Ayushi Mittal  Abhishek K. Singh  Anoop Kumar  Parmanand  Katharina Achazi  Rainer Haag  Sunil K. Sharma 《先进技术聚合物》2020,31(6):1208-1217

Herein, we report on the synthesis of a new class of novel non‐ionic amphiphiles using triglycerol as a core, which is further functionalized with hydrophilic units poly(ethylene glycol) monomethyl ether (M_n: 350 and 550) and a pair of hydrophobic alkyl chains (C₁₈ or C₁₅) via chemo‐enzymatic approach. Fluorescence measurements and dynamic light scattering studies showed that all of the synthesized amphiphilic systems spontaneously self‐ assemble in aqueous solution, which is further confirmed by the transmission electron microscopy. Encapsulation of hydrophobic moieties like Nile red and nimodipine was studied using ultraviolet‐visible (UV‐vis) and fluorescence spectrometer techniques. A cytotoxicity study of the amphiphiles using A549, HeLa, and MCF7 cell, which showed that all of the synthesized nanocarriers are well tolerated at the concentrations studied. The release profile of encapsulated Nile red in synthesized amphiphilic system was studied in the presence of the immobilized enzyme (Novozym 435).  相似文献   

    

Mrinal Jauhari  S.K. Mishra  R. Mittal  S.L. Chaplot 《Journal of Raman spectroscopy : JRS》2019,50(8):1177-1185

Raman spectroscopic measurements are carried out to investigate the structural phase transitions as a function of composition in modified sodium niobate [(1-x) NaNbO₃-xBaTiO₃:NNBTx] for x = 0.0 to 0.15 at room temperature. The characteristic antiferroelectric modes at around 93.4 and 123.6 cm⁻¹, along with a mode at 155.5 cm⁻¹ were found to disappear across the structural phase transition from antiferroelectric orthorhombic phase (Pbcm) to ferroelectric orthorhombic phase (Pmc2₁) for x > 0.02. The redistribution of intensities and positions of the Raman lines in bending (150–350 cm⁻¹) and stretching modes (>550 cm⁻¹) on increasing the concentration x > 0.05, also confirms the occurrence of another phase transition from ferroelectric orthorhombic phase (Pmc2₁) to another ferroelectric orthorhombic phase (Amm2) phase across x~0.10. The phase transitions as observed from Raman measurements are consistent with previous X-ray diffraction study.  相似文献   

    

Vikas Mittal  Ali U. Chaudhry  Nadejda B. Matsko 《哲学杂志》2016,96(20):2143-2160

Adsorption of chlorinated poly(ethylene-co-vinyl acetate)-g-maleic anhydride copolymer and in situ-generated polyaniline (PANI) on thermally reduced graphene oxide (TRGO) platelets was studied in the current study. The adsorption was characterized structurally and morphologically through thermogravimetric analysis, differential scanning calorimetry (DSC), elemental analysis, infra-red and Raman spectroscopy, X-ray diffraction and microscopy. The amount of copolymer adsorption reached a plateau of 0.22 g per g of TRGO, when the initial copolymer to TRGO weight ratio of 1 was used. In the case of PANI modification, much higher extent of adsorption of 0.92 g/g of TRGO (without reaching plateau) was observed due to in situ polymer synthesis and the absence of any steric hindrance to the chains. Shift in the DSC melting transition temperatures of copolymer also indicated that some change in the polymer chain morphology took place after immobilization of polymer on TRGO. PANI modification led to significant reduction in peak melting point from 175C to 140 °C owing to the hindrance in polymer crystallization. The basal plane spacing in the TRGO platelets increased the copolymer adsorption as the 0?0?1 basal plane diffraction shifted from 27° 2Θ for pristine TRGO to 22.5° 2Θ for modified TRGO. For the PANI modified TRGO, no diffraction signal corresponding to TRGO was observed due to extensive adsorption of polymer on the surface. A much thicker polymer phase wrapping the TRGO platelets was observed for PANI modified TRGO. This was also observed through EFTEM and EDX, where the presence of Cl and N (along with other atoms) indicated layer of copolymer and PANI, respectively on the surface of the platelets. EELS analysis also confirmed the semi-crystalline nature of the modified TRGO resulting from the adsorption of semi-crystalline polymers on TRGO. The adsorption approaches used in the study demonstrate successful generation of the functional nanomaterials with tunable extent of surface coverage and potential of employing diverse surface modifications.  相似文献   

    

Niraj K. Shukla  Shiva Mittal 《Numerical Functional Analysis & Optimization》2013,34(4):461-486

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Sanjay Mittal 《国际流体数值方法杂志》2008,56(6):687-702

The receptivity of the separated shear layer for Re = 300 flow past a cylinder is investigated by forced excitation via an unsteady inflow. In order to isolate the shear layer instability, a numerical experiment is set up that suppresses the primary wake instability. Computations are carried out for one half of the cylinder, in two dimensions. The flow past half a cylinder with steady inflow is found to be stable for Re = 300. However, an inlet flow with pulsatile perturbations, of amplitude 1% of the mean, results in the excitation of the shear layer mode. The frequency of the perturbation of the inlet flow determines the frequency associated with the shear layer vortices. For a certain range of forced frequencies the recirculation region undergoes a low‐frequency longitudinal contraction and expansion. An attempt is made to relate this instability to a global mode of the wake determined from a linear stability analysis. Interestingly, this phenomenon disappears when the outflow boundary of the computational domain is shifted sufficiently downstream. This study demonstrates the need of carefully investigating the effect of the location of outflow boundaries if the computational results indicate the presence of low‐frequency fluctuations. The effect of Re and amplitude of unsteadiness at the inlet are also presented. All computations have been carried out using a stabilized finite element formulation of the incompressible flow equations. Copyright © 2007 John Wiley & Sons, Ltd.  相似文献   

