Biomedical subjects

Eric Bertin

Publications and source records attributed to Eric Bertin.

10 recordsLinked to original sources

PubMed2006

Boltzmann and hydrodynamic description for self-propelled particles.

We study analytically the emergence of spontaneous collective motion within large bidimensional groups of self-propelled particles with noisy local interactions, a schematic model for assemblies of biological organisms. As a central result, we derive from the individual dynamics the hydrodynamic equations for the density and velocity fields, thus giving a microscopic foundation to the phenomenological equations used in previous approaches. A homogeneous spontaneous motion emerges below a transition line in the noise-density plane. Yet, this state is shown to be unstable against spatial perturbations, suggesting that more complicated structures should eventually appear.

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PubMed2006

Definition and relevance of nonequilibrium intensive thermodynamic parameters.

We show that intensive thermodynamic parameters associated to additive conserved quantities can be naturally defined from a statistical approach in far-from-equilibrium steady-state systems, under few assumptions, and without any detailed balance requirement. It may apply, e.g., to dissipative systems such as granular gases where volume or mass is still conserved or to systems with periodic boundary conditions where fluxes of conserved quantities are present. We emphasize the usefulness of this concept to characterize the coexistence of different nonequilibrium phases and discuss the influence of the contact between two different systems, in relation with measurement issues.

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PubMed2006

Is there any relationship between pernicious anemia and iron deficiency?

INTRODUCTION: Previous studies have suggested that iron deficiency could be due to atrophic gastritis of the body/fundus. The aim of this study was to determine the prevalence of iron deficiency among patients with pernicious anemia and associated factors. PATIENTS AND METHODS: All patients with pernicious anemia diagnosed at our institution between January 1990 and February 2005 were included. Inclusion criteria were: 1- histological diagnosis of atrophic fundic gastritis and 2- criteria of gastric autoimmune involvement. Histology of gastric biopsies was performed in a blinded manner. Iron deficiency was defined as serum ferritin level<15 microg/L in women and<40 microg/L in men. RESULTS: Ninety-five patients (69 women), mean age 60 years (range: 23-90) were included. Twenty patients (21.1%) had normal blood cell counts; 12 patients (12.6%) had microcytosis with or without anemia and 53 patients (55.8%) macrocytosis with or without anemia. Serum ferritin levels were measured in 58 patients, 16 (27.6%) of whom, all women, had iron deficiency. They were significantly younger (39.2 years) than patients without iron deficiency (61.6 years, P<0.0001). Serum gastrin levels did not differ between the groups with and without iron deficiency. A significantly more severe inflammatory infiltrate of the fundus and endocrine cell hyperplasia was observed in iron deficiency patients. Multivariate analysis showed that iron deficiency was linked to female gender and age<50 years. CONCLUSION: Iron deficiency and microcytic anemia are not rare in patients with pernicious anemia and should not rule out the diagnosis. Iron deficiency does not appear to be related to the degree of atrophic fundic gastritis but is linked to female gender and young age, suggesting menstrual blood loss could play a role. Whether decreased iron absorption due to reduced acid secretion favors the expression of gynecological iron loss cannot be ascertained.

Adult↗

PubMed2005

Global fluctuations and Gumbel statistics.

We explain how the statistics of global observables in correlated systems can be related to extreme value problems and to Gumbel statistics. This relationship then naturally leads to the emergence of the generalized Gumbel distribution Ga(x), with a real index a, in the study of global fluctuations. To illustrate these findings, we introduce an exactly solvable nonequilibrium model describing an energy flux on a lattice, with local dissipation, in which the fluctuations of the global energy are precisely described by the generalized Gumbel distribution.

Journal Article↗

PubMed2005

Subdiffusion and dynamical heterogeneities in a lattice glass model.

We study a kinetically constrained lattice glass model in which continuous local densities are randomly redistributed on neighboring sites with a kinetic constraint that inhibits the process at high densities, and a random bias accounting for attractive or repulsive interactions. The full steady-state distribution can be computed exactly in any space dimension d. Dynamical heterogeneities are characterized by a length scale that diverges when approaching the critical density. The glassy dynamics of the model can be described as a reaction-diffusion process for the mobile regions. The motion of mobile regions is found to be subdiffusive, for a large range of parameters, due to a self-induced trapping mechanism.

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PubMed2005

Nonequilibrium temperatures in steady-state systems with conserved energy.

