Solutions Of Various Concentrations Research Articles

Microscopic Raman-based rapid detection of submicron/nano polypropylene plastics in tea and tea beverages

Polypropylene (PP) is suitable for a broad range of applications and represents the most extensively utilized plastic in food packaging. Micro- and nano-PP plastics are prevalent categories of microplastics (MPs). However, the majority of MPs particles currently utilized in laboratory studies are man-made polystyrene (PS) spheres, and there has been limited research on micrometer- and nanoscale PP plastic particles. This study aims to employ a top-down approach in crafting micro/nanoparticle (M/NPs) models of PP particles, ensuring their enhanced relevance to real-world environments. Micro/nano PP particles, featuring a negatively charged particle size ranging from 203 to 2101 nm, were synthesized through variations in solution concentration and volume. Simultaneously, the devised MPs model was employed to develop a Raman-based qualitative and quantitative detection method for micro/nano PP particles, considering diverse sizes and concentrations. This method integrates Raman spectroscopy and microscopy to measure PP particles with varying sizes, utilizing the coffee ring effect. The Limit of detection (LOD) for 203 nm PP reached 31.25 μg/mL, while those for 382–2101 nm PP were approximately 3.9 μg/mL. The method underwent quantitative analysis by introducing 203 nm PP nanospheres into real food media (i.e., tea beverages, tea leaves), revealing a minimum LOD of approximately 31.25 μg/mL.

Development of products with extended shelf life

The goal of the research is to evaluate the flavor and rheological compositions formed in the process of structuring gel-like solutions of various concentrations into individual processes of the technological scheme for the production of semi-finished products and complex interaction in the structure of the finished product, taking into account the use of gelling agents and dietary supplements. The article presents some features of the flow of physicochemical reactions that make it possible to describe the dynamics of the interaction of nutrients in the formed binary compositions of carbohydrate-fat structures of plant systems in the technological process.Methods. To carry out the tests, the potentiometric method was used and the pH of each sample was determined using the Expert-001-3pH device. Determinations of sugars were carried out according to GOST 8756.13-87 using the permanganate method; dry substances according to GOST 31640-2012; organoleptic assessment according to GOST ISO 6658–2015. Samples of semi-finished products containing 25–30% fruit and citrus juices, 0.1–0.5% freeze-dried aromatic plants, 0.3–0.5% berry or vegetable powders, 0.3–0.6% spices were the objects of the research.The results. It has been established that the use of cellulose and glycerin in the formulation of carbohydrate-fat binary compositions based on fruit, citrus juices, berry or vegetable powders and spicy-aromatic raw materials contributes to the formation of an elastic, delicate film structure and a complex of flavoring and aromatic substances, depending on the type of raw materials and VAD used. With an increase in the concentration of cellulose, the films become denser, and in combination with the main raw materials (juice, powders, spices), the amount of dry substances and extract content increase, the films become opaque and less elastic. It has been found that in all samples, with an increase in spicy-aromatic raw materials, the number of inclusions increases and the films acquire a mosaic appearance. For clarity of experiments, graphs of the dependence of the type of main raw material and VAD on the concentration of the recipe composition and the formation of the flavor and aromatic range have been presented.Conclusion. The experimental data and dependencies obtained will be useful when considering more complex processes of mass transfer, sucrose inversion, and destruction of protein-carotenoid complexes. The perception of flavor and density of edible films is complex: the balance between sweetness, extractivity and threshold values of sensory characteristics are the main criteria for the organoleptic quality of the films being developed. It increases with the concentration of VAD and the type of juices or powders used. A richer and more pronounced taste appears.

