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  • 121951.
    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.

  • 121952.
    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.

  • 121953.
    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.

  • 121954. 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.

  • 121955. 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.

  • 121956. 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.

  • 121957. 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.

  • 121958. 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.

  • 121959. 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.

  • 121960.
    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.

  • 121961. 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

  • 121962.
    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.

  • 121963.
    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.

  • 121964.
    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.

  • 121965.
    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.

  • 121966.
    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.

  • 121967.
    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.

  • 121968.
    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.

  • 121969. Zhao, H.
    et al.
    Yang, Y.
    Li, Q.
    Qiu, Min
    KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
    Sub-wavelength quarter-wave plate based on plasmonic patch antennas2013In: Applied Physics Letters, ISSN 0003-6951, E-ISSN 1077-3118, Vol. 103, no 26, p. 261108-Article in journal (Refereed)
    Abstract [en]

    A quarter-wave plate using plasmonic patch antennas has been investigated. The nanostructures can convert linear polarized light into circular polarized light in the visible range (633 nm). By further exploiting the dimer patch antenna structure composed of different metals, directional emission (with a directivity of 4.8) of circular polarized light (with a conversion efficiency of 27.8%) in an oblique direction with respect to the incident light is enabled. Compared with previous designs, the proposed structures are ultra-thin, and are more suitable for integration applications.

  • 121970.
    Zhao, Hanyue
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Kumar, Mukesh
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Density functional theory study of ordered defect Cu-(In,Ga)-Se compounds2012In: Physica Status Solidi. C, Current topics in solid state physics, ISSN 1610-1634, E-ISSN 1610-1642, Vol. 9, no 7, p. 1600-1603Article in journal (Refereed)
    Abstract [en]

    CuIn1-xGaxSe2 is used as absorber material in thin-film photovoltaics. Presence of defect arrays of 2V(Cu)(-) + X-Cu(2+) complexes (X = In or Ga) in the material results in the formation of ordered defect phases, like for instance Cu(In1-xGax)(3)Se-5 and Cu(In1-xGax)(5)Se-8. An understanding of these defects phases is of considerably importance since they can strongly affect the performance of the solar cell. Density functional theory calculation with a hybrid functional is carried out to study the electronic structures and optical properties of these ordered defect phases. Fundamental properties, such as the band bowing, the band alignment and the absorption coefficients, are presented, and their dependence on material composition is discussed.

  • 121971.
    Zhao, Hanyue
    et al.
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering.
    Persson, Clas
    KTH, School of Industrial Engineering and Management (ITM), Materials Science and Engineering, Applied Material Physics.
    Optical properties of Cu(In,Ga)Se(2) and Cu(2)ZnSn(S,Se)(4)2011In: Thin Solid Films, ISSN 0040-6090, E-ISSN 1879-2731, Vol. 519, no 21, p. 7508-7512Article in journal (Refereed)
    Abstract [en]

    The optical properties of CuInSe(2), CuGaSe(2), Cu(2)ZnSnS(4), and Cu(2)ZnSnSe(4) are investigated using three different first-principles methods, namely the generalized gradient approximation by Perdew. Burke, and Ernzerhof (PBE), the hybrid Hartree-Fock-like functional by Heyd. Scuseria, and Emzerhof (HSE), and a Green's function approach (GW). The density-of-states, the complex dielectric function epsilon(omega) = epsilon(1)(omega) + i epsilon(2)(omega), and the optical absorption coefficient alpha(omega) are determined, providing fundamental understanding of these materials. We find that even though the PBE method generates fairly accurate effective crystal potentials, the HSE and GW methods improve considerably the band-gap energies E(g) and also the localization of the semicore states, thereby describing the optical properties much better. Furthermore, we also present optimized convergence parameters for the self-consistent HSE calculation in order to reduce the computational time of this orbital-dependent method.

  • 121972.
    Zhao, Hao
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    Integrated Security Platform for Mobile Applications2011Licentiate thesis, monograph (Other academic)
    Abstract [en]

    This report describes our concept, design and current implementation of theIntegrated Security Platform for mobile applications.

    The increasing use of mobile applications is the trend of mobile communicationtechnology. Under initiatives of ISO, ETSI, GSMA and other standardization bodies,mobile applications play more and more important role.

    Security is one of the most important issues for mobile applications. Users,applications, their messages and their data need to be protected during storing andtransmitting.

    Integrated Security Platform is a standardized solution for mobile applicationstargeting to provide reliable security. It is based on requirements of operationalenvironments, security extensions and interfaces for security-enhanced applications. Theessence of the idea is to use secure element in the form of Universal Integrated CircuitCard (UICC), which is used to store and run various mobile applications simultaneously.The core of security is a set of secure applications, designed and implemented in theform of Javacard applets, stored in the UICC module. Security process flow guidingmobile applications implementing strong security is also defined in the describedapproach. Security management and all cryptography modules and functions required byapplications in a secure environment are also provided. Integrated Security Platform usesover–the-air (OTA) protocols, like SMS, GPRS, or mobile Internet and over–the–counter(OTC) protocols as communication channels for administration, management andexchange of information with the outside world.

    As a part of this research a mobile application called Secure Mobile Wallet wasdesigned as an example of a security–enhanced application stored in the UICC module. Itprovides to mobile subscribers the possibility to perform various secure mobile financialtransactions. Secure Mobile Wallet comprises several Javacard applets supportingseveral types of financial transactions – mobile banking, mobile payments, mobilecommerce, mobile micro–loans, mobile ticketing, mobile promotions, and so on. Itsupports both, OTA and OTC transactions. Secure Mobile Wallet was also developed inaccordance to requirements for a reliable client’s application as a component of thelarger, secure mobile transactions system.

