Toxizitätsreduktion durch (Grundwasser-) Sanierung?

The usage of an automatized and continuously (on-line) working biomonitor for the surveillance of groundwater remediation is presented and the data are compared to different discontinuous acute biotests. The use of an on-line biomonitor at the SAFIRA groundwater remediation testsite showed to be superior to the discontinuous tests. The long-time surveillance of two different remediation techniques revealed a decrease in remediation efficiency of one technique while the other technique -using activated carbon- did not show any reduction in efficiency. The validation of these results with other acute biotests (algae, fishembryo, daphnia and genotoxicity) indicated a complex groundwater contamination which can not be explained by the quantitatively main contaminant monochlorobenzene. It is suggested to use ecotoxicological biotests and knowledge in parallel to the conventional chemical analysis before a remediation strategy is designed. All anthropogenic contaminations (toxic or unwanted) should be identified beforehand such that the developed remediation techniques would be more target-oriented.     

Chemisorption of oxygen onto activated carbon can enhance the stability of biological perchlorate reduction in fixed bed biofilm reactors

Fixed bed biofilm reactors with granular activated carbon (GAC) or glass beads as support media were used to evaluate the influence of short-term (12h) and long-term (23 days) increases of influent dissolved oxygen (DO) concentrations on biological perchlorate removal. The goal was to evaluate the extent by which chemisorption of oxygen to GAC can enhance the stability of biological perchlorate reduction. Baseline influent concentrations were 50 microg/L of perchlorate, 2 mg/L of acetate as C, and 1mg/L of DO. Perchlorate removal in the glass bead reactor seized immediately after increasing influent DO concentrations from 1 to 4 mg/L since glass beads have no sorptive capacity. In the biologically active carbon (BAC) reactor, chemisorption of oxygen to GAC removed a substantial fraction of the influent DO, and perchlorate removal was maintained during short-term increases of influent DO levels up to 8 mg/L. During long-term exposure to influent DO concentrations of 8.5mg/L, effluent perchlorate and DO concentrations increased slowly. Subsequent exposure of the BAC reactor bed to low DO concentrations partially regenerated the capacity for oxygen chemisorption. Microbial analyses indicated similar microbial communities in both reactors, which confirmed that the differences in reactor performance during dynamic loading conditions could be attributed to the sorptive properties of GAC. Using a sorptive biofilm support medium can enhance biological perchlorate removal under dynamic loading conditions.     

Irradiation effects on AlGaN HFET devices and GaN layers

AlGaN/GaN heterostructure field effect transistors (HFETs) were irradiated with protons as well as carbon, oxygen, iron and krypton ions of high (68 and 120 MeV) and low (2 MeV) energy with fluences in the range from 1 × 10⁷ to 1 × 10¹³ cm^?2. High energy irradiation with protons, carbon and oxygen produced no degradation in devices while krypton irradiation at the fluence of 1 × 10¹⁰ cm^?2 resulted in a small reduction of 2% in the transconductance. Similarly, for GaN samples irradiated with protons, carbon and oxygen at high energy no changes were seen by XRD, PL and Hall effect, while changes in lattice constant and a reduction in PL intensity were observed after irradiation with high energy krypton. Low energy irradiation with carbon and oxygen at a fluence of 5 × 10¹⁰ cm^?2 results in small change in the device performance while remarkable changes in device characteristics are seen at a fluence of 1 × 10¹² cm^?2 for carbon, oxygen, iron and krypton irradiation. Similarly changes are also observed by XRD, PL and Hall effect for the thick GaN layer irradiated at the fluence of 1 × 10¹² cm^?2. The device results and GaN layer properties are strongly correlated.     

Formation of Nanocrystalline Silicon Carbide Powder from Chlorine-Containing Polycarbosilane Precursors

Nanocrystalline ß-SiC particulates with a grain-size range of 5-20 nm were prepared by heating a prepyrolyzed, chlorine-containing polysilane/polycarbosilane (PS/PCS) to 1600°C. The transformation from the prepyrolyzed PS/PCS to nanocrystalline SiC was investigated by differential thermal analysis, thermogravimetric analysis, X-ray diffractometry, mass spectrometry, and infrared spectroscopy. The results indicated that the nanocrystalline ß-SiC was formed by the crystallization of the PS/PCS random network and the crosslinking of Si-Si, Si-Cl, and Si-CH₂-Si bonds. Transmission electron microscopy observation showed that SiC particulates consisted of equiaxed, randomly oriented, ultrafine grains.     

Photoinitiated cationic oligomerization of terminal and internal epoxides

The iodonium salt‐catalyzed, photoinduced cationic oligomerization of terminal and internal monoepoxides from oleochemical as well as the petrochemical origin was studied. The ring‐opening of terminal epoxides (1,2‐octene oxide, phenyl glycidyl ether, 9,10‐epoxy decanoic acid methyl ester and 10,11‐epoxy undecanoic acid methyl ester) predominantly led to macrocyclic oligoethers (M_n = 650—1,100 g/mol) via backbiting in quantitative yields. Mixtures of cyclic and bishydroxy‐terminated oligoethers (M_n = 1,050—1,500 g/mol) were achieved by the conversion of internal epoxides (7,8‐tetradecene oxide and cis‐9,10‐epoxy octadecanoic acid methyl ester) in yields of 80—95%. Macrocyclization was completely suppressed by addition of 20 mol‐% water or ethylene glycol receiving diol‐oligoethers for potential application as soft segments for polyurethanes with molecular weights of approximately 1,300 g/mol.     

