bluuebunny/crossref_metadata_2025 huggingface dataset:
Condensation of the Lennard-Jones fluid on the basis of the Gibbs single-phase approach
Authors: Ushcats M. V.
Published: March 2013

An accurate expression for the cluster expansion of the configuration integral has been considered based on the Gibbs single-phase approach without additional assumptions and approximations. The computational results for the Lennard-Jones fluid demonstrate the beginning of the condensation process at the singularity points of the isothermal compressibility. It has also been shown that the accuracy boundary of the virial equation of state corresponds to these points, not the virial series singularities. At the high density regime, the inappropriate behavior of the cluster expansion has been discovered that may be related to the infinite limits of the cluster integrals, i.e., their independency on the density.
Non-invasive timing of gas gun-launched projectiles using external surface-mounted optical fiber-Bragg grating strain gauges
Authors: Goodwin Peter M. , Marshall Bruce R. , Stevens Gerald D. , Dattelbaum Dana M.
Published: March 2013

Non-invasive detection methods for tracking gun-launched projectiles are important not only for assessment of gun performance but are also essential for timing a variety of diagnostics, for example, to investigate plate-impact events for shock compression experiments. Measurement of the time of passage of a projectile moving inside of the gun barrel can be achieved by detection of the transient hoop strain induced in the barrel of a light-gas gun by the passage of the projectile using external, barrel surface-mounted optical fiber-Bragg grating strain gauges. Optical fiber-Bragg gratings have been implemented and their response characterized on single-stage and two-stage light gas guns routinely used for dynamic experimentation at Los Alamos National Laboratory. Two approaches, using either broadband or narrowband illumination, were used to monitor changes in the Bragg wavelength of the fiber-Bragg gratings. The second approach, using narrowband laser illumination, offered the highest sensitivity. The feasibility of using these techniques to generate early, pre-event signals useful for triggering high-latency diagnostics was demonstrated.
Restricted diffusion in annular geometrical pores
Authors: Ghadirian Bahman , Torres Allan M. , Yadav Nirbhay N. , Price William S.
Published: March 2013

Nuclear magnetic resonance (NMR) diffusion (including diffusion MRI) experiments are only as powerful as the models used to analyse the NMR diffusion data. A major problem, especially with measurements on biological systems, is that the existing models are only very poor approximations of cellular shape. Here, diffusion propagators and pulsed gradient spin-echo attenuation equations are derived in the short gradient pulse limit for diffusion within the annular region of a concentric cylinder of finite length and, similarly, within the annular region of a concentric sphere. The models include the possibility of relaxation at the boundaries and, in the case of the concentric cylinder, having the cylinder arbitrarily oriented with respect to the direction of the applied field gradient. The two models are also of interest due to their direct analogy to optical double slit diffraction. Also expressions for the mean square displacements, which are very useful information for determining the diffusion coefficient within these complex geometries, are obtained as well as for the limiting cases of diffusion on cylindrical and spherical shells and in a ring.
Types of single particle symmetry breaking in transition metal oxides due to electron correlation
Authors: Wagner Lucas K.
Published: March 2013

Very accurate wave functions are calculated for small transition metal oxide molecules. These wave functions are decomposed using reduced density matrices to study the underlying correlation of electrons. The correlation is primarily of left-right type between the transition metals and the oxygen atoms, which is mediated by excitations from the nominal single Slater ground state into antibonding and d-type orbitals. In a localized representation, this correlation manifests itself in a 2-electron hopping term that is off-diagonal. This term is of similar magnitude to the commonly considered Hubbard-type on-site interaction.
Transient swelling, spreading, and drug delivery by a dissolved anti-HIV microbicide-bearing film
Authors: Tasoglu Savas , Rohan Lisa C. , Katz David F. , Szeri Andrew J.
Published: March 2013

There is a widespread agreement that more effective drug delivery vehicles with more alternatives, as well as better active pharmaceutical ingredients (APIs), must be developed to improve the efficacy of microbicide products. For instance, in tropical regions, films are more appropriate than gels due to better stability of drugs at extremes of moisture and temperature. Here, we apply fundamental fluid mechanical and physicochemical transport theory to help better understand how successful microbicide API delivery depends upon properties of a film and the human reproductive tract environment. Several critical components of successful drug delivery are addressed. Among these are: elastohydrodynamic flow of a dissolved non-Newtonian film; mass transfer due to inhomogeneous dilution of the film by vaginal fluid contacting it along a moving boundary (the locally deforming vaginal epithelial surface); and drug absorption by the epithelium. Local rheological properties of the film are dependent on local volume fraction of the vaginal fluid. We evaluated this experimentally, delineating the way that constitutive parameters of a shear-thinning dissolved film are modified by dilution. To develop the mathematical model, we integrate the Reynolds lubrication equation with a mass conservation equation to model diluting fluid movement across the moving vaginal epithelial surface and into the film. This is a complex physicochemical phenomenon that is not well understood. We explore time- and space-varying boundary flux model based upon osmotic gradients. Results show that the model produces fluxes that are comparable to experimental data. Further experimental characterization of the vaginal wall is required for a more precise set of parameters and a more sophisticated theoretical treatment of epithelium.
A general nuclear motion Hamiltonian and non-internal curvilinear coordinates
Authors: Strobusch D. , Scheurer Ch.
Published: March 2013

