bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of particle size and type on 231Pa and 230Th simulation with a global coupled biogeochemical‐ocean general circulation model: A first approach
Authors: Dutay J.‐C. , Lacan F. , Roy‐Barman M. , Bopp L.
Published: January 2009

The oceanic distributions of 231Pa and 230Th are simulated with the global coupled biogeochemical‐ocean general circulation model NEMO‐PISCES. These natural nonconservative tracers, which are removed from the water column by reversible scavenging processes onto particles, have been used to study modern and past ocean circulation. Our model includes three different types of particles: particulate organic matter (POM), calcium carbonate (CaCO3), and biogenic silica (BSi). It also considers two particle classes: small particles (POM) that sink slowly (3 m/d) and large particles (POM, CaCO3, BSi) that sink much more rapidly (50 m/d to 200 m/d) in the water column. 231Pa and 230Th are simulated with a reversible scavenging model that uses partition coefficients between dissolved and particulate phases that depend on particle type and size. Model results are then compared with 231Pa and 230Th observations in the water column and modern sediments. A preliminary evaluation of the particle fields simulated by the PISCES model has revealed that particle concentrations are reasonable at the surface but largely underestimated in the deep ocean. Largely to compensate for this, we find it necessary to use partition coefficients that vary as a function of particle size by significantly more that observed to obtain relatively realistic results. In the water column, 231Pa and 230Th fluxes are mainly controlled by the slowly sinking particles and partition coefficients need to be parameterized as a function of particle flux, as suggested by observations. Considering discrepancies between the modeling particle fields and those observed, we were forced to use exaggerated values for partition coefficients in order to get realistic tracer distributions. These 231Pa and 230Th simulations have provided an opportunity to propose some future developments of the PISCES model, in order to make progress in the simulation of trace elements. Assigning calcium carbonate, biogenic silica, and aluminosilicates to the small particle pool represents a credible approach to increase its concentration and subsequently simulate realistic tracer distributions in the water column using reasonable values for the partition coefficients, as well as a realistic fractionation in the sediments at all depths.
Thermal escape of carbon from the early Martian atmosphere
Authors: Tian Feng , Kasting James F. , Solomon Stanley C.
Published: January 2009

Observations suggest that Mars was wet and warm during the late Noachian, which probably requires a dense CO2 atmosphere. But would a dense CO2 early Martian atmosphere have been stable under the strong EUV flux from the young Sun? Here we show that thermal escape of carbon was so efficient during the early Noachian, 4.1 billion years ago (Ga), that a CO2‐dominated Martian atmosphere could not have been maintained, and Mars should have begun its life cold. By the mid to late Noachian, however, the solar EUV flux would have become weak enough to allow a dense CO2 atmosphere to accumulate. Hence, a sustainable warm and wet period only appeared several hundred million years (Myrs) after Mars formed.
Low‐altitude quasi‐periodic echoes studied using a large database of Gadanki radar observations
Authors: Venkateswara Rao N. , Patra A. K. , Rao S. V. B.
Published: January 2009

In this paper we present studies on low‐altitude quasiperiodic (LQP) echoes based on a large database of Gadanki radar observations. LQP echoes have been observed 33% of the time during daytime and 39% during nighttime. Their occurrence is found to be maximum in the summer (daytime, 58%; nighttime, 57%), followed by the September equinox (daytime, 32%; nighttime, 48%), the March equinox (daytime, 26%; nighttime, 36%), and minimum in the winter (daytime, 25%; nighttime, 26%). Height‐time occurrence of LQP echoes shows two local time maxima: one in the morning (0700–1100 LT) and another in the evening (1900–0000 LT). The most significant results not reported earlier are the large occurrence rate of LQP echoes and the height‐time occurrence maps showing a descending pattern with close resemblance to tidal wind behavior. The Doppler velocities are upward‐northward (downward‐southward) for positive‐ (negative‐) sloped LQP echoes. Also, we find the Doppler spread as high as 200 m s−1 at times underlining the presence of strong plasma turbulence in the collision‐dominated lower E region. These results are discussed in the light of the current understanding of the LQP echoes.
Dynamic motion of the bow shock and the magnetopause observed by THEMIS spacecraft
Authors: Zhang H. , Zong Q.‐G. , Sibeck D. G. , Fritz T. A. , McFadden J. P. , Glassmeier K.‐H. , Larson D.
Published: January 2009

We present an observational study of the dynamic motion of the bow shock and the magnetopause and suggest that the dynamic motion of the bow shock is due to the interaction of an interplanetary shock with the Earth's bow shock. THEMIS B spacecraft crossed the magnetopause, a discontinuity and the bow shock successively in 5 min during its outbound journey on 10 July 2007. Following THEMIS B, THEMIS C, D, E and A consecutively crossed the magnetopause and the discontinuity but not the bow shock. Timing analysis shows that the magnetopause and the discontinuity were moving earthward with speeds of ∼47 km/s and ∼90 km/s, respectively. There is a trend that the discontinuity decelerates as it propagates toward the magnetopause. We suggest that the dynamic motion and the discontinuity are results of the interaction of a weak (MA = 1.4) interplanetary shock with the Earth's bow shock. After the interaction, the transmitted interplanetary shock took the form of a discontinuity where total magnetic field and density increase and the temperature decreases. The rotation of the magnetic field across this discontinuity was similar to that of the interplanetary shock. The expected fast shock ahead of the discontinuity for shock‐shock interaction was not observed.
Timing and localization of near‐Earth tail and ionospheric signatures during a substorm onset
Authors: Gabrielse C. , Angelopoulos V. , Runov A. , Frey H. U. , McFadden J. , Larson D. E. , Glassmeier K.‐H. , Mende S. , Russell C. T. , Apatenkov S. , Murphy K. R. , Rae I. J.
Published: January 2009

