15,660 research outputs found
Discretising Keyfitz' entropy for studies of actuarial senescence and comparative demography
Keyfitz' entropy is a widely used metric to quantify the shape of the survivorship curve of populations, from plants to animals and microbes. Keyfitz' entropy values <1 correspond to life histories with an increasing mortality rate with age (i.e. actuarial senescence), whereas values >1 correspond to species with a decreasing mortality rate with age (negative senescence), and a Keyfitz entropy of exactly 1 corresponds to a constant mortality rate with age. Keyfitz' entropy was originally defined using a continuous-time model, and has since been discretised to facilitate its calculation from discrete-time demographic data. Here, we show that the previously used discretisation of the continuous-time metric does not preserve the relationship with increasing, decreasing or constant mortality rates. To resolve this discrepancy, we propose a new discrete-time formula for Keyfitz' entropy for age-classified life histories. We show that this new method of discretisation preserves the relationship with increasing, decreasing, or constant mortality rates. We analyse the relationship between the original and the new discretisation, and we find that the existing metric tends to underestimate Keyfitz' entropy for both short-lived species and long-lived species, thereby introducing a consistent bias. To conclude, to avoid biases when classifying life histories as (non-)senescent, we suggest researchers use either the new metric proposed here, or one of the many previously suggested survivorship shape metrics applicable to discrete-time demographic data such as Gini coefficient or Hayley's median.</p
Deuteron Magnetic Quadrupole Moment From Chiral Effective Field Theory
We calculate the magnetic quadrupole moment (MQM) of the deuteron at leading
order in the systematic expansion provided by chiral effective field theory. We
take into account parity and time-reversal violation which, at the quark-gluon
level, results from the QCD vacuum angle and dimension-six operators that
originate from physics beyond the Standard Model. We show that the deuteron MQM
can be expressed in terms of five low-energy constants that appear in the
parity- and time-reversal-violating nuclear potential and electromagnetic
current, four of which also contribute to the electric dipole moments of light
nuclei. We conclude that the deuteron MQM has an enhanced sensitivity to the
QCD vacuum angle and that its measurement would be complementary to the
proposed measurements of light-nuclear EDMs
Evidence for precession of the isolated neutron star RX J0720.4-3125
The XMM-Newton spectra of the isolated neutron star RX J0720.4-3125 obtained
over 4.5 years can be described by sinusoidal variations in the inferred
blackbody temperature, the size of the emitting area and the depth of the
absorption line with a period of 7.1 +/- 0.5 years, which we suggest to be the
precession period of the neutron star. Precession of a neutron star with two
hot spots of different temperature and size, probably not located exactly in
antipodal positions, may account for the variations in the X-ray spectra,
changes in the pulsed fraction, shape of the light curve and the phase-lag
between soft and hard energy bands observed from RX J0720.4-3125. An
independent sinusoidal fit to published and new pulse timing residuals from a
coherent analysis covering ~12 years yields a consistent period of 7.7 +/- 0.6
years supporting the precession model.Comment: Accepted for publication in A&A Letters, 5 pages, 5 figure
Crystallization of two forms of a cyclodextrin inclusion complex containing a common organic guest
The isolation and structural elucidation by single crystal Xray diffraction of triclinic and monoclinic modifications of an inclusion complex of b-cyclodextrin with the same guest, methylparaben, are reported
Cantor type functions in non-integer bases
Cantor's ternary function is generalized to arbitrary base-change functions
in non-integer bases. Some of them share the curious properties of Cantor's
function, while others behave quite differently
Molecular Line Profile Fitting with Analytic Radiative Transfer Models
We present a study of analytic models of starless cores whose line profiles
have ``infall asymmetry,'' or blue-skewed shapes indicative of contracting
motions. We compare the ability of two types of analytical radiative transfer
models to reproduce the line profiles and infall speeds of centrally condensed
starless cores whose infall speeds are spatially constant and range between 0
and 0.2 km s-1. The model line profiles of HCO+ (J=1-0) and HCO+ (J=3-2) are
produced by a self-consistent Monte Carlo radiative transfer code. The analytic
models assume that the excitation temperature in the front of the cloud is
either constant (``two-layer'' model) or increases inward as a linear function
of optical depth (``hill'' model). Each analytic model is matched to the line
profile by rapid least-squares fitting.
