Effect of thermal aging on the transport and acoustic properties of partially reticulated polyurethane foams.

This study aims to investigate the acoustic effects of thermal aging on partially reticulated polyurethane (PU) foam. An accelerated test was performed under appropriate test conditions as determined by thermal analyses of the material. Measurements of the absorption coefficient showed that the performance of the partially reticulated PU foam can be significantly reduced by thermal aging. The transport parameters were evaluated to analyze the origin of this change in the absorption behavior. Sensitivity analyses revealed that a decrease in the static airflow resistivity had the greatest effect in terms of reducing the absorption coefficient owing to thermal aging. In addition, observation and characterization of the microstructure of the aged foam to determine the root cause of this acoustic degradation indicated that heat-induced damage to the membrane was the most important factor. To verify this assertion, a periodic unit cell model that mimicked the topology of the cellular structure was constructed, and the mechanism responsible for the change in the acoustic behavior was simulated. The results presented herein can be used as durability guidelines for maintaining the performances of partially reticulated PU foams that are employed in high-temperature environments.

Convolutional neural networks for estimating transport parameters of fibrous materials based on micro-computerized tomography images.

This study proposes a method for estimating the transport parameters of fibrous materials from x-ray micro-computed tomography (CT) images using convolutional neural networks (CNNs). Two-dimensional (2-D) micro-CT images and numerically obtained transport parameters were used to train the CNNs; Stokes flow and potential flow were used to numerically obtain the transport parameters using geometrical models extracted from the raw CT images. Then, analogously to constructing a three-dimensional image of the fibrous material by stacking the 2-D slice images, the volumetric transport parameters of the fibrous materials were calculated using the parameters of each 2-D image predicted by the trained CNN models. The transport parameters of the fibrous volume predicted by the CNN models showed good agreement with the measured values. In addition, the sound absorption coefficient was calculated by applying both the predicted and measured transport parameters to the semi-phenomenological sound propagation model and compared with the measured sound absorption coefficient. The results of the study confirm the feasibility of predicting transport parameters of fibrous materials using a neural network model based on raw micro-CT images.

Estimation and uncertainty analysis of fluid-acoustic parameters of porous materials using microstructural properties.

This study quantified the microstructure of polyurethane foams and elucidated its relationship to fluid-acoustic parameters. The complex morphology derived from the three-dimensional images obtained by micro-computed tomography was analyzed using digital image processing and represented by a pore network model (PNM) and a distance map model. The PNM describes the fluid phase of a porous medium with equivalent spherical pores and circular throats, whereas the distance map model describes the solid phase with the average frame thickness. The porous materials were then modeled by six representative microstructural parameters that describe the geometry and topology of the fluid and solid phases. These parameters were pore radius, throat radius, distance between adjacent pores, coordination number, pore inclination angle, and frame thickness. Semi-phenomenological and empirical approaches were proposed to relate the microstructural properties to the fluid-acoustic parameters. These models effectively described the acoustic parameters and sound absorption performance of six different polyurethane foams. Since the representative microstructural parameters were obtained from small sample volumes of a heterogeneous material, notable variations were observed across different regions of the sample. Hence, this study quantified the effect of the uncertainty in each microstructural parameter on the resulting acoustic parameters using global sensitivity analysis.

Comparison of abdominal and perineal procedures for complete rectal prolapse: an analysis of 104 patients.

PURPOSE: Selecting the best surgical approach for treating complete rectal prolapse involves comparing the operative and functional outcomes of the procedures. The aims of this study were to evaluate and compare the operative and functional outcomes of abdominal and perineal surgical procedures for patients with complete rectal prolapse. METHODS: A retrospective study of patients with complete rectal prolapse who had operations at a tertiary referral hospital and a university hospital between March 1990 and May 2011 was conducted. Patients were classified according to the type of operation: abdominal procedure (AP) (n = 64) or perineal procedure (PP) (n = 40). The operative outcomes and functional results were assessed. RESULTS: The AP group had the younger and more men than the PP group. The AP group had longer operation times than the PP group (165 minutes vs. 70 minutes; P = 0.001) and longer hospital stays (10 days vs. 7 days; P = 0.001), but a lower overall recurrence rate (6.3% vs. 15.0%; P = 0.14). The overall rate of the major complication was similar in the both groups (10.9% vs. 6.8%; P = 0.47). The patients in the AP group complained more frequently of constipation than of incontinence, conversely, in the PP group of incontinence than of constipation. CONCLUSION: The two approaches for treating complete rectal prolapse did not differ with regard to postoperative morbidity, but the overall recurrence tended to occur frequently among patients in the PP group. Functional results after each surgical approach need to be considered for the selection of procedure.

A comparative study of bone formation following grafting with different ratios of particle dentin and tricalcium phosphate combinations.

This study aimed to evaluate the bone regeneration relative to tooth powder and tricalcium phosphate (TCP) mixing ratios using the rabbit cranium defect model. The tooth powder was mixed with TCP in 1:1, 3:1, and 1:3 ratios, and the different ratios were implanted in the rabbit cranium defect for 4 and 8 weeks. Powders crystal structure evaluated using scanning electron microscopy (SEM), attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR), and new bone formation (NBF) was analyzed using micro-computed tomography (CT) and histologic examination. NBF in the control group was restricted to the defect margins. More NBF was observed around the defect margins in the experimental groups compared with the control group. Specifically, active NBF was identified around the implant materials of the centrifugal part of the defect and defect margins in the 3:1 tooth powder: TCP group. Our results suggested that tooth powder and TCP may be useful in bone regeneration.

Effect of platelet-rich plasma and platelet-rich fibrin on peri-implant bone defects in dogs.

The purpose of this study was to evaluate the effect of tooth ash and platelet-rich plasma (PRP), and platelet-rich fibrin (PRF) grafts into bone defects around implants on bone formation. Six adult dogs were used as experimental subjects. Graft materials were used to create a particulate material. Forty-eight tapered-type implants, 3.7 mm in diameter, 10 mm in length, and with surface treated with hydroxyapatite (HA) coating, were used as implant fixtures. Using a trephine bur, four bone defects were formed and implants were placed in the femurs of the adult dogs. Bone grafts were not performed in the control group. Tooth ash was grafted into the defects in group 1. In group 2, a mixture of tooth ash and PRP (1:1 ratio by volume) was grafted into the defects. In group 3, a mixture of tooth ash and PRF (ratio of 1:1) was grafted in the defect area. Animals were sacrificed after 4 or 8 weeks. Based on histopathological examination, the amount and rate of new bone formation were evaluated. Histomorphometric examination revealed that the rate of new bone formation in group 3 of the 4-week group was significantly higher than that in the control group. In addition, in the 8-week group, a significant increase in new bone formation was confirmed in group 3. In this study, a bone graft method using a mixture of tooth ash and PRF was found to increase new bone formation compared to the method using PRP. In addition, it was confirmed that this effect was more prominent in the initial stage of the bone graft.