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  • 121951.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Compact in-plane channel drop filter design using a single cavity with two degenerate modes in 2D photonic crystal slabs2005In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 13, no 7, p. 2596-2604Article in journal (Refereed)
    Abstract [en]

    A compact in-plane channel drop filter design in 2D hexagonal lattice photonic crystal slabs is presented in this paper. The system consists of two photonic crystal waveguides and a single cavity with two degenerate modes. Both modes are able to confine light strongly in the vertical dimension and prove to couple equally into the waveguides. Three dimensional finite difference time domain simulations show that the quality factor is around 3,000. At resonance, power transferred to the drop waveguide is 78% and only 1.6% remains in the bus waveguide. We also show that by carefully tuning the drop waveguide boundary, light remaining in the bus can be further reduced to below 0.4% and thus the channel isolation is larger than 22dB.

  • 121952.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Coupled mode analysis of in-plane channel drop filters with resonant mirrors2005In: Photonics and Nanostructures-Fundamentals and Applications, ISSN 1569-4410, Vol. 3, no 2-3, p. 84-89Article in journal (Refereed)
    Abstract [en]

    A channel drop filter system that consists of two waveguides and three cavities is studied. One cavity couples with both waveguides, while the other two work as resonant mirrors to reflect the selected channel back into the system. The operation of this configuration is analyzed, using coupled mode theory. The conditions to achieve 100% in-plane channel transfer are derived. A method to suppress the side lobes of reflection and backward drop is also proposed. The direct coupling between the cavities is not required. The analysis is verified by two-dimensional finite difference time domain simulations in 2D hexagonal photonic crystals.

  • 121953.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Fabrication tolerance tests on high-Q microcavities in 2D photonic crystal slabs2005In: Conference on Lasers and Electro-Optics Europe: Technical Digest, 2005Conference paper (Refereed)
  • 121954.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Influence of structural variations on high-Q microcavities in two-dimensional photonic crystal slabs2005In: Optics Letters, ISSN 0146-9592, E-ISSN 1539-4794, Vol. 30, no 13, p. 1713-1715Article in journal (Refereed)
    Abstract [en]

    The influence of some critical structural variations in high-Q microcavities in two-dimensional photonic crystal slabs is investigated. All the cavities studied maintain a high Q in a wide range of structural variations, while the resonant frequencies shift on a relatively large scale when the structural variations are comparable to the physical sizes of the cavities.

  • 121955.
    Zhang, Ziyang
    et al.
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Qiu, Min
    KTH, Superseded Departments, Microelectronics and Information Technology, IMIT.
    Small-volume waveguide-section high Q microcavities in 2D photonic crystal slabs2004In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 12, no 17, p. 3988-3995Article in journal (Refereed)
    Abstract [en]

    A series of microcavities in 2D hexagonal lattice photonic crystal slabs are studied in this paper. The microcavities are small sections of a photonic crystal waveguide. Finite difference time domain simulations show that these cavities preserve high Q modes with similar geometrical parameters and field profile. Effective modal volume is reduced gradually in this series of microcavity modes while maintaining high quality factor. Vertical Q value larger than 106 is obtained for one of these cavity modes with effective modal volume around 5.40 cubic half wavelengths [(lambda/2n(slab))(3)]. Another cavity mode provides even smaller modal volume around 2.30 cubic half wavelengths, with vertical Q value exceeding 10(5).

  • 121956.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Andersson, Ulf
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC. KTH, School of Computer Science and Communication (CSC).
    Tong, Limin
    Department of Optical Engineering, Zhejiang University.
    Subwavelength-diameter Silica Wire for Light In-coupling to Silicon-based Waveguide2007In: Chinese optics letters, ISSN 1671-7694, Vol. 5, no 10, p. 577-579Article in journal (Refereed)
    Abstract [en]

    Coupling between subwavelength-diameter silica wires and silicon-based waveguides is studied using the parallel three-dimensional (3D) finite-different time-domain method. Conventional butt-coupling to a silica-substrated silicon wire waveguide gives above 40% transmission at the wavelength range from 1300 to 1750 nm with good robustness against axial misalignments. Slow light can be generated by counter-directional coupling between a silica wire and a two-dimensional (2D) silicon photonic crystal slab waveguide. Through dispersion-band engineering, 82% transmission is achieved over a coupling distance of 50 lattice constants. The group velocity is estimated as 1/35 of the light speed in vacuum.

  • 121957.
    Zhang, Ziyang
    et al.
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Applied Physics, MAP.
    Qui, Min
    KTH, School of Information and Communication Technology (ICT), Microelectronics and Information Technology, IMIT.
    Coupled-mode analysis of a resonant channel drop filter using waveguides with mirror boundaries2006In: Journal of the Optical Society of America. B, Optical physics, ISSN 0740-3224, E-ISSN 1520-8540, Vol. 23, no 1, p. 104-113Article in journal (Refereed)
    Abstract [en]

    The operation of resonant channel drop filters is analyzed using coupled-mode theory. The resonator is chosen to support a single standing-wave mode, and, in the ideal case, one can realize 100% in-plane channel transfer by properly applying mirror boundaries to the waveguides. The presence of the mirrors causes the resonant frequency to shift, and the system Q factor also changes accordingly. The two variables are related by a closed curve depending on the phase introduced by the reflection and wave propagation between the two ports. When one works on different regions of the curve, the system can be tuned to work at different resonant frequencies with minimum Q-factor variations or vice versa. The mirror can be frequency selective. The same single-mode cavity can be used as a resonant mirror to terminate the waveguide. The combined system is analyzed, and we find the conditions to achieve 100% channel transfer as well as to maintain a simple Lorentzian line shape of the transmission spectra. The analysis is verified by two-dimensional (2D) finite-difference time-domain simulations in 2D hexagonal photonic crystals.

  • 121958.
    Zhang, Zizhu
    KTH, School of Architecture and the Built Environment (ABE), Sustainable development, Environmental science and Engineering, Land and Water Resources Engineering.
    An eco-city indicator system for the city of Changsha.2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    With rapid urban development in China, many cities are still concerned about the quantity of the economy growth while ignoring the quality of the growth; ecological systems face a challenging situation. How to evaluate and guide a sustainable devel-opment is a vitally important question to the government of China. The study was partly performed in cooperation with the Institute of Building Research (IBR), who was entrusted by Changsha government of the Hunan Province. To evaluate the sus-tainability of urban development, a comprehensive indicator system was developed and applied, which was consistent to the policy of the so called "Two oriented socie-ty", which means Resource conservation and Environment friendly society. This pa-per shows a logic methodology to develop an indicator system – through the re-search, from literature review to modern concept; it shows clearly the factors that are important to build a sustainable city.

    The indicator system was derived and compared with other existing systems. The comparison showed that the indicator system we developed for the city is operational and integrated with a consistent hierarchy. Thereafter, the established indicator sys-tem was evaluated using an Analytical Hierarchy Process methodology. Indictors of ecological aspects were evaluated using the data collected, including the Changsha green field map, wetland map and ecological control maps. The indicator system was applied and the result was used as decision support in urban planning for 2020. How-ever, a main limitation lied in data collection: since the data we collected was not completely the data we expected. Besides, the indicator system was developed on the base of the policy called the "Two oriented society",which has its preference and limi-tation itself. Still, in sum, the indicator system we built through the research provided a satisfactory framework to the government to guide the development of the society in a macro scale. It needs future involvement to improve the data collection and standardization.

  • 121959.
    Zhang, Zongyin
    KTH, Superseded Departments, Materials Science and Engineering.
    Processing of Nanostructured WC-Co Powders and Sintered Steels2003Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    Processing of nanostructured WC-Co and W-Co powders,modelling of Fe-Mn-Si alloy, swelling of Fe-Cu alloy, andmechanical properties and sintering of Fe-Mn-Si steels havebeen studied in the present thesis.

