22,954 research outputs found
Development of improved single crystal gallium phosphide solar cells final report, jun. 12, 1963 - aug. 12, 1964
Single crystal gallium phosphide solar cell
Normal subgroups of diffeomorphism and homeomorphism groups of R^n and other open manifolds
We determine all the normal subgroups of the group of C^r diffeomorphisms of
R^n, r = 1,2,...,infinity, except when r=n+1 or n=4, and also of the group of
homeomorphisms of R^n (r=0). We also study the group A_0 of diffeomorphisms of
an open manifold M that are isotopic to the identity. If M is the interior of a
compact manifold with nonempty boundary, then the quotient of A_0 by the normal
subgroup of diffeomorphisms that coincide with the identity near to a given end
e of M is simple.Comment: This version corrects an error regarding the diffeomorphism groups of
R^1, since the line has two ends, in contrast to higher dimension
Late-Time Convection in the Collapse of a 23 Solar Mass Star
The results of a 3-dimensional SNSPH simulation of the core collapse of a 23
solar mass star are presented. This simulation did not launch an explosion
until over 600ms after collapse, allowing an ideal opportunity to study the
evolution and structure of the convection below the accretion shock to late
times. This late-time convection allows us to study several of the recent
claims in the literature about the role of convection: is it dominated by an
l=1 mode driven by vortical-acoustic (or other) instability, does it produce
strong neutron star kicks, and, finally, is it the key to a new explosion
mechanism? The convective region buffets the neutron star, imparting a 150-200
km/s kick. Because the l=1 mode does not dominate the convection, the neutron
star does not achieve large (>450 km/s) velocities. Finally, the neutron star
in this simulation moves, but does not develop strong oscillations, the energy
source for a recently proposed supernova engine. We discuss the implications
these results have on supernovae, hypernovae (and gamma-ray bursts), and
stellar-massed black holes.Comment: 31 pages (including 13 figures), submitted to Ap
Design and fabrication of gallium phosphide rectifiers
Design and fabrication of gallium phosphide rectifier
Thermoelectric Amplification of Phonons in Graphene
Amplification of acoustic phonons due to an external temperature gredient
() in Graphene was studied theoretically. The threshold temperature
gradient at which absorption switches over to amplification
in Graphene was evaluated at various frequencies and temperatures
. For and frequency , . The calculation was done in the regime at . The
dependence of the normalized () on the frequency
and the temperature gradient are evaluated numerically and
presented graphically. The calculated for Graphene is lower
than that obtained for homogeneous semiconductors () , Superlattices , Cylindrical Quantum Wire . This makes Graphene a much better material for thermoelectric
phonon amplifier.Comment: 12 Pages, 6 figure
Socially Optimal Mining Pools
Mining for Bitcoins is a high-risk high-reward activity. Miners, seeking to
reduce their variance and earn steadier rewards, collaborate in pooling
strategies where they jointly mine for Bitcoins. Whenever some pool participant
is successful, the earned rewards are appropriately split among all pool
participants. Currently a dozen of different pooling strategies (i.e., methods
for distributing the rewards) are in use for Bitcoin mining.
We here propose a formal model of utility and social welfare for Bitcoin
mining (and analogous mining systems) based on the theory of discounted
expected utility, and next study pooling strategies that maximize the social
welfare of miners. Our main result shows that one of the pooling strategies
actually employed in practice--the so-called geometric pay pool--achieves the
optimal steady-state utility for miners when its parameters are set
appropriately.
Our results apply not only to Bitcoin mining pools, but any other form of
pooled mining or crowdsourcing computations where the participants engage in
repeated random trials towards a common goal, and where "partial" solutions can
be efficiently verified
Pursuing Cardiac Progenitors: Regeneration Redux
Recent studies have questioned the accepted dogma that the regenerative capacity of the heart following injury is limited. Several apparently distinct populations of resident cardiac progenitor cells may have the potential to regenerate functional heart muscle. Despite this progress, the physiologic role and therapeutic potential of cardiac resident progenitor cells remain unclear
Ferrite post in a rectangular wave guide
A thin circular ferrite post magnetized lengthwise is placed in a rectangular wave guide with its axis normal to the direction of propagation of the incident waves. The polarization is such that the electric vector is parallel to the post. The reflected and transmitted waves are calculated both with respect to their intensities and phases. The results are also applied to find the influence of a thin ferrite post upon the resonant frequency of a rectangular cavity
Lower bounds for several online variants of bin packing
We consider several previously studied online variants of bin packing and
prove new and improved lower bounds on the asymptotic competitive ratios for
them. For that, we use a method of fully adaptive constructions. In particular,
we improve the lower bound for the asymptotic competitive ratio of online
square packing significantly, raising it from roughly 1.68 to above 1.75.Comment: WAOA 201
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