Optimising a general repair kit problem with a service constraint

Field services are a particular type of after-sales service performed at the customer’s location where technicians repair malfunctioning machines. The inventory decisions about which spare part types to take to the repair site and in what quantities is called the repair kit problem. This problem is characterized by an order-based performance measure since a customer is only satisfied when all required spare parts are available to fix the machine. As a result, the service level in the decision making process is defined as a job fill rate. In this paper we derive a closed-form expression for the expected service level and total costs for the repair kit problem in a general setting, where multiple units of each part type can be used in a multi-period problem. Such an all-or-nothing strategy is a new characteristic to investigate, but commonly used in practice. Namely, items are only taken from the inventory when all items to perform the repair are available in the right quantity. We develop a new algorithm to determine the contents of the repair kit both for a service and cost model while incorporating this new expression for the job fill rate. We show that the algorithm finds solutions which differ on average 0.2% from optimal costs. We perform a case study to test the performance of the algorithm in practice. Our approach results in service level improvements of more than 30% against similar holding costs.     

Dual biosensor immunoassay-directed identification of fluoroquinolones in chicken muscle by liquid chromatography electrospray time-of-flight mass spectrometry

Fluoroquinolones (FQs) are synthetic antibiotics of broad-spectrum antibacterial activity widely used to treat infections in farmed fish, turkeys, pigs, calves and poultry. Monitoring these substances residues is therefore regulated by law. For the detection of FQs, we studied the feasibility of coupling the simultaneous screening of several FQs, using a dual surface plasmon resonance (SPR) biosensor immunoassay (BIA), in parallel, with an analytical chemical methodology for their identification. Six FQs were simultaneously screened at or below their maximum residue level (MRL) in chicken muscle using a multi-FQ BIA for norfloxacin, ciprofloxacin, enrofloxacin, difloxacin and sarafloxacin, and a specific BIA for flumequine. The two BIAs were serially coupled in a multi-channel SPR biosensor featuring a dual BIA in a competitive inhibition format. The samples non-compliant during the screening with the dual BIA were further concentrated and fractionated with gradient liquid chromatography (LC). The effluent was splitted toward two 96-well fraction collectors resulting in two identical 96-well plates. One was re-screened with the dual BIA to identify the immunoactive fractions and direct the identification efforts toward the relevant fractions in the second well-plate with high resolution LC-electrospray time-of-flight mass spectrometry (ESI-TOFMS). The system not only allows the possibility to screen and identify known FQs, but also to discover unknown chemicals of similar structure which show activity in the dual BIA.     

In vivo XANES measuring technique for studying the arsenic uptake in cucumber plants

New in vivo X‐ray absorption near edge structure measuring technique was developed by using liquid nitrogen steam flow for cooling cucumber samples keeping them under cryogenic conditions during the measurement in order to preserve the original chemical states of arsenic species in the hypocotyl. The aim of this study was to determine the As oxidation state in order to identify the possible metabolic processes during the nutrient uptake in cucumber (Cucumis sativus L. cv Joker) as model plant. The plants were grown in Hoagland's modified nutrient solution. The ratio of the quantity of two As species was determined in the hypocotyls of the cucumber samples: arsenite, As(III) and arsenate, As(V). The ultimate biological goal of the in vivo experiments was to investigate the applicability of the X‐ray absorption near edge structure technique under cryogenic conditions and to specify the resistance level of the plants to arsenic toxicity when different chemical forms of iron, FeCl₃ and Fe‐ascorbate were supplied in the nutrient solution. We have examined the influence of the intense synchrotron radiation beam on the transformation of the oxidation number of both As species when the effect of the reactive oxygen forms was eliminated by the presence of ascorbate. Copyright © 2016 John Wiley & Sons, Ltd.     

Conformational Transmission in DNA

Abstract

This poster presents our recent results on DNA dimers in which a stable trigonal bipyramidal pentacoordinated phosphorus (P^v) structure forms the internucleoside linkage. Conformational analysis of the systems 1-4 with 300 and 500 ¹H NMR has shown that the P^v structure results in a distorted conformation of the backbone structuE (1).     

Homomorphisms and boundedness in topological groups

We consider homomorphisms from a normed space into a topological group. Assuming their boundedness in a neighbourhood (in relative topology) of an extremal point of the unit sphere, we derive their linearity (whenever it makes sense), closedness of the graph or continuity.     

Managing uncertainty in call centres using Poisson mixtures

We model a call centre as a queueing model with Poisson arrivals having an unknown varying arrival rate. We show how to compute prediction intervals for the arrival rate, and use the Erlang formula for the waiting time to compute the consequences for the occupancy level of the call centre. We compare it to the current practice of using a point estimate of the arrival rate (assumed constant) as forecast. Copyright © 2001 John Wiley & Sons, Ltd.     

A regenerable immobilized nadh model IV: Reduction of pyridine-2-carbaldehyde by immobilized 1,4-dihydronicotinamide in the presence of Mg2+ ions

Dihydronicotinamide, anchored to a macroreticular polystyrene resin, reduces pyridine-2-carbaldehyde (PCA) in the presence of Mg²⁺ ions in acetonitrile. The reactions are clean at room temperature, the high rate precluding complications arising from slow side reactions. The influence of Mg²⁺ concentration on the rate of reduction of PCA by polymer-bound reagent and BNAH (1-benzyl-1,4-dihydronicotinamide; low-molar-mass analog) has been studied. Analysis of the kinetic data showed that of the processes contributing to the overall reduction, the reaction between the reductant and the complexed substrate proceeded at the highest rate. In the polymer-bound reagent, “site isolation” on the rigid matrix was observed to prevent bimolecular disproportionation of the neighboring dihydronicotinamides. Regeneration of the polymeric reagent was achieved with an efficiency of 98% per cycle.