Theory Of Reactions Research Articles

A new empirical systematic for (n, 2p) reaction cross sections around 14 MeV

In the present work, we proposed a new empirical systematic with which we can predict the (n, 2p) cross sections as an extension of the empirical rule on the basis of the statistical theory of nuclear reactions. It is obtained by fitting the experimental cross sections as a function of mass number, reaction Q–value, threshold energy and projectile energy. A new analysis of experimental data is performed for (n, 2p) reactions around 14 MeV energy. Besides, the present formula was expressed by a simple systematic with two fitting parameters. The predictions of this formula were discussed and compared with cross section measurements and empirical formulas found in the literature. Results show that the new empirical formula gives a good fit to predict the (n, 2p) cross sections around 14 MeV. This study can provide a reference to the (n, 2p) reaction channel considering the lack of measured cross section values.

Regularity theory for fractional reaction–subdiffusion equation and application to inverse problem

In this paper, we analyze the regularity in time of solutions for nonlinear fractional reaction–subdiffusion equations (FrRSEs). By constituting regularity estimates of resolvent operator and employing fixed point theorems, we establish some results on the global existence and regularity in time of solutions to FrRSE in two different cases of nonlinear perturbations, namely, sublinear and superlinear cases. As an application of these results, several results on the existence and regularity of solutions in an inverse source problem governed by FrRSE with the additional measurements given at terminal time will be shown.

Livelihood Diversification as Political Translation

This article questions the ability of the resistance framework to explain local communities' political reactions to oil palm expansion. Guided by a translation and ethnographic framework, this study investigates the Modang Dayak community's political reaction from below to large-scale land acquisitions in upland East Kalimantan. It shows that, based on their knowledge and everyday life practice, the Modang Dayaks have the agency to negotiate the land scarcity that has accompanied oil palm expansion. This study contributes to reaction theory by arguing that livelihood diversification is a form of political translation used to negotiate the difficulties created by palm oil; as land has become increasingly scarce, the Modang Dayaks have redefined their relationship with it. This reality tends to be ignored in political science debates because researchers generally view political reactions through a resistance paradigm. Ultimately, however, the politics of translation go beyond the politics of resistance.

Renormalization group evolution of optical potentials: Explorations using a “toy” model

To take full advantage of experimental facilities such as FRIB for applications to nuclear astrophysics, nuclear structure, and explorations of neutrinos and fundamental symmetries, we need a better understanding of the interplay of reaction and structure theory. The renormalization group (RG) is the natural tool for maintaining a consistent treatment of reaction and structure. Here we make a first study of RG for optical potentials, which are important ingredients for direct reactions. To simplify the analysis, we use a pedagogical one-dimensional model and evolve toward low RG resolution using the similarity RG (or SRG). We show how SRG decoupling at low resolution carries over to the optical potential and enhances perturbative approximations, and how induced SRG nonlocality compares to the nonlocality of the optical potential. We discuss the results in the larger context of consistent SRG evolution of operators and wave functions in the analysis of direct reactions.

Analysis of thermodynamic properties of moisture-desorption isotherms of Eucalyptus gomphocephala wood

ABSTRACT The aim of this paper was to determine the moisture desorption isotherms and certain thermodynamic properties of Eucalyptus gomphocephala wood using the static gravimetric method at five temperatures: 40°C, 50°C, 60°C, 70°C and 80°C, and relative humidity ranging from 5% to 90%. A “thermodynamic” equation was selected to describe the desorption isotherms under controlled conditions. Desorption isotherms were a “type II” sigmoid. The Clausius–Clapeyron relationship was applied to determine the isosteric heat of desorption. Results showed that for equilibrium moisture content less than 6%, the differential enthalpy and entropy decreased with increasing moisture content according to an exponential law from 26 to 0.5 kJ/mol and from 44 to 0.16 J/(mol K), respectively. The difference in isokinetic and harmonic temperature confirmed the enthalpy-entropy compensation theory of desorption reaction. The negative value of Gibbs free energy (−208.2 kJ/mol) indicated the spontaneous wood-water desorption reaction. Spreading pressure decreased with increasing temperature from 1 J/m² at 40°C to 0.16 J/m² at 80°C and increased with increasing water activity with the rate of 0.014% J/m² per relative humidity.

