996 research outputs found
Entropy Change through Rayleigh-B\'enard Convective Transition with Rigid Boundaries
The previous investigation on Rayleigh-B\'enard convection of a dilute
classical gas [T. Kita: J. Phys. Soc. Jpn. {\bf 75} (2006) 124005] is extended
to calculate entropy change of the convective transition with the rigid
boundaries. We obtain results qualitatively similar to those of the stress-free
boundaries. Above the critical Rayleigh number, the roll convection is realized
among possible steady states with periodic structures, carrying the highest
entropy as a function of macroscopic mechanical variables.Comment: 5 pages, 4 figure
Whirling Hexagons and Defect Chaos in Hexagonal Non-Boussinesq Convection
We study hexagon patterns in non-Boussinesq convection of a thin rotating
layer of water. For realistic parameters and boundary conditions we identify
various linear instabilities of the pattern. We focus on the dynamics arising
from an oscillatory side-band instability that leads to a spatially disordered
chaotic state characterized by oscillating (whirling) hexagons. Using
triangulation we obtain the distribution functions for the number of pentagonal
and heptagonal convection cells. In contrast to the results found for defect
chaos in the complex Ginzburg-Landau equation and in inclined-layer convection,
the distribution functions can show deviations from a squared Poisson
distribution that suggest non-trivial correlations between the defects.Comment: 4 mpg-movies are available at
http://www.esam.northwestern.edu/~riecke/lit/lit.html submitted to New J.
Physic
Flexoelectricity and pattern formation in nematic liquid crystals
We present in this paper a detailed analysis of the flexoelectric instability
of a planar nematic layer in the presence of an alternating electric field
(frequency ), which leads to stripe patterns (flexodomains) in the
plane of the layer. This equilibrium transition is governed by the free energy
of the nematic which describes the elasticity with respects to the
orientational degrees of freedom supplemented by an electric part. Surprisingly
the limit is highly singular. In distinct contrast to the
dc-case, where the patterns are stationary and time-independent, they appear at
finite, small periodically in time as sudden bursts. Flexodomains are
in competition with the intensively studied electro-hydrodynamic instability in
nematics, which presents a non-equilibrium dissipative transition. It will be
demonstrated that is a very convenient control parameter to tune
between flexodomains and convection patterns, which are clearly distinguished
by the orientation of their stripes
Dynamics and Selection of Giant Spirals in Rayleigh-Benard Convection
For Rayleigh-Benard convection of a fluid with Prandtl number \sigma \approx
1, we report experimental and theoretical results on a pattern selection
mechanism for cell-filling, giant, rotating spirals. We show that the pattern
selection in a certain limit can be explained quantitatively by a
phase-diffusion mechanism. This mechanism for pattern selection is very
different from that for spirals in excitable media
Graduating with a Science Major: The Roles of First-Year Science Interests and Educational Aspirations
The purpose of this longitudinal study was to determine whether the degree of science interests and educational aspirations in students’ first year of university would significantly differentiate those students who graduated with a science major from those students who did not graduate with a science major. Moreover, the authors expected that educational aspirations would moderate the relation between science interests and graduating with/without a science major. First-year college students in introductory science courses were surveyed in their first semester and then again upon graduation. These 166 students’ science interests and educational aspirations were assessed at Time 1; their educational major was assessed upon graduation. The findings supported both hypotheses. Science interests and educational aspirations significantly differentiated whether or not students graduated with science majors. Moreover, the interaction of science interests and educational aspirations also significantly differentiated whether or not students graduated with a science major. In short, students who graduated with science majors, compared to their counterparts who graduated with nonscience majors, had significantly higher interests only when they also had higher educational aspirations
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