1,994 research outputs found
Solid State Analog for He-McKellar-Wilkens Quantum Phase
In this letter we investigate the quantum dynamics of a quasiparticle in the
presence of a charged screw dislocation submitted to a uniform magnetic field.
Analysing the quantum scattering for this quasiparticle we observed the
appearance of a topological quantum phase in the solution and demonstrate that
this phenomenon is the solid state analog of the He-McKeller-Wilkens effect.Comment: 7 pages, epl styl
Schr\"odinger formalism for a particle constrained to a surface in
In this work it is studied the Schr\"odinger equation for a non-relativistic
particle restricted to move on a surface in a three-dimensional Minkowskian
medium , i.e., the space equipped with the
metric . After establishing the consistency of the
interpretative postulates for the new Schr\"odinger equation, namely the
conservation of probability and the hermiticity of the new Hamiltonian built
out of the Laplacian in , we investigate the confining
potential formalism in the new effective geometry. Like in the well-known
Euclidean case, it is found a geometry-induced potential acting on the dynamics
which, besides
the usual dependence on the mean () and Gaussian () curvatures of the
surface, has the remarkable feature of a dependence on the signature of the
induced metric of the surface: if the signature is ,
and if the signature is . Applications to surfaces of
revolution in are examined, and we provide examples where the
Schr\"odinger equation is exactly solvable. It is hoped that our formalism will
prove useful in the modeling of novel materials such as hyperbolic
metamaterials, which are characterized by a hyperbolic dispersion relation, in
contrast to the usual spherical (elliptic) dispersion typically found in
conventional materials.Comment: 26 pages, 1 figure; comments are welcom
Coupled electronic and morphologic changes in graphene oxide upon electrochemical reduction
Peer reviewedPostprin
The bound state Aharonov-Bohm effect around a cosmic string revisited
In this article we observe that the self-adjoint extension of the Hamiltonian
of a particle moving around a shielded cosmic string gives rise to a
gravitational analogue of the bound state Aharonov-Bohm effect.Comment: 2 pages, no figure
Bound states in the dynamics of a dipole in the presence of a conical defect
In this work we investigate the quantum dynamics of an electric dipole in a
-dimensional conical spacetime. For specific conditions, the
Schr\"odinger equation is solved and bound states are found with the energy
spectrum and eigenfunctions determined. We find that the bound states spectrum
extends from minus infinity to zero with a point of accumulation at zero. This
unphysical result is fixed when a finite radius for the defect is introduced.Comment: 4 page
The self-energy of a charged particle in the presence of a topological defect distribution
In this work we study a charged particle in the presence of both a continuous
distribution of disclinations and a continuous distribution of edge
dislocations in the framework of the geometrical theory of defects. We obtain
the self-energy for a single charge both in the internal and external regions
of either distribution. For both distributions the result outside the defect
distribution is the self-energy that a single charge experiments in the
presence of a single defect.Comment: 12 pages, Revtex4, two figures,to appear in Int. Joun. Mod. Phys.
Electrostatic self-force in (2+1)-dimensional cosmological gravity
Point sources in (2+1)-dimensional gravity are conical singularities that
modify the global curvature of the space giving rise to self-interaction
effects on classical fields. In this work we study the electrostatic
self-interaction of a point charge in the presence of point masses in
(2+1)-dimensional gravity with a cosmological constant.Comment: 9 pages, Late
Distribuição das Esponjas (Porifera) na Reserva Biológica do Atol das Rocas, Nordeste do Brasil
Due to the richness and uniqueness of its fauna, Atol das Rocas harbours the first Marine Biological Reserve in Brazil, but only six species of sponges were previously recorded from the atoll. In the present study the structure of the sponge community in the Biological Reserve of Atol das Rocas is described through quali- and quantitative sampling in 18 collection sites. Thirty-six sponge species from 24 families were found, which summed with previous records makes a total of 39 species now known from the atoll. At least six species are new, and four (Plakortis sp.3, Clathrina sp., Holoxea violacea and Aplysina sp.) are provisionally endemic of Atol das Rocas. Total species diversity and evenness were moderately high (H=2.38, J=0.71), as well as total sponge abundance (14.2 ind.m-2). Spirastrella hartmani (5.4 ind.m-2) and Chondrilla aff. nucula (1.1 ind.m-2) were the most abundant sponge species in the atoll. Highest sponge diversity (H’= 2.13) and density (70.4 ind.m-2) were found at Fenda site, a cryptic environment with low water movement and 7m depth. The lowest diversity (H’= 0.22) and density (1.7 ind.m-2) were found at the shallow (10-30cm depth), exposed tide pools. Atol das Rocas shares several sponge species with Fernando de Noronha (13/39) and with the littoral of Pernambuco (12/39). The degree of endemism of the sponge community observed in the atoll was low (10%) if compared to New Caledonia reef for example (71%), but this number can increase with more collections and refinement of taxonomic studies.Devido à riqueza e à unicidade de sua fauna, o Atol das Rocas abriga a primeira Reserva Biológica Marinha do Brasil, mas apenas seis espécies de esponjas foram registradas anteriormente no local. Neste trabalho é descrita a estrutura da comunidade de Porifera da Reserva Biológica do Atol das Rocas, através de amostragens quali- e quantitativas em 18 estações de coleta. Foram encontradas 36 espécies de 24 famílias, que somadas aos registros anteriores perfazem 39 espécies conhecidas no atol. Provavelmente seis destas espécies são novas, e quatro (Plakortis sp.3, Clathrina sp., Holoxea violacea e Aplysina sp.) são provisoriamente endêmicas para o Atol das Rocas. A diversidade e a equitabilidade das espécies de esponjas foi moderadamente alta (H=2,38, J=0,71), assim como a abundância total de esponjas (14,2 ind.m-2). Spirastrella hartmani (5,4 ind.m-2) e Chondrilla aff. nucula (1,1 ind.m-2) são as espécies de Porifera mais abundantes na área. O local com a maior diversidade (H’= 2,2) e densidade (70,4 ind.m-2) de esponjas foi a Fenda, um ambiente críptico com baixo hidrodinamismo e 7m de profundidade. As Poças de Maré, rasas e expostas à luz e às ondas, apresentaram a menor diversidade (H’= 0,22) e densidade de esponjas (1,7 ind.m-2). O Atol das Rocas possui muitas espécies de esponjas em comum com Fernando de Noronha (13/39) e com o litoral pernambucano (12/39). O grau de endemismo de esponjas verificado no Atol das Rocas foi baixo (10%) quando comparado por exemplo com o Recife da Nova Caledônia (71%), mas esse número pode aumentar com mais coletas e o refinamento dos estudos taxonômicos
Enzymatic Solid-Phase Reactor Based on Silica Organofunctionalized with p-Phenylenediamine for Electrochemical Detection of Phenolic Compounds
A new biomaterial, based on silica organofunctionalized with p-phenylenediamine (p-PDA) and the enzyme peroxidase, was used in the development of an enzymatic solid-phase reactor. The analytical techniques used in the characterization showed that the organic ligand was incorporated into the silica matrix. Thus, the silica modified with p-PDA allowed the incorporation of peroxidase by the electrostatic interaction between the carboxylic groups present in the enzyme molecules and the amino groups attached to the silica. The enzymatic solid-phase reactor was used for chemical oxidation of phenols in 1 4-benzoquinone that was then detected by chronoamperometry. The system allowed the analysis of hydroquinone with a detection limit of 83.6 nmol L −1 . Thus, the new material has potential in the determination of phenolic compounds river water samples
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