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Dynamics of the radiative recombination in cylindrical nanostructures with type-II band alignment

Physical Review B 2009年第11期79卷 115307-115307页

作者： V. A. Shuvayev I. L. Kuskovsky L. I. Deych Y. Gu Y. Gong G. F. Neumark M. C. Tamargo A. A. Lisyansky Department of Physics Queens College of the City University of New York Flushing New York 11367 USA Department of Physics and Astronomy Materials Science Program Washington State University Pullman Washington 99164 USA Department of Applied Physics and Applied Mathematics Columbia University New York New York 10027 USA Department of Chemistry City College of the City University of New York New York New York 10036 USA

The electron and hole states and confining potential for cylindrical core-shell structure with type-II band alignment are obtained from a numerical solution of the self-consistent Schrödinger-Poisson system of equations. The photoluminescence (PL) kinetics is theoretically analyzed, with the nanostructure size dispersion taken into account. The results are applied to the radiative recombination in the system of ZnTe/ZnSe stacked quantum dots. A good agreement with both cw and time-resolved experimental observations is found. It is shown that size distribution results in the PL decay that has essentially nonexponential behavior even at the tail of the decay where the carrier lifetime is almost the same due to slowly changing overlap of the electron and hole wave functions. Finally, a model situation applicable to colloidal core-shell nanowires is investigated and discussed.

关键词： band structure colloids electron-hole recombination II-VI semiconductors nanowires photoluminescence Poisson equation Schrodinger equation semiconductor quantum dots semiconductor quantum wires time resolved spectra wave functions zinc compounds

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Electrification of granular systems of identical insulators

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Physical Review E 2009年第5期79卷 051304-051304页

作者： Jasper F. Kok Daniel J. Lacks Applied Physics Program University of Michigan Ann Arbor Michigan 48109 USA Atmospheric Oceanic and Space Sciences University of Michigan Ann Arbor Michigan 48109 USA Department of Chemical Engineering Case Western Reserve University Cleveland Ohio 44106 USA

Insulating particles can become highly electrified during powder handling, volcanic eruptions, and the wind-blown transport of dust, sand, and snow. Measurements in these granular systems have found that smaller particles generally charge negatively, while larger particles charge positively. These observations are puzzling since particles in these systems are generally chemically identical and thus have no contact potential difference. We show here that simple geometry leads to a net transfer of electrons from larger to smaller particles, in agreement with these observations. We integrate this charging mechanism into the first quantitative charging scheme for a granular system of identical insulators and show that its predictions are in agreement with measurements. Our theory thus seems to provide an explanation for the hitherto puzzling phenomenon of the size-dependent charging of granular systems of identical insulators.

关键词： particles mechanism insulators Electrification Identical insulators grainstone Volcanic Eruptions

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High Optical Absorption of Indium Sulfide Nanorod Arrays Formed by Glancing Angle Deposition

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MRS Online Proceedings Library 2009年第1期1165卷 1-6页

作者： M. F. Cansizoglu R. Engelken H. W. Seo T. Karabacak Department of Applied Science University of Arkansas at Little Rock Little Rock USA Electrical Engineering Program Arkansas State University State University Jonesboro USA Department of Physics and Astronomy University of Arkansas at Little Rock Little Rock USA

Indium (III) sulfide has recently attracted much attention due to its potential in optical sensors as a photoconducting material and in photovoltaic applications as a wide direct bandgap material. On the other hand, optical absorption properties are key parameters in developing highly photosensitive photodetectors and high efficiency solar cells. We show that indium sulfide nanorod arrays produced by glancing angle deposition techniques have superior absorption and low reflectance properties compared to conventional flat thin film counterparts. We observed an optical absorption value of approximately 96% for nanorods, in contrast to 80% for conventional amorphous-to-polycrystalline thin films of indium sulfide. A photoconductivity response was also observed in the nanorod samples, whereas no measurable photoresponse was detected in conventional thin films. We give a preliminary description of the enhanced light absorption properties of the nanorods by using Shirley-George Model that predicts enhanced diffuse scattering and reduced reflection of light due the rough morphology.

关键词： absorption photoconductivity photovoltaic

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Book Review: The Climate Caper

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Energy & Environment 2009年第8-1期20-21卷 1407-1410页

作者： Christopher Essex Professor of Applied Mathematics and former Director of the Program in Theoretical Physics at the University of Western Ontario Co-Author with Ross McKitrick of Taken by Storm:The Troubled Science Policy and Politics of Global Warming now in its second edition.

