Unsupported State Research Articles

Study on Critical Width of Semi-Coal Rock Roadway of Shallow-Buried Thin Coal Seam Based on Coal Side Self-Stabilization

In the context of a shallow-buried thin coal seam, the surrounding rock deformation in the semi-coal rock roadway is comparatively small, resulting in self-stabilization of the two sides of the roadway without the need for support when the roadway is below a critical width. This study focuses on the transportation roadway of the 2107 working face in the Anzhe Coal Mine, employing a combination of laboratory tests, field tests, theoretical analyses, and numerical simulations. A mechanical model for the layered roof of the semi-coal rock roadway in a shallow-buried thin coal seam is developed, along with a calculation formula for determining the critical width of such roadways. The study also initially examines the correlation between the critical width and factors such as the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata under conditions where the coal sides of the roadway are self-stabilizing. The results showed the following. (1) The calculation formula has good applicability for typical shallow-buried mine roadways in the Niuwu mining area and shallow-buried semi-coal rock roadways with coal thickness below 0.7 m under similar geological conditions. The critical width is related to the tensile strength of the roof, the buried depth of the roadway, and the thickness of the immediate roof strata. The degree of influence is determined by the thickness of the immediate roof strata > the tensile strength of the roof > the buried depth of the roadway. Among these, the tensile strength of the roof, the thickness of the immediate roof strata, and the critical width are basically in a positive exponentially increasing relationship, and the buried depth of the roadway and the critical width are basically in a negative exponentially decreasing relationship. (2) The on-site measurement of the loose circle on both sides of the roadway revealed that the rock mass loose circle had a thickness of 0.2 m, while the coal loose circle had a thickness ranging from 0.6 m to 0.7 m, aligning closely with the results obtained from theoretical calculations. The thickness of the coal loose circle on both sides served as the basis for determining the critical width of the semi-coal rock roadway in the shallow-buried thin coal seam. The calculated critical width of the roadway was 2.9 m, whereas the actual width measured was 2.4 m. Consequently, the two sides of the roadway are deemed capable of self-stabilization in the unsupported state. (3) Following the optimization of the support scheme, engineering analysis indicates that the roof and floor exhibit a maximum convergence of 46.3 mm, while the two sides show a maximum convergence of 18.4 mm. It is observed that the surrounding rock of the roadway satisfies the safety requirements for production. This study can provide theoretical support and a scientific basis for the stability discrimination of two sides and surrounding rock control of semi-coal rock roadways in shallow-buried thin coal seams under similar conditions.

Stress and Deformation Characteristics of Tunnel Surrounding Rock under Alteration

Based on a typical project in an altered rock area, this study carried out numerical simulations using the FLAC3D software to calculate the changes in the stress field, deformation field, and plastic zone of the surrounding rock during the unsupported and supported excavation of a water transfer tunnel. The degree of alteration of the surrounding rock was considered as the base point. The following results were obtained: in the unsupported state, the tunnel surrounding rock was affected by different degrees of alteration, and compressive stress concentration appeared within a certain range at the bottom of the chamber. The value of all-directional stress decreased with the deepening of the degree of alteration, while the opposite was the case for the depth of influence. The displacement changes at the bottom and side walls of the chamber were large and increased significantly with the deepening of the degree of alteration; the displacement monitoring points distributed around the tunnel exhibited the same deformation trend. The plastic zone of the surrounding rock obviously expanded as the degree of alteration deepened. The stress, deformation field, and plastic zone of the tunnel surrounding rock were effectively controlled after the adoption of support measures. The results obtained by this study can be used as a reference for similar projects in altered rock areas.

Application of the Mechanotherapy Devices Simulating Step-Like Movements in Combination with Electrical Stimulation in Spinal Cord Injury Patients

Summarizing the results of the world scientific data on this topic, the possibility to evoke step-like movements in the lower limbs of patients with spinal cord injury (SCI) below the level of damage was noted. That was verified during electrical stimulation in combination with mechanotherapy, the electrodes application to the definite areas of spinal cord. In addition, we stated that these measures led to reduction of muscle hypertonus in the lower limbs, improvement of neuromuscular junction and tolerance towards increasing stimulation that were instrumentally confirmed. We stated that it is impossible to achieve the same effect using only one of these methods isolated. The first studies were carried out by implantation of epidural electrodes in the spinal cord, and later by a combination of electrical stimulation and step-like movements with the same frequency setting manually. During further technology development, stimulation became percutaneous, and the movements were carried out using robotic mechanotherapy. The advantage of this method is obvious: the specialist needs to set the initial parameters which are selected individually for the patient,to monitor the progress of the procedure and to fix changes. These devices include robotic systems which perform movements in the lower extremities with full and partial axial load. Currently a study of the device for robotic therapy in horizontal unsupported state is ongoing in rehabilitation clinic of FSBI NMCC n. a. N.I. Pirogov. Its excellence is support absense, the training is held in conditions of complete body weight unloading. Multimodal electrical stimulation is performed simultaneously with robotic therapy: percutaneous electrical stimulation of the spinal cord and functional electrical stimulation (FES) of the legs, back and abdomen muscles. It was stated that parameters of neurological status were improved significantly. This article presents the results of unsupported robotic mechanotherapy`s clinical testing in the SCI patients rehabilitation.

