bluuebunny/crossref_metadata_2025 huggingface dataset:
Calculation of spin wave spectra in magnetic nanograins and patterned multilayers with perpendicular anisotropy
Authors: Krawczyk M. , Mamica S. , Kłos J. W. , Romero-Vivas J. , Mruczkiewicz M. , Barman A.
Published: June 2011

We study spin-wave excitations in multilayered magnetic nanograins composed of a stack of planes with perpendicular magnetic anisotropy. The inhomogeneity is modeled through the multiple repetition of a unit cell composed of layers of two different magnetic materials. The magnetic inhomogeneity along the central axis is found to split the frequency spectrum of magnetostatic excitations into two bands, while into the number of bands in the spectrum of exchange spin waves. We show that this difference in behavior is a result of the underlying long- and short-range interactions, respectively. We describe a way of increasing the role of the dipolar interactions in the formation of magnonic bands in patterned magnetic multilayers with perpendicular anisotropy, which can allow one to obtain ferromagnetic resonance spectra with two strong absorption peaks in low and high frequencies up to the sub-THz range. Our findings open a new area for modeling the spin-wave spectra of patterned magnetic multilayers with potential applications, and for studying the role of the microscopic magnetic structure in forming spin-wave spectra.
E-H mode transition in low-pressure inductively coupled nitrogen-argon and oxygen-argon plasmas
Authors: Lee Young Wook , Lee Hye Lan , Chung T. H.
Published: June 2011

This work investigates the characteristics of the E-H mode transition in low-pressure inductively coupled N2-Ar and O2-Ar discharges using rf-compensated Langmuir probe measurements and optical emission spectroscopy (OES). As the ICP power increases, the emission intensities from plasma species, the electron density, the electron temperature, and the plasma potential exhibit sudden changes. The Ar content in the gas mixture and total gas pressure have been varied in an attempt to fully characterize the plasma parameters. With these control parameters varying, the changes of the transition threshold power and the electron energy distribution function (EEDF) are explored. In N2-Ar and O2-Ar discharges at low-pressures of several millitorr, the transition thresholds are observed to decrease with Ar content and pressure. It is observed that in N2-Ar plasmas during the transition, the shape of the EEDF changes from an unusual distribution with a flat hole near the electron energy of 3 eV in the E mode to a Maxwellian distribution in the H mode. However, in O2 -Ar plasmas, the EEDFs in the E mode at low Ar contents show roughly bi-Maxwellian distributions, while the EEDFs in the H mode are observed to be nearly Maxwellian. In the E and H modes of O2-Ar discharges, the dissociation fraction of O2 molecules is estimated using optical emission actinometry. During the E-H mode transition, the dissociation fraction of molecules is also enhanced.
Efficient ultrafast optical limiting using single walled carbon nanotubes functionalized noncovalently with free base and metalloporphyrins
Authors: Gupta Jyotsana , Vijayan C. , Maurya Sandeep Kumar , Goswami D.
Published: June 2011

The present work is on the linear and third order nonlinear optical properties of single walled carbon nanotubes functionalized noncovalently with free base porphyrin and a metalloporphyrin separately. The functionalized carbon nanotubes (CNTs) are soluble in dimethylformamide, and the microscopic images show that the porphyrin molecules are attached to the surface of the CNTs. The interaction between CNTs and porphyrins is noncovalent and probably due to π-π interaction as both CNTs and porphyrins have π-electron rich structures. The samples exhibit large ultrafast nonlinear absorption as evident from the open aperture z-scan studies performed using mode-locked Ti:Sapphire femtosecond pulses at 780 nm. The mechanisms of optical nonlinearity of the functionalized CNTs appear to be two photon absorption along with nonlinear scattering with a small contribution from saturable absorption, whereas nonfunctionalized CNTs are known to exhibit saturable absorption. The value of the nonlinear absorption coefficient for the CNTs functionalized with the free base porphyrin is one order smaller than that for CNTs functionalized with metalloporphyrin. Efficient low threshold ultrafast optical limiting is demonstrated for both types of functionalized CNTs.
Electronic and chemical properties of the c-Si/Al2O3 interface
Authors: Werner Florian , Veith Boris , Zielke Dimitri , Kühnemund Lisa , Tegenkamp Christoph , Seibt Michael , Brendel Rolf , Schmidt Jan
Published: June 2011

Using aluminum oxide (Al2O3) films deposited by atomic layer deposition (ALD), the dominant passivation mechanisms at the c-Si/Al2O3 interface, as well as the chemical composition of the interface region, are investigated. The excellent surface passivation quality of thin Al2O3 films is predominantly assigned to a high negative fixed charge density of Qf = − (4 ± 1) × 1012 cm−2, which is located within 1nm of the Si/Al2O3 interface and is independent of the layer thickness. A deterioration of the passivation quality for ultrathin Al2O3 layers is explained by a strong increase in the interface state density, presumably due to an incomplete reaction of the trimethyl-aluminum (TMA) molecules during the first ALD cycles. A high oxygen-to-aluminum atomic ratio resulting from the incomplete adsorption of the TMA molecules is suggested as a possible source of the high negative charge density Qf at the Si/Al2O3 interface.
3D microscale laser dynamic forming: Multiscale modeling and experimental validation
Authors: Gao Huang , Cheng Gary J.
Published: June 2011

