김원정 교수

Nectar drinkers must feed quickly and efficiently due to the threat of predation. While the sweetest nectar offers the greatest energetic rewards, the sharp increase of viscosity with sugar concentration makes it the most difficult to transport. We here demonstrate that the sugar concentration that optimizes energy transport depends exclusively on the drinking technique employed. We identify three nectar drinking techniques: active suction, capillary suction, and viscous dipping. For each, we de

We elucidate the major mechanism of microparticle removal in the megasonic cleaning process through the direct visualization experiments. It is revealed that particles sitting on solids are removed by adjacent microbubbles that oscillate near the substrates and exert interfacial and pressure gradient forces on the particles. Other pressure and streaming effects are shown to be too weak to detach the particles.

Abstract We examine the fluid mechanics of drinking in nature. We classify the drinking strategies of a broad range of creatures according to the principal forces involved, and present physical pictures for each style. Simple scaling arguments are developed and tested against existing data. While suction is the most common drinking strategy, various alternative styles have evolved among creatures whose morphological, physiological and environmental constraints preclude it. Particular attention i

We present the results of a combined experimental and theoretical investigation of the mechanics of self-burial of some plant seeds whose morphologies respond to environmental changes in humidity. The seeds of Erodium and Pelargonium have hygroscopically responsive awns that play a critical role in their self-burial into soil. The awn, coiled in a dry state, uncoils to stretch linearly under highly humid condition because of a tilted arrangement of cellulose microfibrils in one of the layers of

Surface traps, such as electron and hole traps, quench the photoluminescence (PL) of semiconductor nanocrystals. We find a binary ligand system that effectively passivates those surface traps on bare CdSe nanocrystals, thereby making the nanocrystals highly luminescent. Zinc-blende CdSe nanocrystals are prepared by colloidal synthesis, and their optical properties are monitored by varying the amounts of propylamine (PA) and tributylphosphine (TBP) in chloroform at room temperature. The starting

We present the results of a combined experimental and theoretical investigation of the dynamics of drinking in ruby-throated hummingbirds. In vivo observations reveal elastocapillary deformation of the hummingbird's tongue and capillary suction along its length. By developing a theoretical model for the hummingbird's drinking process, we investigate how the elastocapillarity affects the energy intake rate of the bird and how its open tongue geometry reduces resistance to nectar uptake. We note t

We present a combined experimental and theoretical investigation of the dynamics of liquid imbibition through paper. The Washburn equation is widely used to describe the dynamics of capillary flow through paper, but this classical model has limited accuracy, which often makes it difficult to use in developing analytic systems such as paper-based microfluidic devices. We here report that the internal cavity of the cellulose fibres composing paper is significantly responsible for the limited accur

The dynamic actions of cavitation bubbles in ultrasonic fields can clean surfaces. Gas and vapor cavitation bubbles exhibit different dynamic behaviors in ultrasonic fields, yet little attention has been given to the distinctive cleaning effects of gas and vapor bubbles. We present an experimental investigation of surface cleaning by gas and vapor bubbles in an ultrasonic field. Using high-speed videography, we found that the primary motions of gas and vapor bubbles responsible for surface clean

Members of the TNFSF/TNFRSF are involved in the immunoregulation of various immune reactions and diseases. Recently, LIGHT/TR2, GITRL/GITR, and TL1A/DR3 have been reported as playing roles in the inflammatory reactions in atherosclerosis, but a comparative analysis of these molecules has not been conducted. In order to compare their expression patterns, immunohistochemical analyses were performed using six human carotid endoarterectomy samples. The expression of these molecules was detected in t

We propose a portable, non-powered, long-term working suction pump with a high flow rate for microfluidic devices. The pump is driven by a superabsorbent polymer enclosed in a housing with porous fins to accelerate water absorption. We experimentally demonstrate that the pump creates an outstanding flow rate of more than 80 μl min-1 and an absorption volume of ∼20 ml. We address the key design principles underlying the outstanding performance of the pump. As an exemplary application, we construc