Isothermal Approach Research Articles

Influence of contact resistance and natural convection effects on non-dimensional effective thermal conductivity estimation of two-phase materials

In this article, the development of geometry dependent resistance model by considering contact resistance and natural convection effects are used to estimate the effective thermal conductivity of two-phase materials based on the unit cell approach. The algebraic equations have been derived based on isotherm approach for 2-D and 3-D spatially periodic medium. Comparison study has been made between developed models and experimental data. The result agrees well with experimental values.

Effect of grain size on the 85Sr2+ sorption and desorption in columns of crushed granite and infill materials from granitic water under dynamic conditions

The sorption of 85Sr2+ in the form of 10−6 M Sr(NO3)2 in synthetic granitic water (SGW), and its desorption using the same radiotracer-free solution, were investigated under dynamic conditions in columns loaded with crushed granitic materials. The goal of study was to evaluate the influence of grain size on the retardation (R) and distribution (Kd) coefficients of the soluble 85Sr2+, as well as on the other transport parameters type of Peclet number (Pe) and hydrodynamic dispersion coefficient (Dd). Pure granitic sample and granitic fissure infill samples were used, crushed and sieved into 4 different grain size from 0.063 to1.25 mm were used. In order to determine migration parameters, the model based on erfc-function was used, assuming reversible equilibrium linear or non-linear (Freundlich) sorption/desorption isotherms. By means of both model approaches, the experimental breakthrough curves were fitted using non-linear regression procedure according to Newton–Raphson method. The obtained results also validated the applicability of the linear equilibrium isotherms of the 85Sr2+ sorption/desorption in the studied systems. It was found that in the case of linear isotherm approach, both retardation and distribution coefficients increased with decreasing grain size. Moreover, their values for fracture infill samples are higher than comparing to granite. Depending on the grain size, the retardation coefficient R varied between 11 and 25 for pure granite and 33–58 between for fissure infill material. These values correspond to distribution coefficients Kd of 2–7 and 9–24 cm3/g, respectively. Consequently, the sorption capacity of crushed rocks also increases with decreasing grain size and are about 2.5-times higher for fracture infill than in pure granite. The values of Dd increase with increasing grain size. Due to inverse proportion, values of Pe number are decreasing.

Diagnostic devices for isothermal nucleic acid amplification.

Since the development of the polymerase chain reaction (PCR) technique, genomic information has been retrievable from lesser amounts of DNA than previously possible. PCR-based amplifications require high-precision instruments to perform temperature cycling reactions; further, they are cumbersome for routine clinical use. However, the use of isothermal approaches can eliminate many complications associated with thermocycling. The application of diagnostic devices for isothermal DNA amplification has recently been studied extensively. In this paper, we describe the basic concepts of several isothermal amplification approaches and review recent progress in diagnostic device development.

Novel insights in Al-MCM-41 precursor as adsorbent for regulated haloacetic acids and nitrate from water

High concentration of NO (3) (-) in groundwater has raised concern over possible contamination of drinking water supplies. In addition, the formation of haloacetic acids (HAAs) as by-products during disinfection with chlorine-based agents is still a relevant issue, since HAAs pose serious health hazard. In this work, we investigated the affinity of a precursor of Al-MCM-41 (a mesostructured hexagonal aluminosilicate containing the template surfactant) towards nitrate and HAAs, for its possible application in the removal of these pollutants from natural and drinking waters. Additionally, adsorption kinetics and isotherms were studied. The adsorbent was synthesized using cetyltrimethylammonium bromide as surfactant and characterized by physico-chemical techniques. Simulated drinking water was spiked with the EPA-regulated HAAs (monochloroacetic (MCAA), monobromoacetic (MBAA), dichloroacetic (DCAA), dibromoacetic (DBAA), and trichloroacetic (TCAA) acids) and placed in contact with the adsorbent. The effect of matrix composition was studied. Adsorption kinetic studies were performed testing three kinetics models. For the adsorption studies, three adsorption isotherm approaches have been tested to experimental data. The pollutant recoveries were evaluated by suppressed ion chromatography. The affinity of the adsorbent was TCAA = DBAA = DCAA > MBAA > MCAA with DCAA, DBAA, and TCAA completely removed. A removal as high as 77% was achieved for 13mg/L nitrate. The adsorption isotherms of NO (3) (-) and monochloroacetic acid can be modeled by the Freundlich equation, while their adsorption kinetics follow a pseudo-second-order rate mechanism. The adsorbent exhibited high affinity towards HAAs in simulated drinking water even at relevant matrix concentrations, suggesting its potential application for water remediation technologies.

