Exciton-magnon effects in the optical spectrum of MnF2

Exciton and magnon absorption, emission spectra, and fluorescence of antiferromagnetic manganese fluorid

Calcium-Rich Gap Transients: Tidal Detonations of White Dwarfs?

We hypothesize that at least some of the recently discovered class of calcium-rich gap transients are tidal detonation events of white dwarfs (WDs) by black holes (BHs) or possibly neutron stars. We show that the properties of the calcium-rich gap transients agree well with the predictions of the tidal detonation model. Under the predictions of this model, we use a follow-up X-ray observation of one of these transients, SN 2012hn, to place weak upper limits on the detonator mass of this system that include all intermediate-mass BHs (IMBHs). As these transients are preferentially in the stellar haloes of galaxies, we discuss the possibility that these transients are tidal detonations of WDs caused by random flyby encounters with IMBHs in dwarf galaxies or globular clusters. This possibility has been already suggested in the literature but without connection to the calcium-rich gap transients. In order for the random flyby cross-section to be high enough, these events would have to be occurring inside these dense stellar associations. However, there is a lack of evidence for IMBHs in these systems, and recent observations have ruled out all but the very faintest dwarf galaxies and globular clusters for a few of these transients. Another possibility is that these are tidal detonations caused by three-body interactions, where a WD is perturbed toward the detonator in isolated multiple star systems. We highlight a number of ways this could occur, even in lower-mass systems with stellar-mass BHs or neutron stars. Finally, we outline several new observational tests of this scenario, which are feasible with current instrumentation.Comment: 10 pages, 1 figure, accepted for publication in MNRA

Single-Calf Heifer System Profitability Compared to Other North Dakota Beef Production Systems

Production Economics, Productivity Analysis,

A Journey of Pregnancy Loss: From Positivism to Autoethnography

When a dissertation research project exploring the impact of mind - body practices on symptoms of depression and anxiety in pregnant women with a history of miscarriage failed to yield statistically significant results, I struggled with how to demonstrate that I had gleaned knowledge from this project of nearly 3 years. When a series of parallel pregnancy losses occurred in my own life, I realized that I am heavily situated within the context of my research and need to consider my data in a different sense; one that acknowledges my own self within this process while attempting to capture the lived experiences of others. The shift to autoethnography afforded me the opportunity to demonstrate that knowledge can be generated through multiple methodologies, with one approach not being privileged over another. As this dissertation moved from an empirical study to a qualitative, autoethnographic piece, I was able to identify themes surfacing from the literature, my own experiences and participation in a pregnancy loss support group. The themes discussed include: making meaning from the experience, granting personhood status and grieving and other emotional expression

Economics of Establishing a Beef Cattle Feedlot Using By-Products of Ethanol Production in North Dakota

Production Economics, Resource /Energy Economics and Policy, Agribusiness,

Differing Effects of Glycerin on Anaerobic Co-digestion of Mixed Substrates in Bench-Scale Assays and Sub Pilot-Scale Reactors

Bench-scale methods such as Biochemical Methane Potential (BMP) assays and Anaerobic Toxicity Assays (ATAs) are useful tools in evaluating potential feedstocks for anaerobic digestion. The BMP method provides a preliminary indication of substrate biodegradability and methane production, while the ATAs provide an indication of substrate toxicity to anaerobic microbial consortia. Previous research using small (\u3c20 \u3eL) reactors indicated that co-digestion of manures with small amounts of glycerin (ca. 1 – 2 %) can double methane production, but toxicity can result if glycerin exceeds 2% (volumetric basis). This paper investigated the relationship between bench-scale methods (BMPs and ATAs) and sub pilot-scale digester results, using glycerin as a test substrate mixed with a baseline feedstock (beef manure, corn processing wastewater, lagoon liquid, and short-fiber cardboard). The batch-fed, stirred ATAs indicated that glycerin was toxic to methane production at all inclusion levels. The batch-fed, stirred BMPs indicated no significant difference between methane production in the 0.0%to 4.0% addition levels; however at 8.0% addition, methane production tripled. The continuously fed, non-stirred, plug-flow sub pilot-scale reactors indicated toxicity effects in the 2.0% and 4.0% glycerin mixtures and no difference from the control in the 1.0% glycerin mixture. These results demonstrate the variations in scale performance of glycerin as a co-substrate and identify some serious challenges in extrapolating bench-scale assays to large-scale performance of mixed-waste anaerobic digestion systems

