60,233 research outputs found
Random access-random release relay switching matrix
XY relay switching matrix provides complete random access and random release of 400 points. A mercury-wetted bistable relay with independent set and reset coils is the unique feature associated with each point
Cold cathode gauge experiment (ALSEP)
Cold cathode ionization gages were left on the lunar surface as part of ALSEP (Apollo Lunar Surface Experiment Package) on Apollo missions 12, 14, and 15. An instrument prepared for Apollo 13 did not reach the surface because of the abort of that mission. The gages that reached the lunar surface measured the amounts of gas present in the vicinity of the ALSEP sites. The observed daytime gas concentrations were initially about two orders of magnitude greater than the nighttime observations; this was due to contamination of the landing area by the Apollo operations and equipment, and the daytime measurements showed a decrease with time characterized by a time constant of a few months
Numerical Studies of Three-dimensional Breakdown in Trailing Vortex Wakes
Finite element, three dimensional relaxation methods are used to calculate the development of vortex wakes behind aircraft for a considerable downstream distance. The inclusion of a self-induction term in the solution, dependent upon local curvature and vortex core radius, permits calculation of finite lifetimes for systems for which infinite life would be predicted two dimensionally. The associated computer program is described together with single-pair, twin-pair, and multiple-pair studies carried out using it. It is found, in single-pair studies, that there is a lower limit to the wavelengths at which the Crow-type of instability can occur. Below this limit, self-induction effects cause the plane of the disturbance waves to rotate counter to the vortex direction. Self induction in two dimensionally generated twin spiral waves causes an increase in axial length which becomes more marked with decreasing initial wavelength. The time taken for vortex convergence toward the center plane is correspondingly increased. The limited parametric twin-pair study performed suggests that time-to-converge increases with increasing flap span. Limited studies of Boeing 747 configurations show correct qualitative response to removal of the outer flap and to gear deployment, as compared with wind tunnel and flight test experience
Observations of Mare Serenitatis from lunar orbit and their interpretation
Visual observations are investigated of color differences of Serenitatis mare materials from orbit complement photography and other remotely sensed data. The light tan gray inner fill of the Serenitatis basin is younger than the dark blue gray annulus; the latter continues into and appears to be contemporaneous with the fill of Mare Tranquillitatis. Mare ridges occur in both the inner basin fill and the dark annulus of Serenitatis. Ridges are interpreted as the result of structural deformation and up-doming after the solidification of the basaltic lavas. On the southeastern rim of the Serenitatis basin is the darkes blue gray unit within which Apollo 17 landed. Highland massifs surrounding this unit have unstable slopes which are believed to be the result of localized tectonic activity. On the southwest rim of the basin are the dark tan to brown gray mantling materials of the Sulpicius Gallus Formation. Farther west on the rim are dark blue grap patches which resemble the mare material of the Serenitatis dark annulus
Microlensing Halo Models with Abundant Brown Dwarfs
All previous attempts to understand the microlensing results towards the
Large Magellanic Cloud (LMC) have assumed homogeneous present day mass
functions (PDMFs) for the lensing populations. Here, we present an
investigation into the microlensing characteristics of haloes with spatially
varying PDMFs and anisotropic velocity dispersion tensors. One attractive
possibility -- suggested by baryonic dark cluster formation in pregalactic and
protogalactic cooling flows -- is that the inner halo is dominated by stellar
mass objects, whereas low mass brown dwarfs become more prevalent on moving
outwards. The contribution to the microlensing rate must be dominated by dark
remnants (of about 0.5 solar masses) to recover the observed timescales of the
microlensing experiments. But, even though stellar remnants control the rate,
they do not dominate the mass of the baryonic halo, and so the well-known
enrichment and mass budget problems are much less severe. Using a simple ansatz
for the spatial variation of the PDMF, models are constructed in which the
contribution of brown dwarfs to the mass of the baryonic halo is 55 % and to
the total halo is 30 %. An unusual property of the models is that they predict
that the average timescale of events towards M31 is shorter than the average
timescale towards the LMC. This is because the longer line of sight towards M31
probes more of the far halo where brown dwarfs are the most common constituent.Comment: 17 pages, 1 figure, in press at The Astrophysical Journal (Letters
Synchronized voltage contrast display analysis system
An apparatus and method for comparing internal voltage potentials of first and second operating electronic components such as large scale integrated circuits (LSI's) in which voltage differentials are visually identified via an appropriate display means are described. More particularly, in a first embodiment of the invention a first and second scanning electron microscope (SEM) are configured to scan a first and second operating electronic component respectively. The scan pattern of the second SEM is synchronized to that of the first SEM so that both simultaneously scan corresponding portions of the two operating electronic components. Video signals from each SEM corresponding to secondary electron signals generated as a result of a primary electron beam intersecting each operating electronic component in accordance with a predetermined scan pattern are provided to a video mixer and color encoder
Force dependent fragility in RNA hairpins
We apply Kramers theory to investigate the dissociation of multiple bonds
under mechanical force and interpret experimental results for the
unfolding/refolding force distributions of an RNA hairpin pulled at different
loading rates using laser tweezers. We identify two different kinetic regimes
depending on the range of forces explored during the unfolding and refolding
process. The present approach extends the range of validity of the two-states
approximation by providing a theoretical framework to reconstruct free-energy
landscapes and identify force-induced structural changes in molecular
transition states using single molecule pulling experiments. The method should
be applicable to RNA hairpins with multiple kinetic barriers.Comment: Latex file, 4 pages+3 figure
DNA Spools under Tension
DNA-spools, structures in which DNA is wrapped and helically coiled onto
itself or onto a protein core are ubiquitous in nature. We develop a general
theory describing the non-equilibrium behavior of DNA-spools under linear
tension. Two puzzling and seemingly unrelated recent experimental findings, the
sudden quantized unwrapping of nucleosomes and that of DNA toroidal condensates
under tension are theoretically explained and shown to be of the same origin.
The study provides new insights into nucleosome and chromatin fiber stability
and dynamics
The role of the Initial Teacher Training Coordinator in the school based element of partnership: to what extent does the Co-ordinator undertake supervision of aspects of quality assurance?
Over the last 14 years, Universities and colleges have organised school placements and award qualifications whilst teachers, acting as mentors take the lead in guiding, supervising and assessing students on lengthy teaching placements. Partnership developed quickly in response to legislation and Sheffield Hallam University was among the first of the Universities to 'sign up' to the new partnership model in 1992. The Partnership Survey 2006 reported on in this paper has focussed on the Senior Liaison Tutor with a view to finding out their views on their role, and perceived contributions to the quality assurance of the partnership. The survey focussed on some of the key issues identified in previous studies and meetings of the Partnership Management Board.</p
Note on the Kaplan-Yorke dimension and linear transport coefficients
A number of relations between the Kaplan-Yorke dimension, phase space
contraction, transport coefficients and the maximal Lyapunov exponents are
given for dissipative thermostatted systems, subject to a small external field
in a nonequilibrium stationary state. A condition for the extensivity of phase
space dimension reduction is given. A new expression for the transport
coefficients in terms of the Kaplan-Yorke dimension is derived. Alternatively,
the Kaplan-Yorke dimension for a dissipative macroscopic system can be
expressed in terms of the transport coefficients of the system. The agreement
with computer simulations for an atomic fluid at small shear rates is very
good.Comment: 12 pages, 5 figures, submitted to J. Stat. Phy
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