Swarm influences

Swarm Influences The interaction forces described above are modeled based on theory and experiments of single particles in hquids and gases. The effect of neighboring particles on the forces and motion of an individual particle are difficult to grasp. The flow field can no longer be analytically derived, not even for simple flows, as the required symmetry for these analyses is broken by the presence of the surrounding particles. Experimentally, it becomes also much more difficult to obtain relevant information. Therefore, still some empiricism is used in the modeling of swarm effects. 

Most theoretical studies of heat or mass transfer in dispersions have been limited to studies of a single spherical bubble moving steadily under the influence of gravity in a clean system. It is clear, however, that swarms of suspended bubbles, usually entrained by turbulent eddies, have local relative velocities with respect to the continuous phase different from that derived for the case of a steady rise of a single bubble. This is mainly due to the fact that in an ensemble of bubbles the distributions of velocities, temperatures, and concentrations in the vicinity of one bubble are influenced by its neighbors. It is therefore logical to assume that in the case of dispersions the relative velocities and transfer rates depend on quantities characterizing an ensemble of bubbles. For the case of uniformly distributed bubbles, the dispersed-phase volume fraction O, particle-size distribution, and residence-time distribution are such quantities. 

Substituted phenols as well as phenol itself are typical constituents of (bio-)refractory waste waters and can increase a(0> 3 (Gurol and Nekouinaini, 1985). They studied the influence of these compounds in oxygen transfer measurements and attributed this effect to the hindrance of bubble coalescence in bubble swarms, which increases the interfacial area a. When evaluating the effect of these phenols on the ozone mass transfer rate, it is important to note that these substances react fast with ozone (direct reaction, kD= 1.3 103 L mol"1 s 1, pH = 6-8, T = 20 °C, Hoigne and Bader, 1983 b). 

Most of the work in solving the Boltzmann equation for electrons has been for the relatively simple conditions of electron swarm experiments. In these experiments, electrons are released from a cathode in low concentrations and drift under the influence of a uniform applied electric field in a low-pressure gas towards an anode at which the electrons are collected. If... 

Knowing that the quantum mechanical wavepacket follows — at least for short times — the route of a swarm of classical trajectories, it is plausible to surmise that the periodic orbits also influence the motion of the wavepacket ... 

Ledoux M. N., Winston M. L., Higo H., Keeling C. I., Slessor K. N. and LeConte Y. (2001) Queen and pheromonal factors influencing comb construction by simulated honey bee (Apis mellifera L.) swarms. Insectes Soc. 48, 14—20. 

In extraction columns, it is possible to find droplet swarms where the local velocities near the droplet surface are higher, this being due to the lower free area available for the countercurrent flowing continuous phase. Wake and Marangoni influences make the prediction of a physical mass transfer coefficients difficult. With reactive extraction the influence of interfacial kinetics on overall mass transfer is generally not negligible. In any case, a combination of reactive kinetics with any eddy mass transfer model is recommended, whereas the latter could rely on correlations derived for specific column geometries. 

To give an example of the dramatic influence which the geometric parameters can have on coalescence behavior, Fig. 77 shows Y(X) correlations for the industrial-size slot injector which were obtained in a vessel of 30 x 8 m water height. The injector was positioned 1 m above the bottom at the vessel wall in such a way that its axis formed an angle of 0°, + 35° resp. - 35° with the horizontal. Only in the last case, the free jet was pointed towards the floor and decomposed into the bubble swarm just above it. Near the floor, the suction of the free jet is weakest on account of bottom friction. Furthermore, the bubble swarm which has formed does not exert a chimney effect there. Consequently, liquid entrainment into the free jet is suppressed at exactly that point at which it would be particularly supportive of coalescence on account of the weakened kinetic energy of the free jet. 

Momentum-transfer cross sections are normally determined by the electron swarm technique. A detailed discussion of the drift and diffusion of electrons in gases under the influence of electric and magnetic fields is beyond the scope of this book and only a brief summary will be given. The book by Huxley and Crompton (1974) should be consulted for a full description of the experimental methods and analysis procedures. 

