Dominant Path Research Articles

A kinetic and mechanistic study of the self-reaction between two propargyl radicals.

The propargyl radical plays a critical role in various chemical processes, including hydrocarbon combustion, flame synthesis, and interstellar chemistry. Its unique stability arises from the delocalization of π-electrons, allowing it to participate in a wide range of reactions despite being a radical. The self-reaction of propargyl radicals is a fundamental step in synthesizing polycyclic aromatic hydrocarbons. In this work, therefore, a computational study into the C3H3 + C3H3 potential energy surface has been carefully characterized. The calculated results indicate that the reaction can occur by H-abstraction or addition of two propargyl radicals together. The H-abstraction mechanism can create the products P3 (H2CCC + H3CCCH) and P4 (H2CCCH2 + HCCCH) but the energy barriers of the two H-abstraction channels are very high (from 12 to 22kcal/mol). In contrast, the addition mechanism of two propargyl radicals forming the intermediates (I1, I5, I12) and the bimolecular products (P1, P2, P7, P11, P12) are dominant. Among the bimolecular products, the P11 (C6H4 + H2) product is the most energetically favorable, and the channel leading to this product is also the most preferred path compared to all other paths throughout the PES. The calculated enthalpy changes of various reaction paths in this study are in good agreement with the available literature data, indicating that the CCSD(T) method is suitable for the title reaction. The overall rate constant of the reaction depends on both temperature and pressure, reducing with temperature but rising with pressure. The calculated results agree closely with the available experimental values ​​and previous calculated data. Thus, it can be affirmed that in addition to the CASPT2 method as applied in the study of Georgievskii et al. (Phys. Chem. Chem. Phys., 2007, 9, 4259-4268), the CCSD(T) method is also very good for the self-reaction of two propargyl radicals. The M06-2X and CCSD(T) methods with the aug-cc-pVTZ basis set were used to optimize and calculate single-point energies for all species of the reaction. The bimolecular rate constants of the dominant reaction paths were predicted in the temperature and pressure ranges of 300-1800K and 0 - 76,000Torr, respectively, using the VTST and RRKM models with Eckart tunneling correction for the H-shift steps.

Prediction Method for the Distribution of the Effective Dominant Path of Sand Bodies Transporting Oil and Gas and Its Application

To study the oil and gas distribution law in the slope area of a hydrocarbon-bearing basin, one must first define the dominant hydrocarbon transport paths of sand bodies as the superimposed area of the contiguously distributed area of the sand bodies and the paleotectonic ridges at the top interface of the formation. Then, the oil and gas supply area of the oil source faults must be defined, as the overlapped area of the favorable transport paths of oil source faults and the width of their associated fracture zones. Stacking the two areas, we can delineate the distribution of the effective dominant paths of sand bodies transporting oil and gas. The results from our case study of the Qinan area show that the effective dominant paths of sand bodies transporting oil and gas in the lower sub-member within the first member of the Shahejie Formation (Es1L) in the Qinan area are distributed throughout the region, with better development in the west than in the east. And, the effective dominant paths in the eastern part extend from north to south, while those in the western part extend from northeast to southwest. These are favorable for the convergence of oil and gas generated from source rocks in the third member of the Shahejie Formation (Es3) in the main depression of Qikou Sag in the Es1L in the Qinan area. The results are consistent with the fact that oil and gas discovered in the Es1L in the Qinan area are mainly distributed in the central and western regions, with a small amount in the southeast. Therefore, the suggested method is feasible for predicting the effective dominant paths of sand bodies transporting oil and gas.

Fault tracing in multistage gearbox systems based on an improved transfer path analysis method

This study, has developed a novel structural dynamics decoupling method based on TPA. This approach effectively facilitates fault diagnosis and tracing in multistage gearbox systems. Initially, the research explores the relationship between the transfer function of systems with rigid link decoupling and the coupled system’s frequency response function. Compared with Huangfu et al. (2023) , the signal measurement points are reduced. The MWI (Yu et al., 2023) is employed to solve the inverse problem of bearing force identification. Subsequently, the decoupled frequency response and bearing forces are multiplied to calculate the path contribution, determining the dominant fault transfer path and thereby facilitating fault tracing in gearboxes. The effectiveness of this method is validated through numerical simulations and experimental studies, with fault characteristic enhancement exceeding 200%. To evaluate the method’s universality and robustness, experiments on diverse gearbox systems under varying conditions show enhanced fault characteristics across three fault types, confirming its generalizability.

