One-step Transition Research Articles

A novel method for solving response of stochastic vibro-impact systems with two stoppers

The research of stochastic steady-state probability density response of vibration systems including bilateral impacts and gaps is of great theoretical and practical significance. Usually, the non-smooth transformation is introduced in the response calculation, while eliminates the non-smooth characteristics of the systems. Therefore, this paper propose a new method to preserve the velocity jump under the bilateral impact without non-smooth transformation. Based on the generalized cell mapping theory, a complete process is regarded as the one-step transition probability that the stochastic trajectories start from one stopper, and return to the original stopper after impacting with another stopper. Then, the intervals of response are established based on the initial stopper to ensure the continuity of the state space. We analyzed the probability density response of a bilateral Rayleigh vibro-impact oscillator and a piezoelectric energy harvesting device with two symmetric stoppers by utilizing the proposed method, respectively. Comparing with Monte Carlo simulations, it is fully demonstrated the effectiveness of this method. At the same time, the cases using our proposed method are found to have wide applicability under different position of stoppers, restitution coefficient, noise excitation and system parameters.

Theoretical approach to the one-step versus two-step spin transitions in Hofmann-like FeII SCO metal-organic frameworks

Guest molecules in the 3D Hofmann-type FeII spin-crossover (SCO) metal-organic frameworks modulate the magnetic properties of the host, modifying the spin state, transition temperature, width of the hysteresis loop and are responsible for the occurrence of a single-step or multistep spin transition. In this work we explore the guest-dependent SCO properties of the Hofmann-like FeII SCO clathrates with formula {Fe(bpb)[Pt(CN)4]}⋅2G. We use a computational strategy based on DFT periodic calculations on the whole system, CASSCF/NEVPT2 calculations on single metal fragments and plots of the reduced density gradients to identify and quantify the dominant effects governing the occurrence of one-step or two-step spin transitions in these systems. Our results inform about the strength of the ligand field around Fe sites, the relative stability of the different spin states, the amplitude and nature of the host-guest and guest-guest interactions, and the role of the vibronic effects on the SCO properties of Hofmann-type FeII clathrates.

A Markov chain model for geographical accessibility

Accessibility analyses are conducted for a variety of applications, including urban planning and public health studies. These applications may aggregate data at the level of administrative units, such as provinces or municipalities. Accessibility between administrative units can be quantified by travel distance. However, modelling the distances between all administrative units in a region is computationally expensive if a large number of administrative units is considered. We propose a methodology to model accessibility between administrative units as a homogeneous Markov chain, where the administrative units are states and standardised inverse travel distances act as transition probabilities. Single transitions are allowed only between adjacent administrative units, resulting in a sparse one-step transition probability matrix (TPM). Powers of the TPM are taken to obtain transition probabilities between non-adjacent units. The methodology assumes that the Markov property holds for travel between units. We apply the methodology to administrative units within Tshwane, South Africa, considering only major roads for the sake of computation. The results are compared to those obtained using Euclidean distance, and we show that using network distance yields more reasonable results. The proposed methodology is computationally efficient and can be used to estimate accessibility between any set of administrative units connected by a road network.

Thermal-Driven Guest-Induced Spin Crossover Behavior in 3D Fe(II)-Based Porous Coordination Polymers

