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181.
Syndiotactic specific polymerization of styrene has been investigated by ~(13)C NMR analysis and isotopic laelling methods. The value of the activation energy involved in the steric control has been determined. Some information of the number of the active sites and on the life of the catalysts is reported. 相似文献
182.
《Arabian Journal of Chemistry》2022,15(7):103933
In this study, a fingerprint-activity relationship modeling between chemical fingerprints and antirheumatic activity was established, and multivariate statistical analysis was used to evaluate the quality of Taxilli Herba (TH) from different hosts. Characteristic fingerprints of 20 batches of TH samples were generated by high-performance liquid chromatography coupled with triple quadrupole-time of flight tandem mass spectrometry (HPLC-Triple TOF-MS/MS), and the similarity analysis was calculated based on thirteen common characteristic peaks by hierarchical clustering analysis (HCA). Subsequently, nine efficacy markers were discovered by combining fingerprints and antirheumatic activity through grey correlation analysis (GCA) and bivariate correlation analysis (BCA). Meanwhile, the content of 5 constituents in 9 markers was determined by high-performance liquid chromatography coupled with triple quadrupole-linear ion trap tandem mass spectrometry (HPLC-QTRAP-MS/MS). The comprehensive quality of TH was assessed using multivariate statistical analysis, including principal components analysis (PCA) and technique for order preference by similarity to ideal solution (TOPSIS). The results showed that a high dose of TH extract could markedly ameliorate arthritis damage compared to other doses, with flavonoids playing an important role in the antirheumatic activity. The comprehensive quality of samples from Morus alba L. (SS) was superior to those from Liquidambar formosana Hance (FXS). The present study will demonstrate the markers associated with efficacy, and provide an applicable strategy for more comprehensive quality control and evaluation of TH. 相似文献
183.
Establishing a reliable method to predict the global mean temperature (Te) is of great importance because CO2 reduction activities require political and global cooperation and significant financial resources. The current climate models all seem to predict that the earth's temperature will continue to increase, mainly based on the assumption that CO2 emissions cannot be lowered significantly in the foreseeable future. Given the earth's multifactor climate system, attributing atmospheric CO2 as the only cause for the observed temperature anomaly is most likely an oversimplification; the presence of water (H2O) in the atmosphere should at least be considered. As such, Te is determined by atmospheric water content controlled by solar activity, along with anthropogenic CO2 activities. It is possible that the anthropogenic CO2 activities can be reduced in the future. Based on temperature measurements and thermodynamic data, a new model for predicting Te has been developed. Using this model, past, current, and future CO2 and H2O data can be analyzed and the associated Te calculated. This new, esoteric approach is more accurate than various other models, but has not been reported in the open literature. According to this model, by 2050, Te may increase to 15.5 ℃ under "business-as-usual" emissions. By applying a reasonable green technology activity scenario, Te may be reduced to approximately 14.2 ℃. To achieve CO2 reductions, the scenario described herein predicts a CO2 reduction potential of 513 gigatons in 30 years. This proposed scenario includes various CO2 reduction activities, carbon capturing technology, mineralization, and bio-char production; the most important CO2 reductions by 2050 are expected to be achieved mainly in the electricity, agriculture, and transportation sectors. Other more aggressive and plausible drawdown scenarios have been analyzed as well, yielding CO2 reduction potentials of 1051 and 1747 gigatons, respectively, in 30 years, but they may reduce global food production. It is emphasized that the causes and predictions of the global warming trend should be regarded as open scientific questions because several details concerning the physical processes associated with global warming remain uncertain. For example, the role of solar activities coupled with Milankovitch cycles are not yet fully understood. In addition, other factors, such as ocean CO2 uptake and volcanic activity, may not be negligible. 相似文献
184.
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185.
