2,180,706 research outputs found
Space electric power systems study- d-c to d-c converters for nuclear-thermionic energy sources
Direct current converters used in space electric power system for nuclear-electric power suppl
Expanded microchannel heat exchanger: design, fabrication and preliminary experimental test
This paper first reviews non-traditional heat exchanger geometry, laser
welding, practical issues with microchannel heat exchangers, and high
effectiveness heat exchangers. Existing microchannel heat exchangers have low
material costs, but high manufacturing costs. This paper presents a new
expanded microchannel heat exchanger design and accompanying continuous
manufacturing technique for potential low-cost production. Polymer heat
exchangers have the potential for high effectiveness. The paper discusses one
possible joining method - a new type of laser welding named "forward conduction
welding," used to fabricate the prototype. The expanded heat exchanger has the
potential to have counter-flow, cross-flow, or parallel-flow configurations, be
used for all types of fluids, and be made of polymers, metals, or
polymer-ceramic precursors. The cost and ineffectiveness reduction may be an
order of magnitude or more, saving a large fraction of primary energy. The
measured effectiveness of the prototype with 28 micron thick black low density
polyethylene walls and counterflow, water-to-water heat transfer in 2 mm
channels was 72%, but multiple low-cost stages could realize the potential of
higher effectiveness
The density of primes in orbits of z^d + c
Given a polynomial f(z) = z^d + c over a global field K and a_0 in K, we
study the density of prime ideals of K dividing at least one element of the
orbit of a_0 under f. The density of such sets for linear polynomials has
attracted much study, and the second author has examined several families of
quadratic polynomials, but little is known in the higher-degree case. We show
that for many choices of d and c this density is zero for all a_0, assuming K
contains a primitive dth root of unity. The proof relies on several new
results, including some ensuring the number of irreducible factors of the nth
iterate of f remains bounded as n grows, and others on the ramification above
certain primes in iterated extensions. Together these allow for nearly complete
information when K is a global function field or when K=Q(zeta_d).Comment: 27 page
Deciphering Neuropathological Heterogeneity in Alzheimer's Disease: Beyond Plaques and Tangles
Implementing eMental health services in routine mental health care:from barriers to strategies
Primitive prime divisors in the critical orbit of z^d+c
We prove the finiteness of the Zsigmondy set associated to the critical orbit
of f(z) = z^d+c for rational values of c by finding an effective bound on the
size of the set. For non-recurrent critical orbits, the Zsigmondy set is
explicitly computed by utilizing effective dynamical height bounds. In the
general case, we use Thue-style Diophantine approximation methods to bound the
size of the Zsigmondy set when d >2, and complex-analytic methods when d=2.Comment: This version includes numerous typographical changes and expanded
exposition, and a simplified proof of Theorem 6.1. 30 pages, to appear in
International Math Research Notice
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