An exact Hamiltonian for nuclear motions in general curvilinear coordinates is derived. It is demonstrated how this Hamiltonian transforms into well-established expressions, such as the Wilson Howard Hamiltonian or the Meyer Günthard Hamiltonian, if the general coordinates are restricted to be rectilinear or internal. Furthermore, a compact expression for the Hamiltonian expressed in non-internal curvilinear coordinates is provided, which makes this coordinate class available for applications in a simple way, since only the Jacobian matrix with respect to the rotating frame coordinates must be calculated. An example, employing a water model potential, exemplifies how different coordinate systems from all three coordinate classes (rectilinear, internal, and non-internal) lead to vibrational spectra, which are in excellent agreement. Thereby, the applicability of the general Hamiltonian is demonstrated and also its correctness is confirmed.
Influence of Ga doping on rare earth moment ordering and ferromagnetic transition in Nd0.7Sr0.3Co1−xGaxO3
Authors: Kumar Pawan , Maheswar Repaka D. V. , Aparnadevi M. , Tripathi T. S. , Mahendiran R.
Published: March 2013

We report the impact of dilution of Co sublattice by non-magnetic Ga3+ ion on the magnetic, electrical, and magnetoresistive properties in Nd0.7Sr0.3Co1−xGaxO3 for x = 0–0.12. Field-cooled magnetization of the parent compound (x = 0) shows an anomalous maximum at T* = 54.6 K much below the onset of ferromagnetic transition (TC = 160 K) of the Co sublattice, which is attributed to the polarization of Nd-4f moments antiparallel to the Co-3d sublattice. Both TC and T* shift to low temperature with increasing x and the Nd-4f spin reverses from antiparallel to parallel with increasing strength of the magnetic field. While the value of high field magnetization is not seriously affected by Ga doping, coercive field at 10 K increases dramatically with increasing x. Ga substitution transforms ferromagnetic metallic state into ferromagnetic insulating state for x ≥ 0.03 and decreases the magnitude of magnetoresistance from 6% for x = 0% to 0.5% for x = 0.12.
On the levitation force in horizontal core-annular flow with a large viscosity ratio and small density ratio
Authors: Ooms G. , Pourquie M. J. B. M. , Beerens J. C.
Published: March 2013

A numerical study has been made of horizontal core-annular flow: the flow of a high-viscosity liquid core surrounded by a low-viscosity liquid annular layer through a horizontal pipe. Special attention is paid to the question how the buoyancy force on the core, caused by a density difference between the core and the annular layer, is counterbalanced. The volume-of-fluid method is used to calculate the velocities and pressures in the two liquids. At the start of the calculation the core is in a concentric position. Thereafter the core starts to rise under the influence of buoyancy until it reaches an eccentric equilibrium position where the buoyancy force is counterbalanced by hydrodynamic forces generated by the movement of a wave at the core-annular interface with respect to the pipe wall. At high Reynolds number of the flow in the annular layer core levitation is due to inertial forces, whereas at low Reynolds number viscous (lubrication) forces are responsible for levitation. We carried out two types of calculation. In the first we assume the interface to be smooth (without wave) at the start of the calculation and study how the wave develops during the rising period of the core. In the second a wave is already present at the start of the calculation.
Multiferroicity in spin ice Ho2Ti2O7: An investigation on single crystals
Authors: Liu D. , Lin L. , Liu M. F. , Yan Z. B. , Dong S. , Liu J.-M.
Published: March 2013

The single crystals of rare-earth titanate pyrochlore compound Ho2Ti2O7 are grown and their multiferroicity along the [110] and [111] directions is investigated. The ferroelectricity below ∼28 K, with a polarization of ∼2.50 μC/m2 along the ⟨111⟩ direction at 2 K, qualitatively fitting with the theoretical scenario proposed by Khomskii (Nat. Commun. 3, 904 (2012)), is revealed. The magnetoelectric responses along both the [110] and [111] directions are observed, but different underlying mechanisms associated with the specific spin configurations are suggested.
VUV photoionization of gas phase adenine and cytosine: A comparison between oven and aerosol vaporization
Authors: Touboul D. , Gaie-Levrel F. , Garcia G. A. , Nahon L. , Poisson L. , Schwell M. , Hochlaf M.
Published: March 2013

We studied the single photon ionization of gas phase adenine and cytosine by means of vacuum ultraviolet synchrotron radiation coupled to a velocity map imaging electron/ion coincidence spectrometer. Both in-vacuum temperature-controlled oven and aerosol thermodesorption were successfully applied to promote the intact neutral biological species into the gas phase. The photoion yields are consistent with previous measurements. In addition, we deduced the threshold photoelectron spectra and the slow photoelectron spectra for both species, where the close to zero kinetic energy photoelectrons and the corresponding photoions are measured in coincidence. The photoionization close and above the ionization energies are found to occur mainly via direct processes. Both vaporization techniques lead to similar electronic spectra for the two molecules, which consist of broadbands due to the complex electronic structure of the cationic species and to the possible contribution of several neutral tautomers for cytosine prior to ionization. Accurate ionization energies are measured for adenine and cytosine at, respectively, 8.267 ± 0.005 eV and 8.66 ± 0.01 eV, and we deduce precise thermochemical data for the adenine radical cation. Finally, we performed an evaluation and a comparison of the two vaporization techniques addressing the following criteria: measurement precision, thermal fragmentation, sensitivity, and sample consumption. The aerosol thermodesorption technique appears as a promising alternative to vaporize large thermolabile biological compounds, where extended thermal decomposition or low sensitivity could be encountered when using a simple oven vaporization technique.
Measuring time of flight of fusion products in an inertial electrostatic confinement fusion device for spatial profiling of fusion reactions
Authors: Donovan D. C. , Boris D. R. , Kulcinski G. L. , Santarius J. F. , Piefer G. R.
Published: March 2013

