bluuebunny/crossref_metadata_2025 huggingface dataset:
Cool white III-nitride light emitting diodes based on phosphor-free indium-rich InGaN nanostructures
Authors: Soh C. B. , Liu W. , Teng J. H. , Chow S. Y. , Ang S. S. , Chua S. J.
Published: July 2008

Phosphor-free cool white emitting light emitting diodes (LEDs) have been fabricated using a dual stacked InGaN∕GaN multiple quantum wells (MQWs) comprising of a lower set of MQWs emitting yellow and an upper set of MQWs emitting blue. The lower set of MQWs incorporates indium-rich InGaN connected-dot nanostructures with a height of ∼1.0nm in the well. The well is first grown with an InGaN layer serving as the wetting layer, then treated with trimethylindium (TMIn) to initiate nanostructure growth of another InGaN layer to complete the well layer. This gives a broadened yellow emission peak. With the combination of emission from the upper blue emitting InGaN∕GaN MQWs subsequently grown, cool white light emission is achieved. The In-rich nanostructures formed during TMIn treatment enhance indium incorporation in InGaN well and also act as effective radiative recombination sites for carriers at the lower set of MQWs.
Theoretical investigation of the negative differential resistance in squashed C60 molecular device
Authors: Fan Zhi-Qiang , Chen Ke-Qiu , Wan Qing , Zou B. S. , Duan Wenhui , Shuai Z.
Published: July 2008

By applying nonequilibrium Green’s function and first-principles calculation, we investigate the transport behavior of squashed C60 molecular devices. The results show that the electronic transport properties are affected obviously by the deformation of C60 molecule. Negative differential resistance is found in such system and can be tuned by the deformation degree of the molecule. A mechanism for the negative differential resistance behavior is suggested.
Development and characterization of fast responding pressure sensitive microspheres
Authors: Kimura Fletcher , Rodriguez Miguel , McCann Jesse , Carlson Brenden , Dabiri Dana , Khalil Gamal E. , Callis James B. , Xia Younan , Gouterman Martin
Published: July 2008

The response times of pressure sensitive paint (PSP) and pressure sensitive microspheres to passing shockwaves were measured to investigate their ability to accurately determine pressure changes in unsteady flows. The PSPs tested used platinum tetra(pentafluorophenyl)porphine (PtTFPP), platinum octaethylporphine (PtOEP), and a novel set of osmium-based organometallic complexes as pressure sensitive luminophors incorporated into polymer matrices of dimethylsiloxane bisphenol A-polycarbonate block copolymer or polystyrene. Two types of pressure sensitive microspheres were used, the first being PtOEP-doped polystyrene microspheres (PSBeads) and the second being porous silicon dioxide microspheres containing the novel, pressure sensitive osmium complexes. Response times for the platinum-based PSPs ranged from 47.2to53.0μs, while the osmium-based PSPs ranged between 37.6 and 58.9μs. For the microspheres, 2.5μm diameter PSBeads showed a response time of 3.15ms, while the osmium-based silicon dioxide microspheres showed a response time ranging between 13.6 and 18.9μs.
Monocrystalline AlxGa1−xAs heterostructures for high-reflectivity high-Q micromechanical resonators in the megahertz regime
Authors: Cole Garrett D. , Gröblacher Simon , Gugler Katharina , Gigan Sylvain , Aspelmeyer Markus
Published: July 2008

We present high-performance megahertz micromechanical oscillators based on freestanding epitaxial AlxGa1−xAs distributed Bragg reflectors. Compared with dielectric reflectors, the low mechanical loss of the monocrystalline heterostructure gives rise to significant improvements in the achievable mechanical quality factor Q while simultaneously exhibiting near unity reflectivity. Experimental characterization yields an optical reflectivity exceeding 99.98% and mechanical quality factors up to 20 000 at 4K. This materials system is not only an interesting candidate for optical coatings with ultralow thermal noise, but also provides a promising path toward quantum optical control of massive micromechanical mirrors.
Inversionless distributed feedback semiconductor lasers: Ultranarrow linewidth and immunity against spatial hole burning
Authors: Sadeghi S. M. , Li W.
Published: July 2008

We propose and parametrically study an inversionless intrinsically single-mode distributed feedback laser structure. This laser is optically excited by a control laser field that is responsible for transferring a fully transparent waveguide structure into a coherent state, wherein a periodic variation of gain without inversion in the absence of any refractive index perturbation is generated. We show that such a laser can perform under the conditions where its gain is equal or even less than its loss, i.e., zero and negative net gain regimes. The results suggest that, via coherent control of the longitudinal mode intensity profile and standing wave effects, in the negative net gain regime such a laser can be operated at the Bragg wavelength with ultranarrow linewidth and virtual elimination of any sidemode. The inherent resistance of such a laser against spatial hole burning, despite of having strong nonuniform longitudinal mode intensity, and the effects of facet reflectivities are discussed.
Molecular applications of state-specific multireference perturbation theory to HF, H2O, H2S, C2, and N2 molecules
Authors: Mahapatra Uttam Sinha , Chattopadhyay Sudip , Chaudhuri Rajat K.
Published: July 2008

