3,343 research outputs found
An Altitude Chamber for the Study and Calibration of Aeronautical Instruments
The design and construction of an altitude chamber, in which both pressure and temperature can be varied independently, was carried out by the NACA at the Langley Memorial Aeronautical Laboratory for the purpose of studying the effects of temperature and pressure on aeronautical research instruments. Temperatures from +20c to -50c are obtained by the expansion of CO2from standard containers. The chamber can be used for the calibration of research instruments under altitude conditions simulating those up to 45,000 feet. Results obtained with this chamber have a direct application in the design and calibration of instruments used in free flight research
Social Disorganization and Rural/Urban Crime Rates: A County Level Comparison of Contributing Factors
Social disorganization theory (Shaw & McKay, 1929) is a common explanation for crime. However, few studies have examined its significance for the explanation of crime in rural areas. The current study utilizes county level data from the United States Department of Health and Human Services to examine common characteristics of social disorganization for both rural and urban areas and which of these factors greater contribute to crime rates. The findings are consistent with previous research that finds significant differences between urban and rural areas regarding causes of crime. Overall, this study found that common measures of social disorganization such as income, racial heterogeneity, and migration do play a significant role in predicting the crime rate for both urban and rural areas. However, births and international migration play a significant role only in rural areas
Efficient Pattern Matching in Python
Pattern matching is a powerful tool for symbolic computations. Applications
include term rewriting systems, as well as the manipulation of symbolic
expressions, abstract syntax trees, and XML and JSON data. It also allows for
an intuitive description of algorithms in the form of rewrite rules. We present
the open source Python module MatchPy, which offers functionality and
expressiveness similar to the pattern matching in Mathematica. In particular,
it includes syntactic pattern matching, as well as matching for commutative
and/or associative functions, sequence variables, and matching with
constraints. MatchPy uses new and improved algorithms to efficiently find
matches for large pattern sets by exploiting similarities between patterns. The
performance of MatchPy is investigated on several real-world problems
Detection techniques for tenuous planetary atmospheres
The development of new types of detectors for analysis of planetary atmospheres is discussed. Initially, the interest was in detectors for use under partial vacuum conditions; recently, the program has been extended to include detectors for use at one atmosphere and adsorption systems for control and separation of gases. Results to date have included detector for O2 and H2 under partial vacuum conditions. Experiments on detectors for use at high pressures began in 1966; and systems for CO, H2, and O2 were reported in 1967 and 1968. In 1968 studies began on an electrically controlled adsorbent. It was demonstrated that under proper conditions a thin film of semiconductor material could be electrically cycled to absorb and desorb a specific gas. This work was extended to obtain quantitative data on the use of semiconductors as controllable adsorbents
High-precision measurement of the half-life of Ga
The beta-decay half-life of 62Ga has been studied with high precision using
on-line mass separated samples. The decay of 62Ga which is dominated by a 0+ to
0+ transition to the ground state of 62Zn yields a half-life of T_{1/2} =
116.19(4) ms. This result is more precise than any previous measurement by
about a factor of four or more. The present value is in agreement with older
literature values, but slightly disagrees with a recent measurement. We
determine an error weighted average value of all experimental half-lives of
116.18(4) ms.Comment: 9 pages, 5 figures, accepted for publication in PR
Feynman-Schwinger representation approach to nonperturbative physics
The Feynman-Schwinger representation provides a convenient framework for the
cal culation of nonperturbative propagators. In this paper we first investigate
an analytically solvable case, namely the scalar QED in 0+1 dimension. With
this toy model we illustrate how the formalism works. The analytic result for
the self energy is compared with the perturbative result. Next, using a
interaction, we discuss the regularization of various divergences
encountered in this formalism. The ultraviolet divergence, which is common in
standard perturbative field theory applications, is removed by using a
Pauli-Villars regularization. We show that the divergence associated with large
values of Feynman-Schwinger parameter is spurious and it can be avoided by
using an imaginary Feynman parameter .Comment: 26 pages, 9 figures, minor correctio
Conserving Diagrammatic Approximations for Quantum Impurity Models: NCA and CTMA
Self-consistent diagrammatic approximations to the Anderson or Kondo impurity
model, using an exact pseudoparticle representation of the impurity states, are
reviewed. We first discuss the infrared exponents of the pseudoparticle
propagators as indicators of Fermi liquid behavior through their dependence on
the impurity occupation and on magnetic field. Then we discuss the Non-Crossing
Approximation (NCA), identifying its strengths, but also its fundamental
shortcomings. Physical arguments as well as a perturbative renormalization
group analysis suggest that an infinite parquet-type resummation of
two-particle vertex diagrams, the Conserving T-Matrix Approximation (CTMA) will
cure the deficiencies of NCA. We review results on the pseudoparticle spectral
functions, the spin susceptibility and the impurity electron spectral function,
supporting that the CTMA provides qualitatively correct results, both in the
high-temperature regime and in the strong coupling Fermi liquid regime at low
temperatures.Comment: 10 pages, invited article, to appear in a special edition of JPSJ
"Kondo Effect - 40 Years after the Discovery", published version, some minor
typos correcte
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