6,726 research outputs found
Strongly coupled plasma with electric and magnetic charges
A number of theoretical and lattice results lead us to believe that
Quark-Gluon Plasma not too far from contains not only electrically
charged quasiparticles -- quarks and gluons -- but magnetically charged ones --
monopoles and dyons -- as well. Although binary systems like charge-monopole
and charge-dyon were considered in details before in both classical and quantum
settings, it is the first study of coexisting electric and magnetic particles
in many-body context. We perform Molecular Dynamics study of strongly coupled
plasmas with particles and different fraction of magnetic charges.
Correlation functions and Kubo formulae lead to such transport properties as
diffusion constant, shear viscosity and electric conductivity: we compare the
first two with empirical data from RHIC experiments as well as results from
AdS/CFT correspondence. We also study a number of collective excitations in
these systems.Comment: 2nd version, 22 pages, 32 figures: two important new figures have
been included to compare our results with RHIC experiments and AdS/CFT
results; a few new references and comments are added as wel
The differentiation operator on discrete function spaces of a tree
In this paper, we study the differentiation operator acting on discrete
function spaces; that is spaces of functions defined on an infinite rooted
tree. We discuss, through its connection with composition operators, the
boundedness and compactness of this operator. In addition, we discuss the
operator norm and spectrum, and consider when such an operator can be an
isometry. We then apply these results to the operator acting on the discrete
Lipschitz space and weighted Banach spaces, as well as the Hardy spaces defined
on homogeneous trees
Nucleation and crystallization process of silicon using Stillinger-Weber potential
We study the homogeneous nucleation process in Stillinger-Weber silicon in
the NVT ensemble. A clear first-order transition from the liquid to crystal
phase is observed thermodynamically with kinetic and structural evidence of the
transformation. At 0.75 T_m, the critical cluster size is about 175 atoms. The
lifetime distribution of clusters as a function of the maximum size their reach
follows an inverse gaussian distribution as was predicted recently from the
classical theory of nucleation (CNT). However, while there is a qualitative
agreement with the CNT, the free energy curve obtained from the simulations
differs significantly from the theoretical predictions, suggesting that the
low-density liquid phase found recently could play a role in the nucleation
process.Comment: 21 page
Assessing a Hydrodynamic Description for Instabilities in Highly Dissipative, Freely Cooling Granular Gases
An intriguing phenomenon displayed by granular flows and predicted by
kinetic-theory-based models is the instability known as particle "clustering,"
which refers to the tendency of dissipative grains to form transient, loose
regions of relatively high concentration. In this work, we assess a
modified-Sonine approximation recently proposed [Garz\'o et al., Physica A 376,
94 (2007)] for a granular gas via an examination of system stability. In
particular, we determine the critical length scale associated with the onset of
two types of instabilities -vortices and clusters- via stability analyses of
the Navier-Stokes-order hydrodynamic equations by using the expressions of the
transport coefficients obtained from both the standard and the modified-Sonine
approximations. We examine the impact of both Sonine approximations over a
range of solids fraction \phi <0.2 for small restitution coefficients
e=0.25--0.4, where the standard and modified theories exhibit discrepancies.
The theoretical predictions for the critical length scales are compared to
molecular dynamics (MD) simulations, of which a small percentage were not
considered due to inelastic collapse. Results show excellent quantitative
agreement between MD and the modified-Sonine theory, while the standard theory
loses accuracy for this highly dissipative parameter space. The modified theory
also remedies a (highdissipation) qualitative mismatch between the standard
theory and MD for the instability that forms more readily. Furthermore, the
evolution of cluster size is briefly examined via MD, indicating that
domain-size clusters may remain stable or halve in size, depending on system
parameters.Comment: 4 figures; to be published in Phys. Rev.
Incorporating climate change into invasive species management: insights from managers
Invasive alien species are likely to interact with climate change, thus necessitating management that proactively addresses both global changes. However, invasive species managers’ concerns about the effects of climate change, the degree to which they incorporate climate change into their management, and what stops them from doing so remain unknown. Therefore, we surveyed natural resource managers addressing invasive species across the U.S. about their priorities, concerns, and management strategies in a changing climate. Of the 211 managers we surveyed, most were very concerned about the influence of climate change on invasive species management, but their organizations were significantly less so. Managers reported that lack of funding and personnel limited their ability to effectively manage invasive species, while lack of information limited their consideration of climate change in decision-making. Additionally, managers prioritized research that identifies range-shifting invasive species and native communities resilient to invasions and climate change. Managers also reported that this information would be most effectively communicated through conversations, research summaries, and meetings/symposia. Despite the need for more information, 65% of managers incorporate climate change into their invasive species management through strategic planning, preventative management, changing treatment and control, and increasing education and outreach. These results show the potential for incorporating climate change into management, but also highlight a clear and pressing need for more targeted research, accessible science communication, and two-way dialogue between researchers and managers focused on invasive species and climate change
The nuclear spectrum of the radio galaxy NGC 5128 (Centaurus A)
We present near-infrared spectra of the nuclear disk in the nearby radio
galaxy NGC 5128 (Centaurus A). On the basis of the observed strengths of the [S
III] 0.9532um and [Fe II] 1.2567um lines, we classify NGC 5128 as a LINER.