Capture theory models: An overview of their development, experimental verification, and applications to ion-molecule reactions.

Since Arrhenius first proposed an equation to account for the behavior of thermally activated reactions in 1889, significant progress has been made in our understanding of chemical reactivity. A number of capture theory models have been developed over the past several decades to predict the rate coefficients for reactions between ions and molecules-ranging from the Langevin equation (for reactions between ions and non-polar molecules) to more recent fully quantum theories (for reactions at ultracold temperatures). A number of different capture theory methods are discussed, with the key assumptions underpinning each approach clearly set out. The strengths and limitations of these capture theory methods are examined through detailed comparisons between low-temperature experimental measurements and capture theory predictions. Guidance is provided on the selection of an appropriate capture theory method for a given class of ion-molecule reaction and set of experimental conditions-identifying when a capture-based model is likely to provide an accurate prediction. Finally, the impact of capture theories on fields such as astrochemical modeling is noted, with some potential future directions of capture-based approaches outlined.

Creep properties and relevant deformation mechanisms of two low-cost nickel-based single crystal superalloys at elevated temperatures

In this work, the creep properties and relevant deformation mechanisms of the two self-designed low-cost single crystal superalloys were studied under the conditions of 1038 °C/172 MPa and 982 °C/248 MPa. The experimental alloys both displayed superior creep properties than the typical second-generation single crystal superalloy René N5. During high temperature creep tests, the rafted γ′ phase became more and more twisted with the decrease of distance away from the fracture surface, which was caused by the existence of a stress gradient in the gauge length section of the fractured specimen. Under high temperature and low stress conditions, the Re-free alloy displayed denser dislocation networks under both test conditions. Based on the nodal reaction theory, the dislocation networks with different shapes formed by reactions of a/2<110> dislocations at the γ/γ′ interface. Furthermore, the morphology of dislocation networks could transform from initial rectangles to octagons and then to thick hexagons. Under the condition of 982 °C/248 MPa, some parallel dislocation arrays in γ′ particles caused by dislocations pile-up was found in the Re-low alloy, and the main obstacles to the motion of dislocations were K–W locks and a<010> superdislocations. Based on the calculated critical resolved shear stresses, the primary deformation mechanism of the two experimental alloys under elevated temperature and low stress conditions was identified as dislocations slipping in γ matrix and climbing over rafted γ′ phase.

On a Specific Intermolecular Interactions in Nematic Liquid Crystal Systems

The aim of this study was the investigation of the molecular structure of Nematic Liquid Crystal Systems that are based on polar liquid crystals, whose molecules have a large dipole moment directed along the long axis of the molecule. The investigation has a practical importance in the development of the new LC materials for electro-optical systems. In this work, the investigation of a specific intermolecular interaction – the formation of charge transfer complexing (CTC) in LC systems − was carried out by UV and IR spectroscopy. A long−wavelength shift of the CTC absorption band is found. The complicated dependence of optical density of the absorption band of the donor and CTC on the initial donor concentration has been obtained. The correlation between the optical density of the absorption bands of the CTC and donor, on the one hand, and the phase diagram, on the other, was demonstrated to occur in the investigated systems. The analytical expressions for equilibrium constants of complexation process were derived, and the concentrations of the complexes were determined based on the absolute rates reaction theory.

Interfacial dependent reactive oxygen species generation over Pt-ZrO2 nanoparticles for catalytic oxidation of formaldehyde at room temperature

Producing the strong metal-support interaction (SMSI) interface and highly reactive oxygen species is a great challenge for catalytic oxidation of formaldehyde (HCHO) at room temperature over supported metal catalysts. Herein, we report a conceptual oxygen vacancy (VO) associated SMSI interface of Pt-ZrO2 nanoparticles for HCHO catalysis at room temperature, exhibiting interfacial dependent reactive oxygen species (O*) formation. The VO on the ZrO2 support captures and activates the molecular O2, then proceeds to generating the reactive oxygen atom (O*) with a lower activation barrier of 0.3 eV. The generated O* tends to link the (110) surface of ZrO2 and the (111) surface of Pt as an electronic transmission channel for the selective catalytic oxidation of HCHO adsorbed on the (110) surface of ZrO2, accelerating the direct generation of formate species and mineralization of HCHO. The Pt-VO-ZrO2 achieves high HCHO removal and HCHO conversion (>95%) at 20 °C. These findings will consolidate the fundamental theories of room temperature catalytic reactions via constructing the SMSI interface engineering for wide environmental applications.

