Transition Barrier Research Articles

Does Ionic Screening Lower Activation Barriers for Conformational Transitions in Proteins?

In this work, we investigated the kinetics of binding of hen egg-white lysozyme with tri- N-acetylglucosamine in aqueous solutions, at two values of pH, 3.2 and 11, as a function of ionic strength, by a stopped-flow method with tryptophyl fluorescence observation of the transients. We analyzed registered reaction progress curves by employing numerical integration of appropriate chemical master equations. We discriminated between several binding models and established that the process observed in experiments follows a two-step mechanism, composed of four elementary stages: diffusional formation of an encounter complex, dissociation of the encounter complex, conformational transition of the encounter complex to the final complex, and the reverse transformation, i.e., from the final complex to the encounter complex. We evaluated rate constants of these elementary stages and determined their dependencies on solution ionic strength. Regardless of solution pH, rate constants of both forward and reverse conformational transitions increase with an increasing ionic strength. This suggests that ionic screening of intramolecular electrostatic interactions may act to lower the activation barrier for conformational transition in proteins.

Photoactivity and Stability Co-Enhancement: When Localized Plasmons Meet Oxygen Vacancies in MgO.

Durability is still one of the key obstacles for the further development of photocatalytic energy-conversion systems, especially low-dimensional ones. Encouragingly, recent studies show that nanoinsulators such as SiO2 and MgO exhibit substantially enhanced photocatalytic durability than the typical semiconductor p25 TiO2 . Extending this knowledge, MgO-Au plasmonic defect nanosystems are developed that combine the stable photoactivity from MgO surface defects with energy-focusing plasmonics from Au nanoparticles (NPs), where Au NPs are anchored onto monodispersed MgO nanotemplates. Theoretical calculations reveal that the midgap defect (MGD) states in MgO are generated by oxygen vacancies, which provide the main avenues for upward electron transitions under photoexcitation. These electrons drive stable proton photoreduction to H2 gas via water splitting. A synergistic interaction between Au's localized plasmons and MgO's oxygen vacancies is observed here, which enhances MgO's photoactivity and stability simultaneously. Such co-enhancement is attributed to the stable longitudinal-plasmon-free Au NPs, which provide robust hot electrons capable of overcoming the interband transition barrier (≈1.8 eV) to reach proton reduction potential for H2 generation. The demonstrated plasmonic defect nanosystems are expected to open a new avenue for developing highly endurable photoredox systems for the integration of multifunctionalities in energy conversion, environmental decontamination, and climate change mitigation.

Structural phase transition barrier of N-doped MoS2 with charge injection

The electronic properties of transition metal dichalcogenides make them ideal two-dimensional materials for application in electronic devices. Interestingly, structural phase transition (SPT) can be realized by charge injection or charge transfer from intercalants such as lithium and sodium. Unfortunately, SPT generally generates crystal domains and defects, which are usually undesirable. Here, we studied the charging effect on the SPT in N-doped MoS2 based on first-principles calculations. The results suggests the 2H phase is the most stable regardless of doping charge. Therefore, the undesirable SPTs may be avoidable by the covalent nitrogen doping of MoS2. The strain effect on the SPTs was also studied.

Geographic mobility and special education services: Understanding the experiences of Canadian military families

Introduction: American research suggests that stressors associated with growing up in a military family, including geographic mobility, may affect the academic performance and school participation of military-connected children. Students requiring special education may be particularly vulnerable to impacts. Because this issue has not been explored in a Canadian context, the objective of this study was to explore the experience of geographic mobility for Canadian military families and their children’s access to special education services. Methods: Informed by interpretive phenomenological analysis, nine female parents of children with special education needs growing up in Canadian military families were interviewed. Results: Three superordinate themes emerged: Transitioning to new special education systems and services takes an emotional toll on families; active and persistent advocacy and communication strategies to access services are critical; and families struggle to balance securing special education services with career implications. Discussion: Given the common experience of high mobility among military families, future studies should explore different perspectives of the transition experience and barriers to access, including those of educators, school administrators, and active Canadian Armed Forces members.

