The Unimodular Determinant Spectrum Problem

We present results related to the determinant spectrum of matrices with entries restricted to quartic roots of unity. We completely characterize determinant spectra for small orders and present conjectures on the elements and structures of higher-order spectra

Self-buckling and self-writhing of semi-flexible microorganisms

Multi-flagellated microorganisms can buckle and writhe under their own activity as they swim through a viscous fluid. New equilibrium configurations and steady-state dynamics then emerge which depend on the organism's mechanical properties and on the oriented distribution of flagella along its surface. Modeling the cell body as a semi-flexible Kirchhoff rod and coupling the mechanics to a dynamically evolving flagellar orientation field, we derive the Euler-Poincar{\'e} equations governing dynamics of the system, and rationalize experimental observations of buckling and writhing of elongated swarmer {\it P. mirabilis} cells. A sequence of bifurcations is identified as the body is made more compliant, due to both buckling and torsional instabilities. The results suggest that swarmer cells invest no more resources in maintaining membrane integrity than is necessary to prevent self-buckling.Comment: 6 pages, 3 figure

Health trajectories reveal the dynamic contributions of host genetic resistance and tolerance to infection outcome

Resistance and tolerance are two alternative strategies hosts can adopt to survive infections. Both strategies may be genetically controlled. To date, the relative contribution of resistance and tolerance to infection outcome is poorly understood. Here, we use a bioluminescent Listeria monocytogenes (Lm) infection challenge model to study the genetic determination and dynamic contributions of host resistance and tolerance to listeriosis in four genetically diverse mouse strains. Using conventional statistical analyses, we detect significant genetic variation in both resistance and tolerance, but cannot capture the time-dependent relative importance of either host strategy. We overcome these limitations through the development of novel statistical tools to analyse individual infection trajectories portraying simultaneous changes in infection severity and health. Based on these tools, early expression of resistance followed by expression of tolerance emerge as important hallmarks for surviving Lm infections. Our trajectory analysis further reveals that survivors and non-survivors follow distinct infection paths (which are also genetically determined) and provides new survival thresholds as objective endpoints in infection experiments. Future studies may use trajectories as novel traits for mapping and identifying genes that control infection dynamics and outcome. A Matlab script for user-friendly trajectory analysis is provided

(E)-2-(2-Methyl­cyclo­hexyl­idene)hydrazinecarbothio­amide

In the crystal of the title compound, C8H15N3S, mol­ecules are linked by N—H⋯S hydrogen bonds, forming chains along [10]. An intra­molecular N—H⋯N hydrogen bond is also present

The reconstructed Indonesian warm pool sea surface temperatures from tree rings and corals: Linkages to Asian monsoon drought and El Niño–Southern Oscillation

[ 1] The west Pacific warm pool is the heat engine for the globe's climate system. Its vast moisture and heat exchange profoundly impact conditions in the tropics and higher latitudes. Here, September - November sea surface temperature (SST) variability is reconstructed for the warm pool region (15 degrees S - 5 degrees N, 110 - 160 degrees E) surrounding Indonesia using annually resolved teak ring width and coral delta O-18 records. The reconstruction dates from A. D. 1782 - 1992 and accounts for 52% of the SST variance over the most replicated period. Significant correlations are found with El Nino - Southern Oscillation (ENSO) and monsoon indices at interannual to decadal frequency bands. Negative reconstructed SST anomalies coincide with major volcanic eruptions, while other noteworthy extremes are at times synchronous with Indian and Indonesian monsoon drought, particularly during major warm ENSO episodes. While the reconstruction adds to the sparse network of proxy reconstructions available for the tropical Indo-Pacific, additional proxies are needed to clarify how warm pool dynamics have interacted with global climate in past centuries to millennia.</p

Use of multi-trait and random regression models to identify genetic variation in tolerance to porcine reproductive and respiratory syndrome virus