On 16 February 2008, the THEMIS spacecraft (probes) bracketed the near‐Earth signatures of a substorm onset as identified in the THEMIS ground‐based observatories measuring an AETH index up to 180 nT. The main onset was associated with the formation and tailward release of a plasmoid (a proto‐plasmoid) at XGSM = −18.3 RE and a dipolarization in the inner part of the plasma sheet at XGSM = −11.0 RE. The time history and geometry of the event in the tail are consistent with magnetic reconnection as the cause of the substorm expansion onset process. Two activations of the plasma sheet, evidenced by tailward streaming of energetic ions and southward or bipolar signatures of the magnetic field, preceded the main substorm. The first activation was associated with an intensification of a high‐latitude arc, while the second was associated with the onset of ULF pulsations at midlatitude and low‐latitude stations. We conclude that near‐Earth plasma sheet activity that may also be due to reconnection and may be related to nonsubstorm arc intensifications can precede substorm onset by several minutes. In particular, high‐latitude arcs do not appear to result in substorm initiation even though they may occur in close temporal and spatial proximity to the substorm arc.
Variations of ice bed coupling beneath and beyond ice streams: The force balance
Authors: Hughes T.
Published: January 2009

A geometrical force balance that links stresses to ice bed coupling along a flow band of an ice sheet was developed in 1988 for longitudinal tension in ice streams and published 4 years later. It remains a work in progress. Now gravitational forces balanced by forces producing tensile, compressive, basal shear, and side shear stresses are all linked to ice bed coupling by the floating fraction ϕ of ice that produces the concave surface of ice streams. These lead inexorably to a simple formula showing how ϕ varies along these flow bands where surface and bed topography are known: ϕ = hO/hI with hO being ice thickness hI at x = 0 for x horizontal and positive upslope from grounded ice margins. This captures the basic fact in glaciology: the height of ice depends on how strongly ice couples to the bed. It shows how far a high convex ice sheet (ϕ = 0) has gone in collapsing into a low flat ice shelf (ϕ = 1). Here ϕ captures ice bed coupling under an ice stream and hO captures ice bed coupling beyond ice streams.
Global marine gravity from retracked Geosat and ERS‐1 altimetry: Ridge segmentation versus spreading rate
Authors: Sandwell David T. , Smith Walter H. F.
Published: January 2009

Three approaches are used to reduce the error in the satellite‐derived marine gravity anomalies. First, we have retracked the raw waveforms from the ERS‐1 and Geosat/GM missions resulting in improvements in range precision of 40% and 27%, respectively. Second, we have used the recently published EGM2008 global gravity model as a reference field to provide a seamless gravity transition from land to ocean. Third, we have used a biharmonic spline interpolation method to construct residual vertical deflection grids. Comparisons between shipboard gravity and the global gravity grid show errors ranging from 2.0 mGal in the Gulf of Mexico to 4.0 mGal in areas with rugged seafloor topography. The largest errors of up to 20 mGal occur on the crests of narrow large seamounts. The global spreading ridges are well resolved and show variations in ridge axis morphology and segmentation with spreading rate. For rates less than about 60 mm/a the typical ridge segment is 50–80 km long while it increases dramatically at higher rates (100–1000 km). This transition spreading rate of 60 mm/a also marks the transition from axial valley to axial high. We speculate that a single mechanism controls both transitions; candidates include both lithospheric and asthenospheric processes.
Electrical evolution during the decay stage of New Mexico thunderstorms
Authors: Marshall Thomas C. , Stolzenburg Maribeth , Krehbiel Paul R. , Lund Nicole R. , Maggio Chris R.
Published: January 2009

The electric field (E) at the ground beneath a thunderstorm often exhibits an end‐of‐storm oscillation (EOSO) during the storm's decay phase in which E typically undergoes three polarity changes over a period of 30–75 min. To determine why the surface E oscillates, the timing of the EOSO polarity changes of a multicellular storm in New Mexico has been compared to a series of balloon, radar, and lightning data. Three in situ balloon soundings provide vertical profiles of E and inferred charge regions just before and during the EOSO. These data have been compared to the evolving precipitation structure determined from orthogonal range‐height scans of two radars and to several other parameters including lightning mapping array data. Before the EOSO began, the storm had the typical electrical structure of the late mature stage. Estimates of the total charge magnitudes in each of the principal regions before and during the EOSO ranged from 7 to 33 C. The comparisons indicate that surface E polarity changes during the EOSO were (1) primarily owing to the successive fallout of three of the four principal charge regions in the storm's mature stage charge structure, modified by (2) the growth or decay of the charge regions as they descended, and (3) changes in the screening charges at the upper and lower cloud boundaries. More limited data from two other decaying storms indicate that similar in‐cloud evolution was probably occurring during their EOSOs.
Gravity and tectonic patterns of Mercury: Effect of tidal deformation, spin‐orbit resonance, nonzero eccentricity, despinning, and reorientation
Authors: Matsuyama I. , Nimmo F.
Published: January 2009

