534 research outputs found
The Optical Afterglow of GRB 011211
We present early-time optical photometry and spectroscopy of the optical
afterglow of the gamma-ray burst GRB 011211. The spectrum of the optical
afterglow contains several narrow metal lines which are consistent with the
burst occurring at a redshift of 2.140 +/- 0.001. The optical afterglow decays
as a power law with a slope of alpha = 0.83 +/- 0.04 for the first
approximately two days after the burst at which time there is evidence for a
break. The slope after the break is at least 1.4. There is evidence for rapid
variations in the R-band light approximately 0.5 days after the burst. These
variations suggest that there are density fluctuations near the gamma-ray burst
on spatial scales of approximately 40--125 AU. The magnitude of the break in
the light curve, the spectral slope, and the rate of decay in the optical,
suggest that the burst expanded into an ambient medium that is homogeneous on
large scales. We estimate that the local particle density is between
approximately 0.1 and 10 cm^{-3} and that the total gamma-ray energy in the
burst was 1.2--1.9 x 10^{50} erg. This energy is smaller than, but consistent
with, the ``standard'' value of (5 +/- 2) x 10^{50} erg. Comparing the observed
color of the optical afterglow with predictions of the standard beaming model
suggests that the rest-frame V-band extinction in the host galaxy is less than
approximately 0.03 mag.Comment: 17 pages, 4 figures, AASTeX 5.02, to appear in AJ Referee's report
incorporated, minor changes in the tex
Risk-Seeking versus Risk-Avoiding Investments in Noisy Periodic Environments
We study the performance of various agent strategies in an artificial
investment scenario. Agents are equipped with a budget, , and at each
time step invest a particular fraction, , of their budget. The return on
investment (RoI), , is characterized by a periodic function with
different types and levels of noise. Risk-avoiding agents choose their fraction
proportional to the expected positive RoI, while risk-seeking agents
always choose a maximum value if they predict the RoI to be positive
("everything on red"). In addition to these different strategies, agents have
different capabilities to predict the future , dependent on their
internal complexity. Here, we compare 'zero-intelligent' agents using technical
analysis (such as moving least squares) with agents using reinforcement
learning or genetic algorithms to predict . The performance of agents is
measured by their average budget growth after a certain number of time steps.
We present results of extensive computer simulations, which show that, for our
given artificial environment, (i) the risk-seeking strategy outperforms the
risk-avoiding one, and (ii) the genetic algorithm was able to find this optimal
strategy itself, and thus outperforms other prediction approaches considered.Comment: 27 pp. v2 with minor corrections. See http://www.sg.ethz.ch for more
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Squark Loop Correction to W^{+-} H^{-+} Associated Hadroproduction
We study the squark loop correction to W^{+-} H^{-+} associated
hadroproduction via gluon-gluon fusion within the minimal supersymmetric
extension of the standard model. We list full analytic results and
quantitatively analyze the resulting shift in the cross section at the CERN
Large Hadron Collider assuming a supergravity-inspired scenario.Comment: 13 pages (Latex), 5 figures (Postscript
Beyond the exponential horn:a bush-cricket with ear canals which function as coupled resonators
Bush-crickets have dual-input, tympanal ears located in the tibia of their forelegs. The sound will first of all reach
the external sides of the tympana, before arriving at the internal sides through the bush-cricket’s ear canal, the
acoustic trachea (AT), with a phase lapse and pressure gain. It has been shown that for many bush-crickets, the AT has
an exponential horn-shaped morphology and function, producing a significant pressure gain above a certain cut-off frequency. However, the underlying mechanism of different AT designs remains elusive. In this study, we demonstrate
that the AT of the duetting Phaneropterinae bush-cricket Pterodichopetala cieloi function as coupled resonators,
producing sound pressure gains at the sex-specific conspecific calling song frequency, and attenuating the
remainder—a functioning mechanism significantly different from an exponential horn. Furthermore, it is demonstrated
that despite the sexual dimorphism between the P. cieloi AT, both male and female AT have a similar biophysical
mechanism. The analysis was carried out using an interdisciplinary approach, where micro-computed
tomography was used for the morphological properties of the P. cieloi AT, and a finite-element analysis was applied on
the precise tracheal geometry to further justify the experimental results and to go beyond experimental
limitations
Vertically illuminated TW-UTC photodiodes for terahertz generation
More efficient and powerful continuous-wave photonic mixers as terahertz sources are motivated by the need of more versatile local oscillators for submillimeter/terahertz receiver systems. Uni-Travelling Carrier (UTC) photodiodes are very prospective candidates for reaching this objective, but so far only have been reported as lumped-elements or as edge-illuminated optical-waveguide travelling-wave (TW) devices. To overcome the associated power limitations of those implementations, we are developing a novel implementation of the UTC photodiodes which combines a traveling-wave photomixer with vertical velocity-matched illumination in a distributed structure. In this implementation called velocity-matched travelling-wave uni-travelling carrier photodiode, it is possible to obtain in-situ velocity matching of the beat-fringes of the two angled laser beams with the submm/THz-wave on the stripline. In this way, minimum frequency roll-off is achieved by tuning the angle between the two laser beams. A first design of these TW-UTC PDs from our Terahertz Photonics Laboratory at University of Chile has been micro-fabricated at the MC2 cleanroom facility at Chalmers Technical University
Pair production of neutral Higgs bosons at the CERN Large Hadron Collider
We study the hadroproduction of two neutral Higgs bosons in the minimal
supersymmetric extension of the standard model, which provides a handle on the
trilinear Higgs couplings. We include the contributions from quark-antiquark
annihilation at the tree level and those from gluon-gluon fusion, which
proceeds via quark and squark loops. We list compact results for the tree-level
partonic cross sections and the squark loop amplitudes, and we confirm previous
results for the quark loop amplitudes. We quantitatively analyze the hadronic
cross sections at the CERN Large Hadron Collider assuming a favorable
supergravity-inspired scenario.Comment: 22 pages (Latex), 16 figures (Postscript). Discussion of theoretical
uncertainties and background processes added. Accepted for publication in
Phys. Rev.
