Step Interval Research Articles

Liquid Metal Chameleon Tongues: Modulating Surface Tension and Phase Transition to Enable Bioinspired Soft Actuators

Leveraging the unique attributes of functional soft materials to generate force and deformation, significant advancements in soft actuators are driving the evolution of smart robotics. Liquid metals (LMs), known for their high deformability and tunable morphology, demonstrate remarkable actuating capabilities through controllable surface tension. Inspired by the predation method of chameleons, this work introduces a bioinspired LM actuator (BLMA) by modulating the morphology of LM. This BLMA enables high‐strain (up to 170%) actuation by precisely directing LM droplets toward an electrode. Various parameters affecting the BLMA's actuating performance are explored. Notably, the application of a reductive voltage induces rapid solidification of supercooled LM, facilitating phase transition at room temperature. The solidified LM enhances its holding force of BLMA by over 1000 times. To underscore the superior capabilities of the BLMA, diverse applications, such as a complex two‐dimensional plane actuator, a stepper motor with adjustable step intervals, a phase transition‐controlled relay, and a laser code lock actuation gate set, are presented. It is anticipated that the exceptional characteristics of the BLMA will propel advancements in the realms of soft robotics and mechatronics.

Using integrated step selection to determine effects of predation risk on bison habitat selection and movement

AbstractAnimal movement is a fundamental mechanism that shapes communities and ecosystems. Ungulates alter the ecosystems they inhabit and understanding their movements and distribution is critical for linking habitat with population dynamics. Predation risk has been shown to strongly influence ungulate movement patterns, such that ungulates may select habitat where predation risk is lower (refugia), adjust movement rates, temporal patterns, or selection of cover variables in areas with greater predation risk. We evaluated potential predation avoidance behavior in a population of plains bison inhabiting the north rim of Grand Canyon National Park (GRCA) and adjacent Kaibab National Forest (KNF). The KNF has year‐round hunting managed by Arizona Game and Fish Department, whereas hunting is not allowed in GRCA. Human‐maintained water sources on the KNF are particularly important resources for bison wherein they may be exposed to higher predation risk to access these resources. We used 2‐h GPS locations for three years from 31 bison (n = 9 males; n = 22 females), and integrative step selection analysis to test four hypotheses about the potential for bison to reduce their risk from human predation by avoiding areas of high predation risk; moving faster in areas with high predation risk; entering high‐risk areas at night when risk is reduced; and entering high‐risk areas in habitats that provide cover (coniferous forest). The highest performing model indicated bison movement was 1.3 times faster per 2‐h step interval than in areas with no hunting across all vegetation classes (coniferous forest, shrub, quaking aspen, grass‐forb meadow) and across all topography classes (valley, slope, ridge). Bison moved more slowly in grass‐forb meadows than all other vegetation types, and in valleys relative to slopes and ridges. Several radio‐collared individuals had no GPS locations in KNF for the duration of the study. Bison avoided predation risk using two strategies: moving faster while in the KNF, and fully avoiding high‐risk areas by remaining within GRCA. Management that manipulates or reduces timing of hunting seasons may reduce perceived predation risk and encourage bison to distribute into the KNF and across a broader range of available habitat.

Investigation on structural and morphological properties of molybdenum trioxide (MoO3) thin films

Abstract The present study reports on the effect of substrate temperature on structural, morphological and optical properties of MoO3 thin films. MoO3 thin films were deposited on pre-heated glass substrate using spray pyrolysis technique. The substrate temperature was varied from 300 °C to 400°C with a step interval of 50 °C. Structural studies were studied using X-ray diffraction technique. It is observed that all the diffraction peaks exactly match with JCPDS card No. 05-0508. The as –deposited MoO3 thin films exhibits orthorhombic crystal structure. It is found that the crystalline nature increases with the increases of substrate temperature. FESEM micrographs show that the grains are distributed uniformly over the surface without any void. An optical property reveals that the transmission of MoO3 thin film in the visible region increases with increases of deposition temperature.

