Entropic Stochastic Resonance

We present a novel scheme for the appearance of Stochastic Resonance when the dynamics of a Brownian particle takes place in a confined medium. The presence of uneven boundaries, giving rise to an entropic contribution to the potential, may upon application of a periodic driving force result in an increase of the spectral amplification at an optimum value of the ambient noise level. This Entropic Stochastic Resonance (ESR), characteristic of small-scale systems, may constitute a useful mechanism for the manipulation and control of single-molecules and nano-devices.Comment: 4 pages, 3 figure

Damage spreading in the mode-coupling equations for glasses

We examine the problem of damage spreading in the off-equilibrium mode coupling equations. The study is done for the spherical $p$-spin model introduced by Crisanti, Horner and Sommers. For $p>2$ we show the existence of a temperature transition $T_0$ well above any relevant thermodynamic transition temperature. Above $T_0$ the asymptotic damage decays to zero while below $T_0$ it decays to a finite value independent of the initial damage. This transition is stable in the presence of asymmetry in the interactions. We discuss the physical origin of this peculiar phase transition which occurs as a consequence of the non-linear coupling between the damage and the two-time correlation functions.Comment: 5 pages, 2 figures, Revtex fil

Diabetes-associated mitochondrial DNA mutation A3243G impairs cellular metabolic pathways necessary for beta cell function

Aims/hypothesis: Mitochondrial DNA (mtDNA) mutations cause several diseases, including mitochondrial inherited diabetes and deafness (MIDD), typically associated with the mtDNA A3243G point mutation on tRNALeu gene. The common hypothesis to explain the link between the genotype and the phenotype is that the mutation might impair mitochondrial metabolism expressly required for beta cell functions. However, this assumption has not yet been tested. Methods: We used clonal osteosarcoma cytosolic hybrid cells (namely cybrids) harbouring mitochondria derived from MIDD patients and containing either exclusively wild-type or mutated (A3243G) mtDNA. According to the importance of mitochondrial metabolism in beta cells, we studied the impact of the mutation on key parameters by comparing stimulation of these cybrids by the main insulin secretagogue glucose and the mitochondrial substrate pyruvate. Results: Compared with control mtDNA from the same patient, the A3243G mutation markedly modified metabolic pathways leading to a high glycolytic rate (2.8-fold increase), increased lactate production (2.5-fold), and reduced glucose oxidation (−83%). We also observed impaired NADH responses (−56%), negligible mitochondrial membrane potential, and reduced, only transient ATP generation. Moreover, cybrid cells carrying patient-derived mutant mtDNA exhibited deranged cell calcium handling with increased cytosolic loads (1.4-fold higher), and elevated reactive oxygen species (2.6-fold increase) under glucose deprivation. Conclusions/interpretation: The present study demonstrates that the mtDNA A3243G mutation impairs crucial metabolic events required for proper cell functions, such as coupling of glucose recognition to insulin secretio

Thermal noise suppression: how much does it cost?

In order to stabilize the behavior of noisy systems, confining it around a desirable state, an effort is required to suppress the intrinsic noise. This noise suppression task entails a cost. For the important case of thermal noise in an overdamped system, we show that the minimum cost is achieved when the system control parameters are held constant: any additional deterministic or random modulation produces an increase of the cost. We discuss the implications of this phenomenon for those overdamped systems whose control parameters are intrinsically noisy, presenting a case study based on the example of a Brownian particle optically trapped in an oscillating potential.Comment: 6 page

Entropically-induced asymmetric passage times of charged tracers across corrugated channels

We analyze the diffusion of charged and neutral tracers suspended in an electrolyte embedded in a channel of varying cross section. Making use of systematic approximations, the diffusion equation governing the motion of tracers is mapped into an effective 1D equation describing the dynamics along the longitudinal axis of the channel where its varying-section is encoded as an effective entropic potential. This simplified approach allows us to characterize tracer diffusion under generic confinement by measuring their mean first passage time (MFPT). In particular, we show that the interplay between geometrical confinement and electrostatic interactions strongly affect the MFTP of tracers across corrugated channels hence leading to alternative means to control tracers translocation across charged pores. Finally, our results show that the MFPTs of a charged tracer in opposite directions along an asymmetric channel may differ We expect our results to be relevant for biological as well synthetic devices whose dynamics is controlled by the detection of diluted tracer

Fractional quantum Hall effect in CVD-grown graphene

We show the emergence of fractional quantum Hall states in dry-transferred chemical vapor deposition (CVD) derived graphene assembled into heterostructures for magnetic fields from below 3 T to 35 T. Effective composite-fermion filling factors up to $\nu^* = 4$ are visible and higher order composite-fermion states (with four flux quanta attached) start to emerge at the highest fields. Our results show that the quantum mobility of CVD-grown graphene is comparable to that of exfoliated graphene and, more specifically, that the $p/3$ fractional quantum Hall states have energy gaps of up to 30 K, well comparable to those observed in other silicon-gated devices based on exfoliated graphene.Comment: 6 pages, 4 figure

Growth of flat SrRuO3(111) thin films suitable as bottom electrodes in heterostructures

Thin film growth of ferroelectric or multiferroic materials on SrTiO3(111) with a buffer electrode has been hampered by the difficulty of growing flat electrodes on this polar orientation. We report on the growth and characterization of SrRuO3 thin films deposited by pulsed laser deposition on SrTiO3(111). We show that our SrRuO3(111) films are epitaxial and display magnetic bulk-like properties. Films presenting a thickness between 20 and 30nm are found to be very flat (with an RMS of about 0.5 nm) and therefore suitable as bottom electrodes in heterostructures.Comment: Only PDF. 14 pages including 4 color figure

Raman response of quantum critical ferroelectric pb-doped srtio3

A quantum paraelectric SrTiO3 is a material situated in close proximity to a quantum critical point (QCP) of ferroelectric transition in which the critical temperature to the ferroelectric state is suppressed down to 0 K. However, the understanding of the behavior of the phase transition in the vicinity of this point remains challenging. Using the concentration x of Pb in solid solution Sr1−x Pbx TiO3 (PSTx) as a tuning parameter and applying the combination of Raman and dielectric spectroscopy methods, we approach the QCP in PSTx and study the interplay of classical and quantum phenomena in the region of criticality. We obtain the critical temperature of PSTx and the evolution of the temperature-dependent dynamical properties of the system as a function of x to reveal the mechanism of the transition. We show that the ferroelectric transition occurs gradually through the emergence of the polar nanoregions inside the non-polar tetragonal phase with their further expansion on cooling. We also study the ferroelastic cubic-to-tetragonal structural transition, occurring at higher temperatures, and show that its properties are almost concentration-independent and not affected by the quantum criticality.Fil: Linnik, Ekaterina D.. Southern Federal University; RusiaFil: Mikheykin, Alexey S.. Southern Federal University; RusiaFil: Rubi, Diego. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes | Comisión Nacional de Energía Atómica. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología. Unidad Ejecutora Instituto de Nanociencia y Nanotecnología - Nodo Constituyentes; ArgentinaFil: Shirokov, Vladimir B.. No especifíca;Fil: Mezzane, Daoud. No especifíca;Fil: Kondovych, Svitlana V.. No especifíca;Fil: Lukyanchuk, Igor A.. No especifíca;Fil: Razumnaya, Anna G.. Southern Federal University; Rusi