809 research outputs found
Conceptual dead weight device to provide pressure calibration
Dead weight testing device uses a common force plane piston manometer to set accurate gage pressure in pounds per square inch. An additional piston gage easily adapts the device for absolute pressure calibration
Stability of bicontinuous cubic phases in ternary amphiphilic systems with spontaneous curvature
We study the phase behavior of ternary amphiphilic systems in the framework
of a curvature model with non-vanishing spontaneous curvature. The amphiphilic
monolayers can arrange in different ways to form micellar, hexagonal, lamellar
and various bicontinuous cubic phases. For the latter case we consider both
single structures (one monolayer) and double structures (two monolayers). Their
interfaces are modeled by the triply periodic surfaces of constant mean
curvature of the families G, D, P, C(P), I-WP and F-RD. The stability of the
different bicontinuous cubic phases can be explained by the way in which their
universal geometrical properties conspire with the concentration constraints.
For vanishing saddle-splay modulus , almost every phase considered
has some region of stability in the Gibbs triangle. Although bicontinuous cubic
phases are suppressed by sufficiently negative values of the saddle-splay
modulus , we find that they can exist for considerably lower
values than obtained previously. The most stable bicontinuous cubic phases with
decreasing are the single and double gyroid structures since
they combine favorable topological properties with extreme volume fractions.Comment: Revtex, 23 pages with 10 Postscript files included, to appear in J.
Chem. Phys. 112 (6) (February 2000
Complete Embedded Self-Translating Surfaces under Mean Curvature Flow
We describe a construction of complete embedded self-translating surfaces
under mean curvature flow by desingularizing the intersection of a finite
family of grim reapers in general position.Comment: 42 pages, 8 figures. v2: typos correcte
A Multi-Sensor and Modeling Approach for Mapping Light Under Sea Ice During the Ice-Growth Season
Arctic sea ice is shifting from a year-round to a seasonal sea ice cover. This substantial
transformation, via a reduction in Arctic sea ice extent and a thinning of its thickness,
influences the amount of light entering the upper ocean. This in turn impacts underice algal growth and associated ecosystem dynamics. Field campaigns have provided
valuable insights as to how snow and ice properties impact light penetration at fixed
locations in the Arctic, but to understand the spatial variability in the under-ice light
field there is a need to scale up to the pan-Arctic level. Combining information from
satellites with state-of-the-art parameterizations is one means to achieve this. This study
combines satellite and modeled data products to map under-ice light on a monthly
time-scale from 2011 through 2018. Key limitations pertain to the availability of satellitederived sea ice thickness, which for radar altimetry, is only available during the sea ice
growth season. We clearly show that year-to-year variability in snow depth, along with
the fraction of thin ice, plays a key role in how much light enters the Arctic Ocean. This
is particularly significant in April, which in some regions, coincides with the beginning
of the under-ice algal bloom, whereas we find that ice thickness is the main driver of
under-ice light availability at the end of the melt season in October. The extension to the
melt season due to a warmer Arctic means that snow accumulation has reduced, which
is leading to positive trends in light transmission through snow. This, combined with a
thinner ice cover, should lead to increased under-ice PAR also in the summer month
System and method of in-season nitrogen measurement and fertilization of non-leguminous crops from digital image analysis
Systems and methods of determining nitrogen levels from a digital image and in-season nitrogen measurement and fertilization of non-leguminous crops from digital image analysis are disclosed. In particular, a method of determining leaf nitrogen concentration and yield from a digital photograph of a fully developed leaf (collared leaf) of a crop of non-legumes, such as corn, wheat, rice, cotton, potatoes sugarcane, turfgrass or forage grass species. The digital image is processed to determine a dark green color index ( DGCI ), which is closely related to leaf nitrogen concentration and yield. Standardized color disks having known DGCI values are included in the digital photograph and serve as an comparative standard. The comparative standard allows correction of DGCI of samples when using different cameras and/or when lighting conditions change. The DGCI values can then be used to determine the amount of nitrogen fertilizer that should be applied to recover crop yield potential
A Tonnetz Model for pentachords
This article deals with the construction of surfaces that are suitable for
representing pentachords or 5-pitch segments that are in the same class.
