2,864 research outputs found
Precursors and Main-bursts of Gamma Ray Bursts in a Hypernova Scenario
We investigate a "hypernova" model for gamma-ray bursts (GRBs), i.e., massive
C+O star model with relativistic jets. In this model, non-thermal precursors
can be produced by the "first" relativistic shell ejected from the star. Main
GRBs are produced behind the "first"-shell by the collisions of several
relativistic shells. They become visible to distant observers after the
colliding region becomes optically thin. We examine six selected conditions
using relativistic hydrodynamical simulations and simple analyses.
Interestingly, our simulations show that sub-relativistic jets
from the central engine is sufficient to produce highly-relativistic shells. We find that the relativistic shells from such a star can
reproduce observed GRBs with certain conditions. Two conditions are especially
important. One is the sufficiently long duration of the central engine \gsim
100 sec. The other is the existence of a dense-shell somewhere behind the
"first"-shell. Under these conditions, both the existence and non-existence of
precursors, and long delay between precursors and main GRBs can be explained.Comment: 8 pages, 2 figures. Accepted for publication in the Astrophysical
Journal (Letters
Dynamical Susceptibility in KDP-type Crysals above and below Tc II
The path probability method (PPM) in the tetrahedron-cactus approximation is
applied to the Slater-Takagi model with dipole-dipole interaction for
KH2PO4-type hydrogen-bonded ferroelectric crystals in order to derive a small
dip structure in the real part of dynamical susceptibility observed at the
transition temperature Tc. The dip structure can be ascribed to finite
relaxation times of electric dipole moments responsible for the first order
transition with contrast to the critical slowing down in the second order
transition. The light scattering intensity which is related to the imaginary
part of dynamical susceptibility is also calculated above and below the
transition temperature and the obtained central peak structure is consistent
with polarization fluctuation modes in Raman scattering experiments.Comment: 8 pages, 11 figure
Review of CFD Guidelines for Dispersion Modeling
This is the review of CFD (Computational Fluid Dynamics) guidelines for dispersion modeling in the USA, Japan and Germany. Most parts of this review are based on the short report of the special meeting on CFD Guidelines held at the International Symposium on Computational Wind Engineering (CWE2014), University of Hamburg, June 2014. The objective of this meeting was to introduce and discuss the action program to make worldwide guidelines of CFD gas-dispersion modeling. The following six gas-dispersion guidelines including Verification and Validation (V&V) schemes are introduced by each author; (1) US CFD guidelines; (2) COST/ES1006; (3) German VDI (Verein Deutscher Ingenieure) guidelines; (4) Atomic Energy Society of Japan; (5) Japan Society of Atmospheric Environment; (6) Architectural Institute of Japan. All guidelines were summarized in the same format table shown in the main chapters in order to compare them with each other. In addition to the summary of guidelines, the overview of V&V schemes and many guidelines of CFD modeling in the USA are explained
Refining the formation and early evolution of the Eastern North American Margin : new insights from multiscale magnetic anomaly analyses
Author Posting. © American Geophysical Union, 2017. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 122 (2017): 8724–8748, doi:10.1002/2017JB014308.To investigate the oceanic lithosphere formation and early seafloor spreading history of the North Atlantic Ocean, we examine multiscale magnetic anomaly data from the Jurassic/Early Cretaceous age Eastern North American Margin (ENAM) between 31 and 40°N. We integrate newly acquired sea surface magnetic anomaly and seismic reflection data with publicly available aeromagnetic and composite magnetic anomaly grids, satellite-derived gravity anomaly, and satellite-derived and shipboard bathymetry data. We evaluate these data sets to (1) refine magnetic anomaly correlations throughout the ENAM and assign updated ages and chron numbers to M0–M25 and eight pre-M25 anomalies; (2) identify five correlatable magnetic anomalies between the East Coast Magnetic Anomaly (ECMA) and Blake Spur Magnetic Anomaly (BSMA), which may document the earliest Atlantic seafloor spreading or synrift magmatism; (3) suggest preexisting margin structure and rifting segmentation may have influenced the seafloor spreading regimes in the Atlantic Jurassic Quiet Zone (JQZ); (4) suggest that, if the BSMA source is oceanic crust, the BSMA may be M series magnetic anomaly M42 (~168.5 Ma); (5) examine the along and across margin variation in seafloor spreading rates and spreading center orientations from the BSMA to M25, suggesting asymmetric crustal accretion accommodated the straightening of the ridge from the bend in the ECMA to the more linear M25; and (6) observe anomalously high-amplitude magnetic anomalies near the Hudson Fan, which may be related to a short-lived propagating rift segment that could have helped accommodate the crustal alignment during the early Atlantic opening.J. A. G. and
M. T. thank the Department of Geology
and Geophysics at Texas A&M
