2,497 research outputs found
Moment equations in a Lotka-Volterra extended system with time correlated noise
A spatially extended Lotka-Volterra system of two competing species in the
presence of two correlated noise sources is analyzed: (i) an external
multiplicative time correlated noise, which mimics the interaction between the
system and the environment; (ii) a dichotomous stochastic process, whose jump
rate is a periodic function, which represents the interaction parameter between
the species. The moment equations for the species densities are derived in
Gaussian approximation, using a mean field approach. Within this formalism we
study the effect of the external time correlated noise on the ecosystem
dynamics. We find that the time behavior of the order moments are
independent on the multiplicative noise source. However the behavior of the
order moments is strongly affected both by the intensity and the
correlation time of the multiplicative noise. Finally we compare our results
with those obtained studying the system dynamics by a coupled map lattice
model.Comment: 12 pages, 7 figures, to appear in Acta Phys. Pol.
Selecting asteroids for a targeted spectroscopic survey
Asteroid spectroscopy reflects surface mineralogy. There are few thousand
asteroids whose surfaces have been observed spectrally. Determining the surface
properties of those objects is important for many practical and scientific
applications, such as for example developing impact deflection strategies or
studying history and evolution of the Solar System and planet formation.
The aim of this study is to develop a pre-selection method that can be
utilized in searching for asteroids of any taxonomic complex. The method could
then be utilized im multiple applications such as searching for the missing
V-types or looking for primitive asteroids.
We used the Bayes Naive Classifier combined with observations obtained in the
course of the Sloan Digital Sky Survey and the Wide-field Infrared Survey
Explorer surveys as well as a database of asteroid phase curves for asteroids
with known taxonomic type. Using the new classification method we have selected
a number of possible V-type candidates. Some of the candidates were than
spectrally observed at the Nordic Optical Telescope and South African Large
Telescope.
We have developed and tested the new pre-selection method. We found three
asteroids in the mid/outer Main Belt that are likely of differentiated type.
Near-Infrared are still required to confirm this discovery. Similarly to other
studies we found that V-type candidates cluster around the Vesta family and are
rare in the mid/oter Main Belt.
The new method shows that even largely explored large databases combined
together could still be further exploited in for example solving the missing
dunite problem.Comment: accepted to A
Shock absorbing support and restraint means Patent
Shock absorbing couch for body support under high acceleration or deceleration force
Candidate hypervelocity stars of spectral type G and K revisited
Hypervelocity stars (HVS) move so fast that they are unbound to the Galaxy.
When they were first discovered in 2005, dynamical ejection from the
supermassive black hole (SMBH) in the Galactic Centre (GC) was suggested as
their origin. The two dozen HVSs known today are young massive B stars, mostly
of 3-4 solar masses. Recently, 20 HVS candidates of low mass were discovered in
the Segue G and K dwarf sample, but none of them originates from the GC. We
embarked on a kinematic analysis of the Segue HVS candidate sample using the
full 6D phase space information based on new proper motion measurements. Their
orbital properties can then be derived by tracing back their trajectories in
different mass models of our Galaxy. We present the results for 14 candidate
HVSs, for which proper motion measurements were possible. Significantly lower
proper motions than found in the previous study were derived. Considering three
different Galactic mass models we find that all stars are bound to the Galaxy.
We confirm that the stars do not originate from the GC. The distribution of
their proper motions and radial velocities is consistent with predictions for
runaway stars ejected from the Galactic disk by the binary supernova mechanism.
However, their kinematics are also consistent with old disk membership.
Moreover, most stars have rather low metallicities and strong -element
enrichment as typical for thick disk and halo stars, whereas the metallicity of
the three most metal-rich stars could possibly indicate that they are runaway
stars from the thin disk. One star shows halo kinematics.Comment: A&A letter accepte
Prebiotics: a potential treatment strategy for the chemotherapy-damaged gut?
Abstract Mucositis, characterized by ulcerative lesions along the alimentary tract, is a common consequence of many chemotherapy regimens. Chemotherapy negatively disrupts the intestinal microbiota, resulting in increased numbers of potentially pathogenic bacteria, such as Clostridia and Enterobacteriaceae, and decreased numbers of "beneficial" bacteria, such as Lactobacilli and Bifidobacteria. Agents capable of restoring homeostasis in the bowel microbiota could therefore be applicable to mucositis. Prebiotics are indigestible compounds, commonly oligosaccharides, which seek to reverse chemotherapy-induced intestinal dysbiosis through selective colonization of the intestinal microbiota by probiotic bacteria. In addition, evidence is emerging that certain prebiotics contribute to nutrient digestibility and absorption, modulate intestinal barrier function through effects on mucin expression, and also modify mucosal immune responses, possibly via inflammasome-mediated processes. This review examines the known mechanisms of prebiotic action and explores their potential to reduce the severity of chemotherapy-induced mucositis in the intestine.Hanru Wang, Mark S Geier and Gordon S Howart
Simon Says: A Liddle Night Music With those Depreciation Deductions, Please
This 1995 article, co-authored with Joseph M. Dodge, explores why the decision in Simon v. Commissioner, 103 T.C. 247 (1994), was wrong, effectively allowing premature deduction of a capital expenditure and, thus, consumption taxation (as opposed to income taxation)
Quantitative spectral analysis of the sdB star HD 188112: a helium-core white dwarf progenitor
HD 188112 is a bright (V = 10.2 mag) hot subdwarf B (sdB) star with a mass
too low to ignite core helium burning and is therefore considered as a
pre-extremely low mass (ELM) white dwarf (WD). ELM WDs (M 0.3 Msun) are
He-core objects produced by the evolution of compact binary systems. We present
in this paper a detailed abundance analysis of HD 188112 based on
high-resolution Hubble Space Telescope (HST) near and far-ultraviolet
spectroscopy. We also constrain the mass of the star's companion. We use hybrid
non-LTE model atmospheres to fit the observed spectral lines and derive the
abundances of more than a dozen elements as well as the rotational broadening
of metallic lines. We confirm the previous binary system parameters by
combining radial velocities measured in our UV spectra with the already
published ones. The system has a period of 0.60658584 days and a WD companion
with M 0.70 Msun. By assuming a tidally locked rotation, combined with
the projected rotational velocity (v sin i = 7.9 0.3 km s) we
constrain the companion mass to be between 0.9 and 1.3 Msun. We further discuss
the future evolution of the system as a potential progenitor of a
(underluminous) type Ia supernova. We measure abundances for Mg, Al, Si, P, S,
Ca, Ti, Cr, Mn, Fe, Ni, and Zn, as well as for the trans-iron elements Ga, Sn,
and Pb. In addition, we derive upper limits for the C, N, O elements and find
HD 188112 to be strongly depleted in carbon. We find evidence of non-LTE
effects on the line strength of some ionic species such as Si II and Ni II. The
metallic abundances indicate that the star is metal-poor, with an abundance
pattern most likely produced by diffusion effects.Comment: Accepted for publication in A&
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