Laplacesche Integrale und Gammaquotientenreihen in der Theorie der linearen Differentialgleichungen und Volterraschen Integralgleichungen

Ohne Zusammenfassung     

Recent trends and developments in laser ablation-ICP-mass spectrometry

The increased interest in laser technology (e.g. for micro-machining, for medical applications, light shows, CD-players) is a tremendous driving force for the development of new laser types and optical set-ups. This directly influences their use in analytical chemistry. For direct analysis of the elemental composition of solids, mostly solid state lasers, such as Nd:YAG laser systems operating at 1064 nm (fundamental wavelength), 266 nm (frequency quadrupled) and even 213 nm (frequency quintupled) have been investigated in combination with all available inductively coupled plasma mass spectrometers. The trend towards shorter wavelengths (1064 nm - 157 nm) was initiated by access to high quality optical materials which led to the incorporation of UV gas lasers, such as excimer lasers (XeCl 308 nm, KrF 248 nm, ArF 193 nm, and F2 157 nm) into laser ablation set-ups. The flexibility in laser wavelengths, output energy, repetition rate, and spatial resolution allows qualitative and quantitative local and bulk elemental analysis as well as the determination of isotope ratios. However, the ablation process and the ablation behavior of various solid samples are different and no laser wavelength was found suitable for all types of solid samples. This article highlights some of the successfully applied systems in LA-ICP-MS. The current fields of applications are explained on selected examples using 266 nm and 193 nm laser ablation systems.     

Zur Theorie der Systeme linearer Differentialgleichungen mit einer unabhängigen Veränderlichen. I

Ohne Zusammenfassung     

Dynamic scheduling of recreational rental vehicles with revenue management extensions

The rental fleet scheduling problem (RFSP) arises in vehicle-rental operations that offer a wide variety of vehicle types to customers, and allow a rented vehicle to ‘migrate’ to a setdown depot other than the pickup depot.When there is a shortage of vehicles of a particular type at a depot, vehicles may be relocated to that depot, or vehicles of similar types may be substituted.The RFSP involves assigning vehicles to rentals so as to minimise the costs of these operations, and arises in both static and online contexts. The authors have adapted a well-known assignment algorithm for application in the online context. In addition, a network-flow algorithm with more comprehensive coverage of problem conditions is used to investigate the determination of rental pricing using revenue management principles. The paper concludes with an outline of the algorithms’ use in supporting the operations of a large recreational vehicle rental company.     

Hexatic ordering in freely suspended liquid crystal films

In this paper, we report results from synchrotron X-ray scattering studies of thefluid/hexactic/solid phases and phase transitions in both very thick and very thin, freely suspended films of tilted hexatic liquid crystals. Contrary to the thick film case, the higher Fourier coefficients describing the bond orientational order are suppressed in very thin films. This suppression is consistent with a two-dimensional bond orientational order parameter, ₆, rather than the three-dimensional bond orientational order parameter found in very thick films. For a film containing twently-three (23) smectic layers we find that ₆ is two-dimensional whereas the positional order in the crystallineS _J phase is three-dimensional. We present an analysis of the thick film data in terms of the three-dimensionalXY-model and a new mean field theory model which incorporates explicitly the quasi two-dimensional nature of bulk smectic phases.     

Density gradients in packed columns: I. Effects of density gradients on retention and separation speed

Density gradients in packed capillary columns operating under the extreme pressure drops typical for solvating gas chromatography were investigated by on-column spectroscopic measurements and compared to a theoretical model. Laser-induced fluorescence was used to follow the elution of various analytes, and Raman spectroscopy was used to measure the density of the mobile phase, each with respect to column position. Mobile phase linear velocity initially increases gradually, and then rises rapidly near the column outlet. High flow rates near the column outlet are offset by a loss of mobile phase solvating power which ultimately limits the speed of separation. These results represent an extreme case for illuminating factors affecting supercritical fluid separation techniques in general.     

Nucleation and growth during molecular beam epitaxy (MBE) of Si on Si(111)

The nucleation of Si on Si(111) has been studied during deposition in UHV by spot profile analysis of low energy electron diffraction (SPA-LEED). A new method of evaluation is developed by separating the measured spot profile into a central spike and a broad shoulder. The energy dependence of the fraction of the central spike out of the total diffracted intensity provides the vertical distribution of surface atoms over different levels. With this method it is shown that the first nucleation occurs in islands of double height. Only after deposition of several layers a layer-by-layer growth is found with a well defined nucleation of a new layer before the former one is completed.