    Secure Mobile Wallet uses features and security functions provided by UICC moduleto guarantee its security. Implementation and testing of the Integrated Security Platformare performed through Secure Mobile Wallet.

    Expected achievements and contributions of this research are:

    The concept of secure mobile applications stored in the UICC module

    The structure and design of such applications in the form of Javacard applets,including their internal data model and external APIs

    Design and specifications of the middleware between mobile applications stored inmobile phones and supporting security applications in the UICC module

    Specifications of several forms of secure elements and their applications, i.e. as UICCapplets, SIM chip modules or NFC applet

    Design and prototype implementation of Secure Mobile Wallet as mobile phoneapplication using security functions and services follow the concept and principles of theIntegrated Security Platform.

  • 121973.
    Zhao, Hao
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS.
    Secure Management of Multi-Application Mobile Platforms2014Doctoral thesis, monograph (Other academic)
  • 121974.
    Zhao, Hao
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    Muftic, Sead
    KTH, School of Information and Communication Technology (ICT), Communication Systems, CoS, Network Systems Laboratory (NS Lab).
    The concept of secure mobile wallet2011In: World Congress on Internet Security, WorldCIS-2011, 2011, p. 54-58Conference paper (Refereed)
    Abstract [en]

    This paper describes our concept, design and current implementation of the Secure Mobile Wallet. Mobile Wallet is an application stored in mobile phones providing to subscribers the possibility to perform various mobile financial transactions. In our approach Secure Mobile Wallet is stored and running in the Javacard SIM chip, called UICC. It comprises several Javacard applets supporting several types of financial transactions - mobile banking, mobile payments, mobile commerce, mobile micro-loans, mobile ticketing, mobile promotions, and so on. Secure Mobile Wallet supports over-the-air (OTA) transactions based on SMS, GPRS, or mobile Internet protocols and also over-the-counter (OTC) transactions based on NFC or Bluetooth protocols. For users, messages and data stored in the Secure Mobile Wallet are managed and maintained using both, OTA and OTC, protocols. Security is guaranteed by a combination of symmetric and asymmetric cryptography. As a client's application, the Secure Mobile Wallet is integrated into our larger, secure mobile transactions system - SAFE™.

  • 121975.
    Zhao, Hao
    et al.
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    Muftic, Sead
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    Zhang, Feng
    KTH, School of Information and Communication Technology (ICT), Communication: Services and Infrastucture (Closed 20120101), Communication Systems, CoS (closed 2012-01-01).
    The secure mobile wallet: Anytime, anywhere financial transactions2010In: Cutter IT Journal, ISSN 1522-7383, Vol. 23, no 7, p. 32-35Article in journal (Refereed)
  • 121976. Zhao, J.
    et al.
    Chen, X.
    Duan, X.
    Shen, Tong
    KTH, School of Electrical Engineering (EES).
    Study on demand forecasting and allocation of expressway emergency vehicle resource2014In: Journal of Computational Information Systems, ISSN 1553-9105, Vol. 10, no 10, p. 4205-4215Article in journal (Refereed)
    Abstract [en]

    Emergency vehicles are the key resources of expressway for the rescue mission to traffic accidents. For optimal emergency vehicle resources allocation, an improved Case-Based Reasoning (CBR) and an allocation model are established. First, the effecting factors of traffic safety on expressway are analyzed to establish an accident hazard indicator system. A difference coefficient is introduced to improve Case-Based Reasoning for predicting the demand of emergency vehicle resources. Then, the resource allocation model is established based on the objective constrained optimization method, which tries to find the minimum rescue time with constraints such as road hazard, rescue time, resource demand, and the configuration result is obtained by adopting Particle Swarm Optimization (PSO). Finally, according to the study of a bridge case, it shows that the prediction error of resource demands becomes smaller by using the improved case-based reasoning method and the resource allocation results are reasonable through the calculation of objective constrained optimization model.

  • 121977. Zhao, Jiandong
    et al.
    Li, Zhaoxuan
    Zheng, Jun
    Shen, Tong
    KTH, School of Electrical Engineering (EES).
    Walking Stability Compensation Strategy of a Small Humanoid Robot Based on the Error of Swing Foot Height and Impact Force2013In: International Journal of Advanced Robotic Systems, ISSN 1729-8806, E-ISSN 1729-8814, Vol. 10, p. 227-Article in journal (Refereed)
    Abstract [en]

    In order to reduce the impact force of swing legs and improve walking stability when a small humanoid robot is walking, a set of impact dynamics equations based on the second kind Lagrange equation is produced, and an impact compensation control strategy with a BP network optimized by a particle swarm algorithm is designed. The core element of the compensation controller is replacing the error back propagation with a particle swarm algorithm. Due to the regulating joints of the knee, hip and ankle, the walking process is more stable than before. The experiment results show that when the left swing leg lands, the impact force drops by 2N and 1.5N respectively in the moments 4.5s and 10.5s. Therefore, the compensation strategy can reduce the impact force effectively and improve the walking stability.

