Twofold Mechanism Research Articles

Elasto-dynamic analysis of rectangular plates with circular holes

The problem of the free vibrations of a rectangular elastic plate, either clamped or simply supported, with a central circular hole has been investigated by a least-squares point-matching method. The results are given in the form of curves relating the natural frequency of the plate to the hole size for a variety of Poisson's ratios. The curves do not behave monotonically, and the hole size at which the frequency is a minimum is seen to be dependent not only on the boundary conditions but also on Poisson's ratio. A two-fold mechanism of strain relief and mass reduction is proposed to explain these results as well as the results of previous studies on the vibrations of plates with discontinuities.

Investigation of the disposition of surfactant in a latex by the “rate of dialysis method.” Mechanism of detergent dialysis

AbstractThe initial rate of dialysis across a cellophane membrane for sodium dodecylsulfate and dodecylbenzenesulfonate proved to be dependent on surfactant concentration without a break at the critical micelle concentration (cmc) and could, therefore, be used to determine free surfactant concentration in latices over a wide range. Equilibrium dialysis is not a suitable tool, because, if the cmc is exceeded in the dialyzate, diffusion comes practically to a dead stop long before equilibration, at least with ordinary detergents. (Dialysis is, however, resumed at a substantial rate if dialyzate and dialyzed solution are replaced by newly prepared solutions of the same concentration.) An explanation for these phenomena is suggested. Free surfactant concentrations measured by rate of dialysis were far below the cmc in a polystyrene latex and far above the cmc in a comparable poly(vinyl acetate) (PVA) latex. When increasing the surfactant‐polymer ratio in a PVA dispersion by post‐addition complete solubilization of the polymer is observed eventually. Concentrations of free surfactant and of solubilized polymer were measured for the intermediate stages. The experimental data indicate a twofold mechanism for the solubilization process: Surfactant penetrates into the interior of PVA particles taking water with it and causing swelling to the point of disintegration, parallel to which single chains from the outer parts of the particles are already disentangled and solubilized. It is concluded that in a PVA latex only a comparatively small portion of the anionic surfactant will be at the particle surface, a relatively large part being in the aqueous phase and in the particle interior, which may account for this surfactant being a poor stabilizer in vinyl acetate emulsion polymerization at high total solids content.

In VivoGlucose Induced Acceleration of the Inactivation of Fructose Diphosphatase in Wheat Embryos

Abstract The effects of glucose on FDPase have been studied in isolated wheat embryos. The data may be interpreted as showing that glucose (or some derivative), beside repressing FDPase synthesis, also specifically accelerates the rate of FDPase inactivation. It appears, therefore, that under physiological conditions the control of the reaction catalyzed by FDPase is achieved not only through the regulation of the activity of the enzyme, but also by a twofold mechanism of repression of the synthesis of this enzyme and of acceleration of its inactivation.

Mechanism of ozone attack on α‐methyl glucoside and cellulosic materials

AbstractOzone attack on cellulose and related substances was investigated and appears to involve a twofold mechanism. One is a free‐radical chain mechanism involving oxygen in the propagating step. This slow reaction is highly indiscriminate, showing very little, if any, specificity as to the site of attack and resulting in the formation of peroxide, carbonyl, carboxyl, and presumably lactone groups. In the presence of oxygen, kinetic chain lengths of over 100 were measured, but in nitrogen atmosphere the total oxidation of substrate was equivalent to the amount of ozone consumed. The second process appears to be an electrophilic attack which liberates the anomeric carbon of glycosides via an ozone‐catalyzed hydrolysis of glycosidic linkages. This reaction, analogous to a nitronium or chloronium ion‐ or proton‐catalyzed hydrolysis, is postulated since chain degradation of polysaccharides is equally severe in the presence or absence of oxygen, and occurs in buffered solutions or suspensions even in the neutral pH range, and because the main product of ozone attack on α‐methyl glucoside is glucose. Brightness improvement in cellulose involves an electrophilic attack on double bonds and therefore is a direct function of the quantity of ozone used, like chain degradation. It is therefore not surprising that we have found no method of enhancing the specificity of ozone attack on the colored material relative to chain degradation. Because of the topochemical and diffusion‐controlled character of the reaction on cellulose, the use of a different temperature range will cause only a trivial difference in the relative rates of attack.

