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  • 124201.
    Xu, Bo
    et al.
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Zhao, Kun
    Sony Mobile Commun, Network Technol Lab, Res & Technol, SE-22188 Lund, Sweden.;Aalborg Univ, Dept Elect Syst, Antennas Propagat & Radio Networking Sect, DK-9220 Aalborg, Denmark..
    Ying, Zhinong
    Sony Mobile Commun, Network Technol Lab, Res & Technol, SE-22188 Lund, Sweden..
    Sjoberg, Daniel
    Lund Univ, Dept Elect & Informat Technol, SE-22100 Lund, Sweden..
    He, Wang
    Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    He, Sailing
    KTH, School of Electrical Engineering and Computer Science (EECS), Electromagnetic Engineering. Zhejiang Univ, Ctr Opt & Electromagnet Res, Hangzhou 310058, Zhejiang, Peoples R China..
    Analysis of Impacts of Expected RF EMF Exposure Restrictions on Peak EIRP of 5G User Equipment at 28 GHz and 39 GHz Bands2019In: IEEE Access, E-ISSN 2169-3536, Vol. 7, p. 20996-21005Article in journal (Refereed)
    Abstract [en]

    Above 6 GHz, radio frequency (RF) electromagnetic field (EMF) exposure from the mobile communication user equipment (UE) should be assessed in terms of incident power density, rather than specific absorption rate as below 6 GHz. Such regulatory RF EMF restrictions will constrain the transmit power of the UE and its peak equivalent isotropically radiated power (EIRP). This paper provides an analysis of the peak EIRP levels of UE containing code-book-based beamforming arrays at 28 GHz and 39 GHz. Different types of antenna elements, incremental element spacing, 4- and 8-element array configurations, and realistic housing integration are considered. The analysis and results show that in realistic housing integration, the 3GPP requirements on minimum peak EIRP can be generally met under the expected RF EMF exposure restrictions.

  • 124202. Xu, Can T.
    et al.
    Zhan, Qiuqiang
    Liu, Haichun
    Somesfalean, Gabriel
    Qian, Jun
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering. KTH, School of Information and Communication Technology (ICT), Centres, Zhejiang-KTH Joint Research Center of Photonics, JORCEP.
    Andersson-Engels, Stefan
    Upconverting nanoparticles for pre-clinical diffuse optical imaging, microscopy and sensing: Current trends and future challenges2013In: Laser and Photonics Reviews, ISSN 1863-8880, Vol. 7, no 5, p. 663-697Article, review/survey (Refereed)
    Abstract [en]

    Upconverting nanoparticles (UCNPs) are a class of recently developed luminescent biomarkers that - in several aspects - are superior to organic dyes and quantum dots. UCNPs can emit spectrally narrow anti-Stokes shifted light with quantum yields which greatly exceed those of two-photon dyes for fluence rates relevant for deep tissue imaging. Compared with conventionally used Stokes-shifting fluorophores, UCNP-based imaging systems can acquire completely autofluorescence-free data with superb contrast. For diffuse optical imaging, the multiphoton process involved in the upconversion process can be used to obtain images with unprecedented resolution. These unique properties make UCNPs extremely attractive in the field of biophotonics. UCNPs have already been applied in microscopy, small-animal imaging, multi-modal imaging, highly sensitive bioassays, temperature sensing and photodynamic therapy. In this review, the current state-of-the-art UCNPs and their applications for diffuse imaging, microscopy and sensing targeted towards solving essential biological issues are discussed.

  • 124203.
    Xu, Chen
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology.
    EU Energy Situations and Supply Security2008Independent thesis Advanced level (degree of Master (Two Years)), 30 credits / 45 HE creditsStudent thesis
    Abstract [en]

    Energy supply security is a hot topic today. It highly influences energy market, national security and also residents’ daily lives. However, due to different aims and study strategies, definitions of energy supply security are different. In this report, it is defined as stable energy supply processes that result from good infrastructure, delivery of energy sources, carriers and services, which are sturdily controlled by effective energy policies. Prices of energy supply system

    are also maintained on a reasonable level over a continuous period thanks to the efficient crises assessment and management.

    In order to make a comprehensive research, energy situation has been deeply investigated on worldwide, EU and Swedish levels, respectively. Results from these investments obviously certify that due to the big amount of populations, there are significant imbalances between energy supply and demands in developing countries. To make things better, these imbalances don’t exist in developed world, like EU Members including Sweden because of applications of advanced technologies and wide utilizations of renewable energy carriers. Oppositely, greenhouse gases emission is a severe problem in the world, which gives rise to temperature increasing year by year! Besides the global warming, some other factors also bring about uncertainties to energy supply security, so that efficient policies are necessary in order improve the recent

    situations and to create a secure atmosphere for energy supply, such as

    Directive 98/30/EC for natural gas supply security, Directive 2003/55/EC for integration and compatibility of the energy regulation and Directive 2003/54/EC, the first policy that regulates EU electricity market as well as IEM Directive, which is the improvement of Directive 2003/54/EC, etc.

    Although several policies aiming at creation of competitive energy markets and achieving energy supply security, vulnerabilities still exist in EU energy supply system, such as limited primary energy sources and high dependence on nuclear powers, energy network capacity inadequacy, high voltage electricity transmission, etc. Concerning Swedish energy supply system, extreme low temperatures in winter, drilling technologies and high economic budgets for heat sources from underground, hurricanes, thunderstorms to wind turbines and man-made disruptions are all potential vulnerabilities. Regarding these negative aspects, recommendations are given on four different levels, which are global, EU, Swedish and individual perspectives. Specific suggestions to achieve energy supply security include independence of different energy supplies, to enhance international cooperation, periodic assessments and inspections for energy facilities, population control, to keep original energy policies updated, to enhance abilities to resist abnormal weather conditions, to develop heat pump technologies and try to use energy in efficient ways, etc.

  • 124204. Xu, Chen
    et al.
    Qi, Chong
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Liotta, Roberto
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wyss, Ramon
    KTH, School of Engineering Sciences (SCI), Physics, Nuclear Physics.
    Wang, S. M.
    Xu, F. R.
    Jiang, D. X.
    Molecular structure of highly excited resonant states in Mg-24 and the corresponding Be-8+O-16 and C-12+C-12 decays2010In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 81, no 5, p. 054319-Article in journal (Refereed)
    Abstract [en]

    Exotic Be-8 and C-12 decays from high-lying resonances in Mg-24 are analyzed in terms of a cluster model. The calculated quantities agree well with the corresponding experimental data. It is found that the calculated decay widths are very sensitive to the angular momentum carried by the outgoing cluster. It is shown that this property makes cluster decay a powerful tool to determine the spin as well as the molecular structures of the resonances.

  • 124205.
    Xu, Cheng
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    A Segmented Silicon Strip Detector for Photon-Counting Spectral Computed Tomography2012Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Spectral computed tomography with energy-resolving detectors has a potential to improve the detectability of images and correspondingly reduce the radiation dose to patients by extracting and properly using the energy information in the broad x-ray spectrum. A silicon photon-counting detector has been developed for spectral CT and it has successfully solved the problem of high photon flux in clinical CT applications by adopting the segmented detector structure and operating the detector in edge-on geometry. The detector was evaluated by both the simulation and measurements.

    The effects of energy loss and charge sharing on the energy response of this segmented silicon strip detector with different pixel sizes were investigated by Monte Carlo simulation and a comparison to pixelated CdTe detectors is presented. The validity of spherical approximations of initial charge cloud shape in silicon detectors was evaluated and a more accurate statistical model has been proposed.

    A photon-counting energy-resolving application specific integrated circuit (ASIC) developed for spectral CT was characterized extensively by electrical pulses, pulsed laser and real x-ray photons from both the synchrotron and an x-ray tube. It has been demonstrated that the ASIC performs as designed. A noise level of 1.09 keV RMS has been measured and a threshold dispersion of 0.89 keV RMS has been determined. The count rate performance of the ASIC in terms of count loss and energy resolution was evaluated by real x-rays and promising results have been obtained.

    The segmented silicon strip detector was evaluated using synchrotron radiation. An energy resolution of 16.1% has been determined with 22 keV photons in the lowest flux limit, which deteriorates to 21.5% at an input count rate of 100 Mcps mm−2. The fraction of charge shared events has been estimated and found to be 11.1% for 22 keV and 15.3% for 30 keV. A lower fraction of charge shared events and an improved energy resolution can be expected by applying a higher bias voltage to the detector.

  • 124206.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Chen, Han
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Svensson, Christer
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Physics of Medical Imaging.
    Energy resolution of a segmented silicon strip detector for photon-counting spectral CT2013In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 715, p. 11-17Article in journal (Refereed)
    Abstract [en]

    We investigated the energy resolution of a segmented silicon strip detector for photon-counting spectral computed tomography (CT). The detector response to different monochromatic photon energies and various photon fluxes was characterized at the Elettra synchrotron. An RMS energy resolution of 1.50 keV has been demonstrated for 22 keV photons at zero flux, and it deteriorated as a function of input count rate at a rate of 5.13 eV mm2 /Mcps. The charge sharing effect has been evaluated. The results show that around 11.1% of the interacting photons experience charge sharing for 22 keV photons and 15.3% for 30 keV.

