696 research outputs found
Updated F(T) gravity constraints from high redshift cosmography
In the last dozen years a wide and variegated mass of observational data
revealed that the universe is now expanding at an accelerated rate. In the
absence of a well-based theory to interpret the observations, cosmography
provides information about the evolution of the Universe from measured
distances, only assuming that the geometry of the can be described by the
Friedmann-Lemaitre-Robertson -Walker metric. We perform a high-redshift
analysis allows us to put constraints on the cosmographic parameters up to the
5fth order, thus inducing indirect constraints on any gravity theory. Here we
are interested in the so called teleparallel gravity theory, f(T). Actually we
use the analytical expressions of the present day values of f(T) and its
derivatives as functions of the cosmographic parameters to map the cosmography
region of confidences into confidence ranges for f(T) and its derivative.
Moreover, we show how these can be used to test some teleparallel gravity
models without solving the dynamical equations. Our analysis is based on the
Union2 Type Ia Supernovae (SNIa) data set, a set of 28 measurements of the
Hubble parameter, the Hubble diagram constructed from some Gamma Ray Bursts
(GRB) luminosity distance indicators, and gaussian priors on the distance from
the Baryon Acoustic Oscillations (BAO), and the Hubble constant h. To perform
our statistical analysis and to explore the probability distributions of the
cosmographic parameters we use the Markov Chain Monte Carlo Method (MCMC).Comment: International Journal of Modern Physics D, 20 pages, 5 figure
Solid-liquid equilibria for the dimethyl ether plus carbon dioxide binary system
A recently built experimental setup was employed for the estimation of the solid-liquid equilibria of alternative refrigerants systems. The behavior of dimethyl ether (DME) + carbon dioxide was measured down to temperatures of 131.6 K. To confirm the reliability of the apparatus, the triple point of the DME was measured. The triple point data measured revealed a good consistency with the literature. The results obtained for the mixtures were corrected by the Rossini method and interpreted by means of the Schröder equation. © 2010 Akadémiai Kiadó, Budapest, Hungary
Carbon Dioxide + Fluoromethane and Nitrous Oxide + Fluoromethane: Solid−Liquid Equilibria Measurements
A recently built experimental setup was employed for the estimation of the solid-liquid equilibria (SLE) of alternative refrigerant systems. The behavior of two binaries, that is, carbon dioxide + fluoromethane (CO2 + R41) and nitrous oxide + fluoromethane (N2O + R41), was measured down to temperatures of 126.5 K. To confirm the reliability of the apparatus, the triple points of the pure fluids constituent of the binary systems were measured. All triple-point data measured revealed a generally good consistency with the literature. The results obtained for the mixtures were corrected by the Rossini method and interpreted by means of the Schröder equation. © 2010 American Chemical Society
Mafia Inc.: When godfathers become entrepreneurs
We study the investment of criminal organizations in the legal economy. We focus on Italy, a country historically plagued by a conspicuous presence of mafia-type organizations. By using the exogenous credit contraction imposed by the 2007 financial crisis we highlight how the consequences for newly established enterprises have been less severe in areas with organized crime. Although criminal organizations are largely detrimental for local economic conditions, their economic activity might act as an economic stabilizer in the short-run, especially in a context of weak institutional presence. The investment in the legal economy allows criminal organizations to launder money, make profits, and raise social consensus through the provision of alternative sources of social insurance
Copper Nanoparticles in Click Chemistry
Conspectus: The challenges of the 21st century demand scientific and technological achievements that must be developed under sustainable and environmentally benign practices. In this vein, click chemistry and green chemistry walk hand in hand on a pathway of rigorous principles that help to safeguard the health of our planet against negligent and uncontrolled production. Copper-catalyzed azide–alkyne cycloaddition (CuAAC), the paradigm of a click reaction, is one of the most reliable and widespread synthetic transformations in organic chemistry, with multidisciplinary applications. Nanocatalysis is a green chemistry tool that can increase the inherent effectiveness of CuAAC because of the enhanced catalytic activity of nanostructured metals and their plausible reutilization capability as heterogeneous catalysts. This Account describes