A novel instrument is described capable of recording gas electron diffraction (GED) patterns of excited molecular states or transient species with pulsed electron beams. The system incorporates (1) a pulsed optical beam for electronic excitation of materials under study, (2) a synchronously pulsed source of 30–50 keV electrons in a space-charge-limited beam, (3) necessary vacuum environment and sample-handling capabilities, and (4) detection and signal processing equipment using an on-line procedure developed at the University of Arkansas. Data obtained for several test gases demonstrate successful operation of the instrument. The 193 nm laser photofragmentation of carbon disulfide, CS2, is described in detail. In agreement with a recent time-of-flight mass spectrometric study of the same process, carbon monosulfide was observed as the reaction product. This study is the first quantitatively successful joint exercise of on-line multichannel GED data recording and a stroboscopic electron source. The method is expected to be generally useful in determining the structures of excited molecular states or reactive species, and it may enable studies of time-dependent phenomena. The current time resolution is ∼20 ns.
Using experimentally observed processes of linear growth, heterogeneous nucleation, and polymer bending, with no additional assumptions, we have been able to model the two-dimensional formation of polymer domains by sickle hemoglobin. The domains begin with twofold symmetry and proceed toward closure into spherulites at a constant rate. Relationships derived from the simulations presented and the requirements of scaling result in simple expressions for the sensitivity of the closure times to the model input parameters and allow the results to be extended to regions not actually simulated. For concentrations above approximately 25 g/dl, closure times are longer than the time required for the conclusion of the polymerization reaction, and thus incomplete spherulites will be the dominant geometry at high concentrations. Moreover, spherulites are not predicted to form in times less than a few seconds, implying that spherulites will not form during the transit of erythrocytes through the capillaries. Polymer-polymer exclusion, surface nucleation, and monomer exhaustion were also explored and found to have only weak effects on the results.
Plant moisture content (PMC) is used as an indicator of forest flammability, which is assumed to be affected by climate drought. However, the fire-induced drought stress on PMC and its spatial and temporal variations are unclear. Based on a parallel monitoring experiment from 2014 to 2015, this study compared the PMCs and soil moisture contents (SMC) at five post-fire sites in central Yunnan Plateau, Southwest China. The number of years since last fire (YSF), season, topographic position, plant species and tissue type (leaf and branch) were selected as causal factors of the variations in PMC and SMC. A whole year parallel monitoring and sampling in the post-fire communities of 1, 2, 5, 11 and 30 YSF indicated that drought stress in surface soils was the strongest in spring within the first 5 years after burning, and the SMC was regulated by topography, with 64.6% variation in soil moisture accounted for by YSF (25.7%), slope position (22.1%) and season (10.8%). The temporal variations of PMC and SMC differed at both interannual and seasonal scales, but the patterns were consistent across topographic positions. PMC differed significantly between leaves and branches, and among three growth-forms. The mean PMC was lower in broad-leaved evergreen species and higher in conifer species. Season and soil temperature were the primary determinants of PMC, accounting for 19.1% and 8.3% of variation in PMC, respectively. This indicated phenology-related growth rather than drought stress in soil as the primary driver of seasonal changes in PMC. The significant variations of PMC among growth forms and species revealed that seasonal soil temperature change and dominant species in forest communities are useful indicators of fire risk assessment in this region.
The novel insecticide tetrachlorantraniliprole was synthesized utilizing 2,3,5-trichloropyridine as the starting material by a six-step route in 18% yield. The process of simultaneous oxidation and acyl chlorination was studied by in situ FTIR. The molecular structure of tetrachlorantraniliprole was identified by means of NMR, IR, MS, and X-ray diffraction analyses. The single crystal of tetrachlorantraniliprole was formed from toluene solvent, and exhibited monoclinic P2 1 /n group with crystal parameters of a = 15.3316(16) Å, b = 16.7139(16) Å, c = 19.6687(19) Å, V = 4835.2(8) Å 3 , and Z = 4. Moreover, its density = 1.605 g/m 3 , F(000) = 2328.0, µ = 2.17 mm −1 , and 26933 reflections were measured (2.992° 2θ 51.998°).
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