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O'Dea AR Curtis AF Green NJ Timmel CR Hore PJ 《The journal of physical chemistry. A》2005,109(5):869-873
Monte Carlo simulations of the effects of weak magnetic fields on the recombination of interacting radical pairs undergoing free diffusion in solution have been performed, with the aim of determining the influence on the low field effect of the magnetic dipolar coupling between the radicals. The suppression of singlet-triplet interconversion in the radical pair by the dipolar interaction is found to be pronounced at magnetic field strengths comparable to the hyperfine interactions in the radicals, to the extent that the low field effect is completely abolished. The averaging of the dipolar coupling by the translational diffusion of the radicals around one another is relatively efficient in the presence of strong magnetic fields but becomes ineffective in weak applied fields where the strength of the dipolar interaction is independent of the orientation of the inter-radical vector. Low field effects are only likely to be observed if the motion of the radical pair is restricted in some way so as to increase the likelihood that, having separated to the large distance required for the dipolar interaction to have a negligible effect, the radicals subsequently encounter and have the opportunity to recombine. 相似文献
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An unusual ring-expansion reaction of 4-amino-1,1-dioxo-[1,2,3,5]-thiatriazoles has been identified that produces the relatively rare 5-amino-1,1-dioxo-[1,2,4,6]-thiatriazines and. Initial alkylation of the thiatriazole with alpha-halo-esters at N-3 produces alpha-substituted esters which, under basic reaction conditions, undergo opening of the thiatriazole ring and re-closure to a thiatriazine ring. Similar alkylations of with diethyl chloromalonate and ethyl dichloroacetate lead to the loss of SO2 and the production of triazine and triazole, apparently by an initial alkylation at N-5. The reaction of with phenacyl bromides or a phenacyl dibromide forms fully unsaturated 5-amino-1,1-dioxo-[1,2,4,6]-thiatriazines. 相似文献
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M. Dowdall J. P. Gwynn C. Moran C. Davids J. O'Dea B. Lind 《Journal of Radioanalytical and Nuclear Chemistry》2005,266(2):217-223
Summary The role of organic soil as a sink for radioactive contaminants in a High Arctic environment was studied. Samples were obtained
from an area of organic soil located on the Arctic archipelago of Svalbard (79° N) and from a non-organic control site in
the same region. Samples were differentiated into organic layers and the underlying material and measured for a suite of anthropogenic
and natural radionuclides and for a variety of soil chemistry parameters. Results indicated that the organic components of
the soil constitute a sink term for a number of radionuclides. Values for Pu isotopes, 137Cs and 238U were appreciably higher at the study site than at the control site, by up to a factor of 40 for Pu and 20 for 137Cs and 238U. The source of 238U to the site appeared to be enrichment of this isotope from surface or melt water via adsorption to to either iron hydroxides
or organic matter although the situation pertaining to Pu and 137Cs remains less clear. 相似文献
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A Gurtu P K Malhotra I S Mittra P M Sood SC Gupta VK Gupta GL Kaul LK Mangotra Y Prakash NK Rao ML Sharma 《Pramana》1974,3(5):311-322
This is a continuation of our earlier investigation (Gurtuet al 1974Phys. Lett. 50 B 391) on multiparticle production in proton-nucleus collisions based on an exposure of emulsion stack to 200 GeV/c beam at the NAL. It is found that the ratioR em = 〈n s〉/〈n ch〉, where 〈n ch〉 is the charged particle multiplicity in pp-collisions, increases slowly from about 1 at 10 GeV/c to 1·6 at 68 GeV/c and attains a constant value of 1·71 ± 0·04 in the region 200 to 8000 GeV/c. Furthermore,R em = 1·71 implies an effectiveA-dependence ofR A =A 0.18,i.e., a very weak dependence. Predictions ofR em on various models are discussed and compared with the emulsion data. Data seem to favour models of hadron-nucleon collisions in which production of particles takes place through adouble step mechanism,e.g., diffractive excitation, hydrodynamical and energy flux cascade as opposed to models which envisage instantaneous production. 相似文献
