bluuebunny/crossref_metadata_2025 huggingface dataset:
Electroluminescence from monocrystalline silicon solar cell
Authors: Cheng T.-H. , Kuo P.-S. , Ko C.-Y. , Chen C.-Y. , Liu C. W.
Published: May 2009

The band edge emission with the peak at 1.15 μm is observed at room temperature from monocrystalline silicon solar cell at forward bias. The electroluminescence spectra can be fitted by electron hole plasma recombination model. The temporal response of electroluminescence is used to characterize the minority carrier lifetime by fitting the time evolution of radiative recombination using the Shockley–Read–Hall, radiative, and Auger recombination models. The minority carrier lifetime is almost constant (1.8 ms) for excess carrier density lower than 4×1015 cm−3, and then decreases at higher concentration.
Nonreciprocal microwave devices based on magnetic nanowires
Authors: Kuanr Bijoy K. , Veerakumar V. , Marson Ryan , Mishra Sanjay R. , Camley R. E. , Celinski Z.
Published: May 2009

We use magnetic nanowires in an alumina matrix as the active element in microwave nonreciprocal resonance isolators. The design is related to waveguide E-plane isolators but is planar and much smaller than typical waveguide isolators. There is a nonreciprocal attenuation of the wave in forward and reverse directions. The isolation is about 6 dB/cm at 23 GHz. The bandwidth of the device is relatively large (5–7 GHz) in comparison to ferrite-based devices. The central frequency of the device can be tuned with the application of magnetic field.
Direct imaging of current-driven domain walls in ferromagnetic nanostripes
Authors: Uhlig W. C. , Donahue M. J. , Pierce D. T. , Unguris J.
Published: May 2009

To better understand the response of domain walls to current-induced spin transfer torques, we have directly imaged the internal magnetic structure of domain walls in current-carrying ferromagnetic nanostripes. Domain wall images were acquired both while a constant current was flowing through the wire, and after applying current pulses. Domain walls ranging from vortex walls in wide (1 μm) wires to transverse walls in narrow (100 nm) wires were quantitatively analyzed using scanning electron microscopy with polarization analysis. The domain wall motion is characterized by strong interactions with random pinning sites along the wire. The walls either jump with the electron flow between pinning sites, or the pinned walls are distorted by the current. The domain wall propagation is also associated with transverse motion of the vortex core.
Enhanced luminescence of Tb3+/Eu3+ doped tellurium oxide glass containing silver nanostructures
Authors: Kassab Luciana R. P. , de Almeida Ricardo , da Silva Davinson M. , de Assumpção Thiago A. A. , de Araújo Cid B.
Published: May 2009

We report on energy transfer studies in terbium (Tb3+)—europium (Eu3+) doped TeO2–ZnO–Na2O–PbO glass containing silver nanostructures. The samples excitation was made using ultraviolet radiation at 355 nm. Luminescence spectra were recorded from ≈480 to ≈700 nm. Enhanced Eu3+ luminescence at ≈590 nm (transition D50−F71) and ≈614 nm (transition D50−F72) are observed. The large luminescence enhancement was obtained due to the simultaneous contribution of the Tb3+–Eu3+ energy transfer and the contribution of the intensified local field on the Eu3+ ions located near silver nanostructures.
Polarization anisotropy of transient carrier and phonon dynamics in carbon nanotubes
Authors: Kim Ji-Hee , Park Jaegyu , Lee Bong Yeon , Lee Donghan , Yee Ki-Ju , Lim Yong-Sik , Booshehri Layla G. , Hároz Erik H. , Kono Junichiro , Baik Sung-Hoon
Published: May 2009

We report on polarization-dependent transient carrier dynamics and coherent phonon oscillations in single-walled carbon nanotubes by determining the relation between the nanotube axis and the incident light polarization. Due to the anisotropic shape of nanotubes, optical absorption strongly depends on the polarization direction. We observed three decay components when the excitation wavelength was resonant with the E22 transition energy and observed two-decay components under off-resonance conditions. The transient absorption and coherent phonon amplitudes were measured as a function of the angle between the pump and probe polarizations and were analyzed based on the absorption anisotropy of carbon nanotubes.
On the physical understanding of quantum rings self-assembly upon droplet epitaxy
Authors: Li X. L. , Yang G. W.
Published: May 2009

A quantitatively kinetic model has been established to address the quantum rings (QRs) self-assembly upon the droplet epitaxy. Taking the GaAs system as an example, we found that the diffusion of Ga atoms away from the droplet and the trapping of As atoms play crucial roles in the final shape formation of GaAs nanostructures. By calculating the amounts of the produced GaAs in each point, we performed the shape evolution of GaAs nanostructures during the crystallization process. The proposed kinetic theory nicely elucidates the physical mechanisms of the self-assembly of GaAs nanostructures including the single and double QRs and the holed nanostructure upon the droplet epitaxy.
Three-dimensional model of magnetized capacitively coupled plasmas
Authors: Rauf Shahid , Kenney Jason , Collins Ken
Published: May 2009

