Kinetic Point Research Articles

Experimental investigation on the possibility of defining the feasibility of CO2/CH4 exchange into a natural gas hydrate marine reservoir via fast analysis of sediment properties

The present work deals with an experimental investigation on methane hydrate and carbon dioxide hydrate formation in presence of two different types of sand, which acted as seabed simulators. The first typology of sand consists in pure quartz and is commonly used for laboratory experiments on gas hydrate. The other type is named TS-2 and originated from the Tunisian seabed of the Mediterranean Sea. It is silica-based (≈99%), however it also contains other elements and its grains have different shape, size and porosity. Experiments were carried out in order to verify if the specific characteristic of the seabed, in which the hydrate reservoir is present, may intervene or not on the CO2/CH4 replacement process and if such contribution may improve or reduce the process efficiency. Results proved that physical and chemical properties of materials which composed the seabed, may strongly intervene on the replacement process. In particular, experiments revealed that sand TS-2 acted as kinetic and thermodynamic inhibitor for methane hydrate formation, while it promoted CO2 hydrate formation under the kinetic point of view. In this sense, sand TS-2 represents a strong ally for improving the replacement efficiency, due to its capability to both improving the kinetic of the process and reducing the methane hydrate re-formation phenomena. The present study revealed that, with a simple analysis of properties of sediments containing hydrate reservoirs, it would be possible to establish the convenience of intervening with a replacement strategy instead of a classical application for simple methane recovery.

Case analysis of kinetics investigations in toxicity studies of pesticides to identify the nonlinearity of internal exposure and the influences of nonlinearity on the toxicological interpretation of pesticide residue

The nonlinearity of internal exposure to 8 pesticides was investigated in toxicity studies using kinetics to identify nonlinearity visually and to investigate the influence of nonlinearity on toxicological evaluation. Data were obtained from risk assessment reports published by the Food Safety Commission (FSCJ). Nonlinearity was defined using 2 indicators: the lowest visual inflection point (LVIP) and the second lowest visual inflection point (SVIP) of kinetics by drawing a linear distribution chart. The area under the curve and 24-h urine concentrations were stable parameters used to identify the LVIP/SVIP. The sampling timing affected the blood concentrations, and the LVIP/SVIP was detected for 6 pesticides using the parent compounds or their metabolites as analytes. The subproportional nonlinearity was significant for these pesticides. The LVIP/SVIP values were consistent in the same species up to a 1-year period, but the values showed species-specific differences in several compounds. In all compounds found to be nonlinear, apical outcomes were observed at the SVIP or above. The presence of nonlinearity was recognized by the FSCJ. The recognition influenced their judgment of no-observed-adverse-effect levels (NOAELs) for carcinogenicity or health-based guidance values, indicating the importance of appropriate kinetics to identify the nonlinearity for toxicological evaluation of pesticide residue.

Highly energy-efficient degradation of antibiotics in soil: Extensive cold plasma discharges generation in soil pores driven by high voltage nanopulses

Cold atmospheric plasma (CAP) is a green and promising soil remediation approach with significant advantages in terms of energy consumption, removal efficiency and treatment time. The most critical factor for exploiting CAP is the accomplishment of very low remediation cost, while in parallel, the limited penetration of plasma species at soil layers holds back its wider implementation. In this study, we developed a novel dielectric barrier discharge plasma reactor driven by high voltage nanosecond pulses (NSP) able to generate micro-discharges within the interconnected soil pores facilitating the effective transport of reactive species within soil layers. Key-role parameters were investigated such as pulse voltage and pulse frequency, soil thickness and air flow rate. The effectiveness of the method was identified against different types of soil (sandy soil and loam soil), both under high and low ciprofloxacin concentration in soil, while soil moisture impact on degradation efficiency was also explored. An energy efficiency of 21.2 mg of pollutant/kJ was accomplished, which is the highest ever reported for CAP-based soil remediation. The most stable intermediate degradants of ciprofloxacin, and the associated degradation pathways were identified in a kinetic point of view, while the elimination of the toxic intermediates after treatment was ensured. The present effort provides a new highly energy efficient perspective for future development of a CAP-based soil remediation technology as it maximizes the transfer and penetration of plasma species in soil layers under very low estimated remediation cost (~0.4-1.2 €/tn of soil).

