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91.
G. S. Agarwal 《Applied physics. B, Lasers and optics》1995,60(2-3):271-273
The possibility of observing Ramsey fringes in situations where the time separation between two interaction zones is larger than the lifetime is discussed. The spectral characteristics of emission exhibit interferences which are shown to be due to the fact that the spontaneous emission event can occur in two different zones and thus erasing any Welcher-Weg information.It is indeed a great honor for me to contribute an article on the occasion of H. Walther's 60th birthday 相似文献
92.
Numerical simulations are done of Langevin dynamics for a uniform-orderparameter, field-swept Landau model,= –|a/2|m
2+|b/4|m
4–mh(t) , to study hysteresis effects. The field is swept at a constant rateh(t)=h(0)+ht. The stochastic jump values of the field {hJ from an initially prepared metastable minimumm(0) are recorded, on passage to a global minimum m(). The results are: (a) The mean jump¯h
J(h) increases (hysteresis loop widens) with h, confirming a previous theoretical criterion based on rate competition between field-sweep and inverse mean first-passage time (FPT); (b) The broad jump distribution(h
J,h) is related to intrinsically large FPT fluctuations (
2–2)/
2 O(1), and can be quantitatively understood. Possible experimental tests of the ideas are indicated. 相似文献
93.
S Chandrasekhar G Chandrashekar B Nagendra Babu K Vijeender K Venkatram Reddy 《Tetrahedron letters》2004,45(28):5497-5499
A facile synthesis of symmetrical and unsymmetrical ethers is achieved by reductive coupling of carbonyl compounds with alkoxysilanes. This reaction is performed using inert polymethylhydrosiloxane as the hydride source and B(C6F5)3 as the catalytic activator of the PMHS. 相似文献
94.
Nisha CK Manorama SV Ganguli M Maiti S Kizhakkedathu JN 《Langmuir : the ACS journal of surfaces and colloids》2004,20(6):2386-2396
Complete biophysical characterization of complexes (polyplexes) of cationic polymers and DNA is needed to understand the mechanism underlying nonviral therapeutic gene transfer. In this article, we propose a new series of synthesized random cationic polymers (RCPs) from methoxy poly(ethylene glycol) monomethacrylate (MePEGMA) and (3-(methacryloylamino)propyl)trimethylammonium chloride with different mole ratios (32:68, 11:89, and 6:94) which could be used as a model system to address and answer the basic questions relating to the mechanism of the interaction of calf thymus DNA (CT-DNA) and cationic polymers. The solubility of the complexes of CT-DNA and RCP was followed by turbidity measurements. It has been observed that complexes of RCP with 68 mol % MePEGMA precipitate near the charge neutralization point, whereas complexes of the other two polymers are water-soluble and stable at all compositions. Dnase 1 digestion experiments show that DNA is inaccessible when it forms complexes with RCP. Ethidium bromide exclusion and gel electrophoretic mobility show that both polymers are capable of binding with CT-DNA. Atomic force microscopy images in conjunction with light scattering experiments showed that the complexes are spherical in nature and 75-100 nm in diameter. Circular dichroism spectroscopy studies indicated that the secondary structure of DNA in the complexes is not perturbed due to the presence of poly(ethylene glycol) segments in the polymer. Furthermore, we used a combination of spectroscopic and calorimetric techniques to determine complete thermodynamic profiles accompanying the helix-coil transition of CT-DNA in the complexes. UV and differential scanning calorimetry melting experiments revealed that DNA in the complexes is more stable than in the free state and the extent of stability depends on the polymer composition. Isothermal titration calorimetry experiments showed that the binding of these RCPs to CT-DNA is associated with small exothermic enthalpy changes. A complete thermodynamic profile showed that the RCP/DNA complex formation is entropically favorable. Much broader opportunities to vary the architecture of the polymers studied here make these systems promising in addressing various basic and practical problems in gene delivery systems. 相似文献
95.
《Journal of photochemistry and photobiology. A, Chemistry》2006,177(2-3):170-176
Novel photochromic benzimidazol[1,2a]pyrrolidin-2-ones, which give thermally stable highly coloured photochromes, have been synthesised by condensation of 2-methyl-3-benzothienylethylidene(isopropylidene)succinic anhydride with 1,2-diaminobenzene and its 4,5-dimethyl and 4,5-dimethoxy derivatives. The photochromic properties are reported. 相似文献
96.
A new and efficient formal total synthesis of (3S,4S)-balanol, a potent protein kinase C inhibitor, was accomplished from tri-O-acetyl-d-glucal. Balanol and ophiocordin consists of a chiral hexahydro azepine-containing fragment and a benzophenone fragment. The azepine core was prepared in chiral form through intramolecular aza Wittig reaction. A triphenylphosphine mediated ring expansion process was employed to form the seven-membered nitrogen heterocycle. The aldehyde equivalent key intermediate was treated with triphenylphosphine to give the azepine core. To demonstrate the applicability of the new route, a synthesis of the balanol is described. 相似文献
97.
Micelles of different amphiphiles adopt different shapes and internal packing arrangements in water, depending on their chemical
structures and the conditions of the medium. Two microenvironmental features, namely the polarity and the microviscosity that
the aggregate offers to a solubilized molecule, have been monitored using extrinsic fluorescence probes. While the differences
between micelles of spherical and rod-like shapes are not always distinct, stacked micelles and peptide micelles offer distinctly
lower polarity and higher microviscosity to solubilizates than the others. 相似文献
98.
The site of proton abstraction by OH? ion in some 4-substituted-3,5,6-triphenyl-Δ′-cyclohexenes has been established from labelling studies. The further fragmentation mode of (M-H)? ion depends on its structure and stereochemistry. The and nitro isomers exhibit stereochemical differences in the elimination of HNO2 while the amino and cyano analogues show stereochemically controlled RDA fragmentation mode. 相似文献
99.
A simple and efficient method for the preparation of isonucleoside 7 is described. The preparation of 1,4-anhydroxylitol 4, a key intermediate, is described by intramolecular cyclization of (2S,3R,4R)-3,5-dibenzyloxypentan-1,2,4-triol 3 using diethyl carbonate and NaH. 相似文献
100.
Water helices surrounding the nano-channels of trichlorophloroglucinol and tribromophloroglucinol have different handedness, PMPMPM and PPPMMM (P = right-handed, M = left-handed), depending on halogenhalogen interactions between the host molecules. 相似文献