3,301 research outputs found
Deep 1.4 GHZ Follow Up of the Steep Spectrum Radio Halo in Abell 521
In a recent paper we reported on the discovery of a radio halo with very
steep spectrum in the merging galaxy cluster Abell 521 through observations
with the Giant Metrewave Radio Telescope (GMRT). We showed that the steep
spectrum of the halo is inconsistent with a secondary origin of the
relativistic electrons and supports a turbulent acceleration scenario. At that
time, due to the steep spectrum, the available observations at 1.4 GHz
(archival NRAO - Very Large Array - VLA CnB-configuration data) were not
adequate to accurately determine the flux density associated with the radio
halo. In this paper we report the detection at 1.4 GHz of the radio halo in
Abell 521 using deep VLA observations in the D-configuration. We use these new
data to confirm the steep-spectrum of the object. We consider Abell 521 the
prototype of a population of very-steep spectrum halos. This population is
predicted assuming that turbulence plays an important role in the acceleration
of relativistic particles in galaxy clusters, and we expect it will be unveiled
by future surveys at low frequencies with the LOFAR and LWA radio telescopes.Comment: 11 pages, 3 figures (figure 1 available in gif format only). Requires
aastex.cls - Accepted by Ap.
The XMM-Newton Detection of Diffuse Inverse Compton X-rays from Lobes of the FR-II Radio Galaxy 3C98
The XMM-Newton observation of the nearby FR-II radio galaxy 3C 98 is
reported. In two exposures on the target, faint diffuse X-ray emission
associated with the radio lobes was significantly detected, together with a
bright X-ray active nucleus, of which the 2 -- 10 keV intrinsic luminosity is
(4 -- 8) \times 10^{42} erg s-1. The EPIC spectra of the northern and southern
lobes are reproduced by a single power law model modified by the Galactic
absorption, with a photon index of 2.2-0.5+0.6 and 1.7-0.6+0.7 respectively.
These indices are consistent with that of the radio synchrotron spectrum, 1.73
+- 0.01 The luminosity of the northern and southern lobes are measured to be
8.3-2.6+3.3 \times 10^{40} erg s-1 and 9.2-4.3+5.7 \times 10^{40} erg s-1,
respectively, in the 0.7 -- 7 keV range. The diffuse X-ray emission is
interpreted as an inverse-Compton emission, produced when the
synchrotron-emitting energetic electrons in the lobes scatter off the cosmic
microwave background photons. The magnetic field in the lobes is calculated to
be about 1.7 \mu G, which is about 2.5 times lower than the value estimated
under the minimum energy condition. The energy density of the electrons is
inferred to exceed that in the magnetic fields by a factor of 40 -- 50.Comment: 23 pages, 7 figures. Accepted for publication in the Astrophysical
Journa
A KAT-7 view of a low-mass sample of galaxy clusters
Radio observations over the last two decades have provided evidence that
diffuse synchrotron emission in the form of megaparsec-scale radio halos in
galaxy clusters is likely tracing regions of the intracluster medium where
relativistic particles are accelerated during cluster mergers. In this paper we
present results of a survey of 14 galaxy clusters carried out with the
7-element Karoo Array Telescope at 1.86 GHz, aimed to extend the current
studies of radio halo occurrence to systems with lower masses (M M). We found upper limits at the Watt Hz level for of the sample, confirming that
bright radio halos in less massive galaxy clusters are statistically rare.Comment: 7 pages, 4 figures. Conference proceeding of "The many facets of
extragalactic radio surveys: towards new scientific challenges", 20-23
October 2105, Bologna, Ital
Spatial variability of maximum and minimum monthly temperature in Spain during 1981–2010 evaluated by correlation decay distance (CDD)
The spatial variability of monthly diurnal and nocturnal mean values of temperature in Spain has been analysed to evaluate the optimal threshold distance between neighbouring stations that make a meteorological network (in terms of stations’ density) well representative of the conterminous land of Spain. To this end, the correlation decay distance has been calculated using the highest quality monthly available temperature series (1981–2010) from AEMet (National Spanish Meteorological Agency). In the conterminous land of Spain, the distance at which couples of stations have a common variance above the selected threshold (50 %, r Pearson ~0.70) for both maximum and minimum temperature on average does not exceed 400 km, with relevant spatial and temporal differences, and in extended areas of Spain, this value is lower than 200 km. The spatial variability for minimum temperature is higher than for maximum, except in cold months when the reverse is true. Spatially, highest values are located in both diurnal and nocturnal temperatures to the southeastern coastland and lower spatial variability is found to the inland areas, and thus the spatial variability shows a clear coastland-to-inland gradient at annual and monthly scale. Monthly analyses show that the highest spatial variability in maximum and minimum temperatures occur in July and August, when radiation is maximum, and in lowland areas, (<200 m o.s.l.), which coincide with the mostly transformed landscapes, particularly by irrigation and urbanization. These results highlight local factors could play a major role on spatial variability of temperature. Being maximum and minimum temperature interstation correlation values highly variable in Spanish land, an average of threshold distance of about 200 km as a limit value for a well representative network should be recommended for climate analyses,
A new climatology of maximum and minimum temperature (1951–2010) in the Spanish mainland: a comparison between three different interpolation methods
