Papers by Keyword: Metastable State

Abstract: The work investigates the accuracy of the Kramers approximate formula describing the decay rate of a metastable state. The study was performed by comparing the rate obtained through Kramers formula with the quasistationary rate derived by dynamical modeling that was performed by solving the Langevin equation. We have demonstrated that the non-correlation between Kramers rate and dynamical rate reached 15%, while a better correlation was expected. The study allowed us to generate corrections to Kramers formula by accounting for the higher derivatives of the potential. The rate obtained by the corrected formula exhibits the correlation with the dynamic rate of better than 1%.

Abstract: In the framework of the generalized Kramers theory of physical and chemical kinetics the relation for the decay rate of the metastable state is obtained. The peculiarity of the system is the ratio of the potential barrier height to temperature of the system. This ratio is much less than unity. To study the process we introduce the concept of the effective square of the potential barrier. It is shown that in the limiting case the obtained relation becomes the standard formula (Kramers formula) for the decay rate.

Abstract: By analyzing the condition of safe deceleration, a new CA traffic model emphasizing high safety was simulated. In order to describe the impact of the safety deceleration on the model, using computer to design and implement safety deceleration CA model simulation program. Computer numerical simulations have been carried out. The flow-density diagrams indicate the increase of flow and the stability of the entire system, and show the presence of meta-stable state near the critical density. With the increase of safety deceleration probability, the traffic flow is higher than that with the former model in the situations of both mid density and mid-low density.

Abstract: The SDNS cellular automata (CA) traffic model is chosen as the method to point out the fault in the original model by analyzing the condition of safety deceleration. An improved CA model is proposed in this paper through adjustment of the evolution steps and the redefinition of safe deceleration conditions. Thousands of simulations have been carried out. Comparing with SDNS model and original safety deceleration model with the proposed model in this paper, when emerging congestion, the combined action of urging and safe deceleration enabled system self-adjustment so that efficiently mitigated congestion. This proves that the stop status of the whole traffic flow has been improved, which have been observed in real traffic.

Abstract: Based on the SDNS cellular automata (CA) traffic model, the safe driving CA model has been proposed by considering the condition of having a stationary vehicle ahead. In this paper, this model was improved by analyzing the condition of safe deceleration, and also another single lane traffic CA model emphasizing high safety was proposed. The new safe driving rule was introduced based on the ascertained deceleration and distance ahead. Numerical simulations have been carried out. The results indicate the increase of traffic flow and the stability of the whole system, and also reveal the presence of meta-stable state near the critical density.

Abstract: Based on the SDNS cellular automaton (CA) traffic model, an improved single lane traffic CA model with considering the urged acceleration and safe deceleration was proposed. The model not only simulated the interaction between vehicles, but also reproduced nonlinear phenomena which tallies with real traffic such as the synchronism flow and the metastable state. The time-space diagram of new model shows a gray synchronous band zone rather than that black blocking band zone. The range of synchronization is smaller when p_s is bigger, urging has less function, congestion area is wider. Comparing with SDNS model, with the proposed model in this paper, when emerging congestion, the combined action of urging and safe deceleration enabled system self-adjustment so that efficiently mitigated congestion.

Abstract: The studies of X-ray diffraction, magnetization, magnetocaloric effect, and 57Fe Mössbauer spectra have been performed in a bulk sample of RhFe compound synthesized under high pressure. It have been found that RhFe has fcc-type of crystal structure at room temperature and, shows the first order magnetic transition from the antiferromagnetic-like to ferromagnetic state close to 338 K at 5T magnetic field. This type of behavior has been verified by differential scanning calorimetry, magnetization and Mössbauer techniques. The irreversible transition from antiferromagnetic to stable ferromagnetic state has been observed after heating of sample up to 573K.

Abstract: In the present work, rapidly solidified Al-21Si-0.8Mg-1.5Cu-0.5Mn alloys strips was prepared by melt-spinning method. The microstructures, phase and morphology characteristics of the experimental alloy were characterized by means of scanning electron microscopy, transmission electric microscopy. The results show that the microstructures are changed obviously compared with conventional condition. The nucleation and growth of primary silicon are suppressed and primary silicon can not deposited, meanwhile, α-Al phase is nucleated which prior to eutectic. The microstructures of the rapidly solidified alloys are composed of primary micro-nanostructure α phase and feather-needles-like (α+Si) eutectic which set in the α phase. The mechanism of formation for microstructures of melt-spinning Al-Si alloy have also been discussed.

Abstract: In the present work, rapidly solidified hypereutectic Al-Si-Cu-Mg alloys strips was prepared by single roller melt-spinning method. The microstructures, phase and morphology characteristics of the resultant strips were characterized by means of SEM, TEM and XRD technique. The results show that the grains are refined after rapid solidification processing, and the micro-nanocrystals are formed. Compared with equilibrium solidification, the microstructures are changed obviously. The nucleation and growth of primary silicon are suppressed and primary silicon can not deposited, meanwhile, α-Al phase is nucleated which prior to eutectic. Therefore, the microstructures become into the metastable state. The microstructures of the strips are composed of primary micro-nanostructure α phase and feather-needles-like (α+Si) eutectic which set in the α phase. The mechanism of the formation for microstructures of melt-spinning Al–Si alloy have also been discussed.