bluuebunny/crossref_metadata_2025 huggingface dataset:
The generalized active space concept in multiconfigurational self-consistent field methods
Authors: Ma Dongxia , Li Manni Giovanni , Gagliardi Laura
Published: August 2011

A multiconfigurational self-consistent field method based on the concept of generalized active space (GAS) is presented. GAS wave functions are obtained by defining an arbitrary number of active spaces with arbitrary occupation constraints. By a suitable choice of the GAS spaces, numerous ineffective configurations present in a large complete active space (CAS) can be removed, while keeping the important ones in the CI space. As a consequence, the GAS self-consistent field approach retains the accuracy of the CAS self-consistent field (CASSCF) ansatz and, at the same time, can deal with larger active spaces, which would be unaffordable at the CASSCF level. Test calculations on the Gd atom, Gd2 molecule, and oxoMn(salen) complex are presented. They show that GAS wave functions achieve the same accuracy as CAS wave functions on systems that would be prohibitive at the CAS level.
Role of magnesium in band gap engineering of sub-monolayer type-II ZnTe quantum dots embedded in ZnSe
Authors: Zhang Qiang , Shen Aidong , Kuskovsky Igor L. , Tamargo Maria C.
Published: August 2011

Modification of the bandgap of sub-monolayer type-II ZnTe quantum dots (QDs), by means of direct incorporation of magnesium in the QDs, is reported. Nitrogen co-doped QDs embedded in a ZnSe matrix have been grown by a migration-enhanced molecular beam epitaxy technique. Incorporation of Mg in the ZnTe QDs decreases the valence band discontinuity, leading to reduced localization of the holes, which results in a higher electrical conductivity in the samples as deduced from the Hall effect measurements. The type-II alignment of the bands in the QDs is supported by intensity dependent and time-resolved photoluminescence measurements. Hall effect measurements indicate that the material has p-type conductivity with mid-1015 carriers/cm3 and hole mobilities in the 5–50 cm2/V·s range.
Direct magnetocaloric measurements of Fe-B-Cr-X (X = La, Ce) amorphous ribbons
Authors: Law J. Y. , Franco V. , Ramanujan R. V.
Published: August 2011

A procedure has been developed to directly measure the adiabatic temperature change of amorphous melt-spun Fe-based ribbons displaying attractive room temperature magnetocaloric properties. Polycrystalline Gd ribbons are used as a reference material to compensate for the contribution of the sample holder to the experimental values. Fe78B12Cr8Ce2 and Fe75B12Cr8Ce5 melt-spun ribbons exhibited a peak adiabatic temperature change (ΔTadpk) ∼ 58% larger than Co82.9Si5.9Fe4.5Cr4B2.7 amorphous ribbons. The ΔTadpk in Fe78B12Cr8Ce2, Fe75B12Cr8Ce5, and Fe79B12Cr8La1 ribbons displayed ∼ 18-33% enhanced ΔTadpk compared to a GdAl2 alloy.
A full-dimensional coupled-surface study of the photodissociation dynamics of ammonia using the multiconfiguration time-dependent Hartree method
Authors: Giri Kousik , Chapman Emma , Sanz Cristina Sanz , Worth Graham
Published: August 2011

Full-dimensional quantum mechanical computations are carried out to investigate the photodissociation dynamics of \documentclass[12pt]{minimal}\begin{document}$\tilde{A}$\end{document}Ã state NH3 and ND3 using the multiconfiguration time-dependent Hartree (MCTDH) method with recently developed coupled ab initio potential energy surfaces (PESs) [Z. H. Li, R. Valero, and D. G. Truhlar, Theor. Chim. Acc. 118, 9 (2007)10.1007/s00214-006-0237-7]. To use the MCTDH method efficiently the PESs are represented as based on the high-dimensional model representation. The \documentclass[12pt]{minimal}\begin{document}$\tilde{A}$\end{document}Ã ← \documentclass[12pt]{minimal}\begin{document}$\tilde{X}$\end{document}X̃ absorption spectra for both isotopomers were calculated for the zeroth vibrational state of the ground electronic state. With a view to treating larger systems, Jacobi coordinates are used. Computations on the coupled PES are carried out for two-, three-, five-, and six-dimensional model systems to understand the validity of reduced-dimensional calculations. In addition to the fully coupled calculations, the effect of nonadiabatic coupling on absorption spectra is shown by propagating the initial wavepacket only in the \documentclass[12pt]{minimal}\begin{document}$\tilde{A}$\end{document}Ã electronic state. The calculated absorption spectra are shown to be in good agreement with available theoretical and experimental observations. Comparisons with calculations using Radau and valence coordinates show the effect of including the symmetry of the system explicitly. Finally, branching ratios for loss of a hydrogen atom via the two available channels are calculated. These predict that the nonadiabatic product increases with the dimension of the calculations and confirm the importance of the full-dimensional calculations.
True-green (11-22) plane optically pumped laser with cleaved m-plane facets
Authors: Sizov Dmitry , Bhat Rajaram , Heberle Albert , Visovsky Nick , Zah Chung-en
Published: August 2011