Microscale laser dynamic forming (μLDF) shows great potential in fabricating robust and high-aspect-ratio metallic microcomponents. Experiments revealed that strain rate and sample size play important roles in determining the dynamic plasticity and final results of μLDF. To further understand these effects, a multiscale modeling methodology is adopted to characterize the microscale dynamic plasticity considering the evolutions of nano-to-submicron dislocations avalanches under shock loading. In this methodology, 3D discrete dislocation dynamics simulations are implemented to derive the yield strength and the initial strain hardening dependence on size and strain rate. It is observed that there exist three dynamic stages during deformation process. The initial strain hardening rate in Stage II increases with strain rate. The mechanical threshold stress model, intrinsically equipped with strain-rate-dependent flow stress and initial hardening, is chosen and modified to incorporate size effect quantitatively. This scale-dependent model, implemented in abaqus/explicit, provides deformation depths and thickness variations in good agreement with experimental results in μLDF.
Negative permeability characterization of gyrotropic hexaferrite in the millimeter wave band for engineering of double-negative devices
Authors: Yang Bin , Donnan Robert S. , Dubrovka Rostyslav , Tang Wenxuan
Published: June 2011

Thin, square, hexaferrite plates, with magnetization normal to the broad faces, are investigated as fundamental components for creating metamaterials with double-negative character in the millimeter wave band. The intrinsic, chiral, magneto-optical properties of a newly discovered special hexaferrite ceramic (named FB6H), are characterized using a general-purpose, free-space, quasioptical, millimeter wave reflectometer that measures with high numerical and operational efficiency to high accuracy. The FB6H material proves itself to be amenable to possible adaption for delivery of low-loss, broadband double-negative devices and for more challenging reaches into the millimeter/submillimeter wave band due to its stable, broadband negative permeability and promising natural, low-loss properties.
Giant enhancement of n-type carrier mobility in highly strained germanium nanostructures
Authors: Murphy-Armando F. , Fahy S.
Published: June 2011

First-principles electronic structure methods are used to predict the rate of n-type carrier scattering due to phonons in highly-strained Ge. We show that strains achievable in nanoscale structures, where Ge becomes a direct bandgap semiconductor, cause the phonon-limited mobility to be enhanced by hundreds of times that of unstrained Ge, and over a thousand times that of Si. This makes highly tensile strained Ge a most promising material for the construction of channels in CMOS devices, as well as for Si-based photonic applications. Biaxial (001) strain achieves mobility enhancements of 100 to 1000 with strains over 2%. Low temperature mobility can be increased by even larger factors. Second order terms in the deformation potential of the Γ valley are found to be important in this mobility enhancement. Although they are modified by shifts in the conduction band valleys, which are caused by carrier quantum confinement, these mobility enhancements persist in strained nanostructures down to sizes of 20 nm.
Surface and shape anisotropy effects in LaFeO3 nanoparticles
Authors: Wang Dan , Gong Menglian
Published: June 2011

The magnetic properties of the LaFeO3 nanospheres and nanotubes prepared by using the molten salt method have been investigated by magnetization measurements. The zero-field-cooled (ZFC) curve for the LaFeO3 nanospheres exhibits a maximum at 44 K while the ZFC curve for the LaFeO3 nanotubes exhibits two maxima: one, at 48 K, and the other, at 5 K. The maximums at 44 K and 48 K are ascribed to the average blocking temperature of the core moment. The maximum at 5 K in the ZFC curves for the LaFeO3 nanotubes and the rapid increase of magnetization below 10 K in the field-cooled (FC) curves for the LaFeO3 nanotubes are attributed to the surface spin freezing and the tube morphology. Hysteresis loops for the LaFeO3 nanospheres and nanotubes are measured. Loop shift for the LaFeO3 nanospheres is observed and discussed.
Electrodes controlling phase diagrams of symmetric ferroelectric tunneling junctions or capacitors
Authors: Chen W. J. , Zheng Yue , Wang Biao
Published: June 2011

Electrodes controlling the “misfit strain-temperature” phase diagrams of symmetric ferroelectric tunneling junctions or capacitors have been investigated. Taking into account effect of the imperfect charge screening in electrodes, it is found that the phase diagrams can be significantly shifted with changing coefficients of electrodes. Results about the dielectric constants also indicate promising controllability of other properties for ferroelectric tunnel junction or capacitor by adjusting electrodes.
Temperature-dependent photoluminescence properties of MnF2: Configurational-coordinate model analysis
Authors: Arai Takahiro , Adachi Sadao
Published: June 2011

A white MnF2 powder is synthesized by chemical etching of Mn shots in an aqueous HF solution. The optical properties of this synthesized powder are investigated using photoluminescence (PL) analysis, PL excitation spectroscopy, diffuse reflectivity, and PL decay measurements. The MnF2 powder exhibits PL peaks in the red (∼600 nm) and infrared spectral regions (∼780 nm) under visible to ultraviolet excitation. These PL peaks are asymmetric with a tail on the long-wavelength side. Such spectral features and temperature-dependent PL intensities are well interpreted by a newly developed model with Huang-Rhys’s factor as the electron-local vibration coupling strength. The ground- and excited-state energy level diagram for the Mn2+ ions in MnF2 is also proposed.
Point design targets, specifications, and requirements for the 2010 ignition campaign on the National Ignition Facility
Authors: Haan S. W. , Lindl J. D. , Callahan D. A. , Clark D. S. , Salmonson J. D. , Hammel B. A. , Atherton L. J. , Cook R. C. , Edwards M. J. , Glenzer S. , Hamza A. V. , Hatchett S. P. , Herrmann M. C. , Hinkel D. E. , Ho D. D. , Huang H. , Jones O. S. , Kline J. , Kyrala G. , Landen O. L. , MacGowan B. J. , Marinak M. M. , Meyerhofer D. D. , Milovich J. L. , Moreno K. A. , Moses E. I. , Munro D. H. , Nikroo A. , Olson R. E. , Peterson K. , Pollaine S. M. , Ralph J. E. , Robey H. F. , Spears B. K. , Springer P. T. , Suter L. J. , Thomas C. A. , Town R. P. , Vesey R. , Weber S. V. , Wilkens H. L. , Wilson D. C
Published: June 2011

