3,908 research outputs found
Development of three dimensional constitutive theories based on lower dimensional experimental data
Most three dimensional constitutive relations that have been developed to
describe the behavior of bodies are correlated against one dimensional and two
dimensional experiments. What is usually lost sight of is the fact that
infinity of such three dimensional models may be able to explain these
experiments that are lower dimensional. Recently, the notion of maximization of
the rate of entropy production has been used to obtain constitutive relations
based on the choice of the stored energy and rate of entropy production, etc.
In this paper we show different choices for the manner in which the body stores
energy and dissipates energy and satisfies the requirement of maximization of
the rate of entropy production that leads to many three dimensional models. All
of these models, in one dimension, reduce to the model proposed by Burgers to
describe the viscoelastic behavior of bodies.Comment: 23 pages, 6 figure
Probabilistic structural analysis verification studies
The basic objective of this verification effort is to apply probabilistic structural analysis methods developed and implemented in the Numerical Evaluation of Stochastic Structures Under Stress (NESSUS) code to typical space propulsion components. The chosen typical components are turbine blade, high pressure duct, Lox post, and transfer tube liners. Since analysis options of increasing levels of sophistication are implemented in NESSUS incrementally, the verification efforts are also tailored to have increasing levels of sophistication during the progression of the contract. The current released version of the code is limited to linear structural analysis
A numerical study of fluids with pressure dependent viscosity flowing through a rigid porous medium
In this paper we consider modifications to Darcy's equation wherein the drag
coefficient is a function of pressure, which is a realistic model for
technological applications like enhanced oil recovery and geological carbon
sequestration. We first outline the approximations behind Darcy's equation and
the modifications that we propose to Darcy's equation, and derive the governing
equations through a systematic approach using mixture theory. We then propose a
stabilized mixed finite element formulation for the modified Darcy's equation.
To solve the resulting nonlinear equations we present a solution procedure
based on the consistent Newton-Raphson method. We solve representative test
problems to illustrate the performance of the proposed stabilized formulation.
One of the objectives of this paper is also to show that the dependence of
viscosity on the pressure can have a significant effect both on the qualitative
and quantitative nature of the solution
A thermodynamic framework to develop rate-type models for fluids without instantaneous elasticity
In this paper, we apply the thermodynamic framework recently put into place
by Rajagopal and co-workers, to develop rate-type models for viscoelastic
fluids which do not possess instantaneous elasticity. To illustrate the
capabilities of such models we make a specific choice for the specific
Helmholtz potential and the rate of dissipation and consider the creep and
stress relaxation response associated with the model. Given specific forms for
the Helmholtz potential and the rate of dissipation, the rate of dissipation is
maximized with the constraint that the difference between the stress power and
the rate of change of Helmholtz potential is equal to the rate of dissipation
and any other constraint that may be applicable such as incompressibility. We
show that the model that is developed exhibits fluid-like characteristics and
is incapable of instantaneous elastic response. It also includes Maxwell-like
and Kelvin-Voigt-like viscoelastic materials (when certain material moduli take
special values).Comment: 18 pages, 5 figure
A scheme for amplification and discrimination of photons
A scheme for exploring photon number amplification and discrimination is
presented based on the interaction of a large number of two-level atoms with a
single mode radiation field. The fact that the total number of photons and
atoms in the excited states is a constant under time evolution in Dicke model
is exploited to rearrange the atom-photon numbers. Three significant
predictions emerge from our study: Threshold time for initial exposure to
photons, time of perception (time of maximum detection probability), and
discrimination of first few photon states.Comment: 8 pages, 3 figures, RevteX, Minor revision, References adde
Separability bounds on multiqubit moments due to positivity under partial transpose
Positivity of the density operator reflects itself in terms of sequences of
inequalities on observable moments. Uncertainty relations for non-commuting
observables form a subset of these inequalities. In addition, criterion of
positivity under partial transposition (PPT) imposes distinct bounds on
moments, violations of which signal entanglement. We present bounds on some
novel sets of composite moments, consequent to positive partial transposition
of the density operator and report their violation by entangled multiqubit
states. In particular, we derive separability bounds on a multiqubit moment
matrix (based on PPT constraints on bipartite divisions of the density matrix)
and show that three qubit pure states with non-zero tangle violate these PPT
moment constraints. Further, we recover necessary and sufficient condition of
separability in a multiqubit Werner state through PPT bounds on moments.Comment: 16 pages, no figures, minor revisions, references added; To appear in
Phys. Rev.
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