Direct Cooled Ceramic Substrate for Thermal Control of Automotive Power Electronics

As electric vehicle technology develops, manufacturers would like to move toward hotter coolants for power electronic components to reduce system level costs. Thus, unique designs of inverter designs were sought to enable operation with 105°C coolant. The proposed solution in this research incorporated flow channels into the ceramic layer of the direct-bonded copper substrate typically found in power electronic packages. The focus of this research details the design and analysis of the direct cooled ceramic substrate from the perspective of its thermal performance and innovative packaging concept. The research was directed to pursue alumina as the substrate ceramic because of its low cost. Alumina, which has the lowest thermal conductivity among four materials considered, requires a larger substrate cross-sectional area to result in a viable design. Based on preliminary model parameters, two flow channel designs with larger alumina substrates were shown to meet the design goals. Experiments were conducted to characterize the pressure drop across metal foam inserts which were used to enhance the heat transfer in the flow channels. Other experiments were conducted to validate the thermal performance and model configuration. The results of thermal validation experiment showed that the assumed effective thermal conductivity of the metal foam – fluid matrix was too large. The small contact area between the metal foam inserts and ceramic substrate reduces the effective thermal conductivity. Based on the data reduction method, the model parameters were modified to produce temperature distributions that better reflected the experimental data. Simulations were updated with the modified model parameters. These models showed that the cross-sectional area of the alumina substrate had to increase further in order to adequately manage the heat load. In parallel efforts, the overall inverter package was considered. A linear manifold package resulted in the highest power density. Technical review of the inverter package raised concerns about stray inductance. Incorporating the entire inverter leg on one substrate would alleviate these losses. Future research can use the parameters determined in this work to more confidently predict the performance of direct cooled ceramic substrate designs

Does Quality Design Have a Value

Abstract Not Provided

Co-evolution of Rock Strength, Erosion, and Steep Topography

Rock-mass strength is recognized as an important control in geomorphology that influences the morphology of landscapes and modulates feedbacks between surface processes, tectonics, and climate. Despite this general recognition, many of the factors controlling rock-mass strength in the near-surface are not widely understood, largely due to challenges in quantifying strength over the appropriate spatial scales. Although the strength of small rock samples can be readily measured with laboratory techniques, fractures and weathering gradients at progressively larger spatial scales dramatically reduce the strength of rock masses compared to their intact (unfractured) counterparts. Due to a lack of approaches that incorporate discontinuities into strength estimates, the contribution of rock-mass properties to geomorphic processes and topographic relief remains unquantified. In this dissertation, I address gaps in our understanding of the role of rock mass strength in geomorphology by testing new methods for quantifying scale-dependent rock mass strength, using these new tools to quantify gradients in strength across environmental variables, and assessing the contribution of rock strength to topographic form and erosion. Research activities focus on an inverted sedimentary basin within the Western Transverse Ranges of southern California, USA, where differences in fault activity have exposed sedimentary rocks with variable burial histories. With Chapters 2 and 3, I test new approaches to quantifying outcrop- and hillslope-scale near-surface rock-mass strength using slope-stability models and field methods. With these new techniques, I resolve order-of-magnitude differences in strength that appear to be related to diagenetic changes associated with the maximum burial depth of young clastic sedimentary rocks. I resolve smaller differences in strength (300 kPa – 1.5 MPa) that are positively correlated with mean erosion rates, which I hypothesize reflects decreased weathering extents with increasing erosion rates for mountain ranges experiencing faster fault slip rates. Assessing the contribution of rock-mass properties to the evolution of landscapes requires recognizing patterns of long-term fault activity and erosion. In Chapter 4, I resolve differences in the timing of reverse fault localization, initiation, and propagation, as well as long-term erosion rates, using low-temperature thermochronometry. Inverse thermal modelling of Miocene to Pleistocene apatite (U-Th-Sm)/He cooling ages and partially reset zircon (U-Th)/He cooling ages on eleven vertical transects reveal that deformation localization was likely driven by contrasts in the rheology and strength of the lithosphere, rather than by restraining bend tectonism. With estimates of near-surface rock-mass strength and long-term erosion rates mapped across the landscape in Chapters 2-4, I evaluate the contribution of rock-mass strength to topography in Chapter 5. Where erosion rates and climate are spatially uniform, I find a non-linear relationship between topographic metrics and rock-mass shear strength, implying that rock-mass strength sets the topographic structure of the mountain range. Chapter 6 builds on this observation, and I find that post-wildfire erosion as quantified from repeat airborne-LiDAR surveys is positively correlated with local slope and the strength of the underlying bedrock. Rather than setting the erodibility of earth materials directly, I hypothesize that rock-mass strength controls event-driven erosion by setting the steepness of the overlying landscape. Collectively, interpretations put forward in this dissertation highlight the complex interplay between tectonics, erosion, topography, and the mechanical evolution of rock to transportable, erodible materials.PHDEarth and Environmental SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/169827/1/kirkft_1.pd

