5,887 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
Resonating bipolarons
Electrons coupled to local lattice deformations end up in selftrapped
localized molecular states involving their binding into bipolarons when the
coupling is stronger than a certain critical value. Below that value they exist
as essentially itinerant electrons. We propose that the abrupt crossover
between the two regimes can be described by resonant pairing similar to the
Feshbach resonance in binary atomic collision processes. Given the
intrinsically local nature of the exchange of pairs of itinerant electrons and
localized bipolarons, we demonstrate the occurrence of such a resonance on a
finite-size cluster made out of metallic atoms surrounding a polaronic ligand
center.Comment: 7 pages, 4 figures, to be published in Europhysics Letter
Finite VEVs from a Large Distance Vacuum Wave Functional
We show how to compute vacuum expectation values from derivative expansions
of the vacuum wave functional. Such expansions appear to be valid only for
slowly varying fields, but by exploiting analyticity in a complex scale
parameter we can reconstruct the contribution from rapidly varying fields.Comment: 39 pages, 16 figures, LaTeX2e using package graphic
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
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
Detection of Acetylene toward Cepheus A East with Spitzer
The first map of interstellar acetylene (C2H2) has been obtained with the
infrared spectrograph onboard the Spitzer Space Telescope. A spectral line map
of the vibration-rotation band at 13.7 microns carried out toward the
star-forming region Cepheus A East, shows that the C2H2 emission peaks in a few
localized clumps where gas-phase CO2 emission was previously detected with
Spitzer. The distribution of excitation temperatures derived from fits to the
C2H2 line profiles ranges from 50 to 200 K, a range consistent with that
derived for gaseous CO2 suggesting that both molecules probe the same warm gas
component. The C2H2 molecules are excited via radiative pumping by 13.7 microns
continuum photons emanating from the HW2 protostellar region. We derive column
densities ranging from a few x 10^13 to ~ 7 x 10^14 cm^-2, corresponding to
C2H2 abundances of 1 x 10^-9 to 4 x 10^-8 with respect to H2. The spatial
distribution of the C2H2 emission along with a roughly constant N(C2H2)/N(CO2)
strongly suggest an association with shock activity, most likely the result of
the sputtering of acetylene in icy grain mantles.Comment: 11 pages, 5 figures, accepted for publication in ApJ Letter
Determination of the influence of specific building regulations in smart buildings
The automation of domestic services began to be implemented in buildings since the late nineteenth century, and today we are used to terms like ‘intelligent buildings’, ‘digital home’ or ‘domotic buildings’. These concepts tell us about constructions which integrate
new technologies in order to improve comfort, optimize energy consumption or enhance the security of users. In conjunction, building regulations have been updated to suit the needs of society and to regulate these new facilities in such structures. However, we are not always
sure about how far, from the quantitative or qualitative point of view, legislation should
regulate certain aspects of the building activity. Consequently, content analysis is adopted in
this research to determine the influence of building regulations in the implementation of
new technologies in the construction process. This study includes the analysis of different
European regulations, the collection and documentation of such guidelines that have been
established and a study of the impact that all of these have had in the way we start thinking an architectural project. The achievements of the research could be explained in terms of the regulatory requirements that must be taken into account in order to achieve a successful implementation of a home automation system, and the key finding has been the confirmation of how the design of smart buildings may be promoted through specific regulatory requirements while other factors, such as the global economic situation, do not seem to affect directly the rate of penetration of home automation in construction
Hurst Coefficient in long time series of population size: Model for two plant populations with different reproductive strategies
Can the fractal dimension of fluctuations in population size be used to estimate extinction risk? The problem with estimating this fractal dimension is that the lengths of the time series are usually too short for conclusive results. This study answered this question with long time series data obtained from an iterative competition model. This model produces competitive extinction at different perturbation intensities for two different germination strategies: germination of all seeds vs. dormancy in half the seeds. This provided long time series of 900 years and different extinction risks. The results support the hypothesis for the effectiveness of the Hurst coefficient for estimating extinction risk
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