A three-dimensional plasma model is used to understand the characteristics of magnetized capacitively coupled plasma discharges. The simulations consider plasmas generated using high frequency (13.5 MHz) and very high frequency (162 MHz) sources, electropositive (Ar) and electronegative (O2) gases, and spatially uniform and nonuniform magnetic fields. Application of a magnetic field parallel to the electrodes is found to enhance the plasma density due to improved electron confinement and shift the plasma due to the E×B drift. The plasma is electrically symmetric at 162 MHz so it drifts in opposite directions adjacent to the two electrodes due to the E×B drift. On the other hand, the 13.5 MHz plasma is electrically asymmetric and it predominantly moves in one direction under the influence of the E×B drift. The E×B drift focuses the plasma into a smaller volume in regions with convex magnetic field lines. Conversely, the E×B drift spreads out the plasma in regions with concave magnetic field lines. In a magnetized O2 plasma, the overall plasma is found to move in one direction due to the E×B drift while the plasma interior moves in the opposite direction. This behavior is linked to the propensity of negative ions to reside in regions of peak plasma potential, which moves closer to the chamber center opposite to the E×B drift direction.
Internal transport barriers in the National Spherical Torus Experiment
Authors: Yuh H. Y. , Levinton F. M. , Bell R. E. , Hosea J. C. , Kaye S. M. , LeBlanc B. P. , Mazzucato E. , Peterson J. L. , Smith D. R. , Candy J. , Waltz R. E. , Domier C. W. , Luhmann N. C. , Lee W. , Park H. K.
Published: May 2009

In the National Spherical Torus Experiment [M. Ono et al., Nucl. Fusion 41, 1435 (2001)], internal transport barriers (ITBs) are observed in reversed (negative) shear discharges where diffusivities for electron and ion thermal channels and momentum are reduced. While neutral beam heating can produce ITBs in both electron and ion channels, high harmonic fast wave heating can also produce electron ITBs (e-ITBs) under reversed magnetic shear conditions without momentum input. Interestingly, the location of the e-ITB does not necessarily match that of the ion ITB (i-ITB). The e-ITB location correlates best with the magnetic shear minima location determined by motional Stark effect constrained equilibria, whereas the i-ITB location better correlates with the location of maximum E×B shearing rate. Measured electron temperature gradients in the e-ITB can exceed critical gradients for the onset of electron thermal gradient microinstabilities calculated by linear gyrokinetic codes. A high-k microwave scattering diagnostic shows locally reduced density fluctuations at wave numbers characteristic of electron turbulence for discharges with strongly negative magnetic shear versus weakly negative or positive magnetic shear. Reductions in fluctuation amplitude are found to be correlated with the local value of magnetic shear. These results are consistent with nonlinear gyrokinetic simulations predicting a reduction in electron turbulence under negative magnetic shear conditions despite exceeding critical gradients.
p
-GaN
/
InGaN
/
n
-GaN
pedestal nanorods: Effect of postgrowth annealing on the electrical performance
Authors: Seo H. W. , Tu L. W. , Lin Y. T. , Ho C. Y. , Chen Q. Y. , Yuan L. , Norman D. P. , Ho N. J.
Published: May 2009

Pedestal p-GaN/InGaN/n-GaN nanorods have been fabricated on n-type Si (111) substrates by properly reducing the growth temperature of the p-GaN surface layer. Continuous p-GaN layers were formed on the top region by accelerated lateral growth, while keeping the underlying nanostructures and physical properties of InGaN and n-GaN intact, making it feasible for large-scale vertical integration. Growth of the p-GaN layer at 500 °C followed by annealing at 600–800 °C improved crystal structures and the overall electrical and luminescence properties of pedestal nanorods.
Fabrication and electromechanical properties of microscale 1–3-type piezoelectric composites using (Na,K)NbO3-based Pb-free piezoceramics
Authors: Shen Zong-Yang , Xu Ying , Li Jing-Feng
Published: May 2009

Microscale 1–3-type piezoceramic/epoxy composites using Li/Ta-modified (Na,K)NbO3 (NKN-LT) lead-free piezoelectric ceramics were fabricated via a modified dice-fill method, by which the NKN-LT ceramic rods were miniaturized to a lateral width of 150 μm with an aspect ratio (height/width) higher than 3.5. The piezoelectric properties of the 1–3 composites as a function of ceramic volume fraction were measured and compared with theoretical predictions. In addition to a high electromechanical coupling coefficient (kt∼50%) and low acoustic impedances (Z∼10 Mrayls), the developed composites show a clear single thickness mode with a high resonance frequency over 3.5 MHz. The present Pb-free piezocomposites are suitable for medical imaging devices embedded in the human body.
Confocal and force probe imaging system for simultaneous three-dimensional optical and mechanical spectroscopic evaluation of biological samples
Authors: Lin Feilong , Elliott Kevin E. , Parker Wes , Chakraborty Nilay , Teo Chek Sing , Smith Stuart T. , Elliott Gloria D. , Moyer Patrick J.
Published: May 2009

We present the design and operation of a novel instrument for the simultaneous three-dimensional measurements of localized properties using optical and mechanical probes. In this instrument the mechanical and optical probes are stationary relative to the instrument frame while the specimen can be navigated in three-dimensional space in the probing field, translating over a range of 64.5 μm by 49.7 μm by 31.5 μm in each axis, respectively, at closed loop speeds of 10 Hz. A large aperture is provided in the center of the moving platform so that an optical lens can image the specimen from below. An additional z-direction translator has been integrated with this instrument to independently move a force probe that contacts the specimen from above with a translation range of 16 μm. Furthermore, there is an additional seven degrees of freedom providing adjustments to independently position and/or align the scanner and force probe relative to the optical imaging lens. Initial results of both optical and mechanical scans demonstrate 6 nm localization from single molecule fluorescence measurements, as well as single pair fluorescence energy transfer measurements indicating molecular separations of about 2 nm.
Thermodynamic study on phase stability in nanocrystalline Sm–Co alloy system
Authors: Xu W. W. , Song X. Y. , Li E. D. , Wei J. , Zhang J. X.
Published: May 2009

