Exponential Rate Equation Research Articles

In-situ characterization of the relative humidity at the surface of building materials

Standardized laboratory testing is normally used for characterization of building materials and components. In real life, especially when assessing buildings in terms of water-damaged building materials, built-in moisture, rising damp or other problems, information on the hygrothermal state of the constructions may be relevant, but is often sparse. This paper presents a study where application of a newly developed non-destructive experimental method is used to measure the relative humidity (RH) at the surface of four types of building materials. Knowing the RH at the surface, a risk assessment of fungal growth can be made. The materials include concrete, brick, aerated concrete, and gypsum, with and without a surface treatment. The method is based on the idea of establishing a water vapor transport towards equilibrium within a small air volume in contact with the surface of interest. In the laboratory the specimens were conditioned at respectively 65 % RH and 90 % RH in a climate chamber, and then transferred to conditions with 50 % RH. The open side of a Petri dish, equipped with a temperature and relative humidity sensor, was attached to the materials using reusable adhesive. The development of the relative humidity over time within the petri dish was monitored and parameterized mathematically, solving an exponential rate equation. The parameterization and certain sets of assumptions allow among other things a calculation of time to equilibrium which makes it possible to assess the reproducibility and comparison in between materials. As the materials were tested with and without surface treatment, it was possible to estimate the effect of a typical surface treatment on the moisture transport. The measurements compared well to simulations made by a model, though the model predicts slightly faster achievement of equilibrium. Despite the limited number of cases in the current study, the presented results are promising with regards to enable rough estimates of RH at the surface of building materials outside the laboratory with a very simple, inexpensive, and non-destructive method.

Evaluation of Cr(VI) Reduction Using Indigenous Bacterial Consortium Isolated from a Municipal Wastewater Sludge: Batch and Kinetic Studies

Hexavalent Chromium (Cr(VI)) has long been known to be highly mobile and toxic when compared with the other stable oxidation state, Cr(III). Cr(VI)-soluble environmental pollutants have been detected in soils and water bodies receiving industrial and agricultural waste. The reduction of Cr(VI) by microbial organisms is considered to be an environmentally compatible, less expensive and sustainable remediation alternative when compared to conventional treatment methods, such as chemical neutralization and chemical precipitation of Cr. This study aims to isolate and identify the composition of the microbial consortium culture isolated from waste activated sludge and digested sludge from a local wastewater treatment plant receiving high loads of Cr(VI) from an abandoned chrome foundry in Brits (North Waste Province, South Africa). Furthermore, the Cr(VI) reduction capability and efficiency by the isolated bacteria were investigated under a range of operational conditions, i.e., pH, temperature and Cr(VI) loading. The culture showed great efficiency in reduction capability, with 100% removal in less than 4 h at a nominal loading concentration of 50 mg Cr(VI)/L. The culture showed resilience by achieving total removal at concentrations as high as 400 mg Cr(VI)/L. The consortia exhibited considerable Cr(VI) removal efficiency in the pH range from 2 to 11, with 100% removal being achieved at a pH value of 7 at a 37 ± 1 °C incubation temperature. The time course reduction data fitted well on both first and second-order exponential rate equation yielding first-order rate constants in the range 0.615 to 0.011 h−1 and second order rate constants 0.0532 to 5 × 10−5 L·mg−1·h−1 for Cr(VI) concentration of 50–400 mg/L. This study demonstrated the bacterial consortium from municipal wastewater sludge has a high tolerance and reduction ability over a wide range of experimental conditions. Thus, show promise that bacteria could be used for hexavalent chromium remediate in contaminated sites.

