Empty Hole Research Articles

TÉCNICA ANALÍTICA PARA LA EVALUACIÓN DE LA CONTRIBUCIÓN A LA ENERGÍA MEDIA DE EXCITACIÓN DEL AGUA LÍQUIDA DEBIDO A LOS NIVELES DE EXCITACIÓN MOLECULARES

The mean excitation energy <I> is a fundamental quantity in radiation physics, concerning energy deposition in matter and absorbed dose analytical estimations for charged particles. The stopping of swift ions in different materials strongly depends on this parameter among others. This work intends to fill in part, an empty hole in the theory of stopping power: the need of analitically and theoretically assess the hIi-value for materials. The definition of the mean excitation energy using the dielectric response function is analytically integrable if the inelastic cross section parameters are known. Some dielectric models were studied, aimed at calculating the hIi-value for liquid water by theoretical means, reaching the conclusion that a decay of the order of ω −2 in frequency (energy) is needed as weak condition of the optical energy-loss function for the integrals to converge. Afterwards, the first four discrete excitation levels and the diffuse bands for water are treated in a fully analytical scheme, and further compared with numerical results, providing the contribution of these levels to hIi, with the aim of testing the proposed analytical model.

Use of cable ties in ilizarov frame assembly: A simple method to prevent wire-related injuries during postoperative care

Introduction Ilizarov ring fixators are usually applied for ailments such as open fractures, infected nonunions, malunions, growth disturbances, and angular deformities. Moreover, such conditions are often complicated by factors such as concomitant infection, compromised soft tissue cover, compromised vascularity, and disturbed metabolic milieu.[12] Treatment of such conditions often requires prolonged external fixations and pin site care plays a vital role in the prevention of infection, increasing longevity of fixation, keeping soft tissues supple, and increasing compliance to weight-bearing regimen.[3] Compliance to pin site care has prudent correlation with surgical outcome. Due to prolonged external fixation periods, usually home-based self-care of pin sites and frame assembly is prescribed to the patient rather than hospital-based care.[4] Problems with Conventional Methods Conventionally, tensioned Ilizarov wires outside wire fixation boltsare bent in loop shape and cut end is pushed under ring towards nearby empty hole.[5] We found such bending to be counterproductive for pin site care, frame maneuvers, and overall compliance of the patient. Multiple bending of wires in adjacent rings decreases available space for any pin site dressing and any correction maneuver. Their loose, sharp ends may potentially prick or scratch hands during any care maneuver. Such bends even impede any possible retensioning of wires in postoperative phase by grossly reducing stress endurance of wires and making them breakage prone [Figure 1a and b].Figure 1: (a) Conventional method of wire management with 2 bends and positioning under Ilizarov ring. (b) Conventional method critically decreases maneuverable space between Ilizarov rings and predisposes to wire-related injuries during frame careImprovisation and its Benefits After learning about practical difficulties being faced by patients in Ilizarov frame care and comprehending multiple feedbacks from patients, we started using nylon cable ties for fastening loose wire ends of Ilizarov wires with adjacent rings [Figure 2a and b].Figure 2: (a) Nylon cable ties – 4-inch length. (b) Clinical use of nylon cable ties with sharp ends of wires fastened to ring and allowing safe assess to pin sitesSuch wire fastenings neatly arrange all wires' ends parallel to ring either to its sides or its undersurface. It frees up maneuverable space between two rings and facilitates better pin site care. It gives practical benefit of saving hands from scratching protruding wire ends and decreasing wire-related injuries during pin site care. Since only one soft bend is given to any Ilizarov wire, it can be easily retensioned without risk of wire breakage during any possible retensioning. Better pin site care prevents local infections and increases comfort of patient. Nylon cable ties are easily available, cheap, and can be easily applied. Such fastening of ilizarov wires does not infringe on any biomechanical principle of Ilizarov methodology and positively contributes to important aspect of postoperative frame care in Ilizarov surgeries. Conclusion Nylon cable ties are easily available, cost-effective, simpler way to organize loose ends of Ilizarov wires which gives more maneuverable space, facilitates better pin site care, and prevents wire-related injuries. Use of cable ties positively influences follow-up care and overall surgical outcome. Financial support and sponsorship Nil. Conflicts of interest There are no conflicts of interest.

