1,224 research outputs found
Development Of Disease Caused By The Parasite, Perkinsus-Marinus And Defense-Related Hemolymph Factors In 3 Populations Of Oysters From The Chesapeake Bay, Usa
The development of infection caused by the protozoan parasite, Perkinsus marinus (Dermo) and some specific potential defense-related cellular and humoral components in oysters collected from three geographic areas, Deepwater Shoal of James River (DW), Wachapreague (WP), and Mobjack Bay (MJ) were examined over time. Oysters were maintained in estuarine water (salinity = 20 ppt) or in water at a salinity similar to the ambient salinity of the collection sites. Oysters were sampled at the initiation of the experiment (day 0), day 35, and day 100 to determine defense-related parameters and disease prevalence and intensity. All populations experienced a significant increase in P. marinus infection prevalence and intensity from the initiation of the experiment to the termination of the study. Oyster mortality differed between oyster populations. None of the DW oysters perished while cumulative mortalities for WP at 32 ppt and 20 ppt and MJ oysters were respectively, 23, 25, and 35%. The experimental oyster populations demonstrated significant differences with respect to cellular and humoral defense-related variables. As the study progressed, the mean number of total hemocytes declined in the WP and MJ populations and increased in the DW population. The percentage of granulocytes in DW oysters was consistently higher than other populations. DW oysters also had the highest concentrations of protein and lysozyme. This pattern persisted throughout the experimental period. Oyster condition index significantly decreased during the course of the study in all populations except the DW oysters at 10 ppt. Results suggest that the increase of hemocyte number and higher percentage of granulocytes, and lysozyme concentration in DW oysters may have contributed to the high (100%) survival rate of this population. Salinity may have affected disease development. Disease prevalence and intensity tended to be lower in the WP oysters maintained at low salinity than those maintained at high salinity. In the DW population, unexpectedly, oysters maintained at 20 ppt had lower infection prevalence and intensity than oysters maintained at 10 ppt. Salinity induced, to some extent, changes in certain hemolymph components: lysozyme concentration tended to be higher in oysters maintained at low salinity than those maintained at high salinity. Increase in percentage of granulocytes was also observed in WP oysters after transferring to a salinity lower than ambient salinity
On the structure pf genealogical trees in the presence of selection
We investigate through numerical simulations the effect of selection on two
summary statistics for nucleotide variation in a sample of two genes from a
population of N asexually reproducing haploid individuals. One is the mean time
since two individuals had their most recent common ancestor (), and
the other is the mean number of nucleotide differences between two genes in the
sample (). In the case of diminishing epistasis, in which the
deleterious effect of a new mutation is attenuated, we find that the scale of
with the population size depends on the mutation rate, leading then
to the onset of a sharp threshold phenomenon as N becomes large.Comment: 6 page
Reflecting on the first three years of Topex/Poseidon
satellite, in orbit since August 1992, is the first global ocean observing system specifically de-signed to study ocean dynamics. The satellite uses a state-of-the-art radar altimeter system to determine the sea level-the height of sea sur-face relative to a reference ellipsoid-with an unprecedented accuracy. It is supplying a wealth of new information on ocean circula-tion and the patterns of the global seasonal cy-cle, low-frequency wave dynamics, gyre-scale variabilities, ocean tides, and global mean sea level variations. These observations are being used to test ocean circulation theories and the ever-maturing computer models of ocean gen-eral circulation. T/P observations cover the global oceans from 66"s to 66"N every 10 days, allowing oceanographers to routinely monitor the dy-namic global ocean. For the first time, the ocean is being accurately sampled with suffi-cient spatial and temporal resolution to ad-dress its variability at frequencies and wavenumbers (spatial frequency) previously unattainable by in situ observations. The mis-sion was also designed to measure ocean tides, resulting in the most accurate deep ocean tide models to date. The tidal signals were then removed from the sea level measure-ments to make the data suitable for ocean cir-culation studies. The radar altimeter also measures wind speed and wave height, which are part of the mission's data product in addi-tion to sea level. Many results from the mission have been published in two special issues o
Structural and Magnetic Properties of Trigonal Iron
First principles calculations of the electronic structure of trigonal iron
were performed using density function theory. The results are used to predict
lattice spacings, magnetic moments and elastic properties; these are in good
agreement with experiment for both the bcc and fcc structures. We find however,
that in extracting these quantities great care must be taken in interpreting
numerical fits to the calculated total energies. In addition, the results for
bulk iron give insight into the properties of thin iron films. Thin films grown
on substrates with mismatched lattice constants often have non-cubic symmetry.
