Untersuchungen des Zeitstandverhaltens von Schweißverbindungen der Werkstoffe X 20 CrMoV 12 1 und GS-17 CrMoV 5 11

Untersucht wird das Zeitstandverhalten gleichartiger Schweißverbindungen des Werkstoffs X 20 CrMoV 12 1 sowie ungleichartiger Verbindungen zwischen diesem und dem Werkstoff GS-17 CrMoV 5 11. Bei quer entnommenen Kleinproben zeigt sich ein Abfall der Zeitstandfestigkeit gegenüber dem Grundwerkstoff. Große Querproben aus einer ungleichartigen Verbindung weisen eine höhere Zeitstandfestigkeit auf als entsprechende Kleinproben. Zur Klärung der in den Schweißverbindungen auftretenden Spannungs- und Dehnungsumlagerungen wurden inelastische Finite-Elemente-(FE-)Berechnungen durchgeführt. Dabei wurde das Zeitdehnverhalten von Grundwerkstoffen, Schweißgut und thermisch simulierten Gefügen der Wärmeeinflußzone berücksichtigt. Die Anwendung spannungsbezogener Kriterien zur Bestimmung der Anrißdauer der Proben auf die FE-Ergebnisse läßt eine Voraussage des Versagensorts sowie eine sichere Abschätzung der Versagenszeit zu.     

Teachers' perceptions of students' reading abilities: An examination of the relationship between teachers' judgments and students' performance across a continuum of rating methods.

Teacher perceptions about students' academic abilities are important for several reasons (e.g., instructional decision making, special education entitlement decisions). Not surprisingly, researchers have investigated the accuracy of teachers' decisions. Although some data reveal that teachers are relatively good judges of academic performance, other findings have suggested otherwise. A likely explanation for conflicting findings is the varying assessment methods (e.g., direct vs. indirect, norm-referenced vs. peer-independent) and different data analysis procedures that have been used across studies. The purpose of this study was to investigate a continuum of teacher-perception assessment methods as they corresponded to students' oral reading fluency performance. Participants included 10 teachers and 87 first, second, and third grade students from a suburban school in the northeast. Overall results suggested that teachers were generally accurate when estimating students' performance when students had strong oral reading fluency skills, but teachers had more difficulty judging students with average to low oral reading fluency. Further, data interpretation of teachers' judgment accuracy differed somewhat depending upon the statistical method employed. Implications, limitations, and suggestions for future research related to this study are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Zeitstandverhalten warmfester Stähle bei zyklischer und bei intermittierender Beanspruchung

Creep and Creep Rupture Behaviour of Heat Resistant Steels under Cyclic and Intermittent Loading Conditions On typical heat resistant steels creep and creep rupture tests under rectangular cyclical conditions of tension stress or/and temperature were continued. Comparable creep and creep rupture tests with tension and compression phases and with intermittent loading conditions were started. Besides this single-stage loading conditions, double-stage loading conditions were investigated. The test results are analysed with the modified life fraction rule. Concepts of relative life are improved and partly new established.     

70 Jahre Verfahrenstechnik an der TU Dresden

At the Technische Hochschule Dresden, the predecessor institution of the TU Dresden, a specialization “Engineer for Process Engineering” was established in 1953 with the filling of the specialist professorship for chemical engineering, and the present Institute for Process and Environmental Engineering was founded. Since then, the profile in education and research of the institute within the Faculty of Mechanical Science and Engineering of the Technische Universität Dresden (TUD) has been considerably extended. Based on this development, the current main research areas of the five chairs and research groups are presented.     

Intrinsically Ductile Failure in a Nanocrystalline Beta Titanium Alloy

A nanocrystalline bcc Ti_67.4Nb_24.6Zr₅Sn₃ alloy is shown to fracture in an intrinsically ductile manner with exceptionally large dimples (up to 10 µm) which are two orders of magnitude greater than the grain size (≈ 40 nm). This large plasticity length scale is attributed to a combination of low shear modulus (≈ 27 GPa), high Poisson's ratio (≈ 0.4) and ultrahigh strength (UTS ≈ 1.1 GPa), close to the ideal shear stress, which facilitates ideal shear deformation to promote transgranular shear.     

Sulfat-dominierter BTEX-Abbau im Grundwasser eines ehemaligen Gaswerksstandortes

In the area of a former gas-works in Düsseldorf (Germany) a soil and groundwater contamination with up to 100 mg/l BTEX (benzene, toluene, ethylbenzene and xylenes) was investigated. Benzene is the dominant aromatic hydrocarbon in the groundwater. The investigations show a natural biodegradation of BTEX by oxygen, manganese oxides, nitrate, ferric hydroxide and sulfate in the sand and gravel aquifer. Sulfate reduction is the most important degradation process in the contamined groundwater. As a product of sulfate reducion, sufids were formed in the sediments of the aquifer. A balance of oxidants is presented as a tool to quantify BTEX degradation and to differ this from sorption and dilution processes. In the contaminated area the degradation of aromatic hydrocarbons leads to the release of carbon dioxide. The highest free CO ₂ -concentration was found in the region of the groundwater table. Outgassing of CO ₂ is important and was verified by deep-specific soil-gas sampling. The knowledge of these processes in the subsoil is a requirement for making predictions for in-situ remediation effects.     

Dendrite fragmentation by catastrophic elastic remelting

A new fragmentation mechanism of dendrite arms is proposed. The theoretical basis of this mechanism is a shift in the thermodynamical equilibrium at the solid–liquid interface due to the presence of elastic energy. This effect is modelled by the generalized Gibbs–Thomson condition [Larché FC, Cahn JW. Acta Metallurgica. 1973;21:1051], where each term is calculated analytically using a simple Bernoulli–Euler beam model. The resulting non-linear system of ordinary differential equations is integrated in time using a fully implicit scheme. It is demonstrated that there is a critical level of loading, exceeding which causes a catastrophic reduction in the neck cross section, leading to dendrite detachment.     

Periviscerokinin-like immunoreactivity in the nervous system of the American cockroach

A highly specific polyclonal antiserum has been raised against periviscerokinin, the first neuropeptide isolated from the perisympathetic organs of insects (Predel et al. 1995). In this study, two different neuronal systems with periviscerokinin-like immunoreactivity were distinguished in the central nervous system of the American cockroach: (1) An intrinsic neuronal network, restricted to the head-thoracic region, was formed by intersegmental projecting neurons of the brain, suboesophageal ganglion and metathoracic ganglion. In addition, groups of local interneurons occurred in the proto- and tritocerebrum. (2) A typical neurohormonal system was stained exclusively in the abdomen; it was represented by abdominal perisympathetic organs which were supplied by three cell clusters located in each unfused abdominal ganglion. As revealed by nickel backfills, most neurons with axons entering the perisympathetic organs contained a periviscerokinin-like peptide. Immunoreactive fibres left the perisympathetic organs peripherally, innervated the hyperneural muscle and ran via the link nerves/segmental nerves to the heart and segmental vessels. All visceral muscles innervated by periviscerokinin-immunoreactive fibres were shown to be sensitive to periviscerokinin, whereas the hindgut gave no specific response to this peptide.