On Compressive Brittle Fragmentation

Dynamic brittle fragmentation is typically described using analytical and computational approaches for tensile stress‐states. However, most fragmentation applications (e.g., impact, blast) involve very large initial compressive stresses and deformations. In this study, the compressive fragmentation of brittle materials is investigated experimentally across a range of materials: silicon carbide, boron carbide, spinel, basalt and a stony meteorite. Analysis of our experimental results suggests that there exists two different regimes in the fragment size distributions, based on two brittle fragmentation mechanisms. The first is a mechanism that produces larger fragments and is associated with the structural failure of the sample being tested. This mechanism is influenced by the loading conditions (rate, stress state) and sample geometry. The second fragmentation mechanism produces comparatively smaller fragments and arises from the coalescence of fractures initiating and coalescence between defects in regions of large stresses and contact forces (e.g., between two fractured surfaces from the larger fragments). A framework is developed for comparing experimental compressive fragmentation results with tensile fragmentation theories. The compressive experimental results are shown to be adequately described by the theories using the new framework.     

Enantioselective Preference and High Antennal Sensitivity for (−)-Ipsdienol in Scent-Collecting Male Orchid Bees, <Emphasis Type="Italic">Euglossa cyanura</Emphasis>

Male neotropical orchid bees (Euglossini) collect volatile chemicals from their environment, store them in tibial pouches, and later expose their “perfumes” during a courtship display. Here, we showed that enantiomeric selectivity plays an important role in the choice of volatiles by male Euglossa cyanura in southern Mexico, and that behavioral selectivity is linked to antennal sensitivity. In field bioassays with equal concentrations of (+)-ipsdienol, (−)-ipsdienol, and racemate, males preferred the (−)-isomer to the racemate, while neglecting the (+)-isomer. Correspondingly, antennae of male E. cyanura showed larger electroantennographic responses to the (−)-isomer than to the (+)-isomer. In comparison, antennae of male Euglossa mixta, which are not attracted to any form of ipsdienol, showed lower electroantennographic responses to (−)-ipsdienol than did antennae of E. cyanura, and also did not differ in sensitivity with respect to the (+)- or (−)-isomers. We suggest that (−)-ipsdienol is an important component of perfume signals in male E. cyanura, which have undergone selection in favor of increased antennal sensitivity to that enantiomer.     

Thermal plasma vitrification process as an effective technology for fly ash and chromium‐rich sewage sludge utilization

The main goal of the vitrification process for environmental research is the destruction of hazardous waste. This study proposes the use of a thermal plasma treatment process to transform fly ash and chromium‐rich sewage sludge into glassy products called vitrificates that can be stored on the land without harmful environmental effects. This is achieved by: (i) decreasing the temperature and energy used to adjust process cost minimization; and (ii) stabilization of vitrificates for different compositions of waste mixture. The chemical stabilization of final products was examined by heavy metals leachability tests. Hardness tests were done to verify the physical stabilization of vitrificates. The most stable vitrificates were obtained from a sample consisting of 90 wt% fly ash and 10 wt% chromium sludge. The thermal plasma treatment is an effective method which can be used to convert hazardous waste mixtures into less toxic or inert glassy products. The chemical composition of raw materials influenced the chemical and physical properties of the vitrificates and determined their internal structures. Mixtures of two different hazardous wastes reduces the process cost without negative environmental impact, which is an innovation in thermal plasma treatment technology. © 2013 Society of Chemical Industry     

On the uniqueness of Web browsing history patterns

We present the results of the first large-scale study of the uniqueness of Web browsing histories, gathered from a total of 368,284 Internet users who visited a history detection demonstration website. Our results show that for a majority of users (69 %), the browsing history is unique and that users for whom we could detect at least four visited websites were uniquely identified by their histories in 97 % of cases. We observe a significant rate of stability in browser history fingerprints: for repeat visitors, 38 % of fingerprints are identical over time, and differing ones were correlated with original history contents, indicating static browsing preferences (for history subvectors of size 50). We report a striking result that it is enough to test for a small number of pages in order to both enumerate users’ interests and perform an efficient and unique behavioral fingerprint; we show that testing 50 Web pages is enough to fingerprint 42 % of users in our database, increasing to 70 % with 500 Web pages.     

Genetic algorithm approach to calculation of geometric configurations of 2D clusters of uniformly charged classical particles

The genetic algorithms in the variant developed earlier and in that improved by the mechanism of niches have been exploited in the analysis of global and local minima of the potential energy depending either on the inverse distance between particles (as in Coulomb interactions) or on the logarithm of this distance. The number N of point-charge particles is finite and they are confined by the parabolic potential. Solutions of the optimization problems yield for 9?N?30 the ground-state configurations and a number of the metastable configurations as well as some saddle points. For the model with the logarithmic interactions, the new ground-state configuration is found for N=20, whereas for the Coulomb model, some new configurations, observed earlier in the molecular dynamics simulations, are determined.     

Influence of Plasma Waves on the Photoacoustic Signal of Silicon Samples

This article presents the results of theoretical and experimental studies of the influence of plasma waves on the photoacoustic signals of Si samples. The aim of these investigations was to find and examine the sensitive measurement configurations and the configurations of the sample in the photoacoustic cell for detection and measurement of the lifetime of excess carriers. Two measurement configurations were examined: transmission and phase lag and two configurations of the sample in the photoacoustic cell. This article demonstrates that both configurations for samples with differently prepared surfaces are effective for observation and detection of plasma waves with the photoacoustic method.     

Electrochemical studies of four organometallic redox couples as possible reference redox systems in 1-ethyl-3-methylimidazolium tetrafluoroborate

The electrochemical behavior of four organometallic redox couples has been studied in the room temperature ionic liquid 1-ethyl-3-methylimidazolium tetrafluoroborate. Diffusion controlled anodic and cathodic peaks were found for the redox couples Fc/Fc⁺ (ferrocene/ferrocenium), Cc/Cc⁺ (cobaltocene/cobaltocenium) on glassy carbon, platinum and gold. Bis(biphenyl)chromium(I) tetraphenylborate (BCr/BCr⁺) yielded a well-behaved diffusion controlled pair of cathodic-anodic peaks only on glassy carbon and gold as working electrodes. The electrode reaction of decamethylferrocene was affected by adsorption of the reduced form on all of the three working electrodes employed by us. The applicability of three of the four redox couples studied as candidates for reference redox systems in this ionic liquid is discussed.