Path Changes Research Articles

A modified mixed-mode Timoshenko-based peridynamics model considering shear deformation

The original two-dimensional bond-based peridynamic (BBPD) framework, which only considers the pairwise forces (compression and tension) between two material points, is extended by incorporating the effect of shear deformation in the calculations and its influence on the failure of the bonds. To this end, each bond is considered as a short Timoshenko beam, and by doing so, the traditional BBPD is enhanced into a more comprehensive model known as multi-polar peridynamic (MPPD). The proposed novel approach explicitly considers the shear influence factor used in Timoshenko beams and introduces a strain-based shear deformation failure criterion. The model is then validated against two benchmark experimental tests (i.e., a standard pure mode I edge crack, and a Kalthoff-Winkler configuration) reported in the literature under in-plane dynamic loading and plane stress conditions. In most cases, the developed model is shown to be more accurate in predicting the crack paths obtained from the experimental results when compared to other theoretical methods delineated in the literature. Furthermore, a noticeable change in crack branching and crack path is observed in a study on the effects of Poisson's ratio and the loading rate. This investigation also demonstrated that the proposed MPPD model can accommodate materials with Poisson's ratios up to 1/3, expanding the range beyond the traditional BBPD limitations.

How has the relationship between major financial markets changed during the Russia–Ukraine conflict?

Geopolitics events have a significant impact on financial markets in the process of global economic integration and financial liberalization. Focusing on the 2022 Russia-Ukraine conflict, this paper utilizes the TVP-VAR network connectedness approach to investigate its specific impacts on the connectedness of major global financial markets. It examines the dynamic evolution of high-frequency and low-frequency shocks on market correlations during the pre-conflict, initial, and stalemate stages, revealing the changes in risk transmission paths. Findings show that the conflict led to increased market interconnectedness. Low-frequency became a major part of the total spillover, signaling long-term structural changes. The stock and foreign exchange market initially responded swiftly, serving as starting points for risk diffusion. The commodity market has been risk receivers throughout the conflict period. Intra-market and cross-market linkages have also changed. The German stock market was the main source of risk spillovers in the conflict, influencing international market linkages. In the global financial market network, several stock markets were the primary risk transmitters in the early stage of the conflict, while foreign exchange markets took on this role during the stalemate period. In addition, gold continues to play a safe-haven role. Furthermore, the TVP-VAR model is used to quantitatively assess the extent of the impact of the conflict on the spillover effects of major global financial markets at different time points and lags. Based on these findings, this paper constructs diversified portfolios and proposes a series of targeted risk management recommendations, which provide a theoretical basis for future policy formulation under similar crises.

Analyzing and Modeling the Dynamic Electrical Characteristics of Nanocomposite Large-Range Strain Gauges.

Flexible high-deflection strain gauges have been demonstrated to be cost-effective and accessible sensors for capturing human biomechanical deformations. However, the interpretation of these sensors is notably more complex compared to conventional strain gauges, particularly during dynamic motion. In addition to the non-linear viscoelastic behavior of the strain gauge material itself, the dynamic response of the sensors is even more difficult to capture due to spikes in the resistance during strain path changes. Hence, models for extracting strain from resistance measurements of the gauges most often only work well under quasi-static conditions. The present work develops a novel model that captures the complete dynamic strain-resistance relationship of the sensors, including resistance spikes, during cyclical movements. The forward model, which converts strain to resistance, comprises the following four parts to accurately capture the different aspects of the sensor response: a quasi-static linear model, a spike magnitude model, a long-term creep decay model, and a short-term decay model. The resulting sensor-specific model accurately predicted the resistance output, with an R-squared value of 0.90. Additionally, an inverse model which predicts the strain vs. time data that would result in the observed resistance data was created. The inverse model was calibrated for a particular sensor from a small amount of cyclic data during a single test. The inverse model accurately predicted key strain characteristics with a percent error as low as 0.5%. Together, the models provide new functionality for interpreting high-deflection strain sensors during dynamic strain measurement applications, including wearables sensors used for biomechanical modeling and analysis.