Bisecting three classes of lines

We consider the following problem: Let L be an arrangement of n lines in R3 in general position colored red, green, and blue. Does there exist a vertical plane P such that a line in P simultaneously bisects all three classes of points induced by the intersection of lines in L with P? Recently, Schnider used topological methods to prove that such a cross-section always exists. In this work, we give an alternative proof of this fact, using only methods from discrete geometry. With this combinatorial proof at hand, we devise an O(n2log2⁡(n)) time algorithm to find such a plane and a bisector of the induced cross-section. We do this by providing a general framework, from which we expect that it can be applied to solve similar problems on cross-sections and kinetic points.

Investigation of smart water imbibition assisted with microwave radiation as a novel hybrid method of enhanced oil recovery

This research aims to investigate the efficiency of a new hybrid method of smart water imbibition assisted with microwave (MW) radiation. Some experiments including the contact angle measurement, attenuated total reflectance (ATR), zeta potential evaluation, oil viscosity measurement, and smart water imbibition were studied to find the effect of the MW radiation on the performance of the smart water imbibition. To capture the controlling mechanisms, it was essential to sustain the temperature in some of the MW treatments. Hence, the rock sections were treated by two methods of dry (MW treating the sections without immersion in the brine water) and immersed (MW treating the sections when they are immersed in the brine water) treatments. It was shown that the contact angle of an aged rock section could be reduced from 170° at the initial condition to almost 37° due to treating by smart water and the MW radiation. Divalent cations of Mg2+ and SO42- were discovered to be more efficient in the wettability improvement than Ca2+, and this fact was discussed in detail from thermodynamic and kinetic points of view. Also, it was found that the MW thermal effect is not the only reason for the wettability improvement and organic compound desorption, but also the MW treatment could destabilize the organic compounds on the rock surface through generating oscillating electric fields. This fact was confirmed by the results of the immersed MW treatment, where the contact angle reduction was found to be almost as efficient as the dry MW treatment. Based on the ATR spectrums, the MW radiation can desorb the polar and non-polar compounds in two different mechanisms of thermal desorption and destabilization caused by oscillating electric fields. Furthermore, it was shown that the oil viscosity was reduced due to temperature rising caused by the microwave treatment, but when the temperature of the oil sample reduced to the room temperature, the viscosity reduction was not observed. The oil viscosity, after the treatment for 2 min, with the radiation power of 20, 40, 60, 80, and 100 maximum power increased to 52.5, 53.1, 55.5, 54.2, and 53.1 cp, respectively. Finally, it was shown that the oil recovery was increased 9% during the MW radiation for 16 min in the smart water imbibition test. Based on the observed results in this research, it is concluded that the hybrid of smart water imbibition assisted with MW radiation could be considered as a novel EOR method resulting in more oil recovery.

High Temperature Oxidation Behavior of Conventional and Nb-Modified MAR-M246 Ni-Based Superalloy

The present investigations focused on the thermal oxidation of two variants of MAR-M246 alloy having the same contents of Ta and Nb in at. pct, considering the effects of total replacement of Ta by Nb. The alloys were produced by investment casting using high purity elements in induction furnace under vacuum atmosphere. The alloys were oxidized pseudo-isothermally at 800 °C, 900 °C and 1000 °C up to 1000 hours under lab air. Protective oxidation products growing on the surface of the oxidized samples were mainly Al2O3, Cr2O3. Other less protective oxide such as spinels (NiCr2O4 and CoCr2O4) and TiO2 were also detected as oxidation products. The conventional alloy exhibited slight internal oxidation at 800 °C and an enhanced resistance at 900 °C and 1000 °C. The Nb-modified alloy presented an exacerbated internal oxidation and nitridation at 900 °C and 1000 °C and an enhanced resistance at 800 °C. At 1000 °C, Nb-modified alloy was particularly affected by excessive spalling as the main damage mechanisms. From a kinetic point of view, both alloys exhibit the same behavior at 800 °C and 900 °C, with kp values typical of alumina forming alloys (2 × 10−14 to 3.6 × 10−13 g2 cm−4 s−1). However, Ta modified alloys exhibited superior oxidation resistance at 1000 °C when compared to the Nb modified alloy due to better adherence of the protective oxide scale.

