Biomedical subjects

Yoshiki Kohmura

Publications and source records attributed to Yoshiki Kohmura.

4 recordsLinked to original sources

PubMed2006

Three-dimensional GaN-Ga2O3 core shell structure revealed by x-ray diffraction microscopy.

In combination of direct phase retrieval of coherent x-ray diffraction patterns with a novel tomographic reconstruction algorithm, we, for the first time, carried out quantitative 3D imaging of a heat-treated GaN particle with each voxel corresponding to 17 x 17 x 17 nm3. We observed the platelet structure of GaN and the formation of small islands on the surface of the platelets, and successfully captured the internal GaN-Ga2O3 core shell structure in three dimensions. This work opens the door for nondestructive and quantitative imaging of 3D morphology and 3D internal structure of a wide range of materials at the nanometer scale resolution that are amorphous or possess only short-range atomic organization.

Journal Article↗

PubMed2006

Reconstruction of complex-valued electron density with x-ray in-line holograms.

A reconstruction algorithm is proposed to analyze the complex-valued electron-density distribution in an object with x-ray in-line holograms. The real and imaginary parts of the electron density correspond to local variations of x-ray phase shift and absorption, respectively. In the algorithm, the least-squares error of the holograms is iteratively minimized under sign constraints on the real and imaginary parts. The constraints, which are derived from the physical conditions in the interaction between x rays and materials, facilitate robust reconstruction. The reconstruction was applied to holograms of a biological specimen that caused both phase shift and absorption.

Journal Article↗

PubMed2005

Quantitative image reconstruction of GaN quantum dots from oversampled diffraction intensities alone.

The missing data problem, i.e., the intensities at the center of diffraction patterns cannot be experimentally measured, is currently a major limitation for wider applications of coherent diffraction microscopy. We report here that, when the missing data are confined within the centrospeckle, the missing data problem can be reliably solved. With an improved instrument, we recorded 27 oversampled diffraction patterns at various orientations from a GaN quantum dot nanoparticle and performed quantitative image reconstruction from the diffraction intensities alone. This work in principle clears the way for single-shot imaging experiments using x-ray free electron lasers.

Journal Article↗

PubMed2004

The role of pigment cells in the brain of ascidian larva.

The functions of melanin in the pigment cells, the ocellus and the otolith, of ascidian larvae were studied by their swimming behavior and cell morphology with and without 1-phenyl-2-thiourea (PTU), an inhibitor of vertebrate tyrosinase. Melanin formation in both the otolith and the ocellus of PTU-treated larvae at 12 hours of development was completely inhibited. These larvae were unable to swim because of abnormal tail development, but expression of rhodopsin in the outer segments of the photoreceptor was normal. In the PTU-treated larvae at 15 hours of development, melanin formation in the ocellus was inhibited, but that in the otolith seemed to be normal. The photic behavior of these larvae was normal, as was rhodopsin expression in the outer segments. However, the treated larvae lost upward swimming behavior. Synchrotron radiation X-ray fluorescence images showed that metallic elements of K, Ca, and Zn in the statocyte of larva were greatly decreased by PTU treatment, which may result in lowering the specific gravity of the pigment mass. SEM observations showed that the statocyte of Ciona intestinalis was supported by three parts, a foot-piece of the statocyte itself and two fibrous spring-like structures produced from protuberances. All three structures were synaptotagmin-positive. Movement of the statocyte would be detected by these three structures and thus would be responsible for the gravitational orientation.

Animals↗