32,795 research outputs found
Electric vehicle power train instrumentation: Some constraints and considerations
The application of pulse modulation control (choppers) to dc motors creates unique instrumentation problems. In particular, the high harmonic components contained in the current waveforms require frequency response accommodations not normally considered in dc instrumentation. In addition to current sensing, accurate power measurement requires not only adequate frequency response but must also address phase errors caused by the finite bandwidths and component characteristics involved. The implications of these problems are assessed
Performance characteristics of the 12 GHz, 200 watt transmitter experiment package for CTS
The experiment package consists of a 200 W output stage tube (OST) powered by a power processing system (PPS). Descriptions of both the PPS and OST are given. The PPS provides the necessary voltages with a measured dc/dc conversion efficiency of 89 percent. The OST, a traveling wave tube with multiple collectors, has a saturated rf output power of 224 W and operates at an overall efficiency exceeding 40 percent over an 85 MHz bandwidth at 12 GHz. OST performance given includes frequency response, saturation characteristics, group delay, AM to PM conversion, inter-modulation distortion, and two channel gain suppression. Single and dual channel FM video performance is presented. It was determined that for 12 MHz peak to peak frequency deviation on each channel, dual channel FM television signals can be transmitted through the TEP at 60 W, each channel, with 40 MHz channel spacing (center to center)
Normal ground state of dense relativistic matter in a magnetic field
The properties of the ground state of relativistic matter in a magnetic field
are examined within the framework of a Nambu-Jona-Lasinio model. The main
emphasis of this study is the normal ground state, which is realized at
sufficiently high temperatures and/or sufficiently large chemical potentials.
In contrast to the vacuum state, which is characterized by the magnetic
catalysis of chiral symmetry breaking, the normal state is accompanied by the
dynamical generation of the chiral shift parameter . In the chiral
limit, the value of determines a relative shift of the longitudinal
momenta (along the direction of the magnetic field) in the dispersion relations
of opposite chirality fermions. We argue that the chirality remains a good
approximate quantum number even for massive fermions in the vicinity of the
Fermi surface and, therefore, the chiral shift is expected to play an important
role in many types of cold dense relativistic matter, relevant for applications
in compact stars. The qualitative implications of the revealed structure of the
normal ground state on the physics of protoneutron stars are discussed. A
noticeable feature of the parameter is that it is insensitive to
temperature when , where is the chemical potential, and
{\it increases} with temperature for . The latter implies that the
chiral shift parameter is also generated in the regime relevant for heavy ion
collisions.Comment: 28 pages, 6 figures; v2: title changed in journa
Solution of the Percus-Yevick equation for hard discs
We solve the Percus-Yevick equation in two dimensions by reducing it to a set
of simple integral equations. We numerically obtain both the pair correlation
function and the equation of state for a hard disc fluid and find good
agreement with available Monte-Carlo calculations. The present method of
resolution may be generalized to any even dimension.Comment: 9 pages, 3 figure
Time delay occultation data of the Helios spacecraft for probing the electron density distribution in the solar corona
S-band time delay measurements were collected from the spacecraft Helios A and B during three solar occultations in 1975/76 within heliocentric distances of about 3 and 215 earth radius in terms of range, Doppler frequency shift, and electron content. Characteristic features of measurement and data processing are described. Typical data sets are discussed to probe the electron density distribution near the sun (west and east limb as well) including the outer and extended corona. Steady-state and dynamical aspects of the solar corona are presented and compared with earth-bound-K-coronagraph measurements. Using a weighted least squares estimation, parameters of an average coronal electron density profile are derived in a preliminary analysis to yield electron densities at r = 3, 65, 215 earth radius. Transient phenomena are discussed and a velocity of propagation v is nearly equal to 900 km/s is determined for plasma ejecta from a solar flare observed during an extraordinary set of Helios B electron content measurements
An Interval Newton Method
We introduce an interval Newton method for bounding solutions of systems of nonlinear equations. It entails three subalgorithms. The first is a Gauss-Seidel-type step. The second is a real (noninterval) Newton iteration. The third solves the linearized equations by elimination. We explain why each subalgorithm is desirable and how they fit together to provide solutions in as little as one-third or one-quarter the time required by Krawczyk\u27s method [7] in our implementations
Probing Disordered Substrates by Imaging the Adsorbate in its Fluid Phase
Several recent imaging experiments access the equilibrium density profiles of
interacting particles confined to a two-dimensional substrate. When these
particles are in a fluid phase, we show that such data yields precise
information regarding substrate disorder as reflected in one-point functions
and two-point correlations of the fluid. Using Monte Carlo simulations and
replica generalizations of liquid state theories, we extract unusual two-point
correlations of time-averaged density inhomogeneities induced by disorder.
Distribution functions such as these have not hitherto been measured but should
be experimentally accessible.Comment: 10 pages revtex 4 figure
Evaluation of a ln tan integral arising in quantum field theory
We analytically evaluate a dilogarithmic integral that is prototypical of
volumes of ideal tetrahedra in hyperbolic geometry. We additionally obtain new
representations of the Clausen function Cl_2 and the Catalan constant
G=Cl_2(\pi/2), as well as new relations between sine and Clausen function
values.Comment: 24 pages, no figure
Design considerations for large space electric power systems
As power levels of spacecraft rise to the 50 to 100 kW range, it becomes apparent that low voltage (28 V) dc power distribution and management systems will not operate efficiently at these higher power levels. The concept of transforming a solar array voltage at 150 V dc into a 1000 V ac distribution system operating at 20 kHz is examined. The transformation is accomplished with series-resonant inverter by using a rotary transformer to isolate the solar array from the spacecraft. The power can then be distributed in any desired method such as three phase delta to delta. The distribution voltage can be easily transformed to any desired load voltage and operating frequency. The reasons for the voltage limitations on the solar array due to plasma interactions and the many advantages of a high voltage, high frequency at distribution system are discussed
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