Earthquake science in resilient societies

Earthquake science is critical in reducing vulnerability to a broad range of seismic hazards. Evidenceâ based studies drawing from several branches of the Earth sciences and engineering can effectively mitigate losses experienced in earthquakes. Societies that invest in this research have lower fatality rates in earthquakes and can recover more rapidly. This commentary explores the scientific pathways through which earthquakeâ resilient societies are developed. We highlight recent case studies of evidenceâ based decision making and how modern research is improving the way societies respond to earthquakes.Key PointsThe level of seismic risk depends in part on societal investment in earthquake scienceMultidisciplinary investigations involving earthquake scientists and engineers greatly reduce casualties in earthquakesRecent examples highlight the utility of earthquake science in building resilient societies and the need for further research to reduce seismic riskPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/137197/1/tect20552_am.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/137197/2/tect20552.pd

Employing Respondent Driven Sampling (RDS) to recruit people who inject drugs (PWID) and other hard-to-reach populations during COVID-19: Lessons learned

Background: Respondent Driven Sampling (RDS) is an effective sampling strategy to recruit hard-to-reach populations but the impact of the COVID-19 pandemic on the use of this strategy in the collection of data involving human subjects, particularly among marginalized and vulnerable populations, is not known. Based on an ongoing study using RDS to recruit and study the interactions between HIV infection, injection drug use, and the microbiome in Puerto Rico, this paper explores the eectiveness of RDS during the pandemic and provided potential strategies that could improve recruitment and data collection. Results: RDS was employed to evaluate its effectiveness in recruiting a group of people who inject drugs (PWID) and controls (N = 127) into a study in the midst of the COVID-19 pandemic. The participants were distributed among three subsets: 15 were HIV+ and PWID, 58 were HIV- PWID, and 54 were HIV+ and not PWID. Findings: Results showthat recruitment through peer networks using RDS was possible across all sub-groups. Yet, while those in the HIV+ PWID sub-group managed to recruit from other-sub groups of HIV- PWID and HIV+, this occurred at a lower frequency. Conclusion: Despite the barriers introduced by COVID-19, it is clear that even in this environment, RDS continues to play a powerful role in recruiting hard-to-reach populations. Yet, more attention should be paid at how future pandemics, natural disasters, and other big events might affect RDS recruitment of vulnerable and hard-to-reach populations

Anisotropic inverse Compton scattering of photons from the circumstellar disc in PSR B1259-63

The gamma-ray binary system PSR B1259-63 consists of a 48 ms pulsar orbiting a Be star. The system is particularly interesting because it is the only gamma-ray binary system where the nature of the compact object is known. The non-thermal radiation from the system is powered by the spin-down luminosity of the pulsar and the unpulsed radiation originates from the stand-off shock front which forms between the pulsar and stellar wind. The Be star/optical companion in the system produces an excess infrared flux from the associated circumstellar disc. This infrared excess provides an additional photon source for inverse Compton scattering. We discuss the effects of the IR excess near periastron, for anisotropic inverse Compton scattering and associated gamma-ray production. We determine the infrared excess from the circumstellar disc using a modified version of a curve of growth method, which takes into account the changing optical depth through the circumstellar disc during the orbit. The model is constrained using archive data and additional mid-IR observations obtained with the VLT during January 2011. The inverse Compton scattering rate was calculated for three orientations of the circumstellar disc. The predicted gamma-ray light curves show that the disc contribution is a maximum around periastron and not around the disc crossing epoch. This is a result of the disc being brightest near the stellar surface. Additional spectroscopic and near-infrared observations were obtained of the system and these are discussed in relation to the possibility of shock heating during the disc crossing epoch.Comment: 15 pages, 14 figures and 4 tables. MNRAS in press. Updated references, correction of typos in a few of the equations in sec. 5.2 and appendix, and other minor typo correction

Antimicrobial resistance among migrants in Europe: a systematic review and meta-analysis

