We present simple methods for fabricating high aspect-ratio polymer nanostructures on a solid substrate by rigiflex lithography with tailored capillarity and adhesive force. In the first method, a thin, thermoplastic polymer film was prepared by spin coating on a substrate and the temperature was raised above the polymer's glass transition temperature ($T_g$) while in conformal contact with a poly(urethane acrylate) (PUA) mold having nano-cavities. Consequently, capillarity forces the polymer film to rise into the void space of the mold, resulting in nanostructures with an aspect ratio of ${\sim}4$. In the second method, very high aspect-ratio (>20) nanohairs were fabricated by elongating the pre-formed nanostructures upon removal of the mold with the aid of tailored capillarity and adhesive force at the mold/polymer interface. Finally, these two methods were further used to fabricate micro/nano hierarchical structures by sequential application of the molding process for mimicking nature's functional surfaces such as a lotus leaf and gecko foot hairs.

유(流)세포분석기(flow cytometer)는 일정한 체적 내에 존재하는 세포의 종류 및 개체 수 등을 계측하는 장비로써 생체에서 추출한 유액상태(혈액 또는 림프액)의 세포를 모세관(micro-channel)을 통과시킬 때 발생하는 산란 및 형광 빛을 이용하여 계측한다. 유세포 분석기는 신약의 투석 후 세포수의 증감, 암세포의 전이 및 세포주기의 분석 등을 연구하는 데 사용되며 현재 Becton-Dickinson's 등에서 상용화된 제품을 생산 판매하고 있으며, 계측을 위해서는 생체에서 세포를 추출해야 한다는 단점을 가지고 있다. Harvard 의과대학에서 최근에 개발한 생체 유세포분석기(In vivo Flow Cytometer)는 생체에서 세포를 추출하지 않고 세포의 수를 계측할 수 있다[1]. 레이저가 혈관의 특정한 부위에 조사되고 있고, 이곳을 세포가 통과하면서 발생하는 형광을 계측함으로써 주어진 시간 동안 특정세포군이 얼마나 지나가는 지를 계측할 수 있는 장비이다. 본 특별기사에서는 혈류 가시화 분야의 독자를 위해 최근에 "Optics Express"에 "In vivo imaging flow cytometer"라는 제목으로 최근에 개제된 논문의 내용을 하여 소개한다[2].

Macromolecule diffusion in cells and tissues is important for cell signaling, metabolism and locomotion. Biophysical methods, including non-invasive or minimally invasive in-vivo photobleaching techniques and single quantum-dot tracking, have been used to measure the rates of macromolecule diffusion in living cells and tissues, including central nervous system and tumors. Mathematical modeling and statistical analysis of experimental data revealed various modes of diffusion, which are strongly coupled with spatiotemporal changes in nanoscale structures and material properties.

In the present study, naturally generated bubbles were investigated to be sure if they could be adopted as the tracer for PIV techniques. The bubble can be grown from the nuclei melted in the water of tunnel and the size of bubbles is changed through the variation of tunnel pressure. Since the trace ability and appropriate size of tracer are so important for PIV techniques, the characteristics of bubbles as tracer are revealed in terms of trace ability and bubble size with the variation of flow speed and tunnel pressure in this study. In addition, PIV measurements of (low behind a rotating propeller are conducted to confirm the trace ability of bubbles even in a highly vortical flow.

The global environment is deteriorating at an alarming rate, despite of enhanced international environmental regulation. Many studies have been performed to reduce toxic pollutants. Recently, plant-based phytoremediation technology for moving toxic contaminants from soil and water has been receiving large attention. Arsenic-contaminated soil is one of the major pollutant sources for drinking water. Pteris erotica has been known as a hyper-accumulator of arsenic from soils. In this study, we investigated the effect of arsenic absorption on sap flow inside xylem vessels of Pteris. The synchrotron X-ray micro-imaging technique was employed to monitor the refilling process of water containing arsenic inside the xylem vessels of Pteris's leaves and stems non-invasively. The captured phase-contrast X-ray images show both anatomy of internal structure and transport of water inside Pteris. The exposure of Pteris to arsenic solution was found to increase largely the water raise speed in xylem vessels. The present results would provide important information needed for understanding the mechanisms of accumulation and transportation of toxic materials in plants.

Reverse flow occurs in a channel when there is an obstruction at the entry. However it has been shown recently that reverse flow can be realized without an obstruction, by staggering the sides of the channel and placing it at an angle of attack to the oncoming flow. In this study the latter flow is computationally investigated. Studies have been carried out for different widths (gap between the two walls forming the channel), and at an angle of attack of 30. The results have captured all the essential features of this complex phenomenon and show the time dependent pumping mechanism which leads to the occurrence of reverse flow.

Micro-PIV(particle image velocimetry) has been widely used to measure the velocity of micro flow. Although this micro-PIV method can give accurate 2D instantaneous velocity information of mea-surement plane, it cannot resolve the out of plane component of velocity vectors. Lots of the micro fluidic devices generate three-dimensional flow and 3D measurement of velocity is useful to understand the physics of micro flow phenomena. In this study, we constructed stereoscopic micro-PIV(SMPIV) system and applied this method to the impinging micro jet flow. The results show that this method can produce accu-rate 3D reconstruction of micro jet flow.