Multifunctional Coordination Compounds: Design and Properties [and Discussion]

M. Verdaguer

A Genetic Algorithm to associate optical measurements and estimate orbits of geocentric objects

Cataloging geocentric objects can be put in the framework of Multiple Target Tracking (MTT). Current work tends to focus on the S = 2 MTT problem because of its favorable computational complexity of O(n²). The MTT problem becomes NP-hard for a dimension of S˃3. The challenge is to find an approximation to the solution within a reasonable computation time. To effciently approximate this solution a Genetic Algorithm is used. The algorithm is applied to a simulated test case. These results represent the first steps towards a method that can treat the S˃3 problem effciently and with minimal manual intervention.

Associating optical measurements and estimating orbits of geocentric objects through population-based meta-heuristic methods

Currently several thousands of objects are being tracked in the MEO and GEO regions through optical means. The problem faced in this framework is that of Multiple Target Tracking (MTT). In this context both, the correct associations among the observations and the orbits of the objects have to be determined. The complexity of the MTT problem is defined by its dimension S. The number S corresponds to the number of fences involved in the problem. Each fence consists of a set of observations where each observation belongs to a different object. The S ≥ 3 MTT problem is an NP-hard combinatorial optimization problem. There are two general ways to solve this. One way is to seek the optimum solution, this can be achieved by applying a branch-and- bound algorithm. When using these algorithms the problem has to be greatly simplified to keep the computational cost at a reasonable level. Another option is to approximate the solution by using meta-heuristic methods. These methods aim to efficiently explore the different possible combinations so that a reasonable result can be obtained with a reasonable computational effort. To this end several population-based meta-heuristic methods are implemented and tested on simulated optical measurements. With the advent of improved sensors and a heightened interest in the problem of space debris, it is expected that the number of tracked objects will grow by an order of magnitude in the near future. This research aims to provide a method that can treat the correlation and orbit determination problems simultaneously, and is able to efficiently process large data sets with minimal manual intervention.

Iodine-129: Sample preparation, quality control and analyses of pre-nuclear materials and of natural waters from Lower Saxony, Germany

Sample preparation procedures for AMS measurements of 129I and 127I in environmental materials and some methodological aspects of quality assurance are discussed. Measurements from analyses of some pre-nuclear soil and thyroid gland samples and of a systematic investigation of natural waters in Lower Saxony, Germany, are described. Although the up-to-now lowest 129I/127I ratios in soils and thyroid glands were observed, they are still suspect to contamination since they are significantly higher than the pre-nuclear equilibrium ratio in the marine hydrosphere. A survey on all available 129I/127I isotopic ratios in precipitation shows a dramatic increase until the middle of the 1980s and a stabilization since 1987 at high isotopic ratios of about (3.6–8.3)×10−7. In surface waters, ratios of (57–380)×10−10 are measured while shallow ground waters show with ratios of (1.3–200)×10−10 significantly lower values with a much larger spread. The data for 129I in soils and in precipitation are used to estimate pre-nuclear and modern 129I deposition densities.

Electrochemical CO2 Reduction - A Critical View on Fundamentals, Materials and Applications

The electrochemical reduction of CO2 has been extensively studied over the past decades. Nevertheless, this topic has been tackled so far only by using a very fundamental approach and mostly by trying to improve kinetics and selectivities toward specific products in half-cell configurations and liquid-based electrolytes. The main drawback of this approach is that, due to the low solubility of CO2 in water, the maximum CO2 reduction current which could be drawn falls in the range of 0.01–0.02 A cm–2. This is at least an order of magnitude lower current density than the requirement to make CO2-electrolysis a technically and economically feasible option for transformation of CO2 into chemical feedstock or fuel thereby closing the CO2 cycle. This work attempts to give a short overview on the status of electrochemical CO2 reduction with respect to challenges at the electrolysis cell as well as at the catalyst level. We will critically discuss possible pathways to increase both operating current density and conversion efficiency in order to close the gap with established energy conversion technologies.

