bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent advances in direct solar thermal power generation
Authors: Deng Yue-Guang , Liu Jing
Published: October 2009

The recent energy crisis and environmental burden are becoming increasingly urgent and drawing enormous attention to solar-energy utilization. Direct solar thermal power generation technologies, such as thermoelectric, thermionic, magnetohydrodynamic, and alkali-metal thermoelectric methods, are among the most attractive ways to provide electric energy from solar heat. On the one hand, these methods have the potential to be more efficient than traditional ways since they can convert heat to electricity directly without experiencing the conventional intermediate mechanical energy conversion process; on the other hand, these electricity generators are generally silent, reliable, and scalable, making them very suitable to serve as a distributed power generation system for certain specialized fields, such as military and space applications. A lot of effort has been devoted to investigate the energy conversion theory and practical applications thus far. This paper is intended to present a thorough review on recent advances in developing the thermoelectric, thermionic, magnetohydrodynamic, and alkali-metal thermoelectric technologies for direct solar thermal power generation. Both the fundamental issues and latest application research are illustrated and critical issues are discussed. The paper concludes with a description of future developments expected in the subjects covered.
Enhancement of (BH)max in a hard-soft-ferrite nanocomposite using exchange spring mechanism
Authors: Roy Debangsu , Kumar P. S. Anil
Published: October 2009

We have observed the exchange spring behavior in the soft (Fe3O4)-hard (BaCa2Fe16O27)-ferrite composite by tailoring the particle size of the individual phases and by suitable thermal treatment of the composite. The magnetization curve for the nanocomposite heated at 800 °C shows a single loop hysteresis showing the existence of the exchange spring phenomena in the composite and an enhancement of 13% in (BH)max compared to the parent hard ferrite (BaCa2Fe16O27). The Henkel plot provides the proof of the presence of the exchange interaction between the soft and hard grains as well as its dominance over the dipolar interaction in the nanocomposite.
Inadequacies in the conventional treatment of the radiation field of moving sources
Authors: Ardavan Houshang , Ardavan Arzhang , Singleton John , Fasel Joseph , Schmidt Andrea
Published: October 2009

There is a fundamental difference between the classical expression for the retarded electromagnetic potential and the corresponding retarded solution of the wave equation that governs the electromagnetic field. While the boundary contribution to the retarded solution for the potential can always be rendered equal to zero by means of a gauge transformation that preserves the Lorenz condition, the boundary contribution to the retarded solution of the wave equation governing the field may be neglected only if it diminishes with distance faster than the contribution of the source density in the far zone. In the case of a source whose distribution pattern both rotates and travels faster than light in vacuo, as realized in recent experiments, the boundary term in the retarded solution governing the field is by a factor of the order of R1/2 larger than the source term of this solution in the limit that the distance R of the boundary from the source tends to infinity. This result is consistent with the prediction of the retarded potential that part of the radiation field generated by a rotating superluminal source decays as R−1/2, instead of R−1, a prediction that is confirmed experimentally. More importantly, it pinpoints the reason why an argument based on a solution of the wave equation governing the field in which the boundary term is neglected (such as appears in the published literature) misses the nonspherical decay of the field.
Artificial molecular quantum rings under magnetic field influence
Authors: Castelano L. K. , Hai G.-Q. , Partoens B. , Peeters F. M.
Published: October 2009

The ground states of a few electrons confined in two vertically coupled quantum rings in the presence of an external magnetic field are studied systematically within the current spin-density functional theory. Electron-electron interactions combined with inter-ring tunneling affect the electronic structure and the persistent current. For small values of the external magnetic field, we recover the zero magnetic field molecular quantum ring ground state configurations. Increasing the magnetic field many angular momentum, spin, and isospin transitions are predicted to occur in the ground state. We show that these transitions follow certain rules, which are governed by the parity of the number of electrons, the single-particle picture, Hund’s rules, and many-body effects.
Characterization of damage induced by heavy neutron irradiation on multilayered L6iF-single crystal chemical vapor deposition diamond detectors
Authors: Almaviva S. , Angelone M. , Marinelli Marco , Milani E. , Pillon M. , Prestopino G. , Tucciarone A. , Verona C. , Verona-Rinati G.
Published: October 2009

High performance neutron detectors sensitive to both thermal and fast neutrons are of great interest to monitor the high neutron flux produced, e.g., by fission and fusion reactors. An obvious requirement for such an application is neutron irradiation hardness. This is why diamond based neutron detectors are currently under test in some of these facilities. In this paper the damaging effects induced in chemical vapor deposition (CVD) diamond based detectors by a neutron fluence of ∼2×1016 neutrons/cm2 have been studied and significant changes in spectroscopic, electrical, and optical properties have been observed. The detectors are fabricated using high quality synthetic CVD single crystal diamond using the p-type/intrinsic/Schottky metal/L6iF layered structure recently proposed by Marinelli et al. [Appl. Phys. Lett. 89, 143509 (2006)], which allows simultaneous detection of thermal and fast neutrons. Neutron radiation hardness up to at least 2×1014 n/cm2 fast (14 MeV) neutron fluence has been confirmed so far [see Pillon et al., (Fusion Eng. Des. 82, 1174 (2007)]. However, at the much higher neutron fluence of ∼2×1016 neutrons/cm2 damage is observed. The detector response to 5.5 MeV A241m α-particles still shows a well resolved α-peak, thus confirming the good radiation hardness of the device but a remarkable degradation and a significant instability with time of charge collection efficiency and energy resolution arise. Symmetric, nearly Ohmic I-V (current-voltage) characteristics have been recorded from the metal/intrinsic/p-doped diamond layered structure, which before neutron irradiation acted as a Schottky barrier diode with a strong rectifying behavior. The nature and the distribution of the radiation induced damage have been deeply examined by means of cathodoluminescence spectroscopy. A more heavily damaged area into the intrinsic diamond at the same position and with the same extension of the L6iF layer has been found, the increased damage being ascribed to the highly ionizing particles produced in the L6iF layer by thermal neutrons through the nuclear reaction L6i(n,α)T.
On the sensitivity to noise of a Boolean function
Authors: Matache Mihaela T. , Matache Valentin
Published: October 2009