To study the phase stability and the phase transformation behavior in the nanocrystalline (NC) stoichiometric alloys, a thermodynamic model has been developed in the present paper. Using the NC Sm–Co alloy as an example, the thermodynamic properties of various phases in the alloy system were evaluated systematically. In particular, the grain-size-dependence of the Gibbs free energy of each alloy phase at different temperatures was provided. Based on the model calculations, the stabilities of different phases in the NC Sm–Co system were analyzed. As distinctly different from the phase stability in the conventional polycrystalline alloys, the Gibbs free energies of some NC phases become positive at the room temperature when the nanograin size is reduced to below a certain critical value, which implies that these phases cannot stably exist at the room temperature. In order to verify the thermodynamic model, the stoichiometric Sm–Co alloy was prepared, and the grain structure and the phase constitution of the alloy were characterized by combining x-ray diffraction and transmission electron microscopy analyses. The experimental findings have confirmed the thermodynamic model predictions for the NC alloy system.
One- and two-dimensional anisotropic diffractive gratings formed by periodic orthogonal molecular alignment in a hydrogen-bonded liquid crystalline polymer
Authors: Emoto Akira , Manabe Sayaka , Shioda Tatsutoshi , Ono Hiroshi , Kawatsuki Nobuhiro
Published: May 2009

Anisotropic diffractive gratings having periodic orthogonal molecular alignments are formed by a linearly polarized ultraviolet (LPUV) exposure through a photomask in hydrogen (H)-bonding liquid crystalline polymers (H-LCPs) using a unique molecular reorientation behavior. H-bonded side-chain groups of H-LCPs play an important role in the molecular reorientation and the resultant optical anisotropy originating from an intermolecular network composition. To evaluate its potential for optical applications, one- and two-dimensional diffractive gratings were fabricated and analyzed by both polarization optical microscopy and diffraction characteristics. As a result, anisotropic gratings using H-LCP were obtained with a high diffraction efficiency that was 80% of the theoretical maximum efficiency (33.9%) of thin diffractive gratings. Results of experimental and theoretical investigation reveal that the resultant molecular direction and optical anisotropy are generated and controlled by LPUV exposure.
Interfacial misfit array formation for GaSb growth on GaAs
Authors: Huang Shenghong , Balakrishnan Ganesh , Huffaker Diana L.
Published: May 2009

The manuscript reports that the initial strain relaxation of highly mismatched GaSb layers grown on GaAs (001) is governed by the two-dimensional (2D), periodic interfacial misfit (IMF) dislocation array growth mode. Under optimized growth conditions, only pure 90° dislocations are generated along both [110] and [11¯0] directions that are located at GaSb/GaAs interface, which leads to very low threading dislocation density propagated along the growth direction. The long-range uniformity and subsequent strain relaxation of the 2D and periodic IMF array are demonstrated via transmission electron microscopy and scanning transmission electron microscopy images at GaSb/GaAs interface.
Structure and magnetic properties of nanocrystalline Sm1−s(Fe,Mo)5+2s
Authors: Khazzan S. , Mliki N. , Bessais L.
Published: May 2009

Materials based on rare-earth and iron have drawn much attention due to their high performance properties for permanent magnet application. Substitution of Fe by a transition metal remains of considerable interest owing to the relatively modest magnetic properties of the binary Sm–Fe compounds. The structure of the nanocrystalline Sm1−s(Fe,Mo)5+2s alloys is governed by the s Sm vacancy rate and the x amount of Mo. In this work, the Rietveld analysis shows that for s=0.33 the structure is R3¯m of Th2Zn17-type, for s=0.5 the structure is I4∕mmm of ThMn12-type. For s=0.38, the results show a 3∕29 phase, which can be described as A2∕m space group. The solubility of Mo in the 2∕17 structure predicted by atomistic simulation has been demonstrated. The Mössbauer spectra analysis corroborates the x-ray structure results whereas Mo atoms are located in the 6c position (dumbbell site). In contrast, Si and Ga substituting for Fe are located in 18h site. Thermomagnetic measurements indicate that the Curie temperature (TC) of the 2∕17 phase increases up to 434K, for the 3∕29 and 1∕12 phases, TC is equal to 459 and 551K, respectively. The saturation magnetic moment is measured at 9T.
Analysis of GaAs∕GaSb∕GaAs structures under optical excitation considering surface states as an electron reservoir
Authors: Hsieh Hong-Wen , Yen Shun-Tung
Published: May 2009

We present a self-consistent model for the analysis of the carrier distribution, the band profile, and the transition energy of type-II aligned GaAs∕GaSb∕GaAs structures under optical excitation. The model considers the surface states as an electron reservoir, associated with pinning of the conduction band Fermi level at the midgap. In our model, the optical generated holes in the GaSb quantum well causes a potential well on one side of the GaSb layer, which can efficiently accommodate the optically generated electrons. Accordingly, we derive a relation connecting the excitation power to the carrier density. Using the relation and the effective triangular potential approximation, we obtain a simple formula for the transition energy shift as a function of the excitation power, which follows the cube-root rule quite well. The calculation allows the determination of the band offset of a type-II heterointerface by comparison with data from photoluminescence measurement. The result suggests the unstrained valence band offset of GaSb∕GaAs to lie between 0.5 and 0.55eV. We also present a simplified model for analyzing the electronic and optical properties of type-II heterostructures without the need of a self-consistent calculation.
Simplified ultrafast pulse shaper for tailored polarization states using a birefringent prism
Authors: Kupka David , Schlup Philip , Bartels Randy A.
Published: May 2009

