15,341 research outputs found
Beam profiles measured with thermoluminescent dosimeters
Beam profilometer, using thermoluminescent dosimeters, gives a quantitative and qualitative representation of the focus of an external protron beam of a synchrotron. The total number of particles in the beam, particle distribution, and the shape of the beam are determined
Atmospheric leakage and condensate production in NASA's biomass production chamber. Effect of diurnal temperature cycles
A series of tests were conducted to monitor atmospheric leakage rate and condensate production in NASA's Biomass Production Chamber (BPC). Water was circulated through the 64 plant culture trays inside the chamber during the tests but no plants were present. Environmental conditions were set to a 12-hr photoperiod with either a matching 26 C (light)/20 C (dark) thermoperiod, or a constant 23 C temperature. Leakage, as determined by carbon dioxide decay rates, averaged about 9.8 percent for the 26 C/20 C regime and 7.3 percent for the constant 23 C regime. Increasing the temperature from 20 C to 26 C caused a temporary increase in pressure (up to 0.5 kPa) relative to ambient, while decreasing the temperature caused a temporary decrease in pressure of similar magnitude. Little pressure change was observed during transition between 23 C (light) and 23 C (dark). The lack of large pressure events under isothermal conditions may explain the lower leakage rate observed. When only the plant support inserts were placed in the culture trays, condensate production averaged about 37 liters per day. Placing acrylic germination covers over the tops of culture trays reduced condensate production to about 7 liters per day. During both tests, condensate production from the lower air handling system was 60 to 70 percent greater than from the upper system, suggesting imbalances exist in chilled and hot water flows for the two air handling systems. Results indicate that atmospheric leakage rates are sufficiently low to measure CO2 exchange rates by plants and the accumulation of certain volatile contaminants (e.g., ethylene). Control system changes are recommended in order to balance operational differences (e.g., humidity and temperature) between the two halves of the chamber
Quantum Darwinism in quantum Brownian motion: the vacuum as a witness
We study quantum Darwinism -- the redundant recording of information about a
decohering system by its environment -- in zero-temperature quantum Brownian
motion. An initially nonlocal quantum state leaves a record whose redundancy
increases rapidly with its spatial extent. Significant delocalization (e.g., a
Schroedinger's Cat state) causes high redundancy: many observers can measure
the system's position without perturbing it. This explains the objective (i.e.
classical) existence of einselected, decoherence-resistant pointer states of
macroscopic objects.Comment: 5 page
The existence of time
Of those gauge theories of gravity known to be equivalent to general
relativity, only the biconformal gauging introduces new structures - the
quotient of the conformal group of any pseudo-Euclidean space by its Weyl
subgroup always has natural symplectic and metric structures. Using this metric
and symplectic form, we show that there exist canonically conjugate,
orthogonal, metric submanifolds if and only if the original gauged space is
Euclidean or signature 0. In the Euclidean cases, the resultant configuration
space must be Lorentzian. Therefore, in this context, time may be viewed as a
derived property of general relativity.Comment: 21 pages (Reduced to clarify and focus on central argument; some
calculations condensed; typos corrected
Changing trends in the labor force: a survey
The composition of the American workforce has changed dramatically over the past half century as a result of both the emergence of married women as a substantial component of the labor force and an increase in the number of minority workers. The aging of the population has contributed to this change as well. In this paper, the authors review the evidence of changing labor force participation rates, estimate the trends in labor force participation over the past 50 years, and find that aggregate participation has stabilized after a period of persistent increases. Moreover, they examine the disparate labor force participation experiences of different demographic groups. Finally, they survey some of the studies that have provided explanations for these differences.Labor supply ; Labor market
The Shape of Cas A
Based on optical, IR and X-ray studies of Cas A, we propose a geometry for
the remnant based on a "jet-induced" scenario with significant systematic
departures from axial symmetry. In this model, the main jet axis is oriented in
the direction of strong blue-shifted motion at an angle of 110 - 120 degrees
East of North and about 40 - 50 degrees to the East of the line of sight.