In view of the initial success of the complete active space (CAS) based size-extensive state-specific multireference perturbation theory (SS-MRPT) [J. Phys. Chem. A 103, 1822 (1999)] for relatively diverse yet simple chemically interesting systems, in this paper, we present the computation of the potential energy curves (PEC) of systems with arbitrary complexity and generality such as HF, H2O, H2S, C2, and N2 molecules. The ground states of such systems (and also low-lying singlet excited states of C2) possess multireference character making the description of the state difficult with single-reference (SR) methods. In this paper, we have considered the Møller–Plesset (MP) partitioning scheme [SS-MRPT(MP)] method. The accuracy of energies generated via SS-MRPT(MP) method is tested through comparison with other available results. Comparison with FCI has also been provided wherever available. The accuracy of this method is also demonstrated through the calculations of NPE (nonparallelism error) and the computation of the spectroscopic constants of all the above mentioned systems. The quality of the computed spectroscopic constants is established through comparison with the corresponding experimental and FCI results. Our numerical investigations demonstrate that the SS-MRPT(MP) approach provides a balanced treatment of dynamical and non-dynamical correlations across the entire PECs of the systems considered.
Observation of the nd Δ1g (n=6, 7, and 8) Rydberg states of Na2 by optical-optical double resonance spectroscopy: L uncoupling and perturbations
Authors: Chaudhuri Chanchal , Chang Ray-Yuan , Tsai Chin-Chun , Cheng Chuen-Ping , Whang Thou-Jen
Published: July 2008

The nd Δ1g (n=6, 7, and 8) Rydberg states of Na2 correlating with the asymptotic limits of Na(3s)+Na(nd) have been observed using high-resolution cw optical-optical double resonance spectroscopy corresponding to the rovibrational transitions X Σ1g+(v″,J″)+hνpump→B Π1u(v′,J′)+hνprobe→nd Δ1g(v,J). Totals of 104, 83, and 45 identified rovibrational e/f-parity levels in the ranges of v=0–11, 11≤J≤83; v=0–10, 11≤J≤83; and v=0–10, 11≤J≤65, have been assigned to the 6d Δ1g, 7d Δ1g, and 8d Δ1g states, respectively. Using the observed quantum levels, molecular constants were determined from the Dunham fits of the e-parity levels and the Rydberg–Klein–Rees potential curves were constructed for the nd Δ1g(n=6–8) states. The characteristics of the estimated Λ-doubling splitting constants (q0, qv, and μ) with n(=5–8) of the nd Δ1g series have been explored. Detailed investigations reveal that the nd Δ1g(n=6–8) states involve L uncoupling from the internuclear axis and each of these states is affected by an asymmetric perturbation caused by the up and down adjacent states. The rotational-branch intensity and position anomalies in the observed spectra of the nd Δ1g series (n=5–8) of Na2 lead to the conclusion that due to the effects of the L-uncoupling perturbations, the same l complexes approaching the same ion-core limits result in the same l-mixing processes which lead to the formation of the supercomplexes due to the anisotropy of the molecular-ion [Na2+(3s)] field. This would open up opportunities to study the effects of L uncoupling and perturbations in the nd series and high Rydberg states of other alkali dimers.
Uniform and stable field emission from printed carbon nanotubes through oxygen trimming
Authors: Kim Yong C. , Nam J. W. , Hwang M. I. , Kim I. H. , Lee C. S. , Choi Y. C. , Park J. H. , Kim H. S. , Kim Jong M.
Published: July 2008

When carbon nanotube field emitters are operated, a few highly protruded ones generate most of the emission currents that cause spatial nonuniformity and fast decay in lifetime behavior. We present a cost-effective means to solve this problem using selective oxidation on those nanotubes emitting higher currents, which is assisted by Joule heating generated during field emission. Our simple technique is potentially useful for the field emission devices such as display, backlight, x-ray tube, and others using multiple carbon nanotube emitters.
Room temperature ferromagnetism and ferroelectricity in cobalt-doped LiNbO3 film
Authors: Song C. , Wang C. Z. , Yang Y. C. , Liu X. J. , Zeng F. , Pan F.
Published: July 2008

( 5 at. % ) cobalt-doped LiNbO3 (Co:LN) films were prepared by combinatorial laser molecular-beam epitaxy on Si (100). The Co:LN films with Co2+ replacing Nb exhibit room temperature ferromagnetism of 1.2μB∕Co and Curie temperature of ∼540K. Through a Ag∕Co:LN∕Si metal-ferroelectric-semiconductor field effect transistor configuration, ferroelectric measurements show that the films display hysteresis loops at 300K and ferroelectric transition temperature of ∼610K. The hysteresis and the asymmetry in capacitance-voltage and leakage-voltage curves are ascribed to trapping/detrapping process of charges at the Co:LN/Si interface. The coexistence of room temperature ferromagnetism and ferroelectricity makes Co:LN a promising single-phase multiferroic.
Relation between magnetoresistance and nanostructure of current-perpendicular-to-plane giant-magnetoresistance film with current-confined-path nano-oxide layer
Authors: Yuasa Hiromi , Hara Michiko , Fukuzawa Hideaki
Published: July 2008

Nanostructure of a current-perpendicular-to-plane giant-magnetoresistance film with a current-confined-path (CCP) nano-oxide layer was analyzed by high-resolution transmission electron microscopy and three-dimensional atom probe. It was found that the CCP of a film with a higher magnetoresistance (MR) ratio has better crystalline orientation and higher purity than the CCP of a film with a smaller MR ratio. Moreover, the free layer on the CCP of a film with a high MR ratio is well crystallized. Both the CCP with the good crystalline orientation and high purity and the well-crystallized free layer diminish the diffusive electron scattering, which improves an MR ratio.
First principles molecular dynamics study of CdS nanostructure temperature-dependent phase stability
Authors: Wen Bin , Melnik Roderick V. N.
Published: July 2008