In this paper we generate upper and lower bounds for the sensitivity to noise of a Boolean function using relaxed assumptions on input choices and noise. The robustness of a Boolean network to noisy inputs is related to the average sensitivity of that function. The average sensitivity measures how sensitive to changes in the inputs the output of the function is. The average sensitivity of Boolean functions can indicate whether a specific random Boolean network constructed from those functions is ordered, chaotic, or in critical phase. We give an exact formula relating the sensitivity to noise and the average sensitivity of a Boolean function. The analytic approach is supplemented by numerical results that illustrate the overall behavior of the sensitivities as various Boolean functions are considered. It is observed that, for certain parameter combinations, the upper estimates in this paper are sharper than other estimates in the literature and that the lower estimates are very close to the actual values of the sensitivity to noise of the selected Boolean functions.
Electrostatics of pyroelectric accelerators
Authors: Fullem T. Z. , Danon Y.
Published: October 2009

Derivations for equations for calculating the potential and field strength in both single-crystal and two-crystal pyroelectric accelerators are presented. Such expressions for the single-crystal system are well established in the literature, but with cursory derivations. We provide a rigorous derivation of the single-crystal system and expand upon this physical understanding to derive expressions for the potential and field in a two-crystal system. The expressions are verified with finite element modeling and compared with experimental results. This allows for better understanding of pyroelectric accelerators.
Photochemistry of the water dimer: Time-dependent quantum wave-packet description of the dynamics at the S1-S conical intersection
Authors: Chmura Bartosz , Lan Zhenggang , Rode Michal F. , Sobolewski Andrzej L.
Published: October 2009

The photoinduced electron-driven proton-transfer dynamics of the water-dimer system has been investigated by time-dependent quantum wave-packet calculations. The main nuclear degrees of freedom driving the system from the Frank–Condon region to the S0-S1 conical intersection are the distance between the oxygen atoms and the displacement of the hydrogen atom from the oxygen-oxygen bond center. Two important coupling modes have been investigated: Rotation of the H-donating water dangling proton and asymmetric stretching of the H-accepting water dangling protons’ OaH bonds. Potential energy surfaces of the ground and lowest excited electronic states have been constructed on the basis of ab initio calculations. The time-dependent quantum wave-packet propagation has been employed within the (2 + 1)-dimensional systems for the description of the nonadiabatic dynamics of water dimer. The effects of the initial vibrational state of the system on the electronic population transfer and dissociation dynamics are presented. To approximate the photochemical behavior of water dimer in bulk water, we add a boundary condition into the (2 + 1)-dimensional systems to simulate the existence of water bulk. The results provide insight into the mechanisms of excited state deactivation of the water-dimer system in gas phase and in bulk water through the electron-driven proton-transfer process.
Independent component analysis for beam measurements
Authors: Pang X. , Lee S. Y.
Published: October 2009

Independent component analysis (ICA) has been used for data mining in many branches of science. In beam physics, ICA can be applied to analyze turn-by-turn beam position monitor data of beam motion. The narrow-band filtering of ICA provides us methods to identify and extract information on the linear betatron and synchrotron motion, effects of wake fields, etc. We show that the ICA is also a powerful tool to measure nonlinear magnetic field in accelerators. Numerical simulations are used to demonstrate the ability to obtain sextupole strengths at high precision. The methods can be extended to other higher order multipoles.
Asymptotic stability of the stationary solution to an initial boundary value problem for the Mullins equation of fourth order
Authors: Zhu Peicheng
Published: October 2009

In the present article we first study the existence of the stationary solution to an initial boundary value problem for the Mullins equation of fourth order, which was proposed by Mullins [“Two-dimensional motion of idealized grain boundaries,” J. Appl. Phys. 27, 900 (1956)] to describe the groove development, due to the surface diffusion, at the grain boundaries of a heated polycrystal. Then employing an energy method we prove that this stationary solution is asymptotically stable in a suitable norm as time goes to infinity.
A study of the orthogonal polynomials associated with the quantum harmonic oscillator on constant curvature spaces
Authors: Vignat C. , Lamberti P. W.
Published: October 2009

