bluuebunny/crossref_metadata_2025 huggingface dataset:
The form and orientation of Langmuir cells for misaligned winds and waves
Authors: Van Roekel L. P. , Fox‐Kemper B. , Sullivan P. P. , Hamlington P. E. , Haney S. R.
Published: March 2012

Large eddy simulations of the Craik‐Leibovich equations are used to assess the effect of misaligned Stokes drift and wind direction on Langmuir cells in the ocean mixed layer. Misalignments from 0° to 135° are examined and Langmuir turbulence structures are evident in all cases. The Stokes drift is modeled using a broadband empirical spectrum, and cases with and without the Coriolis effect, wind waves, and an initial mixed layer are examined. The expected scaling for the vertical velocity variance is recovered in the aligned simulations and is adapted here to the misaligned cases. The adjusted scaling projects the friction velocity (aligned with the wind stress) into the dominant axial direction of the Langmuir cells. The turbulent Langmuir number is generalized through a similar projection into the axial direction of the Langmuir cells, which reduces its value in realistic conditions. For known Langmuir cell orientations, the strength of Langmuir turbulence for misaligned cases can be estimated using the projected Langmuir number. A prediction for the angle between the wind stress and cell direction is obtained using the law of the wall; this prediction only requires the wind stress, Stokes drift, and boundary layer depth. Conditional analyses show that, with increasing misalignment, the typically antisymmetric Langmuir cell pairs become asymmetric. This asymmetry is due, in part, to the advection by cross cell flow of vorticity from one vortex tube onto the other, and in part due to an asymmetry induced by the stretching of vertical vorticity into cross cell vorticity.
Mesospheric concentric gravity waves generated by multiple convective storms over the North American Great Plain
Authors: Vadas Sharon , Yue Jia , Nakamura Takuji
Published: March 2012

We report on six continuous hours of OH airglow imager observations (at z ∼ 87 km) of convectively generated gravity waves (GWs) near Fort Collins, Colorado, on the evening of 08 September 2005. These GWs appeared as nearly concentric rings, and had epicenters near the locations of deep convection in three thunderstorms in Colorado, Nebraska and South Dakota. Using GOES satellite and weather radar observations, we show that the GWs closely follow the thunderstorms. Using the background wind from a nearby radar, the intrinsic wave parameters and vertical wavelengths are calculated. The temperature perturbations are estimated to be
∼ 1–3% for GWs with horizontal wavelengths λh∼ 20–40 km and horizontal phase speeds ∼40–60 m/s. The horizontal wavelengths of GWs from a convective cluster decreased in time from 30 to 15 km. We employ convective plume and ray‐trace models to simulate the GW‐induced OH intensity perturbations from convective plumes, clusters and complexes. We find that the results using the background model wind (radiosonde/TIME‐GCM) agree well with the late‐time observations, when the images are dominated by southwestward, short‐wavelength, high‐frequency GWs. These late‐time GWs propagate against the background wind, and haveλh ∼ 30–40 km and periods of τ ∼ 20–30 min. The OH intensity perturbations are enhanced because the vertical wavelengths λz increased,
increased, and the vertical velocity perturbations w′ decreased (because the GWs were near their reflection levels). We also find that these short‐wavelength GWs were created ∼5 h earlier by an extremely energetic, deep convective plume in South Dakota, thereby showing that small‐scale, convective GWs directly link the troposphere and mesopause region.
Retrieval of the aerosol direct radiative effect over clouds from spaceborne spectrometry
Authors: de Graaf M. , Tilstra L. G. , Wang P. , Stammes P.
Published: March 2012

The solar radiative absorption by an aerosol layer above clouds is quantified using passive satellite spectrometry from the ultraviolet (UV) to the shortwave infrared (SWIR). UV‐absorbing aerosols have a strong signature that can be detected using UV reflectance measurements, even when above clouds. Since the aerosol extinction optical thickness decreases rapidly with increasing wavelength for biomass burning aerosols, the properties of the clouds below the aerosol layer can be retrieved in the SWIR, where aerosol extinction optical thickness is sufficiently small. Using radiative transfer computations, the contribution of the clouds to the reflected radiation can be modeled for the entire solar spectrum. In this way, cloud and aerosol effects can be separated for a scene with aerosols above clouds. Aerosol microphysical assumptions and retrievals are avoided by modeling only the pure (aerosol‐free) cloud spectra. An algorithm was developed using the spaceborne spectrometer Scanning Imaging Absorption Spectrometer for Atmospheric Chartography (SCIAMACHY). The aerosol direct radiative effect (DRE) over clouds over the South Atlantic Ocean west of Africa, averaged through August 2006 was found to be 23 ± 8 Wm−2 with a mean variation over the region in this month of 22 Wm−2. The largest aerosol DRE over clouds found in that month was 132 ± 8 Wm−2. The algorithm can be applied to any instrument, or a combination of instruments, that measures UV, visible and SWIR reflectances at the top of the atmosphere (TOA) simultaneously.
Warming‐enhanced preferential microbial mineralization of humified boreal forest soil organic matter: Interpretation of soil profiles along a climate transect using laboratory incubations
Authors: Li Jianwei , Ziegler Susan , Lane Chad S. , Billings Sharon A.
Published: March 2012

