NEC violation in mimetic cosmology revisited

In the context of Einstein gravity, if the null energy condition (NEC) is satisfied, the energy density in expanding space-times always decreases while in contracting space-times the energy density grows and the universe eventually collapses into a singularity. In particular, no non-singular bounce is possible. It is, though, an open question if this energy condition can be violated in a controlled way, i.e., without introducing pathologies, such as unstable negative-energy states or an imaginary speed of sound. In this paper, we will re-examine the claim that the recently proposed mimetic scenario can violate the NEC without pathologies. We show that mimetic cosmology is prone to gradient instabilities even in cases when the NEC is satisfied (except for trivial examples). Most interestingly, the source of the instability is always the Einstein-Hilbert term in the action. The matter stress-energy component does not contribute spatial gradient terms but instead makes the problematic curvature modes dynamical. We also show that mimetic cosmology can be understood as a singular limit of known, well-behaved theories involving higher-derivative kinetic terms and discuss ways of removing the instability.Comment: 7 page

Deterministic dynamics of stimulated Brillouin scattering in optical fibres

Abstract unavailable please refer to PD

Cardiovascular Magnetic Resonance Imaging for the Investigation of Patients with Coronary Heart Disease

Objectives To evaluate the role of stress perfusion cardiovascular magnetic resonance (CMR) in the investigation of stable coronary artery disease (CAD). Background Coronary artery disease remains the biggest cause of morbidity and mortality. The multi-parametric CMR examination is established as an investigative strategy for the investigation of CAD. Methods Study 1 & 2: Patients with stable coronary artery disease underwent a multi-parametric CMR protocol assessing 4 components: i) left ventricular function; ii) myocardial perfusion; iii) viability (late gadolinium enhancement (LGE)) and iv) coronary magnetic resonance angiography (MRA). The diagnostic accuracy of the individual components were assessed. The ischaemic burden of stress CMR Vs. Single Photon Emission Computed Tomography (SPECT) was determined. Study 3: Volunteers and patients were scanned with perfusion sequence which adapts the spatial resolution to the available scanning time and field-of-view. Study 4: A multi-centre pragmatic randomised controlled trial of patients with stable angina comparing CMR guided-care Vs. SPECT guided-care Vs. National Institute of Health and Care Excellence guided-care. Results Study 1 demonstrated the stress perfusion component of the multi-parametric CMR exam was the single most important component for overall diagnostic accuracy. However, the full combined multi-parametric protocol was the optimal approach for disease rule-out, and the LGE component best for rule-in. Study 2 showed that there was reasonable agreement of the summed stress scores between CMR and SPECT (a well established investigation with significant amounts of prognostic data). In study 3, a perfusion pulse sequence which automatically adapts the acquisition sequence to the available scanning time results in spatial resolution improvement and reduction in dark rim artefact. Finally in study 4 in patients with suspected angina using CMR as an initial investigative strategy produced a significantly lower probability of unnecessary angiography compared to NICE guidance. There were similar rates of CAD detection were comparable suggesting no penalty for using functional imaging as a gatekeeper for angiography. Conclusion CMR has high diagnostic accuracy for the detection of coronary artery disease; with similar detection of ischaemic burden to established tests and can be used safely and effectively as a gate keeper to invasive coronary angiography

Economic restructuring and technological change : resistance and control among inside workers and letter carriers at Canada Post Corporation, St. John's, Newfoundland

