Singularity-Free Breit Equation from Constraint Two-Body Dirac Equations

We examine the relation between two approaches to the quantum relativistic two-body problem: (1) the Breit equation, and (2) the two-body Dirac equations derived from constraint dynamics. The Breit equation is known to be pathological when singularities appear at finite separations $r$ in the reduced set of coupled equations for attractive potentials even when the potentials themselves are not singular there. They then give rise to unphysical bound states and resonances. In contrast, the two-body Dirac equations of constraint dynamics do not have these pathologies in many nonperturbative treatments. To understand these marked differences, we first express these contraint equations in a hyperbolic form. These coupled equations are then re-cast into two equivalent equations: (1) a covariant Breit-like equation with potentials that are exponential functions of certain ``generator'' functions, and (2) a covariant orthogonality constraint on the relative momentum. This reduction enables us to show in a transparent way that finite-$r$ singularities do not appear as long as the the exponential structure is not tampered with and the exponential generators of the interaction are themselves nonsingular for finite $r$. These Dirac or Breit equations, free of the structural singularities which plague the usual Breit equation, can then be used safely under all circumstances, encompassing numerous applications in the fields of particle, nuclear, and atomic physics which involve highly relativistic and strong binding configurations.Comment: 38 pages (REVTeX), (in press in International Journal of Modern Physics

Effect of milling time on microstructure, crystallite size and dielectric properties of Srtio3 ceramic synthesized via mechanical alloying method

SrTiO3 sample has been successfully prepared by mechanical alloying (MA) method. The effect of milling time on microstructure, crystallite size and dielectric properties of SrTiO3 were studied. The results revealed that the mean crystallite size of milled powders decreased from 84.56 to 12.87 nm with increasing milling time. However, the average lattice strain of milled powders increased from 0.2 to 0.93% with increasing milling time. A single phase SrTiO3 could not be formed with milling alone and required annealing process. A transformation of anatase-TiO2 to rutile-TiO2 was observed at 16 h of milling. After the milled powders were subjected to sintering process at 1200°C, formation of single-phase SrTiO3-type cubic (Pm-3m) perovskite structure was observed. The peak intensities of the sintered SrTiO3 samples decreased as the milling time was increased. For microstructural observations, the average grain size of the sintered SrTiO3 sample milled for 8 h showed the largest. For dielectric measurements, the dielectric constant of the sintered SrTiO3 sample milled for 8 h showed the highest among others. This could be due to the largest grain size obtained for sintered SrTiO3 sample milled for 8 h. The decrease in the grain size with increasing milling time resulted to the decrease in dielectric constant

Fall-related attendance and associated hospitalisation of children and adolescents in Hong Kong: a 12-year retrospective study

Objectives: The present study aimed to examine the trends and characteristics of fall-related attendance in accident and emergency department (AED) by injury type and the trend in associated average length of stay (LOS) among children and adolescents in Hong Kong. Design: A retrospective approach was adopted. Setting: AED, involving all local public emergency departments from 2001 to 2012. Participants: 63 557 subjects aged 0–19 years with fall injury record were included in the analysis. Primary outcome measures: Fall-related injury number and rates were calculated and reported. Poisson and negative binomial regression models were used to study the trends of injury incidence rate at different body regions. Results: AED fall-related attendance rate increased significantly with an annual percentage change of 4.45 (95% CI 3.43 to 5.47%, p<0.0001). The attendance number of male subjects was persistently higher than female subjects. The standardised rate of fracture injury increased by 1.31% (95% CI 0.56 to 2.05%, p<0.0001) and that of non-fracture injury increased by 9.23% (95% CI 7.07 to 11.43%, p<0.0001) annually. Upper limb was the most frequently fractured location. It included forearm/elbow, shoulder/upper arm and wrist/hand with descending order of frequency. On the contrary, head was the most frequent non-fracture location, followed by forearm/elbow. Conclusions: The rates of fall-related attendance have been increasing and still remain high. There were significant increases in non-fracture injuries. Fractures were most frequently found in the upper extremity of a child while the most common non-fracture location was head. It appears that more efforts should be made and preventive measures should be implemented for children and adolescents in Hong Kong

