The impact of loops on the game of cops and robbers on graphs

In the game of cops and robbers on graphs, the cops and the robber are allowed to pass their turn if they are located on a looped vertex. This paper explores the effect of loops on the cop number and the capture time. We provide examples of graphs where the cop number almost doubles when the loops are removed, graphs where the cop number decreases when the loops are removed, graphs where the capture time is quadratic in the number of vertices and copwin graphs where the cop needs to move away from the robber in optimal play.     

Surface energy gradient driven convection for generating nanoscale and microscale patterned polymer films using photosensitizers

The Marangoni effect describes how fluid flows in response to gradients in surface energy. This phenomenon could be broadly harnessed to pattern the surface topography of polymer films if generalizable techniques for programming surface energy gradients existed. Here, a near UV–visible light (NUV–vis) photosensitizer, 9,10‐dibromo‐anthracene (DBA), was doped into thin films of a model polymer, poly(isobutyl methacrylate). After exposure to light through a photomask and heating above the glass transition, thermolysis of photo‐oxidized DBA and grafting to the polymer promoted flow of the film material into the exposed regions. This mechanism did not significantly alter the molecular weight of PiBMA or the film's glass transition temperature, but resulted in an increase in film surface energy as indicated by a decrease in water contact angle. Film height variations of 580 nm were produced using a mask with 12.5 μm features; a mask with 800 nm features was also employed to generate topographic features of corresponding width without expensive contacting equipment. Due to the broad absorbance spectra of DBA, highly accessible and/or unconventional light sources may be employed in this process; this advantage was demonstrated by patterning with sunlight. The nonspecific radical‐mediated nature of the DBA grafting reaction makes this a promising approach for many classes of polymers. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2014 , 52, 1195–1202     

Meltblown fibers: Influence of viscosity and elasticity on diameter distribution

Both melt viscosity (η_o) and elasticity (correlated here with the longest melt relaxation time λ₁) were found to control the diameter distribution of meltblown fibers. Fibers were formed by melt blowing binary polystyrene (PS) blends containing widely differing component molecular weights using a custom-built laboratory apparatus. Varying the concentration and molecular weight of a high molecular weight PS provided independent control over η_o and λ₁. These rheological parameters influence the average diameter (d_av) and the distribution of diameters (coefficient of variation, CV) of meltblown fibers in different ways. Increasing η_o leads to an increase in d_av but has little impact on CV. On the other hand, increasing λ₁ beyond a threshold value reduces CV while simultaneously increasing d_av. A one-dimensional slender-jet theoretical model with both upper convected Maxwell and Phan–Thien and Tanner constitutive equations was developed to investigate the influence of viscoelasticity and processing parameters on the properties of meltblown fibers. This model predicts a strong dependence of fiber diameter on the air shear stress and variations in fiber diameter with viscoelasticity that are in qualitative agreement with the experimental results. We believe these results suggest that carefully controlling the viscoelastic profile of polymers used in melt blowing is a viable approach for producing nanofibers with narrow fiber diameter distributions using current commercial equipment.     

Dark uncertainty

Standard uncertainties obtained by the GUM approach for a range of analytical methods are compared directly and indirectly with estimates of reproducibility standard deviation for the same methods. Results were obtained from both routine analysis and international key comparisons. A general tendency for the uncertainty to be substantially less than the reproducibility standard deviation was found.     

Method validation in analytical sciences: discussions on current practice and future challenges

Accreditation and Quality Assurance - Eurachem held a workshop on method validation in analytical sciences in Gent, Belgium, on 9–10 May 2016. A summary of the working group discussions is...     

House-of-security approach to measurement in analytical chemistry: quantification of human error using expert judgments

A new technique for quantification of human errors in chemical analysis using expert judgments is described. This technique is based on the house-of-security approach developed recently in the field of safety and security for prevention of terrorist and criminal attacks against an organization. The following relative quantification parameters (expressed in %) are proposed in the technique: (a) likelihood score of human error in a chemical analytical measurement/testing method, (b) severity score of human error for reliability of the test results, (c) importance score of a component of a laboratory quality system, and (d) effectiveness score of the quality system as a whole in preventing/blocking human error. As an example, 34 scenarios of human error in pH measurement of groundwater are discussed and quantified.     

A scale mixer model for sis waveguide receivers

We report results from measurements of a scale mixer model, built to investigate the embedding impedance presented to a superconductor-insulator-superconductor (SIS) tunnel junction detector in a full height waveguide with two tuning elements. The embedding impedance is measured as a function of junction position across the waveguide channel. The results are compared to i) computer simulations of the embedding impedance using waveguide theory, ii) a lumped element circuit derived from the theory, iii) an SIS receiver operating between 200 and 280 GHz.     

三维光存储中折射率失配引起的球差补偿

为实现三维光存储中折射率失配引起的球差补偿,建立了光学存储系统模型,获得了折射率失配引起的波前偏差函数与存储深度的表达式.采用泽尔尼克循环多项式对波前偏差函数进行补偿展开.在双光子荧光和单光子共焦荧光读出方式下,均可获得读出荧光强度与存储深度的关系:在折射率失配引起的球差未得到补偿矫正的情况下,存储深度在200 μm左右读出荧光强度基本上下降为零;当折射率失配引起的初级球差被补偿矫正后,读出荧光强度随存储深度的下降得到较好改善;当折射率失配引起的二级球差被补偿矫正后,存储深度在1 mm内存储点强度随深度基本上没有明显地变化.并且对像差补偿方法进行了具体地分析.