Point design targets have been specified for the initial ignition campaign on the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 443, 2841 (2004)]. The targets contain D-T fusion fuel in an ablator of either CH with Ge doping, or Be with Cu. These shells are imploded in a U or Au hohlraum with a peak radiation temperature set between 270 and 300 eV. Considerations determining the point design include laser-plasma interactions, hydrodynamic instabilities, laser operations, and target fabrication. Simulations were used to evaluate choices, and to define requirements and specifications. Simulation techniques and their experimental validation are summarized. Simulations were used to estimate the sensitivity of target performance to uncertainties and variations in experimental conditions. A formalism is described that evaluates margin for ignition, summarized in a parameter the Ignition Threshold Factor (ITF). Uncertainty and shot-to-shot variability in ITF are evaluated, and sensitivity of the margin to characteristics of the experiment. The formalism is used to estimate probability of ignition. The ignition experiment will be preceded with an experimental campaign that determines features of the design that cannot be defined with simulations alone. The requirements for this campaign are summarized. Requirements are summarized for the laser and target fabrication.
Capsule implosion optimization during the indirect-drive National Ignition Campaign
Authors: Landen O. L. , Edwards J. , Haan S. W. , Robey H. F. , Milovich J. , Spears B. K. , Weber S. V. , Clark D. S. , Lindl J. D. , MacGowan B. J. , Moses E. I. , Atherton J. , Amendt P. A. , Boehly T. R. , Bradley D. K. , Braun D. G. , Callahan D. A. , Celliers P. M. , Collins G. W. , Dewald E. L. , Divol L. , Frenje J. A. , Glenzer S. H. , Hamza A. , Hammel B. A. , Hicks D. G. , Hoffman N. , Izumi N. , Jones O. S. , Kilkenny J. D. , Kirkwood R. K. , Kline J. L. , Kyrala G. A. , Marinak M. M. , Meezan N. , Meyerhofer D. D. , Michel P. , Munro D. H. , Olson R. E. , Nikroo A. , Regan S. P. , Suter L. J. , Thomas C. A. , Wilson D. C.
Published: June 2011

Capsule performance optimization campaigns will be conducted at the National Ignition Facility [G. H. Miller, E. I. Moses, and C. R. Wuest, Nucl. Fusion 44, 228 (2004)] to substantially increase the probability of ignition. The campaigns will experimentally correct for residual uncertainties in the implosion and hohlraum physics used in our radiation-hydrodynamic computational models using a variety of ignition capsule surrogates before proceeding to cryogenic-layered implosions and ignition experiments. The quantitative goals and technique options and down selections for the tuning campaigns are first explained. The computationally derived sensitivities to key laser and target parameters are compared to simple analytic models to gain further insight into the physics of the tuning techniques. The results of the validation of the tuning techniques at the OMEGA facility [J. M. Soures et al., Phys. Plasmas 3, 2108 (1996)] under scaled hohlraum and capsule conditions relevant to the ignition design are shown to meet the required sensitivity and accuracy. A roll-up of all expected random and systematic uncertainties in setting the key ignition laser and target parameters due to residual measurement, calibration, cross-coupling, surrogacy, and scale-up errors has been derived that meets the required budget. Finally, we show how the tuning precision will be improved after a number of shots and iterations to meet an acceptable level of residual uncertainty.
The experimental plan for cryogenic layered target implosions on the National Ignition Facility—The inertial confinement approach to fusion
Authors: Edwards M. J. , Lindl J. D. , Spears B. K. , Weber S. V. , Atherton L. J. , Bleuel D. L. , Bradley D. K. , Callahan D. A. , Cerjan C. J. , Clark D , Collins G. W. , Fair J. E. , Fortner R. J. , Glenzer S. H. , Haan S. W. , Hammel B. A. , Hamza A. V. , Hatchett S. P. , Izumi N. , Jacoby B. , Jones O. S. , Koch J. A. , Kozioziemski B. J. , Landen O. L. , Lerche R. , MacGowan B. J. , MacKinnon A. J. , Mapoles E. R. , Marinak M. M. , Moran M. , Moses E. I. , Munro D. H. , Schneider D. H. , Sepke S. M. , Shaughnessy D. A. , Springer P. T. , Tommasini R. , Bernstein L. , Stoeffl W. , Betti R. , Boehly T. R. , Sangster T. C. , Glebov V. Yu. , McKenty P. W. , Regan S. P. , Edgell D. H. , Knauer J. P. , Stoeckl C. , Harding D. R. , Batha S. , Grim G. , Herrmann H. W. , Kyrala G. , Wilke M. , Wilson D. C. , Frenje J. , Petrasso R. , Moreno K. , Huang H. , Chen K. C. , Giraldez E. , Kilkenny J. D. , Mauldin M. , Hein N. , Hoppe M. , Nikroo A. , Leeper R. J.
Published: June 2011

