Greater Rigidity Research Articles

A comparative study of the data of intraoperative neurophysiological monitoring in the surgical correction of severe scoliosis with and without preoperative halo-traction

BACKGROUND: The use of intraoperative neurophysiological monitoring (IONM) during corrective spinal surgery is the gold standard. Maintaining the integrity of the nervous system during surgery is importance. We use various types of halo-traction in the preoperative period in patients with severe scoliotic spinal deformities also to reduce the risk of neurological complications. A comparative study of changes in IONM during operations to correct scoliosis in patients who underwent preoperative halo-gravity training and without it was conducted. AIM: A comparative analysis of the results of IONM during surgery to correct scoliosis with and without preoperative halo-gravity traction. MATERIALS AND METHODS: An observational monocenter retrospective uncontrolled study of the results of IONM was conducted in 88patients with severe scoliotic deformities who received surgical treatment to correct scoliosis using halo-traction. The patients were divided into 2groups. GroupI (52people) received halo-gravity traction as preoperative preparation. GroupII (36people) was operated under conditions of intraoperative halo-traction. A comparative analysis of signaling criteria with the threat of developing neurological deficit of the lower extremities during surgery, the values of the deformation angles before and after surgery, mobility indicators, the volume of blood loss and the time of surgery was performed. RESULTS: An intergroup comparison of the obtained parameters of changes in deformation angles, IONM data revealed that in group I patients had a more pronounced deformation in terms of the angles, their greater rigidity and a smaller number of patients with a normal indicator of the level of MEP, which is statistically reliably confirmed (p0.05). In 12patients signaling criteria with the threat of developing neurological deficits were registered: 7 in groupI, 5 in groupII. In two patients of group II, the recovery of the MEP indicators of the lower extremities did not occur and permanent neurological deficit could not be avoided. CONCLUSION: Preoperative halo-traction makes it possible to prepare nerve structures for the correction of severe deformities and reduce intraoperative effects on the nervous system, reducing the risks of neurological complications in patients with severe spinal deformities compared with simultaneous correction in conditions of intraoperative traction.

Elastic and radiation shielding properties of zinc borotellurite glass systems: The impact of gadolinium oxide

Using the formula [(TeO2)70(B2O3)30], this study examines the impact of Gd2O3 on the elasticity and radiation shielding characteristics of zinc borotellurite glass. Glass samples containing 1–5% mol% Gd2O3 were created by employing the melt quench technique. XRD verified that they are amorphous in nature, and the existence of TeO3, TeO4, BO3, and BO4 vibrational groups was revealed by infrared spectra. The structural alterations were shown by the range of longitudinal and shear ultrasonic velocities, which were 3908–4076 m/s and 2222–2277 m/s, respectively. The glass's rigidity was improved by the large rise in elastic moduli, such as bulk (45 GPa), longitudinal (80 GPa), shear (25 GPa), and Young's moduli (60 GPa), with a higher Gd2O3 content. Higher concentrations of Gd2O3 resulted in a rise in the mass attenuation coefficient (μρ), as measured by WinXcom, which enhanced gamma-ray shielding. The half-value layer (HVL) and mean free path (MFP) at 0.662 MeV decreased with increasing Gd2O3 in a consistent manner. The maximum density and optimum gamma-ray shielding performance were found in the glass containing 5 mol% Gd2O3. These results show Gd2O3 for applications needing greater rigidity and better radiation protection by demonstrating how it affects the elastic and radiation-shielding efficiency of the glass network.

The “buddy stent technique” to overcome poor support for cover stent implantation to treat coronary perforation

An 86-year-old woman was managed for a non-ST-segment elevation myocardial infarction. Coronary angiography revealed significant stenoses at the left anterior descending, left ostial circumflex (LCX), obtuse first marginal, and a Medina 1.0.1 bifurcation lesion at the middle LCX/ second obtuse marginal (OM2). During percutaneous coronary intervention, the rupture of the pre-dilatation balloon was complicated by a type III coronary perforation at the level of the LCX/OM2 bifurcation, leading to cardiac tamponade. Hemodynamics were stabilized by percutaneous pericardial drainage. The placement of a covered stent (BeGraft, Bentley InnoMed), to seal the coronary perforation, was not possible due to its great rigidity and the angulation towards the OM2, even with the use of a guiding catheter extension (Guidezilla, Boston Scientific). To further increase support, we decided to use the flexibility of a regular drug-eluting stent which we implanted from the LCX to the OM2, thereby creating a rail-like path in which the covered stent could then be positioned and deployed successfully, allowing the perforation to be sealed with a good final result. This is what we called the “buddy stent technique”.

