Anomalous diffusion, Localization, Aging and Sub-aging effects in trap models at very low temperature

We study in details the dynamics of the one dimensional symmetric trap model, via a real-space renormalization procedure which becomes exact in the limit of zero temperature. In this limit, the diffusion front in each sample consists in two delta peaks, which are completely out of equilibrium with each other. The statistics of the positions and weights of these delta peaks over the samples allows to obtain explicit results for all observables in the limit $T \to 0$. We first compute disorder averages of one-time observables, such as the diffusion front, the thermal width, the localization parameters, the two-particle correlation function, and the generating function of thermal cumulants of the position. We then study aging and sub-aging effects : our approach reproduces very simply the two different aging exponents and yields explicit forms for scaling functions of the various two-time correlations. We also extend the RSRG method to include systematic corrections to the previous zero temperature procedure via a series expansion in $T$. We then consider the generalized trap model with parameter $\alpha \in [0,1]$ and obtain that the large scale effective model at low temperature does not depend on $\alpha$ in any dimension, so that the only observables sensitive to $\alpha$ are those that measure the `local persistence', such as the probability to remain exactly in the same trap during a time interval. Finally, we extend our approach at a scaling level for the trap model in $d=2$ and obtain the two relevant time scales for aging properties.Comment: 33 pages, 3 eps figure

Random walks and polymers in the presence of quenched disorder

After a general introduction to the field, we describe some recent results concerning disorder effects on both `random walk models', where the random walk is a dynamical process generated by local transition rules, and on `polymer models', where each random walk trajectory representing the configuration of a polymer chain is associated to a global Boltzmann weight. For random walk models, we explain, on the specific examples of the Sinai model and of the trap model, how disorder induces anomalous diffusion, aging behaviours and Golosov localization, and how these properties can be understood via a strong disorder renormalization approach. For polymer models, we discuss the critical properties of various delocalization transitions involving random polymers. We first summarize some recent progresses in the general theory of random critical points : thermodynamic observables are not self-averaging at criticality whenever disorder is relevant, and this lack of self-averaging is directly related to the probability distribution of pseudo-critical temperatures $T_c(i,L)$ over the ensemble of samples $(i)$ of size $L$. We describe the results of this analysis for the bidimensional wetting and for the Poland-Scheraga model of DNA denaturation.Comment: 17 pages, Conference Proceedings "Mathematics and Physics", I.H.E.S., France, November 200

Tree mode of death and mortality risk factors across Amazon forests

AbstractThe carbon sink capacity of tropical forests is substantially affected by tree mortality. However, the main drivers of tropical tree death remain largely unknown. Here we present a pan-Amazonian assessment of how and why trees die, analysing over 120,000 trees representing \u3e 3800 species from 189 long-term RAINFOR forest plots. While tree mortality rates vary greatly Amazon-wide, on average trees are as likely to die standing as they are broken or uprooted—modes of death with different ecological consequences. Species-level growth rate is the single most important predictor of tree death in Amazonia, with faster-growing species being at higher risk. Within species, however, the slowest-growing trees are at greatest risk while the effect of tree size varies across the basin. In the driest Amazonian region species-level bioclimatic distributional patterns also predict the risk of death, suggesting that these forests are experiencing climatic conditions beyond their adaptative limits. These results provide not only a holistic pan-Amazonian picture of tree death but large-scale evidence for the overarching importance of the growth–survival trade-off in driving tropical tree mortality

Asymptomatic oral yeast carriage in HIV-infected patients: frequency and fluconazole susceptibility profile.

