bluuebunny/crossref_metadata_2025 huggingface dataset:
Conformational dynamics of the inner pore helix of voltage-gated potassium channels
Authors: Choe Seungho , Grabe Michael
Published: June 2009

Voltage-gated potassium (Kv) channels control the electrical excitability of neurons and muscles. Despite this key role, how these channels open and close or gate is not fully understood. Gating is usually attributed to the bending and straightening of pore-lining helices at glycine and proline residues. In this work we focused on the role of proline in the Pro-Val-Pro (PVP) motif of the inner S6 helix in the Kv1.2 channel. We started by developing a simple hinged-rod model to fully explore the configurational space of bent helices and we related these configurations to the degree of pore opening. We then carried out fully atomistic simulations of the S6 helices and compared these simulations to the hinged-rod model. Both methods suggest that Kv1 channels are not tightly closed when the inner helices are straight, unlike what is seen in the non-PVP containing channels KcsA and KirBac. These results invite the possibility that the S6 helices may be kinked when Kv1 channels are closed. Our simulations indicate that the wild-type helix adopts multiple spatially distinct configurations, which is consistent with its role in adopting a closed state and an open state. The two most dominant configurational basins correspond to a 6 Å movement of the helix tail accompanied by the PVP region undergoing a local α-helix to 310-helix transition. We explored how single point mutations affect the propensity of the S6 helix to adopt particular configurations. Interestingly, mutating the first proline, P405 (P473 in Shaker), to alanine completely removed the bistable nature of the S6 helix possibly explaining why this mutation compromises the channel. Next, we considered four other mutations in the area known to affect channel gating and we saw similarly dramatic changes to the helix’s dynamics and range of motion. Our results suggest a possible mechanism of helix pore closure and they suggest differences in the closed state of glycine-only channels, like KcsA, and PVP containing channels.
Magnetic response of core-shell cobalt ferrite nanoparticles at low temperature
Authors: Maaz K. , Usman M. , Karim S. , Mumtaz A. , Hasanain S. K. , Bertino M. F.
Published: June 2009

Cobalt ferrite nanoparticles (size: 26±4nm) have been synthesized by coprecipitation route. The coercivity of nanoparticles follows a simple model of thermal activation of particle moments over the anisotropy barrier in the temperature range of 30–300K in accordance with Kneller’s law; however, at low temperatures (<30K), the coercivity shows some deviation from this law. The saturation magnetization follows the modified Bloch’s law in the temperature range of 10–300K. Exchange bias (Hex) studies of the samples show that Hex increases with decreasing temperature of the sample. A strong increase in the Hex values is found below 30K for the low applied field (±20kOe), while a smaller increase is found for the high applied field (±90kOe). The slow increase in the exchange bias at high applied field has been attributed to the high field effects on the surface (shell) spins. These shell spins align along the field direction that weakens the core-shell interface interactions leading to the reduction in the exchange bias at lower temperatures.
An understanding and implications of the coverage of surface free sites in heterogeneous catalysis
Authors: Wang Haifeng , Guo Yanglong , Lu Guanzhong , Hu P.
Published: June 2009

The crucial roles of the coverage of surface free sites in determining catalytic activity trend are quantitatively addressed with the help of density functional theory and microkinetics. First, by analyzing activity trends of NO oxidation catalyzed by Ru, Rh, Pd, Os, Ir, and Pt surfaces with full kinetic considerations, we identify that the activity trend is in general determined by the competition between the reaction barrier and the coverage of surface free sites. Second, since the dissociation of many important molecules, such as the dissociation of N2, O2, and CO, follows the same Brønsted-Evans-Polanyi relationship, the coverage of surface free sites is usually a decisive term that affects the overall activity. Third, an equation is derived for the coverage of surface free sites and it is found that the coverage of surface free sites contains not only all the key thermodynamic parameters but also all the kinetic properties in the catalytic system.
Decay kinetics of luminescence and electron emission from MgO crystal powders in ac plasma display panels
Authors: Okada Takeru , Naoi Taro , Yoshioka Toshihiro
Published: June 2009

Decay kinetics of luminescence at 5.2 eV and those of sustained electron emission from MgO crystal powders were investigated in order to understand the mechanism of discharge delay in ac plasma display panels and sustained electron emission from insulator. The decay of UV-luminescence was nonexponential and the decay was enhanced by increasing the temperature after showing negligible temperature dependence at low temperature. Existence of carrier traps was indicated by thermoluminescence measurements. As a possible mechanism, luminescence from a donor-acceptor pair in combination with thermal activation from carrier traps was introduced. The electron emission properties were evaluated by the measurement of statistical discharge delay time in ac plasma display panels as an indicator. By coating MgO crystal powders on the MgO protective film, the intensity of electron emission increased and its time and temperature dependence was reduced. A comparison under the same excitation revealed that the decay of UV-luminescence was steeper than that of electron emission. To explain the experimental data, we proposed the involvement of direct electron emission from electron traps synchronized with measuring voltages in addition to luminescence-associated electron emission.
Assessing thermodynamic-dynamic relationships for waterlike liquids
Authors: Johnson Margaret E. , Head-Gordon Teresa
Published: June 2009

