Kissing Bonds in Diffusion Bonded Parts

The widespread application of diffusion bonding has been hindered, in part, by concerns over kissing bonds. Kissing bonds are generally considered to be conditions where a bond has little or no strength and the concern is that such conditions might escape detection. At Rohr we differentiate between an intimate contact disbond (which has no bond between the surfaces but is detectable by careful ultrasonic testing) and a kissing bond (which also has no bond between the surfaces but is not detectable using current ultrasonic technology). These definitions will be used throughout

Characterization of Corrosion in Aluminum Alloys Using Nuclear Magnetic Resonance

With an ever increasing emphasis on extending the life of both military and commercial aircraft, it is critical to have nondestructive evaluation (NDE) methods capable of detecting corrosion in its earliest stages of formation. The consequences of corrosion left undetected are material thinning and a subsequent reduction in strength. Conventional NDE methods such as ultrasonics, eddy current and radiography are capable of detecting the resultant exfoliation caused by corrosion; however, some material loss must occur before reliable detection can be made using the referenced methods

Evaluation of Solid-Solid Bonds Nondestructively Using Ultrasound

The need for quantitative nondestructive characterization of solid-solid bonds has grown in response to the increasing industrial demand for production. The work to be reported here is restricted to diffusion bonds in metallic systems and is devoted to a correlation of the bond strength with ultrasonic results. Bond strength is defined as the ultimate stress in a uniaxial tensile test at slow strain rate. Reductions in strength are assumed to occur due to a lack of bonding over a fraction of the surfaces due to non-optimum bonding conditions. The voids produced in the unbonded areas are considered to be crack-like, containing a vacuum or at most a low-pressure gas. Diffusion of the species from the two sides to be bonded is the only process considered, thus neglecting for the moment such effects as precipitate reactions, phase transformations and grain growth. The initial work was performed using identical materials on either side, thus considering only the ultrasonic response of the voids produced at the bonded interface. This paper reports on initial studies using dissimilar materials, necessitating inclusion of the effect of the acoustic impedance mismatch. During the work on dissimilar materials, production of a brittle layer at the bond interface was examined. This brittle layer was caused by a thin layer of carbon present at the bond interface. The challenge of detection of this brittle layer is posed for the nondestructive evaluation community</p

Case Report: Burkitt’s lymphoma patients in Northwest Cameroon have a lower incidence of sickle cell trait (Hb AS) than healthy controls

Contradictory findings have been reported from Africa with regard to the risk of  developing Burkitt’s lymphoma (BL) in sickle cell trait (AS) carriers. Haemoglobin electrophoresis was performed in 78 BL patients in the Northwest region of Cameroon, and in 78 nearest-neighbour controls of the same age, sex and tribe from the same village. AS was confirmed in 4 of 78 (5.13%) BL patients and in 11 of 78 (14.10%) controls (χ2, p=0.052; Fisher’s exact, one-tailed, p=0.050). Sickle cell trait carriers had a marginal statistically reduced risk of developing BL

Greenland subglacial lakes detected by radar

This is the final version of the article. Available from AGU via the DOI in this record.Subglacial lakes are an established and important component of the basal hydrological system of the Antarctic ice sheets, but none have been reported from Greenland. Here we present airborne radio echo sounder (RES) measurements that provide the first clear evidence for the existence of subglacial lakes in Greenland. Two lakes, with areas ~8 and ~10 km2, are found in the northwest sector of the ice sheet, ~40 km from the ice margin, and below 757 and 809 m of ice, respectively. The setting of the Greenland lakes differs from those of Antarctic subglacial lakes, being beneath relatively thin and cold ice, pointing to a fundamental difference in their nature and genesis. Possibilities that the lakes consist of either ancient saline water in a closed system or are part of a fresh, modern open hydrological system are discussed, with the latter interpretation considered more likely.Funding was provided by NERC grant NE/ H020667. Additional support was provided by NASA grant NNX11AD33G and the G. Unger Vetlesen foundation

