Controlled beat-wave Brillouin scattering in the ionosphere.

Stimulated Brillouin scattering experiments in the ionospheric plasma using a single electromagnetic pump wave have previously been observed to generate an electromagnetic sideband wave, emitted by the plasma, together with an ion- acoustic wave. Here we report results of a controlled, pump and probe beat-wave driven Brillouin scattering experiment, in which an ion-acoustic wave generated by the beating of electromagnetic pump and probe waves, results in electromagnetic sideband waves that are recorded on the ground. The experiment used the EISCAT facility in northern Norway, which has several high power electromagnetic wave transmitters and receivers in the radio frequency range. An electromagnetic pump consisting of large amplitude radio waves with ordinary (O) or extraordinary (X) mode polarization was injected into the overhead ionosphere, along with a less powerful probe wave, and radio sideband emissions observed on the ground clearly show stimulated Brillouin emissions at frequencies agreeing with, and changing with, the pump and probe frequencies. The experiment was simulated using a numerical full-scale model which clearly supports the interpretation of the experimental results. Such controlled beat-wave experiments demonstrate a way of remotely investigating the ionospheric plasma parameters.

Comparing antiviral strategies against COVID-19 via multiscale within-host modelling.

Within-host models of COVID-19 infection dynamics enable the merits of different forms of antiviral therapy to be assessed in individual patients. A stochastic agent-based model of COVID-19 intracellular dynamics is introduced here, that incorporates essential steps of the viral life cycle targeted by treatment options. Integration of model predictions with an intercellular ODE model of within-host infection dynamics, fitted to patient data, generates a generic profile of disease progression in patients that have recovered in the absence of treatment. This is contrasted with the profiles obtained after variation of model parameters pertinent to the immune response, such as effector cell and antibody proliferation rates, mimicking disease progression in immunocompromised patients. These profiles are then compared with disease progression in the presence of antiviral and convalescent plasma therapy against COVID-19 infections. The model reveals that using both therapies in combination can be very effective in reducing the length of infection, but these synergistic effects decline with a delayed treatment start. Conversely, early treatment with either therapy alone can actually increase the duration of infection, with infectious virions still present after the decline of other markers of infection. This suggests that usage of these treatments should remain carefully controlled in a clinical environment.

Guideline on the peri-operative management of patients with sickle cell disease: Guideline from the Association of Anaesthetists.

Sickle cell disease is a multisystem disease characterised by chronic haemolytic anaemia, painful vaso-occlusive crises and acute and chronic end-organ damage. It is one of the most common serious inherited single gene conditions worldwide and has a major impact on the health of affected individuals. Peri-operative complications are higher in patients with sickle cell disease compared with the general population and may be sickle or non-sickle-related. Complications may be reduced by meticulous peri-operative care and transfusion, but unnecessary transfusion should be avoided, particularly to reduce the risk of allo-immunisation. Planned surgery and anaesthesia for patients with sickle cell disease should ideally be undertaken in centres with experience in caring for these patients. In an emergency, advice should be sought from specialists with experience in sickle cell disease through the haemoglobinopathy network arrangements. Emerging data suggest that patients with sickle cell disease are at increased risk of COVID-19 infection but may have a relatively mild clinical course. Outcomes are determined by pre-existing comorbidities, as for the general population.

Collisionless shock acceleration in the corona of an inertial confinement fusion pellet with possible application to ion fast ignition.

Two-dimensional particle-in-cell simulations are used to explore collisionless shock acceleration in the corona plasma surrounding the compressed core of an inertial confinement fusion pellet. We show that an intense laser pulse interacting with the long scale-length plasma corona is able to launch a collisionless shock around the critical density. The nonlinear wave travels up-ramp through the plasma reflecting and accelerating the background ions. Our results suggest that protons with characteristics suitable for ion fast ignition may be achieved in this way. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

Preparations for a European R&D roadmap for an inertial fusion demo reactor.

A European consortium of 15 laboratories across nine nations have worked together under the EUROFusion Enabling Research grants for the past decade with three principle objectives. These are: (a) investigating obstacles to ignition on megaJoule-class laser facilities; (b) investigating novel alternative approaches to ignition, including basic studies for fast ignition (both electron and ion-driven), auxiliary heating, shock ignition, etc.; and (c) developing technologies that will be required in the future for a fusion reactor. A brief overview of these activities, presented here, along with new calculations relates the concept of auxiliary heating of inertial fusion targets, and provides possible future directions of research and development for the updated European Roadmap that is due at the end of 2020. This article is part of a discussion meeting issue 'Prospects for high gain inertial fusion energy (part 2)'.

New criteria for efficient Raman and Brillouin amplification of laser beams in plasma.

