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IEEE Photonics Conference (IPC)

作者： Burak Guzelturk Talha Erdem Emre Unal Sedat Nizamoglu Donus Tuncel Hilmi Volkan Demir Department of Electrical and Electronics Engineering Department of Physics Department of Chemistry and UNAM-Institute of Materials Science and Nanotechnology Bilkent University Ankara Turkey School of Electrical & Electronic Engineering Division of Microelectronics School of Mathematical and Physical Sciences Luminous Semiconductor Lighting and Display Center of Excellence Nanyang Technological University Singapore Singapore

Semiconductor nanocrystal quantum dots with their tunable optical properties, narrow photoluminescence, and high photostability have generated great interest in light-emitting device applications. [1, 2] Such colloidal quantum dots that are directly electrically driven in light-emitting diode (LED) structures have been extensively studied in the last decade. However, these LEDs unfortunately suffer from the fundamental problem of poor charge injection into these nanocrystals, which have high potential barriers due to their ligands surrounding them. This problem has been investigated and attempted to be minimized through various optimization methods. [3, 4] As a result, although today the device external quantum efficiencies can now reach ca 2.7 % [5], the main problem with charge injection still exists. On the other hand, conjugated conductive polymers are being used for organic based LEDs for several decades. These LEDs can reach higher quantum efficiencies over 20 % [6]. But these devices suffer in most of the cases from instabilities and degradation of the polymer active layers. To combine the advantages of each material system, hybrid organic-inorganic structures have also previously been investigated to obtain more ingenious devices. However, in all of these hybrid devices, the basic operation has mainly been based on the same mechanism of conventional charge injection into the nanocrystal active material.

关键词： Quantum dots Plastics Energy exchange Light emitting diodes Nanocrystals Photoluminescence

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Observation of anisotropic emission from semiconductor quantum dots in nanocomposites of metal nanoparticles

Observation of anisotropic emission from semiconductor quant...

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IEEE Photonics Conference (IPC)

作者： Tuncay Ozel Sedat Nizamoglu Mustafa A. Sefunc Olga Samarskaya Ilkem O. Ozel Evren Mutlugun Vladimir Lesnyak Nikolai Gaponik Alexander Eychmuller Sergey V. Gaponenko Hilmi Volkan Demir Department of Physics Department of Electrical and Electronics Engineering and UNAM-Institute of Materials Science and Nanotechnology Bilkent University Ankara Turkey Physical Chemistry Technical University of Dresden Dresden Germany Stepanov Institute of Physics National Academy of Science of Belarus Minsk Belarus School of Electrical & Electronic Engineering Division of Microelectronics School of Mathematical and Physical Sciences Luminous Semiconductor Lighting and Display Center of Excellence Nanyang Technological University Singapore Singapore

This paper investigates and demonstrates anisotropic enhanced emission from semiconductor quantum dots placed in multilayered plasmon resonator nanocomposite s using strong plasmon-exciton interactions . In these metal nanoparticle (MNP) resonator architectures, we show that highly isotropic nature of QD emission c an desirably be altered through modifying emission kinetics by plasmon coupling, while also enhancing the overall QD emission.

关键词： Plasmons Films Nanoparticles Gold Couplings Quantum dots

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Angular spectral plane-wave expansion of nonstationary random fields in stochastic mode-stirred reverberation processes

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physical Review E 2010年第4期81卷 041133-041133页

作者： Luk R. Arnaut Time Quantum and Electromagnetics Division National Physical Laboratory Teddington TW11 0LW United Kingdom and Department of Electrical and Electronic Engineering Imperial College of Science Technology and Medicine South Kensington Campus London SW7 2AZ United Kingdom

We derive an integral expression for the plane-wave expansion of the time-varying (nonstationary) random field inside a mode-stirred reverberation chamber. It is shown that this expansion is a so-called oscillatory process, whose kernel can be expressed explicitly in closed form. The effect of nonstationarity is a modulation of the spectral density of the field on a time scale that is a function of the cavity relaxation time. It is also shown how the contribution by a nonzero initial value of the field can be incorporated into the expansion. The results are extended to a special class of second-order processes, relevant to the reception of a mode-stirred reverberation field by a device under test with a first-order (relaxation-type) frequency response.

关键词： Reverberation

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Polar vs. nonpolar InGaN/GaN quantum heterostructures: Opposite quantum confined electroabsorption and carrier dynamics behavior

Polar vs. nonpolar InGaN/GaN quantum heterostructures: Oppos...