Enhancing sensitivity of trace copper detection based on coupled optoelectronic oscillator

We propose to employ coupled optoelectronic oscillator (COEO) for trace copper detection to achieve an enhanced sensitivity and stability. By replacing the optical source of the traditional OEO with an optical feedback loop, the oscillation frequency is determined by the cavity loop length in conjunction with the laser output wavelength. The sensing head, which is fabricated by inserting a fusion spliced fiber with large lateral offset fusion splicing in a Sagnac loop, act as a wavelength selection component in the laser loop. Hence, the oscillation frequency changes with the varying solution concentration. Benefitting from the matching of the laser loop and the OEO loop, the final oscillation mode is more stable. By comparing the performance of the COEO-based, single-loop and dual-loop OEO-based sensors, the highest sensitivity of 41.1 Hz/(uMol/L) is obtained by the COEO-based sensor. Since the positive feedback of two loops, the single mode oscillation can be implemented without additional devices.

COMPLEXATION OF IRON(III) WITH TSC AND FTSC IN H2SO4 SOLUTIONS OF VARIABLE COMPOSITION

The process of complex formation of iron (III) with thiosemicarbazide and 1-formyl-3-thiosemicarbazide in H2SO4 solutions of various concentrations was studied using the potentiometric method. The stability constants of the resulting complexes were calculated, and the ionization constants of the ligands were estimated under the same conditions. It was shown that the stepwise nature of complex formation does not depend on the concentration of hydrogen ions. However, the stability of the complexes decreases with increasing pH. A study of the complex formation of iron(III) with thiosemicarbazide and its acyl derivative showed that there are both similarities and differences in the nature of complex formation. Both ligands react with iron(III) in a stepwise manner, forming stable complexes. With increasing temperature, the stability of the complexes increases. Changing the ionic strength of the solution and the concentration of H2SO4 equally affect the stability of the complexes. At the same time, moving from thiosemicarbazide to 1-formyl-3-thiosemicarbazide, the number of particles formed in the solution decreases, and the stability of the complexes decreases.

Identification of lubricant viscosity to minimize the frictional impact of colonoscopy on colonic mucosa

Applying a lubricant to the colonic mucosa and reducing the dynamic friction coefficient (DFC) between the endoscopic shaft and colonic mucosa may reduce colonoscopy invasiveness. However, the ideal lubricant viscosity remains unknown. Here, we developed a DFC measurement model integrating samples of colonic mucosa from forensic autopsy specimens into a simulated bowel bend and determined the low-friction lubricant viscosity that minimizes the DFC. Carboxymethyl cellulose, xanthan gum, hydroxyethyl cellulose, sodium alginate, and sodium polyacrylate aqueous solutions of various concentrations were used as lubricants. Low-friction lubricants minimized the load on the colonic mucosa during colonoscope insertion and reduced the total endoscopy insertion time. The highest correlation was between the DFC and the lubricant viscosity at a shear rate of 100 1/s. The lowest DFC was almost constant at approximately 0.09, irrespective of the chemical composition of the lubricant, and the low-friction lubricant viscosity (100 1/s) was 0.031–0.086 (median: 0.059). The viscosities of conventional colonoscopic lubricants were suitable for lubricating the anorectal skin owing to their low DFC, but too high for lubricating the colonic mucosa because of their high DFC. The utilization of the low-friction lubricants with the optimal viscosity can reduce the stress on colonic mucosa during colonoscopy.

Reinforcement of nanostructured polyacrylamide hydrogels through the generation of secondary physical network using the nanoparticles’ functional groups

The main drawback regarding hydrogels utilization in biomedical engineering is represented by their weak mechanical properties and it is often addressed either by using nanospecies as fillers or by generating secondary networks that strengthen the material. Our study validates a new synthesis route of obtaining double-network nanostructured materials making use of the functional groups of an adsorbed glyco-protein on carbon-based nanospecies. Following a simple procedure, the decorated nanospecies were embedded in a synthetic polymer and subsequently formed a secondary hydrogen-bond based network through incubation in natural polyphenol solutions of various concentrations. The natural macromolecule's adsorption was evaluated through FTIR and DLS measurements. When compared to the single-network nanostructured materials, the double-network hydrogels exhibited lower affinity to aqueous media and improved ability to dissipate energy upon mechanical stress, depending on the amount of the employed natural crosslinker. As a result of generating the second network through incubation in polyphenol aqueous solution, the surface storage and loss moduli exceed the values of the bulk ones, as indicated by rheology and nanoindentation tests. The properties of the double-network hydrogels can also be tailored towards more hydrophilic surfaces with increased roughness through the control of the supplementary crosslinker amount. Considering the studied physical-chemical properties, and especially their mechanical characteristics, the obtained materials hold great promise for biomedical applications, particularly for the fabrication of scaffolds for wound dressing, soft or low load bearing tissue regeneration and repair.

