Analysis of KrF excimer laser beam modification resulting from ablation under closed thick film flowing filtered water

The application of closed thick film liquid to immerse the ablation etching mechanism of an excimer laser poses interesting possibilities concerning debris control, modification of machined feature topography and modification of ablation rate. Further more, these parameters have been shown to be dependant on flow velocity; hence offering further user control of machining characteristics. However the impact of this technique requires investigation. This contribution offers comparison of the calculated ablation pressure and the effect on feature surface characteristics given for laser ablation of bisphenol A polycarbonate using KrF excimer laser radiation in ambient air against laser ablation of the same substrate under closed thick film flowing filtered water immersion. Also, the impact of such immersion equipment on the optical performance of the micromachining centre used is quantified and reviewed. The pressure is calculated to have risen some 53% when using the liquid immersed ablation technique. This increase in pressure is proposed to have promoted the frequency of surface Plasmons and asperities with a surface area less than 16 µm2. The focal length of the optical system was accurately predicted to be increased by 2.958 mm when using the equipment composed of a 5 mm thick ultraviolet grade fused silica window covering a 1.5 mm thick film of filtered water flowing at 1.85 m/s. This equipment was predicted to have increased the optical depth of focus via reduction in the angle of convergence of the two defining image rays, yet the perceived focus, measured by mean feature wall angle as a discrete indication, was found to be 25% smaller when using the closed thick film flowing filtered water immersion technique than when laser ablating in ambient air. A compressed plume interaction is proposed as a contributing factor in this change

Effects of closed immersion filtered water flow velocity on the ablation threshold of bisphenol A polycarbonate during excimer laser machining

A closed flowing thick film filtered water immersion technique ensures a controlled geometry for both the optical interfaces of the flowing liquid film and allows repeatable control of flow-rate during machining. This has the action of preventing splashing, ensures repeatable machining conditions and allows control of liquid flow velocity. To investigate the impact of this technique on ablation threshold, bisphenol A polycarbonate samples have been machined using KrF excimer laser radiation passing through a medium of filtered water flowing at a number of flow velocities, that are controllable by modifying the liquid flow rates. An average decrease in ablation threshold of 7.5% when using turbulent flow velocity regime closed thick film filtered water immersed ablation, compared to ablation using a similar beam in ambient air; however, the use of laminar flow velocities resulted in negligible differences between closed flowing thick film filtered water immersion and ambient air. Plotting the recorded threshold fluence achieved with varying flow velocity showed that an optimum flow velocity of 3.00 m/s existed which yeilded a minimum ablation threshold of 112 mJ/cm2. This is attributed to the distortion of the ablation plume effected by the flowing immersion fluid changing the ablation mechanism: at laminar flow velocities Bremsstrahlung attenuation decreases etch rate, at excessive flow velocities the plume is completely destroyed, removing the effect of plume etching. Laminar flow velocity regime ablation is limited by slow removal of debris causing a non-linear etch rate over ‘n’ pulses which is a result of debris produced by one pulse remaining suspended over the feature for the next pulse. The impact of closed thick film filtered water immersed ablation is dependant upon beam fluence: high fluence beams achieved greater etch efficiency at high flow velocities as the effect of Bremsstrahlung attenuation is removed by the action of the fluid on the plume; low fluences loose efficiency as the beam makes proportionally large fluence losses at it passes through the chamber window and immersion medium

Interpreting Language in Context in CommandTalk

This paper will focus on how two representations of context are used in CommandTalk to correctly interpret the user's spoken utterances: situational context represents the current state of the simulation, and linguistic context represents the history of the user's linguistic acts

The length of ministerial tenure in the UK 1945-1997

We analyse the determinants of ministerial hazard rates in the UK from 1945-1997. We focus on three sets of attributes i) personal characteristics of the minister; ii) political characteristics of the minister and iii) characteristics pertaining to the government in which the minister serves. We find that educational background increases ministers’ capacity to survive, that female ministers have lower hazard rates and older ministers have higher hazard rates. Experienced ministers have higher hazard than newly appointed ministers. Ministerial rank increases a ministers’ capacity to survive, with full cabinet members having the lowest hazard rates in our sample. We use different strategies to controls for the characteristics of the government the ministers serve in. Our results are robust to any of these controls

Individual and Collective Performance and the Tenureof British Ministers 1945-1997

We study the effects of individual and collective ministerial performance on the length oftime a minister serves in British government from 1945-97, using the number ofresignation calls for a minister as an individual performance indicator and the cumulativenumber of such calls as an indicator of government performance. Our analysis lendssupport to a 'two-strike rule': ministers facing a second call for their resignation have asignificantly higher hazard than those facing their first, irrespective of the performance ofthe government. A minister's hazard rate is decreasing in the cumulative number ofresignation calls; but conditional on receiving a first resignation call, the hazard rateincreases with the number of calls that all government ministers have faced in the past.Our message is that collective ministerial performance is a key determinant of whether aminister survives his first resignation call.