This thesis is a comparative study of the changing work experience and relations of two groups of Canadian postal employees in St. John's, Newfoundland. Two related factors are identified as underwriting these changes: technological based reorganization of work and the demand of a conservative state for a move to a private sector model of operations. The latter factor includes the requirement for a deficit free, and even profit-generating, operation at Canada Post Corporation and the divestment of public ownership. Underlying this empirical analysis is a theoretical interest in the labour process, technology and the managerial problem of control. -- I argue in this thesis that among inside postal workers, members of the Canadian Union of Postal Workers, technological change and the bureaucratic reorganization of work which has surrounded it has undermined their ability to resist management incursions on the shop floor. The subsequent shift in the frontier of control has enabled management to implement a number of productivity and efficiency measures, which from the workers' point of view, has had a major negative effect on their work experience and relations. Moreover, the recent move toward privatization and the generation of more flexible, casual labour further undermines the ability of workers to defend themselves. -- While inside workers have had a continuous history of conflict over the degradation of work through technological change, letter carriers have experienced a relatively stable, institutionalized relationship with management during the past 15 years. This relationship, in contrast to the inside workers', may be characterized as "consent" based. However, with growing pressure on management to solve the economic "crisis" at Canada Post, the status quo between letter carriers and management is eroding and an ultimately antagonistic set of interests is being revealed. -- The data from this comparative study lead to the conclusion that recent interest in the notion of consent within the labour process literature has definite theoretical and empirical limits which become apparent in examining production relations in periods of economic instability. On the other hand, the question of control of labour and technologicl change cannot be addressed in formulistic, determinist fashion. Rather, the unique organizational and historical characteristics of "each" labour process must be understood in its own context

Force plate-derived countermovement jump normative data and benchmarks for professional Rugby League players

The countermovement jump (CMJ) is an important test in rugby league (RL), and the force plate is the recommended assessment device, as it permits the calculation of several variables that explain jump strategy, alongside jump height. The purpose of this study was to produce normative CMJ data and objective benchmarks for professional RL forwards and backs. Normative data for jump height, modified reactive strength index, and jump momentum are provided for 121 professional RL players (66 forwards and 55 backs) who completed CMJ testing on a portable force plate during preseason training. Standardized T-scores (scaled from 0 to 100) were calculated from the respective positional group mean and standard deviation to create CMJ performance bands that were combined with a qualitative description (ranging from extremely poor to excellent) and a traffic light system to facilitate data interpretation and objective benchmark setting by RL practitioners. The jump height and modified reactive strength index benchmarks were larger for the lighter backs, whereas the jump momentum benchmarks were larger for the heavier forwards. The presented novel approach to compiling and presenting normative data and objective benchmarks may also be applied to other data (i.e., from other tests or devices) and populations

EFFECT OF THE NORDIC HAMSTRING EXERCISE ABILITY ON IN-VIVO FASCICLE DYNAMICS DURING VARIATIONS OF THE NORDIC HAMSTRING EXERCISE.

The purpose of this study was to determine if the ability to perform the Nordic hamstring exercise (NHE) impacts upon the fascicle dynamics of the bicep femoris long head during the NHE performed flat, declined and inclined. 10 physically active individuals (8 males and 2 females, age 24.1±3.9 years, body mass 81.8±8.9kg, height 178.8±7.7cm) with a history of performing the NHE, were separated into two equal groups of high and low performers of the NHE via break point angle assessed using 3D motion capture. Dynamic ultrasound (US) videos were collected using a 10cm probe, while semi-automatic software analysed the dynamic US videos. Fascicle lengthening during the NHE is dependent on NHE performance ability, with likely differences (non- overlapping control limits) between high and low performers. While absolute fascicle change was greater in the incline NHE for low performers, greater FL change was observed in the flat NHE for high performers. This could be as a result of the high performers possessing greater resting fascicle length and eccentric hamstring strength

Power and the Production of Science. Assessing Cod Stocks as the Mechanistic Fishery Collapses

This paper discusses power relations in the production of knowledge claims and the validation of management strategies. The experience of doing stock assessment science and creating management plans for Canada’s east coast cod fishery illustrates this general process. We demonstrate that the cyborgization of fisheries-management is limited by its inability to produce power for stabilizing the relations between managers, fishers, technology and fish. Lack of stability forces scientists and managers either to ignore a threat or to intervene by changing their strategy. Consensus is unlikely. Scientists and managers must reconsider reasons for action or lack of it, thus producing a new rationality. Managers attempt to control that reconstruction process in the interests of resolving shortterm challenges. Some scientists resist change and protect their earlier positions against new evidence or re-interpretations. The winning rationality has more to do with the power of the claimant than with the quality of reasoning