Model Of Transitions Research Articles

Near-infrared photoluminescence radiation from the interface of an annealed ZnO nano thin film/silicon heterostructure array

In this study, the photoluminescence (PL) features of an annealed ZnO nano thin film/silicon heterostructure array were investigated. PL spectra were observed, which were closely related to the annealing temperature and covered visible–near infrared (NIR) region among 500–900 nm (1.37 eV–1.59 eV), especially two unexpected NIR peaks at 1.44 eV, 1.57 eV were detected. silicon array was synthesized by hydrothermal corrosion by using the solution composed of ferric nitrate and hydrofluoric acid. A regular array surface was obtained and exhibited a red PL emission with a slight position shift as the excitation wavelength varied. Oxygen defects in the array structure and silicon nanoparticles were responsible for the red PL. ZnO nano thin film/silicon heterostructure array was prepared by heating the Zn film coated array, which was obtained by magnetron sputtering. As the heating temperature increased to 350–400 °C, the PL intensity of the ZnO nano thin film/silicon heterostructure array decreased to approximately half that of the original, and the orange-red PL peaks was substituted by NIR radiations gradually. The models of electrons transition at the interface were analyzed to explain the emissions. The results demonstrated that the potential of ZnO/silicon heterostructure array as a NIR-emitting material.

Building models of topological quantum criticality from pivot Hamiltonians

Progress in understanding symmetry-protected topological (SPT) phases has been greatly aided by our ability to construct lattice models realizing these states. In contrast, a systematic approach to constructing models that realize quantum critical points between SPT phases is lacking, particularly in dimension d>1d>1. Here, we show how the recently introduced notion of the pivot Hamiltonian—generating rotations between SPT phases—facilitates such a construction. We demonstrate this approach by constructing a spin model on the triangular lattice, which is midway between a trivial and SPT phase. The pivot Hamiltonian generates a U(1)U(1) pivot symmetry which helps to stabilize a direct SPT transition. The sign-problem free nature of the model—with an additional Ising interaction preserving the pivot symmetry—allows us to obtain the phase diagram using quantum Monte Carlo simulations. We find evidence for a direct transition between trivial and SPT phases that is consistent with a deconfined quantum critical point with emergent SO(5)SO(5) symmetry. The known anomaly of the latter is made possible by the non-local nature of the U(1)U(1) pivot symmetry. Interestingly, the pivot Hamiltonian generating this symmetry is nothing other than the staggered Baxter-Wu three-spin interaction. This work illustrates the importance of U(1)U(1) pivot symmetries and proposes how to generally construct sign-problem-free lattice models of SPT transitions with such anomalous symmetry groups for other lattices and dimensions.

Markovian RNN: An Adaptive Time Series Prediction Network With HMM-Based Switching for Nonstationary Environments.

We investigate nonlinear regression for nonstationary sequential data. In most real-life applications such as business domains including finance, retail, energy, and economy, time series data exhibit nonstationarity due to the temporally varying dynamics of the underlying system. We introduce a novel recurrent neural network (RNN) architecture, which adaptively switches between internal regimes in a Markovian way to model the nonstationary nature of the given data. Our model, Markovian RNN employs a hidden Markov model (HMM) for regime transitions, where each regime controls hidden state transitions of the recurrent cell independently. We jointly optimize the whole network in an end-to-end fashion. We demonstrate the significant performance gains compared to conventional methods such as Markov Switching ARIMA, RNN variants and recent statistical and deep learning-based methods through an extensive set of experiments with synthetic and real-life datasets. We also interpret the inferred parameters and regime belief values to analyze the underlying dynamics of the given sequences.

Non-analyticity in holographic complexity near critical points

The region near a critical point is studied using holographic models of second-order phase transitions. In a previous paper, we argued that the quantum circuit complexity of the vacuum (C 0) is the largest at the critical point. When deforming away from the critical point by a term the complexity has a piece non-analytic in τ, namely . Here, as usual, and ξ is the correlation length and there are possible logarithmic corrections to this expression. That was derived using numerical results for the Bose–Hubbard model and general scaling considerations. In this paper, we show that the same is valid in the case of holographic complexity providing evidence that the results are universal, and at the same time providing evidence for holographic computations of complexity.

Can models of evolutionary transition clarify the debates over the Neolithic Revolution?

