Stagnant Solution Research Articles

Volumetric interpretation of protein adsorption: Kinetics of protein-adsorption competition from binary solution

The standard solution-depletion method is implemented with SDS-gel electrophoresis as a multiplexing, separation-and-quantification tool to measure competition between two proteins ( i and j) for adsorption to the same hydrophobic adsorbent particles (either octyl sepharose or silanized glass) immersed in binary-protein solutions. Adsorption kinetics reveals an unanticipated slow protein-size-dependent competition that controls steady-state adsorption selectivity. Two sequential pseudo-steady-state adsorption regimes (State 1 and State 2) are frequently observed depending on i, j solution concentrations. State 1 and State 2 are connected by a smooth transition, giving rise to sigmoidally-shaped adsorption-kinetic profiles with a downward inflection near 60 min of solution/adsorbent contact. Mass ratio of adsorbed i, j proteins ( m i / m j ) remains nearly constant between States 1 and 2, even though both m i and m j decrease in the transition between states. State 2 is shown to be stable for 24 h of continuous-adsorbent contact with stagnant solution whereas State 2 is eliminated by continuous mixing of adsorbent with solution. In sharp contrast to binary-competition results, adsorption to hydrophobic adsorbent particles from single-protein solutions (pure i or j) exhibits no detectable kinetics within the timeframe of experiment from either stagnant or continuously mixed solution, quickly achieving a single steady-state value in proportion to solution concentration. Comparison of binary competition between dissimilarly-sized protein pairs chosen to span a broad molecular-weight (MW) range demonstrates that selectivity between i and j scales with MW ratio that is proportional to protein-volume ratio (ubiquitin, Ub, MW = 10.7 kDa; human serum albumin, HSA, MW = 66.3 kDa; prothrombin, FII, 72 kDa; immunoglobulin G, IgG, MW = 160 kDa; fibrinogen, Fib, MW = 341 kDa). Results are interpreted in terms of a kinetic model of adsorption that has protein molecules rapidly diffusing into an inflating interphase that is spontaneously formed by bringing a protein solution into contact with a physical surface (State 1). State 2 follows by rearrangement of proteins within this interphase to achieve the maximum interphase concentration (dictated by energetics of interphase dehydration) within the thinnest (lowest volume) interphase possible by ejection of interphase water and initially-adsorbed proteins. Implications for understanding biocompatibility are discussed using a computational example relevant to the problem of blood–plasma coagulation.

Functional and chemical comparison of apoplastic barriers to radial oxygen loss in roots of rice (Oryza sativa L.) grown in aerated or deoxygenated solution

Radial oxygen loss (ROL) and root porosity of rice (Oryza sativa L.) plants grown in either aerated or deoxygenated (stagnant) conditions were combined for the first time with extensive histochemical and biochemical studies of the apoplastic barriers in the roots' peripheral cell layers. Growth in stagnant solution significantly affected structural and, consequently, the physiological features of rice roots. It increased adventitious root porosity by about 20% and decreased the ROL towards the base to zero at a distance of 40 mm from the apex. By contrast, roots of plants grown in aerated solutions revealed the highest rates of ROL at 30 mm from the apex. Differences in the ROL pattern along the root were related to histochemical studies, which showed an early development of Casparian bands and suberin lamellae in the exodermis, and lignified sclerenchyma cells in roots of plants grown in deoxygenated solution. In agreement with anatomical studies, absolute contents of suberin and lignin in the outer part of the roots (OPR) were higher in plants grown in deoxygenated solution. Regardless of growth conditions, the levels of suberin and lignin increased along the roots towards the base. It is concluded that radial oxygen loss can be effectively restricted by the formation of a suberized exodermis and/or lignified sclerenchyma in the OPR. However, the relative contribution of suberin and lignin in the formation of a tight barrier is unclear. Knowing the permeability coefficient across OPR for roots of plants grown in both conditions will allow a more precise understanding of the mechanisms controlling ROL.

