Hesjedal T.,University of Waterloo |
Hesjedal T.,Clarendon Laboratory
Applied Physics Letters | Year: 2011
Few-layer graphene is obtained in atmospheric chemical vapor deposition on polycrystalline copper in a roll-to-roll process. Raman and x-ray photoelectron spectroscopy were employed to confirm the few-layer nature of the graphene film, to map the inhomogeneities, and to study and optimize the growth process. This continuous growth process can be easily scaled up and enables the low-cost fabrication of graphene films for industrial applications. © 2011 American Institute of Physics.
Steane A.M.,Clarendon Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2015
We present two results in the treatment of self-force of accelerating bodies. If the total force on an extended rigid object is calculated from the change of momentum summed over planes of simultaneity of successive rest frames, then we show that an ideal fluid, moving rigidly, exerts a net force on its boundary that is independent of both pressure and orientation. Under this same definition of total force, we find the electromagnetic self-force for a spherical charged shell of proper radius R accelerating with constant proper acceleration g is (2e2g/R)[1/12-n=0(gR)2n((2n-3)(2n-1)(2n+1)2)-1]. © 2015 American Physical Society.
Steane A.M.,Clarendon Laboratory
American Journal of Physics | Year: 2015
We consider radiation reaction and energy conservation in classical electromagnetism. We first treat the well-known problem of energy accounting during radiation from a uniformly accelerating particle. This gives rise to the following paradox: when the self-force vanishes, the system providing the applied force does only enough work to give the particle its kinetic energy-so where does the energy that is eventually radiated away come from? We answer this question using a modern treatment of radiation reaction and self-force, as it appears in the expression due to Eliezer and Ford and O'Connell. We clarify the influence of the Schott force, and we find that the radiated power is 2q2a0 · f0/(3mc3), which differs from Larmor's formula. Finally, we present a simple and highly visual argument that enables one to track the radiated energy without the need to appeal to the far field in the distant future (the "wave zone"). © 2015 American Association of Physics Teachers.
Steane A.M.,Clarendon Laboratory
American Journal of Physics | Year: 2014
It is widely believed that classical electromagnetism is either unphysical or inconsistent, owing to pathological behavior when self-force and radiation reaction are non-negligible. We argue that there is no inconsistency as long as it is recognized that certain types of charge distribution are simply impossible, such as, for example, a point particle with finite charge and finite inertia. This is owing to the fact that negative inertial mass is an unphysical concept in classical physics. It remains useful to obtain an equation of motion for small charged objects that describes their motion to good approximation without requiring knowledge of the charge distribution within the object. We give a simple method to achieve this, leading to a reduced-order form of the Abraham-Lorentz-Dirac equation, essentially as proposed by Eliezer, Landau, and Lifshitz and derived by Ford and O'Connell. © 2015 American Association of Physics Teachers.
Ingram W.,Clarendon Laboratory |
Ingram W.,UK Met Office
Climate Dynamics | Year: 2013
The water vapour feedback probably makes the largest contribution to climate sensitivity, and the second-largest contribution to its uncertainty, in the sense of disagreement between General Circulation Models (GCMs, the most physically detailed models of climate we have). Yet there has been no quantification of it which allows these differences to be attributed physically with the aim of constraining the true value. This paper develops a new breakdown of the non-cloud LW (longwave) response to climate change, which avoids the problems of the conventional breakdown, and applies it to a set of 4 GCMs. The basic physical differences are that temperature is used as the vertical coordinate, and relative humidity as the humidity variable. In this framework the different GCMs' feedbacks look more alike, consistent with our understanding that their water vapour responses are physically very similar. Also, in the global mean all the feedback components have the same sign, allowing us to conveniently attribute the overall response fractionally (e. g. about 60% from the "partly-Simpsonian" component). The systematic cancellation between different feedback components in the conventional breakdown is lost, so now a difference in a feedback component actually contributes to a difference in climate sensitivity, and the differences between these GCMs in the non-cloud LW part of this can be traced to differences in formulation, mean climate and climate change response. Physical effects such as those due to variations in the formulation of LW radiative transfer become visible. Differences in the distribution of warming no longer dominate comparison of GCMs. The largest component depends locally only on the GCM's mean climate, so it can in principle be calculated for the real world and validated. However, components dependent on the climate change response probably account for most of the variation between GCMs. The effect of simply changing the humidity variable in the conventional breakdown is also examined. It gives some of this improvement-the loss of the cancellations that leave the conventional breakdown of no use to understand differences between GCMs' climate sensitivities-but not the link to mean climate. © 2012 Crown Copyright.
