bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetized and collimated millimeter scale plasma jets with astrophysical relevance
Authors: Brady Parrish C. , Quevedo Hernan J. , Valanju Prashant M. , Bengtson Roger D. , Ditmire Todd
Published: February 2012

Magnetized collimated plasma jets are created in the laboratory to extend our understanding of plasma jet acceleration and collimation mechanisms with particular connection to astrophysical jets. In this study, plasma collimated jets are formed from supersonic unmagnetized flows, mimicking a stellar wind, subject to currents and magnetohydrodynamic forces. It is found that an external poloidal magnetic field, like the ones found anchored to accretion disks, is essential to stabilize the jets against current-driven instabilities. The maximum jet length before instabilities develop is proportional to the field strength and the length threshold agrees well with Kruskal-Shafranov theory. The plasma evolution is modeled qualitatively using MHD theory of current-carrying flux tubes showing that jet acceleration and collimation arise as a result of electromagnetic forces.
Amended conjecture on an upper bound to time-dependent space-charge limited current
Authors: Griswold M. E. , Fisch N. J. , Wurtele J. S.
Published: February 2012

Notwithstanding the recent conjecture that the upper bound on the time-averaged current across a space-charge-limited diode is equal to the steady state Child-Langmuir limit (JCL), Zhu and Ang used a one-dimensional (1D) particle in cell (PIC) code to show that in the regime where space charge effects limit the current to only a few electrons at a time, the time-averaged current can exceed JCL by up to 13% [Y. Zhu and L. K. Ang, Appl. Phys. Lett. 98, 051502 (2011)]. These results are, in fact, verified using our own 1D PIC code. However, the increase in the current is due to special boundary conditions that pertain in this regime and not to the time dependence of the current. To rule out discreteness effects, the conjecture on the upper bound may be reformulated to include only the case when the electric field at the cathode does not fall below zero.
Density dependence of capillary plasma on the pressure and applied voltage
Authors: Uhm Han S. , Jang Dong G. , Kim Min S. , Suk Hyyong
Published: February 2012

Based on a simple theoretical model, the density properties of the electrical discharge in a capillary plasma system are investigated in terms of the hydrogen pressure and applied voltage. The electron density in the capillary during the electrical discharge is calculated from a theoretical model and compared with experimental observations, providing valuable information pertaining to the ionization ratio and conductivity of discharge plasma. The electron density increases almost linearly with the applied voltage for a specified pressure. Meanwhile, the ionization ratio is inversely proportional to the square root of the hydrogen gas pressure.
Mg impurity in helium droplets
Authors: Navarro J. , Mateo D. , Barranco M. , Sarsa A.
Published: February 2012

Within the diffusion Monte Carlo approach, we have determined the structure of isotopically pure and mixed helium droplets doped with one magnesium atom. For pure 4He clusters, our results confirm those of Mella et al. [J. Chem. Phys. 123, 054328 (2005)10.1063/1.1982787] that the impurity experiences a transition from a surface to a bulk location as the number of helium atoms in the droplet increases. Contrarily, for pure 3He clusters Mg resides in the bulk of the droplet due to the smaller surface tension of this isotope. Results for mixed droplets are presented. We have also obtained the absorption spectrum of Mg around the 3s3p 1P1 ← 3s2 1S0 transition.
Infrared absorption by collisional H2–He complexes at temperatures up to 9000 K and frequencies from 0 to 20 000 cm−1
Authors: Abel Martin , Frommhold Lothar , Li Xiaoping , Hunt Katharine L. C.
Published: February 2012

Quantum chemical methods have been used elsewhere to obtain the potential energy surface (PES) and the induced dipole surface (IDS) of H2–He collisional complexes at eight different H–H bond distances, fifteen atom-molecule separations, and 19 angular orientations each [X. Li, A. Mandal, E. Miliordos, and K. L. C. Hunt, J. Chem. Phys. 136, 044320 (2012)]10.1063/1.3676406. An atom-molecule state-to-state scattering formalism is employed, which couples the collisional molecular complex to the electromagnetic radiation field. In this way, we obtain theoretical collision-induced absorption (CIA) spectra of H2–He complexes for frequencies from 0 to 20 000 cm−1 and temperatures up to 9000 K. The work is based on the fundamental theory and is motivated by current research of certain astronomical objects, such as cool white dwarf stars, cool main sequence stars, M dwarfs, exoplanets, so-called “first” stars. We compare our theoretical results to existing laboratory measurements of CIA spectra; very close agreement of theory and measurement is observed. We also discuss similar previous theoretical efforts.
Free energy landscapes for homogeneous nucleation of ice for a monatomic water model
Authors: Reinhardt Aleks , Doye Jonathan P. K.
Published: February 2012

We simulate the homogeneous nucleation of ice from supercooled liquid water at 220 K in the isobaric-isothermal ensemble using the MW monatomic water potential. Monte Carlo simulations using umbrella sampling are performed in order to determine the nucleation free energy barrier. We find the Gibbs energy profile to be relatively consistent with that predicted by classical nucleation theory; the free energy barrier to nucleation was determined to be ∼18 kBT and the critical nucleus comprised ∼85 ice particles. Growth from the supercooled liquid gives clusters that are predominantly cubic, whilst starting with a pre-formed subcritical nucleus of cubic or hexagonal ice results in the growth of predominantly that phase of ice only.
Stability and breakup of confined threads
Authors: Janssen P. J. A. , Meijer H. E. H. , Anderson P. D.
Published: February 2012

