bluuebunny/crossref_metadata_2025 huggingface dataset:
Recent volcanic events and the distribution of hydrothermal venting at the Lucky Strike hydrothermal field, Mid‐Atlantic Ridge
Authors: Ondréas H. , Cannat M. , Fouquet Y. , Normand A. , Sarradin P. M. , Sarrazin J.
Published: February 2009

We present new high‐resolution bathymetry and backscatter data acquired in 2006 with the ROV Victor 6000 over the Lucky Strike hydrothermal field, Mid‐Atlantic Ridge. As long‐term monitoring of the Lucky Strike area (MoMAR project) is being implemented, these new high‐resolution data offer an unprecedented view of the distribution of hydrothermal edifices, eruptive facies, and small‐scale tectonic features in the Lucky Strike vent field. We show that vents located in the NW and NE correspond with wide expanses of lumpy seafloor which we interpret as primarily made of broken chimneys and sulfide edifices. They are found above scarps with relief >50 m or on associated mass wasting deposits. By contrast, the SE and SW vents correspond with small expanses of lumpy seafloor and are located near smaller scarps which we interpret as more recent faults. Hydrothermal edifices in the SW venting area appear very recent, postdating the emplacement and faulting of the most recent lava. We propose that this difference in the age of hydrothermal edifices does not mean that hydrothermal venting itself is more recent in the southern part of the Lucky Strike field because preexisting sulfide deposits there may have been buried by recent volcanic deposits. Instead, the older edifices in the northern part of the hydrothermal field may have been allowed more time to grow because they are set above the level of recent lava flows. The formation of a lava lake is the most recent eruptive event detected at Lucky Strike. Lava drainback is evidenced by benches and lava pillars, suggesting a close connection with an underlying magma reservoir, which probably corresponds to the melt body imaged by Singh et al. (2006). We have found no evidence that this lake was active for months to decades, as lava lakes at terrestrial volcanoes. It may instead have formed as a lava pond, with successive lava flows covering the eruptive vents, as proposed for similar features at the EPR. The horizontal surface of the lake is deformed only near its southwestern shore, along a NNE‐trending set of faults and fissures, which appear to control the distribution of hydrothermal chimneys.
Water and gas chemistry at Lake Kivu (DRC): Geochemical evidence of vertical and horizontal heterogeneities in a multibasin structure
Authors: Tassi F. , Vaselli O. , Tedesco D. , Montegrossi G. , Darrah T. , Cuoco E. , Mapendano M. Y. , Poreda R. , Delgado Huertas A.
Published: February 2009

Waters and dissolved gases collected along vertical profiles in the five basins (Main, Kabuno Bay, Kalehe, Ishungu, and Bukavu) forming the 485 m deep Lake Kivu (Democratic Republic of the Congo) were analyzed to provide a geochemical conceptual model of the several processes controlling lake chemistry. The measured horizontal and vertical variations of water and gas compositions suggest that each basin has distinct chemical features produced by (1) different contribution from long circulating fluid system containing magmatic CO2, responsible of the huge CO2(CH4)‐rich reservoir hosted within the deep lake water; (2) spatial variations of the biomass distribution and/or speciation; and (3) solutes from water‐rock interactions. The Kabuno Bay basin is characterized by the highest rate of magmatic fluid input. Accordingly, this basin must be considered the most hazardous site for possible gas outburst that could be triggered by the activity of the Nyiragongo and Nyamulagira volcanoes, located a few kilometers north of the lake.
Magnetic ordering in the ilmenite‐hematite solid solution: A computational study of the low‐temperature spin glass region
Authors: Harrison Richard J.
Published: February 2009

Magnetic ordering in the ilmenite‐hematite solid solution (Fe2‐xTixO3) has been investigated using Monte Carlo simulations, with particular emphasis on the low‐temperature spin glass region of the phase diagram. Complex magnetic behavior is observed due to the presence of two competing magnetic order parameters: a “hematite‐like” ordering with a two‐layer repeat (Q2) and an “ilmenite‐like” ordering with a four‐layer repeat (Q4). The susceptibility and degree of magnetic order were calculated from the Fourier transform of the layer‐averaged spin distribution, allowing long‐range and short‐range contributions from Q2 and Q4 to be analyzed separately. For x < 0.8, the ferrimagnetic (FM) phase remains stable down to 0 K. For x ≥ 0.8 a heterogeneous FM phase (HFM) followed by a modulated FM phase (MFM) develops. There is an increasing contribution from Q4 with increasing x, and a pronounced cusp in both Q2 and Q4 susceptibilities develops at 30 K. The superposition of Q2 and Q4 leads to frustrated layers containing dynamically disordered spins. Freezing of this spin disorder below 30 K is responsible for the cusp in susceptibility, which can be classified as a reentrant spin glass (RSG) transition. A gradual loss of long‐range FM order occurs as the percolation threshold is approached, resulting in a conventional spin glass (CSG) with no long‐range order below 30 K for x ≥ 0.92. For x > 0.95, a transition to an antiferromagnetic (AF) phase occurs at 40–55 K, followed by an RSG transition at 20–30 K. Changes to the phase diagram caused by chemical clustering are determined using a preannealing algorithm. Clustering expands the AF field to x > 0.9 and the HFM field to x ≥ 0.55. The topology of the simulated phase diagram compares favorably with experiments but suggests that the nature of some phase boundaries should be reexamined from both experimental and computational perspectives.
Deformation of Mexico from continuous GPS from 1993 to 2008
Authors: Marquez‐Azua B. , DeMets C.
Published: February 2009

