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61.
Rodolfo Cuevas Juan-Carlos Ferrer Mathias Klapp Juan-Carlos Muñoz 《Journal of Scheduling》2016,19(1):91-106
The potential benefits of using human resources efficiently in the service sector constitute an incentive for decision makers in this industry to intelligently manage the work shifts of their employees, especially those dealing directly with customers. In the long term, they should attempt to find the right balance between employing as few labor resources as possible and keeping a high level of service. In the short run (e.g., 1 week), however, contracted staff levels cannot be adjusted, and management efforts thus focus on the efficient assignment of shifts and activities to each employee. This article proposes a mixed integer program model that solves the short-term multi-skilled workforce tour scheduling problem, enabling decision makers to simultaneously design workers’ shifts and days off, assign activities to shifts and assign those to employees so as to maximize and balance coverage of a firm’s demand for on-duty staff across multiple activities. Our model is simple enough to be solved with a commercial MIP solver calibrated by default without recurring to complex methodologies, such as extended reformulations and exact and/or heuristic column generation subroutines. A wide computational testing over 1000 randomly generated instances suggests that the model’s solution times are compatible with daily use and that multi-skilling is a significant source of labor flexibility to improve coverage of labor requirements, in particular when such requirements are negatively correlated and part-time workers are a scarce resource. 相似文献
62.
Mathias Breimesser Stefan Ritter Hans-Peter Seifert Sannakaisa Virtanen Thomas Suter 《Corrosion Science》2012
The electrochemical microcapillary technique was applied for the first time to study the electrochemical dissolution signals from single growing cracks due to stress corrosion cracking of thermally sensitised AISI 304 stainless steel in potassium tetrathionate solution. Potentiostatic current measurements on initiating cracks along grain boundaries were performed. Typical current signals of potentiostatic and potentiodynamic measurements consisted of a series of current peaks showing fast rise and exponential decay, sometimes interrupted by passive phases. The results indicate that stress corrosion crack growth is a discontinuous process of passive and active phases, which might be explained by the film rupture model. 相似文献
63.
Impact of coagulation and adsorption on DOC fractions of secondary effluent and resulting fouling behaviour in ultrafiltration 总被引:2,自引:0,他引:2
Membrane fouling by macromolecular dissolved organic compounds is still a fundamental drawback in low-pressure membrane filtration of secondary effluent. In this study, pre-treatment of secondary effluent by coagulation and/or adsorption was investigated in terms of removal of different dissolved organic carbon (DOC) fractions, especially macromolecular substances. DOC fractionation has been characterised by size exclusion chromatography. Adsorption tests using four commercially available activated carbons yielded a removal of small as well as larger organic compounds, revealing differences in the affinity towards macromolecules depending on the type of applied activated carbon. By contrast, coagulation removed predominantly larger molecules, i.e., biopolymers and humic substances. In terms of DOC reduction, the coagulant ferric chloride was superior to aluminium chloride. A combination of coagulation and adsorption resulted in the addition of individual removal efficiencies, suggesting that different fractions of organic compounds were involved in each of the processes. After removal of macromolecular organic compounds either by coagulation or by adsorption, a significant reduction of membrane fouling was observed in tests using two different types of ultrafiltration flat-sheet membranes in 20-h cross-flow filtration tests. 相似文献
64.
Dr. Umberto Maria Battisti Dr. Chunxia Gao Oscar Nilsson Dr. Fady Akladios Dr. Aleksei Lulla Dr. Agnieszka Bogucka Dr. Amalyn Nain-Perez Dr. Liliana Håversen Dr. Woonghee Kim Prof. Jan Boren Prof. Marko Hyvönen Prof. Mathias Uhlen Prof. Adil Mardinoglu Prof. Morten Grøtli 《Chembiochem : a European journal of chemical biology》2023,24(1):e202200339
Enzymes are effective biological catalysts that accelerate almost all metabolic reactions in living organisms. Synthetic modulators of enzymes are useful tools for the study of enzymatic reactions and can provide starting points for the design of new drugs. Here, we report on the discovery of a class of biologically active compounds that covalently modifies lysine residues in human liver pyruvate kinase (PKL), leading to allosteric activation of the enzyme (EC50=0.29 μM). Surprisingly, the allosteric activation control point resides on the lysine residue K282 present in the catalytic site of PKL. These findings were confirmed by structural data, MS/MS experiments, and molecular modelling studies. Altogether, our study provides a molecular basis for the activation mechanism and establishes a framework for further development of human liver pyruvate kinase covalent activators. 相似文献
65.
