Francesco Sciortino

Bio: Francesco Sciortino is an academic researcher from Sapienza University of Rome. The author has contributed to research in topics: Critical point (thermodynamics) & Phase transition. The author has an hindex of 90, co-authored 536 publications receiving 28956 citations. Previous affiliations of Francesco Sciortino include National Center for Simulation & Arizona State University.

Phase behaviour of metastable water

Abstract: THE metastable extension of the phase diagram of liquid water exhibits rich features that manifest themselves in the equilibrium properties of water. For example, the density maximum at 4 °C and the minimum in the isothermal compressibility at 46 °C are thought to reflect the presence of singularities in the behaviour of thermodynamic quantities occurring in the supercooled region1 2. The 'stability–limit conjecture'3–5 suggests that these thermodynamic anomalies arise from a single limit of mechanical stability (spinodal line), originating at the liquid–gas critical point, which determines the limit of both superheating at high temperatures and supercooling at low temperatures. Here we present a comprehensive series of molecular dynamics simulations which suggest that, instead, the supercooling anomalies are caused by a newly identified critical point, above which the two metastable amorphous phases of ice (previously shown to be separated by a line of first-order transitions6,7) become indistinguishable. The two amorphous ice phases are thus incorporated into our understanding of the liquid state, providing a more complete picture of the metastable and stable behaviour of water.

Long-range correlations in nucleotide sequences

Abstract: DNA sequences have been analysed using models, such as an n-step Markov chain, that incorporate the possibility of short-range nucleotide correlations. We propose here a method for studying the stochastic properties of nucleotide sequences by constructing a 1:1 map of the nucleotide sequence onto a walk, which we term a 'DNA walk'. We then use the mapping to provide a quantitative measure of the correlation between nucleotides over long distances along the DNA chain. Thus we uncover in the nucleotide sequence a remarkably long-range power law correlation that implies a new scale-invariant property of DNA. We find such long-range correlations in intron-containing genes and in nontranscribed regulatory DNA sequences, but not in complementary DNA sequences or intron-less genes.

Gelation of particles with short-range attraction

Abstract: Nanoscale or colloidal particles change the properties of materials, imparting solid-like behaviour to a wide variety of complex fluids. This behaviour arises when particles aggregate to form mesoscopic clusters and networks. Numerous scenarios for gelation have been proposed, but no consensus has emerged. Lu et al. report experiments showing that gelation of spherical particles with isotropic, short-range attractions is initiated by spinodal decomposition; this thermodynamic instability triggers the formation of density fluctuations, leading to spanning clusters that dynamically arrest to create a gel. This simple picture of gelation should apply to any particle system with short-range attractions. Solid-like behaviour arises in a wide variety of complex fluids upon gelation — aggregation of particles to form mesoscopic clusters and networks. The authors show that gelation of spherical particles with isotropic, short-range attractions is initiated by spinodal decomposition. Nanoscale or colloidal particles are important in many realms of science and technology. They can dramatically change the properties of materials, imparting solid-like behaviour to a wide variety of complex fluids1,2. This behaviour arises when particles aggregate to form mesoscopic clusters and networks. The essential component leading to aggregation is an interparticle attraction, which can be generated by many physical and chemical mechanisms. In the limit of irreversible aggregation, infinitely strong interparticle bonds lead to diffusion-limited cluster aggregation3 (DLCA). This is understood as a purely kinetic phenomenon that can form solid-like gels at arbitrarily low particle volume fraction4,5. Far more important technologically are systems with weaker attractions, where gel formation requires higher volume fractions. Numerous scenarios for gelation have been proposed, including DLCA6, kinetic or dynamic arrest4,7,8,9,10, phase separation5,6,11,12,13,14,15,16, percolation4,12,17,18 and jamming8. No consensus has emerged and, despite its ubiquity and significance, gelation is far from understood—even the location of the gelation phase boundary is not agreed on5. Here we report experiments showing that gelation of spherical particles with isotropic, short-range attractions is initiated by spinodal decomposition; this thermodynamic instability triggers the formation of density fluctuations, leading to spanning clusters that dynamically arrest to create a gel. This simple picture of gelation does not depend on microscopic system-specific details, and should thus apply broadly to any particle system with short-range attractions. Our results suggest that gelation—often considered a purely kinetic phenomenon4,8,9,10—is in fact a direct consequence of equilibrium liquid–gas phase separation5,13,14,15. Without exception, we observe gelation in all of our samples predicted by theory and simulation to phase-separate; this suggests that it is phase separation, not percolation12, that corresponds to gelation in models for attractive spheres.

