105 research outputs found
Bed-parallel slip : Identifying missing displacement in mass transport deposits
RW was supported by the Israel Science Foundation (ISF grant No. 868/17). SM acknowledges the Israel Science Foundation (ISF grant No. 1645/19). TL acknowledges the Israeli government GSI DS project 40706.Peer reviewedPostprin
Coiling Instabilities in Multilamellar Tubes
Myelin figures are densely packed stacks of coaxial cylindrical bilayers that
are unstable to the formation of coils or double helices. These myelin figures
appear to have no intrinsic chirality. We show that such cylindrical membrane
stacks can develop an instability when they acquire a spontaneous curvature or
when the equilibrium distance between membranes is decreased. This instability
breaks the chiral symmetry of the stack and may result in coiling. A
unilamellar cylindrical vesicle, on the other hand, will develop an
axisymmetric instability, possibly related to the pearling instability.Comment: 6 pages, 2 figure
A First Step Towards Automatically Building Network Representations
To fully harness Grids, users or middlewares must have some knowledge on the
topology of the platform interconnection network. As such knowledge is usually
not available, one must uses tools which automatically build a topological
network model through some measurements. In this article, we define a
methodology to assess the quality of these network model building tools, and we
apply this methodology to representatives of the main classes of model builders
and to two new algorithms. We show that none of the main existing techniques
build models that enable to accurately predict the running time of simple
application kernels for actual platforms. However some of the new algorithms we
propose give excellent results in a wide range of situations
The ideal trefoil knot
The most tight conformation of the trefoil knot found by the SONO algorithm
is presented. Structure of the set of its self-contact points is analyzed.Comment: 11 pages, 8 figure
Morphology of axisymmetric vesicles with encapsulated filaments and impurities
The shape deformation of a three-dimensional axisymmetric vesicle with
encapsulated filaments or impurities is analyzed by integrating a dissipation
dynamics. This method can incorporate systematically the constraint of a fixed
surface area and/or a fixed volume. The filament encapsulated in a vesicle is
assumed to take a form of a rod or a ring so as to imitate cytoskeletons. In
both cases, results of the shape transition of the vesicle are summarized in
phase diagrams in the phase space of the vesicular volume and a rod length or a
ring radius.
We also study the dynamics of a vesicle with impurities coupled to the
membrane curvature. The phase separation and the associated shape deformation
in the early stage of the dynamical evolution can well be explained by the
linear stability analysis. Long runs of simulation demonstrate the nonlinear
coarsening of the wavy deformation of the vesicle in the late stage.Comment: 9 pages, 9 figure
The Velocity Function of Galaxies
We present a galaxy circular velocity function, Psi(log v), derived from
existing luminosity functions and luminosity-velocity relations. Such a
velocity function is desirable for several reasons. First, it enables an
objective comparison of luminosity functions obtained in different bands and
for different galaxy morphologies, with a statistical correction for dust
extinction. In addition, the velocity function simplifies comparison of
observations with predictions from high-resolution cosmological N-body
simulations.