Stranks S.D.,Clarendon Laboratory |
Snaith H.J.,Clarendon Laboratory
Nature Nanotechnology | Year: 2015
Metal-halide perovskites are crystalline materials originally developed out of scientific curiosity. Unexpectedly, solar cells incorporating these perovskites are rapidly emerging as serious contenders to rival the leading photovoltaic technologies. Power conversion efficiencies have jumped from 3% to over 20% in just four years of academic research. Here, we review the rapid progress in perovskite solar cells, as well as their promising use in light-emitting devices. In particular, we describe the broad tunability and fabrication methods of these materials, the current understanding of the operation of state-of-the-art solar cells and we highlight the properties that have delivered light-emitting diodes and lasers. We discuss key thermal and operational stability challenges facing perovskites, and give an outlook of future research avenues that might bring perovskite technology to commercialization. © 2015 Macmillan Publishers Limited. All rights reserved.
Snaith H.J.,Clarendon Laboratory
Journal of Physical Chemistry Letters | Year: 2013
Over the last 12 months, we have witnessed an unexpected breakthrough and rapid evolution in the field of emerging photovoltaics, with the realization of highly efficient solid-state hybrid solar cells based on organometal trihalide perovskite absorbers. In this Perspective, the steps that have led to this discovery are discussed, and the future of this rapidly advancing concept have been considered. It is likely that the next few years of solar research will advance this technology to the very highest efficiencies while retaining the very lowest cost and embodied energy. Provided that the stability of the perovskite-based technology can be proven, we will witness the emergence of a contender for ultimately low-cost solar power. © 2013 American Chemical Society.
Palmer T.N.,Clarendon Laboratory
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences | Year: 2014
This paper sets out a new methodological approach to solving the equations for simulating and predicting weather and climate. In this approach, the conventionally hard boundary between the dynamical core and the sub-grid parametrizations is blurred. This approach is motivated by the relatively shallow power-law spectrum for atmospheric energy on scales of hundreds of kilometres and less. It is first argued that, because of this, the closure schemes for weather and climate simulators should be based on stochastic-dynamic systems rather than deterministic formulae. Second, as high-wavenumber elements of the dynamical core will necessarily inherit this stochasticity during time integration, it is argued that the dynamical core will be significantly overengineered if all computations, regardless of scale, are performed completely deterministically and if all variables are represented with maximum numerical precision (in practice using double-precision floatingpoint numbers). As the era of exascale computing is approached, an energy- and computationally efficient approach to cloud-resolved weather and climate simulation is described where determinism and numerical precision are focused on the largest scales only. © 2014 The Author(s) Published by the Royal Society. All rights reserved.
Steane A.M.,Clarendon Laboratory
Physical Review D - Particles, Fields, Gravitation and Cosmology | Year: 2014
We calculate the self-force of a constantly accelerating electric dipole, showing, in particular, that classical electromagnetism does not predict that an electric dipole could self-accelerate, nor could it levitate in a gravitational field. We also resolve a paradox concerning the inertial mass of a longitudinally accelerating dipole, showing that the combined system of dipole plus field can be assigned a well-defined energy-momentum four-vector, so that the principle of relativity is satisfied. We then present some general features of electromagnetic phenomena in a reference frame described by the Rindler metric, showing in particular that an observer fixed in a gravitational field described everywhere by the Rindler metric will find any charged object supported in the gravitational field to possess an electromagnetic self-force equal to that observed by an inertial observer relative to which the body undergoes rigid hyperbolic motion. It follows that the principle of equivalence is satisfied by these systems. © 2014 American Physical Society.
