Unloading Phase Research Articles

Obstructive sleep Apnea detection and alerting system using Piezoelectric sensor array embedded Quilt

Obstructive sleep apnea (OSA) is a prevalent and serious sleep disorder. OSA causes involuntary cessation of breathing for brief periods of time during sleep. Usually a person may not be aware of breath interruption during sleep which may lead to nocturnal death. We proposed a novel body movement sensing method for detecting apneic episodes. Body movement signals were acquired using piezoelectric sensor array embedded inside a quilt. Acquired signals were digitally processed and peak response of the sensor during loading and unloading phase was analyzed. Alerting system will be activated whenever the movement signal time duration exceeds the threshold (t > 10 s). Also vibration stimulation is applied to the user whenever the breathing pause exceeds preset threshold (t > 20 s) using a vibration motor disc placed inside the quilt. This method was evaluated with 10 subjects in a normal sleep environment. Experimental results revealed that the proposed method efficiently detects and alerts the user within 10 seconds of breathing cessation. The proposed method can also assist in early detection of OSA in asymptomatic individuals.

Experimental Study on Acoustic Emission and Resistivity Response of Sandstone under Constant Amplitude Cyclic Loading

A lot of engineering practice shows that, during the construction and operation of rock mass projects, in addition to the static load, the rock is more subjected to cyclic load. Constant amplitude cyclic load is one of the simpler cyclic loading methods. The damage of rocks gradually accumulates under the action of periodic cyclic load, and finally, fatigue damage occurs, which affects the stability of the project. Therefore, it is necessary to study the mechanical properties of the rock under the action of constant amplitude cyclic load. Acoustic emission (AE) parameters and resistivity are both sensitive to the damage process of the rock and can well describe the damage evolution law of the rock. Under the action of constant amplitude cyclic loading, different loading conditions, different state specimens, and so on, factors will make a big difference to the AE signal and resistivity, such as the difference in stress amplitude, loading rate, and saturation. Therefore, in this paper, the typical sandstone in the Chongqing area is taken as the research object, the AE characteristics and resistivity characteristics of sandstone under different test conditions such as different stress amplitude, different loading frequency, and different saturation are tested, and the evolution of AE is found. It also has a three‐stage rule: in the initial stage, the deformation is faster and the AE signal is strong; in the constant velocity stage, the deformation develops slowly and the AE signal is also stable; in the acceleration stage, the deformation develops sharply and the AE signal also becomes more intense. With the increase of cyclic loading stress amplitude, or the decrease of cyclic loading frequency, or the decrease of rock sample saturation, the acoustic emission signal generated in each cycle will be stronger. The resistivity as a whole shows a rapid decline in the loading phase and a rapid rebound in the unloading phase. The changes in resistivity at different stress amplitudes show differences in the first few cycles; the overall change trend of resistivity at different frequencies is consistent, but the rate of change increases with decreasing frequency, and the variation trend of resistivity is very different under different saturation.

Digital image correlation of additively manufactured CFRTP composite systems in static tensile testing

Additive manufacturing of polymers results in low strength and inherently defective parts with limited application, hence the reason for selectively reinforcing the material using continuous fibers for improving the mechanical properties for which there are indications deviation from the classical laminate theory (CLT) theory and the rule of mixture, as well as a significant influence of manufacturing defects on the overall mechanical properties. Although the results in the mechanical behavior analysis of these materials are scarce today, authors up to date have documented some mechanical properties under tensile loading without interruption. Therefore, eight sets of CFRTP test specimens were designed and additively manufactured according to ASTM-D3039 varying the layer stacking sequences and prepared for digital image correlation (DIC) measurement. Finally, the prepared specimens were statically tested over three consecutive phases of progressive tensile loading and unloading using an axial testing machine, while the displacements were monitored and measured using the GOM-Aramis DIC system.

Effect of fluoride on mechanical properties of NiTi and CuNiTi orthodontic archwires: an in vitro study.