Raman or Brillouin amplification of a laser beam in plasma has long been seen as a way to reach multi-PW powers in compact laser systems. However, no significant plasma-based Raman amplification of a laser pulse beyond 0.1 TW has been achieved in nearly 20 years, and only one report of Brillouin amplification beyond 1 TW. In this paper, we reveal novel non-linear criteria for the initial seed pulse that will finally open the door to efficient Raman and Brillouin amplification to petawatt powers and Joule-level energies. We show that the triple product of the coupling constant [Formula: see text], seed pulse duration [Formula: see text] and seed pulse amplitude a for the Raman seed pulse (or [Formula: see text] for Brillouin) must exceed a specific minimum threshold for efficient amplification. We also analyze the plasma-based Raman and Brillouin amplification experiments to date, and show that the seed pulses used in nearly all experiments are well below our new threshold, which explains the poor efficiency obtained in them. Finally, we analyze a recent Brillouin amplification experiment that used increased seed pulse power to obtain Joule-level amplification, and find excellent agreement with our theory.

Orbital Angular Momentum Coupling in Elastic Photon-Photon Scattering.

In this Letter, we investigate the effect of orbital angular momentum (OAM) on elastic photon-photon scattering in a vacuum for the first time. We define exact solutions to the vacuum electromagnetic wave equation which carry OAM. Using those, the expected coupling between three initial waves is derived in the framework of an effective field theory based on the Euler-Heisenberg Lagrangian and shows that OAM adds a signature to the generated photons thereby greatly improving the signal-to-noise ratio. This forms the basis for a proposed high-power laser experiment utilizing quantum optics techniques to filter the generated photons based on their OAM state.

Expression, purification and metal utilization of recombinant SodA from Borrelia burgdorferi.

Borrelia are microaerophilic spirochetes capable of causing multisystemic diseases such as Lyme disease and Relapsing Fever. The ubiquitous Fe/Mn-dependent superoxide dismutase (SOD) provides essential protection from oxidative damage by the superoxide anion. Borrelia possess a single SOD enzyme - SodA that is essential for virulence, providing protection against host-derived reactive oxygen species (ROS). Here we present a method for recombinant expression and purification of Borrelia burgdorferi SodA in E. coli. Metal exchange or insertion into the Fe/Mn-SOD is inhibited in the folded state. We therefore present a method whereby the recombinant Borrelia SodA binds to Mn under denaturing conditions and is subsequently refolded by a reduction in denaturant. SodA purified by metal affinity chromatography and size exclusion chromatography reveals a single band on SDS-PAGE. Protein folding is confirmed by circular dichroism. A coupled enzyme assay demonstrates SOD activity in the presence of Mn, but not Fe. The apparent molecular weight determined by size exclusion corresponds to a dimer of SodA; a homology model of dimeric SodA is presented revealing a surface Cys distal to the dimer interface. The method presented of acquiring a target metal under denaturing conditions may be applicable to the refolding of other metal-binding proteins.

Supersonic plasma turbulence in the laboratory.

The properties of supersonic, compressible plasma turbulence determine the behavior of many terrestrial and astrophysical systems. In the interstellar medium and molecular clouds, compressible turbulence plays a vital role in star formation and the evolution of our galaxy. Observations of the density and velocity power spectra in the Orion B and Perseus molecular clouds show large deviations from those predicted for incompressible turbulence. Hydrodynamic simulations attribute this to the high Mach number in the interstellar medium (ISM), although the exact details of this dependence are not well understood. Here we investigate experimentally the statistical behavior of boundary-free supersonic turbulence created by the collision of two laser-driven high-velocity turbulent plasma jets. The Mach number dependence of the slopes of the density and velocity power spectra agree with astrophysical observations, and supports the notion that the turbulence transitions from being Kolmogorov-like at low Mach number to being more Burgers-like at higher Mach numbers.

Magnetic Field Generation in Plasma Waves Driven by Copropagating Intense Twisted Lasers.

We present a new magnetic field generation mechanism in underdense plasmas driven by the beating of two, copropagating, Laguerre-Gaussian orbital angular momentum laser pulses with different frequencies and also different twist indices. The resulting twisted ponderomotive force drives up an electron plasma wave with a helical rotating structure. To second order, there is a nonlinear rotating current leading to the onset of an intense, static axial magnetic field, which persists over a long time in the plasma (ps scale) after the laser pulses have passed by. The results are confirmed in three-dimensional particle-in-cell simulations and also theoretical analysis. For the case of 300 fs duration, 3.8×10^{17} W/cm^{2} peak laser intensity we observe magnetic field of up to 0.4 MG. This new method of magnetic field creation may find applications in charged beam collimation and microscale pinch.

