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Spaceflight results in marked muscle atrophy and a corresponding loss in muscle strength. Methods to evaluate spaceflight-induced changes to muscle size and strength are difficult to achieve within the tight confines of spacecrafts. Therefore, convenient methods to non-invasively monitor muscle that are predictive of actual muscle function are critical for future missions to ensure the health and safety of crew members. Evaluate the ability of non-invasive in vivo electrical impedance myography (EIM) combined with statistical models to predict muscle size and strength in rodent models of micro- and partial gravity. Male and female Fisher rats (N = 120), half gonadectomized, were divided into three different weightbearing (WB) conditions of 40 animals each, including 0%WB (0 % of weight-bearing, simulated microgravity), 40%WB (40 % of weight-bearing, simulated Martian gravity), and 100%WB (100 % of weight-bearing, full weight-bearing controls). Rats remained in designated interventions for 28 days. Afterward, rats underwent a series of musculoskeletal strength assessments and measurement of EIM. Rats were then euthanized and gastrocnemius tissues collected. Machine-learning (ML) algorithms were applied to full spectrum EIM data to predict various muscle parameters. 40%WB and 0%WB rats had lower grip strength and plantar flexion compared to 100%WB. Correspondingly, 40%WB and 0%WB also had reduced gastrocnemius mass compared to 100%WB. EIM resistance values demonstrated a dose-dependency response, with greater resistance values associated with reduced gravitational load. ML-enhanced EIM yielded strong predictions of muscle plantar flexion force and muscle mass, with root mean squared errors of 18.4 % of 22.0 %, and R2 values of 0.87 an 0.88, respectively. ML-enhanced EIM may be a helpful tool to non-invasively monitor muscle changes predictive of muscle force production and mass during exposure to reduced gravity. • Electrical impedance myography (EIM) data can be used to predict muscle mass in rats exposed to reduced loading. • EIM data can be used to predict muscle force in rats exposed to reduced loading. • These data support that EIM may find use as a predictor of muscle function in human spaceflight. [ABSTRACT FROM AUTHOR]

Rock excavation is essentially an unloading behavior, and its mechanical properties are significantly different from those under loading conditions. In response to the current deficiencies in the peak strength prediction of rocks under unloading conditions, this study proposes a hybrid learning model for the intelligent prediction of the unloading strength of rocks using simple parameters in rock unloading tests. The XGBoost technique was used to construct a model, and the PSO-XGBoost hybrid model was developed by employing particle swarm optimization (PSO) to refine the XGBoost parameters for better prediction. In order to verify the validity and accuracy of the proposed hybrid model, 134 rock sample sets containing various common rock types in rock excavation were collected from international and Chinese publications for the purpose of modeling, and the rock unloading strength prediction results were compared with those obtained by the Random Forest (RF) model, the Support Vector Machine (SVM) model, the XGBoost (XGBoost) model, and the Grid Search Method-based XGBoost (GS-XGBoost) model. Meanwhile, five statistical indicators, including the coefficient of determination (R2), mean absolute error (MAE), mean absolute percentage error (MAPE), mean square error (MSE), and root mean square error (RMSE), were calculated to check the acceptability of these models from a quantitative perspective. A review of the comparison results revealed that the proposed PSO-XGBoost hybrid model provides a better performance than the others in predicting rock unloading strength. Finally, the importance of the effect of each input feature on the generalization performance of the hybrid model was assessed. The insights garnered from this research offer a substantial reference for tunnel excavation design and other representative projects. [ABSTRACT FROM AUTHOR]

It is unknown whether activity-based physical therapy (ABPT) modalities that mobilize the paralyzed limbs improve bone integrity at the highly fracture-prone epiphyseal regions of the distal femur and proximal tibia following severe spinal cord injury (SCI). In this study, 4-mo-old skeletally mature littermate-matched male Sprague-Dawley rats received either SHAM surgery or severe contusion SCI. At 1 wk postsurgery, SCI rats were stratified to undergo no-ABPT, two 20-min bouts/day of quadrupedal bodyweight-supported treadmill training (qBWSTT), or hindlimb passive isokinetic bicycle (cycle) training, 5 days/wk for another 3 wk. We assessed locomotor recovery and plantar flexor muscle mass, tracked cancellous and cortical bone microstructure at the distal femoral and proximal tibial epiphyses using in vivo microcomputed tomography (microCT), and evaluated bone turnover at the tibial epiphysis with histomorphometry. All SCI animals displayed persistent hindlimb paralysis and pervasive muscle atrophy. Over the initial 2 wk, which included 1 wk of no exercise and 1 wk of ABPT acclimation, a similar magnitude of bone loss developed in all SCI groups. Thereafter, cancellous bone loss and cortical bone decrements increased in the SCI no-ABPT group. qBWSTT attenuated this trabecular bone loss but did not prevent the ongoing cortical bone deficits. In comparison, twice-daily cycle training increased the number and activity of osteoblasts versus other SCI groups and restored all bone microstructural parameters to SHAM levels at both epiphyseal sites. These data indicate that a novel passive isokinetic cycle training regimen reversed cancellous and cortical bone deterioration at key epiphyseal sites after experimental SCI via osteoblast-mediated bone anabolic mechanisms, independent of locomotor recovery or increased muscle mass. NEW & NOTEWORTHY: This study was the first to assess how quadrupedal bodyweight-supported treadmill training or passive isokinetic bicycle (cycle) training impacts bone recovery at the distal femoral and proximal tibial epiphyses in a rat model of severe contusion spinal cord injury. Our results demonstrate that passive isokinetic cycle training completely restored cancellous and cortical bone microstructural parameters at these sites via osteoblast-mediated bone anabolic actions, independent of locomotor recovery or increased plantar flexor muscle mass. [ABSTRACT FROM AUTHOR]

Copyright of Packaging & Food Machinery is the property of Packaging & Food Machinery Magazine and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

In order to investigate the effect of intermediate principal stress on the progressive damage and permeability characteristics of unloading sandstone, the unloading test was carried out under different intermediate principal stress conditions based on a multifunctional true triaxial fluid-solid coupling test system with gas-bearing sandstone as the research object; the exponential permeability model related to the cracked volume strain and damage variable were obtained. The results show that the crack closure stress, crack initiation stress and damage stress increase with the increase of intermediate principal stress, and the percentage of elastic section and microcrack extension stage in the pre-peak strain increases. The deformation in the direction of the intermediate principal stress is restrained in the microcrack extension stage, and the compression effect on the direction of the minimum principal stress is enhanced with the increase of the intermediate principal stress; in the macroscopic crack extension stage, the damage stress is closer to the peak stress, and the damage of the specimen is brittle in character. With the increase of the intermediate principal stress, the initial permeability reduction shows a decreasing trend and the point of elevated permeability shifts backward.

