An automated HPLC determination of meticlorpindol in eggs with UV absorbance detection, using on-line dialysis and pre-concentration as sample clean-up; occurrence in and carry over to eggs

Summary A fully automated HPLC determination of the coccidiostat meticlorpindol in whole egg, egg white and yolk is described. The sample homogenate is dialysed online against water. The dialysate is concentrated on-line on a short reversed-phase (RP) column. The contents of this column are transferred to the reversed-phase analytical column by means of the mobile phase. Meticlorpindol is detected using an absorbance detector at 270 nm. Linear calibration graphs are obtained in the range 40–900 ng/g in whole egg and egg white (detection limit 10 ng/g) and 80–1800 ng/g in yolk (detection limit 20 ng/g). Out of 111 commercially obtained egg samples 12 contained meticlorpindol with levels varying from 10 to 433 ng/g. A group of laying hens, kept in cages, received 10 mg/kg of Lerbek (meticlorpindol and methylbenzoquate; Dow Chemical) in the feed for 10 days. Meticlorpindol residues in the eggs rose to a level of 622 ng/g. Meticlorpindol was found in the eggs until 6 days after withdrawal of the medicated feed. Another group received 110 mg/kg in the feed. Meticlorpindol residues rose to levels of 4480 ng/g in the eggs, 5880 ng/g in the egg white and 2660 ng/g in the yolk. Meticlorpindol was found in the eggs and the egg white until 14 days and in the yolk until 8 days after withdrawal of the medicated feed.

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Eine automatisierte HPLC-Methode zur Bestimmung von Meticlorpindol in Eiern mit UV-Detektion und Probenaufarbeitung mit direkter Dialyse und direkter Vorkonzentrierung; Übertragung (Carry-over) und Vorkommen in Eiern

Zusammenfassung Mit dem beschriebenen Verfahren können Rückstände von Meticlorpindol in Eiern, Eiklar und Dotter automatisch bestimmt werden. Homogenisierte Proben werden gegen Wasser dialysiert. Das Dialysat wird an einer Vorkonzentrierungssäule konzentriert. Mit der mobilen Phase wird das Konzentrat auf die analytische Säule gebracht. Der Nachweis wird mit einem UV-Absorption-Detektor ausgeführt (Wellenlänge 270 nm). Der Zusammenhang zwischen Meßwert und Meticlorpindolgehalt ist linear in dem Bereich von 40 bis 900 ng/g Meticlorpindol in Vollei und Eiklar (Nachweisgrenze etwa 10 ng/g) und von 80 bis 1800 ng/g in Dotter (Nachweisgrenze etwa 20 ng/g). Bei der Untersuchung von 111 Handelsproben wurden in 12 Proben Rückstände von Meticlorpindol nachgewiesen mit Konzentrationen zwischen 10 und 433 ng/g. Eine Gruppe von Legehennen erhielt 10 mg/kg Lerbek (Meticlorpindol und Methylbenzoquate; Dow Chemical) im Futter während 10 Tagen. Die Eier wiesen bis zum 6. Tag nach dem Absetzen des Futterzusatzes nachweisbare Meticlorpindol-Rückstände auf (Höchstgehalt 622 ng/g in Vollei). Eine zweite Gruppe erhielt 110 mg/kg im Futter. In den Volleiproben und Eiklarproben dieser Gruppe konnten bis zum 14. Tag nach dem Absetzen Rückstände von Meticlorpindol nachgewiesen werden (Höchstgehalte 4480 und 5880 ng/g), in den Dotterproben bis zum 8. Tag (Höchstgehalt 2660 ng/g).

     

Morphological impact of zinc oxide layers on the device performance in thin-film transistors

Zinc oxide thin-films are prepared either by spin coating of an ethanolic dispersion of nanoparticles (NP, diameter 5 nm) or by spray pyrolysis of a zinc acetate dihydrate precursor. High-resolution electron microscopy studies reveal a monolayer of particles for the low temperature spin coating approach and larger crystalline domains of more than 30 nm for the spray pyrolysis technique. Thin-film transistor devices (TFTs) based on spray pyrolysis films exhibit higher electron mobilities of up to 24 cm2 V(-1) s(-1) compared to 0.6 cm2 V(-1) s(-1) for NP based TFTs. These observations were dedicated to a reduced number of grain boundaries within the transistor channel.     

Automatic particle detection in microscopy using temporal correlations

One of the fundamental problems in the analysis of single particle tracking data is the detection of individual particle positions from microscopy images. Distinguishing true particles from noise with a minimum of false positives and false negatives is an important step that will have substantial impact on all further analysis of the data. A common approach is to obtain a plausible set of particles from a larger set of candidate particles by filtering using manually selected threshold values for intensity, size, shape, and other parameters describing a particle. This introduces subjectivity into the analysis and hinders reproducibility. In this paper, we introduce a method for automatic selection of these threshold values based on maximizing temporal correlations in particle count time series. We use Markov Chain Monte Carlo to find the threshold values corresponding to the maximum correlation, and we study several experimental data sets to assess the performance of the method in practice by comparing manually selected threshold values from several independent experts with automatically selected threshold values. We conclude that the method produces useful results, reducing subjectivity and the need for manual intervention, a great benefit being its easy integratability into many already existing particle detection algorithms. Microsc. Res. Tech., 76:997–1006, 2013. © 2013 Wiley Periodicals, Inc.     