Initial Phase of Replication of Plus-Stranded RNA Viruses

The author presents theoretical mean-field analysis of the initial phase of the kinetics of intracellular replication of plus-stranded RNA viruses, which are abundant and include, e.g., the hepatitis C virus (HCV). The treatment is based on the conventional concept that the replication process of such viruses takes place at the membrane complexes formed with participation of viral proteins, e.g., NS5A in the HCV case. The key novel prediction supported by Monte Carlo calculations is that this scheme may be insufficient in order to describe the very initial phase of the process, because the initial intracellular viral RNA and protein populations may in this case go extinct rather than overcome the kinetic barrier for transition to the full-scale infection of a host cell. Practically, this means that in such situations, the conventional replication scenario should be complemented by another pathway, e.g., by replication outside the membrane without viral proteins, which operates in the very beginning.

Measuring dynamic public transit accessibility to local centres in Warsaw

Abstract Over the last decade the number of studies on public transit accessibility has significantly increased. The aim of the study was to analyse the scope of application of measurements of the dynamic time accessibility in transportation systems for evaluation purposes. It was assumed that the indicator is a feasible measure for basic analysis however additional indicators are needed for reliable assessment. The study included assessing access to the global centre of Warsaw and to local and district centres in particular units. Public transit accessibility was analysed using schedule-based travel time and the population data statistic. The results of the study confirm the dynamic character of public transit time accessibility and its usefulness as a measure. Spatial and transit barriers were identified in local distribution centres and public transit operation. The work presented in the paper highlights the relevance of the in-depth evaluation of the public transit system in relation to the major congestion problems in Warsaw.

Effect of High Pressure on the Crystal Structure and Vibrational Properties of Olivine-Type LiNiPO4.

In this work, we present an experimental and theoretical study of the effects of high pressure and high temperature on the structural properties of olivine-type LiNiPO4. This compound is part of an interesting class of materials primarily studied for their potential use as electrodes in lithium-ion batteries. We found that the original olivine structure (α-phase) is stable up to ∼40 GPa. Above this pressure, the onset of a new phase is observed, as put in evidence by the X-ray diffraction (XRD) experiments. The structural refinement shows that the new phase (known as β-phase) belongs to space group Cmcm. At room temperature, the two phases coexist at least up to 50 GPa. A complete conversion to the β-phase was only obtained at high-pressure and high-temperature conditions (973 K, 6.5 GPa), as confirmed by both XRD and Raman spectroscopy. Ab initio calculations support the same structural sequence. The need of high-temperature conditions to obtain the complete transformation of the α-phase into the β-phase is indicative of the existence of a kinetic barrier for the phase transition. Here, we report the evolution of crystallographic parameters as a function of pressure for both phases, comparing them with the theoretical predictions. We also discuss the influence of pressure on the polyhedral units and report room-temperature equations of state. The dependence of the Raman phonons of both phases on pressure is also studied, assigning to each phonon its respective symmetry by comparison with the results of the ab initio simulations.

Identifying Barriers Toward a Post-growth Economy – A Political Economy View

In this paper, we take a political economy perspective on barriers that inhibit a transition beyond the growth-paradigm – that is, we frame transition barriers as looming conflicts of interest. Specifically, we investigate potential transition barriers within three case studies. First, unemployment represents the most commonly cited reason why economic growth is considered indispensable. Second, alternative indicators to Gross Domestic Product (GDP) have not succeeded in replacing GDP as a standard metric of economic welfare. Third, pension schemes rely on economic growth to offset demographic change. In each of these three examples, we identify actor-interest constellations that foster the status quo of a growth economy. We conclude that compensating some of those actors who would presumably be worse off in a post-growth economy may be necessary – though not sufficient – for a transition.

Numerical Study for a Large-Volume Droplet on the Dual-Rough Surface: Apparent Contact Angle, Contact Angle Hysteresis, and Transition Barrier.

The profile, apparent contact angle (ACA), contact angle hysteresis (CAH), and wetting state transmission energy barrier (WSTEB) are important static and dynamic properties of a large-volume droplet on the hierarchical surface. Understanding them can provide us with important insights into functional surfaces and promote the application in corresponding areas. In this paper, we establish three theoretical models (models 1-3) and the corresponding numerical methods, which were obtained by the free energy minimization and the nonlinear optimization algorithm, to predict the profile, ACA, CAH, and WSTEB of a large-volume droplet on the horizontal regular dual-rough surface. In consideration of the gravity, the energy barrier on the contact circle, the dual heterogeneous structures and their roughness on the surface, the models are more universal and accurate than the previous models. It showed that the predictions of the models were in good agreement with the results from the experiment or literature. The models are promising to become novel design approaches of functional surfaces, which are frequently applied in microfluidic chips, water self-catchment system, and dropwise condensation heat transfer system.