3D porous coordination polymers [Fe(bpb)2dca]ClO4·0.5CH3OH·Guest (bpb = 1,4-bis(4-pyridyl)benzene; Guest = chloroform or dichloromethane) (1·3CHCl3 and 1·2.5CH2Cl2, 1 = [Fe(bpb)2dca]ClO4·0.5CH3OH) were synthesized and characterized by single-crystal X-ray diffraction, thermogravimetric, magnetic, optical, and calorimetric measurements. The 3D polymer 1·3CHCl3 displays upon cooling an incomplete one-step transition centered at T1/2 ∼ 85 K according to SQUID measurements. The 3D polymer 1·2.5CH2Cl2, however, displays a two-step incomplete spin crossover behavior located between T1/2 ∼ 218 K for the highest transition and T1/2 ∼ 124 K for the lower one. In addition, these materials show different colors due to accommodating chloroform (yellow color) or dichloromethane (orange color) molecules in their cavities. Cryogenic optical microscopy was used to image the spatiotemporal properties of the thermal transition at the scale of a single crystal of both compounds. A gradual transition with a homogeneous color change was detected in 1·3CHCl3 around 90 K, in fair agreement with magnetic data. In contrast, a cooperative hysteretic thermal transition accompanied by delamination and the appearance of well spatially organized microcracks was evidenced in 1·2.5CH2Cl2 around 140 K. The complex two-step spatiotemporal front transformations observed in this system are attributed to the interplay between the SCO and the structural transition. In light of all the above elements, it is thus inferred that host–guest interactions in the crystal cavity can modulate these polymers’ magnetic and optical properties. Such materials can realize the interconversion of high-spin and low-spin states under the stimulation of guest molecules, thus having potential applications as reusable storage for chemical and gas sensors.

Te-doped NiFe2O4 stabilized by amorphous carbon layers derived from one-step topological transitions of NiFe LDHs with significantly enhanced oxygen evolution reaction

Constructing efficient oxygen evolution reaction (OER) electrocatalysts that can stably operate under high temperatures and strong alkaline conditions still faces great challenges for industrial hydrogen production from water electrolysis. Herein, a self-supported tellurium (Te)-doped spinel NiFe2O4 with a carbon-stabilized nanosheet structure anodic catalyst on nickel foam (NF) (Te-NiFe2O4@C/NF) is successfully synthesized by calcination of a layered double hydroxide precursor (NiFe LDH). Benefiting from Te doping as well as coupling with the amorphous carbon layer and the unique superhydrophilic/aerophobic surface property, which provides efficient mass transport channels and rapid electron transport, the optimized Te-NiFe2O4@C/NF requires an overpotential of 220 mV to achieve a current density of 10 mA cm−2 for the OER in 1 M KOH at 25 ℃. Furthermore, an extremely low overpotential of 180 mV is required to achieve 500 mA cm−2 in 6 M KOH at 80 ℃ and maintains superior stability over 60 h under such harsh quasi-industrial conditions. Density functional theory calculations further reveal that Te doping can effectively modulate the local electronic environment of the Ni and Fe sites, which optimizes the intermediate (*OH) adsorption and facilitates the OER kinetics. This work may open up opportunities to explore efficient electrocatalysts for scalable hydrogen production.

Visualizing ultrafast weak-field-induced rotational revivals of air molecules at room temperature.

The ability to observe quantum coherence and interference is crucial for understanding quantum effects in nonlinear optical spectroscopy and is of fundamental interest in quantum mechanics. Here, we present an experimental study combined with theoretical analysis and numerical simulations to identify the underlying process behind the rotational revivals induced by a pair of time-delayed ultrafast femtosecond laser pulses for air molecules under ambient conditions. Our time-resolved two-dimensional alignment measurements confirm that one-step non-resonant Raman transitions from initial states of mixed molecules play a dominant role, showing a signature of weak-field-induced rotational revivals. Furthermore, we demonstrate that such rotational revival spectra can simultaneously measure the entire pure rotational Raman spectra and observe the quantum interference between two transition pathways from a given initial state. This work provides a powerful tool to observe, control, and identify the rotational dynamics of mixed molecular samples under weak-field excitations.

