Determinants of polling accuracy: the effect of opt-in Internet surveys

<p>With the changing polling environment and the difficulties in correctly measuring public opinion, it is crucial to study the effects of polling practices. Elections provide an opportunity to examine how well polls measure support for political parties and how polling practices influence the accuracy of polls. Based on 110 pre-election polls conducted in Sweden, a multiparty system, we find that probability-based samples yield more accurate polls compared to opt-in Internet samples. Thus, our results point to a tradeoff between inexpensive online polls and accuracy.</p

Investigation of the absorption Ångström exponent and its relation to physicochemical properties for mini-CAST soot

<p>In this work, a mini-CAST soot generator was used to produce soot with different optical and physicochemical characteristics. Absorption Ångström exponents (<i>AAE</i>) expressing the absorption wavelength dependence were assessed by multiwavelength <i>in-situ</i> and filter-based (aethalometer) laser extinction. The two optical techniques showed good agreement. For the chosen mini-CAST operating conditions, <i>AAE</i>s between 1 and 3.5 were found. Soot with high mass-fractions of organic carbon (OC) and pyrolytic carbon (PC) determined with thermal optical analysis were associated with <i>AAE</i>s significantly higher than 1. Heating to 250 and 500°C removed the majority of polycyclic aromatic hydrocarbons. However, the thermal-optical analysis revealed that OC and PC were abundant in the soot with <i>AAE</i> > 2 also after heating the aerosol. Analysis of mass absorption cross section ratios for elemental carbon and OC indicated that elevated <i>AAEs</i> also after heating to 500°C could be related to persistent OC and PC components and/or the refractory soot. By comparing the mini-CAST soot optical properties with soot properties derived from <i>in-situ</i> extinction measurements in a premixed flame, mini-CAST soot with a higher <i>AAE</i> could be identified as less mature soot.</p> <p>Copyright © 2018 The Authors</p