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排序方式: 共有143条查询结果,搜索用时 31 毫秒
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22.
Ghanshyam S. Chauhan Surya K. Dhiman Lalit K. Guleria Inderjeet Kaur 《应用聚合物科学杂志》2002,83(7):1490-1500
In an attempt to develop an alternative to petro‐based polymers, we graft‐copolymerized cellulose isolated from the needles of Pinus roxburghii with styrene in a limited aqueous medium in air by simultaneous irradiation using gamma rays as the initiator. The optimum conditions for obtaining maximum grafting were determined as a function of monomer concentration, total dose of irradiation, and amount of water. Maximum percentage of grafting (Pg; 79.9) was obtained at a total dose of 1.152 × 104 Gy with 1.325 × 10?4 mol of styrene. The effect of methanol, LiNO3, Cu(NO3)2, Mohr's salt, H2SO4, HNO3, and AcOH on Pg was studied. All the additives were found to decrease graft yield, contrary to some reported studies. Total percentage conversion and rates of polymerization, grafting, and homopolymerization were evaluated. Evidence of grafting was provided by the characterization of cellulose and its graft copolymers by Fourier transform infrared spectroscopy, thermogravimetry, and observation of the swelling behavior in some solvents. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 83: 1490–1500, 2002 相似文献
23.
Ghanshyam S. Chauhan Baljit Singh Sandeep Chauhan Surya K. Dhiman Dinesh Kumar 《应用聚合物科学杂志》2006,100(2):1522-1530
In continuation to our earlier work to use bioresource for developing alternate materials for use at the interface of biotechnology and polymer science, we have utilized pine needles as a renewable stock of cellulose to synthesize graft copolymers of vinyl imidazole. Kinetics of N‐VIm by simultaneous γ‐irradiation method has been investigated as a function of total dose, monomer concentration, and amount of water. Effect of water–methanol solvent composition on graft yields and polymerization kinetics has also been studied at the optimum grafting conditions of the total dose and monomer concentration. Effect of some additives such as ZnCl2, Mohr salt, tetramethylethylene diamine, potassium persulfate, ammonium persulfate as grafting accelerators and promoters has also been studied. Graft copolymers have been characterized by elemental analysis, FTIR, and swelling studies. The graft copolymers have been used as supports for metal ions sorption, enzyme immobilization, and as potential biomimicking catalysts. Sorption behavior of Fe2+ ions and Cu2+ ions and the immobilization of bovine serum albumin and protease as a function of graft yield has been reported. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1522–1530, 2006 相似文献
24.
The objective of this work was to apply the response surface approach in the development of buccal bioadhesive tablets of 5-fluorouracil (5-FU). Experiments were performed according to a 3(2) factorial design to evaluate the effects of two polymers, Gantrez MS-955 (X(1)) and hydroxypropylmethyl cellulose (HPMC) K15M (X(2)) on the bioadhesive force, percentage drug release in 8 h (Rel(8 h)), time taken for 50% drug release (t(50%)), and diffusion coefficient (n). The effect of the two independent variables on the response variables was studied by response surface plots and contour plots generated by the Design Expert software. The compatibility between 5-FU and the tablet excipients was confirmed by differential scanning calorimetry (DSC) and Fourier transform infrared (FTIR) studies. Both the polymers were found to have synergistic effect on bioadhesion but the effect of Gantrez was more pronounced. A nonlinear twisted relationship was obtained for Rel(8 h) at the intermediate and high levels of the polymers, which indicated an interaction between them at the corresponding factor levels. Kinetic treatment to the dissolution profiles revealed that the drug release ranged from Fickian to anomalous transport, which was mainly dependent on both the independent variables. The desirability function was used to optimize the response variables, and the observed responses were in agreement with the experimental values. 相似文献
25.
Krokhin OV Ying S Cortens JP Ghosh D Spicer V Ens W Standing KG Beavis RC Wilkins JA 《Analytical chemistry》2006,78(17):6265-6269
A new algorithm, sequence-specific retention calculator, was developed to predict retention time of tryptic peptides during RP HPLC fractionation on C18, 300-A pore size columns. Correlations of up to approximately 0.98 R2 value were obtained for a test library of approximately 2000 peptides and approximately 0.95-0.97 for a variety of real samples. The algorithm was applied in conjunction with an exclusion protocol based on mass (15 ppm tolerance) and retention time (2-min tolerance for 0.66% acetonitrile/min gradient), MART criteria to significantly reduce the instrument time required for complete MS/MS analysis of a digest separated by RP HPLC. This was confirmed by reanalyzing the set of HPLC-MALDI MS/MS data with no loss in protein identifications, despite the number of virtually executed MS/MS analyses being decreased by 57%. 相似文献
26.
A design of a parallel flow solar air heater with packed material in its upper channel and capable of providing a higher heat flux compared to the conventional non-porous bed double flow systems is presented. An analytical model describing the various temperatures and heat transfer characteristics of such a parallel flow packed bed solar air heater (PFPBSAH) has been developed and employed to study the effects of the mass flow rate and varying porosities of the packed material on its thermal performance. The model employs an iterative solution procedure to solve the governing energy balance equations describing the complex heat and mass exchanges involved. To validate the proposed analytical model, comparisons between theoretical and experimental results showed that good agreement is achieved with reasonable accuracy. Also, PFPBSAH is found to perform more efficiently than the conventional non-porous double flow solar air heaters with 10–20% increase in its thermal efficiency. Furthermore, the effect of the fraction of mass flow rate in the upper or lower flow channel of PFPBSAH device on its performance, has also investigated theoretically. The fraction of the mass flow rate in the respective channels of the PFPBSAH is shown to be dominant parameter in determining the effective thermal efficiency of the heater. 相似文献
27.
