13,150 research outputs found
The astroclimatological comparison of the Paranal Observatory and El Roque de Los Muchachos Observatory
The new extremely large telescope projects need accurate evaluation of the
candidate sites. In this paper we present the astroclimatological comparison
between the Paranal Observatory, located on the coast of the Atacama Desert
(Chile), and the Observatorio del Roque de Los Muchachos (ORM), located in La
Palma (Canary Islands). We apply a statistical analysis using long term
databases from Paranal and Carlsberg Meridian Telescope (CAMC) weather
stations. Significant differences between the two analyzed sites have been
found.Comment: Accepted for publication in MNRAS. 11 pages, 12 figures, 12 table
APM z>4 QSO Survey: Distribution and Evolution of High Column Density HI Absorbers
Eleven candidate damped Lya absorption systems were identified in 27 spectra
of the quasars from the APM z>4 survey covering the redshift range
2.83.5). High resolution echelle spectra (0.8A FWHM)
have been obtained for three quasars, including 2 of the highest redshift
objects in the survey. Two damped systems have confirmed HI column densities of
N(HI) >= 10^20.3 atoms cm^-2, with a third falling just below this threshold.
We have discovered the highest redshift damped Lya absorber known at z=4.383 in
QSO BR1202-0725. The APM QSOs provide a substantial increase in the redshift
path available for damped surveys for z>3. We combine this high redshift sample
with other quasar samples covering the redshift range 0.008 < z < 4.7 to study
the redshift evolution and the column density distribution function for
absorbers with log N(HI)>=17.2. In the HI column density distribution
f(N)=kN^-beta we find evidence for breaks in the power law, flattening for
17.221.2. The column density
distribution function for the data with log N(HI)>=20.3 is better fit with the
form f(N)=(f*/N*)(N/N*)^-beta exp(-N/N*). Significant redshift evolution in the
number density per unit redshift is evident in the higher column density
systems with an apparent decline in N(z) for z>3.5.Comment: To appear in MNRAS. Latex file (10 pages of text) plus 14 separate
postscript figure files. Requires mn.sty. Postscript version with figures
embedded is available at http://www.ociw.edu/~lisa/publications.htm
El Roque de Los Muchachos Site Characteristics. III. Analysis of Atmospheric Dust and Aerosol Extinction
Canary Islands are normally interested by dominant North-East winds that, in
some meteorological conditions, can transport sand at high altitude from the
Sahara desert. The dust may affect the efficiency of the telescopes and
decreases the transparency of the sky. In order to maximize the scientific
return of the telescopes located at the ORM, we present an analysis of the
atmospheric dust content and its effects on astronomical observations. B, V and
I dust aerosol astronomical extinction are derived. Using a 5 years series
database of data taken from the four channel TNG dust monitor, we compute a
mean hourly and daily values of the dust content. We have detected particles
having size 0.3, 0.5, 1.0 and 5.0 um. Using a power law we have derived the
content of 10.0 um particles. We found a typical local dust concentration
ranging from 3x10^6 particles per cubic meter at 0.3 um, to 10^3 at 5.0 um and
10 at 10.0 um, increasing up to 3 order of magnitudes during the dust storms,
with a relative higher increase of 1.0, 5.0 and 10.0 um particles. The number
of local dust storm events is the same in winter- and summertime, but, the
average background and storm-related increases in the dust concentration in
summer are significantly higher than in winter. In a uniform approximation,
during the dust storms, an average height of the dust layer of 2.5 km above the
telescope is inferred. During the sand storms La Palma Island is affected by an
almost uniform layer extending up to 5 km above the sea level, down, at least
the height of the telescope. The visible extinction is dominated by particles
at 1.0, 5.0 and 10.0 um. In agreement with the results from Carlsberg Automatic
Meridian Circle (CAMC) we find a typical extinction during dust storms of about
0.2 mag/airmass.Comment: Accepted for publication in A&A. 9 pages, 11 figures. This work is
the continuation of a series of papers concerning a detailed study of the
Astroclimatology at ORM. The two previous papers (both Lombardi et al.) have
reference PASP.2006.118.1198-1204 and PASP.2007.119.292-30
Evolution of Neutral Gas at High Redshift -- Implications for the Epoch of Galaxy Formation
Though observationally rare, damped Lya absorption systems dominate the mass
density of neutral gas in the Universe. Eleven high redshift damped Lya systems
covering 2.84 QSO Survey,
extending these absorption system surveys to the highest redshifts currently
possible. Combining our new data set with previous surveys we find that the
cosmological mass density in neutral gas, omega_g, does not rise as steeply
prior to z~2 as indicated by previous studies. There is evidence in the
observed omega_g for a flattening at z~2 and a possible turnover at z~3. When
combined with the decline at z>3.5 in number density per unit redshift of
damped systems with column densities log N(HI)>21 atoms cm^-2, these results
point to an epoch at z>3 prior to which the highest column density damped