ABSTRACTIntroduction: After debonding, white spot may appear on the area below the bracket, which is the early clinical sign of carious lesion. There is increased caries risk underneath and adjacent to orthodontic bands and brackets, which call for maximum use of caries preventive procedures using various fluoride application methods. Objective: The aim of the study was to evaluate alterations in the mechanical properties (modulus of elasticity and yield strength) in loading and unloading phases for different orthodontic archwires (nickel-titanium [NiTi] and copper-nickel-titanium [CuNiTi]) when exposed routinely to fluoride prophylactic agents for a predetermined period of time. Methods: Preformed rectangular NiTi and CuNiTi wires were immersed in fluoride solution and artificial saliva (control) for 90 minutes at 37ºC. After immersion, specimens were tested using a 3-point bend test on a universal testing machine.Results: There is a significant reduction in the unloading yield strength when the NiTi and CuNiTi wires were exposed to APF gel. Conclusion: The result suggests that use of topical fluoride agents affect the mechanical properties of the wires, leading to increase in treatment duration. Fluoride prophylactic agents must be used with caution in patients undergoing orthodontic treatment. Injudicious use of these agents may cause corrosive effects on the orthodontic wire surfaces, with alteration in their mechanical properties.

Mining‐Induced Pressure‐Relief Mechanism of Coal‐Rock Mass for Different Protective Layer Mining Modes

The protective layer mining method of the traditional deep coal seam in has been confronted with great challenges, and it is difficult for coal and gas to be extracted together. Taking the occurrence conditions of III1 mining area of Luling Coal Mine located at Huaibei, China, as engineering background, the influence law of the lithology on stress environment in front of the stope was analyzed by theoretical analysis and numerical simulations. The mining‐induced mechanical effect of coal‐rock mass was studied under different protective layer mining modes. The results showed that the peak value of the advanced abutment pressure decreased with the decrease of lithologic strength under the same mining conditions. For simulated geological conditions, the stress concentration coefficient of soft rock and coal seam protective layer mining modes was 1.9 and 1.7, respectively. Under the mining stress path of different protective layers, the ratio of axial stress increase and confining pressure unloading in secondary unloading phase were 2 : 1 and 1.5 : 1, respectively. The axial stress‐strain curves of different protective layer mining modes had similar trends, and they had a volume expansion at the end of unloading (failure stage). In addition, it revealed the pressure‐relief antireflection mechanism of the protective layer mining. Under the same confining pressure condition, the peak stress and peak strain increased with the increase of loading and unloading velocity ratio. The reduced value of the confining pressure increased, while the volume expansion decreased at failure. The results were applied to III1 mining area in soft rock protective layer mining, which created the mining way of traditional coal seam protective layer. Furthermore, the gas control technology of soft rock protective layer working face was put forward for deep coal seam with low permeability and high gas, enriching the pressure‐relief mining theory of protective layer.

Optimal Thread-In and Thread-Out Strategies for Heavy Plate Levelers

Abstract In this paper, a method to determine optimal adjustment trajectories for the loading and unloading phases of heavy plate levelers is proposed. Due to the high leveling forces, the elastic structure of the leveler is deformed. The available adjustment possibilities of the machine are typically used to actively compensate for the deflection of its work rolls. However, only a small subset of the available degrees of freedom of the leveler may be controlled under load. Therefore, the optimal adjustment is typically determined for the highest expected load and uniformly applied during the whole leveling process. As a consequence, the deflection is overcompensated during the loading and unloading phases of the plate and the head and tail ends of the plate might develop ski-ends. To avoid such an overcompensation, the adjustable degrees of freedom of the leveler can be used. Based on an accurate deflection model of the leveler, the loading and unloading phases of the plate are simulated and the input trajectories for the adjustable degrees of freedom of the leveler are optimized. The proposed approach is validated with simulations.

Prediction and numerical simulation of the face‐slab extrusion damage of Dashixia concrete faced rock‐fill dam

AbstractOne of the core issues affecting the safety of high concrete faced rock‐fill dams (CFRDs) is the extrusion damage of the concrete face slabs. In this paper, the causes of the face‐slab extrusion damage under long‐term operational conditions are studied. It is found that not only the creep behavior of the dam materials but also the circulating water load in the reservoir is responsible for the uneven deformation of the dam that induces the extrusion damage of the face slabs. The possibility of the potential extrusion damage of the face slab of the Dashixia dam, which is now under construction in Xinjiang, China, is further predicted by means of a three‐dimensional finite element analysis (FEA). In the FEA, a unified generalized plasticity model that can reflect the volumetric contraction property during the unloading phase of coarse‐grained materials is adopted to overcome the shortcomings of previous studies where the effects of the circulating water load are neglected because of model limitations. Then, combined with an incremental creep model, the long‐term operational characteristics of the Dashixia dam are predicted and thoroughly discussed. Moreover, a submodel of the face slab is developed and introduced in the analysis to simulate the compressive stress along the thickness of the face slab. According to the results, it can be concluded that extrusion damage of the face slab of the Dashixia dam may occur under the current design conditions, and it is recommended to take some engineering measures to strengthen the slab.