A boundary-integral method for periodic arrays of drops, threads or sheets between parallel walls is presented. The Green’s functions take the form of a far-field Hele-Shaw description, which is used to generate periodic Green’s functions for the parallel-wall configuration. The method is applied to study the effect of confinement on the breakup of threads. A comparison is made with classical Tomotika’s theory and growth rates parallel and perpendicular to the walls are determined as a function of confinement ratio. Contrary to existing belief, we find that confined threads are not stable, but that the time for breakup increases with confinement and viscosity ratio, at least for threads whose diameter is smaller than the wallspacing. We also show the in-phase and out-of-phase breakup for an array of threads, as well as the stabilizing effect of shear flow.
Numerical study of an 8 mm third-harmonic peniotron with a gradual reversal of the magnetic field
Authors: Wu Xinhui , Li Jiayin , Hu Biao , Zhao Xiaoyun , Li Tianming
Published: February 2012

A novel large-orbit electron gun with a gradual reversal of the magnetic field for the 8 mm third-harmonic peniotron is numerically studied in this paper. In the permanent magnetic condition, an electron beam with axial velocity spread of 4.78%, guiding center deviation of 7.18%, and velocity ratio of 2.2 is generated in the gun, satisfying the special requirements of beam-wave interaction in the third-harmonic peniotron. Compared with the traditional three stage method, it is unnecessary here to generate a thin tubular electron beam before the reversal point and the mutational distribution of reversal magnetic field. In addition, the emission band can be placed in the area of axial magnetic field where its magnitude decreases gradually, which reduces the structure complexity and the difficulties in tube-making process greatly. Finally, the peniotron is predicted to yield an output power of 31.9 kW at 30 GHz, with its microwave conversion efficiency of up to 49.4%, which shows the perfect matching between its high frequency system and its electron-optical system. According to the numerical calculations, the device performance is very sensitive to the relative axial position between the magnetic system and the electrode system. If the magnetic system shifts 0.8 mm to the right, the device efficiency would decrease from 49.4% to 31.7%. This phenomenon provides meaningful information in the device hot-test.
Inversion of a general hyperelliptic integral and particle motion in Hořava–Lifshitz black hole space-times
Authors: Enolski Victor , Hartmann Betti , Kagramanova Valeria , Kunz Jutta , Lämmerzahl Claus , Sirimachan Parinya
Published: February 2012

The description of many dynamical problems such as the particle motion in higher dimensional spherically and axially symmetric space-times is reduced to the inversion of hyperelliptic integrals of all three kinds. The result of the inversion is defined locally, using the algebro-geometric techniques of the standard Jacobi inversion problem and the foregoing restriction to the θ-divisor. For a representation of the hyperelliptic functions the Klein–Weierstraß multi-variable σ-function is introduced. It is shown that all parameters needed for the calculations such as period matrices and abelian images of branch points can be expressed in terms of the periods of holomorphic differentials and θ-constants. The cases of genus two, three, and four are considered in detail. The method is exemplified by the particle motion associated with genus one elliptic and genus three hyperelliptic curves. Applications are for instance solutions to the geodesic equations in the space-times of static, spherically symmetric Hořava–Lifshitz black holes.
Creating a high temperature environment at high pressure in a gas piston cylinder apparatus
Authors: Burnley P. C. , Getting I. C.
Published: February 2012

An internal heater capable of 1400 K has been developed for use with a gas piston cylinder apparatus capable of achieving in excess of 3 GPa with an argon pressure medium. The heated gas piston cylinder produces a truly hydrostatic environment for samples up to 3 mm in diameter and 8 mm in length. The apparatus can be used to study systems that are sensitive to stress or samples that cannot withstand shear tractions. The gas piston cylinder apparatus was developed in an effort to reduce experimental uncertainty in the pressure scale and has been used to improve understanding of the Bi I-II transition at 298 K. We estimate that the pressure during a high temperature soak in the gas piston cylinder can be known to within ±0.01 GPa.
Spectral approach to finite Reynolds number effects on Kolmogorov’s 4/5 law in isotropic turbulence
Authors: Tchoufag J. , Sagaut P. , Cambon C.
Published: February 2012

