Suddenly Released Research Articles

Research on the Characteristics of Coal Bump and Monitoring and Early Warning in Hujiahe Coal Mine

Under the high intensity mining disturbance, coal bump is easily triggered by the sudden release of large amount of elastic energy contained in the coal body, which seriously affects coal mine safety production. Triaxial experiments were used to study the damage characteristics of coal samples subjected to loading at the 401103 working face of Hujiahe coal mine, and the critical value of peak strength of coal samples was investigated. Based on the characteristics of the mechanical damage behavior of coal samples obtained from the triaxial experiment, the statistics of the occurrence of coal bump events at the 401103 working face were conducted through numerical simulation and field monitoring to study the areas that need to be focused on prevention and control, with a view to providing basic research for deep coal mining. The results show the following: (1) the strength of coal samples is “weakened” by stress loading, and the fracture penetrates the coal body interface leading to the formation of tensile-shear damage of coal samples. The value of the damage variable for the coal sample in the initial damage stage is 0; at the damage stabilization stage, the values of damage variables were derived to be located at 0.03~0.14. The bearing capacity of the coal sample decreases rapidly during the accelerated development period. (2) According to the simulation and field monitoring, it is known that 0~100 m in front of the coal mining face belongs to the key monitoring area. (3) With the advancement of the working face, different coal pillar widths have obvious effects on the vertical stress, and stress increase and decrease zones appear on both sides of the coal column, and the peak stress shows the characteristics of increasing first and then decreasing with the advancement of the working face. The width of the working face has a great influence on the change of vertical stress. When the sensitivity of the vertical stress to the width of the working face increases, the stress concentration phenomenon will occur, and a large amount of elastic energy gathered in the coal body is suddenly released to induce coal bump.

Numerical study on the mechanism of spontaneous ignition of high-pressure hydrogen during its sudden release into a tube

Hydrogen is regarded as the promising energy carrier in the 21st century and high-pressure storage is selected as the best option. However, spontaneous ignition would be induced if high-pressure hydrogen is suddenly released. Three cases were numerically conducted to gain an insight into the mechanism of the spontaneous ignition and to validate against our previous experimental results. Result show that a hemispherical shock wave is first produced. Then it is reflected as reflected shock wave after hitting the tube wall and interacts with other reflected shock waves to form the Mach disk, shock triple point and a barrel shock. The height of the Mach disk gradually decreases and finally it disappears. Meanwhile, the shape of hydrogen jet changes from a forward convex shape to a backward concave shape and hydrogen/air mixture layer is formed near the tube wall and the center of the tube. The temperature of the shock-affected region gradually increases and its area thickens. After maintenance of high temperature for a period of time, spontaneous ignition firstly occurs at the tube boundary. Present numerical results not only reproduce the ignition conditions but also the ignition positions indicating that the model is an effective tool for hydrogen safety engineering.

Abdominal draw-in maneuver changes neuromuscular responses to sudden release from trunk loading in patients with non-specific chronic low back pain

BackgroundAbdominal draw-in maneuver (ADIM) has been recommended to achieve appropriate trunk muscle response for patients with non-specific chronic low back pain (CLBP). However, it has remained unclear whether the intervention with ADIM could change the trunk muscle response to sudden release from loading, which is considered to contribute mechanical circumstances to low back pain. The purpose of the present study was to investigate the effects of the intervention with ADIM on electromyography (EMG) activities of trunk muscles following sudden release from loading. MethodsSeventeen subjects with non-specific CLBP participated. Subjects resisted trunk flexion or extension loading in semi-seated position, and then the loading was suddenly released. EMG recordings of 6 trunk muscles were acquired using a wireless surface EMG system. Onset and offset times were calculated from the EMG data. The intervention with ADIM was provided for 4 weeks. The onset and offset times were compared between pre- and post-intervention with ADIM. ResultsAt the post-intervention, the onset of trunk flexors following release from trunk flexion loading became significantly earlier than pre-intervention (P = 0.028). The offset of flexors following release from trunk extension loading of post-intervention was significantly earlier than that of pre-intervention (P = 0.001). ConclusionsWe showed that the intervention with ADIM changed the EMG activity of trunk flexors in response to sudden release from loading. These results suggest a possibility that ADIM might be effective to improve the neuromuscular control of trunk flexors for the treatment of young patients with non-specific CLBP.

