27,991 research outputs found
Spectral universality of strong shocks accelerating charged particles
As a rule, the shock compression controls the spectrum of diffusively
accelerated particles. We argue that this is not so if the backreaction of
these particles on the shock structure is significant. We present a
self-similar solution in which the accelerated particles change the flow
structure near the shock so strongly that the total shock compression may
become arbitrarily large. Despite this, the energy spectrum behind the shock is
close to E^{-3/2} independently of anything at all.Comment: Submitted to ApJL, 4 pages, 1 figure, uses revtex and boxedep
The Structure of the Outer Halo of the Galaxy and its Relationship to Nearby Large-Scale Structure
We present evidence to support an earlier indication that the Galaxy is
embedded in an extended, highly inclined, triaxial halo outlined by the spatial
distribution of companion galaxies to the Milky Way. Signatures of this spatial
distribution are seen in 1) the angular variation of the radial-velocity
dispersion of the companion galaxies, 2) the spatial distribution of the M~31
sub-group of galaxies, 3) the spatial distribution of the isolated, mainly
dwarf irregular, galaxies of the Local Group, 4) the velocity anisotropy
quadrupole of a sub-group of high-velocity clouds, and 5) the spatial
distribution of galaxies in the Coma-Sculptor cloud. Tidal effects of M~31 and
surrounding galaxies on the Galaxy are not strong enough to have affected the
observed structure. We conclude that this distribution is a reflection of
initial conditions. A simple galaxy formation scenario is proposed which ties
together the results found here with those of Holmberg (1969) and Zaritsky et
al. (1997) on the peculiar distribution of satellites around a large sample of
spiral galaxies.Comment: Accepted for publication in the Astron J., March 2000, 12 pages with
1 figur
Non-thermal Origin of the EUV and Soft X-rays from the Coma Cluster - Cosmic Rays in Equipartition with the Thermal Medium
The role of cosmic rays (CR) in the formation and evolution of clusters of
galaxies has been much debated. It may well be related to other fundamental
questions, such as the mechanism which heats and virializes the intracluster
medium (ICM), and the frequency at which the ICM is shocked. There is now
compelling evidence both from the cluster soft excess (CSE) and the `hard-tail'
emissions at energies above 10 keV, that many clusters are luminous sources of
inverse-Compton (IC) emission. This is the first direct measurement of cluster
CR: the technique is free from our uncertainties in the ICM magnetic field, and
is not limited to the small subset of clusters which exhibit radio halos. The
CSE emitting electrons fall within a crucial decade of energy where they have
the least spectral evolution, and where most of the CR pressure resides.
However their survival times do not date them back to the relic CR population.
By using the CSE data of the Coma cluster, we demonstrate that the CR are
energetically as important as the thermal ICM: the two components are in
pressure equiparition. Thus, contrary to previous expectations, CR are a
dominant component of the ICM, and their origin and effects should be explored.
The best-fit CR spectral index is in agreement with the Galactic value.Comment: ApJ accepted; 10 pages LaTeX; 2 figures and 1 table in PostScrip
Recommended from our members
Globalization of Capital Markets: Implications for Firm Strategies
© 2016 Elsevier Inc. The integration of international capital markets makes it easier for firms to access capital outside of their home countries. To date international business (IB) scholars have developed a rich tradition of research on how globalization of product markets may affect a firm's organizational form and business strategy. Unfortunately, there is a paucity of studies that explore the challenges firms face in capital markets beyond their domestic boundaries, be it equity, debt, or venture capital markets. The objective of this Special Issue is to address these theoretical and empirical gaps in prior IB studies. This paper outlines the main differences between product and capital markets, and explores theoretical and empirical challenges these differences present for international management scholars. We also provide a brief summary of papers in the Special Issue and outline promising avenues for future research
New Bell inequalities for the singlet state: Going beyond the Grothendieck bound
Contemporary versions of Bell's argument against local hidden variable (LHV)
theories are based on the Clauser Horne Shimony and Holt (CHSH) inequality, and
various attempts to generalize it. The amount of violation of these
inequalities cannot exceed the bound set by the Grothendieck constants.
However, if we go back to the original derivation by Bell, and use the perfect
anti-correlation embodied in the singlet spin state, we can go beyond these
bounds. In this paper we derive two-particle Bell inequalities for traceless
two-outcome observables, whose violation in the singlet spin state go beyond
the Grothendieck constants both for the two and three dimensional cases.
