Ratio Of Rate Constants Research Articles

Slowed Singlet Exciton Fission Enhances Triplet Exciton Transport in Select Perylenediimide Crystals.

Singlet fission (SF) materials used in light-harvesting devices must not only efficiently produce spin-triplet excitons but also transport them to an energy acceptor. N,N'-Bis(2-phenylethyl)-3,4,9,10-perylenedicarboximide (EP-PDI) is a promising SF chromophore due to its photostability, large extinction coefficient, and high triplet yield, but the energy transport mechanisms in EP-PDI solids are minimally understood. Herein, we use transient absorption microscopy to directly characterize exciton transport in EP-PDI crystals. We find evidence for singlet-mediated transport in which pairs of triplet excitons undergo triplet fusion (TF), producing spin-singlet excitons that rapidly diffuse. This interchange of singlet and triplet excitons shuttles triplets as far as 205 nm within the first 500 ps after photoexcitation. This enhanced transport comes at a cost, however, as it necessitates favoring triplet recombination and thus requires fine-tuning of SF dynamics to balance triplet yields with triplet transport lengths. Through numerical modeling, we predict tuning the ratio of SF and TF rate constants, kSF/kTF, to between 1.9 and 3.8 allows for an optimized triplet transport length (425-563 nm) with minimal loss (7-10%) in triplet yield. Interestingly, by adjusting the size of EP-PDI crystals, we find that we can subtly tune their crystal structure and thereby alter their SF and TF rates. By slowing SF within small EP-PDI crystals, we are able to boost their triplet transport length by ∼20%. Although counterintuitive, our work suggests slowing SF by introducing moderate structural distortions can be preferential when optimizing triplet exciton transport, provided singlet exciton transport is not significantly hindered.

Mild Catalyst- and Additive-Free Three-Component Synthesis of 3-Thioisoindolinones and Tricyclic γ-Lactams Accelerated by Microdroplet Chemistry.

Isoindolinones, bearing both γ-lactam and aromatic rings, draw extensive interest in organic, pharmaceutical, and medicinal communities as they are important structural motifs in many natural products, bioactive compounds, and pharmaceuticals. As the main contributor to isoindolinone synthesis, metal catalysis is associated with many drawbacks including essential use of toxic/precious metals and excessive additives, high reaction temperatures, specially predesigned starting materials, and long reaction times (typically 8-30 h). In this study, we developed a catalyst- and additive-free, minute-scale, and high-yield microdroplet method for tricomponent isoindolinone synthesis at mild temperatures. By taking advantage of the astonishing reaction acceleration (1.9 × 102-9.4 × 103 acceleration factor range with a typical rate acceleration factor of 1.51 × 103 for the prototype reaction as the ratio of rate constants by microdroplet and bulk phase), 12 3-thioisoindolinones and two tricyclic γ-lactams were synthesized using various 2-acylbenzaldehydes, amines, and thiols with satisfactory yields ranging from 85% to 97% as well as a scale-up rate of 3.49 g h-1. Because of the advantages (no use of any catalysts or additives, mild temperature, rapid and satisfactory conversion, broad substrate scope, and gram scalability), the microdroplet method represents an attractive alternative to metal catalysis for laboratory synthesis of isoindolinones and their derivatives.

Revealing the Size and Potential Dependent D2O Microkinetics on Pt Nanoparticles Using Grand Canonical Ensemble Modeling.

Revealing the potential and nanoparticle size effect is significant for understanding the electrochemical microkinetic behaviors under real reaction conditions. Herein, an efficient strategy of combining the robust fully converged constant potential (FCP) algorithm and the size dependent site distribution rule assumption was proposed. A simple reaction of isotopic D2O/H2O adsorption and dissociation on Pt nanoparticles was set as the model reaction. The results show that the cathodic negative potential and the anodic positive potential would result in the D2O orientation of the D-down/O-down physisorption configuration. Microkinetic simulations by this strategy obtained electrochemical widows for D2O/H2O dissociation, and the optimal Pt nanoparticle diameter was predicted to be 1.8 nm, which agrees well with the experimental observation of ∼2 nm threshold. The kinetic isotope effect (KIE) rate constant ratio at the optimal potential of -0.80 V vs SHE was calculated to be ∼1.83. This work provides a guideline in studying electrochemical electrode-electrolyte interactions on nanoparticles.

