Tonsils at Telethon: developing a standardised collection of tonsil photographs for group A streptococcal (GAS) research

Introduction

Group A streptococcus (GAS) infections, such as pharyngitis and impetigo, can lead to rheumatic fever and rheumatic heart disease (RHD). Australian Aboriginal and Torres Strait Islander populations experience high rates of RHD and GAS skin infection, yet rates of GAS pharyngitis are unclear. Anecdotally, clinical presentations of pharyngitis, including tonsillar hypertrophy and sore throat, are uncommon. This study aimed to develop a standardised set of tonsil photographs and determine tonsil size distribution from an urban paediatric population.

Methods

A prospective cohort of children aged 3-15 years were recruited at the public events "Discover Day" and "Telethon Weekend" (October 2017) in Perth, Western Australia, Australia. Tonsil photographs, symptomatology, and GAS rapid antigen detection tests (RADT) were collected. Tonsil size was graded from the photographs using the Brodsky Grading Scale of tonsillar hypertrophy (Brodsky) by two independent clinicians, and inter-rater reliability calculated. Pharyngitis symptoms and GAS RADT were correlated, and immediate results provided.

Results

Four hundred and twenty-six healthy children participated in the study over three days. The median age was seven years [interquartile range (IQR) 5.9-9.7 years]. Tonsil photographs were collected for 92% of participants, of which 62% were rated as good-quality photographs and 79% were deemed of adequate quality for assessment by both clinicians. When scored by two independent clinicians, 57% received the same grade. Average Brodsky grades (between clinicians) were 11%, 35%, 28%, 22% and 5% of grades 0,1,2,3 and 4, respectively. There was moderate agreement in grading using photographs, and minimal to weak agreement for signs of infection. Of 394 participants, 8% reported a sore throat. Of 334 GAS RADT performed, <1% were positive.

Discussion

We report the first standardised use of paediatric tonsil photographs to assess tonsil size in urban-living Australian children. This provides a proof of concept from an urban-living cohort that could be compared with children in other settings with high risk of GAS pharyngitis or rheumatic fever such as remote-living Australian Indigenous populations.

The role of geographic disparities in outcomes after orthopaedic trauma surgery

INTRODUCTION

Healthcare disparities linked to patient rurality and socioeconomic status are known to exist, but few studies have examined the effect of urban versus rural status on outcomes after orthopedic trauma surgery. The aim of this study was to examine the correlation between patient rurality, socioeconomic status, and outcomes after orthopedic trauma.

MATERIALS AND METHODS

This is a retrospective cohort study of patients diagnosed with a hip or long bone fracture between January 2016 and December 2017. Data were collected from the Nationwide Inpatient Sample (NIS), a 20% weighted sample of 95% of the U.S. inpatient population. Patients were stratified into 3 groups: isolated hip fracture, isolated long bone fracture, and polytrauma. Bivariate analysis was completed using chi-squared tests for categorical variables and t-tests for continuous variables. Multivariable analysis was completed using population-weighted logistic regression models, based on a conceptual model derived selection of covariates.

RESULTS

We included 235,393 patients diagnosed with a hip or extremity fracture. These were weighted to represent 1,176,965 patients nationally. In the hip fracture group, rural patient status was associated with higher odds of mortality (OR 1.32, P < 0.001) but not complications (OR 0.95, P = 0.082). In the extremity fracture and polytrauma groups, rural patient status was not associated with significantly higher odds of mortality or complications. In the urban polytrauma group, zip code with below-median income was associated with increased odds of mortality (OR 1.23, P = 0.002) but not complications. In the rural polytrauma group, zip code with below-median income was not associated with significantly increased odds of mortality or complications. In the hip fracture and extremity fracture groups, below-median income was not associated with significantly higher odds of mortality.

CONCLUSION

We found that rural patients with hip fracture have higher mortality compared to urban patients and that socioeconomic disparities in mortality after a polytrauma exist in urban settings. These results speak to the ongoing need to develop objective measures of disparity-sensitive healthcare and optimize trauma systems to better serve low-income patients and patients in rural areas.

Use of a Six-Item Modified Frailty Index to Predict 30-day Adverse Events, Readmission, and Mortality in Older Patients Undergoing Surgical Fixation of Lower Extremity, Pelvic, and Acetabular Fractures

INTRODUCTION

This is a retrospective study evaluating the use of a new six-item modified frailty index (MF-6) to predict short-term outcomes of patients receiving surgery for lower extremity fractures.

METHODS

Patients older than 65 years undergoing open reduction and internal fixation for lower extremity, pelvic, and acetabulum fractures were identified from the American College of Surgeons National Surgical Quality Improvement Program. The MF-6 was calculated by assigning one point for each of six common conditions. Multivariable analysis was used to compare patients with an MF-6 of <3 and ≥3. Outcome measures included complications, mortality, readmission, revision surgery, and length of stay. An area under the curve receiver operator analysis was conducted to compare the MF-6 with MF-5, an existing five-item frailty index.

RESULTS

Nine thousand four hundred sixty-three patients were included. Patients with an MF-6 of ≥3 were at markedly higher risk of discharge destination other than home (Exp[B] = 2.09), mortality (Exp[B] = 2.48), major adverse events (Exp[B] = 2.16), and readmission (Exp[B] = 1.82). Receiver-operating curve analysis demonstrated an area under the curve of 0.65 for mortality, 0.62 for major adverse events, and 0.62 for discharge destination other than home, all of which outperformed the MF-5.

DISCUSSION

The MF-6 was correlated with a 30-day postoperative incidence of infectious complications, readmission, and discharge destination. MF-6 scores can be used to risk-stratify patient populations as shifts to value-based care continue to develop.

