4,784 research outputs found
Method and apparatus for optically monitoring the angular position of a rotating mirror
An optical system monitors the angular position of a rotating scanning mirror to indicate the effective start and end of each scan. At a certain angular position, a ray of energy transmitted to the mirror is reflected a plurality of times between the reflectors associated with the optical system and the line on the mirror parallel to the axis, and then to a detector to sense that angular position. A single optical system may be arranged to sense a plurality of different angular positions for each revolution of the mirror
High pressure compressor component performance report
A compressor optimization study defined a 10 stage configuration with a 22.6:1 pressure ratio, an adiabatic efficiency goal of 86.1%, and a polytropic efficiency of 90.6%; the corrected airflow is 53.5 kg/s. Subsequent component testing included three full scale tests: a six stage rig test, a 10 stage rig test, and another 10 stage rig test completed in the second quarter of 1982. Information from these tests is used to select the configuration for a core engine test and an integrated core/low spool test. The test results will also provide data base for the flight propulsion system. The results of the test series with both aerodynamic and mechanical performance of each compressor build are presented. The second 10 stage compressor adiabatic efficiency was 0.848 at a cruise operating point versus a test goal of 0.846
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
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
Helios-2 Vela-Ariel-5 gamma-ray burst source position
The gamma-ray burst of 28 January 1976, one of 18 events thus far detected in interplanetary space with Helios-2, was also observed with the Vela-5A, -6A and the Ariel-5 satellites. A small source field is obtained from the intersection of the region derived from the observed time delays between Helios-2 and Vela-5A and -6A with the source region independently found with the Ariel-5 X-ray detector. This area contains neither any steady X-ray source as scanned by HEAO-A nor any previously catalogued X-ray, radio or infrared sources, X-ray transients, quasars, seyferts, globular clusters, flare stars, pulsars, white dwarfs or high energy gamma-ray sources. The region is however, within the source field of a gamma-ray transient observed in 1974, which exhibited nuclear gamma-ray line structure
Can codimension-two branes solve the cosmological constant problem?
It has been suggested that codimension-two braneworlds might naturally
explain the vanishing of the 4D effective cosmological constant, due to the
automatic relation between the deficit angle and the brane tension. To
investigate whether this cancellation happens dynamically, and within the
context of a realistic cosmology, we study a codimension-two braneworld with
spherical extra dimensions compactified by magnetic flux. Assuming Einstein
gravity, we show that when the brane contains matter with an arbitrary equation
of state, the 4D metric components are not regular at the brane, unless the
brane has nonzero thickness. We construct explicit 6D solutions with thick
branes, treating the brane matter as a perturbation, and find that the universe
expands consistently with standard Friedmann-Robertson-Walker (FRW) cosmology.
The relation between the brane tension and the bulk deficit angle becomes
for a general equation of state. However, this
relation does not imply a self-tuning of the effective 4D cosmological constant
to zero; perturbations of the brane tension in a static solution lead to
deSitter or anti-deSitter braneworlds. Our results thus confirm other recent
work showing that codimension-two braneworlds in nonsupersymmetric Einstein
gravity do not lead to a dynamical relaxation of the cosmological constant, but
they leave open the possibility that supersymmetric versions can be compatible
with self-tuning.Comment: Revtex4, 17 pages, references added, typos corrected, minor points
clarified. Matches published versio
Transient domain walls and lepton asymmetry in the Left-Right symmetric model
It is shown that the dynamics of domain walls in Left-Right symmetric models,
separating respective regions of unbroken SU(2)_L and SU(2)_R in the early
universe, can give rise to baryogenesis via leptogenesis. Neutrinos have a
spatially varying complex mass matrix due to CP-violating scalar condensates in
the domain wall. The motion of the wall through the plasma generates a flux of
lepton number across the wall which is converted to a lepton asymmetry by
helicity-flipping scatterings. Subsequent processing of the lepton excess by
sphalerons results in the observed baryon asymmetry, for a range of parameters
in Left-Right symmetric models.Comment: v2 version accepted for publication in Phys. Rev. D. Discussion in
Introduction and Conclusion sharpened. Equation (12) corrected. 16 pages, 3
figure files, RevTeX4 styl
Interesting consequences of brane cosmology
We discuss cosmology in four dimensions within a context of brane-world
scenario.Such models can predict chaotic inflation with very low reheat
temperature depending on the brane tension. We notice that the gravitino
abundance is different in the brane-world cosmology and by tuning the brane
tension it is possible to get extremely low abundance. We also study
Affleck-Dine baryogenesis in our toy model.Comment: 5 pages, Trivial changes to match the published versio
Transient Accelerated Expansion and Double Quintessence
We consider Double Quintessence models for which the Dark Energy sector
consists of two coupled scalar fields. We study in particular the possibility
to have a transient acceleration in these models. In both Double Quintessence
models studied here, it is shown that if acceleration occurs, it is necessarily
transient. We consider also the possibility to have transient acceleration in
two one-field models, the Albrecht-Skordis model and the pure exponential.
Using separate conservative constraints (marginalizing over the other
parameters) on the effective equation of state , the relative density
of the Dark Energy and the present age of the universe, we
construct scenarios with a transient acceleration that has already ended at the
present time, and even with no acceleration at all, but a less conservative
analysis using the CMB data rules out the last possibility. The scenario with a
transient acceleration ended by today, can be implemented for the range of
cosmological parameters and .Comment: Version accepted in Phys. Rev. D, 22 pages, 10 figures, 4 table
Collision of Domain Walls and Reheating of the Brane Universe
We study a particle production at the collision of two domain walls in
5-dimensional Minkowski spacetime. This may provide the reheating mechanism of
an ekpyrotic (or cyclic) brane universe, in which two BPS branes collide and
evolve into a hot big bang universe. We evaluate a production rate of particles
confined to the domain wall. The energy density of created particles is given
as where is a coupling
constant of particles to a domain-wall scalar field, is the number of
bounces at the collision and is a fundamental mass scale of the domain
wall. It does not depend on the width of the domain wall, although the
typical energy scale of created particles is given by . The
reheating temperature is evaluated as . In order to have the baryogenesis at the electro-weak energy scale,
the fundamental mass scale is constrained as m_\eta \gsim 1.1\times 10^7 GeV
for .Comment: 10 pages, 12 figure
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