Showing papers by "University of Twente published in 1977"

Biodegradability and tissue reaction of random copolymers of L-leucine, L-aspartic acid, and L-aspartic acid esters

Abstract: A series of copoly(α-amino acids) with varying percentages of hydrophilic (l-aspartic acid) and hydrophobic monomers (l-leucine, s-methyl-l-aspartate, and s-benzyl-l-aspartate) were implanted subcutaneously in rats and the macroscopic degradation behavior was studied. Three groups of materials (A, B, C) with different ranges of hydrophilicity were distinguished: A) hydrophobic materials showed no degradation after 12 weeks; B) more hydrophilic materials revealed a gradual reduction in size of the samples, but were still present after 12 weeks; and C) hydrophilic copolymers disappeared within 24 hr. The tissue reactions caused by the materials of group A resembled that of silicone rubber, whereas those of group B showed a more cellular reaction.

Designing curved surfaces with analytical functions

Abstract: Shaping and computer-interactive design of curved surfaces of industrial objects, where artistic freedom is allowed for the outward appearance, is a time-consuming job particularly when feeding the computer program with the necessary geometrical input data. A design method is presented together with practical results of designed surfaces composed of simple analytical functions. Human input of geometrical and artistic data has been minimized. Smoothness and fairness are created by the surface composing functions.

Extensions of Language Families and Canonical Forms for Full AFL-Structures

Abstract: We consider the following ways of extending a family of languages $K$ to an "enriched" family $X(K)$: (i) hyper-algebraic extension ($X = H$) based on iterated parallel substitution, (ii) algebraic extension ($X = A$) obtained by nested iterated substitution, (iii) rational extension ($X = R$) achieved by not-self-embedding nested iterated substitution, and (iv) a few subrational extensions ($X = M, S, P, F, C$) based on several kinds of substitution. We introduce full $X$-AFL's, i.e. nontrivial families closed under finite substitution, intersection with regular sets and under $X$, which turn out to be equivalent to well-known AFL-structures such as full hyper-AFL ($X = H$), super-AFL ($A$), substitution-closed AFL ($R$), semi-AFL ($S$), etc. Then we establish Canonical Forms for the smallest full $X$-AFL $\hat{\cal X}(K)$ containing $K$, i.e. we decompose the operator $\hat{\cal X}$ into simpler operators. Using Canonical Forms for full $X$-AFL's we obtain expressions for the smallest full $X$-AFL containing the result of substituting a family of languages into another family.

Are Inclined Screw-Blades for Vertical Grain Augers Advantageous?

Abstract: DUE to modern technology, screw-blades are often manufactured by rolling them out of one single strip of steel. When simultaneously some blade-inclination is applied, less residual stresses and/or larger possible ratios between outer- and shaft-diameter are claimed by some manufacturers, which seems plausible. However, it is sometimes also claimed that the efficiency of the conveyors is increased by such an inclined blade. The underlying idea is that the blade will cause extra pressure between the material to be conveyed and the tube of the conveyor. This in turn would delay the angular speed of the material, thus resulting in a steeper upward motion. In order to investigate this phenomenon previous investigations based upon the conveyance of a single pointmass have been modified for an inclined screw-blade. It appeared that such a blade has no significant advantages over a normal one, which was confirmed by a series of tests. For completeness also tests were carried out with a leading screw, resulting in worse results. In case the pitch equals the diameter and for friction-coefficients of 0.3 at both screw-blade and tube-wall, an increase of no more than 5 percent in capacity will occur, even for blade inclination-angles up to 30 deg. At the same time, however, the efficiency can drop by 15 percent.

Three Notes on Controlled Hyper-Algebraic and Dhyper-Algebraic Extensions

Abstract: (1) Regular control does not increase the generating power of 1-restricted [d]$K$-iteration grammars provided that $K\supseteq{\rm SYMBOL}$, and $K$ is closed under isomorphism and under union with ${\rm SYMBOL}$-languages. (2) Let $\Gamma$ be a prequasoid closed under the regular operations. If $K$ is a prequasoid [pseudoid], then $H(\Gamma)\subseteq H(\Gamma,K)$ [$\eta(\Gamma) \subseteq\eta(\Gamma,K)$. In particular we have $H(\Gamma) \subseteq (\Gamma){\rm ETOL}$ and $\eta(\Gamma) \subseteq (\Gamma){\rm EDTOL}$.(3) Underweak assumptions on $\Gamma$ and $K$, the decidability of the emptiness problem for $\Gamma$ and $K$ implies the decidability of the emptiness problem and the membership problem for the families $\eta(\Gamma,K)$ and $\eta(K)$.