Student and alumni perspectives on paths into and out of biomedical engineering

Biomedical engineering (BME) has one of the highest proportion of women students of any discipline in Canada, and at University of British Columbia (UBC). Anecdotal evidence, based on instructors' interactions with senior students, suggests that women and gender-minority students in UBC’s BME program might leave engineering post-graduation, at higher numbers and for careers in health sciences/medicine. Our aim was to examine reasons for choosing BME, changes in career goals degree and post-graduation career paths of alumni. We conducted 21 semi-structured interviews with current/past BME students and identified five themes related to pursuing/continuing in BME: Positive and Negative Family Influences; Safety Net of a BME Degree; Dual Identities as Engineer and Physician; Perceived Need for High Grade Averages as a Barrier; and Social Environment as a Factor in Choosing Disciplines. These themes are interconnected, and a combination of themes is needed to explain why students choose to pursue/continue in BME.

Advanced temporal analysis of anode activity during mode transitions in high current vacuum arcs

Abstract Anode activity in high current vacuum arcs leads to the formation of various high current modes and transitions between them. Intense material evaporation during the anode spot mode and formation of a neutral vapour cloud during the anode plume mode modify the arc plasma properties and, hence, can have a crucial impact in applications, like e.g. reduction of interruption performance of switching devices. The influence of anode mode appearance on arc plasma parameters and on anode surface temperature was studied in detail by a novel optical diagnostic technique—intensified video optical emission spectroscopy. Employing advanced diagnostic methods, the ground state density, excitation temperature and pressure profiles close to the anode surface have been determined. For the anode plume mode, higher copper vapour pressure was found in the plume shell compared to its core. The copper ion density distribution shows a maximum outside of the plume shell. Consequently, a higher electrical conductivity in the surrounding area of the plume might be expected, i.e. the arc current flows around the plume rather than through it. Analysis of the temporal evolution of electrical and optical signals reveals that voltage jumps and drops during the mode transitions are accompanied by noticeable changes in the anode surface temperature. Thus, the formation of the anode plume leads to temperature lowering while the transition to the anode spot mode is accompanied by a temperature increase. In general, a clear correlation between electrode surface temperature and arc voltage in the case of constricted anode attachment is found. The results of this study give new insights into anode plume properties and consequences of anode mode transitions. Reversible mode transitions and correlations between arc voltage and anode surface temperature, as well as changes in the current path during anode plume mode, have to be considered as factors for optimization of electrode design and choice of materials for switching applications.

Analysis of cell characteristics using back oxide trap charge effect in various channel structures of 3D-NAND flash

Abstract This study investigates how trap charges in the back oxide layer affect the memory performance of 3D NAND flash memory. We used TCAD to simulate the effect on cell reliability, focusing on retention and interference characteristics, based on changes in current paths and program speed as initial cell characteristics. Additionally, we applied these findings to various channel structures — planar, concave, and convex — that can occur in 3D NAND. Our results indicate that the optimal trap charge for enhancing cell performance lies between -10¹¹ and -10¹⁰ /cm³ and should not exceed -1011 /cm3. Through this research, we can expect the potential for effectively inserting trap charges in actual manufacturing processes to improve the performance characteristics of 3D NAND cells.

Model-free active noise control using second-order simultaneous perturbation stochastic approximation algorithm for periodic noise

Model-free active noise control (ANC) using simultaneous perturbation stochastic approximation (SPSA) algorithm has recently attracted interest of researchers since it avoids the problem of secondary path modeling (SPM). However, the existing SPSA-based ANC methods are all based on the first-order SPSA algorithm and the convergence rate of these methods are significantly lower than that of the Filtered-x least mean square (FxLMS) algorithm. In order to enhance the convergence performance, this paper introduces the second-order SPSA algorithm into the ANC system. During the implementation of the second-order SPSA algorithm, a novel method of matrix positive definite transformation based on eigenvalue decomposition (EVD) is proposed. Convergence performance and tracking performance of ANC using the second-order SPSA algorithm are compared with ANC using the FxLMS algorithm and the standard SPSA through simulation and experimental verification. Simulation and experimental verification results show that ANC using the second-order SPSA algorithm can not only achieve the convergence rate comparable to that of ANC using the FxLMS algorithm, but also track the secondary path change.