    W-Co precursors made by chemical synthesis were used toproduce nanostructured WCCo and W-Co powders by calcination,reduction and carburization. The phase constituents in thecalcined powders depend on temperature and atmospheres. Cobaltcan accelerate the reduction rate of the W-Co precursors as acatalyst, and cobalt influences the formation of intermediatephases during the reduction of the precursors.

    The ratio of carbon monoxide to carbon dioxide controlscarburization process, gives different intermediate phases andcarburization rates. There exist several intermediate phases: W6Co6C, W3Co3C, W2C due to varying carbon monoxide content in thecarburization gases. Nanostructured WC-Co powders with aparticle size of 20-50 nm have been obtained.

    The effect of silicon content on the particle sizedistribution of milled Fe-Mn-Si master alloy powders is muchmore significant than that of manganese content. A finer finalparticle size can be obtained in the alloy powders with highersilicon compositions. Long time milling results in theagglomeration of small particles. The grinding process can bedescribed using classic batch grinding equation based on thepopulation balance model. A swelling model for Fe-Cu alloyssintered at the temperatures above the melting point of copperhas been established based on the penetration mechanism. In themodel, the particle coordination number and heating rate wereused to express the porosity and the thickness of the diffusionlayers between iron and copper particles respectively.

    The effects of sintering temperature and time on theproperties of sintered steels have been studied. Fe-Mn-Simaster alloys made by cast-milling, atomizing, and acombination of atomization and milling have been covered. Themilled, and atomizationmilled alloy steels showed goodmechanical properties with small dimensional change. Transientliquid phase of the Fe-Mn-Si alloys accelerates densification,and offer fast diffusion of alloying elements. The addition ofa small amount of Fe-Mn-Si master alloy to Astaloy 85Mo powdercan lead to high strength with zero dimensional change.

    Key words:Processing; Modelling; Nanostructured powder;WC-Co; W-Co; Calcination; Reduction; Carburization; Particlesize; Sintered steel; Fe-Cu alloy; Swelling; Fe-Mn-Si masteralloy; Mechanical properties; Sintering parameters.

  • 121960.
    Zhang, Zongyin
    KTH, Superseded Departments, Materials Science and Engineering.
    Thermochemical processing of nanostructured W-Co and WC-Co powders2001Licentiate thesis, comprehensive summary (Other scientific)
  • 121961.
    Zhang, Zongyin
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Frisk, K.
    Salwen, A.
    Sandström, Rolf
    KTH, Superseded Departments, Materials Science and Engineering.
    Mechanical properties of Fe-Mo-Mn-Si-C sintered steels2004In: Powder Metallurgy, ISSN 0032-5899, E-ISSN 1743-2901, Vol. 47, no 3, p. 239-246Article in journal (Refereed)
    Abstract [en]

    Four Fe-Mn-Si master alloy powders with the compositions Fe-35%Mn-14%Si, Fe-35%Mn-20%Si, Fe-45%Mn-20%Si and Fe-60%Mn-14%Si were made by the cast milling method, and used to produce Fe-Mo-Mn-Si-C sintered steels. The effects of master alloy composition and sintering atmosphere on the mechanical properties and dimensional change of the sintered steels were studied. The steels were sintered either at 1250 degreesC for 30 min in hydrogen-30% nitrogen or at 1120 degreesC for 30 min in hydrogen and nitrogen-10% hydrogen with different dewpoints. After transient liquid phase sintering, the ultimate tensile strength, yield strength and hardness increase and elongation decreases with increasing contents of manganese and carbon. The dewpoint of sintering atmospheres had little effect on the properties, probably as the addition of manganese and silicon was in the form of a master alloy. The highest tensile strength and smallest dimensional change were obtained in a steel with a composition of Fe-0.85%Mo-1.40% Mn-0-8%Si-0.7%C.

  • 121962.
    Zhang, Zongyin
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Sandström, Rolf
    KTH, Superseded Departments, Materials Science and Engineering.
    Fe-Mn-Si master alloy steel by powder metallurgy processing2004In: Journal of Alloys and Compounds, ISSN 0925-8388, E-ISSN 1873-4669, Vol. 363, no 02-jan, p. 194-202Article in journal (Refereed)
    Abstract [en]

    Fe-Mn-Si master alloy powders were produced by three methods: milling, atomising, and a combination of atomisation and milling. The effects of sintering temperature, time and atmosphere on the properties of sintered steels with these Fe-Mn-Si master alloy powders were studied. The density of the compacts increases with sintering temperature and time. The ultimate tensile strength and hardness increases with sintering temperature and time mainly due to increasing amounts of bainite and martensite after cooling. Elongation is initially raised with sintering temperature and time probably due to improved bonding between powder particles. The compacts with the milled and atomised-milled master alloy showed about the same mechanical properties. On the other hand, the steel with the atomised powder gave lower strength and elongation in both hydrogen and argon-5% hydrogen. Small dimensional changes have been obtained in the steels with milled and atomised-milled Fe-Mn-Si master alloys sintered at 1200degreesC. It was shown that transient liquid phase sintering accelerates the sintering process, which leads to improved mechanical properties.

  • 121963.
    Zhang, Zongyin
    et al.
    KTH, Superseded Departments, Materials Science and Engineering.
    Wahlberg, Sverker
    KTH, Superseded Departments, Materials Science and Engineering.
    Wang, Mingsheng
    KTH, Superseded Departments, Materials Science and Engineering.
    Muhammed, Mamoun
    KTH, Superseded Departments, Materials Science and Engineering.
    Processing of nanostructured WC-Co powder from precursor obtained by co-precipitation1999In: Nanostructured materials, ISSN 0965-9773, E-ISSN 1872-9150, Vol. 12, no 1-4, p. 163-166Article in journal (Refereed)
    Abstract [en]

    The paper reports the processing of a homogenous cobalt tungstate salt synthesised by co-precipitation starting from ammonium paratungstate and cobalt hydroxide. Different processing parameters such as temperatures and times of reduction and carburization and the composition of the carburization gas were studied. Powders of W and Co were obtained after the reduction of the precursor at 600 'C, 650 'C and 700 'C. The specific surface area of W-Co powders increased with decreasing reduction temperature. The carburization was carried out at 700 'C for 3 hours in different CO/CO2 - mixtures. The extent of the reaction was found to depend on the CO/CO2 - ratio. A nanophase WC-Co powder agglomerated at the micrometer scale was obtained after carburization in a 90%CO/10%CO2 gas-mixture.

  • 121964.
    Zhang, Zuotai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Synthesis and Characterization of MgA1ON-BN refractories2006Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In order to meet the need of metallurgical industry in the world, a new MgAlON-BN composite which can be used for example in special refractory nozzles, tubes and break rings for the continuous casting of steel was studied in the present thesis. The aim was to understand the mechanism of synthesis and their physicochemical properties during the application. Thus, the thermodynamic properties, synthesis process, mechanical properties, thermal shock behaviour, thermal diffusivity/conductivity as well as corrosion resistance to molten iron containing oxygen and molten slag of MgAlON and MgAlON-BN composites have been investigated.

    The Gibbs energy of formation of MgAlON was estimated using the method proposed by Kaufman. The phase stability diagram of Mg-Al-O-N-B was investigated, and consequently the synthesis parameters were determined. MgAlON and MgAlON-BN composites were fabricated by hot-pressing method. The composites obtained this way were characterized by XRD, SEM, TEM and HREM analyses. A Matrix-flushing method was employed in the quantitative XRD analysis for the multi-component samples to understand the mechanism of synthesis.

    The relationship between mechanical properties and microstructure of the composites was investigated. The experimental results indicated that BN addition has significant influence on the mechanical properties of the composites. These can be explained by the fact that BN has low Young’s modulus, density and non-reactive nature as well as considerable anisotropy of many properties such as thermal expansion, thermal diffusivity/conductivity. Thus, the addition of BN in MgAlON is likely to lead to the presence of microcracks caused by the mismatch of thermal expansion coefficient. The microcracks result in the enhancement of the strength at elevated temperature and thermal shock durability of the composites.