  • 124207.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Evaluation of Energy Loss and Charge Sharing in Cadmium Telluride Detectors for Photon-Counting Computed Tomography2011In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 58, no 3, p. 614-625Article in journal (Refereed)
    Abstract [en]

    We present estimates of energy loss and charge sharing for a pixelated cadmium telluride (CdTe) detector used for photon-counting spectral computed tomography (CT). In a photon-counting pixelated CdTe detector, several physical effects lead to detected events with reduced energies, including Compton scattering, fluorescence emission, charge diffusion, trapping of charge carriers and slow-hole-motion-induced incomplete charge collection. Charge sharing is the result of the lost energy being collected by adjacent pixels. We simulated the photon transport and the charge-collection process with a Monte Carlo-based simulation and evaluated these effects on the detector performance. The trapping effect and poor hole collection have been studied together using an analytical model. We also investigated the detector response under the influence of only the fluorescence effect. We conclude that the charge sharing effects should be taken into account when the pixel is smaller than 1 mm(2). A straightforward way to decrease the double counting of X-rays from events with charge sharing is to increase the electronic threshold. However, increasing the threshold comes at the cost of losing low-energy events, which is undesirable, at least in applications such as pediatric imaging.

  • 124208.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics. KTH, School of Biotechnology (BIO), Centres, Albanova VinnExcellence Center for Protein Technology, ProNova.
    Validity of spherical approximations of initial charge cloud shape in silicon detectors2011In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 648, no SUPPL. 1, p. 190-193Article in journal (Refereed)
    Abstract [en]

    Spherical approximation has been used extensively in low-energy X-ray imaging to represent the initial charge cloud produced by photon interactions in silicon detectors, mainly because of its simplicity. However, for high-energy X-rays, where the initial charge distribution is as important as the diffusion process, the spherical approximation will not result in a realistic detector response. In this paper, we present a bubble-line model that simulates the initial charge cloud in silicon detectors for photons in the energy range of medical imaging. An initial charge cloud can be generated by sampling the center of gravity and the track size from statistical distributions derived from Monte Carlo generated tracks and by distributing a certain proportion of photon energy into a bubble (68%) and a line portion uniformly. The simulations of detector response demonstrate that the new model simulates the detector response accurately and corresponds well to Monte Carlo simulation.

  • 124209.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Svensson, Christer
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Performance characterization of a silicon strip detector for spectral computed tomography utilizing a laser testing system2011In: MEDICAL IMAGING 2011: PHYSICS OF MEDICAL IMAGING / [ed] Pelc, NJ; Samei, E; Nishikawa, RM, 2011, Vol. 7961Conference paper (Refereed)
    Abstract [en]

    A new silicon strip detector with sub-millimeter pixel size operated in single photon-counting mode has been developed for use in spectral computed tomography (CT). An ultra fast application specific integrated circuit (ASIC) specially designed for fast photon-counting application is used to process the pulses and sort them into eight energy bins. This report characterizes the ASIC and detector in terms of thermal noise (0.77 keV RMS), energy resolution when electron-hole pairs are generated in the detector diode (1.5 keV RMS) and Poissonian count rate with retained count rate linearity and energy resolution (200 Mcps.mm(-2)). The performance of the photon-counting detector has been tested using a picosecond pulsed laser system to inject energy into the detector, simulating x-ray interactions. The laser testing results indicate a good energy-discriminating capability of the detector, assigning the pulses to higher and higher energy bins as the intensity of the laser pulses are increased.

  • 124210.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Svensson, Christer
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Preliminary evaluation of a silicon strip detector for photon-counting spectral CT2012In: Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, ISSN 0168-9002, E-ISSN 1872-9576, Vol. 677, p. 45-51Article in journal (Refereed)
    Abstract [en]

    An edge-on silicon strip detector designed for photon-counting spectral computed tomography (CT) is presented. Progress on the development of an application specific integrated circuit (ASIC) to process the pulses and sort them into energy bins is reported upon. The ASIC and detector are evaluated in terms of electronic noise, energy resolution, count rate linearity under high-frequency periodic pulses, threshold variation and gain. The high-frequency periodic pulses are injected both by means of an external pulse generator and a pulsed laser illuminating the silicon diode. The pulsed laser system has similar to 100 ps pulse width and thus generates near instantaneous pulses in the diode, thus mimicking real X-ray conversions. The evaluation shows a low thermal noise level of 0.77 key RMS, an energy resolution of 1.5 keV RMS when electron-hole pairs are generated in the detector diode by the laser injection. The test results furthermore indicate a good energy-discriminating capability of the detector with the thresholds spread out, assigning the external pulses to higher and higher energy bins as the pulse intensity is increased.

  • 124211.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Persson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Chen, Han
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Svensson, Christer
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Evaluation of a Second-Generation Ultra-Fast Energy-Resolved ASIC for Photon-Counting Spectral CT2013In: IEEE Transactions on Nuclear Science, ISSN 0018-9499, E-ISSN 1558-1578, Vol. 60, no 1, p. 437-445Article in journal (Refereed)
    Abstract [en]

    A second-generation ultra-fast energy-resolved application specific integrated circuit (ASIC) has been developed for photon-counting spectral computed tomography (CT). The energy resolution, threshold dispersion and gain of the ASIC were characterized with synchrotron radiation at Diamond Light Source. The standard deviation of threshold offsets at zero keV is 0.89 keV. An RMS energy resolution of 1.09 keV has been demonstrated for 15 keV photon energy at a count rate of 40 kcps, and it deteriorates at a rate of 0.29 keV/Mcps with the increase of output cout rate. The count rate performance of the ASIC has also been evaluated with 120 kV polychromatic x-rays produced by a tungsten anode tube and the results are presented.

  • 124212.
    Xu, Cheng
    et al.
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Yveborg, Moa
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Chen, Han
    KTH, School of Engineering Sciences (SCI), Physics.
    Danielsson, Mats
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Karlsson, Staffan
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Svensson, C.
    Bornefalk, Hans
    KTH, School of Engineering Sciences (SCI), Physics, Medical Imaging.
    Evaluation of an ultra-fast photon-counting energy-resolved ASIC for spectral CT2012In: Progress in Biomedical Optics and Imaging - Proceedings of SPIE, SPIE - International Society for Optical Engineering, 2012, Vol. 8313, p. 83130Y-Conference paper (Refereed)
    Abstract [en]

    We have developed an ultra-fast photon-counting energy-resolved application specific integrated circuit (ASIC) for spectral computed tomography (CT). A comprehensive characterization has been carried out to investigate the performance of the ASIC in terms of energy resolution under different photon flux rates and the count rate linearity in photon-counting mode. An energy resolution of 4.7 % has been achieved for 59.5 keV low flux photons. The count rate performance of the ASIC was measured with 120 kVp polychromatic x-rays. The results indicate that the count rate linearity can be kept for a flux rate up to 150 Mphotons s -1 mm -2 with retained energy information, and this value is increased to be 250 Mphotons s -1 mm -2 in photon-counting mode.

  • 124213.
    Xu, Chenzhi
    KTH, School of Information and Communication Technology (ICT).
    Optical Spectrocopy on Nanostructrured Materials2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    Solar cells are designed to transform the optical energy into electrical energy. Using solar energy is the best way for humans to solve the energy shortage problem. Dye sensitized solar cell(DSSC) has a low cost and helps people to obtain the solar energy expediently. The DSSC is based on nano structured TiO2 ; and dye molecules help the particles of TiO2 to absorb more photons. Hence DSSC has higher efficiency than SC(solar cell without dye). This thesis elaborates and analyzes the dye which is sensitized to TiO2. The absorption spectrum of the dye was achieved. Two kinds of dye sample were made on the basis of their places in structure of TiO2. One dye sample is solution, nanopowder of the dye in aceton. The other dye sample is film, thin film on a quartz plate. The absorption spectrums of the samples have been measured in laboratory. The measurement suggests that the dye works improves the absorption of solar energy in DSSC. This thesis mainly contains the following sections: Chapter I reviews the solar energy technology development, the research purposes, and the principles of DSSC. Chapter II introduces the theory of optical spectroscopy. Chapter III and Chapter IV describe the apparatus employed in this experimental system, the experimental method, and the testing results. Chapter V gives the conclusions drawn from the experiments.

