Per-pass analysis of recanalization and good neurological outcome in thrombectomy for stroke: Systematic review and meta-analysis

Background and aim First pass effect (FPE) is defined as achieving a complete recanalization with a single thrombectomy device pass. Although clinically desired, FPE is reached in less than 30% of thrombectomy procedures. Multiple device passes are often necessary to achieve successful or complete recanalization. We performed a systematic review and meta-analysis to determine the recanalization rate after each pass of mechanical thrombectomy and its association with good neurological outcome. Methods A literature search was performed for studies reporting the number of device passes required for either successful (mTICI 2b or higher) or complete (mTICI 2c or higher) recanalization. Using random-effect meta-analysis, we evaluated the likelihood of recanalization and good neurological outcome (measured with the modified Rankin Score <2 at 90 days) after each device pass. Results Thirteen studies comprising 4197 patients were included. Among cases with failed first pass, 24% of them achieved final complete recanalization and 45% of them achieved final successful recanalization. Independently to the total number of previously failed attempts, the likelihood of achieving successful recanalization was 30% per pass, and the likelihood to achieve complete recanalization was about 20% per pass. The likelihood of good neurological outcome in patients with final successful recanalization decreased after each device pass: 55% after the first pass, 48% after the second pass, 42% after the third pass, 36% after the fourth pass, and 26% for 5 passes or more. Conclusion Each pass is associated with a stable likelihood of recanalization but a decreased likelihood of good neurological outcome.

Microstructure and Mechanical Properties of the Ni/Ti/Nb Multilayer Composite Manufactured by Accumulative Pack-Roll Bonding

In this work, accumulative pack-roll bonding successfully manufactured the Ni/Ti/Nb multilayer composite. The microstructure evolution and mechanical properties of the composite during the accumulative roll bonding (ARB) process were investigated by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), transmission electron microscopy (TEM), micro-hardness test, and tensile tests. The results showed that the deformation of each layer was relatively uniform in the initial stage of the ARB process. After the fourth pass, the Ni/Ti interface was still relatively straight, while the Ti/Nb interface was unevenly deformed. After the fourth pass, the microstructure of the Ni layer was equiaxed grains with a decreased grain size of 200 nm, and finer equiaxed grains were observed at the interface. No dynamic recrystallization occurred in the Ti and Nb layers. The laminar structure of the Nb layer was observed, and the grains were oriented parallel to the rolling direction. Moreover, the tensile strength and micro-hardness significantly increased as the number of ARB increased. After five passes of the ARB process, the tensile strength of the composite reached 792.3 MPa, and the micro-hardness of Ni, Ti, and Nb were increased to 270.2, 307.4, and 243.4 HV, respectively.

Analisa Gaya Penekanan pada Proses ECAP Batang Kuningan CuZn 70/30

Telah dilakukan percobaan severe plastic deformation (SPD) dengan metodeequal channel angular pressing (ECAP) pada batang kuningan CuZn 70/30 diameter 10 mm sampai 5 pas. Gaya penekanan meningkat secara signifikan pada awal langkah penekanan dan mencapai nilai maksimum lalu melandai. Pada pas pertama gaya penekanan mencapai 115 kN, pas kedua 130 kN, pas ketiga mecapai 150 kN dan pada pas keempat 165 kN. Dari pengukuran luas area di bawah kurva gaya penekanan diperoleh energi total pembentukan pada proses ECAP batang kuningan persatuan panjang adalah 95 Joule/mm pada pas pertama, sampai 130 Joule/mm pada pas ketiga, dan turun 125 Juole/mm pada pas keempat. Secara kumulatif total energi persatuan panjang meningkat secara linier sesuai dengan peningkatan jumpah pas, dimana pada pas keempat mencapai 597 MPa. Peningkatan gaya penekanan dan energi penekanan sebanding dengan terjadinya peningkatan kekerasan pada batang kuningan dan terjadinya penghalusan butir.Kata kunci: ECAP, gaya penekanan, energi pembentukan, kekerasan, penghalusan butir, kuningan.AbstractExperiments of severe plastic deformation (SPD) have been carried out by the method of equal channel angular pressing (ECAP) on brass rods CuZn 70/30 diameter 10 mm to 5 pas. Pressing force significantly is increased emphasis on early steps and reaches a maximum value and then ramp. At the first pas the pressing force reached 115 kN, the second pass 130 kN, the third pass 150 kN and fouth pass is 165. From measurements of the area under the curve of pressing force, the total forming energy per unit length generated to form the brass rod in ECAP is 95 Joule / mm at the first pass, 130 Joules / mm at third pass and down to 125 Joule/mm at fouth pass. Cumulatively, the total forming energy per unit length increases linearly according to the increase in number of ECAP pass, where the fourth pass reach 597 Joule/mm. Increased emphasis pressing load and forming energy is proportional to the increase in hardness of the brass rod and the grain refinement.Keywords: ECAP, pressing load, forming energy, hardness, grain refinement, Brass

Effect of accumulative roll bonding process on textural evolution and its comparison with normal rolled AA7005 aluminum alloy