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Dr. Ain Uddin Seth R. Allen Adrian K. Rylski Connor J. O'Dea Dr. Jack T. Ly Dr. Tod A. Grusenmeyer Dr. Sean T. Roberts Dr. Zachariah A. Page 《Angewandte Chemie (International ed. in English)》2023,62(22):e202219140
The use of visible light to drive polymerizations with spatiotemporal control offers a mild alternative to contemporary UV-light-based production of soft materials. In this spectral region, photoredox catalysis represents the most efficient polymerization method, yet it relies on the use of heavy-atoms, such as precious metals or toxic halogens. Herein, spin-orbit charge transfer intersystem crossing from boron dipyrromethene (BODIPY) dyads bearing twisted aromatic groups is shown to enable efficient visible light polymerizations in the absence of heavy-atoms. A ≈5–15× increase in polymerization rate and improved photostability was achieved for twisted BODIPYs relative to controls. Furthermore, monomer polarity had a distinct effect on polymerization rate, which was attributed to charge transfer stabilization based on ultrafast transient absorption and phosphorescence spectroscopies. Finally, rapid and high-resolution 3D printing with a green LED was demonstrated using the present photosystem. 相似文献
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Alexander W. Bassett Kayla R. Sweet Robert M. O'Dea Amy E. Honnig Claire M. Breyta Julia H. Reilly John J. La Scala Thomas H. Epps III Joseph F. Stanzione III 《Journal of polymer science. Part A, Polymer chemistry》2020,58(5):673-682
Dual-functional monomers consist of two distinctly different functional groups that enable chemical versatility. The most readily available epoxy-methacrylate dual-functional monomer is glycidyl methacrylate (GMA). In an effort to produce bio-based, aromatic complements to GMA, asymmetric phenolic diols (vanillyl alcohol, syringyl alcohol, gastrodigenin, and tyrosol) were identified and selectively epoxidized at the aromatic hydroxyl followed by subsequent esterification at the aliphatic hydroxyl to prepare dual functional monomers, vanillyl alcohol epoxy-methacrylate (VAEM), syringyl alcohol epoxy-methacrylate (SAEM), gastrodigenin epoxy-methacrylate (GDEM), and tyrosol epoxy-methacrylate (TEM). These monomers are viable platforms for a multitude of applications due to their unique chemical functionalities. VAEM, SAEM, GDEM, and TEM were homopolymerized individually to produce aromatic, bio-based epoxy-functional thermoplastics analogous to poly(GMA). The molecular weight distributions and thermal properties of each polymer were evaluated, as were the surface characteristics of flow-coated thin films from these polymers. Most of the newly prepared epoxy-functional thermoplastics exhibited increased thermal stability (initial decomposition temperatures >260 °C in air) relative to poly(GMA), while retaining similar glass transition temperatures (~ 65 °C) and surface energies (~ 53 mJ m−2); thus, these materials could be substituted for poly(GMA) and enable use in higher-temperature applications. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 673–682 相似文献
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Background
Our previous work described the neural processes of motor response inhibition during a stop signal task (SST). Employing the race model, we computed the stop signal reaction time (SSRT) to index individuals' ability in inhibitory control. The pre-supplementary motor area (preSMA), which shows greater activity in individuals with short as compared to those with long SSRT, plays a role in mediating response inhibition. In contrast, the right inferior prefrontal cortex (rIFC) showed greater activity during stop success as compared to stop error. Here we further pursued this functional differentiation of preSMA and rIFC on the basis of an intra-subject approach. 相似文献10.
在静止汞滴电极上用吸附方波伏安法研究了9个单偶氮化合物的表面电化学反应,观察到3种类型的方波伏安图,其中两类可用提出的4电子二步还原反应机理解释。第一步为准可逆还原,第二步为完全不可逆。第三种类型的伏安图可解释为4电子一步还原。以这两种反应机理为数学模型,用非线性最小二乘法分析实验伏安图,理论曲线与实验曲线吻合极好。获得了各偶氮化合物表面电化学反应的动力学参数,初步归纳出反应机理与取代基的关系,为研究其在生物体内的降解反应及致癌性提供了有参考价值的化学信息。 相似文献
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