Commensurability oscillations due to pinned and drifting orbits in a two-dimensional lateral surface superlattice

We have simulated conduction in a two-dimensional electron gas subject to a weak two-dimensional periodic potential, $V_x \cos(2\pi x/a) + V_y \cos(2\pi y/a)$. The usual commensurability oscillations in $\rho_{xx}(B)$ are seen with $V_x$ alone. An increase of $V_y$ suppresses these oscillations, rather than introducing the additional oscillations in $\rho_{yy}(B)$ expected from previous perturbation theories. We show that this behavior arises from drift of the guiding center of cyclotron motion along contours of an effective potential. Periodic modulation in the magnetic field can be treated in the same way.Comment: 3 pages text, 4 eps figures, revte

A review of the genus Agapetus Curtis (Trichoptera: Glossosomatidae) in eastern and central North America, with description of 12 new species

Twenty-nine species of caddisflies in the genus Agapetus Curtis in eastern and central North America are reviewed. Twelve are described as new species: Agapetus aphallus (known only from females); Agapetus baueri, Agapetus flinti, Agapetus harrisi, Agapetus hesperus, Agapetus ibis, Agapetus kirchneri, Agapetus meridionalis, Agapetus pegram, Agapetus ruiteri, Agapetus stylifer, and Agapetus tricornutus. Agapetus rossi Denning 1941 is recognized as a junior subjective synonym of Agapetus walkeri (Betten and Mosely 1940), new synonym. A key to males is provided, and species’ distributions are mapped

The use of home experimentation kits for distance students in first-year undergraduate electronics

Laboratory and practical classes are an important part of the education of students in electronics and electrical engineering. &quot;Hands-on&quot; experience is critical for any engineer working in these fields in particular. For many years, delivering engineering practicals to distance-education students has been a tremendous challenge for universities. For a number of years now, students enrolled in the common first-year electronics course by distance mode at Deakin University have received a home experimentation kit. Using the kit and a laboratory manual, students are required to complete a number of experiments based on components included in the kit. The kit supports a full range of practical activities for digital electronics, and a more limited range of activities for analog electronics. With the kit, off campus students are supplied software for simulating AC electronic circuits, such as amplifiers and rectifiers. In this report we examine the past use of this kit and software,review anecdotal student experiences with the package, and propose changes to it and to other curriculum resources, aiming to enhance the use of the kit by distance students. Key curriculum resources planned are a web-based \u27companion\u27 for the components in and the use of the kit, and two additions to the kit itself: a battery powered function generator, and a PC-based oscilloscope.<br /

B799: Field Appraisal of Resource Management Systems Farms Crop Yield and Quality Relationships with Soil Erosion

This document presents objectives and preliminary results of the Field Appraisal of Resource Management Systems (FARMS) study. This study assumes that estimates of soil erosion using the Universal Soil Loss Equation (USLE) represent long-term rather than short- term effects. The FARMS study randomly sampled 2400 plots over a three year period, 1980-82, for: crop management, soils, conservation practices and management, crop yields, soil chemistry, and sociological data. This report presents analyses from the 800 plots sampled in 1980. Statistics of rill and sheet soil erosion, as estimated by the Universal Soil Loss Equation (USLE), are presented. Data are presented for each of the factors in the USLE, for potato yields and quality, for yield of other field crops, and for soil nutrient analyses. A significant response of yield to erosion was found when the dataset was limited to the most commonly found soil, Caribou (144 plots). Data analyses including potato yields for all varieties and soils (429 plots) do not show any relation to predicted erosion. Regression analysis predicts that for each ton increase in soil erosion per acre per year up to 12 tons, a decrease of 2.3 hundred- weight of potatoes per acre will occur. The cover and management factor (C) was found to be the most important variable in the USLE in predicting potato yield decreases. With each increase of 0.1 C, the predicted yield decrease amounted to 17 hundredweight gross for potatoes, and 20 hundredweight decrease for US-1 potatoes per acre.https://digitalcommons.library.umaine.edu/aes_bulletin/1113/thumbnail.jp

