Deposizione di rivestimenti in Al2O3 mediante High Velocity Suspension Flame Spraying (HVSFS): caratteristiche dei riporti ed effetto dei parametri operativi

La tecnica denominata HVSFS (High Velocity Suspension Flame Spraying) è un processo di termospruzzaturainnovativo che, alimentando la torcia con una sospensione di particelle finissime (micro- o nano-metriche)disperse in una fase liquida, permette la deposizione di rivestimenti ceramici ad alta densità e basso spessore(<100 ?m). Per approfondire la relazione fra caratteristiche dei riporti e proprietà della sospensione, varirivestimenti a base di Al2O3 sono stati depositati utilizzando sospensioni di particelle sia micrometriche, siananometriche. Indipendentemente dai parametri di processo selezionati, una sospensione di particellemicrometriche sufficientemente disperse garantisce maggior efficienza di deposizione (>50%) e producerivestimenti costituiti da un’ottima sovrapposizione di lamelle fortemente coese, con maggior durezza(?1200 HV0.05) e minor rugosità (Ra ? 1.3 ?m) rispetto ai rivestimenti ottenibili con sospensioni dinanoparticelle. Sebbene i rivestimenti ottenuti da sospensioni di particelle micrometriche siano anche soggettia tensioni residue trattive più elevate (fra 50 MPa e 100 MPa), la loro eccellente densità e ottima coesione lirendono molto più resistenti all’usura per strisciamento (studiata con test “ball on disk”) rispetto a riporti diAl2O3 prodotti sia con sospensioni di nanoparticelle, sia con tecniche di termospruzzatura convenzionali

Peripapillary Microvascular and Neural Changes in Diabetes Mellitus: An OCT-Angiography Study

Purpose: To evaluate peripapillary vessel density and morphology in patients with diabetes mellitus (DM) without clinical signs of diabetic retinopathy (DR) and with mild, nonproliferative DR and to correlate with peripapillary nerve fiber layer (NFL) thickness.Methods: One hundred seventeen eyes (34 healthy controls, 54 patients with DM without DR [noDR group] and 24 patients with mild DR [DR group]) were prospectively evaluated. All subjects underwent peripapillary and macular optical coherence tomography angiography (OCT-A). Peripapillary NFL thickness was also recorded. OCT-A slab of radial peripapillary plexus (RPC) and macular superficial capillary plexus (SCP) were analysed in order to calculate perfusion density (PD) and vessel density (VD). Further an image analysis of RPC slab was performed to identify number of branches (NoB) and total branches length (tBL).Results: In peripapillary area there was a significant decrease in VD (P = 0.003), NoB (P < 0.001), and tBL (P < 0.001) in noDR group versus controls; PD values were not different among groups (P = 0.126); there was a significant decrease in average NFL thickness in DR versus controls (P = 0.008) and in the inferior quadrant in noDR group versus controls (P = 0.03); there was a significant correlation between OCT-A and NFL thickness values (\u3c1 ranging from 0.19-0.57). In macular region PD and VD were decreased only in DR group (P < 0.05).Conclusions: There are early changes in the peripapillary vessel morphology and VD of the RPC in patients with DM without DR that correlate to NFL thinning. Earlier changes in superficial vessel density are documented in the peripapillary than in the macular region. These data may confirm a coexistence of an early neuronal and microvascular damage in patients with DM without clinical signs of DR

Conversion factors for effective dose and organ doses with the air Kerma area product in hysterosalpingography

Histerosalpingography (HSG) remains the dominant diagnostic tool for investigation of infertility in women. Conversion factors used to estimate effective (E) and organ doses (HT) from air Kerma area product (KAP) are needed to estimate patient doses in HSG, performed with state-of-the-art fluoroscopic X-ray systems with digital detectors. In this study, estimates of E and HT for six critical organs/tissues, were derived on an individual basis in 120 HSG procedures and in 1410 irradiation events, performed on two X-ray systems from information available through the radiation dose structured report using Monte Carlo methods. Mean values of E and Hovaries were1.0 \ub1 0.9 mSv and 5.6 \ub1 5.4 mGy. E/KAP conversion factors of 0.13; 0.18; 0.28 and 0.35 mSv Gy 121cm 122 were established for irradiation events with a Cu filtration of 0.0; 0.1; 0.4 and 0.9 mm. A high agreement was obtained between E estimated through Monte Carlo methods and E/KAP conversion factors accounting separately for the different modes of fluoroscopy and the radiography component of HSG, with a systematic error of 0 mSv and lower/upper limits of agreement of 120.6 and 0.5 mSv. On the contrary, the use of a single coefficient of conversion did not provide accurate estimates of E, showing a bias of 120.4 mSv and lower and upper limits of agreement of 121.9 and 1.2 mSv. An algorithm for the estimation of effective and organ doses from KAP has been established in HSG procedures depending on the Cu filtration in the X-ray irradiation events