    Effective thermal conductivities were evaluated from the present experimental results of thermal diffusivities, heat capacity and density. A model suitable for present composites has been derived based on Luo’s model. The predicted lines calculated by the model were in good agreement with experimental results.

    The reactions between the composites and molten iron as well as the slag were investigated by ‘‘finger’’ experiments and sessile drop experiments. Both experimental results indicated that the BN addition has positive influence on the corrosion resistance. These are attributed to the excellent corrosion resistance of BN to molten iron and slag, such as the higher contact angle between BN substrate and liquid iron and molten slag compared with that obtained for pure MgAlON.

  • 121965.
    Zhang, Zuotai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wenchao
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Thermal diffusivity/conductivity of MgAlON-BN Composites2006In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 4, p. 615-621Article in journal (Refereed)
    Abstract [en]

    Thermal diffusivity and heat capacity of MgAlON and MgAlON-BN composites were measured in the temperature range of 25 degrees C to 1300 degrees C using a laser flash technique and a differential scanning calorimeter (DSC) technique, respectively. Based on these measurements, effective thermal conductivity of the composites was calculated using the values measured earlier in the same substance. The experimental effective thermal conductivity results of the composites containing different BN contents were found to show the similar trend, which decreased rapidly with increasing temperature below 900 degrees C followed by a slow decrease with further increasing temperature. This can be explained by the fact that thermal conduction in both components, MgAlON and BN, was dominated by phonons. The phonon mean free path decreased with increasing temperature, limited by the characteristic length between two neighboring atoms. The BN addition has significant influence on the effective thermal conductivity. The effective thermal conductivity of the composites containing BN exhibited a small degree of anisotropy with respect to preferred orientation of the BN phase. The degree of anisotropy of the composites increased with increasing BN content, which is particularly pronounced at the higher BN additions. An equation suitable for the present composites has been derived based on Luo's model. The model was slightly modified in the present article. The predicted values calculated by the model were in good agreement with experimental results.

  • 121966.
    Zhang, Zuotai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Matsushita, Taishi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wenchao
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Investigation of Wetting Characteristics of Liquid Iron on Dense MgAlON-based Ceramics by X-Ray Sessile Drop Technique2006In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 37, no 3, p. 421-429Article in journal (Refereed)
    Abstract [en]

    The wetting characteristics of liquid iron on dense MoAlON-based composite ceramics were investigated using X-ray sessile drop technique. The contact angles were measured on substrates of different composites as functions of temperature and varying partial pressures of oxygen. The results with pure argon gas showed that contact angles kept almost constant in the temperature range 1823 to 1873 K. The contact angle was found to show a slight increase with increasing boron nitride (BN) content in MgAlON-BN composites. These are attributed to the higher contact angle between BN substrate and liquid iron drop compared with that obtained for MgAlON substrate. When the CO-CO2-Ar gas mixtures were introduced into the system, the contact angle showed an initial quick decrease followed by a slow decrease and then a period of nearly constant contact angle at a given temperature corresponding to the steady-state condition. Even in this case, BN seemed to cause an increase in the equilibrium contact angle. The equilibrium contact angle was found to decrease with increasing temperature. XRD results indicated that the substrate was oxidized and the oxidation products combined with FeO formed by the oxidation of the iron drop to form FeAl2O4 and Mg1-xFexO. These were likely to form a ternary FeO-Al2O3-MgO slag or a quaternary slag by combining with B2O3. An interesting observation is that the iron drop moved away from the original site, probably due to the Marangoni effect.

  • 121967.
    Zhang, Zuotai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Matsushita, Taishi
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wenchao
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Reactions between MgAlON-BN composites and CaO-SiO2-Al2O3-MgO-''FeO'' slag2007In: Metallurgical and materials transactions. B, process metallurgy and materials processing science, ISSN 1073-5615, E-ISSN 1543-1916, Vol. 38, no 2, p. 231-241Article in journal (Refereed)
    Abstract [en]

    The reactions between MgAlON and MgAlON-BN composites and synthetic CaO-SiO2-Al2O3MgO-"FeO" slag at different temperatures were investigated under stagnant condition using the "finger" experiment as well as X-ray sessile drop methods. The corrosion rate was denoted by the radius difference between the initial radius of the specimen rod and the unreacted core at definite time intervals. The experimental results showed that the radius difference is linear with the square root of time. This indicated that the diffusion of ions in the slag through the product layer is the rate-determining step. One product layer was observed between the unreacted core and slag. X-ray images showed that gas bubbles were generated during the slag penetration. The slag penetration process depends strongly on the temperature. The apparent activation energy was evaluated to be 376.4 kJ/mol. The FeO addition into slag increased the slag corrosion rate. This is most probably due to the decrease of the slag viscosity, because the Fe+2 generally behaves as a network breaker. Furthermore, MgAlON and boron nitride (BN) can be oxidized by FeO, which also increased the slag corrosion rate. The slag corrosion rate decreased with increasing BN content. This can be explained by the fact that the grain boundary interfacial energy decreases with the increase of BN content and nonwetting of BN by molten slag compared to pure MgAlON.

  • 121968.
    Zhang, Zuotai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Seetharaman, Seshadri
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wenchao
    Wang, Xidong
    Synthesis and characterization of MgAlON-BN composites2007In: INTERNATIONAL JOURNAL OF MATERIALS RESEARCH, ISSN 1862-5282, Vol. 98, no 1, p. 64-71Article in journal (Refereed)
    Abstract [en]

    In the present paper the Gibbs energy of formation of MgAlON was evaluated, and on this basis the phase stability diagram of Mg-Al-O-N-B was established. Dense magnesium aluminium oxynitride-boron nitride (MgAlON-BN) composites with 0-30 vol.% BN were synthesized by hot pressing in the temperature range 1750-1850 degrees C in the phase stability region. The phase compositions of the composites analyzed by X-ray diffraction indicated that the main phases were MgAlON and h-BN and no impurities were found. The microstructures of the composites analyzed by transmission electron microscopy, scanning electron microscopy, and high-resolution electron microscopy showed that the MgAlON did not react with BN, and the latter was distributed on the grain boundary of MgAlON homogeneously. Excessive BN (> 20 vol.%) resulted in a discontinuous microstructure for MgAlON. A matrix-flushing method was employed in the quantitative X-ray diffraction analysis for the multi-component MgAlON-BN composites. The results showed that the relative MgAlON content decreased in the process of sintering MgAlON-BN composites. Thermodynamic analysis showed that some Al2O3, AlN, and MgO escaped under the reaction conditions. The lattice parameters of MgAlON in the composites have also been evaluated.

  • 121969.
    Zhang, Zuotai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Teng, Li-Dong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wenchao
    Mechanical Properties and Microstructures of hot-pressed MgAlON-BN Composites2007In: Journal of the European Ceramic Society, ISSN 0955-2219, E-ISSN 1873-619X, Vol. 27, no 1, p. 319-326Article in journal (Refereed)
    Abstract [en]

    The relationship between the mechanical properties and microstructure of hot-pressed MgAlON-BN composite materials was investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution electron microscopy (HREM) and X-ray diffraction (XRD) techniques. The phase compositions of hot-pressed samples prepared from starting mixtures of Al2O3, AlN, MgO and h-BN consisted of MgAlON phases as a matrix and BN phases as the second phase. The density, bending strength at room temperature, fracture toughness and Vickers hardness were measured. The results indicated that the density, strength and Vickers hardness decrease with increasing h-BN content due to the non-reactive nature and layered structure of h-BN. The fracture toughness, however increased with increasing h-BN addition, reaching a maximum of 3.64 MPa m(0.5); it decreased with further increase of BN content. The increase of fracture toughness was attributed to the presence of microcracks and the decrease was considered to be the discontinuous microstructure of the MgAlON phases. Temperature dependence of bending strength remained constant at low temperature, followed by an increase at 800 degrees C and then, dropped quickly. The increase in the bending strength of the composite was attributed to the decrease of residual stress and to the interwoven microstructure of the composites which prevented grain boundary slip and reduced the attenuation rate of high temperature strength. The machinability of the composites was examined. The results indicate that the composite materials with BN content more than 15 vol.% exhibit excellent machinability and could be drilled using conventional hard metal alloy drills

