This work presents a comparative study on the reliability of auxetic (re-entrant honeycomb) and non-auxetic (diamond lattice and conventional honeycomb) lattice composites. The analyzed specimen ...consists of two unidirectional carbon fiber reinforced composite (CFRP) face sheets and a 3D-printed polymeric core. Low velocity impact tests are conducted first to characterize the unit cell deformation pattern, and we further explore its influence on core structure behavior as well as sandwich panel performance. It is found that the re-entrant topology exhibits lower energy absorption capacity but superior robustness and durability. Consequently, the re-entrant panel performs best in both force mitigation and energy dissipation, provided that the impact energy is appropriate. Furthermore, employing re-entrant core not only stabilizes the occurrences of the face sheet penetration as the impact energy increases, but also grants the sandwich panel consistent behaviors under multi-cycle impacts. These unique performances are due to the global instability of the auxetic structure, which yields more compliant deformation and less stress concentration. Resultant discrepancies shall be interpreted with the sandwich core deformation for validation. These findings pave the way for developing new class of auxetic lattice composites, especially under cyclic loading conditions, through a combination of rational design and 3D printing.
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•Auxetic core exhibits lower energy absorption capacity but superior robustness and durability compared with non-auxetic design.•Only if the impact energy is appropriate will the auxetic panel yield best performance in mitigating impact load.•The robust auxetic core shows same deformation pattern under various impact energy, and thus stabilizes face sheet penetration occurrence.•The durable auxetic core remains intact after multi-cycle impacts, and correspondingly grants lattice composites consistent performance.
Metasurfaces can be programmed for a spatial transformation of the wavefront, thus allowing parallel optical signal processing on-chip within an ultracompact dimension. On-chip metasurfaces have been ...implemented with two-dimensional periodic structures, however, their inherent scattering loss limits their large-scale implementation. The scattering can be minimized in single layer high-contrast transmitarray (HCTA) metasurface. Here we demonstrate a one-dimensional HCTA based lens defined on a standard silicon-on-insulator substrate, with its high transmission (<1 dB loss) maintained over a 200 nm bandwidth. Three layers of the HCTAs are cascaded for demonstrating meta-system functionalities of Fourier transformation and differentiation. The meta-system design holds potential for realizing on-chip transformation optics, mathematical operations and spectrometers, with applications in areas of imaging, sensing and quantum information processing.
Interpenetrating phase composite (IPC), also known as co-continuous composite, is one type of material that may exhibit an unusual combination of high stiffness, strength, energy absorption, and ...damage tolerance. Here we experimentally demonstrate that IPCs fabricated by 3D printing technique with rationally designed architectures can exhibit a fracture toughness 16 times higher than that of conventionally structured composites. The toughening mechanisms arise from the crack-bridging, process zone formation and crack-deflection, which are intrinsically controlled by the rationally designed interpenetrating architectures. We further show that the prominently enhanced fracture toughness in the architected IPCs can be tuned by tailoring the stiffness contrasts between the two compositions. The findings presented here not only quantify the fracture behavior of complex architected IPCs but also demonstrate the potential to achieve tailorable mechanical properties through the integrative rational design and the state-of-the-art advanced manufacturing technique.
Carbon fiber reinforced polymer (CFRP) composites are increasingly used in civil, naval, aerospace, and wind energy applications, where they can be frequently exposed to harsh temperature conditions ...and under static and dynamic loads. The extreme temperature conditions and dynamic loading are critical for CFRP composites structural design as the constituent polymer properties are highly sensitive to temperature and strain rate. This work experimentally investigates the effect of temperature, ranging from −100 °C to 100 °C, on the mechanical properties of CFRP composites under static and dynamic three-point bending tests. The results reveal that CFRP composites provide enhanced flexural strength, maximum deflection, and energy absorption at lower temperatures (−60 °C, −100 °C) while relatively poor performance at a higher temperature (100 °C). Experimental images from the post-mortem photographs, scanning electron microscopy, and high speed videos are implemented to observe various failure behaviors including microbuckling, kinking, and fiber breakage at different temperatures. Analytical modeling is further applied to reveal the underlying mechanisms responsible for these temperature dependent mechanical behaviors. The findings reported here provide insights into the study of the temperature effect on the mechanical response of CFRP composites, which expands the way to design stiffer, stronger and tougher CFRP composites.
