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Biomedical subjects

JM Lee

Publications and source records attributed to JM Lee.

9 recordsLinked to original sources
PubMed2000

Development of a three-dimensional data acquisition method for standardization of beta-emitting nuclides

We have developed a three-dimensional data-acquisition system with which pulse heights from an array of detectors can be multi-scaled with dwell times as short as 31 ns. The main part of the system consists of three ADCs of SAR (Successive Approximation Register) type, a 32 MHz oscillation clock and DRAM (Dynamic Random Access Memory) of 192 Mbyte capacity. The clock time is determined by count the clock pulse generated by 28 bits synchronous counter. Both the pulse height and the time information are stored at an array of DRAM, of 40-bits width, 12-bits for pulse height and 28-bits for clock time. The technique is particularly suitable for experiments such as both double and triple coincidence distributions are required. Virtues of the method are demonstrated by measuring the activity of 14C with a 3-PM liquid scintillation counting system. The computer discrimination together with the MCTS (multi-channel time scaling) technique is applied for efficiency variation method in the analysis.

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PubMed2000

Correlation effect in activity measurement of 59Fe

Correlation effects due to the cascade transition of gamma-rays with gates on the relevant peaks have been studied in activity measurement of 59Fe using the bi-dimensional coincidence counting method. Extrapolation curves were obtained at three gamma gates of 1099.2 keV, 1291.6 keV, and that covering both photo-peaks by a computer discrimination method. Of these extrapolation curves, only that obtained at (950-1350) keV gamma gate shows a linear variation, but those of two single gamma gates are not linearly varied in the high efficiency region. This nonlinearity obtained at the gamma gate of 1099.2 keV photo-peak was caused by the correlation effects due to 1-3 coincidence relation via unobserved 192 keV gamma-ray transitions.

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PubMed2000

Eigenmode analysis of arbitrarily shaped two-dimensional cavities by the method of point-matching

In the proposed method, as in the boundary element method (BEM), a field problem is solved on its boundary along which nodes are distributed. The distinct feature of the proposed method is related to the fact that no interpolation functions between the nodes are required, so that the basic collocation method is employed to satisfy a given boundary condition. This approach reduces a large amount of numerical calculation induced due to the interpolation functions. Unlike the method of auxiliary sources (MAS), in the proposed method only the regular functions that have finite functional values everywhere including the origins are employed as basis functions. As a result, the proposed method does not need the auxiliary surface, the construction of which is a troublesome work because its form, dimension, shifting, etc. strongly influence the accuracy of the MAS. The eigenvalues calculated by the proposed method rapidly converge to the exact values thanks to the simplicity of the method. Moreover, the method gives mode shapes successfully without using the interpolation functions between the nodes. The efficiency and accuracy of the method are verified through several applications.

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PubMed1998

Mechanical properties of the tadpole tail fin

The tadpole tail fin is a simple double layer of skin overlying loose connective tissue. Collagen fibres in the fin are oriented at approximately +/-45 degrees from the long axis of the tail. Three tests were conducted on samples of the dorsal tail fin from 6-10 Rana catesbeiana tadpoles to establish the fin's viscoelastic properties under (1) large-deformation cyclic loading at 1 and 3 Hz, (2) small-deformation forced vibration at 1 and 3 Hz, and (3) stress relaxation under a 0.1 s loading time. The fin was very fragile, failing easily under tensile loads less than 7 g. It was also strikingly viscoelastic, as demonstrated by 72+/-1 % hysteresis loss (at 3 Hz), 16+/-3 % stress remaining after 100 s of stress relaxation and a phase angle of 18+/-1 degrees in forced vibration. As a consequence of its viscoelastic properties, the fin was three times stiffer in small than in large deformation. This may account for the ability of the fin to stay upright during normal undulatory swimming, despite the absence of any skeletal support. Tadpoles in nature are often found with damaged tails. We suggest that the unusually viscoelastic and fragile nature of the fin helps tadpoles escape the grasp of predators. Because the fin deforms viscoelastically and tears easily, tadpoles can escape predators and survive otherwise lethal attacks with only minor lacerations to the fin. Recent studies have shown that certain tadpoles develop taller fins in the presence of predators. This developmental plasticity is consistent with the tail fin acting as a protective but expendable 'wrap' around the core muscle tissue.

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PubMed1997

Preparation of Silica-Based Mesoporous Materials From Fluorosilicon Compounds: Gelation of H2SiF6 in Ammonia Surfactant Solution

The silica-based mesoporous molecular sieves were synthesized from fluorosilicon compounds and Al, Ti with the hydrolysis reaction of H2SiF6 in an ammonia-surfactant mixed solution. Well-crystalline mesoporous molecular sieves were obtained after several hours at the atmospheric conditions. The solid products were characterized by X-ray powder diffraction, nitrogen adsorption/desorption, transmission electron microscopy and solid-state NMR spectroscopy. The solid products show high specific surface areas in the range of 627-1040 m2/g, depending on the amount of Al and Ti. Also, they exhibit narrow pore size distributions in the range of 31-35 A according to the addition of Al and Ti. 29Si MAS NMR indicate that all samples mainly contain Q4 types sites. Also, the peak intensity of Q3 sites decreases with increasing amount of aluminum. In 27Al MAS NMR spectra, all samples give intense lines from 4-coordinate aluminum. These results show that aluminum species are incorporated into the framework of Si-MMS. As the amount of Al increases, the intensity line from 6-coordinate aluminum increases. This result represents the increase of the fraction of amorphous aluminum species.

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