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

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

Statistical properties of the GALEX spectroscopic stellar sample

The GALEX General Data Release 4/5 includes 174 spectroscopic tiles, obtained from slitless grism observations, for a total of more than 60,000 ultraviolet spectra. We have determined statistical properties of the sample of GALEX stars. We have defined a suitable system of spectroscopic indices, which measure the main mid-UV features at the GALEX low spectral resolution and we have employed it to determine the atmospheric parameters of of stars in the range 4500<Teff<9000 K. Our preliminary results indicate that the sample is formed by a majority of main sequence F- and G-type stars, with metallicity [M/H]>-1 dex.Comment: 9 pages, 9 figures, accepted for publication in Astrophysics & Space Science, UV universe special issu

Customer integration and operational performance: The mediating role of information quality

Much supply chain integration literature tends to be biased towards its positive impact on operational performance. However, inconclusive results demand investigation of the mechanisms through which supply chain integration can lead to superior operational performance. The purpose of this study is to identify empirically the mediating role of information quality on the relationship between customer integration and operational performance, and the direct relationship between customer integration and operational performance. The study is based on a questionnaire sent to 228 manufacturing companies in the Republic of Ireland, and the relationships between the constructs are analyzed through regression analysis. The results indicate that information quality partially mediates the relationship between customer integration and quality, delivery and flexibility. Further, information quality was found to fully mediate the relationship between customer integration and cost

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 $300$ nm, whereas its temperature accuracy is $\pm 2$ 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 $T(r) \propto ln(r)$ in the diffusive limit. The case of large temperature gradients within the membranes leads to an exponential decay of the thermal field, $T \propto exp[-A \cdot ln(r)]$. 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

On the behavior of site effects in central Mexico (the Mexican volcanic belt &ndash; MVB), based on records of shallow earthquakes that occurred in the zone between 1998 and 2011

The Mexican volcanic belt (MVB) is a seismogenic zone that transects the central part of Mexico with an east–west orientation. The seismic risk and hazard of this seismogenic zone has not been studied in detail due to the scarcity of instrumental data as well as because seismicity in the continental regime of central Mexico is not too frequent. However, it is known that there are precedents of large earthquakes (<i>M</i>_w > 6.0) that have taken place in this zone. The valley of Mexico City (VM) is the sole zone, within the MVB, that has been studied in detail. Studies have mainly focused on the ground amplification during large events such as the 1985 subduction earthquake that occurred off coast of Michoacán. The purpose of this article is to analyze the behavior of site effects in the MVB zone based on records of shallow earthquakes (data not reported before) that occurred in the zone between 1998 and 2011. We present a general overview of site effects in the MVB, a classification of the stations in order to reduce the uncertainty in the data when obtaining attenuation parameters in future works, as well as some comparisons between the information presented here and that presented in previous studies. <br><br> A regional evaluation of site effects and Fourier acceleration spectrum (FAS) shape was estimated based on 80 records of 22 shallow earthquakes within the MVB zone. Data of 25 stations were analyzed. Site effects were estimated by using the horizontal-to-vertical spectral ratio (HVSR) methodology. The results show that seismic waves are less amplified in the northeast sites of the MVB with respect to the rest of the zone and that it is possible to classify two groups of stations: (1) stations with negligible site amplification (NSA) and (2) stations with significant site amplification (SSA). Most of the sites in the first group showed small (<3) amplifications while the second group showed amplifications ranging from 4 to 6.5 at frequencies of about 0.35, 0.75, 15 and 23 Hz. With these groups of stations, average levels of amplification were contrasted for the first time with those caused by the subduction zone earthquakes. With respect to the FAS shapes, most of them showed similarities at similar epicentral distances. Finally, some variations of site effects were found when compared to those obtained in previous studies on different seismicity regions. These variations were attributed to the location of the source. <br><br> These aspects help to advance the understanding about the amplification behavior and of the expected seismic risk on central Mexico due to large earthquakes within the MVB seismogenic zone

Direct evidence for efficient ultrafast charge separation in epitaxial WS₂/graphene heterostructures

We use time- and angle-resolved photoemission spectroscopy (tr-ARPES) to investigate ultrafast charge transfer in an epitaxial heterostructure made of monolayer WS2 and graphene. This heterostructure combines the benefits of a direct-gap semiconductor with strong spin-orbit coupling and strong light-matter interaction with those of a semimetal hosting massless carriers with extremely high mobility and long spin lifetimes. We find that, after photoexcitation at resonance to the A-exciton in WS2, the photoexcited holes rapidly transfer into the graphene layer while the photoexcited electrons remain in the WS2 layer. The resulting charge-separated transient state is found to have a lifetime of ∼1 ps. We attribute our findings to differences in scattering phase space caused by the relative alignment of WS2 and graphene bands as revealed by high-resolution ARPES. In combination with spin-selective optical excitation, the investigated WS2/graphene heterostructure might provide a platform for efficient optical spin injection into graphene