Model Of First-order Transition Research Articles

Accounting for informative observation process in transition models of binary longitudinal outcome: Application to medical record data.

When extracting medical record data to form a retrospective cohort, investigators typically focus on a pre-specified study window, and select subjects who had hospital visits during that study window. However, such data extraction may suffer from an informative observation process, since sicker patients may have hospital visits more frequently. For example, Consecutive Pregnancy Study is a retrospective cohort study of women with multiple pregnancies in 23 Utah hospitals from 2003 to 2010, where the interest is to understand the risk factors of recurrent pregnancy outcomes, such as preterm birth. The observation process is informative in the sense that, women with adverse pregnancy outcomes may be less likely/willing/able to endure subsequent pregnancies. We proposed a three-part joint model with shared random effects structure to address this analytic complication. Particularly, a first-order transition model is used to model the longitudinal binary outcome; a gamma regression model is assumed for the inter-pregnancy intervals; a continuation ratio model specifies the probability of continuing with more births in the future. We note that the latter two parts give rise to a parametric cure-rate survival model. The performance of the proposed method was examined in extensive simulation studies, with both correctly and mis-specified models. The analyses of Consecutive Pregnancy Study data further demonstrate the inadequacies of fitting the transition model alone ignoring the informative observation process.

Interfacial mobility scale determines the scale of collective motion and relaxation rate in polymer films.

Thin polymer films are ubiquitous in manufacturing and medical applications, and there has been intense interest in how film thickness and substrate interactions influence film dynamics. It is appreciated that a polymer-air interfacial layer with enhanced mobility plays an important role in the observed changes and recent studies suggest that the length scale ξ of this interfacial layer is related to film relaxation. In the context of the Adam-Gibbs and random first-order transition models of glass formation, these results provide indirect evidence for a relation between ξ and the scale of collective molecular motion. Here we report direct evidence for a proportionality between ξ and the average length L of string-like particle displacements in simulations of polymer films supported on substrates with variable interaction strength and rigidity. This relation explicitly links ξ to the theoretical scale of cooperatively rearranging regions, offering a promising route to experimentally determine this scale of cooperative motion.

Magnetocaloric materials: The search for new systems

The prospect of efficient solid-state refrigeration at room temperature is driving research into magnetic cooling engine design and magnetic phase transition-based refrigerants. I construct what I believe is the first Ashby-style map of magnetic refrigerant properties, comparing popular materials with limits derived from an idealized first-order transition model. This comparison demonstrates the potential for new magnetocaloric material systems to be established through structural control and optimization at the atomic-, nano- and microscales.

On a doubly nonlinear phase-field model for first-order transitions with memory

Solid-liquid transitions in thermal insulators and weakly conducting media are modeled through a phase-field system with memory. The evolution of the phase variable ${\varphi}$ is ruled by a balance law which takes the form of a Ginzburg-Landau equation. A thermodynamic approach is developed starting from a special form of the internal energy and a nonlinear hereditary heat conduction flow of Coleman-Gurtin type. After some approximation of the energy balance, the absolute temperature ${\theta}$ obeys a doubly nonlinear ``heat equation" where a third-order nonlinearity in ${\varphi}$ appears in place of the (customarily constant) latent-heat. The related initial and boundary value problem is then formulated in a suitable setting and its well--posedness and stability is proved.

A phase-field approach to non-isothermal transitions

The purpose of the paper is to set up a phase-field model for first-order transitions. The phase field is identified with the concentration of a phase and hence is subject to the continuity equation with a mass growth due to the progression of the transition. The continuity equation is viewed as a differential constraint. The body, in the transition layer, is regarded as a viscous material with time- and space-dependent fields for the mass density, the (absolute) temperature, and the phase-field. Consistency of the model suggests that gradients up to third order are considered. The thermodynamic restrictions are derived by letting the second law be expressed by the Clausius–Duhem inequality and allowing for an extra-entropy flux which, eventually, proves essential to the whole thermodynamic scheme. Results are obtained by using the Helmholtz and Gibbs free energies. As a check of the model, Clapeyron’s equation is derived by means of the Gibbs free energy. A maximum theorem is proved which shows that the phase field takes values between 0 and 1 if it so does at an initial time.

