bluuebunny/crossref_metadata_2025 huggingface dataset:
One-way mode transmission in one-dimensional phononic crystal plates
Authors: Zhu Xuefeng , Zou Xinye , Liang Bin , Cheng Jianchun
Published: December 2010

We investigate theoretically the band structures of one-dimensional phononic crystal (PC) plates with both antisymmetric and symmetric structures, and show how unidirectional transmission behavior can be obtained for either antisymmetric waves (A modes) or symmetric waves (S modes) by exploiting mode conversion and selection in the linear plate systems. The theoretical approach is illustrated for one PC plate example where unidirectional transmission behavior is obtained in certain frequency bands. Employing harmonic frequency analysis, we numerically demonstrate the one-way mode transmission for the PC plate with finite superlattice by calculating the steady-state displacement fields under A modes source (or S modes source) in forward and backward direction, respectively. The results show that the incident waves from A modes source (or S modes source) are transformed into S modes waves (or A modes waves) after passing through the superlattice in the forward direction and the Lamb wave rejections in the backward direction are striking with a power extinction ratio of more than 1000. The present structure can be easily extended to two-dimensional PC plate and efficiently encourage practical studies of experimental realization which is believed to have much significance for one-way Lamb wave mode transmission.
Commutativity of the adiabatic elimination limit of fast oscillatory components and the instantaneous feedback limit in quantum feedback networks
Authors: Gough John E. , Nurdin Hendra I. , Wildfeuer Sebastian
Published: December 2010

We show that, for arbitrary quantum feedback networks consisting of several quantum mechanical components connected by quantum fields, the limit of adiabatic elimination of fast oscillator modes in the components and the limit of instantaneous transmission along internal quantum field connections commute. The underlying technique is to show that both limits involve a Schur complement procedure. The result shows that the frequently used approximations, for instance, to eliminate strongly coupled optical cavities, are mathematically consistent.
Exactness of the Bogoliubov approximation in random external potentials
Authors: Jaeck Thomas , Zagrebnov Valentin A.
Published: December 2010

We investigate the validity of the Bogoliubov c-number approximation in the case of interacting Bose-gas in a homogeneous random media. To take into account the possible occurence of type III generalized Bose–Einstein condensation (i.e., the occurrence of condensation in an infinitesimal band of low kinetic energy modes without macroscopic occupation of any of them) we generalize the c-number substitution procedure to this band of modes with low momentum. We show that, as in the case of the one-mode condensation for translation-invariant interacting systems, this procedure has no effect on the exact value of the pressure in the thermodynamic limit, assuming that the c-numbers are chosen according to a suitable variational principle. We then discuss the relation between these c-numbers and the (total) density of the condensate.
Communication: Polarization-angle-scanning two-dimensional infrared spectroscopy of antiparallel β-sheet polypeptide: Additional dimensions in two-dimensional optical spectroscopy
Authors: Choi Jun-Ho , Cho Minhaeng
Published: December 2010

A theoretical description of polarization-angle-scanning (PAS) two-dimensional infrared (2DIR) spectroscopy, where the incident beam polarization directions are considered to be novel dimensions in coherent two-dimensional (2D) optical spectroscopy, is presented. To shed light on the underlying principles and to illustrate a potential use of this measurement method, we investigate the PAS 2DIR spectroscopy of an alanine-based antiparallel β-sheet, using the relationships between cross-peak amplitudes and incident beam polarization directions and carrying out numerical simulations. The numerically simulated PAS 2DIR spectra of the antiparallel β-sheet show that the magnitude and sign of the cross peak reflecting the correlation between the two characteristic amide I vibrations change for varying beam polarization directions. This suggests that each individual cross peak in a given 2D spectrum can be selectively eliminated with an appropriate beam polarization configuration, which in turn provides information on the transition dipole angle and possibly on the structure of coupled multichromophoric systems. This novel measurement method combining the polarization-angle-scanning technique with 2D vibrational or electronic spectroscopy would be a useful tool for probing structural changes of nonequilibrium molecular systems and to investigate transfers of population and coherence by monitoring the time-dependent changes of angles between transition dipoles.
Polarity inversion of N-face GaN using an aluminum oxide interlayer
Authors: Wong Man Hoi , Wu Feng , Speck James S. , Mishra Umesh K.
Published: December 2010

The polarity of GaN grown by plasma-assisted molecular beam epitaxy was inverted from N-face to Ga-face by inserting a composite AlN/aluminum oxide (AlOx) interlayer structure at the inversion interface. The change in polarity was verified in situ by reflection high energy electron diffraction via intensity transients and postgrowth surface reconstructions, and ex situ by convergent beam electron diffraction and etch studies in an aqueous potassium hydroxide solution. The inverted materials showed smooth surfaces and good electrical properties. AlGaN/GaN high electron mobility transistors fabricated on the inverted epilayers showed good dc and high frequency performance. A current-gain cutoff frequency (fT) of 21 GHz and maximum oscillation frequency (fmax) of 61 GHz were measured in devices with a gate length of 0.7 μm. These data compare favorably to those of Ga-face AlGaN/GaN devices with a similar structure grown on Si-face SiC substrates.
A study of the role of dislocation density, indium composition on the radiative efficiency in InGaN/GaN polar and nonpolar light-emitting diodes using drift-diffusion coupled with a Monte Carlo method
Authors: Lu I-Lin , Wu Yuh-Renn , Singh Jasprit
Published: December 2010