Bait-lamina test for assessment of polluted soils: Rough vs. Precise scales

The bait-lamina test is one of the few available methods for measuring the functional activity of soil animals, which was standardized for soil health assessment by ISO 18311. The bait consumption is measured visually on discrete scales. A two-point scale (0 or 1) is used more often, but the threshold for bait consumption scores varies from study to study: 1 point is assigned either to a hole that has been perforated to any extent, or to a hole that has been at least half perforated, or to a fully empty hole. Less often, a three-point scale (0, 0.5, and 1) or a five-point scale (0, 0.25, 0.5, 0.75, and 1) can be used. We investigated how much the use of different scales can influence statistical inferences.We have established that a point on a five-point scale is directly proportional to the proportion of the mass consumption of bait, so in this scale the value of feeding activity is an acceptable surrogate for the bait consumption rate. We analyzed outcomes of the bait-lamina test for 7 measurement rounds at the control area and an area highly polluted with metals near the copper smelter. We assumed the most accurate five-point scale to be the reference and compared it to six less precise scales with fewer points (two three-point and four two-point scales). The difference between the reference and such rough scales depends on the percentage of intermediate points (0.25, 0.5, and 0.75). It turned out that intermediate values are by no means rare (from 11% to 100% of all non-zero values), and in the polluted area they are almost twice as common as in the control area (66% and 28%, respectively). Because of this, the relative difference between the reference scale and rough scales is 2–4 times greater at the polluted site than at the control site. This can lead to a bias in the effect size index: for the rough scales, the log Response Ratio can either double or decrease by one-third relative to the reference scale. This increases the probability of type I and II errors in statistical hypothesis testing.Thus, the outcomes of the bait-lamina test are not invariant relative to the measuring procedure. The three-point scale and ISO 18311 two-point scale are the least biased relative to the reference scale. The use of other rough scales carries a risk of artifacts and should be avoided.

Investigation of Burn Cut Parameters and Model for One-Step Raise Excavation Based on Damage Evolution Mechanisms

One-step raise excavation with burn cut is a kind of technology which use the drilling and blasting method to excavate the raise quickly. Due to the limitation of the free surface in burn cut, determination of cut parameters such as the length of burden and diameters of empty hole and charge hole is important to achieve a good effect of cut blasting. Meanwhile, the choice of the cut model is also crucial to form a proper opening. In this study, a modified Holmquist-Johnson-Cook (HJC) model, in which the tension-compression damage model and tension-compression strain rate effect model are considered, is embedded in the LS-DYNA software to investigate the damage evolution of rock in cut blasting. A simplified numerical model of burn cut is built in the LS-DYNA. The numerical results indicate that there is a threshold value of the burden length to maximize the opening. The empty hole has the effect of transferring blasting energy, and the effect becomes more obvious with the increase of the hole size. Moreover, the linear charge density of the prime cut hole can affect the compression and tension damage. Further, the comparison among four typical burn cut models are conducted based on numerical results. It demonstrates that triangular prism cut and doliform cut, which have more empty holes arrangement surrounding the prime cut hole, are better than spiral cut and diamond cut that with less empty holes locating one side of the prime cut hole in terms of energy efficiency and damage zone control.

Study on crack propagation of the CO2 presplitting blasting empty hole effect in coal seam

AbstractCO2 presplitting blasting is an effective method to increase coal seams permeability and improve gas drainage efficiency. During the blasting process, the empty holes in the coal and rock mass have a significant effect on crack growth. In the experiment, a sample containing empty holes was used for CO2 presplitting blasting. The VIC‐3D was used to observe the change in the surface displacement of the sample; and the amplitude of the wave during the blasting process was collected using ultrasonic waves. Here, we calculated the attenuation coefficient α, analyzed the internal crack damage of the coal and rock mass, and compared the LS‐DYNA simulation results to analyze the empty hole effect on the crack growth of the coal and rock mass. The results show that: (a) radial tensile stress is generated due to the superposition of compression waves and reflected waves during blasting, resulting in an approximately straight main crack channel between the blast hole and the empty hole; (b) When both the stress and the attenuation coefficient reach their peaks, a main crack is formed and the most severe damage occurs inside the coal and rock mass; (c) the main crack channel was formed at 0.13 seconds, and the energy consumption reached the peak at 0.18 seconds, the negative linear correlation between energy and stress was obtained. Therefore, the empty hole effect provides a good guide for the crack propagation of the coal and rock mass and provides a new experimental scheme for increasing the permeability of coal seams.

