Non-linear metric perturbation enhancement of primordial gravitational waves

We present the evolution of the full set of Einstein equations during preheating after inflation. We study a generic supersymmetric model of hybrid inflation, integrating fields and metric fluctuations in a 3-dimensional lattice. We take initial conditions consistent with Eintein's constraint equations. The induced preheating of the metric fluctuations is not large enough to backreact onto the fields, but preheating of the scalar modes does affect the evolution of vector and tensor modes. In particular, they do enhance the induced stochastic background of gravitational waves during preheating, giving an energy density in general an order of magnitude larger than that obtained by evolving the tensors fluctuations in an homogeneous background metric. This enhancement can improve the expectations for detection by planned gravitational waves observatories.Comment: 5 pages, 4 eps figures, matches Phys. Rev. Lett. versio

Effect of acylation on the interaction of the N-Terminal segment of pulmonary surfactant protein SP-C with phospholipid membranes.

AbstractSP-C, the smallest pulmonary surfactant protein, is required for the formation and stability of surface-active films at the air–liquid interface in the lung. The protein consists of a hydrophobic transmembrane α-helix and a cationic N-terminal segment containing palmitoylated cysteines. Recent evidence suggests that the N-terminal segment is of critical importance for SP-C function. In the present work, the role of palmitoylation in modulating the lipid–protein interactions of the N-terminal segment of SP-C has been studied by analyzing the effect of palmitoylated and non-palmitoylated synthetic peptides designed to mimic the N-terminal segment on the dynamic properties of phospholipid bilayers, recorded by spin-label electron spin resonance (ESR) spectroscopy. Both palmitoylated and non-palmitoylated peptides decrease the mobility of phosphatidylcholine (5-PCSL) and phosphatidylglycerol (5-PGSL) spin probes in dipalmitoylphosphatidylcholine (DPPC) or dipalmitoylphosphatidylglycerol (DPPG) bilayers. In zwitterionic DPPC membranes, both peptides have a greater effect at temperatures below than above the main gel-to-liquid-crystalline phase transition, the palmitoylated peptide inducing greater immobilisation of the lipid than does the non-palmitoylated form. In anionic DPPG membranes, both palmitoylated and non-palmitoylated peptides have similar immobilizing effects, probably dominated by electrostatic interactions. Both palmitoylated and non-palmitoylated peptides have effects comparable to whole native SP-C, as regards improving the gel phase solubility of phospholipid spin probes and increasing the polarity of the bilayer surface monitored by pK shifts of fatty acid spin probes. This indicates that a significant part of the perturbing properties of SP-C in phospholipid bilayers is mediated by interactions of the N-terminal segment. The effect of SP-C N-terminal peptides on the chain flexibility gradient of DPPC and DPPG bilayers is consistent with the existence of a peptide-promoted interdigitated phase at temperatures below the main gel-to-liquid-crystalline phase transition. The palmitoylated peptide, but not the non-palmitoylated version, is able to stably segregate interdigitated and non-interdigitated populations of phospholipids in DPPC bilayers. This feature suggests that the palmitoylated N-terminal segment stabilizes ordered domains such as those containing interdigitated lipids. We propose that palmitoylation may be important to promote and facilitate association of SP-C and SP-C-containing membranes with ordered lipid structures such as those potentially existing in highly compressed states of the interfacial surfactant film

Bioethanol production from autohydrolyzed Sargassum muticum

Currently, the high demand of energy has led to the seek of new renewable sources, cutting down with fossil fuels. An interesting and novel way may be the use of macoralgae as raw material to obtain third generation bioethanol. Sargassum muticum is an invasive seaweed highly spread in Asia, Europe and America, which has not been commercially used yet. It has an abundant quantity of polysaccharides which can be used in the production of biofuels. In order to employ them, it is necessary to pretreat the material, and the hydrothermal treatments (as autohydrolysis) have demonstrated to be highly effective, simple, environmentally friendly and economic. In this work, the study of the autohydrolysis of Sargassum muticum has been studied. Consequently, Simultaneous Saccharification and Fermentation took place, using different industrial strains of Saccharomyces cerevisiae and two type of experiments: i) using only the autohydrolyzed solid phase, ii) using the liquid and solid phase from the autohydrolysis procedure.info:eu-repo/semantics/publishedVersio

Enhancement of the enzymatic hydrolysis of Paulownia wood using non-ionic surfactant