Odilia I Bermudez Claire Toher Gabriela Montenegro-Bethancourt Marieke Vossenaar Paul Mathias Colleen Doak Noel W Solomons 《Nutrition journal》2010,9(1):20
Background
Consumption of healthy diets that contribute with adequate amounts of fat and fatty acids is needed for children. Among Guatemalan children, there is little information about fat intakes. Therefore, the present study sought to assess intakes of dietary fats and examine food sources of those fats in Guatemalan children. 相似文献66.
Several carbon‐black filled styrene‐butadiene rubbers are subjected to monotonic uniaxial tension tests in order to investigate the effects of the amount of fillers and of the crosslink density on their mechanical properties. The Young modulus, the volume changes associated with material damage and the stretch to failure are extracted and discussed. Results compare well to the literature results when exist and quantitative analysis are proposed when possible. Results show that filled rubbers are not incompressible when submitted to uniaxial tension tests and their volume changes are strongly dependent of the amount of fillers but are unaffected by the crosslink density. The latter shows strong impact on the filled rubbers stretch to failure but more interestingly this impact is comparable to what is encountered in unfilled rubbers. The stretch to failure is improved by the addition of fillers with an optimum for material filled around 30 phr. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013 相似文献
67.
Eugene A Smirnov Maria A Meledina Alexey V Garshev Vitaly I Chelpanov Sven Frost Jan U Wieneke Mathias Ulbricht 《Polymer International》2013,62(5):836-841
Titania microspheres with narrow size distribution and diameters of about 1 µm were prepared and subsequently functionalized using surface‐initiated atom transfer radical polymerization (ATRP) of N‐isopropylacrylamide. The ATRP initiator was immobilized on the particle surface via acylation of surface hydroxyl groups with α‐bromoisobutyryl bromide. Subsequently, an established ATRP reaction system was used for the preparation of titania surface‐grafted poly(N‐isopropylacrylamide) (PNiPAAm). Characterization was performed with electron microscopies, X‐ray diffraction, infrared spectroscopy and dynamic light scattering. It was found that the particle size in aqueous dispersions changed reversibly with temperature as expected for a shell of PNiPAAm, a polymer with a lower critical solution temperature at 32 °C. This confirmed the successful preparation of functional, stimuli‐responsive TiO2 microparticles via a straightforward controlled surface‐initiated polymerization method. 相似文献
68.
Mathias Herrmann Jan RäthelSören Höhn Jens EichlerAlexander Michaelis 《Journal of the European Ceramic Society》2011,31(13):2401-2406
Hexagonal boron nitride/titanium diboride composites are widely used as evaporation boats for aluminium deposition to produce functional and decorative layers on different target materials. The lifetime of such a material is limited mainly by the interaction of the metal with the ceramic substrate, but the corrosion mechanism has still not yet been thoroughly investigated and understood. In this article the corrosion mechanism for the evaporation boats used was investigated using thermodynamic calculations, FESEM, EDX and XRD phase analysis. The analysis showed that hexagonal boron nitride (hBN), which is thermodynamically less stable than TiB2, is passivated during the application process through the formation of AlN surface layers, whereas the thermodynamically more stable TiB2 phase dissolves and Ti-rich components precipitate in cooler regions of the evaporation boats. 相似文献
69.
70.
Schwede Torsten F.; Badeker Mathias; Langer Martin; Retey Janos; Schulz Georg E. 《Protein engineering, design & selection : PEDS》1999,12(2):151-153
Histidase (histidine ammonia-lyase, EC 4.3.1.3) from Pseudomonasputida was expressed in Escherichia coli and purified. In theabsence of thiols the tetrameric enzyme gave rise to undefinedaggregates and suitable crystals could not be obtained. Thesolvent accessibility along the chain was predicted from theamino acid sequence. Among the seven cysteines, only one waslabeled as `solvent-exposed'. The exchange of this cysteineto alanine abolished all undefined aggregations and yieldedreadily crystals diffracting to 1.8 Å resolution. 相似文献