Queueing Models of Call Centers: An Introduction

This is a survey of some academic research on telephone call centers. The surveyed research has its origin in, or is related to, queueing theory. Indeed, the queueing-view of call centers is both natural and useful. Accordingly, queueing models have served as prevalent standard support tools for call center management. However, the modern call center is a complex socio-technical system. It thus enjoys central features that challenge existing queueing theory to its limits, and beyond.The present document is an abridged version of a survey that can be downloaded from www.cs.vu.nl/obp/callcenters and ie.technion.ac.il/serveng.     

Boundedness and continuity of additive and convex functionals

Summary It is shown that for any real Baire topological vector spaceX the set classesA(X):={T : for any open and convex setD T, every Jensen-convex functional, defined onD and bounded from above onT, is continuous} andB(X):={T : every additive functional onX, bounded from above onT, is continuous} are equal. This generalizes a result of Marcin E. Kuczma (1970) who has shown the equalityA( ⁿ )=B( ⁿ ) However, the infinite dimensional case requires completely different methods; therefore, even in the caseX = ⁿ we obtain a new (and perhaps simpler) proof than that given by M. E. Kuczma.     

Mapping Grape Berry Photosynthesis by Chlorophyll Fluorescence Imaging: The Effect of Saturating Pulse Intensity in Different Tissues

Grape berry development and ripening depends mainly on imported photosynthates from leaves, however, fruit photosynthesis may also contribute to the carbon economy of the fruit. In this study pulse amplitude modulated chlorophyll fluorescence imaging (imaging‐PAM) was used to assess photosynthetic properties of tissues of green grape berries. In particular, the effect of the saturation pulse (SP) intensity was investigated. A clear tissue‐specific distribution pattern of photosynthetic competence was observed. The exocarp revealed the highest photosynthetic capacity and the lowest susceptibility to photoinhibition, and the mesocarp exhibited very low fluorescence signals and photochemical competence. Remarkably, the seed outer integument revealed a photosynthetic ability similar to that of the exocarp. At a SP intensity of 5000 μmol m^?2 s^?1 several photochemical parameters were decreased, including maximum fluorescence in dark‐adapted (F_m) and light‐adapted (F'_m) samples and effective quantum yield of PSII (Φ_II), but the inner tissues were susceptible to a SP intensity as low as 3200 μmol m^?2 s^?1 under light‐adapted conditions, indicating a photoinhibitory interaction between SP and actinic light intensities and repetitive exposure to SP. These results open the way to further studies concerning the involvement of tissue‐specific photosynthesis in the highly compartmentalized production and accumulation of organic compounds during grape berry development.     

Biosensor immunoassay for flumequine in broiler serum and muscle

Flumequine (Flu) is one of the fluoroquinolones most frequently applied for the treatment of broilers in The Netherlands. For the detection of residues of Flu in blood serum of broilers, a biosensor immunoassay (BIA) was developed which was fast (7.5 min per sample) and specific (no cross-reactivity with other (fluoro)quinolones). This inhibition assay was based on a rabbit polyclonal anti-Flu serum and a CM5 biosensor chip coated with Flu which could be detected in the range of 15-800 ng mL(-1). For the detection of Flu in muscle, an easy extraction procedure in buffer was selected and the measuring range was from 24 to 4000 ng g(-1). Average recoveries of 66 till 75% were found with muscle samples spiked at 0.5, 1 and 2 times the maximum residue limit (MRL in muscle = 400 ng g(-1)) and the decision limit (CCalpha) and the detection capability (CCbeta) were determined as 500 and 600 ng g(-1), respectively. Incurred muscle samples were analysed by the BIA and by LC-MS/MS and a good correlation was found (R2 = 0.998). Serum and muscle samples from with Flu treated broilers were analysed and the concentrations found in serum were always higher than those found in muscle (average serum/muscle ratio was 3.5) and this proved the applicability of the BIA in serum as predictor of the Flu concentration in muscle.     

A Concise Total Synthesis of (+)‐Tetrabenazine and (+)‐α‐Dihydrotetrabenazine

Highly concise asymmetric total syntheses of (+)‐tetrabenazine ( 1 ), a drug for the treatment of chorea associated with Huntington’s disease, and of (+)‐α‐dihydrotetrabenazine ( 2 ), an active metabolite of 1 , have been accomplished. Our synthetic route features a trans‐selective enol etherification, followed by an unprecedented cation‐dependent aza‐Claisen rearrangement to establish the carbon framework and two stereogenic centers of tetrabenazine. The syntheses consist of seven steps (34 % overall yield) for (+)‐ 2 and eight steps (22 % overall yield) for (+)‐ 1 .     

Development and evaluation of an interface for coupled capillary supercritical fluid chromatography/magnetic sector mass spectrometry. Application to thermally unstable and high molecular mass compounds

An interface for coupling supercritical fluid chromatography to a magnetic sector mass spectrometer was developed and evaluated. The interface is based on direct introduction of the mobile phase, carbon dioxide, into the ion-source of the mass spectrometer. The SFC-MS system was optimized with respect to the signal-to-noise ratio. Under optimized conditions, the estimated detection limit for n-pentadecane is approximately 30 ppm. Spectra obtained in the electron-impact ionization mode show a very good similarity with library spectra. The performance of the SFC-MS system was evaluated by the analysis of a number of test mixtures. A sample containing several low molecular mass, thermally unstable compounds, which could neither be analyzed by GC-MS nor by LC-MS, was analyzed. Also for the analysis of high molecular mass compounds, the coupled system showed a good performance.     

Selective oxidative para C-C dimerization of 2,6-dimethylphenol

Mechanistic investigations on the oxidative coupling of 2,6-dimethylphenol have led to the development of a selective and efficient procedure to prepare 3,5,3',5'-tetramethyl-biphenyl-4,4'-diol, via a C-C coupling, mediated by a hypervalent form of iodine, i.e. (diacetoxyiodo)benzene and for which a mechanism is proposed.