9,832 research outputs found
Antenna beam-shaping apparatus Patent
Device for improving efficiency of parabolic horn antenna system for linearly polarized signal
Parabolic reflector horn feed with spillover correction Patent
Device for improving efficiency of parabolic reflector horn for linearly or circularly polarized wave
Insertion loss measuring apparatus having transformer means connected across a pair of bolometers Patent
High impedance alternating current sensing transformer device between two bolometers for measuring insertion loss of test componen
Host-Parasite Co-evolution and Optimal Mutation Rates for Semi-conservative Quasispecies
In this paper, we extend a model of host-parasite co-evolution to incorporate
the semi-conservative nature of DNA replication for both the host and the
parasite. We find that the optimal mutation rate for the semi-conservative and
conservative hosts converge for realistic genome lengths, thus maintaining the
admirable agreement between theory and experiment found previously for the
conservative model and justifying the conservative approximation in some cases.
We demonstrate that, while the optimal mutation rate for a conservative and
semi-conservative parasite interacting with a given immune system is similar to
that of a conservative parasite, the properties away from this optimum differ
significantly. We suspect that this difference, coupled with the requirement
that a parasite optimize survival in a range of viable hosts, may help explain
why semi-conservative viruses are known to have significantly lower mutation
rates than their conservative counterparts
The COLD-SAT Experiment for Cryogenic Fluid Management Technology
Future national space transportation missions will depend on the use of cryogenic fluid management technology development needs for these missions. In-space testing will be conducted in order to show low gravity cryogenic fluid management concepts and to acquire a technical data base. Liquid H2 is the preferred test fluid due to its propellant use. The design of COLD-SAT (Cryogenic On-orbit Liquid Depot Storage, Acquisition, and Transfer Satellite), an Expendable Launch Vehicle (ELV) launched orbital spacecraft that will perform subcritical liquid H2 storage and transfer experiments under low gravity conditions is studied. An Atlas launch vehicle will place COLD-SAT into a circular orbit, and the 3-axis controlled spacecraft bus will provide electric power, experiment control, and data management, attitude control, and propulsive accelerations for the experiments. Low levels of acceleration will provide data on the effects that low gravity might have on the heat and mass transfer processes used. The experiment module will contain 3 liquid H2 tanks; fluid transfer, pressurization and venting equipment; and instrumentation
A Selective Advantage for Conservative Viruses
In this letter we study the full semi-conservative treatment of a model for
the co-evolution of a virus and an adaptive immune system. Regions of viability
are calculated for both conservatively and semi-conservatively replicating
viruses interacting with a realistic semi-conservatively replicating immune
system. The conservative virus is found to have a selective advantage in the
form of an ability to survive in regions with a wider range of mutation rates
than its semi-conservative counterpart. This may help explain the existence of
a rich range of viruses with conservatively replicating genomes, a trait which
is found nowhere else in nature.Comment: 4 pages, 2 figure
Do columnar defects produce bulk pinning?
From magneto-optical imaging performed on heavy-ion irradiated YBaCuO single
crystals, it is found that at fields and temperatures where strong single
vortex pinning by individual irradiation-induced amorphous columnar defects is
to be expected, vortex motion is limited by the nucleation of vortex kinks at
the specimen surface rather than by half-loop nucleation in the bulk. In the
material bulk, vortex motion occurs through (easy) kink sliding. Depinning in
the bulk determines the screening current only at fields comparable to or
larger than the matching field, at which the majority of moving vortices is not
trapped by an ion track.Comment: 5 pages, 5 figures, submitted to Physical Review Letter
Cold Formed Steel Tension Members with Two and Three Staggered Bolts
The second edition of the North American Specification for the Design of Cold Formed Steel Structural Members was published in October of 2007 for use in Canada, Mexico, and the United States. This Specification contains two country specific a ppe ndices, namely Appendix A (ANSI/AISI S100- 07) for use in the US and Mexico and Appendix B (CSA S136- 07) for use in Canada. Both Appendix A and B require that a bolt stagger reduction factor of 0.90 be used when calculating the tearing failure strength [resistance] of a cold formed steel member in tension with staggered bolts. This 10% reduction was based on limited testing that was carried out by Dr. Roger LaBoube of the University of Missouri-Rolla, which has now changed its name to the Missouri University of Science & Technology . The objective of this study was to establish if this bolt stagger reduction factor is indeed necessary since the stagger term of [s 2 /4g] has been used in the steel industry for many years without such a reduction. Experimental testing of two and three staggered bolt tension members was carried out in the Structures Laboratory of the Department of Civil Engineering at the University of Waterloo. Based on the test results of the 1.6 mm, 2.1 mm, 2.9 mm, 4 mm, 5 mm, and 6 mm thick steel sheet, it can be concluded that the 0.90 bolt stagger reduction factor is not necessary for the steel plate thicknesses tested
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