In this paper, we apply the Poisson, drift-diffusion, and Schrodinger solver coupled with the Monte Carlo method to study the in-plane carrier dynamics in the InGaN c-plane and nonpolar plane quantum well light-emitting diode device. Carrier diffusion, scattering, radiative recombination, and trapping by dislocation defects in the quantum well are studied. The impact of carrier dynamics on the internal quantum efficiency (IQE) in the quantum well with different indium compositions, dislocation densities, polarization effect, and interface roughness is studied. Our results show that (for dislocations densities in typical devices) due to the large radiative lifetime from the quantum confined Stark effect, nonradiative recombination caused by the dislocation defects plays a dominated role in limiting the IQE. In the nonpolar quantum well, the IQE is much better than in the c-plane case but is still strongly influenced by dislocation density. Our results show that to achieve 100% IQE, the dislocation density levels need to be lower than 106 cm−2 and 107 cm−2 for c-plane and nonpolar plane InGaN quantum well, respectively. Our results are also compared with published experimental work and have shown a good agreement.
Evidence for decoupled two-dimensional vortex behavior of YBa2Cu3O7−δ in La0.7Sr0.3MnO3/YBa2Cu3O7−δ/La0.7Sr0.3MnO3 trilayer
Authors: Samal D. , Anil Kumar P. S.
Published: December 2010

We investigate the vortex behavior of YBa2Cu3O7−δ thin films sandwiched between two ferromagnetic layers (La0.7Sr0.3MnO3/YBa2Cu3O7−δ/La0.7Sr0.3MnO3). The magnetization study on La0.7Sr0.3MnO3/YBa2Cu3O7−δ/La0.7Sr0.3MnO3 trilayers conspicuously shows the presence of both ferromagnetic and diamagnetic phases. The magnetotransport study on the trilayers reveals a significant reduction in the activation energy (U) for the vortex motion in YBa2Cu3O7−δ. Besides, the “U” exhibits a logarithmic dependence on the applied magnetic field which directly indicates the existence of decoupled two-dimensional (2D) pancake vortices present in the CuO2 layers. The evidence of 2D decoupled vortex behavior in La0.7Sr0.3MnO3/YBa2Cu3O7−δ/La0.7Sr0.3MnO3 is believed to arise from (a) the weakening of superconducting coherence length along the c-axis and (b) enhanced intraplane vortex–vortex interaction due to the presence of ferromagnetic layers.
Microwave reflection characteristics of surface-modified Fe50Ni50 fine particle composites
Authors: Wei Jianqiang , Zhang Zhaoqi , Wang Bochong , Wang Tao , Li Fashen
Published: December 2010

Surface-modified planar-anisotropy Fe50Ni50 particle-resin composites have been studied in the microwave frequency range. After surface modification, the eddy current effect is suppressed effectively while the permeability is almost unchanged. High permeability and appropriate permittivity are obtained at the meantime. Simulated microwave reflection result shows that the matching thickness, corresponding frequency, μ and ε is coincident with the quarter wavelength matching condition. The surface-modified Fe50Ni50/resin composites can be attractive candidates for thinner microwave absorbers in L-band (1–2 GHz).
Liquid filling in standard circular well microplates
Authors: Lu Gabriel , Tan Han Yen , Neild Adrian , Liew Oi Wah , Yu Yang , Ng Tuck Wah
Published: December 2010

It is often assumed that droplets dispensed into standard microplate wells will automatically fill their bottoms. We show here by computational simulation and experimental verification that the ability to fill the well bottom is dependent on the surface wetting characteristics. The release of droplets at the center was also found to fill the well bottom better than droplet dispensation in contact with the well wall. Hydrophobic surfaces required higher liquid volumes to fill the well bottom; unlike the case with capillary wells microplates. This renders standard microplate wells less amenable for use in small volume liquid handling; a feature that is increasingly sought after in screening and studies involving scarce agents.
A surface-layer model of ferroelectric nanowire
Authors: Zhang Yihui , Hong Jiawang , Liu Bin , Fang Daining
Published: December 2010

In this paper, a surface-layer model is established to study the axial polarization distributions and critical diameters of nanowires with different surface compositions. Analytical solutions are obtained based on this model, which are validated by the ab initio results for small-size nanowires and can also predict the behaviors of large-size specimen. Compared to the traditional Landau–Ginzburg–Devonshire theory using an extrapolation length, the present model describes more microstructure information of the surface-layer, and is thus capable of characterizing the influences of different surface compositions. Furthermore, this model may shed insight into the mechanisms of the size effect and polarization distribution patterns in nanoscale ferroelectrics.
Interfacial reactions in Ru metal-electrode/HfSiON gate stack structures studied by synchrotron-radiation photoelectron spectroscopy
Authors: Kamada H. , Toyoda S. , Tanimura T. , Kumigashira H. , Oshima M. , Liu G. L. , Liu Z. , Sukegawa T.
Published: December 2010

We have investigated the thermal stability and interfacial reactions of a Ru/HfSiON gate stack structure, annealed in a nitrogen ambient, using synchrotron-radiation photoelectron spectroscopy. We find that in HfSiON films with Ru metal, competition between catalyst-induced oxidation and oxygen or SiO desorption arises upon high-temperature annealing, unlike in the same films without Ru. The desorption reaction during high-temperature annealing at 1050 °C could be caused by the decomposition of an unstable Si oxide component, formed by catalytic oxidation at the interface between the HfSiON layer and the Si substrate after annealing below 850 °C.
Focused electron beam induced etching of silicon by chlorine gas: Negative effects of residual gas contamination on the etching process
Authors: Roediger P. , Wanzenboeck H. D. , Hochleitner G. , Bertagnolli E. , Buehler W.
Published: December 2010