The Fabrication and Testing of Unmanned Aerial Vehicle (UAV) Wing Structure Using 3D Printing and Carbon Fibre Skinning Method

This study examines the efficacy of integrating 3D printing with carbon fibre skinning to construct wing structures for Unmanned Aerial Vehicles (UAVs). The primary objective is to enhance the structural integrity and material characteristics. The study performs static load tests, which demonstrate that wings reinforced with carbon fibre lamination can endure a substantially greater maximum stress of 29.43 N, in contrast to 14.391 N for wings produced only by 3D printing. The carbon fibre laminated wings have a greater load-bearing capability, as evidenced by the safety factor study. This analysis reveals that the permitted loads for carbon fibre laminated wings (19.61 N) are higher compared to 3D printed wings (9.594 N). The tensile testing of the specimens reveals that carbon fibre laminated wings demonstrate enhanced ductility, stiffness, and yield strength. Additionally, they withstand greater levels of maximum stress and strain, except for a slightly higher stiffness seen in 3D printed wings. This research highlights that carbon fibre laminated wings are typically more durable and versatile for many uses, although 3D printed wings may be favoured in situations when greater rigidity is necessary. In conclusion, the study effectively showcases the advantages of combining 3D printing with carbon fibre skinning in the construction of UAV wings. This research significantly contributes to the progress of UAV design and provides fresh insights in the fields of aeronautical engineering and materials science. It is particularly valuable for applications that require UAVs with exceptional performance, durability, and reliability.

Fiber-Reinforced Composites for Full-Arch Implant-Supported Rehabilitations: An In Vitro Study.

Background: Fiber-reinforced composites (FRCs) have been proposed as an alternative to traditional metal alloys for the realization of frameworks in full-arch implant-supported prostheses. The aim of the present in vitro study was to evaluate the deflection under load of seven prostheses endowed with frameworks made of different materials, including different types of fiber-reinforced composites (FRCs). Methods: A master cast with four implant analogues in correspondence with the two lateral incisors and the two first molars was used to create full-arch fixed prostheses with the same shape and different materials. Prostheses were made of the following different materials (framework+veneering material): gold alloy+resin (Au+R), titanium+resin (Ti+R), FRC with multidirectional carbon fibers+resin (ICFRC+AR), FRC with unidirectional carbon fibers+composite (UCFRC+C), FRC with glass fibers+resin (GFRC+AR), FRC with glass fibers+composite (GFRC+C), and resin (R, fully acrylic prosthesis). Flexural tests were conducted using a Zwick/Roell Z 0.5 machine, and the deflection of the lower surface of the prosthesis was measured in order to obtain load/deflection graphs. Results: Greater rigidity and less deflection were recorded for UCFRC+C and GFRC+C, followed by Ti+R and Au+R. The greatest deformations were observed for resin alone, ICFRC+R, and GFRC+R. The results were slightly different in the incisal region, probably due to the greater amount of veneering material in this area. Conclusions: When used to realize full-arch frameworks, Au and Ti allow for predictable mechanical behavior with gradual deformations with increasing load. UCFRC also demonstrated good outcomes and less deflection than ICFRCs when loaded. The GFRC full-arch framework may be a valid alternative, although it showed greater deflections. Further studies are needed in order to evaluate how different prosthesis designs and material thicknesses might affect the outcomes.