First principles molecular dynamics simulations are used to determine the relative stability of wurtzite, graphitic, and rocksalt phases of the CdS nanostructure at various temperatures. Our results indicate that in the temperature range from 300to450K, the phase stability sequence for the CdS nanostructure is rocksalt, wurtzite, and graphitic phases. The same situation holds for bulk CdS crystals under high pressure and 0K. Our work also demonstrates that although the temperature can affect the total energy of the CdS nanostructure, it cannot change its phase stability sequence in the temperature range studied in this letter.
The steady structures of dust voids in electronegative plasmas
Authors: Zheng Xiang , Gan Baoxia , Hu Zuquan , Huang Feng , Shi Guifen , Chen Yinhua
Published: July 2008

The steady structures of dust voids in electronegative plasmas for different ionization rates are investigated using fluid theory. The effects of the concentration of negative ions in plasmas on the distributions of the electric field and the potential in the region of voids as well as Mach number are analyzed numerically. The results show that when the ionization rate is lower, the steady structures do not appear. With an increase of the ionization rate, the steady structures can be formed. The latter are affected by the concentration of the negative ions. With increasing negative ions, the potential decays, and the Mach number as well as the electric field increases. It is also found that increasing both the concentration of the negative ions and the ionization rate can gives rise to contraction of the steady void structures.
Effect of metallic buffer layers on the antiphase boundary density of epitaxial Fe3O4
Authors: Magen C. , Snoeck E. , Lüders U. , Bobo J. F.
Published: July 2008

We report a strong variation of the magnetic properties and of the antiphase boundaries (APBs) density of Fe3O4(001) epitaxial thin films grown on thin Fe(001) and Cr(001) buffer layers on a MgO(001) substrate in comparison with similar magnetite films grown directly on MgO(001). The magnetization of the Fe∕Fe3O4 and Cr∕Fe3O4 bilayers presents a more squared hysteresis loop and reach saturation at much lower magnetic field (∼10–15kOe) than the Fe3O4 thin films of same thickness, which hardly saturate at 70kOe. The magnetization of the magnetite layers has been estimated on both the Fe- and Cr-based samples and a value close to that of the bulk Fe3O4 has been obtained, which points to the magnetic saturation of the Fe3O4 layer induced by the metallic buffers. Transmission electron microscopy has been used to investigate the possible structural origin of this phenomenon studying the APB network of Fe3O4 in the three types of samples. The calculation of the average domain size reveals that the APB density in the bilayers is substantially reduced in comparison with their counterparts without buffer. The domain sizes obtained in Fe and Cr samples are similar, which points to a structural origin probably due to the strain caused by the lattice misfit between the buffers and the magnetite. A lower APB density statistically reduces the influence of the antiferromagnetic interactions existing across some of the boundaries, achieving the saturation of the Fe3O4 layer at much lower magnetic fields.
Transverse vibrations driven negative thermal expansion in a metallic compound GdPd3B0.25C0.75
Authors: Pandey Abhishek , Mazumdar Chandan , Ranganathan R. , Tripathi S. , Pandey D. , Dattagupta S.
Published: July 2008

We have observed negative thermal expansion (NTE) in a metallic, polycrystalline, and structurally ordered cubic compound GdPd3B0.25C0.75. Our analysis suggest that the NTE observed in this compound does not stems from valence or magnetic instability of lattice ions, which is in general the case of metallic compounds exhibiting such an anomaly. We propose a possible alternative mechanism, namely, the transverse vibrations at low temperatures arising from site anisotropy, that induce the lattice contraction thereby resulting in isotropic NTE. The observed NTE also reflects its effect on the electrical transport properties of this compounds.
Influence of bismuth incorporation on the valence and conduction band edges of GaAs1−xBix
Authors: Pettinari G. , Polimeni A. , Capizzi M. , Blokland J. H. , Christianen P. C. M. , Maan J. C. , Young E. C. , Tiedje T.
Published: July 2008

We investigate the electronic properties of GaAs1−xBix by photoluminescence at variable temperature (T=10–430K) and high magnetic field (B=0–30T). In GaAs0.981Bi0.019, localized state contribution to PL is dominant up to 150K. At T=180K the diamagnetic shift of the free-exciton states reveals a sizable increase in the carrier effective mass with respect to GaAs. Such an increase cannot be accounted for by an enhanced localized character of the valence band states, solely. Instead, it suggests that also the Bloch states of the conduction band are heavily affected by the presence of bismuth atoms.
Effects of hydrogen on the optical properties of ZnCdO∕ZnO quantum wells grown by molecular beam epitaxy
Authors: Buyanova I. A. , Wang X. J. , Pozina G. , Chen W. M. , Lim W. , Norton D. P. , Pearton S. J. , Osinsky A. , Dong J. W. , Hertog B.
Published: July 2008

Temperature-dependent cw- and time-resolved photoluminescence (PL), as well as optically detected magnetic resonance (ODMR) measurements are employed to evaluate effects of deuterium (2H) doping on optical properties of ZnCdO∕ZnO quantum well structures grown by molecular beam epitaxy. It is shown that incorporation of H2 from a remote plasma causes a substantial improvement in radiative efficiency of the investigated structures. Based on transient PL measurements, the observed improvements are attributed to efficient passivation by hydrogen of competing nonradiative recombination centers via defects. This conclusion is confirmed from the ODMR studies.
Effective thermostat induced by coarse graining of simple point charge water
Authors: Eriksson Anders , Jacobi Martin Nilsson , Nyström Johan , Tunstrøm Kolbjørn
Published: July 2008

