Twisted Laguerre-Gaussian lasers, with orbital angular momentum and characterized by doughnut-shaped intensity profiles, provide a transformative set of tools and research directions in a growing ...range of fields and applications, from super-resolution microcopy and ultra-fast optical communications to quantum computing and astrophysics. The impact of twisted light is widening as recent numerical calculations provided solutions to long-standing challenges in plasma-based acceleration by allowing for high-gradient positron acceleration. The production of ultra-high-intensity twisted laser pulses could then also have a broad influence on relativistic laser-matter interactions. Here we show theoretically and with ab initio three-dimensional particle-in-cell simulations that stimulated Raman backscattering can generate and amplify twisted lasers to petawatt intensities in plasmas. This work may open new research directions in nonlinear optics and high-energy-density science, compact plasma-based accelerators and light sources.
Pectin Conformation in Solution Alba, K; Bingham, R J; Gunning, P A ...
The journal of physical chemistry. B,
07/2018, Letnik:
122, Številka:
29
Journal Article
Recenzirano
Odprti dostop
The interplay of degree of methylesterification (DM), pH, temperature, and concentration on the macromolecular interactions of pectin in solution has been explored. Small-angle X-ray scattering ...complemented by atomic force microscopy and molecular dynamics was employed to probe chain dimensions and solution structure. Two length scales have been observed with the first level of structure characterising chain clusters with sizes ranging between 100-200 nm. The second level of structure arises from single biopolymer chains with a radius of gyration between ∼6 and 42 nm. The development of a range of macromolecular dimensions in vitro and in silico shows that the chain flexibility increases with DM and at acidic pH, whereas hydrogen bonding is the responsible thermodynamic driving force for cluster formation. High methyl pectins create structures of lower fractal dimension with less efficient packing. This work unveils pectin conformations covering most of its industrially and biologically relevant environments, enabling rational design of advanced biomaterials based on pectin.
Detecting thermal Unruh radiation from accelerated electrons has presented a formidable challenge due not only to technical difficulties but also for lack of conceptual clarity about what is actually ...seen by a laboratory observer. We give a summary of the current interpretations along with a simpler heuristic description that draws on the analogy between the Unruh effect and radiation from a two-level atomic system. We propose an experiment to test whether there is emission of thermal photons from an accelerated electron.
Interannual variations associated with El Niño‐Southern Oscillation can alter the surface‐pressure distribution and moisture transport over Antarctica, potentially affecting the contribution of the ...Antarctic ice sheet to sea level. Here, we combine satellite gravimetry with auxiliary atmospheric data sets to investigate interannual ice‐mass changes during the extreme 2015–2016 El Niño. Enhanced precipitation during this event contributed positively to the mass of the Antarctic Peninsula and West Antarctic ice sheets, with the mass gain on the peninsula being unprecedented within GRACE's observational record. Over the coastal basins of East Antarctica, the precipitation‐driven mass loss observed in recent years was arrested, with pronounced accumulation over Terre Adélie dominating this response. Little change was observed over Central Antarctica where, after a brief pause, enhanced mass‐loss due to weakened precipitation continued. Overall, precipitation changes over this period were sufficient to temporarily offset Antarctica's usual (approximately 0.4 mm yr−1) contribution to global mean sea level rise.
Plain Language Summary
Given that the Antarctic Ice Sheet has the potential to raise sea level by over 50 m if completely melted, it is crucial that we fully understand the factors controlling its stability. Presently, changes in rates of mass loss and mass gain over the ice sheet vary from short (seasonal/interannual) to long (decadal) timescales. Previous research has shown that one potential factor influencing Antarctica on interannual timescales is the El Niño‐Southern Oscillation, a large‐scale interaction between the Pacific Ocean and the overlying atmosphere that fluctuates between warm (El Niño) and cold (La Niña) states every 2–7 years. Here, we show an unprecedented increase in accumulation over the Antarctic Peninsula and West Antarctic sectors during the extreme 2015–2016 El Niño, along with a brief stabilization in mass loss over East Antarctica. Overall, precipitation changes during this event were sufficient to temporarily offset Antarctica's usual (approximately 0.4 mm yr−1) contribution to global mean sea level rise.
