434 research outputs found
Impurity and boundary effects in one and two-dimensional inhomogeneous Heisenberg antiferromagnets
We calculate the ground-state energy of one and two-dimensional spatially
inhomogeneous antiferromagnetic Heisenberg models for spins 1/2, 1, 3/2 and 2.
Our calculations become possible as a consequence of the recent formulation of
density-functional theory for Heisenberg models. The method is similar to
spin-density-functional theory, but employs a local-density-type approximation
designed specifically for the Heisenberg model, allowing us to explore
parameter regimes that are hard to access by traditional methods, and to
consider complications that are important specifically for nanomagnetic
devices, such as the effects of impurities, finite-size, and boundary geometry,
in chains, ladders, and higher-dimensional systems.Comment: 4 pages, 4 figures, accepted by Phys. Rev.
The Case Against Commodity Agreements
Depth sensing nano-indentation investigations have been performed to determine the radial dependence of the hardness through the cross section of a Fe-based bulk glassy rod. We have found the hardness of the material decreases along radius from the center to the outermost surface. This phenomenon is attributed to the ‘cooling rate induced surface softening’. Furthermore, a significant change (~15 %) in elastic modulus is noticed along the radius as well. QC 20120906Hero-
With mouse age comes wisdom : a review and suggestions of relevant mouse models for age-related conditions
Ageing is a complex multifactorial process that results in many changes in physiological changes processes that ultimately increase susceptibility to a wide range of diseases. As such an ageing population is resulting in a pressing need for more and improved treatments across an assortment of diseases. Such treatments can come from a better understanding of the pathogenic pathways which, in turn, can be derived from models of disease. Therefore the more closely the model resembles the disease situation the more likely relevant the data will be that is generated from them. Here we review the state of knowledge of mouse models of a range of diseases and aspects of an ageing physiology that are all germane to ageing. We also give recommendations on the most common mouse models on their relevance to the clinical situations occurring in aged patients and look forward as to how research in ageing models can be carried out. As we continue to elucidate the pathophysiology of disease, often through mouse models, we also learn what is needed to refine these models. Such factors can include better models, reflecting the ageing patient population, or a better phenotypic understanding of existing models
The impact of Basic Fibroblast Growth Factor on Photoreceptor function and morphology
To assess the impact of basic fibroblast growth factor (bFGF) on photoreceptor function and morphology.
METHODS:
Impact was assessed in two models. In one, the endogenous expression of bFGF in photoreceptors was raised by sectioning one optic nerve of rats 3 to 4 weeks before study. In the other, bFGF was injected into the vitreous chamber in rats and cats. Retinal function was assessed from the electroretinogram (ERG), and retinal morphology was studied using DNA dyes, immunolabeling, and in situ hybridization.
RESULTS:
In both models of bFGF upregulation, the ERG b-wave was suppressed over a wide stimulus range and in light- and dark-adapted conditions. The a-wave was not suppressed by either procedure and at the brightest intensities was enhanced by both procedures. In nerve-sectioned eyes, outer retina appeared normal histologically, but levels of bFGF protein in the inner and outer nuclear layers were raised, whereas bFGF mRNA levels remained unchanged. In both models, levels of synaptophysin in the outer plexiform layer and of cytochrome oxidase in inner segments were raised in association with increases in bFGF protein levels.
CONCLUSIONS:
bFGF increased the ability of photoreceptors to respond to light but attenuated the transmission of this response to inner retinal cells, presumably by blocking the photoreceptor-bipolar synapse. If the expression of bFGF protein is upregulated in human photoreceptor dystrophies, it may contribute a reversible component to the loss of vision. The relationship between these actions of bFGF and its ability to protect photoreceptors from stress remains to be established
Continuous slice functional calculus in quaternionic Hilbert spaces
The aim of this work is to define a continuous functional calculus in
quaternionic Hilbert spaces, starting from basic issues regarding the notion of
spherical spectrum of a normal operator. As properties of the spherical
spectrum suggest, the class of continuous functions to consider in this setting
is the one of slice quaternionic functions. Slice functions generalize the
concept of slice regular function, which comprises power series with
quaternionic coefficients on one side and that can be seen as an effective
generalization to quaternions of holomorphic functions of one complex variable.
The notion of slice function allows to introduce suitable classes of real,
complex and quaternionic --algebras and to define, on each of these
--algebras, a functional calculus for quaternionic normal operators. In
particular, we establish several versions of the spectral map theorem. Some of
the results are proved also for unbounded operators. However, the mentioned
continuous functional calculi are defined only for bounded normal operators.
