35 research outputs found
A topos for algebraic quantum theory
The aim of this paper is to relate algebraic quantum mechanics to topos
theory, so as to construct new foundations for quantum logic and quantum
spaces. Motivated by Bohr's idea that the empirical content of quantum physics
is accessible only through classical physics, we show how a C*-algebra of
observables A induces a topos T(A) in which the amalgamation of all of its
commutative subalgebras comprises a single commutative C*-algebra. According to
the constructive Gelfand duality theorem of Banaschewski and Mulvey, the latter
has an internal spectrum S(A) in T(A), which in our approach plays the role of
a quantum phase space of the system. Thus we associate a locale (which is the
topos-theoretical notion of a space and which intrinsically carries the
intuitionistic logical structure of a Heyting algebra) to a C*-algebra (which
is the noncommutative notion of a space). In this setting, states on A become
probability measures (more precisely, valuations) on S(A), and self-adjoint
elements of A define continuous functions (more precisely, locale maps) from
S(A) to Scott's interval domain. Noting that open subsets of S(A) correspond to
propositions about the system, the pairing map that assigns a (generalized)
truth value to a state and a proposition assumes an extremely simple
categorical form. Formulated in this way, the quantum theory defined by A is
essentially turned into a classical theory, internal to the topos T(A).Comment: 52 pages, final version, to appear in Communications in Mathematical
Physic
Non-local Realistic Theories and the Scope of the Bell Theorem
According to a widespread view, the Bell theorem establishes the untenability
of so-called 'local realism'. On the basis of this view, recent proposals by
Leggett, Zeilinger and others have been developed according to which it can be
proved that even some non-local realistic theories have to be ruled out. As a
consequence, within this view the Bell theorem allows one to establish that no
reasonable form of realism, be it local or non-local, can be made compatible
with the (experimentally tested) predictions of quantum mechanics. In the
present paper it is argued that the Bell theorem has demonstrably nothing to do
with the 'realism' as defined by these authors and that, as a consequence,
their conclusions about the foundational significance of the Bell theorem are
unjustified.Comment: Forthcoming in Foundations of Physic
Does quantum nonlocality irremediably conflict with Special Relativity?
We reconsider the problem of the compatibility of quantum nonlocality and the
requests for a relativistically invariant theoretical scheme. We begin by
discussing a recent important paper by T. Norsen [arXiv:0808.2178] on this
problem and we enlarge our considerations to give a general picture of the
conceptually relevant issue to which this paper is devoted.Comment: 18 pages, 1 figur
Deposição de tecidos e componentes quÃmicos corporais em bovinos Nelore de diferentes classes sexuais
Development of an Aeroelastic Tool for Wind Turbine design
The work focuses on the unsteady aerodynamics and aeroelastic properties of a small-medium sized wind-turbine blade operating under ideal conditions. A tapered/twisted blade representative of commercial blades used in an experiment setup at the National Renewable Energy Laboratory is considered. The aerodynamic loads are computed using Computational Fluid Dynamics (CFD) techniques. A commercial finite-volume code, FLUENT, that solves the Navier-Stokes and the Reynolds-Averaged Navier-Stokes (RANS) equations is used. Turbulence effects in the 2-D simulations are modeled using Wilcox k-ω model for validation of the CFD approach. For the 3-D aerodynamic simulations, the unsteady laminar Navier-Stokes equations were used to determine the unsteady loads acting on the blades. Five different blade pitch angles were considered and their aerodynamic performance compared. The structural dynamics of the flexible wind-turbine blade undergoing significant elastic displacements has been described by a nonlinear flap-lag-torsion slender-beam differential model. The aerodynamic quasi-steady forcing terms needed for the aeroelastic governing equations have been predicted through a strip-theory based on a simple 2-D model, and the pertinent aerodynamic coefficients and the distribution over the blade span of the induced velocity derived using CFD. The resulting unsteady hub loads are achieved by a first space integration of the aeroelastic equations by applying the Galerkin's approach - using as shape functions the bending and torsion free vibration modes of the structure - and by a time integration using a harmonic balance scheme. Comparison among two- and three- dimensional computations for the unsteady aerodynamic load, the flap, lag and torsional deflections, forces and moments are presented in the paper. Results, discussions and pertinent conclusions are outlined
CYP4Fs Expression in Rat Brain Correlates with Changes in LTB4 Levels after Traumatic Brain Injury
Cytochrome P450 (CYP) 4Fs constitute a subgroup of the cytochrome P450 superfamily and are involved in cellular protection and metabolism of numerous molecules, including drugs, toxins, and eicosanoids. CYP4Fs are widely distributed in rat brain with each isoform having a unique distribution pattern throughout different brain regions. The present study shows that traumatic brain injury (TBI) triggers inflammation and elicits changes in mRNA expression of CYP4Fs in the frontal and occipital lobes and the hippocampus. At 24 h post-injury, almost all CYP4F mRNA expression is suppressed compared with sham control throughout these three regions, while at 2 weeks post-injury, all CYP4F mRNAs increase, reaching levels higher than those at 24 h post-injury or uninjured controls. These changes in CYP4F levels inversely correlate with levels of leukotriene B4 (LTB4) levels in the brain following injury at the same time points. TBI also causes changes in CYP4F protein expression and localization around the injury site. CYP4F1 and CYP4F6 immunoreactivity increases in surrounding astrocytes, while CYP4F4 immunoreactivity shifts from endothelia of cerebral vessels to astrocytes
Perceived economic pressures and farmer ethics
We hypothesize that an increase in the economic pressures a farmer feels could result in that farmer being more tolerant of unethical conduct than farmers not experiencing economic pressures. To test this hypothesis, we use data from a survey of 3,000 Missouri farmers with farm sales in excess of $10,000 in 2005 in which farmers were asked how acceptable they considered various unethical or questionable farming practices. The survey also contained questions designed to measure perceived economic pressures. We find evidence that economic pressures result in a greater willingness of farmers to tolerate unethical conduct, particularly in the case of actions that have the potential of causing harm or that are influenced by law or contract. We also find that the more frequently a farmer reports observing an unethical action, the more accepting he is of it. Copyright (c)2008 International Association of Agricultural Economists.