7,726 research outputs found
Diffusion and Interdiffusion in Binary Metallic Melts
We discuss the dependence of self- and interdiffusion coefficients on
temperature and composition for two prototypical binary metallic melts, Al-Ni
and Zr-Ni, in molecular-dynamics (MD) computer simulations and the
mode-coupling theory of the glass transition (MCT). Dynamical processes that
are mainly entropic in origin slow down mass transport (as expressed through
self diffusion) in the mixture as compared to the ideal-mixing contribution.
Interdiffusion of chemical species is a competition of slow kinetic modes with
a strong thermodynamic driving force that is caused by non-entropic
interactions. The combination of both dynamic and thermodynamic effects causes
qualitative differences in the concentration dependence of self-diffusion and
interdiffusion coefficients. At high temperatures, the thermodynamic
enhancement of interdiffusion prevails, while at low temperatures, kinetic
effects dominate the concentration dependence, rationalized within MCT as the
approach to its ideal-glass transition temperature . The Darken equation
relating self- and interdiffusion qualitatively reproduces the
concentration-dependence in both Zr-Ni and Al-Ni, but quantitatively, the
kinetic contributions to interdiffusion can be slower than the lower bound
suggested by the Darken equation. As temperature is decreased, the agreement
with Darken's equation improves, due to a strong coupling of all kinetic modes
that is a generic feature predicted by MCT.Comment: 16 pages, 12 figure
Two-temperature coronal flow above a thin disk
We extended the disk corona model (Meyer & Meyer-Hofmeister 1994; Meyer, Liu,
& Meyer-Hofmeister 2000a) to the inner region of galactic nuclei by including
different temperatures in ions and electrons as well as Compton cooling. We
found that the mass evaporation rate and hence the fraction of accretion energy
released in the corona depend strongly on the rate of incoming mass flow from
outer edge of the disk, a larger rate leading to more Compton cooling, less
efficient evaporation and a weaker corona. We also found a strong dependence on
the viscosity, higher viscosity leading to an enhanced mass flow in the corona
and therefore more evaporation of gas from the disk below. If we take accretion
rates in units of the Eddington rate our results become independent on the mass
of the central black hole. The model predicts weaker contributions to the hard
X-rays for objects with higher accretion rate like narrow-line Seyfert 1
galaxies (NLS1s), in agreement with observations. For luminous active galactic
nuclei (AGN) strong Compton cooling in the innermost corona is so efficient
that a large amount of additional heating is required to maintain the corona
above the thin disk.Comment: 17 pages, 6 figures. ApJ accepte
Predictive Analytics im Human Capital Management : Status Quo und Potentiale
First Online: 23 December 2015
Erworben im Rahmen der Schweizer Nationallizenzen (http://www.nationallizenzen.ch)Unternehmen verfĂŒgen mittlerweile ĂŒber fortgeschrittene analytische Informationssysteme, die es erlauben die wachsenden Datenmengen nahezu automatisiert auszuwerten und Aussagen ĂŒber zukĂŒnftige Entwicklungen zu treffen. Predictive Analytics befinden sie sich im Human Capital Management noch in den AnfĂ€ngen. Datengetriebene Unternehmen wie Google oder Hewlett-Packard nutzen Predictive Analytics bereits, um Personalbeschaffung und -erhaltung zu verbessern. Obwohl jedoch die Personalbereiche ĂŒber umfangreiche Daten verfĂŒgen, beschrĂ€nkt sich deren Nutzung nach unserer Erfahrung und einer von uns durchgefĂŒhrten Befragung in den meisten FĂ€llen immer noch auf reaktives Excel-Reporting und einfachste Prognosen z. B. zur Personalanzahl. Data Mining-Verfahren werden hingegen selten genutzt, obwohl sich daraus fĂŒr das Human Capital Management und andere Unternehmensbereiche Vorteile ergeben könnten. In diesem Beitrag stellen wir anhand von Praxisbeispielen und ausgewĂ€hlter Fachliteratur Potentiale von Predictive Analytics im Human Capital Management vor, untersuchen die Verbreitung sowie die Einsatzmöglichkeiten von personalbezogenen Analysen und gehen auch auf die spezifischen Herausforderungen der Nutzung von Personaldaten ein
Work function of few layer graphene covered nickel thin films measured with Kelvin probe force microscopy
Few layer graphene and graphite are simultaneously grown on a similar to 100 nm thick polycrystalline nickel film. The work function of few layer graphene/Ni is found to be 4.15 eV with a variation of 50 meV by local measurements with Kelvin probe force microscopy. This value is lower than the work function of free standing graphene due to peculiar electronic structure resulting from metal 3d-carbon 2p(pi) hybridization. (C) 2016 AIP Publishing LLC