Numerical investigation of the effect of enforced air flow in a closed cavity on temperature distribution of ammonium dihydrogen phosphate crystal with a large aperture

The temperature distribution of a novel Final optics assembly (FOA) made of a square ammonium dihydrogen phosphate (ADP) crystal with a large aperture is examined numerically in this noncritical phase-matching simulation (NCPM). The temperature of the cavity wall is maintained by temperature-controlled, continuously flowing (0.1 m/s) water (313.5 k). The thermal study was first performed numerically inside the cavity with different configurations using the finite volume technique. One fan was placed on one side of the ADP crystal to evaluate the temperature distribution within the cavity and between the crystals. The fan speed is then varied from 10 to 40 rad/s with a step interval of 10 rad/s to evaluate the effect of forced convection. Furthermore, the investigation showed that 20 rad/s is more effective than the other cases. To measure the impact of temperature distribution caused by fan orientation, the fan orientation was adjusted to three different tilt angles (10, 20, and 30 degrees) while the fan rotational speed was maintained at 20 rad/s. The two fans on the side and the two fans on either side of the ADP crystal were also investigated, with different orientations (0, 10, and 20 degrees) and speeds (0, 10, 20, 30, and 40 rad/s). According to the fan speed, direction, number of speeds, and fan locations, the high-temperature spot of ADP crystals can be symmetric, asymmetric, diagonally dominant, center dominant, bottom dominant, or top dominant.

Bridge pier under coupled earthquake and wave - Current actions: Numerical model establishing, optimization and structural response analysis

Bridges located in earthquake-prone areas may be subjected to earthquake, wave and current actions simultaneously. Current investigations on bridge piers under these complex loading conditions were generally performed through underwater shaking table (UST) tests, which required advanced test setups and great expenses. With the aim of eliminating these limits and developing a comprehensive understanding of the performance of deep-water bridge piers under coupled earthquake and wave-current actions, the present study carried out systematic numerical investigations. Wave generation and propagation were first simulated, for which thorough sensitivity analysis was conducted to obtain the optimal parameters, including mesh size, time step intervals, damping zone length and damping coefficients. Numerical models which are able to simulate nonlinear wave-current interactions were then established and validated. Following this, structural responses of bridge piers under wave, wave-current and coupled earthquake and wave-current actions were numerically simulated and validated by test results. Finally, parametric analysis was conducted on a pile of a practical deep-water bridge in China using the validated model with consideration of various water depth levels, diverse wave heights, different current velocities, varied earthquakes and different peak ground accelerations to reveal the influence of different excitation parameters on structural responses.

Pore-network modelling of transverse dispersion in porous media under non-Darcy flow conditions

This work is concerned, for the first time, with estimating the transverse dispersion coefficient under non-Darcy laminar flow conditions in porous media using pore-network modeling. The pore-network modelling approach and the mixed cell method are adopted to simulate both the steady laminar flow and the transient transport of solute for Berea and Bentheimer sandstone samples. For non-Darcy flow, the inertial effect is attributed to the quadratic increase of the pore throat mean velocity, which is embedded in the pressure head losses at either expansion or contraction located at the two ends of any pore throat. A time dependent function, based on both Péclet number and average residence time within the pore throat, is used to incorporate the effect of nonuniform pore throat velocity in the dispersion coefficient. A restrictive upper limit of the time step interval is introduced to prevent numerical overshoots of the concentrations calculated over time. For the same pressure gradient through the sample, the results show a decrease in both Péclet number and the coefficient of transverse dispersion in case of adopting the non-Darcy flow condition instead of the Darcy flow one. The percentage of decrease is up to 20 % for the maximum applied pressure gradient through the sample.

Limitations of estimating branch volume from terrestrial laser scanning

Quantitative structural models (QSMs) are frequently used to simplify single tree point clouds obtained by terrestrial laser scanning (TLS). QSMs use geometric primitives to derive topological and volumetric information about trees. Previous studies have shown a high agreement between TLS and QSM total volume estimates alongside field measured data for whole trees. Although already broadly applied, the uncertainties of the combination of TLS and QSM modelling are still largely unexplored. In our study, we investigated the effect of scanning distance on length and volume estimates of branches when deriving QSMs from TLS data. We scanned ten European beech (Fagus sylvatica L.) branches with an average length of 2.6 m. The branches were scanned from distances ranging from 5 to 45 m at step intervals of 5 m from three scan positions each. Twelve close-range scans were performed as a benchmark. For each distance and branch, QSMs were derived. We found that with increasing distance, the point cloud density and the cumulative length of the reconstructed branches decreased, whereas individual volumes increased. Dependent on the QSM hyperparameters, at a scanning distance of 45 m, cumulative branch length was on average underestimated by − 75%, while branch volume was overestimated by up to + 539%. We assume that the high deviations are related to point cloud quality. As the scanning distance increases, the size of the individual laser footprints and the distances between them increase, making it more difficult to fully capture small branches and to adjust suitable QSMs.