The 'Neolithic Revolution,' sometimes referred to as the emergence of agriculture at its earliest in the southern Levant, is the most significant shift in human history, shaping the world we live in today. Yet, after 100 years of study, its major cause, tempo (gradual or revolutionary), and impact of human intentionality remain disputed. Here, we examine the research potential of an evolutionary transition in individuality (ETI) to clarify this dramatic shift. Applying an ETI research perspective reveals how different causes and conditions lead to the same result, enabling a holistic view rather than a reduction of 'Neolithic' to 'agriculture,' or to one major climatic condition, inheritance system or standard evolutionary model, thus allowing us to clarify and bypass some of these heated, unresolved disputes. Additionally, unlike current archaeological emphasis on 'where,' 'when,' 'why' and 'how' questions, the ETI perspective offers a productive path for resolving a fundamental preliminary anomaly: why and how could the Neolithic lifeway evolve at all, given the selfish interest of individuals in a hunter-gatherer group? We do not intend to solve the shift to Neolithic lifeways, only to offer a fresh lens for examining it, emphasizing the relevance of tracking within and between group differences. This article is part of the theme issue 'Human socio-cultural evolution in light of evolutionary transitions'.

Shape-specific characterization of colorectal adenoma growth and transition to cancer with stochastic cell-based models

Colorectal adenoma are precursor lesions on the pathway to cancer. Their removal in screening colonoscopies has markedly reduced rates of cancer incidence and death. Generic models of adenoma growth and transition to cancer can guide the implementation of screening strategies. But adenoma shape has rarely featured as a relevant risk factor. Against this backdrop we aim to demonstrate that shape influences growth dynamics and cancer risk. Stochastic cell-based models are applied to a data set of 197,347 Bavarian outpatients who had colonoscopies from 2006-2009, 50,649 patients were reported with adenoma and 296 patients had cancer. For multi-stage clonal expansion (MSCE) models with up to three initiating stages parameters were estimated by fits to data sets of all shapes combined, and of sessile (70% of all adenoma), peduncular (17%) and flat (13%) adenoma separately for both sexes. Pertinent features of adenoma growth present themselves in contrast to previous assumptions. Stem cells with initial molecular changes residing in early adenoma predominantly multiply within two-dimensional structures such as crypts. For these cells mutation and division rates decrease with age. The absolute number of initiated cells in an adenoma of size 1 cm is small around 103, related to all bulk cells they constitute a share of about 10-5. The notion of very few proliferating stem cells with age-decreasing division rates is supported by cell marker experiments. The probability for adenoma transiting to cancer increases with squared linear size and shows a shape dependence. Compared to peduncular and flat adenoma, it is twice as high for sessile adenoma of the same size. We present a simple mathematical expression for the hazard ratio of interval cancers which provides a mechanistic understanding of this important quality indicator. We conclude that adenoma shape deserves closer consideration in screening strategies and as risk factor for transition to cancer.

Data-driven remanufacturing planning with parameter uncertainty

We consider the problem of remanufacturing planning in the presence of statistical estimation errors. Determining the optimal remanufacturing timing, first and foremost, requires modeling of the state transitions of a system. The estimation of these probabilities, however, often suffers from data inadequacy and is far from accurate, resulting in serious degradation in performance. To mitigate the impacts of the uncertainty in transition probabilities, we develop a novel data-driven modeling framework for remanufacturing planning in which decision makers can remain robust with respect to statistical estimation errors. We model the remanufacturing planning problem as a robust Markov decision process, and construct ambiguity sets that contain the true transition probabilities with high confidence. We further establish structural properties of optimal robust policies and provide insights for remanufacturing planning. A computational study on the NASA turbofan engine shows that our data-driven robust decision framework consistently yields better out-of-sample reward and higher reliability of the performance guarantee, compared to the nominal model that uses the maximum likelihood estimates of the transition probabilities without considering parameter uncertainty.

Modeling of the interband transitions in the optical conductivity of doped two-dimensional materials in the terahertz to the infrared frequency range: the case studies of graphene and phosphorene

We use Kramers-Kronig analysis and ab initio calculations to develop a simple analytical method for including the effects of high-energy interband electron transitions in the density polarization function of doped graphene and doped phosphorene in the optical limit. The resulting formulas are suitable for applications in the terahertz to the mid-infrared range of frequencies, where the interband electron transitions are shown to give rise to static screening with a suitably chosen in-plane polarizability. In the case of phosphorene, each component of its static polarizability tensor can be computed from a sum-rule–like formula using the ab initio data for the real part of the corresponding component of the full optical interband conductivity tensor of that material.

