Evaluation of formulations for predicting the shear strength of concrete filled circular holes in steel plates

Since the development of perforated plate shear connectors, different formulations have been proposed to predict their shear strength. Most of these formulations were derived from standard push-tests on multiple concrete filled holes (CFH) specimens simulating specific steel-concrete composite beam applications. Aiming at a more general application of these connectors in composite structures and the understanding of the physical and geometric parameters that influence their shear strength, the present work evaluated the use of 12 different formulations to predict 92 test results of single-hole specimens extracted from the literature. Such tests were chosen because the single-hole configuration allows better isolation of the connection behavior which facilitates comparative analysis. The predictions were statistically evaluated, and it was considered that the best formulations were those that showed lower scatter of data and a correction factor closer to one. Also, it was investigated if the individual terms that constitute the formulations adequately describe or show relation to the mechanics that govern the connection. It was verified that the best statistically rated formulations were also the ones showing clearer relation to the connector mechanical behavior. Among the evaluated formulations, three were significantly better than the others for strength prediction, however, it was noted that they can be further improved by considering the influence of concrete confinement and plate thickness on the hole’s strength.

Dynamics of string-like states of a hole in a quantum antiferromagnet: A diagrammatic Monte Carlo simulation

The dynamics of a hole motion in a quantum antiferromagnet has been studied in the past three decade because of its relationship to models related to superconductivity in cuprates. The same problem has received significant attention because of its connection to very recent experiments of the dynamics of ultra-cold atoms in optical lattices where models of strongly correlated electrons can be simulated. In this paper we apply the diagrammatic Monte Carlo method to calculate the single-hole Green's function in the t-J model, where the $J$ term is linearized, in a wide range of imaginary-time with the aim to examine the polaron formation and in particular the details of the contribution of the so-called {\it string excitations} found in such recent experiments. We calculate the single-hole spectral function by analytic continuation from imaginary to real time and study the various aspects that constitute the string picture, such as, the energy-momentum dependence of the main quasiparticle peak and its residue, the {\it internal excitations} of the string which appear as multiple peaks in the spectral function as well as their momentum dependence. We find that the earlier analysis of the spectral function based on a mobile-hole connected with a string of overturn spins and the contribution of the internal string excitations as obtained from the non-crossing approximation is accurate.

Mechanism of Hard-Roof Rock Burst Control by the Deep-Hole Blasting: Numerical Study Based on Particle Flow

In underground coal mines, the deep-hole blasting (DHB) technology is generally adopted for thick hard-roof control. This technology uses the energy released by explosives to weaken the energy storage capacity of hard roof so as to prevent hard-roof rock burst disasters. In this paper, a numerical simulation model of roof DHB was established based on particle flow and the damage range of single-hole blasting with concentrated cylindrical charge was studied. The temporal and spatial evolutions of overlying strata, the distribution of the force chain structure, and the working resistance of hydraulic pressure in the mining process before and after the application of DHB were contrastively analyzed. The following beneficial conclusions were drawn. The blasting-induced single-hole damage range is generally characterized by annular zoning. After the application of DHB, overall the collapse morphology of the key strata in the mining process changes from long-distance instantaneous slipping instability to stratified short-arm stepped synergistic subsidence. The density and strength of force chains in the overburden are notably reduced; the peak value of compressive force chain strength in the key strata in the mining process falls by 17.85% as a result of DHB. The monitoring results of the working resistance of hydraulic support reveal that the DHB technology can effectively shorten the step distance of periodic weighting and reduce the variation amplitude of overburden load during weighting. In summary, the mechanism of hard-roof rock burst control by DHB is reflected by both static load reduction and dynamic load reaction.

Study on the technology of enhancing permeability by deep hole presplitting blasting in Sanyuan coal mine

To reduce gas disasters in low permeability and high gas coal seams and improve gas predrainage efficiency, conventional deep hole presplitting blasting permeability increasing technology was refined and perfected. The damage degree of coal and rock blasting was quantitatively evaluated by using the value range of the damage variable D. According to the actual field test parameters of coal seam #3 in the Sanyuan coal mine, Dlim = 0.81 ~ 1.0 was the coal rock crushing area, Dlim = 0.19 ~ 0.81 was the coal rock crack area, and Dlim = 0 ~ 0.19 was the coal rock disturbance area. The blasting models under different blasting parameters were established by ANSYS/LS-DYNA software. The influence radius of single-hole blasting was 3.1 m, the hole diameter of double-hole blasting was 113 mm, the hole spacing was 5.5 m, and the delayed blasting time was 25 ms. According to the numerical simulation results, the determined parameters were tested on the working face of the 1312 transportation roadway in coal seam #3 of the Sanyuan coal mine. The results show that after blasting, the permeability of the original coal seam was increased by more than 30 times, the gas concentration was increased by 2.16 times, and the single hole purity and mixing volume were increased by 4.73 and 4.27 times, respectively. The positive effects of deep hole presplitting blasting permeability enhancement technology on the pressure relief and permeability enhancement of a low pressure and high gas coal seam were determined.

Improved Sound Absorption Properties in Polyurethane Foams by the Inclusion of Al2O3 Nanoparticles

At present, the scale of China’s power grid is becoming larger and larger, and the control of low-frequency noise in substations (especially for transformers) is very important. The sound-absorbing materials have become one of the important ways to control low-frequency noise. The single polyurethane material cannot satisfy the requirements for reducing low-frequency noise, so it is very necessary to study its composite with other materials. In the paper, the flexible polyurethane foam and Al2O3 nanoparticle composites were obtained by the impregnation method. The method was simple, safe, and easy to control. The morphology and sound absorption coefficient of the foam materials before and after filling were analyzed. Single-hole acoustic cavity models of PU and Al2O3-PU composite were established through the finite element. The absorption and dissipation process of sound pressure for single hole was studied to understand the energy dissipation process. Meanwhile, through studying acoustic energy storage and acoustic energy dissipation, the loss factor of a single hole was obtained, which can predict the change rule of the sound absorption coefficient for PU foam and Al2O3-PU.

Application of Single-Hole Laparoscopy and Sentinel Lymph Node Imaging in Early Endometrial Carcinoma in Special Population

Aim. To explore the clinical efficacy of single-hole laparoscopy combined with sentinel lymph node imaging in the treatment of early endometrial carcinoma in a special population. Method. A retrospective analysis was made on the clinicopathological data of 8 patients with early endometrial carcinoma who underwent extra fascial total hysterectomy plus double adnexal resection and pelvic sentinel lymphadenectomy by transumbilical single-hole laparoscopy in Jiaxing Maternal and Child Health Hospital from Apr. 2019 to Apr. 2021. Result. Single-hole laparoscopy and sentinel lymph node imaging were successfully performed in 8 patients with early endometrial carcinoma, and none of them was converted to porous or laparotomy. At the same time, all 8 patients have a high demand for body shape. All FIGO pathological grades were grade I before operation. Operation time is 160.87 ± 40.61 min , amount of bleeding is 68.75 ± 12.31 ml , the catheter was removed for 2 days, anal exhaust time is 30.13 ± 10.99 h , and postoperative hospital stay is 4.00 ± 1.07 d . There was no related organ injury during the operation, no case of blood transfusion, or case of poor wound healing. The evaluation of postoperative satisfaction was very satisfactory. Conclusion. The application of single-hole laparoscopy and sentinel lymph node imaging in the treatment of early endometrial carcinoma in the special population should be safe and feasible with high satisfaction.