[show abstract][hide abstract] ABSTRACT: We propose a theoretical explanation for the experimentally observed feature in phase contrast images of micropipes in silicon carbide in a white synchrotron radiation (SR) beam, which consists in the fact that the contrast of various micropipes or various regions of the same micropipe is of different colors. The contrast is most often white (the intensity is higher than the background) at the center and black at the edges; however, the sign sometimes changes, and the contrast becomes black at the center and white at the edges. We discuss the results of experiments performed at the SR source in Pohang, Republic of Korea. The cause of the contrast change can be a change in the angle between the micropipe axis and the SR beam direction. At not overly small angles, the phase progression in a section of the micropipe is small and the contrast is standard. If the angle becomes very small, the size of the longitudinal section of the micropipe by the beam increases, which leads to wave field oscillations in the region of the section. At large distances in the white beam, these oscillations are averaged, and averaging results in black contrast.
Journal of Surface Investigation X-ray Synchrotron and Neutron Techniques 08/2013; 6(5). · 0.36 Impact Factor
[show abstract][hide abstract] ABSTRACT: Numerous cell types have shown a remarkable ability to detect and move along gradients in stiffness of an underlying substrate-a process known as durotaxis. The mechanisms underlying durotaxis are still unresolved, but generally believed to involve active sensing and locomotion. Here, we show that simple liquid droplets also undergo durotaxis. By modulating substrate stiffness, we obtain fine control of droplet position on soft, flat substrates. Unlike other control mechanisms, droplet durotaxis works without imposing chemical, thermal, electrical, or topographical gradients. We show that droplet durotaxis can be used to create large-scale droplet patterns and is potentially useful for many applications, such as microfluidics, thermal control, and microfabrication.
Proceedings of the National Academy of Sciences 06/2013; · 9.74 Impact Factor
[show abstract][hide abstract] ABSTRACT: Recently, nanowire (NW) photodetectors with broad spectral response from
ultraviolet (UV)-visible to near-infrared (NIR) have been suggested for
many applications, such as communications and remote control. In this
connection, the development of the NW photodetectors that enable to
discriminate UV and Visible lights has been requested. In this study, we
report on the fabrication of single NW photodetectors that are capable
of discriminating UV and Visible lights. Specifically,
nanoparticles hybrid NWs were directly grown on Au electrode by the
meniscus-guided method. In fact, the single NW photodetector showed
spectral discrimination behavior by a negative photocurrent under UV but
by a positive under Visible light. The different photocurrent behaviors
were attributed to charge transfer between PEDOT:PSS and ZnO
nanoparticles. We also demonstrated single NW photodetector array with
selectively positioned photodetectors on Au electrodes. Each single
photodetector of the array showed its own spectral discrimination
behavior. We believe that our NW photodetectors with the characteristics
of spectral discrimination would contribute to advanced photosensing and
remote control in nanophotonic devices.
[show abstract][hide abstract] ABSTRACT: One of the major concerns in designing waveguides is unavoidable bending
that causes energy loss due to the distortion of modal field. Bending
loss in nanowire waveguides has been studied while including substrate
coupling loss. Pure bending loss unaffected by substrate coupling in
nanowire waveguides still remains unclear. A challenging task in study
of pure bending loss is to introduce bending on nanowire waveguides in
the air and to tune the radius of bending. We report the
characterization of pure bending loss in nanowire waveguides by bending
a vertical freestanding nanowire in the air. Specifically, vertical
freestanding active nanowire waveguides of MEH-PPV have been fabricated
by our meniscus-guided method. To characterize pure bending loss,
desired bending was remotely introduced by applying electrostatic force
near the top end of the waveguide. Finite-difference-time-domain
simulation was performed to confirm the experimental result. We show
that the bending losses, by conventional experimental approaches of
nanowires rested on substrates, were strongly overestimated attributed
to the coupling of the enhanced evanescent field to the substrate. We
suggest that our system could be also utilized for studying various
intrinsic properties of nanowire waveguides.