Theoretical study of OH− nucleophilic attack on cobalt(II)-verdoheme complex

OH[Formula: see text] attack on a four, five and six-coordinated cobalt(II)-verdoheme-coordinated with imidazole (1 M) while the axial ligand was studied using B3LYP method. Different spin multiplicities were considered, namely doublet, quartet, and sextet. Results show the most positive charge to be concentrated at the cobalt and carbon atoms adjacent to the oxygen in the cobalt(II)-verdoheme complex. Data obtained show that a stable intermediate was formed by a nucleophilic attack on one of the latter carbon atoms. The intermediate is initially formed by a nucleophilic attack on one of the aforementioned carbon atoms. This intermediate is then directly converted to a helical open-ring complex by passing it through a transition state. It is specified that if every nucleophilic attack is considered separately, then the OH[Formula: see text] attack on cobalt(II)-verdoheme occurred at all spin multiplicity and coordination states, from a thermodynamics and kinetics point of view, all except an OH[Formula: see text] attack on five-coordinated cobalt(II)-verdoheme at quartet state. However, comparison of reaction paths with different spin in the same coordination show that such a nucleophilic attack is not proceeded, while the reactant is a four and six-coordinated cobalt(II)-verdoheme because the latter reaction spin state is not conserved. It is clear that OH[Formula: see text] attack on five-inatedcoordinated Co(II)-verdoheme at doublet spin multiplicity is the most stable reaction path. Moreover, these findings were confirmed by NBO analysis and molecular orbital calculations.

Improvement of Barrier Properties of Biodegradable Polybutylene Succinate/Graphene Nanoplatelets Nanocomposites Prepared by Melt Process.

Polybutylene Succinate (PBS)/Graphene nanoplatelets (GnP) nanocomposites over a range of GnP from 0 to 1.35 wt.%. were prepared by a melt process. A mixture of individual graphene nanosheets and aggregates was obtained by the addition of GnP in the PBS matrix. The presence of these fillers did not significantly modify the morphology, crystalline microstructure of the matrix or its thermal stability. However, a slight reinforcement effect of PBS was reported in the presence of GnP. The water sorption isotherm modelling with Guggenheim, Andersen and De Boer (GAB) equation and Zimm-Lundberg theory allowed a phenomenological analysis at the molecular scale. The presence of GnP did not modify the water sorption capacity of the PBS matrix. From a kinetic point of view, a decrease of the diffusion coefficient with the increasing GnP content was obtained and was attributed to a tortuosity effect. The influence of water activity was discussed over a range of 0.5 to 1 and 0 to 0.9 for water and dioxygen permeability. Improvement of the barrier properties by 38% and 35% for water and dioxygen permeability respectively were obtained.

Tin recovery from a low-grade tin middling with high Si content and low Fe content by reduction—sulfurization roasting with anthracite coal

A new method for separating and recovering tin from a low-grade tin middling with high Si content and low Fe content by roasting with anthracite coal was researched by studying the reaction mechanism and performing an industrial test, in which the Sn was sulfurized into SnS(g) and then collected using a dust collector. The Fe-Sn alloy may be formed at roasting temperatures above 950°C, and like the roasting temperature increases, the Sn content and Sn activity in this Fe-Sn alloy decrease. Also, more FeS can be formed at higher temperatures and then the formation of FeO-FeS with a low melting point is promoted, which results in more serious sintering of this low-grade tin middling. And from the thermodynamics and kinetics points of view, the volatilization of the Sn decreases at extremely high roasting temperatures. The results of the industrial test carried out in a coal-fired rotary kiln show that the Sn volatilization rate reaches 89.7% and the Sn is concentrated in the collected dust at a high level, indicating that the Sn can be effectively extracted and recovered from the low-grade tin middling with a high Si content and low Fe content through a reduction—sulfurization roasting process.

