632 research outputs found
Risks perceptions and risk management instruments in the European Union: Do farmers have a clear idea of what they need?
This paper explores and analyzes farmersâ risk perceptions, risk management instrumentsâ demand and usage in five Member States (Hungary, Spain, the Netherlands, Germany and Poland). A survey completed by 1047 representative farmers of these EU Member Status collected information that allowed us to set apart two focus areas: the first looks at the declared importance of several sources of farmsâ risk and income instability, and at the actual means that farmers pursue to manage and face them. The second area focuses on the demand for risk management instruments. The paperâs objective is to determine the factors that explain farmersâ responses in the first area, and based on those factors, analyse the demands for two instruments (insurance, and future & option markets). After carrying out basic descriptive statistic analyses, we perform factor analysis in order to establish the linkages between the perceptions and ranking of risks with the declared strategies to manage them. Logit models were fit to determine potential demand of insurance, and futures & options based on the three factors, and other variables like activity types and other controls, like nationality. Results from the factor analysis show that the perception of risk and actual use of risk management are very diverse. Logit models show that insurance is clearly an alternative instrument to diversification, but its demand is poorly explained by the other factors. Furthermore the demand for the use of futures and options is explained by the three factors, with the volatility factor, positively linked; market access /contractual risks; and diversification, negatively linked. In conclusion, policy makers should proceed with caution selecting the most adequate risk management instruments for farmers. It appears that the expected demand of risk management tools does not fit perfectly with the stated perception of risks
From caging to Rouse dynamics in polymer melts with intramolecular barriers: a critical test of the Mode Coupling Theory
By means of computer simulations and solution of the equations of the Mode
Coupling Theory (MCT), we investigate the role of the intramolecular barriers
on several dynamic aspects of non-entangled polymers. The investigated dynamic
range extends from the caging regime characteristic of glass-formers to the
relaxation of the chain Rouse modes. We review our recent work on this
question, provide new results and critically discuss the limitations of the
theory. Solutions of the MCT for the structural relaxation reproduce
qualitative trends of simulations for weak and moderate barriers. However a
progressive discrepancy is revealed as the limit of stiff chains is approached.
This disagreement does not seem related with dynamic heterogeneities, which
indeed are not enhanced by increasing barrier strength. It is not connected
either with the breakdown of the convolution approximation for three-point
static correlations, which retains its validity for stiff chains. These
findings suggest the need of an improvement of the MCT equations for polymer
melts. Concerning the relaxation of the chain degrees of freedom, MCT provides
a microscopic basis for time scales from chain reorientation down to the caging
regime. It rationalizes, from first principles, the observed devations from the
Rouse model on increasing the barrier strength. These include anomalous scaling
of relaxation times, long-time plateaux, and non-monotonous wavelength
dependence of the mode correlators.Comment: 15 pages, 14 figure
Usefulness of a quantitative real-time PCR assay using serum samples to discriminate between inactive, serologically positive and active human brucellosis
AbstractDiagnosis of brucellosis can be difficult in certain scenarios where conventional microbiological techniques have important limitations. The aim of this study was to develop a LightCycler Quantitative PCR assay in serum samples to discriminate between active and past brucellosis. In total, 110 serum samples from 46 brucellosis patients and 64 controls, including persons who had recently been treated for brucellosis, asymptomatic persons exposed to brucellosis, and patients with febrile syndromes involving a differential diagnosis with brucellosis, were studied. Brucella spp.-specific sequences of the PCR primers and probe were selected from the gene encoding an immunogenic membrane protein of 31 kDa (BCSP31). The analytical sensitivity was 1 Ă 101 fg of Brucella DNA. The mean threshold cycles for brucellosis patients and controls were 31.8 ± 1.7 and 35.4 ± 1.1, respectively (p <0.001). The best cut-off for bacterial DNA load was 5 Ă 103 copies/mL. At this cut-off, the area under the receiver operating characteristic curves was 0.963 (95% CI 0.920â1.005), with a sensitivity of 93.5% and a specificity of 98.4%. Under the assay conditions, the LightCycler Quantitative PCR in serum samples seems to be highly reproducible, rapid, sensitive and specific. It is therefore a useful method for both the initial diagnosis and the differentiation between past and active brucellosis