We consider the effect of spin‐orbit resonance, nonzero eccentricity, despinning, and reorientation on Mercury's gravity and tectonic pattern. Large variations of the gravity and shape coefficients from the synchronous rotation and zero eccentricity values,J2/C22= 10/3 and (b−c)/(a−c) = 1/4, arise because of nonsynchronous rotation and nonzero eccentricity even in the absence of reorientation or despinning. Reorientation or despinning induces additional variations. The large gravity coefficientsJ2= (6 ± 2) × 10−5andC22= (1 ± 0.5) × 10−5estimated from the Mariner 10 flybys cannot be attributed to Caloris alone since the required mass excess in this case would have caused Caloris to migrate to one of Mercury's hot poles. Similarly, a large remnant bulge due to a smaller semimajor axis and spin‐orbit resonance can be dismissed since the required semimajor axis is unphysically small (<0.1 AU). Reorientation of a large remnant bulge recording an epoch of faster rotation (without significant semimajor axis variations) can explain the large gravity coefficients. This requires initial rotation rates ≳20 times the present value and a positive gravity anomaly associated with Caloris capable of driving ∼10°–45° equatorward reorientation. The required gravity anomaly can be explained by infilling of the basin with material of thicknesses ≳7 km or an annulus of volcanic plains emplaced around the basin with an annulus width ∼1200 km and fill thicknesses ≳2 km. The predicted tectonic pattern due to these despinning and reorientation scenarios, including some radial contraction, is in good agreement with the lobate scarp pattern observed by Mariner 10. We also predict that lobate scarps will follow a NE–SW orientation in the eastern hemisphere and a positive gravity anomaly (of a few hundred mGal) associated with Caloris.
Analytical modeling of polycyclic aromatic hydrocarbon loading and transport via road runoff in an urban region of Beijing, China
Authors: Zhang Wei , Keller Arturo A. , Wang Xuejun
Published: January 2009

An analytical runoff water quality model is developed for simulating polycyclic aromatic hydrocarbon (PAH) loading and transport via road runoff in an urban area. The model considers buildup and washoff processes of suspended solids in storm runoff and considers dissolved and particle‐bound PAHs. Pollutant deposition and removal processes, which have typically been treated with a constant rate in previous models, are depicted as functions of relative humidity and wind speed to reflect the influence of meteorological conditions and are integrated into the pollutant buildup function. Pollutant input via rainwater and canopy throughfall from roadside trees is considered in the washoff model. The model is calibrated and verified with field data from an urban catchment in Beijing, China. The verification indicates that the runoff model is capable of providing results in good agreement with field measurements. A Monte Carlo framework is used to evaluate the uncertainty of PAH loading under various scenarios of atmospheric conditions.
Forward and backward temporal probability distributions of sorbing solutes in groundwater
Authors: Neupauer R. M. , Wilson J. L. , Bhaskar A.
Published: January 2009

The travel time of a contaminant particle in an aquifer can be used to identify the release time of contamination from a known source, to delineate captures zones around wells, and for other applications. The travel time is uncertain because of spatial variability of hydrogeologic properties and fluctuations of groundwater velocity and therefore is often represented as a random variable. A forward travel time probability density function (pdf) describes the random time that a particle will reach a downgradient location, while the backward travel time pdf describes the time in the past when the particle was at an upgradient location, such as the source location. For sorbing solutes, the particle may have been in either the aqueous phase or the sorbed phase at the location of interest. Since a particle can only travel through the aquifer in the aqueous phase, the random travel time accounts only for particles in the aqueous phase. We develop new probabilistic expressions to characterize the random time in the past that a contaminant particle was sorbed at a location of interest. For a solute that exhibits linear equilibrium sorption, we develop forward and backward pdfs for the time of sorption, defined as the random time at which the particle is at a location of interest in the sorbed phase. For the linear nonequilibrium sorption case, we develop expressions for the forward and backward sorbed phase probability, defined as the discrete probability that a particle will be sorbed at a location of interest at a deterministic time. Although forward pdfs and probabilities produce the same information as backward pdfs and probabilities, backward probabilistic expressions can be calculated more efficiently when the number of observations is small relative to the number of possible source locations or release times.
Proper expression of helix–loop–helix protein Id2 is important to chondrogenic differentiation of ATDC5 cells
Authors: Yang Liu , Ma Xiaoyun , Lyone Anne , Zou Junhui , Blackburn Michael L. , Pan Jing , Yang Dingqiao , Matsushita Hiroshi , Mei Bin , Zielinska-Kwiatkowska Anna , Chansky Howard A.
Published: January 2009

The process of chondrogenesis can be mimicked in vitro by insulin treatment of mouse ATDC5 chondroprogenitor cells. To identify novel factors that are involved in the control of chondrogenesis, we carried out a large-scale screening through retroviral insertion mutagenesis and isolated a fast-growing ATDC5 clone incapable of chondrogenic differentiation. Inverse-PCR analysis of this clone revealed that the retroviral DNA was inserted into the promoter region of mouse Id2 (inhibitor of DNA-binding protein 2) gene. This retroviral insertion increased Id2 protein levels to twice those found in normal ATDC5 cells. To investigate whether an elevated level of Id2 protein was responsible for inhibition of chondrogenic differentiation, ATDC5 cells were infected with a retrovirus to stably express Id2. ATDC5 cells expressing ectopic Id2 exhibited signs of de-differentiation, such as rapid growth, and insulin failed to induce expression of Sox9 (Sry-type high-mobility-group box 9) or matrix genes such as type II collagen (COL2) in these cells. When endogenous Id2 was knocked down by siRNA (small interfering RNA) in ATDC5 cells, expression of Sox9 and COL2 was increased and chondrogenic differentiation was accelerated. To examine how Id2 is expressed in chondrocytes in vivo, we carried out immunostaining of E16.5 mouse embryos and found that Id2 is expressed in articular chondrocytes and proliferating chondrocytes, but barely detectable in hypertrophic chondrocytes. Our results suggest that proper expression of Id2 is important to achieving a fine balance between growth and differentiation during chondrogenesis.
Serial changes in adiponectin and BNP in ACS patients: paradoxical associations with each other and with prognosis
Authors: Ang Donald S. C. , Welsh Paul , Watt Pauline , Nelson Scott M. , Struthers Allan , Sattar Naveed
Published: January 2009

