The Labusch Parameter of a Driven Flux Line Lattice in YBa2_2Cu3_3O7_7 Superconducting Films

We have investigated the influence of a driving force on the elastic coupling (Labusch parameter) of the field-cooled state of the flux line lattice (FLL) in 400 nm thick YBa$_2$Cu$_3$O$_7$ superconducting films. We found that the FLL of a field-cooled state without driving forces is not in an equilibrium state. Results obtained for magnetic fields applied at $0^\circ$ and 30$^\circ$ relative to CuO$_2$ planes, show an enhancement of the elastic coupling of the films at driving current densities several orders of magnitude smaller than the critical one. Our results indicate that the FLL appears to be in a relatively ordered, metastable state after field cooling without driving forces.Comment: 4 Figure

Escape of mass in zero-range processes with random rates

We consider zero-range processes in ${\mathbb{Z}}^d$ with site dependent jump rates. The rate for a particle jump from site $x$ to $y$ in ${\mathbb{Z}}^d$ is given by $\lambda_xg(k)p(y-x)$, where $p(\cdot)$ is a probability in ${\mathbb{Z}}^d$, $g(k)$ is a bounded nondecreasing function of the number $k$ of particles in $x$ and $\lambda =\{\lambda_x\}$ is a collection of i.i.d. random variables with values in $(c,1]$, for some $c>0$. For almost every realization of the environment $\lambda$ the zero-range process has product invariant measures $\{{\nu_{\lambda, v}}:0\le v\le c\}$ parametrized by $v$, the average total jump rate from any given site. The density of a measure, defined by the asymptotic average number of particles per site, is an increasing function of $v$. There exists a product invariant measure ${\nu _{\lambda, c}}$, with maximal density. Let $\mu$ be a probability measure concentrating mass on configurations whose number of particles at site $x$ grows less than exponentially with $\|x\|$. Denoting by $S_{\lambda}(t)$ the semigroup of the process, we prove that all weak limits of $\{\mu S_{\lambda}(t),t\ge 0\}$ as $t\to \infty$ are dominated, in the natural partial order, by ${\nu_{\lambda, c}}$. In particular, if $\mu$ dominates ${\nu _{\lambda, c}}$, then $\mu S_{\lambda}(t)$ converges to ${\nu_{\lambda, c}}$. The result is particularly striking when the maximal density is finite and the initial measure has a density above the maximal.Comment: Published at http://dx.doi.org/10.1214/074921707000000300 in the IMS Lecture Notes Monograph Series (http://www.imstat.org/publications/lecnotes.htm) by the Institute of Mathematical Statistics (http://www.imstat.org

On the nature of bias and defects in the software specification process

Implementation bias in a specification is an arbitrary constraint in the solution space. This paper describes the problem of bias. Additionally, this paper presents a model of the specification and design processes describing individual subprocesses in terms of precision/detail diagrams and a model of bias in multi-attribute software specifications. While studying how bias is introduced into a specification we realized that software defects and bias are dual problems of a single phenomenon. This was used to explain the large proportion of faults found during the coding phase at the Software Engineering Laboratory at NASA/GSFC

Ultra-Compact Dwarfs around NGC 3268

We present radial velocities (from Gemini/GMOS) of the second sample of ultra-compact dwarfs (UCDs) and bright globular clusters (GCs) in the Antlia cluster. Twenty-three objects are located around the giant elliptical NGC 3268, and one is close to the fainter lenticular NGC 3273. Together with previously found UCDs around NGC 3258 a total of 35 UCDs and bright GCs has been now identified in the Antlia cluster. Their colours and magnitudes are compared with those of the nuclei of dE,N galaxies already confirmed as Antlia members. For a subsample that lie on ACS images and are brighter than M_V = -9 mag, the effective radii (R_eff) have been measured, the maximum radius being approximately 10 pc. In addition to the radial velocity sample, we find 10 objects in the magnitude range corresponding to GCs but with 10 < R_eff < 17 pc, resembling the so-called `extended clusters'. By number and magnitude, the new UCDs fit to the GC luminosity function, supporting their interpretation as bright GCs. Additionally, we use a tracer mass estimator to calculate the mass enclosed up to ~47 kpc from NGC 3268, which results in 2.7 x 10^12 M_o.Comment: 10 pages, 5 figures, to be published in MNRA

Tidal Disruption of White Dwarfs from Ultra-close Encounters with Intermediate-mass Spinning Black Holes

We present numerical relativity results of tidal disruptions of white dwarfs from ultra-close encounters with a spinning, intermediate-mass black hole (IMBH). These encounters require a full general relativistic treatment of gravity. We show that the disruption process and prompt accretion of the debris strongly depend on the magnitude and orientation of the black hole (BH) spin. However, the late-time accretion onto the BH follows the same decay, Ṁ ∝ t^(-5/3), estimated from Newtonian gravity disruption studies. We compute the spectrum of the disk formed from the fallback material using a slim disk model. The disk spectrum peaks in the soft X-rays and sustains Eddington luminosity for 1-3 yr after the disruption. For arbitrary BH spin orientations, the disrupted material is scattered away from the orbital plane by relativistic frame dragging, which often leads to obscuration of the inner fallback disk by the outflowing debris. The disruption events also yield bursts of gravitational radiation with characteristic frequencies of ~3.2 Hz and strain amplitudes of ~10^(–18) for galactic IMBHs. The optimistic rate of considered ultra-close disruptions is consistent with no sources found in the ROSAT all-sky survey. Future missions like Wide-Field X-ray Telescope could observe dozens of events

On the use of the Bingham statistical distribution in microsphere-based constitutive models for arterial tissue

Constitutive models for arterial tissue have been an active research field during the last years. The main micro-constituents of blood vessels are different types of cells and the extra-cellular matrix formed by an isotropic high water content ground substance and a network composed of elastin and collagen fibres. Usually the arterial tissue has been modelled as a hyperelastic material within the framework of continuum mechanics, whereas inclusion of structural tensors into constitutive laws is the most widely used technique to introduce the anisotropy induced by the fibres. Though the different existing fibre bundles present a clear preferential direction, the dispersion inherent to biological tissue advices using of constitutive models including representative structural information associated to the spatial probabilistic distribution of the fibres. Lately, microsphere-based models have demonstrated to be a powerful tool to incorporate this information. The fibre dispersion is incorporated by means of an Orientation Density Function (ODF) that weights the contribution of each fibre in each direction of the micro-sphere. In previous works the rotationally symmetric von Mises ODF was successfully applied to the modelling of blood vessels. In this study, the inclusion of the Bingham ODF into microsphere-based model is analysed. This ODF exhibits some advantages with respect to the von Mises one, like a greater versatility and a comparable response to simple tension and equibiaxial tension tests.Peer ReviewedPostprint (author's final draft