The combustion mechanism of aluminium in the steam/carbon dioxide mixed atmosphere

AbstractThe ignition and combustion characteristics of aluminium (Al) in the steam/carbon dioxide (H2O/CO2) mixed atmosphere were calculated by using a close homogeneous catch reactor and premixed laminar flame‐speed of CHEMKIN‐PRO. The effects of initial reaction temperature and H2O/CO2 ratios on the system temperature, products, and ignition delay time were explored. The main reaction paths were analyzed by the temperature sensitivity. Al (l) entered the system with a pronounced phase transition and only one heating stage, but there are two heating stages in the Al (g) system. The reaction of Al in the H2O/CO2 mixed atmosphere has a positive effect on the ignition delay time of the system. The high contents of CO2 in the H2O/CO2 mixed atmosphere can increase the maximum temperature of system and decrease the ignition delay time. Temperature sensitivity analysis shows that AlO, Al2O, and AlOH are important intermediate products, and Al2O2 is the main substance that produces Al2O3. The dominant reaction path is Al → AlOH→AlO → Al2O → Al2O2 → Al2O3. In addition, when the initial temperature was 2300 K, the laminar flame velocity was calculated to reach 35.6 m/s.

Beekeeping and agropastoralism interactions through floral resources in the French Mount Lozère

Beekeeping has faced increasing difficulties during the past decades, among which is the decline in floral resources. Agriculture provides essential floral resources for beekeeping, but some farming practices have also been shown to be responsible for their decline. To provide floral resources for beekeeping, what type of agricultural transformation should be promoted, and how? To answer these questions, we still lack knowledge about the floral resources that are used by beekeeping and about the technical-economic obstacles that farmers face in implementing more favorable farming practices, particularly in agropastoral settings. To help fill these gaps, we develop a novel approach that frames both agropastoral farming and beekeeping as farming systems, by characterizing the beekeeping systems of a given place, the floral resources they use, and the impacts these farming systems have on floral resources. This approach is applied to the agropastoral landscapes of Mount Lozère, southern France, using a methodology based on semi-structured interviews with farmers and beekeepers addressing the agronomical functioning of their farms. We demonstrate that the floral resources used by beekeepers on Mount Lozère are threatened by the current dominant agricultural development paths, which seek to maximize the material productivity of labor. Such paths lead to the intensification of agricultural practices in harvested areas and the extensification of rangelands. These pathways are reinforced by the low remuneration of agropastoral labor and by the current rules of the European Union Common Agricultural Policy. “Frugal” farming, a farming system based on reduced inputs and investments, and labor-intensive practices, namely, a labor-intensive use of pasture, seems an effective way to produce floral resources. Both, agropastoral farmers and beekeepers, would benefit from an increase in the number of agricultural workers in agropastoral landscapes. This calls for public policies that promote a better remuneration of agropastoral labor, either directly or by driving market mechanisms.

Phase-space path integral approach to the kinetics of black hole phase transition in massive gravity

The dynamics of the state-switching process of black holes in dRGT massive gravity theory is presented using free energy landscape and stochastic Langevin equations. The free energy landscape is constructed using the Gibbons-Hawking path integral method. The black hole phases are characterized by taking its horizon radius as the order parameter. The free energy landscape provides three black hole phases: small, intermediate, and large. The small and large black holes are thermodynamically stable whereas the intermediate one is unstable. The Martin–Siggia–Rose–Janssen–de Dominicis (MSRJD) functional describes the stochastic dynamics of black hole phase transition. The Hamiltonian flow lines are obtained from the MSRJD functional and are used to analyze the stability and the phase transition properties. The dominant kinetic path between different phases is discussed for various configurations of the free energy landscape. We discuss the effect of black hole charge and the graviton mass on the critical behavior of black hole phase transition.

Analysis on typical characteristics and causes of coal mine gas explosion accidents in China.

