1,077 research outputs found
Slow inactivation does not affect movement of the fast inactivation gate in voltage-gated Na+ channels.
Voltage-gated Na+ channels exhibit two forms of inactivation, one form (fast inactivation) takes effect on the order of milliseconds and the other (slow inactivation) on the order of seconds to minutes. While previous studies have suggested that fast and slow inactivation are structurally independent gating processes, little is known about the relationship between the two. In this study, we probed this relationship by examining the effects of slow inactivation on a conformational marker for fast inactivation, the accessibility of a site on the Na+ channel III-IV linker that is believed to form a part of the fast inactivation particle. When cysteine was substituted for phenylalanine at position 1304 in the rat skeletal muscle sodium channel (microl), application of [2-(trimethylammonium)ethyl]methanethiosulfonate (MTS-ET) to the cytoplasmic face of inside-out patches from Xenopus oocytes injected with F1304C RNA dramatically disrupted fast inactivation and displayed voltage-dependent reaction kinetics that closely paralleled the steady state availability (hinfinity) curve. Based on this observation, the accessibility of cys1304 was used as a conformational marker to probe the position of the fast inactivation gate during the development of and the recovery from slow inactivation. We found that burial of cys1304 is not altered by the onset of slow inactivation, and that recovery of accessibility of cys1304 is not slowed after long (2-10 s) depolarizations. These results suggest that (a) fast and slow inactivation are structurally distinct processes that are not tightly coupled, (b) fast and slow inactivation are not mutually exclusive processes (i.e., sodium channels may be fast- and slow-inactivated simultaneously), and (c) after long depolarizations, recovery from fast inactivation precedes recovery from slow inactivation
Faraday conversion and magneto-ionic variations in Fast Radio Bursts
The extreme, time-variable Faraday rotation observed in the repeating fast
radio burst (FRB) 121102 and its associated persistent synchrotron source
demonstrates that some FRBs originate in dense, dynamic and possibly
relativistic magneto-ionic environments. Here we show that besides rotation of
the linear-polarisation vector (Faraday rotation), such media can generally
convert linear to circular polarisation (Faraday conversion). We use
non-detection of Faraday conversion, and the temporal variation in Faraday
rotation and dispersion in bursts from FRB\,121102 to constrain models where
the progenitor inflates a relativistic nebula (persistent source) confined by a
cold dense medium (e.g. supernova ejecta). We find that the persistent
synchrotron source, if composed of an electron-proton plasma, must be an
admixture of relativistic and non-relativistic (Lorentz factor )
electrons. Furthermore we independently constrain the magnetic field in the
cold confining medium, which provides the Faraday rotation, to be between
and mG. This value is close to the equipartition magnetic field of the
confined persistent source implying a self-consistent and over-constrained
model that can explain the observations.Comment: Submitted to MNRAS; An error in arguments of sec 2.2 of the previous
version has been correcte
GOOD GOVERNANCE AND PUBLIC POLICY IN INDIA
Good Governance is required to ensure that the public policies have their desired effect. In the recent past, issues of governance have received serious attention from the researchers, policy makers and international development community. Today, ‘governance’ not only occupies centre stage in the development discourse but is also considered as a crucial element to be incorporated in the development strategy. The major focus of the study is on Good Governance and public policy process in India. In this context the present research paper discusses the basic concepts and elements of Good Governance in the first part of the article. The need of the Good Governance in the effective implementation of public policies has been elaborately discussed and the nature of public policy has been mentioned in the next part Various stages and constraints that are involved in public policy process and need for an effective policy has been discussed in detail in subsequent parts. 
On associating Fast Radio Bursts with afterglows
A radio source that faded over six days, with a redshift of
host, has been identified by Keane et al. (2016) as the transient afterglow to
a fast radio burst (FRB 150418). We report follow-up radio and optical
observations of the afterglow candidate and find a source that is consistent
with an active galactic nucleus. If the afterglow candidate is nonetheless a
prototypical FRB afterglow, existing slow-transient surveys limit the fraction
of FRBs that produce afterglows to 0.25 for afterglows with fractional
variation, , and 0.07 for , at 95%
confidence. In anticipation of a barrage of bursts expected from future FRB
surveys, we provide a simple framework for statistical association of FRBs with
afterglows. Our framework properly accounts for statistical uncertainties, and
ensures consistency with limits set by slow-transient surveys.Comment: Accepted version (ApJL
Scintillation noise in widefield radio interferometry
In this paper, we consider random phase fluctuations imposed during wave
propagation through a turbulent plasma (e.g. ionosphere) as a source of
additional noise in interferometric visibilities. We derive expressions for
visibility variance for the wide field of view case (FOV deg) by
computing the statistics of Fresnel diffraction from a stochastic plasma, and
provide an intuitive understanding. For typical ionospheric conditions
(diffractive scale km at MHz), we show that the resulting
ionospheric `scintillation noise' can be a dominant source of uncertainty at
low frequencies ( MHz). Consequently, low frequency widefield
radio interferometers must take this source of uncertainty into account in
their sensitivity analysis. We also discuss the spatial, temporal, and spectral
coherence properties of scintillation noise that determine its magnitude in
deep integrations, and influence prospects for its mitigation via calibration
or filtering.Comment: Accepted versio
Faraday conversion and magneto-ionic variations in fast radio bursts
The extreme, time-variable Faraday rotation observed in the repeating fast radio burst (FRB) 121102 and its associated persistent synchrotron source demonstrates that some FRBs originate in dense, dynamic, and possibly relativistic magneto-ionic environments. Besides rotation of the linear polarization vector (Faraday rotation), such media can generally convert linear to circular polarization (Faraday conversion). We use non-detection of Faraday conversion, and the temporal variation in Faraday rotation and dispersion in bursts from FRB 121102 to constrain models where the progenitor inflates a relativistic nebula (persistent source) confined by a cold dense medium (e.g. supernova ejecta). We find that the persistent synchrotron source, if composed of an electron–proton plasma, must be an admixture of relativistic and non-relativistic (Lorentz factor γ < 5) electrons. Furthermore, we independently constrain the magnetic field in the cold confining medium, which provides the Faraday rotation, to be between 10 and 30 mG. This value is close to the equipartition magnetic field of the confined persistent source implying a self-consistent and overconstrained model that can explain the observations
Prospects for detecting the 21cm forest from the diffuse intergalactic medium with LOFAR
We discuss the feasibility of the detection of the 21cm forest in the diffuse
IGM with the radio telescope LOFAR. The optical depth to the 21cm line has been
derived using simulations of reionization which include detailed radiative
transfer of ionizing photons. We find that the spectra from reionization models
with similar total comoving hydrogen ionizing emissivity but different
frequency distribution look remarkably similar. Thus, unless the reionization
histories are very different from each other (e.g. a predominance of UV vs.
x-ray heating) we do not expect to distinguish them by means of observations of
the 21cm forest. Because the presence of a strong x-ray background would make
the detection of 21cm line absorption impossible, the lack of absorption could
be used as a probe of the presence/intensity of the x-ray background and the
thermal history of the universe. Along a random line of sight LOFAR could
detect a global suppression of the spectrum from z>12, when the IGM is still
mostly neutral and cold, in contrast with the more well-defined, albeit broad,
absorption features visible at lower redshift. Sharp, strong absorption
features associated with rare, high density pockets of gas could be detected
also at z~7 along preferential lines of sight.Comment: 12 pages, 13 figures. MNRAS, in pres
Endovascular Thrombus Removal for Acute Iliofemoral Deep Vein Thrombosis: Analysis from a Stratified Multicenter Randomized Trial
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