Bioreduction of hexavalent chromium by Exiguobacterium indicum strain MW1 isolated from marine water of Paradip Port, Odisha, India

ABSTRACTHexavalent chromium-tolerant (1500 mg/L) bacterium MW1 was isolated from harbour water of Paradip Port and evaluated for Cr(VI) reduction potential. The isolate was identified as Exiguobacterium indicum by biochemical and 16S rRNA gene sequence methods. Salt tolerance of the bacterium was evaluated in a wide range of NaCl concentrations (0.5–13%, w/v). The Cr(VI) reduction of the strain was evaluated and optimised with varied Cr(VI) concentrations (100–1000 mg/L), pH (5.0–9.0), temperature (30–40°C) and shaking velocity (100–150 rpm) in two different minimal media (M9 and Acetate). Under optimised conditions, after 192 h of incubation nearly 92%, 50% and 46% reduction in the M9 minimal medium and 91%, 47% and 40% reduction in the acetate minimal medium were observed for 100, 500 and 1000 mg/L of Cr(VI), respectively. The exponential rate equation for Cr(VI) reduction yielded higher rate constant value, that is, 1.27 × 10−2 h−1 (M9) and 1.17 × 10−2 h−1 (Acetate) in case of 100 mg/L and became lower for 500 and 1000 mg/L Cr(VI) concentrations. Further, the association of bacterial cells with reduced product was ascertained by Fourier transform infrared spectrometer, UV–Vis–DRS and field-emission scanning electron microscope–energy-dispersive X-ray analyses. The above study suggests that the higher reducing ability of the marine bacterium E. indicum MW1 will be suitable for Cr(VI) reduction from saline effluents.

Characterizing toxic Cr(VI) contamination in chromite mine overburden dump and its bacterial remediation

Cr(VI) generated due to natural oxidation of chromite mineral present in chromite mine overburden (COB) dumps of Sukinda, India, has been characterized by different physico-chemical methods. The Cr(VI) was found to be associated with goethite matrix at a contamination level of 500mgCr(VI)kg−1 of COB. Bacillus sp. isolated from the overburden sample exhibiting high tolerance to the hexavalent chromium, was used for the remediation of Cr(VI) in the overburden. The process was optimized while varying the parameters such as pH (2–9), pulp density (10–60%) and temperature (25–40°C). Optimal reduction of more than 98% of Cr(VI) in the COB sample was achieved in 16h at pH∼7.0 and 60% pulp density with the Bacillus sp. (4.05×107cellsmL−1) in absence of media. The exponential rate equation yielded rate constant value of 2.14×10−1h−1 at 60% pulp density. The mode of bio-reduction of Cr(VI) in the overburden sample was established by FT-IR, XRD, EPMA and SEM-EDS studies.

Optimization and characterization of chromium(VI) reduction in saline condition by moderately halophilic Vigribacillus sp. isolated from mangrove soil of Bhitarkanika, India

A Gram-positive moderately halophilic Cr(VI) tolerant bacterial strain H4, isolated from saline mangrove soil, was identified as Vigribacillus sp. by biochemical characterization and 16S rRNA analysis. In LB medium, the strain could tolerate up to 1000mgL−1 Cr(VI) concentration and reduced 90.2 and 99.2% of 100mgL−1 Cr(VI) under optimized set of condition within 70h in absence and presence of 6wt.% NaCl, respectively. The fitting of time course reduction data to an exponential rate equation yielded the Cr(VI) reduction rate constants in the range (0.69–5.56)×10−2h−1. Analyses of total chromium and bacterial cell associated with reduced product by AAS, SEM/EDS, TEM/SAED, FT-IR and UV–vis–DRS indicated the formation of about 35% of insoluble Cr(III) either as Cr(OH)3 precipitate in nanometric size or immobilized on the bacterial cell surface while the remaining 65% of reduced chromium was present as soluble Cr(III) in the growth medium. Powder XRD analysis revealed the amorphous nature of the precipitated Cr(OH)3. The high Cr(VI) reducing ability of the strain under saline condition suggests the Vigribacillus sp. as a new and efficient strain capable of remediating highly saline Cr(VI) polluted industrial effluents.

Reduction of hexavalent chromium by Bacillus sp. isolated from chromite mine soils and characterization of reduced product