Ignition requires precisely controlled, high convergence implosions to assemble a dense shell of deuterium-tritium (DT) fuel with ρR>∼1 g/cm2 surrounding a 10 keV hot spot with ρR ∼ 0.3 g/cm2. A working definition of ignition has been a yield of ∼1 MJ. At this yield the α-particle energy deposited in the fuel would have been ∼200 kJ, which is already ∼10 × more than the kinetic energy of a typical implosion. The National Ignition Campaign includes low yield implosions with dudded fuel layers to study and optimize the hydrodynamic assembly of the fuel in a diagnostics rich environment. The fuel is a mixture of tritium-hydrogen-deuterium (THD) with a density equivalent to DT. The fraction of D can be adjusted to control the neutron yield. Yields of ∼1014−15 14 MeV (primary) neutrons are adequate to diagnose the hot spot as well as the dense fuel properties via down scattering of the primary neutrons. X-ray imaging diagnostics can function in this low yield environment providing additional information about the assembled fuel either by imaging the photons emitted by the hot central plasma, or by active probing of the dense shell by a separate high energy short pulse flash. The planned use of these targets and diagnostics to assess and optimize the assembly of the fuel and how this relates to the predicted performance of DT targets is described. It is found that a good predictor of DT target performance is the THD measurable parameter, Experimental Ignition Threshold Factor, ITFX ∼ Y × dsf 2.3, where Y is the measured neutron yield between 13 and 15 MeV, and dsf is the down scattered neutron fraction defined as the ratio of neutrons between 10 and 12 MeV and those between 13 and 15 MeV.
Levitation and oscillations of neutral particles in a constant electric field
Authors: Dolinsky Yu. , Elperin T.
Published: June 2011

We investigate oscillations of polarized particles embedded in a host liquid and subjected to a constant electric field. In the considered range of parameters there exist repulsion forces between particles which can cause particle levitation and oscillations in the system. We study the eigenfrequencies of oscillations of the levitated particle and demonstrate that oscillations frequency decreases when the amplitude of the electric field grows. Consequently, the lower frequency cut-off of the excited oscillations is determined by the maximum strength of the external electric field whereby the particle motion is not overdamped. The upper bound of the oscillations frequency is determined by the minimum strength of the electric field which is required for particle levitation. We analyze two simple geometrical configurations when a spherical particle is levitated by another immobilized spherical particle and the particle is levitated above the plane interface between two half-spaces with different permittivity and electric conductivity.
Diameter dependence of phase relaxation time and third-order nonlinear susceptibilities in semiconducting single-walled carbon nanotubes
Authors: Ichida Masao , Saito Shingo , Kiyohara Yumie , Nakano Tadashi , Miyata Yasumitsu , Kataura Hiromichi , Ando Hiroaki
Published: June 2011

Diameter dependence of the phase relaxation time T2 in semiconducting single-walled carbon nanotubes was measured using a two-beam time-resolved degenerate four-wave mixing method. The T2 value increases with increasing tube diameter. This experimental trend can be understood by the diameter dependence of exciton-phonon interaction. We also discuss the origin of diameter dependence of third-order nonlinearity connected with relaxation times.
Impurity effects on the generation and velocity of dislocations in Ge
Authors: Murao Yu , Taishi Toshinori , Tokumoto Yuki , Ohno Yutaka , Yonenaga Ichiro
Published: June 2011

The dynamic behavior of dislocations in heavily impurity (Ga, As, O) -doped Ge crystals was investigated as a function of stress and temperature by means of the etch-pit technique. The Ga and O impurities effectively suppressed dislocation generation from a surface scratch, while the As impurity did not strongly do so. Dislocations in Ga- and O-doped Ge crystals were supposed to be immobilized by the stable complexes formed through the impurity segregation and reaction. Remarkably, the O impurity, even at a low concentration of 1016 cm−3, induced the suppression of dislocation generation. The As impurity enhanced and the Ga impurity retarded dislocation velocity in motion. The O impurity had no effect on the velocity of the dislocations.
Ultra-broadband infrared pump-probe spectroscopy using synchrotron radiation and a tuneable pump
Authors: Carroll Lee , Friedli Peter , Lerch Philippe , Schneider Jörg , Treyer Daniel , Hunziker Stephan , Stutz Stefan , Sigg Hans
Published: June 2011

Synchrotron infrared sources have become popular mainly because of their excellent broadband brilliance, which enables spectroscopically resolved spatial-mapping of stationary objects at the diffraction limit. In this article we focus on an often-neglected further advantage of such sources – their unique time-structure – to bring such broadband spectroscopy to the time domain, for studying dynamic phenomenon down to the 100 ps limit. We describe the ultra-broadband (12.5 to 1.1 μm) Fourier transform pump-probe setup, for condensed matter transmission- and reflection-spectroscopy, installed at the X01DC infrared beam-line of the Swiss Light Source (SLS). The optical pump consists of a widely tuneable 100 ps 1 kHz laser system, covering 94% of the 16 to 1.1 μm range. A thorough description of the system is given, including (i) the vector-modulator providing purely electronic tuning of the pump-probe overlap up to 1 ms with sub-ps time resolution, (ii) the 500 MHz data acquisition system interfaced with the experimental physics and industrial control system (EPICS) based SLS control system for consecutive pulse sampling, and (iii) the step-scan time-slice Fourier transform scheme for simultaneous recording of the dual-channel pumped, un-pumped, and difference spectra. The typical signal/noise ratio of a single interferogram in a 100 ps time slice is 300 (measured during one single 140 s TopUp period). This signal/noise ratio is comparable to that of existing gated Globar pump-probe Fourier transform spectroscopy, but brings up to four orders of magnitude better time resolution. To showcase the utility of broadband pump-probe spectroscopy, we investigate a Ge-on-Si material system similar to that in which optically pumped direct-gap lasing was recently reported. We show that the mid-infrared reflection-spectra can be used to determine the optically injected carrier density, while the mid- and near-infrared transmission-spectra can be used to separate the strong pump-induced absorption and inversion processes present at the direct-gap energy.
The role of attractive forces in viscous liquids
Authors: Berthier Ludovic , Tarjus Gilles
Published: June 2011