  • 121970.
    Zhang, Zuotai
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Teng, Li-Dong
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Li, Wenchao
    Thermal shock Behavior of MgAlON and MgAlON-BN CompositesArticle in journal (Refereed)
  • 121971.
    Zhao, Amanda Yushu
    KTH, Superseded Departments, Electric Power Systems.
    Effektförluster orsakade av övertoner1998Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
  • 121972.
    Zhao, Bokang
    KTH, School of Industrial Engineering and Management (ITM), Industrial Economics and Management (Dept.).
    Innovation Capability in SMEs2012Independent thesis Advanced level (degree of Master (One Year)), 10 credits / 15 HE creditsStudent thesis
  • 121973.
    Zhao, Chengyuan
    KTH, School of Architecture and the Built Environment (ABE), Land and Water Resources Engineering (moved 20130630), Water, Sewage and Waste technology.
    Effect of Temperature on Biogas Production in Anaerobic Treatment of Domestic Wastewater UASB System in Hammarby Sjöstadsverk.2011Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The upflow anaerobic sludge blanket (UASB) reactor is widely used around the world to treat variety of domestic andindustrial wastewater with three main advantages: production of biogas as renewable energy, no need of support structure for development of microorganisms and high rate treatment efficiency with low rate of biomass production.

    This study evaluates the effect of temperature on biogas production and CODtotal removal in Line 4-UASB system treating domestic wastewater in Hammarby Sjöstadsverk. Eight parameters were examined including the following: Influent and effluent temperature, pH, influent CODtotal, influent rate, effluent CODtotal, volatile fatty acids, biogas production rate and methane concentration. There are eight set temperature and each is stabilized for seven days. The biogas production analysis is focus on UASB 1. Temperature rising from 19°C to 35°C achieves a general benefit result in methane yield rate and CODtotal removal efficiency. The best methane yield rate and CODtotal removal rate are 0.167l/gCODtotal and 56.84% respectively at highest working temperature 33.4°C with OLR 3.072gCODtotal/(l*day) and HRT 4.2h.

  • 121974. Zhao, Chunyan
    et al.
    Matthews, Jason
    Tujague, Michel
    Wan, Jinghong
    KTH, School of Biotechnology (BIO), Proteomics.
    Ström, Anders
    Toresson, Gudrun
    Lam, Eric W-F.
    Cheng, Guojun
    Gustafsson, Jan-Åke
    Dahlman-Wright, Karin
    Estrogen receptor beta 2 negatively regulates the transactivation of estrogen receptor alpha in human breast cancer cells2007In: Cancer Research, ISSN 0008-5472, E-ISSN 1538-7445, Vol. 67, no 8, p. 3955-3962Article in journal (Refereed)
    Abstract [en]

    Estrogens, by binding to and activating two estrogen receptors (ER alpha and ER beta), are critically involved in the development of the mammary gland and breast cancer. An isoform of ER beta, ER beta 2 (also called ER beta cx), with an altered COOH-terminal region, is coexpressed with ER alpha. in many human breast cancers. In this study, we generated a stable cell line from MCF7 breast cancer cells expressing an inducible version of ER beta 2, along with endogenous ER alpha, and examined the effects of ER beta 2 on the ER alpha protein levels and function. We showed that ER beta 2 inhibited ER alpha-mediated transactivation via estrogen response element and activator protein-1 sites of reporter constructs as well as the endogenous genes pS2 and MMP-1. Chromatin immunoprecipitation assays revealed that ER beta 2 expression caused a significant reduction in the recruitment of ER alpha to both the pS2 and MMP-1 promoters. Furthermore, ER beta 2 expression induced proteasome-dependent degradation of ER alpha. The inhibitory effects of ER beta 2 on ER alpha activity were further confirmed in HEK293 cells that lack functional endogenous ER alpha. We also showed that ER beta 2 can interact with ER alpha both in vitro and in mammalian cells' which is compatible with a model where ER beta 2/ER alpha heterodimers are targeted to the proteasome. Finally, in human breast cancer samples, we observed that expression of ER beta 2 significantly correlated with ER alpha-negative phenotype. Our data suggest that ER beta 2 could influence ER alpha-mediated effects relevant for breast cancer development, including hormone responsiveness.

  • 121975. Zhao, Chunyan
    et al.
    Qiao, Yichun
    Jonsson, Philip
    Wang, Jian
    Xu, Li
    Rouhi, Pegah
    Sinha, Indranil
    Cao, Yihai
    Williams, Cecilia
    Dahlman-Wright, Karin
    Genome-wide profiling of AP-1-regulated transcription provides insights into the invasiveness of triple-negative breast cancer.2014In: Cancer Research, ISSN 0008-5472, E-ISSN 1538-7445, Vol. 74, no 14, p. 3983-3994Article in journal (Refereed)
    Abstract [en]

    Triple-negative breast cancer (TNBC) is an aggressive clinical subtype accounting for up to 20% of all breast cancers, but its malignant determinants remain largely undefined. Here, we show that in TNBC the overexpression of Fra-1, a component of the transcription factor AP-1, offers prognostic potential. Fra-1 depletion or its heterodimeric partner c-Jun inhibits the proliferative and invasive phenotypes of TNBC cells in vitro. Similarly, RNAi-mediated attenuation of Fra-1 or c-Jun reduced cellular invasion in vivo in a zebrafish tumor xenograft model. Exploring the AP-1 cistrome and the AP-1-regulated transcriptome, we obtained insights into the transcriptional regulatory networks of AP-1 in TNBC cells. Among the direct targets identified for Fra-1/c-Jun involved in proliferation, adhesion, and cell-cell contact, we found that AP-1 repressed the expression of E-cadherin by transcriptional upregulation of ZEB2 to stimulate cell invasion. Overall, this work illuminates the pathways through which TNBC cells acquire invasive and proliferative properties.

  • 121976. Zhao, D.
    et al.
    Chuwongin, S.
    Yang, H.
    Seo, J. -H
    Berggren, Jesper
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Ma, Z.
    Zhou, W.
    Transfer printed photonic crystal nanomembrane lasers on silicon with low optical pumping threshold2012In: Group IV Photonics (GFP), 2012 IEEE 9th International Conference on, IEEE , 2012, p. 632418-Conference paper (Refereed)
    Abstract [en]

    We report here an ultra-compact membrane lasers on silicon with very low pumping threshold. The laser consists of InGaAsP QW active region sandwiched in between two single-layer Fano resonance silicon photonic crystal nanomembrane reflectors, based on transfer printing technique.

  • 121977. Zhao, D.
    et al.
    Liu, S.
    Yang, H.
    Ma, Z.
    Reuterskiöld-Hedlund, C.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhou, W.
    Printed Large-Area Single-Mode Photonic Crystal Bandedge Surface-Emitting Lasers on Silicon2016In: Scientific Reports, ISSN 2045-2322, E-ISSN 2045-2322, Vol. 6Article in journal (Refereed)
    Abstract [en]

    We report here an optically pumped hybrid III-V/Si photoic crystal surface emitting laser (PCSEL), consisting of a heterogeneously integrated III-V InGaAsP quantum well heterostructure gain medium, printed on a patterned defect-free Si photonic crystal (PC) bandedge cavity. Single mode lasing was achieved for a large area laser, with a side-mode suppression ratio of 28 dB, for lasing operation temperature ∼200 K. Two types of lasers were demonstrated operating at different temperatures. Detailed modal analysis reveals the lasing mode matches with the estimated lasing gain threshold conditions. Our demonstration promises a hybrid laser sources on Si towards three-dimensional (3D) integrated Si photonics for on-chip wavelength-division multiplex (3D WDM) systems for a wide range of volume photonic/electronic applications in computing, communication, sensing, imaging, etc.

