Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Times, implied operation

Since div ( ) mid div 3 (x) commute with 8(x ) and 3 t (x ) for x0 —x, they have vanishing commutators with the hamiltonian and hence, they are time-independent operators. In fact, their constancy in tame implies that they commute with 3 (x) and S(x) at all times and hence they must be c-number multiples of the unit operator. If these c-numbers are set equal to zero initially, they will remain zero for all times. With this initial choice for div 8(x) and div 3tf(x), the operators S and satisfy all of the Maxwell equations (these now are operator equations ) ... [Pg.563]

Double-resonance spectroscopy involves the use of two different sources of radiation. In the context of EPR, these usually are a microwave and a radiowave or (less common) a microwave and another microwave. The two combinations were originally called ENDOR (electron nuclear double resonance) and ELDOR (electron electron double resonance), but the development of many variations on this theme has led to a wide spectrum of derived techniques and associated acronyms, such as ESEEM (electron spin echo envelope modulation), which is a pulsed variant of ENDOR, or DEER (double electron electron spin resonance), which is a pulsed variant of ELDOR. The basic principle involves the saturation (partially or wholly) of an EPR absorption and the subsequent transfer of spin energy to a different absorption by means of the second radiation, leading to the detection of the difference signal. The requirement of saturability implies operation at close to liquid helium, or even lower, temperatures, which, combined with long experimentation times, produces a... [Pg.226]

It is important to point out that the quality of analytical results is not immediate it can only be achieved if an extensive set of measures are adopted and complied with. Therefore, in parallel to the development of the QA concept, QC systems were introduced as an important tool supporting the QA of chemical measurements. The QC process of examination of laboratory performance in time should always follow QA. QC thus comprises a set of operational techniques and activities used to check whether the requirements for quality are fulfilled. In practice, QC in an analytical chemistry laboratory implies operations carried out daily during the collection, preparation, and analysis of samples, which are designed to ensure that the laboratory can provide accurate and precise results. QC procedures are intended to ensure the quality of results for specific samples or batches of samples and include the analysis of reference materials (RMs), blind samples, blanks, spiked samples, duplicate, and other control samples.2... [Pg.390]

Whatever representation is used, the reduced density operator d should satisfy some basic requirements that can provide important consistency checks. The fact that Tr/5(/ j = 1 at all time implies that we should have Trsd (/) = 1, as was indeed verified in Section 10.4.7. In addition, the reduced density operator ct should satisfy some other basic requirements ... [Pg.389]

We can now use our projection technique to recover averaged time evolution operators in which some of the system coordinates are considered as fast. An interesting case is given by the model in which the solvent polarization relaxes faster than the reorientational molecular modes, that is, the equivalent of equation (1.16). Note that now the matrices Uj 2 (where the subscripts 1, 2 imply we are referring to both U, and U2), are simply given by (-sin (, 2, cos <, 2)" and the resulting diagonal elements of the final friction matrix are constant, so... [Pg.106]

Related to the question of how to define the rate of chemical reaction is the use of the time derivative, dMi/dt or dNi/dt. This implies that things are changing with time and may tempt one to associate the appearance of reaction rate terms in mass conservation equations with unsteady-state processes. This is not necessarily true in general, one must make a distinction between the ongoing time of operation of some process (i.e., that measured by an observer) and individual phenomena such as chemical reactions that occur at a steady rate in an operation that does not vary with time (steady-state). Later we will encounter both steady- and unsteady-state types of processes involving chemical reaction, to be sure, but this depends on the process itself the reaction rate definition has been made without regard to a particular process. [Pg.4]

This form of Onsager s reciprocity implies that the time shift operator, exp(kt), which generates reciprocal relations between kinetic curves, is also symmetric. Obviously, the next step is to address the following questions (Constales et al., 2015) ... [Pg.194]

As the name implies the company basically rents the rig and crew on a per day basis. Usually the oil company also manages the drilling operation and has full control over the drilling process. This type of contract actually encourages the contractor to spend as much time as acceptable on location . With increased cost consciousness, day rate contracts have become less favoured by most oil companies. [Pg.62]

Where Ui denotes input number i and there is an implied summation over all the inputs in the expression above A, Bj, C, D, and F are polynomials in the shift operator (z or q). The general structure is defined by giving the time delays nk and the orders of the polynomials (i.e., the number of poles and zeros of the dynamic models trom u to y, as well as of the noise model from e to y). Note that A(q) corresponds to poles that are common between the dynamic model and the noise model (useful if noise enters system close to the input). Likewise Fj(q) determines the poles that are unique for the dynamics from input number i and D(q) the poles that are unique for the noise N(t). [Pg.189]

Close inspection of equation (A 1.1.45) reveals that, under very special circumstances, the expectation value does not change with time for any system properties that correspond to fixed (static) operator representations. Specifically, if tlie spatial part of the time-dependent wavefiinction is the exact eigenfiinction ). of the Hamiltonian, then Cj(0) = 1 (the zero of time can be chosen arbitrarily) and all other (O) = 0. The second tenn clearly vanishes in these cases, which are known as stationary states. As the name implies, all observable properties of these states do not vary with time. In a stationary state, the energy of the system has a precise value (the corresponding eigenvalue of //) as do observables that are associated with operators that connmite with ft. For all other properties (such as the position and momentum). [Pg.14]

It is stated in the standard that the standard can also be applied throughout the automotive supply chain. This implies that vehicle manufacturers should apply the requirements to their own operations, but obviously such application is voluntary. In due course, ISO/TS 16949 will become a condition of any contract to supply products and services to the vehicle manufacturers. The supply chain includes vehicle distribution and dealers. However, it is not intended that ISO/TS 16949 be applied beyond the vehicle manufacturers at this time. [Pg.46]

The complexity and reduced time constants of modern processes imply the adoption of high performance programmable controllers. This requires not only higher processing speed but also more advanced control algorithms that can optimize the process operation in real time. [Pg.296]


See other pages where Times, implied operation is mentioned: [Pg.177]    [Pg.108]    [Pg.18]    [Pg.212]    [Pg.30]    [Pg.430]    [Pg.401]    [Pg.355]    [Pg.561]    [Pg.278]    [Pg.177]    [Pg.218]    [Pg.76]    [Pg.533]    [Pg.301]    [Pg.149]    [Pg.807]    [Pg.227]    [Pg.122]    [Pg.563]    [Pg.396]    [Pg.1103]    [Pg.510]    [Pg.60]    [Pg.296]    [Pg.365]    [Pg.2401]    [Pg.61]    [Pg.7]    [Pg.386]    [Pg.457]    [Pg.323]    [Pg.292]    [Pg.114]    [Pg.218]    [Pg.236]    [Pg.210]   
See also in sourсe #XX -- [ Pg.16 ]




SEARCH



Implied operation

Operational times

Time, operating

© 2024 chempedia.info