Multiple lump, generalized breathers, Akhmediev breather, manifold periodic and rogue wave solutions for generalized Fitzhugh-Nagumo equation: Applications in nuclear reactor theory

Based on ansatz functions technique, we construct many types of novel wave structures and multiple lump-soliton solutions to the generalized Fitzhugh-Nagumo (gFN)-equation. In particular, we obtain entirely exciting lump, lump 1-kink, lump 2-kink, lump-periodic, manifold periodic-soliton, periodic cross-rational, kink cross-rational (KCR) solutions, interaction of the multi-lump and periodic solutions as well as breather style of solitary wave solutions. Using a transformation of dependent variable, which contain a controlling parameter (can control the direction, wave height and angle of the traveling wave), we build generalized breathers, rogue wave, Akhmediev breather, homoclinic breather, Ma breather, Kuznetsov-Ma breather and their relating rogue waves, multiwave, M-shaped rational and some various interactions. We show the results of our solutions graphically in distinct dimensions by assigning different values to the parameters.

Investigation on the Basic Characteristics of Semi-Fixed Abrasive Grains Polishing Technique for Polishing Sapphire (α-Al2O3).

Single-crystal sapphire (α-Al2O3) is an important material and widely used in many advanced fields. The semi-fixed abrasive grain processing method based on solid-phase reaction theory is a prominent processing method for achieving ultra-precision damage-free surfaces. In order to develop the proposed method for polishing sapphire, the basic characteristics of the semi-fixed abrasive grains polishing tool for polishing sapphire were determined. Weight analysis was used to study the influence rules of parameters on surface roughness and material removal rates using an orthogonal experiment. Then, the optimized polishing tool was obtained through a mixture of abrasive particle sizes to reduce the difficulty in molding the polishing tool. Finally, polishing experiments using different polishing tools were carried out to investigate polishing performance by considering the surface roughness, material removal rate and the surface morphology during polishing. The results showed that (1) external load affects the surface roughness and material removal rate the most, followed by abrasive particle size, sand bond ratio, revolution speed of the workpiece and he polishing tool; (2) the difficulty in manufacturing the polishing tool could be reduced by mixing larger abrasive particles with small abrasive particles; (3) the polishing tool with 200 nm and 1 μm particle sizes performed best in the first 210 min polishing.

Climate Controls on River Chemistry

AbstractHow does climate control river chemistry? Existing literature has examined extensively the response of river chemistry to short‐term weather conditions from event to seasonal scales. Patterns and drivers of long‐term, baseline river chemistry have remained poorly understood. Here we compile and analyze chemistry data from 506 minimally impacted rivers (412,801 data points) in the contiguous United States (CAMELS‐Chem) to identify patterns and drivers of river chemistry. Despite distinct sources and diverse reaction characteristics, a universal pattern emerges for 16 major solutes at the continental scale. Their long‐term mean concentrations (Cm) decrease with mean discharge (Qm), with elevated concentrations in arid climates and lower concentrations in humid climates, indicating overwhelming regulation by climate compared to local Critical Zone characteristics such as lithology and topography. To understand the CmQm pattern, a parsimonious watershed reactor model was solved by bringing together hydrology (storage–discharge relationship) and biogeochemical reaction theories from traditionally separate disciplines. The derivation of long‐term, steady state solutions lead to a power law form of CmQm relationships. The model illuminates two competing processes that determine mean solute concentrations: solute production by subsurface biogeochemical and chemical weathering reactions, and solute export (or removal) by mean discharge, the water flushing capacity dictated by climate and vegetation. In other words, watersheds function primarily as reactors that produce and accumulate solutes in arid climates, and as transporters that export solutes in humid climates. With space‐for‐time substitution, these results indicate that in places where river discharge dwindles in a warming climate, solute concentrations will elevate even without human perturbation, threatening water quality and aquatic ecosystems. Water quality deterioration therefore should be considered in the global calculation of future climate risks.