Influence of Charge Hole Spacing on the Crack Propagation Behavior under the Effect of Empty‐Hole Directional Blasting

In order to explore the reasonable spacing of charge holes in empty‐hole directional blasting, based on the action mechanism of empty‐hole directional blasting, the influence of charge hole spacing on crack propagation is studied, the calculation formula of charge hole spacing is deduced, and the blasting excavation process in Shijiazhuang South Ring Expressway Tunnel is simulated by finite element software. The results show that by setting empty holes on both sides of the charge holes in the peripheral blasting, the guiding cracks can be formed in the connecting direction between the empty hole and the charge hole, the propagation of cracks in other directions can be suppressed, and the spacing of charge holes can be enlarged. Reasonable charge hole spacing is very important to realize the effect of empty‐hole directional blasting; the spacing is small, the rock will be overbroken, and the utilization ratio of explosives is reduced; large spacing, the guiding effect of empty holes is weak, and the effective directional cracks cannot be formed. The spacing between charge holes is closely related to the mechanical properties of rock, detonation parameters of explosive, and aperture of the charge hole and empty hole. According to the simulation results of crack propagation in different spacing, the blasting performance is the best when the charge hole spacing is 800–1000 mm, which is completely consistent with the theoretical calculation result of charge hole spacing 948 mm.

Gob‐Side Entry Retaining Technology with Advanced Empty Hole Butterfly‐Shaped Weakening in Three‐Soft Coal Seam in China

China has a large number of coal resources in “three‐soft” geological conditions. The roof of these coal seams is soft and has low strength. Under this condition, gob‐side entry retaining can be carried out under the guidance of roof leading holes to achieve the goal of nonblasting roof cutting and roadway retaining. In this paper, the technology of void weakening, roof cutting, and pressure relief along gob retaining roadway is investigated. The force model of void is established, and the stress concentration of void and interference effect of stress superposition between holes is simulated by COMSOL numerical simulation software. The influence of different factors on stress distribution surrounding round holes is then studied by orthogonal experiment. The results show that the distribution of the plastic zone in circular holes varies with the lateral pressure ratio. With the increase of lateral pressure ratio, the shape of the plastic zone will gradually change from circular to elliptical, and eventually to butterfly, and the size of the butterfly plastic zone is positively correlated with the aperture. On this basis, the technology of “empty hole weakening + dense pillar” roof cutting and gob‐side entry retaining is presented. The methodology is then applied to an auxiliary air intake roadway of 21309 working face in the Xiangshan Mine. Industrial testing of three‐soft seams using advanced empty hole without blasting roof cutting and gob‐side entry retaining is then successfully carried out. The advanced weakening hole replaces the original blasting cutting technology, omits the blasting cutting link in the existing gob‐side entry retaining technology, shortens the retaining time, solves the problems such as large coal dust concentration and bad construction environment in the blasting process, and provides scientific theoretical basis for the gob‐side entry retaining technology without blasting under such geological conditions.

