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

Continuum field description of crack propagation

We develop continuum field model for crack propagation in brittle amorphous solids. The model is represented by equations for elastic displacements combined with the order parameter equation which accounts for the dynamics of defects. This model captures all important phenomenology of crack propagation: crack initiation, propagation, dynamic fracture instability, sound emission, crack branching and fragmentation.Comment: 4 pages, 5 figures, submitted to Phys. Rev. Lett. Additional information can be obtained from http://gershwin.msd.anl.gov/theor

Steady State Properties of Lock-On Current Filaments in GaAs

Collective impact ionization has been used to explain lock-on in semi-insulating GaAs under high-voltage bias. The authors have used this theory to study some of the steady state properties of lock-on current filaments. In steady state, the heat gained from the field is exactly compensated by the cooling due to phonon scattering. In the simplest approximation, the carrier distribution approaches a quasi-equilibrium Maxwell-Boltzmann distribution. In this report they examine the validity of this approximation. They find that this approximation leads to a filament carrier density which is much lower than the high density needed to achieve a quasiequilibrium distribution. Further work on this subject is in progress

Miscibility of polystyrene-based ionomers with poly(2,6-dibromo-1,4-phenylene oxide)

Blends of poly(2,6-dibromo-1,4-phenylene oxide) (PDBrPO) with 4.8 mol % sulfonated polystyrene (4.8SPS), Na-neutralized 1.7 mol % sulfonated polystyrene (Na1.7SPS), Mn-neutralized 3.8 mol % sulfonated polystyrene (Mn3.8SPS), and Zn-neutralized 3.8 mol % sulfonated polystyrene (Zn3.8SPS) ionomers were investigated for their miscibilities with varying compositions by dilute solution viscometry (DSV), scanning electron microscopy (SEM), and differential scanning calorimetry (DSC). Deltab, mu, and alpha parameters by W. R. Krigbaum and F. J. Wall (J Polym Sci 1950, 5, 505), K. K. Chee (Eur Polym J 1990, 4, 423), and Z. Sun et al. (Eur Polyrn J 1992, 28, 1259), respectively, were calculated from DSV data to determine miscibility. Na1.7SPS is immiscible with PDBrPO in no relation to the blend compositions. On the other hand, the increasing extent of miscibility of the blends reflected by the data is as follows: 4.8SPS < Mn3.8SPS < Zn3.8SPS. DSC and SEM results are also in agreement with the DSV data except for the alpha parameter, which showed some disagreements with Deltab and mu parameters in a few blends. (C) 2001 John Wiley & Sons, Inc

Music and Substance Use: A Meta-analytic Review

While previous research has documented a relation between music and substance use among consumers, to date, there are no meta-analytic reviews of the literature, making our meta-analysis the first in this area. Results from 31 studies, yielding a total of 330,652, indicated that music had a significant effect on substance use, with both music format and genre being significant contributors. The effect of music on substance use also varied by substance type. In addition, participant biological sex and location of data collection were found to moderate the effect of music on substance use. Theoretical implications are discussed along with directions for future research. FAU - Wright, Chrysalis