3.4 μm mid-infrared pulse train laser based on stepped acousto-optic <i>Q</i>-switched external cavity pumped MgO:PPLN optical parametric oscillator

3.4 μm mid-infrared pulse train laser generates the characteristic spectral lines of absorption peaks of CH<sub>4</sub>, NO<sub>2</sub> and other molecules. Its pulse train working mode can increase the signal-to-noise ratio of laser detection echo signal. It has broad application prospects in radar detection, environmental monitoring, spectral analysis and other fields, which has aroused great interest of scientists. Compared with the traditional intra-cavity control method, the step <i>Q</i>-switching method has the advantages of simple structure, high energy utilization rate and accurate control. Therefore, in this paper, both the theoretical study and the experimental study of a 3.4 μm mid-infrared pulse train laser pumped by a step-type acousto-optic <i>Q</i>-switched external cavity in MgO:PPLN optical parametric oscillator are carried out. The theoretical model of fundamental frequency step acousto-optic <i>Q</i>-switching is established. The change trends of photon number density at different step intervals are simulated. The optimal trigger time of step signal required for step acousto-optic <i>Q</i>-switching is obtained. The possibility of obtaining pulse train laser output by step acousto-optic <i>Q</i>-switching is determined. In the simulation, the single pulse envelope contains 3 sub-pulse train waveforms. The pulse width of the sub-pulse in the pulse envelope gradually increases, the sub-pulse interval is 5 μs, and the pulse envelope repetition frequency is 20 kHz. At the same time, the optimal trigger times for the step signal are obtained to be 16.00, 21.00, 26.00, 50.00 μs. The mid-infrared pulse train laser experiment of step acousto-optic <i>Q</i>-switched external cavity pumped MgO:PPLN optical parametric oscillator is carried out, and the 3.4 μm mid-infrared pulse train laser output containing three sub-pulses in a single pulse envelope is obtained. The sub-pulse interval is 5 μs, the narrowest pulse width is 12.8 ns, and the pulse envelope repetition frequency is 20 kHz, when the maximum average output power is 1.08 W, the maximum optical-to-optical conversion efficiency of 1064 nm fundamental light and 3.4 μm parametric light is 10.05%, and the beam quality factor <inline-formula><tex-math id="Z-20240205221930">\begin{document}$M^2$\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231348_Z-20240205221930.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20231348_Z-20240205221930.png"/></alternatives></inline-formula> is 2.01. The output position of the sub pulses in each repetition period in the experiment is basically consistent with the simulation result, and it is found in both simulation and experiment that the width of the sub pulses within each pulse envelope gradually increases. The experimental results show that 3.4 μm mid-infrared pulse train laser output can be obtained by using step AOQS combined with OPO. This innovative method provides theoretical and technical support for detecting atmospheric pollutant concentration by using mid-infrared pulse train laser.

Convergent evolution in a large cross-cultural database of musical scales

Scales, sets of discrete pitches that form the basis of melodies, are thought to be one of the most universal hallmarks of music. But we know relatively little about cross-cultural diversity of scales or how they evolved. To remedy this, we assemble a cross-cultural database (Database of Musical Scales: DaMuSc) of scale data, collected over the past century by various ethnomusicologists. Statistical analyses of the data highlight that certain intervals (e.g., the octave, fifth, second) are used frequently across cultures. Despite some diversity among scales, it is the similarities across societies which are most striking: step intervals are restricted to 100-400 cents; most scales are found close to equidistant 5- and 7-note scales. We discuss potential mechanisms of variation and selection in the evolution of scales, and how the assembled data may be used to examine the root causes of convergent evolution.