We derive velocity functions from five different data sets and find rough
agreement among them, but about a factor of 2 variation in amplitude. These
velocity functions are then compared with N-body simulations of a LCDM model
(corrected for baryonic infall) in order to demonstrate both the utility and
current limitations of this approach. The number density of dark matter halos
and the slope of the velocity function near v_*, the circular velocity
corresponding to an ~L_* spiral galaxy, are found to be comparable to that of
observed galaxies. The primary sources of uncertainty in construction of
Psi(log v) from observations and N-body simulations are discussed and
explanations are suggected to account for these discrepancies.Comment: Latex. 28 pages, 4 figures. Accepted by Ap
Coiling Instability of Multilamellar Membrane Tubes with Anchored Polymers
We study experimentally a coiling instability of cylindrical multilamellar
stacks of phospholipid membranes, induced by polymers with hydrophobic anchors
grafted along their hydrophilic backbone. Our system is unique in that coils
form in the absence of both twist and adhesion. We interpret our experimental
results in terms of a model in which local membrane curvature and polymer
concentration are coupled. The model predicts the occurrence of maximally tight
coils above a threshold polymer occupancy. A proper comparison between the
model and experiment involved imaging of projections from simulated coiled
tubes with maximal curvature and complicated torsions.Comment: 11 pages + 7 GIF figures + 10 JPEG figure
Plant-Expressed Cocaine Hydrolase Variants of Butyrylcholinesterase Exhibit Altered Allosteric Effects of Cholinesterase Activity and Increased Inhibitor Sensitivity
Butyrylcholinesterase (BChE) is an enzyme with broad substrate and ligand specificities and may function as a generalized bioscavenger by binding and/or hydrolyzing various xenobiotic agents and toxicants, many of which target the central and peripheral nervous systems. Variants of BChE were rationally designed to increase the enzymeâs ability to hydrolyze the psychoactive enantiomer of cocaine. These variants were cloned, and then expressed using the magnICON transient expression system in plants and their enzymatic properties were investigated. In particular, we explored the effects that these site-directed mutations have over the enzyme kinetics with various substrates of BChE. We further compared the affinity of various anticholinesterases including organophosphorous nerve agents and pesticides toward these BChE variants relative to the wild type enzyme. In addition to serving as a therapy for cocaine addiction-related diseases, enhanced bioscavenging against other harmful agents could add to the practicality and versatility of the plant-derived recombinant enzyme as a multivalent therapeutic
Multibudded tubules formed by COPII on artificial liposomes
COPII-coated vesicles form at the endoplasmic reticulum for cargo transport to the Golgi apparatus. We used in vitro reconstitution to examine the roles of the COPII scaffold in remodeling the shape of a lipid bilayer. Giant Unilamellar Vesicles were examined using fast confocal fluorescence and cryo-electron microscopy in order to avoid separation steps and minimize mechanical manipulation. COPII showed a preference for high curvature structures, but also sufficient flexibility for binding to low curvatures. The COPII proteins induced beads-on-a-string-like constricted tubules, similar to those previously observed in cells. We speculate about a mechanical pathway for vesicle fission from these multibudded COPII-coated tubules, considering the possibility that withdrawal of the Sar1 amphipathic helix upon GTP hydrolysis leads to lipid bilayer destabilization resulting in fission
Chromosomal aberration frequency in lymphocytes predicts the risk of cancer: results from a pooled cohort study of 22 358 subjects in 11 countries
Mechanistic evidence linking chromosomal aberration (CA) to early stages of cancer has been recently supported by the results of epidemiological studies that associated CA frequency in peripheral lymphocytes of healthy individuals to future cancer incidence. To overcome the limitations of single studies and to evaluate the strength of this association, a pooled analysis was carried out. The pooled database included 11 national cohorts and a total of 22 358 cancer-free individuals who underwent genetic screening with CA for biomonitoring purposes during 1965â2002 and were followed up for cancer incidence and/or mortality for an average of 10.1 years; 368 cancer deaths and 675 incident cancer cases were observed. Subjects were classified within each laboratory according to tertiles of CA frequency. The relative risk (RR) of cancer was increased for subjects in the medium [RR = 1.31, 95% confidence interval (CI) = 1.07â1.60] and in the high (RR = 1.41; 95% CI = 1.16â1.72) tertiles when compared with the low tertile. This increase was mostly driven by chromosome-type aberrations. The presence of ring chromosomes increased the RR to 2.22 (95% CI = 1.34â3.68). The strongest association was found for stomach cancer [RRmedium = 1.17 (95% CI = 0.37â3.70), RRhigh = 3.13 (95% CI = 1.17â8.39)]. Exposure to carcinogens did not modify the effect of CA levels on overall cancer risk. These results reinforce the evidence of a link between CA frequency and cancer risk and provide novel information on the role of aberration subclass and cancer type
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