Results 1 - 10 of 1067
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[en] We evaluate the ability of process based models to reproduce observed global mean sea-level change. When the models are forced by changes in natural and anthropogenic radiative forcing of the climate system and anthropogenic changes in land-water storage, the average of the modelled sea-level change for the periods 1900–2010, 1961–2010 and 1990–2010 is about 80%, 85% and 90% of the observed rise. The modelled rate of rise is over 1 mm yr−1 prior to 1950, decreases to less than 0.5 mm yr−1 in the 1960s, and increases to 3 mm yr−1 by 2000. When observed regional climate changes are used to drive a glacier model and an allowance is included for an ongoing adjustment of the ice sheets, the modelled sea-level rise is about 2 mm yr−1 prior to 1950, similar to the observations. The model results encompass the observed rise and the model average is within 20% of the observations, about 10% when the observed ice sheet contributions since 1993 are added, increasing confidence in future projections for the 21st century. The increased rate of rise since 1990 is not part of a natural cycle but a direct response to increased radiative forcing (both anthropogenic and natural), which will continue to grow with ongoing greenhouse gas emissions. (letter)
[en] We study Lorentz-violating models of massive gravity which preserve rotations and are invariant under time-dependent shifts of the spatial coordinates. In the linear approximation the Newtonian potential in these models has an extra confining term proportional to the distance from the source. We argue that during cosmological expansion the Universe may be driven to an attractor point with larger symmetry which includes particular simultaneous dilatations of time and space coordinates. The confining term in the potential vanishes as one approaches the attractor. In the vicinity of the attractor the extra contribution is present in the Friedmann equation which, in a certain range of parameters, gives rise to the cosmic acceleration
[en] Terahertz (THz) radiation generation by nonlinear mixing of lasers, obliquely incident on a plasma slab is investigated. Two cases are considered: (i) electron density profile is parabolic but density peak is below the critical density corresponding to the beat frequency, (ii) plasma boundaries are sharp and density is uniform. In both cases, nonlinearity arises through the ponderomotive force that gives rise to electron drift at the beat frequency. In the case of inhomogeneous plasma, non zero curl of the nonlinear current density gives rise to electromagnetic THz generation. In case of uniform plasma, the sharp density variation at the plasma boundaries leads to radiation generation. In a slab width of less than a terahertz wavelength, plasma density one fourth of terahertz critical density, laser intensities ∼1017 W/cm2 at 1 μm, one obtains the THz intensity ∼1 GW/cm2 at 3 THz radiation frequency
[en] We present a publicly-available toolkit of flight-proven hardware and software to retrieve 5 TB of data or small physical samples from a stratospheric balloon platform. Before launch, a capsule is attached to the balloon, and rises with it. Upon remote command, the capsule is released and descends via parachute, continuously transmitting its location. Software to predict the trajectory can be used to select a safe but accessible landing site. We dropped two such capsules from the SUPERBIT telescope, in September 2019. The capsules took 37 minutes to descend from 30 km altitude. They drifted 32 km and 19 km horizontally, but landed within 300 m and 600 m of their predicted landing sites. We found them easily, and successfully recovered the data. We welcome interest from other balloon teams for whom the technology would be useful.
[en] Vortices exist in wedge-shaped corners in Stokes flow. In seeking an analogous eigensolution structure in three dimensions, an analytic construction is derived for a rectangular corner. This restriction mirrors the only corner type for which computed streamlines are available for comparison and explanation. The dominant eigenvalue is complex, giving rise to localized eddies. Hence trapped fluid is predicted near the corner. (paper)
[en] Highlights: • Conducts in-depth interviews with 35 climate adaptation actors in Caribbean islands. • Most are aware of the global temperature limits but pessimistic about their achievement. • Global temperature targets must be translated into local adaptation project designs. • Varied understanding of top-down, donor-driven resilience & transformation concepts. • Critical to have common understanding of resilience & transformation across actors. - Abstract: The 2015 Paris Climate Agreement signifies the commitment of the international community to limit global temperature rise to 2°C above pre-industrial levels and further to 1.5°C. To prepare for increasing temperatures, climate adaptation actors are prioritizing climate resilience- and transformation-based activities. There is, however, limited understanding of actors’ knowledge of and attitudes and practices towards these global temperature targets and concepts. Using the case of Caribbean small island developing states, we qualitatively analyze in-depth interviews with 35 climate change donors and project implementers. We find that most actors are aware of the 2°C and 1.5°C targets but that all are pessimistic about their achievement. Project implementers do not have a clear way to incorporate these targets into their adaptation projects. We also find that there is no uniform understanding of ‘resilience’ and ‘transformation’, though actors commonly define ‘resilience’ as the ability to ‘bounce back’ from extreme events and note ‘transformation’ as requiring the disruption of current socio-economic and political systems. Actors are further pessimistic about achieving resilience goals within short programming and funding cycles. Our study highlights the need for the global temperature targets to be urgently translated into the design and implementation of adaptation projects. We also highlight that the concepts of resilience and transformation are top-down and donor-driven, and that there is a need for donors to facilitate the creation of a shared vision of these concepts across all stakeholders.
[en] The paper introduces the principle of using the streak camera to measure the longitudinal distribution of the macro pulse derived by the pulse stacking method. The hardware configuration of the measurement system and the principle of pulse stacking are presented, and the software measurement procedure and user interface are described. The measurement results show that, when the FWHM of the original pulse is 3.82 ps, the FWHM of the stacked macro pulse is 15.3 ps; the plat-top width of the stacked macro pulse is 11.5 ps, and both the rise edge and the fall edge are 1.9 ps. (authors)
[en] In situ solution mining of uranium technology faces uncertainties in policy and regulatory practices. The major environmental laws which are applicable are briefly outlined. The key issue for uranium solution mining is groundwater protection. Its regulation is considered. Also discussed are the evolving regulatory policies for waste disposal and surface reclamation
[en] We employ techniques from optimal transport in order to prove the decay of transfer operators associated with iterated functions systems and expanding maps, giving rise to a new proof without requiring a Doeblin–Fortet (or Lasota–Yorke) inequality.Our main result is the following. Suppose T is an expanding transformation acting on a compact metric space M and a given fixed Hölder function, and denote by the Ruelle operator associated with A. We show that if is normalized (i.e. if ), then the dual transfer operator is an exponential contraction on the set of probability measures on M with the 1-Wasserstein metric.Our approach is flexible and extends to a relatively general setting, which we name Iterated Contraction Systems. We also derive from our main result several dynamical consequences; for example we show that Gibbs measures depends in a Lipschitz-continuous way on variations of the potential. (paper)
[en] Self-organization by bacterial cells often leads to the formation of a highly complex spatially-structured biofilm. In such a bacterial biofilm, cells adhere to each other and are embedded in a self-produced extracellular matrix (ECM). Bacillus substilis bacteria utilize localized cell-death patterns which focuses mechanical forces to form wrinkled sheet-like structures in three dimensions. A most intriguing feature underlying this biofilm formation is that vertical buckling and ridge location is biased to occur in region of high cell-death. Here we present a spatially extended model to investigate the role of the bacterial secreted ECM during the biofilm formation and the self-organization of cell-death. Using this reaction-diffusion model we show that the interaction between the cell's motion and the ECM concentration gives rise to a self-trapping instability, leading to variety of cell-death patterns. The resultant spot patterns generated by our model are shown to be in semi-quantitative agreement with recent experimental observation. (paper)