  • 121978. Zhao, Jianghua
    et al.
    Yang, Xichuan
    Cheng, Ming
    Li, Shifeng
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Molecular Design and Performance of Hydroxylpyridium Sensitizers for Dye-Sensitized Solar Cells2013In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 5, no 11, p. 5227-5231Article in journal (Refereed)
    Abstract [en]

    Four hydroxylpyridium organic dyes were synthesized and applied in dye-sensitized solar cells (DSSCs). Hydroxylpyridium was introduced as an electron acceptor in donor-pi-conjugated bridge-acceptor (D-pi-A) system. The traditional anchoring groups, such as the carboxyl group, were replaced by hydroxyl group. It was found that the existence of the hydroxylpyridium exhibits a large effect on the absorption spectra of dyes JH401-JH404. For JH series of dyes, hexylthiophene was employed as the pi-conjugated bridge, and triphenylamine, phenothiazine, and their derivatives were used as the electron donor. The performances of the dyes with different structure were investigated by photophysical, photovoltaic, and electrochemical methods. When applied in the DSSCs, the sensitizer JH401 yields the best efficiency, 2.6% (J(sc) = 6.35 mA/cm(2), V-oc = 605 mV, FF = 67.696) under 100 mW/cm(2) light illumination. Its maximum incident photon-to-current conversion efficiency (IPCE) is 80% at 440 nm light wavelength, which is the highest IPCE value achieved with hydroxyl group adsorbent organic dyes so far.

  • 121979. Zhao, Jianghua
    et al.
    Yang, Xichuan
    Cheng, Ming
    Li, Shifeng
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    New Organic Dyes with a Phenanthrenequinone Derivative as the pi-Conjugated Bridge for Dye-Sensitized Solar Cells2013In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 117, no 25, p. 12936-12941Article in journal (Refereed)
    Abstract [en]

    A series of organic dyes based on a phenanthrenequinone derivative have been employed for the first time as a it-conjugated bridge in the molecular design of D-pi-A structured organic dyes. Photophysical and electrochemical properties of dyes JH201-JH203 have been systematically investigated. The result shows that dye JH202 exhibits a higher molar extinction coefficient and widened absorption spectrum than dye JH201. Upon replacing the butoxyltriphenylamiine electron donor with phenothiazine, a bathochromic shift absorption spectrum for dye JH203 was observed. When applied in dye-sensitized solar cells (DSSCs), the device sensitized by JH203 yields the best photo-to-current conversion efficiency of 6.0% under standard AM 1.5G illumination (100 rnW/cm(2)) with a short-circuit photocurrent density (J(sc)) of 11.1 mA/cm(2), an open circuit photovoltage (V-oc) of 720 mV, and a fill factor (ff) of 74.9%. The maximum incident photo-to-current conversion efficiency reaches 87% at 460 nm.

  • 121980. Zhao, Jianghua
    et al.
    Yang, Xichuan
    Cheng, Ming
    Li, Shifeng
    Wang, Xiuna
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Highly efficient iso-quinoline cationic organic dyes without vinyl groups for dye-sensitized solar cells2013In: Journal of Materials Chemistry A, ISSN 2050-7488, Vol. 1, no 7, p. 2441-2446Article in journal (Refereed)
    Abstract [en]

    Four organic dyes without a vinyl group are synthesized and applied in dye-sensitized solar cells (DSSCs). The iso-quinoline cation is employed firstly as an electron acceptor in the dye molecular structure. The effect of different dye structures on the photo-electrochemical properties and the performance of the DSSCs are systematically studied. The photovoltaic performances of the DSSCs sensitized by the JH304 dye exhibit the best conversion efficiency of 7.3% (under standard AM 1.5G illumination (100 mW cm(-2))) with a short-circuit current density (J(sc)) of 14.4 mA cm(-2), an open-circuit voltage (V-oc) of 684 mV and a fill factor (ff) of 74.4%. In comparison, the device sensitized by the N719 dye shows an efficiency of 7.9%. The DSSC device sensitized by JH304 also exhibits excellent soaking stability under sunlight for 1000 h.

  • 121981. Zhao, Jianghua
    et al.
    Yang, Xichuan
    Cheng, Ming
    Wang, Weihan
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry. KTH, School of Chemical Science and Engineering (CHE), Centres, Centre of Molecular Devices, CMD.
    Influence of different methylene units on the performance of rhodanine organic dyes for dye-sensitized solar cells2014In: RSC Advances, ISSN 2046-2069, E-ISSN 2046-2069, Vol. 4, no 10, p. 4811-4816Article in journal (Refereed)
    Abstract [en]

    In D-p-A structured organic dyes, rhodanine acetic acid and its derivates have served as electron acceptors successfully. In this work, two single rhodanine organic dyes with different methylene units have been synthesized and applied in dye-sensitized solar cells (DSSCs). The photophysical, electrochemical and photovoltaic properties have been studied systematically. The results show that dye with double methylene units produces a higher photon-to-electron conversion efficiency (eta) of 4.5% than that of a single methylene unit dye with a eta of 4.1%. Also, it is interesting to notice that the lengthened distance between electron acceptor and TiO2 surface does not decrease the short-circuit current density (J(sc)) and IPCE response for both structured dyes. On the contrary, rhodanine dye bearing double methylene units exhibits a better J(sc) and IPCE response than the single methylene unit. The explanation for this trend is probably due to the fact that increased methylene units could suppress regeneration between the injected electron and the oxidized dye effectively.