Pectin Conformation in Solution.

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.

Laboratory evidence of dynamo amplification of magnetic fields in a turbulent plasma.

Magnetic fields are ubiquitous in the Universe. The energy density of these fields is typically comparable to the energy density of the fluid motions of the plasma in which they are embedded, making magnetic fields essential players in the dynamics of the luminous matter. The standard theoretical model for the origin of these strong magnetic fields is through the amplification of tiny seed fields via turbulent dynamo to the level consistent with current observations. However, experimental demonstration of the turbulent dynamo mechanism has remained elusive, since it requires plasma conditions that are extremely hard to re-create in terrestrial laboratories. Here we demonstrate, using laser-produced colliding plasma flows, that turbulence is indeed capable of rapidly amplifying seed fields to near equipartition with the turbulent fluid motions. These results support the notion that turbulent dynamo is a viable mechanism responsible for the observed present-day magnetization.

Brilliant X-rays using a Two-Stage Plasma Insertion Device.

Particle accelerators have made an enormous impact in all fields of natural sciences, from elementary particle physics, to the imaging of proteins and the development of new pharmaceuticals. Modern light sources have advanced many fields by providing extraordinarily bright, short X-ray pulses. Here we present a novel numerical study, demonstrating that existing third generation light sources can significantly enhance the brightness and photon energy of their X-ray pulses by undulating their beams within plasma wakefields. This study shows that a three order of magnitude increase in X-ray brightness and over an order of magnitude increase in X-ray photon energy is achieved by passing a 3 GeV electron beam through a two-stage plasma insertion device. The production mechanism micro-bunches the electron beam and ensures the pulses are radially polarised on creation. We also demonstrate that the micro-bunched electron beam is itself an effective wakefield driver that can potentially accelerate a witness electron beam up to 6 GeV.

Dense plasma heating by crossing relativistic electron beams.

Here we investigate, using relativistic fluid theory and Vlasov-Maxwell simulations, the local heating of a dense plasma by two crossing electron beams. Heating occurs as an instability of the electron beams drives Langmuir waves, which couple nonlinearly into damped ion-acoustic waves. Simulations show a factor 2.8 increase in electron kinetic energy with a coupling efficiency of 18%. Our results support applications to the production of warm dense matter and as a driver for inertial fusion plasmas.

Mesoscopic structure of pectin in solution.

Mesoscopic structure of pectin with different molecular characteristics was investigated by means of small angle X-ray scattering (SAXS), electrokinetic measurements and data modelling. The influence of a broad range of pH (2-7) on chain conformation in the dilute and semi-diluted regime was investigated. Scattering data and concomitant analysis revealed two length scales at all environmental conditions studied. pH showed greater influence at acidic values (pH 2.0) enhancing the globular component of the structure due to association of galacturonic acid residues. Double logarithmic scattering intensity plots revealed fractal dimensions of 1.9 ± 0.2 in the low-q regime and 1.5 ± 0.2 in the high q-region, irrespectively of the specific environment. Increase in branching of RG-I regions of the polysaccharide chains enhanced the compact conformation irrespectively of the pH or concentration. The present work shows that radical changes in pectin conformation can be induced only under strongly acidic conditions a finding that has important consequences in tailoring the technological performance of these biopolymers.

AAGBI guidelines: the use of blood components and their alternatives 2016.

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.

Identification of novel RNA secondary structures within the hepatitis C virus genome reveals a cooperative involvement in genome packaging.

The specific packaging of the hepatitis C virus (HCV) genome is hypothesised to be driven by Core-RNA interactions. To identify the regions of the viral genome involved in this process, we used SELEX (systematic evolution of ligands by exponential enrichment) to identify RNA aptamers which bind specifically to Core in vitro. Comparison of these aptamers to multiple HCV genomes revealed the presence of a conserved terminal loop motif within short RNA stem-loop structures. We postulated that interactions of these motifs, as well as sub-motifs which were present in HCV genomes at statistically significant levels, with the Core protein may drive virion assembly. We mutated 8 of these predicted motifs within the HCV infectious molecular clone JFH-1, thereby producing a range of mutant viruses predicted to possess altered RNA secondary structures. RNA replication and viral titre were unaltered in viruses possessing only one mutated structure. However, infectivity titres were decreased in viruses possessing a higher number of mutated regions. This work thus identified multiple novel RNA motifs which appear to contribute to genome packaging. We suggest that these structures act as cooperative packaging signals to drive specific RNA encapsidation during HCV assembly.

Amplification and generation of ultra-intense twisted laser pulses via stimulated Raman scattering.

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.