Flightless I Negatively Regulates Macrophage Surface TLR4, Delays Early Inflammation, and Impedes Wound Healing

TLR4 plays a pivotal role in orchestrating inflammation and tissue repair. Its expression has finally been balanced to initiate the early, robust immune response necessary for efficient repair without excessively amplifying and prolonging inflammation, which impairs healing. Studies show Flightless I (Flii) is an immunomodulator that negatively regulates macrophage TLR4 signalling. Using macrophages from Flii^+/−, WT, and Flii^Tg/Tg mice, we have shown that elevated Flii reduces early TLR4 surface expression, delaying and reducing subsequent TNF secretions. In contrast, reduced Flii increases surface TLR4, leading to an earlier robust TNF peak. In Flii^+/− mice, TLR4 levels peak earlier during wound repair, and overall healing is accelerated. Fewer neutrophils, monocytes and macrophages are recruited to Flii^+/− wounds, leading to fewer TNF-positive macrophages, alongside an early peak and a robust shift to M2 anti-inflammatory, reparative Ym1⁺ and IL-10⁺ macrophages. Importantly, in diabetic mice, high Flii levels are found in plasma and unwounded skin, with further increases observed in their wounds, which have impaired healing. Lowering Flii in diabetic mice results in an earlier shift to M2 macrophages and improved healing. Overall, this suggests Flii regulation of TLR4 reduces early inflammation and decreases the M2 macrophage phenotype, leading to impaired healing.

Prognostic Value of Early Fluorodeoxyglucose-Positron Emission Tomography Response Imaging and Peripheral Immunologic Biomarkers: Substudy of a Phase II Trial of Risk-Adaptive Chemoradiation for Unresectable Non-Small Cell Lung Cancer

Purpose

We sought to examine the prognostic value of fluorodeoxyglucose-positron emission tomography (PET) imaging during chemoradiation for unresectable non-small cell lung cancer for survival and hypothesized that tumor PET response is correlated with peripheral T-cell function.

Methods and Materials

Forty-five patients with American Joint Committee on Cancer version 7 stage IIB-IIIB non-small cell lung cancer enrolled in a phase II trial and received platinum-doublet chemotherapy concurrent with 6 weeks of radiation (NCT02773238). Fluorodeoxyglucose-PET was performed before treatment start and after 24 Gy of radiation (week 3). PET response status was prospectively defined by multifactorial radiologic interpretation. PET responders received 60 Gy in 30 fractions, while nonresponders received concomitant boosts to 74 Gy in 30 fractions. Peripheral blood was drawn synchronously with PET imaging, from which germline DNA sequencing, T-cell receptor sequencing, and plasma cytokine analysis were performed.

Results

Median follow-up was 18.8 months, 1-year overall survival (OS) 82%, 1-year progression-free survival 53%, and 1-year locoregional control 88%. Higher midtreatment PET total lesion glycolysis was detrimental to OS (1 year 87% vs 63%, P < .001), progression-free survival (1 year 60% vs 26%, P = .044), and locoregional control (1 year 94% vs 65%, P = .012), even after adjustment for clinical/treatment factors. Twenty-nine of 45 patients (64%) were classified as PET responders based on a priori definition. Higher tumor programmed death-ligand 1 expression was correlated with response on PET (P = .017). Higher T-cell receptor richness and clone distribution slope were associated with improved OS (P = .018-0.035); clone distribution slope was correlated with PET response (P = .031).

Conclusions

Midchemoradiation PET imaging is prognostic for survival; PET response may be linked to tumor and peripheral T-cell biomarkers.

Acceptability of OP/Na swabbing for SARS-CoV-2: a prospective observational cohort surveillance study in Western Australian schools

OBJECTIVES

When the COVID-19 pandemic was declared, Governments responded with lockdown and isolation measures to combat viral spread, including the closure of many schools. More than a year later, widespread screening for SARS-CoV-2 is critical to allow schools and other institutions to remain open. Here, we describe the acceptability of a minimally invasive COVID-19 screening protocol trialled by the Western Australian Government to mitigate the risks of and boost public confidence in schools remaining open. To minimise discomfort, and optimise recruitment and tolerability in unaccompanied children, a combined throat and nasal (OP/Na) swab was chosen over the nasopharyngeal swab commonly used, despite slightly reduced test performance.

DESIGN, SETTING AND PARTICIPANTS

Trialling of OP/Na swabbing took place as part of a prospective observational cohort surveillance study in 79 schools across Western Australia. Swabs were collected from 5903 asymptomatic students and 1036 asymptomatic staff in 40 schools monthly between June and September 2020.

OUTCOME MEASURES

PCR testing was performed with a two-step diagnostic and independent confirmatory PCR for any diagnostic PCR positives. Concurrent surveys, collected online through the REDCap platform, evaluated participant experiences of in-school swabbing.

RESULTS

13 988 swabs were collected from students and staff. There were zero positive test results for SARS-CoV-2, including no false positives. Participants reported high acceptability: 71% of students reported no or minimal discomfort and most were willing to be reswabbed (4% refusal rate).

CONCLUSIONS

OP/Na swabbing is acceptable and repeatable in schoolchildren as young as 4 years old and may combat noncompliance rates by significantly increasing the acceptability of testing. This kind of minimally-invasive testing will be key to the success of ongoing, voluntary mass screening as society adjusts to a new 'normal' in the face of COVID-19.

TRIAL REGISTRATION NUMBER

Australian New Zealand Clinical Trials Registry-ACTRN12620000922976.