The Kolmogorov’s 4/5 law is often considered as the sole exact relationship of inertial range statistics. Its asymptotic character, however, has been evidenced, investigating the finite Reynolds number (FRN) effect for the third-order structure function S3(r) (e.g., for longitudinal velocity increments with r separation length) using variants of the Kármán-Howarth equation in physical space. Similar semi-empirical fits were proposed for the maximum of the normalized structure function, C3 = −maxrS3(r)/(ɛr), expressing C3 − 4/5 as a power law of the Taylor-based Reynolds number. One of the most complete studies in this domain is by Antonia and Burratini [J. Fluid Mech. 550, 175 (2006)]. Considering that these studies are based on a model for the unsteady second-order structure function S2(r,t), with no explicit model for the third-order structure function itself, we propose to revisit the FRN effect by a spectral approach, in the line of Qian [Phys. Rev. E 55, 337 (1997), Phys. Rev. E 60, 3409 (1999)]. The spectral transfer term T(k,t), from which S3(r,t) is derived by an exact quadrature, is directly calculated by solving the Lin equation for the energy spectrum E(k,t), closed by a standard triadic (or three-point) theory, here Eddy Damped Quasi Normal Markovian. We show that the best spectral approach to the FRN effect is found by separately investigating the negative (largest scales) and positive (smaller scales) bumps of the transfer term, and not only by looking at the maximum of the spectral flux or maxk∫k∞T(p,t)dp→ɛ. In the forced case, previous results are well reproduced, with Reynolds numbers as high as Reλ = 5 000 to nearly recover the 4/5 value. In the free decay case, the general trend is recovered as well, with an even higher value of Reλ = 50 000, but the EDQNM plots are systematically below those in Antonia and Burattini [J. Fluid Mech. 550, 175 (2006)]. This is explained by the sensitivity to initial data for E(k) in solving the Lin equation at moderate Reynolds numbers. Accordingly, an ad hoc initialization yields results consistent with the experimental spectrum measurements of Comte-Bellot and Corrsin [J. Fluid Mech. 48(2), 273 (1971)], from which S3(r) are recalculated. Present results show that the dispersion observed in existing data at low Reynolds number may be due to sensitivity to initial spectrum shape, a feature of the flow which is not under control in most of laboratory experiments.
Direct simulation Monte Carlo-based expressions for the gas mass flow rate and pressure profile in a microscale tube
Authors: Gallis M. A. , Torczynski J. R.
Published: February 2012

The direct simulation Monte Carlo (DSMC) method of Bird is used to develop simple closed-form expressions for the mass flow rate and the pressure profile for the steady isothermal flow of an ideal gas through a microscale tube connecting two infinite reservoirs at different pressures but at the temperature of the tube wall. Gas molecules reflect from the tube wall according to the Maxwell model (a linear combination of specular and diffuse reflections at the wall temperature) with a unity or sub-unity value of the accommodation coefficient (the probability that molecules reflect diffusely from the wall). The DSMC-based expressions have four parameters. Two parameters are specified so that the mass flow rate reduces to the known expression in the free-molecular regime. One parameter was previously determined by comparison to DSMC simulations in the slip regime. The remaining parameter is determined by comparison to DSMC simulations for pressures spanning the transition regime with several values of the accommodation coefficient. The expressions for the mass flow rate and the pressure profile agree well with the DSMC simulations (rms and maximum differences of 2% and 5% for all cases examined), with other more complicated expressions and with recent experiments involving microscale tubes and channels for all flow regimes.
Reynolds number effect on the velocity increment skewness in isotropic turbulence
Authors: Bos Wouter J. T. , Chevillard Laurent , Scott Julian F. , Rubinstein Robert
Published: February 2012

Second and third order longitudinal structure functions and wavenumber spectra of isotropic turbulence are computed using the eddy-damped quasi-normal Markovian model (EDQNM) and compared to results of the multifractal formalism. It is shown that both the multifractal model and EDQNM give power-law corrections to the inertial range scaling of the velocity increment skewness. For the multifractal formalism, this is an intermittency correction that persists at any high Reynolds number. For EDQNM, this correction is a finite Reynolds number effect, and it is shown that very high Reynolds numbers are needed for this correction to become insignificant with respect to intermittency corrections. Furthermore, the two approaches yield realistic behavior of second and third order statistics of the velocity fluctuations in the dissipative and near-dissipative ranges. Similarities and differences are highlighted, in particular, the Reynolds number dependence.
Effect of the range of repulsions on the existence of a stable liquid phase
Authors: Larsen Ryan J. , Zukoski Charles F.
Published: February 2012

Experimental and theoretical results have established that the range of the attraction plays a critical role in determining whether a particle system exhibits a stable liquid phase. Changes to the range of the repulsions can similarly affect the existence of a stable liquid phase; however, these effects have not been clearly elucidated. We demonstrate that an increase in the range of repulsions can either enhance or decrease the stability of the liquid phase, depending on the form of the interaction potential. For either case, the critical variable that controls the stability of the liquid phase is the ratio of the representative energies of the liquid and solid phases.
Solution-phase photochemistry of a [FeFe]hydrogenase model compound: Evidence of photoinduced isomerisation
Authors: Kania Rafal , Frederix Pim W. J. M. , Wright Joseph A. , Ulijn Rein V. , Pickett Christopher J. , Hunt Neil T.
Published: February 2012