An Assessment of the Drivers and Barriers for the Deployment of Urban Phosphorus Recovery Technologies: A Case Study of The Netherlands

Phosphorus (P), being one of the building blocks of life, is essential for a multitude of applications, primarily for fertilizer usage. Sustainable management of phosphorus is becoming increasingly important in light of adverse environmental effects, ambiguous reserves, increasing global demand and unilateral dependence. Recovery of phosphorus from the biggest loss stream, communal wastewater, has the potential to tackle each of these problems. The implementation of phosphorus recovery technologies at wastewater treatment plants is not widespread, despite prolonged efforts primarily done by researchers over the past decade. This study aimed to assess the drivers and barriers of a phosphorus recovery transition. Several key stakeholders involved in this transition in The Netherlands were interviewed. The Netherlands was taken as a case study, since it serves as a frontrunner in the implementation of phosphorus recovery technologies. This study shows that the main barriers from the point of view of fertilizer companies are the different and unclear characteristics of the phosphorus recovery product struvite compared to common fertilizers. Moreover, the end-of-waste status of struvite is mentioned as a prominent barrier for a phosphorus transition, since it hinders free market trade. Many water boards indicate that the main barrier is the high investment cost with an uncertain return on investment for onsite struvite recovery processes. The specified main driver for water boards for onsite struvite phosphorus recovery technology is the reduction of maintenance costs, and for phosphorus recovery from sewage sludge ash, the low organic pollutant in the P recovery product.

Layer-Dependent Chemically Induced Phase Transition of Two-Dimensional MoS2.

Two-dimensional (2D) transition metal dichalcogenides (TMDCs) with layered structures provide a unique platform for exploring the effect of number of layers on their fundamental properties. However, the thickness scaling effect on the chemical properties of these materials remains unexplored. Here, we explored the chemically induced phase transition of 2D molybdenum disulfide (MoS2) from both experimental and theoretical aspects and observed that the critical electron injection concentration and the duration required for the phase transition of 2D MoS2 increased with decreasing number of layers. We further revealed that the observed dependence originated from the layer-dependent density of states of 2H-MoS2, which results in decreasing phase stability for 2H-MoS2 with increasing number of layers upon electron doping. Also, the much larger energy barrier for the phase transition of monolayer MoS2 induces the longer reaction time required for monolayer MoS2 as compared to multilayer MoS2. The layer-dependent phase transition of 2D MoS2 allows for the chemical construction of semiconducting-metallic heterophase junctions and, subsequently, the fabrications of rectifying diodes and all 2D field effect transistors and thus opens a new avenue for building ultrathin electronic devices. In addition, these new findings elucidate how electronic structures affect the chemical properties of 2D TMDCs and, therefore, shed new light on the controllable chemical modulations of these emerging materials.

Implementation of accrual accounting in Thailand’s central government

ABSTRACTThis paper evaluates the outcomes of accrual accounting implementation in Thailand’s central government. A new conceptual framework was used to study transition barriers and their effects. Financial transparency and accountability were shown to have improved. Significant barriers to the transition to accrual accounting include a lack of incentives, a management culture, a lack of accounting manuals, and a failure to understand accrual information.IMPACTThis paper explains the transition barriers Thailand has faced in adopting accrual accounting in its central government and how these barriers are affecting financial reporting in the public sector. The results in this paper can be applied to other countries in terms of evaluating outcomes or planning transition processes.

The evolution of morphology, crystallization and static and dynamic mechanical properties of long glass-fibre–reinforced polypropylene composites under thermo-oxidative ageing

In this work, the static and dynamic mechanical properties, crystallization behaviours, and morphology of long glass-fibre–reinforced polypropylene (PP) composites with thermo-oxidative ageing time from 0 day to 50 days at 120°C were investigated and discussed. The static mechanical properties showed a global decrease in tensile, bending and impact strengths with increasing ageing time. From the results obtained by scanning electronic microscopic observations, interface debonding clearly occurred between the glass fibre and PP matrix in the aged samples. The crystallinity ( Xc) of the composites was analyzed by differential scanning calorimetry; annealing process played the leading role in the early period of ageing, while as ageing progressed, the degradation of PP matrix dominated the ageing process and Xc decreased. The dynamic mechanical analysis results indicated that the storage modulus and glass transition temperature of the composites also decreased with prolonging ageing time. Then, the apparent activation energy ( E) of glass transition was calculated by the Arrhenius equation with different scanning frequencies. A higher value of E was obtained for the samples in the later ageing period, which means a higher energy barrier for glass transition.