In this paper, true triaxial loading and unloading tests under different principal stress conditions were conducted to study the mechanical properties, failure characteristics, and energy evolution laws of coal bodies that are prone to ejection under different loading and unloading paths, aiming to reveal the ejection mechanism of the surrounding rock of roadway that is prone to ejection after excavation and unloading. The results are as follows. Firstly, the damage of coal samples that are prone to ejection was more severe under high stress single-sided unloading than under loading; when the axial pressure is 90% of the peak value, a large shear crack appeared on the surface of the coal samples, the axial strain rate is high, its own damage degree is large, and the ejection phenomenon was obvious; when the axial pressure was 80% and 70% of the peak value, respectively, the coal samples did not undergo overall macroscopic damage, the axial strain rate is low, and the degree of damage is small, only generated tensile cracks on the free face, and the ejection phenomenon was not obvious. Secondly, the increase of the second principal stress had a reinforcing effect on coal samples that are prone to ejection within a certain range, the internal composite cracks of coal samples that are prone to ejection first increase and then decreased, and the failure mode changed from shear failure to tension-shear composite failure, and finally developed into splitting failure; the intensity of ejection first increased and then decreased. Thirdly, in the process of high stress unloading failure, elastic energy was converted into dissipated energy and released instantly, and the proportion of elastic energy increased sharply, causing the fragments being ejected from the mother body with energy; there were obvious cross mesh cracks in the free face, and the ejection phenomenon was obvious. Fourthly, for coal samples that are prone to ejection under high stress after unloading, the tension-shear cracks rapidly expanded and connected, resulting in tension-shear composite failure, and the ejection phenomenon was obvious; Fifth, tension-shear cracks appear in ejectable coal samples of after unloading, RA increased sharply and AF decreased continuously, AE showing the characteristics of high energy, high meter, high amplitude and high frequency. The study results can provide reference for the on trol of micro impact phenomena in unloading surrounding rock during excavation of similar underground engineering.

The purpose of this study is to determine the efforts made to optimize loading and unloading equipment to facilitate loading and unloading in MV. Isa Golden. The method used in this study is qualitative descriptive. The results of the study include efforts made to optimize the maintenance of loading and unloading equipment by planning loading and unloading maintenance on a scheduled basis by following the maintenance checklist that has been determined by the ship management, evaluating at safety meetings or deck meetings to provide solutions to problems if found and provide answers or solutions to each problem, Make coordination in parts of the organization in dividing 2 (two) groups in loading and unloading equipment maintenance activities or other maintenance so that it can run well following the job description. Mualim I is obliged to compile crane spare parts to make it easier to supervise spare parts that are not available. View lists of equipment and spare parts that expire and make replacements if there is equipment that expires or is used by making and submitting a list of spare parts requests to the company

A new unloading contact model of an elastic–perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement. [ABSTRACT FROM AUTHOR]

This article describes a transport planning model which applies a simulation to support decision-making in quarry operations. The analysis of the transport system was used as input for creating the model and the subsequent research. There are five loading points in the quarry from which, according to the plan, the quarry stone is transported to the crusher, where it proceeds for further processing. The required daily capacity of the downstream technological line is 3800 t/day. Based on the analysis, it was found that it was impossible to fulfill this requirement from the two loading points which were the furthest from the unloading point. For this reason, two simulation models of the transport system were created. The first simulation model is a transport system (loading, removal and dumping of quarry stone) from one loading point. Simulation experiments were performed on this model for all loading points. The findings from the analysis confirmed the results of the simulation experiments. Subsequently, a model of the combined quarry stone removal from two loading points was proposed. The model was designed for two variants of dividing the work shift into two work sections. In the model, which had a tabular form, the combinations of loading points and values of the minimum number of unloaded cars for stone removal were suitable to ensure its necessary daily capacity. The last part of this research was expanding the original model with an additional loading point. Several experiments were performed on this model. The aim of these experiments was to verify the combinations of loading points presented in the proposed model and the combinations of unsatisfactory loading points. Based on the research results, the transport planning model and simulation models are suitable additional tools for the decision-making process in removing quarry stone. [ABSTRACT FROM AUTHOR]

To investigate whether tibiofemoral alignment influences early knee osteoarthritis (OA). We hypothesized that varus overload exacerbates early degenerative osteochondral changes, and that valgus underload diminishes early OA. Normal, over- and underload were induced by altering alignment via high tibial osteotomy in adult sheep (n = 8 each). Simultaneously, OA was induced by partial medial anterior meniscectomy. At 6 weeks postoperatively, OA was examined in five individual subregions of the medial tibial plateau using Kellgren-Lawrence grading, quantification of macroscopic OA, semiquantitative histopathological OA and immunohistochemical type-II collagen, ADAMTS-5, and MMP-13 scoring, biochemical determination of DNA and proteoglycan contents, and micro-computed tomographic evaluation of the subchondral bone. Multivariate analyses revealed that OA cartilaginous changes had a temporal priority over subchondral bone changes. Underload inhibited early cartilage degeneration in a characteristic topographic pattern (P ≥ 0.0983 vs. normal), in particular below the meniscal damage, avoided alterations of the subarticular spongiosa (P ≥ 0.162 vs. normal), and prevented the disturbance of otherwise normal osteochondral correlations. Overload induced early alterations of the subchondral bone plate microstructure towards osteopenia, including significantly decreased percent bone volume and increased bone surface–to–volume ratio (all P ≤ 0.0359 vs. normal). The data provide high-resolution evidence that tibiofemoral alignment modulates early OA induced by a medial meniscus injury in adult sheep. Since underload inhibits early OA, these data also support the clinical value of strategies to reduce the load in an affected knee compartment to possibly decelerate structural OA progression. [ABSTRACT FROM AUTHOR]

Copyright of Modern Food Science & Technology is the property of Editorial Office of Modern Food Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Coal Science & Technology (0253-2336) is the property of Coal Science & Technology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Skeletal muscle unloading occurs during a wide range of conditions, from space flight to bed rest. The unloaded muscle undergoes negative functional changes, which include increased fatigue. The mechanisms of unloading-induced fatigue are far from complete understanding and cannot be explained by muscle atrophy only. In this review, we summarize the data concerning unloading-induced fatigue in different muscles and different unloading models and provide several potential mechanisms of unloading-induced fatigue based on recent experimental data. The unloading-induced changes leading to increased fatigue include both neurobiological and intramuscular processes. The development of intramuscular fatigue seems to be mainly contributed by the transformation of soleus muscle fibers from a fatigue-resistant, "oxidative" "slow" phenotype to a "fast" "glycolytic" one. This process includes slow-to-fast fiber-type shift and mitochondrial density decline, as well as the disruption of activating signaling interconnections between slow-type myosin expression and mitochondrial biogenesis. A vast pool of relevant literature suggests that these events are triggered by the inactivation of muscle fibers in the early stages of muscle unloading, leading to the accumulation of high-energy phosphates and calcium ions in the myoplasm, as well as NO decrease. Disturbance of these secondary messengers leads to structural changes in muscles that, in turn, cause increased fatigue. [ABSTRACT FROM AUTHOR]

The construction of deep foundation pits that are adjacent to an operating subway tunnel can cause significant disturbance to the surrounding soil and tunnel structure. Assessing the stability of the soil in the security area of the tunnel is key to controlling the displacement of the tunnel structure. Assuming that the soil behind the wall is in the elastic stage of small deformation, the unloading stress distribution law of the soil on the excavation surface of the side wall is inversely calculated using the horizontal displacement curve of the retaining structure. Based on the analytical solutions for the horizontal displacement and surface settlement of the soil behind the wall proposed in this paper, the spatial distribution characteristics of the deformation transfer of the soil in the security area are obtained. Considering the interaction between the soil in the security area and the tunnel structure, by simplifying the soil in the security area to a Pasternak foundation model, the tunnel displacement that is caused by deformation transfer can be obtained. The correctness of the theoretical model is verified by comparing it with the measured data for the soil displacement behind the wall and the tunnel structure in project cases of foundation pit excavation. [ABSTRACT FROM AUTHOR]

