Approximate queueing models for capacitated multi-stage inventory systems under base-stock control

A queueing analysis is presented for base-stock controlled multi-stage production-inventory systems with capacity constraints. The exact queueing model is approximated by replacing some state-dependent conditional probabilities (that are used to express the transition rates) by constants. Two recursive algorithms (each with several variants) are developed for analysis of the steady-state performance. It is analytically shown that one of these algorithms is equivalent to the existing approximations given in the literature. The system studied here is more general than the systems studied in the literature. The numerical investigation for three-stage systems shows that the proposed approximations work well to estimate the relevant performance measures.     

Global and local behavior of zeros of nonpositive type

A generalized Nevanlinna function Q(z)$Q(z)$ with one negative square has precisely one generalized zero of nonpositive type in the closed extended upper halfplane. The fractional linear transformation defined by _Qτ(z)=(Q(z)−τ)/(1+τQ(z))$Q_{\tau }(z)=(Q(z)-\tau )/(1+\tau Q(z))$, τ∈R∪{∞}$\tau \in \mathbb{R}\cup \{\infty \}$, is a generalized Nevanlinna function with one negative square. Its generalized zero of nonpositive type α(τ)$\alpha (\tau )$ as a function of τ is being studied. In particular, it is shown that it is continuous and its behavior in the points where the function extends through the real line is investigated.     

Molecular model studies based on ab initio calculations of nucleophilic and electrophilic addition‐substitution reactions focused on carbon–halogen compounds

We describe with molecular model studies based on the intrinsic parameters of van't Hoff's regular tetrahedron nucleophilic and electrophilic addition‐substitution reactions via a selected reaction coordinate for the displacement of carbon. Geometries of stable, intermediate transition complexes or transition states are compared with the corresponding ab initio values. Specific attention is given on the hypervalent and nonhypervalent character of carbon supported by ab initio calculations, our model consideration and experimental evidence. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Simultaneous monitoring of protein adsorption at the solid–liquid interface from sessile solution droplets by ellipsometry and axisymmetric drop shape analysis by profile

In this paper two in situ techniques are combined to simultaneously examine protein adsorption at the solid–liquid interface from sessile solution droplets. With axisymmetric drop shape analysis by profile (ADSA-P) the change in solid–liquid interfacial tension is determined, while ellipsometry is employed to measure the amount of protein adsorbed from the same solution droplet at the solid–liquid interface. Three proteins (human serum albumin (HSA), immunoglobulin G (IgG) and fibrinogen (Fb)) were dissolved to a concentration of 0.05 mg ml⁻¹ in PBS (pH 7) and sessile droplets were placed for 2 h on a 47.8 nm thick gold coating on glass. The gold coated glass was positioned onto a quartz prism with immersion oil. The prism was aligned in a rotating analyser ellipsometer and the optical beam was thus allowed to be reflected at the hydrophobic gold surface. The ADSA-P set-up was built in 90° cross-beamed set-up around the prism. By combining the results for the adsorbed amounts and the interfacial tension changes over the two hour adsorption period, two stages in the adsorption process could be distinguished. In the first stage, the adsorbed amounts increase in correspondence with the interfacial tension changes, indicating that the interfacial tension changes are caused by adsorption, whereas in the second stage interfacial tension changes continue despite the adsorbed amounts being constant. Consequently, the second stage must be associated with conformational changes of the adsorbed proteins. For HSA and Fb, the conformational contribution to the interfacial tension changes (7.8 and 5.3 mJ m⁻², respectively) were approximately 2-fold the adsorption contribution, while for IgG both were equal around 3 mJ m⁻².     

Structural elucidation of biologically active neomycin N‐octyl derivatives in a regioisomeric mixture by means of liquid chromatography/ion trap time‐of‐flight mass spectrometry

Structural elucidation of six regioisomers of mono‐N‐octyl derivatized neomycin is achieved using MSⁿ (up to n = 4) on an ion trap time‐of‐flight (IT‐TOF) instrument equipped with electrospray ionization. The mixture of six derivatized neomycin analogues was generated by reductive amination in a shotgun synthetic approach. In parallel to the liquid chromatography/mass spectrometry (LC/MS) detection, the antibacterial activity of the neomycin regioisomers was tested by post‐column addition of buffer and bacterial inocula, subsequent microfractionation of the resulting mixture, incubation, and finally a chemiluminescence‐based bioactivity measurement based on the production of bacterial ATP. The MS‐based high‐resolution screening approach described can be applied in medicinal chemistry to help in designing and producing new antibiotic substances, which is particularly challenging due to the high functionality of most antibiotic substances, therefore requiring advanced (hyphenated) separation and detection techniques for compound mixtures. Copyright © 2010 John Wiley & Sons, Ltd.     

Introduction for the special issue on the Antwerp Conferences

Quality management of laboratory medicine has become a hot topic at many conferences. Also, many national and international organizations have created working groups and committees with the task of working out standards, guidelines or recommendations for quality management of medical laboratories. We have observed that there is a great deal of interest not only from professional and scientific organizations directly involved in medical laboratory tests, but also from accreditation and certification bodies, from test laboratories in general, from in vitro diagnostic devices (IVD) manufacturers and their associations, and from other medical laboratory suppliers. However, we found that all these parties were discussing from their own point of view, without taking into account the position of other involved partners and that there was a need for creating a discussion forum for quality management in clinical laboratories. So in 1995, we started the Antwerp conferences on quality (r)evolution in clinical laboratories. The aim was to bring together all concerned partners and to establish a forum for brainstorming, independently of any pressure group. The leitmotif for the Antwerp conferences (Fig. 1) is a chain model showing the interfaces and relationships between all the partners involved in laboratory tests. During the conferences, this chain model has been examined from different angles and a summary of the concepts evolving from the discussions can be found in the conference abstracts and conference review reports in this journal. A Selection of ideas emerging from these conferences are presented below. Received: 5 October 1998 · Accepted: 20 October 1998     

关于格点覆盖的一个注记

对于一个给定椭球,本文给出了它的任一全等椭球都包含一个整点的一个充分必要条件.     

Tiling Hamming Space with Few Spheres

We show that if the collection of all binary vectors of lengthnis partitioned intokspheres, then eitherk2 orkn+2. Moreover, such partitions withk=n+2 are essentially unique.     

The scope and limitations of liquid-crystalline behaviour in monosaccharide amphiphiles Comparison of the thermal behaviour of several homologous series of D-glucose derived compounds with an amino-linked alkyl chain

A short review of the scope and limitations of liquid-crystalline behaviour in carbohydrate derivatives is presented. In order to investigate the influence of structure variations on the thermal behaviour of monosaccharide amphiphiles, six homologous series of D-glucose and 2-deoxy-D-glucose derivatives with an aminolinked n-alkyl chain were prepared. The observed thermal behaviour could be readily explained with the aid of a refinement of the qualitative model that was presented earlier [1]. All compounds were found to be mesogenic, and the observed mesophase was smectic A_d (i.e. a partially overlapping bilayer structure) in all cases.