2,507 research outputs found
Ambient betatron motion and its excitation by ghost lines in Tevatron
Transverse betatron motion of the Tevatron proton beam is measured and
analyzed. It is shown that the motion is coherent and excited by external
sources of unknown origins. Observations of the time varying ghost lines in the
betatron spectra are reported.Comment: 9 p
Benthic biomass size spectra in shelf and deep-sea sediments
The biomass distributions of marine benthic metazoans (meio- to macro-fauna, 1 ?gâ32 mg wet weight) across three contrasting sites were investigated to test the hypothesis that allometry can consistently explain observed trends in biomass spectra. Biomass (and abundance) size spectra were determined from observations made at the FaroeâShetland Channel (FSC) in the Northeast Atlantic (water depth 1600 m), the Fladen Ground (FG) in the North Sea (150 m), and the hypoxic Oman Margin (OM) in the Arabian Sea (500 m). Observed biomass increased with body size as a power law at FG (scaling exponent, b = 0.16) and FSC (b = 0.32), but less convincingly at OM (b = 0.12 but not significantly different from 0). A simple model was constructed to represent the same 16 metazoan size classes used for the observed spectra, all reliant on a common detrital food pool, and allowing the three key processes of ingestion, respiration and mortality to scale with body size. A micro-genetic algorithm was used to fit the model to observations at the sites. The model accurately reproduces the observed scaling without needing to include the effects of local influences such as hypoxia. Our results suggest that the size-scaling of mortality and ingestion are dominant factors determining the distribution of biomass across the meio- to macrofaunal size range in contrasting marine sediment communities. Both the observations and the model results are broadly in agreement with the "metabolic theory of ecology" in predicting a quarter power scaling of biomass across geometric body size classes
Shot noise measurements in NS junctions and the semiclassical theory
We present a new analysis of shot noise measurements in normal
metal-superconductor (NS) junctions [X. Jehl et al., Nature 405, 50 (2000)],
based on a recent semiclassical theory. The first calculations at zero
temperature assuming quantum coherence predicted shot noise in NS contacts to
be doubled with respect to normal contacts. The semiclassical approach gives
the first opportunity to compare data and theory quantitatively at finite
voltage and temperature. The doubling of shot noise is predicted up to the
superconducting gap, as already observed, confirming that phase coherence is
not necessary. An excellent agreement is also found above the gap where the
noise follows the normal case.Comment: 2 pages, revtex, 2 eps figures, to appear in Phys. Rev.
A role for dual viral hits in causation of subacute sclerosing panencephalitis
Subacute sclerosing panencephalitis (SSPE) is a progressive fatal neurodegenerative disease associated with persistent infection of the central nervous system (CNS) by measles virus (MV), biased hypermutations of the viral genome affecting primarily the matrix (M) gene with the conversion of U to C and A to G bases, high titers of antibodies to MV, and infiltration of B cells and T cells into the CNS. Neither the precipitating event nor biology underlying the MV infection is understood, nor is their any satisfactory treatment. We report the creation of a transgenic mouse model that mimics the cardinal features of SSPE. This was achieved by initially infecting mice expressing the MV receptor with lymphocytic choriomeningitis virus Cl 13, a virus that transiently suppressed their immune system. Infection by MV 10 days later resulted in persistent MV infection of neurons. Analysis of brains from infected mice showed the biased U to C hypermutations in the MV M gene and T and B lymphocyte infiltration. These sera contained high titers of antibodies to MV. Thus, a small animal model is now available to both molecularly probe the pathogenesis of SSPE and to test a variety of therapies to treat the disease
Single-field inflation constraints from CMB and SDSS data
We present constraints on canonical single-field inflation derived from WMAP
five year, ACBAR, QUAD, BICEP data combined with the halo power spectrum from
SDSS LRG7. Models with a non-scale-invariant spectrum and a red tilt n_s < 1
are now preferred over the Harrison-Zel'dovich model (n_s = 1, tensor-to-scalar
ratio r = 0) at high significance. Assuming no running of the spectral indices,
we derive constraints on the parameters (n_s, r) and compare our results with
the predictions of simple inflationary models. The marginalised credible
intervals read n_s = 0.962^{+0.028}_{-0.026} and r < 0.17 (at 95% confidence
level). Interestingly, the 68% c.l. contours favour mainly models with a convex
potential in the observable region, but the quadratic potential model remains
inside the 95% c.l. contours. We demonstrate that these results are robust to
changes in the datasets considered and in the theoretical assumptions made. We
then consider a non-vanishing running of the spectral indices by employing
different methods, non-parametric but approximate, or parametric but exact.