A Transition Model for Analysis of Repeated Measure Ordinal Response Data to Identify the Effects of Different Treatments

A first-order transition model is used to analyze repeated measurement or longitudinal ordinal response data to compare several treatments for which measurements for each subject occur both at baseline and at follow-up. The likelihood function is partitioned to make possible the use of existing software for estimating model parameters. Data from a clinical trial illustrate the application of the transition model. Nagelkerke’s pseudo-R2 is used for the goodness of fit of the model.

Thermodynamics of a first-order phase transition smeared by frozen disorder

The simplified model of first-order transition in a media with frozen long-range transition-temperature disorder is considered. It exhibits the smearing of the transition due to appearance of the intermediate inhomogeneous phase with thermodynamics described by the ground state of the short-range random-field Ising model. Thus the model correctly reproduce the persistence of first-order transition only in dimensions d > 2, which is found in more realistic models. It also allows to estimate the behavior of thermodynamic parameters near the boundaries of the inhomogeneous phase.

Two Species/Nonideal Solution Model for Amorphous/Amorphous Phase Transitions

ABSTRACTA simple macroscopic thermodynamic model for first order transitions between two amorphous phases in a one component liquid is reviewed, augmented and evaluated. The model presumes the existence in the liquid of two species, whose concentrations are temperature and pressure dependent and which form a solution with large, positive deviations from ideality. Application of the model to recent data indicates that water can undergo an amorphous/amorphous phase transition below a critical temperature Tc of 217K and above a critical pressure Pc of 380 atm.

Multiple actions of pinacidil on adenosine triphosphate‐sensitive potassium channels in guinea‐pig ventricular myocytes.

1. The patch-clamp method was used to study the effects of pinacidil on the adenosine 5'-triphosphate (ATP)-sensitive K+ channel current in guinea-pig ventricular myocytes. 2. In the inside-out configuration of the patch membranes, the channel activity revealed a nearly fully open state in the absence of ATP, whereas application of ATP (0.1-5 mM) markedly suppressed the channel opening. Addition of pinacidil (0.02-1.0 mM) antagonized the inhibitory action of ATP and induced channel opening without marked change in conductance. An increase in ATP concentration depressed the maximal effect of pinacidil. Consequently, the dose-response relationship of ATP inhibition was shifted to the right, but the shift approached a limiting value as pinacidil concentration was increased. The results indicate that the antagonism between pinacidil and ATP is not competitive. 3. The dose-response curve for activation of the channel by pinacidil examined at -50 mV showed a sigmoidal shape but at +50 mV it had a convex shape, revealing asymmetry in the activating effects of pinacidil at these two voltages. 4. In the absence of ATP, pinacidil produced a voltage-dependent block at positive voltages by decreasing the mean open time and increasing the mean closed time, whereas no such effects were observed at negative voltages. The concentration-block relation at a given voltage was fitted to a first-order Hill saturation function. The Kd (dissociation constant) decreased with depolarization from 2.2 mM at +20 mV to 0.15 mM at + 80 mV. 5. The kinetics of block and unblock by pinacidil were shown to be slow, and were expressed by a first-order transition model. The blocking and unblocking rate constants were voltage dependent. 6. The slow block of single-channel current showed an exponential decay in the ensemble current. The time constant of the decay was voltage dependent, reaching a maximal value at around +50 mV. 7. In the absence of ATP, the channel activity gradually decreased and eventually stopped within 12-20 min, a process known as run-down of channel activity. Calcium accelerated this run-down process. Application of pinacidil partially reactivated the channel. Such channel reactivation by pinacidil during the course of run-down depended upon the conditions of the patch and the time course of the run-down. Pretreatment of the channel with ATP markedly strengthened the reactivation effect of pinacidil. 8. These results indicate that there are multiple sites or processes for interaction of pinacidil with the ATP-sensitive K+ channel.