bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling light-driven proton pumps in artificial photosynthetic reaction centers
Authors: Ghosh Pulak Kumar , Smirnov Anatoly Yu. , Nori Franco
Published: July 2009

We study a model of a light-induced proton pump in artificial reaction centers. The model contains a molecular triad with four electron states (i.e., one donor state, two photosensitive group states, and one acceptor state) as well as a molecular shuttle having one electron and one proton-binding sites. The shuttle diffuses between the sides of the membrane and translocates protons energetically uphill: from the negative side to the positive side of the membrane, harnessing for this purpose the energy of the electron-charge separation produced by light. Using the methods of quantum transport theory we calculate the range of light intensity and transmembrane potentials that maximize both the light-induced proton current and the energy transduction efficiency. We also study the effect of temperature on proton pumping. The light-induced proton pump in our model gives a quantum yield of proton translocation of about 55%. Thus, our results explain previous experiments on these artificial photosynthetic reaction centers.
Enhancement of charged macromolecule capture by nanopores in a salt gradient
Authors: Chou Tom
Published: July 2009

Nanopores spanning synthetic membranes have been used as key components in proof-of-principle nanofluidic applications, particularly those involving manipulation of biomolecules or sequencing of DNA. The only practical way of manipulating charged macromolecules near nanopores is through a voltage difference applied across the nanopore-spanning membrane. However, recent experiments have shown that salt concentration gradients applied across nanopores can also dramatically enhance charged particle capture from a low concentration reservoir of charged molecules at one end of the nanopore. This puzzling effect has hitherto eluded a physically consistent theoretical explanation. Here, we propose an electrokinetic mechanism of this enhanced capture that relies on the electrostatic potential near the pore mouth. For long pores with diameter much greater than the local screening length, we obtain accurate analytic expressions showing how salt gradients control the local conductivity which can lead to increased local electrostatic potentials and charged analyte capture rates. We also find that the attractive electrostatic potential may be balanced by an outward, repulsive electro-osmotic flow that can in certain cases conspire with the salt gradient to further enhance the analyte capture rate.
Coarse-grained ions without charges: Reproducing the solvation structure of NaCl in water using short-ranged potentials
Authors: DeMille Robert C. , Molinero Valeria
Published: July 2009

A coarse-grained model of NaCl in water is presented where the ions are modeled without charge to avoid computationally challenging electrostatics. A monatomic model of water [V. Molinero and E. B. Moore, J. Phys. Chem. B 113, 4008 (2009)] is used as the basis for this coarse-grain approach. The ability of Na+ to disrupt the native tetrahedral arrangement of water molecules, and of Cl− to integrate within this organization, is preserved in this mW-ion model through parametrization focused on water’s solvation of these ions. This model successfully reproduces the structural effect of ions on water, referenced to observations from experiments and atomistic molecular dynamics simulations, while using extremely short-ranged potentials. Without Coulomb interactions the model replicates details of the ion-water structure such as distinguishing contact and solvent-separated ion pairs and the free energy barriers between them. The approach of mimicking ionic effects with short-ranged interactions results in performance gains of two orders of magnitude compared to Ewald methods. Explored over a broad range of salt concentration, the model reproduces the solvation structure and trends of diffusion relative to atomistic simulations and experimental results. The functional form of the mW-ion model can be parametrized to represent other electrolytes. With increased computational efficiency and reliable structural fidelity, this model promises to be an asset for accessing significantly longer simulation time scales with an explicit solvent in a coarse-grained system involving, for example, polyelectrolytes such as proteins, nucleic acids, and fuel-cell membranes.
Droplet breakup in microfluidic T-junctions at small capillary numbers
Authors: Jullien M.-C. , Tsang Mui Ching M.-J. , Cohen C. , Menetrier L. , Tabeling P.
Published: July 2009

We perform experimental studies of droplet breakup in microfluidic T-junctions in a range of capillary numbers lying between 4×10−4 and 2×10−1 and for two viscosity ratios of the fluids forming the dispersed and continuous phases. The present paper extends the range of capillary numbers explored by previous investigators by two orders of magnitude. We single out two different regimes of breakup. In a first regime, a gap exists between the droplet and the wall before breakup occurs. In this case, the breakup process agrees well with the analytical theory of Leshansky and Pismen [Phys. Fluids 21, 023303 (2009)]. In a second regime, droplets keep obstructing the T-junction before breakup. Using physical arguments, we introduce a critical droplet extension for describing the breakup process in this case.
Analysis of second-harmonic generation of Lamb waves using a combined method in a two-layered solid waveguide
Authors: Xiang Yanxun , Deng Mingxi , Xuan Fu-Zhen
Published: July 2009

Within the second-order perturbation treatment, the present work analyzed the complex second-harmonic generation of Lamb waves in a two-layered solid waveguide by combining the modal analysis method and the nonlinear reflection of acoustic waves at interfaces. The formal solution of the second-harmonic field is obtained on the basis of the modal analysis approach, from which a phase matching modification factor can be determined. The solution of the cumulative second-harmonic displacement field derived from the nonlinear reflection of acoustic waves at interfaces can be modified by multiplying the phase matching modification factor, and then be more general and applicable for the total second-harmonic field of Lamb wave propagation. Numerical computation results show that amplitude of the second-harmonic displacement increases clearly with propagation distance when the phase velocity of a double frequency Lamb wave (DFLW) component is exactly or approximately equivalent to that of the primary Lamb wave propagation, and reveal that the amplitudes of the second harmonics exhibit a decreasing tendency when the relative deviation of phase velocity between the primary Lamb wave and the DFLW component increases. Primary experimental measurements have been performed to verify the results of the numerical simulations in a FeCrNi alloy steel specimen. The research provides a further understanding for the physical process of the cumulative second-harmonic generation in a two-layered solid waveguide.
Direct measurement of the magnetocaloric effect on La(Fe13−x−yCoy)Six compounds near room temperature
Authors: Balli M. , Fruchart D. , Sari O. , Gignoux D. , Huang J. H. , Hu J. , Egolf P. W.
Published: July 2009

