702 research outputs found
Gyrochronology and its usage for main sequence cool star ages
The construction of all age indicators consists of certain basic steps which
lead to the identification of the properties desirable for stellar age
indicators. Prior age indicators for main sequence field stars possess only
some of these properties. The measured rotation periods of cool stars are
particularly useful in this respect because they have well-defined dependencies
that allow stellar ages to be determined with ~20% errors. This method, called
gyrochronology, is explained informally in this talk, shown to have the desired
properties, compared to prior methods, and used to derive ages for samples of
main sequence field stars.Comment: 10 pages, 6 figures, presented at IAU258, Ages of Star
Translocation of a polymer chain driven by a dichotomous noise
We consider the translocation of a one-dimensional polymer through a pore
channel helped by a motor driven by a dichotomous noise with time exponential
correlation. We are interested in the study of the translocation time, mean
velocity and stall force of the system as a function of the mean driving
frequency. We find a monotonous translocation time, in contrast with the mean
velocity which shows a pronounced maximum at a given frequency. Interestingly,
the stall force shows a nonmonotonic behavior with the presence of a minimum.
The influence of the spring elastic constant to the mean translocation times
and velocities is also presented.Comment: 11 pages, 7 figure
Study of contamination of liquid oxygen by gaseous nitrogen First quarterly report, 1 Jul. - 30 Sep. 1964
Analytical model development for contamination study of liquid oxygen by gaseous nitroge
Noise Induced Phenomena in the Dynamics of Two Competing Species
Noise through its interaction with the nonlinearity of the living systems can
give rise to counter-intuitive phenomena. In this paper we shortly review noise
induced effects in different ecosystems, in which two populations compete for
the same resources. We also present new results on spatial patterns of two
populations, while modeling real distributions of anchovies and sardines. The
transient dynamics of these ecosystems are analyzed through generalized
Lotka-Volterra equations in the presence of multiplicative noise, which models
the interaction between the species and the environment. We find noise induced
phenomena such as quasi-deterministic oscillations, stochastic resonance, noise
delayed extinction, and noise induced pattern formation. In addition, our
theoretical results are validated with experimental findings. Specifically the
results, obtained by a coupled map lattice model, well reproduce the spatial
distributions of anchovies and sardines, observed in a marine ecosystem.
Moreover, the experimental dynamical behavior of two competing bacterial
populations in a meat product and the probability distribution at long times of
one of them are well reproduced by a stochastic microbial predictive model.Comment: 23 pages, 8 figures; to be published in Math. Model. Nat. Phenom.
(2016
The Influence of professional doctorates on practice and the workplace
This paper investigates the influence that undertaking a professional doctorate has on the practice of the graduate and their workplace or organisation. There is a growing literature on how undertaking such advanced development influences the individual graduate at the personal and professional level but there is little evidence of a wider impact on practice in general or at the organisational level. This study seeks to address this issue through a qualitative study of practitioners from a range of professional arenas and sectors who have graduated from a professional doctorate within the past 10 years. Through thematic analysis of semi-structured interviews and the candidates’ project reports we explore their experience of applying their learning within their workplaces providing insight into the level and degree of influence such development can have on organisational contexts. The paper does not focus on the academic or personal impact of their experience as the intention of these particular doctoral researchers is the creation of new knowledge embedded in practice
Noise driven translocation of short polymers in crowded solutions
In this work we study the noise induced effects on the dynamics of short
polymers crossing a potential barrier, in the presence of a metastable state.
An improved version of the Rouse model for a flexible polymer has been adopted
to mimic the molecular dynamics by taking into account both the interactions
between adjacent monomers and introducing a Lennard-Jones potential between all
beads. A bending recoil torque has also been included in our model. The polymer
dynamics is simulated in a two-dimensional domain by numerically solving the
Langevin equations of motion with a Gaussian uncorrelated noise. We find a
nonmonotonic behaviour of the mean first passage time and the most probable
translocation time, of the polymer centre of inertia, as a function of the
polymer length at low noise intensity. We show how thermal fluctuations
influence the motion of short polymers, by inducing two different regimes of
translocation in the molecule transport dynamics. In this context, the role
played by the length of the molecule in the translocation time is investigated.Comment: 11 pages, 3 figures, to appear in J. Stat. Mechanics: Theory and
Experiment, 200
Environmental Noise and Nonlinear Relaxation in Biological Systems
We analyse the effects of environmental noise in three different biological
systems: (i) mating behaviour of individuals of \emph{Nezara viridula} (L.)
(Heteroptera Pentatomidae); (ii) polymer translocation in crowded solution;
(iii) an ecosystem described by a Verhulst model with a multiplicative L\'{e}vy
noise.Comment: 32 pages; In "Ecological Modeling" by Ed. Wen-Jun Zhang. ISBN:
978-1-61324-567-5. - Nova Science Publishers, New York, 201
A time-variable, phase-dependent emission line in the X-ray spectrum of the isolated neutron star RXJ0822–4300
RX J0822−4300 is the central compact object associated with the Puppis A supernova remnant. Previous X-ray observations suggested RX J0822−4300 to be a young neutron star with a weak dipole field and a peculiar surface temperature distribution dominated by two antipodal spots with different temperatures and sizes. An emission line at 0.8 keV was also detected. We performed a very deep (130-ks) observation with XMM–Newton, which allowed us to study in detail the phase-resolved properties of RX J0822−4300. Our new data confirm the existence of a narrow spectral feature, best modelled as an emission line, only seen in the ‘soft’-phase interval – when the cooler region is best aligned to the line of sight. Surprisingly, comparison of our recent observations to the older ones yields evidence for a variation in the emission-line component, which can be modelled as a decrease in the central energy from ∼0.80 keV in 2001 to ∼0.73 keV in 2009–10. The line could be generated via cyclotron scattering of thermal photons in an optically-thin layer of gas, or, alternatively, it could originate in low-rate accretion by a debris disc. In any case, a variation in energy, pointing to a variation of the magnetic field in the line-emitting region, cannot be easily accounted for
As low as reasonabily achievable: lowest dose CT angiography in patients with endoleak after endovascular aneurysm repair
Using Magnetic Activity and Galactic Dynamics to Constrain the Ages of M Dwarfs
We present a study of the dynamics and magnetic activity of M dwarfs using
the largest spectroscopic sample of low-mass stars ever assembled. The age at
which strong surface magnetic activity (as traced by H-alpha) ceases in M
dwarfs has been inferred to have a strong dependence on mass (spectral type,
surface temperature) and explains previous results showing a large increase in
the fraction of active stars at later spectral types. Using spectral
observations of more than 40000 M dwarfs from the Sloan Digital Sky Survey, we
show that the fraction of active stars decreases as a function of vertical
distance from the Galactic plane (a statistical proxy for age), and that the
magnitude of this decrease changes significantly for different M spectral
types. Adopting a simple dynamical model for thin disk vertical heating, we
assign an age for the activity decline at each spectral type, and thus
determine the activity lifetimes for M dwarfs. In addition, we derive a
statistical age-activity relation for each spectral type using the dynamical
model, the vertical distance from the Plane and the H-alpha emission line
luminosity of each star (the latter of which also decreases with vertical
height above the Galactic plane).Comment: 8 pages, 5 figures, to appear in the proceedings of IAU 258: The Ages
of Star
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