High-Temperature Oxidation Behavior of High-Aluminum (Co,Ni)-Based Superalloys for Friction Stir Welding (FSW) Tools

The present investigation focuses on the thermal oxidation of two, Nb- and Ta-alloyed (Ni,Co)-based superalloys having in their microstructures high contents of hard phases and considered potential candidates as a tool for friction stir welding process. The alloys were produced by investment casting using high-purity elements in induction furnace under vacuum atmosphere. The alloys were oxidized pseudo-isothermally up to 1000 h in muffle furnace under laboratory air, and the mass change was monitored manually using an analytical balance. External oxidation products growing on the surface of the oxidized samples were mainly Cr2O3 and Al2O3. At 800 and 900 °C, internal oxidation products were also observed and consist of Al2O3 and AlN. From a kinetic point of view, both superalloys presented the same behavior at 800 and 900 °C with kp values typical of alumina formers. However, Ta-alloyed material exhibited superior oxidation resistance at 1000 °C when compared to the alloy containing Nb.

Thermal Stability of Amorphous Solid Dispersions.

Amorphous solid dispersion drug delivery systems (ASD DDS) were proved to be efficient for the enhancement of solubility and bioavailability of poorly water-soluble drugs. One of the major keys for successful preparation of ASD is the selection of appropriate excipients, mostly polymers, which have a crucial role in improving drug solubility and its physical stability. Even though, excipients should be chemically inert, there is some evidence that polymers can affect the thermal stability of active pharmaceutical ingredients (API). The thermal stability of a drug is closely related to the shelf-life of pharmaceutical products and therefore it is a matter of high pharmaceutical relevance. An overview of thermal stability of amorphous solids is provided in this paper. Evaluation of thermal stability of amorphous solid dispersion is perceived from the physicochemical perspective, from a kinetic (motions) and thermodynamic (energy) point of view, focusing on activation energy and fragility, as well all other relevant parameters for ASD design, with a glance on computational kinetic analysis of solid-state decomposition.

Clinical aspects and detection of Zika virus RNA in several tissues of experimentally infected BALB/cAn mice / Aspectos clínicos e detecção de RNA do vírus Zika em diferentes tecidos de camundongos BALB/cAn infectados experimentalmente

Our group infected BALB/cAn mice with Zika virus to evaluate clinical signs and viral load in several tissues at three different kinetic points. We inoculated fifteen mice with a 100µl of a viral solution to collect nine different tissues, from each animal, for RNA extraction and quantification. Infections caused no lethality. Some of them, however, showed great agitation, hair bristling, and itchy skin. Viral RNA was detected in one sample of heart, eight of the spleen, and two of skeletal muscle. Seven positive detections were from the third day after infection. Only spleen yielded positive results at a later time.

Theoretical insight into single Rh atoms anchored on N-doped γ-graphyne as an excellent bifunctional electrocatalyst for the OER and ORR: electronic regulation of graphitic nitrogen.

Reducing the overpotential and increasing the reaction rate, which are respectively determined by the thermodynamics and kinetics of electrocatalysis, are the keys to obtaining high-performance bifunctional electrocatalysts for the OER/ORR. Herein, six late-transition metals (Ru, Rh, Pd, Os, Ir, and Pt) anchored on γ-GY and graphitic N doped γ-GY substrates are screened as electrocatalysts for the OER and ORR via density functional theory, and the effects of electronic regulation due to the presence of graphitic N on the thermodynamics and kinetics of electrocatalysis are investigated in detail. Among the six γ-GY@TM candidates, only γ-GY@Rh exhibits excellent OER activity, with an overpotential of 0.42 V. Furthermore, graphitic N doped graN-γ-GY@Rh shows outstanding bifunctional electrocatalytic activity, with overpotentials of 0.27 V for the OER and 0.33 V for the ORR, which are remarkably superior to the values of 0.43 V for RuO2 and 0.45 V for noble-metal Pt electrocatalysts. The present results present some of the lowest overpotentials for OER/ORR electrocatalysts given by theoretical studies to date. From a kinetics point of view, N-doping also remarkably reduces the activation energy barriers of the catalytic rate-limiting steps of the OER and ORR, accelerating the reaction processes and significantly improving the conductivity. Our work provides a theoretical strategy for designing high-efficiency bifunctional OER/ORR electrocatalysts based on γ-GY materials.

