Separation of wind sea and swell from nearshore ocean wave spectra

Coexistence of wind sea and swell often results in double-peaked spectra. Separation and identification of the wave energies of wind sea and swell from the measured spectra allow us to have a more realistic description of the sea state, which is of great importance to offshore structure design, safety of marine operation, and the study of wind wave dynamics. This paper describes a method based on the peak frequency of a steepness function to separate the wave energies of wind sea and swell from the omnidirectional wave spectra. Using the PM spectral model for the wind sea spectrum, the separation frequency is derived from the peak frequency of the steepness function. This steepness method does not rely on the availability of the information of wind velocities and wave directions and can be easily implemented for operational uses. Verification results using wave data collected of Seoguipo in Korea are presented

Determination of the parity of the pentaquark baryons : Theta^+ and Xi_5

We study determination of the parity of the pentaquark baryons in two different processes. First, we investigate the Theta^+ production via the vec{p} vec{p} -> Sigma^+ Theta^+ reaction process which was proposed to determine unambiguously the parity of Theta^+. We observe the clear differences in the total cross sections and the spin observable A_{xx}. As for the Xi_5 in the bar{K} N -> K Xi_5 reaction process, the total cross section for the positive parity presents about one hundred times lager than that of the negative one due to the huge destructive interference.Comment: 5 pages, 8 figures, Talk given at International Workshop on BARYONS04, Ecole polytechnique, Paris, France, 25-29 Oct 200

Geometrical barriers and lower critical field in MgB2 single crystals

International audienceThe first penetration field sHpd has been deduced from local magnetization and specific heat measurements in magnesium diboride single crystals. For Ha ic, the geometrical barriers (GB) play a dominant role in the irreversibility mechanism. In thin samples, neglecting the GB in this direction would then lead to a large overestimation of Hc1 deduced from Hp through the standard elliptical formula. The lower critical field is found to be isotropic at low temperature (0.11±0.01 T)

Glide and Superclimb of Dislocations in Solid 4^4He

Glide and climb of quantum dislocations under finite external stress, variation of chemical potential and bias (geometrical slanting) in Peierls potential are studied by Monte Carlo simulations of the effective string model. We treat on unified ground quantum effects at finite temperatures $T$. Climb at low $T$ is assisted by superflow along dislocation core -- {\it superclimb}. Above some critical stress avalanche-type creation of kinks is found. It is characterized by hysteretic behavior at low $T$. At finite biases gliding dislocation remains rough even at lowest $T$ -- the behavior opposite to non-slanted dislocations. In contrast to glide, superclimb is characterized by quantum smooth state at low temperatures even for finite bias. In some intermediate $T$-range giant values of the compressibility as well as non-Luttinger type behavior of the core superfluid are observed.Comment: Updated version submitted to JLTP as QFS2010 proceedings; 11 pages, 6 figure

The Transition to a Giant Vortex Phase in a Fast Rotating Bose-Einstein Condensate

We study the Gross-Pitaevskii (GP) energy functional for a fast rotating Bose-Einstein condensate on the unit disc in two dimensions. Writing the coupling parameter as 1 / \eps^2 we consider the asymptotic regime \eps \to 0 with the angular velocity $\Omega$ proportional to (\eps^2|\log\eps|)^{-1} . We prove that if \Omega = \Omega_0 (\eps^2|\log\eps|)^{-1} and $\Omega_0 > 2(3\pi)^{-1}$ then a minimizer of the GP energy functional has no zeros in an annulus at the boundary of the disc that contains the bulk of the mass. The vorticity resides in a complementary `hole' around the center where the density is vanishingly small. Moreover, we prove a lower bound to the ground state energy that matches, up to small errors, the upper bound obtained from an optimal giant vortex trial function, and also that the winding number of a GP minimizer around the disc is in accord with the phase of this trial function.Comment: 52 pages, PDFLaTex. Minor corrections, sign convention modified. To be published in Commun. Math. Phy

Dilute Bose gas in two dimensions: Density expansions and the Gross-Pitaevskii equation

A dilute two-dimensional (2D) Bose gas at zero temperature is studied by the method developed earlier by the authors. Low density expansions are derived for the chemical potential, ground state energy, kinetic and interaction energies. The expansion parameter is found to be a dimensionless in-medium scattering amplitude u obeying the equation 1/u+\ln u=-\ln(na^2\pi)-2\gamma, where na^2 and \gamma are the gas parameter and the Euler constant, respectively. It is shown that the ground state energy is mostly kinetic in the low density limit; this result does not depend on a specific form of the pairwise interaction potential, contrary to 3D case. A new form of 2D Gross-Pitaevskii equation is proposed within our scheme.Comment: 4 pages, REVTeX, no figure