Heartbeat instability as auto-oscillation between dim and bright void regimes

We investigated the self-excited as well as optogalvanically stimulated heartbeat instability in RF discharge complex plasma. Three video cameras measured the motion of the microparticles, the plasma emission, and the laser-induced fluorescence simultaneously. Comprehensive studies of the optogalvanic control of the heartbeat instability revealed that the microparticle suspension can be stabilized by a continuous laser, whereas a modulated laser beam induces the void contraction either transiently or resonantly. The resonance occurred when the laser modulation frequency coincided with the frequency of small breathing oscillations of the microparticle suspension, which are known to be a prerequisite to the heartbeat instability. Based on the experimental results we suggest that the void contraction during the instability is caused by an abrupt void transition from the dim to the bright regime [Pikalev et al., Plasma Sources Sci. Technol. 30, 035014 (2021)PSTEEU0963-025210.1088/1361-6595/abe0a2]. In the bright regime, a time-averaged electric field at the void boundary heats the electrons causing bright plasma emission inside the void. The dim void has much lower electric field at the boundary and exhibits therefore no emission feature associated with it.

"Zyflex": Next generation plasma chamber for complex plasma research in space

In this paper, we give a detailed description of a novel plasma chamber-the Zyflex chamber-that has been specifically designed for complex/dusty plasma research under reduced gravitational influence as realized during parabolic flight or aboard the International Space Station. The cylindrical, radio-frequency driven discharge device includes a variety of innovations that, for example, allow us to flexibly adjust plasma parameters and its volume via enhanced plasma generation control and a movable, multi-segmented electrode system. The new complex/dusty plasma research tool also supports, due to its overall increased size compared to former space based complex plasma experiments such as PKE-Nefedov or PK-3 Plus, much larger particle systems. Additionally, it can be operated at much lower neutral gas pressures, thus reducing the damping of particle motion considerably. Beyond the technical description and particle-in-cell simulation based characterization of the plasma vessel, we show sample results from experiments performed with this device in the laboratory as well as during parabolic flights, both of which clearly demonstrate the new quality of complex/dusty plasma research that becomes accessible with this new plasma device.

Treatment and outcomes of basicervical femoral neck fractures: A systematic review

PURPOSE

This study aims to systematically review the literature comparing surgical treatments options and respective failure rates for basicervical hip fractures.

METHODS

A comprehensive search of databases, including MEDLINE, Embase, Web of Science, and Cochrane Central for studies published in English on or before June 21, 2019 was performed. Selected search terms included "basicervical," "basi cervical," "AO/OTA type 31-B," "femoral neck fracture" AND "bone nails," "bone screws," "fracture fixation," "internal fixation," "arthroplasty," "cephalomedullary," "sliding hip screw," "ORIF," and "treatment outcome." We included studies that assessed outcomes of basicervical fracture fixation using open reduction internal fixation or arthroplasty. Two authors extracted the following data from each paper: study design, country, cohort year, definition of basicervical, intervention type, sample size, patient demographics, follow-up length, percent of fractures that required revision, and the percent of implants that failed.

RESULTS

Sixteen articles encompassing 910 patients were included. The main outcome was the percent of implants that required revision. The total revision rates were 8% (8 studies, 157 patients, range 0%-55%) for cephalomedullary nails, 7% (10 studies, 584 patients, range 0%-18%) for sliding hip screws, 23% (3 studies, 40 patients, range 16%-50%) for cannulated screws, 0% (1 study, 6 patients) for total hip arthroplasty, and 8% (2 studies, 13 patients, range 0%-11%) for hemiarthroplasty.

CONCLUSION

Management of basicervical fractures with SHS and CMN produces similar failure and re-operation rates. Limited evidence is available on the use of cannulated screws and arthroplasty, but available studies suggest that cannulated screws have an unacceptable revision rate (23%) while arthroplasty may be acceptable. Future studies examining the comparative efficacy of various fixation methods would benefit from strict definition of fracture type as well as consistent reporting of functional outcomes, re-operation rates, and mortality.

Plasma-polymerized pericyte patches improve healing of murine wounds through increased angiogenesis and reduced inflammation

Pericytes have the potential to be developed as a cell therapy for the treatment of wounds; however, the efficacy of any cell therapy relies on the successful delivery of intact and functioning cells. Here, the effect of delivering pericytes on wound repair was assessed alongside the development of a surface-functionalized pericyte patch. Plasma polymerization (PP) was used to functionalize the surface of silicone patches with heptylamine (HA) or acrylic acid (AA) monomers. Human pericytes were subsequently delivered to murine excisional wounds by intradermal injection or using the pericyte-laden patches and the comparative effects on wound healing, inflammation and revascularization determined. The AA surface provided the superior transfer of the cells to de-epidermized dermis. Excisional murine wounds treated either with pericytes injected directly into the wound or with the pericyte-laden AA patches showed improved healing with decreased neutrophil infiltration and reduced numbers of macrophages in the wounds. Pericyte delivery also enhanced angiogenesis through a mechanism independent of VEGF signalling. Pericytes, when delivered to wounds, improved healing responses by dampening inflammation and promoting angiogenesis. Delivery of pericytes using PP-AA-functionalized patches was equally as effective as direct injection of pericytes into wounds. Pericyte-functionalized dressings may therefore be a clinically relevant approach for the treatment of wounds.

Long-term evolution of the three-dimensional structure of string-fluid complex plasmas in the PK-4 experiment

Microparticle suspensions in a polarity-switched discharge plasma of the Plasmakristall-4 facility on board the International Space Station exhibit string-like order. As pointed out in [Phys. Rev. Research 2, 033314 (2020)2643-156410.1103/PhysRevResearch.2.033314], the string-order is subject to evolution on the timescale of minutes at constant gas pressure and constant parameters of polarity switching. We perform a detailed analysis of this evolution using the pair correlations and length spectrum of the string-like clusters (SLCs). Average exponential decay rate of the SLC length spectrum is used as a measure of string order. The analysis shows that the improvement of the string-like order is accompanied by the decrease of the thickness of the microparticle suspension, microparticle number density, and total amount of microparticles in the field of view. This suggests that the observed long-term evolution of the string-like order is caused by the redistribution of the microparticles, which significantly modifies the plasma conditions.