The magnetic and magnetocaloric properties of LaFe11.9−yCoySi1.1 compounds with y=0.8 and 0.9 have been investigated. The temperature dependence of magnetization data revealed that LaFe11.1Co0.8Si1.1 and LaFe11Co0.9Si1.1 exhibit a second-order magnetic transition near room temperature at 282 and 294 K, respectively. Under a magnetic field change of 5 T, the maximum values of isothermal entropy change −ΔS are found to be 15 and 13.5 J/kg K for y=0.8 and 0.9, respectively. The refrigerant capacity has been calculated to be 320 J/kg for y=0.8 and 266 J/kg for y=0.9 under a field change of 5 T. Direct measurements of the temperature change for LaFe11.9−yCoySi1.1 compounds around room temperature were also performed. Measurements of ΔT were performed in adiabatic conditions with practice-oriented method by using a specially developed test bench. For both materials, the normalized temperature change was found to be about 1 K/T at their Curie temperatures.
Low energy Ar+ sputtering-induced GaAs quantum dot formation and evolution
Authors: Wang Y. , Yoon S. F. , Ngo C. Y. , Tong C. Z. , Liu C. Y.
Published: July 2009

GaAs quantum dots formed by Ar+ bombardment under normal beam incidence are investigated in both sputtering time and energy domains. When ion energy is maintained at 1000 eV, the surface morphology is found to saturate with high dot uniformity at 3600 s sputtering time. For longer sputtering times, the surface pattern becomes significantly disordered with fluctuations of ∼28 and ∼24 nm in dot height and base width, respectively. The temporal evolution of dots formed at lower ion energies exhibits a similar trend, as observed at 1000 eV. However, the surface morphology develops in a smaller size scale. Based on the experimental results, we propose a power law model to interpret the correlation between sputtering time and energy as well as their impact on the evolution of lateral dot sizes. The experimental results are in good agreement with the theoretical prediction. Furthermore, photoluminescence is performed to characterize the as-grown and annealed GaAs/AlGaAs quantum dots formed by ion sputtering and molecular beam epitaxy. A significant improvement in the integrated photoluminescence signal has been obtained after thermal annealing, indicating that the potential nonradiative defects can be effectively removed by postgrowth annealing of the sputtering-induced GaAs quantum dot system.
Swift heavy ion induced structural changes in CdS thin films possessing different microstructures: A comparative study
Authors: Ison V. V. , Rao A. Ranga , Dutta V. , Kulriya P. K. , Avasthi D. K. , Tripathi S. K.
Published: July 2009

This study is carried out to verify the role of thin film microstructure in determining the energy relaxation processes of swift heavy ions in CdS polycrystalline thin films. Two sets of CdS thin film samples, differing in their microstructures, prepared using thermal evaporation and spray pyrolysis, are irradiated with 100 MeV Ag ions using Pelletron accelerator. It is observed that the effects produced differ significantly in the two films. For the evaporated films, defect annealing dominates for lower irradiation fluences but at higher fluences the effects due to defect creation and their migration are dominant. A transformation from the metastable cubic to hexagonal phase together with the creation of a significant amount of compressive strain is seen in these films for irradiation at the highest fluence. The optical absorption of the samples shows an increase in band gap from 2.34 eV for the as grown film to 2.43 eV for the sample irradiated at the highest fluence that is further confirmed by photoluminescence (PL) studies. In contrast, the spray deposited samples undergo a significant improvement of crystalline quality for all fluences as shown by an increase in x-ray diffraction peak intensity, sharper optical absorption edge, reduction in defect PL intensity, and removal of asymmetry in the line shape of the longitudinal optical phonon on its lower wavenumber side in Raman spectra.
Photoinduced phenomena in amorphous As4Se3 pulsed laser deposited thin films studied by spectroscopic ellipsometry
Authors: Němec P. , Nazabal V. , Frumar M.
Published: July 2009

Amorphous As4Se3 thin films were prepared by pulsed laser deposition technique. Variable angle spectroscopic ellipsometry was used for the study of reversible photoinduced phenomena in well-annealed films. Tauc–Lorentz and Cody–Lorentz models were employed for the analysis of ellipsometric data. Reversible photorefraction and photodarkening were identified by both models; however, Cody–Lorentz model is shown to be more appropriate for the description of amorphous chalcogenide thin films. The behavior of best fit Cody–Lorentz model parameters is discussed in detail.
Hydrostatic pressure (P≤8 GPa) induced metallization of ferromagnetic insulating La0.79Ca0.21MnO3
Authors: Arumugam S. , Ghosh Barnali , Raychaudhuri A. K. , Selvan N. R. Tamil , Nakanishi T. , Yoshino H. , Murata K. , Mukovskii Ya. M.
Published: July 2009

