Experimental Measurements of Ion Diffusion Coefficients and Heating in a Multi-Ion-Species Plasma Shock.

Collisional plasma shocks generated from supersonic flows are an important feature in many astrophysical and laboratory high-energy-density plasmas. Compared to single-ion-species plasma shocks, plasma shock fronts with multiple ion species contain additional structure, including interspecies ion separation driven by gradients in species concentration, temperature, pressure, and electric potential. We present time-resolved density and temperature measurements of two ion species in collisional plasma shocks produced by head-on merging of supersonic plasma jets, allowing determination of the ion diffusion coefficients. Our results provide the first experimental validation of the fundamental inter-ion-species transport theory. The temperature separation, a higher-order effect reported here, is valuable for advancements in modeling HED and ICF experiments.

Ischemic Preconditioning, But Not Priming Exercise, Improves Exercise Performance in Trained Rock Climbers.

ABSTRACT: MacDougall, KB, McClean, ZJ, MacIntosh, BR, Fletcher, JR, and Aboodarda, SJ. Ischemic preconditioning, but not priming exercise, improves exercise performance in trained rock climbers. J Strength Cond Res 37(11): 2149-2157, 2023-To assess the effects of ischemic preconditioning (IPC) and priming exercise on exercise tolerance and performance fatigability in a rock climbing-specific task, 12 rock climbers completed familiarization and baseline tests, and constant-load hangboarding tests (including 7 seconds on and 3 seconds off at an intensity estimated to be sustained for approximately 5 minutes) under 3 conditions: (a) standardized warm-up (CON), (b) IPC, or (c) a priming warm-up (PRIME). Neuromuscular responses were assessed using the interpolated twitch technique, including maximum isometric voluntary contraction (MVC) of the finger flexors and median nerve stimulation, at baseline and after the performance trial. Muscle oxygenation was measured continuously using near-infrared spectroscopy (NIRS) across exercise. Time to task failure (T lim ) for IPC (316.4 ± 83.1 seconds) was significantly greater than CON (263.6 ± 69.2 seconds) ( p = 0.028), whereas there was no difference between CON and PRIME (258.9 ± 101.8 seconds). At task failure, there were no differences in MVC, single twitch force, or voluntary activation across conditions; however, recovery of MVC and single twitch force after the performance trial was delayed for IPC and PRIME compared with CON ( p < 0.05). Despite differences in T lim , there were no differences in any of the NIRS variables assessed. Overall, despite exercise tolerance being improved by an average of 20.0% after IPC, there were no differences in neuromuscular responses at task failure, which is in line with the notion of a critical threshold of peripheral fatigue. These results indicate that IPC may be a promising precompetition strategy for rock climbers, although further research is warranted to elucidate its mechanism of action.

MRI safety, imaging artefacts, and grid distortion evaluated for FFP3 respiratory masks worn throughout the COVID-19 pandemic.

AIM: To determine which filtering face piece (FFP3) respirators worn throughout the COVID-19 pandemic are safe for magnetic resonance imaging (MRI). MATERIALS AND METHODS: Three clinical MRI sequences were performed to assess imaging artefacts, grid distortion, and local heating for eight commercially available FFP3 respirators. All examinations were performed at Cardiff University Brain Research Imaging Centre using a 3 T Siemens Magnetom Prisma with a 64-channel head and neck coil. Each FFP3 mask was positioned on a custom-developed three-dimensional (3D) head phantom for testing. RESULTS: Five of the eight FFP3 masks contained ferromagnetic components and were regarded as "MRI unsafe". One mask was considered "MRI conditional" and only two masks were deemed "MRI safe" for both MRI staff and patients. Temperature strips positioned at the nasal bridge of the phantom did not exhibit local heating. A maximum grid distortion of 5 mm was seen in the anterior portion of the head of the ferromagnetic FFP3 masks. CONCLUSION: This study has demonstrated the importance of assessing respiratory FFP3 masks for use in and around MRI machines. Future research involving FFP3 masks can be conducted safely by following the procedures laid out in this study.

Efficiency of cycling exercise: Quantification, mechanisms, and misunderstandings.

