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排序方式: 共有453条查询结果,搜索用时 15 毫秒
1.
Clemens G. Raab Georg Regensburger Jamal Hossein Poor 《Journal of Pure and Applied Algebra》2021,225(5):106564
A formal computation proving a new operator identity from known ones is, in principle, restricted by domains and codomains of linear operators involved, since not any two operators can be added or composed. Algebraically, identities can be modelled by noncommutative polynomials and such a formal computation proves that the polynomial corresponding to the new identity lies in the ideal generated by the polynomials corresponding to the known identities. In order to prove an operator identity, however, just proving membership of the polynomial in the ideal is not enough, since the ring of noncommutative polynomials ignores domains and codomains. We show that it suffices to additionally verify compatibility of this polynomial and of the generators of the ideal with the labelled quiver that encodes which polynomials can be realized as linear operators. Then, for every consistent representation of such a quiver in a linear category, there exists a computation in the category that proves the corresponding instance of the identity. Moreover, by assigning the same label to several edges of the quiver, the algebraic framework developed allows to model different versions of an operator by the same indeterminate in the noncommutative polynomials. 相似文献
2.
Sameerah Jamal 《Journal of Differential Equations》2019,266(7):4018-4026
A manifold that contains small perturbations will induce a perturbed partial differential equation. The partial differential equation that we select is the Poisson equation – in order to explore the interplay between the geometry of the manifold and the perturbations. Specifically, we show how the problem of symmetry determination, for higher-order perturbations, can be elegantly expressed via geometric conditions. 相似文献
3.
The stability of Ochratoxin A during its extraction using different extraction techniques has been evaluated. Microwave-assisted extraction and pressurised liquid extraction, in addition to two other reference methods of extraction, i.e. ultrasound-assisted and magnetic stirring-assisted extraction, were evaluated. The effect of extraction temperature using the cited techniques was checked.The results show that Ochratoxin A can be extracted using microwave-assisted extraction at temperatures up to 150 °C without degradation. Pressurised liquid extraction can be used at temperatures up to 100 °C, for extraction times of less than 30 min. Further, both ultrasound-assisted extraction and magnetic stirring extraction can be applied at temperatures up to 65 °C.High-performance liquid chromatography combined with fluorescence detection using a Chromolith RP-18e column at a flow rate of 5 mL min−1 was used to quantify the Ochratoxin A. The retention time for the Ochratoxin A was 1.3 min. The limits of detection (LOD) and of quantification (LOQ) were 0.03 and 0.10 μg L−1, respectively. 相似文献
4.
The polarographic behaviour of salicylaldehyde-2-pyridylhydrazone (SAPH) has been studied in aqueous buffer solution containing 40% ethanol using DC and DP polarographic methods. In the pH range 1.8–7.5 the observed single irreversible reduction wave is assigned to the splitting of the N-N bond and reduction of C=N centre. In alkaline medium, a second wave appears at a more negative potential due to the reduction of the salicylaldehyde which is formed by hydrolytic decomposition of the SAPH molecule. The effect of pH on the limiting current andE
1/2 as well as the reduction mechanism are discussed and compared with similar compounds. The kinetic parameters of the electrode reaction have been calculated.The analytical properties of the copper(II)-SAPH system is described. The complex gave rise to a single irreversible well-defined wave (E
1/2=–0.58 V at pH=5.2). The reaction process is diffusion controlled. A method is suggested for the determination of Cu(II) in presence of different metal ions as the difference in theirE
1/2 values is sufficient for the purpose.This work is taken partly from the M. Sc. Thesis of Jamal S. Shalabi 相似文献
5.
John F. Endicott M. D. Jamal Uddin H. Bernhard Schlegel 《Research on Chemical Intermediates》2002,28(7-9):761-777
The metal-to-ligand charge transfer (MLCT) absorption and emission properties of several ruthenium(II)-bipyridine am(m)ine complexes are compared. The Gaussian deconvolution of the spectra indicates that: (a) the emission MLCT bandwidths are smaller than the absorption bandwidths for the first components of the apparent vibronic progressions; (b) the emission bands decrease in energy and width when a polypyridyl is replaced by an am(m)ine. The observations can be interpreted in terms of a two state model and the perturbation theory-based treatment of the attenuation of the effective reorganizational energy, λr =~ λr o(1- 4α2 DA), where λr o is the reorganizational energy corresponding to no mixing between the two electron transfer states and αDA = (HDA/EDA) is the mixing coefficient. Both the solvent and molecular contributions to λr are attenuated. The MLCT excited state lifetimes also decrease with am(m)ine substitution, and the non-radiative decay rate constant at 77 K is roughly proportional to the number of am(m)ine moieties coordinated to the ruthenium center. 相似文献
6.
