Embedded strong discontinuity finite elements for fractured geomaterials with variable friction

The strong discontinuity approach to modelling strain localization, combined with an enhanced strain element, has been used for more than a decade to model strain localization in materials including geomaterials. Most implementations of enhanced strain elements in the post-localization regime use very simple constitutive formulations along the discontinuity, such as linear softening or a constant friction coefficient. However, the softening relations can be much more complex for geomaterials. For rocks this softening is induced by micro-fractures coalescing into macroscopic cracks during a narrow time interval called ‘slip weakening.’ During this interval the cohesive resistance on the nucleating crack decays to zero while the frictional resistance increases. Furthermore, research has shown that the coefficient of friction for these materials is not constant, but in fact is a function both of the slip speed and the state of the material, including wear, temperature, and other factors. In this paper we augment the modelling capabilities of an enhanced strain element by incorporating a cohesive softening law and a popular rate- and state-dependent friction model commonly used for describing the constitutive properties of rocks and rock-like materials sliding along the fractured surface. Copyright © 2007 John Wiley & Sons, Ltd.     

Mosquito bite hypersensitivity

Incidence of gastrointestinal tuberculosis increases in the western world. Exact epidemiological data about this rare extrapulmonological disease are not available in Hungary. Three advanced cases with intestinal tuberculosis have been reported, all of them recognised during surgery due to complications. The clinicopathological correlations are briefly reviewed, and the importance of early diagnosis is emphasized.     

Hypersensitivity to chironomid larvae

BACKGROUND: The aim of this study was to identify the proteolytic activity which triggers the transformation of human alpha2-macroglobulin (alpha2-M) in seminal fluid and its binding to its receptor. METHODS: Measurement of the concentrations of total and transformed alpha2-M in seminal fluid was accomplished by ELISA. Zymography of seminal plasma was performed in SDS-polyacrylamide gels containing casein as proteolytic substrate. Rate electrophoresis, SDS-PAGE, and Western blotting were applied to study the complex formation of prostate-specific antigen (PSA) with alpha-M. Ligand-binding analysis of sperm cells was performed using [125I] labeled proteins. Detection of receptor on sperm cells was achieved by immunofluorescence. RESULTS: The mean concentration of total alpha2-M in a random collection of seminal plasma was 4.6 microg/ml. On average, between 33-98% of the inhibitor was found to be transformed. Zymography of seminal plasma revealed a proteolytic activity which is associated with a 33-kDa protein identified as PSA. Its proteolytic activity could be inhibited by 0.2-M. Both purified PSA and seminal plasma were capable of transforming native alpha2-M. Binding of PSA to alpha2-M triggers the exposition of receptor binding sites in the inhibitor molecule, which causes binding of the complex to alpha2-M-R/LRP identified on spermatozoa. CONCLUSIONS: PSA, the main proteinase in seminal fluid, is responsible for the transformation of alpha2-M and for its binding to alpha2-M-R/LRP present on spermatozoa. The binding of alpha2-M-PSA complexes to the spermatozoa receptor may exert an impact on normal sperm-cell functions.     

Heavy metal removal by microalgae

The liver is one of the principal sites of iron overload in diseases such as hemochromatosis and beta thalassemia. Hence, much effort has been invested in examining the mechanisms of Fe uptake by hepatocytes. In the present study we have examined the effect of small molecular weight (M(r)) Fe complexes on Fe uptake from iron 59-labeled transferrin (Tf) and 59Fe-labeled citrate by primary cultures of hepatocytes. This was important to assess because Fe-citrate and saturated diferric Tf coexist in the serum of patients with untreated Fe overload. Preincubation of hepatocytes with the low-M(r) Fe complex ferric ammonium citrate (FAC; 25 microg/mL; (Fe) = 4.4 microg/mL) followed by incubation with 59Fe-Tf or 59Fe-citrate ((Fe) = 0.25 to 25 micromol/L) resulted in the marked stimulation of 59Fe uptake. For example, at a physiologically relevant Tf-Fe concentration of 25 micromol/L, there was an 8-fold increase in 59Fe uptake by cells incubated with FAC compared to control cells. In contrast, at Tf-Fe concentrations of 0.25 to 2.5 micromol/L, 59Fe uptake in FAC-treated cells was only 1-fold to 3-fold greater than that in the corresponding controls. These data suggest that the FAC-activated Fe uptake process predominates at physiologically relevant Tf concentrations above the saturation of the Tf receptor (TfR). This is the first study to demonstrate that preincubation of hepatocytes with Iow-M(r)Fe complexes can markedly increase Fe uptake from diferric Tf. In conclusion, these results may help to explain the loading of hepatocytes with Fe that occurs in Fe-overload disease despite marked down-regulation of the TfR.     