[show abstract][hide abstract] ABSTRACT: Softness of solids affects a microscopic deformation, called a `wetting
ridge', at a three-phase contact line. We present a direct visualization
of wetting ridges by high-resolution x-ray imaging, which shows a
spatial transition between elastic and fluidic wetting behaviors on a
soft solid. The fluidic behavior that corresponds to Neumann's triangle
occurs at the vicinity of the triple point while the elastic deformation
at xle (the elasto-capillary length). Real-time x-ray imaging clearly
shows temporal variation of wetting ridge.
[show abstract][hide abstract] ABSTRACT: Here we report a tracking X-ray microscopy (TrXM) as a novel methodology by using upper right lung apices alveoli in live intact mice. By enabling tracking of individual alveolar movements during respiration, TrXM identifies alveolar dynamics: individual alveoli in the upper lung apices show a small size increment as 4.9 ± 0.4% (mean ± s.e.m.) during respiration while their shapes look almost invariant. TrXM analysis in alveolar dynamics would be significant for better understanding of alveolar-based diseases, for instance, ventilator induced lung injury (VILI) in acute respiratory distress syndrome (ARDS).
[show abstract][hide abstract] ABSTRACT: Colloidal particles suspended in a fluid usually inhibit complete wetting of the fluid on a solid surface and cause pinning of the contact line, known as self-pinning. We show differences in spreading and drying behaviors of pure and colloidal droplets using optical and confocal imaging methods. These differences come from spreading inhibition by colloids confined at a contact line. We propose a self-pinning mechanism based on spreading inhibition by colloids. We find a good agreement between the mechanism and the experimental result taken by directly tracking individual colloids near the contact lines of evaporating colloidal droplets.
[show abstract][hide abstract] ABSTRACT: The manner in which the nervous system regulates animal behaviors in natural environments is a fundamental issue in biology. To address this question, C. elegans has been widely used as a model animal for the analysis of various animal behaviors. Previous behavioral assays have been limited to two-dimensional (2-D) environments, confining the worm motion to a planar substrate that does not reflect three-dimensional (3-D) natural environments such as rotting fruits or soil. Here, we develop a 3-D worm tracker (3DWT) for freely moving C. elegans in 3-D environments, based on a stereoscopic configuration. The 3DWT provides us with a quantitative trajectory, including the position and movement direction of the worm in 3-D. The 3DWT is also capable of recording and visualizing postures of the moving worm in 3-D, which are more complex than those in 2-D. Our 3DWT affords new opportunities for understanding the nervous system function that regulates animal behaviors in natural 3-D environments.
PLoS ONE 01/2013; 8(2):e57484. · 3.73 Impact Factor
[show abstract][hide abstract] ABSTRACT: Colloidal droplets including micro- and nanoparticles generally leave a ringlike stain, called the "coffee ring," after evaporation. We show that fingering emerges during evaporation inside the coffee ring, resulting from a bidispersed colloidal mixture of micro- and nanoparticles. Microscopic observations suggest that finger formation is driven by competition between the coffee-ring and Marangoni effects, especially when the inward Marangoni flow is overwhelmed by the outward coffee-ring flow. This finding could help to understand the variety of the final deposition patterns of colloidal droplets.
Physical Review E 01/2013; 87(1-1):013003. · 2.31 Impact Factor
[show abstract][hide abstract] ABSTRACT: When a liquid drop impacts a solid surface, air is generally entrapped underneath. Using ultrafast x-ray phase-contrast imaging, we directly visualized the profile of an entrapped air film and its evolution into a bubble during drop impact. We identified a complicated evolution process that consists of three stages: inertial retraction of the air film, contraction of the top air surface into a bubble, and pinch-off of a daughter droplet inside the bubble. Energy transfer during retraction drives the contraction and pinch-off of a daughter droplet. The wettability of the solid surface affects the detachment of the bubble, suggesting a method for bubble elimination in many drop-impact applications.