Estimation of Effective Thermal Conductivity of Two-Phase Materials by Considering the Knudsen Effect: An Analytical Approach

In this article, the analytic model has been developed to estimate the effective thermal conductivity (ETC) of two-phase materials based on the unit cell approach by considering the concentration, conductivity ratio, contact resistance, and Knudsen effect. The derivations of algebraic equations for standard geometry, such as hexagon and octagon cylinder models are developed based on parallel isotherm approach. The developed analytic model has been used to predict the thermal conductivity of various two-phase materials (conductivity ratio, α = 3.11-310.86 and concentration, ν = 0.05 and 0.74). The present models are validated using the standard models and compared with the experimental data. Further the comparison is made between the present models and existing models. The results are in good agreement.

Ultrasensitive electrogenerated chemiluminescence biosensor for the determination of mercury ion incorporating G4 PAMAM dendrimer and Hg(II)-specific oligonucleotide

A novel electrogenerated chemiluminescence (ECL) biosensor for highly sensitive and selective detection of mercury ion was developed on the basis of mercury-specific oligonucleotide (MSO) served as a molecular recognition element and the ruthenium(II) complex (Ru1) as an ECL emitting species. The biosensor was fabricated on a glassy carbon electrode coated with a thin layer of single wall carbon nanotubes, where the ECL probe, NH 2-(CH 2) 6-oligo(ethylene oxide) 6-MSO ↔ Dend-Ru1, was covalently attached. The Dend-Ru1 pendant was prepared by covalent coupling Ru1 with the 4th generation polyamidoamine dendrimer (Dend), in which each dendrimer contained 35 Ru1 units so that a large amplification of ECL signal was obtained. Upon binding of Hg 2+ to thymine (T) bases of the MSO, the T–Hg–T structure was formed, and the MSO changed from its linear shape to a “hairpin” configuration. Consequently, the Dend-Ru1 approached the electrode surface resulting in the increase of anodic ECL signal in the presence of the ECL coreactant tri- n-propylamine. The reported biosensor showed a high reproducibility and possessed long-term storage stability (92.3% initial ECL recovery over 30 day's storage). An extremely low detection limit of 2.4 pM and a large dynamic range of 7.0 pM to 50 nM Hg 2+ were obtained. An apparent binding constant of 1.6 × 10 9 M −1 between Hg 2+ and the MSO was estimated using an ECL based extended Langmuir isotherm approach involving multilayer adsorption. Determination of Hg 2+ contents in real water samples was conducted and the data were consistent with the results from cold vapor atomic fluorescence spectroscopy.

Predicting accelerated aggregation rates for monoclonal antibody formulations, and challenges for low-temperature predictions

Nonnative aggregation is a common degradation route for therapeutic proteins. Control of aggregate levels inherently requires control and/or prediction of aggregation rates at formulation conditions and storage temperatures of practical interest. Additionally, formulation screening often involves generation of accelerated stability data at one or more temperatures. A temperature‐scanning approach for measuring nonnative aggregation rates as a function of temperature is proposed and evaluated here for a monoclonal antibody across different formulation conditions. Observed rate coefficients of aggregation (kobs) were determined from isothermal kinetic studies for a range of pH and salt conditions at several temperatures, corresponding to shelf lives spanning multiple orders of magnitude. Isothermal kobs values were efficiently and quantitatively predicted by the temperature‐scanning monomer loss (TSML) approach at accelerated conditions (half lives of the order 10−1–102 h). At lower temperatures, non‐Arrhenius behavior was apparent in some cases, and was semi‐quantitatively described by nonlinear van't Hoff contributions to monomer unfolding free energies. Overall, the results demonstrate a novel strategy to quantitatively determine aggregation rates at time scales of industrial interest, based on kobs values from TSML, which are sample‐ and time‐sparing as compared with traditional isothermal approaches, and illustrate challenges for shelf‐life prediction with non‐Arrhenius kinetics. © 2011 Wiley‐Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:4234–4243, 2011

Cure Kinetics of Poly(acrylonitrile-butadiene-styrene) Modified Epoxy–Amine System