A new polarization pulse shaping method utilizing a birefringent prism as both the spectrally dispersing and polarization separating element is presented and analyzed. The method of appropriate prism design is first examined, followed by calibration technique and experimental demonstration of the pulse shaper. Using phase-only modulation by means of a spatial light modulator, we obtain near-transform limited pulses. Furthermore, a sinusoidal spectral phase imparted on the pulse is retrieved and qualitatively compares well with the theoretical target field.
Design of a wide bandwidth switchable mirror based on a liquid crystal etalon
Authors: Dorjgotov E. , Bhowmik A. , Bos P.
Published: May 2009

We propose the design for a switchable mirror with high efficiency and a 30 nm bandwidth. The device is based on a liquid crystal filled etalon. Broad bandwidth is achieved through the use of integrated half-wave layers into the dielectric stack design, while high efficiency is achieved using a polarization independent liquid crystal effect. Potential applications in the area of displays are also presented.
Dynamics of stochastic Zakharov equations
Authors: Guo Boling , Lv Yan , Yang Xiaoping
Published: May 2009

The asymptotic behavior of Zakharov equations driven by random force is studied. The force, which is smooth enough and homogeneous in space and white noise in time, acts on both equations of the Zakharov system independently. By some a priori estimates we prove the existence of a solution in energy spaces E1 and E2 via the Galerkin approximation. This solution is defined on the given probability space rather than a martingale solution. Then a global random attractor is constructed in energy space E2 equipped with weak topology. Further the existence of a stationary measure is proved in energy space E2 with usual topology.
Size effect in Quincke rotation: A numerical study
Authors: Peters F. , Lobry L. , Khayari A. , Lemaire E.
Published: May 2009

This paper deals with the Quincke rotation of small insulating particles. This dc electrorotation of insulating objects immersed in a slightly conducting liquid is usually explained by looking at the action of the free charges present in the liquid. Under the effect of the dc electric field, the charges accumulate at the surface of the insulating particle which, in turn, acquires a dipole moment in the direction opposite to that of the field and begins to rotate in order to flip its dipole moment. In the classical Quincke model, the charge distribution around the rotor is supposed to be purely superficial. A consequence of this assumption is that the angular velocity does not depend on the rotor size. Nevertheless, this hypothesis holds only if the rotor size is much larger than the characteristic ion layer thickness around the particle. In the opposite case, we show thanks to numerical calculations that the bulk charge distribution has to be accounted for to predict the electromechanical behavior of the rotor. We consider the case of an infinite insulating cylinder whose axis is perpendicular to the dc electric field. We use the finite element method to solve the conservation equations for the positive and the negative ions coupled with Navier–Stokes and Poisson equations. Doing so, we compute the bulk charge distribution and the velocity field in the liquid surrounding the cylinder. For sufficiently small cylinders, we show that the smaller the cylinder is, the smaller its angular velocity is when submitted to a dc electric field. This size effect is shown to originate both in ion diffusion and electromigration in the charge layer. At last, we propose a simple analytical model which allows calculating the angular velocity of the rotor when electromigration is present but weak and diffusion can be neglected.
Light emitting diode fault detection using p-n junction photovoltaic effect
Authors: Li Ping , Wen Yumei , Cai Youhai , Li Lian
Published: May 2009

This paper proposes an online noncontact fault detection method during light emitting diode (LED) chip packaging, which is based on the photovoltaic effect in p-n junctions. Once a LED chip bonded on a lead frame is illuminated, the photocurrent will flow through the loop circuits formed by the lead frame. Through characterization of the weak photovoltaic response in the lead frame with the 20 LED chips, five LED faults, including chip defects (chip quality and chip contamination) and bonding deficiencies (disconnection, debonding, and rebonding), can be detected before packaging. A high-sensitivity photocurrent detection instrument has been developed to detect different color (red, yellow, green, and blue) and different size LED chips (9–15 mil) on LED assembly line. A key feature of the new instrument is the capability to tune and implement the maximum output power (photocurrent) in the loop lead frame by designing the high-efficiency magnetic core, the magnetic coil and the detecting system. Experiments demonstrate that the photovoltaic behaviors for LED p-n junctions are directly related to the LED electroluminescent characteristics, and the internal optoelectronic characteristics and the external Ohmic contact performances can be derived by detecting the photocurrent of LED chips. The LED online noncontact fault detection instrument based on the photovoltaic effect can be used to substitute for the ordinary electroluminescence online contact fault detection instrument.
Depolarization ratio measurement using single photomultiplier tube in micropulse lidar
Authors: Dubey P. K. , Jain S. L. , Arya B. C. , Kulkarni Pavan S.
Published: May 2009

The conventional dual polarization micropulse lidar uses two separate photomultiplier tubes (PMT) to detect both the copolarized and cross-polarized beam. The prominent sources of error in the depolarization ratio measurement are mismatch in PMT, improper selection of discriminator threshold and unequal PMT high voltage. In the present work a technique for the measurement of lidar depolarization ratio using only one PMT sensor has been developed. The same PMT detects both copolarized and cross-polarized lidar backscatter. A stepper motor is used along with the mirrors to bring both the received polarization signals over the PMT window. Application of the same PMT minimizes the error caused in the depolarization ratio measurement due to error in photon counting of an individual channel. The design description of this technique along with the preliminary results depicting its functionality has been mentioned in this article.
Quantitative displacement measurement of a nanotube cantilever with nanometer accuracy using epifluorescence microscopy
Authors: Park Hyojun , Kwon Soongeun , Kim Soohyun
Published: May 2009

