2,577 research outputs found
Pebble Mine: Fish, Minerals, and Testing the Limits of Alaska’s “Large Mine Permitting Process”
Southern African American Communities: The Portrait Photography of Florestine Perrault Collins and Richard Samuel Roberts
This thesis is about the portrait photographers, Florestine Perrault Collins (1895-1988) and Richard Samuel Roberts (1880-1936), and how their photographs portrayed “non-othering” representations of their sitters. Collin and Roberts’ works are compared to Southern white photographers from the Jim Crow era to argue for how “non-othering” portraits of their community members were produced. This impacts the way identity can be perceived. Religious and educational themed portraits are used to align a visually associated identity with social values the New Orleans Creole and Columbia, South Carolina communities had. This thesis considers Collins’ and Roberts’ portraits in relation to the state of their communities. The portraits in this thesis are discussed through integrating aesthetic evaluation with the Jim Crow era societal state of the New Orleans Creole and the African American Columbia, South Carolina communities. The thesis argues for the importance of these photographers’ role in giving control over visual representation to their respective communities
A Low Noise Receiver for Submillimeter Astronomy
A broadband, low noise heterodyne receiver, suitable for astronomical use, has been built using a Pb alloy superconducting tunnel junction (SIS). The RF coupling is quasioptical via a bowtie antenna on a quartz lens and is accomplished without any tuning elements. In its preliminary version the double sideband receiver noise temperature rises from 205 K at 116 GHz to 815 K at 466 GHz. This is the most sensitive broadband receiver yet reported for sub-mm wavelengths. Its multi-octave sensitivity and low local oscillator power requirements make this receiver ideal for remote ground observatories or space-borne telescopes such as NASA's Large Deployable Reflector. A version of this receiver is now being built for NASA's Kuiper Airborne Observatory
A Study of a Mini-drift GEM Tracking Detector
A GEM tracking detector with an extended drift region has been studied as
part of an effort to develop new tracking detectors for future experiments at
RHIC and for the Electron Ion Collider that is being planned for BNL or JLAB.
The detector consists of a triple GEM stack with a small drift region that was
operated in a mini TPC type configuration. Both the position and arrival time
of the charge deposited in the drift region were measured on the readout plane
which allowed the reconstruction of a short vector for the track traversing the
chamber. The resulting position and angle information from the vector could
then be used to improve the position resolution of the detector for larger
angle tracks, which deteriorates rapidly with increasing angle for conventional
GEM tracking detectors using only charge centroid information. Two types of
readout planes were studied. One was a COMPASS style readout plane with 400
micron pitch XY strips and the other consisted of 2x10mm2 chevron pads. The
detector was studied in test beams at Fermilab and CERN, along with additional
measurements in the lab, in order to determine its position and angular
resolution for incident track angles up to 45 degrees. Several algorithms were
studied for reconstructing the vector using the position and timing information
in order to optimize the position and angular resolution of the detector for
the different readout planes. Applications for large angle tracking detectors
at RHIC and EIC are also discussed.Comment: Submitted to the IEEE Transactions on Nuclear Scienc
Optimizing double-sideband SIS quasiparticle mixers
Calculations based on the quantum theory of mixing in single-particle tunnel junctions show that there is a fairly simple strategy for optimizing the performance of double-sideband superconductor-insulator-superconductor (SIS) quasiparticle mixers. The best mixer noise temperature is obtained when the signal source is matched to the local oscillator (LO) admittance of the junction. This applies over a very wide range of LO and DC bias conditions. These calculations support the contention that it is the energy dissipation in the device which is important in determining the noise performance, not the small signal admittance or the power gain. This appears to be another demonstration of the Callen and Welton fluctuation-dissipation theorem. which states that it is the dissipation of energy which is responsible for the noise generation in a wide range of devices, and it is this energy dissipation mechanism to which the signal should be coupled to minimize the noise
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GLOMERULAR-LIKE DENDRO-DENDRITIC RELATIONSHIP EXISTS BETWEEN PURKINJE AND GOLGI-II CELLS IN THE CAT CEREBELLUM
Bayesian inference for treatment effects under nested subsets of controls
When constructing a model to estimate the causal effect of a treatment, it is
necessary to control for other factors which may have confounding effects.
Because the ignorability assumption is not testable, however, it is usually
unclear which set of controls is appropriate, and effect estimation is
generally sensitive to this choice. A common approach in this case is to fit
several models, each with a different set of controls, but it is difficult to
reconcile inference under the multiple resulting posterior distributions for
the treatment effect. Therefore we propose a two-stage approach to measure the
sensitivity of effect estimation with respect to control specification. In the
first stage, a model is fit with all available controls using a prior carefully
selected to adjust for confounding. In the second stage, posterior
distributions are calculated for the treatment effect under nested sets of
controls by propagating posterior uncertainty in the original model. We
demonstrate how our approach can be used to detect the most significant
confounders in a dataset, and apply it in a sensitivity analysis of an
observational study measuring the effect of legalized abortion on crime rates
Implementation of a Non-Metallic Barrier in an Electric Motor
Electric motors that run in pure oxygen must be sealed, or "canned," for safety reasons to prevent the oxygen from entering into the electrical portion of the motor. The current canning process involves designing a metallic barrier around the rotor to provide the separation. This metallic barrier reduces the motor efficiency as speed is increased. In higher-speed electric motors, efficiency is greatly improved if a very thin, nonmetallic barrier can be utilized. The barrier thickness needs to be approximately 0.025-in. (.0.6-mm) thick and can be made of a brittle material such as glass. The motors, however, designed for space applications are typically subject to high-vibration environments. A fragile, non-metallic barrier can be utilized in a motor assembly if held in place by a set of standard rubber O-ring seals. The O-rings provide the necessary sealing to keep oxygen away from the electrical portion of the motor and also isolate the fragile barrier from the harsh motor vibration environment. The compliance of the rubber O-rings gently constrains the fragile barrier and isolates it from the harsh external motor environment. The use of a non-metallic barrier greatly improves motor performance, especially at higher speeds, while isolating the electronics from the working fluid with an inert liner
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