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排序方式: 共有336条查询结果,搜索用时 15 毫秒
331.
CA Guymon EN Hoggan NA Clark TP Rieker DM Walba CN Bowman 《Science (New York, N.Y.)》1997,275(5296):57-59
Photopolymerizable diacrylate monomers dissolved in fluid-layer smectic A and smectic C liquid crystal (LC) hosts exhibited significant spatial segregation and orientation that depend strongly on monomer structure. Small, flexible monomers such as 1,6-hexanediol diacrylate (HDDA) oriented parallel to the smectic layers and intercalated, whereas rod-shaped mesogen-like monomers such as 1,4-di-(4-(6-acryloyloxyhexyloxy)benzoyloxy)-2-methylbenzene (C6M) oriented normal to the smectic layers and collected within them. Such spatial segregation caused by the smectic layering dramatically enhanced photopolymerization rates; for HDDA, termination rates were reduced, whereas for C6M, both the termination and propagation rates were increased. These polymerization precursor structures suggest novel materials-design paradigms for gel LCs and nanophase-separated polymer systems. 相似文献
332.
Banks JA Nishiyama T Hasebe M Bowman JL Gribskov M dePamphilis C Albert VA Aono N Aoyama T Ambrose BA Ashton NW Axtell MJ Barker E Barker MS Bennetzen JL Bonawitz ND Chapple C Cheng C Correa LG Dacre M DeBarry J Dreyer I Elias M Engstrom EM Estelle M Feng L Finet C Floyd SK Frommer WB Fujita T Gramzow L Gutensohn M Harholt J Hattori M Heyl A Hirai T Hiwatashi Y Ishikawa M Iwata M Karol KG Koehler B Kolukisaoglu U Kubo M Kurata T Lalonde S Li K Li Y Litt A Lyons E Manning G Maruyama T Michael TP 《Science (New York, N.Y.)》2011,332(6032):960-963
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Even in small molecules, the influence of electronic state on rotational and vibrational product energies is not well understood. Here, we use experiments and theory to address this issue in photodissociation of formaldehyde, H2CO, to the radical products H + HCO. These products result from dissociation from the singlet ground electronic state or the first excited triplet state (T1) of H2CO. Fluorescence spectra reveal a sudden decrease in the HCO rotational energy with increasing photolysis energy accompanied by substantial HCO vibrational excitation. Calculations of the rotational distribution using an ab initio potential energy surface for the T1 state are in very good agreement with experiment and strongly support dominance of the T1 state in the dynamics at the higher photolysis energies. 相似文献
336.
Shannon M. Sermons Benjamin G. Wherley Chenxi Zhang Daniel C. Bowman 《Journal of plant nutrition》2017,40(10):1404-1416
As bermudagrass (Cynodon dactylon (L.) Pers.) transitions from winter dormancy to active growth in spring, nitrogen is essential for new tissue growth. We examined the relative contributions of internally stored nitrogen and that taken up by preexisting and newly produced roots. Field-collected dormant bermudagrass was transferred to a nutrient solution culture system in a growth chamber. Cultures were provided either a non-nitrogen-containing solution or one amended with nitrate labeled with the 15N isotope of nitrogen, which allowed tracking of endogenous and exogenous N pools in all tissues as growth began. Nitrogen in stolon internodes was the largest N source for early growth. Though mass increased at the same rate in both N treatments over 3 weeks of growth, the unfertilized treatment showed early signs of nitrogen deficiency: low tissue N, slowed leaf elongation, and fewer but longer roots. Preexisting roots were active in absorption almost immediately; new roots were produced quickly and had even higher N uptake rates. 相似文献