bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetic properties and microstructure of gas atomized MRE2(Fe,Co)14B powder with ZrC addition (MRE=Nd+Y+Dy)
Authors: Tang W. , Wu Y. Q. , Dennis K. W. , Oster N. T. , Kramer M. J. , Anderson I. E. , McCallum R. W.
Published: March 2009

Gas atomization powder with Zr substitutions for the MRE and ZrC additions were systematically studied. The results show that the partial substitutions of Zr and the ZrC additions effectively improved glass formability in the alloys. Scanning electron microscopy (SEM) revealed that the as-atomized powder with a particle size of less than 32 μm is predominately uniform equiaxed grains with an average grain size of 1.5 μm. X-ray diffraction and differential thermal analysis measurements detected very tiny amounts of amorphous phase. After annealing at 700 °C for 15 min, the SEM grain microstructure exhibits a minor change, but magnetic properties are substantially improved. M versus T measurements reveal that the phase composition evolved from 2:14:1 plus a small amount of 2:17 phases to a single 2:14:1 phase during the annealing process. The sieve analysis of the powders showed a particle size distribution with 90 wt % of the powder less than 45 μm. The magnetic properties of the annealed powder varied with particle size. (BH)max first increases with increasing particle size from 5 μm, reaches the peak value in the size range of 20–25 μm, and then decreases with increasing particle size. For the 20–25 μm powder sample annealed at 700 °C for 15 min, the (BH)max of 9.6 MG Oe at room temperature and 5.6 MG Oe at 200 °C were obtained, respectively.
Phase separation versus spin glass behavior in La0.85Sr0.15CoO3
Authors: Samal D. , Balamurugan K. , Shivakumara C. , Kumar P. S. Anil
Published: March 2009

We present comprehensive studies of dc magnetization, ac susceptibility, and magnetotransport of two sets of La0.85Sr0.15CoO3 samples, one exhibits phase separation and the other exhibits spin glass behavior. Our study reveals that the phase separation in La0.85Sr0.15CoO3 is neither inherent nor ubiquitous; rather, it is a consequence of preparation condition. It is realized that the low temperature annealed sample exhibits phase separation while the high temperature annealed one shows the characteristic of spin glass behavior. This study shows that the most probable magnetic state of La0.85Sr0.15CoO3 is spin glass.
Characteristics of thermally assisted magnetic recording in granular perpendicular media
Authors: Shiino Hirotaka , Kawana Mayumi , Miyashita Eiichi , Watanabe Sadayuki , Hayashi Naoto
Published: March 2009

The effect of thermally assisted magnetic recording using granular perpendicular media with a single-pole-trimmed head has been investigated. A read/write experiment using a spin stand in which the media were heated by laser irradiation demonstrated that the track average amplitude strongly depends on both the position of the write head relative to the center of the laser spot in the down-track direction and on the laser power. Although the signal-to-noise ratio increased with the coercivity of the media, the increment was small; this is thought to be caused by an increase in the switching field distribution of the media with temperature. Our results suggest that the magnetic constant of the media must be optimized with respect to the temperature of writing in order for high-density thermally assisted magnetic recording to be realized.
Grain isolated L10 FePt–Ta2O5 nanocomposite films with large coercivity for perpendicular recording applications
Authors: Lim B. C. , Chen J. S. , Hu J. F. , Lwin P. W. , Ding Y. F. , Cher K. M. , Liu B.
Published: March 2009

L 1 0  FePt–Ta2O5 films with (001) texture were synthesized by cosputtering FePt and Ta2O5 targets and in situ heated at 350 °C. The (001) preferred orientation was preserved even when doped with 20 vol % Ta2O5. The out-of-plane coercivity, Hc, increased from 6.7 kOe (for pure FePt film) to 8.8 kOe when doped with 20 vol % Ta2O5. Further increase in the dopant content to 25 and 30 vol % caused Hc to decrease significantly to below 3 kOe. Well-isolated FePt grains of tall column structures were observed for the 12 nm thick FePt film when doped with 20 vol %. The loop slope parameter, α, of such FePt film approached 1.
High sensitivity and multifunctional micro-Hall sensors fabricated using InAlSb/InAsSb/InAlSb heterostructures
Authors: Bando M. , Ohashi T. , Dede M. , Akram R. , Oral A. , Park S. Y. , Shibasaki I. , Handa H. , Sandhu A.
Published: March 2009

Further diversification of Hall sensor technology requires development of materials with high electron mobility and an ultrathin conducting layer very close to the material’s surface. Here, we describe the magnetoresistive properties of micro-Hall devices fabricated using InAlSb/InAsSb/InAlSb heterostructures where electrical conduction was confined to a 30 nm-InAsSb two-dimensional electron gas layer. The 300 K electron mobility and sheet carrier concentration were 36 500 cm2 V−1 s−1 and 2.5×1011 cm−2, respectively. The maximum current-related sensitivity was 2 750 V A−1 T−1, which was about an order of magnitude greater than AlGaAs/InGaAs pseudomorphic heterostructures devices. Photolithography was used to fabricate 1 μm×1 μm Hall probes, which were installed into a scanning Hall probe microscope and used to image the surface of a hard disk.
Quantitative detection of magnetic particles in a chromatographic membrane by a giant magnetoresistance sensor
Authors: Lee Kisu , Lee Seungkyo , Kim Jeong-Ryul , Cho B. K.
Published: March 2009