A new diagnostic has been developed that uses the time of flight (TOF) of the products from a nuclear fusion reaction to determine the location where the fusion reaction occurred. The TOF diagnostic uses charged particle detectors on opposing sides of the inertial electrostatic confinement (IEC) device that are coupled to high resolution timing electronics to measure the spatial profile of fusion reactions occurring between the two charged particle detectors. This diagnostic was constructed and tested by the University of Wisconsin-Madison Inertial Electrostatic Confinement Fusion Group in the IEC device, HOMER, which accelerates deuterium ions to fusion relevant energies in a high voltage (∼100 kV), spherically symmetric, electrostatic potential well [J. F. Santarius, G. L. Kulcinski, R. P. Ashley, D. R. Boris, B. B. Cipiti, S. K. Murali, G. R. Piefer, R. F. Radel, T. E. Radel, and A. L. Wehmeyer, Fusion Sci. Technol. 47, 1238 (2005)]. The TOF diagnostic detects the products of D(d,p)T reactions and determines where along a chord through the device the fusion event occurred. The diagnostic is also capable of using charged particle spectroscopy to determine the Doppler shift imparted to the fusion products by the center of mass energy of the fusion reactants. The TOF diagnostic is thus able to collect spatial profiles of the fusion reaction density along a chord through the device, coupled with the center of mass energy of the reactions occurring at each location. This provides levels of diagnostic detail never before achieved on an IEC device.
Crystal structure, magnetic properties, and the magnetocaloric effect of Gd5Rh4 and GdRh
Authors: Wang C. L. , Zou J. D. , Liu J. , Mudryk Y. , Gschneidner K. A. , Long Y. , Smetana V. , Miller G. J. , Pecharsky V. K.
Published: March 2013

The crystal structures of Gd5Rh4 and GdRh have been studied by powder and single crystal x-ray diffraction. The results show that Gd5Rh4 is isotypic with Pu5Rh4 and the bond length of the short Rh-Rh dimer is 2.943(4) Å. According to heat capacity measurements in zero magnetic field, the magnetic ordering temperature of Gd5Rh4 is 13 K, in agreement with magnetization measurements. Both the heat capacity peak shape and the positive slope of the Arrott plots at Curie temperature (TC) indicate the second-order nature of the magnetic transition. The temperature dependence of magnetization of Gd5Rh4 measured in 1 kOe applied field indicates noncollinear magnetic ordering that may change into nearly collinear ferromagnetic ordering by increasing the magnetic field. GdRh is ferromagnetic below TC = 22 K. Moderate magnetocaloric effects and relatively high refrigerant capacities are observed in Gd5Rh4 and GdRh.
Hierarchical networks, power laws, and neuronal avalanches
Authors: Friedman Eric J. , Landsberg Adam S.
Published: March 2013

We show that in networks with a hierarchical architecture, critical dynamical behaviors can emerge even when the underlying dynamical processes are not critical. This finding provides explicit insight into current studies of the brain's neuronal network showing power-law avalanches in neural recordings, and provides a theoretical justification of recent numerical findings. Our analysis shows how the hierarchical organization of a network can itself lead to power-law distributions of avalanche sizes and durations, scaling laws between anomalous exponents, and universal functions—even in the absence of self-organized criticality or critical points. This hierarchy-induced phenomenon is independent of, though can potentially operate in conjunction with, standard dynamical mechanisms for generating power laws.
Spectroscopic investigations of ammonia gas sensing mechanism in polypyrrole nanotubes/nanorods
Authors: Ishpal  , Kaur Amarjeet
Published: March 2013

In light of spectroscopic and electrical investigations, ammonia gas sensing mechanism in polypyrrole (PPy) nanotubes/nanorods has been discussed. For improvement in the gas sensing properties of PPy and its surface to volume ratio, nanotubes and nanorods have been synthesized by anionic dye and anionic surfactant directed chemical oxidation method. The gas sensing behavior of the prepared samples has been tested by measuring the change in electrical resistance of the samples in ammonia environment. Scanning electron microscopic investigations have confirmed the synthesis of PPy nanotubes having diameter ∼80–90 nm and length ∼1.5–2.0 μm and the PPy nanorods with diameter ∼150–200 nm and length ∼15–20 μm. The chemical analysis and the confirmation of synthesis of PPy were carried out by Fourier transform infrared and Raman spectroscopic techniques. Better sensitivity against ammonia has been observed in PPy nanorods. For the first time with the help of Raman spectroscopic investigations, the mechanism of gas sensing has been discussed in detail.
The SPARC linear accelerator based terahertz source
Authors: Chiadroni E. , Bacci A. , Bellaveglia M. , Boscolo M. , Castellano M. , Cultrera L. , Di Pirro G. , Ferrario M. , Ficcadenti L. , Filippetto D. , Gatti G. , Pace E. , Rossi A. R. , Vaccarezza C. , Catani L. , Cianchi A. , Marchetti B. , Mostacci A. , Palumbo L. , Ronsivalle C. , Di Gaspare A. , Ortolani M. , Perucchi A. , Calvani P. , Limaj O. , Nicoletti D. , Lupi S.
Published: March 2013