Influence of processing parameters on the porosity, thermal expansion, and oxidation behavior of consolidated Fe22Cr stainless steel powder

The objective of this study was to determine the effects of powder metallurgy process parameters on the porosity, coefficient of thermal expansion, and oxidation behaviors of porous ferritic Fe22Cr stainless steel compacts. Optimum values of the process were also investigated. The results showed that, porosity and the coefficient of thermal expansion decrease with increasing process parameters; and changing powder shape from spherical to flaky at a certain extent. The minimum and maximum porosity values of the samples were recorded as 7% and 30%, respectively. While those for the samples produced from milled powders were noted as 3%, and 19%, respectively. The coefficient of thermal expansion values were measured at 800 °C and found to be in the range of 12–14.5 × 10−6 K−1 for spherical powders and flaky powders. From oxidation kinetics point of view, both process parameters and powder shape influenced the oxidation behavior.

Polarization switching in thin doped HfO2 ferroelectric layers

The deployment of ferroelectrics in device concepts such as Ferroelectric Random Access Memory and Ferroelectric Field Effect Transistors requires a good understanding of the polarization switching mechanisms. While several reports already exist involving classical perovskite ferroelectrics, only recently has the switching dynamics in HfO2-based layers started to be addressed. In this work, the Kolmogorov–Avrami–Ishibashi (KAI), the Nucleation Limited Switching (NLS), the Landau–Khalatnikov (LK), and the Inhomogeneous Field Mechanism (IFM) models for polarization switching are surveyed and evaluated with the existing body of literature. Data concerning NLS and IFM are compared to experiments undertaken in this study. After excluding the KAI model because of considerations dealing with film morphology and domain wall energy, we conclude that the NLS, the LK, and the IFM models do not necessarily mutually exclude each other, but rather give a diverse perspective on the switching phenomenon based on thermodynamic, kinetic, statistic, microscopic, and/or macroscopic points of view.

Moment Equations for Kinetic Study of Intermolecular Interaction by Size Exclusion Chromatography

Abstract New moment equations were developed for size exclusion chromatography (SEC), in which chemical reactions simultaneously take place. It is expected that accurate information about affinity kinetics of intermolecular interactions with no immobilization and no chemical modification of solute and ligand molecules can be obtained from elution peak profiles measured by SEC. Moment equations for the first absolute (μ1A) and second central (μ2C) moment of elution peaks were developed on the basis of the Einstein equation for diffusion and the random walk model in order to analytically determine association (ka) and dissociation (kd) rate constant of intermolecular interactions. They were used to predict chromatographic behavior in hypothetical SEC systems to demonstrate their effectiveness. The influence of some parameters on μ1A and μ2C of elution peaks measured in the SEC systems was quantitatively evaluated. It was indicated that the contributions of axial dispersion and reaction kinetics to μ2C depend on some SEC conditions. It is important to control the SEC conditions so that the reaction kinetics has a predominant contribution to μ2C to determine accurate values of ka and kd. The moment equations are effective for optimizing experimental conditions to accurately analyze intermolecular interactions from kinetic points of view.

Molecular Dynamics Simulations of Photo-Induced Free Radical Polymerization.

Curing kinetic models provide insight into how design parameters affect the kinetics of photopolymerization. However, they do not provide insight into how networks form or how they influence the process. This article describes a molecular dynamics simulation framework for simulating photoinitiated, chain growth, free radical polymerization. The framework was applied to simulate the photo-induced polymerization of bisphenol A (EO)10 diacrylate under varying conditions of curing light intensity and photoinitiator concentration. Results from the simulations agree very well with curing kinetic curves and gelation points derived from experiments. The simulations also reveal that: (1) gelation is highly correlated with the formation of giant molecules, (2) differences in the number of free radicals generated at the beginning of polymerization significantly affect polymer network formation at low to intermediate conversion, and thus affect the gelation point, and (3) increasing light intensity or photoinitiator concentration tends to delay the gelation point, but does not affect the ultimate polymer network structure near the latter stages of photopolymerization.