Large-scale coal mine gas explosion (CMGE) accidents have occurred occasionally and exerted a devastating effect on society. Therefore, it is essential to systematically identify the characteristics and association rules of causes of CMGE accidents through analysis on large-scale CMGE accident reports. In this study, 298 large-scale CMGE accidents in China from 2000 to 2021 were taken as the data sample, and mathematical statistical methods were adopted to analyze their general characteristics, coupling cross characteristics, and characteristics of gas accumulation and ignition sources. Moreover, the text mining technology and the Apriori algorithm were used for exploring the formation mechanism of CMGE accidents, during which 46 main causal factors were identified and 59 strong association rules were obtained. Furthermore, an accident causation network was constructed based on the co-occurrence matrix. The key causal items and sets of CMGE accidents were clarified through network centrality analysis. According to the research results, electrical equipment failure, cable short circuit, mine lamp misfire, hot-line work, and blasting spark are the key ignition sources of CMGE. Fan failure, airflow short circuit, and local ventilation fan damage are the main causes of gas accumulation. Besides, the confidence levels of two association rules of "static spark-fan failure" and "blasting spark-airflow short circuit" are higher than 70%, indicating that they are the two dominant risk-coupling paths of gas explosions. In addition, six causes appear frequently in the shortest risk paths of gas explosion and are closely related to other causes, i.e., fan failure, local ventilation fan damage, static sparks, electrical equipment failure, self-heating ignition, and friction impact sparks. This study provides a new perspective on identifying causes of accidents and their complex association mechanisms from accident report data for practical guidance in risk assessment and accident prevention.

Ce anomaly in hemiboreal headwater streams: An indicator of dominant groundwater flow paths through the catchment

The water quality in headwater streams depends on the groundwater origin and its transport pathways before it eventually discharges as surface water. In this case study, we present the Ce anomaly of over 100 hemiboreal headwater streams in Sweden and discuss the potential of the Ce anomaly to define two stream end members as proxies for the stream origin. The data show a relation between topography and the Ce anomaly, with more negative values (−0.8 to −0.4) in hilly catchments with distinct slopes, defined as an oxidized groundwater end member. The second end member is dominated by groundwater discharge from reduced, organic-rich riparian and wetland soils (reduced groundwater) having small Ce anomalies (−0.3 to zero). Element concentrations show a wide range, depending on the end member of the stream. For example, redox elements (Fe, Mn, S and N) show concentrations up to five times in streams with small negative Ce anomalies (reduced groundwater) compared to the concentrations in streams with large negative Ce anomalies. While element concentrations (of the classic redox elements Fe, Mn, S, N) show seasonal variations due to a summer drought period and the resulting reduced conditions, the Ce anomaly is constant, offering an excellent indicator of the dominant groundwater flow paths regardless of seasonal variations.

Unraveling the NH3-SCR-DeNOx Mechanism of Cu-SSZ-13 Variants by Spectroscopic and Transient Techniques.

Commercial SSZ-13 zeolite with different n(Si)/n(Al) ratios and from different suppliers were subjected to a post-synthetic treatment in order to create mesopores of up to 15 nm. Furthermore, the materials were modified with copper ions and thoroughly physico-chemically characterized. The modified textural properties varied the nature of copper species, and thus, activity in the selective catalytic reduction of NOx with ammonia (NH3-SCR-DeNOx). Pulsed-field gradient nuclear magnetic resonance (PFG-NMR) studies with hexane as probe liquid revealed improved intracrystalline diffusion for some Cu-containing SSZ-13 materials. The NH3-SCR-DeNOx pathways are verified via in situ DR UV-Vis, in situ FT-IR and EPR, temperature-programmed studies as well as SSITKA studies that provide a mechanistic understanding of the reaction. Kinetic modelling results demonstrate the highest NH3-SCR-DeNOx reaction rates and up to 20 % lower energy barriers with n(Si)/n(Al) ratio of 6.5 for all modified forms (i. e., (NH4)Cu-SSZ-13_6.5 and Cu-SSZ-13_6.5_NaOH/0.1) and cause only negligible parasitic ammonia oxidation. The modelling of the stop-flow experiments further demonstrates that the SCR pathway via the HONO surface intermediate is present but barely contributes to the overall NO conversion compared to the dominant path between adsorbed NH3 and NO from the gas phase.