Single-Subject Analyses Reveal Altered Performance and Muscle Activation during Vertical Jumping

Effects of barefoot and minimal footwear conditions on performance during jumping (i.e., jump displacement) are unclear with traditional group-level studies because of intra- and interindividual variability. We compared barefoot, minimal, and conventional athletic footwear conditions relative to countermovement vertical jump (CMVJ) performance and muscle activation using a single-subject approach. Fifteen men (1.8 ± 0.6 m; 84.5 ± 8.5 kg; 23.8 ± 2.3 y) performed three CMVJ trials in barefoot, minimal, and conventional footwear conditions while ground reaction forces (GRF) and electromyograms of eight lower extremity muscles were recorded. The Model Statistic procedure (α = 0.05) compared conditions for CMVJ displacement, net impulse, durations of unloading, eccentric, and concentric phases, and average muscle activation amplitudes during the phases. All variables were significantly altered by footwear (p < 0.05) in some participants, but no participant displayed a universal response to all variables with respect to the footwear conditions. Seven of 15 participants displayed different CMVJ displacements among footwear conditions. Additional characteristics should be evaluated to reveal unique individual traits who respond similarly to specific footwear conditions. Considerations for footwear selection when aiming for acute performance enhancement during CMVJ tests should not be determined according to only group analysis results. The current single-subject approach helps to explain why a consensus on the effects of barefoot, minimal, and conventional footwear conditions during the CMVJ remains elusive.

Habituation to Transport Helps Reducing Stress-Related Behavior in Donkeys During Loading

Adopting proper animal management strategies, including training, might reduce to a substantial extent the adverse effects of transport-related stress in animals. The aim of this study was to evaluate the effect of habituation to transport on stress-related behaviors and physiological indicators during loading and unloading in donkeys. Fourteen donkeys were recruited and divided in two treatment groups: Habituation (H; M = 5, F = 2) and Control (C; M = 5, F = 2). H donkeys were gradually habituated to be transported, traveling together with their mothers and other adult donkeys well-accustomed to transport, while C donkeys had never been transported before. Loading and unloading phases were video recorded and behavior was analyzed. Saliva samples for cortisol concentration determination were collected at rest and after unloading. Latency time to load was significantly shorter for H donkeys than C donkeys (Mann-Whitney; p = 0.004). C donkeys also showed significantly more stress-related behaviors (Mann-Whitney; p = 0.026) and required a higher but not statistically significant number of human interventions to load. Cortisol concentration increased in both groups, but no differences were found between them (Mann-Whitney; p > 0.05). These results suggest that habituation to transport could mitigate stress during loading procedures in donkeys reducing loading time, frequency of stress-related behaviors and diminishing the need of human intervention.

Analytical modeling of surface generation in ultrasonic ball burnishing including effects of indentation pile-up/sink-in and chipping fracture

In mechanical based machining processes, the surface topography is generated through series of hierarchical pattern. Plastic deformation as result of contact and kinematic of motion are two main factors which determine evolution of surface generation. To basically optimize the surface quality, accurate predictive model of surface generation and constraints are required. In the present work, analytical models of dimple formation and hierarchical surface generation in ultrasonic assisted ball burnishing process are proposed. Pile-up and sink-in as two phenomena of indentation during both of loading and unloading phases were taken into the developed models. Considering interaction of indentation profile and kinematic of motion, three-dimensional surface topography and surface roughness are also analytically predicted. A criterion for surface failure is defined to perform process without any erosion. Confirmation of results have been made by series of single trace and multi-traces burnishing experiments on AA6061-T6 and AISI 1045. The results of indention profile, surface topography, roughness and failure criterion which were derived from predictive models were completely consistent with confirmatory experiments.

A novel simplified biomechanical assessment of the heel pad during foot plantarflexion.