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37. Ice crystal shapes in antifreeze protein solutions

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Cryobiology 2010年第3期61卷 373-373页

作者： Ido Braslavsky Maya Bar Junjie Liu Yangzhong Qin Yeliz Celik Peter L. Davies J.S. Wettlaufer Department of Physics and Astronomy Ohio University Athens 45701 OH USA Faculty of Agriculture Food and Environment The Hebrew University of Jerusalem Rehovot 76100 Israel Department of Structural Biology Weizmann Institute of Science Rehovot 76100 Israel School of Physical Science and Technology Inner Mongolia University Hohhot 010021 China Department of Biochemistry Queen’s University Kingston Ontario K7L 3N6 Canada Department of Geology and Geophysics Yale University New Haven CT 06520 USA Department of Physics Yale University New Haven CT 06520 USA Program in Applied Mathematics Yale University New Haven CT 06520 USA

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Improving FRET detection in living cells

Improving FRET detection in living cells

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European Conference on Biomedical Optics, ECBO 2009

作者： Chang, Ching-Wei Wu, Mei Merajver, Sofia D. Mycek, Mary-Ann Department of Biomedical Engineering University of Michigan Ann Arbor MI 48109-2099 United States Department of Internal Medicine Division of Hematology and Oncology University of Michigan Ann Arbor MI 48109-2099 United States Comprehensive Cancer Center University of Michigan Ann Arbor MI 48109-2099 United States Applied Physics Program University of Michigan Ann Arbor MI 48109-2099 United States

Unambiguous FRET detection in living cells is often challenging. Here we describe how the advantages of fluorescence lifetime sensing with FLIM, fluorophore selection, and critical environmental controls provide bette... 详细信息

ISBN: (纸本)9780819476432

关键词： Forster resonance energy transfer

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Searches for cosmic-ray electron anisotropies with the Fermi Large Area Telescope

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Physical Review D 2010年第9期82卷 092003-092003页

