Investigation into micro machinability of Mg based metal matrix compostites (MMCs) reinforced with nanoparticles

PhD ThesisAs composite materials with combination of low weight and high engineering strength, traditional metal matrix composites (MMCs) with micro-sized reinforcement (micro-MMCs) have been utilized in numerous area such as aerospace, automobile, medical and advanced weapon systems in the past two decades. With the development of composite materials, metal matrix composites reinforced with small volume fraction of nano-sized reinforcements (nanoMMCs) exhibits an equivalent and even better properties than that reinforced with large volume of micro-sized reinforcement and thus receive increasing attention from academia and industries. MMCs components are typically fabricated in near net shape process such as casting. But micro machining processes are indispensable in order to meet the increasing demands on the component with high dimensional accuracy and complex shapes. However, the enhanced mechanical properties of MMCs and tool-like hardness of reinforced particles bring challenges to machining process. The deteriorative machined surface finish and excessive tool wear have been recognised as the main obstacles during machining of MMCs due to their heterogeneous and abrasive nature. In this research, the detailed material removal mechanism of nano-MMCs in terms of micro machinability, micro tool wear and simulated material removal process with finite element analysis (FEA) is investigated. The systematic experimental studies on micro machining mechanism of magnesium-based MMCs reinforced with nanoparticles (Ti, TiB2, BN, ZnO) are conducted. The cutting force, burr formation, surface roughness and morphology are characterised to investigate the micro machinability under the effect of various machining parameters, particle volume fraction and matrix/reinforcement materials using design of experiment (DoE) and analysis of variance (ANVOA) methods. The micro structure changes of Mg-MMCs by addition of nanoparticles were taken into account. In addition, surface morphology and the minimum chip thickness is obtained and characterised with the aim of examining the specific cutting energy. A comprehensive investigation of tool wear mechanisms in the micro milling of Mg-MMCs is conducted. The tool wear is characterised both quantitatively and qualitatively by observing tool wear patterns and analysing the effect of cutting parameters and tool coating on average flank wear, reduction in tool diameter, cutting forces, surface roughness, and burr formation. The main wear mechanisms at different machining conditions are determined. Finally, the tool wear phenomenon observed from experiments is explained by simulating the tool-particles interaction using finite element modelling, and hence new wear mechanisms are proposed for machining nano-MMCs. iv The two dimensional micromechanical finite element (FE) models are established to study the material removal mechanism of MMCs reinforced with micro-sized and nanoparticles in micro machining process with consideration of size effect. Two phases, namely particle and matrix are modelled in FE cutting models. Particle fracture properties are involved in micro-sized particles to study the fracture behaviours. The cutting force, tool-particles interaction, particle fracture behaviours, stress/strain distribution, chip formation process and surface morphology are investigated in the FE models. The surface defect generation mechanism is studied in details by developing the additional three dimensional (3D) FE models in machining micro-MMCs. Moreover, the cutting mechanism comparison between machining nano-MMCs and microMMCs is conducted to investigate the effect of significant particle size reduction from micro to nano-scale. The model validation is carried out by studying the chip morphology, cutting force, surface morphology obtained from machining experiments and good agreements are found with the simulation results

Hierarchical binding of copperII to N-truncated Ab4–16 peptide

N-Truncated Ab4–42 displays a high binding affinity with CuII. A mechanistic scheme of the interactions between Ab4–42 and CuII has been proposed using a fluorescence approach. The timescales of different conversion steps were determined. This kinetic mechanism indicates the potential synaptic functions of Ab4–42 during neurotransmission

A Review on Nanocomposites. Part 1: Mechanical Properties

Micromachining of nanocomposites is deemed to be a complicated process due to the anisotropic, heterogeneous structure, and advanced mechanical properties of these materials associated with the size effects in micromachining. It leads to poorer machinability in terms of high cutting force, low surface quality, and high rate of tool wear. In part 1 of this two-part review paper, a comprehensive review on mechanical properties of various nanocomposites will be presented while the second part of the paper will focus on the micro-machinability of these nanocomposite materials

A Review on Nanocomposites. Part 2: Micromachining

Micromachining of nanocomposites is deemed to be a complicated process due to the anisotropic, heterogeneous structure and advanced mechanical properties of these materials associated with the size effects in micromachining. It leads to poorer machinability in terms of high cutting force, low surface quality, and high rate of tool wear. A comprehensive review on mechanical properties of nanocomposites aiming to pointout their effects on micro-machinability has been addressed in part 1. In part 2, the subsequent micro-machining processes are critically discussed based on relevant studies from both experimental and modeling approaches. The main findings and limitations of these micro-machining methods in processing nanocomposites have been highlighted together with future prospects

Analysis of Odor Components in Salted Egg Yolk during Thermal Processing Using Gas Chromatography-Mass Spectrometry and Multivariate Statistical Analysis

Odor compounds produced in salted egg yolk during thermal processing were identify by sensory evaluation and gas chromatography-mass spectrometry (GC-MS) combined with multivariate statistical analysis such as hierarchical cluster analysis (HCA), orthogonal partial least squares-discriminant analysis (OPLS-DA) and principal component analysis (PCA). By using quantitative descriptive sensory analysis, it was found that there was a significant difference in the flavor profile between egg yolk samples with and without unpleasant odor, and it was determined that some egg yolks had obvious off-flavor during hot processing. Cluster analysis showed that the six groups of salted egg yolk samples were clearly divided into two categories, which was consistent with the sensory evaluation results. Furthermore, OPLS-DA identified 33 major differential components with variable importance in the projection (VIP) scores greater than one between samples with and without unpleasant odor, and aldehydes and alcohols were the most significant differential components. Finally, the volatile compounds showing a positive correlation with sour odor were screened by PCA, and n-hexanal, n-valeraldehyde, 1-octen-3-ol, trans,trans-2,4-decadienal, styrene, dimethyl disulfide and 2-nonone were identified due to their odor activity values (OAV) greater than one as the major odor compounds of salted egg yolk during thermal processing. The results provide a reference for analysis of the flavor characteristics and possible off-flavor components of salted egg yolk after thermal processing and provide a scientific basis for accessing the quality of salted egg yolk

