7,923 research outputs found
A QUALITATIVE CHOICE ANALYSIS OF FACTORS INFLUENCING POST-CRP LAND USE DECISIONS
The future use of Conservation Reserve Program (CRP) lands is an important agricultural policy issue. To examine the effects of factors that influence landowners' post-contract use of CRP lands, a survey of Texas High Plains CRP contract holders was conducted in 1992. This study analyzes the results of the survey using a qualitative choice model. It was found that the presence of a livestock enterprise in the current contract holder's operation increases the probability of these acres remaining in the established cover. Contract holders who value the commodity base have an increased probability of returning their acres to crop production.Agricultural policy, Conservation Reserve Program, Ordered probit model, Land Economics/Use,
A study of thermal transitions in a new semicrystalline thermoplastic polyimide
A polyimide derive from 4,4'-isophthaloyl diphthalic anhydride (IDPA) and 1,3-bis (4-aminophenoxy 4'-benzoyl) benzene (1,3-BABB) having semicrystalline behavior was prepared and characterized by differential scanning calorimetry (DSC) and wide angle X-ray scattering (WAXS). Thus a poly(amic acid) film cured in air for one hour each at 100 and 200 C displayed an endotherm at 286 C, followed by a crystallization exotherm at 317 C, and a second melting transition at 350 C. The 286 C melting point appeared to result from earlier solvent-induced crystallization. Films cast from DMAc, air dried, and soaked in methylene chloride could not be induced into semicrystallinity. The fully cured polyimide has a Tg of 216 C. Films heated to temperatures as high as 100 C for one hour in air were transparent and light yellow in color. Those films heated to or above 125 C were translucent. Polarized light microscopy revealed the presence of spherulites 608 micrometers in diameter in a sample cured to 275 C in air. Two film samples, one cured to 275 and the other to 325 C, were evaluated for tensile and ultimate strength, modulus, and percent elongation at 25 and 200 C. These values remained essentially constant at each test temperature
A quantum protocol for cheat-sensitive weak coin flipping
We present a quantum protocol for the task of weak coin flipping. We find
that, for one choice of parameters in the protocol, the maximum probability of
a dishonest party winning the coin flip if the other party is honest is
1/sqrt(2). We also show that if parties restrict themselves to strategies
wherein they cannot be caught cheating, their maximum probability of winning
can be even smaller. As such, the protocol offers additional security in the
form of cheat sensitivity.Comment: 4 pages RevTex. Differs from the journal version only in that the
sentences: "The ordering of the authors on this paper was chosen by a coin
flip implemented by a trusted third party. TR lost." have not been remove
Paradoxical popups: Why are they hard to catch?
Even professional baseball players occasionally find it difficult to
gracefully approach seemingly routine pop-ups. This paper describes a set of
towering pop-ups with trajectories that exhibit cusps and loops near the apex.
For a normal fly ball, the horizontal velocity is continuously decreasing due
to drag caused by air resistance. But for pop-ups, the Magnus force (the force
due to the ball spinning in a moving airflow) is larger than the drag force. In
these cases the horizontal velocity decreases in the beginning, like a normal
fly ball, but after the apex, the Magnus force accelerates the horizontal
motion. We refer to this class of pop-ups as paradoxical because they appear to
misinform the typically robust optical control strategies used by fielders and
lead to systematic vacillation in running paths, especially when a trajectory
terminates near the fielder. In short, some of the dancing around when
infielders pursue pop-ups can be well explained as a combination of bizarre
trajectories and misguidance by the normally reliable optical control strategy,
rather than apparent fielder error. Former major league infielders confirm that
our model agrees with their experiences.Comment: 28 pages, 10 figures, sumitted to American Journal of Physic
Distinct Quantum States Can Be Compatible with a Single State of Reality
Perhaps the quantum state represents information about reality, and not
reality directly. Wave function collapse is then possibly no more mysterious
than a Bayesian update of a probability distribution given new data. We
consider models for quantum systems with measurement outcomes determined by an
underlying physical state of the system but where several quantum states are
consistent with a single underlying state---i.e., probability distributions for
distinct quantum states overlap. Significantly, we demonstrate by example that
additional assumptions are always necessary to rule out such a model.Comment: 5 pages, 2 figure
Almost Commuting Matrices, Localized Wannier Functions, and the Quantum Hall Effect
For models of non-interacting fermions moving within sites arranged on a
surface in three dimensional space, there can be obstructions to finding
localized Wannier functions. We show that such obstructions are -theoretic
obstructions to approximating almost commuting, complex-valued matrices by
commuting matrices, and we demonstrate numerically the presence of this
obstruction for a lattice model of the quantum Hall effect in a spherical
geometry. The numerical calculation of the obstruction is straightforward, and
does not require translational invariance or introducing a flux torus.
We further show that there is a index obstruction to approximating
almost commuting self-dual matrices by exactly commuting self-dual matrices,
and present additional conjectures regarding the approximation of almost
commuting real and self-dual matrices by exactly commuting real and self-dual
matrices. The motivation for considering this problem is the case of physical
systems with additional antiunitary symmetries such as time reversal or
particle-hole conjugation.
Finally, in the case of the sphere--mathematically speaking three almost
commuting Hermitians whose sum of square is near the identity--we give the
first quantitative result showing this index is the only obstruction to finding
commuting approximations. We review the known non-quantitative results for the
torus.Comment: 35 pages, 2 figure
Using Analytics To Challenge Conventional Baseball Wisdom
Baseball, like most other sports, has a set of tenets that began early and have survived virtually unquestioned. Modern analytics gives us an opportunity to examine some of these long-held tenets to see if they were founded on solid evidence. This research examines some common baseball wisdom through an initial study utilizing simulation. In particular, the profiles of several baseball teams are constructed and various factors are examined by simulating ten baseball seasons under various configurations with the different teams. Contrary to conventional wisdom, a batting order where high-average hitters bat third in a lineup and the team’s best power hitter bats cleanup (fourth), for example, does not necessarily generate the most runs per game over the long run. Moreover, high-average hitters with less power can generate more runs per game than power hitters with lesser averages. Finally, it appears that hitters who perform well with runners in scoring position are more influential in helping their team score more runs than even more powerful or higher average hitters who do not produce as frequently in such cases. Players with lower star profiles, but who rise to the occasion with runners in scoring position, can often be purchased by baseball clubs that have a more constrained payroll; teams that are less well-off financially may thus purchase or trade for these hitters and still field a team with a competitive level of high run production
Magnetic Gaps related to Spin Glass Order in Fermionic Systems
We provide evidence for spin glass related magnetic gaps in the fermionic
density of states below the freezing temperature. Model calculations are
presented and proposed to be relevant for explaining resistivity measurements
which observe a crossover from variable-range- to activated behavior. The
magnetic field dependence of a hardgap and the low temperature decay of the
density of states are given. In models with fermion transport a new
metal-insulator transition is predicted to occur due to the spin-glass gap,
anteceding the spin glass to quantum paramagnet transition at smaller spin
density. Important fluctuation effects due to finite range frustrated
interactions are estimated and discussed.Comment: 4 pages, 1 Postscript figure, revised version accepted for
publication in Physical Review Letter
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