Spark plasma sintering microscopic mechanisms of metallic systems: Experiments and simulations

The microscopic densification mechanisms of metallic systems (TiAl, Ag-Zn) by spark plasma sintering (SPS) have been studied by simulations and experiments. Finite element simulations showed that, despite very high current densities at the necks between metallic powder particles (≈5 × 10⁴ A/cm²), only very limited Joule overheating can be expected at these locations (<1°C), because of very fast heat diffusion. The microscopic plasticity mechanisms under these high electric currents have been studied by transmission electron microscopy. For this purpose, thin foils have been extracted by focused ion beam at the necks between TiAl powder particles. This is the first time, to the best of our knowledge, that microscopic plasticity mechanisms at the necks between powder particles are investigated by TEM during densification of a metallic powder. Dislocation glide and climb mechanisms were identified, followed by recovery and recrystallization. The elementary mechanism kinetically controlling these phenomena is proposed to be bulk diffusion of Al, which activation energy (360 kJ/mol) is close to the activation energy measured for densification (308 ± 20 kJ/mol). Comparisons of densification kinetics by SPS (≈60-110 A/cm²) and by hot pressing (0 A/cm²) showed no influence of current on these mechanisms. Finally, reaction experiments in the Ag-Zn system did not show any influence of very high currents (>1000 A/cm²) on diffusion kinetics. Consequently, densification by SPS occurs by classical mechanisms not affected by the current.     

Penicillium populations in dry-cured ham manufacturing plants

Seven ham manufacturing plants were sampled for 1 year to assess the mycoflora present in the air and on hams, with special attention given to potential mycotoxin producers. Temperature and relative humidity were recorded in the ripening rooms. Maturing rooms held hams from 2 to 3 through 6 to 7 ripening months, and aging rooms held hams for the following 6 to 7 months, until the 14-month ripening point, when they were ready for the market. Mean temperatures and relative humidities registered during the study were 14.9 degrees C and 62.4%, respectively, in maturing rooms and 16.3 degrees C and 57.6% in aging rooms. Aspergilli and penicillia, potential mycotoxin producers, were isolated in all the plants from the air and the ham. Aspergilli represented 5% of the isolates, while penicillia were largely dominant, with Penicillium nalgiovense being the most represented species (around 60% of the penicillia), followed by Penicillium nordicum, with 10 and 26% of the penicillia isolated, respectively, from the air or the ham. Ochratoxin A production ability, checked in vitro at 250C, was observed in 50% of the P. nordicum isolates obtained both from the air and the ham. Air and ham surface contamination by penicillia was greater in the ripening rooms, where higher temperatures were registered. A certain correlation was also observed between air and ham surface contamination. On the basis of this study, P. nordicum, the ochratoxin A producer that is notable on proteinaceous substrates, is normally present in ham manufacturing plants in Italy, even though not a dominant species. Further studies are necessary to clarify and ensure if dry-curing conditions minimize the potential risk of ochratoxin A formation in the product.     

Structure and function of mammalian DNA methyltransferases

DNA methylation plays an important role in epigenetic signalling, having an impact on gene regulation, chromatin structure, development and disease. Here, we review the structures and functions of the mammalian DNA methyltransferases Dnmt1, Dnmt3a and Dnmt3b, including their domain structures, catalytic mechanisms, localisation, regulation, post-translational modifications and interaction with chromatin and other proteins, summarising data obtained in genetic, cell biology and enzymatic studies. We focus on the question of how the molecular and enzymatic properties of these enzymes are connected to the dynamics of DNA methylation patterns and to the roles the enzymes play in the processes of de novo and maintenance DNA methylation. Recent enzymatic and genome-wide methylome data have led to a new model of genomic DNA methylation patterns based on the preservation of average levels of DNA methylation in certain regions, rather than the methylation states of individual CG sites.     

