Nonparametric Regression using the Concept of Minimum Energy

It has recently been shown that an unbinned distance-based statistic, the energy, can be used to construct an extremely powerful nonparametric multivariate two sample goodness-of-fit test. An extension to this method that makes it possible to perform nonparametric regression using multiple multivariate data sets is presented in this paper. The technique, which is based on the concept of minimizing the energy of the system, permits determination of parameters of interest without the need for parametric expressions of the parent distributions of the data sets. The application and performance of this new method is discussed in the context of some simple example analyses.Comment: 10 pages, 4 figure

Antiferromagnetic spin-coupling between MnII and amminium radical cation ligands: models for coordination polymer magnets

One and two electron oxidation of the manganese(II) complex [L2Mn(hfac)2] {L = 4'',4'''-di-tert-butyl-2',2'',2'''trimethoxy-{4-(4'-diphenylaminophenyl)pyridine} were studied by ultra violet/ visible/ near infra red spectroscopy, cyclic voltammetry and magnetometry. A one-electron oxidation converts the triarylamine ligand to its radical cation and gives a complex in which the antiferromagnetic coupling between the spin on the ligand and that on the metal J/kb is -1.5 K. In a dilute frozen matrix and at low temperature this behaves as an S = 2 system. A two electron oxidation gives [L2Mn(hfac)2]2.+ which at low enough temperatures behaves as an S = 3/2 system but the spin-coupling between the metal and the ligand is weaker (J/kb = -0.3 K). The weakness of these spin-couplings mean that MnII/amminium radical cation complexes are not promising systems on which to base coordination polymer magnets. The equivalent copper(II) complex [L2Cu(hfac)2] was also investigated but this decomposes when an attempt is made to oxidise the ligand to its amminium radical cation

Digital predictions of complex cylinder packed columns

A digital computational approach has been developed to simulate realistic structures of packed beds. The underlying principle of the method is digitisation of the particles and packing space, enabling the generation of realistic structures. Previous publications [Caulkin, R., Fairweather, M., Jia, X., Gopinathan, N., & Williams, R.A. (2006). An investigation of packed columns using a digital packing algorithm. Computers & Chemical Engineering, 30, 1178–1188; Caulkin, R., Ahmad, A., Fairweather, M., Jia, X., & Williams, R. A. (2007). An investigation of sphere packed shell-side columns using a digital packing algorithm. Computers & Chemical Engineering, 31, 1715–1724] have demonstrated the ability of the code in predicting the packing of spheres. For cylindrical particles, however, the original, random walk-based code proved less effective at predicting bed structure. In response to this, the algorithm has been modified to make use of collisions to guide particle movement in a way which does not sacrifice the advantage of simulation speed. Results of both the original and modified code are presented, with bulk and local voidage values compared with data derived by experimental methods. The results demonstrate that collisions and their impact on packing structure cannot be disregarded if realistic packing structures are to be obtained

Comparison of classical and optimal active suspension control systems

British Rail has been designing active suspensions for some 16 years, starting with tilt systems for the Advanced Passenger train. These have been designed using classical control techniques requiring a combination of experience, intuition and frequency response stability techniques, such as Nichols' plots. In order to see if a more systematic approach to control system design could produce improvements in performance and implementation the current investigation was instigated in which controllers designed using classical techniques are compared with controllers designed using linear optimal control theory. The active suspension used for the investigation was an Electro Magnetic active vertical suspension fitted to a service MkIII coach. Design of the actuators is described in the thesis along with the design of analogue and digital control systems. Two classical control systems were designed. a simple "Sky Hook" damper control system and a more sophisticated position control system developed from British Rail’s experience with Maglev suspensions. A regulator designed using linear optimal control theory was found to give very good results in theory. However to implement the regulator it was necessary to design a system observer. In order to achieve a practically realisable observer considerable rationalisation of the vehicle model was required, which drew heavily on experience gained designing classical control systems. The classical control systems proved to be much easier to commission than the optimal controllers as they were designed with implementation in mind. During track testing problems of interaction between vehicles were encountered, as a result the biggest improvements in ride were obtained with the simple Sky Hook damper, as it was less specific to the vehicle than the other configurations. With further development one of the optimal control systems considered will probably turn out to be the most effective as it draws on the attributes of both classical and optimal design techniques

Quantum dot cascade laser: Arguments in favor

Quantum cascade lasers are recognized as propitious candidates for future terahertz optoelectronics. Here we demonstrate several definite advantages of quantum dot cascade structures over quantum well devices, which suffer fundamental performance limitations owing to continuous carrier spectrum. The discrete spectrum of quantum dots opens an opportunity to control the non-radiative relaxation and optical loss and also provides for more flexibility in the choice of an optical and electrical design of the laser.Comment: 4 pages, 2 figures; Proceedings of MSS13 to be published in Physica

Some thoughts on Darcy-type flow simulation for modelling underground CO 2 storage, based on the Sleipner CO 2 storage operation

