23,769 research outputs found
Aerodynamic design for improved manueverability by use of three-dimensional transonic theory
Improvements in transonic maneuver performance by the use of three-dimensional transonic theory and a transonic design procedure were examined. The FLO-27 code of Jameson and Caughey was used to design a new wing for a fighter configuration with lower drag at transonic maneuver conditions. The wing airfoil sections were altered to reduce the upper-surface shock strength by means of a design procedure which is based on the iterative application of the FLO-27 code. The plan form of the fighter configuration was fixed and had a leading edge sweep of 45 deg and an aspect ratio of 3.28. Wind-tunnel tests were conducted on this configuration at Mach numbers from 0.60 to 0.95 and angles of attack from -2 deg to 17 deg. The transonic maneuver performance of this configuration was evaluated by comparison with a wing designed by empirical methods and a wing designed primarily by two-dimensional transonic theory. The configuration designed by the use of FLO-27 had the same or lower drag than the empirical wing and, for some conditions, lower drag than the two-dimensional design. From some maneuver conditions, the drag of the two-dimensional design was somewhat lower
Quasiclassical Coarse Graining and Thermodynamic Entropy
Our everyday descriptions of the universe are highly coarse-grained,
following only a tiny fraction of the variables necessary for a perfectly
fine-grained description. Coarse graining in classical physics is made natural
by our limited powers of observation and computation. But in the modern quantum
mechanics of closed systems, some measure of coarse graining is inescapable
because there are no non-trivial, probabilistic, fine-grained descriptions.
This essay explores the consequences of that fact. Quantum theory allows for
various coarse-grained descriptions some of which are mutually incompatible.
For most purposes, however, we are interested in the small subset of
``quasiclassical descriptions'' defined by ranges of values of averages over
small volumes of densities of conserved quantities such as energy and momentum
and approximately conserved quantities such as baryon number. The
near-conservation of these quasiclassical quantities results in approximate
decoherence, predictability, and local equilibrium, leading to closed sets of
equations of motion. In any description, information is sacrificed through the
coarse graining that yields decoherence and gives rise to probabilities for
histories. In quasiclassical descriptions, further information is sacrificed in
exhibiting the emergent regularities summarized by classical equations of
motion. An appropriate entropy measures the loss of information. For a
``quasiclassical realm'' this is connected with the usual thermodynamic entropy
as obtained from statistical mechanics. It was low for the initial state of our
universe and has been increasing since.Comment: 17 pages, 0 figures, revtex4, Dedicated to Rafael Sorkin on his 60th
birthday, minor correction
Excited nucleon electromagnetic form factors from broken spin-flavor symmetry
A group theoretical derivation of a relation between the N --> Delta charge
quadrupole transition and neutron charge form factors is presented.Comment: 4 pages, Proc. of the 12 th Int'l. Workshop on the Physics of Excited
Nucleons, NSTAR 2009, Beijing, April 19-22, 200
N-body Gravity and the Schroedinger Equation
We consider the problem of the motion of bodies in a self-gravitating
system in two spacetime dimensions. We point out that this system can be mapped
onto the quantum-mechanical problem of an N-body generalization of the problem
of the H molecular ion in one dimension. The canonical gravitational
N-body formalism can be extended to include electromagnetic charges. We derive
a general algorithm for solving this problem, and show how it reduces to known
results for the 2-body and 3-body systems.Comment: 15 pages, Latex, references added, typos corrected, final version
that appears in CQ
Running with Triplets: How Slepton Masses Change With Doubly-Charged Higgses
We examine the slepton masses of SUSYLR models and how they change due the
presence of light-doubly charged higgs bosons. We discover that the measurement
of the slepton masses could bound and even predict the value of the third
generation Yukawa coupling of leptons to the SU(2)_R Triplets. We also consider
the unification prospects for this model with the addition of left-handed, B -
L = 0 triplets--a model we call the Triplet Extended Supersymmetric Standard
Model (TESSM). Finally, we discuss the changes in the slepton masses due to the
presence of the SU(2)_L triplets.Comment: 20 pages, 6 figures, 4 table
A Model for Neutrino and Charged Lepton Masses in Extra Dimensions
We propose a model with one large submm size extra dimension in which the
gravity and right-handed (RH) neutrino propagate, but the three Standard Model
(SM) families are confined to fat branes of TeV^(-1) size or smaller. The
charged leptons and the light neutrinos receive mass from the five dimensional
Yukawa couplings with the SM singlet neutrino via electroweak Higgs, while the
KK excitations of the SM singlet neutrino gets large TeV scale masses from the
five dimensional Yukawa coupling with an electroweak singlet Higgs. The model
gives non-hierarchical light neutrino masses, accommodate hierarchical charged
lepton masses, and naturally explain why the light neutrino masses are so much
smaller compared to the charged lepton masses. Large neutrino mixing is
naturally expected in this scenario. The light neutrinos are Dirac particles in
this model, hence neutrinoless double beta decay is not allowed. The model has
also several interesting collider implications and can be tested at the LHC.Comment: 11 pages, no figure
Exotic fermion multiplets as a solution to baryon asymmetry, dark matter and neutrino masses
We propose an extension to the standard model where three exotic fermion
5-plets and one scalar 6-plet are added to the particle content. By demanding
that all interactions are renormalizable and standard model gauge invariant, we
show that the lightest exotic particle in this model can be a dark matter
candidate as long as the new 6-plet scalar does not develop a nonzero vacuum
expectation value. Furthermore, light neutrino masses are generated radiatively
at one-loop while the baryon asymmetry is produced by the CP-violating decays
of the second lightest exotic particle. We have demonstrated using concrete
examples that there is a parameter space where a consistent solution to the
problems of baryon asymmetry, dark matter and neutrino masses can be obtained.Comment: 17 pages, 2 figures (REVTeX4.1), v2: some refs added, v3: typos
corrected, Sec.VI.B, C modified, this version to appear in PR
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