940 research outputs found
Quasinormal modes of massive scalar fields in four-dimensional wormholes: Anomalous decay rate
In this work we consider a generalized Bronnikov-Ellis wormhole and the tideless Morris-Thorne wormhole and we study the propagation of massive scalar fields. We calculate the quasinormal frequencies using the Wentzel-Kramers-Brillouin method and the pseudospectral Chebyshev method and we show the presence of an anomalous decay rate for the quasinormal modes in the generalized Bronnikov-Ellis wormhole. However, such anomalous behavior is avoided for the fundamental mode in the Morris-Thorne wormhole background.This work is partially supported by ANID Chile through FONDECYT Grant No. 1220871 (P. A. G., and Y. V.). Á. R. is funded by the María Zambrano Contract No. ZAMBRANO21-25 (Spain)
Wigner Surmise For Domain Systems
In random matrix theory, the spacing distribution functions are
well fitted by the Wigner surmise and its generalizations. In this
approximation the spacing functions are completely described by the behavior of
the exact functions in the limits s->0 and s->infinity. Most non equilibrium
systems do not have analytical solutions for the spacing distribution and
correlation functions. Because of that, we explore the possibility to use the
Wigner surmise approximation in these systems. We found that this approximation
provides a first approach to the statistical behavior of complex systems, in
particular we use it to find an analytical approximation to the nearest
neighbor distribution of the annihilation random walk
Structure and application of antifreeze proteins from Antarctic bacteria
Indexación: Web of Science; Scopus.Background: Antifreeze proteins (AFPs) production is a survival strategy of psychrophiles in ice. These proteins have potential in frozen food industry avoiding the damage in the structure of animal or vegetal foods. Moreover, there is not much information regarding the interaction of Antarctic bacterial AFPs with ice, and new determinations are needed to understand the behaviour of these proteins at the water/ice interface. Results: Different Antarctic places were screened for antifreeze activity and microorganisms were selected for the presence of thermal hysteresis in their crude extracts. Isolates GU1.7.1, GU3.1.1, and AFP5.1 showed higher thermal hysteresis and were characterized using a polyphasic approach. Studies using cucumber and zucchini samples showed cellular protection when samples were treated with partially purified AFPs or a commercial AFP as was determined using toluidine blue O and neutral red staining. Additionally, genome analysis of these isolates revealed the presence of genes that encode for putative AFPs. Deduced amino acids sequences from GU3.1.1 (gu3A and gu3B) and AFP5.1 (afp5A) showed high similarity to reported AFPs which crystal structures are solved, allowing then generating homology models. Modelled proteins showed a triangular prism form similar to β-helix AFPs with a linear distribution of threonine residues at one side of the prism that could correspond to the putative ice binding side. The statistically best models were used to build a protein-water system. Molecular dynamics simulations were then performed to compare the antifreezing behaviour of these AFPs at the ice/water interface. Docking and molecular dynamics simulations revealed that gu3B could have the most efficient antifreezing behavior, but gu3A could have a higher affinity for ice. Conclusions: AFPs from Antarctic microorganisms GU1.7.1, GU3.1.1 and AFP5.1 protect cellular structures of frozen food showing a potential for frozen food industry. Modeled proteins possess a β-helix structure, and molecular docking analysis revealed the AFP gu3B could be the most efficient AFPs in order to avoid the formation of ice crystals, even when gu3A has a higher affinity for ice. By determining the interaction of AFPs at the ice/water interface, it will be possible to understand the process of adaptation of psychrophilic bacteria to Antarctic ice.https://microbialcellfactories.biomedcentral.com/articles/10.1186/s12934-017-0737-
Van Hove Singularities in disordered multichannel quantum wires and nanotubes
We present a theory for the van Hove singularity (VHS) in the tunneling
density of states (TDOS) of disordered multichannel quantum wires, in
particular multi-wall carbon nanotubes. We assume close-by gates which screen
off electron-electron interactions. Diagrammatic perturbation theory within a
non-crossing approximation yields analytical expressions governing the
disorder-induced broadening and shift of VHS's as new subbands are opened. This
problem is nontrivial because the (lowest-order) Born approximation breaks down
