A pedagogical introduction to the replica method for fragile glasses

In this note I present a simplified version of the recent computation (Mezard and Parisi 1998, 1999) of the properties of glasses in the low temperature phase in the framework of the replica theory, using an extension of the tools used in liquid theory. I will only consider here the case of the internal energy at T=0, which can be studied in a simple way without introducing replicas.Comment: 7 pages, 1 figure Talk given at Andalo, March 1999; minor errors have been correcte

The unsolved case of “bone-impairing analgesics”. The endocrine effects of opioids on bone metabolism

The current literature describes the possible risks for bone fracture in chronic analgesics users. There are three main hypotheses that could explain the increased risk of fracture associated with central analgesics, such as opioids: 1) the increased risk of falls caused by central nervous system effects, including sedation and dizziness; 2) reduced bone mass density caused by the direct opioid effect on osteoblasts; and 3) chronic opioid-induced hypogonadism. The impact of opioids varies by sex and among the type of opioid used (less, for example, for tapentadol and buprenorphine). Opioid-associated androgen deficiency is correlated with an increased risk of osteoporosis; thus, despite that standards have not been established for monitoring and treating opioid-induced hypogonadism or hypoadrenalism, all patients chronically taking opioids (particularly at doses ≥100 mg morphine daily) should be monitored for the early detection of hormonal impairment and low bone mass density

Postoperative pain surveys in Italy from 2006 and 2012. (POPSI and POPSI-2)

OBJECTIVE: Despite established standards, effective treatments, and evidence-based guidelines, postoperative pain control in Italy and other parts of the world remains suboptimal. Pain control has been recognized as a fundamental human right. Effective treatments exist to control postsurgical pain. Inadequate postoperative analgesia may prolong the length of hospital stays and may adversely impact outcomes. MATERIALS AND METHODS: The same multiple-choice survey administered at the SIAARTI National Congress in Perugia in 2006 (n=588) was given at the SIAARTI National Congress in Naples, Italy in 2012 (n=635). The 2012 survey was analysed and compared to the 2006 results. RESULTS: Postoperative pain control in Italy was less than optimal in 2006 and showed no substantial improvements in 2012. Geographical distinctions were evident with certain parts of Italy offering better postoperative pain control than other. Fewer than half of hospitals represented had an active Acute Pain Service (APS) and only about 10% of postsurgical patients were managed according to evidence-based guidelines. For example, elastomeric pumps for continuous IV infusion are commonly used in Italy, although patient-controlled analgesia systems are recommended in the guidelines. The biggest obstacles to optimal postoperative pain control reported by respondents could be categorized as organizational, cultural, and economic. CONCLUSIONS: There is considerable room for improvement in postoperative pain control in Italy, specifically in the areas of clinical education, evidence-based treatments, better equipment, and implementation of active APS departments in more hospitals. Two surveys taken six years apart in Italy reveal, with striking similarity, that there are many unmet needs in postoperative pain control and that Italy still falls below European standards for postoperative pain control

Numerical evidence for relevance of disorder in a Poland-Scheraga DNA denaturation model with self-avoidance: Scaling behavior of average quantities

We study numerically the effect of sequence heterogeneity on the thermodynamic properties of a Poland-Scheraga model for DNA denaturation taking into account self-avoidance, i.e. with exponent c_p=2.15 for the loop length probability distribution. In complement to previous on-lattice Monte Carlo like studies, we consider here off-lattice numerical calculations for large sequence lengths, relying on efficient algorithmic methods. We investigate finite size effects with the definition of an appropriate intrinsic length scale x, depending on the parameters of the model. Based on the occurrence of large enough rare regions, for a given sequence length N, this study provides a qualitative picture for the finite size behavior, suggesting that the effect of disorder could be sensed only with sequence lengths diverging exponentially with x. We further look in detail at average quantities for the particular case x=1.3, ensuring through this parameter choice the correspondence between the off-lattice and the on-lattice studies. Taken together, the various results can be cast in a coherent picture with a crossover between a nearly pure system like behavior for small sizes N < 1000, as observed in the on-lattice simulations, and the apparent asymptotic behavior indicative of disorder relevance, with an (average) correlation length exponent \nu_r >= 2/d (=2).Comment: Latex, 33 pages with 15 postscript figure