BACKGROUND: Rates of antimicrobial resistance (AMR) are rising globally and there is concern that increased migration is contributing to the burden of antibiotic resistance in Europe. However, the effect of migration on the burden of AMR in Europe has not yet been comprehensively examined. Therefore, we did a systematic review and meta-analysis to identify and synthesise data for AMR carriage or infection in migrants to Europe to examine differences in patterns of AMR across migrant groups and in different settings. METHODS: For this systematic review and meta-analysis, we searched MEDLINE, Embase, PubMed, and Scopus with no language restrictions from Jan 1, 2000, to Jan 18, 2017, for primary data from observational studies reporting antibacterial resistance in common bacterial pathogens among migrants to 21 European Union-15 and European Economic Area countries. To be eligible for inclusion, studies had to report data on carriage or infection with laboratory-confirmed antibiotic-resistant organisms in migrant populations. We extracted data from eligible studies and assessed quality using piloted, standardised forms. We did not examine drug resistance in tuberculosis and excluded articles solely reporting on this parameter. We also excluded articles in which migrant status was determined by ethnicity, country of birth of participants' parents, or was not defined, and articles in which data were not disaggregated by migrant status. Outcomes were carriage of or infection with antibiotic-resistant organisms. We used random-effects models to calculate the pooled prevalence of each outcome. The study protocol is registered with PROSPERO, number CRD42016043681. FINDINGS: We identified 2274 articles, of which 23 observational studies reporting on antibiotic resistance in 2319 migrants were included. The pooled prevalence of any AMR carriage or AMR infection in migrants was 25·4% (95% CI 19·1-31·8; I2 =98%), including meticillin-resistant Staphylococcus aureus (7·8%, 4·8-10·7; I2 =92%) and antibiotic-resistant Gram-negative bacteria (27·2%, 17·6-36·8; I2 =94%). The pooled prevalence of any AMR carriage or infection was higher in refugees and asylum seekers (33·0%, 18·3-47·6; I2 =98%) than in other migrant groups (6·6%, 1·8-11·3; I2 =92%). The pooled prevalence of antibiotic-resistant organisms was slightly higher in high-migrant community settings (33·1%, 11·1-55·1; I2 =96%) than in migrants in hospitals (24·3%, 16·1-32·6; I2 =98%). We did not find evidence of high rates of transmission of AMR from migrant to host populations. INTERPRETATION: Migrants are exposed to conditions favouring the emergence of drug resistance during transit and in host countries in Europe. Increased antibiotic resistance among refugees and asylum seekers and in high-migrant community settings (such as refugee camps and detention facilities) highlights the need for improved living conditions, access to health care, and initiatives to facilitate detection of and appropriate high-quality treatment for antibiotic-resistant infections during transit and in host countries. Protocols for the prevention and control of infection and for antibiotic surveillance need to be integrated in all aspects of health care, which should be accessible for all migrant groups, and should target determinants of AMR before, during, and after migration. FUNDING: UK National Institute for Health Research Imperial Biomedical Research Centre, Imperial College Healthcare Charity, the Wellcome Trust, and UK National Institute for Health Research Health Protection Research Unit in Healthcare-associated Infections and Antimictobial Resistance at Imperial College London

Tasting Soil Fungal Diversity with Earth Tongues: Phylogenetic Test of SATé Alignments for Environmental ITS Data

An abundance of novel fungal lineages have been indicated by DNA sequencing of the nuclear ribosomal ITS region from environmental samples such as soil and wood. Although phylogenetic analysis of these novel lineages is a key component of unveiling the structure and diversity of complex communities, such analyses are rare for environmental ITS data due to the difficulties of aligning this locus across significantly divergent taxa. One potential approach to this issue is simultaneous alignment and tree estimation. We targeted divergent ITS sequences of the earth tongue fungi (Geoglossomycetes), a basal class in the Ascomycota, to assess the performance of SATé, recent software that combines progressive alignment and tree building. We found that SATé performed well in generating high-quality alignments and in accurately estimating the phylogeny of earth tongue fungi. Drawing from a data set of 300 sequences of earth tongues and progressively more distant fungal lineages, 30 insufficiently identified ITS sequences from the public sequence databases were assigned to the Geoglossomycetes. The association between earth tongues and plants has been hypothesized for a long time, but hard evidence is yet to be collected. The ITS phylogeny showed that four ectomycorrhizal isolates shared a clade with Geoglossum but not with Trichoglossum earth tongues, pointing to the significant potential inherent to ecological data mining of environmental samples. Environmental sampling holds the key to many focal questions in mycology, and simultaneous alignment and tree estimation, as performed by SATé, can be a highly efficient companion in that pursuit

Finding Single Copy Genes Out of Sequenced Genomes for Multilocus Phylogenetics in Non-Model Fungi

Historically, fungal multigene phylogenies have been reconstructed based on a small number of commonly used genes. The availability of complete fungal genomes has given rise to a new wave of model organisms that provide large number of genes potentially useful for building robust gene genealogies. Unfortunately, cross-utilization of these resources to study phylogenetic relationships in the vast majority of non-model fungi (i.e. “orphan” species) remains an unexamined question. To address this problem, we developed a method coupled with a program named “PHYLORPH” (PHYLogenetic markers for ORPHans). The method screens fungal genomic databases (107 fungal genomes fully sequenced) for single copy genes that might be easily transferable and well suited for studies at low taxonomic levels (for example, in species complexes) in non-model fungal species. To maximize the chance to target genes with informative regions, PHYLORPH displays a graphical evaluation system based on the estimation of nucleotide divergence relative to substitution type. The usefulness of this approach was tested by developing markers in four non-model groups of fungal pathogens. For each pathogen considered, 7 to 40% of the 10–15 best candidate genes proposed by PHYLORPH yielded sequencing success. Levels of polymorphism of these genes were compared with those obtained for some genes traditionally used to build fungal phylogenies (e.g. nuclear rDNA, β-tubulin, γ-actin, Elongation factor EF-1α). These genes were ranked among the best-performing ones and resolved accurately taxa relationships in each of the four non-model groups of fungi considered. We envision that PHYLORPH will constitute a useful tool for obtaining new and accurate phylogenetic markers to resolve relationships between closely related non-model fungal species