bluuebunny/crossref_metadata_2025 huggingface dataset:
Neural networks to approach potential energy surfaces: Application to a molecular dynamics simulation
Authors: Latino Diogo A. R. S. , Freitas Filomena F. M. , Aires‐De‐Sousa João , Silva Fernandes Fernando M. S.
Published: May 2007

Potential energy surfaces (PES) are crucial to the study of reactive and nonreactive chemical systems by Monte Carlo (MC) or molecular dynamics (MD) simulations. Ideally, PES should have the accuracy provided by ab initio calculations and be set up as fast as possible. Recently, neural networks (NNs) turned out as a suitable approach for estimating PES from ab initio/DFT energy datasets. However, the accuracy of the properties determined by MC and MD simulation methods from NNs surfaces has not yet, to our knowledge, been systematically analyzed in terms of the minimum number of energy points required for training and the usage of different NN‐types. The goal of this work is to train NNs for reproducing PES represented by well‐known analytical potential functions, and then to assess the accuracy of the method by comparing the simulation results obtained from NNs and analytical PES. Ensembles of feed‐forward neural networks (EnsFFNNs) and associative neural networks (ASNNs) are used to estimate the full energy surface. Training sets with different number of points, from 15 differently parameterized Lennard–Jones (LJ) potentials, are used and argon is taken to test the network. MD simulations have been performed using the tabular potential energies, predicted by NNs, for working out thermal, structural, and dynamic properties which are compared with the values obtained from the analytical function. Our results show that, at least for LJ‐type potentials, NNs can be trained to generate accurate PES to be used in molecular simulations. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Core‐ionized and core‐excited states of macromolecules
Authors: Loos Pierre‐François , Assfeld Xavier
Published: May 2007

We report the calculation of core‐ionized states of small organic compounds and macromolecular systems in the framework of a new method based on the local self‐consistent field (LSCF). This new theoretical scheme avoids the variational collapse of the empty core orbital (CO) of the core‐excited states and ensures the orthogonality between the ground state and the excited states. Compared to experimental data and other theoretical methods, accurate carbon 1s ionization energies using the Boys‐Foster (BF) localization criterion for the determination of the CO and the PBE0/6‐311++G**//B3LYP/6‐311++G** level of theory was obtained to calculate both the ground and excited states. The macromolecular systems, a sequence of 15 alanine amino acids in both α‐helix and β‐sheet conformations, are computed using hybrid quantum mechanics/molecular mechanics (QM/MM) method within the LSCF/MM framework. The results show a weak impact of the MM surrounding in the alanine polypeptides cases compared with that of previous studies based on electrically charged residue, such as glutamate in the crambin protein. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2007
Phase Separation of Binary Blends in Polymer Nanoparticles
Authors: Kietzke Thomas , Neher Dieter , Kumke Michael , Ghazy Omayma , Ziener Ulrich , Landfester Katharina
Published: May 2007

Polymer blends in nanoparticles have been studied by transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy. The TEM studies show that blend particles formed from two immiscible polymers by the miniemulsion process exhibit biphasic morphologies. The fact that no core–shell type but Janus‐like structures were found indicates that the surface free energies between both polymers and the solution–water interface (including the surfactant molecules) are similar; therefore, the blend morphology and composition of the individual phases are mainly determined by the interaction between the two polymer components. Both the TEM studies and the PL experiments provide strong evidence that phase separation in these particles strictly follows the Flory–Huggins theory. This highlights the applicability of the nanoparticle approach to fabricate blend systems with well‐controllable properties and to study structure–property relationships under well‐defined conditions.
Mitochondrial Diseases: Therapeutic Approaches
Authors: DiMauro Salvatore , Mancuso Michelangelo
Published: May 2007

Therapy of mitochondrial encephalomyopathies (defined restrictively as defects of the mitochondrial respiratory chain) is woefully inadequate, despite great progress in our understanding of the molecular bases of these disorders. In this review, we consider sequentially several different therapeutic approaches. Palliative therapy is dictated by good medical practice and includes anticonvulsant medication, control of endocrine dysfunction, and surgical procedures. Removal of noxious metabolites is centered on combating lactic acidosis, but extends to other metabolites. Attempts to bypass blocks in the respiratory chain by administration of electron acceptors have not been successful, but this may be amenable to genetic engineering. Administration of metabolites and cofactors is the mainstay of real-life therapy and is especially important in disorders due to primary deficiencies of specific compounds, such as carnitine or coenzyme Q10. There is increasing interest in the administration of reactive oxygen species scavengers both in primary mitochondrial diseases and in neurodegenerative diseases directly or indirectly related to mitochondrial dysfunction. Aerobic exercise and physical therapy prevent or correct deconditioning and improve exercise tolerance in patients with mitochondrial myopathies due to mitochondrial DNA (mtDNA) mutations. Gene therapy is a challenge because of polyplasmy and heteroplasmy, but interesting experimental approaches are being pursued and include, for example, decreasing the ratio of mutant to wild-type mitochondrial genomes (gene shifting), converting mutated mtDNA genes into normal nuclear DNA genes (allotopic expression), importing cognate genes from other species, or correcting mtDNA mutations with specific restriction endonucleases. Germline therapy raises ethical problems but is being considered for prevention of maternal transmission of mtDNA mutations. Preventive therapy through genetic counseling and prenatal diagnosis is becoming increasingly important for nuclear DNA-related disorders. Progress in each of these approaches provides some glimmer of hope for the future, although much work remains to be done.
NF‐κB responds to mechanical strains in osteoblast‐like cells, and lighter strains create an NF‐κB response more readily
Authors: Liu Jun , Zou Ling , Zheng Yi , Zhao Zhihe , Li Yu , Yang Pu , Luo Songjiao
Published: May 2007

