Lot-sizing for a single-stage single-product production system with rework of perishable production defectives

We consider a single-stage single-product production system. Produced units may be non-defective, reworkable defective, or non-reworkable defective. The system switches between production and rework. After producing a fixed number (N) of units, all reworkable defective units are reworked. Reworkable defectives are perishable or can become technologically obsolete. We assume that the rework time and the rework cost increase linearly with the time that a unit is held in stock. Therefore, N should not be too large. On the other hand, N should not be too small either, since there are set-up times and costs associated with switching between production and rework. For a given N, we derive an explicit expression for the average profit (sales revenue minus costs). Using this expression, the optimal value for N can be determined numerically. Moreover, it is easy to perform a sensitivity analysis, as we illustrate. RID="*" ID="*"The research of Dr. Ruud H. Teunter has been made possible by a fellowship of the Royal Netherlands Academy of Arts and Sciences. The research presented in this paper is part of the research on re-use in the context of the EU sponsored TMR project REVersed LOGistics (ERB 4061 PL 97-5650) in which take part the Otto-von-Guericke Universitaet Magdeburg (D), the Erasmus University Rotterdam (NL), the Eindhoven University of Technology (NL), INSEAD (F), the Aristoteles University of Thessaloniki (GR), and the University of Piraeus (GR). We thank the anonymous referees for their many helpful comments. Correspondence to: R. H. Teunter     

Adaptive performance enhancement by iterative identification and control design

In this paper we combine adaptation and robust control by an iterative scheme of system identification and control design. A nominal model is identified for robust control design and the controller is applied to the plant to gather new data for an update of the nominal model. Our objective is to improve the plant performance with every iteration right from the start. We tackle this problem with frequency domain identification and a control design method that optimizes robustness against coprime factor perturbations. Our approach is illustrated by simulated and practical examples.     

Characterization of fat replacers

Effects of commercial fat replacers on rheological properties of emulsions have been studied under a second-order design. The corresponding functions of regression have been calculated to describe the measured effects mathematically. On the basis of a figured three-dimensional plan of response, combinations of variables (fat, fat replacer, water) could be determined showing a similar consistency to the corresponding full-fat foodstuff.

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Zur Charakterisierung von Fettaustauschern

Zusammenfassung Die Wirkung kommerzieller Fettaustauscher auf rheologische Eigenschaften von O/W-Emulsionen wurde unter Nutzung eines quadratischen Prozeßmodells untersucht und die zugehörigen Schätzfunktionen für die mathematische Beschreibung der Effekte ermittelt. Aus der dreidimensionalen Darstellung der Antwortflächen ergab sich eine einfache Möglichkeit zur Bestimmung von Variablenkombinationen (Fett, Fettaustauscher und Wasser), um Konsistenzparameter vergleichbarer Vollfettprodukte zu simulieren.

     

Ubiquitin‐Based Probes Prepared by Total Synthesis To Profile the Activity of Deubiquitinating Enzymes

Epitope‐tagged active‐site‐directed probes are widely used to visualize the activity of deubiquitinases (DUBs) in cell extracts, to investigate the specificity and potency of small‐molecule DUB inhibitors, and to isolate and identify DUBs by mass spectrometry. With DUBs arising as novel potential drug targets, probes are required that can be produced in sufficient amounts and to meet the specific needs of a given experiment. The established method for the generation of DUB probes makes use of labor‐intensive intein‐based methods that have inherent limitations concerning the incorporation of unnatural amino acids and the amount of material that can be obtained. Here, we describe the total chemical synthesis of active‐site‐directed probes and their application to activity‐based profiling and identification of functional DUBs. This synthetic methodology allowed the easy incorporation of desired tags for specific applications, for example, fluorescent reporters, handles for immunoprecipitation or affinity pull‐down, and cleavable linkers. Additionally, the synthetic method can be scaled up to provide significant amounts of probe. Fluorescent ubiquitin probes allowed faster, in‐gel detection of active DUBs, as compared to (immuno)blotting procedures. A biotinylated probe holding a photocleavable linker enabled the affinity pull‐down and subsequent mild, photorelease of DUBs. Also, DUB activity levels were monitored in response to overexpression or knockdown, and to inhibition by small molecules. Furthermore, fluorescent probes revealed differential DUB activity profiles in a panel of lung and prostate cancer cells.     

Kinetics of thermal degradation of vitamin C in marula fruit (Sclerocarya birrea subsp. caffra) as compared to other selected tropical fruits

The kinetics of the thermal degradation of vitamin C of marula, mango and guava pulp at different heat treatments at temperature ranging from 80 to 150 °C were investigated. For temperatures lower than 125 °C, the ascorbic acid in marula pulp was about 15 fold more stable to heat than the ascorbic acid in mango and guava pulp. The results showed that a simple first order degradation model could not describe the vitamin C degradation as biphasic behaviour was observed. Therefore the model was transformed in a two-fraction model in which the vitamin C content is divided in relatively stable and instable fractions. Marula had a low k_d1,100°C of 7.2 × 10^?3 min^?1 compared to k_d1,100°C of 1.2 × 10^?1 min^?1 for guava and 1.3 × 10^?1 min^?1 for mango. Guava had the highest activation energy, E_a of 58 kJ/mol, followed by mango with 39 kJ/mol and then marula with 29 kJ/mol.     

