XPS Binding Energy Shifts in 2D Ti3C2Tz MXene go largely Beyond Intuitive Explanations: Rationalization from DFT Simulations and Experiments.

MXenes are prototypes of surface tunable 2D materials with vast potential for properties tuning. Accurately characterizing their surface functionalization and its role in electronic structure is crucial, X-ray photoelectron spectroscopy (XPS) being among the go-to methods to do so. Despite extensive use, XPS analysis remains however intricate. Focusing on the benchmark MXene Ti3C2Tz, Density Functional Theory (DFT) calculations of core-level binding energy shifts (BE.s.) are combined with experiments in order to provide a quantitative interpretation of XPS spectra. This approach demonstrates that BE.s. are driven by the complex interplay between chemical, structural, and subtle electronic structure effects preventing analysis from intuitive arguments or comparison with reference materials. In particular, it is shown that O terminations induce the largest BE.s. at Ti 2p levels despite lower electronegativity than F. Additionally, F 1s levels show weak sensitivity to the F local environment, explaining the single contribution in the spectrum, whereas O 1s states are significantly affected by the local surface chemistry. Finally, clear indicators of surface group vacancies are given at Ti 2p and O 1s levels. These results demonstrate the combination of calculations with experiments as a method of the highest value for MXenes XPS spectra analysis, providing guidelines for otherwise complex interpretations.

Luminescence Thermochromism of a Noncluster Copper Iodide Complex.

Hybrid copper(I) halide materials are currently attracting significant attention due to their exceptional luminescence properties, offering great potential for the development of multifunctional emissive materials with, in addition, eco-friendly features. A binuclear copper iodide complex, based on the [Cu2I2L4] motif with phosphite derivatives as ligands, has been synthesized and structurally characterized. Photophysical investigations indicate that this complex displays luminescence thermochromic properties, which are characterized by a temperature-dependent change in the relative intensity of two emission bands. The high-contrast luminescence thermochromism, with an important color variation from purple to cyan, is ascribed to the thermal equilibrium of two different excited states. While thermochromism is relatively known for multimetallic complexes, the perfectly controlled thermochromism of the studied compound is unprecedented for a binuclear complex. From theoretical investigations, this original feature is due to the coordination of phosphite ligands, which induces a specific energy layout of the complex, presenting vacant orbitals of varying nature. This single-component, dual-emissive binuclear complex, displaying relevant sensitivity temperature response, presents great potential for luminescence ratiometric thermometry applications. This study underlines the relevance of the ligand engineering strategy in developing original, emissive, and sustainable copper-based materials.

Investigating premotor corticospinal excitability in fast and slow voluntary contractions of the elbow flexors.

Corticospinal excitability (CSE) increases prior to a voluntary contraction; however, the relative contributions of premotor cortical and spinal mechanisms are poorly understood. It is unknown whether the intended voluntary contractile rate affects CSE. Eighteen young, healthy participants (nine females) completed isometric elbow flexion contractions targeting 50% maximal voluntary contraction (MVC) torque, at either fast (fast as possible) or slow (25% MVC/s) contractile rates. Participants were cued to contract with warning (red) and "GO" (green) visual signals. Magnetic and electric stimulations were applied to elicit motor evoked potentials (MEPs), cervicomedullary evoked potentials (CMEPs), and M-waves, in the surface electromyogram (EMG) recorded over the biceps brachii. MEPs and CMEPs were collected at 0, 25, 50 and 75% premotor reaction time (RT - defined as the time between the "GO" cue and onset of biceps brachii EMG) and compared to a resting baseline. MEP amplitude was greater than baseline at 75% RT (p=0.009), and CMEP amplitude was significantly increased at all RT points relative to baseline (p≤0.001). However, there were no differences in MEP and CMEP amplitudes when compared between fast and slow conditions (p≥0.097). Normalized to the CMEP, there was no difference in MEP amplitude from baseline in either contractile condition (p≥0.264). These results indicate that increased premotor CSE is a spinally-mediated response. Furthermore, premotor CSE is not influenced by the intended voluntary contractile rate. CMEP amplitudes were larger for females than males within the premotor RT period (p=0.038), demonstrating that premotor spinal excitability responses may be influenced by sex.

