Theoretical Study Research Articles

Characterization of Deformational Isomerization Potential and Interconversion Dynamics with Ultrafast X-ray Solution Scattering.

Dimeric complexes composed of d8 square planar metal centers and rigid bridging ligands provide model systems to understand the interplay between attractive dispersion forces and steric strain in order to assist the development of reliable methods to model metal dimer complexes more broadly. [Ir2 (dimen)4]2+ (dimen = para-diisocyanomenthane) presents a unique case study for such phenomena, as distortions of the optimal structure of a ligand with limited conformational flexibility counteract the attractive dispersive forces from the metal and ligand to yield a complex with two ground state deformational isomers. Here, we use ultrafast X-ray solution scattering (XSS) and optical transient absorption spectroscopy (OTAS) to reveal the nature of the equilibrium distribution and the exchange rate between the deformational isomers. The two ground state isomers have spectrally distinct electronic excitations that enable the selective excitation of one isomer or the other using a femtosecond duration pulse of visible light. We then track the dynamics of the nonequilibrium depletion of the electronic ground state population─often termed the ground state hole─with ultrafast XSS and OTAS, revealing a restoration of the ground state equilibrium in 2.3 ps. This combined experimental and theoretical study provides a critical test of various density functional approximations in the description of bridged d8-d8 metal complexes. The results show that density functional theory calculations can reproduce the primary experimental observations if dispersion interactions are added, and a hybrid functional, which includes exact exchange, is used.

Theoretical study on the reaction mechanism of Dakin oxidation: influence of methoxy groups

Theoretical study on the reaction mechanism of Dakin oxidation: influence of methoxy groups

Theoretical Studies on the Reaction Mechanism of Schiff Base Formation from Hexoses.

The Maillard reaction is one of the nonenzymatic post-translational modifications of proteins. Products of this reaction are considered to be related to aging diseases and the sensation of taste. In the initial stage of the Maillard reaction, Schiff base formation first occurs by the nucleophilic attack of amine nitrogen in proteins, and then, the reaction proceeds through the formation of 1,2-eminal and Amadori compounds. In this study, we computationally investigated the reaction pathway of Schiff base formation from hexoses. The optimized geometries of energy minima and transition states were calculated by using the density functional theory with the CAM-B3LYP/6-311+G(2d,2p) level of theory. The Schiff base formation progressed through three steps: two steps of carbinolamine formation and one step of dehydration. The dehydration is considered to be the rate-determining step in all hexoses because the activation barrier of the dehydration was higher than that of the carbinolamine formation. Furthermore, the steric configuration of the OH group at positions 2 and 3 affected the activation barrier.

Fatigue characteristics of rubber isolation layers used in high speed railway ballastless tracks: A theoretical and experimental study

In order to enhance operational conditions for high-speed trains on long-span bridges, the utilization of rubber under-ballast mats were taken as a novel isolation layer in ballastless tracks. Due to the increased train axle load, it is imperative to conduct investigation into the fatigue properties of the rubber isolation layer, so as to ensure the smoothness of the railways. In this work, a series of fatigue tests were performed on the rubber isolation layer to obtain the influence of stress amplitude and loading cycles on its fatigue performance. The results demonstrate a pronounced non-linear load–displacement relationship of the rubber isolation layer with increasing load, while the fatigue endurance significantly decreases with escalating the stress amplitude. Moreover, considering the hyperelastic properties of rubber material, the Mooney-Rivlin constitutive model was employed in finite element simulations. Subsequently, the stress distributions of the rubber isolation layer were analyzed, and the fatigue life was evaluated based on Luo stress method. The rubber isolation layer exhibits localized damage that does not affect the overall performance after 32 years of normal service condition. Therefore, the fatigue performance of the rubber isolation layer remains reliability, providing assurance for the application in ballastless tracks on high-speed railway long-span bridges.

Application of Different Animal Fats as Solvents to Extract Carotenoids and Capsaicinoids from Sichuan Chili.