Numerical study of the disordered Poland-Scheraga model of DNA denaturation

We numerically study the binary disordered Poland-Scheraga model of DNA denaturation, in the regime where the pure model displays a first order transition (loop exponent $c=2.15>2$). We use a Fixman-Freire scheme for the entropy of loops and consider chain length up to $N=4 \cdot 10^5$, with averages over $10^4$ samples. We present in parallel the results of various observables for two boundary conditions, namely bound-bound (bb) and bound-unbound (bu), because they present very different finite-size behaviors, both in the pure case and in the disordered case. Our main conclusion is that the transition remains first order in the disordered case: in the (bu) case, the disorder averaged energy and contact densities present crossings for different values of $N$ without rescaling. In addition, we obtain that these disorder averaged observables do not satisfy finite size scaling, as a consequence of strong sample to sample fluctuations of the pseudo-critical temperature. For a given sample, we propose a procedure to identify its pseudo-critical temperature, and show that this sample then obeys first order transition finite size scaling behavior. Finally, we obtain that the disorder averaged critical loop distribution is still governed by $P(l) \sim 1/l^c$ in the regime $l \ll N$, as in the pure case.Comment: 12 pages, 13 figures. Revised versio

Potential energy landscape of finite-size mean-field models for glasses

connected spin-glass models with a discontinuous transition. In the thermodynamic limit the equilibrium properties in the high temperature phase are described by the schematic Mode Coupling Theory of super-cooled liquids. We show that {\it finite-size} fully connected spin-glass models do exhibit properties typical of Lennard-Jones systems when both are near the critical glass transition, where thermodynamics is ruled by energy minima distribution. Our study opens the way to consider activated processes in real glasses through finite-size corrections (i.e. calculations beyond the saddle point approximation) in mean-field spin-glass models.Comment: 8 pages, 3 postscript figures, EPL format, improved versio

Liquid Limits: The Glass Transition and Liquid-Gas Spinodal Boundaries of Metastable Liquids

The liquid-gas spinodal and the glass transition define ultimate boundaries beyond which substances cannot exist as (stable or metastable) liquids. The relation between these limits is analyzed {\it via} computer simulations of a model liquid. The results obtained indicate that the liquid - gas spinodal and the glass transition lines intersect at a finite temperature, implying a glass - gas mechanical instability locus at low temperatures. The glass transition lines obtained by thermodynamic and dynamic criteria agree very well with each other.Comment: 5 pages, 4 figures, to appear in Phys. Rev. Let

Statistical Physics of Structural Glasses

This paper gives an introduction and brief overview of some of our recent work on the equilibrium thermodynamics of glasses. We have focused onto first principle computations in simple fragile glasses, starting from the two body interatomic potential. A replica formulation translates this problem into that of a gas of interacting molecules, each molecule being built of $m$ atoms, and having a gyration radius (related to the cage size) which vanishes at zero temperature. We use a small cage expansion, valid at low temperatures, which allows to compute the cage size, the specific heat (which follows the Dulong and Petit law), and the configurational entropy. The no-replica interpretation of the computations is also briefly described. The results, particularly those concerning the Kauzmann tempaerature and the configurational entropy, are compared to recent numerical simulations.Comment: 21 pages, 6 figures, to appear in the proceedings of the Trieste workshop on "Unifying Concepts in Glass Physics

Numerical simulations on the 4d Heisenberg spin glass

We study the 4d Heisenberg spin glass model with Gaussian nearest-neighbor interactions. We use finite size scaling to analyze the data. We find a behavior consistent with a finite temperature spin glass transition. Our estimates for the critical exponents agree with the results from epsilon-expansion.Comment: 11 pages, LaTeX, preprint ROMA1 n. 105