Snow-cover mapping in forests by constrained linear spectral unmixing of MODIS data

A snow-cover mapping method accounting for forests (SnowFrac) is presented. SnowFrac uses spectral unmixing and endmember constraints to estimate the snow-cover fraction of a pixel. The unmixing is based on a linear spectral mixture model, which includes endmembers for snow, conifer, branches of leafless deciduous trees and snow-free ground. Model input consists of a land-cover fraction map and endmember spectra. The land-cover fraction map is applied in the unmixing procedure to identify the number and types of endmembers for every pixel, but also to set constraints on the area fractions of the forest endmembers. SnowFrac was applied on two Terra Moderate Resolution Imaging Spectroradiometer (MODIS) images with different snow conditions covering a forested area in southern Norway. Six experiments were carried out, each with different endmember constraints. Estimated snow-cover fractions were compared with snow-cover fraction reference maps derived from two Landsat Enhanced Thematic Mapper Plus (ETM+) images acquired the same days as the MODIS images. Results are presented for non-forested areas, deciduous forests, coniferous forests and mixed deciduous/coniferous forests. The snow-cover fraction estimates are enhanced by increasing constraints introduced to the unmixing procedure. The classification accuracy shows that 96% of the pixels are classified with less than 20% error (absolute units) on 7 May 2001 when all forested and non-forested areas are included. The corresponding figure for 4 May 2000 is 88%.     

Micromechanical Testing of Fracture Initiation Sites in Welded High-Strength Low-Alloy Steel

Micropillar compression tests were performed on martensite (M) and retained austenite (A) containing constituents formed in high-strength low-alloy steel after simulated thermal weld heat treatment. Due to the complicated fine microstructure of the constituent, the resulted stress–strain curves were further analyzed by considering the post-mortem scanning electron micrographs and the morphology of the deformation of the pillars. It was possible to obtain relevant data for the uniaxial stress–strain behavior of the M–A constituent in the studied steel. Microvickers measurements, which were converted to macroscopic yield stress by empirical relations, were compared with the micropillar compression test results. Comparison showed that these empirical relations are overestimating the obtained mechanical properties of the M–A constituents.     

Can a safety-in-numbers effect and a hazard-in-numbers effect co-exist in the same data?

Safety-in-numbers denotes a non-linear relationship between exposure (traffic volume) and the number of accidents, characterised by declining risk as traffic volume increases. There is safety-in-numbers when the number of accidents increases less than proportional to traffic volume, e.g. a doubling of traffic volume is associated with less than a doubling of the number of accidents. Hazard-in-numbers, a less-used concept, refers to the opposite effect: the number of accidents increases more than in proportion to traffic volume, e.g. is more than doubled when traffic volume is doubled. This paper discusses whether a safety-in-numbers effect and a hazard-in-numbers effect can co-exist in the same data. It is concluded that both effects can exist in a given data set. The paper proposes to make a distinction between partial safety-in-numbers and complete safety-in-numbers. Another issue that has been raised in discussions about the safety-in-numbers effect is whether the effect found in some studies is an artefact created by the way exposure was measured. The paper discusses whether measuring exposure as a rate or a share, e.g. kilometres travelled per inhabitant per year, will generate a safety-in-numbers effect as a statistical artefact. It is concluded that this is the case. The preferred measure of exposure is a count of the number of road users. The count should not be converted to a rate or to the share any group of road user contribute to total traffic volume.     

Can a road safety measure be both effective and ineffective at the same time? A game-theoretic model of the effects of daytime running lights

Studies that have evaluated the effects on accidents of daytime running lights for cars have consistently found that cars using daytime running lights are involved in fewer multi-party accidents in daylight than cars not using daytime running lights. However, studies evaluating the effects of mandatory use of daytime running lights have not always found an accident reduction. Although findings are mixed, there is a tendency for the aggregate effects of daytime running lights (i.e. the effects of an increasing share of traffic using daytime running lights) to be smaller than the intrinsic effects (i.e. the difference in accident involvement between cars using and not using daytime running lights). This paper presents a game-theoretic model to explain these apparently inconsistent findings. The game-theoretic model is based on so called Schelling-diagrams, originally introduced by Nobel laureate in economics Schelling. The effects of daytime running lights are modelled by means of Schelling-diagrams. It is shown that it is by no means impossible for cars using daytime running lights to always be safer than cars not using daytime running lights, while the total number of accidents remains constant even if the percentage of cars using daytime running lights increases from, say, 10% to 90%.     

