Next Generation Neutron Detection for Next Generation Nuclear Reactors

Track I: Power GenerationIncludes audio file (31 min.)As the demand for nuclear energy increases worldwide, and MO reactors come online, so does the availability of spent fuel that may be used as a medium of terror. That is, fuel for and waste or byproducts from fissile material refining and nuclear reactors (e.g. plutonium) pose a serious threat with respect to radiological dispersal and nuclear bomb detonation. Radiological dispersal can include fallout by means of water or atmospheric transport (e.g., dumping waste in a river) while fissile trafficking can include the transport of plutonium across a border by seaport entry. In order to safely increase the use of nuclear energy in Missouri, sensitive techniques for nuclear detection must be developed. Presently available commercial detectors are not sensitive enough to detect even large (~3kg) quantities of weapons grade plutonium that are hidden in a barrel of water; our borders are effectively open to critical mass sized plutonium transport. Profs. Caruso, Ching and Kruger (UMKC Physics) are developing detectors capable of a ten times increase in detection sensitivity over existing commercial detectors that will provide a critical component to the future Missouri nuclear safeguarding infrastructure

N-Type Boron-Carbide Semiconductor Polytype and Method of Fabricating the Same

A non-doped n-type boron carbide semiconductor polytype and a method of fabricating the same is provided. The n-type boron carbide polytype may be used in a device for detecting neutrons, electric power conversion, and pulse counting. Such a device may include an n-type boron carbide layer coupled with a substrate where the boron carbide may be an electrically active part of the device. This n-type boron carbide layer may be fabricated through the use of closo-1, 7-dicarbadodecaborane (metacarborane). Specifically, the non-doped n-type polytype may be fabricated using SR-CVD by placing the substrate in a vacuum chamber, cooling the substrate, introducing metacarborane into the chamber, adsorbing the metacarborane onto the surface of the substrate through the use of incident X-ray radiation or electron beam irradiation, decomposing the adsorbed metacarborane, and allowing- the substrate to reach ambient temperature. The n-type polytype of the present invention mav also be fabricated bv PECVD

Robust isothermal electric control of exchange bias at room temperature

Voltage-controlled spin electronics is crucial for continued progress in information technology. It aims at reduced power consumption, increased integration density and enhanced functionality where non-volatile memory is combined with highspeed logical processing. Promising spintronic device concepts use the electric control of interface and surface magnetization. From the combination of magnetometry, spin-polarized photoemission spectroscopy, symmetry arguments and first-principles calculations, we show that the (0001) surface of magnetoelectric Cr2O3 has a roughness-insensitive, electrically switchable magnetization. Using a ferromagnetic Pd/Co multilayer deposited on the (0001) surface of a Cr2O3 single crystal, we achieve reversible, room-temperature isothermal switching of the exchange-bias field between positive and negative values by reversing the electric field while maintaining a permanent magnetic field. This effect reflects the switching of the bulk antiferromagnetic domain state and the interface magnetization coupled to it. The switchable exchange bias sets in exactly at the bulk Néel temperature

Topological Constraint Theory Analysis of Rigidity Transition in Highly Coordinate Amorphous Hydrogenated Boron Carbide

Topological constraint theory (TCT) has revealed itself to be a powerful tool in interpreting the behaviors of amorphous solids. The theory predicts a transition between a “rigid” overconstrained network and a “floppy” underconstrained network as a function of connectivity or average coordination number, 〈r〉. The predicted results have been shown experimentally for various glassy materials, the majority of these being based on 4-fold-coordinate networks such as chalcogenide and oxide glasses. Here, we demonstrate the broader applicability of topological constraint theory to uniquely coordinated amorphous hydrogenated boron carbide (a-BC:H), based on 6-fold-coordinate boron atoms arranged into partially hydrogenated interconnected 12-vertex icosahedra. We have produced a substantial set of plasma-enhanced chemical vapor deposited a-BC:H films with a large range of densities and network coordination, and demonstrate a clear threshold in Young\u27s modulus as a function of 〈r〉, ascribed to a rigidity transition. We investigate constraint counting strategies in this material and show that by treating icosahedra as “superatoms,” a rigidity transition is observed within the range of the theoretically predicted 〈r〉c value of 2.4 for covalent solids with bond-stretching and bond-bending forces. This experimental data set for a-BC:H is unique in that it represents a uniform change in connectivity with 〈r〉 and demonstrates a distinct rigidity transition with data points both above and below the transition threshold. Finally, we discuss how TCT can be applied to explain and optimize mechanical and dielectric properties in a-BC:H and related materials in the context of microelectronics applications

