Superconducting thin rings with finite penetration depth

Recently Babaei Brojeny and Clem [Phys. Rev. B 68, 174514 (2003)] considered superconducting thin-film rings in perpendicular magnetic fields in the ideal Meissner state with negligibly small magnetic penetration depth and presented useful analytical limiting expressions and numerical results for the magnetic-field and sheet-current profiles, trapped magnetic flux, self-inductance, magnetic moment, and focusing of magnetic flux into the hole when no net current flows in the ring. The present paper generalizes all these results to rings with arbitrary values of the two-dimensional effective penetration depth \Lambda = \lambda^2 /d (\lambda is the London depth and d < \lambda/2 the film thickness) using a straightforward matrix inversion method. We also present results for the energy of a superconducting ring as a function of the applied magnetic induction B_a and the quantum number N defining the size of the fluxoid N \phi_0 trapped in the hole.Comment: with 19 figures, gives 11.5 page

Topological Defect Densities in Type-I Superconducting Phase Transitions

We examine the consequences of a cubic term addition to the mean-field potential of Ginzburg-Landau theory to describe first order superconductive phase transitions. Constraints on its existence are obtained from experiment, which are used to assess its impact on topological defect creation. We find no fundamental changes in either the Kibble-Zurek or Hindmarsh-Rajantie predictions.Comment: Revtex4, 1 eps figure, 6 pages. Change in title and in sections II and III so to broaden the scope of the paper. Additional author is include

A dual point description of mesoscopic superconductors

We present an analysis of the magnetic response of a mesoscopic superconductor, i.e. a system of sizes comparable to the coherence length and to the London penetration depth. Our approach is based on special properties of the two dimensional Ginzburg-Landau equations, satisfied at the dual point $(\kappa = \frac{1}{\sqrt{2}}).$ Closed expressions for the free energy and the magnetization of the superconductor are derived. A perturbative analysis in the vicinity of the dual point allows us to take into account vortex interactions, using a new scaling result for the free energy. In order to characterize the vortex/current interactions, we study vortex configurations that are out of thermodynamical equilibrium. Our predictions agree with the results of recent experiments performed on mesoscopic aluminium disks.Comment: revtex, 20 pages, 9 figure

Connecting Numerical Relativity and Data Analysis of Gravitational Wave Detectors

Gravitational waves deliver information in exquisite detail about astrophysical phenomena, among them the collision of two black holes, a system completely invisible to the eyes of electromagnetic telescopes. Models that predict gravitational wave signals from likely sources are crucial for the success of this endeavor. Modeling binary black hole sources of gravitational radiation requires solving the Eintein equations of General Relativity using powerful computer hardware and sophisticated numerical algorithms. This proceeding presents where we are in understanding ground-based gravitational waves resulting from the merger of black holes and the implications of these sources for the advent of gravitational-wave astronomy.Comment: Appeared in the Proceedings of 2014 Sant Cugat Forum on Astrophysics. Astrophysics and Space Science Proceedings, ed. C.Sopuerta (Berlin: Springer-Verlag

Eutectic colony formation: A phase field study

Eutectic two-phase cells, also known as eutectic colonies, are commonly observed during the solidification of ternary alloys when the composition is close to a binary eutectic valley. In analogy with the solidification cells formed in dilute binary alloys, colony formation is triggered by a morphological instability of a macroscopically planar eutectic solidification front due to the rejection by both solid phases of a ternary impurity that diffuses in the liquid. Here we develop a phase-field model of a binary eutectic with a dilute ternary impurity and we investigate by dynamical simulations both the initial linear regime of this instability, and the subsequent highly nonlinear evolution of the interface that leads to fully developed two-phase cells with a spacing much larger than the lamellar spacing. We find a good overall agreement with our recent linear stability analysis [M. Plapp and A. Karma, Phys. Rev. E 60, 6865 (1999)], which predicts a destabilization of the front by long-wavelength modes that may be stationary or oscillatory. A fine comparison, however, reveals that the assumption commonly attributed to Cahn that lamella grow perpendicular to the envelope of the solidification front is weakly violated in the phase-field simulations. We show that, even though weak, this violation has an important quantitative effect on the stability properties of the eutectic front. We also investigate the dynamics of fully developed colonies and find that the large-scale envelope of the composite eutectic front does not converge to a steady state, but exhibits cell elimination and tip-splitting events up to the largest times simulated.Comment: 18 pages, 18 EPS figures, RevTeX twocolumn, submitted to Phys. Rev.