Here we investigate a family of isotropic waterlike glass-forming liquids, in which each thermodynamic state point corresponds to a different potential energy surface which is prescribed to reproduce the gOO(r;T,ρ) of the reference TIP4P-Ew water model potential. Although each isotropic potential is simulated separately, together the family of isotropic potentials displays anomalous dynamics with density and fragile diffusivity with temperature. By removing a common energy landscape, and therefore expected thermodynamic trends with temperature within a single potential, we can more rigorously evaluate whether various entropic measures used in popular phenomenological thermodynamic theories can quantitatively predict the diffusivity or viscosity. We find that the Adam–Gibbs relation between diffusion (or viscosity) and the temperature scaled configurational entropy, Sc, is a poor predictor of fragility trends and density anomalies when necessary anharmonic corrections are added. By contrast the Dzugutov scaling relationship that uses the pair correlation approximation to Sexcess∼S2 provides excellent agreement for diffusion anomalies and for fragile dynamics for weakly supercooled states for the family of isotropic potentials, within a single isotropic potential, and for the TIP4P-Ew model, but deviates strongly in all three cases at more deeply supercooled temperatures. By studying the microscopic dynamics at these low temperatures, we find an increased heterogeneity in the mobility of particle populations reflected in a highly non-Gaussian distribution of particle displacements, even at very long time scales. We conclude that after the onset of dynamical heterogeneity, new consideration of higher structural correlations and/or more complex connectivity paths between basins through barriers appear to be critical for the formulation of a predictive theory for dynamics.
Tunable light trapping for solar cells using localized surface plasmons
Authors: Beck F. J. , Polman A. , Catchpole K. R.
Published: June 2009

Effective light management is imperative in maintaining high efficiencies as photovoltaic devices become thinner. We demonstrate a simple and effective method of enhancing light trapping in solar cells with thin absorber layers by tuning localized surface plasmons in arrays of Ag nanoparticles. By redshifting the surface plasmon resonances by up to 200 nm, through the modification of the local dielectric environment of the particles, we can increase the optical absorption in an underlying Si wafer fivefold at a wavelength of 1100 nm and enhance the external quantum efficiency of thin Si solar cells by a factor of 2.3 at this wavelength where transmission losses are prevalent. Additionally, by locating the nanoparticles on the rear of the solar cells, we can avoid absorption losses below the resonance wavelength due to interference effects, while still allowing long wavelength light to be coupled into the cell. Results from numerical simulations support the experimental findings and show that the fraction of light backscattered into the cell by nanoparticles located on the rear is comparable to the forward scattering effects of particles on the front. Using nanoparticle self-assembly methods and dielectrics commonly used in photovoltaic fabrication this technology is relevant for application to large-scale photovoltaic devices.
Tip geometry effects in scanning capacitance microscopy on GaAs Schottky and metal-oxide-semiconductor-type junctions
Authors: Eckhardt C. , Brezna W. , Bethge O. , Bertagnolli E. , Smoliner J.
Published: June 2009

In this work, the influence of the tip geometry in scanning capacitance microscopy is investigated experimentally and theoretically on metal-oxide-semiconductor- (MOS) and Schottky-type junctions on gallium-arsenide (GaAs). Using a two-dimensional model we find that on Schottky-type junctions the electric field around the tip is screened by the surface states and that the essential parameters entering the capacitance versus voltage C(V) characteristics are the doping level and the contact area only. In contrast to that, the electric field from the tip penetrates into the semiconductor on a MOS-type junction, and the tip geometry effects are much larger. C(V) spectra are fitted to the experimental data and allowed a quantitative determination of doping levels, oxide thickness, and contact area without further calibration measurements.
Wall boundary model for primitive chain network simulations
Authors: Okuda Satoru , Inoue Yasuhiro , Masubuchi Yuichi , Uneyama Takasi , Hojo Masaki
Published: June 2009

In condensed polymeric liquids confined in slit channels, the movement of chains is constrained by two factors: entanglement among the chains and the excluded volume between the chains and the wall. In this study, we propose a wall boundary (WB) model for the primitive chain network (PCN) model, which describes the dynamics of polymer chains in bulk based on coarse graining upon the characteristic molecular weight of the entanglement. The proposed WB model is based on the assumptions that (i) polymers are not stuck but simply reflected randomly by the wall, and (ii) subchains below the entanglement length scale behave like those in bulk even near the wall. Using the WB model, we simulate the dynamics of entangled polymer chains confined in slit channels. The results show that as the slit narrows, the chains are compressed in the direction normal to the wall, while they are expanded in the parallel direction. In addition, the relaxation time of the end-to-end vector increases, and the diffusivity of the center of mass decreases. The compression in the normal direction is a natural effect of confinement, while the expansion is introduced by a hooking process near the wall. The trends revealed that the relaxation time and diffusivity depend on the increase in friction due to an increased number of entanglements near the wall, which is also associated with the hooking process in the PCN model. These results are expected within the assumptions of the PCN model. Thus, the proposed WB model can successfully reproduce the effects of wall confinement on chains.
Imaging by silicon on insulator waveguides
Authors: Song Q. , Qian F. , Tien E. K. , Tomov I. , Meyer J. , Sang X. Z. , Boyraz O.
Published: June 2009

