Syntactic

In a recent report (79), a 150—200 mg/cm Parylene C coating provided protection against moisture uptake by three-phase, polyimide, microballoons, and air, syntactic foams. In a previously reported coating of a similar foam, the stated purpose was strengthening (80). 

Syntactic Cellular Polymers. Syntactic cellular polymer is produced by dispersing rigid, foamed, microscopic particles in a fluid polymer and then stabilizing the system. The particles are generally spheres or microhalloons of phenoHc resin, urea—formaldehyde resin, glass, or siUca, ranging 30—120 lm dia. Commercial microhalloons have densities of approximately 144 kg/m (9 lbs/fT). The fluid polymers used are the usual coating resins, eg, epoxy resin, polyesters, and urea—formaldehyde resin. 

PhenoHc MicrobaUoons appHcations in plastics take advantage of low density, porosity, and surface-to-volume ratio to produce lightweight parts. Probably the most notable example is the syntactic foam. 

A mixture of PhenoHc MicrobaUoons and resin binder has a putty-like consistency. It can be molded to shape, troweUed onto surfaces, or pressed into a core. Curing gives a high strength, low density (0.144 g/cm ) foam free of voids and dense areas, and without a brittle skin. Syntactic foams are used in widely diverse appHcations, including boat flotation aids stmctural parts in aircraft, submarines, and missiles stmctural cores for waU panels and ablative heat shields for reentry vehicles and rocket test engines. 

A progressive etching technique (39,40), combined with x-ray diffraction analysis, revealed the presence of a number of a polytypes within a single crystal of sihcon carbide. Work using lattice imaging techniques via transmission electron microscopy has shown that a-siUcon carbide formed by transformation from the P-phase (cubic) can consist of a number of the a polytypes in a syntactic array (41). 

In addition to developing solid RP structures, work has been conducted on sandwich structures such as filament-wound plastic skins with low-density foamed core or a plastic honeycomb core to develop more efficient strength-to-weight structures. Sandwich structures using a syntactic core have been successfully tested so that failures occurred at prescribed high-hydrostatic pressures of 28 MPa (4,000 psi). 

In the Woods Hole Oceanographic Institute s three-man 1,800 m (6,000 ft.) depth vehicles, approximately 5,000 lb. of syntactic foam were used to provide buoyancy. With a specific gravity of 0.68, it required three pounds of material to gain one pound of... 

Property ASTM Test Phenolics Foamedin Syntactic Place Castable Polyvinyl Chloride Rigid Closed Cell Phenylene Oxide Foamable Resin Polycarbonate Polystyrene Medium-Density Foam Polystyrene Molded Extruded Polyurethane Rigid Closed Cell... 

Syntactic foam contains an orderly arrangement of hollow sphere fillers. They are usually glass microspheres approximately 100 microns (4 mils) in diameter, provide strong, impervious supports for otherwise weak, irregular voids. As a result, syntactic foam has attracted considerable attention both as a convenient and relatively lightweight buoyancy material and as a porous solid with excellent shock attenuating characteristics. The latter characteristic is achieved... 

Interest in the use of syntactic foam as a shock attenuator led to studies of its static and dynamic mechanical properties. Particularly important is the influence of loading rate on stiffness and crushing strength, since oversensitivity of either of these parameters can complicate the prediction of the effectiveness of a foam system as an energy absorber. 

Results of uniaxial strain static and gas gun compression tests on syntactic foam have been conducted. The foam was buoyant and composed of hollow glass microspheres (average diameter 100 microns) embedded in an epoxy plastic. Static testing consists of compressing a 0.25 cm x 2.5 cm dia. wafer between carefully aligned 2.5 cm dia. steel pistons. Lateral expansion of the wafer is... 

Test results provides the hypothesis that syntactic foam is rate insensitive and that the static uniaxial strain stress-strain curve actually represents the general constitutive relation. Disagreement between the experimental data and the predicted behavior is greatest at low stresses (1 kbar) where experimental stresses are about double those predicted analytically. The discrepancy decreases at the higher stress levels and virtually disappears at and beyond 7 kbar. This range... 

We use the term philosophical substructure of a curriculum (Van Berkel, 2005, pp. 33, 52), whereas Schwab uses the term syntactical or also methodological substructure. The philosophical substructure of a curriculum contains besides methodological assumptions a number of, often implicit, philosophical foundations of a curricnlnm. 

Schwab (1964a, p. 14) describes the syntactical or methodological snbstmcture of a discipline thus ... 

Further, Schwab (1964b, pp. 10, 11) emphasises that to each of the possible substantive substmctures of a disciphne there corresponds a distinctive syntactical snbstracture ... 

In chemistiy, for example, it is the case that the different substantive substmctures of the atomic-molecular theoiy and thermodynamics correspond to different syntactical substmctures in terms of the manner and the extent to which each can verify its knowledge (...) the kind of evidence, and the degree to which it is evidential (Schwab, 1964b, p. 11). 

Schwab discusses the philosophical (syntactical) sub-stmcture of the disciplines in education or pedagogy, listing and emphasising each time the educational significance of his concepts (Schwab, 1962, p. 205) ... 

Both of these - the conceptual and the syntactical [philosophical] - are different in different diseiplines. The significance for education of these diverse structures lies preeisely in the extent to whieh we want to teach what it is true and have it understood . 

The use of Schwab s idea of the substractures of a discipline, introduced into this book by Van Berkel, Pilot and Bnlte, may serve as a framework for the ideal cnrricnlnm. However, they take a more practical form when setting ont the formal cnrricnlnm. Schwab (1964) divided a discipline into three parts for edncational pnr-poses - the snbstantive, the syntactical and the pedagogical. In an actual curriculum, these three are interlocked. However, for the pnrposes of analysis, taking each in tnm ... 

This is the framework of teaching and learning methods that are nsed to communicate the substantive and syntactical stmcture of a snbject. This framework has been... 

Programming languages for the LCAP systems comprises traditional FORTRAN and FORTRAN-like directives which are interpreted by a precompiler developed in our laboratory. The directives provide syntactical constructs for interprocessor communication and synchronization. A detailed description of the implementation of our quantum chemistry package HONDO has been given elsewhere. (Dupuis, M. Watts, J. D. Theor. Chim. Acta, in press.) Our experience indicates that the calculations done in the study described above were executed in parallel at a very high level of efficiency. 

If a signal is represented by a sequence of triangular episodes, scale-space filtering manipulates the sequences of triangular episodes with very concrete mechanisms. Here is the complete list of syntactic manipulations carried out by scale-space filtering ... 

Fig, 23. (a) The raw data of three distinct records and (b) their corresponding syntactic generalizations. (Reprinted from Bakshi and Stephanopoulos, Representation of Process Trends, Part IV, Computers and Chemical Engineering, 18(4), p. 303, Copyright (1994), with kind permission from Elsevier Science Ltd., The Boulevard, Langford Lane, Kidlington 0X5 1GB. UK). 

Case 2. The syntactic difference is the string B - CD —A) in the middle of the trend, since... 

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