A method to measure the deflection of a nanotube cantilever with nanometer accuracy in an air or liquid environment is presented. We attached fluorescent dyes at the end of a nanotube to detect its deflection. The nanotube cantilever was fabricated with a multiwalled carbon nanotube that is attached to the end of an electrochemically etched tungsten tip, and it was imaged in an epifluorescence microscope system. The fluorescence intensity distribution of the fluorescent particles at the end of the nanotube was approximated with a Gaussian and fitted by least-squares method. Finally, we were able to measure the displacement of the nanotube cantilever during electrostatic actuation with positional accuracy of a few nanometers. This technique can be applied to a manipulator or a force transducer on related a few piconewton forces.
Midwave infrared InAs/GaSb strained layer superlattice hole avalanche photodiode
Authors: Banerjee Koushik , Ghosh Siddhartha , Mallick Shubhrangshu , Plis Elena , Krishna Sanjay , Grein Christoph
Published: May 2009

Midwavelength infrared InAs–GaSb strained layer superlattice n+-n−-p avalanche photodiodes, specifically designed to have hole dominated avalanching, with a zero percent cutoff wavelength of ∼6.3 μm are fabricated and characterized. Maximum multiplication gain of 105 is measured at −3.6 V at 77 K. Measured excess noise factors are significantly improved compared to unity hole to electron ionization ratio and corresponds to a theoretical value between 40 and 50 when compared with the McIntyre model. Exponential nature of the gain as a function of reverse bias along with low excess noise factors confirms single carrier hole dominated impact ionization.
Structural transformations in carbon under extreme pressure: Beyond diamond
Authors: Sun Jian , Klug Dennis D. , Martoňák Roman
Published: May 2009

High-pressure structural transformations of carbon at terapascal pressures are studied using metadynamics and ab initio methods. Diamond transforms to a mechanically stable cubic structure (P4132) at 2.5 TPa and 300 K. At 4000 K and 2 TPa, simple cubic carbon SC1 (Pm-3m) is obtained from cubic diamond. The high-pressure tetrahedrally coordinated BC8 (Ia-3) structure of carbon is obtained by decompression of the SC1 structure at 1 TPa and 5000 K. At 3000 K, with decompression of SC1 carbon to 1 TPa, two new metastable tetrahedrally coordinated structures form, MP8 (P2/c) and OP8 (Pccn) with higher density than that of cubic diamond. The results show the presence of strong kinetic effects and suggest that phase transformations and structures of carbon at extreme pressures are more complex than previously thought.
Ab initio potential energy curve of F2. IV. Transition from the covalent to the van der Waals region: Competition between multipolar and correlation forces
Authors: Bytautas Laimutis , Ruedenberg Klaus
Published: May 2009

The potential energy curve of the fluorine molecule in the ground electronic state Σ1g+ is determined and analyzed in the long-range region. The analysis is based on expressing the potential as the sum of the potential energy curve of the uncorrelated, but properly dissociating wave function and the correlation energy contribution. It is shown that, in the long-range region, the former becomes identical with the interaction between the quadrupoles of the fluorine atoms and the latter becomes the London dispersion interaction. The former is repulsive because of the coaxial quadrupole alignments in the Σ1g+ ground state and proportional to 1/R5. The latter is attractive and proportional to 1/R6. There moreover exists an additional repulsive force due to the loss of spin-orbit coupling upon the bond formation. As a result of these antagonistic interactions, the potential energy curve has a barrier at about 4 Å, with a value about +0.04 mhartree. The descent of the potential toward the minimum, when the atoms approach each other from infinity, begins therefore only at internuclear distances less than about twice the equilibrium distance and is then very steep.
Density-dependent analysis of nonequilibrium paths improves free energy estimates
Authors: Minh David D. L.
Published: May 2009

When a system is driven out of equilibrium by a time-dependent protocol that modifies the Hamiltonian, it follows a nonequilibrium path. Samples of these paths can be used in nonequilibrium work theorems to estimate equilibrium quantities such as free energy differences. Here, we consider analyzing paths generated with one protocol using another one. It is posited that analysis protocols which minimize the lag, the difference between the nonequilibrium and the instantaneous equilibrium densities, will reduce the dissipation of reprocessed trajectories and lead to better free energy estimates. Indeed, when minimal lag analysis protocols based on exactly soluble propagators or relative entropies are applied to several test cases, substantial gains in the accuracy and precision of estimated free energy differences are observed.
Generation of two-dimensional dust vortex flows in a direct current discharge plasma
Authors: Uchida Giichiro , Iizuka Satoru , Kamimura Tetsuo , Sato Noriyoshi
Published: May 2009

The two-dimensional dust vortex flows are observed in a direct current discharge plasma near the edge of a metal plate which is situated in the dust-particle levitation region. Applying negative dc potential to the metal plate, dust particles are strongly accelerated toward the metal plate edge, and two symmetric dust vortex flows are generated on both sides of the metal plate. Numerical calculation including the effect of the ion drag force well demonstrates the dust vortex formation as in the experiment. A mechanism of the dust vortex generation could be explained by effect of an asymmetry of ion drag force near the metal plate.
Vacuum electron acceleration by tightly focused laser pulses with nanoscale targets
Authors: Popov K. I. , Bychenkov V. Yu. , Rozmus W. , Sydora R. D. , Bulanov S. S.
Published: May 2009

