14,257 research outputs found
The oxidation and sublimation of graphite in simulated re-entry environments
Graphite oxidation and sublimation in simulated reentry environment
Effective Labor Regulation and Microeconomic Flexibility
Microeconomic flexibility, by facilitating the process of creative-destruction, is at the core of economic growth in modern market economies. The main reason for why this process is not infinitely fast, is the presence of adjustment costs, some of them technological, other institutional. Chief among the latter is labor market regulation. While few economists would object to such a view, its empirical support is rather weak. In this paper we revisit this hypothesis and find strong evidence for it. We use a new sectoral panel for 60 countries and a methodology suitable for such a panel. We find that job security regulation clearly hampers the creative-destruction process, especially in countries where regulations are likely to be enforced. Moving from the 20th to the 80th percentile in job security, in countries with strong rule of law, cuts the annual speed of adjustment to shocks by a third while shaving off about one percent from annual productivity growth. The same movement has negligible effects in countries with weak rule of law.
The influence of the geomagnetic field and of the uncertainties in the primary spectrum on the development of the muon flux in the atmosphere
In this paper we study the sensitivity of the flux of atmospheric muons to
uncertainties in the primary cosmic ray spectrum and to the treatment of the
geomagnetic field in a calculation. We use the air shower simulation program
AIRES to make the calculation for two different primary spectra and under
several approximations to the propagation of charged particles in the
geomagnetic field. The results illustrate the importance of accurate modelling
of the geomagnetic field effects. We propose a high and a low fit of the proton
and helium fluxes, and calculate the muon fluxes with these different inputs.
Comparison with measurements of the muon flux by the CAPRICE experiment shows a
slight preference for the higher primary cosmic ray flux parametrization.Comment: 24 pages, 13 figures, submitted to Phys.Rev.
Neutron-Proton Correlations in an Exactly Solvable Model
We examine isovector and isoscalar neutron-proton correlations in an exactly
solvable model based on the algebra SO(8). We look particularly closely at
Gamow-Teller strength and double beta decay, both to isolate the effects of the
two kinds of pairing and to test two approximation schemes: the renormalized
neutron-proton QRPA (RQRPA) and generalized BCS theory. When isoscalar pairing
correlations become strong enough a phase transition occurs and the dependence
of the Gamow-Teller beta+ strength on isospin changes in a dramatic and
unfamiliar way, actually increasing as neutrons are added to an N=Z core.
Renormalization eliminates the well-known instabilities that plague the QRPA as
the phase transition is approached, but only by unnaturally suppressing the
isoscalar correlations. Generalized BCS theory, on the other hand, reproduces
the Gamow-Teller strength more accurately in the isoscalar phase than in the
usual isovector phase, even though its predictions for energies are equally
good everywhere. It also mixes T=0 and T=1 pairing, but only on the isoscalar
side of the phase transition.Comment: 13 pages + 11 postscript figures, in RevTe
Measurement and simulation of anisotropic magnetoresistance in single GaAs/MnAs core/shell nanowires
We report four probe measurements of the low field magnetoresistance in
single core/shell GaAs/MnAs nanowires synthesized by molecular beam epitaxy,
demonstrating clear signatures of anisotropic magnetoresistance that track the
field-dependent magnetization. A comparison with micromagnetic simulations
reveals that the principal characteristics of the magnetoresistance data can be
unambiguously attributed to the nanowire segments with a zinc blende GaAs core.
The direct correlation between magnetoresistance, magnetization and crystal
structure provides a powerful means of characterizing individual hybrid
ferromagnet/semiconductor nanostructures.Comment: Submitted to Applied Physics Letters; some typos corrected and a
defective figure replace
Structure of the vacuum states in the presence of isovector and isoscalar pairing correlations
The long standing problem of proton-neutron pairing and, in particular, the
limitations imposed on the solutions by the available symmetries, is revisited.
We look for solutions with non-vanishing expectation values of the proton, the
neutron and the isoscalar gaps. For an equal number of protons and neutrons we
find two solutions where the absolute values of proton and neutrons gaps are
equal but have the same or opposite sign. The behavior and structure of these
solutions differ for spin saturated (single l-shell) and spin unsaturared
systems (single j-shell). In the former case the BCS results are checked
against an exact calculation.Comment: 19 pages, 5 postscript figure
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