The Case Against Cosmology

It is argued that some of the recent claims for cosmology are grossly overblown. Cosmology rests on a very small database: it suffers from many fundamental difficulties as a science (if it is a science at all) whilst observations of distant phenomena are difficult to make and harder to interpret. It is suggested that cosmological inferences should be tentatively made and sceptically received.Comment: 9 pages, no figure

Implementation of radiation shielding calculation methods. Volume 1: Synopsis of methods and summary of results

The work performed in the following areas is summarized: (1) Analysis of Realistic nuclear-propelled vehicle was analyzed using the Marshall Space Flight Center computer code package. This code package includes one and two dimensional discrete ordinate transport, point kernel, and single scatter techniques, as well as cross section preparation and data processing codes, (2) Techniques were developed to improve the automated data transfer in the coupled computation method of the computer code package and improve the utilization of this code package on the Univac-1108 computer system. (3) The MSFC master data libraries were updated

Tax reform and retirement saving incentives: evidence from the introduction of stakeholder pensions in the UK

Faced with ageing populations, OECD governments are seeking policies to increase individual retirement saving. In April 2001, the UK government introduced Stakeholder Pensions – a low cost retirement saving vehicle. The reform also changed the structure of tax-relieved contribution ceilings, increasing their generosity for lower earning individuals. We examine the impact of these changes on private pension coverage and on contributions to personal pension accounts using individual level micro data. We use a difference-in-differences strategy, and where necessary our estimator is modified to allow for dichotomous outcomes. The results suggest that the change to the contribution ceilings affected both coverage rates and contributions to private pensions among lower earnings individuals, especially among women, and those in couples

Ill-health and retirement in Britain: a panel data-based analysis

We examine the role of ill-health in retirement decisions in Britain, using the first eight waves of the British Household Panel Survey (1991-98). As self-reported health status is likely to be endogenous to the retirement decision, we instrument self-reported health by a constructed ‘health stock’ measure using a set of health indicator variables and personal characteristics, as suggested by Bound et al (1999). Using both linear and non-linear fixed effects estimators, we show that adverse individual health shocks are an important predictor of individual retirement behaviour. We compare the impact of our constructed health measure on economic activity with that arising from the use of other health variables in the data set. We also examine the impact of the 1995 reform of disability benefits on the retirement decision

Where has all the neutral hydrogen gone?

Our extremely deep survey for extragalactic HI (HIDEEP) finds no intergalactic gas clouds, and no galaxies with HI at inferred global column-densities below 10^20 cm^-2 when we could have detected such objects down to a completeness limit of 4 x 10^18 cm^-2. We speculate that low surface-density hydrogen is either ionised or locked up in ``frozen discs'', i.e. structures where the local Ly-alpha is insufficient to excite the 21-cm transition to a spin-temperature above the cosmic background. Such ``frozen discs'' might be responsible for many QSOALSs.Comment: 6 pages, 3 figures, to be published in the proceedings of "The IGM/Galaxy Connection

Gradual Certified Programming in Coq

Expressive static typing disciplines are a powerful way to achieve high-quality software. However, the adoption cost of such techniques should not be under-estimated. Just like gradual typing allows for a smooth transition from dynamically-typed to statically-typed programs, it seems desirable to support a gradual path to certified programming. We explore gradual certified programming in Coq, providing the possibility to postpone the proofs of selected properties, and to check "at runtime" whether the properties actually hold. Casts can be integrated with the implicit coercion mechanism of Coq to support implicit cast insertion a la gradual typing. Additionally, when extracting Coq functions to mainstream languages, our encoding of casts supports lifting assumed properties into runtime checks. Much to our surprise, it is not necessary to extend Coq in any way to support gradual certified programming. A simple mix of type classes and axioms makes it possible to bring gradual certified programming to Coq in a straightforward manner.Comment: DLS'15 final version, Proceedings of the ACM Dynamic Languages Symposium (DLS 2015

Seeing Galaxies Through Thick & Thin. III. HST Imaging of the Dust in Backlit Spiral Galaxies

We present analysis of WFPC2 imaging of two spiral galaxies partially backlit by E/S0 systems in the pairs AM1316-241 and AM0500-620, and the spiral foreground system in NGC 1275. Images in B and I are used to determine the reddening curve of in these systems. The spiral component of AM1316-241 shows dust strongly concentrated in discrete arms, with a reddening law very close to the Milky Way mean. The dust distribution is scale-free between about 100 pc and the arm scale. The spiral in AM0500-620 shows dust concentrated in arms and interarm spurs, with measurable interarm extinction as well. Although its dust properties are less well-determined, we find evidence for a steeper extinction law here. The shape of the reddening law suggests that, at least in AM1316-241, we have resolved most of the dust structure. In AM0500-620, the slope of the fractal perimeter-scale relation steepens systematically from low to high extinction. In AM1316-241, we cannot determine a unique fractal dimension from the defining area-perimeter relation, so the projected dust distribution is best defined as fractal-like. In neither galaxy do we see regions even on single-pixel scales in spiral arms with AB > 2.5. The measurements in NGC 1275 are compromised by our lack of independent knowledge of the foreground system's light distribution, but masked sampling of the absorption suggests an effective reddening curve much flatter than the Milky Way mean (perhaps indicating that the foreground system has been affected by immersion in the hot intracluster gas).Comment: Astronomical Journal, in press. 13 figures. Full-size PostScript figures available at http://www.astr.ua.edu/preprints/kee

Why use ROSCAs when you can use banks? Theory and evidence from Ethiopia

Much of the existing literature on the use of informal credit arrangements such as ROSCAs (Rotating and Credit Saving Associations) theorises the use of such institutions as arising from market failures in the development of formal saving and credit mechanisms. As economic development proceeds, formal institutions might therefore be expected to displace ROSCAs. We show, using household data for Ethiopia, that in fact use of formal institutions and ROSCAs can co-exist, even in the same household. We examine usage of both formal and informal institutions across the household income gradient, and provide a theoretical model consistent with these empirical facts

Avoiding the bullwhip effect using Damped Trend forecasting and the Order-Up-To replenishment policy

We study the Damped Trend forecasting method and its bullwhip generating behaviour when used within the Order-Up-To (OUT) replenishment policy. Using z-transform transfer functions we determine complete stability criteria for the Damped Trend forecasting method. We show that this forecasting mechanism is stable for a much larger proportion of the parametrical space than is generally acknowledged in the literature. We provide a new proof to the known fact that the Naïve, Exponential Smoothing and Holts Method forecasting, when used inside the OUT policy, will always generate bullwhip for every possible demand process, for any lead-time. Further, we demonstrate the Damped Trend OUT system behaves differently. Sometimes it will generate bullwhip and sometimes it will not. Bullwhip avoidance occurs when demand is dominated by low frequency harmonics in some instances. In other instances bullwhip avoidance happens when demand is dominated by high frequency harmonics. We derive sufficient conditions for when bullwhip will definitely be generated and necessary conditions for when bullwhip may be avoided. We verify our analytical findings with a numerical investigation