Wavelet compression of three-dimensional time-lapse biological image data.

The use of multifocal-plane, time-lapse recordings of living specimens has allowed investigators to visualize dynamic events both within ensembles of cells and individual cells. Recordings of such four-dimensional (4D) data from digital optical sectioning microscopy produce very large data sets. We describe a wavelet-based data compression algorithm that capitalizes on the inherent redunancies within multidimensional data to achieve higher compression levels than can be obtained from single images. The algorithm will permit remote users to roam through large 4D data sets using communication channels of modest bandwidth at high speed. This will allow animation to be used as a powerful aid to visualizing dynamic changes in three-dimensional structures.     

Employment of detergent-tag/solute interactions in capillary electrophoresis of neutral polysaccharides

Neutral and inherently immobile polysaccharides are induced to migrate in an electric field through interactions with a detergent added to the electrophoretic electrolyte buffer. Before analysis the polysaccharides are converted to fluorescent derivatives to enable detection, but choice of a tag can also be utilized for modulation of the electrophoretic mobility. Three cases are discussed and exemplified, namely detergent-solute, detergent-solute+tag, and detergent-tag interactions. Anionic as well as cationic surfactants were exploited along with different derivatization reagents. Depending on the approach chosen, different kinds of information about sample composition and distribution(s) can be obtained, including degree of substitution, distribution of molecular weight (obtained in free solution without sieving media) and polymer conformation. A shift in polymer conformation upon a change in solvent composition can be monitored.     

Finite-Volume Discretisations for Flow in Fractured Porous Media

Over the last decades, finite-volume discretisations for flow in porous media have been extended to handle situations where fractures dominate the flow. Successful discretisations have been based on the discrete fracture-matrix models to yield mass conservative methods capable of explicitly incorporating the impact of fractures and their geometry. When combined with a hybrid-dimensional formulation, two central concerns are the restrictions arising from small cell sizes at fracture intersections and the coupling between fractures and matrix. Focusing on these aspects, we demonstrate how finite-volume methods can be efficiently extended to handle fractures, providing generalisations of previous work. We address the finite-volume methods applying a general hierarchical formulation, facilitating implementation with extensive code reuse and providing a natural framework for coupling of different subdomains. Furthermore, we demonstrate how a Schur complement technique may be used to obtain a robust and versatile method for fracture intersection cell elimination. We investigate the accuracy of the proposed elimination method through a series of numerical simulations in 3D and 2D. The simulations, performed on fractured domains containing permeability heterogeneity and anisotropy, also demonstrate the flexibility of the hierarchical framework.     

Discrete and continuous time representations and mathematical models for large production scheduling problems: A case study from the pharmaceutical industry

The underlying time framework used is one of the major differences in the basic structure of mathematical programming formulations used for production scheduling problems. The models are either based on continuous or discrete time representations. In the literature there is no general agreement on which is better or more suitable for different types of production or business environments. In this paper we study a large real-world scheduling problem from a pharmaceutical company. The problem is at least NP-hard and cannot be solved with standard solution methods. We therefore decompose the problem into two parts and compare discrete and continuous time representations for solving the individual parts. Our results show pros and cons of each model. The continuous formulation can be used to solve larger test cases and it is also more accurate for the problem under consideration.     

Numerical Modelling of Convection-Driven Cooling,Deformation and Fracturing of Thermo-Poroelastic Media

Transport in Porous Media - Convection-driven cooling in porous media influences thermo-poro-mechanical stresses, thereby causing deformation. These processes are strongly influenced by the...     

Ion-pair LC of sugars at alkaline pH and pulsed electrochemical detection

Summary Sugars, sugar acids, amino sugars and oligomers are separated as ion-pairs with hydrophobic counter ions at alkaline pH using PLRP-S and Hypercarb as solid phases. Important parameters for regulation of retention and selectivity are nature and concentration of the counter ion, pH (hydroxide concentration) and temperature. Reversals in the elution order wer obtained in some cases. Oligosaccharides are highly retained in these systems. The addition of organic modifiers to the mobile phase for elution of the solutes were found to interfere with the pulsed electrochemical detection (PED). Anions added to the mobile phase compete with the solutes for ion-pair retention, hence, decreasing the capacity factors, and phosphate could be used for this purpose in the separation of maltooligomers (M2-M10) from corn syrup.     

Separation of glucuronides from urine by coupled-column separation using underivatized silica as precolumn.

Glucuronides are separated from urine by coupled-column separations (CCSs). The fraction containing the glucuronide(s) is transferred on-line from a silica precolumn to the analytical column (octadecyl derivatized silica), enriched, and separated by ion-pair chromatography. The retention and selectivity on the precolumn are controlled by pH, buffer components, organic modifier, and ion-pair agent. After the injection of filtered urine samples, glucuronides with different chemical properties can be separated. The total analysis of morphine-3-glucuronide and morphine-6-glucuronide is accomplished in less than six minutes, with UV detection at 210 nm.     

Ion-pair LC of carbohydrates at alkaline pH. Separation and retention behaviour of glycoconjugates

Summary A new technique for the separation of carbohydrates as ion-pairs in strongly alkaline solution is presented. Carbohydrates are weakly acidic and partly present as anions at pH12 [1]. They are retained as ion-pairs on polymeric solid phases (PRP-1 and PLRP-S) with a hydrophobic quaternary ammonium counter ion present in the mobile phase. The effects of nature and concentration of mobile phase components on the retention of carbohydrates have been investigated and an ion-pair distribution model is proposed. The influence of temperature indicated no changes in retention mechanism with high counter ion concentration, but the resolution decreased with increasing temperature. Saccharides added to the mobile phase were shown to increase the retention and the selectivity.     

Ligand-exchange chromatography of carbohydrates and glycoconjugates

The current status of ligand-exchange chromatography (LEC) is reviewed in the light of recent developments, especially regarding mobile phase conditions and choice of metal ions. Further, parameters governing selectivity are emphasized. The paper is divided into two parts: LEC at acidic/neutral pH and at alkaline pH. The general characteristics of each part are outlined and illustrated by appropriate applications, including bioanalysis of carbohydrates in complex mixtures. In particular, the exceptionally strong complexation between carbohydrates and certain metal ions at alkaline pH appears promising for enrichment and clean-up possibilities owing to the high degree of inherent selectivity. Finally, future directions are discussed with regard to the intricate isolation and separation problems associated with glycotechnology. Further advances within this field will depend on the development of analytical methodologies for minute amounts (femtomoles) of complex carbohydrate mixtures present on proteins, receptors and cell surfaces and inside the cells.     

Retention studies of sulphated glycosaminoglycan disaccharides on porous graphitic carbon capillary columns

Summary The retention behaviour of highly polar and charged disaccharide isomers has been studied on porous graphitic carbon columns and experimental parameters were varied over wide a range, including concentration and type of mobile phase constituents as well as temperature. The hydrophilic and anionic sugar analytes were highly retained on this stationary phase compared to the octadecyl-derivatized silica packings more commonly used. E.g., an increase in retention with polarity of a solute and with temperature was observed. By isotherm measurements and nonlinear fitting of Langmuirian expressions to the experimental data the graphite surface appeared homogeneous with only one kind of active adsorption site for these kinds of compound which was furthermore supported by the linear Van't Hoff plots obtained by varying the temperature. The gain in free energy was found to be entropically driven after determination of the ΔH° and ΔS° values. However, enthalpy-entropy compensation behavior was not met.