Unloading Cycles Research Articles

Ultrasensitive and self-alarm pressure sensor based on laser-induced graphene and sea urchin-shaped Fe2O3 sandwiched structure

Flexible pressure sensors are widely used in wearable electronics. In recent years, it is still a challenge to prepare high-sensitivity and high-performance pressure sensors, though flexible pressure sensors have made significant progress. Therefore, a new sensor structure is designed in this study. This structure is composed of sea urchin-like Fe2O3 as a spacer layer, which is sandwiched between two laser-induced graphene (LIG)/polyimide (PI) films. Additionally, a flexible multifunctional sensing device with both health monitoring and alarm functions is prepared based on the excellent mechanical properties and thermal conductivity of LIG. Multifunctional sensing devices have high sensitivity, integrated monitoring, and alarm functions. Specifically, the sensitivity of the pressure sensor is 603 kPa−1 for the pressure ranges of 0–10 kPa. The pressure sensor possesses a working range of up to 200 kPa and good cycle stability (for over 3000 loading–unloading cycles). Furthermore, LIG is employed as a heater to realize the alarm function. In this work, the combination of high performance and simple methods provides an effective method for the development of the integration of multifunctional pressure sensors for wearable electronic devices.

Damage characteristics of sandstone with different crack angles subjected to true triaxial cyclic loading and unloading

Cracks in the rock are among crucial defects affecting its deformation and strength characteristics. Particularly in underground or mining engineering, the initiation and development of cracks due to cyclic unloading are critically affected by the fracture of the rock mass. In order to scrutinize the mechanical behavior of rocks with different crack angles, a true triaxial cyclic loading and an unloading test are carried out on sandstone samples with prefabricated cracks of various angles. The cracked sandstone samples do not considerably expand under action of triaxial stresses, commonly exhibit non-ideal elastic characteristics, and mainly undergo shear failure. As the crack angle grows, the tensile properties become pronounced, and the fracture surface morphology of the cracked samples presents a huge difference. The change rules of the irreversible axial and lateral strains are apparently different, and the rate of change of the irreversible lateral strain in terms of the applied stress is more sensitive than that of the axial irreversible strain. The energy evolution law of the hysteresis loop formed in the sample cyclic load test has no evident influence on the crack angle of the sample; however, the larger the crack angle of the sample, the more energy consumption during failure. Based on the equivalent irreversible strain and the hysteretic loop energy dissipation indicators, the damage law of sandstone samples can be described. It is also revealed that the damage rule determined according to the equivalent irreversible strain index is more conducive to characterizing the initial characteristics of damaged samples. Additionally, the damage rule determined based on the hysteretic loop energy dissipation index would better describe the damage rule associated with the understudy samples. There are obvious discrepancies in the morphological characteristics of the fracture surface in the scanning electron microscope images of the typical fracture surface of the samples with various crack angles, indicating that the damage and destruction of the sample acted upon by the shear and tensile shear are wholly dissimilar.

Cyclic Stability of Ni44.8Cu5Ti45.2Hf5 and Zr‐Substituted Ni44.8Cu5Ti40.2Hf5Zr5 Medium‐Entropy Shape Memory Alloys

An experimental investigation on the cyclic stability of solutionized Ni44.8Cu5Ti45.2Hf5 and Zr‐substituted Ni44.8Cu5Ti40.2Hf5Zr5 (atomic percent, at%) medium‐entropy shape memory alloys (MESMAs) was carried out. The shift of the peak temperature for the forward B2B19′ transformation in Ni44.8Cu5Ti45.2Hf5 alloy after 50 differential scanning calorimetry (DSC) cycles was measured to be 23 °C, substituting 5 at% Zr for Ti increased it to 41 °C. No residual strain accumulation was observed in Ni44.8Cu5Ti45.2Hf5 alloy after 10 thermal cycles under a tensile stress of 200 MPa, and meanwhile the shape memory strain increased from 5% to 6.5%. A pseudoelastic strain (εPE) of ≈2.7% was obtained in Zr‐substituted Ni44.8Cu5Ti40.2Hf5Zr5 alloy at 55 °C (Af + 10 °C) for a maximum deformation (εmax.) of 4.4%. In addition, the stability of pseudoelasticity in Ni44.8Cu5Ti40.2Hf5Zr5 alloy during 100 loading–unloading cycles was examined in the solution annealed (1000 °C for 1 h) and aged (400 °C for 1 h) conditions. The results showed that aging treatment could effectively retard the degradation of pseudoelasticity in the alloy. These preliminary findings suggest that the idea of increasing chemical complexity in NiTi‐based SMAs holds promising potential in developing novel SMAs with enhanced cyclic stability.