Ultra-short electron beams, produced through the velocity bunching compression technique, are used to drive the SPARC linear accelerator based source, which relies on the emission of coherent transition radiation in the terahertz range. This paper reports on the main features of this radiation, as terahertz source, with spectral coverage up to 5 THz and pulse duration down to 200 fs, with an energy per pulse of the order of several micro-joule, and as electron beam longitudinal diagnostics.
Self-irradiation damage to the local structure of plutonium and plutonium intermetallics
Authors: Booth C. H. , Jiang Yu , Medling S. A. , Wang D. L. , Costello A. L. , Schwartz D. S. , Mitchell J. N. , Tobash P. H. , Bauer E. D. , McCall S. K. , Wall M. A. , Allen P. G.
Published: March 2013

The effect of self-irradiation damage on the local structure of δ-Pu, PuAl2, PuGa3, and other Pu intermetallics has been determined for samples stored at room temperature using the extended x-ray absorption fine-structure (EXAFS) technique. These measurements indicate that the intermetallic samples damage at a similar rate as indicated in previous studies of PuCoGa5. In contrast, δ-Pu data indicate a much slower damage accumulation rate. To explore the effect of storage temperature and possible room temperature annealing effects, we also collected EXAFS data on a δ-Pu sample that was held at less than 32 K for a two month period. This sample damaged much more quickly. In addition, the measurable damage was annealed out at above only 135 K. Data from samples of δ-Pu with different Ga concentrations and results on all samples collected from different absorption edges are also reported. These results are discussed in terms of the vibrational properties of the materials and the role of Ga in δ-Pu as a network former.
Charge modulation infrared spectroscopy of rubrene single-crystal field-effect transistors
Authors: Uchida R. , Yada H. , Makino M. , Matsui Y. , Miwa K. , Uemura T. , Takeya J. , Okamoto H.
Published: March 2013

Polarized absorption spectra of hole carriers in rubrene single crystal field-effect transistors were measured in the infrared region (725–8000 cm−1) by charge modulation spectroscopy. The absorptions, including the superimposed oscillatory components due to multiple reflections within thin crystals, monotonically increased with decreasing frequency. The spectra and their polarization dependences were well reproduced by the analysis based on the Drude model, in which the absorptions due to holes in rubrene and electrons in the gate electrodes (silicon), and multiple reflections were fully considered. The results support the band transport of hole carriers in rubrene.
Comparative study on strain induced electrical properties modulation of Si p-n junctions
Authors: Wu Wangran , Pu Yu , Wang Junzhuan , Xu Xiangming , Sun Jiabao , Yuan Zhe , Shi Yi , Zhao Yi
Published: March 2013

Understanding the p-n junctions is of great importance because p-n junctions are the essential elements of semiconductor devices. In this study, we experimentally investigated the strain induced electrical properties modulation of Si p+-n and n+-p junctions. It is found that, under the uniaxial tensile stress, the current in the large-forward-bias region increases significantly, while a rather small current increase is observed in the diffusion-current-dominant region. Besides, the ideality factors in the diffusion-current-dominant region and the large-forward-bias region decrease when the amount of the applied stress increases. The observations are explained by the strain induced variations in energy band structure, their effect on minority carrier concentrations, and the piezoresistance effect.
Persistent photoconductivity effects in printed n-channel organic transistors
Authors: Nga Ng Tse , Fujieda Ichiro , Street Robert A. , Veres Janos
Published: March 2013

Persistent photoconductivity of top-gate n-type organic transistors is investigated. The irradiation of green light leads to a negative shift in transistor threshold voltage and an increase in sub-threshold current. These light-induced effects are enhanced when the gate is negatively biased during the light irradiation, and the recovery process is faster at 60 °C than at 25 °C. After storage in dark, full recovery is obtained for a transistor printed with a neat semiconductor, whereas for the device printed with a solution of the same semiconductor mixed with an insulator, only partial recovery is observed after four days at room temperature. Other stress conditions (irradiation with a positive gate bias, irradiation without bias, and bias under dark) do not change the threshold voltage or the sub-threshold current significantly. We attribute this photo phenomenon to holes trapped and released at the dielectric/semiconductor interface and a smaller number of positive fixed charges generated in the bulk of the semiconductor layer.
The flux pinning mechanism, and electrical and magnetic anisotropy in Fe1.04Te0.6Se0.4 superconducting single crystal
Authors: Shahbazi M. , Wang X. L. , Dou S. X. , Fang H. , Lin C. T.
Published: March 2013

The temperature and magnetic field dependences of the magnetization and critical current density of Fe1.04Te0.6Se0.4 single crystals have been investigated, and the flux pinning mechanism has been analysed. The normalized pinning force (fp = Fp/Fp,max) vs. h(H/Hirr) curves, are scaled using the Dew-Hughes' theory, f(h) ≈ hp(1 − h)q with p = 1.35 and q = 3.06. The angular dependence of the resistivity under different magnetic fields shows a dip-like structure, below the superconducting transition temperature. The anisotropic value of 2 was obtained using Ginzburg-Landau theory.
Metamaterial optical refractive index sensor detected by the naked eye
Authors: Wang Xiaonong , Luo Chunrong , Hong Gang , Zhao Xiaopeng
Published: March 2013