University for their support of J. A. G.’s
PhD program. M. T. and M. R. K. thank
the Department of Earth and
Environmental Sciences at Michigan
State University for their support during
M. R. K.’s MS thesis project, included in
this study.2018-05-1
Mucoadhesive chitosan-coated PLGA nanoparticles for oral delivery of ferulic acid
This paper describes the development and in vitro evaluation of poly(lactic-co-glycolic acid) (PLGA) nanoparticles coated with chitosan (CS) for oral delivery of ferulic acid (FA). Nanoparticles were obtained by an emulsion evaporation technique and characterized. Furthermore, we evaluated the scavenging activity over hypochlorous acid (HOCl), the cytotoxicity over tumour cells and the in vitro intestinal permeability. Nanoparticles were spherical with a mean diameter of 242 nm, positive zeta potential and 50% of encapsulation efficiency. The in vitro release in phosphate buffered saline (PBS) (pH 7.4) demonstrated a prolonged and biphasic profile diffusion-controlled. In simulated gastrointestinal fluids, about 15% of FA was released in gastric fluid and a negligible release was observed in the intestinal fluid. In the HOCl scavenging activity and cytotoxicity over B16-F10 and HeLa cells, FA-loaded nanoparticles presented the same efficacy of the free drug. Besides, in the antioxidant and cytotoxic assay, CS contributed to FA effects. In the intestinal permeability study, FA-loaded nanoparticles exhibited a permeation of 6% through the Caco-2 monolayer and 20% through the Caco-2/HT29-MTX/Raji B co-culture. CS-coated PLGA nanoparticles are promising carriers for oral delivery of FA.This study was supported by the CAPES (Coordenação de Aperfeiçoamento de Pessoal de Ńıvel Superior) in the form of doctoral fellowship for I.A. de Lima, Fundação Araucária (17/17) CNPq (Conselho Nacional de Desenvolvimento Científico e tecnológico) and Finep (Financiadora de Estudos and Projetos) for partial financial support
Mucoadhesive chitosan-coated PLGA nanoparticles for oral delivery of ferulic acid
This paper describes the development and in vitro evaluation of poly(lactic-co-glycolic acid) (PLGA) nanoparticles coated with chitosan (CS) for oral delivery of ferulic acid (FA). Nanoparticles were obtained by an emulsion evaporation technique and characterized. Furthermore, we evaluated the scavenging activity over hypochlorous acid (HOCl), the cytotoxicity over tumour cells and the in vitro intestinal permeability. Nanoparticles were spherical with a mean diameter of 242 nm, positive zeta potential and 50% of encapsulation efficiency. The in vitro release in phosphate buffered saline (PBS) (pH 7.4) demonstrated a prolonged and biphasic profile diffusion-controlled. In simulated gastrointestinal fluids, about 15% of FA was released in gastric fluid and a negligible release was observed in the intestinal fluid. In the HOCl scavenging activity and cytotoxicity over B16-F10 and HeLa cells, FA-loaded nanoparticles presented the same efficacy of the free drug. Besides, in the antioxidant and cytotoxic assay, CS contributed to FA effects. In the intestinal permeability study, FA-loaded nanoparticles exhibited a permeation of 6% through the Caco-2 monolayer and 20% through the Caco-2/HT29-MTX/Raji B co-culture. CS-coated PLGA nanoparticles are promising carriers for oral delivery of FA.This study was supported by the CAPES (Coordenação de Aperfeiçoamento de Pessoal de Ńıvel Superior) in the form of doctoral fellowship for I.A. de Lima, Fundação Araucária (17/17) CNPq (Conselho Nacional de Desenvolvimento Científico e tecnológico) and Finep (Financiadora de Estudos and Projetos) for partial financial support
Ferroelectric switching in epitaxial GeTe films
In this paper, using a resonance-enhanced piezoresponse force microscopy approach
supported by density functional theory computer simulations, we have demonstrated
the ferroelectric switching in epitaxial GeTe films. It has been shown that in films with
thickness on the order of several nanometers reversible reorientation of polarization
occurs due to swapping of the shorter and longer Ge-Te bonds in the interior of the
material. It is also hinted that for ultra thin films consisting of just several atomic
layers weakly bonded to the substrate, ferroelectric switching may proceed through
exchange of Ge and Te planes within individual GeTe layers
(2E)-2-(2,4-Dichlorophenylsulfonyl)-3-(4-methylanilino)-3-(methylsulfanyl)acrylonitrile
The title compound, C17H14Cl2N2O2S2, and the 3-methoxyanilino analogue reported in the preceding paper have been used as starting materials to develop benzothiazine derivatives with antimalarial activity. The molecule displays an E (trans) configuration about the central double bond. Due to conjugation in the C=C—C N group, the putative single bond shows a significant shortening [1.418 (3) Å]. The molecule has a six-membered ring involving an intramolecular N—H⋯O(sulfonyl) bond, which is an example of resonance-assisted hydrogen bonding. In the crystal structure, bonds of the C—H⋯O(sulfonyl) and C—H⋯N(cyano) types form double layers of molecules parallel to (01). Within these layers there are π–π interactions between benzene rings of pairs of centrosymmetrically related molecules, with distances of 3.7969 (12) Å between centroids. C—H⋯π interactions are also present
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