Stochastic approach to diffusion inside the chaotic layer of a resonance

We model chaotic diffusion, in a symplectic 4D map by using the result of a theorem that was developed for stochastically perturbed integrable Hamiltonian systems. We explicitly consider a map defined by a free rotator (FR) coupled to a standard map (SM). We focus in the diffusion process in the action, $I$, of the FR, obtaining a semi--numerical method to compute the diffusion coefficient. We study two cases corresponding to a thick and a thin chaotic layer in the SM phase space and we discuss a related conjecture stated in the past. In the first case the numerically computed probability density function for the action $I$ is well interpolated by the solution of a Fokker-Planck (F-P) equation, whereas it presents a non--constant time delay respect to the concomitant F-P solution in the second case suggesting the presence of an anomalous diffusion time scale. The explicit calculation of a diffusion coefficient for a 4D symplectic map can be useful to understand the slow diffusion observed in Celestial Mechanics and Accelerator Physics.Comment: This is the author's version of a work that was submitted to Physical Review E (http://pre.aps.org

Chirikov and Nekhoroshev diffusion estimates: bridging the two sides of the river

We present theoretical and numerical results pointing towards a strong connection between the estimates for the diffusion rate along simple resonances in multidimensional nonlinear Hamiltonian systems that can be obtained using the heuristic theory of Chirikov and a more formal one due to Nekhoroshev. We show that, despite a wide-spread impression, the two theories are complementary rather than antagonist. Indeed, although Chirikov's 1979 review has thousands of citations, almost all of them refer to topics such as the resonance overlap criterion, fast diffusion, the Standard or Whisker Map, and not to the constructive theory providing a formula to measure diffusion along a single resonance. However, as will be demonstrated explicitly below, Chirikov's formula provides values of the diffusion coefficient which are quite well comparable to the numerically computed ones, provided that it is implemented on the so-called optimal normal form derived as in the analytic part of Nekhoroshev's theorem. On the other hand, Chirikov's formula yields unrealistic values of the diffusion coefficient, in particular for very small values of the perturbation, when used in the original Hamiltonian instead of the optimal normal form. In the present paper, we take advantage of this complementarity in order to obtain accurate theoretical predictions for the local value of the diffusion coefficient along a resonance in a specific 3DoF nearly integrable Hamiltonian system. Besides, we compute numerically the diffusion coefficient and a full comparison of all estimates is made for ten values of the perturbation parameter, showing a very satisfactory agreement.Comment: 25 pages, 9 figures. NOTICE: this is the author's version of a work that was accepted for publication in Physica D. Changes resulting from the publishing process, such as peer review, editing, corrections, structural formatting, and other quality control mechanisms may not be reflected in this document. Changes may have been made to this work since it was submitted for publicatio

On the relevance of chaos for halo stars in the Solar Neighbourhood

We show that diffusion due to chaotic mixing in the Neighbourhood of the Sun may not be as relevant as previously suggested in erasing phase space signatures of past Galactic accretion events. For this purpose, we analyse Solar Neighbourhood-like volumes extracted from cosmological simulations that naturally account for chaotic orbital behaviour induced by the strongly triaxial and cuspy shape of the resulting dark matter haloes, among other factors. In the approximation of an analytical static triaxial model, our results show that a large fraction of stellar halo particles in such local volumes have chaos onset times (i.e., the timescale at which stars commonly associated with chaotic orbits will exhibit their chaotic behaviour) significantly larger than a Hubble time. Furthermore, particles that do present a chaotic behaviour within a Hubble time do not exhibit significant diffusion in phase space.Comment: 20 pages, 16 figures. Accepted for publication in MNRA

Chronic Exposure to Arsenic in Drinking Water Causes Alterations in Locomotor Activity and Decreases Striatal mRNA for the D2 Dopamine Receptor in CD1 Male Mice