Isotherms of phenanthrene adsorption on different organoclay complexes were obtained using the HPLC technique to understand the adsorption behavior and to characterize the effect of sodium chloride (NaCl) on the adsorption. The adsorbed amounts of phenanthrene on montmorillonite exchanged by organic cations such as tetraheptylammonium, benzyltrimethylammonium, hexadecyltrimethylammonium, or tetraphenylphosphonium were several times higher than those obtained using montmorillonite clay without surface modification. At the same equilibrium concentration, the adsorbed amount of phenanthrene is higher on clay modified with benzyltrimethylammonium than on clay modified with hexadecyltrimethylammonium or other cations. Adsorption of phenanthrene on clay modified with benzyltrimethylammonium increased dramatically as the concentration of NaCl increased up to 150 g/l in the aqueous solution. The shape of the curves obtained can be classified as S-type. The adsorption data obtained from salinity experiments support a mathematical model that links the Langmuir constant with the salinity constant. This model may be useful to predict the equilibrium concentration of a contaminant in saline solution. FTIR studies showed strong interactions between the aromatic rings of phenanthrene and the preadsorbed benzyltrimethylammonium on clay surfaces. 相似文献
7.
A new method was developed for the analysis of pesticide residues in tobacco. The objective was to significantly increase the number of samples that can be processed by the laboratory and to enable the extension of the current coverage to additional pesticides. A new analytical approach was therefore defined based on two main axes, the automation of the sample preparation and the selectivity of the analyte detection using tandem mass spectrometry. This latter aspect reduces the stringency of the requirements placed on the clean-up of the extracts and on the chromatographic resolution when less selective detectors are used. The extraction of the analytes from the matrix is performed using the pressurized liquid extraction technique. Tobacco samples are extracted at elevated temperature and pressure (100 C and 100 atm; 1 atm = 101,325 Pa) using acetone as an extraction solvent. The resulting extract is then concentrated using a Vortex evaporator. Three different solid-phase extraction (SPE) procedures, adjusted to the chemical properties of the different active ingredients to be measured, are applied to the concentrated extract, thus leading to three extract fractions. The first fraction contains such main classes of active ingredients as organohalogenated and 2,6-dinitroaniline compounds while the second one collects the organophosphorus and acylalanines residues; these two fractions are analyzed by capillary gas chromatography coupled to tandem mass spectrometry using negative chemical ionization and electron impact ionization in the positive mode, respectively. The third extract fraction gathers the N-methylcarbamates residues which are analyzed by HPLC with post-column derivatization and fluorescence detection. The different sample preparation stages from extraction to SPE clean-up have been automated through the use of recent analytical technologies. In combination with the analysis by tandem mass spectrometry, this provided a potential for a high sample throughput. 相似文献
8.
Saeh JC Lyne PD Takasaki BK Cosgrove DA 《Journal of chemical information and modeling》2005,45(4):1122-1133
The combination of 3D pharmacophore fingerprints and the support vector machine classification algorithm has been used to generate robust models that are able to classify compounds as active or inactive in a number of G-protein-coupled receptor assays. The models have been tested against progressively more challenging validation sets where steps are taken to ensure that compounds in the validation set are chemically and structurally distinct from the training set. In the most challenging example, we simulate a lead-hopping experiment by excluding an entire class of compounds (defined by a core substructure) from the training set. The left-out active compounds comprised approximately 40% of the actives. The model trained on the remaining compounds is able to recall 75% of the actives from the "new" lead series while correctly classifying >99% of the 5000 inactives included in the validation set. 相似文献
9.