Recently, Cariñena, et al. [Ann. Phys. 322, 434 (2007)] introduced a new family of orthogonal polynomials that appear in the wave functions of the quantum harmonic oscillator in two-dimensional constant curvature spaces. They are a generalization of the Hermite polynomials and will be called curved Hermite polynomials in the following. We show that these polynomials are naturally related to the relativistic Hermite polynomials introduced by Aldaya et al. [Phys. Lett. A 156, 381 (1991)], and thus are Jacobi polynomials. Moreover, we exhibit a natural bijection between the solutions of the quantum harmonic oscillator on negative curvature spaces and on positive curvature spaces. At last, we show a maximum entropy property for the ground states of these oscillators.
Nonpolar GaN substrates grown by ammonothermal method
Authors: Kucharski R. , Rudziński M. , Zając M. , Doradziński R. , Garczyński J. , Sierzputowski L. , Kudrawiec R. , Serafińczuk J. , Strupiński W. , Dwiliński R.
Published: October 2009

In this letter, the authors demonstrate large size m-plane GaN substrates grown by ammonothermal method. These substrates have excellent structural quality. The concentration of threading dislocation density is below 5×104 cm−2 and the full width at half maximum for the symmetrical and asymmetrical peaks equals 16 and 19 arc sec, respectively. Also good optical quality, the energy gap-related transition is clearly observed at room temperature in photoluminescence and contactless electroreflectance spectra. GaN epilayers deposited on these substrates exhibit intrinsic narrow exciton lines which are very sensitive to the optical selection rules typical for hexagonal symmetry, proving truly nonpolar character of the material.
Quasi-Lie schemes and Emden–Fowler equations
Authors: Cariñena José F. , Leach P. G. L. , de Lucas Javier
Published: October 2009

The recently developed theory of quasi-Lie schemes is studied and applied to investigate several equations of Emden type and a scheme to deal with them and some of their generalizations is given. As a first result we obtain t-dependent constants of the motion for particular instances of Emden equations by means of some of their particular solutions. Previously known results are recovered from this new perspective. Some t-dependent constants of the motion for equations of Emden type satisfying certain conditions are recovered. Finally new exact particular solutions are given for certain cases of Emden equations.
Charge transport at hybrid bulk heterojunction based on CdS nanopillar arrays embedded in a conducting polymer
Authors: Yang Li-Gong , Chen Fei , Xu Hao , Wang Mang , Chen Hong-Zheng
Published: October 2009

Charge transport in hybrid devices based on a quasiordered heterojunction consisting of a CdS film with nanopillarlike nanostructures embedded in a poly[2-methoxy-5-(20ethylhexyloxy)-1,4-phenylenevinylene] (MEH-PPV) layer was investigated. Temperature-dependent photoluminescence spectra indicate that there exist two kinds of defects (sulfur vacancy and sulfur interstitial) in this CdS film, which act as electron and hole traps, respectively. Current (I)-voltage (V) characteristics in dark show that charge recombination is the main mechanism at the hybrid interface when Ohmic contacts are formed at CdS/indium tin oxide and MEH-PPV/Au interfaces. Photocurrent action spectra and I-V performance under illumination indicate that the recombination was enhanced at the interface due to the participation of the defects. In view of these realities, the light intensity dependence of the photocurrent and the photovoltage of the hybrid devices could be understood by a quantitative model including trap-assistant recombination.
Numerical study of boundary layer separation control using magnetogasdynamic plasma actuators
Authors: Kalra Chiranjeev S. , Shneider Mikhail N. , Miles Richard B.
Published: October 2009

In this study, an efficient, time dependent, two-dimensional Navier–Stokes numerical code for shockwave boundary layer interaction in air is developed. Nonthermal surface plasma actuation is evaluated for effective shockwave induced boundary layer separation control within supersonic inlets. Specifically, high speed magnetogasdynamic plasma actuators are of interest. In these, localized ionization is produced close to the wall surface and then the flow is accelerated using strong magnetic fields. To replicate the experiments done at large boundary layer thickness, the code is divided into time independent and time dependent regimes to significantly reduce computation time. Computational results are in good agreement with experiments in terms of the flow structure as shown by Schlieren imaging, acetone planar laser scattering, and the static pressure profile on the test section wall.
The HelCat dual-source plasma device
Authors: Lynn Alan G. , Gilmore Mark , Watts Christopher , Herrea Janis , Kelly Ralph , Will Steve , Xie Shuangwei , Yan Lincan , Zhang Yue
Published: October 2009

The HelCat (Helicon-Cathode) device has been constructed to support a broad range of basic plasma science experiments relevant to the areas of solar physics, laboratory astrophysics, plasma nonlinear dynamics, and turbulence. These research topics require a relatively large plasma source capable of operating over a broad region of parameter space with a plasma duration up to at least several milliseconds. To achieve these parameters a novel dual-source system was developed utilizing both helicon and thermionic cathode sources. Plasma parameters of ne∼0.5–50×1018 m−3 and Te∼3–12 eV allow access to a wide range of collisionalities important to the research. The HelCat device and initial characterization of plasma behavior during dual-source operation are described.
Generalized Langevin models of molecular dynamics simulations with applications to ion channels
Authors: Gordon Dan , Krishnamurthy Vikram , Chung Shin-Ho
Published: October 2009

