Transition Barrier Research Articles

Identifying and controlling the order parameter for ultrafast photoinduced phase transitions in thermosalient materials

The drastic shape deformation that accompanies the structural phase transition in thermosalient materials offers great potential for their applications as actuators and sensors. The microscopic origin of this fascinating effect has so far remained obscure, while for technological applications, it is important to learn how to drive transitions from one phase to another. Here, we present a combined computational and experimental study, in which we have successfully identified the order parameter for the thermosalient phase transition in the molecular crystal 2,7-di([1,1'-biphenyl]-4-yl)-fluorenone. Molecular dynamics simulations reveal that the transition barrier vanishes at the transition temperature. The simulations further show that two low-frequency vibrational-librational modes are directly related to the order parameter that describes this phase transition, which is supported by experimental Raman spectroscopy studies. By applying a computational THz pulse with the proper frequency and amplitude we predict that we can photoinduce this phase transition on a picosecond timescale.

Clean energy challenges and innovation opportunities in Kazakhstan

Abstract Kazakhstan has pledged to transition to a low-carbon economy by implementing national policies and strategies that promote clean energy innovation. However, Kazakhstan is still falling short of its expected targets for energy transition, and there is a lack of knowledge regarding the country’s challenges and opportunities for clean energy development. Towards this end, the current study identifies and assesses the enablers and barriers related to clean energy innovation in Kazakhstan. Using the combination of SWOT analysis, survey data from 41 experts and the DEMATEL decision support tool, we evaluated the key factors affecting Kazakhstan’s clean energy innovation and their implications for energy transition. Assessment results show that the immature business environment, underpinned by technological, institutional, and socioeconomic factors, is perceived as a high-impact constraint for clean energy innovation and green finance deployment in Kazakhstan. Skilled labour shortages, high reliance on hydrocarbons and low retail energy prices are significant challenges to Kazakhstan’s clean energy innovation. The low-profit margin and high investment risk in clean energy projects are identified as transition barriers in the power and energy-intensive industries. In contrast, Kazakhstan’s endowments of resources critical for developing clean energy technologies (rare earth metals, uranium, gas) and the potential of low-carbon investments (e.g. carbon storage) are perceived as prominent enablers of clean energy innovation. Results are consistent across expert subgroups (academia, industry, NGOs, etc). Findings call for policy support to modern and attractive business environments, capacity, and human capital development. The findings can provide helpful insights for countries in Central Asia and beyond with similar socioeconomic structures that aim for a timely energy transition.

Estimating reaction barriers with deep reinforcement learning1

Stable states in complex systems correspond to local minima on the associated potential energy surface. Transitions between these local minima govern the dynamics of such systems. Precisely determining the transition pathways in complex and high-dimensional systems is challenging because these transitions are rare events, and isolating the relevant species in experiments is difficult. Most of the time, the system remains near a local minimum, with rare, large fluctuations leading to transitions between minima. The probability of such transitions decreases exponentially with the height of the energy barrier, making the system’s dynamics highly sensitive to the calculated energy barriers. This work aims to formulate the problem of finding the minimum energy barrier between two stable states in the system’s state space as a cost-minimization problem. It is proposed to solve this problem using reinforcement learning algorithms. The exploratory nature of reinforcement learning agents enables efficient sampling and determination of the minimum energy barrier for transitions.

Career transitions from work-to-entrepreneurship

Moving from a traditional career to entrepreneurship is a significant shift. It means taking on new responsibilities and dealing with uncertainties. Our research examined what motivates people and the skills they need to make this change. We used career identity theory to understand how people match their motivations, interests, and abilities with their chosen careers. By thematically analyzing 21 in-depth interviews conducted with military veterans and career transition organizations, we find that transition barriers and challenges embedded in career contexts can be overcome by leveraging career capital and social capital through a series of adjustments. The value of career transitions to entrepreneurship was linked to improved well-being, increased autonomy, and satisfaction. We contribute to the entrepreneurship and career literature by proposing an integrative model of work-to-entrepreneurship career pathways, which aids in explaining how occupation contexts shape career aspirations, highlighting the importance of career and social capital and identifying career transition pathways. We propose direction for future research and offer practical implications for employers’ talent management practitioners, individuals considering work-to-entrepreneurship career transitions and interorganizational talent management practices in entrepreneurship ecosystems.

Light-Induced Polaronic Crystals in Single-Layer Transition Metal Dichalcogenides.

