74 research outputs found
Techniques for precision interferometry in space
No full textGravitational waves are an important prediction of Einstein's General theory of Relativity. Derived as a solution to the Einstein field equations, they are predicted to be produced in systems where there is an asymmetric acceleration of matter, and exist as a time varying quadrupolar distortion in spacetime.
Due to the rich variety of scientifically interesting astrophysical sources predicted to be producing gravitational radiation, there is significant international effort directed towards their detection. A large network of ground based interferometric detectors is in operation, with upgrades to increase sensitivity already in progress. They operate on the principle of measuring the time varying displacement in the interferometer path length an incident gravitational wave will induce. However, the predicted amplitude of gravitational waves requires the measurement to be made over several kilometres with a displacement sensitivity of less than 10^-18m/sqrt(Hz).
Ground based detectors operate in the ~10-10000 Hz region, and are fundamentally limited at the low frequency end by the noisy gravitational environment of the Earth. To enable detection of low frequency sources, LISA - the Laser Interferometer Space Antenna - is a planned mission to place an interferometric gravitational wave detector in space, sensitive to gravitational waves in the 0.1-1000 mHz region. Consisting of a triangular constellation of three spacecraft, LISA will aim to detect gravitational waves by monitoring the fluctuation in the separation between free-falling test masses over a baseline of 5 million kilometres with an accuracy of around 10pm/sqrt(Hz).
To demonstrate that LISA technology, such as the ability to place test masses into a suitably quiet gravitational free-fall, is viable, a precursor mission - LISA Pathfinder - will launch in the next few years. LISA Pathfinder will monitor the relative displacement between two free-falling inertial test masses using an interferometer, with the goal of verifying that the required quality of free-fall is achievable in LISA. This work presented in this thesis relates to the development of interferometry for LISA Pathfinder and LISA, the construction of the LISA Pathfinder flight model interferometer, and initial work on developing the interferometer for LISA.
The interferometers required for LISA and LISA Pathfinder must be constructed to be durable enough to survive launch and stable enough to measure displacements of a few picometres at frequencies down to a few mHz. Further, to help minimise noise from sources such as residual jitter of the test masses, the beams which probe the test masses must be aligned to within ±25 micrometers of the nominal reflection point. Using ultra low expansion substrates like Zerodur, and attaching optical components with hydroxide catalysis bonding offers one solution which can provide the durability and stability required.
To achieve the accuracy of beam positioning, a system which allows measurement of absolute propagation direction of a laser beam was developed. Combined with a coordinate measuring machine, this allows the absolute position of a mm-scale laser beam to be measured with an accuracy of around ±5 micrometers and ±20 microradians. This system can operate in two modes: first as a measurement system allowing measurement of an existing beam; and secondly as a target, where it can be positioned to a desired theoretical (such as the nominal reflection point of a test mass) and a beam can be aligned onto it. Combined with a method of precision adjusting optical components at the sub-micron and microradian level prior to hydroxide catalysis bonding, it enables absolute alignment of ultra-stable interferometers to micron level.
Using these techniques, the flight model interferometer for LISA Pathfinder was successfully constructed to meet the alignment and performance requirements. The control system that will maintain the test masses in near free-fall requires a very accurate measure of the attitude of the test masses. This measurement will be provided by the interferometer using differential wavefront sensing (DWS). The flight model interferometer was calibrated to establish the coupling factors between the DWS read-out and the attitude of the test mass to ensure maximum performance of the control system.