Electron acceleration using a tightly focused relativistic short laser pulse interacting with a spherical nanocluster, ultrathin foil or preformed mid-dense plasmas is studied by using three-dimensional particle-in-cell simulations with the Stratton–Chu integrals as the boundary conditions for the incident laser fields. The investigation is performed in the regime where the focal spot size is comparable with the laser wavelength. Generation of high-energy electron multibunch jets with quasimonoenergetic or waterbaglike spectra has been demonstrated. The physical process of acceleration and bunching of the electrons is discussed in detail, as well as particles energy and angular distributions for different laser intensities, focusing optics, target parameters, and laser incidence angles.
Ga
2
O
3
(
Gd
2
O
3
)
on Ge without interfacial layers: Energy-band parameters and metal oxide semiconductor devices
Authors: Chu L. K. , Lin T. D. , Huang M. L. , Chu R. L. , Chang C. C. , Kwo J. , Hong M.
Published: May 2009

Ga 2 O 3 ( Gd 2 O 3 ) (GGO) directly deposited on Ge substrate in ultrahigh vacuum, without a passivation layer such as GeOxNy or Si, has demonstrated excellent electrical performances and thermodynamic stability. Energy-band parameters of GGO/Ge have been determined by in situ x-ray photoelectron spectroscopy in conjunction with reflection electron energy loss spectroscopy and current transport of Fowler–Nordheim tunneling. A conduction-band offset and a valence-band offset of ∼2.3 and ∼2.42 eV, respectively, have been obtained. Moreover, self-aligned Ge pMOSFETs of 1-μm-gate length using Al2O3/GGO as the gate dielectrics have shown a high drain current and a peak transconductance of 252 mA/mm, and 143 mS/mm, respectively.
A phase-space study of jet formation in planetary-scale fluids
Authors: Wordsworth R. D.
Published: May 2009

The interaction between planetary waves and an arbitrary zonal flow is studied from a phase-space viewpoint. Using the Wigner distribution, a planetary wave Vlasov equation is derived that includes the contribution of the mean flow to the zonal potential vorticity gradient. This equation is applied to the problem of planetary wave modulational instability, where it is used to predict a fastest growing mode of finite wavenumber. A wave-mean flow numerical model is used to test the analytical predictions, and an intuitive explanation of modulational instability and jet asymmetry is given via the motion of planetary wavepackets in phase space.
Spectral and spatial investigation of midinfrared surface waves on a plasmonic grating
Authors: Ribaudo T. , Adams D. C. , Passmore B. , Shaner E. A. , Wasserman D.
Published: May 2009

A patterned metal film with a periodic array of subwavelength apertures, fabricated upon a semiconductor substrate and designed to possess transmission resonances in the midinfrared is interrogated with a wavelength-tunable external cavity quantum cascade laser. The interaction of the coherent light with this plasmonic structure is studied using a spatially resolved transmission experiment, allowing for the far-field imaging of propagating waves on the surface of the metal film. Spatial and spectral transmission is investigated for a range of near-normal incidence angles. For nonzero angles of incidence, coupling of laser light, at distinct frequencies, to surface waves propagating in opposite directions is demonstrated.
Characterization of string cavitation in large-scale Diesel nozzles with tapered holes
Authors: Gavaises M. , Andriotis A. , Papoulias D. , Mitroglou N. , Theodorakakos A.
Published: May 2009

The cavitation structures formed inside enlarged transparent replicas of tapered Diesel valve covered orifice nozzles have been characterized using high speed imaging visualization. Cavitation images obtained at fixed needle lift and flow rate conditions have revealed that although the conical shape of the converging tapered holes suppresses the formation of geometric cavitation, forming at the entry to the cylindrical injection hole, string cavitation has been found to prevail, particularly at low needle lifts. Computational fluid dynamics simulations have shown that cavitation strings appear in areas where large-scale vortices develop. The vortical structures are mainly formed upstream of the injection holes due to the nonuniform flow distribution and persist also inside them. Cavitation strings have been frequently observed to link adjacent holes while inspection of identical real-size injectors has revealed cavitation erosion sites in the area of string cavitation development. Image postprocessing has allowed estimation of their frequency of appearance, lifetime, and size along the injection hole length, as function of cavitation and Reynolds numbers and needle lift.
Approximate normal mode analysis based on vibrational subsystem analysis with high accuracy and efficiency
Authors: Hafner Jeffrey , Zheng Wenjun
Published: May 2009

Normal mode analysis (NMA) has been proven valuable in modeling slow conformational dynamics of biomolecular structures beyond the reach of direct molecular simulations. However, it remains computationally expensive to directly solve normal modes for large biomolecular systems. In this study, we have evaluated the accuracy and efficiency of two approximate NMA protocols—one based on our recently proposed vibrational subsystem analysis (VSA), the other based on the rotation translation block (RTB), in comparison with standard NMA that directly solves a full Hessian matrix. By properly accounting for flexibility within blocks of residues or atoms based on a subsystem-environment partition, VSA-based NMA has attained a much higher accuracy than RTB and much lower computing cost than standard NMA. Therefore, VSA enables accurate and efficient calculations of normal modes from all-atom or coarse-grained potential functions, which promise to improve conformational sampling driven by low-frequency normal modes.
A highly efficient two level diamond based single photon source
Authors: Simpson D. A. , Ampem-Lassen E. , Gibson B. C. , Trpkovski S. , Hossain F. M. , Huntington S. T. , Greentree A. D. , Hollenberg L. C. L. , Prawer S.
Published: May 2009