The Microsoft HoloLens 2 Provides Accurate Biomechanical Measures of Performance During Military-Relevant Activities in Healthy Adults.

Augmented reality systems, like the HoloLens 2 (HL2), have the potential to provide accurate assessments of mild traumatic brain injury (mTBI) symptoms in military personnel by simulating complex military scenarios while objectively measuring the user's movements with embedded motion sensors. The aim of this project was to determine if biomechanical measures of marching and squatting, derived from the HL2 motion sensors, were statistically equivalent, within 5%, to metrics derived from the gold-standard three-dimensional motion capture (MoCap) system. Sixty-four adults (18-45 years; 34 males) completed a squatting and a marching task under single- (motor) and dual-task (motor + cognitive) conditions. Positional data from the HL2 and MoCap were simultaneously collected during the tasks and used to calculate and compare biomechanical outcomes. The HL2's augmented reality capabilities were utilized to deliver the cognitive component of the marching dual task. Equivalence testing indicated the HL2 and MoCap measures were within 5% in all squatting metrics-trial time, squat duration, squat velocity, squat depth, and dwell time. Marching metrics, including trial time, step count, stepping rate, and step interval, were also equivalent between the two systems. The mean reaction time for responses during the Stroop test was 810 (125) milliseconds per response. Biomechanical outcomes characterizing performance during two common military movements, squatting and marching, were equivalent between the HL2 and MoCap systems in healthy adults. Squatting and marching are two military-relevant tasks that require strength, motor coordination, and balance to perform, all of which are known to be affected by mTBI. Taken together, the data provide support for using the HL2 platform to deliver military-specific assessment scenarios and accurately measure performance during these activities. Utilizing objective and quantitative measures of motor function may enhance the management of military mTBI and reduce unnecessary risk to service members.

Development of artificial neural network and response surface methodology model to optimize the engine parameters of rubber seed oil – Hydrogen on PCCI operation

Identifying the suitable alternative fuel and optimum blend concentration for diesel engine combustion is critical as most biodiesel emits excess smoke and has a lower thermal efficiency due to its high viscosity and carbon residue. In the previous work, rubber seed oil was tested in a single-cylinder diesel engine, and its performance and emission results were compared with those of pure diesel, an RSO-diesel (70:30 by volume) blend, RSO-methyl ester, RSO-diethyl ether, RSO-ethanol, and RSO-hydrogen in a dual fuel operation. The testing was performed at a constant speed of 1500 rpm, with the engine loads varying at 25% step intervals. Results showed that smoke and nitrogen oxides were significantly reduced for RSO, and engine performance was enhanced when RSO was operated with hydrogen and diethyl ether in dual fuel mode. In this study, the experimental results were employed to develop an artificial neural network and response surface methodology model. Brake thermal efficiency, rate of pressure rise, carbon monoxide, hydrocarbon, oxides of nitrogen, and smoke were predicted using response surface methodology and artificial neural network. Though artificial neural network produced the best R2 values (0.87264–0.99929), mean absolute percentage error was relatively lesser in response surface methodology. Thus, the authors conclude that response surface methodology is the best suitable artificial intelligence tool to optimize the engine for accomplishing desired responses.

Influence of coronary artery disease on cardiolocomotor coupling during walking: a preliminary study

The mechanisms involved in the coupling between cardiac and locomotor rhythms in patients with heart disease remain unclear. It was speculated that reduced function of the cardiovascular and/or locomotor systems would increase the coupling of these systems to increase energy efficiency in response to increased energy demand during exercise. We investigated the development of cardiolocomotor coupling (CLC) in patients with coronary artery disease. Eight outpatients with coronary artery disease (CAD group) and eight healthy individuals (control group) underwent cardiopulmonary exercise testing involving a cycle ergometer ramp protocol and treadmill walk test to record CLC strength. The coefficient of determination (R2 value) of the interval between R waves on the electrocardiograph and step interval reflects CLC strength intensity. The Student’s t-test was used to compare cardiopulmonary exercise testing data and R2 values between the study groups. The R2 value was significantly higher in the CAD group than the control group. Peak oxygen uptake and oxygen uptake at the anaerobic threshold were significantly lower in the CAD group than the control group. Our findings showed that CLC intensity was higher in patients with CAD, suggesting that CLC is more likely to occur in individuals with reduced exercise tolerance due to cardiorespiratory deterioration. Key highlights Eight outpatients with coronary artery disease and eight healthy individuals underwent cardiopulmonary exercise and treadmill walk tests to determine cardiolocomotor coupling strength and physiological characteristics. This study reports a stronger cardiolocomotor coupling during exercise in patients with coronary artery disease compared with healthy individuals, suggesting that cardiolocomotor coupling is more likely to occur in people with reduced exercise tolerance attributed to impaired cardiorespiratory function. Our results support the theory that patients with cardiorespiratory impairment due to coronary artery disease have greater dynamic interaction between the locomotor and cardiovascular systems during exercise, which is concurrent with the hypothesis that cardiolocomotor coupling is a compensatory phenomenon for exercise maintenance.

