Synthesis and characterization of soluble (porphyrinato)iron(II) polymers

The use of (tetrakis(4-hexylphenyl)porphyrinato)Fe(II) in polymerization reactions with bidentate ligands such as 9,10-diisocyanoanthracene and 1,4-diisocyanobenzene led to well-defined stacked polymers1 and2 which are still soluble in common organic solvents such as chloroform, dichloromethane, and tetrahydrofurane. They have been completely characterized by¹H-NMR and UV/vis spectropscopy in solution, even allowing end-group analysis for determination of the average degree of polymerization, yieldingn=10 andn=5 for1 and2, respectively. Mößbauer and IR spectroscopy further established the strong Fe-CN bonding reflected by very small isomer shifts and quadrupole splittings (E _Q0.2 mm s^–1) and a large decrease in the IR stretching frequency (v _CN60 cm^–1). The axially stacked polymers exhibit semiconducting properties only upon doping.Presented at the 5th International Symposium on Macromolecule-Metal Complexes (MMV), Summer 1993 in Bremen, Germany.     

Undecidability of accordance for open systems with unbounded message queues

We study asynchronously communicating open systems modeled as Petri nets with an interface. An accordance preorder describes when one open system can be safely replaced by another open system without affecting some behavioral property of the overall system. Although accordance is decidable for several behavioral properties if we assume a previously known bound on the maximal number of pending messages, we show that it is not decidable without this assumption.     

Hierarchical opacity optimization for sets of 3D line fields

The selection of meaningful lines for 3D line data visualization has been intensively researched in recent years. Most approaches focus on single line fields where one line passes through each domain point. This paper presents a selection approach for sets of line fields which is based on a global optimization of the opacity of candidate lines. For this, existing approaches for single line fields are modified such that significantly larger amounts of line representatives are handled. Furthermore, time coherence is addressed for animations, making this the first approach that solves the line selection problem for 3D time‐dependent flow. We apply our technique to visualize dense sets of pathlines, sets of magnetic field lines, and animated sets of pathlines, streaklines and masslines.     

Rheology of poly(n‐butyl methacrylate) and its composites with calcium carbonate

Poly(n‐butyl methacrylate) (PBMA) composites with calcium carbonate (CaCO₃) were prepared by in situ radical copolymerization of butyl methacrylate (BMA) and methacrylic acid (MA) with precipitated calcium carbonate. To compare the different rheological behaviors of the monomer mixtures with CaCO₃ and the composites, the steady and dynamic viscosities of BMA/MA/CaCO₃ and poly(BMA/MA/CaCO₃) were measured by means of steady and oscillatory shear flows. The viscosity of the mixture BMA/MA/CaCO₃ was found to increase evidently with the increasing of CaCO₃%. The influence of MA% on viscosity of BMA/MA/CaCO₃ was slight. During the in situ polymerization, the viscosity of the reacting system was measured to be enhanced by a factor of about 10⁴ from the monomer/CaCO₃ mixture to composites. The dependency of zero‐shear viscosity on molar mass of PBMA was also investigated. The relation between the zero‐shear viscosity and molar mass is η₀ = 10^?15 M_w^3.5. The evolution of the viscosity with the temperature for both PBMA and its composites was obtained and time–temperature superposition was used to build master curves for the dynamic moduli. The flow activation energies were found to be 115.0, 148.6, and 178.7 kJ/mol for PBMA, composite PBMA/CaCO₃ (90/10), and PBMA/MA/CaCO₃ (89/1/10), respectively. The viscosity of the composites containing less than 10% CaCO₃ was lower than that of pure PBMA with the same molar mass. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 1376–1383, 2003     

On stability of signature-based similarity measures for content-based image retrieval