Cryopreservation of horse semen with a liposome and trehalose added extender
The aim of the study was to evaluate the effect of cryopreserved equine semen in the presence of trehalose-loaded liposomes on the integrity and function of sperm cells. Six ejaculations of five stallions collected with an artificial vagina were used. The ejaculates were diluted with INRA 96® 2:1 v/v and transported at 22 °C to the laboratory. Before cryopreservation, the semen was diluted with INRA Freeze® to obtain the following treatments: T1) INRA Freeze® (control), T2) INRA Freeze® + liposomes, T3) INRA Freeze® + liposomes+trehalose. Data were analysed using the Kruskal Wallis test. The percentages of sperm with intact DNA were 54.5, 57.9, and 64.8% for T1, T2 and T3, respectively (P>0.05). When evaluating the acrosomal and capacitation state after filtering with Percoll®, the percentages of spermatozoa without acrosome reaction and without capacitation were 67.8, 79.2 and 68.1% in T1, T2, and T3, respectively (P>0.05), while the capacitated sperm without acrosome reaction and without capacitation was similar in T1 (47%) and T3 (32%) (P>0.05), and lower in T2 (16%) before filtering with Percoll®. The use of liposomes and liposome-trehalose did not affect on the functional status and nuclear chromatin of the equine sperm after freezing, but it did affect the percentage of capacitated sperm without acrosome reaction after selecting the thawed semen using the Percoll® gradient
Right radical hemicolectomy secondary to cecal appendix mucocele: case report
The cecal appendix mucocele is considered a cystic dilation of obstructive etiology that produces an accumulation of mucoid substance. It may be of benign or malignant origin. 50-year-old female, with no significant personal pathological history, presents with repetitive clinical symptoms of abdominal pain, similar to the process of acute appendicitis, without systemic inflammatory response data, which improves with analgesic management, is protocolized by laboratory studies and imaging, diagnosing appendicular tumor, so it is protocolized for surgical resolution, during which it is decided to do right hemicolectomy due to the macroscopic features of ascending colon. The clinical course and prognosis of mucinous appendicular lesions are closely related to their histology and the presence and extent of peritoneal dissemination. With a survival of 91 to 100% after a conventional appendectomy. The cecal appendix mucocele is considered a benign neoplasm; with good survival provided it is diagnosed in time and an appropriate surgical approach is performed; in our case fortunately it could be protocolized correctly; perform a surgical resection with free edges of oncological cells confirmed by histopathology, so our patient could be discharged from the service being free of oncological pathology at this time
Higgs-Boson Production Induced by Bottom Quarks
Bottom quark-induced processes are responsible for a large fraction of the
LHC discovery potential, in particular for supersymmetric Higgs bosons.
Recently, the discrepancy between exclusive and inclusive Higgs boson
production rates has been linked to the choice of an appropriate bottom
factorization scale. We investigate the process kinematics at hadron colliders
and show that it leads to a considerable decrease in the bottom factorization
scale. This effect is the missing piece needed to understand the corresponding
higher order results. Our results hold generally for charged and for neutral
Higgs boson production at the LHC as well as at the Tevatron. The situation is
different for single top quark production, where we find no sizeable
suppression of the factorization scale. Turning the argument around, we can
specify how large the collinear logarithms are, which can be resummed using the
bottom parton picture.Comment: 18 page
W^+- H^-+ Associated Production at the Large Hadron Collider
We study the production of a charged Higgs boson in association with a W
boson at the CERN Large Hadron Collider in the context of the minimal
supersymmetric extension of the standard model. This production mechanism is
particularly promising if the charged Higgs boson is too heavy to be generated
by top-quark decay. We compare the contributions due to b b-bar annihilation at
the tree level and gg fusion, which proceeds at one loop. Apart from the total
cross section, we also consider distributions in transverse momentum and
rapidity. We also assess the viability of W^+- H^-+ associated production at
the Fermilab Tevatron after the installation of the Main Injector and the
Recycler.Comment: 16 pages (Latex), 8 figures (Postscript
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