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Die Permanenz der Revolution
(2001)
Selbstgesteuertes Lernen
(2001)
Ausweichklauseln im deutschen, österreichischen und schweizerischen Internationalen Privatrecht
(2001)
Zwischen Arbeitsmarkt und Sozialintegration : zur Bedeutung des Zweiten Arbeitsmarks im Sport
(2001)
Grundlagen digitaler Systeme
(2001)
Especially sulphur containing compounds are suitable for the separation of noble metals[ , ]. 1,2-Dithioethenes are weak chelate-forming ligands [ ]and in the case of bis(methylthio)maleonitrile[ ] the donor power of both of the sulphur atoms is further decreased by the electron withdrawing effect of the cyanogroups. Crowned dithiomaleonitrile are macrocyclic chelate ligands which extract Pd(II) at sufficient rate in a very good yields. The reason for that extraction behaviour is the fact that Pd(II) favours the square planar coordination geometry in opposite to the 3d- elements. The synthesis of the immobilized ligands proceeds from the 2-allyloxy-1,2-propanediol forming the dicarbon acid which is reduced to the diole. With the help of thionylchloride the dichloro compound is synthesized forming together with a dithiolate (1,2-disodium-1,2-dicyanethene-1,2-dithiolate, 1,2-disodium-4-methylbenzene-1,2-dithiolate [ ]) at high dilution conditions the macrocycle. Than the allysubstituted crown ether is sillylated and the resulting alkoxysilane is immobilised onto activated silca gel. The substituent forms in the same time a spacer should be modified in the future. By immobilisation at an inactive matrix the selectivity of the ligand should be applied for the accumulation of palladium from diluted solutions. The extraction was performed from nitric acid solution with a yield of 93% into a ligand solution (chloroform, kerosine). The extraction equilibrium is reached after 10 min. By atomic absorption spectroscopy the metal concentration in the aqueous phase was determined to calculate the extraction rate. By modification of the cavity of the macrocyclus the extraction rate increases from the acyclic compound through maleonitrile-dithio-21-crown-7, maleonitrile-dithio-15-crown-5 and maleonitrile-18-crown-6. The best results can be observed at the maleonitrile-dithio-12-crown-4. The rise of the function lg D= f(lg L) gives the composition of the extracted compounds as 1:1. The separation is unsatisfactory in the case of Ag(I), Hg(II), Pt(II), Tl (I) and the most 3d-elements. Also Ni(II) as a representative for the 3d-elements shows only separations coefficients of 1.43?103 . Summarizing, a very good separation of palladium from the examined elements can be specified. Additional to the extraction experiments, as well as the crystal structures and by UV spectroscopy the formation constants of selected chelates were determined. The observed order corresponds to that found by the extraction of palladium in the system water/chloroform. In the case of maleonitrile-dithio-15-crown-5 Ag(I) is endocyclic coordinated with all donor atoms of the macrocyclus. Already maleonitrile-dithio-18-crown-6 can include the silver cation into its greater cavity. In these cases a 1:1 complex is formed. A 1:2 sandwich structure was noticed only in the case of the smaller ligand maleonitrile- dithio-12-crown-4. Obviously, the formation of that structure is not favoured in the system water/chloroform from which can be explained the unfavourable extraction results.
Untersuchungen zur Wirksamkeit der naturschutzrechtlichen Eingriffsregelung im Nordraum Leipzig
(2001)
Was ist politisches Handeln?
(2001)
Der Aufsatz stellt die geschichtliche Entwicklung der Menschenrechtsidee überblickartig dar, beschreibt Stationen ihrer Verwirklung und erläutert den gegenwärtigen völkerrechtlichen Menschenrechtsschutz. Die normativen Grundlagen und Möglichkeiten der Überwachung der so gesetzten Standards werden beschrieben. Abschließend nimmt der Aufsatz aktuelle Herausforderungen an den Menschenrechtsschutz zu Beginn des neuen Jahrtausends in den Blick. Es handelt sich um die gekürzte Fassung eines Beitrages, der im Sommer 2001 in einem Sammelband veröffentlicht wird.
100 [Einhundert] Jahre BGB
(2001)
Based on a study of the German Ministry of Research and Technology in 1990 every year about 2.5 t of heavy metals are released per hectare of landfill by aqueous leaching. This leachate contains approximately 2000 t of heavy metals per year. Their decontaminations in accordance with the legal requirements represent an enormous potential for easing the burden on the environment. On the other hand, this potential opens new possibilities in the production and recycling of selected compounds. The composition of a given model solution corresponds to a landfill leachate resulting from a municipal dump leachate produced by an average German city. Actually, in most cases, a decontamination of such solutions occurs by the transfer of the problematic cations into insoluble compounds usually done by precipitation. The result of the procedure is an unspecific separation of all liquid components - and the "cycle of waste" (landfill- leaching-deposition) begins anew, certainly on a higher level. The objective of our work is the simultaneous separation of heavy metals from alkaline earth metals and iron in order to obtain a leachate which we can lead back to the landfill. The reactive extraction as a separation process offers the possibility of a selective separation of cations that is the separation of toxic - from unproblematic components and includes also the possibility of electrolysis or further winning processes to obtain the wished metals. For the realisation of extraction processes, several commercial extractants and technical equipments are available. Apart from iron, LIX 54 could be used advantageously for an extraction process - unfortunately without any considerable extraction of cadmium. But it is favourable to separate non toxic alkaline earth metals from problematic heavy metals. Such a complex task as the separation of cations from natural solutions cannot be solved easily in a one-step-extraction process. Better results should be obtained by the combination of different procedures, e.g. extraction, ion-exchange and precipitation.
Wo Wasser Weiden wachsen läßt : Witterungsbedingte Dynamik von Geosystemen der mongolischen Steppe
(2001)
Ausgleich nur auf dem Papier
(2001)
Die Völkerrechtsverantwortung des Bundesverfassungsgerichts : Bemerkungen zu Art. 100 Abs. 2 GG
(2001)
Ovlivnovani ucebni motivace
(2001)
Lehrende in Schulen
(2001)
The "Weighting Process" in Land Use Planning - Discussion of the Present Practice of "Weighting Out". Owing to the revision of the Building Code from January 1998 the impact regulation in land use planning is now established in the Building Law. This means the local governments have decision-making powers how to precisely implement the impact regulation. This, however, does not mean - as had been said in practice - that the concerns of nature and landscape can be "weighted out". On the contrary, the decision-making process has to include a detailed differentiation depending on the case, according to a verdict of the Supreme Administrative Court from 1997. The concerns of nature and landscape cannot be moved back as "not of furhter relevance". Only precisely described and insurmontable constraints allow cutbacks. Since compensation measures now can be carried out on the ground of adjacent local communities, a lack of sites available cannot be accepted as a reason. The paper makes clear why also in urban land use planning interference into nature has to be fully compensated for.