  • 124214. Xu, Chun Kai
    et al.
    Liu, Wen Jie
    Zhang, Pan Ke
    Li, Meng
    Zhang, Han Jun
    Xu, Ke Zun
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology. University of Science and Technology of China, China.
    Chen, Xiang Jun
    Nonlinear inelastic electron scattering revealed by plasmon-enhanced electron energy-loss spectroscopy2014In: Nature Physics, ISSN 1745-2473, E-ISSN 1745-2481, Vol. 10, no 10, p. 753-757Article in journal (Refereed)
    Abstract [en]

    Electron energy-loss spectroscopy is a powerful tool for identifying the chemical composition of materials(1-5). It relies mostly on the measurement of inelastic electrons, which carry specific atomic or molecular information. Inelastic electron scattering, however, has a very low intensity, often orders of magnitude weaker than that of elastically scattered electrons. Here, we report the observation of enhanced inelastic electron scattering from silver nanostructures, the intensity of which can reach up to 60% of its elastic counterpart. A home-made scanning probe electron energy-loss spectrometer(6) was used to produce highly localized plasmonic excitations, significantly enhancing the strength of the local electric field of silver nanostructures. The intensity of inelastic electron scattering was found to increase nonlinearly with respect to the electric field generated by the tip-sample bias, providing direct evidence of nonlinear electron scattering processes.

  • 124215.
    Xu, Chunlin
    et al.
    KTH, School of Biotechnology (BIO).
    Eckerman, Christer
    Smeds, Annika
    Reunanen, Markku
    Eklund, Patrik C.
    Sjoholm, Rainer
    Willfor, Stefan
    Carboxymethylated spruce galactoglucomannans: preparation, characterisation, dispersion stability, water-in-oil emulsion stability, and sorption on cellulose surface2011In: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 26, no 2, p. 167-178Article in journal (Refereed)
    Abstract [en]

    Natively acetylated galactoglucomannans (GGMs) is the main hemicellulose type in most softwood species and can be utilised as, for example, bioactive polymers, hydrocolloids, papermaking chemicals, or coating polymers. In this study, carboxymethylated GGMs (CM-GGMs) were prepared and characterised by GC-MS, H-1 and C-13 NMR and FTIR spectroscopy, and SEC-MALLS. The thermal stability of the products was investigated by DSC-TGA. The accessibility of different C-positions in mannose and glucose was investigated. The emulsion stability of CM-GGMs in resin dispersion was studied and it was shown that CM-GGMs can stabilise the resin dispersion also in presence of CaCl2. The possibility of using CM-GGMs as emulsifiers in water-in-oil emulsions was assessed. A CM-GGM with a DS value of 0.25 at a concentration higher than 3% performed the best. Finally, the study of sorption of CM-GGM onto cellulose surface exhibited a decrease in binding ability with an increase in the degree of substitution (DS).

  • 124216.
    Xu, Chunlin
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Spadiut, Oliver
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Araujo, Ana Catarina
    KTH, School of Biotechnology (BIO), Glycoscience.
    Nakhai, Azadeh
    KTH, School of Biotechnology (BIO), Glycoscience.
    Willfor, Stefan
    Brumer, Harry
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Chemo-enzymatic assembly of clickable cellulose surfaces via multivalent polysaccharides2012In: Abstract of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 243Article in journal (Other academic)
  • 124217.
    Xu, Chunlin
    et al.
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Spadiut, Oliver
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Araújo, Ana Catarina
    KTH, School of Biotechnology (BIO).
    Nakhai, Azadeh
    KTH, School of Biotechnology (BIO), Glycoscience.
    Brumer, Harry
    KTH, School of Biotechnology (BIO), Glycoscience. KTH, School of Chemical Science and Engineering (CHE), Centres, Wallenberg Wood Science Center.
    Chemo-enzymatic Assembly of Clickable Cellulose Surfaces via Multivalent Polysaccharides2012In: ChemSusChem, ISSN 1864-5631, Vol. 5, no 4, p. 661-665Article in journal (Refereed)
    Abstract [en]

    The chemist′s guide to the galactosyl unit: A chemo-enzymatic process is developed for the multivalent functionalization of cellulose surfaces via regioselective oxidation of heteropolysaccharides with galactose 6-oxidase. Reductive amination, surface sorption, and click chemistry enable the assembly of (bio)chemically active cellulose surfaces for applications ranging from functional biocomposites to in vitro diagnostics.

  • 124218.
    Xu, Derek
    et al.
    KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Kittichokechai, Kittipong
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Oechtering, Tobias J.
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Skoglund, Mikael
    KTH, School of Electrical Engineering (EES), Communication Theory. KTH, School of Electrical Engineering (EES), Centres, ACCESS Linnaeus Centre.
    Secure Successive Refinement with Degraded Side Information2014In: 2014 IEEE International Symposium on Information Theory (ISIT), IEEE , 2014, p. 2674-2678Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the problem of successive refinement with side information (SI) under secrecy constraint. In particular, under classical successive refinement coding scheme, there are degraded SI sequences Y-n and Z(n) at two decoders and E-n at the eavesdropper. Based on the status of two switches, three different cases are investigated. In case 1 and 3, the eavesdropper only observes output of encoder 1 and 2, respectively, while in case 2, the eavesdropper observes outputs of both encoder 1 and 2. The Markov chain X - Y - (Z, E) holds in all cases. The equivocation is measured by the normalized entropy of source sequence conditioned on the observation of eavesdropper. We completely characterize the rate-distortion-equivocation regions for all three cases, and show that layered coding is optimal. Finally, a binary source example is given.

  • 124219.
    Xu, Disheng
    KTH, School of Engineering Sciences (SCI), Mathematics (Dept.).
    Density of positive Lyapunov exponents for symplectic cocycles2019In: Journal of the European Mathematical Society (Print), ISSN 1435-9855, E-ISSN 1435-9863, Vol. 21, no 10, p. 3143-3190Article in journal (Refereed)
    Abstract [en]

    We prove that Sp(2d, R)-cocycles, HSp(2d)-cocycles and pseudo-unitary cocycles with at least one non-zero Lyapunov exponent are dense in all usual regularity classes for non-periodic dynamical systems. For Schrodinger operators on the strip, we prove a similar result about the density of positive Lyapunov exponents. This generalizes a result of A. Avila [2] to higher dimensions.

  • 124220. Xu, F. R.
    et al.
    Satula, W.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Quadrupole pairing interaction and signature inversion2000In: Nuclear Physics A, ISSN 0375-9474, E-ISSN 1873-1554, Vol. 669, no 02-jan, p. 119-134Article in journal (Refereed)
    Abstract [en]

    The signature inversion in the pi h(11/2) x vh(11/2) rotational bands of the odd-odd Cs and La isotopes and the pi h(11/2) x vi(13/2) bands of the odd-odd Tb, Ho and Tm nuclei is investigated using pairing and deformation self-consistent mean-field calculations, The model can rather satisfactorily account for the anomalous signature splitting provided that spin assignments in some of the bands are revised. Our calculations show that signature inversion can appear already at axially symmetric shapes. It is found that this is due to the contribution of the (lambda mu) = (22) component of the quadrupole-pairing interaction to the mean-field potential.

  • 124221. Xu, F. R.
    et al.
    Walker, P. M.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Limit to high-spin isomerism in hafnium isotopes2000In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 6201, no 1Article in journal (Refereed)
    Abstract [en]

    Configuration-constrained nuclear shape calculations are used to show that reinforcing neutron and proton orbital structures create exceptional conditions for the formation of multiquasiparticle isomers in neutron-rich hafnium isotopes, with axially symmetric, prolate shapes. Highly excited, long-lived states are predicted. However, at angular momenta close to 40 (h) over bar, orbital alignment effects for collective oblate rotation lend to a deep potential minimum that competes energetically with the prolate multiquasiparticle states.

  • 124222. Xu, F. R.
    et al.
    Walker, P. M.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Oblate stability of A approximate to 110 nuclei near the r-process path2002In: Physical Review C. Nuclear Physics, ISSN 0556-2813, E-ISSN 1089-490X, Vol. 65, no 2Article in journal (Refereed)
    Abstract [en]

    Even-even A approximate to 110 nuclei approaching the astrophysical r-process path have been investigated using both the cranked and the configuration-constrained shell models. The calculations show that, with increasing neutron number in the Zgreater than or equal to40 nuclides, nuclear shapes evolve from prolate, through triaxial to oblate deformations. In contrast to other regions of the nuclear chart, pronounced oblate shapes dominate the collective rotation from ground states to very high spins (Isimilar to40), when Ngreater than or equal to70. The stability of the oblate shapes is due to the simultaneous upper-shell neutron and proton Fermi surfaces, reinforced by the rotation alignment behavior of both nucleon types. Configuration-constrained calculations predict the coexistence of well-deformed prolate and oblate multiquasiparticle (isomeric) states.

  • 124223. Xu, F. R.
    et al.
    Zhao, E. G.
    Wyss, Ramon
    KTH, Superseded Departments, Physics.
    Walker, P. M.
    Enhanced stability of superheavy nuclei due to high-spin isomerism2004In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 92, no 25, p. 252501-Article in journal (Refereed)
    Abstract [en]

    Configuration-constrained calculations of potential-energy surfaces in even-even superheavy nuclei reveal systematically the existence at low excitation energies of multiquasiparticle states with deformed axially symmetric shapes and large angular momenta. These results indicate the prevalence of long-lived, multiquasiparticle isomers. In a quantal system, the ground state is usually more stable than the excited states. In contrast, in superheavy nuclei the multiquasiparticle excitations decrease the probability for both fission and alpha decay, implying enhanced stability. Hence, the systematic occurrence of multiquasiparticle isomers may become crucial for future production and study of even heavier nuclei. The energies of multiquasiparticle states and their alpha decays are calculated and compared to available data.

