Pushing nanoparticles with light - A femtonewton resolved measurement of optical scattering forces

Optomechanical manipulation of plasmonic nanoparticles is an area of current interest, both fundamental and applied. However, no experimental method is available to determine the forward-directed scattering force that dominates for incident light of a wavelength close to the plasmon resonance. Here, we demonstrate how the scattering force acting on a single gold nanoparticle in solution can be measured. An optically trapped 80 nm particle was repetitively pushed from the side with laser light resonant to the particle plasmon frequency. A lock-in analysis of the particle movement provides a measured value for the scattering force. We obtain a resolution of less than 3 femtonewtons which is an order of magnitude smaller than any measurement of switchable forces performed on nanoparticles in solution with single beam optical tweezers to date. We compared the results of the force measurement with Mie simulations of the optical scattering force on a gold nanoparticle and found good agreement between experiment and theory within a few fN. (C) 2016 Author(s)

Statistical mechanics of random two-player games

Using methods from the statistical mechanics of disordered systems we analyze the properties of bimatrix games with random payoffs in the limit where the number of pure strategies of each player tends to infinity. We analytically calculate quantities such as the number of equilibrium points, the expected payoff, and the fraction of strategies played with non-zero probability as a function of the correlation between the payoff matrices of both players and compare the results with numerical simulations.Comment: 16 pages, 6 figures, for further information see http://itp.nat.uni-magdeburg.de/~jberg/games.htm

European regulatory agenices should employ full time statisticians

No abstract available

Woven fabrics in book conservation: An investigation into the properties of aerolinen and aerocotton

Woven fabrics commonly referred to as ‘aerocotton’ and ‘aerolinen’ are frequently used in the conservation of books and manuscripts and are valued for their strength and flexibility. Although textiles have a long history in the production and repair of books, aerocottons and aerolinens are relatively recent materials adopted from early aircraft production. In 2007, the main supplier of these woven fabrics to the UK conservation community ceased production, and new producers started supplying a range of woven fabrics under the labels of ‘aerocotton’ and ‘aerolinen’. Understanding the strength, composition, and longevity of repair materials is central to conservation practice and this investigation tested two linens and two cottons alongside the discontinued cotton to quantify the relative strengths of the fabrics. Each fabric was tested before and after laundering, and in three directions (warp, weft, and bias). The tests conducted measured mass per unit area, thickness, sett, tensile strength, folding endurance, and dimensional change. In tensile strength tests the bias-cut fabrics were weakest but extended the most, whilst those cut in the weft direction were strongest. The cottons lasted longest in terms of folding endurance and the samples cut on the bias were the fastest to break. The dimensional change tests showed that washing affected the linens more than the cottons and that across all fabrics there was a greater amount of shrinkage in the warp direction. It is hoped that these results will provide concrete information to guide conservators in the preparation and use of aerocottons and aerolinens

Prevalent cases in observational studies of cancer survival: do they bias hazard ratio estimates?

Observational epidemiological studies often include prevalent cases recruited at various times past diagnosis. This left truncation can be dealt with in non-parametric (Kaplan–Meier) and semi-parametric (Cox) time-to-event analyses, theoretically generating an unbiased hazard ratio (HR) when the proportional hazards (PH) assumption holds. However, concern remains that inclusion of prevalent cases in survival analysis results inevitably in HR bias. We used data on three well-established breast cancer prognosticators – clinical stage, histopathological grade and oestrogen receptor (ER) status – from the SEARCH study, a population-based study including 4470 invasive breast cancer cases (incident and prevalent), to evaluate empirically the effectiveness of allowing for left truncation in limiting HR bias. We found that HRs of prognostic factors changed over time and used extended Cox models incorporating time-dependent covariates. When comparing Cox models restricted to subjects ascertained within six months of diagnosis (incident cases) to models based on the full data set allowing for left truncation, we found no difference in parameter estimates (P=0.90, 0.32 and 0.95, for stage, grade and ER status respectively). Our results show that use of prevalent cases in an observational epidemiological study of breast cancer does not bias the HR in a left truncation Cox survival analysis, provided the PH assumption holds true