We present multiphoton imaging based on semiconductor planar waveguide technology which can be used as a transmitter and receiver simultaneously. In particular, silicon on insulator waveguides with p-i-n diode structures are used to demonstrate <5 μm resolution three-photon imaging of Er3+:Y2O3 microparticles by using 1550 nm excitation. Additional theoretical study has been performed to demonstrate the proposed scheme for three-dimensional tomography of micron-sized objects, which could be realized by using multiple transmitter-detector pairs.
Hybrid particle-field molecular dynamics simulations for dense polymer systems
Authors: Milano Giuseppe , Kawakatsu Toshihiro
Published: June 2009

We propose a theoretical scheme for a hybrid simulation technique where self-consistent field theory and molecular dynamics simulation are combined (MD-SCF). We describe the detail of the main implementation issues on the evaluation of a smooth three-dimensional spatial density distribution and its special gradient based on the positions of particles. The treatments of our multiscale model system on an atomic scale or on a specific coarse-grained scale are carefully discussed. We perform a series of test simulations on this hybrid model system and compare the structural correlations on the atomic scale with those of classical MD simulations. The results are very encouraging and open a way to an efficient strategy that possess the main advantages common to the SCF and the atomistic approaches, while avoiding the disadvantages of each of the treatments.
Acoustic collimating beams by negative refraction in two-dimensional phononic crystal
Authors: He Zhaojian , Heng Yaofu , Peng Shasha , Ding Yiqun , Ke Manzhu , Liu Zhengyou
Published: June 2009

We report the realization of acoustic collimating beams by a two-dimensional phononic crystal, which has a negative effective refractive index of small magnitude. The radiation far field of a point source through the phononic crystal with a divergence angle of about 5° is obtained. The measured intensity field distribution in experiment further confirms this collimating property.
The covariant and on-shell statistics in κ-deformed space-time
Authors: Miao Rong-Xin
Published: June 2009

It has been a long-standing issue to construct the statistics of identical particles in κ-deformed space-time. In this letter, we investigate different ideas on this problem. Following the ideas of Young and Zegers, we obtain the covariant and on shell kappa two-particle state in 1+1 D in a simpler way. Finally, a procedure to get such state in higher dimension is proposed.
Cancellation of environmental effects in resonant mass sensors based on resonance mode and effective mass
Authors: Naeli Kianoush , Brand Oliver
Published: June 2009

A novel technique is developed to cancel the effect of environmental parameters, e.g., temperature and humidity, in resonant mass sensing. Utilizing a single resonator, the environmental cancellation is achieved by monitoring a pair of resonant overtones and the effective sensed mass in those overtones. As an eminent advantage, especially compared to dual-mode temperature compensation techniques, the presented technique eliminates any need for previously measured look-up tables or fitting the measurement data. We show that a resonant cantilever beam is an appropriate platform for applying this technique, and derive an analytical expression to relate the actual and effective sensed masses on a cantilever beam. Thereby, it is shown that in applying the presented technique successfully, the effective sensed masses must not be the same in the investigated pair of resonance overtones. To prove the feasibility of the proposed technique, flexural resonance frequencies of a silicon cantilever are measured before and after loading with a strip of photoresist. Applying the presented technique shows significant reductions in influence of environmental parameters, with the temperature and humidity coefficients of frequency being improved from −19.5 to 0.2 ppm °C−1 and from 0.7 to −0.03 ppm %RH−1, respectively.
Characterization of diamond ultraviolet detectors fabricated with high-quality single-crystalline chemical vapor deposition films
Authors: Iwakaji Y. , Kanasugi M. , Maida O. , Ito T.
Published: June 2009

We have fabricated high-performance ultraviolet (UV) detectors with high-quality undoped and B-doped homoepitaxial diamond layers which were sequentially grown on a high-pressure/high-temperature-synthesized (HPHT) type-Ib (100) substrate by means of a high-power microwave-plasma chemical vapor deposition method. The detector performance measured had large quantum efficiencies due to an effective built-in current amplification function, fast temporal responses, and high UV/visible sensing ratios although the HPHT substrate used had considerable amounts of various defects inducing visible light absorptions and slow detector responses. The usefulness of the bilayer detector structure employed is discussed.
Control of phase transition in quasi-one-dimensional atomic wires by electron doping
Authors: Shim Hyungjoon , Yu Sang-Yong , Lee Woosang , Koo Ja-Yong , Lee Geunseop
Published: June 2009

We report on the controlled change in the phase transition in In atomic chains on a Si(111) surface by introducing Na as impurity atoms. The Na-induced changes in the transition temperature (Tc) from a metallic room-temperature 4×1 structure into an insulating low-temperature 8×2 structure were determined by using low-energy electron diffraction. The Tc decreased almost linearly when the amount of deposited Na atoms was increased. The decrease in Tc with the increase in the amount of adsorbed Na atoms is suggested to be due to the doping of electrons from adsorbate to the substrate.
Electronic structure, linear, and nonlinear optical responses in magnetoelectric multiferroic material BiFeO3
Authors: Ju Sheng , Cai Tian-Yi , Guo Guang-Yu
Published: June 2009

