3,539 research outputs found
Laboratory studies on the excitation and collisional deactivation of metastable atoms and molecules in the aurora and airglow
The aeronomy group at the University of Pittsburgh is actively engaged in a series of coordinated satellite, sounding rocket, and laboratory studies designed to expand and clarify knowledge of the physics and chemistry of planetary atmospheres. Three major discoveries have been made that will lead ultimately to a complete and dramatic revision of our ideas on the ionospheres of Mars, Venus, and the Earth and on the origin of their vacuum ultraviolet airglows. The results have already suggested a new generation of ionosphere studies which probably can be carried out best by laser heterodyning techniques. Laboratory studies have also identified, for the first time, the physical mechanism responsible for the remarkable nitric oxide buildup observed in some auroral arcs. This development is an important break-through in auroral physics, and has military ramifications of considerable interest to the Department of Defense. This work may also shed some light on related NO and atomic nitrogen problems in the mesosphere
Beyond the Zipf-Mandelbrot law in quantitative linguistics
In this paper the Zipf-Mandelbrot law is revisited in the context of
linguistics. Despite its widespread popularity the Zipf--Mandelbrot law can
only describe the statistical behaviour of a rather restricted fraction of the
total number of words contained in some given corpus. In particular, we focus
our attention on the important deviations that become statistically relevant as
larger corpora are considered and that ultimately could be understood as
salient features of the underlying complex process of language generation.
Finally, it is shown that all the different observed regimes can be accurately
encompassed within a single mathematical framework recently introduced by C.
Tsallis.Comment: 6 pages and 7 figures; minor changes in text, added referece
A short account of a connection of Power Laws to the Information Entropy
We use the formalism of 'Maximum Principle of Shannon's Entropy' to derive
the general power law distribution function, using what seems to be a
reasonable physical assumption, namely, the demand of a constant mean "internal
order" (Boltzmann Entropy) of a complex, self interacting, self organized
system. Since the Shannon entropy is equivalent to the Boltzmann's entropy
under equilibrium, non interacting conditions, we interpret this result as the
complex system making use of its intra-interactions and its non equilibrium in
order to keep the equilibrium Boltzmann's entropy constant on the average, thus
enabling it an advantage at surviving over less ordered systems, i.e. hinting
towards an "Evolution of Structure". We then demonstrate the formalism using a
toy model to explain the power laws observed in Cities' populations and show
how Zipf's law comes out as a natural special point of the model. We also
suggest further directions of theory.Comment: 7 pages, no figures, accepted for publication in "Physica A
Studies of the airglow, the aurora, the ion and neutral composition, and the chemistry of the terrestrial atmosphere
Results obtained by rocket-borne optical spectrometry are presented. Composition measurements and auroral studies are reported. The production of N (D-2) atoms by photo-absorption processes, and by electron impact excitation of N2 are discussed along with vibrationally excited CO2(+) ions in planetary atmospheres
The meta book and size-dependent properties of written language
Evidence is given for a systematic text-length dependence of the power-law
index gamma of a single book. The estimated gamma values are consistent with a
monotonic decrease from 2 to 1 with increasing length of a text. A direct
connection to an extended Heap's law is explored. The infinite book limit is,
as a consequence, proposed to be given by gamma = 1 instead of the value
gamma=2 expected if the Zipf's law was ubiquitously applicable. In addition we
explore the idea that the systematic text-length dependence can be described by
a meta book concept, which is an abstract representation reflecting the
word-frequency structure of a text. According to this concept the
word-frequency distribution of a text, with a certain length written by a
single author, has the same characteristics as a text of the same length pulled
out from an imaginary complete infinite corpus written by the same author.Comment: 7 pages, 6 figures, 1 tabl
Universality of Zipf's Law
We introduce a simple and generic model that reproduces Zipf's law. By
regarding the time evolution of the model as a random walk in the logarithmic
scale, we explain theoretically why this model reproduces Zipf's law. The
explanation shows that the behavior of the model is very robust and universal.Comment: 5 eps files included. To be published in J. Phys. Soc. Jp
Fractal Power Law in Literary English
We present in this paper a numerical investigation of literary texts by
various well-known English writers, covering the first half of the twentieth
century, based upon the results obtained through corpus analysis of the texts.
A fractal power law is obtained for the lexical wealth defined as the ratio
between the number of different words and the total number of words of a given
text. By considering as a signature of each author the exponent and the
amplitude of the power law, and the standard deviation of the lexical wealth,
it is possible to discriminate works of different genres and writers and show
that each writer has a very distinct signature, either considered among other
literary writers or compared with writers of non-literary texts. It is also
shown that, for a given author, the signature is able to discriminate between
short stories and novels.Comment: 27 pages, 10 tables,15 figures. Revised version accepted in Physica
Energy spectra of metastable oxygen atoms produced by electron impact dissociation of O2
Kinetic energies of metastable oxygen atoms formed by electron impact dissociation of oxygen and measured in time of flight experimen
Excitation of the Werner bands of H2 by electron impact
Absolute cross sections for the excitation of the H2 Werner band system were measured from energy threshold to 300 eV for electron impact on H2. The bands were observed in emission in the wavelength region 1100A to 1250A. The measured cross sections were compared with published transition probabilities, leading to the conclusion that the Werner bands are suitable as the basis for a relative spectral response calibration only when the bands are observed under sufficiently high resolution. The effect of the perturbation between the C 1Pi u and B 1 Sigma-u states of the hydrogen molecule was clearly observed in anomalies in the rotational intensity distribution in bands of the (3 v '') progression
Excitation of atomic nitrogen by electron impact
Absolute cross sections were measured for the excitation of the N I(1134, 1164, 1168, 1200, 1243, and 1743 A) multiplets by electron impact on atomic nitrogen. The presence of vibrationally excited molecular nitrogen in the discharged gas was confirmed, and its effect on the measurements is discussed. The ratio of the oscillator strengths of the 1200 and 1134 A resonance transitions is presented, as well as the branching ratio for the N I(1311/1164 A) multiplets. Striking differences in the distribution of intensity between the spectra of atomic nitrogen and molecular nitrogen excited by energetic electrons suggest an optical method for measuring the density of atomic nitrogen in the upper atmosphere
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