Experimental investigation on effects of CO2 additions on spontaneous ignition of high-pressure hydrogen during its sudden release into a tube

Hydrogen is expected to be an alternative energy carrier in the future. High-pressure hydrogen storage option is considered as the best choice. However, spontaneous ignition tends to occur if hydrogen is suddenly released from a high-pressure tank into a tube. In order to improve the safety of hydrogen application, an experimental investigation on effects of CO2 additions (5%, 10% and 15% volume concentration) on the spontaneous ignition of high-pressure hydrogen during its sudden expansion inside the tube has been conducted. Pressure transducers are used to record the pressure variation and light sensors are employed to detect the possible spontaneous ignition. It is found that the shock wave overpressure and the mean shock wave speed are almost the same inside the tube for different CO2 additions under the close burst pressures. For cases with more CO2 additions, the ignition detected time is longer and the average speed of the flame, the maximum value of light signals and the detected duration time of spontaneous ignition are smaller. It is shown that minimum burst pressure required for spontaneous ignition increase 1.47 times for 15% CO2 additions. The minimum burst pressure required for spontaneous ignition increases from 4.37 MPa (0% CO2) up to 6.41 MPa (15% CO2). With the increasing of CO2 additions, it requires longer distance and longer time for hydrogen and oxygen to mix and thus longer ignition delay distance/time. The results showed that additions of CO2 to air have a good suppressing effect on hydrogen spontaneous ignition.

Spontaneous ignition of high-pressure hydrogen during its sudden release into hydrogen/air mixtures

This paper investigates the effects of hydrogen additions on spontaneous ignition of high-pressure hydrogen released into hydrogen-air mixture. Hydrogen and air are premixed with different volume concentrations (0%, 5%, 10%, 15% and 20% H2) in the tube before high-pressure hydrogen is suddenly released. Pressure transducers are employed to detect the shock waves, estimate the mean shock wave speed and record the shock wave overpressure. Light sensors are used to determine the occurrence of high-pressure hydrogen spontaneous ignition in the tube. A high-speed camera is used to capture the flame propagation behavior outside the tube. It is found that only 5% hydrogen addition could decrease the minimum storage pressure required for spontaneous ignition from 4.37 MPa to 2.78 MPa significantly. When 10% or 15% hydrogen is added to the air, the minimum storage pressure decreases to 2.81 MPa and 1.85 MPa, respectively. When hydrogen addition increases to 20%, the spontaneous ignition even takes place at burst pressure as low as 1.79 MPa inside the straight tube.

Reactive balance control in older adults with diabetes

Diabetes mellitus is a major health problem for older adults worldwide and could be associated with impaired ability to recover balance after postural disturbances. This study compared reactive balance control in three groups of adults, young (YA), healthy non-diabetes older (nonDM-OA) and diabetes older (DM-OA). Twenty participants in each group completed a series of vision, plantar cutaneous sensitivity, grip power and lower limb strength tests. In the reactive balance test, participants stood on a force platform and used the dominant hand to pull the handle of a cord that could be suddenly released to create an imbalancing force. The anteroposterior (AP) and mediolateral (ML) motion of the center of pressure (COP) immediately after the sudden release was calculated to represent the level of imbalance experienced by the participants. Regression analysis entering big toe plantar sensitivity and grip power as independent variable was conducted for COP range for the three groups separately. The results showed that, except for the knee extensor, DM-OA had significantly poorer muscle strength and plantar sensitivity, and greater COP ML motion than YA and nonDM-OA. DM-OA also had significantly greater COP AP motion than YA. Grip power alone and together with plantar sensitivity explained a significant amount of variance in the AP and ML COP motion respectively (r2 = 0.334 and 0.582, respectively) for DM-OA. These findings indicated that diabetes in older adults was associated with declines in reactive balance control, and these changes may be related to muscle weakness and plantar insensitivity.

Multi-objective optimization for sensor placement against suddenly released contaminant in air duct system.