The energetics of cycling represents a well-studied area of exercise science, yet there are still many questions that remain. Efficiency, broadly defined as the ratio of energy output to energy input, is one key metric that, despite its importance from both a scientific as well as performance perspective, is commonly misunderstood. There are many factors that may affect cycling efficiency, both intrinsic (e.g., muscle fiber type composition) and extrinsic (e.g., cycling cadence, prior exercise, and training), creating a complex interplay of many components. Due to its relative simplicity, the measurement of oxygen uptake continues to be the most common means of measuring the energy cost of exercise (and thus efficiency); however, it is limited to only a small proportion of the range of outputs humans are capable of, further limiting our understanding of the energetics of high-intensity exercise and any mechanistic bases therein. This review presents evidence that delta efficiency does not represent muscular efficiency and challenges the notion that the slow component of oxygen uptake represents decreasing efficiency. It is noted that gross efficiency increases as intensity of exercise increases in spite of the fact that fast-twitch fibers are recruited to achieve this high power output. Understanding the energetics of high-intensity exercise will require critical evaluation of the available data.

A comparison of floor surfaces for injury prevention in care settings: impact forces and horizontal pulling force required to move wheeled equipment.

Shock-absorbing flooring is one potential solution to prevent fall-related injuries. No standards exist to characterize shock-absorbing healthcare flooring. This study explores two mechanical tests for impact force reduction and horizontal force required to move wheeled objects. An appropriately designed rubber underlay can reduce peak impact by 25% compared with 1% with standard vinyl. INTRODUCTION: Severe falls often occur in hospitals and care homes. Shock-absorbing flooring is one potential solution to prevent fall-related injuries; however, no standards exist for characterizing flooring as an injury prevention measure. Shock-absorbing flooring use in high-risk settings may influence both patients (injury-saving potential) and staff (manoeuvring equipment). We aimed to explore two tests to characterize floors, to determine shock absorbency and horizontal pulling force required to move wheeled objects. METHODS: Mechanical testing was performed according to the Canadian Standards Association Z325 Hip Protectors document. This test was developed for hip protectors but is applicable to compliant surfaces that form part of the floor. Tests were performed on commercially available floor materials (suitable for care settings) to assess the force required to initiate movement of a wheeled object across the floor. We explored the relationships between horizontal force required to pull wheeled objects, impact force, floor thickness, and core material. RESULTS: Considerable differences were identified between floor samples in their ability to reduce the peak impact force (range 0.7-25%). A peak force reduction of up to 25% can be achieved with a specially designed rubber underlay. Horizontal pulling force increased with floor thickness but was lower for rubber floors. There was no direct relationship between impact attenuation and horizontal pulling force. Whilst thickness and core material explain some variations (66.5% for wheel movement; 82.3% for impact), other unmeasured factors clearly influence floor performance. CONCLUSIONS: These results can inform the development of flooring and the establishment of standards needed to underpin practice, research, and development in this field.

Additional in-series compliance does not affect the length dependence of activation in rat medial gastrocnemius.

NEW FINDINGS: What is the central question of this study? The length dependence of activation (LDA) is typically explained by a length-dependent increase in calcium sensitivity, but recently calcium-independent mechanisms have been suggested: does active muscle shortening provided by a compliant in-series component impact the muscle length at which force output is maximized, thus contributing to LDA? What is the main finding and its importance? Using an in situ rat medial gastrocnemius set-up and varying the magnitude of muscle shortening via an artificial compliant series-elastic component, we were unable to observe any change in optimal length between conditions, contrary to some previous findings. More research is therefore required to explain these discrepancies. ABSTRACT: The force-length relationship dictates the amount of force a muscle can produce as a function of its length, during maximal isometric contractions. When activation is submaximal, it has been shown that the length at which force production is highest (the optimal length) is longer. This is typically explained by a length-dependent increase in Ca2+ sensitivity, known as the 'length dependence of activation'. Recent reports have implicated shortening against in-series compliance to be a potential factor in the observed optimal length (L0 ) of muscle, via the phenomenon of shortening-induced force depression (a phenomenon which describes the relative reduction in muscle force when a muscle is actively shortening to a given length compared to contracting isometrically at that same length). In the current study, rat medial gastrocnemius was stimulated with single and triple pulses (200 Hz) over a range of lengths, both with and without additional in-series compliance provided by a small piece of silicon tubing in series with the muscle, which allowed greater fascicle shortening upon activation. Fascicle length was measured using sonomicrometry crystals, and peak force (Fpeak ) and L0 were estimated by curve-fitting of the force-length data. The additional in-series compliance significantly reduced Fpeak by approximately 14% and 25% for the single and triple pulses, respectively (P = 0.003, P < 0.001), yet L0 remained unchanged (P = 0.405), suggesting that in our model, shortening against in-series compliance does not affect L0 . We offer potential explanations for the discrepancies seen and discuss whether the velocity of shortening may have a role in the length dependence of force.