OBJECTIVES: Fluconazole-resistant oropharyngeal candidiasis (OPC) is a rapidly growing problem in HIV-infected patients. To better understand the pathogenesis of fluconazole resistance in this setting, asymptomatic candidal carriage was determined by means of oral swabs regularly performed in all patients without clinical signs of OPC seen at our HIV outpatient clinic. Controls were 204 asymptomatic healthcare workers without previous exposure to fluconazole. METHODS: Swabs were plated on three solid media and put in a Sabouraud broth. Phenotypically different colonies were identified to the species level. Susceptibility to fluconazole was determined using a disk diffusion test with 50 microg fluconazole disks on yeast nitrogen agar, with a cut-off value of 25 mm. RESULTS: Swabs were performed in 538 consecutive HIV-positive patients, of whom 216 (40%) had had prior episode(s) of OPC and/or were previously exposed to fluconazole. Yeasts were grown in 418/538 HIV-positive patients (78%), compared to 57/204 controls (28%) (p < 0.05). In HIV-positive patients, yeasts were grown in 189/216 (88%) of those with past fluconazole exposure, and in 229/322 (71%) without exposure (p < 0.05). A total of 589 isolates were grown in the 538 HIV-positive patients (451 C. albicans, 88 C. glabrata, 22 C. tropicalis, 11 C. krusei, and 17 isolates from 12 other species). Resistance to fluconazole was present in 121/589 (21%) Candida species isolates in HIV-positive patients and in 2/59 (3%) in controls. Among C. albicans isolates, there were 18 fluconazole-resistant strains in HIV-positive patients (4%) and none in controls.CONCLUSIONS: Using sensitive culture methods, oral yeast colonization was detected significantly more frequently in HIV-infected patients (78%) than in a control group of HIV-negative persons (28%). In addition, yeast colonization was quantitatively more important in patients with lower CD4+ lymphocyte counts and for those who had been exposed to fluconazole for episode(s) of OPC. Fluconazole-resistant C. albicans isolates were observed only in HIV-positive patients, and all patients (17/18) for whom this information could be ascertained had had prior exposure to fluconazole

Efficacy, tolerability and development of resistance in HIV-positive patients treated with fluconazole for secondary prevention of oropharyngeal candidiasis: a randomized, double-blind, placebo-controlled trial.

Over 37 months, we conducted a prospective double-blind, randomized study in a cohort of 138 HIV-infected patients to compare the effect of two different strategies on the prevention and treatment of oropharyngeal candidiasis relapses and on the development of clinical and microbiological resistance to fluconazole. Each episode was treated with a 7 day course of fluconazole 200 mg/day, followed by secondary prophylaxis with fluconazole 150 mg once weekly matched to placebo. The duration of the double-blind phase of the study, from the day of randomization to the first primary end-point, was 347 +/- 186 days for the fluconazole group and 196 +/- 128 days for the placebo group (P < 0.001). A total of 33 patients remained relapse-free during the course of the study. Clinical failure was observed in a total of five patients (four in the fluconazole group, one in the placebo group; P = 0.15). Microbiological resistance was recorded in 12 patients (eight in the fluconazole group, four in the placebo group; P = 0.20). There were no significant treatment group differences in microbiological resistance whether comparisons were made for all cases or for cases up to 1 month post-study. In the few patients who developed clinical and/or microbiological resistance, the cumulative dose of fluconazole before entry into the study was a mean value of 8.6 g (compared with 2.9 g in patients without clinical and/or microbiological resistance). In summary, patients treated with secondary prophylaxis suffered fewer relapses of oropharyngeal candidiasis. Development of resistant candidiasis (clinical and/or microbiological) was rarely seen in either group and its incidence was not significantly different

Trimethoprim, alone or in combination with sulphamethoxazole, decreases the renal excretion of zidovudine and its glucuronide.

Trimethoprim and trimethoprim-sulphamethoxazole (co-trimoxazole) are often prescribed in HIV patients treated with zidovudine. The pharmacokinetics of zidovudine, after a dose of 3 mg kg-1 by constant rate intravenous infusion over 1 h were evaluated in nine HIV patients in an open, randomized, three-phase crossover study, without and with trimethoprim (150 mg) and trimethoprim-sulphamethoxazole (160 and 800 mg). The metabolic clearance of zidovudine was not significantly influenced by trimethoprim-sulphamethoxazole and trimethoprim. However, the renal clearance of zidovudine was decreased by 58 and 48%, respectively, and that of its glucuronide by 27 and 20% (P < 0.05). The fraction of the dose excreted as the parent compound fell by 47 and 39% and the metabolic ratio by 48 and 43% (P < 0.05). This kinetic drug interaction, apparently due solely to trimethoprim, may only be clinically important when hepatic glucuronidation is also impaired by liver disease or inhibited by other drugs