We combine the velocities of 13 continuous Global Positioning System stations from Mexico and 448 North American plate stations to better understand deformation and earthquake cycle effects in Mexico. Velocities estimated at the Mexican sites from high‐quality GPS data collected since 2003 show no evidence for a previously reported eastward bias at sites in and near the Yucatan peninsula. The new velocities are compared to the predictions of two models, one in which all motion in Mexico is attributed to North American plate motion and the second of which attributes site motions to a combination of plate motion and the elastic effects of frictional coupling along the Mexican subduction zone and faults in the Gulf of California. The second model fits the velocities within their estimated uncertainties. Mainland Mexico thus moves with the North American plate to within 1 mm per year and undergoes elastic interseismic deformation far into its interior. Two stations inland from the Guerrero and Oaxaca segments of the Mexican subduction zone have alternated between several‐year‐long periods of landward motion and several‐month‐long periods of trenchward motion frequently since 1993, consistent with previously described, repeating transient slip events along the subduction interface. The motions of two stations inland from the Rivera plate subduction zone are dominated by the coseismic and postseismic effects of the M = 8.0, 9 October 1995 Colima‐Jalisco earthquake and M = 7.5, 22 January 2003 Tecoman earthquake offshore from western Mexico.
Sensitivity of the subpolar Atlantic climate to local winds
Authors: Saenko Oleg A.
Published: February 2009

The mild climate of northern Europe is thought to be in part maintained by the deep water formation in the northern North Atlantic and the associated meridional overturning circulation. It has been argued that this circulation is controlled by the wind stress in the Southern Ocean. Using a coupled climate model it is shown that the subpolar Atlantic wind stress also plays an important role. A partial or a complete suppression of this wind stress results in the low salinity Arctic waters filling the subpolar Atlantic interior. As a result, the regions of deep water sinking shift southward and the associated overturning circulation, convective activity and oceanic heat loss in the northern North Atlantic strongly weaken. The sea ice advances southward and the North Atlantic climate, including over much of Europe, becomes colder.
Effect of the Atlantic hurricanes on the oceanic meridional overturning circulation and heat transport
Authors: Hu Aixue , Meehl Gerald A.
Published: February 2009

Hurricanes have traditionally been perceived as intense but relatively small scale phenomena, with little effect on the large scale climate system. However, recent evidence has suggested that hurricanes could play a much more significant role in global climate. Here we prescribe Atlantic hurricanes in a global coupled climate model to show that, climatically, the strong hurricane winds can strengthen the Atlantic meridional overturning circulation (MOC) that is responsible for an increased northward meridonal heat transport (MHT), and the hurricane rainfall tends to weaken the MOC and to reduce the MHT. The net effect of the hurricanes on the MOC and MHT depends on the outcome of these two competing processes. This result implies that hurricanes may indeed play an important role in the coupled climate system and need to be studied further in high resolution global coupled models.
Immediate impact of the Mt Chaiten eruption on atmosphere from FORMOSAT‐3/COSMIC constellation
Authors: Wang Kuo‐Ying , Lin Song‐Chin , Lee Lou‐Chuang
Published: February 2009

After being dormant for more than 9000 years, Mount Chaiten in southern Chile started to erupt in the early morning (around 0430‐0600 UTC) of 2 May 2008. In this work we combine data from FORMOSAT‐3/COSMIC and the NCEP GFS model to reveal spatial and temporal evolution of temperatures following the eruption. The eruption occurred when there were active synoptic waves passing over South America. As a result, the volcanic plumes were carried downstream in the westerly flow to the eastern South Atlantic over several days following the eruption. Estimated peak temperature reductions of up to 10 K associated with the volcanic plume were confined to downwind locations and at altitudes between 12 and 20 km. Temperature increases in the troposphere at altitudes below 10 km were associated with the transport of warm air from low latitudes toward midlatitudes. This work shows that FORMOSAT‐3/COSMIC is useful for near real‐time global temperature monitoring.
Four‐dimensional data assimilation of atmospheric CO2 using AIRS observations
Authors: Engelen Richard J. , Serrar Soumia , Chevallier Frédéric
Published: February 2009

The European Global and regional Earth‐system (Atmosphere) Monitoring using Satellite and in situ data (GEMS) project has built a system that is capable of assimilating various sources of satellite and in situ observations to monitor the atmospheric concentrations of CO2 and its surface fluxes. This consists of an atmospheric four‐dimensional variational data assimilation system that provides atmospheric fields to a separate variational flux inversion scheme. In this paper, we describe the atmospheric data assimilation system that currently uses radiance observations from the Atmospheric Infrared Sounder (AIRS) to constrain the CO2 mixing ratios of the data assimilation model. We present the CO2 transport model, the bias correction of the observation‐model mismatch, and the estimation of the background error covariance matrix. Data assimilation results are compared to independent CO2 observations from NOAA/ESRL aircraft showing a reduction of the mean difference of up to 50% depending on the altitude of the aircraft observations relative to an unconstrained transport model simulation. In the coming years, observations from dedicated CO2 satellite missions will be added to the system. Together with improved error characterization and bias correction, we hope to show that satellite observations can indeed complement the in situ observation system to get a better estimate of global carbon fluxes.
Size dependence of iron solubility of Asian mineral dust particles
Authors: Ooki Atsushi , Nishioka Jun , Ono Tsuneo , Noriki Shinichiro
Published: February 2009