The solution-phase photochemistry of the [FeFe] hydrogenase subsite model (μ-S(CH2)3S)Fe2(CO)4(PMe3)2 has been studied using ultrafast time-resolved infrared spectroscopy supported by density functional theory calculations. In three different solvents, n-heptane, methanol, and acetonitrile, relaxation of the tricarbonyl intermediate formed by UV photolysis of a carbonyl ligand leads to geminate recombination with a bias towards a thermodynamically less stable isomeric form, suggesting that facile interconversion of the ligand groups at the Fe center is possible in the unsaturated species. In a polar or hydrogen bonding solvent, this process competes with solvent substitution leading to the formation of stable solvent adduct species. The data provide further insight into the effect of incorporating non-carbonyl ligands on the dynamics and photochemistry of hydrogenase-derived biomimetic compounds.
Oxygen vacancy–induced ferromagnetism in un-doped ZnO thin films
Authors: Zhan Peng , Wang Weipeng , Liu Can , Hu Yang , Li Zhengcao , Zhang Zhengjun , Zhang Peng , Wang Baoyi , Cao Xingzhong
Published: February 2012

ZnO films became ferromagnetic when defects were introduced by thermal-annealing in flowing argon. This ferromagnetism, as shown by the photoluminescence measurement and positron annihilation analysis, was induced by the singly occupied oxygen vacancy with a saturated magnetization dependent positively on the amount of this vacancy. This study clarified the origin of the ferromagnetism of un-doped ZnO thin films and provides possibly an alternative way to prepare ferromagnetic ZnO films.
High energy transmission of Al2O3 doped with light transition metals
Authors: Schuster C. , Klimke J. , Schwingenschlögl U.
Published: February 2012

The transmission of transparent colored ceramics based on Al2O3 doped with light transition metals is measured in the visible and infrared range. To clarify the role of the dopands we perform ab initiocalculations. We discuss the electronic structure and present optical spectra obtained in the independent particle approximation. We argue that the gross spectral features of Co- and Ni-doped Al2O3 samples are described by our model, while the validity of the approach is limited for Cr-doped Al2O3.
Electronic transport anisotropy of buckling graphene under uniaxial compressive strain: Ab initio study
Authors: Xu Yang , Gao Haiyuan , Chen Huabin , Yuan You , Zhu Kaicheng , Chen Hongsheng , Jin Zhonghe , Yu Bin
Published: February 2012

Electronic transport properties of graphene under uniaxial compressive strain are studied using ab initio calculations. With approximate thermal perturbation, buckling occurs when strain exceeds a threshold, comparing to flat unperturbed structures. Transmissions of flat graphene compressed along zigzag direction (ZCG) and buckled graphene compressed along armchair direction (ACG) are insensitive to strain, whereas those of buckled ZCG and flat ACG are negatively correlated to strain. Flat graphene has anisotropic resistance along the strain direction, while buckling suppresses the anisotropy by releasing the strain. The insensitivity of buckled graphene on strain direction and out-of-plane deformation makes feasible to implement flexible electronics.
Design and operation of the wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source
Authors: Abernathy D. L. , Stone M. B. , Loguillo M. J. , Lucas M. S. , Delaire O. , Tang X. , Lin J. Y. Y. , Fultz B.
Published: February 2012

The wide angular-range chopper spectrometer ARCS at the Spallation Neutron Source (SNS) is optimized to provide a high neutron flux at the sample position with a large solid angle of detector coverage. The instrument incorporates modern neutron instrumentation, such as an elliptically focused neutron guide, high speed magnetic bearing choppers, and a massive array of 3He linear position sensitive detectors. Novel features of the spectrometer include the use of a large gate valve between the sample and detector vacuum chambers and the placement of the detectors within the vacuum, both of which provide a window-free final flight path to minimize background scattering while allowing rapid changing of the sample and sample environment equipment. ARCS views the SNS decoupled ambient temperature water moderator, using neutrons with incident energy typically in the range from 15 to 1500 meV. This range, coupled with the large detector coverage, allows a wide variety of studies of excitations in condensed matter, such as lattice dynamics and magnetism, in both powder and single-crystal samples. Comparisons of early results to both analytical and Monte Carlo simulation of the instrument performance demonstrate that the instrument is operating as expected and its neutronic performance is understood. ARCS is currently in the SNS user program and continues to improve its scientific productivity by incorporating new instrumentation to increase the range of science covered and improve its effectiveness in data collection.
A tapered undulator experiment at the ELBE far infrared hybrid-resonator oscillator free electron laser
Authors: Asgekar V. , Lehnert U. , Michel P.
Published: February 2012

A tapered undulator experiment was carried out at the ELBE far-infrared free electron laser (FEL). The oscillator FEL makes use of a hybrid optical resonator. The main motivation was to see whether the presence of a dispersive medium in the form of a waveguide in the resonator has any effect on the outcome. The FEL saturated power and the wavelength shifts have been measured as a function of both positive as well as negative undulator field amplitude tapering. In contrast to the typical high-gain FELs where positive tapering proves beneficial for the output power we observed an improvement of performance at negative taper. During the same experiments we studied the characteristics of the detuning curves. The width of the curves indicates a maximum small signal gain for zero taper while the output peak power increases with negative taper. The saturated power output, the detuning curve characteristics, and the wavelength shifts agrees with the theoretical predictions. Details of the experiment are presented.
Speed enhancement of multi-particle chain in a traveling standing wave
Authors: Šiler Martin , Čižmár Tomáš , Zemánek Pavel
Published: February 2012