Optical activity of trans-4-hydroxy-L-proline in sodium chloride solutions

The optical activity oftrans-4-hydroxy-L-prolinein deionized water and sodium chloride solutions of various concentrations has been investigated through polarimetry. The specific rotation of thecompounddecreases in the magnitude in solutions with the salt concentration of 0 to 2.000 Mbut does not change significantly in the concentration range of 2.500 to 3.500 M. The specific rotations at the salt concentrations from 4.000 to 5.000 M are smaller in the magnitude and do not vary significantly. Theconcentration dependence is explained basedon thecorrelation between the specific rotation and the square root of the solutiondielectric constant.

Приготовление растворов различной концентрации

When preparing treatment solutions of fertilizers and pesticides for technological processes, one should mix liquids taking into account the precise dosing of components. However, the existing designs of dosing and mixing devices do not provide qualitative dosing. Moreover, a sharp increase of fraction quantity may result in a hydraulic impact. To eliminate these disadvantages, based on analytical research of available designs and patent search results, the authors worked out a mixer for preparing solutions of various concentrations. The device is also capable of changing the ratio of components in the process of operation. The device provides smooth change of preparation concentrations due to the design of dosing valves forming square-shaped ports with a changing configuration. The port plates move relative to each other both horizontally and vertically. The proposed device smoothly changes the concentration of the solution, thereby providing for more accurate dosing. It was experimentally found that a smoother change in the flow rate of treatment liquid according to the solution concentration is observed at a distance from the axes of symmetry of the dosing device disks to the rotation axis of the distribution ports, equal to 0.04 to 0.1 m. The deviation of the actual treatment liquid flow rate from the calculated one does not exceed 5%. The integration of the developed mixer into the systems of fertigation units, sprayers and other specialized machines will ensure better quality of the fine irrigation of plants, seeds, and soil.

Optimization of Chromium (VI) Adsorption using Microalgae Biomass (Spirulina sp.) and its Application in Leather Tannery Waste

<p class="E-JOURNALAbstractBodyEnglish">This study was conducted to examine the adsorption of Cr (VI) metal using Spirulina sp (inactive) biomass and its application in leather tannery wastewater. The treatment was carried out to determine the influence of independent variables on Cr (VI) adsorption with variations in pH, contact time, and metal solution concentration. The values of the solution pH, adsorption time, and concentration of the best metal solution were used to determine the center points of the optimization variables through Response Surface Methodology (RSM). The results showed that based on the FTIR test, macromolecules present in Spirulina sp biomass included amino, carboxylate, and hydroxy groups. The combination of factor variables that produced the optimum response was at pH 3.165, contact time of 66.58 minutes, and Cr (VI) metal ion solution concentration of 22.9 mg/L, resulting in a Cr (VI) adsorption efficiency of 69.66%. The adsorption pattern was included in the Freundlich adsorption isotherm, and the application of Spirulina sp biomass adsorbent to tannery waste reduced the concentration of Cr (VI) from 3.9 g/L to an undetectable level at <1.4 g/L.</p>

Corrosion and Protection of Synthetic Intermetallic Compounds and Bulk Aluminum Alloy Under Simulated Atmospheric Conditions

