Integration sequencing in complex manufacturing systems

The integration and test phase of complex manufacturing machines, like an ASML lithographic machine, are expensive and time consuming. The tests that can be performed at a certain point within the integration phase depend on the modules that are integrated. Therefore, the test sequence depends on the integration sequence. Thus, by optimizing the integration sequence of these modules, more tests can be done in parallel and valuable integration and test time can be reduced. In this paper, we introduce a mathematical model to describe an integration sequencing problem and we propose an algorithm to solve this problem optimally. Furthermore, we propose two heuristics to solve large industrial problems in limited computation time. Also, we show with a case study within the development of a lithographic machine that the described method can be used to solve real-life problems. TANGRAM, test strategy, test sequencing, manufacturing machines, semiconductor industry, integration sequencing

Minimizing the level of butyric acid bacteria spores in farm tank milk

A year-long survey of 24 dairy farms was conducted to determine the effects of farm management on the concentrations of butyric acid bacteria (BAB) spores in farm tank milk (FTM). The results were used to validate a control strategy derived from model simulations. The BAB spore concentrations were measured in samples of FTM, feces, bedding material, mixed corn and grass silage fed to cows in the barn, and soil. In addition, a questionnaire was used to gather farm management information such as bedding material used and teat cleaning method applied. The average BAB spore concentration in FTM was 2.7 log(10) spores/L, and 33% of the FTM samples exceeded a concentration of 3 log(10) spores/L. Control of the average spore concentration in mixed silage fed was the only aspect of farm management that was significantly related to the concentration of BAB spores in FTM. Farms that fed mixed silage with the lowest average BAB spore concentrations (3.4 log(10) spores/g) produced FTM with the lowest average concentration (2.1 log(10) spores/L). The efficiency of farm management in controlling the BAB spore concentration in FTM depended to a large extent on the ability of farmers to prevent incidents with elevated BAB spore concentrations in mixed silage (>5 log(10) spores/g) and not on the average BAB spore concentration in mixed silage across the year. The survey showed that farmers should aim for a concentration in mixed silage of less than 3 loglo spores/g and should prevent the concentration from exceeding 5 log(10) spores/g to ensure a concentration in FTM of less than 3 loglo spores/L. These results correspond with the previously reported model simulations

Concentrations of butyric acid bacteria spores in silage and relationships with aerobic deterioration

Germination and growth of spores of butyric acid bacteria ( BAB) may cause severe defects in semihard cheeses. Silage is the main source of BAB spores in cheese milk. The objectives of the study were to determine the significance of grass silages and corn silages as sources of BAB spores and to investigate the relationships between high concentrations of BAB spores in corn silage and aerobic deterioration. In the first survey, samples were taken from various locations in silos containing grass and corn silages and from mixed silages in the ration offered to the cows on 21 farms. We demonstrated that the quantity of BAB spores consumed by cows was determined by a small fraction of silage with a high concentration of spores ( above 5 log(10) BAB/g). High concentrations were most often found in corn silage within areas with visible molds ( 69% of the samples). Areas with visible molds in grass silage and surface layers of corn silage contained, respectively, 21 and 19% of the cases of concentrations above 5 log10 BAB spores/g. Based on these results, we concluded that currently in the Netherlands, corn silage is a more important source of BAB than is grass silage. In a second survey, 8 corn silages were divided into 16 sections and each section was studied in detail. High concentrations of BAB spores were found in only the top 50 cm of these 8 silages. Elevated concentrations of BAB spores were associated with different signs of aerobic deterioration. In 13% of the sections in corn silage with more than 5 log10 yeasts and molds/g, more than 5 log10 BAB spores/g were found. Sections with a temperature of more than 5 C above ambient temperature contained, in 21% of the cases, more than 5 log10 BAB spores/g. Concentrations above 5 log10 BAB spores/g were measured in 50% of the sections with a pH above 4.4. All sections with a pH above 4.4 also showed a temperature that was more than 5 C above ambient temperature and a concentration of yeasts and molds above 5 log10 cfu/g. Based on these results, we postulated that high concentrations of BAB spores in corn silage are the result of oxygen penetration into the silage, resulting in aerobic deterioration and the formation of anaerobic niches with an increased pH just below the surface. Growth of BAB in these anaerobic niches with an increased pH caused the locally high concentrations of BAB in corn silage

Predictive modeling of Bacillus cereus spores in farm tank milk during grazing and housing periods

The shelf life of pasteurized dairy products depends partly on the concentration of Bacillus cereus spores in raw milk. Based on a translation of contamination pathways into chains of unit-operations, 2 simulation models were developed to quantitatively identify factors that have the greatest effect on the spore concentration in milk. In addition, the models can be used to determine the reduction in concentration that could be achieved via measures at the farm level. One model predicts the concentration when soil is the source of spores, most relevant during grazing of cows. The other model predicts the concentration when feed is the main source of spores, most relevant during housing of cows. It was estimated that when teats are contaminated with soil, 33% of the farm tank milk (FTM) contains more than 3 log(10) spores/L of milk. When feed is the main source, this is only 2%. Based on the predicted spore concentrations in FTM, we calculated that the average spore concentration in raw milk stored at the dairy processor during the grazing period is 3.5 log(10) spores/L of milk and during the housing period is 2.1 log(10) spores/L. It was estimated that during the grazing period a 99% reduction could be achieved if all farms minimize the soil contamination of teats and teat cleaning is optimized. During housing, reduction of the concentration by 60% should be feasible by ensuring spore concentrations in feed below 3 log(10) spores/g and a pH of the ration offered to the cows below 5. Implementation of these measures at the farm level ensures that the concentration of B. cereus spores in raw milk never exceeds 3 log(10) spores/L