Environmental physical factors produce mitotic aberration and multicellularity in the ovarian cancer cell line SKOV3

The spread of ovarian cancer (OC) to the coelomic cavity triggers the secretion and accumulation of ascitic fluid (AF). Although its biochemical composition has been well studied, less is known about the implications of physical factors such as the pH and the mechanical properties of the AF for the malignancy of tumor cells. In this work, we investigated the effect of pH and the mechanical properties of AF on cell proliferation and mitotic morphology. We employed biopsies from patients with OC and the SKOV3 cell line as an in vitro model of OC with HeLa cells as controls. Sections of each tumor were stained with HE, analyzed, and related to clinical data. AF from patients with OC exhibited an alkaline pH (ranging from 7.3 to 7.8). Compared to control conditions, the 3 AFs significantly enhanced the proliferation of SKOV3 and HeLa cells. These effects were more pronounced at a more alkaline pH. In addition, we found that AFs have different densities that correlated with a significant increase in multinucleated tumor cells and severe morphological defects in cells undergoing mitosis. In agreement with these data, we found that higher concentrations of soft agar provoked significantly higher numbers of multinucleated and morphologically abnormal SKOV3 cells with no effect on HeLa cells.We conclude that an alkaline pH and greater rigidity could enhance the metastatic potential of OC cells. We propose that these two physical factors could be parameters of clinical importance as predictors of malignancy.

The Aerodynamic Effect of Biomimetic Pigeon Feathered Wing on a 1-DoF Flapping Mechanism.

This study focused on designing a single-degree-of-freedom (1-DoF) mechanism emulating the wings of rock pigeons. Three wing models were created: one with REAL feathers from a pigeon, and the other two models with 3D-printed artificial remiges made using different strengths of material, PLA and PETG. Aerodynamic performance was assessed in a wind tunnel under both stationary (0 m/s) and cruising speed (16 m/s) with flapping frequencies from 3.0 to 6.0 Hz. The stiffness of remiges was examined through three-point bending tests. The artificial feathers made of PLA have greater rigidity than REAL feathers, while PETG, on the other hand, exhibits the weakest strength. At cruising speed, although the artificial feathers exhibit more noticeable feather splitting and more pronounced fluctuations in lift during the flapping process compared to REAL feathers due to the differences in weight and stiffness distribution, the PETG feathered wing showed the highest lift enhancement (28% of pigeon body weight), while the PLA feathered wing had high thrust but doubled drag, making them inefficient in cruising. The PETG feathered wing provided better propulsion efficiency than the REAL feathered wing. Despite their weight, artificial feathered wings outperformed REAL feathers in 1-DoF flapping motion. This study shows the potential for artificial feathers in improving the flight performance of Flapping Wing Micro Air Vehicles (FWMAVs).

Mechanical bonding of rigid MORFs using a tetratopic rotaxane.

The preparation of highly rigid cobalt(II)- and copper(II)-organic frameworks incorporating a tetralactam [2]rotaxane as a ligand is described. The interlocked ligand is functionalized with two pairs of carboxylate groups placed at each counterpart, thus limiting its dynamics within the crystal. The solid structure of the metal-organic rotaxane frameworks showed different, unprecedented polycatenation modes of grids, depending on the employed metal, providing great rigidity to the structures. This rigidity has been evaluated by using single crystal X-ray diffraction analyses of the cobalt(II)-organic frameworks embedded in different solvents, observing that the lattices remain unchanged. Thus, this research demonstrates that rigid and robust materials with permanent porosity can be achieved using dynamic ligands.

INVESTIGATION OF THE DRAG FORCES FROM THE SIDE OF THE POWDER ENVIRONMENT ON THE PARTS MOVEMENT DURING THE MAGNETO-ABRASIVE FINISHING IN THE ANNULAR BATH

The influence of the technological parameters of the magneto-abrasive finishing (MAF) process on the drag forces to the parts movement of different sizes and shapes, made of ferro- and paramagnetic materials, which act from the side of the ferro-abrasive powder medium formed from various powders in the magneto-abrasive tool (MAT) was investigated. The features of the interaction of the structural elements of the MAT with the surfaces being finished are determined. The influence of the magnetic field strength on the drag forces of the movement of the parts of different sizes and shapes in the MAT was established. It was shown that the process of interaction of MAT with the surfaces of samples being finished with characteristic dimensions up to 12 mm in the annular bath with a width of 35 mm occurs in the "free flow around" mode, while the MAF of samples with characteristic dimensions larger than 12 mm occurs in the "flow around" and "jamming" mode of representative volumes of the MAT between the pole tips and the surface being finished – in the zone of the formed little moving dead zone.
 With the increase in the size of the MAT particles from 200/100 μm to 400/315 μm, the relative value by which the drag forces increase is 1.25–1.65, which is explained by the greater magnetization of larger powders and their formations in the composition of the MAT and, accordingly its greater rigidity.