If they are thicker than a few monolayers their electronic structure is similar
to a bulk material with an appropriately distorted geometry, as in our trigonal
calculations. We recast our bulk results in terms of an iron film grown on the
(111) surface of an fcc substrate, and find the predicted strain energies and
moments accurately reflect the trends for iron growth on a variety of
substrates.Comment: 11 pages, RevTeX,4 tar'd,compressed, uuencoded Postscript figure
Interesting magnetic properties of FeCoSi alloys
Solid solution between nonmagnetic narrow gap semiconductor FeSi and
diamagnetic semi-metal CoSi gives rise to interesting metallic alloys with
long-range helical magnetic ordering, for a wide range of intermediate
concentration. We report various interesting magnetic properties of these
alloys, including low temperature re-entrant spin-glass like behaviour and a
novel inverted magnetic hysteresis loop. Role of Dzyaloshinski-Moriya
interaction in the magnetic response of these non-centrosymmetric alloys is
discussed.Comment: 11 pages and 3 figure
Observation of Two New N* Peaks in J/psi -> and Decays
The system in decays of is limited to be
isospin 1/2 by isospin conservation. This provides a big advantage in studying
compared with and experiments which mix
isospin 1/2 and 3/2 for the system. Using 58 million decays
collected with the Beijing Electron Positron Collider, more than 100 thousand
events are obtained. Besides two well known
peaks at 1500 MeV and 1670 MeV, there are two new, clear peaks in
the invariant mass spectrum around 1360 MeV and 2030 MeV. They are the
first direct observation of the peak and a long-sought "missing"
peak above 2 GeV in the invariant mass spectrum. A simple
Breit-Wigner fit gives the mass and width for the peak as MeV and MeV, and for the new peak above 2 GeV
as MeV and MeV, respectively
Bayesian inference of population expansions in domestic bovines
The past population dynamics of four domestic and one wild species of bovine were estimated using Bayesian skyline plots, a coalescent Markov chain Monte Carlo method that does not require an assumed parametric model of demographic history. Four domestic species share a recent rapid population expansion not visible in the wild African buffalo (Syncerus caffer). The estimated timings of the expansions are consistent with the archaeological records of domestication
Degree of entanglement for two qubits
In this paper, we present a measure to quantify the degree of entanglement
for two qubits in a pure state.Comment: 5 page
Mesoscopic models for DNA stretching under force: new results and comparison to experiments
Single molecule experiments on B-DNA stretching have revealed one or two
structural transitions, when increasing the external force. They are
characterized by a sudden increase of DNA contour length and a decrease of the
bending rigidity. It has been proposed that the first transition, at forces of
60--80 pN, is a transition from B to S-DNA, viewed as a stretched duplex DNA,
while the second one, at stronger forces, is a strand peeling resulting in
single stranded DNAs (ssDNA), similar to thermal denaturation. But due to
experimental conditions these two transitions can overlap, for instance for
poly(dA-dT). We derive analytical formula using a coupled discrete worm like
chain-Ising model. Our model takes into account bending rigidity, discreteness
of the chain, linear and non-linear (for ssDNA) bond stretching. In the limit
of zero force, this model simplifies into a coupled model already developed by
us for studying thermal DNA melting, establishing a connexion with previous
fitting parameter values for denaturation profiles. We find that: (i) ssDNA is
fitted, using an analytical formula, over a nanoNewton range with only three
free parameters, the contour length, the bending modulus and the monomer size;
(ii) a surprisingly good fit on this force range is possible only by choosing a
monomer size of 0.2 nm, almost 4 times smaller than the ssDNA nucleobase
length; (iii) mesoscopic models are not able to fit B to ssDNA (or S to ss)
transitions; (iv) an analytical formula for fitting B to S transitions is
derived in the strong force approximation and for long DNAs, which is in
excellent agreement with exact transfer matrix calculations; (v) this formula
fits perfectly well poly(dG-dC) and -DNA force-extension curves with
consistent parameter values; (vi) a coherent picture, where S to ssDNA
transitions are much more sensitive to base-pair sequence than the B to S one,
emerges.Comment: 14 pages, 9 figure
Study of flare energy release using events with numerous type III-like bursts in microwaves
The analysis of narrowband drifting of type III-like structures in radio
bursts dynamic spectra allows to obtain unique information about primary energy
release mechanisms in solar flares. The SSRT spatially resolved images and a
high spectral and temporal resolution allow direct determination not only the
positions of its sources but also the exciter velocities along the flare loop.
Practically, such measurements are possible during some special time intervals
when the SSRT (about 5.7 GHz) is observing the flare region in two high-order
fringes; thus, two 1D scans are recorded simultaneously at two frequency bands.
The analysis of type III-like bursts recorded during the flare 14 Apr 2002 is
presented. Using-muliwavelength radio observations recorded by SSRT, SBRS,
NoRP, RSTN we study an event with series of several tens of drifting microwave
pulses with drift rates in the range from -7 to 13 GHz/s. The sources of the
fast-drifting bursts were located near the top of the flare loop in a volume of
a few Mm in size. The slow drift of the exciters along the flare loop suggests
a high pitch-anisotropy of the emitting electrons.Comment: 16 pages, 6 figures, Solar Physics, in press, 201
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