Average Concentration Factor Research Articles

A Theory of Particle-Reinforced Plasticity

A simple, albeit approximate, theory is developed to determine the elastoplastic behavior of particle-reinforced materials. The elastic, spherical particles are uniformly dispersed in the ductile, work-hardening matrix. The method proposed combines Mori-Tanaka’s concept of average stress in elasticity and Hill’s discovery of a decreasing constraint power of the matrix in polycrystal plasticity. Under a monotonic, proportional loading the latter was characterized, approximately, by the secant moduli of the matrix. The theory is established for both traction and displacement-prescribed boundary conditions, under which, the average stress and strain of the constituents and the effective secant moduli of the composite are explicitly given in terms of the secant moduli of the matrix and the volume fraction of particles. In particular, the yield stress and work-hardening modulus of the composite are shown to be inversely proportional to the deviatoric part of average stress concentration factors of the matrix, and therefore will increase (or decrease) with increasing hard (or soft) particle concentration. It is also found that, even if the matrix is plastically incompressible, the composite as a whole is not. Comparison between the theory and the experiment for a silica/epoxy system shows a reasonable agreement. The theory is also compared with a recently developed one by Arsenault and Taya; while both give the same initial yield stress for the composite, the work-hardening modulus predicted by their theory is found to be higher.

ENGRAFTMENT OF STEM-CELL-ENRICHED BONE MARROW FRACTIONS IN MHC-IDENTICAL DOGS AFTER FRACTIONATED TOTAL-BODY IRRADIATION1

Discontinuous albumin density gradients were used to obtain enrichment of hemopoietic stem cells and depletion of T lymphocytes in aspirated dog bone marrow. Colony forming units in agar (CFU-C) were determined to evaluate the degree of enrichment achieved. An average CFU-C concentration factor of 12.4 was obtained. All transplantations in the study were carried out between DLA-identical sibling combinations. The number of CFU-C administered varied from 0.2 to 5.5 X 10(5)/kg and the number of nucleated cells transfused varied from 0.1 to 1.0 X 10(8)/kg. Stem cell concentrates were found more difficult to engraft than unmodified bone marrow following standard conditioning with a single total-body irradiation (TBI) dose of 7.5 Gy. The efficacy of different TBI-fractionation schedules for obtaining sustained engraftment of CFU-C-enriched grafts in identical bone marrow transplantation (BMT) was determined. A total dose of 12 Gy TBI delivered in two equal fractions of 6.0 Gy (72-hr interval) resulted in sustained engraftment of stem cell grafts in 7 of 7 evaluable dogs. A TBI dose of 9 Gy in two fractions of 4.5 Gy (72-hr interval) resulted in sustained engraftment in 5 of 7 evaluable dogs. The two dogs with engraftment failure received low total cell numbers (10(7) cells/kg) and low CFU-C numbers. 9 Gy of TBI in two fractions of 4.5 Gy (24-hr interval) resulted in sustained engraftment in 11 of 12 evaluable dogs. A significant improvement of engraftment was obtained by increasing the total dose of TBI, which necessitates fractionation into two fractions of TBI. The lower-total-dose TBI (9 Gy) produced less early and late toxicity than the total high-dose (12 Gy) TBI. The incidence of engraftment was similar for the two dosages, however the recovery of peripheral leukocyte counts was slower after 9 Gy TBI. In the dog, optimal conditioning for lymphocyte-depleted hemopoietic stem cell grafts can be obtained by increasing the dose of TBI and concomitant fractionation.

Accumulation of Dieldrin in an Alga (Scenedesmus obliquus), Daphnia magna, and the Guppy (Poecilia reticulata)

Scenedesmus obliquus, Daphnia magna, and Poecilia reticulata accumulated dieldrin directly from water; average concentration factors (concentration in organism, dry weight, divided by concentration in water) were 1282 for the alga, 13,954 for D. magna, and 49,307 (estimated) for the guppy. The amount accumulated by each species at equilibrium (after about 1.5, 3–4, and 18 days, respectively) was directly proportional to the concentration of dieldrin in the water. Daphnia magna and guppies accumulated more dieldrin from water than from food that had been exposed to similar concentrations in water. When guppies were fed equal daily rations of D. magna containing different concentrations of insecticide, the amounts of dieldrin accumulated by the fish were directly proportional to the concentration in D. magna; when two lots of guppies were fed different quantities of D. magna (10 and 20 organisms per day) containing identical concentrations of dieldrin, however, the amounts accumulated did not differ substantially.

