Near-Sun observations of an F-corona decrease and K-corona fine structure.

Remote observations of the solar photospheric light scattered by electrons (the K-corona) and dust (the F-corona or zodiacal light) have been made from the ground during eclipses1 and from space at distances as small as 0.3 astronomical units2-5 to the Sun. Previous observations6-8 of dust scattering have not confirmed the existence of the theoretically predicted dust-free zone near the Sun9-11. The transient nature of the corona has been well characterized for large events, but questions still remain (for example, about the initiation of the corona12 and the production of solar energetic particles13) and for small events even its structure is uncertain14. Here we report imaging of the solar corona15 during the first two perihelion passes (0.16-0.25 astronomical units) of the Parker Solar Probe spacecraft13, each lasting ten days. The view from these distances is qualitatively similar to the historical views from ground and space, but there are some notable differences. At short elongations, we observe a decrease in the intensity of the F-coronal intensity, which is suggestive of the long-sought dust free zone9-11. We also resolve the fine-scale plasma structure of very small eruptions, which are frequently ejected from the Sun. These take two forms: the frequently observed magnetic flux ropes12,16 and the predicted, but not yet observed, magnetic islands17,18 arising from the tearing-mode instability in the current sheet. Our observations of the coronal streamer evolution confirm the large-scale topology of the solar corona, but also reveal that, as recently predicted19, streamers are composed of yet smaller substreamers channelling continual density fluctuations at all visible scales.

Picosecond laser filament-guided electrical discharges in air at 1 kHz repetition rate.

Laser-induced filaments have been shown to reduce the voltage necessary to initiate electrical discharges in atmospheric air and guide their propagation over long distances. Here we demonstrate the stable generation of laser filament-guided electrical discharge columns in air initiated by high energy (up to 250 mJ) 1030 nm wavelength laser pulses of 7 ps duration at repetition rates up to 1 kHz and we discuss the processes leading to breakdown. A current proportional to the laser pulse energy is observed to arise as soon as the laser pulse arrives, initiating a high impedance phase of the discharge. Full breakdown, characterized by impedance collapse, occurs 100 ns to several µs later. A record 4.7-fold reduction in breakdown voltage for dc-biased discharges, which remains practically independent of the repetition rate up to 1 kHz, is observed to be primarily caused by a single laser pulse that produces a large (∼80%) density depression. The radial gaps between the filamentary plasma channel and the hollowed electrodes employed are shown to play a significant role in the breakdown dynamics. A rapid increase of 3-4 orders of magnitude in current is observed to follow the formation of localized radial current channels linking the filament to the electrodes. The increased understanding and control of kHz repetition rate filament-guided discharges can aid their use in applications.

Dynamics of Nanosecond Laser Pulse Propagation and of Associated Instabilities in a Magnetized Underdense Plasma.

The propagation and energy coupling of intense laser beams in plasmas are critical issues in inertial confinement fusion. Applying magnetic fields to such a setup has been shown to enhance fuel confinement and heating. Here we report on experimental measurements demonstrating improved transmission and increased smoothing of a high-power laser beam propagating in a magnetized underdense plasma. We also measure enhanced backscattering, which our kinetic simulations show is due to magnetic confinement of hot electrons, thus leading to reduced target preheating.

Wake dynamics of air filaments generated by high-energy picosecond laser pulses at 1 kHz repetition rate.

We investigated the filamentation in air of 7 ps laser pulses of up to 200 mJ energy from a 1.03 µm-wavelength Yb:YAG laser at repetition rates up to f=1kHz. Interferograms of the wake generated show that while pulses in a train of repetition rate f=0.1kHz encounter a nearly unperturbed environment, at f=1kHz, a channel with an axial air density hole of ∼20% is generated and maintained at all times by the cumulative effect of preceding laser pulses. Measurements at f=1kHz show that the energy deposited decreases proportional to the air channel density depletion, becoming more pronounced as the repetition rate and pulse energy increase. Numerical simulations indicate that contrary to filaments generated by shorter duration pulses, the electron avalanche is the dominant energy loss mechanism during filamentation with 7 ps pulses. The results are of interest for the atmospheric propagation of joule-level picosecond pulses from Yb:YAG lasers, of which average powers now surpass 1 kW, and for channeling other directed energy beams.