BiFeO 3 has attracted great interest for its multiferroic property. The spontaneous electric polarization, multiferroism, and static magnetoelectric coupling have been widely studied both experimentally and theoretically. Here, in this paper, we report on the effects of magnetic ordering, spin fluctuation, and external magnetic field on the linear dielectric function and second-harmonic generation (SHG) in multiferroic BiFeO3. First, our generalized gradient approximation plus Hubbard U calculations reproduce very well experimental data of linear dielectric function. In the mean time, it is revealed that SHG susceptibilities differ dramatically between antiferromagnetic configuration and ferromagnetic one, which is due to the enhanced contrast in the double-photon resonance absorption. Further Monte Carlo simulation of the coupling between electric order and spin-pair correlation function is presented for the spin fluctuation dependence of SHG. The significant nonlinear optical magnetoelectric effect around the Néel temperature provides novel route to enhancing magnetoelectric coupling in multiferroic materials.
Combined density functional theory and Landauer approach for hole transfer in DNA along classical molecular dynamics trajectories
Authors: Woiczikowski P. Benjamin , Kubař Tomáš , Gutiérrez Rafael , Caetano Rodrigo A. , Cuniberti Gianaurelio , Elstner Marcus
Published: June 2009

We investigate in detail the charge transport characteristics of DNA wires with various sequences and lengths in the presence of solvent. Our approach combines large-scale quantum/classical molecular dynamics (MD) simulations with transport calculations based on Landauer theory. The quantum mechanical transmission function of the wire is calculated along MD trajectories and thus encodes the influence of dynamical disorder arising from the environment (water, backbone, counterions) and from the internal base dynamics. We show that the correlated fluctuations of the base pair dynamics are crucial in determining the transport properties of the wire and that the effect of fluctuations can be quite different for sequences with low and high static disorders (differences in base ionization potentials). As a result, in structures with high static disorder as is the case of the studied Dickerson dodecamer, the weight of high-transmissive structures increases due to dynamical fluctuations and so does the calculated average transmission. Our analysis further supports the basic intuition of charge-transfer active conformations as proposed by Barton et al. [J. Am. Chem. Soc. 126, 11471 (2004)]. However, not DNA conformations with good stacking contacts leading to large interbase hopping values are necessarily the most important, but rather those where the average fluctuation of ionization potentials along the base stack is small. The reason behind this is that the ensemble of conformations leads to average electronic couplings, which are large enough for sufficient transmission. On the other hand, the alignment of onsite energies is the critical parameter which gates the charge transport.
High power efficiency in Si-nc/SiO2 multilayer light emitting devices by bipolar direct tunneling
Authors: Marconi A. , Anopchenko A. , Wang M. , Pucker G. , Bellutti P. , Pavesi L.
Published: June 2009

We demonstrate experimentally bipolar (electrons and holes) current injection into silicon nanocrystals in thin nanocrystalline-Si/SiO2 multilayers. These light emitting devices have power efficiency of 0.17% and turn-on voltage of 1.7 V. The high electroluminescence efficiency and low onset voltages are attributed to the radiative recombination of excitons formed by both electron and hole injection into silicon nanocrystals via the direct tunneling mechanism. To confirm the bipolar character, different devices were grown, with and without a thick silicon oxide barrier at the multilayer contact electrodes. A transition from bipolar tunneling to unipolar Fowler–Nordheim tunneling is thus observed.
A
site-controlled quantum dot system offering both high uniformity and spectral purity
Authors: Mereni L. O. , Dimastrodonato V. , Young R. J. , Pelucchi E.
Published: June 2009

In this letter we report on the optical properties of site-controlled InGaAs quantum dots with GaAs barriers grown in pyramidal recesses by metalorganic vapor phase epitaxy. The inhomogeneous broadening of excitonic emission from an ensemble of quantum dots is found to be unusually narrow, with a standard deviation of 1.19 meV and the spectral purity of emission lines from individual dots is found to be very high (18–30 μeV), in contrast with other site-controlled dot systems.
Drag coefficient of the weakly ionized plasma in the high Knudsen number regime
Authors: Chu Hong-Yu , Si Man-Chon , Lin Shang-Bin
Published: June 2009

The drag force acting on a micron-sized polystyrene particle in the high Knudsen number regime is investigated. Analysis of the particle trajectories in stationary neutral argon gas environment suggests the damping time constant τ∝p−1.20±0.04 and Epstein drag force coefficient δ=1.40. The neutral drag coefficient is compared with the drag coefficient measurement in dust-free plasma. The phenomena of the reduced drag in weakly viscous and weakly ionized rf plasma are also observed in this report. It is shown that the slight changes in rf power and pressure would enhance the reduced drag effect, which suggests that there is an additional electrostatic force acting along the particle motion in the plasma.
Phenomena associated with complex (dusty) plasmas in the ionosphere during high-speed meteor showers
Authors: Kopnin S. I. , Popel S. I. , Yu M. Y.
Published: June 2009

Formation of dusty plasmas in the Earth’s ionosphere at 80–120 km altitudes during high-speed meteor showers and its detectable manifestations are discussed. Emphasis is given to ground-based observations such as detection of low-frequency (<50 Hz) ionospheric radio noise, ground-based observations of infrasonic waves, and amplification of the intensity of green radiation at 557.7 nm from a layer at the 110–120 km altitude in the lower ionosphere. The physical processes responsible for these manifestations are considered.
Coarse-grained molecular dynamics of ligands binding into protein: The case of HIV-1 protease inhibitors
Authors: Li Dechang , Liu Ming S. , Ji Baohua , Hwang Kehchih , Huang Yonggang
Published: June 2009