Strength characteristics of brittle rocks under multi-stage intermediate principal stress loading

A series of single-stage true triaxial compression (TTC) tests and multi-stage intermediate principal stress (σ2) loading tests were carried out on three types of brittle rock specimens in this study to examine the influence of σ2 and the validity of obtaining strength parameters by using a multi-stage loading method under true triaxial stress conditions. There exists a critical σ2 at which the rock strength attains its ultimate value under both loading conditions. Under the same σ3 level, the critical σ2 is much smaller under the multi-stage σ2 loading compared with under the single-stage TTC. The test results also show that the strength determined under multi-stage σ2 loading is much smaller than that determined under single-stage TTC. The strength difference can attain 39%. A lower strength is measured under multi-stage σ2 loading because the local fracture plane induced by true triaxial stress is parallel to the σ2, and the strength of the rock specimen containing this type of local fracture plane is not affected by σ2. On the contrary, rock damage accumulates during multiple loading and unloading cycles. The current testing results indicate that the multi-stage loading test is not suitable for determining the strength envelope of brittle rock under true triaxial conditions.

Influence of Complex Stress Path on Energy Characteristics of Sandstones under Triaxial Cyclic Unloading Conditions

This paper explores the characteristics of energy accumulation, evolution, and dissipation of sandstone samples under different confining pressure conditions in the triaxial cyclic unloading test. The characteristics of the stress–strain relationship of deformation and failure of rock samples are analyzed in detail. By utilizing the integral method for the area, the densities of total energy, elastic energy, and dissipated energy under different confining pressure are calculated. In addition, the energy evolution laws of rock deformation and failure with cyclic unloading times are researched. The results demonstrate that during the unloading cycle of confining pressure, the total energy density u, elastic energy density ue, axial total energy density u1, and axial elastic energy density ue1 increase, the radial total energy density u3 and the radial elastic energy density ue3 decrease, and the dissipated energy density is almost unchanged. The total energy density u and elastic energy density ue of rock under different confining pressure cycle unloading have a significant linear relationship. Meanwhile, the scanning electron microscope image shows the microstructure characteristics of the cracks in the sandstone samples. The image results are consistent with the analysis of the macroscopic failure characteristics. Under the same stress path, the higher the initial confining pressure, the more severe the failure of the rock sample. The experimental results are expected to enhance the basic research on the energy characteristics under the triaxial unloading behavior of rock.

Study on gas leakage along cement sheath interfaces in salt cavern gas storage well

Cement sheath interfaces, which are potential gas leakage channels, play an important role in the safe operation of salt cavern underground gas storage (UGS) because the wellbore passes through different lithologies. Cement-salt rock specimens were experimentally prepared to measure the permeability changes under cyclic unloading–loading confining pressure. The results showed that after 10 cycles, the permeability decreased by 64.83% and presented a negative exponential correlation with the number of cycles, indicating that an increase in the gas injection–production cycles was beneficial to the zonal isolation of the cement sheath in the salt rock formation. Based on the permeability evolution law, a 3D geological model of the KING-1 cavern of Jintan UGS, was built considering the cavern and wellbore, to investigate the effects of internal gas pressure, operating time, and lithology on gas migration along the cement sheath interfaces. The gas leakage channel during the operation of salt cavern UGS was determined based on numerical simulation results. The results indicated that after the cavern was formed, the horizontal stress above the casing shoe became larger than the vertical stress, and the difference between the horizontal and vertical stresses increased with the number of cycles. After 20 cycles, the maximum micro–annulus widths at the cement–formation interfaces (CFI) in the mudstone–salt rock interface and mudstone layer at 3 MPa gas pressure were 3.50 and 5.34 times, respectively, of those at 9 MPa. The CFI at the mudstone–salt rock interface was a potential gas leakage channel at the early operational stage of gas storage, whereas at the later operational stage, gas leakage occurred along the CFI in the mudstone layer 20 m above the salt rock layer. The results are expected to provide a reference for gas leakage analysis, risk judgment, and long-term safe operation of salt cavern UGS.