We present a new methodology, which combines molecular dynamics and stochastic dynamics, for modeling the permeation of ions across biological ion channels. Using molecular dynamics, a free energy profile is determined for the ion(s) in the channel, and the distribution of random and frictional forces is measured over discrete segments of the ion channel. The parameters thus determined are used in stochastic dynamics simulations based on the nonlinear generalized Langevin equation. We first provide the theoretical basis of this procedure, which we refer to as “distributional molecular dynamics,” and detail the methods for estimating the parameters from molecular dynamics to be used in stochastic dynamics. We test the technique by applying it to study the dynamics of ion permeation across the gramicidin pore. Given the known difficulty in modeling the conduction of ions in gramicidin using classical molecular dynamics, there is a degree of uncertainty regarding the validity of the MD-derived potential of mean force (PMF) for gramicidin. Using our techniques and systematically changing the PMF, we are able to reverse engineer a modified PMF which gives a current-voltage curve closely matching experimental results.
Nonlocal transport model in equilibrium two-component plasmas
Authors: Zheng Zhen , Rozmus W. , Bychenkov V. Yu. , Brantov A. V. , Capjack C. E.
Published: October 2009

The full set of linearized Fokker–Planck kinetic equations with Landau collision terms have been solved as an initial-value problem for equilibrium electron-ion plasmas. This work is a generalization of the nonlocal transport theory by Bychenkov et al. [Phys. Rev. Lett. 75, 4405 (1995)] to both electron and ion components with frequency-dependent responses. Transport closure relations have been obtained for the complete set of electron and ion fluid equations which are valid over the full range of particle collisionality and for an arbitrary ionic charge. The well-known limits of collisionless and strongly collisional plasma transport theory have been recovered. Practical fits based on the numerical calculations have been introduced for nonlocal and frequency-dependent ion transport coefficients.
Electron beam and plasma modes of a channel spark discharge operation
Authors: Gleizer S. , Yarmolich D. , Felsteiner J. , Krasik Ya. E. , Nozar P. , Taliani C.
Published: October 2009

Parameters of a modified pulsed channel spark discharge (CSD), operating at a repetition rate up to 100 Hz at Ar gas pressures of 10−3 and 10−4 Torr and of the generated electron beam, were studied using different electrical, optical, and x-ray diagnostics. It was shown that efficient (up to ∼74%) transfer of the initially stored energy to the energetic electron beam is realized only at the pressure of 10−4 Torr. Conversely, at the pressure of 10−3 Torr, less than 10% of the stored energy is acquired by the energetic electrons. It was found that the energetic electron beam generation is limited by the expansion of the cathode and anode plasmas and by the formation of plasma inside the gap between the CSD capillary output and the anode. It was also found that the plasma, which acquires the hollow cathode potential, is already formed at the beginning of the CSD operation inside the capillary, and the electron emission occurs from the capillary output plasma boundary. Finally, it was shown that the electron beam energy spectrum differs significantly from the energy spectrum, which one may expect in the case of the planar diode operation.
Magnetic field controlled reversal of ferroelectric polarization in conical spin ordered multiferroics: Monte Carlo simulation
Authors: Yao Xiaoyan , Lo Veng Cheong , Liu Jun-Ming
Published: October 2009

To understand the fascinating multiferroicity observed in CoCr2O4, Monte Carlo simulation is performed on a three-dimensional spinel lattice with classical Heisenberg spins. The conical spin order is confirmed to be the origin of the peculiar magnetoelectric behavior with coexisting magnetization and ferroelectric polarization. Furthermore, the simultaneous reversals of magnetization and polarization controlled by the external magnetic field are reproduced, consisting with the experimental observation qualitatively. It is revealed that, from the microscopic structures of spins, the axis of spin cone provides a “handle,” with which the magnetization and polarization can be reversed by the magnetic field easily.
Electrostatic self-aligned placement of single nanodots by protein supramolecules
Authors: Yoshii Shigeo , Kumagai Shinya , Nishio Kazuaki , Kadotani Ayako , Yamashita Ichiro
Published: October 2009

Electrostatic self-aligned positioning of a single 7 nm nanoparticle in the cage-shaped protein ferritin onto an aminosilane disk pattern as large as next-generation photolithography can produce is demonstrated. Genetic modification of the ferritin increased its surface charge density and therefore improved its electrostatic interaction. Single molecules of the recombinant ferritin could achieve self-aligned placement on 32–45 nm disks under the optimal solution condition, which was calculated by numerical analysis. This biological self-aligned placement, incorporated into next-generation photolithography techniques, will be a useful wafer-scale nanofabrication tool.
Modification of the conductance of single fullerene molecules by endohedral doping
Authors: Stróżecka Anna , Muthukumar Kaliappan , Dybek Aneta , Dennis T. John , Larsson J. Andreas , Mysliveček Josef , Voigtländer Bert
Published: October 2009

We use scanning tunneling microscopy to establish controlled contacts to single molecules of endohedrally doped Ce2@C80 fullerenes with C60 as a reference. The stability of the experimental setup allows for the determination of the conductance of Ce2@C80 relative to the conductance of C60. The endohedral doping reduces the conductance of Ce2@C80 by a factor of about five with respect to C60. Ab initio calculations show that the reason for this reduced conductance is the absence of electron orbitals delocalized over the cage of Ce2@C80 in the energy window of the conductance measurement.
Charge-scaled cavities in polarizable continuum model: Determination of acid dissociation constants for platinum-amino acid complexes
Authors: Zimmermann Tomáš , Burda Jaroslav V.
Published: October 2009