We present a detailed experimental study of optical property of green InGaN quantum wells and optically pumped lasers, with cleaved m-plane facets and a lasing wavelength in the range of 520-530 nm, grown on semipolar (11-22) planes. Taking advantage of low transparency carrier density of the lowest-energy valence band and overcoming low differential gain by minimizing the optical loss of the laser structure, we demonstrated a low threshold pumping power of 120 mW.
Electron beam energy and Ge nanocrystal size effects on the minority carrier diffusion length measured by the nano-electron beam induced current technique
Authors: Doan Quang-Tri , El Hdiy Abdelillah , Troyon Michel
Published: August 2011

The near-field electron beam induced current technique is used to study the minority carrier effective diffusion length versus electron beam energy on structures containing spherical Ge nanocrystals (NCs) with diameters of 50 nm and 70 nm formed by a two step dewetting/nucleation process. For both nanocrystal sizes, the effective diffusion length increases with the electron beam energy and then decreases from a threshold energy, which depends on the nanocrystal size. The effective diffusion length is smaller at low energy for NCs of larger size because of their larger surface recombination velocity, due to a better charge trapping efficiency.
Signal transfer in a chain of stray-field coupled ferromagnetic squares
Authors: Vogel Andreas , Martens Michael , Weigand Markus , Meier Guido
Published: August 2011

We study the vortex-core dynamics in a chain of three stray-field coupled permalloy squares. Time-resolved scanning transmission x-ray microscopy is employed to image the out-of-plane magnetization of the cores. After exciting the first element via a short in-plane magnetic field pulse, the excitation can be transferred through the chain via dipolar interaction. The transfer efficiency of the gyrotropic vortex motion strongly depends on the configuration of the core polarizations. For alternating polarizations, a transfer efficiency of about 56% to the third square is achieved. The chain can be switched back and forth between the transmitting and a locking state.
Role of surface vibration modes in Si nanocrystals within light emitting porous Si at the strong confinement regime
Authors: Mahdouani M. , Gardelis S. , Nassiopoulou A. G.
Published: August 2011

In this work, we study theoretically the resonant coupling between longitudinal optical surface vibrations of Si-OH and/or Si-O-Si and electron and hole states in the silicon nanocrystals (Si NCs) within light emitting porous Si (PSi) thin films in the framework of the Fröhlich interaction. The results of this analysis are compared with experimental results, which show considerable enhancement and a redshift of the photoluminescence (PL) spectrum of a fresh as-grown PSi thin film after prolonged laser irradiation or after aging in air. These effects coincide with the formation of Si-OH and Si-O-Si bonds on the surface of PSi. The redshift of the PL spectrum is due to the pinning of the bandgap of the light emitting Si NCs, as both oxidation via laser irradiation in air and aging in air introduce energy states in the Si NC band gaps. According to the theoretical analysis, the PL enhancement is assigned to inhibition of nonradiative channels rather than to an enhancement of radiative channels in the Si NCs within the PSi film, due to a strong coupling of the surface Si-OH and/or Si-O-Si vibrational modes to the electronic sublevels in the Si NCs within the PSi layer.
Perspective: The dawning of the age of graphene
Authors: Flynn George W.
Published: August 2011

Graphene is a single sheet of carbon atoms that constitutes the basic building block of macroscopic graphite crystals. Held together by a backbone of overlapping sp2 hybrids, graphene's 2p orbitals form π state bands that delocalize over an entire 2-dimensional macroscopic carbon sheet leading to a number of unusual characteristics that include large electrical and thermal conductivities. Recent discoveries have provided simple methods (e.g., mechanical cleavage of graphite) for preparing laboratory scale samples that can be used to investigate the fundamental physical and chemical characteristics of graphene. In addition, a number of techniques have emerged that show promise for producing large-scale samples with the ultimate goal of developing devices that take advantage of graphene's unusual properties. As large samples become available, the possibility grows for applications of this material in solar cell technology (as flexible, transparent electrodes), in composite material development, and in electronic devices.
Interferometry-based Kolsky bar apparatus
Authors: Avinadav C. , Ashuach Y. , Kreif R.
Published: August 2011

A new experimental approach of the Kolsky bar system using optical interferometry is presented for determination of dynamic behavior of materials. Conventional measurements in the Kolsky bar system are based on recording the strain histories on the incident and transmitter bars with two strain gauges, and require good adhesion between the gauge and the bar. We suggest an alternative approach, based on measuring the actual velocities of the bars by using fiber-based velocity interferometry. Two fiber focusers illuminate the bars at a small angle and collect reflected Doppler-shifted light, which is interfered with a reference beam. Velocities are calculated from short-time Fourier transform and phase-based analysis, and the dynamic stress-strain curve is derived directly from the measured velocity traces. We demonstrate that the results coincide with those obtained by conventional strain gauge measurements. The new method is non-intervening and thus not affected by bar impacts, making it more robust and reliable than strain gauges.
Soft carrier multiplication by hot electrons in graphene
Authors: Girdhar Anuj , Leburton J. P.
Published: August 2011

By using the Boltzmann formalism, we show that carrier multiplication by impact ionization can take place at relatively low electric fields during electronic transport in graphene. Because of the absence of an energy gap, this effect is not characterized by a field threshold but is a quadratic function of the electric field, unlike in conventional semiconductors. We also show that the resulting current is an increasing function of the electronic temperature but decreases with increasing carrier concentration.
Thermal fluctuations of clusters with the long-range interaction
Authors: Zhukhovitskii D. I.
Published: August 2011

