11,330 research outputs found
New "Bigs" in cosmology
This paper contains a detailed discussion on new cosmic solutions describing
the early and late evolution of a universe that is filled with a kind of dark
energy that may or may not satisfy the energy conditions. The main distinctive
property of the resulting space-times is that they make to appear twice the
single singular events predicted by the corresponding quintessential (phantom)
models in a manner which can be made symmetric with respect to the origin of
cosmic time. Thus, big bang and big rip singularity are shown to take place
twice, one on the positive branch of time and the other on the negative one. We
have also considered dark energy and phantom energy accretion onto black holes
and wormholes in the context of these new cosmic solutions. It is seen that the
space-times of these holes would then undergo swelling processes leading to big
trip and big hole events taking place on distinct epochs along the evolution of
the universe. In this way, the possibility is considered that the past and
future be connected in a non-paradoxical manner in the universes described by
means of the new symmetric solutions.Comment: 7 figures, 13 pages, RevTe
Discovery of a wide companion near the deuterium burning mass limit in the Upper Scorpius association
We present the discovery of a companion near the deuterium burning mass limit
located at a very wide distance, at an angular separation of 4.6+/-0.1 arcsec
(projected distance of ~ 670 AU) from UScoCTIO108, a brown dwarf of the very
young Upper Scorpius association. Optical and near-infrared photometry and
spectroscopy confirm the cool nature of both objects, with spectral types of M7
and M9.5, respectively, and that they are bona fide members of the association,
showing low gravity and features of youth. Their masses, estimated from the
comparison of their bolometric luminosities and theoretical models for the age
range of the association, are 60+/-20 and 14^{+2}_{-8} MJup, respectively. The
existence of this object around a brown dwarf at this wide orbit suggests that
the companion is unlikely to have formed in a disk based on current planet
formation models. Because this system is rather weakly bound, they did not
probably form through dynamical ejection of stellar embryos.Comment: 10 pages, including 4 figures and 2 table
Comparative study of mycotoxin occurrence in Andean and cereal grains cultivated in South America and North Europe
The consumption of high-quality Andean grains (a.k.a. pseudocereals) is increasing worldwide, and yet very little is known about the susceptibility of these crops to mycotoxin contamination. In this survey study, a multi-analyte liquid chromatography–tandem mass spectrometry (LC–MS/MS) method was utilised to determine mycotoxin and fungal metabolite levels in Andean grains (quinoa and kañiwa) in comparison to cereal grains (barley, oats and wheat), cultivated in both South American (Bolivia and Peru) and North European (Denmark, Finland and Latvia) countries. A total of 101 analytes were detected at varying levels, primarily produced by Penicillium spp., Fusarium spp. and Aspergillus spp., depending on the type of crop, geographical location and agricultural practices used. Generally, Andean grains from South America showed lower mycotoxin contamination (concentration and assortment) than those from North Europe, while the opposite occurred with cereal grains. Mycotoxin contamination profiles exhibited marked differences between Andean and cereal grains, even when harvested from the same regions, highlighting the need for crop-specific approaches for mycotoxin risk mitigation. Lastly, the efficacy of grain cleaning in respect to total mycotoxin content was assessed, which resulted in significantly lower levels (overall reduction approx. 50%) in cleaned samples for the majority of contaminants.Peer reviewe
Treatment of a Complex Distal Triceps Tendon Rupture With a New Technique: A Case Report
Introduction: The distal triceps tendon rupture is an uncommon injury. The acute treatment is well-defined, but when a delayed diagnosis is made or when a tendon retraction is present the alternatives or reconstruction are limited and sometimes complex.
Case Presentation: In this case, we report on a 28-year-old man who presented with a chronic disruption of the distal triceps tendon with a gap of approximately 15 cm. The patient was diagnosed in another center with an inveterate breakage of the distal triceps tendon and was initially treated with an Achilles allograft that was complicated by a wound infection and required more than ten surgeries. Nearly 22 months after the initial trauma, and 12 months after the first surgery, we performed a reconstruction with an Achilles tendon allograft using the new technique of distal attachment. At the 12-month follow-up the patient presented a joint balance from -5º to 110º and presented with no pain.