From the standpoint of the theory of small elastoplastic deformations, the stress-strain state of the continuous medium along various unloading trajectories from the state achieved as a result of a simple active process is analyzed. It is shown that if the unloading is disproportionate, then the constitutive relations connecting the deviators of stresses and strains are tensorially nonlinear, i.e., the unit tensors of these deviators do not coincide. It is demonstrated that in the Il'yushin five-dimensional deviatoric space there exists only one full unloading point, and it belongs to the line segment of the preceding active loading. A measure of the nonproportionality of the unloading is introduced, characterizing the degree of deviation of the path of the passive deformation process from the previously mentioned line segment. This measure is calculated for two piece-linear unloadings using the example of a constant annular tube subject to the simultaneous action of -torsion and axial -shear. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Mathematics, Mechanics & Computer Science is the property of Al-Farabi Kazakh National University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Fault reactivations induced by deep excavation can pose significant challenges to underground construction or resource extraction. Laboratory experiments on rock faults demonstrate that unloading‐induced fault reactivations obey the Coulomb failure criterion derived from loading‐induced events. However, the effect of stress path during unloading on the failure criterion and rupture dynamics of fault reactivations remains poorly understood. Here, we present findings from a series of laboratory experiments aimed at elucidating the effect of the unloading path on the failure criterion and rupture dynamics of fault reactivations. We conducted experiments under various stress conditions, examining two cases of unloading paths. In Case I, we unloaded the minimum principal stress, while in Case II, the maximum principal stress was unloaded. Strain gauges and high‐speed photography were employed to capture the transient dynamic rupture process. Our investigations have yielded new insights into the effect of unloading path on the rupture dynamics when the fault is reactivated. In Case I, we observed fault reactivations resembling those loading‐induced events characterized by forward sliding. Conversely, in Case II, fault reactivations associated with stress reversal produce mild reversed sliding with lower stress drop and rupture velocity. Furthermore, we find that there is a remarkable reduction in static friction for reversed sliding, indicating that the failure criterion for fault reactivation is influenced by the stress path. We demonstrate that enhanced stress heterogeneity, caused by stress reversal, serves as a mechanism for reduced static friction. These findings contribute to our understanding of the mechanisms underlying fault reactivations, particularly those involving reversed sliding. Plain Language Summary: It is known that underground excavation, accompanied by stress release, can trigger fault reactivation, resulting in induced earthquakes. Understanding how unloading affects the activation and rupture dynamics of these induced events is crucial. To investigate the role of unloading path, we conducted laboratory experiments to simulate unloading‐induced fault reactivation on analog material containing a fault. Loadings are applied biaxially at the boundary. We observed that unloading the minimum principal stress (i.e., reducing the minimum loading) could reactivate the fault, generating forward sliding resembling loading‐induced rupture events. Conversely, unloading the maximum principal stress (i.e., reducing the maximum loading) induces reversed sliding, featuring smaller stress drop, coseismic slip, and rupture speed compared to forward sliding. Moreover, the static friction coefficient is reduced prior to reversed sliding. We also found that enhanced stress heterogeneity prior to unloading‐induced reversed sliding can account for the difference in static friction coefficient. Therefore, it is necessary to incorporate the effect of loading path into the studies of fault reactivation. Key Points: Rupture process of unloading‐induced fault reactivation is dictated by the initial stress state and stress pathThe static friction of fault is reduced for the unloading‐induced reversed slidingEnhanced stress heterogeneity caused by stress reversal contributes to reduced static friction [ABSTRACT FROM AUTHOR]

Copyright of Journal of Engineering Geology / Gongcheng Dizhi Xuebao is the property of Journal of Engineering Geology and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

With the technological advances made to expand space exploration, astronauts will spend extended amounts of time in space before returning to Earth. This situation of unloading and reloading influences human physiology, and readaptation to full weight‐bearing may significantly impact astronauts' health. On Earth, similar situations can be observed in patients who are bedridden or suffer from sport‐related injuries. However, our knowledge of male physiology far exceeds our knowledge of female's, which creates an important gap that needs to be addressed to understand the sex‐based differences regarding musculoskeletal adaptation to unloading and reloading, necessary to preserve health of both sexes. Using a ground‐based model of total unloading for 14 days and reloading at full weight‐bearing for 7 days rats, we aimed to compare the musculoskeletal adaptations between males and females. Our results reveal the existence of significant differences. Indeed, males experienced bone loss both during the unloading and the reloading period while females did not. During simulated microgravity, males and females showed comparable muscle deconditioning with a significant decline in rear paw grip strength. However, after 7 days of recovery, muscle strength improved. Additionally, sex‐based differences in myofiber size existing at baseline are significantly reduced or eliminated following unloading and recovery. [ABSTRACT FROM AUTHOR]

Bone loss in lower limbs under space microgravity condition can persist even after the astronauts return to Earth's gravitational environment. It is crucial to determine the extent and timing of bone recovery after spaceflight, especially for long-term flights. However, there is a lack of comprehensive descriptions of the recovery of various aspects of bone quality, particularly in terms of compositional characteristics that reflect changes in bone quality. Therefore, the objective of this study is to investigate the alterations in bone mineral density, composition characteristics, and mechanical properties of rat lower limbs during unloading (tail suspension) and the subsequent recovery loading period. Rats were subjected to tail suspension for four weeks (TS4) followed by reloading for an additional four weeks. Bone mineral density (BMD) was measured by μ-CT and analyzed. The mechanical properties of the tibia were assessed by a three-point bending test, and the composition characteristics of bone tissue were evaluated using Raman spectroscopy. Regression analysis was performed to identify main component related to mechanical property. In the metaphysis, BMD of the tibia significant decreased, particularly in trabecular bone. Upon reloading, only the cortical bone showed recovery. In the diaphysis, cortical bone remained unchanged during unloading but demonstrated delayed bone loss during the reloading period. Simultaneously, the mechanical properties of tibia experienced a substantial reduction after four weeks of unloading, The stiffness and maximum strength did not fully recover, though the elastic modulus and the ultimate strength were restored following the reloading process. Raman spectroscopy characterization found an increase in the carbonate substitution and crystal crystallinity of the diaphysis after 4 weeks of unloading. There was an intriguing alteration in the mineralized collagen ratio, that an increase was observed in the diaphysis while a decrease was observed in the metaphysis. During 4 weeks of reloading, the compositional characteristics of the diaphysis recovered earlier than those of the metaphysis, with the exception of crystallinity which remained unrecovered. Regression analysis indicated that carbonate replacement has a strong correlation to bone mechanical properties during the 4 weeks of unloading and subsequent 4 weeks of reloading. The data obtained in this study highlight the incomplete recovery of bone mineral density, mechanical properties, and compositional characteristics during reloading in tail-suspended rats. These findings deepen our understanding of microgravity-induced bone loss and provide valuable information to develop interventions not only for astronauts but also for persons on earth during and after prolonged periods of unloading. • Cortical and cancellous bone exhibit distinct responses to gravitational forces. • The components of load-bearing bone do not immediately recover after recovery from gravity. • The substitution of carbonate during periods of reloading is highly associated with the mechanical properties of bone. [ABSTRACT FROM AUTHOR]

Underground space creation and energy extraction, which induce unloading on rock fractures, commonly occur in various rock engineering projects, and rock engineering projects are subjected to high temperatures with increasing depth. Fluid flow behavior of rock fractures is a critical issue in many subsurface rock engineering projects. Previous studies have extensively considered permeability evolution in rock fractures under loading phase, whereas changes in fracture permeability under unloading phase have not been fully understood. To examine the unloading-induced changes in fracture permeability under different temperatures, we performed water flow-through tests on fractured rock samples subjected to decreasing confining pressures and different temperatures. The experimental results show that the permeability of fracture increases with unloading of confining pressure but decreases with loading-unloading cycles. Temperature may affect fracture permeability when it is higher than a certain threshold. An empirical model of fracture hydraulic aperture including two material parameters of initial normal stiffness and maximum normal closure can well describe the permeability changes in rough rock fracture subjected to loading-unloading cycles and heating. A coupled thermo-mechanical model considering asperity damage is finally used to understand the influences of stress paths and temperatures on fracture permeability.