Modeling of the strengths of these and additional lines suggests that the
nuclear region is powered by shocks rather than photoionization.Comment: 12 pages including 2 figures, accepted by ApJ Letter
Matter-wave bistability in coupled atom-molecule quantum gases
We study the matter-wave bistability in coupled atom-molecule quantum gases,
in which heteronuclear molecules are created via an interspecies Feshbach
resonance involving either two-species Bose or two-species Fermi atoms at zero
temperature. We show that the resonant two-channel Bose model is equivalent to
the nondegenerate parametric down-conversion in quantum optics, while the
corresponding Fermi model can be mapped to a quantum optics model that
describes a single-mode laser field interacting with an ensemble of
inhomogeneously broadened two-level atoms. Using these analogy and the fact
that both models are subject to the Kerr nonlinearity due to the two-body
s-wave collisions, we show that under proper conditions, the population in the
molecular state in both models can be made to change with the Feshbach detuning
in a bistable fashion.Comment: 6 pages, 5 figure
Polyelectrolyte stars in planar confinement
We employ monomer-resolved Molecular Dynamics simulations and theoretical
considerations to analyze the conformations of multiarm polyelectrolyte stars
close to planar, uncharged walls. We identify three mechanisms that contribute
to the emergence of a repulsive star-wall force, namely: the confinement of the
counterions that are trapped in the star interior, the increase in
electrostatic energy due to confinement as well as a novel mechanism arising
from the compression of the stiff polyelectrolyte rods approaching the wall.
The latter is not present in the case of interaction between two
polyelectrolyte stars and is a direct consequence of the impenetrable character
of the planar wall.Comment: 34 pages, 8 figures. Revised version of the manuscript. To appear in
J. Chem. Phys. May, 200
Quantized Response and Topology of Insulators with Inversion Symmetry
We study three dimensional insulators with inversion symmetry, in which other
point group symmetries, such as time reversal, are generically absent. Their
band topology is found to be classified by the parities of occupied states at
time reversal invariant momenta (TRIM parities), and by three Chern numbers.
The TRIM parities of any insulator must satisfy a constraint: their product
must be +1. The TRIM parities also constrain the Chern numbers modulo two. When
the Chern numbers vanish, a magneto-electric response parameterized by "theta"
is defined and is quantized to theta= 0, 2pi. Its value is entirely determined
by the TRIM parities. These results may be useful in the search for magnetic
topological insulators with large theta. A classification of inversion
symmetric insulators is also given for general dimensions. An alternate
geometrical derivation of our results is obtained by using the entanglement
spectrum of the ground state wave-function.Comment: 12 pages main text; 12 pages appendices; 11 figures. Added new refs.
in 2nd versio
Mobile phone and tablet apps to support young people’s management of their physical long-term conditions: a systematic review protocol
Background: The prevalence of long-term or chronic conditions that limit activity and reduce quality of life in young people aged 10-24 years is rising. This group has distinct health care needs and requires tailored support strategies to facilitate increasing personal responsibility for the management of their condition wherever possible, as they mature. Mobile phone and tablet mobile technologies featuring software program apps are already well used by young people for social networking or gaming. They have also been utilized in health care to support personal condition management, using condition-specific and patient-tailored software. Such apps have much potential, and there is an emerging body of literature on their use in a health context making this review timely. Objective: The objective of this paper is to develop a systematic review protocol focused on identifying and assessing the effectiveness of mobile phone and tablet apps that support young people’s management of their chronic conditions. Methods: The search strategy will include a combination of standardized indexed search terms and free-text terms related to the key concepts of young people; long-term conditions and mobile technology. Peer-reviewed journal articles published from 2003 that meet the inclusion and exclusion criteria will be identified through searching the generated hits from 5 bibliographical databases. Two independent reviewers will screen the titles and abstracts to determine which articles focus on testing interventions identified as a mobile phone or tablet apps, and that have been designed and delivered to support the management of long-term conditions in young people aged 10-24 years. Data extraction and quality assessment tools will be used to facilitate consistent analysis and synthesis. It is anticipated that several studies will meet the selection criteria but that these are likely to be heterogeneous in terms of study design, reported outcomes, follow-up times, participants’ age, and health condition. Sub-group analyses will be undertaken and where possible meta-analyses will take place.Results: This review will synthesize available knowledge surrounding tablet and mobile phone apps that support management of long term physical health conditions in young people. The findings will be synthesized to determine which elements of the technologies were most effective for this population. Conclusions: This systematic review aims to synthesize existing literature in order to generate findings that will facilitate the development of an app intervention. The review will form the first phase of development and evaluation of a complex intervention as recommended by the United Kingdom Medical Research Council. The knowledge gained from the review will be verified in subsequent phases, which will include primary qualitative work with health professionals and young people with long term conditions as research participants. Young people living with long-term conditions will be involved as co-researchers and consumer advisors in all subsequent phases to develop and evaluate an app to support the management of long-term physical health conditions
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