Prediction for ( p,n ) charge-exchange reactions with uncertainty quantification

Background: Charge-exchange reactions are a powerful tool for exploring nuclear structure and nuclear astrophysics; however, a robust charge-exchange reaction theory with quantified uncertainties is essential for extracting reliable physics.Purpose: The goal of this work is to determine the uncertainties due to optical potentials used in the theory for charge-exchange reactions to isobaric analog states.Method: We implement a two-body reaction model to study $(p,n)$ charge-exchange transitions and perform a Bayesian analysis. The $(p,n)$ reaction to the isobaric analog states of $^{14}\mathrm{C}$, $^{48}\mathrm{Ca}$, and $^{90}\mathrm{Zr}$ targets are studied over a range of beam energies. We compare predictions using standard phenomenological optical potentials with those obtained microscopically.Results: Charge-exchange cross sections are reasonably reproduced by modern optical potentials. However, when uncertainties in the optical potentials are accounted for, the resulting predictions of charge-exchange cross sections have very large uncertainties.Conclusions: The charge-exchange reaction cross section is strongly sensitive to the input interactions, making it a good candidate to further constrain nuclear forces and aspects of bulk nuclear matter. However, further constraints on the optical potentials are necessary for a robust connection between this tool and the underlying isovector properties of nuclei.

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Catalytic reductive ring opening of epoxides enabled by zirconocene and photoredox catalysis

Information Thermodynamics of the Transition-Path Ensemble.

The reaction coordinate describing a transition between reactant and product is a fundamental concept in the theory of chemical reactions. Within transition-path theory, a quantitative definition of the reaction coordinate is found in the committor, which is the probability that a trajectory initiated from a given microstate first reaches the product before the reactant. Here we develop an information-theoretic origin for the committor and show how selecting transition paths from a long ergodic equilibrium trajectory induces entropy production which exactly equals the information that system dynamics provide about the reactivity of trajectories. This equality of entropy production and dynamical information generation also holds at the level of arbitrary individual coordinates, providing parallel measures of the coordinate's relevance to the reaction, each of which is maximized by the committor.

James W. Truran (1940–2022)

Truran made far-reaching contributions to the theory of nuclear reactions, stellar nucleosynthesis, big bang nucleosynthesis, stellar abundances, solar system formation, galaxy formation and galactic chemical evolution.

Neutron flux effect in silicon-based bipolar junction transistors exposed to californium-252

This study explores the degradation of silicon-based bipolar junction transistors (BJTs) exposed to a californium-252 source. Both n–p–n and p–n–p BJTs received neutron irradiation of different fluxes (6.3 × 104 cm −2 s−1 to 1.5 × 106 cm −2 s−1). The proportion of the change of reciprocal current gain to neutron fluence increases with the decrease of neutron flux, implying that devices exposed to irradiation of lower neutron flux will suffer severer radiation damage if the total neutron fluence is kept constant. Results obtained by eliminating the impact of accompanying gamma irradiation and the impact of different neutron energy spectra from the degradation of BJTs confirmed this conclusion for both types of BJTs. A kinetic model based on the theory of diffusion-limited reactions was used to analyze the microscopic mechanism, and its results agreed with the experimental results. The simulation results also indicate that lower neutron flux favors the formation of stable defects and reduces the recombination of vacancies and interstitials. This work demonstrates that neutron flux effect also exists in silicon-based BJTs exposed to a californium-252 source and it is related to the defect evolution process in irradiated materials.

