Step Transition Research Articles

Molecular dynamics study on the influence of temperature on the mechanical properties of graphene reinforced magnesium-matrix composites

Magnesium and its alloys have been considered the lightest engineering structural metal materials, but their poor plasticity and the degradation of mechanical properties at high temperatures limit their wide application. Therefore, using molecular dynamics simulation, this work examines how the phase structure and mechanical characteristics of pure magnesium under compressive loading are affected by graphene and varying temperatures. The findings demonstrate that adding graphene can significantly increase magnesium's strength. As well as its Young's modulus, and have a great influence on the secondary strain's strengthening. It is noted that the Gr/Mg-based composites have the same plastic deformation behavior as that of pure magnesium, and both of them undergo a transition from a dense hexagonal structure to other structures during plastic deformation, and the introduction of graphene makes the transition more drastic. The number of embedded graphene layers governs the overall deformation of the Gr/Mg composites; however, it does not significantly affect the deformation behavior of the magnesium matrix in the upper and lower regions of the composites. When there is no graphene embedded, the phase transition of magnesium matrix occurs everywhere, while when graphene is embedded, the phase transition of magnesium matrix in the upper and lower parts of graphene extends along the near-interfacial position of graphene without passing through it, which means graphene has the role of changing the nucleation position of dislocations and blocking the movement of dislocations. In addition, the temperature decreases the phase transition step size of Gr/Mg composites, which is similar to that of pure magnesium, while the temperature affects the phase structure of pure magnesium Gr/Mg composites.

Effect of reverse conjugated structure on charge transfer and photoabsorption characteristics of multi-branched molecules

The present work investigates effect of conjugated structure on two-photon absorption (TPA) and charge transfer characteristics of multi-branched molecules by DTF/TD-DFT and visualization methods. Results show that, compared with V-shaped and T-series counterparts, Y-shaped and R-series molecules exhibit great enhancement on TPA response. Strengthened cooperative effect among branches has been obtained by reversing conjugated structure or changing conjugated structure from V-shape to Y-shape, which has been approved by the TDM and CDD maps in the second step transition of TPA process. Our results indicate that constructing typical structures with suitable charge transfer directions is of great significance for improving performance.

Navigating the transition to Principal Investigator.

As the result of many years of training, becoming a Principal Investigator (PI) is an exciting but also stressful and intimidating career transition step. While navigating this transition we quickly find out that the skills we have crafted throughout our scientific training do not necessarily cover those required to successfully run a research group. Although there is not a common path to ensure success for all new PIs, many of us encounter similar hurdles. The aim of this article is to reflect on my recent experience and mistakes 2 years after initiating this transition, in the hope of highlighting some key aspects that may be beneficial for future new PIs.

A novel technology for lithium extraction through low-temperature synergistic roasting of α-spodumene with lepidolite

α-Spodumene and lepidolite have garnered significant attention because of the booming market of lithium (Li) salts. However, α-spodumene requires a high-temperature phase transition step at ≥1050 °C, and lepidolite needs a large amount of sulfate to extract Li. The economic and environmental benefits of these processes need to be improved. Herein, an innovative scheme, low-temperature synergistic roasting of α-spodumene with lepidolite, was proposed to efficiently extract Li. The conditions for phase transition roasting, acid baking, and water leaching were sequentially optimized. The mechanisms underlying the synchronous phase transition of α-spodumene and lepidolite were studied using various characterization methods. Results indicated that lepidolite lowers the transition temperature of spodumene from the α-phase to the β-phase by 150 °C. During the synergistic roasting, fluorine escapes from the lepidolite lattice and attacks SiO, AlO, and LiO bonds within the α-spodumene lattice. Under optimal conditions, 97.60 % of the Li was extracted, while the leaching ratios of Na, K, Al, and Si were only 50.96 %, 10.96 %, 5.75 %, and 0.30 %, respectively. Current scheme is a promising low-carbon technology that synchronously achieves the low-temperature phase transition of α-spodumene and additive-free Li extraction from lepidolite, offering superior economics, environmental benefits, and practicality compared with the existing methods.

