Biomedical Engineering Reference
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surrounding smooth muscle to relax, thus resulting in vasodilation and
increasing blood flow. Nitric oxide is highly reactive (having a lifetime
of a few seconds), yet diffuses freely across membranes. These attributes
make nitric oxide ideal for a transient paracrine (between adjacent cells)
and autocrine (within a single cell) signaling molecule. It is a powerful va-
sodilator with a short half-life of a few seconds in the blood. Long-known
pharmaceuticals like nitroglycerine and amyl nitrite were discovered, more
than a century after their first use in medicine, to be active through the
mechanism of being precursors to nitric oxide. Low levels of nitric ox-
ide production are important in protecting organs such as the liver from
ischemic damage. Chronic expression of NO is associated with various car-
cinomas and inflammatory conditions including Type-1 diabetes, multiple
sclerosis, arthritis and ulcerative colitis.
Discrete object: Finite, spatially extended lattice subdomain of contiguous
sites denoted with the same spin.
Continuous object: Field, i.e., spatiotemporal evolution of a microscopic
entity.
Overdamped force-velocity response: Relation stating that the local ve-
locity of an individual, and not its acceleration, is proportional to the
local force.
Parallel computing: A form of computation in which many calculations are
carried out simultaneously, operating on the principle that large problems
can be divided into smaller ones, which are then solved concurrently (\in
parallel"). There are several dierent forms of parallel computing: bit-
level, instruction level, data, and task parallelism. In recent years, parallel
computing has become the dominant paradigm in computer architecture,
mainly in the form of multicore processors. Parallel computers can be
roughly classified according to the level at which the hardware supports
parallelism, with multi-core and multi-processor computers having mul-
tiple processing elements within a single machine, while clusters, MPPs,
and grids use multiple computers to work on the same task. Specialized
parallel computer architectures are sometimes used alongside traditional
processors, for accelerating specific tasks. Communication and synchro-
nization between the different subtasks are typically some of the greatest
obstacles to getting good parallel program performance. Optimally, the
speed-up from parallelization would be linear doubling the number of
processing elements should halve the runtime, and doubling it a second
time should again halve the runtime. However, very few parallel algo-
rithms achieve optimal speed-up. Most of them have a near-linear speed-
up for small numbers of processing elements, which flattens out into a
constant value for large numbers of processing elements. The potential
speed-up of an algorithm on a parallel computing platform is given by
Amdahl's law, originally formulated by Gene Amdahl in the 1960s. It
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