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排序方式: 共有472条查询结果,搜索用时 46 毫秒
1.
Yu‐Hsiang Hu Chuh‐Yung Chen Chen‐Chien Wang Yao‐Hui Huang Shao‐Ping Wang 《Journal of polymer science. Part A, Polymer chemistry》2004,42(19):4976-4993
The bulk polymerization of styrene initiated by ?‐caprolactam (CL) and n‐dodecyl mercaptan (RSH) has been explored. This novel polymerization system shows living characteristics. For example, the molecular weight of the resulting polymers increases with conversion, and the system has the ability to form diblock copolymers and so forth. The polymer chain end contains thiol and lactam structures, which we have investigated with Fourier transform infrared, 1H NMR, and 13C NMR techniques. Electron spin resonance spectra and theoretical calculations by the Hartree–Fock methods have been used to examine the mechanism. The results reveal that the initial polymerization starts from thiol via a chain‐transfer reaction, and the propagation proceeds by the insertion of a monomer between the terminal group and the intermediate structure of lactam. Finally, the polymerization kinetics have been examined. The polymerization rate varies linearly with the concentration of CL and RSH, and this confirms the mechanism. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 4976–4993, 2004 相似文献
2.
The effects of instanton-anti-instanton interactions in high-temperature QCD with colour SU(2) are studied with and without quarks. The instanton potential proves to have no repulsive core, thus creating troubles with the definition of nonperturbative contributions to physical quantities. Also the chiral condensate is calculated, and it is shown to vanish if number of quark flavoursN f≧2, whereas forN f=1 it is nonzero for the arbitrary high temperature. 相似文献
3.
The products of the reaction of OClO with NO3 were investigated between 220 and 298 K using a flow reactor and infrared, visible, and ultraviolet analysis. At temperatures below 250 K new infrared and ultraviolet absorption features were observed and assigned to the novel compound chloryl nitrate (O2ClONO2). Additionally, ClO and NO2 were observed as reaction products, indicating the existence of a second reaction channel. O2ClONO2 formation predominates at temperatures below 230 K. The reaction rate constant at 220 K is estimated to be on the order of 10(-14) cm3 molecule-1 s-1 in 1-5 Torr of helium. These observations suggest that O2ClONO2 may exist in the terrestrial stratosphere. 相似文献
4.
M. Kashiwara T. Miwa J. -U. H. Petersen C. M. Yung 《Selecta Mathematica, New Series》1996,2(3):415-499
In [S], [KMS] the semi-infinite wedge construction of level 1U
q
(A
n
(1)
) Fock spaces and their decomposition into the tensor product of an irreducibleU
q
(A
n
(1)
)-module and a bosonic Fock space were given. Here a general scheme for the wedge construction ofq-deformed Fock spaces using the theory of perfect crystals is presented.LetU
q
(g) be a quantum affine algebra. LetV be a finite-dimensionalU
q
(g)-module with a perfect crystal base of levell. LetV
aff V [z,z
–1] be the affinization ofV, with crystal base (L
aff,B
aff). The wedge spaceV
aff V
aff is defined as the quotient ofV
aff V
aff by the subspace generated by the action ofU
q
(g) [z
a
z
b
+z
b
z
a
]a,b onv v (v an extremal vector). The wedge space r
V
aff (r ) is defined similarly. Normally ordered wedges are defined by using the energy functionH :B
aff B
aff . Under certain assumptions, it is proved that normally ordered wedges form a base of r
V
aff.Aq-deformed Fock space is defined as the inductive limit of r
V
aff asr , taken along the semi-infinite wedge associated to a ground state sequence. It is proved that normally ordered wedges form a base of the Fock space and that the Fock space has the structure of an integrableU
q
(g)-module. An action of the bosons, which commute with theU
q
(g)-action, is given on the Fock space. It induces the decomposition of theq-deformed Fock space into the tensor product of an irreducibleU
q
(g)-module and a bosonic Fock space.As examples, Fock spaces for typesA
2n
(2)
,B
n
(1)
,A
2n
–1/(2)
,D
n
(1)
andD
n
+1/(2)
at level 1 andA
1
(1)
at levelk are constructed. The commutation relations of the bosons in each of these cases are calculated, using two point functions of vertex operators. 相似文献
5.
Jerzy Strzelbicki Witold A. Charewicz Yung Liu Richard A. Bartsch 《Journal of inclusion phenomena and macrocyclic chemistry》1989,7(3):349-361
Separation efficiencies and selectivities in solvent extraction of Co(II) and Ni(H) ammine cations from aqueous solutions into chloroform and toluene and in transport through bulk toluene membranes by proton-ionizable crown ethers have been determined. Six proton-ionizable crown ethers with differing lipophilicities, polyether cavity sizes and ionizable groups (carboxylic and sulfonic acid functions) were examined. Higher selectivity and efficiency for Co(II) ammine cation extraction was observed for the more lipophilic, proton-ionizable crown ethers. Highly lipophilic crown carboxylic acids provided effective and selective transport of Co(II) ammine cations through bulk toluene membranes.Presented in part at the 6th International Symposium on High Purity Materials in Science and Technology: Preparation, Characterization and Application of Well-Defined Materials, Dresden, GDR, May 1985, Poster D91, Poster Abstracts, pp. 144, 145.All extraction and transport experiments were conducted at this location. 相似文献
6.