Hydrodynamic behavior of heap leach piles: Influence of testing scale and material properties

The dynamics of solution, soluble species, and gas in increasing scales of heap leaching apparatus were quantified with tracer tests to explain differences in their gold leaching behaviors. The tracer methods included tracer injection in the feed solution and monitoring soluble species during rinsing. Hydrodynamics of the heap systems were evaluated during (1) the scale-up from a 350 kg column to a 55 tonne crib to a 6300 tonne heap, and (2) the change in ore properties from run-of-mine to crushed to agglomerated ore in 55 tonne cribs. The tracer data was interpreted by the Levenspiel compartment flow model that considers a packed bed as a black box filled with ore, air, and moisture, the latter occurring as active flow, by-pass flow, plug flow volume, well-mixed volume, and stagnant/dead volume. This model was useful as a diagnostic tool but would not be a predictive tool. It was established that gold recovery could be correlated to the amount of stagnant solution in the system. Columns and cribs that achieved excellent gold recovery had as little as 0% to 18% of the solution retained in a stagnant form. The 6300 tonne heap had poor gold recovery and contained a significant stagnant volume (57% of the total solution retained in the heap). The proportion of stagnant solution was proportional to the proportion of fines in the ore and the lack of structural support (e.g. column walls) in the heap, the latter translating into a higher bed density. In contrast to the wide distribution of particle size in the run-of-mine and crushed ores, the agglomerated ore was more uniformly-sized, which led to a lower proportion of stagnant solution. The agglomerated ore had a lower bulk density of 1.7 t/m 3 ( vs 2 t/m 3) and a lower proportion of stagnant solution 0% ( vs 88%). Gold extraction from the agglomerated ore was aided by the air available in the pores, while good solution transport out of the packed bed was attributed to the absence of stagnant zones. Tracers proved to be simple and effective to quantitatively diagnose the inner workings of heap leaching systems of various scales. A narrow particle size distribution, a low fines content, and a low bed bulk density were keys to achieving good solution, solute, and gas dynamics, hence high gold recovery.

Tolerance of Hordeum marinum accessions to O2 deficiency, salinity and these stresses combined

When root-zone O(2) deficiency occurs together with salinity, regulation of shoot ion concentrations is compromised even more than under salinity alone. Tolerance was evaluated amongst 34 accessions of Hordeum marinum, a wild species in the Triticeae, to combined salinity and root-zone O(2) deficiency. Interest in H. marinum arises from the potential to use it as a donor for abiotic stress tolerance into wheat. Two batches of 17 H. marinum accessions, from (1) the Nordic Gene Bank and (2) the wheat belt of Western Australia, were exposed to 0.2 or 200 mol m(-3) NaCl in aerated or stagnant nutrient solution for 28-29 d. Wheat (Triticum aestivum) was included as a sensitive check species. Growth, root porosity, root radial O(2) loss (ROL) and leaf ion (Na(+), K(+), Cl(-)) concentrations were determined. Owing to space constraints, this report is focused mainly on the accessions from the Nordic Gene Bank. The 17 accessions varied in tolerance; relative growth rate was reduced by 2-38 % in stagnant solution, by 8-42 % in saline solution (aerated) and by 39-71 % in stagnant plus saline treatment. When in stagnant solution, porosity of adventitious roots was 24-33 %; salinity decreased the root porosity in some accessions, but had no effect in others. Roots grown in stagnant solution formed a barrier to ROL, but variation existed amongst accessions in apparent barrier 'strength'. Leaf Na(+) concentration was 142-692 micromol g(-1) d. wt for plants in saline solution (aerated), and only increased to 247-748 micromol g(-1) d. wt in the stagnant plus saline treatment. Leaf Cl(-) also showed only small effects of stagnant plus saline treatment, compared with saline alone. In comparison with H. marinum, wheat was more adversely affected by each stress alone, and particularly when combined; growth reductions were greater, adventitious root porosity was 21 %, it lacked a barrier to ROL, leaf K(+) declined to lower levels, and leaf Na(+) and Cl(-) concentrations were 3.1-9-fold and 2.8-6-fold higher, respectively, in wheat. Stagnant treatment plus salinity reduced growth more than salinity alone, or stagnant alone, but some accessions of H. marinum were still relatively tolerant of these combined stresses, maintaining Na(+) and Cl(-) 'exclusion' even in an O(2)-deficient, saline rooting medium.