Light-induced ordered states can emerge in materials after irradiation with ultrafast laser pulses. However, their prediction is challenging because the inverted band occupation confounds our chemical intuition. Hence, we use a recently developed constrained density functional perturbation theory approach to systematically screen single-layer transition metal dichalcogenides (TMDs) for light-induced ordered states. We demonstrate that all examined single-layer TMDs reveal similar light-induced charge orderings. The corresponding reconstructions are periodic arrangements of polarons (polaronic crystals), characterized by triangular metal clusters and having no equivalent at equilibrium conditions. The polarons are accompanied by localized midgap states in the electronic band structure, detectable by experimental methods. We assess the selenides as the most promising candidates for potential photoexcitation experiments because they transition at low critical fluences, have low transition barriers, and maintain an open band gap under photoexcitation. Our work paves the way for innovative material design approaches targeting light-induced phases.

Mutability of Nucleation Particles in Reactive Salt Hydrate Phase Change Materials.

Nucleation particles, solid phases dispersed throughout a medium to decrease the energy barrier for solidification or other reversible phase transitions, are generally selected on the basis of structural or interfacial energy considerations between the host phase and the solid phase that is crystallizing. However, the existence of chemical reactions between the nucleation particles and the host phase can obscure these underlying relationships, thereby complicating the process of selection of active nucleation particle phases. Here, we reveal the origin of nucleation activity of barium-based nucleation particles in the salt hydrate calcium chloride hexahydrate (CCH), a candidate for near room temperature thermal energy storage. We demonstrate that these compounds undergo a series of cation exchange and secondary precipitation reactions, resulting in an assemblage of solid precipitates with some degree of limited solid solution, which collectively dramatically reduce undercooling in CCH, but which obscure the identification of a single crystalline phase primarily responsible for the nucleation of crystalline CCH from the liquid. Importantly, this result illustrates a pathway to harness in situ chemical reactions to generate stable active nucleation particles in reactive phase change materials, which may not be readily synthesized by alternative methods, or which may not be active or remain stable when added in isolation.

Large out-of-plane piezoelectric response and ultra-low polarization transition barriers in two-dimensional MoGe2N4/MoSi2N4 heterostructures

With the help of the first principle calculations, two-dimensional (2D) MoGe2N4/MoSi2N4 van der Waals (vdW) heterojunction was confirmed as a type II bandgap arrangement with distinct piezoelectric properties dependent on the stacking orders and interlayer interactions. This structural change is facilitated by slip interactions between the layers and is characterized by a process with a low energy barrier, allowing for efficient and responsive phase transition of structures. Notably, this heterojunction exhibits a particularly large out-of-plane piezoelectric coefficient, d33, within a finite thickness. Concurrently, the piezoelectric coefficient can be enhanced by adjusting the vertical strain to a specific value, and the out-of-plane piezoelectric coefficient d33 can be as high as 73.28 pm/V, which is larger than the values of the available 2D materials or their heterojunctions. In addition, we simulated a piezoelectric actuator on a two-dimensional scale, where the deformation of the upper surface of the piezoelectric brake was linearly modulated by adjusting the driving voltage. Thus, our research paves the way for the conceptualization and creation of cutting-edge nanoelectronic devices, electromechanical systems, and multifunctional atomic-scale appliances.

Surprising Dynamics Phenomena in the Diels-Alder Reaction of C60 Uncovered with AI.

We performed an extensive artificial intelligence-accelerated quasi-classical molecular dynamics investigation of the time-resolved mechanism of the Diels-Alder reaction of fullerene C60 with 2,3-dimethyl-1,3-butadiene. In a substantial fraction (10%) of reactive trajectories, the larger C60 noncovalently attracts the 2,3-dimethyl-1,3-butadiene long before the barrier so that the diene undergoes the series of complex motions including roaming, somersaults, twisting, and twisting somersaults around the fullerene until it aligns itself to pass over the barrier. These complicated processes could be easily missed in typically performed quantum chemical simulations with shorter and fewer trajectories. After the barrier is passed, the bonds take longer to form compared to the simplest prototypical Diels-Alder reaction of ethene with 1,3-butadiene despite high similarities in transition states and barrier widths evaluated with intrinsic reaction coordinate (IRC) calculations. C60 is mainly responsible for these differences as its reaction with 1,3-butadiene is similar to the reaction with 2,3-dimethyl-1,3-butadiene: the only substantial difference being that the extra methyl groups double the probability of the prolonged alignment phase in dynamics. These additional calculations of C60 with 1,3-butadiene could be performed via active learning more easily by reusing the data generated for the other two reactions, showing the potential for larger-scale exploration of the effects of different substrates in the same types of reactions.

