9,650 research outputs found
Formation and morphology of anomalous solar circular polarization
The morphology of spectral line polarization is the most valuable observable
to investigate the magnetic and dynamic solar atmosphere. However, in order to
develop solar diagnosis, it is fundamental to understand the different kinds of
anomalous solar signals that have been routinely found in linear and circular
polarization (LP,CP). The goal of this paper has been to explain and
characterize the morphology of solar CP signals by understanding the combined
effect of magnetic fields, velocity gradients, and atomic orientation in
general NLTE regime. To that aim, an analytical two-layer model of the
polarized radiative transfer equation is developed and used to solve the NLTE
problem with atomic polarization in a semi-parametric way. The formation of
polarization is thus insightfully described with certain precision without
resorting in MHD models or sacrifying key physical ingredients. The potential
of the model for reproducing solar anomalous CP is shown with detailed
calculations. The essential physical behavior of dichroism and atomic
orientation is described, introducing the concepts of dichroic inversion,
neutral and reinforcing medium, critic intensity spectrum, and critic source
function. It is shown that the zero-crossings of the CP spectrum are useful to
classify its morphology and understand its formation. This led to identify and
explain the morphology of the seven most characteristics CP signals that a
single (depth-resolved) scattering layer can produce. Futhermore, it is found
that a minimal number of two magnetic layers along the LOS is required to fully
explain anomalous solar CP signals, and that the morphology and polarity of
Stokes V depends on magnetic, radiative and atomic polarities. Some
implications of these results are presented through a preliminar modeling of
anomalous CP signals in the Na I D and Fe I 1564.8 nm lines.Comment: 18 pages, 18 figures. Accepted for publication in A&A. Typos and
language correcte
Competition, restructuring and firm performance: evidence of an inverted-U relationship from a cross-country survey of firms in transition economies
This paper examines the importance of competition in the growth anddevelopment of firms. We draw on a survey of 3,300 firms in 25transition countries to shed light on the factors that influencerestructuring by firms and their subsequent performance. These datahave three main advantages over those used in previous work. First,they measure directly the degree of competition perceived by each firmin its principal market rather than attempting to infer this from marketdata as measured by statistical agencies. Second, the fact that transitioncountries have market structures inherited from the past avoids some ofthe endogeneity problems associated with measures of competition inmarket economies. Third, the breadth of cross-country variationprovides a method of dealing with the fact that firm-level measures ofthe external environment will not be independent of the firm?s ownperformance. We find evidence of a robust inverted-U effect ofcompetition on performance that is both statistically and economicallysignificant. This paper examines the importance of competition in the growth anddevelopment of firms. We draw on a survey of 3,300 firms in 25transition countries to shed light on the factors that influencerestructuring by firms and their subsequent performance. These datahave three main advantages over those used in previous work. First,they measure directly the degree of competition perceived by each firmin its principal market rather than attempting to infer this from marketdata as measured by statistical agencies. Second, the fact that transitioncountries have market structures inherited from the past avoids some ofthe endogeneity problems associated with measures of competition inmarket economies. Third, the breadth of cross-country variationprovides a method of dealing with the fact that firm-level measures ofthe external environment will not be independent of the firm?s ownperformance. We find evidence of a robust inverted-U effect ofcompetition on performance that is both statistically and economicallysignificant
In the balance: report of a research study exploring information for weight management
This paper uses findings from a research study called Net.Weight to examine the concepts of interaction, information quality and Internet-based information from the perspective of people engaged in managing their weight. The Net.Weight study was a two-year project funded by the British government 19s Department of Health and located in the city of Brighton and Hove. It examined the potential for increased, innovative and effective uses of information and communication technologies (ICTs) to support the self management of weight. The study had several inter-related research strands and the findings discussed in the paper emerged primarily from participatory learning workshops and evaluative interviews. The paper demonstrates that the interaction between people is an important aspect of the information process, which is often neglected in the literature. It suggests that exploring the user-user dimension might add to the understanding of information effectiveness. It also suggests that an approach to information and health literacy which includes a social as well as an individual perspective is necessary. On quality assessment, it supports findings from other studies that organisational authority is a key measure of reliability for lay users and that quality assessment tools have a limited role in the assessment process. The Net.Weight participants embraced the Internet as a medium for weight management information only when it added value to their existing information and weight management practices and when it could be integrated into their everyday lives
Quantum discord in spin-cluster materials
The total quantum correlation (discord) in Heisenberg dimers is expressed via
the spin-spin correlation function, internal energy, specific heat or magnetic
susceptibility. This allows one to indirectly measure the discord through
neutron scattering, as well as calorimetric or magnetometric experiments. Using
the available experimental data, we found the discord for a number of binuclear
Heisenberg substances with both antiferro- and ferromagnetic interactions. For
the dimerized antiferromagnet copper nitrate Cu(NO_3)_2*2.5H_2O, the three
independent experimental methods named above lead to a discord of approximately
0.2-0.3 bit/dimer at a temperature of 4 K. We also determined the temperature
behavior of discord for hydrated and anhydrous copper acetates, as well as for
the ferromagnetic binuclear copper acetate complex [Cu_2L(OAc)]*6H_2O, where L
is a ligand.Comment: 7 pages, 6 figure
Inequality as experienced difference: a reformulation of the Gini coefficient
Inequality is typically measured as the degree of dispersion of a distribution of individual attributes, say, wealth, as is captured for example by the Lorenz curve, and its associated statistic, the Gini coefficient. But both the economics and social psychology of experienced inequality are better expressed by differences between an individual and others. There is a natural way to do this using the standard definition of the Gini coefficient as one half the mean difference among individuals, relative to the population mean wealth. Here we show that reformulating the Gini coefficient as a measure of experienced inequality on a complete social network yields a computational algorithm that, unlike the conventional one, is consistent with this definition and irrespective of population size varies from 0 (no differences among individuals) to 1 (one individual owns all the wealth). Our proposed measure also avoids a downward bias in the standard algorithm, which for small populations can be substantial.. Because social networks are far from complete, the pairwise comparisons based on social interactions in which people routinely engage may support a level of experienced inequality that either exceeds or falls short of the Gini coefficient measured on a hypothetical complete network. We illustrate this fact with empirical estimates for a farming community in Nicaragua
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