22,324 research outputs found
Length control of microtubules by depolymerizing motor proteins
In many intracellular processes, the length distribution of microtubules is
controlled by depolymerizing motor proteins. Experiments have shown that,
following non-specific binding to the surface of a microtubule, depolymerizers
are transported to the microtubule tip(s) by diffusion or directed walk and,
then, depolymerize the microtubule from the tip(s) after accumulating there. We
develop a quantitative model to study the depolymerizing action of such a
generic motor protein, and its possible effects on the length distribution of
microtubules. We show that, when the motor protein concentration in solution
exceeds a critical value, a steady state is reached where the length
distribution is, in general, non-monotonic with a single peak. However, for
highly processive motors and large motor densities, this distribution
effectively becomes an exponential decay. Our findings suggest that such motor
proteins may be selectively used by the cell to ensure precise control of MT
lengths. The model is also used to analyze experimental observations of
motor-induced depolymerization.Comment: Added section with figures and significantly expanded text, current
version to appear in Europhys. Let
New light on the ‘Drummer of Tedworth’: conflicting narratives of witchcraft in Restoration England
This paper presents a definitive text of hitherto little-known early documents concerning ‘The Drummer of Tedworth’, a poltergeist case that occurred in 1662-3 and became famous not least due to its promotion by Joseph Glanvill in his demonological work, Saducismus Triumphatus. On the basis of these and other sources, it is shown how responses to the events at Tedworth evolved from anxious piety on the part of their victim, John Mompesson, to confident apologetic by Glanvill, before they were further affected by the emergence of articulate scepticism about the case
Raising Tc in charge density wave superconductor ZrTe3 by Ni intercalation
We report discovery of bulk superconductivity in Ni0.05ZrTe3 at Tc = 3.1 K,
obtained through Ni intercalation. Superconductivity coexists with charge
density wave (CDW) state with TCDW = 41 K. When compared to parent material
ZrTe3, filamentary superconducting transition is substantially increased
whereas TCDW was suppressed. The analysis of superconducting state indicates
that Ni0.05ZrTe3 is an intermediately coupled superconductor.Comment: 5 pages, 5 figure
Global Nonradial Instabilities of Dynamically Collapsing Gas Spheres
Self-similar solutions provide good descriptions for the gravitational
collapse of spherical clouds or stars when the gas obeys a polytropic equation
of state, (with ). We study the behaviors of
nonradial perturbations in the similarity solutions of Larson, Penston and
Yahil, which describe the evolution of the collapsing cloud prior to core
formation. Our global stability analysis reveals the existence of unstable
bar-modes () when . In particular, for the collapse of
isothermal spheres, which applies to the early stages of star formation, the
density perturbation relative to the background, , increases as ,
where denotes the epoch of core formation, and is the cloud
central density. Thus, the isothermal cloud tends to evolve into an ellipsoidal
shape (prolate bar or oblate disk, depending on initial conditions) as the
collapse proceeds. In the context of Type II supernovae, core collapse is
described by the equation of state, and our analysis
indicates that there is no growing mode (with density perturbation) in the
collapsing core before the proto-neutron star forms, although nonradial
perturbations can grow during the subsequent accretion of the outer core and
envelope onto the neutron star. We also carry out a global stability analysis
for the self-similar expansion-wave solution found by Shu, which describes the
post-collapse accretion (``inside-out'' collapse) of isothermal gas onto a
protostar. We show that this solution is unstable to perturbations of all
's, although the growth rates are unknown.Comment: 28 pages including 7 ps figures; Minor changes in the discussion; To
be published in ApJ (V.540, Sept.10, 2000 issue
Type I Superconductivity in YbSb2 Single Crystals
We present evidence of type I superconductivity in YbSb2 single crystals,
from DC and AC magnetization, heat capacity and resistivity measurements. The
critical temperature and critical field are determined to be 1.3 K
and 55 Oe. A small Ginzburg-Landau parameter \kappa = 0.05,
together with typical magnetization isotherms of type I superconductors, small
critical field values, a strong Differential Paramagnetic Effect (DPE) signal,
and a field-induced change from second to first order phase transition, confirm
the type I nature of the superconductivity in YbSb2. A possible second
superconducting state is observed in the radiofrequency (RF) susceptibility
measurements, with 0.41 K and 430 Oe.Comment: 6 pages, 10 figure
Support System Effects on the DLR-F6 Transport Configuration in the National Transonic Facility
An experimental investigation of the DLR-F6 generic transport configuration was conducted in the NASA NTF for use in the Drag Prediction Workshop. As data from this experimental investigation was collected, a large difference in drag values was seen between the NTF test and an ONERA test that was conducted several years ago. After much investigation, it was determined that this difference was likely due to a sting effect correction applied to the ONERA data which NTF does not use. This insight led to the present work. In this study, a computational assessment has been undertaken to investigate model support system interference effects on the DLR-F6 transport configuration. The configurations computed during this investigation were the isolated wing-body, the wing-body with the full support system (blade and sting), the wing-body with just the blade, and the wing-body with just the sting. The results from this investigation show the same trends that ONERA saw when they conducted a similar experimental investigation in the S2MA tunnel. Computational results suggest that the blade contributed an interference type of effect, the sting contributed a general blockage effect, and the full support system combined these effects
Effect of interlayer anions on [NiFe]-LDH nanosheet water oxidation activity
We synthesized nickel–iron layered double hydroxide ([NiFe]-LDH) nanosheets with different interlayer anions to probe their role in water oxidation catalysis. In alkaline electrolyte in ambient air, carbonate rapidly replaced other interlayer anions and catalytic activity was highest. Electrocatalytic water oxidation in virtually carbonate-free alkaline electrolyte revealed that activity was a function of anion basicity. Our [NiFe]-LDH nanosheets, prepared by pulsed laser ablation in liquids, were regenerated in carbonate-containing aqueous KOH. Anion binding motifs were assessed by X-ray photoelectron spectroscopy in combination with density functional theory calculations, suggesting that nitrite species bound to edge-site Fe in the precatalyst correlated with higher water oxidation activity
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