Impact of Ni2+ on the structural, optical, electrical, and dielectric properties of Cu0.25Co0.25Mg0.5-xNixCe0.03Fe1.97O4 spinel ferrites synthesized via sol-gel auto combustion (SGAC) route

The sol–gel auto-combustion (SGAC) route was used to prepare the Cu0.25Co0.25Mg0.5-xNixCe0.03Fe1.97O4 [Ni-CCMCF] (0.0 ≤ x ≤ 0.5 with the step interval of 0.125) spinel ferrites (SFs). The formation of a single-phase spinel matrix was observed by X-ray diffraction (XRD) analysis. Moreover, the sharp peaks of XRD spectra confirmed the high crystallinity of the as-prepared spinel ferrites. The crystallite size (D) was reduced from (57.33–10.51) ± 0.05 nm and for the pure CCMCF sample, the specific surface area was 20.36 m2/g. The variation absorption bands at tetrahedral and octahedral sites along five Raman modes in Raman spectra were also confirmed in the spinel matrix of the Ni-CCMCF samples. The optical bandgap increased from 0.87 eV to 1.68 eV was observed with the replacement of dopant ions. Furthermore, the minimum resistivity was observed both in Ferro and para regions for the pure CCMCF sample. The tangent loss and dielectric constant were reduced, but ac conductivity was enhanced with increasing frequency and all the dielectric parameters have a minimum value for pure the CCMCF sample. X-ray photoelectron spectroscopy (XPS) and Energy Dispersive X-ray Spectroscopy (EDS) confirmed the successful incorporation of Ni2+ in the CCMCF sample. Therefore, due to the low tangent loss, the pure CCMCF sample will be used for high resonant frequency applications.

Effect of time step interval and time integration schemes in Pseudo-Dynamic analysis

Pseudo Dynamic Analysis technique is an alternative method for exploring structural performance by combining analytical and experimental investigation. Compared to shake table tests, it is a more economical method, and its reliability has been proven over many years of the studies. The damage occurrence and process can be monitored on the test sample due to experiments performed at low speeds. In this study, the behaviour of a single degree of freedom, cantilever column system, under the effect of the pulse load and earthquake record was investigated both numerically and experimentally using Pseudo Dynamic Analysis method. The effects of two different time integration schemes and various time step interval values on analyses were examined in the investigations and the results were compared. Numerical analyses were performed by α-operator splitting method and central differences method, and experimental studies were performed by α-operator splitting method. In experimental investigations, approximate results were obtained with numerical studies for certain values of the time step. At small time interval values, experimental results deteriorated. It is purposed to determine the optimum time step interval value that can be utilised in the Pseudo Dynamic Test method.