Validation Results: Utah and Western Sierra Variants of the Forest Vegetation Simulator

The Forest Vegetation Simulator (FVS) is the most widely available and used growth and yield model in the US. It is used in both forest management and research and the basic model framework is integrated with post-processors which can be used for many useful analyses (e.g., fire effects, bark beetle susceptibility, etc.). Recent identification of the nomenclature and a basic validation procedure has resulted in a nation-wide effort to objectively test individual FVS variants following a specific protocol (FVS Validation Subcommittee 2009). Despite the huge range of possibilities for model use, and some independent testing of various model components, (e.g., Pokharel and Froese 2009; Vacchiano et al. 2008) and variants (Lacerte et al. 2004) a comprehensive evaluation of the basic model output has yet to be done. In this project, deliverables identified as necessary to inform an appropriate model testing procedure included: (1) data set description; (2) model verification; (3) model validation; and (4) model sensitivity analysis

The Distance to the Cygnus Loop from Hubble Space Telescope Imaging of the Primary Shock Front

We present a Hubble Space Telescope/WFPC2 narrow-band H-alpha image of a region on the northeastern limb of the Cygnus Loop supernova remnant. This location provides a detailed example of where the primary blast wave first encounters the surrounding interstellar medium. The filament structure is seen in exquisite detail in this image, which was obtained primarily as an EARLY ACQuisition image for a follow-up spectroscopic program. We compare the HST image to a digitized version of the POSS-I red plate to measure the proper motion of this filament. By combining this value for the proper motion with previous measurements of the shock velocity at this position we find that the distance to the Cygnus Loop is 440 (+130, -100) pc, considerably smaller than the canonical value of 770 pc. We briefly discuss the ramifications of this new distance estimate for our understanding of this prototypical supernova remnant.Comment: 18 pages, 3 Figures (2 JPEG and one Postscript

Ferritic nitrocarburising of tool steels

Four different tool steel materials, P20, H13, M2 and D2, were nitrocarburised at 570&deg;C in a fluidised bed furnace. The reactive diffusion of nitrogen and carbon into the various substrate microstructures is compared and related to the different alloy carbide distributions. The effect of carbon bearing gas (carbon dioxide, natural gas) on carbon absorption is reported, as well as its influence on compound layer growth and porosity. Partial reduction of Fe3O4 at the surface resulted in the formation of a complex, epsi-nitride containing oxide layer. In H13, carbon was deeply absorbed throughout the entire diffusion zone, affecting the growth of grain boundary cementite, nitrogen diffusivity and the sharpness of the compound layer: diffusion zone interface. When natural gas was used, carbon became highly concentrated in the compound layer, while surface decarburisation occurred with carbon dioxide. These microstructural effects are discussed in relation to hardness profiles, and compound layer hardness and ductility. The surfaces were characterised using glow discharge optical emission spectroscopy, optical and scanning electron microscopy and X-ray diffraction.<br /

Pin on disc wear investigation of nitrocarburised H13 tool steel

Nitrocarburised H13 disks were tested in dry, sliding wear against a stationary ruby ball (pin). Three different 4 h nitrocarburising treatments were compared, using N2/NH3/CO2, N2/NH3/natural gas and N2/NH3 gas mixtures, resulting in compound layers of varying thickness, hardness, porosity and oxide morphology. During mild, oxidative wear, with the formation of abrasive wear debris, the most brittle and oxidised surfaces performed poorly. Polishing to a bright, reflective finish greatly reduced wear. However, the N2/NH3/CO2 sample also frequently maintained a \u27very mild\u27 wear regime, owing to the formation of a protective film between the wear surfaces, and resulting in a lowering of the friction coefficient. This treated surface was porous and covered in a complex layer of coarse oxide+epsi-carbonitride. Nitrocarburised samples and wear tracks were characterised by optical microscopy, SEM, atomic force microscopy and stylus profilometry.<br /