This study was to examine the early responses of nuclear factor kappa B (NF‐κB) to mechanical strains in MG‐63. MG‐63 cells were subjected to cyclic uniaxial compressive or tensile strain, produced by a four‐point bending system, at 1000 μstrain or 4000 μstrain for 5 min, 15 min, 30 min and 1 h, respectively. Control cells received the same treatment with no mechanical stress loading. Expression of NF‐κB (p60) was measured by Western blotting. NF‐κB responded rapidly to mechanical stimuli in MG‐63 cells. NF‐κB was activated by cyclic uniaxial stretch at 1000 μstrain while it was restrained under a compressive strain environment at 1000 μstrain (P < 0.001). The effects reversed for tension and compression at 4000 μstrain (P < 0.001). Furthermore, strains at 1000 μstrain affected NF‐κB expression much easier than those at 4000 μstrain. This indicates that there may be different responding mechanisms or mechanotransduction pathways for different mechanical stimuli.
Manifold active‐state conformations in GPCRs: Agonist‐activated constitutively active mutant AT1 receptor preferentially couples to Gq compared to the wild‐type AT1 receptor
Authors: Lee ChangWoo , Hwang Si Ae , Jang Sei-Heon , Chung Hye-Shin , Bhat Manjunatha B. , Karnik Sadashiva S.
Published: May 2007

The angiotensin II type I (AT1) receptor mediates regulation of blood pressure and water‐electrolyte balance by Ang II. Substitution of Gly for Asn111 of the AT1 receptor constitutively activates the receptor leading to Gq‐coupled IP3 production independent of Ang II binding. The Ang II‐activated conformation of the AT1N111G receptor was proposed to be similar to that of the wild‐type AT1 receptor, although, various aspects of the Ang II‐induced conformation of this constitutively active mutant receptor have not been systematically studied. Here, we provide evidence that the conformation of the active state of the wild‐type and the constitutively active AT1 receptors are different. Upon Ang II binding an activated conformation of the wild‐type AT1 receptor activates G protein and recruits β‐arrestin. In contrast, the agonist‐bound AT1N111G mutant receptor preferentially couples to Gq and is inadequate in β‐arrestin recruitment.
Rice black‐streaked dwarf virus minor core protein P8 is a nuclear dimeric protein and represses transcription in tobacco protoplasts
Authors: Liu Huijun , Wei Chunhong , Zhong Yongwang , Li Yi
Published: May 2007

Virus‐encoding nuclear transcriptional regulators play important roles in the viral life cycle. Most of these proteins exhibit intrinsic transcriptional activation or repression activity, and are involved in the regulation of the expression of virus genome itself or important cellular genes to facilitate viral replication and inhibit antiviral responses. Here, we report that the minor core protein P8 of Rice black‐streaked dwarf virus, a dsRNA virus infecting host plants and insects, is targeted to the nucleus of insect and plant cells via its N‐terminal 1–40 amino acids and possesses potent active transcriptional repression activity in Bright Yellow‐2 tobacco suspension cells. Moreover, P8, like many transcriptional regulatory proteins, is capable of forming homo‐dimers within insect cells and in vitro. All these data suggest that P8 is likely to enter the nucleus of host cell and play an important role as a negative transcriptional regulator of host gene expression during the process of virus–host interaction.
Maternal and neonatal outcomes of hospital vaginal deliveries in Tibet
Authors: Miller S. , Tudor C. , Nyima  , Thorsten V.R. , Sonam  , Droyoung  , Craig S. , Le P. , Wright L.L. , Varner M.W.
Published: May 2007

Introduction: To determine the outcomes of vaginal deliveries in three study hospitals in Lhasa, Tibet Autonomous Region (TAR), People's Republic of China (PRC), at high altitude (3650 m). Methods: Prospective observational study of 1121 vaginal deliveries. Results: Pre‐eclampsia/gestational hypertension (PE/GH) was the most common maternal complication 18.9% (n = 212), followed by postpartum hemorrhage (blood loss ≥ 500 ml) 13.4%. There were no maternal deaths. Neonatal complications included: low birth weight (10.2%), small for gestational age (13.7%), pre‐term delivery (4.1%) and low Apgar (3.7%). There were 11 stillbirths (9.8/1000 live births) and 19 early neonatal deaths (17/1000 live births). Conclusion: This is the largest study of maternal and newborn outcomes in Tibet. It provides information on the outcomes of institutional vaginal births among women delivering infants at high altitude. There was a higher incidence of PE/GH and low birth weight; rates of PPH were not increased compared to those at lower altitudes.
Rhys-Davies Exsanguinator: A Haven for Bacteria
Authors: BALLAL M. S. G. , EMMS N. , O’DONOGHUE M. , REDFERN T. R.
Published: May 2007

