102 research outputs found
The Microwave Thermal Thruster Concept
The microwave thermal thruster heats propellant via a heat-exchanger then expands it through a rocket nozzle to produce thrust. The heat-exchanger is simply a microwave-absorbent structure through which propellant flows in small channels. Nuclear thermal thrusters are based on an analogous principle, using neutrons rather than microwaves, and have experimentally demonstrated specific impulses exceeding 850 seconds. A microwave equivalent will likely have a similar specific impulse, since both nuclear and microwave thermal thrusters are ultimately constrained by material thermal limits, rather than the energy-density limits of chemical propellants. We present the microwave thermal thruster concept by characterizing a novel variation for beamed-energy launch. In reducing the thruster concept to practice, the enabling physical process is microwave absorption by refractory materials, and we examine semiconductor and susceptor-based approaches to achieving this absorption within the heat-exchanger structure
Suppression of flavor violation in an A4 warped extra dimensional model
In an attempt to simultaneously explain the observed masses and mixing
patterns of both quarks and leptons, we recently proposed a model
(JHEP08(2010)115) based on the non abelian discrete flavor group A4,
implemented in a custodial RS setup with a bulk Higgs. We showed that the
standard model flavor structure can be realized within the zero mode
approximation (ZMA), with nearly tribimaximal (TBM) neutrino mixing and a
realistic CKM matrix with rather mild assumptions. An important advantage of
this framework with respect to flavor anarchic models is the vanishing of the
dangerous tree level KK gluon contribution to \epsilon_K and the suppression of
the new physics one loop contributions to the neutron EDM, \epsilon'/\epsilon,
b->s\gamma and Higgs mediated flavor changing neutral current (FCNC) processes.
These results are obtained beyond the ZMA, in order to account for the the full
flavor structure and mixing of the zero modes and first Kaluza-Klein (KK) modes
of all generations. The resulting constraints on the KK mass scale are shown to
be significantly relaxed compared to the flavor anarchic case, showing
explicitly the role of non abelian discrete flavor symmetries in relaxing
flavor violation bounds within the RS setup. As a byproduct of our analysis we
also obtain the same contributions for the custodial anarchic case with two
SU(2)_R doublets for each fermion generation.Comment: 8 pages, 4 figures; contribution prepared for DISCRETE'10 - Symposium
on Prospects in the Physics of Discrete Symmetrie
Second Generation of the Automated Cobas Amplicor HCV Assay Improves Sensitivity of Hepatitis C Virus RNA Detection and Yields Results That Are More Clinically Relevant
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