8,925 research outputs found
Hidden Variables or Positive Probabilities?
Despite claims that Bell's inequalities are based on the Einstein locality
condition, or equivalent, all derivations make an identical mathematical
assumption: that local hidden-variable theories produce a set of
positive-definite probabilities for detecting a particle with a given spin
orientation. The standard argument is that because quantum mechanics assumes
that particles are emitted in a superposition of states the theory cannot
produce such a set of probabilities. We examine a paper by Eberhard, and
several similar papers, which claim to show that a generalized Bell inequality,
the CHSH inequality, can be derived solely on the basis of the locality
condition, without recourse to hidden variables. We point out that these
authors nonetheless assumes a set of positive-definite probabilities, which
supports the claim that hidden variables or "locality" is not at issue here,
positive-definite probabilities are. We demonstrate that quantum mechanics does
predict a set of probabilities that violate the CHSH inequality; however these
probabilities are not positive-definite. Nevertheless, they are physically
meaningful in that they give the usual quantum-mechanical predictions in
physical situations. We discuss in what sense our results are related to the
Wigner distribution.Comment: 19 pages, 2 ps files This is a second replacement. In this version we
include an analysis of yet another version of Bell's theorem which has been
brought to our attention. We also discuss in what sense our results are
related to the Wigner distributio
Review of \u3cem\u3eWhy I Burned My Book and Other Essays on Disability.\u3c/em\u3e Paul K. Longmore. Reviewed by Juliet Rothman.
Paul K. Longmore, Why I Burned My Book and Other Essays on Disability. Philadelphia: Temple University Press, 2003. $69.50 papercover
Review of \u3cem\u3eVoices from the Edge: Narratives about the Americans with Disabilities Act.\u3c/em\u3e Ruth O\u27Brien. Reviewed by Juliet C. Rothman.
Book review of Ruth O\u27Brien, Voices from the Edge: Narratives about the Americans with Disabilities Act. New York: Oxford University Press, 2004. 16.95 papercover
The Lorentz Force and the Radiation Pressure of Light
In order to make plausible the idea that light exerts a pressure on matter,
some introductory physics texts consider the force exerted by an
electromagnetic wave on an electron. The argument as presented is both
mathematically incorrect and has several serious conceptual difficulties
without obvious resolution at the classical, yet alone introductory, level. We
discuss these difficulties and propose an alternate demonstration.Comment: More or less as in AJ
The First Amendment and the Right(s) of Publicity
The right of publicity protects persons against unauthorized uses of their identity, most typically their names, images, or voices. The right is in obvious tension with freedom of speech. Yet courts seeking to reconcile the right with the First Amendment have to date produced only a notoriously confused muddle of inconsistent constitutional doctrine. In this Article, we suggest a way out of the maze. We propose a relatively straightforward framework for analyzing how the right of publicity should be squared with First Amendment principles.At the root of contemporary constitutional confusion lies a failure to articulate the precise state interests advanced by the right of publicity. We seek to remedy this deficiency by disaggregating four distinct state interests that the right of publicity is typically invoked to protect. We argue that in any given case the right of publicity is characteristically invoked to protect (one or more) of these four interests: the value of a plaintiff’s performance, the commercial value of a plaintiff’s identity, the dignity of a plaintiff, or the autonomous personality of a plaintiff.Plaintiffs’ interests in their identity must always be weighed against defendants’ constitutional interests in their speech. We therefore isolate three constitutional kinds of communication, each with a distinct form of First Amendment protection. A defendant’s misappropriation of a plaintiff’s identity can occur in public discourse, in commercial speech, or in what we call “commodities.” We then discuss how constitutional protections for these three kinds of speech should intersect with the four different interests that right of publicity claims are typically invoked to protect.The upshot is not a mechanical algorithm for producing correct constitutional outcomes, but an illumination of the constitutional stakes at issue in any given right of publicity action. We hope that by carefully surfacing the constitutional and policy stakes that beset the conflict between right(s) of publicity and the First Amendment, we have sketched a map that might substantially assist those who must navigate this tumultuous terrain
Instability of Extremal Relativistic Charged Spheres
With the question, ``Can relativistic charged spheres form extremal black
holes?" in mind, we investigate the properties of such spheres from a classical
point of view. The investigation is carried out numerically by integrating the
Oppenheimer-Volkov equation for relativistic charged fluid spheres and finding
interior Reissner-Nordstr\"om solutions for these objects. We consider both
constant density and adiabatic equations of state, as well as several possible
charge distributions, and examine stability by both a normal mode and an energy
analysis. In all cases, the stability limit for these spheres lies between the
extremal () limit and the black hole limit (). That is, we find
that charged spheres undergo gravitational collapse before they reach ,
suggesting that extremal Reissner-Nordtr\"om black holes produced by collapse
are ruled out. A general proof of this statement would support a strong form of
the cosmic censorship hypothesis, excluding not only stable naked
singularities, but stable extremal black holes. The numerical results also
indicate that although the interior mass-energy obeys the usual stability limit for the Schwarzschild interior solution, the gravitational
mass does not. Indeed, the stability limit approaches as .
