4,311 research outputs found
Monetary policy, firm heterogeneity, and product variety
This study provides new insights on the allocative effect of monetary policy. It shows that contractionary monetary policy exerts a non-trivial reallocation effect by cleansing unproductive firms and enhancing aggregate productivity. At the same time, however, reallocation involves a reduction in the number of product variety that is central to consumer preferences and hurts welfare. A contractionary policy prevents the entry of new firms and insulates existing firms from competition, reducing aggregate productivity. Under demand uncertainty, the gain of the optimal monetary policy diminishes in firm heterogeneity and increases in the preference for product variety. We provide empirical evidence on US data, which corroborates the relevance of monetary policy for product variety that results from firm entry and exit, and provides limited support to the cleansing effect of monetary policy
More Powerful and Reliable Second-level Statistical Randomness Tests for NIST SP 800-22
Random number generators (RNGs) are essential for cryptographic systems, and statistical tests are usually employed to assess the randomness of their outputs. As the most commonly used statistical test suite, the NIST SP 800-22 suite includes 15 test items, each of which contains two-level tests. For the test items based on the binomial distribution, we find that their second-level tests are flawed due to the inconsistency between the assessed distribution and the assumed one. That is, the sequence that passes the test could still have statistical flaws in the assessed aspect. For this reason, we propose Q-value as the metric for these second-level tests to replace the original P-value without any extra modification, and the first-level tests are kept unchanged. We provide the correctness proof of the proposed Q-value based second-level tests. We perform the theoretical analysis to demonstrate that the modification improves not only the detectability, but also the reliability. That is, the tested sequence that dissatisfies the randomness hypothesis has a higher probability to be rejected by the improved test, and the sequence that satisfies the hypothesis has a higher probability to pass it. The experimental results on several deterministic RNGs indicate that, the Q-value based method is able to detect some statistical flaws that the original SP 800-22 suite cannot realize under the same test parameters
Loss of placental growth factor ameliorates maternal hypertension and preeclampsia in mice
Preeclampsia remains a clinical challenge due to its poorly understood pathogenesis. A prevailing notion is that increased placental production of soluble fms-like tyrosine kinase-1 (sFlt-1) causes the maternal syndrome by inhibiting proangiogenic placental growth factor (PlGF) and VEGF. However, the significance of PlGF suppression in preeclampsia is uncertain. To test whether preeclampsia results from the imbalance of angiogenic factors reflected by an abnormal sFlt-1/PlGF ratio, we studied PlGF KO (Pgf-/-) mice and noted that the mice did not develop signs or sequelae of preeclampsia despite a marked elevation in circulating sFLT-1. Notably, PlGF KO mice had morphologically distinct placentas, showing an accumulation of junctional zone glycogen. We next considered the role of placental PlGF in an established model of preeclampsia (pregnant catechol-O-methyltransferase-deficient [COMT-deficient] mice) by generating mice with deletions in both the Pgf and Comt genes. Deletion of placental PlGF in the context of COMT loss resulted in a reduction in maternal blood pressure and increased placental glycogen, indicating that loss of PlGF might be protective against the development of preeclampsia. These results identify a role for PlGF in placental development and support a complex model for the pathogenesis of preeclampsia beyond an angiogenic factor imbalance
Universal mechanism of discontinuity of commensurate-incommensurate transitions in three-dimensional solids: Strain dependence of soliton self-energy
We show that there exists a universal mechanism of long-range soliton
attraction in three-dimensional solids and, therefore, of discontinuity of any
commensurate-incommensurate (C-IC) phase transition. This mechanism is due to
the strain dependence of the soliton self-energy and specific features of the
solid-state elasticity. The role of this mechanism is studied in detail for a
class of C-IC transitions where the IC modulation is one-dimensional, the
anisotropy in the order parameter space is small, and the symmetry of the
systems allows the existence of the Lifshitz invariant. Two other mechanisms of
soliton attraction are operative here but the universal mechanism considered in
this paper is found to be the most important one in some cases. Comparison with
the most extensively studied C-IC transition in shows that the
experimentally observed thermal anomalies can be understood as a result of the
smearing of the theoretically predicted discontinuous transition.Comment: 8 pages (extended version, title changed
Ising Universality in Three Dimensions: A Monte Carlo Study
We investigate three Ising models on the simple cubic lattice by means of
Monte Carlo methods and finite-size scaling. These models are the spin-1/2
Ising model with nearest-neighbor interactions, a spin-1/2 model with
nearest-neighbor and third-neighbor interactions, and a spin-1 model with
nearest-neighbor interactions. The results are in accurate agreement with the
hypothesis of universality. Analysis of the finite-size scaling behavior
reveals corrections beyond those caused by the leading irrelevant scaling
field. We find that the correction-to-scaling amplitudes are strongly dependent
on the introduction of further-neighbor interactions or a third spin state. In
a spin-1 Ising model, these corrections appear to be very small. This is very
helpful for the determination of the universal constants of the Ising model.
