Cumulative Reaction Rates Research Articles

Association between metabolic risk factors and the hepatitis B reactivation of inactive HBsAg carriers in Jiangsu province: a cohort study

Objective: To analyze the impact of metabolic risk factors on the epidemiological characteristics of the reactivation of inactive HBsAg carriers (IHC) and provide effective intervention measures to standardize the management of chronic hepatitis B infections. Methods: Based on the chronic hepatitis B infection cohort established in 2010 in Jiangsu province, six follow-up visits from 2012 to 2020 were conducted to analyze the characteristics and influencing factors of the hepatitis B reactivation of IHC and the impact of metabolic risk factors, including obesity, high blood pressure, diabetes and hyperglycemia. Results: From 2012 to 2020, 2 527 IHC and 17 730 person-years were observed during a median follow-up period of 7.0 person-years. Ninety-eight cases of hepatitis B reactivation, with a cumulative reaction rate, was 3.9%, and the incidence density was 5.53/1 000 person-years. Multivariate Cox proportional risk regression analysis showed that age and baseline HBV DNA were independent risk factors of HBV reactivation. Compared with the patients ≥60 years, 40-49 age group (aHR=2.16, 95%CI:1.20-3.90) and 20-29 age group (aHR=5.48, 95%CI:2.07-14.48) were significantly associated with hepatitis B reactivation. Compared with the HBV DNA negative patients at baseline, the risk of hepatitis B reactivation was higher in the group with low HBV DNA level 100-1 999 IU/ml (aHR=1.67, 95%CI:1.11-2.52). Stratification analysis results showed that compared with those without metabolic risk factors, in the ≥50 age group, patients with ≥2 metabolic risk factors showed adjusted HR of 2.73 (95%CI:1.08-6.96). Conclusions: The risk of hepatitis B being reactive is the persistent existence of IHC in communities in Jiangsu province, especially young adults, low-level HBV DNA carriers, and IHC with ≥2 metabolic risk factors. Follow-up for these IHC should be strengthened to reduce the risk of disease progression by antiviral treatment at the right time.

Fast ion synergistic effects in JET high performance pulses

Fast ion synergistic effects were studied by predictive modelling of JET best performing pulses for various levels of neutral beam injection (NBI) and radio frequency (RF) power. Calculated DD neutron yields were analysed with the intention of separating the impact of RF synergistic effects due to changes in fast ion (FI) distribution function (DF) from secondary effects accompanying the application of RF power, namely changes in Te and Ti. A novel approach in analysing the efficiency of fast ions in fusion reactions based on evaluation of the cumulative reaction rates is outlined and used in the study. Conclusions on the impact of fast ion synergistic effects on fusion performance are based on comparisons of beam-target (BT) and thermal (Th) DD reaction rates. It was found that changes in auxiliary heating power, NBI and RF, by 4 MW will affect DD fusion performance and neutron rates significantly. Simulations of the best performing JET pulses show that for H minority RF heating scheme with available RF power the impact of RF synergistic effects is somewhat lesser than the secondary effects related to changes in Te and Ti. In conditions of much higher RF power the modification in fast ion distribution function (FI DF) and the impact of the fast ions on BT DD fusion becomes significant. The impact of the RF and NBI power on the BT reactivities was found to be of similar order; however, the NBI power has greater impact on reaction rates due to its larger effect on fast ion density.