  • 124224. Xu, Fang
    et al.
    Chen, Hong
    Xu, Jingyi
    Liang, Xue
    He, Xuelan
    Shao, Binhao
    Sun, Xianqiang
    KTH, School of Biotechnology (BIO), Theoretical Chemistry and Biology.
    Li, Bing
    Deng, Xiaoliang
    Yuan, Mu
    Synthesis, structure-activity relationship and biological evaluation of novel arylpiperzines as alpha(1A/1D)-AR subselective antagonists for BPH2015In: Bioorganic & Medicinal Chemistry, ISSN 0968-0896, E-ISSN 1464-3391, Vol. 23, no 24, p. 7735-7742Article in journal (Refereed)
    Abstract [en]

    A series of novel arylpiperazine derivatives as alpha(1A/1D)-adrenergic receptors (AR) subtype selective antagonists were designed, synthesized and evaluated for their antagonistic activities towards alpha(1)-ARs (alpha(1A), alpha(1B), and alpha(1D)). Compounds 9, 12, 13, 15, 17, 18, 21, 22, 25 and 26 exerted strong antagonistic effects on alpha(1A) and/or alpha(1D) subtypes over alpha(1B) in vitro. SAR analysis indicated that chloride at the ortho-phenyl position for compound 17 was beneficial for the highest alpha(1A/D)-AR sub-selectivity. Moreover, molecular docking study of compound 17 with the homology-modeled alpha(1)-ARs (alpha(1A), alpha(1B), and alpha(1D)) structures exhibited differences of key amino resides in the docking pocket which may influence the subtype selectivity. ILE 193 of alpha(1A) was validated as the key residues for binding ligand. This work provides useful information for finding more new potential drugs in clinic in treating benign prostatic hyperplasia (BPH).

  • 124225. Xu, Fang
    et al.
    Mudiyanselage, Kumudu
    Baber, Ashleigh E.
    Soldemo, Markus
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    Weissenrieder, Jonas
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Material Physics, MF.
    White, Michael G.
    Stacchiola, Dario J.
    Redox-Mediated Reconstruction of Copper during Carbon Monoxide Oxidation2014In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 118, no 29, p. 15902-15909Article in journal (Refereed)
    Abstract [en]

    Copper has excellent initial activity for the oxidation of CO, yet it rapidly deactivates under reaction conditions. In an effort to obtain a full picture of the dynamic morphological and chemical changes occurring on the surface of catalysts under CO oxidation conditions, a complementary set of in situ ambient pressure (AP) techniques that include scanning tunneling microscopy, infrared reflection absorption spectroscopy (IRRAS), and X-ray photoelectron spectroscopy were conducted. Herein, we report in situ AP CO oxidation experiments over Cu(111) model catalysts at room temperature. Depending on the CO:O-2 ratio, Cu presents different oxidation states, leading to the coexistence of several phases. During CO oxidation, a redox cycle is observed on the substrate's surface, in which Cu atoms are oxidized and pulled from terraces and step edges and then are reduced and rejoin nearby step edges. IRRAS results confirm the presence of under-coordinated Cu atoms during the reaction. By using control experiments to isolate individual phases, it is shown that the rate for CO oxidation decreases systematically as metallic copper is fully oxidized.

  • 124226. Xu, H.
    et al.
    Liu, J.
    Qin, D.
    Gao, X.
    Yan, Jinyue
    KTH, School of Chemical Science and Engineering (CHE), Chemical Engineering and Technology, Energy Processes.
    Feasibility analysis of solar irrigation system for pastures conservation in a demonstration area in Inner Mongolia2013In: Applied Energy, ISSN 0306-2619, E-ISSN 1872-9118, Vol. 112, no SI, p. 697-702Article in journal (Refereed)
    Abstract [en]

    Pasture lands in Inner Mongolia of China have been deteriorated severely by overgrazing and climate change in the past 30. years. There is a plan to set up a solar irrigation system in Xilamuren area of the region to restore the pastures effectively. In order to design the solar irrigation system based on groundwater, equations for analyzing the optimum irrigation amount were developed in this study, and the main steps to design the system were also given. The coefficients and parameters in the equations are related to meteorological factors, vegetation types and areas, and soil properties. The soil water content is a control variable to decide the water irrigation amount for its effects on maintaining the vegetation growth based on soil water evaporation, plant transpiration and physiological consumption. According to the pasture restoring objectives and water demands during the plants growing periods, proper soil water contents are chosen as evaluation basis for irrigation. The groundwater system should be kept healthy during exploitation; so, the possible supply of local groundwater is a constraint condition in the model. Besides, an optimum irrigation amount process in a whole year is provided for the solar powered system design.

  • 124227.
    Xu, Haifeng
    KTH, School of Information and Communication Technology (ICT).
    Digital Image Processing Algorithms Research Based on FPGA2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    As we can find through the development of TV systems in America, the digital TV related digital broadcasting is just the road we would walk into. Nowadays digital television is prevailing in China, and the government is promoting the popularity of digital television. However, because of the economic development, analog television will still take its place in the TV market during a long period. But the broadcasting system has not been reformed, as a result, we should not only take use of the traditional analog system we already have, but also improve the quality of the pictures of analog system.

    With the high-speed development of high-end television, the research and application of digital television technique, the flaws caused by interlaced scan in traditional analog television, such as color-crawling, flicker and fast-moved object's boundary blur and zigzag, are more and more obvious. Therefore the conversion of interlaced scan to progressing scan, which is de-interlacing, is an important part of current television production. At present there are many kinds of TV sets appearing in the market. They are based on digital processing technology and use various digital methods to process the interlaced, low-field rate video data, including the de-interlacing and field rate conversion.

    The digital process chip of television is the heart of the new-fashioned TV set, and is the reason of visual quality improvement. As a requirement of real time television signal processing, most of these chips has developed novel hardware architecture or data processing algorithm. So far, the most quality effective algorithm is based on motion compensation, in which motion detection and motion estimation will be inevitably involved, in despite of the high computation cost. in video processing chips, the performance and complexity of motion estimation algorithm have a direct impact on speed area and power consumption of chips. Also, motion estimation determined the efficiency of the coding algorithms in video compression.

    This thesis proposes a Down-sampled Diamond NTSS algorithm (DSD-NTSS) based on New Three Step Search (NTSS) algorithm, taking both performance and complexity of motion estimation algorithms into consideration. The proposed DSD-NTSS algorithm makes use of the similarity of neighboring pixels in the same image and down-samples pixels in the reference blocks with the decussate pattern to reduce the computation cost. Experiment results show that DSD-NTSS is a better tradeoff in the terms of performance and complexity. The proposed DSD-NTSS reduces the computation cost by half compared with NTSS when having the equivalent image quality. Further compared with Four Step Search(FSS) Diamond Search(DS)、Three Step Search(TSS) and some other fast searching algorithms, the proposed DSD-NTSS generally surpasses in performance and complexity.

    This thesis focuses on a novel computation-release motion estimation algorithm in video post-processing system and researches the FPGA design of the system.

  • 124228.
    Xu, Hao
    KTH, School of Engineering Sciences (SCI), Applied Physics.
    Fluorescence Properties of Quantum Dots and Their Utilization in Bioimaging2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Quantum dots (QDs), especially colloidal semiconductor QDs, possess properties including high quantum yields, narrow fluorescence spectra, broad absorption and excellent photostability, making them extremely powerful in bioimaging. In this thesis, we studied the fluorescence properties of QDs and attempted multiple ways to boost applications of QDs in bioimaging field.

    By time-correlated single photon counting (TCSPC) measurement, we quantitatively interpreted the fluorescence mechanism of colloidal semiconductor QDs.

    To enhance QD fluorescence, we used a porous alumina membrane as a photonic crystal structure to modulate QD fluorescence.

    We studied the acid dissociation of 3-mercaptopropionic acid (MPA) coated QDs mainly through electrophoretic mobility of 3-MPA coated CdSe QDs and successfully demonstrated the impact of pH change and Ca2+ ions.

    Blinking phenomena of both CdSe-CdS/ZnS core-shell QDs and 3C-SiC nanocrystals (NCs) were studied. A general model on blinking characteristics relates the on-state distribution to CdSe QD surface conditions. The energy relaxation pathway of fluorescence of 3C-SiC NCs was found independent of surface states.

    To examine QD effect on ciliated cells, we conducted a 70-day long experiment on the bioelectric and morphological response of human airway epithelial Calu-3 cells with periodic deposition of 3-MPA coated QDs and found the cytotoxicity of QDs was found very low.