When a chemical or biological agent is suddenly released into a ventilation system, its dispersion needs to be promptly and accurately detected. In this work, an optimization method for sensors layout in air ductwork was presented. Three optimal objectives were defined, i.e. the minimum detection time, minimum contaminant exposure, and minimum probability of undetected pollution events. Genetic algorithm (GA) method was used to obtain the non-dominated solutions of multiobjectives optimization problem and the global optimal solution was selected among all of the non-dominated solutions by ordering solutions method. Since the biochemical attack occurred in a ventilation system was a random process, two releasing scenarios were proposed, i.e. the uniform and the air volume-based probability distribution. It was found that such a probability distribution affected the results of optimal sensors layout and also resulted in different detect time and different probability of undetected events. It was discussed how the objective functions are being compatible and competitive with each other, and how sensor quantity affect the optimal results and computational load. The impact of changes on other parameters was given, i.e. the deposition coefficient, the air volume distribution and the manual releasing. This work presents an angle of air ductwork design for indoor environment protection and expects to help in realizing the optimized sensor system design for sudden contaminant releasing within ventilation systems.

Stratification at the Earth's largest hyperacidic lake and its consequences

Volcanic lakes provide windows into the interior of volcanoes as they integrate the heat flux discharged by a magma body and condense volcanic gases. Volcanic lake temperatures and geochemical compositions therefore typically serve as warnings for resumed unrest or prior to eruptions. If acidic and hot, these lakes are usually considered to be too convective to allow any stratification within their waters. Kawah Ijen volcano, featuring the largest hyperacidic lake on Earth (volume of 27 million m3), is less homogeneous than previously thought. Hourly temperature measurements reveal the development of a stagnant layer of cold waters (<30 °C), overlying warmer and denser water (generally above 30 °C and density ∼1.083 kg/m3). Examination of 20 yrs of historical records and temporary measurements show a systematic thermal stratification during rainy seasons. The yearly rupture of stratification at the end of the rainy season causes a sudden release of dissolved gases below the cold water layer which appears to generate a lake overturn, i.e. limnic eruption, and a resonance of the lake, i.e. a seiche, highlighting a new hazard for these extreme reservoirs. A minor non-volcanic event, such as a heavy rainfall or an earthquake, may act as a trigger. The density driven overturn requires specific salinity-temperature conditions for the colder and less saline top water layer to sink into the hot saline water. Spectacular degassing occurs when the dissolved gases, progressively stored during the rainy season due to a weakened diffusion of carbon dioxide in the top layer, are suddenly released. These findings challenge the homogenization assumption at acidic lakes and stress the need to develop appropriate monitoring setups.

Postural Responses to a Suddenly Released Pulling Force in Older Adults with Chronic Low Back Pain: An Experimental Study.

Chronic low back pain (CLBP), one of the most common musculoskeletal conditions in older adults, might affect balance and functional independence. The purpose of this study was to investigate the postural responses to a suddenly released pulling force in older adults with and without CLBP. Thirty community-dwelling older adults with CLBP and 26 voluntary controls without CLBP were enrolled. Participants were required to stand on a force platform while, with one hand, they pulled a string that was fastened at the other end to a 2-kg or to a 4-kg force in the opposite direction at a random order. The number of times the participants lost their balance and motions of center of pressure (COP) when the string was suddenly released were recorded. The results demonstrated that although the loss of balance rates for each pulling force condition did not differ between groups, older adults with CLBP had poorer postural responses: delayed reaction, larger displacement, higher velocity, longer path length, and greater COP sway area compared to the older controls. Furthermore, both groups showed larger postural responses in the 4-kg pulling force condition. Although aging is generally believed to be associated with declining balance and postural control, these findings highlight the effect of CLBP on reactive balance when responding to an externally generated force in an older population. This study also suggests that, for older adults with CLBP, in addition to treating them for pain and disability, reactive balance evaluation and training, such as reaction and movement strategy training should be included in their interventions. Clinicians and older patients with CLBP need to be made aware of the significance of impaired reactive balance and the increased risk of falls when encountering unexpected perturbations.