H2chemistry in interstellar ices: the case of CO ice hydrogenation in UV irradiated CO:H2ice mixtures

Context.In dense clouds, hydrogenation reactions on icy dust grains are key in the formation of molecules, like formaldehyde, methanol, and complex organic molecules (COMs). These species form through the sequential hydrogenation of CO ice. Although molecular hydrogen (H2) abundances can be four orders of magnitude higher than those of free H-atoms in dense clouds, H2surface chemistry has been largely ignored; several laboratory studies show that H2does not actively participate in “non-energetic” ice chemistry because of the high activation energies required.Aims.For the example of CO ice hydrogenation, we experimentally investigated the potential role of H2molecules on the surface chemistry when energetic processing (i.e., UV photolysis) is involved. We test whether additional hydrogenation pathways become available upon UV irradiation of a CO:H2ice mixture and whether this reaction mechanism also applies to other chemical systems.Methods.Ultra-high vacuum (UHV) experiments were performed at 8–20 K. A pre-deposited solid mixture of CO:H2was irradiated with UV-photons. Reflection absorption infrared spectroscopy (RAIRS) was used as an in situ diagnostic tool. Single reaction steps and possible isotopic effects were studied by comparing results from CO:H2and CO:D2ice mixtures.Results.After UV-irradiation of a CO:H2ice mixture, two photon-induced products, HCO and H2CO, are unambiguously detected. The proposed reaction mechanism involves electronically excited CO in the following reaction steps: CO + hν→CO*, CO*+ H2→HCO + H where newly formed H-atoms are then available for further hydrogenation reactions. The HCO formation yields have a strong temperature dependence for the investigated regime, which is most likely linked to the H2sticking coefficient. Moreover, the derived formation cross section reflects a cumulative reaction rate that mainly determined by both the H-atom diffusion rate and initial concentration of H2at 8–20 K and that is largely determined by the H2sticking coefficient. Finally, the astronomical relevance of this photo-induced reaction channel is discussed.

Cross-section sensitivity and uncertainty analysis of the FNG copper benchmark experiment

A neutronics benchmark experiment on copper assembly was performed end 2014–beginning 2015 at the 14-MeV Frascati neutron generator (FNG) of ENEA Frascati with the objective to provide the experimental database required for the validation of the copper nuclear data relevant for ITER design calculations, including the related uncertainties. The paper presents the pre- and post-analysis of the experiment performed using cross-section sensitivity and uncertainty codes, both deterministic (SUSD3D) and Monte Carlo (MCSEN5). Cumulative reaction rates and neutron flux spectra, their sensitivity to the cross sections, as well as the corresponding uncertainties were estimated for different selected detector positions up to ∼58cm in the copper assembly. This permitted in the pre-analysis phase to optimize the geometry, the detector positions and the choice of activation reactions, and in the post-analysis phase to interpret the results of the measurements and the calculations, to conclude on the quality of the relevant nuclear cross-section data, and to estimate the uncertainties in the calculated nuclear responses and fluxes.Large uncertainties in the calculated reaction rates and neutron spectra of up to 50%, rarely observed at this level in the benchmark analysis using today's nuclear data, were predicted, particularly high for fast reactions. Observed C/E (dis)agreements with values as low as 0.5 partly confirm these predictions. Benchmark results are therefore expected to contribute to the improvement of both cross section as well as covariance data evaluations.

Reevaluation of neutron flux characterization parameters for NIST RT-2 facility

It has been difficult to characterize the thermal to epithermal neutron flux ratio (f) and the measure of the nonideal epithermal neutron flux distribution (α) for the RT-2 pneumatic rabbit facility at the NIST National Bureau of Standards Reactor (NBSR). In a previous paper, only cadmium-covered irradiations yielded physically reasonable parameters. New measurements were performed using chromium, manganese, cobalt, zinc, zirconium, molybdenum, antimony, gadolinium, lutetium, and gold. The neutron temperature (T n ) in RT-2 measured using bare lutetium and gold foils gave unphysical values. The bare foil methods for measuring f and α gave inconsistent results. The underlying reasons are demonstrated via MCNP simulation results for cumulative reaction rates of selected isotopes. To determine expected intervals for f, α and T, parametric methods were explored. Measured reaction rate probability per target atom (R p ) values for the listed elements were fitted to a modified Westcott curve using an iterative least-squares method to verify consistency of measurements and nuclear data. An advanced parametric approach using a detailed MCNP model of the NBSR was used to calculate neutron flux characterization parameters.

