Engineering topics
Publications and source records attributed to Li, Fei.
Lead halide perovskite (LHP) semiconductors with the general chemical formula ABX 3 are now being widely investigated for a variety of applications including but not limited to high-efficiency photovoltaics (PVs) and light-emitting diodes (LEDs).
Trimeric intracellular cation (TRIC) channels are thought to provide counter-ion currents that facilitate the active release of Ca 2+ from intracellular stores. TRIC activity is controlled by voltage and Ca 2+ modulation, but underlying mechanisms have remained unknown. Here we describe high-resolution crystal structures of vertebrate TRIC-A and TRIC-B channels, both in Ca 2+ -bound and Ca 2+ -free states, and we analyze conductance properties in structure-inspired mutagenesis experiments. The TRIC channels are symmetric trimers, wherein we find a pore in each protomer that is gated by a highly conserved lysine residue. In the resting state, Ca 2+ binding at the luminal surface of TRIC-A, on its threefold axis, stabilizes lysine blockage of the pores. During active Ca 2+ release, luminal Ca 2+ depletion removes inhibition to permit the lysine-bearing and voltage-sensing helix to move in response to consequent membrane hyperpolarization. Diacylglycerol is found at interprotomer interfaces, suggesting a role in metabolic control.
Not Available
Direct numerical simulations (DNS) are performed to study potential stabilizing ef- fect of spanwise periodic discrete roughness elements (DREs) on cross ow instabilities in a spatially developing three-dimensional boundary layer over an in nite-swept natural- laminar- ow wing at a freestream Mach number of 0:75 and a chord Reynolds number of approximately 25 million. In the DNS, both the spanwise periodic DREs and distributed roughness in the leading-edge region are implemented to simulate a typical experimen- tal scenario in which multiple steady cross ow modes including the most unstable mode (i.e., the \target" mode) emerge because of the presence of naturally distributed surface roughness in the leading edge region and spanwise periodic control cylinders of subcritical wavelength are used to force small-wavelength disturbances (i.e., the control mode) for damping the target mode. The DNS results show that the e ectiveness of DRE control is sensitive to roughness diameter, height, and chordwise placement. For the DRE parame- ters considered in this study, the stabilizing e ect on the target mode is small within the computational domain that ended at about 35% of the chord.
Not provided.
Electrode materials with high activity and good stability are essential for commercialization of energy conversion systems such as solid oxide fuel cells or electrolysis cells at the intermediate temperature. Modifying the existing perovskite-based electrode surface to form a heterostructure has been widely applied for the rational design of novel electrodes with high performance. Despite many successful developments in enhancing electrode performance by surface modification, some controversial results are also reported in the literature and the mechanisms are still not well understood. In this work, the mechanism of how surface modification impacts the oxygen reduction reaction (ORR) activity and stability of perovskite-based oxides was investigated. We took La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3 (LSCF) as the thin-film model system and modified its surface with additive Pr x Ce 1–x O 2 layers of different thicknesses. We found a strong correlation between surface oxygen defects and the ORR activity of the heterostructure. By inducing higher oxygen vacancy concentration compared to bare LSCF, PrO 2 coating is proved to greatly facilitate the rate of oxygen dissociation, thus significantly enhancing the ORR activity. Because of low oxygen vacancy density introduced by Pr 0.2 Ce 0.8 O 2 and CeO 2 coating, on the one hand, it does not boost the rate of ORR but successfully suppresses surface Sr segregation, leading to an enhanced durability. Our findings will demonstrate the vital role of surface oxygen defects and provide important insights for the rational design of high-performance electrode materials through surface defect engineering.
Lung cancer is a common malignant tumor, the cancer stem cells (CSCs) were regarded responsible for the development of cancer tissue. The effects of amiloride on lung cancer stem cells and the possible mechanism were not much investigated. In this study, human NCI-H1975 lung CSCs were selected by flow cytometry, and the effects of amiloride at different concentrations (0, 12.5, 25, 50, and 100 μmol/L) were evaluated on proliferation, migration, invasion and apoptosis of CSCs using cell counting kit-8 and Transwell migration assays as well as flow cytometry. Wstern blot analysis was performed to investigate the effect of amiloride on the level of proteins in uPA system, NF-kB pathway, and PI3K-AKT-mTOR pathway in CSCs. As a result, we found that amiloride inhibited proliferation, migration and invasion of lung CSCs, and promoted apoptosis. Further, we found that amiloride decreased levels of target proteins in the uPA system, as well as the NF-kB and PI3K-AKT-mTOR pathways. These results indicated that amiloride could inhibit proliferation, migration and invasion of lung CSCs, and promotes apoptosis, these effects may be related to decreased levels of proteins in the uPA system, the NF-kB pathway, and the PI3K-AKT-mTOR pathway.