Statistical Model of Accurately Estimating Service Delay Behavior in Saturated IEEE 802.11 Networks Based on 2-D Markov Chain

To accurately estimate the service delay behavior of IEEE 802.11 networks, this paper comprehensively considers four main factors that affect the performance of IEEE 802.11 networks and establishes a service delay model with statistical characteristics. We analyzed the operation mechanism of 802.11 DCF, using the backoff stage and the backoff counter to portray the dynamic change characteristics of the system regarding the data frame transmission states. Afterward, we calculated the one-step transition probability of these states, establishing a 2-D Markov model, including the ICS procedure and the backoff procedure. Based on this model, we constructed steady-state equations to derive a relationship between the transmission probability and collision probability for each node transmission queue. By analyzing the ICS delay and the backoff delay, we obtained the probability generating function (PGF) of the average idle time. The analytical expressions of other service delays, such as the successful transmission time and collided transmission time, were derived to obtain the PGF of the total service delay. In the numerical simulation, we compared the first two statistical moments of the PGF with the Nav model, and it was found that our delay evaluation results were significantly better than the traditional evaluation results. The average service delay of the Nav model in all the scenarios was larger than that of the proposed model due to the lack of the ICS procedure in the Nav model. Since a DIFS duration is generally much shorter than a random backoff duration, our model saves the bandwidth and improves transmission efficiency.

Balanced Coexistence of Reversible and Irreversible Covalent Bonds in a Conductive Triple Polymeric Network Enables Stretchable Hydrogels with High Toughness and Adhesiveness.

The application of soft hydrogels to stretchable devices has attracted increasing attention in deformable bioelectronics owing to their unique characteristic, "modulus matching between materials and organs". Despite considerable progress, their low toughness, low conductivity, and absence of tissue adhesiveness remain substantial challenges associated with unstable skin-interfacing, where body movements undesirably disturb electrical signal acquisitions. Herein, we report a material design of a highly tough strain-dissipative and skin-adhesive conducting hydrogel fabricated through a facile one-step sol-gel transition and its application to an interactive human-machine interface. The hydrogel comprises a triple polymeric network where irreversible amide linkage of polyacrylamide with alginate and dynamic covalent bonds entailing conjugated polymer chains of poly(3,4-ethylenedioxythiophene)-co-(3-thienylboronic acid) are simultaneously capable of high stretchability (1300% strain), efficient strain dissipation (36,209 J/m2), low electrical resistance (590 Ω), and even robust skin adhesiveness (35.0 ± 5.6 kPa). Based on such decent characteristics, the hydrogel was utilized as a multifunctional layer for successfully performing either electrophysiological cardiac/muscular on-skin sensors or an interactive stretchable human-machine interface.

Impact of first-order phase transitions on dark matter production in the scotogenic model

In this work, we investigate the effects of first-order phase transitions on the singlet fermionic dark matter in the scotogenic model. It is known that this dark matter candidate tends to conflict with the relevant constraints such as the neutrino oscillation data and charged lepton flavor violating processes if its thermal production mechanism is assumed. We find that the dark matter production mechanisms are modified by first-order phase transitions at some specific parameter regions, where the phase transitions can be one-step or two-step depending on the parameters. If the phase transition is one-step, a sufficiently low nucleation temperature is required to reproduce the observed relic abundance of dark matter. If the phase transition is two-step, the dark matter should never be thermalized, otherwise the abundance would remain too much and overclose the universe. This is because the nucleation temperature cannot be low as in the one-step case. Therefore we require another way of dark matter production, the freeze-in mechanism for the two-step case. We show that the freeze-in mechanism is modified by the temporary vacuum expectation value of the inert scalar field. In both cases, the first-order phase transitions could produce observable gravitational wave spectra. In particular for the one-step phase transition, the generated gravitational waves with sizable energy density are intrinsically correlated with the dark matter production mechanism, and can be detectable by future space-based interferometers.