[show abstract][hide abstract] ABSTRACT: Colloids (colloidal particles or nanoparticles) and their in-situ characterizations are important topics in colloid and interface science. In-situ visualization of colloids with X-ray microscopy is a growing frontier. Here, after a brief introduction on the method, we focus on its application for identifying nanoscale wettability of colloidal particles at fluid interfaces, which is a critical factor in colloidal self-assembly. We discuss a quantitative study on colloidal wettability with two microscopic methods: (i) X-ray microscopy by visualizing natural oil–water interfaces and (ii) confocal microscopy by visualizing fluorescently-labeled interfaces. Both methods show consistent estimation results in colloid–fluid interfacial tensions. This comparison strongly suggests a feasibility of X-ray microscopy as a promising in-situ protocol in colloid research, without fluorescent staining. Finally, we address a prospect of X-ray imaging for colloid and interface science.
Current Opinion in Colloid & Interface Science 09/2012; · 6.63 Impact Factor
[show abstract][hide abstract] ABSTRACT: During bubble or droplet coalescence, there is a puzzling tendency for the coalesced bubble or droplet to be preferentially placed closer to the larger of its two parents. We confirm that this preference is a function of parent size ratio by directly visualizing coalescing air bubbles on an oil-water interface and coalescing water droplets immersed in oil. We find that the final position of the coalesced sphere is controlled by surface energy release and is related to the parent size ratio by a power-law relationship.
[show abstract][hide abstract] ABSTRACT: Three human liver tissue samples (∼5 mm × 40 mm × 20 mm) were excised from a cancer patient’s liver during surgery. The microradiology
analysis was performed with a non-standard approach on a synchrotron. High-resolution refractive-index edge-enhanced microradiographs
that cover a larger volume of the liver tissue sample were obtained. The cancer tissue and normal tissue could be clearly
identified and distinguished based on their different textures. Furthermore, new blood vessel hyperplasia was found near the
cancer area. Blood vessels with a diameter smaller than 20 μm could be identified. These findings were fully consistent with
the histopathological examination of the same area. Microradiographs of the newly formed blood vessels at different angles
were also obtained. This result shows that it is possible to further develop this approach into a technique of microradiographic
imaging for clinic diagnosis of liver cancer at the early stage.
Keywordssynchrotron microradiology-liver cancer-histopathology
Chinese Science Bulletin 04/2012; 50(22):2657-2661. · 1.32 Impact Factor
[show abstract][hide abstract] ABSTRACT: The ageing of the population is an issue in wealthy countries worldwide because of increasing costs for health care and welfare. Survival curves taken from demographic life tables may help shed light on the hypotheses that humans are living longer and that human populations are growing older. We describe a methodology that enables us to obtain separate measurements of scale and shape variances in survival curves. Specifically, 'living longer' is associated with the scale variance of survival curves, whereas 'growing older' is associated with the shape variance. We show how the scale and shape of survival curves have changed over time during recent decades, based on period and cohort female life tables for selected wealthy countries. Our methodology will be useful for performing better tracking of ageing statistics and it is possible that this methodology can help identify the causes of current trends in human ageing.
[show abstract][hide abstract] ABSTRACT: Acervuli are calcified concretions in the pineal gland (PG). Particularly interesting are their incidence and size, which are believed to affect neurological disorders and many physiological functions of PG such as regulating circadian rhythm. Despite long investigations for a century, detailed growth mechanism of acervuli has yet to be studied. Here we study the growth morphology of acervuli in human PGs by a direct visualization in 3-dimension (3-D) using a synchrotron X-ray imaging method. For an entire PG, non-aggregated acervuli show Gaussian distribution in size with 47±28 µm. The 3-D volume rendered images of acervuli reveal that the bumpy surfaces developed by lamination result in the mulberry-like structure. In addition, coalescence of multiple acervuli leads to large-scale lamination on the whole aggregate. We suggest a novel hypothesis on the growth patterns of acervuli by their nucleation density (N(d)): i) mulberry-like structure at low N(d), and ii) large-scale lamination on an aggregate at high N(d).
