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61.
The 1H-pyrazole-3-carboxylic acid 2 was converted in good yield (69%) into the corresponding 1H-pyrazole-3-carboxamide 5 via reaction of the acid chloride 3 with 2,3- diaminopyridine (4). A different product, the 3H-imidazo[4,5-b] pyridine derivative 6, was formed from the reaction of 3 with 4 and base in benzene for 5 hours. The structures of the synthesized compounds were determined spectroscopically. The mechanism of the reaction between 3 and 4 was examined theoretically. 相似文献
62.
Fatma Moalla 《Annali di Matematica Pura ed Applicata》1966,73(1):319-365
Résumè Le travail suivant établit des théorèmes globaux relatifs aux variétes finslériennes completes dont le tenseur de courbure
vérifie certaines hypothèses. Le théorème de Hopf-Rinow est d’abord démontrè, puis au moyen du calcul variationnel, on établit
une géneralisation des théoremes de Myers, de Cartan et de L. W. Green. 相似文献
63.
Hagarman A Measey T Doddasomayajula RS Dragomir I Eker F Griebenow K Schweitzer-Stenner R 《The journal of physical chemistry. B》2006,110(13):6979-6986
We measured the temperature-dependent electronic circular dichroism (ECD) spectra of AX, XA, and XG dipeptides in D2O. The spectra of all XA and AX peptides indicate a substantial population of the polyproline II (PPII) conformation, while the ECD spectra of LG, KG, PG, and AG were found to be quantitatively different from the alanine-based dipeptides. Additional UV absorption data indicate that the ECD spectra of the XG peptides stem from electronic coupling between the peptide and the C-terminal group, and that spectral differences reflect different orientations of the latter. We also measured the 1H NMR spectra of the investigated dipeptides to determine the 3JHalphaNH coupling constants for the C-terminal residue. The observed temperature dependence of the ECD spectra and the respective room-temperature 3JHalphaNH coupling constants were analyzed by a two-state model encompassing PPII and a beta-like conformation. The PPII propensity of alanine in the XA series is only slightly modulated by the N-terminal side chain, and is larger than 50%. As compared to AA, XA peptides containing L, P, S, K V, E, T, and I all cause a relative stabilization of the extended beta-strand conformation. The PPII fractions of XA peptides varied between 0.64 for AA and 0.58 for DA, whereas the PPII fractions of AX peptides were much lower. From the investigated AX peptides, only AL and AQ showed the expected PPII propensity. We found that AT, AI, and AV clearly prefer an extended beta-strand conformation. A quantitative comparison of AA, AAA, and AAAA revealed a hierarchy AAAA > AAA approximately AA for the PPII population, in agreement with predictions from MD calculations and results from Raman optical activity studies (McColl et al. J. Am. Chem. Soc. 2004, 126, 5076). 相似文献
64.
Bayrakçeken F Telatar Z Ari F Tunçyürek L Karaaslan I Yaman A 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2006,65(1):143-146
The alpha-methallyl free radical is formed in the flash photolysis of 3-methylbut-1-ene, and cis-pent-2-ene in the vapor phase, and then subsequent reactions have been investigated by kinetic spectroscopy and gas-liquid chromatography. The photolysis flash was of short duration and it was possible to follow the kinetics of the radicals' decay, which occurred predominantly by bimolecular recombination. The measured rate constant for the alpha-methallyl recombination was (3.5+/-0.3) x 10(10) mol(-1) ls(-1) at 295+/-2K. The absolute extinction coefficients of the alpha-methallyl radical are calculated from the optical densities of the absorption bands. Detailed analysis of related absorption bands and lifetime measurements in the original alpha-methallyl high-resolution discrete absorption spectrum image were also carried out by image processing techniques. 相似文献
65.
