Transient process, definition

Process Systems. Because of the large number of variables required to characterize the state, a process is often conceptually broken down into a number of subsystems which may or may not be based on the physical boundaries of equipment. Generally, the definition of a system requires both definition of the system s boundaries, ie, what is part of the system and what is part of the system s surroundings and knowledge of the interactions between the system and its environment, including other systems and subsystems. The system s state is governed by a set of appHcable laws supplemented by empirical relationships. These laws and relationships characterize how the system s state is affected by external and internal conditions. Because conditions vary with time, the control of a process system involves the consideration of the system s transient behavior. 

Time-Dependent Cascade Behavior. The period of time during which a cascade must be operated from start-up until the desired product material can be withdrawn is called the equiUbrium time of the cascade. The equiUbrium time of cascades utilizing processes having small values of a — 1 is a very important quantity. Often a cascade may prove to be quite impractical because of an excessively long equiUbrium time. An estimate of the equihbrium time of a cascade can be obtained from the ratio of the enriched inventory of desired component at steady state, JT, to the average net upward transport of desired component over the entire transient period from start-up to steady state, T . In equation form this definition can be written as... 

One temporal concept to be borne in mind in this context is whether the (bio)chemical reactions and mass transfer separations taking place at the active microzone (one or both of which, by definition, take place simultaneously with detection) are simultaneous or sequential relative to each other. Whether such processes take place at the same or a different time has a marked effect on the sensor performance and type of transient signal obtained. 

Chronopotentiometry, galvanostatic transients, 1411 as analytical technique, 1411 activation overpotential, 1411 Clavilier, and single crystals, 1095 Cluster formation energy of, 1304 and Frumkin isotherm, 1197 Cobalt-nickel plating, 1375 Cold combustion, definition, 1041 Cole-Cole plot, impedance, 1129, 1135 Colloidal particles, 880, 882 and differential capacity, 880 Complex impedance, 1135 Computer simulation, 1160 of adsorption processes, 965 and overall reaction, 1259 and rate determining step, 1260... 

Indeed, the laser oscillation itself frequently is a transient emission that falls into the broad definition of fluorescent lifetimes. In particular, spiking phenomena (5) and Q Switching (4) clearly bear a close relationship to relaxation times and processes. One could say that laser phenomena are associated with the study of fluorescent decays of inverted populations. 

One of the major obstacles to definitively examining the role of formulation components on enterocyte-based processes is the possible effect of excipient inclusion on other complicating factors. For example, the inclusion of lipids or surfactants in in vitro metabolic or transport screens runs the risk of affecting the thermodynamic activity of the drug in solution, thereby obscuring the role of metabolic and transport processes. Similarly, some surfactants and lipid-surfactant conjugates may cause transient increases in intestinal permeability as... 

Many controlled release devices are not membranes by the conventional definition, since only transient release of an active agent, without permeation occurring between an upstream and a downstream, is typical. Nevertheless, some controlled release units do operate with a concentration driving force to achieve effectively steady state release from the internal reservoir of the device to the external surrounding. Such processes are included here for completeness. 

Reversibility begets reusability. The transient nature of complexes is an absolute requirement for all molecules that function as reusable machines. Enzymes are molecule-sized lathes that bind to their substrates, catalyze a reaction, and release the product when done, the enzyme is ready for reuse. Indeed, any chemical catalyst must meet this criterion based on the very definition of a catalyst a species that enhances the rate of a chemical process without itself being changed. Enzymatic... 

It is important to appreciate that some data may be transient and will never be stored to durable media while other transient data may be processed to derive data before being stored. Systems that only handle transient data are excluded from 21 CFR Part 11. These are systems that acquire and temporarily store data in files that have no user access but, as part of normal workflow, pass that data on to a printer or another system before the process task is complete and the data are purged. Electronic buffers (including temporary files) cannot be considered transient data if user modifications to committed data are permitted. Battery backups for retention of temporary storage invalidates the definition of transient data as do situations where multiple cycles of so-called transient data are stored before being purged. 

Relaxation behavior is deduced from measurements of various transient phenomena. Current interpretations of these phenomena dictate the definition of two processes by which the orientations of the nuclear magnetic moments reach the equilibrium distribution. These processes are described by characteristic times, designated Ti and T2. The first, Ti, is called the thermal or longitudinal relaxation time. 

Griller, D. Ingold, K. U. Acc. Chem. Res. 1976, 9, 13. In the context of this review, radicals are called persistent if their lifetimes in liquid solution exceed those of reactive radical species by many orders of magnitude. They may self-terminate slowly or disappear by other reactions, but these processes do not compete with the cross coupling with usual transient radicals. Stable radicals can be isolated in pure form. They are included in our definition of persistence. 

A recently developed modification of the pendent drop method gives definite area changes of the drop surface, which can be used to initiate transient relaxation processes (Miller et al. 1993a, b). A metering system consisting of two syringes (cf Fig. 6.7) is used to form a drop... 

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