Evidence for a New Class of Extreme UV Sources

Most of the sources detected in the extreme ultraviolet (EUV; 100 Ang to 600 Ang) by the Rosat WFC and EUVE all-sky surveys have been identified with active late-type stars and hot white dwarfs that are near enough to escape absorption by interstellar gas. However, about 15% of EUV sources are as of yet unidentified with any optical counterparts. We examine whether the unidentified EUV sources may consist of the same population of late-type stars and white dwarfs. We present B and R photometry of stars in the fields of seven of the unidentified EUV sources. We detect in the optical the entire main-sequence and white-dwarf population out to the greatest distances where they could still avoid absorption. We use colour-magnitude diagrams to demonstrate that, in most of the fields, none of the observed stars have the colours and magnitudes of late-type dwarfs at distances less than 100 pc. Similarly, none are white dwarfs within 500 pc that are hot enough to be EUV-emitters. The unidentified EUV sources we study are not detected in X-rays, while cataclysmic variables, X-ray binaries, and active galactic nuclei generally are. We conclude that some of the EUV sources may be a new class of nearby objects, that are either very faint at optical bands or which mimic the colours and magnitudes of distant late-type stars or cool white dwarfs. One candidate for optically faint objects is isolated old neutron stars, slowly accreting interstellar matter. Such neutron stars are expected to be abundant in the Galaxy, and have not been unambiguously detected.Comment: 8 pages, incl. figures, MNRAS, accepte

Auger Spectra and Different Ionic Charges Following 3s, 3p and 3d Sub-Shells Photoionization of Kr Atoms

The decay of inner-shell vacancy in an atom through radiative and non-radiative transitions leads to final charged ions. The de-excitation decay of 3s, 3p and 3d vacancies in Kr atoms are calculated using Monte-Carlo simulation method. The vacancy cascade pathway resulted from the de-excitation decay of deep core hole in 3s subshell in Kr atoms is discussed. The generation of spectator vacancies during the vacancy cascade development gives rise to Auger satellite spectra. The last transitions of the de-excitation decay of 3s, 3p and 3d holes lead to specific charged ions. Dirac-Fock-Slater wave functions are adapted to calculate radiative and non-radiative transition probabilities. The intensity of Kr^{4+} ions are high for 3s hole state, whereas Kr^{3+} and Kr^{2+} ions have highest intensities for 3p and 3d hole states, respectively. The present results of ion charge state distributions agree well with the experimental data.Comment: Published in SIGMA (Symmetry, Integrability and Geometry: Methods and Applications) at http://www.emis.de/journals/SIGMA

COSMIC RAYS FROM ACCRETING ISOLATED NEUTRON STARS

Interstellar matter that is accreted onto isolated magnetic neutron stars in the Galaxy ($\sim 10^9$ by number) is accelerated and reflected back by MHD shocks, which envelope the stars. The integrated power in the Galaxy $L_{cr,ns}$ is \sgreat 10^{40} {\rm erg \ s^{-1} }, the energy distribution is a power law of spectral index $> 2$, and the particle energy can be raised to $10^6$ GeV, consistent with the power and spectrum of primary cosmic rays in the Galaxy. The major contribution for $L_{cr,ns}$ comes from a minority of $\sim 10^7$ isolated neutron stars which are located within dense clouds. Sources in these clouds, that are generally spread within the Galactic disk, can explain the concentration of high-energy cosmic rays in the Galactic plane, as deduced from pion decay spectra in gamma-ray observations. The soft X-ray luminosity from these neutron stars is consistent with the Galactic X-ray background. The accretion may be associated with ion-neutral bias, that is further enhanced by ion confinement in frozen-in magnetic fields, which can raise the relative abundance of first ionization potential (FIP) elements in the cosmic rays.Comment: 11 pages, simple TEX; to be published in MNRA

Self-Assembly and Self-Propulsion of Colloidal Particles Using Shape and Janus Anisotropy.