Evaluating plantar biomechanics while descending a single step with different heights.

This study aims to investigate the plantar biomechanics of healthy young males as they descend a single transition step from varying heights. Thirty healthy young males participated the experiment using the F-scan insole plantar pressure system in which participants made single transition steps descent from four step heights (5, 15, 25, and 35cm), leading with their dominant or non-dominant foot. Plantar pressure data were collected for 5s during the period between landing touchdown and standing on the ground. Landing at each step height was repeated three times, with a five-minute rest between different height trials. At 5cm and 15cm steps, participants demonstrated a rearfoot landing strategy on both sides. However, forefoot contact was observed at heights of 25cm and 35cm. Parameters related to center of plantar pressure (COP) of the leading foot were significantly larger compared to the trailing foot (P < 0.001), increased with higher step heights. Vertical ground reaction forces for the biped, leading and trailing feet decreased with increasing step height (all P < 0.05). The leading foot had a higher proportion of overall and forefoot loads, and a lower proportion of rearfoot load compared to the trailing foot (P < 0.001). The overall load on the dominant side was lower than that on the non-dominant side for both the leading and trailing feet (P < 0.001). For the trailing foot, forefoot load on the dominant side was lower than that on the non-dominant side, however, the opposite result appeared in rearfoot load (P < 0.001). Upon the leading foot landing, forefoot load exceeded the rearfoot load for the dominant (P < 0.001) and non-dominant sides (P < 0.001). Upon the trailing foot landing, forefoot load was lower than the rearfoot load for the dominant (P < 0.001) and non-dominant sides (P = 0.019). When the characteristics of biomechanical stability are compromised by step height, landing foot, and footedness factors - due to altered foot landing strategies, changing COP, or uneven force distribution - ability to control motion efficiently and respond adaptively to the forces experienced during movement is challenged, increasing the likelihood of loss of dynamic balance, with a consequent increased risk of ankle sprains and falls.

개념적 접근에 따른 교육과정 연계·통합의 가능성과 과제

Purpose: The purpose of this study is to analyze cases of curriculum connection and integration according to the conceptual approach practiced by IB schools, and to discuss the educational possibilities and challenges of such an approach. Method: In order to analyze the characteristics of curriculum connection and integration according to a conceptual approach, unit design plans and class observations of IB PYP schools were analyzed. Results: IB schools clearly recognize that forming students’ conceptual understanding is the most important goal of teaching and learning, and design and implement inductive learning experiences and transition steps toward conceptual understanding through student-led inquiry. Discussion: It is necessary to present cross-curricular key concepts in the national curriculum, prepare differentiated strategies according to the characteristics of elementary and secondary schools, and strengthen teacher capacity.

Lower Extremity Joint Kinetics during Walk-to-Run and Run-to-Walk Transitions

Lower extremity joint kinetic factors are thought to modulate walk-to-run transition (WRT) and run-to-walk transition (RWT). This study aimed to investigate joint stiffness and energetic patterns during the WRT and RWT processes and identify whether gait transitions occur within a single step or not. Ten healthy subjects participated in treadmill WRT (1.8–2.4 m/s) and RWT (2.4–1.8 m/s) tests. We investigated two steps before transition (S–2, S–1), two steps after transition (S1, S2) and the transition step (S0). We found significant differences between S2 and S–2 for ankle joint stiffness during WRT and RWT (p &lt; 0.001); for hip joint stiffness, we found significant differences between S1 and S–1 during WRT and RWT (p ≤ 0.001). Additionally, stance phase mechanical energy generation was observed to transfer from proximal to distal joints at S0 during WRT, and from distal to proximal at S0 during RWT. Transition step ankle kinematic and kinetic patterns were similar to the target locomotion task gait format in both WRT and RWT. Moreover, RWT required longer adaptation time compared with WRT. These findings indicate that WRT and RWT were modulated before and after the actual transitions, not within a single step. Redistribution of joint mechanical work generation was related to gait transition triggers, which modulate the WRT and RWT processes.

