Macroscopic fracture characteristics of random particle systems

This paper deals with determination of macroscopic fracture characteristics of random particle systems, which represents a fundamental but little explored problem of micromechanics of quasibrittle materials. The particle locations are randomly generated and the mechanical properties are characterized by a triangular softening force-displacement diagram for the interparticle links. An efficient algorithm, which is used to repetitively solve large systems, is developed. This algorithm is based on the replacement of stiffness changes by inelastic forces applied as external loads. It makes it possible to calculate the exact displacement increments in each step without iterations and using only the elastic stiffness matrix. The size effect method is used to determine the dependence of the mean macroscopic fracture energy and the mean effective process zone size of two-dimensional particle systems on the basic microscopic characteristics such as the microscopic fracture energy, the dominant inhomogeneity spacing (particle size) and the coefficients of variation of the microstrength and the microductility. Some general trends are revealed and discussed.Walter P. Murphy Professor of Civil Engineering and Materials Science.     

Internal irradiation from nuclear medicine investigations: a comparison between effective dose equivalent and effective dose

Here we report on a girl with diploid/triploid mosaicism followed up to age 5 years. The clinical manifestations are compared to those of other reported cases. In contrast to most cases, our patient was not growth retarded despite severe delays in psychomotor development. We also discuss 2 manifestations that have not received sufficient attention in previous reports: pigmentary dysplasia and truncal obesity.     

Ion-exchangers containing phosphorus in their functional group. Sorption of cations from nitric acid solutions and from acetate medium

A selective sorption of uranyl ions on organic ion-exchangers containing -OPO(OH)₂ or -PO(OH)₂ groups from dilute nitric acid solution and the affinity of various divalent cations to these groups in acetate medium were studied. Practical applications of these ion exchangers for the separation are described.     

On the importance of dimension variation in determining the limiting steps in adsorption kinetics

Information about the limiting processes in adsorption kinetics can be obtained by an analysis of the shape of the uptake curves (first and second statistical moments M₁ and M₂) as well as by an analysis of the dependence of the adsorption time constants on the radii (R) of the adsorbing particles. The sensitivity of these dependences on the various models of adsorption has been investigated by introducing the factors M₁²/M₂ and d ln M₁/d ln R. d ln M₁/d ln R-2 is shown to be a reliable criterion for diffusion-limited adsorption. From the shape of M₁²/M₂ no corresponding criterion can be derived.     

4-Methylimidazol in Caramel und caramelgef?rbten Lebensmitteln

Zusammenfassung Es wird eine spezifische und kochempfindliche Methode zur Bestimmung von 4-Methylimidazol (4-MeI) in Caramel und caramelgefärbten Lebensmitteln beschrieben. Nach der Extraktion wird 4-MeI gaschromatographisch mit einem stickstoffspezifischen elektrochemischen Detektor (Hall) bestimmt. Als weniger spezifische Alternative kann ein thermoionischer Detektor eingesetzt werden. Bei Zusätzen von 5–200 mg 4-MeI/kg Karamel beträgt die Wiederfindungsrate 90–94%.Die Nachweisgrenze der Methode liegt unterhalb 0,1 mg 4-MeI/kg Caramel; in karamelgefärbten Lebensmitteln können weniger als 0,01 mg/kg nachgewiesen werden.

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4-methylimidazole in caramel and caramel-colored foodsDetermination by gas-liquid-chromatography with nitrogen-specific detectors

Summary A specific and highly sensitive method for the determination of 4-methylimidazole (4-MeI) in caramel and caramel-colored foods is described. After extraction the amount of 4-MeI is determined by gas-liquid chromatography with a nitrogen-specific electrochemical detector (Hall). As a less specific alternative a thermoionic detector can be used. With additions in the range of 5–200 mg 4-MeI/kg caramel, recoveries of 90–94% are obtained.The limit of detection is <0.1 mg 4-Mel/kg caramel; in caramel-colored foods less than 0.01 mg/kg can be detected.

     

Crosslinking of polypropylene in the presence of polyfunctional monomers

The crosslinking of atactic and isotactic polypropylene initiated by organic peroxides in presence of diallyl maleate or pentaerythrityl tetramethacrylate was studied. The influence of concentration of the components of the crosslinking system as well as the effect of temperature and reaction time was followed. For high yield of gel, a high rate of initiation is necessary. Also the rate of reaction of double bonds must be similar to the rate of peroxide decomposition.     

Crystal Chemistry of Iron in Non-Metamict Chevkinite-（Ce） ：Valence State and Site Occupation Proportions

Chevkiniteis one of the commonrare earth acces-sory minerals found in a wide occurrence of paragene-sis . About80analyses of samples in the chevkinitegroup have beenreportedto contain FeO(assuming∑Fe as FeO) rangingfrom7.11%to16·88%[1].How-ever ,in mine…     

Tensile and fracture toughness properties of SiC<Subscript>p</Subscript> reinforced Al alloys: Effects of particle size,particle volume fraction,and matrix strength

The goal of this work was to evaluate the effects of particle size, particle volume fraction, and matrix strength on the monotonic fracture properties of two different Al alloys, namely T1-Al2124 and T1-Al6061, reinforced with silicon carbide particles (SiC_p). From the tensile tests, an increase in particle volume fraction and/or matrix strength increased strength and decreased ductility. On the other hand, an increase in particle size reduced strength and increased the composite ductility. In fracture toughness tests, an increase in particle volume fraction reduced the toughness of the composites. An increase in matrix strength reduced both K _crit and δ_crit values. However, in terms of K _Q (5%) values, the Al6061 composite showed a value similar to the corresponding Al2124 composite. This was mainly attributed to premature yielding caused by the high ductility/low strength of the Al6061 matrix and the testpiece dimensions. The effect of particle size on the fracture toughness depends on the type of matrix and toughness parameter used. In general, an increase in particle size decreased the K _Q (5%) value, but simultaneously increased the amount of plastic strain that the matrix is capable of accommodating, increasing both δ_crit and K _crit values.