A strain rate-dependent distortional hardening model for nonlinear strain paths

In this paper, a strain rate-dependent distortional hardening model is firstly proposed to describe strain rate-dependent material behaviors under linear and nonlinear strain paths changes in 0≤θpathchange≤180∘. The proposed model is formulated based on the simplified strain rate-independent distortional hardening model (Choi and Yoon, 2023). Any yield function could be used for the strain rate-dependent isotropic and anisotropic yielding. For the linear strain path, the strain rate-dependent isotropic hardening behavior could be explained by two state variables representing rate-dependent yielding and convergence rate of flow stress under monotonically increasing loading condition, respectively. For the nonlinear strain paths, the strain rate-dependent material behaviors such as Bauschinger effect, yield surface contraction, permanent softening, and nonlinear transient behavior could be described by modifying the evolution equations of the simplified strain rate-independent distortional hardening model with a logarithmic term of strain rate. For the verification purpose, it was used the strain-rate dependent tension-compression experiments of TRIP980 and TWIP980 (Joo et al., 2019). In addition, a high speed U-draw bending test was conducted with original and pre-strained specimens. The springback prediction in high speed U-draw bending test was performed by using strain rate-independent isotropic, strain rate-dependent isotropic-kinematic and distortional hardening models. It is identified that the proposed model showed the most accurate prediction for the pre-strained specimen where the possible bilinear and trilinear path change in 0≤θpathchange≤180∘ is observed while it showed the same accuracy for the original specimen where main strain path change occur in forward-reverse manner (θpathchange=180∘).

Impact of short-term aircraft noise on cardiovascular disease risk in the area surrounding London Heathrow airport: the RISTANCO epidemiological study.

Long-term exposure to aircraft noise has been associated with small increases in cardiovascular disease risk, but there are almost no short-term exposure studies. Research questions were: Is there an association between short-term changes in exposure to aircraft noise and cardiovascular morbidity and mortality? What are the key effect modifiers? Is there variability in risk estimates between areas with consistent versus changing patterns of noise exposure? Do risk estimates differ when using different noise metrics? Descriptive analyses of noise levels and variability at different times of day, analyses of inequalities in noise exposure and case-crossover analyses of cardiovascular events in relation to aircraft noise exposure. Area surrounding London Heathrow airport. 2014-18. Whole population in study area. Cardiovascular disease hospitalisations and mortality. Aircraft noise levels modelled using a standard noise model for: (1) daily equivalent continuous sound levels at different times of day; (2) daily number of events above defined noise thresholds (2018 only). National Health Service digital hospital admission records and Office for National Statistics mortality records for 2014-18 for cardiovascular outcomes, plus individual-level confounders available from healthcare records. Confounder data including road traffic noise (Leicester modelled), rail noise and air pollution (Department for Environment, Food and Rural Affairs), area level deprivation and ethnicity (UK Census). The morning shoulder period (06.00-07.00 hours) was the noisiest of all eight bands (mean: 50.92 dB). The morning shoulder period also had the third highest number of noisy events (flights) > 60 dB per day, with three events across postcodes on average. However, the highest number of noisy events occurred in daytime (highest between 07.00 and 15.00 hours, second highest 15.00 and 19.00 hours). To identify areas with high variability in aircraft noise exposure (due to changes in flight paths because of wind direction and airport operations), we used coefficients of variation (CoV). The period 24.00-04.30 hours had the highest mean CoV (67.33-74.16), followed by 04.30-06.00 hours and 23.00-24.00 hours. Postcodes in the least deprived quintiles of Carstairs index or avoidable death rate had the lowest noise levels. In case-crossover analyses, we observed increased risk for cardiovascular disease hospital admissions for evening noise 19.00-23.00 hours (odds ratio 1.005, 95% confidence interval 1.000 to 1.010 per 5 dB), but not for other periods or mortality. Further analyses suggested that increased risks were occurring in postcodes with low CoV for noise. We found effect modification by age, sex, ethnicity, deprivation and season. The industry standard noise model, the Aviation Environmental Design Tool, used does not take account of wind direction, which may have led to some exposure misclassification. We developed a comprehensive dataset of daily aircraft noise variability. We found small associations between cardiovascular hospitalisations (but not deaths) and evening aircraft noise levels, particularly in areas with low variability of noise. More studies are needed to understand the effect of noise variation and respite/relief on cardiovascular disease. This award was funded by the National Institute for Health and Care Research (NIHR) Public Health Research programme (NIHR award ref: 15/192/13) and is published in full in Public Health Research; Vol. 12, No. 13. See the NIHR Funding and Awards website for further award information.

