158,010 research outputs found
Identification of the youngest meteorites and a discussion of the possibility that they came from Mars
The shergottites are a group of basaltic meteorites which are very similar in appearance to terrestrial basalts. On the Earth basalts are formed by volcanic activity. Because the shergottites so resemble terrestrial basalts and because they are apparently very young ( 1.3 billion years), it has been inferred that they come from a large planet. Small planets and asteroids lose heat from their interiors quickly and stop producing hot basaltic liquids early in their history. It appears that gases trapped in one shergotite found in Antarctica (BETA 79001) are chemically similar to the martian atmosphere (as measured by the Viking mission). The controversial speculation that the shergotites are samples of mars is examined in detail
Lightning tracking system
A system is described for locating lightning strikes by developing the coordinates of a pair of lines, each of which is produced at a reference sensing station. At each station there are a pair of directional antennas which produce analog signals responsive to a lightning stroke. These analog signals are fed to a pair of integrators which integrate the signals for a predetermined period of time so as to produce the X and Y coordinate of a particular line. The analog signals are also fed through a square rooter, a Schmitt trigger circuit, and flip-flops to produce pulses for starting and stopping the integrators. The system at the remote station is similar to that at the central station and is tied to the circuitry at the central station through logic circuits to minimize the chance of error from spurious signals. Computers, printers, and plotters are utilized to plot the exact location of the lightning stroke
An Equivalent Hermitian Hamiltonian for the non-Hermitian -x^4 Potential
The potential -x^4, which is unbounded below on the real line, can give rise
to a well-posed bound state problem when x is taken on a contour in the
lower-half complex plane. It is then PT-symmetric rather than Hermitian.
Nonetheless it has been shown numerically to have a real spectrum, and a proof
of reality, involving the correspondence between ordinary differential
equations and integral systems, was subsequently constructed for the general
class of potentials -(ix)^N. For PT-symmetric but non-Hermitian Hamiltonians
the natural PT metric is not positive definite, but a dynamically-defined
positive-definite metric can be defined, depending on an operator Q. Further,
with the help of this operator an equivalent Hermitian Hamiltonian h can be
constructed. This programme has been carried out exactly for a few soluble
models, and the first few terms of a perturbative expansion have been found for
the potential m^2x^2+igx^3. However, until now, the -x^4 potential has proved
intractable. In the present paper we give explicit, closed-form expressions for
Q and h, which are made possible by a particular parametrization of the contour
in the complex plane on which the problem is defined. This constitutes an
explicit proof of the reality of the spectrum. The resulting equivalent
Hamiltonian has a potential with a positive quartic term together with a linear
term.Comment: New reference [10] added and discussed. Minor typographical
correction
Life in the eucharistic community : an empirical study in psychological type theory and biblical hermeneutics reading John 6:5–15
This study employs psychological type theory to analyse the ways in which a group of 13 newly ordained Anglican priests (in priest’s orders for 3 or 4 months) reflected on the Eucharistic imagery of the Johannine feeding narrative. In the first exercise, the priests worked in two groups distinguished according to their perceiving preference (7 sensing types and 6 intuitive types). In the second exercise, the priests worked in three groups distinguished according to their judging preferences (4 thinking types, 4 feeling types, and 5 feeling types). The data supported the significance of psychological type in shaping the hermeneutical process (the theory underpinning the SIFT method of biblical hermeneutics and liturgical preaching). Sensing types grappled with the plethora of detail within the text. Intuitive types looked for the bigger picture and identified major themes. Thinking types looked for and organised the major issues raised by the passage. Feeling types focused on the human and relational implications of the narrative
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Large-scale climate variability in Antarctica and the Southern Ocean and links to extra-polar climate
Use of composite rotations to correct systematic errors in NMR quantum computation
We implement an ensemble quantum counting algorithm on three NMR
spectrometers with 1H resonance frequencies of 500, 600 and 750 MHz. At higher
frequencies, the results deviate markedly from naive theoretical predictions.
These systematic errors can be attributed almost entirely to off-resonance
effects, which can be substantially corrected for using fully-compensating
composite rotation pulse sequences originally developed by Tycko. We also
derive an analytic expression for generating such sequences with arbitrary
rotation angles.Comment: 8 pages RevTex including 7 PostScript figures (18 subfigures
TTF: a flexible approach to narrowband imaging
The Taurus Tunable Filter (TTF) is a tunable narrowband interference filter
covering wavelengths from 6300 A to the sensitivity drop-off of conventional
CCDs (9600 A), although a blue `arm' (3700-6500 A) is to be added by the end of
1997. The TTF offers monochromatic imaging at the cassegrain foci of both the
Anglo-Australian and William Herschel Telescopes, with an adjustable passband
of between 6 and 60 A. In addition, frequency switching with the TTF can be
synchronized to movement of charge (charge shuffling) on the CCD which has many
important applications in astrophysics. Here we review different modes of TTF.
We maintain a web site at http://msowww.anu.edu.au/~dhj/ttf.html describing all
aspects of TTF and its operation. In addition to general use, the instrument is
available in AAT service time. Details can be found at
http://www.aao.gov.au/local/www/jmc/service/service.html.Comment: 8 pages; Latex; 5 encapsulated postscript figures. Invited talk at
the "AAO/UKST Galactic Plane H-alpha Survey", International Workshop, Sydney,
Australi
A comparison of measured and theoretical predictions for STS ascent and entry sonic booms
Sonic boom measurements have been obtained during the flights of STS-1 through 5. During STS-1, 2, and 4, entry sonic boom measurements were obtained and ascent measurements were made on STS-5. The objectives of this measurement program were (1) to define the sonic boom characteristics of the Space Transportation System (STS), (2) provide a realistic assessment of the validity of xisting theoretical prediction techniques, and (3) establish a level of confidence for predicting future STS configuration sonic boom environments. Detail evaluation and reporting of the results of this program are in progress. This paper will address only the significant results, mainly those data obtained during the entry of STS-1 at Edwards Air Force Base (EAFB), and the ascent of STS-5 from Kennedy Space Center (KSC). The theoretical prediction technique employed in this analysis is the so called Thomas Program. This prediction technique is a semi-empirical method that required definition of the near field signatures, detailed trajectory characteristics, and the prevailing meteorological characteristics as an input. This analytical procedure then extrapolates the near field signatures from the flight altitude to an altitude consistent with each measurement location
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