Study on wavy-edge plunge milling cutter with chip split and cutting load reduction function

The plunge milling feeds along the cutter axis, and the cutting load is concentrated in the cutter axis with greater rigidity, which is a rough machining process that allows greater machining processing parameters. At present, due to the cutting performance of plunge milling cutter, its efficiency advantage is difficult to give full play, and the application scope is very limited. For this reason, this paper introduces the chip split principle of wavy edge into plunge milling, and develop a high-performance plunge milling cutter that can reduce the cutting force and cutting vibration. The mechanism for wavy edge to reduce load is revealed from the perspective of the geometric characteristics of cutting layer, and the cutter structure of radial dislocation matching axial dislocation is proposed. The critical condition for effective chip split is derived, which provides a theoretical basis for cutter design and machining parameter selection. Considering the rough machining characteristics, the model designing, material selection and manufacturing process for the insert blade, cutter head and cutter body of the wavy-edged plunge milling cutter are proposed, and the reasonable value range of its key cutter geometric parameters are clarified. The arranged plunge milling experiment of 40Cr stainless steel shows that the vibration amplitude of wavy edged cutter is reduced by more than 90 % compared with straight edge cutter, and the machining stability is higher. At the same time, the cutting force is reduced by about 50 %, allowing larger feed per tooth.

The choice of optimal parameters of the retaining wall of the pit enclosure in conditions of dense construction, taking into account its spatial rigidity

The results of the study of the interaction of the pit enclosure made of flexible retaining walls, arranged in the conditions of dense construction, with the soil foundation are presented.
 Calculations were carried out by the method of numerical modeling, using the Plaxis software complex. The modeling is performed in a three-dimensional space, which provides an opportunity for a comprehensive assessment of the stress-strain state (SSS) of the elements of the system "soil array - retaining walls - structures of existing buildings" when using complex configurations of retaining walls and taking into account the factor of their spatial stiffness.
 For the analysis of the results, 4 characteristic sections were chosen. Modeling was performed taking into account the following stages:
 1) the initialization stage (formation of the soil massif in its natural state);
 2) installation of a retaining wall;
 3) alternate development of the pit to the design mark;
 4) load from the building at the stage of operation.
 Based on the results of the calculations, the SSS analysis of the elements of the system "soil massif - retaining walls - structures of existing buildings" was performed, and the reinforcement of the retaining walls was selected, and the costs of the main materials were determined.
 It is shown that taking into account the spatial stiffness of the retaining wall of the pit enclosure makes it possible to more effectively estimate the SSS of the retaining wall structure, more correctly estimate the additional deformations of neighboring buildings, due to taking into account the change in the stiffness of the retaining wall of a complex configuration, and therefore, in the future, to more effectively design the constructions of retaining walls.
 According to the results of the calculations, it is shown that retaining walls made in 2 rows in a staggered order, with piles with a diameter of 420 mm, have greater rigidity than retaining walls made in 1 row with piles with a diameter of 620 mm. Therefore, in order to reduce additional subsidence of neighboring buildings and reduce horizontal movements of the retaining wall, the option of the retaining wall made by placing piles in a staggered order is a priority in conditions of dense construction.
 Armature costs for option 1 are 46% higher compared to option 2. These results indicate that the 2nd option of installing a retaining wall is a more economical solution, however, in conditions of dense construction, its use is limited, since the settlement of neighboring buildings in this case will be greater, due to the lower rigidity of the retaining wall.