  • 121982. Zhao, Jianghua
    et al.
    Yang, Xichuan
    Hao, Yan
    Cheng, Ming
    Tian, Jie
    Sun, Licheng
    KTH, School of Chemical Science and Engineering (CHE), Chemistry, Organic Chemistry.
    Effect of Different Numbers of -CH2- Units on the Performance of Isoquinolinium Dyes2014In: ACS Applied Materials and Interfaces, ISSN 1944-8244, E-ISSN 1944-8252, Vol. 6, no 6, p. 3907-3914Article in journal (Refereed)
    Abstract [en]

    Three new dyes have been synthesized to investigate the influence of the distance between the electron acceptor and TiO2 surface on the performance of dye-sensitized solar cells (DSSCs). In these dyes, the isoquinolinium acceptor, with a -(CH2)(n) COOH anchoring group, and a functionalized triphenylamine donor are separated by an oligothiophene bridge. The physical and electrochemical properties of the dyes were investigated systematically. The results prove that different numbers of -CH2- units between the isoquinolinium acceptor and the carboxyl anchoring group have a less pronounced effect on the physical and electrochemical properties of these dyes. However, when applied in DSSCs, a sharp decrease in the short-circuit current (J(SC)) was observed with increasing numbers of -CH2- units. For example, the device containing the organic dye bearing three -CH2- units produced the lowest J(SC) of 7.94 mA.cm(-2). In contrast, the device containing the dye bearing only one -CH2- unit exhibited the highest J(SC) of 13.88 mA.cm(-2). The higher photocurrent obtained with the device incorporating the dye with one -CH2- unit resulted in a higher power conversion efficiency of 6.8%.

  • 121983.
    Zhao, Jianyu
    KTH, School of Architecture and the Built Environment (ABE), Real Estate and Construction Management.
    Risk Assessment on Housing Segments in Stockholm2016Independent thesis Advanced level (degree of Master (Two Years)), 20 credits / 30 HE creditsStudent thesis
  • 121984.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Henriksson, Aron
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Asker, Lars
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Detecting Adverse Drug Events with Multiple Representations of Clinical Measurements2014In: Proceedings - 2014 IEEE International Conference on Bioinformatics and Biomedicine, IEEE BIBM 2014, IEEE Computer Society, 2014, p. 536-543, article id 6999216Conference paper (Refereed)
    Abstract [en]

    Adverse drug events (ADEs) are grossly under-reported in electronic health records (EHRs). This could be mitigated by methods that are able to detect ADEs in EHRs, thereby allowing for missing ADE-specific diagnosis codes to be identified and added. A crucial aspect of constructing such systems is to find proper representations of the data in order to allow the predictive modeling to be as accurate as possible. One category of EHR data that can be used as indicators of ADEs are clinical measurements. However, using clinical measurements as features is not unproblematic due to the high rate of missing values and they can be repeated a variable number of times in each patient health record. In this study, five basic representations of clinical measurements are proposed and evaluated to handle these two problems. An empirical investigation using random forest on 27 datasets from a real EHR database with different ADE targets is presented, demonstrating that the predictive performance, in terms of accuracy and area under ROC curve, is higher when representing clinical measurements crudely as whether they were taken or how many times they were taken by a patient. Furthermore, a sixth alternative, combining all five basic representations, significantly outperforms using any of the basic representation except for one. A subsequent analysis of variable importance is also conducted with this fused feature set, showing that when clinical measurements have a high missing rate, the number of times they were taken by one patient is ranked as more informative than looking at their actual values. The observation from random forest is also confirmed empirically using other commonly employed classifiers. This study demonstrates that the way in which clinical measurements from EHRs are presented has a high impact for ADE detection, and that using multiple representations outperforms using a basic representation.

  • 121985.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Henriksson, Aron
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Asker, Lars
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Predictive modeling of structured electronic health records for adverse drug event detection2015In: BMC Medical Informatics and Decision Making, ISSN 1472-6947, E-ISSN 1472-6947, Vol. 15, no 4, article id S1Article in journal (Refereed)
    Abstract [en]

    Background: The digitization of healthcare data, resulting from the increasingly widespread adoption of electronic health records, has greatly facilitated its analysis by computational methods and thereby enabled large-scale secondary use thereof. This can be exploited to support public health activities such as pharmacovigilance, wherein the safety of drugs is monitored to inform regulatory decisions about sustained use. To that end, electronic health records have emerged as a potentially valuable data source, providing access to longitudinal observations of patient treatment and drug use. A nascent line of research concerns predictive modeling of healthcare data for the automatic detection of adverse drug events, which presents its own set of challenges: it is not yet clear how to represent the heterogeneous data types in a manner conducive to learning high-performing machine learning models. Methods: Datasets from an electronic health record database are used for learning predictive models with the purpose of detecting adverse drug events. The use and representation of two data types, as well as their combination, are studied: clinical codes, describing prescribed drugs and assigned diagnoses, and measurements. Feature selection is conducted on the various types of data to reduce dimensionality and sparsity, while allowing for an in-depth feature analysis of the usefulness of each data type and representation. Results: Within each data type, combining multiple representations yields better predictive performance compared to using any single representation. The use of clinical codes for adverse drug event detection significantly outperforms the use of measurements; however, there is no significant difference over datasets between using only clinical codes and their combination with measurements. For certain adverse drug events, the combination does, however, outperform using only clinical codes. Feature selection leads to increased predictive performance for both data types, in isolation and combined. Conclusions: We have demonstrated how machine learning can be applied to electronic health records for the purpose of detecting adverse drug events and proposed solutions to some of the challenges this presents, including how to represent the various data types. Overall, clinical codes are more useful than measurements and, in specific cases, it is beneficial to combine the two.