Chandra Multiwavelength Project: Normal Galaxies at Intermediate Redshift
(abridged) We have investigated 136 Chandra extragalactic sources without
broad optical emission lines, including 93 galaxies with narrow emission lines
(NELG) and 43 with only absorption lines (ALG). Based on fx/fo, Lx, X-ray
spectral hardness and optical emission line diagnostics, we have conservatively
classified 36 normal galaxies (20 spirals and 16 ellipticals) and 71 AGNs. We
found no statistically significant evolution in Lx/LB, within the limited z
range. We have built log(N)-log(S), after correcting for completeness based on
a series of simulations. The best-fit slope is -1.5 for both S and B energy
bands, which is considerably steeper than that of the AGN-dominated cosmic
background sources, but slightly flatter than the previous estimate, indicating
normal galaxies will not exceed the AGN population until fx ~ 2 x 10-18 erg s-1
cm-2 (a factor of ~5 lower than the previous estimate). A group of NELGs appear
to be heavily obscured in X-rays, i.e., a typical type 2 AGN. After correcting
for intrinsic absorption, their X-ray luminosities could be Lx > 10^44 erg s-1,
making them type 2 quasar candidates. While most X-ray luminous ALGs (XBONG -
X-ray bright, optically normal galaxy candidates) do not appear to be
significantly absorbed, we found two heavily obscured objects, which could be
as luminous as an unobscured broad-line quasar. Among 43 ALGs, we found two E+A
galaxy candidates with strong Balmer absorption lines, but no [OII] line. The
X-ray spectra of both galaxies are soft and one of them has a nearby close
companion galaxy, supporting the merger/interaction scenario rather than the
dusty starburst hypothesis.Comment: 31 pages, 9 figures, accepted for publication in ApJ (20 June 2006,
v644), replaced with minor correction
X-ray Spectra of the RIXOS source sample
We present results of an extensive study of the X-ray spectral properties of
sources detected in the RIXOS survey, that is nearly complete down to a flux
limit of 3e-14 cgs (0.5-2 keV). We show that for X-ray surveys containing
sources with low count rate spectral slopes estimated using simple hardness
ratios in the ROSAT band can be biased. Instead we analyse three-colour X-ray
data using statistical techniques appropriate to the Poisson regime which
removes the effects of this bias. We have then applied this technique to the
RIXOS survey to study the spectral properties of the sample. For the AGN we
find an average energy index of 1.05+-0.05 with no evidence for spectral
evolution with redshift. Individual AGN are shown to have a range of properties
including soft X-ray excesses and intrinsic absorption. Narrow Emission Line
Galaxies also seem to fit to a power-law spectrum, which may indicate a
non-thermal origin for their X-ray emission. We infer that most of the clusters
in the sample have a bremsstrahlung temperature >3 keV, although some show
evidence for a cooling flow. The stars deviate strongly from a power-law model
but fit to a thermal model. Finally, we have analysed the whole RIXOS sample
containing 1762 sources. We find that the mean spectral slope of the sources
hardens at lower fluxes in agreement with results from other samples. However,
a study of the individual sources demonstrates that the hardening of the mean
is caused by the appearance of a population of very hard sources at the lowest
fluxes. This has implications for the nature of the soft X-ray background.Comment: 31,LaTeX file, 2 PS files with Table 2 and 22 PS figures. MNRAS in
pres
Glassy Dynamics of Protein Folding
A coarse grained model of a random polypeptide chain, with only discrete
torsional degrees of freedom and Hookean springs connecting pairs of
hydrophobic residues is shown to display stretched exponential relaxation under
Metropolis dynamics at low temperatures with the exponent , in
agreement with the best experimental results. The time dependent correlation
functions for fluctuations about the native state, computed in the Gaussian
approximation for real proteins, have also been found to have the same
functional form. Our results indicate that the energy landscape exhibits
universal features over a very large range of energies and is relatively
independent of the specific dynamics.Comment: RevTeX, 4 pages, multicolumn, including 5 figures; larger
computations performed, error bars improve
Rapid diagnosis of human brucellosis by SYBR Green I-based real-time PCR assay and melting curve analysis in serum samples
SUMMARYThe aim of this study was to develop a LightCycler-based real-time PCR (LC-PCR) assay and to evaluate its diagnostic use for the detection of Brucella DNA in serum samples. Following amplification of a 223-bp gene sequence encoding an immunogenetic membrane protein (BCSP31) specific for the Brucella genus, melting curve and DNA sequencing analysis was performed to verify the specificity of the PCR products. The intra- and inter-assay variation coefficients were 1.3% and 6.4%, respectively, and the detection limit was 5 fg of Brucella DNA (one genome equivalent). After optimisation of the PCR assay conditions, a standard curve was obtained with a linear range (correlation coefficient = 0.99) over seven orders of magnitude from 107 to 10 fg of Brucella DNA. The LC-PCR assay was found to be 91.9% sensitive and 95.4% specific when tested with 65 negative control samples and 62 serum samples from 60 consecutive patients with active brucellosis. The assay is reproducible, easily standardised, minimises the risk of infection in laboratory workers, and has a total processing time of < 2 h. It could therefore form a promising and practical approach for the rapid diagnosis of human brucellosis
