29,422 research outputs found
Gauge fields in a string-cigar braneworld
In this work we investigate the properties of an Abelian gauge vector field
in a thin and in a smoothed string-like braneworld, the so-called string-cigar
model. This thick brane scenario satisfies the regularity conditions and it can
be regarded as an interior and exterior string-like solution. The source
undergoes a geometric Ricci flow which is connected to a variation of the bulk
cosmological constant. The Ricci flow changes the width and amplitude of the
massless mode at the brane core and recover the usual thin string-like behavior
at large distances. By numerical means we obtain the Kaluza-Klein (KK) spectrum
for both the thin brane and the string-cigar. It turns out that both models
exhibit a mass gap between the massless and the massive modes and between the
high and the low mass regimes. The KK modes are smooth near the brane and their
amplitude are enhanced by the string-cigar core. The analogue Schr\"odinger
potential is also tuned by the geometric flow.Comment: The discussion about the Kaluza-Klein spectrum of the gauge field was
improved. Numerical analysis was adapted to the conventional notation on
Kaluza-Klein number. Some graphics were modified for considering other
notation. Results unchanged. References added. Corrected typos. 17 pages. 6
figures. To match version to appears in Physics Letters
Gravitating Fluxbranes
We consider the effect that gravity has when one tries to set up a constant
background form field. We find that in analogy with the Melvin solution, where
magnetic field lines self-gravitate to form a flux-tube, the self-gravity of
the form field creates fluxbranes. Several exact solutions are found
corresponding to different transverse spaces and world-volumes, a dilaton
coupling is also considered.Comment: 14 pages, 5 figure
VisIVOWeb: A WWW Environment for Large-Scale Astrophysical Visualization
This article presents a newly developed Web portal called VisIVOWeb that aims
to provide the astrophysical community with powerful visualization tools for
large-scale data sets in the context of Web 2.0. VisIVOWeb can effectively
handle modern numerical simulations and real-world observations. Our
open-source software is based on established visualization toolkits offering
high-quality rendering algorithms. The underlying data management is discussed
with the supported visualization interfaces and movie-making functionality. We
introduce VisIVOWeb Network, a robust network of customized Web portals for
visual discovery, and VisIVOWeb Connect, a lightweight and efficient solution
for seamlessly connecting to existing astrophysical archives. A significant
effort has been devoted for ensuring interoperability with existing tools by
adhering to IVOA standards. We conclude with a summary of our work and a
discussion on future developments
Neutrino-induced nucleosynthesis of A>64 nuclei: The nu p-process
We present a new nucleosynthesis process, that we denote nu p-process, which
occurs in supernovae (and possibly gamma-ray bursts) when strong neutrino
fluxes create proton-rich ejecta. In this process, antineutrino absorptions in
the proton-rich environment produce neutrons that are immediately captured by
neutron-deficient nuclei. This allows for the nucleosynthesis of nuclei with
mass numbers A >64. Making this process a possible candidate to explain the
origin of the solar abundances of 92,94Mo and 96,98Ru. This process also offers
a natural explanation for the large abundance of Sr seen in an hyper-metal-poor
star.Comment: 5 pages, 3 figures, submitted to Physical Review Letter
Robotic or three-dimensional (3D) laparoscopy for right colectomy with complete mesocolic excision (CME) and intracorporeal anastomosis? A propensity score-matching study comparison
Background: We describe our preliminary experience in complete mesocolic excision (CME) with central vascular ligation (CVL) and intracorporeal anastomosis for right colon cancer, comparing the robotic and the three-dimensional (3D) laparoscopic approach. Methods: We performed a retrospective observational clinical cohort study on patients who underwent radical curative surgical resection of right colon cancer with CME from January 2014 to June 2019. Propensity scores were calculated by bivariate logistic regression, including the following variables: age, BMI, and size of tumor. Results: Fifty-five patients underwent CME with CVL: 26 by means of robot-assisted surgery and 29 by means of 3D laparoscopic procedure. There were not statistically significant differences about all the intra- and postoperative outcomes (operative time, length of the specimen, time to bowel canalization, time to