Mortars containing wood-based fibres under thermal exposure using cone calorimeter heating

The behaviour of concrete structures under fire can be improved by adding fibers. However, relatively little is known of the details of the possible beneficial features of the fibre addition. The aim of this study was to compare the effects of different wood-based fibres on the thermal properties of a standard laboratory cement mortar at conditions of a developing fire. The cone calorimeter heating method was used, and the sample thickness and heat flux were varied (25 mm or 50 mm, 25 kWm^?2 or 50 kWm^?2) to compare test conditions. The fibres comprised chemical pulp, chemi-thermomechanical pulp, recycled fibres and viscose fibres. The fibre content in the mortar was 0.15–0.5% by weight. Temperature and mass loos measurements of oven-dried specimens (moisture content <0.1%) showed no differences between different wood-based fibre mortars and plain mortar. With increasing moisture content (about 5%), however, the presence of fibres affected the release of moisture from the fibre mortar material. With rapid heating of mortars, which have a moisture content of about 5%, local pressures are easily built up. These pressures are mainly caused by free water vaporization. The rear surface temperature measurements indicate that in mortars containing wood-based fibres (0.15–0.5% by weight) the vaporization temperatures may be 20 –25% lower than in the reference mortar. Some effects on heat transfer can also be observed due to differences in water vaporization and movement processes.     

Organic memory using [6,6]-phenyl-C(61) butyric acid methyl ester: morphology, thickness and concentration dependence studies

We report a simple memory device in which the fullerene-derivative [6,6]-phenyl-C(61) butyric acid methyl ester (PCBM) mixed with inert polystyrene (PS) matrix is sandwiched between two aluminum (Al) electrodes. Transmission electron microscopy (TEM) images of PCBM:PS films showed well controlled morphology without forming any aggregates at low weight percentages (<10?wt%) of PCBM in PS. Energy dispersive x-ray spectroscopy (EDX) analysis of the device cross-sections indicated that the thermal evaporation of the Al electrodes did not lead to the inclusion of Al metal nanoparticles into the active PCBM:PS film. Above a threshold voltage of <3?V, independent of thickness, a consistent negative differential resistance (NDR) is observed in devices in the thickness range from 200 to 350?nm made from solutions with 4-10?wt% of PCBM in PS. We found that the threshold voltage (V(th)) for switching from the high-impedance state to the low-impedance state, the voltage at maximum current density (V(max)) and the voltage at minimum current density (V(min)) in the NDR regime are constant within this thickness range. The current density ratio at V(max) and V(min) is more than or equal to 10, increasing with thickness. Furthermore, the current density is exponentially dependent on the longest tunneling jump between two PCBM molecules, suggesting a tunneling mechanism between individual PCBM molecules. This is further supported with temperature independent NDR down to 240?K.     

Effect of driving experience on anticipatory look-ahead fixations in real curve driving

Anticipatory skills are a potential factor for novice drivers’ curve accidents. Behavioural data show that steering and speed regulation are affected by forward planning of the trajectory. When approaching a curve, the relevant visual information for online steering control and for planning is located at different eccentricities, creating a need to disengage the gaze from the guidance of steering to anticipatory look-ahead fixations over curves. With experience, peripheral vision can be increasingly used in the visual guidance of steering. This could leave experienced drivers more gaze time to invest on look-ahead fixations over curves, facilitating the trajectory planning.     

Nitrogen-doped graphene with enhanced oxygen reduction activity produced by pyrolysis of graphene functionalized with imidazole derivatives

Nitrogen-doped graphene nanoplatelets (N-GNP) with 1.6–3.3 at.% nitrogen content were synthesized by thermal annealing of GNP functionalized with a series of imidazole-based nitrogen-containing precursors of different nature, charge and nitrogen content. The imidazole derivatives included one ionic liquid, 1-butyl-3-methylimidazolium tetrafluoroborate (BMIBF4) and two polymers, a neutral one, poly(vinylimidazole) (PVI) and a poly(ionic liquid), poly(3-butyl-1-vinylimidazolium bromide) (PBVIBr). N-GNP showed enhanced electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline media compared to pristine GNP, with the number of electrons transferred in oxygen-saturated KOH at low overpotentials following the trend: 2.5 (pristine GNP) < 2.9 (N-GNP from PVI–GNP) < 3.3 (N-GNP from BMIBF₄–GNP) < 3.5 (N-GNP from PBVIBr-GNP). Interestingly, ORR catalytic activity did not correlate with total nitrogen content but was more affected by Brunauer–Emmett–Teller (BET) surface area. The most active materials were N-GNP with lowest doping levels and highest surface area resulting from the ionic (imidazolium-based) nitrogen precursors.     

Fibre mortar composites in fire conditions

A small-scale test series was carried out using the heating system (radiant exposure) of a cone calorimeter to detect any differences in the way different fibres affect the thermal properties of a standard mortar. The fibres were different polypropylene, polyacrylonitrile, aramide, carbon or steel. Fibres affect the release of moisture from the fibre mortar material. Local pressures caused by water vaporization due to rapid heating can be decreased by incorporating fibres. Fibres have a weak insulating effect. However, use of polyacrylonitrile fibres in mortar may increase the risk to spalling under rapid thermal exposure such as fire. The moisture level in specimens is highly significant for their thermal properties and hence their fire behavior.     

Online timestamped text indexing

In this paper we present an efficient method to index a text stream on-line in a fashion that allows, at any point in time, to find the longest suffix of the text that has appeared previously, and the closest (farthest) times in which it has appeared. Our algorithms allow efficient answers to these queries.