20,026 research outputs found
Hyperon Nonleptonic Decays in Chiral Perturbation Theory Reexamined
We recalculate the leading nonanalytic contributions to the amplitudes for
hyperon nonleptonic decays in chiral perturbation theory. Our results partially
disagree with those calculated before, and include new terms previously omitted
in the P-wave amplitudes. Although these modifications are numerically
significant, they do not change the well-known fact that good agreement with
experiment cannot be simultaneously achieved using one-loop S- and P-wave
amplitudes.Comment: 14 pages, latex, 3 figures, uses axodraw.sty, minor additions, to
appear in Phys. Rev.
1/N_c Expansion of the Heavy Baryon Isgur-Wise Functions
The 1/N_c expansion of the heavy baryon Isgur-Wise functions is discussed.
Because of the contracted SU(2N_f) light quark spin-flavor symmetry, the
universality relations among the Isgur-Wise functions of \Lambda_b to \Lambda_c
and \Sigma_b^{(*)} to \Sigma_c^{(*)} are valid up to the order of 1/N_c^2.Comment: 7 pages, latex, no figures, to appear in Phys. Rev.
The structure of lightning flashes HF-UHF: 12 September 1975, Atlanta, Georgia
Simultaneous measurement of sferics at 3, 30, 139, and 295 MHz were made during thunderstorms. Wideband electronics and an analogue tape recorder continuously recorded the radiation from lightning with about 300 kHz of bandwidth. The data were obtained during the passage of a cold front. Flashing rate, burst rate and the structure of individual flashes were recorded. The record of a typical flash begins with a sudden burst of closely spaced pulses whose temporal structure is typical of the stepped leader, and ends in a large pulse suggestive of a first return stroke. The remainder of the flash consists of a sequence of pulses of varying amplitude separated by quiet periods of the order of milliseconds. The shape of these pulses and the temporal structure suggest that the first few large pulses are return strokes. Other discharges begin with widely spaced discrete pulses and resemble the preceding discharge less the leader and return stroke phase. The radiation exhibits a similar structure, at each of the frequencies monitored
Effect of dislocations on properties of heteroepitaxial InP solar cells
The apparently unrelated phenomena of temperature dependency, carrier removal and photoluminescence are shown to be affected by the high dislocation densities present in heteroepitaxial InP solar cells. Using homoepitaxial InP cells as a baseline, it is found that the relatively high dislocation densities present in heteroepitaxial InP/GaAs cells lead to increased volumes of dVoc/dt and carrier removal rate and substantial decreases in photoluminescence spectral intensities. With respect to dVoc/dt, the observed effect is attributed to the tendency of dislocations to reduce Voc. Although the basic cause for the observed increase in carrier removal rate is unclear, it is speculated that the decreased photoluminescence intensity is attributable to defect levels introduced by dislocations in the heteroepitaxial cells
NASA-JSC antenna near-field measurement system
Work was completed on the near-field range control software. The capabilities of the data processing software were expanded with the addition of probe compensation. In addition, the user can process the measured data from the same computer terminal used for range control. The design of the laser metrology system was completed. It provides precise measruement of probe location during near-field measurements as well as position data for control of the translation beam and probe cart. A near-field range measurement system was designed, fabricated, and tested
The Decuplet Revisited in PT
The paper deals with two issues. First, we explore the quantitiative
importance of higher multiplets for properties of the decuplet in
chiral perturbation theory. In particular, it is found that the lowest order
one--loop contributions from the Roper octet to the decuplet masses and
magnetic moments are substantial. The relevance of these results to the chiral
expansion in general is discussed. The exact values of the magnetic moments
depend upon delicate cancellations involving ill--determined coupling
constants. Second, we present new relations between the magnetic moments of the
decuplet that are independent of all couplings. They are exact at the
order of the chiral expansion used in this paper.Comment: 7 pages of double column revtex, no figure
Airborne Advanced Reconfigurable Computer System (ARCS)
A digital computer subsystem fault-tolerant concept was defined, and the potential benefits and costs of such a subsystem were assessed when used as the central element of a new transport's flight control system. The derived advanced reconfigurable computer system (ARCS) is a triple-redundant computer subsystem that automatically reconfigures, under multiple fault conditions, from triplex to duplex to simplex operation, with redundancy recovery if the fault condition is transient. The study included criteria development covering factors at the aircraft's operation level that would influence the design of a fault-tolerant system for commercial airline use. A new reliability analysis tool was developed for evaluating redundant, fault-tolerant system availability and survivability; and a stringent digital system software design methodology was used to achieve design/implementation visibility
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