  • 121978.
    Zhao, David Y
    et al.
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Kleijn, W Bastiaan
    KTH, Superseded Departments, Signals, Sensors and Systems.
    Multiple-description vector quantization using translated lattices with local optimization2004In: GLOBECOM: IEEE Global Telecommunications Conference, NEW YORK: IEEE , 2004, p. 41-45Conference paper (Refereed)
    Abstract [en]

    Multiple-description coding is a joint source- and channel coding technique suitable for real-time multimedia transmission over erasure channels. This work improves the previous methods of multiple-description vector quantization using lattice structured codebooks by introducing translated lattices in the single-description codebooks. The quantizer can easily adapt to the current channel condition, using the locally optimized combined-description codebooks, assuming that channel statistics are available at the encoder. Compared to previous methods, the central distortion is greatly reduced for noisy channels, without a significant effect on complexity.

  • 121979.
    Zhao, David Y.
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Samuelsson, Jonas
    Nilsson, Mattias
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Gmm-based entropy-constrained vector quantization2007In: 2007 IEEE International Conference on Acoustics, Speech, and Signal Processing, Vol IV, Pts 1-3, 2007, p. 1097-1100Conference paper (Refereed)
    Abstract [en]

    In this paper, we present a scalable entropy-constrained vector quantizer based on Gaussian mixture models (GMMs), lattice quantization, and arithmetic coding. We assume that the source has a probability density function of a GMM. The scheme is based on a mixture component classifier, the Karhunen Loeve transform of the component, followed by a lattice quantization. The scalar elements of the quantized vector are entropy coded using a specially designed arithmetic coder. The proposed scheme has a computational complexity that is independent of rate, and quadratic with respect to vector dimension. The design is flexible and allows for adjusting the desired target rate on-the-fly. We evaluated the performance of the proposed scheme on speech-derived source vectors. It was demonstrated that the proposed scheme outperforms a fixed-rate GMM based vector quantizer, and performs closely to the theoretical optimum.

  • 121980.
    Zhao, David Yuheng
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Model Based Speech Enhancement and Coding2007Doctoral thesis, comprehensive summary (Other scientific)
    Abstract [en]

    In mobile speech communication, adverse conditions, such as noisy acoustic environments and unreliable network connections, may severely degrade the intelligibility and natural- ness of the received speech quality, and increase the listening effort. This thesis focuses on countermeasures based on statistical signal processing techniques. The main body of the thesis consists of three research articles, targeting two specific problems: speech enhancement for noise reduction and flexible source coder design for unreliable networks.

    Papers A and B consider speech enhancement for noise reduction. New schemes based on an extension to the auto-regressive (AR) hidden Markov model (HMM) for speech and noise are proposed. Stochastic models for speech and noise gains (excitation variance from an AR model) are integrated into the HMM framework in order to improve the modeling of energy variation. The extended model is referred to as a stochastic-gain hidden Markov model (SG-HMM). The speech gain describes the energy variations of the speech phones, typically due to differences in pronunciation and/or different vocalizations of individual speakers. The noise gain improves the tracking of the time-varying energy of non-stationary noise, e.g., due to movement of the noise source. In Paper A, it is assumed that prior knowledge on the noise environment is available, so that a pre-trained noise model is used. In Paper B, the noise model is adaptive and the model parameters are estimated on-line from the noisy observations using a recursive estimation algorithm. Based on the speech and noise models, a novel Bayesian estimator of the clean speech is developed in Paper A, and an estimator of the noise power spectral density (PSD) in Paper B. It is demonstrated that the proposed schemes achieve more accurate models of speech and noise than traditional techniques, and as part of a speech enhancement system provide improved speech quality, particularly for non-stationary noise sources.

    In Paper C, a flexible entropy-constrained vector quantization scheme based on Gaus- sian mixture model (GMM), lattice quantization, and arithmetic coding is proposed. The method allows for changing the average rate in real-time, and facilitates adaptation to the currently available bandwidth of the network. A practical solution to the classical issue of indexing and entropy-coding the quantized code vectors is given. The proposed scheme has a computational complexity that is independent of rate, and quadratic with respect to vector dimension. Hence, the scheme can be applied to the quantization of source vectors in a high dimensional space. The theoretical performance of the scheme is analyzed under a high-rate assumption. It is shown that, at high rate, the scheme approaches the theoretically optimal performance, if the mixture components are located far apart. The practical performance of the scheme is confirmed through simulations on both synthetic and speech-derived source vectors.

  • 121981.
    Zhao, David Yuheng
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Kleijn, Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    HMM-based gain-modeling for enhancement of speech in noise2007In: IEEE transactions on speech and audio processing, ISSN 1063-6676, E-ISSN 1558-2353, Vol. 15, no 3, p. 882-892Article in journal (Refereed)
    Abstract [en]

    Accurate modeling and estimation of speech and noise gains facilitate good performance of speech. enhancement methods using data-driven prior models. In this paper, we propose a hidden Markov model (HMM)-based speech enhancement method using explicit gain modeling. Through the introduction of stochastic gain variables, energy variation in both speech and noise is explicitly modeled in a unified framework. The speech gain models the energy variations of the speech phones, typically due to differences in pronunciation and/or different vocalizations of individual speakers. The noise gain helps to improve the tracking of the time-varying energy of nonstationary noise. The expectationmaximization (EM) algorithm is used to perform offline estimation of the time-invariant model parameters. The time-varying model'parameters are estimated online using the recursive EM algorithm. The. proposed gain modeling techniques are applied to a novel Bayesian speech estimator, and the performance of the proposed enhancement method is evaluated through objective and subjective tests. The experimental results confirm the advantage of explicit gain modeling, particularly for nonstationary noise sources.

  • 121982.
    Zhao, David Yuheng
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Kleijn, Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Ypma, Alexander
    GN ReSound AS, Algorithm R&D, Eindhoven.
    de Vries, Bert
    GN ReSound AS, Algorithm R&D, Eindhoven.
    Online noise estimation using stochastic-gain HMM for speech enhancement2008In: IEEE transactions on speech and audio processing, ISSN 1063-6676, E-ISSN 1558-2353, Vol. 16, no 4, p. 835-846Article in journal (Refereed)
    Abstract [en]

    We propose a noise estimation algorithm for single-channel noise suppression in dynamic noisy environments. A stochastic-gain hidden Markov model (SG-HMM) is used to model the statistics of nonstationary noise with time-varying energy. The noise model is adaptive and the model parameters are estimated online from noisy observations using a recursive estimation algorithm. The parameter estimation is derived for the maximum-likelihood criterion and the algorithm is based on the recursive expectation maximization (EM) framework. The proposed method facilitates continuous adaptation to changes of both noise spectral shapes and noise energy levels, e.g., due to movement of the noise source. Using the estimated noise model, we also develop an estimator of the noise power spectral density (PSD) based on recursive averaging of estimated noise sample spectra. We demonstrate that the proposed scheme achieves more accurate estimates of the noise model and noise PSD, and as part of a speech enhancement system facilitates a lower level of residual noise.

  • 121983.
    Zhao, David Yuheng
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    HMM-based speech enhancement using explicit gain modeling2006In: 2006 IEEE International Conference on Acoustics, Speech and Signal Processing, 2006, p. 161-164Conference paper (Refereed)
    Abstract [en]

    We propose a hidden Markov model (HMM) based speech enhancement method using explicit modeling of speech and noise gains. The gains are considered to be stochastic variables in an HMM framework. The speech gain models the energy variations of speech phones, typically due to differences in pronunciation and/or different vocalizations of individual speakers. The noise gain helps to improve the tracking of the time-varying energy of non-stationary noise. The time-varying parameters of the gain models are estimated on-line using the recursive expectation maximization (EM) algorithm. The performance of the proposed enhancement system is evaluated through both objective and subjective tests. The experimental results confirm the advantage of explicit gain modeling, particularly for non-stationary noise sources.

