Effect of Laser Welding Parameters on Formation of NiTi Shape Memory Alloy Welds

In this work experimental trials of welding of NiTi flat plates with 2.0 mm thickness were conducted using a 4.5 kW continuous wave (CW) Nd:YAG laser. The influences of laser output power, welding speed, defocus amount and side-blow shielding gas flow rate on the morphology, welding depth and width, and quality of the welded seam were investigated. Meanwhile, the effects of heat input on the mechanical and functional properties of welded joints were studied. The results show that laser welding can take better formation in NiTi alloys. The matching curves with laser power and welding speed affecting different formation of welds were experimentally acquired, which can provide references for laser welding and engineering application of NiTi alloy. The heat input has obvious effects on the ultimate tensile strength (UTS) and shape memory behavior of the welded joints

CTP: Towards Vision-Language Continual Pretraining via Compatible Momentum Contrast and Topology Preservation

Vision-Language Pretraining (VLP) has shown impressive results on diverse downstream tasks by offline training on large-scale datasets. Regarding the growing nature of real-world data, such an offline training paradigm on ever-expanding data is unsustainable, because models lack the continual learning ability to accumulate knowledge constantly. However, most continual learning studies are limited to uni-modal classification and existing multi-modal datasets cannot simulate continual non-stationary data stream scenarios. To support the study of Vision-Language Continual Pretraining (VLCP), we first contribute a comprehensive and unified benchmark dataset P9D which contains over one million product image-text pairs from 9 industries. The data from each industry as an independent task supports continual learning and conforms to the real-world long-tail nature to simulate pretraining on web data. We comprehensively study the characteristics and challenges of VLCP, and propose a new algorithm: Compatible momentum contrast with Topology Preservation, dubbed CTP. The compatible momentum model absorbs the knowledge of the current and previous-task models to flexibly update the modal feature. Moreover, Topology Preservation transfers the knowledge of embedding across tasks while preserving the flexibility of feature adjustment. The experimental results demonstrate our method not only achieves superior performance compared with other baselines but also does not bring an expensive training burden. Dataset and codes are available at https://github.com/KevinLight831/CTP.Comment: Accepted by ICCV 2023. Code: https://github.com/KevinLight831/CT

Apical conicity ratio: A new index on left ventricular apical geometry after myocardial infarction

ObjectiveOur objective was to introduce a new index to evaluate left ventricular aneurysm by quantitative analysis of left ventricular apical geometry.MethodsA total of 116 selected subjects underwent magnetic resonance imaging, 28 healthy volunteers, 29 patients with dilated cardiomyopathy, and 59 patients with ischemic heart disease (26 with left ventricular aneurysm; 33 with no aneurysm). The apical conicity ratio was calculated as the ratio of left ventricular apical area over apical triangle.ResultsDiastolic apical conicity ratio of patients with left ventricular aneurysm was 1.62 ± 0.20 and systolic apical conicity ratio was 1.78 ± 0.43. After left ventricular reconstruction, the diastolic apical conicity ratio decreased to 1.47 ± 0.23 and the systolic ratio to 1.51 ± 0.21, which came close to the normal level, whereas other global indices remained. In patients with dilated cardiomyopathy, sphericity index and eccentricity index increased significantly without changes in the apical conicity ratio. Among patients with ischemic heart disease, the apical conicity ratio of the group with left ventricular aneurysm was significantly higher than that of the group without an aneurysm when the other indices between the 2 groups showed no statistically difference. Receiver operating characteristic curves showed only apical conicity ratio had high power of discriminating left ventricular aneurysm from no aneurysm.ConclusionsThe new index, apical conicity ratio, can be used to quantify the regional left ventricular deformation, especially in patients with left ventricular aneurysm resulting from myocardial infarction

AN INNOVATIVE GAS TURBINE CYCLE WITH METHANOL FUELLED CHEMICAL-LOOPING COMBUSTION

ABSTRACT In this paper, a novel gas turbine cycle integrating methanol decomposition and the chemical-looping combustion (CLC) is proposed. The system study on two methanol-fuelled power plants, the new gas turbine cycle with CLC combustion, and a chemically intercooled gas turbine cycle, has been investigated with the aid of the exergy analysis (EUD methodology). In the proposed system, methanol fuel is decomposed into syngas mainly containing H 2 and CO by recovering low-temperature thermal energy from an intercooler of the air compressor. After the decomposition of methanol, the resulting product of syngas is divided into two parts: the most part reacting with Fe 2 O 3 , is sent into the CLC subsystem, and the other part is introduced into a supplement combustor to enhance the inlet temperatures of turbine to 1100-1500 o C. As a result, the new methanol-fuelled gas turbine cycle with CLC had a breakthrough in performance, with at least about 10.7 percentage points higher efficiency compared to the chemically intercooled gas turbine cycle with recovery of CO 2 and is environmentally superior due to the recovery of CO 2 . This new system can achieve 60.6% net thermal efficiency with CO 2 separation. The promising results obtained here indicated that this novel gas turbine cycle with methanol-fuelled chemical looping combustion could provide a promising approach of both effective use of alternative fuel and recovering low-grade waste heat, and offer a technical probability for CLC in applying into the advanced gas turbine with high temperatures above 1300 o C. INTRODUCTION Currently, we face a potentially serious problem of rapid climate change due to anthropogenic emissions of greenhouse gases (e.g. CO 2 ). One of the options to control the greenhouse gas emission is the CO 2 capture technologies from flue gases. In a fossil fuel-fired power plant, CO 2 capture can be carried out mainly through three available technologies: "precombustion," "post-combustion" and "oxy-fuel combustion." The progress in this field has been addressed by Mazen [2] Chemical-looping combustion (CLC) with inherent separation of CO 2 is considered a promising technology proposed by Ishida and Jin in 1994 [4][5] . It is the most attractive energy efficient method for CO 2 capture from fuel conversion in combustion process. Compared to conventional combustion, the chemical-looping combustion involves the use of a metal oxide as an oxygen carrier, which transfers oxygen from the combustion air to the fuel, and the direct contact between fuel and combustion air is avoided. In this way, CO 2 and H 2 O are inherently separated from the other components of flue gases leading to no energy needed for CO 2 separation. It is worthy emphasized that this novel CO 2 capture technology simultaneously resolve both energy and environmental problems in a combustion processes, since the conversion of fuel-based chemical energy into chemical energy in th

Structure, morphology and magnetic properties of flowerlike gamma-Fe2O3@NiO core/shell nanocomposites synthesized from different precursor concentrations

The flowerlike gamma-Fe2O3@NiO core/shell nanocomposites are synthesized by the two-step method. Their structure and morphology can be controlled by tuning the precursor concentration. Microstructural analysis reveals that all the samples have distinct core/shell structure without impurities, and the NiO shells are built of many irregular nanosheets which enclose the surface of gamma-Fe2O3 core. As the precursor concentration decreases (i.e., more NiO content), the NiO grain grows significantly, and the thickness of NiO shells increases. Magnetic experiments are performed to analyze the influences of different microstructures on magnetic properties of samples and we have the following two results. First, at 5 K, along with increasing thickness of NiO shell, the saturation magnetization increases, while the residual magnetization decreases slightly. Second, the hysteresis loops under cooling field demonstrate that the value of exchange bias effect fluctuates between 13 Oe and 17 Oe. This is mainly because of the NiO shell that (i) is composed of irregular nanosheets with disordered orientations, and (ii) does not form a complete coating around gamma-Fe2O3 core