Experimental Study of the Dynamic Tensile Mechanical Properties of a Coal Sandstone Disc with a Central Hole

Deep mine rocks are often subjected to rock burst induced by dynamic load. The existence of initial holes will reduce the mechanical properties of rocks and affect the stability and safety of the tunnel excavating. In order to study the effect of the ratios of inner and outer diameter on disc specimen dynamic mechanical properties and failure modes, we use cylindrical sandstone specimens of Φ50 × 25 mm to process center holes of different diameters, and a series of dynamic splitting test were carried out with a system of split Hopkinson pressure bar (SHPB) with the diameter of Φ50 mm when the pressure is 0.15 MPa, 0.3 MPa, and 0.5 MPa. The results show that (1) the dynamic tensile stress‐time‐history curve exhibited double peak phenomena, and the second peak value is less than the first peak value, (2) the dynamic tensile stress peaks decrease nonlinearly with the increasing of the ratios of inner and outer diameter, and the dependence is more obvious when the pressure is higher, and (3) there is a tensile crack running along the loading direction in the failure modes of the five samples with the ratio of inner to outer diameter under three kinds of impact pressure. Under the same impact pressure, when the ratio of inner diameter to outer diameter is greater than the critical ratio of inner diameter to outer diameter, there is an obvious empty hole effect; that is, the sample develops secondary tensile cracks that develop from the upper and lower ends of the pore disc to the center of the inner hole. With the increase of the ratio of inner diameter to outer diameter, the width of the penetration crack increases. With the increase of impact pressure, the critical ratio of inner diameter to outer diameter decreases gradually. The research results have certain significance for understanding the mechanical properties of porous rocks.

Clinical outcomes of treatment with locking compression plates for distal femoral fractures in a retrospective cohort

BackgroundPlate fixation is one of the standard surgical treatments for distal femoral fractures. There are few reports on the relationship between the screw position and bone union when fixing by the bridging plate (relative stability) method.MethodsThis retrospective study included 71 distal femoral fractures of 70 patients who were treated with the locking compression plate for distal femur (DePuy Synthes Co., Ltd, New Brunswick, CA, USA). The following measurements were evaluated and analyzed: (1) bone union rate, (2) bridge span length (distance between screws across the fracture), (3) plate span ratio (plate length/bone fracture length), (4) number of empty holes (number of screw holes not inserted around the fracture), and (5) medial fracture distance (bone fracture distance on the medial side of the distal femur). Patient demographics (age), comorbidities (smoking, diabetes, chronic steroid use, dialysis), and injury characteristics (AO type, open fracture, infection) were obtained for all participants. Univariate analysis was performed on them.ResultsOf 71 fractures, 26 fractures were simple fractures, 45 fractures were comminuted fractures, and 7 fractures resulted in non-union. Non-union rate was significantly higher in comminuted fractures with bone medial fracture distance exceeding 5 mm.Non-union was founded in simple fractures with bone medial fracture distance exceeding 2 mm, but not significant (p = 0.06). In cases with simple fractures, one non-union case had one empty hole and one non-union case had four empty holes, whereas in cases with comminuted fractures, five non-union cases had two more empty holes.ConclusionsWe concluded that bone fragment distance between fracture fragments is more important than bridge span length of the fracture site and the number of empty holes. Smoking and medial fracture distance are prognostic risk factors of nonunion in distal femoral fractures treated with LCP as bridging plate.

Bouba and Kiki inside objects: Sound-shape correspondence for objects with a hole

Visual holes (cutouts in a surface) have recently intrigued vision scientists as interesting and useful stimuli in the studies of shape perception and as a perceptual conundrum regarding figure/ground organization. Adopting the Bouba/Kiki paradigm, this study addressed a controversial issue of whether the perceived shape of a closed region alters when the region changes from a solid object to an empty hole, in a more direct manner than previous studies did. Observers were presented with two doughnut-like cardboard cutouts, one with a flower-shaped hole and the other with a star-shaped hole, and then matched them with two nonsense words. The curvature profile of the hole boundary was manipulated so that the shape of the interior region (i.e., a hole) and that of the exterior region (i.e., material edges) give rise to opposite shape impressions (i.e., one rounded and the other spiky). The results of Experiment 1 revealed that shape-name matching for holed objects is based on the interior shapes of holes, but not those of materially defined inner edges. The following three experiments replicated the same pattern of results even when holes appeared like oral apertures in animal character faces (Experiments 2–3) and when they were irregular, non-symmetric, and low in semantic association with familiar real-world objects (Experiment 4). Lastly, Experiment 5 showed that shape-name matching for “C”-shaped, negative-part stimuli is also interior-shape-based if the opening of the interior region is relatively small. These findings suggest that the interior shapes of holes are automatically accessible. I conclude with a discussion of my hypothesis that the only global-level, unitary shape representation of a bounded region of a single connected surface is that of the interior region for both objects and holes, imposing an important constraint in visual shape processing.

