1,282 research outputs found
A Central Role for Cohesins in Sister Chromatid Cohesion, Formation of Axial Elements, and Recombination during Yeast Meiosis
AbstractA multisubunit complex, called cohesin, containing Smc1p, Smc3p, Scc1p, and Scc3p, is required for sister chromatid cohesion in mitotic cells. We show here that Smc3p and a meiotic version of Scc1p called Rec8p are required for cohesion between sister chromatids, for formation of axial elements, for reciprocal recombination, and for preventing hyperresection of double-strand breaks during meiosis. Both Rec8p and Smc3p colocalize with chromosome cores independently of synapsis during prophase I and largely disappear from chromosome arms after pachytene but persist in the neighborhood of centromeres until the onset of anaphase II. The eukaryotic cell's cohesion apparatus is required both for the repair of recombinogenic lesions and for chromosome segregation and therefore appears to lie at the heart of the meiotic process
Chaotic Inflationary Universe on Brane
The chaotic inflationary model of the early universe, proposed by Linde is
explored in the brane world considering matter described by a minimally coupled
self interacting scalar field. We obtain cosmological solutions which admit
evolution of a universe either from a singularity or without a singularity. It
is found that a very weakly coupled self-interacting scalar field is necessary
for a quartic type potential in the brane world model compared to that
necessary in general relativity. In the brane world sufficient inflation may be
obtained even with an initial scalar field having value less than the Planck
scale. It is found that if the universe is kinetic energy dominated to begin
with, it transits to an inflationary stage subsequently.Comment: 13 pages, no fig., accepted in Physical Review
Three-dimensional flux states as a model for the pseudogap phase of transition metal oxides
We propose that the pseudogap state observed in the transition metal oxides
can be explained by a three-dimensional flux state, which exhibits
spontaneously generated currents in its ground state due to electron-electron
correlations. We compare the energy of the flux state to other classes of mean
field states, and find that it is stabilized over a wide range of and
. The signature of the state will be peaks in the neutron diffraction
spectra, the location and intensity of which are presented. The dependence of
the pseudogap in the optical conductivity is calculated based on the parameters
in the model.Comment: submitted to Phys. Rev. B on January 8, 200
Unitarity and the Bethe-Salpeter Equation
We investigate the relation between different three-dimensional reductions of
the Bethe-Salpeter equation and the analytic structure of the resultant
amplitudes in the energy plane. This correlation is studied for both the
interaction Lagrangian and the system with -, -,
and -channel pole diagrams as driving terms. We observe that the equal-time
equation, which includes some of the three-body unitarity cuts, gives the best
agreement with the Bethe-Salpeter result. This is followed by other 3-D
approximations that have less of the analytic structure.Comment: 17 pages, 8 figures; RevTeX. Version accepted for publication in
Phys. Rev.
Higher dimensional radiation collapse and cosmic censorship
We study the occurrence of naked singularities in the spherically symmetric
collapse of radiation shells in a higher dimensional spacetime. The necessary
conditions for the formation of a naked singularity or a black hole are
obtained. The naked singularities are found to be strong in the Tipler's sense
and thus violating cosmic censorship conjecture.Comment: 4 pages, ReVTeX, Phys Rev D Vol 62 107502 (2000
Overlevingsplan bos en natuur; monitoring EGM projecten 2000
In het kader van het programma Overlevingsplan Bos en Natuur is een monitoringplan en een meetprotocol opgesteld voor de monitoring van de resultaten van effectgerichte maatregelen . In het monitoringplan zijn de opzet en doel van het monitoringplan en de meetdoelstelling besproken . In de meetprotocollen zijn de meetvariabelen genoemd die gemonitord moeten worden en is aangegeven hoe de opname van de variabelen uitgevoerd moet worden . Er zijn twee protocollen onderscheiden: In Protocol A wordt de monitoring voor steekproefprojecten, dat zijn projecten die in een 10% steekproef van het totale aantal EGM-projecten vallen, beschreven en in Protocol B wordt de monitoring van doelen rode lijstsoorten beschreven wat in alle EGM-projecten uitgevoerd gaat worden
Coronal mass ejections as expanding force-free structures
We mode Solar coronal mass ejections (CMEs) as expanding force-fee magnetic
structures and find the self-similar dynamics of configurations with spatially