For the first time focused electron beam induced etching of silicon using molecular chlorine has been developed as reliable and reproducible process. Around the etched pits the etching process was found to be accompanied by carbonaceous deposition from hydrocarbon contamination of the residual gas typically present in a scanning electron microscope (SEM). This work will focus on the effect of residual gas deposition on this silicon etch process using chlorine. The process mechanisms for residual gas deposition (in the absence of chlorine) as well as the silicon etch process in the presence of chlorine are discussed in terms of precursor replenishment of the sample surface and precursor delivery to the processed area. The formation of carbonaceous deposits from undesired contaminants can block the surface from an etch process. Especially for low beam currents this problem was encountered. Results suggest that the presence of chlorine when processed with a high electron beam current dominates over residual gas deposition. On the other hand, the etch-inhibiting effect of an increased level of SEM chamber contamination (resulting in increased residual gas deposition rates) is shown.
Electronic structure and magnetism of transition metal doped Zn12O12 clusters: Role of defects
Authors: Ganguli Nirmal , Dasgupta Indra , Sanyal Biplab
Published: December 2010

We present a comprehensive study of the energetics and magnetic properties of ZnO clusters doped with 3d transition metals (TMs) using ab initio density functional calculations in the framework of generalized gradient approximation+Hubbard U (GGA+U) method. Our results within GGA+U for all 3d dopants except Ti indicate that antiferromagnetic interaction dominates in a neutral, defect-free cluster. Formation energies are calculated to identify the stable defects in the ZnO cluster. We have analyzed in details the role of these defects to stabilize ferromagnetism when the cluster is doped with Mn, Fe, and Co. Our calculations reveal that in the presence of charged defects the TM atoms residing at the surface of the cluster may have an unusual oxidation state, that plays an important role to render the cluster ferromagnetic. Defect induced magnetism in ZnO clusters without any TM dopants is also analyzed. These results on ZnO clusters may have significant contributions in the nanoengineering of defects to achieve desired ferromagnetic properties for spintronic applications.
Magnetoresistance of lateral semiconductor spin valves
Authors: Zainuddin A. N. M. , Kum Hyun , Basu D. , Srinivasan S. , Siddiqui L. , Bhattacharya P. , Datta S.
Published: December 2010

The magnetoresistance of two terminal lateral semiconductor spin valves with respect to varying mesa size is studied. It is shown theoretically that extended regions outside the spin-current path can act as an additional source of spin-relaxation, decreasing the magnetoresistance response. From a simplified expression of magnetoresistance derived from spin-diffusion equations, we show that it is important to etch away these extended regions for devices with channel lengths much smaller than the spin-diffusion length in order to achieve maximum magnetoresistance. Preliminary experimental data on a two terminal local spin valve are in good agreement with the theory established in this article.
Two-fluid low-collisionality equilibrium model and application to spherical torus plasmas
Authors: Ishida Akio , Steinhauer Loren C. , Peng Y.-K. Martin
Published: December 2010

A two-fluid equilibrium model with low-collisionality is developed including a new flow-singularity condition. This description is applied to the rapidly rotating, high-performance National Spherical Torus eXperiment (NSTX) [Peng et al., Plasma Phys. Controlled Fusion 47, B263 (2005)]. The model replicates the primary features of an example equilibrium, such as the profiles of electron and ion temperatures, density, and toroidal flow of an example equilibrium. This is the first full-two-fluid computation of two-dimensional equilibrium with rapid ion flow near the thermal speed. In consequence several important features emerge: (1) the ion toroidal current exceeds the toroidal plasma current as a result of electron rotational flow reversal; (2) the ion flow in the core region is roughly parallel to the magnetic field, i.e., the ion fluid in the core is nearly force free; (3) E+ui×B differs considerably from zero, so that the E×B drift fails to describe the ion and electron flows perpendicular to the magnetic field. Simpler models of equilibrium, such as the static equilibrium or the one-fluid flowing model, cannot replicate these properties. These results suggest that the rapidly rotating, high-performance NSTX plasma may represent a new parameter regime of fusion plasmas.
Local relaxation and maximum entropy in two-dimensional turbulence
Authors: Servidio S. , Wan M. , Matthaeus W. H. , Carbone V.
Published: December 2010

The phenomenon of vortex merging in two-dimensional hydrodynamics has been investigated through direct numerical simulations. The fast and local processes that occur during the turbulent relaxation of a randomly initialized system in periodic geometry have been examined. The analysis reveals that many of the coherent structures can be described by a local principle of maximization of entropy. The validity of this entropy principle has been further confirmed by time-dependent statistics using a contour-tracking technique. Implications for the description of persistent coherent vortices commonly observed in nature are suggested, including growing evidence for the wide applicability of maximum entropy-based relaxation principles.
Degradation of InGaN-based laser diodes analyzed by means of electrical and optical measurements
Authors: Meneghini M. , Trivellin N. , Orita K. , Takigawa S. , Tanaka T. , Ueda D. , Meneghesso G. , Zanoni E.
Published: December 2010

