Multimillijoule coherent terahertz bursts from picosecond laser-irradiated metal foils.

Ultrahigh-power terahertz (THz) radiation sources are essential for many applications, for example, THz-wave-based compact accelerators and THz control over matter. However, to date none of the THz sources reported, whether based upon large-scale accelerators or high-power lasers, have produced THz pulses with energies above the millijoule (mJ) level. Here, we report a substantial increase in THz pulse energy, as high as tens of mJ, generated by a high-intensity, picosecond laser pulse irradiating a metal foil. A further up-scaling of THz energy by a factor of ∼4 is observed when introducing preplasmas at the target-rear side. Experimental measurements and theoretical models identify the dominant THz generation mechanism to be coherent transition radiation, induced by the laser-accelerated energetic electron bunch escaping the target. Observation of THz-field-induced carrier multiplication in high-resistivity silicon is presented as a proof-of-concept application demonstration. Such an extremely high THz energy not only triggers various nonlinear dynamics in matter, but also opens up the research era of relativistic THz optics.

A tool to evaluate proportionality and necessity in the use of restrictive practices in forensic mental health settings: the DRILL tool (Dundrum restriction, intrusion and liberty ladders).

BACKGROUND: Prevention of violence due to severe mental disorders in psychiatric hospitals may require intrusive, restrictive and coercive therapeutic practices. Research concerning appropriate use of such interventions is limited by lack of a system for description and measurement. We set out to devise and validate a tool for clinicians and secure hospitals to assess necessity and proportionality between imminent violence and restrictive practices including de-escalation, seclusion, restraint, forced medication and others. METHODS: In this retrospective observational cohort study, 28 patients on a 12 bed male admissions unit in a secure psychiatric hospital were assessed daily for six months. Data on adverse incidents were collected from case notes, incident registers and legal registers. Using the functional assessment sequence of antecedents, behaviours and consequences (A, B, C) we devised and applied a multivariate framework of structured professional assessment tools, common adverse incidents and preventive clinical interventions to develop a tool to analyse clinical practice. We validated by testing assumptions regarding the use of restrictive and intrusive practices in the prevention of violence in hospital. We aimed to provide a system for measuring contextual and individual factors contributing to adverse events and to assess whether the measured seriousness of threating and violent behaviours is proportionate to the degree of restrictive interventions used. General Estimating Equations tested preliminary models of contexts, decisions and pathways to interventions. RESULTS: A system for measuring adverse behaviours and restrictive, intrusive interventions for prevention had good internal consistency. Interventions were proportionate to seriousness of harmful behaviours. A 'Pareto' group of patients (5/28) were responsible for the majority (80%) of adverse events, outcomes and interventions. The seriousness of the precipitating events correlated with the degree of restrictions utilised to safely manage or treat such behaviours. CONCLUSION: Observational scales can be used for restrictive, intrusive or coercive practices in psychiatry even though these involve interrelated complex sequences of interactions. The DRILL tool has been validated to assess the necessity and demonstrate proportionality of restrictive practices. This tool will be of benefit to services when reviewing practices internally, for mandatory external reviewing bodies and for future clinical research paradigms.

Control of laser light by a plasma immersed in a tunable strong magnetic field.

The interaction between laser light and an underdense plasma immersed in a spatio-temporally tunable magnetic field is studied analytically and numerically. The transversely nonuniform magnetic field can serve as a magnetic channel, which can act on laser propagation in a similar way to the density channel. The envelope equation for laser intensity evolution is derived, which contains the effects of magnetic channel and relativistic self-focusing. Due to the magnetic field applied, the critical laser power for relativistic self-focusing can be significantly reduced. Theory and particle-in-cell simulations show that a weakly relativistic laser pulse can propagate with a nearly constant peak intensity along the magnetic channel for a distance much longer than its Rayleigh length. By setting the magnetic field tunable in both space and time, the simulation further shows that the magnetized plasma can then act as a lens of varying focal length to control the movement of laser focal spot, decoupling the laser group velocity from the light speed c in vacuum.

