Isotherm Plots Research Articles

Novel Multifunctional Hybrids of Single-Walled Carbon Nanotubes with Nucleic Acids: Synthesis and Interactions with Living Cells

Novel hybrids of fluorescein-labeled poly(ethylene glycol)-modified single-walled carbon nanotubes (SWCNTs) with nucleic acids were prepared. 5'-Pyrene conjugates of oligodeoxyribonucleotides were used to construct the noncovalent hybrids, with the pyrene residues acting as anchor groups, immobilizing an oligonucleotide on the SWCNT surface. The hybrid formation characteristics were studied using ζ-potential measurements and adsorption isotherm plots. Transmission electron microscopy (TEM) of the samples stained with contrast agents proved that the pyrene conjugates of oligonucleotides were adsorbed onto the surfaces of the functionalized SWCNTs. On the basis of the MTT assay, the functionalized SWCNTs and their hybrids with oligonucleotides exhibited low toxicity toward HeLa, KB-3-1, and KB-8-5 cells. A TEM study of ultrathin sections of cells treated with SWCNTs revealed that the nanotubes directly interacted with the cellular surface.

Application of HYDRUS 1D model for assessment of phenol–soil adsorption dynamics

Laboratory-scale batch, vertical, and horizontal column experiments were conducted to investigate the attenuative capacity of a fine-grained clayey soil of local origin in the surrounding of a steel plant wastewater discharge site in West Bengal, India, for removal of phenol. Linear, Langmuir, and Freundlich isotherm plots from batch experimental data revealed that Freundlich isotherm model was reasonably fitted (R (2) = 0.94). The breakthrough column experiments were also carried out with different soil bed heights (5, 10, and 15 cm) under uniform flow to study the hydraulic movements of phenol by evaluating time concentration flow behavior using bromide as a tracer. The horizontal migration test was also conducted in the laboratory using adsorptive phenol and nonreactive bromide tracer to explore the movement of solute in a horizontal distance. The hydrodynamic dispersion coefficients (D) in the vertical and horizontal directions in the soil were estimated using nonlinear least-square parameter optimization method in CXTFIT model. In addition, the equilibrium convection dispersion model in HYDRUS 1D was also examined to simulate the fate and transport of phenol in vertical and horizontal directions using Freundlich isotherm constants and estimated hydrodynamic parameters as input in the model. The model efficacy and validation were examined through statistical parameters such as the coefficient of determination (R (2)), root mean square error and design of index (d).

Effects of an adiabatic inclined fin on the mixed convection heat transfer in a square cavity

In this study, a square cavity with two ventilation ports in the presence of an adiabatic fin placed on the bottom wall of the cavity is numerically analysed for the mixed convection case for a range of Richardson numbers (Ri = 0.1,1, 10, 30) and at Reynolds number of 300. The top and bottom walls of the cavity are kept at constant temperature while the verticals walls are assumed to be adiabatic. The effect of the fin height, inclination angle and Richardson number on the fluid flow and heat characteristics is numerically analysed. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. It is observed that length and inclination angle of the fin significantly alter the streamlines and isotherms and hence the thermal performance of the system. For the best performance at different fin lengths, optimum inclination angle changes.

Effects of an adiabatic fin on the mixed convection heat transfer in a square cavity with two ventilation ports

In this study, a square cavity with two ventilation ports in the presence of an adi-abatic fin of different lengths placed on the walls of the cavity is numerically analyzed for the mixed convection case for a range of Richardson numbers (Ri=0.1,1, 10, 100) and at Reynolds number of 300. The effect of the fin height, placement of the fin on each of the four walls of the cavity and Richardson number on the heat transfer and fluid flow characteristics is numerically analyzed. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. It is observed that for the convection dominated case, fin length and its position on the one of the four walls of the cavity do not alter the thermal performance whereas when the buoyancy effects become important thermal performance increases for high fin length.

Numerical Simulation on Buoyancy-driven Heat Transfer Enhancement of Nanofluids in an Inclined Triangular Enclosure

Heat transfer enhancement in a two-dimensional inclined lid-driven triangular enclosure utilizing nanofluids is investigated numerically for various pertinent parameters. The present model is developed to analyze the heat transfer performance of nanofluids inside an enclosure taking into account the solid volume fraction δ, variable velocity and thermal boundary conditions. Fluid mechanics and conjugate heat transfer, described in terms of continuity, linear momentum and energy equations. The transport equations are solved numerically using the Galerkin finite element method. Results are obtained for a wide range of parameters such as the Grashof numbers. Copper-water nanofluids is used with Prandtl number, Pr = 6.2 and solid volume fraction δ is varied from 0% - 20%. The streamlines, isotherm plots and heat transfer correlation of the average Nusselt number at the hot surface as well as average fluid temperature in the enclosure is presented and discussed in detailed. It is found that heat transfer increased by 28% as volume fraction δ increases from 0% to 20% at Gr =105. Moreover, the variation of the average Nusselt number and average fluid temperature in the cavity is linear with the solid volume fraction.