Objective performance indicators during specific steps of robotic right colectomy can differentiate surgeon expertise

BackgroundCurrent surgical assessment tools are subjective and nonscalable. Objective performance indicators, calculated from robotic systems data, provide automated data regarding surgeon movements and robotic arm kinematics. We identified objective performance indicators that significantly differed among expert and trainee surgeons during specific steps of robotic right colectomy. MethodsEndoscopic videos were annotated to delineate surgical steps during robotic right colectomies. Objective performance indicators were compared during mesenteric dissection, ascending colon mobilization, hepatic flexure mobilization, and bowel preparation for transection. ResultsTwenty-five robotic right colectomy procedures (461 total surgical steps) performed by 2 experts and 8 trainees were analyzed. Experts exhibited faster camera acceleration and jerk during all steps, as well as faster dominant and nondominant arm acceleration and dominant arm jerk during all steps except distal bowel preparation. During mesenteric dissection, experts used faster camera and dominant arm velocity. During medial-to-lateral ascending colon mobilization, experts used less-dominant wrist yaw and pitch, faster nondominant arm velocity, shorter dominant arm path length, and shorter moving times for camera, dominant arm, and nondominant arm. During lateral-to-medial ascending colon mobilization, experts had faster dominant and nondominant arm velocity and third-arm acceleration. During hepatic flexure mobilization, experts exhibited more camera movements, greater velocity for camera, dominant and nondominant arms, and faster third-arm acceleration. During distal bowel preparation, experts used greater dominant wrist articulation, faster camera velocity, and longer nondominant arm path length. During proximal bowel preparation, experts demonstrated faster nondominant arm velocity. ConclusionObjective performance indicators can differentiate experts from trainees during distinct steps of robotic right colectomy. These automated, objective and scalable metrics can provide personalized feedback for trainees.

Dynamic fracture mechanism from a pre-existing flaw in granite: Insights from grain-based modelling

Both heterogeneity and pre-existing flaws are closely associated with the mechanical response of crystalline granite. To uncover the underlying mechanism, grain-based model (GBM) based on particle flow code (PFC), i.e., PFC-GBM, with different contacts between any two grains, was employed to carry out numerical calculations to investigate the effect of a single flaw with various inclination angles on the dynamic behavior of LdB granite. The failure pattern is identified through density and spatial distributions of microcracks, and the primary fracture directions are obtained by microcrack orientations. Microcracks are divided into inter-Grain and intra-Grain types, and these two types are further classified into more subtypes according to mineral composition. IG cracks typically form during the pre-peak stage and tend to emerge earlier than TG cracks. Conversely, TG cracks are predominantly created during the post-peak stage but constitute a significant proportion irrespective of flaw inclination angle. A novel method is also proposed to acquire high-stress particles, which promote the identification of dominant macrocrack paths. Finally, the effect of particle size is also systemically analyzed.

Determination of dominant oscillation section in power system based on MSSA algorithm and dissipated energy

The identification of dominant oscillation paths is one of the key aspects in studying the stability of inter-area power grids. This paper proposes an improved multi-channel singular spectrum analysis (MSSA) algorithm combined with dissipative energy to identify dominant oscillation section in power systems. First, an improved MSSA method is introduced, which determines the order using the singular value energy spectrum and can effectively identify inter-area oscillation modes in power systems. Second, an energy function analysis method is proposed, which is well-suited for determining dominant oscillation section in power systems. This method is minimally affected by time-varying and nonlinear factors and allows for the visualization of generator states. Finally, the IEEE 68-bus system is used to construct an equivalent model, demonstrating the method's versatility. Simulation results validate the noise resistance, computational efficiency, and applicability to topology change scenarios of the proposed method. This method can accurately analyze inter-area oscillation modes and help to establish the dominant oscillation section.

