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排序方式: 共有195条查询结果,搜索用时 10 毫秒
11.
Dmitrenok A. S. Radhika P. Anjaneyulu V. Subrahmanyam C. Subba Rao P. V. Dmitrenok P. S. Boguslavsky V. M. 《Russian Chemical Bulletin》2003,52(8):1868-1872
Sphingolipids and glycolipids including previously unknown (2S,3S,4R)-1,3,4-trihydroxy-2-(2-(R)-hydroxyoctadecanoylamino)octadec-8E-ene, (2S,3R)-1,3-dihydroxy-2-octadecanoylamino-4E,8E-hexadecadiene, and (2-hydroxy-3-hexadecyloxypropyl)--L-fucopyranoside were isolated from soft corals collected on the shelf near the Andaman Islands (Indian Ocean). The structures of all compounds were established by spectroscopic methods and chemical analyses. The lipids possessed antibacterial activity against Bacillus subtilis, Bacillus pumilus, Escherichia coli, and Pseudomonas aeruginosa and antifungal activity against Aspergillus niger, Rhizopus oryzae, and Candida albicans. 相似文献
12.
On the basis of fixed point theorems for linear topological spaces the authors prove existence theorems for the solutions of functional equations that arise in Dynamic Programming. 相似文献
13.
This paper presents the mathematical development of, and a simple solution technique for, an optimal sequential maintenance scheduling problem. The model is shown to satisfy the Kuhn-Tucker conditions, the necessary and sufficient conditions for the existence of an optimal solution. Real-world systems consisting of mixtures of constant and increasing failure rate devices are considered in the model. Sequential preventive maintenance schedules are developed for groups of identical items with increasing failure rates. Provision is made for the corrective maintenance of these groups if failures occur in between the preventive maintenance schedules. Also, constant failure rate devices are accorded corrective maintenance when failures occur. Optimality is achieved by minimizing the total annual maintenance cost, subject to constraints on the system availability, number of maintenance personnel and intervals of preventive maintenance. The model is applied to a coal mine power system example. 相似文献
14.
Mannepalli Lakshmi Kantam Gopaladasu Tirupati Venkanna Kota Balaji Shiva Kumar Vura Bala Subrahmanyam 《Helvetica chimica acta》2010,93(5):974-979
N‐Arylation of N‐containing heterocycles, such as pyrazoles, imidazoles, and benzimidazoles with aryl‐, heteroaryl‐, and vinylboronic acids was efficiently carried out by copper fluorapatite (CuFAP) catalyst in MeOH at room temperature under base‐free conditions. The N‐arylated heterocycles were isolated in good‐to‐excellent yields. 相似文献
15.
The effect of molecular weight on the separation of semiconducting single‐walled carbon nanotubes using poly(2,7‐carbazole)s 下载免费PDF全文
Nicole A. Rice Ayyagari V. Subrahmanyam Scott E. Laengert Alex Adronov 《Journal of polymer science. Part A, Polymer chemistry》2015,53(21):2510-2516
The use of selective interactions between conjugated polymers and single‐walled carbon nanotubes has emerged as a promising method for the separation of nanotubes by electronic type. Although much attention has been devoted to investigating polyfluorenes and their ability to disperse semiconducting carbon nanotubes under specific conditions, other polymer families, such as poly(2,7‐carbazole)s, have been relatively overlooked. Poly(2,7‐carbazole)s have been shown to also preferentially interact with semiconducting carbon nanotubes, however a detailed investigation of polymer parameters, such as molecular weight, has not been performed. We have prepared seven different molecular weights of a poly(2,7‐carbazole), from short chain oligomers to high molecular weight polymers, and have investigated their effectiveness at dispersing semiconducting single‐walled carbon nanotubes. Although all polymer chain lengths were able to efficiently exfoliate carbon nanotube bundles using a mild dispersion protocol, only polymers above a certain threshold molecular weight (Mn ~ 27 kDa) were found to exhibit complete selectivity for semiconducting nanotubes, with no observable signals from metallic species. Additionally, we found the quality of separation to be strongly dependent on the ratio of polymer to carbon nanotube. Contrary to previous reports, we have found that an excess of poly(2,7‐carbazole) leads to incomplete removal of metallic carbon nanotubes. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2015 , 53, 2510–2516 相似文献
16.