We show that application of hydrostatic pressure makes the ferromagnetic insulating phase of La0.79Ca0.21MnO3 metallic at a pressure of ∼1 GPa. On further increase in pressure (∼6 GPa) the high temperature polaronic state also crosses over to a metallic behavior. The application of the pressure also shifts the ferromagnetic TC of the material to higher temperature. We also find that in the process of pressure induced metallization, the material shows a coherence temperature where a highly resistive incoherent metal crosses over to a less resistive band type metal. The metallic phase so created under pressure has no appreciable magnetoresistance.
Effect of film texture on magnetization reversal and switching field in continuous and patterned (Co/Pd) multilayers
Authors: Sbiaa Rachid , Hua Cho Zhong , Piramanayagam S. N. , Law Randall , Aung Kyaw Oo , Thiyagarajah Naganivetha
Published: July 2009

We studied the reversal properties of perpendicular anisotropy (Co/Pd) multilayers with different crystallographic textures. In case of continuous films, an increase in the coercivity and reduction in the switching field distribution (SFD) were observed as the growth is improved. From magnetic force microscopy, a stripe-type domain configuration was observed in films deposited at low gas pressure while a bubble-type domain was observed in high pressure deposited films. In patterned films, the SFD did not vary significantly for samples with different textures although a 2 kOe increase in the switching field was measured. In patterned structures, the controllability of SFD may not be related to the improvement of film crystallographic growth as was observed for unpatterned films. The results from this study indicate that local variation in the intrinsic film properties plays a major role in the SFD.
Different resistance switching behaviors of NiO thin films deposited on Pt and SrRuO3 electrodes
Authors: Choi J. S. , Kim J.-S. , Hwang I. R. , Hong S. H. , Jeon S. H. , Kang S.-O. , Park B. H. , Kim D. C. , Lee M. J. , Seo S.
Published: July 2009

We have compared resistance switching of NiO films deposited on Pt and SrRuO3 (SRO): unipolar switching in Pt/NiO/Pt and bipolar switching in Pt/NiO/SRO. Linear fitted current-voltage curves and capacitance-voltage results show that on- and off-states conductions in unipolar switching are dominated by inductive Ohmic behavior and Poole–Frenkel effect, respectively. However, the conductions of on- and off-states in bipolar switching follow capacitive Ohmic behavior and Schottky effect, respectively. Therefore, we infer that the mechanisms of the unipolar and bipolar switching behaviors in NiO films are related with changes in bulk-limited filamentary conduction and interfacial Schottky barrier, respectively.
A modified scheme of charge sensitive infrared phototransistor
Authors: Wang Zhihai , Komiyama S. , Ueda T. , Nagai N.
Published: July 2009

Charge sensitive infrared phototransistors (CSIP) realized in a GaAs/AlGaAs double quantum well (QW) structure have so far exploited the tunneling of excited electrons from an isolated island of upper QW to the lower two-dimensional electron gas layer. Another type of CSIP is developed by using a GaAs/AlGaAs double QW crystal, in which inter-QW tunneling is suppressed. Instead of “vertical” tunneling, excited electrons in the upper QW flow in and out the isolated island “laterally” via translational motion through gate-induced potential barriers. The scheme is demonstrated for wavelengths ≈14.6 μm but is suitable for expanding toward longer wavelengths.
Low temperature investigations of switching processes in multilayer rings
Authors: Jain S. , Adeyeye A. O.
Published: July 2009

A systematic study of the magnetotransport behavior of multilayer rings for elliptical and rectangular shapes has been performed as a function of temperature. We observed that due to the increase in energy barrier heights with decreasing temperature, there is a dramatic increase in the switching field distribution for both the ring shapes. In particular, for the rectangular rings, the switching field is very sensitive to temperature variations due to decreased thermal excitations and therefore lead to the formation of intermediate horseshoe state. This intermediate metastable state was thermally not favored at room temperature.
Electrical detection of ferromagnetism in Pd nanoparticles by magnetoresistance measurement
Authors: Okamoto Takao , Maki Hideyuki , Oba Yojiro , Yabuuchi Shin , Sato Tetsuya , Ohta Eiji
Published: July 2009

We investigate ferromagnetism of two-dimensional Pd nanoparticle superlattice by a magnetoresistance measurement. Magnetoresistance increases at a coercive field with hysteretic behavior, which is consistent with the result of a magnetization-field curve. This indicates that the ferromagnetism of the Pd nanoparticle superlattice is electrically detected. From the maximum magnetoresistance change, the conduction-electron polarization of the Pd nanoparticle superlattice is estimated to be ∼4%. The ferromagnetism of Pd nanoparticles is evolved ferromagnetism without protective agents; therefore, the origin of ferromagnetism in the chemically prepared Pd nanoparticles is associated with the intrinsic characteristic of the Pd nanoparticles, but not the effect of the existence of a protective agent.
Magnetocaloric effect and refrigerant capacity in charge-ordered manganites
Authors: Bingham N. S. , Phan M. H. , Srikanth H. , Torija M. A. , Leighton C.
Published: July 2009

