Passive millimeter and terahertz wave imaging has become a significant potential technique for human security check and scene monitoring. Due to the small difference of the brightness temperatures ...between human body and concealed objects, the temperature sensitivity and spatial resolution of radiometers are always the key performance indexes which are difficult to improve. Therefore, when the hardware performance is given, improving detectivity becomes a pressing need. In this paper, a physically-based concealed object enhancement method using multi-polarization information is presented. The polarization model and polarization property of human body and concealed objects have been analyzed. By fusing multiple polarization images, we can obtain a complete polarization image in which the contrast between human body and concealed objects is enhanced and stable. The experimental results of simulation and measurement demonstrate the enhancement performance, and Differential Signal Noise Ratio (DSNR) is obviously improved by using the proposed method.
In this study, TiC0.5N0.5 nanoparticles (NPs) are shown to induce a remarkable grain refinement of aluminum at various cooling rates. The grain refinement mechanisms are systematically investigated ...by microstructure observation, edge-to-edge matching (E2EM) model prediction, and first-principles calculations. The experimental results suggest that as the cooling rates increase from 10 K/s to 70 K/s, a transition from intergranular to intragranular distribution of NPs occurs and the Al/TiC0.5N0.5 interface varies from incoherent to coherent. Based on the E2EM analysis combined with first-principles calculation, it is found that TiC0.5N0.5 can act as a potent nucleant for the heterogeneous nucleation of α-Al. By analyzing the NP effects on the nucleation and growth of α-Al, the grain growth restriction and nucleation promotion mechanisms are proposed to elucidate the refinement phenomena at low and high cooling conditions, respectively.
Nanoparticles (NPs) with different shape, size, architecture and composition were studied for their application as photo-thermal agents in the area of cancer nanomedicine. Out of them, gold ...nanoparticles (Au NPs) depending on their in vivo biocompatibility provide a simple thermal ablation platform. However, fabrication of these Au NPs showing appropriate properties for photo-thermal function requires complex routes utilizing hazardous chemicals as capping agents which may cause in vivo concerns. In this study, the fabricated Au NPs utilizing biosynthetic approach having near-infrared (NIR) absorbance assisting photo-thermal treatment could be a possible alternative. Herein, anisotropic Au NPs were fabricated utilizing an aqueous extract of Ceratonia siliqua (carob) which acts as both stabilizing and reducing agent. The biosynthesized Au NPs were exposed to density-gradient centrifugation for the optimization of NIR absorption in 800 to 1000 nm wavelength range. Colloidal Au NPs showed outstanding contrast enrichment for ultrasound imaging, and also Au nanoplates were obtained by density gradient centrifugation can function as a NIR absorbing agent for efficient photothermal killing of Hep-G2 liver tumor cells in vitro with negligible cytotoxicity to active cells. Furthermore, the present approach recommends an innovative way for treating theranostic cancer.
Streaking of photoelectrons with optical lasers has been widely used for temporal characterization of attosecond extreme ultraviolet pulses. Recently, this technique has been adapted to characterize ...femtosecond x-ray pulses in free-electron lasers with the streaking imprinted by far-infrared and terahertz (THz) pulses. Here, we report successful implementation of THz streaking for time stamping of an ultrashort relativistic electron beam, whose energy is several orders of magnitude higher than photoelectrons. Such an ability is especially important for MeV ultrafast electron diffraction (UED) applications, where electron beams with a few femtosecond pulse width may be obtained with longitudinal compression, while the arrival time may fluctuate at a much larger timescale. Using this laser-driven THz streaking technique, the arrival time of an ultrashort electron beam with a 6-fs (rms) pulse width has been determined with 1.5-fs (rms) accuracy. Furthermore, we have proposed and demonstrated a noninvasive method for correction of the timing jitter with femtosecond accuracy through measurement of the compressed beam energy, which may allow one to advance UED towards a sub-10-fs frontier, far beyond the approximate 100-fs (rms) jitter.
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•A global stress constrained bi-material topology optimization with an adjustable compliance.•FEA modeling simulation and experimental validation were conducted to prove the ...effectiveness.•Flexural strength was greatly improved by 120% to 143% compared with that of the zigzag joint.•A new consideration to enhance Cf/SiC composite/superalloy joints from a structural point of view.
High-stress concentrations form in Cf/SiC composite-to-superalloy joints because of their large modulus mismatch. It deteriorates the mechanical performance of the joined parts and even causes failure. This paper proposes a global stress constrained bimaterial topology optimization method with an adjustable compliance objective to design the joint structure to alleviate the stress concentration in Cf/SiC composite-to-superalloy joints and improve their mechanical properties. Using a numerical FEA modeling simulation and experimental method, the effectiveness of the optimized joining structure was validated. The stress concentration in the joints under three-point-bending test was significantly reduced in comparison to that of the traditional flat and zigzag joints, and the flexural strength was greatly improved by 120% to 143% compared with that of the zigzag joint. The present study provides a new consideration to enhance the mechanical properties of Cf/SiC composite-to-superalloy joints from a structural point of view and compensates for the traditional improvement method of only optimizing interlayer materials.
