1,865 research outputs found
Antenna grout replacement system
An epoxy grout suitable for use in mounting and positioning bearing runner plates used in hydrostatic bearing assemblies for rotatably mounting large radio telescope structures to stationary support pedestals is described. The epoxy grout may be used in original mountings or may be used as part of a replacement system for repairing cavities in existing grout resulting from grout deterioration. The epoxy grout has a relatively short work life and cure time even in the presence of hydraulic oil. The epoxy grout cures without shrinking or sagging to form a grout which is sufficiently strong and durable to provide a grout especially well suited for use under the high pressure loading and close tolerance requirements of large hydrostatic bearing assemblies
Direct Laser Sintering of Borosilicate Glass
Despite the advantages that selective laser sintering (SLS) offers in terms of material
availability, many materials have yet to be explored for feasibility and even fewer are
available on a commercial basis. This paper presents initial investigations for one such
material, borosilicate glass, which could be of particular interest to filter manufacturers
because it presents an attractive alternative to the conventional, time-consuming way of
producing filters of various porosity classes. Process results are presented including a
determination of the optimal parameter window and the effect of processing parameters on the
density and surface quality. The effects of thermal post-processing and the inclusion of an
additive are also discussed.Mechanical Engineerin
Modified dot-blot hybridization technique for filamentous fungi.
Colony hybridization (Grunstein & Hogness, 1975 Proc. Nat. Acad. Sci. USA 72:3961-3965) A allows the rapid screening of multiple strains for the presence or absence of particular DNA sequences
Clocked Atom Delivery to a Photonic Crystal Waveguide
Experiments and numerical simulations are described that develop quantitative
understanding of atomic motion near the surfaces of nanoscopic photonic crystal
waveguides (PCWs). Ultracold atoms are delivered from a moving optical lattice
into the PCW. Synchronous with the moving lattice, transmission spectra for a
guided-mode probe field are recorded as functions of lattice transport time and
frequency detuning of the probe beam. By way of measurements such as these, we
have been able to validate quantitatively our numerical simulations, which are
based upon detailed understanding of atomic trajectories that pass around and
through nanoscopic regions of the PCW under the influence of optical and
surface forces. The resolution for mapping atomic motion is roughly 50 nm in
space and 100 ns in time. By introducing auxiliary guided mode (GM) fields that
provide spatially varying AC-Stark shifts, we have, to some degree, begun to
control atomic trajectories, such as to enhance the flux into to the central
vacuum gap of the PCW at predetermined times and with known AC-Stark shifts.
Applications of these capabilities include enabling high fractional filling of
optical trap sites within PCWs, calibration of optical fields within PCWs, and
utilization of the time-dependent, optically dense atomic medium for novel
nonlinear optical experiments
A comparison of single-cycle versus multiple-cycle proof testing strategies
An evaluation of single-cycle and multiple-cycle proof testing (MCPT) strategies for SSME components is described. Data for initial sizes and shapes of actual SSME hardware defects are analyzed statistically. Closed-form estimates of the J-integral for surface flaws are derived with a modified reference stress method. The results of load- and displacement-controlled stable crack growth tests on thin IN-718 plates with deep surface flaws are summarized. A J-resistance curve for the surface-cracked configuration is developed and compared with data from thick compact tension specimens. The potential for further crack growth during large unload/reload cycles is discussed, highlighting conflicting data in the literature. A simple model for ductile crack growth during MCPT based on the J-resistance curve is used to study the potential effects of key variables. The projected changes in the crack size distribution during MCPT depend on the interactions between several key parameters, including the number of proof cycles, the nature of the resistance curve, the initial crack size distribution, the component boundary conditions (load vs. displacement control), and the magnitude of the applied load or displacement. The relative advantages of single-cycle and multiple-cycle proof testing appear to be specific, therefore, to individual component geometry, material, and loading
High-Resolution Particle-In-Cell Simulations of Two-Dimensional Bernstein-Greene-Kruskal Modes
We present two dimensional (2D) particle-in-cell (PIC) simulations of 2D
Bernstein-Greene-Kruskal (BGK) modes, which are exact nonlinear steady-state
solutions of the Vlasov-Poisson equations, on a 2D plane perpendicular to a
background magnetic field, with a cylindrically symmetric electric potential
localized on the plane. PIC simulations are initialized using analytic electron
distributions and electric potentials from the theory. We confirm the validity
of such solutions using high-resolutions up to a 2048^2 grid. We show that the
solutions are dynamically stable for a stronger background magnetic field,
while keeping other parameters of the model fixed, but become unstable when the
field strength is weaker than a certain value. When a mode becomes unstable, we
observe that the instability begins with the excitation of azimuthal
electrostatic waves that ends with a spiral pattern
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Lahar hazard mapping of Mount Shasta, California : a GIS-based delineation of potential inundation zones in Mud and Whitney Creek basins
Mount Shasta, the southernmost stratovolcano in the Cascade Range (41.4°N) has
frequently produced lahars of various magnitudes during the last 10,000 yr. These include
large flows of eruptive origin, reaching more than 40km from the summit, and studies have
shown that at least 70 debris flows of noneruptive origin have occurred during the last
1,000 yr in various stream channels. The Mud and Whitney Creek drainages have
historically produced more debris flows than any other glacier-headed channel on the
volcano. Periods of accelerated glacial melt have produced lahars in Whitney Creek with a
volume of 4 x 106 m3 and a runout distance of about 27 km from the summit. Mud Creek
flows from 1924 – 1931 covered an area of more than 6 km2 near the community of
McCloud with an estimated 23 x 106 m3 of mud. A much older lahar in Big Canyon Creek
may have deposited a volume of 70 x 106 m3 over present day Mount Shasta City and
beyond. A lahar inundation modeling tool developed by USGS analysts is used to
objectively delineate lahar inundation zones on Mount Shasta by embedding predictive
equations in a geographic information system (GIS) that uses a digital elevation model,
hypothetical lahar volumes, and geometric relationships as input. Volumes derived from
these lahar deposits are extrapolated to the selected drainages to generate probable lahar
inundation hazard zones with a focus on mapping and hazards implications
TRiP: Tracking Rhythms in Plants, an Automated Leaf Movement Analysis Program for Circadian Period Estimation
Background: A well characterized output of the circadian clock in plants is the daily rhythmic movement of leaves. This process has been used extensively in Arabidopsis to estimate circadian period in natural accessions as well as mutants with known defects in circadian clock function. Current methods for estimating circadian period by leaf movement involve manual steps throughout the analysis and are often limited to analyzing one leaf or cotyledon at a time.
Methods: In this study, we describe the development of TRiP (Tracking Rhythms in Plants), a new method for estimating circadian period using a motion estimation algorithm that can be applied to whole plant images. To validate this new method, we apply TRiP to a Recombinant Inbred Line (RIL) population in Arabidopsis using our high-throughput imaging platform. We begin imaging at the cotyledon stage and image through the emergence of true leaves. TRiP successfully tracks the movement of cotyledons and leaves without the need to select individual leaves to be analyzed
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