Binding dynamics and pathways of ligands or inhibitors to target proteins are challenging both experimental and theoretical biologists. A dynamics understanding of inhibitors interacting with protein is essential for the design of novel potent drugs. In this work we applied a coarse-grained molecular dynamics method for simulating inhibitors entering the binding cavity of human immunodeficiency virus type 1 protease (PR). It shows that the coarse-grained dynamics, consistent with the experimental results, can capture the essential molecular dynamics of various inhibitors binding into PR. The primary driving force for the binding processes is the nonbond interaction between inhibitors and PR. The size and topology of inhibitors and the interacting strength between inhibitors and PR have great influence on the binding mode and processes. The interaction strength between the PR and various inhibitors is also analyzed by atomistic molecular mechanics and Poisson–Boltzmann solvation area method.
Application of the Wang–Landau algorithm to the dimerization of glycophorin A
Authors: Gervais Claire , Wüst Thomas , Landau D. P. , Xu Ying
Published: June 2009

A two-step Monte Carlo procedure is developed to investigate the dimerization process of the homodimer glycophorin A. In the first step, the energy density of states of the system is estimated by the Wang–Landau algorithm. In the second step, a production run is performed during which various energetical and structural observables are sampled to provide insight into the thermodynamics of the system. All seven residues LIxxGVxxGVxxT constituting the contact interface play a dominating role in the dimerization, however at different stages of the process. The leucine motif and to some extent the GxxxG motif are involved at the very beginning of the dimerization when the two helices come into contact, ensuring an interface already similar to the native one. At a lower temperature, the threonine motif stabilizes by hydrogen bonding the dimer, which finally converges toward its native state at around 300 K. The power and flexibility of the procedure employed here makes it an interesting alternative to other Monte Carlo methods for the study of similar protein systems.
The inertial lift on a spherical particle settling in a horizontal viscous flow through a vertical slot
Authors: Asmolov Evgeny S. , Osiptsov Andrei A.
Published: June 2009

The inertial lift force exerted on a small rigid sphere settling due to gravity in a horizontal channel flow between vertical walls is investigated. The method of matched asymptotic expansions is used to obtain solutions for the disturbance flow on the length scales of the particle radius and the channel width (inner and outer regions, respectively). The channel Reynolds number is finite, while the particle Reynolds numbers that are based on the slip velocity and the mean shear rate are small. The inner flow is described by the linear Stokes equations. The outer problem is governed by the linear Oseen-like equations with the particle effect approximated by a point force. The outer equations are solved numerically using the two-dimensional Fourier transform of the disturbance velocity field. The lift coefficient is evaluated as a function of governing dimensionless parameters: the particle coordinate across the channel, the channel Reynolds number, and the slip parameter. The particle always migrates away from the walls, with an equilibrium position being on the channel centerline. Close to the walls, the lift coefficient is the same regardless of the slip velocity and the channel Reynolds number. At large channel Reynolds numbers, a local maximum of the migration velocity forms near the channel centerline due to a combined effect of the slip, the linear shear, and the curvature of the undisturbed velocity profile. The results obtained are extended to the case when the drag on a particle has components both parallel and perpendicular to the undisturbed flow. One of primary applications of the results is modeling of the cross-flow migration of settling particles during particle transport in a hydraulic fracture.
Experimental and theoretical studies of isolated neutral and ionic 2-propanol and their clusters
Authors: Shin Joong-Won , Bernstein Elliot R.
Published: June 2009

Infrared plus vacuum ultraviolet (IR/VUV) nonresonant photoionization spectroscopy and VUV/IR photodissociation spectroscopy are employed to study fragmentation pathways and structures of neutral and ionic 2-propanol ((CH3)2CHOH) (IPA) and their relevant clusters of size up to the pentamer. Only the gauche monomer is generated in the supersonic expansion; its VUV induced fragmentation pathways involve Cα–Cβ bond dissociation. The clusters consist of both gauche and trans conformers and their VUV induced fragmentation pathways are size dependent. The IR spectra of neutral clusters (IPA)n suggest that the dimer has a chainlike structure, whereas larger clusters have cyclic structures. VUV ionization of the neutral gauche 2-propanol generates two parent cation isomers whose Cα–Cβ bond dissociations are facilitated by excitation of the OH vibrations. The IR spectra of ionic molecular complex clusters (IPA)n−1⋅CH3CHOH+ and protonated clusters (IPA)n−1⋅H+, generated by VUV ionization of neutral clusters, show that both cluster types adopt open structures with at least one free OH group. Qualitative structural assignments are generated for the neutral species based on MP2/aug-cc-pVDZ, MP2/6-31G, and B3LYP/6-31+G(d) calculations.
Three-dimensional spatial resolution of the nonlinear photoemission from biofunctionalized porous silicon microcavity
Authors: Martin M. , Palestino G. , Cloitre T. , Agarwal V. , Zimányi L. , Gergely C.
Published: June 2009