Studying the problems of youth "transitions" in European countries

This article analyzes the research of European youth policy. The subject of the study is the main trends, typology and principles of functioning of youth "transitions" in European countries. The question of the need to study the phenomenon of youth "transitions" is relevant and timely, since today there is no generally accepted view on the ways to study these processes. The methodological basis of the study was analysis and synthesis, institutional, systemic and comparative approaches. Based on the studied material, the authors conclude that when considering strategies for youth "transitions", it is necessary to take into account several institutional areas, such as the type of socially-oriented state and the specifics of the transition from study to work. The interaction of these strategies gives different models of youth transitions. These studies highlight important interethnic differences depending on the modes of distribution of social assistance, types of capitalism, as well as growth strategies.Thus, we have considered various strategies structuring the transition to adulthood: in order to explain the different models of youth "transitions", it is necessary to take into account several institutional areas, such as the type of socially-oriented state and the specifics of the transition from study to work. The interaction of these strategies gives different models of youth transitions. Although many European researchers argue that age policy is important in this regard due to the aging of society and the growth of "gray power", most of the works devoted to this issue actually refute the hypothesis of bias in favor of the elderly: these studies emphasize important interethnic differences depending on the modes of distribution of social assistance, types of capitalism, as well as growth strategies. As a result, we come to the conclusion that young people should be considered as part of society as a whole, and, therefore, in order to understand how they move into adulthood, it is necessary to see the full institutional, political and economic picture.

OPTIMAL TEMPERATURE DISTRIBUTION FOR A NONISOTHERMAL CAHN-HILLIARD SYSTEM IN TWO DIMENSIONS WITH SOURCE TERM AND DOUBLE OBSTACLE POTENTIAL

In this note, we study the optimal control of a nonisothermal phase field system of Cahn-Hilliard type that constitutes an extension of the classical Caginalp model for nonisothermal phase transitions with a conserved order parameter. It couples a Cahn-Hilliard type equation with source term for the order parameter with the universal balance law of internal energy. In place of the standard Fourier form, the con­stitutive law of the heat flux is assumed in the form given by the theory developed by Green and Naghdi, which accounts for a possible thermal memory of the evolution. This has the consequence that the balance law of internal energy becomes a second-order in time equation for the thermal displacement or freezing index, that is, a primitive with respect to time of the temperature. Another particular feature of our system is the presence of the source term in the equation for the order parameter, which entails further mathematical difficulties because the mass conservation of the order parameter is no longer satisfied. In this paper, we study the case that the double-well potential driving the evolution of the phase transition is given by the nondifferentiable dou­ble obstacle potential, thereby complementing recent results obtained for the differentiable cases of regular and logarithmic potentials. Be­sides existence results, we derive first-order necessary optimality condi­tions for the control problem. The analysis is carried out by employing the so-called deep quench approximation in which the nondifferentiable double obstacle potential is approximated by a family of potentials of logarithmic structure for which meaningful first-order necessary opti­mality conditions in terms of suitable adjoint systems and variational inequalities are available. Since the results for the logarithmic poten­tials crucially depend on the validity of the so-called strict separation property which is only available in the spatially two-dimensional situ­ation, our whole analysis is restricted to the two-dimensional case.

On the classical critical behavior of the specific heat capacity of a model of structural phase transitions with a long-range interaction

The critical specific heat capacity c of a d-dimensional model describing structural phase transitions in an anharmonic crystal with a long-range interaction (decreasing at large distances r as r −d−σ , 0 < σ ≤ 2) is studied near the classical critical point Tc . At temperatures T > Tc and for dimensions σ < d < 2σ (σ and 2σ are the lower and the upper critical dimensions, respectively) the critical specific heat capacity is obtained in the form c ≈ 1 − Dεαs , where D > 0 and αs < 0 depend only on the ratio d/σ, and ε = T/Tc −1 is a measure of the deviation from the critical point. For three fixed values of the ratio d/σ the dependence c ≈ c(ε) is graphically presented. It is shown that at all temperatures T ≤ Tc the specific heat capacity retains its maximum value, c max = 1. The critical exponent αs , obtained here, coincides with that of the known mean spherical model, while c max is different for the two models.

Keynote lecture. Constitutive modelling of phase transitions in granular soils

The use of numerical codes for simulating the propagation phase of fast landslides requires the definition of constitutive relationships suitable for the description of the mechanical behaviour of granular soils, under both solid and fluid conditions. In this paper, the authors briefly illustrate a constitutive modelling approach interpreting the material as a bi-phasic continuum, according to which the solid phase may behave like a solid, under quasi-static conditions, and a fluid, under collisional/dynamic conditions. The model presented seems to satisfactorily reproduce a series of results obtained by using a discrete element numerical code on mono and polydisperse granular specimens. The constitutive model has been implemented in a Material Point Method code to solve boundary value problems, in which strain rate large values are expected to influence the material response.

