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871.
J. Szade W. Burian Z. Celiski T. OKeevan M. Zangrando F. Bondino E. Magnano 《Surface science》2005,580(1-3):163-166
Resonant photoemission was used to investigate the EuF3 ultrathin layer for the photon energies within the Eu 4d → 4f excitation region. Photoemission from the valence band in resonance showed the lines which can be attributed to two Eu valence states (Eu+3 and Eu+2) whereas the off resonance spectra of EuF3 ultrathin layer do not exhibit divalent states of Eu. An explanation of that effect is proposed which is based on the charge transfer from the ligand. 相似文献
872.
Introduction Strontiumaluminumpentafluoride SrAlF5isagoodhostforthespectralresearchofdopedrareearthionsduetoitsweakcrystalfieldenvironment.Forthefirsttime ,Hewesetal.1foundthef→flineemissionoftheEu2 + inSrAlF5matrix ,andfournonequivalentsitesforRE2 + inSrAlF5havealsobeenreported .2 Theobservationofthetunable laserofCr3+ from 85 2to 94 7nminSrAlF5hasat tractedconsiderableattention3andtheferroelectricbehav ior4 ofSrAlF5hasextendeditsapplicablefield .Twogener almethods,high temperatur… 相似文献
873.
Dar‐Jong Lin Cheng‐Liang Chang Chi‐Lin Chang Tzung‐Chin Chen Liao‐Ping Cheng 《Journal of Polymer Science.Polymer Physics》2004,42(5):830-842
Poly(vinylidene fluoride) (PVDF) membranes were prepared by the isothermal immersion and precipitation of PVDF/N‐methyl‐2‐pyrollidone dope solutions in either harsh or soft nonsolvent baths. Low‐voltage field emission scanning electron microscopy imaging of the formed membranes at high magnifications (e.g., 300,000×) revealed their nanoscale fine structures, particularly dendrites observed on the surfaces of the macrovoids, cellular pores, and the membrane skin, which have never been successfully presented in the literature. Evidence of crystallization was also demonstrated by X‐ray diffraction and differential scanning calorimetry measurements. The phase diagram at 25 °C, including a binodal, tie lines, and a crystallization‐induced gelation line, was determined both experimentally and theoretically. These results were further used in mass‐transfer calculations to obtain diffusion trajectories and concentration profiles for the membrane region, which were useful for elucidating the relationship between the membrane preparation conditions and the obtained membrane morphologies. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 830–842, 2004 相似文献
874.
《Tetrahedron letters》2004,45(21):4135-4138
The application of natural phosphates doped with potassium fluoride as heterogeneous catalysts for the Michael addition of aromatic and aliphatic amines to α,β-unsaturated carbonyl compounds is presented. The natural phosphate catalyst can be regenerated and reused without loss of activity, which makes it an attractive alternative to homogeneous basic reagents. Doping natural phosphate with potassium fluoride significantly enhances the rate and yield of the reaction. 相似文献
875.
Xin Hong Shengbo Wang Dahao Guo Hongxing Wu Jie Wang Yusheng Dai Xiaoping Xia Yanning Xie 《Optics and Lasers in Engineering》1998,29(6):447-455
In this paper the characteristics (such as amplitude, width) of a laser-induced shock wave under confining conditions is studied. For engineering applications, a physical study of this method is useful in order to optimize this technique. We have first introduced a new pressure gauge – PVDF (polyvenyliden fluoride) gauge with short rise time and wide linear response range. Experimentally, by measuring the generated pressures under different confining materials, the relationship between the pressures and the acoustic impedance of confining materials, is illustrated, which somewhat agrees with the theoretical calculation. We have also found that under confining conditions laser-induced shock waves persist longer than a laser pulse. Then, the effects of black paint overlay (absorptive overlay) is studied. We experimentally point out that a black paint overlay placed before an irradiated target can greatly increase the generated pressure under any confining material in our experiments for its beneficial effect on the plasma-generating process. To our surprise, comparing the impulse (
), which the shock wave induced under absorptive overlay executes on the target, to that induced under no black paint overlay, the increase ratio is approximately equal. 相似文献
876.
