Time-Dependent Anisotropic Wetting Behavior of Deterministic Structures of Different Strut Widths on Ti6Al4V

This study investigated the wetting behavior of Ti6Al4V surfaces that were groove-structured by means of femtosecond laser irradiation. The material was treated under ambient air conditions by use of a laser wavelength of 1030 nm and a pulse duration of 300 fs. Highly accurate structures with a gap width of 20 µm, a gap depth of 10 µm, and varying strut widths (1–300 µm) were generated and the contact angles in parallel and perpendicular direction were determined using sessile drop method with ultrapure water 1, 8, and 15 days after irradiation. All deterministic surfaces exhibited a pronounced contact angle change over time. The structures showed a strong anisotropic wetting behavior with a maximum contact angle aspect ratio of 2.47 at a strut width of 40 µm and a maximum difference between the parallel and perpendicular contact angle of 47.9° after 1 day.

Non-deterministic structures of computation

Divergence and non-determinism play a fundamental role in the theory of computation, and their combined effect on computational equality deserves further study. By looking at the issue from the point of view of both computation and interaction, we are led to a canonical equality for non-deterministic computation, revealing its rich algebraic structure. We study this structure in three ways. First, we construct a complete equational system for finite-state non-deterministic computation. The challenge with such a system is to find an equational alternative to fixpoint inductionà laMilner. We establish a negative result in the form of the non-existence of a finite equational system for the canonical equality of non-deterministic computation to support our approach. We then investigate infinite-state non-deterministic computation in the light of definability and show that every recursively enumerable set is generated by an unobservable process. Finally, we prove that, as far as computation is concerned, the effect produced jointly by divergence and non-determinism is model independent for a large class of process models.We use C-graphs, which are interesting in their own right, as abstract representations of the computational objects throughout the paper.

Application of Proper Orthogonal Decomposition Technique in Wind Engineering of Structures

Dynamic wind pressures acting on structures are complicated functions of both time and space. The proper orthogonal decomposition technique (POD) is a method of detecting a new coordinate system which can most efficiently represent such random wind pressure fields to identify hidden deterministic structures. In this paper, the POD technique is applied to dynamic wind pressures on spatial structures in order to investigate the properties of these pressures and enable to understand the phenomena better. The results indicate that the POD technique can greatly reduce the amount of data that needs to be stored to re-examine the random wind pressure, which can be reconstructed by only a few dominant modes. It requires 5 modes with an accumulative proportion of 70~80% approximately. Moreover, the dominant modes can describe the spatial distributions of the fluctuating wind load effectively.