Position Measurements Obeying Momentum Conservation

We present a hitherto unknown fundamental limitation to a basic measurement: that of the position of a quantum object when the total momentum of the object and apparatus is conserved. This result extends the famous Wigner-Araki-Yanase (WAY) theorem, and shows that accurate position measurements are only practically feasible if there is a large momentum uncertainty in the apparatus

Approximating relational observables by absolute quantities : a quantum accuracy-size trade-off

The notion that any physical quantity is defined and measured relative to a reference frame is traditionally not explicitly reflected in the theoretical description of physical experiments where, instead, the relevant observables are typically represented as 'absolute' quantities. However, the emergence of the resource theory of quantum reference frames as a new branch of quantum information science in recent years has highlighted the need to identify the physical conditions under which a quantum system can serve as a good reference. Here we investigate the conditions under which, in quantum theory, an account in terms of absolute quantities can provide a good approximation of relative quantities. We find that this requires the reference system to be large in a suitable sense

Cretaceous gnetalean yields first preserved plant gum

Some liquid plant exudates (e.g. resin) can be found preserved in the fossil record. However, due to their high solubility, gums have been assumed to dissolve before fossilisation. The visual appearance of gums (water-soluble polysaccharides) is so similar to other plant exudates, particularly resin, that chemical testing is essential to differentiate them. Remarkably, Welwitschiophyllum leaves from Early Cretaceous, Brazil provide the first chemical confirmation of a preserved gum. This is despite the leaves being exposed to water twice during formation and subsequent weathering of the Crato Formation. The Welwitschiophyllum plant shares the presence of gum ducts inside leaves with its presumed extant relative the gnetalean Welwitschia. This fossil gum presents a chemical signature remarkably similar to the gum in extant Welwitschia and is distinct from those of fossil resins. We show for the first time that a water-soluble plant exudate has been preserved in the fossil record, potentially allowing us to recognise further biomolecules thought to be lost during the fossilisation process

Developing new approaches to measuring NHS outputs and productivity

The Centre for Health Economics and National Institute of Economic and Social Research have recently completed a project funded by the Department of Health to improve measurement of the productivity of the NHS. The researchers have suggested better ways of measuring both outputs and inputs to improve estimates of productivity growth. Past estimates of NHS output growth have not taken account of changes in quality. The CHE/NIESR team conclude that the routine collection of health outcome data on patients is vital to measure NHS quality. They also propose making better use of existing data to quality adjust output indices to capture improvements in hospital survival rates and reductions in waiting times. With these limited adjustments the team estimate that annual NHS output growth averaged 3.79% between 1998/99 and 2003/04.The research team has also developed improved ways of measuring NHS inputs, particularly by drawing on better information about how many people are employed in the NHS and by recognising that staff are becoming increasingly better qualified. There have been substantial increases in staffing levels, pharmaceutical use and investment in equipment and buildings since 1998/99. The net effect of this growth in both outputs and inputs is that, according to the research team’s estimates, NHS productivity declined by about 1.59% a year since 1998/99. This is not out of line with estimates of growth rates in other UK and US service sectors, including insurance and business services. Nor is it surprising that recent years have seen negative growth in the NHS. There are at least two reasons. First, there has been an unprecedented increase in NHS expenditure. The NHS has had to employ more staff to meet the requirements of the European Working Time Directive and hospital consultants and general practitioners, in particular, have benefited from new pay awards.Second, the NHS collects very little information about what actually happens to patients as a result of their contact with the health service. Until there is routine collection of health outcomes data, measurement of the quality of NHS output will remain partial and productivity growth is likely to be underestimated.

Deep uncertainty, public reason, the conservation of biodiversity and the regulation of markets for lion skeletons

Public reason is a formal concept in political theory. There is a need to better understand how public reason might be elicited in making public decisions that involve deep uncertainty, which arises from pernicious and gross ignorance about how a system works, the boundaries of a system, and the relative value (or disvalue) of various possible outcomes. This article is the third in a series to demonstrate how ethical argument analysis—a qualitative decision-making aid—may be used to elicit public reason in the presence of deep uncertainty. The first article demonstrated how argument analysis is capable of probing deep into a single argument. The second article demonstrated how argument analysis can analyze a broad set of arguments and how argument analysis can be operationalized for use as a decision-making aid. This article demonstrates (i) the relevance of argument analysis to public reasoning, (ii) the relevance of argument analysis for decision-making under deep uncertainty, an emerging direction in decision theory, and (iii) how deep uncertainty can arise when the boundary between facts and values is inescapably entangled. This article and the previous two make these demonstrations using, as an example, the conservation and sustainable use of lions

Investigation of cycling-induced microstructural degradation in silicon-based electrodes in lithium-ion batteries using X-ray nanotomography

