Comparison of neuromuscular junction dynamics following ischemic and aged skeletal muscle

Both aging and neuromuscular diseases lead to significant changes in the morphology and functionality of the neuromuscular synapse. Skeletal muscles display a remarkable regenerative capacity, however, are still susceptible to diseases of aging and peripheral nerve perturbations. In this study, we assessed how neuromuscular synapses differ in aged and injured skeletal muscle using an improved neuromuscular junction (NMJ) staining and imaging method. We found that both aged and ischemic skeletal muscle display Wallerian degeneration of the presynaptic motor axons and fragmentation of postsynaptic acetylcholine receptors (AChRs). Quantifiable measurements of various metrics of the NMJs provide a more concrete idea of the dynamics that are occurring in the muscle microenvironment. We questioned whether neuronal degradation precedes myofiber atrophy or vice versa. Previously, it was shown that a cellular crosstalk exists among the motor neurons, myofibers, vasculature, and mitochondria within the muscle microdomain. It is apparent that lack of blood flow to motor neurons in ischemic skeletal muscle disrupts the structure of NMJs, however it is unclear if the aging condition experiences similar dynamics. We demonstrated that both aged and ischemic skeletal muscle demonstrate similar patterns of degeneration, characterized by a smaller percentage overlap of presynaptic and postsynaptic sides, greater fragmentation of AChRs, and a smaller area of AChR clusters. Together, these results reveal high resolution, precise parallels between the aged and ischemic NMJs.

Effect of Aging on the Properties of Intermetallic Layers in SAC+Bi Solder Joints

A major problem faced by electronic packaging industries is the poor reliability of lead free solder joints. One of the most common methods utilized to tackle this problem is by doping the alloy with other elements, especially bismuth. Researches have shown Bismuth doped solder joints to mostly fail near the Intermetallic (IMC) layer rather than the bulk of the solder joint as commonly observed in traditional SAC305 solder joints. An understanding of the properties of this IMC layer would thus provide better solutions on improving the reliability of bismuth doped solder joints. In this study, the authors have used three different lead free solders doped with 1%, 2% and 3% bismuth. Joints of these alloys were created on copper substrates. The joints were then polished to clearly expose the IMC layers. These joints were then aged at 125 °C for 0, 1, 2, 5 and 10 days. For each aging condition, the elastic modulus and the hardness of the IMC layers were evaluated using a nanoindenter. The IMC layer thickness and the chemical composition of the IMC layers were also determined for each alloy at every aging condition using Scanning Electron Microscopy (SEM) and EDS. The results from this study will give a better idea on how the percentage of bismuth content in lead free solder affects the IMC layer properties and the overall reliability of the solder joints.

Relationship between Rheological Indices and Cracking Performance of Virgin, Recycled, and Rejuvenated Asphalt Binders and Mixtures

Long-term cracking performance of asphalt mixtures is heavily influenced by asphalt binder rheology, and changes in binder stiffness, ductility, and aging condition significantly affect the cracking resistance of the corresponding asphalt mixture. This study evaluated the effectiveness of several common and recently developed binder rheological indices in capturing the effects of binder performance grade (PG) and source, recycled binder content, recycling agent (rejuvenator) dose, and long-term aging. These binder rheological indices included the Superpave intermediate-temperature PG (PGI), the Glover-Rowe (G-R) parameter, the crossover temperature (Tδ = 45°), the rheological index (R-value), and ΔTc. This study also directly compared the binder rheological indices with the cracking performance of corresponding asphalt mixtures to explore possible correlations and their robustness. Asphalt mixture cracking performance was evaluated using the Illinois Flexibility Index Test (I-FIT) for intermediate-temperature cracking, and the disk-shaped compact tension (DCT) test and the uniaxial thermal stress and strain test (UTSST) for low-temperature cracking. Results indicated that all the binder rheological indices (except PGI) consistently captured the effects of binder blend composition and proportions and aging condition, with a few exceptions. Results also showed that the G-R parameter, the crossover temperature (Tδ = 45°), and ΔTc had the best correlation to asphalt mixture and field core cracking performance as compared with other rheological indices (PGI and R-value), with ΔTc demonstrating the overall best correlation to mixture cracking performance.

Experimental Study of Low Temperature Performance of Porous Asphalt Mixture

Porous asphalt mixture can be used as a road surface paving material with the remarkable advantage to prevent water accumulation and ponding. However, the performance of porous asphalt mixture in low temperature environment has not been thoroughly investigated, and this forms the subject of research in the present study. The mineral aggregate gradation of porous asphalt mixture was designed based on Bailey method, and the low temperature performance of porous asphalt mixture was studied by means of the low temperature bending test. The factors affecting the low temperature performance of porous asphalt mixture were analyzed through the orthogonal experimental design method, and the effects of porosity, modifier content, aging condition, and test temperature on the low temperature performance of porous asphalt mixture were evaluated. The results showed that the modifier content was the most important factor affecting the low temperature performance of porous asphalt mixture, followed by the test temperature, while the porosity and the aging condition were the least. Among the three performance evaluation indicators, namely the flexural tensile strength, maximum bending strain, and bending stiffness modulus, the maximum bending strain had the highest sensitivity to the porosity. It can be seen from the single factor influence test of porosity that there existed an approximately linear relationship between the maximum bending strain and the porosity of porous asphalt mixture, and the maximum bending strain decreased with increasing porosity. Furthermore, in order to ensure the good working performance of porous asphalt mixture in low temperature environment, the porosity should also satisfy the required limits of the maximum bending strain.

Investigation of Different Laboratory Aging Methods of Bituminous Mixtures

The predicted performance and service life of the pavement depend largely on the properties of bitumen used in the mixtures. The most important feature of bitumen, which has profound effect on the performance of the road is durability. The durability of bitumen is expressed as the resistance to aging. In this study, the bituminous mixture aging was performed instead of bitumen aging in order to represent the aging in the field in the best possible way. The aim of this paper is to evaluate different proposed laboratory aging methods (NCHRP 09-52, NCHRP 09-54 and RILEM) in relation with the current Standard AASHTO R30 (Standard Practice For Mixture Conditioning of Hot Mix Asphalt standard) and to make comparison with the samples performance taken from the field in terms of Indirect Tensile Strength (ITS). The level of aging has also been compared with the samples taken from recently constructed pavement surface and from the five years old pavement surface. Results depicted that, laboratory aging methods revealed the field aging properties on the unaged bitumen. Based on the results, 2 hours forced draft oven aging at 135°C is recommended as short term aging condition because, 2 hours or 4 hours short term forced draft oven aging did not yield significant variation in terms of ITS values. Additionally, 120 hours (5 days) oven aging of compacted samples at 85°C can be recommended as long term aging condition.

Experimental Investigation of PV Array Interconnection Topologies at Nonuniform Aging Condition for Power Maximization

In vast Photovoltaic (PV) power plant the output power production decreases significantly due to the fact of non-uniform aging of PV modules. The non-uniform aging of PV modules increases current-voltage (I-V) mismatch among the array modules and causes mismatch power loss (MPL). There are different interconnection topologies of the PV module in an array to minimize MPL and thus maximize the array output power. This paper investigates four different interconnection topologies experimentally on a 4×4 nonuniformly aged PV array. Three different patterns of PV module rearrangement are used to investigate the performance of each interconnection topology in terms of array output power and MPL. The experimental results show that the proposed interconnection topology is yields about 3.28% (average) higher output power than that of the most commonly used series-parallel array topology. GUB JOURNAL OF SCIENCE AND ENGINEERING, Vol 6(1), Dec 2019 P 39-45