News Article | November 22, 2016
Home > Press > Oxford Nanoimaging report on how the Nanoimager, a desktop microscope delivering single molecule, super-resolution performance, is being applied at the MRC Centre for Molecular Bacteriology & Infection Abstract: Oxford Nanoimaging Limited manufacture and sell microscopes offering super-resolution and single-molecule performance to research users. Today, the company reports on the work of early-adopters for their Nanoimager technology at the MRC Centre for Molecular Bacteriology and Infection located at Imperial College, London. The MRC Centre for Molecular Bacteriology and Infection is uniquely focused on disease-causing bacteria. Ramesh Wigneshweraraj is a Professor of Microbiology leading a group that is working at the leading edge of understanding the behaviour of small proteins produced by viruses that infect bacteria (phages) at the single cell level to ultimately inspire and inform the development of truly novel drugs against antibiotic-resistant bacterial pathogens. Networking in science is so often the provider for new discoveries and collaborations. A meeting at Cambridge proved the point here with Professor Wigneshweraraj (Ramesh) meeting Oxford physicist, Professor Achillefs Kapanidis of the Clarendon Laboratory. Discussing their research over a drink on a warm summer evening, Professor Kapanidis pulled out his laptop and showed results of an experiment very relevant to that being defined by his colleague, Ramesh. One thing led to another and an early demonstration for the Nanoimager, a high resolution single molecule imaging technique developed over a number of years by the Kapanidis group. When, in May 2016, newly-formed company Oxford Nanoimaging (ONI) launched the commercial version of the Nanoimager, Ramesh set out to get funding for the system. With support from the Wellcome Trust, one of ONI's first installations was made at Imperial College in September. Since its arrival, the Nanoimager has been put through its paces by PhD student, Amy Switzer. Without a background in microscopy, Amy has been able to define what she needs from the instrument to satisfy her research needs. Now working alongside ONI's development team, she is evaluating new data processing software to enable her to produce data at the super-resolution levels. Having a multifunctional system is enabling her to use a variety of imaging methods to achieve live cell imaging at the single molecule level. Techniques at the single molecule level including immunofluorescence, tracking PALM and dSTORM, will now help Amy and Ramesh to work quickly on their goal the rapid evaluation of how phage-derived small proteins inhibit bacteria and how bacterial enzymes behave in response to the diverse stresses they are subjected to. The Nanoimager, seen below, is a very small unit measuring just 21 cm x 21 cm. It requires no special environmental conditions like an isolation table as it has been designed to compensate for acoustic and vibrational issues. As Amy says, I am very fortunate to be one of the first users of the Nanoimager. I can work directly with the inventors including Bo Jing from the Kapanidis team. I am able to request new iterations of software and these are delivered with enthusiasm by the ONI folks. Timing is very important and here Ramesh takes up the story. My meeting with Achillefs and the acquisition of the Nanoimager has come at the right time for my research needs. It enables me to understand the behaviour of individual proteins within single bacterial cells. Given the appropriate experimental protocols, I am able to easily detect specific proteins in mixed populations of bacteria. Looking ahead, I can envisage an application of the NanoImager in early diagnostics of bacterial infections, thus enabling rapid species identification and ensuring the correct medication is prescribed, and thereby improving patient welfare while reducing costs. We are really excited to work with ONI in the on-going development of diverse applications for the Nanoimager and, more importantly, to advance fundamental bacteriology in this new and exciting direction. Oxford Nanoimaging has launched a new website providing insight into the applications and technology of the Nanoimager. Visit www.oxfordni.com for more information. About Oxford Nanoimaging Limited Oxford Nanoimaging Limited is a company originating in the Clarendon Laboratory, Department of Physics at the University of Oxford. Professor Achillefs Kapanidis and PhD student, Bo Jing, lead a collaborative, inter-disciplinary team that has pioneered innovative technologies to produce an elegant benchtop super-resolution microscope. The Nanoimager has a footprint of just 21 cm x 21 cm yet packs the capability of a much larger, conventional microscopy platform delivering super-resolution and single-molecule performance. With a significantly lower cost of entry, researchers will now be able to obtain benchtop nanoscale imaging at a fraction of the price of earlier systems without the need for a large laboratory and skilled operators. As Professor Kapanidis says, I wish I had this when I was a graduate student. For more information, please click If you have a comment, please us. 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