Showing papers by "University of Oldenburg published in 1978"

On the Complexity of Clustering Problems

Abstract: The class of discrete optimization problems may be partitioned into two subclasses PS and P?. PS is the subclass of problems which are known to be polynomial solvable. P? is the subclass of problems for which it is not yet known whether an algorithm exists which is polynomial bounded. The subclass P? contains the class NPC of NP-complete discrete optimization problems. NPC has the important property that if only one member of NPC can be shown to be polynomial solvable all members of NPC as well as a large number of other combinatorial problems are polynomial solvable. However, it seems to be very unlikely that all NP-complete problems are polynomial solvable.

Der soziologische konnex der 47 häufigsten makrophyten der gewässer mitteleuropas

Abstract: Phytosociological species groups within the classes Lemnetea and Potametea are investigated on the basis of 3000 releves. The relations between species are calculated with the coefficient of Hamming and a % MathType!MTEF!2!1!+-% feaafeart1ev1aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn% hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr% 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq-Jc9% vqaqpepm0xbba9pwe9Q8fs0-yqaqpepae9pg0FirpepeKkFr0xfr-x% fr-xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaGaeq4Xdm2aaW% baaSqabeaacaqGYaaaaaaa!3885!\[\chi ^{\text{2}} \]. The results are presented in the form of a table with the species ordered in a linear sequence as well as in a plexus diagram. The 47 most frequent species are grouped into 4 clusters and the significance of these phyto-sociological species groups for the syntaxonomy of aquatic communities is discussed. Cluster 1 shows many high contingency values. It comprises the pleustophytic species of the Lemnetea. The isolated position of Utricularia vulgaris, the almost identical contingency profiles of Lemna minor and Spirodela polyrrhiza, the contrast between Lemna gibba versus Lemna trisulca, Riccia fluitans and Ricciocarpus natans, and the strong relation between Hydrocharis and Stratiotes are emphasized.

Versuche zur Darstellung von (R,S)‐2,7‐Dioxabicyclo[2.2.1]‐heptan ( = 1,5‐Anhydro‐2,3‐didesoxy‐β‐D‐glycero‐pentofuranose = 1,4‐Anhydro‐2,3‐didesoxy‐α‐D‐glycero‐pentopyranose)

Abstract: Corey-Winter-Eliminierung aus dem Thionocarbonat 2 der 1.5-Anhydro-β-D-ribofuranose (1) zum ungesattigten Derivat 3 gelingt nicht und somit auch nicht die Darstellung der Titelverbindung 12 auf diesem Wege. Stattdessen entsteht der Orthoester 4. Hingegen gelingt die Eliminierungsreaktion am Derivat 6 des Methyl-5-O-trityl-D-ribofuranosids (5) leicht. Vollstandige Hydrierung des Olefinzuckers 9 fuhrt zu den Anomeren des Methyl-2,3-didesoxy-D-glycero-pentofuranosids (11). die sich in geringer Ausbeute zum Bicyclus 12 cyclisieren lassen. Preparation of (R,S)-2,7-Dioxabicyclo[2.2.1]heptane ( = 1,5-Anhydro-2,3-dideoxy-β-D-glycero-pentofuranose = 1,4-Anhydro-2,3-dideoxy-α-D-glycero-pentopyranose) Corey-Winter elimination of the thionocarbonate 2 of 1,5-anhydro-β-D-ribofuranose (1) does not yield the unsaturated derivative 3 and therefore attempts to prepare the title compound 12via3 failed. Instead the orthoester 4 is formed. On the other hand the elimination reaction of the derivative 6 of methyl 5-O-trityl-D-ribofuranoside (5) proceeds smoothly. Hydrogenation and hydrogenolysis of the unsaturated sugar 9 gives the anomers of methyl 2,3-dideoxy-D-glycero-pentofuranoside (11). which can be cyclisized in moderate yield to the bicyclus 12.

Anhydrozucker mit 2,7‐Dioxabicyclo[2.2.1]heptan‐System: 2,6‐Anhydrohexulosen

Abstract: Vakuumpyrolyse der freien Ketosen D-Fructose, D-Tagatose, D-Psicose und L-Sorbose liefert die 2,6-Anhydrozucker 1a–4a nach Reinigung uber die Acetate 1b–4b in Ausbeuten um ca. 1%. 1a kann auch aus Inulin erhalten werden. Die 270-MHz-1H-NMR-Spektren der Acetate konnten vollstandig interpretiert werden. Anhydro Sugars with 2,7-Dioxabicyclo[2.2.1]heptane System: 2,6-Anhydrohexuloses Vacuum pyrolysis of the free ketoses D-fructose, D-tagatose, D-psicose, and L-sorbose gives the corresponding 2,6-anhydro sugars 1a–4a purified via the acetates 1b–4b in yields of about 1%. 1a is also prepared from inulin. 270 MHz 1H NMR spectra of the acetates are completely interpreted.

Atkinson's "risk preference" model: Should it be revised?

Abstract: Several revisions of Atkinson's risk preference model have been proposed in the last 10 years. The advantage of such revisions, shifting the maximum of the approach tendency to the difficult range in predicting choice behavior, is discussed. After summarizing the results of a series of studies on choice behavior in achievement-related situations, the conclusion is drawn that such a revision is unnecessary. Choice behavior is in agreement with the prediction of the original model when expectancies are assessed in the proper way. There may be other good reasons to revise Atkinson's original model. However, the tendency to choose difficulty levels with objective success probabilities less than .50 is not a reason.

Explizite Lösung des dreidimensionalen Minimax-Standortproblems in der City-Block-Distanz

Abstract: Minimax-Standortprobleme in der City-Block-Distanz sind sowohl in der Ebene als auch im dreidimensionalen Anschauungsraum von praktischer Bedeutung. Das Problem kann in ein lineares Programm umformuliert werden, fur dessen Optimallosungen im Fall der Ebene eine gewisse untere Schranke der Zielfunktion stets angenommen wird und die samtlich explizit angegeben werden konnen. Verallgemeinert man dieses Vorgehen auf den Raum, so stellt man fest, das die entsprechende untere Schranke nicht in allen Fallen angenommen wird. Hier erhalt man dann schlieslich alle Losungen explizit, indem man auf das duale Problem ubergeht. Numerische Beispiele werden angegeben.

Between Tradition and Progress: Oldenburg University's Model Plan for Comprehensive Teacher Training

Abstract: Since early 1974, a pilot project for integrated teacher training has been in progress at Oldenburg University. This is currently the only extensive teacher training reform which exist in the German Federal Republic. All plans for this integrated training program are designed to provide training normally encompassed by the traditional two‐stage programm. The integrated training program includes: - studies in the areas of education and social science; - studies in two major subjects which are later to be taught at school; - practical studies and activities. The new model leads to the following degrees: - nine semesters of study for a Certificate of Qualification for primary and lower‐level secondary school; - eleven semesters for a Certificate of Qualification for higher‐level secon dary school and the education of exceptional children. Theoretic training in major subject areas and related didactic training as well as education and social studies take place chiefly in the form of projects. A basic...