The heel pad (HP) which is located below the calcaneus comprises a composition of morphometrical and morphological arrangements of soft tissues that are influenced by factors such as gender, age and obesity. It is well known that HP pain and Achilles tendonitis consist of discomfort, pain and swelling symptoms that usually develop from excessive physical activities such as walking, jumping and running. The purpose of this study was to develop biomechanical techniques to evaluate the function and characteristics of the HP. Ten healthy participants (five males and five females) participated in this laboratory-based study, each performing a two-footed heel raise to mimic the toe-off phase during human locomotion. Twenty-six (3 mm) retroreflective markers were attached to the left and right heels (thirteen markers on each heel). Kinematic data was captured using three-dimensional motion analysis cameras synchronised with force plates. Descriptive and multivariate statistical tests were used in this study. In addition, a biomechanical technique that utilises only six markers from 26 markers to assess HP deformation and function has been developed and used in this study. Overall HP displacement was significantly higher in males on the most lateral part of the right heel (p < 0.05). No significant differences were evident when comparing the non-dominant and dominant heels during the baseline, unloading and loading phases (p > 0.05). Findings from this study suggested that biomechanical outputs expressed as derivatives from tracked HP marker movements can morphologically and morphometrically characterise HP soft tissue deformation changes. The outcome of this study highlights the importance of 3D motion analysis being used as a potential prospective intervention to quantify the function / characteristics of the heel pad soft tissues.

Test-retest reliability of a clinical foot assessment device for measuring first metatarsophalangeal joint quasi-stiffness

BackgroundThe stiffness of the first metatarsophalangeal joint (MTPJ) is of interest in cases such as hallux rigidus and apropulsive gait. Subjective rating of joint mobility as ‘hypermobile, normal, or stiff’ is an unreliable method. Previous instruments for the assessment of first MTPJ stiffness can be too hard and uncomfortable for test subjects. Recently, a new device using a load cell and optical fiber with fiber Bragg grating (FBG) sensors was developed to provide a comfortable means of clinical foot assessment. This study aimed to evaluate the test-retest reliability of this FBG-load cell device in measuring the first MTPJ quasi-stiffness. MethodsThe left foot of 13 female subjects were measured twice for their first MTPJ quasi-stiffness, approximately seven days apart. The FBG-load cell device measured the MTPJ range of motion from a resting position to maximum dorsiflexion and then returning to the resting start-position. The force applied by a clinician to displace the toe was simultaneously recorded using the load cell. The quasi-stiffness over the “working range” in loading and unloading directions were determined from the slope of the torque-angular displacement graph. The test-retest reliability of the MTPJ quasi-stiffness was evaluated using intra-class correlation coefficient [ICC (2,1)]. ResultsThe reliability was almost perfect for MTPJ quasi-stiffness over the loading phase (ICC = 0.814), moderate for MTPJ quasi-stiffness over the unloading phase (ICC = 0.477) and moderate for MTPJ maximum range (ICC = 0.486). ConclusionThe foot assessment device comprising FBG and load cell was able to reliably measure the first MTPJ quasi-stiffness in a clinical setting. The measurement reliability was higher during the loading phase than the unloading phase.

Formation of prismatic dislocation loops during unloading in nanoindentation

The formation of prismatic dislocation loops during nanoindentation of bcc iron is simulated with discrete dislocation plasticity. Interestingly, it is not the loading phase, but the unloading phase of the test which is found to be crucial for prismatic loop formation when indenting a (001) crystal surface. In this case, prismatic loops do not form during loading, but develop as the indenter is removed, in contrast to (111) indentation where prismatic loops are nucleated almost immediately upon loading.

The effect of autonomous systems on the crew size of ships – a case study

ABSTRACT Recently, autonomous ships have gotten a lot more attention both in the media and in research. However, very little research has focussed on the effects of automation on the size of the crew. This paper analyses the effects of added automation on the required size and composition of the crew on a 750 TEU short sea container vessel. A Crew Analysis Algorithm is used to determine the cheapest crew composition to perform the tasks required to operate a ship. Using this algorithm, two potential automation options are investigated: automating the navigation tasks and automating the mooring tasks. Automating the navigation tasks decreases the required crew size in the normal sailing and arrival & departure phases by 3 and 1 crew members, respectively. The loading & unloading phase is unaffected. Automating the mooring tasks reduces the required crew in the arrival & departure phase to 2. It is concluded that since individual automation options do not affect the crew requirements for all travel phases, their effect on crew reduction is limited unless several options are combined. However, with a change in task assignment and different training of crew members, a reduction of the required number of crew members is possible.