Adsorption characteristics of ethanol root extract of Portulaca oleracea as eco-friendly inhibitor of corrosion of mild steel in H2SO4medium

The adsorption of ethanolic root extract of Portulaca oleracea as corrosion inhibitor for the corrosion of mild steel in H2SO4 medium at the temperature range of 305K to 315 K was studied using weight loss method and characterized using the common adsorption isotherms. The inhibition efficiency, IE%, was found to increase with both increase in the inhibitor concentration and rise in temperature. The increase in IE% with rise in temperature is suggestive of chemisorption. The adsorption best fitted the Langmuir, El-Awady, Temkin and Adejo-Ekwenchi isotherms. Evaluated values of free energy, ΔGads, of the adsorption process were found to be all negative, indicative of spontaneity of the adsorption process and values obtained through the Temkin were above -20 kJ/mol, supportive of the chemisorption. The fact that the slopes and intercepts of the ideal Langmuir isotherm (ILI) plots were not unity and zero, respectively, signifies a deviation from this isotherm but the deviation cannot be said to be much as ΔGads values obtained through modified Langmuir isotherm (MLI) are not quite different from those of ILI. The adherence of the adsorption to the Temkin isotherm is evidence evident of chemisorption, which was made evidently made clear from the Adejo-Ekwenchi b parameter. The exact number of water molecules replaced by inhibitor molecules could not be ascertained by Bockris-Swinkels isotherm.

Magnetoconvective Transport in a Vertical Lid-Driven Cavity Including a Heat Conducting Square Cylinder with Joule Heating

The hydromagnetic mixed convection flow and heat transfer in a vertical lid-driven square enclosure is numerically simulated following a finite volume approach based on the SIMPLEC algorithm. Both the top and bottom horizontal walls of the enclosure are insulated, and the left and right vertical walls are kept isothermal with different temperatures. The left vertical wall is translating in its own plane at a uniform speed, while all other walls are stationary. Two cases of translational lid motion, viz. vertically upward and downward, are considered. A uniform magnetic field is applied along the horizontal direction normal to the translating wall. A heat conducting horizontal solid square cylinder is placed centrally within the outer enclosure. Simulations are conducted for various controlling parameters, such as the Richardson number (1 ≤ Ri ≤ 10), Hartmann number (0 ≤ Ha ≤ 50), and Joule heating parameter (0 ≤ J ≤ 5), keeping the Reynolds number based on lid velocity fixed as Re = 100. The flow and thermal fields are analyzed through streamline and isotherm plots for various Ha, J, and Ri. Furthermore, the pertinent transport quantities such as the drag coefficient, Nusselt number, and bulk fluid temperature are also plotted to show the effects of Ha, J, and Ri on them.

Role of ZnO in Dc Electrical Conductivity of Lithium Bismuthate Glasses

Glasses of various compositions belonging to the Bi2O3-B2O3-ZnO-Li2O quaternary system were prepared using melt quench technique. Dc electric measurements were done on the samples, and activation energies are determined. Arrhenius plots showed straight line behaviour. It is observed that the conductivity of the samples increased with temperature and also with Li2O content, whereas the activation energy decreased with Li2O content. The isothermal plots for constant ZnO and constant Bi2O3glasses revealed that the conduction in these glasses is due to lithium ions only. The isothermal plots for constant lithium containing glasses varied nonlinearly with two maxima, which is attributed to mixed former effect. The variation is explained based on Anderson-Stuart model.

Hydromagnetic Mixed Convective Transport in a Vertical Lid-Driven Cavity Including a Heat Conducting Rotating Circular Cylinder

