19,938 research outputs found
Free fermionic propagators on a lattice
A method used recently to obtain a formalism for classical fields with
non-local actions preserving chiral symmetry and uniqueness of fermion fields
yields a discrete version of Huygens' principle with free discrete propagators
that recover their continuum forms in certain limit.Comment: LaTex document, 13 pages, 1 figure. Minor changes, two references
adde
Impact of the commercial fishery on the population of bait shrimp (Penaeus spp.) in Biscayne Bay, 1986
Monthly population size of bait shrimp in the Bay was estimated from December 1984 to July 1985. Growth rates for male and female P. duorarum showed that pink shrimp
exhibit a mean residence time in the nursery area (Biscayne Bay) of approximately 21 weeks. Monthly mortality rates were determined for each sex of pink shrimp. It was
estimated that 23% and 26% of the male and female monthly population size, respectively, was absorbed by both the fishery and ecosystem monthly. Monthly proportion of the standing stock expected to die exclusively through fishing was 6.5% and 6.0% for males and females respectively. Estimates of emigration rates showed that approximately 4.0% of the population was lost from the Bay system each month. This surplus production was about 50% of the average monthly catch by the fleet. Fishing mortality represents only 8 - 9% of the losses to the shrimp population. The
biggest source of loss is emigration, suggesting that most shrimp beyond the size at recruitment (to the fishery) are not utilized for food while in the Bay. Thus, it appears
that the direct impact of the fishery on the bait shrimp population is relatively small. (PDF contains 46 pages
Selecting SUDS in the Valencia Region of Spain
This paper reports on a study of the implementation of sustainable urban drainage systems (SUDS) in two Spanish towns (Xàtiva and Benaguasil) as part of the EU LIFE+ Project AQUAVAL, which has been conceived to introduce examples of sustainable drainage to the Valencia Region of Spain. Six sites in a range of common urban spaces and land uses are selected and appropriate SUDS techniques proposed by means of a decision-support process. This primarily consisted of the systematic application of key selection criteria through matrices and scores, followed by a brief sustainability analysis. Stakeholders’ preferences and opinions as well as educational and social opportunities are highly considered throughout the process. General monitoring requirements and major limitations in using the methodology are outlined, stressing the need for improvement of four main aspects: local data regarding SUDS performance, detail of the sustainability analysis, support through comprehensive modelling tools, and level of stakeholder engagement. The importance of creating showcases for SUDS in Mediterranean Regions, thus adapting key selection criteria as to foster sustainable drainage understanding and expertise is highlighted
The age-metallicity dependence for white dwarfs
We present a theoretical study on the metallicity dependence of the
initialtofinal mass relation and its influence on white dwarf age
determinations. We compute a grid of evolutionary sequences from the main
sequence to K on the white dwarf cooling curve, passing through
all intermediate stages. During the thermally-pulsing asymptotic giant branch
no third dredge-up episodes are considered and thus the photospheric C/O ratio
is below unity for sequences with metallicities larger than . We
consider initial metallicities from to , accounting for
stellar populations in the galactic disk and halo, with initial masses below
. We found a clear dependence of the shape of the
initialtofinal mass relation with the progenitor metallicity, where metal
rich progenitors result in less massive white dwarf remnants, due to an
enhancement of the mass loss rates associated to high metallicity values. By
comparing our theoretical computations with semi empirical data from globular
and old open clusters, we found that the observed intrinsic mass spread can be
accounted for by a set of initialtofinal mass relations characterized by
different metallicity values. Also, we confirm that the lifetime spent before
the white dwarf stage increases with metallicity. Finally, we estimate the mean
mass at the top of the white dwarf cooling curve for three globular clusters
NGC 6397, M4 and 47 Tuc, around , characteristic of old stellar
populations. However, we found different values for the progenitor mass, lower
for the metal poor cluster, NGC 6397, and larger for the younger and metal rich
cluster 47 Tuc, as expected from the metallicity dependence of the
initialtofinal mass relation.Comment: Accepted for publication in MNRA
MASS SEGREGATION IN DARK MATTER MODELS.
