Advanced ceramics: evaluation of the mechanism of stock removal and ground surface quality

The aim of this work is to evaluate the mechanism of stock removal and the ground surface quality of advanced ceramics machined by a surface grinding process using diamond grinding wheels. The analysis of the grinding performance was done regarding the cutting surface wear behavior of the grinding wheel for ceramic workpieces. The ground surface was evaluated using Scanning Electron Microscopy (SEM). As a result it can be said that the mechanism of material removal in the grinding of ceramic is largely one of brittle fracture. The increase of the h max can reduce the tangential force required by the process. Although, it results in an increase in the surface damage, reducing the mechanical properties of the ground component.

Interphase cytogenetics using fluorescence in situ hybridization: an overview of its application to diffuse and solid tissue

Interphase cytogenetics, utilizing fluorescence in situ hybridization (FISH) techniques, has been successfully applied to diffuse and solid tissue specimens. Most studies have been performed on isolated cells, such as blood or bone marrow cells; a few have been performed on cells from body fluids, such as amniotic fluid, urine, sperm, and sputum. Mechanically or chemically disaggregated cells from solid tissues have also been used as single cell suspensions for FISH. Additionally, intact organized tissue samples represented by touch preparations or thin tissue sections have been used, especially in cancer studies. Advantages and pitfalls of application of FISH methodology to each type of specimen and some significant biological findings achieved are illustrated in this overview.

E. coli a-hemolysin: a membrane-active protein toxin

Alpha-Hemolysin is synthesized as a 1024-amino acid polypeptide, then intracellularly activated by specific fatty acylation. A second activation step takes place in the extracellular medium through binding of Ca2+ ions. Even in the absence of fatty acids and Ca2+ HlyA is an amphipathic protein, with a tendency to self-aggregation. However, Ca2+-binding appears to expose hydrophobic patches on the protein surface, facilitating both self-aggregation and irreversible insertion into membranes. The protein may somehow bind membranes in the absence of divalent cations, but only when Ca2+ (or Sr2+, or Ba2+) is bound to the toxin in aqueous suspensions, i.e., prior to its interaction with bilayers, can a-hemolysin bind irreversibly model or cell membranes in such a way that the integrity of the membrane barrier is lost, and cell or vesicle leakage ensues. Leakage is not due to the formation of proteinaceous pores, but rather to the transient disruption of the bilayer, due to the protein insertion into the outer membrane monolayer, and subsequent perturbations in the bilayer lateral tension. Protein or glycoprotein receptors for a-hemolysin may exist on the cell surface, but the toxin is also active on pure lipid bilayers.

Biflavonoids inhibit the production of aflatoxin by Aspergillus flavus

The biflavonoids 6,6"-bigenkwanin, amenthoflavone, 7,7"-dimethoxyagastisflavone and tetradimethoxybigenkwanin isolated from Ouratea species were tested for inhibitory activity on Aspergillus flavus cultures. Suspensions of Aspergillus flavus spores were inoculated into 50 ml of YES medium at different biflavonoid concentrations: 5 and 10 µg/ml for 6,6"-bigenkwanin, amenthoflavone and 7,7"-dimethoxyagastisflavone, and 5, 10, 15 and 20 µg/ml for tetradimethoxybigenkwanin. The four biflavonoids showed inhibitory activity on aflatoxin B1 and B2 production (P<0.001), but did not inhibit fungal growth at the concentration tested (P>0.05). These results show that biflavonoids can be used for the development of agents to control aflatoxin production.