Two-dimensional numerical simulation is performed for the hydromagnetic mixed convective transport in a vertical lid-driven square enclosure filled with an electrically conducting fluid in the presence of a heat conducting and rotating solid circular cylinder. Both the top and bottom horizontal walls of the enclosure are considered thermally insulated, and the left and right vertical walls are kept isothermal with different temperatures. The left wall is moving in the upward direction at a uniform speed, while all other walls are stationary. A uniform magnetic field is applied along the horizontal direction normal to the moving wall. A heat conducting circular cylinder is placed centrally within the outer enclosure. The cylinder is made to rotate in its own plane about its centroidal axis. Both the clockwise and counterclockwise rotations of the cylinder are considered. All solid walls are assumed electrically insulated. Simulations are performed for various controlling parameters, such as the Richardson number (1 ≤ Ri ≤ 10), Hartmann number (0 ≤ Ha ≤ 50), and dimensionless rotational speed (−5 ≤ Ω ≤ 5) keeping the Reynolds number based on lid velocity fixed as Re = 100. The flow and thermal fields are analyzed through streamline and isotherm plots for various Ha, Ω, and Ri. Furthermore, the pertinent transport quantities such as the drag coefficient, Nusselt number, and bulk fluid temperature are also computed to understand the effects of Ha, Ω, and Ri on them. It is observed that the heat transfer greatly depends on the rotational speed of the cylinder.

Unsteady buoyancy-driven heat transfer enhancement of nanofluids in an inclined triangular enclosure

Heat transfer enhancement in a two-dimensional inclined lid-driven triangular enclosure utilizing nanofluids is investigated numerically for various pertinent parameters. The present model is developed to analyze unsteady heat transfer performance of nanofluids inside an enclosure taking into account the solid volume fraction δ, variable velocity and variable thermal boundary conditions. Fluid mechanics and conjugate heat transfer described in terms of continuity, linear momentum and energy equations. The transport equations are solved numerically using the Galerkin finite element method. Results are obtained for a wide range of parameters such as the Grashof numbers (103≤Gr≤106), and time step (0.01≤τ≤1). Copper-water nanofluids is used with Prandtl number, Pr=6.2 and solid volume fraction δ is varied from 0% to 25%. The streamlines, isotherm plots and heat transfer correlation of the average Nusselt number at the hot surface as well as average fluid temperature in the enclosure is presented and discussed in detail. It is found that heat transfer increased by 31.85% as volume fraction δ increases from 0% to 25% at Gr=105 for τ=0.01. Moreover, the variation of the average Nusselt number and average fluid temperature in the cavity is linear with the solid volume fraction.

Numerical Investigation and POD-Based Interpolation of Natural Convection Cooling of Two Heating Blocks in a Square Cavity

In this study, natural convection cooling of two heating blocks placed in a square cavity is numerically investigated. The cavity is cooled from vertical walls and the surface of the heating blocks are kept at constant temperature. The effect of placing the heating blocks at top, middle and bottom of the cavity, and the distance between the blocks on the heat transfer characteristic is numerically analyzed for the range of Grashof numbers between 103 and 106. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. A POD-based interpolation method is also employed to predict the flow field and heat transfer characteristic for the case where the heating blocks are placed in the middle of the cavity. Nusselt number variation with respect to Grashof number is captured well with this approach of POD-based interpolation compared to the CFD calculations.

Numerical Study of Three-Dimensional Mixed Convection in an Eccentric Annulus

Mixed convection of air with a Prandtl number of 0.7 in eccentric horizontal annuli is numerically investigated. The inner cylinder is at a higher temperature, while the inner and outer cylinders can be rotated either clockwise or counterclockwise with a constant angular velocity. The effects of various parameters, such as the eccentricity of the annulus and the Rayleigh number, are studied using a three-dimensional model. The Navier–Stokes equations, along with the energy equation, are solved in an orthogonal structured grid of a bipolar coordinate system employing a finite volume method based on the SIMPLE algorithm. Here, both steady and unsteady results are presented in two separate codes. Three-dimensional considerations lead to a complicated flow pattern, whereas Taylor vortices have a major role on heat and flow characteristics. It is shown that the axial component of velocity in some configurations has a considerable value, therefore, flow pattern and heat transfer characteristics change in comparison with a two-dimensional approach. Eccentricity leads to a different flow pattern in the upper and lower parts of the annulus. Mean and local heat transfer results are obtained. The physics of the flow underlying the observed heat transfer behavior is revealed by the velocity vectors and the isotherm plots of the numerical solutions. Results show that flow and heat transfer are strongly influenced by the eccentricity of the inner cylinder and Raleigh number, and that three-dimensionality consideration is inevitable.