The Role of Intramolecular Barriers on the Glass Transition of Polymers: Computer Simulations vs. Mode Coupling Theory
We present computer simulations of a simple bead-spring model for polymer
melts with intramolecular barriers. By systematically tuning the strength of
the barriers, we investigate their role on the glass transition. Dynamic
observables are analyzed within the framework of the Mode Coupling Theory
(MCT). Critical nonergodicity parameters, critical temperatures and dynamic
exponents are obtained from consistent fits of simulation data to MCT
asymptotic laws. The so-obtained MCT -exponent increases from standard
values for fully-flexible chains to values close to the upper limit for stiff
chains. In analogy with systems exhibiting higher-order MCT transitions, we
suggest that the observed large -values arise form the interplay
between two distinct mechanisms for dynamic arrest: general packing effects and
polymer-specific intramolecular barriers. We compare simulation results with
numerical solutions of the MCT equations for polymer systems, within the
polymer reference interaction site model (PRISM) for static correlations. We
verify that the approximations introduced by the PRISM are fulfilled by
simulations, with the same quality for all the range of investigated barrier
strength. The numerical solutions reproduce the qualitative trends of
simulations for the dependence of the nonergodicity parameters and critical
temperatures on the barrier strength. In particular, the increase of the
barrier strength at fixed density increases the localization length and the
critical temperature. However the qualitative agreement between theory and
simulation breaks in the limit of stiff chains. We discuss the possible origin
of this feature
A Medium Survey of the Hard X-Ray Sky with ASCA. II.: The Source's Broad Band X-Ray Spectral Properties
A complete sample of 60 serendipitous hard X-ray sources with flux in the
range \ecs to \ecs (2 - 10
keV), detected in 87 ASCA GIS2 images, was recently presented in literature.
Using this sample it was possible to extend the description of the 2-10 keV
LogN(>S)-LogS down to a flux limit of \ecs (the
faintest detectable flux), resolving about a quarter of the Cosmic X-ray
Background. In this paper we have combined the ASCA GIS2 and GIS3 data of these
sources to investigate their X-ray spectral properties using the "hardness"
ratios and the "stacked" spectra method. Because of the sample statistical
representativeness, the results presented here, that refer to the faintest hard
X-ray sources that can be studied with the current instrumentation, are
relevant to the understanding of the CXB and of the AGN unification scheme.Comment: 28 pages plus 6 figures, LaTex manuscript, Accepted for publication
in the Astrophysical Journal, Figure 5 can retrieved via anonymous ftp at
ftp://ftp.brera.mi.astro.it/pub/ASCA/paper2/fig5.ps.g
CONNECTIVITY BETWEEN POPULATIONS OF THE MARINE CRAB LIOCARCINUS DEPURATOR IN THE ATLANTO-MEDITERRANEAN TRANSITION: A FIVE YEAR SERIES
Abstract: We carried out a spatial and temporal genetic differentiation analysis using seven populations of the marine crab Liocarcinus depurator to elucidate the effect of three oceanographic discontinuities in the Atlanto-Mediterranean coast: Gibraltar Strait, Almeria-Oran Front and Ibiza Channel. To conduct this study, a 527 bp fragment of the mitochondrial COI gene was sequenced in individuals captured in the period 2014-2018 from the following Iberian coast populations: CĂĄdiz, West Alboran, East Alboran, Alacant, Valencia, Ebro Delta and North Catalonia. Two haplogroups were detected; one characteristic of Atlantic waters and the other of Mediterranean. Their differential distribution allowed understanding the connectivity between populations. The effect of the oceanographic fronts on gene flow varied over time. Their effects were significant for the Gibraltar Strait (2014 and 2017), Almeria Oran Front (2013, 2014, 2015, 2016 and 2017) and Ibiza Channel (2015). Interestingly, the joint analysis of West Alboran, East Alboran and Alacant populations allowed a more precise detection of the location of the Almeria Oran Front biological effects. Finally, significant differences were observed in connectivity between Valencia and Ebro Delta in 2015, although there is not an oceanographic discontinuity between them. The main conclusion is that the gene flow is mediated by oceanographic fronts, but their intensity and effects change over time.CTM2017-88080 AEI/FEDER, UE) (CTM2015-66400-C3-3-R MINECO/FEDER) (2017 SGR 1120)
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