Genetic drift at expanding frontiers promotes gene segregation

Competition between random genetic drift and natural selection plays a central role in evolution: Whereas non-beneficial mutations often prevail in small populations by chance, mutations that sweep through large populations typically confer a selective advantage. Here, however, we observe chance effects during range expansions that dramatically alter the gene pool even in large microbial populations. Initially well-mixed populations of two fluorescently labeled strains of Escherichia coli develop well-defined, sector-like regions with fractal boundaries in expanding colonies. The formation of these regions is driven by random fluctuations that originate in a thin band of pioneers at the expanding frontier. A comparison of bacterial and yeast colonies (Saccharomyces cerevisiae) suggests that this large-scale genetic sectoring is a generic phenomenon that may provide a detectable footprint of past range expansions.Comment: Please visit http://www.pnas.org/content/104/50/19926.abstract for published articl

Next-to-leading order QCD predictions for the hadronic WHWH+jet production

We calculate the next-to-leading order(NLO) QCD corrections to the $WH^0$ production in association with a jet at hadron colliders. We study the impacts of the complete NLO QCD radiative corrections to the integrated cross sections, the scale dependence of the cross sections, and the differential cross sections ($\frac{d \sigma}{d\cos\theta}$, $\frac{d \sigma}{dp_T}$) of the final $W$-, Higgs-boson and jet. We find that the corrections significantly modify the physical observables, and reduce the scale uncertainty of the LO cross section. Our results show that by applying the inclusive scheme with $p_{T,j}^{cut}=20 GeV$ and taking $m_H=120 GeV$, $\mu=\mu_0\equiv\frac{1}{2}(m_W+m_H)$, the K-factor is 1.15 for the process $p\bar p \to W^{\pm}H^0j+X$ at the Tevatron, while the K-factors for the processes $pp \to W^-H^0j+X$ and $pp \to W^+H^0j+X$ at the LHC are 1.12 and 1.08 respectively. We conclude that to understand the hadronic associated $WH^0$ production, it is necessary to study the NLO QCD corrections to $WH^0j$ production process which is part of the inclusive $WH^0$ production.Comment: 26 pages, 27 figures, accepted by Phys. Rev.

Topographic shading influences cryoconite morphodynamics and carbon exchange

Cryoconite holes are the most active and diverse microbial habitats on glacier and ice-sheet surfaces. In this article the authors demonstrate that the shape of cryoconite holes varies depending on ice-surface topography and that this has implications for the carbon cycling regime within. Net ecosystem production is shown to be controlled primarily by sediment thickness within holes. The authors show that irregular hole shapes are indicative of hole migration away from topographic shade, which promotes carbon fixation at the mesoscale on ice surfaces. A cellular automaton is used in conjunction with sediment-delivery experiments to show that migration is the result of simple sediment transfer processes, implying a relationship between ice-surface evolution and cryoconite biogeochemistry that has not previously been examined.The authors gratefully acknowledge funding from the British Society for Geomorphology, Mount Everest Foundation, Gino Watkins Memorial Fund, Andrew Croft Memorial Fund, Scottish Arctic Club, Gilchrist Educational Fund, and Rolex Awards for Enterprise and Gradconsult. JC also acknowledges UK-funded Natural Environment Research Council Consortium Grant “Black and Bloom” (NE/ M021025/1)