Plasma adiponectin is inversely associated with the risk of coronary heart disease in healthy people. However, adiponectin and BNP (B-type natriuretic peptide) are both known to be positively associated with a risk of poor outcome, and with each other, in ACS (acute coronary syndrome) patients. Serial changes in plasma adiponectin and BNP following ACS have not been assessed previously, and may clarify these apparently paradoxical associations. In the present study, adiponectin, BNP, classical risk markers and clinical parameters were measured in plasma from 442 consecutive ACS patients in an urban teaching hospital, with repeat measures at 7 weeks (n=338). Patients were followed-up for 10 months. Poor outcome was defined as mortality or readmission for ACS or congestive heart failure (n=90). In unadjusted analysis, the change in adiponectin (but not baseline or 7-week adiponectin) was significantly associated with the risk of an adverse outcome {odds ratio (OR), 5.42 [95% CI (confidence interval), 2.78–10.55]}. This association persisted after adjusting for classical risk factors and clinical markers, but was fully attenuated by adjusting for the 7-week BNP measurement [OR, 1.13 (95% CI, 0.27–4.92)], which itself remained associated with risk [OR, 5.86 (95% CI, 1.04–32.94)]. Adiponectin and BNP positively correlated at baseline and 7 weeks, and the change in both parameters over 7 weeks also correlated (r=0.39, P<0.001). In conclusion, increases in plasma adiponectin (rather than absolute levels) after ACS are related to the risk of an adverse outcome, but this relationship is not independent of BNP levels. The results of the present study allude to a potential direct or indirect relationship between adiponectin and BNP post-ACS which requires further investigation.
Electron source of triode type with radial converging electron flow for irradiation of cylindrical targets
Authors: Engelko V. I. , Kuznetsov V. S. , Müller Georg
Published: January 2009

Design of an electron source of triode type is described, which produces a radial converging electron beam employed for modification of the outer surface of fuel element claddings. Experimental investigations of the source showed that beam current magnitude, efficiency of beam focusing to the target, stability of source operation, and beam pulse duration become worse when the target diameter drops below certain values. A method for the calculation of the source operation was developed. Calculations showed that the reason of worse source operation is the initial angular spread of electrons when the target diameter is small. Because of the angular spread a part of electrons passes by the target and oscillates between the target and cathode. The space charge of the oscillating electrons lowers the emission current magnitude and leads to the formation of a virtual cathode in the grid-target gap despite the fact that the emission beam current is less than the limiting one. Formation of a virtual cathode is a reason for the unstable source operation and restriction of the beam pulse duration. Recommendations for the improvement of the source design are suggested.
Broadband dielectric spectroscopy of Ruddlesden–Popper Srn+1TinO3n+1 (n=1,2,3) thin films
Authors: Orloff N. D. , Tian W. , Fennie C. J. , Lee C. H. , Gu D. , Mateu J. , Xi X. X. , Rabe K. M. , Schlom D. G. , Takeuchi I. , Booth J. C.
Published: January 2009

We explore the frequency-dependent relative permittivity of Ruddlesden–Popper series Srn+1TinO3n+1 (n=1,2,3) thin films as a function of temperature and dc electric field. Interdigitated capacitors and coplanar waveguides were used to extract the frequency response from 500 Hz to 40 GHz. At room temperature, the in-plane relative permittivities (ϵ11) obtained for Srn+1TinO3n+1 (n=1,2,3) were 42±3, 54±3, and 77±2, respectively, and were independent of frequency. At low temperatures, ϵ11 increases and electric field tunability develops in Sr4Ti3O10.
Density and temperature distributions in the plasma expanding from an exploded wire in vacuum
Authors: Beilis I. I. , Shashurin A. , Baksht R. B. , Oreshkin V.
Published: February 2009

The plasma expansion from an exploded wire with characteristic times of energy deposition in the wire of tens of microseconds was studied. The probe method was used to measure the plasma temperature and plasma density distributions. Tungsten wires 25, 50, 75, and 125 μm in diameter and a copper wire 100 μm in diameter were used. The waveforms of discharge voltage Ud, discharge current Id, and floating potential showed that Ud was close to a constant, while Id decreased, indicating that the wire resistance increased until plasma appeared. Immediately after the appearance of plasma, Id was observed to peak, while the voltage decreased stepwise from ∼110 to about 70 V. A relatively high electron temperature (about 12 eV) was observed in the expanding plasma even at r=2 cm from the wire axis. The plasma density was a maximum of 2×1013 cm−3 at r=2 cm, and it decreased with increasing r. For r<2 cm, unusual electrical parameters were observed, indicating the probe activity and a significantly increased plasma density in the region close to the wire core.
Artificially controlled magnetic domain structures in ferromagnetic dots∕ferroelectric heterostructures
Authors: Taniyama Tomoyasu , Akasaka Kyohei , Fu Desheng , Itoh Mitsuru
Published: January 2009