We investigate how the transport properties of a united atom fluid with a dissipative particle dynamics thermostat depend on the functional form and magnitude of both the conservative and the stochastic interactions. We demonstrate how the thermostat strongly affects the hydrodynamics, especially diffusion, viscosity, and local escape times. As model system we use simple point charge (SPC) water, from which projected trajectories are used to determine the effective interactions in the united atom model. The simulation results support our argument that the thermostat should be viewed as an integral part of the coarse-grained dynamics rather than a tool for approaching thermal equilibrium. As our main result we show that the united atom model with the adjusted effective interactions approximately reproduces the diffusion constant and the viscosity of the underlying detailed SPC water model.
The importance of polarizability in the modeling of solubility: Quantifying the effect of solute polarizability on the solubility of small nonpolar solutes in popular models of water
Authors: Dyer Peter J. , Docherty Hugh , Cummings Peter T.
Published: July 2008

In recent work by Paschek [J. Chem. Phys. 120, 6674 (2004)] and others [see H. Docherty et al., J. Chem. Phys. 125, 074510 (2006) for a review] it has been suggested that, when coupled to a simple Lennard-Jones model for various small nonpolar solute molecules, the most common models of water (e.g., SPC/E and TIP4P) fail to reproduce quantitatively the solubility of small nonpolar solute molecules in water due in part to failing to account for polarization of the solute molecule. Given the importance of such systems as test-case prototype models of the solubility of proteins and biomolecules, in this work, we investigate the impact of using a polarizable solute model with the SPC/E, TIP3P, TIP4P, TIP4P-Ew, and TIP4P/2005 rigid water models. Specifically we consider Ne, Ar, Kr, Xe, and methane as solutes. In all cases we observe that the use of a polarizable solute improves agreement between experiment and simulations, with the best agreement seen for the largest solutes, Kr, CH4, and Xe and the modern reparametrizations of the TIP4P model, i.e., the TIP4P-Ew and TIP4P/2005 models.
Transport properties of Mie(14,7) fluids: Molecular dynamics simulation and theory
Authors: Eskandari Nasrabad Afshin , Oghaz Nader Mansoori , Haghighi Behzad
Published: July 2008

An extensive computer simulation study is presented for the self-diffusion coefficient, the shear viscosity, and the thermal conductivity of Mie(14,7) fluids. The time-correlation function formalism of Green–Kubo is utilized in conjunction with molecular dynamics (MD) simulations. In addition to molecular simulations, the results of a recent study [A. Eskandari Nasrabad, J. Chem. Phys. 128, 154514 (2008)] for the mean free volume are applied to calculate the self-diffusion coefficients within a free volume theory framework. A detailed comparison between the MD simulation and free volume theory results for the diffusion coefficient is given. The density fluctuation theory of shear viscosity is used to compute the shear viscosity and the results are compared to those from MD simulations. The density and temperature dependences of different time-correlation functions and transport coefficients are studied and discussed.
Viewing-angle controllable liquid crystal display using a fringe- and vertical-field driven hybrid aligned nematic liquid crystal
Authors: Jeong Eun , Lim Young Jin , Chin Mi Hyung , Kim Jin Ho , Lee Seung Hee , Ji Seung Hoon , Lee Gi-Dong , Park Kyoung Ho , Choi Hyun Chul , Ahn Byung Chul
Published: July 2008

Viewing-angle controllable liquid crystal display (LCD) without using an additional panel or pixel division is proposed. In the device, hybrid aligned nematic liquid crystal using a liquid crystal with negative dielectric anisotropy is used. The device shows narrow viewing angle when it is driven only by fringe-electric field, however, it exhibits wide viewing angle if driven by vertical- as well as fringe-electric field. With the approach, the viewing angle of the LCD can be controlled from 120° to 20° in horizontal direction.
Femtosecond real-time probing of transition state dynamics in a surface photoreaction: Methyl desorption from CH3I on MgO(100)
Authors: Vaida Mihai E. , Hindelang Peter E. , Bernhardt Thorsten M.
Published: July 2008

A novel experimental approach to the investigation of surface adsorbate reaction dynamics is presented. The direct time-resolved monitoring of the surface reaction transition state and product formation dynamics were accomplished via pump-probe mass spectrometry. As an example, methyl iodide molecules adsorbed at submonolayer coverage on an ultrathin magnesia film on Mo(100) were photoexcited to the A-band by ultrafast laser pulse irradiation. Employing time-delayed multiphoton ionization the dynamics of the dissociative methyl iodide transition state and of the emerging methyl photoproduct could be detected with femtosecond resolution. The reaction times deduced from the temporal evolution of the methyl ion mass signal indicate a strong interaction of the methyl fragment with the substrate surface prior to desorption.
A practical method to avoid bond crossing in two-dimensional dissipative particle dynamics simulations
Authors: Liu Hong , Xue Yao-Hong , Qian Hu-Jun , Lu Zhong-Yuan , Sun Chia-Chung
Published: July 2008