[show abstract][hide abstract] ABSTRACT: It has been generally accepted that any reaction between micropipes in silicon carbide (SiC) crystals requires a direct contact of the micropipes. We propose a new model of contact-free reactions that are realized through the emission and absorption of full-core dislocations by micropipes. This model can explain the correlated reduction in micropipe radii in the samples with low micropipe densities which has been observed in synchrotron radiation (SR) phase contrast images supported by computer simulations. We provide a theoretical description of a contact-free reaction between two parallel micropipes.
physica status solidi (a) 01/2012; 209(8):1432–1437. · 1.21 Impact Factor
[show abstract][hide abstract] ABSTRACT: The Vaccinia-related kinase 1(VRK1), which is generally implicated in modulating cell cycle, plays important roles in mammalian gametogenesis. Female infertility in VRK1-deficient mice was reported to be caused by defective meiotic progression in oocyte at postovulatory stage. VRK1 roles in folliculogenesis, however, remain largely unknown. Here, accurate quantification of folliculogenesis is performed by a direct visualization of 'intact' ovary in 3-dimensions (3-D) using a synchrotron X-ray microtomography. In VRK1-deficient ovaries, the numbers of pre-antral and antral follicles are significantly reduced by 38% and 46%, respectively, comparing to control. The oocytes volumes in antral and Graffian follicles also decrease by 42% and 37% in the mutants, respectively, indicating defects in oocyte quality at preovulatory stage. Genetic analysis shows that gene expressions related to folliculogenesis are down-regulated in VRK1-deficient ovaries, implying defects in folliculogenesis. We suggest that VRK1 is required for both follicle development and oocyte growth in mammalian female reproduction system.
[show abstract][hide abstract] ABSTRACT: The X-ray synchrotron is quite different from conventional radiation sources. This technique may expand the capabilities of conventional radiology and be applied in novel manners for special cases. To evaluate the usefulness of X-ray synchrotron radiation systems for real time observations, mouse fetal skeleton development was monitored with a high resolution X-ray synchrotron. A non-monochromatized X-ray synchrotron (white beam, 5C1 beamline) was employed to observe the skeleton of mice under anesthesia at embryonic day (E)12, E14, E15, and E18. At the same time, conventional radiography and mammography were used to compare with X-ray synchrotron. After synchrotron radiation, each mouse was sacrificed and stained with Alizarin red S and Alcian blue to observe bony structures. Synchrotron radiation enabled us to view the mouse fetal skeleton beginning at gestation. Synchrotron radiation systems facilitate real time observations of the fetal skeleton with greater accuracy and magnification compared to mammography and conventional radiography. Our results show that X-ray synchrotron systems can be used to observe the fine structures of internal organs at high magnification.
[show abstract][hide abstract] ABSTRACT: Sliced SiC boule grown by physical vapor transport is investigated using synchrotron white beam phase contrast imaging combined with Bragg diffraction. The evolution of defects is revealed. In the early growth stage, foreign polytype inclusions not only induce massive generation of full-core dislocations and dislocated micropipes but also attract them, forming slit-type pores at the boundaries of inclusions.In the intermediate stage, when inclusions stop to grow and become overgrown by the matrix, the pore density significantly reduces, which is attributed to their transformation into new micropipes. In the later stage, the micropipe density decreases, providing evidence for their partial annihilation and healing. Mechanisms for the evolution from inclusions to pores and finally to micropipes during the crystal growth are further discussed.
Physica Status Solidi (A) Applications and Materials 01/2011; 208(4):819 - 824. · 1.46 Impact Factor