In this paper we present a detailed analysis of the degradation of InGaN-based laser diodes carried out by means of electrical and optical techniques. The study is based on the comparison between the degradation kinetics of laser diodes and light-emitting diode (LED)-like samples, i.e., devices with the same epitaxial structure as the lasers, but with no ridge and facets. Results described in the following indicate that degradation of lasers and LED-like samples is due to the same mechanism, possibly involving the generation of point defects within the active region of the devices. Furthermore, since degradation occurs both in lasers and in LED-like samples (i.e., structures with no current confinement), results suggest that degradation of lasers is not correlated with the geometry of the devices, nor to worsening of current confinement under the ridge.
Onset and cessation of time-dependent, dissolution-driven convection in porous media
Authors: Slim Anja C. , Ramakrishnan T. S.
Published: December 2010

Motivated by convection in the context of geological carbon dioxide sequestration, we present the conditions for free, dissolution-driven convection in a horizontal, ideal porous layer from a time-dependent, pure-diffusion base state. We assume that solute as a separate phase is instantaneously placed in the pores above a given horizontal level at time zero, and gradually diffuses into the underlying liquid. As the concentration of dissolved solute in the liquid increases, its density increases and the system may eventually become gravitationally unstable and convection may begin. We define the amplitude of a perturbation as the mean square of the difference of the concentration profile and the pure-diffusion profile. To identify instability, we calculate the maximum possible instantaneous growth rate of the amplitude over all possible infinitesimal and finite perturbations. Instability exists where this growth rate is positive. We consider two scenarios. In the first scenario, the underlying liquid cannot penetrate into the upper region occupied by the separate, solute-rich phase. In this case, no instability is possible for thin porous layers corresponding to Rayleigh–Darcy numbers less than 32.50. For thicker layers, convection can occur at finite, nonzero times and wavenumbers. The earliest possible onset becomes independent of layer thickness for Rayleigh–Darcy numbers above about 75, and occurs at a time of approximately 47.9D(μϕ/[KΔρ(1−ci∗/cm∗)g])2 after solute placement, where D is the effective diffusivity, μ the liquid viscosity, ϕ the porosity and K the permeability of the medium, g the acceleration due to gravity, Δρ=ρm−ρ0 with ρm the density of saturated liquid and ρ0 the density of pure liquid, cm∗ the maximum solute concentration, and ci∗ the initial average concentration. In the second scenario, the liquid phase in the upper layer remains connected; the liquid beneath can penetrate the horizontal boundary between the two layers and immediately becomes saturated. In this case, the onset occurs sooner and increasingly so for thicker layers. We also present the mode profiles and discuss the implications for sequestration.
Gravitational Chern–Simons and the adiabatic limit
Authors: McLellan Brendan
Published: December 2010

We compute the gravitational Chern–Simons term explicitly for an adiabatic family of metrics using standard methods in general relativity. We use the fact that our base three-manifold is a quasiregular K-contact manifold heavily in this computation. Our key observation is that this geometric assumption corresponds exactly to a Kaluza–Klein Ansatz for the metric tensor on our three-manifold, which allows us to translate our problem into the language of general relativity. Similar computations have been performed by Guralnik et al. [Ann. Phys. 308, 222 (2008)], although not in the adiabatic context.
Room temperature coherent and voltage tunable terahertz emission from nanometer-sized field effect transistors
Authors: Boubanga-Tombet S. , Teppe F. , Torres J. , El Moutaouakil A. , Coquillat D. , Dyakonova N. , Consejo C. , Arcade P. , Nouvel P. , Marinchio H. , Laurent T. , Palermo C. , Penarier A. , Otsuji T. , Varani L. , Knap W.
Published: December 2010

We report on reflective electro-optic sampling measurements of terahertz emission from nanometer-gate-length InGaAs-based high electron mobility transistors. The room temperature coherent gate-voltage tunable emission is demonstrated. We establish that the physical mechanism of the coherent terahertz emission is related to the plasma waves driven by simultaneous current and optical excitation. A significant shift of the plasma frequency and the narrowing of the emission with increasing channel’s current are observed and explained as due to the increase in the carriers’ density and drift velocity.
Ion and electron beam nanofabrication of the which-way double-slit experiment in a transmission electron microscope
Authors: Frabboni Stefano , Gazzadi Gian Carlo , Pozzi Giulio
Published: December 2010

We have realized a which-way experiment closely resembling the original Feynman’s proposal exploiting focused ion beam milling to prepare two nanoslits and electron beam induced deposition to grow, selectively over one of them, electron transparent layers of low atomic number amorphous material to realize a which-way detector for high energy electrons. By carrying out the experiment in an electron microscope equipped with an energy filter, we show that the inelastic scattering of electron transmitted through amorphous layers of different thicknesses provides the control of the dissipative interaction process responsible for the localization phenomena which cancels out the interference effects.
Increased critical thickness for high Ge-content strained SiGe-on-Si using selective epitaxial growth
Authors: Kim Meekyung , Hashemi Pouya , Hoyt Judy L.
Published: December 2010

The onset of misfit dislocation formation, i.e., the critical thickness for heteroepitaxy, is studied for selective epitaxial growth of high Ge-content, strained SiGe on oxide-patterned Si wafers. Misfit dislocation spacing was analyzed as a function of film thickness using plan-view transmission-electron microscopy. For selective epitaxial growth at 450 °C, the critical thickness for Si0.33Ge0.67 is found to be 8.5 nm. This is a twofold increase compared to the 4.0 nm theoretical equilibrium critical thickness and the 4.5 nm critical thickness measured for growth on bare Si wafers. The misfit dislocation density for selective epitaxial growth is strongly influenced by the shape and orientation of the growth area.
Exploring the limits of ultrafast polymerase chain reaction using liquid for thermal heat exchange: A proof of principle
Authors: Maltezos George , Johnston Matthew , Taganov Konstantin , Srichantaratsamee Chutatip , Gorman John , Baltimore David , Chantratita Wasun , Scherer Axel
Published: December 2010

