15,965 research outputs found
Gravitational instability in suspension flow
The gravity-driven flow of non-neutrally buoyant suspensions is shown to be unstable to spanwise perturbations when the shearing motion generates a density profile that increases with height. The instability is simply due to having heavier material over light – a Rayleigh–Taylor-like instability. The wavelength of the fastest growing disturbance is on the order of the thickness of the suspension layer. The parameters important to the problem are the angle of inclination of the layer relative to gravity, the relative density difference between the particles and the fluid, the ratio of the particle size to the thickness of the layer and the bulk volume fraction of particles. The instability is illustrated for a range of these parameters and shown to be most pronounced at intermediate values thereof. This instability mechanism may play an important role in pattern formation in multiphase flows
Inertial Effects on the Stress Generation of Active Fluids
Suspensions of self-propelled bodies generate a unique mechanical stress
owing to their motility that impacts their large-scale collective behavior. For
microswimmers suspended in a fluid with negligible particle inertia, we have
shown that the virial `swim stress' is a useful quantity to understand the
rheology and nonequilibrium behaviors of active soft matter systems. For larger
self-propelled organisms like fish, it is unclear how particle inertia impacts
their stress generation and collective movement. Here, we analyze the effects
of finite particle inertia on the mechanical pressure (or stress) generated by
a suspension of self-propelled bodies. We find that swimmers of all scales
generate a unique `swim stress' and `Reynolds stress' that impacts their
collective motion. We discover that particle inertia plays a similar role as
confinement in overdamped active Brownian systems, where the reduced run length
of the swimmers decreases the swim stress and affects the phase behavior.
Although the swim and Reynolds stresses vary individually with the magnitude of
particle inertia, the sum of the two contributions is independent of particle
inertia. This points to an important concept when computing stresses in
computer simulations of nonequilibrium systems---the Reynolds and the virial
stresses must both be calculated to obtain the overall stress generated by a
system
Sterilizable liquid propulsion system Quarterly progress report, 2 Jan. - 31 Mar. 1967
Basic design, component selection, and materials compatibility tests for sterilizable liquid bipropellant propulsion syste
Practical implementation of a dependently typed functional programming language
Types express a program's meaning, and checking types ensures that a program has the intended meaning. In a dependently typed programming language types are predicated on values, leading to the possibility of expressing invariants of a program's behaviour in its type. Dependent types allow us to give more detailed meanings to programs, and hence be more confident of their correctness. This thesis considers the practical implementation of a dependently typed programming language, using the Epigram notation defined by McBride and McKinna. Epigram is a high level notation for dependently typed functional programming elaborating to a core type theory based on Lu๙s UTT, using Dybjer's inductive families and elimination rules to implement pattern matching. This gives us a rich framework for reasoning about programs. However, a naive implementation introduces several run-time overheads since the type system blurs the distinction between types and values; these overheads include the duplication of values, and the storage of redundant information and explicit proofs. A practical implementation of any programming language should be as efficient as possible; in this thesis we see how the apparent efficiency problems of dependently typed programming can be overcome and that in many cases the richer type information allows us to apply optimisations which are not directly available in traditional languages. I introduce three storage optimisations on inductive families; forcing, detagging and collapsing. I further introduce a compilation scheme from the core type theory to G-machine code, including a pattern matching compiler for elimination rules and a compilation scheme for efficient run-time implementation of Peano's natural numbers. We also see some low level optimisations for removal of identity functions, unused arguments and impossible case branches. As a result, we see that a dependent type theory is an effective base on which to build a feasible programming language
Scanning training for rehabilitation of visual field loss due to stroke: identifying and exploring training tools in use
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