1,801 research outputs found
Chemical Equilibration in Hadronic Collisions
We study chemical equilibration in out-of-equilibrium Quark-Gluon Plasma
using the first principles method of QCD effective kinetic theory, accurate at
weak coupling. In longitudinally expanding systems--relevant for relativistic
nuclear collisions--we find that for realistic couplings chemical equilibration
takes place after hydrodynamization, but well before local thermalization. We
estimate that hadronic collisions with final state multiplicities
live long enough to reach approximate
chemical equilibrium, which is consistent with the saturation of strangeness
enhancement observed in proton-proton, proton-nucleus and nucleus-nucleus
collisions.Comment: 7 pages, 3 figures, see also our companion paper arXiv:1811.03068, v2
small changes, published versio
Innovations adoption levels of small ruminant farmers in Tolon-Kumbungu district of Ghana: The Role of Farmer Socio-Economic Characteristics
The rearing of small ruminants plays a major role in the farming system of the people of the Tolon-Kumbungu District of the Northern Region of Ghana. Small ruminant production is a major source of livelihood to over 70% of the inhabitants of the District. However, poor husbandry practices have often served as a major constraint to achieving production and productivity increases. This implies that small ruminant farmers need to adopt innovations in order to promote and sustain small ruminant production. This paper assesses the extent to which innovations introduced to the farmers in the study area are adopted, especially the role of farmer socio-economic characteristics in influencing the innovations adoption levels of small ruminants. A total of 120 small ruminant farmers were selected for the study using simple random sampling, and questionnaires and personal observations employed for the data collection. Twelve communities were randomly selected from four Ministry of Food and Agriculture operational zones. Data were analyzed using SPSS computer software package and descriptive statistics computed based on the data. Cross tabulation and other test statistics were used to determine the relationship between adoption levels and the variables studied. The findings show that, socio-economic characteristics such as extension contacts and credit access showed significance with respect to adoption of most of the innovations. Therefore, if adoption level is to be enhanced, attention should be focused more on training of more agriculture extension agents (AEAs) to increase their number in the area, as well as making affordable credit available and accessible to the farmers to expand their farms.KEY DESCRIPTORS: Adoption, animals, credit, extension and small ruminant
Anomalous Breaking of Anisotropic Scaling Symmetry in the Quantum Lifshitz Model
In this note we investigate the anomalous breaking of anisotropic scaling
symmetry in a non-relativistic field theory with dynamical exponent z=2. On
general grounds, one can show that there exist two possible "central charges"
which characterize the breaking of scale invariance. Using heat kernel methods,
we compute these two central charges in the quantum Lifshitz model, a free
field theory which is second order in time and fourth order in spatial
derivatives. We find that one of the two central charges vanishes.
Interestingly, this is also true for strongly coupled non-relativistic field
theories with a geometric dual described by a metric and a massive vector
field.Comment: 26 pages; major revision (results were unaffected), published versio
VEZF1 elements mediate protection from DNA methylation
There is growing consensus that genome organization and long-range gene regulation involves partitioning of the genome into domains of distinct epigenetic chromatin states. Chromatin insulator or barrier elements are key components of these processes as they can establish boundaries between chromatin states. The ability of elements such as the paradigm β-globin HS4 insulator to block the range of enhancers or the spread of repressive histone modifications is well established. Here we have addressed the hypothesis that a barrier element in vertebrates should be capable of defending a gene from silencing by DNA methylation. Using an established stable reporter gene system, we find that HS4 acts specifically to protect a gene promoter from de novo DNA methylation. Notably, protection from methylation can occur in the absence of histone acetylation or transcription. There is a division of labor at HS4; the sequences that mediate protection from methylation are separable from those that mediate CTCF-dependent enhancer blocking and USF-dependent histone modification recruitment. The zinc finger protein VEZF1 was purified as the factor that specifically interacts with the methylation protection elements. VEZF1 is a candidate CpG island protection factor as the G-rich sequences bound by VEZF1 are frequently found at CpG island promoters. Indeed, we show that VEZF1 elements are sufficient to mediate demethylation and protection of the APRT CpG island promoter from DNA methylation. We propose that many barrier elements in vertebrates will prevent DNA methylation in addition to blocking the propagation of repressive histone modifications, as either process is sufficient to direct the establishment of an epigenetically stable silent chromatin stat
Strings on Semisymmetric Superspaces
Several string backgrounds which arise in the AdS/CFT correspondence are
described by integrable sigma-models. Their target space is always a Z(4)
supercoset (a semi-symmetric superspace). Here we list all semi-symmetric
cosets which have zero beta function and central charge c<=26 at one loop in
perturbation theory.Comment: 25 pages, 1 figur
Thermodynamics and phase diagram of anisotropic Chern-Simons deformed gauge theories
We consider 3+1-dimensional gauge theories at finite temperature and a finite
density of charges which couple to a 2+1-dimensional Chern-Simons operator,
giving rise to a theta-term with constant spatial gradient of theta. The
strong-coupling limit of thermal N=4 super-Yang-Mills theory with this kind of
anisotropic deformation has been used in the context of the AdS/CFT
correspondence as a model for strongly coupled anisotropic quark-gluon plasma.
In this paper we work out the thermodynamics and the (nontrivial) phase diagram
in the limit of vanishing gauge coupling and compare with the corresponding
strong-coupling results.Comment: 23 pages, 7 figures, v2: low temperature expansion corrected,
references added, some discussion expande
Constraints on the Progenitor System of the Type Ia Supernova SN 2011fe/PTF11kly
Type Ia supernovae (SNe) serve as a fundamental pillar of modern cosmology,
owing to their large luminosity and a well-defined relationship between
light-curve shape and peak brightness. The precision distance measurements
enabled by SNe Ia first revealed the accelerating expansion of the universe,
now widely believed (though hardly understood) to require the presence of a
mysterious "dark" energy. General consensus holds that Type Ia SNe result from
thermonuclear explosions of a white dwarf (WD) in a binary system; however,
little is known of the precise nature of the companion star and the physical
properties of the progenitor system. Here we make use of extensive historical
imaging obtained at the location of SN 2011fe/PTF11kly, the closest SN Ia
discovered in the digital imaging era, to constrain the visible-light
luminosity of the progenitor to be 10-100 times fainter than previous limits on
other SN Ia progenitors. This directly rules out luminous red giants and the
vast majority of helium stars as the mass-donating companion to the exploding
white dwarf. Any evolved red companion must have been born with mass less than
3.5 times the mass of the Sun. These observations favour a scenario where the
exploding WD of SN 2011fe/PTF11kly, accreted matter either from another WD, or
by Roche-lobe overflow from a subgiant or main-sequence companion star.Comment: 22 pages, 6 figures, submitte
Enhancing lepton flavour violation in the supersymmetric inverse seesaw beyond the dipole contribution
In minimal supersymmetric models the -penguin usually provides
sub-dominant contributions to charged lepton flavour violating observables. In
this study, we consider the supersymmetric inverse seesaw in which the
non-minimal particle content allows for dominant contributions of the
-penguin to several lepton flavour violating observables. In particular, and
due to the low-scale (TeV) seesaw, the penguin contribution to, for instance,
\Br(\mu \to 3e) and conversion in nuclei, allows to render some of
these observables within future sensitivity reach. Moreover, we show that in
this framework, the -penguin exhibits the same non-decoupling behaviour
which had previously been identified in flavour violating Higgs decays in the
Minimal Supersymmetric Standard Model.Comment: 29 pages, 9 figures, 4 tables; v2: minor corrections, version to
appear in JHE
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