1,804 research outputs found
Lovelock gravity from entropic force
In this paper, we first generalize the formulation of entropic gravity to
(n+1)-dimensional spacetime. Then, we propose an entropic origin for
Gauss-Bonnet gravity and more general Lovelock gravity in arbitrary dimensions.
As a result, we are able to derive Newton's law of gravitation as well as the
corresponding Friedmann equations in these gravity theories. This procedure
naturally leads to a derivation of the higher dimensional gravitational
coupling constant of Friedmann/Einstein equation which is in complete agreement
with the results obtained by comparing the weak field limit of Einstein
equation with Poisson equation in higher dimensions. Our study shows that the
approach presented here is powerful enough to derive the gravitational field
equations in any gravity theory. PACS: 04.20.Cv, 04.50.-h, 04.70.Dy.Comment: 10 pages, new versio
Using the local density approximation and the LYP, BLYP, and B3LYP functionals within Reference--State One--Particle Density--Matrix Theory
For closed-shell systems, the local density approximation (LDA) and the LYP,
BLYP, and B3LYP functionals are shown to be compatible with reference-state
one-particle density-matrix theory, where this recently introduced formalism is
based on Brueckner-orbital theory and an energy functional that includes exact
exchange and a non-universal correlation-energy functional. The method is
demonstrated to reduce to a density functional theory when the
exchange-correlation energy-functional has a simplified form, i.e., its
integrand contains only the coordinates of two electron, say r1 and r2, and it
has a Dirac delta function -- delta(r1 - r2) -- as a factor. Since Brueckner
and Hartree--Fock orbitals are often very similar, any local exchange
functional that works well with Hartree--Fock theory is a reasonable
approximation with reference-state one-particle density-matrix theory. The LDA
approximation is also a reasonable approximation. However, the Colle--Salvetti
correlation-energy functional, and the LYP variant, are not ideal for the
method, since these are universal functionals. Nevertheless, they appear to
provide reasonable approximations. The B3LYP functional is derived using a
linear combination of two functionals: One is the BLYP functional; the other
uses exact exchange and a correlation-energy functional from the LDA.Comment: 26 Pages, 0 figures, RevTeX 4, Submitted to Mol. Phy
Three geographically separate domestications of Asian rice
Domesticated rice (Oryza sativa L.) accompanied the dawn of Asian civilization(1) and has become one of world's staple crops. From archaeological and genetic evidence various contradictory scenarios for the origin of different varieties of cultivated rice have been proposed, the most recent based on a single domestication(2,3). By examining the footprints of selection in the genomes of different cultivated rice types, we show that there were three independent domestications in different parts of Asia. We identify wild populations in southern China and the Yangtze valley as the source of the japonica gene pool, and populations in Indochina and the Brahmaputra valley as the source of the indica gene pool. We reveal a hitherto unrecognized origin for the aus variety in central India or Bangladesh. We also conclude that aromatic rice is a result of a hybridization between japonica and aus, and that the tropical and temperate versions of japonica are later adaptations of one crop. Our conclusions are in accord with archaeological evidence that suggests widespread origins of rice cultivation(1,4). We therefore anticipate that our results will stimulate a more productive collaboration between genetic and archaeological studies of rice domestication, and guide utilization of genetic resources in breeding programmes aimed at crop improvement.European Research Council [339941]info:eu-repo/semantics/publishedVersio
Towards an analytical framework of science communication models
This chapter reviews the discussion in science communication circles of models for public communication of science and technology (PCST). It questions the claim that there has been a large-scale shift from a ‘deficit model’ of communication to a ‘dialogue model’, and it demonstrates the survival of the deficit model along with the ambiguities of that model. Similar discussions in related fields of communication, including the critique of dialogue, are briefly sketched. Outlining the complex circumstances governing approaches to PCST, the author argues that communications models often perceived to be opposed can, in fact, coexist when the choices are made explicit. To aid this process, the author proposes an analytical framework of communication models based on deficit, dialogue and participation, including variations on each
Microscopic observation of magnon bound states and their dynamics
More than eighty years ago, H. Bethe pointed out the existence of bound
states of elementary spin waves in one-dimensional quantum magnets. To date,
identifying signatures of such magnon bound states has remained a subject of
intense theoretical research while their detection has proved challenging for
experiments. Ultracold atoms offer an ideal setting to reveal such bound states
by tracking the spin dynamics after a local quantum quench with single-spin and
single-site resolution. Here we report on the direct observation of two-magnon
bound states using in-situ correlation measurements in a one-dimensional
Heisenberg spin chain realized with ultracold bosonic atoms in an optical
lattice. We observe the quantum walk of free and bound magnon states through
time-resolved measurements of the two spin impurities. The increased effective
mass of the compound magnon state results in slower spin dynamics as compared
to single magnon excitations. In our measurements, we also determine the decay
time of bound magnons, which is most likely limited by scattering on thermal
fluctuations in the system. Our results open a new pathway for studying
fundamental properties of quantum magnets and, more generally, properties of
interacting impurities in quantum many-body systems.Comment: 8 pages, 7 figure
Non-singlet Baryons in Less Supersymmetric Backgrounds
We analyze the holographic description of non-singlet baryons in various
backgrounds with reduced supersymmetries and/or confinement. We show that they
exist in all AdS_5xY_5 backgrounds with Y_5 an Einstein manifold bearing five
form flux, for a number of quarks 5N/8< k< N, independently on the
supersymmetries preserved. This result still holds for gamma_i deformations. In
the confining Maldacena-Nunez background non-singlet baryons also exist,
although in this case the interval for the number of quarks is reduced as
compared to the conformal case. We generalize these configurations to include a
non-vanishing magnetic flux such that a complementary microscopical description
can be given in terms of lower dimensional branes expanding into fuzzy baryons.
