883 research outputs found
ZMYM2 inhibits NANOG-mediated reprogramming [version 1; peer review: 2 approved, 1 approved with reservations]
A Stochastic Analysis of Proposals for the New US Farm Bill
Most of the large scale modeling systems used in the analysis of agricultural policies produce deterministic projections. In reality, however, the agricultural sector is subject to a high degree of uncertainty as a result of fluctuations in exogenous factors such as the weather or macroeconomic variation. A stochastic approach can provide additional information to policy makers regarding the implications of this uncertainty, through the use of stochastically generated projections. This paper also shows how deterministic analysis may result in systematic errors in the projection of some variables. As an applied example, the FAPRI model of the US agricultural sector is simulated stochastically to analyse the impact of proposals for the new US farm bill.Stochastic simulation, US Farm Bill, policy analysis, Agricultural and Food Policy,
Surface-Generated Mesoscale Eddies Transport Deep-Sea Products from Hydrothermal Vents
International audienceAtmospheric forcing, which is known to have a strong influence on surface ocean dynamics and production, is typically not considered in studies of the deep sea. Our observations and models demonstrate an unexpected influence of surface-generated mesoscale eddies in the transport of hydrothermal vent efflux and of vent larvae away from the northern East Pacific Rise. Transport by these deep-reaching eddies provides a mechanism for spreading the hydrothermal chemical and heat flux into the deep-ocean interior and for dispersing propagules hundreds of kilometers between isolated and ephemeral communities. Because the eddies interacting with the East Pacific Rise are formed seasonally and are sensitive to phenomena such as El Niño, they have the potential to introduce seasonal to interannual atmospheric variations into the deep sea
Boundary non-crossings of Brownian pillow
Let B_0(s,t) be a Brownian pillow with continuous sample paths, and let
h,u:[0,1]^2\to R be two measurable functions. In this paper we derive upper and
lower bounds for the boundary non-crossing probability
\psi(u;h):=P{B_0(s,t)+h(s,t) \le u(s,t), \forall s,t\in [0,1]}. Further we
investigate the asymptotic behaviour of with
tending to infinity, and solve a related minimisation problem.Comment: 14 page
Momentum transfer using chirped standing wave fields: Bragg scattering
We consider momentum transfer using frequency-chirped standing wave fields.
Novel atom-beam splitter and mirror schemes based on Bragg scattering are
presented. It is shown that a predetermined number of photon momenta can be
transferred to the atoms in a single interaction zone.Comment: 4 pages, 3 figure
Spacetime Noncommutativity and Antisymmetric Tensor Dynamics in the Early Universe
This paper investigates the possible cosmological implications of the
presence of an antisymmetric tensor field related to a lack of commutatitivity
of spacetime coordinates at the Planck era. For this purpose, such a field is
promoted to a dynamical variable, inspired by tensor formalism. By working to
quadratic order in the antisymmetric tensor, we study the field equations in a
Bianchi I universe in two models: an antisymmetric tensor plus scalar field
coupled to gravity, or a cosmological constant and a free massless
antisymmetric tensor. In the first scenario, numerical integration shows that,
in the very early universe, the effects of the antisymmetric tensor can prevail
on the scalar field, while at late times the former approaches zero and the
latter drives the isotropization of the universe. In the second model, an
approximate solution is obtained of a nonlinear ordinary differential equation
which shows how the mean Hubble parameter and the difference between
longitudinal and orthogonal Hubble parameter evolve in the early universe.Comment: 25 pages, Revtex file, 4 figures in attachmen
FAPRI 2002 World Agricultural Outlook
Crop Production/Industries, Livestock Production/Industries,
Quasi-particle model for lattice QCD: quark-gluon plasma in heavy ion collisions
We propose a quasi-particle model to describe the lattice QCD equation of
state for pure SU(3) gauge theory in its deconfined state, for .
The method involves mapping the interaction part of the equation of state to an
effective fugacity of otherwise non-interacting quasi-gluons. We find that this
mapping is exact. Using the quasi-gluon distribution function, we determine the
energy density and the modified dispersion relation for the single particle
energy, in which the trace anomaly is manifest. As an application, we first
determine the Debye mass, and then the important transport parameters, {\it
viz}, the shear viscosity, and the shear viscosity to entropy density
ratio, . We find that both and
are sensitive to the interactions, and that the interactions significantly
lower both and .Comment: 10 pages, 8 figures, epj class file, version accepted for publication
in Euro. Phys.J
Natural Theories of Ultra-Low Mass PNGB's: Axions and Quintessence
We consider the Wilson Line PNGB which arises in a U(1)^N gauge theory,
abstracted from a latticized, periodically compactified extra dimension U(1).
Planck scale breaking of the PNGB's global symmetry is suppressed, providing
natural candidates for the axion and quintessence. We construct an explicit
model in which the axion may be viewed as the 5th component of the U(1)_Y gauge
field in a 1+4 latticized periodically compactified extra dimension. We also
construct a quintessence PNGB model where the ultra-low mass arises from
Planck-scale suppressed physics itself.Comment: 20 pages, fixed typo and reference
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