Exponential Decay Equation Research Articles

Rhamnolipids biosurfactants as potential modulators of phase and partitioning behavior in micellar systems of aliphatic alcohol ethoxylate surfactants

Abstract The impact of rhamnolipids (RL) biosurfactants presence on the phase-separation equilibrium, micellar properties and partitioning behavior of systems containing the aliphatic non-ionic surfactant Tergitol 15-S-7 (Tg7) was studied in this work. The cloud points of Tg7 solutions (1‐ 10% w/w) in water and sodium citrate (NaCit) buffers pH 7.00 were increased after the RL addition (0.25% w/w) while they were decreased in NaCit pH 5.00. The most marked changes were verified for those systems with low Tg7 concentrations ( 7°). As expected, the zeta potential (ζ) of non-ionic Tg7 systems was close to zero; however, ζ became clearly negative (≅ −20 mV) in NaCit pH 7.00 after the addition of RL. This finding suggested that RL, which is negatively charged at pH 7.00, self-incorporated into Tg7 micelles and conferred them its charge. Hydrodynamic diameter (Dh) was either increased (in citrate media) or decreased (in water) by the RL, depending on the changes caused in the critical packing parameter of mixed micelles. Interestingly, an exponential decay equation, useful for predictive purpose, was found to correlate the cloud point with the hydrodynamic diameter, thus evidencing the crucial role of micelle size/shape on the phase separation. The partitioning behavior of cibacron blue (CB) and malaquite green (MG), negatively and positively charged dyes respectively, in Tg7 aqueous micellar two-phase systems (AMTPS) was significantly affected by the RL 0.25% w/w. In AMTPS with pH 7.00, the RL induced opposite effects, either duplicating the partition coefficient of MG or reducing it to a half for CB. Attractive and repulsive electrostatic interactions between the negatively charged mixed micelles and the partitioned molecules would be responsible of these trends. These results demonstrate the role of RL as a modulator of partitioning behavior of charged molecules and its potential use to improve recoveries and selectivity in a purification protocol.

Temperature sensitivity increases with decreasing soil carbon quality in forest ecosystems across northeast China

Soil respiration universally exhibits exponential temperature dependence (Respiration = R0 eβT & Q10 = e10β), and temperature sensitivity (Q10) and soil organic carbon quality (as expressed by basal respiration rate at 0 °C, R0) are the key parameters. Despite their importance for predicting the responses of forest ecosystems to climate change and quantifying the magnitude of soil CO2 efflux, the controlling factors of temperature sensitivity and soil carbon quality and their relationships among various forest types at a regional scale are as yet unknown. Here, we present a comprehensive analysis of Q10, R0, and their related variables by assembling 154 independent temperature–respiration functions under a common standard in forest ecosystems across northeast China (41°51′–51°24′ N, 118°37′–129°48′ E). The R0 values ranged from 0.1700 to 2.1194 μmol m−2 s−1 (mean = 0.8357 μmol m−2 s−1), and the Q10 values from 1.29 to 5.42 (mean = 2.72). The relationships between Q10 and R0 could be best expressed with exponential decay equations (R2 = 0.460–0.611, P < 0.01). They indicated that the temperature sensitivity decreased with increasing the soil carbon quality, and then tended to level off when the R0 values were larger than ~1 μmol m−2 s−1. Soil carbon quality (R0) was closely related with the minimum soil temperature and its corresponding soil respiration rate during the growing season (R2 = 0.696–0.857, P < 0.01). Such a synthesis is necessary to fully understand the spatial heterogeneity in the temperature sensitivity of soil respiration and to increase our ability to make robust predictions about the future carbon budget.

