1,351 research outputs found
Wandering globular clusters: the first dwarf galaxies in the universe?
In the last decade we witness an advent of new types of dwarf stellar systems
in cluding ultra-compact dwarfs, ultra-faint dwarf spheroidals, and exotic
globular clusters, breaking the old simple paradigm for dwarf galaxies and
globular clusters. These objects become more intriguing, and understanding of
these new findings be comes more challenging. Recently we discovered a new type
of large scale structure in the Virgo cluster of galaxies: it is composed of
globular clusters. Globular clusters in Virgo are found wandering between
galaxies (intracluster globular clusters) as well as in galaxies. These
intracluster globular clusters fill a significant fraction in the area of the
Virgo cluster and they are dominated by blue globular clusters. These
intracluster globular clusters may be closely related with the first dwarf
galaxies in the universe.Comment: 6 pages, 3 figures, Conference Proceedings: "A Universe of Dwarf
Galaxies", 14-18 June 2010, Lyon, Franc
Efficacy and tolerability of the Galanin Analog NAX 5055 in the multiple-hit rat model of symptomatic infantile spasms
Infantile spasms are seizures manifesting in infantile epileptic encephalopathies that are associated with poor epilepsy and cognitive outcomes. The current therapies are not always effective or are associated with serious side effects. Early cessation of spasms has been proposed to improve long-term outcomes. To identify new therapies for infantile spasms with rapid suppression of spasms, we are using the multiple-hit rat model of infantile spasms, which is a model of refractory infantile spasms. Here, we are testing the efficacy and tolerability of a single dose of the galanin receptor 1 preferring analog, NAX 5055, in the multiple-hit model of spasms. To induce the model, postnatal day 3 (PN3) male Sprague-Dawley rats underwent right intracerebral infusions of doxorubicin and lipopolysaccharide; p-chlorophenylalanine was then injected intraperitoneally (i.p.) at PN5. After the onset of spasms at PN4, 11-14 rats/group were injected i.p. with either NAX 5055 (0.5, 1, 2, or 4mg/kg) or vehicle. Video monitoring for spasms included a 1h pre-injection period, followed by 5h of recording post-injection, and two 2h sessions on PN5. The study was conducted in a randomized, blinded manner. Neurodevelopmental reflexes were assessed daily as well as at 2h after injection. Respiratory function, heart rate, pulse distension, oximetry and blood glucose were measured 4h after injection. The relative expression of GalR1 and GalR2 mRNA over β-actin in the cerebral cortex and hippocampus was determined with real time reverse transcription polymerase chain reaction. There was no acute effect of NAX 5055 on spasm frequency after the single dose of NAX 5055 (n=11-13 rats/group, following exclusions). Neurodevelopmental reflexes, vital signs, blood glucose measured 4h post-injection, and survival were not affected. A reduction in pulse and breath distention of unclear clinical significance was observed with the 7mg/kg NAX 5055 dose. GalR1 mRNA was present in the cerebral cortex and hippocampus of PN4 and adult rats. The hippocampal - but not the cortical - GalR1 mRNA expression was significantly lower in PN4 pups than in adults. GalR1 mRNA was also at least 20 times less abundant in the PN4 cortex than GalR2 mRNA. In conclusion, a single dose of NAX 5055 has no acute efficacy on spasms or toxicity in the multiple hit rat model of medically refractory infantile spasms. Our findings cannot exclude the possibility that repetitive NAX 5055 administration may show efficacy on spasms. The higher expression of GalR2 in the PN4 cortex suggests that GalR2-preferring analogs may be of interest to test for efficacy on spasms
Eruptions of Magnetic Ropes in Two Homologous Solar Events on 2002 June 1 and 2: a Key to Understanding of an Enigmatic Flare
The goal of this paper is to understand the drivers, configurations, and
scenarios of two similar eruptive events, which occurred in the same solar
active region 9973 on 2002 June 1 and 2. The June 2 event was previously
studied by Sui, Holman, and Dennis (2006, 2008), who concluded that it was
challenging for popular flare models. Using multi-spectral data, we analyze a
combination of the two events. Each of the events exhibited an evolving
cusp-like feature. We have revealed that these apparent ``cusps'' were most
likely mimicked by twisted magnetic flux ropes, but unlikely to be related to
the inverted Y-like magnetic configuration in the standard flare model. The
ropes originated inside a funnel-like magnetic domain whose base was bounded by
an EUV ring structure, and the top was associated with a coronal null point.
