Arrhenius Concept Research Articles

Energy Barriers for Steroid Hormone Transport in Nanofiltration.

Nanofiltration (NF) membranes can retain micropollutants (MPs) to a large extent, even though adsorption into the membrane and gradual permeation result in breakthrough and incomplete removal. The permeation of MPs is investigated by examining the energy barriers (determined using the Arrhenius concept) for adsorption, intrapore diffusion, and permeation encountered by four different steroid hormones in tight and loose NF membranes. Results show that the energy barriers for steroid hormone transport in tight membrane are entropically dominated and underestimated because of the high steric exclusion at the pore entrance. In contrast, the loose NF membrane enables steroid hormones partitioning at the pore entrance, with a permeation energy barrier (from feed toward the permeate side) ranging between 96 and 116 kJ/mol. The contribution of adsorption and intrapore diffusion to the energy barrier for steroid hormone permeation reveals a significant role of intrapore diffusive transport on the obtained permeation energy barrier. Overall, the breakthrough phenomenon observed during the NF of MPs is facilitated by the low energy barrier for adsorption. Experimental evidence of such principles is relevant for understanding mechanisms and ultimately improving the selectivity of NF.

CONCEPTUAL DIFFICULTIES OF SECONDARY SCHOOL STUDENTS IN UNDERSTANDING ACID-BASE CHEMISTRY

The dissemination of scientific knowledge has enormous transformative potential. As a result, a nation's progress and growth can't get off the ground without a solid foundation in scientific literacy. From this perspective, the education of science is crucial to cultivating a scientific worldview and boosting students' scientific knowledge. The motivation for this study stems from researchers' previous observations of secondary school students' conceptual difficulties in acid-base chemistry. The study used a descriptive, quantitative research approach to investigate common misconceptions about acid-base chemistry held by high school pupils. A special test instrument labelled as test designed to measure the conceptual difficulties in acid-base chemistry (TCDAB) was developed to measure the conceptual difficulties of secondary school students in Acid-Base chemistry. The Punjab Text Book Board, Lahore, version January 2020, 10th chapter Chemistry Text Book was used as a reference for the creation of the test (TCDAB). A table of the specification was used and was delimited to the first three levels of the cognitive domain of Bloom’s taxonomy. TCDAB has been validated by well-known chemists and educators. Test re-tests method was used to determine the reliability and the correlation coefficient (r) was 0.92. The internal consistency of the instrument was also evaluated using SPSS, and the resulting Cronbach alpha coefficient was 0.83. All the students studying chemistry in public secondary school of the district Bahawalnagar of the Punjab, Pakistan were population of this study (Dist. BWN consist of five tehsils which having total 250 schools). To conduct the survey of this study, a sample of 500 students from twenty (20) secondary schools, four (4) secondary schools (2 boys and 2 girls) from each five tehsils was selected by using the convenient sampling technique due to covid-19 in district Bahawalnagar city. The results of the analysis of TCDAB indicated that 60% concept-based items in acid-base chemistry were difficult like Arrhenius concept, Lowry Bronsted concept and Lewis Concepts, amphoteric compounds, conjugate acids and bases, chemical properties of acids and bases, concentration of acid base chemistry, strength of acid base chemistry, Uses of acids and bases, PH scale, and indicators. Keywords: Acid-base chemistry, conceptual difficulties, table of specification, cognitive domain

Durability of glass fiber-reinforced polymer bars conditioned in moist seawater-contaminated concrete under sustained load

