It\u27s Not So Simple: The Role of Simplicity in Science and Theory.

The principle of simplicity (parsimony) has long been invoked as a regulative principle that helps guide theory selection in science. However, it is unclear if there is justification for a globally applicable criterion of parsimony. This paper briefly reviews the salient features of what it means for something to be simple, as well as argues for simplicity as relevant only to a set of background assumptions

Mixing rates across the Gulf Stream, Part 1: On the formation of Eighteen Degree Water

Microstructure profiles taken in February 2007 across the Gulf Stream (GS) measured the temporal and spatial variability of the intense mixing that forms Eighteen Degree Water (EDW). Strong winds, gusting to 30 m s–1, and heat fluxes up to 1000 W m–2 produced moderate-to-strong mixing in the surface mixed layer and the entrainment zone, as well as in the thermocline. In the limit of a vertically balanced heat budget, EDW formation is driven primarily by surface heat loss to the atmosphere across a region extending O(100) km south from the GS core, where entrainment heat fluxes based on dissipation rates were relatively low, O(10) to O(100) W m–2. Near the GS core, much larger entrainment fluxes, O(100) to O(1000) W m–2, contribute significantly to cooling the mixed layer, but less so to overall EDW formation due to its smaller volume. Relationships between observed dissipation rates and the atmospheric and local shear forcing scales are examined for this limited data set and compared with empirical scalings both within the mixed layer and in the entrainment zone. Below the mixed layer near the GS, diapycnal diffusivities in the thermocline averaged about O(10–4) m2 s–1, and are approximately 10 times levels previously observed in the GS during other seasons. Horizontally coherent shear structures, with shoaling phase and clockwise rotation, indicate that downward-propagating near-inertial waves are responsible for much of this enhanced subsurface mixing

Multilayered printed circuit boards inspected by X-ray laminography

Technique produces high resolution cross-sectional radiographs with close interplane spacing for inspecting multilayer boards to be used in providing circuitry routing and module structural support

Mixing rates across the Gulf Stream, Part 2: Implications for nonlocal parameterization of vertical fluxes in the surface boundary layers

The turbulent kinetic energy (TKE) budget of the surface mixed layer is evaluated at wintertime stations occupied in the vicinity of the strong Gulf Stream (GS) jet. The nonlocal K-profile parameterization (KPP) of vertical fluxes is combined with observed hydrography and meteorology to diagnose TKE production. This KPP-based production is averaged over the surface mixed layer and compared with corresponding averages of observed TKE dissipation rate from microstructure measurements, under assumptions of a homogeneous steady-state balance for the layer-averaged TKE budget. The KPP-based TKE production estimates exceed the mean observed boundary layer dissipation rates at occupied stations by up to an order of magnitude. In cases with strong upper ocean shear, the boundary layer depths predicted by the bulk Richardson number criteria of KPP tend to be deeper than indicated by observed dissipation rates, and thereby including strong entrainment zone shear contributes excessively to the KPP-based diagnosis of TKE production. However, even after correcting this diagnosis of mixed layer depth, the layer-averaged production still exceeds observed dissipation rates. These results have several possible implications, including: (1) KPP tends to overestimate vertical momentum flux in cases with strong shear due to geostrophically balanced thermal wind, unbalanced submesoscale dynamics, or entrainment driven by mixed layer inertial oscillations; (2) a mean local TKE balance does not hold in baroclinic mixed layers due to radiation of inertial waves, divergence in horizontal TKE flux or an inverse cascade to larger scales; and (3) both the boundary layer depth and the remaining TKE budget discrepancies indicate the limited validity of mixed layer models in the simulation of submesoscale ocean phenomena

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe - Part II: Thorium fuel cycle

Full recycling of transuranic (TRU) isotopes can in theory lead to a reduction in repository radiotoxicity to reference levels in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. In Part I of this paper, TRU recycle over up to 5 generations of light water reactors (LWRs) or sodium-cooled fast reactors (SFRs) is considered for uranium (U) fuel cycles. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance. U-fuelled SFRs operating a break-even fuel cycle are not particularly effective at reducing repository radiotoxicity as the final core load dominates over a very long timeframe. In this paper, the analysis is extended to the thorium (Th) fuel cycle. Closed Th-based fuel cycles are well known to have lower equilibrium radiotoxicity than U-based fuel cycles but the time taken to reach equilibrium is generally very long. Th burner fuel cycles with SFRs are found to result in very similar radiotoxicity to U burner fuel cycles with SFRs for one less generation of reactors, provided that protactinium (Pa) is recycled. Th-fuelled reduced-moderation boiling water reactors (RBWRs) are also considered, but for burner fuel cycles their performance is substantially worse, with the waste taking ∼3–5 times longer to decay to the reference level than for Th-fuelled SFRs with the same number of generations. Th break-even fuel cycles require ∼3 generations of operation before their waste radiotoxicity benefits result in decay to the reference level in ∼1000 years. While this is a very long timeframe, it is roughly half that required for waste from the Th or U burner fuel cycle to decay to the reference level, and less than a tenth that required for the U break-even fuel cycle. The improved performance over burner fuel cycles is due to a more substantial contribution of energy generated by 233U leading to lower radiotoxicity per unit energy generation. To some extent this an argument based on how the radiotoxicity is normalised: operating a break-even fuel cycle rather than phasing out nuclear power using a burner fuel cycle results in higher repository radiotoxicity in absolute terms. The advantage of Th break-even fuel cycles is also contingent on recycling Pa, and reprocessing losses are significant also for a small number of generations due to the need to effectively burn down the TRU. The integrated decay heat over the scenario timeframe is almost twice as high for a break-even Th fuel cycle than a break-even U fuel cycle when using SFRs, as a result of much higher 90Sr production, which subsequently decays into 90Y. The peak decay heat is comparable. As decay heat at vitrification and repository decay heat affect repository sizing, this may weaken the argument for the Th cycle.The first author would like to acknowledge the UK Engineering and Physical Sciences Research Council (EPSRC) and the Institution of Mechanical Engineers for providing funding towards this work.This is the final version of the article. It first appeared from Elsevier at http://dx.doi.org/10.1016/j.pnucene.2014.11.01