DETECT Schools Study Protocol: A Prospective Observational Cohort Surveillance Study Investigating the Impact of COVID-19 in Western Australian Schools

Introduction: Amidst the evolving COVID-19 pandemic, understanding the transmission dynamics of the SARS-CoV-2 virus is key to providing peace of mind for the community and informing policy-making decisions. While available data suggest that school-aged children are not significant spreaders of SARS-CoV-2, the possibility of transmission in schools remains an ongoing concern, especially among an aging teaching workforce. Even in low-prevalence settings, communities must balance the potential risk of transmission with the need for students' ongoing education. Through the roll out of high-throughput school-based SARS-CoV-2 testing, enhanced follow-up for individuals exposed to COVID-19 and wellbeing surveys, this study investigates the dynamics of SARS-CoV-2 transmission and the current psychosocial wellbeing impacts of the pandemic in school communities. Methods: The DETECT Schools Study is a prospective observational cohort surveillance study in 79 schools across Western Australia (WA), Australia. To investigate the incidence, transmission and impact of SARS-CoV-2 in schools, the study comprises three "modules": Module 1) Spot-testing in schools to screen for asymptomatic SARS-CoV-2; Module 2) Enhanced surveillance of close contacts following the identification of any COVID-19 case to determine the secondary attack rate of SARS-CoV-2 in a school setting; and Module 3) Survey monitoring of school staff, students and their parents to assess psycho-social wellbeing following the first wave of the COVID-19 pandemic in WA. Clinical Trial Registration: Trial registration number: ACTRN12620000922976.

Attenuation of Flightless I Increases Human Pericyte Proliferation, Migration and Angiogenic Functions and Improves Healing in Murine Diabetic Wounds

Pericytes are peri-vascular mural cells which have an important role in the homeostatic regulation of inflammatory and angiogenic processes. Flightless I (Flii) is a cytoskeletal protein involved in regulating cellular functions, but its involvement in pericyte activities during wound healing is unknown. Exacerbated inflammation and reduced angiogenesis are hallmarks of impaired diabetic healing responses, and strategies aimed at regulating these processes are vital for improving healing outcomes. To determine the effect of altering Flii expression on pericyte function, in vitro and in vivo studies were performed to assess the effect on healing, inflammation and angiogenesis in diabetic wounds. Here, we demonstrated that human diabetic wounds display upregulated expression of the Flii protein in conjunction with a depletion in the number of platelet derived growth factor receptor β (PDGFRβ) +/ neural glial antigen 2 (NG2) + pericytes present in the dermis. Human pericytes were found to be positive for Flii and attenuating its expression in vitro through siRNA knockdown led to enhanced proliferation, migration and angiogenic functions. Genetic knockdown of Flii in a streptozotocin-induced murine model of diabetes led to increased numbers of pericytes within the wound. This was associated with dampened inflammation, an increased rate of angiogenic repair and improved wound healing. Our findings show that Flii expression directly impacts pericyte functions, including proliferation, motility and angiogenic responses. This suggests that Flii regulation of pericyte function may be in part responsible for the changes in pericyte-related processes observed in diabetic wounds.

Relapse Rates in Patients with Clubfoot Treated Using the Ponseti Method Increase with Time: A Systematic Review

BACKGROUND

The Ponseti method is the preferred technique to manage idiopathic clubfoot deformity; however, there is no consensus on the expected relapse rate or the percentage of patients who will ultimately require a corrective surgical procedure. The objective of the present systematic review was to determine how reported rates of relapsed deformity and rates of a secondary surgical procedure are influenced by each study's length of follow-up.

METHODS

A comprehensive literature search using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines was performed to identify relevant articles. The definition of relapse, the percentage of patients who relapsed, the percentage of feet that required a surgical procedure, and the mean duration of follow-up of each study were extracted. Pearson correlations were performed to determine associations among the following variables: mean follow-up duration, percentage of patients who relapsed, percentage of feet that required a joint-sparing surgical procedure, and percentage of feet that required a joint-invasive surgical procedure. Logarithmic curve fit regressions were used to model the relapse rate, the rate of joint-sparing surgical procedures, and the rate of joint-invasive surgical procedures as a function of follow-up time.

RESULTS

Forty-six studies met the inclusion criteria. Four distinct definitions of relapse were identified. The reported relapse rates varied from 3.7% to 67.3% of patients. The mean duration of follow-up was strongly correlated with the relapse rate (Pearson correlation coefficient = 0.44; p < 0.01) and the percentage of feet that required a joint-sparing surgical procedure (Pearson correlation coefficient = 0.59; p < 0.01). Studies with longer follow-up showed significantly larger percentages of relapse and joint-sparing surgical procedures than studies with shorter follow-up (p < 0.05).

CONCLUSIONS

Relapses have been reported to occur at as late as 10 years of age; however, very few studies follow patients for at least 8 years. Notwithstanding that, the results indicated that the rate of relapse and percentage of feet requiring a joint-sparing surgical procedure increased as the duration of follow-up increased. Longer-term follow-up studies are required to accurately predict the ultimate risk of relapsed deformity. Patients and their parents should be aware of the possibility of relapse during middle and late childhood, and, thus, follow-up of these patients until skeletal maturity may be warranted.

LEVEL OF EVIDENCE

Therapeutic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Dynamics of spinning particle pairs in a single-layer complex plasma crystal

Spontaneous formation of spinning pairs of particles, or torsions, is studied in a single-layer complex plasma crystal by reducing the discharge power at constant neutral gas pressure. At higher gas pressures, torsions spontaneously form below a certain power threshold. Further reduction of the discharge power leads to the formation of multiple torsions. However, at lower gas pressures the torsion formation is preceded by mode-coupling instability (MCI). The crystal dynamics are studied with the help of the fluctuation spectra of crystal particles' in-plane velocities. Surprisingly, the spectra of the crystal with torsions and MCI are rather similar and contain hot spots at similar locations on the (k,ω) plane, despite very different appearances of the respective particle trajectories. The torsion rotation speed is close (slightly below) to the maximum frequency of the in-plane compressional mode. When multiple torsions form, their rotation speeds are distributed in a narrow range slightly below the maximum frequency.

