5,167 research outputs found
Impact of Power Allocation and Antenna Directivity in the Capacity of a Multiuser Cognitive Ad Hoc Network
This paper studies the benefits that power control and antenna directivity can bring to the capacity of a multiuser cognitive radio network. The main objective is to optimize the secondary network sum rate under the capacity constraint of the primary network. Exploiting location awareness, antenna directivity, and the power control capability, the cognitive radio ad hoc network can broaden its coverage and improve capacity. Computer simulations show that by employing the proposed method the system performance is significantly enhanced compared to conventional fixed power allocation
A GIT interpretration of the Harder-Narasimhan filtration
An unstable torsion free sheaf on a smooth projective variety gives a GIT
unstable point in certain Quot scheme. To a GIT unstable point, Kempf
associates a "maximally destabilizing" 1-parameter subgroup, and this induces a
filtration of the torsion free sheaf. We show that this filtration coincides
with the Harder-Narasimhan filtration.Comment: 19 pages; Comments of the referees and references added. The
construction for holomorphic pairs (Sections 6 and 7 from previous version)
will appear in a further publication. To appear in Rev. Mat Complutens
Quasar Feedback in the Ultraluminous Infrared Galaxy F11119+3257: Connecting the Accretion Disk Wind with the Large-Scale Molecular Outflow
In Tombesi et al. (2015), we reported the first direct evidence for a quasar
accretion disk wind driving a massive molecular outflow. The target was
F11119+3257, an ultraluminous infrared galaxy (ULIRG) with unambiguous type-1
quasar optical broad emission lines. The energetics of the accretion disk wind
and molecular outflow were found to be consistent with the predictions of
quasar feedback models where the molecular outflow is driven by a hot
energy-conserving bubble inflated by the inner quasar accretion disk wind.
However, this conclusion was uncertain because the energetics were estimated
from the optically thick OH 119 um transition profile observed with Herschel.
Here, we independently confirm the presence of the molecular outflow in
F11119+3257, based on the detection of broad wings in the CO(1-0) profile
derived from ALMA observations. The broad CO(1-0) line emission appears to be
spatially extended on a scale of at least ~7 kpc from the center. Mass outflow
rate, momentum flux, and mechanical power of (80-200) R_7^{-1} M_sun/yr,
(1.5-3.0) R_7^{-1} L_AGN/c, and (0.15-0.40)% R_7^{-1} L_AGN are inferred from
these data, assuming a CO-to-H_2 conversion factor appropriate for a ULIRG (R_7
is the radius of the outflow normalized to 7 kpc and L_AGN is the AGN
luminosity). These rates are time-averaged over a flow time scale of 7x10^6
yrs. They are similar to the OH-based rates time-averaged over a flow time
scale of 4x10^5 yrs, but about a factor 4 smaller than the local
("instantaneous"; <10^5 yrs) OH-based estimates cited in Tombesi et al. The
implications of these new results are discussed in the context of time-variable
quasar-mode feedback and galaxy evolution. The need for an energy-conserving
bubble to explain the molecular outflow is also re-examined.Comment: 15 pages, 6 figures, 4 tables, accepted for publication in Ap
Windows through the Dusty Disks Surrounding the Youngest Low Mass Protostellar Objects
The formation and evolution of young low mass stars are characterized by
important processes of mass loss and accretion ocurring in the innermost
regions of their placentary circumstellar disks. Because of the large
obscuration of these disks at optical and infrared wavelengths in the early
protostellar stages (Class 0 Sources), they were previously detected only at
radio wavelengths using interferometric techniques. We have detected with the
Infrared Space Observatory (ISO) the mid-infrared emission associated with the
Class 0 protostar VLA1 in the HH1-2 region located in the Orion nebula. The
emission arises in the three wavelength windows at 5.3, 6.6 and 7.5 micras
where the absorption due to ices and silicates has a local minimum that exposes
the central parts of the youngest protostellar systems to mid-infrared
investigations. The mid-infrared emission arises from a central source with 4
AU diameter at an averaged temperature of 700 K, deeply embedded in a dense
region with a visual extinction of Av=80-100mag.Comment: The article is here and on pres
The Excitation of NH in Interstellar Molecular Clouds. I - Models
We present LVG and non-local radiative transfer calculations involving the
rotational and hyperfine structure of the spectrum of NH with
collisional rate coefficients recently derived by us. The goal of this study is
to check the validity of the assumptions made to treat the hyperfine structure
and to study the physical mechanisms leading to the observed hyperfine
anomalies.
