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排序方式: 共有187条查询结果,搜索用时 15 毫秒
31.
The most sensitive atomic spectrometric technique has been ETA-AAS for many years. Recently, ICP-MS has emerged as an approach which provides even lower detection limits, but at considerably higher instrument and running costs. Flame AAS, on the other hand, is still being used widely in many laboratories in world. Therefore, alternative approaches for better sensitivity using flame AAS should be relevant and important. 相似文献
32.
33.
In this study, firstly, we give curvature conditions of AW(k)-type (1≤k≤3) curves. Then considering AW(k)-type curves, we investigate Bertrand curves γ:I→L3 with κ1(s)≠0 and κ2(s)≠0. We show that there are Bertrand curves of AW(1)-type and AW(3)-type. Moreover, we study weak AW(2)-type and AW(3)-type conical geodesic curves in L3. 相似文献
34.
In the last years, there has been great interest to the formulation and application of wavelet transformation in variety of fields to investigate the characteristics of dynamical systems. Recently, a method based on the scalogram analysis of the continuous wavelet transform, the scale index has been proposed to measure aperiodicity and determine the transitions from aperiodic behaviour to periodic behaviour in nonlinear dynamical systems. In this work we test the scale index method by performing the analysis of the deterministic behaviour of the fermion-like two-dimensional Akdeniz–Smailagic instanton solution in Thirring Model. We show that the scale index method can also be considered to detect the periodic behaviours of the fermion-like instanton solutions. 相似文献
35.
Söhretoğlu D Sakar MK Sabuncuoğlu SA Ozgüneş H Duman H Sterner O 《Natural product research》2012,26(13):1261-1264
Chromatographic studies on the EtOAc soluble portion of the MeOH extract of Geranium lasiopus led to the isolation of eight flavonoids (kaempferol (1), quercetin (2), quercetin 3-O-β-glucopyranoside (3), quercetin 3-O-β-galactopyranoside (4), kaempferol 3-O-α-rhamnopyranosyl-(1?→?6)-β-glucopyranoside (5), quercetin 3-O-α-rhamnopyranosyl-(1?→?6)-β-glucopyranoside (6), kaempferol 3-O-α-rhamnopyranosyl-(1?→?2)-β-glucopyranoside (7) and quercetin 3-O-α-rhamnopyranosyl-(1?→?2)-β-glucopyranoside (8)), two simple phenolic compounds (gallic acid (9) and its methyl ester (10)) and a hydrolysable tannin (pusilagin (11)). The structures of the compounds were elucidated by 1- and 2-dimensional NMR techniques ((1)H, (13)C, COSY, HMBC, HMQC) and ESI-TOF-MS spectrometry. Inhibitory effects on H(2)O(2)-induced lipid peroxidation in human red blood cells of the different extracts of G. lasiopus, as well as isolated compounds, were investigated. All tested compounds showed comparable or higher activity than that of ascorbic acid and trolox. 相似文献
36.
Mahmut Erzengin Ismet Basaran Umit Cakir Aynur Aybey Selma Sinan 《Applied biochemistry and biotechnology》2012,168(6):1540-1548
Human serum paraoxonase 1 (PON1; EC 3.1.8.1) is a high-density lipoprotein associated, calcium-dependent enzyme that hydrolyses aromatic esters, organophosphates and lactones and can protect the low-density lipoprotein against oxidation. In this study, in vitro inhibition effect of some dihydroxy coumarin compounds namely 6,7-dihydroxy-3-(2-methylphenyl)-2H-chromen-2-one (A), 6,7-dihydroxy-3-(3-methylphenyl)-2H-chromen-2-one (B) and 6,7-dihydroxy-3-(4-methylphenyl)-2H-chromen-2-one (C) on purified PON1 were investigated by using paraoxon as a substrate. PON1 was purified using two-step procedures, namely ammonium sulphate precipitation and Sepharose-4B-l-tyrosine-1-naphthylamine hydrophobic interaction chromatography. The purified enzyme had a specific activity of 11.76?U/mg. The dihydroxy coumarin derivatives of A and B compounds inhibited PON1 enzyme activity in a noncompetitive inhibition manner with K i of 0.0080?±?0.256 and 0.0003?±?0.018?mM values, respectively. C compound exerted an uncompetitive inhibition of PON1 enzyme activity with K i of 0.0010?±?0.173?mM. Moreover, dihydroxy coumarin derivatives of A, B and C compounds were effective inhibitors on purified human serum PON1 activity with IC50 of 0.012, 0.022 and 0.003?mM values, respectively. IC50 value of unsubstituted 6,7 dihydroxy coumarin was found as 0.178?mM. The present study has demonstrated that PON1 activity is very highly sensitive to studied coumarin derivatives. 相似文献
37.