Risk factors for dirty dairy cows in Norwegian freestall systems

Cow cleanliness is important for ensuring hygienic milk production and the well-being of dairy cows. The aim of this cross-sectional field study was to describe cow cleanliness in freestall-housed dairy herds and to examine risk factors related to thigh cleanliness. Cow cleanliness (n = 2,335), management-related variables (e.g., ventilation and use of sawdust-bedded stalls), and housing-related variables (e.g., freestall design and number of cows per stall) were recorded in 232 Norwegian freestall-housed dairy herds. Cleanliness was scored on a 4-point scale ranging from clean (1) to very dirty (4). The cows were relatively clean on the udder and belly, dirtier on thigh and the rear part of the body, and dirtiest on the legs, with cleanliness scores (mean ± SD) of 1.64 ± 0.62, 1.62 ± 0.65, 2.02 ± 0.75, 1.77 ± 0.58, and 2.30 ± 0.59, respectively. With dirty thighs as the response variable, several variables were tested in a logistic regression mixed model and with repeated measurements within herd and cow. A high number of cows per freestall [odds ratio (OR) = 3.45], no use of sawdust as bedding (OR = 3.24) versus use of sawdust, and a low-positioned (<0.85 m above stall floor) upper head rail “enclosing” the front of the stall (OR = 1.42 to 2.13) versus a position >0.85 m were all risk factors for dirty thighs on the cows. Furthermore, liquid manure (score 2) versus more consistent manure (score 1; OR = 1.66) and less tame cows (score 2) versus tame cows (score 1) were associated with an increased risk of dirty thighs (OR = 1.24). The cleanest cows were associated with indoor temperatures in the range from 10 to 15°C. For each 10-percentage-unit increase in relative air humidity, the risk of dirty thighs increased (OR = 1.32). Freestalls with a construction hindering normal lying, rising, and standing movements should be avoided. Furthermore, focus is needed on indoor climate and manure consistency to obtain cows with clean thighs.     

Associations of soft flooring materials in free stalls with milk yield, clinical mastitis, teat lesions, and removal of dairy cows

The objective was to test if there was an association between free-stall base softness and milk yield, incidence of clinical mastitis (CM), teat lesions, and removal of cows. In a questionnaire sent to 1,923 dairy farms presumed to be using free-stall housing, farmers were asked for information regarding housing and stall base; for example, the year of installation and the product name or brand of their mats or mattresses. This information was merged with data for milk yield, CM, teat lesions, and removal of cows extracted from the Norwegian Dairy Herd Recording System for the years after installation of mats or mattresses. After exclusion of invalid contributions, the data set consisted of 29,326 lactations for milk yield distributed over 363 free-stalled herds in Norway. The farms were stratified into 5 categories according to the softness of the stall surface measured as millimeter impact of a sphere with a diameter of 120 mm at 2-kN load: 1 = concrete, softness of 0 mm; 2 = rubber, softness of 1 to 8 mm; 3 = soft mats, softness of 9 to 16 mm; 4 = multilayer mats, softness of 17 to 24 mm; and 5 = mattresses, softness over 24 mm. Lactation curves were estimated as modified Wood's lactation curves using test-day data and mixed models with repeated measurements, adjusting for days in milk, parity, and softness of free-stall flooring. Herds on concrete free-stall bases yielded 6,727 ± 146 kg of milk from 5 to 305 days in milk. In comparison, herds showed a decrease of 0.3% on rubber, an increase of 2.4% on soft mats, an increase of 4.5% on multilayer mats, and an increase of 3.9% on mattresses. Compared with concrete, the hazard ratio (HR) of CM was less on rubber, multilayer mats, and mattresses [HR = 0.89 (0.79-0.99), 0.85 (0.73-0.996), and 0.80 (0.73-0.88), respectively]. Compared with concrete, the HR of teat lesions was less on rubber, soft mats, multilayer mats, and mattresses [HR = 0.41 (0.26-0.65), 0.33 (0.24-0.44), 0.12 (0.04-0.38), and 0.47 (0.33-0.67), respectively]. The HR of removal of cows was less on mattresses compared with concrete, rubber, soft mats, and multilayer mats, with HR = 0.90 (0.84-0.97), 0.88 (0.80-0.97), 0.86 (0.80-0.93), and 0.85 (0.76-0.95), respectively. A soft free-stall base contributed significantly to increased milk yield and fewer incidences of CM, teat lesions, and removal of cows.