Abstract With depth increase of many mines, the damage of surrounding rock by high ground stress cannot be ignored under the blasting excavation method. In view of the strong disturbance of surrounding rock caused by dynamic excavation and unloading under high initial rock stress conditions, based on the elastic unloading theory, the analytical solution of dynamic excavation and unloading stress is given using the residue theorem and Laplace inverse transform. The stress field distribution under the coupling effect of blasting load and initial rock stress is described. By making a rock model and implementing biaxial loading using a drop hammer to simulate the impact load, radial cracks generated by the impact stress wave and circumferential cracks generated by unloading during excavation were captured, and the stress change curve during excavation was monitored. The monitoring curve and theoretical curve have consistency in trend. Under the coupling effect of blasting load and initial stress, surrounding rock will generate tensile stress and broken, and the unloading effect of initial stress occurs after the blasting load, which causes tensile damage to the surrounding rock. The stress field curve plotted by the theory explains well the crack propagation caused by the coupling effect of blasting load and initial stress.

Rock excavation is essentially an unloading behavior, and its mechanical properties are significantly different from those under loading conditions. In response to the current deficiencies in the peak strength prediction of rocks under unloading conditions, this study proposes a hybrid learning model for the intelligent prediction of the unloading strength of rocks using simple parameters in rock unloading tests. The XGBoost technique was used to construct a model, and the PSO-XGBoost hybrid model was developed by employing particle swarm optimization (PSO) to refine the XGBoost parameters for better prediction. In order to verify the validity and accuracy of the proposed hybrid model, 134 rock sample sets containing various common rock types in rock excavation were collected from international and Chinese publications for the purpose of modeling, and the rock unloading strength prediction results were compared with those obtained by the Random Forest (RF) model, the Support Vector Machine (SVM) model, the XGBoost (XGBoost) model, and the Grid Search Method-based XGBoost (GS-XGBoost) model. Meanwhile, five statistical indicators, including the coefficient of determination (R2), mean absolute error (MAE), mean absolute percentage error (MAPE), mean square error (MSE), and root mean square error (RMSE), were calculated to check the acceptability of these models from a quantitative perspective. A review of the comparison results revealed that the proposed PSO-XGBoost hybrid model provides a better performance than the others in predicting rock unloading strength. Finally, the importance of the effect of each input feature on the generalization performance of the hybrid model was assessed. The insights garnered from this research offer a substantial reference for tunnel excavation design and other representative projects.

We compared neuromechanical adjustments between traditional and eccentric load reduction weighted jump squats (WJSs). On separate visits, sixteen strength‐trained men performed three sets of six consecutive WJS with 0% (traditional WJS) or 50% eccentric loading reduction with a mechanical braking unit, while concentric load was set at 30% of 1 RM in all trials. A force platform and a motion capture system were used to assess neuromechanical parameters during eccentric and concentric phases of WJS. Peak power output (+4.5 ± 4.1%; p < 0.001), maximal concentric velocity (+3.2 ± 3.6%; p = 0.004), jump height (+19.6 ± 17.4%; p < 0.001), and reactive strength index (+28.2 ± 20.0%; p < 0.001) were higher when eccentric load was reduced by 50% versus 0%. Compared with traditional jump squat, eccentric phase duration (−6.7 ± 9.9%; p = 0.014), contact time (−6.3 ± 7.2%; p = 0.004), and time to reach peak power output (−7.8 ± 7.6%; p < 0.001) were shorter, while peak vertical force (−15.2 ± 17.5%; p = 0.005) and eccentric mechanical work (−23.9 ± 6.6%; p < 0.001) were lower with eccentric load reduction. Eccentric depth (p = 0.613), eccentric velocity (p = 0.070), amortization time (p = 0.060), maximal concentric force (p = 0.727), and concentric mechanical work (p = 0.396) did not differ significantly between conditions. Compared with traditional isoinertial loading, eccentric load reduction promoted more favorable neuromechanical adjustments during landing and propulsion phases in turn maximizing WJS performance. Highlights: Eccentric load reduction weighted jump squat is a form of plyometric exercise during which a rapid, eccentrically braked downward movement is immediately followed by a maximal effort jump.In strength‐trained men, we found this approach advantageous compared with no braking for potentiating weighted jump squat performance due to more favorable eccentric‐ and concentric‐phase metrics.It is possible that smaller training volumes could be completed in each exercise session without compromising on concentric outputs. Under such circumstances, employing eccentric load reduction weighted jump squat might be a more suitable approach when attempting to execute greater workloads while minimizing fatigue. [ABSTRACT FROM AUTHOR]

High overpressure is a critical drilling issue in the Lower Kutai Basin. Typical pore pressure prediction approaches involve an empirical relationship, such as Eaton's method using sonic log data. In areas with high geothermal gradients, such as the Lower Kutai Basin, there is evidence for additional overpressure from gas generation such that sediment unloading must be considered to interpret pore pressure correctly. In this paper a repeatable deterministic model is presented for pore pressure from sonic data and, using selected wells from the Lower Kutai Basin, also the use of the resistivity log in a similar model. In the Lower Kutai Basin, sonic logs are often absent from the logging suite or otherwise running over limited intervals, making an alternative log-based prediction method particularly valuable. As a caveat, shallow freshwater encroachment is reported in the Lower Kutai Basin, means the shallow resistivity data can be problematic to use to define both top of overpressure and a normal compaction trend. Care must therefore be taken if resistivity is to be used for the interpretation of unloaded pore pressure, and chiefly applied and this likely to be more successful where encroachment is less pronounced, such as pro-delta shales. Assuming the additional care needed in using resistivity data, this paper suggests that resistivity can be a useful tool for pore pressure prediction in unloaded shale at elevated temperatures within the Lower Kutai Basin. At present the technique has been applied to only a limited dataset due to data availability limitations, but it is hoped with further refinement it will form a helpful additional approach in the pore pressure prediction toolkit. [ABSTRACT FROM AUTHOR]

