No abstract

Rock dynamic fracture is a complex problem and has received considerable attention during the last few decades. In this paper, tensile crack softening failure criterion is used to study impact‐induced crack initiation and propagation in rocks. In order to examine applicability of the criterion, under realistic loading and boundary conditions, three boundary conditions were analyzed in details and an impacting experiment using single cleavage semicircle compression (SCSC) specimens had been successfully simulated. A good agreement was achieved between the simulation and experimental results. It was concluded that the boundary conditions play an important role in rock dynamic fracturing. When a stress wave propagates from a material with low wave impedance to a material of high wave impedance, the compression wave is partially reflected back and the process of fast cracking is suppressed. In addition, with the change of the tensile strength and the fracture energy, the crack initiation modes can be divided into four types.

Biomass burning is a dominant source of ultrafine particulate matter in the atmosphere. Particulate matter is a leading health risk factor on a global scale, causing millions of premature deaths annually. Biomass burning also emits short-term climate forcers which contribute to the warming of the Earth’s atmosphere. Wood and animal dung are widely employed in the developing world as the primary sources of household energy. While wood burning is well studied, emissions from dung remain largely uncharacterized. Emissions from a given burn are highly complex chemical mixtures. While specific biomass tracerssuch as levoglucosanare employed to track burns, a fundamental chemical understanding of biomass emissions is required to predict their impacts. Herein, we conducted comprehensive sets of chemical analyses for particles emitted from biomass burning. Samples were generated using a tube furnace allowing reproducible, precise control of conditions. Emission factor data for levoglucosan and its isomers were measured from extracted particulate matter. We found that the levoglucosan emission factors from two distinct types of cow dung were consistently lower than that from wood. The water-extractable fraction of dung emissions exhibited light-absorptive properties greater than wood. Nontargeted chemical characterization was achieved through deconvolution of high-resolution mass spectrometry data. Overall, we present that the key differences between wood and dung emissions mirror the differences in their fuel compositions. The complexity of the extracted spectra and the unique characteristics of dung emissions accentuate the need for further study on biomass types less common within the Western context.