共查询到20条相似文献,搜索用时 9 毫秒
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Thermodynamic properties of fluids are generally calculated from the PVT relations through equations of state. The majority of existing equations of state require the critical properties or intermolecular potential energy parameters as their input data. In many cases, such properties are neither available nor they can be accurately estimated.
One accessible and accurately measurable property of substances is the velocity of sound. In this report a method is introduced through which one can predict the PVT behavior of fluids using the velocity of sound data. A general mathematical relationship,
expressing the velocity of sound, c, in terms of the hard-core velocity of sound, chs, and thermodynamic properties is derived. One may use this equation to extract PVT data from cVT data, or vice versa. As an example the virial coefficients, the Lennard-Jones intermolecular potential parameters, and the constants of the van der Waals equation of state for a number of pure fluids are calculated using the velocity of sound data. Utility of this method is particularly attractive for such compounds as heavy hydrocarbons, unstable fluids, and newly designed molecules for which intermolecular parameters and critical properties are not available. 相似文献5.
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Sârbu C 《Journal of AOAC International》2000,83(6):1463-1467
A new fuzzy regression algorithm was successfully applied to calibration in thin-layer chromatography (TLC)/densitometry. Different regression techniques were also considered, and objective quality coefficients were used for evaluation of the results. Depending on the structure of the data, the fuzzy procedure can improve the results dramatically. From the results reported in this paper and other unpublished results, it appears clear that the calibration procedure based on fuzzy regression is the most suitable regression method in quantitative TLC. 相似文献
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The classification of absorption bands in the acene series (, p, β-bands) was first based on the annellation effect and later on the polarization of the bands with regard to the molecular axes (Lb,La,Bb,Ba-bands). Both give the same result since annelation axes and molecular axes coincide. This is not so in the pyrene series. Annellation axes and molecular axes are different and it is shown that the classification of bands can be based only on the annellation effects. Moreover, the electronic asymmetry of the pyrene system is demonstrated by a striking asymmetric annellation effect. A number of higher annellated pyrenes have been synthesized:
1·-benzonaphtho-(2″·3″ :6·7)-pyrene, dinaphto-(2'·3 :1·2)-(2″·3″:6·7)-pyrene, 1·14,4·5-dibenzo-pentacene, 5·,15·16-dibenzohexacene, 6·7,16·17-dibenzoheptacene, 1·16,4·5-dibenzohexacene and 7·8,17·18-dibenzo-octacene. 相似文献
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A regression tree (RT) was extensively utilized in quantitative structure-activity relationship studies (QSAR), due to its inherently promising attributes. The issues of instability and inclination to overfitting and suboptima, however, often occur in RT. In the present study, a robust version of boosting was invoked to simultaneously improve the stability and generalization ability of RT, forming a new method called robust boosting regression tree (RBRT). RBRT works by sequentially employing the RT method to model the robustly reweighted versions of the original training set and then aggregating these resultant predictors via weighted median. The designed RBRT was applied to predict the bioactivities of flavoniod derivatives and the anti-HIV activities of HIV-1 inhibitors, compared with boosting RT (BRT) and RT. The results of these two data sets demonstrated that the introduction of robust boosting drastically enhances the stability and generalization ability of RT, and RBRT is superior to BRT in QSAR studies. 相似文献
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Majumder SK Gupta A Gupta S Ghosh N Gupta PK 《Journal of photochemistry and photobiology. B, Biology》2006,85(2):109-117
We report development of a direct multi-class spectroscopic diagnostic algorithm for discrimination of high-grade cancerous tissue sites from low-grade as well as precancerous and normal squamous tissue sites of human oral cavity. The algorithm was developed making use of the recently formulated theory of total principal component regression (TPCR). The in vivo autofluorescence spectral data acquired from patients screened for neoplasm of oral cavity at the Government Cancer Hospital, Indore, was used to train and validate the algorithm. The diagnostic algorithm based on TPCR was found to provide satisfactory performance in classifying the tissue sites in four different classes - high-grade squamous cell carcinoma, low-grade squamous cell carcinoma, leukoplakia, and normal squamous tissue. The classification accuracy for these four classes was observed to be approximately 94%, 100%, 100% and 91% for the training data set (based on leave-one-out cross-validation), and was approximately 90%, 90%, 85% and 88%, respectively for the corresponding classes for the independent validation data set. 相似文献
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Zohreh Fasihi Parvin Zakeri-Milani Ali Nokhodchi Jafar Akbari Mohammad Barzegar-Jalali Raimar Loebenberg Hadi Valizadeh 《Journal of Thermal Analysis and Calorimetry》2017,130(3):1371-1382