Dielectric loss of boron-based dielectrics on niobium resonators

Advanced solid-state quantum bits (qubits) are likely to require a variety of dielectrics for wiring crossovers, substrates, and Josephson junctions. Microwave superconducting resonators are an excellent tool for measuring the internal dielectric loss of materials. We report the dielectric loss of boron-based dielectric films using a microwave coplanar waveguide (CPW) resonator with heterostructure geometry. Power-dependent internal quality factors of magnetron-sputtered boron carbide ( B4C ) and boron nitride (BN) were measured and are compared to silicon oxide ( SiO2 ), a common material used in wiring crossovers. The internal dielectric loss due to two-level systems for B4C , and BN is less than silicon dioxide ( SiO2 ), which demonstrates the existence of low-loss sputtered materials. We also found that niobium (Nb) CPW resonators suffer a decrease in internal quality factor after deposition of B4C at temperatures above 150 ∘C . This result is consistent with the idea that the oxidation of the surface of the superconducting metal can contribute to loss in a device

Carbon‐Enriched Amorphous Hydrogenated Boron Carbide Films for Very‐Low‐k Interlayer Dielectrics

A longstanding challenge in ultralarge‐scale integration has been the continued improvement in low‐dielectric‐constant (low‐k) interlayer dielectric materials and other specialized layers in back‐end‐of‐the‐line interconnect fabrication. Modeled after the success of carbon‐containing organosilicate materials, carbon‐enriched amorphous hydrogenated boron carbide (a‐BxC:Hy) films are grown by plasma‐enhanced chemical vapor deposition from ortho‐carborane and methane. These films contain more extraicosahedral sp3 hydrocarbon groups than nonenriched a‐BxC:Hy films, as revealed by FTIR and NMR spectroscopy, and also exhibit lower dielectric constants than their nonenriched counterparts, notably due to low densities combined with a low distortion and orientation contribution to the total polarizability. Films with dielectric constant as low as 2.5 are reported with excellent electrical stability (leakage current of 10−9 A cm−2 at 2 MV cm−1 and breakdown voltage of >6 MV cm−1), good thermal conductivity of 0.31 ± 0.03 W m−1 K−1, and high projected Young’s modulus of 12 ± 3 GPa. These properties rival those of leading SiOC:H materials, and position a‐BxC:Hy as an important complement to traditional Si‐based materials to meet the complex needs of next‐generation interconnect fabrication.Carbon‐enriched amorphous hydrogenated boron carbide films are demonstrated with dielectric constant (k) as low as 2.5—attributed to low densities combined with network‐rigidifying CH2 bridging groups—as well as excellent electrical, thermal, and mechanical properties, rivaling those of state‐of‐the‐art silicon‐based low‐k dielectric materials.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/1/aelm201700116_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/141869/2/aelm201700116.pd

Robust isothermal electric switching of interface magnetization: A route to voltage-controlled spintronics

Roughness-insensitive and electrically controllable magnetization at the (0001) surface of antiferromagnetic chromia is observed using magnetometry and spin-resolved photoemission measurements and explained by the interplay of surface termination and magnetic ordering. Further, this surface in placed in proximity with a ferromagnetic Co/Pd multilayer film. Exchange coupling across the interface between chromia and Co/Pd induces an electrically controllable exchange bias in the Co/Pd film, which enables a reversible isothermal (at room temperature) shift of the global magnetic hysteresis loop of the Co/Pd film along the magnetic field axis between negative and positive values. These results reveal the potential of magnetoelectric chromia for spintronic applications requiring non-volatile electric control of magnetization.Comment: Single PDF file: 27 pages, 6 figures; version of 12/30/09; submitted to Nature Material

Desert Farming Benefits from Microbial Potential in Arid Soils and Promotes Diversity and Plant Health