Biomechanical testing of hip protectors following the Canadian Standards Association express document.

A variety of hip protectors are available, but it is not clear which is the most effective and there is no standard test to evaluate their performance. This is the first study that uses a standard mechanical test on hip protectors. Some protectors perform well but others are almost ineffective, providing little to no protection to the wearer during a fall. INTRODUCTION: Each year, over 70,000 patients are admitted to hospital in the UK with hip fractures. There are a variety of commercial hip protectors currently available. However, it is not explicitly clear which is the most effective with regard to maximum force attenuation, whilst still being both comfortable for the user and providing reasonable force reduction if misplaced from the intended position. The numerous test methods reported in the literature have given conflicting results, making objective comparison difficult for users, researchers, and manufacturers alike. The Canadian Standards Association (CSA) has therefore published an express document (EXP-08-17) with a draft standard test method. This paper presents initial results for a range of hip protectors. METHODS: Eighteen commercially available hip protectors were tested according to EXP-08-17. Each hip protector was impacted five times in correct anatomical alignment over the greater trochanter and once at 50 mm displacements in the anterior, posterior, and lateral directions. RESULTS: Considerable differences were identified between individual hip protectors in their ability to reduce impact forces on the femur (between 3% and 36% reduction in peak force). The performance was reduced when misplaced in many cases (maximum reduction only 20%). CONCLUSIONS: This is the first study that uses a standard mechanical test on hip protectors. Previous studies have used a variety of methods, making it difficult to interpret results. We hope that these results using a standard test method will facilitate the effective comparison of results, as well as providing useful data for clinicians, users, and purchasers.

Observations of Multiple Nuclear Reaction Histories and Fuel-Ion Species Dynamics in Shock-Driven Inertial Confinement Fusion Implosions.

Fuel-ion species dynamics in hydrodynamiclike shock-driven DT^{3}He-filled inertial confinement fusion implosion is quantitatively assessed for the first time using simultaneously measured D^{3}He and DT reaction histories. These reaction histories are measured with the particle x-ray temporal diagnostic, which captures the relative timing between different nuclear burns with unprecedented precision (∼10 ps). The observed 50±10 ps earlier D^{3}He reaction history timing (relative to DT) cannot be explained by average-ion hydrodynamic simulations and is attributed to fuel-ion species separation between the D, T, and ^{3}He ions during shock convergence and rebound. At the onset of the shock burn, inferred ^{3}He/T fuel ratio in the burn region using the measured reaction histories is much higher as compared to the initial gas-filled ratio. As T and ^{3}He have the same mass but different charge, these results indicate that the charge-to-mass ratio plays an important role in driving fuel-ion species separation during strong shock propagation even for these hydrodynamiclike plasmas.

Detection of influenza virus by electrochemical surface plasmon resonance under potential modulation.

In this study we report the development of a novel viral pathogen immunosensor technology based on the electrochemical modulation of the optical signal from a surface plasmon wave interacting with a redox dye reporter. The device is formed by incorporating a sandwich immunoassay onto the surface of a plasmonic device mounted in a micro-electrochemical flow cell, where it is functionalized with a monoclonal antibody aimed to a specific target pathogen antigen. Once the target antigen is bound to the surface, it promotes the capturing of a secondary polyclonal antibody that has been conjugated with a redox-active methylene blue dye. The methylene blue displays a reversible change in the complex refractive index throughout a reduction-oxidation transition, which generates an optical signal that can be electrochemically modulated and detected at high sensitivity. For proof-of-principle measurements, we have targeted the hemagglutinin protein from the H5N1 avian influenza A virus to demonstrate the capabilities of our device for detection and quantification of a critical influenza antigen. Our experimental results of the EC-SPR-based immunosensor under potential modulation showed a 300 pM limit of detection for the H5N1 antigen.

