Endurance testing of downstream cathodes on a low-power MPD thruster

A low-power MPD thruster with downstream cathode was tested for endurance with a series of hollow cathode designs. Failure modes and failure mechanisms were identified. A new hollow cathode (with rod inserts) has emerged which shows promise for long life. The downstream positioning of the cathode was also changed from an on-axis location to an off-axis location. Data are presented for a 1332-hour life test of this new hollow cathode located at the new off-axis location. Xenon propellant was used

Measuring the Alfvenic Nature of the Interstellar Medium: Velocity Anisotropy Revisited

The dynamics of the interstellar medium (ISM) are strongly affected by turbulence, which shows increased anisotropy in the presence of a magnetic field. We expand upon the Esquivel & Lazarian method to estimate the Alfven Mach number using the structure function anisotropy in velocity centroid data from position-position-velocity maps. We utilize 3D magnetohydrodynamic (MHD) simulations of fully developed turbulence, with a large range of sonic and Alfvenic Mach numbers, to produce synthetic observations of velocity centroids with observational characteristics such as thermal broadening, cloud boundaries, noise, and radiative transfer effects of carbon monoxide. In addition, we investigate how the resulting anisotropy-Alfven Mach number dependency found in Esquivel & Lazarian (2011) might change when taking the second moment of the position-position-velocity cube or when using different expressions to calculate the velocity centroids. We find that the degree of anisotropy is related primarily to the magnetic field strength (i.e. Alfven Mach number) and the line-of-sight orientation, with a secondary effect on sonic Mach number. If the line-of-sight is parallel to up to ~45 deg off of the mean field direction, the velocity centroid anisotropy is not prominent enough to distinguish different Alfvenic regimes. The observed anisotropy is not strongly affected by including radiative transfer, although future studies should include additional tests for opacity effects. These results open up the possibility of studying the magnetic nature of the ISM using statistical methods in addition to existing observational techniques

Canada–US Border Communities: What the People Have to Say

This paper investigates the Canada-U.S. borderlands relationship along the two geographic corridors as bounded by Lake Superior: Sault Ste. Marie, Ontario–Sault Ste. Marie, Michigan and Thunder Bay, Ontario–Duluth, Minnesota. Borderland communities—driven by their shared cultural characteristics (ethnicity, language, religion)—are said to challenge the border as a dividing device and undermine the very essence of international borders. Moreover, borderlands regions are dynamic and overlapping, providing the first point of contact and interaction between nations. We use interviews of over 200 people living in these borderlands regions to investigate the cross-border relationships of Canada-U.S. border communities. We find that despite the challenges of crossing the border, these communities retain a strong sense of shared values

Differences That Matter: Canada, the United States and Environmental Policymaking

Does the way Canada, as a nation state, approach international environmental policymaking make a difference with respect to solving environmental problems in the Americas? We argue that it does, and it is a difference that matters. Canadian efforts toward multilateralism and toward inclusiveness (e.g., willingness to work with weaker nations) serve as a counter balance to the growing unilateralism and ever present exceptionalism of the United States, currently the most powerful country in the world, and Canada’s southern neighbor and regional partner in developing environmental policy that affects the northern Americas directly and all of the Americas indirectly. Our argument is made first generally, and then specifically using involvement and reaction to the goals set out by the Commission for Environmental Cooperation (CEC), where, along with Mexico, Canada and the United States play leading roles. The basic contention of this paper is that the vision for and goals of the CEC are much more aligned with the way Canada perceives the way international environmental policymaking should be implemented, and that by fostering that vision, Canada tries to counter the tendency of the present-day United States administration to go at it alone, and thereby provides a linkage to other countries in the Americas to position themselves for participation in regional environmental policymaking

