Ultrasonic measurement of core material temperature, phase 1

High temperature ultrasonic temperature measurements in nuclear rocket engine to determine feasibility of rhenium sensor as high temperature senso

Ultrasonic measurement of core material temperature, phase 2

Sheaths for pulse-echo ultrasonic temperature senso

Critical assessment of failure criteria for adhesively bonded composite repair design

Due to the high stress concentration and non-linear deformation in bonded joints, accurate strength prediction remains challenge. The aim of this paper is to evaluate the accuracies of different failure criteria and computational methodologies for bonded composite joints and their suitability as an engineering design tool. A total of four analytical and four numerical predictive models were evaluated against experimental results obtained from single lap and skin-doubler joints. Experimental observations reveal two main failure modes: cohesive and first-ply fracture. Strain-based models based on cohesive properties were found to be applicable only to joints exhibiting cohesive failure. Fracture mechanics-based models, on the other hand, can predict both cohesive and composite ply failure

Symptomatology under storm conditions in the north atlantic in control subjects and in persons with bilateral labyrinthine defects

Motion sickness under conditions of stress and anxiety - role of vestibular apparatu

Scaling parameter for fatigue delamination growth in composites under varying load ratios

Fatigue delamination growth in composite laminates is strongly influenced by mean loads or load ratios. Description of this behaviour currently relies on empirical curve fitting, which renders it difficult to predict fatigue lives of composite structures subjected to variable amplitude fatigue loading. This paper presents a new scaling parameter that is consistent with the similitude concept and incorporates the crack-tip shielding effects of fibre bridging under fatigue loading. Static and fatigue experiments were carried out on IM7/977-3 composite laminates under mode I and mode II. Large-scale fibre bridging was observed as a major toughening mechanism under both static and fatigue loading. To correctly account for the effect of fibre bridging, an inverse method was developed to determine the traction stresses acting in the crack wake. The new scaling parameter, accounting for the effect of bridging by cross-over fibres, is shown to unify the fatigue growth rates under different load ratios obtained in this study

Plasticity induced crack closure in adhesively bonded joints under fatigue loading

The mean load of a cyclic loading has a large effect on fatigue crack growth rates in metallic materials and bonded joints. In metallic structures, this effect has been attributed to plasticity-induced crack closure, but little is known about the mechanism responsible for this mean load effect on fatigue crack growth in adhesively bonded joints. This paper presents a computational investigation of the plasticity-induced crack closure mechanism affecting disbond growth in adhesively bonded joints under fatigue loading. The results show that the ratios of crack-opening and crack-closure are approximately independent of the level of plastic constraint, indicated by the ratio between the plastic zone size and the adhesive thickness. An effective strain-energy release rate parameter, which accounts for the crack closure behaviour, has been developed as a new correlating parameter for disbond growth. Comparisons with the experimental results pertinent to four different adhesive bonded joints reveal that this new correlating parameter is capable of unifying the fatigue growth rates by eliminating the effect of mean loads

The bispectrum of matter perturbations from cosmic strings

We present the first calculation of the bispectrum of the matter perturbations induced by cosmic strings. The calculation is performed in two different ways: the first uses the unequal time correlators (UETCs) of the string network - computed using a Gaussian model previously employed for cosmic string power spectra. The second approach uses the wake model, where string density perturbations are concentrated in sheet-like structures whose surface density grows with time. The qualitative and quantitative agreement of the two gives confidence to the results. An essential ingredient in the UETC approach is the inclusion of compensation factors in the integration with the Green's function of the matter and radiation fluids, and we show that these compensation factors must be included in the wake model also. We also present a comparison of the UETCs computed in the Gaussian model, and those computed in the unconnected segment model (USM) used by the standard cosmic string perturbation package CMBACT. We compare numerical estimates for the bispectrum of cosmic strings to those produced by perturbations from an inflationary era, and discover that, despite the intrinsically non-Gaussian nature of string-induced perturbations, the matter bispectrum is unlikely to produce competitive constraints on a population of cosmic strings

Constraining Galileon inflation

In this short paper, we present constraints on the Galileon inflationary model from the CMB bispectrum. We employ a principal-component analysis of the independent degrees of freedom constrained by data and apply this to the WMAP 9-year data to constrain the free parameters of the model. A simple Bayesian comparison establishes that support for the Galileon model from bispectrum data is at best weak

Discriminating among Earth composition models using geo-antineutrinos

It has been estimated that the entire Earth generates heat corresponding to about 40 TW (equivalent to 10,000 nuclear power plants) which is considered to originate mainly from the radioactive decay of elements like U, Th and K, deposited in the crust and mantle of the Earth. Radioactivity of these elements produce not only heat but also antineutrinos (called geo-antineutrinos) which can be observed by terrestrial detectors. We investigate the possibility of discriminating among Earth composition models predicting different total radiogenic heat generation, by observing such geo-antineutrinos at Kamioka and Gran Sasso, assuming KamLAND and Borexino (type) detectors, respectively, at these places. By simulating the future geo-antineutrino data as well as reactor antineutrino background contributions, we try to establish to which extent we can discriminate among Earth composition models for given exposures (in units of kt$\cdot$ yr) at these two sites on our planet. We use also information on neutrino mixing parameters coming from solar neutrino data as well as KamLAND reactor antineutrino data, in order to estimate the number of geo-antineutrino induced events.Comment: 24 pages, 10 figures, final version to appear in JHE

Optimal bispectrum constraints on single-field models of inflation

We use WMAP 9-year bispectrum data to constrain the free parameters of an 'effective field theory' describing fluctuations in single-field inflation. The Lagrangian of the theory contains a finite number of operators associated with unknown mass scales. Each operator produces a fixed bispectrum shape, which we decompose into partial waves in order to construct a likelihood function. Based on this likelihood we are able to constrain four linearly independent combinations of the mass scales. As an example of our framework we specialize our results to the case of 'Dirac-Born-Infeld' and 'ghost' inflation and obtain the posterior probability for each model, which in Bayesian schemes is a useful tool for model comparison. Our results suggest that DBI-like models with two or more free parameters are disfavoured by the data by comparison with single parameter models in the same class