We use the moments of counts of neighbors as given by the Generalized
Correlation Integrals, to study the clustering properties of Dark Matter Halos
(DH) in Cold Dark Matter (CDM) and Cold+Hot Dark Matter (CHDM) models. We
compare the results with those found in the CfA and SSRS galaxy catalogs. We
show that if we apply the analysis in redshift space, both models reproduce
equally well the observed clustering of galaxies. Mass segregation is also
found in the models: more massive DHs are more clustered compared with less
massive ones. In redshift space, this mass segregation is reduced by a factor
2-3 due to the peculiar velocities. Observational catalogs give an indication
of luminosity and size segregation, which is consistent with the predictions of
the models. Because the mass segregation is smaller in redshift space, it is
suggestive that the real luminosity or size segregation of galaxies could be
significantly larger than what it is found in redshift catalogs.Comment: 13 pages including 9 figures (220 KB) in uuencoded compressed
Postscript format. To appear in The Astrophysical Journal, June 10. Latex
file and figures available at ftp://astrohp.ft.uam.es/pub/preprints/masse
Cerebral and cardiovascular effects of analgesic doses of ketamine during a target controlled general anesthesia: a prospective randomized study
Introduction: Ketamine is increasingly being used in various pain settings. The purpose of this study was to
assess the effect of an analgesic dose of ketamine in the bispectral index (BIS), spectral edge frequency (SEF-95), density spectral array (DSA), cerebral oximetry (rSO2) and mean arterial pressure (MAP) during general
anaesthesia with a target controlled infusion.
Methods: A prospective, single-blinded and randomized study on adult patients scheduled for elective spine
surgery was carried out. After anaesthesia induction with propofol, remifentanil and rocuronium, when a stable BIS
value (45-55) was achieved, an automatic recording of BIS, SEF-95, rSO2 and MAP values during 9 min was
performed to establish patients baseline values. Subsequently, patients were randomly assigned to receive a
ketamine bolus dose of 0.2 mg/kg, 0.5 mg/kg or 1 mg/kg; all variables were recorded for additional 9 min after the
ketamine bolus, in the absence of any surgical stimulus. A p-value <0.05 was considered significant in the statistical
analysis.
Results and discussion: Thirty-nine patients were enrolled in the study. Our results show a dose-related
increase of SEF-95 and BIS values. DSA demonstrate a shift in the frequency range and power distribution towards
higher frequencies. Our results do not show significant differences in MAP and rSO2 values.
Conclusion: When ketamine is used intraoperatively in analgesic doses, the anaesthetist should anticipate an
increase in SEF-95 and BIS values which will not be associated with the level of anaesthesia.info:eu-repo/semantics/publishedVersio
Stabilization of Extra Dimensions and The Dimensionality of the Observed Space
We present a simple model for the late time stabilization of extra
dimensions. The basic idea is that brane solutions wrapped around extra
dimensions, which is allowed by string theory, will resist expansion due to
their winding mode. The momentum modes in principle work in the opposite way.
It is this interplay that leads to dynamical stabilization. We use the idea of
democratic wrapping \cite{art5}-\cite{art6}, where in a given decimation of
extra dimensions, all possible winding cases are considered. To simplify the
study further we assumed a symmetric decimation in which the total number of
extra dimensions is taken to be where N can be called the order of the
decimation. We also assumed that extra dimensions all have the topology of
tori. We show that with these rather conservative assumptions, there exists
solutions to the field equations in which the extra dimensions are stabilized
and that the conditions do not depend on . This fact means that there exists
at least one solution to the asymmetric decimation case. If we denote the
number of observed space dimensions (excluding time) by , the condition for
stabilization is for pure Einstein gravity and for dilaton
gravity massaged by string theory parameters.Comment: Final versio
Critical phenomena of thick branes in warped spacetimes
We have investigated the effects of a generic bulk first-order phase
transition on thick Minkowski branes in warped geometries. As occurs in
Euclidean space, when the system is brought near the phase transition an
interface separating two ordered phases splits into two interfaces with a
disordered phase in between. A remarkable and distinctive feature is that the
critical temperature of the phase transition is lowered due to pure geometrical
effects. We have studied a variety of critical exponents and the evolution of
the transverse-traceless sector of the metric fluctuations.Comment: revtex4, 4 pages, 4 figures, some comments added, typos corrected,
published in PR
- …