What would you do? An investigation of stated-response data

When analysing choices or policy impacts, economists generally rely on what people actually do, rather than what they say they would do. The "stated response" approach is treated with scepticism due, for example, to concerns regarding the effect of strategic or social considerations on what people say, and a belief that people may not adequately consider such a hypothetical question. This paper evaluates an example of this approach; the direct questioning of parents as to whether they would withdraw their children from school if the Familias en Accion education subsidies were withdrawn. Our results suggest that these concerns are not entirely invalid but that the stated responses do provide important information and correlate in the expected manner with child and household characteristics. We conclude by emphasising the importance of good question design, which may allow researchers to use the "stated response" method as a complement to more typical quantitative methodologies

Measuring Empowerment: A Program Evaluation of the Youth Organization Sal y Luz in Medellin, Colombia

The 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

Techniques for precision interferometry in space

Gravitational 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

Superballistic Diffusion of Entanglement in Disordered Spin Chains

We study the dynamics of a single excitation in an infinite XXZ spin chain, which is launched from the origin. We study the time evolution of the spread of entanglement in the spin chain and obtain an expression for the second order spatial moment of concurrence, about the origin, for both ordered and disordered chains. In this way, we show that a finite central disordered region can lead to sustained superballistic growth in the second order spatial moment of entanglement within the chain.Comment: 5 pages, 1 figur

Walkability Means What, To Whom?:Difficulties and Challenges in Defining Walkability

There has been considerable growth in public health research investigating the influence of the built environment on physical activity. Simultaneously, transport and planning professionals have been promoting a change from inactive to active transport modes to reduce traffic congestion and air pollution. A core concept in both areas of research is ‘walkability’. Walkable areas are varied and professional opinion on the level of walkability of an area can be contradictory. This study used a researcher-developed questionnaire to assess the environmental factors that influence walking behaviour. Professionals working within the areas of planning, architecture, politics, advocacy, public health and engineering were invited to complete the online questionnaire. All professions agreed that the presence of local quality functional walking routes, the availability of numerous destinations within walking distance and the perception of safety were all key factors that influence the walkability of an area. However, professions disagreed on the role of aesthetic factors; visual interest along a route was given a higher priority by some professions than others. It was concluded that different professions have different understandings of the concept of walkability, and future research should employ qualitative methodologies to investigate these differences further

Construction and testing of the optical bench for LISA pathfinder

eLISA is a space mission designed to measure gravitational radiation over a frequency range of 0.1–100 mHz (European Space Agency LISA Assessment Study Report 2011). It uses laser interferometry to measure changes of order $10\,{\rm pm /\sqrt{Hz}}$ in the separation of inertial test masses housed in spacecraft separated by 1 million km. LISA Pathfinder (LPF) is a technology demonstrator mission that will test the key eLISA technologies of inertial test masses monitored by laser interferometry in a drag-free spacecraft. The optical bench that provides the interferometry for LPF must meet a number of stringent requirements: the optical path must be stable at the few ${\rm pm /\sqrt{Hz}}$ level; it must direct the optical beams onto the inertial masses with an accuracy of better than ±25 μm, and it must be robust enough not only to survive launch vibrations but to achieve full performance after launch. In this paper we describe the construction and testing of the flight optical bench for LISA Pathfinder that meets all the design requirements

Child education and work choices in the presence of a conditional cash transfer programme in rural Colombia

This research is part of a large evaluation effort, undertaken by a consortium formed by IFS, Econometria and SEI, which has considered the effects of Familias en Accion on a variety of outcomes one year after its implementation. In early reports, we focussed on the effects of the programme on school enrolment. In this paper, we both expand those results, by carefully analysing anticipation effects along with other issues, and complement them with an analysis of child labour - both paid and unpaid (including domestic) work. The child labour analysis is made possible due to a rich time use module of the surveys that has not previously been analysed. We find that the programme increased the school participation rates of 14 to 17 year old children quite substantially, by between 5 and 7 percentage points, and had lower, but non-negligible effects on the enrolment of younger children of between 1.4 and 2.4 percentage points. In terms of work, the effects are generally largest for younger children whose participation in domestic work decreased by around 10 to 12 percentage points after the programme but whose participation in income-generating work remained largely unaffected by the programme. We also find evidence of school and work time not being fully substitutable, suggesting that some, but not all, of the increased time at school may be drawn from children's leisure time

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

Inequalities in body mass index, diet and physical activity in the UK: Longitudinal evidence across childhood and adolescence

We use longitudinal data across a key developmental period, spanning much of childhood and adolescence (age 5 to 17, years 2006–2018) from the UK Millennium Cohort Study, a nationally representative study with an initial sample of just over 19,000. We first examine the extent to which inequalities in overweight, obesity, BMI and body fat over this period are consistent with the evolution of inequalities in health behaviours, including exercise and healthy diet markers (i.e., skipping breakfast) (n = 7,220). We next study the links between SES, health behaviours and adiposity (BMI, body fat), using rich models that account for the influence of a range of unobserved factors that are fixed over time. In this way, we improve on existing estimates measuring the relationship between SES and health behaviours on the one hand and adiposity on the other. The advantage of the individual fixed effects models is that they exploit within-individual changes over time to help mitigate biases due to unobserved fixed characteristics (n = 6,883). We observe stark income inequalities in BMI and body fat in childhood (age 5), which have further widened by age 17. Inequalities in obesity, physical activity, and skipping breakfast are observed to widen from age 7 onwards. Ordinary Least Square estimates reveal the previously documented SES gradient in adiposity, which is reduced slightly once health behaviours including breakfast consumption and physical activity are accounted for. The main substantive change in estimates comes from the fixed effects specification. Here we observe mixed findings on the SES associations, with a positive association between income and adiposity and a negative association with wealth. The role of health behaviours is attenuated but they remain important, particularly for body fat

Construction of rugged, ultrastable optical assemblies with optical component alignment at the few microradian level

A 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