439 research outputs found
Breaking and restoring symmetries within the nuclear energy density functional method
We review the notion of symmetry breaking and restoration within the frame of
nuclear energy density functional methods. We focus on key differences between
wave-function- and energy-functional-based methods. In particular, we point to
difficulties to formulate the restoration of symmetries within the energy
functional framework. The problems tackled recently in connection with
particle-number restoration serve as a baseline to the present discussion.
Reaching out to angular-momentum restoration, we identify an exact mathematical
property of the energy density that could be used to
constrain energy density functional kernels. Consequently, we suggest possible
routes towards a better formulation of symmetry restorations within energy
density functional methods.Comment: 16 pages, 3 figures, contribution to the "Focus issue on Open
Problems in Nuclear Structure", Journal of Physics
The tensor part of the Skyrme energy density functional. I. Spherical nuclei
We perform a systematic study of the impact of the J^2 tensor term in the
Skyrme energy functional on properties of spherical nuclei. In the Skyrme
energy functional, the tensor terms originate both from zero-range central and
tensor forces. We build a set of 36 parameterizations, which covers a wide
range of the parameter space of the isoscalar and isovector tensor term
coupling constants, with a fit protocol very similar to that of the successful
SLy parameterizations. We analyze the impact of the tensor terms on a large
variety of observables in spherical mean-field calculations, such as the
spin-orbit splittings and single-particle spectra of doubly-magic nuclei, the
evolution of spin-orbit splittings along chains of semi-magic nuclei, mass
residuals of spherical nuclei, and known anomalies of charge radii. Our main
conclusion is that the currently used central and spin-orbit parts of the
Skyrme energy density functional are not flexible enough to allow for the
presence of large tensor terms.Comment: 38 pages, 36 figures; Minor correction
Pairing renormalization and regularization within the local density approximation
We discuss methods used in mean-field theories to treat pairing correlations
within the local density approximation. Pairing renormalization and
regularization procedures are compared in spherical and deformed nuclei. Both
prescriptions give fairly similar results, although the theoretical motivation,
simplicity, and stability of the regularization procedure makes it a method of
choice for future applications.Comment: 10 pages, 8 figures, submitted to Phys. Rev.
Chiral three-nucleon forces and pairing in nuclei
We present the first study of pairing in nuclei including three-nucleon
forces. We perform systematic calculations of the odd-even mass staggering
generated using a microscopic pairing interaction at first order in chiral
low-momentum interactions. Significant repulsive contributions from the leading
chiral three-nucleon forces are found. Two- and three-nucleon interactions
combined account for approximately 70% of the experimental pairing gaps, which
leaves room for self-energy and induced interaction effects that are expected
to be overall attractive in nuclei.Comment: 4 pages, 3 figure
New analysis method of the halo phenomenon in finite many-fermion systems. First applications to medium-mass atomic nuclei
A new analysis method to investigate halos in finite many-fermion systems is
designed, as existing characterization methods are proven to be
incomplete/inaccurate. A decomposition of the internal wave-function of the
{-body} system in terms of overlap functions allows a model-independent
analysis of medium-range and asymptotic properties of the internal one-body
density. The existence of a spatially decorrelated region in the density
profile is related to the existence of three typical energy scales in the
excitation spectrum of the {-body} system. A series of model-independent
measures, taking the internal density as the only input, are introduced. The
new measures allow a quantification of the potential halo in terms of the
average number of fermions participating to it and of its impact on the system
extension. Those new "halo factors" are validated through simulations and
applied to results obtained through energy density functional calculations of
medium-mass nuclei. Performing spherical Hartree-Fock-Bogoliubov calculations
with state-of-the-art Skyrme plus pairing functionals, a collective halo is
predicted in drip-line Cr isotopes, whereas no such effect is seen in Sn
isotopes.Comment: 27 Pages, 29 Figures. Accepted for publication in Phys. Rev. C
back-to-back with second part (arXiv:0711.1275
Pandemic influenza control in Europe and the constraints resulting from incoherent public health laws