Studies on Electronic Structure and Optical Properties of MoS2/X (X = WSe2, MoSe2, AlN, and ZnO) Heterojunction by First Principles

The single-layer MoS2 is a highly sought-after semiconductor material in the field of photoelectric performance due to its exceptional electron mobility and narrow bandgap. However, its photocatalytic efficiency is hindered by the rapid recombination rate of internal photogenerated electron–hole pairs. Currently, the construction of heterojunctions has been demonstrated to effectively mitigate the recombination rate of photogenerated electron–hole pairs. Therefore, this paper employs the first principles method to calculate and analyze the four heterojunctions formed by MoS2/WSe2, MoS2/MoSe2, MoS2/AlN, and MoS2/ZnO. The study demonstrates that the four heterojunctions exhibit structural stability. The construction of heterojunctions, as compared to a monolayer MoS2, leads to a reduction in the band gap, thereby lowering the electron transition barrier and enhancing the light absorption capacity of the materials. The four systems exhibit II-type heterojunction. Therefore, the construction of heterojunctions can effectively enhance the optical properties of these systems. By forming heterojunctions MoS2/WSe2 and MoS2/MoSe2, the absorption coefficient in the visible light region is significantly increased, resulting in a greater ability to respond to light compared to that of MoS2/ZnO and MoS2/AlN. Consequently, MoS2-based heterojunctions incorporating chalcogenide components WSe2 and MoSe2, respectively, exhibit superior catalytic activity compared to MoS2 heterojunctions incorporating non-chalcogenide components ZnO and AlN, respectively. The absorption spectrum analysis reveals that MoS2/MoSe2 exhibits the highest light responsivity among all investigated systems, indicating its superior photoelectric performance.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation.

Perylene diimides (PDIs) have garnered considerable attention due to its immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI-PDA, by linking an ortho-substituted PDI with p-phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron transfer dynamics, leading to a ten-fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI-PDA compared to the PDI molecular counterpart, achieving yields exceeding 90%. Electron property studies and density functional theory calculations show that the PDI-PDA with its well-defined crystal structure, enhances π-π stacking and lowers the electron transition barrier. Moreover, the strong electron-withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI-PDA suppressing the rapid recombination of photogenerated electron-hole pairs and improving charge separation efficiency to give high photocatalytic efficiency. This study provides a brief yet effective way for the improvement of the photocatalytic efficiency of commonly used PDI-based dyes by integrating them into a framework skeleton.

Integration of Perylene Diimide into a Covalent Organic Framework for Photocatalytic Oxidation

AbstractPerylene diimides (PDIs) have garnered considerable attention due to their immense potential in photocatalysis. However, manipulating the molecular packing within their aggregates and enhancing the efficiency of photogenerated carrier recombination remain significant challenges. In this study, we demonstrate the incorporation of a PDI unit into a covalent organic framework (COF), named PDI‐PDA, by linking an ortho‐substituted PDI with p‐phenylenediamine (PDA) to control its intermolecular aggregation. The incorporation enables precise modulation of electron‐transfer dynamics, leading to a ten‐fold increase in the efficiency of photocatalytic oxidation of thioether to sulfoxide with PDI‐PDA compared to the PDI molecular counterpart, with yields exceeding 90 %. Electron property studies and density functional theory calculations show that the PDI‐PDA with its well‐defined crystal structure, enhances π–π stacking and lowers the electron transition barrier. Moreover, the strong electron‐withdrawing ability of the PDI unit promotes the spatial separation of the valency band maximum and conduction band minimum of PDI‐PDA, suppressing the rapid recombination of photogenerated electron‐hole pairs and improving the charge‐separation efficiency to give high photocatalytic efficiency. This study provides a brief but effective way for improving the photocatalytic efficiency of commonly used PDI‐based dyes by integrating them into a framework skeleton.

Microscopic in situ observation of electromechanical instability in a dielectric elastomer actuator utilizing transparent carbon nanotube electrodes.

Electromechanical instability (EMI) restricts the performance of dielectric elastomer actuators (DEAs), leading to premature electrical breakdown at a certain voltage. However, macro-level observations using traditional carbon grease electrodes have failed to capture the detailed features of EMI. In this study, we investigated EMI at the microscopic scale by fabricating transparent and conductive single-walled carbon nanotube (SWCNT) electrodes. Our findings reveal that EMI predominantly occurs in highly localized regions with dimensions on the order of tens of micrometers. This snap-through instability is likely induced by pre-existing defects within the elastomer, such as air voids or conductive particles, which reduce the critical voltage required for EMI in the flawed areas. From the perspective of phase transition principles, these defects act as heterogeneous nucleation sites for new phase embryos, thereby lowering the energy barrier for the electromechanical phase transition (i.e., EMI) compared to homogeneous nucleation in an ideally impurity-free elastomer. This study clarifies the longstanding discrepancy between theoretically predicted deformation bursts and the experimentally observed macroscopic continuous expansion of DEAs under low pre-stretch conditions. Additionally, it underscores the critical importance of material purity in mitigating electromechanical instability.