Serial swabs were taken from the inner and outer surfaces of a new Rhys-Davies exsanguinator before and after use on the limbs of patients to exsanguinate limbs prior to tourniquet inflation and surgery. Both surfaces of the exsanguinator showed increasing levels of contamination with bacterial colonisation with use starting from the first use. The organisms grown included potentially harmful bacteria such as Pseudomonas sp. The Rhys-Davies exsanguinator can harbour potentially harmful organisms and, thus, may raise the risk of infection transmission between patients when used without cleaning between uses. Methods of effective cleaning of the exsanguinator between uses are discussed.
Outcome of Open Trigger Digit Release
Authors: LIM M-H. , LIM K. -K. , RASHEED M. Z. , NARAYANAN S. , BENG-HOI TAN A.
Published: May 2007

This study was undertaken to review the outcome of open trigger digit release of 483 digits in 373 consecutive patients over a 1 year period. Parameters were obtained from case records. The patients were followed up for a minimum of 6 months postoperatively. The most commonly affected digits were the ring (42%) and middle (26%) fingers. Based on the classification by Wolfe [Tenosynovitis. In: Green DP (Ed). Operative hand surgery, 5th Edn. New York, Churchill Livingstone, 2005: 2137–2159], Grade II (51%) and III (33%) trigger digits accounted for majority of affected digits. Non-operative treatment was the first line modality for 82% of the patients. Primary surgical release (18% of patients) was performed for patients who had refractory conditions, grade IV triggering and those who requested this treatment. The overall complication rate was 1%. These included superficial wound dehiscence, extension lag and postoperative residual stiffness. There were no recurrences of triggering. Steroid injection is recommended as the first line treatment. Surgical release is recommended for refractory and severe triggering.
Sedimentology, stratigraphy, and glacier dynamics, western scottish Highlands
Authors: Golledge Nicholas R.
Published: May 2007

Glacial sediments of the western Scottish Highlands are comprehensively described and characterized here for the first time, enabling the first glacial stratigraphy for the area to be proposed. This classification is based on the results of extensive geological mapping and field investigation of sedimentary sequences and their structures, X-ray diffraction and particle size distribution analyses, and comparison with deposits formed in contemporary glaciated environments. These new data are subsequently appraised in terms of their implications for late Pleistocene glacier evolution and dynamics. Together, the data suggest that much of the landscape is palimpsest, and can be attributed to the Weichselian (Late Devensian) glaciation. Subsequent glacier advance during the Younger Dryas did little to modify the area, suggesting that ice flow was dominated by sliding on a meltwater-lubricated rigid bed, with deformation of basal sediments playing a more limited role. Final deglaciation was marked by a significant increase in basal meltwater flux, reflecting the warming climate and increasing precipitation. These new palaeoglaciological and palaeoenvironmental insights advance our understanding of former glacier dynamics in the western Scottish Highlands, improve our knowledge of Pleistocene landscape evolution of this area, and enable comparisons to be made with sedimentary sequences elsewhere.
Global hydrometeor occurrence as observed by CloudSat: Initial observations from summer 2006
Authors: Mace Gerald G. , Marchand Roger , Zhang Qiquing , Stephens Graeme
Published: May 2007

Measurements of global hydrometeor coverage and occurrence frequencies as observed by the cloud radar on CloudSat are summarized using data collected during Summer 2006. CloudSat was launched on 28 April 2006 and began collecting data routinely on 7 June 2006. In this article we document the distribution of cloudiness from the ITCZ to the Polar regions as observed by CloudSat during the first summer of operations. The overall global hydrometeor coverage as observed by CloudSat is found to be 0.506. The vertical distribution of zonally averaged hydrometeor occurrence shows the relationship of clouds with components of the atmospheric general circulation such as the Hadley Cell, the ubiquitous storms over the Southern Ocean, and the subtropical stratocumulus regimes.
Atmospheric volcanic loading derived from bipolar ice cores: Accounting for the spatial distribution of volcanic deposition
Authors: Gao Chaochao , Oman Luke , Robock Alan , Stenchikov Georgiy L.
Published: May 2007

Previous studies have used small numbers of ice core records of past volcanism to represent hemispheric or global radiative forcing from volcanic stratospheric aerosols. With the largest‐ever assembly of volcanic ice core records and state‐of‐the‐art climate model simulations of volcanic deposition, we now have a unique opportunity to investigate the effects of spatial variations on sulfate deposition and on estimates of atmospheric loading. We have combined 44 ice core records, 25 from the Arctic and 19 from Antarctica, and Goddard Institute for Space Studies ModelE simulations to study the spatial distribution of volcanic sulfate aerosols in the polar ice sheets. We extracted volcanic deposition signals by applying a high‐pass loess filter to the time series and examining peaks that exceed twice the 31‐year running median absolute deviation. Our results suggest that the distribution of volcanic sulfate aerosol follows the general precipitation pattern in both regions, indicating the important role precipitation has played in affecting the deposition pattern of volcanic aerosols. We found a similar distribution pattern for sulfate aerosols from the 1783–1784 Laki and 1815 Tambora eruptions, as well as for the total β activity after the 1952–1954 low‐latitude Northern Hemisphere and 1961–1962 high‐latitude Northern Hemisphere atmospheric nuclear weapon tests. This confirms the previous assumption that the transport and deposition of nuclear bomb test debris resemble those of volcanic aerosols. We compare three techniques for estimating stratospheric aerosol loading from ice core data: radioactive deposition from nuclear bomb tests, Pinatubo sulfate deposition in eight Antarctic ice cores, and climate model simulations of volcanic sulfate transport and deposition following the 1783 Laki, 1815 Tambora, 1912 Katmai, and 1991 Pinatubo eruptions. By applying the above calibration factors to the 44 ice core records, we have estimated the stratospheric sulfate aerosol loadings for the largest volcanic eruptions during the last millennium. These loadings agree fairly well with estimates based on radiation, petrology, and model simulations. We also estimate the relative magnitude of sulfate deposition compared with the mean for Greenland and Antarctica for each ice core record, which provides a guideline to evaluate the stratospheric volcanic sulfate aerosol loading calculated from a single or a few ice core records.
Inorganic chlorine and bromine in coastal New England air during summer
Authors: Keene William C. , Stutz Jochen , Pszenny Alexander A. P. , Maben John R. , Fischer Emily V. , Smith Allen M. , von Glasow Roland , Pechtl Susanne , Sive Barkley C. , Varner Ruth K.
Published: May 2007

