5,992 research outputs found
Plasmons in Sodium under Pressure: Increasing Departure from Nearly-Free-Electron Behavior
We have measured plasmon energies in Na under high pressure up to 43 GPa
using inelastic x-ray scattering (IXS). The momentum-resolved results show
clear deviations, growing with increasing pressure, from the predictions for a
nearly-free electron metal. Plasmon energy calculations based on
first-principles electronic band structures and a quasi-classical plasmon model
allow us to identify a pressure-induced increase in the electron-ion
interaction and associated changes in the electronic band structure as the
origin of these deviations, rather than effects of exchange and correlation.
Additional IXS results obtained for K and Rb are addressed briefly.Comment: 5 pages, 4 figure
Defect formation in superconducting rings: external fields and finite-size effects
Consistent with the predictions of Kibble and Zurek, scaling behaviour has
been seen in the production of fluxoids during temperature quenches of
superconducting rings. However, deviations from the canonical behaviour arise
because of finite-size effects and stray external fields.
Technical developments, including laser heating and the use of long Josephson
tunnel junctions, have improved the quality of data that can be obtained. With
new experiments in mind we perform large-scale 3D simulations of quenches of
small, thin rings of various geometries with fully dynamical electromagnetic
fields, at nonzero externally applied magnetic flux. We find that the outcomes
are, in practice, indistinguishable from those of much simpler Gaussian
analytical approximations in which the rings are treated as one-dimensional
systems and the magnetic field fluctuation-free.Comment: 10 pages, 3 figures, presentation at QFS2012, to appear in JLT
Characterizing Diffused Stellar Light in simulated galaxy clusters
[Abridged] In this paper, we carry out a detailed analysis of the performance
of two different methods to identify the diffuse stellar light in cosmological
hydrodynamical simulations of galaxy clusters. One method is based on a
dynamical analysis of the stellar component. The second method is closer to
techniques commonly employed in observational studies. Both the dynamical
method and the method based on the surface brightness limit criterion are
applied to the same set of hydrodynamical simulations for a large sample about
80 galaxy clusters.
We find significant differences between the ICL and DSC fractions computed
with the two corresponding methods, which amounts to about a factor of two for
the AGN simulations, and a factor of four for the CSF set. We also find that
the inclusion of AGN feedback boosts the DSC and ICL fractions by a factor of
1.5-2, respectively, while leaving the BCG+ICL and BCG+DSC mass fraction almost
unchanged. The sum of the BCG and DSC mass stellar mass fraction is found to
decrease from ~80 per cent in galaxy groups to ~60 per cent in rich clusters,
thus in excess of what found from observational analysis.
We identify the average surface brightness limits that yields the ICL
fraction from the SBL method close to the DSC fraction from the dynamical
method. These surface brightness limits turn out to be brighter in the CSF than
in the AGN simulations. This is consistent with the finding that AGN feedback
makes BCGs to be less massive and with shallower density profiles than in the
CSF simulations. The BCG stellar component, as identified by both methods, are
slightly older and more metal-rich than the stars in the diffuse component.Comment: 18 Pages, 15 figures. Matches to MNRAS published versio
Observation of the onset of strong scattering on high frequency acoustic phonons in densified silica glass
The linewidth of longitudinal acoustic waves in densified silica glass is
obtained by inelastic x-ray scattering. It increases with a high power alpha of
the frequency up to a crossover where the waves experience strong scattering.
We find that \alpha is at least 4, and probably larger. Resonance and
hybridization of acoustic waves with the boson-peak modes seems to be a more
likely explanation for these findings than Rayleigh scattering from disorder.Comment: 4 pages, 4 figures, to appear in Phys. Rev. Letter
The cloud-in-cloud problem for non-Gaussian density fields
The cloud-in-cloud problem is studied in the context of the extension to
non-Gaussian density fields of the Press-Schechter approach for the calculation
of the mass function. As an example of a non-Gaussian probability distribution
functions (PDFs) we consider the Chi-square, with various degrees of freedom.
