6,181 research outputs found
What is Known About Species Richness and Distribution on the Outer-Shelf South Texas Banks?
The outer-shelf South Texas Banks, also known as the snapper banks, are known by fishermen to be excellent fishing grounds. However, few scientific studies have been conducted to describe the ecology of these uncommon but distinctive habitats. This paper describes results of a literature review and an assessment to determine what is known about the biota of the South Texas Banks and to assist in developing renewed interest and focus on these topographic highs. The outer-shelf South Texas Banks include relict coralgal reefs and relict barrier islands, and we also include data for a nearshore site, which is geographically and geologically separated from the offshore banks. Obtainable scientific literature was reviewed, and biodiversity data were compiled. Results indicate that one of the most studied sites, Southern Bank, could be used as a surrogate to describe potential biodiversity at other, less studied South Texas Banks. Conclusions support the need for more biological studies at all of the South Texas Banks. Results of future studies, when combined with existing results, could be used to identify sites as potential candidates for place-based protection
h-Principles for the Incompressible Euler Equations
Recently, De Lellis and Sz\'ekelyhidi constructed H\"older continuous,
dissipative (weak) solutions to the incompressible Euler equations in the torus
. The construction consists in adding fast oscillations to the
trivial solution. We extend this result by establishing optimal h-principles in
two and three space dimensions. Specifically, we identify all subsolutions
(defined in a suitable sense) which can be approximated in the -norm by
exact solutions. Furthermore, we prove that the flows thus constructed on
are genuinely three-dimensional and are not trivially obtained
from solutions on .Comment: 29 pages, no figure
The Complexity of Nash Equilibria in Simple Stochastic Multiplayer Games
We analyse the computational complexity of finding Nash equilibria in simple
stochastic multiplayer games. We show that restricting the search space to
equilibria whose payoffs fall into a certain interval may lead to
undecidability. In particular, we prove that the following problem is
undecidable: Given a game G, does there exist a pure-strategy Nash equilibrium
of G where player 0 wins with probability 1. Moreover, this problem remains
undecidable if it is restricted to strategies with (unbounded) finite memory.
However, if mixed strategies are allowed, decidability remains an open problem.
One way to obtain a provably decidable variant of the problem is restricting
the strategies to be positional or stationary. For the complexity of these two
problems, we obtain a common lower bound of NP and upper bounds of NP and
PSPACE respectively.Comment: 23 pages; revised versio
Identification of A-colored Stars and Structure in the Halo of the Milky Way from SDSS Commissioning Data
A sample of 4208 objects with magnitude 15 < g* < 22 and colors of main
sequence A stars has been selected from 370 square degrees of Sloan Digital Sky
Survey (SDSS) commissioning observations. The data is from two long, narrow
stripes, each with an opening angle of greater than 60 deg, at Galactic
latitudes 36 < abs(b) < 63 on the celestial equator. An examination of the
sample's distribution shows that these stars trace considerable substructure in
the halo. Large overdensities of A-colored stars in the North at (l,b,R) =
(350, 50, 46 kpc) and in the South at (157, -58, 33 kpc) and extending over
tens of degrees are present in the halo of the Milky Way. Using photometry to
separate the stars by surface gravity, both structures are shown to contain a
sequence of low surface gravity stars consistent with identification as a blue
horizontal branch (BHB). Both structures also contain a population of high
surface gravity stars two magnitudes fainter than the BHB stars, consistent
with their identification as blue stragglers (BSs). From the numbers of
detected BHB stars, lower limits to the implied mass of the structures are
6x10^6 M_sun and 2x10^6 M_sun. The fact that two such large clumps have been
detected in a survey of only 1% of the sky indicates that such structures are
not uncommon in the halo. Simple spheroidal parameters are fit to a complete
sample of the remaining unclumped BHB stars and yield (at r < 40 kpc) a fit to
a halo distribution with flattening (c/a = 0.65+/-0.2) and a density falloff
exponent of alpha = -3.2+/-0.3.Comment: AASTeX v5_0, 26 pages, 1 table, 20 figures, ApJ accepte
Behavioral implications of shortlisting procedures
We consider two-stage “shortlisting procedures” in which the menu of alternatives is first pruned by some process or criterion and then a binary relation is maximized. Given a particular first-stage process, our main result supplies a necessary and sufficient condition for choice data to be consistent with a procedure in the designated class. This result applies to any class of procedures with a certain lattice structure, including the cases of “consideration filters,” “satisficing with salience effects,” and “rational shortlist methods.” The theory avoids background assumptions made for mathematical convenience; in this and other respects following Richter’s classical analysis of preference-maximizing choice in the absence of shortlisting
Solution of the X-ray edge problem for 2D electrons in a magnetic field
The absorption and emission spectra of transitions between a localized level
and a two-dimensional electron gas, subjected to a weak magnetic field, are
calculated analytically. Adopting the Landau level bosonization technique
developed in previous papers, we find an exact expression for the relative
intensities of spectral lines. Their envelope function, governed by the
interaction between the electron gas and the core hole, is reminescent of the
famous Fermi edge singularity, which is recovered in the limit of a vanishing
magnetic field.Comment: 4 pages, 1 figur
Decision Problems for Nash Equilibria in Stochastic Games
We analyse the computational complexity of finding Nash equilibria in
stochastic multiplayer games with -regular objectives. While the
existence of an equilibrium whose payoff falls into a certain interval may be
undecidable, we single out several decidable restrictions of the problem.
First, restricting the search space to stationary, or pure stationary,
equilibria results in problems that are typically contained in PSPACE and NP,
respectively. Second, we show that the existence of an equilibrium with a
binary payoff (i.e. an equilibrium where each player either wins or loses with
probability 1) is decidable. We also establish that the existence of a Nash
equilibrium with a certain binary payoff entails the existence of an
equilibrium with the same payoff in pure, finite-state strategies.Comment: 22 pages, revised versio
Faculty Retraining: A Strategic Response to Changing Resources and Technology
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/66742/2/10.1177_009155218301100201.pd
Dissipative continuous Euler flows
We show the existence of continuous periodic solutions of the 3D
incompressible Euler equations which dissipate the total kinetic energy
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