Anisotropic colloidal particles can serve as the building block for a variety of complex materials with a range of different functional properties. We demonstrate the properties of anisotropic particles that are complex in shape and surface properties in three different systems. Shape anisotropy is achieved by increasing particle eccentricity from spheres to ellipsoids. Surface anisotropy introduces distinct physical and/or chemical halves to colloidal particles, called Janus particles. In this dissertation, we utilize shape and biphasic properties to generate interesting kinetic and thermodynamic properties of materials. In particular, experimental and theoretical studies allow us control over the self-assembly and self-propulsion of colloids by influencing anisotropic features. Working with metallodieletric Janus spheres – polystyrene colloids with a hemispheric gold cap – the role of hydrophobicity and gold thickness in salt-induced self-assembly is studied. We quantify experimentally and with modeling, the distinct surface interactions. Modeling these biphasic spheres as multilayered systems predicted the interactions at short and long-range. Metallodieletric colloids can also be ellipsoidal and patterned with other metals, thereby introducing shape anisotropy with biphasic interactions. We study the active motion of dilute dispersions of prolate spheroidal polystyrene particles half-coated with platinum along its major axis. Hydrogen peroxide is catalytically decomposed to water and oxygen at the platinum surface and the chemical energy is converted into autonomous motion. We discuss the physical origins of the observed trajectories of motion and extract the forces and torques generated from active motion as a function of particle eccentricity. Lastly, shape anisotropy can be useful for self-assembly. We examine how oblate spheroids (discoids) densify during field-assisted assembly. We report the application of direct current (dc) electric fields and visible light to suspensions of discoids to achieve localized dense three-dimensional packings that are both disordered and ordered.The application of the dc electric field enables particle assembly and the use of light promotes packing to higher densities. Taken together, we find that particle anisotropy plays a decisive role in these three different colloidal systems. By systematically exploring its impact, we further identify the utility of anisotropy in designing colloidal systems with functional interactions as well as dynamic properties.PHDChemical EngineeringUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/135804/1/shemio_1.pd

E-commerce and entrepreneurship in SMEs : the case of myBot

Purpose:The adoption of e-commerce in Small and Medium enterprises (SMEs) is a much-researched topic in developed and developing nations. The application of mobile devices, and social media networks (SMN) such as Facebook has revolutionised the e-commerce adoption process in SMEs. However, research into this area is still developing and there is a dearth of knowledge on how SMEs in developing countries enact and apply this phenomenon. This paper explains how e-commerce entrepreneurship using SMN is conceptualised and applied in SMEs, and highlights factors that influence this e-commerce innovation. Design/Methodology/Approach:An interpretive and qualitative case study approach was adopted as a methodological foundation in a firm pseudo-named, myBot. The study employed Contextualism theory as a meta-theoretical framework to conceptualise and analyse the e-commerce entrepreneurship process in the firm. The study employed face-to-face semi-structured and unstructured interviews with the manager as primary means of obtaining in-depth information. Further information was obtained through website content analysis and document analysis of the firm’s reports and observations. Findings:The results unearth a socially-constructed feature of e-commerce entrepreneurship that draws from myBot’s manager’s innovative ability to use Facebook and e-mail to increase sales through its niche market. Factors that propelled e-commerce entrepreneurial activities using Facebook include trust, commitment and innovativeness. Originality/Value:The study provides a theoretical lens into the understanding of an ecommerce entrepreneurship process using a Contextualism theory. The paper showcases how e-commerce using Facebook can be portrayed in a developing country context. Keywords:E-commerce, Entrepreneurship, SMN, Contextualism, SMEs, Interpretive, Case study

Semiclassical Hartree-Fock theory of a rotating Bose-Einstein condensation

In this paper, we investigate the thermodynamic behavior of a rotating Bose-Einstein condensation with non-zero interatomic interactions theoretically. The analysis relies on a semiclassical Hartree-Fock approximation where an integral is performed over the phase space and function of the grand canonical ensemble is derived. Subsequently, we use this result to derive several thermodynamic quantities including the condensate fraction, critical temperature, entropy and heat capacity. Thereby, we investigate the effect of the rotation rate and interactions parameter on the thermodynamic behavior. The role of finite size is discussed. Our approach can be extended to consider the rotating condensate in optical potential