  • 121986.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Henriksson, Aron
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Cascading Adverse Drug Event Detection in Electronic Health Records2015In: 2015 IEEE International Conference on Data Science and Advanced Analytics (DSAA): Proceedings, IEEE Computer Society, 2015, p. 810-817, article id 7344869Conference paper (Refereed)
    Abstract [en]

    The ability to detect adverse drug events (ADEs) in electronic health records (EHRs) is useful in many medical applications, such as alerting systems that indicate when an ADE-specific diagnosis code should be assigned. Automating the detection of ADEs can be attempted by applying machine learning to existing, labeled EHR data. How to do this in an effective manner is, however, an open question. The issues addressed in this study concern the granularity of the classification task: (1) If we wish to predict the occurrence of ADE, is it advantageous to conflate the various ADE class labels prior to learning, or should they be merged post prediction? (2) If we wish to predict a family of ADEs or even a specific ADE, can the predictive performance be enhanced by dividing the classification task into a cascading scheme: predicting first, on a coarse level, whether there is an ADE or not, and, in the former case, followed by a more specific prediction on which family the ADE belongs to, and then finally a prediction on the specific ADE within that particular family? In this study, we conduct a series of experiments using a real, clinical dataset comprising healthcare episodes that have been assigned one of eight ADE-related diagnosis codes and a set of randomly extracted episodes that have not been assigned any ADE code. It is shown that, when distinguishing between ADEs and non-ADEs, merging the various ADE labels prior to learning leads to significantly higher predictive performance in terms of accuracy and area under ROC curve. A cascade of random forests is moreover constructed to determine either the family of ADEs or the specific class label; here, the performance is indeed enhanced compared to directly employing a one-step prediction. This study concludes that, if predictive performance is of primary importance, the cascading scheme should be the recommended approach over employing a one-step prediction for detecting ADEs in EHRs.

  • 121987.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Henriksson, Aron
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Detecting Adverse Drug Events Using Concept Hierarchies of Clinical Codes2014In: 2014 IEEE International Conference on Healthcare Informatics: Proceedings, IEEE Computer Society, 2014, p. 285-293, article id 7052501Conference paper (Refereed)
    Abstract [en]

    Electronic health records (EHRs) provide a potentially valuable source of information for pharmacovigilance. However, adverse drug events (ADEs), which can be encoded in EHRs with specific diagnosis codes, are heavily under-reported. To provide more accurate estimates for drug safety surveillance, machine learning systems that are able to detect ADEs could be used to identify and suggest missing ADE-specific diagnosis codes. A fundamental consideration when building such systems is how to represent the EHR data to allow for accurate predictive modeling. In this study, two types of clinical code are used to represent drugs and diagnoses: the Anatomical Therapeutic Chemical Classification System (ATC) and the International Statistical Classification of Diseases and Health Problems (ICD). More specifically, it is investigated whether their hierarchical structure can be exploited to improve predictive performance. The use of random forests with feature sets that include only the original, low-level, codes is compared to using random forests with feature sets that contain all levels in the hierarchies. An empirical investigation using thirty datasets with different ADE targets is presented, demonstrating that the predictive performance, in terms of accuracy and area under ROC curve, can be significantly improved by exploiting codes on all levels in the hierarchies, compared to using only the low-level encoding. A further analysis is presented in which two strategies are employed for adding features level-wise according to the concept hierarchies: top-down, starting with the highest abstraction levels, and bottom-up, starting with the most specific encoding. The main finding from this subsequent analysis is that predictive performance can be kept at a high level even without employing the more specific levels in the concept hierarchies.

  • 121988.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Henriksson, Aron
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Kvist, Maria
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Asker, Lars
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Handling Temporality of Clinical Events for Drug Safety Surveillance2015In: AMIA Annual Symposium Proceedings, ISSN 1559-4076, Vol. 2015, p. 1371-1380Article in journal (Refereed)
    Abstract [en]

    Using longitudinal data in electronic health records (EHRs) for post-marketing adverse drug event (ADE) detection allows for monitoring patients throughout their medical history. Machine learning methods have been shown to be efficient and effective in screening health records and detecting ADEs. How best to exploit historical data, as encoded by clinical events in EHRs is, however, not very well understood. In this study, three strategies for handling temporality of clinical events are proposed and evaluated using an EHR database from Stockholm, Sweden. The random forest learning algorithm is applied to predict fourteen ADEs using clinical events collected from different lengths of patient history. The results show that, in general, including longer patient history leads to improved predictive performance, and that assigning weights to events according to time distance from the ADE yields the biggest improvement.

  • 121989.
    Zhao, Jing
    et al.
    Logist Engn Univ, Dept Math, Chongqing 400016, Peoples R China.;Second Mil Med Univ, Dept Nat Med Chem, Coll Pharm, Shanghai, Peoples R China..
    Holme, Petter
    KTH, School of Computer Science and Communication (CSC), Computational Biology, CB.
    Three Faces of Metabolites: Pathways, Localizations and Network Positions2010In: COMPUTATIONAL SYSTEMS BIOLOGY / [ed] Chen, L Zhang, XS Shen, B Wu, LY Wang, Y, WORLD PUBLISHING CORPORATION , 2010, Vol. 13, p. 13-+Conference paper (Refereed)
    Abstract [en]

    In this study, we investigate the relative organization of three (not independent) categorizations of metabolites pathways, subcellular localizations and network clusters both qualitatively and quantitatively and further characterize the categories from topological point of view. The picture of the metabolism we obtain is that of peripheral modules, characterized both by being dense network clusters and localized to organelles, connected by a central, highly connected core. Pathways typically run through several network clusters and localizations, connecting them-laterally. The significant overlap between organelles, pathways and network clusters suggest that, to some extent, the topology of metabolic networks could spell out the spatial isolations of cellular architectures and functional coherence of metabolic systems. Such systems level analysis of the correlation between different categorizations is helpful for understanding the influence of intracellular organization on the regulation of metabolic processes.