作者： M. Ackermann M. Ajello W. B. Atwood L. Baldini J. Ballet G. Barbiellini D. Bastieri K. Bechtol R. Bellazzini B. Berenji E. D. Bloom E. Bonamente A. W. Borgland A. Bouvier J. Bregeon A. Brez M. Brigida P. Bruel R. Buehler T. H. Burnett S. Buson G. A. Caliandro R. A. Cameron P. A. Caraveo S. Carrigan J. M. Casandjian C. Cecchi Ö. Çelik E. Charles A. Chekhtman C. C. Cheung J. Chiang S. Ciprini R. Claus J. Cohen-Tanugi J. Conrad A. Cuoco C. D. Dermer A. de Angelis F. de Palma S. W. Digel G. Di Bernardo E. do Couto e Silva P. S. Drell R. Dubois C. Favuzzi S. J. Fegan W. B. Focke M. Frailis Y. Fukazawa S. Funk P. Fusco D. Gaggero F. Gargano S. Germani N. Giglietto P. Giommi F. Giordano M. Giroletti T. Glanzman G. Godfrey D. Grasso I. A. Grenier J. E. Grove S. Guiriec M. Gustafsson D. Hadasch A. K. Harding K. Hayashi E. Hays R. E. Hughes G. Jóhannesson A. S. Johnson W. N. Johnson T. Kamae H. Katagiri J. Kataoka M. Kerr J. Knödlseder M. Kuss J. Lande L. Latronico S.-H. Lee M. Lemoine-Goumard M. Llena Garde F. Longo F. Loparco M. N. Lovellette P. Lubrano A. Makeev M. N. Mazziotta J. E. McEnery J. Mehault P. F. Michelson T. Mizuno A. A. Moiseev C. Monte M. E. Monzani E. Moretti A. Morselli I. V. Moskalenko S. Murgia T. Nakamori M. Naumann-Godo P. L. Nolan E. Nuss T. Ohsugi A. Okumura N. Omodei E. Orlando J. F. Ormes D. Paneque J. H. Panetta D. Parent V. Pelassa M. Pepe M. Pesce-Rollins F. Piron T. A. Porter S. Profumo S. Rainò R. Rando M. Razzano A. Reimer O. Reimer T. Reposeur J. Ripken S. Ritz M. Roth H. F.-W. Sadrozinski A. Sander T. L. Schalk C. Sgrò J. Siegal-Gaskins E. J. Siskind D. A. Smith P. D. Smith G. Spandre P. Spinelli M. S. Strickman A. W. Strong D. J. Suson H. Takahashi T. Takahashi T. Tanaka J. B. Thayer J. G. Thayer D. J. Thompson L. Tibaldo D. F. Torres G. Tosti A. Tramacere Y. Uchiyama T. L. Usher J. Vandenbroucke V. Vasileiou N. Vilchez V. Vitale A. P. Waite P. Wang B. L. Winer K. S. Wood Z. Yang T. Ylinen G. Zaharijas M. Ziegler W. W. Hansen Experimental Physics Laboratory Kavli Institute for Particle Astrophysics and Cosmology Department of Physics and SLAC National Accelerator Laboratory Stanford University Stanford California 94305 USA Santa Cruz Institute for Particle Physics Department of Physics and Department of Astronomy and Astrophysics University of California at Santa Cruz Santa Cruz California 95064 USA Istituto Nazionale di Fisica Nucleare Sezione di Pisa I-56127 Pisa Italy Laboratoire AIM CEA-IRFU/CNRS/Université Paris Diderot Service d’Astrophysique CEA Saclay 91191 Gif sur Yvette France Istituto Nazionale di Fisica Nucleare Sezione di Trieste I-34127 Trieste Italy Dipartimento di Fisica Università di Trieste I-34127 Trieste Italy Istituto Nazionale di Fisica Nucleare Sezione di Padova I-35131 Padova Italy Dipartimento di Fisica “G. Galilei ” Università di Padova I-35131 Padova Italy Istituto Nazionale di Fisica Nucleare Sezione di Perugia I-06123 Perugia Italy Dipartimento di Fisica Università degli Studi di Perugia I-06123 Perugia Italy Dipartimento di Fisica “M. Merlin” dell’Università e del Politecnico di Bari I-70126 Bari Italy Istituto Nazionale di Fisica Nucleare Sezione di Bari 70126 Bari Italy Laboratoire Leprince-Ringuet École polytechnique CNRS/IN2P3 Palaiseau France Department of Physics University of Washington Seattle Washington 98195-1560 USA Institut de Ciencies de l’Espai (IEEC-CSIC) Campus UAB 08193 Barcelona Spain INAF-Istituto di Astrofisica Spaziale e Fisica Cosmica I-20133 Milano Italy NASA Goddard Space Flight Center Greenbelt Maryland 20771 USA Center for Research and Exploration in Space Science and Technology (CRESST) and NASA Goddard Space Flight Center Greenbelt Maryland 20771 USA Department of Physics and Center for Space Sciences and Technology University of Maryland Baltimore County Baltimore Maryland 21250 USA Space Science Division Naval Research Laboratory Washington D.C. 20375 USA George Mason University Fairfax Virgin

The Large Area Telescope on board the Fermi satellite (Fermi LAT) detected more than 1.6×106 cosmic-ray electrons/positrons with energies above 60 GeV during its first year of operation. The arrival directions of these events were searched for anisotropies of angular scale extending from ∼10° up to 90°, and of minimum energy extending from 60 GeV up to 480 GeV. Two independent techniques were used to search for anisotropies, both resulting in null results. Upper limits on the degree of the anisotropy were set that depended on the analyzed energy range and on the anisotropy’s angular scale. The upper limits for a dipole anisotropy ranged from ∼0.5% to ∼10%.

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Resonance effects due to the excitation of surface Josephson plasma waves in layered superconductors

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Physical Review B 2009年第21期79卷 214501-214501页

作者： V. A. Yampol’skii A. V. Kats M. L. Nesterov A. Yu. Nikitin T. M. Slipchenko Sergey Savel’ev Franco Nori Advanced Science Institute The Institute of Physical and Chemical Research (RIKEN) Wako-shi Saitama 351-0198 Japan A.Ya. Usikov Institute for Radiophysics and Electronics Ukrainian Academy of Sciences 61085 Kharkov Ukraine Department of Physics Loughborough University Loughborough LE11 3TU United Kingdom Department of Physics Center for Theoretical Physics Applied Physics Program Center for the Study of Complex Systems University of Michigan Ann Arbor Michigan 48109-1040 USA

We analytically examine the excitation of surface Josephson plasma waves (SJPWs) in layered superconductors by an incident electromagnetic wave. The mechanism of excitation is related to the diffraction of the incident wave due to a small periodic modulation in the ab plane of the maximum c-axis Josephson current density. We show that the absorption of the incident wave can be substantially increased, for certain incident angles, due to the resonance excitation of SJPWs. The absorption increase is accompanied by a decrease in the specular reflection. Moreover, we find the dependence of the resonance value of the incident angle on the parameters of the superconductor and the frequency of the incident wave, and the depth of the modulations guaranteeing the total absorption (and total suppression of the specular reflection). Numerical examples of the resonance effects are presented for Bi2212 superconductors.

