Macroporous Polymer-Derived Ceramic Monoliths for Cryogenic Applications Manufactured by Water-Based Freeze Casting

Macroporous SiOC ceramics were prepared by a water-based freeze casting process, using polysiloxanes as precursors and silica sol as water phase and binder. The obtained porous monoliths have anisotropic porous structure and thermal and mechanical properties. The macroporous SiOC aimed at cryogenic applications which involve mass transport and thermal transport processes. The first part of the thesis focuses on manufacturing macroporous monoliths, in which process the surface characteristics of preceramic polymers in terms of hydrophobicity/hydrophilicity were modified to be used in the water-based freeze casting process. Two approaches were chosen for the surface modification. The first approach to modify the wettability of the precursor was pyrolysis of hydrophobic methyl phenyl polysiloxanes (H44) in inert gas at low temperature, by which hybrid ceramic materials (H44-derived filler) were generated. Depending on the pyrolysis temperatures, the surface characteristics can be varied from hydrophobic to hydrophilic. H44-derived fillers obtained by pyrolyzing methyl phenyl polysiloxane at 600 degree Celsius were hydrophilic enough to be used as solid phase in water-based process. The influence of solid loading, freeze temperatures and pyrolysis temperatures on porosity and specific surface areas were investigated. The combination of polymer derived filler materials with freezing casting method resulted in the trimodal pore structure (micro/meso/macropore) at pyrolysis temperature of 600 to 700 degree Celsius. Even at pyrolysis temperature of 1000 degree Celsius, the specific surface area was be as high as 74 square meter per gram. The pore shape can be tailored from lamellar to tubular depending on freezing temperatures. The second approach to modify the wettability was to introduce more hydrophilic groups to the hydrophobic methyl polysiloxane (MK) by cross-linking with (3-Aminopropyl)triethoxysilane (APTES). The molar ratios between MK and APTES and pyrolysis temperature led to different amounts of aminopropyl groups in the cross-linked products, which altered the basicity and hydrophilicity. For both approaches, besides the surface characteristics, surface charges also account for stable suspension to prepare final homogenous monoliths. Filler material prepared with MK: APTES molar ratio of 1:1, pyrolyzed at 600 degree Celsius was applicable for freeze casting considering the wettability and suspension stability. The monolith prepared with MK-APTES derived filler had also a hierarchical micro/meso/macroporous structure. The vapor adsorption indicated that the high content of silica sol improved the hydrophilicity greatly, and pyrolysis temperature also influenced the hydrophilicity to a minor degree. Notably, the silica sol is responsible for the formation of mesopores. The second part of the thesis was to investigate the mechanical and thermal properties of the obtained unidirectional porous SiOC ceramics prepared with MK and H44 at cryogenic and room temperatures. The compressive strength of monoliths was investigated both in air (293 Kelvin) and in liquid nitrogen (77 Kelvin). The influence of both liquid and cryogenic temperature on compressive strength was investigated. The compressive strength of monoliths showed not only anisotropy, but also a significant increase in liquid nitrogen. This increase may be due to the liquid nitrogen trapped inside the porous structures and cryogenic temperature. The linear thermal expansion coefficients (CTE), thermal conductivity and specific heat capacity of porous SiOC, were studied from cryogenic to room temperature. Both monoliths show anisotropic linear expansion coefficients, with the parallel direction having almost twice the shrinkage of the perpendicular direction. The monolith prepared with H44 showed thermal shrinkage twice as much as that prepared with MK and APTES, which might be due to the composition differences and measurement condition. The thermal conductivities of both monoliths made from two precursors showed anisotropic features and similar values. The minimum and maximum values for thermal conductivity are 0.2 and 0.9 Watts per meter per Kelvin. Thermal conductivities and specific heat capacities displayed an upward trend from low temperature to room temperature. It was assumed that the maximum heat conductivities of these materials were determined mainly by the macroporosity and the thermal conductivity of the hybrid material

A Method for Identifying the Key Performance Shaping Factors to Prevent Human Errors during Oil Tanker Offloading Work

Acknowledgments: The authors would like to appreciate the experts and the engineers working in the Beihai Oil Terminal for their constructive supports during the development of this work. The authors would also like to thank the editors and the anonymous reviewers for their valuable comments.Peer reviewedPublisher PD

HBX-Mediated Migration of HBV-Replicating HepG2 Cells: Insights on Development of Hepatocellular Carcinoma

Hepatitus B virus (HBV) is a major cause of the development of hepatpcellular carcinoma (HCC). One of the significant characteristics of tumor progression is cell migration which is reflective of cytoskeletal dynamics. The Rho GTPases contribute to a multiple cellular processes, including the cellular cytoskeletal reorganization and motility. It has been found that some Rho GTPases have oncogenic activity and can promote cancer cell invasion. Here we discuss one of the Rho GTPases, Rac1 can be activated by HBV replication and such activation results in the high motility of HBV-replicating cells. The enhanced cell motility can be interestingly alleviated by the mutation at the sites of proline rich domain located in HBX. Our findings may provide new insights on the mechanism of HCC development associated with chronic HBV infection

Rheological properties of polyurethane-based magnetorheological gels

© 2019 Zhang, Li, Wang and Wang. The paper tests the influence of mass fractions of carbonyl iron particles (CIPs) on the rheological properties of magnetorheological (MR) gels. Polyurethane-based MR gels with different weight fraction of CIPs, i.e., 40, 60, and 80%, were firstly prepared by mechanical mixing, respectively. The changes of shear stress and viscosity with shear rate under different magnetic flux density were tested and analyzed. It was found that the shear stress increases with mass fraction under magnetic flux density. The viscoelastic properties of MRGs were achieved by oscillatory shear measure. The effects of strain amplitude and frequency on viscoelastic of MRGs under different magnetic flux density were measured and analyzed. The study results shown that the elastic characteristics become more obvious with the increase of CIPs mass fraction. However, it has opposite effect on the viscous properties of materials