Applying a Phase-Separation Parameterization in Modeling Secondary Organic Aerosol Formation from Acid-Driven Reactive Uptake of Isoprene Epoxydiols under Humid Conditions.

Secondary organic aerosol (SOA) from acid-driven reactive uptake of isoprene epoxydiols (IEPOX) contributes up to 40% of organic aerosol (OA) mass in fine particulate matter. Previous work showed that IEPOX substantially converts particulate inorganic sulfates to surface-active organosulfates (OSs). This decreases aerosol acidity and creates a viscous organic-rich shell that poses as a diffusion barrier, inhibiting additional reactive uptake of IEPOX. To account for this "self-limiting" effect, we developed a phase-separation box model to evaluate parameterizations of IEPOX reactive uptake against time-resolved chamber measurements of IEPOX-SOA tracers, including 2-methyltetrols (2-MT) and methyltetrol sulfates (MTS), at ~ 50% relative humidity. The phase-separation model was most sensitive to the mass accommodation coefficient, IEPOX diffusivity in the organic shell, and ratio of the third-order reaction rate constants forming 2-MT and MTS ( ). In particular, had to be lower than 0.1 to bring model predictions of 2-MT and MTS in closer agreement with chamber measurements; prior studies reported values larger than 0.71. The model-derived rate constants favor more particulate MTS formation due to 2-MT likely off-gassing at ambient-relevant OA loadings. Incorporating this parametrization into chemical transport models is expected to predict lower IEPOX-SOA mass and volatility due to the predominance of OSs.

Clinical Analysis and in Vitro Correlation of BCRP-Mediated Drug-Drug Interaction in the Gastrointestinal Tract.

Breast cancer resistance protein (BCRP) is a drug efflux transporter expressed on the epithelial cells of the small intestine and on the lateral membrane of the bile duct in the liver; and is involved in the efflux of substrate drugs into the gastrointestinal lumen and secretion into bile. Recently, the area under the plasma concentration-time curve (AUC) of rosuvastatin (ROS), a BCRP substrate drug, has been reported to be increased by BCRP inhibitors, and BCRP-mediated drug-drug interaction (DDI) has attracted attention. In this study, we performed a ROS uptake study using human colon cancer-derived Caco-2 cells and confirmed that BCRP inhibitors significantly increased the intracellular accumulation of ROS. The correlation between the cell to medium (C/M) ratio of ROS obtained by the in vitro study and the absorption rate constant (ka) ratio obtained by clinical analysis was examined, and a significant positive correlation was observed. Therefore, it is suggested that the in vitro study using Caco-2 cells could be used to quantitatively estimate BCRP-mediated DDI with ROS in the gastrointestinal tract.

Ozonolysis of 2-Methyl-2-pentenal: New Insights from Master Equation Modeling.

Experimental and theoretical studies were carried out to investigate the ozonolysis of trans-2-methyl-2-pentenal. The experiments were conducted in atmospheric simulation chambers coupled to a Fourier transform infrared (FTIR) spectrometer and a gas chromatograph-mass spectrometer at room temperature and atmospheric pressure in the presence of an excess of cyclohexane in dry conditions (RH < 1%). The ozonolysis reaction was investigated theoretically from the results of accurate density functional (M06-2X) and ab initio [CCSD(T)] computations, employing the AVTZ basis set. The sequence of reaction steps was established, and the system of kinetics equations was modeled using MESMER. In the first step, a primary ozonide is formed, which then decomposes along two pathways. The principal ozonolysis products are propanal, methylglyoxal, ethylformate, and a secondary ozonide. An interesting competition between sequential reaction steps and well-skipping is found, which leads to an inversion of the expected methylglyoxal/propanal product ratio at temperatures below 210 K. The mechanism of the "hot ester" reaction channel of the Criegee intermediate was revisited. The computed ozonolysis rate constant and product branching ratio are in excellent agreement with the experimental data that are also reported in the present work.