Design of Alkali-Activated Materials and Geopolymer for Deep Soilmixing: Interactions with Model Soils.

This study focuses on the use of alkali-activated materials and geopolymer grouts in deep soilmixing. Three types of grouts, incorporating metakaolin and/or slag and activated with sodium silicate solution, were characterized at different scales to understand the development of their local structure and macroscopic properties. The performance of the soilmix was assessed by using combinations of the grouts and model soils with different clay contents. Feret's approach was used to understand the development of compressive strength at different water-to-solid ratios ranging from 0.65 to 1. The results suggested that incorporating calcium reduced the water sensitivity of the materials, which is crucial in soilmixing. Adding soils to grouts resulted in improved mechanical properties, due to the influence of the granular skeleton. Based on strength results, binary soilmix mixtures containing 75% of metakaolin and 25% of slag, with H2O/Na2O ratios ranging from 28 to 42 demonstrated potential use for soilmixing due to the synergistic reactivity of metakaolin and slag. The optimization of compositions is necessary for achieving the desired properties of soil mixtures with higher H2O/Na2O ratios.

Differential effects of stimulation frequency on isometric and concentric isotonic contractile function in human quadriceps.

Electrically evoked contractions are used to assess the relationship between frequency input and contractile output to characterize inherent muscle function, and these have been done mostly with isometric contractions (i.e., no joint rotation). The purpose was to compare the electrically stimulated frequency and contractile function relationship during isometric (i.e., torque) with isotonic (i.e., concentric torque, angular velocity, and mechanical power) contractions. The knee extensors of 16 (5 female) young recreationally active participants were stimulated (∼1-2.5 s) at 14 frequencies from 1 to 100 Hz. This was done during four conditions, which were isometric and isotonic at loads of 0 (unloaded), 7.5%, and 15% isometric maximal voluntary contraction (MVC), and repeated on separate days. Comparisons across contractile parameters were made as a % of 100 Hz. Independent of the load, the mechanical power-frequency relationship was rightward shifted compared with isometric torque-frequency, concentric torque-frequency, and velocity-frequency relationships (all P ≤ 0.04). With increasing load (0%-15% MVC), the isotonic concentric torque-frequency relationship was shifted leftward systematically from 15 to 30 Hz (all P ≤ 0.04). Conversely, the same changes in load caused a rightward shift in the velocity-frequency relationship from 1 to 40 Hz (all P ≤ 0.03). Velocity was leftward shifted of concentric torque in the unloaded isotonic condition from 10 to 25 Hz (all P ≤ 0.03), but concentric torque was leftward shifted of velocity at 15% MVC isotonic condition from 10 to 50 Hz (all P ≤ 0.03). Therefore, isometric torque is not a surrogate to evaluate dynamic contractile function. Interpretations of evoked contractile function differ depending on contraction type, load, and frequency, which should be considered relative to the specific task.NEW & NOTEWORTHY In whole human muscle, we showed that the electrically stimulated power-frequency relationship was rightward shifted of the stimulated isometric torque-frequency relationship independent of isotonic load, indicating that higher stimulation frequencies are needed to achieve tetanus. Therefore, interpretations of evoked contractile function differ depending on contraction type (isometric vs. dynamic), load, and frequency. And thus, isometric measures may not be appropriate as a surrogate assessment when evaluating dynamic isotonic contractile function.

Influence of stimulation frequency on early and late phase rate of torque and velocity development.