This study presents a new climatology of monthly temperature for mainland Spain (1951–2010), performed with the highest quality and spatially dense, up-to-date monthly temperature dataset available in the study area (MOTEDAS). Three different interpolation techniques were evaluated: the Local Weighted Linear Regression (LWLR), the Regression-Kriging (RK) and the Regression-Kriging with stepwise selection (RKS), a modification of RK. The performances of the different models were evaluated by the leave-one-out validation procedure, comparing the results from the models with the original data and calculating different error measurements. The three techniques performed better for Tmax than for Tmin, and for the cold, rather than warmer months, also at lower altitude than highland areas. The best results were achieved with LWLR applied for the first time on temperatures in the Spanish mainland. This method improved the accuracy of the temperature reconstruction with respect to RK and RKS. We present a collection of Tmax and Tmin monthly charts, using the same temperature legend to prevent any visual bias in the interpretation of the results. The dataset is available upon request
Advantages of robotic right colectomy over laparoscopic right colectomy beyond the learning curve: a systematic review and meta-analysis
Background: With the widespread application of robotic systems and the increasing number of studies comparing robotic right colectomy (RRC) and laparoscopic right colectomy (LRC), there is a need for an up-to-date systemic review and meta-analysis assessing the advantages of this technique. Methods: The systemic review was performed in Medline, Scopus, Embase, Cochrane Oral Health Group Specialized Register and Google Scholar databases searching for studies comparing RRC and LRC, with no date restriction but limited to English and French literature. Two independent reviewers performed data extraction and qualitative synthesis. Random-effects models were used to summarize the risk ratio (RR) and mean differences (MD) with 95% confidence interval (CI). Results: Twenty-six non-randomized clinical trials (NRCTs) and 1 RCT were included. Overall, 2,314 patients underwent RRC and 17,791 LRC. Operative time was significantly longer for RRC with a MD of 45.36 min (95% CI: 31.75-58.97; P<0.00001). Conversion rate was significantly lower in the RRC group with a RR of 0.47 (95% CI: 0.27-0.81; P=0.007, I-2=33%). Also, the number of harvested lymph node was significantly higher in the RRC group than the LRC group, with a MD of 2.03 (95% CI: 0.45-3.61; P=0.01, I-2=68%). Estimated blood loss favored RRC, with a MD of-8.68 (95% CI:-17.27 to-0.08; P=0.05, I-2=46%). There was no difference in the overall complication rate, mortality, anastomotic leakage, and time to first flatus. However, a significantly shorter hospital stay was associated with RRC, with a MD of -0.60 (95% CI:-1.01 to-0.19; P=0.004, I-2=64%). No quantitative analysis could be performed for oncological outcomes. RRC was associated with significantly higher costs (MD 3,185.50 USD; 95% CI: 720.98-5650.02; P=0.01, I-2=94%). Conclusions: RRC is a safe procedure that may offer certain advantages over LRC as lower conversion rate, blood loss, hospital stay. However, this should be balanced out with increased operative time and higher costs
Causal Perturbation Theory and Differential Renormalization
In Causal Perturbation Theory the process of renormalization is precisely
equivalent to the extension of time ordered distributions to coincident points.
This is achieved by a modified Taylor subtraction on the corresponding test
functions. I show that the pullback of this operation to the distributions
yields expressions known from Differential Renormalization. The subtraction is
equivalent to BPHZ subtraction in momentum space. Some examples from Euclidean
scalar field theory in flat and curved spacetime will be presented.Comment: 15 pages, AMS-LaTeX, feynm
The Unruh-deWitt Detector and the Vacuum in the General Boundary formalism
We discuss how to formulate a condition for choosing the vacuum state of a
quantum scalar field on a timelike hyperplane in the general boundary
formulation (GBF) using the coupling to an Unruh-DeWitt detector. We explicitly
study the response of an Unruh-DeWitt detector for evanescent modes which occur
naturally in quantum field theory in the presence of the equivalent of a
dielectric boundary. We find that the physically correct vacuum state has to
depend on the physical situation outside of the boundaries of the spacetime
region considered. Thus it cannot be determined by general principles
pertaining only to a subset of spacetime.Comment: Version as published in CQ
Spectral up- and downshifting of Akhmediev breathers under wind forcing
We experimentally and numerically investigate the effect of wind forcing on
the spectral dynamics of Akhmediev breathers, a wave-type known to model the
modulation instability. We develop the wind model to the same order in
steepness as the higher order modifcation of the nonlinear Schroedinger
equation, also referred to as the Dysthe equation. This results in an
asymmetric wind term in the higher order, in addition to the leading order wind
forcing term. The derived model is in good agreement with laboratory
experiments within the range of the facility's length. We show that the leading
order forcing term amplifies all frequencies equally and therefore induces only
a broadening of the spectrum while the asymmetric higher order term in the
model enhances higher frequencies more than lower ones. Thus, the latter term
induces a permanent upshift of the spectral mean. On the other hand, in
contrast to the direct effect of wind forcing, wind can indirectly lead to
frequency downshifts, due to dissipative effects such as wave breaking, or
through amplification of the intrinsic spectral asymmetry of the Dysthe
equation. Furthermore, the definitions of the up- and downshift in terms of
peak- and mean frequencies, that are critical to relate our work to previous
results, are highlighted and discussed.Comment: 30 pages, 11 figure
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