We used streptavidin-coated magnetic particles (Dynabeads® M-280) for an immunochromatographic test, instead of colloidal gold particles, which was widely used in a conventional technique. The concentration of magnetic particles in a membrane was quantitatively analyzed by using a giant magnetoresistance (GMR) sensor with a sensitivity of 0.17%/Oe. As a specific zone with a localized concentration of the magnetic particles passed through a GMR sensor, it was observed that the magnitude of sensing signals is proportional to the density of magnetic particles. Therefore, this result suggests that a GMR sensor, which was studied in this paper, can be used for the quantitative detection with a high sensitivity of specific analytes in the immunochromatographic assays, when the analytes were coated on magnetic particles.
CoRuCr-oxide intermediate layers for perpendicular magnetic recording media
Authors: Piramanayagam S. N. , Srinivasan K.
Published: March 2009

CoRuCr-oxide based intermediate layers have been introduced as a replacement for pure Ru-based intermediate layers in perpendicular recording media. It was observed that the CoRuCr intermediate layers provide better C-axis orientation than the Ru intermediate layers. The introduction of oxygen during the deposition of CoRuCr increases the C-axis dispersion slightly but it is still comparable to that of Ru intermediate layer. Grain size and grain size distribution were reduced with CoRuCr-oxide intermediate layers. Magnetic properties were also optimized, indicating that the CoRuCr-oxide intermediate layers are good candidates for perpendicular recording media.
Evaluation of distribution of exchange coupling in CoFe/Ru/CoFe synthetic antiferromagnetic structure after annealing
Authors: Takenaga Takashi , Takada Hiroshi , Tomohisa Shingo , Furukawa Taisuke , Kuroiwa Takeharu , Yoshiara Kiichi
Published: March 2009

We investigated the exchange-coupling fields of CoFe/Ru (tRu)/CoFe synthetic antiferromagnetic (SyAF) structures with a Ru underlayer and capping layer before and after annealing at 300 and 350 °C. Exchange-coupling field Hex decreased after annealing and distribution increases in Hex were observed in the structure of smaller tRu, especially at tRu≤0.7 nm. Remanence magnetizations increased at smaller tRu. These results indicate that distribution is caused by the existence of the antiferromagnetic coupling of locally various coupling fields due to annealing. A larger exchange-coupling field after high temperature annealing can be obtained by suppressing the distribution of the exchange coupling in the SyAF structure.
Microscopic surface photovoltage spectroscopy of the CdSe/ZnCdMgSe quantum dots structures
Authors: Malikova L. , Holden Todd , Perez-Paz M. Noemi , Muñoz M. , Tamargo M. C.
Published: March 2009

We present room temperature microscopic (100 nm resolution) surface photovoltage spectra of three CdSe/ZnCdMgSe quantum dot structures with different CdSe deposition times. Observed spectroscopic features were attributed to absorption in the barrier, quantum dot, and wetting layer. Good agreement with photoluminescence measurements was observed. Our results indicate that photogenerated carriers are confined within large quantum dots, but for small quantum dots there is significant tunneling of photogenerated holes to surface states. Our study shows that surface photovoltage spectroscopy is a useful tool for studying carrier tunneling and vertical coupling between quantum dots.
Preparation of soft magnetic FeCo-based films for writers
Authors: Wang Xuan , Zheng Fu , Liu Zhaoyang , Liu Xiaoxi , Wei Dan , Wei Fulin
Published: March 2009

New soft magnetic head materials, the nanocrystalline FeCoAlOC thin films, were prepared by introducing C element in epoxy resin during rf sputtering of FeCoAlO films. When Al2O3 was cosputtered with FeCo, soft magnetic properties of thin films were highly improved: the coercive force decreases from dozen of oersted to several oersted (Hch∼4.8 Oe and Hce∼6.5 Oe). With further addition of carbon, the thin films exhibit excellent soft magnetic properties and good high frequency response: the coercivity is as low as 1.0 Oe, with saturation Bs>20 kG, permeability μ′>500 when f≤1.0 GHz, and cutoff frequency around 1.7 GHz. The measurement of microstructure shows that the good magnetic properties are correlated with the small gain size of film.
Facile hydrothermal preparation and characterizations of single crystalline Ge dioxide nanowires
Authors: Pei L. Z. , Zhao H. S. , Tan W. , Zhang Q. F.
Published: March 2009

Bulk-quantity single crystalline Ge dioxide nanowires (GeONWs) have been prepared via a facile and simple hydrothermal deposition process using GeO2 powder. Transmission electron microscopy (TEM) observations show that the GeONWs have a high purity, diameter ranging from 30 to 300 nm, and length of longer than 10 μm. X-ray diffraction, Fourier transform infrared, high-resolution TEM, and selected area electron diffraction pattern of the GeONWs indicate that the nanowires are single crystalline GeO2 with hexagonal structure. Room temperature photoluminescence measurement shows that the synthesized GeONWs have intense violet light emission and blue light emission at 370 and 476 nm, respectively. It is proposed that the GeONWs may follow the vapor-solid growth mechanism.
Origin of high strength and nanophotonic properties of crab shell (Paralithodes camtschaticus)
Authors: Aurognzeb Deeder
Published: March 2009