Highly Resolved Measurements of a Developing Strong Collisional Plasma Shock.

The structure of a strong collisional shock front forming in a plasma is directly probed for the first time in laser-driven gas-jet experiments. Thomson scattering of a 526.5 nm probe beam was used to diagnose temperature and ion velocity distribution in a strong shock (M∼11) propagating through a low-density (ρ∼0.01 mg/cc) plasma composed of hydrogen. A forward-streaming population of ions traveling in excess of the shock velocity was observed to heat and slow down on an unmoving, unshocked population of cold protons, until ultimately the populations merge and begin to thermalize. Instabilities are observed during the merging, indicating a uniquely plasma-phase process in shock front formation.

Relationships between MRI fat distributions and sleep apnea and obesity hypoventilation syndrome in very obese patients.

PURPOSE: Obesity is associated with both obstructive sleep apnea (OSA) and obesity hypoventilation. Differences in adipose tissue distribution are thought to underlie the development of both OSA and hypoventilation. We explored the relationships between the distribution of upper airway, neck, chest, abdominal and muscle fat in very obese individuals. METHODS: We conducted a cross-sectional cohort study of individuals presenting to a tertiary sleep clinic or for assessment for bariatric surgery. Individuals underwent magnetic resonance (MR) imaging of their upper airway, neck, chest, abdomen and thighs; respiratory polygraphy; 1 week of autotitrating CPAP; and morning arterial blood gas to determine carbon dioxide partial pressure and base excess. RESULTS: Fifty-three individuals were included, with mean age of 51.6 ± 8.4 years and mean BMI of 44.3 ± 7.9 kg/m2; there were 27 males (51%). Soft palate, tongue and lateral wall volumes were significantly associated with the AHI in univariable analyses (p < 0.001). Gender was a significant confounder in these associations. No significant associations were found between MRI measures of adiposity and hypoventilation. CONCLUSIONS: In very obese individuals, our results indicate that increased volumes of upper airway structures are associated with increased severity of OSA, as previously reported in less obese individuals. Increasingly large upper airway structures that reduce pharyngeal lumen size are likely to lead to OSA by increasing the collapsibility of the upper airway. However, we did not show any significant association between regional fat distribution and propensity for hypoventilation, in this population.

Adhesion molecule increases in sleep apnea: beneficial effect of positive airway pressure and moderation by obesity.

BACKGROUND: Elevated levels of intercellular adhesion molecule 1 (ICAM-1) and vascular cell adhesion molecule 1 (VCAM-1) may contribute to cardiovascular disease and are associated with obstructive sleep apnea (OSA) and obesity. The relationship between OSA and obesity in determining ICAM-1 and VCAM-1 levels, and the effect of treatment, is unclear. OBJECTIVE: Our aim was to study whether positive airway pressure (PAP) usage resulted in changes in ICAM-1 and VCAM-1 after 2 years within 309 OSA patients from the Icelandic Sleep Apnea Cohort, and determine how obesity affected such changes. SUBJECTS/METHODS: The mean body mass index (BMI) was 32.4±5.1 kg m(-2); subjects had moderate-to-severe OSA (apnea-hypopnea index=45.0±20.2) and 79% were male. There were 177 full PAP users (⩾4 h per night and ⩾20 of last 28 nights), 44 partial (<4 h per night or <20 nights) and 88 nonusers. RESULTS: ICAM-1 (P<0.001) and VCAM-1 (P=0.012) change was significantly different among the PAP groups. The largest ICAM-1 differences were among the most obese subjects (P<0.001). At follow-up, nonusers had increased ICAM-1 compared with decreased levels in full users. All groups had increased VCAM-1, but nonusers had a significantly larger increase than full users. CONCLUSIONS: Within moderate-to-severe OSA patients, PAP usage prevents increases in adhesion molecules observed in nonusers after 2 years. For ICAM-1, the largest effect is in the most obese subjects. As OSA and obesity commonly coexist, the usage of PAP to limit increases in adhesion molecules may decrease the rate of progression of OSA-related cardiovascular disease.

The validity and reliability of quadriceps twitch force as a measure of skeletal muscle fatigue while cycling.

