Simulation elevated temperatures

Reduce stress on molecules caused by a simulation at elevated temperatures. The cooling process, called simulated annealing, takes new, high energy conformational states toward stable conform ations. 

For a conformation in a relatively deep local minimum, a room temperature molecular dynamics simulation may not overcome the barrier and search other regions of conformational space in reasonable computing time. To overcome barriers, many conformational searches use elevated temperatures (600-1200 K) at constant energy. To search conformational space adequately, run simulations of 0.5-1.0 ps each at high temperature and save the molecular structures after each simulation. Alternatively, take a snapshot of a simulation at about one picosecond intervals to store the structure. Run a geometry optimization on each structure and compare structures to determine unique low-energy conformations. 

The procedures used for estimating the service life of solid rocket and gun propulsion systems include physical and chemical tests after storage at elevated temperatures under simulated field conditions, modeling and simulation of propellant strains and bond tine characteristics, measurements of stabilizer content, periodic surveillance tests of systems received after storage in the field, and extrapolation of the service life from the detailed data obtained (21—33). 

The kinetic parameters associated with the synthesis of norbomene are determined by using the experimental data obtained at elevated temperatures and pressures. The reaction orders with respect to cyclopentadiene and ethylene are estimated to be 0.96 and 0.94, respectively. According to the simulation results, the conversion increases with both temperature and pressure but the selectivity to norbomene decreases due to the formation of DMON. Therefore, the optimal reaction conditions must be selected by considering these features. When a CSTR is used, the appropriate reaction conditions are found to be around 320°C and 1200 psig with 4 1 mole ratio of ethylene to DCPD in the feed stream. Also, it is desirable to have a Pe larger than 50 for a dispersed PFR and keep the residence time low for a PFR with recycle stream. 

In the case of reservoir systems that rely on the cohesivity of the blend due to interparticle interactions, studies are required on vibrational stability in simulated storage, transport, and use tests, including determination of the effects of elevated temperature and humidity. 

The conditions under which the material is tested are crucial. The top of the exposure chamber must be sealed and the tank should contain no free air space. A stirring mechanism in the tank keeps the leachate mixture homogeneous and a heater block keeps it at an elevated temperature as required for the test. Stress conditions of the material in the field should also be simulated as closely as possible. The original U.S. EPA Method 9090 test included a rack to hold specimens under stress conditions but was revised when some materials shrank in the leachate. Due to the hazardous nature of the material, testing should be performed in a contained environment and safety procedures should be rigorously followed. 

Kumar, S. K. Szleifer, I. Panagiotopoulos, A. Z., Molecular simulation of the pure n-hexadecane vapor-liquid equilibria at elevated temperature, Phys. Rev. Lett. 1991, 66, 2935... 

Several conditions must be met for successful ETEM investigations. Thin, electron-transparent samples are necessary—this requirement can usually be met with most catalyst powders. Ultrahigh-purity heater materials and sample grids capable of withstanding elevated temperature and gases are required (such as those made of stainless steel or molybdenum). The complex nature of catalysis with gas environments and elevated temperatures requires a stable design of the ETEM instrument to simulate realistic conditions at atomic resolution. 

In some situations we have performed finite temperature molecular dynamics simulations [50, 51] using the aforementioned model systems. On a simplistic level, molecular dynamics can be viewed as the simulation of the finite temperature motion of a system at the atomic level. This contrasts with the conventional static quantum mechanical simulations which map out the potential energy surface at the zero temperature limit. Although static calculations are extremely important in quantifying the potential energy surface of a reaction, its application can be tedious. We have used ah initio molecular dynamics simulations at elevated temperatures (between 300 K and 800 K) to more efficiently explore the potential energy surface. 

Visual detection of surface layers on cathodes using microscopy techniques such as SFM seems to be supportive of the existence of LiF as a particulate-type deposition.The current sensing atomic force microscope (CSAFM) technique was used by McLarnon and co-workers to observe the thin-film spinel cathode surface, and a thin, electronically insulating surface layer was detected when the electrode was exposed to either DMC or the mixture FC/DMC. The experiments were carried out at an elevated temperature (70 °C) to simulate the poor storage performance of manganese spinel-based cathodes, and degradation of the cathode in the form of disproportionation and Mn + dissolution was ob-served. °° This confirms the previous report by Taras-con and co-workers that the Mn + dissolution is acid-induced and the electrolyte solute (LiPFe) is mainly responsible. 

Generally, one would expect that the most volatile component would evaporate first, and this would probably be the diluent. In several cases of operating simulated solvent extraction processes at temperatures up to 70°C, it has been noted that the diluent is rapidly volatilized [G. M. Ritcey and B. H. Lucas, unpublished data]. Problems of volatilization appear not to have occurred to any great extent in the past (perhaps the losses were not measured), but any trend to the use of elevated temperatures would require that this form of solvent loss be thoroughly investigated. 

Sunaryo GR, Katsumura Y, Ishigure K (1995) Radiolysis of water at elevated temperatures-III. Simulation of radiolytic products at 25 and 250°C under the irradiation with y rays and fast neutrons. Rad Phys Chem 45 703-714... 

T o grasp the chemical condition of water in the pressure vessel, direct measurement is practically impossible because of high pressure, high temperature, and intense radiation. In order to predict the concentrations of water decomposition products, a computer simulation should be applied. This idea was found in 1960s [1-3]. To perform the simulation, both a set of G-values for water decomposition products and a set of reactions for transient species are necessary. For these two decades, much effort has been made in Sweden, Denmark, United Kingdom, Canada, and Japan to evaluate the G-values and rate constants of the reactions at elevated temperatures up to 300 °C, and now there are practically enough accumulated data. There are several reviews of water radiolysis at elevated temperatures [4-7] and examples of practical application of the radiolysis in reactors [8,9]. 

Consider a fluidized bed operated at an elevated temperature, e.g. 800°C, and under atmospheric pressure with ah. The scale model is to be operated with air at ambient temperature and pressure. The fluid density and viscosity will be significantly different for these two conditions, e.g. the gas density of the cold bed is 3.5 times the density of the hot bed. In order to maintain a constant ratio of particle-to-fluid density, the density of the solid particles in the cold bed must be 3.5 times that in the hot bed. As long as the solid density is set, the Archimedes number and the Froude number are used to determine the particle diameter and the superficial velocity of the model, respectively. It is important to note at this point that the rale of similarity requires the two beds to be geometrically similar in construction with identical normalized size distributions and sphericity. It is easy to prove that the length scales (Z, D) of the ambient temperature model are much lower than those in the hot bed. Thus, an ambient bed of modest size can simulate a rather large hot bed under atmospheric pressure. 

Using a realistic model for PE, the molecular dynamics technique is used to simulate atomic motion in a crystal. The calculations reveal conformational disorder above a critical temperature. The customarily assumed RIS model is found to be a poor description of the crystal at elevated temperature. 

Menichelli, Effects of Nuclear Radiation and Elevated Temperature Storage on Electroexplosive Devices , JSpacecraft Rockets 13,15 (1976) 250) R.A. Benham, Simulation of... 

As shown in Fig. 18, the simulation conductivity data were generally consistent with the experimental results. However, there are appreciable differences between the simulation and experimental results. At some points, the differences can be 100%. The other observation is that the simulation must underestimate the activation energies of the conduction. The primary reason for this discrepancy is that these simulation models do not take into account interaction between the membrane itself and its environment. In reality, the water uptake at elevated temperatures may be greater than that at room temperature. In the simulations, it was assumed that both... 

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