Key Points
Precipitation‐derived mass anomalies are estimated for the Antarctic Ice Sheet over the GRACE period
An unprecedented increase in accumulation over the Antarctic Peninsula and West Antarctica coincides with the extreme 2015–2016 El Niño
This was sufficient to temporarily offset Antarctica's usual (≈0.4 mm yr−1) contribution to global mean sea level rise
In the open ocean, sea level variability is primarily steric in origin. Steric sea level is given by the depth integral of the density field, raising the question of how tide gauges, which are ...situated in very shallow water, feel deep ocean variability. Here this question is examined in a high‐resolution global ocean model. By considering a series of assumptions we show that if we wish to reconstruct coastal sea level using only local density information, then the best assumption we can make is one of no horizontal pressure gradient, and therefore no geostrophic flow, at the seafloor. Coastal sea level can then be determined using density at the ocean's floor. When attempting to discriminate between mass and volume components of sea level measured by tide gauges, the conventional approach is to take steric height at deep‐ocean sites close to the tide gauges as an estimate of the steric component. We find that with steric height computed at 3000 m this approach only works well in the equatorial band of the Atlantic and Pacific eastern boundaries. In most cases the steric correction can be improved by calculating steric height closer to shore, with the best results obtained in the depth range 500–1000 m. Yet, for western boundaries, large discrepancies remain. Our results therefore suggest that on time scales up to about 5 years, and perhaps longer, the presence of boundary currents means that the conventional steric correction to tide gauges may not be valid in many places.
Key Points
Topography modifies the relationship between steric and total sea level
This allows deep ocean steric variability to be observed at tide gauges
How best to estimate the steric tide gauge signal depends on local dynamics
Summary
Blood transfusion can be life‐saving. Anaesthetists regularly request and administer blood components to their patients. All anaesthetists must be familiar with indications and appropriate ...use of blood and blood components and their alternatives, but close liaison with haematology specialists and their local blood sciences laboratory is encouraged. Considerable changes in approaches to optimal use of blood components, together with the use of alternative products, have become apparent over the past decade, leading to a need to update previous guidelines and adapt them for the use of anaesthetists working throughout the hospital system.
The flagship congress of the European Federation of Corrosion (EFC), EUROCORR 2019, was held under the theme of ‘New Times, New Materials, New Corrosion Challenges’ at the Barcelo Sevilla ...Renacimiento, Seville, Spain, from 9 to 13 September. This major corrosion event will be reviewed in four parts over four issues, with the present instalment summarising the various coatings-related technical sessions (Organic, Inorganic, Self-healing/smart and Metallic coatings, Pre-treatments, Polymers in organic coatings and Advanced materials), along with the technical sessions on CO2 corrosion in industrial applications, Corrosion control in aerospace, Corrosion in concrete and cathodic protection, Corrosion of steel in concrete and Marine corrosion.
X-ray1, 2, 3 and radio4, 5, 6 observations of the supernova remnant Cassiopeia A reveal the presence of magnetic fields about 100 times stronger than those in the surrounding interstellar medium. ...Field coincident with the outer shock probably arises through a nonlinear feedback process involving cosmic rays2, 7, 8. The origin of the large magnetic field in the interior of the remnant is less clear but it is presumably stretched and amplified by turbulent motions. Turbulence may be generated by hydrodynamic instability at the contact discontinuity between the supernova ejecta and the circumstellar gas9. However, optical observations of Cassiopeia A indicate that the ejecta are interacting with a highly inhomogeneous, dense circumstellar cloud bank formed before the supernova explosion10, 11, 12. Here we investigate the possibility that turbulent amplification is induced when the outer shock overtakes dense clumps in the ambient medium13, 14, 15. We report laboratory experiments that indicate the magnetic field is amplified when the shock interacts with a plastic grid. We show that our experimental results can explain the observed synchrotron emission in the interior of the remnant. The experiment also provides a laboratory example of magnetic field amplification by turbulence in plasmas, a physical process thought to occur in many astrophysical phenomena.
The GOCE satellite mission was launched in 2009 and the first gravity models were released in July 2010. Here we present an initial assessment of the GOCE data in terms of the mean circulation of the ...North Atlantic. We show that with just two months of data, the estimated circulation from GOCE is already superior to a similar estimate based on 8 years of GRACE observations. This result primarily depends on the fact that the GOCE mean dynamic topography (MDT) is generally less noisy than that obtained from the GRACE data. It therefore requires less smoothing and so there is less attenuation of the oceanographic signal. Our results provide a strong validation of the GOCE mission concept, and we anticipate further substantial improvements as the mission progresses.
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