12,025 research outputs found
Radial oscillations of neutral and charged hybrid stars
We construct stellar models of hadron stars and hybrid stars and calculate
the frequencies of their lowest radial mode of vibration. Chandrasekhar's
equation for radial oscillations is generalized for stars with internal
electric fields and earlier versions of that generalization are simplified. For
the hybrid stars a Gibbs construction is employed. It is found that the
softening of the equation of state associated with the presence of deconfined
quarks reduces the oscillation frequency. We show that a slight charge
inbalance should lead to increased maximum mass, decreased central density and
lower oscillation frequencies
Quantum quenches in the Dicke model: statistics of the work done and of other observables
We study the statistics of the work done in a zero temperature quench of the
coupling constant in the Dicke model describing the interaction between a gas
of two level atoms and a single electromagnetic cavity mode. When either the
final or the initial coupling constants approach the critical coupling
that separates the normal and superradiant phases of the system,
the probability distribution of the work done displays singular behavior. The
average work tends to diverge as the initial coupling parameter is brought
closer to the critical value . In contrast, for quenches ending
close to criticality, the distribution of work has finite moments but displays
a sequence of edge singularities. This contrasting behavior is related to the
difference between the processes of compression and expansion of a particle
subject to a sudden change of its confining potential. We confirm this by
studying in detail the time dependent statistics of other observables, such as
the quadratures of the photons and the total occupation of the bosonic modes.Comment: 8 pages, 2 figure
Residence time of symmetric random walkers in a strip with large reflective obstacles
We study the effect of a large obstacle on the so called residence time,
i.e., the time that a particle performing a symmetric random walk in a
rectangular (2D) domain needs to cross the strip. We observe a complex
behavior, that is we find out that the residence time does not depend
monotonically on the geometric properties of the obstacle, such as its width,
length, and position. In some cases, due to the presence of the obstacle, the
mean residence time is shorter with respect to the one measured for the
obstacle--free strip. We explain the residence time behavior by developing a 1D
analog of the 2D model where the role of the obstacle is played by two defect
sites having a smaller probability to be crossed with respect to all the other
regular sites. The 1D and 2D models behave similarly, but in the 1D case we are
able to compute exactly the residence time finding a perfect match with the
Monte Carlo simulations
Decentralised Coordination of Low-Power Embedded Devices Using the Max-Sum Algorithm
This paper considers the problem of performing decentralised coordination of low-power embedded devices (as is required within many environmental sensing and surveillance applications). Specifically, we address the generic problem of maximising social welfare within a group of interacting agents. We propose a novel representation of the problem, as a cyclic bipartite factor graph, composed of variable and function nodes (representing the agents’ states and utilities respectively). We show that such representation allows us to use an extension of the max-sum algorithm to generate approximate solutions to this global optimisation problem through local decentralised message passing. We empirically evaluate this approach on a canonical coordination problem (graph colouring), and benchmark it against state of the art approximate and complete algorithms (DSA and DPOP). We show that our approach is robust to lossy communication, that it generates solutions closer to those of DPOP than DSA is able to, and that it does so with a communication cost (in terms of total messages size) that scales very well with the number of agents in the system (compared to the exponential increase of DPOP). Finally, we describe a hardware implementation of our algorithm operating on low-power Chipcon CC2431 System-on-Chip sensor nodes
Softening of the equation of state of matter at large densities and temperatures: chiral symmetry restoration vs. quark deconfinement
We discuss two models for describing the behavior of matter at large
densities and intermediate temperatures. In both models a softening of the
equation of state takes place due to the appearance of new degrees of freedom.
The first is a hadronic model in which the softening is due to chiral symmetry
restoration. In the second model the softening is associated with the formation
of clusters of quarks in the mixed phase. We show that both models allow a
significant softening but, in the first case the bulk modulus is mainly
dependent on the density, while in the mixed phase model it also strongly
depends on the temperature. We also show that the bulk modulus is not vanishing
in the mixed phase due to the presence of two conserved charges, the baryon and
the isospin one. Only in a small region of densities and temperatures the
incompressibility becomes extremely small. Finally we compare our results with
recent analysis of heavy ion collisions at intermediate energies.Comment: 4 pages, 4 figures, editorially accepted versio
Exotic Heavy Quarkonium Spectroscopy: A Mini-review
Since nine years experiments have been observing a host of exotic states
decaying into heavy quarkonia. The interpretation of most of them still remains
uncertain and, in some cases, controversial, notwithstanding a considerable
progress has been made on the quality of the experimental information available
and a number of ideas and models have been put forward to explain the
observations. In this mini-review we will summarize the measurements, with the
most recent updates, and list the useful ones yet to be done. We will discuss
the problem of the spin of the X, which could hide some major surprise on its
interpretation, and review some more phenomenological issues debated in the
field.Comment: 14 pages, 2 figures, 5 tables. To appear in Mod. Phys. Lett.
