Interaction between U/UO2 bilayers and hydrogen studied by in-situ X-ray diffraction

This paper reports experiments investigating the reaction of H$_{2}$ with uranium metal-oxide bilayers. The bilayers consist of $\leq$ 100 nm of epitaxial $\alpha$-U (grown on a Nb buffer deposited on sapphire) with a UO$_{2}$ overlayer of thicknesses of between 20 and 80 nm. The oxides were made either by depositing via reactive magnetron sputtering, or allowing the uranium metal to oxidise in air at room temperature. The bilayers were exposed to hydrogen, with sample temperatures between 80 and 200 C, and monitored via in-situ x-ray diffraction and complimentary experiments conducted using Scanning Transmission Electron Microscopy - Electron Energy Loss Spectroscopy (STEM-EELS). Small partial pressures of H$_{2}$ caused rapid consumption of the U metal and lead to changes in the intensity and position of the diffraction peaks from both the UO$_{2}$ overlayers and the U metal. There is an orientational dependence in the rate of U consumption. From changes in the lattice parameter we deduce that hydrogen enters both the oxide and metal layers, contracting the oxide and expanding the metal. The air-grown oxide overlayers appear to hinder the H$_{2}$-reaction up to a threshold dose, but then on heating from 80 to 140 C the consumption is more rapid than for the as-deposited overlayers. STEM-EELS establishes that the U-hydride layer lies at the oxide-metal interface, and that the initial formation is at defects or grain boundaries, and involves the formation of amorphous and/or nanocrystalline UH$_{3}$. This explains why no diffraction peaks from UH$_{3}$ are observed. {\textcopyright British Crown Owned Copyright 2017/AWE}Comment: Submitted for peer revie

Further Developments in Gold-stud Bump Bonding

As silicon detectors in high energy physics experiments require increasingly complex assembly procedures, the availability of a wide variety of interconnect technologies provides more options for overcoming obstacles in generic R&D. Gold ball bonding has been a staple in the interconnect industry due to its ease of use and reliability. However, due to some limitations in the standard technique, alternate methods of gold-stud bonding are being developed. This paper presents recent progress and challenges faced in the development of double gold-stud bonding and 0.5 mil wire gold-stud bonding at the UC Davis Facility for Interconnect Technology. Advantages and limitations of each technique are analyzed to provide insight into potential applications for each method. Optimization of procedures and parameters is also presented.Comment: TWEPP 2011 conference proceeding, 8 pages, 7 figure

Transforming gender relations in an ageing world : a policy discussion paper

This policy discussion paper explores the way in which intersecting inequalities affect life courses and gender relations in older age. It argues for a gendered lifecourse perspective within the Sustainable Development Goals framework

Ocean-atmosphere interactions in the tropical Atlantic seasonal cycle and multidecadal variability of ENSO

The interaction between the ocean and atmosphere drives changes in the climate system in a wide variety of timescales. The strong annual cycle in the equatorial Atlantic, especially over the east, has been object of extensive research but the role of ocean-atmosphere interactions in driving the seasonal cycle remains to be fully understood in this region. The west African monsoon and the Atlantic cold tongue are the main phenomena controlling the seasonal variability in the equatorial Atlantic and a better understanding of their interaction is crucial for a complete comprehension of the dynamics of the annual cycle. Ocean atmosphere interactions are the main driver of ENSO, which is the leading mode of ocean-atmosphere variability at interannual timescales in the tropics. ENSO properties have experienced large changes in the last few decades but the drivers behind those changes are still in debate. The three studies presented in this thesis are based in climate model simulations. In the first and second papers the atmosphere and ocean components of NorESM model are used to investigate the dynamics of the seasonal cycle in the equatorial Atlantic. The third paper focuses on the identification of multidecadal modulation of ENSO properties by means of a strongly simplified model: the conceptual recharge oscillator model. The first part of this thesis presents an in-depth study of the mechanisms of the seasonal cycle in the equatorial Atlantic with special focus on the quantification of the role of the coupling between the ocean and the atmosphere. My results show that thermodynamic coupling is the main driver of the seasonal cycle in the western equatorial Atlantic and indicate that the dynamical Bjerknes feedback plays a secondary role. In the east, ocean dynamics and the monsoon are the main drivers of the seasonal cycle in the ocean and atmosphere, respectively, with ocean-atmosphere interactions contributing to the amplification of the annual cycle. In the second part of this thesis, I study the changes in observed ENSO properties at multidecadal timescales. The large observed changes in ENSO in the recent decades are reproduced with a conceptual model based on the recharge and discharge of the Pacific equatorial upper ocean heat content. This indicates that dynamic coupling is the main driver of ENSO in the last decades with the thermocline feedback being the mechanism responsible of the amplification of the SST anomalies in the eastern equatorial Pacific

Unexpected phase locking of magnetic fluctuations in the multi-k magnet USb

The spin waves in the multi-k antiferromagnet USb soften and become quasielastic well below the antiferromagnetic ordering temperature TN. This occurs without a magnetic or structural transition. It has been suggested that this change is in fact due to dephasing of the different multi-k components: a switch from 3-k to 1-k behavior. In this work, we use inelastic neutron scattering with tridirectional polarization analysis to probe the quasielastic magnetic excitations and reveal that the 3-k structure does not dephase. More surprisingly, the paramagnetic correlations also maintain the same clear phase correlations well above TN (up to at least 1.4TN)