Crop response of greenhouse soil-grown cucumber to total available N in a Nitrate Vulnerable Zone

Abstract Intensive vegetable production in soil is commonly associated with low N use efficiency (NUE) and consequently appreciable N losses that have negative environmental impacts. Improved N management practices for intensive vegetable crops require detailed knowledge of crop response to N supply. This study evaluated the effects of increasing total available N (TAN, i.e. the sum of soil mineral N at planting, N mineralized from organic matter, and mineral fertilizer N applied by fertigation) on cucumber grown in soil in a greenhouse. Parameters assessed were: yield, dry matter production (DMP), crop N uptake, nitrogen use efficiency (NUE) and potential NO3− leaching loss. The study was conducted in three growing seasons, in autumn, spring and late spring. Three commercial cultivars were examined, in the Late Spring crop, to assess possible cultivar differences. Five N treatments were applied, in the Autumn and Spring crops, as different N concentrations in nutrient solution that were applied in all irrigations throughout the crops. The applied N concentrations were N1: 0.7–1.0 mmol L-1, N2: 4.7–5.7 mmol L-1, N3: 12.1–13.8 mmol L-1, N4: 16.3–17.6 mmol L-1 and N5: 19.7–21.1 mmol L-1. The cultivar ´Strategos´ was used in both crops. Three N treatments (N1: 2.4 mmol L-1; N2: 8.5 mmol L-1and N3: 14.8 mmol L-1) were continuously applied throughout the Late Spring crop to three different cultivars (´Strategos´, ´Padrera´, and ´Mitre´). Total and marketable yield, relative to maximum value, and DMP were strongly related to TAN in linear-plateau relationships for the three growing seasons and three cultivars. Using relationships that include data from the three cropping seasons and the three cultivars, TAN values for maximum DMP, total yield, and marketable yield were 222 ± 15 kg ha−1, 221 ± 14 kg ha−1 and 228 ± 15 kg ha−1, respectively, for the Autumn, Spring and Late Spring crops. The relationships of crop N uptake to TAN, and DMP to crop N uptake, were described by a logarithmic equation. The relationship of N uptake efficiency to TAN (i.e. N uptake/TAN) was described by an exponential decay equation. Considering all crops and cultivars, these relationships were described by individual equations with R2 values of 0.75-0.96. The consistency of these relationships indicate that there are general responses of greenhouse-grown cucumber to N, which is not affected by growing season or cultivar. Measured NO3− leaching losses were low because of good irrigation management. Residual mineral N was considered to be indicative of the potential NO3− leaching loss; residual soil mineral N increased exponentially with TAN, being 196 and 330 kg N ha−1 for the highest N treatments in the Autumn and Spring crops, respectively. The information provided by this study will enable the total N supply (TAN) to be matched to cucumber crop N requirements thereby reducing excessive N supply and consequent negative environmental impacts.

Measured saline and sodic solutions effects on soil saturated hydraulic conductivity, electrical conductivity and sodium adsorption ratio

Hydraulic conductivity is important in the transport of water and salts in salt affected soils. The objective of this study was to determine how saturation of soil columns with saline and sodic solutions changes soil saturated hydraulic conductivity (Ksat) and subsequent salt leaching on a variety of soil textures and smectite clay content. Soil columns were capillary wetted with solutions of varying electrical conductivity (EC) and sodium adsorption ratio (SAR). Ksat was measured by infiltrating deionized water at the soil surface. Ksat as a function of leachate pore volume was fit with an exponential decay equation and a pedotransfer function was created to predict the decay coefficients. Higher salt contents in waters were more successful at increasing soil SAR as compared to low salt content waters. The pedotransfer functions performed similar to the McNeal and Simunek and Suarez models to predict Ksat change due to solution composition without the need of X-ray diffraction of the soil clay fraction. Soils with a greater clay content and specifically smectite clay content have larger changes in saturated water flow rates whether from one time wetting or under long term use of irrigation waters at high EC and Low SAR. High clay smectitic soils require careful management when they are saline-sodic and have a smaller range of safe irrigation waters to prevent reduction in hydraulic conductivity from SAR.

Multistage Signals Based on Cyclic Chemiluminescence for Decoding Complex Samples.