The Portsmouth protocol for intra-operative ultrasound of the small bowel in Crohn's disease.

AIM: Bowel preservation is paramount in Crohn's disease surgery as affected patients are typically young adults at risk of having several abdominal surgical procedures during their lifetime. Intra-operative assessment of the extent and location of Crohn's disease is not standardized and is left to a mixture of the surgeon's experience, tactile feedback, macroscopic appearance and preoperative imaging. The aim of this study was to describe the technical steps of a standardized protocol for intra-operative ultrasound assessment of the small bowel in patients undergoing surgery for ileocolic Crohn's disease. METHOD: After laparoscopic mobilization of the bowel, a periumbilical incision is performed for extracorporeal division of the mesentery and the resection and anastomosis. A gastrointestinal consultant radiologist, with expertise in Crohn's disease imaging and abdominal ultrasound, performs full intra-operative assessment of the small bowel by applying a sterile ultrasound probe directly to the bowel, prior to resection being performed by the surgeon. The bowel is assessed through the wound protector with a sterile technique and the length, location and number of segments is documented together with further quantitative assessment using the METRIC (MR enterography or ultrasound in Crohn's disease) scoring guide. RESULTS: A step-by-step protocol for intra-operative ultrasound evaluation of the entire small bowel is described. CONCLUSIONS: A standardized approach to intra-operative evaluation of the extent and location of Crohn's disease is desirable. Intra-operative ultrasound may provide added value for assessment of proximal and multifocal Crohn's disease.

Feasibility of intraoperative ultrasound of the small bowel during Crohn's disease surgery.

BACKGROUND: Intraoperative assessment of the extent and location of Crohn's disease is not standardised and relies on a mixture of surgeons' experience, tactile feedback and macroscopic appearance. To overcome this variability, we developed a protocol for full intraoperative ultrasound scan of the small bowel and we here report the results of "Assessing the Feasibility and Safety of Using Intraoperative Ultrasound in Ileocolic Crohn's Disease-The IUSS CROHN Study". METHODS: This is a prospective single centre observational study with enrolment of all patients undergoing elective surgery for terminal ileal Crohn's disease from January 2019 to March 2020. Patients underwent laparoscopic ileocolic resection, according to a standardised technique. Ultrasound intraoperative quantitative assessment was performed according to the METRIC (MREnterography or ulTRasound in Crohn's disease) scoring guide. RESULTS: Intraoperative ultrasound was successfully performed in 6 patients from the ileocaecal valve to the proximal jejunum. The median time required was 23.5 min (range 17-37 min) as compared to 6.5 min (5-12 min) required for the macroscopic evaluation performed by the surgeon. In 3 patients, intraoperative ultrasound identified more disease than surgical evaluation. CONCLUSIONS: This feasibility study demonstrated the safety of intraoperative ultrasound and allowed the development of a standardised protocol for intraoperative ultrasound and the data collection required to inform a randomised multicentre study.

An optically multiplexed single-shot time-resolved probe of laser-plasma dynamics.

We introduce a new approach to temporally resolve ultrafast micron-scale processes via the use of a multi-channel optical probe. We demonstrate that this technique enables highly precise time-resolved, two-dimensional spatial imaging of intense laser pulse propagation dynamics, plasma formation and laser beam filamentation within a single pulse over four distinct time frames. The design, development and optimization of the optical probe system is presented, as are representative experimental results from the first implementation of the multi-channel probe with a high-power laser pulse interaction with a helium gas jet target.

Dual Ion Species Plasma Expansion from Isotopically Layered Cryogenic Targets.

A dual ion species plasma expansion scheme from a novel target structure is introduced, in which a nanometer-thick layer of pure deuterium exists as a buffer species at the target-vacuum interface of a hydrogen plasma. Modeling shows that by controlling the deuterium layer thickness, a composite H^{+}/D^{+} ion beam can be produced by target normal sheath acceleration (TNSA), with an adjustable ratio of ion densities, as high energy proton acceleration is suppressed by the acceleration of a spectrally peaked deuteron beam. Particle in cell modeling shows that a (4.3±0.7) MeV per nucleon deuteron beam is accelerated, in a directional cone of half angle 9°. Experimentally, this was investigated using state of the art cryogenic targetry and a spectrally peaked deuteron beam of (3.4±0.7) MeV per nucleon was measured in a cone of half angle 7°-9°, while maintaining a significant TNSA proton component.