Jamal Afzal Yaomei Fu Tian-Xiang Luan Zhongmin Su Pei-Zhou Li 《Molecules (Basel, Switzerland)》2022,27(13)
Developing a low-cost and effective proton-conductive electrolyte to meet the requirements of the large-scale manufacturing of proton exchange membrane (PEM) fuel cells is of great significance in progressing towards the upcoming “hydrogen economy” society. Herein, utilizing the one-pot acylation polymeric combination of acyl chloride and amine precursors, a polyamide with in-built -SO3H moieties (PA-PhSO3H) was facilely synthesized. Characterization shows that it possesses a porous feature and a high stability at the practical operating conditions of PEM fuel cells. Investigations of electrochemical impedance spectroscopy (EIS) measurements revealed that the fabricated PA-PhSO3H displays a proton conductivity of up to 8.85 × 10−2 S·cm−1 at 353 K under 98% relative humidity (RH), which is more than two orders of magnitude higher than that of its -SO3H-free analogue, PA-Ph (6.30 × 10−4 S·cm−1), under the same conditions. Therefore, matrix-mixed membranes were fabricated by mixing with polyacrylonitrile (PAN) in different ratios, and the EIS analyses revealed that its proton conductivity can reach up to 4.90 × 10−2 S·cm−1 at 353 K and a 98% relative humidity (RH) when the weight ratio of PA-PhSO3H:PAN is 3:1 (labeled as PA-PhSO3H-PAN (3:1)), the value of which is even comparable with those of commercial-available electrolytes being used in PEM fuel cells. Additionally, continuous tests showed that PA-PhSO3H-PAN (3:1) possesses a long-life reusability. This work demonstrates, using the simple acylation reaction with the sulfonated module as precursor, that low-cost and highly effective proton-conductive electrolytes for PEM fuel cells can be facilely achieved. 相似文献
10.
Tabassum Jannat Md. Jamal Hossain Ahmed M. El-Shehawi Md. Ruhul Kuddus Mohammad A. Rashid Sarah Albogami Ibrahim Jafri Mohamed El-Shazly Mohammad Rashedul Haque 《Molecules (Basel, Switzerland)》2022,27(13)
The aim of the study was to conduct phytochemical and pharmacological investigations of Wrightia coccinea (Roxb. ex Hornem.) Sims via several in vitro, in vivo, and in silico models. A total of four compounds were identified and isolated from the methanol extract of the bark and the methanol extract of the seed pulp of W. coccinea through successive chromatographic techniques and were characterized as 3β-acetyloxy-olean-12-en-28-ol (1), wrightiadione (2), 22β-hydroxylupeol (3), and β-sitosterol (4) by spectroscopic analysis. The aqueous fraction of the bark and chloroform fraction of the fruits provided the most potent antioxidant capacity (IC50 = 7.22 and 4.5 µg/mL, respectively) in DPPH free radical scavenging assay compared with the standard ascorbic acid (IC50 = 17.45 µg/mL). The methanol bark extract and the methanol fruit coat extract exerted anti-diarrheal activity by inhibiting 74.55 ± 0.67% and 77.78 ± 1.5% (mean ± SEM) of the diarrheal episode in mice, respectively, after four hours of loading the samples. In the hypoglycemic test, the methanol bark extract and the methanol fruit coat extract (400 mg/kg) produced a significant (p < 0.05) reduction in the blood glucose level in mice. Both doses of the plant extracts (200 mg/kg and 400 mg/kg) used in the study induced a significant (p < 0.05) increase in pain reaction time. The in vitro and in vivo findings were supported by the computational studies. The isolated compounds exhibited higher binding affinity compared with the standard drugs towards the active binding sites of glutathione reductase, epidermal growth factor receptor (EGFR), kappa opioid receptor, glucose transporter 3 (GLUT 3), Mu opioid receptor, and cyclooxygenase 2 (COX-2) proteins due to their potent antioxidant, cytotoxic, anti-diarrheal, hypoglycemic, and central and peripheral analgesic properties, respectively. The current findings concluded that W. coccinea might be a potential natural source for managing oxidative stress, diarrhea, hyperglycemia, and pain. Further studies are warranted for extensively phytochemical screening and establishing exact mechanisms of action. 相似文献