Humified soil organic matter storage in boreal forests is large, and its responses to warming over relatively long timescales is critical for predicting soil feedbacks to climate change. To derive information relevant across decades to centuries from manipulative short‐term experiments, we conducted incubations of soils from two forested sites along the Newfoundland‐Labrador Boreal Ecosystem Latitude Transect in eastern Canada and assessed linkages between incubation data and these sites' profile characteristics. The sites differ in mean annual temperature by 3.4°C, but vegetation and soil types are similar. Organic soils (Oe + Oa) were incubated for 120 days at 15°C and 20°C, with and without a replaced Oi subhorizon possessing a distinct δ13C signature. Laboratory warming induced significantly greater mineralization and leaching of humified SOM relative to replaced Oi, congruent with greater warming‐induced increases in phenol oxidase activity relative to enzymes associated with labile C acquisition (percent increases of 101% versus 50%, respectively). These data suggest that warming can influence microbial communities and their enzymatic dynamics such that relative losses of humified SOM are disproportionately enhanced. This is consistent with stable isotopic, C:N, and radiocarbon profile differences between the two sites, which suggest a greater degree of microbial processing and greater relative losses of older SOC over the preceding decades at the warmer site, given our knowledge of organic inputs in these soils. This study is a first step toward linking the divergent timescales represented by soil profiles and laboratory manipulations, an important goal for biogeochemists assessing climate change impacts on SOM dynamics.
Interfacing a one‐dimensional lake model with a single‐column atmospheric model: Application to the deep Lake Geneva, Switzerland
Authors: Goyette Stéphane , Perroud Marjorie
Published: March 2012

A single column atmospheric model (SCM) coupled to a one‐dimensional lake model devised for climate simulations is described in this paper. As a test case, this coupled model is applied to the deepest section of Lake Geneva in Switzerland. Both atmospheric and lake models require a minimal set of adjustable parameters to reproduce the local observations of temperature, moisture, and wind as well as those of the lake thermal profiles. A number of simulations have been performed to produce a sorted set of optimal model parameters that reproduces the mean and the variability of the seasonal evolution of the thermal profiles in the lake as well as those of the mean and the variability of the surface air temperature, moisture, and winds. The lake water temperature is reproduced realistically using the optimal calibration parameter values with a seasonal‐ and depth‐averaged error of 0.41°C in summer, −0.15°C in autumn, 0.01°C in winter, and 0.27°C in spring when compared to the lake observations. Also, the errors of the seasonally averaged simulated anemometer‐level wind speed, screen‐level air temperature, and specific humidity to the station‐derived values are 0.04 m s−1, 1.04°C, and 0.74 g kg−1, respectively. Results of this study contribute to the understanding of the air‐lake interactions present over the deep Lake Geneva. In addition, the sensitivity experiments carried out in this paper serve as the basis for experiments aiming at studying the thermal response of the deep Swiss Lake Geneva under future global climate change conditions reported in a companion paper.
Modulation of cellular S1P levels with a novel, potent and specific inhibitor of sphingosine kinase-1
Authors: Schnute Mark E. , McReynolds Matthew D. , Kasten Tom , Yates Matthew , Jerome Gina , Rains John W. , Hall Troii , Chrencik Jill , Kraus Michelle , Cronin Ciaran N. , Saabye Matthew , Highkin Maureen K. , Broadus Richard , Ogawa Shinji , Cukyne Kristin , Zawadzke Laura E. , Peterkin Vincent , Iyanar Kaliapan , Scholten Jeffrey A. , Wendling Jay , Fujiwara Hideji , Nemirovskiy Olga , Wittwer Arthur J. , Nagiec Marek M.
Published: March 2012

SphK (sphingosine kinase) is the major source of the bioactive lipid and GPCR (G-protein-coupled receptor) agonist S1P (sphingosine 1-phosphate). S1P promotes cell growth, survival and migration, and is a key regulator of lymphocyte trafficking. Inhibition of S1P signalling has been proposed as a strategy for treatment of inflammatory diseases and cancer. In the present paper we describe the discovery and characterization of PF-543, a novel cell-permeant inhibitor of SphK1. PF-543 inhibits SphK1 with a Ki of 3.6 nM, is sphingosine-competitive and is more than 100-fold selective for SphK1 over the SphK2 isoform. In 1483 head and neck carcinoma cells, which are characterized by high levels of SphK1 expression and an unusually high rate of S1P production, PF-543 decreased the level of endogenous S1P 10-fold with a proportional increase in the level of sphingosine. In contrast with past reports that show that the growth of many cancer cell lines is SphK1-dependent, specific inhibition of SphK1 had no effect on the proliferation and survival of 1483 cells, despite a dramatic change in the cellular S1P/sphingosine ratio. PF-543 was effective as a potent inhibitor of S1P formation in whole blood, indicating that the SphK1 isoform of sphingosine kinase is the major source of S1P in human blood. PF-543 is the most potent inhibitor of SphK1 described to date and it will be useful for dissecting specific roles of SphK1-driven S1P signalling.
Structure-based analysis of VDAC1: N-terminus location, translocation, channel gating and association with anti-apoptotic proteins
Authors: Geula Shay , Ben-Hail Danya , Shoshan-Barmatz Varda
Published: March 2012