Asian mineral dust was sampled at Hokkaido, northern Japan, in spring 2004 and 2006. Iron solubility of the bulk aerosol, the size‐segregated aerosol (0.45 < D < 11 μm), the snow containing a lot of mineral dust, and a simulated Asian dust standard (CJ‐2) were measured by an iron dissolution experiment using a newly developed continuous leaching method. The iron solubility of the bulk aerosol samples was 1.2–2.2%. Within the 1.1 < D < 11 μm size range, iron solubility (0.52–8.2%) was higher in the smaller fractions of the size‐segregated aerosol samples. We considered that the preferential removal of larger mineral dust particles from the air by snow resulted in the low iron solubility of the snow samples. Iron solubility of mineral dust was relatively lower in the 4.7 < D < 11 μm fraction of the size‐segregated aerosol samples (0.52%), in the snow samples (0.20–0.57%), and in the CJ‐2 standard (0.33%), which are dominated by large size particles (D > 4.7 μm). We suggest that an iron solubility of around 0.4% is typical for Asian mineral dust of large particles transported to Hokkaido. In the high‐nutrient low‐chlorophyll region of the western subarctic North Pacific near the Asian continent, where the mineral dust deposition is dominated by large particles, the iron solubility of the mineral dust entering the ocean is around 0.4%.
Supervision: The Sensitivity Awareness Supervision Model
Authors: Kosta Joan C. , Brice Alejandro
Published: February 2009

Clinical supervisors are faced with supervising students who represent differences from “traditional” students that include spoken language, dialect, interpersonal communication styles, and attitudes. The training of culturally and linguistically diverse (CLD) speech-language pathologists is therefore a priority in order to serve the growing CLD population. The issues of cultural and linguistic diversity present major challenges for the clinical training of student clinicians. The need to develop specific styles and guidelines relating to supervision of CLD students is critical. This paper highlights concepts used in a supervision model designed for use with CLD student clinicians.
A monatomic system with a liquid-liquid critical point and two distinct glassy states
Authors: Xu Limei , Buldyrev Sergey V. , Giovambattista Nicolas , Angell C. Austen , Stanley H. Eugene
Published: February 2009

We study the glass transition (GT) in a model system that exhibits the presence of more than one liquid or glassy state (“polyamorphism”) using molecular dynamics simulations. We study the Jagla model [E. A. Jagla, J. Chem. Phys. 111, 8980 (1999)], a two-scale spherically symmetric ramp potential with both attractive and repulsive interactions. The Jagla model is particularly interesting since, depending on its parametrization, it predicts two phases (“polyamorphism”) not only in the glassy state but also in equilibrium as a liquid-liquid phase transition (LLPT). The Jagla model may also be useful in understanding a recent observation of polyamorphism in metallic glasses containing cerium. We use a parametrization for which crystallization can be avoided and the GT and LLPT are clearly separated, providing a unique opportunity to study the effects of the LLPT on the GT. We follow the experimental protocol employed in the classical differential scanning calorimetry experiments used to characterize the GT, cooling and heating the system through the GT and calculating the constant-pressure specific heat CP and the thermal expansion coefficient αP. At pressures below and well above the LLPT, the same basic GT phenomenology of metallic glasses is observed, i.e., a single peak in CP (typical of ergodicity restoration) occurs upon heating across the GT. At pressures above the LLPT, a second peak in CP develops at higher temperature above the GT. This second peak in CP arises from the presence of a Widom line TW defined as the locus of maximum correlation length in the one-phase region above the liquid-liquid critical point (LLCP). The behavior of αP is different across the GT and Widom line. Near the GT temperature Tg, αP displays a small peak upon heating, which makes a negligible contribution to the CP peak. On the other hand, near TW, αP displays a much larger peak, which makes a substantial contribution to the CP peak at higher temperature. We find that Tg is almost independent of pressure for each of the two coexisting liquids, but shows an apparent discontinuity upon crossing the LLPT line, to a lower value for the higher-entropy phase. We compare the entropies of both phases, and the corresponding temperature dependencies, with those of the crystal phase. We also study the dependence of the GT on heating rate and find that for pressures below the LLCP, slow heating results in crystallization, as occurs in laboratory experiments. Regarding the thermal expansion properties of the Jagla model, we study the interplay of the density minimum recently observed in confined water and the GT.
Franck–Condon analysis of laser-induced fluorescence excitation spectrum of anthranilic acid: Evaluation of geometry change upon S→S1 excitation
Authors: Leśniewski Sebastian , Kolek Przemyslaw , Pirowska Katarzyna , Sobolewski Andrzej L. , Najbar Jan
Published: February 2009

Geometry and vibrational modes of the anthranilic acid molecule in the S0 and S1 states were computed using ab initio methods: Hartree–Fock (HF) and configuration interaction of singly excited configurations (CIS) as well as the density functional theory with time-dependent perturbation (TD-DFT). The intensity distribution in the laser-induced fluorescence excitation spectra was modeled in two ways: using displacement parameters for independent modes and using multidimensional Franck–Condon integrals. The change in the molecular geometry upon excitation was calculated from the band intensities within the above two models. Displacement parameters of eight in-plane modes active in the excitation spectrum were optimized to reproduce the experimental intensities of about 40 most intensive and well-separated vibrational bands, while displacement parameters of other in-plane modes were kept frozen at the values resulting from the quantum chemical calculations. The intramolecular hydrogen bond is significantly stronger in the S1 state than in the ground state. Additionally, bond lengths and angles in the aromatic ring, within the substituents and between the ring and the substituents undergo significant changes and they induce the presence of strong fundamentals in the excitation spectrum.
Direct lithographic top contacts for pentacene organic thin-film transistors
Authors: Kuo C.-C. , Jackson T. N.
Published: February 2009