A variation in the magnetization and magnetic domain structures of epitaxial Fe dots on a single crystal BaTiO3 substrate is demonstrated in association with the structural phase transition of ferroelectric BaTiO3. The temperature dependent magnetization of Fe dots drops suddenly at 282K and increases again at 189K with decreasing temperature. The variations clearly correspond to the successive structural phase transitions of BaTiO3 from tetragonal to orthorhombic phases and from orthorhombic to rhombohedral phases. After a thermal cycle between room temperature and 150K passing through these phase transitions, the initial magnetic domain structure of Fe dots with an enclosed magnetic flux structure changes to a single-domain-like structure due to interfacial strain between Fe and BaTiO3 arising from possible switching of c-axis orientation of BaTiO3 substrate.
Ab initio calculation of intrinsic spin Hall conductivity of Pd and Au
Authors: Guo G. Y.
Published: January 2009

An ab initio relativistic band structure calculation of spin Hall conductivity (SHC) (σxyz) in Pd and Au metals has been performed. It is found that at low temperatures, intrinsic SHCs for Pd and Au are, respectively, ∼1400 and ∼400(ℏ∕e)(Ωcm)−1. The large SHC in Pd comes from the resonant contribution from the spin-orbit splitting of the doubly degenerated 4d bands near the Fermi level at symmetry Γ and X points, and the smaller SHC in Au is due to the broad free-electron-like 6s6p bands. However, as the temperature increases, the SHC in Pd decreases monotonically and reduces to ∼330(ℏ∕e)(Ωcm)−1 at 300K, while the SHC in Au increases steadily and reaches ∼750(ℏ∕e)(Ωcm)−1 at room temperature. This indicates that the gigantic spin Hall effect [σxyz≈105(ℏ∕e)(Ωcm)−1] observed recently in the Au∕FePt system [T. Seki et al., Nature Mater. 7, 125 (2008)] is due to the extrinsic mechanisms such as the skew scattering by the impurities in Au.
Contribution of Eu 4f states to the magnetic anisotropy of EuO
Authors: Arenholz E. , Schmehl A. , Schlom D. G. , van der Laan G.
Published: January 2009

Anisotropic x-ray magnetic linear dichroism (AXMLD) provides a novel element-, site-, shell-, and symmetry-selective techniques to study the magnetic anisotropy induced by a crystalline electric field. The weak Eu2+ M4,5 AXMLD observed in EuO(001) indicates that the Eu 4f states are not rotationally invariant and hence contribute weakly to the magnetic anisotropy of EuO. The results are contrasted with those obtained for 3d transition metal oxides.
A model of laser heater undulator system for self-amplified free electron lasers
Authors: Dattoli G. , Migliorati M.
Published: January 2009

The laser heater has been proposed to damp the microbunching instability affecting the operation of free electron laser (FEL) self-amplified spontaneous emission (SASE) devices. The heater may be provided by an external laser or by a FEL oscillator using the same electron beam driving the SASE-FEL operation. The second solution offers undoubtful advantages, which will be discussed in this paper. We present simple physical arguments which allow the derivation of a criterion yielding the amount of laser power necessary to damp the instability, without compromising the FEL SASE operation.
Effect of substitution of Co for Fe on the magnetic hysteresis loss and the refrigerant capacity in the La0.5Pr0.5Fe11.5Si1.5 compounds
Authors: Shen Jun , Li Yang-Xian , Hu Feng-Xia , Sun Ji-Rong
Published: January 2009

Magnetic hysteresis loss and refrigerant capacity of the NaZn13-type La0.5Pr0.5Fe11.5−xCoxSi1.5 (0⩽x⩽1.0) compounds have been investigated. The substitution of Co in the La0.5Pr0.5Fe11.5Si1.5 causes the order of phase transition at TC to change from first order to second order at x=0.6. Although the magnetic entropy change decreases with increasing Co concentration, the hysteresis loss at TC also reduces remarkably from 94.8J∕kg for x=0to1.8J∕kg for x=0.4 because an increase in Co content can weaken the itinerant electron metamagnetic transition. The effective refrigerant capacity remains at a high value ranging from 355to433J∕kg for a field change of 0–5T as x varies from 0 to 1.0.
Tuning magnetic properties of yttrium iron garnet film with oxygen partial pressure in sputtering and annealing process
Authors: Yang Qing-Hui , Zhang Huai-Wu , Wen Qi-Ye , Liu Ying-Li , Xiao John Q.
Published: January 2009

In this paper, the magnetic properties of these films which deposited and annealed at different atmospheres were investigated. The experimental results show that the magnetic properties of yttrium iron garnet films prepared by rf magnetron sputtering method can be tuned with oxygen partial pressure in sputtering and annealing processes. The optimal condition is depositing in atmosphere of R=0 and annealing at 0.5Pa O2, or depositing in atmosphere of R=2% and annealed in vacuum.
Origin of asymmetry of tunneling conductance in CoFeB∕MgO∕CoFeB tunnel junction
Authors: Jang Youngman , Lee Kisu , Lee Seungkyo , Yoon Seungha , Cho B. K. , Cho Y. J. , Kim K. W. , Kim Kwang-seok
Published: January 2009