It is a generalization of the well known \"Ottingen-Riemann torus for triads of
neo-Riemannian theories. Two pentachords are near if they differ by a
particular set of contextual inversions and the whole contextual group of
inversions produces a Tiling (Tessellation) by pentagons on the surfaces. A
description of the surfaces as coverings of a particular Tiling is given in the
twelve-tone enharmonic scale case.Comment: 27 pages, 12 figure
Quality control in resting-state fMRI: the benefits of visual inspection
Background: A variety of quality control (QC) approaches are employed in resting-state functional magnetic resonance imaging (rs-fMRI) to determine data quality and ultimately inclusion or exclusion of a fMRI data set in group analysis. Reliability of rs-fMRI data can be improved by censoring or “scrubbing” volumes affected by motion. While censoring preserves the integrity of participant-level data, including excessively censored data sets in group analyses may add noise. Quantitative motion-related metrics are frequently reported in the literature; however, qualitative visual inspection can sometimes catch errors or other issues that may be missed by quantitative metrics alone. In this paper, we describe our methods for performing QC of rs-fMRI data using software-generated quantitative and qualitative output and trained visual inspection.
Results: The data provided for this QC paper had relatively low motion-censoring, thus quantitative QC resulted in no exclusions. Qualitative checks of the data resulted in limited exclusions due to potential incidental findings and failed pre-processing scripts.
Conclusion: Visual inspection in addition to the review of quantitative QC metrics is an important component to ensure high quality and accuracy in rs-fMRI data analysis
ProtoDESI: First On-Sky Technology Demonstration for the Dark Energy Spectroscopic Instrument
The Dark Energy Spectroscopic Instrument (DESI) is under construction to
measure the expansion history of the universe using the baryon acoustic
oscillations technique. The spectra of 35 million galaxies and quasars over
14,000 square degrees will be measured during a 5-year survey. A new prime
focus corrector for the Mayall telescope at Kitt Peak National Observatory will
deliver light to 5,000 individually targeted fiber-fed robotic positioners. The
fibers in turn feed ten broadband multi-object spectrographs. We describe the
ProtoDESI experiment, that was installed and commissioned on the 4-m Mayall
telescope from August 14 to September 30, 2016. ProtoDESI was an on-sky
technology demonstration with the goal to reduce technical risks associated
with aligning optical fibers with targets using robotic fiber positioners and
maintaining the stability required to operate DESI. The ProtoDESI prime focus
instrument, consisting of three fiber positioners, illuminated fiducials, and a
guide camera, was installed behind the existing Mosaic corrector on the Mayall
telescope. A Fiber View Camera was mounted in the Cassegrain cage of the
telescope and provided feedback metrology for positioning the fibers. ProtoDESI
also provided a platform for early integration of hardware with the DESI
Instrument Control System that controls the subsystems, provides communication
with the Telescope Control System, and collects instrument telemetry data.
Lacking a spectrograph, ProtoDESI monitored the output of the fibers using a
Fiber Photometry Camera mounted on the prime focus instrument. ProtoDESI was
successful in acquiring targets with the robotically positioned fibers and
demonstrated that the DESI guiding requirements can be met.Comment: Accepted versio
Weak Lensing from Space I: Instrumentation and Survey Strategy
A wide field space-based imaging telescope is necessary to fully exploit the
technique of observing dark matter via weak gravitational lensing. This first
paper in a three part series outlines the survey strategies and relevant
instrumental parameters for such a mission. As a concrete example of hardware
design, we consider the proposed Supernova/Acceleration Probe (SNAP). Using
SNAP engineering models, we quantify the major contributions to this
telescope's Point Spread Function (PSF). These PSF contributions are relevant
to any similar wide field space telescope. We further show that the PSF of SNAP
or a similar telescope will be smaller than current ground-based PSFs, and more
isotropic and stable over time than the PSF of the Hubble Space Telescope. We
outline survey strategies for two different regimes - a ``wide'' 300 square
degree survey and a ``deep'' 15 square degree survey that will accomplish
various weak lensing goals including statistical studies and dark matter
mapping.Comment: 25 pages, 8 figures, 1 table, replaced with Published Versio
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