Labor Force Transitions of Older Married Couples in Germany

This study investigates the labor force behavior of older married couples in Germany. Monthly observations from the first eleven waves of the German Socio-Economic Panel (GSOEP) are used to describe and analyze the relationship between the labor force behavior of husbands and wives. The empirical model is a discrete time, competing risks hazard model of transitions among labor force states defined by the employment status of both spouses. The analysis indicates that the probability of one spouse exiting employment is much larger if the other spouse is not employed than if the other spouse is employed. Similarly, one member of a couple is much more likely to enter employment if the spouse is employed than if the spouse is not employed. Observed covariates including wages and retirement benefits help to explain these patterns, but unobserved preferences for shared leisure also appear to play an important role.

From philosophical traditions to scientific developments: reconsidering the response to Brouwer’s intuitionism

Brouwer’s intuitionistic program was an intriguing attempt to reform the foundations of mathematics that eventually did not prevail. The current paper offers a new perspective on the scientific community’s lack of reception to Brouwer’s intuitionism by considering it in light of Michael Friedman’s model of parallel transitions in philosophy and science, specifically focusing on Friedman’s story of Einstein’s theory of relativity. Such a juxtaposition raises onto the surface the differences between Brouwer’s and Einstein’s stories and suggests that contrary to Einstein’s story, the philosophical roots of Brouwer’s intuitionism cannot be traced to any previously established philosophical traditions. The paper concludes by showing how the intuitionistic inclinations of Hermann Weyl and Abraham Fraenkel serve as telling cases of how individuals are involved in setting in motion, adopting, and resisting framework transitions during periods of disagreement within a discipline.

Photovoltaic systems and sustainable communities: New social models for ecological transition. The impact of incentive policies in profitability analyses

The issue of energy independence and sustainability are two major challenges in energy decision-making models. Prosumer development and sustainable community models are identified as drivers to achieve the ecological transition. This work proposes an economic analysis based on Net Present Value (NPV) also supported by the assessment of alternative scenarios (sensitivity, scenario and risk analysis). This study concerns a photovoltaic (PV) plant located in a mature market (Italy) under a collective self-consumption (CSC) scheme.The first aim is to assess the profitability of a PV plant by considering different political (tax deduction, subsidies) and market (purchase price, selling price) contexts. The results show significant economic returns with very modest levels of risk. The NPV varies in the range 2136–8084 €/kW in the baseline policy scenario and 1919–7868 €/kW in the alternative policy scenario, and thus the variations in NPV are more significant in the market scenarios than in the policy scenarios.The second aim seeks to propose how benefits among renewable self-consumers can be divided, and three scenarios are proposed for a CSC scheme: i) revenues split equally; ii) revenues shared entirely according to energy consumption profile and iii) revenues shared according to a partial energy consumption profile. The share of self-consumption plays a key role, but soaring energy costs also push prosumers to make a choice for the future and make their contribution to the development of a sustainable community.

Spectral variability of the uranyl silicates uranophane-α and uranophane-β: polymorphism and luminescence

The luminescence of the uranyl cation UO22+ depends on the local crystalline environment and is sensitive to structural influences. Steady-state photoluminescence emission spectra of the related uranyl silicates uranophane-α, uranophane-β, sklodowskite and haiweeite from various locations are presented and discussed in the light of structure–property relation. The four mineral species were chosen for their close relationships: uranophane-α and uranophane-β are polymorphs and share the underlaying topology with sklodowskite. Haiweeite, with different topology, shares the composing elements Ca, U, Si, O with uranophane, while in sklodowskite Mg replaces Ca. All species show some variability in their spectra, parameterized as a variation of the centroid wavelength. Those variations are linked to defects and structural disorder, relevant in studies of uranyl speciation and migration. We present empiric spectra of the four mineral species with the least influence of structural disorder. As an unexpected feature, a prominent—partly dominating—double peak structure occurs in the case of uranophane-α only, while it is absent in the spectra of the other species. Considering a model of luminescent transitions in the uranyl ion in more detail, this observation is discussed in the light of the polymorphism of uranophane. We show evidence that variable amounts of uranophane-β phase embedded in uranophane-α are possibly at the origin of this spectral signature. Growth of those uranophane-β clusters might be induced by defects in the uranophane-α lattice and further promoted by the polymorphism of uranophane.