Building upon the experience gained in developing and building the LISA Pathfinder interferometer, a prototype of the LISA optical bench is in development. The LISA interferometer is significantly more complicated than that of LISA Pathfinder. Some of its features include: imaging systems to minimise coupling of beam tilt to displacement noise; a precision beam expander to generate a beam appropriate for the telescope; a redundant fibre injector system, creating two beams collinear to within a few microns and 10-20 microradians; and polarisation optics for beam steering. The development and current state of the design for the prototype optical bench is presented, along with an overview of its features
Construction of rugged, ultrastable optical assemblies with optical component alignment at the few microradian level
No full textA method for constructing quasimonolithic, precision-aligned optical assemblies is presented. Hydroxide-catalysis bonding is used, adapted to allow optimization of component fine alignment prior to the bond setting. We demonstrate the technique by bonding a fused silica mirror substrate to a fused silica baseplate. In-plane component placement at the submicrometer level is achieved, resulting in angular control of a reflected laser beam at the sub-10-μrad level. Within the context of the LISA Pathfinder mission, the technique has been demonstrated as suitable for use in space-flight applications. It is expected that there will also be applications in a wide range of areas where accuracy, stability, and strength of optical assemblies are important
Lost in translation: The power of language
No full textThis paper brings together ideas about culture, difference and the importance of translation and interpretation in educational contexts. A key component of this paper is the promotion of curriculum based on a dialogical framework.The paper developed an argument of the impossibility of perfect translation, and points towards linguistic hospitality as the ethical dimension to the inadequate representation of the ‘other’. It highlights the complex role of teacher as translator – an activity that is relational and creative - and the child in translation as a process of metamorphosis rather than reproduction. We were asked to submit this paper to a special Special Issue on Power and Language for Education Philosophy and Theory after presenting a paper on a similar theme at the Philosophy of Education Conference, Brisbane, December, 2008. This special issue is to be re-published in book form in 2012. Educational Philosophy and Theory has an ERA research journal ranking of A+ and a Q score of 19.93. This paper brings together ideas about culture, difference and the importance of translation and interpretation in educational contexts. A key component of this paper is the promotion of curriculum based on a dialogical framework.The paper developed an argument of the impossibility of perfect translation, and points towards linguistic hospitality as the ethical dimension to the inadequate representation of the ‘other’. It highlights the complex role of teacher as translator – an activity that is relational and creative - and the child in translation as a process of metamorphosis rather than reproduction. We were asked to submit this paper to a special Special Issue on Power and Language for Education Philosophy and Theory after presenting a paper on a similar theme at the Philosophy of Education Conference, Brisbane, December, 2008. This special issue is to be re-published in book form in 2012. Educational Philosophy and Theory has an ERA research journal ranking of A+ and a Q score of 19.93. My contribution Each author contributed equally to the structure, organization, development and writing of the paper. Peter Fitzsimons contributed the writing on Nietszche, and I contributed the writing on linguistic hospitality. We worked equally on the theorizing of translation in regard to Foucault and Derrida. My specific contribution develops Ricoeurean concepts in particular the writing on linguistic hospitality. This concept promotes the importance of shared understandings, the role of metaphor in creating new understandings, and the critical role of readership in interpretation
Measuring Empowerment: A Program Evaluation of the Youth Organization Sal y Luz in Medellin, Colombia
No full textThe concept of empowerment is critical to the development of youths\u27 ability to recognize themselves as stakeholders in their community and as participants in civic engagement (Kohlfeldt, 2011; Langhout, 2010). However, programs or groups with goals to foster ideals of empowerment face myriad challenges, such as the social and environmental context of the youth, and the status that the youth maintain in their communities (Kohlfeldt, 2011; Langhout, 2010; Zimmerman, 2004). To measure empowerment, the current study draws observations from a focus-group affiliated with a youth-centered community group known as Sal y Luz located in a disadvantaged comuna of Medellin, Colombia. Using photo elicitation, the group took pictures in response to eleven different concepts associated with feelings of empowerment. Then, each participant attended a focus-group discussion of the photos to assist the researcher with photo interpretation. The input from both the photos and the focus group discussions reveal that this particular group displays the ideals of empowerment to a greater extent than anticipated; for example, in response to a prompt regarding the makeup of community, both the photos and related discussion centered on the idea that community is made up of multiple factors, including geographical location, borders, people, job availability and cultural context. The group was quick to note that these are all things that must be taken into consideration when they\u27re planning their next projects, especially the risks that are taken by crossing neighborhood borders. The final product aims to advise Sal y Luz administration regarding some limitations to empowerment identified by the study, as well as allow the author to learn more about youth empowerment associated with an organization that does look exclusively at youth-dedicated issues. Although the study took place in the span of only eight days, such an evaluation process brought on by the study lends support to Sal y Luz\u27s efforts at establishing a more vocal and active youth in an historically violent and complex area of Medellin, Colombia
Aspects of optical meterology systems for space-borne gravitational wave detectors
No full textThis thesis is an account of the research carried out by the author in developing a range of necessary components for future gravitational wave detectors, between October 2009 and September 2013 in the Institute for Gravitational Research at the University of Glasgow.
The aims of this thesis were to design, develop and test technologies which enable future space-borne interferometric gravitational wave detectors.
The research was as part of a large international collaboration focused on developments for a space-borne gravitational wave detector by the name of LISA an all of her variants.