Problem-based learning (PBL) and science, technology, engineering, and mathematics (STEM) are two acronyms widely visible in education literature today. However, few studies have explored these in connection with one another, specifically with regard to teacher preparation. This study investigated how 47 prospective elementary teachers developed PBL units and how they integrated STEM and other disciplines into those units. It also addressed the affordances and constraints of integrated STEM as perceived by the prospective elementary teachers. Data sources in this multimethod study included PBL units and interviews. Findings revealed that all of the units integrated at least two of the STEM disciplines, as well as literacy, in a variety of ways. The prospective teachers articulated perceived benefits of integrated STEM, such as: making connections across content areas, preparing students for the real world, teaching students that failure is not a bad thing, and providing future opportunities. They also addressed perceived barriers of integrated STEM, such as: having limited experience with the content, diminishing the effect of individual content areas, and needing better curriculum alignment. Overall, this study provides evidence that PBL can be a pedagogical approach to integrate STEM. Implications for teachers, teacher educators, and curriculum specialists are discussed. 相似文献
66.
Fatma Fakhfakh 《Complex Analysis and Operator Theory》2018,12(8):2003-2018
This paper is devoted to the investigation of the perturbation problem of right (left) Browder linear relations and lower (upper) semi-Browder linear relations under commuting compact linear relations. Further, our results are used to show the invariance of Browder’s spectrum. 相似文献
67.
Özlem Türker Bayrak Ay?en D. Akkaya 《Journal of Computational and Applied Mathematics》2010,233(8):1763-1772
We consider a multiple autoregressive model with non-normal error distributions, the latter being more prevalent in practice than the usually assumed normal distribution. Since the maximum likelihood equations have convergence problems (Puthenpura and Sinha, 1986) [11], we work out modified maximum likelihood equations by expressing the maximum likelihood equations in terms of ordered residuals and linearizing intractable nonlinear functions (Tiku and Suresh, 1992) [8]. The solutions, called modified maximum estimators, are explicit functions of sample observations and therefore easy to compute. They are under some very general regularity conditions asymptotically unbiased and efficient (Vaughan and Tiku, 2000) [4]. We show that for small sample sizes, they have negligible bias and are considerably more efficient than the traditional least squares estimators. We show that our estimators are robust to plausible deviations from an assumed distribution and are therefore enormously advantageous as compared to the least squares estimators. We give a real life example. 相似文献
68.
We study the existence of oscillatory and periodic solutions of a class of first order scalar impulsive delay differential
equations with piecewise constant argument. 相似文献
69.
Ultraviolet and visible spectroscopic measurements were used to investigate prepared undoped and Mn-doped sodium phosphate glasses before and after successive gamma irradiation. The effects of both glass composition and MnO2 content on the generation of radiation-induced defects were investigated. Undoped sodium phosphate glass shows strong UV absorption, which is attributed to the presence of trace iron impurities present in the raw materials. Mn-doped glasses reveal an additional visible broad band centered at about 500 nm due to Mn3+, which has recently been related to the 5Eg →5T2g transition. The radiation-induced bands are correlated with the generation of liberated electron–hole pairs during the process of gamma irradiation and the possibility of photochemical reactions especially with trace iron impurities and manganese ions. The intensity and the position of the induced bands are observed to depend on the type and composition of glass, concentration of the dopant and also on the irradiation dose. Manganese ions when present in relatively higher content have been found to show a shielding behavior towards the effects of progressive gamma irradiation causing a retardation of the growth of the induced defects. Infrared and Raman spectra of the undoped and Mn-doped glasses were measured to investigate the structural phosphate groups present and the effect of MnO2 on the network structure. An ESR investigation was carried out to confirm the state of manganese ions in the prepared sodium phosphate glasses. 相似文献
70.
Celal Bayrak 《光谱学快报》2013,46(2):133-140
ABSTRACT New Hofmann–Td-type clathrates of the forms Cd(CPA)2M(CN)4.C6H6 (CPA = cyclopropylamine; M?Cd or Hg) prepared in powder form and characterized by FT-IR, FT-Raman, far-IR spectra, X-ray diffraction, and elemental analyses are reported. Vibrational assignments are proposed for the bands of the host lattice and guest molecule. It is shown that the spectra are consistent with a proposed crystal structure for the compounds derived from X-ray diffraction measurements. The C, H, and N analyses were carried out for all the compounds. All the vibrational modes of coordinated CPA are characterized. The spectral features suggest that these compounds are similar in structure to the Hofmann–Td-type clathrates. 相似文献