This study presents an easy and quick method for the synthesis of graphene from graphite in a set of solvents, including n-Hexadecane (n-Hexa), dimethylsulfoxide (DMSO), sodium hydroxide (NaOH), 1-octanol (OCTA), perchloric acid (PA), N,N-Dimethylformamide (DMF), ethylene glycol (EG), and ethylene diamine (ED), via microwave (MW) energy. The properties of final products were determined by X-ray diffraction spectroscopy (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet-visible (UV-Vis) spectroscopy, and the four-point probe technique. The XRD spectra of most of the MW-assisted graphene products showed peaks at 2θ = 26.5° and 54°. Layer numbers extend from 2 and 25, and the leading comes about were gotten by having two-layered products, named as graphene synthesized in dimethylsulfoxide (G-DMSO), graphene synthesized in ethylene glycol (G-EG), and graphene synthesized in 1-octanol (G-OCTA). G-DMF has the highest electrical conductivity with 22 S/m. The electrical conductivity is higher when the dipole moment of the used solvent is between 2 and 4 Debye (D). The FTIR spectra of most of the MW-assisted graphene products are in line with commercial graphene (CG). The UV-Vis spectra of all MW-assisted graphene products showed a peak at 223 nm referring to characteristic sp2 C=C bonds and 273 nm relating to the n → π * transition of C-O bonds. 相似文献
38.
A new phthalocyanine-subphthalocyanine heterodyad ( 5 ) was prepared by Pd(0)-catalyzed Sonogashira coupling reaction between an asymmetrical phthalocyanine ( 3 ) bearing monoiodo and multiple triazolide moieties on its backbone and a subphthalocyanine ( 4 ) bearing axially propargyl group. The structure of this heterodyad ( 5 ) was subsequently confirmed by the conventional spectroscopic techniques. The photophysical and photochemical properties including; fluorescence and singlet oxygen generation of ( 5 ) along with its building chromophores ( 3 ) and ( 4 ) were also investigated. Interestingly, a purple colored solution was observed by this novel dyad which was significantly different from those colors (green or blue) obtained by phthalocyanine-subphthalocyanine conjugates. Based on steady state absorption spectroscopic data and transient absorption results, the synthesized dyad 5 was free of aggregation and there is good energy transfer occurs between Pc and subPc moieties. This result was confirmed using density functional theory (DFT) and time-dependent DFT (TDDFT) analyses: B3LYP exchange-correlation functional and the 6–31 + G(d) basis set. 相似文献
39.
Shaul K. Bar-Lev Mahmut Parlar David Perry Wolfgang Stadje Frank A. Van der Duyn Schouten 《European Journal of Operational Research》2007
A population of items is said to be “group-testable”, (i) if the items can be classified as “good” and “bad”, and (ii) if it is possible to carry out a simultaneous test on a batch of items with two possible outcomes: “Success” (indicating that all items in the batch are good) or “failure” (indicating a contaminated batch). In this paper, we assume that the items to be tested arrive at the group-testing centre according to a Poisson process and are served (i.e., group-tested) in batches by one server. The service time distribution is general but it depends on the batch size being tested. These assumptions give rise to the bulk queueing model M/G(m,M)/1, where m and M(>m) are the decision variables where each batch size can be between m and M. We develop the generating function for the steady-state probabilities of the embedded Markov chain. We then consider a more realistic finite state version of the problem where the testing centre has a finite capacity and present an expected profit objective function. We compute the optimal values of the decision variables (m, M) that maximize the expected profit. For a special case of the problem, we determine the optimal decision explicitly in terms of the Lambert function. 相似文献
40.
Nuriye Kocak Mustafa Sahin Ilker Akin Mahmut Kus Mustafa Yilmaz 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(10):776-779
Chitosan nanoparticles (CHN) were prepared based on ionotropic gelation between low moleculer weight chitosan and sodium tripolyphosphate (TPP) under microwave irradiation. Particle size, zeta potential, and FT-IR techniques were used for characterization of CHN. The influence of reaction time on the nanoparticle size distribution was investigated, and the results showed that the microwave irradiation method evidently decreases the reaction times and particle size over the conventional method. It was determined by the results of the zeta potential measurements that synthesized CHN under microwave irradiation clearly exhibits more homogeneous and stable dispersion. 相似文献