The main aim of this study is the calculation of acid dissociation constants of the products of cisplatin reaction with the amino acids cysteine and methionine. In the first step, a suitable procedure for the calculation of solvation Gibbs free energies is found, based on the comparison of the calculated and experimental pKas of both amino acids and simple platinum complexes. The resulting approach combines the DFT/B3LYP density functional, 6-311++G(2df,2pd) basis set, the D-PCM formulation of the continuum solvation model, and modified UAHF cavities. Since the main area of applicability of the UAHF model is solvation of organic molecules, a minor modification of the UAHF algorithm was necessary to improve the accuracy when applying it to the transition metal complexes. Instead of the integer (or semi-integer) formal charges used in the original formulation, more realistic partial charges obtained from the electronic density using the NPA procedure are used to generate molecular cavity. All other parameters of the model remain unchanged. This simple modification of the UAHF model works markedly better than the original formulation. The root mean square error of calculated pKas over a set of molecules including zwitterions and divalent diaquaplatinum cation is equal to 0.74. In the second step, pKas of platinum amino-acid complexes with the total charge ranging from 0e to 2e were computed. It was found that the pKas of all ionizable groups of both amino acids are highly variable among the complexes studied. They range from −5 (in complexes containing protonated thiol or carboxyl groups directly bonded to platinum) to 14 (in monodentate complexes containing a positively charged amino group, which is stabilized by intramolecular hydrogen bonds).
Scanning flow-impedance microscopy: A simple imaging technique based on hydrodynamics
Authors: Kim Tae Young , Kim Dong-Kwon , Kim Sung Jin
Published: October 2009

We introduce the concept of scanning flow-impedance microscopy (SFIM) which is an imaging technique based on hydrodynamics. Using a simple experimental setup including a mass flow controller and a manometer, the operating principle of SFIM is validated under atmospheric pressure and temperature conditions. Experimental results show that the flow impedance strongly depends on the relative distance between a probe and a specimen. SFIM micrographs of microscale patterns with various linewidths are presented.
Edge-passivation induced half-metallicity of zigzag zinc oxide nanoribbons
Authors: Chen Qian , Zhu Liyan , Wang Jinlan
Published: October 2009

The electronic and magnetic properties of zigzag zinc oxide (ZnO) nanoribbons with or without hydrogen passivation are investigated using ab initio calculations. The ribbon is found to be half-metallic ferromagnet when edge zinc atoms are passivated only. Moreover, the half-metallicity only emerges in the ribbons with relatively large width. Besides, the half-metallic ferromagnet can also be achieved when the passivatator H is replaced by CH3 or NH2. These diverse electronic and magnetic properties might open ZnO materials great possibility in future spintronics.
Duty ratio-dependent fluorescence enhancement through surface plasmon resonance in Ag-coated gratings
Authors: Cui Xiaoqiang , Tawa Keiko , Hori Hironobu , Nishii Junji
Published: October 2009

One-dimensional gratings with different duty ratios were designed and implemented for enhanced fluorescence detection and imaging. Verified by finite difference time domain simulations, our results showed that the enhancement strongly depended on the duty ratio of the land width to pitch of the grating structure. The maximum enhancement factor was achieved when the duty ratio was equal to 0.50 in our trapezoidal gratings with pitch=400 nm and depth=20 nm. Such a facile grating mold will exert a considerable influence on microarray biosensors and fluorescence microscopy.
Nonlinear evolution of Buneman instability and its implication for electron acceleration in high Mach number collisionless perpendicular shocks
Authors: Amano Takanobu , Hoshino Masahiro
Published: October 2009

Nonlinear evolution of the Buneman instability and its application to electron acceleration in collisionless shocks are discussed. Two-dimensional particle-in-cell simulations show that the saturation level of the instability is reduced from one-dimensional simulation results. It is demonstrated that the reduced saturation level is due to the resonant wave-particle interactions with large amplitude obliquely propagating waves. A new estimate for the saturation level is given by considering the interactions with oblique modes. The effects of the large amplitude oblique modes on electron shock surfing acceleration that is mainly controlled by the Buneman instability are also investigated. Two-dimensional particle-in-cell simulations of the shock transition region are performed by adopting a local model with the periodic boundary condition. The results indicate that the presence of oblique modes introduces a stochastic behavior to the trajectories of energetic electrons. The maximum energy is limited by the finite lifetime of the instability in the present periodic model. However, this will not be the case in the realistic shock transition region. The application to realistic shocks with Mach numbers typical of supernova remnants is also discussed.
Entrainment of a film on a surface from the meniscus of a liquid wedge during coating
Authors: Reznik S. N. , Salalha W. , Sorek Y. , Avramov D. , Zussman E.
Published: October 2009

