467 research outputs found
Characterization of putative steroid receptors in the membrane, cytosol and nuclear fractions from the olfactory tissue of brown and rainbow trout
Specific binding sites for testosterone have been detected in three compartments of olfactory tissue from brown and rainbow trout. Binding of 3H-testosterone to the membrane fraction of olfactory tissue is of high affinity (KD = 0.5 - 1.9 nM) and limited capacity (NMAX = 30 - 60 fmol mg-1 protein). Binding is reversible, and is eliminated by protease treatment. The membrane binding site exhibits a high degree of ligand specificity; 11β-hydroxytestosterone, 11-ketotestosterone, 17α-hydroxyprogesterone, 17α, 20β-dihydroxy-4-pregnen-3-one, cortisol, and estradiol-17β all fail to displace testosterone at 20-fold excess while testosterone itself competes successfully. These attributes are consistent with the presence of specific steroid receptor proteins. Binding of testosterone within the cytosol is of moderate affinity (KD = 9.0 - 23.0 nM) and high capacity (Nmax = 0.5 - 2.9 pmol mg-1 protein) and is more readily displaced by a number of steroid competitors than is the case for the membrane site. The rate of association and dissociation of testosterone from the cytosolic binding site is markedly more rapid than the equivalent processes in the membrane fraction. Binding of testosterone to the nuclear extract is of high affinity (KD ~ 3.0 nM) and limited capacity (Nmax ~ 50 fmol mg-1 protein).
There are no substantial differences between species or between sexes in the affinity or capacity of testosterone-binding sites in nuclear extract or membrane fraction. However, cytosolic testosterone-binding sites are three- to four-fold more abundant in rainbow trout than in brown trout, and female rainbow trout have more cytosolic binding sites than male rainbow trout, but a lower affinity for testosterone than male sites.
Preliminary evidence supports the involvement of the membrane-associated testosterone-binding site in olfactory processes. Rainbow trout display an EOG response to testosterone at a concentration (10-9 M) which is consistent with the equilibrium dissociation constant (KD) of the membrane-associated testosterone-binding site. Binding of 3H-testosterone to the membrane-associated site shows a pH dependancy which is comparable to the effects of pH on the EOG response to testosterone in intact fish. The attributes of the intracellular testosterone-binding sites are common to testosterone receptors in other fish tissues which are known androgen target tissues. This suggests that the development and/or function of salmonid olfactory tissue may be susceptible to influence by endogenous testosterone
A new optimal packing algorithm for telecommunications networks planning
AbstractIn telecommunications network planning, the problem of multiplexing low speed lines onto high speed transmission channels provides opportunities for attractive economic solutions. In many cases, the overall costs for transmission channels runs into hundreds of thousands of dollars per year. Thus, the problem of finding the minimum number of transmission channels to support low speed lines might be very important.This paper describes an exact packing algorithm (OPTPACK) for determining the packing of low speed lines onto high speed channels in such a way that the number of required channels is minimized
Features of Unstable Carotid Plaque During and After the Hyperacute Period Following TIA/Stroke
Two-point microrheology and the electrostatic analogy
The recent experiments of Crocker et al. suggest that microrheological
measurements obtained from the correlated fluctuations of widely-separatedprobe
particles determine the rheological properties of soft, complex materials more
accurately than do the more traditional particle autocorrelations. This
presents an interesting problem in viscoelastic dynamics. We develop an
important, simplifing analogy between the present viscoelastic problem and
classical electrostatics. Using this analogy and direct calculation we analyze
both the one and two particle correlations in a viscoelastic medium in order to
explain this observation
Homologous Flares and Magnetic Field Topology in Active Region NOAA 10501 on 20 November 2003
We present and interpret observations of two morphologically homologous
flares that occurred in active region (AR) NOAA 10501 on 20 November 2003. Both
flares displayed four homologous H-alpha ribbons and were both accompanied by
coronal mass ejections (CMEs). The central flare ribbons were located at the
site of an emerging bipole in the center of the active region. The negative
polarity of this bipole fragmented in two main pieces, one rotating around the
positive polarity by ~ 110 deg within 32 hours. We model the coronal magnetic
field and compute its topology, using as boundary condition the magnetogram
closest in time to each flare. In particular, we calculate the location of
quasiseparatrix layers (QSLs) in order to understand the connectivity between
the flare ribbons. Though several polarities were present in AR 10501, the
global magnetic field topology corresponds to a quadrupolar magnetic field
distribution without magnetic null points. For both flares, the photospheric
traces of QSLs are similar and match well the locations of the four H-alpha
ribbons. This globally unchanged topology and the continuous shearing by the
rotating bipole are two key factors responsible for the flare homology.