Метод перехода от хранилищ данных к озерам данных геоинформационных систем на основе Лямбда-архитектуры

This paper discusses the transition from traditional data warehouses to data lakes in geographic information systems using Lambda architecture. Provides an overview of the key transition steps, including planning, data collection and processing, data querying, data analytics, and metadata management. Particular attention is paid to the interaction of data lakes and GIS, as well as sample big data processing code based on Lambda architecture. The advantages of using data lakes in GIS and the possibilities o integrating modern data processing technologies are considered.

Enhancing Ni/Co Activity by Neighboring Pt Atoms in NiCoP/MXene Electrocatalyst for Alkaline Hydrogen Evolution

AbstractDensity functional theory (DFT) calculations demonstrate neighboring Pt atoms can enhance the metal activity of NiCoP for hydrogen evolution reaction (HER). However, it remains a great challenge to link Pt and NiCoP. Herein, we introduced curvature of bowl‐like structure to construct Pt/NiCoP interface by adding a minimal 1 ‰‐molar‐ratio Pt. The as‐prepared sample only requires an overpotential of 26.5 and 181.6 mV to accordingly achieve the current density of 10 and 500 mA cm−2 in 1 M KOH. The water dissociation energy barrier (Ea) has a ~43 % decrease compared with NiCoP counterpart. It also shows an ultrahigh stability with a small degradation rate of 10.6 μV h−1 at harsh conditions (500 mA cm−2 and 50 °C) after 3000 hrs. X‐ray photoelectron spectroscopy (XPS), soft X‐ray absorption spectroscopy (sXAS), and X‐ray absorption fine structure (XAFS) verify the interface electron transfer lowers the valence state of Co/Ni and activates them. DFT calculations also confirm the catalytic transition step of NiCoP can change from Heyrovsky (2.71 eV) to Tafel step (0.51 eV) in the neighborhood of Pt, in accord with the result of the improved Hads at the interface disclosed by in situ electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests.

Enhancing Ni/Co Activity by Neighboring Pt Atoms in NiCoP/MXene Electrocatalyst for Alkaline Hydrogen Evolution.

Density functional theory (DFT) calculations demonstrate neighboring Pt atoms can enhance the metal activity of NiCoP for hydrogen evolution reaction (HER). However, it remains a great challenge to link Pt and NiCoP. Herein, we introduced curvature of bowl-like structure to construct Pt/NiCoP interface by adding a minimal 1 ‰-molar-ratio Pt. The as-prepared sample only requires an overpotential of 26.5 and 181.6 mV to accordingly achieve the current density of 10 and 500 mA cm-2 in 1 M KOH. The water dissociation energy barrier (Ea) has a ~43 % decrease compared with NiCoP counterpart. It also shows an ultrahigh stability with a small degradation rate of 10.6 μV h-1 at harsh conditions (500 mA cm-2 and 50 °C) after 3000 hrs. X-ray photoelectron spectroscopy (XPS), soft X-ray absorption spectroscopy (sXAS), and X-ray absorption fine structure (XAFS) verify the interface electron transfer lowers the valence state of Co/Ni and activates them. DFT calculations also confirm the catalytic transition step of NiCoP can change from Heyrovsky (2.71 eV) to Tafel step (0.51 eV) in the neighborhood of Pt, in accord with the result of the improved Hads at the interface disclosed by in situ electrochemical impedance spectroscopy (EIS) and scanning electrochemical microscopy (SECM) tests.