An optical refractive index sensor that can be detected by the naked eye is presented in this paper. The sensor is developed based on the theory that metamaterials can completely absorb incident electric and magnetic field near its resonant frequencies. By inserting different mediums in the sensor or by dropping the mediums on the surface of the sensor, we detect the medium with a different refractive index through qualitative and quantitative analysis. The sensor is convenient for the detection of the liquid refractive index.
A density functional theory study of epitaxial graphene on the (3×3)-reconstructed C-face of SiC
Authors: Deretzis I. , Magna A. La
Published: March 2013

We study the electronic properties of epitaxial graphene on the (3×3)-reconstructed SiC(0001¯) plane within the density functional theory. Our results show that the interface interaction is inherently weak. The first graphene layer above the substrate is almost planar and sp2-hybridized. The substrate's contribution in the low-energy electronic spectrum is present through (a) interface states deriving from SiC surface atoms with bands that disperse around the Dirac point, (b) a mild n-type doping, and (c) a ∼20 meV band-gap opening. Substrate interference is, therefore, an issue also in the case of graphene grown on the C-face of SiC.
Communication: Importance sampling including path correlation in semiclassical initial value representation calculations for time correlation functions
Authors: Pan Feng , Tao Guohua
Published: March 2013

Full semiclassical (SC) initial value representation (IVR) for time correlation functions involves a double phase space average over a set of two phase points, each of which evolves along a classical path. Conventionally, the two initial phase points are sampled independently for all degrees of freedom (DOF) in the Monte Carlo procedure. Here, we present an efficient importance sampling scheme by including the path correlation between the two initial phase points for the bath DOF, which greatly improves the performance of the SC-IVR calculations for large molecular systems. Satisfactory convergence in the study of quantum coherence in vibrational relaxation has been achieved for a benchmark system-bath model with up to 21 DOF.
Breather-like penetration of ultrashort linearly polarized laser into over-dense plasmas
Authors: Wu Dong , Zheng C. Y. , Yan X. Q. , Yu M. Y. , He X. T.
Published: March 2013

The penetration of an ultrashort laser pulse into an overdense plasma in the relativistic transparency regime is reexamined. The interaction is governed by the Maxwell and relativistic hydrodynamic equations and investigated using a fully implicit energy-conserving numerical scheme. It is found that for a circularly polarized laser, the penetrated pulse has the expected soliton structure. However, for a linearly polarized laser, the penetrated light exhibits a breather structure, and energy exchange between it and the plasma is at twice the laser frequency.
Theory and experiments characterizing hypervelocity impact plasmas on biased spacecraft materials
Authors: Lee Nicolas , Close Sigrid , Goel Ashish , Lauben David , Linscott Ivan , Johnson Theresa , Strauss David , Bugiel Sebastian , Mocker Anna , Srama Ralf
Published: March 2013

Space weather including solar activity and background plasma sets up spacecraft conditions that can magnify the threat from hypervelocity impacts. Hypervelocity impactors include both meteoroids, traveling between 11 and 72 km/s, and orbital debris, with typical impact speeds of 10 km/s. When an impactor encounters a spacecraft, its kinetic energy is converted over a very short timescale into energy of vaporization and ionization, resulting in a small, dense plasma. This plasma can produce radio frequency (RF) emission, causing electrical anomalies within the spacecraft. In order to study this phenomenon, we conducted ground-based experiments to study hypervelocity impact plasmas using a Van de Graaff dust accelerator. Iron projectiles ranging from 10−16 g to 10−11 g were fired at speeds of up to 70 km/s into a variety of target materials under a range of surface charging conditions representative of space weather effects. Impact plasmas associated with bare metal targets as well as spacecraft materials were studied. Plasma expansion models were developed to determine the composition and temperature of the impact plasma, shedding light on the plasma dynamics that can lead to spacecraft electrical anomalies. The dependence of these plasma properties on target material, impact speed, and surface charge was analyzed. Our work includes three major results. First, the initial temperature of the impact plasma is at least an order of magnitude lower than previously reported, providing conditions more favorable for sustained RF emission. Second, the composition of impact plasmas from glass targets, unlike that of impact plasmas from tungsten, has low dependence on impact speed, indicating a charge production mechanism that is significant down to orbital debris speeds. Finally, negative ion formation has a strong dependence on target material. These new results can inform the design and operation of spacecraft in order to mitigate future impact-related space weather anomalies and failures.
Characteristics of the dynamic shielding on the Wannier-ridge electron escapes by electron impact in weakly coupled plasmas
Authors: Ki Dae-Han , Jung Young-Dae
Published: March 2013

The influence of the dynamic shielding on the Wannier ridge electron escapes into the continuum states by the electron-impact is investigated in weakly coupled plasmas. The dynamically shielded renormalized electron charge and screened Wannier exponent are obtained by considering the equation of motion in the Wannier configuration mode with the effective interaction potential as functions of the charge of the residual ion, Debye length, projectile energy, and thermal energy. The result shows that the dynamic renormalized effective electron charge decreases with an increase of the thermal energy, especially for large distances. It is found that the dynamic shielding effect enhances the Wannier exponent for the double-electron escape. The variation of the dynamic shielding effect on the screened Wannier exponent is also discussed.
Oxygen-vacancy-related dielectric relaxations in SrTiO3 at high temperatures
Authors: Wang C. C. , Lei C. M. , Wang G. J. , Sun X. H. , Li T. , Huang S. G. , Wang H. , Li Y. D.
Published: March 2013

