Search Results

You are looking at 1 - 7 of 7 items

  • Author: Longfei Wang x
Clear All Modify Search

Abstract

The present work studied the carbides in forged and annealed H13 hot work die steel. The carbides were examined by scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and X-ray diffraction (XRD) and analyzed with quantitative chemical analysis method. The carbide types, qualities and compositions in dependence on temperatures were thermodynamically calculated by Thermo-Calc software and compared with the experimental results. In the final, methods for carbide improvement were discussed. The results are as follows. The primary carbides and the carbide segregation are improved after the hot-forging operation. The carbides in the hot-forged and annealed H13 steel are M7C3, M6(C, N) and M(C, N) which is accordance with the calculated results. Trace Mg added to the H13 steel leads to an increase of primary carbide nucleation and a decrease of primary carbide size.

Abstract

Patients with amnestic mild cognitive impairment (aMCI) are at an increased risk of further deterioration and eventually developing Alzheimer’s disease (AD). Therefore, the identification of specific markers for this disease such as radiological markers is of great diagnostic and clinical significance. Our previous work has shown that magnetic resonance imaging (MRI) is a powerful tool to identify unique imaging features in patients with aMCI. Herein, we calculated the gray matter volume by structural magnetic resonance imaging (sMRI), and spontaneous low frequency fluctuations (LFF) using resting-state functional MRI (rs-fMRI) in 11 patients with aMCI and 22 normal control patients. Compared with the control group, patients with aMCI showed significant reduction of gray matter volume in the inferior frontal gyrus, inferior parietal lobule, anterior cingulated cortex, and insula and superior temporal gyrus. Patients with aMCI also showed significantly lower amplitudes of low-frequency fluctuations (ALFF) in the posterior cingulate cortex, precuneus, temporal gyrus and inferior parietal lobule when compared with the control group. However, in several other brain regions including the occipital lobe and cerebellum, the ALFF in patients with aMCI was significantly increased. The variation in ALFF between the two groups remained significant after adjustment for structural differences. Our results obtained in this pilot study are consistent with our previous finding and collectively show that patients with aMCI have abnormal MRI imaging findings. The pathological basis of these imaging features in patients with aMCI needs to be further explored.

Abstract

Pitch uncertainty and line edge roughness are among the critical quality attributes of a pitch standard and normally the analyses of these two parameters are separate. The analysis of self-traceable Cr atom lithography nano-gratings shows a positive relevance and sensitivity between LER and evaluated standard deviation of pitch. Therefore, LER can be used as an aided pre-evaluation parameter for the pitch calculation method, such as the gravity center method or the zero-crossing points method. The optimization of the nano-grating evaluation method helps to obtain the accurate pitch value with fewer measurements and provide a comprehensive characterization of pitch standards.

Abstract

Recently, ionic polymer-metal composites (IPMCs), which are becoming an increasingly popular material, have been used as soft actuators because of their inherent properties of light weight, flexibility, softness, especially efficient transformation from electrical energy to mechanical energy with large bending strain response under low activation voltage. This paper mainly focuses on a review on optical and micromanipulation applications of IPMCs as soft actuators. After presenting the general mechanism of sensing and actuating in IPMCs, recent progresses are discussed about the preparation process and practical technologies, especially for aided manufacturing techniques defined as the methods to fabricate IPMC into all kinds of shapes in terms of the demands, which are reviewed for the first time. Then, a number of recent IPMC applications for optical actuators, grippers and catheters are reviewed and investigated in this paper. Further developments and suggestions for IPMCs are also discussed. Extensive previous researches are provided for references in detail.

Abstract

Ribs effects on the heat transfer performance and cooling air flow characteristics in various aspect ratios (AR) U-shaped channels under different working conditions are numerically investigated. The ribs angle and channel orientation are 45° and 90°, respectively, and the aspect ratios are 1:2, 1:1, 2:1. The inlet Reynolds number changes from 1e4 to 4e4 and rotational speeds include 0, 550 rpm, 1,100 rpm. Local heat transfer coefficient, endwall surface heat transfer coefficient ratio and augmentation factor are the three primary criteria to measure channel heat transfer. Ribs increase the heat transfer area and improve heat transfer coefficient of ribbed surfaces significantly, especially in the 1st pass, while the endwall surface contributes more to channel heat transfer because of the larger area and relatively smaller heat transfer coefficient. The wide channel (AR=2:1) owns the better augmentation factor than the narrow channel (AR=1:2) and ribs heat transfer weight increases with an increase of the inlet Reynolds number. Rotating slightly reduces the ribs heat transfer weight in channel and the trailing surface in 1st pass is the main influence object of rotating.

Abstract

The numerical simulations are used to conduct the comparative study of pin-fins cooling channel and multi-impingement cooling channel on the heat transfer and flow, and to design the multi-impingement channel through the parameters of impinging distance and impingement-jet-plate thickness. The Reynolds number ranges from 1e4 to 6e4. The dimensionless impinging distance is 0.60, 1.68, 2.76, respectively, and the dimensionless impinging-jet-thickness is 0.5, 1.0, 1.5, respectively. The endwall surface, pin-fins surface, impinging-jet-plate surface are the three object surfaces to investigate the channel heat transfer performance. The heat transfer coefficient h and augmentation factor Nu/Nu0 are selected to measure the surface heat transfer, and the friction coefficient f is chosen to evaluate the channel flow characteristics. The impinging-jet-plate surface owns higher heat transfer coefficient and larger area than pin-fins surface, which are the main reasons to improve the heat transfer performance of multi-impingement cooling channel. Reducing the impinging distance can improve the endwall surface heat transfer obviously and enhance impingement plate surface heat transfer to some extent, decreasing the thickness of impinging-jet-plate can significantly increase its own heat transfer coefficient, which both all increase the cooling air flow loss.