Search for Evergreens in Science: A Functional Data Analysis

Evergreens in science are papers that display a continual rise in annual citations without decline, at least within a sufficiently long time period. Aiming to better understand evergreens in particular and patterns of citation trajectory in general, this paper develops a functional data analysis method to cluster citation trajectories of a sample of 1699 research papers published in 1980 in the American Physical Society (APS) journals. We propose a functional Poisson regression model for individual papers' citation trajectories, and fit the model to the observed 30-year citations of individual papers by functional principal component analysis and maximum likelihood estimation. Based on the estimated paper-specific coefficients, we apply the K-means clustering algorithm to cluster papers into different groups, for uncovering general types of citation trajectories. The result demonstrates the existence of an evergreen cluster of papers that do not exhibit any decline in annual citations over 30 years.Comment: 40 pages, 9 figure

Testing, simulation and optimisation of additively manufactured structural hollow sections

Additive manufacturing (AM) is gaining increasing prominence in the construction industry, offering the potential for enhanced design freedom and reduced material use. However, the performance of additively manufactured metallic structural elements and the possible benefits associated with the attainable optimised geometries have seldom been investigated. The primary aim of this study is therefore to conduct an experimental and numerical investigation of additively manufactured metallic components, considering material behaviour, welded components and optimised tubular profiles. An experimental investigation was first conducted to examine the microstructural and mechanical properties of AM materials. Two grades of powder bed fusion (PBF) stainless steel (316L and CX) were considered, and the weldability and joining characteristics of PBF 316L stainless steel were also examined. The underlying microstructures were characterised and correlated with the measured mechanical properties from tensile coupon tests. At the cross-sectional level, axial compression tests were carried out on PBF circular hollow sections; advanced measuring techniques, including 3D laser-scanning and digital image correlation, were employed in the tests. Finite element (FE) models were developed to replicate the test results and to generate supplementary cross-sectional resistance data. Comparisons between design predictions and the test and FE data were made to evaluate the applicability of the existing codified design rules to additively manufactured cross-sections. In order to increase the axial compressive resistance and to reduce the imperfection sensitivity of very slender circular cross-sections (or cylindrical shells), optimised corrugated shells were sought through the use of the Particle Swarm Optimisation algorithm in conjunction with cross-section profile generation and numerical analyses. An experimental investigation into the cross-sectional behaviour of the resulting optimised shells, additively manufactured by PBF in 316L and CX stainless steels, was undertaken. The test results verified that the corrugated cylindrical shells achieved significantly higher capacities than their circular counterparts and with reduced imperfection sensitivity.Open Acces

ARTERIAL WAVEFORM MEASUREMENT USING A PIEZOELECTRIC SENSOR

This study aims to develop a new method to monitor peripheral arterial pulse using a PVDF piezoelectric sensor. After comparing different locations of sensor placement, a specific sensor wrap for the finger was developed. Its composition, size, and location make it inexpensive and very convenient to use. In order to monitor the effectiveness of the sensor at producing a reliable pulse waveform, a monitoring system, including the PZT sensor, ECG, pulse-oximeter, respiratory sensor, and accelerometer was setup. Signal analysis from the system helped discover that the PZT waveform is relative to the 1st derivative of the artery pressure wave. Also, the system helped discover that the first, second, and third peaks in PZT waveform represent the pulse peak, inflection point, and dicrotic notch respectively. The relationship between PZT wave and respiration was also analyzed, and, consequently, an algorithm to derive respiratory rate directly from the PZT waveform was developed. This algorithm gave a 96% estimating accuracy. Another feature of the sensor is that by analyzing the relationship between pulse peak amplitude and blood pressure change, temporal artery blood pressure can be predicted during Valsalva maneuver. PZT pulse wave monitoring offers a new type of pulse waveform which is not yet fully understood. Future studies will lead to a more broadly applied use of PZT sensors in cardiac monitoring applications