Ultrasonic characterization of microstructure in powder metal alloy

The ultrasonic wave propagation characteristics were measured for IN-100, a powder metallurgy alloy used for aircraft engine components. This material was as a model system for testing the feasibility of characterizing the microstructure of a variety of inhomogeneous media including powder metals, ceramics, castings and components. The data were obtained for a frequency range from about 2 to 20 MHz and were statistically averaged over numerous volume elements of the samples. Micrographical examination provided size and number distributions for grain and pore structure. The results showed that the predominant source for the ultrasonic attenuation and backscatter was a dense (approx. 100/cubic mm) distribution of small micropores (approx. 10 micron radius). Two samples with different micropore densities were studied in detail to test the feasibility of calculating from observed microstructural parameters the frequency dependence of the microstructural backscatter in the regime for which the wavelength is much larger than the size of the individual scattering centers. Excellent agreement was found between predicted and observed values so as to demonstrate the feasibility of solving the forward problem. The results suggest a way towards the nondestructive detection and characterization of anomalous distributions of micropores when conventional ultrasonic imaging is difficult. The findings are potentially significant toward the application of the early detection of porosity during the materials fabrication process and after manufacturing of potential sites for stress induced void coalescence leading to crack initiation and subsequent failure

Palaeoenvironmental signatures revealed from rare earth element (REE) compositions of vertebrate microremains of the Vesiku Bone Bed (Homerian, Wenlock), Saaremaa Island, Estonia

The Estonian Journal of Earth Sciences is an open access journal and applies the Creative Commons Attribution 4.0 International License CC BY to all its papers (http://creativecommons.org/licenses/by/4.0/). The attached file is the published version of the article

The smallest known Devonian tetrapod shows unexpectedly derived features.

A new genus and species of Devonian tetrapod, Brittagnathus minutus gen. et sp. nov., is described from a single complete right lower jaw ramus recovered from the Acanthostega mass-death deposit in the upper part of the Britta Dal Formation (upper Famennian) of Stensiö Bjerg, Gauss Peninsula, East Greenland. Visualization by propagation phase contrast synchrotron microtomography allows a complete digital dissection of the specimen. With a total jaw ramus length of 44.8 mm, Brittagnathus is by far the smallest Devonian tetrapod described to date. It differs from all previously known Devonian tetrapods in having only a fang pair without a tooth row on the anterior coronoid and a large posterior process on the posterior coronoid. The presence of an incipient surangular crest and a concave prearticular margin to the adductor fossa together cause the fossa to face somewhat mesially, reminiscent of the condition in Carboniferous tetrapods. A phylogenetic analysis places Brittagnathus crownward to other Devonian tetrapods, adjacent to the Tournaisian genus Pederpes. Together with other recent discoveries, it suggests that diversification of 'Carboniferous-grade' tetrapods had already begun before the end of the Devonian and that the group was not greatly affected by the end-Devonian mass extinction

Measurements of Scattering from Bulk Defects

This report presents results of measurements of longitudinal wave ultrasonic scattering from complex defects embedded in Ti-alloy by the diffusion bonding process. The defects examined are: circular and elliptical cracks, two overlapping voids consisting of a sphere and a prolate spheroid, two adjacent spherical voids, and a spherical void with an encircling crack. Representative plots are given for the raw waveforms, magnitude (and sometimes the phase) of the deconvolved Fourier transform, and in some cases the time impulse response function. The data are compared to or analyzed in terms of several current theories. While good quantitative agreement was observed over certain ranges, the comparisons point to definite (in some cases not unexpected) limitations in either the pertaining theory or experiment or both. Finally, the results are discussed with an eye toward applications

Multiple Discourses On Sexuality Implications For Translating Sexual Wellness Concept Into Action Strategies In A Kenyan Context

This Paper attemps to map, drawing mainly from HIV and AIDS prevention interventions, the multiple discourses on sexuality. The aim is to provide a picture of the challenges and opportunities in transforming the concept of sexual wellness currently being articulated. This is a move from the commonly held view of sexuality as a threat to health, to one promoting sexual wellness or positive view of sexuality. A postcolonial conceptual perspective is used to help grasp the multiple-realities emerging from the historical influences on Africa and for reflexivity on the ambivalences and representations of Africa and African culture including sexuality.Key words: sexuality, complexity, moral sensitivity, postcolonial, HIV and AI

Crack Depth Measurements with the Aid of SAW NDE

This report presents results of measurements of crack depth with the aid of acoustic bulk and surface waves. Both simulated and real fatigue cracks were examined. Two techniques were employed, one took advantage of the very efficient mode conversion between acoustic surface waves and shear waves at the crack tip; the other technique used the diffraction of shear waves at the crack tip. Both techniques were used on a number of simulated {spark eroded) and real cracks in Al 2024. In one fatigue specimen which contained an elliptical crack 4.5 mm in length and 1.25 mm in depth, crack closure studies were carried out. The precision of crack depth determination was judged to be better than 10%

Low Frequency Characterization of Flaws in Ceramics

There is an increasing need for the characterization of small flaws in ceramic components. This project is concerned with detecting and characterizing flaws in the bulk of ceramic parts. Cylindrical tensile test specimens of hot pressed Si3N4 are being prepared and, when available, will be inspected. In preparation for the arrival of the samples, measurement techniques have been developed for inspection of cylindrical shaped samples, signal processing techniques have been developed for obtaining flaw scattering data over a broad range of frequencies and analysis techniques have been developed to automatically extract flaw characteristics from measured data

Vascularization and odontode structure of a dorsal ridge spine of Romundina stellina Ørvig 1975

There are two types of dermal skeletons in jawed vertebrates: placoderms and osteichthyans carry large bony plates (macromery), whereas chondrichthyans and acanthodians are covered by small scales (micromery). Fin spines are one of the last large dermal structures found on micromeric taxa and offer a potential source of histology and morphology that can be compared to those found on macromeric groups. Dermal fin spines offer a variety of morphology but aspects of their growth modes and homology are unclear. Here, we provide detailed descriptions of the microstructure and growth of a dorsal ridge spine from the acanthothoracid placoderm, Romundina stellina, using virtual three-dimensional paleohistological datasets. From these data we identify several layers of dentine ornamentation covering the lateral surfaces of the spine and reconstructed their growth pattern. We show that this spine likely grew posteriorly and proximally from a narrow portion of bone located along the leading edge of the spine. The spine is similarly constructed to the scales with a few exceptions, including the absence of polarized fibers distributed throughout the bone and the presence of a thin layer of perichondral bone. The composition of the spine (semidentine odontodes, dermal bone, perichondral bone) is identical to that of the Romundina dermal plates. These results illustrate the similarities and differences between the dermal tissues in Romundina and indicate that the spine grew differently from the dentinous fin spines from extant and fossil chondrichthyans. The morphology and histology of Romundina is most similar to the fin spine of the probable stem osteichthyan Lophosteus, with a well-developed inner cellular bony base and star-shaped odontodes on the surface. Results from these studies will undoubtedly have impact on our understanding of fossil fin spine histology and evolution, contributing to the on-going revision of early gnathostome phylogeny