排序方式: 共有189条查询结果,搜索用时 15 毫秒
91.
Azadeh Nakhai 《Tetrahedron》2009,65(11):2298-9445
The reaction of hydrazine derivatives with α,β-unsaturated ketones, such as cyclohexenyl(phenyl)methanone and (E)-2-benzylidenecyclohexanone, were investigated.The reaction between methylhydrazine and e.g., cyclohexenyl(phenyl)methanone was particularly interesting as 3a,4,5,6,7,7a-hexahydro-1-methyl-3-phenyl-1H-indazole was obtained as the major product together with 4,5,6,7-tetrahydro-2-methyl-3-phenyl-2H-indazole as a minor product. 相似文献
92.
93.
A sensitive and simple solid‐phase preconcentration procedure for the determination of trace amount of lead by flame atomic absorption spectrometry (FAAS) is developed. The method is based on the adsorption of Pb2+ on the column of fine grinded eucalyptus stem adsorbent, elution of the column by nitric acid and subsequent determination by FAAS. The effect of different variables such as pH, eluent type, flow rate and interfering ions on the recovery of the analyte was investigated and optimum conditions were established. The adsorption of lead onto fine grinded eucalyptus stem can formally be described by a Langmuir equation with a maximum adsorption capacity of 4.49 mg g?1. A preconcentration factor of 50 was achieved using the optimum conditions. The calibration graph was linear in the range 10–125 ng mL?1 of lead in the initial solution with r = 0.9982. The limit of detection based on 3Sb criterion was 4.5 ng mL?1 and the relative standard deviation for eight replicate measurements of 30 and 80 ng mL?1 of iron was 3.6 and 2.8%, respectively. The method was successfully applied to the determination of lead added to well, tap and wastewater samples. 相似文献
94.
Many biosensors have been developed to detect Hg(2+) using thymine-rich DNA. While sensor response to various cations is often studied to demonstrate selectivity, the effect of anions has been largely overlooked. Anions may compete with DNA for metal binding and thus produce a false negative result. Anions cannot be added alone; the cation part of a salt may cause DNA compaction and other effects, obscuring the role of anions. We find that the sensitivity of a FRET-based Hg(2+) probe is independent of Na(+) concentration. Therefore, by using various sodium salts, any change in sensitivity can be attributed solely to the effect of anions. Halide salts, sulfides, and amines are strong inhibitors; anions containing oxo or hydroxyl groups (e.g. nitrate, sulfate, phosphate, carbonate, acetate, and citrate) do not interfere with Hg(2+) detection even at 100 mM concentration. Mercury hydrolysis and its diffusion into polypropylene containers can also strongly affect the detection results. We conclude that thymine-rich DNA should be useful for Hg(2+) detection in many environmental water samples. 相似文献
95.
Microfluidic system for measuring neutrophil migratory responses to fast switches of chemical gradients 总被引:4,自引:0,他引:4
Experimental systems that provide temporal and spatial control of chemical gradients are required for probing into the complex mechanisms of eukaryotic cell chemotaxis. However, no current technique can simultaneously generate stable chemical gradients and allow fast gradient changes. We developed a microfluidic system with microstructured membranes for exposing neutrophils to fast and precise changes between stable, linear gradients of the known chemoattractant Interleukin-8 (IL-8). We observed that rapidly lowering the average concentration of IL-8 within a gradient, while preserving the direction of the gradient, resulted in temporary neutrophil depolarization. Fast reversal of the gradient direction while increasing or decreasing the average concentration also resulted in temporary depolarization. Neutrophils adapted and maintained their directional motility, only when the average gradient concentration was increased and the direction of the gradient preserved. Based on these observations we propose a two-component temporal sensing mechanism that uses variations of chemokine concentration averaged over the entire cell surface and localized at the leading edge, respectively, and directs neutrophil responses to changes in their chemical microenvironment. 相似文献
96.
Analysis of the magnetic losses in iron-based soft magnetic composites with MgO insulation produced by sol-gel method 总被引:3,自引:0,他引:3
Amir Hossein Taghvaei Azadeh Ebrahimi Kamal Janghorban 《Journal of magnetism and magnetic materials》2010,322(23):3748-3754
This work investigated the magnetic losses of heat treated iron-based soft magnetic composites with a thin MgO insulating layer produced by sol-gel method. The samples were characterized by energy dispersive X-ray spectroscopy, X-ray analysis and Fourier transform infrared spectroscopy. The results show that the surface of the powders contains a thin layer of MgO insulation. The loss results indicate that the hysteresis part for both the core loss and total loss factor was approximately the same for the MgO-insulated compacts and conventional SOMALOYTM samples with phosphate insulation after annealing at 600 °C. But the MgO-insulated compacts exhibited significantly lower eddy current contribution of both core loss and total loss factor with respect to SOMALOYTM samples after annealing. Also the contribution of eddy current in the iron particles for MgO insulated compacts (kp=0.91) was noticeably higher than this contribution for SOMALOYTM samples (kp=0.18) after annealing due to the higher electrical resistivity of the MgO-insulated compacts. 相似文献
97.
