Slipping approach

Asakawa M, Ashton PR, Ballardini R, Balzani V, Belohradsky M, Gandolfi MT, Kocian O, Prodi L, Raymo EM, Stoddart JF, Venturi M (1997) The slipping approach to self-assembling [n]rotaxanes. J Am Chem Soc 119 302-310... 

Figure 12. The slipping approach to the [2]rotaxane 14-PF6 and its solid-state structure.

The synthesis of 94 is noteworthy, because no templating interactions seem to be required to form the rotaxane in preparative yields The slipping approach performed in the melt seems to offer universal access to otherwise not obtainable rotaxanes. The absence of solvent not only assists this slipping by guaranteeing high concentrations, but also eases the reaction because no desolvation processes need to take place. 

Figure 35. Schematic representation depicting the self organization of rotaxane-like entities using the slipping approach in the melt (high concentrations of wheel and axle). R Rotax-ane where the hydrogen bonds between wheel and axle have not yet been formed. R Rot-axane with hydrogen bonds between wheel and axle. Entropy loss upon formation of the mechanical bond is not considered in the graph.

The amide hydrogen-bonding motif has been shown to support the clipping, threading, and slipping approaches to the formation of rotaxanes. The wide scope of the neutral template synthesis is enriched by the promising possibilities of the non-template synthesis performed in the melt. Numerous rotaxanes were obtained on a preparative scale and are available for further chemistry. 

Slipping approach is effective for the preparation of oligorotaxane based on crown ether and secondary ammonium salt because the inclusion complex is fairly stable. When dibenzo-30-crown-10 (DB30C10) was used as the wheel component, 3,5-di-ferf-butylphenyl group is the complementary end-cap to the crown ether. DB30C10 slips over the 3,5-di-ferf-butylphenyl group... 

When conferred with a hydrophilic head (in this case a substituted trityl unit), and a hydrophobic (benzylic alcohol) tail, rotaxanes - branched [55] or otherwise - can be formed into Langmuir films in a manner similar to catenanes. Rotaxane 224+ - synthesized from its corresponding thread via the slipping approach - when incorporated into a device in a manner similar to the catenane 214+ also exhibited interesting electron-transport properties [56], Unlike the catenane-based device, there is no switching element built into the molecule. However, like the switchable catenane, the rotaxane 224+ has electroactive bipyridinium sites, whose presence can mediate the tunneling of... 

The slip approach defines the onset of surface defects as related to a slippage of the polymer at the die wall. Accordingly, the zero-wall velocity concept, as used in the constitutive approach, does not apply. Many attempts have been made to experimentally measure the velocity at the wall, however, with mixed success. Still, theories have been developed which support a shear-dependent slippage at a polymer/ solid interface. Slippage may be understood as the buildup of a layer of polymer molecules bonded to the die surface, which undergo a coil-stretch transition under the shear stress. In light of this understanding, the microscopic shp layer development may be in line with the possible formation of a macroscopic surface layer as a consequence of a many... 

Ceramic slips approach Newtonian behaviour when completely deflocculated. (cf. bingham body dilatancy rheopexy thixotropy) Nextel. Trade-name. 3M Corp. Mullite fibres. 

The presence of surface conductance behind the slip plane alters the relationships between the various electrokinetic phenomena [83, 84] further complications arise in solvent mixtures [85]. Surface conductance can have a profound effect on the streaming current and electrophoretic mobility of polymer latices [86, 87]. In order to obtain an accurate interpretation of the electrostatic properties of a suspension, one must perform more than one type of electrokinetic experiment. One novel approach is to measure electrophoretic mobility and dielectric spectroscopy in a single instrument [88]. 

Clearly then, the continuum approach as outlined above is faulty. Furthermore, since our erroneous result depends only on the non-slip boundary condition for V together with the Navier-Stokes equation (4.3), one or... 