Equation to Predict Riverine Transport of Suddenly Discharged Pollutants

AbstractPollution discharge to rivers is the leading cause of freshwater pollution. This paper presents a method for predicting the concentrations of a pollutant that is suddenly released into a river. The prediction method is based on a first-order Gaussian function. The coefficients of the Gaussian function are calculated using three power equations. These equations have six parameters whose values are optimized with the genetic algorithm (GA). The results of this paper’s case study are compared with those obtained with the artificial neural network method (ANN), genetic programming (GP), and from the analytical solution of the differential equation for riverine transport of suddenly released pollutants. The proposed equation is applied in a case study that confirms its suitability for estimating the concentration of pollutants downstream from a sudden release location in a river. The correlation coefficient (R2) and the root mean square error (RMSE) of the training and testing data obtained from the ap...

Effects of fatigue on trunk stability in elite gymnasts

The aim of the present study was to test the hypothesis that fatigue due to exercises performed in training leads to a decrement of trunk stability in elite, female gymnasts. Nine female gymnasts participated in the study. To fatigue trunk muscles, four series of five dump handstands on the uneven bar were performed. Before and after the fatigue protocol, participants performed three trials of a balancing task while sitting on a seat fixed over a hemisphere to create an unstable surface. A force plate tracked the location of the center of pressure (CoP). In addition, nine trials were performed in which the seat was backward inclined over a set angle and suddenly released after which the subject had to regain balance. Sway amplitude and frequency in unperturbed sitting were determined from the CoP time series and averaged over trials. The maximum displacement and rate of recovery of the CoP location after the sudden release were determined and averaged over trials. After the fatigue protocol, sway amplitude in the fore-aft direction was significantly increased (p = 0.03), while sway frequency was decreased (p = 0.005). In addition, the maximum displacement after the sudden release was increased (p = 0.009), while the rate of recovery after the perturbation was decreased (p = 0.05). Fatigue induced by series of exercises representing a realistic training load caused a measurable decrement in dynamic stability of the trunk in elite gymnasts.

Experimental investigation on the self-ignition of pressurized hydrogen released by the failure of a rupture disk through tubes

Hydrogen is expected to be used as a clean energy carrier. However, when high-pressure hydrogen is suddenly released into the air through tubes, self-ignition can occur by a diffusion ignition mechanism. In this paper, the phenomena of self-ignition and flame propagation during the sudden release of high-pressure hydrogen were investigated experimentally. Experimental results show that self-ignition can occur when bursting pressure is sufficiently high in spite of the shortness of the tube. For example, self-ignition was observed at a bursting pressure as high as 23.5 MPa with 50 mm long tube. When self-ignition successfully occurs, a hydrogen jet flame is produced by the ignition. The flame is then stabilized at the tube outlet. From photodiode signals and flame images, the propagation of a flame inside the tube is confirmed and the flame is detected near the rupture disk as the bursting pressure increases. When the tube length is not long enough to produce self-ignition, a hydrogen flame is observed in the only boundary layer at the end of tube and it quenches after the flame exits the tube. Consequently, the formation of a complete flame across the tube is important to initiate self-ignition, which sustains a diffusion flame after jetting out of the tube into the air. Also, in order to establish a complete flame across the tube, it is necessary to have sufficient length such that the mixing region is generated by multi-dimensional shock–shock interactions.

Collision of a suddenly released bent carbon nanotube with a circular graphene sheet

Molecular dynamics (MD) simulations were used to investigate the mechanical strain energy release of a bent single wall carbon nanotube (CNT) and its mechanical collision with a circular graphene sheet that is fixed at its edges. The MD simulations show that the CNT is able to store a vast amount of mechanical strain energy because of the formation of kinks on its wall at the regions of maximum curvature. The sudden release of the strain energy upon releasing the bent CNT can cause its tip to approach a speed of 7000 m/s. Even with such a high speed collision with a monolayer graphene sheet, the CNT and the monolayer graphene sheet remain completely intact and do not suffer any damage. The instantaneous average impact pressure between the CNT and the graphene sheet is calculated to be in the range of 1–10 GPa for different temperatures and aspect ratios of the CNT. These results indicate the promising application of a CNT and a graphene sheet as a nanoknife and a nanocutting board, respectively, for nanocleavage processes such as sequence-specific DNA cleaving processes.