Electrical field enhanced CO2 permeation through a carbon molecular sieve membrane: A combined density functional based tight binding and computational fluid dynamics study

An important challenge in membrane technology for gas separation is to simultaneously improve their permeability and selectivity. Often, the increase in one performance leads to the decline of the other. This study presents a solution to that problem by utilizing electrical field coupling to improve CO2 permeation through a nitrile-containing poly (arylene-ether-ketone) (PEK-C(CN)) carbon molecular sieve membrane. Density functional based tight binding simulations of CO2, CH4, and N2 adsorption on PEK-C(CN) monolayer were conducted without and with electric field. The findings revealed that the electric field strength and orientation affected the molecules bond lengths, atomic charges, and bond angles. Investigation of their adsorption energy dominantly favored CO2 adsorption. Analysis of the partial density of states confirmed that adsorption interactions with the membrane were due to CO2 responses to the applied electric field. It additionally proved the electrical stability of PEK-C(CN) membrane. Computational fluid dynamics simulations of gas permeation through PEK-C(CN) membrane were performed without and with electric field. Results indicated an average pore distribution around 0.5 nm. The velocity flow distribution aided locate the interconnected pores, bringing to the fore the dominant transportation paths of gas molecules. It was uncovered that although the application of an electric field significantly improved the membrane gas permeability, it was not necessarily beneficial to its selectivity. −5 V was determined to be the optimum potential for an improvement of CO2 permeability from 57.32 Barrer (no field) to 15924.91 Barrer, while also enhancing the selectivity. This work demonstrates the benefits of the electric field and its promising application in gas separation processes.

Comparing, slurry infiltration characteristics between calcareous and silica sands based on slurry infiltration column tests and CT scanning

Calcareous sand, also known as bioclastic deposits, has distinct composition and morphological characteristics compared to siliceous sand. The exploration of the South China Sea has revealed a high potential for slurry pressure balanced (SPB) shield tunnelling in coastal areas that pass through calcareous sand strata. However, the impact of the differences between calcareous sand and siliceous sand on filter cake formation remains unclear. This study aimed to investigate the slurry infiltration characteristics of calcareous sand and siliceous sand (with Fujian sand as a representative) with the same permeability coefficient through micro slurry infiltration column tests. The macroscopic differences in slurry infiltration between the two media were observed. The sand columns were scanned before and after slurry infiltration using a CT scanner, allowing for the reconstruction of both the original particles’ topology and the pore network of the sand column. A pore network model was established, and the Dijkstra algorithm was used to identify the dominant particle infiltration paths, with flow resistance serving as the weight criterion for evaluating pore connectivity performance. The study found that the differences in particle topology and connectivity of the pore network were the fundamental mechanisms underlying the macroscopic slurry infiltration behaviors between different types of sands. These differences also explained the influence of particle size on the slurry infiltration characteristics for the same type of sand. The findings shed light on the fundamental mechanisms driving the differences in slurry infiltration behaviors and provide insights into the influence of particle size on slurry infiltration characteristics within the same type of sand.

Enhancement of Cu-to-Cu bonding property by residual stress in Cu substrate

This study investigated the use of copper nanoparticles (Cu NPs) as a novel material for interconnecting joints in advanced electronic packaging technology. Cu NPs offered a promising alternative due to their excellent electrical and thermal properties. Cu NPs were characterized as single crystals by a transmission electron microscope, and electron backscatter diffraction confirmed that the grain size of the Cu substrate was about 11 μm and only became slightly larger after thermal annealing. Surface diffusion was determined to be the dominant kinetic path for Cu NP sintering on the substrate. An additional driving force for sintering was validated by measuring the stress state using X-ray diffraction. The characterization results provided evidence for proposing a mechanism to explain how residual stress influenced atomic behavior during the sintering process. High residual stress enhanced the strength of the Cu NP joints and improved the reliability of electronic devices.

Numerical study on gas reaction path of InN-MOVPE with three typical reactors

This study investigates the controversies about the gas-phase reaction path in the InN MOVPE process. Numerical modeling of the reaction-transport processes in three typical reactors was conducted for main reaction paths. By comparisons of the molar concentrations of the major In-containing species, it was determined that the different approaches of the gas mixing and heating led to three distinct reaction paths. When the non-premixed gas precursors are heated very fast upon entering the reactor, the adduct/amide formation path predominates and the pyrolysis path is negligible (Path 1). When the precursors are mixed at room temperature and heated gradually, the adduct TMIn:NH3 dissociates back into TMIn, with the pyrolysis path dominating. However, the formation of amides DMInNH2 intensifies the generation of nanoparticles (Path 2). When mixing occurs at warm temperature and heated fast, both the pyrolysis and adduct paths co-exist, but their effects are different (path 3). In the CCS reactor the dominant reaction path will be Path 1, while in the vertical reactor with a greater height, Path 2 is predominant. In the pre-mixed horizontal reactor, Path 3 is dominant, the pyrolysis path forms a competition with the adduct path near the substrate, and the adduct path dominating at the top of the reactor.