    In a brief summary, our study of QD could benefit in bioimaging and biosensing. Especially, super-resolution fluorescent bioimaging, such as, stochastic optical reconstruction microscopy (STORM) and photo-activated localization microscopy (PALM), may benefit from the modulation of the QD blinking in this study. And fluorescence lifetime imaging (FLIM) microscopy could take advantage of lifetime modulation based on our QD lifetime study.

  • 124229.
    Xu, Hao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cellular Biophysics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Influence of surface states on blinking characteristics of single colloidal CdSe-CdS/ZnS core-multishell quantum dot2017In: Journal of Colloid and Interface Science, ISSN 0021-9797, E-ISSN 1095-7103, Vol. 505, p. 528-536Article in journal (Refereed)
    Abstract [en]

    We carefully characterized the fluorescence blinking of single colloidal CdSe-CdS/ZnS core-multishell quantum dots (QDs) with different surface modifications, including octadecylamine (ODA) coated QDs dispersed in chloroform, aqueous 3-mercaptopropionic acids (3MPA) coated QDs in HEPES solution treated by Ca2+ ions and ethylene glycol tetraacetic acid (EGTA, Ca2+ chelator), and aqueous 3MPA-QDs treated by glycerol. It was found that the on- and off-state probability density distributions displayed different rules. The off-state probability density distributions of all QDs complied well with the inverse power law, while the on-state probability density distributions bended upwards in log-log scale, and the degree of the upwards-bending correlated strongly with QD surface modification and fluorescence brightness of the single QD. Further autocorrelation analysis revealed that the fluorescence time series of a single QD was more random when the single QD showed a stronger fluorescence. Realistic numerical simulations with input parameters from quantum mechanical calculations showed that the QD exciton was first generated by an excitation photon; It radiatively recombined to give QD's fluorescence response, i.e., the on-state, which displayed the upwards-bended on-state probability density distribution profile; The electron and/or the hole of the photoexcited exciton in the QD core, after tunneling to the QD surface, randomly walked through the two-dimensional network of the QD surface states, resulting in the off-state probability density distribution profile of the inverse power law. Surface modification modified the QD surface-state network, in turn modifying the on/off probability density distribution profiles. Our findings provide us with a novel highway of applying colloidal QDs to study microscopic physical, and chemical, processes in many fields including in vivo and in vitro imaging, sensing and labelling.

  • 124230.
    Xu, Hao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Understand blinking of single colloidal CdSe-CdS/ZnS quantum dot by surface modificationManuscript (preprint) (Other academic)
  • 124231.
    Xu, Hao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Understand blinking of single colloidal CdSe-CdS/ZnS quantum dot by surface modificationManuscript (preprint) (Other academic)
  • 124232.
    Xu, Hao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Chmyrov, Volodymyr
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Widengren, Jerker
    KTH, School of Engineering Sciences (SCI), Applied Physics, Experimental Biomolecular Physics.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics.
    Mechanisms of fluorescence decays of colloidal CdSe-CdS/ZnS quantum dots unraveled by time-resolved fluorescence measurement2015In: Physical Chemistry, Chemical Physics - PCCP, ISSN 1463-9076, E-ISSN 1463-9084, Vol. 17, no 41, p. 27588-27595Article in journal (Refereed)
    Abstract [en]

    By narrowing the detection bandpass and increasing the signal-to-noise ratio in measuring the time-resolved fluorescence decay spectrum of colloidal CdSe-CdS/ZnS quantum dots (QDs), we show that directly after the photoexcitation, the fluorescence decay spectrum is characterized by a single exponential decay, which represents the energy relaxation of the photogenerated exciton from its initial high-energy state to the ground exciton state. The fluorescence decay spectrum of long decay time is in the form of beta/t(2), where beta is the radiative recombination time of the ground-state exciton and t is the decay time. Our findings provide us with a direct and quantitative link between fluorescence decay measurement data and fundamental photophysics of QD exciton, thereby leading to a novel way of applying colloidal QDs to study microscopic, physical and chemical processes in many fields including biomedicine.

  • 124233.
    Xu, Hao
    et al.
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Li, Li
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Manneberg, Otto
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Russom, Aman
    KTH, School of Engineering Sciences (SCI), Applied Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Gylfason, Kristinn B.
    KTH, School of Electrical Engineering (EES), Micro and Nanosystems.
    Brismar, Hjalmar
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Fu, Ying
    KTH, School of Engineering Sciences (SCI), Applied Physics, Cell Physics. KTH, Centres, Science for Life Laboratory, SciLifeLab.
    Modulated fluorescence of colloidal quantum dots embedded in a porous alumina membrane2013In: Journal of Physical Chemistry B, ISSN 1520-6106, E-ISSN 1520-5207, Vol. 177, no 45, p. 14151-14156Article in journal (Refereed)
    Abstract [en]

    The fluorescence spectrum of CdSe core-CdS/ZnS shell colloidal quantum dots (QDs) embedded in porous alumina membrane was studied. Small peaks, superimposed on the principal QD fluorescence spectrum, were observed. Finite-difference time-domain simulation indicates that the QD point radiation emitting from within the membrane is strongly modulated by the photonic band structure introduced by the membrane pores, leading to the observed fine spectral features. Moreover, the principal QD fluorescence peak red-shifted when the optical excitation power was increased, which is attributed to QD material heating due to emitted phonons when the photoexcited electron and hole relax nonradiatively from high-energy states to the ground exciton state before fluorescence.

  • 124234.
    Xu, Haoxin
    KTH, School of Industrial Engineering and Management (ITM), Energy Technology, Heat and Power Technology.
    Numerical Study on the Thermal Performance of a Novel Impinging Type Solar Receiver for Solar Dish-Brayton System2013Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    An impinging type solar receiver has been designed for potential applications in a future Brayton Solar Dish System. The EuroDish system is employed as the collector, and an externally fired micro gas turbine (EFMGT) has been chosen as the power conversion unit. In order to reduce the risks caused by the quartz glass window, which is widely used in traditional air receiver designs, a cylinder cavity absorber without a quartz window has been adopted. Additionally, an impinging design has been chosen as the heat exchange system due to its high heat transfer coefficient compared to other single-phase heat exchange mechanisms. This thesis work introduces the design of an solar air receiver without a glass window, which features jet impingement to maximize the heat transfer rate. A detailed study of the thermal performance of the designed solar receiver has been conducted using numerical tools from the ANSYS FLUENT package.

    Concerning receiver performance, an overall thermal efficiency of 72.9% is attained and an output air temperature of 1100 K can be achieved, according to the numerical results. The total thermal power output is 38.05 kW, enough to satisfy the input requirements of the targeted micro gas turbine. A preliminary design layout is presented and potential optimization approaches for future enhancement of the receiver are proposed, regarding local thermal stress and pressure loss reduction.

    This thesis project also introduces a ray-thermal coupled numerical design method, which combines ray tracing techniques (using FRED®), with thermal performance analysis (using ANSYS Workbench).

  • 124235.
    Xu, Huan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Graphene Oxide Technology to Advance the Performance of Poly(lactic acid) Materials2016Doctoral thesis, monograph (Other academic)
    Abstract [en]

    In the past two decades, a burgeoning biorefinery concept has grown in concert with the materials science, contributing to the rise of biobased materials that respect environment and are versatile for various applications. An excellent example is poly(lactic acid) (PLA) that exhibits high strength and desirable degradability. Unfortunately, PLA suffers from poor mechanical ductility and toughness, and low resistance to heat and water/gas permeation. In order to promote the performance of PLA and thus to broaden the application areas, this study brings to light the morphological and structural specificities for fabrication of high-performance PLA films. The proposed strategy hinges on innovative uses of graphene oxide (GO) nanostructures, giving the possibility to simultaneously tailor the crystalline morphology, mechanical and barrier properties, and degradation behavior for PLA.

    While recognizing the GO-enabled function in controlling the crystalline morphology of racemic PLA, the nucleation mechanism induced by GO nanosheets was elucidated as a first step. In addition to the observation of random lamellae induced by the basal planes of GO nanosheets, it was of particular interest to reveal that the ultrathin edges of nanosheets were ready to trigger the ordered alignment of PLA lamellae. The high nucleation activity of GO was further employed to preferentially accelerate the stereocomplex crystallization of PLA, which subsequently suppressed the development of homo-crystals by generation of spatial hindrance. As a result of the decoration of GO nanosheets with sterecomplex crystals, an impressive combination of barrier and thermal properties, and mechanical strength and ductility was achieved for the racemic PLA/GO composites.

    As a parallel approach, the morphology and structure of GO were tailored to enhance PLA-GO interactions and to improve GO dispersion: (1) few-layer nanosheets were firmly immobilized onto microsized starch particles by hydrogen bonding, permitting the creation of strong and active nanointerfaces in PLA biocomposites that enhanced interfacial interactions and facilitated filler dispersion; (2) the planar dimensionality of GO was shrunk to quasi-zero, conferring the generation of higher density of oxygen functional groups and enhanced interactions with PLA matrix, and resulting in higher nucleation activity and accelerated hydrolytic degradation.

