Linear Stochastic Fluid Networks: Rare-Event Simulation and Markov Modulation

We consider a linear stochastic fluid network under Markov modulation, with a focus on the probability that the joint storage level attains a value in a rare set at a given point in time. The main objective is to develop efficient importance sampling algorithms with provable performance guarantees. For linear stochastic fluid networks without modulation, we prove that the number of runs needed (so as to obtain an estimate with a given precision) increases polynomially (whereas the probability under consideration decays essentially exponentially); for networks operating in the slow modulation regime, our algorithm is asymptotically efficient. Our techniques are in the tradition of the rare-event simulation procedures that were developed for the sample-mean of i.i.d. one-dimensional light-tailed random variables, and intensively use the idea of exponential twisting. In passing, we also point out how to set up a recursion to evaluate the (transient and stationary) moments of the joint storage level in Markov-modulated linear stochastic fluid networks

A low cost direct writing process for flexible circuit and interconnect fabrication

This thesis investigates the development of a low cost fabrication process for flexible electronics and interconnects. By using a ‘direct writing’ process, the use of vacuum-­‐based metal evaporation and photoresist steps is not necessary and so less complex equipment is needed. The process forms silver embedded on top of a polyimide substrate and was first tested using a UV laser to perform writing before switching to a blue laser due to excessive substrate degradation observed from UV exposures. The blue light was combined with a biologically friendly photo reducing agent, which was found to be much more efficient at the creation of silver. The methods of silver formation by various means are the main focus of investigation in this thesis but process expansion and improvement were the main goals. To this end, a chemical, rather than light-­‐based, process for silver creation was found to produce more consistent silver coatings, however the patterning by this method was found to be more challenging. The process was also extended to a different substrate in polyetherimide

Automated precision alignment of optical components for hydroxide catalysis bonding

We describe an interferometric system that can measure the alignment and separation of a polished face of a optical component and an adjacent polished surface. Accuracies achieved are ∼ 1μrad for the relative angles in two orthogonal directions and ∼ 30μm in separation. We describe the use of this readout system to automate the process of hydroxide catalysis bonding of a fused-silica component to a fused-silica baseplate. The complete alignment and bonding sequence was typically achieved in a timescale of a few minutes, followed by an initial cure of 10 minutes. A series of bonds were performed using two fluids - a simple sodium hydroxide solution and a sodium hydroxide solution with some sodium silicate solution added. In each case we achieved final bonded component angular alignment within 10 μrad and position in the critical direction within 4 μm of the planned targets. The small movements of the component during the initial bonding and curing phases were monitored. The bonds made using the sodium silicate mixture achieved their final bonded alignment over a period of ∼ 15 hours. Bonds using the simple sodium hydroxide solution achieved their final alignment in a much shorter time of a few minutes. The automated system promises to speed the manufacture of precision-aligned assemblies using hydroxide catalysis bonding by more than an order of magnitude over the more manual approach used to build the optical interferometer at the heart of the recent ESA LISA Pathfinder technology demonstrator mission. This novel approach will be key to the time-efficient and low-risk manufacture of the complex optical systems needed for the forthcoming ESA spaceborne gravitational waves observatory mission, provisionally named LISA

Black ceiling tiles reduce occupational UV exposure for staff in clinical area containing phototherapy cabinets

Phototherapy clinics administer UV light to patients via phototherapy cabinets. The UV radiation from these cabinets reflects on the white ceiling tiles of the clinic and is directed towards both staff and patients in the area. This is particularly problematic for clinical technologists who must undertake dosimetry in these areas and have a particular time (often as low as 30 minutes) before they reach their maximum exposure limit. By replacing the white tiles with black alternatives which absorb the stray radiation, we have been able to reduce these reflections by almost 90%, prolonging the time to maximum exposure by nearly 10 times. We therefore present these findings to encourage similar clinics to undertake the simple protocols outlined which will significantly improve staff and patient safety.</p

Storageless and caching Tier-2 models in the UK context

Operational and other pressures have lead to WLCG experiments moving increasingly to a stratified model for Tier-2 resources, where ``fat" Tier-2s (``T2Ds") and ``thin" Tier-2s (``T2Cs") provide different levels of service. In the UK, this distinction is also encouraged by the terms of the current GridPP5 funding model. In anticipation of this, testing has been performed on the implications, and potential implementation, of such a distinction in our resources. In particular, this presentation presents the results of testing of storage T2Cs, where the ``thin" nature is expressed by the site having either no local data storage, or only a thin caching layer; data is streamed or copied from a ``nearby" T2D when needed by jobs. In OSG, this model has been adopted successfully for CMS AAA sites; but the network topology and capacity in the USA is significantly different to that in the UK (and much of Europe). We present the result of several operational tests: the in-production University College London (UCL) site, which runs ATLAS workloads using storage at the Queen Mary University of London (QMUL) site; the Oxford site, which has had scaling tests performed against T2Ds in various locations in the UK (to test network effects); and the Durham site, which has been testing the specific ATLAS caching solution of ``Rucio Cache" integration with ARC's caching layer

Black ceiling tiles reduce occupational UV exposure for staff in clinical area containing phototherapy cabinets

Phototherapy clinics administer UV light to patients via phototherapy cabinets. The UV radiation from these cabinets reflects on the white ceiling tiles of the clinic and is directed towards both staff and patients in the area. This is particularly problematic for clinical technologists who must undertake dosimetry in these areas and have a particular time (often as low as 30 minutes) before they reach their maximum exposure limit. By replacing the white tiles with black alternatives which absorb the stray radiation, we have been able to reduce these reflections by almost 90%, prolonging the time to maximum exposure by nearly 10 times. We therefore present these findings to encourage similar clinics to undertake the simple protocols outlined which will significantly improve staff and patient safety.</p