Numerical and Experimental Study of Liquid Breakup Process in Solid Rocket Motor Nozzle

Rocket propulsion is an important travel method for space exploration and national defense, rockets needs to be able to withstand wide range of operation environment and also stable and precise enough to carry sophisticated payload into orbit, those engineering requirement makes rocket becomes one of the state of the art industry. The rocket family have been classified into two major group of liquid and solid rocket based on the fuel phase of liquid or solid state. The solid rocket has the advantages of simple working mechanism, less maintenance and preparing procedure and higher storage safety, those characters of solid rocket make it becomes popular in aerospace industry. Aluminum based propellant is widely used in solid rocket motor (SRM) industry due to its avalibility, combusion performance and economical fuel option, however after aluminum react with oxidant of amonimum perchrate (AP), it will generate liquid phase alumina (Al2O3) as product in high temperature (2,700~3,000 K) combustion chamber enviornment. The liquid phase alumina particles aggromorate inside combustion chamber into larger particle which becomes major erosion calprit on inner nozzle wall while alumina aggromorates impinge on the nozzle wall surface. The erosion mechanism result nozzle throat material removal, increase the performance optimized throat diameter and reduce nozzle exit to throat area ratio which leads to the reduction of exhaust gas velocity, Mach number and lower the propulsion thrust force. The approach to avoid particle erosion phenomenon taking place in SRM’s nozzle is to reduce the alumina particle size inside combustion chamber which could be done by further breakup of the alumina droplet size in SRM’s combustion chamber. The study of liquid breakup mechanism is an important means to smaller combustion chamber alumina droplet size and mitigate the erosion tack place on rocket nozzle region. In this study, a straight two phase air-water flow channel experiment is set up for liquid breakup phenomenon observation. The liquid water material in this experiment will play a comparison role as liquid alumina in high temerature enviornment. The method proposed to control the liquid breakup size of liquid droplet is done by the means of changing the liquid properties of surface tension. The surface tenion of liquid plays an inportant role of providing major liquid droplet bounding pressure or Laplace pressure. By reduceing surface tension of liquid leads to lower Laplace pressure of droplet and result in less droplet dynamic stability which could be breakup under external pressure difference. The reduction of surface tension of liquid aluminum could be achieved by adding magnisium and strontium, it is reported that the surface tension reeducation level could reach 10%~15% when those additive mension above are adding to aluminum. This study of liquid breakup mechanism include two major part, first part is straight two-phase channel experiment and simulation comparison which provide a validation work of CFD simulation performance when compare to experiment. Second part is single droplet breakup experiment, in this experiment the relation of surface tension and liquid breakup behavior is carefully studied. The straight two-phase flow channel experiment setting will enable to us to study the liquid breakup process in macro scale. The quantification method is achieved by analyzing high-speed camera image by MatLab image process code develop in UW-Milwaukee wind tunnel lab which extract data in images and provide information including liquid droplet count and size distribution, wave frequency and time averaging two-phase free boundary. It was found that liquid breakup mechanism proportional to gas-droplet velocity difference square, gas density and liquid droplet size and inverse proportional to liquid surface tension. The single droplet experiment part is provide a close up view of liquid breakup and prove the reduced surface tension will enhance liquid breakup activity. In this study, we could observe the evidence of enhance liquid breakup activity by the reduced surface tension of liquid. Therefor the approach of reducing surface tension of Solid Rocket Motor (SRM) fuel reacting product is a high potential solution to SRM nozzle erosion

Psychosocial Determinants of Insomnia in Adolescents: Roles of Mental Health, Behavioral Health, and Social Environment

The theoretical explanation of human problems is derived from the complex interplay of psychological, social, economic, political, and physical factors. Aims: This study examined the roles of behavioral health (i.e., alcohol abuse and suicidality) and social environment (i.e., family support, school connectedness, and favorable neighborhood) and mental health [i.e., depression, anxiety, and attention deficit hyperactivity disorder (ADHD)] in predicting insomnia in adolescents in an ecological perspective. Methods: Approximately 6445 high school students in Taiwan were administered an anonymous self-report survey. Hierarchical multiple regression was performed to examine how multidimensional social environment, behavioral health, and mental health factors were associated with insomnia in adolescents. Results: The prevalence rate of insomnia in the sample was 30%. The results indicated that alcohol abuse (β = 0.04), suicidality (β = 0.06), depression (β = 0.29), anxiety (β = 0.14), and ADHD (β = 0.11) were positively associated with insomnia (p \u3c 0.001), whereas family support (β = −0.06), school connectedness (β = −0.05), and favorable neighborhood (β = −0.10) were negatively associated with insomnia (p \u3c 0.001). Sex did not predict insomnia, but age was positively associated with insomnia (β = 0.09, p \u3c 0.001). Among all predictors of insomnia in the study, mental health factors, especially depression, play a major role on insomnia among adolescents, and is as much important as social environment factors. Conclusion: This study demonstrated how both psychosocial variables (social environment and behavioral health) and psychological symptoms were associated with insomnia in adolescents when the demographic variables (sex and age) were controlled and provided valuable information and evidence for clinicians, social workers, and health professionals who provide support to adolescents with insomnia. Applying an ecological approach in practice can aid in understanding at individual, family, school, and community levels and in identifying the strengths and weaknesses of their interactions with each other. Implications: This perspective enables practitioners in effectively treating problems and addressing the needs of the various levels, including the individual, family, school, and the broader community. Thus, prevention and intervention of insomnia in adolescents should focus on multidimensional risk and protective factors, including mental health, behavioral health, and social environment, in the context of an ecological system

