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Kinetic Theory of Transient Condensation and Evaporation at a Plane Surface
The phenomenon of transient condensation onto, or evaporation from, a liquid sheet in contact
with its pure vapor is treated from a kinetic theory viewpoint. The Maxwell moment method is used
to formulate the detailed transient problem. A steady surface mass flux rate exists for times large in
comparison with the collision time, that is, in the continuum regime, and explicit formulas are given
for this limit. The complete gasdynamic field, however, is nonsteady for all times. The calculations are
carried out utilizing four moments, and the effects of incorporating additional moments are negligible.
Finally, the analysis is extended to incorporate imperfect mass and temperature accommodation.
Examination of the transient solution and a matched asymptotic "quasisteady" solution shows that
the gasdynamic field consists of a diffusion process near the liquid surface coupled through an expansion
or compression wave to the constant far field state
Gravitational Correction to Running of Gauge Couplings
We calculate the contribution of graviton exchange to the running of gauge
couplings at lowest non-trivial order in perturbation theory. Including this
contribution in a theory that features coupling constant unification does not
upset this unification, but rather shifts the unification scale. When
extrapolated formally, the gravitational correction renders all gauge couplings
asymptotically free.Comment: 4 pages, 2 figures; v2: Clarified awkward sentences and notations.
Corrected typos. Added references and discussion thereof in introduction.
Minor copy editting changes to agree with version to be published in Physical
Review Letter
On the degenerated soft-mode instability
We consider instabilities of a single mode with finite wavenumber in
inversion symmetric spatially one dimensional systems, where the character of
the bifurcation changes from sub- to supercritical behaviour. Starting from a
general equation of motion the full amplitude equation is derived
systematically and formulas for the dependence of the coefficients on the
system parameters are obtained. We emphasise the importance of nonlinear
derivative terms in the amplitude equation for the behaviour in the vicinity of
the bifurcation point. Especially the numerical values of the corresponding
coefficients determine the region of coexistence between the stable trivial
solution and stable spatially periodic patterns. Our approach clearly shows
that similar considerations fail for the case of oscillatory instabilities.Comment: 16 pages, uses iop style files, manuscript also available at
ftp://athene.fkp.physik.th-darmstadt.de/pub/publications/wolfram/jpa_97/ or
at http://athene.fkp.physik.th-darmstadt.de/public/wolfram_publ.html. J.
Phys. A in pres
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