Reference period

In perturbation theories of fluids, the pair total potential is divided into a reference part and a perturbation  [c.503]

The first step is to divide the total potential into two parts a reference part and the remainder treated as a perturbation. A coupling parameter X is introduced to serve as a switch which turns the perturbation on or off.  [c.503]

A very successfiil first-order perturbation theory is due to Weeks, Chandler and Andersen pair potential u r) is divided into a reference part u r) and a perturbation w r)  [c.508]

The long-term OES is 50 ppm (8 hr TWA), set to protect against CNS effects, which will also protect against liver or kidney damage and initation. The short-term OES is 1000 ppm (15 minute reference period) to minimize exposures at initant levels.  [c.139]

The Occupational Exposure Standards imposed for trichloroethylene are Maximum Exposure Limits of 100 ppm (8 hr TWA) and 150 ppm (15 minute reference period). A skin notation Sk is applicable because of the potential for skin absorption. Because of its volatility, trichloroethylene is not recommended for cold cleaning it is normally used in partially enclosed vapour degreasing equipment provided with local exhaust ventilation.  [c.141]

Reference, Period of Cancer site/ No.  [c.243]

It is normal to establish OELs for long periods (TWAs) in relation to a reference period of 8 hours, which is a typical working-day schedule. Values above the OEL are allowed provided these are compensated by equivalent excursions below the TWA during the working day. OELs are also normally set on the basis of a nominal 40-hour work week, with a maximum of 240 work ing days in a year and for a working lifetime that might reach 45 years. Fhe long reference period could be a different one, such as a month, a year, and so on. In general, an 8-hour OEL is recommended as the most satisfactory and practical way of monitoring airborne agents for the purpose of preventing adverse health effects, although, in any case, OELs do not constitute an absolute dividing line between harmless and harmful concentrations.  [c.366]

Instantaneous OELs represent concentrations that should not be exceeded during any part of the working exposure that is, they represent the maximum permissible concentration of a chemical compound (or element) present in the air within a working area that, according to current knowledge, generally does not impair the health of the employee or cause undue annoyance. These OELs are also called ceiling values and are used for agents that present acute effects such as irritants or for other type of substances that present chronic and acute effects simultaneously and therefore may be used with appropriate medical surveillance. This OEL uses no specific time reference period, but for some situations instantaneous monitoring is not feasible, requiring the use of a 15-minute sampling period.  [c.367]

For this reason, in order to save time and money, it may be convenient to subdivide the exposed workers into more or less homogeneous groups with respect to exposure—that it is to say, based on similar work patterns—and take direct measurements of air samples within the breathing zone of a worker in the area or areas in which the work activities are carried out during a reference period. However, the use of homogeneous groups should be reconsidered if any individual exposure differs greatly from the average value of the group, which may occur if workers do not perform repetitive tasks.  [c.370]

Maximum exposure limit (MEL) The maximum concentration of an airborne substance, averaged out over a reference period to which employees may be exposed by inhalation.  [c.1457]

Reference period A specified time period allowed for human exposure to a specific concentration of a biological agent or chemical.  [c.1471]

Design and Installation of Pressure-Release Systems in References Part 1 -Design , API Recommended Practice 520, 4 ed., American Petroleum Institute, Wasliington DC, 1976,  [c.248]

The relative importance of tlie different excitations may qualitatively be understood by noting tliat the doubles provide electron correlation for electron pairs, Quadruply excited determinants are important as they primarily correspond to products of double excitations. The singly excited determinants allow inclusion of multi-reference charactei in the wave function, i.e. they allow the orbitals to relax . Although the HF orbitals are optimum for the single determinant wave function, that is no longer the case when man) determinants are included. The triply excited determinants are doubly excited relative tc the singles, and can then be viewed as providing correlation for the multi-reference part of the Cl wave function.  [c.108]

To ensure disposal water quality is in line with regulatory requirements (usually 40 ppm), the oil content in water is monitored by solvent extraction and infrared spectroscopy. The specification of 40 ppm refers to an oil in water content typically averaged over a one month period.  [c.249]

The last part, following the method to analyse radioscopy and acoustic emission values, will be to correlate the characteristic values of the radioscopic detection of casting defects with extracted characteristic values of the acoustic emission analysis. The correlation between the time based characteristic values of acoustic emission analysis and the defect characterizing radioscopy values did not come to very satisfactory results referring the low frequency measurements. The reason can be found in the  [c.16]