AbstractBACKGROUND: The reduction of highly mobile and toxic hexavalent chromium by bacterial strains is considered to be a viable alternative to reduce Cr(VI) contamination, in soils and water bodies, emanating from the overburden dumps of chromite ores and mine drainage. The present study reports the isolation of Cr(VI) resistant bacterial strains from an Indian chromite mine soil and their potential use in reduction of hexavalent chromium.RESULTS: Among the isolates, a bacterial strain (CSB‐4) was identified as Bacillus sp. based on standard biochemical tests and partial 16SrRNA gene sequencing, which was tolerant to as high as 2000 mg L−1 Cr(VI) concentration. The strain was capable of reducing Cr(VI) to Cr(III) in different growth media. Under the optimized conditions pH ∼7.0, 100 mg L−1 Cr(VI), 35 °C temperature and stirring speed 100 rpm, CSB‐4 reduced more than 90% of Cr(VI) in 144 h. The time course reduction data fitted well an exponential rate equation yielding rate constants in the range 3.22 × 10−2 to 6.5 × 10−3 h−1 for Cr(VI) concentration of 10–500 mg L−1. The activation energy derived from temperature dependence rate constants between 25 and 35 °C was found to be 99 kJ mol−1. The characterization of reduced product associated with bacterial cells by SEM‐EDS, FT‐IR and XRD was also reported.CONCLUSION: Reasonably high tolerance and reduction ability of indigenous Bacillus sp. (CSB‐4) for Cr(VI) under a wide range of experimental conditions show promise for its possible use in reclamation of chromite ore mine areas including soils and water bodies. Copyright © 2010 Society of Chemical Industry

Kinetics of DTPA extraction of zinc from calcareous soils

Abstract The kinetics of Zn extraction by diethylenetriaminepentaacetic acid (DTPA) from the ≤ 2 mm fraction of 12 calcareous soils was investigated using surface soil (0–30 cm) samples. Soils were equilibrated with 0.005 M, DTPA solution for 0.25 to 192 h. Zero-, first-, second-, third-order, parabolic diffusion and simple Elovich equations did not adequately describe Zn extraction kinetics. The best model for describing extraction data for all soils was the exponential rate equation ( q = a t b ). q is the amount of Zn desorption (mg Zn kg − 1 ), a is the Zn desorption magnitude constant (mg Zn kg − 1 h − 1 ) and b is the desorption rate constant. Constant a ranged from 21 to 79.8 with a mean of 41.4 and b from 0.19 to 0.33 with a mean of 0.25. The differences in a value presumably reflect the quite different properties and constituents of these soil types. The magnitude constant a , was positively correlated ( r = 0.76⁎⁎) to organic carbon content and negatively to pH ( r = − 0.67⁎). The rate constant b was not related to any of the measured soil properties such as pH, cation exchange capacity, carbonate calcium equivalent, active calcium carbonate equivalent, clay content, organic carbon and specific surface area or to any combination of these properties.

Membrane fusion: A new function of non steroidal anti-inflammatory drugs

Membrane fusion is an important event in many biological processes and is characterized by several intermediate steps of which content mixing between the two fusing vesicles signals the completion of the process. Fusion induced solely by small drug molecules is not a common event. Non Steroidal Anti-Inflammatory Drugs (NSAIDs), that control pain and inflammation, are also capable of exhibiting diverse functions. In this study we present a new function of NSAIDs belonging to the oxicam group, as membrane fusogenic agents. Small Unilamellar Vesicles (SUVs) formed by the phospholipid, dimyristoylphosphatidylcholine (DMPC), were used as model membranes. Fluorescence assays using terbium/dipicolinic acid (Tb/DPA) were used to monitor content mixing and corresponding leakage in presence of the drugs. Transmission Electron Microscope (TEM) was also used to image fusion bodies in drug treated vesicles as compared to the untreated ones. The results show that the three oxicam NSAIDs viz. Meloxicam, Piroxicam and Tenoxicam can induce fusion of DMPC vesicles and lead the fusion process to completion at a very low drug to lipid ratio (D/L) of 0.045. The oxicam drugs exhibit differential fusogenic behavior as reflected in the kinetics of content mixing and leakage, both of which can be described by a single exponential rate equation. Moreover, not all NSAIDs can induce membrane fusion. Indomethacin, an acetic acid group NSAID and ibuprofen, a propionic acid group NSAID, did not induce fusion of vesicles. This new property of NSAIDs has important applications in biochemical processes.

