Search

New developments concerning geotextile concrete mattresses for revetment construction Geotextile concrete mattresses provide a more than 50 years lasting history. Their initial application has been documented for coastal and river protection works as well as for mountain stream rehabilitations. Due to several reasons, their application has become more popular again over the last years. Although the system has been in use for decades, there are still some uncertainties left concerning the basic working principles of concrete mattresses. This paper is intended to explain the basic concrete mattress technology in conjunction with the four‐point bending tests carried out at the University of Applied Sciences in Münster. Furthermore it describes the research concerning the hydraulic roughness recently carried out at the RWTH Aachen University and the ice load testing performed in Russia. Finally, applications for the mattress as revetment system for canals, waterways and overflow sections are provided. [ABSTRACT FROM AUTHOR]

Bearing capacity failure of geogrid reinforced retaining walls Retaining structures are one of the commonly used applications of geogrid reinforced soil. Most design codes such as EBGEO and other international regulations assume a quasi-monolithic reinforced block securing adequate bearing capacity for retaining walls. Due to flexible behavior of the geogrid reinforcement the assumption of a rigid foundation base is questionable. Consequently, laboratory model tests have been developed at the Geotechnical Institute of RWTH Aachen University to investigate the bearing capacity behavior of both rigid and flexible retaining structures. Laboratory model tests are carried out to illustrate the failure kinematics of reinforced and cantilever retaining structures qualitatively. A path-controlled punching force is increased on top of the structure until failure of the subsoil is observed. The deformation of the specimens is evaluated with digital image correlation (DIC) method in order to analyze the failure mechanism qualitatively. The test results indicate different failure modes for rigid and flexible walls. Bearing capacity failure occurred in cases of flexible geogrid reinforced walls, whereas a comparable rigid wall failed by sliding. The load resistance of bearing capacity was considerably higher compared to sliding. Moreover, a considerable increase in bearing capacity is observed with enlarged reinforcement length resulting in an improved bearing resistance. [ABSTRACT FROM AUTHOR]

Pollen germination may occur via the so-called germination pores or directly through the pollen wall at the site of contact with the stigma. In this study, we addressed what processes take place during pollen hydration (i.e. before tube emergence), in a species with extra-poral pollen germination, Arabidopsis thaliana., A T- DNA mutant population was screened by segregation distortion analysis. Histological and electron microscopy techniques were applied to examine the wild-type and mutant phenotypes., Within 1 h of the start of pollen hydration, an intine-like structure consisting of cellulose, callose and at least partly de-esterified pectin was formed at the pollen wall. Subsequently, this 'germination plaque' gradually extended and opened up to provide passage for the cytoplasm into the emerging pollen tube. BURSTING POLLEN ( BUP) was identified as a gene essential for the correct organization of this plaque and the tip of the pollen tube. BUP encodes a novel Golgi-located glycosyltransferase related to the glycosyltransferase 4 ( GT4) subfamily which is conserved throughout the plant kingdom., Extra-poral pollen germination involves the development of a germination plaque and BUP defines the correct plastic-elastic properties of this plaque and the pollen tube tip by affecting pectin synthesis or delivery. [ABSTRACT FROM AUTHOR]

Objective. The aim of this study was to investigate whether (a) overgeneralization is restricted to negative attributions directed at the self; or whether it also extends to positive self-attributions and to attributions of situations in the outside world, and (b) whether the valence and direction (positively or negatively, to the self- or across situations) of overgeneralization processes vary among different patient populations. Methods. Patients with major depressive disorder (MDD, n = 34), borderline personality disorder (BPD, n = 18), or both ( n = 35), and never-depressed non-patients (NPs; n = 50) completed various measures of overgeneralization. Results. Patients with MDD show higher levels of negative overgeneralization but lower levels of positive overgeneralization to the self- and across situations than NPs. Patients with MDD show more negative than positive overgeneralization to the self: a negative bias. They, however, do show higher levels of positive than negative overgeneralization across situations. Patients with BPD show the same pattern for overgeneralization to the self, but their higher levels of negative overgeneralization across situations are not exceeded by their positive counterpart. Conclusions. Results indicate that patient groups differ from NPs not only with respect to negative, but also with respect to positive overgeneralization. Furthermore, the valence and direction of overgeneralization processes vary among MDD and BPD patient populations. More specifically, findings suggest that, as compared to never-depressed individuals, patients with BPD and patients with MDD alike, lack a buffer against negative overgeneralization directed at the self. In patients with BPD, not only the high level of overgeneralization to the self, but also the high level of overgeneralization across situations seems to be problematic, since both types of overgeneralization appear not to be buffered by their positive counterparts. [ABSTRACT FROM AUTHOR]

Summary A major question in pollen tube growth in planta remains: do the pollen tube walls form a barrier to interaction with the environment? Using cryo-FESEM, we directly assessed the 3D construction and porosity of tobacco pollen tube walls. Fractured mature primary walls showed a 40-50 nm spaced lattice of continuous fibers interconnected by short rods in the primary wall. These observations agree with TEM observations of sectioned walls. In the secondary callose wall, for which no structure is visible using TEM, cryo-FESEM also revealed a 50 nm lattice consisting of longer fibers, approximately 10-15 nm wide, with rod-like, thinner interconnections at angles of approximately 90° with the longer fibers. Such architecture may reflect functional needs with respect to porosity and mechanical strength. The wall does not form a mechanical barrier to interaction with the environment and is gained at low cost. Cryo-FESEM additionally revealed another special feature of the wall: the tubes were tiled with scales or rings that were highly conspicuous after pectin extraction with EDTA. These rings cause the typical banding patterns of pectin that are commonly seen in pollen tubes during oscillatory growth, as confirmed by staining with toluidine blue as well as by DIC microscopy. Growth analysis by VEC-LM showed that the ring- or scale-like structures of the primary wall consist of material deposited prior to the growth pulses. The alternating band pattern seen in the callose wall is probably imposed by constrictions resulting from the rings of the primary wall. [ABSTRACT FROM AUTHOR]