We take three flow simulators, all based on Darcy’s Law but with different numerical solver implementations, to assess some of the issues surrounding their use to model underground CO2 storage. We focus on the Sleipner CO2 injection project, which, with its seismic monitoring datasets, provides unique insights into CO2 plume development during a large-scale injection operation. The case studies firstly compare simulator performance in terms of outputs and run-times on carefully matched model scenarios; then we compare numerical with analytical Darcy solutions to explore the potential for modelling simplification; finally we look at the effects of including conservation of energy in the simulations. The initial case-study used simplified axisymmetric model geometry to simulate the upward flux of CO2 through a heterogeneous reservoir, incorporating multiphase flow with coupled CO2 dissolution into formation brine. All three codes produced near-identical results with respect to CO2 migration velocity and total upward CO2 flux at the reservoir top. The second case-study involved 3D modelling of the growth of the topmost layer of CO2 trapped and migrating beneath topseal topography. Again the three codes showed excellent agreement. In the third case-study the simulators were tested against a simplified analytical solution for gravity currents to model the spreading of a single CO2 layer beneath a flat caprock. Neglecting capillary effects, the numerical models showed similar layer migration and geometry to the analytical model, but it was necessary to minimise the effects of numerical dispersion by adopting very fine cell thicknesses. The final case-study was designed to test the non-isothermal effects of injecting CO2 into a reservoir at non-ambient temperature. Only two of the simulators solve for conservation of energy, but both showed a near identical thermal anomaly, dominated by Joule-Thomson effects. These can be significant, particularly where reservoir conditions are close to the critical point for CO2 where property variations can significantly affect plume mobility and also seismic response. In conclusion, the three simulators show robust consistency, any differences far less than would result from geological parameter uncertainty and limitations of model resolution. In this respect the three implementations are significantly different in terms of computing resource requirement and it is clear that approaches with simplified physics will pay rich dividends in allowing more detailed reservoir heterogeneity to be included. Contrary to this, including conservation of energy is heavier on computing time but is likely to be required for storage scenarios where the injectant stream is significantly different in temperature to the reservoir and most critically for shallower storage reservoirs where CO2 is close to its critical point

CO 2 storage: setting a simple bound on potential leakage through the overburden in the North Sea Basin

So-called ‘gas chimneys’ are likely to provide the main geological risk for out-of-reservoir CO2 migration in thick post-rift overburden successions such as typify the central and northern North Sea. Here we postulate that, in the North Sea, such chimneys formed in the geological past, with a likely peak activity at the end of the ice-age, and are currently rather dormant. With this postulate we set a bound on possible bulk migration rates considering both advective and diffusive flow and based on a hypothetical CO2 storage site at 800 m depth. Calculated migration velocities into the overburden, by either advection or diffusion, are very low, at less than one metre per thousand years. Consequently flux rates are also very low, several orders of magnitude below the leakage thresholds that have been suggested as ensuring effective mitigation performance. Time-lapse seismic reflection data from the Sleipner storage site, which is located beneath some small chimney features, show no evidence of CO2 migration into the overburden. This cannot prove the postulate, because the time interval spanned by the seismic surveys is just a few years, but it is nevertheless consistent with it

Design and application of a multi-modal process tomography system

This paper presents a design and application study of an integrated multi-modal system designed to support a range of common modalities: electrical resistance, electrical capacitance and ultrasonic tomography. Such a system is designed for use with complex processes that exhibit behaviour changes over time and space, and thus demand equally diverse sensing modalities. A multi-modal process tomography system able to exploit multiple sensor modes must permit the integration of their data, probably centred upon a composite process model. The paper presents an overview of this approach followed by an overview of the systems engineering and integrated design constraints. These include a range of hardware oriented challenges: the complexity and specificity of the front end electronics for each modality; the need for front end data pre-processing and packing; the need to integrate the data to facilitate data fusion; and finally the features to enable successful fusion and interpretation. A range of software aspects are also reviewed: the need to support differing front-end sensors for each modality in a generic fashion; the need to communicate with front end data pre-processing and packing systems; the need to integrate the data to allow data fusion; and finally to enable successful interpretation. The review of the system concepts is illustrated with an application to the study of a complex multi-component process

Geology of Exeter and its environs

A 225 km² area around Exeter, described in this report, extends from the villages of Brampford Speke and Whimple in the north to Aylesbeare, Exminster and Woodbury in the south. It is underlain by Carboniferous, Permian, and Triassic solid formations and by a variety of Quaternary superficial deposits. The Namurian Crackington Formation comprises mainly tightly folded shales with subordinate sandstone interbeds. The Permian rocks consist of a lower, predominantly: breccia, sequence (Whipton Formation, Teignmouth Breccia, Monkerton Member) that thins and disappears northwards against a possibly fault-controlled ridge of Crackington Formation; the breccias are overlain by sandstones and mudstones (Dawlish Sandstone and Aylesbeare Mudstone). Volcanic rocks occur at the base of the Permian sequence and possibly within the Dawlish Sandstone. The latter splits into five alternating sandstone and mudstone members when traced northwards from Exeter into the Crediton Trough (an area of thick Permian sediments). The Aylesbeare Mudstone is divisible south of Aylesbeare into two members, the lower containing impersistent sandstones. It is overlain by the basal Triassic gravels (Budleigh Salterton Pebble Beds) which are in turn succeeded by the Otter Sandstone