The shape evolution of an entrained film from the meniscus of a liquid wedge is studied, both experimentally and theoretically. The liquid wedge is formed by a droplet of liquid injected between a substrate and a tilted plate. When the substrate moves relative to the tilted plate with a constant velocity, a film of a constant slope is entrained on it, while another film remains on the tilted plate. The numerical and analytical investigation of the process provides the dependence of the length and slope of the entrained film after the end of drawing process, as well as the maximum thickness of the film on the tilted plate, on the capillary number. The length of the entrained film was found to be minimal for infinitely large capillary numbers when the surface tension effects are negligibly small. Experimental data confirm the predicted characteristic geometry of the film for capillary numbers up to 0.75.
Suppression of the perpendicular anisotropy at the CoO Néel temperature in exchange-biased CoO/[Co/Pt] multilayers
Authors: Shipton E. , Chan K. , Hauet T. , Hellwig O. , Fullerton E. E.
Published: October 2009

We performed high field torque magnetometry measurements on CoO/[Co/Pt] magnetic multilayers that exhibit perpendicular exchange bias. We find that the antiferromagnet CoO layers strongly modify the uniaxial anisotropy of the multilayer structures. The strongest effects due to the CoO layers occur in the vicinity of the Néel temperature, where we observe a suppression of the first-order anisotropy and a smaller enhancement of the second-order anisotropy. This results in a nonmonotonic variation of the anisotropy with temperature and for selected samples a transition from perpendicular to in-plane and back to perpendicular anisotropy with increasing temperature.
Electrically pumped continuous-wave vertical-cavity surface-emitting lasers at ∼2.6 μm
Authors: Arafin Shamsul , Bachmann Alexander , Kashani-Shirazi Kaveh , Amann Markus-Christian
Published: October 2009

In this paper, electrically pumped GaSb-based vertical-cavity surface-emitting lasers operating continuous wave at a record long emission wavelength of ∼2.6 μm are presented. Owing to the excellent thermal heat management, the devices exhibit single-mode operation up to a heat-sink temperature of 55 °C. Lateral current confinement and index guiding in the device are accomplished by utilizing the buried tunnel junction concept. Devices with aperture diameters of 6 μm show maximum output powers of 0.3 mW at room temperature with quantum efficiencies around 10%.
Relaxation of strained pseudomorphic SixGe1−x layers on He-implanted Si/δ-Si:C/Si(100) substrates
Authors: Buca D. , Minamisawa R. A. , Trinkaus H. , Holländer B. , Nguyen N. D. , Loo R. , Mantl S.
Published: October 2009

In this letter we present a method to increase the efficiency of SiGe layer relaxation by He+ ion implantation and annealing. Preferential nucleation of He platelets along a δ-impurity layer grown in the Si substrate below the SiGe layer results in planar localization and homogenization of dislocation loop sources inducing a more uniform distribution of misfit dislocations. We demonstrate this for a thin Si:C layer grown by reduced pressure chemical vapor deposition. The optimization of the conditions for efficient relaxation and layer quality is studied with respect to the position of the Si:C layer and the process parameters. Relaxation degrees up to 85% are obtained for Si0.77Ge0.23 layers.
Enhancement of the output power of a terahertz parametric oscillator with recycled pump beam
Authors: Wu Dong Ho , Ikari Tomofumi
Published: October 2009

We report a technique for the terahertz parametric oscillator, in which we recycle the pump beam in order to increase the efficiency and enhance the terahertz beam output. In our experiments, the pump laser beam is injected into a doped LiNbO3 crystal with 5% MgO, and the exiting pump beam is redirected back through the nonlinear crystal. Our data show that the terahertz beam output power increases almost four times in magnitude, when the pump beam is recycled once in crossed-beam geometry.
Improved contrast radially polarized coherent anti-Stokes Raman scattering microscopy using annular aperture detection
Authors: Lin Jian , Lu Fake , Wang Haifeng , Zheng Wei , Sheppard Colin JR , Huang Zhiwei
Published: October 2009

We propose a unique annular aperture detection scheme in radially polarized coherent anti-Stokes Raman scattering (RP-CARS) microscopy for significantly removing nonresonant background for high contrast vibrational imaging. Our finite-difference time-domain calculations show that the maximum radiation patterns of RP-CARS signals from the scatterers vary with the scatterer’s sizes, which are different from nonresonant CARS radiation from surrounding water. By applying appropriate sizes of annular stop apertures in the detection path, the nonresonant background from water can be effectively suppressed, yielding over 110-fold improvements in signal-to-background ratio for the forward-detected RP-CARS, while over 50-fold improvements for the backward RP-CARS detection.
Improving efficiency roll-off in organic light emitting devices with a fluorescence-interlayer-phosphorescence emission architecture
Authors: Zheng Tianhang , Choy Wallace C. H. , Ho Cheuk-Lam , Wong Wai-Yeung
Published: October 2009

Organic light emitting devices (OLEDs) with a fluorescence-interlayer-phosphorescence emission layer structure (FIP EML) has been proposed to solve the efficiency roll-off issue effectively. Efficient green OLED based on FIP EML exhibiting only 26% roll-off in the luminance efficiency, which is lower than the typical roll-off of 51% for conventional phosphorescent OLEDs with single EML operated at 5–150 mA/cm2 range, has been demonstrated. Such enhancement should be attributed to the improved carrier balance, the exciton redistribution in recombination zone, the suppression of nonradiative exciton quenching processes, and the elimination of energy transfer loss offered by the FIP EML structure.
Nonmodal and nonlinear dynamics of a volatile liquid film flowing over a locally heated surface
Authors: Tiwari Naveen , Davis Jeffrey M.
Published: October 2009