soft oral intake, length of hospital stay, postoperative complication, number of retrieved lymph nodes, number of positive lymph nodes and lymph node ratio) between the robotic and the 3D laparoscopic approach. After the matching procedure, 20 patients of the robotic group and 20 patients of the 3D laparoscopic group were selected for the analysis. There were no differences in any of the analyzed variables between the two groups except for longer operative time in the robotic group (p = 0.002). Conclusion: The 3D vision revealed an important advantage in order to achieve the correct identification of surgical anatomy allowing a safe and effective right colectomy with CME, CVL, and intracorporeal anastomosis, either using laparoscopic or with robotic approach, providing similar short-term outcomes. Taking into account the high costs and the longer operative time of robotic procedure, the 3D laparoscopy could be considered in performing right colectomy with CME, while the robotic approach should be considered as a first choice approach for challenging situations (obese patient, complex associated procedures)
Multi-black hole solutions in five dimensions
Using a recently developed generalized Weyl formalism, we construct an
asymptotically flat, static vacuum Einstein solution that describes a
superposition of multiple five-dimensional Schwarzschild black holes. The
spacetime exhibits a U(1)\times U(1) rotational symmetry. It is argued that for
certain choices of parameters, the black holes are collinear and so may be
regarded as a five-dimensional generalization of the Israel-Khan solution. The
black holes are kept in equilibrium by membrane-like conical singularities
along the two rotational axes; however, they still distort one another by their
mutual gravitational attraction. We also generalize this solution to one
describing multiple charged black holes, with fixed mass-to-charge ratio, in
Einstein-Maxwell-dilaton theory.Comment: 23 pages, 6 figure
Multi-shell gold nanowires under compression
Deformation properties of multi-wall gold nanowires under compressive loading
are studied. Nanowires are simulated using a realistic many-body potential.
Simulations start from cylindrical fcc(111) structures at T=0 K. After
annealing cycles axial compression is applied on multi-shell nanowires for a
number of radii and lengths at T=300 K. Several types of deformation are found,
such as large buckling distortions and progressive crushing. Compressed
nanowires are found to recover their initial lengths and radii even after
severe structural deformations. However, in contrast to carbon nanotubes
irreversible local atomic rearrangements occur even under small compressions.Comment: 1 gif figure, 5 ps figure
Minimal Trinification
We study the trinified model, SU(3)_C x SU(3)_L x SU(3)_R x Z_3, with the
minimal Higgs sector required for symmetry breaking. There are five Higgs
doublets, and gauge-coupling unification results if all five are at the weak
scale, without supersymmetry. The radiative see-saw mechanism yields sub-eV
neutrino masses, without the need for intermediate scales, additional Higgs
fields, or higher-dimensional operators. The proton lifetime is above the
experimental limits, with the decay modes p -> \bar\nu K^+ and p -> \mu^+ K^0
potentially observable. We also consider supersymmetric versions of the model,
with one or two Higgs doublets at the weak scale. The radiative see-saw
mechanism fails with weak-scale supersymmetry due to the nonrenormalization of
the superpotential, but operates in the split-SUSY scenario.Comment: 23 pages, uses axodra
Radiation Damping in FRW Space-times with Different Topologies
We study the role played by the compactness and the degree of connectedness
in the time evolution of the energy of a radiating system in the
Friedmann-Robertson-Walker (FRW) space-times whose spacelike
sections are the Euclidean 3-manifold and six topologically
non-equivalent flat orientable compact multiply connected Riemannian
3-manifolds. An exponential damping of the energy is present in the
case, whereas for the six compact flat 3-spaces it is found
basically the same pattern for the evolution of the energy, namely relative
minima and maxima occurring at different times (depending on the degree of
connectedness) followed by a growth of . Likely reasons for this
divergent behavior of in these compact flat 3-manifolds are discussed
and further developments are indicated. A misinterpretation of Wolf's results
regarding one of the six orientable compact flat 3-manifolds is also indicated
and rectified.Comment: 13 pages, RevTeX, 5 figures, To appear in Phys. Rev. D 15, vol. 57
(1998
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