  • 121990.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Karlsson, Isak
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Asker, Lars
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Applying Methods for Signal Detection in Spontaneous Reports to Electronic Patient Records2013In: Proceedings of the  19th ACM SIGKDD International Conference on Knowledge Discovery and Data Mining, Association for Computing Machinery (ACM), 2013Conference paper (Refereed)
    Abstract [en]

    Currently, pharmacovigilance relies mainly on disproportionality analysis of spontaneous reports. However, the analysis of spontaneous reports is concerned with several problems, such as reliability, under-reporting and insucient patient information. Longitudinal healthcare data, such as Electronic Patient Records (EPRs) in which comprehensive information of each patient is covered, is a complementary source of information to detect Adverse Drug Events (ADEs). A wide set of disproportionality methods has been developed for analyzing spontaneous reports to assess the risk of reported events being ADEs. This study aims to investigate the use of such methods for detecting ADEs when analyzing EPRs. The data used in this study was extracted from Stockholm EPR Corpus. Four disproportionality methods (proportional reporting rate, reporting odds ratio, Bayesian condence propagation neural network, and Gamma-Poisson shrinker) were applied in two dierent ways to analyze EPRs: creating pseudo spontaneous reports based on all observed drug-event pairs (event-level analysis) or analyzing distinct patients who experienced a drug-event pair (patient-level analysis). The methods were evaluated in a case study on safety surveillance of Celecoxib. The results showed that, among the top 200 signals, more ADEs were detected by the event-level analysis than by the patient-level analysis. Moreover, the event-level analysis also resulted in a higher mean average precision. The main conclusion of this study is that the way in which the disproportionality analysis is applied, the event-level or patient-level analysis, can have a much higher impact on the performance than which disproportionality method is employed.

  • 121991.
    Zhao, Jing
    et al.
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Papapetrou, Panagiotis
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Asker, Lars
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Boström, Henrik
    Stockholms universitet, Institutionen för data- och systemvetenskap.
    Learning from heterogeneous temporal data from electronic health records2017In: Journal of Biomedical Informatics, ISSN 1532-0464, E-ISSN 1532-0480, Vol. 65, p. 105-119Article in journal (Refereed)
    Abstract [en]

    Electronic health records contain large amounts of longitudinal data that are valuable for biomedical informatics research. The application of machine learning is a promising alternative to manual analysis of such data. However, the complex structure of the data, which includes clinical events that are unevenly distributed over time, poses a challenge for standard learning algorithms. Some approaches to modeling temporal data rely on extracting single values from time series; however, this leads to the loss of potentially valuable sequential information. How to better account for the temporality of clinical data, hence, remains an important research question. In this study, novel representations of temporal data in electronic health records are explored. These representations retain the sequential information, and are directly compatible with standard machine learning algorithms. The explored methods are based on symbolic sequence representations of time series data, which are utilized in a number of different ways. An empirical investigation, using 19 datasets comprising clinical measurements observed over time from a real database of electronic health records, shows that using a distance measure to random subsequences leads to substantial improvements in predictive performance compared to using the original sequences or clustering the sequences. Evidence is moreover provided on the quality of the symbolic sequence representation by comparing it to sequences that are generated using domain knowledge by clinical experts. The proposed method creates representations that better account for the temporality of clinical events, which is often key to prediction tasks in the biomedical domain.

  • 121992. Zhao, K.
    et al.
    Li, H. Y.
    Liu, J. C.
    Wang, C. K.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Dipolar effects on propagation of ultrashort laser pulse in one-dimensional para-nitroaniline (pNA) molecules2005In: Journal of Physics B: Atomic, Molecular and Optical Physics, ISSN 0953-4075, E-ISSN 1361-6455, Vol. 38, no 23, p. 4235-4245Article in journal (Refereed)
    Abstract [en]

    The dynamic behaviour of ultrashort (femtosecond) laser pulses in a molecular medium is studied by solving the full Maxwell-Bloch equations beyond the limits of the slowly varying envelope approximation and the rotating-wave approximation under the resonant and the non-resonant conditions. A one-dimensional asymmetric charge-transfer molecule, para-nitroaniline, is used as a model molecule whose electronic properties are calculated with the time-dependent hybrid density functional theory. Under the one-photon resonant condition, 4 pi pulse is separated into two sub-pulses. The weight of the second-harmonic component mainly contributed by the two-photon excitation becomes stronger with longer propagation time. Under the two-photon resonant condition, the separation of 4 pi pulse is not induced and many higher-order spectral components beyond the second-harmonic generation occur. Interestingly, when the pulse propagates for long enough, the carrier modification becomes so significant that a continuous spectrum is generated. The Fourier transform of the high-harmonic spectrum demonstrates that an even shorter laser pulse can be produced in both resonant and non-resonant propagations. The effects of permanent dipole moments on the pulse evolution are discussed.