During summer 2004, a comprehensive suite of reactive trace gases (including halogen radicals and precursors, ozone, reactive N, soluble acids, and hydrocarbons), the chemical and physical characteristics of size‐resolved aerosols, actinic flux, and related physical conditions were measured at Appledore Island, Maine, as part of the International Consortium for Atmospheric Research on Transport and Transformation (ICARTT). Sea‐salt mass averaged 4 to 8 times lower than that over the open North Atlantic Ocean. Production in association with sea salt was the primary source for inorganic Cl and Br. Acid displacement of sea‐salt Cl− primarily by HNO3 sustained high HCl mixing ratios (often >2000 pptv) during daytime. Median pHs for the larger sea‐salt size fractions (geometric mean diameters, GMDs ≥ 2.9 μm) ranged from 3.1 to 3.4; median pHs for sub‐μm size fractions were ≤ 1.6. Cl* (including HOCl and Cl2) ranged from <20 to 421 pptv Cl but was less than the detection limit (DL) during most sampling intervals. Periods during which Cl* was consistently detectable corresponded to relatively clean conditions, multiday transport over water, and relatively low actinic flux. At high HCl mixing ratios (>1000 pptv), HCl + OH sustained steady state Cl‐atom concentrations in the range of 104 cm−3. When detectable, photolysis of Cl* was generally the dominant source of atomic Cl; steady state concentrations of Cl atoms were frequently in the range of 104 to 105 cm−3. At these concentrations, Cl played an important role in the chemical evolution of polluted coastal air. Br radical chemistry was relatively unimportant.
UV measurements in the 3000–5000 m altitude region in Tibet
Authors: Dahlback Arne , Gelsor Norsang , Stamnes Jakob J. , Gjessing Yngvar
Published: May 2007

We present measurements of solar UV radiation performed with multichannel moderate‐bandwidth NILU‐UV filter instruments during winter and summer in 2003 in the altitude region from 3000 m to 5000 m at 29°N in the Lhasa region in Tibet. During summer the UV index was found frequently to exceed 15 on clear days and occasionally to exceed 20 on partially cloudy days. High altitudes, low ozone column amounts, clean atmospheres, and relatively low latitudes are factors that contribute to the high UV levels on the Tibetan plateau. UV index values of 12 were measured in late winter for a solar zenith angle of 40° at a snow‐covered 5000 m altitude site. This is a 35% increase compared to a corresponding snow‐free surface. Our measurements show that the solar UV radiation increases with altitude. For clear‐sky and snow‐free conditions the altitude increase is 7–8% per km for erythemal UV dose rates and 3% per km at a wavelength of 340 nm. Results from clear‐sky calculations using a multiple‐scattering radiative transfer model were found to agree within 5% with clear‐sky UV measurements. Radiative transfer calculations combined with measurements were used to estimate the influence of clouds on the UV radiation at the surface. On the average the variable cloud cover in Lhasa reduced the daily integrated erythemal UV dose by 25%. The NILU‐UV instruments also provide total ozone column amounts. The mean difference between daily total ozone column amounts derived from NILU‐UV measurements and from Earth Probe TOMS data was −1.4% ± 3.2% (1σ).
A comparative study of the turbulent flow field with and without a pebble cluster in a gravel bed river
Authors: Lacey R. W. Jay , Roy André G.
Published: May 2007

This paper investigates the processes and spatial patterns of the turbulent flow around a naturally formed in situ pebble cluster and the interactions with large‐scale coherent flow structures. Instantaneous high‐frequency velocities were measured using the simultaneous deployment of four acoustic Doppler velocimeters, with the pebble cluster and after the cluster was removed. Results indicate a twofold increase in turbulent kinetic energy over the sampling area when the pebble cluster is present. Individual vertical component velocity spectra in the wake of the pebble cluster contain a marked peak which decreases in frequency from 1.8 Hz near the cluster to 1.0 Hz farther downstream. This peak is associated with eddies shedding from the shear layer in the lee of the cluster, and it agrees well with the values estimated using a Strouhal number of 0.18. Space‐time correlations indicate the presence of coherent depth‐scale macroturbulent flow structures. These structures in the intermediate flow region are relatively unaffected by eddies shedding from the pebble cluster. The results suggest the effects of the pebble cluster on the surrounding flow dynamics are quite localized and limited to the near‐bed region.
Dual‐scale transport of sensible heat and water vapor over a short canopy under unstable conditions
Authors: Saito Makoto , Asanuma Jun , Miyata Akira
Published: May 2007