Aluminum alloy 7075-D6 is often used for aircraft parts and is thus exposed to atmospheric conditions. AA7075-D6 is susceptible to corrosion due to high Zn, Mg and Cu contents in the form of various intermetallic particles having more or less noble electrochemical potential regarding the matrix (1,2). Usually, corrosion of aluminum alloys is simulated using solutions of various concentrations of chloride ions. However, aircraft are exposed to atmospheric conditions, where Cl- is not the only pollutant. Namely, in industrial and urban areas, major inorganic species such as ammonium (NH4 +), sulfate (SO4 2−) and nitrate (NO3 −) ions are found in the form of NH4NO3 and (NH4)2SO4 (or NH4HSO4). Therefore, these should also be considered because they represent corrosive agents for many aluminum alloys (3). Corrosive conditions may be thus better simulated by the so-called dilute Harrisonʼs solution (DHS) (0.35 wt.% (NH4)2SO4 + 0.05 wt.% NaCl), which in addition to Cl− also contains SO4 2− and nitrate NO3 − reflecting the environmental and atmospheric conditions. The first part of our study was focused on the corrosion of AA7075-T6 in DHS and comparison with NaCl solution. In addition to AA7075-T6, major intermetallic compounds (IMCs) synthesized in bulk form to represent the major intermetallic constituents (Al2Cu, Al2CuMg, Al7Cu2Fe and MgZn2) were also investigated. For IMCs, electrochemical measurements were performed using a microcell, and a standard cell was used to study the bulk alloy.Bulk AA7075-T6 was less susceptible to corrosion in DHS than in chloride solution stemming from the beneficial presence of sulfate ions and lower chloride concentration. The susceptibility of IMCs to corrosion in DHS increased as Al2Cu < Al7Cu2Fe < Al2CuMg < MgZn2 due to the increased dissolution of Mg in the presence of ammonium ions. The relative nobility of IMCs was determined based on the galvanic current density.In the second part of our study, we addressed the role of cerium salts in the corrosion protection of AA7075-T6 in DHS. Cerium salts are non-toxic compounds and demonstrate corrosion inhibition by inhibiting redox reactions by forming a protective cerium-containing precipitated conversion layer (4). Ce salts acted as inhibitors for the alloy during 14-day testing, forming a Ce hydroxide layer. The degree of protection depended on the type of anion, being the highest for Ce acetate. For the IMC, however, inhibition by Ce salts did not occur during short measurements, indicating the importance of galvanic interaction with the alloy matrix in the inhibition, which was confirmed by long-term measurements of the alloy. Micro and macro approaches give essential information on the galvanic relation between the IMPs and Al matrix under different conditions in the presence and absence of different cerium salts or other inhibitions (5). This brought about valuable information concerning corrosion inhibition and synergism with other ions in the corrosion media. Figure. Schematic presentation of (a) effect of various anions (NH4 +, SO4 2 - and Cl-) in dilute Harrison’s solution, and (b) effect of cerium(III) cations and corresponding anions (Cl-, NO3 - and CH3COO-) on the surface of AA7075-T6. Corrosion inhibition due to the deposition of the cerium layer is presented in (c). The precipitation of Ce species proceeds mainly on the cathodic sites and progressively spreads over the alloy surface; meanwhile, the Mg and Al are slowly dissolved from the anodic sites.

The Effect of electrolyte concentration and temperature at electroplating with copper on the plate thickness and corrosion rate of plated gray cast iron

This study aims to determine the effect of variations in electrolyte solution concentration and copper electroplating temperature on gray cast iron to achieve the desired copper layer thickness and reduce the corrosion rate of gray cast iron impeller pumps. A total of 30 test specimens made from gray cast iron were used, with dimensions conforming to the ASTM G31-72 standard for corrosion rate testing. The specimens were coated with copper electroplating using three different solutions: solution 1 (195 g/L copper sulfate, 45 g/L sulfuric acid), solution 2 (205 g/L copper sulfate, 50 g/L sulfuric acid), and solution 3 (215 g/L copper sulfate, 55 g/L sulfuric acid). Each solution was used with dipping temperatures of 30 – 34 °C, 40 – 44 °C, and 50 – 54 °C. After being coated with copper, the layer thickness was measured using a digital coating thickness gauge (F&amp;NF type). The corrosion rate was then tested using the weight loss method, following the ASTM G31-72 standard, by immersing the specimens in seawater for 240 hours. The test results showed that the highest average thickness was achieved with solution 3 and a plating temperature of 50 – 54 °C, measuring 27.46 μm. The lowest average thickness was with solution 1 and a plating temperature of 30 – 34 °C, measuring 26.23 μm. The lowest corrosion rate was observed with solution 3 and a plating temperature of 50 – 54 °C, at 0.0041 mmpy, whereas the highest corrosion rate was found with solution 1 and a plating temperature of 30 – 34 °C, at 0.0079 mmpy. For comparison, the average corrosion rate of uncoated specimens was 2.2947 mmpy.