Variability of the discrepancy between manufacturer and measured CTDI100 values by scanner type, acquisition parameters and phantom size

According to the EU directive 2013/59, the computed tomography (CT) equipments shall be able to inform the practitioner of parameters for assessing the patient dose. The aim of this study was to measure the accuracy of the CTDI100 with respect to the values stipulated in the manufacturer manual for different manufacturers/models of CT and to assess the impact of acquisition parameters on CTDI100 accuracy. Ten CT from 4 different manufacturers were included in the study. The discrepancy with the manufacturer value CTDI100 was checked with a dosimeter with traceable calibration. Manufacturer values for the CTDI100 were derived from the equipment's manual. The impact of the kVp, CT model, primary collimation and phantom size on the discrepancy of the CTDI100, was assessed by a four-way ANOVA. All the factors had a statistically significant impact on CTDI100 discrepancy (P\u202f<\u202f0.05). In a head to head comparison, the greater discrepancies were found on average for 80\u202fkV (15.4\u202f\ub1\u202f10.7%), sixteen channels CT (10.3\u202f\ub1\u202f5.1%) and for thick collimations (13.2\u202f\ub1\u202f6.8%), whilst no significant differences were found between head and body phantoms. For sixteen channels CT and acquisition protocols involving the use of low kV or thick primary collimation, the discrepancies with the manufacturer value CTDI100 can be higher than 20%, which is the suspension level indicated in the EC RP N.162 Publication. This suggests the need of individual calibration of CT X-ray tubes by the manufacturers and the necessity of including this check in the quality control programs for CT

Conversion factors for effective dose and organ doses with the air kerma area product in patients undergoing percutaneous transhepatic biliary drainage and trans arterial chemoembolization

Conversion factors used to estimate effective (E) and organ doses (HT) from air Kerma area product (KAP) are required to estimate population doses in percutaneous transhepatic biliary drainage (PTBD) and trans arterial chemoembolization (TACE) interventional procedures. In this study, E and HT for ten critical organs/tissues, were derived in 64 PTBD and 48 TACE procedures and in 14,540 irradiation events from dosimetric, technical and geometrical information included in the radiation dose structured report using the PCXMC Monte Carlo model, and the ICRP 103 organ weighting factors. Conversion factors of: 0.13; 0.19; 0.26 and 0.32 mSv Gy−1 cm−2 were established for irradiation events characterized by a Cu filtration of 0.0; 0.1; 0.4 and 0.9 mm, respectively. While a single coefficient of conversion is not able to provide estimates of E with enough accuracy, a high agreement is obtained between E estimated through Monte Carlo methods and E estimated through E/KAP conversion factors accounting separately for the different modes of fluoroscopy and the fluorography component of the procedures. An algorithm for the estimation of effective and organ doses from KAP has been established in biliary procedures which considers the Cu filtration in the X-ray irradiation events. A similar algorithm could be easily extended to other interventional procedures and incorporated in radiation dose monitoring systems to provide dosimetric estimates automatically with enough accuracy to assess population doses

Damage tolerant functionally graded WC-Co/Stainless Steel HVOF coatings

In this paper, effective damage tolerance of a functionally graded coating (FGC) deposited by high velocity oxygen fuel (HVOF) spraying is observed. The thick FGC (≈1.2 mm) consists of 6 layers with a stepwise change in composition from 100 vol.% ductile AISI316 stainless steel (bottom layer) to 100 vol.% hard WC-12Co (top layer) deposited onto an AISI316 stainless steel substrate. Damage tolerance is observed via 1) an increase in compliance with depth, and 2) an increase in fracture resistance by containment, arrest and deflection of cracks. A smooth gradation in the composition and hardness through the coating thickness is found by scanning electron microscopy and depth-sensing microindentation, respectively. The in-situ curvature measurement technique reveals that during the deposition of the FGC, compressive stresses exist in the lower, metallic layers owing to peening effect of successive impact, and these gradually evolve to high tensile, in the top layers. Tensile stresses appear to be due to quenching alone; thermal stresses are low because of the gradation. All of this is beneficial for the deposition of a thick coating.The FGC structure shows the ability to reduce cracking with increased compliance in the top layer during static and dynamic normal contact loading, while retaining excellent sliding wear resistance (ball-on-disk tests). Results are discussed in comparison to the behavior and properties of coatings of similar individual compositions and thicknesses, as well as a thick monolithic WC-12Co sprayed coating. Further improvements in the processing are proposed to enhance the adhesion strength and avoid coating delamination under high load contact-fatigue conditions