A BIPV/T System Design Based on Simulation and its Application in Integrated Heating System

AbstractIn order to better master the internal airflow distribution characteristics of photovoltaic thermal (PV/T) collector on air source heat pump (ASHP) system heating performance, CFD software was applied in studying the building-integrated photovoltaic thermal (BIPV/T) sys-tem. A mathematical model of BIPV/T and ASHP integrated heating system was established. Numerical simulation of the system was conducted based on the typical meteorological data in Shenyang area. The influence of the inlet and outlet velocity, internal flow field distribution and temperature field distribution of the BIPV/T system were analyzed on the system thermal efficiency. The relationship between optimal COP and the inlet and outlet velocity of ASHP system was studied. The optimal inlet velocity of the BIPV/T – ASHP integrated system was determined to be 4 m/s, and the COP reached 4.6

Geometric and kinematic analysis of faults bordering the Andaman sea continental shelves: a 3D seismic case study

To clarify the tectonic evolution of M15 block in the Andaman Sea, we perform a delicate study of fault geometry and dynamics using a 3D seismic data. The data reveal eight sequence interfaces from the Early Oligocene to the Quaternary, large scale and multi angle extensional strike-slip faults, and a series of normal faults. The two large scale faults F1 and F2 start in the Eocene and end in the Quaternary, controlling the regional structure. The NNE-SSW strike-slip F1 fault belongs to the South Sagaing fault and the NNE-SSW strike-slip F2 is the eastern Andaman fault, the strike-slip movement of which are controlled by the impact of the collision between the Indian plate and the Eurasian plate. Through the analysis of the fault development history by the method of the ancient drop and the growth index, we find that most of the large or secondary scale faults reach the maximum drop and growth index in the Miocene, indicating that the Miocene is a significant period of plate collision enhancing and faults generating. The regional stress field is dominated by E-W tension. The continental crust has expanded rapidly from the Oligocene to the Miocene which results in the rapid subsidence of the crust. This regional stress intensity becomes weak after the Miocene. The activities of the faults caused a large difference in terrain height between the west and the east in the study area, forming a pattern of the western depression and the eastern terrace. Many NNE-SSW, NE-SW or NEE-SWW trend strike-slip faults and minor faults develop in the Miocene. It echoes the event that the convergence and subduction of the Indian plate from SW to NE direction led to the right rotation and N-NNE strike-slip of the West Myanmar block in the Miocene, thus forming a regional large strike-slip fault. All of the faults affect the structure of the region

Measurement of Young’s modulus of thin SmS films by Nanoindentation and surface acoustic wave

Nanoindentation was used to measure the elastic modulus of thin semiconducting form of Samarium Sulphide (SmS) thin films with nominal thickness of 100 nm, 200 nm and 400 nm on silicon substrate at different loads. The indentation results are fitted with modified King’s model [1] to exclude the effect of substrate, of which the Young’s moduli of films are consistent with measurement from Laser Surface Acoustic Wave system (LaWave) and calculated results from literature [2]. [1] [1] R. Saha, W. D. Nix, Acta Mater. 50 (2002) 23. [2] E. G. Soboleva et al, Appl. Mech. Mater. 770 (2015) 137; V. V. Kaminskiy et al, Sol. Sys. Res., 48 (2014) 561

How far is brain-inspired artificial intelligence away from brain?

Fueled by the development of neuroscience and artificial intelligence (AI), recent advances in the brain-inspired AI have manifested a tipping-point in the collaboration of the two fields. AI began with the inspiration of neuroscience, but has evolved to achieve a remarkable performance with little dependence upon neuroscience. However, in a recent collaboration, research into neurobiological explainability of AI models found that these highly accurate models may resemble the neurobiological representation of the same computational processes in the brain, although these models have been developed in the absence of such neuroscientific references. In this perspective, we review the cooperation and separation between neuroscience and AI, and emphasize on the current advance, that is, a new cooperation, the neurobiological explainability of AI. Under the intertwined development of the two fields, we propose a practical framework to evaluate the brain-likeness of AI models, paving the way for their further improvements

Rectifying interphases for preventing Li dendrite propagation in solid-state electrolytes

Solid-state electrolytes have emerged as the grail for safe and energy-dense Li metal batteries but still face significant challenges of Li dendrite propagation and interfacial incompatibility. In this work, an interface engineering approach is applied to introduce an electronic rectifying interphase between the solid-state electrolyte and Li metal anode. The rectifying behaviour restrains electron infiltration into the electrolyte, resulting in effective dendrite reduction. This interphase consists of a p-Si/n-TiO2 junction and an external Al layer, created using a multi-step sputter deposition technique on the surface of garnet pellets. The electronic rectifying behaviour is investigated via the asymmetric I-V responses of on-chip devices and further confirmed via the one-order of magnitude lower current response by electronic conductivity measurements on the pellets. The Al layer contributes to interface compatibility, which is verified from the lithiophilic surface and reduced interfacial impedance. Electrochemical measurements via Li symmetric cells show a significantly improved lifetime from dozens of hours to over two months. The reduction of the Li dendrite propagation behaviour is observed through 3D reconstructed morphologies of the solid-state electrolyte by X-ray computed tomography