© 2010 Martin et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.Background: With the emergence of influenza H1N1v the world is facing its first 21st century global pandemic. Severe Acute Respiratory Syndrome (SARS) and avian influenza H5N1 prompted development of pandemic preparedness plans. National systems of public health law are essential for public health stewardship and for the implementation of public health policy[1]. International coherence will contribute to effective regional and global responses. However little research has been undertaken on how law works as a tool for disease control in Europe. With co-funding from the European Union, we investigated the extent to which laws across Europe support or constrain pandemic preparedness planning, and whether national differences are likely to constrain control efforts. Methods: We undertook a survey of national public health laws across 32 European states using a questionnaire designed around a disease scenario based on pandemic influenza. Questionnaire results were reviewed in workshops, analysing how differences between national laws might support or hinder regional responses to pandemic influenza. Respondents examined the impact of national laws on the movements of information, goods, services and people across borders in a time of pandemic, the capacity for surveillance, case detection, case management and community control, the deployment of strategies of prevention, containment, mitigation and recovery and the identification of commonalities and disconnects across states. Results: Results of this study show differences across Europe in the extent to which national pandemic policy and pandemic plans have been integrated with public health laws. We found significant differences in legislation and in the legitimacy of strategic plans. States differ in the range and the nature of intervention measures authorized by law, the extent to which borders could be closed to movement of persons and goods during a pandemic, and access to healthcare of non-resident persons. Some states propose use of emergency powers that might potentially override human rights protections while other states propose to limit interventions to those authorized by public health laws. Conclusion: These differences could create problems for European strategies if an evolving influenza pandemic results in more serious public health challenges or, indeed, if a novel disease other than influenza emerges with pandemic potential. There is insufficient understanding across Europe of the role and importance of law in pandemic planning. States need to build capacity in public health law to support disease prevention and control policies. Our research suggests that states would welcome further guidance from the EU on management of a pandemic, and guidance to assist in greater commonality of legal approaches across states.Peer reviewe
Are Shakespeare's plays always metatheatrical?
The ambiguity of the term "metatheatre" derives in part from its text of origin, Lionel Abel's 1963 book of the same name. By his own admission, Abel's use of the term was "loose and sometimes erratic" (v). If we use the term in its broadest sense—to describe any theater that in some way draws attention to its own artifice—it becomes evident that early modern drama is always "metatheatrical" to some extent: these plays are designed never entirely to lose sight of the material realities of their performance, or of the physical co-presence of their audiences. If this is the case, how useful is the term "metatheatre"? Indeed, are Shakespeare's plays always metatheatrical? This article unpicks some of the conflicting notions of metatheatre suggested in Abel's book, and suggests a modified conceptual model based on the work of Arthur Koestler. Arguing against the tendency to see early modern theatrical self-consciousness as a form of proto-Brechtian alienation, it uses Koestler's concept of bisociation to think about the delight produced by "universes of discourse colliding, frames getting entangled, or contexts getting confused" (40). It considers several examples from performance, especially moments from productions at the reconstructed Shakespeare's Globe, to argue that metatheatre functions as a kind of imaginative game. This game may be prompted by cues in the written text, but it is one that can be played only in performance. While Harry Newman's essay for this special issue argues that metatheatricality was available to early modern readers "on the paper stage of printed playbooks" (104), my essay posits a decidedly more theatrical definition of the term, contending that the agency of the actors plays a central role in determining the metatheatricality of particular moments on stage
Halo phenomenon in finite many-fermion systems. Atom-positron complexes and large-scale study of atomic nuclei
The analysis method proposed in Ref. \cite{rotival07a} is applied to
characterize halo properties in finite many-fermion systems. First, the
versatility of the method is highlighted by applying it to light and
medium-mass nuclei as well as to atom-positron and ion-positronium complexes.