This study examines the nature of vertical transport of sensible heat and water vapor density due to mesoscale motions and how they are observed with surface eddy covariance systems. For this purpose, turbulence data measured above a flat and irrigated rice paddy field under unstable conditions were analyzed. It was shown that the larger‐scale component in the measured time series represents mesoscale motions. Wavelet cospectra of the scalar fluxes revealed the presence of vertical transport at horizontal scales larger than the cospectral gap. A time series and the eddy covariance flux were decomposed into a turbulence and a mesoscale component using the identified cospectral gap. The mesoscale transport component of sensible heat and water vapor were found to be related to the wind direction and therefore characteristic of the upwind surface conditions at this scale. In contrast, the turbulence flux component exhibits universal attributes resulting from the local surface characteristics.
InAs/InP quantum dots with bimodal size distribution: Two evolution pathways
Authors: Bansal Bhavtosh , Gokhale M. R. , Bhattacharya Arnab , Arora B. M.
Published: May 2007

The evolution of InAs quantum dots grown on InP substrates by metal-organic vapor phase epitaxy is studied as a function of InAs coverage. Under specific growth conditions, the onset of the two- to three-dimensional transition proceeds via two distinct pathways: through (i) an abrupt appearance of quantum dots as expected in the usual Stranski-Krastanov growth picture and (ii) a continuous evolution of small surface features into well-developed quantum dots. The average size of the features in both these families increases with coverage, leading to a bimodal distribution in dot sizes at an intermediate stage of growth evolution. On further deposition of material, the two families merge into a single broad unimodal distribution of sizes. Complementary information obtained from independent measurements of photoluminescence spectra and surface morphology is correlated and is found to be independently consistent with the picture of growth proposed.
Intrinsic phase shift between a spin torque oscillator and an alternating current
Authors: Zhou Yan , Persson J. , Åkerman Johan
Published: May 2007

We report on a preferred phase shift Δϕ0 between a spin torque oscillator (STO) and an alternating current (Iac) injected at the intrinsic frequency (fSTO) of the STO. In the in-plane (IP) precession mode the STO adjusts to a state where its resistance (or voltage) lags Iac about a quarter of a wavelength [Δϕ0=(87–94)°]. In the IP mode Δϕ0 increases somewhat with the direct current. As the precession changes into the out-of-plane (OOP) mode, Δϕ0 jumps by about 180°, i.e., the STO resistance now precedes Iac about a quarter of a wavelength (Δϕ0=–86°). At the IP/OOP boundary, the alternating current mixes the two oscillation modes and both periodic and chaotic oscillations are observed. As a consequence of mixing, subharmonic terms appear in the STO signal. The intrinsic Δϕ0 will impact any circuit design based on STO technology and will, e.g., have direct consequences for phase locking in networks of serially connected STOs.
Mössbauer studies of multiferroic spinel CoCr1.98Fe0.0257O4
Authors: Choi Kang Ryong , Kim Sung Baek , Kim Chul Sung
Published: May 2007

In order to elucidate the role of Cr ions in CoCr2O4 exhibiting multiferroic property, we have substituted a small amount of Fe ions for Cr sites and investigated the magnetic behavior of Fe ions on atomic scale, using Mössbauer measurement. Polycrystalline CoCr1.98Fe0.0257O4 compound was prepared by wet-chemical process. The crystal structure was found to be a single-phase cubic spinel with space group of Fd-3m. The lattice constant (a0) and the internal structural parameter (x) of the oxygen were determined to be 8.340 and 0.264Å, respectively. Mössbauer absorption spectra at 4.2K show that the well developed two sextets are superposed with small difference in hyperfine field. Isomer shift values (δ) of the two sextets are found to be 0.34 and 0.35mm∕s relative to the Fe metal, which are consistent with the high spin Fe3+ charge state. With increasing temperature, the sextets gradually split into two subspectra, and then around 28K the absorption line broadening of outer sextet appears rapidly. Above the Néel temperature (TN=97K) the paramagnetic doublets are observed. The sudden change of outer sextet is observed above 28K, which corresponds to the spin transition temperature. Mössbauer measurement results suggest that Cr3+ ions have two different magnetic sites, and the temperature dependent magnetic property is attributable to the different behaviors of magnetic ions in the two sites.
Reversible and quasireversible information in first-order reversal curve diagrams
Authors: Béron Fanny , Clime Liviu , Ciureanu Mariana , Ménard David , Cochrane Robert W. , Yelon Arthur
Published: May 2007

Two methods for extracting information from first-order reversal curves (FORCs) obtained on low coercivity samples are presented. The proportion of reversibility as a function of applied field can be extracted by calculating the ratio of the initial slope of each FORC to the susceptibility on the major hysteresis loop upper branch at the same field. This gives us the part of the reversal process, a process occurring with zero coercivity, that is, where H=Hr, during the magnetization reversal. In order to be able to see the nonperturbed trace coming from the irreversible processes with a small coercivity compared to the FORC domain, some points have to be added in the H<Hr area in a way that minimizes the discontinuities near H=Hr. This is done by using two functions characterizing the behavior of the magnetization on the H=Hr axis (“extrapolated FORCs”). These methods were used to characterize a CoFeB nanowire array with the applied field perpendicular to the nanowire axis.
Time relaxation of flux rotation and dimensional crossover in La1.85Sr0.15CuO4
Authors: Bruckental Y. , Shaulov A. , Yeshurun Y.
Published: May 2007