The early (≤50 ms) rate of torque development (RTD) is dependent upon the speed of neuromuscular activation; however, few studies have evaluated the determinants of rate of velocity development (RVD), which may be load-dependent. The purpose here was to explore the relationship between stimulation frequency with the early and late (≥100 ms) phase isometric RTD and isotonic RVD. The knee extensors of 16 (five female) young recreationally active participants were stimulated using 14 frequencies from 1 to 100 Hz during isometric and isotonic ("unloaded" and 7.5% of the isometric maximal voluntary contraction [MVC]) contractions. Isometric RTD and isotonic RVD were evaluated for the early (0-50 ms) and late (0-100 ms) phases from torque and velocity onset, respectively. Sigmoid functions were fit and bilinear regressions were used to examine the slopes of the steep portion of the curve and the plateau frequency. RTD- and RVD-frequency relationships were well described by a sigmoid function (all r2 > 0.96). Compared with the late phase, early isometric RTD, and unloaded RVD displayed lower slopes (all P ≤ 0.001) and higher plateau frequencies (all P < 0.001). In contrast, early and late RVD of a moderately loaded isotonic contraction did not display different slopes (P = 0.055) or plateau frequencies (P = 0.690). Early isometric RTD and unloaded isotonic RVD are more dependent on changes in stimulation frequency compared with late phases. However, RVD for a moderately loaded isotonic contraction displayed similar responses for the early and late phases. Therefore, a high frequency of activation is critical for early torque and velocity generation but dependent upon the load for isotonic contractions.NEW & NOTEWORTHY We show that during an "unloaded" isotonic contraction, the early phase rate of velocity development is more dependent upon a high electrical activation frequency compared with the late phase, similar to isometric torque. However, early and late phase rates of velocity development of moderately loaded isotonic contractions display similar responses. These results indicate that the determinants of isotonic shortening function are dependent on the externally applied load, highlighting the importance of task-specificity of contraction.

Voluntary activation of human knee extensors during isotonic shortening contractions.

PURPOSE: The interpolated twitch technique (ITT) is often used to assess voluntary activation during isometric contractions; however, this may have limited relevance to dynamic contractions. Although the ITT has been applied to relatively slow isokinetic contractions (< 150°/s), it has received limited consideration during unconstrained velocity (i.e., isotonic) contractions, despite their relevance to natural movements. Here, we explored the ITT during isotonic knee extension contractions using a modified dynamometer. METHODS: Young males (n = 6) and females (n = 4) performed isometric and isotonic knee extension contractions of sub-maximal and maximal intensities with doublet (150 Hz) muscle belly stimulations to assess voluntary activation. Following each voluntary isotonic contraction (velocity range ~ 35°/s to ~ 275°/s), resting potentiated doublets were evaluated during passive joint rotation at the same angular velocity achieved during voluntary efforts, to account for force-velocity characteristics. Correlations between voluntary activation and the proportion of maximal torque or power were evaluated for isometric and isotonic contractions, respectively. RESULTS: Isometric voluntary activation was strongly correlated with increasing torque output (r = 0.96, p < 0.001). Doublet torque during passive joint rotation displayed a hyperbolic relationship with increasing angular velocity (r = 0.98, p < 0.001). Isotonic voluntary activation was strongly correlated with increasing power output (r = 0.89, p < 0.001). During maximal effort contractions, no differences were observed in voluntary activation between isometric and isotonic conditions (89.4% vs. 89.2%, p = 0.904). CONCLUSIONS: The ITT is a valid approach to evaluate voluntary activation during an isotonic contraction using a modified dynamometer. Participants were able to achieve a similar high level of voluntary activation during isometric and isotonic contractions.

Micro- and nanostructured layered-kagome zinc orthovanadate BaZn3(VO4)2(OH)2.