Structural studies place the VDAC1 (voltage-dependent anion channel 1) N-terminal region within the channel pore. Biochemical and functional studies, however, reveal that the N-terminal domain is cytoplasmically exposed. In the present study, the location and translocation of the VDAC1 N-terminal domain, and its role in voltage-gating and as a target for anti-apoptotic proteins, were addressed. Site-directed mutagenesis and cysteine residue substitution, together with a thiol-specific cross-linker, served to show that the VDAC1 N-terminal region exists in a dynamic equilibrium, located within the pore or exposed outside the β-barrel. Using a single cysteine-residue-bearing VDAC1, we demonstrate that the N-terminal region lies inside the pore. However, the same region can be exposed outside the pore, where it dimerizes with the N-terminal domain of a second VDAC1 molecule. When the N-terminal region α-helix structure was perturbed, intra-molecular cross-linking was abolished and dimerization was enhanced. This mutant also displays reduced voltage-gating and reduced binding to hexokinase, but not to the anti-apoptotic proteins Bcl-2 and Bcl-xL. Replacing glycine residues in the N-terminal domain GRS (glycine-rich sequence) yielded less intra-molecular cross-linked product but more dimerization, suggesting that GRS provides the flexibility needed for N-terminal translocation from the internal pore to the channel face. N-terminal mobility may thus contribute to channel gating and interaction with anti-apoptotic proteins.
Drosophila: A Model for Understanding Obesity and Diabetic Complications
Authors: Teleman A. , Ratzenböck I. , Oldham S.
Published: March 2012

The molecular mechanisms underlying development of obesity and diabetic complications are not well understood. Drosophila has become a popular model organism for studying a variety of human diseases. We discuss here emerging Drosophila models of obesity and diabetic complications.
Liver: A Target of Late Diabetic Complications
Authors: Herzig S.
Published: March 2012

Whereas many studies have implicated metabolic liver dysfunction as a causative factor for obesity-related type 2 diabetes and the Metabolic Syndrome, its role as a long-term complication of diabetic metabolism is still mostly unexplored.

In contrast to the well-described late diabetic micro- and macro-vascular complications in response to hyperglycemic conditions such as nephro- and retinopathy as well as atherosclerosis, only recent studies have highlighted disturbances of liver function as a novel aspect of diabetic late complications that may substantially impact the overall disease outcome and determine mortality rates in diabetic subjects. Here we will discuss recent developments in this area, particularly focusing on transcriptional regulators of hepatic dysfunction as a long-term consequence of established diabetes.
Murine Models of Diabetic Nephropathy
Authors: Peters V. , Schmitt C.
Published: March 2012

Diabetic nephropathy is the leading cause of end stage renal diseases worldwide. Even though several diabetic animal models exist, not a single one develops renal changes sufficiently reflecting those seen in humans. This review provides an overview on mouse models presenting with various features of diabetic nephropathy. The critical analysis and comparison of existing mouse models substantially enhances our understanding of the disease process and should provide a guide for choosing the most suitable mouse model for the investigation of diabetic nephropathy.
Control of in-plane uniaxial anisotropy of Fe72Si14B14 magnetostrictive thin film using a thermal expansion coefficient
Authors: Shin Jaewon , Hoon Kim Sung , Suwa Yasuaki , Hashi Shuichiro , Ishiyama Kazushi
Published: March 2012

This paper introduces an in-plane uniaxial anisotropy control method of Fe72Si14B14 magnetostrictive thin-film for high sensitivity of MI sensor. The anisotropy can be controlled by inverse-magnetostriction and inducing a bias stress using the difference of thermal expansion coefficient in bimetal structure. We can control the uniaxiality of anisotropy by the structure of the thin-film. Our proposed methods are useful in solving the problems and inconveniences of existing methods. To verify the proposed methods, we carried out experiments as well as FEM simulation. Looking at the FEM simulation and magnetic domain observation results, we confirmed that the in-plane uniaxial anisotropy could be controlled by a difference of a thermal expansion coefficient. Moreover, changes in the length of the conductive layer provides the local (edge section) control of the uniaxial anisotropy.
Spin-reorientation in the antiferromagnetic ordering of LiFe1-xMnxPO4 investigated with Mössbauer spectroscopy
Authors: Jun Kwon Woo , Lee In Kyu , Hyuk Rhee Chan , Kim Chul Sung
Published: March 2012

The crystal structures of LiFe1-xMnxPO4 (x = 0.1, 0.3, 0.5) samples have been characterized with x-ray diffraction (XRD) and were determined to be orthorhombic with space group Pnma by Rietveld refinement method. The temperature dependence of the magnetization curves showed abnormal antiferromagnetic behavior as well as a decrease in Néel temperature (TN) with Mn substitution from superconducting quantum interference device (SQUID) measurement. The magnetization decreases until the temperature reaches the spin-reorientation temperature (TS), and then increases with temperature up to TN. The Mössbauer spectra of the LiFe1-xMnxPO4 show that the magnetic hyperfine field (Hhf) and electric quadrupole splitting (ΔEQ) values change with increasing temperature, compared to values at TS, which is caused by the strong electric crystalline field originating from distorted octahedral symmetry. The decrease in TS of LiFe1-xMnxPO4 can be explained by the Mn-concentration-dependent crystal field and spin-orbit coupling in the Fe2 + site.
A novel linear and rotary Halbach permanent magnet actuator with two degrees-of-freedom
Authors: Jin Ping , Fang Shuhua , Lin Heyun , Wang Xianbin , Zhou Shigui
Published: March 2012