Porous Elastomer Based Wide Range Flexible Pressure Sensor for Autonomous Underwater Vehicles

This work presents the design and implementation of a porous polydimethylsiloxane (PDMS)-based wide-range flexible pressure sensor for autonomous underwater vehicles. The capacitive sensor, with porous PDMS as dielectric, is encapsulated in bulk PDMS polymer. The fabricated sensor was evaluated over a wide pressure range (0-230 kPa), which is similar to pressures experienced up to approx. 23 m below the sea level. The sensors showed linear response when tested in air and near-linear response (98%) when submerged in water. The sensor showed much higher sensitivity (0.375 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) in water than in the air environment. However, the sensor exhibited the performance and sensitivity similar to the air condition (0.005 kPa <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">−1</sup> ) when the readout electronics (encapsulated inside a watertight enclosure) was also submerged inside the water along with the sensor. The fabricated sensor also exhibited fast response and recovery time (190 ms), as well as excellent repeatability and stability (no drift) over tested range of 50 loading and unloading cycles. These results demonstrate the suitability of presented sensors for potential use in applications requiring a wide range of pressure, particularly the underwater robotics where real-time pressure monitoring is critical for autonomous operation.

Macroscale modelling of 3D-woven composites: Elasto-plasticity and progressive damage

There is a growing need across multiple industries for lightweight materials with improved material performance and reduced manufacturing costs. Composites with 3D-woven reinforcement could help fill this need. Their use however, requires the development of computationally efficient and industrially applicable material models to predict their non-linear behaviour. This work proposes a macroscale elasto-plasticity and damage model to capture the experimentally observed inelastic strains and stiffness reductions. The model is general, thermodynamically consistent and allows for various non-linear phenomena to be added and calibrated in a modular fashion depending on loading direction. Further it allows for a simplified parameter identification routine in which the damage and hardening laws are identified directly from experimental curves without the need for complex calibration routines.In order to demonstrate the applicability of the proposed macroscale model, focus is given to predicting the material response of a 3D glass fibre reinforced epoxy material system. The damage and hardening parameters are identified based on uniaxial tensile and in-plane shear experimental curves with unloading cycles. The model performance is validated against an off-axis tensile test with unloading cycles and shows good agreement to the experimental result.

Impact of unloading kinematics on the occurrence of capping during the production of pharmaceutical tablets

Capping is a common defect that can occur during the manufacturing of pharmaceutical tablets. Several studies showed that decreasing the unloading speed of the manufacturing cycle plays a role in the occurrence of such defects. Following this idea, we study in this work the influence of the unloading step on capping using a compaction simulator.Measuring the die wall pressure made it possible to detect precisely that tablets capped just after the unloading (some milliseconds only). To evaluate the impact of the unloading speed on capping, we developed a two-step unloading phase controlled by three manufacturing parameters. It was possible to mitigate capping by decreasing the speed at which the contact between the punches and the tablet was lost. Capping seemed due to dynamical effects related to the release of the axial pressure. The modification of the unloading step to mitigate capping led to significant changes in tablet density but no clear trends were found for the residual die-wall pressure and tablet strength.This work made it possible to improve the understanding of capping. Moreover, the two-step unloading cycle gave a new idea for possible modifications that could be done on rotary presses in order to mitigate capping.

A Comprehensive Study of Fracture Toughness Determination from Conventional and Unconventional Methods

In this work fracture toughness is determined by the Toughness model; Critical Stress-Strain Model and Energy release rate model using unconventional test method referred to as Spherical Indentation test (SIT) to reduce the large and costly experimental set up as required in Conventional Fracture Toughness Test. The toughness model correlates the indentation energy to fracture with fracture toughness, Critical Stress-Strain Model assumes that the critical fracture toughness is equal to the critical plastic work done by the material when a crack tends to propagate and as per the Energy release rate model, indentation depth is given by loading-unloading cycles. The unloading slope which is elastic provides the reduced Young’s Modulus of the material from each unloading cycle which reflects the occurrence of damage in the material. For the determination of contact radius at different indentation points, finite element analysis is performed using the material data obtained from the tensile test result obtained from the previous work of the author. Conventional method using the Compact Tension (CT) and Three-Point Bending (TPB) specimens for the same material is used to determine the fracture toughness and compared with the above-described model.