The ropes appear to be the major drivers for the events, but their rise was not
triggered by reconnection in the coronal null point. We propose a scenario and
a three-dimensional scheme for these events in which the filament eruptions and
flares were caused by interaction of the ropes.Comment: 22 pages, 11 figure
In vitro evaluation of electrospun blends of gelatin and PCL for application as a partial thickness corneal graft
The advent of innovative surgical procedures utilizing partial thickness corneal grafts has created a need for the development of synthetic implants to recreate corneal stromal tissue. This work evaluates electrospun gelatin and polycaprolactone (PCL) scaffolds as a potential biomaterial suitable for use in regeneration of corneal stromal tissue. Electrospun gelatin has been used for many years in tissue engineering, however, post‐production modification, such as crosslinking, is usually required to mechanically strengthen such scaffolds. This paper aims therefore to compare glutaraldehyde (GA) cross‐linked electrospun gelatin scaffolds with electrospun blends of gelatin and PCL at different ratios. Scaffolds were fabricated using electrospinning and characterized by scanning electron microscopy, Attenuated Total Reflectance‐Fourier Transform Infrared Spectroscopy (ATR‐FTIR), and tensile testing. To evaluate biocompatibility, primary human corneal stromal cells (hCSC) were seeded upon the scaffolds to assess adherence, proliferation and phenotype. Results demonstrated that scaffolds fabricated from mixtures of gelatin and PCL showed increased mechanical strength and plasticity compared to scaffolds fabricated from GA cross‐linked gelatin alone. In addition, scaffolds fabricated from PCL and gelatin showed comparable support of hCSC adhesion and proliferation. In conclusion, blended mixtures of gelatin and PCL can be considered as an option in the selection of corneal repair materials in the future
Coronal Shock Waves, EUV waves, and their Relation to CMEs. II. Modeling MHD Shock Wave Propagation Along the Solar Surface, Using Nonlinear Geometrical Acoustics
We model the propagation of a coronal shock wave, using nonlinear geometrical
acoustics. The method is based on the Wentzel-Kramers-Brillouin (WKB) approach
and takes into account the main properties of nonlinear waves: i) dependence of
the wave front velocity on the wave amplitude, ii) nonlinear dissipation of the
wave energy, and iii) progressive increase in the duration of solitary shock
waves. We address the method in detail and present results of the modeling of
the propagation of shock-associated extreme-ultraviolet (EUV) waves as well as
Moreton waves along the solar surface in the simplest solar corona model. The
calculations reveal deceleration and lengthening of the waves. In contrast,
waves considered in the linear approximation keep their length unchanged and
slightly accelerate.Comment: 15 pages, 7 figures, accepted for publication in Solar Physic
Polarimetric Properties of Flux-Ropes and Sheared Arcades in Coronal Prominence Cavities
The coronal magnetic field is the primary driver of solar dynamic events.
Linear and circular polarization signals of certain infrared coronal emission
lines contain information about the magnetic field, and to access this
information, either a forward or an inversion method must be used. We study
three coronal magnetic configurations that are applicable to polar-crown
filament cavities by doing forward calculations to produce synthetic
polarization data. We analyze these forward data to determine the
distinguishing characteristics of each model. We conclude that it is possible
to distinguish between cylindrical flux ropes, spheromak flux ropes, and
sheared arcades using coronal polarization measurements. If one of these models
is found to be consistent with observational measurements, it will mean
positive identification of the magnetic morphology that surrounds certain
quiescent filaments, which will lead to a greater understanding of how they
form and why they erupt.Comment: 22 pages, 8 figures, Solar Physics topical issue: Coronal Magnetis
Extreme Ultra-Violet Spectroscopy of the Lower Solar Atmosphere During Solar Flares
The extreme ultraviolet portion of the solar spectrum contains a wealth of
diagnostic tools for probing the lower solar atmosphere in response to an
injection of energy, particularly during the impulsive phase of solar flares.
These include temperature and density sensitive line ratios, Doppler shifted
emission lines and nonthermal broadening, abundance measurements, differential
emission measure profiles, and continuum temperatures and energetics, among
others. In this paper I shall review some of the advances made in recent years
using these techniques, focusing primarily on studies that have utilized data
from Hinode/EIS and SDO/EVE, while also providing some historical background
and a summary of future spectroscopic instrumentation.Comment: 34 pages, 8 figures. Submitted to Solar Physics as part of the
Topical Issue on Solar and Stellar Flare
Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of "EIT waves", Type II Radio Bursts, and Leading Edges of CMEs
We show examples of excitation of coronal waves by flare-related abrupt
eruptions of magnetic rope structures. The waves presumably rapidly steepened
into shocks and freely propagated afterwards like decelerating blast waves that
showed up as Moreton waves and EUV waves. We propose a simple quantitative
description for such shock waves to reconcile their observed propagation with
drift rates of metric type II bursts and kinematics of leading edges of coronal
mass ejections (CMEs). Taking account of different plasma density falloffs for
propagation of a wave up and along the solar surface, we demonstrate a close
correspondence between drift rates of type II bursts and speeds of EUV waves,
Moreton waves, and CMEs observed in a few known events.Comment: 30 pages, 15 figures. Solar Physics, published online. The final
publication is available at http://www.springerlink.co
High-Energy Aspects of Solar Flares: Overview of the Volume
In this introductory chapter, we provide a brief summary of the successes and
remaining challenges in understanding the solar flare phenomenon and its
attendant implications for particle acceleration mechanisms in astrophysical
plasmas. We also provide a brief overview of the contents of the other chapters
in this volume, with particular reference to the well-observed flare of 2002
July 23Comment: This is the introductory article for a monograph on the physics of
solar flares, inspired by RHESSI observations. The individual articles are to
appear in Space Science Reviews (2011
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