The present study is a comparative study of three equations, namely the Clausius–Clapeyron, Van’t Hoff and Hildebrand (to calculate crystal–liquid fugacity ratio (CLFR) of drug compounds), to select the best model in predicting the intestinal absorption and develop a new classification system based on dose number (D o) and CLFR. The required thermodynamic parameters [melting point, enthalpy of fusion (ΔH m) and the differential molar heat capacity (?C pm)] were experimentally obtained by differential scanning calorimetry. Pharmacokinetic data [the human intestinal absorption (F a) and apparent permeability of Caco-2 (P app _Caco-2)] and D o were obtained from the literature. The highest value of CLFR was found for diclofenac with the value of 88.78, 87.29, and 87.84 mol% from Clausius–Clapeyron, Van’t Hoff, and Hildebrand approaches, respectively. The lowest CLFR value was seen for memantine with the value of 14.3 × 10?17 and 26 × 10?12 mol% from Van’t Hoff and Hildebrand equations, respectively. Statistical comparison with the Wilcoxon signed rank test showed that the CLFR values calculated by three equations are different. CLFR values of more than 1 mol% correspond to the complete intestinal absorption (F a). There was a sigmoidal dependency between CLFR and F a, similar to the dependency between P app _Caco-2 and F a. In these modeling, the excellent correlations were obtained in all three models as evidenced by a good coefficient of determination (r 2 ) without a significant difference in the average absolute error. A new classification system from Hildebrand model based on D o and CLFR was developed and was in agreement with the biopharmaceutics classification system (70.5%) and the biopharmaceutical drug disposition system (65.6%). This modeling approach can be a valuable tool for scientists as an alternative for intestinal permeability in the biopharmaceutical classification system to develop new oral drugs. The CLFR obtained from Hildebrand model is also more convenient than the Clausius Clapeyron model, because the former does not need to calculate ?C pm (difficult step in calculating CLFR) for drug compounds. This new classification can help to develop the new drug product in industrial and academic research, without necessary in vivo experiments. 相似文献
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Marco Grotti Maria Luisa Abelmoschi Francesco Soggia Christian Tiberiade Roberto Frache 《Spectrochimica Acta Part B: Atomic Spectroscopy》2000,55(12):1847-1860
The multivariate effects of Na, K, Mg and Ca as nitrates on the electrothermal atomisation of manganese, cadmium and iron were studied by multiple linear regression modelling. Since the models proved to efficiently predict the effects of the considered matrix elements in a wide range of concentrations, they were applied to correct the interferences occurring in the determination of trace elements in seawater after pre-concentration of the analytes. In order to obtain a statistically significant number of samples, a large volume of the certified seawater reference materials CASS-3 and NASS-3 was treated with Chelex-100 resin; then, the chelating resin was separated from the solution, divided into several sub-samples, each of them was eluted with nitric acid and analysed by electrothermal atomic absorption spectrometry (for trace element determinations) and inductively coupled plasma optical emission spectrometry (for matrix element determinations). To minimise any other systematic error besides that due to matrix effects, accuracy of the pre-concentration step and contamination levels of the procedure were checked by inductively coupled plasma mass spectrometric measurements. Analytical results obtained by applying the multiple linear regression models were compared with those obtained with other calibration methods, such as external calibration using acid-based standards, external calibration using matrix-matched standards and the analyte addition technique. Empirical models proved to efficiently reduce interferences occurring in the analysis of real samples, allowing an improvement of accuracy better than for other calibration methods. 相似文献
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Gardana C Simonetti P Berti C Pietta P 《Rapid communications in mass spectrometry : RCM》2007,21(23):3849-3854
Propolis has various biological activities such as antibacterial, antiviral, antioxidant, immunostimulating and antiinflammatory, which are generally ascribed to the polyphenolic fraction. The aim of this study was to evaluate the absorption of the main polyphenols [caffeic acid (CA), pinobanksin-5methyl ether (P-5ME), pinobanksin (Pb), chrysin (C), pinocembrin (P), galangin (G), pinobanksin-3-acetate, pinobanksin esters and caffeic acid phenylethyl ester (CAPE)] from a dewaxed and standardized extract of propolis (EPID). Fifteen healthy volunteers consumed 5 mL EPID in water, corresponding to 125 mg of flavonoids. Blood samples were collected before, each hour for 8 h and 24 h after EPID intake. After deconjugation by beta-glucuronidase/sulfatase the plasma samples were analyzed by a selective liquid chromatography/tandem mass spectrometry (LC/MS/MS) method using morin as internal standard (I.S.). A kinetic profile characterized by two t(max), respectively at 1 h and about 5 h post-ingestion, was observed in all the subjects. The two peaks may be due to enterohepatic cycling. Among the various polyphenols ingested, only P-5ME, Pb, C, P and G were detected in plasma and C(max)t(1h) were 65.7 +/- 13.3, 46.5 +/- 12.7, 79.5 +/- 18.6, 168.1 +/- 16.3 and 113.7 +/- 16.8 ng/mL, respectively. These levels decreased significantly after 8 h and were no longer detectable 24 h after EPID intake. The recovery of the extraction for CA, Pb, C, P, G and I.S. from spiked plasma was 95.2 +/- 3.1, 93.1 +/- 3.6, 91 +/- 2.5, 96.4 +/- 4.2, 93.4 +/- 2.4 and 85.5 +/- 2.4%, respectively. The results of this study evidence that flavonoids from EPID are absorbed, metabolized and Pb-5ME and G seem to have apparent absorption, measured as (AUC/dose), higher than C, P and Pb. 相似文献