Verfahren zur Konditionierung von Rohgasen — Teil 1: Konditionierung durch elektrische Maßnahmen

The operating performance of plant for removal of particulates from gases can be positively influenced by crude gas conditioning and other additive measures. These processes involved introduction of additional material or additional energy into the plant. Set goals are the reduction of particle emissions, reduction of operating costs, adaptation to new boundary conditions, or the opening of new applications for the separators concerned. In the first of three surveys, conditioning by electrical means is considered. An account of the principles of electrically induced agglomeration is followed by a presentation and discussion of the possibilities and consequences of electrical effects applied to filtering separators, inertial separators, and wet separators. Wherever possible, points of practical relevance are also evaluated.     

Crosslinking during radical polymerization of dodecyl methacrylate

A much more efficient formation of crosslinks was observed in the free‐radical polymerization of dodecyl methacrylate with respect to the amount of decomposed peroxide than it would correspond to the additional peroxide crosslinking of formed poly(dodecyl methacrylate). Polymer crosslinking also proceeds after using 2,2´‐azoisobutyronitrile as initiator of the polymerization of dodecyl methacrylate, although with a substantially lower efficiency compared to the initiation by peroxide under comparable conditions. The efficient formation of crosslinked structures can be explained by branching and copolymerization of monomer with multifunctional dead polymer. Multifunctionality of the formed macromolecules is a result of transfer and addition reactions of the present free radicals with the formed polymer. The difference in the influence of the initiator follows from the higher reactivity of oxy radicals in transfer reactions with monomer dodecyl methacrylate which results in a greater number of polymerizable double bonds built in the polymer chain.     

Dietary fat in the prevention of cardiovascular disease — a review

In developed countries atherosclerotic cardiovascular disease is the reason for about 50% of all deaths. With growing prosperity coronary heart disease (CHD) is becoming the major cause of premature death. Most complications of atherosclerosis occur unexpectedly and more than 50% of the patients developing a myocardial infarction do not survive more than one year. Because of the severe morbidity and high mortality primary prevention is likely to be the only solution. Epidemiological studies show a strong, positive relationship between plasma cholesterol concentrations and the incidence of CHD. People who immigrate from low‐risk to high‐risk areas usually acquire similar plasma cholesterol levels as the native population and a similar CHD risk. This demonstrates that environmental rather than genetic factors lead to the differences in cardiovascular risk and supports the notion that nutrition and lifestyle play a major role. The association between dietary intake of fat and cholesterol and the extent of atherosclerosis and CHD has been recognized in previous studies. The amount of saturated fat in the diet correlates stronger with the incidence of CHD than with total fat intake. The consumption of unsaturated fatty acids, however, appears to be beneficial, since it is inversely correlated with the plasma cholesterol concentration and risk of myocardial infarction. Lately additional nutritional factors like trans fatty acids with a negative influence on risk as well as positive factors like linolenic acid have attracted much attention. In conclusion, as a challenge to public health, preventive medicine needs to focus on changes in dietary habits with priority, particularly fat modification. A nutrition low in total fat primarily avoiding saturated and trans fatty acids, but rich in fruit and vegetables should be recommended.     

Aliphatic polyamides prepared by ester-amine polycondensation as potential drug carrier polymers

Aliphatic polyamides of interest as macromolecular drug carriers are synthesized by base-catalyzed polycondensation of aliphatic diesters with diamines. The reactions are conducted in the presence of anhydrous sodium carbonate at temperatures ranging from ambient to 65°C, initially in the undilute state. The addition of aprotic solvent at a later stage serves to maintain sufficiently low viscosity for proper homogenization. The comonomers, diethyl 3,6,9-trioxaundecanedioate and 4,7,10-trioxa-1,13-tridecanediamine, copolymerize to form polymer 1, a straight-chain polyamide devoid of specific functionality. Use of diethyl tartrate in lieu of the aforementioned diester leads to polyamide 2 possessing hydroxyl side groups. Other experiments in which diamines incorporating additional (secondary) amino groups are employed afford polyamides 3–8 containing such secondary amine functions as main-chain constituents. The water-soluble target polymers are crudely fractionated by aqueous dialysis (12000–14000 molecular mass cut-off) and collected by freeze-drying in yields of 20 to 40%. The low-yield range has been accepted in this investigation as the price to be paid for the realization of linear polyamide structures in accordance with compositional expectations, a requirement vital for the proper functioning of the polymers as drug carriers. The practicability of drug binding (conjugating) is exemplified by the coupling of ferrocene as a drug model to polyamide 5 via amide linkage. The water-soluble conjugate 5-Fc features an iron content corresponding to one ferrocene group in the repeat unit. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 73: 2143–2150, 1999