Major clinical approaches of prefabricated and customized prostheses for the temporomandibular joint: a systematic review

Introduction: The temporomandibular joint (TMJ) is composed of dense fibrocartilage formed between the mandibular condyle and the temporal bone. The high collagen content of this disc provides great rigidity and durability. Osteoarthritis-like degenerative joint disease belonging to temporomandibular disorder (TMD) is a destruction of bone and cartilage with a consequent inflammation that enhances tissue destruction. As a treatment, the implantation of a total alloplastic TMJ prosthesis is an innovative approach to the treatment of TMD. There are two types of prefabricated (stock) and custom computer-aided design/computer-aided manufacturing (CAD/CAM) systems. Objective: The present study aimed to carry out a concise systematic review of the major clinical approaches of prefabricated and customized prostheses for the temporomandibular joint. Methods: The systematic review rules of the PRISMA Platform were followed. The search was carried out from February to May 2023 in the Scopus, PubMed, Science Direct, Scielo, and Google Scholar databases, using articles from 2018 to 2023. Results and Conclusion: A total of 107 articles were found, 34 articles were evaluated and 19 were included and developed in this systematic review study. Considering the Cochrane tool for risk of bias, the overall assessment resulted in 21 studies with a high risk of bias and 15 studies that did not meet GRADE. It was concluded that the clinical results of the stock and CAD/CAM prostheses suggested major improvements in mouth opening and reduced pain as a result of the rehabilitation of temporomandibular joint function. The results showed comparable data for the two types of prosthesis design at 6 months postoperatively. Thus, both temporomandibular joint and custom implants work well despite the additional advantages of custom prostheses, along with increasing access to digital technology, which may result in custom devices dominating the market in total temporomandibular joint replacement systems.

Comparative Study of Different Types of Slab for Same Structural Condition.

The regular slab is often supported by a beam in modern construction, With a modest slab width and a big beam deep, the weight is transmitted from beam to column. Because of the flat slab, architects may construct partition walls wherever they are required. It is popular since it assists with weight reduction, stimulates quick development, and is did-not expensive. Similarly, since its debut, the classic slab has brought benefits such as greater rigidity. It offers a higher weight bearing capacity while also being good and economical. Grid slabs are required if the span is higher than one span, while grid beams are given if the span is less than one span. Grid slabs are good for longer spans with large loads because they eliminate voids that would otherwise result in dead load. Some slabs are less costly and more resistant to vibration. The study’s purpose is to determine which of the three slab varieties, regular slab, flat slab with drop, and grid slab, is the most benefits. a G+5 This study looked at storey displacement, shear force, bending moment, and storey drift in a residential multi-story structure with different slab.

High-Power Ultrasound in Enology: Is the Outcome of This Technique Dependent on Grape Variety?

The disruptive effect exerted by high-power ultrasound (US) on grape cell walls is established as the reason behind the chromatic, aromatic and mouthfeel improvement that this treatment causes in red wines. Given the biochemical differences that exist between the cell walls of different grape varieties, this paper investigates whether the effect of the application of US in a winery may vary according to the grape variety treated. Wines were elaborated with Monastrell, Syrah and Cabernet Sauvignon grapes, applying a sonication treatment to the crushed grapes using industrial-scale equipment. The results showed a clear varietal effect. The wines made with sonicated Syrah and Cabernet Sauvignon grapes showed an important increase in the values of color intensity and concentration of phenolic compounds, and these increases were higher than those observed when sonication was applied to Monastrell crushed grapes, whereas Monastrell wines presented the highest concentration in different families of polysaccharides. These findings correlate with the differences in the composition and structure of their cell walls since those of Monastrell grapes presented biochemical characteristics associated with a greater rigidity and firmness of the structures.

Preliminary findings from a study relating the effects of hearing loss and listening conditions on postural sway to fall risk in older adults

Hearing loss is associated with increased fall risk in older adults, but multiple mechanisms have been proposed to account for this. Hearing loss may reduce spatial awareness and/or increase cognitive load, both of which may increase fall risk but may be ameliorated by hearing aid use. Here, we present preliminary results from an in-progress study comparing fall incidence in daily life with postural sway measured under various listening conditions in older adults with and without hearing aids. Seventeen adults aged 65 to 81 years (7 using bilateral hearing aids, 10 without) stood with feet together and eyes closed, listening to noise vocoded speech (4, 8, 16 channels) and spatially distributed environmental sounds (silence, 1, 3 sources) for 1min per condition while postural sway was recorded in the lab. Participants subsequently reported daily near-falls and falls for 4 months. Results suggest hearing aid users show less postural sway, potentially indicating greater rigidity which has been associated with greater fall risk. However, near-fall incidence was lower for hearing aid users. Further analyses showed higher near-fall rates associated with higher auditory thresholds, but hearing aid use may mitigate this trend. We are currently collecting more data with a wider variety of participants.