Thermal ramp rate is a major limiting factor in using real-time polymerase chain reaction (PCR) for routine diagnostics. We explored the limits of speed by using liquid for thermal exchange rather than metal as in traditional devices, and by testing different polymerases. In a clinical setting, our system equaled or surpassed state-of-the-art devices for accuracy in amplifying DNA/RNA of avian influenza, cytomegalovirus, and human immunodeficiency virus. Using Thermococcus kodakaraensis polymerase and optimizing both electrical and chemical systems, we obtained an accurate, 35 cycle amplification of an 85-base pair fragment of E. coli O157:H7 Shiga toxin gene in as little as 94.1 s, a significant improvement over a typical 1 h PCR amplification.
Reduced efficiency roll-off in electrophosphorescent devices by a short-living rhenium emitter with well-matched energy levels
Authors: Li Xiao , Zhang Dongyu , Chi Haijun , Xiao Guoyong , Dong Yan , Wu Shuanghong , Su Zisheng , Zhang Zhiqiang , Lei Peng , Hu Zhizhi , Li Wenlian
Published: December 2010

We demonstrated reduced efficiency roll-off in electrophosphorescent devices based on a rhenium [Re(I)] complex, {9, 9-Di-[9′-(4″-phenoxybutyl)-9′H-carbazyl]-9-H-4,5-Diazafluorene Re(CO)3Br} (Re-PCDF). The devices based on Re-PCDF exhibited the peak luminance of 7888 cd/m2 and the maximum efficiency of 7.41 cd/A, respectively. Remarkably, the devices exhibited very small efficiency roll-off with only ca. 28%, which is much better than the reported Re(I) complexes based devices. Such excellent performances could be ascribed to the short luminescent lifetime of Re-PCDF and well-matched energy levels between the singlet host and the triplet emitter. The detailed mechanisms of such small efficiency roll-off were also investigated.
Magnetoresistance in a lithography defined single constrained domain wall spin-valve
Authors: Wang Yudong , de Groot C. H. , Claudio-Gonzalez D. , Fangohr Hans
Published: December 2010

We have measured domain wall magnetoresistance in a single lithographically constrained domain wall. An H-shaped Ni nanobridge was fabricated by e-beam lithography with the two sides being single magnetic domains showing independent magnetic switching. The connection between the sides constrains the domain wall when the sides line up antiparallel. The magnetoresistance curve clearly identifies the magnetic configurations that are expected from a spin-valvelike structure. The value of the magnetoresistance at room temperature is around 0.1% or 0.4 Ω. This value is shown to be in agreement with a theoretical formulation based on spin accumulation. Micromagnetic simulations show that it is possible to reduce the size of the domain wall further by shortening the length of the bridge.
Biological cell controllable patch-clamp microchip
Authors: Penmetsa Siva , Nagrajan Krithika , Gong Zhongcheng , Mills David , Que Long
Published: December 2010

A patch-clamp (PC) microchip with cell sorting and positioning functions is reported, which can avoid drawbacks of random cell selection or positioning for a PC microchip. The cell sorting and positioning are enabled by air bubble (AB) actuators. AB actuators are pneumatic actuators, in which air pressure is generated by microheaters within sealed microchambers. The sorting, positioning, and capturing of 3T3 cells by this type of microchip have been demonstrated. Using human breast cancer cells MDA-MB-231 as the model, experiments have been demonstrated by this microchip as a label-free technical platform for real-time monitoring of the cell viability.
Interface roughness scattering in laterally coupled InGaAs quantum wires
Authors: Kunets Vas. P. , Teodoro M. D. , Dorogan V. G. , Lytvyn P. M. , Tarasov G. G. , Sleezer R. , Ware M. E. , Mazur Yu. I. , Krasinski J. S. , Salamo G. J.
Published: December 2010

Conductivity of In0.38Ga0.62As quantum wires grown on the (311)A plane of GaAs was studied using temperature dependent Hall effect. Detailed analysis of the scattering phenomena which control electron mobility along the wires indicates that the most significant scattering mechanism which limits electron mobility at low temperatures is scattering from interface roughness. This finding contributes to the general understanding of the potential to use self-assembled semiconductor quantum wires in the fabrication of thermoelectric devices where one-dimensionality and enhanced scattering at rough boundaries are important.
Quasiparticle energies and uniaxial pressure effects on the properties of SnO2
Authors: Saniz R. , Dixit H. , Lamoen D. , Partoens B.
Published: December 2010

We calculate the quasiparticle energy spectrum of SnO2 within the GW approximation, properly taking into account the contribution of core levels to the energy corrections. The calculated fundamental gap is of 3.85 eV. We propose that the difference with respect to the experimental optical gap (3.6 eV) is due to excitonic effects in the latter. We further consider the effect applied on uniaxial pressure along the c-axis. Compared to GW, the effect of pressure on the quasiparticle energies and band gap is underestimated by the local-density approximation. The quasiparticle effective masses, however, appear to be well described by the latter.
Different longitudinal optical—transverse optical mode amplification in tip enhanced Raman spectroscopy of GaAs(001)
Authors: Gucciardi Pietro Giuseppe , Valmalette Jean-Christophe
Published: December 2010