Numerical simulation of the effect of empty hole between adjacent blast holes in the perforation process of blasting

Numerical simulation of the effect of empty hole between adjacent blast holes in the perforation process of blasting

Bouba and Kiki inside objects: Sound-shape correspondence for objects with a hole

Visual holes (cutouts in a surface) have recently intrigued vision scientists as interesting and useful stimuli in the studies of shape perception and as a perceptual conundrum regarding figure/ground organization. Adopting the Bouba/Kiki paradigm, this study addressed a controversial issue of whether the perceived shape of a closed region alters when the region changes from a solid object to an empty hole, in a more direct manner than previous studies did. Observers were presented with two doughnut-like cardboard cutouts, one with a flower-shaped hole and the other with a star-shaped hole, and then matched them with two nonsense words. The curvature profile of the hole boundary was manipulated so that the shape of the interior region (i.e., a hole) and that of the exterior region (i.e., material edges) give rise to opposite shape impressions (i.e., one rounded and the other spiky). The results of Experiment 1 revealed that shape-name matching for holed objects is based on the interior shapes of holes, but not those of materially defined inner edges. The following three experiments replicated the same pattern of results even when holes appeared like oral apertures in animal character faces (Experiments 2-3) and when they were irregular, non-symmetric, and low in semantic association with familiar real-world objects (Experiment 4). Lastly, Experiment 5 showed that shape-name matching for C-shaped, negative-part stimuli is also interior-shape-based if the opening of the interior region is relatively small. These findings suggest that the interior shapes of holes are automatically accessible. I conclude with a discussion of my hypothesis that the only global-level, unitary shape representation of a bounded region of a single connected surface is that of the interior region for both objects and holes, imposing an important constraint in visual shape processing.

Use of Micro X-ray Computed Tomography with Phosphotungstic Acid Preparation to Visualize Human Fibromuscular Tissue.

Manual dissection and histological observation are common methods used to investigate human tissues. However, manual dissection can damage delicate structureswhile processing and histological observation provide limited information through cross-sectional imaging. Micro X-ray computed tomography (microCT) is an effective tool for obtaining three-dimensional information without damaging specimens. However, it shows limited efficiency in differentiating soft tissue parts. Use of contrast-enhancing agents, like phosphotungstic acid (PTA), can solve this problem by improving soft tissue contrast. We implemented microCT with PTA to investigate the human orbicularis retaining ligament (ORL), which is a delicate structure in the orbit area. In this method, harvested specimens are fixed in formalin, dehydrated in serial ethanol solutions, and stained with a PTA solution. After staining, microCT scanning, 3D reconstruction, and analysis are performed. Skin, ligaments, and muscles can be clearly visualized using this method. The specimen size and duration of staining are essential features of the method. The suitable specimen thickness was about 5-7 mm, above which the process was slowed, and the optimum duration was 5-7 days, below which an empty hole in the central area occasionally occurred. To maintain the location and direction of small pieces during cutting, sewing on the same region of each part is recommended. Furthermore, preliminary analyses of the anatomical structure are needed to correctly identify each piece. Parafilm can be used to prevent drying, but care should be taken to prevent specimen distortion. Our multidirectional observation showed that the ORL is composed of a multilayered meshwork of continuous plates, rather than thread-like fibers, as reported previously. These results suggest that microCT scanning with PTA is useful for examining specific compartments within complex structures of human tissue. It may be helpful in the analyses of cancer tissues, nerve tissues, and various organs, like the heart and liver.