We report a process to fabricate metallic source and drain contacts on pentacene thin films with channel resolution less than 10μm. Organic thin-film transistors (OTFTs) made by this method can have field-effect mobility of 0.3cm2/V−s. Contact resistance extracted from these OTFTs is about (5×107)–(5×108)Ωμm which is lower than that typical for bottom contact devices. Such performance in OTFTs demonstrates this method’s value for fabricating organic electronics.
Time-resolved and energy-dispersed spin excitation in ferromagnets and clusters under influence of femtosecond laser pulses
Authors: Hartenstein T. , Lefkidis G. , Hübner W. , Zhang G. P. , Bai Y.
Published: February 2009

When an ultrafast laser impinges a magnetic material, it excites charge and then, via spin-orbit-coupling, spin. This holds great promise for the future magnetic storage. However, the coupling of the two dynamics is far from clear, which hampers the experimental effort in femtosecond magnetism. Since not every excitation induces the same spin excitation, a clear understanding of the correlation between charge and spin is crucial. In this paper we investigate in a complete first-principles manner the energy dispersion of the spin-moment change in ferromagnetic Ni and the effect of the distance between the magnetic centers upon the spin localization and local-spin-flip times in metallic chains. Thus we establish the missing link between the spin-momentum change and the density-of-states change, and derive rules-of-thumb for localized spin manipulation.
Spectra broadening of point-contact Andreev reflection measurement on GaMnAs
Authors: Chiang T. W. , Chiu Y. H. , Huang S. Y. , Lee S. F. , Liang J. J. , Jaffrès H. , George J. M. , Lemaitre A.
Published: February 2009

Point-contact Andreev reflection measurements on Ga0.94Mn0.06As were investigated using Pb tips. The observed conductance versus voltage spectra exhibited behaviors which were described by the modified Blonder–Tinkham–Klapwijk model but with significant broadening. We propose a model by introducing a spreading resistance and compare with an existing model which included effective temperature as a parameter. In as-grown/annealed Ga0.94Mn0.06As samples, we extracted conduction electron spin polarization of 76%/74% from our model, instead of 90%/82% from the one with the effective temperature.
Thiol-capped ferromagnetic Au nanoparticles investigated by Au L3 x-ray absorption spectroscopy
Authors: Garitaonandia J. S. , Goikolea E. , Insausti M. , Suzuki M. , Kawamura N. , Osawa H. , Gil del Muro I. , Suzuki K. , Cashion J. D. , Gorria C. , Plazaola F. , Rojo T.
Published: February 2009

Different dodecanethiol capped Au nanoparticles (NP) with similar sizes (∼2nm) but different ferromagnetic signals at room temperature have been investigated by means of x-ray absorption spectroscopy at the Au L3-edge. The reversion of the x-ray magnetic circular dichroism signal with the change of sign of the external applied magnetic field confirms the location of the magnetism at the Au atoms. In comparison with the Au foil, all the samples present accentuated white lines at the x-ray absorption near-edge structure (XANES) indicating generation of 5d holes in the Au atoms located at surface of the NPs as consequence of a localized charge transfer from the Au surface atoms to the S atoms of the capping agent. XANES spectra reflect differences among the electronic structure of the Au NPs which are compared with the observed different macroscopic magnetic signals.
Re-entrant ferromagnet PrMn2Ge0.8Si1.2: Magnetocaloric effect
Authors: Wang J. L. , Campbell S. J. , Zeng R. , Poh C. K. , Dou S. X. , Kennedy S. J.
Published: February 2009

The structural and magnetic properties of the re-entrant ferromagnet PrMn2Ge0.8Si1.2 have been investigated by various experimental methods. Similar to the canonical re-entrant ferromagnet SmMn2Ge2, multiple magnetic phase transitions have been detected in PrMn2Ge0.8Si1.2 over the temperature range from 10to550K with re-entrant ferromagnetism occurring around ∼54K. The magnetocaloric effect has been measured in terms of the isothermal magnetocaloric entropy change and found to be positive at the re-entrant ferromagnetic transition with a maximum value of around 1.9J∕kgK at 58K for a magnetic field change of 0–3T. On the other hand, the entropy change becomes negative (∼−0.5J∕kgK) at the antiferromagnetic to ferromagnetic transition for the same field change.
Point-contact search for antiferromagnetic giant magnetoresistance
Authors: Wei Zhen , Sharma Amit , Bass Jack , Tsoi Maxim
Published: February 2009

We report the first measurements of effects of large current densities on current-perpendicular-to-plane magnetoresistance (MR) of magnetic multilayers containing two antiferromagnetic (AFM) layers separated by a nonmagnetic layer. These measurements were intended to search for a recently predicted antiferromagnetic giant magnetoresistance (AGMR) similar to giant magnetoresistance seen in multilayers containing two ferromagnetic (F) layers separated by a nonmagnetic layer. We report on MR measurements for current injected from point contacts into sandwiches containing different combinations of layers of F=CoFe and AFM=FeMn. In addition to AFM/N/ AFM, F/AFM/N/AFM, and F/AFM/N/AFM/F structures, initial results led us to examine also AFM/F/N/AFM, F/AFM, and single F- and AFM-layer structures. At low currents, no MR was observed in any samples, and no MR was observed at any current densities in samples containing only AFMs. Together, these results indicate that no AGMR is present in these samples. In samples containing F layers, high current densities sometimes produced a small positive MR—largest resistance at high fields. For a given contact resistance, this MR was usually larger for thicker F layers, and for a given current, it was usually larger for larger contact resistances (smaller contacts). We tentatively attribute this positive MR to suppression at high currents of spin accumulation induced around and within the F layers.
Study on strengthening and toughening of sintered rare-earth permanent magnets
Authors: Li W. , Li A. H. , Wang H. J. , Pan W. , Chang H. W.
Published: February 2009