Exploring the nigrostriatal and digestive interplays in Parkinson's disease using dynamic total-body [11C]CFT PET/CT.

Dynamic total-body imaging enables new perspectives to investigate the potential relationship between the central and peripheral regions. Employing uEXPLORER dynamic [11C]CFT PET/CT imaging with voxel-wise simplified reference tissue model (SRTM) kinetic modeling and semi-quantitative measures, we explored how the correlation pattern between nigrostriatal and digestive regions differed between the healthy participants as controls (HC) and patients with Parkinson's disease (PD). Eleven participants (six HCs and five PDs) underwent 75-min dynamic [11C]CFT scans on a total-body PET/CT scanner (uEXPLORER, United Imaging Healthcare) were retrospectively enrolled. Time activity curves for four nigrostriatal nuclei (caudate, putamen, pallidum, and substantia nigra) and three digestive organs (pancreas, stomach, and duodenum) were obtained. Total-body parametric images of relative transporter rate constant (R1) and distribution volume ratio (DVR) were generated using the SRTM with occipital lobe as the reference tissue and a linear regression with spatial-constraint algorithm. Standardized uptake value ratio (SUVR) at early (1-3min, SUVREP) and late (60-75min, SUVRLP) phases were calculated as the semi-quantitative substitutes for R1 and DVR, respectively. Significant differences in estimates between the HC and PD groups were identified in DVR and SUVRLP of putamen (DVR: 4.82 ± 1.58 vs. 2.58 ± 0.53; SUVRLP: 4.65 ± 1.36 vs. 2.84 ± 0.67; for HC and PD, respectively, both p < 0.05) and SUVREP of stomach (1.12 ± 0.27 vs. 2.27 ± 0.65 for HC and PD, respectively; p < 0.01). In the HC group, negative correlations were observed between stomach and substantia nigra in both the R1 and SUVREP values (r=-0.83, p < 0.05 for R1; r=-0.94, p < 0.01 for SUVREP). Positive correlations were identified between pancreas and putamen in both DVR and SUVRLP values (r = 0.94, p < 0.01 for DVR; r = 1.00, p < 0.001 for SUVRLP). By contrast, in the PD group, no correlations were found between the aforementioned target nigrostriatal and digestive areas. The parametric images of R1 and DVR generated from the SRTM model, along with SUVREP and SUVRLP, were proposed to quantify dynamic total-body [11C]CFT PET/CT in HC and PD groups. The distinction in correlation patterns of nigrostriatal and digestive regions between HC and PD groups identified by R1 and DVR, or SUVRs, may provide new insights into the disease mechanism.

Changes in Mechanism and Transition State Structure for Solvolysis Reactions of Ring Substituted Benzyl Chlorides in Aqueous Solution.

Rate and product data are reported for the solvolysis reactions of twenty-seven mono, di (3,4) and tri (3,4,5) ring-substituted benzyl chlorides. The first order rate constant for solvolysis in 20% acetonitrile in water decrease from k solv = 2.2 s-1 for 4-methoxybenzyl chloride to 1.1 x 10-8 s-1 for 3,4-dinitrobenzyl chloride. The product rate constant ratios k MeOH/k TFE for solvolysis in 70/27/3 (v/v/v) HOH/TFE/MeOH range from a minimum of k MeOH/k TFE = 8 to a maximum of 110. The rate data were fit to a four-parameter Hammett equation that separates the resonance and polar effects of the aromatic ring substituents on the reaction rate. Increases in the values of the Hammett reaction constants and are observed as the substituent constants or are increased. A sharp decrease in the product selectivity k MeOH/k TFE = 26 for stepwise solvolysis of 4-methoxybenzyl chloride is observed as electron-withdrawing meta-substituents are added to 4-methoxybenzyl ring due to a Hammond-effect on the position of the transition state for solvent addition to the substituted 4-methoxybenzyl carbocation reaction intermediates. Sharp increases in the selectivity k MeOH/k TFE are observed with decreasing reactivity of other 3,4,5-subsituted benzyl chlorides due to anti-Hammond shifts on a two-dimensional More-O'Ferrall reaction coordinate diagram in the position of the transition state for a concerted solvolysis reaction.