Elderly Subjects' Ability to Recover Balance With a Single Backward Step Associates With Body Configuration at Step Contact

In the event of a slip or trip, one's ability to recover a stable upright stance by stepping should depend on (a) the configuration of the body at the instant of step contact and (b) the forces generated between the foot and ground during step contact. In this study, we tested whether these two variables associate with elderly subjects' ability to recover balance by taking a single backward step after sudden release from an inclined position. Twenty-six community-dwelling subjects (12 women, 14 men) of mean age 75+/-4 (SD) years each underwent five trials in which they were suddenly released from a backward inclination of 7 degrees and instructed to "recover balance with a single step." Body segment motions and foot contact forces were analyzed to determine step contact times, stepping angles, body lean angles at step contact, and the magnitudes and times (after step contact) of peak foot-floor contact forces and peak sagittal-plane torques at the ankle, knee, and hip of the stepping leg. Fifty percent of subjects were predominantly single steppers (successful at recovering with a single step in greater than three of five trials), 27% were multiple steppers (successful in less than two of five trials), and 23% were mixed response steppers (successful in two of five or three of five trials). Recovery style associated with the ratio of stepping angle divided by body lean angle at step contact (p = .003), which averaged 1.4+/-0.5 for single steppers and 0.6+/-0.5 for multiple steppers, but not with step contact time, stepping angle, or contact forces and joint torques during step contact. These results suggest that elderly subjects' ability to recover balance with a single backward step depends primarily on the configuration of the body (in particular, the ratio of stepping angle to body lean angle) at step contact.

Modeling Sediment Deposition Patterns Arising From Suddenly Released Fixed‐Volume Turbulent Suspensions

Models presented in several recent papers [1–3] dealing with particle transport by, and deposition from, bottom gravity currents produced by the sudden release of dilute, well‐mixed fixed‐volume suspensions have been relatively successful in duplicating the experimentally observed long‐time, distal, areal density of the deposit on a rigid horizontal bottom. These models, however, fail in their ability to capture the experimentally observed proximal pattern of the areal density with its pronounced dip in the region initially occupied by the well‐mixed suspension and its equally pronounced local maximum at roughly the one‐third point of the total reach of the deposit. The central feature of the models employed in [1–3] is that the particles are always assumed to be vertically well‐mixed by fluid turbulence and to settle out through the bottom viscous sublayer with the Stokes settling velocity for a fluid at rest with no re‐entrainment of particles from the floor of the tank. Because this process is assumed from the outset in the models of [1–3], the numerical simulations for a fixed‐volume release will not take into account the actual experimental conditions that prevail at the time of release of a well‐mixed fixed‐volume suspension. That is, owing to the vigorous stirring that produces the well‐mixed suspension, the release volume will initially possess greater turbulent energy than does an unstirred release volume, which may only acquire turbulent energy as a result of its motion after release through various instability mechanisms. The eddy motion in the imposed fluid turbulence reduces the particle settling rates from the values that would be observed in an unstirred release volume possessing zero initial turbulent energy.We here develop a model for particle bearing gravity flows initiated by the sudden release of a fixed‐volume suspension that takes into account the initial turbulent energy of mixing in the release volume by means of a modified settling velocity that, over a time scale characteristic of turbulent energy decay, approaches the full Stokes settling velocity. Thereafter, in the flow regime, we assume that the turbulence persists and, in accord with current understanding concerning the mechanics of dense underflows, that this turbulence is most intense in the wall region at the bottom of the flow and relatively coarse and on the verge of collapse (see [22]) at the top of the flow where the density contrast is compositionally maintained. We capture this behavior by specifying a “shape function” that is based upon experimental observations and provides for vertical structure in the volume fraction of particles present in the flow. The assumption of vertically well‐mixed particle suspensions employed in [1–5] corresponds to a constant shape function equal to unity.Combining these two refinements concerning the settling velocity and vertical structure of the volume fraction of particles into the conservation law for particles and coupling this with the fluid equations for a two‐layer system, we find that our results for areal density of deposits from sudden releases of fixed‐volume suspensions are in excellent qualitative agreement with the experimentally determined areal densities of deposit as reported in [1, 3, 6]. In particular, our model does what none of the other models do in that it captures and explains the proximal depression in the areal density of deposit.

Factors affecting the transient tension change after applying stepwise length change to glycerol-treated muscle fibers. Effects of temperature, divalent cations, and modification with p-chloromercuribenzoate.

