6,531 research outputs found
The contact angle in inviscid fluid mechanics
We show that in general, the specification of a contact angle condition at
the contact line in inviscid fluid motions is incompatible with the classical
field equations and boundary conditions generally applicable to them. The
limited conditions under which such a specification is permissible are derived;
however, these include cases where the static meniscus is not flat. In view of
this situation, the status of the many `solutions' in the literature which
prescribe a contact angle in potential flows comes into question. We suggest
that these solutions which attempt to incorporate a phenomenological, but
incompatible, condition are in some, imprecise sense `weak-type solutions';
they satisfy or are likely to satisfy, at least in the limit, the governing
equations and boundary conditions everywhere except in the neighbourhood of the
contact line. We discuss the implications of the result for the analysis of
inviscid flows with free surfaces.Comment: 13 pages, no figures, no table
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
Exact Haldane mapping for all and super universality in spin chains
The low energy dynamics of the anti-ferromagnetic Heisenberg spin chain
in the semiclassical limit is known to map onto the O(3) nonlinear
model with a term in 1+1 dimension. Guided by the underlying
dual symmetry of the spin chain, as well as the recently established
topological significance of "dangling edge spins," we report an {\em exact}
mapping onto the O(3) model that avoids the conventional large
approximation altogether. Our new methodology demonstrates all the super
universal features of the angle concept that previously arose in the
theory of the quantum Hall effect. It explains why Haldane's original ideas
remarkably yield the correct answer in spite of the fundamental complications
that generally exist in the idea of semiclassical expansions
Spectral reflectance measurements of a virus host model
A technique has been developed to detect the characteristic spectral signatures of healthy and infected St. Augustine grass. It is possible to predict the coverage of the infected area provided ground truth coverage shows positive St. Augustine grass turf. Qualitative measurements from photographs of plants in the blue and red regions with polarization show that light reflected from healthy plants is more strongly polarized than that from diseased plants. Photographs taken through the blue Wratten 47 filter in conjuction with a polarizer show an excellent differentiation. A large photographic difference also appears in the red region. Much smaller differences were noted in the 540 to 550 nm region. Although the intensity in the near-IR region is much higher than the visible region of the spectrum, differences in the healthy and diseased plants' reflectance were quite small
A computational model for three-dimensional incompressible wall jets with large cross flow
A computational model for the flow field of three dimensional incompressible wall jets prototypic of thrust augmenting ejectors with large cross flow is presented. The formulation employs boundary layer equations in an orthogonal curvilinear coordinate system. Simulation of laminar as well as turbulen wall jets is reported. Quantification of jet spreading, jet growth, nominal separation, and jet shrink effects due to corss flow are discussed
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