It is well known that the bone loss which may lead to bone fracture risk occurs under microgravity and disuse. Besides bone mineral density (BMD), the role of collagen as the main component of bone in the mechanism has unknown. In addition, myofascia, which is also mainly composed of collagen, plays an important role in the force transmission in musculoskeletal system. In this study, the collagen alternations of hindlimb tibia and myofascia in tail-suspension rats, which hindlimb unloading as a model to simulate microgravity and/or disuse, were investigated and further the correlations with the mechanical properties were analyzed. The collagen fiber orientations were observed by second-harmonic generation (SHG) microscopy and quantitatively analyzed in MATLAB. Bone mechanical properties were measured by three-point-bending test and nanoindentation. Myofascial mechanical properties were explored by tensile test. The results showed: 1) the collagen fibers orientation both in bone and myofascia were dispersed, as standard deviation of collagen fiber orientation increased.2) the mechanical properties of tibia were decreased by unloading both at macro level (maximum load, breaking load and stiffness, etc.) and micro level (hardness). In myofascia, the yield strain and ultimate strain were significantly decreased. 3) correlation analysis showed bone collagen orientation was related to bone hardness/elastic modulus, and myofascial collagen orientation was related to myofascial elastic modulus and yield limit. Additionally, myofascial mechanical properties were related to bone mechanical properties. These suggested disordered collagen orientation may be related to the deterioration of mechanical properties in both bone and myofascia under simulated microgravity. The alternation of myofascial mechanical property may have a certain impact on the deterioration of bone mechanical properties through affecting the force transmission from muscle to bone. • The collagen fibers orientation both in bone and myofascia were dispersed under microgravity • The bone collagen orientation was related to bone hardness and elastic modulus • The myofascial collagen orientation was related to myofascial elastic modulus and yield limit • The myofascial mechanical properties were related to bone mechanical properties • The alternation of myofascial mechanical property may have a certain impact on the deterioration of bone mechanical properties through affecting the force transmission from muscle to bone [ABSTRACT FROM AUTHOR]

Raw materials are usually stored in the form of particles in silos, such as the food, chemical, and pharmaceutical field. The motion of granular materials can vary greatly in the flow of gases and liquids, due to their discrete particle aggregates. It is difficult to accurately explain using traditional theories, such as solid or fluid mechanics, and condensed matter physics. Particularly, the silo can serve as one of the most important carriers to store the particulate matter. It is still lacking in a comprehensive unified theory for the silo subjected to complex forces. Among them, the irregularity of rice seeds has a significant impact on the unloading in the silo, due to the nature of loose particles. Therefore, it is of great significance to clarify the impact of rice seed discharge flow in the silo. Auxiliary devices can also be added to transform the central into the overall flow bin. Simple and effective fluid modification can be used to adjust the structure of silos for the better particle flow. This study aims to explore the impact mechanism of different fluid modifications on the flow of rice seed particles during discharge in the silo. The transformation of the population flow pattern was achieved from the central to the overall flow for better population flow. The discrete element method (DEM) was selected to construct the traditional silo, vertical disturbance, and horizontal disturbance silo models. Rice seed particle models were established for the discharge simulation. The flow pattern was compared with the actual discharge experiment in the silo. A series of experiments was also conducted to verify the accuracy of the discrete element model and numerical simulation. The mass flow index (MFI) and z-axis particle velocity indicated that the particle velocity in the central region of traditional and vertically disturbed silos decreased with the increase of particle stacking height, whereas, the particle velocity increased in the sidewall region. There was a decrease in the particle velocity in the sidewall area of the horizontally disturbed silo, as the particle stacking height increased, whereas, the particle velocity increased in the central area. Traditionally, the conversion heights of the flow pattern were 130, 118, and 130 mm, respectively, in the vertically and horizontally disturbed silos. There was a variation in the vertical, horizontal, and angular velocity in the different areas of the silo. Specifically, the vertical velocity of the population decreased by 34.82% and 83.46%, respectively, compared with the traditional flow area of the silo under the action of the vertical and horizontal fluid. The fluctuation of population horizontal velocity increased, as the height of particle accumulation decreased in the silo population. The standard deviations of particle horizontal velocity were 0.027 3, 0.018 7, and 0.010 3, respectively, in the traditional silos, vertical and horizontal disturbance silos. There were similar changes in the particle angular velocity in the center and sidewall areas of traditional and vertical disturbance silos. The peak angular velocity was smaller in the center area of vertical disturbance silos, compared with the traditional silos. The variation of particle angular velocity was similar to the traditional silo in the flow area of a horizontal disturbance. But there was a small variation of particle angular velocity in a horizontal disturbance silo. The finding can provide the theoretical reference for the fluid design standards, structural and positional parameters, particularly for the high available area of the silo. [ABSTRACT FROM AUTHOR]

Background contextFor chronic low back pain, the causal mechanisms between pathological features from imaging and patient symptoms are unclear. For instance, disc herniations can often be present without symptoms. There remains a need for improved knowledge of the pathophysiological mechanisms that explore spinal tissue damage and clinical manifestations of pain and disability. Spaceflight and astronaut health provides a rare opportunity to study potential low back pain mechanisms longitudinally. Spaceflight disrupts diurnal loading on the spine and several lines of evidence indicate that astronauts are at a heightened risk for low back pain and disc herniation following spaceflight.PurposeTo examine the relationship between prolonged exposure to microgravity and the elevated incidence of postflight disc herniation, we conducted a longitudinal study to track the spinal health of twelve NASA astronauts before and after approximately 6 months in space. We hypothesize that the incidence of postflight disc herniation and low back complaints associates with spaceflight-included muscle atrophy and pre-existing spinal pathology.Study designThis is a prospective longitudinal study.Patient sampleOur sample included a cohort of twelve astronaut crewmembers.Outcome measuresFrom 3T MRI, we quantified disc water content (ms), disc degeneration (Pfirrmann grade), vertebral endplate irregularities, facet arthropathy and/ fluid, high intensity zones, disc herniation, multifidus total cross-sectional area (cm2), multifidus lean muscle cross-sectional area (cm2), and muscle quality/composition (%). From quantitative fluoroscopy we quantified, maximum flexion-extension ROM (°), maximum lateral bending ROM (°), and maximum translation (%). Lastly, patient outcomes and clinical notes were used for identifying postflight symptoms associated with disc herniations from 3T MRI.MethodsAdvanced imaging data from 3T MRI were collected at three separate time points in relation to spending six months in space: (1) within a year before launch ("pre-flight"), (2) within a week after return to Earth ("post-flight"), and (3) between 1 and 2 months after return to Earth ("recovery"). Fluoroscopy of segmental kinematics was collected at preflight and postflight timepoints. We assessed the effect of spaceflight and postflight recovery on longitudinal changes in spinal structure and function, as well as differences between crew members who did and did not present a symptomatic disc herniation following spaceflight.ResultsHalf of our astronauts (n=6) experienced new symptoms associated with a new or previously asymptomatic lumbar disc protrusion or extrusion following spaceflight. We observed decreased multifidus muscle quality following spaceflight in the lower lumbar spine, with a reduced percentage of lean muscle at L4L5 (-6.2%, p=.009) and L5S1 (-7.0%, p=.006) associated with the incidence of new disc herniation. Additionally, we observed reduced lumbar segment flexion-extension ROM for L2L3 (-17.2%, p=.006) and L3L4 (-20.5%, p=.02) following spaceflight, and furthermore that reduced ROM among the upper three lumbar segments (-24.1%, p=.01) associated with the incidence of disc herniation. Existing endplate pathology was most prevalent in the upper lumbar spine and associated with reduced segmental ROM (-20.5%, p=.02).ConclusionsIn conclusion from a 10-year study investigating the effects of spaceflight on the lumbar spine and risk for disc herniation, we found the incidence of lumbar disc herniation following spaceflight associates with compromised multifidus muscle quality and spinal segment kinematics, as well as pre-existing spinal endplate irregularities. These findings suggest differential effects of spinal stiffness and muscle loss in the upper versus lower lumbar spine regions that may specifically provoke risk for symptomatic disc herniation in the lower lumbar spine following spaceflight. Results from this study provide a unique longitudinal assessment of mechanisms and possible risk factors for developing disc herniations and related low back pain. Furthermore, these findings will help inform physiologic countermeasures to maintain spinal health in astronauts during long-duration missions in space.

