Implementation of a New Linear Control Technique Based on Experimentally Validated Small-Signal Model of Three-Phase Three-Level Boost-Type Vienna Rectifier

In this paper, the design and implementation of a new multiple-input-multiple-output linear control technique based on a theoretically established and experimentally validated small- signal model for the three-phase three-level boost-type ac/dc Vienna converter are presented. Averaging and local linearization techniques are used to derive the dynamic model expressed in the dqo reference frame. The resulted transfer functions are discretized for the sake of a digital controller design. Multiple-loop control strategy is adopted and consists of inner current feedback loops, which are based on the straightforward looping technique that neglects interactions between the dq components of control inputs and currents, respectively, and of an outer voltage loop, which is designed to ensure dc voltage regulation by adjusting the magnitude of the references for the inner current loops. The output dc voltage unbalance is also controlled in the inner loops. The proposed modeling and control approaches are first simulated and then validated on a 1.5-kW laboratory prototype supported by the DS 1104 digital real-time controller board of dSPACE. The obtained results prove the accuracy of the proposed new small-signal model and, therefore, its reliability for dynamic analysis and control design purposes. It is also proved that a judicious choice of controller parameters, as well as an adequate rating of boost inductors, allows one to meet the IEEE standard requirements in terms of ac line-current total harmonic distortion and power factor. The efficiency of the proposed control technique is maintained in case of disturbances occurring on both source and load sides.     

Changes in skin cell wall composition during the maturation of four premium wine grape varieties

BACKGROUND: Grape skin cell walls form a barrier against the diffusion of colour. The colour of red wines is mainly due to anthocyanins, although their concentration in wine is not always correlated with the anthocyanin content of grape skins. The cell wall composition changes during fruit ripening, so it was thought that a study of the ripening behaviour of four premium varieties might provide information on how the composition changes during ripening and explain the technological differences. RESULTS: The largest quantities of skin cell wall material (CWM) were isolated from Monastrell grapes, probably owing to the greater number of cell layers they contain and the thicker cell walls. During ripening, a loss of skin CWM (e.g. 120–60 and 65–45 mg CWM g^?1 fresh skin for Monastrell J and Cabernet Sauvignon respectively) and galactose (e.g. 36–20 and 55–30 mg g^?1 CWM for Cabernet Sauvignon and Monastrell J respectively) was observed, together with a decrease in the degree of pectin methylation and acetylation, except in Syrah, in which pectin methylation remained unchanged. These changes were accompanied by the accumulation of glucose, while other neutral sugars showed no significant variations. A correlation was found between the degree of ripening and those constituents changing in the grape skin cell wall. CONCLUSION: The cell wall composition differs sufficiently between grape varieties to allow discrimination between them. Ripening was associated with a decrease in the quantity of CWM and galactose in the cell walls. Monastrell showed the largest quantities of both throughout ripening. The differences observed between Monastrell and the other varieties would explain the technological differences between them. Copyright © 2007 Society of Chemical Industry     

Identification of tet(M) in two Lactococcus lactis strains isolated from a Spanish traditional starter-free cheese made of raw milk and conjugative transfer of tetracycline resistance to lactococci and enterococci

Specific PCR and sequencing showed that a tet(M) gene was present in two tetracycline-resistant Lactococcus lactis strains isolated from a raw milk, starter-free cheese. Hybridisation experiments using as a probe an internal segment of the gene obtained by PCR associated tet(M) with plasmids of around the same size (30 kbp) in both strains. Molecular analysis of the tetracycline resistance loci, including the upstream and downstream regions of the genes, showed them to be identical to one other and to the tet(M) encoded by the conjugative transposon Tn916. Amplification of Tn916-derived segments suggested the transposon was complete in the two L. lactis strains. Further, curing of the tetracycline resistance was accompanied by a reduction in size of the plasmids comparable to that expected for Tn916. Tetracycline resistance could be transferred by conjugation to plasmid-free Lactococcus and Enterococcus strains. However, no plasmid DNA was detected among the transconjugants while both tet(M) and transposon-related sequences were amplified by PCR. This suggested that only the transposon was mobilized.     

Proteolytic regulation of the extent of dietary proteins with skin grape proanthocyanidin and anthocyanidin's interactions

During technological processing, proanthocyanidins and anthocyanidins could be partly lost due to the complexation phenomena, affecting food and beverage nutritional properties, organoleptic properties and health-promoting potentials. A common issue is encountered when processing food and beverage which is binding of phenolics to dietary proteins. The present investigation aims at evaluating the proteolysis contribution, using pure protease (Pepsin, 3000 units g⁻¹), to protein–anthocyanidin and protein–proanthocyanidin interactions. Bovine serum albumin (BSA), ovalbumin (OVA) and casein (CAS) dietary protein models were used. High-performance liquid chromatography coupled to diode array detector (HPLC-DAD) and size exclusion chromatography analyses proved that pepsin treatment significantly (P > 0.05) decreased the ratio of flavonoids’ interaction with tested proteins . The proteolysis reduced anthocyanidin interactions with CAS, OVA and BSA by 64.88%, 57.37% and 42.87% respectively. Similarly, proanthocyanidins interaction with CAS, OVA and BSA were reduced by 34.23%, 13.74% and 2.39% respectively. This study provides the basis to develop innovative technologies to limit protein–flavonoid complexation during food and beverage processing.     

The Requirements for the Calibration Conditions in Large-Aperture Fizeau Interferometers

The problems that arise during the calibration of the reference plates of large-aperture interferometers are discussed and the methods for solving them are presented. It is shown that the repeatability of shapes of the reference plates after their rearrangements can be provided by selecting the mechanism of their fixing in place. It is demonstrated that the temperature deformations of the reference-plate surfaces can be determined from a numerical model. These measures have made it possible to calibrate the reference plates of the 630-mm interferometer with an accuracy of λ/1000 RMS (λ = 632.8 nm).     

Influence of the Cross-Sectional Shape of Hot Semifinished Rolled Products on the Formation of the Plot of Specific Tension in Cold-Rolled Strips

Metallurgist - In view of the increasing competition in the market of rolled products, the problem of evaluation of the quality of strips in various stages of the process of rolling seems to be...     

Simulation of liquid micro-jet in free expanding high-speed co-flowing gas streams

We present the development of an experimentally validated computational fluid dynamics model for liquid micro jets. Such jets are produced by focusing hydrodynamic momentum from a co-flowing sheath of gas on a liquid stream in a nozzle. The numerical model based on laminar two-phase, Newtonian, compressible Navier–Stokes equations is solved with finite volume method, where the phase interface is treated by the volume of fluid approach. A mixture model of the two-phase system is solved in axisymmetry using?~?300,000 finite volumes, while ensuring mesh independence with the finite volumes of the size 0.25 µm in the vicinity of the jet and drops. The numerical model is evaluated by comparing jet diameters and jet lengths obtained experimentally and from scaling analysis. They are not affected by the strong temperature and viscosity changes in the focusing gas while expanding at nozzle outlet. A range of gas and liquid-operating parameters is investigated numerically to understand their influence on the jet performance. The study is performed for gas and liquid Reynolds numbers in the range 17–1222 and 110–215, and Weber numbers in the range 3–320, respectively. A reasonably good agreement between experimental and scaling results is found for the range of operating parameters never tackled before. This study provides a basis for further computational designs as well as adjustments of the operating conditions for specific liquids and gases.