Vector magnetization measurements in La1.85Sr0.15CuO4 under a steady field H tilted relative to the ab plane show that the induction B rotates toward H with time. The rate of rotation as a function of temperature exhibits two peaks separated by a dip around 12K. Measurements of the remnant induction show that for temperatures below ∼12K, B rotates towards the c axis, whereas for temperatures above ∼12K, B rotates towards the ab planes. We argue that these data are consistent with a two-dimensional and a three-dimensional behavior below and above the dimensional crossover temperature, ∼12K, respectively.
Single electron effects and Bloch oscillations in high-TC superconductive tunneling junctions
Authors: Alvarez G. A. , Wang X. L. , Dou S. X. , Wu M. Z.
Published: May 2007

We investigated the effects of single electron charging energy in high-TC superconductors. Various phenomena originated from Coulomb blockade were observable in c-axis NdBa2Cu3O7−δ∕PrBa2Cu3O7−δ∕NdBa2Cu3O7−δ superconducting tunnel junctions. The current-voltage characteristics show a Coulomb gap for Cooper pair tunneling when the charging energy exceeds the Josephson coupling energy. A crossover from Coulomb blockade of Cooper pair tunneling to a supercurrent is observed when the ratio of Josephson coupling energy to charging energy is increased. We found a regime in which aspects of the Coulomb blockade of tunneling coexist with features typical of Josephson tunneling. Under microwave irradiation of frequency f, the dynamic resistance dV∕dI as a function of the current I showed sharp singularities at I=2nef, n=±1,±2,…. This behavior appears to be very similar to the one predicted by the semiclassical theory of Bloch oscillations.
Magnetic properties of Fe-based toroidal cores prepared by continuous Joule heating under tensile stress
Authors: Yanai T. , Shimada A. , Takagi K. , Takahashi K. , Nakano M. , Fukunaga H. , Yoshizawa Y.
Published: May 2007

Fe-based toroidal cores with a permeability value of several hundreds were prepared by the continuous Joule heating method under tensile stress at a high moving velocity of 120cm∕min, corresponding to an effective annealing time of approximately 1.8s, and their magnetic properties were evaluated. The prepared core showed a constant permeability value up to 2MHz and a low magnetic loss compared with those for conventional cores with controlled permeability. An investigation of dc-bias properties of the core suggested that the core has constant and good magnetic properties below the dc-bias field of 1kA∕m which is approximately 50% of the anisotropy field. Consequently, the continuous Joule heating under a tensile stress method at high moving velocity enables us to prepare a long annealed ribbon in a short time with simple equipment and improves productivity for the fabrication process of high performance Fe-based toroidal cores with controlled permeability.
Actuation field in martensitic Ni49.0Mn23.5Ga27.5
Authors: Zhao Peng , Cullen James , Wuttig Manfred
Published: May 2007

The singular point detection technique has been applied to determine the magnetic anisotropy constant K1 of small martensitic Ni49.0Mn23.5Ga27.5 (wt %) single crystals with a martensitic transformation temperature TM of 276K. As expected, K1 increases with decreasing temperatures below TM, following a magnetization power law K1(T)∕K1(0)=[Ms(T)∕Ms(0)]3. At 5K, K1 reaches 3.24×105J∕m3. The force required to initiate twin boundary motion increases exponentially with decreasing temperature. The combination of both temperature dependences leads to a very restricted temperature window for magnetic actuation using this alloy.
Ferromagnetic resonance in the proximity of the unstable perpendicular equilibrium: A study in Permalloy thin films and nanoscale dots
Authors: Yu Chengtao , Pechan Michael J. , Bennett Ryan , Katine Jordan , Folks Liesl , Carey Matthew
Published: May 2007

We are investigating the magnetization dynamics of a ferromagnetic system in the proximity of the unstable perpendicular equilibrium. The test system utilized is Permalloy in thin film and dot arrays with the applied field along a small angle off the film normal. Frequency∕field dispersion curves (up to 15GHz) obtained at different small angles (θH) reveal significant deviations from the perpendicular linear dispersion at low frequencies, and they form almost frequency independent flat plateau with a local minimum near the demagnetization field. The existence of the local minimum results in three resonances in a constant frequency∕swept field scans. Such behavior is modeled successfully, in particular, in the film case, by using an approach for oblique angle resonance [P. E. Tannenwald, Phys. Rev. 105, 377 (1957)]. For the dots, additional influence from either induced in-plane anisotropy or vortex formation is discussed.
Mechanisms of magnetization reversals in elliptical thin films
Authors: Wei Zung-Hang , Lai Mei-Feng
Published: May 2007

The size dependence of reversal mechanisms and the corresponding switching fields of elliptical Permalloy thin films are studied by micromagnetic simulation. From the simulated spin configurations, it is shown that for ellipses with different dimensions there exist three reversal mechanisms: the buckling-instability mode, the vortex-propagation mode, and the mixed mode of buckling-instability and vortex-propagation modes.
Measuring exchange anisotropy in Fe∕MnPd using inductive magnetometry
Authors: Kennewell K. J. , Ji X. , Hu J. , Krishnan K. M. , Stamps R. L.
Published: May 2007

Local effective fields created in Fe by MnPd through exchange anisotropy are studied using an inductive ferromagnetic resonance technique. The bilayers were prepared on single crystal MgO(001) using ion beam sputtering in high vacuum and have a highly orientated crystalline structure with a [001] orientation as determined by x-ray diffraction. Unidirectional and fourfold anisotropies are measured using a stripline resonance geometry. Experiments with the field applied along different crystalline directions indicate that the fourfold axes are well defined with magnitudes consistent with values expected for bulk Fe. Anomalies in the frequency studied as a function of applied field are interpreted as evidence for a distribution of unidirectional anisotropy field orientations and strengths.
Temperature dependent x-ray magnetic circular dichroism in Er2Fe17
Authors: Lee Y. , Harmon B. N. , Goldman A. I. , Lang J. C.
Published: May 2007