In recent years, we have a systematic investigation on the mechanical properties, fracture behavior and micromechanism, strengthening and toughening, and impact stability of sintered rare-earth permanent magnets (being abbreviated to “REPM”) at the aim of improving the workability and increasing the dynamic applications of REPM. A scanning electron microscope was used to study the fracture behavior and micromechanism of the experimental magnets. The impact stability of REPM was investigated using a falling-weight impact tester and an impact-acceleration standard device based on laser interference technique. The brittleness index of B=Hv∕KC was used to appraise the workability of REPM. It shows that the fracture mechanism of sintered NdFeB magnets mainly appears intergranular fracture. Sintered Sm-Co magnets tend to cleavage fracture. The fracture behavior REPM obviously exhibit anisotropy. The mechanical strength of the experimental magnets prepared by dual-alloy sintering method surpassed 390MPa without a sacrifice of magnetic properties. The impact stability increased from 2.5×104g for the ordinary magnet specimens to 11×104g for the strengthened and roughened specimens (g represents the gravity acceleration). It was found that Ti-doping decreased the Vickers-hardness Hv. Presumably, the workability of NdFeB magnets maybe improved with Ti-doping.
Crystal structure and magnetic properties of melt spun Sm(Co,V)7 ribbons
Authors: Hsieh C. C. , Chang H. W. , Chang C. W. , Guo Z. H. , Yang C. C. , Chang W. C.
Published: February 2009

The crystal structure and magnetic properties of melt spun Sm(Co,V)7 ribbons have been investigated. It was found that SmCo7−xVx ribbons may crystallize in pure TbCu7-type structure for x=0.1–0.3 spun at a high wheel speed of 40 m/s. The structure refinement results show that the doping element V prefers to occupy the 2e site of TbCu7-type structure. Besides, transmission electron microscopy images show that with increasing V content, the grain size was refined from 200–400 nm for x=0.1 to 40–100 nm for x=0.3. As a result, the intrinsic coercivity enhances effectively from 1.9 kOe for SmCo7 ribbon to 11.5 kOe for SmCo6.7V0.3 ribbon. It is also verified that a slight addition of C to SmCo7−xVx could further refine the microstructure, resulting in the improvement of the magnetic properties of SmCo7−xVx ribbons. The optimal magnetic properties of σr=58.7 emu/g, Hic=13.5 kOe, and (BH)max=9.3 MG Oe can be obtained for SmCo6.9V0.1C0.1 ribbon.
Generation of nanosecond magnetic pulse field for switching experiments on a single Co/Pt nanodot
Authors: Kikuchi N. , Okamoto S. , Kitakami O.
Published: February 2009

A one-turn Cu microcoil being able to generate a large perpendicular pulse field was fabricated on a Co/Pt multilayer dot of 300 nm in diameter covered with electrodes for anomalous Hall effect measurement. Rectangular electric pulses with the maximum amplitude of 160 V and the duration τp=1.8–20.8 ns were transmitted through the coil without any significant distortion. The magnetization of the dot was successfully switched solely by the pulse field with the maximum value of 2.7 kOe. No significant dependence of the nucleation field for a reversed embryo in the dot was found over the range of τp examined in the present study. Based on the Néel–Arrhenius model, the activation energy for nucleation of the reversed embryo was evaluated to be 6×10−12 erg.
Exchange bias of ferromagnetic/antiferromagnetic in FePt/FeRh bilayers
Authors: Nam Nguyen T. , Lu W. , Suzuki T.
Published: February 2009

A systematic investigation of structural and magnetic properties of FePt/FeRh bilayers has been carried out. The transition temperature of single FeRh layer is higher than that of FePt/FeRh bilayer. A sharp decrease in coercivity is observed at transition temperature for FePt/FeRh bilayer. The thickness FePt dependence of exchange bias field and unidirectional anisotropy constant are discussed. Of interest is the exchange bias effect that appears in FePt/FeRh bilayer and the unidirectional anisotropy constant, which is very large (up to 0.8 erg/cm2), suggesting that this system can be applied for spin-valve sensors and heat assisted magnetic recording medium. It may also provide some useful information for better understanding of the mechanism of exchange bias.
X-ray photoemission study in Re0.7Ca0.3MnO3 epitaxial films
Authors: Hsu Daniel , Mani Awadhesh , Chuang C. H. , Chen C. H. , Lin Minn-Tsong , Lin J. G.
Published: February 2009