Simultaneous polarization transformation and amplification of multi-petawatt laser pulses in magnetized plasmas.

With increasing laser peak power, the generation and manipulation of high-power laser pulses become a growing challenge for conventional solid-state optics due to their limited damage threshold. As a result, plasma-based optical components that can sustain extremely high fields are attracting increasing interest. Here, we propose a type of plasma waveplate based on magneto-optical birefringence under a transverse magnetic field, which can work under extremely high laser power. Importantly, this waveplate can simultaneously alter the polarization state and boost the peak laser power. It is demonstrated numerically that an initially linearly polarized laser pulse with 5 petawatt peak power can be converted into a circularly polarized pulse with a peak power higher than 10 petawatts by such a waveplate with a centimeter-scale diameter. The energy conversion efficiency of the polarization transformation is about 98%. The necessary waveplate thickness is shown to scale inversely with plasma electron density ne and the square of magnetic field B0, and it is about 1 cm for ne = 3 × 1020 cm-3 and B0 = 100 T. The proposed plasma waveplate and other plasma-based optical components can play a critical role for the effective utilization of multi-petawatt laser systems.

Dense relativistic electron mirrors from a Laguerre-Gaussian laser-irradiated micro-droplet.

We investigate dense relativistic electron mirror generation from a micro-droplet driven by circularly polarized Laguerre-Gaussian lasers. The surface electrons are expelled from the droplet by the laser's radial electric field and evolve into dense sheets after leaving the droplet. These electrons are trapped in the potential well of the laser's transverse ponderomotive force and are steadily accelerated to about 100 MeV by the longitudinal electric field. Particle-in-cell simulations indicate that the relativistic electron mirrors are characterized by high beam charge, narrow energy spread, and large angular momentum, which can be utilized for bright X/γ-ray emission and photon vortex formation.

Bacterial Contamination in Tips of Electrocautery Devices During Total Hip Arthroplasty.

Surgical equipment can become contaminated during surgery. It is unknown if electrocautery tips can become contaminated in clean orthopedic procedures despite the produced heat. Therefore, we conducted a prospective study to address this concern. The tips from 25 primary and 25 aseptic revision THAs were collected and an additional 5 sterile tips served as negative controls. Aerobic and anaerobic cultures were incubated for a minimum of 3 days. There were 3 positive cultures (6%); one in primary THA (4%) with Lactobacillus and Enterococcus faecalis; two among revisions (8%), one with E. faecalis and another one with alpha hemolytic streptococci and coagulase negative Staphylococcus. The mean exposure time of the contaminated tips was 132.3 minutes. Patients were followed for 90 days postoperatively and none of them developed surgical site infection. This is the first study to demonstrate that electrosurgical devices can become contaminated during THA in laminar flow equipped operating rooms.

Energy coupling in short pulse laser solid interactions and its impact for space debris removal.

Significant advances have been made over the last decade to improve the performance, efficiency, and contrast of high peak and average power laser systems, driven by their use in a wide variety of fields, from the industrial to the scientific. As the contrast of the lasers has improved, interactions with contrasts of 1012 are now routinely undertaken. At such high contrasts, there is negligible preplasma formation and the ionized surface layer created by subpicosecond-duration pulses typically forms a highly reflective "plasma mirror" capable of reflecting between 70% and 90% of the incident energy. Although such interactions are of significant interest for applications such as harmonic source production and to enable the underlying physics to be studied, their low absorption can limit their usefulness for applications such as space debris removal.

Laser harmonic generation with independent control of frequency and orbital angular momentum.