    In addition to the fundamental insights into the PLA-GO interaction mechanisms, the methodologies proposed here can shape new routes to high-performance PLA materials with promising potential in a diversity of applications.

  • 124236.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Bai, Yuge
    Xie, Lan
    Li, Jinlai
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Heat-Resistant and Microwaveable Poly(Iactic acid) by Quantum-Dot Promoted Stereocomplexation2017In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 5, no 12, p. 11607-11617Article in journal (Refereed)
    Abstract [en]

    Nanofiller-tailored stereocomplexation signifies a promising and feasible pathway to develop heat-resistant poly (lactic acid) (PLA) materials. However, this pathway is thwarted by the potential adverse environmental issues of traditional nanofillers and the challenges in facilitating the nanofiller dispersion and selective formation of stereocomplex crystals (SCs). Here we unravel a microwave-assisted approach to exploit biobased quantum dots (QDs) featuring excellent capability to preferably nucleate PLA SCs. The combination of ultrasmall dimension and high oxygenation degree of QDs conferred intimate interactions with stereocomplexed PLA chains, readying complete exfoliation and uniform dispersion of QDs to promote stereocomplexation. The well-dispersed QDs provided perfect UV shielding for PLA composites, while sustaining high transmission to visible light comparable to pure PLA. Strong interfacial interactions and high concentration of SCs were created around the nanoscale surfaces of QDs, accounting for the greatly increased resistance to oxygen permeation, thermal deformation, and microwave heating. This was accompanied by substantial rise in tensile modulus and elongation at break (up to 74 and 51%) compared to that of pure PLA, affording the demonstration of unusual reinforcing and toughening mechanisms imparted by the PLA-affinitive QDs. The robust structural integrity under harsh usage environments, coupled with high gas barrier, prominent light management and evasion of flexibility and extensibility sacrifices, may prompt low-cost and ecofriendly PLA nanocomposites suitable for diverse applications including microwaveable food packaging.

  • 124237.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology. College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, China.
    Feng, Zhaoxuan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Xie, L.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Graphene Oxide-Driven Design of Strong and Flexible Biopolymer Barrier Films: From Smart Crystallization Control to Affordable Engineering2016In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 4, no 1, p. 334-349Article in journal (Refereed)
    Abstract [en]

    Development of multifunctional, versatile biobased polymers can greatly benefit from the discovery and application of 2D sheet-like materials. For instance, the hybrid system integrating graphene oxide (GO) nanosheets with enantiomeric poly(lactic acid) (PLA) showcases several key properties that can address emerging multifunction needs such as good gas barrier and high thermal resistance. Here we revealed that large specific surface area and homogeneous dispersion of GO conferred the construction of interconnected networks in PLA even with relatively low GO contents (0.1 and 0.5 wt %). These well-extended GO nanosheets were ready to provide enormous and active platforms to nucleate preferentially the neighboring stereocomplex chains, prompting the prevailing development of stereocomplex crystals (SCs). The notable scenario associated with the GO distribution was imaged by 2D Fourier transform infrared spectroscopy, and was further elucidated by dynamic crystallization. More importantly, the nanosheets decorated with ordered PLA lamellae, in turn, contributed to the impressive enhancement in barrier and mechanical properties and chemical resistance. For example, a distinct decrease of 98.5% in oxygen permeability coefficient was observed for the composite films containing 0.5 wt % GO (6.264 × 10-17 cm3 cm cm-2 s-1 Pa-1) compared to the control sample crystallized at 150 °C (4.214 × 10-15 cm3 cm cm-2 s-1 Pa-1). The performance distinction was accompanied by the unusual combination of high tensile strength (73.5 MPa) and high elongation (13.6%), displaying an increase of 31.7% and 183.3% compared to the counterpart, respectively. This may provide a broader context for exploiting 2D nanosheets as robust cells to advance the function and property of PLA, which helps to outline the roadmap for fashioning high-performance, affordable bioplastics.

  • 124238.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hua, Geng
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Odelius, Karin
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Stereocontrolled Entanglement-Directed Self-Alignment of Poly(lactic acid) Cylindrites2016In: Macromolecular Chemistry and Physics, ISSN 1022-1352, E-ISSN 1521-3935Article in journal (Refereed)
    Abstract [en]

    The concept of stereocontrolled entanglements, in which the tunable H-bonded chiral pairs serve as crosslinks to create topological constraints on the local chain dynamics, is introduced to tailor the crystalline morphology of stereocomplex poly(lactic acid). For the entanglements to be interconnected and activated, poly(d-lactic acid) with statistical branched architecture is incorporated, enabling the construction of 3D association with linear poly(l-lactic acid) chains. With thermodynamically graded disentanglement relaxation for the blends, the profound influence of entanglements on the crystalline morphology is revealed during isothermal crystallization. Orderly aligned cylindrites some with an exceptional length of over 500 μm, resembling the structural features of the classical shish-kebab superstructure, are observed in the blends penetrated with dense entanglement constraints. By contrast, only dendritic spherulites are formed in the highly disentangled blends. The selectively suppressed homo-crystallization by the entanglements offers insights into the contribution of constraints. This bottom-up strategy opens up pathways to engender oriented crystals of long-range order under quiescent conditions, which has potential implications for other chiral polymers.

  • 124239.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Feng, Zhaoxuan
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Adolfsson, Karin H.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Sichuan Univ, Dept Polymer Sci & Engn, Chengdu, Sichuan, Peoples R China..
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Enhancing the function of graphene oxide nanosheets by crystallization control: Unexpected harvest of strength, ductility and thermal stability for poly(lactic acid) barrier films2016In: Abstracts of Papers of the American Chemical Society, ISSN 0065-7727, Vol. 251Article in journal (Other academic)
  • 124240.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, L.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Thermostable and impermeable "nano-barrier walls" constructed by poly(lactic acid) stereocomplex crystal decorated graphene oxide nanosheets2015In: Macromolecules, ISSN 0024-9297, E-ISSN 1520-5835, Vol. 48, no 7, p. 2127-2137Article in journal (Refereed)
    Abstract [en]

    In contrast to the relatively clear understanding of epitaxial crystallization induced by one-dimensional nanofillers, the underlying interfacial interactions between polymer crystals and two-dimensional graphene oxide (GO) nanosheets are something of a mystery. Here, the GO-assisted formation of poly(lactic acid) (PLA) stereocomplex crystals (SCs) is disclosed from the quantitative structural analysis to the direct morphological observations at multiscale and the interaction mechanism at the molecular level. It is unexpected to observe that the edges of GO featuring rich grooves and ultralow thickness were ready to induce a layer of ordered lamellae, in clear contrast to the random growth of lamellae on the basal planes. The origin of GO-induced crystallization was appraised from the interaction point of view as indicated by the evident red-shift of a set of functional groups in the Fourier transform infrared spectroscopy spectra. More importantly, the GO nanosheets, albeit presented at an extremely low content (0.05 wt %), decorated by the preferred formation of SCs enabled the simultaneous enhancement of gas barrier properties and resistance to heat distortion. Specifically, the unique combination of greatly improved heat deformation temperature (HDT) and low oxygen permeability coefficient (P<inf>O</inf><inf>2</inf>) for the composite crystallized at 165 °C was demonstrated (146.5 °C and 0.95 × 10-15 cm3 cm cm-2 s-1 Pa-1), outperforming pure PLA with an increment of 75% and a decrease of 77% in HDT and P<inf>O</inf><inf>2</inf>, respectively. The proposed methodology affords elucidation of well-tailored thermal and barrier properties, which may motivate further extension of this rational design to other material combinations.

  • 124241.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Sichuan University, China.
    Xie, L.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Coffee-Ground-Derived Quantum Dots for Aqueous Processable Nanoporous Graphene Membranes2017In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 5, no 6, p. 5360-5367Article in journal (Refereed)
    Abstract [en]

    Carbon-based quantum dots (QDs) with ultralow dimensions and controllable surface chemistry have unique properties appealing to diverse applications. Here, we disclose a high-throughput transformation of spent coffee grounds into uniform QDs assembled by few-layer graphene oxide nanosheets, employing a microwave-assisted strategy under aqueous reaction conditions. Given the low dimensions (30 nm) and high structural integrity, the highly oxygenated QDs exhibited excellent dispersibility in water with tunable fluorescence. The structural attributes of QDs conferred excellent affinity to graphene nanosheets, permitting aqueous processing of nanoporous graphene membranes applicable to removing a broad spectrum of water pollutants ranging from organic compounds to heavy metals while sustaining a high flux rate. The proposed "trash-to-treasure" strategy opens up new possibilities for aqueous processing of nanoporous graphene membranes with great potential in the environmental field.

