4,268 research outputs found
Species and the Good in Anne Conway's Metaethics
Anne Conway rejects the view that creatures are essentially members of any natural kind more specific than the kind 'creature'. That is, she rejects essentialism about species membership. This chapter provides an analysis of one of Anne Conway's arguments against such essentialism, which (as I argue) is drawn from metaethical rather than metaphysical premises. In her view, if a creature's species or kind were inscribed in its essence, that essence would constitute a limit on the creature's potential to participate in the divine good. It is this consideration that ultimately leads her to reject essentialism about species membership. The chapter concludes with an examination of some of the metaethical consequences of Conway's view as well as a lesson it can teach us about ideal adviser accounts of the good
Eddy current proximity gage for the determination of thickness of Portland cement concrete pavements
Multiple tests with eddy current proximity gage for determining thickness of concrete pavement
Avalanche multiplication in AlxGa1-xAs (x=0to0.60)
Electron and hole multiplication characteristics, Me and Mh, have been measured in AlxGa1-xAs (x=0-0.60) homojunction p+-i-n+ diodes with i-region thicknesses, w, from 1 μm to 0.025 μm and analyzed using a Monte Carlo model (MC). The effect of the composition on both the macroscopic multiplication characteristics and microscopic behavior is therefore shown for the first time. Increasing the alloy fraction causes the multiplication curves to be shifted to higher voltages such that the multiplication curves at any given thickness are practically parallel for different x. The Me/Mh ratio also decreases as x increases, varying from ~2 to ~1 as x increases from 0 to 0.60 in a w=1 μm p+-i-n+. The Monte-Carlo model is also used to extract ionization coefficients and dead-space distances from the measured results which cover electric field ranges from ~250 kV/cm-1200 kV/cm in each composition. These parameters can be used to calculate the nonlocal multiplication process by solving recurrence equations. Limitations to the applicability of field-dependent ionization coefficients are shown to arise however when the electric-field profile becomes highly nonunifor
Faster all-pairs shortest paths via circuit complexity
We present a new randomized method for computing the min-plus product
(a.k.a., tropical product) of two matrices, yielding a faster
algorithm for solving the all-pairs shortest path problem (APSP) in dense
-node directed graphs with arbitrary edge weights. On the real RAM, where
additions and comparisons of reals are unit cost (but all other operations have
typical logarithmic cost), the algorithm runs in time
and is correct with high probability.
On the word RAM, the algorithm runs in time for edge weights in . Prior algorithms used either time for
various , or time for various
and .
The new algorithm applies a tool from circuit complexity, namely the
Razborov-Smolensky polynomials for approximately representing
circuits, to efficiently reduce a matrix product over the algebra to
a relatively small number of rectangular matrix products over ,
each of which are computable using a particularly efficient method due to
Coppersmith. We also give a deterministic version of the algorithm running in
time for some , which utilizes the
Yao-Beigel-Tarui translation of circuits into "nice" depth-two
circuits.Comment: 24 pages. Updated version now has slightly faster running time. To
appear in ACM Symposium on Theory of Computing (STOC), 201
Altitude performance of a low-noise-technology fan in a turbofan engine with and without a sound suppressing nacelle
Test variables were inlet Reynolds number index (0.2 to 0.5), flight Mach number (0.2 to 0.8), and flow distortion (tip radial and combined circumferential - tip radial patterns). Results are limited to fan bypass and overall engine performance. There were no discernible effects of Reynolds number on fan performance. Increasing flight Mach number shifted the fan operating line such that pressure ratio decreased and airflow increased. Inlet flow distortion lowered stall margin. For a Reynolds number index of 0.2 and flight Mach number of 0.54, the sound suppressing nacelle lowered fan efficiency three points and increased specific fuel consumption about 10 percent
Inclusions Among Mixed-Norm Lebesgue Spaces
A mixed LP norm of a function on a product space is the
result of successive classical Lp norms in each variable,
potentially with a different exponent for each. Conditions to
determine when one mixed norm space is contained in another are
produced, generalizing the known conditions for embeddings
of Lp spaces.