Search for β+\beta^+EC and ECEC processes in 112^{112}Sn and β−β−\beta^-\beta^- decay of 124^{124}Sn to the excited states of 124^{124}Te

Limits on $\beta^+$EC and ECEC processes in $^{112}$Sn and on $\beta^-\beta^-$ decay of $^{124}$Sn to the excited states of $^{124}$Te have been obtained using a 380 cm$^3$ HPGe detector and an external source consisting of natural tin. A limit with 90% C.L. on the $^{112}$Sn half-life of $0.92\times 10^{20}$ y for the ECEC(0$\nu$) transition to the $0^+_3$ excited state in $^{112}$Cd (1871.0 keV) has been established. This transition is discussed in the context of a possible enhancement of the decay rate by several orders of magnitude given that the ECEC$(0\nu)$ process is nearly degenerate with an excited state in the daughter nuclide. Prospects for investigating such a process in future experiments are discussed. The $\beta^-\beta^-$ decay limits for $^{124}$Sn to the excited states of $^{124}$Te were obtained on the level of $(0.8-1.2)\times 10^{21}$ y at the 90% C.L.Comment: 17 pages, 5 figure

Effect of disorder in MgB2 thin films

We report on scanning tunneling spectroscopy studies of magnesium diboride (MgB2) thin films grown by different techniques. The films have critical temperatures ranging between 28 and 41 K with very different upper critical fields. We find that the superconducting gap associated with the sigma band decreases almost linearly with decreasing critical temperature while the gap associated with the pi band is only very weakly affected in the range of critical temperatures above 30 K. In the sample with the lowest critical temperature (28 K) we observe a small increase of the pi gap that can only be explained in terms of an increase in the interband scattering. The tunneling data was analyzed in the framework of the two-band model. The magnetic-field-dependent tunneling spectra and the upper critical field measurements of these disordered samples can be consistently explained in terms of an increase of disorder that mostly affects the pi band in samples with reduced critical temperatures

Photoproduction of Theta baryon from the neutron

We study photoproduction reactions for Theta^+, which was recently observed as a candidate of an exotic five quark state uudd(bar s). We employ effective lagrangian interactions in the linear and non-linear formalism of chiral symmetry and investigate two cases of spin and parity of Theta^+, J^P = 1/2^+ and 1/2^-. We calculate cross sections and discuss possibilities to discriminate one from the other.Comment: 14 pages, 19 figure

Anisotropic Superparamagnetism of Monodispersive Cobalt-Platinum Nanocrystals

Based on the high-temperature organometallic route (Sun et al. Science 287, 1989 (2000)), we have synthesized powders containing CoPt_3 single crystals with mean diameters of 3.3(2) nm and 6.0(2) nm and small log-normal widths sigma=0.15(1). In the entire temperature range from 5 K to 400 K, the zero-field cooled susceptibility chi(T) displays significant deviations from ideal superparamagnetism. Approaching the Curie temperature of 450(10) K, the deviations arise from the (mean-field) type reduction of the ferromagnetic moments, while below the blocking temperature T_b, chi(T) is suppressed by the presence of energy barriers, the distributions of which scale with the particle volumes obtained from transmission electron microscopy (TEM). This indication for volume anisotropy is supported by scaling analyses of the shape of the magnetic absorption chi''(T,omega) which reveal distribution functions for the barriers being also consistent with the volume distributions observed by TEM. Above 200 K, the magnetization isotherms M(H,T) display Langevin behavior providing 2.5(1) mu_B per CoPt_3 in agreement with reports on bulk and thin film CoPt_3. The non-Langevin shape of the magnetization curves at lower temperatures is for the first time interpreted as anisotropic superparamagnetism by taking into account an anisotropy energy of the nanoparticles E_A(T). Using the magnitude and temperature variation of E_A(T), the mean energy barriers and 'unphysical' small switching times of the particles obtained from the analyses of chi''(T,omega) are explained. Below T_b hysteresis loops appear and are quantitatively described by a blocking model, which also ignores particle interactions, but takes the size distributions from TEM and the conventional field dependence of E_A into account.Comment: 12 pages with 10 figures and 1 table. Version accepted for publication in Phys. Rev. B . Two-column layou