Stabilization of novel N‐heterocyclic germylenes: A computational perspective

AbstractIn this theoretical survey, N‐heterocyclic Germylenes (NHGes; 1–13) are compared and contrasted at DFT. All singlet (s) and triplet (t) states of NHGes turn out as minima for showing no negative force constant on their energy surfaces. Yet, only s states appear as global minima. From thermodynamic view point, the scrutinized NHGes show singlet‐triplet energy gap (ΔEs–t) larger than that of VI and VII germylenes, in the range of 51.45–60.37 versus 49.72 and 42.83 kcal/mol, respectively. In addition, all species are found less stable than NHGes synthesized by Veith (V) and more stable than the NHGes synthesized by Herrmann (VI) and Driess (VII) and so except for 9s–13s structures, reminder singlet divalent species have minimum vibrational frequencies (υmin) more than 100 cm−1. From kinetic view point, the ΔEHOMO–LUMO (band gap) of all singlet NHGes under study is higher than that of Driess's germylene. Henceforth, 1s–8s structures as stable molecules satisfy the identified conditions by Hoffmann, Schleyer, and Schaefer. Dimer of the singlet 1H‐4‐germapyridine‐4‐ylidene (1s), is found 11.44 kcal/mol less thermodynamically stable than its corresponding aromatic monomer. Endothermicity of head‐to‐head dimerization indicates that the reaction is unfavorable for 1, just as 8, while exothermicity shows that head‐to‐head dimerization is favorable for the others especially 9. This survey indicates the substitution effects of fused rings on thermodynamic and kinetic stabilities of NHGes hoping to prompt the experimental attentions toward them.

Fatty acid profile, oxidative status, and content of volatile organic compounds in raw and cooked meat of different chicken strains

Chicken meat is rich in unsaturated fatty acids. Therefore, it is more susceptible to lipid oxidation and production of volatile organic compounds (VOC). In this study, we evaluated the fatty acids, antioxidants, and VOC profiles of raw and cooked meat samples derived from 4 strains of chicken differing in their growth rates, which were as follows: slow-growing (SG, Leghorn), medium-growing (MG, Hubbard and Naked Neck), and fast-growing (FG, Ross). The VOC profile of meat was measured using proton-transfer reaction–mass spectrometry (PTR–MS). The VOC were identified using PTR–time of flight-MS (PTR-ToF-MS). The data were analyzed using both univariate and multivariate models. Twenty main VOC were identified, which were classified into the following chemical categories: aldehydes, alkadienes, alkenes, furans, amides, alcohols, and other compounds. Our results revealed that the chicken genotype and the method of cooking strongly influenced the VOC profile of the meat. Identifying the relationships between these traits allowed us to highlight the trade-off of the main substrates such as n-3 and n-6 polyunsaturated fatty acids (PUFA), protective substances (antioxidants), and degradation products (VOC) of the poultry meat produced during cooking. The extent of VOC production and n-3 loss was found to be higher for the SG genotype. Reduction of n-6 was higher in MG, whereas small losses in antioxidants and PUFA were observed in the FG genotype, consequently, resulting in the lowest production of VOC. The SG and MG are genotypes more active from a kinetic point of view respect to the FG ones. For this reason, in the FG genotypes, the antioxidants are less involved in the oxidative stress induced by the movement; thus, they were available to protect the lipid of the meat during the cooking process. These results suggested that the use of SG and MG genotypes requires a specific dietary protocol (i.e., increasing the antioxidants content) to counteract the lipid oxidations in all the phases: in vivo, postmortem, and during/after cooking.

Dielectronic recombination in non-LTE plasmas

Novel phenomena and methods related to dielectronic capture and dielectronic recombination are studied for non-local thermodynamic equilibrium (LTE) plasmas and for applications to non-LTE ionization balance. It is demonstrated that multichannel autoionization and radiative decay strongly suppress higher-order contributions to the total dielectronic recombination rates, which are overestimated by standard approaches by orders of magnitude. Excited-state coupling of dielectronic capture is shown to be much more important than ground-state contributions, and electron collisional excitation is also identified as a mechanism driving effective dielectronic recombination. A theoretical description of the effect of angular-momentum-changing collisions on dielectronic recombination is developed from an atomic kinetic point of view and is visualized with a simple analytical model. The perturbation of the autoionizing states due to electric fields is discussed with respect to ionization potential depression and perturbation of symmetry properties of autoionization matrix elements. The first steps in the development of statistical methods are presented and are realized in the framework of a local plasma frequency approach. Finally, the impact of collisional–radiative processes and atomic population kinetics on dielectronic recombination is critically discussed, and simple analytical formulas are presented.