Inspired by the proved dissolving power of vegetable oils for non-polar and low-polar natural compounds, animal fats with triglycerides as the major components were investigated as food-grade solvents in this study for the simultaneous extraction of carotenoids and capsaicinoids from Sichuan chili. The dissolving power of lard, beef tallow, chicken fat and basa fish oil in the extraction of er jing tiao chili was firstly compared, where animal oils with worse extraction ratios for carotenoids (0.79 mg/g in average) performed better for the extraction of capsaicinoids (0.65 mg/g in average). Furthermore, the solvent effect of animal fats on the oleo-extracts was evaluated in terms of fatty acid composition, oil quality indexes, crystal polymorphism, melting and crystallization behaviors, where no significant differences were observed between animal fats before and after extraction. The oxidative stability of animal fats could be 1.02- up to 2.73-fold enhanced after extraction and the pungency degree could reach the same spicy level as commercial hotpot oil. In addition, the Hansen solubility parameters of solvents and solutes were predicted for further theoretical miscibility study, which helps to make a better comprehension of the dissolving mechanism behind such oleo-extraction. Overall, animal fats demonstrated their considerable solvent power for extracting carotenoids and capsaicinoids simultaneously from Sichuan chili, which showed significant potential for developing a novel Sichuan spicy hotpot oil with enhanced flavor and stability.

Synthesis and evaluation of benzo[1,2,3]selenadiazole-isoxazoles as corrosion inhibitors for copper in NaCl: An integrated experimental and theoretical approach

In this study, we investigate the protective capabilities of two synthetic compounds, 5-methyl-5-(4-methylbenzo[d][1,2,3]selenadiazol-7-yl)-3-phenyl-4,5-dihydro-isoxazole (BHP) and 5-methyl-5-(4-methylbenzo[d][1,2,3]selenadiazol-7-yl)-3-(4-nitrophenyl)-4,5-dihydro-isoxazole (BNP), as corrosion inhibitors for copper in a 3.5 wt% NaCl solution. The chemical structure of these benzo[1,2,3]selenadiazolyl-isoxazole derivatives combines a benzo[1,2,3]selenadiazole core, which to our knowledge has not been previously studied for its anticorrosive activity on copper, with an isoxazole nucleus known in the literature as one of the most effective azoles in preventing copper corrosion. The efficiency and mechanism of copper corrosion inhibition were evaluated through electrochemical, theoretical, and morphological studies. Potentiodynamic polarization (PDP) showed that both BHP and BNP were effective in inhibiting copper corrosion. At 10−3 M, BHP showed a maximum inhibition efficiency of 80.24 %, while BNP achieved an even higher efficiency of 89.83 %. Adsorption behavior analysis indicated that both compounds followed the Langmuir isotherm. In addition, the high value of Kads (103 M−1) indicates a strong adsorption capacity of our molecules on the copper surface. The negative adsorption free energy (ΔG°ads=−34.14kJ/mol for BHP and ΔG°ads=−34.00kJ/mol for BNP) indicates a spontaneous adsorption process. Electrochemical impedance spectroscopy (EIS) showed that both compounds formed a thin protective layer on the copper surface, a finding further supported by surface morphology studies using scanning electron microscopy (SEM-EDX) and ATR-FTIR analysis.

A diminished North Atlantic nutrient stream during Younger Dryas climate reversal

The high rate of biological productivity in the North Atlantic is stimulated by the advective supply of nutrients into the region via the Gulf Stream (nutrient stream). It has been proposed that the projected future decline in the Atlantic Meridional Overturning Circulation (AMOC) will cause a reduction in nutrient supply and resulting productivity. In this work, we examine how the nutrient stream changed over the Younger Dryas climate reversal that marked the transition out of the last ice age. Gulf Stream nutrient content decreased, and oxygen content increased at the Florida Straits during this time of weakened AMOC. The decreased nutrient stream was accompanied by a reduction in biological productivity at higher latitudes in the North Atlantic, which supports the link postulated in theoretical and modeling studies.

Controlled Growth Lateral/Vertical Heterostructure Interface for Lithium Storage.