constant \alpha, where {\bf J} =\alpha {\bf B}, in spherical and cylindrical
geometries, expanding spheromaks and expanding Lundquist fields
correspondingly. The field structures remain force-free, under the conventional
non-relativistic assumption that the dynamical effects of the inductive
electric fields can be neglected. While keeping the internal magnetic field
structure of the stationary solutions, expansion leads to complicated internal
velocities and rotation, induced by inductive electric field. The structures
depends only on overall radius R(t) and rate of expansion \dot{R}(t) measured
at a given moment, and thus are applicable to arbitrary expansion laws. In case
of cylindrical Lundquist fields, the flux conservation requires that both axial
and radial expansion proceed with equal rates. In accordance with observations,
the model predicts that the maximum magnetic field is reached before the
spacecraft reaches the geometric center of a CME.Comment: 19 pages, 9 Figures, accepted by Solar Physic
Nuclear organisation and replication timing are coupled through RIF1-PP1 interaction
Three-dimensional genome organisation and replication timing are known to be correlated, however, it remains unknown whether nuclear architecture overall plays an instructive role in the replication-timing programme and, if so, how. Here we demonstrate that RIF1 is a molecular hub that co-regulates both processes. Both nuclear organisation and replication timing depend upon the interaction between RIF1 and PP1. However, whereas nuclear architecture requires the full complement of RIF1 and its interaction with PP1, replication timing is not sensitive to RIF1 dosage. The role of RIF1 in replication timing also extends beyond its interaction with PP1. Availing of this separation-of-function approach, we have therefore identified in RIF1 dual function the molecular bases of the co-dependency of the replication-timing programme and nuclear architecture
Interchange Slip-Running Reconnection and Sweeping SEP Beams
We present a new model to explain how particles (solar energetic particles;
SEPs), accelerated at a reconnection site that is not magnetically connected to
the Earth, could eventually propagate along the well-connected open flux tube.
Our model is based on the results of a low-beta resistive magnetohydrodynamics
simulation of a three-dimensional line-tied and initially current-free bipole,
that is embedded in a non-uniform open potential field. The topology of this
configuration is that of an asymmetric coronal null-point, with a closed fan
surface and an open outer spine. When driven by slow photospheric shearing
motions, field lines, initially fully anchored below the fan dome, reconnect at
the null point, and jump to the open magnetic domain. This is the standard
interchange mode as sketched and calculated in 2D. The key result in 3D is
that, reconnected open field lines located in the vicinity of the outer spine,
keep reconnecting continuously, across an open quasi-separatrix layer, as
previously identified for non-open-null-point reconnection. The apparent
slipping motion of these field lines leads to form an extended narrow magnetic
flux tube at high altitude. Because of the slip-running reconnection, we
conjecture that if energetic particles would be traveling through, or be
accelerated inside, the diffusion region, they would be successively injected
along continuously reconnecting field lines that are connected farther and
farther from the spine. At the scale of the full Sun, owing to the super-radial
expansion of field lines below 3 solar radii, such energetic particles could
easily be injected in field lines slipping over significant distances, and
could eventually reach the distant flux tube that is well-connected to the
Earth
Higher Dimensional Cosmology with Some Dark Energy Models in Emergent, Logamediate and Intermediate Scenarios of the Universe
We have considered N-dimensional Einstein field equations in which
four-dimensional space-time is described by a FRW metric and that of extra
dimensions by an Euclidean metric. We have chosen the exponential forms of
scale factors a and d numbers of b in such a way that there is no singularity
for evolution of the higher dimensional Universe. We have supposed that the
Universe is filled with K-essence, Tachyonic, Normal Scalar Field and
DBI-essence. Here we have found the nature of potential of different scalar
field and graphically analyzed the potentials and the fields for three scenario
namely Emergent Scenario, Logamediate Scenario and Intermediate Scenario. Also
graphically we have depicted the geometrical parameters named statefinder
parameters and slow-roll parameters in the higher dimensional cosmology with
the above mentioned scenarios.Comment: 21 pages, 36 figure
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