The Resistance Factor

Expert systems are still a mystery to a large part of the scientific community. This is partially due to the volitional mystification that unfortunately can be found in many scientific areas. Additional confusion comes with the discussion about whether the system shall be called expert systems or knowledge-based systems, which is basically a valid discussion but does not really help to raise the level of acceptance. One of the most obvious factors is, Which expert would like to be replaced by an expert system It is important to understand that expert systems rely on experts and that withont the knowledge base they are essentially nseless. 

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Pressure drop is calculated by k x velocity pressure, where k is the resistance factor for the above items other than duct friction and is found from Table 29.1 or similar references. Velocity pressure is found by density x velocity, taking standard density at 1.2kg/m°, or from Table 29.2. 

The water stress Incurred by trees growing on the south site Is hypothesized to have modified foliage quality such that trees became highly susceptible to the budworm. This appears to have been primarily due to the decrease In the resistance factors beta-plnene and bornyl acetate accompanied by an Increase In alpha-plnene. If alpha-plnene consistently Increases In stressed Douglas-flr trees. It Is then possible that budworm may use It as an attractant or cue In locating suitable hosts. 

A porous solid of volume V consists of the volume Vg of the solid material and VG = V — Vs the volume of the solid-free spaces. We call p = VG/V the void fraction. The resistance factor depends on the voidage of the porous body and on a diversion or winding factor /j,p such that the relationships... 

With the Reynolds number Res = wsdP/v and the previously defined Archimedes number, the resistance factor can also be written as... 

As the resistance factor cR in flow around a sphere is dependent on the Reynolds number, according to (3.278), a relationship between the Reynolds number formed with the falling velocity urs and the Archimedes number can be derived, Res = f(Ar). 

In process engineering the main interest lies in the region Res < 104. The area above Res = 105, in which the transition from laminar to turbulent boundary layer occurs, can generally be disregarded for chemical engineering tasks. By solving the Navier-Stokes equation up to Re = 80 and comparing this with experiments enabled Brauer and co-workers [3.42] to find a very accurate empirical law, for values up to Re = 104, for the resistance factor... 

Pyrethroid resistance in some strains of H. armigera is largely due to overproduction of specific esterase isoenzymes (Rni 0.24 0.33) which are thought to sequester and hydrolyse pyrethroids. The resistance factor is positively correlated to esterase litre, so that increasing resistance is accompanied by increasing esterase activity (Gunning et at.. 1996). Unfortunately, conventional esterase inhibitors, such as profenofos, have failed to synergize pyrethroids... 

In 1984 resistance to Dl>l, lindane, organopbosphorus compounds, carbaryI. bioresmethrin and pyrethrins was detected in O. surimmensis taken from the held Attia and Frecker, 1984). The resistance factor was low for pyrethrins (2,3) and bioresmethrin (3 8) but very high for fenitrothion (>160). The inclusion of PBO in the assays reduced the latter to 10 or less. 

Miller, L. H., S. J. Mason, D. F. Clyde and M. H. McGinniss (1976). The resistance factor to Plasmodium vivax in blacks. The Duffy-blood-group genotype, FyFy. N Engl J Med 295(6) 302-304. 

The ability of this protein to efflux drug out of the tumor cell provides the tumor cell a significant means of protection. Further, the lack of chemical specificity of the protein provides the tumor cell protection from a variety of drugs once the membrane protein is expressed. An obvious question to be asked at this point is, If the protein pumps drugs out of the cell could we not inhibit the pump and thereby obviate the resistance factor the protein provides Yet another approach would be to develop anticancer drugs not affected by the Pgp. In fact there exist a variety of drugs that are not substrates of the membrane pump but unfortunately some of our most important anticancer drugs such as doxorubicin, vincristine, and taxol are affected by this pump. 

In order to determine the relevant parameters, the coefficients of the Van Deemter plot Aj and Q are measured (Section 6.5.3.1). Additionally the void fraction (Section 2.2.2) and the resistance factor tp (Section 2.3.5) are measured or estimated. 

