Characterization of asphalt fume composition under simulated road paving conditions by GC/MS and microflow LC/quadrupole time-of-flight MS

A highly sensitive, selective, and reliable analytical method has been developed and validated for characterization of asphalt fume generated under simulated road paving conditions. A dynamic asphalt fume generation system was modified to provide consistent test atmospheres at simulated asphalt road paving conditions. In the process of fume generation, asphalt was initially preheated in an oven to 170 degrees C, pumped to a large kettle, which maintained the asphalt temperature between 150 and 170 degrees C, and then transferred to the generator. The fume was conducted from the generator to an exposure chamber through a heated transfer line. Characterization of the asphalt fume test atmospheres included the following: (1) determination of the consistency of the asphalt aerosol composition within the generation system; (2) quantification of total organic matter of the asphalt fume by electron impact ionization of isotope dilution gas chromatography/ mass spectrometry); and (3) identification of individual priority polycyclic aromatic hydrocarbons (PAHs) in asphalt fume by selected ion monitoring. With the developed method, asphalt fumes could be characterized into three fractions: (1) filter collection of a large molecular size fraction over a range of mass-to-charge (m/z) ratios of 173-309; (2) XAD-2 trapping of a medium molecular size fraction over a range of m/z ratios of 121-197; and (3) charcoal trapping of a small molecular size fraction that contained mainly the volatile vapor fraction over a range of m/z ratios of 57-141. Total organic matter of the asphalt fume was quantified over the 5 exposure days. Sixteen specific priority PAHs were monitored and identified. These PAHs were determined at trace levels on the filter fraction. A novel approach, which utilizes collision-induced dissociation of fragmentation pathway leading to a characteristic fragmentation pattern by coupling microflow liquid chromatography to atmospheric pressure chemical ionization of quadrupole time-of-flight mass spectrometry, was used to further clarify the trace amount of key components present in simulated road paving asphalt fumes. These results demonstrate that asphalt fume composition could be characterized and specific priority PAHs could be identified by this method. The major advantages of this method are its highly sensitivity, selectivity, and reliability for chemical hazard characterization in a complex mixture. This method is suitable for support toxicity studies using simulated occupational exposure to asphalt fumes.     

High-Temperature Nanoindentation of SiC/SiC Composites

JOM - The results of high-temperature nanoindentation testing on both a control and a neutron-irradiated silicon carbide matrix silicon carbide fiber composite sample are presented. The mechanical...     

Multiple-input multiple-output over-thehorizon radar: experimental results

Results from an experiment that applied one class of multiple-input multiple-output (MIMO) waveform techniques to over-the-horizon radar (OTHR) are reported. The experiment objective was to demonstrate that adaptive transmitter beamforming could be used in an appropriately design radar to reject spatially discrete Doppler-spread clutter. In the particular MIMO radar architecture that the authors call non-causal transmit beamforming, conventional or adaptive transmitter beamforming occurs following waveform transmission, propagation, scatter from targets and clutter sources, return propagation and finally signal reception. In the case reported herein spatially discrete clutter was successfully rejected to the noise floor of the radar return with rejection in excess of 35 dB achieved using common adaptive algorithms and straightforward training data selection. As part of the rejection algorithm the transmitted waveform direction-of-departure (DOD) from the transmitter array to the target was estimated and used as the preserved steer direction in the adaptive beamformer. The DOD estimates agree well with the geometrically determined true values. The demonstration of non-causal transmit beamforming suggests that it will be possible to create multiple simultaneous adaptive range-dependent transmitter beams with an appropriately designed OTHR. This has several applications including for the mitigation of Doppler-spread clutter.     

Riverine turtles select habitats maintained by natural discharge regimes in an unimpounded large river

Turtle populations are imperiled worldwide, but limited ecological information from unaltered systems hampers science‐based management and conservation of some species, especially riverine turtles such as the spiny softshell (Apalone spinifera). We therefore investigated movements and spatial habitat selection of 54 A. spinifera in 633 river kilometres (rkm) of the least‐altered river in the conterminous United States—the Yellowstone River in Montana—from 2005 to 2009. Movement rates and home ranges were smaller than in fragmented, altered river systems because nesting and overwintering habitats were common and in close proximity. Habitat selection also differed. A. spinifera in the Yellowstone River overwintered in unaltered bluff pools and summered in complex reaches with side channels, islands, and diverse habitats. However, those in the highly altered Missouri River used deep alluvial pools for overwintering and flooded, inundated, or backwatered tributary mouths in spring and summer. Importantly, selected habitats in both rivers were functionally similar, including complex river reaches (with multiple channels, islands, and diverse habitats) and natural pool types. Unfortunately, these are the very habitats that are limited in rivers affected by dams, bank stabilization, and channelization. Therefore, preservation of natural and diverse riverine habitats—and the fluvial dynamics that maintain them—may enhance conservation of A. spinifera in large rivers.     

支持外观造型创新设计的计算机辅助设计环境

介绍一个计算机辅助设计环境，该环境利用进化计算及可视化技术生成二维草图及三维图像，以支持设计人员的创新设计．用一个艺术设计实例介绍了该环境所采用的基于树结构的遗传算法，实例用一般的数学表达式生成艺术品底座外形，用复合函数表达式生成艺术花卉的三维图像．实例表明：文中方法能够生成一些有创意的解，并展示了进化的计算方法在创新设计中的潜力。     

Noncausal Adaptive Spatial Clutter Mitigation in Monostatic MIMO Radar: Fundamental Limitations

The problem of a point target detection masked by clutter distributed over range and Doppler, including the range and Doppler of the target, is considered for a multimode propagation scenario commonly encountered in quasimonostatic HF over-the-horizon radars (OTHR). Here, a clutter signal spread in Doppler frequency due to propagation via a disturbed ionospheric layer competes with a target and narrowband clutter returns propagating via a stable ionospheric layer with the same group delay (radar range). Mitigation over all ranges of spread clutter propagating via a “mixed mode” path with indistinguishable direction-of-arrival (DoA) relative to the target requires (potentially adaptive) transmit beamforming to exploit the direction-of-departure (DoD) difference, which varies as a function of radar range. This range-dependent beamforming can be implemented only via the use of multiple-input multiple-output radar technology. In this paper, we explore the fundamental limitations that exist for the maximal dimension of the area in range-Doppler space occupied by spread clutter and the required properties (cardinality) of the orthogonal waveform set for efficient spread clutter mitigation.