Search

High-resolution synthetic aperture radar presents a significant challenge to imaging algorithms and computing power. Slide spotlight is an important mode that has both high resolution and wide azimuth swath. Generally, in the slide spotlight mode, the performance of conventional frequency domain imaging algorithms degrades because of orbit curvature, the time-variant azimuth chirp rate, and other factors. We adopt the Back-Projection (BP) algorithm in this study to counteract this limitation. We also propose a CPU/GPU heterogeneous BP algorithm to deal with the high computing complexity O(N3) of the BP algorithm. This heterogeneous BP algorithm makes full use of computing resources and accelerates imaging progress, and the design of a scheduling thread improves the flexibility of the algorithm.

To improve the tribological characteristics of dimples on the surface of 45 steel, the dimples were filled with MoS2 and MoS2 modified by dopamine (MoS2 @ DA), and ball‐disk friction and wear tests were conducted. Specifically, the dimple filling gap, abrasion depth, and surface cross‐sectional area of 45 steel were measured. The wear morphology of the friction ball and exfoliation of MoS2 in the dimples and the bending characteristics of the specimens were studied. The surface friction coefficient of MoS2 @ DA‐filled specimen was 17.9% lower than MoS2‐filled specimen, and the dimple filling gap was 70.1% lower, the surface abrasion depth was 5.8% lower, and the abrasion cross‐sectional area was 17.7% smaller. Moreover, the bending strength of the MoS2 @ DA specimen was 3.27 times greater than that of the MoS2 specimen, and the exfoliation of MoS2 was slowed by filling with the MoS2 @ DA. Finally, the tribological characteristics were also superior for the specimens prepared with MoS2 @ DA. [ABSTRACT FROM AUTHOR]

α‐SiAlON is well known for its excellent mechanical properties, but its thermal properties are less investigated. In this work, we investigate the thermal conductivity of Ca α‐SiAlON ceramics with varying m and n values and prepared samples by spark plasma sintering (SPS) at 1600°C or gas pressure sintering (GPS) at 1800°C and 1900°C. The prepared Ca α‐SiAlON ceramics showed thermal conductivities ranging from 4.6 to 10.7 W/(mK) at 25°C. It was found that the thermal conductivity of the α‐SiAlON samples could be reduced by increasing either m or n or both. Besides, the samples prepared by SPS had lower thermal conductivity compared with those by GPS due to their smaller grain size, and the effect of m and n would be minor after m reached 2. These results provide basic knowledge for tuning α‐SiAlON's thermal conductivity for applications concerning thermal management. [ABSTRACT FROM AUTHOR]

Direct numerical simulations of temporally evolving turbulent channel flows with a weak spanwise rotation are conducted at a rotation number of 0.05 and Mach numbers of 0.3, 1.5, and 3.0 to investigate the influence of compressibility effects on turbulent statistics and large-scale structures. The corresponding Reynolds numbers are 2820, 3000, and 4880. Investigation shows that many asymmetric characteristics for incompressible flow also hold for compressible flow. The mean and fluctuating turbulent statistics distributions are similar to those for incompressible flows and shift from the suction side toward the pressure side. Weak spanwise rotation alters the mean the Mach number. The recovery enthalpy collapses between the pressure and suction sides and is independent of the Mach number. The Reynolds shear stress distributions are similar for compressible flows but with larger slopes than incompressible flows. When introducing semi-local scaling, the turbulent kinetic energy budget at pressure side is insensitive to compressibility effects. The average spanwise spacing of near-wall streaks increases as with the Mach number. The number of Taylor–Görtler vortex pairs is determined primarily by the aspect ratio of the computational domain, and is independent of the compressibility effects. [ABSTRACT FROM AUTHOR]

Background: With concerns about depletion of fossil fuel and environmental pollution, synthesis of biofuels such as isobutanol from low-cost substrate by microbial cell factories has attracted more and more attention. As one of the most promising carbon sources instead of food resources, acetate can be utilized by versatile microbes and converted into numerous valuable chemicals. Results: An isobutanol synthetic pathway using acetate as sole carbon source was constructed in E. coli. Pyruvate was designed to be generated via acetyl-CoA by pyruvate-ferredoxin oxidoreductase YdbK or anaplerotic pathway. Overexpression of transhydrogenase and NAD kinase increased the isobutanol titer of recombinant E. coli from 121.21 mg/L to 131.5 mg/L under batch cultivation. Further optimization of acetate supplement concentration achieved 157.05 mg/L isobutanol accumulation in WY002, representing the highest isobutanol titer by using acetate as sole carbon source. Conclusions: The utilization of acetate as carbon source for microbial production of valuable chemicals such as isobutanol could reduce the consumption of food-based substrates and save production cost. Engineering strategies applied in this study will provide a useful reference for microbial production of pyruvate derived chemical compounds from acetate. [ABSTRACT FROM AUTHOR]