We report on tip enhanced Raman spectroscopy of GaAs(100) crystals taking advantage of the fields polarization to maximize the near-field contrast. Excitation parallel to either the [100] or the [110] crystallographic axis provide minimum far-field background provided that cross- or parallel-component of the Raman field are detected. Experiments highlight a tip-induced selective enhancement of the one-phonon longitudinal optical mode with respect to the transverse optical mode. We interpret this effect in terms of depolarization of the excitation field and beam deflection which breaks the polarization-based selection rules of the Raman scattering.
Ambipolar bistable switching effect of graphene
Authors: Shin Young Jun , Kwon Jae Hyun , Kalon Gopinadhan , Lam Kai-Tak , Bhatia Charanjit S. , Liang Gengchiau , Yang Hyunsoo
Published: December 2010

Reproducible current hysteresis is observed in graphene with a back gate structure in a two-terminal configuration. An opposite sequence of switching with different charge carriers, holes, and electrons is found. The charging and discharging effect is proposed to explain this ambipolar bistable hysteretic switching. To confirm this hypothesis, one-level transport model simulations including charging effect are performed and the results are consistent with our experimental data. Methods of improving the on/off ratio of graphene resistive switching are suggested.
Protease activated receptor-1 inhibits the Maspin tumor-suppressor gene to determine the melanoma metastatic phenotype
Authors: Villares Gabriel J. , Zigler Maya , Dobroff Andrey S. , Wang Hua , Song Renduo , Melnikova Vladislava O. , Huang Li , Braeuer Russell R. , Bar-Eli Menashe
Published: December 2010

The thrombin receptor protease activated receptor-1 (PAR-1) is overexpressed in metastatic melanoma cell lines and tumor specimens. Previously, we demonstrated a significant reduction in tumor growth and experimental lung metastasis after PAR-1 silencing via systemic delivery of siRNA encapsulated into nanoliposomes. Gene expression profiling identified a 40-fold increase in expression of Maspin in PAR-1–silenced metastatic melanoma cell lines. Maspin promoter activity was significantly increased after PAR-1 silencing, suggesting that PAR1 negatively regulates Maspin at the transcriptional level. ChIP analyses revealed that PAR-1 decreases binding of Ets-1 and c-Jun transcription factors to the Maspin promoter, both known to activate Maspin transcription. PAR-1 silencing did not affect Ets-1 or c-Jun expression; rather it resulted in increased expression of the chromatin remodeling complex CBP/p300, as well as decreased activity of the CBP/p300 inhibitor p38, resulting in increased binding of Ets-1 and c-Jun to the Maspin promoter and higher Maspin expression. Functionally, Maspin expression reduced the invasive capability of melanoma cells after PAR-1 silencing, which was abrogated after rescuing with PAR-1. Furthermore, tumor growth and experimental lung metastasis was significantly decreased after expressing Maspin in a metastatic melanoma cell line. Moreover, silencing Maspin in PAR-1–silenced cells reverted the inhibition of tumor growth and experimental lung metastasis. Herein, we demonstrate a mechanism by which PAR-1 negatively regulates the expression of the Maspin tumor-suppressor gene in the acquisition of the metastatic melanoma phenotype, thus attributing an alternative function to PAR-1 other than coagulation.
Adapting North American wheat production to climatic challenges, 1839–2009
Authors: Olmstead Alan L. , Rhode Paul W.
Published: December 2010

The Intergovernmental Panel on Climate Change projects that temperatures in the major grain-growing areas of North America will rise by 3–4 °C by 2100. Such abrupt changes will create major challenges, significantly altering the area suitable for wheat. The historical record offers insight into the capability of agriculture to adapt to climatic challenges. Using a new county-level dataset on wheat production and climate norms, we show that during the 19th and 20th centuries North American grain farmers pushed wheat production into environments once considered too arid, too variable, and too harsh to cultivate. As summary measures, the median annual precipitation norm of the 2007 distribution of North American wheat production was one-half that of the 1839 distribution, and the median annual temperature norm was 3.7 °C lower. This shift, which occurred mostly before 1929, required new biological technologies. The Green Revolution associated with the pioneering work of Norman Borlaug represented an important advance in this longer process of biological innovation. However, well before the Green Revolution, generations of North American farmers overcame significant climatic challenges.
Coesite and stishovite in a shocked lunar meteorite, Asuka-881757, and impact events in lunar surface
Authors: Ohtani E. , Ozawa S. , Miyahara M. , Ito Y. , Mikouchi T. , Kimura M. , Arai T. , Sato K. , Hiraga K.
Published: December 2010

Microcrystals of coesite and stishovite were discovered as inclusions in amorphous silica grains in shocked melt pockets of a lunar meteorite Asuka-881757 by micro-Raman spectrometry, scanning electron microscopy, electron back-scatter diffraction, and transmission electron microscopy. These high-pressure polymorphs of SiO
2
in amorphous silica indicate that the meteorite experienced an equilibrium shock-pressure of at least 8–30 GPa. Secondary quartz grains are also observed in separate amorphous silica grains in the meteorite. The estimated age reported by the
39
Ar/
40
Ar chronology indicates that the source basalt of this meteorite was impacted at 3,800 Ma ago, time of lunar cataclysm; i.e., the heavy bombardment in the lunar surface. Observation of coesite and stishovite formed in the lunar breccias suggests that high-pressure impact metamorphism and formation of high-pressure minerals are common phenomena in brecciated lunar surface altered by the heavy meteoritic bombardment.
Behavioral consequences of dopamine deficiency in the
Drosophila
central nervous system
Authors: Riemensperger Thomas , Isabel Guillaume , Coulom Hélène , Neuser Kirsa , Seugnet Laurent , Kume Kazuhiko , Iché-Torres Magali , Cassar Marlène , Strauss Roland , Preat Thomas , Hirsh Jay , Birman Serge
Published: December 2010

