21,816 research outputs found
A study of some reactor shielding problems for spacecraft applications
Programs to calculate single-scattered neutron and gamma fluxes from reactor-powered spacecraft radiators and sample calculations from unshielded SNAP-
RECENT IMPROVEMENTS IN MADCAP
MADCAP is a programming language admitting subscripts, superscripts and certain forms of displayed formulas. The basic implementation of this language was described in a previous paper [MADCAP: A scientific compiler for a displayed formula textbook language,
Comm. ACM 4
(Jan. 61), 31-36]. This paper discusses recent improvements in the language in three areas: complex display, logical control, and subprogramming. In the area of complex display, the most prominent improvements are a notation for integration and for the binomial coefficients. In the area of logical control the chief new feature is a notation for variably nested looping. The discussion of subprogramming is focused on MADCAP's notation for and use of “procedures.”
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Concepts and procedures used to determine certain sea wave characteristics
A technique and its application are presented by which wave parameters, critical to spacecraft water impact load analysis, may be determined
Spin Correlations in the Two-Dimensional Spin-5/2 Heisenberg Antiferromagnet Rb2MnF4
We report a neutron scattering study of the instantaneous spin correlations
in the two-dimensional spin S=5/2 square-lattice Heisenberg antiferromagnet
Rb_2MnF_4. The measured correlation lengths are quantitatively described, with
no adjustable parameters, by high-temperature series expansion results and by a
theory based on the quantum self-consistent harmonic approximation. Conversely,
we find that the data, which cover the range from about 1 to 50 lattice
constants, are outside of the regime corresponding to renormalized classical
behavior of the quantum non-linear sigma model. In addition, we observe a
crossover from Heisenberg to Ising critical behavior near the Neel temperature;
this crossover is well described by a mean-field model with no adjustable
parameters.Comment: 8 pages, LaTeX, with 6 included EPS figures, submitted to EPJ
Anomalous Phase Transition in Strained SrTiO Thin Films
We have studied the cubic to tetragonal phase transition in epitaxial
SrTiO films under various biaxial strain conditions using synchrotron X-ray
diffraction. Measuring the superlattice peak associated with TiO octahedra
rotation in the low temperature tetragonal phase indicates the presence of a
phase transition whose critical temperature is a strong function of strain,
with T as much as 50K above the corresponding bulk temperature.
Surprisingly, the lattice constants evolve smoothly through the transition with
no indication of a phase change. This signals an important change in the nature
of the phase transition due to the epitaxy strain and substrate clamping
effect. The internal degrees of freedom (TiO rotations) have become
uncoupled from the overall lattice shape.Comment: 4 pages, 3 figures, REVTeX
EAGLE ISS - A modular twin-channel integral-field near-IR spectrograph
The ISS (Integral-field Spectrograph System) has been designed as part of the
EAGLE Phase A Instrument Study for the E-ELT. It consists of two input channels
of 1.65x1.65 arcsec field-of-view, each reconfigured spatially by an
image-slicing integral-field unit to feed a single near-IR spectrograph using
cryogenic volume-phase-holographic (VPH) gratings to disperse the image
spectrally. A 4k x 4k array detector array records the dispersed images. The
optical design employs anamorphic magnification, image slicing, VPH gratings
scanned with a novel cryo-mechanism and a three-lens camera. The mechanical
implementation features IFU optics in Zerodur, a modular bench structure and a
number of high-precision cryo-mechanisms.Comment: 12 pages, to be published in Proc SPIE 7735: Ground-based & Airborne
Instrumentation for Astronomy II
Direct Evidence for the Source of Reported Magnetic Behavior in "CoTe"
In order to unambiguously identify the source of magnetism reported in recent
studies of the Co-Te system, two sets of high-quality, epitaxial CoTe films
(thickness 300 nm) were prepared by pulse laser deposition (PLD).
X-ray diffraction (XRD) shows that all of the films are epitaxial along the
[001] direction and have the hexagonal NiAs structure. There is no indication
of any second phase metallic Co peaks (either or ) in the XRD
patterns. The two sets of CoTe films were grown on various substrates with
PLD targets having Co:Te in the atomic ratio of 50:50 and 35:65. From the
measured lattice parameters for the former and
for the latter, the compositions CoTe (63.1% Te) and CoTe
(63.8% Te), respectively, are assigned to the principal phase. Although XRD
shows no trace of metallic Co second phase, the magnetic measurements do show a
ferromagnetic contribution for both sets of films with the saturation
magnetization values for the CoTe films being approximately four times
the values for the CoTe films. Co spin-echo nuclear magnetic
resonance (NMR) clearly shows the existence of metallic Co inclusions in the
films. The source of weak ferromagnetism reported in several recent studies is
due to the presence of metallic Co, since the stoichiometric composition "CoTe"
does not exist.Comment: 19 pages, 7 figure
Comparative analysis of rigidity across protein families
We present a comparative study in which 'pebble game' rigidity analysis is applied to multiple protein crystal structures, for each of six different protein families. We find that the main-chain rigidity of a protein structure at a given hydrogen bond energy cutoff is quite sensitive to small structural variations, and conclude that the hydrogen bond constraints in rigidity analysis should be chosen so as to form and test specific hypotheses about the rigidity of a particular protein. Our comparative approach highlights two different characteristic patterns ('sudden' or 'gradual') for protein rigidity loss as constraints are removed, in line with recent results on the rigidity transitions of glassy networks
Compensatory Consumption and Consumer Compromises: A State of the Art Review
Compensatory consumption has been an increasingly researched yet widely debated area of consumer behaviour over the last 20 years. Extant research formulates the term as overwhelmingly negative, largely due to the simplistic and fragmented conceptualisations assumed in prior work. The purpose of the current paper is to present a comprehensive review of the umbrella term of compensatory consumption, incorporating a continuum of behaviours and accounting for the pre- and post-consumption periods including both positive and negative viewpoints. In addition, expanding upon the theory of need satisfaction, the current paper introduces a novel conceptual distinction between compensation and compromise. Finally, a proposed theoretical framework is presented that differentiates between compensatory and compromisory consumption based on the extent of consumer consciousness, rationality and rationalisation. Future research directions are offered
Transcutaneous measurement of volume blood flow
Blood flow velocity measurements, using Doppler velocimeter, are described. The ability to measure blood velocity using ultrasound is derived from the Doppler effect; the change in frequency which occurs when sound is reflected or transmitted from a moving target. When ultrasound of the appropriate frequency is transmitted through a moving blood stream, the blood cells act as point scatterers of ultrasonic energy. If this scattered ultrasonic energy is detected, it is found to be shifted in frequency according to the velocity of the blood cells, nu, the frequency of the incident sound, f sub o, the speed of sound in the medium, c, and the angle between the sound beam and the velocity vector, o. The relation describing this effect is known as the Doppler equation. Delta f = 2 f sub o x nu x cos alpha/c. The theoretical and experimental methods are evaluated
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