Ricerche Sull'Azione Promovente della Follicolina nel Duplice Meccanismo della Carcinogenesi

Studies were undertaken on an eventual initiating or promoting action of follicular hormone in the twofold mechanism of carcinogenesis on the mouse skin. Animals were grouped into two series. The first series was divided into two groups: one was painted with a folliculin oleous solution (Estrene 5) every 3 days, the other with a 5 per cent dilution of croton oil in estrene. The mice of the second series, previously submitted to three paintings with 3:4-benzpyrene, were divided into four groups: 1) control group, 2) painted with Estrene every 3 days, 3) treated with 5 per cent croton oil solution in olive oil, and 4) treated with 5 per cent dilution of croton oil in oleous solution of follicular hormone. Results show that the follicular hormone, either alone or combined with croton oil, fails to produce any initiating and promoting action when painted on mouse skin previously treated with sub-maximal doses of 3:4-benzpyrene. Folliculin, on the contrary, enhances considerably the promoting action of croton oil when painted with it on the skin sensitized with benzpyrene: a rather early appearance of epithelial projections without basal membrane and composed of atypical elements is seen, whereas in animals of the same series, long treated with paintings of croton oil diluted with olive oil or with oleous folliculin this picture is not observed.

Histological and clinical considerations on the effects of estrogen in cancer of the prostate

26 histological controls have been carried out on patients bearing prostata carcinoma and treated with estrogens. Results are exposed. The opinion is stressed that estrogens act on prostata carcinoma by a twofold mechanism, i.e. both by a hormonal and a direct cystostatical action.

Observations on the Occurrence, Characteristics and Specificity of Natural Agglutinins

1. A study has been made of natural agglutination as exemplified by the reactions of the serum of nine animal species with a variety of bacteria.2. End-titres are recorded, and the fact is noted that sera of different animal species show an order of agglutinating activity which is almost constant for all organisms used. Ox, pig and horse sera give consistently strong reactions, while specimens from rabbit, guinea-pig and rat react weakly or not at all. Sheep, human and cat sera occupy an intermediate position. Variations are noted, however, with different individual specimens of serum from the same species.3. Organisms of the series tested can also be grouped in order according to their apparent susceptibility to agglutination by normal sera.4. The serum of young animals is found to be deficient in the agglutinating principle.5. The agglutinating effect shows a thermolability intermediate between that of complement and the immune agglutinins. Complete inactivation occurs as a rule after exposure to 60° C.–65° C. for half-an-hour. For certain strains the serum principle is inactivated at much lower temperatures.6. Lability curves show marked irregularity. In certain cases a zone of relative inactivation is produced at a temperature of 55° C.7. The natural agglutinating substance is found to be present in greater degree in the carbonic acid insoluble fraction of serum than in the carbonic acid soluble fraction. In this respect it differs from the immune agglutinins, which are chiefly located in the carbonic acid soluble moiety.8. The agglutinating principle for each organism can be absorbed completely by the homologous strain, when a variable lowering of the end-titre for other unrelated organisms results. A similar lowering of activity for these organisms may be produced by treating the serum with non-specific physical absorbents. Charcoal and Kieselguhr were used to demonstrate this.9. By the technique of double absorption it can be shown that agglutination depends on non-specific and specific factors and it is concluded that normal serum agglutinates bacteria in virtue of a twofold mechanism:(a) A non-specific effect reacting in varying degree with all organisms and removable by treatment with a finely divided absorbent.(b) A series of specific effects reacting as true “natural antibodies.” These specific antibody-like principles exist for a wide variety of organisms. Absorption of any one organism removes the homologous effect leaving the remainder quantitatively unimpaired.10. The question of bacterial variation and receptor analysis in relation to the natural agglutinins is being studied and will be reported on at a later date.