Boundary layer flows are a special class of flows in which the flow far from the surface of an object is inviscid, and the effects of viscosity are manifest only in a thin region near the surface where steep velocity gradients occur to satisfy the no-slip condition at the solid surface. The thin layer where the velocity decreases from the inviscid, potential flow velocity to zero (relative velocity) at the sohd surface is called the boundary layer The thickness of the boundary layer is indefinite because the velocity asymptotically approaches the free-stream velocity at the outer edge. The boundaiy layer thickness is conventionally t en to be the distance for which the velocity equals 0.99 times the free-stream velocity. The boundary layer may be either laminar or turbulent. Particularly in the former case, the equations of motion may be simphfied by scaling arguments. Schhchting Boundary Layer Theory, 8th ed., McGraw-HiU, New York, 1987) is the most comprehensive source for information on boundary layer flows. 

As flooding is approached, the slip velocity continues to decrease until at the flood point is zero and the following relationship apphes ... 

When the size of a particle approaches the same order of magnitude as the mean free path of the gas molecules, the setthng velocity is greater than predicted by Stokes law because of molecular shp. The slip-flow correc tion is appreciable for particles smaller than 1 [Lm and is allowed for by the Cunningham correc tion for Stokes law (Lapple, op. cit. Licht, op. cit.). The Cunningham correction is apphed in calculations of the aerodynamic diameters of particles that are in the appropriate size range. 

The use of a model of human error allows a systematic approach to be adopted to the prediction of human failures in CPI operations. Although there are difficulties associated with predicting the precise forms of mistakes, as opposed to slips, the cognitive approach provides a framework which can be used as part of a comprehensive qualitative assessment of failure modes. This can be used during design to eliminate potential error inducing conditions. It also has applications in the context of CPQRA methods, where a comprehensive qualitative analysis is an essential precursor of quantification. The links between these approaches and CPQRA will be discussed in Chapter 5. 

The slip for this type of compressor is similar to that of the lobe units however, the passages are basically different, and this changes the approach to slip correction. The manufacturer should be consulted for data specific to a particular unit. The slip is dependent on the pressure differential across the unit and the gas density. It does not vary with speed or length of the rotor. 

The above results show close agreement between the experimental and theoretical friction factor (solid line) in the limiting case of the continuum flow regime. The Knudsen number was varied to determine the influence of rarefaction on the friction factor with ks/H and Ma kept low. The data shows that for Kn < 0.01, the measured friction factor is accurately predicted by the incompressible value. As Kn increased above 0.01, the friction factor was seen to decrease (up to a 50% X as Kn approached 0.15). The experimental friction factor showed agreement within 5% with the first-order slip velocity model. 

In the absence of diffusion, all hydrodynamic models show infinite variances. This is a consequence of the zero-slip condition of hydrodynamics that forces Vz = 0 at the walls of a vessel. In real systems, molecular diffusion will ultimately remove molecules from the stagnant regions near walls. For real systems, W t) will asymptotically approach an exponential distribution and will have finite moments of all orders. However, molecular diffusivities are low for liquids, and may be large indeed. This fact suggests the general inappropriateness of using to characterize the residence time distribution in a laminar flow system. Turbulent flow is less of a problem due to eddy diffusion that typically results in an exponentially decreasing tail at fairly low multiples of the mean residence time. 

Since the middle of the 1990s, another computation method, direct simulation Monte Carlo (DSMC), has been employed in analysis of ultra-thin film gas lubrication problems [13-15]. DSMC is a particle-based simulation scheme suitable to treat rarefied gas flow problems. It was introduced by Bird [16] in the 1970s. It has been proven that a DSMC solution is an equivalent solution of the Boltzmann equation, and the method has been effectively used to solve gas flow problems in aerospace engineering. However, a disadvantageous feature of DSMC is heavy time consumption in computing, compared with the approach by solving the slip-flow or F-K models. This limits its application to two- or three-dimensional gas flow problems in microscale. In the... 

In summary, sliding can be regarded as a process during which interfacial atoms would experience a series of stick-slip motions, similar to the jump in and out in the adhesion case, and it is the energy loss in this approach/separation cycle that determines the level of friction. 

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