The cure kinetics of epoxy based on the diglycidyl ether of bisphenol A (DGEBA) modified with different amounts of poly(acrylonitrile-butadiene-styrene) (ABS) and cured with 4,4′-diaminodiphenylsulfone (DDS) was investigated by employing differential scanning calorimetry (DSC). The curing reaction was followed by using an isothermal approach over the temperature range 150–180°C. The amount of ABS in the blends was 3.6, 6.9, 10 and 12.9 wt%. Blending of ABS in the epoxy monomer did not change the reaction mechanism of the epoxy network formation, but the reaction rate seems to be decreased with the addition of the thermoplastic. A phenomenological kinetic model was used for kinetic analysis. Activation energies and kinetic parameters were determined by fitting the kinetic model with experimental data. Diffusion control was incorporated to describe the cure in the latter stages, predicting the cure kinetics over the whole range of conversion. The reaction rates for the epoxy blends were found to be lower than that of the neat epoxy. The reaction rates decreased when the ABS contents was increased, due to the dilution effect caused by the ABS on the epoxy/amine reaction mixture.

Polymer-induced recovery of nanoparticles from microemulsions

A new isothermal approach to the recovery of inorganic nanoparticles (NPs) is demonstrated. The NPs can be incorporated into a background microemulsion (ME) supporting fluid, and they can be recovered by addition of non-adsorbing polymer. A clean liquid-liquid (L-L) phase transition can be readily induced by addition of polymer to the MEs. Furthermore, the L-L transitions are also observed in the presence of added NPs, but now the nanoparticles concentrate in the lower co-existing ME phases. Once recovered, the NPs can be redispersed by adding extra ME as a solvent.

Simulations of direct collisions of gas clouds with the central black hole

We perform numerical simulations of clouds in the Galactic Centre (GC) engulfing the nuclear super-massive black hole and show that this mechanism leads to the formation of gaseous accretion discs with properties that are similar to the expected gaseous progenitor discs that fragmented into the observed stellar disc in the GC. As soon as the cloud hits the black hole, gas with opposite angular momentum relative to the black hole collides downstream. This process leads to redistribution of angular momentum and dissipation of kinetic energy, resulting in a compact gaseous accretion disc. A parameter study using thirteen high resolution simulations of homogeneous clouds falling onto the black hole and engulfing it in parts demonstrates that this mechanism is able to produce gaseous accretion discs that could potentially be the progenitor of the observed stellar disc in the GC. A comparison of simulations with different equations of state (adiabatic, isothermal and full cooling) demonstrates the importance of including a detailed thermodynamical description. However the simple isothermal approach already yields good results on the radial mass transfer and accretion rates, as well as disc eccentricities and sizes. We find that the cloud impact parameter strongly influences the accretion rate whereas the impact velocity has a small affect on the accretion rate.

Comparison of geometry dependent resistance models with conventional models for estimation of effective thermal conductivity of two-phase materials

The geometry dependent resistance models are used to estimate the effective thermal conductivity of two-phase materials based on the unit cell approach. The algebraic equations are derived based on isotherm approach for various geometries. The effective thermal conductivity of the above models are found and compared with experimental data with a minimum and maximum deviation of ±3.976 and ±19.55%, respectively. The present models are good agreement with experimental results.

Double Covalent Coupling Method for the Fabrication of Highly Sensitive and Reusable Electrogenerated Chemiluminescence Sensors

A double covalent coupling method for the fabrication of a highly sensitive and reusable electrogenerated chemiluminescence (ECL) chemical sensor for the detection of tertiary amines and ECL aptamer-based (ECL-AB) biosensor for the detection of cocaine is reported. The ECL sensors were constructed by covalent coupling of amino-containing Ru(bpy)(3)(2+) derivatives (Ru1, Ru(bpy)(3)(2+) = tris(2,2'-bipyridyl)ruthenium(II)) or cocaine aptamer-Ru1 to the surface of a paraffin-impregnated graphite electrode that had been covalently modified with a monolayer of 4-aminobenzene sulfonic acid via electrochemical oxidations. ECL performance of the newly developed chemical sensors was evaluated using tri-n-propylamine (TPrA) and metoclopramide (MCP) as model analytes. The sensors exhibited excellent sensitivity, stability, and reproducibility with a detection limit of 30 nM for TPrA and 2.0 nM for MCP, and relative standard deviations (RSDs) of 2.1% over 90 cyclic potential cycles (0 to 1.50 V vs Ag/AgCl) and 2.6% over 45 cycles (0.60 to +1.30 V vs Ag/AgCl) at 400 mV/s for 50 nM TPrA and 200 nM MCP, respectively. For the ECL-AB biosensor, it showed an extremely low detection limit of 10 pM for cocaine, and offered a good selectivity toward cocaine, heroin, and caffeine. This detection limit was about 4-6 orders of magnitude lower than that reported on the basis of alternating current (AC) voltammetry and optical aptamer-based cocaine biosensors. Additionally, the ECL-AB biosensor was highly reusable (RSD = 2.8%, n = 7) and possessed long-term storage stability (96.8% initial ECL recovery over 21 days storage). A binding constant of 4.6 +/- 0.3 x 10(9) M(-1) between cocaine and its aptamer was estimated using an ECL based Langmuir isotherm approach. Wide ranging applications of the presently reported strategy in fabricating various chemical sensors or biosensors are expected.

