143 research outputs found
Cosmic magnetic fields from velocity perturbations in the early Universe
We show, using a covariant and gauge-invariant charged multifluid
perturbation scheme, that velocity perturbations of the matter-dominated dust
Friedmann-Lemaitre-Robertson-Walker (FLRW) model can lead to the generation of
cosmic magnetic fields. Moreover, using cosmic microwave background (CMB)
constraints, it is argued that these fields can reach strengths of between
10^{-28} and 10^{-29} G at the time the dynamo mechanism sets in, making them
plausible seed field candidates.Comment: 11 pages, 1 figure, IOP style, minor changes and typos correcte
Genetically discrete populations of Trypanosoma congolense from livestock on the Kenyan coast
Twenty-seven stocks of Nannomonas trypanosomes isolated from livestock in 1982 on a ranch at Kilifi on the Kenyan coast were characterized by isoenzyme electrophoresis and by the abilities of the parasite's DNA to hybridize to two repetitive sequence DNA probes. Allthe Kilifi stocks which were examined had isoenzyme patterns which were markedly different from the 75 patterns previously described from 78 stocks of Trypanosoma congolense. On average only 15% of the enzyme bands present in the Kilifi stocks were present in those stocks of T. congolense which had previously been surveyed for isoenzymes. The DNA from all the Kilifi stocks which had been examined for isoenzymes hybridized with only the repetitive sequence probe isolated from a clone of a Kilifi stock. In contrast, the DNA from all 27 Kilifi stocks failed to hybridize with a repetitive sequence probe isolated from a clone from a different stock of T. congolense. Thus, the trypanosomes in all the Kilifi stocks examined were both phenotypically and genotypically discrete. These genetically discrete trypanosomes have also been detected in 2 stocks isolated from livestock from another location on the Kenyan coast. The results show that there is a wide range of genetic heterogeneity within the trypanosomes currently classified as T. congolense. We suggest that the limits of this genetic heterogeneity could represent incipient speciatio
Scalar field and electromagnetic perturbations on Locally Rotationally Symmetric spacetimes
We study scalar field and electromagnetic perturbations on Locally
Rotationally Symmetric (LRS) class II spacetimes, exploiting a recently
developed covariant and gauge-invariant perturbation formalism. From the
Klein-Gordon equation and Maxwell's equations, respectively, we derive
covariant and gauge-invariant wave equations for the perturbation variables and
thereby find the generalised Regge-Wheeler equations for these LRS class II
spacetime perturbations. As illustrative examples, the results are discussed in
detail for the Schwarzschild and Vaidya spacetime, and briefly for some classes
of dust Universes.Comment: 22 pages; v3 has minor changes to match published versio
Primordial magnetic fields from second-order cosmological perturbations: Tight coupling approximation
We explore the possibility of generating large-scale magnetic fields from
second-order cosmological perturbations during the pre-recombination era. The
key process for this is Thomson scattering between the photons and the charged
particles within the cosmic plasma. To tame the multi-component interacting
fluid system, we employ the tight coupling approximation. It is shown that the
source term for the magnetic field is given by the vorticity, which signals the
intrinsically second-order quantities, and the product of the first order
perturbations. The vorticity itself is sourced by the product of the
first-order quantities in the vorticity evolution equation. The magnetic fields
generated by this process are estimated to be Gauss on the
horizon scale at the recombination epoch. Although our rough estimate suggests
that the current generation mechanism can work even on smaller scales, more
careful investigation is needed to make clear whether it indeed works in a wide
range of spatial scales.Comment: 10pages, minor corrections, accepted for publication in Class. Quant.
Gra
Maxwell-Kosteleck\'y Electromagnetism and Cosmic Magnetization
The Lorentz violating term in the photon sector of Standard Model Extension,
\mathcal{L}_K = -{\frac14} (k_F)_{\alpha \beta \mu \nu} F^{\alpha \beta}
F^{\mu \nu} (here referred to as the Kosteleck\'{y} term), breaks conformal
invariance of electromagnetism and enables a superadiabatic amplification of
magnetic vacuum fluctuations during inflation. For a wide range of values of
parameters defining Lorentz symmetry violation and inflation, the present-day
magnetic field can have an intensity of order of nanogauss on megaparsec scales
and then could explain the large-scale magnetization of the universe.Comment: 10 pages, 1 figure, minor revisions; accepted for publication in
Physics Letters
Robot-assisted pelvic floor reconstructive surgery: an international Delphi study of expert users.
Robotic surgery has gained popularity for the reconstruction of pelvic floor defects. Nonetheless, there is no evidence that robot-assisted reconstructive surgery is either appropriate or superior to standard laparoscopy for the performance of pelvic floor reconstructive procedures or that it is sustainable. The aim of this project was to address the proper role of robotic pelvic floor reconstructive procedures using expert opinion.
We set up an international, multidisciplinary group of 26 experts to participate in a Delphi process on robotics as applied to pelvic floor reconstructive surgery. The group comprised urogynecologists, urologists, and colorectal surgeons with long-term experience in the performance of pelvic floor reconstructive procedures and with the use of the robot, who were identified primarily based on peer-reviewed publications. Two rounds of the Delphi process were conducted. The first included 63 statements pertaining to surgeons' characteristics, general questions, indications, surgical technique, and future-oriented questions. A second round including 20 statements was used to reassess those statements where borderline agreement was obtained during the first round. The final step consisted of a face-to-face meeting with all participants to present and discuss the results of the analysis.
The 26 experts agreed that robotics is a suitable indication for pelvic floor reconstructive surgery because of the significant technical advantages that it confers relative to standard laparoscopy. Experts considered these advantages particularly important for the execution of complex reconstructive procedures, although the benefits can be found also during less challenging cases. The experts considered the robot safe and effective for pelvic floor reconstruction and generally thought that the additional costs are offset by the increased surgical efficacy.
Robotics is a suitable choice for pelvic reconstruction, but this Delphi initiative calls for more research to objectively assess the specific settings where robotic surgery would provide the most benefit
Physiological Roles of Orexin Receptors on Sleep/Wakefulness Regulation
Hypothalamic neuropeptides orexin-A and orexin-B play critical roles in the regulation of sleep/wakefulness, as well as in a variety of physiological functions including emotion, reward and energy homeostasis. The effects of orexin peptides are mediated by two receptors, orexin 1 (OX1R) and orexin 2 (OX2R) receptors. These receptors show differential expression patterns depending on brain regions and neuron types, suggesting their differential roles. Here, we review the current understanding of the physiological roles of each orexin receptor subtype, focusing on the regulation of sleep/wakefulness. © Springer International Publishing Switzerland 2015. All rights reserved.Book Chapter, Embargo Period 12 month
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