Pure micro- and nanocrystalline powders of the layered-kagome zinc orthovanadate BaZn3(VO4)2(OH)2 have been successfully prepared and thoroughly characterised. Microstructured samples (BaZn3-MPs) have been produced by hydrothermal reaction using synthetic martyite Zn3V2O7(OH)2·2H2O as the starting reagent. Nanoparticles (NPs) with an average size of ≈ 60 nm (BaZn3-NPs-7h) or ≈ 50 nm (BaZn3-NPs-25min) have been obtained by using a coprecipitation method at ambient pressure, and by varying the stirring time. Rietveld refinements of X-ray diffraction data indicate that micro- and nanostructured BaZn3(VO4)2(OH)2 both crystallize in a R3̄m structure very similar to that of the known layered-kagome compound BaCo3(VO4)2(OH)2. Transmission electron microscopy observation of BaZn3-NPs-7h and BaZn3-NPs-25min reveals crystallized NPs with homogenous distributions of Ba, Zn, and V elements. FT-IR and Raman spectra show subtle differences between micro- and nanostructured samples which cannot be linked to any differences in the average crystal structures. The high resolution 51V MAS NMR spectrum of BaZn3-MPs shows a single isotropic line attributed to VO43- groups with C3v point group. The spectra of the nanostructured samples reveal the presence of a weak additional signal which decreases in intensity with increasing the NPs size, and which has been tentatively assigned to the presence at the surface of the NPs of a small amount of V5+ ions in a different chemical environment. Nanostructuring also impacts the optical properties of BaZn3(VO4)2(OH)2. The UV-vis absorption spectra of NPs exhibit an additional weak transition in the visible domain which is not observed for the microstructured sample.

Electrically Evoked Isotonic Plantar Flexion Contractions Are Impaired Less than Voluntary After a Dynamic Fatiguing Task.

PURPOSE: Evaluating central and peripheral processes responsible for reduced power after dynamic fatiguing tasks are often limited to isometric torque, which may not accurately reflect dynamic contractile performance. Here, we compare voluntary and electrically evoked peak power (and its determinants: dynamic torque and velocity) and rate of velocity development (RVD) before and after a dynamic fatiguing task using concentric Plantar flexion contractions. METHODS: Young (18-32 yr) males ( n = 11) and females ( n = 2) performed maximal-effort isotonic Plantar flexion contractions using a load of 20% isometric torque until an approximately 75% reduction in peak power. Voluntary and electrically evoked (300 Hz tibial nerve stimulation) contractions loaded to 20% and 40% isometric torque through 25° ankle joint range of motion were compared before and 0, 2.5, 5, and 10 min after task termination. RESULTS: At task termination, peak power and RVD of voluntary contractions at both loads were reduced more (~40% to 50% reduction) than electrically evoked (~25% to 35% reduction) contractions ( P < 0.001 and P = 0.003). Throughout the recovery period, electrically evoked peak power and RVD returned to baseline sooner (<5 min) than voluntary contractions, which were still depressed at 10 min. Reductions in peak power for the 20% load were equally due to impaired dynamic torque and velocity, whereas velocity was impaired more than dynamic torque ( P < 0.001) for the 40% load. CONCLUSIONS: The relative preservation of electrically evoked power and RVD compared with voluntary contractions at task termination and quicker recovery to baseline indicates that the reductions in dynamic contractile performance after task termination are due to both central and peripheral processes; however, the relative contribution of dynamic torque and velocity is load dependent.

Coordinatively Cross-Linked Binders for Silicon-Based Electrodes for Li-Ion Batteries: Beneficial Impact on Mechanical Properties and Electrochemical Performance.

A simple and versatile preparation of Zn(II)-poly(carboxylates) reticulated binders by the addition of Zn(II) precursors (ZnSO4, ZnO, or Zn(NO3)2) into a preoptimized poly(carboxylic acids) binder solution is proposed. These binders lead systematically to a significantly improved electrochemical performance when used for the formulation of silicon-based negative electrodes. The formation of carboxylate-Zn(II) coordination bonds formation is investigated by rheology and FTIR and NMR spectroscopies. Mechanical characterizations reveal that the coordinated binder offers a better electrode coating cohesion and adhesion to the current collector, as well as higher hardness and elastic modulus, which are even preserved in the presence of a carbonate solvent (i.e., in battery operation conditions). Ultimately, as shown from operando dilatometry experiments, the electrode expansion during lithiation is reduced, mitigating electrode mechanical failure. Such coordinatively reticulated electrodes outperform their uncoordinated counterparts with an improved capacity retention of over 30% after 60 cycles.