The efficacy of high-load resistance training in combination with aerobic training in patients with coronary artery disease: a dose-dependent randomised, controlled clinical trial

Abstract Funding Acknowledgements Type of funding sources: Public grant(s) – National budget only. Main funding source(s): Slovenian Research Agency Background The combination of resistance training (RT) and aerobic training (AT) was shown to be superior compared to AT, although most studies applied only low-loads (LL) to moderate-loads in RT. Therefore, it remains to be elucidated whether high-load (HL) RT elicits greater improvement in maximal aerobic capacity and maximal muscle strength compared to low-load (LL) RT in combination to AT in patients with coronary artery disease (CAD). Purpose The aim of our study was to investigate the effects of HL-RT and LL-RT combined with AT in comparison to AT on maximal aerobic capacity, muscle strength and health-related quality of life. Methods We randomised 79 patients with CAD to HL-RT+AT (70 %-80% of one repetition maximum [1-RM]), LL-RT+AT (35%-40% of 1-RM) or AT group and 59 patients with mean (SD) age 61 (8) years and left ventricular ejection fraction 53 (9) % completed 12 weeks (36 training sessions) of the study. After the initial ambulatory screening by cardiologist and cardiopulmonary exercise test, patients were familiarised with proper lifting and breathing technique, and performed 1-RM test on leg press machine. During the training, the RT load progressively increased from 70% of 1-RM (6–11 repetitions per set) to 80% of 1-RM (6–8 reps per set) in HL-RT group and from 35% of 1-RM (12–22 reps per set) to 40% of 1-RM (12–16 reps per set) in LL-RT group in the first seven weeks of the intervention. Following re-evaluation of 1-RM, the training load in HL-RT group was progressed from 70% 1-RM (11 reps per set) to 80% 1-RM (6–8 reps per set), and the load in LL-RT group was progressed from 35% 1-RM (22 reps per set) to 40% 1-RM (12–16 reps per set). All patients performed AT consisted of 3-5 min of work-load interval cycling separated by 2 min of unloaded cycling progressing from 50% to 80% maximal workload achieved at baseline cardiopulmonary exercise test. We measured maximal aerobic capacity (VO2 max), maximal voluntary contraction (MVC) and quality of life at baseline and post-training. Results Exercise training was safe and associated with improvement in VO2 max (p &amp;lt; 0.01) in all training groups, whereas only LL-RT and HL-RT group improved MVC (both p &amp;lt; 0.001). Following training, VO2 max increased more in HL-RT group compared to AT group (+18 %, p = 0.032), and MVC increased more in HL-RT group compared to LL-RT group (+7 %, p = 0.018) and AT group (+16 %, p &amp;lt; 0.001). HL-RT group improved mental functioning component of short form 12-item quality of life questionnaire (+6 points, p = 0.003), with no significant difference compared to other training modalities. Conclusions RT on top of routine CR management, is safe and efficacious training modality for patients with CAD enrolled in cardiac rehabilitation.

Shakedown response of recycled rubber–granular waste mixtures under cyclic loading

Understanding and quantifying the long-term deformation behaviour of granular materials under repeated loads is imperative for ensuring the longevity of railway tracks. One of the most relevant characteristics of granular materials under repeated cycles of loading and unloading is their ability to achieve a relatively stable state (shakedown) after being subjected to initial compression. The shakedown response of blended rubber–granular waste mixtures under triaxial test conditions has been investigated in past studies highlighting the influence of the rubber content, confining stress and cyclic loading amplitude. However, a clear methodology for estimating shakedown yield limits of these granular mixtures has not been discussed in detail. The current study highlights the influence of the peak shear strength of these mixtures under static loading on their shakedown response in cyclic loading conditions. It is observed that the variation of static shear strength with rubber contents and confining stresses is found to affect the shakedown response. A unified method of estimating the shakedown limit is proposed by analysing permanent axial strains with normalised cyclic stress ratio at different loading cycles. The proposed method is validated through two independent sets of drained cyclic triaxial test data on coal wash–rubber crumb mixtures and rail ballast.

