Background levels

The P-radiation was shown to cause the positive deviation from the background level (approx. 3 times) before the earthquake. 

Referring to figure BLIP. 7 consider electrons from the event under study as well as from other events all arriving at the two detectors. The electrons from the event under study are correlated in time and result in a peak in the time spectrum centred approximately at the delay time. There is also a background level due to events that bear no fixed time relation to each other. If the average rate of tlie background events in each detector is R and i 2> then the rate that two such events will be recorded within time Ax is given by i g, where... 

Cq ), where is the blended impurity concentration of impurity a Cq, the background impurity level and the multiplication constant. Possible sources of background response include instmment noise, sample system outgassing, or interference from other impurity response signals. Proper setup, purging, and operation of the instmment should reduce background levels weU below ippb. 

In the final product, the formaldehyde has completely reacted to form a very inert thermoset resin. Spontaneous emission of formaldehyde from high pressure laminates is measured at approximately the accepted background level of 0.035 ppm (15). Melamine surfaced laminates are tested and approved for food service equipment by the National Sanitation Foundation (16). 

Figure 7 Microanalysis of a CuO/ZnO methanol synthesis catalyst with a field-emission STEM (a) EOS data showing Cu and Zn K-lines and (b) EELS data showing Cu and Zn L-edges with dotted lines indicating background levels. Spectra were taken simultaneously from a 2-nm diameter area. Signal intensities above background show that approximately the same relative amounts of Cu and Zn were measured by each method.

Background level The concentration of a particular substance present in the air without any local source of the pollutant, or the concentration of the pollutant at some distance from its source. 

In onshore drilling there is no need for chlorides above these background levels. Potassium chloride has been added to some drilling fluids as an aid to controlling problem shale formations drilled. Potassium acetate or potassium carbonate are acceptable substitutes in most of these situations. 

Heavy metals are present in drilled formation solids and in naturally occurring materials used as mud additives. The latter include barite, bentonite, lignite, and mica (sometimes used to stop mud losses downhole). There are background levels of heavy metals in trees that carry through into lignosulfonate made from them. 

The standard rates the offending noise according to its nature 5dB(A) is added where the noise has a definite continuous note and a further 5 dB(A) added for noise of an intermittent nature. The number of occasions that happen in an 8-hour period is then plotted on a graph and the correction for intermittency is derived. When these calculations have been performed, the noise level is compared to the background level. The standard states that where the noise exceeds the background by 5 dB or more, the nuisance is to be classed as marginal, and where the background is exceeded by lOdB(A) or more, complaints are to be expected. 

It is stressed in this standard that it is not intended to be a criterion but most local authorities tend to use it as a guide. Other methods are available or may have value for individual circumstances. Particular problems occur when a noise is of a very tonal nature or contains discernible information (i.e. music or voice). It is quite possible for music to become a nuisance at no more than 3dB(A) above ambient background level. 

Count Rate of an Attache Case. Filled with Dynamite vs Background Levels.. . . Comparison of % N by Weight in Some Materials Found in Typical Luggage... 

Another way of demonstrating currently achievable performance with the above system is shown in Table 13. Here, the peak counts/sec from a typical empty suitcase, leather attache case, and the leather attache case containing six sticks of Dynamite are compared to the background level. The attache case, in both cases, was also filled with common nitrogen-rich materials such as wool, vitamins Bj and B12t pills, rayon, saccharin, silk and other materials such as paper, cotton and brass ... 

Count Rate of an Attache Case Filled with Dynamite vs Background Levels... 

First value given is mean calculated from data of Appendix A, Forstner and Wittmann, 1979, (23). Second value (in parentheses) is average world background level (Table 28, Forstner and Wittmann, 1979), (23). 

Syers, J.K. Iskandar, I.K. Keeney, D.R. Distribution and Background Levels of Mercury in Sediment Cores from Selected Wisconsin Lakes. Water Air Soil Pollut. 1973 2, 105-118. 

Heavy metals. The profiles of sediment and pollutant depositions and the relationships of concentrations with time have been reconstructed. For most metals the highest accumulations took place between the fifties and the sixties, when the fastest industrial development of Porto Marghera took place. In Figure 2 the concentration profiles of three of the most interesting metals (Hg, Pb, Cd) are plotted vs. depth. Data were "normalized" (i.e. divided) by the background levels, as metals have different natural presence in the environment. This leads to accumulation factors, referred to pre-industrial background values. Any derived data tell... 

Atmospheric fluxes of lead in the United States rose steadily from the first decades of this century, reaching a maximum in the early 1970s (see Eisenrich et al., 1986 and references therein). Passage of the Clean Air Act of 1972 and its subsequent amendments resulted in dramatic reductions in atmospheric lead concentrations, although lead fluxes worldwide still remain 10-1000 times background levels (Settle et al, 1982 Settle and Patterson, 1982). 

The transport rate of mercury flowing from the land to the oceans in rivers has been increased by a factor of about three by human activity. While the increased rate is still relatively less important than the total transport of Hg through the atmosphere, it can represent a significant stress on the exposed organisms, particularly since the increased flux is unevenly distributed. That is, human activity has created local environments where the transport of mercury or its concentration in a river or estuary is many tens of times higher than background levels. 

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