Conclusions: The use of an Achilles tendon allograft provides excellent results in complex distal triceps tendon ruptures. We report the use of a new technique to anchor a distal Achilles allograft
Radio-frequency performance comparison of several H-plane rectangular waveguide filters loaded with circular dielectric posts
This paper is a postprint of a paper submitted to and accepted for publication in IET Microwaves Antennas and Propagation and is subject to Institution of Engineering and Technology Copyright. The copy of record is available at IET Digital LibraryThe study presents a radio-frequency performance comparison between several H-plane geometry filters based on rectangular waveguide technology. The basic all-metal filter of resonant cavities is compared with filters loaded with circular dielectric resonators, either in propagative or evanescent mode. The use of these resonators is claimed to reduce the length of the filter, increase the rejection band until the first spurious frequency and to improve the voltage magnification factor (VMF), at the cost of increasing the losses. Therefore, in order to properly assess and quantify the possible advantages of these filters, an accurate analysis of six of them has been developed. All the filters have been designed to have the same electrical response, and the length, losses, rejection band, VMF, and fabrication cost for all the filters are compared.Our acknowledgement to the Val Space Consortium for its contribution - Laboratories co-funded by the European Regional Development Fund - A way of making Europe.Bachiller Martin, MC.; Esteban González, H.; Diaz, F.; Morro, JV.; Boria Esbert, VE. (2016). Radio-frequency performance comparison of several H-plane rectangular waveguide filters loaded with circular dielectric posts. IET Microwaves Antennas and Propagation. 10(5):536-545. doi:10.1049/iet-map.2014.0738S53654510
Supersymmetric Model of Muon Anomalous Magnetic Moment and Neutrino Masses
We propose the novel lepton-number relationship , which
is uniquely realized by the interaction in supersymmetry and may account for a possibly large
muon anomalous magnetic moment. Neutrino masses (with bimaximal mixing) may be
generated from the spontaneous and soft breaking of this lepton symmetry.Comment: 10 pages, including 2 figure
Can slow roll inflation induce relevant helical magnetic fields?
We study the generation of helical magnetic fields during single field
inflation induced by an axial coupling of the electromagnetic field to the
inflaton. During slow roll inflation, we find that such a coupling always leads
to a blue spectrum with , as long as the theory is treated
perturbatively. The magnetic energy density at the end of inflation is found to
be typically too small to backreact on the background dynamics of the inflaton.
We also show that a short deviation from slow roll does not result in strong
modifications to the shape of the spectrum. We calculate the evolution of the
correlation length and the field amplitude during the inverse cascade and
viscous damping of the helical magnetic field in the radiation era after
inflation. We conclude that except for low scale inflation with very strong
coupling, the magnetic fields generated by such an axial coupling in single
field slow roll inflation with perturbative coupling to the inflaton are too
weak to provide the seeds for the observed fields in galaxies and clusters.Comment: 33 pages 6 figures; v4 to match the accepted version to appear in
JCA
Detecting Higgs Boson Decay to Neutralinos at Hadron Supercolliders
We examine prospects for detecting the neutral Higgs bosons of minimal
supersymmetric models (MSSM) when their decays into neutralino pairs are
kinematically allowed. The best signature appears to be
H_h,H_p\to\tz_2\tz_2\to 4\ell +\eslt. We argue that Standard Model
contributions to this signature are negligible, and examine regions of MSSM
parameter space where the four lepton mode should be observable at the Large
Hadron Collider. The same signal can also come from continuum neutralino pair
production. We propose a set of cuts to illustrate that the neutralino decay
mode of the Higgs bosons provides a viable signal over a substantial range of
model parameters, and show that it may be separable from continuum neutralino
production if sufficient integrated luminosity can be accumulated.Comment: 15 pages (REVTEX), 7 figures available by regular mail,
FSU-HEP-940204, UH-511-781-9
Can black holes be torn up by phantom dark energy in cyclic cosmology?
Infinitely cyclic cosmology is often frustrated by the black hole problem. It
has been speculated that this obstacle in cyclic cosmology can be removed by
taking into account a peculiar cyclic model derived from loop quantum cosmology
or the braneworld scenario, in which phantom dark energy plays a crucial role.
In this peculiar cyclic model, the mechanism of solving the black hole problem
is through tearing up black holes by phantom. However, using the theory of
fluid accretion onto black holes, we show in this paper that there exists
another possibility: that black holes cannot be torn up by phantom in this
cyclic model. We discussed this possibility and showed that the masses of black
holes might first decrease and then increase, through phantom accretion onto
black holes in the expanding stage of the cyclic universe.Comment: 6 pages, 2 figures; discussions adde
- …