Uwe Beginn Reza Najjar Jürgen Ellmann Rostislav Vinokur Roland Martin Martin Mller 《Journal of polymer science. Part A, Polymer chemistry》2006,44(3):1299-1316
Vinylidene difluoride and hexafluoropropene are copolymerized in supercritical carbon dioxide at 280 bar and 50 °C by means of free radical copolymerization, initiated by diethyl peroxydicarbonate. The first stages of the reaction were monitored by turbidity measurements and the time/conversion curve was followed gravimetrically to measure the initial rates of polymerization. The obtained copolymers possessed bimodal molecular weight distributions, their average comonomer composition was well described by the Lewis‐Mayo equation with the copolymerization parameters rVDF = 4.8 and rHFP = 0. The glass transition and melting temperatures of the copolymers are similar to that of the materials resulting from aqueous emulsion polymerization. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 1299–1316, 2006 相似文献
877.
Muhamad Nasir Hidetoshi Matsumoto Tetsuya Danno Mie Minagawa Toshihira Irisawa Masatoshi Shioya Akihiko Tanioka 《Journal of Polymer Science.Polymer Physics》2006,44(5):779-786
Poly(vinylidene fluoride) (PVDF) nanofibers were prepared by electrospray deposition (ESD). To control the diameter, morphology, and structure of PVDF nanofibers, some parameters were investigated, such as polymer concentration, nozzle‐to‐ground collector distance, feeding rate of the polymer solution, and applied voltage. The fabricated fiber was 80–700 nm in diameter. The increase in the polymer concentration caused an increase in the polymer viscosity and fiber diameter. At low polymer concentration (5 wt %), polymer nanoparticles were formed. An increase in applied voltage will increase the fiber diameter. Variation in the nozzle‐to‐ground collector distance did not result in significant changes in the fiber diameter. Increase in the feeding rate of the polymer solution decreased the fiber diameter. Differential scanning calorimetry (DSC) and wide angle X‐ray diffraction (WAXD) measurements showed that the melting point and total crystallinity were decreased. Fourier transform infrared spectroscopy (FTIR) measurement revealed that ESD process induced the formation of the oriented β‐phase PVDF structures. It was also demonstrated that the addition of hydrofluorocarbon solvent to polymer solution remarkably enhanced the formation of β‐phase crystalline structure of PVDF nanofiber. © 2006 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 779–786, 2006 相似文献
878.
Kohji Tashiro Sono Sasaki Seishi Saragai 《Journal of Polymer Science.Polymer Physics》2004,42(22):4175-4181
The time‐resolved measurement of wide‐angle X‐ray scattering was performed with a synchrotron radiation source during the processes of the isothermal crystallization and ferroelectric phase transition of a vinylidene fluoride/trifluoroethylene copolymer with 73 mol % vinylidene fluoride. When the sample was cooled rapidly from the melt to the temperature region of the paraelectric high‐temperature phase, the peak position of the 200/110 reflection shifted toward the higher angle side and the half‐width became narrower. This indicated an increase in the crystallite size with a more compact chain‐packing mode. Even when the temperature jump was made from the melt into the region of the ferroelectric or low‐temperature phase, the crystallization of the high‐temperature phase was first observed before the appearance of the low‐temperature phase. This was consistent with a prediction based on the so‐called Ostwald state rule: the thermodynamically unstable but kinetically preferable high‐temperature phase can appear first even when the thermodynamically more stable low‐temperature phase should be created. The time‐dependent intensity changes were analyzed with the Avrami kinetic equation. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 4175–4181, 2004 相似文献
879.
880.
A new iron fluoride assisted convenient and efficient strategy for the preparation of 4H-pyrimido[2,1-b]benzothiazoles derivatives in solvent-free media is described. The reactions can be performed at low-catalyst loadings with excellent functional group tolerance. The catalyst can be readily recovered and reused for next reaction for at least three runs without any significant impact on the yields of the products. The easy recovery of the catalyst and high yield of the products make the protocol attractive, sustainable, and economic. 相似文献