13,965 research outputs found
Launching Delta Alliance, final report of phase 2
Delta Alliance is a network that aims to improve the resilience of the world’s deltas. It provides a foundation and framework for international knowledge sharing and development around delta issues. Phase 2 focussed on three components: developing the Delta Alliance organization, initiating network activities and (development of) research and knowledge sharing projects
The Circadian Clock Gene Period1 Connects the Molecular Clock to Neural Activity in the Suprachiasmatic Nucleus.
The neural activity patterns of suprachiasmatic nucleus (SCN) neurons are dynamically regulated throughout the circadian cycle with highest levels of spontaneous action potentials during the day. These rhythms in electrical activity are critical for the function of the circadian timing system and yet the mechanisms by which the molecular clockwork drives changes in the membrane are not well understood. In this study, we sought to examine how the clock gene Period1 (Per1) regulates the electrical activity in the mouse SCN by transiently and selectively decreasing levels of PER1 through use of an antisense oligodeoxynucleotide. We found that this treatment effectively reduced SCN neural activity. Direct current injection to restore the normal membrane potential partially, but not completely, returned firing rate to normal levels. The antisense treatment also reduced baseline [Ca(2+)]i levels as measured by Fura2 imaging technique. Whole cell patch clamp recording techniques were used to examine which specific potassium currents were altered by the treatment. These recordings revealed that the large conductance [Ca(2+)]i-activated potassium currents were reduced in antisense-treated neurons and that blocking this current mimicked the effects of the anti-sense on SCN firing rate. These results indicate that the circadian clock gene Per1 alters firing rate in SCN neurons and raise the possibility that the large conductance [Ca(2+)]i-activated channel is one of the targets
Consequences of the Factorization Hypothesis in pbar p, pp, gamma p and gamma gamma Collisions
Using an eikonal analysis, we examine the validity of the factorization
theorem for nucleon-nucleon, gamma p and gamma gamma collisions. As an example,
using the additive quark model and meson vector dominance, we directly show
that for all energies and values of the eikonal, that the factorization theorem
sigma_{nn}/sigma_{gamma p} = sigma_{gamma p}/sigma_{gamma gamma} holds. We can
also compute the survival probability of large rapidity gaps in high energy
pbar p and pp collisions. We show that the survival probabilities are identical
(at the same energy) for gamma p and gamma gamma collisions, as well as for
nucleon-nucleon collisions. We further show that neither the factorization
theorem nor the reaction-independence of the survival probabilities depends on
the assumption of an additive quark model, but, more generally, depends on the
opacity of the eikonal being independent of whether the reaction is n-n, gamma
p or gamma gamma.Comment: 8 pages, Revtex, no figures. Expanded discussion, minor correction
A new numerical method for obtaining gluon distribution functions , from the proton structure function
An exact expression for the leading-order (LO) gluon distribution function
from the DGLAP evolution equation for the proton structure
function for deep inelastic scattering has
recently been obtained [M. M. Block, L. Durand and D. W. McKay, Phys. Rev.
D{\bf 79}, 014031, (2009)] for massless quarks, using Laplace transformation
techniques. Here, we develop a fast and accurate numerical inverse Laplace
transformation algorithm, required to invert the Laplace transforms needed to
evaluate , and compare it to the exact solution. We obtain accuracies
of less than 1 part in 1000 over the entire and spectrum. Since no
analytic Laplace inversion is possible for next-to-leading order (NLO) and
higher orders, this numerical algorithm will enable one to obtain accurate NLO
(and NNLO) gluon distributions, using only experimental measurements of
.Comment: 9 pages, 2 figure
Gravitational torques in spiral galaxies: gas accretion as a driving mechanism of galactic evolution
The distribution of gravitational torques and bar strengths in the local
Universe is derived from a detailed study of 163 galaxies observed in the
near-infrared. The results are compared with numerical models for spiral galaxy
evolution. It is found that the observed distribution of torques can be
accounted for only with external accretion of gas onto spiral disks. Accretion
is responsible for bar renewal - after the dissolution of primordial bars - as
well as the maintenance of spiral structures. Models of isolated, non-accreting
galaxies are ruled out. Moderate accretion rates do not explain the
observational results: it is shown that galactic disks should double their mass
in less than the Hubble time. The best fit is obtained if spiral galaxies are
open systems, still forming today by continuous gas accretion, doubling their
mass every 10 billion years.Comment: 4 pages, 2 figures, Astronomy and Astrophysics Letters (accepted
Biodiversity in drinking water distribution systems:a brief review
In drinking water distribution systems, three groups of living organisms are usually found in the biofilm and circulating water: heterotrophic bacteria, free-living protozoa, and macro-invertebrates. Indirect evidence suggests that protozoa grazing in distribution systems can partially eliminate biomass production and accidental microbiological pollution. This paper examines the biodiversit in drinking water distribution systems
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