Millisecond time interval

DESI Probing reactions occurring in millisecond time intervals Perry et al. [109]... 

The cause of this difficulty therefore resides within the counter itself. The difficulty is described by saying that the Geiger counter has a dead time, by which is meant the time interval after a pulse during which the counter cannot respond to a later pulse. This interval, which is usually well below 0.5 millisecond, limits the useful maximum counting rate of the detector. The cause of the dead time is the slowness with which the positive-ion space charge (2.5) leaves the central wire under the influence of the electric field. This reduction in observed counting rate is known as the coincidence loss. 

The maximum time step depends on the highest frequencies (usually R-H bonds). The main problem in dynamics calculations is that the movements leading to appreciable conformational changes usually have lower frequencies (milliseconds e.g., torsions). The computation of such long time intervals is usually prohibitive due to the CPU time involved. 

The de-excitation of the excited primary products may produce secondary excited products. The latter, in turn, may undergo deexcitation or dissociation within < 10-1° sec. The species that survive this time interval may still be highly reactive intermediates that react with each other, with the solvent or with other solutes. These intermediates seldom survive longer than milliseconds thereafter they form the secondary or tertiary more stable products. 

The explosive charges are successively initiated at time intervals as short as 20-100 milliseconds with the aid of millisecond detonators... 

This phenomenon has recently been analyzed by studying the oxidation of ethanol at ZnS-particles [187, 189]. As already discussed above (Sect. 5.2.), the oxidation of ethanol occurs in two steps, i.e. in the first step, a radical is formed by hole transfer at the surface of an individual particle. Since it takes in the average several milliseconds before another hole is generated by photon absorption in the same individual 3 nm-particle, the radical can diffuse into the solution. There, the radicals can disproportionate and dimerize according to Eqs. (90a) and (90b) leading to the formation of acetoaldehyde and butanediol, respectively, as proved with 3 nm ZnS-particles. Performing the same experiment with much larger particles (4/im), no butanediol was found [187, 189]. Since the time interval between the absorption of two photons in one particle is... 

When adsorption from solution Is monitored by the depletion method. It Is very difficult to measure changes in bulk concentration over time Intervals down to milliseconds. Perhaps this Is the reason that such systematic studies are not abundant in the literature. Fast measurements require stopped-flow, pressure-jump or temperature-jump techniques. The method used to determine concentrations must also be fast suitable methods include certain spectroscopies and, for charged substances, conductivity. When adsorption on Fresnel surfaces Is studied, say by reflectometry, concentration measurements in the solution are not needed. 

The catalysts used in Fluid Catalytic Cracking (FCC) are reversibly deactivated by the deposition of coke. Results obtained in a laboratory scale entrained flow reactor with a hydrowax feedstock show that coke formation mainly takes place within a time frame of milliseconds. In the same time interval conversions of 30-50% are found. After this initial coke formation, only at higher catalyst-to-oil ratios some additional coke formation was observed. In order to model the whole process properly, the coke deposition and catalyst deactivation have to be divided in an initial process (typically within 0.15 s) and a process at a larger time scale. When the initial effects were excluded from the modeling, the measured data could be described satisfactory with a constant catalytic activity. 

We tend to think that what we usually do is appropriate. This is often true in our daily life. However, it is not necessarily true in the field of science. For example, we usually run reactions in a centimeter size flask in an organic chemistry laboratory. Why The reason is probably, that the sizes of the flasks are similar to the size of our hands. However, the sizes of the flasks are not necessarily appropriate from a molecular-level viewpoint. Flasks are often too big for the control of molecular reactions. Scientifically, smaller reactors such as microreactors provide a much better molecular environment for reactions. What about reaction times Reactions in laboratory synthesis usually take minutes to hours to obtain a product in a sufficient amount. Why It is probably because a time interval of minutes to hours is acceptable and convenient for human beings. In such a range of time, we can recognize how the reaction proceeds. We start a reaction, wait for a while, and stop it in this range of time. If reactions are too fast, it is difficult to determine how the reaction proceeds, because the reaction is complete too soon after it is started. Therefore, we have chosen reactions that complete in a range of minutes to hours. Another reason is that we are able to conduct only such reactions that require minutes to hours for completion in a controlled way. In other words, in laboratory synthesis, we cannot conduct faster reactions that complete within milliseconds to seconds, because they are too fast to control. In such cases, significant amounts of unexpected compounds are obtained as byproducts. In addition, extremely fast reactions sometimes lead to explosions. However, we should keep in mind that such limitations of reaction... 

Considering the sequences of physical and chemical events, at the beginning an extremely rapid energy deposition occurs in the first 10 x e"18 to 10 x e 12 s time interval. The chemical processes follow in the next milliseconds (10 x e 3 to 1 s). Some transitional degradation products however are much more stable in polymers. The frozen-in free radicals are long living enough (10 x e3 to 10 x e9 s, or more up to years ) to use them for later practical applications [5, 6],... 

The time between neutron generations is the time between a neutron being produced and the time it is absorbed, into either a fissile or non-fissile nucleus. In reality this time interval will vary between individual neutrons, but we will make the simplifying assumption that the lifetime of all neutrons may be characterized by the average neutron lifetime, /, which is typically 1 millisecond in a commercial thermal reactor. Neutrons are being bom continuously in a reactor, and we may assume that at any instant of time the neutrons have a uniform spread of all ages between 0 and I seconds. Let us divide the neutron lifetime. /, into a large number, M, of time intervals. Si, where... 

The accuracy of all methods, over time intervals from several seconds to hours, is usually 0.1 mN/m. Special instruments enable measurements in the millisecond time scale. Such studies are performed with less accuracy, sometimes of the order of 1.0 mN/m. 

The maximum bubble pressure method, realised as the set-up discussed above, allows measurements in a time interval from 1 ms up to several seconds and longer. At present, it is the only commercial apparatus which produces adsorption data in the millisecond and even sub-millisecond range (Fainerman Miller 1994b, cf. Appendix G). Otherwise data in this time interval can be obtained only from laboratory set-ups of the oscillating jet, inclined plate or other, even more sophisticated, methods. The accuracy of surface tension measurements in... 

A comparison of the bubble pressure method with the oscillating jet method was also performed with aqueous Triton X-100 solutions. Some results are given in Fig. 5.29 as a y/log X3 - plot. In contrast to the inclined plate, the oscillating jet only yields data in the time interval of few milliseconds. Also in this time interval the agreement with the maximiun bubble pressure method is excellent and shows deviations only within the limits of the accuracy of the two methods. 

---