The combined effect of sustained loading and moist seawater-contaminated concrete environment on the durability performance of two types of glass fiber-reinforced polymer (GFRP) bars was investigated. A sustained load of 25% of the ultimate tensile strength was applied to concrete-encased GFRP bars immersed in tap water for up to 15 months at temperatures of 20, 40, and 60 °C. None of the loaded specimens conditioned at 20 °C were creep-ruptured during conditioning. In contrast, many bars were creep-ruptured during conditioning at the higher temperatures of 40 and 60 °C. At a conditioning temperature of 20 °C, Type I and II GFRP bars retained 84 and 70% of their original tensile strength after 15 months of conditioning under a sustained load. At the higher temperature of 60 °C, trivial tensile strength retentions of 15 and 12% were recorded for Type I and Type II GFRP bars, respectively, after 15 months of conditioning under a sustained load. A comparative analysis between results of loaded and unloaded specimens demonstrated the detrimental effect of the presence of a sustained load during conditioning on the tensile strength retention of GFRP bars. The detrimental effect of the sustained load was intensified at the higher temperatures. The accelerated aging test data along with Arrhenius concept were employed to develop a durability design model that can predict the tensile strength retention of both types of GFRP bars in moist seawater-contaminated concrete.

Durability of glass fiber-reinforced polymer composites under the combined effects of moisture and sustained loads

This paper deals with durability of glass fiber-reinforced polymer composites under sustained loads and simultaneously exposed to either saltwater or tap water. The tensile properties of the specimens before and after conditioning were evaluated along with their moisture uptaking behavior to reveal the durability of the specimens under combined effects. The mass change curves under saltwater and tap water immersion exhibited dual-stage diffusion process. The first stage followed Fickian profile, while mass loss occurred in the second stage with increasing immersion time, attributed to hydrolysis of resin. The weight gain in saltwater was greater than that in tap water. Moreover, the mass change curves under varying percentage of sustained loadings exhibited similar trends, while the maximum moisture uptake was obviously affected by the loading conditions. Based on Fick’s second law, the diffusion coefficients in the first stage under different conditions were determined through the least-square regression technique. It was observed that the tensile strength and modulus were increasing initially upon immersion, which was attributed to curing beyond the initial cure during manufacture. Then, the tensile properties decreased with continued immersion in saltwater or tap water. After 180 days of immersion, the tensile properties degraded at a smaller rate, both for specimens with and without sustained loading. For the saltwater immersion of 360 days, the tensile properties decreased significantly as the sustained loading increased. However, the tap water immersion had less detrimental effect on tensile properties of glass fiber-reinforced polymer. Furthermore, based on Arrhenius concept coupled with fracture mechanics principle, a new model was proposed to describe the combined effects of immersion and sustained load.

Long-term durability prediction models for GFRP bars in concrete environment

This article presents a durability study of glass fiber reinforced polymer (GFRP) bars within concrete environment and provides recommendations for effective accelerated ageing methods, data reduction and validation, and formulation of master curves for long-term predictions. Concrete beams reinforced with GFRP bars were immersed in tap water inside temperature-controlled tanks. Sustained load was applied to beam samples, and elevated temperatures were used to accelerate the ageing of GFRP bars. After exposure, GFRP bars were tested for residual tensile strength, which was considered as a measure of the durability performance of the specimens. Scanning electron microscopy (SEM) images were used to evaluate the microstructural changes of conditioned specimens. Short-term (up to 270 days) results showed that compared to alkalinity and low sustained load, moisture and elevated temperature played much more important roles in accelerating environmental attack to GFRP bars. Based on the short-term test results, the dominant degradation mechanism for GFRP bars in concrete was found as the deterioration of fiber/matrix interface. A degradation model based on Arrhenius concept and prediction procedures are given, and correlations with other studies and field data are provided. The tensile strength retentions for GFRP bars in saturated concrete subjected to sustained load were predicted. It was found that degradation rates decreased rapidly, but tensile strength retentions at different exposure temperatures converge to a constant value with the increase of exposure time. Beyond fiber-matrix debonding, there is a possibility that other degradation mechanisms such as fiber corrosion may start to dominate the deterioration process of GFRP bars with time.

