Browsing by Author "Wu, Hao"

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Amoeboid motion in confined geometry
(2015-11-04)
Wu, Hao
;
Thiebaud, M.
;
Hu, W. -F.
;
Farutin, A.
;
Rafai, S.
Many eukaryotic cells undergo frequent shape changes (described as amoeboid motion) that enable them to move forward. We investigate the effect of confinement on a minimal model of amoeboid swimmer. A complex picture emerges: (i) The swimmer's nature (i.e., either pusher or puller) can be modified by confinement, thus suggesting that this is not an intrinsic property of the swimmer. This swimming nature transition stems from intricate internal degrees of freedom of membrane deformation. (ii) The swimming speed might increase with increasing confinement before decreasing again for stronger confinements. (iii) A straight amoeoboid swimmer's trajectory in the channel can become unstable, and ample lateral excursions of the swimmer prevail. This happens for both pusher- and puller-type swimmers. For weak confinement, these excursions are symmetric, while they become asymmetric at stronger confinement, whereby the swimmer is located closer to one of the two walls. In this study, we combine numerical and theoretical analyses.
Amoeboid swimming in a channel
(2016)
Wu, Hao
;
Farutin, Alexander
;
Hu, Wei-Fan
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Thiebaud, Marine
;
Rafai, Salima
Several micro-organisms, such as bacteria, algae, or spermatozoa, use flagellar or ciliary activity to swim in a fluid, while many other micro-organisms instead use ample shape deformation, described as amoeboid, to propel themselves either by crawling on a substrate or swimming. Many eukaryotic cells were believed to require an underlying substratum to migrate (crawl) by using membrane deformation (like blebbing or generation of lamellipodia) but there is now increasing evidence that a large variety of cells (including those of the immune system) can migrate without the assistance of focal adhesion, allowing them to swim as efficiently as they can crawl. This paper details the analysis of amoeboid swimming in a confined fluid by modeling the swimmer as an inextensible membrane deploying local active forces (with zero total force and torque). The swimmer displays a rich behavior: it may settle into a straight trajectory in the channel or navigate from one wall to the other depending on its confinement. The nature of the swimmer is also found to be affected by confinement: the swimmer can behave, on average over one swimming cycle, as a pusher at low confinement, and becomes a puller at higher confinement, or vice versa. The swimmer\'s nature is thus not an intrinsic property. The scaling of the swimmer velocity V with the force amplitude A is analyzed in detail showing that at small enough A, V similar to A(2)/eta(2) (where eta is the viscosity of the ambient fluid), whereas at large enough A, V is independent of the force and is determined solely by the stroke cycle frequency and the swimmer size. This finding starkly contrasts with models where motion is based on ciliary and flagellar activity, where V similar to A/eta. To conclude, two definitions of efficiency as put forward in the literature are analyzed with distinct outcomes. We find that one type of efficiency has an optimum as a function of confinement while the other does not. Future perspectives are outlined.
Linking Insomnia to Workplace Injuries: A Moderated Mediation Model of Supervisor Safety Priority and Safety Behavior
(2016-01)
Kao, Kuo-Yang
;
Spitzmueller, Christiane
;
Cigularov, Konstantin
;
Wu, Hao
;
管理科學系
This study investigated why and how insomnia can relate to workplace injuries, which continue to have high human and economic costs. Utilizing the self-regulatory resource theory, we argue that insomnia decreases workers\' safety behaviors, resulting in increased workplace injuries. Moreover, in order to ultimately derive organizational interventions to alleviate the detrimental impact of insomnia on workplace injuries, we propose that supervisor safety priority can create situational strength that can prevent workers from behaving unsafely despite experiencing insomnia. Our theoretical model was examined and empirically supported using hierarchically nested data collected from supervisors (N = 482) and workers (N = 2,737) in a midsized construction services company. Results were consistent with the proposed conceptual framework; the relationship between insomnia and injuries is explained by the influence of insomnia on safety behaviors. For workers supervised by supervisors with high safety priority, both the relationship between insomnia and safety behaviors and the indirect relationship between insomnia and workplace injuries were weaker. We provide theoretical implications for future safety research and suggest tentative directions for practitioners working to reduce workplace injuries through sleep-oriented interventions.
Linking Insomnia to Workplace Injuries: A Moderated Mediation Model of Supervisor Safety Priority and Safety Behavior
(2016-01-01)
Kao, Kuo-Yang
;
Spitzmueller, Christiane
;
Cigularov, Konstantin
;
Wu, Hao
;
管理科學系
This study investigated why and how insomnia can relate to workplace injuries, which continue to have high human and economic costs. Utilizing the self-regulatory resource theory, we argue that insomnia decreases workers\' safety behaviors, resulting in increased workplace injuries. Moreover, in order to ultimately derive organizational interventions to alleviate the detrimental impact of insomnia on workplace injuries, we propose that supervisor safety priority can create situational strength that can prevent workers from behaving unsafely despite experiencing insomnia. Our theoretical model was examined and empirically supported using hierarchically nested data collected from supervisors (N = 482) and workers (N = 2,737) in a midsized construction services company. Results were consistent with the proposed conceptual framework; the relationship between insomnia and injuries is explained by the influence of insomnia on safety behaviors. For workers supervised by supervisors with high safety priority, both the relationship between insomnia and safety behaviors and the indirect relationship between insomnia and workplace injuries were weaker. We provide theoretical implications for future safety research and suggest tentative directions for practitioners working to reduce workplace injuries through sleep-oriented interventions.