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81.
Csaba Szántay Jr. 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):334-352
The problem of signals generated in and received from regions outside the active coil area is discussed in the context of using standard measurement techniques. Some of the conceptual and practical consequences of the existence of such transition-band signals are highlighted. Examples include radiation damping, pulse-width calibration, lineshape and radiofrequency homogeneity tests, improper saturation, and exchange- and relaxation-rate determinations. One interesting implication is that apparent sample-to-sample variations in the calibrated 90° pulse width values are a function not only of probe tuning and bulk susceptibility effects, but also of the linewidths involved. A semi-quantitative treatment of the phenomenon is also given. 相似文献
82.
83.
Ossi Horovitz Gheorghe Tomoaia Csaba Racz Aurora Mocanu Liviu-Dorel Bobos Maria Tomoaia-Cotisel 《Central European Journal of Chemistry》2006,4(3):489-501
The surface pressure versus molecular area isotherms of some carotenoids: β,β-carotene-4-one (echinenone, ECH), β,β-carotene-4,4′-dione
(canthaxanthin, CAN) and 4,4′-diapo-ω,ω-carotene-4,4′-dial (APO), spread at the air/water interface, are reported. A van der
Waals type state equation is used to describe the high molecular area portions of the compression isotherms and interaction
parameters within monolayers are derived. Quantum chemical semi-empirical SCF MO calculations (AM1 and PM3) are performed
for the optimized geometries of molecules and dipole moments are calculated. Similar theoretical magnitudes are obtained by
both methods. Surface properties, like collapse pressure, surface compressional modulus and interaction parameters are discussed
in terms of dipole-dipole interactions, and correlations with the calculated quantities for the carotenoid molecules are analyzed.
The orientation of the different carotenoid molecules in the monolayer is discussed. 相似文献
84.
We propose a new variant of the two-stage recourse model. It can be used e.g., in managing resources in whose supply random
interruptions may occur. Oil and natural gas are examples for such resources. Constraints in the resulting stochastic programming
problems can be regarded as generalizations of integrated chance constraints. For the solution of such problems, we propose
a new decomposition method that integrates a bundle-type convex programming method with the classic distribution approximation
schemes. Feasibility and optimality issues are taken into consideration simultaneously, since we use a convex programming
method suited for constrained optimization. This approach can also be applied to traditional two-stage problems whose recourse
functions can be extended to the whole space in a computationally efficient way. Network recourse problems are an example
for such problems. We report encouraging test results with the new method.
相似文献
85.
86.
Zsuzsanna Kardos-Balogh Ferenc Sóti Mária Incze Mária Kajtár Mária Kajtár-Peredy Csaba Szántay 《Tetrahedron letters》1985,26(45):5593-5596
A stable 3-acylindolenine derivative (2) has been prepared intramolecular electrophilic acylation. The reactivity of 2 has been studied. 相似文献
87.
The reactions of trihydroxybenzenes 1a-c and 3-methylbut-2-enoic acid ( 2 ) in a zinc chloride/water/phosphoryl chloride system afford either the new trihydroxyphenylbutenone derivatives 3b,c or dihydroxy-2,2-dimethyl-4-chromanones 4a-c in good yields. Compounds 3b,c can be cyclized in high yields to 4b,c in 5% sodium hydroxide solution. Regioselective O-alkylation of 4a-c leads to 5a-f in good yields. O-Alkylation of 5a-f , followed by reduction and dehydration, results in the formation of precocene 3 ( 7d ) and its regioisomer 7a-c,e,f . Methylation of 4a-c gives 6g-i . Subsequent reduction and dehydration affords precocene 2 ( 7h ) and its regioisomers 7g,i . 相似文献
88.
Capillary electrochromatography of proteins with polymer-based strong-cation-exchanger microspheres 总被引:1,自引:0,他引:1
Monodisperse poly(glycidyl methacrylate-divinylbenzene) microspheres were functionalized with propyl sulfonic acid moieties to obtain beads negatively charged in a wide pH range. They were packed into fused-silica capillary of 50 micro, I.D. in order to separate proteins by capillary electrochromatography (CEC). Baseline separation of four basic proteins as well as three cytochrome c variants with an average column efficiency of 60,000 theoretical plates was obtained under isocratic elution conditions. The high efficiency is attributed to the uniformity of the column packing and the hydrophilic surface coverage of the polymer beads derived from the functionalization process. The effect of pH and salt concentration on protein separations was investigated and the results showed that the CEC separation mechanism is the combination of chromatographic retention and electrophoretic migration. Moreover, the column packed with the strongly acidic poly(glycidyl methacrylate-divinylbenzene) beads was also suitable for protein separations by micro-HPLC with a salt gradient. The comparison between the two kinds of elution modes shows that the column described here exhibited higher peak efficiency with isocratic elution in CEC than with gradient elution in micro-HPLC. 相似文献
89.
Jnos les Gyrgy Kalaus Lajos Szab
Albert Lvai Istvn Greiner Mria Kajtr‐Peredy Pl Szab
Csaba Szntay 《Journal of heterocyclic chemistry》2002,39(4):767-771
The oxidation of (‐)‐tabersonine ( 1 ) with dimethyldioxirane (DMD) in neutral and acidic medium gave 16‐hydroxytabersonine‐N‐oxide ( 3 ) and the didehydrovincamine isomers 4 and 5 , respectively. (+)‐14,15‐Didehydro‐quebrachamine ( 7 ) furnished the hydroxyindolenine 9 , and the pentacyclic derivative 11 . (+)‐Quebrachamine ( 8 ) and DMD in neutral medium gave (7S,20S)‐(+)‐rhazidigenine ( 12 ) which was converted to (2R,7S,20S)‐(+)‐rhazidine ( 13b ) with hydrochloric acid. 相似文献
90.