    

T. K. Prasanth  S. Mittal 《国际流体数值方法杂志》2008,58(10):1063-1080

The effect of the blockage on vortex‐induced vibrations of a circular cylinder of low non‐dimensional mass (m^*=10) in the laminar flow regime is investigated in detail. A stabilized space–time finite element formulation is utilized to solve the incompressible flow equations in primitive variables form in two dimensions. The transverse response of the cylinder is found to be hysteretic at both ends of synchronization/lock‐in region for 5% blockage. However, for the 1% blockage hysteresis occurs only at the higher Re end of synchronization/lock‐in region. Computations are carried out at other blockages to understand its effect on the hysteretic behavior. The hysteresis loop at the lower Re end of the synchronization decreases with decrease in blockage and is completely eliminated for blockage of 2.5% and less. On the other hand, hysteresis persists for all values of blockage at the higher Re end of synchronization/lock‐in. Although the peak transverse oscillation amplitude is found to be same for all blockage (～0.6D), the peak value of the aerodynamic coefficients vary significantly with blockage. The r.m.s. values show lesser variation with blockage. The effect of streamwise extent of computational domain on hysteretic behavior is also studied. The phase between the lift force and transverse displacement shows a jump of almost 180° at, approximately, the middle of the synchronization region. This jump is not hysteretic and is independent of blockage. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

    

Nikhil Kumar  Anant Diwakar  Sandeep Kumar Attree  Sanjay Mittal 《国际流体数值方法杂志》2013,71(12):1494-1508

A new method for shape optimization with relatively large number of design variables is proposed. It is well known that gradient‐based methods converge to a local optimum. As a result, utilization of a richer design space does not necessarily lead to a better design. This is demonstrated via the design of an airfoil for maximum lift for Re = 1000 and α = 4° flow. The airfoil is represented by fourth‐order non‐uniform rational B‐splines, and the control points are used as design variables. Starting with a NACA0012 airfoil, it is found that the optimal airfoil obtained with 13 control points has far superior aerodynamic performance than the ones obtained with 39 and 61 control points. For effective utilization of a richer design space, it is proposed that the number of design variables be increased gradually. The method is demonstrated by designing high lift airfoils for Re = 1000 and 1 × 10⁴. The objective function is the maximization of the time‐averaged lift coefficient for α = 4°. The optimization cycle with 27 control points is initiated with the optimal airfoil obtained with 13 control points. The process is continued with gradual increase in the number of design variables. Beyond a certain number of control points, the optimization leads to a spontaneous appearance of corrugations on the upper surface of the airfoil. The corrugations are responsible for the generation of small vortices that add to the suction on the upper surface of the airfoil and lead to enhanced lift. A stabilized finite element method is used to solve the unsteady flow and adjoint equations. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

    

D. N. Srinath  S. Mittal 《国际流体数值方法杂志》2009,61(4):355-381

Flow over NACA 0012 airfoil is studied at α = 4^° and 12^° for Re?500. It is seen that the flow is very sensitive to Re. A continuous adjoint based method is formulated and implemented for the design of airfoils at low Reynolds numbers. The airfoil shape is parametrized with a non‐uniform rational B‐splines (NURBS). Optimization studies are carried out using different objective functions namely: (1) minimize drag, (2) maximize lift, (3) maximize lift to drag ratio, (4) minimize drag and maximize lift and (5) minimize drag at constant lift. The effect of Reynolds number and definition of the objective function on the optimization process is investigated. Very interesting shapes are discovered at low Re. It is found that, for the range of Re studied, none of the objective functions considered show a clear preference with respect to the maximum lift that can be achieved. The five objective functions result in fairly diverse geometries. With the addition of an inverse constraint on the volume of the airfoil the range of optimal shapes, produced by different objective functions, is smaller. The non‐monotonic behavior of the objective functions with respect to the design variables is demonstrated. The effect of the number of design parameters on the optimal shapes is studied. As expected, richer design space leads to geometries with better aerodynamic properties. This study demonstrates the need to consider several objective functions to achieve an optimal design when an algorithm that seeks local optima is used. Copyright © 2008 John Wiley & Sons, Ltd.  相似文献   

    

S. Mittal  Ashoke De  Vinod Kumar 《International Journal of Computational Fluid Dynamics》2013,27(8):563-577

Flow past multi-element airfoil is studied via two-dimensional numerical simulations. The incompressible Reynolds averaged Navier–Stokes equations, in primitive variables, are solved using a stabilized finite element formulation. The Spalart–Allmaras and Baldwin–Lomax models are employed for turbulence closure. The implementation of the Spalart–Allmaras model is verified by computing flow over a flat plate with a specified trip location. Good agreement is seen between the results obtained with the two models for flow past a NACA 0012 airfoil at 5° angle of attack. Results for the multi-element airfoil, with the two turbulence models, are compared with experiments for various angles of attack. In general, the pressure distribution, from both the models matches quite well with the experimental results. However, at larger angles of attack, the computational results overpredict the suction peak on the slat. The velocity profiles from the Baldwin–Lomax model are, in general, more diffused compared to those from the Spalart–Allmaras model. The agreement between the computed and experimental results is not too good in the flap region for large angles of attack. Both the models are unable to predict the stall; the flow remains attached even for relatively large angles of attack. Consequently, the lift coefficient is over predicted at large α by the computations. Overall, compared to the Baldwin–Lomax model, the predictions from the Spalart–Allmaras model are closer to experimental measurements.  相似文献   

    

Roy L  Mittal S  Paul A 《Angewandte Chemie (International ed. in English)》2012,51(17):4152-4156

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