At small distances S = r — R — R2 between particles surfaces, the resistance factor behaves as j5 for rigid particles [13], and as Xjs/d for drops [39] having mobile surface. We will still limit ourselves to the case of rigid particles. For them, at small clearance between particles, the fador of resistance is... 

A decrease of the clearance d between drops Si and S2 results in the velocity figuring in the dependences (11.82). To take a proper account of the influence of distortion of the velocity field at small 3, one has to include the resistance factors into (11.82). It should be kept in mind that resistance factors have different forms for the motion of drop S2 parallel and perpendicular to the surface Si, therefore... 

Let us adduce the asymptotic expressions for the resistance factors of rigid particles. Introduce a dimensionless distance from the center of the large particle Si to the surface of the small partide St along the line of centers, jci = (r — Rt)lR. For small values of the clearance (1 < < 1.5), it is possible to use the near-... 

A detailed analysis of relative motion of drops along the line of centers for small clearances between drops is performed in [49]. The approximate expression for the resistance factor of drop S2 looks like... 

The parameter m characterizes the mobility of the drop surface. So, at m 1, the drop surface is almost completely retarded and from the hydrodynamic standpoint, it behaves like a solid particle. The resistance factor is then... 

The expression (11.89) coincides with the first term of asymptotic relations (11.85) for fcr. From the form of the resistance factor, it follows that it has a non-integrable singularity at <5 0, so drops with fully retarded surface cannot come into contact in a finite time under the action of a finite force. 

Another limiting case m 1 corresponds to an almost fully mobile surface. Then the drop behaves as a gas bubble and the resistance factor has the form... 

To summarize, note that asymptotic expressions were found in paper [39] for the resistance factors of relative motion of two spherical drops with different internal viscosities and placed into a liquid of viscosity for d —> 0... 

If one of the drops has a fully retarded surface, which corresponds to the case of relative motion between a drop and a rigid particle, the asymptotic expression for the resistance factor at 0 looks like... 

Here u is the drop velocity, R - the drop radius, U - the velocity of the liquid, E - strength of the electric field. We shall assume from now on that the electric field is strong enough, so the resistance factor f in the expression for the hydro-dynamic force can be put equal to unity when considering the capture of a drop by a cylindrical wire. 

Introduce the resistance factor of drop 2 into its motion relative to the other drop... 

ACCase prepared from the resistant L. multiflorum biotype, which had been selected by field use of didofop, was inhibited by the APPs diclofop, haloxyfop and quizalofop with IC50S (herbicide cone, needed for 50% enzyme inhibition) that were 28-, 9- and 10-times higher than for ACCase from a susceptible biotype. There was no cross-resistance to the CHD herbicides sethoxydim or dethodim [32]. ACCase resistance was subsequently also confirmed for L. multiflorum biotypes from other countries. In a resistant biotype selected by didofop in Normandy, the resistance factor (ratio of the IC50 for ACCase from the resistant to the IC50 for ACCase from the susceptible biotype) was 19 for diclofop and 5 for haloxyfop, but only 2 for the CHDs dethodim and sethoxydim [33]. Interestingly,... 

Biotypes with target-site-based resistance to ACCase inhibitors were also selected in wild oat species [Avena fatua, A. sterilis). The resistance patterns were found to be variable. For example, the resistance factors for ACCase from the Canadian A. fatua biotype UMl were 105 for sethoxydim, 10 for tralkoxydim, and 10 for didofop and fenoxaprop, whereas for the Aoena fatua biotype UM33 from Canada the ratios were 10.5 for fenoxaprop, 1.2 for diclofop, 5 for sethoxydim and 1.7 for tralkoxydim. It was proposed that this was due to different point mutations, each being assodated with a characteristic resistance pattern [37]. Another reason could be the frequency of homozygote and heterozygote resistant and susceptible plants within a tested population. 

Recall from the tube model of Section 11.3 that losses in the model are caused exclusively by wave propagation from the ends of the tube no losses occur within the tube itself Recall also from Section 11.5.3 that the resistance factors which cause the losses have... 

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