Re-entrants

Targets and spirals have been observed in the CIMA/CDIMA system [13] and also in dilute flames (i.e. flames close to their lean flammability limits) in situations of enlianced heat loss [33]. In such systems, substantial fiiel is left unbumt. Spiral waves have also been implicated in the onset of cardiac arrhytlnnia [32] the nomial contractive events occurring across the atria in the mannnalian heart are, in some sense, equivalent to a wave pulse initiated from the sino-atrial node, which acts as a pacemaker. If this pulse becomes fragmented, perhaps by passing over a region of heart muscle tissue of lower excitability, then spiral structures (in 3D, these are scroll waves) or re-entrant waves may develop. These have the incorrect... 

Solvent-excluded surfaces correlate with the molecular or Connolly surfaces (there is some confusion in the literature). The definition simply proceeds from another point of view. In this c ase, one assumes to be inside a molecaile and examines how the molecule secs the surrounding solvent molecules. The surface where the probe sphere does not intersect the molecular volume is determined. Thus, the SES embodies the solvent-excluded volume, which is the sum of the van der Waals volume and the interstitial (re-entrant) volume (Figures 2-119. 2-120). 

Fig. l.fi. The van tier Waals (vdw) surface of a molecule corresponds to the outward-facing surfaces of the van der Waak spheres of the atoms. The molecular surface is generated hy rolling a spherical probe (usually of radius 1.4 A to represent a mater molecule) on the van der Wools surface. The molecular surface is consiructed from contact and re-entrant surface elements. The centre of the probe traces out the accessible surface. 

Etch Profiles. The final profile of a wet etch can be strongly influenced by the crystalline orientation of the semiconductor sample. Many wet etches have different etch rates for various exposed crystal planes. In contrast, several etches are available for specific materials which show Httle dependence on the crystal plane, resulting in a nearly perfect isotropic profile. The different profiles that can be achieved in GaAs etching, as well as InP-based materials, have been discussed (130—132). Similar behavior can be expected for other crystalline semiconductors. It can be important to control the etch profile if a subsequent metallisation step has to pass over the etched step. For reflable metal step coverage it is desirable to have a sloped etched step or at worst a vertical profile. If the profile is re-entrant (concave) then it is possible to have a break in the metal film, causing an open defect. 

Electrolytic plating rates ate controUed by the current density at the metal—solution interface. The current distribution on a complex part is never uniform, and this can lead to large differences in plating rate and deposit thickness over the part surface. Uniform plating of blind holes, re-entrant cavities, and long projections is especiaUy difficult. 

A situation which is frequently encountered in tire production of microelectronic devices is when vapour deposition must be made into a re-entrant cavity in an otherwise planar surface. Clearly, the gas velocity of the major transporting gas must be reduced in the gas phase entering the cavity, and transport down tire cavity will be mainly by diffusion. If the mainstream gas velocity is high, there exists the possibility of turbulent flow at tire mouth of tire cavity, but since this is rare in vapour deposition processes, the assumption that the gas widrin dre cavity is stagnant is a good approximation. The appropriate solution of dre diffusion equation for the steady-state transport of material tlrrough the stagnant layer in dre cavity is... 

De Bruyne [41] has applied the same principles to other idealised shapes for pores. As would be expected, penetration into a re-entrant ink bottle pore is much less than for cylinders (Fig. 6). The critical importance of contact angle in determining the extent of penetration should be noted. 

Fig. 6. Penetration of a liquid into (a) a cylindrical and (b) a re-entrant pit (after de Bruyne [41 ]). Pit depth 100 pm, diameter at mouth 1 pm, re-entrant angle 45°.

This concept may be invoked to account for electrolyte formation in microcracks in a metal surface or in the re-entrant angle formed by a dust particle and the metal surface. More importantly, it can also explain electrolyte formation in the pores of corrosion product and hence the secondary critical humidity discussed earlier. Ferric oxide gel is known to exhibit capillary condensation characteristic and pore sizes deduced from measurements of its adsorptive capacity are of the right order of magnitude to explain a secondary critical relative humidity as70 7o for rusted steel . 

Sharp changes in direction, especially where liquids are moving at high velocities, and re-entrant angles, dead spaces and other details where stagnant conditions may result should be avoided. This is particularly important if inhibitors are to be used. 

For protection of sheet-steel piling, the anodes are normally mounted within the re-entrants of the piles to prevent mechanical damage by berthing ships, dredging, etc. (Fig. 10.30). 

The importance of twins lies in the existence of a permanent re-entrant corner at the twin boundary for cases a) and b) — and possibly for c) where it is too small to be detected — and therefore a position at the surface where there is no... 

Many technological applications of liquid crystals, as in electro-optic display devices, are based on multicomponent mixtures. Such systems offer a route to the desired material properties which cannot be achieved simultaneously for single component systems. Mixtures also tend to exhibit a richer phase behaviour than pure systems with features such as re-entrant nematic phases [3] and nematic-nematic transitions possible. In this section, we describe simulations which have been used to study mixtures of thermotropic calamitic mesogens. 

Moreover, the new smectic phases with the broken head-to-tail inversion symmetry (of the type of A, A2, A, etc.) and the re-entrant effects (i.e. the reentrance of the less ordered phase at temperatures below those of a more ordered phase) were found among strongly asymmetric mesogens [11-13, 30] (Fig. 2). These observations indicate that with asymmetric molecules, dipolar and steric interactions are important for the liquid crystalline behaviour. 

These structures were firstly observed for terminally polar mesogens [11, 12]. However, recent experiments give clear evidence of the presence of smectic A layering [37, 38], re-entrant nematic behaviour [39], two-dimensional lattices [40, 41] and smectic layering with incommensurate periodicities [42] for non-polar sterically asymmetric LCs. 

Typical re-entrant piston-bowl design for a small, high-speed direct-injection Cl engine. (From Kook, S., Bae, C., Miles, P.C., Choi, D., Bergin, M., and Reitz, R.D., The Effect of Swirl Ratio and Fuel Injection Parameters on CO emission and Fuel Conversion Efficiency for High-Dilution, Low-Temperature Combustion in an Automotive Diesel Engine, SAE, 2006-01-019 2006. With permission.)... 

RAPP c, LANTZSCH H J, DROCHNER w (2001) Hydrolysis of ph)dic acid hy intrinsic plant and supplemented microbial phytase Aspergillus niger) in the stomach and small intestine of minipigs fitted with re-entrant cannnlas. 3. Hydrolysis of ph)dic acid (1P6) and occurrence of hydrolysis products (1P5,1P4, 1P3 and 1P2). JAnim Physiol Anim Nutr (Berl). 85 420-30. 

Finished multiple seals of this type are shown in Figure 40, 7F and V. The outer tube may be sealed directly to the apparatus for which it is required, or a Dewar seal may first be formed as shown in Figure 50, VII, making the multiple seal re-entrant. The re-entrant form is very useful when, for example, the vnres are directly attached to, and are supporting, electrodes (see p. 157). 

Re-entrant foam provides a counter-intuitive demonstration of processing (5). Polyurethane can be isotropically compressed in a mold and heated to about 170 °C. The microstructure of the resulting solid yields a material that bulges in cross section when stretched More information on polymers will be available from John Droske s complementary NSF-funded project (described in the preceding section). 

Shaped charge. An explosive charge designed to produce specific effects by the inclusion of a re-entrant conical or V shape usually lined with metal. 

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