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Biomedical subjects

K Hozumi

Publications and source records attributed to K Hozumi.

At least 37 records · Page 2Linked to original sources
PubMed1993

Characterization of the T cells in aged rat bone marrow.

In this study, we determined the characteristics of CD3-positive (CD3+) T cells existing in rat bone marrow (BM). In contrast to splenic T cells, BM CD3+ T cells are composed of a higher proportion of CD8+ T cells, and the number of both cell types increased with age. Such CD3+ T cells in aged rats showed a similar usage of TCR V beta as splenic T cells, suggesting that BM CD3+ T cells are thymus-dependent and composed of an ordinary population in view of the expression of the TCR beta-chain. Purified T cells obtained from aged rat BM showed a markedly proliferative response by stimulation with immobilized anti-CD3 mAb, as did splenic T cells. However, the addition of BM non-T cells completely inhibited the response of both BM and splenic T cells in vitro. These results suggest that T cells in rat BM are negatively regulated by BM non-T cells in their response to the TCR-mediated signal not to disrupt the microenvironment of the BM.

Aging↗
PubMed1993

A growth model of a single sugi (Cryptomeria japonica) tree based on the dry matter budget of its aboveground parts.

Growth of a single sugi (Cryptomeria japonica (L.f.) D. Don.) tree was analyzed on the basis of a dry matter budget. The aboveground net production rate and death rate were defined as the anabolic rate and catabolic rate, respectively. Growth rate of aboveground tree weight, v(w) (kg(dw) year(-1)), was defined as follows: v(w) = v(p) - v(d) (1) where v(p) (kg(dw) year(-1)) is the aboveground net production rate and v(d) (kg(dw) year(-1)) is the aboveground death rate. The value of v(d) is obtained by measuring the monthly clippings of new dead leaves and branches attached to a sample tree. The value of v(w) was calculated as the annual difference in the estimated aboveground tree weight, w(T) (kg(dw)). Finally, the value of v(p) was estimated as the sum of the values of v(d) and v(w). The following allometric relationships were found between v(p) and w(T) and between v(d) and w(T): v(p) = aw(T) (alpha), v(d) = bw(T) (beta) (2). Combining Equations 1 and 2 gives a growth equation, Bertalanffy's equation, of the sample tree. dw(T)/dt = v(w) = aw(T) (alpha) - bw(T) (beta) (3). Because the growth curve of w(T) was derived from Equation 3, the analysis of the growth of w(T) is based on direct measurement of the dry matter budget.

Journal Article↗
PubMed1992

Long-term respiration in relation to growth and maintenance processes of the aboveground parts of a hinoki forest tree.

Over a three-year period, CO(2) exchange rates were measured continuously on the aboveground parts of a 13-year-old hinoki (Chamaecyparis obtusa (Sieb. et Zucc.) Endl.) tree in the field, using an open gas-exchange system tracking ambient temperature. The relationship between daily aerial respiratory consumption and daily gross production, which was analyzed monthly, closely resembled McCree's equation. The value of the coefficient of growth respiration ranged between 0.0 in winter and 0.16 in summer and increased with increasing monthly mean temperature. A clockwise loop was observed for monthly change in the relationship between the coefficient of growth respiration and temperature. Maintenance respiration could be formulated as a power function of aboveground dry weight. The exponent of the equation ranged from 0.3 to 1.1. A value of 1.1 in May and June, when trees were growing most actively, indicated that maintenance respiration was directly proportional to aboveground weight. In March, April, July, and August, maintenance respiration was not proportional to aboveground weight, but it was closely proportional to surface area. The exponent value exhibited seasonal change with a clockwise loop in response to monthly average temperature. During the dormant season, respiration was used only for maintenance purposes, whereas during the growing season both growth and maintenance respiration occurred. Annual growth and maintenance respiration increased with increasing tree age. The average annual contribution to total respiratory consumption was 21% for growth respiration and 79% for maintenance respiration.

Journal Article↗
PubMed1986

An estimate of the photosynthetic production of individual trees in a Chamaecyparis obtusa plantation.

A Weibull function was used to model the vertical distribution of leaf area of individual trees in a 25-year-old Chamaecyparis obtusa (Siebold & Zucc.) Endl. plantation. The parameter representing the shape of the leaf distribution was independent of tree size. A scale parameter tended to decrease with tree size suggesting a critical minimum height for retention of foliage by trees. On the basis of leaf distribution, the photosynthetic production of individual trees was estimated from the canopy photosynthetic production, which was determined from a model of canopy photosynthesis. The data indicated that the photosynthesis of a tree was proportional to the corresponding tree weight to the power of 1.84. Furthermore, the photosynthetic production varied as the 3/2nd power of total leaf area of the tree. Thus, it was concluded that the photosynthetic production per unit of leaf area, that is, the mean photosynthetic activity of a tree, is proportional to the stem girth at clear length, or the square root of the leaf area of the tree.

Journal Article↗
PubMed1982

Measurements of radionuclides induced in the accelerator structure of the KEK-PS.

Radionuclides induced in accelerator structures were measured during each long shut-down by using a pure Ge detector and a portable multichannel pulse height analyzer. Variation in the nuclide composition for various points in the accelerator tunnel was investigated. The decay of the exposure rate was calculated using the measured nuclide composition. Radionuclide measurements of the vacuum chamber removed from the accelerator were also performed. The relation between the variation of the residual exposure rate and that of the nuclide composition was examined and it was found that the proportion of 48V, 54Mn and 56Co corresponds to variation in the beam loss pattern.

Particle Accelerators↗