Calcaneal tendon stiffness is not associated with dynamic time-dependent contractile output.

The ability to rapidly generate muscular torque and velocity is important in specialized activities and daily tasks of living. Tendon stiffness is one factor in the neuromuscular system that influences musculoskeletal torque transmission. Previous studies have reported weak-to-moderate correlations between tendon stiffness and rate of torque development (RTD). However, these correlations have been reported only for isometric contractions, which may not be relevant to contractions involving joint rotation (i.e., dynamic). The purpose was to investigate the effect of calcaneal tendon stiffness on the dynamic RTD and rate of velocity development (RVD) in plantar flexor muscles. Young adult males (n = 13) and females (n = 2) performed prone isometric- and isotonic-mode maximal voluntary plantar flexion contractions (MVC). Ultrasound imaging was used to quantify tendon morphological characteristics to estimate Young's elastic modulus (YM). Maximal voluntary and electrically evoked (300 Hz) isometric- and isotonic-mode (at 10% and 40% MVC loads) contractions were evaluated for RTD and RVD through a 25° ankle joint range of motion. YM was correlated with isometric RTD, but only for evoked contractions (RTD0-50 ms: r = 0.54, p = 0.02, RTD0-200 ms: r = 0.62, p = 0.01). Conversely, YM was not correlated with dynamic RTD (voluntary: r = -0.07-0.41, p = 0.06-0.40, evoked: r = -0.2-0.3, p = 0.14-0.24) nor RVD (voluntary: r = -0.08-0.24, p = 0.27-0.40, evoked: r = 0.12-0.3, p = 0.14-0.34). These correlations would indicate that calcaneal tendon stiffness is an important factor for rapid isometric torque development, but less so for isotonic contractions. The determinants of dynamic contractile rates are more complex and warrant further study.

Assessing the Surface Chemistry of 2D Transition Metal Carbides (MXenes): A Combined Experimental/Theoretical 13C Solid State NMR Approach.

The surface functionalization of 2D transition metal carbides or nitrides, so-called MXenes, is one of the fundamental levers allowing to deeply modify their physicochemical properties. Beyond new approaches to control this pivotal parameter, the ability to unambiguously assess their surface chemistry is thus key to expand the application fields of this large class of 2D materials. Using a combination of experiments and state of the art density functional theory calculations, we show that the NMR signal of the carbon─the element common to all MXene carbides and corresponding MAX phase precursors─is extremely sensitive to the MXene functionalization, although carbon atoms are not directly bonded to the surface groups. The simulations include the orbital part to the NMR shielding and the contribution from the Knight shift, which is crucial to achieve good correlation with the experimental data, as demonstrated on a set of reference MXene precursors. Starting with the Ti3C2Tx MXene benchmark system, we confirm the high sensitivity of the 13C NMR shift to the exfoliation process. Developing a theoretical protocol to straightforwardly simulate different surface chemistries, we show that the 13C NMR shift variations can be quantitatively related to different surface compositions and number of surface chemistry variants induced by the different etching agents. In addition, we propose that the etching agent affects not only the nature of the surface groups but also their spatial distribution. The direct correlation between surface chemistry and 13C NMR shift is further confirmed on the V2CTx, Mo2CTx, and Nb2CTx MXenes.

Methodological and Clinimetric Evaluation of Inspiratory Respiratory Muscle Ultrasound in the Critical Care Setting: A Systematic Review and Meta-Analysis.