Understanding biomaterial is very important for superior material development. Here, we report structural and nanophotonic properties of crab shell. The fibrous shell is composed of nanocrystalline calcite, which gives the structure very high strength. Scanning electron microscope cross section and energy dispersive x-ray shows top surface (reddish) is fibrous with metal nanoparticle segregation, while the bottom layer is composed of layered nanohole array similar to air-dielectric photonic lattice structure. The air-dielectric nanohole arrays are disordered but correlated with fractal dimension >1 and able to block infrared. Nanocrystalline calcite and metal nanoparticles can also block extreme level of UV.
Temperature dependence of refractive index and electronic polarizability of KNbGeO5 glass and its nanocrystallized glasses
Authors: Honma Tsuyoshi , Ito Noriko , Dimitrov Vesselin , Komatsu Takayuki
Published: March 2009

The refractive indices (n) and densities (ρ) of a glass and transparent nanocrystallized glasses with the composition of 25K2O-25Nb2O5–50GeO2 (i.e., KNbGeO5) are measured in the temperature range of 30–150 °C in order to clarify the temperature dependences of the electronic polarizability of oxide ions (αO2−) and optical basicity (Λ). It is found that the values of n, αO2−, and Λ increase almost linearly with increasing temperature, and the values of the temperature dependence of these properties, i.e., dn/dT, dαO2−/dT, and dΛ/dT, tend to decrease slightly due to the nanocrystallization. It is clarified that the temperature dependence of the electronic polarizability of oxide ions in the precursor glass and nanocrystallized glasses has a large contribution for the temperature dependence of the refractive index in comparison with the contribution of density (volume thermal expansion). The features in the temperature dependences of αO2− and Λ in the present glass system is related to the large optical basicities of the constituent oxides of K2O, Nb2O5, and GeO2.
Observation of two elastic thresholds in GexAsySe1−x−y glasses
Authors: Wang R. P. , Smith A. , Luther-Davies B. , Kokkonen H. , Jackson I.
Published: March 2009

We have prepared GexAsySe1−x−y glasses with mean coordination numbers (MCNs) from 2.2 to 2.86. Tg was found to generally increase with increasing MCN while the glass density showed a maximum at MCN≈2.45 and a minimum at MCN≈2.65. The elastic moduli of the glasses were estimated from the shear and compressional wave velocities measured by ultrasonic pulse interferometry. For the first time we simultaneously observed two elastic transition thresholds, the first at MCN≈2.45 and the second at MCN≈2.65, which appear closely correlated with changes in the glass microstructure. The elastic moduli of two groups of samples with the same MCN=2.4 and 2.64 but different compositions suggest that the chemical compositions also have an influence on the elastic properties.
Effects of π-stacking interactions on the near carbon K-edge x-ray absorption fine structure: A theoretical study of the ethylene pentamer and the phthalocyanine dimer
Authors: Linares Mathieu , Stafström Sven , Norman Patrick
Published: March 2009

X-ray absorption spectra have been determined for ethylene and free base phthalocyanine at the carbon K-edge with use of the complex polarization propagator method combined with Kohn–Sham density functional theory and the Coulomb attenuated method B3LYP exchange-correlation functional. Apart from isolated molecules, the study includes π-stacked systems of the phthalocyanine dimer and the ethylene dimer, trimer, tetramer, and pentamer. For ethylene, π-stacking involves a reduction in transition energy of the valence π∗-band by some 70 meV and large spectral changes (regarding also shape and intensity) of the Rydberg bands. For phthalocyanine, there are large spectral changes in the entire valence π∗-part of the spectrum.
Effect of mechanical strain on 1/f noise in metal-oxide semiconductor field-effect transistors
Authors: Lim Ji-Song , Acosta Antonio , Thompson Scott E. , Bosman Gijs , Simoen Eddy , Nishida Toshikazu
Published: March 2009

The drain current 1/f noise power spectral density (PSD) is measured on industrial long channel metal-oxide-semiconductor field-effect transistors (MOSFETs) under externally applied mechanical stress. It is observed that 1/f noise PSD increases for both n-channel MOSFETs under uniaxial tensile stress and p-channel MOSFETs under uniaxial compressive stress. The strain-induced noise PSD change is also frequency dependent with larger changes at lower frequencies. The change in noise PSD magnitude is shown to be primarily due to mechanical strain-induced mobility change while the change in noise index α in the 1/fα spectrum is attributed to strain-induced energy level shift in the inversion layer and/or trap redistribution in energy and space.
Microwave switches based on graphene
Authors: Dragoman M. , Dragoman D. , Coccetti F. , Plana R. , Muller A. A.
Published: March 2009

We investigated a double-clamped graphene device positioned over a planar waveguide in which propagate electromagnetic fields up to 60 GHz. Several double-clamped graphene flakes display good characteristics in enabling and disabling the propagation of high-frequency electromagnetic fields. The same characteristics were retrieved in a graphene switch based on the rapid change in the resistivity due to an applied gate voltage. Both devices are among the fastest switches, the switching time being very short less than 1 ns.
Two-stage-like glass transition and the glass-forming ability of a soft magnetic Fe-based glassy alloy
Authors: Zhang Wei , Jia Fei , Zhang Xingguo , Xie Guoqiang , Kimura Hisamichi , Inoue Akihisa
Published: March 2009