The renormalization exponents of the Ising model are determined as y_t = 1.587
(2), y_h = 2.4815 (15) and y_i = -0.82 (6). The universal ratio Q =
^2/ is equal to 0.6233 (4) for periodic systems with cubic symmetry.
The critical point of the nearest-neighbor spin-1/2 model is K_c=0.2216546
(10).Comment: 25 pages, uuencoded compressed PostScript file (to appear in Journal
of Physics A
Improved high-temperature expansion and critical equation of state of three-dimensional Ising-like systems
High-temperature series are computed for a generalized Ising model with
arbitrary potential. Two specific ``improved'' potentials (suppressing leading
scaling corrections) are selected by Monte Carlo computation. Critical
exponents are extracted from high-temperature series specialized to improved
potentials, achieving high accuracy; our best estimates are:
, , , ,
. By the same technique, the coefficients of the small-field
expansion for the effective potential (Helmholtz free energy) are computed.
These results are applied to the construction of parametric representations of
the critical equation of state. A systematic approximation scheme, based on a
global stationarity condition, is introduced (the lowest-order approximation
reproduces the linear parametric model). This scheme is used for an accurate
determination of universal ratios of amplitudes. A comparison with other
theoretical and experimental determinations of universal quantities is
presented.Comment: 65 pages, 1 figure, revtex. New Monte Carlo data by Hasenbusch
enabled us to improve the determination of the critical exponents and of the
equation of state. The discussion of several topics was improved and the
bibliography was update
Measurement of the quasi-elastic axial vector mass in neutrino-oxygen interactions
The weak nucleon axial-vector form factor for quasi-elastic interactions is
determined using neutrino interaction data from the K2K Scintillating Fiber
detector in the neutrino beam at KEK. More than 12,000 events are analyzed, of
which half are charged-current quasi-elastic interactions nu-mu n to mu- p
occurring primarily in oxygen nuclei. We use a relativistic Fermi gas model for
oxygen and assume the form factor is approximately a dipole with one parameter,
the axial vector mass M_A, and fit to the shape of the distribution of the
square of the momentum transfer from the nucleon to the nucleus. Our best fit
result for M_A = 1.20 \pm 0.12 GeV. Furthermore, this analysis includes updated
vector form factors from recent electron scattering experiments and a
discussion of the effects of the nucleon momentum on the shape of the fitted
distributions.Comment: 14 pages, 10 figures, 6 table
Search for the W-exchange decays B0 --> Ds(*)- Ds(*)+
We report a search for the decays , , in a sample of 232
million decays to \BBb ~pairs collected with the \babar detector
at the PEP-II asymmetric-energy storage ring. We find no significant
signal and set upper bounds for the branching fractions: and at 90% confidence level.Comment: 8 pages, 2 figures, submitted to PRD-R
Study of Upsilon(3S,2S) -> eta Upsilon(1S) and Upsilon(3S,2S) -> pi+pi- Upsilon(1S) hadronic trasitions
We study the Upsilon(3S,2S)->eta Upsilon(1S) and Upsilon(3S,2S)->pi+pi-
Upsilon(1S) transitions with 122 million Upsilon(3S) and 100 million
Upsilon(2S) mesons collected by the BaBar detector at the PEP-II asymmetric
energy e+e- collider. We measure B[Upsilon(2S)->eta
Upsilon(1S)]=(2.39+/-0.31(stat.)+/-0.14(syst.))10^-4 and Gamma[Upsilon(2S)->eta
Upsilon(1S)]/Gamma[Upsilon(2S)-> pi+pi-
Upsilon(1S)]=(1.35+/-0.17(stat.)+/-0.08(syst.))10^-3. We find no evidence for
Upsilon(3S)->eta Upsilon(1S) and obtain B[Upsilon(3S)->eta Upsilon(1S)]<1.0
10^-4 and Gamma[Upsilon(3S)->eta Upsilon(1S)]/Gamma[Upsilon(3S)->pi+pi-
Upsilon(1S)]<2.3 10^-3 as upper limits at the 90% confidence level. We also
provide improved measurements of the Upsilon(2S) - Upsilon(1S) and Upsilon(3S)
- Upsilon(1S) mass differences, 562.170+/-0.007(stat.)+/-0.088(syst.) MeV/c^2
and 893.813+/-0.015(stat.)+/-0.107(syst.) MeV/c^2 respectively.Comment: 8 pages, 16 encapsulated postscript figures, submitted to Phys.Rev.
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