The x-ray magnetic circular dichroism spectra of the erbium L2 and L3 edges in Er2Fe17 have been investigated experimentally as a function of temperature and theoretically using first principles electronic structure calculations. The spectral changes with temperature are rather dramatic and are related to the interplay between the Fe-3d and the Er-4f orbitals causing spin polarization of the 5d states.
Structural analysis of the CoFeB thin film in Ru∕CoFeB and MgO∕CoFeB layers
Authors: Kim Dong Joon , Bae Ji Young , Lim Woo Chang , Kim Kee Won , Lee Taek Dong
Published: May 2007

In the last few years, magnetic tunnel junctions with MgO barrier have attracted attention due to the theoretically predicted and experimentally verified huge TMR. In the present work, crystallization behavior of CoFeB layer adjacent to the MgO or Ru layer was studied by annealing at various temperatures for 1h. The crystallization started at MgO∕CoFeB interface but crystallization temperature changed with materials and thickness of adjacent layer. When the thickness of MgO layer increased in MgO∕CoFeB bilayer, crystallization temperature decreased. This strongly suggests that B from CoFeB layer diffused into adjacent layer to crystallize at lower temperature and MgO can serve as a sink of B. Details will be discussed.
Numerical simulation of magnetization process in epitaxial Co2MnSi∕Cr∕Co2MnSi trilayers with oscillatory interlayer coupling
Authors: Wang H. , Mitani S. , Sato A. , Saito K. , Takanashi K. , Yakushiji K.
Published: May 2007

Numerical simulation is carried out to investigate the magnetization process of epitaxial Co2MnSi∕Cr∕Co2MnSi trilayers with oscillatory interlayer exchange coupling. A series of the magnetization curves is successfully fitted by using a very simple model, in which the absent 180° coupling is assumed while 90° coupling and the lowest order cubic anisotropy are considered. The 90° coupling energy and the anisotropy constant can be uniquely determined, and it is revealed that the strength of 90° coupling decreases exponentially with the spacer layer thickness.
Band structures, and magnetic and transport properties of La doped two dimensional Sr2CoO4
Authors: Yao Q. W. , Wang X. L. , Cheng Z. X. , Peleckis G. , Dou S. X. , Nigam R. , Zhao G. P.
Published: May 2007

In this work, we report on our studies on the band structure calculations, structures, transport, and magnetic properties in two dimensional layer structured perovskite compounds Sr2−xLaxCoO4. Structure refinement results reveal that these compounds crystallized in K2NiF4-type structures with space group I4∕mmm. The temperature dependence of resistivity shows a semiconductorlike behavior over a wide range of temperatures, a metal-insulator transition at 240K, and an upturn at 160K for the x=1, 1.25, and 0.75 samples. A coercive field is about 1T for the sample with x=0.75, while it is about 0.05T for x=0.75 and 0.1T for the x=1.25 samples. A negative field hysteresis magnetoresistance in close correlation with the coercive field has been observed and can be explained by the grain boundary tunneling effect. The first-principles band structure calculations were carried out for Sr1.5La0.5CoO4 and the results indicate that the system is metallic with a high spin polarization which is responsible for the observed large magnetoresistance.
Effect of growth temperature on the magnetic, microwave, and cation inversion properties on NiFe2O4 thin films deposited by pulsed laser ablation deposition
Authors: Chinnasamy C. N. , Yoon S. D. , Yang Aria , Baraskar Ashish , Vittoria C. , Harris V. G.
Published: May 2007

First principles band structure calculations suggest that the preferential occupation of Ni2+ ions on the tetrahedral sites in NiFe2O4 would lead to an enhancement of the exchange integral and subsequently the Néel temperature and magnetization. To this end, we have deposited NiFe2O4 films on MgO substrates by pulsed laser deposition. The substrate temperature was varied from 700to900°C at 5mTorr of O2 pressure. The films were annealed at 1000°C for different times prior to their characterization. X-ray diffraction spectra showed either (100) or (111) orientation with the spinel structure dependent on the substrate orientation. Magnetic studies showed a magnetization value of 2.7kG at 300K. The magnetic moment was increased to the bulk value as a result of postdeposition annealing at 1000°C. The as produced films show that the ferromagnetic resonance linewidth at 9.61GHz was 1.5kOe, and it was reduced to 0.34kOe after postannealing at 1000°C. This suggests that the annealing led to the redistribution of Ni2+ ions to their equilibrium octahedral sites. Further, it is shown that the magnetically preferred direction of Ha can be aligned perpendicular to the film plane when films are grown with a fixed oxygen pressure of 5mTorr for films deposited at 700 and 900°C.
High spin polarization in a two phase quaternary Heusler alloy Co2MnAl1−XSnX
Authors: Rajanikanth A. , Kande D. , Takahashi Y. K. , Hono K.
Published: May 2007

