3,192 research outputs found
Respiration as a percentage of daily photosynthesis in whole plants is homeostatic at moderate, but not high, growth temperatures
• Here, we investigated the impact of temperature on the carbon economy of two Plantago species from contrasting habitats. • The lowland Plantago major and the alpine Plantago euryphylla were grown hydroponically at three constant temperatures: 13, 2
Are Post-Newtonian templates faithful and effectual in detecting gravitational signals from neutron star binaries?
We compute the overlap function between Post-Newtonian (PN) templates and
gravitational signals emitted by binary systems composed of one neutron star
and one point mass, obtained by a perturbative approach. The calculations are
performed for different stellar models and for different detectors, to estimate
how effectual and faithful the PN templates are, and to establish whether
effects related to the internal structure of neutron stars may possibly be
extracted by the matched filtering technique.Comment: 14 pages, 3 figures, accepted for publication in Phys. Rev.
Evolution and CNO yields of Z=10^-5 stars and possible effects on CEMP production
Our main goals are to get a deeper insight into the evolution and final fates
of intermediate-mass, extremely metal-poor (EMP) stars. We also aim to
investigate their C, N, and O yields. Using the Monash University Stellar
Evolution code we computed and analysed the evolution of stars of metallicity Z
= 10^-5 and masses between 4 and 9 M_sun, from their main sequence until the
late thermally pulsing (super) asymptotic giant branch, TP-(S)AGB phase. Our
model stars experience a strong C, N, and O envelope enrichment either due to
the second dredge-up, the dredge-out phenomenon, or the third dredge-up early
during the TP-(S)AGB phase. Their late evolution is therefore similar to that
of higher metallicity objects. When using a standard prescription for the mass
loss rates during the TP-(S)AGB phase, the computed stars lose most of their
envelopes before their cores reach the Chandrasekhar mass, so our standard
models do not predict the occurrence of SNI1/2 for Z = 10^-5 stars. However, we
find that the reduction of only one order of magnitude in the mass-loss rates,
which are particularly uncertain at this metallicity, would prevent the
complete ejection of the envelope, allowing the stars to either explode as an
SNI1/2 or become an electron-capture SN. Our calculations stop due to an
instability near the base of the convective envelope that hampers further
convergence and leaves remnant envelope masses between 0.25 M_sun for our 4
M_sun model and 1.5 M_sun for our 9 M_sun model. We present two sets of C, N,
and O yields derived from our full calculations and computed under two
different assumptions, namely, that the instability causes a practically
instant loss of the remnant envelope or that the stars recover and proceed with
further thermal pulses. Our results have implications for the early chemical
evolution of the Universe.Comment: 12 pages, 13 figures, accepted for publication in A&
The Role of Oxidation Compounds in Biofilm Growth on Polyethylene Geomembrane Barriers Used in Landfill
In a model study, polyethylene was preoxidized and incubated for a period of 7 months at 40°C in two different municipal solid waste leachates. During the postexperimental analyses, specific attention was paid to the carbonyl species and carboxylic acid depletion during the environmental exposure because it is well known that carboxylic acids are believed to be a potential substrate for the development of microorganisms. The results showed that the carbonyl as well as the carboxylic acid depletion observed follows first-order kinetics. The biofilm formation was characterized using a suite of analytical techniques, and its formation was compared with the carboxylic acid and carbonyl depletion profil
TransverseDiff gravity is to scalar-tensor as unimodular gravity is to General Relativity
Transverse Diffeomorphism (TDiff) theories are well-motivated theories of
gravity from the quantum perspective, which are based upon a gauge symmetry
principle. The main contribution of this work is to firmly establish a
correspondence between TransverseDiff and the better-known scalar-tensor
gravity --- in its more general form ---, a relation which is completely
analogous to that between unimodular gravity and General Relativity. We then
comment on observational aspects of TDiff. In connection with this proof, we
derive a very general rule that determines under what conditions the procedure
of fixing a gauge symmetry can be equivalently applied before the variational
principle leading to the equations of motion, as opposed to the standard
procedure, which takes place afterwards; this rule applies to gauge-fixing
terms without derivatives.Comment: 10 pages; amsart style; v3: version as appeared in JCAP, redaction
improve
Temperature and magnetic field dependences of the elastic constants of Ni-Mn-Al magnetic Heusler alloys
We report on measurements of the adiabatic second order elastic constants of