Role of magnesium acetate in hydration and carbonation of magnesium oxide-based cements

MgO-based cements have the potential for low carbon binders especially when MgO is sourced from non‑carbonate minerals. Understanding the reaction kinetics and products formed are the keys to pave the way for these binders as construction materials. In this study, the influence of acetate on hydration and subsequent carbonation of reactive MgO is investigated. MgO hydrated in Mg-acetate solution of various concentrations (0 to 0.5 M) and CO2 cured afterward was characterized at different reaction times. Magnesium acetate in addition to enhancing the hydration kinetics modifies the morphology and crystallinity of the precipitated brucite. Acetate also influences the carbonate phases formed when samples are cured with CO2. Giorgiosite, a lesser-known hydrated magnesium carbonate, was formed in the presence of acetate, while the control specimens prepared with neat water produced nesquehonite. The findings reported here give insights into the use of organic additives in improving the reaction kinetics of MgO and the possibility to tune the formation pathways of different magnesium carbonates.

Modeling the flux of volatile fatty acid in a membrane distillation with the effect of pH

This study aims to develop a mathematical model to estimate the initial flux of volatile fatty acids (VFAs) in the direct contact membrane distillation (DCMD) process. VFAs are toxic and emit odors. However, they have recently been recognized as valuable raw materials. Water and VFAs can be separated together using membrane distillation (MD). Water vapor and volatile compounds can pass through the membrane pores. They move toward the permeate side. Flux occurs not only for water but also for VFAs in DCMD process due to the volatility of VFAs. Parameters affecting the flux of VFAs were identified. Their relationship was confirmed experimentally. Acetic acid, butyric acid, and valeric acid were selected as target compounds because they have different Henry's constants and hydrophobicity. The ionization of acid solution varies depending on pH. MD tests were performed under various pH conditions. The flux of VFAs was observed to vary depending on the pH. The flux of VFAs was found to be proportional to the ionization fraction (α0) of the feed solution. Therefore, the model was developed to reflect the ionization fraction. An empirical formula was derived to predict the flux of VFAs using experimental data. A statistical analysis supported that the flux predicted by the model fitted very well with the observed flux. Additionally, experiments were performed with acid solutions of various concentrations. The concentration range applicable to the derived empirical formula was validated. The developed model can provide further insight into the relationship between flux and pH.

The effect of temperature on permittivity measurements of aqueous solutions of glucose for the development of non-invasive glucose sensors based on electromagnetic waves