  • 121984.
    Zhao, David Yuheng
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Kleijn, W. Bastiaan
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    On noise gain estimation for HMM-based speech enhancement2005In: 9th European Conference on Speech Communication and Technology, 2005, p. 2113-2116Conference paper (Refereed)
    Abstract [en]

    To address the variation of noise level in non-stationary noise signals, we study the noise gain estimation for speech enhancement using hidden Markov models (HMM). We consider the noise gain as a stochastic process and we approximate the probability density function (PDF) to be log-normal distributed. The PDF parameters are estimated for every signal block using the past noisy signal blocks. The approximated PDF is then used in a Bayesian speech estimator minimizing the Bayes risk for a novel cost function, that allows for an adjustable level of residual noise. As a more computationally efficient alternative, we also derive the maximum likelihood (ML) estimator, assuming the noise gain to be a deterministic parameter. The performance of the proposed gain-adaptive methods are evaluated and compared to two reference methods. The experimental results show significant improvement under noise conditions with time-varying noise energy.

  • 121985.
    Zhao, David Yuheng
    et al.
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    Samuelsson, Jonas
    Dolby Labs, Stockholm.
    Nilsson, Mattias
    KTH, School of Electrical Engineering (EES), Sound and Image Processing.
    On entropy-constrained vector quantization using gaussian mixture models2008In: IEEE Transactions on Communications, ISSN 0090-6778, E-ISSN 1558-0857, Vol. 56, no 12, p. 2094-2104Article in journal (Refereed)
    Abstract [en]

    A flexible and low-complexity entropy-constrained vector quantizer (ECVQ) scheme based on Gaussian mixture models (GMMs), lattice quantization, and arithmetic coding is presented. The source is assumed to have a probability density function of a GMM. An input vector is first classified to one of the mixture components, and the Karhunen-Loeve transform of the selected mixture component is applied to the vector, followed by quantization using a lattice structured codebook. Finally, the scalar elements of the quantized vector are entropy coded sequentially using a specially designed arithmetic coder. The computational complexity of the proposed scheme is low, and independent of the coding rate in both the encoder and the decoder. Therefore, the proposed scheme serves as a lower complexity alternative to the GMM based ECVQ proposed by Gardner, Subramaniam and Rao [1]. The performance of the proposed scheme is analyzed under a high-rate assumption, and quantified for a given GMM. The practical performance of the scheme was evaluated through simulations on both synthetic and speech line spectral frequency (LSF) vectors. For LSF quantization, the proposed scheme has a comparable performance to [1] at rates relevant for speech coding (20-28 bits per vector) with lower computational complexity.

  • 121986. Zhao, Deyin
    et al.
    Liu, Shihchia
    Yang, Hongjun
    Ma, Zhenqiang
    Reuterskiöld-Hedlund, Carl
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Hammar, Mattias
    KTH, School of Information and Communication Technology (ICT), Integrated Devices and Circuits.
    Zhou, Weidong
    Design and Characterization of Photonic Crystal Bandedge Surface-emitting Lasers on Silicon2015In: 2015 PHOTONICS CONFERENCE (IPC), IEEE conference proceedings, 2015Conference paper (Refereed)
    Abstract [en]

    We report the detailed design and experimental realization of single mode photonic crystal bandedge surface-emitting lasers on silicon based on a transfer process. By improving the coupling efficiency, the single mode operation regime can be shifted to higher temperatures.

  • 121987. Zhao, Ding
    et al.
    Gong, Hanmo
    Yang, Yuanqing
    Li, Qiang
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Realization of an extraordinary transmission window for a seamless Ag film based on metal-insulator-metal structures2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 102, no 20, p. 201109-Article in journal (Refereed)
    Abstract [en]

    A polarization-sensitive, wide-angle operating antireflection coating based on a metal-insulator-metal structure is investigated. In both visible and near-infrared regions, it dramatically reduces the reflection and enhances the transmission through a seamless Ag film near a specifically designed frequency due to the surface plasmon resonance. By achieving above 70% transmission through a 20 nm-thickness Ag film theoretically, this antireflection coating is able to open an extraordinary transmission window for a metallic layer without any slits or holes.

  • 121988. Zhao, Ding
    et al.
    Meng, Lijun
    Gong, Hanmo
    Chen, Xingxing
    Chen, Yiting
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Yan, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Li, Qiang
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Ultra-narrow-band light dissipation by a stack of lamellar silver and alumina2014In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 104, no 22, p. 221107-Article in journal (Refereed)
    Abstract [en]

    An ultra-narrow band absorber consisting of continuous silver and alumina films is investigated. Owing to Fabry-Perot resonance and silver's inherent loss, an ultra-narrow spectral range of light can be entirely trapped in the structure. By varying thicknesses of metallic and dielectric films, absorption peak shifts in visible and near-infrared regions. When two such metal-insulator-metal stacks are cascaded, experimental results show that an ultra-narrow absorption bandwidth of 7 nm is achieved, though theoretical results give that of 2 nm. Features of high-efficiency and ultra-narrow band absorption have huge potential in optical filtering, thermal emitter design, etc.

  • 121989. Zhao, Feng
    et al.
    Johnsson, Lennart
    KTH, School of Computer Science and Communication (CSC), Centres, Centre for High Performance Computing, PDC.
    The Parallel Multipole Method on the Connection Machine1991In: SIAM Journal on Scientific and Statistical Computing, Vol. 12, no 6, p. 1420-1437Article in journal (Refereed)
    Abstract [en]

    This paper reports on a fast implementation of the three-dimensional nonadaptive Parallel Multipole Method (PMM) on the Connection Machine system model CM-2. The data interactions within the decomposition tree are modeled by a hierarchy of three-dimensional grids forming a pyramid in which parent nodes have degree eight- The base of the pyramid is embedded in the Connection Machine as a three-dimensional grid. The standard grid embedding feature is used. For 10 or more particles per processor the communication time is insignificant. The evaluation of the potential field for a system with 128k particles takes 5 seconds, and a system of a million particles about 3 minutes. The maximum number of particles that can be represented in 2G bytes of primary storage is approximately 50 million. The execution rate of this implementation of the PMM is at about 1.7 Gflops/sec for a particle-processor-ratio of 10 or greater. A further speed improvement is possible by an improved use of the memory hierarchy associated with each floating-point unit in the system.

  • 121990. Zhao, G.
    et al.
    Imran, M. A.
    Pang, Zhibo
    KTH, School of Electrical Engineering and Computer Science (EECS), Information Science and Engineering.
    Chen, Z.
    Li, L.
    Toward Real-Time Control in Future Wireless Networks: Communication-Control Co-Design2019In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 57, no 2, p. 138-144, article id 8558500Article in journal (Refereed)
    Abstract [en]

    Wireless networks are undergoing a transition from connecting people to connecting things, which will allow human interaction with the physical world in a real-time fashion, for example, Tactile Internet, industrial automation, self-driving vehicles, and remote surgery. Therefore, future wireless networks need to support real-time control since it is the essential function enabling such emerging applications. In this article, some fundamental design capabilities needed to realize real-time control in future wireless networks are discussed, with primary emphasis given to communication-control because both communication and control systems have strong dynamics and interdependencies, and they tightly interact with each other. A case study is provided to demonstrate the necessity of such co-design.

