129 research outputs found
Gigahertz Peaked Spectrum sources from the Jodrell Bank-VLA Astrometric Survey
Observations with MERLIN at 408 MHz have been used to establish the
low-frequency part of the spectra of more than a hundred compact radio sources
taken from the part of the Jodrell Bank--VLA Astrometric Survey limited by 35
deg. < \delta < 75 deg. These sources were selected from JVAS and other
catalogues to have convex spectra between 1.4 and 8.4 GHz, characteristic of
Gigahertz Peaked Spectrum (GPS) sources. We have confirmed convex shapes of the
spectra of 76 objects (one half of our initial candidates) thereby yielding the
largest genuine sample of GPS sources compiled so far. Seven of 17 identified
quasars in the sample have large (z\ga 2) redshifts.Comment: 18 pages, 2 figures, minor corrections. To appear in: A&A Suppl. vol.
135 (March 1999
The biomechanics and energetics of human running using an elastic knee exoskeleton
While the effects of series compliance on running biomechanics are well documented, the effects of parallel compliance are known only for the simpler case of hopping. As many practical exoskeletal and orthotic designs act in parallel with the leg, it is desirable to understand the effects of such an intervention. Spring-like forces offer a natural choice of perturbation for running, as they are both biologically motivated and energetically inexpensive to implement. To this end, we investigate the hypothesis that the addition of an external elastic element at the knee during the stance phase of running results in a reduction in knee extensor activation so that total joint quasi-stiffness is maintained. An exoskeletal knee brace consisting of an elastic element engaged by a clutch is used to provide this stance phase extensor torque. Motion capture of five subjects is used to investigate the consequences of running with this device. No significant change in leg stiffness or total knee stiffness is observed due to the activation of the clutched parallel knee spring. However, this pilot data suggests differing responses between casual runners and competitive long-distance runners, whose total knee torque is increased by the device. Such a relationship between past training and effective utilization of an external force is suggestive of limitations on the applicability of assistive devices
Quantum energy inequalities and local covariance II: Categorical formulation
We formulate Quantum Energy Inequalities (QEIs) in the framework of locally
covariant quantum field theory developed by Brunetti, Fredenhagen and Verch,
which is based on notions taken from category theory. This leads to a new
viewpoint on the QEIs, and also to the identification of a new structural
property of locally covariant quantum field theory, which we call Local
Physical Equivalence. Covariant formulations of the numerical range and
spectrum of locally covariant fields are given and investigated, and a new
algebra of fields is identified, in which fields are treated independently of
their realisation on particular spacetimes and manifestly covariant versions of
the functional calculus may be formulated.Comment: 27 pages, LaTeX. Further discussion added. Version to appear in
General Relativity and Gravitatio
Observations of the bright radio sources in the North Celestial Pole region at the RATAN-600 radio telescope
A survey of the North Celestial Pole region using the RATAN-600 radio
telescope at five frequencies in the range 2.3 to 21.7 GHz is described.
Sources were chosen from the NVSS catalogue. The flux densities of 171 sources
in the Declination range +75 to +88 are presented; typical flux density errors
are 5-10 percent including calibration errors. About 20 percent of the sources
have flat spectra or a flat component.Comment: 21 pages, 7 figures; to be published in Astronomy and Astrophysics
(without last figure with the spectra of the observed sources
Acute Appendicitis after Liver Transplantation: A Case Report and Review of the Literature
Acute appendicitis is one of the most common etiologies for acute abdomen. However, fewer than 30 cases of acute appendicitis after liver transplantation have so far been reported in the literature. Previous case studies have concluded that acute appendicitis after liver transplantation may present differently than in non-immunosuppressed patients and thus may lead to more complications. Herein, we describe the fourth case of laparoscopic appendectomy in a 40-year-old female presenting with an acute abdomen, 10 years after orthotopic liver transplantation for autoimmune hepatitis. Additionally, we review the literature, and emphasize the importance for laparoscopic, rather than open appendectomy after liver transplantation. Overall, despite the small number of reported cases of appendicitis after orthotopic liver transplantation, we found the incidence and clinical presentation are similar to patients without liver transplantation. The etiologies for appendicitis in patients after liver transplantation may be different than in those not chronically immunosuppressed, with significantly less lymphoid hyperplasia and increased fecalith and cytomegaloviral infections. Preliminary results showed that laparoscopic appendectomy after liver transplantation results in decreased hospital stays and fewer complications
ISO observations of a sample of Compact Steep Spectrum and GHz Peaked Spectrum Radio Galaxies
We present results from observations obtained with ISOPHOT, on board the ISO
satellite, of a representative sample of seventeen CSS/GPS radio galaxies and
of a control sample of sixteen extended radio galaxies spanning similar ranges
in redshift (0.2 = 10^26 W/Hz).
The observations have been performed at lambda = 60, 90, 174 and 200 microns.
Seven of the CSS/GPS sources have detections >= 3 sigma at one or more
wavelengths, one of which is detected at >= 5 sigma. By co-adding the data we
have obtained average flux densities at the four wavelengths. We found no
evidence that the FIR luminosities of the CSS/GPS sources are significantly
different from those of the extended objects and therefore there is not any
support for CSS/GPS sources being objects "frustrated" by an abnormally dense
ambient medium. The two samples were then combined, providing FIR information
on a new sample of radio galaxies at intermediate redshifts. We compare this
information with what previously known from IRAS and discuss the average
properties of radio galaxies in the redshift range 0.2 - 0.8. The FIR emission
cannot be accounted for by extrapolation of the synchrotron radio spectrum and
we attribute it to thermal dust emission. The average FIR luminosity is >=
6*10^11 L_sun. Over the observed frequency range the infrared spectrum can be
described by a power law with spectral index alpha >~1.0 +/- 0.2. Assuming the
emission to be due to dust, a range of temperatures is required, from >=80 K to
\~25 K. The dust masses required to explain the FIR emission range from 5*10^5
M_sun for the hotter component up to 2*10^8 M_sun for the colder one.
(abridged)Comment: Astronomy & Astrophysics, in press, 16 pages, 2 Figure
Radio interferometric observations of two core-dominated triple radio sources at z>3
Aims. We selected two radio quasars (J1036+1326 and J1353+5725) based on
their 1.4-GHz radio structure, which is dominated by a bright central core and
a pair of weaker and nearly symmetric lobes at ~10" angular separation. They
are optically identified in the Sloan Digital Sky Survey (SDSS) at
spectroscopic redshifts z>3. We investigate the possibility that their
core-dominated triple morphology can be a sign of restarted radio activity in
these quasars, involving a significant repositioning of the radio jet axis.
Methods. We present the results of high-resolution radio imaging observations
of J1036+1326 and J1353+5725, performed with the European Very Long Baseline
Interferometry (VLBI) Network (EVN) at 1.6 GHz. These data are supplemented by
archive observations from the Very Large Array (VLA).We study the large- and
small-scale radio structures and the brightness temperatures, then estimate
relativistic beaming parameters. Results. We show that the central emission
region of these two high-redshift, core-dominated triple sources is compact but
resolved at ~10 milli-arcsecond resolution. We find that it is not necessary to
invoke large misalignment between the VLBI jet and the large-scale radio
structure to explain the observed properties of the sources.Comment: 5 pages, 4 figures, accepted for publication in A&
- …