629 research outputs found
Electron-positron annihilation into two photons in an intense plane-wave field
The process of electron-positron annihilation into two photons in the
presence of an intense classical plane wave of an arbitrary shape is
investigated analytically by employing light-cone quantization and by taking
into account the effects of the plane wave exactly. We introduce a general
description of second-order 2-to-2 scattering processes in a plane-wave
background field, indicating the necessity of considering the localization of
the colliding particles and achieving that by means of wave packets. We define
a local cross section in the background field, which generalizes the vacuum
cross section and which, though not being directly an observable, allows for a
comparison between the results in the plane wave and in vacuum without relying
on the shape of the incoming wave packets. Two possible cascade or two-step
channels have been identified in the annihilation process and an alternative
way of representing the two-step and one-step contributions via a "virtuality"
integral has been found. Finally, we compute the total local cross section to
leading order in the coupling between the electron-positron field and the
quantized photon field, excluding the interference between the two
leading-order diagrams arising from the exchange of the two final photons, and
express it in a relatively compact form. In contrast to processes in a
background field initiated by a single particle, the pair annihilation into two
photons, in fact, also occurs in vacuum. Our result naturally embeds the vacuum
part and reduces to the vacuum expression, known in the literature, in the case
of a vanishing laser field.Comment: 26 pages, 2 figure
Características distintivas do apoio administrativo e legal à segurança nacional nos EUA e na Rússia: fundamentos conceituais
This article is devoted to a comparative analysis of the experience of strategic administrative and legal regulation and ensuring national security in the US and Russia. It is established and systematized the distinctive features of the Western (North American) and Eastern (Russian) approaches to the issues of strategic planning and development of policy documents in this area. It is defined common approaches to understanding national security in the US and Russia.Este artículo está dedicado a un análisis comparativo de la experiencia de la regulación administrativa y legal estratégica y a garantizar la seguridad nacional en los EE. UU. Y Rusia. Se establecen y sistematizan las características distintivas de los enfoques occidental (norteamericano) y oriental (ruso) a los temas de planificación estratégica y desarrollo de documentos de políticas en esta área. Se definen enfoques comunes para entender la seguridad nacional en los EE. UU. Y RusiaEste artigo é dedicado a uma análise comparativa da experiência de regulamentação administrativa e legal estratégica e garantindo a segurança nacional nos EUA e na Rússia. Estabelece-se e sistematiza-se as características distintivas das abordagens ocidental (norte-americana) e oriental (russa) para as questões de planejamento estratégico e desenvolvimento de documentos de política nessa área. São definidas abordagens comuns para entender a segurança nacional nos EUA e na Rússia
Loss of Melanoregulin (MREG) Enhances Cathepsin-D Secretion by the Retinal Pigment Epithelium
Cathepsin-D (Cat-D) is a major proteolytic enzyme in phagocytic cells. In the retinal pigment epithelium (RPE), it is responsible for the daily degradation of photoreceptor outer segments (POSs) to maintain retinal homeostasis. Melanoregulin (MREG)-mediated loss of phagocytic capacity has been linked to diminished intracellular Cat-D activity. Here, we demonstrate that loss of MREG enhances the secretion of intermediate Cat-D (48 kDa), resulting in a net enhancement of extracellular Cat-D activity. These results suggest that MREG is required to maintain Cat-D homeostasis in the RPE and likely plays a protective role in retinal health. In this regard, in the Mreg dsu/dsu mouse, we observe increased basal laminin. Loss of the Mreg dsu allele is not lethal and therefore leads to slow age-dependent changes in the RPE. Thus, we propose that this model will allow us to study potential dysregulatory functions of Cat-D in retinal disease
Loss of Melanoregulin (MREG) Enhances Cathepsin-D Secretion by the Retinal Pigment Epithelium
Abstract Cathepsin-D (Cat-D) is a major proteolytic enzyme in phagocytic cells. In the retinal pigment epithelium (RPE), it is responsible for the daily degradation of photoreceptor outer segments (POSs) to maintain retinal homeostasis. Melanoregulin (MREG)-mediated loss of phagocytic capacity has been linked to diminished intracellular Cat-D activity. Here, we demonstrate that loss of MREG enhances the secretion of intermediate Cat-D (48 kDa), resulting in a net enhancement of extracellular Cat-D activity. These results suggest that MREG is required to maintain Cat-D homeostasis in the RPE and likely plays a protective role in retinal health. In this regard, in the Mreg dsu/dsu mouse, we observe increased basal laminin. Loss of the Mreg dsu allele is not lethal and therefore leads to slow age-dependent changes in the RPE. Thus, we propose that this model will allow us to study potential dysregulatory functions of Cat-D in retinal disease. Copyright © Cambridge University Press, 2013