systems are still forming. We find that over the redshift range 2<z<4 the total
mass in neutral gas is marginally comparable with the total visible mass in
stars in present day galaxies. However, if one considers the total mass visible
in stellar disks alone, ie excluding galactic bulges, the two values are
comparable. We are observing a mass of neutral gas comparable to the mass of
visible disk stars. Lanzetta, Wolfe & Turnshek (1995) found that omega_g(z~3.5)
was twice omega_g(z~2), implying a much larger amount of star formation must
have taken place between z=3.5 and z=2 than is indicated by metallicity
studies. This created a `cosmic G-dwarf problem'. The more gradual evolution of
omega_g we find alleviates this. These results have profound implications for
theories of galaxy formation.Comment: To appear in MNRAS. Latex file (4 pages of text) plus 3 separate
postscript figure files. Requires mn.sty. Postscript version with figures
embedded is available at http://www.ociw.edu/~lisa/publications.htm
Soliton core filling in superfluid Fermi gases with spin-imbalance
In this paper the properties of dark solitons in superfluid Fermi gases with
spin-imbalance are studied by means of a recently developed effective field
theory [S. N. Klimin, J. Tempere, G. Lombardi, J. T. Devreese, Eur. Phys. J. B
88, 122 (2015)] suitable to describe the BEC-BCS crossover in ultracold gases
in an extended range of temperatures as compared to the usual Ginzburg-Landau
treatments. The spatial profiles for the total density and for the density of
the excess-spin component, and the changes of their properties across the
BEC-BCS crossover are examined in different conditions of temperature and
imbalance. The presence of population imbalance is shown to strongly affect the
structure of the soliton excitation by filling its core with unpaired atoms.
This in turn influences the dynamical properties of the soliton since the
additional particles in the core have to be dragged along thus altering the
effective mass.Comment: 9 pages, 9 figure
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The use of social media for improving energy consumption awareness and efficiency: An overview of existing tools
Raising consumers’ awareness of energy consumption is one of the first steps in encouraging the adoption of energy saving behaviours that result in energy efficiency. Green information systems are becoming recognised as a solution to many environmental problems although information technology (e.g. disposal of IT devices) has also been associated with causing detrimental effects on the environment. Researchers and practitioners have begun to focus on Green ICT but there is little scholarly research on the use of ICT tools such as social media from an energy efficiency context to raise consumer awareness and improve their engagement in tackling environmental issues. Therefore, the aim of this paper is to explore the use of social media and existing tools for the interaction of people on energy saving discussions and for generating awareness and engagement (which thereby leads to energy efficiency behaviour). In this paper the authors provide a state of the art review around the concept of energy awareness, models of consumer engagement, and more importantly the use of social media in the energy efficiency context. This research is based on a desk-based normative review and seeks to provide a better understanding to both scholars and practitioners involved in the use of ICT for driving energy consumer awareness and engagement for energy efficiency.This work evolved in the context of the project DAREED (Decision support Advisor for innovative business models and useR engagement for smart Energy Efficient Districts), www.dareed.eu, a project co-funded by the EC within FP7, Grant agreement no: 609082
Finite temperature effective field theory and two-band superfluidity in Fermi gases
We develop a description of fermionic superfluids in terms of an effective
field theory for the pairing order parameter. Our effective field theory
improves on the existing Ginzburg - Landau theory for superfluid Fermi gases in
that it is not restricted to temperatures close to the critical temperature.
This is achieved by taking into account long-range fluctuations to all orders.
The results of the present effective field theory compare well with the results
obtained in the framework of the Bogoliubov - de Gennes method. The advantage
of an effective field theory over Bogoliubov - de Gennes calculations is that
much less computation time is required. In the second part of the paper, we
extend the effective field theory to the case of a two-band superfluid. The
present theory allows us to reveal the presence of two healing lengths in the
two-band superfluids, to analyze the finite-temperature vortex structure in the
BEC-BCS crossover, and to obtain the ground state parameters and spectra of
collective excitations. For the Leggett mode our treatment provides an
interpretation of the observation of this mode in two-band superconductors.Comment: 17 pages, 11 figures. In the published version [EPJB 88, 122 (2015)],
there is a misprint in expressions (20) and (21). There must be "E_k" instead
of "\xi_k" in the arguments of the functions "f_n" in those two formulae. In
the present version, this misprint is correcte
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