Predicting potassium fertilizer requirement using exchange isotherm approach in relation to soil characteristics

Determining potassium (K) fertilizer requirement using sorption isotherms is considered more accurate than conventional soil K tests. A total of 59 surface soil samples were used to establish K exchange isotherm. To evaluate K requirement sorption test, a glasshouse experiment using perennial ryegrass (Lolium perenne, cv. Roper) was carried out on 10 soil samples. The experiment was laid out as a completely randomized design with four replications and four K levels (K0, K20, K40, K80). Concentrations of K in solution established by adding K in the pots estimated from the sorption curve ranged from 20 to 80 mg K l−1 including check treatment (no K). Dry matter yield of ryegrass in most soils approached maximum as adjusted K levels were increased to 20 mg K l−1. The amounts of K required to bring the soils to 20 mg l−1 in soil solution varied among soils and ranged from 99 to 399 mg kg−1, on average 205 mg kg−1 soil. It was found that a useful regression model for the prediction of standard K requirement (K20) included the combination of plant available K extracted by NH4OAc (Av-K) and clay content: K20 = −41 − 0.63 Av-K + 9.0 Clay (R2 = 0.61, p < 0.001, n = 59).

Effective thermal conductivity modeling with primary and secondary parameters for two-phase materials

In this article, the collocated parameter models are used to estimate the effective thermal conductivity of the two-phase materials including the effect of various inclusions in the unit cell. The algebraic equations are derived using unit cell based isotherm approach for two dimensional spatially periodic medium. The geometry of the medium is considered as a matrix of touching and non-touching in-line octagon and hexagon cylinders. The models are used to predict the thermal conductivity of numerous two-phase materials (maximum conductivity ratio of 1000 and concentration ranging between 0 and 1). The estimated thermal conductivity data is in good agreement with the experimental data within ?15.84%, ?18.14% maximum deviation, respectively, from octagon and hexagon cylinders for various two-phase systems. The obtained results are compared with a wide range of experimental data for various geometrical configurations to estimate the effective thermal conductivity of two-phase materials.

Estimation of Effective Thermal Conductivity of Two-Phase Materials Using Collocated Parameter Model

In this article, the collocated parameter models are used to estimate the effective thermal conductivity of the two-phase materials. The algebraic equations are derived using a unit-cell-based isotherm approach for a two- and three-dimensional spatially periodic medium. The geometry of the medium is considered as matrix of touching and nontouching in-line square and circular cylinders as well as touching and nontouching in-line solid and hollow cubes. The models are used to predict the thermal conductivity of numerous two-phase materials (maximum conductivity ratio of 1000 and concentration ranging between 0 and 1). The estimated thermal conductivity data is in good agreement with experimental data within ± 16.67% deviation for various two-phase systems. The results are compared with the standard models and experimental data for different types of two-phase systems; it is shown that the touching in-line solid cube model predicts better as compared to other geometrical configurations.

Modeling Nonlinear Sorption of Alcohol Ethoxylates to Sediment: The Influence of Molecular Structure and Sediment Properties

The nonlinear sorption of individual alcohol ethoxylate (AE) homologues was studied as a function of the chemical structure of AE and properties of six marine sediments and three clay minerals. All sorption data for both sediments and clays are well described by a dual-mode model, combining a Langmuir and linear sorption term. The nonlinear isotherms of a single homologue on different substrates almost overlap when sorbed concentrations are expressed per specific surface area. Below and above the Langmuir maximum capacity, isotherms approach linearity. Accordingly, it is demonstrated for nine individual AE that the two linear sorption coefficients for the clay mineral illite are predictive within a factor of two for a North Sea sediment. The linear sorption term at high concentrations is likely related to bilayer formation on the mineral surfaces, for both clays and sediments. Adsorption and bilayer formation to mineral surfaces dominate the sorption behavior of most AE homologues to the tested marine sediments. The two fitted sorption coefficients correlate well with the polar and nonpolar chain lengths of the AE. The enhanced nonlinearity of isotherms for AE with longer ethoxylate chains is explained by both an increasing adsorption coefficient and a decreasing bilayer formation affinity with additional ethoxylate units.