International transferability of accident modification functions for horizontal curves

Studies of the relationship between characteristics of horizontal curves and accident rate have been reported in several countries. The characteristic most often studied is the radius of a horizontal curve. Functions describing the relationship between the radius of horizontal curves and accident rate have been developed in Australia, Canada, Denmark, Germany, Great Britain, New Zealand, Norway, Portugal, Sweden, and the United States. Other characteristics of horizontal curves that have been studied include deflection angle, curve length, the presence of transition curves, super-elevation in curves and distance to adjacent curves. This paper assesses the international transferability of mathematical functions (accident modification functions) that have been developed to relate the radius of horizontal curves to their accident rate. The main research problem is whether these functions are similar, which enhances international transferability, or dissimilar, which reduces international transferability. Accident modification functions for horizontal curve radius developed in the countries listed above are synthesised. The sensitivity of the functions to other characteristics of curves than radius is examined. Accident modification functions developed in different countries have important similarities. The functions diverge with respect to accident rate in the sharpest curves.     

Modeling and Simulation of an Integrated Micro Packed Bed Reactor-Heat Exchanger Configuration for Direct Dimethyl Ether Synthesis

The application of an integrated micro packed bed reactor-heat exchanger for highly exothermic syngas conversion to dimethyl ether was investigated by numerical simulation. A three-dimensional pseudo-homogeneous model was developed to describe concentration and temperature distributions inside a single reaction slit. The model was adopted at low Reynolds numbers (small catalyst particles and long residence times). The simulation results reveal that the micro packed reaction slit is close to isothermal, and a negligible temperature gradient is predicted also for a doubling of the critical reaction slit dimension, i.e. the reaction slit height. The flow in the reaction slit was modelled by Brinkman??s equation and it was found that the pressure drop in wide range of gas velocity was not significant. The reactor simulation showed good agreement with experimental results and could be further developed to assess the potential of microstructured packed bed reactors to intensify large-scale industrial processes.     

Norwegian‐grown Jerusalem artichoke (Helianthus tuberosus L.): morphology and content of sugars and fructo‐oligosaccharides in stems and tubers

BACKGROUND: Two field trials growing Jerusalem artichoke (Helianthus tuberosus L.) are discussed. Twenty genetic variants were compared in order to find genotypes suitable for Norwegian production. A second trial investigated the above‐ground part of early and late variants. RESULTS: The highest yield (28.7 t ha^?1) and highest amount of tubers per plant was obtained in early variants, e.g. the white Tysnes gave 1.72 kg tubers plant^?1. Early variants had a markedly lower portion of smooth tubers. Late variants gave the most preferable tuber shape, but low yield. Only a weak correlation was found between dry matter content and total content of fructo‐oligosaccharides (FOS) (r = 0.255) in the tubers. The mean content of FOS including sucrose through all variants was found to be 116 g kg^?1 fresh weight (FW) or 550 g kg^?1 dry weight (DW). The average chain length of FOS in the tubers was found to be DP3.9. There was no difference in tuber FOS content between early and late variants. The highest above‐ground amount biomass was found for the late variants when harvested in September. The content of soluble carbohydrates was found to be highest in stalks in August (sucrose and FOS major compounds). CONCLUSION: Early variants give the highest tuber yield under Norwegian growing conditions. Late variants give highest above‐ground biomass. Copyright © 2010 Society of Chemical Industry     

Parameterization and analysis of the optical absorption and scattering coefficients in a western Norwegian fjord: a case II water study

Based on statistical analyses of optical properties measured during a whole year of monthly cruises in a Norwegian fjord, we constructed a two-component model for the absorption and scattering coefficients for visible light. The input to the model is the concentrations of yellow substance and chlorophyll a. Because of the presence of a significant amount of nonalgal particles in coastal water, we assume that the absorption and scattering coefficients approach constant background values when the concentration of chlorophyll a approaches zero. The model works reasonably for a variety of optical conditions encountered throughout the year, with a possible exception during a bloom of the Emiliania huxleyi algae in June.