  • 121991. Zhao, Guang-Jiu
    et al.
    Chen, Rui-Kui
    Sun, Meng-Tao
    Liu, Jian-Yong
    Li, Guang-Yue
    Gao, Yun-Ling
    Han, Ke-Li
    Yang, Xi-Chuan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Photoinduced intramolecular charge transfer and S-2 fluorescence in thiophene-pi-conjugated donor-acceptor systems: Experimental and TDDFT studies2008In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 14, no 23, p. 6935-6947Article in journal (Refereed)
    Abstract [en]

    Experimental and theoretical methods were used to study newly synthesized thiophene-pi-cojugated donor-acceptor compounds, which were found to exhibit efficient intramolecular charge-transfer emission in polar solvents with relatively large Stokes shifts and strong solvatochromism. To gain insight into the solvatochromic behavior of these compounds, the dependence of the spectra on solvent polarity was studied on the basis of Lippert-Mataga models. We found that intramolecular charge transfer in these donor-acceptor systems is significantly dependent on the electron-with-drawing substituents at the thienyl 2-position. The dependence of the absorption and emission spectra of these compounds in methanol on the concentration of trifluoroacetic acid was used to confirm intramolecular charge-tranfer emission. Moreover, the calculated absorption and emission energies, which are in accordance with the experimental values, suggested that fluorescence can be emitted from different geometric confirmations. In addition, a novel S-2 fluorescence phenomenon for some of these compounds was also be observed. The fluorescence excitation spectra were used to confirm the S-2 fluorescence. We demonstrate that S-2 fluorescence can be explained by the calculated energy gap between the S-2 and S-1 states of these molecules. Furthermore, nonlinear optical behavior of the thiophene-pi-conjugated compound with diethylcyanomethylphosphonate substituents was predicted in theory.

  • 121992.
    Zhao, Guanyi
    KTH, School of Architecture and the Built Environment (ABE), Urban Planning and Environment, Geodesy and Satellite Positioning.
    Fusion of Ladybug3 omnidirectional camera and Velodyne Lidar2015Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    The advent of autonomous vehicles expedites the revolution of car industry. Volvo Car Corporation has an ambition of developing the next generation of autonomous vehicle. In the Volvo Car Corporation, Active Safety CAE group, enthusiastic engineers have initiated a series of relevant research to enhance the safety function for autonomous vehicle and this thesis work is also implemented at Active Safety CAE with their support.   

    Perception of vehicle plays a pivotal role in autonomous driving, therefore an idea of improving vision by fusing two different types of data from Velodyne HDL-64E S3 High Definition LiDAR Sensor and Ladybug3 camera respectively, is proposed.

     This report presents the whole process of fusion of point clouds and image data. An experiment is implemented for collecting and synchronizing multi-sensor data streams by building a platform which supports the mounting of Velodyne, Ladybug 3 and their accessories, as well as the connection to GPS unit, laptop. Related software/programming environment for recording, synchronizing and storing data will also be mentioned.

    Synchronization is mainly achieved by matching timestamps between different datasets. Creating log files for timestamps is the primary task in synchronization.

    External Calibration between Velodyne and Ladybug3 camera for matching two different datasets correctly is the focus of this report. In the project, we will develop a semi-automatic calibration method with very little human intervention using a checkerboard for acquiring a small set of feature points from laser point cloud and image feature correspondences. Based on these correspondences, the displacement is computed. Using the computed result, the laser points are back-projected into the image. If the original and back-projected images are sufficiently consistent, then the transformation parameters can be accepted. Displacement between camera and laser scanner are estimated through two separate steps: first, we will estimate the pose for the checkerboard in image and get its depth information in camera coordinate system; and then a transformation relation between the camera and the laser scanner will be computed within three dimensional space. 

    Fusion of datasets will finally be done by combing color information from image and range information from point cloud together. Other applications related to data fusion will be developed as the support of future work. 

    In the end, a conclusion will be drawn. Possible improvements are also expected in future work. For example, better accuracy of calibration might be achieved with other methods and adding texture to cloud points will generate a more realistic model.

  • 121993. Zhao, Gui-Ling
    et al.
    Ullah, Farman
    Deiana, Luca
    Lin, Shuangzheng
    Zhang, Qiong
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Sun, Junliang
    Ibrahem, Ismail
    Dziedzic, Pawel
    Córdova, Armando
    Dynamic Kinetic Asymmetric Transformation (DYKAT) by Combined Amine- and Transition-Metal-Catalyzed Enantioselective Cycloisomerization2010In: Chemistry - A European Journal, ISSN 0947-6539, E-ISSN 1521-3765, Vol. 16, no 5, p. 1585-1591Article in journal (Refereed)
    Abstract [en]

    The first examples of one-pot highly chemo- and enantioselective dynamic kinetic asymmetric transformations (DYKATs) involving alpha,beta-unsaturated aldehydes and proparaylated carbon acids are presented. These DYKATs, which proceed by a combination of catalytic iminium activation, enamine activation, and Pd-0-catalyzed enyne cycloisomerization, give access to functionalized cyclopentenes wit. It up to. 99% ee and can be used for the generation of all-carbon quaternary stereocenters

  • 121994.
    Zhao, Guo-Hua
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    High-performance Load-bearing Alloys2017Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The aim of this thesis is to study advanced metallic alloys as load-bearing componentsfor engineering and biomedical applications. The investigations have been focusing onthe improvement of the properties and performance of existing materials as well assynthesizing and developing completely new materials. This thesis covers alloy design,microstructure characterizations, mechanical and electrochemical tests, together withevaluating the tribocorrosion performances under the combined action of wear andcorrosion. The thesis consists of three parts:In part one (paper I and II), two types of multicomponent Ti-Fe-Sn-Nb alloys weredeveloped showing superior mechanical properties with distinct microstructures. Firstlythe hypoeutectic alloy consisting of ductile dendrites and ultrafine eutectic presentedsuperior yield strength and enhanced ductility compared to those of bulk metallicglasses (BMGs). Secondly, the β-type alloys completely retaining of β-Ti phasedisplayed outstanding plasticity without sacrificing the high mechanical strength.In part two (paper III), a series of Ti-based glassy alloys containing no biological toxicelements e.g. Ni, Cu and Al, were designed by a novel method coupling thermodynamiccalculations and topological instability criterion. A self-consistent thermodynamicdatabase was constructed based on the CALPHAD (Calculation of Phase Diagrams)approach. The experimental verifications matched reasonably well with the theoreticalcalculation, suggesting this method provides an effective approach for glass formingpredictions.In part three (paper IV and V), the degradation mechanisms of the load-bearing Zrbased BMGs were evaluated under the effects of tribological wear and electrochemicalcorrosion. Comparatively the tribo-electrochemical performances of the surfacemodified (plasma nitriding or diamond-like carbon) conventional metallic biomaterialsi.e. medical grade pure Ti, stainless steel and CoCrMo alloys, were investigated in linewith that of the BMGs.

  • 121995.
    Zhao, Guohua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. NTNU Norwegian University of Science and Technology, Norway.
    Aune, R. E.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Espallargas, N.
    Degradation of Zr-based bulk metallic glasses used in load-bearing implants: A tribocorrosion appraisal2016In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 60, p. 56-67Article in journal (Refereed)
    Abstract [en]

    Owing to the amorphous structure, Bulk Metallic Glasses (BMGs) have been demonstrating attractive properties for potential biomedical applications. In the present work, the degradation mechanisms of Zr-based BMGs with nominal compositions Zr55Cu30Ni5Al10 and Zr65Cu18Ni7Al10 as potential load-bearing implant material were investigated in a tribocorrosion environment. The composition-dependent micro-mechanical and tribological properties of the two BMGs were evaluated prior to the tribocorrosion tests. The sample Zr65-BMG with a higher Zr content exhibited increased plasticity but relatively reduced wear resistance during the ball-on-disc tests. Both BMGs experienced abrasive wear after the dry wear test under the load of 2N. The cross-sectional subsurface structure of the wear track was examined by Focused Ion Beam (FIB). The electrochemical properties of the BMGs in simulated body fluid were evaluated by means of potentiodynamic polarization and X-ray Photoelectron Spectroscopy (XPS). The spontaneous passivation of Zr-based BMGs in Phosphate Buffer Saline solution was mainly attributed to the highly concentrated zirconium cation (Zr4+) in the passive film. The tribocorrosion performance of the BMGs was investigated using a reciprocating tribometer equipped with an electrochemical cell. The more passive nature of the Zr65-BMG had consequently a negative influence on its tribocorrosion resistance, which induced the wear-accelerated corrosion and eventually speeded-up the degradation process. It has been revealed the galvanic coupling was established between the depassivated wear track and the surrounding passive area, which is the main degradation mechanism for the passive Zr65-BMG subjected to the tribocorrosion environment.