Effect of fluid–particle-interactions on dispersing nano-particles in epoxy resins using stirred-media-mills and three-roll-mills

Fibre reinforced composites are indispensable in the field of modern lightweight structures, such as used in aerospace, automotive industry or in wind power plants. Those materials provide high weight savings and increase the efficiency of a structure significantly. Therefore, various efforts are made to continuously improve the quality of the matrix and the fibres. By embedding nano-particles into the epoxy matrix, the mechanical properties as well as the electrical and thermal characteristics can significantly be improved [1]. In most cases these nano-sized particles are produced as dry powders not as single primary particles but rather as particle collectives consisting out of several primary particles. For the application in reinforced composites the particles must be suspended in epoxy resin as separately dispersed primary particles or in a certain aggregate size. Generally, the influencing parameters to break up the aggregates in a dispersion process can be divided into the stress mechanism, the intensity and the frequency of the dispersing machine itself, the properties of the dispersed particles (e.g. the particle–particle interactions) the properties of the homogenous phase and the particle–resin-interactions. Besides the effect of the chosen dispersing machine the optimization of the dispersing process was investigated by applying modified particle surfaces and varying the fluid properties. The results show that the surface properties of the particles must fit to the epoxy resin properties and the attractive forces between the primary particles must be reduced or the stabilization improved, respectively. An indication for an improved stabilization and adjustment of the particles surface properties to the fluid properties can be obtained by measurements of the contact angle and the rheological properties. Generally, an increase of viscosity and mass fraction of the product leads to a higher energetic efficiency of the dispersion process in the stirred media mill and three-roll-mill.     

Pattern formation and transient thermocapillary flow in a rectangular side-heated open cavity

Marangoni convection in an open, side-heated container of a rectangular cross-section is investigated experimentally. The cavity’s length is much larger than the distance between the heated walls. Therefore, the flow is quasi-two-dimensional if the thermocapillary Reynolds number and the Rayleigh number are small. On an increase of the temperature difference between the side walls the flow becomes three-dimensional. We measure the onset of the three-dimensional flow and its structure. Morover, microgravity experiments have been performed using the Drop Tower facility of ZARM at the University of Bremen. In these latter experiments the dynamics of the flow upon a step change from 1g to μg was measured. The result of the experiments and corresponding numerical simulations show a significant change of the flow pattern within the first 1.5 seconds after the step change.     

Addressable Microfluidic Polymer Chip for DNA‐Directed Immobilization of Oligonucleotide‐Tagged Compounds

A microfluidic polymer chip for the self‐assembly of DNA conjugates through DNA‐directed immobilization is developed. The chip is fabricated from two parts, one of which contains a microfluidic channel produced from poly(dimethylsiloxane) (PDMS) by replica‐casting technique using a mold prepared by photolithographic techniques. The microfluidic part is sealed by covalent bonding with a chemically activated glass slide containing a DNA oligonucleotide microarray. The dimension of the PDMS–glass microfluidic chip is equivalent to standard microscope slides (76 × 26 mm²). The DNA microarray surface inside the microfluidic channels is configured through conventional spotting, and the resulting DNA patches can be conveniently addressed with compounds containing complementary DNA tags. To demonstrate the utility of the addressable surface within the microfluidic channel, DNA‐directed immobilization (DDI) of DNA‐modified gold nanoparticles (AuNPs) and DNA‐conjugates of the enzymes glucose oxidase (GOx) and horseradish peroxidase (HRP) are carried out. DDI of AuNPs is used to demonstrate site selectivity and reversibility of the surface‐modification process. In the case of the DNA–enzyme conjugates, the patterned assembly of the two enzymes allows the establishment and investigation of the coupled reaction of GOx and HRP, with particular emphasis on surface coverage and lateral flow rates. The results demonstrate that this addressable chip is well suited for the generation of fluidically coupled multi‐enzyme microreactors.     

What makes a scientific article influential? The case of demographers

In this paper we examine, by means of a citation analysis, which factors influence the impactof articles published in demography journals between 1990 and 1992. Several quantifiablecharacteristics of the articles (characteristics with respect to authors, visibility, content andjournals) are strongly related to their subsequent impact in the social sciences. Articles are mostfrequently cited when they deal with empirical, ahistorical research focusing on populations in thedeveloped world, when they are prominently placed in a journal issue, when they are written inEnglish and when they appear in core demography journals. Furthermore, although eminentscholars are likely to be cited on the basis of their reputation, the effect of reputation appears to besmall in demography.     

Modeling and simulation of the engagement dynamics of a wet friction clutch system subjected to degradation: An application to condition monitoring and prognostics

In this paper, a friction model appropriate for wet friction clutches based on the extension of the Generalized Maxwell Slip (GMS) friction model is integrated to a four-DOF lumped-mass-spring-damper system which represents a typical SAE#2 test setup. Degradation models expressing the evolutions of the friction model parameters are also proposed, where the structure of the degradation models is inspired from experimental results obtained in the earlier work. This way, the engagement dynamics of the clutch system during the useful lifetime can be simulated. It appears that the previously developed pre-and postlockup features extracted from the simulated signals obtained in this study are qualitatively in agreement with the experimental results. Those features show their predictive behaviors that confirm their feasibility to be used for clutch monitoring and prognostics. Furthermore, the models and simulation procedure discussed in this paper can be employed for developing and evaluating prognostics algorithms for wet friction clutch applications.