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排序方式: 共有162条查询结果,搜索用时 31 毫秒
101.
102.
D. I. Bower D. A. Jarvis I. M. Ward 《Journal of Polymer Science.Polymer Physics》1986,24(7):1459-1479
A study of molecular orientation in a series of five one-way-drawn sheets of poly(ethylene terephthalate) is reported. Five orientation averages P which characterize the benzene-ring orientation were determined directly by Raman spectroscopy. Two further averages P and P were determined from a combination of Raman spectroscopy and refractive index measurements on the basis of two different conformational models. As in a previous publication, the seven averages P were used to estimate all the P up to fourth order for the benzene rings on the assumption that in each case the actual distribution of orientations is close to the most probable distribution. The seven orientation averages P for each drawn sheet were also compared with those calculated on the basis of two simple models for the development of molecular orientation during drawing, the pseudoaffine deformation scheme and the rubber network model. It was shown that the orientation of the chain axes is closer to that predicted by the rubber network model, the pseudoaffine deformation scheme greatly overestimating the degree of chain biaxiality. The results also show that the benzene ring planes are preferentially oriented toward the planes of the sheets. The chain axis orientation is, however, nearly uniaxial and similar to that observed for uniaxially drawn samples, suggesting that there is no direct connection between the processes of chain axis orientation and preferential orientation of the benzene-ring planes. 相似文献
103.
It is shown that, by assuming that each of the peaks resolved in the CCl stretching region of the Raman spectra of a series of poly(vinyl chloride) gels can be associated with a definite triad structure, most of the peaks can he assigned to syndiotactic, isotactic, or heterotactic triad configurations without reference to the spectra of model compounds or to vibrational calculations. The results are in general agreement with most previous assignments except for the assignment of the peak at 646 cm–1. Previously this was assigned to syndiotactic material, but it is here assigned to a structure consisting of consecutive syndiotactic, isotactic, and syndiotactic placements in a conformation not very distorted from the planar zigzag conformation. 相似文献
104.
Vullev VI Wan J Heinrich V Landsman P Bower PE Xia B Millare B Jones G 《Journal of the American Chemical Society》2006,128(50):16062-16072
A facile nonlithographic method for expedient fabrication of microfluidic devices of poly(dimethylsiloxane) is described. Positive-relief masters for the molds are directly printed on smooth substrates. For the formation of connecting channels and chambers inside the polymer components of the microfluidic devices, cavity-forming elements are adhered to the surfaces of the masters. Using this nonlithographic approach, we fabricated microfluidic devices for detection of bacterial spores on the basis of enhancement of the emission of terbium (III) ions. 相似文献
105.
Controlling the phase delay of light transmitted through double-layer metallic subwavelength slit arrays 总被引:1,自引:0,他引:1
Marcet Z Paster JW Carr DW Bower JE Cirelli RA Klemens F Mansfield WM Miner JF Pai CS Chan HB 《Optics letters》2008,33(13):1410-1412
We demonstrate that the phase of light transmitted through double-layer subwavelength metallic slit arrays can be controlled through lateral shift of the two layers. Our samples consist of two aluminum layers, each of which contains an array of subwavelength slits. The two layers are placed in sufficient proximity to allow coupling of the evanescent fields at resonance. By changing the lateral shift between the layers from zero to half the period, the phase of the transmitted electromagnetic field is increased by pi, while the transmitted intensity remains high. Such a controllable phase delay could open new capabilities for nanophotonic devices that cannot be achieved with single-layer structures. 相似文献
106.
Olivia Boyd Gang‐Wei Wang Olga O. Sokolova Adam D. J. Calow Sophie M. Bertrand John F. Bower 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):19020-19024
Aminocyclopropanes equipped with pendant nucleophiles undergo carbonylative heterocyclization triggered by C?C bond activation to generate eight‐membered N‐heterocycles. In these processes, intramolecular “capture” of a rhodacyclopentanone intermediate by an aryl or N‐based nucleophile is followed by C?C or C?N bond‐forming “collapse” to the targets. These studies demonstrate how the combination of cyclopropane strain release and the templating effect of catalytically generated metallacycles can be harnessed to enable otherwise challenging medium ring closures. 相似文献
107.