Assessment of O2 diffusivity across the barrier to radial O2 loss in adventitious roots of Hordeum marinum.

The subapical regions of wetland plant roots can develop a barrier to radial O2 loss (ROL), but barrier resistance has rarely been quantified in terms of its O2 diffusivity. Barrier resistance in adventitious roots of the waterlogging-tolerant Hordeum marinum was assessed from measurements of ROL using cylindrical platinum electrodes while either varying shoot O2 partial pressures or cooling the rooting medium. Anatomical features were examined using fluorescence microscopy. When grown in stagnant agar nutrient solution, a barrier to ROL was induced over the basal half of 100-120-mm-long roots. Autofluorescence in hypodermal cell walls indicated that putative suberin deposition was coincident with barrier expression. Root cooling revealed a significant respiratory component in barrier resistance. Eliminating the respiration effect by manipulating shoot O2 partial pressures revealed an O2 diffusivity for the barrier of 5.96 x 10(-7) cm2 s(-1), 96% less than that at the apex, which was > or = 1.59 x 10(-5) cm2 s(-1). It is concluded that the ROL barrier is a manifestation of two components acting synergistically: a physical resistance caused principally by secondary cell-wall deposits in the outer hypodermal layer; and respiratory activity in the hypodermal/epidermal layers; with physical resistance being the dominant component.

Volumetric interpretation of protein adsorption: Ion-exchange adsorbent capacity, protein pI, and interaction energetics

Adsorption of lysozyme (Lys), human serum albumin (HSA), and immunoglobulin G (IgG) to anion- and cation-exchange resins is dominated by electrostatic interactions between protein and adsorbent. The solution-depletion method of measuring adsorption shows, however, that these proteins do not irreversibly adsorb to ion-exchange surfaces, even when the charge disparity between adsorbent and protein inferred from protein pI is large. Net-positively-charged Lys (pI = 11) and net-negatively-charged HSA (pI = 5.5) adsorb so strongly to sulfopropyl sepharose (SP; a negatively-charged, strong cation-exchange resin, −0.22 mmol/mL exchange capacity) that both resist displacement by net-neutral IgG (pI = 7.0) in simultaneous adsorption competition experiments. By contrast, IgG readily displaces both Lys and HSA adsorbed either to quaternary ammonium sepharose (Q; a positively-charged, strong anion exchanger, +0.22 mmol/mL exchange capacity) or to octadecyl sepharose (ODS; a neutral hydrophobic resin, 0 mmol/mL exchange capacity). Thus it is concluded that adsorption results do not sensibly correlate with protein pI and that pI is actually a rather poor predictor of affinity for ion-exchange surfaces. Adsorption of Lys, HSA, and IgG to ion-exchange resins from stagnant solution leads to adsorbed multi-layers, into or onto which IgG adsorbs in adsorption competition experiments. Comparison of adsorption to ion-exchange resins and neutral ODS leads to the conclusion that the apparent standard free-energy of adsorption Δ G ads ° of Lys, HSA, and IgG is not large in comparison to thermal energy due to energy-compensating interactions between water, protein, and ion-exchange surfaces that leaves a small net Δ G ads ° . Thus water is found to control protein adsorption to a full range of substratum types spanning hydrophobic (poorly water wettable) surfaces, hydrophilic surfaces bearing relatively-weak Lewis acid/base functionalities that wet with (hydrogen bond to) water but do not exhibit ion-exchange properties, and surfaces with strong Lewis acid/base functional groups that exhibit ion-exchange properties in the conventional chemistry sense of ion-exchange.

Electrodeposited Free-Standing Single-Crystal Indium Nanowires

Single-crystal indium nanowires were grown from arrays of holes 150–300 nm in diameter etched into a 300 nm dielectric by potentiostatic electrodeposition from stagnant InCl3-based solutions. The monocrystallinity of the nanowires was confirmed by electron backscattered diffraction measurements. For given experimental conditions, indium wires several micrometers in length grew out of the shallow templates without significant lateral overgrowth, resulting in high-aspect-ratio one-dimensional nanowires. This unusual observation is attributed to a perturbation of the local diffusion field by the neighboring holes or nanowires.