The dynamic properties of cross-bridge movement were investigated in glycerol-treated muscle fibers under various conditions by analyzing tension responses to two types of length change. First, the fiber bundles were stretched linearly with time for 0.3 s from the rest length (L0) by 2.5% of L0, suddenly released, then fixed at L0 (sudden release of the slow stretch). Second, they were stretched for 0.01 s by 2.5% of L0, then held at the plateau length (a quick stretch). 1. The transient tension responses following both length changes were divided into three phases: (i) very quick recovery of tension (0 approximately 0.05 s), (ii) quick recovery (0.05 approximately 0.3-0.4 s), and (iii) gradual recovery (0.3-0.4 s approximately several seconds). 2. The effects of activating conditions on the rates of the quick phases (0 approximately 0.3-0.4 s) were not associated with those on the nucleoside triphosphatase [EC 3.6.1.3] rates: the rates of the quick phases increased with increase in temperature and Mg2+-ATP concentration, with decrease in Ca2+ concentration, and also on replacement of Mg2+-ATP by Mg2+-ITP or Mn2+-ATP. Only a small amount of ADP, 0.07 mol per mol of myosin (Fig. 24 in the preceding paper), was liberated during the quick recovery phases. 3. The remaining slow tension recovery was concluded to be associated with one cycle of ATP splitting, and progressed very smoothly. This suggests that most of the cross-bridges do not exist in a synchronously dissociated state during one cycle of ATP splitting.

Acceleration of the ATPase activity of glycerol-treated muscle fibers by repeated stretch-release cycles.

Glycerol-treated muscle fiber bundles were fixed at their rest length in 50 mM KC1, 2 mM MgC1(2), and 10 micron CaC1(2) at pH 7.8 and 0 degrees C in the presence of sufficient amounts of ATP, creatine kinase, and creatine phosphate. The fiber bundles were stretched linearly with time for 0.3 s at a constant amplitude, suddenly released, then fixed at the rest length for a constant time interval (alpha seconds). The stretch-release cycle was repeated, and the ATPase activity (the rate of ADP liberation) [EC 3.6.1.3] was measured. It was found that: 1. ATPase was activated by repeated stretch-release. As repetitive stretch-release of 1--2% of the rest length caused maximum activation, we usually selected a value of 2.5% of the rest length. The activation of ATPase was found to be a function of the duration, alpha, of the isometric phase after sudden release from stretching. The ATPase activity of fiber bundles was almost unaffected when they were oscillated by a simple stretch-release without an isometric phase after the sudden release (alpha=0). 2. The ATPase activity of oscillated muscle fibers increased with increase in the value of alpha, reached a maximal level, then decreased gradually with further increase of alpha to a value slightly larger than that of static fibers. At 0 degrees C, the value of alpha for the maximum activation was observed at about 2 s, and the maximum activity was about 2.5 times that of static fibers. At 20 degrees C, the alpha value for maximum activation was about 0.5 s, and the maximum activity was about 1.8 times that of static fibers. 3. The time course of ADP liberation after one stretch-release cycle could be easily calculated from the ATPase activity of the summed durations of the isometric phase, alpha, assuming that the ATPase activation was turned off and on by the stretching and release, respectively, and that the state of cross-bridges immediately after the stretch-release was independent of alpha of the cycle. The rate of ADP liberation after stretch-release thus obtained showed a short lag phase, a sigmoidal increase, a decrease to almost zero, then a return to nearly the original level (the rate of static fibers). About 1.3 mol of ATP per mol of myosin was hydrolyzed at both 0 degrees C and 20 degrees C during one cycle of the changes in the rate of ADP liberation.

Objective signs of inferior alveolar nerve anesthesia in exodontia

Objective determination of the adequacy of inferior alveolar nerve anesthesia is difficult. A dependable objective test based upon clinical observation of hundreds of patients during extraction of mandibular teeth, is presented. Following routine inferior alveolar nerve block anesthesia, time is allowed for subjective signs of “tingling” of the lower lip. Fully aware that the patient may respond to pressure in the absence of pain, the tooth to be extracted is tested. Gradual pressure of increasing intensity is applied with extracting forceps for 3 seconds, then suddenly released, providing a sudden stimulus. If the patient immediately moves or “jumps,” this response indicates inadequate anesthesia. If the patient does not respond to the sudden release of pressure, that tooth can be removed painlessly even though the patient may still respond to pressure.