Analysing Magnetism Using Scanning SQUID Microscopy

Scanning superconducting quantum interference device microscopy (SSM) is a scanning probe technique that images local magnetic flux, which allows for mapping of magnetic fields with high field and spatial accuracy. Many studies involving SSM have been published in the last decades, using SSM to make qualitative statements about magnetism. However, quantitative analysis using SSM has received less attention. In this work, we discuss several aspects of interpreting SSM images and methods to improve quantitative analysis. First, we analyse the spatial resolution and how it depends on several factors. Second, we discuss the analysis of SSM scans and the information obtained from the SSM data. Using simulations, we show how signals evolve as a function of changing scan height, SQUID loop size, magnetization strength and orientation. We also investigated 2-dimensional autocorrelation analysis to extract information about the size, shape and symmetry of magnetic features. Finally, we provide an outlook on possible future applications and improvements.Comment: 16 pages, 10 figure

A New Radio - X-Ray Probe of Galaxy Cluster Magnetic Fields

Results are presented of a new VLA-ROSAT study that probes the magnetic field strength and distribution over a sample of 16 ``normal'' low redshift (z < 0.1) galaxy clusters. The clusters span two orders of magnitude in X-ray luminosity, and were selected to be free of (unusual) strong radio cluster halos, and widespread cooling flows. Consistent with these criteria, most clusters show a relaxed X-ray morphology and little or no evidence for recent merger activity. Analysis of the rotation measure (RM) data shows cluster-generated Faraday RM excess out to ~0.5 Mpc from cluster centers. The results, combined with RM imaging of cluster-embedded sources and ROSAT X-ray profiles indicates that the hot intergalactic gas within these ``normal'' clusters is permeated with a high filling factor by magnetic fields at levels of = 5-10 (l/10 kpc)^{-1/2} microGauss, where l is the field correlation length. These results lead to a global estimate of the total magnetic energy in clusters, and give new insight into the ultimate energy origin, which is likely gravitational. These results also shed some light on the cluster evolutionary conditions that existed at the onset of cooling flows.Comment: 6 pages, 1 figure, uses emulateapj5.sty, accepted by ApJ

A strategic study of energy efficient and hybrid energy system options for a multi-family building in Korea

This study is to identify performance of energy efficiency measures and to match low-carbon and renewable energy (RE) systems supplies to demands in the context of multi-family residential buildings in Korea. An approach to the evaluation of the hybrid energy systems was investigated, including consideration of heat and power demand profiles, energy system combinations, building design options and strategies for matching supply to demand. The approach is encapsulated within an integrated software environment. Building energy simulation technology was exploited to make virtual energy use data. Low-carbon and RE system modelling techniques were used to predict energy supply profiles. A series of demand/supply matching-based analyses were made to identify the effect of energy efficient demand measures (e.g. roof-top gardens, innovative underfloor heating system) and evaluate the capacity utilisation factor from the hybrid energy systems. On the basis of performance information obtained at the conceptual design stage, the design team can pinpoint the most energy efficient demand/supply combination, and consequently, maximise the impact of hybrid energy systems adoption