the off-stoichiometric NiMnAl single crystalline Heusler
alloy. The variation in the temperature dependence of the elastic constants has
been investigated across the magnetic transition and over a broad temperature
range. Anomalies in the temperature behaviour of the elastic constants have
been found in the vicinity of the magnetic phase transition. Measurements under
applied magnetic field, both isothermal and variable temperature, show that the
value of the elastic constants depends on magnetic order, thus giving evidence
for magnetoelastic coupling in this alloy system.Comment: 7 pages, 5 figures. Accepted for publication in Physical the Review
Gravitational signals emitted by a point mass orbiting a neutron star: effects of stellar structure
The effects that the structure of a neutron star would have on the
gravitational emission of a binary system are studied in a perturbative regime,
and in the frequency domain. Assuming that a neutron star is perturbed by a
point mass moving on a close, circular orbit, we solve the equations of stellar
perturbations in general relativity to evaluate the energy lost by the system
in gravitational waves. We compare the energy output obtained for different
stellar models with that found by assuming that the perturbed object is a black
hole with the same mass, and we discuss the role played by the excitation of
the stellar modes. Ouresults indicate that the stellar structure begins to
affect the emitted power when the orbital velocity is v >0.2c (about 185 Hz for
a binary system composed of two canonical neutron stars). We show that the
differences between different stellar models and a black hole are due mainly to
the excitation of the quasinormal modes of the star. Finally, we discuss to
what extent and up to which distance the perturbative approach can be used to
describe the interaction of a star and a pointlike massive body.Comment: 22 pages, 6 figures, to appear in Phys. Rev. D. Revised version,
added one table and extended discussio
Observables, gauge invariance, and the role of the observers in the limit from general relativity to special relativity
Some conceptual issues concerning general invariant theories, with special
emphasis on general relativity, are analyzed. The common assertion that
observables must be required to be gauge invariant is examined in the light of
the role played by a system of observers. Some features of the reduction of the
gauge group are discussed, including the fact that in the process of a partial
gauge fixing the reduction at the level of the gauge group and the reduction at
the level of the variational principle do not commute. Distinctions between the
mathematical and the physical concept of gauge symmetry are discussed and
illustrated with examples. The limit from general relativity to special
relativity is considered as an example of a gauge group reduction that is
allowed in some specific physical circumstances. Whether and when the
Poincar\'e group must be considered as a residual gauge group will come out as
a result of our analysis, that applies, in particular, to asymptotically flat
spaces.Comment: 17 page
Neutrino Opacities in Neutron Stars with Kaon Condensates
The neutrino mean free paths in hot neutron-star matter are obtained in the
presence of kaon condensates. The kaon-induced neutrino absorption process,
which is allowed only in the presence of kaon condensates, is considered for
both nondegenerate and degenerate neutrinos. The neutrino mean free path due to
this process is compared with that for the neutrino-nucleon scattering. While
the mean free path for the kaon-induced neutrino absorption process is shown to
be shorter than the ordinary two-nucleon absorption process by several orders
of magnitude when temperature is not very high, the neutrino-nucleon scattering
process has still a dominant contribution to the neutrino opacity. Thus, the
kaon-induced neutrino absorption process has a minor effect on the thermal and
dynamical evolution of protoneutron stars.Comment: 35 pages, 4 figure
Double Fe-impurity charge state in the topological insulator BiSe
The influence of individual impurities of Fe on the electronic properties of
topological insulator BiSe is studied by Scanning Tunneling Microscopy.
The microscope tip is used in order to remotely charge/discharge Fe impurities.
The charging process is shown to depend on the impurity location in the
crystallographic unit cell, on the presence of other Fe impurities in the close
vicinity, as well as on the overall doping level of the crystal. We present a
qualitative explanation of the observed phenomena in terms of tip-induced local
band bending. Our observations evidence that the specific impurity neighborhood
and the position of the Fermi energy with respect to the Dirac point and bulk
bands have both to be taken into account when considering the electron
scattering on the disorder in topological insulators.Comment: 10 pages, accepted for publication in Applied Physics Letters, minor
bugs were correcte
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