Mechanism and kinetics of the electrochemical formation of polypyrrole under forced convection conditions

This work studies the process of electrochemical formation of polypyrrole onto a vitreous carbon rotating disk electrode, from a pyrrole aqueous solution containing sodium nitrate, applying different potentials to the electrode for both conditions: stagnant and forced convection. It was found that the analyses of the experimental current transients, in both cases, could be done using the same theoretical model. The latter involves three different contributions: a first one due to pyrrole oxidation on the vitreous carbon surface, to form different oligomers in solution, a second one related with bidimensional nucleation of the oligormeric form of pyrrole (formed during the first stage) that saturated the solution near the electrode surface and a final contribution due to oxidation of pyrrole and/or its oligomers onto the surface of the polypyrrole film deposited during the 2D nucleation. The last contribution can be related to the polypyrrole three dimensional growth through direct incorporation of the monomer to the polymeric film or to a similar processes as described on the first two stages. For the stagnant solution the contribution related with the third stage was the highest observed, for a given applied potential, however, when hydrodynamic conditions were imposed, at a constant potential, the contribution due to this stage diminishes with the angular speed of the RDE electrode, because the more reactive oligomeric forms of pyrrole are forced away from the electrode surface, to practically reach a steady value. From AFM images it is shown that toroidal structures became apparent when deposition was done potentiodynamically and that the whole electrode surface was covered by small nuclei which possess an average height that is quite similar to that theoretically predicted by the deposition model here proposed to explain the potentiostatic Ppy electrodeposition.

Effect of nitrate fertilization and saline stress on the contents of active constituents of Echinacea angustifolia DC

In this study, the effect of nitrogen form (nitrate and ammonium in the molar ratio of 1:1 or 1:0), supplied to the plant or NaCl salinity (up to a concentration of 50 mol m −3) of the feeding solution, on the content of selected caffeic acid derivatives and the activities of phenylalanine ammonia lyase (PAL; EC. 4.3.1.5) and shikimate dehydrogenase (SKDH; EC 1.1.1.25) were investigated in the leaves and the roots of Echinacea angustifolia DC, grown hydroponically. Two experiments were conducted under glasshouse conditions with seedlings transplanted in aerated stagnant nutrient solution (floating raft system) four weeks after emergence. The nitrate/ammonium ratio in the nutrient solution did not affect plant growth or dry matter partitioning, but it influenced the concentration of determined metabolites; in particular, the root concentrations of chlorogenic acid, echinacoside and caffeic acid were significantly higher in the plants grown with nitrate as sole source of nitrogen. NaCl salinity reduced plant growth, by reducing the biomass allocated to the inflorescences, and enhanced the accumulation of chlorogenic acid and cichoric acids, at least in the roots.

Electrochemical Behavior of Chemical Conversion Coated Aluminum ASA6061 in Chromic Acid

The corrosion behavior of bare and chemical conversion coated (through anodizing) aluminum ASA 606 I in stagnant chromic acid solutions . Solutions of 2, 6 & J O wt. % Cr03 at 45°C, have been investigated using polarization technique. The anodizing experiments were conducted under fixed conditions of 35 minute exposure time and 30 volt supplied voltage. The most important feature achieved was the great difference in behavior between the anodic polarization curves for bare and anodized aluminum in different concentrations of chromic acid solutions.

Degree of Supersaturation-Regulated Chiral Symmetry Breaking in One Crystal

This paper aimed at studying chiral symmetry-breaking phenomena in one crystal. Preferential crystallization of racemic asparagines was carried out in nonseeded stagnant solutions through slow cooling. By varying the supersaturation, only one transparent crystal could be obtained at enough low supersaturation of dl-asparagine, and the crystal was not pure enantiomer with crystal enantiomeric excess increasing inversely with the degree of supersaturation. Crystal enantiomeric excess can amount up to 85% in one transparent crystal. Because no secondary nucleation occurred except for stochastic primary nucleation, we suggest that primary nucleation and competition between l- and d-nuclei were considered to be a mechanism for asymmetry amplification. High-performance capillary electrophoresis coupled with laser-induced fluorescence was used to separate and quantify l- and d-asparagine and the enantiomeric excess value can be calculated according to their concentration.