TurbuStat: Turbulence Statistics in Python

We present TurbuStat (v1.0): a Python package for computing turbulence statistics in spectral-line data cubes. TurbuStat includes implementations of fourteen methods for recovering turbulent properties from observational data. Additional features of the software include: distance metrics for comparing two data sets; a segmented linear model for fitting lines with a break-point; a two-dimensional elliptical power-law model; multi-core fast-fourier-transform support; a suite for producing simulated observations of fractional Brownian Motion fields, including two-dimensional images and optically-thin HI data cubes; and functions for creating realistic world coordinate system information for synthetic observations. This paper summarizes the TurbuStat package and provides representative examples using several different methods. TurbuStat is an open-source package and we welcome community feedback and contributions.Comment: Accepted in AJ. 21 pages, 8 figure

Magnetohydrodynamics (MHD) Engineering Test Facility (ETF) 200 MWe power plant. Design Requirements Document (DRD)

A description and the design requirements for the 200 MWe (nominal) net output MHD Engineering Test Facility (ETF) Conceptual Design, are presented. Performance requirements for the plant are identified and process conditions are indicated at interface stations between the major systems comprising the plant. Also included are the description, functions, interfaces and requirements for each of these major systems. The lastest information (1980-1981) from the MHD technology program are integrated with elements of a conventional steam electric power generating plant

Bridges and Barriers: The Lake Superior Borderlands

This paper investigates the Canada–US borderlands relationship along the two geographic corridors as bounded by Lake Superior: Sault Ste. Marie, Ontario–Sault Ste. Marie, Michigan and Thunder Bay, Ontario–Duluth, Minnesota. Borderland communities—driven by their shared cultural characteristics (ethnicity, language,religion)—are said to challenge the border as a dividing device and undermine the very essence of international borders. Moreover, borderlands regions are dynamic and overlapping, providing the first point of contact and interaction between nations. Our results depict inherent differences between these particular border regions, with each illustrating characteristics that both connect and divide. Despite the passage of time and both countries’ determined efforts to make the passage safe and less demanding, the peoples in these border regions perceive a continuing frustration with crossing the border and connecting to the people on the other side of the border

Late stages of the evolution of A-type stars on the main sequence: comparison between observed chemical abundances and diffusion models for 8 Am stars of the Praesepe cluster

Aims. We aim to provide observational constraints on diffusion models that predict peculiar chemical abundances in the atmospheres of Am stars. We also intend to check if chemical peculiarities and slow rotation can be explained by the presence of a weak magnetic field. Methods. We have obtained high resolution, high signal-to-noise ratio spectra of eight previously-classified Am stars, two normal A-type stars and one Blue Straggler, considered to be members of the Praesepe cluster. For all of these stars we have determined fundamental parameters and photospheric abundances for a large number of chemical elements, with a higher precision than was ever obtained before for this cluster. For seven of these stars we also obtained spectra in circular polarization and applied the LSD technique to constrain the longitudinal magnetic field. Results. No magnetic field was detected in any of the analysed stars. HD 73666, a Blue Straggler previously considered as an Ap (Si) star, turns out to have the abundances of a normal A-type star. Am classification is not confirmed for HD 72942. For HD 73709 we have also calculated synthetic Delta-a photometry that is in good agreement with the observations. There is a generally good agreement between abundance predictions of diffusion models and values that we have obtained for the remaining Am stars. However, the observed Na and S abundances deviate from the predictions by 0.6 dex and >0.25 dex respectively. Li appears to be overabundant in three stars of our sample.Comment: Accepted for publication on A&

Normal-metal quasiparticle traps for superconducting qubits

The presence of quasiparticles in superconducting qubits emerges as an intrinsic constraint on their coherence. While it is difficult to prevent the generation of quasiparticles, keeping them away from active elements of the qubit provides a viable way of improving the device performance. Here we develop theoretically and validate experimentally a model for the effect of a single small trap on the dynamics of the excess quasiparticles injected in a transmon-type qubit. The model allows one to evaluate the time it takes to evacuate the injected quasiparticles from the transmon as a function of trap parameters. With the increase of the trap size, this time decreases monotonically, saturating at the level determined by the quasiparticles diffusion constant and the qubit geometry. We determine the characteristic trap size needed for the relaxation time to approach that saturation value.Comment: 11 pages, 5 figure