Recent Advances in Our Understanding of the Role of Meltwater in the Greenland Ice Sheet System

Nienow, Sole and Cowton’s Greenland research has been supported by a number of UK NERC research grants (NER/O/S/2003/00620; NE/F021399/1; NE/H024964/1; NE/K015249/1; NE/K014609/1) and Slater has been supported by a NERC PhD studentshipPurpose of the review:  This review discusses the role that meltwater plays within the Greenland ice sheet system. The ice sheet’s hydrology is important because it affects mass balance through its impact on meltwater runoff processes and ice dynamics. The review considers recent advances in our understanding of the storage and routing of water through the supraglacial, englacial, and subglacial components of the system and their implications for the ice sheet Recent findings:   There have been dramatic increases in surface meltwater generation and runoff since the early 1990s, both due to increased air temperatures and decreasing surface albedo. Processes in the subglacial drainage system have similarities to valley glaciers and in a warming climate, the efficiency of meltwater routing to the ice sheet margin is likely to increase. The behaviour of the subglacial drainage system appears to limit the impact of increased surface melt on annual rates of ice motion, in sections of the ice sheet that terminate on land, while the large volumes of meltwater routed subglacially deliver significant volumes of sediment and nutrients to downstream ecosystems. Summary:  Considerable advances have been made recently in our understanding of Greenland ice sheet hydrology and its wider influences. Nevertheless, critical gaps persist both in our understanding of hydrology-dynamics coupling, notably at tidewater glaciers, and in runoff processes which ensure that projecting Greenland’s future mass balance remains challenging.Publisher PDFPeer reviewe

Overcoming systemic barriers preventing healthy urban development in the UK: Main findings from interviewing senior decision-makers during a 3-year planetary health pilot

This paper sets out the main findings from two rounds of interviews with senior representatives from the UK’s urban development industry: the third and final phase of a 3-year pilot, Moving Health Upstream in Urban Development’ (UPSTREAM). The project had two primary aims: firstly, to attempt to value economically the health cost-benefits associated with the quality of urban environments and, secondly, to interview those in control of urban development in the UK in order to reveal the potential barriers to, and opportunities for, the creation of healthy urban environments, including their views on the use of economic valuation of (planetary) health outcomes. Much is known about the ‘downstream’ impact of urban environments on human and planetary health and about how to design and plan healthy towns and cities (‘midstream’), but we understand relatively little about how health can be factored in at key governance tipping points further ‘upstream’, particularly within dominant private sector areas of control (e.g. land, finance, delivery) at sub-national level. Our findings suggest that both public and private sector appeared well aware of the major health challenges posed by poor-quality urban environments. Yet they also recognized that health is not factored adequately into the urban planning process, and there was considerable support for greater use of non-market economic valuation to help improve decision-making. There was no silver bullet however: 110 barriers and 76 opportunities were identified across a highly complex range of systems, actors and processes, including many possible points of targeted intervention for economic valuation. Eight main themes were identified as key areas for discussion and future focus. This findings paper is the second of two on this phase of the project: the first sets out the rationale, approach and methodological lessons learned

Thermodynamic Analysis of Air-compression Refrigerating Machine Based on the Exergy Cost Theory

On the basis of the exergy cost theory, a procedure has been developed for carrying out an in-depth thermodynamic analysis of air-compression refrigerating machines and thermal pumps taking into consideration nonequivalence of exergy losses in various links of thermotransformation process and their effect on consumption of exergy supplied to the system. A thermoeconomic model of a single-stage air-compression refrigerating machine was proposed which takes into consideration structural and topological features of the process scheme and interrelation between its elements. For an equivalent mapping of structural and topological features of the refrigerating machine scheme, a parametric flow graph was developed. The procedure uses a matrix form of recording exergy balances which is the most convenient for representation of the thermoeconomic models. In order to obtain reference operating mode of the refrigerating machine, the principle of thermodynamic process idealizing was used. Application of the structural theory of thermoeconomics has made it possible to establish the portion of endogenous and exogenous destruction of exergy in the elements of the refrigerating machine.Numerical implementation of the proposed procedure has made it possible to reveal influence of internal irreversibility in the cycle determined by non-isentropic compression processes in the compressor and expansion in the expander. A significant effect of efficiency of the expansion process in the expander on the exergy efficiency of the air-compression refrigerating machine was established.Influence of the change of ambient temperature on the character of consumption of exergy by each element of the refrigeration machine was estimated. It has been revealed that even a slight change of the ambient temperature significantly affects consumption of “fuel” by each element of the system, while the dependence is linear.Generalized dependences of exergy indicators on variable factors have been obtained which enabled finding of unfavorable operating conditions for equipment with increased energy consumption. It was established that the efficiency factor of the turboexpander has the greatest influence on the change of consumption of exergy of “fuel” in the system

Grounding Line Migration through the Calving Season at Jakobshavn Isbræ, Greenland, observed with Terrestrial Radar Interferometry

