6,791 research outputs found
The Goddard program of gamma ray transient astronomy
Gamma ray burst studies are reviewed. The past results, present status and future expectations are outlined regarding endeavors using experiments on balloons, IMP-6 and -7, OGO-3, ISEE-1 and -3, Helios-2, Solar Maximum Mission, the Einstein Observatory, Solar Polar and the Gamma Ray Observatory, and with the interplanetary gamma ray burst networks, to which some of these spacecraft sensors contribute. Additional emphasis is given to the recent discovery of a new type of gamma ray transient, detected on 1979 March 5
The protein import apparatus of chloroplasts
Routing of cytosolically synthesized precursor proteins into chloroplasts is a specific process which involves a multitude of soluble and membrane components. In this review we wil1 focus on early events of the translocation pathway of nuclear coded plastidic precursor proteins and compare import routes for polypeptide of the outer chloroplast envelope to that of internal chloroplast compartments. A number of proteins housed in the chloroplast envelopes have been implied to be involved in the translocation process, but so far a certain function has not been assigned to any of these proteins. The only exception could be an envelope localized hsc 70 homologue which could retain the import competence of a precursor protein in transit into the organelle
Spontaneous Symmetry Breaking in General Relativity. Vector Order Parameter
Gravitational properties of a hedge-hog type topological defect in two extra
dimensions are considered in General Relativity employing a vector as the order
parameter. All previous considerations were done using the order parameter in
the form of a multiplet in a target space of scalar fields. The difference of
these two approaches is analyzed and demonstrated in detail. Regular solutions
of the Einstein equations are studied analytically and numerically. It is shown
that the existence of a negative cosmological constant is sufficient for the
spontaneous symmetry breaking of the initially plain bulk. Regular
configurations have a growing gravitational potential and are able to trap the
matter on the brane. If the energy of spontaneous symmetry breaking is high,
the gravitational potential has several points of minimum. Identical in the
uniform bulk spin-less particles, being trapped within separate minima, acquire
different masses and appear to the observer on brane as different particles
with integer spins.Comment: 23 pages, 6 figure
Leptogenesis with Left-Right domain walls
The presence of domain walls separating regions of unbroken and
is shown to provide necessary conditions for leptogenesis which
converts later to the observed Baryon aymmetry. The strength of lepton number
violation is related to the majorana neutrino mass and hence related to current
bounds on light neutrino masses. Thus the observed neutrino masses and the
Baryon asymmetry can be used to constrain the scale of Left-Right symmetry
breaking.Comment: References added, To appear in Praman
Status of Electroweak Phase Transition and Baryogenesis
I review recent progress on the electroweak phase transition and
baryogenesis, focusing on the minimal supersymmetric standard model as the
source of new physics.Comment: 10 pp, 6 figures; plenary talk given at 6th Workshop on High Energy
Physics Phenomenology, 4 Jan. 2000, Chennai, India. v.2: added reference
Postsynaptic calcium/calmodulin-dependent protein kinase II is required to limit elaboration of presynaptic and postsynaptic neuronal arbors
Neuronal dendritic and axonal arbors grow to a characteristic size and then stabilize their structures. Activity-dependent stop-growing signals may limit neuronal process elaboration. We tested whether endogenous calcium/calmodulin-dependent protein kinase II (CaMKII) activity in postsynaptic optic tectal cells is required to restrict the elaboration of neuronal processes in the Xenopus tadpole retinotectal projection. Optic tectal cells were infected with vaccinia viruses that express CaMKII-specific inhibitory peptides. In vivo time-lapse imaging revealed that expression of CaMKII inhibitors blocked the growth restriction that normally occurs during maturation of tectal cell dendritic arbors. Postsynaptic CaMKII inhibition also increased the growth of presynaptic retinotectal axon arbors. The results indicate that endogenous postsynaptic CaMKII activity is required to limit the growth of presynaptic and postsynaptic arbor structures in vivo
A New Source for Electroweak Baryogenesis in the MSSM
One of the most experimentally testable explanations for the origin of the
baryon asymmetry of the universe is that it was created during the electroweak
phase transition, in the minimal supersymmetric standard model. Previous
efforts have focused on the current for the difference of the two Higgsino
fields, , as the source of biasing sphalerons to create the baryon
asymmetry. We point out that the current for the orthogonal linear combination,
, is larger by several orders of magnitude. Although this increases
the efficiency of electroweak baryogenesis, we nevertheless find that large
CP-violating angles are required to get a large enough baryon
asymmetry.Comment: 4 pages, 2 figures; numerical error corrected, which implies that
large CP violation is needed to get observed baryon asymmetry. We improved
solution of diffusion equations, and computed more accurate values for
diffusion coefficient and damping rate
Using fluid inclusions to constrain ore fluid properties at the goldstrike carlin-type gold system, Nevada, USA
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