Bounds on geometric wakefields in collimators and step transitions of arbitrary cross sections

We present the wakefield conformal mapping technique that can be readily applied to the analysis of the radiation generated by an ultra-relativistic particle in the step transition and a collimator. We derive simple analytical expressions for the lower and upper bounds of both longitudinal and transverse wake potentials. We test the derived expressions against well-known formulas in several representative examples. The proposed method can greatly simplify the optimization of collimating sections and can become a useful tool in the shape optimization problems.

The influence of women’s age and fall history on foot and lower limb kinematics during transition step descent

Falls are a major public health concern, with older women being at the greatest risk to experience a fall. Step descent increases the likelihood of a fall injury, yet the influence of age and fall history on lower extremity kinematics have not been extensively studied. The purpose of this study was to examine lower extremity and foot kinematics of women with and without a fall history during single step descent. Hip, knee, and foot kinematics of young women (n = 15, age = 22.6 ± 3.2 years), older women with no recent falls (n = 15, age = 71.6 ± 4.4 years), and older women with a fall history (n = 15, age = 71.5 ± 5.0 years) as they descended a 17 cm step were examined. Differences in initial contact angles and ROM during landing were examined with between group MANOVA tests. Distal foot initial contact angles were not significant between groups. For range of motion, both older groups went through greater hip extension (p = 0.003, partial η2 = 0.25), but less hip adduction (p = 0.002, partial η2 = 0.27) and less lateral midfoot dorsiflexion (p = 0.001, partial η2 = 0.28) than the younger women. The older fall group had reduced knee flexion (p = 0.004, partial η2 = 0.23) than the younger group, and the older non-fallers slightly plantarflexed at the medial midfoot (p = 0.005, partial η2 = 0.23) while the young women dorsiflexed. Thelanding phase ROMdifferences exhibited by the older adult groupsmayincrease the likelihood of a misstep, which may result in a fall.

Unraveling potential phase transition mechanism of NBT-based systems: From an interesting view to survey ferroelectric loops

As for assessing strain performances of Na0.5Bi0.5TiO3-based systems, the driving field level is a critical parameter. Currently, both current density and strain rate evaluation methods have been utilized to characterize the driving field. However, we find that some discrepancies indeed exist between these two evaluation methods, especially for the highly ergodic condition. By means of the typical ferroelectric theory, the initial analysis for discrepant current density and strain rate loops reveals that the relaxor-ferroelectric transition is likely to be a multi-step transition process. Dynamic dielectric loss/permittivity evolution further confirms the speculation and suggests that partial transition steps may be consisted of successive transition events. Ferroelectric and dielectric loops not only provide a fantastic view to unravel the multi-step relaxor-ferroelectric transition process, but also guides to regulate the strain appraisal system.

C−C Coupling in CO2 Electroreduction on Single Cu‐Modified Covalent Triazine Frameworks: A Static and Dynamic Density Functional Theory Study

AbstractThe electrochemical reduction of CO2 into C2+ products represents a promising solution to completing the carbon cycle, thereby fostering a sustainable energy supply. Single‐atom electrocatalysts (SAECs) have garnered significant attention as efficient electrocatalysts for the CO2 reduction reaction. Herein, we carried out a first‐principles study on the mechanism of C−C bond formation on single‐Cu‐atom‐modified covalent triazine frameworks (Cu‐CTFs), which are a promising platform for SAECs. Static density functional calculations indicated that the dimerization of CO, which is the main mechanism for C−C bond formation on bulk Cu metals, was not favorable for Cu‐CTFs because of the lack of adjacent Cu sites for co‐adsorption of CO molecules. Rather than CO dimerization, the reaction between adsorbed *CHO and CO to produce *COCHO has a relatively low reaction energy barrier. Constrained ab initio molecular dynamics analyses revealed that the C−C bond‐forming reaction proceeds via insertion of CO at the *CHO intermediate, which has a modest activation energy of 0.09 eV. Specifically, when CO molecule is constrained to be brought close to *CHO, CO insertion between *CHO and Cu occurs at a C−C distance of 1.8 Å. This insertion reaction is the transition step for this C−C bond formation.