  • 121993. Zhao, K.
    et al.
    Liu, J. C.
    Wang, C. K.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Resonant propagation of femtosecond laser pulse in DBASVP molecule: one-dimensional asymmetric organic molecule2005In: Chinese Physics (Beijing), ISSN 1009-1963, E-ISSN 1741-4199, Vol. 14, no 10, p. 2014-2018Article in journal (Refereed)
    Abstract [en]

    We have investigated the resonant propagation of femtosecond laser pulse in 4-trans-[p-(N, N-Di-n-butylamino)-p-stilbenyl vinyl] pyridine medium with permanent dipole moments. The electronic structures and parameters for the compound have been calculated by using density functional theory. In the optical regime, there is one charge-transfer state, and the molecule can thus be simplified as a two-level system. Both the one- and two-photon transitions occur between the ground and charge-transfer states. The numerical results show that the permanent dipole moments have an obvious effect on the propagation of the ultrashort pulse laser. The ideal self-induced transparency disappears for 2 pi pulse, and second harmonic spectral components occur significantly due to the two-photon absorption process. For the 6 pi pulse, continuum frequency generation is produced and a shorter duration pulse in time domain with 465 as is obtained.

  • 121994. Zhao, K.
    et al.
    Sun, Y. H.
    Wang, C. K.
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Zhang, X.
    Yu, X. Q.
    Jiang, M. H.
    Studies on two-photon absorption cross-sections of 1,4-dimethoxy-2,5-divinyl-benzene derivatives2005In: Wuli xuebao, ISSN 1000-3290, Vol. 54, no 6, p. 2662-2668Article in journal (Refereed)
    Abstract [zh]

    The one-photon and two-photon absorption properties of a series of 1, 4-dimethoxy-2, 5-divinyl-benzene derivatives are investigated by use of the analytic response theory at HF level. The one-photon and two-photon fluorescence spectra of E, E-2-5Bis[4'-(N, N-di-n-butylamino) styryl]-1 4-dimenthoxybenzene are measured. The numerical results show that these molecules have strong two-photon absorption cross sections. In the visible light region, the maximal one-photon absorption strengths of the molecules occur in the first excited state. Furthermore, the maximal two-photon absorption cross sections of the D-pi-A typed molecules still appear in the first state, but for D-pi-D typed molecules the second excited state has the maximal two-photon absorption cross-section. The optical properties of the molecules are closely related to the electric property of the donor and acceptor. The symmetrically substituted molecules can not be determined to have a larger two-photon absorption cross section than the asymmetrically substituted molecules for such a kind of pi-center. The charge-transfer process for the charge-transfer states is displayed, and then the mechanism of photopolymerization is discussed qualitatively.

  • 121995. Zhao, K.
    et al.
    Zhang, S.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    CLOSELY-LOCATED MIMO ANTENNAS OF TRI-BAND FOR WLAN MOBILE TERMINAL APPLICATIONS2010In: Journal Electromagnetic Waves and Applications, ISSN 0920-5071, E-ISSN 1569-3937, Vol. 24, no 2-3, p. 363-371Article in journal (Refereed)
    Abstract [en]

    A closely-located MIMO antennas of tri-band with an inter-PIFA (Planner Inverted-F Antenna) spacing of only 20mm is proposed for WLAN mobile terminal applications. Two L-shaped slots etched on each PIFA are introduced appropriately to achieve high isolation at higher frequencies and tri-band property. The MIMO antenna can operate in the bands of 2.4-2.4812 GHz, 5.07-5.4 GHz and 5.64-6.61 GHz, and the mutual couplings are less than -16.5 dB, -27 dB and -23 dB, respectively. Radiation pattern, gain and efficiency are also measured. Our designed antenna has the advantages of closely-located structure, tri-band, high isolation, small variation of gain and high efficiency.

  • 121996. Zhao, K.
    et al.
    Zhang, Shuai
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    He, Sailing
    KTH, School of Electrical Engineering (EES), Electromagnetic Engineering.
    ENHANCE THE BANDWIDTH OF A ROTATED RHOMBUS SLOT ANTENNA WITH MULIPLE PARASITIC ELEMENTS2010In: Journal Electromagnetic Waves and Applications, ISSN 0920-5071, E-ISSN 1569-3937, Vol. 24, no 14-15, p. 2087-2094Article in journal (Refereed)
    Abstract [en]

    The bandwidth of a printed antenna with a rotated rhombus slot is enhanced further by introducing 7 parasitic stripes, one of which is embedded on an edge of the rhombus slot downside while the others are on the upside. The mechanism of the wideband antenna is explained. The measured results indicate a large impedance bandwidth of 122.6% (1.59GHz-6.63 GHz) for VSWR < 2. The radiation patterns are also measured and relatively stable throughout the whole operating band.

  • 121997.
    Zhao, Kangqiao
    et al.
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Amir, Saifullah
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Meng, Xiaozhou
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Ali, Muhammad Mohsin
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Gustafsson, Martin
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Elnaggar, Mohammed Ismail
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    Rusu, Ana
    KTH, School of Information and Communication Technology (ICT), Electronic, Computer and Software Systems, ECS.
    A reconfigurable successive approximation ADC in 0.18μm CMOS technology2008In: 15th IEEE International Conference on Electronics, Circuits and Systems, 2008. ICECS 2008, IEEE conference proceedings, 2008, p. 646-649Conference paper (Refereed)
    Abstract [en]

    This paper presents the design of a reconfigurable successive approximation analog to digital converter (ADC) for both ultra wideband and Bluetooth applications. The behavioral level design is presented along with the circuit implementation. The ADC architecture employs a split capacitor array DAC which reduces the power consumption. The ADC is implemented in a 0.18mum CMOS process and circuit level simulation results show that the ADC can achieve 28.9 dB SINAD at 66 MSPS in the UWB mode, and 53.9 dB SINAD at 1 MSPS in the Bluetooth mode.

