Publishing and Bookselling (Book Review)

published or submitted for publicatio

Predicting the influence of strain on crack length measurements performed using the potential drop method

The potential drop (PD) crack growth measurement technique is sensitive to strain accumulation which is often erroneously interpreted as crack extension. When testing ductile materials these errors can be significant, but in many cases the optimum method of minimising or supressing them remains unknown because it is extremely difficult to measure them experimentally in isolation from other sources of error, such non-ideal crack morphology. In this work a novel method of assessing the influence of strain on PD, using a sequentially coupled structural electrical finite element (FE) model, has been developed. By comparing the FE predictions with experimental data it has been demonstrated that the proposed FE technique is extremely effective at predicting trends in PD due to strain. It has been used to identify optimum PD configurations for compact tension, C(T), and single edge notched tension, SEN(T), fracture mechanics specimens and it has been demonstrated that the PD configuration often recommended for C(T) specimens can be subject to large errors due to strain accumulation. In addition, the FE technique has been employed to assess the significance of strain after the initiation of stable tearing for a monotonically loaded C(T) specimen. The proposed FE technique provides a powerful tool for optimising the measurement of crack initiation and growth in applications where large strains are present, e.g. J-R curve and creep crack growth testing

The power spectrum of the circular noise

The circular noise is important in connection to Mach's principle, and also as a possible probe of the Unruh effect. In this letter the power spectrum of the detector following the Trocheries-Takeno motion in the Minkowski vacuum is analytically obtained in the form of an infinite series. A mean distribution function and corresponding energy density are obtained for this particular detected noise. The analogous of a non constant temperature distribution is obtained. And in the end, a brief discussion about the equilibrium configuration is given.Comment: accepted for publication in GR

Detection of negative energy: 4-dimensional examples

We study the response of switched particle detectors to static negative energy densities and negative energy fluxes. It is demonstrated how the switching leads to excitation even in the vacuum and how negative energy can lead to a suppression of this excitation. We obtain quantum inequalities on the detection similar to those obtained for the energy density by Ford and co-workers and in an `operational' context by Helfer. We revisit the question `Is there a quantum equivalence principle?' in terms of our model. Finally, we briefly address the issue of negative energy and the second law of thermodynamics.Comment: 10 pages, 7 figure

Improvements in the Measurement of Creep Crack Initiation and Growth Using Potential Drop

To predict the residual life of components operating in the creep regime, it is vital to accurately identify crack initiation, and measure subsequent crack growth, in laboratory tests. Potential drop (PD) measurements, used for this purpose, are susceptible to errors caused by the accumulation of creep strain. For creep ductile materials, this can result in highly conservative crack initiation models and the implementation of unnecessary inspection and maintenance programmes that can cost millions of pounds in lost revenue. Conversely, the crack growth models can be non-conservative. Using a novel combination of interrupted creep crack growth (CCG) tests and sequentially coupled structural-electrical finite element analyses a new method of interpreting PD data has been developed and validated. It uses an increase in gradient on a plot of PD vs. load-line displacement to accurately identify crack initiation. This has been compared to the current method in ASTM E1457-15 by reanalysing data from CCG tests performed on a range of materials at various temperatures and loads. The initiation times, measured using the current ASTM method, were underestimated by factors of up to 23 and the subsequent crack growth rates were underestimated by factors of up to 1.5

Long-term variations in Iceland–Scotland overflow strength during the Holocene

The overflow of deep water from the Nordic seas into the North Atlantic plays a critical role in global ocean circulation and climate. Approximately half of this overflow occurs via the Iceland–Scotland (I–S) overflow, yet the history of its strength throughout the Holocene (~ 0–11 700 yr ago, ka) is poorly constrained, with previous studies presenting apparently contradictory evidence regarding its long-term variability. Here, we provide a comprehensive reconstruction of I–S overflow strength throughout the Holocene using sediment grain size data from a depth transect of 13 cores from the Iceland Basin. Our data are consistent with the hypothesis that the main axis of the I–S overflow on the Iceland slope was shallower during the early Holocene, deepening to its present depth by ~ 7 ka. Our results also reveal weaker I–S overflow during the early and late Holocene, with maximum overflow strength occurring at ~ 7 ka, the time of a regional climate thermal maximum. Climate model simulations suggest a shoaling of deep convection in the Nordic seas during the early and late Holocene, consistent with our evidence for weaker I–S overflow during these intervals. Whereas the reduction in I–S overflow strength during the early Holocene likely resulted from melting remnant glacial ice sheets, the decline throughout the last 7000 yr was caused by an orbitally induced increase in the amount of Arctic sea ice entering the Nordic seas. Although the flux of Arctic sea ice to the Nordic seas is expected to decrease throughout the next century, model simulations predict that under high emissions scenarios, competing effects, such as warmer sea surface temperatures in the Nordic seas, will result in reduced deep convection, likely driving a weaker I–S overflow

Dynamical modelling of the elliptical galaxy NGC 2974

In this paper we analyse the relations between a previously described oblate Jaffe model for an ellipsoidal galaxy and the observed quantities for NGC 2974, and obtain the length and velocity scales for a relevant elliptical galaxy model. We then derive the finite total mass of the model from these scales, and finally find a good fit of an isotropic oblate Jaffe model by using the Gauss-Hermite fit parameters and the observed ellipticity of the galaxy NGC 2974. The model is also used to predict the total luminous mass of NGC 2974, assuming that the influence of dark matter in this galaxy on the image, ellipticity and Gauss-Hermite fit parameters of this galaxy is negligible within the central region, of radius $0.5R_{\rm e}.$Comment: 7 figure

Automated analysis of atrial late gadolinium enhancement imaging that correlates with endocardial voltage and clinical outcomes: A 2-center study

This work was supported by the British Heart Foundation PG/10/37/28347, RG/10/11/28457, NIHR Biomedical Research Centre funding, and the ElectroCardioMaths Programme of the Imperial BHF Centre of Research Excellence