The neuromodulatory function of dopamine (DA) is an inherent feature of nervous systems of all animals. To learn more about the function of neural DA in
Drosophila
, we generated mutant flies that lack tyrosine hydroxylase, and thus DA biosynthesis, selectively in the nervous system. We found that DA is absent or below detection limits in the adult brain of these flies. Despite this, they have a lifespan similar to WT flies. These mutants show reduced activity, extended sleep time, locomotor deficits that increase with age, and they are hypophagic. Whereas odor and electrical shock avoidance are not affected, aversive olfactory learning is abolished. Instead, DA-deficient flies have an apparently “masochistic” tendency to prefer the shock-associated odor 2 h after conditioning. Similarly, sugar preference is absent, whereas sugar stimulation of foreleg taste neurons induces normal proboscis extension. Feeding the DA precursor
l
-DOPA to adults substantially rescues the learning deficit as well as other impaired behaviors that were tested. DA-deficient flies are also defective in positive phototaxis, without alteration in visual perception and optomotor response. Surprisingly, visual tracking is largely maintained, and these mutants still possess an efficient spatial orientation memory. Our findings show that flies can perform complex brain functions in the absence of neural DA, whereas specific behaviors involving, in particular, arousal and choice require normal levels of this neuromodulator.
Expression and functional role of a transcribed noncoding RNA with an ultraconserved element in hepatocellular carcinoma
Authors: Braconi Chiara , Valeri Nicola , Kogure Takayuki , Gasparini Pierluigi , Huang Nianyuan , Nuovo Gerard J. , Terracciano Luigi , Croce Carlo M. , Patel Tushar
Published: December 2010

Although expression of non–protein-coding RNA (ncRNA) can be altered in human cancers, their functional relevance is unknown. Ultraconserved regions are noncoding genomic segments that are 100% conserved across humans, mice, and rats. Conservation of gene sequences across species may indicate an essential functional role, and therefore we evaluated the expression of ultraconserved RNAs (ucRNA) in hepatocellular cancer (HCC). The global expression of ucRNAs was analyzed with a custom microarray. Expression was verified in cell lines by real-time PCR or in tissues by in situ hybridization using tissue microarrays. Cellular ucRNA expression was modulated with siRNAs, and the effects on global gene expression and growth of human and murine HCC cells were evaluated. Fifty-six ucRNAs were aberrantly expressed in HepG2 cells compared with nonmalignant hepatocytes. Among these ucRNAs, the greatest change was noted for ultraconserved element 338 (uc.338), which was dramatically increased in human HCC compared with noncancerous adjacent tissues. Although uc.338 is partially located within the poly(rC) binding protein 2 (
PCBP2
) gene, the transcribed ncRNA encoding uc.338 is expressed independently of
PCBP2
and was cloned as a 590-bp RNA gene, termed TUC338. Functional gene annotation analysis indicated predominant effects on genes involved in cell growth. These effects were experimentally demonstrated in both human and murine cells. siRNA to TUC338 decreased both anchorage-dependent and anchorage-independent growth of HCC cells. These studies identify a critical role for TUC338 in regulation of transformed cell growth and of transcribed ultraconserved ncRNA as a unique class of genes involved in the pathobiology of HCC.
Pravastatin induces placental growth factor (PGF) and ameliorates preeclampsia in a mouse model
Authors: Kumasawa Keiichi , Ikawa Masahito , Kidoya Hiroyasu , Hasuwa Hidetoshi , Saito-Fujita Tomoko , Morioka Yuka , Takakura Nobuyuki , Kimura Tadashi , Okabe Masaru
Published: December 2010

Preeclampsia is a relatively common pregnancy-related disorder. Both maternal and fetal lives will be endangered if it proceeds unabated. Recently, the placenta-derived anti-angiogenic factors, such as soluble fms-like tyrosine kinase-1 (sFLT1) and soluble endoglin (sENG), have attracted attention in the progression of preeclampsia. Here, we established a unique experimental model to test the role of sFLT1 in preeclampsia using a lentiviral vector-mediated placenta-specific expression system. The model mice showed hypertension and proteinuria during pregnancy, and the symptoms regressed after parturition. Intrauterine growth restriction was also observed. We further showed that pravastatin induced the VEGF-like angiogenic factor placental growth factor (PGF) and ameliorated the symptoms. We conclude that our experimental preeclamptic murine model phenocopies the human case, and the model identifies low-dose statins and PGF as candidates for preeclampsia treatment.
Determination of second-order elliptic operators in two dimensions from partial Cauchy data
Authors: Imanuvilov Oleg Y. , Uhlmann Gunther , Yamamoto Masahiro
Published: December 2010