A new sensitive method of dissociation constants determination based on the isohydric solutions principle

The paper provides a new formulation and analytical proposals based on the isohydric solutions concept. It is particularly stated that a mixture formed, according to titrimetric mode, from a weak acid (HX, C 0 mol/L) and a strong acid (HB, C mol/L) solutions, assumes constant pH, independently on the volumes of the solutions mixed, provided that the relation C 0 = C + C 2 · 10 p K 1 is valid, where p K 1 = −log K 1, K 1 the dissociation constant for HX. The generalized formulation, referred to the isohydric solutions thus obtained, was extended also to more complex acid–base systems. Particularly in the (HX, HB) system, the titration occurs at constant ionic strength ( I) value, not resulting from presence of a basal electrolyte. This very advantageous conjunction of the properties provides, among others, a new, very sensitive method for verification of p K 1 value. The new method is particularly useful for weak acids HX characterized by low p K 1 values. The method was tested experimentally on four acid–base systems (HX, HB), in aqueous and mixed-solvent media and compared with the literature data. Some useful (linear and hyperbolic) correlations were stated and applied for validation of p K 1 values. Finally, some practical applications of analytical interest of the isohydricity (pH constancy) principle as one formulated in this paper were enumerated, proving the usefulness of such a property which has its remote roots in the Arrhenius concept.

Integral and differential cross sections of reactions relevant to astrochemistry

In recent years, kinetic experiments have shown that, contrary to the Arrhenius concept, many neutral-neutral reactions remain fast at very low temperature. Such behaviour ranks them as important processes to be considered in the chemical networks that model the synthesis and the fate of molecules observed in the interstellar medium. This Perspective Article aims to review complementary crossed beam experiments of relevant neutral-neutral reactions performed in the low collision energy regime. A few selected reactions are considered, with particular emphasis on carbon-atom reactions with unsaturated hydrocarbons. It is shown, with the example of the C + C(2)H(2) system, that the conjunction of kinetic and dynamic experiments can provide a consistent set of detailed rate coefficients for a multichannel reaction, relevant to astrochemical models.

What is the science? What have people instead of, and why do we need corrosiology?

People need a science comprehending both their and its own destination, universal, far-seeing, harmonizing the whole biosphere, and preventing from mistakes. It was such a science, Ya.M. Kolotyrkin has dreamt about, and such was its own ancient trend. However,... Having substantially accelerated its development and pragmatized it, the industrial revolution split it into a handy set of narrow-seeing weakly bound branches, and thus deprived them of panoramic sight and ability to distinguish between the essence and illusion. At first sight, everything is OK (especially after the Scientific-technological revolution that has illusively conquered crises): the science finds mineral deposits, discovers the ways of and teaches how to make something of them, invents and develops everything that fills our everyday life, serves and substitutes for us in industry, joins the continents, and so on. But in essence... this is the shortest way to the hell for our children’s children. We do pave it ourselves by exhausting the mines and wells so as if the mineral resources, which were created by the Supreme Intelligence (by means of the numerous past biospheres for billions of years!), do not have a price that hundreds and thousands times exceeds the market cost of everything we produce of them. By means of a thorough analysis, unbreakable semantic definitions of the basic triad of scientific categories Life, Science, and Verity are clarified. As an example of the quality of theories that are still in use, absolutely feebleness of the S. Arrhenius concept of electrolytic dissociation (which has stopped the development of electrochemistry for more than a century) is shown. The reunion and closest cooperation between the science and Church is the last chance for the man to get the True Science and Life!

Theoretical consideration of the general validity of the Equivalent Point Method in thermal process evaluation

The general validity of the Equivalent Point Method as an evaluation technique in thermal processing is considered. An analysis, based on analytical expressions for the impact of a heat treatment on food quality attributes indicates that the basic assumption of the methodology, i.e. a unique intersection point for a series of thermal reduction relationships, is only warranted theoretically for isothermal heating processes. Under time-variable temperature conditions, the difference between the impact on a target quality attribute calculated from the equivalent point and the impact evaluated directly from the temperature profile increases with increasing deviation from the isothermal heating. This conclusion is proven for process evaluation, based on both the Arrhenius concept and the Thermal Death Time model.

Pediococci and biotechnology.