The intermediate principal stress and unloading have an important influence on the shear failure characteristics of rock. Based on the multifunctional true triaxial fluid-structure interaction test system, the loading and unloading failure tests of sandstone under different intermediate principal stress conditions were carried out. The deformation characteristics and strength characteristics were analyzed, and the influence of the two on the angle of shear deformation zone was studied by establishing the constitutive relationship and the shear deformation zone angle prediction model. The test results show that with the increase of intermediate principal stress, the deflected shear stress at the peak of the rock sample increases, and the increase under unloading conditions is small. The maximum compression point of the rock sample shows a trend of increasing first and then stabilizing, and after reaching the maximum compression point, the volume strain of the rock sample gradually changes from expansion to compression under loading conditions, while the expansion trend occurs under unloading conditions. With the increase of intermediate principal stress, the deflection shear strain of the rock sample increases sharply, and the steep increase under unloading conditions occurs early. At the peak, the stress and strain Lode angles under the unloading condition are larger than those under the loading condition, and the difference between the two types of Lode angles under the two conditions increases with the increase of the intermediate principal stress. The intermediate principal stress and unloading can reflect the yield characteristics of the rock through the stress Lode angle, and reflect the internal fracture evolution direction of the rock through the strain Lode angle. The equivalent plastic strain was used to characterize the internal friction angle and dilatancy angle, and to establish a hardening intrinsic relationship consisting of three stress invariants. Comparing the experimental values, it was found that the model predicted well. With the increase of the intermediate principal stress, the angle of the deformation zone first decreases and then stabilizes. The unloading effect will reduce the angle of the deformation zone, and the angle decrease level is reduced under the influence of the intermediate principal stress.

Dynamic unloading is instantaneous, and the transient unloading effect has important influence on deep rock blasting excavation. In order to study the deformation law and failure mechanism of surrounding rock under dynamic excavation with unloading condition. And tunderstand further dynamic characteristics and the dynamic effects of transient unloading in rock mass excavation. There used a self-developed simulation test device for simulating the process of dynamic excavation in confining pressure loading. The experimental model was made similar material, and used the test device to impact it. It focus on monitoring the unloading effect in real time with the help of strain gauge, high-speed camera and fiber grating sensor. These devices that monitored effective strain-time curves, crack propagation image and the tensile state or compressive state of rock mass after excavation. The test results show that surrounding rock stress of model have experienced five stages that were called initial stress stage, dynamic loading stage, dynamic unloading stage, initial stress unloading stage and creep stage respectively. After model was impacted, each monitoring point occured different strain variation, and some occured compressive strrain, others occured tensile strain. The whole model in compressived state. The model showed creep phenonmen after excavation. Through observing crack propagation image, crack propagation process shown clearly. Firstly, radial cracks were rapidly generated during dynamic excavation. Then, with the free face increase constantly, the stored energy of surrounding rock of model was rapidly released toward the free face, resulting in annular crack occured. Annular crack belongs to tensile faiure, which was generated in vertical radial crack direction and propagated along the adjacent radial crack. Finally, annular crack was parallelled with the free face. The simulation test device system monitored the unloading effect of rock-like marterial well in whole time. Unloading strain value varied with distance, the rock mass model can be divided into near unloading area, middle unloading area and far unloading area after excavation.

This article describes a transport planning model which applies a simulation to support decision-making in quarry operations. The analysis of the transport system was used as input for creating the model and the subsequent research. There are five loading points in the quarry from which, according to the plan, the quarry stone is transported to the crusher, where it proceeds for further processing. The required daily capacity of the downstream technological line is 3800 t/day. Based on the analysis, it was found that it was impossible to fulfill this requirement from the two loading points which were the furthest from the unloading point. For this reason, two simulation models of the transport system were created. The first simulation model is a transport system (loading, removal and dumping of quarry stone) from one loading point. Simulation experiments were performed on this model for all loading points. The findings from the analysis confirmed the results of the simulation experiments. Subsequently, a model of the combined quarry stone removal from two loading points was proposed. The model was designed for two variants of dividing the work shift into two work sections. In the model, which had a tabular form, the combinations of loading points and values of the minimum number of unloaded cars for stone removal were suitable to ensure its necessary daily capacity. The last part of this research was expanding the original model with an additional loading point. Several experiments were performed on this model. The aim of these experiments was to verify the combinations of loading points presented in the proposed model and the combinations of unsatisfactory loading points. Based on the research results, the transport planning model and simulation models are suitable additional tools for the decision-making process in removing quarry stone.

A new unloading contact model of an elastic–perfectly plastic half-space indented by an elastic spherical indenter is presented analytically. The recovered deformation of the elastic indenter and the indented half-space has been found to be dependent on the elastic modulus ratio after fully unloading. The recovered deformation of the indented half-space can be calculated based on the deformation of the purely elastic indenter. The unloading process is assumed to be entirely elastic, and then the relationship of contact force and indentation can be determined based on the solved recovered deformation and conforms to Hertzian-type. The model can accurately predict the residual indentation and residual curvature radius after fully unloading. Numerical simulations are performed to demonstrate the assumptions and the unloading model. The proposed unloading model can cover a wide range of indentations and material properties and is compared with existing unloading models. The cyclic behavior including loading and unloading can be predicted by combining the proposed unloading law with the existing contact loading model. The combined model can be employed for low-velocity impact and nanoindentation tests and the comparison results are in good agreement.

Skeletal muscle unloading occurs during a wide range of conditions, from space flight to bed rest. The unloaded muscle undergoes negative functional changes, which include increased fatigue. The mechanisms of unloading-induced fatigue are far from complete understanding and cannot be explained by muscle atrophy only. In this review, we summarize the data concerning unloading-induced fatigue in different muscles and different unloading models and provide several potential mechanisms of unloading-induced fatigue based on recent experimental data. The unloading-induced changes leading to increased fatigue include both neurobiological and intramuscular processes. The development of intramuscular fatigue seems to be mainly contributed by the transformation of soleus muscle fibers from a fatigue-resistant, “oxidative“ “slow” phenotype to a “fast” “glycolytic“ one. This process includes slow-to-fast fiber-type shift and mitochondrial density decline, as well as the disruption of activating signaling interconnections between slow-type myosin expression and mitochondrial biogenesis. A vast pool of relevant literature suggests that these events are triggered by the inactivation of muscle fibers in the early stages of muscle unloading, leading to the accumulation of high-energy phosphates and calcium ions in the myoplasm, as well as NO decrease. Disturbance of these secondary messengers leads to structural changes in muscles that, in turn, cause increased fatigue.

One of the early changes upon tuber induction is the switch from apoplastic to symplastic unloading. Whether and how this change in unloading mode contributes to sink strength has remained unclear. In addition, developing tubers also change from energy to storage-based sucrose metabolism. Here, we investigated the coordination between changes in unloading mode and sucrose metabolism and their relative role in tuber sink strength by looking into callose and sucrose metabolism gene expression combined with a model of apoplastic and symplastic unloading. Gene expression analysis suggests that callose deposition in tubers is decreased by lower callose synthase expression. Furthermore, changes in callose and sucrose metabolism are strongly correlated, indicating a well-coordinated developmental switch. Modelling indicates that symplastic unloading is not the most efficient unloading mode per se. Instead, it is the concurrent metabolic switch that provides the physiological conditions necessary to potentiate symplastic transport and thereby enhance tuber sink strength .

