Control of optical bandgap energy and optical absorption coefficient by geometric parameters in sub-10 nm silicon-nanodisc array structure

A sub-10 nm, high-density, periodic silicon-nanodisc (Si-ND) array has been fabricated using a new top-down process, which involves a 2D array bio-template etching mask made of Listeria-Dps with a 4.5 nm diameter iron oxide core and damage-free neutral-beam etching (Si-ND diameter: 6.4 nm). An Si-ND array with an SiO(2) matrix demonstrated more controllable optical bandgap energy due to the fine tunability of the Si-ND thickness and diameter. Unlike the case of shrinking Si-ND thickness, the case of shrinking Si-ND diameter simultaneously increased the optical absorption coefficient and the optical bandgap energy. The optical absorption coefficient became higher due to the decrease in the center-to-center distance of NDs to enhance wavefunction coupling. This means that our 6 nm diameter Si-ND structure can satisfy the strict requirements of optical bandgap energy control and high absorption coefficient for achieving realistic Si quantum dot solar cells.     

Effect of operating parameters and chemical treatment on the tribological performance of natural fiber composites: A review

The demand for high-performance engineering products made from natural resources is increasing because of the low-cost, low-density, biodegradability, renewable nature and lighter than synthetic fibers. With these characteristics, the tribological performance of natural fiber composite has become an important element to be considered in most industrial and manufacturing functions. This paper presents an overview of the factors that influence the tribological performance of natural fiber composites, which include applied load, sliding distance, sliding velocity and fiber orientation. Influences of chemical treatment is also reviewed and illustrated through scanning electron microscope (SEM) observations. This review will focus on kenaf fibers (KFs) and oil palm fibers (OPFs) which have been widely exploited over the past few years among the available natural resources. The results show that the operating parameter, fiber orientation and chemical treatment has significant effects on the tribological performance of natural composite. A clear understanding of the factors that affect the tribological performance is very essential in performance improvement on natural fibers reinforced polymer composite for potential applications.     

Recent Advances on the Role of Brain-Derived Neurotrophic Factor (BDNF) in Neurodegenerative Diseases

Neurotrophins, such as brain-derived neurotrophic factor (BDNF), are essential for neuronal survival and growth. The signaling cascades initiated by BDNF and its receptor are the key regulators of synaptic plasticity, which plays important role in learning and memory formation. Changes in BDNF levels and signaling pathways have been identified in several neurodegenerative diseases, including Alzheimer’s disease, Parkinson’s disease, and Huntington’s disease, and have been linked with the symptoms and course of these diseases. This review summarizes the current understanding of the role of BDNF in several neurodegenerative diseases, as well as the underlying molecular mechanism. The therapeutic potential of BDNF treatment is also discussed, in the hope of discovering new avenues for the treatment of neurodegenerative diseases.     

Assessment of stable tearing on fatigue fracture surfaces

Fatigue fracture surfaces in a range of structural metals sometimes exhibit bands, visible as dull crescent-shaped regions which contrast to the “bright” background fatigue surface. Such bands are believed to be created within a single load cycle under either constant-amplitude or variable-amplitude load conditions. Microscopically, crack advance by tearing has similarity to the final unstable fracture of the component, with the difference that the tearing is stable: it arrests after a certain distance of crack front advance, which is then followed by further fatigue crack growth. Multiple stable tearing bands, separated by regions created by fatigue crack growth, may be visible on a single fracture surface, to the extent that they may even make up the majority of the fracture surface area.Post-failure analysis of fracture surfaces often relies on quantitative fractography to relate various crack-front progression markings to specific loads in the load history, in order to estimate the crack growth history in the component. Matching this data to predicted crack growth, however, is complicated by the fact that stable tearing is not included in fatigue predictive models, and so the presence of significant tearing can greatly complicate the derivation of a crack growth history which can be matched to a crack growth model. The post-failure analysis of fracture surfaces is particularly difficult in cases where the load history record is poor, and that process has been observed to be much more difficult when significant tearing is present. Several empirical models and concepts have been proposed to assist with post-failure analysis of tearing, but as yet we do not have a good understanding of the parameters which influence both the onset and the arrest of the tearing, and the factors which control crack shape change as tearing progresses. As a result, the interpretation of tearing on service fracture surfaces remains difficult.This paper reviews the existing empirical models for tearing analysis, and describes a series of tests which produced tearing in an aircraft aluminium alloy, with the aim of developing a better understanding of these fracture surface features. The analysis of the tearing shapes indicates that one of the empirical models may have broad value as an engineering analysis tool, since it correlates reasonably well with tearing characteristics in these tests. The study reveals that the stress intensity factor is one of the key controlling parameters in tearing onset and arrest, although simple methods for estimation of relevant stress intensity values are problematic because of the key role of crack front curvature. The main conclusions relate to the notable differences between tearing under constant-amplitude and variable-amplitude loading. The constant-amplitude conditions confer some resistance to stable tearing, and this is believed to result from the high loading prior to tear onset; several mechanisms could be involved. This research is part of a program which is developing improved analytical and prognostic models for stable tearing.     

A simulation of the comminution process of homogenized lithium-ion battery models

The simulation of the comminution process of a lithium-ion battery model and evaluation of the performance of three cylindrical battery models derived from previous studies were achieved in the present study. The finite element method (FEM) was used along with dynamic simulation procedures. The models were classified based on the battery material model parameters used in the analysis, namely type A, B, and C models. The battery material models of type A and C were unable to provide results that were consistent with real-world circumstances. In contrast, the type B model gives a realistic battery dynamic reaction. Additional testing on the type B model was performed in terms of battery shard size, fracture energy, comminution pressures, element displacement, battery element velocity, and device capacity calculation. The simulation results revealed that the type B model in this study is capable of properly predicting the dynamic response of the battery, notably when compared to the other two models. The study in the present research could be used in the future to identify the proper cutting tool geometry, estimate the size of the comminution product, and play an important role in the design and optimization of the comminution machine.

     

Comparative effects of palm vitamin E and α-tocopherol on healing and wound tissue antioxidant enzyme levels in diabetic rats

The effect of supplementing 200 mg/kg body weight palm vitamin E (PVE) and 200 mg/kg body weight α-tocopherol (α-loc) on the healing of wounds in streptozotocin-induced diabetic rats was evaluated. The antioxidant potencies of these two preparations of vitamin E were also evaluated by determining the antioxidant enzyme activities, namely, glutathione peroxidase (GPx) and superoxide dismutase (SOD), and malondialdehyde (MDA) levels in the healing of dermal wounds. Healing was evaluated by measuring wound contractions and protein contents in the healing wounds. Cellular redistribution and collagen deposition were assessed morphologically using cross-sections of paraffin-embedded day-10 wounds stained according to the Van Gieson method. GPx and SOD activities as well as MDA levels were determined in homogenates of day-10 dermal wounds. Results showed that PVE had a greater potency to enhance wound repair and induce the increase in free radical-scavenging enzyme activities than α-Toc. Both PVE and α-Toc, however, were potent antioxidants and significantly reduced the lipid peroxidation levels in the wounds as measured by the reduction in MDA levels.