2,123 research outputs found
Irreversible investment and uncertainty : an empirical study of rice mills in the Mekong river delta, Vietnam
This paper investigates the irreversibility of investments and the impact this has on the nature of the relationship between investment and uncertainty. The empirical analysis uses firm-level data and is based on a survey of 210 rice-milling firms in the Mekong River Delta in Vietnam, which was carried out during the year 2000.We show that the relationship between investment and uncertainty is influenced by the extent to which investments are irreversible. In particular, the results indicate that when the degree of irreversibility increases, this increases the negative association between uncertainty and investment.
The seismic properties of low-mass He-core white dwarf stars
We present here a detailed pulsational study applied to low-mass He-core
white dwarfs, based on full evolutionary models representative of these
objects. The background stellar models on which our pulsational analysis was
carried out were derived by taking into account the complete evolutionary
history of the progenitor stars, with special emphasis on the diffusion
processes acting during the white dwarf cooling phase. We computed nonradial
-modes to assess the dependence of the pulsational properties of these
objects with stellar parameters such as the stellar mass and the effective
temperature, and also with element diffusion processes. We also performed a g-
and p-mode pulsational stability analysis on our models and found well-defined
blue edges of the instability domain, where these stars should start to exhibit
pulsations. We found substantial differences in the seismic properties of white
dwarfs with and the extremely low-mass (ELM) white
dwarfs (). Specifically, -mode pulsation modes
in ELM white dwarfs mainly probe the core regions and are not dramatically
affected by mode-trapping effects by the He/H interface, whereas the opposite
is true for more massive He-core white dwarfs. We found that element diffusion
processes substantially affects the shape of the He/H chemical transition
region, leading to non-negligible changes in the period spectrum of low-mass
white dwarfs. Our stability analysis successfully predicts the pulsations of
the only known variable low-mass white dwarf (SDSS J184037.78+642312.3), and
also predicts both - and -mode pulsational instabilities in a significant
number of known low-mass and ELM white dwarfs.Comment: 14 pages, 15 figures, 2 tables. To be published in Astronomy &
Astrophysic
3D Model Atmospheres for Extremely Low-Mass White Dwarfs
We present an extended grid of mean three-dimensional (3D) spectra for
low-mass, pure-hydrogen atmosphere DA white dwarfs (WDs). We use CO5BOLD
radiation-hydrodynamics 3D simulations covering Teff = 6000-11,500 K and logg =
5-6.5 (cgs units) to derive analytical functions to convert spectroscopically
determined 1D temperatures and surface gravities to 3D atmospheric parameters.
Along with the previously published 3D models, the 1D to 3D corrections are now
available for essentially all known convective DA WDs (i.e., logg = 5-9). For
low-mass WDs, the correction in temperature is relatively small (a few per cent
at the most), but the surface gravities measured from the 3D models are lower
by as much as 0.35 dex. We revisit the spectroscopic analysis of the extremely
low-mass (ELM) WDs, and demonstrate that the 3D models largely resolve the
discrepancies seen in the radius and mass measurements for relatively cool ELM
WDs in eclipsing double WD and WD + milli-second pulsar binary systems. We also
use the 3D corrections to revise the boundaries of the ZZ Ceti instability
strip, including the recently found ELM pulsators.Comment: 11 pages, 8 figures, accepted for publication in the Astrophysical
Journa
Reply to Comment on "Reevaluation of the parton distribution of strange quarks in the nucleon"
A Comment on the recently published reevaluation of the polarization-averaged
parton distribution of strange quarks in the nucleon using final data on the
multiplicities of charged kaons in semi-inclusive deep-inelastic scattering is
reviewed. Important features of the comparison of one-dimensional projections
of the multidimensional HERMES data are pointed out. A test of the
leading-order extraction of xS(x) using the difference between charged-kaon
multiplicities is repeated. The results are consistent with leading-order
predictions within the uncertainties in the input data, and do not invalidate
the earlier extraction of xS(x).Comment: Reply Comment to arXiv:1407.372
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A Status Report On A Planet Search Around White Dwarf Stars
We have continued monitoring a pilot sample of 15 isolated, pulsating DA white dwarfs for center-of-mass motion caused by a planetary companion. Roughly 7 years into our survey, we have preliminary evidence for periodic variations in pulse arrival times for at least two white dwarfs in our sample. The variations in these systems are unlikely to be caused by secular evolution and are possibly the result of motion of the white dwarf around a center of mass. We have yet to claim confirmation of a planet. GD66 is a previously published candidate system, with a modulation in pulse arrival times that could be caused by a 2.0 M-J sin i planetary companion with an 8.3 year orbital period. Another candidate system, WD1354+0108, has a phase modulation consistent with a 0.7 M-J sin i planet at 2.3 AU (a 4.5 year orbit). We see similar behavior in two independent frequencies within this star, and while a sinusoid is currently a marginally better fit to the data than a straight line (as we might expect from cooling alone in a DAV), we are hesitant to over-interpret our results. Finally, we have a third system, WD0018+0031, that shows a change in pulse arrival times inconsistent with cooling alone; a 2.7 M-J planet at an orbit of about 5 AU could cause the observed trend. Observations of these candidate systems are ongoing in order to constrain any planetary companions that may be present.Astronom
Crystallization in suspensions of hard spheres: A Monte Carlo and Molecular Dynamics simulation study
The crystallization of a metastable melt is one of the most important non
equilibrium phenomena in condensed matter physics, and hard sphere colloidal
model systems have been used for several decades to investigate this process by
experimental observation and computer simulation. Nevertheless, there is still
an unexplained discrepancy between simulation data and experimental nucleation
rate densities. In this paper we examine the nucleation process in hard spheres
using molecular dynamics and Monte Carlo simulation. We show that the
crystallization process is mediated by precursors of low orientational
bond-order and that our simulation data fairly match the experimental data
sets
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