Tuning structural, electrical, dielectric and magnetic properties of Mg–Cu–Co ferrites via dysprosium (Dy3+) doping

In current research work, Dy3+ substituted Mg0.5Cu0.25Co0.25Fe2‒xDyxO4 (0.0 ≤ x ≤ 0.04 with the step interval of 0.01) soft ferrites were synthesized by the sol–gel auto combustion method. The prepared samples were characterized by the techniques using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), Fourier transform infrared (FTIR) spectroscopy, current–voltage (I–V) measurement, LCR meter, vibrating sample magnetometer (VSM) and Raman. XRD data reveal that the average crystallite size is 49.71 nm and the lattice constant is 0.83703 nm for sample x = 0.03. The non-uniform grain growth was demonstrated by micrographs and impurity-free elemental composition was observed from EDX analysis. The DC resistivity has an increasing and decreasing trend in ferromagnetic and paramagnetic regions with an increase in temperature. Moreover, the high resistivity is observed with the order of 1010 Ω·cm, and the activation energy is 0.944 eV for samples x = 0.03. The dielectric parameters including dielectric constant, dielectric losses, and impedance gradually decrease with the increase in frequency from 8 Hz to 8 MHz. The minimum dielectric loss at high frequency is found for sample x = 0.03. The coercivity (Hc) and saturation magnetization (Ms) are found in the ranges of 520.82–544.02 Oe and 20.5841–21.1473 emu/g, respectively. These observations confirm that dysprosium (x = 0.03) doped MCC-soft ferrites may be applicable in transformer cores, microwave absorbance, and telecommunication devices.

Statistical Optimization of Carbon Dioxide Capture Performance by Tri-Solvent System of MEA-DEA-PZ from the Stored Gas Reservoir

Aims/Objective: The current study evaluates the effectiveness of a blended tri-solvent system composed of monoethanolamine (MEA), diethanolamine (DEA), and piperazine (PZ) for removing the carbon dioxide (CO2) from the stored gas reservoir. The developed system is intended to be both environmentally benign and productive. Methods: The CO2 absorption was carried out for the total solvent (5, 10, and 15% v/v), during the course of three temperature ranges (20, 25, and 30°C) while maintaining the reservoir pressure of 1.5, 2, and 2.5 bar. The fraction of DEA: MEA has been restricted to 0.2, 0.5, and 0.8, with simultaneous loading of anhydrous PZ ranging from 0 to 2 gm. and agitation speed for step intervals of 300, 600, and 900 rpm. For the purpose of investigating the synergetic effects of the process parameters on the rapid absorption of CO2 (ξ) and the initial CO2 absorption rate (ε0), Box-Behnken Design (BBD) of response surface methodology (RSM) has been exploited. The design of experiments (DoE) assisted artificial neural network (ANN) and metaheuristic approach of hybridising ANN-whale optimization algorithm (WOA) was also developed and utilised to train and test the developed model. Three optimization models based on RSM, DoE-WOA and ANN-WOA were compared. Under the optimized operating conditions pertaining to DoE, DoE-WOA and DoE-ANN-WOA, (ε0 = 3.340, 3.460 3.513 gm./min-250 mL) and (ξ = 17.114, 18.069, 18.145 gm./250 mL) were obtained. Results: The hybridised DoE-ANN-WOA shows promising results in correlation with the experimental outcomes having error % for ε0 & ξ of 0.790 & 1.31. Conclusion: The DoE-ANN-WOA tends to be selected to predict the optimal absorption conditions as compared to other optimization techniques used in current article.

An Accuracy-preserving Block Hybrid Algorithm for the Integration of Second-order Physical Systems with Oscillatory Solutions

It is a known fact that in most cases, to integrate an oscillatory problem, higher order A-stable methods are often needed. This is because such problems are characterized by stiffness, chaos and damping, thus making them tedious to solve. However, in this research, an accuracy-preserving relatively lower order Block Hybrid Algorithm (BHA) is proposed for solution of second-order physical systems with oscillatory solutions. The sixth order algorithm was derived using interpolation and collocation of power series within a single step interval [tn; tn+1]. In order to circumvent the Dahlquist-barrier and also obtain an accuracy-preserving algorithm, four o-step points were incorporated within the single step interval. A number of special cases of oscillatory problems were solved using the proposed method and the results obtained clearly showed that it outperformed other existing methods we compared our results with even though the BHA is of lower order relative to such methods. Some of the second-order physical systems considered were the Kepler, Bessel and damped problems. Some important properties of the BHA were also analyzed and the results of the analysis showed that it is consistent, zero-stable and convergent

Physical activity is a potential measure of physical resilience in older adults receiving hemodialysis.

