2,281 research outputs found
Description of a digital computer simulation of an Annular Momentum Control Device (AMCD) laboratory test model
A description of a digital computer simulation of an Annular Momentum Control Device (AMCD) laboratory model is presented. The AMCD is a momentum exchange device which is under development as an advanced control effector for spacecraft attitude control systems. The digital computer simulation of this device incorporates the following models: six degree of freedom rigid body dynamics; rim warp; controller dynamics; nonlinear distributed element axial bearings; as well as power driver and power supply current limits. An annotated FORTRAN IV source code listing of the computer program is included
Neutrinos from the Propagation of a Relativistic Jet Through a Star
We discuss the neutrino signature of a relativistic jet propagating through a
stellar envelope, a scenario realized in the collapsar model for Gamma Ray
Bursts (GRBs). It is shown that the dramatic slowing of the jet deep within the
star is accompanied by inelastic neutron-nucleon collisions and the conversion
of a substantial fraction of the jet kinetic energy to neutrinos. These
neutrinos have observed energies in the range two to tens of GeV and an
estimated detection rate comparable to or larger than the detection rate of GeV
neutrinos from other GRB-related processes. The time delay between the arrival
of these neutrinos and the GRB photons is tens of seconds. An observation of
this delay would provide an indication that the GRB jet originated in a massive
star.Comment: To appear in Ap
Measurement of the Width Difference of B_d Mesons
We estimate \Delta Gamma_d/\Gamma_d, including 1/m_b contributions and part
of the next-to-leading order QCD corrections, and find it to be around 0.3%. We
show the methods to measure \Delta Gamma_d/\Gamma_d by using at least two
different final states on the untagged B_d decay. The nonzero width difference
can also be used to identify new physics effects and to resolve a twofold
discrete ambiguity in the B_d-\bar{B}_d mixing phase. With the high statistics
and accurate time resolution of the upcoming LHC experiment, the measurement of
\Delta Gamma_d seems to be possible. This measurement would be important for an
accurate measurement of \sin2\phi_1 at the LHC. We also derive an upper bound
on the value of \Delta Gamma_d/\Gamma_d in the presence of new physics.Comment: 3 pages, LaTeX, Presented at the 5th KEK Topical Conference(KEKTC5
The Probability Density of the Higgs Boson Mass
The LEP Collaborations have reported a small excess of events in their
combined Higgs boson analysis at center of mass energies up to about 208 GeV.
In this communication, I present the result of a calculation of the probability
distribution function of the Higgs boson mass which can be rigorously obtained
if the validity of the Standard Model is assumed. It arises from the
combination of the most recent set of precision electroweak data and the
current results of the Higgs searches at LEP 2.Comment: 3 pages, 2 figure
An Assessment of Integrated Flywheel System Technology
The current state of the technology in flywheel storage systems and ancillary components, the technology in light of future requirements, and technology development needs to rectify these shortfalls were identified. Technology efforts conducted in Europe and in the United States were reviewed. Results of developments in composite material rotors, magnetic suspension systems, motor/generators and electronics, and system dynamics and control were presented. The technology issues for the various disciplines and technology enhancement scenarios are discussed. A summary of the workshop, and conclusions and recommendations are presented
Analysis and simulation of a magnetic bearing suspension system for a laboratory model annular momentum control device
A linear analysis and the results of a nonlinear simulation of a magnetic bearing suspension system which uses permanent magnet flux biasing are presented. The magnetic bearing suspension is part of a 4068 N-m-s (3000 lb-ft-sec) laboratory model annular momentum control device (AMCD). The simulation includes rigid body rim dynamics, linear and nonlinear axial actuators, linear radial actuators, axial and radial rim warp, and power supply and power driver current limits
Quark Mass Matrices from a Softly Broken U(1) Symmetry
Assigning U(1) charges to the quarks of the standard model, and allowing one
extra scalar doublet with m^2 > 0, the correct pattern of the up and down quark
mass matrices is obtained, together with their charged-current mixing matrix.Comment: 10 pages, no figur
Neutral top-pion and the rare top decays
We study the rare top decays in the
framework of topcolor-assisted technicolor() models. We find that the
neutral top-pion can produce significant contributions to these
processes via the flavor changing couplings and
. For the mass and
the parameter , the branching ratio (t can
reach . Taking into account the constraints of the present
experimental limit of the process on the free parameters of
models, we find that the value of ()() is in the range of
1.8.Comment: To be published in Phys.
Z decay into two massless gauge bosons in a magnetic field
An investigation of the processes Z to gluon-gluon and Z to photon-photon in
a background magnetic field is presented. For homogeneous fields corrections to
the charged fermion propagator can be calculated in leading orders of the
magnetic field. This work examines the first order contributions of the
corrected propagator to decays that are otherwise zero. Results of the decay
rates for varying field strengths are included.Comment: 14 pages, 2 figures, needs RevTeX4; typos corrected, appendix added,
references added, format changed to preprint mod
Improved Temperature Performance of 1.31-mu/m Quantum Dot Lasers by Optimized Ridge Waveguide Design
In this letter, we demonstrate the importance of the fabricated device structure for the external differential efficiency, threshold current density, and maximum operating temperature for ground state operation of a 1.31-mu/m quantum dot laser. The introduction of a shallow ridge etch design and selective electroplating of the gold bondpads is demonstrated to offer improved performance in comparison to a deep ridge etch design with thinner evaporated gold bondpads
- …