We present evidence from computer simulation that the slowdown of relaxation of a standard Lennard-Jones glass-forming liquid and that of its reduction to a model with truncated pair potentials without attractive tails are quantitatively and qualitatively different in the viscous regime. The pair structure of the two models is however very similar. This finding, which appears to contradict the common view that the physics of dense liquids is dominated by the steep repulsive forces between atoms, is characterized in detail, and its consequences are explored. Beyond the role of attractive forces themselves, a key aspect in explaining the differences in the dynamical behavior of the two models is the truncation of the interaction potentials beyond a cutoff at typical interatomic distance. This leads us to question the ability of the jamming scenario to describe the physics of glass-forming liquids and polymers.
Two-component natural spinors from two-step spin-orbit coupled wave functions
Authors: Zeng Tao , Fedorov Dmitri G. , Schmidt Michael W. , Klobukowski Mariusz
Published: June 2011

We developed an algorithm to obtain the natural orbitals (natural spinors) from the two-step spin-orbit coupled wave functions. These natural spinors are generally complex-valued, mixing two spin components, and they can have similar symmetry properties as the j-j spinors from the one-step spin-orbit coupling calculations, if the reduced density equally averages all the components of a multi-dimensional irreducible representation. Therefore, the natural spinors can serve as an approximation to the j-j spinors and any wave function analysis based on the j-j spinors can also be performed based on them. The comparison between the natural spinors and the j-j spinors of three representative atoms, Tl, At, and Lu, shows their close similarity and demonstrates the ability of the natural spinors to approximate the j-j spinors.
Pressure induced crystallization in amorphous silicon
Authors: Pandey K. K. , Garg Nandini , Shanavas K. V. , Sharma Surinder M. , Sikka S. K.
Published: June 2011

We have investigated the high pressure behavior of amorphous silicon (a-Si) using x-ray diffraction and Raman scattering techniques. Our experiments show that a-Si undergoes a polyamorphous transition from the low density amorphous to the high density amorphous phase, followed by pressure induced crystallization to the primitive hexagonal (ph) phase. On the release path, the sequence of observed phase transitions depends on whether the pressure is reduced slowly or rapidly. Using the results of our first principles calculations, pressure induced preferential crystallization to the ph phase is explained in terms of a thermodynamic model based on phenomenological random nucleation and the growth process.
Effect of vacancy on the sliding of an iron grain boundary
Authors: Zhou Hong-Bo , Liu Yue-Lin , Duan Chen , Jin Shuo , Zhang Ying , Gao Fei , Shu Xiaolin , Lu Guang-Hong
Published: June 2011

We perform a first-principles calculation to investigate the effect of a vacancy on the sliding of an iron (Fe) Σ5 (310) [001] tilt grain boundary (GB). We calculate vacancy formation energies in order to determine the site preference of the vacancy at the Fe GB. We show that vacancies can easily segregate to the GB region, which is attributed to special atomic configurations of the GB. We demonstrate that the maximal sliding energy barrier of the GB with a monovacancy is 2.78 J/m2, 15% lower than that of the vacancy-free GB, suggesting that the presence of vacancy at the GB increases the GB mobility.
Improvement of sensitivity in high-resolution Rutherford backscattering spectroscopy
Authors: Hashimoto H. , Nakajima K. , Suzuki M. , Sasakawa K. , Kimura K.
Published: June 2011

The sensitivity (limit of detection) of high-resolution Rutherford backscattering spectroscopy (HRBS) is mainly determined by the background noise of the spectrometer. There are two major origins of the background noise in HRBS, one is the stray ions scattered from the inner wall of the vacuum chamber of the spectrometer and the other is the dark noise of the microchannel plate (MCP) detector which is commonly used as a focal plane detector of the spectrometer in HRBS. In order to reject the stray ions, several barriers are installed inside the spectrometer and a thin Mylar foil is mounted in front of the detector. The dark noise of the MCP detector is rejected by the coincidence measurement with the secondary electrons emitted from the Mylar foil upon the ion passage. After these improvements, the background noise is reduced by a factor of 200 at a maximum. The detection limit can be improved down to 10 ppm for As in Si at a measurement time of 1 h under ideal conditions.
I−·(CH3I)2 photoexcitation: The influence of dipole bound states on detachment and fragmentation
Authors: Van Duzor Matthew , Mbaiwa Foster , Lasinski Joshua , Holtgrewe Nicholas , Mabbs Richard
Published: June 2011

We present the results of a photoelectron imaging study of the I−·(CH3I)2 cluster anion over excitation wavelengths 355–260 nm. The resulting spectra and photoelectron angular distributions (PADs) suggest extensive electron-molecule interaction following photoexcitation. Fragmentation channels are observed subsequent to excitation between 355 and 330 nm. The origin of these features, which begin 200 meV and peak 70 meV below the X band direct detachment threshold, is described in terms of a predissociative dipole bound state. The nature of the fragments detected and the energetics of the channel opening argue strongly in favor of an asymmetric, head to tail cluster anion geometry posited by Dessent et al. [Acc. Chem. Res. 31, 527 (1998)]10.1021/ar950061f. Above the direct detachment threshold, PADs display evidence of phenomena akin to electron-molecule scattering. The fragment anions disappear above the X band threshold but reappear some distance below the second (A) direct detachment band. At these energies there is also rapid variation of the X band PAD, an observation attributed to autodetachment via spin-orbit relaxation of the iodine core of the cluster.
Enhanced piezoelectric and magnetic properties of Bi1−xCaxFe1−x/2Nbx/2O3 solid solutions
Authors: Troyanchuk I. O. , Tereshko N. V. , Karpinsky D. V. , Kholkin A. L. , Kopcewicz M. , Bärner K.
Published: June 2011