MHD Mixed Convection in a Lid-Driven Cavity Including a Heated Source

Numerical simulations are performed to understand the thermo-magneto-convective transport of fluid and heat in a vertical lid-driven square enclosure following a finite volume approach based on the SIMPLEC algorithm. The enclosure is filled with an electrically conducting fluid and having a heated source on the right vertical wall. Two different types of sources, such as a semicircular and a rectangular one, are considered. Both the top and bottom horizontal walls and the right vertical wall, except the source of the enclosure, are assumed insulated and the left vertical wall and the sources are kept isothermal with different temperatures. The left vertical wall is also translating in its own plane at a uniform speed, while all other walls are stationary. Two cases of translational lid motion, viz., vertically upward and downward are considered. A uniform magnetic field is applied along the horizontal direction normal to the translating wall. Shear forces due to lid motion, buoyancy forces as a result of differential heating, and magnetic forces within the electrically conducting fluid act simultaneously. Heat transfer due to forced flow, natural convection, and Joule dissipation are taken into account. Simulations are conducted for various controlling parameters, such as the Rayleigh number (103 ≤ Ra ≤ 105), Hartmann number (0 ≤ Ha ≤ 100), and Joule heating parameter (0 ≤ J ≤ 5), keeping the Reynolds number based on lid velocity fixed as Re = 100. The flow and thermal fields are analyzed through streamline and isotherm plots for various Ha and J. Furthermore, the pertinent transport quantities such as the drag coefficient, Nusselt number, and bulk fluid temperature are also plotted to show the effects of Ha, J, and Ra on them.

Direct incorporation method for the synthesis of molybdophosphate/MCM-41 silica composite: Adsorption study of heavy metals from aqueous solutions

The direct incorporation of α-Keggin structure, [PMo12O40]3−, derived from ammonium molybdophosphate into the mesopores of MCM-41 silica to synthesis MP/MCM-41 composite was carried out using soft-templating approach which based on surfactant self-assembly. The aimed composite material was characterized by XRD, FT-IR, SEM and BET techniques. Sorption properties of the synthesized composite powder were evaluated through sorption of lead, copper and cadmium ions from their multicomponent aqueous solutions. Preliminary studies of cation hydrolysis using MINTEQA2 software program was accomplished indicating that at pH of 5 the highest percent of free Pb2+, Cu2+ and Cd2+ was attained. Batch sorption tests were carried out at different initial heavy metal ion concentrations revealing that the synthesized composite has great selectivity to lead ions over copper and cadmium ions. The experimentally obtained sorption results were analyzed using pseudo-1st and -2nd order kinetic models to stand on the possible sorption mechanisms indicating the sorption behavior of the studied ions onto MP/MCM-41 composite belonged to the pseudo 2nd order kinetic model and the sorption process was a chemical process. Isotherm plots were constructed and analyzed using Langmuir and Freundlich isotherm models. Results indicated that the best fitting to the experimentally obtained data was obtained when Langmuir isotherm model was applied.

Free Energy Changes and Components Implicit in the MWC Allosteric Model for the Cooperative Oxygen Binding of Hemoglobin

Hill's plots of oxygen binding isotherms reveal the presence of a transition between two different oxygen affinities at the beginning and end of the isotherm. They correspond to the two conformations anticipated by the MWC model, namely, the T and R conformations at the beginning and end of oxygen binding, when the lower affinity of the T form develops into the higher affinity of the R form. The difference between the binding Gibbs free energy changes of the two affinities (Δ G(L)) is the free energy of binding cooperativity. Notably, Δ G(L) is positive in favor of the T form, which moves to a higher energy level upon oxygen release. Osmotic stress reveals a higher volume/surface ratio of deoxyhemoglobin, with a positive Δ G(W) also in favor of the T form. An increasing protein concentration shifts the isotherms to the right, indicating the formation of intermediate polymeric forms. The enthalpy of the intermediates shows a strong absorption of heat at the third oxygenation step because of polymer formation with quinary, and higher-order, structures. The disassembly of intermediate polymers releases energy with a negative Δ G that compensates and allows the positive values of Δ G(L). High-energy polymers are the barrier preventing the relaxation of the T and R conformations into one another. The MWC allosteric model is the best justification of oxygen binding cooperativity.

Crystallization behavior of Si-added amorphous Ga19Sb81 films for phase-change memory

Crystallization behavior of Si-added amorphous Ga19Sb81 films was studied by measuring electrical resistance (R) versus temperature (T) at various heating rates. The crystallization temperatures obtained from the R–T curves increase from 228 to 284°C measured at the heating rate 10°C/min with increasing Si content to 14at.%. All films with full-crystallization show phases of Sb and GaSb. At 9at.% Si the activation energy of crystallization and the rate factor reach the maxima of 9.1eV and 6.8×1084min−1, respectively. The kinetic exponent (n) of the film with 9at.% Si is below 1.5 which indicates growth-dominated crystallization, while that of other films falls in 1.5≤n≤2.5 which denotes decreasing nucleation rate during nuclei growth. Time of 90% crystallization slightly decreases owing to Si addition as estimated using JMA theory. The temperature corresponding to 10-year failure-time obtained through isothermal Arrhenius plot effectively increases from 156 to 217°C as Si content is from 0 to 14at.%. The melting temperature slightly reduces from 591 to 581°C with Si addition. The reset voltage of test cells based on Si4(Ga19Sb81)96 is reduced by 0.5V to ~2.75V and can be set–reset switched within pulse-widths of 40–200ns.

