Introduction to Library Trends 44 (2) Fall 1995: The Library and Undergraduate Education

published or submitted for publicatio

Gating of high-mobility InAs metamorphic heterostructures

We investigate the performance of gate-defined devices fabricated on high mobility InAs metamorphic heterostructures. We find that heterostructures capped with In$_{0.75}$Ga$_{0.25}$As often show signs of parallel conduction due to proximity of their surface Fermi level to the conduction band minimum. Here, we introduce a technique that can be used to estimate the density of this surface charge that involves cool-downs from room temperature under gate bias. We have been able to remove the parallel conduction under high positive bias, but achieving full depletion has proven difficult. We find that by using In$_{0.75}$Al$_{0.25}$As as the barrier without an In$_{0.75}$Ga$_{0.25}$As capping, a drastic reduction in parallel conduction can be achieved. Our studies show that this does not change the transport properties of the quantum well significantly. We achieved full depletion in InAlAs capped heterostructures with non-hysteretic gating response suitable for fabrication of gate-defined mesoscopic devices

Characterization of a high-pressure diesel fuel injection system as a control technology option to improve engine performance and reduce exhaust emissions

Test results from a high pressure electronically controlled fuel injection system are compared with a commercial mechanical injection system on a single cylinder, diesel test engine using an inlet boost pressure of 2.6:1. The electronic fuel injection system achieved high pressure by means of a fluid intensifier with peak injection pressures of 47 to 69 MPa. Reduced exhaust emissions were demonstrated with an increasing rate of injection followed by a fast cutoff of injection. The reduction in emissions is more responsive to the rate of injection and injection timing than to high peak injection pressure

Addressing Soil Carbon Sequestration Response from Multispecies Dairy Forage Systems and Modeling Rangeland Beef Cow Dry Matter Intake Using Precision Enteric Emissions Measurements

Regenerative agriculture is a pressing matter for the dairy industry to address cropland sustainability and carbon sequestration. One regenerative management practice that has been identified to help with row crop sustainability for key metrics like soil organic carbon (SOC) is complex covers. When producers use complex covers one of the main challenges is that it takes time to detect a change in SOC. However, simulation models are a tool that can be used to help determine if a regenerative practice is a strategy that gives the best results (i.e., increased SOC) while aligning with long-term production goals. Therefore, our objectives were to 1) modify the DAYCENT model to simulate soil carbon and flux with complex cover practices and 2) simulate different conventional and regenerative cropping scenarios on United States dairy farms in Wisconsin and Michigan to assess differences in soil carbon (C). The Soil Carbon CareTaker model used parameters from DAYCENT that were modified to estimate SOC with different complex cover and tillage practices over 30 years for dairy fields (n = 12) within Michigan. The calibrated model was shown to lack precision (R2 = 0.07) but was highly accurate [mean bias = -0.26 (MB)]. We simulated a base case for each field along with four different scenarios: no-till (NoTill), 30 years of continuous corn (CornOnly), cover crops with tillage (CC), and cover crops with no-till (CC NoTill). The Michigan dairy fields were split into three different regions: west (n = 4), central (n = 2), and east (n = 6). Within these regions, we observed an average least percent soil C change from the base case of -14% (west), -12% (central), and -15% (east) from the CornOnly scenario, while the greatest average percent change from the base for each region was 350% (west), 361% (central), and 278% (east) for the CC NoTill scenario. Thus, the Soil Carbon CareTaker model can be used as a tool for producers to assess regenerative management strategies that will enhance C sequestration, meet sustainability goals, and provide cost-effective regenerative dairy products to meet shifting consumer demands. Another goal for sustainable agriculture is assessing range cattle dry matter intake (DMI). DMI is an essential component to determining nutrient supply and for evaluating grazing management. Not only is DMI a major concern for cattle management, but it is also a key component regarding the rising pressure to assess the impact of enteric gas emissions from cattle on the environment. Since DMI and enteric emissions are directly correlated, this provides a potential to leverage enteric emissions to predict DMI. Obtaining data for beef cattle DMI and enteric emissions on forage-based diets similar to extensive rangelands is needed to develop an equation capable of predicting DMI for grazing cattle. Therefore, our objectives were to: 1) measure CH4, CO2, and O2 emissions, and DMI of dry beef cows and 2) use these data to develop a mathematical model capable of predicting grazing DMI. The predictive equation or precision system model (PSM) was developed using data from two feeding trials that were conducted using technology to measure enteric emissions (GreenFeed™), daily DMI (SmartFeed Pro™), and front-end body weights (SmartScale™). This study was conducted in western South Dakota during the winter of 2022. Two feeding trials used non-lactating beef cows (n = 7) receiving low (6% CP) or moderate (15% CP) quality grass hay using a 14-day adaptation period and a 14-day data collection period. Average CH4 (g/day), CO2 (g/day), and O2 (g/day) were 265 + 8.78, 7,953 + 228.83, 5,690 + 1,488.19, for the low and 215 + 13.63, 6,863 + 393.79, 5,244 + 328.32 for the moderate treatments, respectively. The PSM was evaluated for accuracy [mean bias (MB)] and precision (R2). Initial models were less than desirable for individual DMI with a range of R2 of 0.01- 0.36 for single and multiple linear regression. Using herd-level data and a 3-day smoothing, the CH4 model produced the best results with an R2 and MB of 0.91 and -255.00, respectively. A major limitation was poor GreenFeed™ use rates resulting in a limited sample size to compare with individual daily DMI data. Advances in DMI estimates for grazing cattle will have the potential to enhance stocking rate estimates, supplementation, and individual animal efficiency, leading to lower cost, optimized resources, and enhanced environmental sustainability

