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71.
An application in magnetic resonance spectroscopy quantification models a signal as a linear combination of nonlinear functions. It leads to a separable nonlinear least squares fitting problem, with linear bound constraints on some variables. The variable projection (VARPRO) technique can be applied to this problem, but needs to be adapted in several respects. If only the nonlinear variables are subject to constraints, then the Levenberg–Marquardt minimization algorithm that is classically used by the VARPRO method should be replaced with a version that can incorporate those constraints. If some of the linear variables are also constrained, then they cannot be projected out via a closed-form expression as is the case for the classical VARPRO technique. We show how quadratic programming problems can be solved instead, and we provide details on efficient function and approximate Jacobian evaluations for the inequality constrained VARPRO method. 相似文献
72.
O. Sima 《Journal of Radioanalytical and Nuclear Chemistry》1991,155(2):75-78
An analytical expression for the equivalent thickness of a sample measured in a Marinelli geometry is reported. Using it as input in the formula proposed by Dryak et al.1, self-absorption corrections for Marinelli beakers with arbitrary dimensions can be computed. 相似文献
73.
Belman N Israelachvili JN Li Y Safinya CR Ezersky V Rabkin A Sima O Golan Y 《Physical chemistry chemical physics : PCCP》2011,13(11):4974-4979
We describe methodology for producing highly uniform, ordered and reproducible superstructures of surfactant-coated ZnS nanorod and nanowire assemblies, and propose a predictive multiscale "packing model" for superstructure formation based on electron microscopy and powder X-ray diffraction data on the superstructure, as well as on individual components of the nanostructured system. The studied nanoparticles showed a hierarchical structure starting from the individual faceted ZnS inorganic cores, onto which the crystalline surfactant molecules are adsorbed, to the superstructure of the nanoparticle arrays. Our results point out the critical role of the surfactant headgroup and polarity in nanoparticle assembly, and demonstrate the relationship between the molecular structure of the surfactant and the resulting superstructure of the nanoparticle assemblies. 相似文献
74.
Tyrosinase immobilized magnetic nanobeads for the amperometric assay of enzyme inhibitors: application to the skin whitening agents 总被引:1,自引:0,他引:1
The immobilization of tyrosinase onto glutaraldehyde activated streptavidine magnetic particles and subsequent retention onto a magnetized carbon paste electrode for the amperometric assay of tyrosinase inhibitors is described. Tyrosine was used as substrate as it is the first substrate in the melanogenesis process. The sensing mode is based on monitoring the decrease of the amperometric signal corresponding to the electrochemical reduction of dopaquinone enzymatically generated. This current decrease is due to the presence of inhibitors acting directly on the enzyme or inhibitors acting on the product of the enzymatic reaction, i.e. dopaquinone. The methodology is designed for the evaluation of the inhibitory potency of the most frequently used active substances in cosmetic marketed products against hyperpigmentation such as kojic acid, azelaic acid and benzoic acid. These compounds bind to the tyrosinase active center. Ascorbic acid is also investigated as it interrupts the synthesis pathway of melanin by reducing the melanin intermediate dopaquinone back to l-dopa. By comparing the obtained IC50, under the same experimental conditions, the order of their inhibitory potency was: kojic acid (IC50 = 3.7 × 10−6 M, Ki = 8.6 × 10−7 M), ascorbic acid (IC50 = 1.2 × 10−5 M), benzoic acid (IC50 = 7.2 × 10−5 M, Ki = 2.0 × 10−5 M) and azelaic acid (IC50 = 1.3 × 10−4 M, Ki = 4.2 × 10−5 M) in close agreement with literature spectrophotometric inhibition data using the soluble tyrosinase. 相似文献
75.
Sima Ahmadi-Shooli 《Journal of Macromolecular Science: Physics》2013,52(7):619-633
The properties of (50/50?wt%) styrene butadiene rubber/epoxidized (50%) natural rubber (SBR/ENR50) blends containing nanoclay (NC, 5 or 10phr) without and with carbon black (CB 20phr) cured by sulfur or by electron beam (EB) irradiation (50 and 100kGy), were compared. A sulfur cured compound containing 35phr CB was prepared as a reference sample. Dynamic mechanical thermal analysis (DMTA) indicated that the sulfur cured sample containing 10phr NC and 20phr CB and the 100kGy irradiated sample with 5phr NC and 20phr CB had higher crosslink density, storage modulus, and tensile strength, and less loss factor and loss modulus, compared to the reference sample. Scanning electron microscopy (SEM) images of cryo- fractured surfaces confirmed the DMA and crosslink density results. We suggest a light weight 100kGy irradiated sample containing the lowest amount of NC and 20phr CB with a uniform distribution of the –C–C– bonds crosslinks, for high thermal stability applications and also for passenger cars tire treads, for its ice grip and wet skid properties especially for icy and wet roads, with improvements of 23% and 20%, respectively as compared to the reference sample. 相似文献
76.