Relation between the Widom line and the dynamic crossover in systems with a liquid–liquid phase transition

Abstract: We investigate, for two water models displaying a liquid–liquid critical point, the relation between changes in dynamic and thermodynamic anomalies arising from the presence of the liquid–liquid critical point. We find a correlation between the dynamic crossover and the locus of specific heat maxima (“Widom line”) emanating from the critical point. Our findings are consistent with a possible relation between the previously hypothesized liquid–liquid phase transition and the transition in the dynamics recently observed in neutron scattering experiments on confined water. More generally, we argue that this connection between and dynamic crossover is not limited to the case of water, a hydrogen bond network-forming liquid, but is a more general feature of crossing the Widom line. Specifically, we also study the Jagla potential, a spherically symmetric two-scale potential known to possess a liquid–liquid critical point, in which the competition between two liquid structures is generated by repulsive and attractive ramp interactions.

Phase Diagram of Patchy Colloids: Towards Empty Liquids

Abstract: We report theoretical and numerical evaluations of the phase diagram for patchy colloidal particles of new generation. We show that the reduction of the number of bonded nearest neighbors offers the possibility of generating liquid states (i.e., states with temperature T lower than the liquid-gas critical temperature) with a vanishing occupied packing fraction (� ), a case which can not be realized with spherically interacting particles. Theoretical results suggest that such reduction is accompanied by an increase of the region of stability of the liquid phase in the (T-� ) plane, possibly favoring the establishment of homogeneous disordered materials at small � , i.e., stable equilibrium gels. The physico-chemical manipulation of colloidal particles is growing at an incredible pace. The large freedom in the control of the interparticle potential has made it possible to design colloidal particles which significantly extend the possibilities offered by atomic systems [1]. An impressive step further is offered by the newly developed techniques to assemble (and produce with significant yield) colloidal molecules, particles decorated on their surface by a predefined number of attractive sticky spots, i.e., particles with specifically designed shapes and interaction sites [2 ‐ 5]. These new particles, thanks to the specificity of the built-in interactions, will be able not only to reproduce molecular systems on the nano and micro scale, but will also show novel collective behaviors. To guide future applications of patchy colloids, to help in designing bottom-up strategies in self-assembly [6 ‐8], and to tackle the issue of interplay between dynamic arrest and crystallization —a hot-topic related, for example, to the possibility of nucleating a colloidal diamond crystal structure for photonic applications [9]—it is crucial to be able to predict the region in the (T-� ) plane in which clustering, phase separation, or even gelation is expected. While design and production of patchy colloids is present-day research, unexpectedly theoretical studies of the physical properties of these systems have a longer history, starting in the eighties in the context of the physics of associated liquids [10 ‐15]. These studies, in the attempt to pin down the essential features of association, modeled molecules as hardcore particles with attractive spots on the surface, a realistic description of the recently created patchy colloidal particles. A thermodynamic perturbation theory (TPT) appropriate for these models was introduced by Wertheim [16] to describe association under the hypothesis that a sticky site on a particle cannot bind simultaneously to two (or more) sites on another particle. Such a condition can be naturally implemented in colloids, due to the relative size of the particle as compared to the range of the sticky interaction. These old studies provide a very valuable starting point for addressing the issue of the phase diagram of this new class of colloids, and, in particular, of the role of the patches number. In this Letter, we study a system of hard-sphere particles with a small number M of identical short-ranged, squarewell attraction sites per particle (sticky spots), distributed on the surface with the same geometry as the recently produced patchy colloidal particles [4]. We identify the number of possible bonds per particle as the key parameter controlling the location of the critical point, as opposed to the fraction of surface covered by attractive patches. We present results of extensive numerical simulations of this model in the grand-canonical ensemble [17] to evaluate the location of the critical point of the system in the (T-� ) plane as a function of M. We complement the simulation results with the evaluation of the region of thermodynamic instability according to the Wertheim theory [16,18,19]. Both theory and simulation confirm that, on decreasing the number of sticky sites, the critical point moves toward ���������������� �

疟原虫var基因转换速率变化导致抗原变异[英]／Paul H, Robert P, Christodoulou Z, et al//Proc Natl Acad Sci U S A

Abstract: 抗原变异可使得多种致病微生物易于逃避宿主免疫应答。表达在感染红细胞表面的恶性疟原虫红细胞表面蛋白1（PfPMP1）与感染红细胞、内皮细胞、树突状细胞以及胎盘的单个或多个受体作用，在黏附及免疫逃避中起关键的作用。每个单倍体基因组var基因家族编码约60种成员，通过启动转录不同的var基因变异体为抗原变异提供了分子基础。

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

“Bioinformatics” 특집을 내면서

Abstract: BIOE 402. Medical Technology Assessment. 2 or 3 hours. Bioentrepreneur course. Assessment of medical technology in the context of commercialization. Objectives, competition, market share, funding, pricing, manufacturing, growth, and intellectual property; many issues unique to biomedical products. Course Information: 2 undergraduate hours. 3 graduate hours. Prerequisite(s): Junior standing or above and consent of the instructor.