Semi-blind sparse channel estimation using regularized expectation maximization

In Massive multiple-input multiple-output (MIMO) systems, channel estimation is crucial. The large size of the antennas causes a significant pilot and feedback overhead, making it challenging to estimate channels in massive MIMO systems. Besides, the studies have shown that mmWave channels are sparse due to the limited number of dominant propagation paths. Therefore, the motivation of this paper is to exploit the inherent sparsity of the massive mmWave MIMO channels to develop a semi-blind channel estimation with reduced number of pilots. To this goal, an expectation maximization (EM) based technique has been developed which leverages the sparsity of the underlying channel for its better estimation. An iterative approach is proposed to solve the modeled problem which simultaneously updates the channel coefficients and data symbols using available data and system structure at each iteration. The proposed method imposes sparsity with the aid of Smoothed L0 norm (SL0) in the M-step. The simulation results demonstrate the proposed method have quick convergence and lower channel estimation error compared to the existing methods. As a quantitative evaluation, the proposed method attains the normalized mean square error of 9×10−2 and 7×10−3 at SNR=5dB and SNR=15dB, respectively.

Dissociative adsorption of supersonic CH3Cl on Cu oxide Surfaces: Cu2O(111) and bulk Cu2O precursor “29”-Structure on Cu(111)

To examine the elementary steps of the Rochow-Müller process we placed copper oxides, viz., Cu2O(111) and the bulk Cu2O precursor “29”-structure on Cu(111), under supersonic molecular beams (SSMB) of CH3Cl. The SSMB energies range from 0.5-1.9 eV. We employed X-ray photoemission spectroscopy (XPS) in conjunction with synchrotron radiation (SR) to determine the resulting adsorbed species present. We identified two reaction paths, viz., Reaction I and Reaction II. Reaction I involves dissociative adsorption of CH3Cl. In Reaction II, CH3Cl also dissociates, but with Cl as the dominant adsorbed species (higher than that of adsorbed carbonaceous species, as observed for Reaction I). For the incident energies and exposure conditions considered, we found Reaction II as the dominant reaction path for CH3Cl reaction on both Cu2O(111) and the “29”-structure on Cu(111).

Electroluminescent vertical tunneling junctions based on WSe2 monolayer quantum emitter arrays: Exploring tunability with electric and magnetic fields

We experimentally demonstrate the creation of defects in monolayer WSe2 via nanopillar imprinting and helium ion irradiation. Based on the first method, we realize atomically thin vertical tunneling light-emitting diodes based on WSe2 monolayers hosting quantum emitters at deterministically specified locations. We characterize these emitters by investigating the evolution of their emission spectra in external electric and magnetic fields, as well as by inducing electroluminescence at low temperatures. We identify qualitatively different types of quantum emitters and classify them according to the dominant electron-hole recombination paths, determined by the mechanisms of intervalley mixing occurring in fundamental conduction and/or valence subbands.

Analysis of geothermal heat recovery from abandoned coal mine water for clean heating and cooling: A case from Shandong, China

Exploiting heat from abandoned mine water using heat pumps is attracting increasing attention worldwide. China has a large number of abandoned coal mines, but there are few applications of geothermal heat recovery from mine water. Here, we report a new case from Shandong, North China. Based on actual geological and underground space structures, numerical analysis is performed to study the flow and heat transfer in the complex connection network among roadways. For given temperature differences on the source side, the underground heat transfer is greatly influenced by flow rates in roadways. Under the acceptable performances and long-term stability of heat pumps, the maximum heat transfer capacity of roadways reaches 697.3 kW at the flow rate of 100 m3/h, with the power per unit length of 151.3 W/m, indicating a promising heat recovery potential. When switching between the extraction and injection well, both fluid directions and the distribution of flow rates in roadways change obviously, thereby affecting the underground heat transfer. Besides dominant flow paths, there exist weak flow paths, which can be identified by numerical analysis, and necessary blocking can be applied to optimize the flow and heat transfer. Excessively long horizontal straight roadways for heat exchange should be avoided.