A moving array of optical traps created by interference of two counter-propagating evanescent waves has been used for delivery of particle chains up to 18 micro-particles long immersed in water. The particles were optically self-arranged into a linear chain with well-separated distances between them. We observed a significant increase in the delivery speed of the whole structure as the number of particles in the chain increased. This could provide faster sample delivery in microfluidic systems. We quantified the contributions to the speed enhancement caused by the optical and hydrodynamic interactions between the particles.
Contact transport of focused ion beam-deposited Pt to Si nanowires: From measurement to understanding
Authors: Ke J. J. , Tsai K. T. , Dai Y. A. , He J. H.
Published: February 2012

The Si nanowires (NWs) were contacted by focused ion beam (FIB)-deposited Pt as the Ohmic contacts. Ultralow specific contact resistivity of 1.2 × 10−6 Ω-cm2 has been measured. Due to the focused ion beam-induced amorphization of Si NWs, contact behavior is explained by diffusion theory, allowing accurate estimation of electron concentration, electron mobility, effective barrier height, and ideality factor. This study can be the guidance to correct measurement and understanding of the contact transport, which is useful for NWs device design and fabrication.
Multiple pulse-heating experiments with different current to determine total emissivity, heat capacity, and electrical resistivity of electrically conductive materials at high temperatures
Authors: Watanabe Hiromichi , Yamashita Yuichiro
Published: February 2012

A modified pulse-heating method is proposed to improve the accuracy of measurement of the hemispherical total emissivity, specific heat capacity, and electrical resistivity of electrically conductive materials at high temperatures. The proposed method is based on the analysis of a series of rapid resistive self-heating experiments on a sample heated at different temperature rates. The method is used to measure the three properties of the IG-110 grade of isotropic graphite at temperatures from 850 to 1800 K. The problem of the extrinsic heating-rate effect, which reduces the accuracy of the measurements, is successfully mitigated by compensating for the generally neglected experimental error associated with the electrical measurands (current and voltage). The results obtained by the proposed method can be validated by the linearity of measured quantities used in the property determinations. The results are in reasonably good agreement with previously published data, which demonstrate the suitability of the proposed method, in particular, to the resistivity and total emissivity measurements. An interesting result is the existence of a minimum in the emissivity of the isotropic graphite at around 1120 K, consistent with the electrical resistivity results.
Ultrahigh resolution soft x-ray emission spectrometer at BL07LSU in SPring-8
Authors: Harada Yoshihisa , Kobayashi Masaki , Niwa Hideharu , Senba Yasunori , Ohashi Haruhiko , Tokushima Takashi , Horikawa Yuka , Shin Shik , Oshima Masaharu
Published: February 2012

An extremely high resolution flat field type slit less soft x-ray emission spectrometer has been designed and constructed for the long undulator beamline BL07LSU in SPring-8. By optimizing the ruling parameters of two cylindrical gratings, a high energy resolution ΔE < 100 meV and/or an E/ΔE ∼ 10 000 are expected for the energy range of 350 eV – 750 eV taking into account the broadening by the spatial resolution (25 μm) of a CCD detector. A coma-free operation mode proposed by Strocov et al., is also applied to eliminate both defocus and coma aberrations. The spectrometer demonstrated experimentally that E/ΔE = 10 050 and 8046 for N 1s (402.1 eV) and Mn 2p (641.8 eV) edges, respectively.
An in situ approach to study trace element partitioning in the laser heated diamond anvil cell
Authors: Petitgirard S. , Borchert M. , Andrault D. , Appel K. , Mezouar M. , Liermann H.-P.
Published: February 2012

Data on partitioning behavior of elements between different phases at in situ conditions are crucial for the understanding of element mobility especially for geochemical studies. Here, we present results of in situ partitioning of trace elements (Zr, Pd, and Ru) between silicate and iron melts, up to 50 GPa and 4200 K, using a modified laser heated diamond anvil cell (DAC). This new experimental set up allows simultaneous collection of x-ray fluorescence (XRF) and x-ray diffraction (XRD) data as a function of time using the high pressure beamline ID27 (ESRF, France). The technique enables the simultaneous detection of sample melting based to the appearance of diffuse scattering in the XRD pattern, characteristic of the structure factor of liquids, and measurements of elemental partitioning of the sample using XRF, before, during and after laser heating in the DAC. We were able to detect elements concentrations as low as a few ppm level (2–5 ppm) on standard solutions. In situ measurements are complimented by mapping of the chemical partitions of the trace elements after laser heating on the quenched samples to constrain the partitioning data. Our first results indicate a strong partitioning of Pd and Ru into the metallic phase, while Zr remains clearly incompatible with iron. This novel approach extends the pressure and temperature range of partitioning experiments derived from quenched samples from the large volume presses and could bring new insight to the early history of Earth.
Spin transport in poly(metalarenylsilane)
Authors: Matsuura Yukihito
Published: February 2012