Direct numerical simulations (DNS) are performed to examine the receptivity to roughness in a spatially developing three-dimensional boundary layer over an in finite-swept natural-laminar-flow wing at a free stream Mach number of 0:75 and a chord Reynolds number of approximately 25 million based on the long, swept chord. Stationary cross ow disturbances are excited by applying either critically spaced discrete cylinders of micron size or naturally occurring distributed roughness in the leading-edge region. The DNS data show that the spanwise spectral content of the excited cross ow disturbances is highly dependent upon the shape of roughness elements, and the initial growth of the cross ow structures is a nonlinear function of the element height. The linear growth rate of the excited cross ow disturbances predicted by DNS shows good agreement with linear parabolized stability equations. The receptivity study lays the foundation for investigating the stabilization of the naturally most unstable steady cross ow mode by using spanwise periodic DREs.
In this study, the carbothermal reduction of pellets composed of quartz and carbon at temperatures between 1898 K and 1948 K (1625 °C and 1675 °C) are investigated. The main product from this reaction is silicon carbide (SiC). The reduction of quartz with carbon black, charcoal, coke, coal, and pre-heated coal in the pellet were compared to investigate the different carbon resources used in silicon production. Charcoal and coke have high SiO reactivity, while carbon black and coal (pre-heated coal) have low SiO reactivity. Charcoal and carbon black show better matching between quartz/carbon reactivity and SiO reactivity, and will lose less SiO gas than coke and pre-heated coal. Coal has a high volatile content and is thus not recommended as a raw material for the pellets.
The kinetic modeling for the carbothermal reduction reaction rate in quartz and carbon black pellets is studied at different temperatures, under varying CO partial pressures in ambient atmosphere, varying carbon contents, different quartz particle sizes, and different crucible opening areas. Carbon black is produced by the cracking of natural gas. The activation energy of the SiC-producing step was determined to be 594 kJ/mol. The averaged pre-exponential factor A obtained from 1898 K, 1923 K, and 1948 K (1625 °C, 1650 °C, and 1675 °C) is 2.62E+16 min -1 . The reaction rate of the gas-solid interface factor, fix-C content (X fix-C ), temperature (T), and CO partial pressure (X CO ) can be expressed as follows:((d pct)/(dt))=(1-0.40×X fix-C -0.86 ×pct)×2.62×10 16 ×exp(-(594000/(RT)))×(2.6-0.015×X co ).
Kinetic modeling of quartz and carbon pellet at temperatures of 1898 K, 1923 K, and 1948 K (1625 °C, 1650 °C, and 1675 °C) was investigated in this study. The carbon materials used were charcoal, coke, coal, and preheated coal. The overall SiC producing reaction can be described by the reaction SiO 2 + 3C = SiC + 2CO. In the SiC-producing step, the reaction rate of quartz and carbon pellet can be expressed as ((d pct)/(dt)) = (1 - 0.40 × X fix - C -0.86 × F C × pct) × A × exp(-(E/(RT))) The carbon factor F C was used to describe the influence of different carbon materials that effect the gas–solid interface reaction. For charcoal, coke, coal, and preheated coal, the F C values were 0.83, 0.80, 0.94, and 0.83, respectively. The pre-exponential factor A values for the preceding four carbon materials were 1.06 × 10 16 min -1 , 4.21 × 10 15 min -1 , 3.85 × 10 9 min -1 , and 1.00 × 10 25 min -1 , respectively. The activation energies E for the SiC-producing step were 570, 563, 336, and 913 kJ/mole for charcoal, coke, coal, and preheated coal pellets, respectively.
