39,799 research outputs found
Micromagnetic Simulations of Ferromagnetic Rings
Thin nanomagnetic rings have generated interest for fundamental studies of
magnetization reversal and also for their potential in various applications,
particularly as magnetic memories. They are a rare example of a geometry in
which an analytical solution for the rate of thermally induced magnetic
reversal has been determined, in an approximation whose errors can be estimated
and bounded. In this work, numerical simulations of soft ferromagnetic rings
are used to explore aspects of the analytical solution. The evolution of the
energy near the transition states confirms that, consistent with analytical
predictions, thermally induced magnetization reversal can have one of two
intermediate states: either constant or soliton-like saddle configurations,
depending on ring size and externally applied magnetic field. The results
confirm analytical predictions of a transition in thermally activated reversal
behavior as magnetic field is varied at constant ring size. Simulations also
show that the analytic one dimensional model continues to hold even for wide
rings
Coupled-resonator-induced transparency with a squeezed vacuum
We present the first experimental observation of quantum fluctuation spectra
in two coupled optical cavities with an injected squeezed vacuum light. The
quadrature components of the reflected squeezed vacuum spectra are measured by
phase sensitive homodyne detector. The experimental results demonstrate
coupled-resonator-induced transparency in the quantum regime, in which
electromagnetically-induced-transparency-like characteristic of the absorption
and dispersion properties of the coupled optical cavities determines the
line-shape of the reflected quantum noise spectra.Comment: 4 pages, 4 figures, appear in Phys. Rev. Let
Bioconversion of rape straw into a nutritionally enriched substrate by Ganoderma lucidum and yeast
This work aims to select biological treatments and conditions for the bioconversion of rape straw by the mixed-strain fermentation of Ganoderma lucidum and yeasts (Saccharomyces cerevisiae, Candida tropicalis and Candida utilis), into an enriched substrate with increased crude protein and digestibility. Orthogonal experiment showed that the optimal experimental condition for the crude protein enrichment was: 10% (v/w) C. utilis inoculum was added to the rape straw medium after 7 days of G. lucidum growth; the crude protein content of the substrate was 16.23%; the yield rate were increased by 75.70 and 225.90%, respectively when compared to the G. lucidum individual-fermentation and without fermentation substrate. The results in this study also indicated that: the co-culture of 2 fungi (G. lucidum + C. utilis) was better than individual (G. lucidum) culture on the degradation of cellulose and lignin of rape straw substrate and the secretion of ligninolytic enzyme system including laccase (Lac), manganese peroxidase (MnP) and lignin peroxidase (LiP).Key words: Bioconversion, rape straw, nutritionally enrichment, Ganoderma lucidum, yeast
Scaling in directed dynamical small-world networks with random responses
A dynamical model of small-world network, with directed links which describe
various correlations in social and natural phenomena, is presented. Random
responses of every site to the imput message are introduced to simulate real
systems. The interplay of these ingredients results in collective dynamical
evolution of a spin-like variable S(t) of the whole network. In the present
model, global average spreading length \langel L >_s and average spreading time
_s are found to scale as p^-\alpha ln N with different exponents.
Meanwhile, S behaves in a duple scaling form for N>>N^*: S ~ f(p^-\beta
q^\gamma t'_sc), where p and q are rewiring and external parameters, \alpha,
\beta, \gamma and f(t'_sc) are scaling exponents and universal functions,
respectively. Possible applications of the model are discussed.Comment: 4 pages, 6 Figure
Searching for Ground Truth: a stepping stone in automating genre classification
This paper examines genre classification of documents and
its role in enabling the effective automated management of digital documents by digital libraries and other repositories. We have previously presented genre classification as a valuable step toward achieving automated extraction of descriptive metadata for digital material. Here, we present results from experiments using human labellers, conducted to assist in genre characterisation and the prediction of obstacles which need to be overcome by an automated system, and to contribute to the process of creating a solid testbed corpus for extending automated genre classification and testing metadata extraction tools across genres. We also describe the performance of two classifiers based on image and stylistic modeling features in labelling the data resulting from the agreement of three human labellers across fifteen genre classes.