Experimental Study on Progressive Damage Evolution in Rocks Subjected to Post-peak Cyclic Loading History

Abstract Because of the release of in situ rock stress, rocks surrounding deep underground excavations are mostly driven into a post-peak damage state. Thus, investigations on cyclic loading-induced damage of rocks are of paramount significance in terms of the long-term stability of rock structures. In this study, using a damage-controlled testing method, the effect of post-peak cyclic loading on the failure behavior of different rock types was comprehensively evaluated. This investigation revealed that post-peak cyclic loading imposes no significant influence on the overall failure behavior of rocks. The evolution of damage variables also indicated that the large portion of axial strain damage (Da) occurs during the first cycle at the peak strength, whereas lateral strain damage (Dl) evolved more rapidly than Da did in the post-peak regime under further loading and unloading cycles. The cumulative permanent axial strain (∑εap) evolved nonlinearly with the axial stress ratio (σi/σa−peak) in the post-peak regime, which was manifested as sparse-dense-sparse hysteretic loops. A rapid reduction in the crack damage stress ratio was observed for rocks in the initial sparse hysteretic loops, which was followed by a lower decrease rate in the subsequent dense hysteretic loops, and an almost constant value was finally reached in the last sparse hysteretic loops. Furthermore, tangent Young’s modulus (Etan) and Poisson’s ratio (υ) evolved in three main stages: One, Etan first increased and then decreased in the initial sparse hysteretic loops, while υ continuously increased, representing significant deformation in the lateral direction. Two, Etan decreased in the dense hysteretic loops, while υ increased at a higher rate for stronger rocks because of the decrease in Da accumulation. Three, the increase rate of υ declined in the second set of sparse hysteretic loops, and Etan decreased until complete failure occurred.

Estimation of the Large Diameter Bored Pile Ultimate Capacity Using Different Design Methods: Assessment Study

In this paper, in situ measurements of two well-instrumented loading tests performed on large diameter bored piles (LDBP) have been utilized to assess the reliability of the predicted ultimate pile capacity using three settlement-based and capacity-based methods. The first test was conducted on a short LDBP with a 1.3m and 9.50 length. This LDBP was constructed in stiff clay soil and loaded till the achievement of the failure. While the second in-situ loading test was performed on a long LDBP with a 1.00 m diameter and 34.00 m length. This LDBP was constructed in multi-layered soil and examined under three axially loading and unloading cycles to obtain the ultimate load settlement relationship. Although this LDBP was loaded with an applied load of three times its working capacity, but no apparent failure was reached at the end of the loading test. Thus, two different methods are adopted to interpret the test data and determine the ultimate pile capacity. The obtained ultimate capacities of the two tests were utilized in an assessment study. The comparative analysis results showed a significant difference between the ultimate capacity obtained using three different methods and field measurements. Out of the three utilized methods in this study, the two settlement-based methods underestimated the LDBP ultimate capacity of the two LDBP cases; conversely, the third capacity-based method overestimated the ultimate capacity of the two LDBP cases.

Impact of aerobic fitness status, menstrual cycle phase, and oral contraceptive use on exercise metabolic flexibility