Analysis of surface fluctuation spectra is performed for a large cluster of particles interacting via a sum of the short-range Lennard-Jones potential and long-range ±1/r potential, where the positive sign corresponds to the gravity, and negative corresponds to the electrostatic interaction. The spectral amplitudes of thermally driven capillary modes in a self-consistent field induced by cluster particles including the modes with no axial symmetry are derived in the approximation of small amplitudes. It is demonstrated that within used approximation, the surface tension is independent of the field strength. The low wave vector amplitudes are damped by attracting field that compresses the cluster and magnified by repulsing field leading to cluster fission. The fission threshold is found to be different from that found by Bohr and Wheeler and Frenkel due to the replacement of the ordinary surface tension by the bare one. Molecular dynamics study of a cluster with the long-range interaction in the vapor environment is performed using a novel integrator for a multiscale system. Simulation scheme implies rotation of the long-range components of forces acting on cluster particles thus vanishing an artificial torque. Simulation results justify theoretical conclusion of modes damping and independence of the surface tension of the field strength. Fission threshold evaluated from simulation data is in a good agreement with theory.
A phase-synchronization and random-matrix based approach to multichannel time-series analysis with application to epilepsy
Authors: Osorio Ivan , Lai Ying-Cheng
Published: August 2011

We present a general method to analyze multichannel time series that are becoming increasingly common in many areas of science and engineering. Of particular interest is the degree of synchrony among various channels, motivated by the recognition that characterization of synchrony in a system consisting of many interacting components can provide insights into its fundamental dynamics. Often such a system is complex, high-dimensional, nonlinear, nonstationary, and noisy, rendering unlikely complete synchronization in which the dynamical variables from individual components approach each other asymptotically. Nonetheless, a weaker type of synchrony that lasts for a finite amount of time, namely, phase synchronization, can be expected. Our idea is to calculate the average phase-synchronization times from all available pairs of channels and then to construct a matrix. Due to nonlinearity and stochasticity, the matrix is effectively random. Moreover, since the diagonal elements of the matrix can be arbitrarily large, the matrix can be singular. To overcome this difficulty, we develop a random-matrix based criterion for proper choosing of the diagonal matrix elements. Monitoring of the eigenvalues and the determinant provides a powerful way to assess changes in synchrony. The method is tested using a prototype nonstationary noisy dynamical system, electroencephalogram (scalp) data from absence seizures for which enhanced cortico-thalamic synchrony is presumed, and electrocorticogram (intracranial) data from subjects having partial seizures with secondary generalization for which enhanced local synchrony is similarly presumed.
Second virial coefficient for the dipolar hard sphere fluid
Authors: Henderson Douglas
Published: August 2011

The dipolar hard sphere fluid is a useful model for a polar fluid. Some years ago, the second virial coefficient, B2, of this fluid was obtained as a series expansion in the inverse temperature or (dipole strength) by Keesom. Little work on this problem seems to have been done since that time. Using a result of Chan and Henderson for the spherical average of the Boltzmann factor of this fluid, more complete results are obtained for B2. The more complete results are more negative than the Keesom series, as one would expect, but his expansion is remarkably accurate. This method can be used to obtain the second virial coefficient of the dipolar Lennard-Jones (Stockmayer) or dipolar Yukawa fluids.
Temperature induced transition from hexagonal to circular pits in graphite oxidation by O2
Authors: Delehouzé Arnaud , Rebillat Francis , Weisbecker Patrick , Leyssale Jean-Marc , Epherre Jean-Francois , Labrugère Christine , Vignoles Gérard L.
Published: August 2011

We report on an in-situ monitoring of graphite oxidation using a high temperature environmental scanning electron microscope. A morphological transition is clearly identified around 1040 K between hexagonal pits at low temperatures and circular pits at high temperatures, with apparently no change in the kinetic law. A kinetic Monte Carlo model allows rationalizing these findings in terms of the competitive oxidation of armchair and zig-zag edge sites and provides an estimate of the rate laws associated to these two events. Extended to three dimensions, the model also explains the “in-depth” transition between the stepwise hexagons and the hemispheres observed by atomic force microscopy.
Reconfigurable gradient index using VO2 memory metamaterials
Authors: Goldflam M. D. , Driscoll T. , Chapler B. , Khatib O. , Marie Jokerst N. , Palit S. , Smith D. R. , Kim Bong-Jun , Seo Giwan , Kim Hyun-Tak , Ventra M. Di , Basov D. N.
Published: August 2011

We demonstrate tuning of a metamaterial device that incorporates a form of spatial gradient control. Electrical tuning of the metamaterial is achieved through a vanadium dioxide layer which interacts with an array of split ring resonators. We achieved a spatial gradient in the magnitude of permittivity, writeable using a single transient electrical pulse. This induced gradient in our device is observed on spatial scales on the order of one wavelength at 1 THz. Thus, we show the viability of elements for use in future devices with potential applications in beamforming and communications.
Enhanced phase stabilization of CoPt in the presence of Ag
Authors: Sehdev Neeru , Medwal Rohit , Annapoorni S.
Published: August 2011