Updated constraints on the Georgi-Machacek model and its electroweak phase transition and associated gravitational waves

With theoretical constraints such as perturbative unitarity and vacuum stability conditions and updated experimental data of Higgs measurements and direct searches for exotic scalars at the LHC, we perform an updated scan of the allowed parameter space of the Georgi-Machacek (GM) model. With the refined global fit, we examine the allowed parameter space for inducing strong first-order electroweak phase transitions (EWPTs) and find only the one-step phase transition is phenomenologically viable. Based upon the result, we study the associated gravitational wave (GW) signals and find most of which can be detected by several proposed experiments. We also make predictions on processes that may serve as promising probes to the GM model in the near future at the LHC, including the di-Higgs productions and several exotic scalar production channels.

The Conformational Transition Pathways and Hidden Intermediates in DFG-Flip Process of c-Met Kinase Revealed by Metadynamics Simulations.

Protein kinases intrinsically translate their conformations between active and inactive states, which is key to their enzymatic activities. The conformational flipping of the three-residue conservative motif, Asp-Phe-Gly (DFG), is crucial for many kinases' biological functions. Obtaining a detailed demonstration of the DFG flipping process and its corresponding dynamical and thermodynamical features could broaden our understanding of kinases' conformation-activity relationship. In this study, we employed metadynamics simulation, a widely used enhanced sampling technique, to analyze the conformational transition pathways of the DFG flipping for the c-Met kinase. The corresponding free energy landscape suggested two distinct transition pathways between the "DFG-in" and "DFG-out" states of the DFG-flip from c-Met. On the basis of the orientation direction of the F1223 residue, we correspondingly named the two pathways the "DFG-up" path, featuring forming a commonly discovered "DFG-up" transition state, and the "DFG-down" path, a unique transition pathway with F1223 rotating along the opposite direction away from the hydrophobic cavity. The free energies along the two pathways were then calculated using the Path Collective Variable (PCV) metadynamics simulation. The simulation results showed that, though having similar free energy barriers, the free energy cuve for the DFG-down path suggested a two-step conformational transition mechanism, while that for the DFG-up path showed the one-step transition feature. The c-Met DFG flipping mechanism and the new intermediate state discovered in this work could provide a deeper understanding of the conformation-activity relationship for c-Met and, possibly, reveal a new conformational state as the drug target for c-Met and other similar kinases.

Supervised learning with probability interpretation in airfoil transition judgment

Transition prediction has always been a frontier issue in the field of aerodynamics. A supervised learning model with probability interpretation for transition judgment based on experimental data was developed in this paper. It solved the shortcomings of the point detection method in the experiment, that which was often only one transition point could be obtained, and comparison of multi-point data was necessary. First, the Variable-Interval Time Average (VITA) method was used to transform the fluctuating pressure signal measured on the airfoil surface into a sequence of states which was described by Markov chain model. Second, a feature vector consisting of one-step transition matrix and its stationary distribution was extracted. Then, the Hidden Markov Model (HMM) was used to pre-classify the feature vectors marked using the traditional Root Mean Square (RMS) criteria. Finally, a classification model with probability interpretation was established, and the cross-validation method was used for model validation. The research results show that the developed model is effective and reliable, and it has strong Reynolds number generalization ability. The developed model was theoretically analyzed in depth, and the effect of parameters on the model was studied in detail. Compared with the traditional RMS criterion, a reasonable transition zone can be obtained using the developed classification model. In addition, the developed model does not require comparison of multi-point data. The developed supervised learning model provides new ideas for the transition detection in flight experiments and other experiments.

Solvent effects on the original molecular recovery from the solvated solute monomers of cyclic nitramine explosives

This work aims to understand the relationship between crystallization phenomena and solvation effects. Three cyclic nitramine explosives, including hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine (HMX) and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, CL-20), are selected to study the solvent effects on the original molecular recovery from the solvated solute monomers in the crystallization process using the quantum mechanical approach. Simulated results indicates that the low energy barrier can be overcome by the positive energy increase during the antisolvent crystallization process, leading to recovering original α-RDX molecules from their solvated monomers through the one-step transition state mechanism. Whereas for the molecules of HMX and HNIW, due to significant solvation effects on the molecular energy, it is suggested that the final presence of these original molecules in the crystalline order of the metastable crystals has to rely on the amorphous nucleus in the two-step nucleation mechanism.