The structure, thermal stability, and crystalline behavior of (Fe0.9Co0.1)67.5Nb4Gd3.5B25 glassy alloy, which exhibits a two-stage-like glass transition phenomenon, were investigated using x-ray diffraction, transmission electron microscopy, and differential scanning calorimetry. The nanoscale metastable (Fe,Co)23B6 phase precipitated in the glassy matrix after annealing, while the two-stage-like glass transition disappeared, indicating the two-stage-like glass transition results from the overlap of the endothermic reaction for the glass transition with the exothermic reaction for the formation of the (Fe,Co)23B6 phase in the supercooled liquid region. The (Fe0.9Co0.1)67.5Nb4Gd3.5B25 glassy alloy exhibits high glass-forming ability, enabling the formation of glassy alloy rods with diameters exceeding 3.0 mm, rather high saturation magnetization of 0.91 T, low coercive force of 2.5 A/m, and high fracture strength of 3870 MPa.
Study of monoclinic-tetragonal-cubic phase transition in Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 single crystals by micro-Raman spectroscopy
Authors: Cheng Juan , Yang Yang , Tong Yan-Hua , Lu Sheng-Bo , Sun Jing-Ya , Zhu Ke , Liu Yu-Long , Siu G. G. , Xu Z. K.
Published: March 2009

The relaxor ferroelectric Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 (PZN–0.08PT) single crystal has been investigated using polarized micro-Raman scattering technique in a wide temperature range from −150 to 350 °C. Raman spectra of the crystal at temperatures lower than 90 °C show 11 modes over a frequency range of 100–1000 cm−1. There are 12 Raman active vibration modes in the monoclinic structure of relaxor ferroelectrics according to the group theory analysis. Thus the structure of PZN-0.08PT single crystal at low temperatures is confirmed as monoclinic. Two structural phase transitions in the crystal were observed when the temperature was increasing. First, the monoclinic-tetragonal (M-T) phase transition happens at 90 °C. Second, the tetragonal-cubic (T-C) phase transition takes place at 170 °C.
Determining the excess carrier lifetime in crystalline silicon thin-films by photoluminescence measurements
Authors: Rosenits Philipp , Roth Thomas , Warta Wilhelm , Reber Stefan , Glunz Stefan W.
Published: March 2009

A valuable nondestructive measurement and analysis method for determining individual excess carrier lifetimes in multilayer systems is presented. This is particularly interesting for the characterization of crystalline silicon thin-film samples consisting of an electrically active epitaxial layer on top of a highly doped crystalline substrate. The analysis principle is based on a comparison between a measured photoluminescence intensity ratio and associated simulated radiative recombination ratios for samples with different epitaxial layer thicknesses. It benefits from the fact that for low excess carrier lifetimes within the epitaxial layer the carrier concentration in the said layer is limited by bulk recombination, while for high carrier lifetimes surface and interface recombination is dominating. In order to verify this measurement and analysis principle, results of a set of crystalline silicon thin-film samples with varying epitaxial layer thickness on a highly doped Czochralski substrate are presented.
Real-time microstructure of shocked LiF crystals: Use of synchrotron x-rays
Authors: Turneaure Stefan J. , Gupta Y. M. , Zimmerman K. , Perkins K. , Yoo C. S. , Shen G.
Published: March 2009

We describe the use of a third generation synchrotron facility to obtain in situ, real-time, x-ray diffraction measurements in plate impact experiments. Subnanosecond duration x-ray pulses were utilized to record diffraction data from pure and magnesium-doped LiF single crystals shocked along the [111] and [100] orientations. The peak stresses were 3.0 GPa for the [111] oriented LiF and between 3.0 and 5.0 GPa for the [100] oriented LiF. For these stresses, shock compression along [111] results in elastic deformation and shock compression along [100] results in elastic-plastic deformation. Because of the quality of the synchrotron x-ray pulses, both shifting and broadening of the diffraction data were obtained simultaneously. As expected, shifts for elastic compression and elastic-plastic compression in shocked LiF were consistent with uniaxial and isotropic lattice compression, respectively. More importantly, diffraction patterns from crystals shocked along [100] exhibited substantial broadening due to elastic-plastic deformation. The broadening indicates that the shocked LiF(100) crystals developed substructure with a characteristic size for coherently diffracting domains (0.1–10 μm) and a distribution of (100) microlattice-plane rotations (∼1° wide). In contrast to the LiF(100) results, broadening of the diffraction pattern did not occur for elastically deformed LiF(111). Another important finding was that the amount of lattice disorder for shocked LiF(100) depends on the loading history; the broadening was larger for the magnesium-doped LiF(100) (large elastic precursor) than for ultrapure LiF(100) (small elastic precursor) shocked to the same peak stress. The data are simulated by calculating the diffraction pattern from LiF(100) with a model microstructure consisting of coherently diffracting domains. The lattice orientation and longitudinal strain is assumed uniform within domains, but they vary from domain to domain with Gaussian distributions. Simulations using such a model are in good agreement with the measured diffraction patterns. The principal finding from the present work is that synchrotron x-rays can provide real-time data regarding microstructure changes accompanying shock-induced deformation and structural changes.
Plume detachment from a magnetic nozzle
Authors: Deline Christopher A. , Bengtson Roger D. , Breizman Boris N. , Tushentsov Mikhail R. , Jones Jonathan E. , Chavers D. Greg , Dobson Chris C. , Schuettpelz Branwen M.
Published: March 2009