Energy barrier of bcc-fcc phase transition via the Bain path in Yukawa system

In the Yukawa system with the dimensionless screening parameter κ>1.5, when bcc-fcc transition occurs via Bain path, we show that spontaneous transitions do not occur even if the system temperature reaches the transition point of bcc-fcc because it is necessary to increase once the free energy in the process of transition from bcc to fcc through Bain deformation. Here, we refer the temporary increment of the free energy during Bain deformation as Bain barrier. Since there are the Bain barriers at the transitions between bcc and fcc phases, these phases may coexist as metastable state in the wide region (not a coexistence line) of κ and the coupling constant Γ. We study the excess energy of the system and the free energy difference between bcc and fcc phases by the Monte Carlo method, where the simulation box is divided into a large number of elements with small volume and a particle in the box is restricted be placed in one of these elements. By this method, we can tabulate the values of the interparticle potential and can calculate the internal energy fast and precisely.

Alloying as a Route to Monolayer Transition Metal Dichalcogenides with Improved Optoelectronic Performance: Mo(S1–xSex)2 and Mo1–yWyS2

On the basis of first-principles and cluster expansion calculations, we propose an effective approach to realize monolayer transition metal dichalcogenides with sizable band gaps and improved optoelectronic performance. We show that monolayer Mo(S1–xSex)2 and Mo1–yWyS2 with x = 1/3, 2/3 and y = 1/3, 1/2, 2/3 are stable according to phonon calculations and realize 1T′ or 1T″ phases. The transition barriers from the 2H phase are lower than for monolayer MoS2, implying that the 1T′ or 1T″ phases can be achieved experimentally. Furthermore, it turns out that the 1T″ monolayer alloys with x = 1/3, 2/3 and y = 1/3, 2/3 are semiconductors with band gaps larger than 1 eV, due to trimerization. The visible light absorption and carrier mobility are strongly improved as compared to 2H monolayer MoS2, MoSe2, and WS2. Thus, the 1T″ monolayer alloys have the potential to expand the applications of transition metal dichalcogenides, for example, in solar cells.

An empirical examination of critical barriers in transitions between technology push and demand pull strategies in manufacturing organizations

PurposeThe purpose of this paper is to examine critical barriers in transitions between technology push (TP) and demand pull (DP) strategies in Indian manufacturing industries for accomplishing sustainable development.Design/methodology/approachThe factors that affect the transitions have been extracted and analyzed using factor analysis technique. For the purpose, various critical barriers are grouped together based on their relevance to TP-DP strategies. The responses to critical barriers have been collected from different Indian manufacturing organizations practicing TP-DP strategies, using a well-framed TP-DP questionnaire. Further, the responses are analyzed using factor analysis which improved the data interpretation.FindingsFour latent factors were extracted from critical barriers and revealed that the manufacturing organizations face these barriers in transitions between TP-DP strategies. The recognition of the outcomes of critical barriers has been perceived to be substantial in the present context.Originality/valueThe research concludes that TP-DP strategies in Indian manufacturing industries encounter relevant critical barriers for accomplishing sustainable development. The outcomes of the study will help TP-DP practitioners, HR executives and organizational managers in manufacturing companies to develop clear understanding about the significant TP-DP strategies to be followed comprehensively for realization of sustainable development. The manufacturing organizations will be able to formulate and express their policies and issues in a more pertinent manner. Hence, the knowledge obtained from the empirical examination of critical barriers in transitions between TP and DP strategies will be helpful in improving the overall performance of manufacturing industries involved in the present study.

Structural and energetic properties of tautomeric forms of phosphonyl thioamides

Stable tautomeric forms in a series of phosphonyl thioamides have been studied using DFT methods. The molecules studied in this contribution present a phosphonyl group in β-position of the C–S bond connected to the amine group. The three most stable tautomeric forms with double bonds on either C=N, C=S, or adjacent C=C have been described, and their relative energies together with the transition barriers have been evaluated. In such molecules a six-member ring can be formed by a hydrogen bond between the oxygen of the phosphonyl group and the H–N bond of the thioamide. The tautomeric form involving a C=N double bond is found less stable than the two other forms by more than 10 kcal/mol. The transition barriers between the various tautomers are calculated to be as large as 40 kcal/mol for the isolated molecules, but less than 30 kcal/mol in the presence of one water molecule. Similar results are obtained with various substituents on the phosphorus or on the nitrogen atom. Electronic vertical spectra have been calculated using the TD-DFT approach for the three stable tautomeric forms in a series of six substituted phosphonyl thioamides, and it is found that the signature of each tautomer is sufficiently specific to allow for their clear identification in a mixture using UV–Vis spectroscopy.

