1,242 research outputs found
Purification of a phospholipase C froM Bacillus cereus
Phospholipase C activity present in the growth medium of Bacillus cereus was purified 20-fold by chromatography on polyethyleneimine-cellulose columns, or by treatment with protamine sulfate and subsequent chromatography on DEAE-cellulose columns. Purified enzyme preparations retained the ability to hydrolyze ethanolamine phosphoglycerides in the absence of choline phosphoglycerides. A typical preparation had a specific activity of about 9 [mu]moles/min per mg toward purified diacyl glycerophosphoryl ethanolamine and a specific activity of about 15-20 [mu]moles/ min per mg toward diacyl glycerophosphorylmonomethylethanolamine and diacyl glycerophosphoryl choline. Monoacyl glycerophosphate was not hydrolyzed under similar conditions.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/32856/1/0000232.pd
Mechanism of thermally activated c-axis dissipation in layered High-T superconductors at high fields
We propose a simple model which explains experimental behavior of -axis
resistivity in layered High-T superconductors at high fields in a limited
temperature range. It is generally accepted that the in-plane dissipation at
low temperatures is caused by small concentration of mobile pancake vortices
whose diffusive motion is thermally activated. We demonstrate that in such
situation a finite conductivity appears also in -direction due to the phase
slips between the planes caused by the mobile pancakes. The model gives
universal relation between the components of conductivity which is in good
agreement with experimental data.Comment: RevTeX, 4 pages, 2 Postscript figure
The Canonical Model of a Singular Curve
We give refined statements and modern proofs of Rosenlicht's results about
the canonical model C' of an arbitrary complete integral curve C. Notably, we
prove that C and C' are birationally equivalent if and only if C is
nonhyperelliptic, and that, if C is nonhyperelliptic, then C' is equal to the
blowup of C with respect to the canonical sheaf \omega. We also prove some new
results: we determine just when C' is rational normal, arithmetically normal,
projectively normal, and linearly normal.Comment: 28 pages, no figures, IV Congresso Iberoamericano de Geometria
Complex
The BARD1 C-Terminal Domain Structure and Interactions with Polyadenylation Factor CstF-50†
The BARD1 N-terminal RING domain binds BRCA1 while the BARD1 C-terminal ankyrin and tandem BRCT repeat domains bind CstF-50 to modulate mRNA processing and RNAP II stability in response to DNA damage. Here we characterize the BARD1 structural biochemistry responsible for CstF- 50 binding. The crystal structure of the BARD1 BRCT domain uncovers a degenerate phosphopeptide binding pocket lacking the key arginine required for phosphopeptide interactions in other BRCT proteins.Small angle X-ray scattering together with limited proteolysis results indicates that ankyrin and BRCT domains are linked by a flexible tether and do not adopt a fixed orientation relative to one another. Protein pull-down experiments utilizing a series of purified BARD1 deletion mutants indicate that interactions between the CstF-50 WD-40 domain and BARD1 involve the ankyrin-BRCT linker but do not require ankyrin or BRCT domains. The structural plasticity imparted by the ANK-BRCT linker helps to explain the regulated assembly of different protein BARD1 complexes with distinct functions in DNA damage signaling including BARD1-dependent induction of apoptosis plus p53 stabilization and interactions. BARD1 architecture and plasticity imparted by the ANK-BRCT linker are suitable to allow the BARD1 C-terminus to act as a hub with multiple binding sites to integrate diverse DNA damage signals directly to RNA polymerase
The 3′ processing factor CstF functions in the DNA repair response
Following DNA damage, mRNA levels decrease, reflecting a coordinated interaction of the DNA repair, transcription and RNA processing machineries. In this study, we provide evidence that transcription and polyadenylation of mRNA precursors are both affected in vivo by UV treatment. We next show that the polyadenylation factor CstF, plays a direct role in the DNA damage response. Cells with reduced levels of CstF display decreased viability following UV treatment, reduced ability to ubiquitinate RNA polymerase II (RNAP II), and defects in repair of DNA damage. Furthermore, we show that CstF, RNAP II and BARD1 are all found at sites of repaired DNA. Our results indicate that CstF plays an active role in the response to DNA damage, providing a link between transcription-coupled RNA processing and DNA repair
Easily retrievable objects among the NEO population