We investigated the top and bottom interfaces of a CoFeB∕MgO∕CoFeB tunnel junction using transmission electron microscope (TEM) and x-ray photoemission spectroscopy (XPS) in order to understand the origin of the asymmetry of dI∕dV in terms of bias polarity. It was found, from a TEM image, that there is no clear cut at the top interface, while the bottom interface has relatively clean boundary. Furthermore, XPS data show that more hydroxides were formed at the top interface than at the bottom interface. These indicate that the hydroxides would hinder the epitaxial crystallinity at the interface in CoFeB∕MgO∕CoFeB tunnel junctions. Therefore, it is most likely that the asymmetry of dI∕dV is caused by the disappearance of minority Bloch state, which is closely correlated with the existence of hydroxides at the top interface of a CoFeB∕MgO∕CoFeB tunnel junction.
Quantitative analysis of the angle dependence of planar Hall effect observed in ferromagnetic GaMnAs film
Authors: Kim Jungtaek , Yoo Taehee , Chung Sunjae , Lee Sanghoon , Liu X. , Furdyna J. K.
Published: January 2009

The angle dependence of the planar Hall effect has been analyzed based on the magnetic free energy including the magnetic anisotropy and the Zeeman effects. The Zeeman effect dominated the magnetic anisotropy in high field and only a single energy minimum is shown in free energy over entire field angle, which leads to the coherent rotation of the magnetization in the form of a single domain state. When the field strength is reduced below 300Oe, multiple energy minima appear in the angle dependence of free energy due to the increase in the relative importance of magnetic anisotropy. In the low field region, reorientation of magnetization experiences abrupt transition between the free energy minima. The pinning fields obtained from the analysis showed systematic dependence on the strength of external field, which was used to rotate magnetization. We understood such pinning energy dependence in terms of the difference in the free energy density profile for the different field strengths.
Current-perpendicular-to-plane magnetoresistance of a domain wall confined in a nano-oxide layer
Authors: Sato Jun , Matsushita Katsuyoshi , Imamura Hiroshi
Published: January 2009

We theoretically study the current-perpendicular-to-plane magnetoresistance (MR)of a domain wall confined in a current-confined-path (CCP) structure made of a nano-oxide layer. In order to calculate the MR ratio of the system, the continuity equations for charge and spin currents are numerically solved with the three-dimensional CCP geometry by the use of the finite element method. It is confirmed that the MR ratio is enhanced by the CCP structure, which is consistent with the experimental results.
Combined angular effects of spin polarization and magnetic field on magnetic element switching
Authors: Wang Xiaobin , Zhu Wenzhong , Gao Zheng , Xi Haiwen , Dimitrov Dimitar
Published: February 2009

We explore the combined effects of polarization direction and magnetic field direction on magnetization switching. Optimal polarization and magnetic field angles are obtained for the most effective magnetization switching. Analytical results are obtained for specific symmetric configurations based upon spin torque magnetization dynamics symmetry. Modeling results are used to understand experimental measurements for spin torque switching of a magnetic tunneling junction with canted pinning layers from nanosecond region to second region.
The band gap of ultrathin amorphous and well-ordered Al2O3 films on CoAl(100) measured by scanning tunneling spectroscopy
Authors: Rose V. , Franchy R.
Published: January 2009

The structural and electronic properties of ultrathin insulator Al2O3 films on CoAl(100) have been studied using a combination of scanning tunneling spectroscopy and microscopy. The analysis of the differential conductance yields a band gap of 2.6–2.9eV for amorphous Al2O3. In the case of a well-ordered alumina film, the band gap is increased to 4.5eV. On each of the oxide phases, the barrier height is to a large extent independent of local variations such as the surface corrugations or oxide steps.
Tunnel magnetoresistance effect in magnetic tunnel junctions using epitaxial Co2FeSi Heusler alloy electrode
Authors: Oogane Mikihiko , Shinano Masatsugu , Sakuraba Yuya , Ando Yasuo
Published: January 2009

Magnetic tunnel junctions (MTJs) using epitaxially grown (100)-oriented and (110)-oriented Co2FeSi Heusler alloy bottom electrodes and amorphous Al-oxide barriers were fabricated. The tunnel magnetoresistance (TMR) ratios were 80% at 2 K and 48% at room temperature for the MTJ with the (100)-Co2FeSi bottom electrode. The MTJ with the (100)-Co2FeSi bottom electrode had a smaller TMR ratio than the MTJ with (100)-Co2FeSi electrode. The TMR ratio in MTJs with Co2FeSi electrode is smaller than that of a MTJ with Co2MnSi electrode. Tunnel conductance characteristics were investigated, revealing no half-metallic character in MTJs with Co2FeSi electrode in the conductance-voltage curves.
Magnetic behavior and phase diagram of Gd4(Co1−xCux)3 compounds
Authors: Seixas T. M. , Salgueiro da Silva M. A. , Braun H. F. , Eska G.
Published: January 2009

In order to study the effects caused by substituting Co for Cu on the magnetic properties of Gd4(Co1−xCux)3 compounds with x=0.05, 0.1, 0.2, and 0.3, superconducting quantum interference device magnetization measurements were performed on polycrystalline samples in the temperature range of 5–300 K using applied magnetic fields from 0 to 5 T. Experimental results show that the substitution of Co for Cu produces an increase in magnetic anisotropy, which is accompanied by important changes in the magnetic ordering of these ferrimagnetic compounds with respect to that of Gd4Co3. A magnetic T-x phase diagram comprised of c-axis, canted, and possibly partially disordered ferrimagnetic phases, is proposed. The calculated average saturation magnetic moment of Co atoms decreases exponentially with increasing Cu content. Such behavior of MCo(x) may originate from the combined effect of the 3d band filling by 4s electrons from Cu atoms and a strong dependence of Co moment on the number of local Co neighboring atoms.
Particle-in-cell simulations of short-pulse, high intensity light impinging on structured targets
Authors: Lasinski B. F. , Langdon A. B. , Still C. H. , Tabak M. , Town R. P. J.
Published: January 2009