The stability of a thin, volatile liquid film falling under the influence of gravity over a locally heated, vertical plate is analyzed in the noninertial regime using a model based on long-wave theory. The model is formulated to account for evaporation that is either governed by thermodynamic considerations at the interface in the one-sided limit or limited by the rate of mass transfer of the vapor from the interface. The temperature gradient near the upstream edge of the heater induces a gradient in surface tension that opposes the gravity-driven flow, and a pronounced thermocapillary ridge develops in the streamwise direction. Recent theoretical analyses predict that the ridge becomes unstable above a critical value of the Marangoni parameter, leading to the experimentally observed rivulet structure that is periodic in the direction transverse to the bulk flow. An oscillatory, thermocapillary instability in the streamwise direction above the heater is also predicted for films with sufficiently large heat loss at the free surface due to either evaporation or strong convection in the adjoining gas. This present work extends the recent linear stability analysis of such flows by Tiwari and Davis [Phys. Fluids 21, 022105 (2009)] to a nonmodal analysis of the governing non-self-adjoint operator and computations of the nonlinear dynamics. The nonmodal analysis identifies the most destabilizing perturbations to the film and their maximum amplification. Computations of the nonlinear dynamics reveal that small perturbations can be sufficient to destabilize a linearly stable film for a narrow band of wave numbers predicted by the nonmodal, linearized analysis. This destabilization is linked to the presence of stable, discrete modes that appear as the Marangoni parameter approaches the critical value at which the film becomes linearly unstable. Furthermore, the thermocapillary instability leads to a new, time-periodic base state. This transition corresponds to a Hopf bifurcation with increasing Marangoni parameter. A linear stability analysis of this time-periodic state reveals further instability to transverse perturbations, with the wave number of the most unstable mode about 50% smaller than for the rivulet instability of the steady base state and exponential growth rate about three times larger. The resulting film behavior is reminiscent of inertial waves on locally heated films, although the wave amplitude is larger in the present case near the heater and decays downstream where the Marangoni stress vanishes. The film’s heat transfer coefficient is found to increase significantly upon the transition to the time-periodic flow.
10 fs ultrafast all-optical switching in polystyrene nonlinear photonic crystals
Authors: Liu Ye , Qin Fei , Wei Zhi-Yi , Meng Qing-Bo , Zhang Dao-Zhong , Li Zhi-Yuan
Published: October 2009

An ultrafast all-optical switching with the response time on the order of 10 fs is demonstrated in a three-dimensional opal polystyrene nonlinear photonic crystal by means of precise femtosecond pump-probe technique. The switching is realized by the shift in the photonic band gap under external optical pumping of 8 fs Ti:sapphire pulse laser with a peak pump power of 20.6 GW/cm2. The good performance of optical switching is attributed to the very strong and fast Kerr nonlinear optical response of the polystyrene material.
Ni
@
B
80
: A single molecular magnetic switch
Authors: Li J. L. , Yang G. W.
Published: October 2009

We theoretically performed that the magnetic moment of Ni-encapsulated B80 (Ni@B80) can be greatly tuned by changing the position of Ni atom inside the hollow cage of B80. There are three stable configurations of Ni@B80 with Ni atom located at center, pentagon, and hexagonal-in, respectively. Compared with that of Ni@B80 with Ni atom located at center, all the magnetic moments of Ni@B80’s with Ni atom located at pentagon and hexagon-in in the hollow cage of B80 are zero. These fascinating findings imply that Ni@B80 may be a promising candidate for single molecular magnetic switch.
Effect of donor-acceptor concentration ratios on nonradiative energy transfer in closely packed CdTe quantum dots
Authors: Lin Y. C. , Wang W. J. , Chung H. L. , Chou W. C. , Chen W. K. , Chang W. H. , Susha A. S. , Rogach A. L.
Published: October 2009

This study investigates the dependence of Förster resonance energy transfer (FRET) on donor-acceptor (D/A) concentration ratios in mixed-size CdTe quantum dots (QDs) films by using photoluminescence (PL) and time-resolved PL spectroscopy. Experimental results indicate that an increasing donor concentration significantly quenches the emission intensity and lifetime in donor QDs and enhances that in acceptor QDs, providing clear evidence of increased FRET efficiency. When D/A ratio exceeds 6, however, the emission intensity and the lifetime of acceptors start to decline, reflecting a decreasing FRET efficiency because of a markedly declining availability of acceptor QDs.
Dripping to jetting transitions observed from supercritical fluid in liquid microcoflows
Authors: Marre S. , Aymonier C. , Subra P. , Mignard E.
Published: October 2009

Dripping to jetting transition from liquid-liquid to liquid-gas systems has been widely studied in microfluidics. Recent developments have permitted the use of supercritical fluids at high pressure and various temperatures in microfluidic systems to develop sustainable processes. In this article, we use this strategy to demonstrate the possibility to generate stable droplets and reversible dripping to jetting transitions at microscale from supercritical carbon dioxide-liquid water microcoflows.
Photon-number resolving performance of the InGaAs/InP avalanche photodiode with short gates
Authors: Chen Xiuliang , Wu E , Xu Lilin , Liang Yan , Wu Guang , Zeng Heping
Published: October 2009