We consider the inverse boundary value problem in two dimensions of determining the coefficients of a general second-order elliptic operator from the Cauchy data measured on a nonempty arbitrary relatively open subset of the boundary. We give a complete characterization of the set of coefficients yielding the same partial Cauchy data. As a corollary we prove several uniqueness results in determining coefficients from partial Cauchy data for the isotropic conductivity equation, the Schrödinger equation, the convection–diffusion equation, the anisotropic conductivity equation modulo a group of diffeomorphisms that are the identity at the boundary, and the magnetic Schrödinger equations modulo gauge transformations. The key step is the construction of novel complex geometrical optics solutions using Carleman estimates.
Holin triggering in real time
Authors: White Rebecca , Chiba Shinobu , Pang Ting , Dewey Jill S. , Savva Christos G. , Holzenburg Andreas , Pogliano Kit , Young Ry
Published: December 2010

During λ infections, the holin S105 accumulates harmlessly in the membrane until, at an allele-specific time, suddenly triggering to form irregular holes of unprecedented size (>300 nm), releasing the endolysin from the cytoplasm, resulting in lysis within seconds. Here we used a functional S105–GFP chimera and real-time deconvolution fluorescence microscopy to show that the S105–GFP fusion accumulated in a uniformly distributed fashion, until suddenly, within 1 min, it formed aggregates, or rafts, at the time of lethal triggering. Moreover, the isogenic fusion to a nonlethal S105 mutant remained uniformly distributed, whereas a fusion to an early-lysing mutant showed early triggering and early raft formation. Protein accumulation rates of the WT, early, and nonlethal alleles were identical. Fluorescence recovery after photobleaching (FRAP) revealed that the nonlethal mutant and untriggered WT hybrids were highly mobile in the membrane, whereas the WT raft was essentially immobile. Finally, an antiholin allele,

S105
ΔTMD1

–
mcherryfp
, in the product of which the S105 sequence deleted for the first transmembrane domain was fused to mCherryFP. This hybrid retained full antiholin activity, in that it blocked lethal hole formation by the S105–GFP fusion, accumulated uniformly throughout the host membrane and prevented the S105–GFP protein from forming rafts. These findings suggest that phage lysis occurs when the holin reaches a critical concentration and nucleates to form rafts, analogous to the initiation of purple membrane formation after the induction of bacteriorhodopsin in halobacteria. This model for holin function may be relevant for processes in mammalian cells, including the release of nonenveloped viruses and apoptosis.
Cytoplasmic cAMP-sensing domain of hyperpolarization-activated cation (HCN) channels uses two structurally distinct mechanisms to regulate voltage gating
Authors: Wicks Nadine L. , Wong Tammy , Sun Jinyi , Madden Zarina , Young Edgar C.
Published: December 2010

Voltage gating of hyperpolarization-activated cation (HCN) channels is potentiated by direct binding of cAMP to a cytoplasmic cAMP-sensing domain (CSD). When unliganded, the CSD inhibits hyperpolarization-dependent opening of the HCN channel gate; cAMP binding relieves this autoinhibition so that opening becomes more favorable thermodynamically. This autoinhibition-relief mechanism is conserved with that of several other cyclic nucleotide receptors using the same ligand-binding fold. Besides its thermodynamic effect, cAMP also modulates the depolarization-dependent deactivation rate by kinetically trapping channels in an open state. Here we report studies of strong open-state trapping in an HCN channel showing that the well-established autoinhibition-relief model is insufficient. Whereas deletion of the CSD mimics the thermodynamic open-state stabilization usually associated with cAMP binding, CSD deletion removes rather than mimics the kinetic effect of strong open-state trapping. Substitution of different CSD sequences leads to variation of the degree of open-state trapping in the liganded channel but not in the unliganded channel. CSD-dependent open-state trapping is observed during a voltage-dependent deactivation pathway, specific to the secondary open state that is formed by mode shift after prolonged hyperpolarization activation. This hysteretic activation–deactivation cycle is preserved by CSD substitution, but the change in deactivation kinetics of the liganded channel resulting from CSD substitution is not correlated with the change in autoinhibition properties. Thus the liganded and the unliganded forms of the CSD respectively provide the structural determinants for open-state trapping and autoinhibition, such that two distinct mechanisms for cAMP regulation can operate in one receptor.
B cell homeostasis and plasma cell homing controlled by Krüppel-like factor 2
Authors: Winkelmann Rebecca , Sandrock Lena , Porstner Martina , Roth Edith , Mathews Martina , Hobeika Elias , Reth Michael , Kahn Mark L. , Schuh Wolfgang , Jäck Hans-Martin
Published: December 2010

Krüppel-like factor 2 (KLF2) controls T lymphocyte egress from lymphoid organs by regulating sphingosin-1 phosphate receptor 1 (S1Pr1). Here we show that this is not the case for B cells. Instead, KLF2 controls homeostasis of B cells in peripheral lymphatic organs and homing of plasma cells to the bone marrow, presumably by controlling the expression of β7-integrin. In mice with a B cell-specific deletion of KLF2, S1Pr1 expression on B cells was only slightly affected. Accordingly, all splenic B cell subsets including B1 cells were present, but their numbers were increased with a clear bias for marginal zone (MZ) B cells. In contrast, fewer peyers patches harboring fewer B cells were found, and fewer B1 cells in the peritoneal cavity as well as recirculating B cells in the bone marrow were detected. Upon thymus-dependent immunization, IgG titers were diminished, and antigen-specific plasma cells were absent in the bone marrow, although numbers of antigen-specific splenic plasmablasts were normal. KLF2 plays also a role in determining the identity of follicular B cells, as KLF2-deficient follicular B cells showed calcium responses similar to those of MZ B cells and failed to down-regulate MZ B cell signature genes, such as CD21 and CXCR7.