We report the synthesis of CoPt and CoPt–Ag nanoparticles by the simultaneous reduction of platinum(II) acetylacetonate (Pt(acac)2), cobalt(II)acetylacetonate (Co(acac)2), and silver nitrate (AgNO3) (for CoPt–Ag) in the presence of poly(N-vinyl-2-pyrrolidone) (PVP). Here the changes in the structural and magnetic properties of these nanoparticles subjected to heat treatment and the effect of adding silver to CoPt in comparison to pure CoPt have been investigated. TEM observations reveal a narrow size distribution with particle diameter of about 2–3 nm. The XRD studies reveal a disordered fcc phase for the as synthesized nanoparticles which after annealing at higher temperatures show peaks corresponding to an ordered L10 phase. The structural phase transition is also followed by enhanced magnetic properties. The magnetic measurements show the transition of a magnetically soft alloy to a magnetically hard material with a maximum coercivity of ∼1 T after annealing at 700 °C. The addition of silver (Ag) to CoPt alloy induces a reduction in the ordering temperature by 100 °C compared to pure CoPt, with an increased coercivity of 1.2 T. Such thermally stable and structurally ordered hard magnetic nanoparticles are promising candidates for magnetic storage applications.
Efficient calculation of α- and β-nitrogen free energies and coexistence conditions via overlap sampling with targeted perturbation
Authors: Tan Tai Boon , Schultz Andrew J. , Kofke David A.
Published: August 2011

A recently introduced solid-phase free-energy calculation method that is based upon overlap sampling with targeted free-energy perturbation is further developed and extended to systems with orientational degrees of freedom. Specifically we calculate the absolute free energy of the linear-molecular nitrogen model of Etter et al., examining both the low-temperature low-pressure α-N2 structure and the orientationally disordered β-N2 phase. In each perturbation (for the α-N2 phase) to determine the free-energy difference between systems at adjacent temperatures, harmonic coordinate scaling is applied to both the translational and rotational degrees of freedom in the nitrogen molecule to increase the phase-space overlap of the two perturbing systems and consequently, improve the free-energy difference results. For the plastic β-N2 phase, a novel method that requires several perturbation paths is introduced to calculate its absolute free energy. Through these methods, the absolute free energies for both the α-N2 and β-N2 phase can be accurately and precisely determined. We find again that the anharmonic contribution to the free energy has weak dependence on system size. The transition properties for the α-N2 and β-N2 phase are also investigated. The α-β phase transition for the model at atmospheric pressure (0.1 MPa) is found to occur at 40.35 ± 0.01 K with volumetric and entropy changes of 0.44 ± 0.01 cm3/mol and 1.99 ± 0.01 cal/mol.K respectively.
Spin transistor based on T-shaped graphene junctions
Authors: Li Hang , Chen Yuan Ping , Xie Yue E. , Zhong JianXin
Published: August 2011

We propose a spin device based on a T-shaped graphene junction (TGJ) in which a ferromagnetic insulator and a metallic gate are deposited on the sidearm. Spin transport properties of the TGJ are studied by using the Green’s function method. It is found that spin-polarized transport can be achieved both far away from and near the Dirac point. The spin polarization far away from the Dirac point is correlated with the quasi-bound states in the junction, while the spin polarization near the Dirac point is due to the destruction of edge states. By varying the strength of the potential, i.e., the gate voltage on the sidearm, the spin polarization can be tuned quasi-periodically from −100% to 100%. In addition, the size of the sidearm also shows obvious influence on the spin polarization of TGJ.
Dewetting growth of crystalline water ice on a hydrogen saturated Rh(111) surface at 135 K
Authors: Beniya Atsushi , Koitaya Takanori , Mukai Kozo , Yoshimoto Shinya , Yoshinobu Jun
Published: August 2011

We investigated the water (D2O) adsorption at 135 K on a hydrogen pre-adsorbed Rh(111) surface using temperature programmed desorption and infrared reflection absorption spectroscopy (IRAS) in ultrahigh vacuum. With increasing the hydrogen coverage, the desorption temperature of water decreases. At the saturation coverage of hydrogen, dewetting growth of water ice was observed: large three-dimensional ice grains are formed. The activation energy of water desorption from the hydrogen-saturated Rh(111) surface is estimated to be 51 kJ/mol. The initial sticking probability of water decreases from 0.46 on the clean surface to 0.35 on the hydrogen-saturated surface. In IRAS measurements, D-down species were not observed on the hydrogen saturated surface. The present experimental results clearly show that a hydrophilic Rh(111) clean surface changes into a hydrophobic surface as a result of hydrogen adsorption.
Energy maps, side chain conformational flexibility, and vibrational features of polar amino acids L-serine and L-threonine in aqueous environment
Authors: Hernández Belén , Pflüger Fernando , Adenier Alain , Nsangou Mama , Kruglik Sergei G. , Ghomi Mahmoud
Published: August 2011

A comprehensive description of the energetic, conformational, and vibrational features of the two amino acids (AAs) with polar side chains, i.e., serine and threonine, in aqueous environment, is provided. To adequately analyze the side chain conformational flexibility of these amino acids, we resorted to quantum mechanical calculations with the use of density functional theory, which allowed the determination of the energetic features of these AAs through 236 clusters. Each cluster contains a zwitterionic AA surrounded by seven explicit water molecules. The obtained data could evidence the effect of the side chain conformational angle (χ1 and χ2) as well as the location of water molecules on the energy landscapes of both AAs. Four of the lowest energy clusters of each AA, which give rise to distinct side chain conformations, were selected in order to reproduce the FT-IR and Raman spectra recorded in aqueous solutions and to assign the vibrational modes responsible of the main observed bands.
Role of oxygen-bonds in the degradation process of phosphorescent organic light emitting diodes
Authors: de Moraes Ines Rabelo , Scholz Sebastian , Lüssem Björn , Leo Karl
Published: August 2011

