Three-Dimensional Magnetohydrodynamics Simulations Of Counter-Helicity Spheromak Merging In The Swarthmore Spheromak Experiment

Recent counter-helicity spheromak merging experiments in the Swarthmore Spheromak Experiment (SSX) have produced a novel compact torus (CT) with unusual features. These include a persistent antisymmetric toroidal magnetic field profile and a slow, nonlinear emergence of the n = 1 tilt mode. Experimental measurements are inconclusive as to whether this unique CT is a fully merged field-reversed configuration (FRC) with strong toroidal field or a partially merged doublet CT configuration with both spheromak- and FRC-like characteristics. In this paper, the SSX merging process is studied in detail using three-dimensional resistive MHD simulations from the Hybrid Magnetohydrodynamics (HYM) code. These simulations show that merging plasmas in the SSX parameter regime only partially reconnect, leaving behind a doublet CT rather than an FRC. Through direct comparisons, we show that the magnetic structure in the simulations is highly consistent with the SSX experimental observations. We also find that the n = 1 tilt mode begins as a fast growing linear mode that evolves into a slower-growing nonlinear mode before being detected experimentally. A simulation parameter scan over resistivity, viscosity, and line-tying shows that these parameters can strongly affect the behavior of both the merging process and the tilt mode. In fact, merging in certain parameter regimes is found to produce a toroidal-field-free FRC rather than a doublet CT. (C) 2011 American Institute of Physics. [doi:10.1063/1.3660533

Pushing the limits of excited-state gg-factor measurements

Current developments in excited-state $g$-factor measurements are discussed with an emphasis on cases where the experimental methodology is being extended into new regimes. The transient-field technique, the recoil in vacuum method, and moment measurements with LaBr$_3$ detectors are discussed.Comment: 5 pages, 6 figure

Manganese Oxide Thin Films Prepared by Nonaqueous Sol-Gel Processing: Preferential Formation of Birnessite

High quality manganese oxide thin films with smooth surfaces and even thicknesses have been prepared with a nonaqueous sol–gel process involving reduction of tetraethylammonium permanganate in methanol. Spin-coated films have been cast onto soft glass, quartz, and Ni foil substrates, with two coats being applied for optimum crystallization. The addition of alkali metal cations as dopants results in exclusive formation of the layered birnessite phase. By contrast, analogous reactions in bulk sol–gel reactions yield birnessite, tunneled, and spinel phases depending on the dopant cation. XRD patterns confirm the formation of well-crystallized birnessite. SEM images of Li-, Na-, and K–birnessite reveal extremely smooth films having uniform thickness of less than 0.5 μm. Thin films of Rb– and Cs–birnessite have more fractured and uneven surfaces as a result of some precipitation during the sol–gel transformation. All films consist of densely packed particles of about 0.1 μm. When tetrabutylammonium permanganate is used instead of tetraethylammonium permanganate, the sol–gel reaction yields amorphous manganese oxide as the result of diluted Mn sites in the xerogel film. Bilayer films have been prepared by casting an overcoat of K–birnessite onto an Na–birnessite film. However, Auger depth profiling indicates considerable mixing between the adjacent layers

The Impact of Mentoring and Scholarships on Teacher Candidates

The study examines data from surveys and interviews with teacher candidates and local education mentors at a Midwestern university who were involved in a Grow Your Own program; this article focuses on results for the teacher candidates. Using data based on demographics, financial need, and academic performance, the researchers identified eight educator preparation candidates from under-represented backgrounds. Each teacher candidate was invited to receive an academic scholarship of $1,500 per semester for two terms, fall 2022 and spring 2023, with the understanding each scholarship recipient would be paired with a university mentor and an in-district mentor from one of two rural school districts with close proximity to the Midwest university. Teacher candidates were required to attend introductory meetings, professional learning, and culminating sessions in order to receive and retain the scholarship funds. Researchers sought to understand perceptions on mentoring, financial support, and professional development from the teacher candidates while investigating the impact of mentoring on retention. The qualitative case study included a pre- and post-survey for scholarship recipients. The scholarship recipients also participated in a focus group interview. Findings included the importance of the scholarship funds to the teacher candidates that went beyond financial implications, and being selected to participate made them “feel special.” The relationships formed with the university faculty and the local education mentors became a “network” allowing the teacher candidates to feel confident and valued; they became the educators they will continue to rely on throughout their careers. The professional development provided opportunities for participants to see, in real-time, the concepts that were discussed in abstract during their education courses. Key Words: mentoring teacher candidates, teacher preparation, relationships, grow your ow

Hydrogeology and Hydrochemistry of the Falls City Uranium Mine Tailings Remedial Action Project, Karnes County, Texas

Oxidized uranium ore deposits were discovered in the Deweesville sandstone (also referred to as the Stones Switch; Bunker and MacKallor [1973]) in the Falls City region in the 1950s. Uranium was mined and milled in the small community of Deweesville by Susquehanna-Western, Inc. (SWI) from April 1961 to August 1973. Tailings composed of sediment residue from the sulfuric acid milling process and residual sulfuric acid solutions were disposed of in six ponds on the outcrop of the Deweesville, within the mined-out uranium pits in the Deweesville, and on the outcrop of the Conquista, creating a set of large tailings impoundments (figs. 1.1 and 1.2). From 1978 to 1982 Solution Engineering, Inc. (SEI) conducted a secondary recovery of the remaining uranium in the tailings piles by in situ leaching. In 1984, the ponds on top of two of the tailings piles were spray evaporated and a clay cap was placed over the piles to prevent additional percolation of water through the piles and into the underlying aquifers. Acidic tailings solutions have been recharging the underlying aquifers since initial tailings disposal and may still be leaking into these aquifers. Several hydrogeologic investigations have been conducted to assess whether there has been groundwater contamination from the tailings. Early studies were conducted by Turk, Kehle and Associates (1976), and Ford, Bacon & Davis Utah (1978, 1981). Each of these studies included only minor investigations of the hydrogeology and hydrochemistry of the site and, in general, underestimated the extent of contamination from the site. Investigations conducted by the U.S. Department of Energy (DOE) from 1985 to 1991 have since revealed the true extent of contamination (U.S. Department of Energy, 1991).Bureau of Economic Geolog