To better understand the energy response of the Antineutrino Detector (AD), the Daya Bay Reactor Neutrino Experiment installed a full Flash ADC readout system on one AD that allowed for simultaneous data taking with the current readout system. This paper presents the design, data acquisition, and simulation of the Flash ADC system, and focuses on the PMT waveform reconstruction algorithms. For liquid scintillator calorimetry, the most critical requirement to waveform reconstruction is linearity. Several common reconstruction methods were tested but the linearity performance was not satisfactory. A new method based on the deconvolution technique was developed with 1% residual non-linearity, which fulfills the requirement. Here, the performance was validated with both data and Monte Carlo (MC) simulations, and 1% consistency between them has been achieved.
Highlights: • Disruption of LRRK2 in Zebrafish leads to hyperactivity at adult stage. • Neurological and immunological pathways are disrupted in LRRK2 mutant. • Disruption of LRRK2 in Zebrafish leads to a weakened antibacterial response. As a protein with complex domain structure and roles in kinase, GTPase and scaffolding, LRRK2 is believed to be an important orchestration node leading to several cascades of signal transduction rather than one specific pathway. LRRK2 variants were found to be associated with Parkinson's disease, Crohn's disease and leprosy. Here we disrupt LRRK2 in zebrafish and found hyperactivity rather than hypoactivity in adult zebrafish mutants. By RNA-seq we found genes involved in infectious disease and immunological disease were notably affected. Functional studies also revealed a weakened antibacterial response in LRRK2 mutant. This mutant can be further explored for revealing molecular mechanisms and modeling of LRRK2 related diseases.
The Colorado potato beetle is one of the most challenging agricultural pests to manage. It has shown a spectacular ability to adapt to a variety of solanaceaeous plants and variable climates during its global invasion, and, notably, to rapidly evolve insecticide resistance. To examine evidence of rapid evolutionary change, and to understand the genetic basis of herbivory and insecticide resistance, we tested for structural and functional genomic changes relative to other arthropod species using genome sequencing, transcriptomics, and community annotation. Two factors that might facilitate rapid evolutionary change include transposable elements, which comprise at least 17% of the genome and are rapidly evolving compared to other Coleoptera, and high levels of nucleotide diversity in rapidly growing pest populations. Adaptations to plant feeding are evident in gene expansions and differential expression of digestive enzymes in gut tissues, as well as expansions of gustatory receptors for bitter tasting. Surprisingly, the suite of genes involved in insecticide resistance is similar to other beetles. Finally, duplications in the RNAi pathway might explain why Leptinotarsa decemlineata has high sensitivity to dsRNA. In conclusion, the L. decemlineata genome provides opportunities to investigate a broad range of phenotypes and to develop sustainable methods to control this widely successful pest.
The state of the boundary layer on space re-entry vehicles significantly affects the design of the thermal protection system. However, the physical mechanism that leads to the laminar-turbulent boundary-layer transition on blunt spherical capsules remains an open question in literature. This work numerically assesses the potential of roughness-induced non-modal disturbance growth on re-entry capsules with a spherical-section forebody by optimal transient-growth theory and direct numerical simulation. Two different sets of wind-tunnel experiments are considered. Optimal transient-growth studies have been performed for the blunt capsule experiments at Mach 5.9 in the Hypersonic Ludwieg tube Braunschweig (HLB) of the Technische Universitat Braunschweig. In some of these measurements, the capsule model was equipped with a specifically designed patch of distributed micron-sized surface roughness. The transient-growth results for the HLB capsule are compared to corresponding numerical data for a Mach 6 blunt capsule experiment in the Adjustable Contour Expansion (ACE) facility of the Texas A&M University (TAMU) at lower Reynolds number. Similar trends are observed for both configurations. In particular, a rather low maximum energy gain is noted for the surface temperature conditions of the experiments. It is shown that the surface temperature dependence of the optimal transient-growth results is very similar for both capsule configurations. Moreover, the generation of stationary disturbances by well-defined roughness patches on the capsule surface is studied for the conditions of the HLB experiment using direct numerical simulations (DNS). To help explain the observed laminar-turbulent transition downstream of the roughness patch in some of the HLB capsule experiments, additional simulations were carried out to study the evolution of unsteady perturbations within the steady disturbance flow field due to the roughness patch. However, the DNS did not provide any indication of modal or non-modal disturbance growth in the wake of the roughness patch, and hence, the physical mechanism underlying the observed onset of transition remains unknown.