Water attenuation

WATR, WEFT and Water-PRESS. If the transverse relaxation of the water is faster than the spins of interest, suppression can be achieved using the CPMG-based WATR (water attenuation by T2 relaxation) method. ° The T2 relaxation time of the water can be selectively decreased through the... 

T-90°-data acquisition [9] in which the time interval, x, is chosen such that the water resonance, which is expected to have the longest T, in the sample, has zero magnetization after the 90° pulse [113, 114], The CPMG spin-echo pulse sequence 90°-(t-180°-t) n-data acquisition (n = number of repetitions), has been used with the pulse interval, r, adjusted to attenuate the water signal, for example, from erythrocyte and protein suspensions [113], The technique is improved by the addition of ionic species such as ammonium chloride which increases the chemical exchange of the water protons and thus shortens T2 relative to the compounds of interest. This method is known as WATR (Water Attenuation by T2 Relaxation) [114]. Solvent suppression can also be achieved by selective excitation of the spectrum with special pulses such that the water resonance occurs at a point of null excitation [115-119]. However, distortion of peaks near the null point may occur. 

There is a great similarity in the catalytic transformation of ethanol and of methanol on a HZSM-5 zeolite, either concerning the reaction mechanism [4], or in the spectra of products [5,6], Nevertheless, the high content of water in the feed in the BTG process markedly influences the distribution of products and catalyst deactivation [5-7], It has been proven that water attenuates deactivation by coke at moderate temperatures [6], but causes irreversible deactivation by dealumination of the zeolite at high temperatures. 

The investigation of the ester hydrolysis reaction can take advantage of the suppression of the water signal by means of the WATR technique (water attenuation by T2 relaxation). Using this method, signals in the region of J = 4-5 ppm can easily be observed. In this manner, the kinetics of hydrolysis of neostigmine bromide in weak acid aqueous solution... 

In one case, in particular, Roush observed the elimination of a silyl ether even with an anhydrous preparation of TASF. However, inclusion of several equivalents of water attenuated the basicity of the fluoride and produced the desired product in good yield without competitive elimination. Anhydrous TASF does foster similar side reactions with some highly sensitive substrates, such as those found during the synthesis of bafilomycin Al, (—)-osmundalactone, and (—)-muricatacin. While HF pyridine andHF EtsN are alternative reagents for base sensitive substrates, reactivity problems are often encountered, leading to very slow or incomplete reactions, or even no reaction. However, TASF in a solution of DMF/water (2-3 equiv of water relative to the amount of TASF) appears to be even milder than the anhydrous reagent, as shown in the synthesis of bafilomycin Al. ... 

Fig. 4 shows the variation of the water attenuation coefficient (water being similar from this point of view to thyroid and extra-thyroid tissue) in function of energy in the range 30 - 100 keV. The thyroid lies from 0 to 50 mm under the skin, and thus we have set out in Fig. 5 the transmission of a photon beam through 3 tissues thicknesses 10, 20 and 50 mm, each one of there curves being normalized against a standard value for 35 keV. 

Attenuation is also an important factor in air-bome ultrasound. For exampe, attenuation in air at 1 MHz is 1.2 dB/cm, compared with a figure of 0.0022 dB/cm in water [1]. In addition, environmental conditions (temperature, turbulences) can affect the inspection with air-bome... 

Figure Bl.14.13. Derivation of the droplet size distribution in a cream layer of a decane/water emulsion from PGSE data. The inset shows the signal attenuation as a fiinction of the gradient strength for diflfiision weighting recorded at each position (top trace = bottom of cream). A Stokes-based velocity model (solid lines) was fitted to the experimental data (solid circles). The curious horizontal trace in the centre of the plot is due to partial volume filling at the water/cream interface. The droplet size distribution of the emulsion was calculated as a fiinction of height from these NMR data. The most intense narrowest distribution occurs at the base of the cream and the curves proceed logically up tlirough the cream in steps of 0.041 cm. It is concluded from these data that the biggest droplets are found at the top and the smallest at the bottom of tlie cream.