An investigation of the crystal structure, the magnetic and the piezoelectric properties of polycrystalline Bi1-xCaxFe1-x/2Nbx/2O3 (I) and Bi1-xPbxFe1-x/2Nbx/2O3 (II) systems was performed by x-ray diffraction, Mössbauer spectroscopy, vibrating sample magnetometry, and piezoresponse force microscopy. It is shown that an increasing niobium content induces a polar-to-nonpolar morphotropic boundary near x = 0.19 (I) and x = 0.3 (II). Within the polar region of the system (I), (0.15 ≤x ≤0.18), the solid solutions are homogeneous weak ferromagnets whereas compounds of the system (II) do not exhibit an appreciable spontaneous magnetization. It is assumed that chemical substitutions leading to a decrease of the initial volume of the unit cell favor the stabilization of the weak ferromagnetic state within the rhombohedral ferroelectric phase. The piezoresponse is significantly enhanced near the morphotropic boundary. The piezoelectric properties of the parent antiferromagnet BiFeO3, harboring a cycloidal spatially modulated spin structure, are compared with those of the polar weak ferromagnet Bi0.82Ca0.18Fe0.91Nb0.09O3.
Correlated barrier hopping in ZnO nanorods
Authors: Soosen Samuel M. , Chandran Anoop , Koshy Jiji , George K. C.
Published: June 2011

The ac conduction in ZnO nanorods has been investigated in the frequency range of 100 Hz−1 MHz and at various temperatures between 303 and 543 K. An agreement between experimental and theoretical results suggests that the ac conduction in ZnO nanorods can be successfully explained by Correlated Barrier Hopping model. PL spectrum gives the evidence of surface defects in ZnO nanorods which contribute to this type of conduction mechanism. The different physical parameters such as hopping distance, density of charged defect states, etc. are calculated from the experimental data.
Multiwavelength erbium-doped fiber laser based on intensity-dependent transmission in a linear cavity
Authors: Tian Jiajun , Yao Yong , Xiao Jun Jun , Xu Xiaochuan , Chen Deying
Published: June 2011

A multiwavelength erbium-doped fiber laser with linear cavity configuration is proposed and demonstrated. A power-symmetric nonlinear optical loop mirror (NOLM) serves as the laser’s output coupler and has an intensity-induced increase in transmission (IIT) that leads to higher cavity loss for oscillating wavelengths with higher power. The IIT feature of the NOLM suppresses the mode competition in the erbium-doped fiber and ensures stable multiwavelength operation at room temperature. Both the wavelength number and the output power of the laser can be flexibly controlled by adjusting the work state of the NOLM via a quarter wave plate and/or a polarization controller.
Acceleration of the effect of solute on the entropy-volume cross fluctuation density in aqueous 2-butoxyethanol, 1-propanol, and glycerol: The fourth derivative of Gibbs energy
Authors: Yoshida Koh , Baluja Shipra , Inaba Akira , Koga Yoshikata
Published: June 2011

Using a differential pressure perturbation calorimetry developed by us recently [K. Yoshida, S. Baluja, A. Inaba, K. Tozaki, and Y. Koga, “Experimental determination of third derivative of G (III): Differential pressure perturbation calorimetry (II),” J. Solution Chem. (in press)], we experimentally determined the partial molar S–V cross fluctuation density of solute B, SVδB , in binary aqueous solutions for B = 1-propanol (1P) and glycerol (Gly). This third derivative of G provides information about the effect of solute B on the S–V cross fluctuation density, SVδ, in aqueous solution as the concentration of B varies. Having determined SVδB by better than 1% uncertainty, we evaluated for the first time the fourth derivative quantity SVδB−B = N(∂SVδB /∂nB) for B = 1P and Gly graphically without resorting to any fitting functions within several percent. This model-free quantity gives information about the acceleration of the effect of solute B on SVδ. By comparing fourth derivative quantities, SVδB−B , among B = 1P, Gly, and 2-butoxyethanol obtained previously, the distinction of the effect of solute on H2O becomes clearer than before when only the third derivative quantities were available.
Two-dimensional electron gas transport anisotropy in N-polar GaN/AlGaN heterostructures
Authors: Umana-Membreno G. A. , Fehlberg T. B. , Kolluri S. , Brown D. F. , Keller S. , Mishra U. K. , Nener B. D. , Faraone L. , Parish G.
Published: June 2011

Magnetic-field dependent Hall-effect measurements and mobility spectrum analysis were employed to study anisotropic transport in N-polar GaN/Al0.3Ga0.7N heterostructures grown on vicinal sapphire substrates. The significant anisotropy in the mobility in the parallel and perpendicular directions to the miscut direction was accompanied by a slight anisotropy in charge density. A single electron species was found in the direction parallel to the steps resulting from growth on the vicinal substrates; while in the perpendicular direction two distinct electrons peaks were evident at T≤150 K. The lower average mobility in the perpendicular direction is attributed to interface roughness scattering.
Size-dependent photochromism-based holographic storage of Ag/TiO2 nanocomposite film
Authors: Han Runyuan , Zhang Xintong , Wang Lingling , Dai Rui , Liu Yichun
Published: June 2011

