229 research outputs found
Infanticide in wolves: seasonality of mortalities and attacks at dens support evolution of territoriality
Evidence for territoriality is usually correlative or post hoc as we observe the results of past selection that are challenging to detect. Wolves (Canis lupus) are considered territorial because of competition for food (resource defense), yet they exhibit classic intrinsic behaviors of social regulation (protection against infanticide). This emphasis on prey and infrequent opportunity to observe wild wolf behavior has led to little investigation into the causes of or competitive underpinnings in the evolution of wolf territoriality. We report 6 cases of territorial wolf packs attacking neighboring packs at or near their den; 2 attacks were observed in detail. In all cases, except perhaps one, the attacking pack killed adult wolves either at the den or near it; in 4 cases, pups were probably lost. Loss of pups led to future loss of territory and in one case pack cessation. Intraspecific killing (measured in collared adults only) peaked in April, the month when pups were born and helpless in dens, even though aggressive interactions were at their seasonal low. Twelve of 13 (92%) of the wolves killed during the denning season (March, April, May) were reproductive (males and females), and 8 of 12 were dominant individuals (highest ranking wolf for that sex in the pack). Wolf–wolf killings were also high in October and December, the beginning and middle of the nomadic season, respectively. Aggressive interactions were more frequent during the nomadic season when wolves were roaming their territory as a group compared to the denning season when wolf activity was centered on the den and pack members less cohesive. We conclude that attacks on dens are a more effective form of interpack competition than interference during the breeding season, the current best-supported hypothesis, and that protected pup-rearing space is the primary cause of wolf territoriality
Pre-galactic metal enrichment - The chemical signatures of the first stars
The emergence of the first sources of light at redshifts of z ~ 10-30
signaled the transition from the simple initial state of the Universe to one of
increasing complexity. We review recent progress in our understanding of the
formation of the first stars and galaxies, starting with cosmological initial
conditions, primordial gas cooling, and subsequent collapse and fragmentation.
We emphasize the important open question of how the pristine gas was enriched
with heavy chemical elements in the wake of the first supernovae. We conclude
by discussing how the chemical abundance patterns conceivably allow us to probe
the properties of the first stars and subsequent stellar generations, and allow
us to test models of early metal enrichment.Comment: 52 pages, 20 figures, clarifications, references added, accepted for
publication in the Reviews of Modern Physic
Star Formation in the Milky Way and Nearby Galaxies
We review progress over the past decade in observations of large-scale star
formation, with a focus on the interface between extragalactic and Galactic
studies. Methods of measuring gas contents and star formation rates are
discussed, and updated prescriptions for calculating star formation rates are
provided. We review relations between star formation and gas on scales ranging
from entire galaxies to individual molecular clouds.Comment: 55 pages, 15 figures, in press for Annual Reviews of Astronomy and
Astrophysics; Updated with corrected equation 5, improved references, and
other minor change
Towards the field binary population: Influence of orbital decay on close binaries
Surveys of the binary populations in the solar neighbourhood have shown that
the periods of G- and M-type stars are log-normally distributed. However,
observations of young binary populations suggest a log-uniform distribution.
Clearly some process(es) change the period distribution over time. Most stars
form in star clusters, in which two important dynamical processes occur: i)
gas-induced orbital decay of embedded binary systems and ii) destruction of
soft binaries in three-body interactions. The emphasis here is on orbital decay
which has been largely neglected so far. Using a combination of Monte-Carlo and
dynamical nbody modelling it is demonstrated here that the cluster dynamics
destroys the number of wide binaries, but leaves short-period binaries
basically undisturbed even for a initially log-uniform distribution. By
contrast orbital decay significantly reduces the number and changes the
properties of short-period binaries, but leaves wide binaries largely
uneffected. Until now it was unclear whether the short period distribution of
the field is unaltered since its formation. It is shown here, that orbital
decay is a prime candidate for such a task. In combination the dynamics of
these two processes, convert an initial log-uniform distribution to a
log-normal period distribution. The probability is 94% that the evolved and
observed period distribution were sampled from the same parent distribution.
