Quadrature Mismatch Shaping for Digital-to-Analog Converters

Quadrature sigma-delta analog-to-digital converters require a feedback path for both the I and the Q parts of the complex feedback signal. If two separate multibit feedback digital-to-analog converters (DACs) are used, mismatch among the unit DAC elements leads to additional mismatch noise in the output spectrum as well as an I/Q imbalance. This paper proposes new quadrature bandpass (QBP) mismatch shaping techniques. In our approach, the I and Q DACs are merged into one complex DAC, which leads to near-perfect I/Q balance. To select the unit DAC elements of the complex multibit DAC, the well-known butterfly shuffler and tree structure are generalized towards a complex structure, and necessary constraints for their correct functioning are derived. Next, a very efficient first-order QBP shaper implementation is proposed. Finally, the newly presented complex structures are simulated to prove their effectiveness and are compared with each other with respect to performance     

New Ferro Powder for Selective Laser Sintering of Dense Parts

The paper describes a new powder composition specially developed for selective laser sintering (SLS). The aim is to obtain a ferro powder that can be sintered without need for a (sacrificial) polymer binder and that results in quasi dense parts that do not need any post-processing like furnace sintering, infiltration or HIP. The powder is a mixture of different types of particles (Fe, Cu, Ni and Fe₃P). The composition and mixture ratio are justified by using phase diagrams. The powder has been tested using an own developed Nd: YAG SLS machine. The influence of process parameters (laser power, scan velocity, scan spacing and scan strategy) and the microstructural characteristics have been investigated. Attention is devoted to the binding mechanism (liquid phase sintering, through melting) and to the quality of resulting parts (density, balling effect,…).     

Visual association encoding activates the medial temporal lobe: a functional magnetic resonance imaging study

The involvement of structures in the medial temporal lobe during the encoding of visual associations was studied with functional magnetic resonance imaging. In 11 out of 12 normal healthy volunteers this task resulted in activation in posterior portions of the parahippocampal region, close to the collateral sulcus. In seven subjects activation was encountered in the hippocampal formation. The visual association task as adapted for this study may provide a sensitive measure to study anterograde amnesia prevalent in Alzheimer's disease. Therefore, the present paradigm enables the study of individual changes in learning and memory capacities over time.     

Prevalence of potentially pathogenic Bacillus cereus in food commodities in The Netherlands

Randomly selected food commodities, categorized in product groups, were investigated for the presence and number of Bacillus cereus bacteria. If positive, and when possible, five separate colonies were isolated and investigated for the presence of four virulence factors: presence of genes encoding three enterotoxins (hemolysin BL [HBL], nonhemolytic enterotoxin [NHE], and cytotoxin K) and the ability to produce cereulide. In addition, the presence of psychrotrophic and mesophilic signatures was determined. The genes for NHE are found in more than 97% of the isolates, those for HBL in approximately 66% of the isolates, and the gene for cytotoxin K in nearly 50% of the isolates. Significant associations between product groups and (combinations of) virulence factors were the relatively low percentage of isolates from the "flavorings" group containing genes encoding NHE and the higher-than-average occurrence of both the genes encoding HBL and NHE in the "pastry" group. Cereulide was produced by 8.2% of the isolates but only in combination with the presence of genes for one or more other virulence factors. Most isolates (89.9%) were mesophilic; minorities of the isolates were psychrotrophic (4.4%) or of intermediate signature (5.7%). In the product group "milk and milk products," the incidence of strains with psychrotrophic or intermediate signatures is significantly higher than in the other product groups. In the product groups "flavorings," "milk and milk products," "vegetable(s) and vegetable products," "pastry," and "ready-to-eat foods," a relatively high number of samples contain high numbers of B. cereus bacteria. Within the product group "ready-to-eat foods," the products containing rice and pasta show a relatively high incidence of high numbers of B. cereus bacteria.     

Health and growth of veal calves fed milk replacers with or without probiotics

Four experiments with 1-wk-old veal calves were conducted to assess the influence of probiotics on growth and health indicators. In experiments 1 and 2, the liquid probiotic supplements were administered daily from experimental d 1 to 15. The treatment period in experiments 3 and 4 was extended to 56 d. The probiotics used were a multispecies probiotic (MSPB) containing different probiotic species of human origin, or a calf-specific probiotic (CSPB) containing 6 Lactobacillus species isolated from calf feces and selected on the basis of a combination of characteristics.When the data for the 4 experiments were pooled, the probiotics enhanced growth rate during the first 2 wk. During the 8-wk experimental period, average daily gain and feed efficiency were significantly improved in the probiotic-treated groups. The MSPB-induced increase in weight gain was greater when the control calves were considered less healthy based on a health score (an index of diarrhea and therapeutic treatments). Probiotic treatment tended to diminish mortality. The CSPB treatment reduced the incidence of diarrhea and the fecal counts of coliforms. When therapeutic treatment was intensive in the control calves, the ingestion of probiotics reduced the percentage of calves that required therapy and the amount of treatments needed against digestive or respiratory diseases. There was no clear difference in the efficiency of the MSPB and CSPB preparations. Further research is necessary to identify underlying mechanisms and to evaluate the potential of probiotics to improve respiratory health in veal calf production.     