The measurement of skeletal muscle fatigue in response to cycling exercise is commonly done in isometric conditions, potentially limiting its ecological validity, and creating challenges in monitoring the time course of muscle fatigue across an exercise bout. This study aimed to determine if muscle fatigue could be reliably assessed by measuring quadriceps twitch force evoked while pedaling, using instrumented pedals. Nine participants completed three laboratory visits: a step incremental test to determine power output at lactate threshold, and on separate occasions, two constant-intensity bouts at a power output 10% above lactate threshold. Femoral nerve electrical stimulation was applied to elicit quadriceps twitch force both while pedaling (dynamic) and at rest (isometric). The test-retest reliability of the dynamic twitch forces and the agreement between the dynamic and isometric twitch forces were evaluated. Dynamic twitch force was found to have excellent reliability in an unfatigued state (intraclass correlation coefficient (ICC) = 0.920 and mean coefficient of variation (CV) = 7.5%), and maintained good reliability at task failure (ICC = 0.846 and mean CV = 11.5%). When comparing dynamic to isometric twitch forces across the task, there was a greater relative decline in the dynamic condition (P = 0.001). However, when data were normalized to the 5 min timepoint when potentiation between conditions was presumed to be more similar, this difference disappeared (P = 0.207). The reliability of this method was shown to be commensurate with the gold standard method utilizing seated isometric dynamometers and offers a new avenue to monitor the kinetics of muscle fatigue during cycling in real time.

Acute performance fatigability following continuous versus intermittent cycling protocols is not proportional to total work done.

Classical training theory postulates that performance fatigability following a training session should be proportional to the total work done (TWD); however, this notion has been questioned. This study investigated indices of performance and perceived fatigability after primary sessions of high-intensity interval training (HIIT) and constant work rate (CWR) cycling, each followed by a cycling time-to-task failure (TTF) bout. On separate days, 16 participants completed an incremental cycling test, and, in a randomized order, (i) a TTF trial at 80% of peak power output (PPO), (ii) an HIIT session, and (iii) a CWR session, both of which were immediately followed by a TTF trial at 80% PPO. Central and peripheral aspects of performance fatigability were measured using interpolated twitch technique, and perceptual measures were assessed prior to and following the HIIT and CWR trials, and again following the TTF trial. Despite TWD being less following HIIT (P = 0.029), subsequent TTF trial was an average of 125 s shorter following HIIT versus CWR (P < 0.001), and this was accompanied by greater impairments in voluntary and electrically evoked forces (P < 0.001), as well as exacerbated perceptual measures (P < 0.001); however, there were no differences in any fatigue measure following the TTF trial (P ≥ 0.149). There were strong correlations between the decline in TTF and indices of peripheral (r = 0.70) and perceived fatigability (r ≥ 0.80) measured at the end of HIIT and CWR. These results underscore the dissociation between TWD and performance fatigability and highlight the importance of peripheral components of fatigability in limiting endurance performance during high-intensity cycling exercise.

Impact of mid-Z gas fill on dynamics and performance of shock-driven implosions at the OMEGA laser.

Shock-driven implosions with 100% deuterium (D_{2}) gas fill compared to implosions with 50:50 nitrogen-deuterium (N_{2}D_{2}) gas fill have been performed at the OMEGA laser facility to test the impact of the added mid-Z fill gas on implosion performance. Ion temperature (T_{ion}) as inferred from the width of measured DD-neutron spectra is seen to be 34%±6% higher for the N_{2}D_{2} implosions than for the D_{2}-only case, while the DD-neutron yield from the D_{2}-only implosion is 7.2±0.5 times higher than from the N_{2}D_{2} gas fill. The T_{ion} enhancement for N_{2}D_{2} is observed in spite of the higher Z, which might be expected to lead to higher radiative loss, and higher shock strength for the D_{2}-only versus N_{2}D_{2} implosions due to lower mass, and is understood in terms of increased shock heating of N compared to D, heat transfer from N to D prior to burn, and limited amount of ion-electron-equilibration-mediated additional radiative loss due to the added higher-Z material. This picture is supported by interspecies equilibration timescales for these implosions, constrained by experimental observables. The one-dimensional (1D) kinetic Vlasov-Fokker-Planck code ifp and the radiation hydrodynamic simulation codes hyades (1D) and xrage [1D, two-dimensional (2D)] are brought to bear to understand the observed yield ratio. Comparing measurements and simulations, the yield loss in the N_{2}D_{2} implosions relative to the pure D_{2}-fill implosion is determined to result from the reduced amount of D_{2} in the fill (fourfold effect on yield) combined with a lower fraction of the D_{2} fuel being hot enough to burn in the N_{2}D_{2} case. The experimental yield and T_{ion} ratio observations are relatively well matched by the kinetic simulations, which suggest interspecies diffusion is responsible for the lower fraction of hot D_{2} in the N_{2}D_{2} relative to the D_{2}-only case. The simulated absolute yields are higher than measured; a comparison of 1D versus 2D xrage simulations suggest that this can be explained by dimensional effects. The hydrodynamic simulations suggest that radiative losses primarily impact the implosion edges, with ion-electron equilibration times being too long in the implosion cores. The observations of increased T_{ion} and limited additional yield loss (on top of the fourfold expected from the difference in D content) for the N_{2}D_{2} versus D_{2}-only fill suggest it is feasible to develop the platform for studying CNO-cycle-relevant nuclear reactions in a plasma environment.