НАПРЯЖЕННО-ДЕФОРМИРОВАННОЕ СОСТОЯНИЕ В КОСТИ И ИНТЕРФЕЙСЕ «ИМПЛАНТАТ — КОСТЬ»

Introduction. This article presents the results of mathematical modeling of the stress-strain state in the bone tissue surrounding the implant and the implant-bone connection depending on the diameter and length of the implant in the case of different directions of force application and the implant-bone implant installation angle.
 Target. To study the effect of the diameter, length of the implant and the load angle on the stress fields in a three-dimensional implant-bone system with finite elements and determine the effect of the load angle on the stress fields with a change in diameter and length.
 Materials and methods. To study the distribution and analysis of the stress-strain state in the bone tissue around implants of different diameters and lengths during dental implantation, a three-dimensional finite element model of the lower jaw was created. Three models were developed using computed tomography and the Universal Surgical Integration System software.
 Results. In all cases studied, the maximum stresses were achieved in the cortical bone due to its greater rigidity. However, since cortical and cancellous bone have different strength characteristics, it was necessary to consider the stress in these areas separately.
 In the cortical bone, the maximum stresses were always reached near the edge of the hole and the contact with the implant, respectively. In cancellous bone, in many cases, the maximum stresses were noted in the region of the implant apex. At the same time, when the implant is placed at an angle or in the buccolingual direction of load application, the stresses are redistributed in favor of the cancellous bone.
 Findings. Thus, in general, it can be concluded that an increase in the length and diameter of the implant leads to a noticeable decrease in stresses in the bone tissue surrounding the implant and in the implant-bone junction. The obtained results demonstrated that implants of small diameter and length, installed in the jawbone at an oblique loading angle, are the least favorable option for stress distribution at the implant-bone interface.

Lateral load-displacement response of flexure-dominant concrete-encased steel columns based on ASCE/SEI 41

Concrete-encased steel (CES) column, in which structural steel is encased in an RC section, is widely used in high-rise or heavily-loaded structures due to its great load-carrying capacity, rigidity, and durability. Nevertheless, the development of performance-based seismic design is still insufficient for CES structures, especially for evaluating the lateral load-displacement relationship. As a commonly-used performance-based seismic design (PBSD) guidance, current ASCE/SEI 41 guides global engineers to conduct the seismic evaluation of RC, steel, masonry, and timber structures. Nevertheless, ASCE/SEI 41 fails to give the modeling parameters for CES members owing to insufficient research concerning the steel-concrete interaction. In this paper, a lateral load-displacement curve for flexure-dominant CES columns under a nonlinear static procedure is proposed based on the provisions of RC members in the current ASCE/SEI 41. In the proposed curve, different constitutive laws are applied to consider different confinement of concrete; the slip between the structural steel and surrounding concrete is considered by reduced lateral stiffness; meanwhile, the end rotation caused by the bar-slip in RC is also taken into account to simulate the lateral behavior better. With a detailed calculation procedure, a comparison with experimental results of 42 CES columns in different references is reported to verify the applicability of the proposed curve. It can be concluded that the proposed curve can produce reasonable predictions of cracking load, cracking displacement, yield load, yield displacement, peak displacement, and strength degradation of flexure-dominant CES columns, leading to a feasible way to evaluate the lateral response of CES columns in practical design.

Impact of Fiber Buildup Stacking Sequence on Thermo-Mechanical Behaviour of Natural Fiber–Reinforced Anamide Composites

This article focuses on the viscoelastic behaviour of the anamide composites using a dynamic mechanical study developed by hot compression moulding technology at higher temperatures. The frequency range for this analysis is 1 Hz. In the nitrogen atmosphere, thermogravimetry analysis differential scanning calorimetry was used to investigate the thermal stability of composite laminates with various fiber orientations. The findings showed that a glass transition temperature close to 100°C can be achieved at 1 Hz to increase the fiber orientation of the basalt fiber-enhanced anamide compounds. Through the thermo-gravimetric analysis experiments, the excellent thermal stability of composite laminates at temperatures above 600°C was conspicuous. Analysis using the Fourier transform infrared (FTIR) spectroscopy envisioned the surface chemical properties of anamide films at various fiber orientations, and the interaction properties between fiber and matrix were determined. Scanning electron microscopy on composite laminate surfaces proclaimed that the interface relationship between the basalt fiber and the anamide material is superior with FTIR findings being assisted. The findings demonstrate that composite laminates may be a good replacement for high-performance and high-temperature applications since they are thermally extremely robust with great rigidity.