Minimum inhibitory concentration (MIC) of sodium lactate for pathogens and spoilage organisms occurring in meat products

Pathogens and spoilage organisms occuring in meat products were screened in laboratory media, according to a method of Eklund (1983), in order to determine the specific inhibitory effect of lactate on growth of these microorganisms under optimum growth conditions (pH 6.5, 20°C). In general, Gram-positive bacteria were more sensitive towards lactate than Gram-negative bacteria. It was shown especially, that strains that were able to grow at water activities of 0.95 and below in the presence of NaCl (Staphylococcus aureus, Listeria monocytogenes, Brochothrix thermosphacta) were inhibited by sodium lactate (NaL). It appeared, that yeasts were resistant to large amounts of NaL (> 10% w/v). However, NaL had a specific inhibitory effect on growth of these organisms when compared to the effect of NaCl. These results indicate that lactate addition to food products with a pH near neutrality offers good prospects for shelf life prolongation.     

Effect of environmental conditions during soya-bean fermentation on the growth of Staphylococcus aureus and production and thermal stability of enterotoxins A and B

During tempe manufacture, Staphylococcus aureus was able to survive in newly started soya-bean soaks (final pH 4.7), whereas it died during soaks with accelerated souring (final pH 4.0). No S. aureus were detected after subsequent heat treatment of soaked beans. S. aureus strain S6 could produce enterotoxins A and B if inoculated on cooked soya-beans. Its growth and enterotoxin production were not influenced by inoculation rate nor by the presence of actively growing Rhizopus oligosporus, the fungus responsible for tempe formation. Enterotoxin levels were highest after 48 h fermentation. Presence of lactobacilli (L. brevis or L. plantarum) during the tempe fermentation did not influence staphylococcal growth, but enterotoxin levels were reduced. Reduced oxygen pressure did not affect staphylococcal growth, but resulted in lower enterotoxin levels after 48 h incubation. The thermal stability of enterotoxin A in tempe was significantly lower than in Brain Heart Infusion broth of comparable pH. Heating of enterotoxin-containing tempe mash reduced enterotoxin A by 99.7% as measured with ELISA and animal feeding methods.     

An on-line respirographic biosensor for the characterization of load and toxicity of wastewaters

A respirographic biosensor is presented that is capable of monitoring the waste load and potential toxicity of wastewaters, both off-line in a laboratory or on-line at the wastewater treatment plant. The principles of the sensors' operation have been developed and implications of the design choices evaluated. Short term BOD values were obtained every 30 min. The linear dynamic range spanned concentrations differing by a factor of 5000. This range could be expanded by a factor of 10 by adjusting the aeration rate of the bioreactor in the sensor. The response time for toxicity detection was approximately 1 h. The use in the sensor of activated sludge from the plant concerned ensured relevant toxicity information was obtained. To check the condition of the sludge, an independent respiration measurement is proposed. When a siginificant activity change is observed, the sludge in the sensor must be replaced. The presence of oxidoreduction chemicals can cause interferences that may lead to measurement errors. Based on a difference in reaction kinetics, their presence can be assessed and the effect eliminated. Both on-line and laboratory applications in the chemical industry are presented. Special emphasis is given to the usefulness of the sensor data for waste management of production divisions. On-line assessment of load variations and hydrogen peroxide spills are given as illustrations of the implementation of the sensor on the treatment plant. Attention is drawn to the potential application of the data for process control and improved performance of the treatment plant.     

In vitro digestibility of Bacillus fermented soya bean

Bacillus fermented legume products include among others dawadawa and soumbala made from African locust bean, and natto and kinema made from soya bean. Bacillus subtilis is the dominant species involved in the fermentation. During Bacillus fermentation for 48 h of autoclaved soya bean the quantity of soluble and dialyzable matter increased from 22% and 6% up to 65% and 40%, respectively. Protein and carbohydrate degradation during fermentation of soya bean with several Bacillus spp. was investigated and appeared to be substantial during the first 18 h of fermentation resulting in the release of high levels of peptides and oligosaccharides. In vitro digestibility was increased from 29% up to 33–43% after Bacillus fermentation for 48 h. It was shown that Bacillus spp. were able to degrade soya bean macromolecules to a large extent resulting in water-soluble low molecular weight compounds. In vitro digestion of Bacillus fermented soya bean using gastrointestinal enzymes only slightly increased the amount of dialyzable matter, which clearly demonstrated the beneficial effect of Bacillus fermentation on food nutrient availability.