We focused on the spin transport properties of polymers containing ferrocene and the related transition-metal-benzene sandwich compound (metal = Cr and V) with a silicon bridge such as poly(ferrocenylsilane) and poly(metalarenylsilane). As a model system, a sulfur-substituted oligomer was put on gold electrodes via the sulfur-gold interaction. Spin transport between the two gold electrodes was calculated using a non-equilibrium Green’s function formalism and density functional theory. We have found that the oligomer containing Cr or V atoms exhibited an almost perfect spin filter behavior in which all the 3dz2 orbitals contributed to the electron transport.
Design, construction, and calibration of an isothermal titration calorimeter and its application in the study of the adsorption of phenolic compounds
Authors: Moreno-Piraján Juan Carlos , Giraldo Liliana
Published: February 2012

An isothermal calorimetric titration was designed and built, and some of the results obtained are presented here. For this purpose, a Calvet heat-conducting microcalorimeter was developed and connected to a titration unit built for this experiment to record titration thermograms. The microcalorimeter was electrically calibrated to establish its sensitivity and reproducibility, obtaining K = 13.56 ± 0.21 W V−1. Additionally, the equipment was tested using the heat of neutralisation for the tris-hydroxymethyl-aminomethane-HCl (THAM-HCl) system, obtaining ΔH = −30.92 ± 0.03 kJ mol−1. The unit was assembled to obtain titration heats and the corresponding thermodynamic variables (ΔH, ΔG, ΔS, and Ke) with a system of phenolic derivatives-activated carbon (synthesised from potato peel).
Growth and valence band offset measurement of PbTe/InSb heterojunctions
Authors: Lee Kyoung-Keun , Priyantha Weerasinghe , Myers Thomas H.
Published: February 2012

InSb (111)B and (211)B substrates were investigated for the growth of PbTe. The PbTe/InSb (111)B showed slip features caused by stain relaxation during cooling down, while growth of PbTe/InSb (211)B resulted in a better surface morphology. The valence band offset of PbTe/InSb (211)B was measured by high resolution x-ray photoemission spectroscopy and ultraviolet photoemission spectroscopy with the value of 0.38 ± 0.05 eV. The PbTe/InSb (211)B heterojunction structure forms a type-III—broken gap heterostructure with the conduction band offset of 0.23 ± 0.05 eV.
Gas refractometry using a hollow-core photonic bandgap fiber in a Mach-Zehnder-type interferometer
Authors: Shavrin I. , Novotny S. , Shevchenko A. , Ludvigsen H.
Published: February 2012

We present the design of a fiber-optic gas refractometer that enables spectrally resolved measurements of both real and imaginary parts of the complex refractive index. The proposed concept is based on a Mach-Zehnder-type interferometer with a hollow-core photonic bandgap fiber in one of the interferometer’s arms. The fiber is used simultaneously as an optical waveguide and an analyte containing cell. We demonstrate the performance of the device by measuring the complete complex refractive index of an air-acetylene gas mixture within the optical C-band. The introduced concept leads towards versatile applications in optics as well as atomic and molecular physics.
Omni-directional selective shielding material based on amorphous glass coated microwires
Authors: Ababei G. , Chiriac H. , David V. , Dafinescu V. , Nica I.
Published: February 2012

The shielding effectiveness of the omni-directional selective shielding material based on CoFe-glass coated amorphous wires in 0.8 GHz-3 GHz microwave frequency range is investigated. The measurements were done in a controlled medium using a TEM cell and in the free space using horn antennas, respectively. Experimental results indicate that the composite shielding material can be developed with desired shielding effectiveness and selective absorption of the microwave frequency range by controlling the number of the layers and the length of microwires.
Quasi-periodic functions on the torus and sl(n)-elliptic Lie algebra
Authors: Skrypnyk T.
Published: February 2012

We investigate properties of the sl(n) automorphic elliptic algebra \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n))$\end{document}E(sl(n)). We prove it to be \documentclass[12pt]{minimal}\begin{document}$\mathbb {Z}$\end{document}Z quasi-graded Lie algebra which could be viewed as a deformation of a graded loop algebra. We show that it admits the decomposition into the direct sum of two subalgebras: \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n))= \mathfrak {E}(sl(n))_+ + \mathfrak {E}(sl(n))_-$\end{document}E(sl(n))=E(sl(n))++E(sl(n))− consistent with the described quasi-grading. We prove that \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n))^*_{\pm }=\mathfrak {E}(sl(n))_{\mp }$\end{document}E(sl(n))±*=E(sl(n))∓, i.e., Lie algebras \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n)),$\end{document}E(sl(n)), \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n))_+ ,$\end{document}E(sl(n))+, and \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n))_-$\end{document}E(sl(n))− constitute the Manin triple. We explicitly construct a central extension of \documentclass[12pt]{minimal}\begin{document}$\mathfrak {E}(sl(n))$\end{document}E(sl(n)). We find its algebra of differentiations and its central extension which coincide with the quasi-graded deformation of the Virasoro algebra.
Boundary-enhanced momentum relaxation of longitudinal optical phonons in GaN
Authors: Ma N. , Shen B. , Lu L. W. , Xu F. J. , Guo L. , Wang X. Q. , Lin F. , Feng Z. H. , Dun S. B. , Liu B.
Published: February 2012