BACKGROUND: To convert deserts into arable, green landscapes is a global vision, and desert farming is a strong growing area of agriculture world-wide. However, its effect on diversity of soil microbial communities, which are responsible for important ecosystem services like plant health, is still not known. METHODOLOGY/PRINCIPAL FINDINGS: We studied the impact of long-term agriculture on desert soil in one of the most prominent examples for organic desert farming in Sekem (Egypt). Using a polyphasic methodological approach to analyse microbial communities in soil as well as associated with cultivated plants, drastic effects caused by 30 years of agriculture were detected. Analysing bacterial fingerprints, we found statistically significant differences between agricultural and native desert soil of about 60%. A pyrosequencing-based analysis of the 16S rRNA gene regions showed higher diversity in agricultural than in desert soil (Shannon diversity indices: 11.21/7.90), and displayed structural differences. The proportion of Firmicutes in field soil was significantly higher (37%) than in the desert (11%). Bacillus and Paenibacillus play the key role: they represented 96% of the antagonists towards phytopathogens, and identical 16S rRNA sequences in the amplicon library and for isolates were detected. The proportion of antagonistic strains was doubled in field in comparison to desert soil (21.6%/12.4%); disease-suppressive bacteria were especially enriched in plant roots. On the opposite, several extremophilic bacterial groups, e.g., Acidimicrobium, Rubellimicrobium and Deinococcus-Thermus, disappeared from soil after agricultural use. The N-fixing Herbaspirillum group only occurred in desert soil. Soil bacterial communities were strongly driven by the a-biotic factors water supply and pH. CONCLUSIONS/SIGNIFICANCE: After long-term farming, a drastic shift in the bacterial communities in desert soil was observed. Bacterial communities in agricultural soil showed a higher diversity and a better ecosystem function for plant health but a loss of extremophilic bacteria. Interestingly, we detected that indigenous desert microorganisms promoted plant health in desert agro-ecosystems

IL-1β Suppresses Innate IL-25 and IL-33 Production and Maintains Helminth Chronicity.

Approximately 2 billion people currently suffer from intestinal helminth infections, which are typically chronic in nature and result in growth retardation, vitamin A deficiency, anemia and poor cognitive function. Such chronicity results from co-evolution between helminths and their mammalian hosts; however, the molecular mechanisms by which these organisms avert immune rejection are not clear. We have found that the natural murine helminth, Heligmosomoides polygyrus bakeri (Hp) elicits the secretion of IL-1β in vivo and in vitro and that this cytokine is critical for shaping a mucosal environment suited to helminth chronicity. Indeed in mice deficient for IL-1β (IL-1β(-/-)), or treated with the soluble IL-1βR antagonist, Anakinra, helminth infection results in enhanced type 2 immunity and accelerated parasite expulsion. IL-1β acts to decrease production of IL-25 and IL-33 at early time points following infection and parasite rejection was determined to require IL-25. Taken together, these data indicate that Hp promotes the release of host-derived IL-1β that suppresses the release of innate cytokines, resulting in suboptimal type 2 immunity and allowing pathogen chronicity

Stratification of asthma phenotypes by airway proteomic signatures

© 2019 Background: Stratification by eosinophil and neutrophil counts increases our understanding of asthma and helps target therapy, but there is room for improvement in our accuracy in prediction of treatment responses and a need for better understanding of the underlying mechanisms. Objective: We sought to identify molecular subphenotypes of asthma defined by proteomic signatures for improved stratification. Methods: Unbiased label-free quantitative mass spectrometry and topological data analysis were used to analyze the proteomes of sputum supernatants from 246 participants (206 asthmatic patients) as a novel means of asthma stratification. Microarray analysis of sputum cells provided transcriptomics data additionally to inform on underlying mechanisms. Results: Analysis of the sputum proteome resulted in 10 clusters (ie, proteotypes) based on similarity in proteomic features, representing discrete molecular subphenotypes of asthma. Overlaying granulocyte counts onto the 10 clusters as metadata further defined 3 of these as highly eosinophilic, 3 as highly neutrophilic, and 2 as highly atopic with relatively low granulocytic inflammation. For each of these 3 phenotypes, logistic regression analysis identified candidate protein biomarkers, and matched transcriptomic data pointed to differentially activated underlying mechanisms. Conclusion: This study provides further stratification of asthma currently classified based on quantification of granulocytic inflammation and provided additional insight into their underlying mechanisms, which could become targets for novel therapies