This paper presents a novel linear and rotary Halbach permanent magnet actuator, which is capable of two degrees-of-freedom movements. The magnetic field distributions of the actuator are analytically analyzed using the magnetic scalar potential, where its tubular mover is transferred into a planar one by using a magnetic field curvature factor. The linear cogging force and rotary cogging torque and the stator flux-linkage of the actuator are subsequently predicted validated by the three-dimensional finite element method.
A magnetoelectric energy harvester with the magnetic coupling to enhance the output performance
Authors: Bai Xiaoling , Wen Yumei , Yang Jin , Li Ping , Qiu Jing , Zhu Ying
Published: March 2012

In this research an energy harvester employing the magnetoelectric (ME) transducer to convert mechanical vibration energy into electrical energy is presented, and it is demonstrated that the use of a magnetically coupled cantilever beam can achieve to enhance the output performances of the harvester in terms of improving the electric output and tuning the resonant frequency efficiently. Under the acceleration of 0.2 g (with g = 9.8 ms−2), the resonant frequency is successfully tuned range from 16.1 to 27.9 Hz, and the output power is obviously improved from 42.3 to 151.4 μW with the effect of magnetic coupling.
Shape-induced bi-stable magnetic states in submicrometer structures of permalloy films
Authors: Telepinsky Yevgeniy , Mor Vladislav , Schultz Moty , Klein Lior
Published: March 2012

We pattern submicrometer structures of thin films of permalloy in the form of two crossing ellipses and in the form of one long ellipse crossed by several ellipses where the width of the ellipses varies between 100 and 1000 nm. We find that the crossing area has two stable axes of magnetization, which are perpendicular to each other and which are rotated by 45 degrees relative to the axes of the ellipses. We measure the planar Hall effect (PHE) of the submicrometer structures and demonstrate sharp switching behavior between the two easy axes of the magnetization. The observed behavior is modeled analytically with bi-axial magnetic anisotropy and compared with numerical simulations. We discuss possible application of such submicrometer structures for PHE-based magnetic memory.
L1 CrPt phase formation and magnetic properties
Authors: Zhang Rui , Skomski Ralph , Li Xingzhong , Li Zhen , Manchanda Priyanka , Kashyap Arti , Kirby Roger D. , Liou Sy-Hwang , Sellmyer D. J.
Published: March 2012

L10-ordered antiferromagnetic CrPt is of interest as a pinning material in exchange-biased system due to its many intriguing properties and such alloy with a (001) texture has also been used to serve as an underlayer to promote the L10 phase formation of other materials. Therefore, it is important to control not only the L10 phase formation of such material but also the texture of its ordered phase. A systematic study of the L10 phase formation of CrPt thin film was performed. The anisotropy of CrPt L10 phase has also been investigated both experimentally using CrPt/Fe bilayer system and theoretically using first principle calculation. The experimental result is in consistent with the theoretical estimation within the present thin film limitation.
Enhancing the perpendicular anisotropy of NdDyFeB films by Dy diffusion process
Authors: Gong W. J. , Wang X. , Liu W. , Guo S. , Wang Z. H. , Cui W. B. , Zhu Y. L. , Zhang Y. Q. , Zhang Z. D.
Published: March 2012

A large coercivity and anisotropy enhancement in perpendicular NdDyFeB (120 nm)/Dy (tDy) films has been realized by a Dy grain-boundary diffusion process. The coercivity HC and the ratio Mr/Ms reach their maxima at tDy = 50 nm, and the magnetic domain sizes increase with increasing tDy. The HC and Mr/Ms increasing with tDy is due to the enhancement of the anisotropy of (Nd,Dy)2Fe14B grains by Dy substitution for Nd. The coercivity mechanism is a nucleation-type mechanism. Dy and Nd elements coexist at grain boundaries, forming a (Nd,Dy)-rich phase, which may promote the nucleation of reversal domains.
Multi-scale/multi-physical modeling in head/disk interface of magnetic data storage
Authors: Chung Pil Seung , Smith Robert , Vemuri Sesha Hari , Jhon Young In , Tak Kyungjae , Moon Il , Biegler Lorenz T. , Jhon Myung S.
Published: March 2012

The model integration of the head-disk interface (HDI) in the hard disk drive system, which includes the hierarchy of highly interactive layers (magnetic layer, carbon overcoat (COC), lubricant, and air bearing system (ABS)), has recently been focused upon to resolve technical barriers and enhance reliability. Heat-assisted magnetic recording especially demands that the model simultaneously incorporates thermal and mechanical phenomena by considering the enormous combinatorial cases of materials and multi-scale/multi-physical phenomena. In this paper, we explore multi-scale/multi-physical simulation methods for HDI, which will holistically integrate magnetic layers, COC, lubricants, and ABS in non-isothermal conditions.
Separated Sm-Co hard nanoparticles by an optimization of mechanochemical processes
Authors: Zheng Liyun , Cui Baozhi , Li Wanfeng , Hadjipanayis George C.
Published: March 2012

Sm-Co hard nanoparticles have been synthesized by a modified mechanochemical processing. The phases, microstructure, particle sizes and magnetic properties of the synthesized Sm-Co nanoparticles have been investigated. The results showed that the precursors and milling times had great effects on the structure and magnetic properties of the synthesized Sm-Co nanoparticles. It is interesting to find that either Sm2Co7, SmCo5 or Sm2Co17 hard single phases can be obtained by manipulating the amount and ratio of starting materials of Sm2O3 and Co. After the mixture of Sm2O3, Co, Ca, and CaO powders were milled for 2–12 h, no Sm-Co based hard phases was formed, whereas the Sm-Co hard nanocrystallites were formed by a subsequent annealing at 650 °C for 1 h. The maximum coercivities of the synthesized Sm2Co7, SmCo5, and Sm2Co17 were 37.1, 35.5, and 10.8 kOe, respectively. Separated Sm2Co17 nanoparticles were obtained after washing the annealed powder with a solution of acetic acid aqueous solution. The washed Sm2Co17 particles were single crystals and had an average particle size of 81 nm.
Magnetization processes in micron-scale (CoFe/Pt)n multilayers with perpendicular anisotropy: First-order reversal curves measured by extraordinary Hall effect
Authors: Diao Z. , Decorde N. , Stamenov P. , Rode K. , Feng G. , Coey J. M. D.
Published: March 2012