The effectiveness of full actinide recycle as a nuclear waste management strategy when implemented over a limited timeframe - Part I: Uranium fuel cycle

Disposal of spent nuclear fuel is a major political and public-perception problem for nuclear energy. From a radiological standpoint, the long-lived component of spent nuclear fuel primarily consists of transuranic (TRU) isotopes. Full recycling of TRU isotopes can, in theory, lead to a reduction in repository radiotoxicity to reference levels corresponds to the radiotoxicity of the unburned natural U required to fuel a conventional LWR in as little as ∼500 years provided reprocessing and fuel fabrication losses are limited. This strategy forms part of many envisaged ‘sustainable’ nuclear fuel cycles. However, over a limited timeframe, the radiotoxicity of the ‘final’ core can dominate over reprocessing losses, leading to a much lower reduction in radiotoxicity compared to that achievable at equilibrium. The importance of low reprocessing losses and minor actinide (MA) recycling is also dependent on the timeframe during which actinides are recycled. In this paper, the fuel cycle code ORION is used to model the recycle of light water reactor (LWR)-produced TRUs in LWRs and sodium-cooled fast reactors (SFRs) over 1–5 generations of reactors, which is sufficient to infer general conclusions for higher numbers of generations. Here, a generation is defined as a fleet of reactors operating for 60 years, before being retired and potentially replaced. Over up to ∼5 generations of full actinide recycle in SFR burners, the final core inventory tends to dominate over reprocessing losses, beyond which the radiotoxicity rapidly becomes sensitive to reprocessing losses. For a single generation of SFRs, there is little or no advantage to recycling MAs. However, for multiple generations, the reduction in repository radiotoxicity is severely limited without MA recycling, and repository radiotoxicity converges on equilibrium after around 3 generations of SFRs. With full actinide recycling, at least 6 generations of SFRs are required in a gradual phase-out of nuclear power to achieve transmutation performance approaching the theoretical equilibrium performance – which appears challenging from an economic and energy security standpoint. TRU recycle in pressurized water reactors (PWRs) with zero net actinide production provides similar performance to low-enriched-uranium (LEU)-fueled LWRs in equilibrium with a fleet of burner SFRs. However, it is not possible to reduce the TRU inventory over multiple generations of PWRs. TRU recycle in break-even SFRs is much less effective from a point of view of reducing spent nuclear fuel radiotoxicity.The first author would like to acknowledge the UK Engineering and Physical Sciences Research Council (EPSRC) and the Institution of Mechanical Engineers for providing funding towards this work.This is the final version of the article. It first appeared from Elsevier via http://dx.doi.org/10.1016/j.pnucene.2015.07.02

Intergalactic Globular Clusters

We confirm and extend our previous detection of a population of intergalactic globular clusters in Abell 1185, and report the first discovery of an intergalactic globular cluster in the nearby Virgo cluster of galaxies. The numbers, colors and luminosities of these objects can place constraints on their origin, which in turn may yield new insights to the evolution of galaxies in dense environments.Comment: 2 pages, no figures. Talk presented at JD6, IAU General Assembly XXV, Sydney, Australia, July 2003, to appear in Highlights of Astronomy, Vol. 1

Dehiscence of detached internal limiting membrane in eyes with myopic traction maculopathy with spontaneous resolution

Background: Idjwi, an island of approximately 220,000 people, is located in eastern DRC and functions semi-autonomously under the governance of two kings (mwamis). At more than 8 live births per woman, Idjwi has one of the highest total fertility rates (TFRs) in the world. Rapid population growth has led to widespread environmental degradation and food insecurity. Meanwhile family planning services are largely unavailable.Methods: At the invitation of local leaders, we conducted a representative survey of 2,078 households in accordance with MEASURE DHS protocols, and performed ethnographic interviews and focus groups with key informants and vulnerable subpopulations. Modelling proximate determinates of fertility, we evaluated how the introduction of contraceptives and/or extended periods of breastfeeding could reduce the TFR.Results: Over half of all women reported an unmet need for spacing or limiting births, and nearly 70% named a specific modern method of contraception they would prefer to use; pills (25.4%) and injectables (26.5%) were most desired. We predicted that an increased length of breastfeeding (from 10 to 21 months) or an increase in contraceptive prevalence (from 1% to 30%), or a combination of both could reduce TFR on Idjwi to 6, the average desired number of children. Increasing contraceptive prevalence to 15% could reduce unmet need for contraception by 8%.Conclusions: To meet women’s need and desire for fertility control, we recommend adding family planning services at health centers with NGO support, pursuing a community health worker program, promoting extended breastfeeding, and implementing programs to end sexual- and gender-based violence toward women