Light propagating down a cone and/or impinging on a structured surface in the short-pulse, high intensity laser-matter interaction which generates the hot energetic electrons essential to the fast ignition scheme is studied with particle-in-cell simulations. These more complex geometries lead to both increased laser light absorption and higher temperatures of the resulting energetic electrons as compared to simple slab interactions. But the relatively wide angular distributions of the energetic electrons observed in the simulations needs to be taken into account in fast ignition designs.
Parallel multireference configuration interaction calculations on mini-β-carotenes and β-carotene
Authors: Kleinschmidt Martin , Marian Christel M. , Waletzke Mirko , Grimme Stefan
Published: January 2009

We present a parallelized version of a direct selecting multireference configuration interaction (MRCI) code [S. Grimme and M. Waletzke, J. Chem. Phys. 111, 5645 (1999)]. The program can be run either in ab initio mode or as semiempirical procedure combined with density functional theory (DFT/MRCI). We have investigated the efficiency of the parallelization in case studies on carotenoids and porphyrins. The performance is found to depend heavily on the cluster architecture. While the speed-up on the older Intel Netburst technology is close to linear for up to 12–16 processes, our results indicate that it is not favorable to use all cores of modern Intel Dual Core or Quad Core processors simultaneously for memory intensive tasks. Due to saturation of the memory bandwidth, we recommend to run less demanding tasks on the latter architectures in parallel to two (Dual Core) or four (Quad Core) MRCI processes per node. The DFT/MRCI branch has been employed to study the low-lying singlet and triplet states of mini-n-β-carotenes (n=3, 5, 7, 9) and β-carotene (n=11) at the geometries of the ground state, the first excited triplet state, and the optically bright singlet state. The order of states depends heavily on the conjugation length and the nuclear geometry. The B1u+ state constitutes the S1 state in the vertical absorption spectrum of mini-3-β-carotene but switches order with the 2 A1g− state upon excited state relaxation. In the longer carotenes, near degeneracy or even root flipping between the B1u+ and B1u− states is observed whereas the 3 A1g− state is found to remain energetically above the optically bright B1u+ state at all nuclear geometries investigated here. The DFT/MRCI method is seen to underestimate the absolute excitation energies of the longer mini-β-carotenes but the energy gaps between the excited states are reproduced well. In addition to singlet data, triplet-triplet absorption energies are presented. For β-carotene, where these transition energies are known from experiment, excellent agreement with our calculations is observed.
Renormalized theory of the ion cyclotron turbulence in magnetic field-aligned plasma shear flow
Authors: Mikhailenko V. S. , Mikhailenko V. V. , Stepanov K. N. , Azarenkov N. A.
Published: January 2009

The analytical treatment of nonlinear evolution of the shear-flow-modified current driven ion cyclotron instability and shear-flow-driven ion cyclotron kinetic instabilities of magnetic field-aligned plasma shear flow is presented. Analysis is performed on the base of the nonlinear dispersion equation, which accounts for a new combined effect of plasma turbulence and shear flow. It consists of turbulent scattering of ions across the shear flow with their convection by shear flow and results in enhanced nonlinear broadening of ion cyclotron resonances. This effect is found to lead to the saturation of ion cyclotron instabilities as well as to the development of nonlinear shear flow driven ion cyclotron instability.
Orientational mobility and relaxation spectra of dendrimers: Theory and computer simulation
Authors: Markelov Denis A. , Lyulin Sergey V. , Gotlib Yuli Y. , Lyulin Alexey V. , Matveev Vladimir V. , Lahderanta Erkki , Darinskii Anatolij A.
Published: January 2009

The developed theory of the orientational mobility of individual segments of a perfectly branched dendrimer is used to calculate the relaxation spectrum of a dendrimer. Frequency dependences of NMR relaxation 1/T1 and of the nuclear Overhauser effect have been theoretically calculated from the Brownian dynamics simulation data. The dendrimer segmental orientational mobility is governed by three main relaxation processes: (i) the rotation of the dendrimer as a whole, (ii) the rotation of the dendrimer’s branch originated from a given segment, and (iii) the local reorientation of the segment. The internal orientational mobility of an individual dendrimer segment depends only on the topological distance between this segment and the terminal shell of the dendrimer. Characteristic relaxation times of all processes and their contributions to the segmental mobility have been calculated. The influence of the number of generations and the number of the generation shell on the relaxation times has been studied. The correlation between the characteristic times and the calculated relaxation spectrum of the dendrimer has been established.
Bifurcation phenomena in the flow through a sudden expansion in a circular pipe
Authors: Mullin T. , Seddon J. R. T. , Mantle M. D. , Sederman A. J.
Published: January 2009

We report the results of an experimental investigation into bifurcation phenomena in laminar and time-dependent flows through a sudden expansion in a circular pipe. The flow state was investigated using high resolution magnetic resonance imaging techniques which have enabled us to identify important qualitative features in the flow field and make quantitative estimates of the velocity distributions. Using these techniques we have uncovered evidence for a steady symmetry breaking bifurcation at a critical value of the Reynolds number. The asymmetric steady state which arises at the bifurcation point eventually gives way to time dependence in the form of bursts of periodic motion with further increase in flow rate.
Electron paramagnetic resonance of Er3+ ions in aluminum nitride
Authors: Yang Shan , Evans S. M. , Halliburton L. E. , Slack G. A. , Schujman S. B. , Morgan K. E. , Bondokov R. T. , Mueller S. G.
Published: January 2009