Some comments on the physical significance of our work are included.Comment: 71 pages, some references added. Accepted for publication in Reviews
in Mathematical Physic
Numerical and experimental analysis of municipal solid wastes gasification process
As the quantity of municipal solid waste (MSW) increases with economic growth,
problems arise in regard to sustainable management solutions. Thermal treatment
presents a valid option for reducing the amounts of post-recycling waste to be
landfilled. Incineration technology, besides reducing the total volume of waste and
making use of the chemical energy in MSW for power generation, has negative
environmental impact from high emission of pollutants. Recent policy to tackle climate
change and resources conservation stimulated the development of renewable energy and
landfill diversion technology, thereby giving gasification technology development
renewed importance. In this work a two-dimensional CFD model for MSW gasification
was developed and an Eulerian-Eulerian approach was used to describe the transport of
mass, momentum and energy for the solid and gas phases. This model is validated using
experimental data from the literature. The numerical results obtained are in good
agreement with the reported experimental results
Aspects of noncommutative Lorentzian geometry for globally hyperbolic spacetimes
Connes' functional formula of the Riemannian distance is generalized to the
Lorentzian case using the so-called Lorentzian distance, the d'Alembert
operator and the causal functions of a globally hyperbolic spacetime. As a step
of the presented machinery, a proof of the almost-everywhere smoothness of the
Lorentzian distance considered as a function of one of the two arguments is
given. Afterwards, using a -algebra approach, the spacetime causal
structure and the Lorentzian distance are generalized into noncommutative
structures giving rise to a Lorentzian version of part of Connes'
noncommutative geometry. The generalized noncommutative spacetime consists of a
direct set of Hilbert spaces and a related class of -algebras of
operators. In each algebra a convex cone made of self-adjoint elements is
selected which generalizes the class of causal functions. The generalized
events, called {\em loci}, are realized as the elements of the inductive limit
of the spaces of the algebraic states on the -algebras. A partial-ordering
relation between pairs of loci generalizes the causal order relation in
spacetime. A generalized Lorentz distance of loci is defined by means of a
class of densely-defined operators which play the r\^ole of a Lorentzian
metric. Specializing back the formalism to the usual globally hyperbolic
spacetime, it is found that compactly-supported probability measures give rise
to a non-pointwise extension of the concept of events.Comment: 43 pages, structure of the paper changed and presentation strongly
improved, references added, minor typos corrected, title changed, accepted
for publication in Reviews in Mathematical Physic
Wightman Functions' Behaviour on the Event Horizon of an Extremal Reissner-Nordstr\"om Black Hole
A weaker Haag, Narnhofer and Stein prescription as well as a weaker Hessling
Quantum Equivalence Principle for the behaviour of thermal Wightman functions
on an event horizon are analysed in the case of an extremal
Reissner-Nordstr\"{o}m black hole in the limit of a large mass. In order to
avoid the degeneracy of the metric in the stationary coordinates on the
horizon, a method is introduced which employs the invariant length of geodesics
which pass the horizon. First the method is checked for a massless scalar field
on the event horizon of the Rindler wedge, extending the original procedure of
Haag, Narnhofer and Stein onto the {\em whole horizon} and recovering the same
results found by Hessling. Afterwards the HNS prescription and Hessling's
prescription for a massless scalar field are analysed on the whole horizon of
an extremal Reissner-Nordstr\"{o}m black hole in the limit of a large mass. It
is proved that the weak form of the HNS prescription is satisfyed for all the
finite values of the temperature of the KMS states, i.e., this principle does
not determine any Hawking temperature. It is found that the
Reissner-Nordstr\"{o}m vacuum, i.e., does satisfy the weak HNS
prescription and it is the only state which satisfies weak Hessling's
prescription, too. Finally, it is suggested that all the previously obtained
results should be valid dropping the requirements of a massless field and of a
large mass black hole.Comment: 27 pages, standard LaTex, no figures, final version containing the
results following from Hessling's principle as they appeared in the other
paper gr-qc/9510016, minor changes in the text and in references, it will
appear on Class. Quant. Gra
Life Span Extension by Calorie Restriction Depends on Rim15 and Transcription Factors Downstream of Ras/PKA, Tor, and Sch9
Calorie restriction (CR), the only non-genetic intervention known to slow aging and extend life span in organisms ranging from yeast to mice, has been linked to the down-regulation of Tor, Akt, and Ras signaling. In this study, we demonstrate that the serine/threonine kinase Rim15 is required for yeast chronological life span extension caused by deficiencies in Ras2, Tor1, and Sch9, and by calorie restriction. Deletion of stress resistance transcription factors Gis1 and Msn2/4, which are positively regulated by Rim15, also caused a major although not complete reversion of the effect of calorie restriction on life span. The deletion of both RAS2 and the Akt and S6 kinase homolog SCH9 in combination with calorie restriction caused a remarkable 10-fold life span extension, which, surprisingly, was only partially reversed by the lack of Rim15. These results indicate that the Ras/cAMP/PKA/Rim15/Msn2/4 and the Tor/Sch9/Rim15/Gis1 pathways are major mediators of the calorie restriction-dependent stress resistance and life span extension, although additional mediators are involved. Notably, the anti-aging effect caused by the inactivation of both pathways is much more potent than that caused by CR
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