Connections and Divisions in On Certainty

The central claim of this paper is that On Certainty (1969)\ud is not to be seen as a "work� of Wittgenstein, but as an\ud assemblage from the enormous collection of material that\ud constitutes the Nachlass (cf. Stern 1996; Ackermann 1998;\ud Hintikka 1991). To substantiate this assertion, I will\ud critically compare the publication to its sources, namely\ud manuscripts 172, 174, 175, 176 and 177 of the Nachlass. I\ud will trace and value the decisions G.E.M. Anscombe and\ud G.H. von Wright have made in gathering this collection.\ud Their claim is twofold: first, Wittgenstein "marked it [On\ud Certainty] off in his notebooks as a separate topic�, and\ud second "it constitutes a single sustained treatment of the\ud topic� (Wittgenstein 1969, Preface). I will show that the first\ud claim is incorrect: not only are Wittgenstein"s "marks�\ud ambiguous, but the editors applied their own demarcations\ud in these notebooks as well. Their second claim is in need\ud of amplification. Wittgenstein"s concern with epistemological\ud issues is not limited to these five manuscripts: other\ud notebooks of the same period also contain entries that\ud strongly relate to topics discussed in On Certainty. I will\ud discuss examples from the undated notebooks MSS 169,\ud 170 and 171, published in Last Writings on the Philosophy\ud of Psychology, Vol. II: The "Inner� and the "Outer� (1992).\ud These show that it is difficult to make strict divisions in the\ud Nachlass in general, and in the late writings of the years\ud 1949-1951 in particular

The effect of the compatibilizer SEBS-g-GMA on the blend PP-PET: virgin and recycled materials

Abstract. In the carpet industry poly(ethylene terephthalate) (PET) and poly(propylene) (PP) are often used together within a single product. Mechanical recycling of these carpets results in a blend of PET and PP, which are immiscible. To enhance impact strength of this waste stream, the compatibilizer SEBS-g-GMA was used. More specific the transferability of earlier results with the compatibilizer, obtained on virgin PET-PP blends with amorphous PET (PETg), was assessed. Firstly, from these blends to blends with semi-crystalline PET (PETe) and secondly, from virgin to recycled materials. Two blends of virgin material were made containing 80 wt% PP and 20 wt% PETg or PETe. The effect of adding 2,5 wt% SEBS-g-GMA was assessed. Subsequently, post-industrial PP (r-PP) and post-consumer PETe (r-PETe) were blended and mechanical properties were measured for blends with and without compatibilizer. An increase in impact strength for the two virgin compatibilized blends (PP:PETg:SEBS-g-GMA and PP:PETe:SEBS-g-GMA) was expected and confirmed. A reduced effect of the compatibilizer on impact strength was observed for the recycled blends, due to the possible presence of contaminants. It was concluded that the results from virgin PETg-PP were directly transferable to virgin PETe-PP, but not entirely to recycled materials

Vascular self-healing of a reinforced concrete beams under 4-point bending

Self-healing materials are inspired on self-healing capabilities of living organisms. For plants, animals and people, the vascular system that distributes nutrients to all parts of the organism is also key for the self-healing capability. In a concrete element, a self-healing approach with an incorporated vascular system possess advantages towards repeatable self-healing and controlled placement of the self-healing system in the areas of interest. This study presents such a vascular system, which is designed to be accessible from outside of the concrete beam. Both clay and inorganic phosphate cement are compared as materials for the vanes of this system. The specimen contain steel reinforcement and are tested by means of 4-point bending, in order to obtain realistic conditions. Ease of construction and placement are discussed. From the experiments it can be seen that repeatable selfhealing is possible, that the system is able to heal multiple cracks at the same time and that cracks can be sealed and mechanical properties restored

In-Plane and Out-of-Plane Charge Dynamics of High-TcT_c Cuprates

We propose a theoretical expression for the $k$- and $\omega$-dependent dielectric function of a stack of two-dimensional layers coupled along the direction perpendicular to the layers, and discuss some of its properties. We argue that the plasma frequencies at $k=0$ should correspond to those which are experimentally obtained from optical measurements on {\em e.g.} La$_{1-x}$Sr$_{x}$CuO$_4$ via the $f$-sum rule analysis, regardless of the fact that such systems are strongly correlated. We discuss some of the ramifications due to strong anisotropy of the charge transport in these systems, and the lack of coherence for the transport in the direction perpendicular to the layers.Comment: 8 pages, postscript, uuencoded gz-compressed .tar fil

Neutron radiography based visualization and profiling of water uptake in (un)cracked and autonomously healed cementitious materials

Given their low tensile strength, cement-based materials are very susceptible to cracking. These cracks serve as preferential pathways for corrosion inducing substances. For large concrete infrastructure works, currently available time-consuming manual repair techniques are not always an option. Often, one simply cannot reach the damaged areas and when making those areas accessible anyway (e.g., by redirecting traffic), the economic impacts involved would be enormous. Under those circumstances, it might be useful to have concrete with an embedded autonomous healing mechanism. In this paper, the effectiveness of incorporating encapsulated high and low viscosity polyurethane-based healing agents to ensure (multiple) crack healing has been investigated by means of capillary absorption tests on mortar while monitoring the time-dependent water ingress with neutron radiography. Overall visual interpretation and water front/sample cross-section area ratios as well as water profiles representing the area around the crack and their integrals do not show a preference for the high or low viscosity healing agent. Another observation is that in presence of two cracks, only one is properly healed, especially when using the latter healing agent. Exposure to water immediately after release of the healing agent stimulates the foaming reaction of the polyurethane and ensures a better crack closure