First-order reversal curves (FORCs) were recorded using the extraordinary Hall effect in micron-sized crosses of [Co90Fe10 (0.5 nm)/Pt (1.0 nm)]n multilayers with n = 10, 20, and 50, which exhibit perpendicular magnetic anisotropy. Both the major hysteresis loop and the FORCs are compared to previous results, where the magnetization was measured directly on unpatterned stacks using alternating gradient force magnetometry. The FORC diagrams are dominated by two “hysteron” peaks, and their separation increases when n becomes larger. A frustrated domain growth process is suggested in our n = 20 and 50 samples.
Effect of magnetic fields on melt-spun Nd2Fe14B-based ribbons
Authors: Van Nguyen Vuong , Rong Chuanbing , Ding Yong , Liu J. Ping
Published: March 2012

The effect of a magnetic field on microstructure and magnetic properties of Nd2Fe14B-based melt-spun ribbons is investigated. The magnetic field was applied in perpendicular or parallel direction to the ribbon plane during quench with a field strength up to several kilo Oersteds. The XRD patterns and TEM graphs show a strong grain size reduction upon the magnetic field application. The magnetic field also enhances the (00l) texture of ribbons when the field is perpendicular to the ribbon plane. The refined microstructure with significantly reduced grain size leads to enhanced magnetic exchange interactions between the hard and soft phases in the Nd2Fe14B/Fe nanocomposite ribbons. This magnetic field-assisted melt-spinning technique is promising for producing nanocomposite magnets with enhanced energy density.
Flux distribution in Fe-based superconducting materials by magneto-optical imaging
Authors: Lin Zhi Wei , Zhu Jian Guo , Guo You Guang , Wang Xiao Lin , Dou Shi Xue , Johansen Tom H. , Shi Xun , Choi K. Y.
Published: March 2012

This paper presents the magnetic flux distributions in Fe-based superconducting materials including single crystal of Ba(Fe1.9Ni0.1)As2 and Ba(Fe1.8Co0.2)As2, as well as polycrystalline SmFeO0.75F0.2As by means of magneto-optical imaging (MOI) technique. The single crystals were grown out of FeAs flux while polycrystalline sample was grown by hot-press. A MOI film with in-plan magnetization was used to visualize flux distributions at the sample surface. A series of magneto-optical images was taken when the samples were zero-field cooled and field cooled. The flux behavior, including penetration into and expelling from the samples, as well as pinning properties were studied. When external fields increase, flux is completely shielded from the crystals, then, gradually penetrates toward the crystal center from the edge. For polycrystalline sample, Meissner state was observed at very low field. With increasing the field further, flux penetrates into the sample easily along grain boundary, then into grain. Compared with high-Tc cuprates, it is found that the flux distributions in Fe-based superconducting materials are very similar to that in high-Tc cuprates with strong pinning strength.
The impact of deposition temperature on L1 formation in FePt films
Authors: Wang Bincheng , Barmak Katayun
Published: March 2012

Binary FePt films with compositions in the range of 42.4 to 54.0 at. % Pt were sputter deposited at temperatures between 100 and 300 °C. Films deposited at 250 and 300 °C were fully L10 ordered, whereas films deposited between 100 and 200 °C were either A1 or a mixture of A1 and L10. Differential scanning calorimetry studies following deposition showed a bifurcation in the post-deposition formation characteristics of the L10 phase for films deposited between 100 and 200 °C depending on film composition. For films with compositions >47 at. % Pt, L10 formation kinetics were identical to those for room-temperature deposited films. In contrast, for films with <47 at. % Pt, significantly higher temperatures were needed for full transformation to the L10 phase. Thus the choice of deposition temperature and film composition is critical to achieving fully L10 films during deposition. The Curie temperature of the L10 phase was not impacted by the deposition temperature.
Low power field generation for magneto-optic fiber-based interferometric switches
Authors: Pritchard John , Mina Mani , Weber Robert J. , Kemmet Sasha
Published: March 2012

A new fiber-based, magneto-optic switch is proposed with a novel approach for low power and efficient operation. The switch, with reasonable switching speed compared to competitive designs, operates at considerably reduced power levels, which makes it a practical deployable solution. The basic switch setup consists of a Faraday rotator in a Sagnac fiber-optic interferometer in which optical switching is controlled by an electronic driving circuit. The electronic system generates a magnetic field through the Faraday rotator by driving current through a specially designed two-coil system. The new coil system allows for sufficient field generation at low quiescent power levels while maintaining very short optical rise and fall times. The design and considerations as well as the effect of mutual inductance between the two coils and its influence on switching times are investigated. The optical system consists of a Sagnac interferometer with a Faraday rotator within the Sagnac loop. Appropriate phase shift for interference is achieved by the proposed field generating system designed for the magneto-optical element. The theory of operation, design, experimental results, and optical and electronic setup are presented and analyzed.
Influences of leakage currents on the transport properties and photoelectric effects in heterojunctions composed of colossal magnetoresistance manganites and Nb-doped titanates
Authors: Wang J. F. , Wu Z. P. , Gao J.
Published: March 2012

