9,181 research outputs found
Feasibility model of a high reliability five-year tape transport, volume 2
Analysis of the design features of the modularized tape transport renders a life expectancy in excess of five years. Tests performed on the tape transport were directed toward determining its performance capability. These tests revealed that the tape jitter and skew are in the range achieved by high quality digital tape transports. Guidance of the tape in the lateral sense by the use of the two hybrid crowned rollers proved to be excellent. Tracking was maintained within less than one thousandth inch (approximately 2 micrometers). The guidance capability demonstrated makes possible the achievement of the performance objective of 7.2 x 10 to the 9th power storage capability employing 1500 ft. of one inch wide tape with a packing density of 5,000 bits per inch per track on 80 tracks. Also, the machine showed excellent characteristics operating over a wide range of tape speeds. The basic design concept lends itself to growth and adaptation to a wide range of recorder requirements
Feasibility model of a high reliability five-year tape transport, Volume 1
The development, performance, and test results for the spaceborne magnetic tape transport are discussed. An analytical model of the tape transport was used to optimize its conceptual design. Each of the subsystems was subjected to reliability analyses which included structural integrity, maintenance of system performance within acceptable bounds, and avoidance of fatigue failure. These subsystems were also compared with each other in order to evaluate reliability characteristics. The transport uses no mechanical couplings. Four drive motors, one for each reel and one for each of two capstans, are used in a differential mode. There are two hybrid, spherical, cone tapered-crown rollers for tape guidance. Storage of the magnetic tape is provided by a reel assembly which includes the reel, a reel support structure and bearings, dust seals, and a dc drive motor. A summary of transport test results on tape guidance, flutter, and skew is provided
Predicting the size and probability of epidemics in a population with heterogeneous infectiousness and susceptibility
We analytically address disease outbreaks in large, random networks with
heterogeneous infectivity and susceptibility. The transmissibility
(the probability that infection of causes infection of ) depends on the
infectivity of and the susceptibility of . Initially a single node is
infected, following which a large-scale epidemic may or may not occur. We use a
generating function approach to study how heterogeneity affects the probability
that an epidemic occurs and, if one occurs, its attack rate (the fraction
infected). For fixed average transmissibility, we find upper and lower bounds
on these. An epidemic is most likely if infectivity is homogeneous and least
likely if the variance of infectivity is maximized. Similarly, the attack rate
is largest if susceptibility is homogeneous and smallest if the variance is
maximized. We further show that heterogeneity in infectious period is
important, contrary to assumptions of previous studies. We confirm our
theoretical predictions by simulation. Our results have implications for
control strategy design and identification of populations at higher risk from
an epidemic.Comment: 5 pages, 3 figures. Submitted to Physical Review Letter
Incommensurate phonon anomaly and the nature of charge density waves in cuprates
While charge density wave (CDW) instabilities are ubiquitous to
superconducting cuprates, the different ordering wavevectors in various cuprate
families have hampered a unified description of the CDW formation mechanism.
Here we investigate the temperature dependence of the low energy phonons in the
canonical CDW ordered cuprate LaBaCuO. We discover
that the phonon softening wavevector associated with CDW correlations becomes
temperature dependent in the high-temperature precursor phase and changes from
a wavevector of 0.238 reciprocal space units (r.l.u.) below the ordering
transition temperature up to 0.3~r.l.u. at 300~K. This high-temperature
behavior shows that "214"-type cuprates can host CDW correlations at a similar
wavevector to previously reported CDW correlations in non-"214"-type cuprates
such as YBaCuO. This indicates that cuprate CDWs may
arise from the same underlying instability despite their apparently different
low temperature ordering wavevectors.Comment: Accepted in Phys. Rev. X; 9 pages; 5 figures; 3 pages of
supplementary materia
Anisotropic softening of magnetic excitations in lightly electron doped SrIrO
The magnetic excitations in electron doped (SrLa)IrO with
were measured using resonant inelastic X-ray scattering at the Ir
-edge. Although much broadened, well defined dispersive magnetic
excitations were observed. Comparing with the magnetic dispersion from the
parent compound, the evolution of the magnetic excitations upon doping is
highly anisotropic. Along the anti-nodal direction, the dispersion is almost
intact. On the other hand, the magnetic excitations along the nodal direction
show significant softening. These results establish the presence of strong
magnetic correlations in electron doped SrLa)IrO with close
analogies to the hole doped cuprates, further motivating the search for high
temperature superconductivity in this system
Fragility and hysteretic creep in frictional granular jamming
The granular jamming transition is experimentally investigated in a
two-dimensional system of frictional, bi-dispersed disks subject to
quasi-static, uniaxial compression at zero granular temperature. Currently
accepted results show the jamming transition occurs at a critical packing
fraction . In contrast, we observe the first compression cycle exhibits
{\it fragility} - metastable configuration with simultaneous jammed and
un-jammed clusters - over a small interval in packing fraction (). The fragile state separates the two conditions that define
with an exponential rise in pressure starting at and an exponential
fall in disk displacements ending at . The results are explained
through a percolation mechanism of stressed contacts where cluster growth
exhibits strong spatial correlation with disk displacements. Measurements with
several disk materials of varying elastic moduli and friction coefficients
, show friction directly controls the start of the fragile state, but
indirectly controls the exponential slope. Additionally, we experimentally
confirm recent predictions relating the dependence of on . Under
repetitive loading (compression), the system exhibits hysteresis in pressure,
and the onset increases slowly with repetition number. This friction
induced hysteretic creep is interpreted as the granular pack's evolution from a
metastable to an eventual structurally stable configuration. It is shown to
depend upon the quasi-static step size which provides the only
perturbative mechanism in the experimental protocol, and the friction
coefficient which acts to stabilize the pack.Comment: 12 pages, 10 figure
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