4,742 research outputs found

    An ASCA Study of the W51 Complex

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    We present the analysis of ASCA archival data from the Galactic source W51. The ASCA spectra show that the soft (kT<= 2.5 keV) X-rays are of thermal origin and are compatible with W51C being a single, isothermal (kT~0.3 keV) supernova remnant at the far-side of the Sagittarius arm. The ASCA images reveal hard (kT>=2.5 keV) X-ray sources which were not seen in previous X-ray observations. Some of these sources are coincident with massive star-forming regions and the spectra are used to derive X-ray parameters. By comparing the X-ray absorbing column density with atomic hydrogen column density, we infer the location of star-forming regions relative to molecular clouds. There are unidentified hard X-ray sources superposed on the supernova remnant and we discuss the possibility of their association.Comment: 13 pages, 11 figures, to be published in Astronomical Journa

    Strategic Implications of Current Small Business Waste Reduction Programs

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    The strategic importance of environmental awareness has received a great deal of recognition recently, but attention has centered primarily on residential or municipal recycling and waste reduction efforts. The small amount of research done on commercial waste reduction policies has focused on the altitudes and programs of large corporations. As governmental agencies impose waste reduction mandates on communities and corporations, many small businesses will be forced 10 adopt waste reduction programs in the future. In addition, a growing body of evidence suggests that environmental programs are associated with profitability, indicating the need for a more strategic approach 10 the management of environmental issues in order to effectively administer required programs. This study presents results of survey research indicating that small businesses are willing 10 commit 10 strategic waste reduction programs, but are concerned primarily with the convenience  of such programs. Although convenience is frequently related 10 operating cost in small businesses, issues regarding the expense of waste reduction programs are of secondary concern 10 small business executives. The implications of these results are discussed, along with recommendations for small business executives, consult­ ants, and policy  makers

    Numerical propagation of high energy cosmic rays in the Galaxy I: technical issues

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    We present the results of a numerical simulation of propagation of cosmic rays with energy above 101510^{15} eV in a complex magnetic field, made in general of a large scale component and a turbulent component. Several configurations are investigated that may represent specific aspects of a realistic magnetic field of the Galaxy, though the main purpose of this investigation is not to achieve a realistic description of the propagation in the Galaxy, but rather to assess the role of several effects that define the complex problem of propagation. Our simulations of Cosmic Rays in the Galaxy will be presented in Paper II. We identified several effects that are difficult to interpret in a purely diffusive approach and that play a crucial role in the propagation of cosmic rays in the complex magnetic field of the Galaxy. We discuss at length the problem of the extrapolation of our results to much lower energies where data are available on the confinement time of cosmic rays in the Galaxy. The confinement time and its dependence on particles' rigidity are crucial ingredients for 1) relating the source spectrum to the observed cosmic ray spectrum; 2) quantifying the production of light elements by spallation; 3) predicting the anisotropy as a function of energy.Comment: 29 pages, 12 figures, submitted to JCA

    Anisotropies in the Diffuse Gamma-Ray Background from Dark Matter with Fermi LAT: a closer look

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    We perform a detailed study of the sensitivity to the anisotropies related to Dark Matter (DM) annihilation in the Isotropic Gamma-Ray Background (IGRB) as measured by the Fermi Large Area Telescope (Fermi-LAT). For the first time, we take into account the effects of the Galactic foregrounds and use a realistic representation of the Fermi-LAT. We consider DM anisotropies of extra-galactic origin and of Galactic origin (which can be generated through annihilation in the Milky Way sub-structures) as opposed to a background of anisotropies generated by sources of astrophysical origin, blazars for example. We find that with statistics from 5 years of observation Fermi is sensitive to a DM contribution at the level of the thermal-relic cross section depending on the DM mass and annihilation mode. The anisotropy method for DM searches has a sensitivity comparable to the usual methods based only on the energy spectrum and thus constitutes an independent and complementary piece of information in the DM puzzle. (abridged)Comment: 17 pages, 9 figures, v2: added discussion on unresolved point sources, matches published version on MNRA

    On a Network Model of Localization in a Random Magnetic Field

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    We consider a network model of snake states to study the localization problem of non-interacting fermions in a random magnetic field with zero average. After averaging over the randomness, the network of snake states is mapped onto MM coupled SU(2N)(2N) spin chains in the N→0N \rightarrow 0 limit. The number of snake states near the zero-field contour, MM, is an even integer. In the large conductance limit g=Me22πℏg = M {e^2 \over 2 \pi \hbar} (M≫2M \gg 2), it turns out that this system is equivalent to a particular representation of the U(2N)/U(N)×U(N){\rm U}(2N) / {\rm U}(N) \times {\rm U}(N) sigma model (N→0N \rightarrow 0) {\it without} a topological term. The beta function β(1/M)\beta (1/M) of this sigma model in the 1/M1/M expansion is consistent with the previously known β(g)\beta (g) of the unitary ensemble. These results and further plausible arguments support the conclusion that all the states are localized.Comment: Revtex, 6 pages, 3 figures appended as an uuencoded fil