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The development of solutions that prevent dehydration or promote adequate re-hydration play a vital role in preventing fatigue during exercise, however, the methods commonly used to assess the hydration ability of such solutions are invasive and often assess the components of absorption separately. This paper describes using a non-invasive deuterium tracer technique that assesses gastric emptying and intestinal absorption simultaneously to evaluate the uptake of water during rest and exercise. The kinetics of absorption are further examined by mathematical modelling of the data generated. For the rest group, 0.05 g/kg of body weight of deuterium, contained in gelatine capsules, was ingested with ordinary tap water and saliva samples were collected every 5 min for one hour while the subject remained seated. The deuterium was administered as above for the exercise group but sample collection was during one hour of exercise on a treadmill at 55% of the subject's maximum heart rate. The enrichment data for each subject were mathematically modelled and the parameters obtained were compared across groups using an independent samples t-test. Compared with the rest condition, the exercise group showed delayed absorption of water as indicated by significant differences for the modelling parameters t2, t1/2, maximum absorption rate and solution absorption amount at t1. Labelling with a deuterium tracer is a good measure of the relative rate ingested fluids are absorbed by the body. Mathematical modelling of the data generates rates of maximum absorption and allows calculation of the percentage of the solution that is absorbed at any given time during the testing period. 相似文献
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The use of regression methods for classifying and predicting the mechanisms of toxic action of phenols was investigated in this study. Multiresponse regression was conducted using a total of six linear and nonlinear regression methods: simple linear regression (LinReg), logistic regression (LogReg), generalized additive model (GAM), locally weighted regression scatter plot smoothing (LOWESS), multivariate adaptive regression splines (MARS), and projection pursuit regression (PPR). A database containing phenols acting by four mechanisms (polar narcosis, weak acid respiratory uncoupling, proelectrophilicity, and soft electrophilicity) was used to assess the performances of the six regression methods in the multiresponse regression approach. For comparison purposes, traditional linear discriminant analysis (LDA) was also conducted as a baseline method to study the potential improvement of prediction accuracy by the multiresponse regression approach. Results showed that compared to LDA, the overall mechanism prediction error rate could be reduced to below 10% by multiresponse regression based on PPR. In addition to prediction accuracy, interpretability of the resultant models was discussed. 相似文献
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Immobilized liposome chromatography to study drug-membrane interactions. Correlation with drug absorption in humans 总被引:1,自引:0,他引:1
For rapid screening of drug-membrane interactions and predicting drug absorption in vivo, unilamellar liposomes were stably immobilized in the pores of gel beads by avidin-biotin binding. Interactions of a diverse set of well-described drugs with the immobilized liposomal membranes were reflected by their elution profiles. The membrane partitioning coefficients (KLM) of the drugs were determined from the retention volumes. The drug retentions on egg phosphatidylcholine (EPC)-phosphatidylserine (PS)-cholesterol (chol) and EPC-PS-phosphatidylethanolamine (PE)-chol columns intended to mimic small intestine membranes were similar, although the positively-charged drugs were more strongly retarded on the negatively-charged liposomes than the negatively-charged drugs. The relationship between log KLM with the drug fraction absorbed in humans showed that the log KLM values obtained with unilamellar liposomes can be used to predict drug passive transcellular absorption, similarly to that previously shown for entrapped multilamellar liposomes. The immobilized liposome chromatography method should be useful for screening compounds at an early stage of the drug discovery process. The avidin-biotin immobilization of the liposomes prolongs the lifetime of the columns. 相似文献
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[structure: see text] The complete stereostructure of glisoprenin A has been predicted via analysis of the 13C NMR behaviors in the presence of (R)- and (S)-Pr(tfc)3. 相似文献