2,109 research outputs found
Superconductivity as a Bose-Einstein condensation?
Bose-Einstein condensation (BEC) in two dimensions (2D) (e.g., to describe
the quasi-2D cuprates) is suggested as the possible mechanism widely believed
to underlie superconductivity in general. A crucial role is played by nonzero
center-of-mass momentum Cooper pairs (CPs) usually neglected in BCS theory.
Also vital is the unique {\it linear} dispersion relation appropriate to
weakly-coupled "bosonic" CPs moving in the Fermi sea--rather than in vacuum
where the dispersion would be quadratic but only for very strong coupling, and
for which BEC is known to be impossible in 2D.Comment: 6 pages included 3 figure
Harmonically Trapped Quantum Gases
We solve the problem of a Bose or Fermi gas in -dimensions trapped by mutually perpendicular harmonic oscillator potentials. From the
grand potential we derive their thermodynamic functions (internal energy,
specific heat, etc.) as well as a generalized density of states. The Bose gas
exhibits Bose-Einstein condensation at a nonzero critical temperature
if and only if , and a jump in the specific heat at if and
only if . Specific heats for both gas types precisely coincide as
functions of temperature when . The trapped system behaves like an
ideal free quantum gas in dimensions. For we recover
all known thermodynamic properties of ideal quantum gases in dimensions,
while in 3D for 1, 2 and 3 one simulates behavior reminiscent of
quantum {\it wells, wires}and{\it dots}, respectively.Comment: 14 pages including 3 figures and 3 table
Water Absorption By Cork
A study of liquid water absorption by cork was carried out in which the anisotropy of cork was taken into account. The changes with time of the mass, volume, and linear dimensions were measured for different orientations of the sections in cork exposed to liquid water at room temperature (20 C) and at 90-100 C. Two regimes of water absorption were identified, namely, a period involving dimensional change and a period with only mass change. Diffusion coefficients at both temperatures were estimated using a special technique. There is a small anisotropy with a faster diffusion in the radial direction. Diffusion coefficients at 90 C are two orders of magnitude larger than at room temperature. Water absorption in the cell walls causes the expansion of cork, which (for the boiled specimens tested) is slightly smaller in the radial direction. The volume increase is proportional to the mass increase and ceases after relatively short immersion times. At this stage, the cell walls are apparently saturated with water. Further immersion results in penetration of water into the cells. The kinetics of absorption is rather slow at long times, but eventually the cells become full of water, the density increases above that of water, and the cork sinks
Filling holes under non-linear constraints
Publisher Copyright:
© 2023, The Author(s).In this paper we handle the problem of filling the hole in the graphic of a surface by means of a patch that joins the original surface with C1-smoothness and fulfills an additional non-linear geometrical constraint regarding its area or its mean curvature at some points. Furthermore, we develop a technique to estimate the optimum area that the filling patch is expected to have that will allow us to determine optimum filling patches by means of a system of linear and quadratic equations. We present several numerical and graphical examples showing the effectiveness of the proposed method.publishersversionpublishe
Avaliação de métodos de enxertia para a gravioleira em Viçosa-MG.
Visando obter informações sobre tĂ©cnicas de enxertia em gravioleira (Annoma muricata L.), foram avaliados, neste trabalho, nove mĂ©todos de enxertia: garfagem Ă inglesa simples com e sem parafina; garfagem Ă inglesa com entalhe com e sem parafina; garfagem no topo em fenda cheia com e sem parafina; borbulhia em placa; borbulhia em janela aberta e borbulhia em T invertido. Os mĂ©todos de garfagem Ă inglesa simples e de garfagem no topo em fenda cheia, ambos com e sem parafinados, apresentaram maiores Ăndices no pegamento e brotamento do enxerto. Apesar de nĂŁo diferirem entre si, os mĂ©todos com uso de grafos parafinados podem ser recomendados por proporcionarem menor custo na produção de mudas enxertadas de graviola.Edição do XI Congresso Brasileiro de Fruticultura
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