In the Appendix we also argue that Hawking radiation will not lead to an
extremal Reissner-Nordstr\"om black hole. All our results are consistent with
the third law of black hole dynamics, as currently understood
Carbon transit through degradation networks
The decay of organic matter in natural ecosystems is controlled by a network of biologically, physically, and chemically driven processes. Decomposing organic matter is often described as a continuum that transforms and degrades over a wide range of rates, but it is difficult to quantify this heterogeneity in models. Most models of carbon degradation consider a network of only a few organic matter states that transform homogeneously at a single rate. These models may fail to capture the range of residence times of carbon in the soil organic matter continuum. Here we assume that organic matter is distributed among a continuous network of states that transform with stochastic, heterogeneous kinetics. We pose and solve an inverse problem in order to identify the rates of carbon exiting the underlying degradation network (exit rates) and apply this approach to plant matter decay throughout North America. This approach provides estimates of carbon retention in the network without knowing the details of underlying state transformations. We find that the exit rates are approximately lognormal, suggesting that carbon flow through a complex degradation network can be described with just a few parameters. These results indicate that the serial and feedback processes in natural degradation networks can be well approximated by a continuum of parallel decay rates.National Science Foundation (U.S.) (Grant EAR-0420592)United States. National Aeronautics and Space Administration (Grant NNA08CN84A
"Quantum Interference with Slits" Revisited
Marcella [arXiv:quant-ph/0703126] has presented a straightforward technique
employing the Dirac formalism to calculate single- and double-slit interference
patterns. He claims that no reference is made to classical optics or scattering
theory and that his method therefore provides a purely quantum mechanical
description of these experiments. He also presents his calculation as if no
approximations are employed. We show that he implicitly makes the same
approximations found in classical treatments of interference and that no new
physics has been introduced. At the same time, some of the quantum mechanical
arguments Marcella gives are, at best, misleading.Comment: 11 pages, 3 figure
Inverse method for estimating respiration rates from decay time series
Long-term organic matter decomposition experiments typically measure the mass lost from decaying organic matter as a function of time. These experiments can provide information about the dynamics of carbon dioxide input to the atmosphere and controls on natural respiration processes. Decay slows down with time, suggesting that organic matter is composed of components (pools) with varied lability. Yet it is unclear how the appropriate rates, sizes, and number of pools vary with organic matter type, climate, and ecosystem. To better understand these relations, it is necessary to properly extract the decay rates from decomposition data. Here we present a regularized inverse method to identify an optimally-fitting distribution of decay rates associated with a decay time series. We motivate our study by first evaluating a standard, direct inversion of the data. The direct inversion identifies a discrete distribution of decay rates, where mass is concentrated in just a small number of discrete pools. It is consistent with identifying the best fitting "multi-pool" model, without prior assumption of the number of pools. However we find these multi-pool solutions are not robust to noise and are over-parametrized. We therefore introduce a method of regularized inversion, which identifies the solution which best fits the data but not the noise. This method shows that the data are described by a continuous distribution of rates, which we find is well approximated by a lognormal distribution, and consistent with the idea that decomposition results from a continuum of processes at different rates. The ubiquity of the lognormal distribution suggest that decay may be simply described by just two parameters: a mean and a variance of log rates. We conclude by describing a procedure that estimates these two lognormal parameters from decay data. Matlab codes for all numerical methods and procedures are provided
Two-dimensional hydrodynamic lattice-gas simulations of binary immiscible and ternary amphiphilic fluid flow through porous media
The behaviour of two dimensional binary and ternary amphiphilic fluids under
flow conditions is investigated using a hydrodynamic lattice gas model. After
the validation of the model in simple cases (Poiseuille flow, Darcy's law for
single component fluids), attention is focussed on the properties of binary
immiscible fluids in porous media. An extension of Darcy's law which explicitly
admits a viscous coupling between the fluids is verified, and evidence of
capillary effects are described. The influence of a third component, namely
surfactant, is studied in the same context. Invasion simulations have also been
performed. The effect of the applied force on the invasion process is reported.
As the forcing level increases, the invasion process becomes faster and the
residual oil saturation decreases. The introduction of surfactant in the
invading phase during imbibition produces new phenomena, including
emulsification and micellisation. At very low fluid forcing levels, this leads
to the production of a low-resistance gel, which then slows down the progress
of the invading fluid. At long times (beyond the water percolation threshold),
the concentration of remaining oil within the porous medium is lowered by the
action of surfactant, thus enhancing oil recovery. On the other hand, the
introduction of surfactant in the invading phase during drainage simulations
slows down the invasion process -- the invading fluid takes a more tortuous
path to invade the porous medium -- and reduces the oil recovery (the residual
oil saturation increases).Comment: 48 pages, 26 figures. Phys. Rev. E (in press
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