Nomenclature changes of pediococci postdate the publication of Bergey's Manual. Pediococci possess both a "group" and a "type" antigen. They are gram positive, asporogenous, nonmotile, generally catalase negative, but may possess catalase-like activity. The pediococci may have either a cytochrome or a flavoprotein enzyme system. Anaerobically they are homofermentative using the PEP:PTS and the EMP pathway. Catalase positive strains utilize glucose aerobically and anaerobically while lactose and glycerol are only used aerobically. Some pentoses are fermented to lactate and acetate. Absolute requirement for folinic acid and nearly all amino acids is observed. Pediococci grow luxuriously in All Purpose Tween (APT) broth and are isolated on Rogosa SL agar. Detection can be done by electrical impedance and fluorescent antibody techniques. The Arrhenius concept was utilized in selecting metabolically efficient strains. Antibiotics, antioxidants, some chloride salts and some spices are detrimental to the pediococci. On the other hand, some chloride salts, manganese, and some spices are stimulant. Dialysis-fermentation and immobilization of pediococcal cells were recorded. Some strains decarboxylate histidine to histamine. The resting cell metabolism and the production of bacteriocin have been utilized in antibiosis. An intra and intergeneric genetic transfer system of plasmids from pediococci was by a conjugation-like mechanism. Formation of bacteriocin and fermentation of carbohydrates were linked to plasmids. Lytic bacteriophages to pediococci have not yet been identified. Industrial cultures are mainly frozen concentrates. Linear equations were developed to model the fermentative activity of pediococci and the effects of environmental factors.

History of blood gas analysis. II. pH and acid-base balance measurements.

Electrometric measurement of the hydrogen ion concentration was discovered by Wilhelm Ostwald in Leipzig about 1890 and described thermodynamically by his student Walther Nernst, using the van't Hoff concept of osmotic pressure as a kind of gas pressure, and the Arrhenius concept of ionization of acids, both of which had been formalized in 1887. Hasselbalch, after adapting the pH nomenclature of Sørensen to the carbonic-acid mass equation of Henderson, made the first actual blood pH measurements (with a hydrogen electrode) and proposed that metabolic acid-base imbalance be quantified as the "reduced" pH of blood after equilibration to a carbon dioxide tension (PCO2) of 40 mm Hg. This good idea, coming 40 years before simple blood pH measurements at 37 degrees C became widely available, was never adopted. Instead, Van Slyke developed a concept of acid-base chemistry that depended on measuring plasma CO2 content with his manometric apparatus, a standard method until the 1960s, when it was displaced by the three-electrode method of blood gas analysis. The 1952 polio epidemic in Copenhagen stimulated Astrup to develop a glass electrode in which pH could be measured in blood at 37 degrees C before and after equilibration with known PCO2. He introduced the interpolative measurement of PCO2 and bicarbonate level (later base excess) using only pH measurements and, with Siggaard-Andersen, developed clinical acid-base chemistry. Controversy arose when blood base excess was noted to be altered by acute changes in PCO2 and when abnormalities of base excess were called metabolic acidosis or alkalosis, even when they represented compensation for respiratory abnormalities in PCO2. In the 1970s it became clear that "in-vivo" or "extracellular fluid" base excess (measured at an average extracellular fluid hemoglobin concentration of 5 g) eliminated the error caused by acute changes in PCO2. Base excess is now almost universally used as the index of nonrespiratory acid-base imbalance.

Experimental measurement of sediment nitrification and denitrification in Hamilton Harbour, Canada

This research examines the role of sediment nitrification and denitrification in the nitrogen cycle of Hamilton Harbour. The Harbour is subject to large ammonia and carbon loadings from a waste-water treatment plant and from steel industries. Spring ammonia concentrations rapidly decrease from 4.5 to 0.5 mg 1−1, while spring nitrate concentrations increase from 1 to 2 mg l−1, by mid-summer. A three-layer sediment model was developed. The first layer is aerobic; in it, oxidation of organics and nitrification occurs. The second layer is for denitrification, and the third layer is for anaerobic processes. Ammonia sources for nitrification include diffusion from the water column, sources associated with the oxidation of organics, sources from denitrification and from anaerobic processes. Diffusion of oxygen, ammonia and nitrate across the sediment-water interface occurs. Temperature effects are modelled using the Arrhenius concept. A combination of zero-order kinetics for nitrate or ammonia consumption with diffusion results in a half-order reaction, with respect to the water column loss rate to sediments.