Coupling of Noncrossing Wave Modes in a Two-Dimensional Plasma Crystal

We report an experimental observation of the coupling of the transverse vertical and longitudinal in-plane dust-lattice wave modes in a two-dimensional complex plasma crystal in the absence of mode crossing. A new large-diameter rf plasma chamber was used to suspend the plasma crystal. The observations are confirmed with molecular dynamics simulations. The coupling manifests itself in traces of the transverse vertical mode appearing in the measured longitudinal spectra and vice versa. We calculate the expected ratio of the trace to the principal mode with a theoretical analysis of the modes in a crystal with finite temperature and find good agreement with the experiment and simulations.

Capacitively coupled rf discharge with a large amount of microparticles: Spatiotemporal emission pattern and microparticle arrangement

The effect of micron-sized particles on a low-pressure capacitively coupled rf discharge is studied both experimentally and using numerical simulations. In the laboratory experiments, microparticle clouds occupying a considerable fraction of the discharge volume are supported against gravity with the help of the thermophoretic force. The spatiotemporally resolved optical emission measurements are performed with different arrangements of microparticles. The numerical simulations are carried out on the basis of a one-dimensional hybrid (fluid-kinetic) discharge model describing the interaction between plasma and microparticles in a self-consistent way. The study is focused on the role of microparticle arrangement in interpreting the spatiotemporal emission measurements. We show that it is not possible to reproduce simultaneously the observed microparticle arrangement and emission pattern in the framework of the considered one-dimensional model. This disagreement can be attributed to the two-dimensional effects (e.g., radial diffusion of the plasma components) or to the lack of the proper description of the sharp void boundary in the frame of fluid approach.

Wake-Mediated Propulsion of an Upstream Particle in Two-Dimensional Plasma Crystals

The wake-mediated propulsion of an "extra" particle in a channel of two neighboring rows of a two-dimensional plasma crystal, observed experimentally by Du et al. [Phys. Rev. E 89, 021101(R) (2014)PRESCM1539-375510.1103/PhysRevE.89.021101], is explained in simulations and theory. We use the simple model of a pointlike ion wake charge to reproduce this intriguing effect in simulations, allowing for a detailed investigation and a deeper understanding of the underlying dynamics. We show that the nonreciprocity of the particle interaction, owing to the wake charges, is responsible for a broken symmetry of the channel that enables a persistent self-propelled motion of the extra particle. We find good agreement of the terminal extra-particle velocity with our theoretical considerations and with experiments.

Density distribution of a dust cloud in three-dimensional complex plasmas

We propose a method of determination of the dust particle spatial distribution in dust clouds that form in three-dimensional (3D) complex plasmas under microgravity conditions. The method utilizes the data obtained during the 3D scanning of a cloud, and it provides reasonably good accuracy. Based on this method, we investigate the particle density in a dust cloud realized in gas discharge plasma in the PK-3 Plus setup onboard the International Space Station. We find that the treated dust clouds are both anisotropic and inhomogeneous. One can isolate two regimes in which a stationary dust cloud can be observed. At low pressures, the particle density decreases monotonically with the increase of the distance from the discharge center; at higher pressures, the density distribution has a shallow minimum. Regardless of the regime, we detect a cusp of the distribution at the void boundary and a slowly varying density at larger distances (in the foot region). A theoretical interpretation of the obtained results is developed that leads to reasonable estimates of the densities for both the cusp and the foot. The modified ionization equation of state, which allows for violation of the local quasineutrality in the cusp region, predicts the spatial distributions of ion and electron densities to be measured in future experiments.

Plasmakristall-4: New complex (dusty) plasma laboratory on board the International Space Station

New complex-plasma facility, Plasmakristall-4 (PK-4), has been recently commissioned on board the International Space Station. In complex plasmas, the subsystem of μm-sized microparticles immersed in low-pressure weakly ionized gas-discharge plasmas becomes strongly coupled due to the high (10³-10⁴ e) electric charge on the microparticle surface. The microparticle subsystem of complex plasmas is available for the observation at the kinetic level, which makes complex plasmas appropriate for particle-resolved modeling of classical condensed matter phenomena. The main purpose of PK-4 is the investigation of flowing complex plasmas. To generate plasma, PK-4 makes use of a classical dc discharge in a glass tube, whose polarity can be switched with the frequency of the order of 100 Hz. This frequency is high enough not to be felt by the relatively heavy microparticles. The duty cycle of the polarity switching can be also varied allowing to vary the drift velocity of the microparticles and (when necessary) to trap them. The facility is equipped with two videocameras and illumination laser for the microparticle imaging, kaleidoscopic plasma glow observation system and minispectrometer for plasma diagnostics and various microparticle manipulation devices (e.g., powerful manipulation laser). Scientific experiments are programmed in the form of scripts written with the help of specially developed C scripting language libraries. PK-4 is mainly operated from the ground (control center CADMOS in Toulouse, France) with the support of the space station crew. Data recorded during the experiments are later on delivered to the ground on the removable hard disk drives and distributed to participating scientists for the detailed analysis.

Quasi-two-dimensional complex plasma containing spherical particles and their binary agglomerates

A unique type of quasi-two-dimensional complex plasma system was observed which consisted of monodisperse microspheres and their binary agglomerations (dimers). The particles and their dimers levitated in a plasma sheath at slightly different heights and formed two distinct sublayers. The system did not crystallize and may be characterized as a disordered solid. The dimers were identified based on their characteristic appearance in defocused images, i.e., rotating interference fringe patterns. The in-plane and interplane particle separations exhibit nonmonotonic dependence on the discharge pressure.