The evolution of cooperation by negotiation in a noisy world.

Cooperative interactions among individuals are ubiquitous despite the possibility of exploitation by selfish free riders. One mechanism that may promote cooperation is 'negotiation': individuals altering their behaviour in response to the behaviour of others. Negotiating individuals decide their actions through a recursive process of reciprocal observation, thereby reducing the possibility of free riding. Evolutionary games with response rules have shown that infinitely many forms of the rule can be evolutionarily stable simultaneously, unless there is variation in individual quality. This potentially restricts the conditions under which negotiation could maintain cooperation. Organisms interact with one another in a noisy world in which cooperative effort and the assessment of effort may be subject to error. Here, we show that such noise can make the number of evolutionarily stable rules finite, even without quality variation, and so noise could help maintain cooperative behaviour. We show that the curvature of the benefit function is the key factor determining whether individuals invest more or less as their partner's investment increases, investing less when the benefit to investment has diminishing returns. If the benefits of low investment are very small then behavioural flexibility tends to promote cooperation, because negotiation enables cooperators to reach large benefits. Under some conditions, this leads to a repeating cycle in which cooperative behaviour rises and falls over time, which may explain between-population differences in cooperative behaviour. In other conditions, negotiation leads to extremely high levels of cooperative behaviour, suggesting that behavioural flexibility could facilitate the evolution of eusociality in the absence of high relatedness.

The accuracy of interpretation of emergency abdominal CT in adult patients who present with non-traumatic abdominal pain: results of a UK national audit.

AIM: To evaluate major/minor discrepancy rates for provisional (initial) and addendum (supplementary senior review) emergency computed tomography (CT) reports in patients presenting with non-traumatic abdominal pain. MATERIALS AND METHODS: Ethical approval for this type of study is not required in the UK. All radiology departments with an approved lead for audit registered with the Royal College of Radiologists were invited to participate in this retrospective audit. The first 50 consecutive patients (25 surgical, 25 non-surgical) who underwent emergency abdominal CT for non-traumatic abdominal pain in 2013 were included. Statistical analyses were performed to identify organisational and report/patient-related variables that might be associated with major discrepancy. RESULTS: One hundred and nine (58%) of 188 departments supplied data to the study with a total of 4,931 patients (2,568 surgical, 2,363 non-surgical). The audit standard for provisional report major discrepancy was achieved for registrars (target <10%, achieved 4.6%), for on-site consultants (target <5%, achieved 3.1%) and consultant addendum (target <5%, achieved 2.9%). Off-site reporters failed to meet the standard target (<5%, achieved 8.7% overall and 12.7% in surgical patients). The standard for patients coming to harm was not met in the surgical group (target <1%, achieved 1.5%) and was narrowly missed overall (target <1%, achieved 1%). CONCLUSION: This study should be used to provide impetus to improve aspects of out-of-hours CT reporting. Clear benefits of CT interpretation/review by on-site and more senior (consultant) radiologists have been demonstrated.

The locus of sexual selection: moving sexual selection studies into the post-genomics era.

Sexual selection drives fundamental evolutionary processes such as trait elaboration and speciation. Despite this importance, there are surprisingly few examples of genes unequivocally responsible for variation in sexually selected phenotypes. This lack of information inhibits our ability to predict phenotypic change due to universal behaviours, such as fighting over mates and mate choice. Here, we discuss reasons for this apparent gap and provide recommendations for how it can be overcome by adopting contemporary genomic methods, exploiting underutilized taxa that may be ideal for detecting the effects of sexual selection and adopting appropriate experimental paradigms. Identifying genes that determine variation in sexually selected traits has the potential to improve theoretical models and reveal whether the genetic changes underlying phenotypic novelty utilize common or unique molecular mechanisms. Such a genomic approach to sexual selection will help answer questions in the evolution of sexually selected phenotypes that were first asked by Darwin and can furthermore serve as a model for the application of genomics in all areas of evolutionary biology.