Study on Surrounding Rock Stability of Long-Span Coal Roadway under Influence of Mining and Support Technology Optimization

Taking stoping safety of large-span working face in a coal mine in Shanxi as the background, the damage and movement law of overlying strata structure in coal roadways under the influence of mining are studied. Combined with the actual production of the mine, the mining pressure characteristics of the working face and the influence range of mining in the working face are mastered. Main research contents and conclusions are that: (1) Numerical simulation of roadway stability is carried out using UDEC software, stimulating the stress and strain variation of surrounding rock under unsupported state. Based on this, the roadway support parameters are simulated and optimized, which provides valuable reference for practical engineering. (2) Study the simplified design process of bolt support parameters, improve the accuracy of bolt support parameters and reduce the cost of coal mine support to increase the incidence of coal mine roof accidents, providing a basis for coal mine safety production.

Stable Switching Control Strategy of the Support Pressure and Velocity of Shield Machine Gripper Shoes

An electro‐hydraulic servo position and pressure compound control method was investigated considering the working principle of a hydraulic stepping motor of a shield machine gripper shoe and its practical working characteristics in the supporting process. The control targets were to improve the support efficiency and reduce the disturbance of gripper shoes on the surrounding rock. In this method, a fuzzy switching controller was used to switch between electro‐hydraulic position control and electro‐hydraulic pressure control. Numerical and prototype simulation experiments were conducted on the control method. The theoretical analysis and experimental results showed that the control method could effectively convert the gripper shoes from an unsupported state to a supported state in a short amount of time, as well as realize surge‐free switching between position control and pressure control. Thus, disturbance of the gripper shoes on the surrounding rock could be reduced. The results of this study provide a theoretical basis for research on control strategies of hydraulic stepping propulsion of shield machines.

Activation of the Highly‐Selective Pd11Bi2Se2 during the Semi‐Hydrogenation of Acetylene

Pd11Bi2Se2 was prepared as single‐phase material and used in an unsupported state as catalyst in the semi‐hydrogenation of acetylene in ethylene excess. After an initial inactive time‐period, Pd11Bi2Se2 activated and showed high acetylene conversion and selectivity towards ethylene at 473 K. In addition, after the initial inactive state, the compound revealed high stability during 100 h time on stream. At 80 % conversion the selectivity to ethylene is higher than 90 %. Post‐catalysis investigations by powder X‐ray diffraction (p‐XRD) and X‐ray photoelectron spectroscopy (XPS) exclude the formation of intermetallic hydrides, decomposition, and the presence of elemental palladium. Furthermore, comparison of XPS before and after catalysis revealed the reason of the inactive state of the intermetallic compound during the first hours of catalysis. An initial surface layer of bismuth oxide is reduced and re‐incorporated into the intermetallic compound. This material change is responsible for the initially observed activation of Pd11Bi2Se2 during the semi‐hydrogenation of acetylene.

Numerical studies on surrounding rock deformation controlled by pressure relief groove in deep roadway

After entering deep mining, the roadway is in a high stress state, the deformation of surrounding rock becomes larger, and the roadway floor is particularly significant under unsupported state, which brings great difficulty to the safe production and support of the coal mine. Pressure relief method can change the stress field of surrounding rocks so that the surrounding rock can be in stress-reducing area. The present paper studied the deformation law of the roadway and the changes in the stress state and plastic zone of the surrounding rocks around the roadway before and after the excavation of pressure relief groove on the bottom floor of the high-stress roadway by using FLAC under the engineering background of one mine in Binchang, analyzed the influence of different groove depths and widths on the floor heave, convergence on both sides and roof subsidence. The simulation results show that: after the roadway floor was grooved in the high stress roadway, a larger stress-relaxed area will be formed near the roadway floor, the stress will be transferred to the deep roadway floor, and the pressure relief groove plays a better control effect on the deformation of the high-stress roadway. With the increase of the width and depth of the pressure relief groove, the convergence of the top and bottom of the roadway will be decreased accordingly, but the effect is not significant, while its influence on the convergence on both sides is relatively significant. After applying the simulation results to the engineering practice, the practice shows that: the combined support of anchor rod, anchor rope plus pressure relief groove can control the deformation of the roadway well and the conclusion obtained can provide some reference values for the study and design of the grooving pressure relief control technology.

