165 research outputs found
Evolution of economic entities under heterogeneous political/environmental conditions within a Bak-Sneppen-like dynamics
A model for economic behavior, under heterogeneous spatial economic
conditions is developed. The role of selection pressure in a Bak-Sneppen-like
dynamics with entity diffusion on a lattice is studied by Monte-Carlo
simulation taking into account business rule(s), like enterprise - enterprise
short range location "interaction"(s), business plan(s) through spin-offs or
merging and enterprise survival evolution law(s). It is numerically found that
the model leads to a sort of phase transition for the fitness gap as a function
of the selection pressure.Comment: 6 figures. to be published in Physica
Early Low Protein Diet Aggravates Unbalance between Antioxidant Enzymes Leading to Islet Dysfunction
BACKGROUND:Islets from adult rat possess weak antioxidant defense leading to unbalance between superoxide dismutase (SOD) and hydrogen peroxide-inactivating enzymatic activities, catalase (CAT) and glutathione peroxidase (GPX) rending them susceptible to oxidative stress. We have shown that this vulnerability is influenced by maternal diet during gestation and lactation. METHODOLOGY/PRINCIPAL FINDINGS:The present study investigated if low antioxidant activity in islets is already observed at birth and if maternal protein restriction influences the development of islet antioxidant defenses. Rats were fed a control diet (C group) or a low protein diet during gestation (LP) or until weaning (LPT), after which offspring received the control diet. We found that antioxidant enzymatic activities varied with age. At birth and after weaning, normal islets possessed an efficient GPX activity. However, the antioxidant capacity decreased thereafter increasing the potential vulnerability to oxidative stress. Maternal protein malnutrition changed the antioxidant enzymatic activities in islets of the progeny. At 3 months, SOD activity was increased in LP and LPT islets with no concomitant activation of CAT and GPX. This unbalance could lead to higher hydrogen peroxide production, which may concur to oxidative stress causing defective insulin gene expression due to modification of critical factors that modulate the insulin promoter. We found indeed that insulin mRNA level was reduced in both groups of malnourished offspring compared to controls. Analyzing the expression of such critical factors, we found that c-Myc expression was strongly increased in islets from both protein-restricted groups compared to controls. CONCLUSION AND SIGNIFICANCE:Modification in antioxidant activity by maternal low protein diet could predispose to pancreatic islet dysfunction later in life and provide new insights to define a molecular mechanism responsible for intrauterine programming of endocrine pancreas
Model of macroeconomic evolution in stable regionally dependent economic fields
We develop a model for the evolution of economic entities within a
geographical type of framework. On a square symmetry lattice made of three
(economic) regions, firms, described by a scalar fitness, are allowed to move,
adapt, merge or create spin-offs under predetermined rules, in a space and time
dependent economic environment. We only consider here one timely variation of
the ''external economic field condition''. For the firm fitness evolution we
take into account a constraint such that the disappearance of a firm modifies
the fitness of nearest neighboring ones, as in Bak-Sneppen population fitness
evolution model. The concentration of firms, the averaged fitness, the regional
distribution of firms, and fitness for different time moments, the number of
collapsed, merged and new firms as a function of time have been recorded and
are discussed. Also the asymptotic values of the number of firms present in the
three regions together with their average fitness, as well as the number of
respective births and collapses in the three regions are examined. It appears
that a sort of selection pressure exists. A power law dependence,
signature of self-critical organization is seen in the birth and collapse
asymptotic values for a high selection pressure only. A lack of
self-organization is also seen at region borders.Comment: 11 figures double columns on 7 page
Simple Model for the Dynamics of Correlations in the Evolution of Economic Entities Under Varying Economic Conditions
From some observations on economic behaviors, in particular changing economic
conditions with time and space, we develop a very simple model for the
evolution of economic entities within a geographical type of framework. We
raise a few questions and attempt to investigate whether some of them can be
tackled by our model. Several cases of interest are reported. It is found that
the model even in its simple forms can lead to a large variety of situations,
including: delocalization and cycles, but also pre-chaotic behavior.Comment: Presented at Bali IEC02 symposium, Aug. 2002; submitted to Physica A
; 8 pages, 5 figure
Discovery of Fragment Molecules That Bind the Human Peroxiredoxin 5 Active Site
The search for protein ligands is a crucial step in the inhibitor design process. Fragment screening represents an interesting method to rapidly find lead molecules, as it enables the exploration of a larger portion of the chemical space with a smaller number of compounds as compared to screening based on drug-sized molecules. Moreover, fragment screening usually leads to hit molecules that form few but optimal interactions with the target, thus displaying high ligand efficiencies. Here we report the screening of a homemade library composed of 200 highly diverse fragments against the human Peroxiredoxin 5 protein. Peroxiredoxins compose a family of peroxidases that share the ability to reduce peroxides through a conserved cysteine. The three-dimensional structures of these enzymes ubiquitously found throughout evolution have been extensively studied, however, their biological functions are still not well understood and to date few inhibitors have been discovered against these enzymes. Six fragments from the library were shown to bind to the Peroxiredoxin 5 active site and ligand-induced chemical shift changes were used to drive the docking of these small molecules into the protein structure. The orientation of the fragments in the binding pocket was confirmed by the study of fragment homologues, highlighting the role of hydroxyl functions that hang the ligands to the Peroxiredoxin 5 protein. Among the hit fragments, the small catechol molecule was shown to significantly inhibit Peroxiredoxin 5 activity in a thioredoxin peroxidase assay. This study reports novel data about the ligand-Peroxiredoxin interactions that will help considerably the development of potential Peroxiredoxin inhibitors
