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61.
Abstract A review is presented of a very general aspect of the response of all metals subjected to displacive irradiation. This aspect is referred to as «persistence» and describes the tendency of both radiation-induced microstructural evolution and the associated changes in material properties or dimensional stability to evolve to saturation states that resist further change upon continued irradiation. It is shown that new persistent states can develop on a longer time frame associated with the late-term loss of existing microstructural components or the gain of new components, especially when transmutation and/or segregation occurs. The persistent states are often dependent on the irradiation conditions, and if these are changed, the material usually adjusts to form the persistent state characteristic of the new conditions, with the memory of the former state often lost, and sometimes leaving no visible record of the former state in the new microstructure. Depending on the microstructural components involved, the transition toward the new persistent state can occur quickly or very slowly. 相似文献
62.
The goal of this study was to determine the extent to which the variability seen in distortion product otoacoustic emissions (DPOAEs), among ears with normal hearing, could be accounted for. Several factors were selected for investigation, including behavioral threshold, differences in middle-ear transmission characteristics either in the forward or the reverse direction, and differences in contributions from the distortion and reflection sources. These variables were assessed after optimizing stimulus parameters for individual ears at each frequency. A multiple-linear regression was performed to identify whether the selected variables, either individually or in combination, explained significant portions of variability in DPOAE responses. Behavioral threshold at the f(2) frequency and behavioral threshold squared at that same frequency explained the largest amount of variability in DPOAE level, compared to the other variables. The combined model explained a small, but significant, amount of variance in DPOAE level at five frequencies. A large amount of residual variability remained, even at frequencies where the model accounted for significant amounts of variance. 相似文献
63.
John Asplund Gregory Clark Garner Cochran va Czabarka Arran Hamm Gwen Spencer Lszl Szkely Libby Taylor Zhiyu Wang 《组合设计杂志》2019,27(10):586-597
The crossing number of a graph is the smallest number of edge crossings over all drawings of in the plane. For any , the ‐planar crossing number of , is defined as the minimum of over all graphs with . Pach et al [Comput. Geom.: Theory Appl. 68 (2018), pp. 2–6] showed that for every , we have and that this bound does not remain true if we replace the constant by any number smaller than . We improve the upper bound to as . For the class of bipartite graphs, we show that the best constant is exactly for every . The results extend to the rectilinear variant of the ‐planar crossing number. 相似文献
64.
Heart rate variability analysis by chaotic global techniques in children with attention deficit hyperactivity disorder
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Rubens Wajnsztejn Tatiana Dias De Carvalho David M. Garner Luiz Carlos Marques Vanderlei Moacir Fernandes Godoy Rodrigo Daminello Raimundo Celso Ferreira Vitor E. Valenti Luiz Carlos De Abreu 《Complexity》2016,21(6):412-419
Attention deficit hyperactivity disorder (ADHD) is characterized by decreased attention span, impulsiveness, and hyperactivity. Autonomic nervous system imbalance was previously described in this population. We aim to compare the autonomic function of children with ADHD and controls by analyzing heart rate variability (HRV). Children with ADHD (22 boys, mean age 9.964 years) and 28 controls (15 boys, mean age 9.857 years) rested in supine position with spontaneous breathing for 20 min. Heart rate was recorded beat by beat. HRV analysis was performed by use of chaotic global techniques. ADHD promoted an increase in the chaotic forward parameter. The algorithm which applied all three chaotic global parameters was only the second optimum statistically measured by Kruskal–Wallis (P < 0.0001) and low standard deviations. It was also highly influential by principal component analysis with almost all variation covered by the first two components. The third algorithm which lacked the (high spectral Detrended Fluctuation Analysis) parameter performed best statistically. However, we chose the algorithm which applied all three chaotic globals due to previous studies mentioned in the text—forward and inverse problems. Comparison of the autonomic function by analyzing HRV with chaotic global techniques suggests an increase in chaotic activity in children with ADHD in relation to the control group. © 2015 Wiley Periodicals, Inc. Complexity 21: 412–419, 2016 相似文献
65.
Mary E. Garner Dr. Stephan Hohloch Prof. Dr. Laurent Maron Prof. Dr. John Arnold 《Angewandte Chemie (International ed. in English)》2016,55(44):13789-13792
Actinide complexes demonstrate unparalleled reactivity towards small molecules. However, utilizing these powerful transformations in a predictable and deliberate manner remains challenging. Therefore, developing actinide systems that not only perform noteworthy chemistry but also demonstrate controllable reactivity is a key goal. We describe a bis(NHC)borate thorium‐bpy complex ( 1 ) that is capable of reductively cleaving the R?NC bond in a series of organic isocyanides. In contrast to most actinide‐mediated bond activations, the dealkylation event mediated by 1 is remarkably general and yields very well‐defined products that assist in mechanistic elucidation. Synthesis of the rearranged but‐3‐enyl product from the reaction of 1 and cyclopropylmethyl isocyanide supports the notion of a radical‐based mechanism. 相似文献
66.
Alkenylalumination of substituted styrene oxides with [alpha-(ethoxycarbonyl)alkenyl]diisobutylaluminum, in the presence of BF(3).Et(2)O, affords the corresponding (Z)-alpha-alkylidene-gamma-aryl-gamma-hydroxy esters in 81-100% Z-selectivity. Chromatographic separation of isomers, followed by lactonization with trifluoroacetic acid, provides isomerically pure (Z)-alpha-alkylidene-gamma-aryl-gamma-butyrolactones in 53-78% overall yield. Isomerization of the (Z)-alkylidene hydroxyl esters using LDA, followed by protonation using a bulky proton source, such as BHT, provides a simple route to the corresponding alpha-(E)-alkylidene-gamma-phenyl-gamma-hydroxy esters in 72-78% yield, which were cyclized to obtain the corresponding (E)-butyrolactones in 78-85% yield. 相似文献
67.
Davies SG Garner AC Goddard EC Kruchinin D Roberts PM Smith AD Rodriguez-Solla H Thomson JE Toms SM 《Organic & biomolecular chemistry》2007,5(12):1961-1969
The diastereoselective conjugate addition of homochiral lithium amides to methyl 4-(N-allyl-N-benzylamino)but-2-enoate has been used as the key step in a simple and efficient protocol for the preparation of 3,4-substituted aminopyrrolidines. This protocol provides a complementary and stereoselective route to both anti- and syn-3-amino-4-alkylpyrrolidines as well as anti- and syn-3-hydroxy-4-aminopyrrolidines, in high de and ee viabeta-amino enolate functionalisation. This methodology has been applied to the synthesis of anti-(3S,4S)- and syn-(3R,4S)-3-methoxy-4-(N-methylamino)pyrrolidine. 相似文献
68.
The alpha-helix is the most abundant secondary structural element in proteins and is an important structural domain for mediating protein-protein and protein-nucleic acid interactions. Strategies for the rational design and synthesis of alpha-helix mimetics have not matured as well as other secondary structure mimetics such as strands and turns. This perspective will focus on developments in the design, synthesis and applications of alpha-helices and mimetics, particularly in the last 5 years. Examples where synthetic compounds have delivered promising biological results will be highlighted as well as opportunities for the design of mimetics of the type I alpha-helical antifreeze proteins. 相似文献
69.