A study reporting the researchers’ findings was published April 13 in the journal Accident Analysis and Prevention.

Traffic accidents involving large trucks in the United States have increased 47 percent according to the National Safety Council, and in 2021, these vehicles were responsible for nine percent of all vehicles involved in fatal crashes. Several studies worldwide have highlighted in particular the severity of collisions related to drowsy driving and their substantial risk of fatality.

A major risk here comes from what researchers term “microsleeps.” A microsleep is a brief episode of sleep that lasts for just a few seconds and can occur involuntarily during wakefulness. It can lead to impaired cognitive and motor performance, including slower reaction times, decreased attention, and even complete loss of consciousness. Microsleep episodes can have a significant impact on driving performance and increase the likelihood of dozing off while driving. In 2022, National Police Agency of Japan announced that falling asleep at the wheel was to be included in the same category of “forward inattention” as distraction, which has been the most frequent cause of fatal traffic accidents in the country for over ten years.

A great deal of research into typical microsleep behaviors has investigated one or more aspects of the problem such as eye closure or changes in pupil diameter. No study has yet performed an analysis that takes a more holistic approach considering multiple aspects of the problem, combining the driver’s eye and mouth movements as well as their entire body and vehicle driving behavior. Most such studies have also only considered driver performance during computer simulations. No research has yet looked at actual collisions of large trucks.

“But in recent years, there has been an explosion in the use of dashcam video recorders,” said Hajime Kumagai, lead author of the paper and a specialist in sleep medicine with the Graduate School of Biomedical and Health Sciences at Hiroshima University.

“This means that a great many traffic accidents, and their possible relationship to episodes of microsleeping have been recorded. This inspired us to employ dashcam footage to investigate microsleep-related behaviors immediately prior to real-world truck collisions.”

In total, the researchers reviewed 3,120 seconds of video footage from interior and exterior dashcams across 52 cases from truck collisions in Japan that had actually happened. They analysed the footage from one minute before the crash right up until the crash. In each incident, the person at the wheel had been a professional driver, and all crashes occurred on either urban roads or highways.

The footage was visually analyzed in a second-by-second manner to simultaneously evaluate any eye changes and microsleep-related activity including the driver’s actions to try to prevent falling asleep (anti-sleepiness behaviors), behavioral signs of microsleep, and abnormal vehicle behavior.

The researchers concluded that the key signs of microsleep include behaviors suggesting a creeping sleepiness, such as the absence of body movement, relaxation of antigravity muscles (the muscles such as back and neck muscles, as well as calves and quadriceps used to support ourselves against the force of gravity), eyes being half-closed, and closure of the eyes for one second or more.

“Up to now, technologies used to attempt to detect and counter falling asleep at the wheel have focused mainly on monitoring the driver’s eyes,” said Toshiaki Shiomi, a co-author of the study. “What we found means that it is crucial to monitor not just the eyes but also the driver’s whole body, as well as vehicle behavior in order to reliably detect microsleep-related activity.”

This should also help in avoiding false alarms by ensuring a clear distinction between microsleep-related and non-microsleep-related behaviors.

Developing advanced safety systems that can detect and alert drivers of potential microsleep episodes involving a whole-of-body approach combined with monitoring of the vehicle for typical microsleep-related abnormal vehicle maneuvers could be an effective intervention for reducing accidents in the trucking industry.

The team hopes now to support work developing such advanced safety systems. These might include technologies that monitor both the inside and outside of the truck using cameras or other sensors, as well as deployment of algorithms that can analyze such data in real-time to detect signs of sleepiness or fatigue. These systems could then alert drivers with an alarm when they are at risk of falling asleep at the wheel.

The PCE (Power-conversion efficiency), a measure of the power generated from a given solar irradiation, is considered a significant benchmark for the performance of photovoltaics (PVs), or solar panels, in power generation. The improved efficiency of over 19% that was achieved by the PolyU researchers constitutes a record for binary OSCs, which have one donor and one acceptor in the photo-active layer.

Led by Prof. LI Gang, Chair Professor of Energy Conversion Technology and Sir Sze-Yen Chung Endowed Professor in Renewable Energy at PolyU, the research team invented a novel OSC morphology-regulating technique by using 1,3,5-trichlorobenzene as a crystallisation regulator. This new technique boosts OSC efficiency and stability.

The team developed a non-monotonic intermediated state manipulation (ISM) strategy to manipulate the bulk-heterojunction (BHJ) OSC morphology, which simultaneously optimises crystallisation dynamics and energy loss of non-fullerene OSCs. Unlike the strategy of using traditional solvent additives, which is based on excessive molecular aggregation in films, the ISM strategy promotes the formation of more ordered molecular stacking and favourable molecular aggregation. As a result, the PCE was considerably increased and the undesirable non-radiative recombination loss was reduced. Notably, non-radiative recombination lowers the light generation efficiency and increases the heat loss.

The research team’s findings are described in the study “19.3% Binary Organic Solar Cell and Low Non-Radiative Recombination Enabled by Non-Monotonic Intermediate State Transition” published in Nature Communications . The conversion of solar energy to electricity is an essential technology for achieving a sustainable environment. Although OSCs are promising devices that harness solar energy cost-effectively, their efficiency must be improved if they are to be used widely in practical applications.

Non-fullerene acceptors based organic solar cells represent the frontier of research in the field of organic photovoltaics due to both the materials and morphology manipulation innovations. Nevertheless, non-radiative recombination loss suppress and performance boosting are in the centre of organic cell research.

Prof. Li said, “Challenges in research came from the existing additive-based benchmark morphology control methods, which suffer from non-radiative recombination loss, thus lowering the open-circuit voltage due to excessive aggregation.” The research team took about two years to devise a non-monotonic ISM strategy for increasing the OSC efficiency and lowering the non-radiative recombination loss. The publication of the study promises to galvanise OSC research.

Prof. Li said, “The new finding will make OSC research an exciting field, and this will likely create tremendous opportunities in applications like portable electronics and building-integrated PVs.” The new door will open when low cost single-junction OSCs can achieve a PCE of over 20%, along with more stable performance and other unique advantages such as flexibility, transparency, stretchability, low weight and tuneable colour.

Prof. Li has been recognised as a Highly Cited Researcher 9 years in a row since 2014, which testifies to his significant impact on global research. His pioneering contributions to research on polymer solar cells since 2005 have brought sustainable influence on printable solar energy development with global recognition.

Underpinning the research on OPV field, Prof LI’s study titled, “High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends,” was published on Nature Materials in 2005. This represented OPV’s first generation research breakthrough which has fuelled solar technology from this frontier study.

In 2010, Prof LI’s study titled “For the Bright Future — Bulk Heterojunction Polymer Solar Cells with Power Conversion Efficiency of 7.4%” was published on Advanced Materials.

Prof. Li said, “The latest study shows a record low non-radiative recombination loss of 0.168 eV in a binary OSC with a PCE of over 19%. This is a very encouraging result for the long-standing research on OSCs that I have conducted over the past two decades. We have already achieved better OSC efficiency, and this will subsequently help accelerate the applications of solar energy.”

References: Nature Materials 4, 864-868 (2005). High-efficiency solution processable polymer photovoltaic cells by self-organization of polymer blends. Advanced Materials Vol. 22, Issue 20 (2010). For the Bright Future — Bulk Heterojunction Polymer Solar Cells with Power Conversion Efficiency of 7.4%.