For improving the lifetime of organic light emitting diodes (OLEDs), it is essential to understand the chemical reaction pathways involved in the degradation process of these devices. Using the laser desorption/ionization time-of-flight mass spectrometry (LDI-TOF-MS) technique, an OLED based on the phosphorescent emitter tris(phenylpyridine)iridium (Ir(ppy)3) was investigated. We show that the chemical dissociation reaction of the Ir(ppy)3 molecule and an additional complexation of its fragments with the used hole blocking material 4,7-diphenyl-1,10-phenanthroline is the main intrinsic degradation mechanism. This finding underlines the exciton induced dissociation mechanism of phosphorescent emitters, even at emitters without any metal-oxygen-bonds in the ligand system.
The effect of Bi composition to the optical quality of GaAs1−xBix
Authors: Mohmad A. R. , Bastiman F. , Hunter C. J. , Ng J. S. , Sweeney S. J. , David J. P. R.
Published: August 2011

GaAs1−xBix alloys grown by molecular beam epitaxy for x up to 0.06 were studied by photoluminescence (PL). The results indicate that dilute fractions of bismuth (Bi) with x < 0.025 improve the material quality of this low temperature growth alloys by reducing the density of gallium (Ga) and/or arsenic related defects. The crystal quality starts to degrade at higher Bi concentration probably due to significant amount of Bi-related defects, BiGa. However, the room temperature PL intensity continues to increase with Bi content for the range studied due to greater band-gap offset between GaAs and GaAs1−xBix. Analysis carried out shows no correlation between localization effects and the room temperature PL enhancement.
Transparent, flexible, ultrathin sound source devices using Indium Tin oxide films
Authors: Tian He , Xie Dan , Yang Yi , Ren Tian-Ling , Wang Yu-Feng , Zhou Chang-Jian , Peng Ping-Gang , Wang Li-Gang , Liu Li-Tian
Published: August 2011

Thermoacoustic effects were observed in 100-nm indium tin oxide (ITO) films. The sound emission from the ITO films was measured as a function of power, distance, and frequency. Significant flat and wide frequency responses occurred between 20 and 50 kHz. The sound pressure and efficiency were in good agreement with theoretical results. This indicates that a thermoacoustic effect exists in metal-oxide materials and that a large family of transparent electrode materials may exhibit similar properties. Using the ultrathin, transparent, and flexible characteristics, we showed promising applications of ITO sound source devices that were integrated with liquid crystal display screens.
An optical magnetic metamaterial working at multiple frequencies simultaneously
Authors: Li Qiuze , Lin Weihua , Wang Guo Ping
Published: August 2011

We theoretically design and experimentally demonstrate a multilayered optical magnetic metamaterial working at multiple frequencies simultaneously. The metamaterial is constructed with tapered ellipsoidal metal-dielectric-metal particles (EMDMPs), which is obtained through alternately depositing multiple layers of Ag and SiO2 films on a dielectric template of ellipsoidal nanohole arrays created by holographic lithography and lift-off procedure. Transmission and reflection spectra measurements reveal that the metamaterial exhibits multiband magnetic resonances at near infrared due to the size variation of EMDMPs in depositing and lift-off procedures. Our results may prove a step towards the construction of realistic metamaterials for various photonics applications.
On the temperature dependence of electron leakage from the active region of GaInN/GaN light-emitting diodes
Authors: Meyaard David S. , Shan Qifeng , Dai Qi , Cho Jaehee , Schubert E. Fred , Kim Min-Ho , Sone Cheolsoo
Published: August 2011

Reduction in the light-output power in GaN-based light-emitting diodes (LEDs) with increasing temperature is a well-known phenomenon. In this work, temperature dependent external-quantum-efficiency versus current curves are measured, and the mechanisms of recombination are discussed. Shockley-Read-Hall recombination increases with temperature and is found to greatly reduce the light output at low current densities. However, this fails to explain the drop in light-output power at high current densities. At typical current density (35 A/cm2), as temperature increases, our results are consistent with increased Shockley-Read-Hall recombination and increased electron leakage from the active region. Both of these effects contribute to the reduction in light-output power in GaInN/GaN LEDs at high temperatures.
Accelerating the L1 ordering transition of FePt(001) nanograins using composite buffer layers
Authors: Li Guoqing , Zheng Yuanping , Hayashi Kenichi , Takanashi Koki
Published: August 2011

This paper reports fabrication of 2-nm-thick L10 FePt films at a low substrate temperature of 400 °C using composite MgO and FeAl buffer layers on (001) MgO substrates. The FeAl buffer layer is crucial in promoting the ordered L10 growth of (001) FePt by allowing additional heat uptake. The MgO buffer layer prevents interlayer diffusion of FeAl into the FePt films and induces (001) texture growth. The deposited FePt films consist of isolated nanograins about 13 nm in size. These films have (001) texture and perpendicular magnetic anisotropy with a coercivity of up to 19 kOe. They have potential applications in perpendicular magnetic recording.
Giant magnetoresistance in zigzag graphene nanoribbon
Authors: Wang Z. F. , Liu Feng
Published: August 2011

