28,035 research outputs found
Primordial magnetic fields constrained by CMB anisotropies and dynamo cosmology
Magneto-curvature stresses could deform magnetic field lines and this would
give rise to back reaction and restoring magnetic stresses [Tsagas, PRL
(2001)]. Barrow et al [PRD (2008)] have shown in Friedman universe the
expansion to be slow down in spatial section of negative Riemann curvatures.
From Chicone et al [CMP (1997)] paper, proved that fast dynamos in compact 2D
manifold implies negatively constant Riemannian curvature, here one applies the
Barrow-Tsagas ideas to cosmic dynamos. Fast dynamo covariant stretching of
Riemann slices of cosmic Lobachevsky plane is given. Inclusion of advection
term on dynamo equations [Clarkson et al, MNRAS (2005)] is considered. In
absence of advection a fast dynamo is also obtained. Viscous and restoring
forces on stretching particles decrease, as magnetic rates increase. From COBE
data (), one computes stretching
.
Zeldovich et al has computed the maximum magnetic growth rate as
. From COBE data one computes
a lower growth rate for the magnetic field as
, well-within Zeldovich et al
estimate. Instead of the Harrison value one obtains the
lower primordial field which yields the
at the Big Bang time.Comment: Dept of theoretical physics-UERJ-Brasi
Surface magnetic canting in a ferromagnet
The surface magnetic canting (SMC) of a semi-infinite film with ferromagnetic
exchange interaction and competing bulk and surface anisotropies is
investigated via a nonlinear mapping formulation of mean-field theory
previously developed by our group [L. Trallori et al., Int. J. Mod. Phys. B 10,
1935-1988 (1996)], and extended to the case where an external magnetic field is
applied to the system. When the field H is parallel to the film plane, the
condition for SMC is found to be the same as that recently reported by Popov
and Pappas [Phys. Rev. B 64, 184401 (2001)]. The case of a field H applied
perpendicularly to the film plane is also investigated. In both cases, the
zero-temperature equilibrium configuration is easily determined by our
theoretical approach.Comment: 4 pages, 3 figure
Antarctic Ocean polynyas
The spatial and temporal variability of sea ice concentrations derived from Nimbus-7 Scanning Multichannel Microwave Radiometer (SMMR) brightness temperatures are presented. Emphasis is on the continental shelf region of the Ross Sea during 1984, when supporting data were obtained from oceanographic stations and moored instruments. The effects of the large spring polynya in the Ross Sea on summer insolation, surface heat layer storage, and late autumn ice formation are described
Instabilities in complex mixtures with a large number of components
Inside living cells are complex mixtures of thousands of components. It is
hopeless to try to characterise all the individual interactions in these
mixtures. Thus, we develop a statistical approach to approximating them, and
examine the conditions under which the mixtures phase separate. The approach
approximates the matrix of second virial coefficients of the mixture by a
random matrix, and determines the stability of the mixture from the spectrum of
such random matrices.Comment: 4 pages, uses RevTeX 4.
Wealth Effects of Banks' Rights to Market and Originate Annuities
We examine wealth effects, for banks and insurers, of bank rights to sell and underwrite annuities. The stock-price reactions to four court and regulatory decisions are consistent with expectations of bank gains at insurers' expense. Cross-sectionally, smaller, riskier insurers with higher distribution costs and substantial annuity business sustain larger wealth losses. Larger, riskier bank holding companies with fee- based and consumer business gain most, consistent with the extension of federal safety-net guarantees as a source of gains. Banking stock-price reactions to the Supreme Court's decision are opposite other findings, possibly reflecting unfulfilled expectations of a broader mandate for expanded bank rights.Annuities, VALIC, financial modernization, deregulation, deposit insurance, Blackfeet National Bank, event studies
Storage and retrieval of vector beams of light in a multiple-degree-of-freedom quantum memory
The full structuration of light in the transverse plane, including intensity,
phase and polarization, holds the promise of unprecedented capabilities for
applications in classical optics as well as in quantum optics and information
sciences. Harnessing special topologies can lead to enhanced focusing, data
multiplexing or advanced sensing and metrology. Here we experimentally
demonstrate the storage of such spatio-polarization-patterned beams into an
optical memory. A set of vectorial vortex modes is generated via liquid crystal
cell with topological charge in the optic axis distribution, and preservation
of the phase and polarization singularities is demonstrated after retrieval, at
the single-photon level. The realized multiple-degree-of-freedom memory can
find applications in classical data processing but also in quantum network
scenarios where structured states have been shown to provide promising
attributes, such as rotational invariance
A Computational Study of the Weak Galerkin Method for Second-Order Elliptic Equations
The weak Galerkin finite element method is a novel numerical method that was
first proposed and analyzed by Wang and Ye for general second order elliptic
problems on triangular meshes. The goal of this paper is to conduct a
computational investigation for the weak Galerkin method for various model
problems with more general finite element partitions. The numerical results
confirm the theory established by Wang and Ye. The results also indicate that
the weak Galerkin method is efficient, robust, and reliable in scientific
computing.Comment: 19 page
Radial glia in the proliferative ventricular zone of the embryonic and adult turtle, Trachemys scripta elegans.
To better understand the role of radial glial (RG) cells in the evolution of the mammalian cerebral cortex, we investigated the role of RG cells in the dorsal cortex and dorsal ventricular ridge of the turtle, Trachemys scripta elegans. Unlike mammals, the glial architecture of adult reptile consists mainly of ependymoradial glia, which share features with mammalian RG cells, and which may contribute to neurogenesis that continues throughout the lifespan of the turtle. To evaluate the morphology and proliferative capacity of ependymoradial glia (here referred to as RG cells) in the dorsal cortex of embryonic and adult turtle, we adapted the cortical electroporation technique, commonly used in rodents, to the turtle telencephalon. Here, we demonstrate the morphological and functional characteristics of RG cells in the developing turtle dorsal cortex. We show that cell division occurs both at the ventricle and away from the ventricle, that RG cells undergo division at the ventricle during neurogenic stages of development, and that mitotic Tbr2+ precursor cells, a hallmark of the mammalian SVZ, are present in the turtle cortex. In the adult turtle, we show that RG cells encompass a morphologically heterogeneous population, particularly in the subpallium where proliferation is most prevalent. One RG subtype is similar to RG cells in the developing mammalian cortex, while 2 other RG subtypes appear to be distinct from those seen in mammal. We propose that the different subtypes of RG cells in the adult turtle perform distinct functions
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