The Legality of Nuclear Weapons: A Response to Corwin

This Article is a response to Journal author David Corwin\u27s contention that the use of nuclear weapons is illegal under international law. In turn, the author carefully examines relevant treaty provisions to support his thesis. Finally, the author contends that the principles of customary international law and state practice provide a foundation by which the use of nuclear weapons is circumscribed under international law

Sparse Graph Codes for Quantum Error-Correction

We present sparse graph codes appropriate for use in quantum error-correction. Quantum error-correcting codes based on sparse graphs are of interest for three reasons. First, the best codes currently known for classical channels are based on sparse graphs. Second, sparse graph codes keep the number of quantum interactions associated with the quantum error correction process small: a constant number per quantum bit, independent of the blocklength. Third, sparse graph codes often offer great flexibility with respect to blocklength and rate. We believe some of the codes we present are unsurpassed by previously published quantum error-correcting codes.Comment: Version 7.3e: 42 pages. Extended version, Feb 2004. A shortened version was resubmitted to IEEE Transactions on Information Theory Jan 20, 200

Solution of a Braneworld Big Crunch/Big Bang Cosmology

We solve for the cosmological perturbations in a five-dimensional background consisting of two separating or colliding boundary branes, as an expansion in the collision speed V divided by the speed of light c. Our solution permits a detailed check of the validity of four-dimensional effective theory in the vicinity of the event corresponding to the big crunch/big bang singularity. We show that the four-dimensional description fails at the first nontrivial order in (V/c)^2. At this order, there is nontrivial mixing of the two relevant four-dimensional perturbation modes (the growing and decaying modes) as the boundary branes move from the narrowly-separated limit described by Kaluza-Klein theory to the well-separated limit where gravity is confined to the positive-tension brane. We comment on the cosmological significance of the result and compute other quantities of interest in five-dimensional cosmological scenarios.Comment: 54 pages, 12 figures, URL updated & 3 references adde

Baseline performance and emissions data for a single-cylinder, direct-injected diesel engine

Comprehensive fuel consumption, mean effective cylinder pressure, and emission test results for a supercharged, single-cylinder, direct-injected, four-stroke-cycle, diesel test engine are documented. Inlet air-to-exhaust pressure ratios were varied from 1.25 to 3.35 in order to establish the potential effects of turbocharging techniques on engine performance. Inlet air temperatures and pressures were adjusted from 34 to 107 C and from 193 to 414 kPa to determine the effects on engine performance and emissions. Engine output ranged from 300 to 2100 kPa (brake mean effective pressure) in the speed range of 1000 to 3000 rpm. Gaseous and particulate emission rates were measured. Real-time values of engine friction and pumping loop losses were measured independently and compared with motored engine values