The intensity of the Raman scattering from uniaxially oriented amorphous poly(ethylene terephthalate) tapes at wave number shifts of 1732, 1616, 1286, 857, and 632 cm?1 has been observed for various combinations of incident and scattered light polarization vectors with respect to the draw direction. An attempt has been made to analyze the data to provide values of 〈P2(ζ)〉 and 〈P4(ζ)〉, where Pn(ζ) is the nth order Legendre polynomial in ζ,ζ is the cosine of the angle between the draw direction and a typtical chain axis in the polymer, and the angle brackets denote the average value over all repeat units. This attempt was successful for the 1616 and 632 cm?1 lines but less successful for the other three, although the data for the 1732 and 1286 cm?1 lines could be analyzed to provide quantities proportional, but not equal, to 〈P2(ζ)〉. In the analysis and discussion two possible models were considered for the conformation of the terephthaloyl residues in the amorphous polymer but it was not possible to reject either model conclusively. The results suggest, in agreement with previous studies by other methods, that the drawing of PET at 80°C takes place essentially as the extension of a rubberlike network which is frozen on subsequent cooling to room temperature. 相似文献
108.
Abe K Abe K Abe T Adam I Akimoto H Aston D Baird KG Baltay C Band HR Barklow TL Bauer JM Bellodi G Berger R Blaylock G Bogart JR Bower GR Brau JE Breidenbach M Bugg WM Burke D Burnett TH Burrows PN Calcaterra A Cassell R Chou A Cohn HO Coller JA Convery MR Cook V Cowan RF Crawford G Damerell CJ Daoudi M Dasu S de Groot N de Sangro R Dong DN Doser M Dubois R Erofeeva I Eschenburg V Etzion E Fahey S Falciai D Fernandez JP Flood K Frey R Hart EL Hasuko K Hertzbach SS Huffer ME Huynh X Iwasaki M 《Physical review letters》2005,94(9):091801
Exploiting the manipulation of the SLAC Linear Collider electron-beam polarization, we present precise direct measurements of the parity-violation parameters A(c) and A(b) in the Z-boson-c-quark and Z-boson-b-quark coupling. Quark-antiquark discrimination is accomplished via a unique algorithm that takes advantage of the precise SLAC Large Detector charge coupled device vertex detector, employing the net charge of displaced vertices as well as the charge of kaons that emanate from those vertices. From the 1996-1998 sample of 400 000 Z decays, produced with an average beam polarization of 73.4%, we find A(c)=0.673+/-0.029(stat)+/-0.023(syst) and A(b)=0.919+/-0.018(stat)+/-0.017(syst). 相似文献
109.
J. Kovermann A. Stahl A. A. Mikhailichenko D. Scott G. A. Moortgat-Pick V. Gharibyan P. Pahl R. Pöschl K. P. Schüler K. Laihem S. Riemann A. Schälicke R. Dollan H. Kolanoski T. Lohse T. Schweizer K. T. McDonald Y. Batygin V. Bharadwaj G. Bower F. -J. Decker C. Hast R. Iverson J. C. Sheppard Z. Szalata D. Walz A. Weidemann G. Alexander E. Reinherz-Aronis S. Berridge W. Bugg Y. Efrimenko 《Pramana》2007,69(6):1165-1169
A longitudinal polarized positron beam is foreseen for the international linear collider (ILC). A proof-of-principle experiment
has been performed in the final focus test beam at SLAC to demonstrate the production of polarized positrons for implementation
at the ILC. The E166 experiment uses a 1 m long helical undulator in a 46.6 GeV electron beam to produce a few MeV photons
with a high degree of circular polarization. These photons are then converted in a thin target to generate longitudinally
polarized e
+ and e
−. The positron polarization is measured using a Compton transmission polarimeter. The data analysis has shown asymmetries
in the expected vicinity of 3.4% and ∼1% for photons and positrons respectively and the expected positron longitudinal polarization
is covering a range from 50% to 90%.
相似文献
110.