Infiltration of biomacromolecules into porous silicon photonic architectures results in biofunctionalized structures with unique properties. Characterization of their optical response and performance optimization in biomacromolecular detection and biophotonic application require a combination of optical and structural studies. Nonlinear optical microscopy is applied to study porous silicon microcavities with and without infiltrated glucose oxidase. The infiltrated protein acts as an internal two-photon-excited fluorescence emitter and second harmonic generator, enabling the in-depth visualization of the porous structure. Enhanced second harmonic generation and fluorescence emission by the porous silicon structure is experimentally associated with the defect layer.
Characterization of AlGaN/GaN metal-oxide-semiconductor field-effect transistors by frequency dependent conductance analysis
Authors: Kordoš P. , Stoklas R. , Gregušová D. , Novák J.
Published: June 2009

We report on the frequency dependent conductance measurements of AlGaN/GaN metal-oxide-semiconductor heterostructure field-effect transistors (MOSHFETs). The properties of the devices with as-deposited and annealed 9-nm-thick Al2O3 gate oxide were investigated. The trap density in the range of 1011 cm−2 eV−1 was evaluated for the nonannealed devices. However, the conductance versus frequency peaks were significantly broader than those expected from theory, which indicates a surface potential fluctuation due to nonuniformities in the oxide charge and interface traps. Additionally, the dependence of the trap state time constant on gate voltage showed a deviation from the expected exponential function. However, the annealed devices (680 °C, 5 min) yielded a slightly lower (∼75%) trap density. Moreover, the conductance versus frequency data and the time constant versus gate voltage dependence of the annealed devices were in full agreement with the theoretical ones. The results show that the frequency dependent conductance analysis can be a useful tool for the characterization of AlGaN/GaN MOSHFETs.
Assembly and magnetic properties of nickel nanoparticles on silicon nanowires
Authors: Ingole S. , Manandhar P. , Wright J. A. , Nazaretski E. , Thompson J. D. , Picraux S. T.
Published: June 2009

The directed assembly of magnetic Ni nanoparticles at the tips of silicon nanowires is reported. Using electrodeposition Ni shells of thickness from 10 to 200 nm were selectively deposited on Au catalytic seeds at the ends of nanowires. Magnetic characterization confirms a low coercivity (≈115 Oe) ferromagnetic behavior at 300 K. This approach to multifunctional magnetic-semiconducting nanostructure assembly could be extended to electrodeposition of other materials on the nanowire ends, opening up additional approaches to device integration. Such magnetically functionalized nanowires offer an approach to developing highly localized magnetic probes for high resolution magnetic resonance force microscopy.
Thickness dependence of the mobility at the LaAlO3/SrTiO3 interface
Authors: Bell C. , Harashima S. , Hikita Y. , Hwang H. Y.
Published: June 2009

The electronic transport properties of a series of LaAlO3/SrTiO3 interfaces were investigated, and a systematic thickness dependence of the sheet resistance and magnetoresistance was found for constant growth conditions. This trend occurs above the critical thickness of four unit cells, below which the LaAlO3/SrTiO3 interface is not conducting. A dramatic decrease in mobility of the electron gas of nearly two orders of magnitude was observed with increasing LaAlO3 thickness from 5 to 25 unit cells.
Aluminum/polyaniline/GaAs metal-insulator-semiconductor solar cell: Effect of tunneling on device performance
Authors: Mangal Sutanu , Adhikari Sarbani , Banerji P.
Published: June 2009

We report fabrication of GaAs based metal-insulator-semiconductor solar cell with polyaniline, a polymeric material, as an insulator. The photovoltaic response of Aluminum/Polyaniline/GaAs metal-insulator-semiconductor diode was measured in the air mass (AM) 1.0 and 1.5. The values of the open circuit voltage, short circuit current and the series resistance at AM 1.0 are measured to be 0.45 mA, 1.07 V and 26 Ω, respectively. It is found that the thickness of the polyaniline layer plays a crucial role in determining various properties of the device. The findings are explained on the basis of the tunneling probability.
Twin formation during the growth of InP on SrTiO3
Authors: Cheng J. , Largeau L. , Patriarche G. , Regreny P. , Hollinger G. , Saint-Girons G.
Published: June 2009

The epitaxial growth of InP on (001)-oriented SrTiO3 (STO) is analyzed, and evidence is shown of the formation of twins during the early stages of the growth. A detailed crystallographic description of these twins is presented, and the origin of their formation is discussed. The elevated interface energy characteristic of the InP/STO system, combined with the initial three-dimensional growth of the semiconductor and with the existence of a commensurate heterointerface between STO and the twinned InP variant are identified as the main causes of twin formation during the growth of this highly heterogeneous epitaxial system.
Low-lying lattice modes of highly uniform pentacene monolayers
Authors: He Rui , Tassi Nancy G. , Blanchet Graciela B. , Pinczuk Aron
Published: June 2009

The authors report that monolayers of pentacene grown on a functionalized polymeric substrate display high uniformity that enable observations of Raman spectra of low-lying optical vibrations. The evolution of the frequencies and widths of the modes has been studied in films reaching the single monolayer level. Raman spectra of low-lying lattice modes display major changes when the film thickness changes from 1 to 2 monolayers, revealing that a phase akin to a thin film phase of pentacene already emerges in films of only 2 monolayers.
Effect of spin frustration and spin-orbit coupling on the ferroelectric polarization in multiferroic YMnO3
Authors: Zhong Chonggui , Jiang Qing , Zhang Hua , Jiang Xuefan
Published: June 2009

