Dynamics and thermodynamics in spinor quantum gases

We discuss magnetism in spinor quantum gases theoretically and experimentally with emphasis on temporal dynamics of the spinor order parameter in the presence of an external magnetic field. In a simple coupled Gross-Pitaevskii picture we observe a dramatic suppression of spin dynamics due to quadratic Zeeman ''dephasing''. In view of an inhomogeneous density profile of the trapped condensate we present evidence of spatial variations of spin dynamics. In addition we study spinor quantum gases as a model system for thermodynamics of Bose-Einstein condensation. As a particular example we present measurements on condensate magnetisation due to the interaction with a thermal bath.Comment: 8 pages, 7 figure

Epithelial Migration and Non-adhesive Periderm Are Required for Digit Separation during Mammalian Development.

The fusion of digits or toes, syndactyly, can be part of complex syndromes, including van der Woude syndrome. A subset of van der Woude cases is caused by dominant-negative mutations in the epithelial transcription factor Grainyhead like-3 (GRHL3), and Grhl3-/-mice have soft-tissue syndactyly. Although impaired interdigital cell death of mesenchymal cells causes syndactyly in multiple genetic mutants, Grhl3-/- embryos had normal interdigital cell death, suggesting alternative mechanisms for syndactyly. We found that in digit separation, the overlying epidermis forms a migrating interdigital epithelial tongue (IET) when the epithelium invaginates to separate the digits. Normally, the non-adhesive surface periderm allows the IET to bifurcate as the digits separate. In contrast, in Grhl3-/- embryos, the IET moves normally between the digits but fails to bifurcate because of abnormal adhesion of the periderm. Our study identifies epidermal developmental processes required for digit separation

An empirical comparison of convertible bond valuation models

This paper empirically compares three convertible bond valuation models. We use an innovative approach where all model parameters are estimated by the Marquardt algorithm using a subsample of convertible bond prices. The model parameters are then used for out-of-sample forecasts of convertible bond prices. The mean absolute deviation is 1.86% for the Ayache-Forsyth-Vetzal model, 1.94% for the Tsiveriotis-Fernandes model, and 3.73% for the Brennan-Schwartz model. For this and other measures of fit, the Ayache-Forsyth-Vetzal and Tsiveriotis-Fernandes models outperform the Brennan-Schwartz model

Applicability of the Broken-Bond Rule to the Surface Energy of the fcc Metals

We apply the Green's function based full-potential screened Korringa-Kohn-Rostoker method in conjunction with the local density approximation to study the surface energies of the noble and the fcc transition and $sp$ metals. The orientation dependence of the transition metal surface energies can be well described taking into account only the broken bonds between first neighbors, quite analogous to the behavior we recently found for the noble metals [see cond-mat/0105207]. The (111) and (100) surfaces of the $sp$ metals show a jellium like behavior but for the more open surfaces we find again the noble metals behavior but with larger deviation from the broken-bond rule compared to the transition metals. Finally we show that the use of the full potential is crucial to obtain accurate surface energy anisotropy ratios for the vicinal surfaces.Comment: 13 pages, 5 figures, to appear in July in Surface Science Vol. 511,1 (2002

Tweaking the spin-wave dispersion and suppressing the incommensurate phase in LiNiPO4 by iron substitution

Elastic and inelastic neutron scattering studies of Li(Ni$_{1-x}$Fe$_{x}$)PO$_4$ single crystals reveal anomalous spin-wave dispersions along the crystallographic direction parallel to the characteristic wave vector of the magnetic incommensurate phase. The anomalous spin-wave dispersion ({\it magnetic soft mode}) indicates the instability of the Ising-like ground state that eventually evolves into the incommensurate phase as the temperature is raised. The pure LiNiPO$_4$ system ($x=0$), undergoes a first-order magnetic phase transition from a long-range incommensurate phase to an antiferromagnetic ground state at {\it T}$_N$ = 20.8 K. At 20% Fe concentrations, although the AFM ground state is to a large extent preserved as that of the pure system, the phase transition is second-order, and the incommensurate phase is completely suppressed. Analysis of the dispersion curves using a Heisenberg spin Hamiltonian that includes inter- and in-plane nearest and next-nearest neighbor couplings reveals frustration due to strong competing interactions between nearest- and a next-nearest neighbor site, consistent with the observed incommensurate structure. The Fe substitution only slightly lowers the extent of the frustration, sufficient to suppress the IC phase. An energy gap in the dispersion curves gradually decreases with the increase of Fe content from $\sim$2 meV for the pure system ($x=0$) to $\sim$0.9 meV for $x=0.2$

