61,717 research outputs found

    Exact and approximate dynamics of the quantum mechanical O(N) model

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    We study a quantum dynamical system of N, O(N) symmetric, nonlinear oscillators as a toy model to investigate the systematics of a 1/N expansion. The closed time path (CTP) formalism melded with an expansion in 1/N is used to derive time evolution equations valid to order 1/N (next-to-leading order). The effective potential is also obtained to this order and its properties areelucidated. In order to compare theoretical predictions against numerical solutions of the time-dependent Schrodinger equation, we consider two initial conditions consistent with O(N) symmetry, one of them a quantum roll, the other a wave packet initially to one side of the potential minimum, whose center has all coordinates equal. For the case of the quantum roll we map out the domain of validity of the large-N expansion. We discuss unitarity violation in the 1/N expansion; a well-known problem faced by moment truncation techniques. The 1/N results, both static and dynamic, are also compared to those given by the Hartree variational ansatz at given values of N. We conclude that late-time behavior, where nonlinear effects are significant, is not well-described by either approximation.Comment: 16 pages, 12 figrures, revte

    Space physics missions handbook

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    The purpose of this handbook is to provide background data on current, approved, and planned missions, including a summary of the recommended candidate future missions. Topics include the space physics mission plan, operational spacecraft, and details of such approved missions as the Tethered Satellite System, the Solar and Heliospheric Observatory, and the Atmospheric Laboratory for Applications and Science

    Clementine Observations of the Zodiacal Light and the Dust Content of the Inner Solar System

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    Using the Moon to occult the Sun, the Clementine spacecraft used its navigation cameras to map the inner zodiacal light at optical wavelengths over elongations of 3-30 degrees from the Sun. This surface brightness map is then used to infer the spatial distribution of interplanetary dust over heliocentric distances of about 10 solar radii to the orbit of Venus. We also apply a simple model that attributes the zodiacal light as being due to three dust populations having distinct inclination distributions, namely, dust from asteroids and Jupiter-family comets (JFCs), dust from Halley-type comets, and an isotropic cloud of dust from Oort Cloud comets. The best-fitting scenario indicates that asteroids + JFCs are the source of about 45% of the optical dust cross-section seen in the ecliptic at 1 AU, but that at least 89% of the dust cross-section enclosed by a 1 AU radius sphere is of a cometary origin. When these results are extrapolated out to the asteroid belt, we find an upper limit on the mass of the light-reflecting asteroidal dust that is equivalent to a 12 km asteroid, and a similar extrapolation of the isotropic dust cloud out to Oort Cloud distances yields a mass equivalent to a 30 km comet, although the latter mass is uncertain by orders of magnitude.Comment: To be published in Icaru

    Habeas Corpus in Peru: Myth and Reality

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    The purpose of the present article is not to criticize the laudable project of those whose object is to secure better protection for fundamental human rights, but rather to examine in detail the theory and practice of habeas corpus in one Latin American country, Peru, and to demonstrate that the greatest encroachments on human rights come not from political tyranny, as is popularly imagined, but from the malfunctioning of the legal system itself, against which even the most perfectly conceived habeas corpus is quite ineffective. It is trite but true that a legal system is only as effective as the human agency engaged in running it. It is sad to relate that, for all their apparent excellence on paper, the majority of Peruvian laws, as anyone with but slight acquaint- ance with the country can testify, are a dead letter. Of nothing is this truer than of the law relating to habeas corpus in Peru

    A Sentencing Problem: How Far Is a Fall from Grace

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    It is now almost universally accepted that there are three possible bases underlying sentences imposed by the Courts, following some breach of the criminal law. These are generally described as retribution, deterrence and reformation. Occasionally these qualities are considered in combination under some such title as the aims of penal measures. Another factor, ever present in a vague though influential form, now seems to be emerging from the shadows to assume more definite shape. Yet to materialize is its relationship to the other established, uncontroverted aims. The emergent element may conveniently be termed public disapproval, under which may be subsumed all those social sentiments, tacit or express, which reflect in the view taken of the offender\u27s conduct. It is increasingly evident that imprecision in regard to the understanding of this factor and its relationship to the accepted sentencing criteria constitutes agreat obstacle to the rationalization of penal policy and is at the root of many of the inconsistencies into which Courts are forced from time to time
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