The blue-asymmetric line profiles with two peaks, or with a blue shifted peak
and a red shifted shoulder, can be well fit by the ``HILL5'' model (a five
parameter version of the hill model), with an RMS error of 0.02 km s-1. A peak
signal to noise ratio of at least 30 in the molecular line observations is
required for performing these analytic radiative transfer fits to the line
profiles.Comment: 48 pages, 20 figures, accepted for publication in Ap
Trehalose is required for the acquisition of tolerance to a variety of stresses in the filamentous fungus Aspergillus nidulans
Trehalose is a non-reducing disaccharide found at high concentrations in Aspergillus nidulans conidia and rapidly degraded upon induction of conidial germination. Furthermore, trehalose is accumulated in response to a heat shock or to an oxidative shock. The authors have characterized the A. nidulans tpsA gene encoding trehalose-6-phosphate synthase, which catalyses the first step in trehalose biosynthesis. Expression of tpsA in a Saccharomyces cerevisiae tps1 mutant revealed that the tpsA gene product is a functional equivalent of the yeast Tps1 trehalose-6-phosphate synthase. The A. nidulans tpsA-null mutant does not produce trehalose during conidiation or in response to various stress conditions. While germlings of the tpsA mutant show an increased sensitivity to moderate stress conditions (growth at 45 °C or in the presence of 2 mM H2O2), they display a response to severe stress (60 min at 50 °C or in the presence of 100 mM H2O2) similar to that of wild-type germlings. Furthermore, conidia of the tpsA mutant show a rapid loss of viability upon storage. These results are consistent with a role of trehalose in the acquisition of stress tolerance. Inactivation of the tpsA gene also results in increased steady-state levels of sugar phosphates but does not prevent growth on rapidly metabolizable carbon sources (glucose, fructose) as seen in Saccharomyces cerevisiae. This suggests that trehalose 6-phosphate is a physiological inhibitor of hexokinase but that this control is not essential for proper glycolytic flux in A. nidulans. Interestingly, tpsA transcription is not induced in response to heat shock or during conidiation, indicating that trehalose accumulation is probably due to a post-translational activation process of the trehalose 6-phosphate synthase
XMM-NEWTON High Resolution Spectroscopy of NGC 5548
We analyze a 137 ks exposure X-ray spectrum of the Seyfert 1 galaxy NGC 5548
obtained with the XMM-Newton Reflection Grating Spectrometer. Due to the long
exposure time, the spectrum is of higher statistical quality than the previous
observations of this AGN. Therefore, we detect for the first time in NGC 5548
inner-shell transitions from O III to O VI ions, and the Unresolved Transition
Array of M-shell iron. The warm absorber found from this X-ray observation
spans three orders of magnitude in ionization parameter. We detect O III, which
is as lowly ionized as the warm absorber detected in the UV band, to Fe XXIV.
For O VI the column density determined from our X-ray data is an order of
magnitude larger than the column density measured in previous UV observations.
We conclude that there is substantially more low ionized material than
previously deduced from UV observations. However, only a few percent of the
warm absorber detected in the X-rays is lowly ionized. A 99.9 % significant
increase in the derived absorbing column density with higher ionization states
is observed. The outflow velocities determined from the X-ray absorption lines
are consistent with those deduced from the UV lines, evidence, together with
the detection of O VI, that the X-ray and UV warm absorber are different
manifestations of the same phenomenon. From a simple mass conservation
argument, we indicate that our data set is consistent with an outflow with
small opening angle formed due to instabilities in the accretion disk. Possible
due to uncertainties in the radiative transport mechanism, an apparent deviant
iron to oxygen abundance is detected. No strong relativistically broadened
emission lines of O VIII, N VII and C VI were detected.Comment: 10 pages, 10 figures, to be published in A&
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