Paraffin Deposition in a Stagnant Fluid Layer inside a Cavity Subjected to a Temperature Gradient

The deposition of high molecular weight paraffins on the inner wall of sub-sea production and transportation pipelines continues to be a critical operational problem faced by the petroleum industry. The accumulation of the deposited material on the inner wall of the lines may lead to increased pumping power, decreased flow rate, or even the total blockage of the line, with an accompanying loss of production and capital investment. In the present work, a critical review of the literature on wax deposition was conducted and concluded that there is not enough experimental evidence to determine which are the relevant mechanisms responsible for wax deposition. Based on the findings of the literature search, a research program was initiated with the aim of identifying the relative importance of the wax deposition mechanisms. To this end, simple, basic experiments were designed and complemented by numerical simulations. The present paper is part of this ongoing research program and reports on experiments on deposition in cavities containing a stagnant solution of paraffin and solvent and submitted to a transverse temperature gradient. The experiments yielded temporal distributions of paraffin deposits. A molecular diffusion-based model underestimated the evolution of the deposit thickness for the stagnant cavity. The results obtained were not sufficient to corroborate the widely accepted hypothesis that the wax deposition process is controlled by molecular diffusion.

Interaction between Taylor bubbles rising in stagnant non-Newtonian fluids

The interaction between Taylor bubbles rising in stagnant non-Newtonian solutions was studied. Aqueous solutions of carboxymethylcellulose (CMC) and polyacrylamide (PAA) polymers were used to study the effect of different rheological properties: shear viscosity and viscoelasticity. The solutions studied covered a range of Reynolds numbers between 10 and 714, and Deborah numbers up to 14. The study was performed with pairs of Taylor bubbles rising in a vertical column (0.032 m internal diameter) filled with stagnant liquid. The velocities of the leading and trailing bubbles were measured by sets of laser diodes/photocells placed along the column. The velocity of the trailing bubble was analysed together with the liquid velocity profile in the wake of a single rising bubble (Particle Image Velocimetry data obtained from the literature). For the less concentrated CMC solutions, with moderate shear viscosity and low viscoelasticity, the interaction between Taylor bubbles was similar to that found in Newtonian fluids. For the most concentrated CMC solution, which has high shear viscosity and moderate viscoelasticity, a negative wake forms behind the Taylor bubbles, inhibiting coalescence since the bubbles maintain a minimum distance of about 1 D between them. For the PAA solutions, with moderate shear viscosity but higher viscoelasticity than the CMC solutions, longer wake lengths are seen, which are responsible for trailing bubble acceleration at greater distances from the leading bubble. Also in the PAA solutions, the long time needed for the fluid to recover its initial shear viscosity after the passage of the first bubble makes the fluid less resistant to the trailing bubble flow. Hence, the trailing bubble can travel at a higher velocity than the leading bubble, even at distances above 90 D.

Electrochemical Behavior of AISI 304SS with Particulate Silica Coating in 0.1 M NaCl

This paper presents electrochemical behavior of AISI 304 stainless steel with a silica layer in a stagnant bulk solution of NaCl. Layers composed of densely packed diam silica particles were deposited cathodically on stainless steel at a constant voltage by electrophoretic deposition (EPD). Quite smooth and crack-free silica layers less than about in thickness were obtained and the thickness of the layer depended linearly on the deposition time. It is proposed that silica layers deposited by EPD can be used as simulated particulate layers to investigate localized corrosion of corrosion-resistant alloys under atmospheric environments. Electrochemical properties of silica-coated stainless steel samples in NaCl were investigated. The cathodic polarization behavior depended on the thickness of the silica layer; the limiting current density for oxygen reduction reaction decreased with increasing silica layer thickness. The effect of the silica layer on anodic polarization behavior was not remarkable.

