Crystallographic structure and mechanical properties of tantalum coatings on steel deposited by DC magnetron sputtering

Tantalum metal exhibits excellent erosion and corrosion resistance property. Hence, tantalum coatings are investigated for protection of steel surface exposed to mechanical stresses, high temperature, and corrosive environment. Such conditions exist inside large army gun barrels. The goal of this work was to contribute to the development of technology for tantalum coating of steel, which would replace the presently used electrochemical chromium deposition. A DC magnetron sputtering process was used to deposit tantalum coatings on steel substrates. In sputtering, tantalum is deposited in two phases: ductile, body-centered cubic (bcc) phase (a-phase) and a metastable, brittle tetragonal ß-phase. Only a-phase of tantalum is considered suitable for protective coatings. Such coatings were successfully deposited on steel substrates heated to 400°C (with Ar sputtering gas) and 350°C (with Kr), and also at room temperature if tantalum nitride interlayers were first deposited on steel substrates. Tantalum phase composition was determined by x-ray diffraction (XRD). The crystallographic phase of the nitride interlayer, studied by XRD, and its composition measured by the nuclear reaction analysis, showed that the stoichiometric TaN is required for a-phase deposition. Adhesion of sputter deposited tantalum coatings was evaluated using a scratch test method. It was found that strongly adhering a-phase tantalum coatings can be deposited on sputter etched steel substrate with tantalum nitride interlayer, and also on substrates heated to elevated temperatures. Adhesion failure of coatings was different for the ductile a-phase or predominantly a-phase coatings, and the brittle ß-phase coatings, which under an optical microscope revealed numerous small cracks, before delamination. This study confirms the superiority of the a-phase tantalum over ß-phase tantalum in protective coating applications. Parameters of DC magnetron sputtering deposition process for obtaining a-phase tantalum coatings were also determined

Efficient tomography with unknown detectors

We compare the two main techniques used for estimating the state of a physical system from unknown measurements: standard detector tomography and data-pattern tomography. Adopting linear inversion as a fair benchmark, we show that the difference between these two protocols can be traced back to the nonexistence of the reverse-order law for pseudoinverses. We capitalize on this fact to identify regimes where the data-pattern approach outperforms the standard one and vice versa. We corroborate these conclusions with numerical simulations of relevant examples of quantum state tomography.Comment: 13 pages, 6 figures. Submitted for publication. Comments most welcome

Optical imaging of strain in two-dimensional crystals

Strain engineering is widely used in material science to tune the (opto-)electronic properties of materials and enhance the performance of devices. Two-dimensional atomic crystals are a versatile playground to study the influence of strain, as they can sustain very large deformations without breaking. Various optical techniques have been employed to probe strain in two-dimensional materials, including micro-Raman and photoluminescence spectroscopy. Here we demonstrate that optical second harmonic generation constitutes an even more powerful technique, as it allows to extract the full strain tensor with a spatial resolution below the optical diffraction limit. Our method is based on the strain-induced modification of the nonlinear susceptibility tensor due to a photoelastic effect. Using a two-point bending technique, we determine the photoelastic tensor elements of molybdenum disulfide. Once identified, these parameters allow us to spatially image the two-dimensional strain field in an inhomogeneously strained sample.Comment: 13 pages, 4 figure

Establishment patterns of bitterbrush

August 1971.Includes bibliographical references (pages 84-87).Covers not scanned.Print version deaccessioned 2021.During the summer of 1969, 50 bitterbrush (Purshia tridentata) plants were collected from each of 25 sites located from approximately 10 to 35 miles west of Fort Collins, Colorado. These sites were selected to represent the range of topographic conditions under which bitterbrush is found in this area. The principle objective was to relate establishment patterns over time, as indicated by the 1969 age structure, to the weather history of the area. The bitterbrush plants were aged by cross-dating techniques using ponderosa pine as a control. The age structure of the sample indicates a severe lack of establishment since 1950. The reason for this reduction in establishment is unknown. There appear to be no differential effects due to weather during the period of good establishment prior to 1950 as compared to the period of poor establishment since. Spring temperature proved to be the best predictor of establishment. The age structures of the 25 plots proved to be significantly different. The growth and vigor were found to be significantly influenced by topography. Maximum stem diameter was found to be the best single predictor of age within the array of measurements taken on the live plant. Even maximum stem diameter is a crude index at best for the ages of plants in the area studied. Both bitterbrush and ponderosa pine were analyzed for growth response to weather. Temperature proved to be more limiting for both species than did moisture

Multiparameter Quantum Metrology of Incoherent Point Sources: Towards Realistic Superresolution

We establish the multiparameter quantum Cram\'er-Rao bound for simultaneously estimating the centroid, the separation, and the relative intensities of two incoherent optical point sources using alinear imaging system. For equally bright sources, the Cram\'er-Rao bound is independent of the source separation, which confirms that the Rayleigh resolution limit is just an artifact of the conventional direct imaging and can be overcome with an adequate strategy. For the general case of unequally bright sources, the amount of information one can gain about the separation falls to zero, but we show that there is always a quadratic improvement in an optimal detection in comparison with the intensity measurements. This advantage can be of utmost important in realistic scenarios, such as observational astronomy.Comment: 5 pages, 3 figures. Comments welcome

Red Ed: Teaching Toward a New Internationalism

In this essay, I narrate part of my experience leading second-language college writing students through an activity that introduces them to some of the basics of ideology critique and critical discourse analysis. I also describe a Language Event Analysis assignment that invites students to analyze international language-related current events. In the process, I try to show why a dialectical multilingualism must be part of any radically internationalist socialist teaching praxis

Influence of ESP collector configuration on reduction of particulate emissions from biomass combustion facility

Development of compact electrostatic precipitators (ESPs) for reduction of particulate emissions from small scale biomass combustion is an actual task. Particle mass collection efficiency of an ESP depends from combustion conditions, geometry of precipitator ionizer, collector stage configuration and ESP operation parameters. The investigation of the influence of collector stage configuration on particle mass collection efficiency of a pilot space charge ESP was in the focus of the study. It was shown that the use of tube collector with integrated grounded plates enhanced particle mass collection efficiency. The loading of plates with aerosol provoked particle re-entrainment and decreased long-term ESP mass collection efficiency. The use of grounded brush electrodes ensured effective reduction of particle emissions but resulted in increase of pressure drop in the precipitator. The optimization of cleaning intervals of the ionizer and collector stages increased particle mass collection efficiency. It was shown, that the integration of automatic systems for ionizer and collector cleaning into the space charge ESP enhanced precipitator long-term operation stability and ensured effective reduction of particulate emissions form small scale biomass combustion