Gastric bands: what the general radiologist should know.

Obesity in the UK is increasing, it is estimated that in England 24% of men and 25% of women are obese.(1,2) In recent years bariatric surgery has become increasingly common and is effective in producing long-term weight loss.(4,5) The most popular form of bariatric surgery in Europe is laparoscopic adjustable gastric banding (LAGB).(6) Radiologists play a key role assessing the normal function of bands, adjusting their filling under fluoroscopic guidance, and in recognizing and managing complications. This review will describe the general principles of LAGB; how they are assessed, how to recognize the most common complications, an overview of the appearances of the bands used in the UK, and novel developments in their use and design.

Density-dependent investment in costly anti-predator defences: an explanation for the weak survival benefit of group living.

A central explanation for group living across animal taxa is the reduced rate of attack by predators. However, many field observations show a weak or non-existent effect of group size on per capita mortality rates. Herein we resolve this apparent paradox. We found that Pieris brassicae larvae defended themselves less readily when in groups than when alone, in that they were more reluctant to regurgitate in response to simulated attacks and produced less regurgitant. Furthermore, a simple model demonstrates that this reluctance was sufficient to cancel out the benefit from being in a group. This conditional strategy can be understood in terms of the costs and benefits of defences. For grouped individuals, defence is less often required because attack rates are lower and the costs of defence may be higher due to competition for resources. These phenomena are likely to be widespread in facultatively gregarious species that utilise anti-predator defences.

Transport of an intense proton beam from a cone-structured target through plastic foam with unique proton source modeling.

Laser-accelerated proton beams are applicable to several research areas within high-energy density science, including warm dense matter generation, proton radiography, and inertial confinement fusion, which all involve transport of the beam through matter. We report on experimental measurements of intense proton beam transport through plastic foam blocks. The intense proton beam was accelerated by the 10ps, 700J OMEGA EP laser irradiating a curved foil target, and focused by an attached hollow cone. The protons then entered the foam block of density 0.38g/cm^{3} and thickness 0.55 or 1.00mm. At the rear of the foam block, a Cu layer revealed the cross section of the intense beam via proton- and hot electron-induced Cu-K_{α} emission. Images of x-ray emission show a bright spot on the rear Cu film indicative of a forward-directed beam without major breakup. 2D fluid-PIC simulations of the transport were conducted using a unique multi-injection source model incorporating energy-dependent beam divergence. Along with postprocessed calculations of the Cu-K_{α} emission profile, simulations showed that protons retain their ballistic transport through the foam and are able to heat the foam up to several keV in temperature. The total experimental emission profile for the 1.0mm foam agrees qualitatively with the simulated profile, suggesting that the protons indeed retain their beamlike qualities.

Influence of spatial-intensity contrast in ultraintense laser-plasma interactions.

Increasing the intensity to which high power laser pulses are focused has opened up new research possibilities, including promising new approaches to particle acceleration and phenomena such as high field quantum electrodynamics. Whilst the intensity achievable with a laser pulse of a given power can be increased via tighter focusing, the focal spot profile also plays an important role in the interaction physics. Here we show that the spatial-intensity distribution, and specifically the ratio of the intensity in the peak of the laser focal spot to the halo surrounding it, is important in the interaction of ultraintense laser pulses with solid targets. By comparing proton acceleration measurements from foil targets irradiated with by a near-diffraction-limited wavelength scale focal spot and larger F-number focusing, we find that this spatial-intensity contrast parameter strongly influences laser energy coupling to fast electrons. We find that for multi-petawatt pulses, spatial-intensity contrast is potentially as important as temporal-intensity contrast.

Imaging manifestations of faecal impaction and stercoral perforation.

Stercoral perforation can be defined as perforation of the bowel due to pressure necrosis from a faecal mass. It is an uncommon but life-threatening complication of unresolved faecal impaction. In this review, we highlight the important computed tomography (CT) findings of faecal impaction and stercoral perforation of the colon and subsequent therapeutic options in the adult population.