Second, the dependence of nuclear halo properties on the characteristics of the
energy density functional used in self-consistent Hartree-Fock-Bogoliubov
calculations is studied. It is found that (a) the low-density behavior of the
pairing functional and the regularization/renormalization scheme must be chosen
coherently and with care to provide meaningful predictions, (b) the impact of
pairing correlations on halo properties is significant and is the result of two
competing effects, (c) the detailed characteristics of the pairing functional
has however only little importance, (d) halo properties depend significantly on
any ingredient of the energy density functional that influences the location of
single-particle levels; i.e. the effective mass, the tensor terms and the
saturation density of nuclear matter. The latter dependencies give insights to
how experimental data on medium-mass drip-line nuclei can be used in the
distant future to constrain some characteristics of the nuclear energy density
functional. Last but not least, large scale predictions of halos among all
spherical even-even nuclei are performed using specific sets of particle-hole
and particle-particle energy functionals. It is shown that halos in the ground
state of medium-mass nuclei will only be found at the very limit of neutron
stability and for a limited number of elements.Comment: 24 Pages, 32 Figures. Accepted for publication in Phys. Rev. C
back-to back with first part (nucl-th/0702050
Etude de la dégradation de quelques composés organochlorés volatils par photolyse du peroxyde d'hydrogène en milieux aqueux
Le travail a eu pour but d'étudier l'efficacité de la photolyse du peroxyde d'hydrogène sur la dégradation de quelques composés organochlorés aliphatiques saturés (chiorométhanes et chloroéthanes) en milieu aqueux (pH 7,5). Les expériences ont été réalisées en réacteur statique, avec une Lampe basse pression à vapeur de mercure et avec des concentrations initiales en produit chloré de l'ordre de 10-6 mol l-1 et en H202 comprises entre 10-5 et 10-3 mol L-.Les résultats montrent que le système H202/UV peut oxyder les composés organochlorés étudiés à l'exception des composés ne possédant pas d'atome d'hydrogène (CCL4 et C2 CL6). Les rendements d'oxydation obtenus avec Le réacteur utilisé dépendent du temps de réaction, de la concentration initiale en H202, du flux photonique et peuvent être nettement diminués par la présence de pièges à radicaux (ions bicarbonates) dans le milieu réactionnel.Par ailleurs, une étude cinétique de la photolyse du peroxyde d'hydrogène en absence de matière organique est également présentée.The aim of this work was to study oxidation of certain volatile polychlorinated hydrocarbons, using hydrogen peroxide photoactivated by UV. This research was carried out with different mixtures of diluted aqueous solutions of chloromethanes (CHCl3, CCl4) and chloroethanes (C2H3Cl3, C2H2Cl4, C2HCl5, CCl6), which are typical halogenated compounds most frequently found in contaminated groundwater. The effect of the hydrogen peroxide concentration, the light intensity and the bicarbonate concentration on the rate of 1,1,2-trichloroethane (TCE) oxidation was determined. A kinetic study on hydrogen peroxide photolysis in a solution free of organic compounds was also carried out.EXPERIMENTATIONExperiments were conducted in a batch reactor (V = 4 l), equipped with an immersed mercury low-pressure lamp. The intensity emitted at 253.7 nm was roughly 2 1019 photons s-1. The temperature of the reaction mixture was maintained with a regulation system at 16 ± 0.5 °C (figure 1).The solutions were prepared in a phosphate buffer µ = 2 10-2 M, pH = 7.5). The outer surface of the lamp was masked with strips of aluminium, so as to obtain various percentages of initial energy (20 to 100 %).The concentration of the hydrogen peroxide of the samples was determined by spectrophotometry and the chlorinated compounds were analysed by electron capture gas chromatography.RESULTKinetics of hydrogen peroxide photolysis : H202 was decomposed by UV tb produce two hydroxyl radicals. In diluted solutions ([H202] < 10-3 M), the concentration decreases in accordante with a first order law. The rate constant depends on the initial light intensity (Io), on the characteristics of the reactor (volume and distance between the lamp and the watt. of the reactor) and on the motar extinction coefficient of the irradiated solution (equation C). The decomposition rate appears to be dependent on pH, the rate of constant rire has been found to be proportional to the dissociation of hydrogen peroxide into its basic form (EH2O2 = 20 mol-1 cm-1,EH2O2_ = 240 mol-1 cm-1) (figure 2 and 3).Oxidation of the chlorinated compounds : H202/UV is very efficient for the removal of organic compounds. Preliminary experiments showed that both UV and H2O2 treatments do not decompose halogenated compounds. Hydroxyl radicals are extremly reactive and attack organic compounds preferentialty by abs-tracting a hydrogen atom from an organic molecule. This is confirmed by the results which show that chloromethanes and chloroethanes with an H atom are eliminated, but net compounds such as tetrachloride and hexachloroethane (figure 4 to 7).The effectiveness of an H202/UV system depends on various parameters. Studies on the TCE elimination show that the oxidation yields an increase when the reaction time, the UV irradiation dose (figure 9b) and the hydrogen peroxide concentration (figure 8) increase. However, the efficiency decreases in the presence of radical traps such as bicarbonate and carbonate ions (figure 10)
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