We have investigated the structure and the spin polarization of Co2MnAl, Co2MnSn, and Co2MnAl0.5Sn0.5 alloys. The structures of the Co2MnAl and Co2MnSn alloys that were annealed for four days at 450°C were B2 and L21, respectively. Co2MnAl0.5Sn0.5 had a dendrite microstructure that was formed by the phase separation into Al-enriched B2 and Sn-enriched L21 phases during solidification. The saturation magnetization values of Co2MnAl, Co2MnAl0.5Sn0.5, and Co2MnSn were 3.66μB, 4.3μB, and 4.9μB, respectively, which are slightly lower than the theoretical values of 4μB, 4.5μB, and 5μB due to the low degree of L21 ordering. The spin polarization P measured by the point contact Andreev reflection technique were 0.56 for B2-Co2MnAl, 0.6 for L21-Co2MnSn, and interestingly, a higher value of 0.63 for the two phase Co2MnAl0.5Sn0.5 alloy.
Domain wall assisted magnetic recording (invited)
Authors: Dobin A. Yu. , Richter H. J.
Published: May 2007

The domain wall assisted switching in the hard/soft composite nanostructures is studied using numerical and analytic micromagnetics. The switching occurs via domain wall nucleation, compression in the applied field, depinning, and propagation through the hard/soft interface. Optimizing hard and soft layer parameters yields a significant increase of the maximum switchable anisotropy for a fixed applied field, and hence an enhancement of the energy barrier that can be translated into grain diameter reduction and magnetic recording density gains. The switching fields for the media with quadratic variation of the anisotropy were calculated and optimized to achieve the largest energy barrier gain. Domain wall assisted switching was studied in the field of a single pole write head.
Influence of hot pressure on the magnetoresistance of CrO2
Authors: Wang Xianjie , Sui Yu , Song Xiudan , Zhu Ruibin , Qian Zhengnan , Su Wenhui , Tang Jinke
Published: May 2007

In this paper, we investigate the influence of high temperature and high pressure (hot pressure) on the magnetic and transport properties of polycrystalline CrO2 samples compacted under high pressure and high temperature of up to 5GPa and 600°C, respectively. The magnetic moment increases with compacting temperature, and a metal-semiconductor transition is observed in hot-pressed samples, different from the cold-pressed samples. These results indicate that the formation of Cr2O3 at the grain boundaries of CrO2 is suppressed by hot pressure. The magnitude of low field magnetoresistance of up to 1T at 5K is enhanced first with the increase of compacting temperature and then decreased under higher compacting temperature. This result can be well explained by the change of spin-dependent tunneling at the modulated grain boundaries of CrO2 due to the transformation from Cr2O3 to CrO2 under hot pressure.
Modeling of magnetostrictive Galfenol sensor and validation using four point bending test
Authors: Datta Supratik , Atulasimha Jayasimha , Flatau Alison B.
Published: May 2007

A magnetomechanical bending model has been developed to predict the magnetic induction, elastic, and magnetostrictive strain and bending stress in a magnetostrictive member subjected simultaneously to bending load and dc magnetic bias field. This model was obtained by coupling Euler-Bernoulli beam theory with an energy-based statistical model. The bending model predictions were within 10% of the experimental results obtained from a uniquely devised four point bending test of Galfenol (nominal composition of 84at.% Fe and 16at.% Ga) performed under different magnetic bias fields.
Magnetic properties of a noninterpenetrating chiral porous cobalt metal-organic framewok
Authors: Yu Chengtao , Ma Shengqian , Pechan Michael J. , Zhou Hong-cai
Published: May 2007

Noninterpenetrating chiral porous cobalt metal-organic framework built from the coplanar triangular H3TATB ligands has been synthesized under solvothermal conditions. X-ray analysis revealed the compound crystallized in the chiral space group either P4132 or P4332, and adopted a trimetallic “hourglass” secondary building unit, in which there are two terminal Td-Co atoms and one central Oh-Co with Td-Co and Oh-Co distance about 3.604Å. Paramagnetic behavior is observed throughout the measured temperature range of 2–300K. Assuming a uniform isotropic interaction between the nearest neighbor Co atoms, susceptibility of the trinuclear Co2+ linear chain has been calculated by following Van Vleck’s quantum model for spin-spin couplings. The resultant fit to the data indicates an antiferromagnetic Co–Co interaction in the molecule, with coupling strength J∼−6.2×10−16erg, θ∼−16K.
Optical response of a strongly anisotropic thin film as a nonmagnetic negative phase velocity material
Authors: Hernández P. H. , Martínez G. , Cocoletzi Gregorio H. , Azucena-Coyotecatl H. , Díaz-Hernández J.
Published: May 2007

We study the optical response of a strongly anisotropic nonmagnetic material. As a first case, it is considered an anisotropic nonmagnetic thin film (medium 2) sandwiched between medium 1 of refraction index n1 and medium 3 of refraction index n3. As a second case, the anisotropic thin film and medium 3 are interchanged. These geometries correspond to the Kretchmann [E. Kretschmann and H. Raether, Z. Naturforsch. A 23, 2135 (1968); E. Kretschmann, Z. Phys. 241, 313 (1971)] and Otto [A. Otto, Z. Phys. 216, 398 (1968)] attenuated total reflectivity arrays, respectively. Our main goal is to obtain a negative phase velocity propagation. To achieve this we choose an index of refraction n1>1 and show how the appropriate angle of incidence allows us to induce a negative phase velocity nonmagnetic material. We focused our attention in two distinct regions that emerge in the reflectivity curves when varying the angle of incidence. In the first region, the minima of the reflectivity are interpreted in terms of the coupling of light with the modes at the interface between the anisotropic material and the medium with refraction index n3. In the second region, the structure of the reflectivity is due to the propagation of light in the highly anisotropic material, with negative phase velocity.