An electron paramagnetic resonance (EPR) spectrum from Er3+ ions has been observed in a bulk single crystal of aluminum nitride (AlN). These Er3+ ions were introduced into the crystal during growth and had a concentration of approximately 2×1016 cm−3. The Er3+ EPR signal, monitored at 4.5 K, exhibits axial symmetry (the unique axis is parallel to the c axis in this wurtzite lattice) and shows well-resolved hyperfine splittings due to E167r nuclei. An absence of site splittings in the EPR angular dependence indicates that these erbium ions, replacing aluminum ions in the AlN crystal, have no nearby defects. Principal values for the g and hyperfine matrices are g∥=4.337, g⊥=7.647, |A∥|=454 MHz, and |A⊥|=796 MHz. Forbidden transitions, appearing in the low-field portion of the hyperfine spectrum when the magnetic field is rotated a few degrees away from the c axis, give |P|=7.8 MHz for the nuclear electric quadrupole parameter.
Study of LiNbO3 and LiTaO3 ferroelectric domain structures using high-resolution x-ray diffraction under application of external electric field
Authors: Roshchupkin D. V. , Irzhak D. V. , Antipov V. V.
Published: February 2009

Regular domain structures formed in ferroelectric LiNbO3 and LiTaO3 crystals by the aftergrowth thermoelectrical treatment technique were studied by high-resolution x-ray diffraction and topography under an external electric field applied to the crystals. The application of an external electric field to the crystal causes longitudinal and shift deformations due to the reverse piezoelectric effect and, as a result, inverse changes in the Bragg angle values in adjacent domains. The changes in the Bragg angle values lead to an increase in the x-ray topographic contrast of the domain structure images and allow the direction of the polar and piezoelectrically active axis in adjacent domains to be unambiguously determined. In addition, it was shown that the x-ray diffraction technique can be used to study the behavior of elastic deformations near domain boundaries under an external electric field applied to crystals.
On the magnetism, thermal- and electrical transport of SrMoO2N
Authors: Logvinovich D. , Hejtmánek J. , Knižek K. , Maryško M. , Homazava N. , Tomeš P. , Aguiar R. , Ebbinghaus S. G. , Reller A. , Weidenkaff A.
Published: January 2009

Physical properties of perovskite-type SrMoO2N phases were studied in the temperature range of 3 K<T<300 K. The oxynitride crystallizes in a cubic unit cell (space group Pm3¯m) as revealed by neutron and x-ray diffraction measurements. The polycrystalline material shows weakly temperature dependent electrical resistivity and low glasslike heat conductivity, both reflecting the unusual strength of the scattering processes in the charge carrier transport. Based on the positive Seebeck coefficient values, holes are identified as the dominating charge carriers in SrMoO2N. Down to 150 K, the magnetic susceptibility is temperature independent and explained as enhanced Pauli paramagnetism (χ∼10−4 emu mol−1 Oe−1). The absolute value of its magnetic susceptibility is, however, half of that for SrMoO3. Simultaneously, the lower Sommerfeld coefficient γ measured for the oxynitride confirms the lower density of states near the Fermi level for SrMoO2N compared to SrMoO3. At low temperature, both SrMoO2N and SrMoO3 show Curie paramagnetism superimposed to the temperature independent Pauli paramagnetism and an anomaly at T=54 K. This anomaly is attributed to the presence of molecular oxygen in the material, while the Curie upturn is likely associated with a small amount of paramagnetic centers.
Outer synchronization of coupled discrete-time networks
Authors: Li Changpin , Xu Congxiang , Sun Weigang , Xu Jian , Kurths Jürgen
Published: January 2009

In this paper, synchronization between two discrete-time networks, called “outer synchronization” for brevity, is theoretically and numerically studied. First, a sufficient criterion for this outer synchronization between two coupled discrete-time networks which have the same connection topologies is derived analytically. Numerical examples are also given and they are in line with the theoretical analysis. Additionally, numerical investigations of two coupled networks which have different connection topologies are analyzed as well. The involved numerical results show that these coupled networks with different connection matrices can reach synchronization.
Simple expression for the dependence of the nanodrop contact angle on liquid-solid interactions and temperature
Authors: Berim Gersh O. , Ruckenstein Eli
Published: January 2009

The density distributions and contact angles of nanodrops on smooth solid surfaces are calculated on the basis of a nonlocal density functional theory in wide ranges of temperature and parameters of the Lennard-Jones potentials representing the fluid-fluid and fluid-solid interactions. A simple linear dependence of the contact angle on the fluid-solid energy parameter ϵfs was found for various temperatures, hard core fluid-solid parameters σfs, and average fluid density of the system. A simple expression is suggested which represents all the above results in a unified form that relates the contact angle θ to the parameters of the interaction potentials and temperature. The most intriguing feature was that for each considered σfs there is a value ϵfs0 of ϵfs for which the contact angle θ=θ0 can be considered independent of temperature and of σfs. It is shown that ϵfs=ϵfs0 divides the materials for which θ increases from those for which θ decreases with increasing temperature. The results obtained for the dependence of the contact angle on the parameters of the model are in qualitative agreement with known molecular dynamics results.