High-powered electric propulsion thrusters utilizing a magnetized plasma require that plasma exhaust detach from the applied magnetic field in order to produce thrust. This paper presents experimental results demonstrating that a sufficiently energetic and flowing plasma can indeed detach from a magnetic nozzle. Microwave interferometer and probe measurements provide plume density, electron temperature, and ion flux measurements in the nozzle region. Measurements of ion flux show a low-beta plasma plume which follows applied magnetic field lines until the plasma kinetic pressure reaches the magnetic pressure and a high-beta plume expanding ballistically afterward. Several magnetic configurations were tested including a reversed field nozzle configuration. Despite the dramatic change in magnetic field profile, the reversed field configuration yielded little measurable change in plume trajectory, demonstrating the plume is detached. Numerical simulations yield density profiles in agreement with the experimental results.
Dielectric relaxation in particle-filled polymer: Influence of the filler particles and thermal treatments
Authors: Adohi B. J.-P. , Brosseau C.
Published: March 2009

Variable-temperature measurements of the frequency-dependent complex effective permittivity are performed on silicon dioxide loaded epoxy resin composites. Two relaxation peaks due to conductivity and α-relaxation processes are identified. The amplitude and relaxation frequency of each peak strongly vary according to filler and material treatments while the activation energy of the Arrhenius ionic conductivity remains unchanged. These trends are compared to previous works. We argue that the changes in amplitude and relaxation frequency can be attributed to ions trapped in silicon dioxide particles and to a significant change in the elasticity network of the polymer chains.
Structure, magnetization, and low-temperature spin dynamic behavior of zincblende Mn-rich Mn(Ga)As nanoclusters embedded in GaAs
Authors: Wang W. Z. , Deng J. J. , Lu J. , Sun B. Q. , Wu X. G. , Zhao J. H.
Published: March 2009

We have fabricated a set of samples of zincblende Mn-rich Mn(Ga)As clusters embedded in GaAs matrices by annealing (Ga,Mn)As films with different nominal Mn content at 650 °C. For the samples with Mn content no more than 4.5%, the Curie temperature reaches nearly 360 K. However, when Mn content is higher than 5.4%, the samples exhibit a spin-glass-like behavior. We suggest that these different magnetic properties are caused by the competing result of dipolar and Ruderman–Kittel–Kasuya–Yosida interaction among clusters. The low-temperature spin dynamic behavior, especially the relaxation effect, shows the extreme creeping effect which is reflected by the time constant τ of ∼1011 s at 10 K. We explain this phenomenon by the hierarchical model based on the mean-field approach. We also explain the memory effect by the relationship between the correlation function and the susceptibility.
Stabilization of ion temperature gradient driven modes by lower hybrid wave in a tokamak
Authors: Kuley Animesh , Tripathi V. K.
Published: March 2009

A gyrokinetic formalism has been developed to study lower hybrid wave stabilization of ion temperature gradient driven modes, responsible for anomalous ion transport in the inner region of tokamak. The parametric coupling between lower hybrid and drift waves produce lower hybrid sideband waves. The pump and the sidebands exert a ponderomotive force on electrons, modifying the eigenfrequency of the drift wave and influencing the growth rate. The longer wavelength drift waves are destabilized by the lower hybrid wave while the shorter wavelengths are suppressed. The requiste lower hybrid power is in the range of ∼900 kW at 4.6 GHz.
Comment regarding “On the Crooks fluctuation theorem and the Jarzynski equality” [J. Chem. Phys. 129, 091101 (2008)] and “Nonequilibrium fluctuation-dissipation theorem of Brownian dynamics” [J. Chem. Phys. 129, 144113 (2008)]
Authors: Crooks G. E.
Published: March 2009

The incongruous “unexpected inapplicability of the Crook’s fluctuation theorem” is due to an inexplicable, inappropriate use of inconsistent expressions. The girding is secure.
Quasilattice approximation of statistical systems with strong superstable interactions: Correlation functions
Authors: Rebenko A. L. , Tertychnyi M. V.
Published: March 2009

A continuous infinite system of point particles interacting via two-body strong superstable potential is considered in the framework of classical statistical mechanics. We define some kind of approximation of main quantities, which describe macroscopical and microscopical characteristics of systems, such as grand partition function and correlation functions. The pressure of an approximated system converges to the pressure of the initial system if the parameter of approximation a→0 for any values of an inverse temperature β>0 and a chemical activity z. The same result is true for the family of correlation functions in the region of small z.
Bounding the electrostatic free energies associated with linear continuum models of molecular solvation
Authors: Bardhan Jaydeep P. , Knepley Matthew G. , Anitescu Mihai
Published: March 2009

The importance of electrostatic interactions in molecular biology has driven extensive research toward the development of accurate and efficient theoretical and computational models. Linear continuum electrostatic theory has been surprisingly successful, but the computational costs associated with solving the associated partial differential equations (PDEs) preclude the theory’s use in most dynamical simulations. Modern generalized-Born models for electrostatics can reproduce PDE-based calculations to within a few percent and are extremely computationally efficient but do not always faithfully reproduce interactions between chemical groups. Recent work has shown that a boundary-integral-equation formulation of the PDE problem leads naturally to a new approach called boundary-integral-based electrostatics estimation (BIBEE) to approximate electrostatic interactions. In the present paper, we prove that the BIBEE method can be used to rigorously bound the actual continuum-theory electrostatic free energy. The bounds are validated using a set of more than 600 proteins. Detailed numerical results are presented for structures of the peptide met-enkephalin taken from a molecular-dynamics simulation. These bounds, in combination with our demonstration that the BIBEE methods accurately reproduce pairwise interactions, suggest a new approach toward building a highly accurate yet computationally tractable electrostatic model.
Explicit algebraic Reynolds stresses and scalar fluxes for density-stratified shear flows
Authors: Violeau D.
Published: March 2009