P. Radhakrishnanand D. V. Subba Rao K. V. Surendranath D. Subrahmanyam V. Himabindu 《Chromatographia》2008,68(7-8):669-673
A new and accurate chiral liquid chromatographic method has been developed for the separation and quantification of (S,R,S)-enantiomer (unwanted enantiomer) and (R,R,R)-isomer (key intermediate) of aprepitant in bulk drug and formulation samples of apprepitant. The elution time was approximately 20 min using an immobilized amylose-based chiral stationary phase (Chiralpak-IA). The mobile phase was n-hexane and ethanol (90:10, v/v) and was delivered at a flow rate of 1.0 mL min?1. Detection was carried out with a wavelength set to 220 nm. The resolution factor between enantiomers was found to be greater than five. Limit of detection for both (S,R,S) enantiomer and (R,R,R) isomer of aprepitant was 0.035 µg, and limit of quantification for both (S,R,S) enantiomer and (R,R,R) isomers of aprepitant was 0.1 µg, for a 10 µL injection. The developed method showed excellent linearity (r > 0.999) for both isomers. When the method was applied to bulk drug samples and in pharmaceutical formulations recoveries were obtained ranging from 97.2 to 103.1%. Aprepitant sample solutions were found to be stable when characterized over a period of 48 h. 相似文献
17.
Dr. Ashok Yadav Meghamala Sarkar Dr. Sappati Subrahmanyam Atul Chaudhary Prof. Dr. Evamarie Hey-Hawkins Prof. Dr. Ramamoorthy Boomishankar 《Chemistry (Weinheim an der Bergstrasse, Germany)》2020,26(19):4209-4213
The design of porous materials for the recognition of multiple hydrocarbons is highly desirable for the energy-efficient separation and recognition of chemical feedstock. Herein, three new iso-structural porous discrete metal–organic cages of formula {[Pd3(NiPr)3PO]4(R-AN)6} (R-AN=anilate linkers) for the selective recognition of substituted aromatic hydrocarbons are reported. The tetrahedral cages 1 , 2 , and 3 containing anilate, chloranilate, and bromanilate linkers exhibited selective encapsulation of mesitylene, o-xylene, and p-xylene, respectively, over other analogous aromatic hydrocarbons. These selective encapsulations were driven by the variations in the portal diameters present at each of these cages and their interactions with the hydrocarbon guests. These observations are supported by mass spectrometry, NMR studies, and theoretical binding-energy calculations. 相似文献
18.
M. Subrahmanyam S. J. Kulkarni B. Srinivas 《Reaction Kinetics and Catalysis Letters》1993,49(2):455-459
N-(2-hydroxyethyl) ethylenediamine reaction was observed over zeolite catalysts giving rise to only dehydrocyclization and over chromite catalysts showing dehydrocyclization together with dehydrogenation. The major product changes from the cyclized compound piperazine to pyrazine when the reactant is switched from zeolite to chromite catalyst. This process stands as a model reaction for characterizing lone acid sites and adjacent acid-base sites over zeolite and chromite catalysts, respectively.IICT Communication No. 3175 相似文献
19.
Some procedures for the gravimetric determination of silica in lead-bearing samples involve the extraction of lead sulphate with ammonium acetate. Results for silica are then low because some silica is dissolved in ammonium acetate solution. Correct results can be obtained only by avoiding fuming with sulphuric acid. If samples contain a large proportion of insoluble silica, preliminary fusion with sodium hydroxide is recommended. 相似文献
20.
Kanchi Suvardhan Kailasa Suresh Kumar Dasari Rekha Pantrangam Subrahmanyam Kapuvedi Kiran Bellum Jayaraj Surasura Ramanaiah Kandhukuri Janardhanam Pattium Chiranjeevi 《Mikrochimica acta》2007,157(3-4):237-244
Cloud point extraction was applied as a method for preconcentration of rhodium after formation of a complex with 2-propylpiperidine-1-carbodithioate
(2-PPC), and later determined by flame atomic absorption spectrometry using TritonX-114 as surfactant. Rhodium was complexed
with 2-PPC in an aqueous phase and kept for 15 min in a thermostatted bath at 40 °C. Separation of the two phases was accomplished
by centrifugation for 15 min at 4000 rpm. The chemical variables affecting the cloud point extraction were optimized and successfully
applied to rhodium determination in various water samples. Under optimized conditions, the preconcentration system (100 mL
sample) permitted an enhancement factor of 50. The detection limits obtained under optimal conditions was 0.052 ng mL−1. The extraction efficiency was investigated at different rhodium concentrations (7.0–42.0 μg mL−1), and good recoveries (96.42–99.14%) were obtained using this method. It has been applied to the determination of rhodium
in water and was compared with reported methods in terms of Student’s ‘t’-test and variance ratio ‘f’-test. 相似文献