Parameteric thermal process models of friction stir welding

A Dissertation for the Master’s Degree in Mechanical Engineering School of Mechanical, Industrial & Aeronautical Engineering Date: 02/02/2017The Friction Stir Welding process is a rotating tool, that consists of a specialy designed shoulder and pin, that is plunged into the joining line of the required material and traverses along this line. The friction is induced by the rotating tool causes the workpiece material to rise to an operating temperature of 70% to 90% of the workpiece material's melting temperature and resulting in, no phase change, nor any defects associated with phase change, occurs in the workpiece. The increased temperature of the material causes the shear yield strength to drastically decrease thus allowing the two pieces to plasticise, easily stir around the tool and subsequently join. As the tool traverses along the workpiece, the softened material cools in the wake of the rotating tool and recrystallises, forming a ne grained microstructure. Attempts to develop an innovative tool to correlate the resulting of thermal models with process parameters are scarce. In this work, 6056-T4 and 6082-T6 Aluminum alloy sheets are friction stir welding at different rotational and translational speeds during the experimental aspect and material 2024-T3 for the analytical calculations. The effects of process parameters on the resulting thermal and mechanical properties are investigated. The results show that the use of coolant during the friction stir weld decrease heat generation substantially, this can also affect the force of the weld. It is also observed that the shear strenght of the processed sheet depends strongly on the rotational and translational speeds as weld as the thermal aspect and varies widely within the processed region, this was shown in this study by evaluating the thermal aspects of different weld types namely the Standard tool, Bobbin tool and the innovative tool. In addition. The proposed approach involves determination of the use of the friction stir welding in different thermal conditions and championing the use of an innovative tool.MT201

P3 response during short-term memory retrieval revisited by a spatio-temporal analysis

The most reported event related potential (ERP) parameter during short-term memory retrieval has been P3 wave and the association has been built on the relation between P3 latency and reaction times. The aim of this study is to identify an ERP component that reflects the memory scanning process preceding the decision making stage which has been associated with the P3 peak. A spatiotemporal analysis was applied on the P3 and pre-P3 period of ERP responses obtained during the retrieval phase of the Sternberg paradigm with two memory load conditions (3 and 5 letters in the memory set). In the easy task condition with the fastest reaction times (positive probes of 3 letters condition), a single P3 was observed, whereas P3 was split into two peaks in responses to probe items of more demanding task conditions. The single P3 peak and the later components of the split P3 peaks displayed the typical P3 topography. On the other hand, the topographic mapping of the earlier peak of the split P3 wave and ascending part of the single P3 peak revealed a right parietal topography. The onset time of this earlier right lateralized topography was stable among all conditions but it persisted longer in the high memory load condition. We conclude that the right-lateralized positivity in the pre-P3 period reflects the memory scanning process followed by the P3 peak with midline parietal topography reflecting the decision making process. © 2012 Elsevier B.V.

Retinal nerve fiber layer, ganglion cell complex, and choroidal thicknesses in migraine

ABSTRACT Purpose: To evaluate the thicknesses of the peripapillary retinal nerve fiber layer (RNFL), ganglion cell complex (GCL), and choroid layer using spectral domain optical coherence tomography (SD-OCT) for investigating the effects of vascular changes on the eye and optic nerve in patients who have migraine with aura. Methods: Forty-five patients who had migraine with aura (migraine group) and 45 healthy individuals (control group) were enrolled in the study. Age, gender, duration after migraine diagnosis, intraocular pressure, and axial length measurements were recorded in each case. RNFL, GCL, and choroid layer thicknesses were measured using SD-OCT in all participants. Results: The mean age was 36.1 ± 6.7 (20-45) years in the migraine group and 35.7 ± 8.6 (19-45) years in the control group. There was no significant difference in the RNFL thicknesses of the temporal and nasal quadrants (p >0.05). The RNFL thicknesses of the superior and inferior quadrants were significantly lower in the migraine group compared with those in the control group (p =0.001, p <0.01, respectively). Measurements for the superior and inferior GCL were not significantly different between the groups (p >0.05). Subfoveal, temporal, and nasal choroidal thickness measurements at 500 µm, 1000 µm, and 1500 µm were significantly lower in the migraine group than in the control group (p =0.001; p <0.01, respectively). Conclusions: Compared with the controls, the RNFL and choroid layer were determined to be thinner in patients who had chronic migraine with aura

The outcomes of transcatheter aortic valve implantation with Edwards SAPIEN or CoreValve devices: Single-center experience in Turkey

Background: This study aims to evaluate early- and midterm outcomes of transcatheter aortic valve implantation

Risk Factors in Post-LASIK Corneal Ectasia

Purpose. To evaluate the risk factors for post-laser in situ keratomileusis (LASIK) ectasia. Materials and Methods. Medical records of 42 eyes of 28 (10 women, 18 men) patients who developed corneal ectasia after LASIK were retrospectively reviewed. Topographical features and surgical parameters of those patients were evaluated. Results. The mean age of patients was 34.73±6.50 (23–48) years and the mean interval from LASIK to the diagnosis of post-LASIK ectasia was 36.0±16.92 (12–60) months. The following factors were determined as a risk factors: deep ablation (>75 μm) in 10 eyes, FFK (forme fruste keratoconus) in 6 eyes, steep cornea (>47 D) in 3 eyes, pellucid marginal degeneration (PMD) in 2 eyes, thin cornea (<500 μm) in 2 eyes, thin and steep cornea in 2 eyes, thin cornea and deep ablation in 5 eyes, FFK and steep cornea in 2 eyes, and FFK, steep cornea, and deep ablation in 1 eye. However no risk factor has been determined in 9 eyes (21.4%). Conclusion. The findings of our study showed that most of the patients who developed post-LASIK ectasia have a risk factor for post-LASIK ectasia. However, the most common risk factor was deep ablation