With the increasing depletion of shallow-earth mineral resources, deep mining will become the primary route of future mineral resources development. However, deep mining technology is a long way from being mature, and there are still a great number of issues that severely limit the growth of resources. In this paper, the acoustic emission (AE) tests of triaxially loaded and unloaded deep diorite are conducted. The results show that when confining pressure is at a low level, the failure mode of rock sample is mainly tension fracture; however as confining pressure increases, the failure mode gradually changes to shear failure. Under different stress paths, AE counting characteristics can be separated into four stages, including initial low-energy zone, pre-peak quiet zone, peak sudden burst zone and post-peak failure intensive zone (post-peak fast attenuation zone or post-peak high density zone). The damage variable is defined as the ratio of the AE count rate of a certain stage to the cumulative AE count rate of the failure process, and it accounts for the largest proportion at the stage of unloading confining pressure. In addition, when confining pressure increases, the damage variable changes from a flat growth to a rapid growth, with the abrupt transition occurring around the peak stress. [ABSTRACT FROM AUTHOR]

Impressively increasing availability of mechanical circulatory/cardiac support systems (MCSs) worldwide, together with the deepening of the knowledge of critical care medical practitioners, has inevitably led to the discussion about further improvements of intensive care associated to MCS. An appealing topic of the left ventricle (LV) overload related to VA ECMO support endangering myocardial recovery is being widely discussed within the scientific community. Unloading of LV leads to the reduction in LV end-diastolic pressure, reduction in pressure in the left atrium, and decrease in the LV thrombus formation risk. Consequently, better conditions for myocardial recovery, with comfortable filling pressures and a better oxygen delivery/demand ratio, are achieved. The combination of VA ECMO and Impella device, also called ECPELLA, seems to be a promising strategy that may bring the improvement of CS mortality rates. The series of presented trials and meta-analyses clearly showed the potential benefits of this strategy. However, the ongoing research has brought a series of new questions, such as whether Impella itself is the only appropriate unloading modality, or any other approach to unload LV would be beneficial in the same way. Benefits and potential risks of LV unloading and its timing are being discussed in this current review. [ABSTRACT FROM AUTHOR]

Coal bump seriously threatens the safe and efficient mining of coal, and the research on the occurrence mechanism of coal bump is of great significance. The roadway coal bump accounts for 86.8% of the total. The occurrence of coal bump in gateroad is summarized. It is considered that hard roof and hard coal are the geological characteristics of coal bump, and the sliding instability of rib coal mass is the failure characteristics of coal bump. Based on the elastic foundation theory, the upward deflection characteristics of the front and lateral roof of the working face under the condition of hard roof are analyzed, and compared with the engineering practice of roof rebounding. Taking the roadway coal mass as the research object, the unloading sliding mechanical model of roof-coal-floor composite structure is established. By analyzing the relationship between horizontal ground stress of coal mass, frictional force of coal-roof and coal-floor and tensile resistance of coal mass, the critical equation of coal bump is established. It is proposed that the vertical pressure of coal seam is reduced due to the upward deflection of the roof, and the coal mass loses its clamping and moves into the roadway after overcoming the friction between roof and floor and the tensile strength of coal mass under the action of horizontal ground stress, that is, the unloading and slippage mechanism of coal bump in hard roof mining roadway. The model reasonably explains the causality of coal bump in hard roof mining roadway. Based on the unloading-slippage model, the principle of influencing factors of coal bump, includes the buried depth, roof strength, roof elastic modulus and roof thickness, coal mass strength and elastic modulus. Finally, two coal bump events, "8.2" coal bump in Tangshan coal mine and "11.11" coal bump in Hongyang mine are analyzed and the unloading-slippage mechanism are the reasoning of two events. [ABSTRACT FROM AUTHOR]

Considering the stress paths of kilometer-deep granite during mining， the triaxial loading and unloading experiments are performed on granite under three stress paths: ascending axial pressure and fixed confining pressure， ascending axial pressure and unloading confining pressure， and fixed axial pressure and unloading confining pressure. The aim is to obtain the deformation and failure characteristics and energy evolution law of rock under mining and unloading conditions. The research results show that under the high confining pressure levels， rock stores more energy before reaching peak failure， and the deformation energy released during failure has a more significant impact on the rock structure， leading to brittle failure of the rock sample. The unloading effect weakens the radial restraint of the confining pressure on the rock sample， causing an increase in radial expansion， and failure occurs at a lower stress level. Furthermore， the rock deformation modulus and generalized Poisson’s ratio reach the extreme point faster， determined by the expansion point， the turning point at which the proportion of elastic energy of the rock sample changes from increasing to decreasing. Compared with the ascending axial pressure and fixed confining pressure test， the ratio of elastic energy to dissipated energy is higher under the unloading conditions， resulting in more severe in rock damage. [ABSTRACT FROM AUTHOR]

To investigate the influence of unloading effect of a circular tunnel face on rockburst process, by innovatively combining rock drilling unloading devices and triaxial systems, the strain rockburst simulation under the entire stress path of “high initial stress + internal unloading + stress adjustment” (HUS test) was realized for the intact cubic red sandstone samples (100 mm × 100 mm × 100 mm). Comparative tests were conducted on cubic red sandstone samples with prefabricated circular holes (φ 25 mm) under the stress path of “prefabricated circular hole + high initial stress + stress adjustment” (PHS test), thereby highlighting the influence of internal unloading on rockburst failure. The test results revealed that with an increase in vertical stress, the sidewalls in both the HUS and PHS tests suffered strain rockburst failure. Compared with the PHS test, the initial failure stress in the HUS test is lower, and it is easier to induce sidewall rockbursts. This indicates that the internal unloading influences the sidewall failure, causing an obvious strength-weakening effect, which becomes more significant with an increase in buried depth. The strain rockburst failure was more severe in the HUS test owing to the influence of internal unloading. V-shaped rockburst pits were formed in the HUS tests, whereas in the PHS test, arc-shaped rockburst pits were produced. It was also found that strain rockburst failure may occur only when the rock has a certain degree of rockburst proneness.

Abstract We aimed to quantify declines from baseline in lower limb skeletal muscle size and strength of uninjured adults following single‐leg disuse. We searched EMBASE, Medline, CINAHL, and CCRCT up to 30 January 2022. Studies were included in the systematic review if they (1) recruited uninjured participants; (2) were an original experimental study; (3) employed a single‐leg disuse model; and (4) reported muscle strength, size, or power data following a period of single‐leg disuse for at least one group without a countermeasure. Studies were excluded if they (1) did not meet all inclusion criteria; (2) were not in English; (3) reported previously published muscle strength, size, or power data; or (4) could not be sourced from two different libraries, repeated online searches, and the authors. We used the Cochrane Risk of Bias Assessment Tool to assess risk of bias. We then performed random‐effects meta‐analyses on studies reporting measures of leg extension strength and extensor size. Our search revealed 6548 studies, and 86 were included in our systematic review. Data from 35 and 20 studies were then included in the meta‐analyses for measures of leg extensor strength and size, respectively (40 different studies). No meta‐analysis for muscle power was performed due to insufficient homogenous data. Effect sizes (Hedges' gav) with 95% confidence intervals for leg extensor strength were all durations = −0.80 [−0.92, −0.68] (n = 429 participants; n = 68 aged 40 years or older; n ≥ 78 females); ≤7 days of disuse = −0.57 [−0.75, −0.40] (n = 151); >7 days and ≤14 days = −0.93 [−1.12, −0.74] (n = 206); and >14 days = −0.95 [−1.20, −0.70] (n = 72). Effect sizes for measures of leg extensor size were all durations = −0.41 [−0.51, −0.31] (n = 233; n = 32 aged 40 years or older; n ≥ 42 females); ≤7 days = −0.26 [−0.36, −0.16] (n = 84); >7 days and ≤14 days = −0.49 [−0.67, −0.30] (n = 102); and >14 days = −0.52 [−0.74, −0.30] (n = 47). Decreases in leg extensor strength (cast: −0.94 [−1.30, −0.59] (n = 73); brace: −0.90 [−1.18, −0.63] (n = 106)) and size (cast: −0.61[−0.87, −0.35] (n = 41); brace: (−0.48 [−1.04, 0.07] (n = 41)) following 14 days of disuse did not differ for cast and brace disuse models. Single‐leg disuse in adults resulted in a decline in leg extensor strength and size that reached a nadir beyond 14 days. Bracing and casting led to similar declines in leg extensor strength and size following 14 days of disuse. Studies including females and males and adults over 40 years of age are lacking.