The non-linear optical process of laser harmonic generation (HG) enables the creation of high quality pulses of UV or even X-ray radiation, which have many potential uses at the frontiers of experimental science, ranging from lensless microscopy to ultrafast metrology and chiral science. Although many of the promising applications are enabled by generating harmonic modes with orbital angular momentum (OAM), independent control of the harmonic frequency and OAM level remains elusive. Here we show, through a theoretical approach, validated with 3D simulations, how unique 2-D harmonic progressions can be obtained, with both frequency and OAM level tuned independently, from tailored structured targets in both reflective and transmissive configurations. Through preferential selection of a subset of harmonic modes with a specific OAM value, a controlled frequency comb of circularly polarised harmonics can be produced. Our approach to describe HG, which simplifies both the theoretical predictions and the analysis of the harmonic spectrum, is directly applicable across the full range of HG mechanisms and can be readily applied to investigations of OAM harmonics in other processes, such as OAM cascades in Raman amplification, or the analysis of harmonic progressions in nonlinear optics.

Acetabular cup size trends in total hip arthroplasty.

BACKGROUND: Total hip arthroplasty (THA) is a common procedure for end stage osteoarthritis. The learning curve for THA is complex and challenging. One of the most difficult skills to master is acetabular reaming. We wish to identify if experience in arthroplasty leads to preservation of more bone stock. AIM: To investigate if increasing surgeon experience will predict an ever decreasing acetabular cup size. METHODS: A retrospective case series of four attending orthopaedic surgeons was completed. All uncemented elective total hip arthroplasties since appointment were selected for inclusion. The size of acetabular cup used was noted and logistic regression was used to identify if a trend to smaller cups existed. RESULTS: A total of 1614 subjects were included with a mean age of 64 years. Overall cups were on average 0.18mm smaller per year (95% confidence interval -0.25 to -0.11, P < 0.001). Individual surgeon trends showed cup sizes to decrease 0.27 mm/year for surgeon A, 0.02 mm/year for surgeon B, 0.15 mm/year for surgeon C and 0.29 mm/year for surgeon D. Three of the four surgeons had a more pronounced trend to smaller cups for male subjects than their female counterparts. CONCLUSION: We found increasing surgeon experience to be associated with an ever-decreasing acetabular cup size. Smaller acetabular cup size may act as a surrogate marker of surgical proficiency by virtue of decreased acetabular reaming.

Development of a portable hypoxia chamber for ultra-high dose rate laser-driven proton radiobiology applications.

BACKGROUND: There is currently significant interest in assessing the role of oxygen in the radiobiological effects at ultra-high dose rates. Oxygen modulation is postulated to play a role in the enhanced sparing effect observed in FLASH radiotherapy, where particles are delivered at 40-1000 Gy/s. Furthermore, the development of laser-driven accelerators now enables radiobiology experiments in extreme regimes where dose rates can exceed 109 Gy/s, and predicted oxygen depletion effects on cellular response can be tested. Access to appropriate experimental enviroments, allowing measurements under controlled oxygenation conditions, is a key requirement for these studies. We report on the development and application of a bespoke portable hypoxia chamber specifically designed for experiments employing laser-driven sources, but also suitable for comparator studies under FLASH and conventional irradiation conditions. MATERIALS AND METHODS: We used oxygen concentration measurements to test the induction of hypoxia and the maintenance capacity of the chambers. Cellular hypoxia induction was verified using hypoxia inducible factor-1α immunostaining. Calibrated radiochromic films and GEANT-4 simulations verified the dosimetry variations inside and outside the chambers. We irradiated hypoxic human skin fibroblasts (AG01522B) cells with laser-driven protons, conventional protons and reference 225 kVp X-rays to quantify DNA DSB damage and repair under hypoxia. We further measured the oxygen enhancement ratio for cell survival after X-ray exposure in normal fibroblast and radioresistant patient- derived GBM stem cells. RESULTS: Oxygen measurements showed that our chambers maintained a radiobiological hypoxic environment for at least 45 min and pathological hypoxia for up to 24 h after disconnecting the chambers from the gas supply. We observed a significant reduction in the 53BP1 foci induced by laser-driven protons, conventional protons and X-rays in the hypoxic cells compared to normoxic cells at 30 min post-irradiation. Under hypoxic irradiations, the Laser-driven protons induced significant residual DNA DSB damage in hypoxic AG01522B cells compared to the conventional dose rate protons suggesting an important impact of these extremely high dose-rate exposures. We obtained an oxygen enhancement ratio (OER) of 2.1 ± 0.1 and 2.5 ± 0.1 respectively for the AG01522B and patient-derived GBM stem cells for X-ray irradiation using our hypoxia chambers. CONCLUSION: We demonstrated the design and application of portable hypoxia chambers for studying cellular radiobiological endpoints after exposure to laser-driven protons at ultra-high dose, conventional protons and X-rays. Suitable levels of reduced oxygen concentration could be maintained in the absence of external gassing to quantify hypoxic effects. The data obtained provided indication of an enhanced residual DNA DSB damage under hypoxic conditions at ultra-high dose rate compared to the conventional protons or X-rays.

