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91.
92.
Environmentally friendly three‐component condensation reactions of an activated C‐H acid, an aldehyde, and alkyl nitriles to afford the corresponding pyran annulated heterocyclic systems in water in good yields, avoiding the addition of any catalyst, are reported. 相似文献
93.
Hamed Najafi Farhood Najafi Sima Shahabi Amirbabak Abrishamkar Fathollah Moztarzadeh 《高分子科学杂志,A辑:纯化学与应用化学》2013,50(11-12):736-746
AbstractIn the study, dental composites of color A2 using Bis-GMA/UDMA/TEGDMA resins (ratios 70/10/20), and silica filler (70%wt, 75%wt, and 80%wt) which is a hybrid of two silica types in nano and micro dimensions were made using two different photoinitiators namely BAPO and camphorquinone. The optimum photoinitiator was selected based on the mechanical tests results after which the composites were subjected to the following tests: FTIR to evaluate polymerization degree, microhardness test, UTM, and SEM micrographs were taken to analyze the surface fracture of samples. The results of photoinitiator selection (flexural strength test) is 36.54?MPa, 37.62?MPa, and 75.08?MPa for BAPO?+?camphorquinone, camphorquinone, and BAPO respectively. The results show that the BAPO photoinitiator exhibits better results over camphorquinone and also BAPO/camphorquinone initiator systems. Then after choosing the photoinitiator system composites with different filler contents show higher mechanical strength than existing dental composites. The results of the mechanical tests for the composites with different filler contents synthesized after initiator system selection were significantly higher than the values specified in ISO 4049:2009 (102?MPa over 80?MPa). FTIR results indicate that the degree of conversion in these composite is 25.41%, 37.68, and 40.94% for composites with different filler amounts. 相似文献
94.
Khosravian Pouya Emadi Sima Mirjalily Ghasem Zamani Behzad 《Wireless Personal Communications》2020,111(2):1235-1254
Wireless Personal Communications - Non-orthogonal multiple access (NOMA) acts as one of the promising multiple access technology for fifth generation communication systems, and has the capability... 相似文献
95.
M. I. Osorio‐Garcia D. M. Sima F. U. Nielsen U. Himmelreich S. Van Huffel 《Journal of Chemometrics》2011,25(4):183-192
Quantification of magnetic resonance spectroscopy (MRS) signals is required for providing metabolite concentrations of the tissue under investigation. For estimating these concentrations several biochemical and acquisition conditions need to be taken into account. It is still a challenge to obtain reliable concentrations, as experimental conditions may have a detrimental effect on the spectral quality. The lineshape of MRS signals is affected, for instance, by inhomogeneities of the static magnetic field arising from imperfect shimming and tissue heterogeneities. To handle this type of distortions, we propose an extension of the self‐deconvolution method, where a common lineshape is estimated and a robust method with local regression is included to improve the smoothing of the estimated damping (or lineshape) function. This common lineshape is imposed in the metabolite quantification method and the spectral parameters (amplitude, frequency, damping and phase corrections) are obtained via nonlinear least squares. In this study, we considered distorted simulated, in vitro and in vivo rat brain signals which were lineshape corrected and quantitative results were compared in all three cases. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
96.
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
97.
Sima M. Cotofana S.D. Vassiliadis S. van Eijndhoven J.T.J. Vissers K.A. 《Very Large Scale Integration (VLSI) Systems, IEEE Transactions on》2004,12(6):622-635
This paper presents a TriMedia processor extended with three reconfigurable designs for entropy decoding (ED), inverse quantization (IQ), and two-dimensional (2-D) inverse discrete cosine transform (IDCT), and assesses the performance gain that is provided by such extensions when performing MPEG2-compliant pel reconstruction. We first describe an extension of the TriMedia architecture, which consists of a multiple-context field programmable gate array (FPGA)-based reconfigurable functional unit (RFU), a configuration unit managing the reconfiguration of the RFU, and their associated instructions. Then, we address the computation of the ED, IQ, and 2-D IDCT tasks, and propose to provide reconfigurable hardware support for a variable-length decoder that can decode two symbols per call (VLD-2), an inverse quantizer that can dequantize four coefficients per call (IQ-4), and an 1-D IDCT (1-D IDCT). The most important aspects concerning the implementation of the FPGA-mapped VLD-2, IQ-4, and 1-D IDCT units, as well as the organization of the software routines calling these FPGA-mapped computing units are outlined. Experimental results indicate that by configuring each of the VLD-2, IQ-4, and 1-D IDCT units on a different FPGA context, and by activating the contexts as needed, the FPGA-augmented TriMedia can perform MPEG2-compliant pel reconstruction with an average speed-up of 1.4/spl times/ over the standard TriMedia. 相似文献
98.
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
99.
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
100.
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