An explicit algebraic model for Reynolds stresses and active scalar turbulent fluxes is proposed for simply stratified, stable shear flows such as atmospheric boundary layers of estuaries, including buoyant effects due to density variations (temperature, salinity). Under equilibrium assumptions, these models lead to explicit functions of the gradient Richardson number Ri that model the damping of the eddy viscosity and eddy diffusivity coefficients. The present model is compared to other existing theoretical approaches, as well as experimental observations, with satisfactory agreement. The evolution of the turbulent Prandtl number as a function of Ri is correctly predicted and its neutral value is consistent with existing values in the literature. The behavior of the model predicts that internal waves are responsible for momentum diffusion at large Ri, consistently with recent publications. The properties of turbulence anisotropy are briefly investigated.
Radiative transitions in P- and B-doped silicon nanocrystals
Authors: de Oliveira E. L. , Albuquerque E. L. , de Sousa J. S. , Farias G. A.
Published: March 2009

The radiative transitions in P- and B-doped Si nanocrystals are investigated by means of first-principle calculations. Using a three-level model, we show that the radiative lifetimes and oscillator strengths of the transitions between the conduction and the impurity bands, as well as the transitions between the impurity and the valence bands are strongly affected by the impurity position. On the other hand, the direct conduction-to-valence band decay is practically unchanged due to the presence of the impurity. In addition, the emission intensity of P(B)-doped nanocrystals with impurities positioned in the surface (anywhere) is higher (lower) than for pure nanocrystals.
Accuracies of the empirical theories of the escape probability based on Eigen model and Braun model compared with the exact extension of Onsager theory
Authors: Wojcik Mariusz , Tachiya M.
Published: March 2009

This paper deals with the exact extension of the original Onsager theory of the escape probability to the case of finite recombination rate at nonzero reaction radius. The empirical theories based on the Eigen model and the Braun model, which are applicable in the absence and presence of an external electric field, respectively, are based on a wrong assumption that both recombination and separation processes in geminate recombination follow exponential kinetics. The accuracies of the empirical theories are examined against the exact extension of the Onsager theory. The Eigen model gives the escape probability in the absence of an electric field, which is different by a factor of 3 from the exact one. We have shown that this difference can be removed by operationally redefining the volume occupied by the dissociating partner before dissociation, which appears in the Eigen model as a parameter. The Braun model gives the escape probability in the presence of an electric field, which is significantly different from the exact one over the whole range of electric fields. Appropriate modification of the original Braun model removes the discrepancy at zero or low electric fields, but it does not affect the discrepancy at high electric fields. In all the above theories it is assumed that recombination takes place only at the reaction radius. The escape probability in the case when recombination takes place over a range of distances is also calculated and compared with that in the case of recombination only at the reaction radius.
Comment on “High-resolution core-level photoemission study on GaAs(111)B surfaces” [J. Appl. Phys. 101, 043516 (2007)]
Authors: Farrell H. H. , Schultz B. D. , Palmstrøm C. J.
Published: March 2009

Photoemission work by Nakamura et al. [J. Appl. Phys. 101, 043516 (2007)] on the GaAs(111)B(√19×√19)R23° surface shows that the surface region contains three different types of As atoms and two different types of Ga atoms. The outstanding feature of their data is the presence of Ga atoms in the outermost layer of the reconstruction, which they conclude is inconsistent with published models. However, there are two published models, which were not identified in the paper, that contain these top-layer Ga atoms. Additionally, one of the two models also contains three distinct types of As surface atoms and two distinct types of Ga surface atoms as identified experimentally by Nakamura et al. [J. Appl. Phys. 101, 043516 (2007)].
Effect of the miscut direction in (111) 3C-SiC film growth on off-axis (111)Si
Authors: Severino A. , Camarda M. , Condorelli G. , Perdicaro L. M. S. , Anzalone R. , Mauceri M. , La Magna A. , La Via F.
Published: March 2009

Two miscut directions of (111) Si substrate on 3C-SiC heteroepitaxial growth have been studied with the resulting 3C-SiC stress and defects as a function of miscut axis direction toward [110] and [112] of (111) Si analyzed. We studied this dependency from an experimental point of view, investigating the structural properties of 3C-SiC, and using a kinetic Monte Carlo method on superlattice to confirm our experimental findings with numerical simulations. Residual stress and stacking fault density were halved by growing on a (111) Si substrate off-cut toward the [110] direction. A different surface morphology was revealed between the two inclinations.
Dust ion-acoustic shocks in quantum dusty pair-ion plasmas
Authors: Misra A. P.
Published: March 2009

The formation of dust ion-acoustic shocks in a four-component quantum plasma whose constituents are electrons, both positive and negative ions, and immobile charged dust grains, is studied. The effects of both the dissipation due to kinematic viscosity and the dispersion caused by the charge separation as well as the quantum tunneling associated with the Bohm potential are taken into account. The propagation of small but finite amplitude dust ion-acoustic waves is governed by the Korteweg–de Vries–Burger equation, which exhibits both oscillatory and monotonic shocks depending not only on the viscosity parameters η±=μ±ωp−/cs2 (where μ± are the coefficients of kinematic viscosity, ωp− is the plasma frequency for negative ions, and cs is the ion-sound speed), but also on the quantum parameter H (the ratio of the electron plasmon to the electron Fermi energy) and the positive to negative ion density ratio β. Large amplitude stationary shocks are recovered for a Mach number (M) exceeding its critical value (Mc). Unlike the small amplitude shocks, quite a smaller value of η+, η−, H and β may lead to the large amplitude monotonic shock structures. The results could be of importance in astrophysical and laser produced plasmas.
The dynamic Jahn–Teller effect in Cu(II) doped MgO
Authors: Riley Mark J. , Noble Christopher J. , Tregenna-Piggott Philip L. W.
Published: March 2009

