8,223 research outputs found
The Dark Energy Equation of State using Alternative High-z Cosmic Tracers
We propose to use alternative cosmic tracers to measure the dark energy
equation of state and the matter content of the Universe [w(z) & Omega_m]. Our
proposed method consists of two components: (a) tracing the Hubble relation
using HII galaxies which can be detected up to very large redshifts, z~4, as an
alternative to supernovae type Ia, and (b) measuring the clustering pattern of
X-ray selected AGN at a median redshift of z~1. Each component of the method
can in itself provide interesting constraints on the cosmological parameters,
especially under our anticipation that we will reduce the corresponding random
and systematic errors significantly. However, by joining their likelihood
functions we will be able to put stringent cosmological constraints and break
the known degeneracies between the dark energy equation of state (whether it is
constant or variable) and the matter content of the universe and provide a
powerful and alternative route to measure the contribution to the global
dynamics and the equation of state of dark energy. A preliminary joint analysis
of X-ray selected AGN (based on the largest to-date XMM survey; the 2XMM) and
the currently largest SNIa sample (Hicken et al.), using as priors a flat
universe and the WMAP5 normalization of the power-spectrum, provides:
Omega_m=0.27+-0.02 and w=-0.96+-0.07. Equivalent and consistent results are
provided by the joint analysis of X-ray selected AGN clustering and the latest
Baryonic Acoustic Oscillation measures, providing: Omega_m=0.27+-0.02 and
w=-0.97+-0.04.Comment: Different versions of this paper appear in the "Dark Universe"
conference (Paris, July 2009) and in the "1st Mediterranean Conference in
Classical & Quantum Gravity" (invited
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Bioinspired snapping-claw apparatus to study hydrodynamic cavitation effects on the corrosion of metallic samples
A creative low-cost and compact mechanical device that mimics the rapid closure of the pistol shrimp claw was used to conduct electrochemical experiments, in order to study the effects of hydrodynamic cavitation on the corrosion of aluminum and steel samples. Current-time curves show significant changes associated with local variations in dissolved O2 concentration, cavitation-induced erosion and changes in the nature of the surface corrosion products
Star Formation History and Extinction in the central kpc of M82-like Starbursts
We report on the star formation histories and extinction in the central kpc
region of a sample of starburst galaxies that have similar far infrared (FIR),
10 micron and K-band luminosities as those of the archetype starburst M82. Our
study is based on new optical spectra and previously published K-band
photometric data, both sampling the same area around the nucleus. Model
starburst spectra were synthesized as a combination of stellar populations of
distinct ages formed over the Hubble time, and were fitted to the observed
optical spectra and K-band flux. The model is able to reproduce simultaneously
the equivalent widths of emission and absorption lines, the continuum fluxes
between 3500-7000 Ang, the K-band and the FIR flux. We require a minimum of 3
populations -- (1) a young population of age < 8 Myr, with its corresponding
nebular emission, (2) an intermediate-age population (age < 500 Myr), and (3)
an old population that forms part of the underlying disk or/and bulge
population. The contribution of the old population to the K-band luminosity
depends on the birthrate parameter and remains above 60% in the majority of the
sample galaxies. Even in the blue band, the intermediate age and old
populations contribute more than 40% of the total flux in all the cases. A
relatively high contribution from the old stars to the K-band nuclear flux is
also apparent from the strength of the 4000 Ang break and the CaII K line. The
extinction of the old population is found to be around half of that of the
young population. The contribution to the continuum from the relatively old
stars has the effect of diluting the emission equivalent widths below the
values expected for young bursts. The mean dilution factors are found to be 5
and 3 for the Halpha and Hbeta lines respectively.Comment: 20 pages, uses emulateapj.cls. Scheduled to appear in ApJ Jan 1, 200
Renewable energy research progress in Mexico: a review
Mexico ranks 9th in the world in crude oil reserves, 4th in natural gas reserves in America and it is also highly rich in renewable energy sources (solar, wind, biomasss, hydropower and geothermal). However, the potential of this type of energy has not been fully exploited. Hydropower is the renewable energy source with the highest installed capacity within the country (11,603 MW), while geothermal power capacity (958 MW) makes Mexico to be ranked 4th in the use of this energy worldwide. Wind energy potential is concentrated in five different zones, mainly in the state of Oaxaca, and solar energy has a high potential due to Mexico's ideal location in the so called Solar Belt. Biomass energy has the highest potential (2635 to 3771 PJ/year) and has been the subject of the highest number of research publications in the country during the last 30 years (1982-2012). Universidad Nacional Autonoma de Mexico has led research publications in hydropower, wind, solar and biomass energy and Instituto de Investigaciones Electricas in geothermal energy during this period. According to the General Law for Climate Change the country has set the goal of generating 35% of its energy needs from renewable sources by 2024. This paper presents an overview of the renewable energy options available in Mexico, current status, main positive results to date and future potential. It also analyses barriers hindering improvements and proposes pertinent solutions. © 2014 The Authors
A novel high resolution contactless technique for thermal field mapping and thermal conductivity determination: Two-Laser Raman Thermometry
We present a novel high resolution contactless technique for thermal
conductivity determination and thermal field mapping based on creating a
thermal distribution of phonons using a heating laser, while a second laser
probes the local temperature through the spectral position of a Raman active
mode. The spatial resolution can be as small as nm, whereas its
temperature accuracy is K. We validate this technique investigating the
thermal properties of three free-standing single crystalline Si membranes with
thickness of 250, 1000, and 2000 nm. We show that for 2-dimensional materials
such as free-standing membranes or thin films, and for small temperature
gradients, the thermal field decays as in the diffusive
limit. The case of large temperature gradients within the membranes leads to an
exponential decay of the thermal field, . The
results demonstrate the full potential of this new contactless method for
quantitative determination of thermal properties. The range of materials to
which this method is applicable reaches far beyond the here demonstrated case
of Si, as the only requirement is the presence of a Raman active mode
Aquatic Feeding by Moose: Selection of Plant Species and Feeding Areas in Relation to Plant Chemical Composition and Characteristics of Lakes
Aquatic feeding by moose was studied with emphasis on (i) the chemical composition of aquatic plants compared with terrestrial browse, (ii) the chemical composition of preferred and unpreferred aquatic plant species and (iii) characteristics of preferred feeding areas. Compared with woody browse, aquatic plants had much higher levels of sodium and iron, and similar levels of other nutrients tested. In a cafeteria selection experiment, moose consistently ate seven species of aquatic plants (preferred plants), consistently rejected five species (unpreferred plants), and gave an intermediate response to seven species. Preferred species had significantly higher sodium content. Those in the intermediate class contained more crude protein and phosphorus than unpreferred species. Of 24 lakes and ponds, 6 were heavily used by moose. 16 were used relatively little, and 2 were difficult to classify. The six heavily used sites had shallower water, a higher mineral content in the lake sediment, and a greater abundance of preferred plant species. Plants growing in heavily used sites had higher levels of sodium, phosphorus, and manganese than the same species growing in lightly used sites. Results suggest that levels of sodium in aquatic plants have a major influence on the animals\u27 selection of aquatic plant species and feeding areas, while phosphorus and protein levels may also influence selection
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