The Bowl Championship Series: A Mathematical Review

We discuss individual components of the college football Bowl Championship Series, compare with a simple algorithm defined by random walks on a biased graph, attempt to predict whether the proposed changes will truly lead to increased BCS bowl access for non-BCS schools, and conclude by arguing that the true problem with the BCS Standings lies not in the computer algorithms, but rather in misguided addition.Comment: 12 pages, 2 figures, submitted to Notices of the AM

Nanoscale spatially resolved infrared spectra from single microdroplets

Droplet microfluidics has emerged as a powerful platform allowing a large number of individual reactions to be carried out in spatially distinct microcompartments. Due to their small size, however, the spectroscopic characterisation of species encapsulated in such systems remains challenging. In this paper, we demonstrate the acquisition of infrared spectra from single microdroplets containing aggregation-prone proteins. To this effect, droplets are generated in a microfluidic flow-focussing device and subsequently deposited in a square array onto a ZnSe prism using a micro stamp. After drying, the solutes present in the droplets are illuminated locally by an infrared laser through the prism, and their thermal expansion upon absorption of infrared radiation is measured with an atomic force microscopy tip, granting nanoscale resolution. Using this approach, we resolve structural differences in the amide bands of the spectra of monomeric and aggregated lysozyme from single microdroplets with picolitre volume.Comment: 5 pages, 3 Figure

HIV/AIDS and Agrarian Livelihoods in Zambia: a Test of the New Variant Famine Hypothesis.

1. Consistent with the New Variant Famine (NVF) hypothesis, the negative impact of drought on crop output and output per hectare is further exacerbated where HIV prevalence rates are relatively high, particularly in the low- and medium rainfall zones of the country (agro-ecological regions I and II). 2. HIV prevalence rates and AIDS-related mortality rates in Zambia are highest in the lowest rainfall and most drought-prone zone of the country (agro-ecological region I). 3. Only for districts in agro-ecological region I do we find evidence of a robust negative effect of HIV/AIDS on agrarian livelihood indicators. Relatively stable food production zones and/or areas with relatively low HIV prevalence rates appear to be less vulnerable to the adverse effects predicted by the NVF hypothesis, which suggests that HIV/AIDS exacerbates the effects of drought and other shocks on agrarian communities. 4. HIV/AIDS reduces the crop production gains associated with fertilizer subsidy increases in the highest rainfall areas. 5. Increases in the percentage of female-headed households in a district are related to declines in agricultural production indicators, but these effects do not appear to worsen when the HIV/AIDS epidemic is severe. 6. Only in districts whose borders encompass both agro-ecological regions II and III do we consistently find weak evidence that HIV/AIDS reduces the contribution of productive assets to crop output and output per unit of land as would be expected under the NVF hypothesis.food security, food policy, Zambia, HIV/AIDS, Food Security and Poverty, Health Economics and Policy, Q20,

Stability of Monomer-Dimer Piles

We measure how strong, localized contact adhesion between grains affects the maximum static critical angle, theta_c, of a dry sand pile. By mixing dimer grains, each consisting of two spheres that have been rigidly bonded together, with simple spherical monomer grains, we create sandpiles that contain strong localized adhesion between a given particle and at most one of its neighbors. We find that tan(theta_c) increases from 0.45 to 1.1 and the grain packing fraction, Phi, decreases from 0.58 to 0.52 as we increase the relative number fraction of dimer particles in the pile, nu_d, from 0 to 1. We attribute the increase in tan(theta_c(nu_d)) to the enhanced stability of dimers on the surface, which reduces the density of monomers that need to be accomodated in the most stable surface traps. A full characterization and geometrical stability analysis of surface traps provides a good quantitative agreement between experiment and theory over a wide range of nu_d, without any fitting parameters.Comment: 11 pages, 12 figures consisting of 21 eps files, submitted to PR

Conventional versus highly cross-linked polyethylene in primary total knee replacement : a comparison of revision rates using data from the National Joint Registry for England, Wales, and Northern Ireland

There is evidence to support the use of highly cross-linked polyethylene (HXLPE) in patients undergoing total hip arthroplasty. However, the benefits for those undergoing total knee arthroplasty are uncertain, with conflicting reports based on previous cohort analyses. The purpose of the present study was to compare the revision rates following primary total knee arthroplasty with use of HXLPE as compared with conventional polyethylene (CPE) using data from the National Joint Registry (NJR) for England, Wales and Northern Ireland. We performed a retrospective analysis of primary total knee arthroplasties recorded in the NJR from 2003 to 2014. Cobalt-chromium (CoCr)-CPE and CoCr-HXLPE bearing surfaces were compared using all-cause revision, aseptic revision, and septic revision as end points. Survival analyses were conducted using rates per 100 years observed, Kaplan-Meier survival estimates, and Cox regression hazard ratios (HRs) adjusted for age, sex, American Society of Anesthesiologists (ASA) classification, body mass index (BMI), lead surgeon grade, and implant constraint. Secondary analyses compared the most commonly used HXLPEs (Zimmer Prolong, DePuy XLK, and Stryker X3) against CPE for the 3 most common total knee arthroplasty systems (NexGen, PFC Sigma, and Triathlon). In the present study of 550,658 total knee arthroplasties, the unadjusted aseptic revision rates were significantly lower following procedures performed with CPE (n = 513,744) as compared with those performed with HXLPE total knee replacements (n = 36,914) (0.29 [95% confidence interval (CI), 0.28 to 0.30] compared to 0.38 [95% CI, 0.35 to 0.42], p 35 kg/m, the "second-generation" Stryker X3 HXLPE demonstrated significantly better survival than its respective CPE, with CPE having an HR of 2.6 (95% CI, 1.2 to 5.9) (p = 0.02). Alternative bearings are marketed as having improved wear properties over traditional CoCr-CPE. This registry-based analysis demonstrated no overall survival benefit of HXLPE after a maximum duration of follow-up of 12 years. Because of their increased cost, the routine use of HXLPE bearings may not be justified. However, they may have a role in specific "higher demand" groups such as patients 35 kg/m. Therapeutic Level III. See Instructions for Authors for a complete list of levels of evidence

Spectral tripartitioning of networks

We formulate a spectral graph-partitioning algorithm that uses the two leading eigenvectors of the matrix corresponding to a selected quality function to split a network into three communities in a single step. In so doing, we extend the recursive bipartitioning methods developed by Newman [Proc. Nat. Acad. Sci. 103, 8577 (2006); Phys. Rev. E 74, 036104 (2006)] to allow one to consider the best available two-way and three-way divisions at each recursive step. We illustrate the method using simple "bucket brigade" examples and then apply the algorithm to examine the community structures of the coauthorship graph of network scientists and of U. S. Congressional networks inferred from roll-call voting similarities.Comment: 12 pages with 4 figures, resubmitted version accepted for publication in Physical Review

Mountains of Maize, Persistent Poverty

The past two years are a tribute to Zambian farmers; they have responded admirably to government efforts to promote maize production. But ironically, rural poverty remains stubbornly high despite the fact that the government has spent over 2% of the nation’s gross domestic product in supporting maize production and subsidizing inputs for farmers. Why is it that maize production has increased so impressively without making a serious dent in rural poverty? And what are the lessons for the new government?maize, poverty, Zambia, Agricultural and Food Policy, Food Security and Poverty,