Short-term outcomes of total knee arthroplasty performed with and without a tourniquet.

INTRODUCTION: Not using a tourniquet could improve early postoperative pain, range of motion (ROM), length of stay (LOS), and thromboembolic risk in patients undergoing total knee arthroplasty (TKA). Our aim was to compare these factors, intraoperative blood loss, and gender-related outcomes in patients undergoing primary TKA with or without a tourniquet. METHODS: We performed a retrospective cohort study of 97 patients undergoing TKA with or without tourniquet from 2018 to 2020. Revisions and bilateral TKAs were excluded. Blood loss was estimated using a validated formula. Postoperative pain was tested using the visual analogue scale (VAS). ROM and quadriceps lag were assessed by a physiotherapist on a postoperative day 2 and discharge. The index of suspicion for a thromboembolic event was defined as the number of embolic-related investigations ordered in the first 6 months post-surgery. The Shapiro-Wilk test was used to assess the distribution of the data, Mann-Whitney for the continuous variables, and Fischer's test for the categorical ones. RESULTS AND DISCUSSION: There was a significant difference in blood loss. The non-tourniquet group lost on average 32% more blood (1291 mL vs. 878 mL, p<0.001 two-tailed). We found no difference in pain, ROM, LOS, and quadriceps lag on day 2 and at discharge. There was one thromboembolic event in the tourniquet group, but the thromboembolic index of suspicion did not differ (p=0.53). With tourniquet use, women had a significantly lower day 2 maximum flexion than men (71.56° vs. 84.67°, p=0.02). In this retrospective cohort study, the results suggest that tourniquet use is associated with lower blood loss and similar postoperative pain, range of motion, quadriceps lag, length of stay, and thromboembolic risk. There might be some differences between how men and women tolerate a tourniquet, with women having worse short-term outcomes compared to men.

Field testing of a new flow-through directional passive air sampler applied to monitoring ambient nitrogen dioxide.

This paper reports the first field deployment and testing of a directional passive air sampler (DPAS) which can be used to cost-effectively identify and quantify air pollutants and their sources. The sampler was used for ambient nitrogen dioxide (NO(2)) over ten weeks from twelve directional sectors in an urban setting, and tested alongside an automatic chemiluminescent monitor. The time-integrated passive directional results were compared with the directional analysis of the active monitoring results using wind data recorded at a weather station. The DPAS discriminated air pollutant signals directionally. The attempts to derive quantitative data yielded reasonable results--usually within a factor of two of those obtained by the chemiluminescent analyser. Ultimately, whether DPAS approaches are adopted will depend on their reliability, added value and cost. It is argued that added value was obtained here from the DPAS approach applied in a routine monitoring situation, by identifying source sectors. Both the capital and running costs of DPAS were <5% of those for the automatic monitor. It is envisaged that different sorbents or sampling media will enable this rotatable DPAS design to be used for other airborne pollutants. In summary, there are reasons to be optimistic that directional passive air sampling, together with careful interpretation of results, will be of added value to air quality practitioners in future.

Extremely brilliant GeV γ-rays from a two-stage laser-plasma accelerator.