[reaction: see text] Ir(III) complex [Cp(PMe(3))IrMe(CH(2)Cl(2))][BAr(f)] (1) was used to introduce deuterium stoichiometrically into substituted naphthalene/benzene templates and several "drug-like" entities. The exchange process is tolerant of a wide array of functional groups. Labeling of warfarin using subatmospheric pressures of T(2) led to specific activities and total activities rivaling current functional group directed tritium labeling methods. When paired with the appropriate deuterium donor, Cp(PMe(3))Ir(H(3))OTf (4) was found to deuterate a number of organic compounds catalytically. 相似文献
7.
The four new lariciresinol‐based lignan glycosides, (?)‐lariciresinol 4′‐(6″‐O‐feruloyl‐β‐D ‐glucopyranoside) ( 1 ), (?)‐lariciresinol 4′‐(4″,6″‐di‐O‐feruloyl‐β‐D ‐glucopyranoside) ( 2 ), 5,5′‐dimethoxylariciresinol 4′‐(4″,6″‐di‐O‐feruloyl)‐β‐D ‐glucopyranoside) ( 3 ), and 4‐O‐[α‐(1,2‐dihydroxyethyl)syringyl]‐5,5′‐dimethoxylariciresinol 4′‐(4″,6″‐di‐O‐feruloyl‐β‐D ‐glucopyranoside) ( 4 ), together with two known ones, lariciresinol 4′‐β‐D ‐glucopyranoside) ( 5 ) and tortoside B ( 6 ), were isolated from the BuOH extract of Rhus javanica var. roxburghiana roots, and their structures were established by means of various spectroscopic techniques. 相似文献
8.
Yu‐Hsiang Hu Chuh‐Yung Chen 《Journal of polymer science. Part A, Polymer chemistry》2002,40(21):3692-3702
The bulk polymerization of methyl methacrylate initiated with 2‐pyrrolidinone and n‐dodecyl mercaptan (R‐SH) has been explored. This polymerization system showed “living” characteristics; for example, the molecular weight of the resulting polymers increased with reaction time by gel permeation chromatographic analysis. Also, the polymer was characterized by Fourier transform infrared spectroscopy, 1H NMR, and 13C NMR techniques. The polymer end with the iniferter structures was found. By the initial‐rate method, the polymerization rate depended on [2‐pyrrolidinone]1.0 and [R‐SH]0. Combining the structure analysis and the polymerization‐rate expression, a possible mechanism was proposed. n‐Dodecyl mercaptan served dual roles—as a catalyst at low conversion and as a chain‐transfer agent at high conversion. Finally, the thermal properties were studied, and the glass‐transition temperature and thermal‐degradation temperature were, respectively, 25 and 80–100 °C higher than that of the azobisisobutyronitrile system. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3692–3702, 2002 相似文献
9.
Self-assembling of metallic nanoparticles to form well-defined nanostructured structures is a field that has been receiving considerable research interest in recent years. In this field, DNA is a commonly used linker molecule to direct the assembly of the nanoscale building blocks because of its unique recognition capabilities, mechanical rigidity, and physicochemical stability. This study reported our novel approach to generate gold nanoparticle-DNA conjugates bearing specially designed DNA linker molecules that can be used as building blocks to construct nanoassemblies with precisely controlled structure or as nanoprobes for quantitative DNA sequence detection analysis. In our approach, gold nanoparticle-DNA conjugates bearing a specific number of long double-stranded DNA strands were prepared by gel electrophoresis. A restriction endonuclease enzyme was then used to manipulate the length of the nanoparticle-bound DNA. This enzymatic cleavage was confirmed by gel electrophoresis, and digestion efficiency of 90% or more was achieved. With this approach, nanoparticle conjugates bearing a specific number of strands of short DNA with less than 20-base can be achieved. 相似文献
10.
Correlated atomic force microscopy and fluorescence lifetime imaging of live bacterial cells 总被引:3,自引:0,他引:3
Micic M Hu D Suh YD Newton G Romine M Lu HP 《Colloids and surfaces. B, Biointerfaces》2004,34(4):205-212
We report on imaging living bacterial cells by using a correlated tapping-mode atomic force microscopy (AFM) and confocal fluorescence lifetime imaging microscopy (FLIM). For optimal imaging of Gram-negative Shewanella oneidensis MR-1 cells, we explored different methods of bacterial sample preparation, such as spreading the cells on poly-L-lysine coated surfaces or agarose gel coated surfaces. We have found that the agarose gel containing 99% ammonium acetate buffer can provide sufficient local aqueous environment for single bacterial cells. Furthermore, the cell surface topography can be characterized by tapping-mode in-air AFM imaging for the single bacterial cells that are partially embedded. Using in-air rather than under-water AFM imaging of the living cells significantly enhanced the contrast and signal-to-noise ratio of the AFM images. Near-field AFM-tip-enhanced fluorescence lifetime imaging (AFM-FLIM) holds high promise on obtaining fluorescence images beyond optical diffraction limited spatial resolution. We have previously demonstrated near-field AFM-FLIM imaging of polymer beads beyond diffraction limited spatial resolution. Here, as the first step of applying AFM-FLIM on imaging bacterial living cells, we demonstrated a correlated and consecutive AFM topographic imaging, fluorescence intensity imaging, and FLIM imaging of living bacterial cells to characterize cell polarity. 相似文献