By using a self-differencing circuit to achieve efficient spike cancellation for the near-infrared single-photon detector based on InGaAs/InP avalanche photodiode, we verified that shortening the gate duration enforced the detection efficiency to saturate at an increased voltage, while increasing the avalanche gain favored the discrimination of the avalanche signals caused by different photon-number states. Photon-number resolving detection was realized by measuring the weak current at the avalanche built-up. The photon-number resolving performance could be improved by shortening the gating pulse duration.
Transparent flexible resistive random access memory fabricated at room temperature
Authors: Won Seo Jung , Park Jae-Woo , Lim Keong Su , Kang Sang Jung , Hong Yun Ho , Yang Ji Hwan , Fang Liang , Sung Gun Yong , Kim Han-Ki
Published: October 2009

We report the room temperature fabrication of highly transparent and flexible resistive random access memory devices based on an ITO (indium tin oxide)/ZnO (zinc oxide)/ITO/Ag/ITO capacitor structure on a polyethersulfone flexible substrate. The ITO/Ag/ITO multilayered bottom electrode provides superior flexibility as well as high transparency compared to devices with ITO single bottom electrode during repetitive bending tests. The devices exhibit a high transmittance and the excellent reliability of data retention. Moreover, they show consistent memory performance, even under thermal stress. The results of this study provide a breakthrough solution for the era of transparent and flexible electronic systems in the near future.
Direct calculations of vibrational absorption and circular dichroism spectra of alanine dipeptide analog in water: Quantum mechanical/molecular mechanical molecular dynamics simulations
Authors: Yang Seongeun , Cho Minhaeng
Published: October 2009

The vibrational absorption (IR) and vibrational circular dichroism (VCD) spectra of alanine dipeptide analog in water are directly calculated by Fourier transforming the time correlation functions of the electric and magnetic dipole moments, which are calculated using the dynamic partial charges and trajectory of the peptide generated from the quantum mechanical/molecular mechanical molecular dynamics simulations. The alanine dipeptide analog is treated at the Hartree–Fock level with 3-21G, 4-31G, 6-31G, and 6-31G∗ basis sets and the solvent H2O is modeled with the TIP3P water. The atomic partial charges are obtained from the Löwdin population analysis, which gives consistent IR spectral profiles irrespective of the basis sets used. The simulated VCD spectrum by a polyproline II(PII)-dominant trajectory is compatible with the previous experimental results of the polyproline peptides, where the amide I and II VCD bands are negative couplets with a weak positive peak to the high frequency region. The sampling efficiency of the PII conformer is much lower than the other ones at all basis levels used. The simulated VCD spectrum of α-helix averaged over five trajectories has the reverse sign pattern compared to the PII spectrum and is found to be consistent with the previously observed spectral features of α-helical polypeptides. The sign patterns of the β-strand VCD spectrum are qualitatively similar to the experimental spectra of β-sheet rich proteins. The VCD spectra obtained from the trajectories containing several extended conformers such as β and PII are not clearly distinguishable from the β-strand-dominant spectra. It is interesting that the PII and the coil VCD spectra coincide in sign pattern and relative intensity for all amide modes. This demonstrates that the negative couplet structures of the amide I and II VCD spectra do not necessarily prove the dominance of either PII or coil conformation. We anticipate that the present method can be used to directly simulate the IR and VCD spectra of structurally heterogeneous biomolecules in condensed phases.
Visible bands of divanadium
Authors: Balfour Walter J. , Li Runhua
Published: October 2009

Observations in laser-induced fluorescence between 570 and 620 nm with vanadium metal and helium can be assigned to Σ3u−−X Σ3g− spectra in the V2 molecule. Dispersed fluorescence data have been collected and rotational analyses performed.
Circle-coupled resonator waveguide with enhanced Sagnac phase-sensitivity for rotation sensing
Authors: Yan Lu , Xiao Zhisong , Guo Xiaoqian , Huang Anping
Published: October 2009

We propose a configuration of integrated waveguide structure consisting of resonators coupled to an arc-shape waveguide. We show theoretically that enhanced sensitivity is given by positive dispersion of the system, and the coupled resonators’ contribution manifests itself as an enhancement of phase shift imparted by Sagnac effect. A more clearly physical analysis indicated that the enhancement is with dependence in form but in physical essence no relation on slow light property predicted in the waveguides. This optimized system is preferable compared with a conventional gyroscope. Such proposed configuration can be used to realize highly compact optical gyroscope for rotation sensing.
Analytical analysis of heat conduction in a suspended one-dimensional object
Authors: Huang X. Y. , Zhang Z. Y. , Liu Y. , Peng L.-M.
Published: October 2009

An analytical solution is given for the self-heating conduction equation of a suspended one-dimensional (1D) object. The conductivity of the 1D object is given by combining Umklapp and second-order three-phonon processes. Using this analytical solution, several relations among some important parameters are discussed and are shown to be consistent with existing experimental results. A method to retrieve the coefficients for thermal conductivity is proposed for a general thermal conductor without knowing the detailed temperature profile along the 1D object.