We study a class of nonequilibrium lattice models describing local redistributions of a globally conserved quantity, which is interpreted as an energy. A particular subclass can be solved exactly, allowing us to define a statistical temperature T(th) along the same lines as in the equilibrium micro-canonical ensemble. We compute the response function and find that when the fluctuation-dissipation relation is linear, the slope T(FD)(-1) of this relation differs from the inverse temperature T(th)(-1). We argue that T(th) is physically more relevant than T(FD), since in the steady-state regime, it takes equal values in two subsystems of a large isolated system. Finally, a numerical renormalization group procedure suggests that all models within the class behave similarly at a coarse-grained level, leading to a parameter that describes the deviation from equilibrium. Quantitative predictions concerning this parameter are obtained within a mean-field framework.

Journal Article↗

PubMed2004

Dynamic phase diagram of the number partitioning problem.

We study the dynamic phase diagram of a spin model associated with the number partitioning problem, as a function of temperature and of the fraction K/N of spins allowed to flip simultaneously. The case K=1 reproduces the activated behavior of Bouchaud's trap model, whereas the opposite limit K=N can be mapped onto the entropic trap model proposed by Barrat and Mézard. In the intermediate case 1< 0 . In this temperature range, the model exhibits a nontrivial fluctuation-dissipation relation leading for K<<N to a single effective temperature equal to T(g) /2 . These results give insights into the relevance and limitations of the picture proposed by simple trap models.

Journal Article↗

PubMed2004

Temperature in nonequilibrium systems with conserved energy.

We study a class of nonequilibrium lattice models which describe local redistributions of a globally conserved energy. A particular subclass can be solved analytically, allowing us to define a temperature T(th) along the same lines as in the equilibrium microcanonical ensemble. The fluctuation-dissipation relation is explicitly found to be linear, but its slope differs from the inverse temperature T(-1)(th). A numerical renormalization group procedure suggests that, at a coarse-grained level, all models behave similarly, leading to a two-parameter description of their macroscopic properties.

Journal Article↗

PubMed2002

Energy restriction with protein restriction increases basal metabolism and meal-induced thermogenesis in rats.

We previously observed an increased sympathetic nervous system (SNS) activity that was partly responsible for a defect in the insulin secretion response to glucose after postweaning protein-energy restriction (PER) in female rats. These results, together with other data on low-protein feeding, suggested that a low protein-to-energy ratio (P/E) in the diet could stimulate energy expenditure (EE), but direct measurements of EE have never been reported under conditions of PER. The goal of the present study was thus to quantify the changes induced by PER to body composition, the various parameters of EE, and plasma triiodothyronine levels. PER induced severe growth retardation, but the subcutaneous white and interscapular brown adipose tissue masses were preserved. Basal metabolism, meal-induced thermogenesis, and triiodothyronine levels were increased, but substrate utilization by the working muscles was unaffected. Meal-induced thermogenesis was increased by spontaneous activity in PER rats only. These results suggest that rats adapt to a low P/E in the diet by burning part of their excess nonprotein energy and storing the remaining excess in subcutaneous adipose tissue.

Animals↗

PubMed2002

Development of beta-cell mass in fetuses of rats deprived of protein and/or energy in last trimester of pregnancy.

Fetal malnutrition is now proposed as a risk factor of later obesity and type II diabetes. We previously analyzed the long-term impact of reduced protein and/or energy intake strictly limited to the last week of pregnancy in Wistar rats. Three protocols of gestational malnutrition were used: 1) low-protein isocaloric diet (5 instead of 15%) with pair feeding to the mothers receiving the control diet, 2) restricted diet (50% of control diet), and 3) low protein-restricted diet (50% of low-protein diet). Only isolated protein restriction induced a long-term beta-cell mass decrease. In the present study, we used the same protocols of food restriction to analyze their short-term impact (on day 21.5 of pregnancy) on beta-cell mass development. A 50% beta-cell mass decrease was present in the three restricted groups, but low-protein diet, either associated or not to energy restriction, increased fetal beta-cell insulin content. Among all the parameters analyzed to further explain our results, we found that the fetal plasma level of taurine was lowered by low-protein diet and was the main predictor of the fetal plasma insulin level (r = 0.63, P < 0.01). In conclusion, rat fetuses exposed to protein and/or energy restriction during the third part of pregnancy have a similar dramatic decrease in beta-cell mass, and their ability to recover beta-cell mass development retardation depends on the type of malnutrition used. Moreover, our results support the hypothesis that taurine might play an important role in fetal beta-cell mass function.

Animals↗