This article presents for the first time an empirical study that shows the importance of considering temperature when analyzing the permittivity (dielectric constant) of aqueous glucose solutions of various concentrations. The permittivity is a parameter that is investigated by researchers as a biomarker for non-invasive measurement of glucose without drawing blood. The development of this technology will allow personalized healthcare diagnostics to monitor and prevent diabetes. Since human glucose levels in the blood vary in the range of a few milligrams per decilitre, estimating such small variations of glucose will require a highly accurate and repeatable sensing technology. Electromagnetic (EM) waves, specifically in the microwave and terahertz frequency ranges, have shown promise in detecting changes in the electrical properties of blood plasma as they relate to glucose concentration. However, it's important to note that while this technology shows promise, it is still in the research and development phase. It is shown here that the body temperature can affect the accuracy of the blood glucose measurements. Experiments were conducted with different glucose concentration solutions under various temperatures and the complex permittivity of the glucose was studied across a wide frequency range from 400 MHz to 11 GHz. The rise in thermal energy normally causes dipolar liquids like water to vibrate and rotate disrupting the alignment of the dipoles in response to an electric field thereby reducing its permittivity. Empirical results however show that for aqueous solution of glucose the permittivity increases with rise in temperature from 16 °C to 37 °C. This is attributed to the polar nature of the water and glucose molecules that becomes more pronounced with increased thermal energy. Based on the experimental results an accurate analytical expression is derived that considers the temperature of the aqueous glucose solution. The accuracy of the analytical expression is shown experimentally to be above 99%. The findings from the study should enable the design of accurate non-invasive glucose monitoring devices based on electromagnetic sensing techniques.

Effect of Natural Dye on the Spectral Response of the Heterojunction Ag/ZnO/Ps/Si/Ag for Photodetector Application

Zinc oxide and dye are utilized to absorb and convert incident photons to electric energy using a sandwich construction with an active area of 1.5 × 1.5 cm2, which improves the photodetector’s performance as a light sensor. A variable variation of solution concentration according to the ratio of mass and volume was used to extract natural dye from Barago officinalis. The Barago officinalis absorbance was investigated by spectrophotometer at a wavelength of 200–1000 nm. This indicates that UV absorption has occurred, and note that when an increase in the spectral response at concentration of 1, there appears an improvement in the infrared region with a wave length of 950 nm and the enhanced sensitivity in the long wavelength region could be attributed to formation of dye aggregates within the devices which led to the highest value of qualitative detection up to 1.3 × 10[Formula: see text] W[Formula: see text] cm Hz[Formula: see text] thus increasing quantum efficiency to (119)% at the wavelength (950 nm).

Structure and diffuseness model of solid-liquid interface for binary alloys

Using the morphological instability at the solid–liquid interface as a basis by the maximum entropy production rate principle (MEPR), a model is presented on the morphological structure and diffuseness of the interface during directional solidification of binary alloys. It is shown that, the independent diffuseness theory of Cahn and the Jackson roughness criterion can be unified at a limiting condition under this new MEPR solidification model. The model under the principle of MEPR is applied to describe the evolution of atomistically smooth and rough interfaces through the evaluation of the size of the solid–liquid interface and the of number atomic layers. The model is tested with data for binary alloys of aluminium, lead, and tin at varying solute concentrations. The results showed strong agreement with available data from experimental measurements.

Chitosan Sponges for Efficient Accumulation and Controlled Release of C-Phycocyanin.

The paper proposed a new porous material for wound healing based on chitosan and C-phycocyanin (C-PC). In this work, C-PC was extracted from the cyanobacteria Arthrospira platensis biomass and purified through ammonium sulfate precipitation. The obtained C-PC with a purity index (PI) of 3.36 ± 0.24 was loaded into a chitosan sponge from aqueous solutions of various concentrations (250, 500, and 1000 mg/L). According to the FTIR study, chitosan did not form new bonds with C-PC, but acted as a carrier. The encapsulation efficiency value exceeded 90%, and the maximum loading capacity was 172.67 ± 0.47 mg/g. The release of C-PC from the polymer matrix into the saline medium was estimated, and it was found 50% of C-PC was released in the first hour and the maximum concentration was reached in 5-7 h after the sponge immersion. The PI of the released C-PC was 3.79 and 4.43 depending on the concentration of the initial solution.