Visual motion-evoked potentials in man

Visual motion-evoked potentials were recorded from the human scalp. The stimulus chosen for most detailed study was sudden reversal of the motion of a patterned field, on the hypothesis that this was likely to activate only mechanisms selectively sensitive to the direction of stimulus motion. A large proportion of the experiments were designed to test this hypothesis; and in fact they supported it. In addition to motion-reversal VEPs, VEPs to the onset and the offset of pattern motion, and to the appearance and disappearance of patterns were recorded and analysed. The relationships between these different types of VEP were investigated. Also, the dependence of the motion-onset, -offset end -reversal VEPs on certain stimulus parameters was studied. Are motion-reversal VEPs produced by direction-selective mechanisms? That direction-selective mechanisms were at least partly responsible for the motion-reversal VEPs was confirmed, since an adapting stimulus moving in the same direction as the motion before reversal produced an effect on the VEP different to that produced by en adapting stimulus moving in the opposite direction. Further investigation indicated that direction-selective mechanisms were probably the sole contributors to the motion-reversal VEPs, since control experiments failed to support any of the most likely alternative ways in which direction-insensitive mechanisms might theoretically have contributed to the motion-reversal VEPs. In particular, considerable attention was devoted to the possibility that mechanisms sensitive to contrast but insensitive to direction of motion might have been activated by a brief increase in the effective contrast of the stimulus pattern at the moment of reversal, and thereby have contributed to the VEP. Such an increase in the effective contrast could in theory have been caused by the brief slowing down which inevitably occurred at the moment of reversal, but several experiments refuted this interpretation. In particular, the VEPs were virtually independent of the time taken for reversal, but were very dependent on the velocity before and after reversal, reducing almost to zero at very high or very low velocities. A sudden step-displacement or change of the pattern at the moment of reversal suppressed the VEP. This effect was not caused by interference with the time-course of slow movement at reversal, since suppression occurred even when the step-displacement took place outside the period of slow movement. A psychophysical effect has been observed which may be connected with this phenomenon. Involuntary eye movements ere apparent~ not implicated in the production of the VEPs, since periodic and aperiodic stimulation yield similar results. Certain other ways in which VEP components might have arisen, even in the absence of eye movements or imperfections in the stimulus motion, have been investigated; but there has been no indication of the occurrence of such components. So the motion-reversal VEPs probably arose almost entirely from direction-selective mechanisms. Component analysis of VEPs The VEPs to the reversal and to the offset of motion apparently comprised three separate component peaks. In this respect they were similar to pattern-appearance VEPs, and the distribution over the scalp of any one of the components was the same for all three kinds of VEP (e.g. the first peak of the motion-reversal VEP had the some scalp-distribution as the first peak of the motion-offset VEP and the first peak of the pattern-appearance VEP). This implied that the corresponding components originated in the same cortical areas, and a correlation analysis of the amplitudes of the various components of motion-reversal VEPs and pattern-appearance VEPs for different subjects supported this conclusion. Now there is convincing evidence (Jeffreys, 1971) that the first component of pattern-appearance VEPs originates in striate cortex end the later components in extrastriate cortex. It is therefore concluded that the first peaks of motion-reversal and. motion-offset VEPs are likewise probably from striate cortex, and the later peaks from extrastriate. The VEP to motion-onset was very different from the above VEPs, however, and appeared to be more closely related to the pattern-disappearance VEP. It is possible that the same mechanisms underlie these two kinds of VEP. Although motion-reversal VEPs appear to be the product of direction-selective mechanisms alone, it is far from certain that this is true of motion-onset and -offset VEPs. Nevertheless, there is evidence that the latter kinds of VEP may share generating mechanisms with the former; since the motion-reversal VEP was, under many conditions though not all, a good approximation to the sum of the motion-onset and -offset VEPs recorded under similar stimulus conditions. The effects of varying stimulus parameters Motion-reversal VEPs were found to be largely independent of brightness except at the lowest levels, but the latency did tend to increase slightly as the brightness was reduced. Despite the discovery (MaCKay & Rietveld, 1968) that the proximity of a stationary reference line enhances the VEP to the onset of motion of a stimulus line,' it appears that the sharp contours comprising the edge of the visual field did not influence the VEPs to the onset, offset or reversal of pattern motion, since replacing the sharp contours by blurred ones did not affect the VEPs. The onset, offset and reversal VEPs did not depend greatly on the direction of motion. Superimposing a steady motion did, however, markedly modify the VEPs. The effects of using patterns other than visual noise were investigated. Checkerboards and visual noise produced similar results, but line rasters produced very different VEPs

Development of an adaptive window-opening algorithm to predict the thermal comfort, energy use and overheating in buildings

This investigation of the window opening data from extensive field surveys in UK office buildings demonstrates: 1) how people control the indoor environment by opening windows; 2) the cooling potential of opening windows; and 3) the use of an ‘adaptive algorithm’ for predicting window opening behaviour for thermal simulation in ESP-r. It was found that when the window was open the mean indoor and outdoor temperatures were higher than when closed, but show that nonetheless there was a useful cooling effect from opening a window. The adaptive algorithm for window opening behaviour was then used in thermal simulation studies for some typical office designs. The thermal simulation results were in general agreement with the findings of the field surveys. The adaptive algorithm is shown to provide insights not available using non adaptive simulation methods and can assist in achieving more comfortable, lower energy buildings while avoiding overheating

Comfort driven adaptive window opening behaviour and the influence of building design

It is important to understand and model the behaviour of occupants in buildings and how this behaviour impacts energy use and comfort. It is similarly important to understand how a buildings design affects occupant comfort, occupant behaviour and ultimately the energy used in the operation of the building. In this work a behavioural algorithm for window opening developed from field survey data has been implemented in a dynamic simulation tool. The algorithm is in alignment with the proposed CEN standard for adaptive thermal comfort. The algorithm is first compared to the field study data then used to illustrate the impact of adaptive behaviour on summer indoor temperatures and heating energy. The simulation model is also used to illustrate the sensitivity of the occupant adaptive behaviour to building design parameters such as solar shading and thermal mass and the resulting impact on energy use and comfort. The results are compared to those from other approaches to model window opening behaviour. The adaptive algorithm is shown to provide insights not available using non adaptive simulation methods and can assist in achieving more comfortable and lower energy buildings

Nonlinear Optics Quantum Computing with Circuit-QED

One approach to quantum information processing is to use photons as quantum bits and rely on linear optical elements for most operations. However, some optical nonlinearity is necessary to enable universal quantum computing. Here, we suggest a circuit-QED approach to nonlinear optics quantum computing in the microwave regime, including a deterministic two-photon phase gate. Our specific example uses a hybrid quantum system comprising a LC resonator coupled to a superconducting flux qubit to implement a nonlinear coupling. Compared to the self-Kerr nonlinearity, we find that our approach has improved tolerance to noise in the qubit while maintaining fast operation.Comment: 5 pages, 3 figure