Artificial heterostructures with structural advancements and customizable electronic interfaces are fundamental for achieving high-performance lithium-ion batteries (LIBs). Here, we propose a design idea for a covalently bonded lateral/vertical black phosphorus (BP)-graphdiyne oxide (GDYO) heterostructure achieved through a facile ball-milling approach. Lateral heterogeneity is realized by the sp2-hybridized mode P-C bonds, which connects the phosphorus atoms at the edges of BP with the carbon atoms of the terminal acetylene in GDYO. The vertical connection of the heterojunction of BP and GDYO is connected by P-O-C bond. Experimental and theoretical studies demonstrate that BP-GDYO incorporates interfacial and structural engineering features, including built-in electric fields, chemical bond interactions, and maximized nanospace confinement effects. Therefore, BP-GDYO exhibits improved electrochemical kinetics and enhanced structural stability. Moreover, through ex- and in-situ studies, we clarified the lithiation mechanism of BP-GDYO, highlighting that the introduction of GDYO inhibits the shuttle/dissolution effect of phosphorus intermediates, hinders volume expansion, provides more reactive sites, and ultimately promotes reversible lithium storage. The BP-GDYO anode exhibits lithium storage performance with high-rate capacity and long-cycle stability (602.6 mAh g-1 after 1000 cycles at 2.0 A g-1). The proposed interfacial and structural engineering are universal and represents a conceptual advance in building high-performance LIBs electrode. This article is protected by copyright. All rights reserved.

Highly efficient degradation and detoxification of antibiotics over C–Dots/siderite heteroaggregates in photo-Fenton systems: The crucial role of C–Dots

The substantial presence of antibiotics in aquatic environments remains as a critical environmental issue that needs to be urgently addressed. In this study, mimetics of C–Dots/siderite heteroaggregates (CSI) were studied in a visible-light-responsive Fenton system as a platform for the degradation of antibiotics in contaminated water. By virtue of the excellent electron transfer of C–Dots, the sustained conversion cycles of Fe(II) → Fe(III) → Fe(II) in CSI were greatly accelerated, and meanwhile the H2O2 utilization was enhanced. The optimized CSI–3 nanocomposite displayed a prominent degradation efficiency towards a series of tetracycline analogs at ppb levels. Density functional theory (DFT) calculations indicated the excellent photo-Fenton catalytic performance of CSI originated from the increased d-band center and electron density, which considerably improves the utilization of H2O2. Both experimental and theoretical studies revealed that the correlated toxicity of degradation intermediates was significantly decreased. Additionally, a continuous flow device integrating the CSI photo-Fenton system maintained a high degradation efficiency after long-term treatment of simulated chlortetracycline wastewater. The presented work thereby confirms a spontaneous remediation process for the decontamination and detoxification of persistent organic pollutants under the action of heteroaggregates formed by engineered nanoparticles and natural minerals.

SM-BIM: A NEW CONCEPTUAL FRAMEWORK FOR MULTI-CRITERIA DECISION-MAKING PROCESS BASED ON SMART MATERIALS AND BUILDING INFORMATION MODELING

ABSTRACT Because the construction sector exerts a considerable environmental effect, especially on building materials, a growing interest in environmental design and construction has emerged. The United Nations has set sustainable development goals (SDGs) for 2030 to protect the environment, including energy conservation and doubling the global rate of improving energy efficiency, because building materials significantly affect energy consumption. Thus, building-material selection at the initial design phase is critical, and random selection of building materials often involves subjectivity, uncertainty, and ambiguity. This process costs time and resources while resulting in the inefficient environmental performance of buildings. Therefore, this study proposes the use of building-information modeling (BIM) as a tool because of its importance in attaining sustainability to aid in the selection process of smart materials (SMs) based on specified criteria and make the selection process faster and more accurate. This method is accomplished through a theoretical study of SMs and using a conceptual framework through four phases for multicriteria decision-making to improve energy efficiency and reduce the energy consumption of buildings. To pursue SDG 7, a theoretical and deductive approach is used.

Design and synthesis of heteroleptic Ni(II) dipyrrin complexes for electrochemical proton reduction reactions: Cyclic voltammetric and theoretical studies

The effect of nuclearity on electrochemical hydrogen generation using new heteroleptic Ni(II) complexes containing redox-active dipyrrin and dithiocarbamate ligands has been described. Complexes 1–2 have been meticulously characterized by spectroscopic studies (ESI-MS, IR, 1H, 13C NMR, UV–vis) and their structures unambiguously confirmed by X-ray single crystal analyses. Electrocatalytic properties of the complexes toward hydrogen evolution reaction have been investigated by cyclic voltammetric studies in an organic medium in the presence of acetic acid as a weak proton source. Notably, complexes 1 and 2 produce H2 via doubly reduced Ni(II) species i.e. Ni(0) in the presence of acetic acid. Further, these complexes exhibited significant electrocatalytic activity (TOF: 264 (1) and 650 s−1 (2). Controlled potential electrolysis established a minimum Faradaic efficiency of 92 (1) and 96 % (2). Complex 2 exhibited higher turnover frequency relative to 1, while 1 showed lower overpotential (0.35 V) in comparison to 2 (0.45 V). The stability of the complexes and the amount of produced H2 has been investigated by bulk electrolysis study. A tentative mechanism (ECEC; E, electrons and C, chemical steps) and involved intermediate species for the proton reduction reaction for 1 has been established by theoretical studies.

