5,018 research outputs found
The thermodynamics and roughening of solid-solid interfaces
The dynamics of sharp interfaces separating two non-hydrostatically stressed
solids is analyzed using the idea that the rate of mass transport across the
interface is proportional to the thermodynamic potential difference across the
interface. The solids are allowed to exchange mass by transforming one solid
into the other, thermodynamic relations for the transformation of a mass
element are derived and a linear stability analysis of the interface is carried
out. The stability is shown to depend on the order of the phase transition
occurring at the interface. Numerical simulations are performed in the
non-linear regime to investigate the evolution and roughening of the interface.
It is shown that even small contrasts in the referential densities of the
solids may lead to the formation of finger like structures aligned with the
principal direction of the far field stress.Comment: (24 pages, 8 figures; V2: added figures, text revisions
Controlled Synchronization of One Class of Nonlinear Systems under Information Constraints
Output feedback controlled synchronization problems for a class of nonlinear
unstable systems under information constraints imposed by limited capacity of
the communication channel are analyzed. A binary time-varying coder-decoder
scheme is described and a theoretical analysis for multi-dimensional
master-slave systems represented in Lurie form (linear part plus nonlinearity
depending only on measurable outputs) is provided. An output feedback control
law is proposed based on the Passification Theorem. It is shown that the
synchronization error exponentially tends to zero for sufficiantly high
transmission rate (channel capacity). The results obtained for synchronization
problem can be extended to tracking problems in a straightforward manner, if
the reference signal is described by an {external} ({exogenious}) state space
model. The results are applied to controlled synchronization of two chaotic
Chua systems via a communication channel with limited capacity.Comment: 8 pages, 2 figure
The Effect of Early vs. Normal Calf Weaning on Feedlot Performance and Herd Management: A Cross-Discipline Case Study
A study of early vs. normal weaning of calves concludes that early weaning improves feedlot production efficiency, reducing per day and per pound feedlot production costs. Early weaned steers finished higher thus feedlot profitability was not affected. Early weaning has a positive affect on cow health and pasture utilization rates.Livestock Production/Industries,
Host cell invasion by Staphylococcus aureus stimulates the shedding of microvesicles
During severe sepsis, microvesicles that are positive for tissue factor (TF) are at increased levels within blood and in pulmonary lavage. These microvesicles potentially disperse TF, the major initiator of the coagulation cascade, throughout multiple organ systems, initiating fibrin deposition and resultant ischemia. The source of these microvesicles has remained incompletely defined. Although TF+ microvesicles are shed from cells that express nascent TF transcript in response to injury, recent findings revealed that circulating, full-length TF protein is detectable prior to these nascent transcripts. This finding suggested that the protein is released from constitutive sources as an acute response. We examined whether Staphylococcus aureus, the Gram-positive bacteria that is emerging as one of the most common etiologic agents in sepsis, is capable of stimulating the release of TF+ microvesicles from a pulmonary cell line that constitutively expresses TF protein. We found that host cell invasion stimulated an acute release of TF+ microvesicles and that these microvesicles mediated the transfer of the protein to TF-negative endothelial cells. We also found that transfer was inhibited by cholesterol-lowering simvastatin. Taken together, our findings reveal that S. aureus pathogenesis extends to the acute release of TF+ microvesicles and that inhibiting dispersal by this mechanism may provide a therapeutic target
A target-cell limited model can reproduce influenza infection dynamics in hosts with differing immune responses
We consider a hierarchy of ordinary differential equation models that describe the within-host viral kinetics of influenza infections: the IR model explicitly accounts for an immune response to the virus, while the simpler, target-cell limited TEIV and TV models do not. We show that when the IR model is fitted to pooled experimental murine data of the viral load, fraction of dead cells, and immune response levels, its parameters values can be determined. However, if, as is common, only viral load data are available, we can estimate parameters of the TEIV and TV models but not the IR model. These results are substantiated by a structural and practical identifiability analysis. We then use the IR model to generate synthetic data representing infections in hosts whose immune responses differ. We fit the TV model to these synthetic datasets and show that it can reproduce the characteristic exponential increase and decay of viral load generated by the IR model. Furthermore, the values of the fitted parameters of the TV model can be mapped from the immune response parameters in the IR model. We conclude that, if only viral load data are available, a simple target-cell limited model can reproduce influenza infection dynamics and distinguish between hosts with differing immune responses
ExELS: an exoplanet legacy science proposal for the ESA Euclid mission. II. Hot exoplanets and sub-stellar systems
The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the
frequency of cold exoplanets down to Earth mass from host separations of ~1 AU
out to the free-floating regime by detecting microlensing events in Galactic
Bulge. We show that ExELS can also detect large numbers of hot, transiting
exoplanets in the same population. The combined microlensing+transit survey
would allow the first self-consistent estimate of the relative frequencies of
hot and cold sub-stellar companions, reducing biases in comparing "near-field"
radial velocity and transiting exoplanets with "far-field" microlensing
exoplanets. The age of the Bulge and its spread in metallicity further allows
ExELS to better constrain both the variation of companion frequency with
metallicity and statistically explore the strength of star-planet tides.
We conservatively estimate that ExELS will detect ~4100 sub-stellar objects,
with sensitivity typically reaching down to Neptune-mass planets. Of these,
~600 will be detectable in both Euclid's VIS (optical) channel and NISP H-band
imager, with ~90% of detections being hot Jupiters. Likely scenarios predict a
range of 2900-7000 for VIS and 400-1600 for H-band. Twice as many can be
expected in VIS if the cadence can be increased to match the 20-minute H-band
cadence. The separation of planets from brown dwarfs via Doppler boosting or
ellipsoidal variability will be possible in a handful of cases. Radial velocity
confirmation should be possible in some cases, using 30-metre-class telescopes.