Bar fraction in lenticular galaxies: dependence on luminosity and environment

We present a study of bars in lenticular galaxies based on a sample of 371 galaxies from the SDSS-DR 7 and 2MASS in optical and near-infrared bands, respectively. We found a bar in 15% of the lenticular galaxies in our sample, which is consistent with recent studies. The barred galaxy fraction shows a luminosity dependence, with faint lenticular galaxies (MK > -24.5, total absolute magnitude in K band) having a larger fraction of bars than bright lenticular galaxies (MK < -24.5). A similar trend is seen when Mr = -21.5, the total absolute magnitude in SDSS r band is used to divide the sample into faint and bright lenticular galaxies. We find that faint galaxies in clusters show a higher bar fraction than their counterparts in the field. This suggests that the formation of bars in lenticular galaxies not only depends on the total luminosity of galaxy but also on the environment of the host galaxy.Comment: Accepted for publication in MNRAS: Letters, 5 pages, 4 figure

White Light Interferometry for Quantitative Surface Characterization in Ion Sputtering Experiments

White light interferometry (WLI) can be used to obtain surface morphology information on dimensional scale of millimeters with lateral resolution as good as ~1 {\mu}m and depth resolution down to 1 nm. By performing true three-dimensional imaging of sample surfaces, the WLI technique enables accurate quantitative characterization of the geometry of surface features and compares favorably to scanning electron and atomic force microscopies by avoiding some of their drawbacks. In this paper, results of using the WLI imaging technique to characterize the products of ion sputtering experiments are reported. With a few figures, several example applications of the WLI method are illustrated when used for (i) sputtering yield measurements and time-to-depth conversion, (ii) optimizing ion beam current density profiles, the shapes of sputtered craters, and multiple ion beam superposition and (iii) quantitative characterization of surfaces processed with ions. In particular, for sputter depth profiling experiments of 25Mg, 44Ca and 53Cr ion implants in Si (implantation energy of 1 keV per nucleon), the depth calibration of the measured depth profile curves determined by the WLI method appeared to be self-consistent with TRIM simulations for such projectile-matrix systems. In addition, high depth resolution of the WLI method is demonstrated for a case of a Genesis solar wind Si collector surface processed by gas cluster ion beam: a 12.5 nm layer was removed from the processed surface, while the transition length between the processed and untreated areas was 150 {\mu}m.Comment: Applied Surface Science, accepted: 7 pages and 8 figure

Development of a tight-binding potential for bcc-Zr. Application to the study of vibrational properties

We present a tight-binding potential based on the moment expansion of the density of states, which includes up to the fifth moment. The potential is fitted to bcc and hcp Zr and it is applied to the computation of vibrational properties of bcc-Zr. In particular, we compute the isothermal elastic constants in the temperature range 1200K < T < 2000K by means of standard Monte Carlo simulation techniques. The agreement with experimental results is satisfactory, especially in the case of the stability of the lattice with respect to the shear associated with C'. However, the temperature decrease of the Cauchy pressure is not reproduced. The T=0K phonon frequencies of bcc-Zr are also computed. The potential predicts several instabilities of the bcc structure, and a crossing of the longitudinal and transverse modes in the (001) direction. This is in agreement with recent ab initio calculations in Sc, Ti, Hf, and La.Comment: 14 pages, 6 tables, 4 figures, revtex; the kinetic term of the isothermal elastic constants has been corrected (Eq. (4.1), Table VI and Figure 4

Low-dimensional Bose gases

We present an improved many-body T-matrix theory for partially Bose-Einstein condensed atomic gases by treating the phase fluctuations exactly. The resulting mean-field theory is valid in arbitrary dimensions and able to describe the low-temperature crossover between three, two and one-dimensional Bose gases. When applied to a degenerate two-dimensional atomic hydrogen gas, we obtain a reduction of the three-body recombination rate which compares favorably with experiment. Supplementing the mean-field theory with a renormalization-group approach to treat the critical fluctuations, we also incorporate into the theory the Kosterlitz-Thouless transition that occurs in a homogeneous Bose gas in two dimensions. In particular, we calculate the critical conditions for the Kosterlitz-Thouless phase transition as a function of the microscopic parameters of the theory. The proposed theory is further applied to a trapped one-dimensional Bose gas, where we find good agreement with exact numerical results obtained by solving a nonlinear Langevin field equation.Comment: 14 pages, 13 figures, revte

Highly anisotropic Bose-Einstein condensates: crossover to lower dimensionality

We develop a simple analytical model based on a variational method to explain the properties of trapped cylindrically symmetric Bose-Einstein condensates (BEC) of varying degrees of anisotropy well into regimes of effective one dimension (1D) and effective two dimension (2D). Our results are accurate in regimes where the Thomas-Fermi approximation breaks down and they are shown to be in agreement with recent experimental data.Comment: 4 pages, 2 figures; significantly more new material added; title and author-list changed due to changes in conten