Mixing down

Fig. 3. Abundances within the hydrogen-burning shell as function of relative mass 5m, defined as ranging from 0 to 1 between the bottom of the shell and the convective envelope. From observational evidence a penetration of extra-mixing down to 5m 0.15 has been inferred...

These layers containing higher concentrations of pollutants provide an important mechanism for transport of ozone, particles, and their precursors to the free troposphere. In addition, in the morning when solar heating causes turbulent mixing (Fig. 2.20), these pollutants are mixed down to the surface. This not only increases the surface concentrations but also provides species that can initiate the VOC-NO chemistry that leads to more ozone formation. As a result, there is a carryover from one day to the next, leading to smog episodes in which the pollutant concentrations increase from day to day. 

The rhodium-102 and cadmium-109 high altitude tracer experiments provide the best information on the pattern and time-scale of downward mixing from the mesosphere to the lower stratosphere and troposphere (20, 21). The 102Rh tracer injected into the lower thermosphere on Aug. 11, 1958, mixed down into the lower stratosphere selectively at high lati-... 

Mixing times are the times required for 6, or A, or Ig to fall from their initial value (before mixing), down to some prescribed small value (for instance 0.05 or 0.01). We shall see that in Lagrangian coordinates, - o /(da /dt) is also a mixing time. 

The shallow-water character of the sea provides rapid propagation of wind and convective mixing down to the bottom, which leads to equalizing the vertical temperature distribution in most cases, the temperature difference is less than 1 °C. Meanwhile, during summertime calm periods, the thermocline is formed which prevents the near-bottom layer from water exchange. 

This paper analyzes the role that mixing can play in this reaction, and tries to divide "mixing" down into its several component fluid mechanic parts, which is helpful in analyzing process results. 

Ozone is of major interest to tropospheric chemists for two reasons It leads to the production of hydroxyl radicals, and it is a greenhouse gas. For many years, tropospheric ozone was believed to be chemically inert. Scientists held that the ozone present in the troposphere was formed initially in the stratosphere — where ultraviolet radiation is of high enough energy to dissociate oxygen — and mixed down into the troposphere. It was postulated further that ozone was removed from the atmosphere primarily by reacting with Earth s surface. 

These diagenetic models have proven effective in understanding the effects of various sedimentary processes on silica dynamics in the seabed (Johnson, 1976 Ragueneau et al., 2000). For example, the effect of bioturbation by benthic fauna on pore-water silicate profiles has been examined (Schinck and Guinasso, 1978). Higher intensities of bioturbation lead to higher asymptotic silicate values at depth because the benthic fauna are mixing down particles from the surface... 

This Nyquist condition quickly brings us to a problem. A typical NMR frequency is of the order of hundreds of MHz but there simply are no ADCs available which work fast enough to digitize such a waveform with the kind of accuracy (i.e. number of bits) we need for NMR. The solution to this problem is to mix down the signal to a lower frequency, as is described in the next section. 

By contrast, in the less cold winter of 1994-95 the core of the gyre only mixed down to 800m (Malanotte-Rizzoli etal., 1996). In that winter, Vidussi etal. (2001) calculated that the depth integrated chlorophyll content of the 0-230 m layer in the Rhodes Gyre was 61.3 g chlorophyll m-2 which was twice the value of the productivity later averaged for the rest of the basin. 

Nonlinear crystals are normally used for frequency doubling and mixing down to 200 nm, where the oxygen bands in air start to absorb. The p-barium borate crystal has a 189 nm cut-off, which is determined by the absorption in the crystal itself. Practically it is used down to about 200 nm, where the radiation is absorbed by oxygen in air. For shorter wavelengths the oxygen has to be removed from the path of the laser radiation. 

Micromrxers provide very fast mixing, down to milliseconds or even below [9, 26]. The concentration profiles are uniform and there is good agreement between experiment and theory, which may make process development more predictable. Results at the laboratory scale may be maintained throughout the scale-out steps, since the fluid dynamics are not changed or at least shift by analogy in a known manner. This is particularly valid for very fast precipitations such as with Yellow 12 manufacture. Here, the seed formation and agglomeration process is impacted... 

It is also important to consider where in the sediment dissolution occurs. Metabolically produced COj released immediately at the sediment-water interface is probably much less effective for carbonate dissolution than in deeper sediment strata, because neutralization with bottom water COj might occur instead of dissolution. If the particulate organic matter is more rapidly mixed down, i.e. by bioturbation, and oxidized in deeper sediment strata, the CO released into the pore waters can probably more effectively dissolve carbonates (Martin and Sayles 1996). 

Thus, approximately five times more heat must be removed to freeze the water than to cool the mix down. 

D NMR pulse sequence. A series of delays and RF pulses culminating in the detection, amplification, mixing down, and digitization of the FID. 

Mixing down. Syn. mixdown. The reduction of an analog signal from a high frequency (typically tens or hundreds of MHz) to a lower frequency range (typically below 100 kHz). 

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