Identification of complex samples presents a difficult challenge for modern analytical techniques, and the differentiation among closely similar mixtures often remains indeterminate. In this article, we designed a simplified cyclic chemiluminescence (CCL) system that is able to measure multistage signals in a single sample injection. The system was used to investigate the CCL reactions of the binary, ternary, and multicomponent mixtures. Results showed that each mixture has a unique exponential decay equation (EDE) with a constant decay coefficient (k-value) to describe the change law of its multistage signals. Further studies found that different brands of liquor, beer, toner, and baby powder have different k-values, and the same brand of the commodities between different batches have the same k-values, which allows facile identification of these complex samples. We then used different catalysts to design digital codes of the k-value for further improving the identifying ability of CCL. Moreover, the multistage signals are like fingerprints and could be used for linear discriminate analysis, which provides another complementary approach for identification of complex samples. Finally, we demonstrated that CCL shows potential applications in certification and quality assurance according to the change of the k-values of the sample. This work demonstrates that excellent discrimination ability of CCL for the identification of complex samples and provides a promising technology for quality assurance.

Classification of beef carcasses from Portugal using animal characteristics and pH/temperature decline descriptors

Previous research showed that meat of optimal tenderness is produced when rigor mortis temperature falls between 12 − 35 °C. This study aimed to classify beef carcasses quality according to the ideal window rule using pH/temperature decay descriptors and animal characteristics. Seventy-four Mirandesa breed and 52 Crossbreds, with an average age of 10.1 ± 2.32 months, were slaughtered at one abattoir located in the Northeast of Portugal. Carcass temperature and pH, logged during 24 h post-mortem, were modelled by exponential decay equations that estimated temperature (kT) and pH (kpH) decay rates. Additionally, other pH/temperature descriptors were estimated from the fitted models. From linear models adjusted to each descriptor, it was found that hot carcass weight, age, breed, gender, age class, fat cover, conformation and transport and lairage time had influence (P < 0.05) on pH and temperature decay rates. Thus, combining the variables kT and kpH, and selected animal/carcass characteristics as linear predictors, a system to classify quality of carcasses was developed.

Diffusion of Re(VII) and Se (IV) in compacted GMZ bentonite in the presence of Bacillus spp.

The effect of Bacillus spp. on Re(VII) and Se(IV) diffusion in compacted GMZ bentonite was investigated by a through-diffusion method. Bacillus spp. had no significance effect on the effective diffusion coefficient (De) and the accessible porosity (eacc) of Re(VII), whereas a decrease of De and an increase of distribution coefficient (Kd) were observed for Se(IV). Moreover, Archie’s law and an exponential decay equation were employed to fit the De value of Re(VII) and Se(IV).

Experimental Modeling of Suspended Sediment Transport Considering the Flow Rate and Grain Size

Bong, T.; Son, Y., and Kim, K.-S., 2019. Experimental modeling of suspended sediment transport considering the flow rate and grain size. Journal of Coastal Research, 35(3), 637–647. Coconut Creek (Florida), ISSN 0749-0208.In this study, laboratory sediment disposal tests were performed using an open channel, and the behavior of soil particles underwater was analyzed according to flow rate and grain size. For each grain size, the deposition distributions of soil particles were demonstrated to have log-normal distributions regardless of the flow rate. The relationships between the average and standard deviation of the deposition distance and the flow rate can be expressed using a quadratic regression equation, and the relationships between the average and standard deviation of deposition distance and the grain size can be expressed using a two-term exponential decay equation. As a result, a simple experimental model was proposed for predicting the soil transportation and deposition distribution considering the flow rate and grain size. The proposed model was validated by comparison with the test results for each grain size and a mixed soil, which was collected from another area, and the proposed model showed good agreement with the experimental results.

Interference of Palmer amaranth (Amaranthus palmeri) Density in Grafted and Nongrafted Watermelon