The influence of first- and second-order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity (RC) of charge-ordered Pr0.5Sr0.5MnO3 has been investigated. The system undergoes a paramagnetic to ferromagnetic transition at TC∼255 K followed by a ferromagnetic charge-disordered to antiferromagnetic charge-ordered transition at TCO∼165 K. While the first-order magnetic transition (FOMT) at TCO induces a larger MCE (6.8 J/kg K) limited to a narrower temperature range resulting in a smaller RC (168 J/kg), the second-order magnetic transition at TC induces a smaller MCE (3.2 J/kg K) but spreads over a broader temperature range resulting in a larger RC (215 J/kg). In addition, large magnetic and thermal hysteretic losses associated with the FOMT below TCO are detrimental to an efficient magnetic RC, whereas these effects are negligible below TC because of the second-order nature of this transition. These results are of practical importance in assessing the usefulness of charge-ordered manganite materials for active magnetic refrigeration, and Pr0.5Sr0.5MnO3 provides an interesting case study in which the influence of first- and second-order transitions on MCE could be compared in the same system in a single experiment.
Shock response of iron between 143 and 1275 K
Authors: Zaretsky E. B.
Published: July 2009

The shock response of polycrystalline iron of 99.995% purity was studied in a series of planar impact experiments using laser interferometer monitoring of the free surface of preheated/precooled samples. On the basis of the recorded waveforms, the dynamic yield and tensile (spall) strengths of iron were determined over the 143–1275 K temperature range. Part of the recorded waveforms had a three-wave (PEL, P1, and P2 waves) structure reflecting a stress-induced phase transformation in the impacted samples. By estimating the stress σtr and the temperature Ttr on the top of the P1 wave, it became possible to determine the upper borders of stability with respect to the shock loading for both the α- and the γ-iron phases. The analysis of the P2 waves of the recorded waveforms showed that irrespective of its initial, α or γ, state the high-pressure phase of iron is the ε-phase. The same analysis yields the width, 5.18 GPa, of the mixed phase region, above which the three-wave structures are substituted by two-wave ones (PEL and P2) with solely the ε-phase behind the front of the overdriven P2 wave.
Magnetoresistance based first-order reversal curve analysis of magnetic tunnel junctions
Authors: Pomeroy J. M. , White T. C. , Grube H. , Read J. C. , Davies J. E.
Published: July 2009

First-order reversal curve (FORC) analysis is conventionally applied to magnetization versus applied magnetic field loops to determine the ensemble properties of multidomain magnetic samples ranging from naturally occurring geological samples to exquisitely engineered materials for use in magnetic storage. We apply FORC analysis to magnetic tunnel junctions (MTJs) by using magnetoresistance instead of magnetization field. By using the MTJ resistance to monitor domain switching, arbitrarily small samples can be studied, as well as functioning devices after lithographic patterning. Experimental data are presented from sub-0.01 mm2 MTJs that illustrate the application of FORC analysis and demonstrate asymmetric switching distributions when mapped in coercive versus interaction field space.
Quantum dynamical simulations for nuclear spin selective laser control of ortho- and para-fulvene
Authors: Belz S. , Grohmann T. , Leibscher M.
Published: July 2009

In the present paper we explore the prospects for laser control of the photoinduced nonadiabatic dynamics of para- and ortho-fulvene with the help of quantum dynamical simulations. Previous investigations [Bearpark et al., J. Am. Chem. Soc. 118, 5253 (1996); Alfalah et al., J. Chem. Phys. 130, 124318 (2009)] show that photoisomerization of fulvene is hindered by ultrafast radiationless decay through a conical intersection at planar configuration. Here, we demonstrate that photoisomerization can nevertheless be initiated by damping unfavorable nuclear vibrations with properly designed laser pulses. Moreover, we show that the resulting intramolecular torsion is nuclear spin selective. The selectivity of the photoexcitation with respect to the nuclear spin isomers can be further enhanced by applying an optimized sequence of two laser pulses.
Electromagnetically induced transparency in a three-level lambda system with permanent dipole moments
Authors: Zhou Fengxue , Niu Yueping , Gong Shangqing
Published: July 2009

Electromagnetically induced transparency in a three-level Λ-type molecular system with nonzero permanent dipole moments is investigated. It is shown that in the (2+2)-transition processes, when the sign of d21, the difference in permanent dipole moments of the probe transition, is positive, perfect electromagnetically induced transparency with steep normal dispersion could be obtained under specific conditions. In contrast, when the sign of d21 is negative, surprisingly gain without inversion with steep anomalous dispersion could be attained.
Fluctuations in a ferrofluid monolayer: An integral equation study
Authors: Luo Liang , Klapp Sabine H. L.
Published: July 2009

Using integral equation theory in the reference hypernetted chain (RHNC) approximation we investigate the structure and phase behavior of a monolayer of dipolar spheres. The dipole orientations of the particles fluctuate within the plane. The resulting angle dependence of the correlation functions is treated via an expansion in two-dimensional rotational invariants. For homogeneous, isotropic states the RHNC correlation functions turn out to be in good agreement with Monte Carlo simulation data. We then use the RHNC theory combined with a stability (fluctuation) analysis to identify precursors of the low-temperature behavior. As expected, the fluctuations point to pair and cluster formation in the range of low and moderate densities. At high densities, there is no clear indication for a ferroelectric transition, contrary to what is found in three-dimensional dipolar fluids. The stability analysis rather indicates an alignment of chains supplemented by local crystal-like order.
Functionalized zinc oxide nanorod with ionophore-membrane coating as an intracellular Ca2+ selective sensor
Authors: Asif M. H. , Fulati A. , Nur O. , Willander M. , Brännmark Cecilia , Strålfors Peter , Börjesson Sara I. , Elinder Fredrik
Published: July 2009