Response Statistics of Single-Degree-of-Freedom Systems with Lévy Noise by Improved Path Integral Method

In this paper, we put forward an improved version of the path integral (PI) method for the response statistics of single-degree-of-freedom (SDOF) system excited by Lévy noise. To overcome the problem of large amount of calculation and storage, the PI method is simplified and parallelized, which makes the PI method for SDOF system with Lévy noise feasible and efficient. As the key to the PI method, the short-time transition probability density function (PDF) of the SDOF system is derived and verified by proving that the PI solution satisfies the corresponding fractional Fokker–Planck–Kolmogorov (FPK) equation. The fractional FPK equation, which is the governing equation of the SDOF system, is derived through the characteristic function and the Chapman–Kolmogorov equation. To solve the problem of large storage and calculations in the PI method, we simplify the one-step iteration formula and perform parallel calculations on the simplified formula. The simplification of the one-step iteration formula reduces one-fold integration, thereby reducing the storage capacity of the one-step transition matrix. Parallel calculation by domain decomposition can effectively reduce the calculation time, which can be seen from the running time of two prototypical examples. Besides, to show the effectiveness of the improved PI method, Monte Carlo solutions and analytical solutions are used as reference solutions.

One-Step versus Two-Step Valence Tautomeric Transitions in Tetraoxolene-Bridged Dinuclear Cobalt Compounds.

The syntheses of valence tautomeric compounds with multistep transitions using new redox-active ligands are the long-term goal of the field of bistable materials. The redox-active tetraoxolene ligand, 2,7-di-tert-butylpyrene-4,5,9,10-tetraone (pyreneQ-Q), is now developed to synthesize a pair of dinuclear compounds {[CoL2]2(pyreneSq-Sq)}[Co(CO)4]2·xCH2Cl2·2C6H5CH3 (1, x = 2, L = 1,10-phenanthroline, phen; 2, x = 1.5, L = 2,2'-bipyridine, bpy). Variable-temperature magnetic susceptibilities and single-crystal X-ray diffraction measurements indicate a partial one-step valence tautomeric transition for 1 and a rare two-step valence tautomeric transition for 2, respectively. DFT calculation results are consistent with the experimental data, revealing the correlation between thermodynamic parameters and the one-step/two-step valence tautomeric behaviors.

Approximate verification of geometric ergodicity for multiple-step Metropolis transition kernels

In many applications involving discrete time Markov chains, the autocorrelation between states corresponding to nearby time points is too high to use all of these states as part of an approximate random sample from a specified target distribution. In these situations, it is common to use the output of a thinned chain, where we take samples every $h$ steps, and $h$ is a positive integer, in order to reduce autocorrelation. In order to justify using central limit theorems in analyses based on the output of a thinned chain, it is necessary to show that the thinned chain is geometrically ergodic. A common way to do this is to show that the chain satisfies a minorization condition and an associated drift condition. In this manuscript, we extend previous results pertaining to one-step transition kernels to handle numerical estimation of minorization and drift coefficients for $h$-step transition kernels for Metropolis algorithms.

Mechanism of diethylamine/DBU-catalyzed cycloaddition of azides to unsaturated aldehydes: A quantum mechanical investigation

Density functional theory (DFT) methods have been used to investigate the mechanism of diethylamine-catalyzed cycloaddition reaction of phenyl azide and pentanal. The single point energies have been computed at M06-2X/6-311+G(d,p)//M06-2X /6-31+G(d,p) levels of theory in the presence of DMSO as a solvent. The computational results indicate that the catalyzed cycloaddition reaction is carried out via two one-step transition states that lead to 1,4- and 1,5-regioisomers, and favors the generation of the 1,4-regioisomer. In the absence of a catalyst, the 32CA reactions of azide and alkyne lack poor regioselectivity. Finally, distortion/interaction analysis along the reaction pathways was used to explain the 1,5-regioselectivity.