Based on the mean-field Hubbard model (J. Guo et al., Appl. Phys. Lett. 92, 163109 (2008)), ballistic spin transport in zigzag graphene nanoribbons is investigated theoretically. A giant magnetoresistance effect is found with 100% change in resistance as the two transverse electrodes switch from the parallel to antiparallel magnetic configuration. Such change is shown to arise from different coupling between the subbands near the Fermi level, which is dependent of the orbital symmetry. In addition, the operating energy window of giant magnetoresistance exists in a wide range of ribbon widths, easing the way for experimental validation of the proposed device.
Giant electric field controlled magnetic anisotropy in epitaxial BiFeO3-CoFe2O4 thin film heterostructures on single crystal Pb(Mg1/3Nb2/3)0.7Ti0.3O3 substrate
Authors: Wang Zhiguang , Yang Yaodong , Viswan Ravindranath , Li Jiefang , Viehland D.
Published: August 2011

We have deposited self-assembled BiFeO3 (BFO)-CoFe2O4 (CFO) thin films on Pb(Mg1/3Nb2/3)0.7Ti0.3O3 (PMN-PT) substrates and studied the change in magnetic anisotropy under different strain conditions induced by an applied electric field. After electric field poling, we observed (i) giant magnetization change: magnetization of original CFO phase is three times larger than that of strained one and (ii) magnetic force microscopy line profiles that exhibited significant change in the CFO magnetic domain response in accordance to magnetization-field (M-H) loops. Together, these results demonstrate good control of the magnetic properties of CFO via an electric field induced strain.
Optical frequency signal detection through surface plasmon polaritons
Authors: Aihara Takuma , Nakagawa Kyohei , Fukuhara Masashi , Ling Yu Yen , Yamaguchi Kenzo , Fukuda Mitsuo
Published: August 2011

We demonstrated experimentally that an optical frequency signal can be detected through surface plasmon polaritons (SPPs) using an optical heterodyne technique. We fabricated an SPP detector consisting of a Au/Si Schottky diode with seven 10-μm-long and 150-nm-wide parallel slits (a multi-slit grating). When two beams of light with slightly different wavelengths irradiated the multi-slit grating of the SPP detector, a beat signal, corresponding to the optical frequency signal, was clearly observed.
Light-addressable electrodeposition of cell-encapsulated alginate hydrogels for a cellular microarray using a digital micromirror device
Authors: Huang Shih-Hao , Hsueh Hui-Jung , Jiang Yeu-Long
Published: August 2011

This paper describes a light-addressable electrolytic system used to perform an electrodeposition of calcium alginate hydrogels using a digital micromirror device (DMD). In this system, a patterned light illumination is projected onto a photoconductive substrate serving as a photo-anode to electrolytically produce protons, which can lead to a decreased pH gradient. The low pH generated at the anode can locally release calcium ions from insoluble calcium carbonate (CaCO3) to cause gelation of calcium alginate through sol-gel transition. By controlling the illumination pattern on the DMD, a light-addressable electrodeposition of calcium alginate hydrogels with different shapes and sizes, as well as multiplexed micropatterning was performed. The effects of the concentration of the alginate and CaCO3 solutions on the dimensional resolution of alginate hydrogel formation were experimentally examined. A 3 × 3 array of cell-encapsulated alginate hydrogels was also successfully demonstrated through light-addressable electrodeposition. Our proposed method provides a programmable method for the spatiotemporally controllable assembly of cell populations into cellular microarrays and could have a wide range of biological applications in cell-based biosensing, toxicology, and drug discovery.
Accurate measurement of sample conductivity in a diamond anvil cell with axis symmetrical electrodes and finite difference calculation
Authors: Yang Jie , Peng Gang , Han Yonghao , Gao Chunxiao
Published: August 2011

We report a relatively precise method of conductivity measurement in a diamond anvil cell with axis symmetrical electrodes and finite difference calculation. The axis symmetrical electrodes are composed of two parts: one is a round thin-film electrode deposited on diamond facet and the other is the inside wall of metal gasket. Due to the asymmetrical configuration of the two electrodes, finite difference method can be applied to calculate the conductivity of sample, which can reduce the measurement error.
Magnetic, dielectric and photo-absorption study of a ferromagnetic semiconductor α-Fe1.4Ga0.6O3
Authors: Naresh N. , Bhowmik R. N.
Published: August 2011

We report the synthesis of α-Fe1.4Ga0.6O3 compound and present its structural phase stability and interesting magnetic, dielectric and photo-absorption properties. In our work Ga doped α-Fe2O3 samples are well stabilized in α phase (rhombohedral crystal structure with space group R3C). Properties of the present composition of Ga doped α-Fe2O3 system are remarkably advanced in comparison with recently most studied FeGaO3 composition. At room temperature the samples are typical soft ferromagnet, as well as direct band gap semiconductor. Dielectric study showed low dielectric loss in the samples with large enhancement of ac conductivity at higher frequencies. Optical absorption in the visible range has been enhanced by 4 to 5%. This composition has exhibited large scope of tailoring room temperature ferromagnetic moment and optical band gap by varying grain size and non-ambient (vacuum) heat treatment of the as prepared samples by mechanical alloying.
High-resolution data demonstrate gravitational lensing of the cosmic microwave background
Authors: Miller Johanna L.
Published: August 2011

