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101.
102.
Evidence is presented which indicates that singlet → triplet intersystem crossing from the charge-transfer singlet state of electron donor-acceptor complexes is efficient only when a locally excited triplet state of a component molecule (donor or acceptor) lies below the charge-transfer singlet state. 相似文献
103.
Tripathi RP Rastogi SK Kundu B Saxena JK Reddy VJ Srivastava S Chandra S Bhaduri AP 《Combinatorial chemistry & high throughput screening》2001,4(3):237-244
A library of 24 glycoconjugates related to glycosylated beta-amino acid derivative (I) was been prepared and screened against DNA topoisomerase-II of the filarial parasite S. cervi. Among these, compound 6 was found to be a potent inhibitor of DNA topoisomerase-II with 95% inhibition at 1.09 microM. Furthermore, compound 6 was at least three times more potent than the lead compound, glycosylated beta-amino acid derivative I. 相似文献
104.
The photo-oxidative degradation and stabilization of poly(2,6-dimethyl-1,4-phenylene oxide) films have been examined in the temperature range 263–313 K in air with u.v. light of 253.7 nm. The changes in weight-average molecular weight, quantum efficiencies, carbonyl index, hydroperoxide concentration and i.r. spectra have been followed in the absence and presence of the stabilizer. The heats of activation of the systems have been calculated and the mechanism of stabilization has been postulated. A saturation limit in photostabilization of the polymer was achieved beyond 0.6 wt% of zinc di-n-hexyl dithiophosphate. 相似文献
105.
S. B. Manohar S. K. Aggarwal S. M. Deshmukh A. R. Parab P. P. Burte H. C. Jain Satya Prakash 《Journal of Radioanalytical and Nuclear Chemistry》1981,63(1):145-153
A gamma-spectrometric method using an intrinsic high resolution germanium detector has been developed for the determination
of isotope ratios of plutonium from samples in solution form. The method is based on the assay of low energy gamma-rays of238Pu,239Pu,240Pu and241Pu and does not require the use of branching intensities or the knowledge of detection efficiencies for different gamma rays.
Since low energy gamma-rays are used, the effect of241Am has also been studied. It is found that results are not affected up to 0.5 wt% of241Am in plutonium samples. An accuracy of 3% is achievable in the determination of240Pu/239Pu and241Pu/239Pu atom ratios as demonstrated by carrying out measurements on isotopic standards of plutonium. 相似文献
106.
Ginotra SK Chhikara BS Singh M Chandra R Tandon V 《Chemical & pharmaceutical bulletin》2004,52(8):989-991
Mild, efficient and eco-friendly oxidation of 17alpha-methylandrostan-3beta-17beta-diol (1) has been studied with three different reagents viz. pentavalent iodine reagent 2-iodoxy benzoic acid (IBX) in DMSO at 65 degrees C, sodium hypochlorite and H2O2/Na2WO4 under phase transfer conditions to give 17beta-hydroxy-17alpha-methylandrostan-3-one (mestanolone 2), a drug intermediate as oxidized product. The H2O2/Na2WO4/PTC gave mestanolone in high yield and purity whereas sodium hypochlorite/PTC system yielded some chlorinated material along with the mestanolone. However, 1 with 2.5 equivalent of IBX gave 17beta-hydroxy-17alpha-methyl-Delta1-androsten-3-one (3) under the similar reaction conditions in good yield and single step reaction. 相似文献
107.
Summary The effect of composition and flow rate of the mobile phase on the HPLC separation of hydrogenated buckminsterfullerene (C60Hn n=2–38) was investigated on BuckySep column. Toluene was used as the basic solvent and hexane, heptane, cyclohexane, THF,
acetonitrile, acetone, ethanol and 2-propanol as co-solvents. The fraction of co-solvents was varied 10–80%, and the flow
rate 1–0.1 mL min−1. Toluene-acetonitrile 65∶35 and toluene-acetone 50∶50 provided the best separation. Under the best conditions complete separation
of C60H2 and almost complete separation of the four most abundant isomers of C60H4 were achieved. Separation of derivatives with higher hydrogen content was very poor.
Presented at: Balaton Symposium on High-Performance Separation Methods, Siófok, Hungary, September 3–5, 1997 相似文献
108.