This description is a first step towards exploring the finite 't Hooft coupling
region.Comment: 36 Pages, 1 figure, Latex, v2: few minor changes, JHEP versio
The role of clathrin in post-golgi trafficking in toxoplasma gondii
Apicomplexan parasites are single eukaryotic cells with a highly polarised secretory system that contains unique secretory organelles (micronemes and rhoptries) that are required for host cell invasion. In contrast, the role of the endosomal system is poorly understood in these parasites. With many typical endocytic factors missing, we speculated that endocytosis depends exclusively on a clathrin-mediated mechanism. Intriguingly, in Toxoplasma gondii we were only able to observe the endogenous clathrin heavy chain 1 (CHC1) at the Golgi, but not at the parasite surface. For the functional characterisation of Toxoplasma gondii CHC1 we generated parasite mutants conditionally expressing the dominant negative clathrin Hub fragment and demonstrate that CHC1 is essential for vesicle formation at the trans-Golgi network. Consequently, the functional ablation of CHC1 results in Golgi aberrations, a block in the biogenesis of the unique secretory microneme and rhoptry organelles, and of the pellicle. However, we found no morphological evidence for clathrin mediating endocytosis in these parasites and speculate that they remodelled their vesicular trafficking system to adapt to an intracellular lifestyle
On effective actions of BPS branes and their higher derivative corrections
We calculate in detail the disk level S-matrix element of one Ramond-Ramond
field and three gauge field vertex operators in the world volume of BPS branes,
to find four gauge field couplings to all orders of up to on-shell
ambiguity. Then using these infinite couplings we find that the massless pole
of the field theory amplitude is exactly equal to the massless pole S-matrix
element of this amplitude for the case to all orders of .
Finally we show that the infinite massless poles and the contact terms of this
amplitude for the case can be reproduced by the Born-Infeld action and
the Wess-Zumino actions and by their higher derivative corrections.Comment: 26 pages, 2 figures, minor corrections,references added and version
published in JHE
Evaluation of a multifaceted "Resident-as-Teacher" educational intervention to improve morning report
BACKGROUND: Resident-led morning report is an integral part of most residency programs and is ranked among the most valuable of educational experiences. The objectives of this study were to evaluate the effect of a resident-as-teacher educational intervention on the educational and teaching experience of morning report. METHODS: All senior internal medicine residents were invited to participate in this study as teaching participants. All internal medicine residents and clerks were invited to participate as audience participants. The educational intervention included reading material, a small group session and feedback after teaching sessions. The educational and teaching experiences were rated prior to and three months after the intervention using questionnaires. RESULTS: Forty-six audience participants and 18 teaching participants completed the questionnaires. The degree to which morning report met the educational needs of the audience was higher after the educational intervention (effect size, d = 0.26, p = 0.01). The perceptions of the audience were that delivery had improved and that the sessions were less intimidating and more interactive. The perception of the teaching participants was that delivery was less stressful, but this group now reported greater difficulty in engaging the audience and less confidence in their medical knowledge. CONCLUSION: Following the educational intervention the audience's perception was that the educational experience had improved although there were mixed results for the teaching experience. When evaluating such interventions it is important to evaluate the impact on both the educational and teaching experiences as results may differ
The deuteron: structure and form factors
A brief review of the history of the discovery of the deuteron in provided.
The current status of both experiment and theory for the elastic electron
scattering is then presented.Comment: 80 pages, 33 figures, submited to Advances in Nuclear Physic
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