55,787 research outputs found
Strategy for Cost-Effective Reduction of the Sum of Health Risk Estimates for Exposures to Mixtures of Toxic Substances
The authors argue that a minimization approach can provide guidance for effective use of funds to reduce the sum of estimated risks or the upper limit of the sum of risk estimates for mixtures of chemicals
Scalable data abstractions for distributed parallel computations
The ability to express a program as a hierarchical composition of parts is an
essential tool in managing the complexity of software and a key abstraction
this provides is to separate the representation of data from the computation.
Many current parallel programming models use a shared memory model to provide
data abstraction but this doesn't scale well with large numbers of cores due to
non-determinism and access latency. This paper proposes a simple programming
model that allows scalable parallel programs to be expressed with distributed
representations of data and it provides the programmer with the flexibility to
employ shared or distributed styles of data-parallelism where applicable. It is
capable of an efficient implementation, and with the provision of a small set
of primitive capabilities in the hardware, it can be compiled to operate
directly on the hardware, in the same way stack-based allocation operates for
subroutines in sequential machines
Structural trends in clusters of quadrupolar spheres
The influence of quadrupolar interactions on the structure of small clusters
is investigated by adding a point quadrupole of variable strength to the
Lennard-Jones potential. Competition arises between sheet-like arrangements of
the particles, favoured by the quadrupoles, and compact structures, favoured by
the isotropic Lennard-Jones attraction. Putative global potential energy minima
are obtained for clusters of up to 25 particles using the basin-hopping
algorithm. A number of structural motifs and growth sequences emerge, including
star-like structures, tubes, shells and sheets. The results are discussed in
the context of colloidal self-assembly.Comment: 8 pages, 6 figure
Test results of a 40-kW Stirling engine and comparison with the NASA Lewis computer code predictions
A Stirling engine was tested without auxiliaries at Nasa-Lewis. Three different regenerator configurations were tested with hydrogen. The test objectives were: (1) to obtain steady-state and dynamic engine data, including indicated power, for validation of an existing computer model for this engine; and (2) to evaluate structurally the use of silicon carbide regenerators. This paper presents comparisons of the measured brake performance, indicated mean effective pressure, and cyclic pressure variations from those predicted by the code. The silicon carbide foam generators appear to be structurally suitable, but the foam matrix showed severely reduced performance
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