Continuous approach for the random-field Ising chain.

We study the random-field Ising chain in the limit of strong exchange coupling. In order to calculate the free energy we apply a continuous Langevin-type approach. This continuous model can be solved exactly, whereupon we are able to locate the crossover between an exponential and a power-law decay of the free energy with increasing coupling strength. In terms of magnetization, this crossover restricts the validity of the linear scaling. The known analytical results for the free energy are recovered in the corresponding limits. The outcomes of numerical computations for the free energy are presented, which confirm the results of the continuous approach. We also discuss the validity of the replica method which we then utilize to investigate the sample-to-sample fluctuations of the finite size free energy

Stability of the splay state in pulse--coupled networks

The stability of the dynamical states characterized by a uniform firing rate ({\it splay states}) is analyzed in a network of globally coupled leaky integrate-and-fire neurons. This is done by reducing the set of differential equations to a map that is investigated in the limit of large network size. We show that the stability of the splay state depends crucially on the ratio between the pulse--width and the inter-spike interval. More precisely, the spectrum of Floquet exponents turns out to consist of three components: (i) one that coincides with the predictions of the mean-field analysis [Abbott-van Vreesvijk, 1993]; (ii) a component measuring the instability of "finite-frequency" modes; (iii) a number of "isolated" eigenvalues that are connected to the characteristics of the single pulse and may give rise to strong instabilities (the Floquet exponent being proportional to the network size). Finally, as a side result, we find that the splay state can be stable even for inhibitory coupling.Comment: 13 pages, 10 figures, submitted for pubblication to Physical Review

Desynchronization in diluted neural networks

The dynamical behaviour of a weakly diluted fully-inhibitory network of pulse-coupled spiking neurons is investigated. Upon increasing the coupling strength, a transition from regular to stochastic-like regime is observed. In the weak-coupling phase, a periodic dynamics is rapidly approached, with all neurons firing with the same rate and mutually phase-locked. The strong-coupling phase is characterized by an irregular pattern, even though the maximum Lyapunov exponent is negative. The paradox is solved by drawing an analogy with the phenomenon of ``stable chaos'', i.e. by observing that the stochastic-like behaviour is "limited" to a an exponentially long (with the system size) transient. Remarkably, the transient dynamics turns out to be stationary.Comment: 11 pages, 13 figures, submitted to Phys. Rev.

Efficacy of vildagliptin for prevention of postpartum diabetes in women with a recent history of insulin-requiring gestational diabetes: A phase II, randomized, double-blind, placebo-controlled study

Objective: Women with insulin-requiring gestational diabetes mellitus (GDM) are at high risk of developing diabetes within a few years postpartum. We implemented this phase II study to test the hypothesis that vildagliptin, a dipeptidyl peptidase-4 inhibitor, is superior to placebo in terms of reducing the risk of postpartum diabetes. Methods: Women with insulin-requiring GDM were randomized to either placebo or 50 mg vildagliptin twice daily for 24 months followed by a 12-month observation period (EudraCT: 2007-000634-39). Both groups received lifestyle counseling. The primary efficacy outcomes were the diagnosis of diabetes (American Diabetes Association (ADA) criteria) or impaired fasting glucose (IFG)/impaired glucose tolerance (IGT). Results: Between 2008 and 2015, 113 patients (58 vildagliptin, 55 placebo) were randomized within 2.2–10.4 (median 8.6) months after delivery. At the interim analysis, nine diabetic events and 28 IFG/IGT events had occurred. Fifty-two women withdrew before completing the treatment phase. Because of the low diabetes rate, the study was terminated. Lifestyle adherence was similar in both groups. At 24 months, the cumulative probability of postpartum diabetes was 3% and 5% (hazard ratio: 1.03; 95% confidence interval: 0.15–7.36) and IFG/IGT was 43% and 22% (hazard ratio: 0.55; 95% confidence interval: 0.26–1.19) in the placebo and vildagliptin groups, respectively. Vildagliptin was well tolerated with no unexpected adverse events. Conclusions: The study did not show significant superiority of vildagliptin over placebo in terms of reducing the risk of postpartum diabetes. However, treatment was safe and suggested some improvements in glycemic control, insulin resistance, and β-cell function. The study identified critical issues in performing clinical trials in the early postpartum period in women with GDM hampering efficacy assessments. With this knowledge, we have set a basis for which properly powered trials could be performed in women with recent GDM. Trial registration number at ClinicalTrials.gov: NCT01018602. Keywords: Gestational diabetes mellitus, Prevention, Dipeptidyl peptidase-4 inhibitor, Postpartum diabetes, Randomized controlled trial, Life-styl