17,508 research outputs found
Lead telluride bonding and segmentation study Semiannual phase report, Aug. 1, 1967 - Jan. 31, 1968
Constitutional studies of SnTe and Si-Ge metal systems, segmented Si-Ge-PdTe thermocouple efficiencies, and pore migration in PbSnTe thermoelement
Lead telluride bonding and segmentation study Interim report, 1 Nov. 1966 - 31 Jul. 1967
Lead telluride bonding and segmentation studies including couple design, test devices, and life testin
Emergence of steady and oscillatory localized structures in a phytoplankton-nutrient model
Co-limitation of marine phytoplankton growth by light and nutrient, both of
which are essential for phytoplankton, leads to complex dynamic behavior and a
wide array of coherent patterns. The building blocks of this array can be
considered to be deep chlorophyll maxima, or DCMs, which are structures
localized in a finite depth interior to the water column. From an ecological
point of view, DCMs are evocative of a balance between the inflow of light from
the water surface and of nutrients from the sediment. From a (linear)
bifurcational point of view, they appear through a transcritical bifurcation in
which the trivial, no-plankton steady state is destabilized. This article is
devoted to the analytic investigation of the weakly nonlinear dynamics of these
DCM patterns, and it has two overarching themes. The first of these concerns
the fate of the destabilizing stationary DCM mode beyond the center manifold
regime. Exploiting the natural singularly perturbed nature of the model, we
derive an explicit reduced model of asymptotically high dimension which fully
captures these dynamics. Our subsequent and fully detailed study of this model
- which involves a subtle asymptotic analysis necessarily transgressing the
boundaries of a local center manifold reduction - establishes that a stable DCM
pattern indeed appears from a transcritical bifurcation. However, we also
deduce that asymptotically close to the original destabilization, the DCM
looses its stability in a secondary bifurcation of Hopf type. This is in
agreement with indications from numerical simulations available in the
literature. Employing the same methods, we also identify a much larger DCM
pattern. The development of the method underpinning this work - which, we
expect, shall prove useful for a larger class of models - forms the second
theme of this article
Conservation of energy and momenta in nonholonomic systems with affine constraints
We characterize the conditions for the conservation of the energy and of the
components of the momentum maps of lifted actions, and of their `gauge-like'
generalizations, in time-independent nonholonomic mechanical systems with
affine constraints. These conditions involve geometrical and mechanical
properties of the system, and are codified in the so-called
reaction-annihilator distribution
Book Reviews
Constitutional Power and World Affairs, Columbia University Lectures, on the George Blumenthal Foundation, for i918, by George Sutherland. New York, Columbia University Press, 1019, pp. vii, 202. This book is one of the most interesting and thoughtful commentaries on certain phases of our Constitution which has appeared in many years. During his two terms in the United States Senate Mr. Sutherland came to be recognized as one of the ablest constitutional lawyers of the country, and his retirement in 1917 was a distinct loss to our public life. The present book is the product not only of exact, scholarly study of the subject, but is enriched by the varied experience of its author in the actual moulding of our governmental institutions during an important period. This appears particularly in the chapters on the treaty-making power
Computing the Casimir energy using the point-matching method
We use a point-matching approach to numerically compute the Casimir
interaction energy for a two perfect-conductor waveguide of arbitrary section.
We present the method and describe the procedure used to obtain the numerical
results. At first, our technique is tested for geometries with known solutions,
such as concentric and eccentric cylinders. Then, we apply the point-matching
technique to compute the Casimir interaction energy for new geometries such as
concentric corrugated cylinders and cylinders inside conductors with focal
lines.Comment: 11 pages, 18 figure
Low Gain Avalanche Detectors (LGAD) for particle physics and synchrotron applications
A new avalanche silicon detector concept is introduced with a low gain in the region of ten, known as a Low Gain Avalanche Detector, LGAD. The detector's characteristics are simulated via a full process simulation to obtain the required doping profiles which demonstrate the desired operational characteristics of high breakdown voltage (500 V) and a gain of 10 at 200 V reverse bias for X-ray detection. The first low gain avalanche detectors fabricated by Micron Semiconductor Ltd are presented. The doping profiles of the multiplication junctions were measured with SIMS and reproduced by simulating the full fabrication process which enabled further development of the manufacturing process. The detectors are 300 μm thick p-type silicon with a resistivity of 8.5 kΩcm, which fully depletes at 116 V. The current characteristics are presented and demonstrate breakdown voltages in excess of 500 V and a current density of 40 to 100 nAcm−2 before breakdown measured at 20oC. The gain of the LGAD has been measured with a red laser (660 nm) and shown to be between 9 and 12 for an external bias voltage range from 150 V to 300 V
Finite to infinite steady state solutions, bifurcations of an integro-differential equation
We consider a bistable integral equation which governs the stationary
solutions of a convolution model of solid--solid phase transitions on a circle.
We study the bifurcations of the set of the stationary solutions as the
diffusion coefficient is varied to examine the transition from an infinite
number of steady states to three for the continuum limit of the
semi--discretised system. We show how the symmetry of the problem is
responsible for the generation and stabilisation of equilibria and comment on
the puzzling connection between continuity and stability that exists in this
problem
Lead telluride bonding and segmentation study Semiannual phase report, 1 Feb. - 31 Jul. 1968
Chemical and physical properties of Co-Si-Ge system and PbTe-MnTe system, and life testing of thermocouple
Goals, Strategies and First Discoveries of AO327, the Arecibo All-Sky 327 MHz Drift Pulsar Survey
We report initial results from AO327, a drift survey for pulsars with the
Arecibo telescope at 327 MHz. The first phase of AO327 will cover the sky at
declinations of -1 to 28 degrees, excluding the region within 5 degrees of the
Galactic plane, where high scattering and dispersion make low-frequency surveys
sub-optimal. We record data from a 57 MHz bandwidth with 1024 channels and 125
us sampling time. The 60 s transit time through the AO327 beam means that the
survey is sensitive to very tight relativistic binaries even with no
acceleration searches. To date we have detected 44 known pulsars with periods
ranging from 3 ms to 2.21 s and discovered 24 new pulsars. The new discoveries
include three millisecond pulsars, three objects with periods of a few tens of
milliseconds typical of young as well as mildly recycled pulsars, a nuller, and
a rotating radio transient. Five of the new discoveries are in binary systems.
The second phase of AO327 will cover the sky at declinations of 28 to 38
degrees. We compare the sensitivity and search volume of AO327 to the Green
Bank North Celestial Cap survey and the GBT350 drift survey, both of which
operate at 350 MHz.Comment: Accepted for publication in Ap
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