Amir Sabet Sarvestani Parviz Abdolmaleki Seyed Javad Mowla Faezeh Ghanati Emran Heshmati Zeinab Tavasoli Azadeh Manoochehri Jahromi 《Micron (Oxford, England : 1993)》2010,41(2):101-104
In order to evaluate the influence of static magnetic fields (SMF) on the progression of cell cycle as a monitor of presumptive genotoxicity of these fields, the effects of a 15 mT SMF on cell cycle progression in rat bone marrow stem cells (BMSC) were examined. The cells were divided into two groups. One group encountered SMF alone for 5 h continuously but the other group exposed with X ray before treatment with SMF. The population of cells did not show any significant difference in the first group but the second group that was exposed with acute radiation before encountering SMF showed a significant increase in the number of cells in G2/M phase. So SMF has intensified the effects of X ray, where SMF alone, did not had any detectable influence on cell cycle.These findings suggest that magnetic fields (MF) play their role by increasing the effects of genotoxic agents and because of the greater concentration of free radicals in the presence of radical pair producers, this effect is better detectable. 相似文献
98.
One‐Pot Synthesis of Cu2O/ZnO Nanoparticles at Present of Folic Acid to Improve UV‐Protective Effect of Cotton Fabrics 下载免费PDF全文
Seyyed Abbas Noorian Nahid Hemmatinejad Azadeh Bashari 《Photochemistry and photobiology》2015,91(3):510-517
In this study, the effect of using folic acid on the in situ synthesis process of nanostructures has been investigated. Folic acid, as a biotemplate for synthesis of Cu2O/ZnO, was used to improve the reducing and stabilizing the ability of cotton fabric and avoid agglomeration of the particles. Scanning electron microscopy images revealed that using folic acid caused the formation of particles with smaller sizes on the cotton fabric and X‐ray diffraction confirmed the same crystalline pattern of nanoparticles in comparison with the previous synthesis process. The effect of using this biotemplate on different properties of treated fabrics including UV‐protection effect, hydrophilicity, crease recovery angle, softness, thickness and mechanical properties has been evaluated. The folic acid had a great influence on UV‐protection effect, in synthesis procedure, decreasing the droplet absorption time, bending length and improving the wrinkle resistance and mechanical properties. Interestingly, the higher tensile strength of the treated cotton fabrics proved the incorporation of nanoparticles into the cotton fibers. An in situ, green and rapid method can be provided by using folic acid for the synthesis of the nanostructures with controlled size. 相似文献
99.
A PVC-based sensor for La3+ ions based on N-[hexahydrocyclopentapyrol-2((1H)yl)amino]carbonyl]-4-methyl benzene sulfonamide (gliclazide) as a novel carrier was prepared. The electrode exhibits a Nernstian response for La3+ over a wide concentration range (1.0×10−1-1.0×10−6 M) with a slope of 20.1 mV per decade. The limit of detection is 8.0×10−7 M. The sensor has a very short response time (<15 s) and a useful working pH range of 4.0-8.0. The proposed membrane sensor shows excellent discriminating ability towards La3+ ions with regard to several alkali, alkaline earth, transition and heavy metal ions. The electrode was successfully applied for determination of La3+ in binary mixtures. 相似文献
100.
Reza Maddahian Azadeh Kebriaee Bijan Farhanieh Bahar Firoozabadi 《Archive of Applied Mechanics (Ingenieur Archiv)》2011,81(4):489-501
In this research, the developing turbulent swirling flow in the entrance region of a pipe is investigated analytically by
using the boundary layer integral method. The governing equations are integrated through the boundary layer and obtained differential
equations are solved with forth-order Adams predictor-corrector method. The general tangential velocity is applied at the
inlet region to consider both free and forced vortex velocity profiles. The comparison between present model and available
experimental data demonstrates the capability of the model in predicting boundary layer parameters (e.g. boundary layer growth,
shear rate and swirl intensity decay rate). Analytical results showed that the free vortex velocity profile can better predict
the boundary layer parameters in the entrance region than in the forced one. Also, effects of pressure gradient inside the
boundary layer is investigated and showed that if pressure gradient is ignored inside the boundary layer, results deviate
greatly from the experimental data. 相似文献