关键词： bismuth compounds calcium current density electromagnetic wave absorption electromagnetic wave diffraction high-temperature superconductors Josephson effect resonance solid-state plasma strontium compounds

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Breast tomosynthesis reconstruction with a multi-beam x-ray source

Breast tomosynthesis reconstruction with a multi-beam x-ray ...

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Medical Imaging 2009: physics of Medical Imaging

作者： Chen, Ying Zhou, Weihua Yang, Guang Qian, Xin Lu, Jianping Zhou, Otto Dept. of Electrical and Computer Engineering Southern Illinois University Carbondale IL 62901 United States Biomedical Engineering Graduate Program Southern Illinois University Carbondale IL 62901 United States Dept. of Physics and Astronomy and Curriculum in Applied Sciences and Engineering University of North Carolina Chapel Hill NC 27599 United States Lineberger Comprehensive Cancer Center University of North Carolina Chapel Hill NC 27599 United States

ISBN: (纸本)9780819475091

As a new three-dimensional breast imaging technique, breast tomosynthesis allows the reconstruction of an arbitrary set of planes in the breast from a limited-angle series of x-ray projection images. The breast tomosynthesis technique has been demonstrated as promising to improve early breast cancer detection. This paper represents a preliminary phantom study and computer simulation results of different breast tomosynthesis reconstruction algorithms with a novel carbon nanotube based multi-beam x-ray source. Five representative tomosynthesis reconstruction algorithms, including back projection (BP), filtered back projection (FBP), matrix inversion tomosynthesis (MITS), maximum likelihood expectation maximization (MLEM), and simultaneous algebraic reconstruction technique (SART) were investigated. Tomosynthesis projection images of a phantom were acquired with the stationary multi-beam x-ray tomosynthesis system. Reconstruction results from different algorithms were studied. A computer simulation study was further done to investigate the sharpness of reconstructed in-plane structures and to see how effective each algorithm is at removing outof- plane blur with parallel-imaging geometries. Datasets with 9 and 25 projection images of a defined 3D spherical object were simulated with a total view angle of 50 degrees. Results showed that the multi-beam x-ray system is capable to generate 3D tomosynthesis images with faster speed compared with current commercial prototype systems. With simulated parallel-imaging geometry, MITS and FBP showed edge enhancement in-plane performance. BP, FBP and MLEM performed better at out-of-plane structure removal with larger number of projection images. © 2009 SPIE.

关键词： Carbon nanotubes

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Drastic change of the Casimir force at the metal-insulator transition

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Physical Review B 2009年第12期80卷 125119-125119页

作者： E. G. Galkina B. A. Ivanov Sergey Savel’ev V. A. Yampol’skii Franco Nori Advanced Science Institute The Institute of Physical and Chemical Research (RIKEN) Wako-shi Saitama 351-0198 Japan Institute of Physics 03028 Kiev Ukraine Institute of Magnetism 03142 Kiev Ukraine National T. Shevchenko University of Kiev 03127 Kiev Ukraine Department of Physics Loughborough University Loughborough LE11 3TU United Kingdom A. Ya. Usikov Institute for Radiophysics and Electronics 61085 Kharkov Ukraine Department of Physics Center for Theoretical Physics Applied Physics Program The University of Michigan Ann Arbor Michigan 48109-1040 USA

The dependence of the Casimir force on material properties is important for both future applications and to gain further insight on its fundamental aspects. Here we apply the general Lifshitz theory of the Casimir force to low-conducting compounds, or poor metals. For distances in the micrometer range, the Casimir force for a large variety of such materials is described by universal equations containing a few parameters: the effective plasma frequency ωp, dissipation rate γ of the free carriers, and electric permittivity ε∞ for ω≥ωp (in the infrared range). This theory of the Casimir force for poor metals can also describe inhomogeneous composite materials containing small regions with different conductivity. The Casimir force for systems involving samples made with compounds that have a metal-insulator transition shows a drastic change of the Casimir force within the transition region, where the metallic and dielectric phases coexist. Indeed, the Casimir force can increase by a factor of 2 near this transition.

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