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IEEE PhotonicsGlobal@Singapore, IPGC

作者： Emre Sari Sedat Nizamoglu Jung Hun Choi Seung Jae Lee Kwang Hyeon Baik In Hwan Lee Jong Hyeob Baek Sung-Min Hwang Hilmi Volkan Demir Department of Electrical and Electronics Engineering Department of Physics Nanotechnology Research Center and National Institute of Materials Science and Nanotechnology UNAM Bilkent University Ankara Turkey School of Advanced Materials Engineering Chonbuk National University of Korea Cheongju South Korea Korea Photonics Technology Institute Gwangju South Korea Optoelectronics Laboratory Korea Electronics and Technology Institute Seongnam Gyeonggi South Korea School of Electrical and Electronic Engineering Microelectronics Division School of Physical and Mathematical Sciences Physics and Applied Physics Division Nanyang Technological University Singapore

We present a study of quantum confined electroabsorption and carrier dynamics in polar c-plane and nonpolar a-plane InGaN/GaN quantum heterostructures. We demonstrate red-shifting absorption edge, due to quantum confined Stark effect, in nonpolar InGaN/GaN quantum structures in response to increased electric field, while we show the opposite effect with blue-shifting absorption spectra in polar quantum structures. Moreover, confirmed by time-resolved photoluminescence measurements, we prove that carrier lifetimes increase with increasing electric field for nonpolar structures, whereas the opposite occurs for polar ones.

关键词： Electric fields Gallium nitride Absorption Electrostatics Physics Materials Charge carrier processes

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Nonspherical laser-induced cavitation bubbles

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physical Review E 2010年第1期81卷 016308-016308页

作者： Kang Yuan Lim Pedro A. Quinto-Su Evert Klaseboer Boo Cheong Khoo Vasan Venugopalan Claus-Dieter Ohl Division of Physics and Applied Physics School of Physical and Mathematical Sciences Nanyang Technological University 21 Nanyang Link Singapore 637371 Singapore Institute of High Performance Computing Fusionopolis 1 Fusionopolis Way #16-16 Connexis Singapore 138632 Singapore Department of Mechanical Engineering National University of Singapore 10 Kent Ridge Crescent Singapore 119260 Singapore Department of Chemical Engineering and Materials Science and Laser Microbeam and Medical Program Beckman Laser Institute University of California Irvine California 92697-2575 USA

The generation of arbitrarily shaped nonspherical laser-induced cavitation bubbles is demonstrated with a optical technique. The nonspherical bubbles are formed using laser intensity patterns shaped by a spatial light modulator using linear absorption inside a liquid gap with a thickness of 40 μm. In particular we demonstrate the dynamics of elliptic, toroidal, square, and V-shaped bubbles. The bubble dynamics is recorded with a high-speed camera at framing rates of up to 300 000 frames per second. The observed bubble evolution is compared to predictions from an axisymmetric boundary element simulation which provides good qualitative agreement. Interesting dynamic features that are observed in both the experiment and simulation include the inversion of the major and minor axis for elliptical bubbles, the rotation of the shape for square bubbles, and the formation of a unidirectional jet for V-shaped bubbles. Further we demonstrate that specific bubble shapes can either be formed directly through the intensity distribution of a single laser focus, or indirectly using secondary bubbles that either confine the central bubble or coalesce with the main bubble. The former approach provides the ability to generate in principle any complex bubble geometry.

关键词： High speed cameras

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Exploring new routes for the development of functional nanomaterials using extreme pressure

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作者： Lipinska, K. Kalita, P. Hemmers, O. Sinogeikin, S. Mariotto, G. Segre, C. Ohki, Y. Department of Chemistry and Harry Reid Center for Environmental Studies University of Nevada Las Vegas NV United States Department of Physics University of Nevada Las Vegas Las Vegas United States Geophysical Laboratory Carnegie Institution of Washington Washington DC United States Faculty of Mathematical Physical and Natural Science University of Verona Verona Italy Physics Division BCPS Department Illinois Institute of Technology Chicago United States Department of Electrical Engineering and Bioscience Waseda University Tokyo Japan

ISBN: (纸本)9780470927151

High-pressure offers the thrilling possibility to synthesize novel solids with unique optical, electronic, magnetic or thermo-mechanical properties that is currently a major challenge in materials science. Some of our recent high-pressure studies of glass-derived nanocrystalline composite using diamond anvil cell technology and synchrotron radiation based x-ray diffraction are presented. We synthesized and investigated pressure-induced transformations occurring in a heterophased, nano-architectured composite that consists of an amorphous matrix and embedded nanocrystals or quantum dots of gallium oxide. We discuss the observed phase transition occurring in the nanocrystals seeded in a host glass matrix and we compare their equation of state and bulk modulus with that of bulk gallium oxide crystals.

关键词： Nanocrystals

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Tracking motor recovery in stroke survivors undergoing rehabilitation using wearable technology

Tracking motor recovery in stroke survivors undergoing rehab...