Repeatability. This refers to two aspects of inspection similarity between objects that are inspected and possibility of maintaining constant inspection conditions (settings) for all the inspections performed. Obviously, interpretation of data in repeatable conditions is significantly simplified. Usually, inspection during or after manufacturing process will be repeatable. Another example of repeatable inspection is inspection of heat exchangers in power nuclear plants, inspection of aircrafts as these are well standardised. However, a large part of the NDT inspection done is not repeatable.  [c.98]

Non Destructive Testing of materials is the main application of Ultrasonic Reflection Tomography (URT). This method results from a linearization of the Inverse Acoustic Scattering Problem, named Inverse Bom Approximation (IBA). URT allows perturbations (theoretically small) of a reference medium to be visualized. For media with weak inhomogeneities, one chooses the reference medium to be homogeneous the mean medium. This leads to a "Constant Background" IBA method, whose practical solution results in regular angular scanning with broad-band pulses, allowing one to cover slice-by-slice the spatial frequency spectrum of the imaged object. This leads to "Reconstruction-From-Projections" algorithms like those used for X-ray Computed Tomography. For media with strong heterogeneities, the problem is quite non-linear and there is in general no single solution. However, for example, one is generally concerned only by flaws, which appear to be strong (but small and localized so that the result is a small disturbance) inhomogeneities in well known media, the part of component to be inspected. In this case, one can use a "Variable Background" IBA method - the reference background being the water-specimen set - to reconstruct the perturbation.  [c.743]

Perdew J P, Burke K and Wang Y 1996 Phys. Rev. B 54 16 533 and references therein  [c.135]

Truncation at the first-order temi is justified when the higher-order tenns can be neglected. Wlien pe [c.508]

The gates referred to above can be created in various ways. For example, suppose that the probe beam goes tlirough the sample, but only half of its physical width (in the sample) is crossed with the pump beam. Now, if we have two photodiodes, one can measure the intensify of the perturbed part of the probe beam, whilst the second measures the unperturbed part as a result of creating spatial gates, the two recorded output signals can be used to measure the  [c.3028]

The i 2 form of the cyclopentadienyl cation was not studied extensively. In [77], it was referred to as an electronically excited state. According to the Jahn-Teller theorem, at a certain geometry it should be part of the ground state, formed by the distortion of the degenerate structure. This requirement is fulfilled, of course, if it is indeed a TS between two ground-state species. We computationally verified this proposition as follows. The exact structure of the system at the degeneracy point was searched for under D5 , symmetry constraint. The C-C bond distance rc-c for the symmetric cation at the conical intersection was found by calculating the energy of the two states point by point with different rc-c values. A minimum energy was obtained at rc-c = 1 -437 A. At this point, the Djf, symmetry was removed, and a search for an electronic state of B2 symmetry was conducted. A structure with the geometry shown in Figure 30 was found. At this geometry, the B2 state is lower in energy than any other, and therefore lies on the ground-state surface. Going either way to the type-VI structure, still on the ground-state surface, the energy decreased—the  [c.363]

OES, OCCUPATIONAL EXPOSURE STANDARD (uk) The Concentration of an airborne substance (averaged over a reference period) at which, according to current knowledge, there is no evidence that it is likely to be injurious to employees if they are exposed by inhalation, day after day. (Specified by HSC in Guidance Note EH40.)  [c.16]

Occupational exposute limits (OELs) have been used fot decades as exposure criteria for air contaminants (see Sections 5.3 and 6.2). OELs are quantitative health standards expressed as a maximum mean concentration of dangerous air contaminants over a given reference period. Although OELs are required for the establishment of health-based standards, the limits entail a gteat deal of uncertainty. They indicate the minimum level of air quality corresponding to the present understanding of what is an acceptable risk, but they do not serve as a criterion for planning a comfortable environment and con-iToi technologies fot the whole life cycle of the system, say over a period of 20  [c.398]

Occupational exposure standards (OES) U.K, standards relating to the concentration of an airborne substance that can be tolerated without harmful effects on workers over a reference period. See Long term exposure limit (LTEL) and Short term exposure limit (STEL),  [c.1462]