The abundance of lignocellulosic biomass from various industries provides a great potential feedstock for the production of value-added products. This lignocellulosic materials can be enzymatically hydrolyzed into sugars for the production of biofuels and biomaterials. However, the presence of lignin is inhibitory, becoming a major obstacle for enzymatic hydrolysis of lignocellulosic materials conducted in high solid loading. This is because the lignin acts as a protective barrier for cellulose and, thus, restricts the accessibility of the enzyme to the cellulose. Addition of surfactants, polymers, and noncatalytic proteins can improve the enzymatic hydrolysis of lignocellulosic materials by blocking the exposed lignin surfaces. In this work, the optimization of enzymatic hydrolysis of Paulownia wood was tested, evaluating the influence of: i) autohydrolysis pretreatment under non-isothermal conditions (TMAX: 210ºC, 220ºC and 230ºC), ii) solid loading (Consistency: 10, 13 and 16 %), iii) enzyme substrate ratio (ESR: 8, 12 and 16 UPF/g Paulownia), and iv) the addition of nonionic surfactant Tween 20 (0, 1.5 and 3 g/L). The enzyme employed was Cellic CTec2 (Novozymes) with an enzyme activity of 160 UFP/mL. This work suggested that autohydrolysis pretreatment could improve the enzymatic hydrolysis significantly and the addition of Tween 20 could reduce the hydrolysis time and enzyme dosage.info:eu-repo/semantics/publishedVersio

Multiple Lambda cosmology: dark fluid with time-dependent equation of state as classical analog of cosmological landscape

We discuss FRW universe with time-dependent EoS dark fluid which leads to multiple de Sitter space. This model (as well as its scalar-tensor version) may be considered as some classical analog of cosmological landscape. The universe expansion history may look as transitions between different deSitter eras what suggests the interesting solution for cosmological constant problem. For specific time-dependent EoS dark fluid the possibility of transitions between universe regions with positive and negative cosmological constant is also established.Comment: LaTeX file, 8 pages, no figure, version to appear in PL

Deux approches pour modifier les activités de résolution de problèmes en physique dans l'enseignement secondaire : une tentative de synthèse

Dans cet article les AA. présentent un cadre théorique pour analyser les activités de résolution de problèmes " papier crayon " issu de la confrontation des recherches menées par deux équipes (Gil Perez D. et Martinez Torregrossa J. en Espagne et Caillot M. et Dumas-Carré A. en France) dans le domaine de la physique. Le point de départ commun des deux équipes est de considérer que l'échec généralisé des élèves ne peut être imputé seulement (ni principalement) à des caractéristiques ou des lacunes des élèves, mais que la plus grande responsabilité doit être cherchée du côté de la didactique habituelle. Ce qui doit être remis en question de façon prioritaire est la conception même des activités de résolution de problèmes. Cette remise en question de la conception didactique commence par une interrogation sur le concept de problème lui-même. De même, le comportement habituellement retenu comme modèle (celui de l'expert) est remis en question| le comportement proposé comme modèle est celui du chercheur scientifiqu

Matching microscopic and macroscopic responses in glasses

We first reproduce on the Janus and Janus II computers a milestone experiment that measures the spin-glass coherence length through the lowering of free-energy barriers induced by the Zeeman effect. Secondly we determine the scaling behavior that allows a quantitative analysis of a new experiment reported in the companion Letter [S. Guchhait and R. Orbach, Phys. Rev. Lett. 118, 157203 (2017)]. The value of the coherence length estimated through the analysis of microscopic correlation functions turns out to be quantitatively consistent with its measurement through macroscopic response functions. Further, non-linear susceptibilities, recently measured in glass-forming liquids, scale as powers of the same microscopic length.Comment: 6 pages, 4 figure

Critical Behavior of Three-Dimensional Disordered Potts Models with Many States

We study the 3D Disordered Potts Model with p=5 and p=6. Our numerical simulations (that severely slow down for increasing p) detect a very clear spin glass phase transition. We evaluate the critical exponents and the critical value of the temperature, and we use known results at lower $p$ values to discuss how they evolve for increasing p. We do not find any sign of the presence of a transition to a ferromagnetic regime.Comment: 9 pages and 9 Postscript figures. Final version published in J. Stat. Mec

The Mpemba effect in spin glasses is a persistent memory effect

The Mpemba effect occurs when a hot system cools faster than an initially colder one, when both are refrigerated in the same thermal reservoir. Using the custom built supercomputer Janus II, we study the Mpemba effect in spin glasses and show that it is a non-equilibrium process, governed by the coherence length \xi of the system. The effect occurs when the bath temperature lies in the glassy phase, but it is not necessary for the thermal protocol to cross the critical temperature. In fact, the Mpemba effect follows from a strong relationship between the internal energy and \xi that turns out to be a sure-tell sign of being in the glassy phase. Thus, the Mpemba effect presents itself as an intriguing new avenue for the experimental study of the coherence length in supercooled liquids and other glass formers.Comment: Version accepted for publication in PNAS. 6 pages, 7 figure