Experimental and modeling investigation on anisotropic plastic flow of metal plates under nonproportional loading conditions

The plastic deformation behavior of metal plates has been proved to be affected by loading paths. Plastic flow is a critical component in the mechanical description of plastic deformation, like yield and hardening. In this work, the anisotropic plastic flow of two metal plates (16MnCr5 and S420MC) under non-proportional loading conditions was investigated. Large specimens manufactured along different orientations were pre-tensioned up to various strain levels; subsequently, small uniaxial tensile specimens were cut from the pre-tensioned specimens along different orientations with the interval of 15°, and then loaded to rupture. Meanwhile, the r-value, a measure of anisotropic plastic flow, was recorded. Result shows that for the studied plates which had constant r-value in the monotonic uniaxial tensile tests, a downward evolution of the r-value against plastic strain was observed when the Schmitt angle of two stage loading directions was greater than 90°. As the plastic strain in the subsequent loading stage accumulated, the r-value dropped from a higher level to its original level within a strain range about 6.0%. Based on the transient r-value evolution, a HEXAH-based evolutionary plastic potential model was constructed within the framework of non-associated flow (non-AF) theory. In the model, a local ellipse-shape distortion of the plastic potential surface was defined during plastic deformation process and when the Schmitt angel exceeded 90°, such distortion caused a downward evolution of the r-value in the subsequent deformation. The calibration result indicates that the model could reproduce the transient r-value response relevant to loading path change. The proposed evolutionary plastic potential model can be applied together with different anisotropic hardening models in the non-AF theory to give a detailed description of the plastic deformation behavior and hopefully provide a solution for the accurate simulation of the complex sheet metal forming process.

Communication Mechanism and User Sentiment Analysis of Public Emergencies on Social Media: A Case Study of the Wenzhou Doctor-Patient Dispute on July 19

This study aims to explore the communication mechanism and user sentiment analysis of public emergencies in social media. Taking the doctor-patient dispute in Wenzhou, China on 7.19 as an example, the study systematically analyses the dissemination path, speed, influence and user sentiment changes of the incident in social media, and through data collection and analysis, the study reveals that the incident Through data collection and analysis, the study reveals the evolution of the incident on social media platforms from the initial release of information, to the buzz of discussion, to the decline of public opinion. The study also adopts a comparative analysis method, comparing the doctor-patient dispute in Wenzhou with the Tangshan man-beating incident, to analyse the differences between the two incidents in terms of speed of dissemination, duration, and users' emotions, and to further explore the characteristics of the dissemination of social emergencies and the influencing factors in the social media. This study provides theoretical support for monitoring and guiding public opinion in social media, and proposes strategies to effectively respond to public opinion crises.

An X-ray diffraction study of the influence of linear and changing strain paths on strain and texture evolution in AA6111-T4 aluminium alloy sheets

Multi-stage automotive stamping processes involve both linear and changing strain paths. While extensive research exists on linear strain paths and discontinuous strain path change, the study of continuous strain path change is limited due to the need for sophisticated experimental procedures. In this paper, the effect of continuous strain path change on strain, strain hardening behaviour, microstructure, and texture evolution was compared with that of discontinuous strain path change in AA6111-T4 aluminium alloy using a novel experimental setup comprising an in-situ mechanical rig and cruciform sample. An X-ray source was used to obtain diffraction patterns, which were analysed to measure diffraction intensities and lattice strains at the {111}, {200}, {220} and {311} lattice planes to study strain hardening behaviour, microstructure, and texture evolution during the loading paths. The experiments were repeated outside the X-ray diffraction chamber to study macroscopic strain evolution and hardening behaviour of the samples using a digital image correlation system. It was found that the absence of unloading and reloading in the continuous strain path change posed challenges for plastic deformation in the next deformation stage, leading to strain softening, premature failure, and relatively weaker textural development. Conversely, the presence of unloading and reloading in the discontinuous strain path change facilitated increased plastic deformation in the next deformation stage, resulting in strain hardening, delayed failure, and stronger textural development.

An online modeling virtual sensing technique based on kriging interpolation for active noise control

Combined with virtual sensing techniques, active noise control can generate quiet zones in places without error microphones. Many existing virtual sensing techniques require pretraining of the system with physical microphones placed temporarily at the control location as well as retraining if the primary sound field or the secondary paths change. This process responds slowly and is infeasible in many application scenarios. In this paper, we propose a virtual sensing technique based on kriging interpolation, which gives an unbiased sound pressure estimator with minimum variance, assuming the spatial correlation model. The proposed method only depends on the distances between physical and virtual microphones and does not depend on the prior information of the primary noise field, implying that the method naturally tracks the variations of the noise sources. Further, when the secondary paths change due to variations in the secondary sources or the position of the virtual microphones, we combine the virtual sensing technique with a secondary path online modeling method, which enables the system to track the time-varying secondary paths and thus ensure the convergence of the active noise control system.

