3,341 research outputs found
Current driven switching of magnetic layers
The switching of magnetic layers is studied under the action of a spin
current in a ferromagnetic metal/non-magnetic metal/ferromagnetic metal spin
valve. We find that the main contribution to the switching comes from the
non-equilibrium exchange interaction between the ferromagnetic layers. This
interaction defines the magnetic configuration of the layers with minimum
energy and establishes the threshold for a critical switching current.
Depending on the direction of the critical current, the interaction changes
sign and a given magnetic configuration becomes unstable. To model the time
dependence of the switching process, we derive a set of coupled Landau-Lifshitz
equations for the ferromagnetic layers. Higher order terms in the
non-equilibrium exchange coupling allow the system to evolve to its
steady-state configuration.Comment: 8 pages, 2 figure. Submitted to Phys. Rev.
Reduction of the Three Dimensional Schrodinger Equation for Multilayered Films
In this paper, we present a method for reducing the three dimensional
Schrodinger equation to study confined metallic states, such as quantum well
states, in a multilayer film geometry. While discussing some approximations
that are employed when dealing with the three dimensionality of the problem, we
derive a one dimensional equation suitable for studying such states using an
envelope function approach. Some applications to the Cu/Co multilayer system
with regard to spin tunneling/rotations and angle resolved photoemission are
discussed.Comment: 14 pages, 1 figur
Glueball spectrum based on a rigorous three-dimensional relativistic equation for two-gluon bound states II: calculation of the glueball spectrum
In the preceding paper, a rigorous three-dimensional relativistic equation
for two-gluon bound states was derived from the QCD with massive gluons and
represented in the angular momentum representation. In order to apply this
equation to calculate the glueball spectrum, in this paper, the equation is
recast in an equivalent three-dimensional relativistic equation satisfied by
the two-gluon positive energy state amplitude. The interaction Hamiltonian in
the equation is exactly derived and expressed as a perturbative series. The
first term in the series describes the one-gluon exchange interaction which
includes fully the retardation effect in it. This term plus the linear
confining potential are chosen to be the interaction Hamiltonian and employed
in the practical calculation. With the integrals containing three and four
spherical Bessel functions in the QCD vertices being analytically calculated,
the interaction Hamiltonian is given an explicit expression in the angular
momentum representation. Numerically solving the relativistic equation with
taking the contributions arising from the retardation effect and the
longitudinal mode of gluon fields into account, a set of masses for the
and glueball states are
obtained and are in fairly good agreement with the predictions given by the
lattice simulatio
Research on the Assembly Pattern of MMC Bolted Flange Joint
AbstractIn a Metal-to-Metal Contact (MMC) bolted flange joint the stress of sealing surfaces is constant. It canwithstand higherbolt load. So, under the operating conditions of high temperature, high pressure or their fluctuations, the sealing effect of MMC bolted flange joints is better than of floating (FLT) bolted flange joints. According to the structure characteristics of MMC bolted flange joints, a new tightening method (SH-Method) was recommended in this work.The bolt forces during the tightening process of a MMC bolted flange joint with SH-Method were calculated and analyzed with the finite element analysis Software ANSYS. The calculating model and results were experimentally verified. Both calculating and experimentally results showed, the new tightening method ‘SH-Method’has the advantages of fewer steps, simpler operation, more uniform bolt force, and better sealing effect, compared to the star pattern and the alternative pattern #3 of ASME PCC-1, in which only the pattern methods for FLT flange joints are recommended
Novel fungal genera and species associated with the sooty blotch and flyspeck complex on apple in China and the USA
Fungi in the sooty blotch and flyspeck (SBFS) complex cause blemishes on apple and pear fruit that result in economic losses for growers. The SBFS fungi colonise the epicuticular wax layer of pomaceous fruit but do not invade the cuticle. Fungi causing fuliginous and punctate mycelial types on apple are particularly difficult to identify based on morphological criteria because many species in the SBFS complex share the same mycelial phenotypes. We compared the morphology and nuclear ribosomal DNA phylogeny (ITS, LSU) of 11 fungal strains isolated from SBFS blemishes on apple obtained from two provinces in China and five states in the USA. Parsimony analysis, supported by cultural characteristics and morphology in vitro, provided support to delimit the isolates into three novel genera, representing five new species. Phaeothecoidiella, with two species, P. missouriensis and P. illinoisensis, is introduced as a new genus with pigmented endoconidia in the Dothideomycetes. Houjia (Capnodiales) is introduced for H. pomigena and H. yanglingensis. Although morphologically similar to Stanjehughesia (Chaetosphaeriaceae), Houjia is distinct in having solitary conidiogenous cells. Sporidesmajora (Capnodiales), based on S. pennsylvaniensis, is distinguished from Sporidesmium (Sordariomycetes) in having long, multiseptate conidiophores that frequently have a subconical, darkly pigmented apical cell, and very long, multi-euseptate conidia