Deep Brain Stimulation Complications in Patients With Parkinson’s Disease and Surgical Modifications: A Single-Center Retrospective Analysis

BackgroundAs a complication-prone operation, deep brain stimulation (DBS) has become the first-line surgical approach for patients with advanced Parkinson’s disease (PD). This study aimed to evaluate the incidence and risk factors of DBS-associated complications.MethodsWe have reviewed a consecutive series of patients with PD undergoing DBS procedures to describe the type, severity, management, and outcome of postoperative complications from January 2011 to December 2018. Both univariate and multivariate analyses were performed to identify statistically significant risk factors. We also described our surgical strategies to minimize the adverse events.ResultsA total of 225 patients underwent 229 DBS implantation procedures (440 electrodes), of whom 20 patients experienced 23 DBS-associated complications, including ten operation-related complications and 13 hardware-related ones. Univariate analysis elucidated that comorbid medical conditions (P = 0.024), hypertension (P = 0.003), early-stage operation (P < 0.001), and unilateral electrode implantation (P = 0.029) as risk factors for overall complications, or more specifically, operation-related complications demonstrated in the stratified analysis. In contrast, no risk factor for hardware-related complications was identified. Statistical significances of hypertension (OR = 3.33, 95% CI: 1.14–9.71, P = 0.027) and early-stage (OR = 11.04, 95% CI: 2.42–50.45, P = 0.002) were further validated via multivariate analysis. As the annual number of DBS procedures increased, the incidence of complications gradually decreased (R = −0.699, P < 0.01). Additionally, there was a strong correlation between surgical complications and unplanned readmission (R = 0.730, P < 0.01).ConclusionThe importance of cumulative experience and relevant technique modifications should be addressed to prevent DBS-associated complications and unplanned readmission

Targeting T Cell Activation and Lupus Autoimmune Phenotypes by Inhibiting Glucose Transporters

CD4+ T cells have numerous features of over-activated cellular metabolism in lupus patients and mouse models of the disease. This includes a higher glycolysis than in healthy controls. Glucose transporters play an essential role in glucose metabolism by controlling glucose import into the cell from the extracellular environment. We have previously shown that treatment of lupus-prone mice with 2-deoxy-D-glucose, which inhibits the first step of glycolysis was sufficient to prevent autoimmune activation. However, direct targeting of glucose transporters has never been tested in a mouse model of lupus. Here, we show that CG-5, a novel glucose transporter inhibitor, ameliorated autoimmune phenotypes in a spontaneous lupus-prone mouse model, B6.NZM2410.Sle1.Sle2.Sle3 (Triple-congenic, TC), and in a chronic graft- vs. host-disease (cGVHD) model of induced lupus. In vitro, CG-5 blocked glycolysis in CD4+ T cells, and limited the expansion of CD4+ T cells induced by alloreactive stimulation. CG-5 also modulated CD4+ T cell polarization by inhibiting Th1 and Th17 differentiation and promoting regulatory T (Treg) induction. Moreover, CG-5 treatment reduced lupus phenotypes including the expansion of germinal center B (GC B) cells, as well as the production of autoantibodies in both TC mice and cGVHD models. Finally, CG-5 blocked glycolysis in human T cells. Overall, our data suggest that blocking glucose uptake with a small molecule inhibitor ameliorates autoimmune activation, at least partially due to its inhibition of glycolysis in CD4+ T cells

Characterizing Acupuncture Stimuli Using Brain Imaging with fMRI - A Systematic Review and Meta-Analysis of the Literature

Background The mechanisms of action underlying acupuncture, including acupuncture point specificity, are not well understood. In the previous decade, an increasing number of studies have applied fMRI to investigate brain response to acupuncture stimulation. Our aim was to provide a systematic overview of acupuncture fMRI research considering the following aspects: 1) differences between verum and sham acupuncture, 2) differences due to various methods of acupuncture manipulation, 3) differences between patients and healthy volunteers, 4) differences between different acupuncture points. Methodology/Principal Findings We systematically searched English, Chinese, Korean and Japanese databases for literature published from the earliest available up until September 2009, without any language restrictions. We included all studies using fMRI to investigate the effect of acupuncture on the human brain (at least one group that received needle-based acupuncture). 779 papers were identified, 149 met the inclusion criteria for the descriptive analysis, and 34 were eligible for the meta-analyses. From a descriptive perspective, multiple studies reported that acupuncture modulates activity within specific brain areas, including somatosensory cortices, limbic system, basal ganglia, brain stem, and cerebellum. Meta-analyses for verum acupuncture stimuli confirmed brain activity within many of the regions mentioned above. Differences between verum and sham acupuncture were noted in brain response in middle cingulate, while some heterogeneity was noted for other regions depending on how such meta-analyses were performed, such as sensorimotor cortices, limbic regions, and cerebellum. Conclusions Brain response to acupuncture stimuli encompasses a broad network of regions consistent with not just somatosensory, but also affective and cognitive processing. While the results were heterogeneous, from a descriptive perspective most studies suggest that acupuncture can modulate the activity within specific brain areas, and the evidence based on meta-analyses confirmed some of these results. More high quality studies with more transparent methodology are needed to improve the consistency amongst different studies