Disinfection of bacteria and viruses under near infrared light by tunable self-assembled nanomaterial NH2-MIL-101-xAu based on photothermal and photodynamic mechanisms

In response to the threat posed by multi-drug resistant "superbugs", a synergistic approach of photothermal therapy (PTT) and photodynamic therapy (PDT) has been developed. In this work, NH2-MIL-101-xAu was prepared by introducing Au nanoparticles on the surface of NH2-MIL-101 n-type semiconductor by means of self-assembly. The introduction of Au nanoparticles greatly improves the light absorption and utilization of nanomaterials. Based on the surface plasma response (SPR), NH2-MIL-101-xAu has an efficient photothermal conversion ability, and under the irradiation of 808 nm (1 W/cm2), NH2-MIL-101–5.0Au (0.50 mg/mL) can be heated to 60℃ in 3 min. And the synergistic effect of plasma-induced interfacial charge-transfer transition and Schottky barriers dramatically enhances the photogenerated carrier separation of NH2-MIL-101-xAu, which in turn generates a large number of reactive oxygen species (ROS). Under the experimental conditions, NH2-MIL-101-xAu with the synergistic effect of PTT and PDT had the sterilization rate of 99.99999 % against Escherichia coli and Staphylococcus aureus, and the inactivation rate of Bacteriophage MS2 was more than 99.9 %. This study shows that NH2-MIL-101-xAu possessing a high degree of tunability is an effective PTT and PDT synergistic means of destroying pathogens, which is very helpful in the application of eliminating drug-resistant bacteria.

The significance of fuzzy boundaries of the barrier regions in single-molecule measurements of failed barrier crossing attempts.

A recent ground-breaking experimental study [Lyons et al., Phys. Rev. X 14(1), 011017 (2024)] reports on measuring the temporal duration and the spatial extent of failed attempts to cross an activation barrier (i.e., "loops") for a folding transition in a single molecule and for a Brownian particle trapped within a bistable potential. Within the model of diffusive dynamics, however, both of these quantities are, on average, exactly zero because of the recrossings of the barrier region boundary. That is, an observer endowed with infinite spatial and temporal resolution would find that finite loops do not exist (or, more precisely, form a set of measure zero). Here we develop a description of the experiment that takes the "fuzziness" of the boundaries caused by finite experimental resolution into account and show how the experimental uncertainty of localizing the point, in time and space, where the barrier is crossed leads to observable distributions of loop times and sizes. Although these distributions generally depend on the experimental resolution, this dependence, in certain cases, may amount to a simple resolution-dependent factor and, therefore, the experiments do probe inherent properties of barrier crossing dynamics.

Mechanism of activation and autophosphorylation of a histidine kinase

Histidine kinases (HK) are one of the main prokaryotic signaling systems. Two structurally conserved catalytic domains inside the HK enable autokinase, phosphotransfer, and phosphatase activities. Here, we focus on a detailed mechanistic understanding of the functional cycle of the WalK HK by a multi-scale simulation approach, consisting of classical as well as hybrid QM/MM molecular dynamics simulation. Strikingly, a conformational transition induced solely in DHp leads to the correct activated conformation in CA crucial for autophosphorylation. This finding explains how variable sensor domains induce the transition from inactive to active state. The subsequent autophosphorylation inside DHp proceeds via a penta-coordinated transition state to a protonated phosphohistidine intermediate. This intermediate is consequently deprotonated by a suitable nearby base. The reaction energetics are controlled by the final proton acceptor and presence of a magnesium cation. The slow rates of the process result from the high energy barrier of the conformational transition between inactive and active states. The phosphorylation step exhibits a lower barrier and down-the-hill energetics. Thus, our work suggests a detailed mechanistic model for HK autophosphorylation.