AbstractWatermelon [Citrullus lanatus(Thunb.) Matsum &amp; Nakai] grafting is commonly used for management of diseases caused by soilborne pathogens; however, little research exists describing the effect of grafting on the weed-competitive ability of watermelon. Field experiments determined the response in yield, fruit number, and fruit quality of grafted and nongrafted watermelon exposed to increasing densities of Palmer amaranth (Amaranthus palmeriS. Watson). Grafting treatments included ‘Exclamation’ triploid (seedless) watermelon grafted on two interspecific hybrid squash rootstocks ‘Carnivor’ and ‘Kazako’, with nongrafted Exclamation as the control. Weed treatments includedA. palmeriat densities of 1, 2, 3, and 4A. palmeriplants per watermelon planting hole (0.76-m row) and a weed-free control. IncreasingA. palmeridensities caused significant reductions (P &lt;0.05) in marketable watermelon yield and marketable fruit number. Watermelon yield reduction was described by a rectangular hyperbola model, and 4A. palmeriplants planting hole−1reduced marketable yield 41%, 38%, and 65% for Exclamation, Carnivor, and Kazako, respectively. Neither grafting treatment norA. palmeridensity had a biologically meaningful effect on soluble solids content or on the incidence of hollow heart in watermelon fruit.Amaranthus palmeriseed and biomass production was similar across weed population densities, but seed number per femaleA. palmeridecreased according to a two-parameter exponential decay equation. Thus, increasing weed population densities resulted in increased intraspecific competition amongA. palmeriplants. While grafting may offer benefits for disease resistance, no benefits regarding weed-competitive ability were observed, and a consistent yield penalty was associated with grafting, even in weed-free treatments.

Tunable color emitting of Ba1-x-ySiO3:xEu,yBi3+ phosphors with the self-reduction of Eu3+ ions calcined in air

A series of Ba1-xSiO3:xEu and Ba0.92-ySiO3:0.08Eu, yBi3+ phosphors have been synthesized using one-step calcination of a precursor prepared by chemical co-precipitation. The self-reduction phenomenon of Eu3+ is observed and verified by photoluminescence (PL), excitation (PLE) spectra and X-ray photoelectron spectroscopy (XPS). Under 353 nm excitation, the Ba1-x-ySiO3:xEu,yBi3+ phosphors exhibit a broad band ranging from 390 nm to 560 nm with a peak centered at 499 nm originating from the 4f65d→4f7 transition of Eu2+ ions and several narrow band emissions peaked at 464 nm, 537 nm, 581 nm, 590 nm, 615 nm, 660 nm and 705 nm can be attributed to 5D2→7F0, 5D1→7F1, 5D0→7F0, 5D0→7F1, 5D0→7F2, 5D0→7F3 and 5D0→7F4 transition of Eu3+, respectively. The self-reduction of Eu3+→Eu2+ in BaSiO3:Eu calcined in air has been explained from the following aspects: the charge compensation mechanism and the structures of 3-D networks composed by SiO4 tetrahedra, helpful for maintaining of the reduction (Eu3+→Eu2+) at a high temperature. Co-doping Bi3+ ions can both enhance the emissions from Eu2+ and Eu3+ because the doped Bi3+ ions not only can make vacancy for Eu2+ but also can enhance the emitting for Eu3+ in BaSiO3. Moreover, when excited by 370 nm, the CIE chromaticity coordinates of Ba0.92SiO3:0.08Eu and Ba0.912SiO3:0.08Eu,0.008Bi3+ are (0.3521, 0.3141) and (0.3558, 0.3408), meanwhile their correlated color temperature (CCT) are 4478 K and 4523 K, which belongs to the warm white light region. Furthermore, the decay curves are measured and can be well fitted with double exponential decay equation. It shows that both the average lifetimes of Eu2+ and Eu3+ are extended with the concentration of Bi3+ ions increasing. Therefore, the Ba1-x-ySiO3:xEu,yBi3+ phosphor is a promising warm white‐light emitting diodes (w-LEDs) integrated with NUV chips.