Cerium Oxide Nanoparticles Act As A Unique Catalyst And Scavenge Nitric Oxide And Peroxynitrite And Decrease Rns In Vitro And In Vivo

Cerium oxide nanoparticles (CeO2 NPs)(nanoceria) have been shown to possess a substantial oxygen storage capacity via the interchangeable surface reduction and oxidation of cerium atoms, cycling between the Ce4+ and Ce3+ redox states. Reduction of Ce4+ to Ce3+ causes oxygen vacancies or defects on the surface of the crystalline lattice structure of the particles, generating a cage for redox reactions to occur. The study of the chemical and biological properties of CeO2 NPs has expanded recently, and the methods used to synthesize these materials are also quite diverse. This has led to a plethora of studies describing various preparations of CeO2 NPs for potential use in both industry and for biomedical research. Our own work has centered on studies that measure the ability of water-based CeO2 NPs materials to reduce reactive oxygen and nitrogen species in biological systems, and correlating changes in surface chemistry and charge to the catalytic nature of the particles. The application in experimental and biomedical research of CeO2 NPs began with the discovery that water-based cerium oxide nanoparticles could act as superoxide dismutase mimetics followed by their ability to reduce hydrogen dioxide similar to catalase. While their ROS scavenging ability was well established, their ability to interact with specific RNS species, specifically nitric oxide (·NO) or peroxynitrite (ONOO- ) was not known. The studies described in this dissertation focus on the study of RNS and cerium oxide nanoparticles. Our in vitro work revealed that CeO2 NPs that have higher levels of reduced cerium sites (3+) at the surface (which are effective SOD mimetics) are also capable of accelerating the iv decay of peroxynitrite in vitro. In contrast, CeO2 NPs that have fewer reduced cerium sites at the particle surface (which also exhibit better catalase mimetic activity) have ·NO scavenging capabilities as well as some reactivity with peroxynitrite. Our studies and many others have shown cerium oxide nanoparticles can reduce ROS and RNS in cell culture or animal models. The accumulation of ROS and RNS is a common feature of many diseases including Alzheimer’s disease (AD). Testing our CeO2 NPS in cortical neurons, we used addition of Aβ peptide as an AD model system. CeO2 NPs delayed Aβ-induced mitochondrial fragmentation and neuronal cell death. When mitochondrial ROS levels are increased, mitochondrial fission is activated by DRP1 S616 phosphorylation. Specifically, our studies showed the reduction of phosphorylated DRP1 S616 in the presence of CeO2 NPs. Results from our studies have begun to unravel the molecule mechanism behind the catalytic nature of how CeO2 NPs reduce ROS/RNS in biological systems and represents an important step forward to test the potential neuroprotective effects of CeO2 NPs in model systems of AD. A plethora of studies describing various preparations of CeO2 NPs for potential use in both industry and for biomedical research have been described in the past five years. It has become apparent that the outcomes of CeO2 NPs exposure can vary as much as the synthesis methods and cell types tested. In an effort to understand the disparity in reports describing the toxicity or protective effects of exposure to CeO2 NPs, we compared CeO2 NPs synthesized by three different methods; H2O2 (CNP1), NH4OH (CNP2) or hexamethylenetetramine (HMT-CNP1). Exposure to HMT-CNP1 led to reduced metabolic activity (MTT) at a 10-fold lower concentration than CNP1 or CNP2 and surprisingly, exposure to HMT-CNP1 led to substantial v decreases in the ATP levels. Mechanistic studies revealed that HMT-CNP1 and CNP2 exhibited robust ATPase (phosphatase) activity, whereas CNP1 lacked ATPase activity. HMT-CNP1 were taken up into HUVECs far more efficiently than the other preparations of CeO2 NPs. Taken together, these results suggest the combination of increased uptake and ATPase activity of HMT-CNP1 may underlie the mechanism of the toxicity of this preparation of CeO2 NPs, and may suggest ATPase activity should be considered when synthesizing CeO2 NPs for use in biomedical applications. Overall the studies have uncovered two new catalytic activities for water-based CeO2 NPs (·NO scavenging and accelerated decay of peroxynitrite), demonstrated their ability to reduce RNS in an AD cell culture model as well as identifying a catalytic activity (phosphatase) that may underlie the observed toxicity of CeO2 NPs reported in other studies

It’s the government, stupid: how governments blame citizens for their own policies

Governments have developed a convenient habit of blaming social problems on their citizens, placing too much emphasis on personal responsibility and pursuing policies to ‘nudge’ their citizens to better behaviour. Keith Dowding argues that responsibility for many of our biggest social crises should be laid at the feet of politicians

A perspective from Kazakhstan

Purpose – The purpose of this paper is to explore the role of the national university in developing sustainable cultural heritage digital preservation practices. Design/methodology/approach – Using Nazarbayev University in Astana, Kazakhstan as an example, this paper discusses current development of cultural heritage digital collections, and looks to the university library’s impact on nationwide digital practices development. Findings – While the university and its digital collections are still nascent, NU will likely have a large impact on the creation of sustainable digital cultural heritage preservation practices due to its international visibility and direct connection to stakeholders. Originality/value – Focused on developing nations, this paper will be of special interest to librarians working in countries facing similar challenges, such as other CIS nations