1,161 research outputs found
Entropic N-bound and Maximal Mass Conjecture Violations in Four Dimensional Taub-Bolt(NUT)-dS Spacetimes
We show that the class of four-dimensional Taub-Bolt(NUT) spacetimes with
positive cosmological constant for some values of NUT charges are stable and
have entropies that are greater than that of de Sitter spacetime, in violation
of the entropic N-bound conjecture. We also show that the maximal mass
conjecture, which states "any asymptotically dS spacetime with mass greater
than dS has a cosmological singularity", can be violated as well. Our
calculation of conserved mass and entropy is based on an extension of the path
integral formulation to asymptotically de Sitter spacetimes.Comment: 37 pages, 22 figures, 3 tables, few typos corrected, version to
appear in Nucl. Phys.
Human Langerhans cells in transplantation: Recipient cells survive conditioning but donor cells predominate at day 100
Reissner-Nordstrom-de Sitter black hole, planar coordinates and dS/CFT
We discuss the Reissner-Nordstrom-de Sitter black holes in the context of
dS/CFT correspondence by using static and planar coordinates. The boundary
stress tensor and the mass of the solutions are computed. Also, we investigate
how the RG flow is changed for different foliations. The Kastor-Traschen
multi-black hole solution is considered as well as AdS counterparts of these
configurations. In particular, we find that in planar coordinates the black
holes appear like punctures in the dual boundary theory.Comment: 30 pages, 3 eps figures, JHEP style v2: new references added,
misprints correcte
Microplastic in wild populations of the omnivorous crab Carcinus aestuarii: A review and a regional-scale test of extraction methods, including microfibres
Microplastic (MP) has become ubiquitous in the marine environment. Its threat to marine organisms has been demonstrated under laboratory conditions, yet studies on wild populations still face methodological difficulties. We reviewed the methods used to separate MP from soft animal tissues and highlighted a lack of standardised methodologies, particularly critical for synthetic microfibres. We further compared enzymatic and a potassium hydroxide (KOH)-based alkaline digestion protocols on wild crabs (Carcinus aestuarii) collected from three coastal lagoons in the north Adriatic Sea and on laboratory-prepared synthetic polyester (PES) of different colour and polypropylene (PP). We compared the cost-effectiveness of the two methods, together with the potential for adverse quantitative or qualitative effects on MP that could alter the capability of the polymers to be recognised via microscopic or spectroscopic techniques. Only 5.5% of the 180 examined crabs contained MP in their gastrointestinal tracts, with a notably high quantitative variability between individuals (from 1 to 117 particles per individual). All MP found was exclusively microfibres, mainly PES, with a mean length (\ub1SE) of 0.5\u202f\ub1\u202f0.03\u202fmm. The two digestion methods provided comparable estimates on wild crabs and did not cause any visible physical or chemical alterations on laboratory-prepared microfibres treated for up to 4 days. KOH solution was faster and cheaper compared to the enzymatic extraction, involving fewer procedural steps and therefore reducing the risk of airborne contamination. With digestion times longer than 4 days, KOH caused morphological alterations of some of the PES microfibres, which did not occur with the enzymatic digestion. This suggests that KOH is effective for the digestion of small marine invertebrates or biological samples for which shorter digestion time is required, while enzymatic extraction should be considered as alternative for larger organisms or sample sizes requiring longer digestion times
Observing Long Colour Flux Tubes in SU(2) Lattice Gauge Theory
We present results of a high statistics study of the chromo field
distribution between static quarks in SU(2) gauge theory on lattices of volumes
16^4, 32^4, and 48^3*64, with physical extent ranging from 1.3 fm up to 2.7 fm
at beta=2.5, beta=2.635, and beta=2.74. We establish string formation over
physical distances as large as 2 fm. The results are tested against Michael's
sum rules. A detailed investigation of the transverse action and energy flux
tube profiles is provided. As a by-product, we obtain the static lattice
potential in unpreceded accuracy.Comment: 66 pages, 29 figures, uuencoded latex file with epsfigures (450 K),
supplementary full colour figures are available via ftp, CERN-TH.7413/94
(extended version
Argon annealing of the oxygen-isotope exchanged manganite La_{0.8}Ca_{0.2}MnO_{3+y}
We have resolved a controversial issue concerning the oxygen-isotope shift of
the ferromagnetic transition temperature T_{C} in the manganite
La_{0.8}Ca_{0.2}MnO_{3+y}. We show that the giant oxygen-isotope shift of T_C
observed in the normal oxygen-isotope exchanged samples is indeed intrinsic,
while a much smaller shift observed in the argon annealed samples is an
artifact. The argon annealing causes the 18O sample to partially exchange back
to the 16O isotope due to a small 16O contamination in the Ar gas. Such a
contamination is commonly caused by the oxygen outgas that is trapped in the
tubes, connectors and valves. The present results thus umambiguously
demonstrate that the observed large oxygen isotope effect is an intrinsic
property of manganites, and places an important constraint on the basic physics
of these materials.Comment: 4 pages, 3 figures, submitted to PR
Structure of isobaric analog states in 91Nb populated by the 90Zr(a,t) reaction
Decay via proton emission of isobaric analog states (IAS's) in
was studied using the reaction at =180 MeV.