Metabolic flexibility is the ability to appropriately store or utilize substrates. Exercise such as high‐intensity interval exercise (HIIE) is also a robust test of one’s ability to shift between substrates to support metabolic demand. Menstrual cycle or oral contraceptive use may impact metabolic responses to exercise. Fitness status also plays an important role in metabolism. We assessed the impact of hormonal fluctuation and fitness status on exercise metabolism in women during HIIE. 25, healthy, active women (24.4±3.6yrs; 165.5±6.9 cm; 65.1±10.5 kg; 38.8±6.6mL/kg/min) experiencing a regular menstrual cycle (n=15) or using oral contraceptives (n=11) completed the study. Participants were split by aerobic fitness status (High: 43.7±4.7mL/kg/min; Low: 33.6±3.9mL/kg/min). Participants completed a baseline and counterbalanced HIIE sessions in the follicular (FOL) and luteal phase (LUT). FOL sessions took place 2‐7d after onset of menstruation or non‐active OC days. LUT sessions took place ~6‐8d following urine ovulation or third week of active OC pills. Exercise was performed on an electrically braked cycle ergometer. High intervals (H1‐H4) were 4x4 min intervals at the power output corresponding to 50% of the difference between the ventilatory threshold and VO2peak, separated with 3min of unloaded cycling (0W; low intervals). RPE and blood lactate assessed via finger stick were taken after each interval. There was no effect of menstrual cycle phase or oral contraceptive use on fat oxidation, carbohydrate oxidation or blood lactate. There was an effect of fitness status on fat oxidation in LUT and FOL (p=0.002). High fit women oxidized more fat during the full session (FOL: p=0.050, LUT: p=0.001), high intervals (FOL: p=0.048, LUT: p=0.001), and low intervals (FOL: p=0.032, LUT: p=0.024) during FOL and LUT, and recovery during LUT (p=0.033). Carbohydrate oxidation (g/kg; p=0.049) and AUC (p=0.024) were greater in high women during FOL, but not LUT. Blood lactate was significantly greater in low fit women during exercise interval H2 through recovery during FOL, but not LUT (p≤0.050). Total change in rate of fat oxidation (Δ g/kg/min) during HIIE intervals was greater in high vs low fitness during FOL (H2: p= 0.018, H3: p=0.004), and LUT (H1: p=0.041, H2: p=0.001, H3: p=0.001, H4: p=0.006). There was a correlation between exercise fat oxidation (g/kg) and lactate AUC (H1‐L4) during FOL (r=‐0.440, p=0.030; n=25) but not LUT (‐30 minute) (r=0.215, p=0.143; n=25). Our results reflect fitness status plays an important role in exercise fat oxidation, carbohydrate oxidation and blood lactate during HIIE in young women. High fitness women benefit from greater exercise metabolic flexibility than their low fit counterparts. These these differences may be unique to the menstrual cycle phase, with low fitness women having poorer exercise metabolic flexibility in the follicular phase.

A New Analytical Model for Deflection of Concrete Beams Reinforced by BFRP Bars and Steel Fibres under Cyclic Loading.

Basalt-fiber-reinforced plastic-bars-reinforced concrete beams (i.e., BFRP-RC beams) usually possess significant deformations compared to reinforced concrete beams due to the FRP bars having a lower Young’s modulus. This paper investigates the effects of adding steel fibers into BFRP-RC beams to reduce their deflection. Ten BFRP-RC beams were prepared and tested to failure via four-point bending under cyclic loading. The experimental variables investigated include steel-fiber volume fraction and shape, BFRP reinforcement ratio, and concrete strength. The influences of steel fibers on ultimate moment capacity, service load moment, and deformation of the BFRP-RC beams were investigated. The results reveal that steel fibers significantly improved the ultimate moment capacity and service load moment of the BFRP-RC beams. The deflection and residual deflection of the BFRP-RC beams reinforced with 1.5% by volume steel fibers were 48.18% and 30.36% lower than their counterpart of the BFRP-RC beams without fibers. Under the same load, the deflection of the beams increased by 11% after the first stage of three loading and unloading cycles, while the deflection increased by only 8% after three unloading and reloading cycles in the second and third stages. Finally, a new analytical model for the deflection of the BFRP-RC beams with steel fibers under cyclic loading was established and validated by the experiment results from this study. The new model yielded better results than current models in the literature.

Correlation of Hemodynamic and Respiratory Parameters in Invasive Cardiopulmonary Exercise Testing (iCPET).

Background: Invasive cardiopulmonary exercise testing (iCPET) is an integral part in the advanced diagnostic workup of pulmonary hypertension (PH). Our study evaluated the relation between hemodynamic and respiratory parameters at two different resting conditions and two defined low exercise levels with a close synchronization of measurements in a broad variety of dyspnea patients. Subjects and methods: We included 146 patients (median age 69 years, range 22 to 85 years, n = 72 female) with dyspnea of uncertain origin. Invasive hemodynamic and gas exchange parameters were measured at rest, 45° upright position, unloaded cycling, 25 and 50 W exercise. All measurements were performed in a single RHC procedure. Results: Oxygen uptake (VO/body mass) correlated significantly with cardiac index (all p ≤ 0.002) at every resting and exercise level and with every method of cardiac output measurement (thermodilution, method of Fick). Mean pulmonary arterial pressure (PAPmean) correlated with all respiratory parameters (respiratory rate, partial end-tidal pressures of oxygen and carbon dioxide [petCO and petO], ventilation/carbon dioxide resp. oxygen ratio [VE/VCO, VE/VO], and minute ventilation [VE], all p < 0.05). These correlations improved with increasing exercise levels from rest via unloaded cycling to 25 W. There was no correlation with right atrial or pulmonary arterial wedge pressure. Summary: In dyspnea patients of different etiologies, the cardiac index is closely linked to VO at every level of rest and submaximal exercise. PAPmean is the only pressure that correlates with different respiratory parameters, but this correlation is highly significant and stable at rest, unloaded cycling and at 25 W.