Weak values are quantum: you can bet on it
The outcome of a weak quantum measurement conditioned to a subsequent
postselection (a weak value protocol) can assume peculiar values. These results
cannot be explained in terms of conditional probabilistic outcomes of
projective measurements. However, a classical model has been recently put
forward that can reproduce peculiar expectation values, reminiscent of weak
values. This led the authors of that work to claim that weak values have an
entirely classical explanation. Here we discuss what is quantum about weak
values with the help of a simple model based on basic quantum mechanics. We
first demonstrate how a classical theory can indeed give rise to non-trivial
conditional values, and explain what features of weak values are genuinely
quantum. We finally use our model to outline some main issues under current
research.Comment: 6 pages, 1 figur
Automatic Genre Classification of Latin Music Using Ensemble of Classifiers
This paper presents a novel approach to the task of automatic music genre classification which is based on ensemble learning. Feature vectors are extracted from three 30-second music segments from the beginning, middle and end of each music piece. Individual classifiers are trained to account for each music segment. During classification, the output provided by each classifier is combined with the aim of improving music genre classification accuracy. Experiments carried out on a dataset containing 600 music samples from two Latin genres (Tango and Salsa) have shown that for the task of automatic music genre classification, the features extracted from the middle and end music segments provide better results than using the beginning music segment. Furthermore, the proposed ensemble method provides better accuracy than using single classifiers and any individual segment
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Studying biological science does not lead to adoption of a healthy lifestyle
Aims:
The lifestyle and physical activity (PA) habits of young people play a key role in the prevention of cardiovascular and metabolic diseases at older ages. The current generation of biological science students at university holds promise for better future medicine and medical technology. However, their physical fitness and lifestyle are often ignored.
Methods:
Lifestyle, PAs and common risk factors for cardiovascular disease before, and at, university were collected from 408 students using self-completed, anonymous surveys between the academic years of 2017 and 2019 from the School of Biological Sciences, University of Reading. Statistical analysis was performed using SAS® 9.4 software.
Results:
Among the 408 participants, 134 were male and 274 were female with a mean (SD) age of 19.6 (2.24). Approximately 19% of participants consumed alcohol beyond the safe limit of <14 units/week (112 g/week). Among them, 65% were males. Before university, 47% of students failed to meet the UK National Physical Activity Guidelines (NPAG) which increased to 56% during university with males exhibiting a steeper incline. Compared to their lifestyles before university, more students had insufficient sleep and displayed greater sedentariness during university. Moreover, 16% of students declared no engagement in PA which was greater than the value of 12% before university. Fitness perceptions worsened by 11% during university particularly for females. Statistical analysis revealed that gender, BMI and fitness perceptions were significantly correlated with PA levels. The most prevalent explanation for inadequacy in meeting NPAG was insufficient time.
Conclusion:
Compared to their pre-university lifestyles, biological science students at university are more likely to adopt unhealthier behaviours with less time for exercise and prolonged sedentary behaviours, which increases the risk for cardiovascular diseases. It is important to raise awareness of their fitness perceptions and to encourage health-promoting programmes at university
Wigner-Weyl isomorphism for quantum mechanics on Lie groups
The Wigner-Weyl isomorphism for quantum mechanics on a compact simple Lie
group is developed in detail. Several New features are shown to arise which
have no counterparts in the familiar Cartesian case. Notable among these is the
notion of a `semiquantised phase space', a structure on which the Weyl symbols
of operators turn out to be naturally defined and, figuratively speaking,
located midway between the classical phase space and the Hilbert space
of square integrable functions on . General expressions for the star product
for Weyl symbols are presented and explicitly worked out for the angle-angular
momentum case.Comment: 32 pages, Latex2
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