Mechanical Properties and Failure Mechanism of the Weakly Cemented Overburden in Deep Mining

With increases in the mining depth and area in the Ordos coal field, the failure law of the super thick sandstone in the Zhidan group leads to frequent disasters, such as rock bursts and mine earthquakes, which have become a significant issue, restricting large-scale continuous mining. To adequately understand the movement mechanism of the super-thick and weakly cemented overburden, and to promote the large-scale mining of the coal resources under it, this study analyzes the physical and mechanical properties, along with the microstructural characteristics, of the weakly cemented overburden of the Yingpanhao Coal Mine through mechanics tests, scanning electron microscope tests (SEM) and hydrolysis experiments. A two-dimensional discrete element model of the survey region is then built to explore the temporal and spatial evolution laws of the overburden failure. The results show that, even though poorly cemented strata such as the Cretaceous Zhidan group sandstone and the Zhiluo group sandstone are weak in lithology, their unique mineral composition and microstructural characteristics give them a greater rigidity when their thickness reaches a certain value. The surface subsidence exhibits a sudden increase, and the dynamic disaster range of the overlying strata is wide when deep multi-face mining was carried out under the super-thick and weakly cemented overburden. The temporal and spatial evolution laws of the strata subsidence and influence boundary are closely related to their depth, and their relationships evolve into the Boltzmann function and Boltzmann–parabolic function, respectively. The failure mode of the super-thick and weakly cemented overburden is ‘beam–arch shell–half arch shell’, and the failure boundary exhibits arch fractures.

STIFFNESS PARAMETERS OF VARIOUS MODIFICATIONS OF RING FIXATOR

Relevance. To date, there is no final solution to the theoretical and practical issues of the problem of external fixation in the treatment of long bone fractures.
 Objective. To determine the rational methods of completing ring retainer (RF) in the treatment of nonunions of the shin bones after fractures of long bones on the basis of clinical and experimental substantiation of the choice, taking into account the peculiarities of the assembly of the apparatus and the implementation of the connection "apparatus-fragments of non-union".
 Materials and methods. In the experimental part, Sawbones® synthetic composite bone was used. The rigidity of fixation of bone fragments of the RF of the wire-rod type was studied. We tested and compared 5 different options for fixation of bone fragments in RF. The samples were tested in 4 modes: compression along the axis of the bone; compression on the head of the bone; twisting; bending. The strength and deformation characteristics of the materials were determined with a maximum force of up to 5 kN using the TIRATEST-2151 universal testing machine. They chose the most optimal configuration of the RF. Then, in the clinical part, the clinical effectiveness of the optimal structures was evaluated based on the analysis of their use in 12 patients with non-union of the shin bones.
 Results. Optimal structures have been determined from the point of view of integral rigidity of the structure. The greatest rigidity was the RF system No. 3, in which 3 spokes are used: 2 of them are held at an angle, 1 - in the plane of the ring. In the case of an increase in the number of spokes, the stiffness of the system increased. When tested in compression along the axis of the bone, the stiffness of System No. 3 is 6.5% greater than that of System No. 2 and 12.5 % greater than System No. 1, in which only 2 spokes are used. Fixing the spokes at an angle to the plane of the ring also increases the rigidity of the system. When tested in compression along the axis of the bone, the stiffness of System No. 3 is 6.5 % greater than that of System No. 2. The stiffening rib affects the stiffness of the entire system. But the bend became the most sensitive. Flexural stiffness decreased by 23 % and compression by 8.5 %. Debris removal during bending increased by 1.5-1.8 times.
 Conclusion. The best indicators of fixation rigidity have options for the arrangement of spokes with a cross not only in the frontal, but also in the sagittal planes. The stability of the fixation of the rod is significantly increased by mounting the "stiffness triangle". The obtained clinical data indicate the promising application of improved ring fixators.