Finding proper factorizations in finite groups

One focus in group theory has been to establish the properties of a finite group that can be written as the product of two proper subgroups whose properties are known. The investigation here will proceed in the other direction by establishing conditions for when a finite group can be written as a product of two proper subgroups and for when a specific proper subgroup is part of a product of proper subgroups that equals the group. A byproduct of this investigation is a classification of those finite groups which cannot be written as the product of any two proper subgroups

Considerations for Using a Geographic Information System to Assess Environmental Supports for Physical Activity

The use of a geographic information system (GIS) to study environmental supports for physical activity raises several issues, including acquisition and development, quality, and analysis. We recommend to public health professionals interested in using GIS that they investigate available data, plan for data development where none exists, ensure the availability of trained personnel and sufficient time, and consider issues such as data quality, analyses, and confidentiality. This article shares information about data-related issues that we encountered when using GIS to validate responses to a questionnaire about environmental supports for physical activity

Dynamics of sediment flux to a bathyal continental margin section through the Paleocene–Eocene Thermal Maximum

The response of the Earth system to greenhouse-gas-driven warming is of critical importance for the future trajectory of our planetary environment. Hyperthermal events – past climate transients with global-scale warming significantly above background climate variability – can provide insights into the nature and magnitude of these responses. The largest hyperthermal of the Cenozoic was the Paleocene–Eocene Thermal Maximum (PETM ∼ 56 Ma). Here we present new high-resolution bulk sediment stable isotope and major element data for the classic PETM section at Zumaia, Spain. With these data we provide a new detailed stratigraphic correlation to other key deep-ocean and terrestrial PETM reference sections. With this new correlation and age model we are able to demonstrate that detrital sediment accumulation rates within the Zumaia continental margin section increased more than 4-fold during the PETM, representing a radical change in regional hydrology that drove dramatic increases in terrestrial-to-marine sediment flux. Most remarkable is that detrital accumulation rates remain high throughout the body of the PETM, and even reach peak values during the recovery phase of the characteristic PETM carbon isotope excursion (CIE). Using a series of Earth system model inversions, driven by the new Zumaia carbon isotope record, we demonstrate that the silicate weathering feedback alone is insufficient to recover the PETM CIE, and that active organic carbon burial is required to match the observed dynamics of the CIE. Further, we demonstrate that the period of maximum organic carbon sequestration coincides with the peak in detrital accumulation rates observed at Zumaia. Based on these results, we hypothesise that orbital-scale variations in subtropical hydro-climates, and their subsequent impact on sediment dynamics, may contribute to the rapid climate and CIE recovery from peak-PETM conditions

Quantification of the performance of chaotic micromixers on the basis of finite time Lyapunov exponents

Chaotic micromixers such as the staggered herringbone mixer developed by Stroock et al. allow efficient mixing of fluids even at low Reynolds number by repeated stretching and folding of the fluid interfaces. The ability of the fluid to mix well depends on the rate at which "chaotic advection" occurs in the mixer. An optimization of mixer geometries is a non trivial task which is often performed by time consuming and expensive trial and error experiments. In this paper an algorithm is presented that applies the concept of finite-time Lyapunov exponents to obtain a quantitative measure of the chaotic advection of the flow and hence the performance of micromixers. By performing lattice Boltzmann simulations of the flow inside a mixer geometry, introducing massless and non-interacting tracer particles and following their trajectories the finite time Lyapunov exponents can be calculated. The applicability of the method is demonstrated by a comparison of the improved geometrical structure of the staggered herringbone mixer with available literature data.Comment: 9 pages, 8 figure

Do residents’ perceptions of being well-placed and objective presence of local amenities match? A case study in West Central Scotland, UK