With our combination of CMB and LSS data, running models are preferred over
power-law models only by a Delta chi^2 ~ 5.8, allowing inflationary stages
producing a sizable negative running -0.063^{+0.061}_{-0.049} and larger
tensor-scalar ratio r < 0.33 at the 95% c.l. This requires large values of the
third derivative of the inflaton potential within the observable range. We
derive bounds on this derivative under the assumption that the inflaton
potential can be approximated as a third order polynomial within the observable
range.Comment: 32 pages, 7 figures. v2: additional references, some typos corrected,
passed to JCAP style. v3: minor changes, matches published versio
Stressed, but not defenceless: no obvious influence of irradiation levels on antifeeding and antifouling defences of tropical macroalgae
The production of defence metabolites is assumed to be costly in metabolic terms. If this holds true, low-light stress should reduce the ability of seaweeds to defend themselves chemically against herbivory and fouling. We investigated the effect of energy limitation on the defensive status of seaweeds by assessing their attractiveness to mesograzers and their activity against a bivalve macrofouler in comparison with non-stressed conspecifics. The macroalgae Codium decorticatum (Woodw.) M. Howe, Osmundaria obtusiloba (C. Agardh) R. E. Norris, Pterocladiella capillacea (S. G. Gmel.) Santel. and Hommer., Sargassum vulgare C. Agardh and Stypopodium zonale (Lamour.) Papenf. collected at the southeastern Brazilian coast were exposed to six levels of irradiation (between 1 and 180 ÎŒmol photons mâ2 sâ1) for 10â14 days. After this period, algae from all treatment levels were: (a) processed as artificial food and offered to an amphipod community dominated by Elasmopus brasiliensis Dana and (b) extracted to test for differences in settlement rates of the fouling mussel Perna perna L. on filter paper loaded with the crude extracts. Generally, photosynthesis rates and growth were reduced under low light conditions. Attractiveness to herbivores and macrofoulers, however, was insensitive to energy limitation. We discuss possible explanations for the observed absence of a relationship between light availability and algal defence including the change in nutritional value of the algal tissue, the allocation of resources towards defence instead of growth and the absence of costs for defence
Parton Distributions in the Valon Model
The parton distribution functions determined by CTEQ at low are used as
inputs to test the validity of the valon model. The valon distributions in a
nucleon are first found to be nearly independent. The parton distribution
in a valon are shown to be consistent with being universal, independent of the
valon type. The momentum fractions of the partons in the valon add up
separately to one. These properties affirm the validity of the valon model. The
various distributions are parameterized for convenient application of the
model.Comment: 9 pages + 9 figures in ep
Probing the primordial power spectra with inflationary priors
We investigate constraints on power spectra of the primordial curvature and
tensor perturbations with priors based on single-field slow-roll inflation
models. We stochastically draw the Hubble slow-roll parameters and generate the
primordial power spectra using the inflationary flow equations. Using data from
recent observations of CMB and several measurements of geometrical distances in
the late Universe, Bayesian parameter estimation and model selection are
performed for models that have separate priors on the slow-roll parameters. The
same analysis is also performed adopting the standard parameterization of the
primordial power spectra. We confirmed that the scale-invariant
Harrison-Zel'dovich spectrum is disfavored with increased significance from
previous studies. While current observations appear to be optimally modeled
with some simple models of single-field slow-roll inflation, data is not enough
constraining to distinguish these models.Comment: 23 pages, 3 figures, 7 tables, accepted for publication in JCA
Met het oog op wachttijd
Zonder een goed functionerend hoornvlies, hierna genoemd cornea, kunnen de ogen hun taak niet goed uitvoeren. Iets meer dan 100 jaar geleden, in 1905, werd de eerstes uccesvolle transplantatie van een cornea van een overleden donor uitgevoerd in TsjechiĂ«, door oogarts Zirm. Mede door de ontwikkeling van operatiemicroscopen, extra dun hechtdraad en het gebruik van antibiotica worden vandaag de dag in Nederland ongeveer 900 corneatransplantaties per jaar uitgevoerd. In Nederland is de Nederlandse transplantatie Stichting (NTS) verantwoordelijk voor het toewijzen van corneaâs aan patiĂ«nten (Bokhorst et al., 2007).\ud
De gemiddelde wachttijd voor een cornea in Nederland is ongeveer een half jaar, ofwel 175 dagen. (Zie figuur 1) De door de NTS en oogartsen meest genoemde oorzaken zijn een tekort aan operatiecapaciteit en corneaâs en de fluctuatie in zowel vraag als aanbod van corneaâs. Ons eerste doel was te onderzoeken in welke mate deze zaken de wachttijd beĂŻnvloeden. Een tweede doel was mogelijke verbeteringen aan te dragen
Associated Production of Heavy Quarkonia and Electroweak Bosons at Present and Future Colliders
We investigate the associated production of heavy quarkonia, with
angular-momentum quantum numbers ^{2S+1}L_J = ^1S_0, ^3S_1, ^1P_1, ^3P_J (J =
0, 1, 2), and photons, Z bosons, and W bosons in photon-photon, photon-hadron,
and hadron-hadron collisions within the factorization formalism of
nonrelativistic quantum chromodynamics providing all contributing partonic
cross sections in analytic form. In the case of photoproduction, we also
include the resolved-photon contributions. We present numerical results for the
processes involving J/psi and chi_{cJ} mesons appropriate for the Fermilab
Tevatron, CERN LHC, DESY TESLA, operated in the e^+ e^- and gamma gamma modes,
and DESY THERA.Comment: 41 pages (Latex), 10 figures (Postscript
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