Investigation on Reaction Mechanisms of Nano-energetic Materials and Application in Joining

Nano-energetic materials, also known as metastable intermetallic composites (MICs), have shown promise in applications such as propellants, pyrotechnics, and explosives. The work in this thesis pursues a deep understanding of the reaction mechanisms of typical nano-thermite composites and the functions of CNTs in nano-thermite reactions. The thesis begins with the development of nano-thermite composites with layered structure using Al and Fe2O3 nanoparticles via the Electrophoretic Deposition (EPD) process. The nano-thermite composites show a consistency in onset temperature even with different ratios of Al and Fe2O3, which suggests uniform interfacial formation, where the nano-thermite reactions are initiated. This work investigates the reaction mechanisms of typical nano-thermite composites: Al/CuO and Al/NiO. The results show that the Al/CuO nano-thermite system exhibits a gas-solid reaction mechanism, whereas the Al/NiO system exhibits a condensed-phase reaction mechanism. Furthermore, the functions of CNTs in nano-thermite reactions are investigated. The mass transfer mechanisms and thermal conductivities affect the energy release and reaction rate. Improvements in thermal conductivity and mass transfer are able to enhance the reactivity of nano-thermite composites. Measurements indicate that CNTs possess extremely high thermal conductivity compared with Al and metal oxidizers. Meanwhile, the NiO nanoparticles and CNTs react to release CO or CO2 at the initial stage of the thermite reaction. The CO or CO2 carry the oxygen atoms to the Al layers, followed by the reaction between Al and CO2. Overall, the function of CNTs in nano-thermite reactions using the Al/NiO nano-thermite composite is to change the reaction from a solid-solid mechanism to a condensed-phase mechanism. Finally, silicon wafers are welded using nano-thermite composites in order to achieve the application attempt. It has been shown that increasing energy release and decreasing apparent activation energy can provide an enhanced amount of energy to the interfacial area, which produces better mechanical strength in the welded zone

Comparative analysis of physiological variations and genetic architecture for cold stress response in soybean germplasm

Soybean (Glycine max L.) is susceptible to low temperatures. Increasing lines of evidence indicate that abiotic stress-responsive genes are involved in plant low-temperature stress response. However, the involvement of photosynthesis, antioxidants and metabolites genes in low temperature response is largely unexplored in Soybean. In the current study, a genetic panel of diverse soybean varieties was analyzed for photosynthesis, chlorophyll fluorescence and leaf injury parameters under cold stress and control conditions. This helps us to identify cold tolerant (V100) and cold sensitive (V45) varieties. The V100 variety outperformed for antioxidant enzymes activities and relative expression of photosynthesis (Glyma.08G204800.1, Glyma.12G232000.1), GmSOD (GmSOD01, GmSOD08), GmPOD (GmPOD29, GmPOD47), trehalose (GmTPS01, GmTPS13) and cold marker genes (DREB1E, DREB1D, SCOF1) than V45 under cold stress. Upon cold stress, the V100 variety showed reduced accumulation of H2O2 and MDA levels and subsequently showed lower leaf injury compared to V45. Together, our results uncovered new avenues for identifying cold tolerant soybean varieties from a large panel. Additionally, we identified the role of antioxidants, osmo-protectants and their posttranscriptional regulators miRNAs such as miR319, miR394, miR397, and miR398 in Soybean cold stress tolerance

Gut Microbiota Aggravates Neutrophil Extracellular Traps-Induced Pancreatic Injury in Hypertriglyceridemic Pancreatitis

Hypertriglyceridemic pancreatitis (HTGP) is featured by higher incidence of complications and poor clinical outcomes. Gut microbiota dysbiosis is associated with pancreatic injury in HTGP and the mechanism remains unclear. Here, we observe lower diversity of gut microbiota and absence of beneficial bacteria in HTGP patients. In a fecal microbiota transplantation mouse model, the colonization of gut microbiota from HTGP patients recruits neutrophils and increases neutrophil extracellular traps (NETs) formation that exacerbates pancreatic injury and systemic inflammation. We find that decreased abundance of Bacteroides uniformis in gut microbiota impairs taurine production and increases IL-17 release in colon that triggers NETs formation. Moreover, Bacteroides uniformis or taurine inhibits the activation of NF-κB and IL-17 signaling pathways in neutrophils which harness NETs and alleviate pancreatic injury. Our findings establish roles of endogenous Bacteroides uniformis-derived metabolic and inflammatory products on suppressing NETs release, which provides potential insights of ameliorating HTGP through gut microbiota modulation

