A GENERALIZED BLOCK BOOTSTRAP FOR SEASONAL TIME SERIES

When time‐series data contain a periodic/seasonal component, the usual block bootstrap procedures are not directly applicable. We propose a modification of the block bootstrap – the generalized seasonal block bootstrap (GSBB) – and show its asymptotic consistency without undue restrictions on the relative size of the period and block size. Notably, it is exactly such restrictions that limit the applicability of other proposals of block bootstrap methods for time series with periodicities. The finite‐sample performance of the GSBB is also illustrated by means of a small simulation experiment.     

Suitability of VVC and HEVC for Video Telehealth Systems

Video compression in medical video streaming is one of the key technologies associated with mobile healthcare. Seamless delivery of medical video streams over a resource constrained network emphasizes the need of a video codec that requires minimum bitrates and maintains high perceptual quality. This paper presents a comparative study between High Efficiency Video Coding (HEVC) and its potential successor Versatile Video Coding (VVC) in the context of healthcare. A large-scale subjective experiment comprising of twenty-four non-expert participants is presented for eight different test conditions in Full High Definition (FHD) videos. The presented analysis highlights the impact of compression artefacts on the perceptual quality of HEVC and VVC processed videos. Our results and findings show that VVC clearly outperforms HEVC in terms of achieving higher compression, while maintaining high quality in FHD videos. VVC requires upto 40% less bitrate for encoding an FHD video at excellent perceptual quality. We have provided rate-quality curves for both encoders and a degree of overlap across both codecs in terms of perceptual quality. Overall, there is a 71% degree of overlap in terms of quality between VVC and HEVC compressed videos for eight different test conditions.     

Growth of thin Ag films produced by radio frequency magnetron sputtering

Thin Ag films in the thickness range D = 14–320 nm were deposited by radio frequency magnetron sputtering on glass substrates at room temperature inside a vacuum chamber with base pressure of about 5 × 10^− 6 Pa. The growth of the films was studied via X-ray diffraction and atomic force microscopy experiments. The two techniques are complementary and give us the opportunity to study the surface roughness, the statistical distribution and the average value of the grain size, as well as the texture of the samples. It is shown that the film roughness increases negligibly within the first 60 atomic layers of growth. The thicker films (D 300 nm) develop a nanocrystalline structure with a root mean square roughness of about 2.5 nm. The grain size evolves linearly with the thickness from 9.4 nm at D = 54 nm to 31.6 nm at D = 320 nm.     

Thermochromic composite fibres containing liquid crystals formed via melt extrusion

A three-layered composite fibre has been generated via a modified wire-coating melt co-extrusion process. The continuous fibre consists of a thermochromic liquid crystalline (TLC) layer encapsulated between a transparent polypropylene outer sheath and a black polyether ether ketone inner core. The fibres exhibit clear thermochromic behaviour consistent with the behaviour of unincorporated TLCs, and have been formed into a textile. The presence of the black inner core was found to be the key for the clear retention of colour within the fibres against both white and black backgrounds. The temperature-sensitive fibres and textiles can be applied to a variety of thermal mapping applications, such as in the medical and engineering fields, due to the tunable nature of TLCs.     

An automatic optimization method for minimizing supporting structures in additive manufacturing

The amount of supporting structure usage has been a major research topic in layer-based additive manufacturing (AM) over the past years as it leads to increased fabrication time and decreased surface quality. Previous studies focused on deformation and topology optimization to eliminate the number of support structures. However, during the actual fabrication process, the properties of shape and topology are essential. Therefore, they should not be modified casually. In this study, we present an optimizer that reduces the number of supporting structures by identifying the prime printing direction. Without rotation, models are projected in each direction in space, and the basis units involved in the generation of support structures are separated. Furthermore, the area of the supporting structures is calculated. Eventually, the prime printing direction with minimal supporting area is obtained through pattern-searching method. The results of the experiment demonstrated that the printing area was reduced by up to 60% for some cases, and the surface quality was also improved correspondingly. Furthermore, both the material consumption and fabrication time were decreased in most cases. In future work, additional factors will be considered, such as the height of the supporting structures and the adhesion locations to improve the efficiency of this optimizer.The full text can be downloaded at https://link.springer.com/content/pdf/10.1007%2Fs40436-019-00277-y.pdf     

Co-located pressure-correction formulations on unstructured 2-D grids

 By extending a Navier–Stokes solution method for structured grids (SGs), a pressure-correction, finite-volume formulation for the numerical solution of laminar, incompressible, 2-D flows on unstructured grids (UGs) with triangular elements has been deviced. Since a co-located storage arrangement for all of the flow variables is used, the velocity and pressure fields should be artificially coupled. This is achieved through the careful extension of the Pressure-Weighted Interpolation Method (PWIM), successfully used for SGs in the past. In the first part of the paper, the method formulation for UGs is analyzed. Then, the PWIM for UGs and the boundary conditions' implementation along solid walls are investigated, on the basis of two flow problems.