Physical resilience, or the ability to recover after a physical stressor, declines with aging. Efforts to preserve physical resilience in the older dialysis population are critically needed; however, validated, patient-centered measures that are sensitive to change are also needed. Our objective was to assess accelerometer-derived step count variability, or a measure of intra-individual variation in physical activity, as a potential measure of physical resilience among older adults receiving hemodialysis. Community-dwelling ambulatory older adults receiving in-center hemodialysis were prospectively enrolled. Participants wore wrist accelerometers during daytime hours on both dialysis and non-dialysis days up to 14 days, and the feasibility of accelerometer use was assessed from wear time. We used accelerometer data to compute step counts in 4-hour blocks and step count variability. Physical function was assessed with the Short Physical Performance Battery (SPPB which includes gait speed test), grip strength, activities of daily living (ADLs) instruments, and life space mobility. We assessed interval fatigue (subjective rating from 0 to 10) on dialysis and non-dialysis days and self-reported recovery time. We assessed the correlations of step count variability with measures of physical function and step count and interval fatigue. Of 37 enrolled participants, 29 had sufficient accelerometer data for analyses. Among the 29 participants, mean (SD) age was 70.6(4.8) years, and 55% (n=16) were male and 72% (n=21) were Black race. Participants were largely sedentary with median (Q1-Q3) self-reported total kilocalories per week of 200 (36-552). Step count variability was positively correlated with measures of physical function: SPPB (r=0.50, p<0.05), gait speed (r=0.59, p<0.05), handgrip strength (r=0.71, p<0.05), Instrumental ADLs (r=0.44, p<0.05) and life space mobility (r=0.54, p<0.05).There was a weak inverse correlation between post-dialysis step counts (4-hour blocks after a dialysis session) and post-dialysis interval fatigue [r=-0.19 (n=102, p=0.06). Physical activity assessment via accelerometer is feasible for older adults receiving hemodialysis. Step count variability correlated with physical function, so it may be a novel measure of physical resilience. Further studies are needed to validate this measure.

Mechanical and microstructural properties of high-performance concrete made with rice husk ash internally cured with superabsorbent polymers

An experimental study was carried out to determine the properties of rice husk ash (RHA) and its effect on high-performance concrete's (HPC) mechanical and microstructural properties. RHA content was placed at 0–30% at 5% step intervals and a constant water-binder ratio (W/B) of 0.3. A slump flow test was carried out to measure the workability property of the fresh HPC. In contrast, the influence of RHA contents on compressive, splitting tensile, flexural strengths and microstructural properties were examined for the hardened HPC specimens. The X-ray fluorescence (XRF), scanning electron microscopy-energy dispersive x-ray (SEM-EDX), X-ray diffraction (XRD), Fourier-transform infrared spectroscopy-Attenuate total reflectance (FTIR-ATR), Thermogravimetry analysis (TGA), Brunauer, Emmett and Teller (BET) specific surface area and laser diffraction particle size distribution (PSD) were used to access the feasibility of RHA in HPC. XRD and SEM/EDX techniques were conducted to investigate the hydration products and microstructure in hardened HPCs. The post-test examination showed increased compressive, splitting tensile and flexural strengths of HPC samples for a 10% RHA content mix, recording the highest compressive strength in all curing ages. As the curing ages increase, the microstructure of the samples with RHA becomes denser than the control due to the refinement of the microstructure by the RHA incorporated. The XRD and SEM/EDX confirmed the lower calcium hydroxides from pozzolanic reactivity and later formation of C–S–H. The results suggest that RHA can be used as a cement replacement for up to 10% in HPC to produce sustainable concrete.

Application of the Generalized Backstepping Control Method for Lotka-Volterra Prey-Predator System with Constant Time Delay

A well-known method, namely the backstepping method, which is used for stabilizing systems of ordinary differential equations is applied in this paper to solve the system of Lotka-Volterra prey-predator with time delay. The followed approach is accomplished with the cooperation of the method of steps, which is a well-known approach followed in solving delay differential equations, to transform the system of nonlinear delay differential equations into an equivalent system of ordinary differential equations. The fundamental concept behind the backstepping method is to construct recursively Lyapunov functions in quadratic form to stabilize the system for each time step interval. Matlab computer software is used to carry out the numerical simulation in order to investigate the effectiveness of the followed approach.