Background:<p></p> Recently there has been growing interest in how neighbourhood features, such as the provision of local facilities and amenities, influence residents’ health and well-being. Prior research has measured amenity provision through subjective measures (surveying residents’ perceptions) or objective (GIS mapping of distance) methods. The latter may provide a more accurate measure of physical access, but residents may not use local amenities if they do not perceive them as ‘local’. We believe both subjective and objective measures should be explored, and use West Central Scotland data to investigate correspondence between residents’ subjective assessments of how well-placed they are for everyday amenities (food stores, primary and secondary schools, libraries, pharmacies, public recreation), and objective GIS-modelled measures, and examine correspondence by various sub-groups.<p></p> Methods:<p></p> ArcMap was used to map the postal locations of ‘Transport, Health and Well-being 2010 Study’ respondents (n = 1760), and the six amenities, and the presence/absence of each of them within various straight-line and network buffers around respondents’ homes was recorded. SPSS was used to investigate whether objective presence of an amenity within a specified buffer was perceived by a respondent as being well-placed for that amenity. Kappa statistics were used to test agreement between measures for all respondents, and by sex, age, social class, area deprivation, car ownership, dog ownership, walking in the local area, and years lived in current home.<p></p> Results:<p></p> In general, there was poor agreement (Kappa <0.20) between perceptions of being well-placed for each facility and objective presence, within 800 m and 1000 m straight-line and network buffers, with the exception of pharmacies (at 1000 m straight-line) (Kappa: 0.21). Results varied between respondent sub-groups, with some showing better agreement than others. Amongst sub-groups, at 800 m straight-line buffers, the highest correspondence between subjective and objective measures was for pharmacies and primary schools, and at 1000 m, for pharmacies, primary schools and libraries. For road network buffers under 1000 m, agreement was generally poor.<p></p> Conclusion:<p></p> Respondents did not necessarily regard themselves as well-placed for specific amenities when these amenities were present within specified boundaries around their homes, with some exceptions; the picture is not clear-cut with varying findings between different amenities, buffers, and sub-groups

Establishing low-power operating limits for liquid metal heat pipes

Liquid metal heat pipes operated at power throughputs well below their design point for long durations may fail as a result of the working fluid migrating to a cold region within the pipe, freezing there, and hot returning to the evaporator section. Eventually sufficient working fluid inventory may be lost to the cold region to cause a local dry-out condition in the evaporator. A joint experimental and analytical effort between the Air Force Phillips Laboratory and Los Alamos National Laboratory is underway to investigate the phenomena. Experiments include both high temperature liquid metal and low temperature organic heat pipes. To date, a low temperature working fluid has been selected and its performance in a heat pipe validated. Additionally, a low-temperature heat pipe has been fabricated and is presently being tested

Assessing the impact of bioturbation on sedimentary isotopic records through numerical models

The disturbance of seafloor sediments by the activities of bottom-dwelling organisms, known as bioturbation, significantly alters the marine paleorecord by redistributing particles in the upper sediment layers. Consequently, ‘proxy’ signals recorded in these sediment particles, such as the size, abundance, or isotopic composition of plankton shells, are distorted by particle mixing. Accordingly, bioturbation can alter the apparent timing, duration, and magnitude of recorded events by smoothing climatic and oceanographic signals. In an extreme scenario, biological mixing can significantly obscure our view of the past by homogenizing the bioturbated layer, destroying sediment layering, and distorting the relative timing and intensity of past climatological events. Here we explore how bioturbation distorts proxy records of environmental events from a modeling perspective. First, we provide an overview and comparison of different numerical models created for simulating the movement and structural alteration of sediment by bioturbation. Next, we use an updated particle resolving model – iTURBO2 – to illustrate how various modes and intensities of bioturbation distort the signature of past climatological events, considering a range of conceptual shapes of vertical proxy profiles. Finally, we demonstrate how sampled proxy records can differ due to the combined effects of particle mixing and differential abundance changes that often concur with environmental transitions. We make the iTURBO2 MATLAB code openly available to facilitate further exploration of proxy biases due to bioturbation to aid the interpretation of the climatological record preserved in marine sediments