Examples of nir analysis are polymer identification (126,127), pharmaceutical manufacturing (128), gasoline analysis (129,130), and on-line refinery process chemistry (131). Nir fiber optics have been used as immersion probes for monitoring pollutants in drainage waters by attenuated total internal reflectance (132). The usefulness of nir for aqueous systems has led to important biological and medical appHcations (133). 

Composition and Methods of Manufacture. Vaccine is produced from the Oka attenuated strain. Vacciae is produced in human diploid cells such as MRC-5. After growth in the cell substrate, the cells themselves are harvested into the growth medium and sonicated to release the cell-associated vims. Sucrose and buffering salts are generally in the medium to help stabiLize the vims. The vacciae is presented in a free2e-dried vial to be reconstituted with sterile distilled water before injection (27). 

Ex situ bioremediation may use various biological wastewater treatment processes, soil piles, or land appHcation. With in situ bioremediation, the basic process is the same microbes, soil, and water working together as a bioreactor. Where the in situ techniques differ are in how contaminants and microbes are brought in contact and how oxygen, nutrients, and other chemical supplements ate distributed in the soil—water—air matrix. Typical in situ bioremediation techniques include natural or intrinsic attenuation, air sparging, and bioventing. 

A comparison of phenol acidity in DMSO versus the gas phase also shows an attenuation of substituent effects, but not nearly as much as in water. Whereas the effect of ubstituents on AG for deprotonation in aqueous solution is about one-sixth that in the gas phase, the ratio for DMSO is about one-third. This result points to hydrogen bonding of the phenolate anion by water as the major difference in the solvating properties of water and DMSO. ... 

Multiple pathways are a major concern since depostion of PIC would have occurred. Specific soil conditions determine attenuation rates of penta PIC leachate. Once penta reaches the water table, other transport and fate processes become important. Penta exists in two forms ionized and non-ionized. The ionized form is soluble in water, while the non-ionized form is not. The ratio of the two forms in water is dependent on the pH of the aquifer. In alkaline environments penta PIC tend to be more soluble and more susceptible to advective transport and biological decay. Half-lives of penta leachate in groundwater have been estimated ranging from 27 days to 58 years. 

Unlike X-rays and gamma rays, electrons are rapidly attenuated. The maximum range of a 1-million-volt electron is about 4 m in air and about 5 cm in water. In... 

Atmospheric attenuation is the consequence of absorption of radiation by the medium present between emitter and receiver. For thermal radiation, atmospheric absorption is primarily due to water vapor and, to a lesser extent, to carbon dioxide. Absorption also depends on radiation wavelength, and consequently, on hie temperature. Duiser approximates transmissivity as... 

The atmospheric attenuation factor takes into account the influence of absorption and scattering by water vapor, carbon dioxide, dust, and aerosol particles. One can assume, as a conservative position, a clear, dry atmosphere for which = 1. 

Velocity and Attenuation of the Pressure Waves. The velocity and attenuation of the mud pulses or waves have been studied theoretically and experimentally. The velocity depends on the mud weight, mud compressibility, and on the drillpipe characteristics, and varies from 4920 ft/s for a light water-base mud to 3,940 ft/s for a heavy water-base mud. An oil-base mud velocity will vary from 3,940 ft/s for a light mud to 3,280 ft/s for a heavy mud. 

The problem has been recognized by many of the developers concerned, who have consequently themselves adopted the environmental standards of other industrialized nations. In the absence of national controls this is a responsible and laudable approach. However, the piecemeal adoption of standards taken from elsewhere does not take account of local conditions. These conditions may either enhance or limit the ability of the environment to disperse and attenuate or assimilate pollutants (e.g. the occurrence of temperature inversions will limit the dispersion of air pollutants). Similarly, the use to which local resources are put may demand particularly high standards of environmental quality (e.g. the use of sea water or river water as the basis of potable water supply). The choice of standards must also take into account local practices and existing local administration. 

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