At the university of Glasgow this collaboration included H.Ward, D.I. Robertson, C. J. Killow, E. D. Fitzsimons, M. Perreur-Lloyd and the author
Mechanisation of Precision Placement and Catalysis Bonding of Optical Components
No full textPrecision-aligned, ultra-stable optical assemblies are needed for an increasing number of space applications, in areas such as science, metrology and geodesy
Automated precision alignment of optical components for hydroxide catalysis bonding
No full textWe 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
RESTORATION OF MOTOR AND NON-MOTOR FUNCTIONS BY NEUROTROPHIC FACTORS IN NONHUMAN PRIMATES WITH DOPAMINE DEPLETION
No full textParkinson’s disease (PD) is a progressive debilitating neurodegenerative disorder characterized by resting tremor, rigidity, bradykinesia and postural instability. As the disease progresses there is a loss of dopamine (DA) neurons in the substantia nigra projecting to the various forebrain and sub-cortical regions. Current treatments for PD are unable to prevent or curtail the neurodegenerative process; so rescuing remaining dopamine in the mid-brain has been the recent focus of research examining the effectiveness of neurotrophic factors (NTFs) in the treatment of PD. In this dissertation, the ability of three novel, recently discovered NTFs to restore DA neurons and motor function in a nonhuman primate model of PD was examined. The NTFs were Cerebral Dopamine Neurotrophic Factor (CDNF) and two variants of Neurturin (NRTN), N2 and N4, that have mutations that prevent binding to heparin sulfate binding sites in the brain. These studies used the unilateral low dose (0.15 ± 0.001 mg/kg) monkey 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD to cause loss of DA neurons. Six groups of monkeys were studied: vehicle-treated (negative control), Glial Cell-line Derived Neurotropic Factor (GDNF, positive control), two groups of CDNF-treated monkeys (450 μg and 150 μg), and N2 and N4-treated groups. After MPTP, monkeys developed moderate symptoms of PD (PD rating scale score=7.9±0.5 on a scale of 0-22, p<0.001), motor dysfunction and increased daytime sleepiness. After three months of infusions, all three NTFs (150 μg CDNF, N2 and N4) significantly increased the number of DA neurons in the substantia nigra, p=0.03, and improved parkinsonian symptoms measured by rating scale, p<0.001. Most motor functions were significantly correlated with the number of DA neurons in the substantia nigra. N4 significantly improved daytime sleep duration, bouts and wake-latency (p=0.02, p=0.06 and p=0.02, respectively). In summary, CDNF, N2 and N4 trophic factors are neurorestorative to DA neurons, motor function is tightly correlated with DA neuronal number, and N4 improved the non-motor symptom of increased daytime sleepiness in this monkey PD model. These factors hold promise for clinical therapy for PD patients
PACE-UP (Pedometer and consultation evaluation - UP) – a pedometer-based walking intervention with and without practice nurse support in primary care patients aged 45–75 years: study protocol for a randomised controlled trial
No full text© 2013 Harris et al.; licensee BioMed Central Ltd.
This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated.Background - Most adults do not achieve the 150 minutes weekly of at least moderate intensity activity recommended for health. Adults’ most common physical activity (PA) is walking, light intensity if strolling, moderate if brisker. Pedometers can increase walking; however, most trials have been short-term, have combined pedometer and support effects, and have not reported PA intensity. This trial will investigate whether pedometers, with or without nurse support, can help less active 45–75 year olds to increase their PA over 12 months. Methods/design: Design: Primary care-based 3-arm randomized controlled trial with 12-month follow-up and health economic and qualitative evaluations. Participants: Less active 45–75 year olds (n = 993) will be recruited by post from six South West London general practices, maximum of two per household and households randomised into three groups. Step-count and time spent at different PA intensities will be assessed for 7 days at baseline, 3 and 12 months by accelerometer. Questionnaires and anthropometric assessments will be completed. Intervention: The pedometer-alone group will be posted a pedometer (Yamax Digi-Walker SW-200), handbook and diary detailing a 12-week pedometer-based walking programme, using targets from their baseline assessment. The pedometer-plus-support group will additionally receive three practice nurse PA consultations. The handbook, diary and consultations include behaviour change techniques (e.g., self-monitoring, goal-setting, relapse prevention planning). The control group will receive usual care.
Outcomes: Changes in average daily step-count (primary outcome), time spent sedentary and in at least moderate intensity PA weekly at 12 months, measured by accelerometry. Other outcomes include change in body mass index, body fat, self-reported PA, quality of life, mood and adverse events. Cost-effectiveness will be assessed by the incremental cost of the intervention to the National Health Service and incremental cost per change in step-count and per quality adjusted life year. Qualitative evaluations will explore reasons for trial non-participation and the interventions’ acceptability. Discussion- The PACE-UP trial will determine the effectiveness and cost-effectiveness of a pedometer-based walking intervention delivered by post or practice nurse to less active primary care patients aged 45–75 years old. Approaches to minimise bias and challenges anticipated in delivery will be discussed.This project was funded by the National Institute for Health Research Health Technology Assessment (NIHR HTA) Programme (project number HTA 10/32/02) and will be published in full in Health Technology Assessment
The shortest way to end disputes about religion. [electronic resource] : In two parts. By the Rev. Robert Manning, Author of England's Conversion and Reformation compared.
No full textWith two final advertisement leaves.Electronic reproduction.English Short Title Catalog,Reproduction of original from British Library
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