Childhood Adversity, Resilience, and Mental Health: A Sequential Mixed-Methods Study of Chinese Young Adults

Resilience is a key health protective factor for those with adverse childhood experiences (ACEs), but little research has explored how it manifests in early adulthood or across cultures. The purpose of this study was to generate a fuller understanding of resilience and its contribution to the relationships between mental health problems and ACEs among Chinese young adults in Hong Kong. Using a sequential explanatory mixed-methods design, 433 Chinese young adults aged 18-24 years were surveyed online to examine the relationships between ACEs, resilience, and mental health problems (depression, anxiety, maladjustment, and post-traumatic stress symptoms). Among them, 34 participants with ACEs were purposively selected and interviewed to explore cultural factors that influenced their resilience. Quantitative data were analyzed using multiple hierarchical regression analyses; qualitative data were analyzed using a qualitative descriptive approach.Higher cumulative ACE exposure was associated with higher severity of adjustment disorder and odds for screening positive for post-traumatic stress disorders, but not for symptoms of depression or anxiety. Resilience significantly contributed to explaining variances across all mental health outcomes over and beyond ACEs and in a protective fashion. Four themes emerged from qualitative interviews: (1) Privacy, emotional restraint, and “saving face”; (2) Conforming to preserve harmony; (3) A will to excel; and (4) Viewing adversity as a matter of luck. These findings suggest Chinese young adults’ resilience was influenced by cultural norms of restraint, conformity, competition, and superstition. The present study provides a model for future studies using a mixed-methods design to deeply examine resilience among younger people exposed to early adversities within sociocultural, historical, or geographical contexts

Laser ignition of iso-octane and n-heptane jets under compression-ignition conditions

This work aims to investigate the effect of laser-induced plasma ignition (LI) on combustion behaviours of isooctane (a gasoline surrogate) at compression-ignition (CI) conditions. A high-energy laser was used to force the fuel ignition at a quiescent-steady environment inside an optically accessible constant-volume combustion chamber with 900 K ambient gas temperature, 22.8 kg∕m3 ambient gas density and 21 vol.% O2 concentration. A diesel surrogate (n-heptane) was tested at a lower charge temperature of 735 K to offset its higher fuel reactivity than the iso-octane, such that the flames of both fuels can have a similar lift-off length. Forced laser ignition was introduced either before or after the natural autoignition timing of the fuels. The laser was focused at the jet axis 15 mm and 30 mm from the nozzle. High-speed schlieren imaging, heat release analysis and flame luminosity measurement were applied to the flames. The high-speed schlieren imaging was used to monitor the flame structure evolution of the natural ignition and LI cases. Due to laser ignition, the flame lift-off lengths decrease, with which the uncertainties in the lift-off distances reduce by more than 80%. The laser-affected flame bases return back to the natural flame base locations. The uncertainties in the lift-off lengths also increase, as the flame stabilisation locations approach the natural lift-off distances. Under the test conditions of this work, the rates at which the iso-octane flames shift downstream are slower than the n-heptane cases. The heat release rate profiles show high heat release from the flames following the LI events, before transitioning to lower steady values. The flame luminosity measurements indicate a strong correlation between the LI affected lift-off length and increased soot formation. The luminosity levels decrease as the flame base shifts downstream over time.Guanxiong Zhai, Sensen Xing, Anthony C.Y. Yuen, Paul R. Medwell, Sanghoon Kook, Guan Heng Yeoh, Qing Nian Cha

Study of ignition and combustion characteristics of consecutive injections with iso-octane and n-heptane as fuels

Gasoline compression ignition (GCI) engines have potential to improve fuel economy and reduce emissions harmful to health and the environment compared with conventional diesel combustion engines. The underpinning knowledge of key phenomena of fuel–air mixture formation, ignition, combustion, and pollutant formation, however, is lacking at present. This work investigated the ignition and combustion interaction processes between two consecutive jets of iso-octane (gasoline surrogate) and n-heptane (diesel surrogate) inside a quiescent steady environment with an ambient density of 22.8 kg/m3, an O2 concentration of 21 vol % but with ambient temperatures of 950 and 780 K, respectively. Three injection schedules were tested, consisting of a double injection that follows a pilot–main injection duration (2.6 ms/6.5 ms) with dwell times of 0.2, 0.7, and 1.2 ms, in addition to single injections with long (9.1 ms) and short (2.6 ms) injection durations as reference cases. Combined high-speed schlieren imaging, pressure trace measurements, combustion luminosity detection using photodiode and closed-homogeneous reactor simulations revealed that under the 950 K condition for iso-octane and 780 K condition for n-heptane, pilot-injection-induced local temperature and flame intermediate changes can considerably affect the preignition reactions of the main injections that followed. It is also found that the interaction effects are dependent on the ignition and combustion characteristics of the fuels involved as well as the temporal separation between the injections.Sensen Xing, Guanxiong Zhai, Haijun Mo, Paul R. Medwell, Anthony C.Y. Yuen, Sanghoon Kook, Guan H. Yeoh, and Qing N. Cha

A review of hydrogen direct injection for internal combustion engines: towards carbon-free combustion

A paradigm shift towards the utilization of carbon-neutral and low emission fuels is necessary in the internal combustion engine industry to fulfil the carbon emission goals and future legislation requirements in many countries. Hydrogen as an energy carrier and main fuel is a promising option due to its carbon-free content, wide flammability limits and fast flame speeds. For spark-ignited internal combustion engines, utilizing hydrogen direct injection has been proven to achieve high engine power output and efficiency with low emissions. This review provides an overview of the current development and understanding of hydrogen use in internal combustion engines that are usually spark ignited, under various engine operation modes and strategies. This paper then proceeds to outline the gaps in current knowledge, along with better potential strategies and technologies that could be adopted for hydrogen direct injection in the context of compression-ignition engine applications—topics that have not yet been extensively explored to date with hydrogen but have shown advantages with compressed natural gas.Ho Lung Yip, Aleš Srna, Anthony Chun Yin Yuen, Sanghoon Kook, Robert A. Taylor, Guan Heng Yeoh, Paul R. Medwell, and Qing Nian Cha