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Annual International Conference of the IEEE engineering in Medicine and Biology Society (EMBC)

作者： Shyamal Patel Richard Hughes Todd Hester Joel Stein Metin Akay Jennifer Dy Paolo Bonato Department of Physical Medicine and Rehabilitation Harvard Medical School Spaulding Rehabilitation Hospital Boston MA USA Biomedical Engineering Department University of Houston Houston TX USA Department of Computer Science University of Texas Austin Austin TX USA Department of Electrical and Computer Engineering Northeastern University Boston MA USA Division of Health Sciences and Technology Harvard and Massachusetts Institute of Technology Cambridge MA USA

Quantitative assessment of motor abilities in stroke survivors undergoing rehabilitation can be a valuable feedback to guide the rehabilitation process. The Functional Ability Scale (FAS) part of Wolf Motor Function Test (WMFT) is used to evaluate movement quality during performance of a set of functional motor tasks. In this paper, we show that information collected using body worn sensors such as accelerometers during performance of functional motor tasks by stroke survivors can be used to build accurate classifiers of FAS scores for individual tasks. We perform feature selection to improve classification accuracy and show that it is possible to estimate the total FAS score from a subset of functional motor tasks taken from the WMFT.

关键词： Feature extraction Accelerometers Indexes Wearable sensors Conferences Data mining Classification algorithms

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Correction to "Multiuser Switched Diversity Scheduling Systems with Per-User Threshold" [May 10 1321-1326]

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IEEE Transactions on Communications 2010年第12期58卷 3631-3631页

作者： Haewoon Nam Mohamed-Slim Alouini Mobile Devices Technology Office Motorola Inc. Austin TX USA Electrical Engineering Program Division of Physical and Chemical Sciences and Engineering King Abdullah University for Science and Technology Thuwal Saudi Arabia

In the above titled paper (ibid., vol. 58, no. 5, pp. 1321-1326), Fig. 1 was incorrectly duplicated in the place of Fig. 2. The correct Fig. 2 is presented here.

关键词： Scheduling Diversity methods

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The valence charge polarization induced by the shorter and stronger bonds between under-coordinated gold atoms

The valence charge polarization induced by the shorter and s...

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IEEE International Nanoelectronics Conference (INEC)

作者： Xi Zhang Jer-lai Kuo Mingxia Gu Xiaofeng Fan Ping Bai Qing Gong Song C.Q. Sun School of Electrical and Electronic Engineering Nanyang Technological University Singapore Singapore School of Physical and Mathematical Science Nanyang Technological University Singapore Singapore Advanced Photonics and Plasmonics Division ASTAR-Institute of High Performance Computing Singapore Advanced Photonics and Plasmonics Division A*STAR Institute of High Performance Computing Singapore School of Science Civil Aviation University of China Tianjin China Sch. of Electr. & Electron. Eng. Nanyang Technol. Univ. Singapore Singapore

ISBN: (纸本)9781424435432

Relativistic density functional theory calculations have been conducted to examine the effect of atomic under-coordination. The calculated results agree exceedingly well with experimental observations: skin-depth bond contraction, chain end stats polarization, potential well depression, core level shift, and the valence charge polarization of gold nanostructures. Consistency between calculations and experimental observations affirms the prediction of the bond-order-length-strength (BOLS) correlation theory [Sun CQ, Phys Rev B 69, 045105 (2004)], asserting that the under-coordinated surface atoms are indeed associated with local strain, quantum trap depression, charge densification and valence charge polarization and that the locally polarized and pinned electrons are responsible for the metal-insulator transition and magnetism present of gold nanoparticles.

关键词： Polarization Gold Density functional theory Potential well Nanostructures Bonding Sun Magnetic field induced strain Quantum mechanics Electron traps

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Fiber-to-bundle registration of white matter tracts

Fiber-to-bundle registration of white matter tracts

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Medical Imaging 2009 - Image Processing

作者： Xu, Qing Anderson, Adam W. Gore, John C. Ding, Zhaohua Vanderbilt University Institute of Imaging Science United States Department of Electrical Engineering and Computer Science Vanderbilt University United States Department of Biomedical Engineering Vanderbilt University United States Chemical and Physical Biology Program Vanderbilt University United States

ISBN: (纸本)9780819475107

Magnetic resonance diffusion tensor imaging (DTI) is being widely used to reconstruct brain white matter (WM) fiber tracts. For further characterization of the tracts, the fibers with similar courses often need to be grouped into a fiber bundle that corresponds to certain underlying WM anatomic structure. In addition, the alignments of fibers from different studies are often desirable for bundle comparisons and group analysis. In this work, a novel registration algorithm based on fiber-to-bundle matching was proposed to address the above two needs. Using an Expectation Maximization (EM) algorithm, the proposed method is capable of estimating a Thin-Plate- Spline transformation that optimally aligns whole-brain target fiber sets with a reference bundle model. Based on the resulting transformations, the fibers from different target datasets can all be warped into the reference coordinate system for comparisons and group analysis. The fibers can be further automatically labeled according to their similarity to the reference model. The algorithm was evaluated with eight human brain DTI data volumes acquired in vivo at 3T. After registration, the warped target bundles exhibit good similarity to the reference bundles. Quantitative experiments further demonstrated that the detected target bundles agree with ground truth obtained by manual segmentation at a sub-voxel accuracy. © 2009 Copyright SPIE - The International Society for Optical engineering.

关键词： Fibers

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