30 research outputs found

    Cone beam computed tomography evaluation of ponticulus posticus in patients with cleft lip and palate: a retrospective radio-anatomic study

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    Background: Ponticulus posticus (PP) is an abnormal bony bridge on the atlas. It plays a significant role in patients undergoing C1 lateral mass screw procedure. Patients with cleft lip and palate (CLP) have higher risk than patients in general population for the appearance of cervical vertebral anomalies. The purpose of the this study was twofold: to determine the prevalence and characteristics of PP in patients with CLP, and to compare the findings with patients in general population using cone beam computed tomography. Materials and methods: Cone beam computed tomography images from 54 individuals who had undergone surgical repair of cleft lip and/or palate were analysed as the study group. For comparison purposes a control group was randomly selected from 108 patients and matched with the CLP subjects. Results: Although 12 of the 54 (22.3%) patients with surgically repaired cleft lip and/or palate in the study group were identified to have PP, only 10 of the 108 (9.2%) patients in the control group had PP. The distribution of the presence of PP between the groups was statistically significant. Conclusions: Ponticulus posticus is an important anomaly and the presence of PP is important for patients. PP can have clinical significance in cervical spine surgery as this study has indicated that the likelihood of encountering PP is higher in patients with CLP. We suggest that PP should be taken into account prior to cervical vertebral surgery in patients with CLP. (Folia Morphol 2018; 77, 1: 72–78)

    Micro-abrasion wear behavior of thermal-spray-coated steel tooth drill bits

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    Wear behavior of four kinds of thermally sprayed coatings on steel tooth drill bits have been investigated by micro-abrasion wear test. The fixed ball micro abrasion wear test was applied for bare substrate and for thermal sprayed substrate of each sample. SiC and Al₂O₃ abrasive powders with grain size of 5 μm were used in the abrasion experiments. Ball rotational speed values of 140 rpm and applied loads of 1, 2 and 3 N were used. Experimental results show that the wear mechanisms of the coatings are micro-grooving and micro-rolling. Application of the coatings was found to have an influence on the wear mechanism of the samples. The results also indicate that wear resistance of thermally sprayed coatings can be correlated to porosity, hardness, plasticity, toughness, and cohesion properties of the coatings. In addition, wear resistance of the coated samples had increased in accordance with the increasing coating thickness

    A new coherent infrared image converter

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    A new model of incoherent-to-coherent IR image converter based on a GaAs photoconductor (PC) joined to an electro-optic (EO) Bi12SiO20 crystal has been analyzed theoretically and experimentally. The possibility of field transfer from the PC to the EO crystal under the infrared (IR) radiation sufficient for realization of the EO (Pockels) effect in the EO crystal was assessed. Based on the electric field parameters and the parameters of the PC and EO crystal, the threshold sensitivity of the converter was estimated. The experimental PC-EO crystal structure by which IR-radiation (0.9–1.5 μm) was converted into the coherent visible radiation was obtained on the basis of theoretical calculations. The limiting resolution of readout image was about 10 lp/mm. The measured threshold sensitivity of the converter, 5 × 10−4 W/cm2, was found to be in the limits of theoretical estimation. The results indicate that this device has the potential for use in a high-speed, high-contrast optically addressed spatial light modulators

    Boride Layer Growth Kinetics of AISI H13 Steel Borided with Nano-Sized Powders

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    Growth kinetics of boride layers in AISI H13 steel was investigated using the pack boriding method at temperatures of 1073, 1173 and 1273 K (800°C, 900°C and 1000°C) for periods of 2, 4 and 6 h with nano-sized boron (NB) and micron-sized Ekabor II powders as boriding agents. The total thickness of the boride layer (including both FeB and Fe2B) after boriding at 1273 K (1000°C) for 6 h was 103.8 μm and 96.5 μm for the NB and Ekabor II specimens, respectively. X-ray diffraction analysis of the boride layers on the surfaces borided with NB and Ekabor II revealed the presence of FeB and Fe2B phases with sawtooth morphology. The FeB/Fe2B volume ratio was higher in the specimens borided with NB. The thickness of the boride layer (FeB + Fe2B) increased with the increasing boriding temperature and time. The FeB layer in the NB specimen displayed a (002) preferred orientation

    Effects of blanking speed on the shear surface of mild steel (St37)

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    Blanking operation is widely used to cut sheet or plates by a shearing process between punch and die. The process of shearing and the conditions of the sheared surface are influenced by the punch, the die, the speed of punching, the clearance between the punch and the die. In this study, effects of high speed blanking on surface quality and corrosion properties of mild steel St37 shear surface have been investigated. The work presented in this paper aims at evaluating the shear surface quality improvements of the St37 resulting from the use of high energy rate forging machine. The appraisal is based on criteria related to surface accuracy and corrosion resistance characterization. For this purpose, St37 mild steels were cut using three different punch speeds hydraulic presses at nearly quasistatic, conventional mechanical presses at low punch velocity (0.2 m/s) and high energy rate forging machine at high punch velocity (10 m/s), for different die clearances (4.5%-6% of sheet thickness). After accelerated corrosion tests, blanks were performed in conjunction with scanning electron microscopy technique to study the cutting process of the blanks at room temperature. In fact, by using high energy rate forging machine, a reduction of more than 25% of the surface roughness (R_{a}) was realized and better resistance to stress corrosion cracking and pitting corrosion was noticed. It was observed that the corrosion resistance of the high energy rate forging-cut specimen was better than that of the hydraulic-cut and mechanical-cut specimens

    Microstructural and mechanical properties of friction stir welded pure lead

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    26-32The present study focuses on the applicability of friction stir welding to pure Pb plates. The joint performances are evaluated by optical microscopy, microhardness measurements, notch impact tests and three point bending tests. The effects of the tool rotational speed (1500, 2000 and 2500 rev/min) and welding speed (72, 100 and 125 mm/min) on the joint performance are determined. The results indicate that the welded joints exhibit similar or higher mechanical properties than those of the base material. Optimal joint performance was achieved with a rotational speed of 1500 rev/min and welding speed of 100 mm/min

    A new approach to sintering and boriding of steels “Boro-sintering”: Formation, microstructure and wear behaviors

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    In this study, sintering and boriding methods are applied as a single step, and it is aimed to gain time and economic advantage. For this purpose, powder mixtures prepared in suitable compositions were subjected to sintering and boro-sintering processes. In the boro-sintering process, the sintering was carried out in the boriding atmosphere and the two processes were carried out together. The processing, microstructure, hardness and dry sliding wear behavior of the samples were studied. The powders were pressed under different pressures, and their effects on the properties of the final component were investigated. The sintering process was carried out for 2 h at 1000 °C, and the boro-sintering process was carried out at 1000 °C for 2, 4 and 6 h. Fe2B and Fe2B + FeB boride phases occurred depending on the boro-sintering process duration. Boride layer thickness varied between 120 and 400 μm according to boro-sintering duration and cold press pressure. Vickers micro-hardness and Ball-on-disc wear tests were performed on the samples. Whereas 205–215 HV hardnesses were obtained in the sintered samples, 1252–1705 HV hardness values were reached by boro-sintering process. Increased cold pressing pressure reduced wear losses. However, the long boro-sintering time increased surface hardness, but reduced wear resistance. © 2020 Elsevier B.V
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