The effects of leakage currents were investigated for Pr0.7Sr0.3MnO3/Nb-SrTiO3 heterojunctions. It was found that small amounts of leakage currents could cause pronounced detriment to the rectifying properties but had very limited impacts on the barrier heights determined from the forward currents. Significant open circuit voltages VOC were observed when the highly rectified junctions were illuminated by a visible light with a wavelength of 532 nm. For the less rectified junctions, the leakage currents reduced VOC severely and resulted in an anomalous temperature dependence of VOC. Theories for semiconductor contacts were employed in order to discuss these results.
Trapping of excess electrons at the microhydrated protonated amino groups in proteins
Authors: Li Wenchao , Zhang Zhenwei , Yang Hongfang , Wu Xiuxiu , Liu Jinxiang , Bu Yuxiang
Published: March 2012

We present a combined first-principles calculation and molecular dynamics simulation study of an excess electron (EE) in condensed phase of a microhydrated protonated amino group in proteins in this work. The protonated amino group, –NH3+, is modeled by a CH3NH3+ and an amount of water molecules are included to form various microhydrated CH3NH3+ clusters, and the states and the dynamics of the trapped EE are analyzed. In addition to the localized and delocalized states observed, the N–H/O–H bond cleavage phenomena followed by escape of a H atom are also observed for some hydrated clusters in which the –NH3+ group exposes on the surface of the cluster and directly participates in binding an EE. The state-to-state conversion is controlled by thermal motion of molecules in the clusters, and the cleavage of the N–H or the O–H bond and the H escape are determined by the binding modes of the EE. The H-escape nature could be attributed to the dissociation of the N–H or O–H bond induced by the trapped EE which transfers to their antibonding orbitals. This work provides a microscopical picture of the EE trapping at a microhydrated hydrophilic group in proteins, long-range electron migration, and the H-evolving mechanisms relevant for the lesions or damages of proteins or DNA. This is the first step in considering increasingly larger peptide fragments for further investigation of the detailed lesion/damage or charge migration mechanisms. Further work about this topic is underway.
Icosahedral to double-icosahedral shape transition of copper clusters
Authors: Jiang Minglong , Zeng Qun , Zhang Tingting , Yang Mingli , Jackson Koblar Alan
Published: March 2012

The lowest-energy isomers of CuN clusters for N = 20–30 are identified using an unbiased search algorithm and density functional theory calculations. The low-energy structures over this size range are dominated by those based on a 13-atom icosahedral (Ih) core and a 19-atom double icosahedron (DIh) core. A transition in the ground-state isomers from Ih-based to DIh-based structures is predicted overt N = 21–23. We discuss this transition in the broader context of the growth pattern for CuN over N = 2–30 that features regions of gradual evolution in which atoms successively add to the cluster surface, separated by sudden changes to a different structural organization and more compact shape. These transitions result from a competition between interatomic bonding energy and surface energy. The implications of this growth pattern for the further evolution of copper from microstructure to bulk are discussed.
Spectroscopic investigations of ThF and ThF+
Authors: Barker Beau J. , Antonov Ivan O. , Heaven Michael C. , Peterson Kirk A.
Published: March 2012

The electronic spectra of ThF and ThF+ have been examined using laser induced fluorescence and resonant two-photon ionization techniques. The results from high-level ab initio calculations have been used to guide the assignment of these data. Spectra for ThF show that the molecule has an X 2Δ3/2 ground state. The upper spin-orbit component, X 2Δ5/2 was found at an energy of 2575(15) cm−1. The low-lying states of ThF+ were probed using dispersed fluorescence and pulsed field ionization - zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy. Vibronic progressions belonging to four electronic states were identified. The lowest energy states were clearly 1Σ+ and 3Δ1. Although the energy ordering could not be rigorously determined, the evidence favors assignment of 1Σ+ as the ground state. The 3Δ1 state, of interest for investigation of the electron electric dipole moment, is just 315.0(5) cm−1 above the ground state. The PFI-ZEKE measurements for ThF yielded an ionization energy of 51 581(3) cm−1. Molecular constants show that the vibrational constant increases and the bond length shortens on ionization. This is consistent with removal of a non-bonding Th-centered 6d or 7s electron. Laser excitation of ThF+ was used to probe electronically excited states in the range of 19 000–21 500 cm−1.
Effect of crystallographic anisotropy on the resistance switching phenomenon in perovskites
Authors: Plecenik T. , Tomášek M. , Belogolovskii M. , Truchly M. , Gregor M. , Noskovič J. , Zahoran M. , Roch T. , Boylo I. , Španková M. , Chromik Š. , Kúš P. , Plecenik A.
Published: March 2012

Resistance switching effects in metal/perovskite contacts based on epitaxial c-axis oriented YBa2Cu3O6+c (YBCO) thin films with different crystallographic orientation have been studied. Three types of Ag/YBCO junctions with the contact restricted to (i) c-axis direction, (ii) ab-plane direction, and (iii) both were designed and fabricated, and their current-voltage characteristics have been measured. The type (i) junctions exhibited conventional bipolar resistance switching behavior, whereas in other two types the low-resistance state was unsteady and their resistance quickly relaxed to the initial high-resistance state. Physical mechanism based on the oxygen diffusion scenario, explaining such behavior, is discussed.
Quantum-dynamics study of the ${\rm H}_5^+$H5+ cluster: Full dimensional benchmark results on its vibrational states
Authors: Valdés Álvaro , Prosmiti Rita , Delgado-Barrio Gerardo
Published: March 2012