Kinetics and thermodynamics of unimolecular dissociation of n-C3H7I

Abstract The present work expands previous studies on the kinetics of the n-C3H7I unimolecular decomposition and the thermodynamic properties of n-C3H7I and i-C3H7I molecules, by providing combined experimental and theoretical data on the rate constant for reaction of n-C3H7I + Ar ⇌ n-C3H7 + I + Ar, as well as thermodynamic data for iodopropane isomers, calculated based on the density functional theory. The n-C3H7I dissociation rate constant has been precisely determined in shock-tube experiments by applying atomic resonance absorption spectrometry (ARAS) at the resonance transition wavelength of atomic iodine (183.0 nm) in a temperature range from 830 to 1230 K at a pressure of 3–4 bar. The resulting expression is presented in the Arrhenius form: k 1st = 1.17 × 1013exp(−191.4 kJ mol−1/RT) (s−1). Theoretical RRKM/ME calculation of the temperature- and pressure-dependent rate constant and channel branching ratio have been based on quantum chemical calculations and were performed over a wide range of thermodynamic conditions (T = 300–2000 K, p = 10−4 to 102 bar). Additionally, the thermochemistry of the reactions of n-C3H7I dissociation and isomerization has been calculated on B3LYP/cc-pVTZ-PP level of theory. Thermodynamic data, which are provided in NASA polynomial format, are in a better agreement with the available experimental data and previous theoretical estimates.

Flotation and oil agglomeration of high ash LVMC coal after deshaling by jigging: a comparative study using different collectors

ABSTRACT LVMC coal with an ash content of 38.70% was initially crushed to −4.0 to +0.50 mm and deshaled using a laboratory model Batac Jig. The resulting concentrate was further size reduced to −0.50 mm and combined with the original fines obtained during crushing. Froth flotation (of −0.50 mm size) and oil agglomeration (of −0.075 mm size) tests conducted using different collectors at varying dosages revealed that the combination of jigging and froth flotation processes can effectively reduce the ash content down to 26.29%. At this stated ash, an acceptable yield of 54.67% was obtained with the highest Separation Efficiency value of 18.20 when the Mahua oil collector was used. Kinetic studies of batch flotation indicated that both ash and non-ash components of the coal reported to concentrate at the same rates, demonstrated by the relative ratios of rate constants ( K N A K A ) , which was equal to 1.0404. It is concluded in the paper that the collector mahua oil outperformed in both the flotation and oil agglomeration processes. The uniqueness of the paper is the approach of beneficiating the newly graded high-high, high-NGM Indian coal using cost-effective bio-degradable oils after deshaling in a Jig. The characteristic size distribution curve plotted for the agglomerates is defined mathematically.

Pressure and temperature dependent kinetics and the reaction mechanism of Criegee intermediates with vinyl alcohol: a theoretical study.

Criegee intermediates (CIs), the key intermediates in the ozonolysis of olefins in atmosphere, have received much attention due to their high activity. The reaction mechanism of the most simple Criegee intermediate CH2OO with vinyl alcohol (VA) was investigated by using the HL//M06-2X/def2TZVP method. The temperature and pressure dependent rate constant and product branching ratio were calculated using the master equation method. For CH2OO + syn-VA, 1,4-insertion is the main reaction channel while for the CH2OO + anti-VA, cycloaddition and 1,2-insertion into the O-H bond are more favorable than the 1,4-insertion reaction. The 1,4-insertion or cycloaddition intermediates are stabilized collisionally at 300 K and 760 torr, and the dissociation products involving OH are formed at higher temperature and lower pressure. The rate constants of the CH2OO reaction with syn-VA and anti-VA both show negative temperature effects, and they are 2.95 × 10-11 and 2.07 × 10-13 cm3 molecule-1 s-1 at 300 K, respectively, and the former is agreement with the prediction in the literature.

