Macro- and micro-cellular porous ceramics from preceramic polymers

Macrocellular and microcellular SiOC open cell ceramic foams were fabricated from a preceramic polymer. Macrocellular foams, with a cell size ranging from about 100–600 μm and a bulk density ranging from about 0.25–0.58 g/cm³, depending on the processing parameters, were fabricated using a direct foaming approach. Microcellular foams, with a cell size of about 8 μm, were fabricated using poly(methyl methacrylate)microbeads as sacrificial templates. The bulk density ranged from about 0.31–0.48 g/cm³, depending on the amount of microbeads in the starting material. The compression strength of the foams increased with increasing relative density, and microcellular foams possessed a 2–5 times higher crushing strength than macrocellular foams of similar density.     

Formal Performance Modelling and Evaluation of an Adaptive Mechanism for Packetised Audio over the Internet

A case study is presented which concerns the design of an adaptive mechanism for packetised audio for use over the Internet. During the design process, the audio mechanism was modelled with the stochastically timed process algebra EMPA and analysed via simulation by the EMPA based software tool TwoTowers in order to predict the percentage of packets that are received in time for being played out. The predicted performance figures obtained from the algebraic model illustrated in advance the adequacy of the approach adopted in the design of the audio playout delay control mechanism. Based on these performance figures, it was possible to implement and develop the complete mechanism without incurring additional costs due to the late discovery of unexpected errors or inefficiency. Performance results obtained from experiments conducted on the field confirmed the predictive simulative results. Received March 1997 / Accepted in revised form July 1998     

The terminal O-acetyltransferase involved in vindoline biosynthesis defines a new class of proteins responsible for coenzyme A-dependent acyl transfer

The gene encoding acetyl CoA:deacetylvindoline 4-O-acetyltransferase (DAT) (EC 2.3.1.107) which catalyzes the last step in vindoline biosynthesis was isolated and characterized. The genomic clone encoded a 50 kDa polypeptide containing the sequences of nine tryptic fragments derived from the purified DAT heterodimer. However, cleavage of DAT protein to yield a heterodimer appears to be an artifact of the protein purification procedure, since the size of the protein (50 kDa) cross-reacting with anti-DAT antibody in seedlings and in leaves of various ages also corresponds to the size of the active recombinant enzyme. Studies with the intact plant and with developing seedlings showed that induction of DAT mRNA, protein accumulation and enzyme activity occurred preferentially in vindoline producing tissues such as leaves and cotyledons of light-treated etiolated seedlings. The ORF of DAT showed significant sequence identity to 19 other plant genes, whose biochemical functions were mostly unknown. The Mr of approximately 50 kDa, a HXXXDG triad, and a DFGWGKP consensus sequence are highly conserved among the 20 plant genes and these criteria may be useful to identify this type of acyltransferase. The involvement of some of these genes in epicuticular wax biosynthesis, fruit-ripening and in benzoyltransfer reactions indicates that the plant kingdom contains a superfamily of multifunctional acyltransferases which operate by a reaction mechanism related to the ancient chloramphenicol O-acetyltransferase and dihydrolipoyl acetyltransferase class of enzymes.     

Molecular characterization of Italian rice cultivars

Random amplified polymorphic DNA (RAPD) is an efficient tool to detect DNA polymorphisms and to distinguish different clones and cultivars. We have applied the RAPD technique to distinguish, starting from a single rice seed, among some Italian rice cultivars from market and from National Institute for research on food and nutrition, Italy. We also estimated the genomic similarity among the rice cultivars object of this study taking advantage of the amplification patterns. Despite the low genomic variability among Italian rice cultivars, RAPD technique allowed us to distinguish among them. This indicates that RAPD can be used routinely to verify the identity of Italian rice cultivars in order to prevent fraudulent commercial activity.     

Stochastic analysis of crude oil procurement and processing under uncertain demand for bunker fuel oil

Bunker fuel oil (ifo), one of the products of petroleum refining, has a strong impact in the production process because it drives the availability of heavy residues that depend on the crude quality. A simplified stochastic model for the Administración Nacional de Combustibles Alcohol y Portland refinery, based on the uncertainty of the demand for ifo, is proposed for comparison with the current approach of deterministic demand. In this model, the benefits of the production process are maximized, taking decisions on the more suitable raw material, intermediate products and final blends in order to fulfill quality and demand requirements of final products. A specific case is analyzed where the maximum benefit is achieved when the most expensive crude quality is purchased, due to a lack of incentive to produce extra amounts of heavy fuel oil that must be exported at a non‐attractive price. Results are compared with the solution of a deterministic model with mean demand. In addition, the stochastic model solution depicts how the refinery should operate for each scenario of ifo demand.     

Mixing logics and rewards for the component-oriented specification of performance measures

Formal notations for system performance modeling need to be equipped with suitable notations for specifying performance measures. These companion notations have been traditionally based on reward structures and, more recently, on temporal logics. In this paper we propose an approach that combines logics and rewards, together with a definition mechanism that allows performance measures to be specified in a component-oriented way, thus facilitating the task for non-experts. The resulting Measure Specification Language (MSL) is interpreted both on action-labeled continuous-time Markov chains and on stochastic process algebras. The latter interpretation provides a compositional framework for performance-sensitive model manipulations and emphasizes the increased expressiveness with respect to traditional reward structures for implicit-state modeling notations.     

