EvoL: The new Padova T-SPH parallel code for cosmological simulations - I. Basic code: gravity and hydrodynamics

We present EvoL, the new release of the Padova N-body code for cosmological simulations of galaxy formation and evolution. In this paper, the basic Tree + SPH code is presented and analysed, together with an overview on the software architectures. EvoL is a flexible parallel Fortran95 code, specifically designed for simulations of cosmological structure formation on cluster, galactic and sub-galactic scales. EvoL is a fully Lagrangian self-adaptive code, based on the classical Oct-tree and on the Smoothed Particle Hydrodynamics algorithm. It includes special features such as adaptive softening lengths with correcting extra-terms, and modern formulations of SPH and artificial viscosity. It is designed to be run in parallel on multiple CPUs to optimize the performance and save computational time. We describe the code in detail, and present the results of a number of standard hydrodynamical tests.Comment: 33 pages, 49 figures, accepted on A&

Practical theories for service life prediction of critical aerospace structural components

A new second-order theory was developed for predicting the service lives of aerospace structural components. The predictions based on this new theory were compared with those based on the Ko first-order theory and the classical theory of service life predictions. The new theory gives very accurate service life predictions. An equivalent constant-amplitude stress cycle method was proposed for representing the random load spectrum for crack growth calculations. This method predicts the most conservative service life. The proposed use of minimum detectable crack size, instead of proof load established crack size as an initial crack size for crack growth calculations, could give a more realistic service life

Integrity in the fresh produce supply chain: solutions and approaches to an emerging issue

Food fraud is the misrepresentation of food in terms of labelling or documentation. The fresh produce supply chain is global with fresh produce grown many thousands of miles from the point of purchase and consumption. Long supply and complex fresh produce supply chains provide opportunity for fraudulent activity to occur especially further processing or re-packing of products to mask opaque practice and non-compliant behaviour. Price premiums for products designated as ‘high-value’, for example, organic produce, produce of particular provenance, or geographical production area provides motivation for less scrupulous actors to present for sale, produce that is mislabelled or misrepresented. People integrity as well as data, product and process integrity are gaining wider attention in the horticultural sector. Types of fraud critiqued in this review paper include mislabelling, substitution or misrepresentation of origin (country or regional location), method of production (organic or conventional) or incorrect varietal declaration. These challenges and the existing and emerging technologies that are both used within a quality assurance programme and alternatively used by regulators when investigating potential instances of fraudulent behaviour are considered. New methodological solutions and approaches are emerging and suc techniques will develop rapidly to meet the growing challenge of fraud and to ensure consumer trust in the industry is maintained especially as types of food fraud evolve and become more sophisticated

Employer Perceptions of Online Degrees: A Literature Review

This literature review explores the research about the perception of online degrees by potential employers or “gatekeepers” in comparison with those earned in a traditional format. This is important because these perceptions can affect the employment opportunities or lack thereof of students and, in turn, institutions

Tests of Spurious Transport in Smoothed Particle Hydrodynamics

We have performed a series of systematic tests to evaluate the effects of spurious transport in three-dimensional smoothed particle hydrodynamics (SPH) calculations. Our tests investigate (i) particle diffusion, (ii) shock heating, (iii) numerical viscosity, and (iv) angular momentum transport. The results are useful for quantifying the accuracy of the SPH scheme, especially for problems where shear flows or shocks are present, as well as for problems where true hydrodynamic mixing is relevant. We examine the different forms of artificial viscosity (AV) which have been proposed by Monaghan, by Hernquist & Katz, and by Balsara. For each form, our tests suggest a single set of values for the AV parameters $\alpha$ and $\beta$ (coefficients of the linear and quadratic terms) which are appropriate in a large number of situations. We also discuss how these parameters should be adjusted depending on the goals of the particular application. We find that both the Hernquist & Katz and Balsara forms introduce relatively small amounts of numerical viscosity. Furthermore, both Monaghan's and Balsara's AV do well at treating shocks and at limiting the amount of spurious mixing. For these reasons, we endorse the Balsara AV for use in a broad range of applications.Comment: 49 pages, 26 figures as 30 postscript files, submitted to The Journal of Computational Physic