Flow and Heat Transfer Phenomena around an Equilateral Triangular Bluff Body: Effect of Wall Confinement
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Amit Kumar Dhiman 《亚洲传热研究》2016,45(7):608-630
This paper focuses on the effects of wall confinements (or blockage ratios) on the flow and heat transfer characteristics around a long equilateral triangular bluff body placed in a horizontal channel for Reynolds number (Re) range 1 to 80 and blockage ratio range 0.1 to 0.5 for air as the working fluid. The governing continuity, Navier–Stokes and energy equations along with appropriate boundary conditions are solved by using a finite volume method‐based commercial solver Ansys Fluent. The total drag coefficient decreases with an increasing value of Re for a fixed value of the blockage ratio; however, it increases with an increasing value of the blockage ratio for a fixed value of Re due to the fact that the channel walls exert an extra retardation force on the obstacle. The onset of flow separation is delayed as the value of the blockage ratio increases. The critical Re (i.e., the transition to a time‐periodic regime) exists between 45 and 46, 46 and 47, 58 and 59, and 79 and 80 for the blockage ratios of 0.1, 0.125, 0.25, and 0.5, respectively. The simple correlations for wake length, total drag coefficient, and average obstacle Nusselt number are obtained for the range of conditions covered. 相似文献
28.
A numerical investigation is conducted to analyze the steady and unsteady laminar flow and heat transfer in a channel with two square bars (of equal diameters) arranged side-by-side. The analysis is carried out for Reynolds number = 10–100, Prandtl number = 0.7–50, for transverse separation distance between the bars (i.e., gap ratio) of 1.5, 2, 2.5, 5, and 10 at the blockage ratio of 1/18. The results found here are in good agreement with previously published data. The effects of gap ratio, Reynolds number, and Prandtl number on the detailed kinematics of the flow and the heat transfer are presented. The engineering parameters such as total drag coefficient, average Nusselt number, and Strouhal number are calculated for the preceding range of conditions. It is observed that the overall drag coefficient decreases with increasing Reynolds number, whereas the average Nusselt number for the square cylinders increases with increasing Reynolds number and/or Prandtl number for all the values of gap ratios studied. The percentage enhancement in the value of the average Nusselt number is found to be more than 76% for the range of settings covered here. 相似文献
29.
The reduction of carbonyl compounds by borohydride supported on a cellulose–anion exchange resin is known. The synthesis of a graft copolymer of cellulose and poly(4‐vinyl pyridine) [CellO‐g‐poly(4‐VP)] has been carried out with ceric ions as a redox initiator. A postgrafting treatment of CellO‐g‐poly(4‐VP) with sodium borohydride has produced CellO‐g‐poly(4‐VP) borane, a polymer‐supported reducing agent. Optimum conditions pertaining to the maximum percentage of grafting have been evaluated as a function of the concentrations of the initiator, monomer, and nitric acid, amount of water, time, and temperature. The maximum percentage of grafting (585%) has been obtained with 0.927 mol/L of 4‐vinyl pyridine and 0.018 mol/L of ceric ammonium nitrate in 120 min at 45°C. The polymeric support, CellO‐g‐poly(4‐VP) borane, has been used for reduction reactions of different carbonyl compounds such as benzaldehyde, cyclohexanone, crotonaldehyde, acetone, and furfural. The graft copolymer has been characterized with IR and thermogravimetric analysis. The grafted cellulose has been found to be thermally stable. The reduced products have been characterized with IR and NMR spectral methods. The reagent has been reused for the reduction of a fresh carbonyl compound, and it has been observed that the polymeric reagent reduces the compounds successfully but with a little lower product yield. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 相似文献
30.
Freezing-induced splashing during impact of molten metal droplets with high Weber numbers 总被引:3,自引:0,他引:3
Rajeev Dhiman Sanjeev Chandra 《International Journal of Heat and Mass Transfer》2005,48(25-26):5625-5638
The impact of molten tin droplets (0.6 mm diameter) on solid surfaces was observed for a range of impact velocities (10–30 m/s), substrate temperatures (25–200 °C) and substrate materials (stainless steel, aluminum and glass). The substrate was mounted on the rim of a rotating flywheel and the collision of single droplets with the moving substrate was photographed. Droplet impact Reynolds number ranged from 2.2 × 104 to 6.5 × 104 and Weber number from 8.0 × 102 to 7.2 × 103. On a hot surface there was no splashing and droplets spread to form disk-like splats with smooth edges. Solidification around the edges of droplets spreading on cold surfaces created a solid rim that obstructed flow and triggered splashing. An analytical model was developed to predict the transition temperature at which splashing disappeared by assuming that the thickness of the solid layer had to equal that of the splat in the time the droplet spread to its maximum extent in order to obstruct liquid flow. The model predicted the transition temperature for aluminum and stainless steel surfaces, assuming that thermal contact resistance between the droplet and substrate varied between 10−6 and 10−7 m2 K/W. The model also predicted that tin droplets would not splash on glass surfaces maintained at or above room temperature, and this was confirmed by experiments. 相似文献