A benchmark for variably saturated variable-density variable-viscosity flow and solute transport in porous media

In natural environments, fluid density and viscosity can be affected by spatial and temporal variations of solute concentration, for example, due to saltwater intrusion in coastal aquifers, leachate infiltration from waste disposal sites, and upconing of saline water from deep aquifers. Potentially unstable situations may arise in which a dense fluid overlies a less dense fluid. This situation can produce instabilities manifested by dense plume fingers moving vertically downwards counterbalanced by vertical upward flow of the less dense fluid. The resulting free convection increases solute transport rates over large distances and times relative to constant-density flow. Unstable brine flow is further complicated if the porous medium is variably saturated. The results from a laboratory experiment of variably saturated variable-density flow and solute transport from Simmons et al. (2002) are used as the physical basis to define a new mathematical benchmark. This benchmark aims at realistically reproducing the experimental fingering patterns. Random hydraulic conductivity fields were used in the simulations as a numerical perturbation method to realistically mimic the observed dense plume fingering. The HydroGeoSphere code coupled with PEST are used to calibrate the parameter set that defines the benchmark. A grid convergence analysis is performed to obtain the adequate spatial and temporal discretizations. The new mathematical benchmark is useful for model comparison and testing of variably saturated variable-density flow in porous media. Simmons CT, Pierini ML, Hutson JL (2002) Laboratory investigation of variable-density flow and solute transport in unsaturated–saturated porous media. Transp Porous Media. 47(2): 215–244, 10.1023/A:1015568724369.

Concentration‐Discharge Patterns Reveal Catchment Controls Over the Stoichiometry of Carbon and Nutrient Supply to Boreal Streams

AbstractCarbon (C), nitrogen (N), and phosphorus (P) export from catchments is strongly regulated by interactions between hydrological flowpaths and their terrestrial use/storage. While concentration‐discharge (c‐Q) relationships have been widely used to understand this interplay for C, N, and P individually, how flow regulates the relative supply of these resources across spatial and temporal scales is not well documented. Here, we analyze c‐Q relationships from 12 years of data to test how seasonal flow regulates the concentrations of inorganic N (Dissolved inorganic nitrogen [DIN]) and P (Dissolved inorganic phosphorus [DIP]), dissolved organic N (DON) and C (dissolved organic carbon [DOC]) and their respective ratios across 12 streams in a boreal landscape. We observed opposing c‐Q relationships between organic and inorganic solutes. DOC and DON tended toward transport limitation with little year‐to‐year change, whereas ammonium (NH4) and DIP were increasingly source limited over time. These different c‐Q relationships translated into large (up to three‐fold) shifts in resource ratios (e.g., DOC:DIN) in response to changes in flow. Our results also highlight strong influences of catchment structure on c‐Q patterns, regardless of solute, season, and longer‐term directional changes. Here, the organic solute c‐Q responses became less transport limited over time; while inorganic solute responses became less source limited with increasing mire/decreasing forest cover. Overall, differences in timing of catchment exports for C, N, and P, create dynamic variation in solute concentrations in streams with subsequent impacts on resource stoichiometry that is central to aquatic ecological processes.

Curious Behavior of Fe3+-As3+ Chemical Interactions and Nucleation of Clusters in Aqueous Medium.

The simultaneous presence of Fe3+ and As3+ ions in groundwater (higher ppb or lower ppm level concentrations at circumneutral pH) as well as in acid mine drainages (AMDs)/industrial wastewater (up to few thousand ppm concentration at strongly acidic pH) are quite common. Therefore, understanding the chemical interactions prevalent between Fe3+ and As3+ ions in aqueous medium leading to nucleation of ionic clusters/solids, followed by aggregation and growth, is of great environmental significance. In the present work, we attempt to probe the nucleation process of Fe3+-As3+ clusters in solutions of various concentrations and pHs (from AMD to groundwater-like) using a combination of experimental and theoretical techniques. Interestingly, our study reveals nucleation of primary FeAs clusters in nearly all of them independent of concentration or pH. Theoretical studies employed density functional theory (DFT) to predict the primary clusters as stable Fe4As4 units. The surprising resemblance of these clusters with known Fe3+-As3+ minerals at the local level was observed experimentally, which provides an important clue about solid-phase growth from a range of Fe3+-As3+ solutions. Our experimental findings are further supported by a stepwise reaction mechanism established from detailed DFT studies.