Manoeuvring urban spaces in-between public and private: female agency in early-twentieth-century Gothenburg

ABSTRACT This article analyses female agency in early twentieth-century Gothenburg. It argues that female urban practices were a major catalyst for the transformation of urban space in the port city, which has traditionally been attributed to male-dominated activities in trade, industry and urban politics. Drawing on women’s personal memories and on insights offered by theoretical studies that consider gender and mobility as constitutive elements of urban space, the article focuses on women’s mobile practices in the rapidly changing industrial port city: on female migration, on how women navigated the labour market, and on their perception as home-makers. In doing so, it places particular emphasis on how women acted in the blurred boundaries between ‘public’ and ‘private’ spaces and thereby on one of the major ordering principles of urban life.

An Improved Multi-point Chord Reference Measurement Device and Error Correction Method for Corrugation Measuring in Sharp Curves

Background: The traditional chord reference method and its device have faced challenges matching the sharp curve track. Thus, it is of utmost importance to research and develop a measurement device and method that can obtain accurate and comprehensive information regarding rail running band corrugation. Aims: It provides a solution for the measurement of the multi-point chord reference method on sharply curved rails and, at the same time, meets the demand for data richness and accuracy in theoretical studies on the causes of rail corrugation and wheel-rail contact relationships. Objective: This paper aims to research and design a measurement device based on the multi-point chord reference method for the rail running band corrugation. Meanwhile, the error in measuring the sharp curve rail is corrected and verified by simulation. Methods: The lateral information of rail running band is obtained by using a line laser profile sensor; the rail corrugation measurement model and error correction model of the rail running band area are established based on multi-point reference system; the simulation of the system model is carried out using Matlab; and the mechanical structure is built for static testing. Results: The measurement model based on the profile sensor and multi-point chord reference system can accurately obtain the rail corrugation waveform of any longitudinal measurement line in the running band area. The measurement results can be accurately corrected for a radius of 200m- 400m, the error parameters can be effectively improved, and the mechanical mechanism of the measurement system runs stably. Conclusion: The results show that the measurement model can accurately measure the rail corrugation of the sharp curve section, and the multi-waveform in the rail running band area has good measurement performance, but the mechanical structure can be optimized and improved in the light weight.

Investigation on bearing resistance of thin-walled circular steel tube subjected to eccentric loading

In the engineering structures using circular steel tube (CST), the eccentric loading of CST members often occurs due to installation error and structural form. Existing research mainly focuses on the bearing resistance of circular steel pipes under the condition of eccentricity at one end. In practical application, both ends of CST members also may be eccentric. And with the increase in eccentricity, material yielding may occur prior to flexural buckling. So far, it’s lack of reports about the mechanical behavior of CST members subjected to eccentric loading at both ends and the boundary between material yielding and flexural buckling. This paper presents experimental, numerical and theoretical studies on bearing resistance of thin-walled circular steel tube with slenderness ratio of 30, 40 and 50, subjected to eccentric loading at one end and both ends, respectively. The study reveals a significant discrepancy in the prediction of bearing resistance for circular tubes subjected to eccentric loading at both ends according to existing design codes. Considering the synthesis of bending moment and deflection caused by eccentric loading at both ends, the calculation method of the bearing resistance based on flexural buckling of CST is established, which enhances the prediction accuracy of test verification. In addition, a theoretical boundary between the two failure modes appearing in CST members under eccentric loading at one and both end(s) - flexural buckling and reaching the material yielding strength - was established as dominated by the slenderness ratio and loading eccentricity.