SUBCELLULAR LOCALIZATION, PURIFICATION AND PROPERTIES OF A CDP-DIACYLGLYCEROL - DEPENDENT PHOSPHATIDYLSERINE SYNTHASE IN BACILLUS LICHENIFORMIS

A CDP-diacylglycerol dependent phosphatidylserine synthase was detected in three species of gram-positive bacilli, viz. Bacillus licheniformis, Bacillus subtilis and Bacillus megaterium; the enzyme in B. licheniformis was studied in detail. The subcellular distribution experiments in cell-free extracts of B. licheniformis using differential centrifugation, sucrose gradient centrifugation and detergent solubilization showed the phosphatidylserine synthase to be tightly associated with the membrane. The enzyme was shown to have an absolute requirement for divalent metal ion for activity with a strong preference for manganese. The enzyme activity was completely dependent upon the addition of CDP-diacylglycerol to the assay system; the role of the liponucleotide was rigorously shown to be that of phosphatidyl donor and not just a detergent-like stimulator. This enzyme was then solubilized from B. licheniformis membranes and purified to near homogeneity. The purification procedure consisted of CDP-diacylglycerol-Sepharose affinity chromatography followed by substrate elution from blue-dextran Sepharose. The purified preparation showed a single band with an apparent minimum molecular weight of 53,000 when subjected to SDS polyacrylamide gel electrophoresis. The preparation was free of any phosphatidylglycerophosphate synthase, CDP-diacylglycerol hydrolase and phosphatidylserine hydrolase activities. The utilization of substrates and formation of products occurred with the expected stoichiometry. Radioisotopic exchange patterns between related substrate and product pairs suggest a sequential BiBi reaction as opposed to the ping-pong mechanism exhibited by the well studied phosphatidylserine synthase of Escherichia coli. Proteolytic digestion of the enzyme yielded a smaller active form of the enzyme (41,000 daltons) which appears to be less prone to aggregation.^ This has been the first detailed study in a well-defined bacillus species of the enzyme catalyzing the CDP-diacylglycerol-dependent formation of phosphatidylserine; this reaction is the first committed step in the biosynthetic pathway to the major membrane component, phosphatidylethanolamine. Further study of this enzyme may lead to understanding of new mechanisms of phosphatidyl transfer and novel modes of control of phospholipid biosynthetic enzymes. ^

EFFECTS OF THE ACTA2 R258C MUTATION ON VASCULAR SMOOTH MUSCLE CELL PHENOTYPE AND PROPERTIES

Thoracic Aortic Aneurysms and Dissections (TAAD) are the fifteenth leading cause of death in the United States. About 15% of TAAD patients have family history of the disease. The most commonly mutated gene in these families is ACTA2, encoding smooth muscle-specific α-actin. ACTA2 missense mutations predispose individuals both to TAAD and to vascular occlusive disease of small, muscular arteries. Mice carrying an Acta2 R258C mutant transgene with a wildtype Acta2 promoter were generated and bred with Acta2-/- mice to decrease the wildtype: mutant Acta2 ratio. Acta2+/+ R258C TGmice have decreased aortic contractility without aortic disease. Acta2+/- R258C TG mice, however, have significant aortic dilatations by 12 weeks of age and a hyperproliferative response to injury. We characterized smooth muscle cells (SMCs) from bothmouse models under the hypothesis that mutant α-actin has a dominant negative effect, leading to impaired contractile filament formation/stability, improper focal adhesion maturation and increased proliferation. Explanted aortic SMCs from Acta2+/+ R258C TG mice are differentiated - they form intact filaments, express higher levels of contractile markers compared to wildtype SMCs and have predominantly nuclear Myocardin-Related Transcription Factor A (MRTF-A) localization. However, ultracentrifugation assays showed large unpolymerized actin fractions, suggesting that the filaments are brittle. In contrast, Acta2+/- R258C TG SMCs are less well-differentiated, with pools of unpolymerized actin, more cytoplasmic MRTF-A and decreased contractile protein expression compared to wildtype cells. Ultracentrifugation assays after treating Acta2+/- R258C TGSMCs with phalloidin showed actin filament fractions, indicating that mutant α-actin can polymerize into filaments. Both Acta2+/+ R258C TGand Acta2+/- R258C TGSMCs have larger and more peripheral focal adhesions compared to wildtype SMCs. Rac1 was more activated in Acta2+/+ R258C TGSMCs; both Rac1 and RhoA were less activated in Acta2+/- R258C TG SMCs, and FAK was more activated in both transgenic SMC lines compared to wildtype. Proliferation in both cell lines was significantly increased compared to wildtype cells and could be partially attenuated by inhibition of FAK or PDGFRβ. These data support a dominant negative effect of the Acta2 R258C mutation on the SMC phenotype, with increasing phenotypic severity when wildtype: mutant α-actin levels are decreased.