  • 121996.
    Zhao, Guo-Hua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Aune, Ragnhild E.
    Espallargas, Nuria
    Tribocorrosion studies of metallic biomaterials: The effect of plasma nitriding and DLC surface modifications2016In: Journal of The Mechanical Behavior of Biomedical Materials, ISSN 1751-6161, E-ISSN 1878-0180, Vol. 63, p. 100-114Article in journal (Refereed)
    Abstract [en]

    The medical grade pure titanium, stainless steel and CoCrMo alloy have been utilized as biomaterials for load-bearing orthopedic prosthesis. The conventional surgery metals suffer from a combined effect of wear and corrosion once they are implanted, which may significantly accelerate the material degradation process. In this work, the tribocorrosion performance of the metallic biomaterials with different surface modifications was studied in the simulated body fluid for the purpose of investigating the effect of the surface treatments on the tribocorrosion performance and eventually finding the most suitable implantation materials. The metals were subjected to surface modifications by plasma nitriding in different treatment temperatures or physical vapor deposition (PVD) to produce diamond-like carbon (DLC) coating, respectively. The dry wear and tribocorrosion properties of the samples were evaluated by using a reciprocating ball-on-disc tribometer equipped with an electrochemical cell. Prior to the tribocorrosion tests, their electrochemical behavior was measured by the potentiodynamic polarization in phosphate buffer saline (PBS) solution at room temperature. Both stainless steel and CoCrMo after low temperature nitriding kept their passive nature by forming an expanded austenite phase. The DLC coated samples presented the low anodic corrosion current due to the chemical inertness of the carbon layer. During the tribocorrosion tests at open circuit potential, the untreated and low temperature nitrided samples exhibited significant potential drop towards the cathodic direction, which was a result of the worn out of the passive film. Galvanic coupling was established between the depassivated (worn) area and the still passive (unworn) area, making the materials suffered from wear-accelerated corrosion. The DLC coating performed as a solid lubricant in both dry wear and tribocorrosion tests, and the resulting wear after the tests was almost negligible.

  • 121997.
    Zhao, Guohua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Norwegian University of Science and Technology (NTNU), Norway.
    Espallargas, N.
    Aune, R. E.
    Tribocorrosion studies on surface modified medical grade stainless steel2015In: TMS2015 Supplemental Proceedings, The Minerals, Metals, and Materials Society, 2015, p. 521-528Conference paper (Refereed)
    Abstract [en]

    Tribocorrosion performance of medical grade A1S1 316L stainless steel with and without surface modification has been studied during exposure to an electrolyte. Some of the samples investigated were surface modified by plasma nitriding (at both 400 and 550 °C), and others by a special arc physical vapor deposition to secure a thin layer of a diamond-like carbon (DLC) coating on the surface of the samples. XRD and SEM were used to characterize the homogeneity and microstructure of all samples. Potentiodynamic polarization measurement and tribocorrosion tests were performed multiple times on all groups of samples. It was established that surface treated SS 316L exhibited totally different passive behaviors, which consequently lead different tribocorrosion performance in the electrolyte. It was also established that the DLC coating performed as a solid lubricant in the ball-on-plate tests, and the resulting wear track after the tribocorrosion tests was almost negligible. On the other hand, the untreated and Nitriding 400 °C samples experienced wear accelerated corrosion due to their passive behavior. The results suggest that the DLC coated SS 316L have the best performance at the combined wear and corrosion environment, while the untreated and Nitriding 400 °C samples should be avoided to apply in biological tribocorrosion conditions.

  • 121998.
    Zhao, Guo-Hua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Tohoku University, Japan.
    Ketov, Sergey V.
    Jiang, Jing
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Louzguine-Luzgin, Dmitri V.
    New Beta-type Ti-Fe-Sn-Nb alloys with superior mechanical strength2017In: Materials Science & Engineering: A, ISSN 0921-5093, E-ISSN 1873-4936, Vol. 705, p. 348-351Article in journal (Refereed)
    Abstract [en]

    Ti-Fe-Sn-Nb alloys comprised of single beta-Ti phase were developed showing excellent mechanical strength and superior plasticity. The alloys exhibited increased yield strength as a function of Fe content, where the Ti80Fe14Sn3Nb3 alloy presented the highest yield stress (1.88 GPa) comparable to that of Ti-based nanocrystalline alloys. Moreover, a significant strain-hardening (520 MPa) was achieved along with the plastic deformation. The excellent mechanical strength was enhanced by the supersaturated beta-Ti and the high density of lattice defects that restrict the dislocation motion.

  • 121999.
    Zhao, Guo-Hua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering. Tohoku University, Japan.
    Ketov, Sergey V.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Borgenstam, Annika
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Louzguine-Luzgin, Dmitri V.
    Ti-Fe-Sn-Nb hypoeutectic alloys with superb yield strength and significant strain-hardening2017In: Scripta Materialia, ISSN 1359-6462, E-ISSN 1872-8456, Vol. 135, p. 59-62Article in journal (Refereed)
    Abstract [en]

    In this letter new Ti-Fe-Sn-Nb hypoeutectic alloy comprised of primary dendritic β-Ti and ultrafine (β-Ti + TiFe) eutectic was developed showing superior mechanical properties. The as-cast Ti67Fe27Sn3Nb3 (at.%) alloy exhibited exceptionally high yield stress (2.18 GPa) comparable to that of bulk metallic glasses. Most importantly, the sample presented significant strain-hardening (320 MPa) and enhanced plasticity. The slip deformation and dislocation accumulation in the β-Ti dendrite contribute to the plasticity and the pronounced strain-hardening, whereas the high strength stems from the ultrafine (β-Ti + TiFe) eutectic structure as well as the solution hardening in the multicomponent system.

  • 122000.
    Zhao, Guo-Hua
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Mao, Huahai
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Louzguine-Luzgin, Dmitri V.
    Glass forming range of the Ti-Fe-Si amorphous alloys: An effective materials-design approach coupling CALPHAD and topological instability criterion2016In: Journal of Applied Physics, ISSN 0021-8979, E-ISSN 1089-7550, Vol. 120, no 20, article id 205106Article in journal (Refereed)
    Abstract [en]

    A method of composition design for metallic glasses was proposed by using the Calculation of Phase Diagrams (CALPHAD) with the assistance of the topological instability criterion. This methodology was demonstrated in the quick and effective searching of glass-forming regions for Ti-Fe-Si and Ti-Zr-Fe-Si alloys containing no biologically toxic elements, e.g., Ni and Cu. In addition, the Ti-Fe-Si system may promote the glass formation owing to the existence of a deep eutectic at the Ti-rich corner. A self-consistent thermodynamic database was constructed based on the CALPHAD approach. The liquidus projection, isothermal sections, and the enthalpy of mixing were calculated by using the database. On the basis of these calculations coupling with the topological instability "lambda lambda criterion," the potential glass-forming alloy compositions in a narrow region were suggested for experimental validation. Thereafter, the isothermal sections of the Ti-Zr-Fe-Si quaternary system were calculated at certain contents of Zr. The designed alloys were prepared by arc-melting and followed by melt-spinning to the ribbon shape. The experimental verifications matched reasonably well with the theoretical calculations. This work offers new insights for predicting glass-forming alloys based on thermodynamic arguments; it shall be of benefit for the exploration of new metallic glasses.

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