Dissipative particle dynamics (DPD) simulation technique is an effective method targeted on mesoscopic simulations in which the interactions between particles are soft. As a result, it inevitably causes bond crossing and interpenetration between particles. Here we develop a practical method based on the two-dimensional DPD model which can extremely reduce the possibility of bond crossing. A rigid core is added to each particle by modifying the form of the conservative force in DPD so that the particles cannot penetrate each other. Then by adjusting the spring constant of the bond, we can impose a simple geometry constraint so that the bond crossing can hardly take place. Furthermore, we take into account an analytic geometry constraint in the polymerization model of DPD by which we can successfully avoid the severe bond crossing problem during bond generation in two dimensions. A parabola fitting between the pressure and the particle number density shows that our modified DPD model with small rigid cores can still be mapped onto the Flory–Huggins model, and the mesoscopic length scale of our simulations does not change. By analyzing the mean-square displacement of the innermost monomer and the center of mass of the chains, we find a t8/15 power law of the polymer dynamics in our model instead of the Rouse prediction supporting the recent results in literature.
Enhanced characteristics of blue InGaN∕GaN light-emitting diodes by using selective activation to modulate the lateral current spreading length
Authors: Lin Ray-Ming , Lu Yuan-Chieh , Chou Yi-Lun , Chen Guo-Hsing , Lin Yung-Hsiang , Wu Meng-Chyi
Published: July 2008

We have studied the characteristics of blue InGaN∕GaN multiquantum-well light-emitting diodes (LEDs) after reducing the length of the lateral current path through the transparent layer through formation of a peripheral high-resistance current-blocking region in the Mg-doped GaN layer. To study the mechanism of selective activation in the Mg-doped GaN layer, we deposited titanium (Ti), gold (Au), Ti∕Au, silver, and copper individually onto the Mg-doped GaN layer and investigated their effects on the hole concentration in the p-GaN layer. The Mg-doped GaN layer capped with Ti effectively depressed the hole concentration in the p-GaN layer by over one order of magnitude relative to that of the as-grown layer. This may suggest that high resistive regions are formed by diffusion of Ti and depth of high resistive region from the p-GaN surface depends on the capped Ti film thickness. Selective activation of the Mg-doped GaN layer could be used to modulate the length of the lateral current path. Furthermore, the external quantum efficiency of the LEDs was improved significantly after reducing the lateral current spreading length. In our best result, the external quantum efficiency was 52.3% higher (at 100mA) than that of the as-grown blue LEDs.
Controlled in situ boron doping of short silicon nanowires grown by molecular beam epitaxy
Authors: Das Kanungo Pratyush , Zakharov Nikolai , Bauer Jan , Breitenstein Otwin , Werner Peter , Goesele Ulrich
Published: July 2008

Epitaxial silicon nanowires (NWs) of short heights (∼280nm) on Si ⟨111⟩ substrate were grown and doped in situ with boron on a concentration range of 1015–1019cm−3 by coevaporation of atomic Si and B by molecular beam epitaxy. Transmission electron microscopy revealed a single-crystalline structure of the NWs. Electrical measurements of the individual NWs confirmed the doping. However, the low doped (1015cm−3) and medium doped (3×1016 and 1×1017cm−3) NWs were heavily depleted by the surface states while the high doped (1018 and 1019cm−3) ones showed volume conductivities expected for the corresponding intended doping levels.
Efficient quantum calculations of vibrational states of vinylidene in full dimensionality: A scheme with combination of methods
Authors: Li Bin , Bian Wensheng
Published: July 2008

Full-dimensional quantum calculations of vibrational states of C2H2 and C2D2 are performed in the high-energy region (above 20400cm−1 relative to the acetylene minimum). The theoretical scheme is a combination of several methods. To exploit the full parity and permutation symmetry, the CC–HH diatom-diatom Jacobi coordinates are chosen; phase space optimization in combination with physical considerations is used to obtain an efficient radial discrete variable representation, whereas a basis contraction scheme is applied for angular coordinates. The preconditioned inexact spectral transform method combined with an efficient preconditioner is employed to compute eigenstates within a desired spectral window. The computation is efficient. More definite assignments on vinylidene states than previous studies are acquired using the normal mode projection; in particular, a consistent analysis of the ν1 (symmetric CH stretch) state is provided. The computed vinylidene vibrational energy levels are in general good agreement with experiment, and several vinylidene states are reported for the first time.
Intense upconversion and infrared emissions in Er3+–Yb3+ codoped Lu2SiO5 and (Lu0.5Gd0.5)2SiO5 crystals
Authors: Han Lin , Song Feng , Chen Shu-Qi , Zou Chang-Guang , Yu Xiao-Chen , Tian Jian-Guo , Xu Jun , Xu Xiao-dong , Zhao Guang-jun
Published: July 2008

High optical quality Lu2SiO5 (LSO) and (Lu0.5Gd0.5)2SiO5 (LGSO) laser crystals codoped with Er3+ and Yb3+ have been fabricated by the Czochralski method. Intense upconversion (UC) and infrared emission (1543nm) are observed under excitation of 975nm. The luminescence processes are explained and the emission efficiencies are quantitatively obtained by measuring the UC efficiency and calculating the emission cross section. The temperature-dependent optical properties of the crystals are also investigated. Our study indicates that Er3+–Yb3+:LSO and Er3+–Yb3+:LGSO crystals are promising gain media for developing the solid-state 1.5μm optical amplifiers and tunable UC lasers.
Preparation of nanochain and nanosphere by self-assembly of gold nanoparticles
Authors: Fang C. , Fan Y. , Kong J. M. , Gao Z. Q. , Balasubramanian N.
Published: July 2008

A self-assembly method is demonstrated to link nanoparticles into nanostructure of nanochain or nanosphere. Gold nanoparticles were covered with capping molecules by forming Au–S bonds with thiol group at one terminate. Another terminating group, carboxylic acid, showed strong complex interaction with inorganic linker Zr4+ to form covalent complex bond. The different nanostructures were obtained by moving a balance between two opposite interactions, the linking interaction of Zr4+ and the electrostatic repulsive interaction of net surface charge. When the capping molecule with different chain length was used, the linked nanochain feature exhibited a tunable interdistance between the neighboring nanoparticles.
Passivation effects on ZnO nanowire field effect transistors under oxygen, ambient, and vacuum environments
Authors: Song Sunghoon , Hong Woong-Ki , Kwon Soon-Shin , Lee Takhee
Published: July 2008