Laser-Sculptured Hierarchical Spinous Structures for Ultra-High-Sensitivity Iontronic Sensors with a Broad Operation Range.

Tactile pressure sensing over a wide operation range (>1 MPa) is challenging for a variety of applications in fields such as aviation, oceanography, and biomedicine. Recently, innovative strategies have been utilized to improve the performances of tactile sensors using specially designed structures, dielectric layers, and electrodes. Here, a hierarchical structural design based on ionic gel films has been utilized to build iontronic pressure sensors with ultrahigh sensitivities and broad operation ranges. Sculptured patterns made by a controlled CO2 laser scanning process have been produced on polyimide films to achieve two kinds of protrusion structures for high specific surface areas and strength to withstand high pressure. The iontronic sensor has been constructed by adding two screen-printed electrodes of high surface areas to achieve an ultrahigh sensitivity of 2593 kPa-1 and a wide pressure range from 0 Pa to 3.36 MPa. The prototype device also has a fast response and recovery time of 26 and 13 ms, respectively, and an excellent mechanical durability in the endurance test of over 2700 repeated loading and unloading cycles under a pressure of 1 MPa. Several application examples have been demonstrated, including the detection of physiological signals on human volunteers, the feedback control of intelligent robots, the grasping operation of underwater soft grippers, and the environmental wind-speed monitoring. As such, this work demonstrates a versatile and economical methodology to produce high-performance flexible sensors for various potential applications.

Microstructure and Superelastic Properties of FeNiCoAlTi Single Crystals with the &lt;100&gt; Orientation under Tension

The microstructure and superelastic response of an Fe41Ni28Co17Al11.5Ti2.5 (at.%) single crystal along the &lt;100&gt; orientation was investigated under tension at room temperature after aging at 600 °C for 24 h. From the superelastic results, the samples aged at 600 °C for 24 h exhibited 4.5% recoverable strain at room temperature. The digital image correlation (DIC) method was used to observe the strain distribution during the 6.5% applied strain loading. The DIC results showed that the strain was uniformly distributed during the loading and unloading cycles. Only one martensite variant was observed from the DIC results. This was related to the aging heat treatment times. The martensite morphology became a single variant with a longer aging time. The thermo-magnetization results indicated that the phase transformation and temperature hysteresis was around 36 °C. Increasing the magnetic field from 0.05 to 7 Tesla, the transformation temperatures increased. The maximum magnetization was 160 emu/g under the magnetic field of 7 Tesla. From the transmission electron microscopy results, the L12 precipitates were around 10 nm in size, and they were high in Ni content and low in Fe content.

Flexible, mechanically robust, multifunctional and sustainable cellulose/graphene nanocomposite films for wearable human-motion monitoring

The recent sensing technology development for flexible electronics has led to applications in intelligent robots, human-machine interfaces and health monitoring. However, it is challenging to combine ultra-light weight, high durability and flexibility, rapid response and simple fabrication within a single sensor. We herein report a cost-effective, sustainable preparation route for such a sensor, through (i) self-assembling cellulose nanofibers (CNFs) and graphene nanoplatelets modified by Triton X-100 (X-100-GNPs) and (ii) simply filtrating the mixture. X-100-GNPs were found to relatively uniformly disperse in the CNF matrix due to strong interfacial interactions. A nanocomposite film containing 23.76 vol% of GNPs displayed an electrical conductivity of 9.67 S/cm with mechanical robustness – Young's modulus of 6.18 GPa and tensile strength of 173 MPa. The efficient conductive GNP network provided the nanocomposite film sensors with integration of rapid response (61 ms under 1.5 KPa) and high flexibility, sensitivity and durability over 10,000 loading and unloading cycles at 1 Hz with 0–0.5% tensile strain. Used as a wearable strain sensor, the film demonstrated remarkable sensing capabilities in physiological signals, voice recognition, repression changes, muscle contraction and joint bending.