Voltammetric Measurements at the Surface of Cotton: Absorption and Catalase Reactivity of a Dinuclear Manganese Complex

Voltammetric measurements at the surface of cotton fabric were conducted after impregnating the surface of the textile with graphite flakes. The resulting conducting surface contact was connected to a conventional basal plane pyrolytic graphite substrate electrode and employed both in stagnant solution and in rotating disc voltammetry mode. Diffusion through the immobilized cotton sample (inter-fiber) is probed with the aqueous Fe(CN)6(4-/3-) redox system. With a small amount of platinum immobilized at the cotton surface, catalase reactivity toward hydrogen peroxide was observed and used to further quantify the diffusion (intra- and inter-fiber) into the reactive zone at the graphite-cotton interface. A well-known catalase model system, the dinuclear manganese metal complex [Mn(IV)2(micro-O)3L2](PF6)2 (with L=1,4,7-trimethyl-1,4,7-triazacyclononane), is investigated in aqueous 0.1 M carbonate buffer at pH 9.8 in contact with cotton fabric. Absorption of the metal complex is monitored and quantified by voltammetric methods. A Langmurian binding constant of approximately K=2x103 M-1 was determined. Voltammetric measurements of the adsorbed metal complex reveal strong absorption and chemically irreversible reduction characteristics similar to those observed in solution. In the presence of hydrogen peroxide, catalyst coverage dependent anodic catalase activity was observed approximately following the rate law rate=k[catalyst]surface[H2O2]solution and with k=3x104 dm3 s-1 mol-1. The catalyst reactivity was modified by the presence of cotton.

Growth and ion relations in response to combined salinity and waterlogging in the perennial forage legumes Lotus corniculatus and Lotus tenuis

Lotus tenuis (Wadst. & Kit.) is a perennial legume widely grown for pasture in the flood-prone and salt affected Pampa region of Argentina. The physiology of salt and waterlogging tolerance in L. tenuis (four cultivars) was evaluated, and compared with Lotus corniculatus (three cultivars); the most widely cultivated Lotus species. Overall, L. tenuis cultivars accumulated less Na+ and Cl−, and more K+ in shoots than L. corniculatus cultivars, when exposed to 200 mM NaCl for 28 days in aerated or in stagnant solutions. Root porosity was higher in L. tenuis cultivars due to greater aerenchyma formation. In a NaCl dose–response experiment (0–400 mM NaCl in aerated solution), L. tenuis (cv. Chaja) accumulated half as much Cl− in its shoots than L. corniculatus (cv. San Gabriel) at all external NaCl concentrations, and about 30% less shoot Na+ in treatments above 250 mM NaCl. Ion distributions in shoots were determined for plants at 200 mM NaCl. L. tenuis (cv. Chaja) again accumulated about half as much Cl− in old leaves, young leaves and stems, compared with concentrations in L. corniculatus (cv. San Gabriel). There were not, however, significant differences between the two species for Na+ concentrations in the various shoot tissues. The higher root porosity, and maintenance of lower shoot Cl− and Na+ concentrations in L. tenuis, compared with L. corniculatus, contributes to the greater tolerance to combined salt and waterlogging stress in L. tenuis. Moreover, significant variation for tolerance to combined salinity and waterlogging stress was identified within both L. tenuis and L. corniculatus.

Corrosion of 304L stainless steel and chrome-plated drainage together with the ordinary black rubber and brass gaskets by stagnant solutions of sodium hypochlorite solutions