The microstructural degradation of a composite silicon electrode at different stages in its cycle life was investigated in 3D using X-ray nano-computed tomography. A reconstructed volume of 36 μm × 27 μm × 26 μm from the composite electrode was imaged in its pristine state and after 1, 10 and 100 cycles. Particle fracturing and phase transformation was observed within the electrode with increased cycling. In addition, a distinct, lower X-ray attenuating phase was clearly resolved, which can be associated with surface film formation resulting from electrolyte breakdown and with silicon particle phase transformation. Changes in quantified microstructural properties such as phase volume fraction and particle specific surface area were tracked. Electrode performance loss is associated with loss of active silicon. These imaging results further highlight the capability of high resolution X-ray tomography to investigate the role of electrode microstructure in battery degradation and failure

Total and tropospheric ozone changes: observations and numerical modelling

A survey has been made of total and tropospheric ozone dynamics in the context of its impacts on climate, human health and ecosystems. Observation data on total ozone content (TOZ) in the atmosphere and relevant numerical modelling results have been discussed as well as similar information for tropospheric ozone, whose formation and changes are being determined by quite different causes. A necessity has been emphasized to get more adequate global observational data on TOZ and tropospheric ozone (this is especially important in the latter case, because information on tropospheric ozone is far from being complete). Unsolved problems relevant to both total and tropospheric ozone have been briefly considered

Porous metal–organic frameworks for enhanced performance silicon anodes in lithium-ion batteries

Maintaining the physical integrity of electrode microstructures in Li-ion batteries is critical to significantly extend their cycle life. This is especially important for high-capacity anode materials such as silicon, whose operational volume expansion exerts huge internal stress within the anode, resulting in electrode destruction and capacity fade. In this study, we demonstrate that by incorporating metal–organic frameworks (MOFs) with carboxylate organic linkers into Si-based anodes, a stable and flexible pore network is generated to maximize and maintain Li-ion flux throughout the electrode’s architecture. We show that the zirconium carboxylate MOF UiO-67 is a versatile comaterial to boost performance and mitigate the rate of anode degradation that presently limits the lifetime of Si anodes. The cage-like pores in UiO-67 and flexural properties of the 4,4′-biphenyldicarboxylate organic linker are proposed to create robust “ionophores” in the anode film to enhance longer term durability and performance

An AMR Study of the Common Envelope Phase of Binary Evolution

The hydrodynamic evolution of the common envelope phase of a low mass binary composed of a 1.05 Msun red giant and a 0.6 Msun companion has been followed for five orbits of the system using a high resolution method in three spatial dimensions. During the rapid inspiral phase, the interaction of the companion with the red giant's extended atmosphere causes about 25% of the common envelope to be ejected from the system, with mass continuing to be lost at the end of the simulation at a rate ~ 2 Msun/yr. In the process the resulting loss of angular momentum and energy reduces the orbital separation by a factor of seven. After this inspiral phase the eccentricity of the orbit rapidly decreases with time. The gravitational drag dominates hydrodynamic drag at all times in the evolution, and the commonly-used Bondi-Hoyle-Lyttleton prescription for estimating the accretion rate onto the companion significantly overestimates the true rate. On scales comparable to the orbital separation, the gas flow in the orbital plane in the vicinity of the two cores is subsonic with the gas nearly corotating with the red giant core and circulating about the red giant companion. On larger scales, 90% of the outflow is contained within 30 degrees of the orbital plane, and the spiral shocks in this material leave an imprint on the density and velocity structure. Of the energy released by the inspiral of the cores, only about 25% goes toward ejection of the envelope.Comment: 18 pages, 11 figures, submitted to ApJ; accepted versio

Synthesis of layered silicon-graphene hetero-structures by wet jet milling for high capacity anodes in Li-ion batteries

While silicon-based negative electrode materials have been extensively studied, to develop high capacity lithium-ion batteries, implementing a large-scale production method that can be easily transferred to industy, has been a crucial challenge. Here, a scalable wet-jet milling method was developed to prepare a silicon-graphene hybrid material to be used as negative electrode in lithium-ion batteries. This synthesized composite, when used as an anode in lithium cells, demonstrated high Li ion storage capacity, long cycling stability and high-rate capability. In particular, the electrode exhibited a reversible discharge capacity exceeding 1763 mAh g-1 after 450 cycles with a capacity retention of 98% and a coulombic efficiency of 99.85% (with a current density of 358 mA g-1). This significantly supersedes the performance of a Si-dominant electrode structures. The capacity fade rate after 450 cycles was only 0.005% per cycle in the 0.05-1 V range. This superior electrochemical performance is ascribed to the highly layered, silicon-graphene porous structure, as investigated via focused ion beam in conjunction with scanning electron microscopy (FIB-SEM) tomography. The hybrid electrode could retain 89% of its porosity (under a current density of 358 mA g-1) after 200 cycles compared with only 35% in a Si-dominant electrode. Moreover, this morphology can not only accommodate the large volume strains from active silicon particles, but also maintains robust electrical connectivity. This confers faster transportation of electrons and ions with significant permeation of electrolyte within the electrode. Physicochemical characterisations were performed to further correlate the electrochemical performance with the microstructural dynamics. The excellent performance of the hybrid material along with the scalability of the synthesizing process is a step forward to realize high capacity/energy density lithium-ion batteries for multiple device applications