We herein present comparative investigation on the dielectric properties of both ceramic and single crystal SrTiO3 samples in the temperature from room temperature to 1073 K. Two relaxations were observed in both samples. They behave as Debye-like and relaxor-like relaxations in ceramic and single crystal samples, respectively. These relaxations were found to be bulk effect related to oxygen-vacancy. In single crystal sample, the relaxations result from the long-range conduction associated with singly and doubly charged oxygen vacancies. In ceramic sample, the oxygen vacancies are more strongly localized in relation to the crystal. This leads to a new phenomenon of formation and dissociation of oxygen vacancy clusters before the vacancies make contribution to the long-range conduction. The low-temperature relaxation in ceramic sample was determined by the clustering and dissociating processes of the oxygen vacancies. The high-temperature relaxation in ceramic sample was found to share the same mechanism as that in the single crystal sample.
Nanoimprint-lithography patterned epitaxial Fe nanowire arrays with misaligned magnetocrystalline and shape anisotropies
Authors: Zhang Wei , Bowden Mark E. , Krishnan Kannan M.
Published: March 2013

We fabricated large area (>1 × 1 cm2), epitaxial Fe nanowire arrays on MgO(001) substrates by nanoimprint lithography with a direct metallization of epitaxial materials through a metallic mask, which avoided the disadvantageous metal-etching process in conventional methods. The magnetization reversals, as revealed by magneto-optic Kerr effect, showed competing effects between Fe cubic magnetocrystalline anisotropy and lithographically induced uniaxial shape anisotropy. Unlike the weakly induced uniaxial anisotropy observed in continuous films, both the magnitude and direction of the uniaxial shape anisotropy can be easily modulated in the nanowires. Complex magnetization reversal processes including two-step and three-step loops were observed when magnetizing the samples along different Fe cubic easy axes, respectively. These modified magnetization reversal processes were explained by the nucleation and propagation of the domain walls along the non-superimposed easy axes of the competing magnetocrystalline and shape anisotropies.
Controlling spontaneous surface structuring of azobenzene-containing polymers for large-scale nano-lithography of functional substrates
Authors: Ambrosio A. , Girardo S. , Camposeo A. , Pisignano D. , Maddalena P.
Published: March 2013

In this work, we investigate the effect of illumination parameters which is light polarization, wavelength, and beam focalization, on the large-scale patterning of the surface of azobenzene-containing polymer films by means of spontaneous surface structuring. This is a phenomenon due to the interference at the sample surface between different light modes originated by scattering from the primary illuminating beam. In particular, the surface patterning in regions of a few squared millimeters with a spatial resolution down to 180 nm is achieved by means of a single beam illumination. The realized topographical structures are both preferentially oriented gratings and isotropically distributed topographical protrusions (dots), with sub-wavelength features.
Improvement of AlGaN/GaN/Si high electron mobility heterostructure performance by hydrogenation
Authors: Mimila-Arroyo J. , Jomard F. , Chevallier J.
Published: March 2013

The charge transport properties of high electron mobility AlGaN/GaN/Si heterostructure are improved by its deuteration under properly designed experimental conditions; an increase of 30% on the two dimensional electron gas electrical conductivity, produced by an equivalent increase on its electron concentration, with unchanged mobility is observed. These parameters dependence with the probe current is reduced as well. The increase on the free electron concentration is explained by the release of captured electrons by the deuterium passivation of ionized acceptors. The improvements might impact not only the structure ability to handle current but other parameters as breakdown voltage and electrical noise.
Molecular beam epitaxial AlGaN/GaN high electron mobility transistors leakage thermal activation on silicon and sapphire
Authors: Fontserè A. , Pérez-Tomás A. , Placidi M. , Baron N. , Chenot S. , Moreno J. C. , Rennesson S. , Cordier Y.
Published: March 2013

GaN-based power switches are expected to play a key role in uncooled electronics at elevated temperatures. In this paper we explore the thermal activation mechanisms taking place in analogous AlGaN/GaN high electron mobility transistors grown on silicon and sapphire. The on-resistance (α = 1.4/1.8 [Si/sapphire]) and saturation current (α = −1.5/−1.8) temperature coefficients, the thermal activation energies (Ea = 0.02–0.30/0.30 eV), the drain current on/off ratio (α = −1.5–9.1/−9.4), or the thermal impedances (Rth = 76.9/125.8 K/W) were determined and comparatively analyzed by means of physical-based models which include polar-optical phonon scattering, Poole-Frenkel trap assisted and Schottky emission, and the channel self-heating.
Large reversible magnetocaloric effects in ErFeSi compound under low magnetic field change around liquid hydrogen temperature
Authors: Zhang H. , Shen B. G. , Xu Z. Y. , Shen J. , Hu F. X. , Sun J. R. , Long Y.
Published: March 2013

