9,277 research outputs found
Electrostatic propulsion system with a direct nuclear electrogenerator Patent
Nuclear electric generator for accelerating charged propellant particles in electrostatic propulsion syste
Reciprocal relativity of noninertial frames: quantum mechanics
Noninertial transformations on time-position-momentum-energy space {t,q,p,e}
with invariant Born-Green metric ds^2=-dt^2+dq^2/c^2+(1/b^2)(dp^2-de^2/c^2) and
the symplectic metric -de/\dt+dp/\dq are studied. This U(1,3) group of
transformations contains the Lorentz group as the inertial special case. In the
limit of small forces and velocities, it reduces to the expected Hamilton
transformations leaving invariant the symplectic metric and the nonrelativistic
line element ds^2=dt^2. The U(1,3) transformations bound relative velocities by
c and relative forces by b. Spacetime is no longer an invariant subspace but is
relative to noninertial observer frames. Born was lead to the metric by a
concept of reciprocity between position and momentum degrees of freedom and for
this reason we call this reciprocal relativity.
For large b, such effects will almost certainly only manifest in a quantum
regime. Wigner showed that special relativistic quantum mechanics follows from
the projective representations of the inhomogeneous Lorentz group. Projective
representations of a Lie group are equivalent to the unitary reprentations of
its central extension. The same method of projective representations of the
inhomogeneous U(1,3) group is used to define the quantum theory in the
noninertial case. The central extension of the inhomogeneous U(1,3) group is
the cover of the quaplectic group Q(1,3)=U(1,3)*s H(4). H(4) is the
Weyl-Heisenberg group. A set of second order wave equations results from the
representations of the Casimir operators
Light Sheets and the Covariant Entropy Conjecture
We examine the holography bound suggested by Bousso in his covariant entropy
conjecture, and argue that it is violated because his notion of light sheet is
too generous. We suggest its replacement by a weaker bound.Comment: 5 pages, to appear in Classical and Quantum Gravit
The speed of gravity in general relativity
The question is discussed of what is the speed of gravity (at the fundamental
non-perturbative level). The question is important, if nowhere else, in
discussing the problem of information "lost" in black holes. It turns out that
the duly defined "gravitational signal" generally may be causal, superluminal
and "semi-superluminal". In the class of globally hyperbolic spacetimes the two
last varieties coincide. And if some (often imposed, but not always satisfied)
conditions hold, the signals may be \emph{only} causal. In this sense the speed
of gravity does not exceed the speed of light.Comment: typos corrected, et
The influence of composition, annealing treatment, and texture on the fracture toughness of Ti-5Al-2.5Sn plate at cryogenic temperatures
The plane strain fracture toughness K sub Ic and conventional tensile properties of two commercially produced one-inch thick Ti-5Al-2.5Sn plates were determined at cryogenic temperatures. One plate was extra-low interstitial (ELI) grade, the other normal interstitial. Portions of each plate were mill annealed at 1088 K (1500 F) followed by either air cooling or furnace cooling. The tensile properties, flow curves, and K sub Ic of these plates were determined at 295 K (room temperature), 77 K (liquid nitrogen temperature), and 20 K (liquid hydrogen temperature)
Solenoidal versus compressive turbulence forcing
We analyze the statistics and star formation rate obtained in high-resolution
numerical experiments of forced supersonic turbulence, and compare with
observations. We concentrate on a systematic comparison of solenoidal
(divergence-free) and compressive (curl-free) forcing, which are two limiting
cases of turbulence driving. Our results show that for the same RMS Mach
number, compressive forcing produces a three times larger standard deviation of
the density probability distribution. When self-gravity is included in the
models, the star formation rate is more than one order of magnitude higher for
compressive forcing than for solenoidal forcing.Comment: 1 page, to appear in the proceedings of the IAU General Assembly
Joint Discussion 14 "FIR2009: The ISM of Galaxies in the Far-Infrared and
Sub-Millimetre", ed. M. Cunningha
Precise nondivergent analytic formulas for the radiative corrections to the beta energy spectrum in hyperon semileptonic decays over the entire Dalitz plot
Very accurate analytical expressions for the radiative corrections of
unpolarized hyperons semileptonic decays of charged and neutral baryons have
been obtained in the recent past. Some of these formulas contain logarithmic
singularities at the edges of the Dalitz plot for the three- and four-body
decays. These singularities are analyzed and integrated analytically to obtain
new divergentless formulas for the energy spectrum of the produced beta
particle. The new equations contain terms of the order alpha times the momentum
transfer, are applicable to any beta decay process and are suitable for a
model-independent experimental analysis.Comment: 22 pages, 4 figure
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