Estimation of the charge carrier localization length from Gaussian fluctuations in the magneto-thermopower of La_{0.6}Y_{0.1}Ca_{0.3}MnO_3
The magneto-thermoelectric power (TEP) of perovskite type
manganise oxide is found to exhibit a sharp peak
at some temperature . By approximating the true shape of the
measured magneto-TEP in the vicinity of by a linear triangle of the
form , we observe that . We adopt the electron localization scenario and
introduce a Ginzburg-Landau (GL) type theory which incorporates the two
concurrent phase transitions, viz., the paramagnetic-ferromagnetic transition
at the Curie point and the "metal-insulator" (M-I) transition at
. The latter is characterized by the divergence of the field-dependent
charge carrier localization length at some characteristic field
. Calculating the average and fluctuation contributions to the total
magnetization and the transport entropy related magneto-TEP
within the GL theory, we obtain a simple relationship between and the
above two critical temperatures ( and ). The observed slope
ratio is found to be governed by the competition between
the electron-spin exchange and the induced magnetic energy . The
comparison of our data with the model predictions produce ,
, , , and for the estimates of
the Curie temperature, the exchange coupling constant, the critical
magnetization, the localization length, and the free-to-localized carrier
number density ratio, respectively.Comment: 6 pages (REVTEX), 2 PS figures (epsf.sty); submitted to Phys.Rev.
Kinetic studies of peroxiredoxin 6 from Arenicola marina: Rapid oxidation by 3 hydrogen peroxide and peroxynitrite but lack of reduction by hydrogen sulfide
, respectively, at pH 7.4 and 25°C. Reduction of tert-butyl hydroperoxide was slower. 34 The pK a of the peroxidatic thiol of AmPrx6 was determined as 5
Benford's law predicted digit distribution of aggregated income taxes: the surprising conformity of Italian cities and regions
The yearly aggregated tax income data of all, more than 8000, Italian
municipalities are analyzed for a period of five years, from 2007 to 2011, to
search for conformity or not with Benford's law, a counter-intuitive phenomenon
observed in large tabulated data where the occurrence of numbers having smaller
initial digits is more favored than those with larger digits. This is done in
anticipation that large deviations from Benford's law will be found in view of
tax evasion supposedly being widespread across Italy. Contrary to expectations,
we show that the overall tax income data for all these years is in excellent
agreement with Benford's law. Furthermore, we also analyze the data of
Calabria, Campania and Sicily, the three Italian regions known for strong
presence of mafia, to see if there are any marked deviations from Benford's
law. Again, we find that all yearly data sets for Calabria and Sicily agree
with Benford's law whereas only the 2007 and 2008 yearly data show departures
from the law for Campania. These results are again surprising in view of
underground and illegal nature of economic activities of mafia which
significantly contribute to tax evasion. Some hypothesis for the found
conformity is presented.Comment: 18 pages, 5 tables, 4 figures, 61 references, To appear in European
Physical Journal
Permanent 125I-seed prostate brachytherapy: early prostate specific antigen value as a predictor of PSA bounce occurrence
<p>Abstract</p> <p>Purpose</p> <p>To evaluate predictive factors for PSA bounce after <sup>125</sup>I permanent seed prostate brachytherapy and identify criteria that distinguish between benign bounces and biochemical relapses.</p> <p>Materials and methods</p> <p>Men treated with exclusive permanent <sup>125</sup>I seed brachytherapy from November 1999, with at least a 36 months follow-up were included. Bounce was defined as an increase ≥ 0.2 ng/ml above the nadir, followed by a spontaneous return to the nadir. Biochemical failure (BF) was defined using the criteria of the Phoenix conference: nadir +2 ng/ml.</p> <p>Results</p> <p>198 men were included. After a median follow-up of 63.9 months, 21 patients experienced a BF, and 35.9% had at least one bounce which occurred after a median period of 17 months after implantation (4-50). Bounce amplitude was 0.6 ng/ml (0.2-5.1), and duration was 13.6 months (4.0-44.9). In 12.5%, bounce magnitude exceeded the threshold defining BF. Age at the time of treatment and high PSA level assessed at 6 weeks were significantly correlated with bounce but not with BF. Bounce patients had a higher BF free survival than the others (100% versus 92%, p = 0,007). In case of PSA increase, PSA doubling time and velocity were not significantly different between bounce and BF patients. Bounces occurred significantly earlier than relapses and than nadir + 0.2 ng/ml in BF patients (17 vs 27.8 months, p < 0.0001).</p> <p>Conclusion</p> <p>High PSA value assessed 6 weeks after brachytherapy and young age were significantly associated to a higher risk of bounces but not to BF. Long delays between brachytherapy and PSA increase are more indicative of BF.</p
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