The Contribution of Melanoregulin to Microtubule-Associated Protein 1 Light Chain 3 (LC3) Associated Phagocytosis in Retinal Pigment Epithelium
A main requisite in the phagocytosis of ingested material is a coordinated series of maturation steps which lead to the degradation of ingested cargo. Photoreceptor outer segment (POS) renewal involves phagocytosis of the distal disk membranes by the retinal pigment epithelium (RPE). Previously, we identified melanoregulin (MREG) as an intracellular cargo-sorting protein required for the degradation of POS disks. Here, we provide evidence that MREG-dependent processing links both autophagic and phagocytic processes in LC3-associated phagocytosis (LAP). Ingested POS phagosomes are associated with endogenous LC3 and MREG. The LC3 association with POSs exhibited properties of LAP; it was independent of rapamycin pretreatment, but dependent on Atg5. Loss of MREG resulted in a decrease in the extent of LC3-POS association. Studies using DQ™-BSA suggest that loss of MREG does not compromise the association and fusion of LC3-positive phagosomes with lysosomes. Furthermore, the mechanism of MREG action is likely through a protein complex that includes LC3, as determined by colocalization and immunoprecipitation in both RPE cells and macrophages. We posit that MREG participates in coordinating the association of phagosomes with LC3 for content degradation with the loss of MREG leading to phagosome accumulation. © 2014, Springer Science+Business Media New York
Collective Modes of Tri-Nuclear Molecules
A geometrical model for tri-nuclear molecules is presented. An analytical
solution is obtained provided the nuclei, which are taken to be prolately
deformed, are connected in line to each other. Furthermore, the tri-nuclear
molecule is composed of two heavy and one light cluster, the later sandwiched
between the two heavy clusters. A basis is constructed in which Hamiltonians of
more general configurations can be diagonalized. In the calculation of the
interaction between the clusters higher multipole deformations are taken into
account, including the hexadecupole one. A repulsive nuclear core is introduced
in the potential in order to insure a quasi-stable configuration of the system.
The model is applied to three nuclear molecules, namely Sr + Be +
Ba, Mo + Be + Te and Ru + Be +
Sn.Comment: 24 pages, 9 figure
The Contribution of Melanoregulin to Microtubule-Associated Protein 1 Light Chain 3 (LC3) Associated Phagocytosis in Retinal Pigment Epithelium
A main requisite in the phagocytosis of ingestedmaterial is a coordinated series of maturation steps which leadto the degradation of ingested cargo. Photoreceptor outersegment (POS) renewal involves phagocytosis of the distaldisk membranes by the retinal pigment epithelium (RPE).Previously, we identified melanoregulin (MREG) as an intra-cellular cargo-sorting protein required for the degradation ofPOS disks. Here, we provide evidence that MREG-dependentprocessing links both autophagic and phagocytic processes inLC3-associated phagocytosis (LAP). Ingested POSphagosomes are associated with endogenous LC3 andMREG. The LC3 association with POSs exhibited propertiesof LAP; it was independent of rapamycin pretreatment, butdependent on Atg5. Loss of MREG resulted in a decrease inthe extent of LC3-POS association. Studies using DQ™-BSAsuggest that loss of MREG does not compromise the associ-ation and fusion of LC3-positive phagosomes with lysosomes.Furthermore, the mechanism of MREG action is likelythrough a protein complex that includes LC3, as determinedby colocalization and immunoprecipitation in both RPE cellsand macrophages. We posit that MREG participates incoordinating the association of phagosomes with LC3 forcontent degradation with the loss of MREG leading tophagosome accumulation
A Global Potential Analysis of the O+Si Reaction Using a New Type of Coupling Potential
A new approach has been used to explain the experimental data for the
O+Si system over a wide energy range in the laboratory system
from 29.0 to 142.5 MeV. A number of serious problems has continued to plague
the study of this system for a couple of decades. The explanation of anomalous
large angle scattering data; the reproduction of the oscillatory structure near
the Coulomb barrier; the out-of-phase problem between theoretical predictions
and experimental data; the consistent description of angular distributions
together with excitation functions data are just some of these problems. These
are long standing problems that have persisted over the years and do represent
a challenge calling for a consistent framework to resolve these difficulties
within a unified approach. Traditional frameworks have failed to describe these
phenomena within a single model and have so far only offered different
approaches where these difficulties are investigated separately from one
another. The present work offers a plausible framework where all these
difficulties are investigated and answered. Not only it improves the
simultaneous fits to the data of these diverse observables, achieving this
within a unified approach over a wide energy range, but it departs for its
coupling potential from the standard formulation. This new feature is shown to
improve consistently the agreement with the experimental data and has made
major improvement on all the previous coupled-channels calculations for this
system.Comment: 21 pages with 12 figure
- …