Feasibility and effectiveness of heat pipe cooling in end milling operations : thermal, structural static, and dynamic analyses : a new approach

In this paper, the feasibility and effectiveness of heat pipe cooling in end milling operations are investigated. A new embedded heat pipe technology was utilized to remove the heat generated at the tool-interface in end milling processes. Numerical studies involved four cases, including dry milling, fluid cooling, heat pipe cooling, and heat pipe cooling with cutting fluid supplied. The thermal, structural static, and dynamic characteristics of the endmill were investigated using a numerical calculation with fast finite element plus solvers based on explicit finite element analysis software. The results demonstrate that the heat pipe end-mill is most feasible and effective in the actual end milling processe

Assessment of gene-covariate interactions by incorporating covariates into association mapping

The HLA region is considered to be the main genetic risk factor for rheumatoid arthritis. Previous research demonstrated that HLA-DRB1 alleles encoding the shared epitope are specific for disease that is characterized by antibodies to cyclic citrullinated peptides (anti-CCP). In the present study, we incorporated the shared epitope and either anti-CCP antibodies or rheumatoid factor into linkage disequilibrium mapping, to assess the association between the shared epitope or antibodies with the disease gene identified. Incorporating the covariates into the association mapping provides a mechanism 1) to evaluate gene-gene and gene-environment interactions and 2) to dissect the pathways underlying disease induction/progress in quantitative antibodies

EXPLORING E-LEARNING BEHAVIOR THROUGH LEARNING DISCOURSES

As many studies predict e-learning behaviors through intention, few of them investigate user’s learning behaviors directly. In addition to intention, individual’s e-learning behaviors may be influenced by technology readiness and group influences, such as social identity and social bond. This research-in-progress study explores how e-learning behaviors vary with intention, technology readiness, social identity and social bond. Our investigation was based on analyzing the speech acts embedded in fourteen learners’ online discourses in an eighteen-week e-learning course. We then compared how speech acts varied among groups with different degree of intention, technology readiness, social identity, and social bond. Our findings contribute e-learning research by clarifying how intention, technology readiness, social identity, and social bond influence learning behaviors in e-learning context

Factors Affecting Occupational Exposure to Needlestick and Sharps Injuries among Dentists in Taiwan: A Nationwide Survey

BACKGROUND: Although the risks of needlestick and sharps injuries (NSIs) for dentists are well recognized, most papers published only described the frequency of occupational exposure to NSIs. Less has been reported assessing factors contributing to exposure to NSIs. The purpose of this study was to update the epidemiology of NSIs among dentists in Taiwan and identify factors affecting NSIs in order to find preventive strategies. METHODOLOGY/PRINCIPAL FINDINGS: A nationwide survey was conducted in dentists at 60 hospitals and 340 clinics in Taiwan. The survey included questions about factors supposedly affecting exposure to NSIs, such as dentist and facility characteristics, knowledge and attitudes about infectious diseases, and practices related to infection control. Univariate and multivariate logistic regression analyses were conducted to determine the association between risk factors and exposure to NSIs. In total, 434 (74.8%) of 580 dentists returned the survey questionnaires, and 100 (23.0%) reported that they had experienced more than one NSI per week. Our data showed that the risk of occupational NSIs is similarly heightened by an older age (odds ratio [OR], 3.18; 95% confidence interval [CI], 1.62-6.25), more years in practice (OR, 2.57; 95% CI, 1.41-4.69), working in clinics (OR, 1.73; 95% CI, 1.08-2.77), exhibiting less compliance with infection-control procedures (OR, 1.82; 95% CI, 1.04-3.18), having insufficient knowledge of blood-borne pathogens (OR, 1.67; 95% CI, 1.04-2.67), and being more worried about being infected by blood-borne pathogens (OR, 1.82; 95% CI, 1.05-3.13). CONCLUSIONS/SIGNIFICANCE: High rates of NSIs and low compliance with infection-control procedures highly contribute to the chance of acquiring a blood-borne pathogen infection and threaten occupational safety. This study reveals the possible affecting factors and helps in designing prevention strategies for occupational exposure to NSIs