Recent developments in laser-wakefield accelerators have led to compact ultrashort X/γ-ray sources that can deliver peak brilliance comparable with conventional synchrotron sources. Such sources normally have low efficiencies and are limited to 107-8 photons/shot in the keV to MeV range. We present a novel scheme to efficiently produce collimated ultrabright γ-ray beams with photon energies tunable up to GeV by focusing a multi-petawatt laser pulse into a two-stage wakefield accelerator. This high-intensity laser enables efficient generation of a multi-GeV electron beam with a high density and tens-nC charge in the first stage. Subsequently, both the laser and electron beams enter into a higher-density plasma region in the second stage. Numerical simulations demonstrate that more than 1012 γ-ray photons/shot are produced with energy conversion efficiency above 10% for photons above 1 MeV, and the peak brilliance is above 1026 photons s-1 mm-2 mrad-2 per 0.1% bandwidth at 1 MeV. This offers new opportunities for both fundamental and applied research.

Two-stage revision of infected hip arthroplasty using a shortened post-operative course of antibiotics.

INTRODUCTION: We present a series of 30 consecutive patients with 31 infected total hip arthroplasties treated by a single surgeon over a 4-year period in whom a shortened post-operative course of antimicrobial chemotherapy was used. METHODS: The treatment protocol consisted of a two-stage exchange with removal of infected components, insertion of an interim antibiotic eluting cement spacer and re-implantation of an extensively coated uncemented prosthesis on the femoral side. Systemic antibiotic treatment following each stage consisted of an abridged course of 5 days post-operative intra-venous administration followed by complete cessation of anti-microbial therapy. RESULTS: At a mean follow-up of 35 months (minimum 24 months), there were no cases of recurrent prosthetic infection and no patient had required revision for aseptic loosening or mechanical instability on the femoral side. The combination of effective-staged surgical joint debridement, a shortened post-operative course of systemic antibiotic treatment and an adequate latent period before re-implantation has led to encourage early results in this series of revised chronic hip joint prosthetic infections.

Author Correction: Relativistic Doppler-boosted γ-rays in High Fields.

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.

Relativistic Doppler-boosted γ-rays in High Fields.

The relativistic Doppler effect is one of the most famous implications of the principles of special relativity and is intrinsic to moving radiation sources, relativistic optics and many astrophysical phenomena. It occurs in the case of a plasma sail accelerated to relativistic velocities by an external driver, such as an ultra-intense laser pulse. Here we show that the relativistic Doppler effect on the high energy synchrotron photon emission (~10 MeV), strongly depends on two intrinsic properties of the plasma (charge state and ion mass) and the transverse extent of the driver. When the moving plasma becomes relativistically transparent to the driver, we show that the γ-ray emission is Doppler-boosted and the angular emission decreases; optimal for the highest charge-to-mass ratio ion species (i.e. a hydrogen plasma). This provides new fundamental insight into the generation of γ-rays in extreme conditions and informs related experiments using multi-petawatt laser facilities.

Attosecond electron bunches from a nanofiber driven by Laguerre-Gaussian laser pulses.

Generation of attosecond bunches of energetic electrons offers significant potential from ultrafast physics to novel radiation sources. However, it is still a great challenge to stably produce such electron beams with lasers, since the typical subfemtosecond electron bunches from laser-plasma interactions either carry low beam charge, or propagate for only several tens of femtoseconds. Here we propose an all-optical scheme for generating dense attosecond electron bunches via the interaction of an intense Laguerre-Gaussian (LG) laser pulse with a nanofiber. The dense bunch train results from the unique field structure of a circularly polarized LG laser pulse, enabling each bunch to be phase-locked and accelerated forward with low divergence, high beam charge and large beam-angular-momentum. This paves the way for wide applications in various fields, e.g., ultrabrilliant attosecond x/γ-ray emission.

Intronic alternative splicing regulators identified by comparative genomics in nematodes.