A full-dimensional quantum dynamics study is carried out for the highly fluxional \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+ cation on a recent reference potential energy surface by using the multi configuration time-dependent Hartree method. With five equivalent light atoms and shallow barriers between various low-lying stationary points on the surface, the spectroscopic characterization of \documentclass[12pt]{minimal}\begin{document}${\rm H}_5^+$\end{document}H5+ represents a huge challenge for accurate quantum dynamics simulations. The present calculation is the first such a study on this cation, which together with its isotope analogies are of primary importance in the interstellar chemistry. The vibrational ground state properties and several vibrationally excited states corresponding to low vibrational frequency motions, not yet directly observable by the experiment, are presented and analyzed.
Investigation of special features of parameters of Schottky barrier contacts caused by a nonlinear bias dependence of the barrier height
Authors: Bozhkov V. G. , Shmargunov A. V.
Published: March 2012

The results of studying the IV-characteristics (IVCs) of the contact Au-n-GaAs obtained by electrochemical deposition are presented. The observed characteristics - the bias dependence of the ideality factor (n), the measured (ϕbm) and effective (ϕbI) barrier heights, an inverse relationship between the measured barrier height and ideality factor, and the edge effects (the dependence of n, ϕbm, and ϕbI on the contact diameter) are explained by the nonlinear bias dependence on the effective barrier height. The explanation is given on the basis of the contact model with an intermediate layer and interface states (Bardeen model), and the intimate contact model with the subsurface states. The nonlinearity of the bias dependence on the barrier height is due to the inhomogeneous energy distribution of the interface states (a decrease in density from the edges to the middle of the bandgap) and the inhomogeneous energy and coordinate (from the surface to the depth) distribution of the subsurface states. An essential feature for every model is also the condition that the barrier height and ideality factor are measured at a constant current (or in a constant range of currents) while studying contacts with different diameters or when measuring the IVCs at different temperatures. This condition is not difficult to achieve, but gives the necessary certainty to different barrier height values used in examining experimental results. Some limitations and shortcomings of the widely used model of inhomogeneous Schottky barrier contact with the “saddle points” are also discussed.
Arbitrary amplitude ion-acoustic soliton coexistence and polarity in a plasma with two ion species
Authors: Verheest Frank , Hellberg Manfred A. , Baluku Thomas K.
Published: March 2012

Using a Sagdeev pseudopotential formalism, large ion-acoustic waves are investigated in a multispecies plasma model consisting of two cold positive ion species in the presence of nonthermal Cairns electrons. Positive solitons are limited in amplitude by infinite compression of the lighter ion species. Negative solitons become possible at a sufficient degree of electron nonthermality, and their amplitudes are limited by the occurrence of double layers. What determines coexistence is the possibility of having parameter ranges for which there are solitons at the acoustic speed, which is a necessary and sufficient condition but unfortunately not an easy criterion to check analytically. For the first time a parameter range has been found where both negative and positive polarity solutions coexist, with the solitons at the acoustic speed always having a positive polarity, contrary to earlier results which seemed to indicate that polarity switches and coexistence ranges were linked. Finally, some useful proofs are presented in an Appendix, concerning the Sagdeev pseudopotential behavior at the acoustic speed, results of which are generic to a range of physical plasma models.
Electric field effects on reduced effective masses of minibands at the mini-Brillouin-zone center and edge in a GaAs/AlAs superlattice
Authors: Nakayama M. , Kawabata T.
Published: March 2012

We have investigated the electric-field-strength dependence of the reduced effective masses of the minibands in a GaAs/AlAs superlattice embedded in a p-i-n diode structure with use of electroreflectance spectroscopy. Frantz-Keldysh (FK) oscillations are observed in the energy region between the n = 1 heavy hole to electron transition at the mini-Brillouin-zone center (kz = 0: Γ point) and that at the edge (kz = π/D: π point), where D is the superlattice period. Analyzing the FK oscillations, we evaluate the reduced effective masses at the Γ and π points as a function of electric field strength. The evaluated reduced effective masses are consistent with the values estimated from the calculated miniband dispersion relations in a low electric field regime. It is found that the reduced effective masses tend to be heavier at a given electric field strength. Considering the electric-field-strength dependence of eigenstates calculated using a transfer-matrix method, we conclude that an increase of the reduced effective masses originates from weak localization of the electron envelope function in the transformation process from the miniband to Stark-ladder states in Wannier-Stark localization.
Left-right loading dependence of shock response of (111)//(112) Cu bicrystals: Deformation and spallation
Authors: An Q. , Han W. Z. , Luo S. N. , Germann T. C. , Tonks D. L. , Goddard W. A.
Published: March 2012

We investigate with molecular dynamics the dynamic response of Cu bicrystals with a special asymmetric grain boundary (GB), (111)//(112)〈110〉, and its dependence on the loading directions. Shock loading is applied along the GB normal either from the left or right to the GB. Due to the structure asymmetry, the bicrystals demonstrate overall strong left-right loading dependence of its shock response, including compression wave features, compression and tensile plasticity, damage characteristics (e.g., spall strength), effective wave speeds and structure changes, except that spallation remains dominated by the GB damage regardless of the loading directions. The presence or absence of transient microtwinning also depends on the loading directions.
Ferromagnetism in hydrogenated N-doped amorphous carbon films
Authors: Liu S. Y. , Zhen C. M. , Li Y. Z. , Pan C. F. , Zhou H. J. , Hou D. L.
Published: March 2012