  • 121998.
    Zhao, Ke
    KTH, School of Biotechnology (BIO).
    Theoretical study of light-molecule nonlinear interactions2007Licentiate thesis, comprehensive summary (Other scientific)
    Abstract [en]

    The work presented in the thesis concerned theoretical study of light-matter nonlinear interactions. Two important aspects of such interactions have been examined, namely the nonlinear optical properties of a series of organic charge transfer molecules in solutions induced by the laser light and the propagation of the ultrafast high power laser through the nonlinear molecular medium.

    Special attention has been paid to understand the solvent effects on the two-photon absorption of a symmetrical diamino substituted distyrylbenzene chromophore, for which time-dependent density functional theory in combination with polarizable continuum model (PCM) have been employed. The dielectric medium alone has a rather small effect both on the bond length alternation and on the one-photon absorption spectrum, but noticeable effects on the two-photon absorption cross section. Both one- and two-photon absorptions are found to be extremely sensitive to the planarity of the molecule. Our calculations indicate that the experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores can not be attributed to the intrinsic properties of a single molecule and its interaction with solvents. With the same theoretical approaches, two-photon absorption properties of interacting polar chromophores have been investigated to examine the validity of the widely used exciton model. Our first principles calculations have shown that the exciton model offers a conceptually simple interpretation for experimental observations, but is lack of predictability.

    The second part of the thesis is to investigate the propagation of ultrashort laser pulse through a one-dimensional asymmetric organic molecular medium by solving full Maxwell-Bloch equations using predictor-corrector finite-difference time-domain method. It focuses on the supercontinuum generation of spectra and the formation of attosecond pulses. It is shown that the supercontinuum generation is strongly modulated by both area and width of the pulse, which results from the interference between the splitting pulses in time-domain and is the implication of the time-energy uncertainty relation. The presence of permanent dipole moment in molecular medium has noticeable effects on the supercontinuum generation. Our calculations show that a well-shaped 132 attosecond pulse can be generated from a two femtosecond incoming pulse under certain conditions. Influences of carrier-envelope phase and time-dependent ionization on the spectral and temporal evolutions of the ultrashort pulses have also been discussed.

  • 121999.
    Zhao, Ke
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Theoretical study on nonlinearoptical properties of organicchromophores in solutions2010Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Inter-molecular interactions have significant influences on linear and nonlinear optical properties of molecules including one- and two-photon absorptions, emissions, and various high order nonlinear polarizations. The related investigation has become an active and challenging research area. The theoretical structure-to-property relationship obtained from quantum chemical calculations of single organic conjugated molecules often can not be directly applied to real materials in condensed phases. One has to consider the effect of environment, that is, inter-molecular interactions, where the model systems experience in real experiments or applications. The change of molecular conformations under all kinds of interactions and its effects on linear and nonlinear optical properties are the central issue of this thesis.

    Special attentions have been paid to symmetrical diamino substituted distyrylbenzene chromophores with different torsional angles, two dipolar merocyanine dyes of various orientations, two isomers of a V-shaped 2-hydroxypyrimidine derivative and their various dimers, and the structural fluctuations of interacting polar chromophores in solutions. Quantum chemical methods in combination with molecular dynamics simulations have been employed to study molecular conformations and optical properties in solutions, in particular the solvent and aggregation effects on one- and two-photon absorption. More specifically, time-dependent density functional theory has been used for all electronic calculations, while the polarizable continuum model and supermolecule approach have also been employed to take into account solvent effects.

    Moreover, the propagation of an ultrashort laser pulse through a one-dimensional asymmetric organic molecular medium which possesses large permanent dipole moments has been simulated by solving full Maxwell-Bloch equations using predictor-corrector finite-difference time-domain method. We have focused on the supercontinuum generation of spectra and the formation of attosecond pulses.

  • 122000.
    Zhao, Ke
    et al.
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Ferrighi, Lara
    Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø.
    Frediani, Luca
    Centre for Theoretical and Computational Chemistry, Department of Chemistry, University of Tromsø.
    Wang, Chuan-Kui
    College of Physics and Electronics, Shandong Normal University, Jinan .
    Luo, Yi
    KTH, School of Biotechnology (BIO), Theoretical Chemistry.
    Solvent effects on two-photon absorption of dialkylamino substituted distyrylbenzene chromophore2007In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690, Vol. 126, no 20Article in journal (Refereed)
    Abstract [en]

    Solvent effects on the two-photon absorption of a symmetrical diamino substituted distyrylbenzene chromophore have been studied using the density functional response theory in combination with the polarizable continuum model. It is shown that the dielectric medium has a rather small effect both on the bond length alternation and on the one-photon absorption spectrum, but it affects significantly the two-photon absorption cross section. It is found that both one- and two-photon absorptions are extremely sensitive to the planarity of the molecule, and the absorption intensity can be dramatically reduced by the conformation distortion. It has led to the conclusion that the experimentally observed anomalous solvent effect on the two-photon absorption of dialkylamino substituted distyrylbenzene chromophores cannot be attributed to the intrinsic properties of a single molecule and its interaction with solvents.

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