71,914 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 Solar Wind Energy Flux
The solar-wind energy flux measured near the ecliptic is known to be
independent of the solar-wind speed. Using plasma data from Helios, Ulysses,
and Wind covering a large range of latitudes and time, we show that the
solar-wind energy flux is independent of the solar-wind speed and latitude
within 10%, and that this quantity varies weakly over the solar cycle. In other
words the energy flux appears as a global solar constant. We also show that the
very high speed solar-wind (VSW > 700 km/s) has the same mean energy flux as
the slower wind (VSW < 700 km/s), but with a different histogram. We use this
result to deduce a relation between the solar-wind speed and density, which
formalizes the anti-correlation between these quantities.Comment: 12 pages, 5 figure
Sum rules in the heavy quark limit of QCD
In the leading order of the heavy quark expansion, we propose a method within
the OPE and the trace formalism, that allows to obtain, in a systematic way,
Bjorken-like sum rules for the derivatives of the elastic Isgur-Wise function
in terms of corresponding Isgur-Wise functions of transitions to
excited states. A key element is the consideration of the non-forward
amplitude, as introduced by Uraltsev. A simplifying feature of our method is to
consider currents aligned along the initial and final four-velocities. As an
illustration, we give a very simple derivation of Bjorken and Uraltsev sum
rules. On the other hand, we obtain a new class of sum rules that involve the
products of IW functions at zero recoil and IW functions at any . Special
care is given to the needed derivation of the projector on the polarization
tensors of particles of arbitrary integer spin. The new sum rules give further
information on the slope and also on the curvature
, and imply, modulo a very natural assumption, the
inequality , and therefore the absolute bound
.Comment: 64 pages, Late
Implementation and Outcome Evaluation of the Intensive Aftercare Program: Final Report
This Report presents the findings from a 5-year, multisite evaluation of the implementation and outcomes of the Intensive Aftercare Program (IAP), which was sponsored by the Office of Juvenile Justice and Delinquency Prevention (OJJDP). IAP was a major initiative in aftercare programming during the 1990s and has received considerable national attention. It addresses a critical problem facing the nation's juvenile justice system: how to effectively intervene with high-risk, incarcerated juvenile offenders who have demonstrated high recidivism rates and continue to offend as adults
Correlation between electric-field-induced phase transition and piezoelectricity in lead zirconate titanate films
We observed that electric field induces phase transition from tetragonal to
rhombohedral in polycrystalline morphotropic lead zirconate titanate (PZT)
films, as reported in 2011 for bulk PZT. Moreover, we evidenced that this
field-induced phase transition is strongly correlated with PZT film
piezoelectric properties, that is to say the larger the phase transition, the
larger the longitudinal piezoelectric coefficient d 33,eff . Although d 33,eff
is already comprised between as 150 to 170 pm/V, our observation suggests that
one could obtain larger d 33,eff values, namely 250 pm/V, by optimizing the
field-induced phase transition thanks to composition fine tuning
Metallicity Evolution in the Early Universe
Observations of the damped Lya systems provide direct measurements on the
chemical enrichment history of neutral gas in the early universe. In this
Letter, we present new measurements for four damped Lya systems at high
redshift. Combining these data with [Fe/H] values culled from the literature,
we investigate the metallicity evolution of the universe from z~1.5-4.5.
Contrary to our expectations and the predictions of essentially every chemical
evolution model, the N(HI)-weighted mean [Fe/H] metallicity exhibits minimal
evolution over this epoch. For the individual systems, we report tentative
evidence for an evolution in the unweighted [Fe/H] mean and the scatter in
[Fe/H] with the higher redshift systems showing lower scatter and lower typical
[Fe/H] values. We also note that no damped Lya system has [Fe/H] < -2.7 dex.
Finally, we discuss the potential impact of small number statistics and dust on
our conclusions and consider the implications of these results on chemical
evolution in the early universe.Comment: 6 pages, 2 encapsulated figures, Latex2e, uses emulateapj.sty and
onecolfloat.sty. Accepted for publication in ApJ Letters: Feb 28, 200
Observation of correlations up to the micrometer scale in sliding charge-density waves
High-resolution coherent x-ray diffraction experiment has been performed on
the charge density wave (CDW) system KMoO. The satellite
reflection associated with the CDW has been measured with respect to external
dc currents. In the sliding regime, the satellite reflection displays
secondary satellites along the chain axis which corresponds to correlations up
to the micrometer scale. This super long range order is 1500 times larger than
the CDW period itself. This new type of electronic correlation seems inherent
to the collective dynamics of electrons in charge density wave systems. Several
scenarios are discussed.Comment: 4 pages, 3 figures Typos added, references remove
Static cylindrical symmetry and conformal flatness
We present the whole set of equations with regularity and matching conditions
required for the description of physically meaningful static cylindrically
symmmetric distributions of matter, smoothly matched to Levi-Civita vacuum
spacetime. It is shown that the conformally flat solution with equal principal
stresses represents an incompressible fluid. It is also proved that any
conformally flat cylindrically symmetric static source cannot be matched
through Darmois conditions to the Levi-Civita spacetime. Further evidence is
given that when the Newtonian mass per unit length reaches 1/2 the spacetime
has plane symmetry.Comment: 13 pages, Late
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