Design and Numerical Evaluation of Cascade-Type Thermoelectric Modules

Thermoelectric (TE) generation performance can be enhanced by stacking several TE modules (so-called cascade-type modules). This work presents a design method to optimize the cascade structure for maximum power output. A one-dimensional model was first analyzed to optimize the TE element dimensions by considering the heat balance including conductive heat transfer, Peltier heat, and Joule heat, assuming constant temperatures at all TE junctions. The number of p–n pairs was successively optimized to obtain maximum power. The power output increased by 1.24 times, from 12.7 W in a conventional model to 15.7 W in the optimized model. Secondly, a two-dimensional numerical calculation based on the finite-volume method was used to evaluate the temperature and electric potential distributions. Voltage–current characteristics were calculated, the maximum power output was evaluated, and the efficiencies of two possible models were compared to select the optimal design. The one-dimensional analytical approach is effective for a rough design, and multidimensional numerical calculation is effective for evaluating the dimensions and performance of cascade-type TE modules in detail

Thermoelectric Generation Using Water Lenses

A solar light concentrator composed of water and plastic transparent film has been designed. This flexible lens design can trace the solar movement through control of the tensile stress and amount of water, and concentrate the solar energy onto the thermoelectric (TE) module surface. An experimental water lens was constructed, and the concentrated intensity was monitored by a photodiode as a function of x–z position; For example, when 3.0 kg water was filled and tension of 69.0 N/m was applied to the transparent vinyl sheet, the concentration ratio was evaluated as the maximum of 28.0 at a depth of 657 mm from the water lens bottom surface. TE generation was tested to show the validity of the water lens. The surface condition of the receiver was found to be critical

Study on the Vibration Effect of Short Footage Blasting Load on Surrounding Rock-Support Structure of Tunnel

In the excavation process of a drilling and blasting tunnel, it takes multiple blasting excavations to form, so it is inevitable to produce multiple blasting impact loads, which will cause certain vibration damage to the surrounding rock-support structure. To solve this problem, based on the attenuation formula of blasting vibration wave and considering the cumulative effect of short footage blasting load, the radial displacement formula of surrounding rock particles is derived, and the analytical solution of vibration velocity field is obtained by using the method of separating variables. Then, taking Cuobuling station of Qingdao Metro as the engineering background, the finite element software is used to simulate the tunnel excavation process under the action of short footage multiple blasting. The vibration damage impact of multiple blasting loads on the surrounding rock-supporting structure is analyzed from the accumulated displacement value and vibration velocity cumulative value of the excavation tunnel. The results show that the damage accumulation effect is produced in the surrounding rock of each section during the blasting construction, among which the accumulation is the largest at the arch bottom. With the increase of blasting times, the damage of the surrounding rock is still accumulating gradually. Compared with the first blasting, the peak value of vibration velocity of the second blasting increased by 114%, and with the increase of blasting times, the variation trend of maximum vibration velocity of the measuring point showed an upward trend, but the subsequent vibration acceleration decreased. Under the condition of grade V surrounding rock, when the thickness of the concrete spray layer is 350 mm, the maximum displacement cumulative value of each measuring point in profile 1-1 is reduced by about 50.4% compared with that without support. According to the displacement nephogram of the concrete spray layer, the displacement of the concrete spray layer accumulates after three times of blasting, which affects the stability of the supporting structure. Finally, an example analysis is carried out and compared with the analytical model results to verify the accuracy of the mechanical model

Using a Water Lens for Light Concentration in Thermoelectric Generation

A water lens is employed to concentrate sunlight on the surface of a thermoelectric module in order to heat it. This water lens can change its shape flexibly and is adjustable to solar altitudes. The lens shape and light path were simulated for the cases when the light is incident at an angle to the water surface, parallel to the central axis of the half-cylindrical water lens, and when the light is focused on a plate. A condensing ratio larger than 70 is achieved when the incident light is closer to the normal of the water surface and if the optimal lens shape is maintained

Study on Stability of Shield Tunnel Excavation Face in Soil-Rock Composite Stratum

In order to study the instability mode of shield excavation face in soil-rock composite stratum and determine the ultimate support pressure of excavation face, this paper selects two typical soil-rock composite strata and uses three-dimensional finite element software to study the failure development process of shield excavation face. Based on the principle of limit equilibrium, a calculation model of limit support pressure for soil-rock composite stratum is proposed and applied to practical engineering. It is found that the shape of “unloading loosening zone” is mainly determined by the properties of upper soil and the properties of lower rock mainly determine the scope and shape of “sliding instability zone.” With the increase of soil proportion coefficient, the ultimate bearing capacity increases nonlinearly and the growth rate decreases gradually. At the same time, the influence of overlying Earth pressure and soil cohesion cannot be ignored