We have performed the x-ray photoemission experiments in the colossal magnetoresistive manganites Re0.7Ca0.3MnO3 with Re=La, Pr, and Nd in order to study the Re dependence of electronic structures in this system. The samples are epitaxial films grown on LaAlO3 substrates with pulsed laser deposition system. It is found that the binding energies of Mn 2p3/2 are 641.7 and 643.1 eV for La0.7Ca0.3MnO3 and Nd0.7Ca0.3MnO3, respectively. The shift of this energy level is related to the change in bond angle and/or bond length between Mn and oxygen. Moreover, two lines of O 1s core level are assigned as Mn–O (530 eV) and Re–O (533 eV). The intensity ratio of these two lines in Nd0.7Ca0.3MnO3 is different from those in La0.7Ca0.3MnO3 and Pr0.7Ca0.3MnO3, suggesting that the ion redistribution between Re–O and Mn–O sites occurs with the Re substitution in these films.
Automated system for the calibration of magnetometers
Authors: Petrucha Vojtech , Kaspar Petr , Ripka Pavel , Merayo Jose M. G.
Published: February 2009

A completely nonmagnetic calibration platform has been developed and constructed at DTU Space (Technical University of Denmark). It is intended for on-site scalar calibration of high-precise fluxgate magnetometers. An enhanced version of the same platform is being built at the Czech Technical University. There are three axes of rotation in this design (compared to two axes in the previous version). The addition of the third axis allows us to calibrate more complex devices. An electronic compass based on a vector fluxgate magnetometer and micro electro mechanical systems (MEMS) accelerometer is one example. The new platform can also be used to evaluate the parameters of the compass in all possible variations in azimuth, pitch, and roll. The system is based on piezoelectric motors, which are placed on a platform made of aluminum, brass, plastic, and glass. Position sensing is accomplished through custom-made optical incremental sensors. The system is controlled by a microcontroller, which executes commands from a computer. The properties of the system as well as calibration and measurement results will be presented.
The spin polarization of Mn atoms in paramagnetic CuMn alloys induced by a Co layer
Authors: Abes M. , Atkinson D. , Tanner B. K. , Charlton T. , Langridge S. , Hase T. P. A. , Ali M. , Marrows C. H. , Neudert A. , Hicken R. J. , Mirone A. , Arena D.
Published: February 2009

Using the surface, interface, and element specificity of x-ray resonant magnetic scattering in combination with x-ray magnetic circular dichroism, we have spatially resolved the polarization, and hence the spin accumulation in Mn high susceptibility material in close proximity to a ferromagnetic layer. The magnetic polarization of Mn and Cu 3d electrons in paramagnetic CuMn layers is detected in a Co/Cu(x)/CuMn structure for varying copper layer thicknesses (x). The size of the Mn and Cu L2–3-edge dichroism shows a decrease in the polarization for increasing copper thickness indicating the dominant interfacial nature of the Cu and Mn spin polarization. The Mn polarization appears to be much higher than that of Cu.
Correlating antiferromagnetic spin structures with ion-beam bombardment in exchange-biased NiFe/Mn bilayers
Authors: Lin K.-W. , Chen T.-J. , Guo J.-Y. , Ouyang H. , Wei D.-H. , van Lierop J.
Published: February 2009

The correlation between the ion-beam bombardment and the exchange bias magnetism in NiFe (10 nm)/Mn (25 nm) bilayers was studied. While the bottom Mn layers bombarded by different Ar ion-beam energies (VEH from 70 to 150 V) retained the same structure, significant differences in exchange bias were observed when in contact with a top NiFe layer. The dependence of the exchange bias field, Hex, with increasing VEH suggests strongly that the Ar ion-beam bombardment process may create uncompensated Mn spins (Hex enhancement) or increase the spin misalignment in ferromagnet (FM)/antiferromagnet (AF) interfaces (Hex decrease), depending on the energy used. A schematic FM/AF spin structure was proposed to explain this unusual exchange bias behavior.
Spin dynamics in CoFe2O4 nanoparticles
Authors: Desautels R. D. , Cadogan J. M. , van Lierop J.
Published: February 2009

The bulk and local magnetisms of ∼10 nm diameter CoFe2O4 nanoparticles have been characterized from 5 to 425 K. Magnetometry results indicate that the nanoparticles have a blocking temperature around 380 K and they exhibit a temperature dependent cubic magnetocrystalline anisotropy similar to that of bulk CoFe2O4 with K(0)∼1.2×106 ergs/cm3. However, the local, atomic-level spin dynamics examined by Mössbauer spectroscopy indicates strongly that rather than exhibiting a typical static, blocked magnetism to superparamagnetism behavior, the CoFe2O4 nanoparticle moments become paramagnetic, with this transition percolating from the surface to the core of the nanoparticle with increasing temperature.
Manipulating the crystallographic properties of Fe/MgO/Fe trilayers
Authors: Liu Xiaoxi , Matsuoka Hidetoshi , Zhang Hong , Morisako Akimitsu
Published: February 2009

An ultrathin MgO/Fe seed layer was introduced to manipulate the crystal orientation and crystallinity of Fe/MgO/Fe trilayers. The crystallographic properties and magnetic properties of the trilayer are investigated. It is concluded that the texture of the MgO layer is strongly dependent on the texture of the Fe layer. (001) oriented Fe layer can assist the growth of (001) oriented MgO barrier upon annealing. A 0.5 nm MgO seed layer can introduce (001) orientation in the following Fe layer. It is also found that the crystal orientation of the Fe/MgO/Fe trilayer is independent of the initial Fe seed layer thickness. However, the crystallinity of both the Fe layer and the MgO layer is dependent on the initial Fe seed layer.
Photochemical formation of HCO and CH3 on the ground S (A1′) state of CH3CHO
Authors: Heazlewood Brianna R. , Rowling Steven J. , Maccarone Alan T. , Jordan Meredith J. T. , Kable Scott H.
Published: February 2009