The Discovery of lambda Bootis Stars -- The Southern Survey II

The $\lambda$ Boo stars are chemically peculiar A-type stars whose abundance anomalies are associated with the accretion of metal-poor material. We searched for $\lambda$ Boo stars in the southern hemisphere in a targeted spectroscopic survey of metal-weak and emission-line stars. Obtaining spectra for 308 stars and classifying them on the MK system, we found or co-discovered 24 new $\lambda$ Boo stars. We also revised the classifications of 11 known $\lambda$ Boo stars, one of which turned out to be a chemically normal rapid rotator. We show that stars previously classified in the literature as blue horizontal branch stars or emission-line A stars have a high probability of being $\lambda$ Boo stars, although this conclusion is based on small-number statistics. Using WISE infrared fluxes, we searched our targets for infrared excesses that might be attributable to protoplanetary or debris discs as the source of the accreted material. Of the 34 $\lambda$ Boo stars in our sample, 21 at various main-sequence ages have infrared excesses, confirming that not all $\lambda$ Boo stars are young.Comment: Accepted for publication in MNRAS. Figures do not have heavy reliance on colour. Online data will be hosted with the journal / Vizier@CD

Stable Spheromak Formation By Merging In An Oblate Flux Conserver

An axisymmetric spheromak formed by the dynamic merging of two smaller spheromaks of the same magnetic helicity in the Swarthmore Spheromak Experiment (SSX) [M. R. Brown, Phys. Plasmas 6, 1717 (1999)] has been observed and characterized. The spheromak is formed in an oblate (tilt stable), trapezoidal, 6 mm wall copper flux conserver in SSX, which is 0.5 m in diameter and L=0.4 m in length at its largest dimensions. This configuration is formed by cohelicity merging of two spheromaks (either both right-handed or both left-handed) in which the merging poloidal fluxes are parallel (i.e., no field reversal for reconnection to occur initially). After a period of dynamic and nonaxisymmetric activity, the configuration ultimately relaxes to an axisymmetric state. A nonaxisymmetric tilted state, very close in total energy to the axisymmetric state, is also sometimes observed. This configuration is characterized by a suite of magnetic probe arrays for magnetic structure B(r,t), ion Doppler spectroscopy for T(i) and flow, and interferometry for ne. The magnetic structures of both states match well to computed eigenstates. (C) 2010 American Institute of Physics. [doi:10.1063/1.3334324

Observation Of A Helical Self-Organized State In A Compact Toroidal Plasma

A nonaxisymmetric stable magnetohydrodynamic (MHD) equilibrium within a prolate cylindrical conducting boundary has been produced experimentally. It has m=1 azimuthal symmetry, helical distortion, and flat lambda profile, all in agreement with the computed magnetically relaxed minimum magnetic energy Taylor state. Despite varied initial conditions determined by two helicity injectors on the device, this same equilibrium consistently emerges as the final state. These results therefore describe a new example of self-organization in an MHD plasma

Quantifying tumour-infiltrating lymphocyte subsets : a practical immuno-histochemical method

Background: Efficient histological quantification of tumour-infiltrating T and B lymphocyte (TIL) subsets in archival tissues would greatly facilitate investigations of the role of TIL in human cancer biology. We sought to develop such a method. Methods: Ten ×40 digital images of 4 μ sections of 16 ductal invasive breast carcinomas immunostained for CD3, CD4, CD8, and CD20 were acquired (a total of 640 images). The number of pixels in each image matching a partition of Lab colour space corresponding to immunostained cells were counted using the ‘Color range’ and ‘Histogram’ tools in Adobe Photoshop 7. These pixel counts were converted to cell counts per mm2 using a calibration factor derived from one, two, three or all 10 images of each case/antibody combination. Results: Variations in the number of labelled pixels per immunostained cell made individual calibration for each case/antibody combination necessary. Calibration based on two fields containing the most labelled pixels gave a cell count minimally higher (+ 5.3%) than the count based on 10-field calibration, with 95% confidence limits − 14.7 to + 25.3%. As TIL density could vary up to 100-fold between cases, this accuracy and precision are acceptable. Conclusion: The methodology described offers sufficient accuracy, precision and efficiency to quantify the density of TIL sub-populations in breast cancer using commonly available software, and could be adapted to batch processing of image files

A Model for the Ultrasonic Scattering from Multi-Branched Cracks

The ultrasonic detection (discrimination from geometrical reflectors) and sizing of intergranular stress corrosion cracks (IGSCC’s) is an essential element in the continued safe operation of nuclear power plants. Unfortunately, these ultrasonic tests are rendered difficult by the complex topography of the cracks, which may include multiple facets and branches which scatter ultrasound in a nearly independent fashion. Thus, the waveforms reflected from such flaws exhibit complex shapes which may not be related to the overall extent of the flaw in a simple fashion