A concentrator for thin-film solar cells

This paper presents a theoretical study of a novel concentrating reflector especially suited to thin-film solar cells. The concentrator consists simply of a V-trough with side-walls which are specularly reflecting and a base to which the solar cells are attached. Mounted with its axis in the east-west direction, the concentrator is designed to track the seasonal, but not diurnal motion of the Sun, by adjustments to its tilt made several times per year. A general method is described for determining the direct-beam concentration factor for any incidence angle, opening angle and side-wall reflectance. Integration of this concentration factor over all of the angles of incidence associated with the diurnal and seasonal motion of the Sun over one year, has yielded the yearly average concentration factor for direct solar radiation. A similar integration over an isotropic sky has yielded the concentration factor for the diffuse component of solar radiation. Total yearly average concentration factors of two or higher appear to be possible with this concentrator design.

Extracellular concentrating of proteins in the cecropia moth follicle.

AbstractYolk proteins, derived from the blood, are incorporated into the oocytes of insects and certain vertebrates by pinocytosis, but reach the oocyte surface only after penetrating the surrounding follicular epithelium via intercellular channels. In an investigation of the events occurring in these intrafollicular spaces, the dense extracellular material present between the follicle cells and in the oocyte's brush border was extracted from vitellogenic cecropia moth follicles by soaking in physiological saline. Quantitative immunochemical determination of several eluted blood proteins revealed that these components had been more concentrated in the extracellular spaces than in the blood. The average concentration factors were 2.5 for the predominant yolk protein, vitellogenin, and 4.5 for the carotenoid protein.Since injected foreign proteins were also accumulated in the spaces, the concentrating mechanism seemed to act on all available proteins. However, in vitro inhibition of yolk formation with dinitrophenol resulted in a selective increase in the amount of extracellular vitellogenin in follicles which had been previously exposed to a medium low in this protein, suggesting accumulation of a factor with a specific affinity for it. Furthermore under certain conditions vitellogenin was more readily released from the concentrate than was the carotenoid protein. These results indicate that, despite apparent lack of discrimination in the binding of blood proteins in the spaces, extracellular interactions may contribute to the selectivity known to occur during vitellogenesis.

Concentration of 137Cs, 65Zn, and 85Sr by fresh‐water algae

AbstractDifferences in the concentration and retention of 137Cs by unicellular diatoms, filamentous green algae, and filamentous blue‐green algae were demonstrated under both batch and continuous‐flow culture conditions. 137Cs concentration factors were generally higher by a factor of 2 in batch tests than in continuous flow tests. In retention studies, 137Cs was desorbed more rapidly from algae under continuous‐flow conditions. Studies with blue‐green algae indicate that 137Cs concentrations in the various species were more closely related to the surface‐to‐volume ratios of algal cells than to the systematic relationships of the three species. Continuous‐flow studies indicated no differences among three species of filamentous green algae in the concentration of 137Cs, 65Zn, and 85Sr. However, the average concentration factors of the radionuclides were considerably different: 3800 for 65Zn, 460 for 137Cs, and 230 for 85Sr. These radionuclides were rapidly desorbed following the transfer of algae to nonradioactive media. The desorption rate was inversely related to the concentration rate.

Environmental contamination with radioruthenium, 1961-1965.

The results of measurements of medium-lived 103Ru and 106Ru in air-borne particles, fall-out, surface soil, river water, sea-water, foodstuffs, complete diet and human muscle and lungs during 1961-1965 are summarized. Main passage route of 103Ru was found through the fresh leafy vegetables, while 106Ru was supplied by different way, i. e., 77% by plant materials raised on land, 6% by foodstuffs of animal origin and the remainder by seaweed ; the concentration was the highest in the last item. Estimation of lung and body burdens was performed on the basis of observed data for inhalation and ingestion and compared with the result of measurements on human materials obtained from cadavers. The mobility of fall-out ruthenium in the sequence between precipitation and run-off from rivers seemed a little larger than strontium and much larger than cesium, reaching 14% of fresh fall-out to be delivered to the sea. Average concentration factor from sea-water to sea food as a whole was found to be 70 or equivalent daily intake of sea-water to be 7 kg. On this basis, the maximum permissible concentration of 106Ru in sea-water was suggested as 3 × 10-6μCi/ml.