Quantum transition state theory: featuring ensemble pre-equilibrium approximation

In this article, we use an ensemble pre-equilibrium approximation to vindicate the use of Heisenberg Equation of Motion and some other approximation for the rate of the change of quasi-equilibrium state in order to derive, based on the most precise and accurate existing theory of reaction rates to date, a rate law for any given elementary step of a chemical reaction that applies even to the condensed phase. The necessity of such a theory arises because first of all, quantum mechanics must be taken into account, and secondly, other molecules and especially the solvent may play an important role in the transition state of any elementary reaction, and we have devised a theory for doing so. Also, the correct theory for reaction rates critically depends on a complete set of wavefunctions of the transition state representing initially the products and finally the reactants, and we show a simple way for deriving it. We also show that several prevailing formulas in the literature for the cumulative reaction rate within the range of applicability of non-relativistic mechanics to the electrons and nuclei of the reacting systems within the reactor are exactly equivalent to each other, even in the condensed phase, and therefore the present theory is exact within the laws of quantum non-relativistic mechanics.

Charged-particle thermonuclear reaction rates: II. Tables and graphs of reaction rates and probability density functions

Numerical values of charged-particle thermonuclear reaction rates for nuclei in the A = 14 to 40 region are tabulated. The results are obtained using a method, based on Monte Carlo techniques, that has been described in the preceding paper of this issue (Paper I). We present a low rate, median rate and high rate which correspond to the 0.16, 0.50 and 0.84 quantiles, respectively, of the cumulative reaction rate distribution. The meaning of these quantities is in general different from the commonly reported, but statistically meaningless expressions, “lower limit”, “nominal value” and “upper limit” of the total reaction rate. In addition, we approximate the Monte Carlo probability density function of the total reaction rate by a lognormal distribution and tabulate the lognormal parameters μ and σ at each temperature. We also provide a quantitative measure (Anderson–Darling test statistic) for the reliability of the lognormal approximation. The user can implement the approximate lognormal reaction rate probability density functions directly in a stellar model code for studies of stellar energy generation and nucleosynthesis. For each reaction, the Monte Carlo reaction rate probability density functions, together with their lognormal approximations, are displayed graphically for selected temperatures in order to provide a visual impression. Our new reaction rates are appropriate for bare nuclei in the laboratory. The nuclear physics input used to derive our reaction rates is presented in the subsequent paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new reaction rates to previous results.

Charged-particle thermonuclear reaction rates: I. Monte Carlo method and statistical distributions

A method based on Monte Carlo techniques is presented for evaluating thermonuclear reaction rates. We begin by reviewing commonly applied procedures and point out that reaction rates that have been reported up to now in the literature have no rigorous statistical meaning. Subsequently, we associate each nuclear physics quantity entering in the calculation of reaction rates with a specific probability density function, including Gaussian, lognormal and chi-squared distributions. Based on these probability density functions the total reaction rate is randomly sampled many times until the required statistical precision is achieved. This procedure results in a median (Monte Carlo) rate which agrees under certain conditions with the commonly reported recommended “classical” rate. In addition, we present at each temperature a low rate and a high rate, corresponding to the 0.16 and 0.84 quantiles of the cumulative reaction rate distribution. These quantities are in general different from the statistically meaningless “minimum” (or “lower limit”) and “maximum” (or “upper limit”) reaction rates which are commonly reported. Furthermore, we approximate the output reaction rate probability density function by a lognormal distribution and present, at each temperature, the lognormal parameters μ and σ. The values of these quantities will be crucial for future Monte Carlo nucleosynthesis studies. Our new reaction rates, appropriate for bare nuclei in the laboratory, are tabulated in the second paper of this issue (Paper II). The nuclear physics input used to derive our reaction rates is presented in the third paper of this issue (Paper III). In the fourth paper of this issue (Paper IV) we compare our new reaction rates to previous results.