An unexplored diamond defect center that is found to emit stable single photons at a measured rate of 1.6 MHz at room temperature is reported. The center, identified in chemical vapor deposition grown diamond crystals, exhibits a sharp zero phonon line at 734 nm with a full width at half maximum of ∼4 nm. The photon statistics confirm that the center is a single emitter and provides direct evidence of a true two level single quantum system in diamond.
A simple design of flat hyperlens for lithography and imaging with half-pitch resolution down to 20 nm
Authors: Xiong Yi , Liu Zhaowei , Zhang Xiang
Published: May 2009

We propose that a hyperlens can be used for photolithography to generate deep subwavelength arbitrary patterns from diffraction-limited masks. Numerical simulation shows that half-pitch resolution down to 20 nm is possible from a mask with 280 nm period at working wavelength 375 nm. We also extend the hyperlens projection concept from cylindrical interfaces to arbitrary interfaces. An example of a flat interface hyperlens is numerically demonstrated for lithography purposes.
Ultralow threshold laser action from toroidal polymer microcavity
Authors: Tulek Abdullah , Akbulut Duygu , Bayindir Mehmet
Published: May 2009

We report laser action from a toroidal microcavity coated with π-conjugated polymer. An ultralow threshold value of ∼200 pJ/pulse is achieved by free space excitation in ambient conditions. This is the lowest threshold energy obtained in microtoroid lasers by free space excitation. The effective refractive index of the polymer, extracted from Fourier analysis of emission spectra, is 1.787, which is very close to measured value of 1.790 indicating that laser modes are located around the circumference of the cavity as whispering gallery resonances.
A global assessment of endemism and species richness across island and mainland regions
Authors: Kier Gerold , Kreft Holger , Lee Tien Ming , Jetz Walter , Ibisch Pierre L. , Nowicki Christoph , Mutke Jens , Barthlott Wilhelm
Published: May 2009

Endemism and species richness are highly relevant to the global prioritization of conservation efforts in which oceanic islands have remained relatively neglected. When compared to mainland areas, oceanic islands in general are known for their high percentage of endemic species but only moderate levels of species richness, prompting the question of their relative conservation value. Here we quantify geographic patterns of endemism-scaled richness (“endemism richness”) of vascular plants across 90 terrestrial biogeographic regions, including islands, worldwide and evaluate their congruence with terrestrial vertebrates. Endemism richness of plants and vertebrates is strongly related, and values on islands exceed those of mainland regions by a factor of 9.5 and 8.1 for plants and vertebrates, respectively. Comparisons of different measures of past and future human impact and land cover change further reveal marked differences between mainland and island regions. While island and mainland regions suffered equally from past habitat loss, we find the human impact index, a measure of current threat, to be significantly higher on islands. Projected land-cover changes for the year 2100 indicate that land-use-driven changes on islands might strongly increase in the future. Given their conservation risks, smaller land areas, and high levels of endemism richness, islands may offer particularly high returns for species conservation efforts and therefore warrant a high priority in global biodiversity conservation in this century.
Structural specializations of A2, a force-sensing domain in the ultralarge vascular protein von Willebrand factor
Authors: Zhang Qing , Zhou Yan-Feng , Zhang Cheng-Zhong , Zhang Xiaohui , Lu Chafen , Springer Timothy A.
Published: May 2009

The lengths of von Willebrand factor (VWF) concatamers correlate with hemostatic potency. After secretion in plasma, length is regulated by hydrodynamic shear force-dependent unfolding of the A2 domain, which is then cleaved by a specific protease. The 1.9-Å crystal structure of the A2 domain demonstrates evolutionary adaptations to this shear sensor function. Unique among VWF A (VWA) domains, A2 contains a loop in place of the α4 helix, and a
cis
-proline. The central β4-strand is poorly packed, with multiple side-chain rotamers. The Tyr-Met cleavage site is buried in the β4-strand in the central hydrophobic core, and the Tyr structurally links to the C-terminal α6-helix. The α6-helix ends in 2 Cys residues that are linked by an unusual vicinal disulfide bond that is buried in a hydrophobic pocket. These features may narrow the force range over which unfolding occurs and may also slow refolding. Von Willebrand disease mutations, which presumably lower the force at which A2 unfolds, are illuminated by the structure.
A Carlitz module analogue of a conjecture of Erdos and Pomerance
Authors: Kuo Wentang , Liu Yu-Ru
Published: May 2009

Let

A
=

F

q

[
T
]

A=\mathbb {F}_q[T]

be the ring of polynomials over the finite field

F

q

\mathbb {F}_q

and

0
≠
a
∈
A

0 \neq a \in A

. Let

C
C

be the

A
A

-Carlitz module. For a monic polynomial

m
∈
A

m\in A

, let

C
(
A

/

m
A
)

C(A/mA)

and

a
¯

\bar {a}

be the reductions of

C
C

and

a
a

modulo

m
A

mA

respectively. Let

f
a

(
m
)

f_a(m)

be the monic generator of the ideal

{
f
∈
A
,

C
f

(

a
¯

)
=

0
¯

}

\{f\in A, C_f(\bar {a}) =\bar {0}\}

on

C
(
A

/

m
A
)

C(A/mA)

. We denote by

ω
(

f
a

(
m
)
)

\omega (f_a(m))

the number of distinct monic irreducible factors of

f
a

(
m
)

f_a(m)

. If

q
≠
2

q\neq 2

or

q
=
2

q=2

and

a
≠
1
,
T

a\neq 1, T

, or

(
1
+
T
)

(1+T)

, we prove that there exists a normal distribution for the quantity
\[
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" alttext="StartStartFraction omega left-parenthesis f Subscript a Baseline left-parenthesis m right-parenthesis right-parenthesis minus one half left-parenthesis log degree m right-parenthesis squared OverOver StartFraction 1 Over StartRoot 3 EndRoot EndFraction left-parenthesis log degree m right-parenthesis Superscript 3 slash 2 Baseline EndEndFraction period">

ω
(

f
a

(
m
)
)
−

1
2

(
log
⁡
deg
⁡
m

)
2

1

3

(
log
⁡
deg
⁡
m

)

3

/

2

.