Short communication: quantification of the transmission of microorganisms to milk via dirt attached to the exterior of teats

Pathogens and spoilage microorganisms can be transmitted to milk via dirt (e.g., feces, bedding material, soil, or a combination of these) attached to the exterior of the cows¿ teats. To determine the relevance of this pathway and to perform quantitative microbial risk analysis of the microbial contamination of farm tank milk (FTM), it is important to know the amount of dirt transmitted to milk via the exterior of teats. In this study at 11 randomly selected Dutch farms the amount of dirt transmitted to milk via the exterior of teats is determined using spores of mesophilic aerobic bacteria as a marker for transmitted dirt. The amount of transmitted dirt to milk varied among farms from 3 to 300 mg/L, with an average of 59 mg/L. The usefulness of the data for microbial risk analyses is briefly illustrated using the contamination of FTM with spores of butyric acid bacteria as a case study. In a similar way the data can be used to identify measures to control the contamination of FTM with other microorganisms or chemical residues

Minimizing the level of Bacillus cereus spores in farm tank milk

In a year-long survey on 24 Dutch farms, Bacillus cereus spore concentrations were measured in farm tank milk (FTM), feces, bedding material, mixed grass and corn silage, and soil from the pasture. The aim of this study was to determine, in practice, factors affecting the concentration of B. cereus spores in FTM throughout the year. In addition, the results of the survey were used in combination with a previously published modeling study to determine requirements for a strategy to control B. cereus spore concentrations in FTM below the MSL of 3 log(10) spores/L. The B. cereus spore concentration in FTM was 1.2 +/- 0.05 log(10) spores/L and in none of samples was the concentration above the MSL. The spore concentration in soil (4.9 +/- 0.04 log(10) spores/g) was more than 100-fold higher than the concentration in feces (2.2 +/- 0.05 log(10) spores/g), bedding material (2.8 +/- 0.07 loglo spores/g), and mixed silage (2.4 +/- 0.07 log(10) spores/g). The spore concentration in FTM increased between July and September compared with the rest of the year (0.5 +/- 0.02 log(10) spores/L difference). In this period, comparable increases of the concentrations in feces (0.4 +/- 0.03 loglo spores/g), bedding material (0.5 +/- 0.05 log(10) spores/g), and mixed silage (0.4 +/- 0.05 log(10) spores/g) were found. The increased B. cereus spore concentration in FTM was not related to the grazing of cows. Significant correlations were found between the spore concentrations in FTM and feces (r = 0.51) and in feces and mixed silage (r = 0.43) when the cows grazed. The increased concentrations during summer could be explained by an increased growth of B. cereus due to the higher temperatures. We concluded that year-round B. cereus spores were predominantly transmitted from feeds, via feces, to FTM. Farmers should take measures that minimize the transmission of spores via this route by ensuring low initial contamination levels in the feeds

Improving farm management by modeling the contamination of farm tank milk with butyric acid bacteria

Control of contamination of farm tank milk (FTM) with the spore-forming butyric acid bacteria (BAB) is important to prevent the late-blowing defect in semi-hard cheeses. The risk of late blowing can be decreased via control of the contamination level of FTM with BAB. A modeling approach was applied to identify an effective control strategy at the farm level. The simulation model developed was based on a translation of the contamination pathway into a chain of unit operations. Using various simulations, the effects of factors related to feed quality, feed management, cattlehouse hygiene, and milking practices on the contamination level of FTM were evaluated. Contamination level of silage was found to be the most important factor. When silage contains on average less than 3 log(10) BAB/g, a basic pretreatment of udder teats before milking (similar to 75% removal of attached spores) is sufficient to assure an FTM contamination level below 1 BAB/mL. When silage contains more than 5 log(10) BAB/g, it should not be fed, because it then becomes almost impossible to assure an FTM contamination level below 1 BAB/mL. Measures aimed at improving cattlehouse hygiene, the contamination via soil, and the contamination level of other feeds contribute only marginally to the control of the contamination of FTM with BAB. Application of the modeling methodology could be beneficial for the control of the contamination of FTM with other microorganisms such as Bacillus cereus

Using interactive model simulations in co-design : An experiment in urban design

This paper presents an experiment in which people performed a co-design task in urban design, using a multi-user touch table application with or without interactive model simulations. We hypothesised that using the interactive model simulations would improve communication and co-operation between co-design participants, would help participants to develop shared understanding and would positively affect the co-design process and its outcomes. However, our experiment (involving 60 people in 20 codesign sessions) only partly confirmed these hypotheses. People positively evaluated the interactive model simulation tools (an interactive map of an urban area, interactive models for traffic, sound, sight and safety, and ‘tangibles’), and these tools promoted communication and co-operation, and the exploration of design solutions. However, people’s experiences of social cohesion and their satisfaction with their own contribution to the co-design process were better without these tools, possibly because using these tools drew people’s attention towards these interactive model simulations and away from the dynamics between the participants. We therefore advocate using such tools selectively, for example, early on in a co-design process, to improve shared understanding of the contents of the problem, rather than later on, when people need to focus on their fellow participants and on the processes of communication and cooperation