Many alternative splicing events are regulated by pentameric and hexameric intronic sequences that serve as binding sites for splicing regulatory factors. We hypothesized that intronic elements that regulate alternative splicing are under selective pressure for evolutionary conservation. Using a Wobble Aware Bulk Aligner genomic alignment of Caenorhabditis elegans and Caenorhabditis briggsae, we identified 147 alternatively spliced cassette exons that exhibit short regions of high nucleotide conservation in the introns flanking the alternative exon. In vivo experiments on the alternatively spliced let-2 gene confirm that these conserved regions can be important for alternative splicing regulation. Conserved intronic element sequences were collected into a dataset and the occurrence of each pentamer and hexamer motif was counted. We compared the frequency of pentamers and hexamers in the conserved intronic elements to a dataset of all C. elegans intron sequences in order to identify short intronic motifs that are more likely to be associated with alternative splicing. High-scoring motifs were examined for upstream or downstream preferences in introns surrounding alternative exons. Many of the high-scoring nematode pentamer and hexamer motifs correspond to known mammalian splicing regulatory sequences, such as (T)GCATG, indicating that the mechanism of alternative splicing regulation is well conserved in metazoans. A comparison of the analysis of the conserved intronic elements, and analysis of the entire introns flanking these same exons, reveals that focusing on intronic conservation can increase the sensitivity of detecting putative splicing regulatory motifs. This approach also identified novel sequences whose role in splicing is under investigation and has allowed us to take a step forward in defining a catalog of splicing regulatory elements for an organism. In vivo experiments confirm that one novel high-scoring sequence from our analysis, (T)CTATC, is important for alternative splicing regulation of the unc-52 gene.

SGEM Hot Off the Press: ultrasound during critical care simulation: a randomized crossover study.

As part of the Canadian Journal of Emergency Medicine's (CJEM) developing social media strategy, 1 we are collaborating with the Skeptics' Guide to Emergency Medicine (SGEM) to summarize and critically appraise the current emergency medicine (EM) literature using evidence-based medicine principles. In the "Hot Off the Press" series, we select original research manuscripts published in CJEM to be featured on the SGEM website/podcast 2 and discussed by the study authors and the online EM community. A similar collaboration is underway between the SGEM and Academic Emergency Medicine. What follows is a summary of the selected article the immediate post-publication synthesis from the SGEM podcast, commentary by the first author, and the subsequent discussion from the SGEM blog and other social media. Through this series, we hope to enhance the value, accessibility, and application of important, clinically relevant EM research. In this, the third SGEM HOP hosted collaboratively with CJEM, we discuss Olszynski et al.'s randomized crossover study evaluating the use of ultrasound simulator devices during critical care simulation. 3.

Ultra-bright γ-ray emission and dense positron production from two laser-driven colliding foils.

Matter can be transferred into energy and the opposite transformation is also possible by use of high-power lasers. A laser pulse in plasma can convert its energy into γ-rays and then e - e + pairs via the multi-photon Breit-Wheeler process. Production of dense positrons at GeV energies is very challenging since extremely high laser intensity ~1024 Wcm-2 is required. Here we propose an all-optical scheme for ultra-bright γ-ray emission and dense positron production with lasers at intensity of 1022-23 Wcm-2. By irradiating two colliding elliptically-polarized lasers onto two diamondlike carbon foils, electrons in the focal region of one foil are rapidly accelerated by the laser radiation pressure and interact with the other intense laser pulse which penetrates through the second foil due to relativistically induced foil transparency. This symmetric configuration enables efficient Compton back-scattering and results in ultra-bright γ-photon emission with brightness of ~1025 photons/s/mm2/mrad2/0.1%BW at 15 MeV and intensity of 5 × 1023 Wcm-2. Our first three-dimensional simulation with quantum-electrodynamics incorporated shows that a GeV positron beam with density of 2.5 × 1022 cm-3 and flux of 1.6 × 1010/shot is achieved. Collective effects of the pair plasma may be also triggered, offering a window on investigating laboratory astrophysics at PW laser facilities.