Anderson acceleration with approximate calculations: Applications to scientific computing

SummaryWe provide rigorous theoretical bounds for Anderson acceleration (AA) that allow for approximate calculations when applied to solve linear problems. We show that, when the approximate calculations satisfy the provided error bounds, the convergence of AA is maintained while the computational time could be reduced. We also provide computable heuristic quantities, guided by the theoretical error bounds, which can be used to automate the tuning of accuracy while performing approximate calculations. For linear problems, the use of heuristics to monitor the error introduced by approximate calculations, combined with the check on monotonicity of the residual, ensures the convergence of the numerical scheme within a prescribed residual tolerance. Motivated by the theoretical studies, we propose a reduced variant of AA, which consists in projecting the least‐squares used to compute the Anderson mixing onto a subspace of reduced dimension. The dimensionality of this subspace adapts dynamically at each iteration as prescribed by the computable heuristic quantities. We numerically show and assess the performance of AA with approximate calculations on: (i) linear deterministic fixed‐point iterations arising from the Richardson's scheme to solve linear systems with open‐source benchmark matrices with various preconditioners and (ii) non‐linear deterministic fixed‐point iterations arising from non‐linear time‐dependent Boltzmann equations.

Structural, magnetic, and electronic properties of a GdAsSe single crystal: Experimental and theoretical studies

Structural, magnetic, and electronic properties of a GdAsSe single crystal: Experimental and theoretical studies

Dyakonov surface waves in dielectric crystals with negative anisotropy

Abstract Since the initial discovery of Dyakonov surface waves at a flat infinite interface of two dielectrics, at least one of which is positively anisotropic, extensive research has been conducted towards their theoretical and experimental studies in materials with positive anisotropy. The potential applications of these waves were initially limited due to the stringent conditions for their existence and the requirement for position anisotropy. In our study, we present the theoretical prediction and experimental observation of a novel type of Dyakonov surface waves that propagate along the flat strip of the interface between two dielectrics with negative anisotropy. We demonstrate that the conditions for surface waves are satisfied for negatively anisotropic dielectrics owing to the specific boundaries of the strip waveguide confined between two metallic plates. We study such modes theoretically by using the perturbation theory in the approximation of weak anisotropy and demonstrate that the electromagnetic field distribution in these modes is chiral. Experimental verification of theoretical predictions is made in the microwave range using 3D-printed negatively anisotropic water-dielectric metamaterial slabs. The existence of Dyakonov surface waves in negative crystals prompts a reassessment of the list of materials suitable for practical realization of these waves in the visible and infrared ranges. Due to the ability of the considered modes to transmit chiral light, they have potential in the sensing of chiral organic molecules.

Theoretical analyses and experimental study on the factors influencing the pressure resistance of the magnetorheological grease seal with pinch mode pole piece

This paper mainly focuses on experimental research and theoretical analysis on the pressure resistance capability of magnetorheological grease rotary shaft sealing with pinch mode pole piece structure. Combining magnetorheological grease and pinch mode pole piece structure, the using of permanent magnet as magnetic source is aiming to reduce the lag of yield stress establishment and release. Herein, the micro-nano composite magnetorheological grease was prepared. Right after the synthesis process, its magnetization properties and rheological properties were scientifically and systematically characterized. The influence of different gaps and tooth widths on the magnetic induction intensity is analyzed by finite element method. Based on the theoretical method, the pressure resistance capacity induced by magnetic force is calculated. By comparing the theoretical calculation and experimental results of the pressure resistance, the cause of error and failure is analyzed.

Exploring Antimicrobial Hydroxypropyl-β-Cyclodextrin Inclusion Complexes for Cheese Preservation: A Combined Theoretical and Experimental Study

Exploring Antimicrobial Hydroxypropyl-β-Cyclodextrin Inclusion Complexes for Cheese Preservation: A Combined Theoretical and Experimental Study

Human capital for the green economy

This study aims to assess the market availability of human capital for the needs of the green economy under the conditions of the changing labour market in Poland. It is a theoretical and analytical study based on desk research and critical analysis of available factual information. Based on an analysis of quantitative data describing the age structure and education of Poles from the perspective of three consecutive decades, a growing labour supply deficit was found. It also points to a possible shortage of competencies needed to green the economy. It was emphasised that, in view of the low effectiveness of the state's prevention policy aimed at preventing the growing demographic crisis, it would be necessary to supplement the shortage of workers from external resources, that is, labour migration. However, this may also be difficult because the labour markets in other European countries become increasingly competitive. Recommended solutions to foster labour market sustainability for the green economy may be to delay the exit of employees from the labour market, boost female economic activity, and make the education system more efficient.