Direct Josephson coupling between superconducting flux qubits
We have demonstrated strong antiferromagnetic coupling between two
three-junction flux qubits based on a shared Josephson junction, and therefore
not limited by the small inductances of the qubit loops. The coupling sign and
magnitude were measured by coupling the system to a high-quality
superconducting tank circuit. Design modifications allowing to continuously
tune the coupling strength and/or make the coupling ferromagnetic are
discussed.Comment: REVTeX 4, 4 pages, 5 figures; v2: completely rewritten, added
finite-temperature results and proposals for ferromagnetic galvanic couplin
Modeling Eclipses in the Classical Nova V Persei: The Role of the Accretion Disk Rim
Multicolor (BVRI) light curves of the eclipsing classical nova V Per are
presented, and a total of twelve new eclipse timings are measured for the
system. When combined with previous eclipse timings from the literature, these
timings yield a revised ephemeris for the times of mid-eclipse given by HJD =
2,447,442.8260(1) + 0.107123474(3) E. The eclipse profiles are analyzed with a
parameter-fitting model that assumes four sources of luminosity: a white dwarf
primary star, a main-sequence secondary star, a flared accretion disk with a
rim, and a bright spot at the intersection of the mass-transfer stream and the
disk periphery. A matrix of model solutions are computed, covering an extensive
range of plausible parameter values. The solution matrix is then explored to
determine the optimum values for the fitting parameters and their associated
errors. For models that treat the accretion disk as a flat structure without a
rim, optimum fits require that the disk have a flat temperature profile.
Although models with a truncated inner disk (R_in >> R_wd) result in a steeper
temperature profile, steady-state models with a temperature profile
characterized by T(r) \propto r^{-3/4} are found only for models with a
significant disk rim. A comparison of the observed brightness and color at
mid-eclipse with the photometric properties of the best-fitting model suggests
that V Per lies at a distance of ~ 1 kpc.Comment: Accepted for publication in The Astrophysical Journal. Thirty-nine
pages, including 9 figures. V2 - updated to include additional references and
related discussion to previous work overlooked in the original version, and
to correct a typo in the ephemeris given in the abstract. V3 - Minor typos
corrected. The paper is scheduled for the 20 June 2006 issue of the ApJ. V4 -
An error in equation (9) has been corrected. The results presented in the
paper were not affected, as all computations were made using the correct
formulation of this equatio
Second moment of the Husimi distribution as a measure of complexity of quantum states
We propose the second moment of the Husimi distribution as a measure of
complexity of quantum states. The inverse of this quantity represents the
effective volume in phase space occupied by the Husimi distribution, and has a
good correspondence with chaoticity of classical system. Its properties are
similar to the classical entropy proposed by Wehrl, but it is much easier to
calculate numerically. We calculate this quantity in the quartic oscillator
model, and show that it works well as a measure of chaoticity of quantum
states.Comment: 25 pages, 10 figures. to appear in PR
A Survey for Massive Giant Planets in Debris Disks with Evacuated Inner Cavities
The commonality of collisionally replenished debris around main sequence
stars suggests that minor bodies are frequent around Sun-like stars. Whether or
not debris disks in general are accompanied by planets is yet unknown, but
debris disks with large inner cavities - perhaps dynamically cleared - are
considered to be prime candidates for hosting large-separation massive giant
planets. We present here a high-contrast VLT/NACO angular differential imaging
survey for eight such cold debris disks. We investigated the presence of
massive giant planets in the range of orbital radii where the inner edge of the
dust debris is expected. Our observations are sensitive to planets and brown
dwarfs with masses >3 to 7 Jupiter mass, depending on the age and distance of
the target star. Our observations did not identify any planet candidates. We
compare the derived planet mass upper limits to the minimum planet mass
required to dynamically clear the inner disks. While we cannot exclude that
single giant planets are responsible for clearing out the inner debris disks,
our observations constrain the parameter space available for such planets. The
non-detection of massive planets in these evacuated debris disks further
reinforces the notion that the giant planet population is confined to the inner
disk (<15 AU).Comment: Accepted for publication in Ap
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