Electric field mediated DNA motion model

Understanding the motion and the governing equations of a molecule's path in tissue is an ultimate requirement for the repeatable, site specific delivery of molecules [Joseph D. Hickey. Modelling the Motion of Ions and Molecules in Electroporation and Electrophoresis Field Conditions. University of South Florida, College of Arts and Sciences, Department of Physics, Tampa, Florida, 2003., Joseph D. Hickey and Richard Gilbert. Modeling the electromobility of ions in a target tissue. DNA and Cell Biology, 22 (12) (2003) 823–828.]. This paper describes a computationally efficient mathematical model and simulation technique for the examination of DNA fragments in a 1% agarose gel. The speed of the individual DNA fragments through the agarose gel was described through two parts. The maximum velocity was calculated using the Coulombic force divided by Stoke's law and that value was retarded by an exponential rate equation. The simulation utilizes previously published techniques modified for this specific application [Joseph D. Hickey and Richard Gilbert. Fluid flow electrophoresis model. Bioelectrochemistry, 63 (2) (2004) 365–367., Joseph D. Hickey and Richard Gilbert. Modeling the electromobility of ions in a target tissue. DNA and Cell Biology, 22 (12) (2003) 823–828.]. Five representative DNA fragment sizes that span the resolution of a 1% agarose gel were chosen for this analysis. The speeds corresponding to these five DNA fragment sizes were converted into discrete values and used in a 50 step simulation. The resultant error comparing the simulation with experimental distance was 7.76%. Through a 1-D optimization procedure, this error was reduced to 3.02% for a 52 step simulation.

A kinetic study on the dissolution of disperse dyes in the presence of intensifying additives

The kinetics controlling the water solubility of a disperse dye in the presence of the intensifiers polyethyleneglycol, caprolactam and combination of both were investigated. An exponential rate equation was found to describe the dissolution process. It was established that the additives increase the rate of dissolution.

Kinetic investigation of the textile bleaching process

A kinetic investigation on the time variation of the degree of whiteness of the textile substrate and the concentration of hydrogen peroxide as a bleaching agent has been undertaken. An exponential rate equation is found valid for the bleaching reaction, while a power rate equation applies to the bleaching agent's decomposition reaction. The effect of the various additives in the bleaching baths is elucidated.

Status of the Substrate Binding Sites of Ribulose Bisphosphate Carboxylase as Determined with 2-C-Carboxyarabinitol 1,5-Bisphosphate

The properties of the tight and specific binding of 2-C-carboxy-d-arabinitol 1,5-bisphosphate (CABP), which occurs only to reaction sites of ribulose 1,5-bisphosphate carboxylase (Rubisco) that are activated by CO(2) and Mg(2+), were studied. With fully active purified spinach (Spinacia oleracea) Rubisco the rate of tight binding of [(14)C]CABP fit a multiple exponential rate equation with half of the sites binding with a rate constant of 40 per minute and the second half of the sites binding at 3.2 per minute. This suggests that after CABP binds to one site of a dimer of Rubisco large subunits, binding to the second site is considerably slower, indicating negative cooperativity as previously reported (S Johal, BE Partridge, R Chollet [1985] J Biol Chem 260: 9894-9904). The rate of CABP binding to partially activated Rubisco was complete within 2 to 5 minutes, with slower binding to inactive sites as they formed the carbamate and bound Mg(2+). Addition of [(14)C]CABP and EDTA stopped binding of Mg(2+) and allowed tight binding of the radiolabel only to sites which were CO(2)/Mg(2+)-activated at that moment. This approach estimated the amount of CO(2)/Mg(2+)-activated sites in the presence of inactive sites and carbamylated sites lacking Mg(2+). The rate of CO(2) fixation was proportional to the CO(2)/Mg(2+)-activated sites. During light-dependent CO(2) fixation with isolated spinach chloroplasts, the amount of carbamylation was proportional to Rubisco activity either initially upon lysis of the plastids or following total activation with Mg(2+) and CO(2). Lysis of chloroplasts in media with [(14)C]CABP plus EDTA estimated those carbamylated sites having Mg(2+). The loss of Rubisco activation during illumination was partially due to the lack of Mg(2+) to stabilize the carbamylated sites.

