896 research outputs found
A phylogenetic comparative analysis on the evolution of sequential hermaphroditism in seabreams (Teleostei : Sparidae)
The Sparids are an ideal group of fish in which to study the evolution of sexual systems since they
exhibit a great sexual diversity, from gonochorism (separate sexes) to protandrous (male-first) and
protogynous (female-first) sequential hermaphroditism (sex-change). According to the size-advantage
model (SAM), selection should favour sex change when the second sex achieves greater reproductive
success at a larger body size than the first sex. Using phylogenetic comparative methods and a sample
of 68 sparid species, we show that protogyny and protandry evolve from gonochorism but evolutionary
transitions between these two forms of sequential hermaphroditism are unlikely to happen. Using male
gonadosomatic index (GSI) as a measure of investment in gametes and proxy for sperm competition,
we find that, while gonochoristic and protogynous species support the predictions of SAM, protandrous
species do not, as they exhibit higher GSI values than expected even after considering mating
systems and spawning modes. We suggest that small males of protandrous species have to invest
disproportionally more in sperm production than predicted not only when spawning in aggregations
with high levels of sperm competition, but also when spawning in pairs due to the need to fertilize
highly fecund females, much larger than themselves. We propose that this compensatory mechanism,
together with Bateman’s principles in sequential hermaphrodites, should be formally incorporated in
the SAM
Strangelet spectra from type II supernovae
We study in this work the fate of strangelets injected as a contamination in
the tail of a "strange matter-driven" supernova shock. A simple model for the
fragmentation and braking of the strangelets when they pass through the
expanding oxygen shell is presented and solved to understand the reprocessing
of this component. We find that the escaping spectrum is a scaled-down version
of the one injected at the base of the oxygen shell. The supernova source is
likely to produce low-energy particles of quite independently
of the initial conditions. However, it is difficult that ultrarrelativistic
strangelets (such as the hypothetical Centauro primaries) can have an origin in
those explosive events.Comment: RevTex file, 5 pp., no figure
Effect of Muons on the Phase Transition in Magnetised Proto-Neutron Star Matter
We study the effect of inclusion of muons and the muon neutrinos on the phase
transition from nuclear to quark matter in a magnetised proto-neutron star and
compare our results with those obtained by us without the muons. We find that
the inclusion of muons changes slightly the nuclear density at which transition
occurs.However the dependence of this transition density on various chemical
potentials, temperature and the magnetic field remains quantitatively the same.Comment: LaTex2e file with four postscript figure
Decay versus survival of a localized state subjected to harmonic forcing: exact results
We investigate the survival probability of a localized 1-d quantum particle
subjected to a time dependent potential of the form with
or . The particle is
initially in a bound state produced by the binding potential . We
prove that this probability goes to zero as for almost all values
of , , and . The decay is initially exponential followed by a
law if is not close to resonances and is small; otherwise
the exponential disappears and Fermi's golden rule fails. For exceptional sets
of parameters and the survival probability never decays to zero,
corresponding to the Floquet operator having a bound state. We show similar
behavior even in the absence of a binding potential: permitting a free particle
to be trapped by harmonically oscillating delta function potential
Measuring ^{12}C(&alpha,&gamma)^{16}O from White Dwarf Asteroseismology
During helium burning in the core of a red giant, the relative rates of the
3&alpha and ^{12}C(&alpha,&gamma)^{16}O reactions largely determine the final
ratio of carbon to oxygen in the resulting white dwarf star. The uncertainty in
the 3&alpha reaction at stellar energies due to the extrapolation from
high-energy laboratory measurements is relatively small, but this is not the
case for the ^{12}C(&alpha,&gamma)^{16}O reaction. Recent advances in the
analysis of asteroseismological data on pulsating white dwarf stars now make it
possible to obtain precise measurements of the central ratio of carbon to
oxygen, providing a more direct way to measure the ^{12}C(&alpha,&gamma)^{16}O
reaction rate at stellar energies. We assess the systematic uncertainties of
this approach and quantify small shifts in the measured central oxygen
abundance originating from the observations and from model settings that are
kept fixed during the optimization. Using new calculations of white dwarf
internal chemical profiles, we find a rate for the ^{12}C(&alpha,&gamma)^{16}O
reaction that is significantly higher than most published values. The accuracy
of this method may improve as we modify some of the details of our description
of white dwarf interiors that were not accessible through previous
model-fitting methods.Comment: 8 pages, 4 figures, 3 tables, uses emulateapj5.sty, Accepted for
publication in the Astrophysical Journa
Diffusive Ionization of Relativistic Hydrogen-Like Atom
Stochastic ionization of highly excited relativistic hydrogenlike atom in the
monochromatic field is investigated. A theoretical analisis of chaotic dynamics
of the relativistic electron based on Chirikov criterion is given for the cases
of one- and three-dimensional atoms. Critical value of the external field is
evaluated analitically. The diffusion coefficient and ionization time are
calculated.Comment: 13 pages, latex, no figures, submitted to PR
Native and non-native egg parasitoids associated with brown marmorated stink bug (Halyomorpha halys [stål, 1855]; hemiptera: Pentatomidae) in western slovenia
Halyomorpha halys (Hemiptera: Pentatomidae), native to East Asia, has become a globally invasive pest, as a serious threat to agricultural production and a notorious nuisance pest in urban areas. Considerable efforts have been made so far to develop effective pest control measures to prevent crop damage. Biological control of this invasive stink bug by egg parasitoids has proven to be the most environmentally sustainable long-term solution. Knowledge of the native egg parasitoid fauna is of key importance when implementing a biological control program. Therefore, the main objective of our study was to detect egg parasitoid species associated with H. halys in the Goriška region (Western Slovenia) and to evaluate their impact on the pest population under field conditions. In the years 2019 and 2020, around 4600 H. halys eggs were collected in the wild and more than 3400 sentinel eggs were exposed to detect parasitoids in the field. Five egg-parasitoid species emerged from H. halys eggs: Anastatus bifasciatus (Hymenoptera: Eupelmidae), Telenomus sp., Trissolcus basalis, Trissolcus mitsukurii (Hymenoptera: Scelionidae) and Ooencyrtus telenomicida (Hymenoptera: Encyrtidae), all of them are new records for Slovenia. The native species, An. bifasciatus, dominated in urban and suburban areas, while non-native Tr. mitsukurii prevailed in agricultural areas. Overall parasitism rates of naturally laid eggs by the parasitoid species complex in 2019 and 2020 was 3.0 and 14.4%, respectively. Rapid recruitment of native parasitoids, early detection of an effective alien parasitoid species and increasing overall parasitism rates are very encouraging results, which need to be followed and verified in future research
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