In the present work, texture evolution of AA7005 aluminum alloy during the accumulative roll bonding and conventionally rolled was investigated by X-ray diffraction. It was found that the dominant texture components of both samples were Brass, Copper, Rotated Cube and Goss components, but the ARB texture evolution was quicker and displayed complex features. When the number of ARB cycle increased, the intensity of texture components decreased at the second and third pass, then enhanced at the fourth pass, and finally decreased. During the ARB process there was a texture transition at the second and third pass from Brass and S to Rotated Cube components due to the shear texture which formed on the surface region and moved to the center during the next pass. The enhancement of texture intensity at the fourth pass might be attributed to the formation of nano shear bands. The texture intensity decreasing at final cycle was correlated to redundant shear strain and continuous recrystallization during the high ARB passes.

Computational Simulation of Dynamic Recrystallization and Severe Deformation of AA7075 Alloy

The empirical model of dynamic recrystallization (DRX) coupled with DEFORM 3D® software (based on the finite element method (FEM)) was used to predict the microstructural evolution of the AA7075 processed by four passes of equal channel angular pressing (ECAP) at 250° C. The DRX model parameters were taken from the literature. The simulation results showed that the DRX exhibited a heterogeneous distribution from the back to the frontal part of the sample and this heterogeneity markedly diminished in the fourth pass. The recrystallized volume fraction reached 50% in most of the sample in the fourth pass and the average grain size did not show significant changes, going from an initial value of 16.4 μm to 12.5 μm. This latter result was attributed to the fact that DRX occurred partially even for the last pass. Experimental testing of ECAP was conducted by using the same conditions of computational simulation. The validation of model was performed by comparison of average grain size values with those obtained experimentally by means of image analysis applied on micrographs that were acquired by means of optical microscopy (OM). Hardness and peak load values also indicated the occurrence of a partial dynamic recrystallization and recovery.

A Goal Oriented, Sequential Process Design of a Multi-Stage Hot Rod Rolling System

The steel manufacturing process is characterized by the requirement of expeditious development of high quality products at low cost through effective and judicious use of available resources. Identifying solutions that meet the conflicting commercially imperative goals of such process chains is hard using traditional search techniques. The complexity embedded in such a problem increases due to the presence of large number of design variables, constraints and bounds, conflicting goals and the complex sequential relationships of the different stages of manufacturing. A classic example of such a manufacturing problem is the design of a rolling system for manufacturing a steel rod. This is a sequential process in which information flows from first rolling stage/pass to last rolling pass and the decisions made at first pass influence the decisions that are made at the later passes. In this paper, we present a method based on well-established empirical models and response surface models developed through simulation experiments (finite element based) along with the compromise Decision Support Problem (cDSP) construct to support integrated information flow across different stages of a multi-stage hot rod rolling system. The method is goal-oriented because the design decisions are first made based on the end requirements identified for the process at the last rolling pass and these decisions are then passed to rolling passes that precede following the sequential order in an inverse manner to design the entire rolling process chain. We illustrate the efficacy of the method by carrying out the design of a multi-stage rolling system. We formulate the cDSP for the second and fourth pass of a four pass rolling chain. The stages are designed by sequentially passing the design information obtained after exercising the cDSP for the last pass for different scenarios and identifying the best combination of design variables that satisfies the conflicting goals. The cDSP for second pass helps in integrated information flow from fourth to first pass and in meeting specified goals imposed by the fourth and third pass designed. The end goals identified for this problem for fourth pass are minimization of ovality (quality) of rod, maximization of throughput (productivity) and minimization of rolling load (performance and cost). The method can be instantiated for other multi-stage manufacturing processes such as the steel making process chain having several unit operations. In future, we plan to use the method for supporting decision workflow in steel making process by formulating cDSPs for the multiple unit operations involved and linking them as a decision network using coupled cDSPs.

Metallographic Analysis of Non-Orientation Silicon Steel W20 in Different Shearing Deformation Area

In order to further understand the relationship between technology and metallographic microstructure for the large-scale production of non-orientation silicon steel, hot assembles rolling mill samples at different shearing deformation strip were selected and analyzed. The results show that the surface microstructure in finishing section at the first meeting to the fourth-pass is band-shape deformed ferrite plus equiaxed recrystallization ferrite, while the center is deformed ferrite. With the increase of shearing deformation, number of rheological ferrite increase, and become more slender.

Effect of Low Temperature Rolling on Microstructure and Properties of ECAE Processed Copper

The changes in the tensile properties, in relation to the phenomenon of shear banding are investigated in copper, rolled at liquid nitrogen temperature and then recrystallized, after initial processing by Equal-Channel Angular Extrusion (ECAE) at room temperature. Increases in ductility and strength up to the fourth pass of ECAE processing were noted, then a decrease of both properties was observed. The decrease was accompanied by twinning and shear banding. In rolled samples, pre-cooled down to the temperature of liquid nitrogen and initially recrystallized, the twinning and shear banding mechanisms were the most probable mechanisms responsible for lowering the mechanical properties.