Nutrient release dynamics from decomposing organic materials and their mulching-effect on pearl millet yields in a low-input Sahelian cropping system

Organic material inputs for increased crop yields are insufficient in the Sahelian West Africa. There is a need for diversifying organic amendment sources for improved nutrient supply in low-input cropping system. The 2-year study aimed to (1) explore the rates of mass losses and nutrient release dynamics from Acacia tumida prunings (AT) and millet straw (MS) under field conditions, (2) assess termite’s contribution to the decomposition of AT and MS, and (3) ascertain the mulching-effect of these organic materials on pearl millet yields. The study was conducted in Niger using field experiment and litterbag methodology and the data modelled using single exponential decay equations. Under field conditions, mulching with AT and MS increased millet grain yield by 35 and 33%, respectively compared to control. The harvest index (HI) in 2014 increased by 21% compared to that obtained in 2013 with the highest HI being recorded for the AT mulched treatment. The results from litterbag experiment indicated a greater dry mass losses from MS decomposition in 2013 whereas relatively higher mass losses were recorded from AT decomposition in 2014. The differences in mass losses among the organic materials could be related to the interaction of soil moisture dynamics and termites’ population which are positively correlated with mass losses. The contribution of termites to the decomposition was estimated to be 36% for MS and 8% for AT. In 2013, at 126 days after litterbags placement, the amounts of N, P, and K released from MS were 16, 1, and 25 kg ha−1 of initial nutrient applied, respectively compared with the 22, 1, and 23 kg ha−1 recorded from AT treatment. During the same period in 2014, the total amounts of N, P and K released from MS were 15, 0.6, and 29 kg ha−1, respectively compared to the 32 kg ha−1 of N, 1 kg ha−1 of P, and 29 kg ha−1 of K released from the AT treatment. The intrinsic organic material quality could explain markedly the variation in nutrient released among the organic material. These results indicate that Acacia tumida prunings have a potential to provide nutrient through mineralization for enhanced crop yield in the Sahel.

Effect of Travel Time and Temperature on Chlorine Bulk Decay in Water Supply Pipes

An experimental study was performed by using the world standard treated drinking water of the city of Ankara. Chlorine is known to be consumed in the bulk liquid phase and at the pipe wall. In the present study the bulk decay pattern was investigated in the absence of pipe wall decay. The test results presented describe how chlorine bulk decay might change with the travel time (residence time) of water in a pipe and the temperature of water in the network. Other than the single constant bulk decay coefficient of chlorine for the first-order exponential decay equation frequently used in many previous studies and models, a parameter coupling residence time of water might be more representative for the water of a city supply network. The test data also showed that chlorine decay of stagnant water in bottles does not differ in magnitude from that of flowing water in a pipe. Additionally, the test results reveal no correlation between initial chlorine concentration level and the bulk decay pattern.

The effect of doping Mg2+ on structure and properties of Sr(1.992-x)MgxSiO4: 0.008Eu2+ blue phosphor synthesized by co-precipitation method

In order to improve the luminescence property of silicate phosphors, a series of Sr(1.992-x)MgxSiO4: 0.008Eu2+(x = 0, 0.25, 0.50, 0.75) blue phosphors have been synthesized using one-step calcination of a precursor prepared by chemical co-precipitation. And then the crystal structure and luminescence properties of the phosphors are investigated by means of X-Ray Diffraction and spectrophotometer. The results show that β-phase existed in the mixed phases of Sr2SiO4 (β+α′) would transform to α′-phase with Mg2+ ions doping into the silicate host until it disappeared. On the other hand, the introduction of Mg2+ ions can enhance the intensity of the excitation spectrum and promote the excitation sensitivity of Sr(1.992-x)MgxSiO4: 0.008Eu2+ phosphors in NUV region. Under NUV excitation at 350 nm, all samples exhibit a broadband emission in range of 400–550 nm due to the 4f65d1→4f7(8S7/2) transition of Eu2+ ions. According to Multi-peak fitting to emission spectra by Gauss method, the broad emission band consists of two single bands with peaks Em1 and Em2 locating at 460 and 490 nm, which corresponds to Eu2+ ions occupying the ten-fold oxygen-coordinated Sr1 site and the nine-fold oxygen-coordinated Sr2 site, respectively. The luminescence intensity of Sr(1.992-x)MgxSiO4:0.008Eu2+(x = 0, 0.25, 0.50, 0.75) blue phosphors has been enhanced remarkably after Mg2+ ions are added. Meanwhile, the chromaticity coordinates change from the blue-green region to the blue region as x moves from 0 to 0.75. Moreover, the decay curves are measured and can be well fitted with double exponential decay equation. It shows that the average lifetime is extended with the concentration of Mg2+ ions increasing. These results indicate that Sr(1.992-x)MgxSiO4: 0.008Eu2+(x = 0, 0.25, 0.50, 0.75) can be used as a potential blue phosphor in near UV-excited white LEDs.