WiSeBE: Window-based Sentence Boundary Evaluation

Sentence Boundary Detection (SBD) has been a major research topic since Automatic Speech Recognition transcripts have been used for further Natural Language Processing tasks like Part of Speech Tagging, Question Answering or Automatic Summarization. But what about evaluation? Do standard evaluation metrics like precision, recall, F-score or classification error; and more important, evaluating an automatic system against a unique reference is enough to conclude how well a SBD system is performing given the final application of the transcript? In this paper we propose Window-based Sentence Boundary Evaluation (WiSeBE), a semi-supervised metric for evaluating Sentence Boundary Detection systems based on multi-reference (dis)agreement. We evaluate and compare the performance of different SBD systems over a set of Youtube transcripts using WiSeBE and standard metrics. This double evaluation gives an understanding of how WiSeBE is a more reliable metric for the SBD task.Comment: In proceedings of the 17th Mexican International Conference on Artificial Intelligence (MICAI), 201

Evaluation of Microwave Methods for Thickness Measurements of Liquid Shim Material

This paper describes the use of a microwave interferometer technique which measures the thickness of liquid shim material applied to composite surfaces. Liquid shim, which is a low dielectric material, is applied to spar cap surfaces in order to maintain wing skin mold-line tolerances while reducing stresses at the location of fastener holes. For this application, the thickness of the shim material must be controlled within specified limits. Microwave reflection techniques provide an alternative nondestructive approach to liquid shim thickness measurements

Basal topographic controls on rapid retreat of Humboldt Glacier, northern Greenland

This is the final version of the article. Available from CUP via the DOI in this record.Discharge from marine-terminating outlet glaciers accounts for up to half the recent mass loss from the Greenland ice sheet, yet the causal factors are not fully understood. Here we assess the factors controlling the behaviour of Humboldt Glacier (HG), allowing us to evaluate the influence of basal topography on outlet glacier response to external forcing since part of HG’s terminus occupies a large overdeepening. HG’s retreat accelerated dramatically after 1999, coinciding with summer atmospheric warming of up to 0.19°C a–1 and sea-ice decline. Retreat was an order of magnitude greater in the northern section of the terminus, underlain by a major basal trough, than in the southern section, where the bedrock is comparatively shallow. Velocity change following retreat was spatially non-uniform, potentially due to a pinning point near HG’s northern lateral margin. Consistent with observations, numerical modelling demonstrates an order-of-magnitude greater sensitivity to sea-ice buttressing and crevasse depth (used as a proxy for atmospheric warming) in the northern section. The trough extends up to 72 km inland, so it is likely to facilitate sustained retreat and ice loss from HG during the 21st century.Funding for this work was provided by a Durham Doctoral Studentship to J.R.C. Radio-echo sounding data were acquired and processed through UK Natural Environment Research Council (NERC) grant NE/H020667 to J.A.D. and P.C. and a G. Unger Vetlesen grant to the University of Texas Institute for Geophysics (UTIG). GrOGG laser altimetry was supported by NNXAD33G to D.D.B. This paper is UTIG contribution No. 2733. S.S.R.J. was supported by UK NERC fellowship NE/J018333/1

Young neutron stars with soft gamma ray emission and anomalous X-ray pulsar

The observational properties of Soft Gamma Repeaters and Ano\-malous X-ray Pulsars (SGR/AXP) indicate to necessity of the energy source different from a rotational energy of a neutron star. The model, where the source of the energy is connected with a magnetic field dissipation in a highly magnetized neutron star (magnetar) is analyzed. Some observational inconsistencies are indicated for this interpretation. The alternative energy source, connected with the nuclear energy of superheavy nuclei stored in the nonequilibrium layer of low mass neutron star is discussed.Comment: 29 pages, 13 figures, Springer International Publishing Switzerland 2016 A.W. Alsabti, P. Murdin (eds.), Handbook of Supernova

Transformation Pathways of Silica under High Pressure

Concurrent molecular dynamics simulations and ab initio calculations show that densification of silica under pressure follows a ubiquitous two-stage mechanism. First, anions form a close-packed sub-lattice, governed by the strong repulsion between them. Next, cations redistribute onto the interstices. In cristobalite silica, the first stage is manifest by the formation of a metastable phase, which was observed experimentally a decade ago, but never indexed due to ambiguous diffraction patterns. Our simulations conclusively reveal its structure and its role in the densification of silica.Comment: 14 pages, 4 figure