Zinc-blende and wurtzite GaAs quantum dots in nanowires studied using hydrostatic pressure

We report both zinc-blende (ZB) and wurtzite (WZ) crystal phase self-assembled GaAs quantum dots (QDs) embedding in a single GaAs/AlGaAs core-shell nanowires (NWs). Optical transitions and single-photon characteristics of both kinds of QDs have been investigated by measuring photoluminescence (PL) and time-resolved PL spectra upon application of hydrostatic pressure. We find that the ZB QDs are of direct band gap transition with short recombination lifetime (~1 ns) and higher pressure coefficient (75-100 meV/GPa). On the contrary, the WZ QDs undergo a direct-to-pseudodirect bandgap transition as a result of quantum confinement effect, with remarkably longer exciton lifetime (4.5-74.5 ns) and smaller pressure coefficient (28-53 meV/GPa). These fundamentally physical properties are further examined by performing state-of-the-art atomistic pseudopotential calculations

NDRG2 Ameliorates Hepatic Fibrosis by Inhibiting the TGF-β1/Smad Pathway and Altering the MMP2/TIMP2 Ratio in Rats

Liver fibrosis is a worldwide clinical issue. It has been well established that activated hepatic stellate cells (HSCs) are responsible for excessive extracellular matrix (ECM) deposition in chronically damaged livers. The identification of key elements that control HSCs activation will help to further our understanding of liver fibrosis and improve the outcome of clinical treatment. This study demonstrates that N-Myc downstream-regulated gene 2 (NDRG2) is a potential regulator of liver fibrosis as NDRG2 mRNA and protein levels were reduced during HSCs activation. In addition, enhanced NDRG2 expression reduced Smad3 transcription and phosphorylation, which inhibited HSCs activation by blocking the TGF-β1 signal. Moreover, NDRG2 contributed to an increase in the ratio of matrix metalloproteinase 2 (MMP2) to tissue inhibitor of matrix metalloproteinase 2 (TIMP2), which may facilitate the degradation of the ECM. In dimethylnitrosamine (DMN)-induced fibrotic rat livers, adenovirus-mediated NDRG2 overexpression resulted in decreased ECM deposition and improved liver function compared with controls. In conclusion, the present findings indicate that the modulation of NDRG2 is a promising strategy for the treatment of liver fibrosis

The Impact of China’s Electricity Deregulation on Coal and Power Industries: Two-stage Game Modeling Approach

The regulated price mechanism in China’s power industry has attracted much criticism because of its incapability to optimize the allocation of resources. To build an “open, orderly, competitive and complete” power market system, the Chinese government launched an unprecedented marketization reform in 2015 to deregulate the electricity price. This paper examines the impact of the electricity price deregulation in the industry level. We first construct two-stage dynamic game models by taking the coal and coal-fired power industries as the players. Using the models, we compare analytically the equilibriums with and without electricity regulation, and examine the changes in electricity price, electricity generation, coal price and coal traded quantity. The theoretical analyses show that there are three intervals of the regulated electricity sales prices which influence the impact of electricity price deregulation. Next, we collect empirical data to estimate the parameters in the game models, and simulate the influence of electricity deregulation on the two industries in terms of market outcome and industrial profitability. Our results suggest that the actual regulated electricity price falls within the medium interval of the theoretical results, which means the price deregulation will result in higher electricity sales price but lower coal price, less coal traded amount and less electricity generation amount. The robustness analysis shows that our results hold with respect to the electricity generation efficiency and price elasticity of electricity demand

Determining Recycling Fees and Subsidies in China’s WEEE Disposal Fund with Formal and Informal Sectors

At present, most of China’s waste electrical and electronic equipment (hereafter referred to as WEEE) flow into the informal recycling sector, which has no official disassembly certification. To regulate the WEEE recycling industry, the policy of the WEEE disposal fund has been implemented to levy recycling fees from producers and subsidize the formal recycling sector. This paper aims to solve the challenging problem of how to optimize recycling fees and subsidies. We first study the competition between the formal and informal sectors, and construct the game models of the dismantling and refurbishing processes. Based on the equilibrium outcomes, we then examine the impact of the disposal fund on producers, as well as the formal and informal recycling sectors. With the goal of maximizing social welfare and maintaining a balanced budget for the disposal fund, we study the optimal recycling fee levied on producers and the corresponding subsidy provided to the formal sector. Social welfare is a function of producer and formal-recycler profits, consumer surplus, and the negative externality caused by informal dismantling and refurbishing, such as environmental pollution and safety problems. Results show that the use of subsidy can increase the acquisition quantity of used products in the formal sector, but the increase will slow down with higher subsidy. If the recycling fee that producers are charged is small, social welfare will be improved. In addition, as the fee is increased, social welfare will rise first and then fall. As such, any excessive increase in recycling fees should be avoided

Analysis on the inception of the magnetohydrodynamic flow instability in the annular linear induction pump channel

Flow instability is the intricate phenomenon in the annular linear induction pump (ALIP) when the pump runs at off-design working condition. A three-dimensional (3D) numerical model is built to simulate the flow in the pump channel. The pump heads at different flow rates are accurately predicted by comparing with experiment. The simulation results show the fluid velocity is circumferentially nonuniform in the pump channel even at the nominal flow rate. The flow in the middle sector continuously decelerates to nearly zero with the reducing flow rate. Reversed flow occurs in the azimuthal plane, followed by vortex flow. The reason for the heterogeneous velocity field is attributed to the mismatch between nonuniform Lorentz force and relatively even pressure gradient. It is seen that the flow in the region of small Lorentz force has to sacrifice its velocity to match with the pressure gradient. An analytic expression of the axial Lorentz force is then developed and it is clearly demonstrated the Lorentz force could be influenced by the profiles of velocity and radial magnetic flux density. The coupling between velocity and magnetic field is studied by analyzing the magnitudes of different terms in the dimensionless magnetic induction equation. It is found the dissipation term is determined by not only the magnetic Reynolds number but also the square of wave number of the disturbance in each direction. The smaller disturbing wave number weakens the dissipating effect, resulting in the larger nonuniform magnetic field and axial Lorentz force

Tuning and Identification of Interband Transitions in Monolayer and Bilayer Molybdenum Disulfide Using Hydrostatic Pressure

Few-layer molybdenum disulfide (MoS₂) is advantageous for application in next-generation electronic and opto­electronic devices. For monolayer MoS₂, it has been established that both the conduction band minimum (CBM) and the valence band maximum (VBM) occur at the K point in the Brillouin zone. For bilayer MoS₂, it is known that the VBM occurs at the Γ point. However, whether the K valley or the Λ valley forms the CBM and the energy difference between them remain disputable. Theoretical calculations have not provided a conclusive answer. In this paper, we demonstrate that a direct K–K to an indirect Λ–K interband transition in bilayer MoS₂ can be optically detected by tuning the hydrostatic pressure. A changeover of the CBM from the K valley to the Λ valley is observed to occur under a pressure of approximately 1.5 GPa. The experimental results clearly indicate that the K valley forms the CBM under zero strain, while the Λ valley is approximately 89 ± 9 meV higher in energy