    The AMCIS 2003 Panels of IS Education-II: The Chicken and the Egg Debate: Positioning Database Content in the Information Systems Curriculum

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    This paper summarizes the results of a panel on how database content is covered in current university programs, with reference to the IS2002 model curriculum. Panelists included information systems (IS) faculty members who are actively involved in determining the coverage of database content at their institutions and in establishing academy-wide database content and technology resources. Topics included positioning database content in the overall curriculum, sequencing of content within the database course(s), and summary suggestions for tailoring database coverage at colleges and universities

    Diagnostic Potential of Cosmic-Neutrino Absorption Spectroscopy

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    Annihilation of extremely energetic cosmic neutrinos on the relic-neutrino background can give rise to absorption lines at energies corresponding to formation of the electroweak gauge boson Z0Z^{0}. The positions of the absorption dips are set by the masses of the relic neutrinos. Suitably intense sources of extremely energetic (102110^{21} -- 102510^{25}-eV) cosmic neutrinos might therefore enable the determination of the absolute neutrino masses and the flavor composition of the mass eigenstates. Several factors--other than neutrino mass and composition--distort the absorption lines, however. We analyze the influence of the time-evolution of the relic-neutrino density and the consequences of neutrino decay. We consider the sensitivity of the lineshape to the age and character of extremely energetic neutrino sources, and to the thermal history of the Universe, reflected in the expansion rate. We take into account Fermi motion arising from the thermal distribution of the relic-neutrino gas. We also note the implications of Dirac vs. Majorana relics, and briefly consider unconventional neutrino histories. We ask what kinds of external information would enhance the potential of cosmic-neutrino absorption spectroscopy, and estimate the sensitivity required to make the technique a reality.Comment: 25 pages, 26 figures (in 46 files), uses RevTe

    Particle Acceleration in Cosmic Sites - Astrophysics Issues in our Understanding of Cosmic Rays

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    Laboratory experiments to explore plasma conditions and stimulated particle acceleration can illuminate aspects of the cosmic particle acceleration process. Here we discuss the cosmic-ray candidate source object variety, and what has been learned about their particle-acceleration characteristics. We identify open issues as discussed among astrophysicists. -- The cosmic ray differential intensity spectrum is a rather smooth power-law spectrum, with two kinks at the "knee" (~10^15 eV) and at the "ankle" (~3 10^18 eV). It is unclear if these kinks are related to boundaries between different dominating sources, or rather related to characteristics of cosmic-ray propagation. We believe that Galactic sources dominate up to 10^17 eV or even above, and the extragalactic origin of cosmic rays at highest energies merges rather smoothly with Galactic contributions throughout the 10^15--10^18 eV range. Pulsars and supernova remnants are among the prime candidates for Galactic cosmic-ray production, while nuclei of active galaxies are considered best candidates to produce ultrahigh-energy cosmic rays of extragalactic origin. Acceleration processes are related to shocks from violent ejections of matter from energetic sources such as supernova explosions or matter accretion onto black holes. Details of such acceleration are difficult, as relativistic particles modify the structure of the shock, and simple approximations or perturbation calculations are unsatisfactory. This is where laboratory plasma experiments are expected to contribute, to enlighten the non-linear processes which occur under such conditions.Comment: accepted for publication in EPJD, topical issue on Fundamental physics and ultra-high laser fields. From review talk at "Extreme Light Infrastructure" workshop, Sep 2008. Version-2 May 2009: adjust some wordings and references at EPJD proofs stag

    Chiral Anomaly and Spin Gap in One-Dimensional Interacting Fermions

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    Semiclassical approach has been developed for the one-dimensional interacting fermion systems. Starting from the incommensurate spin density wave (SDW) mean field state for the repulsive Hubbard model in 1D, the non-Abelian bosonized Lagrangian describing the spin-charge separation is obtained. The Berry phase term is derived from the chiral anomaly, and we obtain the massless Tomonaga-Luttinger liquid in the single chain case while the spin gap opens in the double-chain system. This approach offers a new method to identify the strong-coupling fixed point, and its relation to the Abelian bosonization formalism is discussed on the spin gap state. The generalization to higher dimensions is also discussed.Comment: Revised and enlarged version. 16 pages in REVTE
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