Controlling Three‐Step and Five‐Step Spin Transitions by Polymorphism in an FeIII Spin Crossover Complex

Comprehensive SummaryRegulating spin crossover (SCO) behavior, especially controlling the spin transition steps, is an important scientific issue, mainly because people aim to control spin bistability and multistability. Presently, SCO bistability can be regulated by changing the ligand‐modifying species, non‐coordinated anions, guest molecules, and metal‐ion dopant. However, the control of multistability is extremely challenging, especially in Fe(III) SCO compounds. Here, we report that [FeIII(H‐5‐Br‐thsa)(5‐Br‐thsa)]·H2O (5‐Br‐thsa = (5‐bromo‐2‐hydroxybenzylidene)hydrazinecarbothioamide), a compound we have reported before, exists in two polymorphic forms: polymorph 1 exhibits three‐step SCO, and polymorph 2 shows five‐step SCO, with multi‐step SCO behavior effectively regulated by polymorphism. According to single‐crystal and powder X‐ray diffractometry, polymorphs 1 and 2 crystallize in different space groups during their spin transitions, with two‐step symmetry breaking observed (Pbcn → Pnc2 → Pbcn for polymorph 1; P21/n → Pn → P21/n for polymorph 2). We realized that the behavior of these two polymorphs depends significantly on the structure, including (i) the average Fe—N bond distance, (ii) deformation of octahedral FeIII atoms, and (iii) distinct crystal packing, which account for the large differences observed in magnetic properties.

A Kinematic Model to Predict a Continuous Range of Human-Like Walking Speed Transitions.

While constant speed gait is well understood, far less is known about how humans change walking speed. It is also unknown if the transition steps smoothly morph between speeds, or if they are unique. Using data from a prior study in which subjects transitioned between five speeds while walking on a treadmill, joint kinematic data were decomposed into trend and periodic components. The trend captured the time-varying nature of the gait, and the periodic component captured the cyclic nature of a stride. The start and end of the transition were found by detecting where the trend diverged from a ±2 standard deviation band around the mean of the pre- and post-transition trend. On average, the transition started within half a step of when the treadmill changed speed ( p << 0.001 for equivalence test). The transition length was 2 to 3 steps long. A predictive kinematic model was fit to the experimental data using Bezier polynomials for the trend and Fourier series for the periodic component. The model was fit using 1) only constant speed walking, 2) only speed transition steps, and 3) a random sample of five step types and then validated using the complement of the training data. Regardless of the training set, the model accurately predicted untrained gaits (normalized RMSE , normalized maximum error generally ). Because the errors were similar for all training sets, this implies that joint kinematics smoothly morph between gaits when humans change speed.

Goal-Conditioned Hierarchical Reinforcement Learning With High-Level Model Approximation.

Hierarchical reinforcement learning (HRL) exhibits remarkable potential in addressing large-scale and long-horizon complex tasks. However, a fundamental challenge, which arises from the inherently entangled nature of hierarchical policies, has not been understood well, consequently compromising the training stability and exploration efficiency of HRL. In this article, we propose a novel HRL algorithm, high-level model approximation (HLMA), presenting both theoretical foundations and practical implementations. In HLMA, a Planner constructs an innovative high-level dynamic model to predict the k -step transition of the Controller in a subtask. This allows for the estimation of the evolving performance of the Controller. At low level, we leverage the initial state of each subtask, transforming absolute states into relative deviations by a designed operator as Controller input. This approach facilitates the reuse of subtask domain knowledge, enhancing data efficiency. With this designed structure, we establish the local convergence of each component within HLMA and subsequently derive regret bounds to ensure global convergence. Abundant experiments conducted on complex locomotion and navigation tasks demonstrate that HLMA surpasses other state-of-the-art single-level RL and HRL algorithms in terms of sample efficiency and asymptotic performance. In addition, thorough ablation studies validate the effectiveness of each component of HLMA.