  • 124242.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology. College of Polymer Science and Engineering, State Key Laboratory of Polymer Materials Engineering, Sichuan University, Chengdu, China.
    Xie, Lan
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Beyond a Model of Polymer Processing-Triggered Shear: Reconciling Shish-Kebab Formation and Control of Chain Degradation in Sheared Poly(L-lactic acid)2015In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 3, no 7, p. 1443-1452Article in journal (Refereed)
    Abstract [en]

    Here we disclose an unprecedented methodology toward high-performance poly(L-lactic acid) (PLLA) through generation of dense shish-kebabs, while the normal shear stress-induced chain degradation is controlled. The key elements involve the application of a pulse of strong shear and controlled crystallization. Specifically, the shear featuring a short duration of 1 s and a shear rate high to 100 s(-1) was employed to create shish precursors, which was followed by high-temperature crystallization (at 130, 135, and 140 degrees C) to render the prevailing development of shish-kebabs rather than spherulites. The direct observation of the overgrown shish afforded the demonstration of its origin from shear-aligned bundles of fibrillar chains, implying the crucial importance of chain entanglements in driving the alignment of neighboring chains along the transient shear. For the first time, the shear-aligned shish was revealed to present much higher conformational order, compared to the neighboring kebabs or spherulites. It is of great interest that the application of transient shear flow prevented PLLA from shear-induced degradation, although the PLLA chains are inherently sensitive to external shear stress. The proposed pathway, thus, creates PLLA rich in shish-kebabs with well-preserved high-molecular-weight chains. This signifies a new scenario with respect to previous studies where strong and long-acting shear was required for the formation of oriented structures in PLLA and the property enhancement was to large part hampered by simultaneous chain scissions. Of immense significance is the possibility to utilize these findings during common processing such as extrusion, spinning, and blowing, in which a transient and intensive shear flow is normally generated.

  • 124243. Xu, Huan
    et al.
    Xie, Lan
    Jiang, Xin
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Chen, Jing-Bin
    Zhong, Gan-Ji
    Li, Zhong-Ming
    Structural Basis for Unique Hierarchical Cylindrites Induced by Ultrahigh Shear Gradient in Single Natural Fiber Reinforced Poly(lactic acid) Green Composites2014In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 15, no 5, p. 1676-1686Article in journal (Refereed)
    Abstract [en]

    A local shear flow field was feasibly generated by pulling the ramie fiber in single fiber reinforced poly(lactic acid) (PLA) composites. This was featured by an ultrahigh shear gradient with a maximum shear rate up to 1500 s(-1), a level comparable to that frequently occurring during the practical polymer processing. To distinguish shear-induced self-nucleation and ramie fiber-induced heterogeneous nucleation, the shear history was classified by pulling the fiber for 5 s (pulled sample) and pulling out the fiber during 10 s (pulled-out sample), while the static fiber-induced crystallization was carried out as the counterpart. As a result of the ultrahigh shear gradient, the combination of primary shear-induced nucleation in the central region and secondary nucleation in the outer layer assembled the unique hierarchical superstructures. By comparing the architectural configurations of interphases formed in the static, pulled, and pulled-out samples, it was shown that the hierarchical cylindrites underwent the process of self-nucleation driven by the applied shear flow, very different from the formation of fiber-induced transcrystallinity (TC) triggered by the heterogeneous nucleating sites at the static fiber surface. The twisting of transcrystallized lamellae may take place due to the spatial hindrance induced by the incredibly dense nuclei under the intense shearing flow, as observed in the synchrotron X-ray diffraction patterns. The influence of chain characteristics on the crystalline morphology was further explored by adding a small amount of poly(ethylene glycol) (PEG) to enhance the molecular mobility of PLA. It was of interest to find that the existence of PEG not only facilitated the growth rates of TC and cylindrites but also improved the preferential orientation of PLA chains and thus expanded the ordered regions. We unearthed lamellar units that were composed of rich fibrillar extended chain crystals (diameter of 50-80 nm). These results are of importance to shed light on tailoring crystalline morphology for natural fibers reinforced green composite materials. Of immense practical significance, too, is the crystalline evolution that has been tracked in the simple model penetrated with an ultrahigh shear gradient, which researchers have so far been unable to replicate during the practical melt processing, such as extrusion and injection molding.

  • 124244.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Xie, Lan
    Li, Jinlai
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Coffee Grounds to Multifunctional Quantum Dots: Extreme Nanoenhancers of Polymer Biocomposites2017In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 9, no 33, p. 27972-27983Article in journal (Refereed)
    Abstract [en]

    Central to the design and execution of nanocomposite strategies is the invention of polymer-affinitive and multifunctional nanoreinforcements amenable to economically viable processing. Here, a microwave-assisted approach enabled gram-scale fabrication of polymer-affinitive luminescent quantum dots (QDs) from spent coffee grounds. The ultrasmall dimensions (approaching 20 nm), coupled with richness of diverse oxygen functional groups, conferred the zero-dimensional QDs with proper exfoliation and uniform dispersion in poly(L-lactic acid) (PLLA) matrix The unique optical properties of QDs were inherited by PLLA nano composites, giving intensive luminescence and high visible transparency, as well as nearly 100% UV-blocking ratio in the full-UV region at only 0.5 wt % QDs. The strong anchoring of PLLA chains at the nanoscale surfaces of QDs facilitated PLLA crystallization, which was accompanied by substantial improvements in thermomechanical and tensile properties. With 1 wt % QDs, for example, the storage modulus at 100 degrees C and tensile strength increased over 2500 and 69% compared to those of pure PLLA (4 and 57.3 MPa), respectively. The QD-enabled energy-dissipating and flexibility-imparting mechanisms upon tensile deformation, including the generation of numerous shear bands, crazing, and nanofibrillation, gave an unusual combination of elasticity and extensibility for PLLA nanocomposites. This paves the way to biowaste-derived nanodots with high affinity to polymer for elegant implementation of distinct light management and extreme nanoreinforcements in an ecofriendly manner.

  • 124245.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Wu, Duo
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Immobilized Graphene Oxide Nanosheets as Thin but Strong Nanointerfaces in Biocomposites2016In: ACS Sustainable Chemistry & Engineering, ISSN 2168-0485, Vol. 4, no 4, p. 2211-2222Article in journal (Refereed)
    Abstract [en]

    Graphene oxide (GO) nanosheets featuring high surface activity and large planar dimension may function as robust nanointerfaces in biocomposites, contributing to simultaneous promotion of mechanical and gas barrier properties. Here, a solution-processed, additive-free approach to immobilize few-layer GO nanosheets on starch granule surfaces (GO@starch) by hydrogen bonding is demonstrated. This approach enabled a straightforward pathway to remove the intersheet van der Waals forces (pi-pi stacking) that generally cause reaggregation and poor dispersion of GO in polymer matrices. Incorporation of GO@starch into poly (lactic acid) (PLA) allowed an interesting structure with few-layer nanosheets firmly immobilized at the PLA-starch interfaces. Inheriting the high aspect ratio and surface energy of GO, GO@starch distinctly strengthened the interfacial interactions with PLA, albeit present at ultralow GO concentrations (up to 0.03 wt %), facilitating the dispersion of GO@starch and nucleation of PLA. The morphological regulation rendered composite films with an impressive combination of high thermal stability, mechanical strength and oxygen resistance. A substantial increase of 280% in tensile strength (58.2 MPa) and a prominent decline of 82% in oxygen permeation coefficient (4.0 cm(3) mm cm(-2) day(-1) atm(-1)) were achieved in the composites loaded with 30 wt % GO@starch in comparison with the counterpart. The cost-performance ratio for the nanostructured biocomposites was excellent even compared to the established packaging materials. The multiscale morphological regulation of sheet-like nanofillers by controlled exfoliation and immobilization of GO on microsized starch particle surfaces, the simplicity of manufacturing, together with the versatility of the engineered composites should make our strategy broadly applicable to other material combinations.

  • 124246.
    Xu, Huan
    et al.
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology. Sichuan University, Chengdu, China.
    Yang, Xi
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology.
    Xie, Lan
    Hakkarainen, Minna
    KTH, School of Chemical Science and Engineering (CHE), Fibre and Polymer Technology, Polymer Technology.
    Conformational Footprint in Hydrolysis-Induced Nanofibrillation and Crystallization of Poly(lactic acid)2016In: Biomacromolecules, ISSN 1525-7797, E-ISSN 1526-4602, Vol. 17, no 3, p. 985-995Article in journal (Refereed)
    Abstract [en]

    The origin of hydrolysis-induced nanofibrillation and crystallization, at the molecular level, was revealed by mapping the conformational ordering during long-term hydrolytic degradation of initially amorphous poly(lactic acid) (PLA), a representative model for degradable aliphatic polyesters generally displaying strong interplay between crystallization and hydrolytic erosion. The conformational regularization of chain segments was essentially the main driving force for the morphological evolution of PLA during hydrolytic degradation. For hydrolysis at 37 degrees C, no significant structural variations were observed due to the immobilization of frozen PLA chains. In contrast, conformational ordering in PLA was immediately triggered during hydrolysis at 60 degrees C and was responsible for the transition from random coils to disordered trans and, further, to quasi-crystalline nanospheres. On the surfaces, the head-by-head absorption and joining of neighboring nanospheres led to nanofibrillar assemblies following a gluttonous snake-like manner. The length and density of nanofibers formed were in close relation to the hydrolytic evolution, both of which showed a direct rise in the initial 60 days and then a gradual decline. In the interior, presumably the high surface energy of the nanospheres allowed for the preferential anchoring and packing of conformationally ordered chains into lamellae. In accordance with the well-established hypothesis, the amorphous regions were attacked prior to the erosion of crystalline entities, causing a rapid increase of crystallinity during the initial 30 days, followed by a gradual fall until 90 days. In addition to adequate illustration of hydrolysis-induced variations of crystallinity, our proposed model elucidates the formation of spherulitic nuclei featuring an extremely wide distribution of diameters ranging from several nanometers to over 5 mu m, as well as the inferior resistance to hydrolysis observed for the primary nuclei. Our work fuels the interest in controlling nanofibrillation mechanism during hydrolysis of PLA, opening up possibilities for straightforward nanofiber formation.