We investigated the passivation effects on the electrical characteristics of ZnO nanowire field effect transistors (FETs) under the various oxygen environments of ambient air, dry O2, and vacuum. When the ZnO nanowire FET was exposed to more oxygen, the current decreased and the threshold voltage shifted to the positive gate bias direction, due to electrons trapping to the oxygen molecules at the nanowire surface. On the contrary, the electrical properties of the nanowire FET remained unchanged under different environments with passivation by a polymethyl methacrylate layer, which demonstrates the importance of surface passivation for ZnO nanowire-based electronic device applications.
Electrothermal actuation based on carbon nanotube network in silicone elastomer
Authors: Chen L. Z. , Liu C. H. , Hu C. H. , Fan S. S.
Published: July 2008

The authors report an electrothermal actuator, which is fabricated by involving carbon nanotube network into the silicone elastomer. The actuators exhibit excellent performances as good as normal dielectric elastomer actuators while working under much lower voltages (e.g., 1.5Vmm−1). They are longitudinal actuators and there is no need for stacking or rolling sheets of materials. In addition, they can satisfy the demand of different voltage applications ranging from dozens of voltages to thousands of voltages by using different carbon nanotube loading composites. Visible maximal strain of 4.4% occurs at an electric power intensity around 0.03Wmm−3.
Dependence of field-effect mobility and contact resistance on nanostructure in regioregular poly(3-hexylthiophene) thin film transistors
Authors: Singh K. A. , Sauvé G. , Zhang R. , Kowalewski T. , McCullough R. D. , Porter L. M.
Published: July 2008

The mobility and contact resistance of transistors based on regioregular poly(3-hexylthiophene) (P3HT) with Ti∕Pt electrodes were investigated as a function of the molecular weight (MW) of P3HT. For an increase in MW from 5.5to11kDa, the mobility increased from 0.04to0.16cm2V−1s−1, whereas the contact resistance decreased from 1.7to0.6MΩ. Further increases in MW yielded an apparent saturation in both the mobility and the contact resistance. A nanofibrilar morphology was observed where the width of the nanofibrils increases with MW. A qualitative model based on polymer chain folding is proposed to explain the electrical results.
Cesium hydroxide doped tris-(8-hydroxyquinoline) aluminum as an effective electron injection layer in inverted bottom-emission organic light emitting diodes
Authors: Xiong Tao , Wang Fengxia , Qiao Xianfeng , Ma Dongge
Published: July 2008

We demonstrate highly efficient inverted bottom-emission organic light-emitting diodes (IBOLEDs) by using cesium hydroxide (CsOH) doped tris-(8-hydroxyquinoline) aluminum (Alq3) as the electron injection layer on indium tin oxide cathode, which could significantly enhance the electron injection, resulting in a large increase in luminance and efficiency. The maximum luminance, current efficiency, and power efficiency reach 21000cd∕cm2, 6.5cd∕A, and 3.5lm∕W, respectively, which are 40%–50% higher in efficiency than that of IBOLEDs with cesium carbonate (Cs2CO3) doped Alq3 as the electron injection layer, where the efficiencies are only 4.5cd∕A and 2.2lm∕W. Our results indicate that CsOH doped Alq3 should be an effective electron injection layer on a wide range of electrodes to fabricate high performance OLEDs.
Efficient electrical detection of ambipolar acoustic transport in GaAs
Authors: Batista P. D. , Hey R. , Santos P. V.
Published: July 2008

We demonstrate a photon detector combining the ambipolar transport of electrons and holes by surface acoustic waves with electrical charge detection using a lateral p-i-n junction. By optimizing photon absorption and the acoustic transport, overall quantum efficiencies of 70% have been achieved for ambipolar transport lengths exceeding 100μm.
Optical limiting properties of silver nanoprisms
Authors: Polavarapu Lakshminarayana , Xu Qing-Hua , Dhoni Mohan S. , Ji Wei
Published: July 2008

We report exceptional optical limiting properties of two kinds of Ag nanoprisms (pure Ag nanoprisms and Au@Ag core-shell nanoprisms) in solution that were photochemically prepared. Fluence-dependent transmittance measurements using 7ns laser pulses of 532nm wavelength showed that the optical limiting properties of two kinds of silver nanoprisms in solution are slightly better than that of carbon nanotube suspensions, which is known as a benchmark optical limiter. Nonlinear scattering experiments suggested that nonlinear scattering should play an important role in the observed optical limiting effects.
Epitaxial growth and surface metallic nature of LaNiO3 thin films
Authors: Tsubouchi K. , Ohkubo I. , Kumigashira H. , Matsumoto Y. , Ohnishi T. , Lippmaa M. , Koinuma H. , Oshima M.
Published: July 2008

In situ epitaxial growth control of LaNiO3 (LNO) films at high oxygen pressure has been successfully achieved using a combination of pulsed laser deposition and high-pressure reflection high-energy electron diffraction (RHEED). RHEED oscillations, indicative of epitaxial layer-by-layer growth, were clearly observed during LNO deposition under optimal conditions. The film surfaces were composed of atomically flat terraces and steps. Detailed photoelectron spectroscopy analysis of LNO grown at the optimal oxygen pressure revealed that Ni ions assume a uniform Ni3+ high-valence state and that the resultant metallic properties are preserved even at the surface and in the interface region between LNO and the LaAlO3 substrate.
Stable response to visible light of InGaN photoelectrodes
Authors: Luo Wenjun , Liu Bin , Li Zhaosheng , Xie Zili , Chen Dunjun , Zou Zhigang , Zhang Rong
Published: July 2008