However, our analyses also indicate that different magnetic connectivity
domains of the quadrupolar configuration become unstable during each flare, so
that magnetic reconnection proceeds differently in both events.Comment: 24 pages, 10 figures, Solar Physics (accepted
A Quantitative Model of Energy Release and Heating by Time-dependent, Localized Reconnection in a Flare with a Thermal Loop-top X-ray Source
We present a quantitative model of the magnetic energy stored and then
released through magnetic reconnection for a flare on 26 Feb 2004. This flare,
well observed by RHESSI and TRACE, shows evidence of non-thermal electrons only
for a brief, early phase. Throughout the main period of energy release there is
a super-hot (T>30 MK) plasma emitting thermal bremsstrahlung atop the flare
loops. Our model describes the heating and compression of such a source by
localized, transient magnetic reconnection. It is a three-dimensional
generalization of the Petschek model whereby Alfven-speed retraction following
reconnection drives supersonic inflows parallel to the field lines, which form
shocks heating, compressing, and confining a loop-top plasma plug. The
confining inflows provide longer life than a freely-expanding or
conductively-cooling plasma of similar size and temperature. Superposition of
successive transient episodes of localized reconnection across a current sheet
produces an apparently persistent, localized source of high-temperature
emission. The temperature of the source decreases smoothly on a time scale
consistent with observations, far longer than the cooling time of a single
plug. Built from a disordered collection of small plugs, the source need not
have the coherent jet-like structure predicted by steady-state reconnection
models. This new model predicts temperatures and emission measure consistent
with the observations of 26 Feb 2004. Furthermore, the total energy released by
the flare is found to be roughly consistent with that predicted by the model.
Only a small fraction of the energy released appears in the super-hot source at
any one time, but roughly a quarter of the flare energy is thermalized by the
reconnection shocks over the course of the flare. All energy is presumed to
ultimately appear in the lower-temperature T<20 MK, post-flare loops
Normalization anomalies in level truncation calculations
We test oscillator level truncation regularization in string field theory by
calculating descent relations among vertices, or equivalently, the overlap of
wedge states. We repeat the calculation using bosonic, as well as fermionic
ghosts, where in the bosonic case we do the calculation both in the discrete
and in the continuous basis. We also calculate analogous expressions in field
level truncation. Each calculation gives a different result. We point out to
the source of these differences and in the bosonic ghost case we pinpoint the
origin of the difference between the discrete and continuous basis
calculations. The conclusion is that level truncation regularization cannot be
trusted in calculations involving normalization of singular states, such as
wedge states, rank-one squeezed state projectors and string vertices.Comment: 1+20 pages, 6 figures. v2: Ref. added, typos correcte
4pi Models of CMEs and ICMEs
Coronal mass ejections (CMEs), which dynamically connect the solar surface to
the far reaches of interplanetary space, represent a major anifestation of
solar activity. They are not only of principal interest but also play a pivotal
role in the context of space weather predictions. The steady improvement of
both numerical methods and computational resources during recent years has
allowed for the creation of increasingly realistic models of interplanetary
CMEs (ICMEs), which can now be compared to high-quality observational data from
various space-bound missions. This review discusses existing models of CMEs,
characterizing them by scientific aim and scope, CME initiation method, and
physical effects included, thereby stressing the importance of fully 3-D
('4pi') spatial coverage.Comment: 14 pages plus references. Comments welcome. Accepted for publication
in Solar Physics (SUN-360 topical issue
String Field Theory Projectors for Fermions of Integral Weight
The interaction vertex for a fermionic first order system of weights (1,0)
such as the twisted bc-system, the fermionic part of N=2 string field theory
and the auxiliary \eta\xi system of N=1 strings is formulated in the Moyal
basis. In this basis, the Neumann matrices are diagonal; as usual, the
eigenvectors are labeled by \kappa\in\R. Oscillators constructed from these
eigenvectors make up two Clifford algebras for each nonzero value of \kappa.
Using a generalization of the Moyal-Weyl map to the fermionic case, we classify
all projectors of the star-algebra which factorize into projectors for each
\kappa-subspace. At least for the case of squeezed states we recover the full
set of bosonic projectors with this property. Among the subclass of ghost
number-homogeneous squeezed state projectors, we find a single class of
BPZ-real states parametrized by one (nearly) arbitrary function of \kappa. This
class is shown to contain the generalized butterfly states. Furthermore, we
elaborate on sufficient and necessary conditions which have to be fulfilled by
our projectors in order to constitute surface states. As a byproduct we find
that the full star product of N=2 string field theory translates into a
canonically normalized continuous tensor product of Moyal-Weyl products up to
an overall normalization. The divergent factors arising from the translation to
the continuous basis cancel between bosons and fermions in any even dimension.Comment: LaTeX, 1+23 pages, minor improvements, references adde
Stereoscopic Analysis of the 19 May 2007 Erupting Filament
A filament eruption, accompanied by a B9.5 flare, coronal dimming and an EUV
wave, was observed by the Solar TERrestrial Relations Observatory (STEREO) on
19 May 2007, beginning at about 13:00 UT. Here, we use observations from the
SECCHI/EUVI telescopes and other solar observations to analyze the behavior and
geometry of the filament before and during the eruption. At this time, STEREO A
and B were separated by about 8.5 degrees, sufficient to determine the
three-dimensional structure of the filament using stereoscopy. The filament
could be followed in SECCHI/EUVI 304 A stereoscopic data from about 12 hours
before to about 2 hours after the eruption, allowing us to determine the 3D
trajectory of the erupting filament. From the 3D reconstructions of the
filament and the chromospheric ribbons in the early stage of the eruption,
simultaneous heating of both the rising filamentary material and the
chromosphere directly below is observed, consistent with an eruption resulting
from magnetic reconnection below the filament. Comparisons of the filament
during eruption in 304 A and Halpha show that when it becomes emissive in He
II, it tends to disappear in Halpha, indicating that the disappearance probably
results from heating or motion, not loss, of filamentary material.Comment: Accepted for publication in Solar Physic
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