66,735 research outputs found
A multilayered effective medium model for the roughness effect on the Casimir force
A multilayered effective medium model is proposed to calculate the
contribution of surface roughness to the Casimir force. In this model the rough
layer has its optical properties derived from an effective medium
approximation, with the rough layer considered as the mixing of voids and solid
material. The rough layer can be divided into sublayers consisting of different
volume fractions of voids and solid material as a function of the roughness
surface profile. The Casimir force is then calculated using the generalizations
of the Lifshitz theory for multilayered planar systems. Predictions of the
Casimir force based on the proposed model are compared with those of well known
methods of calculation, usually restricted to be used with large scale
roughness. It is concluded that the effect of short scale roughness as
predicted by this model is considerably larger than what could be expected from
the extrapolation of the results obtained by the other methods
Building and Refining Abstract Planning Cases by Change of Representation Language
ion is one of the most promising approaches to improve the performance of
problem solvers. In several domains abstraction by dropping sentences of a
domain description -- as used in most hierarchical planners -- has proven
useful. In this paper we present examples which illustrate significant
drawbacks of abstraction by dropping sentences. To overcome these drawbacks, we
propose a more general view of abstraction involving the change of
representation language. We have developed a new abstraction methodology and a
related sound and complete learning algorithm that allows the complete change
of representation language of planning cases from concrete to abstract.
However, to achieve a powerful change of the representation language, the
abstract language itself as well as rules which describe admissible ways of
abstracting states must be provided in the domain model. This new abstraction
approach is the core of Paris (Plan Abstraction and Refinement in an Integrated
System), a system in which abstract planning cases are automatically learned
from given concrete cases. An empirical study in the domain of process planning
in mechanical engineering shows significant advantages of the proposed
reasoning from abstract cases over classical hierarchical planning.Comment: See http://www.jair.org/ for an online appendix and other files
accompanying this articl
Towards Model-Driven Development of Access Control Policies for Web Applications
We introduce a UML-based notation for graphically modeling
systems’ security aspects in a simple and intuitive
way and a model-driven process that transforms graphical
specifications of access control policies in XACML. These
XACML policies are then translated in FACPL, a policy
language with a formal semantics, and the resulting policies
are evaluated by means of a Java-based software tool
Approximate methods for the solution of quantum wires and dots : Connection rules between pyramidal, cuboidal, and cubic dots
Energy eigenvalues of the electronic ground state are calculated for rectangular and triangular GaAs/Ga(0.6)Al(0.4)As quantum wires as well as for cuboidal and pyramidal quantum dots of the same material. The wire (dot) geometries are approximated by a superposition of perpendicular independent finite one-dimensional potential wells. A perturbation is added to the system to improve the approximation. Excellent agreement with more complex treatments is obtained. The method is applied to investigate the ground state energy dependence on volume and aspect ratio for finite barrier cubic, cuboidal, and pyramidal quantum dots. It is shown that the energy eigenvalues of cubes are equal to those of cuboids of the same volume and aspect ratio similar to one. In addition, a relationship has been found between the volumes of pyramidal quantum dots (often the result of self-assembling in strain layered epitaxy) and cuboidal dots with the same ground state energy and aspect ratios close to one. © 1999 American Institute of Physics
Modeling the Influence of Antifreeze Proteins on Three-Dimensional Ice Crystal Melt Shapes using a Geometric Approach
The melting of pure axisymmetric ice crystals has been described previously
by us within the framework of so-called geometric crystal growth.
Nonequilibrium ice crystal shapes evolving in the presence of hyperactive
antifreeze proteins (hypAFPs) are experimentally observed to assume ellipsoidal
geometries ("lemon" or "rice" shapes). To analyze such shapes we harness the
underlying symmetry of hexagonal ice Ih and extend two-dimensional geometric
models to three-dimensions to reproduce the experimental dissolution process.
The geometrical model developed will be useful as a quantitative test of the
mechanisms of interaction between hypAFPs and ice.Comment: 15 pages, 5 figures; Proc. R. Soc. A, Published online before print
June 27, 201
Nanoscale roughness and morphology affect the IsoElectric Point of titania surfaces
We report on the systematic investigation of the role of surface nanoscale
roughness and morphology on the charging behaviour of nanostructured titania
(TiO2) surfaces in aqueous solutions. IsoElectric Points (IEPs) of surfaces
have been characterized by direct measurement of the electrostatic double layer
interactions between titania surfaces and the micrometer-sized spherical silica
probe of an atomic force microscope in NaCl aqueous electrolyte. The use of a
colloidal probe provides well-defined interaction geometry and allows
effectively probing the overall effect of nanoscale morphology. By using
supersonic cluster beam deposition to fabricate nanostructured titania films,
we achieved a quantitative control over the surface morphological parameters.
We performed a systematical exploration of the electrical double layer
properties in different interaction regimes characterized by different ratios
of characteristic nanometric lengths of the system: the surface rms roughness
Rq, the correlation length {\xi} and the Debye length {\lambda}D. We observed a
remarkable reduction by several pH units of IEP on rough nanostructured
surfaces, with respect to flat crystalline rutile TiO2. In order to explain the
observed behavior of IEP, we consider the roughness-induced self-overlap of the
electrical double layers as a potential source of deviation from the trend
expected for flat surfaces.Comment: 63 pages, including 7 figures and Supporting Informatio
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