From Foragers to Fisher-Farmers: How the Neolithisation Process Affected Coastal Fisheries in Scandinavia

AbstractThe Neolithisation process altered human dependence on wild food sources, and dominant models of the Neolithic transition in Scandinavia still focus on cultural divisions. This study emphasises the evidence of creolization processes, in particular the exploitation of Atlantic Bluefin tuna (Thunnus thynnus) among Neolithic fisher-farmers north and east of the Skagerrak Sea in Scandinavia (4000–2350 cal BCE). The site Jortveit in Southern Norway, where Bluefin tuna was caught with toggling harpoons, is used as a point of departure. In order to understand this phenomenon, the first empirical review of prehistoric toggling harpoons in Central and Eastern Europe is presented. Toggling harpoons first appeared in the late Vinĉa Culture, then in the Gumelniţa, Cucuteni-Trypillia, and Sredny Stog cultural complexes further east, and finally in Central Europe and Scandinavia during the time of the Funnel Beaker Culture. Considering the accumulated evidence of long distance contact from Eastern to Central Europe and Scandinavia in the early fourth millennium BCE, it is argued that toggling harpoon technology was distributed through trade networks. Its appearance around the Skagerrak Sea in the Neolithic reflects fisher-farmers using a creolized fishing technology, inspired by Eneolithic societies.

Glassy correlated state induced by disorder in the frustrated antiferromagnet Tb2Zr2O7

We study the low-temperature thermomagnetic properties of the polycrystalline material Tb2Zr2O7 through ac susceptibility and specific heat measurements. This zirconate displays a defect-fluorite structure in which the magnetic Tb3+ and nonmagnetic Zr4+ cations sit randomly on the same metal sublattice. No long-range magnetic order is found down to 100 mK, although dominant antiferromagnetic interactions are observed and the spins remain dynamic down to the lowest temperatures investigated. We observed a frequency-dependent peak around 2.5 K which is well described by many models of a canonical spin-glass transition. In-field specific heat measurements and the recovered entropy of the system Rln(4) suggest a two doublets ground state separated by 7 K. Comparisons to the pyrochlores Tb2Ti2O7 and Tb2Hf2O7 reinforce the collective spin-glass-type behavior and the opening for discussions of an exotic Coulomb phase in this material.

Coumarin 337 in aqueous solution: interplay between excitation and hydration

Excitation of the C337, highly fluorescent dye in an aqueous solution was studied by the TD-DFT. Through the B3PW91/6-311++G(d, p)/IEFPCM theory level, we obtained the C337 vibronic absorption spectrum which exactly reproduces the experimental maximum. Significant differences are shown between the results of calculating the transition energies using the models of vertical and vibronic transitions. Upon excitation, the main shift of the electron density occurs from C10 to C4 neighboring atom. Thus, large-scale ICT not occur. The effect of excitation on the vibrational spectra of C337 was analyzed. A single C337 molecule and its five different hydration complexes with strongly bound water molecules have been analyzed. Various hydrate complexes of the dye have been studied, and the effect of hydration on its excitation vibrational properties has been elucidated. It was taken into account that a water molecule can attach to the nitrogen atom N1 ("A" type) and the C=O carbonyl ("B" type), and cyano C≡N ("C" type) groups of the dye.

Simplified Model for Forward-Flight Transitions of a Bio-Inspired Unmanned Aerial Vehicle

A new forward-flight model for bird-like ornithopters is presented. The flight dynamics model uses results from potential, unsteady aerodynamics to characterize the forces generated by the flapping wings, including the effects of the dynamic variables on the aerodynamic formulation. Numerical results of the model, which are validated with flapping flight experimental data of an ornithopter prototype, show that state variables such as the pitch angle and the angle of attack oscillate with the flapping frequency, while their mean values converge towards steady-state values. The theoretical analysis of the system shows a clear separation of timescales between flapping oscillations and transient convergence towards the final forward-flight state, which is used to substantially simplify both the interpretation and the solution of the dynamic equations. Particularly, the asymptotic separation into three timescales allows for dividing the problem into a much simpler set of linear equations. The theoretical approximation, which fits the numerical results, provides a direct look into the influence of the design and control parameters using fewer computational resources. Therefore, this model provides a useful tool for the design, navigation and trajectory planning and control of flapping wing UAVs.