Strain-gradient crystal plasticity model with slip-system level GND tracking: Simulation vs experiment for sequential strain path change in AA6016-T4

Crystal plasticity models that track strain gradients and associated geometrically necessary dislocations (GNDs) typically determine the Nye tensor, mimicking the experimental approach. However, estimating GND densities for each slip-system is then intrinsically ambiguous. This study seeks to build upon current state of the art by quantifying GNDs at the slip-system level in the model using the local strain gradients. The model is exercised by replicating experiments undertaken on AA6016, which are performed under multi-step strain paths; both GND and SSD populations are quantified at various stages using both high resolution EBSD (HREBSD) and XRD. A full 3D volume of the material is extracted using ion beam serial sectioning to enable the creation of a high-fidelity model of the material.The combined modeling and experimental campaigns conclude that: 1) Calculation of the GND content at the slip level gives effectively equivalent GND evolution as the tradition Nye tensor method, but provides the significant advantage of knowing unambiguously the contribution on each slip system. 2) The net hardening predicted by the SGCP model is accurate, including prediction of a rapid increase in hardening (and associated dislocation content) following strain path change; and 3) Comparisons of observed and simulated GND populations reveal that buildup in the real sample is dominated by precipitate distribution rather than by grain boundary (GB) networks; such precipitates are not present in the current model, hence this result was not predicted.

A Study on the Attenuation Patterns of Underground Blasting Vibration and Their Impact on Nearby Tunnels

The natural caving method, as a new technique in underground mining, has been promoted and applied in several countries worldwide. The destruction of the bottom rock mass structure directly impacts the structural stability of underground engineering, resulting in damage and collapse of underground tunnels. Therefore, based on the principles of explosion theory and field monitoring data, a scaled three-dimensional numerical simulation model of underground blasting was constructed using LS-DYNA19.0 software to investigate the attenuation patterns of underground blasting vibrations and their impact on nearby tunnels. The results show that the relative error range between the simulated blasting vibration velocities based on the FEM-SPH (Finite Element Method–Smoothed Particle Hydrodynamics) algorithm and the measured values is between 7.75% and 9.85%, validating the feasibility of this method. Significant fluctuations in blasting vibration velocities occur when the blast center increases to within a range of 10–20 m. As the blast center distance exceeds 25 m, the vibration velocities are increasingly influenced by the surrounding stress. Additionally, greater stress results in higher blasting vibration velocities and stress wave intensities. Fitting the blasting vibration velocities of various measurement points using the Sadovsky formula yields fitting correlation coefficients ranging between 0.92 and 0.97, enabling the prediction of on-site blasting vibration velocities based on research findings. Changes in propagation paths lead to localized fluctuations in the numerical values of stress waves. These research findings are crucial for a deeper understanding of underground blasting vibration patterns and for enhancing blasting safety.

Engineering Triple-Phase Interfaces with Hierarchical Carbon Nanocages for High-Areal-Capacity All-Solid-State Li-S Batteries.

All-solid-state lithium-sulfur batteries (ASSLSBs) have garnered widespread attention due to their advantages of high energy density and enhanced safety. However, the typical composite structure composed of solid-state electrolyte (SE), discrete conducting carbon black, and microsized sulfur (μ-S) with long-range Li+/e- conducting path and huge volume changes, suffers from sluggish charge transport and severe electrochemical-mechanical failure. In this work, a unique hierarchical carbon nanocage (hCNC) is applied as a continuous conducting network where nanosized sulfur are confined. Due to the synergistic effects of multi-dimensional (particle, interface, and electrode) structural engineering, this new sulfur-carbon composite cathode (S@hCNC39) can achieve uniform distribution of sulfur and carbon, and efficiently constructs triple-phase interfaces, showing enhanced charge-carrier transport and improved electrochemical-mechanical stability. Remarkable cycling performance of 89% after 300 cycles at 0.2C at 30°C is realized in ASSLSBs assembled with S@hCNC39. Notably, ASSLSBs achieve an ultrahigh areal capacity of 9.95 mAh cm-2 with stable cycling at 60°C with high sulfur contents of 40% and high sulfur loadings of 6mg cm-2. These results provide critical insights into the design of rational sulfur-carbon composites and offer a viable approach to enhance the overall performance of ASSLSBs.

