Investigations on a hybrid element with cellular metallic material for heating, cooling and ventilation

Surface heating and cooling systems are gaining more and more importance in building energy technology. In order to implement these systems not only on the floor but also on the ceilings and walls, the thermodynamic requirements are supplemented by constructional requirements. In order to fulfil these requirements, the use of open-cell porous metals for such systems will be investigated in more detail. In addition to the design and manufacturing challenges, a large number of numerical and experimental investigations on test samples are also necessary. These investigations are described and explained in more detail in the following article.

Dynamics analysis of a slender ball-screw feed system considering the changes of the worktable position

For a slender ball-screw feed system, the position of the screw–nut joints will change greatly when the moving worktable moves along its whole stroke. Therefore, the compression/tension and torsion stiffness of the screw-shaft on both sides of the screw–nut joints will change. Thus, the system transmission stiffness will also vary and affect its dynamics. In this article, considering the changes of the worktable position and using hybrid element method, a dynamic model was established for the slender ball-screw feed system, and a calculation method of the system stiffness and mass matrix was provided. The experiments on the slender ball-screw feed system with different positions were also performed to verify the proposed dynamic model. Finally, the influences of length, screw-tension force, pitch, nominal diameter of screw and rated dynamic load of screw-nut joints on the slender ball-screw feed system’s natural frequency along its whole stroke were studied. The results showed that the slender ball-screw feed system possesses obvious position-dependent variable dynamics along its whole stroke; the ratio of length to diameter of the screw ( Lf/ d0) would be better designed smaller than 50 in order to obtain the relative uniformity of the system dynamics when manufacturing large machine tools.

The paribhāṣās in the Śrautasūtras: Problems, Opportunities and Premises for an Investigation

What is a paribhāṣā? How does it work in Śrautasūtra-texts? This paper tries to examine these questions and to trace a story of the paribhāṣās in the Śrautasūtras, giving some indications for future researches. Often translated as “meta-rule”, paribhāṣā is a primary derivative from the Sanskrit root “bhāṣ”, which means “to talk”, with the prefix “pari”, which means “around”, “beyond”. The term indicates a specific discourse “around” or “beyond” something. Therefore, it represents the link with the context, a hybrid element placed between text and context. A paribhāṣā is an explanation, an element around discourse that acts as a frame for what is said: it is a rule that is valid in a wider context than that of the object under analysis, that goes “beyond” discourse. It is a unique opportunity to glance at the ritual in itself, at the “ritual string”, in opposition to every “discourse of the ritual”. This rule’s validity is put into effect through the other rules expressed within the text, in other words it is a meta-rule. However, the subject of the relationship between paribhāṣās and the texts of the śruti is still uncharted territory: the categorizations that have so far been suggested are weak or not useful, and need stronger foundations. The present paper pretends to be a first step in this direction.