The tip of a borosilicate glass capillary with functionalized hexagonal ZnO nanorods was used to make a sensitive electrochemical intracellular Ca2+ sensor. To adjust the sensor for Ca2+ measurements with sufficient selectivity and stability, polyvinylchloride membrane containing Ca2+ ionophores were coated on the surface. The membrane covered ZnO nanorods exhibited a Ca2+-dependent electrochemical potential difference versus an Ag/AgCl reference electrode. The potential difference was linear over a large concentration range (100 nM–10 mM). The measurements of Ca2+ concentrations using our ZnO nanorods sensor in human fat cells or in frog egg cells were consistent with values of Ca2+ concentrations reported in the literature. This nanoelectrode device paves the way to measurements of intracellular biochemical species in specific locations within single living cells.
Development and performance analysis of a standard orifice flow calibration system
Authors: Akram H. M. , Maqsood M. , Rashid H.
Published: July 2009

An orifice flow system has been developed indigenously which is a primary standard for the calibration of high vacuum gauges in the range of 10−3–10−6 mbar. It consists of a constant-volume flow meter, designed to generate a known flow rate of a particular gas to the vacuum chamber. This chamber is partitioned into two parts by a plate with an orifice of calculable conductance. The pressures, generated by this standard system, are compared with those of secondary standard, namely, spinning rotor gauge. Different uncertainties and correction factors are calculated. The maximum percentage deviation is from 1.16% to 0.97%. The combined uncertainties over the entire calibration range of the standard system are in the range of 4.0×10−6 mbar.
Luminescent and thermo-optical properties of Nd3+-doped yttrium aluminoborate laser glasses
Authors: Santos C. N. , Mohr D. , Silva W. F. , de Camargo A. S. S. , Eckert H. , Li M. S. , Vermelho M. V. D. , Hernandes A. C. , Ibanez A. , Jacinto C.
Published: July 2009

In this work we performed a thorough spectroscopic and thermo-optical investigation of yttrium aluminoborate glasses doped with neodymium ions. A set of samples, prepared by the conventional melt-quenching technique and with Nd2O3 concentrations varying from 0.1 to 0.75 mol %, were characterized by ground state absorption, photoluminescence, excited state lifetime measurements, and thermal lens technique. For the neodymium emission at 1064 nm (F43/2→I411/2 transition), no significant luminescence concentration quenching was observed and the experimental lifetime values ranged around 70 μs. The obtained values of thermal conductivity and diffusivity of approximately 10.3×10−3 W/cm K and 4.0×10−3 cm2/s, respectively, are comparable to those of commercial laser glasses. Moreover, the fluorescence quantum efficiency of the glasses, calculated using the Judd–Ofelt formalism and luminescence decay, lies in the range from 0.28 to 0.32, larger than the typical values obtained for Nd3+ doped YAl3(BO3)4 crystals.
Long-range-corrected hybrid density functionals including random phase approximation correlation: Application to noncovalent interactions
Authors: Janesko Benjamin G. , Henderson Thomas M. , Scuseria Gustavo E.
Published: July 2009

We recently presented a combination of a short-range density functional approximation with long-range random phase approximation (RPA) correlation [B. G. Janesko, T. M. Henderson, and G. E. Scuseria, J. Chem. Phys. 130, 081105 (2009)]. Here we show that this approach provides very accurate interaction energy predictions for a range of noncovalent complexes. Calculations on representative sets of hydrogen bonded, dipole-dipole, charge transfer, and weakly bound (van der Waals) complexes show that long-range RPA provides statistical errors comparable to CCSD(T) in moderate basis sets. This approach shows promise for providing accurate and computationally tractable models of noncovalent interactions in biological systems.
A nonextensive approach for the instability of current-driven ion-acoustic waves in space plasmas
Authors: Liu Zhipeng , Liu Liyan , Du Jiulin
Published: July 2009

The instability of current-driven ion-acoustic waves in the collisionless magnetic-field-free space plasma is investigated by using a nonextensive approach. The ions and the electrons are thought of in the power-law distributions that can be described by the generalized q-Maxwellian velocity distribution and are considered with the different nonextensive q-parameters. The generalized q-wave frequency and the generalized instability q-growth rate for the ion-acoustic waves are derived. The numerical results show that the nonextensive effects on the ion-acoustic waves are not apparent when the electron temperature is much more than the ion temperature, but they are salient when the electron temperature is not much more than the ion temperature. As compared to the electrons, the ions play a dominant role in the nonextensive effects.
Dislocation structures of Σ3 {112} twin boundaries in face centered cubic metals
Authors: Wang J. , Anderoglu O. , Hirth J. P. , Misra A. , Zhang X.
Published: July 2009

High resolution transmission electron microscopy of nanotwinned Cu films revealed Σ3 {112} incoherent twin boundaries (ITBs), with a repeatable pattern involving units of three {111} atomic planes. Topological analysis shows that Σ3 {112} ITBs adopt two types of atomic structure with differing arrangements of Shockley partial dislocations. Atomistic simulations were performed for Cu and Al. These studies revealed the structure of the two types of ITBs, the formation mechanism and stability of the associated 9R phase, and the influence of stacking fault energies on them. The results suggest that Σ3 {112} ITBs may migrate through the collective glide of partial dislocations.
Oscillations in meta-generalized-gradient approximation potential energy surfaces for dispersion-bound complexes
Authors: Johnson Erin R. , Becke Axel D. , Sherrill C. David , DiLabio Gino A.
Published: July 2009