The two-variable problem (with four Lp exponents, two for
each mixed norm) is studied extensively. The problem\u27s ``unpermuted
case simply reduces to a question of Lp embeddings. The other,
``permuted case further divides, depending on the values of the
Lp exponents. Often, they fit the ``Minkowski case , when
Minkowski\u27s integral inequality provides an easy, complete solution.
In the ``non-Minkowski case , the solution is determined
by the structure of the measures in the component Lp spaces.
When no measure is purely atomic, there can be no mixed-norm
embedding in the non-Minkowski case, so for such measures the
problem is solved.
With at least one purely atomic measure, the non-Minkowski case
divides further based on the structure of the measures and the
values of the exponents. Various necessary conditions and
sufficient conditions are found, solving a number of subcases.
Other subcases are shown to be genuinely complicated, with
their solutions expressed in terms of an optimization problem known
to be computationally difficult.
With some difficult cases already present in the two-variable
problem, it is impractical to cover every case of the
multivariable problem, but results are presented which
fully solve some cases.
When no measure is purely atomic, the multivariable problem
is solved by a reduction to the Minkowski case of certain
two-variable subproblems.
The multivariable problem with
unweighted lp spaces has a similar reduction to
easy two-variable subproblems. It is conjectured that
this applies more generally; that, regardless of the structures
of the involved measures, when every permuted two-variable
subproblem fits the Minkowski case, the full multivariable
mixed norm inclusion must hold
Improving the numerical stability of fast matrix multiplication
Fast algorithms for matrix multiplication, namely those that perform
asymptotically fewer scalar operations than the classical algorithm, have been
considered primarily of theoretical interest. Apart from Strassen's original
algorithm, few fast algorithms have been efficiently implemented or used in
practical applications. However, there exist many practical alternatives to
Strassen's algorithm with varying performance and numerical properties. Fast
algorithms are known to be numerically stable, but because their error bounds
are slightly weaker than the classical algorithm, they are not used even in
cases where they provide a performance benefit.
We argue in this paper that the numerical sacrifice of fast algorithms,
particularly for the typical use cases of practical algorithms, is not
prohibitive, and we explore ways to improve the accuracy both theoretically and
empirically. The numerical accuracy of fast matrix multiplication depends on
properties of the algorithm and of the input matrices, and we consider both
contributions independently. We generalize and tighten previous error analyses
of fast algorithms and compare their properties. We discuss algorithmic
techniques for improving the error guarantees from two perspectives:
manipulating the algorithms, and reducing input anomalies by various forms of
diagonal scaling. Finally, we benchmark performance and demonstrate our
improved numerical accuracy
Low multiplication noise thin Al0.6Ga0.4As avalanche photodiodes
Avalanche multiplication and excess noise were measured on a series of Al0.6Ga0.4As p+in+ and n+ip+ diodes, with avalanche region thickness, w ranging from 0.026 μm to 0.85 μm. The results show that the ionization coefficient for electrons is slightly higher than for holes in thick, bulk material. At fixed multiplication values the excess noise factor was found to decrease with decreasing w, irrespective of injected carrier type. Owing to the wide Al0.6Ga0.4As bandgap extremely thin devices can sustain very high electric fields, giving rise to very low excess noise factors, of around F~3.3 at a multiplication factor of M~15.5 in the structure with w=0.026 μm. This is the lowest reported excess noise at this value of multiplication for devices grown on GaAs substrates. Recursion equation modeling, using both a hard threshold dead space model and one which incorporates the detailed history of the ionizing carriers, is used to model the nonlocal nature of impact ionization giving rise to the reduction in excess noise with decreasing w. Although the hard threshold dead space model could reproduce qualitatively the experimental results, better agreement was obtained from the history-dependent mode
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