The Impact and Process of Transition from Face-to-Face to Online Teaching During a Pandemic: A Grounded Theory Approach

Abstract The COVID-19 pandemic required a “rethinking and retooling” of many educational interactions, especially in schools that offer primarily face-to-face educational models. The sudden necessity for altering teaching formats and styles created challenges and opportunities for faculty and their students. There is little understanding of the impact the abrupt switch had on faculty and students, or the process by which the transition took place. The purpose of this study was to develop a theory about the impact on and the processes used by faculty for implementing online education in response to the pandemic. A total of 24 faculty members from a private southeastern university that primarily uses a face-to-face educational model were interviewed. The grounded theory methods of Corbin and Strauss (2015) and Charmaz (2014) were used to inform the inquiry. The unexpected transition to online teaching impacted faculty and students personally, professionally, and academically. Faculty readiness to teach online was highly dependent on perceptions of self-efficacy, which in turn affected their perceptions of the transition. Study findings reinforce the need for university administrators to provide faculty with structured pedagogical support specifically technological and instructional design assistance, dedicated time to learn and incorporate instructional changes, and mental health services to care for themselves and their students during times of crisis. Determining the process by which the transition took place provides insight regarding both transition facilitators and barriers, which can inform future educational delivery and evaluation.

Mixed Methods Evaluation of a Youth-Friendly Clinic for Young People Living with HIV Transitioning from Pediatric Care.

(1) Background: Adolescents and young adults face challenges when transitioning to adult care due to emerging adulthood and changing providers and insurance. Young people living with HIV (YPLHIV) have additional obstacles with mental health and stigma. During transition, only 55% of YPLHIV are retained in care, and 65% are virally suppressed. To address these challenges, the Adolescent and Young Adult Health Care Transition Clinic (AYAHCTC) was created at Vanderbilt University Medical Center in 2017. This mixed methods study evaluates the initial cohort and solicits YPLHIVs' perspectives on transition barriers and facilitators. (2) Methods: Quantitative analyses (n = 21) characterized patients' demographics, clinical engagement, and retention. Qualitative interviews (n = 5) captured patients' transition experiences. (3) Results: This study, conducted in the Southeastern USA, included a cohort where 47.6% were born abroad, with all participants being US citizens by birth or naturalization. Patients' mean age at first visit was 19.6 years. The average AYAHCTC duration was 2.21 years. First-year engagement and retention were 100% and 95.5%, respectively. Viral suppression rates improved from 66.7% at the first visit to 81.0% at the last visit. Eleven patients transitioned out of AYAHCTC. Qualitative analyses indicate that barriers to transition include leaving trusted providers, reduced parental guidance, developing autonomy, and perceived loss of confidentiality in adult clinic environment. Transition was facilitated by youth-friendly services, clear communication, and strong relationships with AYAHCTC providers. (4) Conclusions: YPLHIV positively viewed AYAHCTC experiences. Future directions include optimizing services to build YPLHIVs' independence, supporting YPLHIV experiencing stigma, assuaging concerns about switching providers, collaborating with adult clinics to maintain confidentiality, and designing interventions focused on adherence during transition.

On the Emergence of Ferromagnetism in LaCoO3 Ultrathin Films

AbstractIt is well known that the properties of a crystal evolve as it increases in size from a single atomic plane to that of the bulk. Such size‐dependent transitions can stem from many different origins and depend on minute changes to crystal bonding and composition. A model example is that of LaCoO3, which is non‐magnetic in the bulk but can display ferromagnetism at the nanoscale. Here, the evolution of structure‐property relationships is studied in the LaCoO3−δ/SrTiO3 (001) system as the thickness of LaCoO3−δ is increased from a single plane to 10 unit cells. In situ synchrotron X‐ray studies are performed during and post‐deposition to probe changes in the interactions between structure, stoichiometry, and magnetic behavior. Structural quantification indicates that the oxygen octahedral rotation pattern evolves with thickness, due to inherent differences in crystal symmetry between the film and substrate. The change in rotation modifies the required energy barrier for the spin state transition via the Co–O bond length and Co–O–Co bond angle, affecting the appearance of ferromagnetism. Our results highlight the contributions of high spin Co2+ and/or high spin Co3+ to respective weak and robust ferromagnetism and the evolution of properties with size in ultrathin LaCoO3−δ heterostructures.

Virtual Community Conversations as Catalysts for Improving Transitions for Youth With Intellectual and Developmental Disabilities.

Youth with intellectual and developmental disabilities (IDD) aspire to participate in a variety of activities after high school, such as attaining paid employment, enrolling in postsecondary education, being involved in their communities, living independently, and building friendships. However, complex and longstanding transition barriers require comprehensive solutions that are tailored to a local community's unique needs and available resources so that local youth with IDD may achieve their desired outcomes. This article presents "virtual community conversations" as a promising approach for bringing together local communities to tackle barriers to good outcomes for residents with IDD. Attendees were able to effectively generate innovative recommendations for addressing issues in their local communities. We offer recommendations for enhancing and extending implementation of this approach.

Investigating the transitional barriers university students face when moving from further education; what are the potential issues they may meet?

Investigating the transitional barriers university students face when moving from further education; what are the potential issues they may meet?