Meta-generalized-gradient approximations (meta-GGAs) in density-functional theory are exchange-correlation functionals whose integrands depend on local density, density gradient, and also the kinetic-energy density. It has been pointed out by Johnson et al. [Chem. Phys. Lett. 394, 334 (2004)] that meta-GGA potential energy curves in dispersion-bound complexes are susceptible to spurious oscillations unless very large integration grids are used. This grid sensitivity originates from the saddle-point region of the density near the intermonomer midpoint. Various dimensionless ratios involving the kinetic-energy density, found in typical meta-GGAs, may be ill-behaved in this region. Grid sensitivity thus arises if the midpoint region is sampled by too sparse a grid. For most meta-GGAs, standard grids do not suffice. Care must be taken to avoid this problem when using, or constructing, meta-GGAs.
Midinfrared electroluminescence from pentanary-quaternary heterojunction light-emitting diodes
Authors: Cook N. B. , Krier A.
Published: July 2009

InAs-GaInAsSbP-InAsSbP double heterojunction light-emitting diodes were fabricated which exhibit electroluminescence near 3.7 μm at room temperature. Radiative recombination from band-tail states associated with alloy disorder and localized potential fluctuations was observed, as well as emission from states localized at the InAs-pentanary heterointerface.
Enhanced photoluminescence in gold nanoparticles doped ferroelectric liquid crystals
Authors: Kumar A. , Prakash J. , Mehta D. S. , Biradar A. M. , Haase W.
Published: July 2009

We report the characterization and photoluminescence (PL) of newly synthesized deformed helix ferroelectric liquid crystal (DHFLC) material having short pitch and high spontaneous polarization. We observed ninefold enhancement in PL intensity in gold nanoparticles doped DHFLC material. This enhancement in the PL intensity has been attributed to the coupling of localized surface plasmon resonance from metal nanoparticles with DHFLC molecules, resulting in the increase in excitation and emission rate of the liquid crystal molecules in the localized electromagnetic field. These studies would provide a cutting edge tool in the realization of enhanced photoluminescent liquid crystal display devices.
Solitary waves and double layers in dense magnetoplasma
Authors: Chatterjee Prasanta , Saha Taraknath , Muniandy Sithi V. , Yap S. L. , Wong C. S.
Published: July 2009

Using Sagdeev’s pseudopotential technique, ion acoustic solitary waves and double layers are studied subject to an external magnetic field in a two-component dense magnetoplasma consisting of ions and degenerate electrons. The ions are described by the hydrodynamic equations, and the electrons are assumed to follow the Thomas–Fermi density distribution. The pseudopotential is derived directly from Poisson’s equation without assuming the quasineutrality condition. The ranges of parameters for which solitary waves and double layers exist are studied in detail using Sagdeev’s technique.
Dual hierarchical biomimic superhydrophobic surface with three energy states
Authors: Chen Ming-Hung , Hsu Tsung-Hsing , Chuang Yun-Ju , Tseng Fan-Gang
Published: July 2009

A low hysteresis surface prepared by two-length-scaled hierarchical textures to mimic the Lotus effect is proposed. The fabricated textures incorporate self-masked nanorods on microextrusions. A high static contact angle (160°) and low hysteresis (∼2.7°) are obtained and comparable to the surface properties of a natural lotus leaf. The stability of hydrophobicity is described with respect to three energy states (nonwetting, microwetting, and nanowetting) based on dynamic contact angle analysis by droplet impinging onto the surface. The estimated texture-induced energy barrier based on the principle of energy conservation is in good agreement to those estimated from Laplace’s law.
Vertical-geometry all-optical switches based on InAs/GaAs quantum dots in a cavity
Authors: Jin C. Y. , Kojima O. , Kita T. , Wada O. , Hopkinson M. , Akahane K.
Published: July 2009

Self-assembled InAs/GaAs quantum dots (QDs) incorporated in an asymmetric GaAs/Al0.8Ga0.2As vertical cavity have been employed as an optical nonlinear medium for reflection-type all-optical switches. Switching time down to 23 ps together with wavelength tuning range over 30 nm have been achieved in this structure. An angle-dependent behavior of the switching time has been observed, which suggests there is a coupling mechanism between the ground and excited states in QDs with different sizes.
Energy current imaging method for time reversal in elastic media
Authors: Anderson Brian E. , Guyer Robert A. , Ulrich Timothy J. , Le Bas Pierre-Yves , Larmat Carène , Griffa Michele , Johnson Paul A.
Published: July 2009

An energy current imaging method is presented for use in locating sources of wave energy during the back propagation stage of the time reversal process. During the back propagation phase of an ideal time reversal experiment, wave energy coalesces from all angles of incidence to recreate the source event; after the recreation, wave energy diverges in every direction. An energy current imaging method based on this convergence/divergence behavior has been developed. The energy current imaging method yields a smaller spatial distribution for source reconstruction than is possible with traditional energy imaging methods.
Epitaxial, cation-ordered, ferroelectric PbSc0.5Ta0.5O3 thin films prepared by pulsed laser deposition
Authors: Chopra Anuj , Birajdar Balaji I. , Kim Yunseok , Vrejoiu Ionela , Alexe Marin , Hesse Dietrich
Published: July 2009

We report on growth and ferroelectric properties of cation-ordered, epitaxial PbSc0.5Ta0.5O3 (100) films. Single phase epitaxial films were grown on vicinal SrTiO3 (100) substrates with a layer of SrRuO3 as bottom electrode by pulsed laser deposition. Their crystal orientation, topography, and microstructure were analyzed by x-ray diffraction, atomic force microscopy, and transmission electron microscopy (TEM), respectively. The in-plane and out-of-plane epitaxial relationships were studied by ϕ and θ-2θ scans, respectively. Superstructure reflections obtained in TEM diffraction patterns of the films confirm cation ordering. Polarization-field and switching current-voltage hysteresis curves demonstrate ferroelectric behavior of the films at room temperature.
Chirality and diameter dependent x-ray absorption of single walled carbon nanotubes
Authors: Gao Bin , Wu ZiYu , Ågren Hans , Luo Yi
Published: July 2009