The electron paramagnetic resonance spectra of Cu(II) doped MgO single crystals have been re-examined in detail within the framework of a dynamic Jahn–Teller effect. The experimental 1.8 K X-band spectra can be modeled in terms of a cubic spin Hamiltonian operating within the set of four Kramers doublets corresponding to the lowest vibronic energy levels of an E⊗e Jahn–Teller problem. This “four state” model must also include vibronic (Ham) reduction factors and a random distribution of the crystal strain. It was found to be important to treat the Zeeman, hyperfine, quadrupole, tunneling, and strain terms without recourse to perturbation theory or other approximations and this has been carried out using the eigenfield method. We find that the first excited singlet is of A2 symmetry, indicating that the CuO6 center has the expected E⊗e Jahn–Teller potential energy surface with three equivalent minima at tetragonally elongated octahedral geometries. Small random crystal strains have a dominant influence on the spectra and we find that the major features can be reproduced by averaging over the strain in the angular direction ϕs with a small magnitude centered about zero. Details of the strain broadening require a distribution of strains centered at zero with a larger spread; however, the use of a single intrinsic linewidth could not account for all linewidth features. Our analysis also differs from that of previous workers in that different hyperfine values (A1=−20.0×10−4 and A2=−86.0×10−4 cm−1) are required as well as a nuclear quadrupole term (P2=+8.75×10−4 cm−1) to account for the observed structure and the angular dependence. The transitions within the lowest excited singlet are observed directly, giving an estimate of the tunneling splitting as ∼4 cm−1. These parameter values are related to the intrinsic Jahn–Teller coupling parameters of the potential energy surface. We conclude that the Cu(II)/MgO system can be described as an almost pure dynamic Jahn–Teller case, with most spectral features accounted for by using a single isolated Γ8(E2) vibronic state.
Binding energies between unlike atoms determined from island densities
Authors: Einax Mario , Dieterich Wolfgang , Maass Philipp
Published: March 2009

Measurements of island densities during submonolayer nucleation and growth can be used to determine adatom diffusion constants and effective binding energies between like atoms. While this “nucleation route” is well established for monocomponent systems, we here present a new procedure to determine effective binding energies between unlike atoms by analyzing island densities obtained from codeposition of different components. The procedure is based on a theory developed recently [M. Einax et al., Phys. Rev. Lett. 99, 016106 (2007); W. Dieterich et al., Eur. Phys. J. Spec. Top. 161, 151 (2008)] and its practical applicability is demonstrated by generating experimental surrogate data by kinetic Monte Carlo simulations.
Swimming speeds of filaments in nonlinearly viscoelastic fluids
Authors: Fu Henry C. , Wolgemuth Charles W. , Powers Thomas R.
Published: March 2009

Many micro-organisms swim through gels and non-Newtonian fluids in their natural environments. In this paper, we focus on micro-organisms which use flagella for propulsion. We address how swimming velocities are affected in nonlinearly viscoelastic fluids by examining the problem of an infinitely long cylinder with arbitrary beating motion in the Oldroyd-B fluid. We solve for the swimming velocity in the limit in which deflections of the cylinder from its straight configuration are small relative to the radius of the cylinder and the wavelength of the deflections; furthermore, the radius of the cylinder is small compared to the wavelength of deflections. We find that swimming velocities are diminished by nonlinear viscoelastic effects. We apply these results to examine what types of swimming motions can produce net translation in a nonlinear fluid, comparing to the Newtonian case, for which Purcell’s “scallop” theorem describes how time-reversibility constrains which swimming motions are effective. We find that a leading order violation of the scallop theorem occurs for reciprocal motions in which the backward and forward strokes occur at different rates.
Luminescence mechanisms of silicon-rich nitride films fabricated by atmospheric pressure chemical vapor deposition in N2 and H2 atmospheres
Authors: Lin Chia-Hung , Uen Wu-Yih , Lan Shan-Ming , Huang Yen-Chin , Liao Sen-Mao , Li Zhen-Yu , Yang Tsun-Neng , Ku Chien-Te , Chen Meng-Chu , Huang Yu-Hsiang
Published: March 2009

This work examines possible luminescence mechanisms of silicon-rich nitride (SRN) films that were fabricated by atmospheric pressure chemical vapor deposition (APCVD). Under an ambient gas of either H2 or N2, two SRN films were deposited using the same precursors of Si and N. While photoluminescence (PL) measurements of both as-deposited specimens revealed an intense luminescence band (1.8–3.8 eV), which was observable by the naked eye, a detailed examination of the high energy band of the PL spectra over 2.8 eV yielded different results for those samples that were fabricated in different ambiences. To determine the reason for these differences, Fourier-transform infrared spectroscopy and x-ray photoelectron spectroscopy were conducted, suggesting unique chemical bonds and elemental ratio of nitrogen to silicon in SRN films. Further analysis involving plan-view high-resolution transmission electron microscopic observations of SRN films demonstrated the embedding of Si quantum dots (Si QDs), but with some differences depending on the deposition environment. Analyses of the results obtained suggest that the emission from SRN films that were deposited by APCVD is not only dominated by the quantum confinement effect of Si QDs, but also subordinately affected by the surface states around these Si QDs.
Efficiency enhancement of a high power microwave generator based on a relativistic backward wave oscillator with a resonant reflector
Authors: Xiao Renzhen , Chen Changhua , Zhang Xiaowei , Sun Jun
Published: March 2009