An improved method for magnetic identification and localization of cracks in conductors

A SQUID magnetometer can be used to measure the magnetic field produced by flaws in a two-dimensional, conducting plate carrying a current. Identification of the flaw-induced magnetic field is difficult because of the large magnetic field associated with the edges of the plate and the current in the leads that connect the plate to the power supply. We have developed a technique by which the wire and edge fields can be cancelled prior to mapping the magnetic field. In this technique, a similar unflawed conducting sheet is placed adjacent to the flawed plate, with a connection between the sheet and the plate at one edge, and with the opposite edges of the sheet and of the plate connected to the two conductors of a coaxial cable. Thus, an applied current will flow along one conductor of the cable, across the cancelling sheet, cross into the flawed plate, return along the plate, and then return to the power supply along the other conductor of the coaxial cable. As a result of this geometry, there is no magnetic field from the lead-in wires because they are coaxial, and the magnetic field due to the edges of the plate is cancelled by the opposing magnetic field of the edges in the adjacent sheet. The extent of cancellation is determined primarily by the separation between the plate and the cancelling sheet, by the thickness of the plate, and by macroscopic inhomogeneities in their electrical conductivities.     

Discrete micromechanics of elastoplastic crystals

The theoretical prediction of elastoplastic behaviour of single crystals is a basic problem which is central to the prediction of the overall behaviour of the crystal aggregate. It is generally well known that quasi-static and isothermal plastic deformation in single crystals arises almost solely from slip on specific crystallographic planes, and that this process occurs when the resolved shear stress on a critical slip system reaches a certain maximum value. What is not obvious is how one can identify the specific slip systems activated by a given load increment, since the process usually involves selection from a pool of linearly dependent slip systems. In this paper we use small-deformation multisurface plasticity theory to phrase properly the problem of crystal slips at infinitesimal increments. We then describe an ‘ultimate’ algorithm for systematically identifying the active slip systems at finite increments. We arrive at the following major conclusions when the ultimate algorithm is applied to f.c.c. crystals: For perfectly plastic crystals the combination of active slip systems may or may not be unique; however, the imposition of the discrete Kuhn-Tucker conditions is sufficient to determine the (unique) final crystal stresses. For Taylor hardening crystals in which active and latent slip systems harden by the same amount, the discrete Kuhn-Tucker conditions are also sufficient to make the mathematical problem of crystal stress integration well posed, i.e. the final stresses can be determined uniquely albeit the combination of active slip systems may not be unique. To illustrate the latter point, an accurate return-mapping algorithm for perfectly plastic and Taylor hardening crystals is described and tested against the ultimate algorithm to demoustrate numerically that it is possible to generate different combinations of active slip systems and yet produce identical final stresses.     

Physicochemical and physiological changes during the ripening of Banana (Musaceae) fruit grown in Colombia

The physicochemical and physiological attributes of three contrasting commercial varieties of Musaceae, Dominico Harton (plantain), Guineo (cooking banana) and Gros Michel (dessert banana), were evaluated and statistically analysed during post-harvest ripening. Quality attributes differed markedly among varieties, both in fresh fruits and during ripening. Variety (V) had a significant effect (P < 0.001) on all attributes except total soluble solids (TSS), carotenes and total chlorophyll. Storage time (ST) had a significant effect on all attributes except colour parameter b* and total carotenes. Starch levels decreased significantly (P < 0.001) during ripening, with nearly complete hydrolysis in Gros Michel, followed by Guineo and Dominico Harton. Discriminant analysis showed that central diameter, TSS of the pulp, colour parameter a* and total starch had the highest weight in the differentiation among varieties. These results point out which parameters may help improve current methods for monitoring ripening of bananas, in particular the commercially important varieties in this study.