The effects of gamma irradiation on the microbiological, physical and sensory qualities of diced tomatoes 总被引:1,自引:0,他引:1
Anuradha Prakash Jacqueline Manley Suresh DeCosta Fred Caporaso Denise Foley 《Radiation Physics and Chemistry》2002,63(3-6):387-390
Diced Roma tomatoes were treated with gamma irradiation and evaluated for changes in microbial, physical, chemical and sensory properties. Dosages for Trial 1 were 0.0, 0.39, 0.56 and 1.82 kGy and in Trial 2, 0.0, 0.50, 1.24 and 3.70 kGy. Irradiation at 3.70 kGy resulted in no aerobic populations through day 12 and significantly fewer colonies through day 15 whereas yeast and mold populations experienced a 2 log reduction through day 12. Color, titratable acidity, and °Brix were not significantly affected by irradiation. Tissue firmness decreased with increasing dose but not with storage time. Treatment with 3.7 kGy decreased firmness by 50% and 20% with 0.5 kGy, however, the reduced firmness induced by 0.50 kGy was undetected by a 9 member trained sensory panel. A significant (p0.05) inverse correlation between changes in texture and water-soluble pectin (WSP) was determined while total pectin remained relatively constant and oxalate soluble pectin content decreased slightly with irradiation dose. The significant inverse correlation between the loss of firmness and WSP indicates that the changes in WSP play an important role in the tissue softening of tomatoes, This study indicates that irradiation at 0.5 kGy can reduce microbial counts substantially to improve microbial shelf life without adverse effects on sensory qualities. 相似文献
109.
M. Prakash Y. R. Waghmare I. Mehrotra 《Zeitschrift für Physik A Hadrons and Nuclei》1976,278(2):155-164
Low-lying spectra of6Li,18F,18O,42Sc,42Ca,58Ni and92Zr are studied with Sussex matrix elements (SME) and their central, spin-orbit and tensor components. It is observed that major contribution to level energies comes from the central part, while the tensor part provides the finer details of spectra, particularly forT=0 levels. The spin-orbit part does not make any appreciable contribution to level energies. A phenomenological renormalization of the SME is carried out to improve the agreement with the experimental results. It turns out that some of the low-lyingT=0 levels can be satisfactorily described if the SME in the3S1 relative state are made (1+α) times their bare interaction value, whereα is a constant to be determined from a comparison with experimental level energies. Similarly, forT=1 levels, better agreement with the experimental results is obtained if aδ-function-plus-quadrupole interaction is added to the SME. 相似文献
110.
V.K. Chandra B.P. Chandra M. Tiwari R.N. Baghel M. Ramrakhiani 《Journal of luminescence》2012,132(6):1532-1539
When a voltage pulse is applied under forward biased condition to a spin-coated bilayer organic light-emitting diode (OLED), then initially the electroluminescence (EL) intensity appearing after a delay time, increases with time and later on it attains a saturation value. At the end of the voltage pulse, the EL intensity decreases with time, attains a minimum intensity and then it again increases with time, attains a peak value and later on it decreases with time. For the OLEDs, in which the lifetime of trapped carriers is less than the decay time of the EL occurring prior to the onset of overshoot, the EL overshoot begins just after the end of voltage pulse. The overshoot in spin-coated bilayer OLEDs is caused by the presence of an interfacial layer of finite thickness between hole and electron transporting layers in which both transport molecules coexist, whereby the interfacial energy barrier impedes both hole and electron passage. When a voltage pulse is applied to a bilayer OLED, positive and negative space charges are established at the opposite faces of the interfacial layer. Subsequently, the charge recombination occurs with the incoming flux of injected carriers of opposite polarity. When the voltage is turned off, the interfacial charges recombine under the action of their mutual electric field. Thus, after switching off the external voltage the electrons stored in the interface next to the anode cell compartment experience an electric field directed from cathode to anode, and therefore, the electrons move towards the cathode, that is, towards the positive space charge, whereby electron–hole recombination gives rise to luminescence. The EL prior to onset of overshoot is caused by the movement of electrons in the electron transporting states, however, the EL in the overshoot region is caused by the movement of detrapped electrons. On the basis of the rate equations for the detrapping and recombination of charge carriers accumulated at the interface expressions are derived for the transient EL intensity I, time tm and intensity Im corresponding to the peak of EL overshoot, total EL intensity It and decay of the intensity of EL overshoot. In fact, the decay prior to the onset of EL overshoot is the decay of number of electrons moving in the electron transporting states. The ratio Im/Is decreases with increasing value of the applied pulse voltage because Im increases linearly with the amplitude of applied voltage pulse and Is increases nonlinearly and rapidly with the increasing amplitude of applied voltage pulse. The lifetime τt of electrons at the interface decreases with increasing temperature whereby the dependence of τt on temperature follows Arrhenius plot. This fact indicates that the detrapping involves thermally-assisted tunneling of electrons. Using the EL overshoot in bilayer OLEDs, the lifetime of the charge carriers at the interface, recombination time of charge carriers, decay time of the EL prior to onset of overshoot, and the time delay between the voltage pulse and onset time of the EL overshoot can be determined. The intense EL overshoot of nanosecond or shorter time duration may be useful in digital communication, and moreover, the EL overshoot gives important information about the processes involving injection, transport and recombination of charge carriers. The criteria for appearance of EL overshoot in bilayer OLEDs are explored. A good agreement is found between the theoretical and experimental results. 相似文献