Central diastolic pressure exponential decay constant and subendocardial flow supply.

Central diastolic pressure exponential decay constant and subendocardial flow supply.

Modeling Endothelial Cell Loss After Descemet Stripping Endothelial Keratoplasty: Data From 5 Years of Follow-up.

To report 5-year outcomes for graft survival and endothelial cell survival after Descemet stripping endothelial keratoplasty (DSEK) including regression modeling for cell survival over time. This is a single-institution, retrospective, consecutive interventional series of 210 primary DSEK grafts operated for low-to-moderate risk indications, specifically Fuchs dystrophy and bullous keratopathy. Primary outcomes were cumulative graft survival and % endothelial cell loss from 3 months through 5 years; the secondary outcome was to trend endothelial cell density over time by least-squares and mixed nonlinear modeling. Cumulative graft survival was high at 99%, 98%, and 94% at 1, 3, and 5 years, respectively. Mean endothelial cell loss was (mean ± SD) 44% ± 16%, 56% ± 17%, and 67% ± 13% at 1, 3, and 5 years. The trend in mean endothelial cell density over time by least square regression was accurately and parsimoniously described by a straight line taking earliest values (3 mo) through to 5 years, with a rate of cell loss of 148 ± 13 cells·mm·yr. Higher-order polynomial and exponential models did not provide a closer regression fit. Mixed nonlinear modeling using exponential decay equations confirmed a relatively stable rate of cell loss for DSEK from 3 months through to 5 years, in contrast to penetrating keratoplasty models using similar techniques in previous studies. DSEK graft survival is high in our series through 5 years. Endothelial cell loss occurs at a relatively constant albeit low-grade rate from the earliest postoperative measurements through 5 years.

Peanut Residue Carbon and Nitrogen Mineralization under Simulated Conventional and Conservation Tillage

Core Ideas Recommendations of 22 to 67 kg N ha−1 credit after peanut are not substantiated. Decomposition of peanut residue in North Carolina and Alabama fit double exponential decay equations. Nitrogen credit to wheat was 14 to 24 kg N ha−1, but to cotton was 2 to 10 kg N ha−1. Nitrogen credits differ by location and placement of residue. Nitrogen credits should be specified to which crop they are applied. Residue management is an important aspect of cropping systems. Availability of plant residue N to succeeding crops depends on N mineralization rates. Cooperative Extension currently recommends 22 to 67 kg N ha−1 credit to subsequent crops following peanut (Arachis hypogaea L.), but these recommendations are not supported in the literature, nor do they specify if the credit is applied to a subsequent winter or spring crop. The objective of this study was to assess N release rates from residues of three peanut cultivars (NC V‐11, GA 02‐C, and ANorden) at two placements (surface and 10‐cm deep) and two locations representing northern and southern extremes of U.S. commercial peanut production (North Carolina and Alabama). Litterbags containing the equivalent of 3.5 Mg ha−1 were placed in a completely randomized design at both locations with four replications and retrieved periodically up to 335 d after application. Results were fit to single or double exponential decay models. Based on empirical models, the N credit to a subsequent winter wheat (Triticum aestivum L.) crop was estimated at 14 to 19 kg N ha−1 when peanut residues were buried after harvest, and 19 to 24 kg N ha−1 when on the soil surface. When N credits were applied to a subsequent cotton (Gossypium hirsutum L.) crop, they were reduced to 2 to 9 kg N ha−1 (buried) and 6 to 10 kg N ha−1 (surface). Current recommendations are higher than the results obtained in this study suggest and warrant re‐examination.