The lack of good understanding on the electronic structure of individual carbon nanotubes severely limited the applications of carbon nanotubes. By employing density functional theory in combination with the equivalent core hole approximation, we are able to provide near edge x-ray absorption fine structure (NEXAFS) spectra of all possible single walled carbon nanotubes (SWCNTs) with diameters below 1.45 nm. It is shown that the π∗ absorption edges in NEXAFS spectra of SWCNTs are converged already at the length of 3 nm, while a good description of the full spectra can only be obtained after 7 nm. A recent high resolution experimental spectrum of a bundle of SWCNTs with diameters 1.37±0.08 nm has been successfully assigned by the calculations. Noticeable chirality and diameter dependence have been identified for the simulated NEXAFS spectra. The collection of calculated spectra serves as a useful reference for experimental identification of individual carbon nanotubes.
Modification of magnetotransport properties across patterned GaMnAs nanoconstrictions by application of high current densities
Authors: Cho Sung Un , Choi Hyung Kook , Yang Chan Uk , Park Yun Daniel , Da Silva Fabio C. S. , Osminer Teresa , Pappas David P.
Published: July 2009

We report on modifications in the magnetotransport properties across patterned GaMnAs nanoconstrictions by the application of high current densities (<107 A/cm2). Initially, we observe controllable changes in the electrical resistance with the direction of the bias current. Repeated biases at high current densities greatly increase the constriction resistances. Subsequent biasing and magnetotransport measurements show nearly a fourfold increase in the magnetoresistances and large changes in the magnetic switching behavior of GaMnAs. The initial reversibility of the changes in resistance suggests that dopant electromigration may locally alter the interstitial concentrations of Mn at the nanoconstriction.
A level set simulation for ordering of quantum dots via cleaved-edge overgrowth
Authors: Niu X. B. , Uccelli E. , Fontcuberta i Morral A. , Ratsch C.
Published: July 2009

Cleaved-edge overgrowth (CEO) is a promising technique to obtain ordered arrays of quantum dots, where the size and position of the dots can be controlled very well. We present level set simulations for CEO. Our simulations illustrate how the quality of the CEO technique depends on the potential energy surface (PES) for adatom diffusion, and thus suggest how variations of the PES can potentially improve the uniformity of quantum dot arrays.
High spin injection polarization at an elevated dc bias in tunnel-junction-based lateral spin valves
Authors: Wang X. J. , Zou H. , Ocola L. E. , Ji Y.
Published: July 2009

Submicron metallic lateral spin valves are fabricated with AlOx tunnel junctions as spin injection and detection barriers. The spin polarization is estimated to be ∼20%, determined by both Hanle effect and variations of device dimensions. The polarization is maintained at a large dc injection current density >2×106 A/cm2. Both the spin polarization and spin diffusion length are weakly temperature dependent.
Evolution of relaxor ferroelectric behavior of poly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) terpolymer nanorods
Authors: Lin Jun-Hong , Lu S. G. , Lin M. , Geuβ Markus , Zhang Q. M.
Published: July 2009

The evolution of relaxor ferroelectric behavior of poly(vinylidene fluoride trifluoroethylene chlorofluoroethylene) [P(VDF-TrFE-CFE)] terpolymer nanorods with diameters reduced from 200 to 25 nm was investigated. It was observed that all the nanorods studied exhibited relaxor ferroelectric behavior, as characterized by the dielectric peak shifting toward high temperatures with increasing frequency. The frequency-permittivity peak temperature characteristics fit well with the Vogel–Fulcher (VF) relation. Moreover, the freezing temperature in the VF relation decreased with the reduction of nanorod diameter, indicating that the scaling down of the lateral size of nanorods influenced the relaxor ferroelectric behavior of the terpolymer.
Interface-induced piezoelectricity in an unpoled Na0.5Bi0.5TiO3-based composite ceramic
Authors: Zhao M. L. , Wang L. H. , Wang C. L. , Zhang J. L. , Gai Z. G. , Wang C. M. , Li J. C.
Published: July 2009

Composite ceramics containing Bi12TiO20 and Na0.5Bi0.5TiO3 grains were fabricated by an ordinary sintering technique. An anomalous piezoelectric response consistent with triclinic symmetry was found in unpoled samples and could be detected up to at least 765 °C. This piezoelectric effect appears concurrently with macroscopic cellular interfaces in as-sintered ceramics, suggesting that it may originate from an interface effect. Since these kinds of composites also have near-zero temperature coefficients of the resonance frequencies over the temperature range from 400 to 520 °C, they have potential as high-temperature piezoelectric materials.
A comparison of viscoelastic stress wakes for two-dimensional and three-dimensional Newtonian drop deformations in a viscoelastic matrix under shear
Authors: Afkhami S. , Yue P. , Renardy Y.
Published: July 2009