The significance of PI-RADS v2.1 score combined with quantitative parameters of DWI and DCE-MRI in differentiating between benign prostatic hyperplasia and prostate cancer

This study investigates the efficacy of the Prostate Imaging Reporting and Data System version 2.1 (PI-RADS v2.1) score combined with quantitative metrics from Diffusion Weighted Imaging (DWI) and Dynamic Contrast Enhancement Magnetic Resonance Imaging (DCE-MRI) in differentiating between benign prostatic hyperplasia (BPH) and prostate cancer (PCa). The data of 65 patients with prostate diseases were retrospectively analyzed, and they were divided into a BPH group (n = 34) and a PCa group (n = 31). All patients underwent a multiparametric MRI (mpMRI) examination, which included conventional MRI, DWI and DCE-MRI scans. Variables analyzed included the PI-RADS v2.1 score, apparent diffusion coefficient (ADC), volume transfer constant (Ktrans), rate constant (Kep) and extravascular space volume ratio (Ve). The diagnostic performance of the PI-RADS v2.1 score, DWI, DCE-MRI and their combined metrics in differentiating BPH from PCa was assessed using Receiver Operating Characteristic (ROC) curve analysis. The results demonstrated that the PI-RADS v2.1 scores, Ktrans and Kep values of the PCa group were significantly higher than those of the BPH group (p &lt; 0.001), while the ADC value of the PCa group was significantly lower than the BPH group (p &lt; 0.001). No significant difference was observed in the Ve value between the two groups (p = 0.596). ROC analysis indicated that the area under the curve (AUC) values for the PI-RADS v2.1 score, ADC, Ktrans, Kep, Ve and their combination parameters were 0.824, 0.916, 0.903, 0.904, 0.625 and 0.990, respectively, with the combined parameters showing higher sensitivity and specificity than any single parameter. These findings suggest that the PI-RADS v2.1 score, along with DWI and DCE-MRI sequences, are valuable tools for differentiating BPH from PCa. The quantitative parameters, including ADC, Ktrans and Kep values, offer significant imaging references for clinical assessment, and the combination parameters can significantly enhance diagnostic accuracy.

Ultraviolet germicidal irradiation: A prediction model to estimate UV-C-induced infectivity loss in single-strand RNA viruses

Ultraviolet germicidal irradiation (UVGI) disinfection technology is effective in inactivating microorganisms. However, its performance can vary against different microorganisms due to their diverse structural and genomic features. Thus, rapid predictions of UV (254 nm) inactivation kinetics are essential, particularly for highly infectious emerging pathogens, such as SARS-CoV-2, during the extemporary COVID-19 pandemic. In this study, aiming at single-strand RNA (ssRNA) viruses, an improved genomic model was introduced to predict the UV inactivation kinetics of viral genomes using genome sequence data. First, the overall virus infectivity loss in an aqueous matrix was estimated as the sum of damage to both the entire genome and the protein capsid. Then, the “UV rate constant ratio of aerosol and liquid” was used to convert the UV rate constant for viruses in a liquid-based matrix to an airborne state. The prediction model underwent both quantitative and qualitative validation using experimental data from this study and the literature. Finally, with the goal of mitigating potential airborne transmission of ssRNA viruses in indoor environments, this paper summarizes existing in-duct UVGI system designs and evaluates their germicidal performance. The prediction model may serve as a preliminary tool to assess the effectiveness of a UVGI system for emerging or unculturable viruses or to estimate the required UV dose when designing such a system.

