5,366 research outputs found
Quantum radiation in a plane cavity with moving mirrors
We consider the electromagnetic vacuum field inside a perfect plane cavity
with moving mirrors, in the nonrelativistic approximation. We show that low
frequency photons are generated in pairs that satisfy simple properties
associated to the plane geometry. We calculate the photon generation rates for
each polarization as functions of the mechanical frequency by two independent
methods: on one hand from the analysis of the boundary conditions for moving
mirrors and with the aid of Green functions; and on the other hand by an
effective Hamiltonian approach. The angular and frequency spectra are discrete,
and emission rates for each allowed angular direction are obtained. We discuss
the dependence of the generation rates on the cavity length and show that the
effect is enhanced for short cavity lengths. We also compute the dissipative
force on the moving mirrors and show that it is related to the total radiated
energy as predicted by energy conservation.Comment: 17 pages, 1 figure, published in Physical Review
Asymptotic enumeration of incidence matrices
We discuss the problem of counting {\em incidence matrices}, i.e. zero-one
matrices with no zero rows or columns. Using different approaches we give three
different proofs for the leading asymptotics for the number of matrices with
ones as . We also give refined results for the asymptotic
number of incidence matrices with ones.Comment: jpconf style files. Presented at the conference "Counting Complexity:
An international workshop on statistical mechanics and combinatorics." In
celebration of Prof. Tony Guttmann's 60th birthda
Parabolic dunes in north-eastern Brazil
In this work we present measurements of vegetation cover over parabolic dunes
with different degree of activation along the north-eastern Brazilian coast. We
are able to extend the local values of the vegetation cover density to the
whole dune by correlating measurements with the gray-scale levels of a high
resolution satellite image of the dune field. The empirical vegetation
distribution is finally used to validate the results of a recent continuous
model of dune motion coupling sand erosion and vegetation growth.Comment: 18 pages, 14 figures, aubmitted to Geomorpholog
Mitochondrial Uncoupling Proteins In Mammals And Plants
Uncoupling proteins (UCPs) belong to a distinct cluster of the mitochondrial anion carrier family. Up to five different uncoupling protein types were found in mitochondria of mammals and plants, and recently in fishes, fungi and protozoa. They exhibit a significantly conserved structure with several motifs specific to either the whole cluster or protein type. Uncoupling proteins, as well as the whole mitochondrial anion carrier gene family, probably emerged in evolution before the separation of animal, fungi, and plant kingdoms and originate from an anion/nucleotide or anion/anion transporter ancestor. Mammalian UCP1, UCP2, UCP3, and plant uncoupling proteins pUCP1 and pUCP2 are similar and seem to form one subgroup, whereas UCP4 and BMCP1 belong to a different group. Molecular, biochemical, and phylogenic data suggest that UCP2 could be considered as an UCP-prototype. UCP1 plays its biological role mainly in the non-shivering thermogenesis while the role of the other types is unknown. However, hypotheses have suggested that they are involved in the general balance of basic energy expenditure, protection from reactive oxygen species, and, in plants, in fruit ripening and seed ontogeny.212201212Kuan, J., Saier M.H., Jr., (1993) Res. Microbiol., 144, pp. 671-672Kuan, J., Saier M.H., Jr., (1993) Crit. Rev. Biochem. Mol. Biol., 28, pp. 209-233El Moualij, B., Duyckaerts, C., Lamotte-Brasseur, J., Sluse, F.E., (1997) Yeast, 13, pp. 573-581Palmieri, F., Indiveri, C., Bisaccia, F., Krämer, R., (1993) J. Bioenerg. Biomembr., 25, pp. 525-535Ježek, P., Garlid, K.D., (1990) J. Biol. Chem., 265, pp. 19303-19311Ricquier, D., Kader, J.-C., (1976) Biochem. Biophys. Res. 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The mathematical description of the electrosynthesis of composites of oxy-hydroxycompounds cobalt with polypyrrole overooxidazed
The electrosynthesis of the composite with of the overoxidized polypyrrole with cobalt oxy-hydroxide in strongly acidic media has been described mathematically, using linear stability theory and bifurcation analysis. The steadystates stability conditions and oscillatory and monotonic instability requirements have been described too. The system´s behavior was compared with behavior of other systems with overoxidation, electropolymerization of heterocyclic compounds and electrosynthesis of the cobalt oxy-hydroxides
Clinical Usefulness of Streptococcus pneumoniae Urinary Antigen in Patients Hospitalized with Non-Nosocomial Pneumonia
Introduction : Community acquired pneumonia (CAP) is a major cause of hospital admissions and mortality in developed countries. Nevertheless, in about half of the cases a microbial etiology can`t be determined. The need to improve the diagnostic tools of this disease has led to the development of new techniques, such as Streptococcus pneumoniae urinary antigen. Objectives : To analyse the usefulness of the urinary antigen in determining the etiologic diagnosis of pneumonias and its influence in the antibiotherapy modification. Methods : Retrospective analysis of hospitalized patients in 2010 with CAP (n=226) and healthcare associated pneumonia (HCAP) [n=64] diagnosis whose urinary pneumococcal antigen has been analyzed. Results: Median age was significantly greater in HCAP. HCAP patients had more co-morbidities and higher severity scores. Twenty-one patients in the CAP group and 4 patients in the HCAP group had positive pneumococcal antigen. The sensibility of urinary antigen in determining pneumococcal pneumonias was 36% and the specificity 89%. Almost one quarter of the 25 patients with positive urinary antigen had appropriate reductions in antimicrobial spectra, which was not statistically significant when compared with the group with negative urinary antigen. There was a significant relation between a positive urinary antigen and pneumonia severity. Conclusions: Considering its high specificity, the urinary antigen is useful to confirm the presence of pneumococcal pneumonia.
Potentially urinary antigen can help to avoid unnecessary treatments in hospitalized patients with CAP
Inertial forces in the Casimir effect with two moving plates
We combine linear response theory and dimensional regularization in order to
derive the dynamical Casimir force in the low frequency regime. We consider two
parallel plates moving along the normal direction in dimensional space. We
assume the free-space values for the mass of each plate to be known, and obtain
finite, separation-dependent mass corrections resulting from the combined
effect of the two plates. The global mass correction is proportional to the
static Casimir energy, in agreement with Einstein's law of equivalence between
mass and energy for stressed rigid bodies.Comment: 9 pages, 1 figure; title and abstract changed; to appear in Physical
Review
Dynamic model of gene regulation for the lac operon
Gene regulatory network is a collection of DNA which interact with each other and with other matter in the cell. The lac operon is an example of a relatively simple genetic network and is one of the best-studied structures in the Escherichia coli bacteria. In this work we consider a deterministic model of the lac operon with a noise term, representing the stochastic nature of the regulation. The model is written in terms of a system of simultaneous first order differential equations with delays. We investigate an analytical and numerical solution and analyse the range of values for the parameters corresponding to a stable solution
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