Sedimentation Phenomena in Swine Waste Slurries: Model Development

ABSTRACT ANALYTICAL models were developed to describe the complex mechanisms associated with the sedimentation phenomena of swine slurries. Solids concentration at any given depth and time could be determined from the model's relationship among the physical forces and the material characteristics. Temperature in the range of 1 to 20C had no significant effect on the model's ability to predict settling rates. The derivation moves from the simple discrete settling to the more complex nondiscrete flocculant and zone settling. The data from flushed swine waste using a laboratory settling column, which simulated the ideal assumptions of the mathematical models, was used to develop empirical relationships from which the coefficient of the models were determined. Each coefficient was related to specific floe growth characteristics of the particles in wastewater and the dimension of the sedimentation system. All results point to modifying the first-order rate equation to include a second or third-order term to account for the higher flocculation and zone formation associated with the higher concentrated organic slurries in swine manure than those present in municipal and industrial wastewaters. The basic form of the equation will be an exponential rate equation with the independent factors of initial concentration, depth, and time in a power series.

Inhibition of acetylcholinesterase by diisocyanates and its spontaneous reactivation.

The inhibition of human acetylcholinesterase (AchE) by 4,4'-diphenylmethane diisocyanate (MDI) is determined and compared with the previously described inhibition of this enzyme by two other industrially used diisocyanates: toluene diisocyanate (TDI) and hexamethylene diisocyanate (HDI). The inhibition potency of these three diisocyanates is found to be in the oder HDI greater than TDI greater than MDI. The spontaneous reactivation of inhibited AchE is reanalysed with the help of a computer program designed to fit the reactivation data to the exponential rate equation Vt = Vinf (1 - e-Kobs X (t - to) ). The enzyme inhibited by HDI and MDI undergoes very slow and limited spontaneous reactivation. The rate of delivery of diisocyanates into the respiratory tract of an exposed worker may be faster than the rate of spontaneous reactivation of the inhibited enzyme. These results are discussed in connection with the obstructive lung disease observed in approximately 5% of the workers employed in the isocyanate industry.

The double exponential rate equation for thermally activated dislocation motion

The double exponential rate equation for dislocation motion developed by Nichols is examined. It is shown that for the usual case where the back activation area is greater than the forward activation area, a plot of dislocation velocity versus effective stress, τ, exhibits an inflexion point at intermediate levels of effective stress. In this case the stress sensitivity of dislocation velocity, n, is shown to assume values of less than unity near the inflexion point. At lower τ levels n approaches unity and decreases with increasing τ while at higher values of τ, n increases in a manner characteristic of a single exponential function. Since this behaviour is at variance with experimental evidence it is concluded that the basic assumptions required in the application of the equation to experimental results are possibly invalid.

Exponential kinetic equation for the process of hypochlorite treatment of pulps

An explanation is proposed for the exponential rate equation obtained in a kinetic study of the interaction between calcium hypochlorite and different kinds of commucial pulp. It has been confirmed that this kinetic equation describes the reaction of delignification of pulp. The importance of the entropy factor has been explained with the net-structure of lignin and its modifications.

Proton scattering as a tool for the study of crystal structures: R S Nelson, Metallurgy Division, AERE, Harwell, Berkshire, England

The kinetics of Zn extraction by diethylenetriaminepentaacetic acid (DTPA) from the ≤ 2 mm fraction of 12 calcareous soils was investigated using surface soil (0–30 cm) samples. Soils were equilibrated with 0.005 M, DTPA solution for 0.25 to 192 h. Zero-, first-, second-, third-order, parabolic diffusion and simple Elovich equations did not adequately describe Zn extraction kinetics. The best model for describing extraction data for all soils was the exponential rate equation (q = atb). q is the amount of Zn desorption (mg Zn kg− 1), a is the Zn desorption magnitude constant (mg Zn kg− 1 h− 1) and b is the desorption rate constant. Constant a ranged from 21 to 79.8 with a mean of 41.4 and b from 0.19 to 0.33 with a mean of 0.25. The differences in a value presumably reflect the quite different properties and constituents of these soil types. The magnitude constant a, was positively correlated (r = 0.76⁎⁎) to organic carbon content and negatively to pH (r = − 0.67⁎). The rate constant b was not related to any of the measured soil properties such as pH, cation exchange capacity, carbonate calcium equivalent, active calcium carbonate equivalent, clay content, organic carbon and specific surface area or to any combination of these properties.