Black Hole Entropy, Verlinde’s Entropy Gravity Proposal and Unruh Formula in Projection Gravitation

In the projection gravitation theory, there exists a merging model of black hole formation. Particles that meet the merging condition can be combined together to form a black hole. The essence of a black hole is an empty hole. A black hole is not a single object, it is a composite particles system. From this model, the black hole entropy formula can be easily derived out. This merging condition is equivalent to a temperature condition. From this black hole model, we can easily derive out the Verlinde’s entropy gravity proposal formula and the Unruh formula. It is also proved that the Verlinde’s entropy gravity proposal formula and the Unruh formula are actually equivalent. The Verlinde’s entropy gravity proposal theory is not universally correct, but only in special circumstances. The gravitational acceleration produced by an object has a maximum value. Projection gravitation theory has important research value.

Stress concentration factor near loaded hole contacting with the bolt in the monolayer of orthotropic composite material

Purpose. To suggest a method to predict the stress concentration factor near loaded hole contacting with the bolt in the monolayer of orthotropic composite material to be independent of difficult calculations. And to verify the factor with use results of numerical calculations using the finite element method in contact formulation. Methodology. The analysis of known outcomes in the literature is carried out. Several assumptions have been formulated about the changes of stress concentration factor depending on the ratio of the hole diameter to the plate width, as well as on orthotropy in the plate material. Assumptions are confirmed by calculated results, graphs. The finite element method was used. Results. A formula is proposed that predicts the stress concentration factor without carrying out difficult calculations of contact problems using known approximations for an isotropic material and the Lekhnitsky-Soldatov solution for a stretched orthotropic infinite plate with an empty hole. Using the results of numerical calculations of contact boundary problems with the finite element method the proposed formula was verified, its good accuracy was shown in the practically applicable range of the ratio of the hole diameter to the plate width. Originality. A four-step method is developed - simple formulas that allow rapid prediction of the stress concentration factor near loaded hole contacting with the bolt in a monolayer of orthotropic composite material using only of the elastic characteristics of the plate material, proven approximations and simple solutions.

Bone remodeling effect of a chitosan and calcium phosphate-based composite.

Chitosan is a biocompatible polymer that has been widely studied for tissue engineering purposes. The aim of this research was to assess bone regenerative properties of an injectable chitosan and calcium phosphate-based composite and identify optimal degree of deacetylation (%DDA) of the chitosan polymer. Drill holes were generated on the left side of a mandible in Sprague-Dawley rats, and the hole was either left empty or filled with the implant. The animals were sacrificed at several time points after surgery (7–22 days) and bone was investigated using micro-CT and histology. No significant new bone formation was observed in the implants themselves at any time points. However, substantial new bone formation was observed in the rat mandible further away from the drill hole. Morphological changes indicating bone formation were found in specimens explanted on Day 7 in animals that received implant. Similar bone formation pattern was seen in control animals with an empty drill hole at later time points but not to the same extent. A second experiment was performed to examine if the %DDA of the chitosan polymer influenced the bone remodeling response. The results suggest that chitosan polymers with %DDA between 50 and 70% enhance the natural bone remodeling mechanism.

The “Sleeper” plate: A technical note

Context: A tension band plate (TBP) for guided growth of angular deformity is typically removed after the deformity is corrected to prevent overcorrection. After TBP removal, rebound deformity may occur, necessitating reinsertion of a new TBP. Aims: This study aims to describe a minimally invasive technique for partial removal of TBP to deactivate the TBP when correction is achieved. The technique also allows minimally invasive reactivation of the construct when desired. Settings and Design: This is retrospective case series study. Subjects and Methods: The surgery consists of removing the metaphyseal screw only and keeping the plate and the epiphyseal screw. The procedure is done through a 1-cm incision with fluoroscopy. The metaphyseal edge of the plate is elevated off the bone to break the seal between it and the bone, to prevent tethering. Bone wax is injected in the empty plate hole to prevent bone ingrowth, as this could also cause re-tethering. In case of a subsequent rebound deformity, the metaphyseal screw may be re-inserted percutaneously to reactivate (“wake-up”) the “sleeper plate”. Statistical Analysis Used: Descriptive analysis. Results: The sleeper plate technique was done in eight patients (three males and five females). Four patients had genu valgum and four had genu varum. Mean age at surgery was 11 years (7–14 years). Metaphyseal screw removal was done in a mean period of 14 months (range from 7.4 to 22 months) after the index procedure. Rebound of the deformity happened in three patients and required plate reactivation by reinsertion of the metaphyseal screw. Conclusion: The sleeper plate technique is a minimally invasive procedure and can be an alternative to the removal of the whole TBP construct if the patient is skeletally immature with a risk of deformity rebound. Level of Evidence: IV