Numerical analysis and identification of mixed convection in pulsating flow in a square cavity with two ventilation ports in the presence of a heating block

In this study, a square cavity with two ventilation ports in the presence of a isothermal heating block placed in the middle of the cavity is numerically analyzed for the mixed convection case in pulsating flow for a range of Richardson numbers (Ri = 1, 10, 100) and at Reynolds number of 300. At the inlet of the ventilation port, pulsating velocity is imposed for Strouhal numbers of 0.1, 0.5, 1, 2.5, 5 and velocity amplitude ratio of 0.3, 0.6 and 0.9. The effect of the pulsation frequency, amplitude and Richardson number on the heat transfer and fluid flow characteristics is numerically analyzed. The results are presented in terms of streamlines, isotherm plots and averaged Nusselt number plots. A neural network-based identification approach is utilized for the low amplitude of pulsating velocity to obtain an input–output model for the heat transfer for a range of pulsating frequencies.

Selective Separation of Aluminum from Biological and Environmental Samples Using Glyoxal-bis(2-hydroxyanil) Functionalized Amberlite XAD-16 Resin: Kinetics and Equilibrium Studies

A new glyoxal-bis(2-hydroxyanil) anchored Amberlite XAD-16 chelating resin was synthesized and characterized by elemental analyses and scanning electron microscopy along with energy dispersive X-ray spectroscopy (SEM/EDAX), infrared spectral, and thermal studies. The resin was found to selectively bind aluminum in aqueous medium over a large number of competitive cations, at pH 9. Experimental conditions, for effective sorption of Al(III) were optimized systematically and were found to have fast kinetics (t1/2 10 min), high preconcentration flow rate (5.0 mL min–1), very high sorption capacity (24.28 mg g–1), regenerability up to 66 sample loading/elution cycles, and low preconcentration limit (3.3 ppb) from test solutions of different interferent to analyte ratio. The chemisorption and identical, independent binding site behavior were evaluated by Dubinin–Radushkevich isotherm and Scatchard plot analysis. Equilibrium data fit well to Langmuir adsorption isotherms (r2 = 0.998) indicating a typical monolayer sorption. We confirmed the analytical reliability of the method by the analysis of standard reference materials (SRMs), recovery experiments, and precision expressed as coefficient of variation (<5%). The applicability of the proposed method was demonstrated by preconcentration of trace Al(III) in dialysis fluid, packaged drinking water, rum, and soft drink samples.

Numerical Prediction of Heat Transfer from Localized Heating in Enclosure Using CIP Method

In this paper, two-dimensional laminar natural-convection heat transfer of air has been numerically solved by Cubic Interpolated Method known as CIP which is based on the Eulerian mesh grid generation. For this investigation a cavity has been selected as a geometry which is being heated from bottom of the cavity at three different positions, the sides of the cavity are cold and the top of the cavity is adiabatic and no heat exchange exist there. The cavity is being heated from three different position of the bottom which is equal in length and equal but in three different position of left, center and right in equally distance. The whole simulation takes place in two various Grasshof number and air has been taken as fluid inside cavity. Prantl number has been set to 0.7 throughout the simulation. Results are presented in the form of streamlines and isothermal plots inside the cavity. The results illustrate the heat for middle heated plate is distributed symmetrically through the cavity.

Dilatometric sintering study of fine-grained ceramics from ultradispersed admixture composed of Ce0.09Zr0.91O2 and MgO–Al2O3

Abstract The experiment was carried out to produce fine-grained ceramics with a grain size of less than 5 μm. Ultradispersed oxide mixture MgO–Al 2 O 3 (weight ratio MgO/Al 2 O 3 value was 3/97) and solid solution Ce 0.09 Zr 0.91 O 2− δ were used as initial nanopowders with a crystallite size less than 10 nm. Dilatometric investigation was carried out at the temperature interval 1100–1550 °C using three temperature modes, included various heating and cooling rates and isothermal plots. Initial metal oxide powders were obtained by modified sol–gel technique using N-containing organic compounds for sol stabilization. It was shown that the role of MgO in nanopowdery composition for sintering is to accelerate the sintering due to the formation of the liquid phase with spinel MgAl 6 O 10 . It was determined, that the presence of interim isotherms on the temperature rise curves does not impact the rate and quality of sintering.