This study provides information about the damping mechanism of these states.
Decay to the ground state and low-lying phonon states in was
observed. The experimental data are compared with theoretical predictions
wherein the IAS `single-particle' proton escape widths are calculated in a
continuum RPA approach. The branching ratios for decay to the phonon states are
explained using a simple model.Comment: 3 figures. submitted to Phys. Lett.
Cosmological Black Holes on Branes
We examined analytically a cosmological black hole domain wall system. Using
the C-metric construction we derived the metric for the spacetime describing an
infinitely thin domain wall intersecting a cosmological black hole. We studied
the behaviour of the scalar field describing a self-interacting cosmological
domain wall and find the approximated solution valid for large distances. The
thin wall approximation and the back raection problem were elaborated finding
that the topological kink solution smoothed out singular behaviour of the zero
thickness wall using a core topological and hence thick domain wall. We also
analyze the nucleation of cosmological black holes on and in the presence of a
domain walls and conclude that the domain wall will nucleate small black holes
on it rather than large ones inside.Comment: 13 pages, Revtex, to be published in Phys.Rev. D1
Pion photoproduction on the nucleon in the quark model
We present a detailed quark-model study of pion photoproduction within the
effective Lagrangian approach. Cross sections and single-polarization
observables are investigated for the four charge channels, , , , and .
Leaving the coupling strength to be a free parameter, we obtain a
reasonably consistent description of these four channels from threshold to the
first resonance region. Within this effective Lagrangian approach, strongly
constrainted by the quark model, we consider the issue of double-counting which
may occur if additional {\it t}-channel contributions are included.Comment: Revtex, 35 pages, 16 eps figures; version to appear on PR
Model confidence sets and forecast combination: an application to age-specific mortality
Background: Model averaging combines forecasts obtained from a range of models, and it often produces more accurate forecasts than a forecast from a single model.
Objective: The crucial part of forecast accuracy improvement in using the model averaging lies in the determination of optimal weights from a finite sample. If the weights are selected sub-optimally, this can affect the accuracy of the model-averaged forecasts. Instead of choosing the optimal weights, we consider trimming a set of models before equally averaging forecasts from the selected superior models. Motivated by Hansen et al. (2011), we apply and evaluate the model confidence set procedure when combining mortality forecasts.
Data & Methods: The proposed model averaging procedure is motivated by Samuels and Sekkel (2017) based on the concept of model confidence sets as proposed by Hansen et al. (2011) that incorporates the statistical significance of the forecasting performance. As the model confidence level increases, the set of superior models generally decreases. The proposed model averaging procedure is demonstrated via national and sub-national Japanese mortality for retirement ages between 60 and 100+.
Results: Illustrated by national and sub-national Japanese mortality for ages between 60 and 100+, the proposed model-average procedure gives the smallest interval forecast errors, especially for males. Conclusion: We find that robust out-of-sample point and interval forecasts may be obtained from the trimming method. By robust, we mean robustness against model misspecification
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