Hydrocarbon generation kinetics and in-situ conversion temperature conditions of Chang 7 Member shale in the Ordos Basin, China

In-situ conversion technology has been more popular lately as an effective way to realize the industrial development of extensive medium- and low-mature shale oil/oil shale resources in China. The Ordos Basin has been recognized as the main basin containing the largest in-situ conversion recoverable resources of China. Researchers have revealed the hydrocarbon generation kinetics of low mature oil shales in the 7th Member of the Yanchang Formation (Chang 7 Member). However, the kinetics of medium mature shales may be different from those of low mature shales, and they can also be used as potential targets for in-situ conversion. At present, there is a lack of research on the in-situ hydrocarbon generation kinetics of medium- and low-mature shale oil/oil shale. In this paper, open system pyrolysis experiments were carried out on natural shales and shale samples derived from semi-open system pyrolysis with different maturities in the Chang 7 Member of the Ordos Basin respectively. Using the parallel first-order reaction theory, the frequency factor of low-mature shale was calculated to be 5.47 × 1010 s−1, and the distribution of activation energy ranged from 38 kcal/mol to 61 kcal/mol. The main peak of activation energy was 49 kcal/mol, and accounted for 66.91% of all shales. With the increase in maturity, the average activation energy becomes higher, and therefore more in-situ conversion energy is needed. At the same time, the hydrocarbon generation potential characterized by S2 peak of pyrolysis decreases during the maturation process. The activation energy is divided into three groups according to its distribution characteristics: low, main peak and high activation energy groups, representing <47 kcal/mol, ranging from 47 kcal/mol to 52 kcal/mol and >52 kcal/mol respectively. The proportion of low and high activation energy groups increased with the increase in maturity, while the proportion of main peak activation energy groups decreased. When the kinetic parameters are extrapolated to the condition of in-situ conversion, it is better to choose shales with low maturity (RO <1 .0%) and fully transform them by rapid heating to the main hydrocarbon generation stage, and different conversion temperature ranges should be set for different maturity samples.

Study of the deformed halo nucleus 31Ne with Glauber model based on microscopic self-consistent structures

The exotic deformed nucleus 31Ne is studied with an approach that combines self-consistent structure and reaction theories. The deformed relativistic Hartree-Bogoliubov theory in continuum (DRHBc) is utilized to demonstrate that deformation and pairing correlations give rise to a halo structure with a large-amplitude p-wave configuration in 31Ne. Then the valence nucleon wave functions and angle-averaged density distributions of 30Ne from this theory are used as input for the Glauber reaction model to study the observables of neutron-rich neon isotopes to search halo signatures. With NL1 effective interaction, our predictions of the reaction cross sections for these exotic neon isotopes on a carbon target can better reproduce the experimental data than those from the relativistic mean field model for a spherical shape with resonances and pairing correlation contributions, and are roughly 3.3% (∼ 50 mb) larger than those with Gaussian function-fitted densities of the core nuclei. The calculated one-neutron removal cross section at 240 MeV/nucleon, and the inclusive longitudinal momentum distribution of the 30Ne residues from the 31Ne breakup reaction are largely improved over previous theoretical predictions and agree well with data. These reaction evaluations indicate a dilute density distribution in coordinate space and are a canonical signature of a halo structure. Moreover, our predictions with the NL3 and PK1 effective interactions give slightly better descriptions of reaction observables for exotic neon isotopes.

Generator coordinate method for transition-state dynamics in nuclear fission

Since its beginnings, fission theory has assumed that low-energy induced fission takes place through transition-state channels at the barrier tops. Nevertheless, up to now there is no microscopic theory applicable to those conditions. We suggest that modern reaction theory is suitable for this purpose, and propose a methodology based on a configuration-interaction framework using the generator coordinate method (GCM). Simple reaction-theoretic models are constructed with the Gaussian overlap approximation to parametrize both the dynamics within the channels and their incoherent couplings to states outside the barrier. The physical characteristics of the channels examined here are their effective bandwidths and the quality of the coupling to compound-nucleus states as measured by the transmission factor $T$. We also investigate the spacing of GCM states with respect to their degree of overlap. We find that a rather coarse mesh provides an acceptable accuracy for estimating the bandwidths and transmission factors. The common numerical stability problem in using the GCM is avoided due to the choice of meshes and the finite bandwidths of the channels. The bandwidths of the channels are largely controlled by the zero-point energy with respect to the collective coordinate in the GCM configurations.