\frac {\omega (f_a(m))-\frac {1}{2}(\log \deg m)^2}{\frac {1}{\sqrt {3}}{(\log \deg m)^{3/2}}}.

\]
This result is analogous to an open conjecture of Erdős and Pomerance concerning the distribution of the number of distinct prime divisors of the multiplicative order of

b
b

modulo

n
n

, where

b
b

is an integer with

|

b

|

>
1

|b|>1

, and

n
n

a positive integer.
Oscillations of a given size of some arithmetic error terms
Authors: Kaczorowski Jerzy , Wiertelak Kazimierz
Published: May 2009

A general method of estimating the number of oscillations of a given size of arithmetic error terms is developed. Special attention is paid to the remainder terms in the prime number formula, in the Dirichlet prime number theorem for primes in arithmetic progressions and to the remainder term in the asymptotic formula for the number of square free divisors of an integer.
A 𝑐₀-saturated Banach space with no long unconditional basic sequences
Authors: Lopez-Abad J. , Todorcevic S.
Published: May 2009

We present a Banach space

X

\mathfrak X

with a Schauder basis of length

ω
1

\omega _1

which is saturated by copies of

c
0

c_0

and such that for every closed decomposition of a closed subspace

X
=

X
0

⊕

X
1

X=X_0\oplus X_1

, either

X
0

X_0

or

X
1

X_1

has to be separable. This can be considered as the non-separable counterpart of the notion of hereditarily indecomposable space. Indeed, the subspaces of

X

\mathfrak X

have “few operators” in the sense that every bounded operator

T
:
X
→

X

T:X \rightarrow \mathfrak {X}

from a subspace

X
X

of

X

\mathfrak {X}

into

X

\mathfrak {X}

is the sum of a multiple of the inclusion and a

ω
1

\omega _1

-singular operator, i.e., an operator

S
S

which is not an isomorphism on any non-separable subspace of

X
X

. We also show that while

X

\mathfrak {X}

is not distortable (being

c
0

c_0

-saturated), it is arbitrarily

ω

1

\omega _{1}

-distortable in the sense that for every

λ
>
1

\lambda >1

there is an equivalent norm

‖

|

⋅
‖

|

\| |\cdot \| |

on

X

\mathfrak {X}

such that for every non-separable subspace

X
X

of

X

\mathfrak {X}

there exist

x
,
y
∈

S
X

x,y\in S_X

such that

‖

|

x
‖

|

/

‖

|

y
‖

|

≥
λ

\| |x\| |/\| |y\| |\ge \lambda

.
Rashes in Pregnancy
Authors: Alsop Rebecca
Published: May 2009

The hormonal, physiological and physical changes that occur during pregnancy can lead to a number of skin conditions being exacerbated, occurring for the first time or appearing in an altered form. In addition to this, there are a number of systemic infections in which skin symptoms or rash may be the presenting complaint. It is important to be able to distinguish between those rashes which represent potential complications for the pregnant woman and developing foetus and those which do not. Where the diagnosis is unclear, it is useful to have a management strategy to exclude serious causes.
Gastro-Intestinal Bleeding
Authors: Mehta Chirag , Chang Joy
Published: May 2009

Acute gastro-intestinal (GI) bleeding is defined as bleeding into the GI tract. GI bleeding is a common medical problem that can vary in presentation from being an insidious chronic blood loss to being potentially life threatening. Although 80% of acute GI bleeds stop spontaneously, it is essential to determine the source of bleeding and establish a diagnosis in order to attempt to prevent a recurrence and so that the most appropriate management may be given in future episodes. Also, an accurate diagnosis will allow a patient to be treated optimally for the underlying condition.
The Role of the GP within the Practice Management Structure
Authors: Morton Anna , Simon Chantal
Published: May 2009

T here are now many different models of primary care operating within the UK. However, the traditional practice owned and run by GPs, almost always with the assistance of a practice manager, is still the most usual model of primary care provision. In some cases, the practice manager is also a stakeholder in the business, in others simply an employee. This section focuses on the management roles of the GPs within traditional style practices.
Nd2(WO4)3
Authors: Weil Matthias , Stöger Berthold , Aleksandrov Lyubomir
Published: May 2009

The title compound, dineodymium(III) tris[tungstate(VI)], is a member of the Eu2(WO4)3structure family and crystallizes isotypically with other rare earth tungstates and molybdates of this formula type. The structure is a derivative of the scheelite (CaWO4) structure and can be considered as an ordered defect variant with a threefold scheelite supercell and one rare earth (RE) site unoccupied. The Nd3+cations are coordinated by eight O atoms in form of a distorted bicapped trigonal prism. The two unique W cations are tetrahedrally surrounded by O atoms. One WO4tetrahedron has 2 symmetry and is relatively undistorted whereas the other tetrahedron differs considerably from an ideal geometry. This is caused by an additional remote O atom at a distance of 2.149 (4) Å. The resulting WO4 + 1polyhedra form W2O8dimers through edge-sharing. Together with the WO4and NdO8units, the three-dimensional set-up is accomplished.