Phase diagram of the vortex system in layered superconductors with strong columnar pinning

We present the results of a detailed investigation of the low-temperature properties of the vortex system in strongly anisotropic layered superconductors with a random array of columnar pinning centers. Our method involves numerical minimization of a free energy functional in terms of the time-averaged local vortex density. It yields the detailed vortex density distribution for all local free-energy minima, and therefore allows the computation of any desired correlation function of the time-averaged local vortex density. Results for the phase diagram in the temperature vs. pin concentration plane at constant magnetic induction are presented. We confirm that for very low pin concentrations, the low-temperature phase is a Bragg glass, which melts into an interstitial liquid phase via two first-order steps, separated by a Bose glass phase. At higher concentrations, however, the low-temperature phase is a Bose glass, and the melting transition becomes continuous. The transition is then characterized by the onset of percolation of liquid-like regions across the sample. Inhomogeneous local melting of the Bose glass is found to occur. There is also a depinning crossover between the interstitial liquid and a completely unpinned liquid at higher temperatures. At sufficiently large pin concentrations, the depinning line merges with the Bose glass to interstitial liquid transition. Many of the features we find have been observed experimentally and in simulations. We discuss the implications of our results for future experimental and theoretical work.Comment: 15 pages including Figure

The phase diagram of vortex matter in layered superconductors with tilted columnar pinning centers

We study the vortex matter phase diagram of a layered superconductor in the presence of columnar pinning defects, {\it tilted} with respect to the normal to the layers. We use numerical minimization of the free energy written as a functional of the time averaged vortex density of the Ramakrishnan-Yussouff form, supplemented by the appropriate pinning potential. We study the case where the pin density is smaller than the areal vortex density. At lower pin concentrations, we find, for temperatures of the order of the melting temperature of the unpinned lattice, a Bose glass type phase which at lower temperatures converts, via a first order transition, to a Bragg glass, while, at higher temperatures, it crosses over to an interstitial liquid. At somewhat higher concentrations, no transition to a Bragg glass is found even at the lowest temperatures studied. While qualitatively the behavior we find is similar to that obtained using the same procedures for columnar pins normal to the layers, there are important and observable quantitative differences, which we discuss.Comment: 12 pages, including figure

The role of binaries in the enrichment of the early Galactic halo. I. r-process-enhanced metal-poor stars

The detailed chemical composition of most metal-poor halo stars has been found to be highly uniform, but a minority of stars exhibit dramatic enhancements in their abundances of heavy neutron-capture elements and/or of carbon. The key question for Galactic chemical evolution models is whether these peculiarities reflect the composition of the natal clouds, or if they are due to later mass transfer of processed material from a binary companion. If the former case applies, the observed excess of certain elements was implanted within selected clouds in the early ISM from a production site at interstellar distances. Our aim is to determine the frequency and orbital properties of binaries among these chemically peculiar stars. This information provides the basis for deciding whether mass transfer from a binary companion is necessary and sufficient to explain their unusual compositions. This paper discusses our study of a sample of 17 moderately (r-I) and highly (r-II) r-process-element enhanced VMP and EMP stars. High-resolution, low signal-to-noise spectra of the stars were obtained at roughly monthly intervals over 8 years with the FIES spectrograph at the Nordic Optical Telescope. From these spectra, radial velocities with an accuracy of ~100 m/s were determined by cross-correlation against an optimized template. 14 of the programme stars exhibit no significant RV variation over this period, while 3 are binaries with orbits of typical eccentricity for their periods, resulting in a normal binary frequency of ~18+-6% for the sample. Our results confirm our preliminary conclusion from 2011, based on partial data, that the chemical peculiarity of the r-I and r-II stars is not caused by any putative binary companions. Instead, it was imprinted on the natal molecular clouds of these stars by an external, distant source. Models of the ISM in early galaxies should account for such mechanisms.Comment: 14 pages, 3 figures, accepted for publication in Astronomy and Astrophysic

Mobile application platform heterogeneity: Android vs Windows phone vs iOS vs Firefox OS