Dust interferometers in plasmas

An interferometric imaging technique has been proposed to instantly measure the diameter of individual spherical dust particles suspended in a gas discharge plasma. The technique is based on the defocused image analysis of both spherical particles and their binary agglomerates. Above a critical diameter, the defocused images of spherical particles contain stationary interference fringe patterns and the fringe number increases with particle diameters. Below this critical diameter, the particle size has been measured using the rotational interference fringe patterns which appear only on the defocused images of binary agglomerates. In this case, a lower cutoff limit of particle diameter has been predicted, below which no such rotational fringe patterns are observed for the binary agglomerates. The method can be useful as a diagnostics for complex plasma experiments on earth as well as under microgravity conditions.

Plasma crystal dynamics measured with a three-dimensional plenoptic camera

Three-dimensional (3D) imaging of a single-layer plasma crystal was performed using a commercial plenoptic camera. To enhance the out-of-plane oscillations of particles in the crystal, the mode-coupling instability (MCI) was triggered in it by lowering the discharge power below a threshold. 3D coordinates of all particles in the crystal were extracted from the recorded videos. All three fundamental wave modes of the plasma crystal were calculated from these data. In the out-of-plane spectrum, only the MCI-induced hot spots (corresponding to the unstable hybrid mode) were resolved. The results are in agreement with theory and show that plenoptic cameras can be used to measure the 3D dynamics of plasma crystals.

Anisotropic confinement effects in a two-dimensional plasma crystal

The spectral asymmetry of the wave-energy distribution of dust particles during mode-coupling-induced melting, observed for the first time in plasma crystals by Couëdel et al. [Phys. Rev. E 89, 053108 (2014)PLEEE81539-375510.1103/PhysRevE.89.053108], is studied theoretically and by molecular-dynamics simulations. It is shown that an anisotropy of the well confining the microparticles selects the directions of preferred particle motion. The observed differences in intensity of waves of opposed directions are explained by a nonvanishing phonon flux. Anisotropic phonon scattering by defects and Umklapp scattering are proposed as possible reasons for the mean phonon flux.

Observation of particle pairing in a two-dimensional plasma crystal

The observation is presented of naturally occurring pairing of particles and their cooperative drift in a two-dimensional plasma crystal. A single layer of plastic microspheres was suspended in the plasma sheath of a capacitively coupled radio-frequency discharge in argon at a low pressure of 1 Pa. The particle dynamics were studied by combining the top-view and side-view imaging of the suspension. Cross-analysis of the particle trajectories allowed us to identify naturally occurring metastable pairs of particles. The lifetime of pairs was long enough for their reliable identification.

Synchronization of particle motion induced by mode coupling in a two-dimensional plasma crystal

The kinematics of dust particles during the early stage of mode-coupling induced melting of a two-dimensional plasma crystal is explored. It is found that the formation of the hybrid mode causes the particle vibrations to partially synchronize at the hybrid frequency. Phase- and frequency-locked hybrid particle motion in both vertical and horizontal directions (hybrid mode) is observed. The system self-organizes in a rhythmic pattern of alternating in-phase and antiphase oscillating chains of particles. The spatial orientation of the synchronization pattern correlates well with the directions of the maximal increment of the shear-free hybrid mode.

Network analysis of three-dimensional complex plasma clusters in a rotating electric field

Network analysis was used to study the structure and time evolution of driven three-dimensional complex plasma clusters. The clusters were created by suspending micron-size particles in a glass box placed on top of the rf electrode in a capacitively coupled discharge. The particles were highly charged and manipulated by an external electric field that had a constant magnitude and uniformly rotated in the horizontal plane. Depending on the frequency of the applied electric field, the clusters rotated in the direction of the electric field or remained stationary. The positions of all particles were measured using stereoscopic digital in-line holography. The network analysis revealed the interplay between two competing symmetries in the cluster. The rotating cluster was shown to be more cylindrical than the nonrotating cluster. The emergence of vertical strings of particles was also confirmed.

Cold atmospheric plasma for local infection control and subsequent pain reduction in a patient with chronic post-operative ear infection

Following surgery of cholesteatoma, a patient developed a chronic infection of the external auditory canal, including extended-spectrum β-lactamase producing Escherichia coli, which caused severe pain. The application of cold atmospheric plasma resulted in a significant reduction in pain and clearance of bacterial carriage, allowing antibiotics and analgesics to be ceased.

High-voltage nanosecond pulses in a low-pressure radio-frequency discharge

An influence of a high-voltage (3-17 kV) 20 ns pulse on a weakly-ionized low-pressure (0.1-10 Pa) capacitively coupled radiofrequency (RF) argon plasma is studied experimentally. The plasma evolution after pulse exhibits two characteristic regimes: a bright flash, occurring within 100 ns after the pulse (when the discharge emission increases by 2-3 orders of magnitude over the steady-state level), and a dark phase, lasting a few hundreds μs (when the intensity of the discharge emission drops significantly below the steady-state level). The electron density increases during the flash and remains very large at the dark phase. 1D3V particle-in-cell simulations qualitatively reproduce both regimes and allow for detailed analysis of the underlying mechanisms. It is found that the high-voltage nanosecond pulse is capable of removing a significant fraction of plasma electrons out of the discharge gap, and that the flash is the result of the excitation of gas atoms, triggered by residual electrons accelerated in the electric field of immobile bulk ions. The secondary emission from the electrodes due to vacuum UV radiation plays an important role at this stage. High-density plasma generated during the flash provides efficient screening of the RF field (which sustains the steady-state plasma). This leads to the electron cooling and, hence, onset of the dark phase.