Arsenic exposure has been associated with sensory, motor, memory, and learning alterations in humans and alterations in locomotor activity, behavioral tasks, and neurotransmitters systems in rodents. In this study, CD1 mice were exposed to 0.5 or 5.0 mg As/L of drinking water for 6 months. Locomotor activity, aggression, interspecific behavior and physical appearance, monoamines levels, and expression of the messenger for dopamine receptors D1 and D2 were assessed. Arsenic exposure produced hypoactivity at six months and other behaviors such as rearing and on-wall rearing and barbering showed both increases and decreases. No alterations on aggressive behavior or monoamines levels in striatum or frontal cortex were observed. A significant decrease in the expression of mRNA for D2 receptors was found in striatum of mice exposed to 5.0 mg As/L. This study provides evidence for the use of dopamine receptor D2 as potential target of arsenic toxicity in the dopaminergic system

Role of the gp85/Trans-Sialidases in Trypanosoma cruzi Tissue Tropism: Preferential Binding of a Conserved Peptide Motif to the Vasculature in Vivo

Background: Transmitted by blood-sucking insects, the unicellular parasite Trypanosoma cruzi is the causative agent of Chagas' disease, a malady manifested in a variety of symptoms from heart disease to digestive and urinary tract dysfunctions. the reasons for such organ preference have been a matter of great interest in the field, particularly because the parasite can invade nearly every cell line and it can be found in most tissues following an infection. Among the molecular factors that contribute to virulence is a large multigene family of proteins known as gp85/trans-sialidase, which participates in cell attachment and invasion. But whether these proteins also contribute to tissue homing had not yet been investigated. Here, a combination of endothelial cell immortalization and phage display techniques has been used to investigate the role of gp85/trans-sialidase in binding to the vasculature.Methods: Bacteriophage expressing an important peptide motif (denominated FLY) common to all gp85/trans-sialidase proteins was used as a surrogate to investigate the interaction of this motif with the endothelium compartment. for that purpose phage particles were incubated with endothelial cells obtained from different organs or injected into mice intravenously and the number of phage particles bound to cells or tissues was determined. Binding of phages to intermediate filament proteins has also been studied.Findings and Conclusions: Our data indicate that FLY interacts with the endothelium in an organ-dependent manner with significantly higher avidity for the heart vasculature. Phage display results also show that FLY interaction with intermediate filament proteins is not limited to cytokeratin 18 (CK18), which may explain the wide variety of cells infected by the parasite. This is the first time that members of the intermediate filaments in general, constituted by a large group of ubiquitously expressed proteins, have been implicated in T. cruzi cell invasion and tissue homing.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)Universidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilUniv São Paulo, Inst Quim, Dept Bioquim, BR-01498 São Paulo, BrazilUniv Texas MD Anderson Canc Ctr, David H Koch Ctr, Houston, TX 77030 USAUniv Texas MD Anderson Canc Ctr, Dept Canc Biol, Houston, TX 77030 USAUniversidade Federal de São Paulo, Dept Microbiol Imunol & Parasitol, São Paulo, BrazilFAPESP: 2004/03303-5FAPESP: 2008/54.806-8Web of Scienc

BRCA1 genetic testing in 106 breast and ovarian cancer families from southern Italy (Sicily): a mutation analyses.

PURPOSE: To evaluate the contribution of germline BRCA1 mutations in the incidence of hereditary and familial Breast Cancer (BC) and/or Ovarian Cancer (OC) in patients from Southern Italy (in the region of Sicily) and to identify a possible association between the higher frequency of BRCA1 mutations and a specific familial profile. EXPERIMENTAL DESIGN: A consecutive series of 650 patients with BC and/or OC diagnosed between 1999 and 2005 were recruited from the Southern Italian region of Sicily, after interview at the "Regional Reference Centre for the Characterization and Genetic Screening of Hereditary Tumors" at the University of Palermo. Genetic counselling allowed us to recruit a total of 106 unrelated families affected with breast and/or ovarian cancer screened for mutations occurring in the whole BRCA1 gene by automatic direct sequencing. RESULTS: Germline BRCA1 mutations were found in 17 of 106 (16%) Sicilian families. The HBOC profile had a major frequency (66%) of mutations (P < 0.01). A total of 28 sequence variants was identified. Seven of these were pathogenic, 5 unknown biological variant (UV) and 16 polymorphisms. We also identified a pathological mutation (4843delC) as a possible Sicilian founder mutation. CONCLUSIONS: The present study is the first BRCA1 disease-associated mutations analysis in Southern Italian families. The early age of onset of such tumors and the association with the HBOC familial profile could be two valid screening factors for the identification of BRCA1 mutation carriers. Finally, we identified a BRCA1 mutation with a possible founder effec