OBJECTIVE: Significant variations exist in the use of respiratory muscle ultrasound in intensive care with no society-level consensus on the optimal methodology. This systematic review aims to evaluate, synthesize, and compare the clinimetric properties of different image acquisition and analysis methodologies. DATA SOURCES: Systematic search of five databases up to November 24, 2021. STUDY SELECTION: Studies were included if they enrolled at least 50 adult ICU patients, reported respiratory muscle (diaphragm or intercostal) ultrasound measuring either echotexture, muscle thickness, thickening fraction, or excursion, and evaluated at least one clinimetric property. Two independent reviewers assessed titles, abstracts, and full text against eligibility. DATA EXTRACTION: Study demographics, ultrasound methodologies, and clinimetric data. DATA SYNTHESIS: Sixty studies, including 5,025 patients, were included with 39 studies contributing to meta-analyses. Most commonly measured was diaphragm thickness (DT) or diaphragm thickening fraction (DTF) using a linear transducer in B-mode, or diaphragm excursion (DE) using a curvilinear transducer in M-mode. There are significant variations in imaging methodology and acquisition across all studies. Inter- and intrarater measurement reliabilities were generally excellent, with the highest reliability reported for DT (ICC, 0.98; 95% CI, 0.94-0.99). Pooled data demonstrated acceptable to excellent accuracy for DT, DTF, and DE to predicting weaning outcome after 48 to 72 hours postextubation (DTF AUC, 0.79; 95% CI, 0.73-0.85). DT imaging was responsive to change over time. Only three eligible studies were available for intercostal muscles. Intercostal thickening fraction was shown to have excellent accuracy of predicting weaning outcome after 48-hour postextubation (AUC, 0.84; 95% CI, 0.78-0.91). CONCLUSIONS: Diaphragm muscle ultrasound is reliable, valid, and responsive in ICU patients, but significant variation exists in the imaging acquisition and analysis methodologies. Future work should focus on developing standardized protocols for ultrasound imaging and consider further research into the role of intercostal muscle imaging.

Test-retest repeatability of electrically evoked isotonic power and isometric torque in the plantar flexors.

Electrically evoked isometric torque has good to excellent repeatability, but the degree of repeatability for electrically evoked isotonic power is unknown. We evaluated the test-retest repeatability of plantar flexion isometric torque and isotonic power evoked using brief tetanic trains at 10 and 50 Hz. Both torque and power had excellent (intraclass correlation coefficient >0.9) repeatability at low and high frequencies. Similar to isometric torque, electrically evoked isotonic power is a stable measure for studying dynamic muscle function.

Associations between Pretreatment Body Composition Features and Clinical Outcomes among Patients with Metastatic Clear Cell Renal Cell Carcinoma Treated with Immune Checkpoint Blockade.

PURPOSE: High body mass index (BMI) may lead to improved immune-checkpoint blockade (ICB) outcomes in metastatic clear cell renal cell carcinoma (mccRCC). However, BMI is a crude body size measure. We investigated BMI and radiographically assessed body composition (BC) parameters association with mccRCC ICB outcomes. EXPERIMENTAL DESIGN: Retrospective study of ICB-treated patients with mccRCC. BMI and BC variables [skeletal muscle index (SMI) and multiple adiposity indexes] were determined using pretreatment CT scans. We examined the associations between BMI and BC variables with ICB outcomes. Therapeutic responses per RECIST v1.1 were determined. We compared whole-transcriptomic patterns with BC variables in a separate cohort of 62 primary tumor samples. RESULTS: 205 patients with mccRCC were included in the cohort (74% were male, 71% were overweight/obese, and 53% were classified as low SMI). High-BMI patients experienced longer overall survival (OS) than normal-weight patients [unadjusted HR, 0.66; 95% confidence interval (CI), 0.45-0.97; P = 0.035]. The only BC variable associated with OS was SMI [unadjusted HR comparing low vs. high SMI 1.65 (95% CI: 1.13-2.43); P = 0.009]. However, this OS association became nonsignificant after adjusting for International Metastatic Renal Cell Carcinoma Database Consortium score and line of therapy. No OS association was seen for adiposity and no BC variable was associated with progression-free survival or radiological responses. Tumors from patients with low SMI displayed increased angiogenic, inflammatory, and myeloid signals. CONCLUSIONS: Our findings highlight the relevance of skeletal muscle in the BMI paradox. Future studies should investigate if addressing low skeletal muscle in metastatic patients treated with ICB can improve survival.

Comparison of prolonged low-frequency force depression assessed using isometric torque and isotonic power following a dynamic fatiguing task.