Based on density functional theory, we investigate the mechanism of ferroelectric polarization of hexagonal YMnO3 with noncollinear magnetic structure calculations. By comparing the electronic structure of different magnetic ordering, we are surprised that, due to triangular spin frustration and spin-orbit (SO) coupling, the Y 4d states are strongly hybridized with O(3,4) 2p ones, while the hybridizations of Mn 3d with O(1,2) 2p states are reduced correspondingly. The large anomalies in Born effective charges on off-centering Y and O ions manifest that the Y d0-ness with rehybridization is the driving force for the ferroelectricity, which provides a first-principle understanding of multiferroicity in YMnO3.
Characterization of near-infrared n-type β-FeSi2/p-type Si heterojunction photodiodes at room temperature
Authors: Shaban Mahmoud , Nomoto Keita , Izumi Shota , Yoshitake Tsuyoshi
Published: June 2009

n -type β-FeSi2/p-type Si heterojunctions were fabricated from β-FeSi2 films epitaxially grown on Si(111) by facing-target direct-current sputtering. Sharp film-substrate interfaces were confirmed by scanning electron microscopy. The current-voltage and photoresponse characteristics were measured at room temperature. They exhibited good rectifying properties and a change of approximately one order of magnitude in the current at a bias voltage of −1 V under illumination by a 6 mW, 1.31 μm laser. The estimated detectivity was 1.5×109 cm √Hz W at 1.31 μm. The results suggest that the β-FeSi2/Si heterojunctions can be used as near-infrared photodetectors that are compatible with silicon integrated circuits.
Two-wave structure of liquid film and wave interrelation in annular gas-liquid flow with and without entrainment
Authors: Alekseenko Sergey , Antipin Vladimir , Cherdantsev Andrey , Kharlamov Sergey , Markovich Dmitry
Published: June 2009

The wavy structure of liquid film in downward annular gas-liquid flow with and without liquid entrainment is examined for a wide range of gas velocities using high-speed laser-induced fluorescence technique. It is shown that the wavy structure is always represented by two types of waves, long-lived and short-lived waves with the latter always generated at the back slopes of the long-lived waves. Main regularities of short-lived wave generation and evolution are also described.
Very simple metallic subwavelength cell for constructing left-handed metamaterial
Authors: Wang Zhiyu , Wang Dongxing , Jiang Tao , Peng Liang , Huangfu Jiangtao , Ran Lixin
Published: June 2009

In this letter, a very simple metallic subwavelength cell is designed for constructing left-handed metamaterial. The conductive current mode inside the metallic resonator of this cell imitates one reported displacement current mode inside a dielectric subwavelength resonator. We show by simulation and experiments that an artificial metamaterial composed of cells with such kind of current mode can behave simultaneously negative permittivity and permeability. The metallic cell with double negative property obtained in this letter is suitable for the applications in the high frequency band, such as in millimeter or even terahertz bands.
Impact of disorder on surface plasmons in two-dimensional arrays of metal nanoparticles
Authors: Khurgin J. B. , Sun G.
Published: June 2009

We study the impact of disorder on the properties of surface plasmons (SP) in metal nanoparticle arrays and develop analytical expressions enabling us to ascertain the degree of localization and mixing between the SP states. We show that it might be advantageous to intentionally introduce a certain degree of disorder in order to engineer the improved sensors and detectors.
L
1
CoPt–Ta2O5 exchange coupled multilayer media for magnetic recording
Authors: Pandey K. K. M. , Chen J. S. , Chow G. M. , Hu J. F.
Published: June 2009

Exchange coupled L10 CoPt–Ta2O5 multilayer media of gradually reducing coercivity from bottom to top layer were demonstrated to reduce the coercivity of hardest layer. The coercivity of different layers was tuned by adjusting the Ta2O5 content. The coercivity of 12 nm hardest layer was reduced by factor of three using multilayer media of total thickness 20 nm. The exchange coupled media comprising 12 nm hardest layer and 8 nm softest layer was able to reduce the coercivity only by factor of two. This indicates that multilayer media is more effective to reduce the switching field than the exchange coupled media.
Moderately anisotropic field-effect mobility in dinaphtho[2,3-b:2′,3′-f]thiopheno[3,2-b]thiophenes single-crystal transistors
Authors: Uno Mayumi , Tominari Y. , Yamagishi M. , Doi I. , Miyazaki E. , Takimiya K. , Takeya J.
Published: June 2009

Anisotropy of carrier mobility is measured for dinaphtho[2,3-b:2′,3′-f]thiopheno[3,2-b]thiophenes single-crystal transistors. We have developed a method of “local gating” to restrict carrier-accumulated channels elongated radially within the herringbone planes of submillimeter crystals so that mixture of conductivity off the intended directions is minimized in the measurement. The highest mobility 4 cm2/V s is achieved for the a-axis direction due to the highest orbital overlaps, while the lowest mobility measured in the perpendicular direction is still as high as 2.5 cm2/V s. The moderate anisotropy favors high performance in polycrystalline thin-film transistors of the compound, where charge transport is inevitably mixed for all directions.
Temperature stability of ([Na0.5K0.5NbO3]0.93–[LiTaO3]0.07) lead-free piezoelectric ceramics
Authors: Skidmore Thomas A. , Comyn Tim P. , Milne Steven J.
Published: June 2009