With the complication of the power system, features of the resonance interaction behave diversely and pose a threat to the effectiveness of the resonance suppression strategies. Existing resonance ...suppression strategies are usually designed for specific scenarios which are in close correlation with the impedance frequency-amplitude distribution, and their adaptability under different scenarios is hard to evaluate. In this paper, the resonance suppression domain of a DC distribution network is derived based on the node impedance variation before/after the resonance is suppressed. The derived criterion takes the admittance change of the resonance suppression strategies as variables, and the conservative/ideal suppression domain criteria are defined. On this basis, a method for evaluating the effectiveness of resonance suppression strategies is proposed, which simplifies the evaluation process and avoids a complicated matrix inverse process to each resonance suppression strategy during the system impedance calculation. Furthermore, a DC active damper control strategy based on the resonance suppression strategy evaluation is proposed, and the proposed strategy could suppress resonances under different scenarios by a targeted design of the reshaping admittance parameters. Time domain simulations with a 5-node distribution network are carried out to verify the proposed method.
•Community ‘cohesion’ index increased by 54.45% under light grazing compared to heavy grazing.•Identify the indicate plant species of each grazing intensity treatment with the SPEC-OCCU plot.•Plant ...factors mainly affect the plant community stability under light gazing practice.•Soil factors regulate the plant community stability under light gazing practice.
On the Tibetan Plateau, most alpine meadows have undergone various degree of degradation due to heavy grazing practices. Assessing the progress of grazing succession, identify the indicator species for different grazing managements is crucial to facilitate the effective restoration of degraded alpine meadows. In this study, specific areas with varying levels of grazing intensity were selected to assess the stability of plant communities, to identify the indicator species for each stage, and to examine the driving factors influencing community stability. The results showed that (i) plant community stability was found to be highest under light and moderate levels of grazing. In comparison to heavy grazing treatment, the community “cohesion” index (|Negative cohesion|) increased by 54.45% under light grazing treatment and by 23.24% under moderate grazing treatment. (ii) the indicator species varied across different succession stages and played distinct roles. Dominant species were identified as indicator species with no grazing and light grazing treatment, whereas rare poisonous species served as indicators under heavy grazing treatment. (iii) the driving factors and mechanisms influencing community stability differed throughout gradient of grazing intensity. Plant-related factors primarily influenced community stability under light grazing, while soil-related factors began to play a joint role under heavy grazing. This empirical knowledge contributes to establishing a scientific basis for the rational utilization and management of alpine meadow ecosystems.
Lentil protein isolate (LPI)-κ-carrageenan (κ-C) and -ι-carrageenan (ι-C) based microcapsules were prepared through spray-drying and freeze-drying to encapsulate flaxseed oil in order to reach final ...oil levels of 20% and 30%. Characteristics of the corresponding emulsions and their dried microcapsules were determined. For emulsion properties, all LPI-κ-C and LPI-ι-C emulsions remained 100% stable after 48 h, while the LPI emulsions destabilized quickly (p < 0.05) after homogenization mainly due to low emulsion viscosity. For spray-dried microcapsules, the highest yield was attributed to LPI-ι-C with 20% oil, followed by LPI-κ-C 20% and LPI-ι-C 30% (p < 0.05). Flaxseed oil was oxidized more significantly among the spray-dried capsules compared to untreated oil (p < 0.05) due to the effect of heat. Flaxseed oil was more stable in all the freeze-dried capsules and showed significantly lower oil oxidation than the untreated oil after 8 weeks of storage (p < 0.05). As for in vitro oil release profile, a higher amount of oil was released for LPI-κ-C powders under simulated gastric fluid (SGF), while more oil was released for LPI-ι-C powders under simulated gastric fluid and simulated intestinal fluid (SGF + SIF) regardless of drying method and oil content. This study enhanced the emulsion stability by applying carrageenan to LPI and showed the potential to make plant-based microcapsules to deliver omega-3 oils.
In this work, the effects of TiCN and γ-Al2O3 nanoparticle (NP) addition on the microstructural evolution of cast AZ91 alloys at the cooling rate ranging from 15 to 120 K/s have been systematically ...investigated. Experimental results reveal that grain coarsening occurs in cast AZ91 alloys when the cooling rate exceeds 90 K/s, while it can be effectively inhibited upon addition of NPs. The marked inhibition effect may originate from the formation of TiCN or γ-Al2O3 NP-induced undercooling zone ahead of solid/liquid (S/L) front of α-Mg, which not only can restrict grain growth effectively, but also can reactivate the native nucleants that are inactive in AZ91 melts to participate in nucleation events. And if possessing high nucleation potency, NPs can also promote further nucleation events and lead to significant grain refinement. An analytical model has been established to quantitatively account for the restriction effect of NPs on grain growth. The present work may shed a new light on the grain coarsening of cast alloys during fast cooling and provide an effective approach to circumvent it.
The sand castings of Mg–Y–RE–Zr series alloys are widely utilized in the large scales and complex shapes in the aerospace industry, as a result of which there are always some cast defects in the ...products. In this study, the feasibility of repair welding of sand-cast Mg–4Y–3RE–0.5Zr alloy by tungsten inert gas (TIG) welding was scrutinized with different welding currents from 150 to 210 A. The results indicated that defect-free repaired joints with good appearance could be acquired at 170 and 190 A. Interestingly, the grain size of the fusion zone (FZ) was refined initially and then increased with the linear increment of welding current. Because at the higher heat inputs, although the cooling rate of the molten pool was reduced, substantial constitutional supercooling for the grain refinement was attained after the Zr particles were transformed into Zr solutes. The tensile strength of the repaired joint at 170 A was 195 MPa with the maximum joint efficiency of 87.8%, and the elongation reached to 124.4% of the sand-cast base material (BM). However, serious grain coarsening and continuous eutectic structures generated in heat-affected zone (HAZ) above 190 A resulted in the weakening of the joint due to the brittle intergranular fracture.
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