Ultrasonic wave propagation in heterogenous media

The non-destructive testing of austenitic steel welds using ultrasound is of vital importance for assessing safety critical structures such as those found in the nuclear industry. The internal geometry of these welds is heterogeneous and highly scattering and this makes it dicult to detect and characterise any defects within them. To help overcome these diculties the use of ultrasound transducer arrays and the associated Full Matrix Capture is becoming more widespread. There is a need therefore to develop post-processing algorithms that best utilise the data from such devices. This paper considers the use of a time-frequency domain method known as the Decomposition of the Time Reversal Operator (DORT) method. To develop this method and to demonstrate its ecacy in tackling this problem a series of simulated data sets are used. The simulated data is generated using a finite element method (PZFLEX) with the heterogeneous internal microstructure of the weld being given by previous Electron Backscatter Diraction measurements. A range of artificial flaws are then inserted into this geometry. By varying the flaw size and type a comparison is conducted between the DORT method and the Total Focusing Method (TFM) and their relative ability to perform flaw detection assessed. Importantly, however, the DORT method relies on a Singular Value Decomposition in time and frequency space and this spectral information contains information about the flaw size and shape

Isolation, Effects and Characterization of a Peripheral Tissue Injury Extract Causing Endothelial Cell Dysfunction, Ileus and a Precipitous Death

Undergraduate Basi

Reactive-infiltration instabilities in rocks. Fracture dissolution

A reactive fluid dissolving the surface of a uniform fracture will trigger an instability in the dissolution front, leading to spontaneous formation of pronounced well-spaced channels in the surrounding rock matrix. Although the underlying mechanism is similar to the wormhole instability in porous rocks there are significant differences in the physics, due to the absence of a steadily propagating reaction front. In previous work we have described the geophysical implications of this instability in regard to the formation of long conduits in soluble rocks. Here we describe a more general linear stability analysis, including axial diffusion, transport limited dissolution, non-linear kinetics, and a finite length system.Comment: to be published in J. Fluid. Mec

Building a spindle of the correct length in human cells requires the interaction between TPX2 and Aurora A

To assemble mitotic spindles, cells nucleate microtubules from a variety of sources including chromosomes and centrosomes. We know little about how the regulation of microtubule nucleation contributes to spindle bipolarity and spindle size. The Aurora A kinase activator TPX2 is required for microtubule nucleation from chromosomes as well as for spindle bipolarity. We use bacterial artificial chromosome–based recombineering to introduce point mutants that block the interaction between TPX2 and Aurora A into human cells. TPX2 mutants have very short spindles but, surprisingly, are still bipolar and segregate chromosomes. Examination of microtubule nucleation during spindle assembly shows that microtubules fail to nucleate from chromosomes. Thus, chromosome nucleation is not essential for bipolarity during human cell mitosis when centrosomes are present. Rather, chromosome nucleation is involved in spindle pole separation and setting spindle length. A second Aurora A–independent function of TPX2 is required to bipolarize spindles

Autosomal dominant retinitis pigmentosa with apparent incomplete penetrance: a clinical, electrophysiological, psychophysical, and molecular genetic study

7 páginas, 7 figuras, 4 tablas.-- Licence Creative Commons, attribution, Non-commercial licence.-- et al.Twenty five symptomatic individuals and six asymptomatic obligate gene carriers from four families with autosomal dominant retinitis pigmentosa (adRP) showing apparent incomplete penetrance have been studied. Symptomatic individuals from three families showed early onset of night blindness, non-recordable rod electroretinograms, and marked elevation of both rod and cone thresholds in all subjects tested. In the fourth family, there was more variation in the age of onset of night blindness and some symptomatic individuals showed well preserved rod and cone function in some retinal areas. All asymptomatic individuals tested had evidence of mild abnormalities of rod and cone function, indicating that these families show marked variation in expressivity rather than true non-penetrance of the adRP gene. No mutations of the rhodopsin or RDS genes were found in these families and the precise genetic mutation(s) remain to be identified.This study was supported by the Medical Research Council (UK), The Weilcome Trust, British Retinitis Pigmentosa Society, and the National Retinitis Pigmentosa Society, Fighting Blindness, USA.Peer reviewe

The nature and causes of coastal landsliding on the Maungatapu Peninsula, Tauranga, New Zealand