  • 124247. Xu, J.
    et al.
    Huan, Yuxiang
    KTH, School of Electrical Engineering and Computer Science (EECS).
    Zheng, L. -R
    Zou, Z.
    A Low-Power Arithmetic Element for Multi-Base Logarithmic Computation on Deep Neural Networks2019In: International System on Chip Conference, IEEE Computer Society , 2019, p. 260-265Conference paper (Refereed)
    Abstract [en]

    Computational complexity and memory intensity are crucial in deep convolutional neural network algorithms for deployment to embedded systems. Recent advances in logarithmic quantization has manifested great potential in reducing the inference cost of neural network models. However, current base-2 logarithmic quantization suffers from performance upper limit and there is few work that studies hardware implementation of other bases. This paper presents a multi-base logarithmic scheme for Deep Neural Networks (DNNs). The performance of Alexnet is studied with respects to different quantization resolutions. Base -\sqrt2 logarithmic quantization is able to raise the ceiling of top-5 classifying accuracy from 69.3% to 75.5% at 5-bit resolution. A segmented logarithmic quantization method that combines both base-2 and base \sqrt2 is then proposed to improve the network top-5 accuracy to 72.3% in 4-bit resolution. The corresponding arithmetic element hardware has been designed, which supports base sqrt2 logarithmic quantization and segmented logarithmic quantization respectively. Evaluated in UMC 65nm process, the proposed arithmetic element operating at 500MHz and 1.2V consumes as low as 120 μW. Compared with 16-bit fixed point multiplier, our design achieves 58.03% smaller in area, with 73.74% energy reduction.

  • 124248. Xu, J.
    et al.
    Luo, P.
    Lu, B.
    Wang, H.
    Wang, X.
    Wu, J.
    Yan, Jinyue
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Chemical Engineering, Energy Processes.
    Energy-water nexus analysis of wastewater treatment plants (WWTPs) in China based on statistical methodologies2018In: CLEANER ENERGY FOR CLEANER CITIES / [ed] Wang, H; Wang, X; Yan, J; Wu, J; Yang, Y; Li, H, Elsevier, 2018, Vol. 152, p. 259-264Conference paper (Refereed)
    Abstract [en]

    Wastewater treatment plants (WWTPs) are considered as energy-intensive facilities. Against the background of stricter policy requirements and discharge standard, thousands of municipal WWTPs are experiencing upgrading and reconstruction in China. However, the accompanying energy consumption cannot be ignored. Based on the statistical analysis of energy consumption and relevant factors from data of more than six thousand WWTPs over China, in this paper we analyzed the most influential factors related to energy consumption, which include treatment technology, wastewater amount, removed pollutants, social and economic characteristics, etc. Furthermore, we set up systematic method of energy performance assessment for WWTPs and explored the potential of energy saving in WWTPs. Results showed that processing capacity, organic pollutant concentration, discharge standard and economic factors have major effects on energy efficiency. Although sludge treatment and disposal normally consume intensive energy, it is possible to recover energy from biomass in the sludge. The results indicate that there is huge potential for energy saving and recovery in WWTPs, and we propose a conceptual roadmap for energy efficiency improving in WWTPs in China.

  • 124249. Xu, J.
    et al.
    Pupurs, A.
    Lindbergh, G.
    KTH, School of Chemical Science and Engineering (CHE).
    Varna, J.
    Multifunctional composites: Modeling intercalation induced stresses in constituents of micro-battery2016In: ECCM 2016 - Proceeding of the 17th European Conference on Composite Materials, European Conference on Composite Materials, ECCM , 2016Conference paper (Refereed)
    Abstract [en]

    A structural battery that simultaneously carries mechanical loads while storing electrical energy offers the potential of significantly reduced total vehicle weight owing to the multifunctionality. Carbon fiber is employed as negative electrode of the battery and also as a composite reinforcement material. It is coated with a solid polymer electrolyte working as an ion conductor and separator whilst transferring mechanical loads. The coated fiber is surrounded by a conductive positive electrode material. This paper demonstrates a methodology for addressing mechanical stresses arising in a conceptualized micro battery cell during electrochemical cycling, caused by time dependent gradients in lithium ion concentration distribution in the carbon fiber. 

  • 124250.
    Xu, Jia Cheng
    KTH, School of Engineering Sciences in Chemistry, Biotechnology and Health (CBH), Biomedical Engineering and Health Systems.
    Evaluation of Thoracic Injury Risk of Heavy Goods Vehicle Occupants during Steering Wheel Rim Impacts to Different Rib Levels2019Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The interior of heavy goods vehicles (HGVs) differs from passenger cars. Both the steering wheel and the occupant are positioned differently in a HGV and increases the risk of steering wheel rim impacts. Such impact scenarios are relatively unexplored compared to passenger car safety studies that are more prevalent within the field of injury biomechanics. The idea with using human body models (HBMs) is to complement current crash test dummies with biomechanical data. Furthermore, the biofidelity of a crash dummy for loading similar to a steering wheel rimimpact is relatively unstudied and especially to different rib levels. Therefore, the aim with this thesis was to evaluate HGV occupant thoracic response between THUMS v4.0 and Hybrid III (H3) during steering wheel rim impacts with respect to different rib levels (level 1-2, 3-4, 6-7, 7-8, 9-10) with regards to ribs, aorta, liver, and spleen.

    To the author’s best knowledge, use of local injury risk functions for thoracic injuries is fairly rare compared to the predominant usage of global injury criteria that mainly predicts the most commonthoracic injury risk, i.e. rib fractures. Therefore, local injury criteria using experimental test datahave been developed for the ribs and the organs. The measured parameters were chest deflectionand steering wheel to thorax contact force on a global level, whilst 1st principal Green-Lagrangestrains was assessed for the rib and the organ injury risk. The material models for the liver and

    the spleen were remodelled using an Ogden material model based on experimental stress-strain data to account for hyperelasticity. Rate-dependency was included by iteration of viscoelastic parameters. The contact modelling of the organs was changed from a sliding contact to a tied contact to minimize unrealistic contact separations during impact.

    The results support previous findings that H3 needs additional instrumentation to accurately

    register chest deflection for rib levels beyond its current range, namely at ribs 1-2, 7-8, and 9-10. For THUMS, the chest deflection were within reasonable values for the applied velocities, but there were no definite injury risk. Fact is, the global injury criteria might overpredict the AIS3 injury risk (rib fractures) for rib level 1-2, 7-8, and 9-10. The rib strains could not be correlated with the measured chest deflections. This was explained by the unique localized loading characterized by pure steering wheel rim impact that mainly affected the sternum and the rib cartilage while minimizing rib deformation. The organ strains indicate some risk of rupture where the spleen deforms the most at rib levels 3-4 and 6-7, and the liver and the aorta at rib levels 6-7 and 7-8.

    This study provides a framework for complementing H3 with THUMS for HGV occupant safety

    with emphasis on the importance of using local injury criteria for functional injury prediction,

    i.e. prediction of injury risk using parameters directly related to rib fracture or organ rupture.

    Local injury criteria are thus a powerful safety assessment tool as it is independent on exterior loading such as airbag, steering wheel hub, or seat belt loading. It was noticed that global injury criteria with very localized impacts such as rim impacts have not been studied and will affect rib fracture risk differently than what has been studied using airbag or seat belt restraints. However, improvements are needed to accurately predict thoracic injury risk at a material level by finding more data for the local injury risk functions.

    Conclusively, it is clear that Hybrid III has insufficient instrumentation and is in need of upgrades to register chest deflections at multiple rib levels. Furthermore, the following are needed: better understanding of global injury criteria specific for HGV occupant safety evaluation, more data for age-dependent (ribs) and rate-dependent (organs) injury risk functions, a tiebreak contact with tangential sliding for better organ kinematics during impacts, and improving the biofidelity of the material models using data from tissue level experiments.

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