The photoelectrochemical properties of InxGa1−xN∕GaN (0⩽x⩽0.20) epitaxial films on sapphire (0001) substrates have been investigated. The flatband potential of InxGa1−xN is shifted to more positive voltages with increasing indium incorporation. In aqueous HBr solution, the turnover number of the In0.20Ga0.80N electrode reaches 847 after 4000s illumination, which suggests that In0.20Ga0.80N has good photostability. Moreover, In0.20Ga0.80N shows highest visible-light response among InxGa1−xN (0⩽x⩽0.20) and the incident photon conversion efficiency is about 9% at 400–430nm in the HBr solution.
Spin-torque oscillator with tilted fixed layer magnetization
Authors: Zhou Yan , Zha C. L. , Bonetti S. , Persson J. , Åkerman Johan
Published: July 2008

A spin-torque oscillator with a fixed layer magnetization tilted out of the film plane is capable of strong microwave signal generation in zero magnetic field. Through numerical simulations, we study the microwave signal generation as a function of drive current for two realistic tilt angles. The tilted magnetization of the fixed layer can be achieved by using a material with high out-of-plane magnetocrystalline anisotropy, such as L10 FePt.
UV survey finds 40% of the baryons missing from the nearby universe
Authors: Day Charles
Published: July 2008

Most baryons exist in the near vacuum between clusters of galaxies. Accounting for all the baryons continues to challenge astronomers.
Statistical mechanics elucidates constraints on the ultimate accuracy of biochemical sensing
Authors: Day Charles
Published: July 2008

Some biochemical interactions are akin to detecting a sporadic signal against a noisy background.
Passenger jets collect data for research on climate change and pollution
Authors: Feder Toni
Published: July 2008

Next time you settle in for a long flight, consider that instruments for sampling the outside air for atmospheric research may also be on board.
DOE urged to proceed more deliberately with global plan to expand nuclear power
Authors: Kramer David
Published: July 2008

Critics of the Global Nuclear Energy Partnership say the Department of Energy is rushing to commercialize unproven technologies.
Social networks link interdisciplinary scientists
Authors: Matthews Jermey N.A.
Published: July 2008

Analysis of social networks has become a many-body problem, attracting physicists and uniting once-divergent disciplines.
Grand challenges in basic energy sciences
Authors: Fleming Graham R. , Ratner Mark A.
Published: July 2008

Research focused in five related areas will allow unprecedented control over the microscopic world and could be the key to a sustainable future
Designing payments for ecosystem services: Lessons from previous experience with incentive-based mechanisms
Authors: Jack B. Kelsey , Kousky Carolyn , Sims Katharine R. E.
Published: July 2008

Payments for ecosystem services (PES) policies compensate individuals or communities for undertaking actions that increase the provision of ecosystem services such as water purification, flood mitigation, or carbon sequestration. PES schemes rely on incentives to induce behavioral change and can thus be considered part of the broader class of incentive- or market-based mechanisms for environmental policy. By recognizing that PES programs are incentive-based, policymakers can draw on insights from the substantial body of accumulated knowledge about this class of instruments. In particular, this article offers a set of lessons about how the environmental, socioeconomic, political, and dynamic context of a PES policy is likely to interact with policy design to produce policy outcomes, including environmental effectiveness, cost-effectiveness, and poverty alleviation.
Efficiency of incentives to jointly increase carbon sequestration and species conservation on a landscape
Authors: Nelson Erik , Polasky Stephen , Lewis David J. , Plantinga Andrew J. , Lonsdorf Eric , White Denis , Bael David , Lawler Joshua J.
Published: July 2008

We develop an integrated model to predict private land-use decisions in response to policy incentives designed to increase the provision of carbon sequestration and species conservation across heterogeneous landscapes. Using data from the Willamette Basin, Oregon, we compare the provision of carbon sequestration and species conservation under five simple policies that offer payments for conservation. We evaluate policy performance compared with the maximum feasible combinations of carbon sequestration and species conservation on the landscape for various conservation budgets. None of the conservation payment policies produce increases in carbon sequestration and species conservation that approach the maximum potential gains on the landscape. Our results show that policies aimed at increasing the provision of carbon sequestration do not necessarily increase species conservation and that highly targeted policies do not necessarily do as well as more general policies.
Ecological and socioeconomic effects of China's policies for ecosystem services
Authors: Liu Jianguo , Li Shuxin , Ouyang Zhiyun , Tam Christine , Chen Xiaodong
Published: July 2008