Maximalist shoes do not alter performance or joint mechanical output during the countermovement jump

ABSTRACT This study examined potential differences between maximally cushioned (MAX) shoes and standard cushioned (STND) shoes during countermovement vertical jump (CMVJ) performance. Twenty-one males (23[2] y; 86.5[15.4] kg; 179.8[6.3] cm) completed eight jumps each in MAX and STND shoes while three-dimensional kinematic and kinetic data were collected. Paired-samples t-tests (α = 0.05) and Cohen’s d effect sizes (ES) were used to compare the following variables: vertical jump displacement, jump time, hip, knee and ankle joint angles at the start of the countermovement, the end of the unloading phase, the end of the eccentric phase, and at takeoff, peak joint power, and the joint contributions to total lower extremity work during the eccentric and concentric phases. The ankle was more dorsiflexed at the end of the countermovement in the MAX shoe (p = 0.002; ES = 0.55) but greater plantarflexion occurred in the STND shoes at takeoff (p = 0.028; ES = 0.56). No other differences were observed. The result of this study suggests that unique ankle joint angular positioning may be employed when wearing MAX versus STND shoes. Since the unique ankle joint positioning did not alter jump performance, potential MAX footwear users might not need to consider the potential for altered CMVJ performance when determining whether to adopt MAX footwear.

Influence of seismic strain rates on the co‐ and post‐seismic response of civil engineering buildings

SummaryThe elastic properties of buildings change during earthquakes. In particular, fundamental frequencies are observed to shift rapidly during the co‐seismic phase and to recover slowly once the strong motion has finished. Although the frequency shift is usually correlated with loading amplitude, the co‐seismic frequency variations observed in real structures are not only determined by the absolute amplitude of the strain value. In order to interpret the uncertainties of the prediction of engineering demand parameters for a given intensity measure, we analyze the influence of loading rates (i.e., strain rates) on resonance frequency variations in buildings with different structural states during the loading and unloading phases caused by seismic events. Our observations suggest the existence of a strain rate threshold that activates the nonlinear response of the structure, characterizing the activation of cracking and indicating a strong nexus between the elastic structural response, structural state, and the loading process.

Masonry subjected to semi-cyclic compression: Inelastic response modelling

A series of load tests on unreinforced masonry elements (triplets and wallettes with inclined bed joints) subjected to semi-cyclic compression have been performed in order to investigate the response of masonry under such loading conditions. The specimens exhibited inelastic and extremely nonlinear response and substantially different behaviour during the loading, unloading and reloading phases. Further investigations revealed that the observed behaviour was governed by the response of the block-mortar interfaces. A new mechanical model has been developed, which combines the conventional stress–strain model for the masonry with a non-linear model describing the response of the block-mortar interfaces. The model was calibrated using the Monte-Carlo simulation method and validated against the semi-cyclic compression tests on masonry specimens. The model developed is expected to improve significantly the simulation of the force–displacement response of unreinforced masonry walls subjected to seismic loading.

Sex differences in heel pad stiffness during in vivo loading and unloading.

Due to conflicting data from previous studies a new methodological approach to evaluate heel pad stiffness and soft tissue deformation has been developed. The purpose of this study was to compare heel pad (HP) stiffness in both limbs between males and females during a dynamic unloading and loading activity. Ten males and 10 females volunteered to perform three dynamic trials to unload and load the HP. The dynamic protocol consisted of three continuous phases: foot flat (baseline phase), bilateral heel raise (unloading phase) and foot flat (loading phase) with each phase lasting two seconds. Six retroreflective markers (3 mm) were attached to the skin of the left and right heels using a customised marker set. Three‐dimensional motion analysis cameras synchronised with force plates collected the kinematic and kinetic data throughout the trials. Three‐way repeated measures ANOVA together with a Bonferroni post hoc test were applied to the stiffness and marker displacement datasets. On average, HP stiffness was higher in males than females during the loading and unloading phases. ANOVA results revealed no significant differences for the stiffness and displacement outputs with respect to sex, sidedness or phase interactions (p > .05) in the X, Y and Z directions. Irrespective of direction, there were significant differences in stiffness between the baseline and unloading conditions (p < .001) but no significant differences between the baseline and loaded conditions (p = 1.000). Post hoc analyses for the marker displacement showed significant differences between phases for the X and Z directions (p < .032) but no significant differences in the Y direction (p > .116). Finally, females portrayed lower levels of mean HP stiffness whereas males had stiffer heels particularly in the vertical direction (Z) when the HP was both unloaded and loaded. High HP stiffness values and very small marker displacements could be valuable indicators for the risk of pathological foot conditions.