Normal to this axis would be an expanding torus as predicted by jet-induced
models. In the proposed geometry, iron-peak elements in the main jet-like flow
could appear "beyond" the portions of the remnant rich in silicon by projection
effects, not the effect of mixing. In the context of the proposed geometry, the
displacement of the compact object from the kinematic center of the remnant at
a position angle of ~169 degrees can be accommodated if the motion of the
compact object is near to, but slightly off from, the direction of the main
"jet" axis by of order 30 degrees. In this model, the classical NE "jet," the
SW "counter-jet" and other protrusions, particularly the "hole" in the North,
are non-asymmetric flows approximately in the equatorial plane, e.g., out
through the perimeter of the expanding torus, rather than being associated with
the main jet. We explore the spoke-like flow in the equatorial plane in terms
of Rayleigh-Taylor, Richtmyer-Meshkov and Kelvin-Helmholz instabilities and
illustrate these instabilities with a jet-induced simulation.Comment: 25 pages, 4 figures. Accepted for publication in the Astrophysical
Journa
Endothelial HO-1 induction by model TG-rich lipoproteins is regulated through a NOX4-Nrf2 pathway
Circulating levels of chylomicron remnants (CMRs) increase postprandially and their composition directly reflects dietary lipid intake. These TG-rich lipoproteins likely contribute to the development of endothelial dysfunction, albeit via unknown mechanisms. Here, we investigated how the FA composition of CMRs influences their actions on human aortic endothelial cells (HAECs) by comparing the effects of model CMRs—artificial TG-rich CMR-like particles (A-CRLPs)—containing TGs extracted from fish, DHA-rich algal, corn, or palm oils. HAECs responded with distinct transcriptional programs according to A-CRLP TG content and oxidation status, with genes involved in antioxidant defense and cytoprotection most prominently affected by n-3 PUFA-containing A-CRLPs. These particles were significantly more efficacious inducers of heme oxygenase-1 (HO-1) than n-6 PUFA corn or saturated FA-rich palm CRLPs. Mechanistically, HO-1 induction by all CRLPs requires NADPH oxidase 4, with PUFA-containing particles additionally dependent upon mitochondrial reactive oxygen species. Activation of both p38 MAPK and PPARβ/δ culminates in increased nuclear factor erythroid 2-related factor 2 (Nrf2) expression/nuclear translocation and HO-1 induction. These studies define new molecular pathways coupling endothelial cell activation by model CMRs with adaptive regulation of Nrf2-dependent HO-1 expression and may represent key mechanisms through which dietary FAs differentially impact progression of endothelial dysfunction
The economic performance of cities: a Markov-switching approach
This paper examines the determinants of employment growth in metro areas. To obtain growth rates, we use a Markov-switching model that separates a city’s growth path into two distinct phases (high and low), each with its own growth rate. The simple average growth rate over some period is, therefore, the weighted average of the high-phase and low-phase growth rates, with the weight being the frequency of the two phases. We estimate the effects of a variety of factors separately for the high-phase and low-phase growth rates, along with the frequency of the low phase. We find that growth in the high phase is related to human capital, industry mix, and average firm size. In contrast, we find that growth in the low phase is mostly related to industry mix, specifically, the relative importance of manufacturing. Finally, the frequency of the low phase appears to be related to the level of non-education human capital, but to none of the other variables. Overall, our results strongly reject the notion that city-level characteristics influence employment growth equally across the phases of the business cycle.Business cycles ; Cities and towns
Measuring Which-Path Information with Coupled Electronic Mach-Zehnder Interferometers
We theoretically investigate a generalized "which-path" measurement on an
electronic Mach-Zehnder Interferometer (MZI) implemented via Coulomb coupling
to a second electronic MZI acting as a detector. The use of contextual values,
or generalized eigenvalues, enables the precise construction of which-path
operator averages that are valid for any measurement strength from the
available drain currents. The form of the contextual values provides direct
physical insight about the measurement being performed, providing information
about the correlation strength between system and detector, the measurement
inefficiency, and the proper background removal. We find that the detector
interferometer must display maximal wave-like behavior to optimally measure the
particle-like which-path information in the system interferometer,
demonstrating wave-particle complementarity between the system and detector. We
also find that the degree of quantum erasure that can be achieved by
conditioning on a specific detector drain is directly related to the ambiguity
of the measurement. Finally, conditioning the which-path averages on a
particular system drain using the zero frequency cross-correlations produces
conditioned averages that can become anomalously large due to quantum
interference; the weak coupling limit of these conditioned averages can produce
both weak values and detector-dependent semi-weak values.Comment: 17 pages, 12 figures, published version including appendi
New representation and a vacuum state for canonical quantum gravity
A new representation for canonical gravity and supergravity is presented,
which combines advantages of Ashtekar's and the Wheeler~DeWitt representation:
it has a nice geometric structure and the singular metric problem is absent. A
formal state functional can be given, which has some typical features of a
vacuum state in quantum field theory. It can be canonically transformed into
the metric representation. Transforming the constraints too, one recovers the
Wheeler~DeWitt equation up to an anomalous term. A modified Dirac quantization
is proposed to handle possible anomalies in the constraint algebra.Comment: 28 pages, LaTe
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