We find that the usual hypothesis of identical excitation temperatures for
all hyperfine components of the =1-0 transition is not correct within the
range of densities existing in cold dense cores, i.e., a few 10 \textless
n(H) \textless a few 10 cm. This is due to different radiative
trapping effects in the hyperfine components. Moreover, within this range of
densities and considering the typical abundance of NH, the total
opacity of rotational lines has to be derived taking into account the hyperfine
structure. The error made when only considering the rotational energy structure
can be as large as 100%. Using non-local models we find that, due to
saturation, hyperfine anomalies appear as soon as the total opacity of the
=1-0 transition becomes larger than 20. Radiative scattering in
less dense regions enhance these anomalies, and particularly, induce a
differential increase of the excitation temperatures of the hyperfine
components. This process is more effective for the transitions with the highest
opacities for which emerging intensities are also reduced by self-absorption
effects. These effects are not as critical as in HCO or HCN, but should be
taken into account when interpreting the spatial extent of the NH
emission in dark clouds.Comment: 13 pages, 12 figure
Erratum: Long range correlations in DNA: scaling properties and charge transfer efficiency (vol 91, art no 228101, 2003)
©2004 The American Physical Society.Depto. de Física de MaterialesFac. de Ciencias FísicasTRUEpu
D-brane probes on L^{abc} Superconformal Field Theories
We study supersymmetric embeddings of D-brane probes of different
dimensionality in the AdS_5xL^{abc} background of type IIB string theory. In
the case of D3-branes, we recover the known three-cycles dual to the dibaryonic
operators of the gauge theory and we also find a new family of supersymmetric
embeddings. Supersymmetric configurations of D5-branes, representing fractional
branes, and of spacetime filling D7-branes (which can be used to add flavor)
are also found. Stable non supersymmetric configurations corresponding to fat
strings and domain walls are found as well.Comment: 20 pages, LaTeX;v2: minor improvements, references adde
Herschel PACS Spectroscopic Diagnostics of Local ULIRGs: Conditions and Kinematics in Mrk 231
In this first paper on the results of our Herschel PACS survey of local
Ultraluminous Infrared Galaxies (ULIRGs), as part of our SHINING survey of
local galaxies, we present far-infrared spectroscopy of Mrk 231, the most
luminous of the local ULIRGs, and a type 1 broad absorption line AGN. For the
first time in a ULIRG, all observed far-infrared fine-structure lines in the
PACS range were detected and all were found to be deficient relative to the far
infrared luminosity by 1 - 2 orders of magnitude compared with lower luminosity
galaxies. The deficits are similar to those for the mid-infrared lines, with
the most deficient lines showing high ionization potentials. Aged starbursts
may account for part of the deficits, but partial covering of the highest
excitation AGN powered regions may explain the remaining line deficits. A
massive molecular outflow, discovered in OH and 18OH, showing outflow
velocities out to at least 1400 km/sec, is a unique signature of the clearing
out of the molecular disk that formed by dissipative collapse during the
merger. The outflow is characterized by extremely high ratios of 18O / 16O
suggestive of interstellar medium processing by advanced starbursts.Comment: Accepted for publication in the Astronomy and Astrophysics Herschel
Special Issue, 5 pages, 4 figure
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