Effect of Hydroxychloroquine on the Retinal Layers: A Quantitative Evaluation with Spectral-Domain Optical Coherence Tomography

Purpose. To evaluate the effect of hydroxychloroquine on retinal pigment epithelium- (RPE-) Bruch’s membrane complex, photoreceptor outer segment, and macular ganglion cell-inner plexiform layer (GCIPL) thicknesses using spectral-domain optical coherence tomography (SD-OCT). Methods. In this prospective case-control study, 51 eyes of 51 hydroxychloroquine patients and 30 eyes of 30 healthy subjects were included. High-quality images were obtained using a Cirrus HD-OCT with 5-line raster mode; the photoreceptor inner segment (IS) and outer segment (OS), sum of the segments (IS + OS), and RPE-Bruch’s membrane complex were analyzed. Results. The thicknesses of the IS + OS and OS layers were significantly lower in the hydroxychloroquine subjects compared to the control subjects (P<0.05). RPE-Bruch’s membrane complex thicknesses were significantly higher in the hydroxychloroquine subjects than for those of the control subjects (P<0.05). The minimum and temporal-inferior macular GCIPL thicknesses were significantly different between the patients with hydroxychloroquine use and the control subjects (P=0.04 and P=0.03, resp.). Conclusions. The foveal photoreceptor OS thinning, loss of GCIPL, and RPE-Bruch’s membrane thickening were detected in patients with hydroxychloroquine therapy. This quantitative approach using SD-OCT images may have important implications to use as an early indicator of retinal toxicity without any visible signs of hydroxychloroquine retinopathy

Effect of Hydroxychloroquine on the Retinal Layers: A Quantitative Evaluation with Spectral-Domain Optical Coherence Tomography

Purpose. To evaluate the effect of hydroxychloroquine on retinal pigment epithelium-(RPE-) Bruch's membrane complex, photoreceptor outer segment, and macular ganglion cell-inner plexiform layer (GCIPL) thicknesses using spectral-domain optical coherence tomography (SD-OCT). Methods. In this prospective case-control study, 51 eyes of 51 hydroxychloroquine patients and 30 eyes of 30 healthy subjects were included. High-quality images were obtained using a Cirrus HD-OCT with 5-line raster mode; the photoreceptor inner segment (IS) and outer segment (OS), sum of the segments (IS + OS), and RPE-Bruch's membrane complex were analyzed. Results. The thicknesses of the IS + OS and OS layers were significantly lower in the hydroxychloroquine subjects compared to the control subjects (P < 0.05). RPE-Bruch's membrane complex thicknesses were significantly higher in the hydroxychloroquine subjects than for those of the control subjects (P < 0.05). The minimum and temporal-inferior macular GCIPL thicknesses were significantly different between the patients with hydroxychloroquine use and the control subjects (P = 0.04 and P = 0.03, resp.). Conclusions. The foveal photoreceptor OS thinning, loss of GCIPL, and RPE-Bruch's membrane thickening were detected in patients with hydroxychloroquine therapy. This quantitative approach using SD-OCT images may have important implications to use as an early indicator of retinal toxicity without any visible signs of hydroxychloroquine retinopathy

Hematologic and Clinical Parameters After Transcatheter Aortic Valve Implantation (TAVI) in Patients With Severe Aortic Stenosis

Background: Previous studies have demonstrated that platelet activation occurs in patients with aortic stenosis (AS). This study sought to evaluate the changes in hematologic and clinical parameters noted with the improvement in AS following transcatheter aortic valve implantation (TAVI) in patients with severe AS at high risk of surgery

Electrophysiological Evaluation of Atrioventricular Conduction Disturbances in Transcatheter Aortic Valve Implantation With Edwards SAPIEN Prosthesis

Aims. Permanent pacemaker requirement is a known complication after transcatheter aortic valve implantation (TAVI). The aim of the present study was to analyze the effects of Edwards SAPIEN prosthesis implantation on atrioventricular conduction. Methods. The study included 28 patients who underwent TAVI due to severe aortic valve stenosis. An electrophysiological study was performed in the catheterization room immediately before the initial balloon valvuloplasty and immediately after Edwards SAPIEN prosthesis implantation. Results. His-ventricle interval was significantly prolonged postprocedure (55.9 +/- 11.5 ms) vs preprocedure (47.3 +/- 7.8 ms) (P<.001). The antegrade Wenckebach point was observed to be significantly prolonged postprocedure (354.4 +/- 41.3 ms) vs preprocedure (333.7 +/- 45.4 ms) (P=.001). Despite atrial-His interval prolongation, it was not statistically significant. After the procedure, we observed significant conduction disturbances in 3 patients (10.7%). These conduction problems recovered before discharge. One of the patients (3.6%) with right bundle branch block + left anterior fascicular block required permanent pacemaker implantation. At postprocedure electrocardiogram, QRS duration increased, QRS axis shifted to the left, and both of the values became normal before discharge. The patient's echocardiographic and clinical parameters were improved during follow-up. Conclusion. The effect of Edwards SAPIEN on the conduction system was mostly infranodal and temporary. The physical properties of the Edwards SAPIEN prosthesis may explain this observation. This complication may be lessened if the frame height characteristics can be improved