close to the VHS. Interestingly, compared to the bulk case, the boundary TDOS
shows drastically altered VHS, even in the clean limit.Comment: 4 pages, 2 figures, accepted with revisions in PR
Influence of the collision energy on the O(1D) + RH --> OH(X2Pi) + R (RH=CH4, C2H6, C3H8) Reaction Dynamics. A laser Induced Fluorescence and Quasiclassical Trajectory Study
The influence of the collision energy (ET) on the O(1D) + RH OH(X2H) + R (RH = CH4, C2H6, and C3H8) reaction dynamics has been studied, using the N2O photodissociation at 193 nm as O(1D) precursor (ET = 0.403 eV) and probing the OH v = 0 and 1 levels by LIF. A triatomic QCT study of the reaction with CH4 on a fully ab initio based analytical PES has also been performed, and a quite good agreement with the experimental OH rovibrational distributions has been obtained. Our experimental results are similar to those obtained when the O3 photodissociation is used to produce O(1D) (ET = 0.212 eV), as expected on the basis of the available energy in products and also from the QCT calculations. The P(v=0)/P(v= 1) populations ratio values reported for C2H6 and C3H8 in a very recent work (Wada and Obi, J. Phys. Chem. A 1998, 102, 3481), where the N2O was also used to generate O(1D), are probably largely underestimated. The rotational distributions obtained are similar to those obtained in other experiments, and a quite good agreement has been obtained for the spin-orbit and A-doublet populations. The reaction takes place near exclusively through the insertion of the O(1D) atom into a C-H bond below 0.6 eV, and the mechanism may be direct or nondirect (mainly through short-lived (CH3)OH collision complexes) with about the same probability. The OH vibrational distribution arising from the direct mechanism is inverted, while the nondirect one leads to a noninverted distribution. At higher ET, the abstraction mechanism also contributes appreciably to reactivity. © 2000 American Chemical Society
Particle collisons near a three-dimensional warped AdS black hole
In this paper we consider the warped AdS 3 black hole solution of topologically massive gravity with a negative cosmological constant, and we study the possibility that it acts as a particle accelerator by analyzing the energy in the center of mass (CM) frame of two colliding particles in the vicinity of its horizon, which is known as the Bañnados, Silk and West (BSW) process. Mainly, we show that the critical angular momentum (Lc) of the particle decreases when the warping parameter(ν) increases. Also, we show that despite the particle with Lc being able to exist for certain values of the conserved energy outside the horizon, it will never reach the event horizon; therefore, the black hole cannot act as a particle accelerator with arbitrarily high CM energy on the event horizon. However, such a particle could also exist inside the outer horizon, with the BSW process being possible on the inner horizon. On the other hand, for the extremal warped AdS 3 black hole, the particle with Lc and energy E could exist outside the event horizon and, the CM energy blows up on the event horizon if its conserved energy fulfills the condition E2>(ν2+3)l23(ν2-1), with the BSW process being possible
Monitoring of the morphologic reconstruction of deposited ablation products in laser irradiation of silicon
Using electron microscopy, atomic force microscopy, X-ray microanalysis, and IR spectroscopy, it was established that, in the regime of continuous laser irradiation of silicon at P = 170 W in different gaseous atmospheres with an oxygen impurity, SiOx composite films with a complex morphology form. The main components of ablation products are clusters that form during flight of ablation products and as a result of separation of SiOx-clusters from the zone of the irradiation channel. The roughness and density of the films depend on the heating temperature of the target surface and the type of deposited clusters
Silk-ELR co-recombinamer covered stents obtained by electrospinning
Producción CientíficaIn the field of tissue engineering the choice of materials is of great importance given the possibility
to use biocompatible polymers produced by means of biotechnology. A large number of synthetic
and natural materials have been used to this purpose and processed into scaffolds using
Electrospinning technique. Among materials that could be used for the fabrication of scaffold and
degradable membranes, natural polymers such as collagen, elastin or fibroin offer the possibility
to design structures strictly similar to the extracellular matrix (ECM). Biotechnology and genetic engineering
made possible the advent of a new class of biopolymers called protein-based polymers.
