27,754 research outputs found
DMRG study of the Bond Alternating \textbf{S}=1/2 Heisenberg ladder with Ferro-Antiferromagnetic couplings
We obtain the phase diagram in the parameter space and an
accurate estimate of the critical line separating the different phases. We show
several measuments of the magnetization, dimerization, nearest neighbours
correlation, and density of energy in the different zones of the phase diagram,
as well as a measurement of the string order parameter proposed as the non
vanishing phase order parameter characterizing Haldane phases. All these
results will be compared in the limit with the behaviour of the
Bond Alternated Heisenberg Chain (BAHC). The analysis of our
data supports the existence of a dimer phase separated by a critical line from
a Haldane one, which has exactly the same nature as the Haldane phase in the
BAHC.Comment: Version 4. 8 pages, 15 figures (12 figures in document
Structure of fish assemblages on coastal rocky shores of the Azores
Bol. Mus. Mun. Funchal, Sup. N.º 6: 127-138, 2001The structure of fish assemblages was investigated from the surface down to 25 m depth on Azorean rocky shores. A total of 57 fish species was recorded by visual censuses, most species (66%) occurring in the whole depth range studied. Fish abundance was dominated by 11 species, mainly sparids, labrids, carangids and pomacentrids, which constituted over 88% of the total number of individuals recorded. The trophic structure of the fish assemblages studied in the Azores was characterized by the dominance of benthic mesocarnivores and high proportions of herbivores and pelagic macrocarnivores.A estrutura das comunidades ictiológicas dos fundos rochosos dos Açores foi estudada desde a superfície até aos 25 m de profundidade. Um total de 57 espécies de peixes foi identificado com recurso a censos visuais. A maioria das espécies (66%) ocorreu em toda a gama de profundidades estudada. A fauna ictiológica era dominada, em termos de abundância, por 11 espécies, principalmente pertencentes às famílias Sparidae, Labridae, Carangidae e Pomacentridae, os quais constituíram mais de 88% do número total de indivíduos observados. A estrutura trófica das comunidades ictiológicas estudadas nos Açores apresentouse dominada por meso-carnívoros bentónicos e proporções elevadas de herbívoros e macro-carnívoros pelágico
Neutral heavy lepton production at next high energy linear colliders
The discovery potential for detecting new heavy Majorana and Dirac neutrinos
at some recently proposed high energy colliders is discussed. These
new particles are suggested by grand unified theories and superstring-inspired
models. For these models the production of a single heavy neutrino is shown to
be more relevant than pair production when comparing cross sections and
neutrino mass ranges.
The process is calculated
including on-shell and off-shell heavy neutrino effects.
We present a detailed study of cross sections and distributions that shows a
clear separation between the signal and standard model contributions, even
after including hadronization effects.Comment: 4 pages including 15 figures, 1 table. RevTex. Accepted in Physical
Review
Bifurcations in the theory of current transfer to cathodes of dc discharges and observations of transitions between different modes
General scenarios of transitions between different spot patterns on
electrodes of dc gas discharges and their relation to bifurcations of
steady-state solutions are analyzed. In the case of cathodes of arc discharges,
it is shown that any transition between different modes of current transfer is
related to a bifurcation of steady-state solutions. In particular, transitions
between diffuse and spot modes on axially symmetric cathodes, frequently
observed in the experiment, represent an indication of the presence of
pitchfork or fold bifurcations of steady-state solutions. Experimental
observations of transitions on cathodes of dc glow microdischarges are analyzed
and those potentially related to bifurcations of steady-state solutions are
identified. The relevant bifurcations are investigated numerically and the
computed patterns are found to conform to those observed in the course of the
corresponding transitions in the experiment
MUTAÇÕES NA REGIÃO AMINOTERMINAL DO GENE COL1A2 E A MANIFESTAÇÃO DA OSTEOGÊNESE IMPERFEITA 2011
A Osteogênese Imperfeita (OI) é uma doença genética associada a alterações na molécula do colágeno tipo I. Caracteriza-se clinicamente por fragilidade e deformidade ósseas. A grande maioria dos casos relatados são alterações autossômicas dominantes nos genes COL1A1 e COL1A2, codificadores da molécula do colágeno tipo I. Entretanto, existem casos isolados e há relatos de herança autossômica recessiva da OI, fazendo da OI um grupo clinicamente e geneticamente heterogêneo. A diversidade clínica e genética apresentada pelos pacientes com OI evidencia a necessidade de estudos moleculares dos genes associados à OI. Essa pesquisa tem como objetivo caracterizar o padrão de mutações da região aminoterminal do gene COL1A2 em pacientes com OI. Foram estudados os exons 1 a 26 em 33 pacientes não aparentados com OI de Vitória-ES por PCR-SSCP e sequenciamento. Foi observada uma alteração no padrão de bandas de DNA, localizada no fragmento do exon 16 do gene COL1A2 na amostra de um paciente do sexo feminino com quadro clínico moderado de OI. O sequenciamento dessa amostra permitiu a identificação da alteração, c.739 G>C, uma substituição nucleotídica (p.Gly247Arg) com descrição clínica distinta de um relato prévio na literatura portador da mesma alteração genética. As diferenças observadas justificam o desenvolvimento de pesquisas nos genes associados à formação e maturação da molécula do colágeno tipo I. Os resultados dessa pesquisa poderão contribuir com o entendimento clínico da doença, e, consequentemente, auxiliar no desenvolvimento de tratamentos mais adequados aos pacientes.
Palavras-chave
Thermal entanglement witness for materials with variable local spin lengths
We show that the thermal entanglement in a spin system using only magnetic
susceptibility measurements is restricted to the insulator materials. We
develop a generalization of the thermal entanglement witness that allows us to
get information about the system entanglement with variable local spin lengths
that can be used experimentally in conductor or insulator materials. As an
application, we study thermal entanglement for the half-filled Hubbard model
for linear, square and cubic clusters. We note that it is the itinerancy of
electrons that favors the entanglement. Our results suggest a weak dependence
between entanglement and external spin freedom degrees.Comment: 4 pages, 3 figure
- …