Dose-finding study of paclitaxel and cyclophosphamide in advanced breast cancer

Background The toxicity profile of prolonged infusions of paclitaxel in combination with cyclophosphamide in metastat-ic breast cancer has already been defined. The objective of this dose-finding study was to determine the maximum tolerable doses (MTDs) of shorter (three-hour) infusions of paclitaxel in combination with i.v. bolus cyclophosphamide in patients who had previously received a maximum of one chemotherapy for advanced breast carcinoma. The MTD of the same regimen with granulocyte colony-stimulating factor (G-CSF) support was then established. Patients and methods Eighty women with metastatic breast cancer received a total of 352 fully evaluable courses of therapy. The starting doses were paclitaxel 135 mg/m2 and cyclophosphamide 750 mg/m2 given every three weeks. At least three patients were treated at each dose level and if there were dose-limiting toxic effects during the first cycles three additional patients were entered. G-CSF support (5 ug/kg s.c.) was added to the second cycle if specific dose-limiting toxicities had occurred during the first cycle. The MTD was defined as the dose level at which more than two of six patients presented dose-limiting toxicities during the first cycle. Results Febrile neutropenia (n = 4) and severe thrombo-cytopenia (n - 1) defined the MTDs of paclitaxel as 200 mg/m2 and of cyclophosphamide as 2,000 mg/m2 with or without G-CSF in patients with and, respectively, without prior chemotherapy for advanced disease. Non-hematologic toxicity was moderate. Recommended doses were 200 mg/m2 of paclitaxel and 1,750 mg/m2 of cyclophosphamide with or without G-CSF in patients with and, respectively, without prior chemotherapy. The overall response rate was 25% and 50%, respectively, in patients with and without prior chemotherapy for metastatic disease. Complete remissions (9%) were reported only in patients without prior chemotherapy; antitumour activity in women with anthracycline-resistant disease, with an 8% response rate (95% CI: 1%-26%), was poor. Conclusion Paclitaxel at 200 mg/m2 and cyclophosphamide at 1,750 mg/m2 can be safely administered every three weeks to women with advanced breast cancer. The moderate antitumour activity observed with the schedule tested argues against its use as initial therapy for advanced breast cance

Inference of population splits and mixtures from genome-wide allele frequency data

Many aspects of the historical relationships between populations in a species are reflected in genetic data. Inferring these relationships from genetic data, however, remains a challenging task. In this paper, we present a statistical model for inferring the patterns of population splits and mixtures in multiple populations. In this model, the sampled populations in a species are related to their common ancestor through a graph of ancestral populations. Using genome-wide allele frequency data and a Gaussian approximation to genetic drift, we infer the structure of this graph. We applied this method to a set of 55 human populations and a set of 82 dog breeds and wild canids. In both species, we show that a simple bifurcating tree does not fully describe the data; in contrast, we infer many migration events. While some of the migration events that we find have been detected previously, many have not. For example, in the human data we infer that Cambodians trace approximately 16% of their ancestry to a population ancestral to other extant East Asian populations. In the dog data, we infer that both the boxer and basenji trace a considerable fraction of their ancestry (9% and 25%, respectively) to wolves subsequent to domestication, and that East Asian toy breeds (the Shih Tzu and the Pekingese) result from admixture between modern toy breeds and "ancient" Asian breeds. Software implementing the model described here, called TreeMix, is available at http://treemix.googlecode.comComment: 28 pages, 6 figures in main text. Attached supplement is 22 pages, 15 figures. This is an updated version of the preprint available at http://precedings.nature.com/documents/6956/version/

Investigation of structure property relationships in liquid processible, solvent free, thermally stable bismaleimide-triazine (BT) resins

Three cyanate ester monomer or oligomer species: 2,2-bis(4-cyanatophenyl)propane 1, 1-1-bis(4-cyanatophenyl)ethane (2), and the oligomeric phenolic cyanate (PrimasetTM PT30) (3), are blended in various ratios with bis(4-maleimidophenyl)methane, (4), to form binary and ternary mixtures (11 in total) and cured, in the absence of catalysts (3 K/min to 150 °C + 1 hour; 3 K/min to 200 °C + 3 hours), followed by a post cure (3 K/min to 260 °C + 1 hour). The use of liquid monomer, (2), offers the possibility of liquid processing in blends containing minority compositions of bismaleimide. Glycidylmethacrylate is explored as a reactive diluent (2.5-10 wt %) to linked interpenetrating network polymer structures comprising cyanate ester and bismaleimide components with glass transition temperatures of 267-275 ºC, depending on composition; the onset of thermo-oxidative degradation ranges from 386-397 ºC. When a binary blend of (2) and (3) (with the former in the minority) is co-cured with (4), an excellent balance of properties is achieved with liquid processing, a Tg greater than 400 C and onset of degradation of 425 ºC in static air. Kinetic analysis of DSC data using Ozawa and Kissinger methods yield activation energies of between 107- 112 kJ/mole for a binary blend of (1)90-(4)10, which is in good agreement with literature. Molecular dynamics simulation of the same blend in cured form gave a simulated glass transition temperature of 250 C that is in very close agreement with empirical DMTA data