Delayed fluorescence of InP:Mn/ZnS nanocrystals

The photoluminescence properties of ZnS-capped Mn-doped InP nanocrystals are shown to be determined by the high ratio of the radiative rate constants of the host and dopant emission, by the polydispersity-induced inhomogeneous broadening, and by the rapid establishment of thermal equilibrium in the distribution of the excitation between the energy levels of the quantum dot and the dopant ion. Because of the combination of these factors, the resulting photoluminescence includes the delayed host fluorescence and the quenched dopant phosphorescence, both having very broad lifetime distributions.

KINETIC EQUATIONS FOR RADICAL-CHAIN OXIDATION INVOLVING PROCESS-INHIBITING ALKYL (OR HYDRO)TETRAOXYL FREE RADICAL

The derivation of kinetic equations for the oxidation processes by the free-radical nonbranched-chain mechanism is shown. This derivation is based on the proposed reaction scheme for the initiated addition of free radicals to the multiple bond of the molecular oxygen includes the addition reaction of the peroxyl free radical to the oxygen molecule to form the tetraoxyl free radical. This reaction competes with chain propagation reactions through a reactive free radical. The chain evolution stage in this scheme involves a few of free radicals, one of which – alkyl(or hydro)tetraoxyl – is relatively low-reactive and inhibits the chain process by shortening of the kinetic chain length. The rate equations (containing one to three parameters to be determined directly) are deduced using the quasi-steady-state treatment. These kinetic equations were used to describe the γ-induced nonbranched-chain processes of free-radical oxidation of liquid o-xylene at 373 K and hydrogen dissolved in water containing various amounts of oxygen at 296 K. The ratios of rate constants of competing reactions and rate constants of addition reactions to the molecular oxygen are defined. In these processes the oxygen with the increase of its concentration begins to act as an oxidation autoinhibitor (or an antioxidant), and the rate of peroxide formation as a function of the dissolved oxygen concentration has a maximum. It is shown that a maximum in these curves arises from the competition between hydrocarbon (or hydrogen) molecules and dioxygen for reacting with the emerging peroxyl 1:1 adduct radical. From the energetic standpoint possible nonchain pathways of the free-radical oxidation of hydrogen and the routes of ozone decay via the reaction with the hydroxyl free radical in the upper atmosphere (including the addition yielding the hydrotetraoxyl free radical, which can be an intermediate in the sequence of conversions of biologically hazardous UV radiation energy) were examined. The energetics of the key radical-molecule gas-phase reactions is considered.

Kinetics of three commercial textile dyes decomposition by UV/H2O2 and UV/acetone processes: An experimental comparative study and DFT calculations

Acetone photolysis was investigated and compared with the UV/H2O2 process for the removal of three commercial textile dyes, Reactive Red 184 (RR184), Reactive Orange 4 (RO4), and Direct Red 80 (DR80), in aqueous solution at 254 nm, pH = 6.5–6.8, and T = 20 ± 2 °C. The removal efficiency of RR184, RO4, and DR80 by UV/H2O2 was 35 %, 59 %, and 69 %, respectively, whereas UV/acetone exhibited a removal efficiency of 81 %, 99 %, and 88 %, within 30 min ([Dye]0 = 0.1 mM and [acetone]0 = [H2O2]0 = 50 mM). However, as the initial doses of H2O2 and acetone were increased, the decolorization increased, and the experimental kinetic data always agreed with the pseudo-first-order reaction model (R2 = 0.94–0.99). Additionally, UV/acetone was consistently shown to be significantly more efficient than UV/H2O2 under all conditions tested. For instance, the rate constant ratios kUV/acetone/kUV/H2O2 are 3.19, 1.95, and 1.67 for RR184, RO4, and DR80, respectively ([Dye]0 = 0.1 mM and [acetone]0 = [H2O2]0 = 50 mM). Scavenging tests using specific probes revealed that •OH and •CH3 radicals were the main responsible for dyes degradation (greater than80 %) in the UV/H2O2 and UV/acetone processes, respectively. In both systems, the dyes' reactivity order was found to be RO4 > DR80 > RR184, indicating that chemical structure is an important factor in evaluating the efficiency of the degradation process. This reactivity order was supported by the density functional theory (DFT)-based thermodynamic calculations used to explain the HO•-initiated degradation of the studied azo dyes in the UV/H2O2 process.

