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排序方式: 共有1102条查询结果,搜索用时 484 毫秒
1.
D. Amutha Rani Y. Yamamoto S. Mohri M. Sivakumar Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2003,41(3):269-273
In this study, a novel stepwise extraction method has been examined. The guest molecules housed between the helices of the clathrate δ form of syndiotactic polystyrene can be removed completely with this method. A systematic study of the preparation of a solvent‐free mesophase (emptied clathrate) membrane, its helical and residual solvent contents, and its structural transformations has been performed. In this first attempt, an enhancement in the TTGG helical content has been observed in the extracted membrane, and a conceptual mechanism is proposed. © 2002 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 269–273, 2003 相似文献
2.
S. Mohri D. Amutha Rani Y. Yamamoto Y. Tsujita H. Yoshimizu 《Journal of Polymer Science.Polymer Physics》2004,42(2):238-245
Syndiotactic polystyrene (sPS) has various crystalline forms such as α, β, γ, and δ forms, and a mesophase depending on the preparation method. In this study, we focused on the mesophase with the molecular cavity of sPS, which is obtained by step‐wise extraction of the guest molecules from the sPS δ form. To prepare the mesophase containing different shapes and sizes of the cavity, two kinds of the sPS δ form membrane cast from either toluene or chloroform solution were first prepared and then the guest molecules were removed by a step‐wise extraction method using acetone and methanol. We could succeed in the preparation of two kinds of mesophase with different shapes and sizes of the molecular cavity. Either toluene or chloroform vapor sorption to the sPS mesophase membranes was examined at 25 °C. Sorption analysis indicates that the mesophase with large molecular cavities can mainly sorb large molecules; on the other hand, the mesophase with small cavities can sorb only the small molecules, and is unable to sorb a large amount of large molecule because the cavity was too small to sorb the large molecules. Therefore, the sPS mesophase membrane has sorption selectivity based on the size of the molecular cavity. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 238–245, 2004 相似文献
3.
We analyze the spectra of pions and protons in heavy-ion collisions at relativistic energies from 2 A GeV to 65+65 A GeV by
using a jet-implemented hadron-string cascade model. In this energy region, hadron transverse mass spectra first show softening
until SPS energies, and re-hardening may emerge at RHIC energies. Since hadronic matter is expected to show only softening
at higher energy densities, this re-hardening of spectra can be interpreted as a good signature of the quark-gluon plasma
formation 相似文献
4.
A short and efficient enantioselective synthesis of sulfobacin A has been achieved using the Sharpless asymmetric dihydroxylation and the regiospecific nucleophilic opening of a cyclic sulfate as the key steps. 相似文献
5.
We investigate certain classes of normal completely positive (CP) maps on the hyperfinite II1 factorA. Using the representation theory of a suitable irrational rotation algebra, we propose some computable invariants for such
CP maps.
Dedicated to Professor K B Sinha 相似文献
6.
M K Parida Nita Sinha B Adhikary B Allanach A Alok K S Babu B Brahmachari D Choudhury E J Chun P K Das A Ghosal D Hitlin W S Hou S Kumar H N Li E Ma S K Majee G Majumdar B Mishra G Mohanty S Nandi H Pas M K Parida S D Rindani J P Saha N Sahu Y Sakai S Sen C Sharma C D Sharma S Shalgar N N Singh S Uma Sankar N Sinha R Sinha F Simonetto R Srikanth R Vaidya 《Pramana》2006,67(5):849-860
This is the report of flavor physics and model building working group at WHEPP-9. While activites in flavor physics have been
mainly focused on B-physics, those in model building have been primarily devoted to neutrino physics. We present summary of working group discussions
carried out during the workshop in the above fields, and also briefly review the progress made in some projects subsequently. 相似文献
7.
A convenient method for the two-step synthesis of arenediynes from 1,2-arenedialdehydes is reported. Dibromomethylenation of dialdehydes under Corey-Fuchs conditions (CBr4, Ph3P, Zn) provides the tetrabromides in excellent yields. Treatment of the tetrabromides with n-BuLi or LDA affords 3,4-unsaturated 1,5-diynes, the key structural moiety present in several naturally occurring antitumour antibiotics, in varying yields. The key intermediates in these transformations appear to be vinylidenecarbenes or carbenoids, generated in situ via metal-halogen exchange and elimination. 相似文献
8.
Sivananda Misra Gangadhar Sahu 《Journal of polymer science. Part A, Polymer chemistry》1985,23(10):2647-2657
Kinetics of polymerization of acrylamide initiated by Thallium(III) perchlorate was investigated in aqueous perchloric acid medium in the temperature range of 55–70°C. The rates of polymerization were measured varying the concentration of the monomer, initiator, and perchloric acid. The rate of polymerization was found to increase with increase of temperature, monomer concentration, initiator concentration, and perchloric acid concentration. The effect of additives like different solvents, surfactants, and retarders on the rate of polymerization was studied. Molecular weights of the polymer were determined by viscometry. The chain transfer constants for the monomer (CM) and that for the solvent dioxan (Cs) were calculated to be 7.33 × 10?3 and 6.66 × 10?3, respectively. From the Arrhenius plot, the overall activation energy (Ea) was calculated to be 10.68 kcal/mol. The energy of initiation was calculated to be 12.36 kcal/mol. Depending on the results obtained, a suitable reaction mechanism has been suggested and a rate equation has been derived. 相似文献
9.
Priti Gupta 《Tetrahedron letters》2005,46(38):6571-6573
A short and practical enantioselective synthesis of tarchonanthuslactone has been achieved in high diastereomeric excess using iterative Jacobsen’s hydrolytic kinetic resolution and ring closing metathesis as the key steps. 相似文献
10.
Many-body interaction in glycine-(water)3 complex using density functional theory method 总被引:4,自引:0,他引:4
Various configurations were investigated to find the most stable structures of glycine-(water)3 complex. Five different optimized conformers of glycine-(water)3 complex are obtained from density functional theory calculations using 6-311++G* basis set. Relaxation energy and many body interaction energies (two, three, and four body) are also calculated for these conformers. Out of the five conformers, the most stable conformer has the BSSE corrected total energy -513.917 967 7 Hartree and binding energy -27.28 Kcal/mol. It has been found that the relaxation energies, two body energies and three body energies have significant contribution to the total binding energy whereas four body energies are very small. The chemical hardness and chemical potential also confirmed the stability of the conformer having lowest total energy. 相似文献