Similarity between craze morphology and shear-band morphology in polystyrene

The formation of shear bands and crazes in thin films as well as in bulk samples of polystyrene were examined in the electron microscope using a variety of replication techniques. The morphologies of shear bands and crazes are quite similar both depending initially upon the relative shear displacement of 400 to 1000 Å domains. As deformation continues and orientation increases, fibrils varying from 50 to 700 Å are formed within the deformation zone, lateral constraint of the normal Poisson contraction causing voids to form in the crazes but not in the shear bands. Shear-band width was found not to be a unique function of either temperature or strain-rate and both craze and shear-band morphologies were found not to be strong functions of molecular weight. Regardless of molecular weight, fibrils formed within the deformation zone were always on the order of a few hundred Angstroms in diameter. However, for thin films of molecular weight less than 20 000 insufficient numbers of tie molecules between fundamental structural units or domains made it difficult for these fibres to span the craze width.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44785/1/10853_2004_Article_BF00632758.pd

FEG-SEM investigation of α\alpha-alumina scales formed on FeCrAlY alloys oxidised at 1200∘^{\circ}C

This work is part of an ongoing European funded project, “SMILER”, with the aim of improving the performance of alumina forming Fe-20Cr-5Al-Y alloys for high temperature industrial applications. One aspect of the project is to investigate the influence of additives on the oxidation behaviour of these alloys. During this study a LEO 1550 FESEM (field emission scanning electron microscope), equipped with INCA X-ray microanalysis facilities was used. Ultra-high-purity model alloys, where the levels of additives (Hf, Zr, Ti, Si, La and Y) were carefully controlled, and two commercial Aluchrom YHfAl and Kanthal AMPT alloys were oxidised at 1200$^{\circ}$C for up to 3100h (100h/cycle).
The YHfAl, (Y+Ti+Zr)- and (Y+Zr+Hf)-containing alloys showed the highest oxidation rates when oxidised, whereas the La-containing alloy showed the lowest oxidation rate. However, the La-containing alloy spalled the most, while the (Y+Zr+Hf)-containing and YHfAl alloys showed little spallation, and the additives appeared to have a major influence on the spallation of the $\alpha$-alumina scale formed. On the alloys with La and Si respectively, the scale spalled at the scale/metal interface (adhesively), whereas on alloys containing (Y+Hf+Ti) and (Y+Hf+Zr) and the YHfAl alloy, the scale spalled mainly in a cohesive manner (within the scale). Also, the added elements affected the scale topography. In general the scale had a columnar structure at the scale/metal interface, whereas the grains were equiaxed at the scale/gas interface. However, in the case of YHfAl and (Y+Zr+Hf)-containing alloys, a sunflower type structure was observed in both fractured samples, in the regions where the scale spalled cohesively. Preliminary EDX analyses revealed that, in the case of YHfAl, for example, the center of the sunflower structure was rich in Mg. This suggests that there may be inhomogeneities in the metal substrate, prior to oxidation, where high concentrations of Mg increase the local oxide growth rate

The barley (Hordeum vulgare) cellulose synthase-like D2 gene (HvCslD2) mediates penetration resistance to host-adapted and nonhost isolates of the powdery mildew fungus

Cell walls and cellular turgor pressure shape and suspend the bodies of all vascular plants. In response to attack by fungal and oomycete pathogens, which usually breach their host's cell walls by mechanical force or by secreting lytic enzymes, plants often form local cell wall appositions (papillae) as an important first line of defence. The involvement of cell wall biosynthetic enzymes in the formation of these papillae is still poorly understood, especially in cereal crops. To investigate the role in plant defence of a candidate gene from barley (Hordeum vulgare) encoding cellulose synthase-like D2 (HvCslD2), we generated transgenic barley plants in which HvCslD2 was silenced through RNA interference (RNAi). The transgenic plants showed no growth defects but their papillae were more successfully penetrated by host-adapted, virulent as well as avirulent nonhost isolates of the powdery mildew fungus Blumeria graminis. Papilla penetration was associated with lower contents of cellulose in epidermal cell walls and increased digestion by fungal cell wall degrading enzymes. The results suggest that HvCslD2-mediated cell wall changes in the epidermal layer represent an important defence reaction both for nonhost and for quantitative host resistance against nonadapted wheat and host-adapted barley powdery mildew pathogens, respectively.Dimitar Douchkov, Stefanie Lueck, Goetz Hensel, Jochen Kumlehn, Jeyaraman Rajaraman, Annika Johrde, Monika S. Doblin, Cherie T. Beahan, Michaela Kopischke, Ren, e Fuchs, Volker Lipka, Rients E. Niks, Vincent Bulone, Jamil Chowdhury, Alan Little, Rachel A. Burton, Antony Bacic, Geoffrey B. Fincher and Patrick Schweize