Key Blasting Parameters for Deep‐Hole Excavation in an Underground Tunnel of Phosphorite Mine

Ever increasing mine production capacity and mechanized operations enable advanced drilling equipment to be widely adopted in underground mines. In order to achieve satisfactory blasting performance in tunnel advance, there is a critical need to optimize the blasting technique to match the large deep‐hole drilling capability. In this study, through theoretical analysis of tunnel blasting, the layout of cutting holes was found to be the key factor controlling the blasting performance. The deep‐hole cutting effect was first investigated by analyzing the influence of the free surface of a hollow hole using the fluid‐structure interaction modeling method in ANSYS/LS‐DYNA. Then the rock dynamic evolution processes of blasting using a double‐cavity grooving and a four‐cavity grooving were compared and analyzed towards an understanding of the influence of the spacing and layout of cutting holes on the blasting performance. The comparison results show that four empty hole cut layouts yield larger effective free surface than that of the two empty hole cut layouts. This is because larger compensation space for breaking of rock and expansion of gas is more conducive to improving the energy utilization rate of explosives and thus improving the blasting performance and the footage of cyclic blasting. The results indicated that the blasting performance can be improved by reserving reasonable compensation space in the grooving area.

Empty Hole Entropy and Black Hole Entropy in Gravitation

In the projection gravitation theory, the center of a gravitational source is an empty hole, not black hole. The gravitation can be understood as a new kind of Lorentz symmetry breaking. Multiple empty holes can merge together to form a large empty hole. So the empty holes form a thermodynamic system. So the empty hole has thermodynamic properties, such as entropy and temperature. We discuss two models of empty holes merging. The first model derives out a result that empty hole entropy is proportional to the radius of the empty hole. The second model can simply derive out the formula of black hole entropy in General Relativity. The black hole entropy is just a special case in empty hole. Two models get the same result that the temperature of the empty hole is inversely proportional to its radius. The empty hole has a new statistical distribution mode, that is the empty hole distribution. In the new projection gravitation, the Planck energy and the Planck length have a new and different physical meaning. The two constants represent a special kind of association relationship that has not yet been understood by humans.

A study of cut blasting for one-step raise excavation based on numerical simulation and field blast tests

Over the past several decades, raise excavation has been widely employed in underground mining, civil engineering and military engineering. One-step raise excavation with burn cuts, where all the boreholes are pre-drilled and detonated at one time and no workers need to be underneath the freshly blasted and dangerous ground, is an important and promising method in raise excavation. Cut parameters, especially the parameters of prime cut which used empty hole as a free surface and swelling space, have significant influence on the effect of raise formed. In this study, two small-scale experimental methods, spiral hole spacing method and observation hole method, are designed to determine the prime cut parameters such as hole spacing (L), stemming length (Ls1, Ls2) and air deck length (La) which are normally determined by empirical formula. In order to study the feasibility of the two methods, numerical analysis and experimental tests are conducted in V zone of Sandaozhuang molybdenum mine (SMM), in which there are large numbers of underground goafs need to be controlled by filled raise. The Riedel–Hiermaier–Thoma (RHT) material model, which considers compression damage and tension damage effect under blasting loading, is employed in the LS-DYNA software to study the rock damage zone. Meanwhile, the field tests are carried out according to the two small-scale experimental methods. The comparison results show that the damage zone of numerical simulation has a good agreement with the experimental data. Further, the optimal prime cut parameters obtained from experimental tests are applied in one-step filled-raise excavation, and a 23 m raise that meets the design requirements is formed through the proposed technology. The results indicate that these cut parameters determined by the small-scale experiments are suited for one-step raise excavation. This study can provide two simple field experiments to determine the important prime cut parameters of one-step raise excavation.