Background: A host can adopt two response strategies to infection: resistance (reduce pathogen load) and tolerance (minimize impact of infection on performance). Both strategies may be under genetic control and could thus be targeted for genetic improvement. Although there is evidence that supports a genetic basis for resistance to porcine reproductive and respiratory syndrome (PRRS), it is not known whether pigs also differ genetically in tolerance. We determined to what extent pigs that have been shown to vary genetically in resistance to PRRS also exhibit genetic variation in tolerance. Multi-trait linear mixed models and random regression sire models were fitted to PRRS Host Genetics Consortium data from 1320 weaned pigs (offspring of 54 sires) that were experimentally infected with a virulent strain of PRRS virus to obtain genetic parameter estimates for resistance and tolerance. Resistance was defined as the inverse of within-host viral load (VL) from 0 to 21 (VL21) or 0 to 42 (VL42) days post-infection and tolerance as the slope of the reaction-norm of average daily gain (ADG21, ADG42) on VL21 or VL42. Results: Multi-trait analysis of ADG associated with either low or high VL was not indicative of genetic variation in tolerance. Similarly, random regression models for ADG21 and ADG42 with a tolerance slope fitted for each sire did not result in a better fit to the data than a model without genetic variation in tolerance. However, the distribution of data around average VL suggested possible confounding between level and slope estimates of the regression lines. Augmenting the data with simulated growth rates of non-infected half-sibs (ADG0) helped resolve this statistical confounding and indicated that genetic variation in tolerance to PRRS may exist if genetic correlations between ADG0 and ADG21 or ADG42 are low to moderate. Conclusions: Evidence for genetic variation in tolerance of pigs to PRRS was weak when based on data from infected piglets only. However, simulations indicated that genetic variance in tolerance may exist and could be detected if comparable data on uninfected relatives were available. In conclusion, of the two defense strategies, genetics of tolerance is more difficult to elucidate than genetics of resistance.</p

Corals record long-term Leeuwin current variability including Ningaloo Niño/Niña since 1795

Variability of the Leeuwin current (LC) off Western Australia is a footprint of interannual and decadal climate variations in the tropical Indo-Pacific. La Niña events often result in a strengthened LC, high coastal sea levels and unusually warm sea surface temperatures (SSTs), termed Ningaloo Niño. The rarity of such extreme events and the response of the southeastern Indian Ocean to regional and remote climate forcing are poorly understood owing to the lack of long-term records. Here we use well-replicated coral SST records from within the path of the LC, together with a reconstruction of the El Niño-Southern Oscillation to hindcast historical SST and LC strength from 1795 to 2010. We show that interannual and decadal variations in SST and LC strength characterized the past 215 years and that the most extreme sea level and SST anomalies occurred post 1980. These recent events were unprecedented in severity and are likely aided by accelerated global ocean warming and sea-level rise. © 2014 Macmillan Publishers Limited

Learning from Communities: The Local Dynamics of Formal and Informal Volunteering in Korogocho, Kenya

Taking the Korogocho community as its starting point, this article explores the respective roles, dynamics and relationship between formal and informal volunteering. Following an overview of the research's participatory systemic action research (SAR) methodology, the article outlines how the widespread use of stipends and allowances by external development organisations has blurred the distinction between formal volunteerism and low?paid work – something that disincentivises volunteering through local organisations who lack the resources to pay allowances. It examines informal volunteering, such as mutual aid and self?help groups, and highlights how they add significant value when they emerge in response to a directly experienced community need. Finally, it discusses the risks and opportunities associated with formal and informal volunteering. Issues include how volunteering can be used in complementary ways to address community needs, the scales at which they are most effective, and their potential in promoting greater inclusion and more equitable gender roles

Effects of memory biases on variability of temperature reconstruction

L.L. was supported by a studentship from the Natural Environment Research Council (NERC) E3 Doctoral training partnership [grant number NE/L002558/1]. A.S. and G.H. were supported by NERC under the Belmont forum, Grant PacMedy [NE/P006752/1]. G.H. was supported by NCAS [R8/H12/83/029]. G.H. was further funded by the Wolfson Foundation and the Royal Society as a Royal Society Wolfson Research Merit Award [WM130060] holder. We acknowledge the National Center for Atmospheric Research (NCAR) for producing and making publicly available their model output. We acknowledge the Northern Hemisphere Tree-Ring Network Development (N-TREND) for providing publicly available data.Quantifying past climate variation and attributing its causes improves our understanding of the natural variability of the climate system. Tree-ring based proxies have provided skilfull and highly resolved reconstructions of temperature and hydroclimate of the last Millennium. However, like all proxies, they are subject to uncertainties, arising from varying data quality, coverage and reconstruction methodology. Previous studies have suggested that biological-based memory processes could cause spectral biases in climate reconstructions. This study determines the effects of such biases on reconstructed temperature variability and the resultant implications for detection and attribution studies. We find that introducing persistent memory, reflecting the spectral properties of tree-ring data, can change the variability of pseudo proxy reconstructions compared to the surrogate climate and resolve model-proxy-discrepancies. This is especially the case for proxies based on ring-width data. Such memory inflates the difference between the Medieval Climate Anomaly and the Little Ice Age, and suppresses and extends the cooling in response to volcanic eruptions. When accounting for memory effects climate model data can reproduce long-term cooling after volcanic eruptions as seen in proxy reconstructions. Results of detection and attribution studies show that signals in reconstructions as well as residual unforced variability are consistent with those in climate models when the model fingerprints reflect autoregressive memory as found in tree-rings.Publisher PDFPublisher PDFPeer reviewe