4,962 research outputs found
High energy factorization predictions for the charm structure function F2^c at HERA
High energy factorization predictions for F2^c are derived using BFKL
descriptions of the proton structure function F2 at HERA. The model parameters
are fixed by a fit of F2 at small x. Two different approaches of the non
perturbative proton input are shown to correspond to the factorization at the
gluon or quark level, respectively. The predictions for F2^c are in agreement
with the data within the present error bars. However, the photon wave-function
formulation (factorization at quark level) predicts significantly higher F2^c
than both gluon factorization and a next-leading order DGLAP model.Comment: latex file + 6 encapsulated figures, 28 page
Evaluation of an urban NMHC emission inventory by measurements and impact on CTM results
This paper presents an evaluation of the consistency of an urban state-of-the-art hydrocarbon (HC) emission inventory. The evaluation was conducted through the comparison of this inventory with hourly HC measurements during two summer months in the centre of Marseille, on the Mediterranean French coast. Factors of under or overestimation could be calculated for each compound on the basis of a systematic HC to HC ratio analysis. These results, associated with a deep analysis of the speciation profiles, show that most of the common and highly concentrated hydrocarbons (such as butanes) are too much predominant in the emission speciation, while the heavy and less common species (branched alkanes, substituted aromatics) are under-represented in the inventory. The urban diffuse sources appear here as one critical point of the inventories. The disagreements were shown to have a strong incidence on the representation of the air mass reactivity. In a last step, the identified uncertainties in emissions were implemented in an air-quality model for sensitivity studies. It was shown that the observed biases in the inventory could affect the regional ozone production, with a probable impact on ozone peaks of 2-10 ppbv over the area. © 2010 Elsevier Ltd
Medium-modified average multiplicity and multiplicity fluctuations in jets
The energy evolution of average multiplicities and multiplicity fluctuations
in jets produced in heavy-ion collisions is investigated from a toy
QCD-inspired model. In this model, we use modified splitting functions
accounting for medium-enhanced radiation of gluons by a fast parton which
propagates through the quark gluon plasma. The leading contribution of the
standard production of soft hadrons is enhanced by a factor while
next-to-leading order (NLO) corrections are suppressed by , where
the parameter accounts for the induced-soft gluons in the medium. Our
results for such global observables are cross-checked and compared with their
limits in the vacuum.Comment: 8 pages and 4 figures. Version to be published in EPJ
Caecidae (Mollusca: Gastropoda) in Broward County, Florida
Caecidae is a widespread family of minute gastropod snails. Although a few species have previously been found in abundance in a few localized studies in Broward County waters, little is known about their richness, diversity, abundance and distribution in different habitats throughout local waters. This project examined species assemblages both qualitatively and quantitatively in a range of benthic habitats across Broward County. Samples were collected from five different habitat types from northern and southern Broward Country, and included two of each of the following five sites: mangrove, Intracoastal Waterway, creek, reef and rubble. Caecid specimens were removed from general samples, separated by species or developmental stage and preserved in 95% ethanol. Also, as artificial substrates have become an increasingly important resource enhancement technique, this project also compared Caecidae assemblages on artificial vs. natural substrates using a large dataset previously used primarily to examine amphipod crustacean assemblages. Species recorded in Broward County include Caecum pulchellum, C. imbricatum, C. floridanum, C. textile and Meioceras nitidum. Published records exist for 14 additional species collected elsewhere in South Florida (e.g., Palm Beach County). Descriptions, distributional data and synonymies summarizing available information are given for all 19 species. Nearly 97% of the specimens, including Caecum pulchellum, Caecum floridanum and Meioceras nitidum, were found on the reef and rubble habitats; approximately 2.5% percent were found in the Intracoastal; approximately 0.5% were found in the creek, and all taxa were absent in both mangrove habitats. A repeated measures MANOVA indicated no significant differences among any of the factors (reef type, substrate or genus) over time; (RM MANOVA, F=0.112, 2.596, 0.018, 4.604), p values = 0.769, 0.248, 0.906, 0.141) suggesting that there were no preferences in substrate material among the species investigated
On the degrees of freedom of a semi-Riemannian metric
A semi-Riemannian metric in a n-manifold has n(n-1)/2 degrees of freedom,
i.e. as many as the number of components of a differential 2-form. We prove
that any semi-Riemannian metric can be obtained as a deformation of a constant
curvature metric, this deformation being parametrized by a 2-for
DAMA detection claim is still compatible with all other DM searches
We show that the annual modulation signal observed by DAMA can be reconciled
with all other negative results from dark matter searches with a conventional
halo model for particle masses around 5 to 9 GeV. We also show which particular
dark matter stream could produce the DAMA signal.Comment: Talk given at TAUP2005, Sept. 10-14 2005, Zaragoza (Spain). 3 pages,
4 figure
Measuring emission coordinates in a pulsar-based relativistic positioning system
A relativistic deep space positioning system has been proposed using four or
more pulsars with stable repetition rates. (Each pulsar emits pulses at a fixed
repetition period in its rest frame.) The positioning system uses the fact that
an event in spacetime can be fully described by emission coordinates: the
proper emission time of each pulse measured at the event. The proper emission
time of each pulse from four different pulsars---interpolated as
necessary---provides the four spacetime coordinates of the reception event in
the emission coordinate system. If more than four pulsars are available, the
redundancy can improve the accuracy of the determination and/or resolve
degeneracies resulting from special geometrical arrangements of the sources and
the event.
We introduce a robust numerical approach to measure the emission coordinates
of an event in any arbitrary spacetime geometry. Our approach uses a continuous
solution of the eikonal equation describing the backward null cone from the
event. The pulsar proper time at the instant the null cone intersects the
pulsar world line is one of the four required coordinates. The process is
complete (modulo degeneracies) when four pulsar world lines have been crossed
by the light cone.
The numerical method is applied in two different examples: measuring emission
coordinates of an event in Minkowski spacetime using pulses from four pulsars
stationary in the spacetime; and measuring emission coordinates of an event in
Schwarzschild spacetime using pulses from four pulsars freely falling toward a
static black hole.
These numerical simulations are merely exploratory, but with improved
resolution and computational resources the method can be applied to more
pertinent problems. For instance one could measure the emission coordinates,
and therefore the trajectory, of the Earth.Comment: 9 pages, 2 figures, v3: replaced with version accepted by Phys. Rev.
Bioactive flavanones from Luma chequen
A bioassay-guided chemical study of a methanolic extract of fresh leaves of Luma chequen led to the isolation of lumaflavanones A (1), B (2) and C (3) whose structures are proposed on the basis of NMR spectroscopic data. The structure of lumaflavanone A was confirmed by X-ray analysis. Antifeedant (Spodoptera littoralis), brine shrimp (Artemia salina) and fungistatic (Botrytis cinerea) bioassays showed that while 3 was the most active in the first two assays the mixture of 1 and 2 was more effective as a fungistatic
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