The influence of size distribution of Ag nanoparticles (NPs) on photochromic behavior and holographic storage dynamics of Ag/TiO2 films was investigated using a 532 nm laser as excitation source and recording beams, respectively. Experimental results suggest that small Ag NPs are subject to easier photoinduced oxidative dissolution than large Ag NPs under the 532 nm excitation, and contribute to the rapid growth of holographic grating in the initial stage. These observations were discussed in terms of size-dependent silver redox potential influencing both interfacial electron transfer among Ag NPs and TiO2 matrix and subsequent dissolution of Ag NPs, as well as surface plasmon resonance absorption property of Ag NPs also related to their size distribution.
Electronic properties of hydrogenated silicene and germanene
Authors: Houssa M. , Scalise E. , Sankaran K. , Pourtois G. , Afanas’ev V. V. , Stesmans A.
Published: June 2011

The electronic properties of hydrogenated silicene and germanene, so called silicane and germanane, respectively, are investigated using first-principles calculations based on density functional theory. Two different atomic configurations are found to be stable and energetically degenerate. Upon the adsorption of hydrogen, an energy gap opens in silicene and germanene. Their energy gaps are next computed using the HSE hybrid functional as well as the G0W0 many-body perturbation method. These materials are found to be wide band-gap semiconductors, the type of gap in silicane (direct or indirect) depending on its atomic configuration. Germanane is predicted to be a direct-gap material, independent of its atomic configuration, with an average energy gap of about 3.2 eV, this material thus being potentially interesting for optoelectronic applications in the blue/violet spectral range.
Two-dimensional measurement of the nonlinearity parameter B/A in excised biological samples
Authors: Saito Shigemi , Kim Jung-Ho
Published: June 2011

The method previously developed for measuring the acoustic nonlinearity parameter B/A in a liquid sample with a volume as small as 0.1 ml [S. Saito, J. Acoust. Soc. Am. 127, 51(2010)] has been automated and applied to two-dimensional measurements of excised biological samples using a LabVIEW program. The focus of the sound beam is laterally shifted on the 3 × 3 mm2 area of the sample while measuring the B/A successively. By displaying the result of 256 time repeated measurements with an interval of 0.2 mm in two dimensions, a C-mode image was generated for B/A. The images of linear properties such as density, sound speed, and attenuation coefficient are also obtained. The image, whose pattern can be different from those of the density and sound speed, has the capability to reveal the detailed structure of the B/A, which varies from region to region in a single biological sample. The application of the method to small samples is also demonstrated by measuring a thermally coagulated biological sample.
Generalized scattering control using cut-wire-based metamaterials
Authors: Wakatsuchi Hiroki , Christopoulos Christos
Published: June 2011

We numerically show how multiple band scattering parameters for arbitrary polarization can be easily designed by using cut-wire-based (CW-based) metamaterials, which enable us to control six fundamental scattering properties, i.e., reflection, transmission, absorption, and polarization independence, dependence and change. The structure shown here is composed of three-independent metamaterial designs, each of which has a different scattering profile. The use of the simple CW-based metamaterials is expected to facilitate complex scattering parameter design, which potentially contributes to the development of more complex and multiple band metamaterial applications.
Note: Direct measurement of the point-to-point resolution for microns-thick specimens in the ultrahigh-voltage electron microscope
Authors: Wang Fang , Cao Meng , Zhang Hai-Bo , Nishi Ryuji , Takaoka Akio
Published: June 2011

We report on a direct measurement method and results of the point-to-point resolution for microns-thick amorphous specimens in the ultrahigh-voltage electron microscope (ultra-HVEM). We first obtain the ultra-HVEM images of nanometer gold particles with different sizes on the top surfaces of the thick epoxy-resin specimens. Based on the Rayleigh criterion, the point-to-point resolution is then determined as the minimum distance between centers of two resolvable tangent gold particles. Some values of resolution are accordingly acquired for the specimens with different thicknesses at the accelerating voltage of 2 MV, for example, 18.5 nm and 28.4 nm for the 5 μm and 8 μm thick epoxy-resin specimens, respectively. The presented method and results provide a reliable and useful approach to quantifying and comparing the achievable spatial resolution for the thick specimens imaged in the mode of transmission electron including the scanning transmission electron microscope.
Seasonal changes in morphology and steroid receptor expression in the prostate of the brushtail possum (Trichosurus vulpecula): an animal model for the study of prostate growth?
Authors: Martyn Helen , Pugazhenthi Kamali , Gould Maree , Fink Jo W. , McLeod Bernie , Nicholson Helen D.
Published: June 2011

The prostate of the brushtail possum undergoes growth and regression during the year. The present study investigated the morphological changes and expression of androgen and oestrogen receptors during the breeding and non-breeding seasons. Prostate tissue was collected from adult possums at 2-monthly intervals. The periurethral and outer glandular areas were separated and the volume of stromal, epithelial and luminal tissues measured in each area. Immunohistochemistry was used to investigate cell proliferation with proliferating cell nuclear antigen (PCNA) and to localise androgen receptor (AR) and oestrogen receptors α and β (ERα, ERβ). Seasonal changes in expression of the three receptors were investigated using quantitative PCR and western blot analysis. During the breeding season the volume of stromal tissue in the periurethral area and the luminal volume in the glandular area significantly increased. The change in periurethral volume was associated with increased PCNA-immunopositive cells. While the localisation of AR to the stromal and epithelial cells did not change, there was a significant increase in receptor expression before the main breeding season. ERα and ERβ expression and localisation did not alter during the year. Similarities in receptor expression and localisation suggest that the possum may be a suitable animal model for the study of human prostate growth.
Boar semen can tolerate rapid cooling rates prior to freezing
Authors: Juarez Jorge D. , Parrilla Inma , Vazquez Juan M. , Martinez Emilio A. , Roca Jordi
Published: June 2011