Three-dimensional structure of Mach cones in monolayer complex plasma crystals

The structure of Mach cones in a crystalline complex plasma has been studied experimentally using an intensity sensitive imaging, which resolved particle motion in three dimensions. This revealed a previously unknown out-of-plane cone structure, which appeared due to excitation of the vertical wave mode. The complex plasma consisted of micron sized particles forming a monolayer in a plasma sheath of a gas discharge. Fast particles, spontaneously moving under the monolayer, created Mach cones with multiple structures. The in-plane cone structure was due to compressional and shear lattice waves.

Kinetics of the melting front in two-dimensional plasma crystals: Complementary analysis with the particle image and particle tracking velocimetries

Melting of a two-dimensional plasma crystal occurring due to a mode-coupling instability is studied using particle tracking and particle image velocimetry techniques. By combining these techniques, it is possible to identify the location of a propagating melting front and find a characteristic scale length for the temperature gradient across the front. It is found that the measurements of heat transport are consistent with a simple two-dimensional model allowing us to estimate the thermal diffusivity. The measured values for the thermal diffusivity are consistent with previously measured values.

Nonviscous motion of a slow particle in a dust crystal under microgravity conditions

Subsonic motion of a large particle moving through the bulk of a dust crystal formed by negatively charged small particles is investigated using the PK-3 Plus laboratory onboard the International Space Station. Tracing the particle trajectories shows that the large particle moves almost freely through the bulk of the plasma crystal, while dust particles move along characteristic α-shaped pathways near the large particle. In the hydrodynamic approximation, we develop a theory of nonviscous dust particle motion about a large particle and calculate particle trajectories. Good agreement with experiment validates our approach.

Fluid-solid phase transitions in three-dimensional complex plasmas under microgravity conditions

Phase behavior of large three-dimensional (3D) complex plasma systems under microgravity conditions onboard the International Space Station is investigated. The neutral gas pressure is used as a control parameter to trigger phase changes. Detailed analysis of structural properties and evaluation of three different melting-freezing indicators reveal that complex plasmas can exhibit melting by increasing the gas pressure. Theoretical estimates of complex plasma parameters allow us to identify main factors responsible for the observed behavior. The location of phase states of the investigated systems on a relevant equilibrium phase diagram is estimated. Important differences between the melting process of 3D complex plasmas under microgravity conditions and that of flat 2D complex plasma crystals in ground based experiments are discussed.

Freezing and melting of 3D complex plasma structures under microgravity conditions driven by neutral gas pressure manipulation

Freezing and melting of large three-dimensional complex plasmas under microgravity conditions is investigated. The neutral gas pressure is used as a control parameter to trigger the phase changes: Complex plasma freezes (melts) by decreasing (increasing) the pressure. The evolution of complex plasma structural properties upon pressure variation is studied. Theoretical estimates allow us to identify the main factors responsible for the observed behavior.

Kinetics of fluid demixing in complex plasmas: role of two-scale interactions

Using experiments and combining theory and computer simulations, we show that binary complex plasmas are particularly good model systems to study the kinetics of fluid-fluid demixing at the "atomistic" (individual particle) level. The essential parameters of interparticle interactions in complex plasmas, such as the interaction range(s) and degree of nonadditivity, can be varied significantly, which allows systematic investigations of different demixing regimes. The critical role of competition between long-range and short-range interactions at the initial stage of the spinodal decomposition is discussed.

Direct observation of mode-coupling instability in two-dimensional plasma crystals

Dedicated experiments on melting of two-dimensional plasma crystals were carried out. The melting was always accompanied by spontaneous growth of the particle kinetic energy, suggesting a universal plasma-driven mechanism underlying the process. By measuring three principal dust-lattice wave modes simultaneously, it is unambiguously demonstrated that the melting occurs due to the resonance coupling between two of the dust-lattice modes. The variation of the wave modes with the experimental conditions, including the emergence of the resonant (hybrid) branch, reveals exceptionally good agreement with the theory of mode-coupling instability.

First direct measurement of optical phonons in 2D plasma crystals

Spectra of phonons with out-of-plane polarization were studied experimentally in a 2D plasma crystal. The dispersion relation was directly measured for the first time using a novel method of particle imaging. The out-of-plane mode was proven to have negative optical dispersion at small wave numbers, comparison with theory showed good agreement. The effect of the plasma wakes on the dispersion relation is briefly discussed.

Formation of bubbles, blobs, and surface cusps in complex plasmas

Investigations of the dynamical evolution of a complex plasma, in which a vertical temperature gradient compensates gravity, were carried out. At low power the formation of microparticle bubbles, blobs, and spraying cusps was observed. This activity can be turned on and off by changing control parameters, such as the rf power and the gas pressure. Several observational effects indicate the presence of surface tension, even at small "nanoscales" of a few 100's of particles. By tracing the individual microparticle motion the detailed (atomistic) dynamics can be studied as well as the pressure dependence of the forces. A possible mechanism that could drive the observed phenomena is analogous to the Rayleigh-Taylor instability.

Dissipative dark soliton in a complex plasma

The observation of a dark soliton in a three-dimensional complex plasma containing monodisperse microparticles is presented. We perform our experiments using neon gas in the bulk plasma of an rf discharge. A gas temperature gradient of 500K/m is applied to balance gravity and to levitate the particles in the bulk plasma. The wave is excited by a short voltage pulse on the electrodes of the radio frequency discharge chamber. It is found that the wave propagates with constant speed. The propagation time of the dark soliton is approximately 20 times longer than the damping time.

Dynamics of lane formation in driven binary complex plasmas

The dynamical onset of lane formation is studied in experiments with binary complex plasmas under microgravity conditions. Small microparticles are driven and penetrate into a cloud of big particles, revealing a strong tendency towards lane formation. The observed time-resolved lane-formation process is in good agreement with computer simulations of a binary Yukawa model with Langevin dynamics. The laning is quantified in terms of the anisotropic scaling index, leading to a universal order parameter for driven systems.