The dynamics of the photodissociation of CH3CHO into CH3+HCO products have been investigated at energies between 30 953 and 31 771 cm−1, spanning the threshold for radical production on the triplet (T1) surface. A barrierless pathway to CH3+HCO radical products formed on the ground state (S0) surface was discovered and established to be an important reaction channel in acetaldehyde photodissociation throughout this wavelength range. HCO laser induced fluorescence (LIF) spectra recorded from CH3CHO dissociated above and below the T1 barrier energy are quite different; HCO produced on S0 yields a more congested LIF spectrum with sharp rotational transitions, while HCO formed on the T1 surface displays fewer, more intense, Doppler-broadened lines. These differences have been further explored in the populations of the HCO Ka=1 doublets. Despite the upper and lower levels being almost isoenergetic, HCO formed on T1 preferentially populates the upper Kc state due to the geometry of the T1 transition state structure. In contrast, HCO formed on S0 produces equal population in each of the upper and lower Ka=1 components. Product state distributions (PSDs) showed that HCO formed on S0 is born with an approximately statistical distribution of population in the available product states, modeled well by phase space theory. HCO formed on the T1 surface, in contrast, has a PSD that can be characterized as arising from “impulsive” dynamics. Previous discrepancies in the height of the T1 barrier are discussed following the observation that, once the T1 channel is energetically accessible, there is competition between the S0 and T1 pathways, with the dominance of the triplet channel increasing with increasing photolysis energy.
Photodissociation dynamics of lithium chloride: Contribution of interferometric predissociation
Authors: Hosseini B. H. , Weck P. F. , Sadeghpour H. R. , Kirby K. , Stancil P. C.
Published: February 2009

Continuum photoabsorption of lithium chloride (LiCl) was investigated using a coupled-channel time-dependent wave packet approach. Photodissociation cross sections for the production of ground-state Li and Cl atoms were computed up to temperatures of 1500 K for a thermal distribution of rotational levels. At such temperatures, LiCl is believed to be the primary Li-bearing gas in cool stellar atmospheres. Narrow Rydberg resonances in the total absorption spectrum are found to dominate the thermally averaged cross section due to the large density of Rydberg states in the predissociation gap. Comparison with measured photoabsorption cross sections, where available, is made.
Bi-nanoparticle (CdTe and CdSe) mixed polyaniline hybrid thin films prepared using spin coating technique
Authors: Verma Deepak , Dutta V.
Published: February 2009

Polyaniline (Pani) films containing CdTe, CdSe, and both nanoparticles were deposited using spin coating technique. Pani was chemically synthesized by oxidation method, whereas surfactant free CdTe and CdSe nanoparticles were prepared using solvothermal method. Binanoparticle films showed an increase in the absorption from 350 nm to the near IR region. Absorption spectra also showed charge transfer complex formation for the binanoparticle hybrid thin films prepared with weight ratio of [Pani (camphor sulfonic acid, CSA):CdTe:CdSe] 200:100:75. Photoluminescence measurement for the bi-nanoparticle hybrid thin films confirmed that the required dissociation of excitons was taking place at the interface. Scanning electron microscopy images showed homogeneity and an interconnected network on the surface of the films prepared with Pani (CSA):CdTe:CdSe weight ratios of 200:100:50 and 200:100:75, respectively. Cyclic voltammetry confirmed better stability for the bi-nanoparticle hybrid films in comparison to Pani film. It also established the process of electrochemical charge transfer between the nanoparticles and the polymer matrix.
Analysis of aftercavity interaction in gyrotrons
Authors: Sinitsyn Oleksandr V. , Nusinovich Gregory S.
Published: February 2009

This paper is devoted to the analysis of a so-called “aftercavity interaction” in gyrotrons. The term “aftercavity interaction” is used for defining the cyclotron resonance interaction between electrons in a spent beam exiting the cavity and traveling electromagnetic waves propagating from the cavity exit into the output part of a tube. A simple theory allowing one to analyze the role of aftercavity interaction in gyrotron operation has been developed. With the use of only two parameters characterizing the profile of the waveguide wall and the profile of the magnetic field, one can find conditions resulting in weakening this parasitic effect. Also, the simulations for the gyrotron efficiency in the presence of aftercavity interaction are performed for an existing device. Results of these simulations agree with analytical predictions. They also show how the axial distribution of the magnetic field in an existing cryomagnet should be modified in order, first, to use the aftercavity interaction for improving the interaction efficiency and, second, for weakening the role of this interaction in degrading the wall-plug efficiency in gyrotrons with depressed collectors. Results of such analysis can be beneficial for the gyrotron efficiency enhancement.
Parametric studies of nonlinear magnetosonic waves in two-dimensional quantum magnetoplasmas
Authors: Mushtaq A. , Qamar A.
Published: February 2009

Using the effective one fluid quantum magnetohydrodynamic (QMHD) model, magnetosonic waves propagating obliquely to an external magnetic field are studied in an electron-ion (e-i) Fermi plasma. In the linear approximation, the effect of quantum corrections on the fast and slow magnetosonic waves are discussed. It is shown that the system of QMHD equations admit the Kadomstev–Petviashvilli soliton due to the balance between nonlinearity and dispersion caused by the obliqueness and quantum diffraction effects. It is observed that for both modes, the angle θ, the electron quantum diffraction, and statistic effects modify the shape of the solitary structure. It is also found that the results obtained for the quantum plasma differ significantly from the classical e-i plasmas.
Simulation of the control of vortex breakdown in a closed cylinder using a small rotating disk
Authors: Tan Boon Thong , Liow Keith Y. S. , Mununga Lewis , Thompson Mark C. , Hourigan Kerry
Published: February 2009