The influence of the channel geometry on the high-field electron transport properties has been investigated in n-type GaN at room temperature. It is found that electrons in narrow channels drift much faster than those in wide channels. This discrepancy is attributed to the boundary-enhanced momentum relaxation of longitudinal optical (LO) phonons, which increases the electron drift velocity through enhancing the electron energy dissipation while weakening the momentum relaxation. In narrow channels, the effective LO-phonon momentum relaxation time is about ∼0.67 ps. The suggested theoretical analysis coincides well with the important features of the experimental results.
Note: Absolute calibration of two DRZ phosphor screens using ultrashort electron bunch
Authors: Wu Y. C. , Zhu B. , Dong K. G. , Yan Y. H. , Gu Y. Q.
Published: February 2012

This article gives the absolute calibration of two types phosphor screens (DRZ) that were used to detect and characterize electron bunches driven by laser-plasma accelerator. The test was performed with picoseconds electron bunch at a radio frequency linear electron accelerator in Tsinghua University. The photons emitted from DRZ screens showed good linear responses to the charge of incident electron bunch and cosine angular distribution in space. An energy conversional efficiency of effective scintillant matter was also calculated.
Electrical phase transition of poly(4,4′-aminotriphenylene hexafluoroisopropylidenediphthalimide) by photogenerated charged carrier injection
Authors: Lee Kyoung-Jae , Min Kim Dong , Ihm Kyuwook , Ree Moonhor , Kang Tai-Hee , Chung Sukmin
Published: February 2012

We show a set-up of poly(4,4′-aminotriphenylene hexafluoroisopropylidenediphthalimide) (6F-TPA PI)/Al sample in which holes are injected by photoelectron emission process instead of direct charge carrier injection via metal electrode. In this process, an irreversible electrical phase transition of 6F-TPA PI is found in contrast to the Al/6F-TPA PI/Al structure, leading to a write-once-read-many behavior. The photoelectron spectroscopy results measured before and after the switching process revealed that the irreversible electrical phase transition of 6F-TPA PI is attributed to the chemical modification of the carbonyl group in phthalimide moiety.
Effect of the graded electron blocking layer on the emission properties of GaN-based green light-emitting diodes
Authors: Zhang Ning , Liu Zhe , Wei Tongbo , Zhang Lian , Wei Xuecheng , Wang Xiaodong , Lu Hongxi , Li Jinmin , Wang Junxi
Published: February 2012

We report on the effect of a graded AlGaN electron blocking layer (GEBL) on the emission properties of InGaN/GaN multiple quantum wells light-emitting diode (LED). The adoption of GEBL in the LED enhances the electroluminescence intensity and reduces the wavelength blue-shift with increasing injection current. The light output power of the GEBL LED is enhanced by 163% and 415% at 20 and 350 mA, respectively. Moreover, the forward voltage of the GEBL LED is reduced by 0.38 V at the forward current of 20 mA.
Spin-inversion in nanoscale graphene sheets with a Rashba spin-orbit barrier
Authors: Ahmadi Somaieh , Esmaeilzadeh Mahdi , Namvar Esmaeil , Pan Genhua
Published: February 2012

Spin-inversion properties of an electron in nanoscale graphene sheets with a Rashba spin-orbit barrier is studied using transfer matrix method. It is found that for proper values of Rashba spin-orbit strength, perfect spin-inversion can occur in a wide range of electron incident angle near the normal incident. In this case, the graphene sheet with Rashba spin-orbit barrier can be considered as an electron spin-inverter. The efficiency of spin-inverter can increase up to a very high value by increasing the length of Rashba spin-orbit barrier. The effect of intrinsic spin-orbit interaction on electron spin inversion is then studied. It is shown that the efficiency of spin-inverter decreases slightly in the presence of intrinsic spin-orbit interaction. The present study can be used to design graphene-based spintronic devices.
Electronic structure, lattice energies and Born exponents for alkali halides from first principles
Authors: Gopikrishnan C. R. , Jose Deepthi , Datta Ayan
Published: February 2012

First principles calculations based on DFT have been performed on crystals of halides (X = F, Cl, Br and I) of alkali metals (M = Li, Na, K, Rb and Cs). The calculated lattice energies (U0) are in good agreement with the experimental lattice enthalpies. A new exact formalism is proposed to determine the Born exponent (n) for ionic solids. The values of the Born exponent calculated through this ab-initio technique is in good agreement with previous empirically derived results. Band Structure calculations reveal that these compounds are wide-gap insulators that explains their optical transparency. Projected density of states (PDOS) calculations reveal that alkali halides with small cations and large anions, have small band gaps due to charge transfer from X → M. This explains the onset of covalency in ionic solids, which is popularly known as the Fajans Rule.
Electrical transport across metal/two-dimensional carbon junctions: Edge versus side contacts
Authors: Wu Yihong , Wang Ying , Wang Jiayi , Zhou Miao , Zhang Aihua , Zhang Chun , Yang Yanjing , Hua Younan , Xu Baoxi
Published: February 2012

