Absolute Determination of Stress in Textured Materials

The continuum theory of elastic wave propagation in deformed, anisotropic solids is reviewed with emphasis on those features which might be used to distinguish between stress induced changes in ultrasonic velocity and changes due to material anisotropy, such as would be produced by preferred grain orientation in a polycrystalline metal As noted by previous authors, one such feature is the difference in velocity of two shear waves, whose directions of propagation and polarization have been interchanged. In particular, when these directions fall along the symmetry axes of a rolled plate (assuming orthorhombic symmetry) and these are also the directions of principal stress, then the theory predicts that ρ(V 12 2−V 21 2) = T1−T2 where ρ is the density, Vij is the velocity of a shear wave propagating along the i-axis and polarized along the j-axis, and Ti is a principal stress component. In addition to being independent of the degree of texture, this relationship has the advantage that no microstructurally dependent acoustoelastic coefficient is involved. The applicability of this prediction of continuum theory to heterogeneous engineering materials such as metal polycrystals is discussed using previously reported stress dependencies of ultrasonic velocities, and new experiments to answer some remaining questions are described. A possible configuration for using the effect to measure the value of a uniform stress in a plate of unknown texture is proposed

Effect of Texture on Ultrasonic Backscattering Coefficient in Pure Titanium Plate

Ultrasonic grain noise is one of the important factors which limit the detectability of small defects. The intensity of the grain noise may be represented by the ultrasonic backscattering coefficient which directly relates microstructure to the grain noise intensity. Various microstructures affect the backscattering coefficient, as reported in previous volumes of this series of proceedings1–3. In the present article, the effect of texture will be quantitatively discussed.</p

Analysis of the seismic performance of a two storey log house

The dearth of knowledge on the load resistance mechanisms of log houses and the need for developing numerical models that are capable of simulating the actual behaviour of these structures has pushed efforts to research the relatively unexplored aspects of log house construction. The aim of the research that is presented in this paper is to build a working model of a log house that will contribute toward understanding the behaviour of these structures under seismic loading. The paper presents the results of a series of shaking table tests conducted on a log house and goes on to develop a numerical model of the tested house. The finite element model has been created in SAP2000 and validated against the experimental results. The modelling assumptions and the difficulties involved in the process have been described and, finally, a discussion on the effects of the variation of different physical and material parameters on the results yielded by the model has been drawn up.The research leading to these results has received funding from the European Union‘s Seventh Framework Programme [FP7/2007-2013] under grant agreement n°227887 (SERIES)

Using biology to teach adolescents about STD transmission and self-protective behaviors

The effects of a prevention program designed to teach 7th grade students about the different risk behaviors associated with human immunodeficiency virus (HIV), chlamydia, and gonorrhea transmission were examined. Over 3 days, the students were taught how to reason about self-protective behaviors using information about the biological causal mechanisms of these sexually transmitted diseases (STDs). Results revealed that these students displayed more biology knowledge and greater certainty in their responses to open-ended risk behavior questions than did a control group of students who learned the same information from a standard rote approach in the same amount of time. Importantly, increased biological reasoning was linked to better performance at identifying risk behaviors for less well-known STDs. The findings support the premise that a biological approach to STD education minimizes the cognitive burden related to memorizing a list of seemingly unconnected facts. Biologically based health instruction can be an effective tool for teaching adolescents about various STDs beyond HIV infection. © 2006 Elsevier Inc. All rights reserved.link_to_subscribed_fulltex

Arthropod 'rain' into tropical streams: The importance of intact riparian forest and influences on fish diets

Terrestrial arthropods might represent an important energy source for stream predators, but these trophic linkages have seldom been studied in the tropics. Terrestrial arthropod inputs (essentially, arthropod 'rain') into four streams with different riparian vegetation (two draining shrublands and two draining forests) were measured over three consecutive seasons (dry, wet, dry) from 2005 to 2007 in monsoonal Hong Kong. Predatory minnows, Parazacco spilurus (Cyprinidae), were collected and their consumption of terrestrial arthropods was estimated. Inputs of arthropods were dominated by Diptera, Collembola, Formicidae and aerial Hymenoptera, accounting for ≥73% of the arthropod abundance. Seasonal variation was marked: numbers in the dry seasons were approximately half (47-57%) those in the wet season, and biomass fell to one-third (33-37%) of the wet-season value. Shrubland streams received 19-43% fewer individuals and 6-34% less biomass than shaded forest streams. An analysis of fish diets in three of the four streams showed that terrestrial insects and spiders were more important prey in the two forest streams, accounting for 35-43% of prey abundance (39-43% by volume) v. 28% (27%) in the shrubland stream. Because riparian vegetation is the source of terrestrial arthropod inputs to streams, degradation of streamside forests that reduce these inputs will have consequences for the diets of stream fishes. © CSIRO 2008.link_to_subscribed_fulltex