Modern smartphones have a rich spectrum of increasingly sophisticated features, opening opportunities for software-led innovation. Of the large number of platforms to develop new software on, in this paper we look closely at three platforms identified as market leaders for the smartphone market by Gartner Group in 2013 and one platform, Firefox OS, representing a new paradigm for operating systems based on web technologies. We compare the platforms in several different categories, such as software architecture, application development, platform capabilities and constraints, and, finally, developer support. Using the implementation of a mobile version of the tic-tac-toe game on all the four platforms, we seek to investigate strengths, weaknesses and challenges of mobile application development on these platforms. Big differences are highlighted when inspecting community environments, hardware abilities and platform maturity. These inevitably impact upon developer choices when deciding on mobile platform development strategies

Every Cloud Has a Push Data Lining: Incorporating Cloud Services in a Context-Aware Application

We investigated context-awareness by utilising multiple sources of context in a mobile device setting. In our experiment we developed a system consisting of a mobile client, running on the Android platform, integrated with a cloud-based service. These components were integrated using pushmessaging technology.One of the key featureswas the automatic adaptation of smartphones in accordance with implicit user needs. The novelty of our approach consists in the use of multiple sources of context input to the system, which included the use of calendar data and web based user configuration tool, as well as that of an external, cloud-based, configuration file storing user interface preferences which, pushed at log-on time irrespective of access device, frees the user from having to manually configure its interface.The systemwas evaluated via two rounds of user evaluations (n = 50 users), the feedback of which was generally positive and demonstrated the viability of using cloud-based services to provide an enhanced context-aware user experience

North Atlantic Deep Water Formation

Various studies concerning differing aspects of the North Atlantic are presented. The three major topics under which the works are classified include: (1) oceanography; (2) paleoclimate; and (3) ocean, ice and climate modeling

The effect of schooling and ability on achievement test scores

This paper develops two methods for estimating the effect of schooling on achievement test scores that control for endogeneity of schooling by postulating that both schooling and test scores are generated by a common unobserved latent ability. These methods are applied to data on schooling and test scores. Estimates from the two methods are in close agreement. We find that the effects of schooling on test scores are roughly linear across schooling levels. The effects of schooling on measured test scores are slightly larger for lower latent ability levels. We find that schooling increases the AFQT score on average between 2 and 4 percentage points, roughly twice as large as the effect claimed by Herrnstein and Murray (1994) but in agreement with estimates produced by Neal and Johnson (1996) and Winship and Korenman (1997). We extend the previous literature by estimating the impact of schooling on measured test scores at various quantiles of the latent ability distribution.Education; ability; latent variables; selection; MCMC

An exact formalism to study the thermodynamic properties of hard-sphere systems under spherical confinement

This paper presents a modified grand canonical ensemble which provides a new simple and efficient scheme to study few-body fluid-like inhomogeneous systems under confinement. The new formalism is implemented to investigate the exact thermodynamic properties of a hard sphere (HS) fluid-like system with up to three particles confined in a spherical cavity. In addition, the partition function of this system was used to analyze the surface thermodynamic properties of the many-HS system and to derive the exact curvature dependence of both the surface tension and adsorption in powers of the density. The expressions for the surface tension and the adsorption were also obtained for the many- HS system outside of a fixed hard spherical object. We used these results to derive the dependence of the fluid-substrate Tolman length up to first order in density.Comment: 6 figures. The paper includes new exact results about hard spheres fluid-like system

Eighth-order phase-field-crystal model for two-dimensional crystallization

We present a derivation of the recently proposed eighth order phase field crystal model [Jaatinen et al., Phys. Rev. E 80, 031602 (2009)] for the crystallization of a solid from an undercooled melt. The model is used to study the planar growth of a two dimensional hexagonal crystal, and the results are compared against similar results from dynamical density functional theory of Marconi and Tarazona, as well as other phase field crystal models. We find that among the phase field crystal models studied, the eighth order fitting scheme gives results in good agreement with the density functional theory for both static and dynamic properties, suggesting it is an accurate and computationally efficient approximation to the density functional theory