our contribution to click chemistry using unsupported and supported copper nanoparticles (CuNPs) as catalysts prepared by chemical reduction. Cu(0)NPs (3.0 ± 1.5 nm) in tetrahydrofuran were found to catalyze the reaction of terminal alkynes and organic azides in the presence of triethylamine at rates comparable to those achieved under microwave heating (10–30 min in most cases). Unfortunately, the CuNPs underwent dissolution under the reaction conditions and consequently could not be recovered. Compelling experimental evidence on the in situ generation of highly reactive copper(I) chloride and the participation of copper(I) acetylides was provided. The supported CuNPs were found to be more robust and efficient catalyst than the unsupported counterpart in the following terms: (a) the multicomponent variant of CuAAC could be applied; (b) the metal loading could be substantially decreased; (c) reactions could be conducted in neat water; and (d) the catalyst could be recovered easily and reutilized. In particular, the catalyst composed of oxidized CuNPs (Cu2O/CuO, 6.0 ± 2.0 nm) supported on carbon (CuNPs/C) was shown to be highly versatile and very effective in the multicomponent and regioselective synthesis of 1,4-disubstituted 1,2,3-triazoles in water from organic halides as azido precursors; magnetically recoverable CuNPs (3.0 ± 0.8 nm) supported on MagSilica could be alternatively used for the same purpose under similar conditions. Incorporation of an aromatic substituent at the 1-position of the triazole could be accomplished using the same CuNPs/C catalytic system starting from aryldiazonium salts or anilines as azido precursors. CuNPs/C in water also catalyzed the regioselective double-click synthesis of β-hydroxy-1,2,3-triazoles from epoxides. Furthermore, alkenes could be also used as azido precursors through a one-pot CuNPs/C-catalyzed azidosulfenylation–CuAAC sequential protocol, providing β-methylsulfanyl-1,2,3-triazoles in a stereo- and regioselective manner. In all types of reaction studied, CuNPs/C exhibited better behavior than some commercial copper catalysts with regard to the metal loading, reaction time, yield, and recyclability. Therefore, the results of this study also highlight the utility of nanosized copper in click chemistry compared with bulk copper sources.This work was supported by the Spanish Ministerio de EconomÃa y Competitividad, the Generalitat Valenciana, Fondo Europeo de Desarrollo Regional, the Argentinian Consejo Nacional de Investigaciones CientÃficas y Técnicas and Agencia Nacional de Promoción CientÃfica Tecnológica, and the Instituto de SÃntesis Orgánica (Universidad de Alicante)
Quantifying Volume Changing Perturbations in a Wave Chaotic System
A sensor was developed to quantitatively measure perturbations which change
the volume of a wave chaotic cavity while leaving its shape intact. The sensors
work in the time domain by using either scattering fidelity of the transmitted
signals or time reversal mirrors. The sensors were tested experimentally by
inducing volume changing perturbations to a one cubic meter mixed chaotic and
regular billiard system. Perturbations which caused a volume change that is as
small as 54 parts in a million were quantitatively measured. These results were
obtained by using electromagnetic waves with a wavelength of about 5cm,
therefore, the sensor is sensitive to extreme sub-wavelength changes of the
boundaries of a cavity. The experimental results were compared with Finite
Difference Time Domain (FDTD) simulation results, and good agreement was found.
Furthermore, the sensor was tested using a frequency domain approach on a
numerical model of the star graph, which is a representative wave chaotic
system. These results open up interesting applications such as: monitoring the
spatial uniformity of the temperature of a homogeneous cavity during heating up
/ cooling down procedures, verifying the uniform displacement of a fluid inside
a wave chaotic cavity by another fluid, etc.Comment: 13 pages, 13 figure
Trust and fertility in uncertain times
Recent studies have shown higher uncertainty to be associated with fertility decline. This study considers the role of social trust as a coping mechanism when general uncertainty increases. We analyse the fertility data of Italian provinces from 2004 to 2013, thereby incorporating the period of economic recession, which unexpectedly and exogenously increased uncertainty across the population. We find a robust and significantly positive impact of social trust on fertility, which is stronger among younger age groups. Moreover, we find that the buffer effect of trust decreases with the level of public childcare provision, suggesting that low trust endowments may be counterbalanced through public policy
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