Drag resistance

Cattaneo M (2004) Aspirin and clopidogrel efficacy, safety, and the issue of drag resistance. Arterioscler Thromb Vase Biol 24 1980-1987... 

The hydrodynamic forces are usually described by a linear relation between drag resistance and relative fluid velocity ... 

In this equation, % is a proportionality factor known as the bead-solvent friction coefficient which purports to account in some kind of average way for the complex molecular interactions as the polymer segments (schematized by the bead) move about in the solvent. Following Stokes law of drag resistance, this friction coefficient is usually given as = 67trisa, with a equal to the bead radius. 

Efficacy of enfuvirtide in patients infected with drag-resistant HIV-1 in Europe and Australia, N Engl J Med 348 2186-2195... 

Anderson et al., 2003) eventually leading to larger drag resistances than chemically-active AF coatings (Holm et al., 2004 Schultz, 2004). Additionally, the AF properties of pure PDMS are rather poor after relatively short immersion times, so foul-release coatings must incorporate leaching additives which can act as potent non-specific biocides (Rittschof, 2001), the environmental side-effects of which have not been fully assessed yet. 

Laboratory rotors have been used to evaluate the drag resistance of immersed surfaces as well. The rotational frequency of the innermost cylinder is adjusted to the relevant speed (monitored by a tachometer) and after about 30 minutes of flow stabilisation a 50 Nm strain gauge transducer picks up the torque, M,. All measurements are based on the average of three replicate tests. A sketch of the set-up is shown in Figure 13 details on the set-up and calculations are described in Weinell et al. (2003). 

Figure 13 The set-up for evaluation of drag resistance of immersed surfaces.

Weinell, C. E., Olsen, K.N., Christoffersen, M.W., Kiil. S. (2003) Experimental Study of Drag Resistance Using a Laboratory Scale Rotary Set-up, Biofouling, Vol. 19(supplement), 45-51. 

Cabot, M. C., Giulano, A. E., Han, T-Y., and Liu, Y-Y., 1999, SDZ PSC 833, the cyclosporin A analog and multidrug resistance modulator, activates ceramide synthesis and increases vinblastine sensitivity in drug-sensitive and drag-resistant cancer cells. Cancer Res. 59 880-885. 

Hawkshead JJ (2008) Hospital wastewater containing pharmaceuticals active compounds and drag-resistant organisms a source of environmental toxicity and increased antibiotic resistance. J Residual Sci Tech 5 51-60... 

We have to realize that sometimes requirements concerning physical properties of model materials exist that cannot be implemented. In such cases only a partial similarity can be realized. For this, essentially only two procedures are available (for details see Refs. 5 and 10). One consists of a well-planned experimental strategy in which the process is divided into parts, which are then investigated separately under conditions of complete similarity. This approach was first applied by William Froude (1810-1879) in his efforts to scale-up the drag resistance of the ship s hull. 

The maximum attainable reductions in drag resistance and their corresponding peripheral conditions are summarized in Table 6. The list of values shows that the respective effectiveness maxima of individual molecular weights lie at different Reynolds numbers (see Fig. 24). 

Summary. We demonstrate that in a wide range of temperatures Coulomb drag between two weakly coupled quantum wires is dominated by processes with a small interwire momentum transfer. Such processes, not accounted for in the conventional Luttinger liquid theory, cause drag only because the electron dispersion relation is not linear. The corresponding contribution to the drag resistance scales with temperature as T2 if the wires are identical, and as T5 if the wires are different. 

In this paper we demonstrate that the drag resistivity between weakly coupled wires is dominated by the forward scattering in a wide temperature range. Even for identical wires, which is the most favorable for backscattering case, ro oc T2 wins over r2kF at all T above T ep(lo/hkF )1/(1+7. For different wires, r2kF is exponentially small at T < udn, whereas ro has a power-law low-temperature asymptotics here Sn is the mismatch of the electron densities between the wires and u is the characteristic plasma velocity hereafter we sc I, h 1. 

Drag Resistance in Terms of the Density-Density Correlation Function... 

Fig. 2. Sketch of the temperature dependence of the drag resistivity between identical wires. The small momentum transfer contribution considered in this paper dominates at T > T the ratio T /cf is exponentially small for kpd > 1. ...

Equation 1.32 for the region close to the wall is illustrated in Fig. 1.6. The flow velocity is maximal at the plane of shear and then decays quickly as we move away from the wall. This should not be surprising as in a column packed with uncharged particles, EOF is generated at the tube wall and the interior of the tube contributes only the drag resistance. It should be noted that the flow velocity falls significantly as soon as we move a distance of one particle diameter away from the column wall. Previous experimental studies on packed beds that have been published in the literature support these findings [55]. 

For more information, see the recent review on the progress in overcoming drag resistance and on the development of new antibiotics [57]. 

When appropriate material systems are not available for model experiments, accurate simulation of the working conditions of an industrial plant on a laboratory- or bench-scale may not be possible. Under such conditions, experiments on differently sized equipment are customarily performed before extrapolation of the results to the full-scale operation. Sometimes this expensive and basically unreliable procedure can be replaced by a well-planned experimental strategy. Namely, the process in question can be either divided up into parts which are then investigated separately (Example 9 Drag resistance of a ship s hull after Froude) or certain similarity criteria can be deliberately abandoned and then their effect on the entire process checked (Example 41/2 Simultaneous mass and heat transfer in a catalytic fixed bed reactor after Damkohler). 

Naturally, the results of dimensional analysis discussed above and their consequences were not known to the ship builders of the 19th century. Since the time of Rankine, the total drag resistance of a ship has been divided into three parts the surface friction, the stern vortex and the bow wave. However, the concept of Newtonian mechanical similarity, known at that time, only stated that for mechanically similar processes the forces vary as F p l2 v2. Scale-up was not considered for assessing the effect of gravity. 

J. Pawlowski [21] discussed an interesting alternative experimental approach to this scale-up problem. He also started by splitting the drag resistance into friction, depending only on Re, and a bow wave resistance, depending only on Fr ... 

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