Moreover, creating a higher dimensional analog of perfect correlations, and
applying a recent result of Alon and his associates (Invent. Math. 163 499
(2006)) we prove that there are two-particle Bell inequalities for traceless
two-outcome observables whose violation increases to infinity as the dimension
and number of measurements grow. Technically these result are possible because
perfect correlations (or anti-correlations) allow us to transport the indices
of the inequality from the edges of a bipartite graph to those of the complete
graph. Finally, it is shown how to apply these results to mixed Werner states,
provided that the noise does not exceed 20%.Comment: 18 pages, two figures, some corrections and additional references,
published versio
Hyperfine frequency shift in two-dimensional atomic hydrogen
We propose the explanation of a surprisingly small hyperfine frequency shift
in the two-dimensional (2D) atomic hydrogen bound to the surface of superfluid
helium below 0.1 K. Owing to the symmetry considerations, the microwave-induced
triplet-singlet transitions of atomic pairs in the fully spin-polarized sample
are forbidden. The apparent nonzero shift is associated with the
density-dependent wall shift of the hyperfine constant and the pressure shift
due to the presence of H atoms in the hyperfine state not involved in the
observed transition. The interaction of adsorbed atoms with one
another effectively decreases the binding energy and, consequently, the wall
shift by the amount proportional to their density. The pressure shift of the
resonance comes from the fact that the impurity -state atoms
interact differently with the initial -state and final -state atoms and
is also linear in density. The net effect of the two contributions, both
specific for 2D hydrogen, is comparable with the experimental observation. To
our knowledge, this is the first mentioning of the density-dependent wall
shift. We also show that the difference between the triplet and singlet
scattering lengths of H atoms, pm, is exactly twice smaller
than the value reported by Ahokas {\it et al.}, Phys. Rev. Lett. {\bf101},
263003 (2008).Comment: 4 pages, no figure
National evaluation of the neighbourhood nurseries: impact report
This study assessed the impact of NNI on parental employment, use of formal childcare, and take-up of benefits and tax credits, particularly for disadvantaged groups such as lone parents, low income families and ethnic minority groups
Synthetic Spectra and Color-Temperature Relations of M Giants
As part of a project to model the integrated spectra and colors of elliptical
galaxies through evolutionary synthesis, we have refined our synthetic spectrum
calculations of M giants. After critically assessing three effective
temperature scales for M giants, we adopted the relation of Dyck et al. (1996)
for our models. Using empirical spectra of field M giants as a guide, we then
calculated MARCS stellar atmosphere models and SSG synthetic spectra of these
cool stars, adjusting the band absorption oscillator strengths of the TiO bands
to better reproduce the observational data. The resulting synthetic spectra are
found to be in very good agreement with the K-band spectra of stars of the
appropriate spectral type taken from Kleinmann & Hall (1986) as well. Spectral
types estimated from the strengths of the TiO bands and the depth of the
bandhead of CO near 2.3 microns quantitatively confirm that the synthetic
spectra are good representations of those of field M giants. The broad-band
colors of the models match the field relations of K and early-M giants very
well; for late-M giants, differences between the field-star and synthetic
colors are probably caused by the omission of spectral lines of VO and water in
the spectrum synthesis calculations. Here, we present four grids of K-band
bolometric corrections and colors -- Johnson U-V and B-V; Cousins V-R and V-I;
Johnson-Glass V-K, J-K and H-K; and CIT/CTIO V-K, J-K, H-K and CO -- for models
having 3000 K < Teff < 4000 K and -0.5 < log g < 1.5. These grids, which have
[Fe/H] = +0.25, 0.0, -0.5 and -1.0, extend and supplement the color-temperature
relations of hotter stars presented in a companion paper (astro-ph/9911367).Comment: To appear in the March 2000 issue of the Astronomical Journal. 60
pages including 15 embedded postscript figures (one page each) and 6 embedded
postscript tables (10 pages total
Galactic Globular Cluster Relative Ages
Based on a new large, homogeneous photometric database of 35 Galactic
globular clusters (GGCs), a set of distance and reddening independent relative
age indicators has been measured. The observed D(V-I)_2.5 and D(V)(HB-TO) vs.
metallicity relations have been compared with the relations predicted by two
recent updated libraries of isochrones. Using these models and two independent
methods, we have found that self-consistent relative ages can be estimated for
our GGC sample. Based on the relative age vs. metallicity distribution, we
conclude that: (a) there is no evidence of an age spread for clusters with
[Fe/H]<-1.2, all the clusters of our sample in this range being old and coeval;
(b) for the intermediate metallicity group (-1.2<=[Fe/H]<-0.9) there is a clear
evidence of age dispersion, with clusters up to ~25% younger than the older
members; and (c) the clusters within the metal rich group ([Fe/H]>=-0.9) seem
to be coeval within the uncertainties (except Pal12), but younger (~17%) than
the bulk of the Galactic globulars. The latter result is totally model
dependent. From the distribution of the GGC ages with the Galactocentric
distance, we can present a possible scenario for the Milky Way formation: The
GC formation process started at the same zero age throughout the halo, at least
out to ~20 kpc from the Galactic center. According to the present stellar
evolution models, the metal-rich globulars are formed at a later time (~ 17%
lower age). And finally, significantly younger halo GGCs are found at any
R(GC)>8 kpc. For these, a possible scenario associated with mergers of dwarf
galaxies to the Milky Way is suggested.Comment: 47 pages, 9 figures. To be published in the Astronomical Journal,
November issu
- âŠ