We expect secondary eclipses, and reflection and emission from planets to be
detectable in up to ~100 systems in both VIS and NISP-H. Transits of ~500
planetary-radius companions will be characterised with two-colour photometry
and ~40 with four-colour photometry (VIS,YJH), and the albedo of (and emission
from) a large sample of hot Jupiters in the H-band can be explored
statistically.Comment: 18 pages, 16 figures, accepted MNRA
The Use of Gamma-ray Bursts as Direction and Time Markers in SETI Strategies
When transmitting a signal over a large distance it is more efficient to send
a brief beamed signal than a continuous omni-directional transmission but this
requires that the receiver knows where and when to look for the transmission.
For SETI, the use of various natural phenomena has previously been suggested to
achieve the desired synchronization. Here it is proposed that gamma-ray bursts
may well the best ``synchronizers'' of all currently known phenomena due to
their large intrinsic luminosities, high occurrence rate, isotropic sky
distribution, large distance from the Galaxy, short duration, and easy
detectability. For targeted searches, precise positions for gamma-ray bursts
are required together with precise distance measurements to a target star. The
required burst position determinations are now starting to be obtained, aided
in large part by the discovery of optical afterglows. Good distance
measurements are currently available from Hipparcos and even better
measurements should be provided by spacecraft now being developed. For
non-targeted searches, positional accuracies simply better than a detector's
field of view may suffice but the time delay between the detection of a
gamma-ray burst and the reception of the transmitted signal cannot be predicted
in an obvious way.Comment: 8 pages, accepted for publication in PAS
Large Deformation Effects in the N = Z 44Ti Compound Nucleus
The N = Z 44Ti* nucleus has been populated in Fusion Evaporation process at
very high excitation energies and angular momenta using two entrance channels
with different mass-asymmetry. The deformation effects in the rapidly rotating
nuclei have been investigated through the energy distribution of the
alpha-particle combined to statistical-model calculations. In the case of
low-multiplicity events, the ratio between first particle emitted has been
measured and shows significant disagreement with the predictions of the
statistical-model. This may explain The large discrepancies observed in proton
energy spectra measured in previous experiments performed in the same mass
region.Comment: Proceeding of the 10th International Conference on Nuclear Reaction
Mechanisms, Varenna Italy, June 9-13 2003. 10 pages, 6 figures, 1 tabl
ExELS: an exoplanet legacy science proposal for the ESA Euclid mission. II. Hot exoplanets and sub-stellar systems
The Exoplanet Euclid Legacy Survey (ExELS) proposes to determine the
frequency of cold exoplanets down to Earth mass from host separations of ~1 AU
out to the free-floating regime by detecting microlensing events in Galactic
Bulge. We show that ExELS can also detect large numbers of hot, transiting
exoplanets in the same population. The combined microlensing+transit survey
would allow the first self-consistent estimate of the relative frequencies of
hot and cold sub-stellar companions, reducing biases in comparing "near-field"
radial velocity and transiting exoplanets with "far-field" microlensing
exoplanets. The age of the Bulge and its spread in metallicity further allows
ExELS to better constrain both the variation of companion frequency with
metallicity and statistically explore the strength of star-planet tides.
We conservatively estimate that ExELS will detect ~4100 sub-stellar objects,
with sensitivity typically reaching down to Neptune-mass planets. Of these,
~600 will be detectable in both Euclid's VIS (optical) channel and NISP H-band
imager, with ~90% of detections being hot Jupiters. Likely scenarios predict a
range of 2900-7000 for VIS and 400-1600 for H-band. Twice as many can be
expected in VIS if the cadence can be increased to match the 20-minute H-band
cadence. The separation of planets from brown dwarfs via Doppler boosting or
ellipsoidal variability will be possible in a handful of cases. Radial velocity
confirmation should be possible in some cases, using 30-metre-class telescopes.
We expect secondary eclipses, and reflection and emission from planets to be
detectable in up to ~100 systems in both VIS and NISP-H. Transits of ~500
planetary-radius companions will be characterised with two-colour photometry
and ~40 with four-colour photometry (VIS,YJH), and the albedo of (and emission
from) a large sample of hot Jupiters in the H-band can be explored
statistically.Comment: 18 pages, 16 figures, accepted MNRA
On the Possibility of Observing the Shapiro Effect for Pulsars in Globular Clusters
For pulsars in globular clusters, we suggest using observations of the
relativistic time delay of their radiation in the gravitational eld of a
massive body (the Shapiro effect) located close to the line of sight to detect
and identify invisible compact objects and to study the distribution of both
visible and dark matter in globular clusters and various components of the
Galaxy. We have derived the dependences of the event probability on the
Galactic latitude and longitude of sources for two models of the mass
distribution in the Galaxy: the classical Bahcall-Soneira model and the more
recent Dehnen-Binney model. Using three globular clusters (M15, 47 Tuc, Terzan
5) as an example, we show that the ratios of the probability of the events due
to the passages of massive Galactic objects close to the line of sight to the
parameter f2 for pulsars in the globular clusters 47 Tuc and M15 are comparable
to those for close passages of massive objects in the clusters themselves and
are considerably higher than those for the cluster Terzan 5. We have estimated
the rates of such events. We have determined the number of objects near the
line of sight toward the pulsar that can produce a modulation of its pulse
arrival times characteristic of the effect under consideration; the population
of brown dwarfs in the Galactic disk, whose concentration is comparable to that
of the disk stars, has been taken into account for the first time.Comment: 26 pages, 9 figure
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