Lengths of cliffed coastline in Quaternary sediments around Tauranga Harbour, and particularly on the Maungatapu Peninsula, have been subjected to major landsliding episodes during and after rainstorms in recent years. This study is intended to broaden the database concerning coastal landsliding by documenting a descriptive and analytical study of the landslides, and to provide information useful for those attempting to control the effects of the landslides. A field mapping project was undertaken, associating patterns of landslide scars, marine erosion and groundwater seepage from cliff faces. More intensive studies at three sample sites included surveying, soil strength and physical index testing, hydraulic conductivity determinations and groundwater table observations. A number of working hypotheses, concerning the nature and causes of the landslide events, are erected and tested using the results of these descriptive studies. The hypotheses are further evaluated in factor sensitivity studies, using a simplified Janbu slope stability analysis program, which was written as part of the study. It has been found that the landslide events occur as parts of one of two cliff evolutionary sequences observed on the Maungatapu Peninsula. Where the rate of basal erosion by tidal currents and wind driven waves exceeds the rate of cliff crest retreat due to various cliff face modifying processes, the cliff segment gradually steepens. Failures in the material above an impermeable clay bed in the Pahoia Tuffs are triggered by high pore water pressures. Critical pore water pressures occur when long wet periods, culminating in medium to long return period storms, produce high seepage flows through the sandy material above the impermeable clay bed. The failures initially occur in a rotational manner, apparently causing the liquefaction of a bed of low bulk density silty sand lenses within a denser sandy mud matrix. Subsequent movements are therefore rapid and translatory, producing elongate annular debris lobes extending from the cliff base. The results of the study are then applied in formulating coastal management strategies, and in suggesting appropriate site stabilisation techniques

A Maximum Eigenvalue Approximation for Crack-Sizing Using Ultrasonic Arrays

Ultrasonic phased array systems are becoming increasingly popular as tools for the inspection of safety-critical structures with in the non-destructive testing industry. The datasets captured by these arrays can be used to image the internal microstructure of individual components, all owing the location and nature of any defects to be deduced. Unfortunately, many of the current imaging algorithms require an arbitrary threshold at which the defect measurements can be taken and this aspect of subjectivity can lead to varying characterisations of a flaw between different operators. This paper puts forward an objective approach based on the Kirchoff scattering model and the approximation of the resulting scattering matrices by Toeplitz matrices. A mathematical expression relating the crack size to the maximum eigenvalue of the associated scattering matrix is thus derived. The formula is analysed numerically to assess its sensitivity to the system parameters and it is shown that the method is most effective for sizing defects that are commensurate with the wavelength of the ultrasonic wave (or just smaller than. The method is applied to simulated FMC data arising from finite element calculations where the crack length to wavelength ratios range between 0.6 and 1.8. The recovered objective crack size exhibits an error of 12%

The detection of flaws in austenitic welds using the decomposition of the time reversal operator

The non-destructive testing of austenitic welds using ultrasound plays an important role in the assessment of the structural integrity of safety critical structures. The internal microstructure of these welds is highly scattering and can lead to the obscuration of defects when investigated by traditional imaging algorithms. This paper proposes an alternative objective method for the detection of flaws embedded in austenitic welds based on the singular value decomposition of the time-frequency domain response matrices. The distribution of the singular values is examined in the cases where a flaw exists and where there is no flaw present. A lower threshold on the singular values, specific to austenitic welds, is derived which, when exceeded, indicates the presence of a flaw. The detection criterion is successfully implemented on both synthetic and experimental data. The datasets arising from welds containing a flaw, are further interrogated using the decomposition of the time reversal operator (DORT) method and the total focussing method (TFM) and it is shown that images constructed via the DORT algorithm typically exhibit a higher signal to noise ratio than those constructed by the TFM algorithm

Cereal based diets modulate some markers of oxidative stress and inflammation in lean and obese Zucker rats

Extent: 10p.Background: The potential of cereals with high antioxidant capacity for reducing oxidative stress and inflammation in obesity is unknown. This study investigated the impact of wheat bran, barley or a control diet (α-cellulose) on the development of oxidative stress and inflammation in lean and obese Zucker rats. Methods: Seven wk old, lean and obese male Zucker rats (n = 8/group) were fed diets that contained wheat bran, barley or α-cellulose (control). After 3 months on these diets, systolic blood pressure was measured and plasma was analysed for glucose, insulin, lipids, oxygen radical absorbance capacity (ORAC), malondialdehyde, glutathione peroxidase and adipokine concentration (leptin, adiponectin, interleukin (IL)-1β, IL-6, TNFα, plasminogen activator inhibitor (PAI)-1, monocyte chemotactic protein (MCP)-1). Adipokine secretion rates from visceral and subcutaneous adipose tissue explants were also determined. Results: Obese rats had higher body weight, systolic blood pressure and fasting blood lipids, glucose, insulin, leptin and IL-1β in comparison to lean rats, and these measures were not reduced by consumption of wheat bran or barley based diets. Serum ORAC tended to be higher in obese rats fed wheat bran and barley in comparison to control (p = 0.06). Obese rats had higher plasma malondialdehyde (p < 0.01) and lower plasma glutathione peroxidase concentration (p < 0.01) but these levels were not affected by diet type. PAI-1 was elevated in the plasma of obese rats, and the wheat bran diet in comparison to the control group reduced PAI-1 to levels seen in the lean rats (p < 0.05). These changes in circulating PAI-1 levels could not be explained by PAI-1 secretion rates from visceral or subcutaneous adipose tissue. Conclusions: A 3-month dietary intervention was sufficient for Zucker obese rats to develop oxidative stress and systemic inflammation. Cereal-based diets with moderate and high antioxidant capacity elicited modest improvements in indices of oxidative stress and inflammation.Damien P Belobrajdic, Yan Y Lam, Mark Mano, Gary A Wittert and Anthony R Bir