From the data’s statistical properties, researchers can determine that the background has been gravitationally distorted without their knowing where the distorting foreground structures are.
Nanodiamonds are promising quantum probes of living cells
Authors: Wilson R. Mark
Published: August 2011

Even in a complex electromagnetic environment, the spin of a single point defect in diamond can be used as a sensitive magnetometer.
Kinetic experiments shed light on protein-folding thermodynamics
Authors: Smart Ashley G.
Published: August 2011

Perturbing biomolecules and then watching them relax may be the kind and gentle way to determine their free-energy landscapes.
DOE looks hard at taking over deep underground site
Authors: Feder Toni
Published: August 2011

At stake is US leadership in the particle-physics intensity frontier.
Harnessing consumer mobile devices for science
Authors: Matthews Jermey N. A.
Published: August 2011

Researchers are exploring ways to utilize the sensors and software inside cell phones and mobile tablets.
NASA art: 50 years of exploration
Authors: Crouch Tom D.
Published: August 2011

For half a century, selected artists have been invited to express their visions of NASA’s undertakings. A new exhibit shares those visions with the public.
The enactive approach
Authors: Froese Tom , Di Paolo Ezequiel A.
Published: August 2011

There is a small but growing community of researchers spanning a spectrum of disciplines which are united in rejecting the still dominant computationalist paradigm in favor of the enactive approach. The framework of this approach is centered on a core set of ideas, such as autonomy, sense-making, emergence, embodiment, and experience. These concepts are finding novel applications in a diverse range of areas. One hot topic has been the establishment of an enactive approach to social interaction. The main purpose of this paper is to serve as an advanced entry point into these recent developments. It accomplishes this task in a twofold manner: (i) it provides a succinct synthesis of the most important core ideas and arguments in the theoretical framework of the enactive approach, and (ii) it uses this synthesis to refine the current enactive approach to social interaction. A new operational definition of social interaction is proposed which not only emphasizes the cognitive agency of the individuals and the irreducibility of the interaction process itself, but also the need for jointly co-regulated action. It is suggested that this revised conception of ‘socio-cognitive interaction’ may provide the necessary middle ground from which to understand the confluence of biological and cultural values in personal action.
Can robots have phobias?
Authors: Savage Tony
Published: August 2011

This paper evaluates the use of synthetic modeling to investigate the relationship between organic and artificial forms of behavioral mal-adaptability. In particular, it addresses the character of organic phobias and the issue of testing the validity of artificial models of these phobias. The two main accounts of organic phobias, the biological or evolutionary and the associative learning explanation, are used as the starting points of this exercise. The learning approach is explored in terms of a probability based model which uses a discrepancy mechanism to represent the artificial phobia, while the endogenous aspect of artificial phobias is discussed in terms of the potential offered by evolutionary learning. Several methods of assessing the construct validity of artificial phobias are outlined.
Algebraic independence of periods and logarithms of Drinfeld modules
Authors: Chang Chieh-Yu , Papanikolas Matthew
Published: August 2011

Let

ρ
\rho

be a Drinfeld

A
A

-module with generic characteristic defined over an algebraic function field. We prove that all of the algebraic relations among periods, quasi-periods, and logarithms of algebraic points on

ρ
\rho

are those coming from linear relations induced by endomorphisms of

ρ
\rho

.
Itération d’applications rationnelles dans les espaces de matrices
Authors: Cerveau Dominique , Déserti Julie
Published: August 2011

The iteration of rational maps is well understood in dimension

1
1

but less so in higher dimensions. We study some maps on spaces of matrices which present a weak complexity with respect to the ring structure. First, we give some properties of certain rational maps; the simplest example is the rational map which sends the matrix

M

\mathrm {M}

onto

M

2

\mathrm {M}^2

for which we exhibit some dynamical properties. Finally, we deal with some small perturbations of this map.
Characterization of the tunable response of highly strained compliant optical metamaterials
Authors: Pryce Imogen M. , Aydin Koray , Kelaita Yousif A. , Briggs Ryan M. , Atwater Harry A.
Published: August 2011

Metamaterial designs are typically limited to a narrow operating bandwidth that is predetermined by the fabricated dimensions. Various approaches have previously been used to introduce post-fabrication tunability and thus enable active metamaterials. In this work, we exploit the mechanical deformability of a highly compliant polymeric substrate to achieve dynamic, tunable resonant frequency shifts greater than a resonant linewidth. We investigate the effect of metamaterial shape on the plastic deformation limit of resonators. We find that, for designs in which the local strain is evenly distributed, the response is elastic under larger global tensile strains. The plastic and elastic limits of resonator deformation are explored and the results indicate that, once deformed, the resonators operate within a new envelope of elastic response. We also demonstrate the use of coupled resonator systems to add an additional degree of freedom to the frequency tunability and show that compliant substrates can be used as a tool to test coupling strength. Finally, we illustrate how compliant metamaterials could be used as infrared sensors, and show enhancement of an infrared vibration absorption feature by a factor of 225.
Local investigation of the optical properties of subwavelength rectangular holes with a focused beam of electrons
Authors: Prangsma J. C. , van Oosten D. , Kuipers L.
Published: August 2011