The X-ray Ridge Surrounding Sgr A* at the Galactic Center

We present the first detailed simulation of the interaction between the supernova explosion that produced Sgr A East and the wind-swept inner ~ 2-pc region at the Galactic center. The passage of the supernova ejecta through this medium produces an X-ray ridge ~ 9'' to 15'' to the NE of the supermassive black hole Sagittarius A* (Sgr A*). We show that the morphology and X-ray intensity of this feature match very well with recently obtained Chandra images, and we infer a supernova remnant age of less than 2,000 years. This young age--a factor 3--4 lower than previous estimates--arises from our inclusion of stellar wind effects in the initial (pre-explosion) conditions in the medium. The supernova does not clear out the central ~ 0.2-pc region around Sgr~A* and does not significantly alter the accretion rate onto the central black hole upon passage through the Galactic center.Comment: 10 pages, 3 figures, submitted to ApJ

Composition Mixing during Blue Straggler Formation and Evolution

We use smoothed-particle hydrodynamics to examine differences between direct collisions of single stars and binary star mergers in their roles as possible blue straggler star formation mechanisms. We find in all cases that core helium in the progenitor stars is largely retained in the core of the remnant, almost independent of the type of interaction or the central concentration of the progenitor stars. We have also modelled the subsequent evolution of the hydrostatic remnants, including mass loss and energy input from the hydrodynamical interaction. The combination of the hydrodynamical and hydrostatic models enables us to predict that little mixing will occur during the merger of two globular cluster stars of equal mass. In contrast to the results of Proctor Sills, Bailyn, & Demarque (1995), we find that neither completely mixed nor unmixed models can match the absolute colors of observed blue stragglers in NGC 6397 at all luminosity levels. We also find that the color distribution is probably the crucial test for explanations of BSS formation - if stellar collisions or mergers are the correct mechanisms, a large fraction of the lifetime of the straggler must be spent away from the main sequence. This constraint appears to rule out the possibility of completely mixed models. For NGC 6397, unmixed models predict blue straggler lifetimes ranging from about 0.1 to 4 Gyr, while completely mixed models predict a range from about 0.6 to 4 Gyr.Comment: AASTeX, 28 pg., accepted for ApJ, also available at http://ucowww.ucsc.edu/~erics/bspaper.htm

Equilibrium Configurations of Strongly Magnetized Neutron Stars with Realistic Equations of State

We investigate equilibrium sequences of magnetized rotating stars with four kinds of realistic equations of state (EOSs) of SLy (Douchin et al.), FPS (Pandharipande et al.), Shen (Shen et al.), and LS (Lattimer & Swesty). Employing the Tomimura-Eriguchi scheme to construct the equilibrium configurations. we study the basic physical properties of the sequences in the framework of Newton gravity. In addition we newly take into account a general relativistic effect to the magnetized rotating configurations. With these computations, we find that the properties of the Newtonian magnetized stars, e.g., structure of magnetic field, highly depends on the EOSs. The toroidal magnetic fields concentrate rather near the surface for Shen and LS EOSs than those for SLy and FPS EOSs. The poloidal fields are also affected by the toroidal configurations. Paying attention to the stiffness of the EOSs, we analyze this tendency in detail. In the general relativistic stars, we find that the difference due to the EOSs becomes small because all the employed EOSs become sufficiently stiff for the large maximum density, typically greater than $10^{15}\rm{g} \rm{cm}^{-3}$. The maximum baryon mass of the magnetized stars with axis ratio $q\sim 0.7$ increases about up to twenty percents for that of spherical stars. We furthermore compute equilibrium sequences at finite temperature, which should serve as an initial condition for the hydrodynamic study of newly-born magnetars. Our results suggest that we may obtain information about the EOSs from the observation of the masses of magnetars.Comment: submitted to MNRA