Magnetic properties and magnetocaloric effects (MCEs) of ternary intermetallic ErFeSi compound have been investigated in detail. It is found that ErFeSi exhibits a second-order magnetic transition from ferromagnetic to paramagnetic states at the Curie temperature TC = 22 K, which is quite close to the liquid hydrogen temperature (20.3 K). A thermomagnetic irreversibility between zero-field-cooling and field-cooling curves is observed below TC in low magnetic field, and it is attributed to the narrow domain wall pinning effect. For a magnetic field change of 5 T, the maximum values of magnetic entropy change (−ΔSM) and adiabatic temperature change (ΔTad) are 23.1 J/kg K and 5.7 K, respectively. Particularly, the values of −ΔSM and refrigerant capacity reach as high as 14.2 J/kg K and 130 J/kg under a magnetic field change of 2 T, respectively. The large MCE without hysteresis loss for relatively low magnetic field change suggests that ErFeSi compound could be a promising material for magnetic refrigeration of hydrogen liquefaction.
A computational study of the thermoelectric performance of ultrathin Bi2Te3 films
Authors: Maassen Jesse , Lundstrom Mark
Published: March 2013

The ballistic thermoelectric performance of ultrathin films of Bi2Te3, ranging in thickness from 1 to 6 quintuple layers, is analyzed using density functional theory combined with the Landauer approach. Our results show that the thinnest film, corresponding to a single quintuple layer, has an intrinsic advantage originating from the particular shape of its valence band, leading to a large power factor and figure-of-merit exceeding bulk Bi2Te3. The interaction between the top and bottom topological surface states is key. The thinnest film yields a six-fold increase in power factor compared to bulk.
Size-dependent deformation in nanograins and nanotwins
Authors: Gu Pei , Dao Ming
Published: March 2013

This paper discusses three aspects that have not been looked into within mechanistic model for rationalizing observed behavior of nanocrystalline materials. (1) For the nano-materials with low energy barrier to emit the trailing partial after the leading partial, such as nanocrystalline Al (nc-Al), both partials extend intra-granularly in strengthening effect. (2) In the transition grain-size region between strengthening and softening, the coupled effect of intra-granular dislocation extension and grain boundary deformation contributes to flow stress. (3) Reformulating the non-homogeneous nucleation model, the activation volume is further examined.
Novel anomalies for like-charged attraction between curved surfaces and formulation of a hydrogen bonding style mechanism
Authors: Zhou Shiqi
Published: March 2013

For the first time, the classical density functional theory (DFT) is numerically solved in three- and two-dimensional spaces for a two sphere model of electrostatic interactions between two spherical nanoscale colloids immersed in a primitive model electrolyte solution. Two scientific anomalies are found that (i) contrary to what is often asserted that presence of multivalent counter ion is necessary to induce a like-charge attraction (LCA), univalent counter ion also induces the LCA only if bulk electrolyte concentration and colloid surface charge are high enough, and (ii) although the LCA in general becomes stronger with the bulk electrolyte concentration, adverse effects unexpectedly occur if the colloid surface charge quantity rises sufficiently. In addition, effects of counter ion and co-ion diameters in eliciting the LCA are first investigated and several novel phenomena such as monotonic and non-monotonic dependence of the LCA well depth on the counter ion diameter in different colloid surface charge zones are confirmed. Based these findings, a hydrogen bonding style mechanism is suggested and surprisingly, by appealing to fairly common-sense concepts such as bond energy, bond length, number of hydrogen bonds formed, and counter ion single-layer saturation adsorption capacity, self-consistently explains origin of the LCA between two spherical nanoscale particles, and all phenomena previously reported and observed in this study.
Peculiarly strong room-temperature ferromagnetism from low Mn-doping in ZnO grown by molecular beam epitaxy
Authors: Zuo Zheng , Morshed Muhammad , Beyermann W. P. , Zheng Jian-Guo , Xin Yan , Liu Jianlin
Published: March 2013

Strong room-temperature ferromagnetism is demonstrated in single crystalline Mn-doped ZnO thin films grown by molecular beam epitaxy. Very low Mn doping concentration is investigated, and the measured magnetic moment is much larger than what is expected for an isolated ion based on Hund's rules. The ferromagnetic behavior evolves with Mn concentration. Both magnetic anisotropy and anomalous Hall effect confirm the intrinsic nature of ferromagnetism. While the Mn dopant plays a crucial role, another entity in the system is needed to explain the observed large magnetic moments.
Influence of organic matter, clay mineralogy, and pH on the effects of CROSS on soil structure is related to the zeta potential of the dispersed clay
Authors: Marchuk Alla , Rengasamy Pichu , McNeill Ann
Published: March 2013

The high proportion of adsorbed monovalent cations in soils in relation to divalent cations affects soil structural stability in salt-affected soils. Cationic effects on soil structure depend on the ionic strength of the soil solution. The relationships between CROSS (cation ratio of soil structural stability) and the threshold electrolyte concentration (TEC) required for the prevention of soil structural problems vary widely for individual soils even within a soil class, usually attributed to variations in clay mineralogy, organic matter, and pH. The objective of the present study was to test the hypothesis that clay dispersion influenced by CROSS values depends on the unique association of soil components, including clay and organic matter, in each soil affecting the net charge available for clay–water interactions.
Experiments using four soils differing in clay mineralogy and organic carbon showed that clay dispersion at comparable CROSS values depended on the net charge (measured as negative zeta potential) of dispersed clays rather than the charge attributed to the clay mineralogy and/or organic matter. The effect of pH on clay dispersion was also dependent on its influence on the net charge. Treating the soils with NaOH dissolved the organic carbon and increased the pH, thereby increasing the negative zeta potential and, hence, clay dispersion. Treatment with calgon (sodium hexametaphosphate) did not dissolve organic carbon significantly or increase the pH. However, the attachment of hexametaphosphate with six charges on each molecule greatly increased the negative zeta potential and clay dispersion. A high correlation (R2 = 0.72) was obtained between the relative clay content and relative zeta potential of all soils with different treatments, confirming the hypothesis that clay dispersion due to adsorbed cations depends on the net charge available for clay–water interactions. The distinctive way in which clay minerals and organic matter are associated and the changes in soil chemistry affecting the net charge cause the CROSS–TEC relationship to be unique for each soil.
HDAC6
mutations rescue human tau-induced microtubule defects in
Drosophila
Authors: Xiong Ying , Zhao Kai , Wu Jiaxi , Xu Zhiheng , Jin Shan , Zhang Yong Q.
Published: March 2013

