POLISHING OF POLYCRYSTALLINE DIAMOND COMPOSITES

This thesis aims to establish a sound scientific methodology for the effective and efficient polishing of thermally stable PCD composites (consisting of diamond and SiC) for cutting tools applications. The surface roughness of industrial PCD cutting tools, 0.06 μm Ra is currently achieved by mechanical polishing which is time consuming and costly because it takes about three hours to polish a 12.7 mm diameter PCD surface. An alternative technique, dynamic friction polishing (DFP) which utilizes the thermo-chemical reactions between the PCD surfaces and a catalytic metal disk rotating at high peripheral speed has been comprehensively investigated for highly efficient abrasive-free polishing of PCD composites. A special polishing machine was designed and manufactured in-house to carry out the DFP of PCD composites efficiently and in a controllable manner according to the requirements of DFP. The PCD polishing process and material removal mechanism were comprehensively investigated by using a combination of the various characterization techniques: optical microscopy, SEM and EDX, AFM, XRD, Raman spectroscopy, TEM, STEM and EELS, etc. A theoretical model was developed to predict temperature rise at the interface of the polishing disk and PCD asperities. On-line temperature measurements were carried out to determine subsurface temperatures for a range of polishing conditions. A method was also developed to extrapolate these measured temperatures to the PCD surface, which were compared with the theoretical results. The material removal mechanism was further explored by theoretical study of the interface reactions under these polishing conditions, with particular emphasis on temperature, contact with catalytic metals and polishing environment. Based on the experimental results and theoretical analyses, the material removal mechanism of dynamic friction polishing can be described as follows: conversion of diamond into non-diamond carbon takes place due to the frictional heating and the interaction of diamond with catalyst metal disk; then a part of the transformed material is detached from the PCD surface as it is weakly bonded; another part of the non-diamond carbon oxidizes and escapes as CO or CO2 gas and the rest diffuses into the metal disk. Meanwhile, another component of PCD, SiC also chemically reacted and transformed to amorphous silicon oxide/carbide, which is then mechanically or chemically removed. Finally an attempt was made to optimise the polishing process by investigating the effect of polishing parameters on material removal rate, surface characteristics and cracking /fracture of PCD to achieve the surface roughness requirement. It was found that combining dynamic friction polishing and mechanical abrasive polishing, a very high polishing rate and good quality surface could be obtained. The final surface roughness could be reduced to 50 nm Ra for two types of PCD specimens considered from pre-polishing value of 0.7 or 1.5 μm Ra. The polishing time required was 18 minutes, a ten fold reduction compared with the mechanical abrasive polishing currently used in industry

2-Nitro-N′-[1-(pyridin-2-yl)ethyl­idene]benzohydrazide

In the title compound, C14H12N4O3, the dihedral angle between the benzene ring and the pyridine ring is 60.9 (2)°. The major twist in the mol­ecule occurs about the (NH)—(CO)—Car—Car (ar = aromatic) bond, the relevant torsion angle being 63.97 (12)°. In the crystal, inversion dimers linked by pairs of N—H⋯O hydrogen bonds generate R 2 2(8) loops

Modeling Information Acquisition and Social Learning Dynamics: A Rational Inattention Perspective

Social learning, a fundamental process through which individuals shape their beliefs and perspectives via observation and interaction with others, is critical for the development of our society and the functioning of social governance. Prior works on social learning usually assume that the initial beliefs are given and focus on the update rule. With the recent proliferation of online social networks, there is an avalanche amount of information, which may significantly influence users' initial beliefs. In this paper, we use the rational inattention theory to model how agents acquire information to form initial beliefs and assess its influence on their adjustments in beliefs. Furthermore, we analyze the dynamic evolution of belief distribution among agents. Simulations and social experiments are conducted to validate our proposed model and analyze the impact of model parameters on belief dynamics.Comment: 10 pages, 6 figures, submitted to ICASSP 202

Periodontal health and quality of life in patients with chronic obstructive pulmonary disease

SummaryObjectiveTo evaluate the association of periodontal health and parameters of quality of life assessed in 306 Chinese patients with chronic obstructive pulmonary disease (COPD).MethodsPeriodontal status and respiratory function in 306 COPD patients were clinically evaluated and their quality of life was assessed using the standardized St George’s Respiratory Questionnaire (SGRQ).ResultsThe SGRQ scores were all significantly correlated with major lung function parameters (r2 = −0.37 to −0.28; all p < 0.0001) and Medical Research Council dyspnoea scale (r2 = 0.23 to 0.30; all p < 0.0001). The SGRQ scores also correlated with the 6-min walk test (r2 = −0.15 to −0.13; all p < 0.05). Of periodontal health parameters, missing tooth number and plaque index appeared to be related to the scores of quality of life. The age- and gender-adjusted Pearson’s correlation coefficients between missing teeth and total score, symptoms score, and activity score were 0.09, 0.12, and 0.12, respectively (all p < 0.05). The Pearson’s correlation coefficients between plaque index and symptoms score and activity score were 0.09 and 0.09 (p < 0.05). After adjusting for age, gender, body mass index, and smoking status, missing teeth remained significantly associated with symptom score (p = 0.030) and activity score (p = 0.033) while plaque index was significantly associated with symptom score (p = 0.007).ConclusionsPoor periodontal health as reflected by missing teeth and plaque index was significantly associated with lower quality of life in COPD patients. Our findings indicate the importance of promoting dental care in current public health strategies to improve the quality of life in COPD patients