One example is represented by the silk-elastin-proteins that combine the elasticity and resilience of
elastin with the high tensile strength of silk-fibroin and display engineered bioactive sequences. In
this work, we use electrospinning technique to produce a fibrous scaffold made of the corecombinamer
Silk-ELR. Obtained fibres have been characterized from the morphological point of
view. Homogeneity and morphology have been explored using Scanning Electron Microscopy. A
thorough study regarding the influence of Voltage, flow rate and distance have been carried out to
determine the appropriate parameters to obtain the fibrous mats without defects and with a good
distribution of diameters. Cytocompatibility has also been in vitro tested. For the first time we use
the co-recombinamer Silk-ELR for the fabrication of a 2.5 angioplasty balloon coating. This structure
could be useful as a coated scaffold for the regeneration of intima layer of vessels.“THE GRAIL” (Tissue in Host Engineering Guided Regeneration of Arterial Intima Layer) projectEuropean Union’s ‘Seventh Framework’ Programme for research, technological development and demonstration (grant HEALTH.2011.1.4-2-278557)European Commission (NMP-2014- 646075, MSCA-ITN-2014-642687)Ministerio de Economía, Industria y Competitividad (grant PCIN-2015-010, MAT2015-68901-R, MAT2016- 78903-R)Junta de Castilla y León (VA015U16)Centro en Red de Medicina Regenerativa y Terapia Celular de Castilla y Leó
Expansion for the solutions of the Bogomolny equations on the torus
We show that the solutions of the Bogomolny equations for the Abelian Higgs
model on a two-dimensional torus, can be expanded in powers of a quantity
epsilon measuring the departure of the area from the critical area. This allows
a precise determination of the shape of the solutions for all magnetic fluxes
and arbitrary position of the Higgs field zeroes. The expansion is carried out
to 51 orders for a couple of representative cases, including the unit flux
case. We analyse the behaviour of the expansion in the limit of large areas, in
which case the solutions approach those on the plane. Our results suggest
convergence all the way up to infinite area.Comment: 26 pages, 8 figures, slightly revised version as published in JHE
A functional BH3 domain in an aquaporin from Leishmania infantum.
Despite the absence of sequences showing significant similarity to any of the members of the Bcl-2 family of proteins in protozoa, experiments carried out in yeast or trypanosomatids have demonstrated that ectopic expression of some of these members alters their response to different death stimuli. Because the BH3 domain is the smallest common signature in all the proteins of this family of apoptosis regulators and also because they are essential for molecular interactions between antagonistic members, we looked for sequences with significant similarity to the BH3 motif in the Leishmania infantum genome. Among the top scoring ones, we found the MYLALQNLGDEV amino-acid stretch at the C terminus of a previously described aquaporin, now renamed as Li-BH3AQP. This motif is highly conserved in homologous proteins from other species of the Leishmania genus. The association of Li-BH3AQP with human Bcl-XL was demonstrated by both co-immunoprecipitation and yeast two-hybrid experiments. Ectopic expression of Li-BH3AQP reduced viability of HeLa cells and this deleterious effect was abrogated by the simultaneous overexpression of Bcl-XL. Although we were not able to demonstrate a reduction in parasite viability when the protein was overexpressed in Leishmania promastigotes, a prodeath effect could be observed when the parasites overexpressing Li-BH3AQP were treated with staurosporine or antimycin A. Surprisingly, these parasites were more resistant, compared with wild-type parasites, to hypotonic stress or nutrient deprivation. The prodeath activity was abolished upon replacement of two highly conserved amino acids in this BH3 domain. Taken together, these results point to Li-BH3AQP as the first non-enzymatic protein ever described in trypanosomatids that is involved in cell death
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