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Modified Green's Functions for Shallow Water Acoustic Wave Propagation
This article presents an assessment of alternative forms of the Greenâs function for boundary element simulations of acoustic wave propagation in shallow water. It is assumed that the problem is two-dimensional, the source of acoustic disturbance is time-harmonic, the velocity of sound is constant and the medium in the absence of perturbations is quiescent.
Efficient implementations of the boundary element method for underwater acoustics should employ Green's functions which directly satisfy the boundary conditions on the free surface and the horizontal parts of the bottom boundary. In the present work, these Green's functions are constructed by using different techniques, namely the method of images, eigenfunction expansions and the Ewaldâs method
High resolution imaging of the early-type galaxy NGC 1380: an insight into the nature of extended extragalactic star clusters
NGC 1380 is a lenticular galaxy located near the centre of the Fornax Cluster
northeast of NGC 1399. The globular cluster system of this galaxy was
previously studied only from the ground. Recent studies of similar early-type
galaxies, specially lenticular ones, reveal the existence of star clusters that
apparently break up the traditional open/globular cluster dichotomy. With
higher quality photometry from HST/WFPC2 we study the star clusters in NGC
1380, measuring their magnitudes, colours, sizes and projected distances from
the centre of the galaxy. We used deep archival HST/WFPC2 in the B and V bands.
We built colour magnitude diagrams from which we selected a sample of cluster
candidates. We also analysed their colour distribution and measured their
sizes. Based on their location in the luminosity-size diagram we estimated
probabilities of them being typical globular clusters as those found in the
Galaxy. A total of about 570 cluster candidates were found down to V=26.5. We
measured sizes for approximately 200 of them. The observed colour distribution
has three apparent peaks. Likewise for the size distribution. We identified the
smaller population as being mainly typical globular clusters, while the more
extended objects have small probabilities of being such objects. Different
correlations between absolute magnitudes, sizes, colours and location were
inferred for these cluster sub-populations. Most extended clusters (Reff > 4
pc) share similar properties to the diffuse star clusters reported to inhabit
luminous early-type galaxies in the Virgo galaxy cluster such as being of low
surface brightness and fainter than MV ~ -8. We also report on a small group of
(Reff ~ 10 pc), -8< MV < -6, red clusters located near the centre of NGC 1380,
which may be interpreted as faint fuzzies.Comment: accepted for publication in A&
Mating Patterns and Post-Mating Isolation in Three Cryptic Species of the Engystomops Petersi Species Complex
Determining the extent of reproductive isolation in cryptic species with dynamic geographic ranges can yield important insights into the processes that generate and maintain genetic divergence in the absence of severe geographic barriers. We studied mating patterns, propensity to hybridize in nature and subsequent fertilization rates, as well as survival and development of hybrid F1 offspring for three nominal species of the Engystomops petersi species complex in YasunĂ National Park, Ecuador. We found at least two species in four out of six locations sampled, and 14.3% of the wild pairs genotyped were mixed-species (heterospecific) crosses. We also found reduced fertilization rates in hybrid crosses between E. petersi females and E. âmagnusâ males, and between E. âmagnusâ females and E. âselvaâ males but not in the reciprocal crosses, suggesting asymmetric reproductive isolation for these species. Larval development times decreased in F1 hybrid crosses compared to same species (conspecific) crosses, but we did not find significant reduction in larval survival or early metamorph survival. Our results show evidence of post-mating isolation for at least two hybrid crosses of the cryptic species we studied. The general decrease in fertilization rates in heterospecific crosses suggests that sexual selection and reinforcement might have not only contributed to the pattern of call variation and behavioral isolation we see between species today, but they may also contribute to further signal divergence and behavioral evolution, especially in locations where hybridization is common and fertilization success is diminished
Mating Patterns and Post-Mating Isolation in Three Cryptic Species of the Engystomops Petersi Species Complex
Determining the extent of reproductive isolation in cryptic species with dynamic geographic ranges can yield important insights into the processes that generate and maintain genetic divergence in the absence of severe geographic barriers. We studied mating patterns, propensity to hybridize in nature and subsequent fertilization rates, as well as survival and development of hybrid F1 offspring for three nominal species of the Engystomops petersi species complex in YasunĂ National Park, Ecuador. We found at least two species in four out of six locations sampled, and 14.3% of the wild pairs genotyped were mixed-species (heterospecific) crosses. We also found reduced fertilization rates in hybrid crosses between E. petersi females and E. âmagnusâ males, and between E. âmagnusâ females and E. âselvaâ males but not in the reciprocal crosses, suggesting asymmetric reproductive isolation for these species. Larval development times decreased in F1 hybrid crosses compared to same species (conspecific) crosses, but we did not find significant reduction in larval survival or early metamorph survival. Our results show evidence of post-mating isolation for at least two hybrid crosses of the cryptic species we studied. The general decrease in fertilization rates in heterospecific crosses suggests that sexual selection and reinforcement might have not only contributed to the pattern of call variation and behavioral isolation we see between species today, but they may also contribute to further signal divergence and behavioral evolution, especially in locations where hybridization is common and fertilization success is diminished
Next-to-next-to-leading order fits to CCFR'97 data and infrared renormalons
We briefly summarize the outcomes of our recent improved fits to the
experimental data of CCFR collaboration for structure function of deep-inelastic scattering at the next-to-next-to-leading order. Special
attention is paid to the extraction of and the parameter of the
infrared renormalon model for -correction at different orders of
perturbation theory. The results can be of interest for planning similar
studies using possible future data of Neutrino Factories.Comment: 3 pages, presented at WG3 of 4th NuFact'02 Workshop, London 1-6 July,
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The Gribov horizon and the one-loop color-Coulomb potential
We recalculate the color-Coulomb potential to one-loop order, under the
assumption that the effect of the Gribov horizon is to make i) the transverse
gluon propagator less singular; and ii) the color-Coulomb potential more
singular, than their perturbative behavior in the low-momentum limit. As a
first guess, the effect of the Gribov horizon is mimicked by introducing a
transverse momentum-dependent gluon mass term, leading to a propagator of the
Gribov form, with the prescription that the mass parameter should be adjusted
to the unique value where the infrared behavior of the Coulomb potential is
enhanced. We find that this procedure leads to a Coulomb potential rising
asymptotically as a linear term modified by a logarithm.Comment: 15 pages, 2 figure
Microscopic phenomena and a modern approach to turbulence
The use of an arc driven shock tube as a technique in the study of turbulence and evidence to support a kinetic theory of turbulence are described. Topics covered include: (1) reaction rate distortion in turbulent flow; (2) turbulent bursts in a shock tube; (3) driver gas flow with fluctuations; (4) improving the Mach number capabilities of arc driver shock tubes; and (5) resonant absorption in an argon plasma at thermal equilibrium
Cylindrically symmetric spinning Brans-Dicke spacetimes with closed timelike curves
We present here three new solutions of Brans-Dicke theory for a stationary
geometry with cylindrical symmetry in the presence of matter in rigid rotation
with . All the solutions have eternal closed timelike curves
in some region of the spacetime, the size of which depends on .
Moreover, two of them do not go over a solution of general relativity in the
limit .Comment: revtex, 10 pages, 1 figure in p
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