Retrieving similar images from large image databases is a challenging task for today’s content-based retrieval systems. Aiming at high retrieval performance, these systems frequently capture the user’s notion of similarity through expressive image models and adaptive similarity measures. On the query side, image models can significantly differ in quality compared to those stored on the database side. Thus, similarity measures have to be robust against these individual quality changes in order to maintain high retrieval performance. In this paper, we investigate the robustness of the family of signature-based similarity measures in the context of content-based image retrieval. To this end, we introduce the generic concept of average precision stability, which measures the stability of a similarity measure with respect to changes in quality between the query and database side. In addition to the mathematical definition of average precision stability, we include a performance evaluation of the major signature-based similarity measures focusing on their stability with respect to querying image databases by examples of varying quality. Our performance evaluation on recent benchmark image databases reveals that the highest retrieval performance does not necessarily coincide with the highest stability.     

Engineering microfluidic papers: effect of fiber source and paper sheet properties on capillary-driven fluid flow

In the present study, we introduce a novel approach to control and modulate fluid transport inside microfluidic papers using lab-engineered paper sheets. Lab-sheets consisting of different fiber sources (eucalyptus sulfate and cotton linters pulp) and varying porosities were designed and further modified with small millimeter-scaled channels using hydrophobic barriers consisting of fiber-attached, hydrophobic polymers. The capillary-driven transport of an aqueous solution was monitored visually, and the influence of parameters such as fiber source, paper grammage, and channel width on the flow rates through the channel was investigated. The experimental results were compared with those obtained with commercially available filter papers. Our findings suggest that accurate control of fluid transport processes with standard filter papers is complex. Additionally, if the channel width is smaller than the mean fiber length, flow rates become dependent on the geometric parameters of the channel because of the formation of dead-end pores at the hydrophobic barriers. Finally, control of the paper sheets porosity, by varying the fiber density of the lab-made paper, affords the fabrication of chemically identical sheets whereby capillary flow is largely influenced and can be modulated accordingly by simple papermaking processes.     

Dynamic mechanical properties and morphology of high‐density polyethylene/CaCO3 blends with and without an impact modifier

Dynamic mechanical analysis and differential scanning calorimetry were used to investigate the relaxations and crystallization of high‐density polyethylene (HDPE) reinforced with calcium carbonate (CaCO₃) particles and an elastomer. Five series of blends were designed and manufactured, including one series of binary blends composed of HDPE and amino acid treated CaCO₃ and four series of ternary blends composed of HDPE, treated or untreated CaCO₃, and a polyolefin elastomer [poly(ethylene‐co‐octene) (POE)] grafted with maleic anhydride. The analysis of the tan δ diagrams indicated that the ternary blends exhibited phase separation. The modulus increased significantly with the CaCO₃ content, and the glass‐transition temperature of POE was the leading parameter that controlled the mechanical properties of the ternary blends. The dynamic mechanical properties and crystallization of the blends were controlled by the synergistic effect of CaCO₃ and maleic anhydride grafted POE, which was favored by the core–shell structure of the inclusions. The treatment of the CaCO₃ filler had little influence on the mechanical properties and morphology. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 3907–3914, 2007     

Detailed Molecular Structure Modeling – A Path Forward to Designing Application Properties of ldPE

Summary: This paper describes a step on the ambitious aim to “design” application properties of ldPE by first simulating the detailed molecular structure of a high‐pressure tubular reactor product. The reactor of a certain configuration produces under well‐defined operating conditions. The next step is to correlate the structure with the application properties. Finally, the sequence will be reversed in order to deduce the operating conditions, which lead to the desired product quality. Two‐dimensional distributions, in molecular weight and branching frequency, as well a two compartment models with a core and a shell stream were simulated and compared with experimental results. Therefore, CFD simulations were carried out to discretize the reaction medium. Samples were taken from both pilot and commercial plants. The TREF‐SEC analytical method was successfully applied in order to measure the microscopic structure of the material. The tremendous numerical problems were solved with the help of the software PREDICI .

Detailed MWD for a pilot scale reactor product.