Immunologic transplant reactions after non-mechanical corneal trepanation with the excimer laser

Nonmechanical trephination has been established as the standard procedure in penetrating keratoplasty (PK) for avascular corneal diseases at our institution. The purpose of this study was to analyze the incidence and reversibility of immunologic graft reactions after nonmechanical trephination and to detect potentially causative factors. Out of a total series of 400 nonmechanical PKs, 286 consecutive procedures with sufficient follow-up performed between 07/1989 and 09/1997 were included in the study (104 x keratoconus, 78 x Fuchs' dystrophies, 31 x bullous keratopathies, 28 x ulcers, 25 x avascular scars, 12 x stromal dystrophies, 4 x buphthalmos, 4 x others; 202 x PK only, 84 x combined procedures; 276 first PK). The age of the 138 females and 148 males at the time of surgery ranged from 16 to 89 (mean 55 +/- 19) years. The recipient and donor trephinations were performed from the epithelial side using an 193-mm excimer laser (MEL50 or MEL60, Aesculap-Meditec, 1.5 x 1.5 mm spot mode, 16-24 mJ/pulse, repetition rate 30 or 25/s; metal masks). The shape of the recipient trephination was either circular with four or eight "orientation teeth" (n = 251; 5.0-8.0 mm diameter) or elliptical (n = 35, 6.0 x 7.0 to 7.5 x 8.5 mm diameter). In 62% of procedures fresh or short-term-preserved donor tissue was used, and in 38% of procedures the donor tissue was organ-culture-preserved. During a mean follow-up of 22 +/- 18 months (maximum 7.7 years), 10 acute diffuse (3 irreversible; 1.0%) and 3 chronic focal endothelial graft reactions occurred (4.5%) not earlier than 4 months and not later than 35 months after PK. Elective procedures (3.5%) resulted in significantly (P = 0.01) less reactions than acute corneal ulcers (14.3%). After 1, 2 and 3 years, the cumulative reaction rates (Kaplan-Meier values) were 1.3%, 6.3% and 13.9% in elective procedures, none of which, however, occurred after 26 elliptical trephinations. With fresh or short-term-preserved donor tissue (4.2%), graft reactions did not happen more frequently but earlier (12 +/- 6 months) than with organ-culture-preserved donor tissue (2.2%, 30 +/- 6 months). In patients with keratoconus (4.9%), reactions occurred more frequently (P = 0.05, LogRank) and earlier than in patients with Fuchs' dystrophy (1.3%). In addition to well-established optical advantages, nonmechanical trephination seems to have no immunologic drawbacks.

Cage effects in recombination of allyl radicals in irradiated polyethylene. II. Cumulative reaction rates and decay kinetic processes

AbstractHwang and Cheng have studied the recombination reaction of allyl radicals in irradiated polyethylene by including the effects of (i) diffusion of macroradicals by jumps of finite size in the crystalline phase and (ii) a caging reaction with a finite rate in the disordered region. In this work their results are used to analyze cumulative reaction rate data on the decay of allyl radicals in extended‐chain and Marlex film polyethylene. The kinetic parameters obtained show the effects of reaction temperature, irradiation dose, and morphological differences.

Effects of jump diffusion rates on reaction kinetics in solids

Applying Torrey’s treatment of jump diffusion in solids to the study of reaction kinetics, a method is presented to describe the dynamics of caging processes in solids in which the reactants are confined to the cages. We put our attention to the study of three measures of time-dependent reactivity; namely, the observed reaction rate, cumulative reaction rate, and the fraction of correlated recovery. The consistency of the present approach is checked by comparison between Noyes’ particle pair model and diffusion model. Based on correlated recovery, a theoretical expression is obtained which describes the recovery and includes a parameter that characterizes the initial distribution function. Application of a jump diffusion model shows significant differences in the reactivity functions from those resulting from the Brownian model for the time region characterized by the average jump time.