Bioactive compounds and antioxidant potential in fresh and dried Jaffa® sweeties,a new kind of citrus fruit

Bioactive compounds in the edible parts of fresh and dried Jaffa^® sweeties, a new kind of citrus fruit, were analysed and their antioxidant capacities were assessed. Antioxidant‐rich fractions were extracted from fresh and dried sweeties with 1.2 M HCl in methanol/water (1:1 v/v), and the antioxidant activities of these extracts were evaluated. Using the β‐carotene/linoleate model system, the extracts from equivalent quantities of fresh and dried sweeties showed 89 and 87% antioxidant activity respectively. Similarly, using the DPPH radical‐scavenging method, the extracts showed 87 and 85% antioxidant activity respectively. The best correlations were between caffeic acid content and β‐carotene and DPPH antioxidant activity values (r = 0.9849 and 0.9798 respectively, p = 0.005). Both fresh and dried sweeties are bioactive natural products; when fresh fruits are not available, properly dried sweeties could be used as a substitute. Copyright © 2004 Society of Chemical Industry     

Retention of mineral constituents in frozen brassicas depending on the method of preliminary processing of the raw material and preparation of frozen products for consumption

The content of ash, P, K, Ca, Mg, Na, Fe, Zn, Mn, Cu, Cr and Ni was determined in four species of brassicas: Brussels sprouts, broccoli, and green and white cauliflowers. The investigation covered the raw material, the material blanched or cooked before freezing and frozen products after 12 months of refrigerated storage and prepared for consumption. Frozen products were obtained by the traditional method of freezing the blanched material or by the modified method of freezing the cooked material. The processing of vegetables before freezing (washing, grinding, blanching or cooking) caused statistically significant decreases in most constituents analysed. Blanching did not basically change the content of sodium and calcium; or that of chromium in both types of cauliflower; copper and nickel in white cauliflower; and nickel and phosphorus in Brussels sprouts. Cooking in brine, however, caused increases in the content of ash, sodium and calcium in white cauliflower, decreases in the content of potassium and iron and, in some species, of the remaining constituents. In comparison with the traditional method, a greater content of most analysed elements was found in frozen products obtained by the modified technology and prepared for consumption. However, no significant differences were noted in the level of chromium in all the samples; in the level of calcium in broccoli and green cauliflower; of nickel in broccoli; of nickel, copper and zinc in white cauliflower; and of copper in green cauliflower.     

Dose intercomparison studies for 60Co gamma-ray and electron beam irradiation in the year 2002

1 Introduction With the rapid development of radiation process- ing by electron beam irradiation in China, it is more Ever since 1962, alanine/EPR dosimetry system and more needed to establish a transfer dosimetryhas been used to measure the absorbed dose.[1] Its ad- system with high accuracy to assure the quality of thevantages over othe…     

Atorvastatin Modulates the Efficacy of Electroporation and Calcium Electrochemotherapy

Electroporation is influenced by the features of the targeted cell membranes, e.g., the cholesterol content and the surface tension of the membrane. The latter is eventually affected by the organization of actin fibers. Atorvastatin is a statin known to influence both the cholesterol content and the organization of actin. This work analyzes the effects of the latter on the efficacy of electroporation of cancer cells. In addition, herein, electroporation was combined with calcium chloride (CaEP) to assess as well the effects of the statin on the efficacy of electrochemotherapy. Cholesterol-rich cell lines MDA-MB231, DU 145, and A375 underwent (1) 48 h preincubation or (2) direct treatment with 50 nM atorvastatin. We studied the impact of the statin on cholesterol and actin fiber organization and analyzed the cells’ membrane permeability. The viability of cells subjected to PEF (pulsed electric field) treatments and CaEP with 5 mM CaCl₂ was examined. Finally, to assess the safety of the therapy, we analyzed the N-and E-cadherin localization using confocal laser microscopy. The results of our investigation revealed that depending on the cell line, atorvastatin preincubation decreases the total cholesterol in the steroidogenic cells and induces reorganization of actin nearby the cell membrane. Under low voltage PEFs, actin reorganization is responsible for the increase in the electroporation threshold. However, when subject to high voltage PEF, the lipid composition of the cell membrane becomes the regulatory factor. Namely, preincubation with atorvastatin reduces the cytotoxic effect of low voltage pulses and enhances the cytotoxicity and cellular changes induced by high voltage pulses. The study confirms that the surface tension regulates of membrane permeability under low voltage PEF treatment. Accordingly, to reduce the unfavorable effects of preincubation with atorvastatin, electroporation of steroidogenic cells should be performed at high voltage and combined with a calcium supply.