Effect of pH on Boron Adsorption-Desorption Hysteresis of Soils

Lime is regularly used to increase soil pH, which will increase boron (B) fixation in soils. The effects of raising pH on B adsorption and the reversibility of adsorbed B in acid soils are essential for soil B management. In this study, B adsorption and desorption in limited concentration as a function of pH were measured in five fine-textured red soils. Immediately after adsorption of B, four consecutive desorption steps were carried out by successive dilution. The sorption results were described well by the Freundlich equation. Boron adsorption markedly increased as pH increased. This increase was more pronounced when Ca(OH)2, as opposed to NaOH, was used for pH adjustment. The presentation of desorption data was based on the traditional isotherm approach and on time-dependent isotherms. Apparent hysteresis was observed in that both derivational families of desorption isotherms deviated from the adsorption isotherm for the five soils at their original pH. Moreover, hysteresis coefficients, ndes/nads and λtrad for the traditional approach, had a positive correlation with organic carbon content, but they had a negative correlation with free Fe2O3 and free Al2O3 content. As pH increased, the hysteresis diminished, and adsorbed B became more likely to be desorbed. This finding may be because B adsorption and raising pH increase the negative charge on the surface, which creates electrostatic repulsion and results in an increase in desorption as pH increases.

Cure properties of self‐extinguishing epoxy resin systems with microencapsulated latent catalysts for halogen‐free semiconductor packaging materials

AbstractThe cure properties of self‐extinguishing epoxy resin systems with different microencapsulated latent catalysts were investigated, which are composed of YX4000H and NC3000H as a biphenyl epoxy resin, MEH‐7800SS as a hardener, and triphenylphosphine (TPP) microencapsulated with various polymers as a latent catalyst. The cure kinetics of these systems were analyzed by differential scanning calorimetry using an isothermal approach, and the kinetic parameters of all systems were reported in generalized kinetic equations with diffusion effects. Both the epoxy resin systems with microencapsulated latent catalysts showed lower cure conversion rate and higher critical cure reaction conversion than those with TPP. These different cure conversion rates could be explained by the decrease of crystallinity of the biphenyl epoxy resin and the activation energy of these epoxy resin systems. The cure conversion rates of the epoxy resin systems with the microencapsulated latent catalyst would be dependent on the activation energy of these systems. The storage stability tests for these systems were performed, and a good shelf‐life was observed in both the epoxy resin systems with EPCAT‐PAM, a core–shell‐type latent catalyst. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009

Studies of hydrate nucleation with high pressure differential scanning calorimetry

Current models for hydrate formation in subsea pipelines require an arbitrary assignment of a subcooling criterion for nucleation. In reality hydrate nucleation times depend on both the degree of subcooling and the amount of time the fluid has been subcooled. In this work, differential scanning calorimetry was applied to study hydrate nucleation for gas phase hydrate formers. Temperature ramping and isothermal approaches were combined to explore the probability of hydrate nucleation for both methane and xenon. A system-dependent subcooling of around 30 K was necessary for hydrate nucleation from both guest molecules. In both systems, hydrate nucleation occurred over a narrow temperature range (2–3 K). The system pressure had a large effect on the hydrate nucleation temperature but the ice nucleation temperature was not affected over the range of pressures investigated (3–20 MPa). Cooling rates in the range of (0.5–3 K/min) did not have any statistically significant effect on the nucleation temperature for each pressure investigated. In the isothermal experiments, the time required for nucleation decreased with increased subcooling.

Adsorption of dissolved organic carbon to mineral soils: A comparison of four isotherm approaches

The partitioning of dissolved organic carbon (DOC) within mineral soils is primarily controlled by adsorption to soil particle surfaces. We compare the theoretical limitations and modeling accuracy of four isotherm approaches to describe DOC partitioning to soil surfaces. We use 52 mineral soil samples to create linear initial mass (IM), non-linear, and Langmuir isotherms, all relating the initial solution concentration ( X i) to the amount of DOC adsorbed or released from soil surfaces. The Langmuir isotherm is also used with final concentration ( X f). The IM isotherm failed to meet theoretical assumptions and provided poor fits to experimental data. The non-linear and Langmuir X i approaches had good fits to experimental data, and the Langmuir X i approach had the most robust estimates of desorption capacity. Both Langmuir X i and X f isotherms hold the advantage of estimating the maximum adsorption capacity, yet the X f isotherm is a better reflection of adsorption processes.