Metal/two-dimensional carbon junctions are characterized by using a nanoprobe in an ultrahigh vacuum environment. Significant differences were found in bias voltage (V) dependence of differential conductance (dI/dV) between edge- and side-contact; the former exhibits a clear linear relationship (i.e., dI/dV ∝ V), whereas the latter is characterized by a nonlinear dependence, dI/dV ∝ V3/2. Theoretical calculations confirm the experimental results, which are due to the robust two-dimensional nature of the carbon materials under study. Our work demonstrates the importance of contact geometry in graphene-based electronic devices.
Cartesian vortex theory, cosmic vortices, and the route to cosmogony
Authors: Wettlaufer John S.
Published: February 2012

Supplemental material for the Quick study "The universe in a cup of coffee" PHYSICS TODAY, May 2011, page 66.
The Large Hadron Collider yields tantalizing hints of the Higgs boson
Authors: Schwarzschild Bertram M.
Published: February 2012

There’s not yet enough data for a convincing sighting of standard particle theory’s long-sought capstone. But there’s less and less room for it to hide.
Multiple exciton generation enhances a working solar cell
Authors: Miller Johanna L.
Published: February 2012

A single energetic photon can excite more than one electron in a nanocrystal. Collecting those electrons may be a path to higher photovoltaic efficiencies.
Reluctant to train, reluctant to prescribe: barriers to general practitioner prescribing of opioid substitution therapy
Authors: Longman Christine , Temple-Smith Meredith , Gilchrist Gail , Lintzeris Nicholas
Published: February 2012

Opioid substitution therapy (OST) is a well-recognised, evidence-based treatment for opioid dependence. Since the early 1990s, Australia has used a community-based general practitioner (GP) model of prescribing, particularly within the state of Victoria, where over 85% of OST prescribing is undertaken by GPs in community settings. Yet the majority of GPs invited to complete the required OST training decline the offer, while of those who complete training, the majority prescribe to few or no patients. This study aimed to determine the reasons for this. Twenty-two in-depth interviews were conducted with Victorian GPs exploring the reasons why the majority declined training, and for trained GPs, why they prescribed to few or no patients in the first 12 months after training. General practitioners who declined to train were predominantly influenced by negative experiences with drug-seeking patients, although other secondary reasons also affected their decision. Some GPs who completed the training were prevented from prescribing by several structural and operational barriers, many of which could be addressed. Fear of deskilling with time became a further impediment. General practitioners who became regular prescribers were highly committed with lengthy general practice experience. Concerns exist about the recruitment process for OST prescriber training, where nearly all GPs decline the offer of training, and the barriers that prevent GPs prescribing after training. Action is needed to address barriers to GP OST training and prescribing, and further research is necessary to ascertain measures required to facilitate long-term prescribing.
Effects of water content and temperature on the surface conductivity of bentonite clay
Authors: Mojid M. A. , Cho H.
Published: February 2012

This study explored the effects of water content and temperature on the mobility of exchangeable cations (termed the surface ionic mobility and hereafter ionic mobility) in the hydration layers of bentonite clay. The ionic mobility directly governs the surface conductivity of the clay. The investigation was done by measuring the bulk electrical conductivity (EC) of four sand–bentonite mixtures of different proportions for a wide range of water contents under constant temperature, and three bentonite samples at different water contents over 5–90°C. The ionic mobility was determined from the surface conductivity at the mean ionic strength of the hydration layers. The ionic mobility in the sand–bentonite samples increased with an increase in hydration layer thickness. For a given thickness of the hydration layer, the greater the bentonite content of a sample, the smaller was the ionic mobility. The ionic mobility in the bentonite samples at different water contents also increased, at reduced rates, with a rise in temperature. Consequently, the surface conductivity of the samples increased non-uniformly, at two different rates, with an increase in temperature. The increasing rate of this conductivity depended on temperature; over the low temperature range which depended on the water content, the rate was 0.013 dS/m.K, and over higher temperature range, the rate decreased to 0.008 dS/m.K. The commonly used temperature correction factor, 0.019 dS/m.K, for EC therefore did not hold true for the bentonite samples.
Soft currencies, cash economies, new monies: Past and present
Authors: Guyer Jane I.
Published: February 2012

Current variation in the forms of money challenges economic anthropologists and historians to review theory and comparative findings on multiple currency systems. There are four main sections to the paper devoted to (
i
) the present continuum of hard to soft currencies as an instance of multiplicity, including discussion of different combinations of the classic four functions of money, especially the relationship between store of value and medium of exchange; (
ii
) the logic of anthropological inquiry into multiple currency economies; (
iii
) the case of the monies of Atlantic Africa, applying the analytics of exchange rates as conversions to African transactions; and (
iv
) the return to economic life in a present day Nigerian economy lived in soft currency and cash. The paper identifies five findings that suggest foci for future research. (
i
) The widespread occurrence of conversions, which bring together ranking principles within transactions. (
ii
) Several types of positional ranking ranging from simple stepwise ordinal scales to iconic ordinality that creates a parabolic curve of value. (
iii
) Fictional units of account that serve to mediate both the memorization of nonreductive transactions and their nature as conversions. (
iv
) The importance of the temporal reach of what constitutes wealth: over the short run, the life span, intergenerational succession, and in (legal) perpetuity (as for corporate and sovereign debts and specified assets). (
v
) The social niches in which these qualities are brought together in transactional regimes. In conclusion, the paper returns to the exchange function of cash, soft currencies, and new money forms.