This paper presents the results of corrosion of 304L stainless steel sink, chrome-plated waste/drainage, brass and ordinary black rubber gaskets and putty by stagnant solutions of sodium hypochlorite. Three sets of experiments ( Case A, Case B and Case C) were performed. In each experiment four 500 ml beakers were labeled solution 1, solution 2, solution 3 and solution 4. Each beaker contained a solution of sodium hypochlorite, a chrome-plated drainage (with ordinary black rubber and brass gaskets), and a sample of the 304L stainless steel cut from a 304L stainless steel domestic sink. For the cases (Case A and Case C) where the chemical resistance of the putty was tested another set of four beakers labeled solution 1, solution 2, solution 3 and solution 4 were used for the putty samples. Two sets of four concentrations were used. The concentrations considered were: Case A: 50 ml of sodium hypochlorite solution per litre of water, 40 ml of sodium hypochlorite per litre of water, 30 ml of sodium hypochlorite per litre of water and 20 ml of sodium hypochlorite per litre of water. The other set of concentrations used were: Case B and C: 50 ml of sodium hypochlorite per 5 l of water, 40 ml of sodium hypochlorite per 5 l of water, 30 ml of sodium hypochlorite per 5 l of water and 20 ml of sodium hypochlorite per 5 l of water. In the Case B experiments the solutions in the beakers were replaced with freshly prepared ones every two days during the observation of the samples. All the experiments were run at room temperature for 30 days. Case A: The results show that highly concentrated stagnant solutions of sodium hypochlorite corrode the chrome-plated waste/drainage, the brass gasket and dissolve the ordinary black rubber and the putty used to hold the chrome-plated waste/drainage in place. Case B: The formation of black/blue deposit was noted on the threaded part of all the chrome-plated waste/drainage in each of the four beakers. The amount of deposits formed increased with the duration of experiment. The changing of the solution every two days increased the amount of deposits formed. The ordinary black rubber gaskets were chemically resistant to all the solutions. Case C: Peeling off of chrome plating (from inside the chrome-plated waste/drainage) was observed in all of the beakers during the initial stage of the experiment and black deposits appeared on the top surface of the chrome-plated waste/drainage. The ordinary black rubber gaskets were chemically resistant to all the solutions. The putty samples became slightly blackish in all the four solutions. The 304L stainless steel sink sample did not corrode in all the solutions.

Morphological and physiological responses of rice (Oryza sativa) to limited phosphorus supply in aerated and stagnant solution culture.

Rain-fed lowland rice commonly encounters stresses from fluctuating water regimes and nutrient deficiency. Roots have to acquire both oxygen and nutrients under adverse conditions while also acclimating to changes in soil-water regime. This study assessed responses of rice roots to low phosphorus supply in aerated and stagnant nutrient solution. Rice (Oryza sativa 'Amaroo') was grown in aerated solution with high P (200 micro m) for 14 d, then transferred to high or low (1.6 micro m) P supply in aerated or stagnant solution for up to 8 d. After only 1 d in stagnant conditions, root radial oxygen loss (ROL) had decreased by 90 % in subapical zones, whereas near the tip ROL was maintained. After 4 d in stagnant conditions, maximum root length was 11 % less, and after 8 d, shoot growth was 25 % less, compared with plants in aerated solution. The plants in stagnant solution had up to 19 % more adventitious roots, 24 % greater root porosity and 26 % higher root/shoot ratio. Rice in low P supply had fewer tillers in both stagnant and aerated conditions. After 1-2 d in stagnant solution, relative P uptake declined, especially at low P supply. Aerated roots at low P supply maintained relative P uptake for 4 d, after which uptake decreased to the same levels as in stagnant solution. Roots responded rapidly to oxygen deficiency with decreased ROL in subapical zones within 1-2 d, indicating induction of a barrier to ROL, and these changes in ROL occurred at least 2 d before any changes in root morphology, porosity or anatomy were evident. Relative P uptake also decreased under oxygen deficiency, showing that a sudden decline in root-zone oxygen adversely affects P nutrition of rice.

Comment on “Theorems of Electrochemical Mass Transport in Dilute Solutions of Mixtures of Electrolytes Including Weak Electrolytes and Hydrolysis Reactions” [ J. Electrochem. Soc. , 152 , E282 (2005)

In corollary 1 of theorem 7, the author states, “In an isothermal, stagnant, and dilute electrolytic solution of a mixture of neutral strong electrolytes, without chemical reactions and with one-dimensional mass transport, the electrochemical mass transport at steady state is characterized by linear concentration distribution for all species.”

Microfluidic voltammetry: simulation of the chronoamperometric response of microband electrodes sited within microreactors

A computationally efficient fully implicit approach to the simulation of the chronoamperometric response of microband electrodes sited within microscale rectangular ducts is reported. The current response is reported for stagnant solution and where electrolyte is pumped through the cell under microfluidic control. The generality of the method is illustrated with reference to the simple case of a reversible one-electron-transfer reaction. The influence of flow rate and the effects of axial, lateral and normal diffusion upon the electrolysis current are examined and the results compared to approximate analytical behaviour where appropriate.