We generate density fields in cubic boxes with periodic boundary conditions and
then determine the number of points considered collapsed at each scale through
an hierarchy of smoothing windows. We find that the mass function we obtain
differs from that predicted using the Extended Press-Schechter formalism,
particularly for low values of and for those PDFs most distinct from a
Gaussian.Comment: 5 pages, LaTex using mn.sty, matches published version, results for
the Inverted Chi-square distribution withdraw
High-throughput screening with the Eimeria tenella CDC2-related kinase2/cyclin complex EtCRK2/EtCYC3a
The poultry disease coccidiosis, caused by infection with Eimeria spp. apicomplexan parasites, is responsible for enormous economic losses to the global poultry industry. The rapid increase of resistance to therapeutic agents, as well as the expense of vaccination with live attenuated vaccines, requires the development of new effective treatments for coccidiosis. Because of their key regulatory function in the eukaryotic cell cycle, cyclin-dependent kinases (CDKs) are prominent drug targets. The Eimeria tenella CDC2-related kinase 2 (EtCRK2) is a validated drug target that can be activated in vitro by the CDK activator XlRINGO (Xenopus laevis rapid inducer of G2/M progression in oocytes). Bioinformatics analyses revealed four putative E. tenella cyclins (EtCYCs) that are closely related to cyclins found in the human apicomplexan parasite Plasmodium falciparum. EtCYC3a was cloned, expressed in Escherichia coli and purified in a complex with EtCRK2. Using the non-radioactive time-resolved fluorescence energy transfer (TR-FRET) assay, we demonstrated the ability of EtCYC3a to activate EtCRK2 as shown previously for XlRINGO. The EtCRK2/EtCYC3a complex was used for a combined in vitro and in silico high-throughput screening approach, which resulted in three lead structures, a naphthoquinone, an 8-hydroxyquinoline and a 2-pyrimidinyl-aminopiperidine-propane-2-ol. This constitutes a promising starting point for the subsequent lead optimization phase and the development of novel anticoccidial drugs
Academic freedom in Europe: reviewing UNESCOâs recommendation
This paper examines the compliance of universities in the European Union with the UNESCO Recommendation concerning the Status of HigherâEducation Teaching Personnel, which deals primarily with protection for academic freedom. The paper briefly surveys the European genesis of the modern research university and academic freedom, before evaluating compliance with the UNESCO recommendation on institutional autonomy, academic freedom, university governance and tenure. Following from this, the paper examines the reasons for the generally low level of compliance with the UNESCO Recommendation within the EU states, and considers how such compliance could be improved
Elastic constant dishomogeneity and dependence of the broadening of the dynamical structure factor in disordered systems
We propose an explanation for the quadratic dependence on the momentum ,
of the broadening of the acoustic excitation peak recently found in the study
of the dynamic structure factor of many real and simulated glasses. We ascribe
the observed law to the spatial fluctuations of the local wavelength of
the collective vibrational modes, in turn produced by the dishomegeneity of the
inter-particle elastic constants. This explanation is analitically shown to
hold for 1-dimensional disordered chains and satisfatorily numerically tested
in both 1 and 3 dimensions.Comment: 4 pages, RevTeX, 5 postscript figure
Gauge-theoretic invariants for topological insulators: A bridge between Berry, Wess-Zumino, and Fu-Kane-Mele
We establish a connection between two recently-proposed approaches to the
understanding of the geometric origin of the Fu-Kane-Mele invariant
, arising in the context of 2-dimensional
time-reversal symmetric topological insulators. On the one hand, the
invariant can be formulated in terms of the Berry connection and
the Berry curvature of the Bloch bundle of occupied states over the Brillouin
torus. On the other, using techniques from the theory of bundle gerbes it is
possible to provide an expression for containing the square root
of the Wess-Zumino amplitude for a certain -valued field over the
Brillouin torus.
We link the two formulas by showing directly the equality between the above
mentioned Wess-Zumino amplitude and the Berry phase, as well as between their
square roots. An essential tool of independent interest is an equivariant
version of the adjoint Polyakov-Wiegmann formula for fields , of which we provide a proof employing only basic homotopy theory and
circumventing the language of bundle gerbes.Comment: 23 pages, 1 figure. To appear in Letters in Mathematical Physic
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