Life Cycie In late summer females deposit elongate masses of eggs in soil eggs hatch in spring nymphs develop for 40-60 days until molting to adults. Adults feed until killed by cold weather. Swarms appear as a result of interaction of weather and biological influences. 

When a perforated plate is used as a gas sparger in a bubble column, the mean gas holdup b is influenced by the size and arrangement of holes as well as column diameter as a result of change in both of bubble size and the flow pattern of the bubble swarm. These effects have been reviewed and correlated by Kato and Nishiwaki (K6) for air-water systems where a sparger is perforated uniformly. When the hole diameter 8 is smaller than 1.0-1.4 mm and the gas velocity f/c is low, 5 for a given diameter column... 

Swarm PF, Coe AM, Mace R. 1984. Ethanol and dimethylnitrosamine and diethylnitrosamine metabolism and disposition in the rat. Possible relevance to the influence of ethanol on human cancer incidence. Carcinogenesis 5 1337-1343. 

The effects of energy on ion-molecule rate processes have been investigated by a variety of methods. The influence of reactant translational energy, as studied by SIFDT (selected ion-flow drift-tube) techniques in swarm experiments, by ICR, and by beam and other single-collision techniques, is reviewed in other parts of this chapter or of this book. In this section, we will concentrate specifically on the influence of reactant internal energy on ion-molecule reactions. There are basically two sources of data that address this problem ... 

Variable-temperature swarm methods provide data on ion-molecule reactions over a wide range of temperatures and reveal the influence of vibrational and rotational energy of the reactants on reactivity. 

In swarm experiments, an important step forward was the development of a new method in which the SIFT techniques were combined with laser-induced-fluorescence (LIF) detection for monitoring the ion vibrational states (Kato et al., 1993). In this way, both the vibrational states of the reactant ion and the vibrational states of some reaction products could be detected, and the influence of vibrational energy on reaction rates of thermal ions (where the translational-to-vibrational energy transfer is negligible) could be studied. The method was primarily used to study reactions of Nj(t) = 0 to 4) with Ar (which will be discussed separately), N2 and O2 (Kato et al., 1993), Kr (Kato et al., 1996), H2 (de Grouw et al., 1995), and HCl (Krishnamurthy et al., 1997). In the reaction... 

Hay, NA., Tipper, D.J., Gygi, D. and Hughes, C. (1999). A novel membrane protein influencing cell shape and multicellular swarming of Proteus mirabdis. J. Bacteriol. 181, 2008—2016. 

C,H,202, Mr 152.19, a pheromone isolated from the feces of the desert locust Schistocerca gregaria that influences aggregation (formation of swarms) and is supposed to have other physiological activities. However, in recent studies, the substance could not be detected, at least in S. gregaria, instead a mixture of various phenols and phenylacetonitrile (CgH7NO, Mr 133.15) was reported. For general information on the pheromones of grasshoppers, see Ut . 

The width of the waveform pulse applied to wires in an ion shutter is the key parameter in establishing peak widths in a mobility spectrum since the minimum possible width of an ion swarm, before normal diffusion and other influences in the drift region, is set by the shutter pulse time. The minimum time of a pulse, even in a well-designed and well-built instrument, is fixed by the time for ions, under mobility control of the superimposed electric field of the drift tube, to pass from one side of a shutter grid set (reaction region) to the other side (drift region). Injection pulses of about 100 ps are... 

When an electric field is imposed on the ion swarm in the supporting atmosphere, ion motion will be influenced by this field. In contrast, neutral molecules will barely be affected, if at aU, by the electric field, and any effect will depend on the dipole or quadrupole moments of the gases. An additional factor is the electrostatic interaction between the ion and gas molecules the ion may attract gas molecules that have permanent dipole, quadrupole, or higher moments. The electrostatic forces would also lead to ion-induced dipole interactions with the gas molecules, the magnitude of which depends on the polarizability of the gas. The interaction potential used to represent these forces is discussed in Section 10.3. 

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