In vivo18F-DOPA PET imaging identifies a dopaminergic deficit in a rat model with a G51D α-synuclein mutation.

Parkinson's disease (PD) is a neurodegenerative condition with several major hallmarks, including loss of substantia nigra neurons, reduction in striatal dopaminergic function, and formation of α-synuclein-rich Lewy bodies. Mutations in SNCA, encoding for α-synuclein, are a known cause of familial PD, and the G51D mutation causes a particularly aggressive form of the condition. CRISPR/Cas9 technology was used to introduce the G51D mutation into the endogenous rat SNCA gene. SNCAG51D/+ and SNCAG51D/G51D rats were born in Mendelian ratios and did not exhibit any severe behavourial defects. L-3,4-dihydroxy-6-18F-fluorophenylalanine (18F-DOPA) positron emission tomography (PET) imaging was used to investigate this novel rat model. Wild-type (WT), SNCAG51D/+ and SNCAG51D/G51D rats were characterized over the course of ageing (5, 11, and 16 months old) using 18F-DOPA PET imaging and kinetic modelling. We measured the influx rate constant (Ki) and effective distribution volume ratio (EDVR) of 18F-DOPA in the striatum relative to the cerebellum in WT, SNCAG51D/+ and SNCAG51D/G51D rats. A significant reduction in EDVR was observed in SNCAG51D/G51D rats at 16 months of age indicative of increased dopamine turnover. Furthermore, we observed a significant asymmetry in EDVR between the left and right striatum in aged SNCAG51D/G51D rats. The increased and asymmetric dopamine turnover observed in the striatum of aged SNCAG51D/G51D rats reflects one aspect of prodromal PD, and suggests the presence of compensatory mechanisms. SNCAG51D rats represent a novel genetic model of PD, and kinetic modelling of 18F-DOPA PET data has identified a highly relevant early disease phenotype.

Experimental Measurement of Pure and Mixed-Gas Kinetics of Ethylene and Ethane Adsorption onto Mordenite, Zeolite 13X, and ZJU-74a: Insights into the Value of Single- vs Mixed-Gas Kinetics, Validity of IAST and Sips Isotherm Models, and Temperature/Pressure Relationships for Process Modeling

Adsorption processes can be applied to the separation of alkane/alkene mixtures. Process modeling is a key tool used to assess if the operating and capital cost of these processes can compete with the industry standard (e.g., cryogenic distillation for ethylene/ethane). These process models rely on experimental adsorbent data, which, due to simplicity, is typically gathered using only pure gases at equilibrium conditions. Gas separations are fundamentally mixed-gas processes, raising the following question: is equilibrium pure gas adsorption data suitable to predict mixed-gas separation performance? To answer this, our work provides process modeling data sets for ethylene and ethane on Mordenite, Zeolite 13X, and ZJU-74a and illustrates that pure gas kinetic measurements are sufficient to predict mixed-gas behavior and provides caution on relying on equilibrium conditions predicted by the ideal adsorbed solution theory (IAST) and extended-Sips methods. Using a modification of the volumetric method for measuring adsorption, we report pure gas kinetics as a function of temperature (20–80 °C) and pressure (<100 kPa) for the adsorption of ethylene and ethane onto Mordenite, Zeolite 13X, and ZJU-74a to supplement isotherms and aid in process modeling. At 293 K, the pseudo-second-order adsorption rate constants of ethylene and ethane, respectively, on Mordenite (4.2 and 2.0 kg·mol–1·s–1) and Zeolite 13X (6.4 and 10 kg·mol–1·s–1) increase with increasing pore size, whereas ZJU-74a (4.9 and 6.6 kg·mol–1·s–1) does not. Only Mordenite exhibited kinetic selectivity (3.2), with the ratio of rate constants for Zeolite 13X and ZJU-74a near unity, suggesting that process models of Zeolite 13X and ZJU-74a will not benefit from considering kinetics. Rate constants of all materials follow an Arrhenius trend with temperature, and the effect of pressure was within measurement error and considered negligible, allowing for simple implementation of these results into process models. Additionally, we show that the extended-Sips isotherm and IAST methods for predicting binary equilibria from pure isotherms perform poorly at predicting the equilibrium condition observed in mixed-gas kinetic experiments.