Adherence to growth hormone (GH) therapy in na\uefve to treatment GH-deficient children: data of the Italian Cohort from the Easypod Connect Observational Study (ECOS)

Background: With the use of non-objective measurement, adherence to growth hormone (GH) therapy has been reported suboptimal in a large proportion of patients, and poor adherence has been shown to affect short-term growth response in patients receiving GH treatment. Objective: The Easypod\u2122 electronic device allows objective measurement of adherence. In this study, we report 3-year prospective adherence data of the Italian cohort of na\uefve GH deficient (GHD) children extrapolated from the Easypod Connect Observational Study (ECOS) database. Patients and methods: Seventy-three GHD children na\uefve to GH treatment were included in the analysis. 22 Italian centers participated in the study. Results: Mean adherence rate was consistently above 85% across the 3-year observation period. Particularly, mean adherence was 88.5%, 86.6%, and 85.7% after 1, 2 and 3\ua0years, respectively. Mean (\ub1 SD) height-SDS increase after the first year was 0.41 (\ub1 0.38). Conclusions: The majority of na\uefve GHD children starting GH treatment with Easypod maintained an adherence rate > 85% up to 3\ua0years. Easypod is a useful tool to follow-up patients\u2019 adherence allowing timely intervention to improve optimal treatment for these patients

Adherence to growth hormone (GH) therapy in naïve to treatment GH-deficient children: data of the Italian Cohort from the Easypod Connect Observational Study (ECOS)

Background: With the use of non-objective measurement, adherence to growth hormone (GH) therapy has been reported suboptimal in a large proportion of patients, and poor adherence has been shown to affect short-term growth response in patients receiving GH treatment. Objective: The Easypod™ electronic device allows objective measurement of adherence. In this study, we report 3-year prospective adherence data of the Italian cohort of naïve GH deficient (GHD) children extrapolated from the Easypod Connect Observational Study (ECOS) database. Patients and methods: Seventy-three GHD children naïve to GH treatment were included in the analysis. 22 Italian centers participated in the study. Results: Mean adherence rate was consistently above 85% across the 3-year observation period. Particularly, mean adherence was 88.5%, 86.6%, and 85.7% after 1, 2 and 3 years, respectively. Mean (± SD) height-SDS increase after the first year was 0.41 (± 0.38). Conclusions: The majority of naïve GHD children starting GH treatment with Easypod maintained an adherence rate > 85% up to 3 years. Easypod is a useful tool to follow-up patients’ adherence allowing timely intervention to improve optimal treatment for these patients

A 6 day course of liposomal amphotericin B in the treatment of infantile visceral leishmaniasis: the Italian experience

OBJECTIVES: To evaluate in a retrospective analysis the efficacy and safety of a 6 day course of liposomal amphotericin B (L-AmB) in infantile cases of Mediterranean visceral leishmaniasis (VL) diagnosed over a 10 year period in Italy. PATIENTS AND METHODS: Patients included were diagnosed as having VL consecutively admitted from December 1992 to December 2001 at four main referral children's hospitals in Italy and treated with six intravenous doses of 3 mg/kg L-AmB given on days 1-5 and 10 (a total dose of 18 mg/kg). Demographic data, nutritional status, underlying diseases, clinical and laboratory findings, and therapy outcome were considered. RESULTS: A total of 164 HIV-negative children (median age 1.6 years; range 4 months to 14 years) were enrolled. All patients were initially cured by the given treatment, and did not present adverse events related to drug infusion. Seven patients (4.3%) had a clinical and parasitological relapse 3-15 months after therapy. All relapses were successfully retreated with 3 mg/kg L-AmB for 10 consecutive days (a total dose of 30 mg/kg). CONCLUSIONS: This study highlights the efficacy (>95%) and safety of the six dose L-AmB regimen and validates it as a first-line treatment for Mediterranean VL in children