Structural and doping effects in the half-metallic double perovskite A2A_2CrWO6_6

he structural, transport, magnetic and optical properties of the double perovskite $A_2$CrWO$_6$ with $A=\text{Sr, Ba, Ca}$ have been studied. By varying the alkaline earth ion on the $A$ site, the influence of steric effects on the Curie temperature $T_C$ and the saturation magnetization has been determined. A maximum $T_C=458$ K was found for Sr$_2$CrWO$_6$ having an almost undistorted perovskite structure with a tolerance factor $f\simeq 1$. For Ca$_2$CrWO$_6$ and Ba$_2$CrWO$_6$ structural changes result in a strong reduction of $T_C$. Our study strongly suggests that for the double perovskites in general an optimum $T_C$ is achieved only for $f \simeq 1$, that is, for an undistorted perovskite structure. Electron doping in Sr$_2$CrWO$_6$ by a partial substitution of Sr$^{2+}$ by La$^{3+}$ was found to reduce both $T_C$ and the saturation magnetization $M_s$. The reduction of $M_s$ could be attributed both to band structure effects and the Cr/W antisites induced by doping. Band structure calculations for Sr$_2$CrWO$_6$ predict an energy gap in the spin-up band, but a finite density of states for the spin-down band. The predictions of the band structure calculation are consistent with our optical measurements. Our experimental results support the presence of a kinetic energy driven mechanism in $A_2$CrWO$_6$, where ferromagnetism is stabilized by a hybridization of states of the nonmagnetic W-site positioned in between the high spin Cr-sites.Comment: 14 pages, 10 figure

Associations between dimensions of anorexia nervosa and obsessive–compulsive disorder: An examination of personality and psychological factors in patients with anorexia nervosa

Objective: Anorexia nervosa (AN) and obsessive–compulsive disorder (OCD) are highly comorbid. However, the factors that account for this comorbidity are poorly understood. We examined the core dimensions of AN and OCD and psychological and personality factors shared by both disorders. Method: In path analyses (N = 732 women with either current AN or recovered from AN), we examined which factors were uniquely and independently associated with the core dimensions of AN and OCD. We also examined recovery from AN as a moderator. Results: When individuals with AN reported greater concern over mistakes, they endorsed more severity in both AN and OCD core dimensions. These unique associations existed above and beyond all other transdiagnostic personality and psychological factors and regardless of AN recovery status. Conclusions: Concern over mistakes partially accounts for severity in the core dimensions of both AN and OCD. Concern over mistakes may represent an important target in the aetiology of AN and OCD

Observation of hard scattering in photoproduction events with a large rapidity gap at HERA

Events with a large rapidity gap and total transverse energy greater than 5 GeV have been observed in quasi-real photoproduction at HERA with the ZEUS detector. The distribution of these events as a function of the $\gamma p$ centre of mass energy is consistent with diffractive scattering. For total transverse energies above 12 GeV, the hadronic final states show predominantly a two-jet structure with each jet having a transverse energy greater than 4 GeV. For the two-jet events, little energy flow is found outside the jets. This observation is consistent with the hard scattering of a quasi-real photon with a colourless object in the proton.Comment: 19 pages, latex, 4 figures appended as uuencoded fil

Measurement of the B0-anti-B0-Oscillation Frequency with Inclusive Dilepton Events

The $B^0$-$\bar B^0$ oscillation frequency has been measured with a sample of 23 million \B\bar B pairs collected with the BABAR detector at the PEP-II asymmetric B Factory at SLAC. In this sample, we select events in which both B mesons decay semileptonically and use the charge of the leptons to identify the flavor of each B meson. A simultaneous fit to the decay time difference distributions for opposite- and same-sign dilepton events gives $\Delta m_d = 0.493 \pm 0.012{(stat)}\pm 0.009{(syst)}$ ps$^{-1}$.Comment: 7 pages, 1 figure, submitted to Physical Review Letter