36,298 research outputs found
Necrotic tumor growth: an analytic approach
The present paper deals with a free boundary problem modeling the growth
process of necrotic multi-layer tumors. We prove the existence of flat
stationary solutions and determine the linearization of our model at such an
equilibrium. Finally, we compute the solutions of the stationary linearized
problem and comment on bifurcation.Comment: 14 pages, 3 figure
Multi- nuclei and kaon condensation
We extend previous relativistic mean-field (RMF) calculations of multi- nuclei, using vector boson fields with SU(3) PPV coupling constants and
scalar boson fields constrained phenomenologically. For a given core nucleus,
the resulting separation energy , as well as the
associated nuclear and -meson densities, saturate with the number
of mesons for . Saturation
appears robust against a wide range of variations, including the RMF nuclear
model used and the type of boson fields mediating the strong interactions.
Because generally does not exceed 200 MeV, it is argued that
multi- nuclei do not compete with multihyperonic nuclei in providing
the ground state of strange hadronic configurations and that kaon condensation
is unlikely to occur in strong-interaction self-bound strange hadronic matter.
Last, we explore possibly self-bound strange systems made of neutrons and
mesons, or protons and mesons, and study their properties.Comment: 21 pages, 8 figures, revised text and reference
Testing Einstein's time dilation under acceleration using M\"ossbauer spectroscopy
The Einstein time dilation formula was tested in several experiments. Many
trials have been made to measure the transverse second order Doppler shift by
M\"{o}ssbauer spectroscopy using a rotating absorber, to test the validity of
this formula. Such experiments are also able to test if the time dilation
depends only on the velocity of the absorber, as assumed by Einstein's clock
hypothesis, or the present centripetal acceleration contributes to the time
dilation. We show here that the fact that the experiment requires -ray
emission and detection slits of finite size, the absorption line is broadened;
by geometric longitudinal first order Doppler shifts immensely. Moreover, the
absorption line is non-Lorenzian. We obtain an explicit expression for the
absorption line for any angular velocity of the absorber.
The analysis of the experimental results, in all previous experiments which
did not observe the full absorption line itself, were wrong and the conclusions
doubtful. The only proper experiment was done by K\"{u}ndig (Phys. Rev. 129
(1963) 2371), who observed the broadening, but associated it to random
vibrations of the absorber. We establish necessary conditions for the
successful measurement of a transverse second order Doppler shift by
M\"{o}ssbauer spectroscopy. We indicate how the results of such an experiment
can be used to verify the existence of a Doppler shift due to acceleration and
to test the validity of Einstein's clock hypothesis.Comment: 11 pages, 4 figure
Modification of turbulent transport with continuous variation of flow shear in the Large Plasma Device
Continuous control over azimuthal flow and shear in the edge of the Large
Plasma Device (LAPD) has been achieved using a biasable limiter which has
allowed a careful study of the effect of flow shear on pressure-gradient-driven
turbulence and transport in LAPD. LAPD rotates spontaneously in the ion
diamagnetic direction (IDD); positive limiter bias first reduces, then
minimizes (producing a near-zero shear state), and finally reverses the flow
into the electron diamagnetic direction (EDD). Degradation of particle
confinement is observed in the minimum shearing state and reduction in
turbulent particle flux is observed with increasing shearing in both flow
directions. Near-complete suppression of turbulent particle flux is observed
for shearing rates comparable to the turbulent autocorrelation rate measured in
the minimum shear state. Turbulent flux suppression is dominated by amplitude
reduction in low-frequency (kHz) density fluctuations. An increase in
fluctuations for the highest shearing states is observed with the emergence of
a coherent mode which does not lead to net particle transport. The variations
of density fluctuations are fit well with power-laws and compare favorably to
simple models of shear suppression of transport.Comment: 10 pages, 5 figures; Submitted to Phys. Rev. Let
Unitarity Restoration in the Presence of Closed Timelike Curves
A proposal is made for a mathematically unambiguous treatment of evolution in
the presence of closed timelike curves. In constrast to other proposals for
handling the naively nonunitary evolution that is often present in such
situations, this proposal is causal, linear in the initial density matrix and
preserves probability. It provides a physically reasonable interpretation of
invertible nonunitary evolution by redefining the final Hilbert space so that
the evolution is unitary or equivalently by removing the nonunitary part of the
evolution operator using a polar decomposition.Comment: LaTeX, 17pp, Revisions: Title change, expanded and clarified
presentation of original proposal, esp. with regard to Heisenberg picture and
remaining in original Hilbert spac
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