164,757 research outputs found

    Nonuniversal Effects in the Homogeneous Bose Gas

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    Effective field theory predicts that the leading nonuniversal effects in the homogeneous Bose gas arise from the effective range for S-wave scattering and from an effective three-body contact interaction. We calculate the leading nonuniversal contributions to the energy density and condensate fraction and compare the predictions with results from diffusion Monte Carlo calculations by Giorgini, Boronat, and Casulleras. We give a crude determination of the strength of the three-body contact interaction for various model potentials. Accurate determinations could be obtained from diffusion Monte Carlo calculations of the energy density with higher statistics.Comment: 24 pages, RevTex, 5 ps figures, included with epsf.te

    On the extension of 2- polynomials

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    Let XX be a three dimensional real Banach space. Ben\'itez and Otero \cite {BeO} showed that if the unit ball of XX is is an intersection of two ellipsoids, then every 2-polynomial defined in a linear subspace of XX can be extended to XX preserving the norm. In this article, we extend this result to any finite dimensional Banach space

    A remark on contraction semigroups on Banach spaces

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    Let XX be a complex Banach space and let J:XXJ:X \to X^* be a duality section on XX (i.e. x,J(x)=J(x)x=J(x)2=x2\langle x,J(x)\rangle=\|J(x)\|\|x\|=\|J(x)\|^2=\|x\|^2). For any unit vector xx and any (C0C_0) contraction semigroup T={etA:t0}T=\{e^{tA}:t \geq 0\}, Goldstein proved that if XX is a Hilbert space and if T(t)x,J(x)1|\langle T(t) x,J(x)\rangle| \to 1 as tt \to \infty, then xx is an eigenvector of AA corresponding to a purely imaginary eigenvalue. In this article, we prove the similar result holds if XX is a strictly convex complex Banach space

    Joint Vertex Degrees in an Inhomogeneous Random Graph Model

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    In a random graph, counts for the number of vertices with given degrees will typically be dependent. We show via a multivariate normal and a Poisson process approximation that, for graphs which have independent edges, with a possibly inhomogeneous distribution, only when the degrees are large can we reasonably approximate the joint counts as independent. The proofs are based on Stein's method and the Stein-Chen method with a new size-biased coupling for such inhomogeneous random graphs, and hence bounds on distributional distance are obtained. Finally we illustrate that apparent (pseudo-) power-law type behaviour can arise in such inhomogeneous networks despite not actually following a power-law degree distribution.Comment: 30 pages, 9 figure

    Quantum Transport Calculations Using Periodic Boundary Conditions

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    An efficient new method is presented to calculate the quantum transports using periodic boundary conditions. This method allows the use of conventional ground state ab initio programs without big changes. The computational effort is only a few times of a normal ground state calculation, thus it makes accurate quantum transport calculations for large systems possible.Comment: 9 pages, 6 figure

    On the dispersion management of fluorite whispering-gallery mode resonators for Kerr optical frequency comb generation in the telecom and mid-infrared range

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    Optical whispering gallery mode (WGM) resonators have been very attracting platforms for versatile Kerr frequency comb generations. We report a systematic study on the material dispersion of various optical materials that are capable of supporting quality factors above 10910^9. Using an analytical approximation of WGM resonant frequencies in disk resonators, we investigate the effect of the geometry and transverse mode order on the total group-velocity dispersion (GVDGVD). We demonstrate that the major radii and the radial mode indices play an important role in tailoring the GVDGVD of WGM resonators. In particular, our study shows that in WGM disk-resonators, the polar families of modes have very similar GVDGVD, while the radial families of modes feature dispersion values that can differ by up to several orders of magnitude. The effect of these giant dispersion shifts are experimentally evidenced in Kerr comb generation with magnesium fluoride. From a more general perspective, this critical feature enables to push the zero-dispersion wavelength of fluorite crystals towards the mid-infrared (mid-IR) range, thereby allowing for efficient Kerr comb generation in that spectral range. We show that barium fluoride is the most interesting crystal in this regard, due to its zero dispersion wavelength (ZDWZDW) at 1.93μm1.93 \rm{\mu m} and an optimal dispersion profile in the mid-IR regime. We expect our results to facilitate the design of different platforms for Kerr frequency comb generations in both telecommunication and mid-IR spectral ranges
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