A polymorphic phase transition (PPT) is often engineered into lead-free materials to generate high piezoelectric activity at room temperature, limiting their temperature stability. We report [Na0.5K0.5NbO3]0.93–[LiTaO3]0.07 tetragonal ceramics with favorable properties over a broad temperature range due to a high Curie temperature at 447 °C and PPT at −15 °C involving a transition to a monoclinic rather than low temperature orthorhombic phase. Piezoelectric k31 and d31 coefficients varied from 0.19 to 0.14 and −53 to −33 pC/N, respectively, over the range of −15 to 300 °C. Strain-electric field loops provided strains of ∼0.2% and a high-field d33 of 205 pm/V.
Spatial Effects on Temporal Categorisation
Authors: Roussel Marie-Ève , Grondin Simon , Killeen Peter
Published: June 2009

We examined the influence of spatial factors in temporal processing. Participants categorised as short or long empty intervals marked by two brief flashes delivered from locations differing in height and depth (experiment 1), or from two of three locations on a vertical plane (experiment 2). The perceived duration of intervals, as determined by the point of subjective equality, was affected by the height and depth of the signals (experiment 1). Experiment 2 showed that the point of fixation plays a critical role in perceived duration. The duration of an interval located in the upper visual field is perceived as longer when participants fixate the higher visual source and shorter when the fixation point is set in the middle; this latter result also generally applies when the fixation point is in the lower source. Finally, for the sensitivity level, there was a significant segment (upper versus lower) × direction (descending versus ascending) interaction in experiment 1; a similar interaction effect varied according to the fixation point in experiment 2. In experiment 2, the Weber fractions were around 0.22. Most results can be explained in terms of the need to shift attention from one visual source—for marking time intervals—to another.
Apparent Visual Motion of the Observer's Own Limbs
Authors: Ekroll Vebjørn , Scherzer Tom R
Published: June 2009

We describe how illusory apparent motion of one's own fingers and other body parts can easily be experienced in spite of grossly conflicting proprioceptive signals. This simple illusion may be used to shed light on the crossmodal integration of visual and proprioceptive signals. Our preliminary observations suggest that the visual and proprioceptive signals do not merge into a common crossmodal percept. Instead, mutually inconsistent visual and bodily sensations are experienced simultaneously.
Widespread reorganization of metabolic enzymes into reversible assemblies upon nutrient starvation
Authors: Narayanaswamy Rammohan , Levy Matthew , Tsechansky Mark , Stovall Gwendolyn M. , O'Connell Jeremy D. , Mirrielees Jennifer , Ellington Andrew D. , Marcotte Edward M.
Published: June 2009

Proteins are likely to organize into complexes that assemble and disassemble depending on cellular needs. When ≈800 yeast strains expressing GFP-tagged proteins were grown to stationary phase, a surprising number of proteins involved in intermediary metabolism and stress response were observed to form punctate cytoplasmic foci. The formation of these discrete physical structures was confirmed by immunofluorescence and mass spectrometry of untagged proteins. The purine biosynthetic enzyme Ade4-GFP formed foci in the absence of adenine, and cycling between punctate and diffuse phenotypes could be controlled by adenine subtraction and addition. Similarly, glutamine synthetase (Gln1-GFP) foci cycled reversibly in the absence and presence of glucose. The structures were neither targeted for vacuolar or autophagosome degradation nor colocalized with P bodies or major organelles. Thus, upon nutrient depletion we observe widespread protein assemblies displaying nutrient-specific formation and dissolution.
Localized olfactory representation in mushroom bodies of
Drosophila
larvae
Authors: Masuda-Nakagawa Liria M. , Gendre Nanaë , O'Kane Cahir J. , Stocker Reinhard F.
Published: June 2009

Odor discrimination in higher brain centers is essential for behavioral responses to odors. One such center is the mushroom body (MB) of insects, which is required for odor discrimination learning. The calyx of the MB receives olfactory input from projection neurons (PNs) that are targets of olfactory sensory neurons (OSNs) in the antennal lobe (AL). In the calyx, olfactory information is transformed from broadly-tuned representations in PNs to sparse representations in MB neurons (Kenyon cells). However, the extent of stereotypy in olfactory representations in the calyx is unknown. Using the anatomically-simple larval olfactory system of
Drosophila
in which odor ligands for the entire set of 21 OSNs are known, we asked how odor identity is represented in the MB calyx. We first mapped the projections of all larval OSNs in the glomeruli of the AL, and then followed the connections of individual PNs from the AL to different calyx glomeruli. We thus established a comprehensive olfactory map from OSNs to a higher olfactory association center, at a single-cell level. Stimulation of single OSNs evoked strong neuronal activity in 1 to 3 calyx glomeruli, showing that broadening of the strongest PN responses is limited to a few calyx glomeruli. Stereotypic representation of single OSN input in calyx glomeruli provides a mechanism for MB neurons to detect and discriminate olfactory cues.