The optical properties of rectangular subwavelength holes in a gold film are investigated using the light generated when a focused beam of electrons impinges on the sample close to the hole. Using this technique, multi-spectral maps of the holes are obtained with a resolution beyond the optical diffraction limit. The results show the influence of hole shape on the spectrum of locally scattered light. Rectangular holes of varying shape and size are investigated, and the spatial distribution of the polarization of the observed light is measured. The influence of neighbouring holes is investigated by measuring small clusters of holes.
The genome as a life-history character: why rate of molecular evolution varies between mammal species
Authors: Bromham Lindell
Published: August 2011

DNA sequences evolve at different rates in different species. This rate variation has been most closely examined in mammals, revealing a large number of characteristics that can shape the rate of molecular evolution. Many of these traits are part of the mammalian life-history continuum: species with small body size, rapid generation turnover, high fecundity and short lifespans tend to have faster rates of molecular evolution. In addition, rate of molecular evolution in mammals might be influenced by behaviour (such as mating system), ecological factors (such as range restriction) and evolutionary history (such as diversification rate). I discuss the evidence for these patterns of rate variation, and the possible explanations of these correlations. I also consider the impact of these systematic patterns of rate variation on the reliability of the molecular date estimates that have been used to suggest a Cretaceous radiation of modern mammals, before the final extinction of the dinosaurs.
In Situ Hybridization to Polytene Chromosomes in Drosophila Using Tritium-Labeled Probes
Authors: Pardue Mary-Lou
Published: August 2011

INTRODUCTION

In situ hybridization to polytene chromosomes frequently is used to find the chromosomal site of a cloned DNA sequence, as well as to investigate the distribution of families of repeated sequences in the chromosome set and to measure the amount of a repeated sequence at different sites. These different experimental goals are best accomplished by variations of the technique. Quantitation of sequences at different chromosomal sites, for example, is best done using radioactive probes where the signal is measured directly from the bound probe, rather than after the one or two subsequent steps (e.g., antibody or streptavidin binding, enzymatic color production, etc.) that are required to detect nonradioactive probes. Tritium (3H) is by far the best radioisotope for in situ hybridization because of the very low energy of the beta particle that is emitted. These beta particles travel <1 µm through autoradiographic emulsion, giving a precise localization for the probe. In addition, 3H probes can reliably detect sequences on polytene chromosomes significantly shorter than those detected by nonradioactive probes. The simplest and most successful probes are made by random primer labeling of gel-purified fragments of cloned DNA. The DNA can be labeled while still in the gel slice or it can be purified with a minicolumn. This protocol describes a procedure for 3H labeling of DNA in agarose and for performing in situ hybridization using the resulting radiolabeled probe.
A synthesis of Cenozoic sedimentation in the North Sea
Authors: Anell Ingrid , Thybo Hans , Rasmussen Erik
Published: August 2011

The North Sea Basin contains an almost complete record of Cenozoic sedimentation, separated by clear regional unconformities. The changes in sediment characteristics, rate and source, and expression of the unconformities reflect the tectonic, eustatic and climatic changes that the North Sea and its margins have undergone. While the North Sea has been mapped locally, we present the first regional mapping of the Cenozoic sedimentary strata. Our study provides a new regional sub‐division of the main seismic units in the North Sea together with maps of depocentres, influx direction and source areas. Our study provides a regional synthesis of sedimentation based on a comprehensive interpretation of a regionally covering reflection seismic data set. We relate observations of sediment characteristics and unconformities to the geological evolution. The timing, regional expression and stratigraphic characteristics of many unconformities indicate that they were generated by eustatic sea‐level fall, often in conjunction with other processes. Early Cenozoic unconformities, however, relate to tectonism associated with the opening of the North Atlantic. From observation on a regional scale, we infer that the sediment influx into the North Sea during the Cenozoic is more complex than previously suggested clockwise rotation from early northwestern to late southern sources. The Shetland Platform supplied sediment continuously, although at varying rates, until the latest Cenozoic. Sedimentation around Norway changed from early Cenozoic influx from the southwestern margin, to almost exclusively from the southern margin in the Oligocene and from all of southern Norway in the latest Cenozoic. Thick Eocene deposits in the Central Graben are sourced mainly from a western and a likely southern source, indicating that prominent influx from the south did not only occur from the mid‐Miocene onwards. We infer a new age for the increased progradational sediment influx in the Pleistocene of 2.5 Ma, coeval with Fennoscandian glaciation.
Implementing Local Safeguarding Children Boards: managing complexity and ambiguity
Authors: Munro Emily R. , France Alan
Published: August 2011

Local Safeguarding Children Boards (LSCBs) were established under the Children Act 2004 and have responsibility for coordinating and ensuring the effectiveness of the work of partner bodies to safeguard and promote the welfare of children. Drawing on data from a Department for Children, Schools and Families and Department of Health‐funded evaluation, the paper examines the development of LSCBs and the challenges and issues that have been encountered by Boards in implementing new arrangements. In doing so, the paper contributes to current debates about some of the limitations of New Labour's safeguarding reforms as a vehicle for improving outcomes for children and families.