Guest-Induced Multistep-to-One-Step Reversible Spin Transition with Enhanced Hysteresis in a 2D Hofmann Framework.

The interplay of host-guest interactions and controlled modulation of spin-crossover (SCO) behavior is one of the most exploited topics regarding data storage, molecular sensing, and optical technologies. In this work, we demonstrate the experimental approach of tuning the SCO behavior via controlled modulation of the spin-state cooperativity in a 2D Hofmann coordination polymer, [FeIIPd(CN)4(L)2]·1.3MeOH (1·1.3MeOH; L = methyl isonicotinate). Removal of the solvent changes the four-step transition to a complete one-step spin transition with an enhanced hysteresis width (∼20 K). Structural analysis of solvated (1·1.3MeOH) and partially desolvated (1·0.3MeOH) compounds reveals that the crystal system changes from a monoclinic C2/c space group to an orthorhombic Imma space group, where the FeII sites are present in a more symmetrically equivalent environment. Consequently, the axial ligand-field (LF) strength and face-to-face interactions of the ligands were increased by removing the guest, which is reflected in the highly cooperative SCO in 1 (desolvated compound). Also, the shift of the CN bond stretching frequencies and decrease of their relative intensities from the variable-temperature Raman spectroscopic measurements further corroborate the SCO behavior. Besides, theoretical calculations reveal that the singlet (1Γ) LF terms decrease by removing guest molecules, enhancing the molecular population in the low-spin state at low temperature, as experimentally observed for 1. Notably, fine tuning of the SCO behavior via host-guests interactions provides a great opportunity to design potential chemosensors.

Dynamic response and bifurcation for Rayleigh-Liénard oscillator under multiplicative colored noise

The generalized mixed Rayleigh-Liénard (R-L) oscillator with both periodic and parametric excitations subjected to multiplicative colored noise is investigated in this paper. First, the deterministic global properties are calculated by the iterative compatible cell mapping method, showing the coexistence of chaotic attractor and periodic attractor. Then, under different damping control parameters, the evolutionary processes of transient and steady-state probability density functions (PDFs) of the response under multiplicative colored noise are discussed by the generalized cell mapping based on the short-time Gaussian approximation (GCM/STGA). To solve the storage problem and improve the computational efficiency of one-step transition probability density matrix, we propose to introduce the block matrix procedure into the GCM/STGA method. The results show that the evolutionary direction of PDFs is in accordance with the shape of the unstable manifold. We also observe that it takes longer to achieve the steady state for the case with the coexistence of chaotic attractor and periodic attractor than the case with only periodic attractor. Besides, the stochastic P-bifurcation occurs with changing the intensity and the correlation time for the colored noise. The GCM/STGA scheme shows good agreement with Monte Carlo simulations, which proves the effectiveness of the proposed strategy for systems with chaotic attractor and multiplicative colored noise.

Generation and Application of Directly Reprogrammed Endothelial Cells.

Cell-based therapy has emerged as a promising option for treating advanced ischemic cardiovascular disease by inducing vascular regeneration. However, clinical trials with adult cells turned out disappointing in general. As a newer approach, direct reprogramming has emerged to efficiently generate endothelial cells (ECs), which can promote neovascularization and vascular regeneration. This review provides recent updates on the direct endothelial reprogramming. In general, directly reprogrammed ECs can be generated by two approaches: one by transitioning through a plastic intermediate state and the other in a one-step transition without any intermediate states toward pluripotency. Moreover, the methods to deliver reprogramming factors and chemicals for the fate conversion are highlighted. Next, the therapeutic effects of the directly reprogrammed ECs on animal models are reviewed in detail. Other applications using directly reprogrammed ECs, such as tissue engineering and disease modeling, are also discussed. Lastly, the remaining questions and foremost challenges are addressed.