Hirsch P.B.,Parks Road
Philosophical Magazine | Year: 2010
This introductory paper to the special conference marking the retirement of Professor David Cockayne gives a brief outline of his career. It highlights some of his many seminal contributions in research, and also refers briefly to his outstanding contributions to the promotion, dissemination and teaching of electron microscopy not covered in the scientific programme of the conference. © 2010 Taylor & Francis Group, LLC. All rights reserved.
McQuillan A.,Oxford Astrophysics |
Aigrain S.,Oxford Astrophysics |
Roberts S.,Parks Road
Astronomy and Astrophysics | Year: 2012
We investigate the variability properties of main sequence stars in the first month of Kepler data, using a new astrophysically robust systematics correction. We find that the fraction of stars with variability greater than that of the Sun is 60%, which is marginally consistent with previous studies, and confirm the trend of increasing variability with decreasing effective temperatures. We define low and high variability samples, with a cut corresponding to twice the variability level of the active Sun, and compare the properties of the stars belonging to each sample. We show tentative evidence that the more active stars have lower proper motions and may be located closer to the galactic plane. We also investigate the frequency content of the variability, finding clear evidence for periodic or quasi-periodic behaviour in 16% of stars, and showing that there exist significant differences in the nature of variability between spectral types. Of the periodic objects, most A and F stars have short periods (<2 days) and highly sinusoidal variability, suggestive of pulsations, whilst G, K and M stars tend to have longer periods (>5 days, with a trend towards longer periods at later spectral types) and show a mixture of periodic and stochastic variability, indicative of activity. Finally, we use auto-regressive models to characterise the stochastic component of the variability, and show that its typical amplitude and time-scale both increase towards later spectral types, which we interpret as a corresponding increase in the characteristic size and life-time of active regions. © 2012 ESO.
O'Brien D.,Parks Road
Proceedings of the 2013 18th European Conference on Network and Optical Communications, NOC 2013 and 2013 8th Conference on Optical Cabling and Infrastructure, OC and I 2013 | Year: 2013
Two high-speed optical wireless demonstrators were produced within the EU funded framework 7 OMEGA project. One of these operates at 1.25Gbit/s demonstrating high data rates, and the other offering 'room scale' coverage at 280 Mbits/s. Details of design, implementation and testing of each are reviewed, together with the challenges of such systems and future directions for work in this area. © 2013 IEEE.
Aslam Z.,Parks Road |
Nicholls R.,Parks Road |
Koos A.,Parks Road |
Nicolosi V.,Parks Road |
Grobert N.,Parks Road
Advanced Functional Materials | Year: 2011
Multi-walled carbon nanotubes (MWCNTs) have long been anticipated as candidates for electrical components in an increasingly miniaturized electronics industry due to their inherent electrical properties. It is possible to manipulate and control these properties by introducing dopants such as N, B, and P. Although some current-induced structural changes in MWCNTs have been observed, no systematic study has been carried out to explore the correlation of changes in the internal structure with the electronic behavior of doped-MWCNTs in terms of the current densities present. In situ transmission electron microscopy (TEM) investigations are presented here of individual, N-doped MWNCT (N-MWCNTs) using the in situ TEM/scanning tunneling microscopy (TEM/STM) Nanofactory© holder. It is observed for the first time that N-MWCNTs not only undergo current-induced structural transformation; i.e., from the typical bamboo structure of N-MWCNTs to the stacked cones, but also-and most importantly-the complete removal of the dopant causes a significant change in the electronic behavior. This has serious implications for the use of doped CNTs as electronic components, especially since tremendous efforts are being made to synthesize CNTs with controlled dopant concentrations. For N-doped multi-walled carbon nanotubes (CNTs) to be fully exploited as electrical components in the miniaturized electronics industry, their behavior in the presence of an applied current must be fully understood. Current-induced restructuring of CNTs has a dominant effect on the dopant which in turn influences their electronic properties. Copyright © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Whelan M.J.,Parks Road
Philosophical Magazine | Year: 2010
A short review is provided of the way the weak-beam technique was developed for observing dislocations at higher resolution than previously attained. Some of the early applications of the technique are described. © 2010 Taylor & Francis.