Comparison of Methane Production from Bench- and Sub Pilot-Scale Anaerobic Digesters

Design and construction of full-scale anaerobic digesters that co-digest manure with other substrates, such as food processing wastes, is challenging because of the large number of potential mixtures that can be fed to the digester. In this work we examine the relationship between results from bench-scale methods such as biochemical methane potential assays (BMPs) and sub pilot-scale reactors. The baseline feedstock for this study was beef manure from concrete feedlot pens (open and covered) in eastern Iowa. Additional co-digestion substrates tested were short-fiber cardboard, corn processing wastewater, enzyme processing wastewater and lagoon liquid. Substrates were characterized for total solids (TS), volatile solids (VS), chemical oxygen demand (COD), pH, alkalinity, and ammonia, after which BMPs were conducted on all substrates. Based on the BMP and anaerobic toxicity assay (ATA) results, a mixture was created and evaluated using BMPs and tested in 100-L sub pilot-scale reactors. This study showed that results from BMPs of feedstock co-digestion mixtures accurately estimated the range of methane produced from three 100-L, plug flow reactors

Approaches for Selecting Anaerobic Digestion Co-Substrates for a Full-Scale Beef Manure Digester Using Biochemical Methane Potentials and Anaerobic Texicity Assays

Design and construction of full-scale anaerobic digesters that co-digest manure with various materials requires analysis of each substrate. Substrate combinations should be analyzed through a scale up procedure in which substrates are characterized, and then evaluated using biochemical methane potential assays (BMPs) and anaerobic toxicity assays (ATAs). The BMPs provide a preliminary indication of the biodegradability of a substrate and of its potential to produce methane via anaerobic digestion, while ATAs determine the degree to which a particular substrate inhibits methane production. Mixture combinations that perform well in BMPs and ATAs should be tested in laboratory-scale anaerobic digesters. Once proven in lab-scale reactors for at least three hydraulic retention times, the best mixture should be tested in a pilot-scale reactor. This paper focuses on the first steps in this process using BMPs and ATAs results to select mixtures for laboratory-scale digester testing. The baseline feedstock was beef manure obtained from concrete feedlot pens (open and covered) in eastern Iowa. Various bedding materials were available, including oat hulls, corn stover, and wood shavings. To provide additional energy production, industrial byproducts from cardboard manufacturing, enzyme production, and corn and soybean processing were also potential substrates. Substrates were characterized for TS, VS, COD, pH, alkalinity, and ammonia. Then BMPs were completed on all substrates and ATAs were performed as needed. The results reported here were used to develop mixtures for use in laboratory-scale anaerobic digester testing

Ultrahigh Bandwidth Spin Noise Spectroscopy: Detection of Large g-Factor Fluctuations in Highly n-Doped GaAs

We advance all optical spin noise spectroscopy (SNS) in semiconductors to detection bandwidths of several hundred gigahertz by employing an ingenious scheme of pulse trains from ultrafast laser oscillators as an optical probe. The ultrafast SNS technique avoids the need for optical pumping and enables nearly perturbation free measurements of extremely short spin dephasing times. We employ the technique to highly n-doped bulk GaAs where magnetic field dependent measurements show unexpected large g-factor fluctuations. Calculations suggest that such large g-factor fluctuations do not necessarily result from extrinsic sample variations but are intrinsically present in every doped semiconductor due to the stochastic nature of the dopant distribution.Comment: 5 pages, 3 figure