The exchange energy is by far the largest contributor to xc- For the neon atom, for example, the exchange energy is —12.11 a.u., while the correlation energy is — 0.39 a.u. (as calculated by wave mechanics methods). Since the exchange energy dominates xo one may reasonably ask why we do not calculate diis term exactly from orbitals (analogously to the kinetic energy), by the formula known from wave mechanics (eq. (3.33)), and only calculate die computationally difficult part, the correlation energy, by DFT Although this has been tried, it gives poor results. The basic problem is that the DFT definitions of exchange and correlation energies are not completely equivalent to their wave mechanics counterparts. The correlation energy in wave mechanics is defined as the difference between the exact energy and the corresponding Hartree-Fock value, and die exchange energy is die total electron-electron repulsion minus the Coulomb energy. These energies have both a short- and long-range part (in terms of the distance between two electrons). The long-range correlation is essentially the static correlation energy (i.e. die multi-reference part, see Section 4.6) while the short-range part is the dynamical correlation. The long-range part of the exchange energy in wave mechanics effectively cancels the long-range part of the correlation energy. The dehnitions of exchange and correlation in DFT, however, are local (short range), they only depend on the density at a given point and in die immediate vicinity (via derivatives of the density). The cancellation at long range is (or should be) implicitly built into the exchange-correlation functional. Calculating the exchange energy by wave mechanics and the correlation by DFT thus destroys the cancellation.  [c.180]

Figure 14.11 demonstrates that, despite the anticipation of an incremental project (e.g. gas compression) during the decline period, the actual opex diverges significantly from the estimate during the decline period. Under-estimates of 50-100% are common. This difference does not dramatically affect the NPV of the project economics when discounting back to a reference date at the development planning stage, because the later expenditure is heavily discounted. However, for a company managing the project during the decline period, the difference is very real the company is faced with actual increases in the expected opex of up to 100%. Such increases in planned expenditure may threaten the profitability of a project in its decline period the opex may exceed the cost oil allowance under a production sharing contract.  [c.344]

Attention should be given in the fact, that penetration of eddy currents in residual austenite will be slightly deeper than in the martensite structure of steel, as austenite shows low electrical conductivity. The signal originatimg from the austenite structure will be amplified in effect of the influence of the structure found at greater depth. There will be no error as the method of measurement is compartable and the samples made for reference purposes will have the same structure as the studied part.  [c.21]

SQUID electronics The output voltage of the bare SQUID is not linear in the input flux, but it is periodic with a flux period of = 2- 10 D Vs. In order to linearize the output signal of the SQUID it is driven in a negative feed back loop (flux locked loop) The output voltage of the loop generates a flux at the SQUID inductance in order to compensate the input flux. The sensor works as a null detector. To keep the SQUID in a proper setpoint we use a carrier frequency method at 6 MHz. This SQUID electronics is shown in the upper right part of fig. 5. The lower right part of fig. 5 shows the Eddy current part of the electronics. An oscillator, variable in frequency, provides the power for Eddy current excitation. Sirtrultaneously it gives a frequency reference to a two channel lock in demodulator in the signal path. The phase setting of the demodidator is variable, but the phase relation of both chatmels is frxed orthogonal. So a phase plane monitoring is possible.  [c.301]

In principle, the pictures with the indications to be valuated where stored. The regions of interest where cut out and rearranged in a new picture for further processing as shown for example in Fig. 3. You see a part of the reference block No. 1 with indications from 3 wetting procedures (horizontal) of 6 detection media (vertical).  [c.672]

Figure 3 shows the result of UT of a section of the case of a high-pressure process column, in which metal delaminations were found. In the Figure different colours denote the depth of the discontinuities location. The the colour-depth correspondence is given on the left side of the figure. The metal delaminations shown in Figure 3 can be assessed quantitatively (depth of location, thickness of the damaged layer, amplitude of reflection or area of discontinuity, etc.). Based on analysis of repeated UT patterns and their characteristics in terms of fracture mechanics, the strength potential of the structure at a given moment can be evaluated. It is much more complicated to forecast the safe service is the speed (acceleration) of discontinuities development, i.e. increment of the characteristics (area) of the discontinuities over a certain period of time. As there exists a dependence between the rate of discontinuities development and mechanical stresses in the metal, the characteristics of the rate of discontinuities development should be taken as one of the criteria of prefailure condition. Figure 4 is given as the example of monitoring the development of discontinuities. Figure 4,a shows a discontinuity selected as the reference one, for its subsequent monitoring. Figure 4,b shows the same discontinuity after as certain time (about a year). The settings and schematics of scanning are, naturally, identical. Quite obvious are the qualitative differences which confirm the development of delaminations in the metal. Quantitative estimates are more complicated and are a subject of specific study and determination of the degree of degradation, while their assessment is based on the fracture mechanics theory and specific characteristics of the construction (steel grade, environment, design features, etc.), but it is sufficient to note here that performance of quantitative measurements of discontinuities by the data of Figure 4 is quite real.  [c.791]