Hutton E.W.H.,University of Colorado at Boulder |
Syvitski J.P.M.,University of Colorado at Boulder |
Watts A.B.,Parks Road
Computers and Geosciences | Year: 2013
Sea level has risen on order of 100. m since the last glacial maximum (LGM), increasing the load on continental shelves and inducing lithospheric flexure. An analytic solution for the deflection of a linear slope due to sea level fluctuations is derived, based on a one-dimensional elastic plate model. This analytic solution provides deflection estimates of global continental shelves, due only to increases in water loading, effective elastic thickness (which is a proxy for the strength of the lithosphere with 2°×2° resolution) and the local shape of LGM continental margins (one-arc minute resolution). Changes in eustatic sea level are thus disengaged from changes in relative sea level. Variations in water loading can alter the slopes of continental shelves on the order of 30%, but importantly the magnitude is regionally variable. Hydro-isostasy adds to the magnitude of a sea-level rise, long after the eustatic component of the sea-level rise has ended. A sea-level rise will produce a steepening of a continental shelf, while a sea-level drop causes a decrease in shelf gradient and an increase in the total shoreline regression. Quantifying this effect is essential to reconstructing stream gradients, estimating sediment delivered by rivers, for estimating accommodation space through a sea-level cycle, and to support the use of paleo-shoreline to estimate eustatic sea-level fluctuations. © 2012 Elsevier Ltd.
Gelabert J.,Parks Road |
Edwards D.J.,Parks Road |
Stevens C.J.,Parks Road
Electronics Letters | Year: 2011
A novel concept of the use of an ultra-wide bandwidth (UWB) ultra-small-scale wireless interconnect scheme inside an electrically small enclosure is proposed. The concept is presented using a PC tower case as a model environment in which a channel measurement campaign has been made with two different types of antennas. Ricean K factor analysis was conducted for different positions of the antennas to identify the multipath behaviour of the channel, as well as channel capacity. An average maximum channel capacity of almost 6Gbit/s is achieved using the whole UWB band for one of the antennas, assuming a signal-to-noise ratio of 25dB. This work supports the proposal that a high-capacity UWB wireless interconnect scheme for communicating different devices within a PC case scenario may be used to replace wired interconnections, providing a wireless backplane system. © 2011 The Institution of Engineering and Technology.
Kendall M.J.,Parks Road |
Siviour C.R.,Parks Road
Polymer (United Kingdom) | Year: 2013
Polymers are frequently used in applications in which they may be exposed to high rate or impact loading and there is growing industrial importance in understanding their mechanical behavior at different strain rates. This paper describes research that has been performed to better understand and predict the dependence on strain rate of mechanical properties such as yield and flow stress, by investigating the relationship between rate dependence and temperature dependence. In particular, the mechanical behavior of poly(vinyl chloride) with 20 wt% plasticizer has been studied at strain rates from 0.001 s-1 to 4700 s-1 and temperatures from -60 to +80 C. In addition to the use of time-temperature superposition, this paper presents a novel experimental method in which the yield stress and the effects of adiabatic heating at high strain rates are simulated in the low rate loading. © 2013 Elsevier Ltd. All rights reserved.
Lubenko I.,Parks Road |
Ker A.D.,Parks Road
Proceedings of SPIE - The International Society for Optical Engineering | Year: 2012
With most image steganalysis traditionally based on supervised machine learning methods, the size of training data has remained static at up to 20000 training examples. This potentially leads to the classifier being undertrained for larger feature sets and it may be too narrowly focused on characteristics of a source of cover images, resulting in degradation in performance when the testing source is mismatched or heterogeneous. However it is not difficult to obtain larger training sets for steganalysis through simply taking more photos or downloading additional images. Here, we investigate possibilities for creating steganalysis classifiers trained on large data sets using large feature vectors. With up to 1.6 million examples, naturally simpler classification engines must be used and we examine the hypothesis that simpler classifiers avoid overtraining and so perform better on heterogeneous data. We highlight the possibilities of online learners, showing that, when given sufficient training data, they can match or exceed the performance of complex classifiers such as Support Vector Machines. This applies to both their accuracy and training time. We include some experiments, not previously reported in the literature, which provide benchmarks of some known feature sets and classifier combinations. © 2012 Copyright Society of Photo-Optical Instrumentation Engineers (SPIE).
Robinson D.P.,Parks Road |
Das S.,Parks Road |
Searle M.P.,Parks Road
Tectonophysics | Year: 2010
Motivated by the observation that the rare earthquakes which propagated for significant distances at supershear speeds occurred on very long straight segments of faults, we examine every known major active strike-slip fault system on land worldwide and identify those with long (>100km) straight portions capable not only of sustained supershear rupture speeds but having the potential to reach compressional wave speeds over significant distances, and call them "fault superhighways". The criteria used for identifying these are discussed. These superhighways include portions of the 1000. km long Red River fault in China and Vietnam passing through Hanoi, the 1050. km long San Andreas fault in California passing close to Los Angeles, Santa Barbara and San Francisco, the 1100. km long Chaman fault system in Pakistan north of Karachi, the 700. km long Sagaing fault connecting the first and second cities of Burma, Rangoon and Mandalay, the 1600 km Great Sumatra fault, and the 1000. km Dead Sea fault. Of the 11 faults so classified, nine are in Asia and two in North America, with seven located near areas of very dense populations. Based on the current population distribution within 50. km of each fault superhighway, we find that more than 60. million people today have increased seismic hazards due to them. © 2010.