This means binaries can be formed with periods that are sampled from the
log-uniform distribution. As the cluster evolves, short-period binaries are
merged to single stars by the gas-induced orbital decay while the dynamical
evolution in the cluster destroys wide binaries. The combination of these two
equally important processes reshapes a initial log-uniform period distribution
to the log-normal period distribution, that is observed in the field
(abridged).Comment: 9 pages, 9 figure
Using AI/ML to predict blending performance and process sensitivity for Continuous Direct Compression (CDC)
Utilising three artificial intelligence (AI)/machine learning (ML) tools, this study explores the prediction of fill level in inclined linear blenders at steady state by mapping a wide range of bulk powder characteristics to processing parameters. Predicting fill levels enables the calculation of blade passes (strain), known from existing literature to enhance content uniformity. We present and train three AI/ML models, each demonstrating unique predictive capabilities for fill level. These models collectively identify the following rank order of feature importance: RPM, Mixing Blade Region (MB) size, Wall Friction Angle (WFA), and Feed Rate (FR). Random Forest Regression, a machine learning algorithm that constructs a multitude of decision trees at training time and outputs the mode of the classes (classification) or mean prediction (regression) of the individual trees, develops a series of individually useful decision trees. but also allows the extraction of logic and breakpoints within the data. A novel tool which utilises smart optimisation and symbolic regression to model complex systems into simple, closed-form equations, is used to build an accurate reduced-order model. Finally, an Artificial Neural Network (ANN), though less interrogable emerges as the most accurate fill level predictor, with an r2 value of 0.97. Following training on single-component mixtures, the models are tested with a four-component powdered paracetamol formulation, mimicking an existing commercial drug product. The ANN predicts the fill level of this formulation at three RPMs (250, 350 and 450) with a mean absolute error of 1.4%. Ultimately, the modelling tools showcase a framework to better understand the interaction between process and formulation. The result of this allows for a first-time-right approach for formulation development whilst gaining process understanding from fewer experiments. Resulting in the ability to approach risk during product development whilst gaining a greater holistic understanding of the processing environment of the desired formulation.</p
Evolution of the binary population in young dense star clusters
Context: Field stars are not always single stars, but can often be found in
bound double systems. Since binary frequencies in the birth places of stars,
young embedded clusters, are sometimes even higher than on average the question
arises of how binary stars form in young dense star clusters and how their
properties evolve to those observed in the field population.
Aims: We assess, the influence of stellar dynamical interactions on the
primordial binary population in young dense cluster environments.
Methods: We perform numerical N-body simulations of the Orion Nebula Cluster
like star cluster models including primordial binary populations using the
simulation code nbody6++.
Results: We find two remarkable results that have yet not been reported: The
first is that the evolution of the binary frequency in young dense star
clusters is independent predictably of its initial value. The time evolution of
the normalized number of binary systems has a fundamental shape. The second
main result is that the mass of the primary star is of vital importance to the
evolution of the binary. The more massive a primary star, the lower the
probability that the binary is destroyed by gravitational interactions. This
results in a higher binary frequency for stars more massive than 2\Msun
compared to the binary frequency of lower mass stars. The observed increase in
the binary frequency with primary mass is therefore most likely not due to
differences in the formation process but can be entirely explained as a
dynamical effect.
Conclusions: Our results allow us to draw conclusions about the past and the
future number of binary systems in young dense star clusters and demonstrate
that the present field stellar population has been influenced significantly by
its natal environments.Comment: 8 pages, 6 figure
Variable Accretion Rates and Fluffy First Stars
We combine the output of hydrodynamical simulations of Population III star
cluster formation with stellar evolution models, and calculate the evolution of
protostars experiencing variable mass accretion rates due to interactions
within a massive disk. We find that the primordial protostars are extended
'fluffy' objects for the bulk of their pre-main-sequence lifetimes. Accretion
luminosity feedback from such objects is high, but as shown in previous work,
has a minimal effect on the star cluster. The extended radii of the protostars,
combined with the observation of close encounters in the simulations, suggests
that mergers will occur in such systems. Furthermore, mass transfer between
close protostellar binaries with extended radii could lead to massive tight
binaries, which are a possible progenitor of gamma ray bursts.Comment: 7 pages, 6 figures, 2 tables. To be published in MNRA
Ultrafast Electronic Band Gap Control in an Excitonic Insulator
We report on the nonequilibrium dynamics of the electronic structure of the layered semiconductor Ta2NiSe5 investigated by time- and angle-resolved photoelectron spectroscopy. We show that below the critical excitation density of FC=0.2 mJ cm-2, the band gap narrows transiently, while it is enhanced above FC. Hartree-Fock calculations reveal that this effect can be explained by the presence of the low-temperature excitonic insulator phase of Ta2NiSe5, whose order parameter is connected to the gap size. This work demonstrates the ability to manipulate the band gap of Ta2NiSe5 with light on the femtosecond time scale
The Effects of Accretion Luminosity upon Fragmentation in the Early Universe
We introduce a prescription for the luminosity from accreting protostars into
smoothed particle hydrodynamics simulation, and apply the method to simulations
of five primordial minihalos generated from cosmological initial conditions. We
find that accretion luminosity delays fragmentation within the halos, but does
not prevent it. In halos that slowly form a low number of protostars, the
accretion luminosity can reduce the number of fragments that are formed before
the protostars start ionising their surroundings. However, halos that rapidly
form many protostars become dominated by dynamical processes, and the effect of
accretion luminosity becomes negligible. Generally the fragmentation found in
the halos is highly dependent on the initial conditions. Accretion luminosity
does not substantially affect the accretion rates experienced by the
protostars, and is far less important than dynamical interactions, which can
lead to ejections that effectively terminate the accretion. We find that the
accretion rates onto the inner regions of the disks (20 AU) around the
protostars are highly variable, in contrast to the constant or smoothly
decreasing accretion rates currently used in models of the pre-main sequence
evolution of Population III stars.Comment: 12 pages, 10 figures and 3 tables. Accepted by MNRA
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