Hong Kong dentists' preparedness for medical emergency in dental clinics

Aim: The aim of this study was to investigate the Hong Kong dentists’ and dental clinics’ preparedness for medical emergency in the dental clinic. Methods: Two custom designed questionnaires were developed, one for dentists and another for dental clinics, to collect the required information. The sampling frame for participants was the list of registered dentists published by the Hong Kong Dental Council on its website in January 2016. A total of 434 dentists and 143 dental clinics were selected from the list by systematic random sampling. The latter sample was supplemented by 10 randomly selected government dental clinics. The questionnaires were mailed the selected dentists together with a cover letter and a stamped return envelope. A reminder letter and another copy of the questionnaire were sent out two weeks after the first mailing. Results: 167 (38%) completed dentist questionnaires and 53 (35%) clinic questionnaires were collected. Most of the respondent dentists had some deficient knowledge on basic life support (BLS), their mean score was 3.5 out of a maximum of 5. Most (>60%) of the respondents thought they were competent in performing medical emergency procedures except giving intravenous injection. Moreover, most (>60%) of them held positive attitude towards having immediate availability of essential medical emergency equipment and drugs in their clinic. Dentists who were more recent graduates, those with postgraduate qualifications, and those who work with accompaniment generally had higher mean BLS knowledge scores. In the dental clinics, the most commonly kept medical emergency equipment/drug was instant glucose (70%) and followed by antihistamine (62%). Only a quarter of the clinics were equipped with AED, and 45% were equipped with oxygen cylinder. For 8 out of the 11 items, a higher proportion of the bigger clinics (>2 dental chairs) than the smaller clinics had the medical emergency equipment/drug available (Chi-square test, p<0.05). Conclusion: Hong Kong dentists have a moderate level of knowledge on BLS which should be enhanced through regular attendance at CE courses. Their knowledge level is affected by a number of their background and professional activities factors. Most dental clinics in Hong Kong have only few of the essential medical emergency equipment and drugs while the larger clinics are better equipped than the smaller clinics.published_or_final_versio

An Algorithm for Modelling Escalator Fixed Loss Energy for PHM and sustainable energy usage

Prognostic Health Management (PHM) is designed to assess and monitor the health status of systems, anticipate the onset of potential failure, and prevent unplanned downtime. In recent decades, collecting massive amounts of real-time sensor data enabled condition monitoring (CM) and consequently, detection of abnormalities to support maintenance decision-making. Additionally, the utilization of PHM techniques can support energy sustainability efforts by optimizing energy usage and identifying opportunities for energy-saving measures. Escalators are efficient machines for transporting people and goods, and measuring energy consumption in time can facilitate PHM of escalators. Fixed loss energy, or no-load energy, of escalators denotes the energy consumption by an unloaded escalator. Fixed loss energy varies over time indicating varying operating conditions. In this paper, we propose to use escalators' fixed loss energy for PHM. We propose an approach to compute daily fixed loss energy based on energy consumption sensor data. The proposed approach is validated using a set of experimental data. The advantages and disadvantages of each approach are also presented, and recommendations are given. Finally, to illustrate PHM, we set up an EWMA chart for monitoring the fixed loss over time and demonstrate the potential in reducing energy costs associated with escalator operation

Remaining Useful Life Modelling with an Escalator Health Condition Analytic System

The refurbishment of an escalator is usually linked with its design life as recommended by the manufacturer. However, the actual useful life of an escalator should be determined by its operating condition which is affected by the runtime, workload, maintenance quality, vibration, etc., rather than age only. The objective of this project is to develop a comprehensive health condition analytic system for escalators to support refurbishment decisions. The analytic system consists of four parts: 1) online data gathering and processing; 2) a dashboard for condition monitoring; 3) a health index model; and 4) remaining useful life prediction. The results can be used for a) predicting the remaining useful life of the escalators, in order to support asset replacement planning and b) monitoring the real-time condition of escalators; including alerts when vibration exceeds the threshold and signal diagnosis, giving an indication of possible root cause (components) of the alert signal.Comment: 14 pages, 12 figures, 7 table

In situ Proteomic Profiling of Curcumin Targets in HCT116 Colon Cancer Cell Line

To date, the exact targets and mechanism of action of curcumin, a natural product with anti-inflammatory and anti-cancer properties, remain elusive. Here we synthesized a cell permeable curcumin probe (Cur-P) with an alkyne moiety, which can be tagged with biotin for affinity enrichment, or with a fluorescent dye for visualization of the direct-binding protein targets of curcumin in situ. iTRAQ™ quantitative proteomics approach was applied to distinguish the specific binding targets from the non-specific ones. In total, 197 proteins were confidently identified as curcumin binding targets from HCT116 colon cancer cell line. Gene Ontology analysis showed that the targets are broadly distributed and enriched in the nucleus, mitochondria and plasma membrane, and they are involved in various biological functions including metabolic process, regulation, response to stimulus and cellular process. Ingenuity Pathway Analysis™ (IPA) suggested that curcumin may exert its anticancer effects over multiple critical biological pathways including the EIF2, eIF4/p70S6K, mTOR signaling and mitochondrial dysfunction pathways. Functional validations confirmed that curcumin downregulates cellular protein synthesis, and induces autophagy, lysosomal activation and increased ROS production, thus leading to cell death