Peter Scharfenberg 《Theoretical chemistry accounts》1980,58(1):73-79
A simple classification scheme is proposed for critical points, based only on rankr and signatures of the (n,n)-matrixG of harmonic force constants. The determination ofr ands, e.g. by the well-known factorizationG=L
T
gL (L: triangular matrix,g: diagonal matrix), has several theoretical as well as practical (computational) advantages over the inspection of eigenvalues ofG, so far used in quantum chemistry. The eigenvalues are sufficient butnot necessary for a classification whereas rank and signature are the only necessary and sufficient prerequisites for solving the task. For the purpose of presenting a working example, by calculating only a 2×2 torque constant matrix, it is shown that the coplanar ethylbenzene is unstable in the CNDO/2 picture. 相似文献
186.
The PF6 salts of the new cationic hexamethylborazinerhodium(I) complexes of general formula [Rh(Me3B3N3Me3)(LL′)]+ (LL′= 1,5-cyclooctadiene, norbornadiene, tetrafluorobenzobarrelene, trimethyltetrafluorobenzobarrelene, L = L′ = ethylene, CO) have been prepared from the reaction between [RhCl(LL′)]2, Me3B3NMe3, and AgPF6 in dichloromethane. These complexes are very labile, undergoing rapid ring ligand exchange in solution with σ and π-donor ligands. The synthesis of [Rh(η6-naphthalene)(COD)]PF6 is also described. The properties and NMR and IR spectroscopic characteristics of the new compounds are briefly discussed. 相似文献
187.
A method is described for the simultaneous quantitative determination of monoamines and related compounds from urine and brain tissue samples in the pg-range, using a GC/MF instrument LKB-2091 provided with a multiple ion detection (MID) system and capillary columns. The simultaneous detection of “fingerprints” with fourteen and more compounds during one single GC run was achieved after the intoduction of “time gates” for the detection of the different characteristic masses. Several modifications to the LKB equipment permitted exact reproducibility of retention times, which is essential for the use of “time gates”. The detection of “fingerprints” with these acidic, basic and alcoholic substances was achieved by the extraction of the dried biological samples with silylating agents. 相似文献
188.
The Golay-Giddings and Poiseuille equations are used to derive equations for the calculation of the maximum plate number and minimum time conditions for given columns at fixed, but selectable, outlet pressures. In addition, expressions are presented for the determination of minimum analysis times for separation problems requiring given plate numbers. In this instance, the optimum column length can be calculated as a function of outlet pressure. A Basic computer program, incorporating the equations for the various optima, together with the H-ū curves, is described. Input variables are either column length or desired plate number, column diameter, film thickness, capacity ratio of the solute, column outlet pressure, seperation temperature, and carrier gas. The carrier gas viscosity is automatically calculated in the case of hydrogen, helium, or nitrogen. For these gases, and if the solute is a n-alkane, the diffusivity of the solute in the mobile phase is calculated. In this case, the carbon number of the solute is needed in the computation. For high molecular weight polydimethylsilicone phases (e.g. SE-30), the program can approximate the diffusivity of n-alkanes in the stationary phase at the given temperature as a function of the carbon number. Of course, manually entered values of viscosity and diffusion coefficients can be included in the calculations. 相似文献
189.
Jean Diebolt 《Journal of Theoretical Probability》1991,4(4):655-667
We consider the Markov chainX
n+1=T(X
n
)+
n
, where {
n
;n1} is a
d
-valued random sequence of independent identically distributed random variables, and the functionT:
d
d
is measurable and satisfies a suitable growth condition. Under certain conditions involvingT and the probability distribution of
n
, we show that this Markov chain is ergodic. Moreover, we obtain sharp upper bounds for the tail of the corresponding stationary probability density function. In our proofs, we make use of the Leray-Schauder fixed-point theorem. 相似文献
190.
A study was undertaken to determine the interfering effects of arsenic, bismuth, germanium, lead, selenium, tin and tellurium on trace determination of antimony by atomic-absorption spectrometry with hydride-generation. A 1% NaBH(4) solution was used as reductant and a small amount of oxygen was added to the hydrogen produced, to support the combustion and atomization of SbH(3). The interference from selenium in the determination of antimony is removed if potassium iodide-ascorbic acid solution or copper sulphate is added to the sample solution. The interference of tin and tellurium can also be avoided by adding potassium iodide-ascorbic acid solution. A possible interference mechanism is discussed. 相似文献