The calculation of the decomposition products of C5F10O–CO2 mixtures with a chemical kinetic model

This paper presents a chemical kinetic model to investigate the physicochemical process in C5F10O-CO2 mixtures. The model contains 12 ions, including e, C+, O+, C2 +, O2 +, CO+, CO2 +, O−, C−, C2 −, O2 −, O3 − and 38 neutral species, containing C, O, C2, O2, CO, CO2, O3, C5F10O, C4F7Oa, C4F7Ob, C4F7Oc, C4F7Od, C3F5O, C3F4Oa, C3F4Ob, C3F4Oc, C3F4Od, C3F4Oe, C3F3Oa, C3F3Ob, COCF3, C2F2Oa, C2F2Ob, COFC, COF, C3F7a, C3F7b, C3F6a, C3F6b, C2F5, C2F4a, C2F4b, C2F3a, C2F3b, C2F2, CF3, CF2, CF. The total number of 180 reactions are considered. For the reactions whose forward and reverse rate constants can be obtained, the reactions are split into two one-way reactions. In addition, the reactions which produce photons are also considered as one-way reactions. The other reactions are reversable. The reverse rate constants can be obtained by the ratio of the forward rate constants and the equilibrium constants. The molar fractions of the decomposition products in C5F10O-CO2 mixtures with the C5F10O content to be 5%, 7% and 13% are calculated in the temperature range of 500–3500 K. The ratio of the electron temperature to the temperature of the heavy species is calculated to obtain the deviation from local thermodynamic equilibrium in different temperatures. The characteristic decomposition products in different temperature ranges are determined. In addition, the main reaction pathways for the main species are determined by analyzing the contributions of the corresponding reactions to the generation and consumption of the species. In order to validate the chemical kinetic model, the molar fractions of the species in pure CO2 are compared with those by Gibbs free energy minimization in a wide temperature range. This model can help better understand the physicochemical process from the aspect of the reactions during the over-heat fault, and the characteristic decomposition products in different temperature range can help identify the potential fault to avoid great power accidents.

Evaluation of Short-Term Oxidation Mechanism of Laser Cladded Ni–Cr–C Coating on Titanium Aluminide Substrate

In the present investigation, a NiCr–Cr3C2 powder mixture was deposited on titanium aluminide substrate by laser cladding. The kinetics and mechanism of oxidation of the substrate and coating were studied at 800–1100 °C using XRD, SEM, ToF–SIMS and XPS characterization techniques. The results demonstrated that the Ni–Cr–C coating had improved oxidation resistance, as compared to the substrate. The oxidized surface of the coating was covered with Cr2O3 and NiCr2O4 phases at the early stages of the oxidation. The formation of NiCr2O4 could be attributed to the reaction of NiO (an oxidation product of the NiCr phase) and Cr2O3 (an oxidation product of the chromium carbide phase) during oxidation. Increasing the oxidation time at 900 °C led to the partial formation of CrO3 as a result of the oxidation of Cr2O3. It was also found that the parabolic rate constant ratio of $$\left( {K_{{\text{p}}}^{{{\text{substrate}}}} /K_{{\text{p}}}^{{{\text{coating}}}} } \right)$$ increased with the temperature, which showed, comparatively, the better oxidation resistance of the coating at higher temperatures.