Studies of beam ion confinement to enhance plasma performance on EAST

A key physics issue for achieving steady-state high-performance plasmas on EAST tokamak is to decrease beam-ion losses to improve plasma confinement during neutral beam injections (NBIs). To decrease the beam losses, previous counter-I p NBI injections are upgraded to co-I p injections. Analysis shows that due to the reversed direction of drift across the flux surfaces caused by the pitch angle, the beam prompt loss fraction decreases from about 49% to 3% after the upgrade. Moreover, because of the change of entire beam path, beam shine-through (ST) loss fraction for counter-I p tangential and counter-I p perpendicular injections is reversed to co-I p tangential and co-I p perpendicular injections, respectively. Due to the change in the initial trapped-confined beam ion fraction caused by the peaked pitch profiles, the losses induced by toroidal ripple field are also reversed after the upgrade. To further improve the beam-ion confinement under the present NBI layout, the amplitudes of toroidal field are increased from 1.75 to 2.20 T. Result shows that, due to the smaller orbit width and peaked pitch angle profile, the beam prompt loss power is lower with higher toroidal field. Due to the synergy of higher initial trapped-confined beam ion fraction and narrower Goldston-White-Boozer (GWB) boundary, the loss induced by ripple diffusion is higher with higher toroidal field. The combined effect of beam ST loss, prompt loss and ripple loss, contributes to the increase in beam ion density. The decrease in beam loss power enhances beam heating efficiency, especially the fraction of beam heating ions. Finally, comparison between simulation and measurement by 235U fission chamber (FC) indicates that the increase in neutron rate is mainly contributed by improvement of beam-ion confinement. This study can provide potential support for beam operation and high-T i experiment on EAST tokamak.

Synthetic iterative scheme for thermal applications in hotspot systems with large temperature variance

A synthetic iterative scheme is developed for thermal applications in hotspot systems with large temperature variance. Different from previous work with linearized equilibrium state and small temperature difference assumption, the phonon equilibrium distribution shows a nonlinear relationship with temperature and mean free path changes with the spatial temperature when the temperature difference of system is large, so that the same phonon mode may suffer different transport processes in different geometric regions. In order to efficiently capture nonlinear and multiscale thermal behaviors, the Newton method is used and a macroscopic iteration is introduced for preprocessing based on the iterative solutions of the stationary phonon BTE. Macroscopic and mesoscopic physical evolution processes are connected by the heat flux, which is no longer calculated by classical Fourier’s law but obtained by taking the moment of phonon distribution function. These two processes exchange information from different scales, such that the present scheme could efficiently deal with heat conduction problems from ballistic to diffusive regime. Numerical tests show that the present scheme could efficiently capture the multiscale heat conduction in hotspot systems with large temperature variances. In addition, a comparison is made between the solutions of the present scheme and effective Fourier’s law by several heat dissipations problems under different sizes or selective phonon excitation. Numerical results show that compared to the classical Fourier’s law, the results of the effective Fourier’s law could be closer to the BTE solutions by adjusting effective coefficients. However, it is still difficult to capture some local nonlinear phenomena in complex geometries.

Subthalamic nucleus deep brain stimulation modulates speech graphs in patients with Parkinson’s disease

Graph theory enables a direct quantification of topological properties of any arbitrary network. Its application in neuroscience has unveiled topological changes of brain networks associated with various neurodegenerative diseases. This study used the graph theory to understand speech deficits in patients with Parkinson’s disease (PD). In particular, this study investigated the effect of subthalamic nucleus deep brain stimulation (STN-DBS) on the topology of speech graphs. Sixty patients with PD completed a standard semantic fluency test with DBS switched ON and OFF. A control group of sixty matched nonsurgical PD patients completed the test once. All verbal responses were recorded, transcripted, and transformed into directed speech graphs. Volumes of tissue activated (VTA) were estimated for three STN subregions, including sensorimotor, associative, and limbic parts. First, the patients with DBS OFF produced smaller and denser speech graphs than nonsurgical patients, showing fewer nodes, higher density, shorter diameter, and shorter average shortest path. Second, DBS partially reversed the effect of surgery, leading to larger and sparser speech graphs with more nodes, lower density, longer diameter, and longer average shortest path (ON versus OFF). Third, however, the left associative VTA negatively correlated with the DBS-induced diameter and average shortest path changes (ON versus OFF), suggesting that the patients with greater left associative STN stimulation tended to produce smaller and denser speech graphs. This study demonstrates that STN-DBS can partially restore the topological structure of speech graphs in PD patients. However, stimulating the left associative STN appears to disrupt speech graphs.

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.