Neurons from the brains of Alzheimer’s disease (AD) and related tauopathy patients contain neurofibrillary tangles composed of hyperphosphorylated tau protein. Tau normally stabilizes microtubules (MTs); however, tau hyperphosphorylation leads to loss of this function with consequent MT destabilization and neuronal dysfunction. Accordingly, MT-stabilizing drugs such as paclitaxel and epothilone D have been shown as possible therapies for AD and related tauopathies. However, MT-stabilizing drugs have common side effects such as neuropathy and neutropenia. To find previously undescribed suppressors of tau-induced MT defects, we established a
Drosophila
model ectopically expressing human tau in muscle cells, which allow for clear visualization of the MT network. Overexpressed tau was hyperphosphorylated and resulted in decreased MT density and greater fragmentation, consistent with previous reports in AD patients and mouse models. From a genetic screen, we found that a
histone deacetylase 6
(
HDAC6
) null mutation rescued tau-induced MT defects in both muscles and neurons. Genetic and pharmacological inhibition of the tubulin-specific deacetylase activity of HDAC6 indicates that the rescue effect may be mediated by increased MT acetylation. These findings reveal HDAC6 as a unique potential drug target for AD and related tauopathies.
Runx1 and p21 synergistically limit the extent of hair follicle stem cell quiescence in vivo
Authors: Lee Jayhun , Hoi Charlene S. L. , Lilja Karin C. , White Brian S. , Lee Song Eun , Shalloway David , Tumbar Tudorita
Published: March 2013

Mechanisms of tissue stem cell (SC) quiescence control are important for normal homeostasis and for preventing cancer. Cyclin-dependent kinase inhibitors (CDKis) are known inhibitors of cell cycle progression. We document CDKis expression in vivo during hair follicle stem cell (HFSC) homeostasis and find p21 (cyclin-dependent kinase inhibitor 1a, Cdkn1a), p57, and p15 up-regulated at quiescence onset. p21 appears important for HFSC timely onset of quiescence. Conversely, we find that Runx1 (runt related transcription factor 1), which is known for promoting HFSC proliferation, represses p21, p27, p57, and p15 transcription in HFSC in vivo. Intriguingly, in cell culture, tumors, and normal homeostasis, Runx1 and p21 interplay modulates proliferation in opposing directions under the different conditions. Unexpectedly, Runx1 and p21 synergistically limit the extent of HFSC quiescence in vivo, which antagonizes the role of p21 as a cell cycle inhibitor. Importantly, we find in cultured keratinocytes that Runx1 and p21 bind to the p15 promoter and synergistically repress p15 mRNA transcription, thereby restraining cell cycle arrest. This documents a surprising ability of a CDKi (p21) to act as a direct transcriptional repressor of another CDKi (p15). We unveil a robust in vivo mechanism that enforces quiescence of HFSCs, and a context-dependent role of a CDKi (p21) to limit quiescence of SCs, potentially by directly down-regulating mRNA levels of (an)other CDKi(s).
Advection of surface-derived organic carbon fuels microbial reduction in Bangladesh groundwater
Authors: Mailloux Brian J. , Trembath-Reichert Elizabeth , Cheung Jennifer , Watson Marlena , Stute Martin , Freyer Greg A. , Ferguson Andrew S. , Ahmed Kazi Matin , Alam Md. Jahangir , Buchholz Bruce A. , Thomas James , Layton Alice C. , Zheng Yan , Bostick Benjamin C. , van Geen Alexander
Published: March 2013

Chronic exposure to arsenic (As) by drinking shallow groundwater causes widespread disease in Bangladesh and neighboring countries. The release of As naturally present in sediment to groundwater has been linked to the reductive dissolution of iron oxides coupled to the microbial respiration of organic carbon (OC). The source of OC driving this microbial reduction—carbon deposited with the sediments or exogenous carbon transported by groundwater—is still debated despite its importance in regulating aquifer redox status and groundwater As levels. Here, we used the radiocarbon (
14
C) signature of microbial DNA isolated from groundwater samples to determine the relative importance of surface and sediment-derived OC. Three DNA samples collected from the shallow, high-As aquifer and one sample from the underlying, low-As aquifer were consistently younger than the total sediment carbon, by as much as several thousand years. This difference and the dominance of heterotrophic microorganisms implies that younger, surface-derived OC is advected within the aquifer, albeit more slowly than groundwater, and represents a critical pool of OC for aquifer microbial communities. The vertical profile shows that downward transport of dissolved OC is occurring on anthropogenic timescales, but bomb
14
C-labeled dissolved OC has not yet accumulated in DNA and is not fueling reduction. These results indicate that advected OC controls aquifer redox status and confirm that As release is a natural process that predates human perturbations to groundwater flow. Anthropogenic perturbations, however, could affect groundwater redox conditions and As levels in the future.