A high power microwave generator based on a relativistic backward wave oscillator with a resonant reflector (BWO-RR) has been proposed in order to improve microwave conversion efficiency. In this device, the slow wave structure is separated by a modulation cavity, which significantly decreases the energy spread of the modulated beam electrons. At the end of the slow wave structure, an extraction cavity is employed to increase the beam-wave interaction and optimize the extraction of the output power. Particle-in-cell simulations show that a microwave efficiency of 46% has been obtained compared with that of 34% obtained with the BWO-RR.
Effect of external electrostatic charge on condensed phase domains at the air-water interface: Experiment and shape equation analysis
Authors: Ou-Yang Wei , Weis Martin , Yamamoto Tetsuya , Manaka Takaaki , Iwamoto Mitsumasa
Published: March 2009

The effect of external electrostatic charge on the shapes of liquid condensed (LC) phase domains in monolayer at the air/water interface was investigated. For this reason the thermodynamic properties, domain size, and spontaneous polarization were analyzed by surface pressure—area isotherms, Brewster angle microscopy (BAM), and Maxwell displacement current technique. The analysis indicated magnesium ions preferred to bond with dipalmitoyl phosphatidylcholine negative head group in liquid expanded phase and/or at domain boundary at low ion concentration and got an access to binding with molecules inside of the LC domains for higher ion concentration. Domain size increase characterized by BAM was discussed in respect to the shape equation on the basis of electrostatic energy contribution. Although molecular repulsive force increased by adding of ions into subphase, the growth of domain size exceeded this tendency. Following shape equation analysis it was suggested that this effect corresponded to change in dipole moment orientation represented by increase in spontaneous polarization in normal projection. This demonstrated impact of local electrostatic field on molecular dipoles and free energy of LC domains.
A spectral characterization for generalized quantum gates
Authors: Du Hong-Ke , Dou Yan-Ni
Published: March 2009

In this article, we prove that a contraction A on a separable Hilbert space is not a generalized quantum gate (or a convex combination of unitaries) if and only if A is a semi-Fredholm with ind A≠0 and a compact perturbation of a partial isometry.
Electrical tuning of intersubband transition in a semiconductor quantum ring
Authors: Bhattacharyya S. , Das N. R. , Sen Susmita
Published: March 2009

In this paper, the intersubband transition energy in an n-type semiconductor quantum ring has been investigated in the presence of an electric field perpendicular to the plane of the ring. The analysis has been done considering the effect of band nonparabolicity of the semiconductor. The results show that at high electric field energy varies nonlinearly with field and the optical transition between the two lowest quantized subbands can be controlled by the electric field. It has also been shown how this fine wavelength tuning by electric field depends on the band gap of the semiconductor.
Temperature measurement of an atmospheric pressure arc discharge plasma jet using the diatomic CN (BΣ+2-XΣ+2, violet system) molecular spectra
Authors: Moon Se Youn , Kim D. B. , Gweon B. , Choe W.
Published: March 2009

The CN (BΣ+2-XΣ+2) molecular emission spectrum is used to measure both the vibrational and rotational temperatures in atmospheric pressure arc jet discharges. The vibrational and rotational temperature effects on the synthetic diatomic molecular spectra were investigated from the (v′,v″)=(0,0) band to the (5,5) band. The temperatures obtained from the synthetic spectra compared with the experimental result of a low-frequency arc discharge show a vibrational temperature of (4250–5010)K and a rotational temperature of (3760–3980)K for the input power in the range of (80–280)W. As the (0,0) band is isolated from other vibrational transition bands, determination of the rotational temperature is possible based only on the (0,0) band, which simplifies the temperature measurement. From the result, it was found that the CN molecular spectrum can be used as a thermometer for atmospheric pressure plasmas containing carbon and nitrogen.
Vacuum-ultraviolet-induced charge depletion in plasma-charged patterned-dielectric wafers
Authors: Upadhyaya G. S. , Kruger J. B. , Shohet J. L.
Published: March 2009

Plasma-induced charging of patterned-dielectric structures during device fabrication can cause structural and electrical damage to devices. In this work, we report on vacuum-ultraviolet (VUV) radiation-induced charge depletion in plasma-charged patterned-silicon-oxide dielectric wafers. Charge depletion is studied as a function of photon energy and the aspect ratio of hole structures. The wafers were charged in a plasma and subsequently exposed to monochromatic-synchrotron-VUV. Surface-potential measurements after VUV exposure showed that photon energies less than 11 eV were beneficial in depleting the plasma-induced charge from the patterned-dielectric wafers. In addition, for a given photon-flux density and for photon energies less than 11 eV, VUV-induced charge depletion decreases with increasing hole aspect ratio. The results are explained with a physically plausible equivalent-circuit model, which suggests that both electron photoinjection from Si into the oxide and oxide surface conductivity play an important role in the charge-depletion process.