Modulation of mitochondrial DNA copy number in a model of glioblastoma induces changes to DNA methylation and gene expression of the nuclear genome in tumours
BACKGROUND:There are multiple copies of mitochondrial DNA (mtDNA) present in each cell type, and they are strictly regulated in a cell-specific manner by a group of nuclear-encoded mtDNA-specific replication factors. This strict regulation of mtDNA copy number is mediated by cell-specific DNA methylation of these replication factors. Glioblastoma multiforme, HSR-GBM1, cells are hyper-methylated and maintain low mtDNA copy number to support their tumorigenic status. We have previously shown that when HSR-GBM1 cells with 50% of their original mtDNA content were inoculated into mice, tumours grew more aggressively than non-depleted cells. However, when the cells possessed only 3% and 0.2% of their original mtDNA content, tumour formation was less frequent and the initiation of tumorigenesis was significantly delayed. Importantly, the process of tumorigenesis was dependent on mtDNA copy number being restored to pre-depletion levels. RESULTS:By performing whole genome MeDIP-Seq and RNA-Seq on tumours generated from cells possessing 100%, 50%, 0.3% and 0.2% of their original mtDNA content, we determined that restoration of mtDNA copy number caused significant changes to both the nuclear methylome and its transcriptome for each tumour type. The affected genes were specifically associated with gene networks and pathways involving behaviour, nervous system development, cell differentiation and regulation of transcription and cellular processes. The mtDNA-specific replication factors were also modulated. CONCLUSIONS:Our results highlight the bidirectional control of the nuclear and mitochondrial genomes through modulation of DNA methylation to control mtDNA copy number, which, in turn, modulates nuclear gene expression during tumorigenesis.Xin Sun and Justin C. St Joh
Theory of Current-Induced Magnetization Precession
We solve appropriate drift-diffusion and Landau-Lifshitz-Gilbert equations to
demonstrate that unpolarized current flow from a non-magnet into a ferromagnet
can produce a precession-type instability of the magnetization. The fundamental
origin of the instability is the difference in conductivity between majority
spins and minority spins in the ferromagnet. This leads to spin accumulation
and spin currents that carry angular momentum across the interface. The
component of this angular momentum perpendicular to the magnetization drives
precessional motion that is opposed by Gilbert damping. Neglecting magnetic
anisotropy and magnetostatics, our approximate analytic and exact numerical
solutions using realistic values for the material parameters show (for both
semi-infinite and thin film geometries) that a linear instability occurs when
both the current density and the excitation wave vector parallel to the
interface are neither too small nor too large. For many aspects of the problem,
the variation of the magnetization in the direction of the current flows makes
an important contribution.Comment: Submitted to Physical Review
Flow-induced elastic anisotropy of metallic glasses
As-cast bulk metallic glasses are isotropic, but anisotropy can be induced by thermomechanical treatments. For example, the diffraction halo in the structure function S(Q) observed in transmission becomes elliptical (rather than circular) after creep in uniaxial tension or compression. Published studies associate this with frozen-in anelastic strain and bond-orientational anisotropy. Results so far are inconsistent on whether viscoplastic flow of metallic glasses can induce anisotropy. Preliminary diffraction data suggest that the anisotropy, if any, is very low, while measurements of the elastic properties suggest that there is induced anisotropy, opposite in sign to that due to anelastic strain. We study three bulk metallic glasses, Ce65Al10Cu20Co5, La55Ni10Al35, and Pd40Ni30Cu10P20. By using resonant ultrasound spectroscopy to determine the full elasticity tensor, the effects of relaxation and rejuvenation can be reliably separated from uniaxial anisotropy (of either sign). The effects of viscoplastic flow in tension are reported for the first time. We find that viscoplastic flow of bulk metallic glasses, particularly in tension, can induce significant anisotropy that is distinct from that associated with frozen-in anelastic strain. The conditions for inducing such anisotropy are explored in terms of the Weissenberg number (ratio of relaxation times for primary relaxation and for shear strain rate). There is a clear need for further work to characterize the structural origins of flow-induced anisotropy and to explore the prospects for improved mechanical and other properties through induced anisotropy
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