Phosphoinositide Modulation of Heteromeric Kv1 Channels Adjusts Output of Spiral Ganglion Neurons from Hearing Mice
Spiral ganglion neurons (SGNs) relay acoustic code from cochlear hair cells to the brainstem, and their stimulation enables electrical hearing via cochlear implants. Rapid adaptation, a mechanism that preserves temporal precision, and a prominent feature of auditory neurons, is regulated via dendrotoxin-sensitive low-threshold voltage-activated (LVA) K(+) channels. Here, we investigated the molecular physiology of LVA currents in SGNs cultured from mice following the onset of hearing (postnatal days 12-21). Kv1.1- and Kv1.2-specific toxins blocked the LVA currents in a comparable manner, suggesting that both subunits contribute to functional heteromeric channels. Confocal immunofluorescence in fixed cochlear sections localized both Kv1.1 and Kv1.2 subunits to specific neuronal microdomains, including the somatic membrane, juxtaparanodes, and the first heminode, which forms the spike initiation site of the auditory nerve. The spatial distribution of Kv1 immunofluorescence appeared mutually exclusive to that of Kv3.1b subunits, which mediate high-threshold voltage-activated currents. As Kv1.2-containing channels are positively modulated by membrane phosphoinositides, we investigated the influence of phosphatidylinositol-4,5-bisphosphate (PIP2) availability on SGN electrophysiology. Reducing PIP2 production using wortmannin, or sequestration of PIP2 using a palmitoylated peptide (PIP2-PP), slowed adaptation rate in SGN populations. PIP2-PP specifically inhibited the LVA current in SGNs, an effect reduced by intracellular dialysis of a nonhydrolysable analog of PIP2. PIP2-PP also inhibited heterologously expressed Kv1.1/Kv1.2 channels, recapitulating its effect in SGNs. Collectively, the data identify Kv1.1/Kv1.2 heteromeric channels as key regulators of action potential initiation and propagation in the auditory nerve, and suggest that modulation of these channels by endogenous phosphoinositides provides local control of membrane excitability
Edge Shear Flows and Particle Transport near the Density Limit in the HL-2A Tokamak
Edge shear flow and its effect on regulating turbulent transport have long
been suspected to play an important role in plasmas operating near the
Greenwald density limit . In this study, equilibrium profiles as well as
the turbulent particle flux and Reynolds stress across the separatrix in the
HL-2A tokamak are examined as is approached in ohmic L-mode discharges.
As the normalized line-averaged density is raised, the
shearing rate of the mean poloidal flow drops, and the
turbulent drive for the low-frequency zonal flow (the Reynolds power ) collapses. Correspondingly, the turbulent particle
transport increases drastically with increasing collision rates. The geodesic
acoustic modes (GAMs) gain more energy from the ambient turbulence at higher
densities, but have smaller shearing rate than low-frequency zonal flows. The
increased density also introduces decreased adiabaticity which not only
enhances the particle transport but is also related to a reduction in the
eddy-tilting and the Reynolds power. Both effects may lead to the cooling of
edge plasmas and therefore the onset of MHD instabilities that limit the plasma
density
Origin of the spin reorientation transitions in (FeCo)B alloys
Low-temperature measurements of the magnetocrystalline anisotropy energy
in (FeCo)B alloys are reported, and the origin of this
anisotropy is elucidated using a first-principles electronic structure
analysis. The calculated concentration dependence with a maximum near
and a minimum near is in excellent agreement with experiment.
This dependence is traced down to spin-orbital selection rules and the filling
of electronic bands with increasing electronic concentration. At the optimal Co
concentration, depends strongly on the tetragonality and doubles under a
modest 3% increase of the ratio, suggesting that the magnetocrystalline
anisotropy can be further enhanced using epitaxial or chemical strain.Comment: 4 pages + supplementary material, 6 figures. Accepted in Applied
Physics Letter
Free field realization of the exceptional current superalgebra \hat{D(2,1;\a)}_k
The free-field representations of the D(2,1;\a) current superalgebra and
the corresponding energy-momentum tensor are constructed. The related screening
currents of the first kind are also presented.Comment: Latex file, 10 page
Using high-throughput virtual screening to explore the optoelectronic property space of organic dyes; finding diketopyrrolopyrrole dyes for dye-sensitized water splitting and solar cells
Organic dyes based on conjugated chromophores such as diketopyrrolopyrrole (DPP) have a large range of uses beyond providing colour to other materials, such as in dye-sensitized solar cells, dye-sensitized photoelectrochemical cells, dye-sensitized colloidal photocatalysts and organic photovoltaics. We perform a high-throughput virtual screening using the xTB family of density functional tight-binding methods to map the optoelectronic property space of ∼45 000 DPP dyes. The large volume of data at our disposal allows us to probe the difference between symmetric and asymmetric dyes and to identify the apparent boundaries of the optoelectronic property space for these dyes, as well as which substituents give access to particular combinations of properties. Finally, we use our dataset to screen for DPP dyes that can drive the reduction of protons to molecular hydrogen when illuminated as part of dye-sensitized photoelectrochemical cells or dye-sensitized colloidal photocatalysts, or as dyes for TiO2-based dye-sensitized solar cells
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