Two experiments were performed in the present study that demonstrated that boar spermatozoa are capable of surviving rapid cooling rates within a range of 15–5°C before freezing. Boar ejaculates diluted in Beltsville thawing solution (BTS) (1 : 1, v/v) were held at 17–20°C and shipped over a 24-h time period from two AI centres to a cryobiology laboratory, where they were pooled (Experiment 1) or cryopreserved individually (Experiment 2) using a standard 0.5-mL straw freezing protocol. The effects of cooling before freezing were assessed after thawing through the objective evaluation of sperm motility and flow cytometric analysis of membrane integrity, acrosomal status, changes in membrane lipid architecture monitored by merocyanine and annexin V binding and intracellular production of reactive oxygen species. In Experiment 1 (six replicates), two semen pools (five ejaculates per pool) were cooled from 15 to 5°C at rates of 0.08, 0.13, 0.40 and 1.50°C min–1. These cooling rates did not result in any significant differences (P > 0.05) in any of the post-thaw sperm assessments, even in thawed samples incubated under capacitation conditions. In Experiment 2, three individual ejaculates from 16 boars were slowly (0.08°C min–1) or rapidly (1.5°C min–1) cooled before freezing. A consistent interboar variability (P < 0.01) was detected, which was independent of the cooling rate used. Cooling rate only significantly influenced (P < 0.05) sperm assessments in four of 16 boars, which exhibited slightly higher percentages of motile cells and intact plasma and acrosomal membranes in the samples that had been cooled slowly. These findings demonstrate that boar spermatozoa undergoing cryopreservation can withstand rapid cooling rates before freezing.
Leukaemia inhibitory factor mediated proliferation of HTR-8/SVneo trophoblast cells is dependent on activation of extracellular signal-regulated kinase 1/2
Authors: Prakash Golla Jaya , Suman Pankaj , Prieto Diana M. Morales , Markert Udo R. , Gupta Satish K.
Published: June 2011

Leukaemia inhibitory factor (LIF) is one of the cytokines that is indispensable for embryo implantation. The aim of the present study was to investigate the role of activation of extracellular signal-regulated kinase (ERK) 1/2 in LIF-mediated proliferation of HTR-8/SVneo cells. Stimulation of HTR-8/SVneo cells with LIF (50 ng mL–1) resulted in an increase in cell proliferation (P < 0.05) via increased transition of cells to the G2/M phase of cell cycle. Stimulation with LIF resulted in the activation of both signal transducer and activator of transcription (STAT) 3 Tyr705 and ERK1/2, but inhibition of ERK1/2 signalling by pretreatment of cells with U0126 (10 µM) for 2 h resulted in abrogation of LIF-mediated increases in G2/M transition, with a significant decrease (P < 0.05) in absolute cell numbers compared with control. Although STAT3 silencing had no effect on LIF-dependent proliferation of HTR-8/SVneo cells, it did result in an increase in cell apoptosis, which increased further upon inhibition of ERK1/2 activation irrespective of LIF stimulation. Stimulation of cells with LIF increased the Bcl-2/Bax ratio, whereas ERK1/2 inhibition decreased the Bcl-2/Bax ratio, even after LIF stimulation. Hence, it can be inferred that ERK1/2 activation is essential for LIF-mediated increases in proliferation and that both STAT3 and ERK1/2 activation are important for the survival of HTR-8/SVneo cells.
Increased Wingless (
Wnt
) signaling in pituitary progenitor/stem cells gives rise to pituitary tumors in mice and humans
Authors: Gaston-Massuet Carles , Andoniadou Cynthia Lilian , Signore Massimo , Jayakody Sujatha A. , Charolidi Nicoletta , Kyeyune Roger , Vernay Bertrand , Jacques Thomas S. , Taketo Makoto Mark , Le Tissier Paul , Dattani Mehul T. , Martinez-Barbera Juan Pedro
Published: June 2011

Wingless (Wnt)/β-catenin signaling plays an essential role during normal development, is a critical regulator of stem cells, and has been associated with cancer in many tissues. Here we demonstrate that genetic expression of a degradation-resistant mutant form of β-catenin in early Rathke's pouch (RP) progenitors leads to pituitary hyperplasia and severe disruption of the pituitary-specific transcription factor 1-lineage differentiation resulting in extreme growth retardation and hypopituitarism. Mutant mice mostly die perinatally, but those that survive weaning develop lethal pituitary tumors, which closely resemble human adamantinomatous craniopharyngioma, an epithelial tumor associated with mutations in the human β-catenin gene. The tumorigenic effect of mutant β-catenin is observed only when expressed in undifferentiated RP progenitors, but tumors do not form when committed or differentiated cells are targeted to express this protein. Analysis of affected pituitaries indicates that expression of mutant β-catenin leads to a significant increase in the total numbers of pituitary progenitor/stem cells as well as in their proliferation potential. Our findings provide insights into the role of the Wnt pathway in normal pituitary development and demonstrate a causative role for mutated β-catenin in an undifferentiated RP progenitor in the genesis of murine and human craniopharyngioma.