A Fully Differential CMOS Current Memory Cell for Space-Embedded Analog-to-Digital Converters

This paper presents a radiation-hardened high-resolution current memory cell (CMC) that can be used to implement current-mode analog-to-digital converters (ADCs) for space-embedded, charge-coupled device processors. This CMC is based on a fully differential structure and on the Miller effect to reduce charge-injection errors. Using a commercial 0.35-μm 3.3-V complementary metal-oxide-semiconductor (CMOS) process, the radiation tolerance of this CMC has been enhanced by designing enclosed n-channel MOS transistors, using p-channel MOS switches only, and introducing guard rings wherever necessary. Results show that the CMC accuracy is 10 bits and that its estimated linearity error is &3x000B1;50 nA for a [-200 μA; 200 μA] dynamic input current range. Experimental results point out that signal-dependent charge injections are divided 23 times at least, which improves the CMC accuracy by approximately 4 bits. The measured acquisition time for a 200-μA input step transition to achieve a 10-bit settling accuracy is 50 ns. The active chip area and the power consumption of the proposed CMC are 0.042 mm 2 and 6 mW, respectively.

Chemoselective reduction of aromatic nitro compounds (o-nitrophenol derivatives) using simple borane-THF without transition metal catalysts, additives, or ligands

Chemoselective reduction of aromatic nitro compounds (ortho-nitrophenol derivatives) using Borane in THF (BH3-THF) at room temperature, without using an additional metal catalyst is reported. Interestingly, nitroarenes containing two or three groups, a selective reduction of the nitro group adjacent to the hydroxy group is observed which happens to be the first Chemoselective reduction protocol for nitro groups using BH3-THF. The presence of the phenolic hydroxyl group is found to be the key that aids in hydrogen transfer to the nitro group through a cyclic transition step.

A Ramp versus Step Transition to Constant Work Rate Exercise Decreases Steady-State Oxygen Uptake.

This study aimed to investigate whether a ramp-to-constant WR (rCWR) transition compared with a square-wave-to-constant WR (CWR) transition within the heavy-intensity domain can reduce metabolic instability and decrease the oxygen cost of exercise. Fourteen individuals performed (i) a ramp-incremental test to task failure, (ii) a 21-min CWR within the heavy-intensity domain, and (iii) an rCWR to the same WR. Oxygen uptake (V̇O 2 ), lactate concentration ([La - ]), and muscle oxygen saturation (SmO 2 ) were measured. V̇O 2 and V̇O 2 gain (V̇O 2 -G) during the first 10-min steady-state V̇O 2 were analyzed. [La - ] before, at, and after steady-state V̇O 2 and SmO 2 during the entire 21-min steady-state exercise were also examined. V̇O 2 and V̇O 2 -G during rCWR (2.49 ± 0.58 L·min -1 and 10.7 ± 0.2 mL·min -1 ·W -1 , respectively) were lower ( P < 0.001) than CWR (2.57 ± 0.60 L·min -1 and 11.3 ± 0.2 mL·min -1 ·W -1 , respectively). [La - ] before and at steady-state V̇O 2 during the rCWR condition (1.94 ± 0.60 and 3.52 ± 1.19 mM, respectively) was lower than the CWR condition (3.05 ± 0.82 and 4.15 ± 1.25 mM, respectively) ( P < 0.001). [La - ] dynamics after steady-state V̇O 2 were unstable for the rCWR ( P = 0.011). SmO 2 was unstable within the CWR condition from minutes 4 to 13 ( P < 0.05). The metabolic disruption caused by the initial minutes of square-wave exercise transitions is a primary contributor to metabolic instability, leading to an increased V̇O 2 -G compared with the rCWR condition approach. The reduced early reliance on anaerobic energy sources during the rCWR condition may be responsible for the lower V̇O 2 -G.