Carbon nitride is a promising photocatalyst, but its catalytic performance is inhibited by a low charge-transfer rate and a limited surface area. Herein, a carbon (C)-doped carbon nitride nanotube with abundant π-electrons was developed by using nicotinamide and melamine as precursors through a supramolecular self-assembly method. The experiments and density functional theory (DFT) analysis prove the important function of doped C in catalytic performance. Carbon doping endows carbon nitride with plentiful π-electrons, which effectively promote charge migration and separation. Besides, the nanotubular structure provides unique porous channels for water splitting and an improved light-harvesting ability. Benefiting from the synergic effects of carbon doping and tubular texture, carbon-doped carbon nitride exhibits an excellent H2 evolution rate of 10 089 μmol h–1 g–1 with Pt and triethanolamine (TEOA) as a cocatalyst and a sacrificial agent, respectively, under λ ≥ 400 nm, which is superior to bulk CN (920 μmol h–1 g–1). This significant method offers guidance for the adjustment of the texture and electron density within carbon nitride. [ABSTRACT FROM AUTHOR]

Poly(ε-caprolactone) (PCL)-based semi-crystalline polymers are shape memory polymers that have been extensively used in various applications ranging from biological, soft robots and flexible electronic devices. Despite the large number of studies aiming at constructing the well-defined crosslinked polymer networks, detailed investigations in terms of structural factors that influence the thermal-mechanical and shape memory properties are still poorly understand and investigated. In this work, PCL crosslinked networks with different molecular weight of diacrylate PCL macromonoter (Mn) are prepared via base-catalyzed thiol-ene Michael addition. The results indicate that the melting temperature, the crystallization temperature and the crystallinity of the polymer networks exhibit an upward trend with increment of Mn. Besides that, the tensile strength and shape memory properties are also correlated with Mn. Controlled-strain DMA characterization on shape memory properties show that the cPCL-10000 network exhibits the most remarkable shape fixity and shape recovery ratio, indicative of lowering cross-linking density and chains mobility. In particular, permanent shape reconfiguration can also be achieved by triggering transesterification within the same polymer network, and a possible molecular mechanism responsible for the elasticity-based shape memory effect and plasticity-based permanent shape reconfigurability is proposed and combined to present the 2D-to-3D shape-morphing behaviors. [ABSTRACT FROM AUTHOR]

In this study, nano-TiNb2O7/carbon nanotubes (nano-TNO/CNTs) composites were prepared by solvothermal process, ball-milling and subsequent high-temperature calcination. The effects of CNTs content on the microstructure and electrochemical performances of nano-TNO/CNTs composites were investigated. The results indicate nano-TNO/CNTs-20 composites exhibit superior high-rate and cycling performance. Their specific capacities at 0.1, 0.3, 0.5, 1.0 and 2.0 A·g−1 are 374, 351, 339, 320 and 300 mAh·g−1, respectively. Moreover, the capacity retention ratios are up to 94.7% and 82% after 500 and 770 cycles at 0.3 and 1.0 A·g−1, respectively. The excellent electrochemical performances should be attribute to the nanoscale TNO particles and conductive network formed by CNTs around nano-TNO particles in composites, enabling facile Li+ diffusion and electronic conductivity, and a significant pseudocapacitive contribution to the rate capability was also demonstrated. [ABSTRACT FROM AUTHOR]

Tumor microenvironment (TME) consists of a dynamic network of non-tumoral stromal cells, including cancer-associated fibroblasts, endothelial cells, tumor-associated macrophages (TAMs), B and T cells. In the TME, TAMs support tumor initiation, progression, invasion and metastasis by promoting angiogenesis and immunosuppression of the tumor cells. There is close crosstalk between TAMs and tumor cells. Notably, chemokines are a significant messenger mediating the crosstalk between tumor cells and TAMs. TAMs can promote tumor progression via secretion of chemokines. Various chemokines secreted by tumors are involved in the generation and polarization of TAMs, the infiltration of TAMs in tumors, and the development of TAMs' suppressive function. This paper reviews CCL2-CCR2, CCL3/5-CCR5, CCL15-CCR1, CCL18-CCR8, CX3CL1/CCL26-CX3CR1, CXCL8-CXCR1/2, CXCL12-CXCR4/CXCR7 signaling pathways, their role in the recruitment, polarization and exertion of TAMs, and their correlation with tumor development, metastasis and prognosis. Furthermore, we present the current research progress on modulating the effects of TAMs with chemokine antagonists and discuss the prospects and potential challenges of using chemokine antagonists as therapeutic tools for cancer treatment. The TAMs targeting by chemokine receptor antagonists in combination with chemotherapy drugs, immune checkpoint inhibitors or radiotherapy appears to be a promising approach. [ABSTRACT FROM AUTHOR]