First observation of electrorheological plasmas

We report the experimental discovery of "electrorheological (ER) complex plasmas," where the control of the interparticle interaction by an externally applied electric field is due to distortion of the Debye spheres that surround microparticles (dust) in a plasma. We show that interactions in ER plasmas under weak ac fields are mathematically equivalent to those in conventional ER fluids. Microgravity experiments, as well as molecular dynamics simulations, show a phase transition from an isotropic to an anisotropic (string) plasma state as the electric field is increased.

High speed laser tomography system

A high speed laser tomography system was developed capable of acquiring three-dimensional (3D) images of optically thin clouds of moving micron-sized particles. It operates by parallel-shifting an illuminating laser sheet with a pair of galvanometer-driven mirrors and synchronously recording two-dimensional (2D) images of thin slices of the imaged volume. The maximum scanning speed achieved was 120,000 slices/s, sequences of 24 volume scans (up to 256 slices each) have been obtained. The 2D slices were stacked to form 3D images of the volume, then the positions of the particles were identified and followed in the consecutive scans. The system was used to image a complex plasma with particles moving at speeds up to cm/s.

Highly resolved self-excited density waves in a complex plasma

Experimental results on self-excited density waves in a complex plasma are presented. An argon plasma is produced in a capacitively coupled rf discharge at a low power and gas pressure. A cloud of microparticles is subjected to effective gravity in the range of 1-4 g by thermophoresis. The cloud is stretched horizontally (width/height approximately 45 mm/8 mm). The critical pressure for the onset of the waves increases with the temperature gradient. The waves are propagating in the direction of the ion drift. The wave frequency, phase velocity, and wavelength are measured, and particle migrations affected by the waves are analyzed at a time scale of 1 ms/frame and a subpixel space resolution.

Void Closure in Complex Plasmas under Microgravity Conditions

We describe the first observation of a void closure in complex plasma experiments under microgravity conditions performed with the Plasma-Kristall (PKE-Nefedov) facility on board the International Space Station. The void--a grain-free region in the central part of the discharge where the complex plasma is generated--has been formed under most of the plasma conditions and thought to be an inevitable effect. However, we demonstrate in this Letter that an appropriate tune of the discharge parameters allows the void to close. This experimental achievement along with its theoretical interpretation opens new perspectives in engineering new experiments with large quasi-isotropic void-free complex plasma clouds in microgravity conditions.

Measurement of the interaction force among particles in three-dimensional plasma clusters

The interaction forces between particles have been studied in a 3D plasma cluster under weak external confinement. A suitable combination of dc and rf applied to a small electrode provided gravity compensation, uniform over dimensions much larger than the cluster itself. The forces acting on the particles could be reconstructed due to unique three-dimensional diagnostics, which allow us to obtain coordinates and velocities of all the particles simultaneously. The measurements yield a maximum (external) confinement force of 1.4 x 10(-15)N and interparticle force that is repulsive at short distances and attractive at larger distances, with a maximum attractive force of 2.4 X 10(-14)N at particle separation 195 microm.

Critical point in complex plasmas

The occurrence of liquid-vapor phase transition and the possible existence of a critical point in complex plasmas--systems that consist of charged micrograins in a neutralizing plasma background--is investigated theoretically. An analysis based on the consideration of the intergrain interaction potential suggests that under certain conditions systems near and at the critical point should be observable. Measurements under microgravity conditions would appear to be required. The analysis aims at determining the plasma parameter regime most suitable for planned experimental investigations.

Force field inside the void in complex plasmas under microgravity conditions

Observations of complex plasmas under microgravity conditions onboard the International Space Station performed with the Plasma-Kristall experiment-Nefedov facility are reported. A weak instability of the boundary between the central void (region free of microparticles) and the microparticle cloud is observed at low gas pressures. The instability leads to periodic injections of a relatively small number of particles into the void region (by analogy this effect is called the "trampoline effect"). The trajectories of injected particles are analyzed providing information on the force field inside the void. The experimental results are compared with theory which assumes that the most important forces inside the void are the electric and the ion drag forces. Good agreement is found clearly indicating that under conditions investigated the void formation is caused by the ion drag force.

Molecular tagging of a senescence gene by introgression mapping of a stay-green mutation from Festuca pratensis

* Intergeneric hybrids between Lolium multiflorum and Festuca pratensis (Lm/Fp) and their derivatives exhibit a unique combination of genetic and cytogenetic characteristics: chromosomes undergo a high frequency of homoeologous recombination at meiosis; the chromosomes of the two species can easily be discriminated by genomic in situ hybridization (GISH); recombination occurs along the entire length of homoeologous bivalents; a high frequency of marker polymorphism is observed between the two species. * This combination of characters has been used to transfer and isolate a F. pratensis chromosome segment carrying a mutant 'stay-green' gene conferring a disrupted leaf senescence phenotype into L. multiflorum. * The genetic location within the introgressed F. pratensis segment of the senescence gene has been mapped using amplified fragment length polymorphisms (AFLPs), and F. pratensis-specific AFLP markers closely flanking the green gene have been cloned. * The use of these cloned sequences as markers for the stay-green locus in marker-assisted selection programmes has been tested. The potential application of Lm/Fp introgressions as a tool for the map-based cloning of introgressed Fp genes is discussed.

Diagnostics of the electronegative plasma sheath at low pressures using microparticles

Levitated particles are a new powerful diagnostic of the midplasma sheath region. They can reveal features undetectable either to plasma or to surface measurements. The equilibrium position of microparticles suspended in an oxygen plasma sheath, together with a model of the levitation force and Langmuir probe measurements, gives evidence of secondary electropositive plasmas in the already established plasma sheath, in the range of parameters where the modified Bohm criterion breaks down into multiple solutions.