The enhancement or suppression of vortex breakdown in a closed cylinder caused by a small rotating disk embedded in the nonrotating endwall is simulated in this study. This paper shows that corotation or counter-rotation of the control disk with respect to the driving lid is able to promote or suppress the “bubble-type” vortex breakdown. This is achieved using only a small fraction of the power required to drive the main lid. The simulations show that the vortex breakdown induced or suppressed by flow control displays similar characteristics near the breakdown region as produced by varying the flow Reynolds number. These include near-axis swirl, centerline axial velocity, and centerline pressure. The influence of the size of the control disk is also quantified.
Mass spectrometry study of decomposition of exo-tetrahydrodicyclopentadiene by low-power, low-pressure rf plasma
Authors: Jiao Charles Q. , Ganguly Biswa N. , Garscadden Alan
Published: February 2009

The plasma cracking of exo-tetrahydrodicyclopentadiene (JP-10) (C10H16) is investigated using a quadrupole mass spectrometer. The relative densities of the JP-10 molecule and its principal decomposition products, including H2, are determined for varying rf powers in the range of 3–30 W, using the measured ion intensities combined with ionization cross section data from the literature. The extent of the cracking of JP-10 and the formation of H2 as functions of the rf power are discussed.
Normal and anomalous diffusion in highly confined hard disk fluid mixtures
Authors: Ball C. D. , MacWilliam N. D. , Percus J. K. , Bowles R. K.
Published: February 2009

Monte Carlo simulation is used to study binary mixtures of two-dimensional hard disks, confined to long, narrow, structureless pores with hard walls, in a regime of pore sizes where the large particles exhibit single file diffusion while the small particles diffuse normally. The dynamics of the small particles can be understood in the context of a hopping time, τ21, that measures the time it takes for a small particle to escape the single file cage formed by its large particle neighbors, and can be linked to the long time diffusion coefficient. We find that τ21 follows a power law as a function of the reduced pore radius for a wide range of particle size ratios with an exponent, α, that is independent of the size ratio, but linearly dependent on the Monte Carlo step size used in the dynamic scheme. The mean squared displacement of the small particles as a function of time exhibits two dynamic crossovers. The first, from normal to anomalous diffusion, occurs at intermediate times then the system returns to normal diffusion in the long time limit. We also find that the diffusion coefficient is related to τ21 through a power law with exponent β=−0.5, as predicted by theory. Finally, we show that particle separation in a binary mixture will be optimal at the pore radius that causes the large particles to undergo their transition from normal to anomalous diffusion.
Growth and capping of InAs/GaAs quantum dots investigated by x-ray Bragg-surface diffraction
Authors: Freitas Raul O. , Quivy Alain A. , Morelhão Sérgio L.
Published: February 2009

An x-ray diffraction method, based on the excitation of a surface diffracted wave, is described to investigate the capping process of InAs/GaAs (001) quantum dots (QDs). It is sensitive to the tiny misorientation of (111) planes at the surface of the buffer layer on samples with exposed QDs. After capping, the misorientation occurs in the cap-layer lattice faceting the QDs and its magnitude can be as large as 10° depending on the QDs growth rates, probably due to changes in the size and shape of the QDs. A slow strain release process taking place at room temperature has also been observed by monitoring the misorientation angle of the (111) planes.
Development of pressure cell for specific heat measurement at low temperature and high Magnetic field
Authors: Kawae T. , Yaita K. , Yoshida Y. , Inagaki Y. , Ohashi M. , Oomi G. , Matsubayashi K. , Matsumoto T. , Uwatoko Y.
Published: February 2009

We report the performance of Ag–Pd–Cu alloy as the material of a pressure cell to carry out specific heat measurements at low temperatures and high magnetic fields. The Ag–Pd–Cu alloy is advantageous to reduce the background due to the nuclear specific heat in the pressure cell growing at low temperatures and high magnetic fields. We prepared 70-20-10 alloy composed of 70 mass % of Ag, 20 mass % of Pd, and 10 mass % of Cu. The maximum hardness over 100 HRB (Rockwell-B scale) is achieved by the heat treatment. The magnetization and susceptibility results show that the alloy includes a small amount of magnetic ions, whose concentration is smaller than that in the Be–Cu alloy. We confirm that the specific heat of a piston cylinder cell made of the 70-20-10 alloy increases smoothly from 0.2 to 9 K and the nuclear specific heat decreases drastically in magnetic field compared to that expected in the Be–Cu alloy. The pressure value in the cell at low temperature increases almost linearly up to P=0.4 GPa, which is nearly the limit of the inner piston made of the 70-20-10 alloy, with increasing of the load applied at room temperature.
Effect of sample structure on reconstruction quality in computed tomography
Authors: Cao Meng , Zhang Hai-Bo , Li Chao , Nishi Ryuji
Published: February 2009

We have investigated the effect of a sample structure on reconstruction quality in computed tomography (CT). A power spectrum with respect to a projection angle is used to represent the sample structure. The condition for high quality reconstruction is then analyzed with the simulation and the electron tomography experiment based on an ultrahigh voltage electron microscope. The truncated terms in the power spectrum are suggested to be less than 10−3 for high quality reconstruction. The effect of the sample structure is believed to be an important factor for high quality reconstruction of complex samples in various CT techniques.