Genetic susceptibility for ischemic infarction and arteriolosclerosis based on neuropathologic evaluations.

BACKGROUND: Recent genetic studies of stroke and related risk factors have identified a growing number of susceptibility loci; however, the relationship of these alleles to ischemic stroke is unknown. The challenge in finding reproducible loci of ischemic stroke susceptibility may be in part related to the etiologic heterogeneity in clinically defined stroke subtypes. In this study, we tested whether known single nucleotide polymorphisms (SNPs) associated with stroke or putative stroke risk factors are associated with neuropathologically defined micro- or macroscopic infarcts and with arteriolosclerosis. METHODS: Measures of neuropathology and genotyping were available from 755 deceased participants from the Religious Orders Study and the Rush Memory and Aging Project. All donated brains were examined by a board-certified neuropathologist using standardized protocol for the presence of microscopic infarct, macroscopic infarct and arteriolosclerosis (lipohyalinosis). In primary analysis, 74 candidate SNPs previously associated (p < 5 × 10(-8)) with ischemic stroke or known risk factors, including atrial fibrillation (AF), hypertension, diabetes, low-density lipoprotein (LDL) level and carotid artery stenosis, were evaluated for association with neuropathologic endpoints. We performed a secondary exploratory analysis to include 93 additional SNPs associated with putative ischemic stroke risk factors including SNPs associated with high-density lipoprotein (HDL), triglyceride serum levels, myocardial infarction (MI), coronary artery disease and cerebral white matter disease. Regression models relating SNPs to cerebrovascular neuropathology were adjusted for age at death, gender and cohort membership. RESULTS: The strongest associations seen for both macroscopic and microscopic infarcts were risk variants associated with diabetes. The diabetes risk variant rs7578326 located near the IRS1 locus was associated with both macroscopic (OR = 0.73, p = 0.011) and microscopic (OR = 0.71, p = 0.009) infarct pathology. Another diabetes susceptibility locus (rs12779790) located between the calcium/calmodulin-dependent protein kinase ID (CAMK1D) and cell division cycle 123 homolog (CDC123) genes is also associated with both macroscopic (OR = 1.40, p = 0.0292) and microscopic infarcts (OR = 1.43, p = 0.0285). The diabetes risk variant rs864745 within JAZF1 was associated with arteriolosclerosis (OR = 0.80, p = 0.014). We observed suggestive associations with the diabetes risk variant rs7961581 (p = 0.038; between TSPAN8 and LGR5) and rs5215 (p = 0.043; KCNJ11), the LDL risk variant rs11206510 (p = 0.045; PCSK9), as well as the AF risk locus ZFHX3. The CDKN2A/B locus (rs2383207, 9p21), identified initially as a susceptibility allele for MI and recently implicated in large vessel stroke, was associated with macroscopic infarct pathology in our autopsy cohort (OR = 1.26, p = 0.031). CONCLUSION: Our results suggest replication of the candidate CDKN2A/B stroke susceptibility locus with directly measured macroscopic stroke neuropathology, and further implicate several diabetes and other risk variants with secondary, pleiotropic associations to stroke-related pathology in our autopsy cohort. When coupled with larger sample sizes, cerebrovascular neuropathologic phenotypes will likely be powerful tools for the genetic dissection of susceptibility for ischemic stroke.