PURPOSE: Prolonged low-frequency force depression (PLFFD) occurs following both dynamic and static fatiguing tasks, but it has been assessed predominately using measures of isometric torque. However, it is unknown whether PLFFD induced during dynamic tasks is adequately characterized by isometric torque, which excludes velocity and power. The purpose of this study was to compare PLFFD assessed using isometric torque and isotonic power following a concentric fatiguing task. METHODS: Young (18-31 years) males (n = 9) and females (n = 4) performed isotonic plantar flexion contractions until a ~ 75% reduction in peak power. Isotonic and isometric contractions were electrically evoked at 10 Hz and 50 Hz via tibial nerve stimulation. Isotonic and isometric PLFFD was assessed as the ratio of 10 to 50 Hz for power and torque, respectively. Recovery was assessed immediately, and at 2.5, 5, 10, 20, and 30 min after task termination. RESULTS: Relative to baseline, 10:50 Hz ratio assessed using isotonic power was reduced more than isometric torque (30 min 41 ± 17 vs. 25 ± 12% reduction, p = 0.001); however, both contraction modes displayed similar trajectories throughout recovery (p = 0.906). The larger reduction in isotonic 10:50 Hz ratio was due to greater impairments in 10 Hz power compared to 10 Hz isometric torque (30 min 38 ± 20 vs. 21 ± 11% reduction, p < 0.001). CONCLUSION: The similar trajectories of 10:50 Hz ratios throughout recovery indicate that PLFFD can be adequately characterized using either isometric torque or isotonic power.

Age-related performance fatigability: a comprehensive review of dynamic tasks.

Adult aging is associated with a myriad of changes within the neuromuscular system, leading to reductions in contractile function of old adults. One of the consequences of these age-related neuromuscular adaptations is altered performance fatigability, which can limit the ability of old adults to perform activities of daily living. Whereas age-related fatigability during isometric tasks has been well characterized, considerably less is known about fatigability of old adults during dynamic tasks involving movement about a joint, which provides a more functionally relevant task compared with static contractions. This review provides a comprehensive summary of age-related fatigability during dynamic contractions, where the importance of task specificity is highlighted with a brief discussion of the potential mechanisms responsible for differences in fatigability between young and old adults. The angular velocity of the task is critical for evaluating age-related fatigability, as tasks that constrain angular velocity (i.e., isokinetic) produce equivocal age-related differences in fatigability, whereas tasks involving unconstrained velocity (i.e., isotonic-like) consistently induce greater fatigability for old compared with young adults. These unconstrained velocity tasks, which are more closely associated with natural movements, offer an excellent model to uncover the underlying age-related mechanisms of increased fatigability. Future work evaluating the mechanisms of increased age-related fatigability during dynamic tasks should be evaluated using contraction modes that are specific to the task (i.e., dynamic), rather than isometric, particularly for the assessment of spinal and supra spinal components. Advancing our understanding of age-related fatigability is likely to yield novel insights and approaches for improving mobility limitations in old adults.

Frequency-dependent coexistence of muscle fatigue and potentiation assessed by concentric isotonic contractions in human plantar flexors.