Evaluations of the Mechanism of Disintegrant Action

The disintegrant properties of eight tablet disintegrants (a cation exchange resin, cross-linked carboxymethyl cellulose, sodium starch glycolate, U.S.P., Crospovidone, U.S.P., corn starch, an insoluble anionic cellulose polymer, a modified food starch, and a soybean cellulose derivative) have been evaluated. Three techniques were applied to some or all of the materials. Water uptake rates and capacities were determined for all disintegrants in bulk powders. Disintegration times of tablets formulated with varying concentrations of the different disintegrants in a matrix comprising 75% unmilled dibasic calcium phosphate dihydrate and 25% anhydrous lactose were measured. For four disintegrants, a novel computer assisted cinsphotomicrographic technique was applied to investigate the interaction of water with individual disintegrant particles, both in terms of swelling rate and maximum water capacity

Comparative evaluation of tablet disintegrants and studies of the mechanism of disintegrant action have quite properly attracted the attention of a number of pharmaceutical scientists. (1-16) However, it is clear that at present there is no concensus concerning a general theory rationalizing disintegrant action and at least five separate mechanism have been proposed (1, 2, 4)

In the present paper, the disintegrant action of eight disintegrants has been studied using three separate approaches. Firstly, the rate and capacity of the bulk powders to take up water and to swell as a result has been evaluated using an apparatus similar to that used by Nogami and coworkers (5). Secondly, the disintegration times of tablets containing varying concentrations of disintegrant and compressed using a matrix of 75% unmilled dibasic calcium phosphate dihydrate and 25% anhydrous lactose were determined in a manner similar to that described by Rudnic and his associates (6). Thirdly, the authors are able to report - apparently for the first time - the use of a new method for evaluating the rate and extent of swelling of individual units in an assembly of disintegrant particles. This method exploits a cinephotomicrographic technique in which groups of disintegrant particles are photographed under a microscope by a high speed movie camera with the resultant film being analyzed by a special computer technique which allows the size of both individual and all particles, in any given visual field, to be followed over the very short period of time which elapses during the interaction of the disintegrant particles with water. The results presented in this paper demonstrate that a combination of the three methods described above and, in particular, the computer assisted cinemicrophotographic technique allow considerable insight to be gained of the disintegration process     

Curcumin and the cellular stress response in free radical-related diseases

Free radicals play a main pathogenic role in several human diseases such as neurodegenerative disorders, diabetes, and cancer. Although there has been progress in treatment of these diseases, the development of important side effects may complicate the therapeutic course. Curcumin, a well known spice commonly used in India to make foods colored and flavored, is also used in traditional medicine to treat mild or moderate human diseases. In the recent years, a growing body of literature has unraveled the antioxidant, anticarcinogenic, and antinfectious activity of curcumin based on the ability of this compound to regulate a number of cellular signal transduction pathways. These promising data obtained in vitro are now being translated to the clinic and more than ten clinical trials are currently ongoing worldwide. This review outlines the biological activities of curcumin and discusses its potential use in the prevention and treatment of human diseases.     

Modifications in membrane fatty acid composition of Salmonella typhimurium in response to growth conditions and their effect on heat resistance

The effects of growth temperature (in the range 10-45 degrees C) and acidification up to pH 4.5 of the culture medium (Brain Heart Infusion, BHI) with different organic acids (acetic, citric and lactic) and hydrochloric acid on membrane fatty acid composition and heat resistance of Salmonella typhimurium CECT 443 were studied. The heat resistance was maximal in cells grown at 45 degrees C (cells grown in non-acidified BHI showed a D58-value of 0.90 min) and decreased with decreasing growth temperature up to 10 degrees C (D58-value of 0.09 min). The growth of cells in acidified media caused an increase in their heat resistance. In general, acid adapted cells showed D-values of between 1.5 and 2 times higher than the corresponding for non-acid adapted control cells. This cross-protection response, which has important implications in food processing, was not dependent on the pH value and the acid used to acidify the growth medium. A membrane adaptation corresponding to an increase in the unsaturated to saturated fatty acids ratio (UFA/SFA) and membrane fluidity was observed at low growth temperature. Moreover, the acidification of the growth medium caused a decrease in UFA/SFA ratio and in the C18:1 relative concentration, and an increase in cyclopropane fatty acids (CFA) content mainly due to the increase in cyc19 relative concentration. Thus, acid adapted cells showed CFA levels 1.5 times higher than non-acid adapted control cells. A significant proportion of unsaturated fatty acids were converted to their cyclopropane derivatives during acid adaptation. These changes in membrane fatty acid composition result in cells with decreased membrane fluidity. A clear relation between membrane fatty acid composition and heat resistance was observed. In general, D-values were maximum for cells with low UFA/SFA ratio, and, consequently, with low membrane fluidity. Moreover, CFA formation played a major role in protecting acid adapted cells from heat inactivation. However, changes observed in membrane fatty acid composition are not enough to explain the great thermotolerance of cells grown at 45 degrees C. Thus, other mechanisms, such as the synthesis of Heat Shock Proteins, could be responsible for this increase in the bacterial heat resistance.