To address devastating environmental crises and to improve human well-being, China has been implementing a number of national policies on payments for ecosystem services. Two of them, the Natural Forest Conservation Program (NFCP) and the Grain to Green Program (GTGP), are among the biggest programs in the world because of their ambitious goals, massive scales, huge payments, and potentially enormous impacts. The NFCP conserves natural forests through logging bans and afforestation with incentives to forest enterprises, whereas the GTGP converts cropland on steep slopes to forest and grassland by providing farmers with grain and cash subsidies. Overall ecological effects are beneficial, and socioeconomic effects are mostly positive. Whereas there are time lags in ecological effects, socioeconomic effects are more immediate. Both the NFCP and the GTGP also have global implications because they increase vegetative cover, enhance carbon sequestration, and reduce dust to other countries by controlling soil erosion. The future impacts of these programs may be even bigger. Extended payments for the GTGP have recently been approved by the central government for up to 8 years. The NFCP is likely to follow suit and receive renewed payments. To make these programs more effective, we recommend systematic planning, diversified funding, effective compensation, integrated research, and comprehensive monitoring. Effective implementation of these programs can also provide important experiences and lessons for other ecosystem service payment programs in China and many other parts of the world.
Autophagy is an adaptive response in desmin-related cardiomyopathy
Authors: Tannous Paul , Zhu Hongxin , Johnstone Janet L. , Shelton John M. , Rajasekaran Namakkal S. , Benjamin Ivor J. , Nguyen Lan , Gerard Robert D. , Levine Beth , Rothermel Beverly A. , Hill Joseph A.
Published: July 2008

A missense mutation in the αB-crystallin (CryAB) gene triggers a severe form of desmin-related cardiomyopathy (DRCM) characterized by accumulation of misfolded proteins. We hypothesized that autophagy increases in response to protein aggregates and that this autophagic activity is adaptive. Mutant CryAB (CryAB
R120G
) triggered a >2-fold increase in cardiomyocyte autophagic activity, and blunting autophagy increased the rate of aggregate accumulation and the abundance of insoluble CryAB
R120G
-associated aggregates. Cardiomyocyte-restricted overexpression of CryAB
R120G
in mice induced intracellular aggregate accumulation and systolic heart failure by 12 months. As early as 2 months (well before the earliest declines in cardiac function), we detected robust autophagic activity. To test the functional significance of autophagic activation, we crossed CryAB
R120G
mice with animals harboring heterozygous inactivation of
beclin 1
, a gene required for autophagy. Blunting autophagy
in vivo
dramatically hastened heart failure progression with a 3-fold increase in interstitial fibrosis, greater accumulation of polyubiquitinated proteins, larger and more extensive intracellular aggregates, accelerated ventricular dysfunction, and early mortality. This study reports activation of autophagy in DRCM. Further, our findings point to autophagy as an adaptive response in this proteotoxic form of heart disease.
The
RPG
gene of
Medicago truncatula
controls
Rhizobium
-directed polar growth during infection
Authors: Arrighi Jean-François , Godfroy Olivier , de Billy Françoise , Saurat Olivier , Jauneau Alain , Gough Clare
Published: July 2008

Rhizobia can infect roots of host legume plants and induce new organs called nodules, in which they fix atmospheric nitrogen. Infection generally starts with root hair curling, then proceeds inside newly formed, intracellular tubular structures called infection threads. A successful symbiotic interaction relies on infection threads advancing rapidly at their tips by polar growth through successive cell layers of the root toward developing nodule primordia. To identify a plant component that controls this tip growth process, we characterized a symbiotic mutant of
Medicago truncatula
, called
rpg
for rhizobium-directed polar growth. In this mutant, nitrogen-fixing nodules were rarely formed due to abnormally thick and slowly progressing infection threads. Root hair curling was also abnormal, indicating that the
RPG
gene fulfils an essential function in the process whereby rhizobia manage to dominate the process of induced tip growth for root hair infection. Map-based cloning of
RPG
revealed a member of a previously unknown plant-specific gene family encoding putative long coiled-coil proteins we have called RRPs (RPG-related proteins) and characterized by an “RRP domain” specific to this family.
RPG
expression was strongly associated with rhizobial infection, and the RPG protein showed a nuclear localization, indicating that this symbiotic gene constitutes an important component of symbiotic signaling.
Divergent sodium channel defects in familial hemiplegic migraine
Authors: Kahlig Kristopher M. , Rhodes Thomas H. , Pusch Michael , Freilinger Tobias , Pereira-Monteiro José M. , Ferrari Michel D. , van den Maagdenberg Arn M. J. M. , Dichgans Martin , George Alfred L.
Published: July 2008

Familial hemiplegic migraine type 3 (FHM3) is a severe autosomal dominant migraine disorder caused by mutations in the voltage-gated sodium channel Na
V
1.1 encoded by
SCN1A
. We determined the functional consequences of three mutations linked to FHM3 (L263V, Q1489K, and L1649Q) in an effort to identify molecular defects that underlie this inherited migraine disorder. Only L263V and Q1489K generated quantifiable sodium currents when coexpressed in tsA201 cells with the human β
1
and β
2
accessory subunits. The third mutant, L1649Q, failed to generate measurable whole-cell current because of markedly reduced cell surface expression. Compared to WT-Na
V
1.1, Q1489K exhibited increased persistent current but also enhanced entry into slow inactivation as well as delayed recovery from fast and slow inactivation, thus resulting in a predominantly loss-of-function phenotype further demonstrated by a greater loss of channel availability during repetitive stimulation. In contrast, L263V exhibited gain-of-function features, including delayed entry into, as well as accelerated recovery from, fast inactivation; depolarizing shifts in the steady-state voltage dependence of fast and slow inactivation; increased persistent current; and delayed entry into slow inactivation. Notably, the two mutations (Q1489K and L1649Q) that exhibited partial or complete loss of function are linked to typical FHM, whereas the gain-of-function mutation L263V occurred in a family having both FHM and a high incidence of generalized epilepsy. We infer from these data that a complex spectrum of Na
V
1.1 defects can cause FHM3. Our results also emphasize the complex relationship between migraine and epilepsy and provide further evidence that both disorders may share common molecular mechanisms.