Asteroids and comets are of strategic importance for science in an effort to understand the formation, evolution and composition of the Solar System. Near-Earth Objects (NEOs) are of particular interest because of their accessibility from Earth, but also because of their speculated wealth of material resources. The exploitation of these resources has long been discussed as a means to lower the cost of future space endeavours. In this paper, we consider the currently known NEO population and define a family of so-called Easily Retrievable Objects (EROs), objects that can be transported from accessible heliocentric orbits into the Earth’s neighbourhood at affordable costs. The asteroid retrieval transfers are sought from the continuum of low energy transfers enabled by the dynamics of invariant manifolds; specifically, the retrieval transfers target planar, vertical Lyapunov and halo orbit families associated with the collinear equilibrium points of the Sun-Earth Circular Restricted Three Body problem. The judicious use of these dynamical features provides the best opportunity to find extremely low energy Earth transfers for asteroid material. A catalogue of asteroid retrieval candidates is then presented. Despite the highly incomplete census of very small asteroids, the ERO catalogue can already be populated with 12 different objects retrievable with less than 500 m/s of Δv. Moreover, the approach proposed represents a robust search and ranking methodology for future retrieval candidates that can be automatically applied to the growing survey of NEOs
Pinning-induced transition to disordered vortex phase in layered superconductors
Destruction of the vortex lattice by random point pinning is considered as a
mechanism of the ``second peak'' transition observed experimentally in weakly
coupled layered high temperature superconductors. The transition field
separating the topologically ordered quasilattice from the amorphous vortex
configuration is strongly influenced by the layered structure and by the
nonlocal nature of the vortex tilt energy due to the magnetic interlayer
coupling. We found three different regimes of transition depending on the
relative strength of the Josephson and magnetic couplings. The regimes can be
distinguished by the dependence of the transition fieldComment: 8 pages, 3 Postscript figures. Accepted to Phys. Rev.B. (regular
article
New Experimental Limits on Macroscopic Forces Below 100 Microns
Results of an experimental search for new macroscopic forces with Yukawa
range between 5 and 500 microns are presented. The experiment uses 1 kHz
mechanical oscillators as test masses with a stiff conducting shield between
them to suppress backgrounds. No signal is observed above the instrumental
thermal noise after 22 hours of integration time. These results provide the
strongest limits to date between 10 and 100 microns, improve on previous limits
by as much as three orders of magnitude, and rule out half of the remaining
parameter space for predictions of string-inspired models with low-energy
supersymmetry breaking. New forces of four times gravitational strength or
greater are excluded at the 95% confidence level for interaction ranges between
200 and 500 microns.Comment: 25 Pages, 7 Figures: Minor Correction
Nonlinear Magneto-Optical Response of - and -Wave Superconductors
The nonlinear magneto-optical response of - and -wave superconductors
is discussed. We carry out the symmetry analysis of the nonlinear
magneto-optical susceptibility in the superconducting state. Due to the surface
sensitivity of the nonlinear optical response for systems with bulk inversion
symmetry, we perform a group theoretical classification of the superconducting
order parameter close to a surface. For the first time, the mixing of singlet
and triplet pairing states induced by spin-orbit coupling is systematically
taken into account. We show that the interference of singlet and triplet
pairing states leads to an observable contribution of the nonlinear
magneto-optical Kerr effect. This effect is not only sensitive to the
anisotropy of the gap function but also to the symmetry itself. In view of the
current discussion of the order parameter symmetry of High-T
superconductors, results for a tetragonal system with bulk singlet pairing for
various pairing symmetries are discussed.Comment: 21 pages (REVTeX) with 8 figures (Postscript
Ground State Vortex Lattice Structures in d-wave Superconductors
We show in a realistic symmetry gap model for a cuprate
superconductor that the clean vortex lattice has discontinuous structural
transitions (at and near T=0), as a function of the magnetic field along
the c-axis. The transitions arise from the singular nonlocal and anisotropic
susceptibility of the superconductor to the perturbation
caused by supercurrents associated with vortices. The susceptibility, due to
virtual Dirac quasiparticle-hole excitation, is calculated carefully, and leads
to a ground state transition for the triangular lattice from an orientation
along one of the crystal axis to one at 45 to them, i.e, along the gap zero
direction. The field scale is seen to be 5 Tesla , where is the gap maximum, is the
nearest neighbour hopping, is the lattice constant, and is the
flux quantum. At much higher fields () there is a discontinuous
transition to a centred square structure. The source of the differences from
existing calculations, and experimental observability are discussed, the latter
especially in view of the very small (a few degrees per vortex) differences
in the ground state energy.Comment: To be published in Phys. Rev.
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