The purpose was to investigate whether postactivation potentiation (PAP) mitigates power (i.e., torque × angular velocity) loss during dynamic fatiguing contractions and subsequent recovery by enhancing either muscle torque or angular velocity in human plantar flexors. In 12 participants, electrically stimulated (1, 10, and 50 Hz) dynamic contractions were done during a voluntary isotonic fatiguing protocol until a 75% loss in voluntary peak power, and throughout 30 min of recovery. At the initial portion of fatigue (20% decrease), power responses of evoked low frequencies (1 and 10 Hz) were enhanced due to PAP (156% and 137%, respectively, P < 0.001), whereas voluntary maximal efforts were depressed due to fatiguing mechanisms. Following the fatiguing task, prolonged low-frequency force depression (PLFFD) was evident by reduced 10:50 Hz peak power ratios (21%-24%) from 3 min onward during the 30-min recovery (P < 0.005). Inducing PAP with maximal voluntary dynamic contractions during PLFFD enhanced the peak power responses of low frequencies (1 and 10 Hz) by 128%-160%, P < 0.01. This PAP response mitigated the effects of PLFFD as the 1:50 (P < 0.05) and 10:50 (P > 0.4) Hz peak power ratios were greater or not different from the prefatigue (baseline) values. In addition, PAP enhanced peak torque more than peak angular velocity during both baseline and fatigue measurements (P < 0.03). These results indicate that PAP can ameliorate PLFFD acutely when evaluated during concentric isotonic contractions and that peak torque is enhanced to a greater degree compared with peak angular velocity at baseline and in a fatigued state.NEW & NOTEWORTHY Postactivation potentiation (PAP) enhanced stimulated low frequencies (1 and 10 Hz) during muscle fatigue development when assessed with power (torque × angular velocity) in a voluntary isotonic fatiguing task. Following the task during 30 min of recovery, prolonged low-frequency force depression (PLFFD) was evident, and inducing PAP with brief maximal contractions during this state ameliorated the effects of PLFFD. PAP enhanced peak torque more than peak angular velocity during both baseline and fatiguing conditions.

Templating effect of trans-2,5-dimethylpiperazine (TDMP) on the structural dimensionality of hybrid metal halides.

Templating effects are commonly investigated by comparing different organic structure-directing agents in a specific inorganic system. Herein, a specific secondary diamine, the trans-2,5-dimethylpiperazine, has been selected for different metal halide anions with the aim to analyze its influence on different inorganic networks. Thus, five new trans-2,5-dimethylpiperazine-1,4-diium based compounds with [CuBr4]2-, [CdBr4]2-, [CuBr2]-, [AgCl2]-, and [AgBr2]- have been synthesized, structurally characterized and compared to eight previously reported compounds containing [ZnCl4]2-, [ZnBr4]2-, [CoCl4]2-, [PbCl4]2-, [PbBr4]2-, [SnBr4]2-, [CuCl4]2-, and [CdCl4]2-. Despite the different crystal structures (space-groups, inorganic frameworks, etc.), the dimensionalities (from 0D to 2D) of the inorganic networks of these 13 hybrid materials could be rationalized according to only two parameters: the oxidation state (+1 or +2) and the coordination sphere (tetrahedron or octahedron) of the metal ions. The luminescence properties of the new hybrid silver bromide have been analyzed and discussed by comparing the luminescence mechanisms of the other previously reported trans-2,5-dimethylpiperazine-1,4-diium metal halides.

Local environment of iodine dissolved as iodate in high-pressure aluminoborosilicate glasses: A I K-edge x-ray absorption spectroscopic study.

The use of high-pressure synthesis conditions to produce I-bearing aluminoborosilicate represents a promising issue for the immobilization of 129I radioisotope. Furthermore, iodine appears to be more solubilized in glasses under its iodate (I5+) form rather than its iodide (I-) form. Currently, the local atomic environment for iodine is poorly constrained for I- and virtually unknown for I5+ or I7+. We used I K-edge x-ray absorption spectroscopy conducted at 20 K for determining the local atomic environment of iodine dissolved as I-, I5+, and I7+ in a series of aluminoborosilicate glasses. We determined that I- is surrounded by either Na+ or Ca2+ in agreement with previous studies. The signal collected from EXAFS reveals that I5+ is surrounded invariably by three oxygen atoms forming an IO3 - cluster charge compensated by Na+ and/or Ca2+. The I-O distance in iodate dissolved in glass is comparable to the I-O distance in crystalline compounds at ∼1.8 Å. The distance to the second nearest neighbor (Na+ or Ca2+) is also constant at ∼3.2 Å. This derived distance is identical to the distance between I- and Na+ or Ca2+ in the case of iodide local environment. For one sample containing iodate and periodate, the distinction between the local environment of I5+ and I7+ could not be made, suggesting that both environments have comparable EXAFS signals.