Sing (see Ref. 207 and earlier papers) developed a modification of the de Boer r-plot idea. The latter rests on the observation of a characteristic isotherm (Section XVII-9), that is, on the conclusion that the adsorption isotherm is independent of the adsorbent in the multilayer region. Sing recognized that there were differences for different adsorbents, and used an appropriate standard isotherm for each system, the standard isotherm being for a nonporous adsorbent of composition similar to that of the porous one being studied. He then defined a quantity = n/nx)s where nx is the amount adsorbed by the nonporous reference material at the selected P/P. The values are used to correct pore radii for multilayer adsorption in much the same manner as with de Boer. Lecloux and Pirard [208] have discussed further the use of standard isotherms.  [c.667]

This definition holds for multiple dimensions as well for A particles, the classical transition state is a saddle point that is unbound along the reaction coordinate but bound along the 3N- 7 remaining coordinates. A cut tlirough the surface at the transition state perpendicular to the reaction coordinate represents a 3A - 7 dimensional dividing surface that acts as a bottleneck between reactants and products. The nature of the transition state and, more generally, the region of the potential energy in the vicinity of the transition state (referred to above as the transition-state region) therefore plays a major role in detennining many of the experimental observables of a reaction such as the rate constant and the product energy and angrilar distributions. For this reason, the transition-state region is the most important part of the potential energy surface from a computational (and experunental) perspective.  [c.871]

Cracking (or hydrocracking, as it is referred to when carried out in the presence of Fl2) reactions are an integral part of petroleum refining. Flydrocracking is used to lower the average molecular weight (MW) of a higher MW hydrocarbon mixture so that it can then be blended and sold as gasoline. The interest in the fiindamentals of catalytic cracking reactions is strong and it has been thoroughly researched.  [c.947]

In this chapter we shall first outline the basic concepts of the various mechanisms for energy redistribution, followed by a very brief overview of collisional intennoleciilar energy transfer in chemical reaction systems. The main part of this chapter deals with true intramolecular energy transfer in polyatomic molecules, which is a topic of particular current importance. Stress is placed on basic ideas and concepts. It is not the aim of this chapter to review in detail the vast literature on this topic we refer to some of the key reviews and books [U, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, and 32] and the literature cited therein. These cover a variety of aspects of tire topic and fiirther, more detailed references will be given tliroiighoiit this review. We should mention here the energy transfer processes, which are of fiindamental importance but are beyond the scope of this review, such as electronic energy transfer by mechanisms of the Forster type [33, 34] and related processes.  [c.1046]

Before looking more elosely at these, it is important to reeognize another eategory of pump-probe Raman experiments. These are often referred to as transient Raman pump-probe studies. In these, a given system is pumped mto a transient eondition sueh as an exeited vibronie state, or a photoehemieal event sueh as dissoeiation or radieal fonnation [, M ai d Ml- Sueh pumping ean be aehieved by any means—even by high energy radiation [66, 67 and 68]—though nonnally laser pumping is used. The produet(s) fonned by the pump step is then studied by a Raman probe (often simply spontaneous Raman, sometimes CARS). Sinee the transient state is nonnally at low eoneentrations, the Raman probing seeks out resonant enhaneement, as we are deseribing, and also means must be taken to stay away from the lumineseenee baekground that is invariably eaused by the pump event. Often, time gated Fourier transfonn Raman in the near-IR is employed  [c.1202]

Consider now the adiabatic approximation [38,39] to the solution of Schtodinger s equation. Such an approximation is based on the fact that the nuclear masses are much larger than the electronic ones and therefore, on average, the nuclei move much more slowly than the electrons. The latter are thns able to follow the nuclear displacements Their distribution in space is detemiined by the instantaneous nuclear configuration. To a first approximation, the nuclei may then be regarded as fixed. Accordingly, the total molecular wave function can be divided in two parts one refers to the electronic wave function s R), the other to the nuclear wave function Xnllc(R ) Regarding the nuclear wave function, it is possible to separate the translational part if the interaction between the translational and the other (rotational and vibrational) nuclear degrees of freedom can be ignored. This case is typical in studies of spectroscopy and collisional dynamics where the measured properties depend on the motions of the interacting species relative to each other but not on the motion of the system as a whole (the space is assumed to be uniform and  [c.554]

See pages that mention the term Reference period : [c.460]    [c.365]    [c.105]    [c.16]    [c.29]    [c.1096]    [c.1586]    [c.1902]    [c.1908]    [c.2305]    [c.2533]    [c.2642]    [c.74]    [c.197]   
Industrial ventilation design guidebook (2001) -- [ c.1472 ]