Addressing electronic effects in the semi-hydrogenation of ethyne by InPd2 and intermetallic Ga–Pd compounds

The intermetallic compound InPd2 was prepared as single-phase material and used in an unsupported state as catalyst in the semi-hydrogenation of ethyne in a large excess of ethene. InPd2 showed high activity and selectivity (up to 93%) toward ethene in the temperature range from 478 to 508K. In addition, the compound revealed high stability during 20h time on stream at 473K at 80% selectivity and >90% conversion. Investigations by differential thermal analysis combined with thermogravimetry (DTA/TG) in H2 and near-ambient pressure X-ray photoelectron spectroscopy (NAP-XPS) exclude the formation of intermetallic hydrides, phase transitions, decomposition, and the presence of elemental palladium. The stability of InPd2 under reaction conditions allows addressing the influence of electronic factors on the catalytic properties by comparison with Ga–Pd intermetallic compounds. From the joint results of experiments and first-principles calculations, the electronic influence on the catalytic selectivity is found to be minor; selectivity seems to be largely governed by geometric effects – as suggested earlier by the site-isolation concept – as well as the absence of hydridic hydrogen.

Photocatalytic Decomposition of Formic Acid on Mo2C-Containing Catalyst

The photocatalytic behavior of pure and supported Mo2C was investigated in the vapor-phase decomposition of formic acid. IR studies showed that illumination promoted the dissociation of molecularly adsorbed HCOOH and the decomposition of formate species formed on Mo2C/TiO2 sample. Mo2C prepared on TiO2 enhanced the extent of the photocatalytic decomposition exhibited by TiO2. Both the dehydrogenation and dehydration reactions occurred. Interestingly, Mo2C had photocatalytic properties even in unsupported state and also on an inert SiO2 surface. Its photoactivity was dramatically increased by the presence of potassium prepared by the carburization of K2MoO4, when the dehydrogenation came into prominence. Pure and K-doped Mo2C showed an appreciable photocatalytic effect in the visible light, which was attributed to their lower bandgap. Photocatalytic decomposition of HCOOH on pure and K-doped Mo2C at 300 K. (A) conversion of HCOOH; (B) Formation of CO2; (C) CO/CO2 ratio.

Democratic Aspirations and Destabilizing Outcomes in Afghanistan

The United States and its allies, in control of Afghanistan since October 2001, failed to support the development of an inclusive, legitimate and accountable political system. This paper examines how the imposition of an inappropriate model of democracy, the prioritization of American interests over those of Afghans, and a pattern of expedient political decisions have contributed to the destabilization of the country. The democracy and state-building model imposed on Afghanistan was stymied from the outset by critical foundational flaws. These include the return to power of discredited warlords reviled by most Afghans, the marginalization of particular groups including the remnants of the Taliban movement, and the concentration of power in an executive Presidency at the expense of a weak parliamentary structure. In 2014, along with the drawdown of US and NATO troops, Afghanistan’s disputed election saga ended in a no-victor deal that effectively discarded the (as yet unknown) results of the ballot box. Once again, Washington politics reinforced the grip of a warlord-dominated elite on the machinery of the state and exposed the hollowness of the US-led and UN-supported state building project.

Aspects of temperature-programmed analysis of some gas–solid reactions. Part 1.—Dispersion effects in temperature-programmed bulk reduction and temperature-programmed desorption

The reduction of hexachloroplatinic acid and the desorption of adsorbed hydrogen have been followed by temperature-programmed methods. Both the temperature-programmed bulk reduction (t.p.b.r.) and the temperature-programmed desorption (t.p.d.) profiles reveal several maxima at temperatures which vary with the ultimate Pt dispersion and the support used. Reductions commenced at subambient temperatures and good separation of all three t.p.b.r. peaks was only achieved on starting t.p.b.r. at least as low as 223 K. T.p.b.r. temperatures of maximum reduction rates for samples supported on porous silica decreased with increasing dispersion but were higher for the supported rather than the unsupported state. The maximum quantities of hydrogen consumed in t.p.b.r. exceed that expected for complete reduction in some silica-supported samples, but the contribution of the high-temperature γ-peak (possibly associated with spillover) increased with increasing Pt dispersion. T.p.d. liberated less gaseous hydrogen (41–84%) from silica-supported samples than the total quantity of preadsorbed hydrogen, but the percentage increased (and the temperatures at which desorption rates were a maximum decresed) as the Pt dispersion increased. Alumina- and titania-supported samples produced more complex t.p.d. and t.p.b.r. profiles than those of silica. It is argued that it is not justified to interpret these or other equivalent temperature-programmed profiles in terms of processes occurring on chemically distinct and distinguishable solid or surface states. The activation energy for diffusion is critically important and diffusion may be too slow in t.p.b.r. and too fast in t.p.d. to allow temperature-programmed profiles to arise from processes occurring to such distinguishable and identifiable species. In t.p.d. surface residence times are also important in defining the fraction of adsorbate subsequently desorbed.