To study the fracture propagation and meso damage evolution law of saturated sandstone under unloading (unloading confining pressure), three unloading confining pressure tests of sandstone under different initial axial pressures were designed. By means of nuclear magnetic resonance (NMR) technology, the variation characteristics of rock porosity and T2 spectrum curves were analyzed, the relationship between damage degree and unloading confining pressure ratio was established, and the fractal characteristics of NMR were analyzed. The results show that: (1) The larger the initial axial compression, the larger the axial strain and the smaller the radial strain when unloading failure occurs. With the increase of unloading confining pressure ratio, the elastic modulus decreases, and the Poisson's ratio and strain increase. (2) T2 spectrum peak shows that the pore size increases with the increase of unloading confining pressure ratio. The larger the initial axial compression, the larger the pore size. (3) Porosity increases exponentially with the increase of unloading confining pressure ratio, in which the number of micropores continues to increase, the number of mesopores and macropores first decreases and then increases. The initial axial pressure promotes the development and expansion of pores. (4) The relationship between pore characteristics, energy and damage degree is generally consistent, and the fractal characteristics of three sizes of pores show different changing rules with the increase of unloading confining pressure ratio. Highlights: With the increase of unloading confining pressure ratio, the rock gradually changes from elastic deformation to plastic deformation. The failure of the sample is caused by the sharp increase of the number and size of pores. Porosity increases exponentially with the increase of unloading confining pressure ratio. With the increase of unloading confining pressure ratio, the number of micropores continues to increase, and the number of mesopores and macropores first decreases and then increases. [ABSTRACT FROM AUTHOR]

Background and Objectives: Sex-specific outcome in patients with acute myocardial infarction-related cardiogenic shock (AMI-CS) receiving temporary mechanical circulatory support remains controversial. Materials and Methods: Patients with AMI-CS who received Impella support were prospectively enrolled in the Japanese registry for Percutaneous Ventricular Assist Device. Patients enrolled between January 2021 and December 2022 were considered to be eligible. Patients with out-of-hospital cardiac arrest and those without revascularization were excluded. The sex disparity in the 30-day survival after the initiation of Impella support was evaluated. Results: A total of 924 patients (median age 73 years; 21% female) were included. Female patients were older and had a smaller physiques than male patients (p < 0.05 for both). Female sex was significantly associated with a higher 30-day mortality after adjustment for four other potential confounders with a hazard ratio of 1.365 (95% confidence interval 1.026–1.816, p = 0.0324). In the female cohort, patients who received Impella prior to revascularization (N = 138) had a greater survival rate compared to those who received Impella after revascularization (68.1% versus 44.8%, p = 0.0015). Conclusions: Among the patients with AMI-CS who received Impella support and underwent revascularization, female sex was independently associated with a lower 30-day survival. For female patients, early initiation of Impella support prior to revascularization may improve their clinical outcomes. [ABSTRACT FROM AUTHOR]

Introduction: This study investigated kinematic and EMG changes in gait across simulated gravitational unloading levels between 100% and 20% of normal body weight. This study sought to identify if each level of unloading elicited consistent changes—particular to that percentage of normal body weight—or if the changes seen with unloading could be influenced by the previous level(s) of unloading. Methods: 15 healthy adult participants (26.3 ± 2.5 years; 53% female) walked in an Alter-G anti-gravity treadmill unloading system (mean speed: 1.49 ± 0.37 mph) for 1 min each at 100%, 80%, 60%, 40% and 20% of normal body weight, before loading back to 100% in reverse order. Lower-body kinematic data were captured by inertial measurement units, and EMG data were collected from the rectus femoris, biceps femoris, medial gastrocnemius, and anterior tibialis. Data were compared across like levels of load using repeated measures ANOVA and statistical parametric mapping. Difference waveforms for adjacent levels were created to examine the rate of change between different unloading levels. Results: This study found hip, knee, and ankle kinematics as well as activity in the rectus femoris, and medial gastrocnemius were significantly different at the same level of unloading, having arrived from a higher, or lower level of unloading. There were no significant changes in the kinematic difference waveforms, however the waveform representing the change in EMG between 100% and 80% load was significantly different from all other levels. Discussion: This study found that body weight unloading from 100% to 20% elicited distinct responses in the medial gastrocnemius, as well as partly in the rectus femoris. Hip, knee, and ankle kinematics were also affected differentially by loading and unloading, especially at 40% of normal body weight. These findings suggest the previous level of gravitational load is an important factor to consider in determining kinematic and EMG responses to the current level during loading and unloading below standard g. Similarly, the rate of change in kinematics from 100% to 20% appears to be linear, while the rate of change in EMG was non-linear. This is of particular interest, as it suggests that kinematic and EMG measures decouple with unloading and may react to unloading uniquely. [ABSTRACT FROM AUTHOR]

Spinal cord injury (SCI) causes severe and resistant sublesional disuse bone loss. Abaloparatide, a modified parathyroid hormone related peptide, is an FDA approved drug for treatment of severe osteoporosis with potent anabolic activity. The effects of abaloparatide on SCI‐induced bone loss remain undefined. Thus, female mice underwent sham or severe contusion thoracic SCI causing hindlimb paralysis. Mice then received subcutaneous injection of vehicle or 20 μg/kg/day abaloparatide for 35 days. Micro‐computed tomography (micro‐CT) analysis of the distal and midshaft femoral regions of the SCI‐vehicle mice revealed reduced trabecular fractional bone volume (56%), thickness (75%), and cortical thickness (80%) compared to sham‐vehicle controls. Treatment with abaloparatide did not prevent SCI‐induced changes in trabecular or cortical bone. However, histomorphometry evaluation of the SCI‐abaloparatide mice demonstrated that abaloparatide treatment increased osteoblast (241%) and osteoclast (247%) numbers and the mineral apposition rate (131%) compared to SCI‐vehicle animals. In another independent experiment, treatment with 80 μg/kg/day abaloparatide significantly attenuated SCI‐induced loss in cortical bone thickness (93%) when compared to SCI‐vehicle mice (79%) but did not prevent SCI‐induced trabecular bone loss or elevation in cortical porosity. Biochemical analysis of the bone marrow supernatants of the femurs showed that SCI‐abaloparatide animals had 2.3‐fold increase in procollagen type I N‐terminal propeptide, a bone formation marker than SCI‐vehicle animals. SCI groups had 70% higher levels of cross‐linked C‐telopeptide of type I collagen, a bone resorption marker, than sham‐vehicle mice. These findings suggest that abaloparatide protects the cortical bone against the deleterious effects of SCI by promoting bone formation. [ABSTRACT FROM AUTHOR]