Particle size effect on the catalyst attrition in a lab‐scale fluidized bed

Catalysts readily suffer from particle attrition in fluidized beds. In this article, a commercial fluid catalytic cracking catalyst was sieved into several particle‐size intervals to investigate the size effect on particle attrition. It is shown that an exponential decay equation presents a suitable description of attrition and that catalyst attrition is dependent on particle size. Steady‐state specific attrition rate decreases with increasing particle size; however, initial specific attrition rate and decay time parameter change irregularly. For comparison of attrition resistances, a long attrition test is required to reach steady‐state attrition, and the steady‐state specific attrition rate is recommended. It is seen that the smallest particle‐size interval is the most seriously attrited, while the two largest particle‐size intervals are the most attrition‐resistant. Furthermore, weak interactions appear among attrition behaviors of different intervals, and a linear combination method is effective to combine all interval samples to predict the attrition of the original full‐sized sample. © 2016 American Institute of Chemical Engineers AIChE J, 63: 914–920, 2017

Kinetic analysis of simultaneous denitrification and biomineralization of novel Acinetobacter sp. CN86

A novel aerobic denitrification and biomineralization strain CN86 was isolated from the Qu Jiang artificial lake. Based on phylogenetic characteristics, the isolated strain was identified as Acinetobacter species. Strain CN86 was confirmed to have the ability to perform simultaneous denitrification and biomineralization. Exponential decay equation was used for the matching of kinetic processes on denitrification and biomineralization. A highest nitrate removal rate was achieved at the pH7.0, organic concentration of 1.5g/L and temperature of 30°C. An optimal hardness removal rate was obtained at the pH9.0, organic concentration of 2.0g/L and temperature of 30°C. Strain CN86 is a suitable candidate for the simultaneous removal of nitrate and hardness in groundwater treatment.

Drag Reduction Characteristics of Polyacrylamide in a Rotating Disk Apparatus

The drag reduction efficiency of Polyacrylamide has been tested in this study with different parameters using rotating disc apparatus. The polymer is tested at various concentrations (500, 700, 1000, 1500 and 2000) ppm and under turbulent conditions at different rotation speed up to 3000 rpm. The results show that maximum percent of drag reduction is (28, 30, 33, 35 and 36) % for the above concentrations respectively. The mechanical degradation of the polymer with time is also investigated and analyzed using empirical exponential decay function. The fractional exponential decay equation was found to fit the experimental data of low polymer concentration, while better fitting of single exponential decay model is found for experimental data of higher polymer concentration. The drag reduction decrease with increasing polymer concentration.

A Charged Residue in the HCN Channel C-Linker Stabilizes the Open State

Hyperpolarization- and cyclic nucleotide-activated (HCN) channels are regulated by a voltage sensing domain (VSD) as well as a cyclic nucleotide binding domain (CNBD) coupled to the pore by a C-linker. We previously found a mutation in the VSD that slows deactivation kinetics by creating a highly stable open state (Open State Trapping, OST) that is dependent on cAMP binding; deletion of the CNBD and C-linker (ΔC) completely removed OST. I introduced point mutations in the C-linker in an OST mutant, and tested their effects on the stable open conformation. Deactivation kinetics of the mutants, and the ΔC construct, were studied in Xenopus laevis oocytes using two electrode voltage clamp, and fitted to an exponential decay equation. Arginine substitution of a conserved glutamate significantly decreased the deactivation time constant (τ) at +20 mV by ∼3.5 fold when compared to wild type. The same mutation shifted the isochronal deactivation midpoint voltage (Vdeact) by −41 mV. For ΔC, ΔVdeact was −55 mV relative to wild type and τ was ∼8 fold faster than wild type. Therefore, the charge reversal mutation removed a substantial portion of the OST effect on τ and the majority of the OST effect on Vdeact. In comparison, mutating the same residue to glutamine or cysteine partially removed the OST effects, with τ decreased by ∼1.5 fold and 3 fold respectively, and with ΔVdeact of −9 mV and −19 mV respectively. We conclude the native glutamate stabilizes the open state during OST, possibly due to C-linker interactions with other channel regions. Future research will explore how and when this stabilization occurs, for example if it can still occur in the absence of cAMP binding or of the OST mechanism.