Heating time

For constant energy simulations without temperature regulation, use heating steps of about 0.5 ps and a healing time of 20-30 ps. In gen eral, short h eating tim es and large temperature steps perturb th e initial system m ore than Ion gcr heating times and small tern -perature steps. 

The choice of heating time depends on the purpose of the molecular dynamics simulation. If the simulation is for conformational searches, the heating step is not critical for a successful calculation. The heating step may be rapid to induce large structural changes that provide access to more of the conformational space. 

If the heating time t or cooling time t are non-zero, or if the run time tj. is non-zero and constant temperature is selected, velocities are adjusted (rescaled) during the molecular dynamics run to change the temperature of the system. 

Conversion at Equilibrium. The maximum urea conversion at equilibrium attainable at 185°C is ca 53% at infinite heating time. The conversion at equiUbtium can be increased either by raising the reactor temperature or by dehydrating ammonium carbamate in the presence of excess ammonia. Excess ammonia shifts the reaction to the right side of the overall equation ... 

After the allotted pressing/heating time, the pressure is released and the press moves to the open position. By this time, the loader is again ready and as each veneer assembly is moved into its respective opening, the pressed panels are pushed out into the unloader on the opposite side of the press. As the press begins the next cycle, the unloader moves to deposit the pressload of panels into a stack. 

Dye sublimation requires more heat dissipation and a longer (>10 ms) heating period to make a dark mark than does thermal transfer. Carehil manipulation of heating time and temperature can proportion mark size and dye content to cover a wide density range (0 to ca 2 optical density). 

Fig. 11. Logarithm of heating time compared with temperature to attain various degrees of degradation of wood (35). No parentheses indicates weight loss on oven heating a single parenthesis indicates modulus of mpture on oven heating and double parentheses indicates weight loss on heating beneath...

Seam correlations, measurements of rank and geologic history, interpretation of petroleum (qv) formation with coal deposits, prediction of coke properties, and detection of coal oxidation can be deterrnined from petrographic analysis. Constituents of seams can be observed over considerable distances, permitting the correlation of seam profiles in coal basins. Measurements of vitrinite reflectance within a seam permit mapping of variations in thermal and tectonic histories. Figure 2 indicates the relationship of vitrinite reflectance to maximum temperatures and effective heating time in the seam (11,15). 

Fig. 2. Relation of vittinite reflectance (R in percent to maximum temperature and effective heating time (/ ) where = activation energy in kj...

A measure of the heat resistance can be obtained by the weight loss at various temperatures. Table 18.12 gives details of the weight loss of three poly-pyromellitimides after various heating times at 325°C. 

The heating time is kept to a minimum in order to reduce the darkening of the solution, which increases as the heating time is extended. 

Alternatively, for a heating eondition, the heating time required for seale-up is ... 

T-Jumps can also be produced by microwave heating and by laser pulse absorption. These methods remove the restriction to low-resistance solvents any solvent capable of absorbing energy of the applied frequency may be used. The heating time can be extremely short with laser heating. ... 

It was found that when the heating time was reduced to three hours and a reaction temperature of 190°C to 200"t was maintained, equivalent yields (40 to 50%) were obtained, but that the yields were appreciably lowered when the heating time was further reduced to two hours. It was also found that when the temperature was lowered to the range of 1 70t to lOO t the yield was significantly lowered. 

Polymerization conditions Heating time to the polymerization temperature (min) ... 

Example of a Thermoplastic Processing Heat-Time Profile Cycle... 

Fig. 6-3 Melting characteristics of TPs and TSs based on their heat-time processing profiles.

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