On-Line Solid Phase Extraction–Gas Chromatography–Cryotrapping–Infrared Spectrometry for the Trace-Level Determination of Microcontaminants in Aqueous Samples

A large-volume on-column GC–cryotrapping–IR system was developed for injections of up to 100 μl of organic extracts. Considerable reduction of the solvent-and-water background and enhanced analyte detectability was achieved by using an open-split interface between the GC column and the IR detector and improving the leak-tightness of the system. The system was combined with solid-phase extraction to yield on-line SPE–GC–IR. With this set-up, sample volumes of only 20 ml sufficed to detect, and identify, microcontaminants in tap and surface water at the 0.1–1 μg/L level. Detection limits were on the order of 15 ng/L for tap water when using appropriate functional-group chromatograms. Or, in other words, SPE–GC–IR is a suitable technique for the screening of environmental water samples for functional groups, i.e. classes of compounds, of interest.     

High-strain tensile deformation of a sphere-forming triblock copolymer/mineral oil blend

Films of a blend of styrene–isoprene triblock copolymer and mineral oil have been simple-cast and roll-cast from a toluene solution. Their microstructure has been analyzed by transmission electron microscopy and small-angle X-ray scattering. The blend formed polystyrene spheres arranged on a body-centered cubic lattice in a matrix composed of polyisoprene and mineral oil, and the samples display large grain sizes and very long-range order. The roll-cast sample exhibits approximately uniaxial symmetry around the rolling direction, which corresponds to the [111] crystallographic direction of the lattice. The glassy spheres act as physical crosslinks of known crosslinking functionality in the soft rubbery matrix. The high-strain deformation mechanism of this oriented cubic material has been studied by a simultaneous tensile–SAXS experiment, where the sample was stretched up to 300% along the [111] direction. By monitoring the position of the (222) and (11 0) reflections, the deformation of the lattice is shown to be affine with the macroscopic deformation of the sample, and the Poisson's ratio is approximately 0.46. The first zero of the sphere form factor in the SAXS patterns remains also essentially unchanged up to 300% deformation indicating that the reinforcing glassy PS domains retain their spherical shape throughout the deformation. Deformation of the microstructure is totally reversible upon unloading. A model of {hk0} faults is proposed to describe the microstructural changes induced by high-strain deformation. © 1998 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 36: 1625–1636, 1998     

pH‐Controlled Macromolecule Encapsulation in and Release from Polyelectrolyte Multilayer Nanocapsules

pH‐Controlled encapsulation in and release of macromolecules from polyelectrolyte capsules of a few microns in diameter is demonstrated. Capsules were prepared via alternating adsorption of the oppositely charged polymers poly(allylamine hydrochloride) and poly(styrene sulfonate) onto decomposable melamin formaldehyde cores. The capsules were open for macromolecules at pH values below 6 and closed at pH > 8.     

Potential of Flame Ionization Detection Coupled On‐Line with Microcolumn Liquid Chromatography Using Aqueous Eluents and an Eluent‐Jet Interface

The potential of the on‐line coupling of microcolumn liquid chromatography (μLC) using aqueous eluents with a flame ionization detector (FID) was evaluated. An eluent‐jet interface was modified to allow the efficient introduction of the eluent into the FID. The potential of the method is demonstrated by the μLC–FID determination of lower alcohols and bis(2‐hydroxyethylthio)alkanes on porous and non‐porous stationary phases, respectively. Flow injection analysis (FIA)–FID experiments with highly polar, thermolabile, semi‐volatile and non‐volatile compounds like amino acids, organic acids, alkylphosphonic acids, and carbohydrates showed the developed configuration to be a promising approach for the detection of a wide range of analytes. Compared with a nebulization interface, the eluent‐jet interface showed 4–10 times higher peaks for citric acid. Detection limits by FIA for all compounds were in the range of 0.2–5 ng injected. With ribose as test compound, plots of peak height vs. amount injected showed good linearity (r² > 0.999) in the range of 75–12,000 μg/mL. The repeatability showed relative standard deviations of less than 5%.     

Separation of Lutidine Isomers by Inclusion

Structures of the inclusion compounds formed between the host compound 1,4-bis(9-hydroxy-9-fluorenyl)benzene and three lutidine regioisomers, 2,4-, 3,5-, and 2,6-lutidine, have been elucidated. Competition experiments were performed to investigate the degree of host selectivity for complexation with the lutidine isomers. Lattice energy calculations explain the results of the competition experiments, and thermal analysis shows that the desolvation reactions are complex.     

Dynamics of Ship–Motion

The ship capsizing problem is one of the major challenges in naval architecture. The IMO criterion regarding capsize stability is still the righting lever curve of static stability calculated for calm water. For the prediction of large–amplitude motions the dynamic loads have to be included. The capsizing of a ship in regular waves is resulting from a sequence of bifurcations in the ship's motion: The determination of bifurcations is possible using path‐following techniques of nonlinear dynamics. Existing tools are, however, without adaption not readily applicable for the determination of bifurcations. The main and until now unsolved problem is the necessity of including memory integrals to describe the ship hydrodynamics. First results with simple algorithms show two different scenarios leading to capsizing due to increasing wave amplitudes.     

Subharmonic motion of floating cranes

As an example of the nonlinear phenomena in offshore engineering the subharmonic motion of a floating crane is investigated. This nonlinear behavior was observed in experiments [1] as well as simulations [3] for a periodically forced floating crane. The range of operation, in which initial conditions and disturbances influence the type of motion significantly, are of special interest – as well as bifurcation points, where the dynamics change qualitatively due to a small change of one of the parameters. Two different mathematical tools for the investigation of these critical ranges are described: The multiple scales method allows for the analysis of the oscillating system in frequency domain. Path following algorithms are applied in the numerical bifurcation analysis. The results of both tools are in good agreement and can assist in the evaluation of operating conditions.     

A Memory-Efficient Encoding Method for Processing Mixed-Type Data on Machine Learning

The most common machine-learning methods solve supervised and unsupervised problems based on datasets where the problem’s features belong to a numerical space. However, many problems often include data where numerical and categorical data coexist, which represents a challenge to manage them. To transform categorical data into a numeric form, preprocessing tasks are compulsory. Methods such as one-hot and feature-hashing have been the most widely used encoding approaches at the expense of a significant increase in the dimensionality of the dataset. This effect introduces unexpected challenges to deal with the overabundance of variables and/or noisy data. In this regard, in this paper we propose a novel encoding approach that maps mixed-type data into an information space using Shannon’s Theory to model the amount of information contained in the original data. We evaluated our proposal with ten mixed-type datasets from the UCI repository and two datasets representing real-world problems obtaining promising results. For demonstrating the performance of our proposal, this was applied for preparing these datasets for classification, regression, and clustering tasks. We demonstrate that our encoding proposal is remarkably superior to one-hot and feature-hashing encoding in terms of memory efficiency. Our proposal can preserve the information conveyed by the original data.