Room temperature ferromagnetism has been observed in hydrogenated N-doped amorphous carbon films (a-CNx:H) prepared by plasma enhanced chemical vapor deposition. The magnetization of the films changed depending on the ratio (R) of the flow rate of nitrogen to that of methane during deposition and on the annealing temperature. The highest magnetization of the as-deposited samples was obtained with R = 4. Annealing the films at 300 °C resulted in a significant increase in the magnetic moment compared to that of the as-deposited films. When the annealing temperature was above 500 °C, the magnetic moment of the samples decreased. No ferromagnetic impurities could be detected. The ferromagnetism of the a-CNx:H film is attributed mainly to spin-polarization of the p orbitals of the N adatoms on the surface or in the interlayers of irregular carbon.
High power impulse magnetron sputtering discharges: Instabilities and plasma self-organization
Authors: Ehiasarian A. P. , Hecimovic A. , de los Arcos T. , New R. , Schulz-von der Gathen V. , Böke M. , Winter J.
Published: March 2012

We report on instabilities in high power impulse magnetron sputtering plasmas which are likely to be of the generalized drift wave type. They are characterized by well defined regions of high and low plasma emissivity along the racetrack of the magnetron and cause periodic shifts in floating potential. The azimuthal mode number m depends on plasma current, plasma density, and gas pressure. The structures rotate in E→×B→ direction at velocities of ∼10 km s−1 and frequencies up to 200 kHz. Collisions with residual gas atoms slow down the rotating wave, whereas increasing ionization degree of the gas and plasma conductivity speeds it up.
Whittaker pairs for the Virasoro algebra and the Gaiotto-Bonelli-Maruyoshi-Tanzini states
Authors: Felińska Ewa , Jaskólski Zbigniew , Kosztołowicz Michał
Published: March 2012

Whittaker modules for two families of Whittaker pairs related to the subalgebras of the Virasoro algebra generated by Lr, …, L2r and L1, Ln are analyzed. The structure theorems for the corresponding universal Whittaker modules are proved and some of their consequences are derived. All the Gaiotto [e-print arXiv:0908.0307] and the Bonelli-Maruyoshi-Tanzini [J. High Energy Phys. 1202, 031 (2012)10.1007/JHEP02(2012)031] states in an arbitrary Virasoro algebra Verma module are explicitly constructed.
Wall-plug efficiency of mid-infrared quantum cascade lasers
Authors: Yang Q. K. , Schilling C. , Ostendorf R. , Hugger S. , Fuchs F. , Wagner J.
Published: March 2012

We present a comprehensive analysis of the wall-plug efficiency of mid-infrared (λ ∼ 4–10 μm) quantum cascade (QC) lasers, by taking into account the transition efficiency of the active region, the light out-coupling efficiency from the emission facet, the voltage efficiency across the superlattice, and the current efficiency including the leakage and thermal backfilling current densities at threshold. All relevant parameters including their interdependencies have been taken into account and analyzed in order to optimize the wall-plug efficiency of practical QC lasers. Expressions for optimizing the extraction energy Δinj and the mirror loss αm are deduced, which are then used to maximize the wall-plug efficiency of QC lasers. Finally, predictions for the wall-plug efficiency of realistic QC lasers are made both at room temperature and at low temperature. Good agreement is found with corresponding experimental data from the literature.
Numerical analysis of formation properties of a high-field dipole domain for submicron GaAs field-effect transistor devices
Authors: Jyegal Jang
Published: March 2012

A typical 0.3-μm gate-length submicron GaAs metal-semiconductor field-effect transistor (MESFET) is simulated using a complete energy model that solves a complete form of the energy conservation equation, and also using a simplified energy model that only neglects heat flux for electrons. The simulations are carried out with the same device physical and bias conditions, and a transient analysis is made to investigate thermal electron conduction effects on the formation property of a high-field dipole domain in the submicron GaAs MESFET. It is shown that the simplified model leads to the existence of a very unstable Gunn domain oscillating between the gate and drain, but the more accurate complete model gives a stable high-field domain confined well in the gate region due to thermal electron conduction. The crucial reason for this discrepancy between the two results is associated with the capable limits of accuracy in the simplified model. That is, this model gives rise to an unduly large retardation in the energy-gaining rate of electrons in the gate channel, so that the production of the negative differential resistance phenomenon by the electrons is largely delayed under the gate. Therefore, a traveling Gunn domain can be exhibited for submicron GaAs field-effect transistors in the simulation by a simplified energy model. It is demonstrated that even though simplified energy models are capable of reflecting the nonstationary effect of velocity overshoot properly, it is quite improper to apply these for studying device physics related to dipole domain properties; thermal electron conduction plays a pivotal role in forming a stable dipole domain in the submicron GaAs MESFET. In addition, the average effective valley-transition force for channel electrons (a new physical quantity first defined in the paper) is used to show that simplified energy models give a much larger magnitude for the force (approximately 1.8 eV/μm) compared to 1.2 eV/μm given by the complete energy model. Furthermore, the force is given closer to the drain end of the gate in the former models. Therefore, simplified energy models have a high possibility of creating a traveling domain for submicron devices.