A model identification approach to quantify impact of whole-body vertical vibrations on limb compliant dynamics and walking stability

Extensive research is ongoing in the field of orthoses/exoskeleton design for efficient lower limbs assistance. However, despite wearable devices reported to improve lower limb mobility, their structural impacts on whole-body vertical dynamics have not been investigated. This study introduced a model identification approach and frequency domain analysis to quantify the impacts of orthosis-generated vibrations on limb stability and contractile dynamics. Experiments were recorded in the motion capture lab using 11 unimpaired subjects by wearing an adjustable ankle–foot orthosis (AFO). The lower limb musculoskeletal structure was identified as spring-mass (SM) and spring-mass-damper (SMD) based compliant models using the whole-body centre-of-mass acceleration data. Furthermore, Nyquist and Bode methods were implemented to quantify stabilities resulting from vertical impacts. Our results illustrated a significant decrease (p < 0.05) in lower limb contractile properties by wearing AFO compared with a normal walk. Also, stability margins quantified by wearing AFO illustrated a significant variance in terms of gain-margins (p < 0.05) for both loading and unloading phases whereas phase-margins decreased (p < 0.05) only for the respective unloading phases. The methods introduced here provide evidence that wearable orthoses significantly affect lower limb vertical dynamics and should be considered when evaluating orthosis/prosthesis/exoskeleton effectiveness.

Phase-Specific Predictors of Countermovement Jump Performance That Distinguish Good From Poor Jumpers.

Krzyszkowski, J, Chowning, LD, and Harry, JR. Phase-specific predictors of countermovement jump performance that distinguish good from poor jumpers. J Strength Cond Res 36(5): 1257-1263, 2022-The modified-reactive strength index (RSImod) is commonly examined during the countermovement vertical jump (CMJ) to assess neuromuscular characteristics (i.e., explosiveness, fatigue, adaptation, etc.) of an athlete. However, both phase-specific variables explaining RSImod and corresponding differences between good and poor jumpers are not well understood in trained populations. This study sought to (a) identify predictors of RSImod during the CMJ based on phase-specific temporal and rate of force development (RFD) variables, and (b) identify differences in those predictors between performers with high and low RSImod performances from a sample of collegiate male basketball players (n = 22; 20 ± 2 years; 1.99 ± 0.06 month; 93.8 ± 7.5 kg). Subjects performed 3 maximal effort CMJ trials while ground reaction force data was recorded using 2 force platforms. Phase-specific temporal and RFD variables were calculated and entered into separate stepwise regression models using backward elimination to identify predictors RSImod. Individuals were then categorized into high (n = 11; RSImod = 0.68 ± 0.10) and low (n = 11; RSImod = 0.48 ± 0.04) RSImod groups according to the overall median RSImod (RSImod = 0.55). Independent t-tests (α = 0.05) were conducted and supplemented by Cohen's d effect sizes (d ≥ 1.2, large) to compare groups relative to significant predictors identified by the linear regression models and related variables. The temporal regression model (R2 = 0.530) retained unloading time and concentric time, whereas the RFD regression model (R2 = 0.429) retained unloading RFD and braking RFD. The high RSImod group exhibited significantly greater RSImod scores (d = 2.51, p < 0.001) and jump heights (d = 1.58, p < 0.001), shorter times to takeoff (d = 1.27, p = 0.007) and concentric times (d = 1.51, p = 0.002), and a greater braking RFD (d = 1.41, p = 0.005) than the low RSImod group. Individuals targeting enhanced CMJ performance may consider exploring strategies or interventions to develop quicker unloading and concentric phases and increasing eccentric RFD abilities.