Ground attenuation

Fig 31 Schematic diagram of transducer mounted in a charge assembly. The probe shield is electrically connected to the grounded attenuator plate, to the wall of the explosive container, and to the ground lead of the signal cable... 

LASL, Los Alamos, NM. The transducer described in his paper and shown in Fig 31 was in the form of an uncharged parallel-plate capacitor which had an explosive as a dielectric. One plate was connected to the signal input terminal of an oscilloscope, while the other plate was grounded and acted as part of the attenuator in the boosting system. When the shock wave in the grounded attenuator plate hir the explosive, a voltage appeared across the capacitor and a pulse appeared on the oscilloscope. Two oscilloscopes were used to record the waveform of the current in the transducer circuit which consisted of a small capacitance shunted by the small resistance of the signal cable. 

Atomic Absorption Spectroscopy. Mercury, separated from a measured sample, may be passed as vapor iato a closed system between an ultraviolet lamp and a photocell detector or iato the light path of an atomic absorption spectrometer. Ground-state atoms ia the vapor attenuate the light decreasiag the current output of the photocell ia an amount proportional to the concentration of the mercury. The light absorption can be measured at 253.7 nm and compared to estabUshed caUbrated standards (21). A mercury concentration of 0.1 ppb can be measured by atomic absorption. 

Cooling-Tower Plumes. An important consideration in the acceptabiHty of either a mechanical-draft or a natural-draft tower cooling system is the effect on the environment. The plume emitted by a cooling tower is seen by the surrounding community and can lead to trouble if it is a source of severe ground fog under some atmospheric conditions. The natural-draft tower is much less likely to produce fogging than is the mechanical-draft tower. Nonetheless, it is desirable to devise techniques for predicting plume trajectory and attenuation. 

The inductive reactance, Xl, will tend to offset the ground capacitive reactance X,j and diminish the denominator to a certain value of Xl, say, until it completely offsets the content of X. (Xl= X, ). At higher ratios, when Xl > 3 X. g, the denominator will rise more rapidly than the numerator and will tend to attenuate the Fg a as withand X, but at a slightly higher value of max (Figure 20.7, curve 3). 

The addition of this stage of filtering will bring the very high-frequeney attenuation under eontrol and further attenuate any differential-mode noise on the earth ground lead. It will also produee a eombined attenuation of -36 dB at the switehing frequency of the power supply. 

United States, where most recorded earthquake data are in MM intensity units, there are two approaches for determining the attenuation of ground motion. Method 1 is an intensity-atte ition... 

Ground radiation is from deposited radioactive particles. The deposition rate from a radioactive cloud without rain (dry deposition) is so low that the ground radiation dose is about the same as the inhalation dose. A heavy rain, however, may wash out enough particles from the plume to make ground radiation the dominant contributor to the total dose in a limited area. Rain will also attenuate radiation by leaching the radioactivity to be shielded by the soil and by moving it to streams for further removal. 

These coefficients must be multiplied by the density of air and tissue, respectively. Figure 15.7.2-1 depicts a radiation fallout field. Let C be the curie activity/m. The radiation into a unit area receptor at z = 1 m above the ground. The area is emitting C r dr d0 gammas/s. These are attenuated in the air as exp(-p, R) and geometrically as l/(4 7t R). The radiation received by the receptor is given by equation 15.7.2-1 which becomes 15.7.2-2 by a change of... 

Schirmer M, JF Barker (1998) A study of long-term MTBE attenuation in the Borden aquifer, Ontario, Canada. Ground Water Monitoring and Remediation. 113-122. 

Natural attenuation relies on natural processes to clean up or attenuate pollution in soil and ground-water. Natural attenuation occurs at most polluted sites. However, the right conditions must exist underground to clean sites properly. If not, cleanup will not be quick enough or complete enough. Scientists monitor or test these conditions to make sure natural attenuation is working. This is called monitored natural attenuation (MNA)94-96... 

U.S. EPA, Technical Protocol for Evaluating Natural Attenuation of Chlorinated Solvents in Ground Water, National Risk Management Research Laboratory, United States Environmental Protection Agency, Washington, DC, October 1998. 

Palmer C.D., Puls R.W. Natural attenuation of hexavalent chromium in ground water and soils. EPA/540/S-94/505, 1994. 

It is concluded that the selectivities of electrophilic additions are not directly related to the reactivities but to the transition-state positions. Extensive comparison with similar data on the bromination and hydration of other ethylenic compounds bearing a conjugated group shows that this unexpected reactivity-selectivity behaviour can arise from an imbalance between polar and resonance effects (Ruasse, 1985). Increasing resonance in the ground state would make the transition state earlier and attenuate the kinetic selectivity more strongly than it enhances the reactivity. Hydration and halogenation probably respond differently to this imbalance. 

If a substance is irradiated with electromagnetic radiation, the energy of the incident photons may be transferred to the atoms or molecules raising them from the ground state to an excited state. This process, known as absorption, is accompanied by attenuation of the incident radiation at a particular frequency and can occur only when the energy difference between the two levels is exactly matched by the energy of the photons. The frequency of the radiation is given by... 

Self-absorption is a phenomenon whereby emitted radiation is reabsorbed as it passes outwards from the central region of the flame (cf. arc/spark spectrometry). It occurs because of interaction with ground state atoms of the analyte in the cooler outer fringes of the flame and results in attenuation of the intensity of emission. It is particularly noticeable for lines originating from the lowest excited level and increases with the concentration of the analyte solution (Figure 8.24). 

This contribution summarizes state-of-the-science with respect to USGS research on the hydrogeochemistry of trace-element mobilization and attenuation from mineralized areas during transport in surface and ground waters. The primary aspects are ... 

The objectives of this research were to determine the potential for contamination of Snow Lake which provides drinking water for the town of Snow Lake, and the local environment by identifying the source of arsenic in the ground water at MW17 and the mechanisms by which arsenic is being transported and attenuated. 

From MW17, the ground water flows initially SE beneath the NATA but due to rock outcrops veers N to combine with surface water in the RA. The sediment in this area has been contaminated with As from the surficial runoff from the ARS as well as earlier mining operations. The As in the surface water is then attenuated by ferric (Fe(lll)) oxyhydroxides (HFO) so that by the time it reaches Snow Lake level of As are significantly reduced to <0.005 mg/L. 

In a simple electron microscope, a primary beam of electrons is produced using a conventional electron gun, where a heated cathode, maintained at ground potential, emits electrons which are drawn out by a positive potential (typically 30 kV) to form a high energy electron beam. This beam is easily electrostatically and/or magnetically focused (since electrons are charged particles) to a few microns across, and can be directed to any point on the sample by a series of magnetic lenses. The system must be evacuated to reduce attenuation and scatter of the electron beam. When an electron beam strikes the sample, a number of processes take place (Fig. 5.6 Pollard and Heron 1996 51). 

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