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Mixed-Member Electoral Systems
Mixed-member electoral systems may well be the electoral reform of the 21st century. In the view of many electoral reformers, mixed systems offer the best of both the traditional British single-seat district system and PR systems. This book seeks to evaluate: why these systems have recently appealed to many countries with diverse electoral historie.
eBook
Fast response of cold ice-rich permafrost in northeast Siberia to a warming climate
The ice- and organic-rich permafrost of the northeast Siberian Arctic lowlands (NESAL) has been projected to remain stable beyond 2100, even under pessimistic climate warming scenarios. However, the numerical models used for these projections lack processes which induce widespread landscape change termed thermokarst, precluding realistic simulation of permafrost thaw in such ice-rich terrain. Here, we consider thermokarst-inducing processes in a numerical model and show that substantial permafrost degradation, involving widespread landscape collapse, is projected for the NESAL under strong warming (RCP8.5), while thawing is moderated by stabilizing feedbacks under moderate warming (RCP4.5). We estimate that by 2100 thaw-affected carbon could be up to three-fold (twelve-fold) under RCP4.5 (RCP8.5), of what is projected if thermokarst-inducing processes are ignored. Our study provides progress towards robust assessments of the global permafrost carbon–climate feedback by Earth system models, and underlines the importance of mitigating climate change to limit its impacts on permafrost ecosystems.
Siberian Arctic permafrost contains vast stores of carbon, the fate of which is dependent on the climate. Here the authors use models of future scenarios to show that under the direst climate changes up to 2/3 of the stored organic carbon could thaw.
Journal Article
Detection of a Spinning Object Using Light's Orbital Angular Momentum
The linear Doppler shift is widely used to infer the velocity of approaching objects, but this shift does not detect rotation. By analyzing the orbital angular momentum of the light scattered from a spinning object, we observed a frequency shift proportional to product of the rotation frequency of the object and the orbital angular momentum of the light. This rotational frequency shift was still present when the angular momentum vector was parallel to the observation direction. The multiplicative enhancement of the frequency shift may have applications for the remote detection of rotating bodies in both terrestrial and astronomical settings.
Journal Article
HBR's 10 must reads on mental toughness
Our professional lives are full of challenges and setbacks, but those who achieve elite performance are able to consistently rally their emotional strength in the pursuit of their goals--no matter what gets thrown at them. If you read nothing else on mental toughness, read these ten articles by experts in the field. We've combed through hundreds of articles in the Harvard Business Review archive and selected the most important ones to help you build your emotional strength and resilience--and to achieve high performance. This book will inspire you to: Thrive on pressure like an Olympic athlete Manage and overcome negative emotions by acknowledging them Plan short-term goals to achieve long-term aspirations Surround yourself with the people who will push you the hardest Use challenges to become a better leader Use creativity to move past trauma Understand the tools your mind uses to recover from setbacks-- Provided by publisher.
Book
Direct observations of evolving subglacial drainage beneath the Greenland Ice Sheet
Simultaneous observations of moulins and boreholes in western Greenland show that water delivery to the base of the ice sheet via moulins affects short-term ice velocity fluctuations, but not late-season ice velocity decelerations.
Ice velocity response to subglacial pressure variation
Increased meltwater delivery to the base of the Greenland Ice Sheet will increase the ice sheet velocity, accelerating its inevitable rush towards the ocean and subsequent sea level rise. Or will it? Debate on this topic is at the forefront of cryospheric research, but has been hampered by the lack of simultaneous observations of hydraulic head in moulins, vertical shafts that deliver water to the base of the ice sheet, and boreholes, which monitor basal water pressure. Lauren Andrews and colleagues now provide these observations from a small region in western Greenland and reveal that water delivery by moulins into channelized basal flow is indeed linked to short-term fluctuations in ice velocity. Late season decelerations in ice velocity, however, seem to be controlled by changes in unchannelized flow, rather than any shifts in the moulin system.
Seasonal acceleration of the Greenland Ice Sheet is influenced by the dynamic response of the subglacial hydrologic system to variability in meltwater delivery to the bed
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via crevasses and moulins (vertical conduits connecting supraglacial water to the bed of the ice sheet). As the melt season progresses, the subglacial hydrologic system drains supraglacial meltwater more efficiently
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, decreasing basal water pressure
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and moderating the ice velocity response to surface melting
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. However, limited direct observations of subglacial water pressure
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mean that the spatiotemporal evolution of the subglacial hydrologic system remains poorly understood. Here we show that ice velocity is well correlated with moulin hydraulic head but is out of phase with that of nearby (0.3–2 kilometres away) boreholes, indicating that moulins connect to an efficient, channelized component of the subglacial hydrologic system, which exerts the primary control on diurnal and multi-day changes in ice velocity. Our simultaneous measurements of moulin and borehole hydraulic head and ice velocity in the Paakitsoq region of western Greenland show that decreasing trends in ice velocity during the latter part of the melt season cannot be explained by changes in the ability of moulin-connected channels to convey supraglacial melt. Instead, these observations suggest that decreasing late-season ice velocity may be caused by changes in connectivity in unchannelized regions of the subglacial hydrologic system. Understanding this spatiotemporal variability in subglacial pressures is increasingly important because melt-season dynamics affect ice velocity beyond the conclusion of the melt season
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Journal Article
Space-time wave packets localized in all dimensions
Optical wave packets that are localized in space and time, but nevertheless overcome diffraction and travel rigidly in free space, are a long sought-after field structure with applications ranging from microscopy and remote sensing, to nonlinear and quantum optics. However, synthesizing such wave packets requires introducing non-differentiable angular dispersion with high spectral precision in two transverse dimensions, a capability that has eluded optics to date. Here, we describe an experimental strategy capable of sculpting the spatio-temporal spectrum of a generic pulsed beam by introducing arbitrary radial chirp via two-dimensional conformal coordinate transformations of the spectrally resolved field. This procedure yields propagation-invariant ‘space-time’ wave packets localized in all dimensions, with tunable group velocity in the range from 0.7
c
to 1.8
c
in free space, and endowed with prescribed orbital angular momentum. By providing unprecedented flexibility in sculpting the three-dimensional structure of pulsed optical fields, our experimental strategy promises to be a versatile platform for the emerging enterprise of space-time optics.
Propagation-invariant wave packets confined in space and time can be useful for optical sensing, imaging, and nonlinear and quantum optics. Here the authors demonstrate control over the angular dispersion of optical wave packets in two-transverse dimensions to synthesize space-time wave packets localized in all dimensions.
Journal Article