Non-isothermal crystallization kinetics of Fe75Cr5P9B4C7 metallic glass with a combination of desired merits

The non-isothermal crystallization kinetics of our previously reported Fe75Cr5P9B4C7 metallic glass (MG) was systematically evaluated by X-ray diffraction (XRD), transmission electron microscopy (TEM) and differential scanning calorimeter (DSC). The primary crystalline phases of the present alloy annealed under non-isothermal heating conditions were mainly identified as nanocrystalline α-(Fe,Cr), (Fe,Cr)3P, (Fe,Cr)3C and (Fe,Cr)23(C,B)6 embedded in amorphous matrix by XRD and TEM. The apparent activation energy (E) for characteristic temperatures determined by Kissinger method is similar to that determined by Ozawa method. The Eg for the glass transition temperature is larger than both of the Ex for the onset crystallization temperature and the Ep for the peak temperature, indicating that the energy barrier for the glass transition is higher than that for the crystallization. Furthermore, the local activation energy evaluated by Kissinger-Akahira-Sunose (KAS) method and Ozawa-Flynn-Wall (OFW) method shows similar trend of gradual increase with the progressing of the crystallization process, implying that the improved difficulty of crystallization. Additionally, the local Avrami exponents gradually decreased from the values larger than 2.5 to the values smaller than 2.5, which implies a typical diffusion-controlled growth with variable crystallization mechanisms during the whole process.

Attitudes and experiences of childhood cancer survivors transitioning from pediatric care to adult care.

Survivors of pediatric cancer are prone to late effects which require ongoing medical care. Young adult survivors often transition from specialist pediatric care to adult-oriented or community-based healthcare. This study aims to describe the attitudes and experiences of survivors and their parents towards transition barriers and enablers. Long-term survivors and parents (of survivors < 16years) were recruited from 11 hospitals in Australia and New Zealand to participate in a semi-structured telephone interview regarding their transition experiences. Transcribed interviews were coded and content analysis was used to number participants within themes. Thirty-three participants were interviewed, of which 18 were survivors (mean age 26years, SD = 6.3; mean time since treatment completion 13.3years, SD = 6.1) and 15 were parents (mean survivor age 15years, SD = 1.9; mean time since treatment completion 8.4years, SD = 2.8). Participants described their transition attitudes as positive (55%), neutral (15%), or negative (30%). Key barriers to transition included dependence on pediatric healthcare providers, less confidence in primary care physicians (PCPs), inadequate communication, and cognitive difficulty. Enablers included confidence in and proximity to physicians, good communication, information, independence, and age. Many survivors face barriers to their transition out of pediatric care. Early introduction to transition, greater collaboration between healthcare professionals, and better information provision to survivors may improve the transition process. Future research of survivors' experience of barriers/enablers to transition is needed. Development of interventions, such as those that address self-management skills, is required to facilitate transition and encourage long-term engagement.

Steered molecular dynamics simulations for uncovering the molecular mechanisms of drug dissociation and for drug screening: A test on the focal adhesion kinase.

Drug-binding kinetics could play important roles in determining the efficacy of drugs and has caught the attention of more drug designers. Using the dissociation of 1H-pyrrolo[2,3-b]-pyridines from the focal adhesion kinase as an example, this work finds that steered molecular dynamics simulations could help screen compounds with long-residence times. It also reveals a two-step mechanism of ligand dissociation resembling the release of ADP from protein kinase A reported earlier. A phenyl group attaching to the pyrrole prolongs residence time by creating a large activation barrier for transition from the bound to the intermediate state when it becomes exposed to the solvent. Principal component analysis shows that ligand dissociation does not couple with large-scale collective motions of the protein involving many of its amino acids. Rather, a small subset of amino acids dominates. Some of these amino acids do not contact the ligands directly along the dissociation pathways and could exert long-range allosteric effects. © 2018 Wiley Periodicals, Inc.