Ice velocity variations near the terminus of Jakobshavn Isbræ, Greenland, were observed with a terrestrial radar interferometer (TRI) during three summer campaigns in 2012, 2015, and 2016. We estimate a  ∼ 1km wide floating zone near the calving front in early summer of 2015 and 2016, where ice moves in phase with ocean tides. Digital elevation models (DEMs) generated by the TRI show that the glacier front here was much thinner (within 1km of the glacier front, average ice surface is  ∼ 100 and  ∼ 110m above local sea level in 2015 and 2016, respectively) than ice upstream (average ice surface is  \u3e 150m above local sea level at 2–3km to the glacier front in 2015 and 2016). However, in late summer 2012, there is no evidence of a floating ice tongue in the TRI observations. Average ice surface elevation near the glacier front was also higher,  ∼ 125m above local sea level within 1km of the glacier front. We hypothesize that during Jakobshavn Isbræ\u27s recent calving seasons the ice front advances  ∼ 3km from winter to spring, forming a  \u3e 1km long floating ice tongue. During the subsequent calving season in mid- and late summer, the glacier retreats by losing its floating portion through a sequence of calving events. By late summer, the entire glacier is likely grounded. In addition to ice velocity variation driven by tides, we also observed a velocity variation in the mélange and floating ice front that is non-parallel to long-term ice flow motion. This cross-flow-line signal is in phase with the first time derivative of tidal height and is likely associated with tidal currents or bed topography

Thermoeconomic Optimization of Supercritical Refrigeration System with the Refrigerant R744 (CO2)

We developed a thermoeconomic model of refrigeration plant that works by the supercritical CO2 cycle as refrigerating medium. The model is built for the plant of the “air – air” type and makes it possible at the optimization of design and the selection of economical operating modes to simultaneously consider both thermodynamic and economic parameters. Resulting expenses for the creation and operation of the system over the projected life cycle were accepted as objective function for analysis of the model. The minimum of resulting expenses corresponds to the optimum system characteristics while maintaining amount and quality of produced cold. Development of the model allowed us to represent objective function in the form of expanded analytical expressions, which consider interrelation between all optimizing parameters of the system.One of the benefits of the method consists in the fact that the obtained unique analytical solution in the form of a system of equations of partial derivatives from objective function of the resulting expenses is applicable for the thermoeconomic optimization of regime parameters of operation of any refrigeration system that works according to the examined scheme and with a similar type of equipment.Numerical solution of the thermoeconomic optimization problem of refrigeration plant of the “air – air” type (conditioner), with CO2 as refrigerant, that works in the supercritical region made it possible to find optimum parameters of the system, which provide for the conditions of reaching minimum level of the resulting expenses at different values of tariffs for electric power. We examined effect of the value of tariff for electric power on the character of optimization of the system.An application of this technique in practice should contribute to the reduction in financial costs for the creation and operation of conditioners that work on CO2, to an increase in their competitivness compared with traditional freon systems and contribute to the creation of conditions for their large-scale implementation in Ukraine

On the spectrum of moderated neutrons emitted by the isotropic source in the gas fuel

Analytical formula for the equation of the neutron scattering for isotropic neutron source, which includes the temperature of the moderating medium as the parameter, was first obtained in the given work in the framework of gas model of the medium. The obtained equation of the scattering is based on the solution of the kinematic problem of elastic scattering of neutron at the nucleus in “L”-system in general case, when before the scattering not only neutron but the nucleus also have the arbitrary velocity vector in “L”-system of coordinates. The neutron flux and moderating spectra depending on the media temperature were found for this new equation of the scattering. Obtained expression for the moderating neutron spectra allows the new interpretation of the processes, which determine neutron spectra in the thermal area

Parametric effects in the frictional interaction of a tool with a billet in the process of its treatment by pressure

Purpose. Justification of the influence of pulsating dynamic loads in the surface layers of parts obtained by plastic deformation methods on the quality of finished products during cold rolling, knurling, running in, drawing and stamping. Research methodology. A schematization was adopted in which the workpiece or part is an anisotropic medium elastically bonded along the surface of the junction of external reinforced layers with the internal mass of the part. On the basis of the proposed physical model, conditions were found under which under the action of cyclic surface loads, violations of the integrity of the appearance of fracturing and waviness of external fibers in the process of strengthening the treatment of semi-finished products and parts are possible. Findings. The obtained data allows us to establish the frequency characteristics of the process of unstable parametric oscillations caused by nonlinear friction between the forming element and the workpiece (part), which lead to a deterioration in the quality of finished products. In addition, for the steady-state operating modes of machines for cold metal forming, the dependence of the amplitudes of deformation waves, as functions of the maximum pulsations of the “periodic” components of surface forces, was obtained, and measures were proposed to reduce vibroactivity in the area of tool interaction with the workpiece and machine parts for cold processing. Originality. It consists in formulating and solving the second dynamic problem for the surface layers of the workpiece at the interface of the processed layers and the workpiece array. Depending on the occurring periodic forces for the surface layers, the conditions of steady and unstable operation of the shaping tool and the whole machine for metal forming by pressure, as a whole, are determined. Practical value of the work lies in the fact that safe modes of operation of metal forming machines have been identified, conditions for improving the design of machines for cold metal forming have been created, under which the possibility of occurrence of parametric oscillations, as well as the reduction of vibratory activity of machines for cold metal forming in minimized whole. Keywords: running in, knurling, drawing, plastic deformation, roller, tool, workpiece, the amplitude of oscillations, load, excitation coefficient, steady amplitude, deformation wave.</jats:p