Systematic study and characterization of silicon carbide films produced via micro cold spray

Micro cold spray (MCS) has emerged in the past three decades as a novel technology for depositing dense, patterned, thick films without the need for high temperature treatments or chemical precursors. MCS film deposition has been demonstrated with a number of ceramics, but very limited work has been published on the deposition of silicon carbide (SiC), which possesses a high melting temperature and notable wear and chemical resistance properties. This dissertation aims to understand particle deformation and film formation mechanisms that occur during MCS through computational and experimental studies of SiC deposition. A molecular dynamics simulation study is first presented of SiC particle impact on an atomically flat SiC substrate by systematically varying particle impact velocity, impact angle, and particle orientation. Quantitative analysis of the simulations indicates that impact conditions favoring amorphization also favor increased deformation and deposition efficiency, establishing amorphization as the primary mechanism for SiC particle deformation during MCS deposition. The remaining studies focus on SiC films experimentally deposited using a custom MCS machine. In the next chapter, observation of SiC film deposition by multiple powder feedstocks of different particle size distributions is discussed. Additionally, the effect of particle impact velocity is explored by systematic variation of MCS processing conditions using powder feedstock with a nominal size of 500 nm to deposit SiC films on 304 stainless steel. Imaging performed via scanning electron microscopy (SEM) and atomic force microscopy indicate that the films contain larger microstructural features and lower porosity with increasing particle impact velocity. Further characterization is performed on 25 × 25 mm films. Optical profilometry and ion milling with SEM imaging is used to characterize film thickness and x-ray diffraction is used to characterize crystallinity. Adhesion and wear/erosion testing is used to assess the strength and wear resistance of the films. Results indicate that the films are primarily amorphous, consolidated, and are 2–11 μm thick. The adhesion strength of the films exceeds 5 MPa, but measured wear/erosion exceeded that of the reference substrate. The low wear resistance was attributed to the significant roughness of the substrate which suggests improved properties may be possible.Materials Science and Engineerin

Study of the Ethiopian live cattle and beef value chain

Rats achieve remarkable texture discriminations by sweeping their facialwhiskers along surfaces. This work explores how neurons at two levels of the sensory pathway, trigeminal ganglion and barrel cortex, carry information about such stimuli. We identified two biologically plausible coding mechanisms, spike counts and patterns, and used “mutual information” to quantify how reliably neurons in anesthetized rats reported texture when “decoded” according to these candidate mechanisms. For discriminations between surfaces of different coarseness, spike counts could be decoded reliably and rapidly (within 30 ms after stimulus onset in cortex). Information increased as responseswere considered as spike patterns with progressively finer temporal precision. At highest temporal resolution (spike sequences across six bins of 4ms), the quantity of “information” in patterns rose 150% for ganglion neurons and 110% for cortical neurons above that in spike counts. In some cases, patterns permitted discriminations not supported by spike counts alone

A stochastic proximal alternating method for non-smooth non-convex optimization

We introduce SPRING, a novel stochastic proximal alternating linearized minimization algorithm for solving a class of non-smooth and non-convex optimization problems. Large-scale imaging problems are becoming increasingly prevalent due to advances in data acquisition and computational capabilities. Motivated by the success of stochastic optimization methods, we propose a stochastic variant of proximal alternating linearized minimization (PALM) algorithm \cite{bolte2014proximal}. We provide global convergence guarantees, demonstrating that our proposed method with variance-reduced stochastic gradient estimators, such as SAGA \cite{SAGA} and SARAH \cite{sarah}, achieves state-of-the-art oracle complexities. We also demonstrate the efficacy of our algorithm via several numerical examples including sparse non-negative matrix factorization, sparse principal component analysis, and blind image deconvolution.Comment: 28 pages, 11 page appendi

Images in cardiovascular medicine. Cardiac tuberculoma.

A 43-year–old man with a 6-month history of cough, dyspnea, nocturnal sweats, and weight loss was reviewed in the clinic. Clinical examination revealed cervical lymphadenopathy and indicated constrictive physiology. Initial tests, including chest radiography, sputum examination, QuantiFERON-TB Gold test, and lymph node biopsy, were unyielding. HIV serology was nonreactive

Buried alive: Aquatic plants survive in ‘ghost ponds’ under agricultural fields

The widespread loss of wetlands due to agricultural intensification has been highlighted as a major threat to aquatic biodiversity. However, all is not lost as we reveal that the propagules of some aquatic species could survive burial under agricultural fields in the sediments of ‘ghost ponds’ - ponds in-filled during agricultural land consolidation. Our experiments showed at least eight aquatic macrophyte species to germinate from seeds and oospores, following 50–150 years of dormancy in the sediments of ghost ponds. This represents a significant proportion of the expected macrophyte diversity for local farmland ponds, which typically support between 6 and 14 macrophyte species. The rapid (< 6 months) re-colonisation of resurrected ghost ponds by a diverse aquatic vegetation similarly suggests a strong seed-bank influence. Ghost ponds represent abundant, dormant time capsules for aquatic species in agricultural landscapes around the globe, affording opportunities for enhancing landscape-scale aquatic biodiversity and connectivity. While reports of biodiversity loss through agricultural intensification dominate conservation narratives, our study offers a rare positive message, demonstrating that aquatic organisms survive prolonged burial under intensively managed agricultural fields. We urge conservationists and policy makers to consider utilizing and restoring these valuable resources in biodiversity conservation schemes and in agri-environmental approaches and policies

Written evidence from the NCECJS to the HoC Justice Committee: implications of Brexit for justice

Forensic biometric sharing within the EU (Prüm) is a specialist form of cooperation. Nevertheless research into this activity and the context in which it occurs places some of the implications of Brexit into sharp relief: a) Brexit (in any form) will not result in a major reduction in the need for effective criminal justice and security cooperation. The UK will still receive millions of foreign citizens a year and a very small proportion of them will be serious criminals who present major threats. The challenge is to identify this small group within the generally law-abiding and tax-paying crowd. b) The effectiveness, continued extension and form of such cooperation will also have a major impact on the safety and rights of UK citizens abroad, whether they are in the diaspora or simply travelling for work or holidays. c) The value of individual criminal justice and security cooperation agreements (however good) will only be realised fully within a comprehensive framework (e.g. with access to the European Arrest Warrant (EAW)) that is underpinned institutionally (e.g. by Europol and Eurojust) and subject to parliamentary and legal scrutiny. d) UK global economic and political status was significantly reduced on 23rd June and a badly handled Brexit will further diminish this country’s influence. There will be little or no scope for UK bespoke arrangements for police and judicial cooperation or scientific standardisation. e) The resilience of both UK science and technology, and our criminal justice system – including responses to transnational cybercrime - are likely to be weakened significantly if British forensic scientists are no longer influential within EU collaborative scientific research, professional working groups and standardisation decisions. Opting-out of the EU arrangements, such as Prüm, the European Criminal Records Information System (ECRIS) and EAW, to which the UK belongs only after recent Protocol 36 reviews by criminal justice professionals, government and Parliament would be inexplicable and may prove to be reckless