A new method for the efficient synthesis of aldehydes, ketones, and oxophosphonates from various types of amines (primary and secondary) and aminophosphonates via oxidative deamination by nicotinium dichromate (=3‐carboxypyridinium dichromate; NDC) is described. 相似文献
77.
Hosseinzadeh Maral Nikjoo Shadi Zare Najme Delavar Delaram Beigoli Sima Chamani Jamshidkhan 《Research on Chemical Intermediates》2019,45(2):401-423
Research on Chemical Intermediates - Through the incorporation of spectorescopic and molecular methods of modeling, the researchers investigated the interaction between Carbon Nanotubes (CNTs) and... 相似文献
78.
The Girard's reagent P derivative of canthaxanthin ((GRP)2 -canthaxanthin), a dicationic carotenoid, forms a highly water-dispersible complex with (2-hydroxypropyl)-γ-cyclodextrin. The UV–visible light spectrum of the complex is consistent with some degree of aggregation, but the spectrum is independent of concentration from 7.5 to 750 μ m . Stern-Vomer plots for singlet-oxygen quenching by the complex are linear over a concentration range of 0–20 μ m . In the presence of 1 m m (2-hydroxypropyl)-γ-cyclodextrin, the singlet-oxygen quenching constant for the complex is 7.9 ± 0.9 × 108 m −1 s−1 . This is about an order of magnitude lower than the singlet-oxygen quenching constants for (GRP)2 -canthaxanthin in various organic solvents. The properties of the complex are also compared with the properties of (GRP)2 -canthaxanthin solubilized in neat water and in water containing various detergents. The singlet-oxygen quenching constant for (GRP)2 -canthaxanthin in micelles depends strongly on the specific detergent used, varying from 9.4 × 108 m −1 s−1 for hexadecyltrimethylammonium bromide (CTAB) to 1.24 ± 0.4 × 1010 m −1 s−1 for sodium dodecyl sulfate. The small quenching constant in CTAB micelles correlates with spectroscopic evidence for aggregation of the (GRP)2 -canthaxanthin in this detergent. 相似文献
79.
F. Sima N. Stefan I.N. Mihailescu L.E. Sima E. Palcevskis I. Zalite 《Applied Surface Science》2009,255(10):5312-5317
We studied the influence of porous Al2O3 substrates on Ce-stabilized ZrO2-doped hydroxyapatite thin films morphology pulsed laser deposited on their top. The porosities of substrates were monitored by changing sintering temperatures and measured with a high pressure Hg porosimeter.The depositions were conducted in 50 Pa water vapors by multipulse ablation of the targets with an UV KrF* (λ = 248 nm, τ ∼ 25 ns) excimer laser. The surface morphology of synthesized nanostructures was investigated by scanning electron microscopy and atomic force microcopy. Ca/P ratio within the range 1.67-1.70 was found for hydroxyapatite coatings by energy dispersive spectroscopy.The films were further seeded with mesenchymal stem cells for in vitro tests. The cells showed good attachment and spreading uniformly covering the entire surface of samples. The complexity of film morphology which is increasing with substrate porosity was shown to have a positive influence on cultivated cells density. 相似文献
80.
Frank J.Filippelli S. E. Reeg F.Sima Sariaslani M. W. Duffel J. P. N. Rosazza 《Photochemistry and photobiology》1988,48(3):265-269
Abstract— Photooxidation of 16-O-acetylvindoline in methanol using chlorpromazine-HCl as a photosensitizing agent produces nearly quantitative yields of an iminium derivative. The 16-O-acetylvindol-ine-iminium product was characterized spectrally by proton NMR and mass spectrometry; and by chemical reduction with sodium borodeuteride. Proton NMR and mass spectral analyses of the reduced product revealed that deuterium was stereospecifically incorporated into the 3-a-position. The iminium product formed by photochemical oxidation is identical to that produced by copper oxidases and peroxidase. Photochemical oxidation provides direct evidence for the involvement of free radicals in Aspidosperma alkaloid transformations. 相似文献