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941.
942.
MesomorphicCharacteristicsofInducedChiralNematicPhaseof[SmecticLCP,PS(4BC/DM)/NematicLC,E7/ChiralDopant,CB┐15]┐TernaryComposi... 相似文献
943.
Osamu Kikuchi Toshio Watanabe Yusuke Satoh Yuichi Inadomi 《Journal of Molecular Structure》2000,507(1-3):53-62
Ab initio MO GB theory which includes the continuum model of solvent effect using generalized Born formula has been applied to the dimerization reaction of HCN in aqueous solution which is the starting step in prebiotic synthesis of purine precursors from aqueous hydrogen cyanide. Three steps considered were: (i) the reaction of HCN and H2O to produce the CN− anion, (ii) the reaction of CN− with HCN to give the NC–CH=N− anion, and (iii) the addition of a proton to the anion to give iminoacetonitrile. The formation of CN− ion from HCN in aqueous solution requires 15.1 kcal/mol (the experimental value estimated from the dissociation constant of HCN in water is 14.8 kcal/mol). The reaction of CN− with HCN requires the activation energy of 32.2 kcal/mol (MP2/6-31++G**//HF/6-31++G**) to give the dimer. This barrier height is reduced to 26.1 kcal/mol when HCN is associated with H3O+. In the presence of NH3 in aqueous solution, CN− is produced easily by the reaction of HCN and NH3 with a low activation energy of 4.3 kcal/mol. It was shown that the formation of CN− becomes easier in ammoniacal solution, and the dimerization occurs efficiently in aqueous solutions which contain NH3. 相似文献
944.
Preparation of SnO2 Monolithic Gel by Sol-Gel Method 总被引:2,自引:0,他引:2
Haruhisa Shiomi Chisato Kakimoto Atsushi Nakahira Shinichi Takeda 《Journal of Sol-Gel Science and Technology》2000,19(1-3):759-763
The effects of aging of a wet gel at room temperature and a use of a drying control chemical additive (DCCA) were investigated on the prevention of cracking of the gel during drying. N,N-Dimethylformamide (DMF) having low surface tension was used as a DCCA in this study. Before drying, the aged wet gel was immersed in DMF for several days to replace the pore liquid in the wet gel with DMF.The longer the aging and DMF immersing times became, a fewer cracks generated during drying. Especially, the immersion in DMF for over 8 days made it possible to obtain the SnO2 gel monolith without cracking from the wet gel aged for short time (1 day). However, the wet gel aged for long time without immersing in DMF could not be dried without cracking. Therefore, the replacement of the pore liquid in the wet gel with DMF having low surface tension is thought to be more effective on avoiding a crack generation than aging. From a pore size distribution measurement by N2 gas adsorption, it was found that the pore size and the breadth of the pore size distribution of the dried gel became larger and narrower respectively with increasing DMF immersing time. DMF is thought to be capable of forming strong hydrogen bonding to hydroxyl groups remaining on the surface of the wet gel and providing a shielding cage around the reactants (Sn–OH), thus further condensation reaction is probably suppressed. Consequently, a large pore distribution is developed in the gel, which reduces the magnitude of capillary stress induced during drying. 相似文献
945.
Kimiko Makino Mebae Umetsu Yuko Goto Asami Nakayama Tomomi Suhara Jun Tsujii Akihiko Kikuchi Hiroyuki Ohshima Yasuhisa Sakurai Teruo Okano 《Colloids and surfaces. B, Biointerfaces》1999,13(6):2327-297
Four types of hydrophilic gel microcapsules containing water have been prepared by an interfacial polymerization method. Each type of microcapsules has a membrane of different composition. Using three kinds of monomers, N,N-dimethylacrylamide (DMAAm), 4-(aminomethyl)styrene (AmSt), and N,N-dimethylaminopropylacrylamide (DMAPAA), one type of aqueous copolymer having primary and tertiary amino groups was obtained. By the polymerization of three kinds of monomers, DMAAm, AmSt, and 2-[(methacryloyloxy)ethyl] trimethylammoniumchloride (METAC), another type of aqueous copolymer having primary and quaternary ammonium groups was also obtained. Two more types of copolymers were synthesized by copolymerization of -acryloxy-ω-methoxy-poly(ethylene glycol) (a-PEG) with the above two kinds of monomer mixture. These copolymers were polymerized with terephthaloyldichloride at the water/oil interface to prepare four types of microcapsules containing water, i.e., poly(DMAAm-co-DMAPAA-co-AmSt-alt-terephthalic acid) microcapsules, poly(DMAAm-co-DMAPAA-co-AmSt-co-PEG-alt-terephthalic acid) microcapsules, poly (DMAAm-co-METAC-co-AmSt-alt-terephthalic acid) microcapsules, and poly (DMAAm-co-METAC-co-AmSt-co-PEG-alt-terephthalic acid) microcapsules, which will be abbreviated to MC 1, MC 2, MC 3, and MC 4, respectively. It has been predicted that the microcapsule membranes are hydrophilic and soft and have two-sublayer structures from electrophoretic mobility measurements and from the analysis of the data with Ohshima’s electrokinetic theory for soft particles. The outer sublayers of MC 1 and MC 2 are negatively charged and those of MC 3 and 4 are slightly positively charged. Also, the surfaces of MC 1 and MC 2 are harder than those of MC 3 and 4. By PEGylation, the surface charge density in the membranes decreases and the surface becomes softer. It has been found that the membrane of red blood cells (RBC) is also soft and is composed of two-sublayers, the outer sublayer of which is negatively charged and the inner one is positively charged. The interaction of four types of microcapsules with RBC has been studied. It was found that microcapsules with soft surfaces (MC 3 and MC 4) do not interact with RBC, even though the microcapsule surfaces are positively charged and the surface of RBC is negatively charged. On the other hand, microcapsules with negatively charged but harder surfaces (MC 1) interact with RBC to introduce hemolysis. The membrane surface of MC 2, which is obtained by PEGylation of MC 1, becomes softer than that of MC 1 so that the interaction with RBC was weakly suppressed. From these, it was concluded that the dominant factor to control the interaction between synthetic polymer surfaces and biological cell surfaces is not the surface charges carried by the polymer surfaces but the softness of the polymer surfaces. 相似文献
946.
K. Masumoto T. Ohtsuki K. Sueki K. Kikuchi T. Mitsugashira 《Journal of Radioanalytical and Nuclear Chemistry》1999,241(1):201-206
The11C and14C labeled fullerenes were produced by charged-particle and neutron irradiation, of C60, C70 and their mixture. It was found that a carbon atom of fullerence can be easily exchanged with a radioactive carbon atom produced
by a nuclear reaction. The HPLC method was effective for identification and purification of various labeled fullerene families
as chemically stable compounds. The radiochemically interesting aspect of the results is not only the production of11C and14C labeled fullerenes but also the formation of radioactive higher fullerenes which can be simultaneously produced with high
yield and in carrier-free form. 相似文献
947.
948.
蓝宝石衬底上RF-MBE生长的GaN中的极性控制和螺旋位错的降低 总被引:1,自引:1,他引:0
近年来人们报道了用MBE方法生长GaN的飞速进展,利用RF-MBE方法可以获得高的GAN生长速率和高的电子迁移率.本文讨论了用RF-MBE方法在蓝宝石衬底上生长GaN过程中的极性控制和螺旋位错的降低.在充分氮化的蓝宝石衬底上直接生长GaN,使GaN的极性控制为N-极性,并用高温生长的AlN核化层实现GaN的Ga-极性.对于N-和Ga-极性的GaN这两种情况,高温生长的AlN中间迭层的引入,可以有效地抑制螺旋位错的扩散.位错的降低使GaN的室温电子迁移率得到提高,对于Ga-极性的GaN,其值为332cm2/V·s;而对于N-极性的GaN,其值为688cm2/V·s. 相似文献
949.
μSR spectra on the spin frustrating spinel antiferromagnet Zn(Cr
x
Ga1−x
)2O4 (x=0.9,1.0) have been measured. For x=1.0 compound, both the relaxation rate and the initial asymmetry showed distinct anomalies at the Néel temperature. The magnetic
susceptibility for the x=0.9 compound was known to have a faint peak at around 12 K, whose origin was not clear so far. Our μSR study revealed that
this temperature is the onset temperature of development of the magnetic correlation accompanied by appreciable spin fluctuations.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献
950.
Mekata M. Kikuchi H. Watanabe I. Nagamine K. Itoh S. Mamiya H. Kojima K. M. 《Hyperfine Interactions》2001,136(3-8):263-268
The magnetic ordering process of Ising spins on diluted square lattice was studied by muon spin relaxation using model compounds
Rb2Co
c
Mg1−c
F4. Muon relaxation shows an anomaly at a remarkably higher temperature T
N
μSR than the transition temperature determined by neutron Bragg scattering T
N
ND near the percolation threshold for square lattice (c
p=0.593). The difference between the two temperatures amounts to 50% of T
N
ND just above c
p. The field cooling effect of DC magnetic susceptibility is appreciable below T
N
ND while the temperature of the anomaly in AC susceptibility approaches to T
N
μSR as the frequency is increased. It was concluded that there is a crossover from two-dimensional ordering at T
N
μSR to three-dimensional ordering at T
N
ND but the two-dimensional order between T
N
μSR and T
N
ND has slow fluctuations due to the fractal structure with a plenty of weak links.
This revised version was published online in September 2006 with corrections to the Cover Date. 相似文献