A recent experimental study of a Newtonian drop suspended in a viscoelastic matrix undergoing simple shear displays a transient overshoot in drop deformation which is qualitatively similar to two-dimensional (2D) numerical simulation results. Despite the similarity, an interpretation in light of the 2D result is misleading because the overshoot is absent in the fully three-dimensional (3D) simulation. This motivates a study of regimes where qualitatively different and interesting features such as overshoots in deformation occur for a 2D drop but not for a 3D drop. The influence of viscoelastic “wakes” that emanate from the drop tips is reported. The viscoelastic wakes are larger and of higher magnitude in 3D than in 2D, and lead to more deformation in 3D. During drop evolution, the less deformed drop is found to be aligned more with the flow direction. As the drop-to-matrix viscosity ratio increases from 1 to past 3, drop rotation is promoted, with accompanying retraction when the capillary number is sufficiently high. Thus, a 3D overshoot in deformation is promoted with increasing viscosity ratio.
Atomic hydrogen adsorption and incipient hydrogenation of the Mg(0001) surface: A density-functional theory study
Authors: Li Yanfang , Zhang Ping , Sun Bo , Yang Yu , Wei Yinghui
Published: July 2009

We investigate the atomic hydrogen adsorption on Mg(0001) by using density-functional theory within the generalized gradient approximation and a supercell approach. The coverage dependence of the adsorption structures and energetics is systematically studied for a wide range of coverage Θ [from 0.11 to 2.0 monolayers (ML)] and adsorption sites. In the coverage range 0<Θ<1.0, the most stable among all possible adsorption sites is the on-surface fcc site followed by the hcp site, and the binding energy increases with the coverage, thus indicating the higher stability of on-surface adsorption and a tendency to the formation of H islands (clusters) when increasing the coverage within the region 0<Θ<1.0. The on-surface diffusion path energetics of atomic hydrogen as well as the activation barriers for hydrogen penetration from the on-surface to the subsurface sites are also presented at low coverage. At high coverage of 1.0<Θ≤2.0, it is found that the coadsorption configuration with 1.0 monolayer of H residing on the surface fcc sites and the remaining (Θ−1.0) monolayer of H occupying the subsurface tetra-I sites is most energetically favorable. The resultant H–Mg–H sandwich structure for this most stable coadsorption configuration displays similar spectral features to the bulk hydride MgH2 in the density of states. The other properties of the H/Mg(0001) system including the charge distribution, the lattice relaxation, the work function, and the electronic density of states are also studied and discussed in detail. It is pointed out that the H–Mg chemical bonding during surface hydrogenation displays a mixed ionic/covalent character.
Full dimensional (15 dimensional) quantum-dynamical simulation of the protonated water-dimer IV: Isotope effects in the infrared spectra of D(D2O)2+, H(D2O)2+, and D(H2O)2+ isotopologues
Authors: Vendrell Oriol , Gatti Fabien , Meyer Hans-Dieter
Published: July 2009

The infrared spectra of H(H2O)2+, D(D2O)2+, H(D2O)2+, and D(H2O)2+ isotopologues of the Zundel cation in the spectral range of 0–4000 cm−1 are computed by quantum dynamics in full dimensionality using the multiconfiguration time-dependent Hartree method. The spectra present dramatic isotope effects in the middle spectral region between 600 and 2000 cm−1. Not only the expected line shifts due to isotopic substitution take place but the intensities of the peaks and the number of absorptions with appreciable intensity vary. The most complex spectrum is the one of H(D2O)2+, in which a group of at least four coupled vibrational modes is found in a narrow spectral range between 1000 and 1500 cm−1 and is responsible for the three peaks found in this spectral region. The simplest spectrum of the series corresponds to D(H2O)2+. In this case deuteration of the central position induces decoupling of the vibrational modes, especially of the asymmetric central proton mode and the ungerade water bending, leading to a spectrum which is easy to assign and interpret. Zero-point energies and low energy vibrational eigenstates of each isotopologue related to the wagging (pyramidalization) and water-water internal relative rotation are computed using the block improved relaxation algorithm. The effect of isotopic substitution on these states is discussed. The reported simulations provide detailed information on the dynamics and vibrational spectroscopy of the Zundel cation and contribute to our general understanding of protonated water clusters and the hydrated proton.
High-performance dinaphtho-thieno-thiophene single crystal field-effect transistors
Authors: Haas Simon , Takahashi Yukihiro , Takimiya Kazuo , Hasegawa Tatsuo
Published: July 2009

We fabricated high-performance single crystal organic field-effect transistors (SC-OFETs) based on dinaphtho[2,3-b:2′,3′-f]thieno[3,2-b]-thiophene (DNTT). Among various device geometries and contact types, best performance is obtained for a lamination-type SC-OFET composed of a Cytop-treated SiO2 gate dielectric and top-contact gold/tetrathiafulvalene-tetracyanoquinodimethane electrodes, which results in hysteresis-free device characteristics with optimum mobility of 8.3 cm2/V s and an on/off ratio of >108. The achieved performance is promising for use of the air-stable DNTT in future studies of intrinsic properties of molecular crystals.
Fractal network dimension determining the relation between the strength of bulk metallic glasses and the glass transition temperature
Authors: Klein D. J. , March N. H. , Alonso J. A.
Published: July 2009

[Ma et al., Nat. Mater. 8, 30 (2009)] have uncovered the fractal dimension Df=2.31 associated with the medium-range order in a variety of bulk metallic glasses, reflected in the first sharp diffraction peak q1 determined from neutron and x-ray measurements. Here, based on the proposal in this journal of [Yang et al., Appl. Phys. Lett. 88, 221911 (2006)], which related the strength σy of bulk metallic glasses to the glass transition temperature Tg, we show that the product q1Dfσy is linear in Tg.