Particle air pollution has adverse health effects, and low-cost monitoring among a large population group is an effective method for performing environmental health studies. However, concern about ...the accuracy of low-cost monitors has affected their popularization in monitoring projects.
To calibrate a low-cost particle monitor (HK-B3, Hike, China) through a controlled exposure experiment.
Our study used a MicroPEM monitor (RTI, America) as a standard particle concentration measurement device to calibrate the Hike monitors. A machine learning model was established to calibrate the particle concentration obtained by the low-cost PM2.5 monitors, and ten-fold validation was used to test the model. In addition, we used a linear regression model to compare the results of the machine learning model. A calibration method was established for the low-cost monitors, and it can be used to apply the monitors in future air pollution monitoring projects.
The values of the random forest model calibration results and observations were more condensed around the regression line y = 0.99x + 0.05, and the R squared value (R2 = 0.98) was higher than that for the linear regression (R2 = 0.87). The random forest model showed better performance than the traditional linear regression model.
Our study provided an effective calibration method to support the accuracy of low-cost monitors. The machine learning method based on the calibration model established in our study can increase the effectiveness of future air pollution and health studies.
•A machine learning method was used to establish a random forest model for calibrating low-cost PM2.5 monitors.•The random forest model showed better performance than the traditional linear regression model.•Our study provided a calibration method for low-cost monitors under indoor air pollution conditions.
A dynamic surface pattern with a topography and fluorescence in response to environmental stimulus can enable information recording, hiding, and reading. Such patterns are therefore widely used in ...information security and anticounterfeiting. Here, we demonstrate a dynamic dual pattern using a supramolecular network comprising a copolymer containing pyridine (P4VP-nBA-S) and hydroxyl distyrylpyridine (DSP-OH) as the skin layer for bilayer wrinkling systems, in which both the wrinkle morphology and fluorescence color can be simultaneously regulated by visible light-triggered isomerization of DSP-OH, or acids. Acid-induced protonation of pyridines can dynamically regulate the cross-linking of the skin layer through hydrogen bonding, and the fluorescence of DSP-OH. On selective irradiation with 450 nm visible light or acid treatment, the resulting hierarchical patterned surface becomes smooth and wrinkled reversibly, and simultaneously its fluorescence changes dynamically from blue to orange-red. The smart surfaces with dynamic hierarchical wrinkles and fluorescence can find potential application in anticounterfeiting.
Auxetic materials exhibiting a negative Poisson's ratio are of great research interest due to their unusual mechanical responses and a wide range of potential deployment. Efforts have been devoted to ...exploring novel 2D and 3D auxetic structures through rational design, optimization, and taking inspiration from nature. Here we report a 3D architected lattice system showing a negative Poisson's ratio over a wide range of applied uniaxial stretch. 3D printing, experimental tests, numerical simulation, and analytical modeling are implemented to quantify the evolution of the Poisson's ratio and reveal the underlying mechanisms responsible for this unusual behavior. We further show that the auxetic behavior can be controlled by tailoring the geometric features of the ligaments. The findings reported here provide a new routine to design architected metamaterial systems exhibiting unusual properties and having a wide range of potential applications.
Abstract
Background
Alteration of the gut microbiota may contribute to the development of inflammatory bowel disease (IBD). Epigallocatechin-3-gallate (EGCG), a major bioactive constituent of green ...tea, is known to be beneficial in IBD alleviation. However, it is unclear whether the gut microbiota exerts an effect when EGCG attenuates IBD.
Results
We first explored the effect of oral or rectal EGCG delivery on the DSS-induced murine colitis. Our results revealed that anti-inflammatory effect and colonic barrier integrity were enhanced by oral, but not rectal, EGCG. We observed a distinct EGCG-mediated alteration in the gut microbiome by increasing
Akkermansia
abundance and butyrate production. Next, we demonstrated that the EGCG pre-supplementation induced similar beneficial outcomes to oral EGCG administration. Prophylactic EGCG attenuated colitis and significantly enriched short-chain fatty acids (SCFAs)-producing bacteria such as
Akkermansia
and SCFAs production in DSS-induced mice. To validate these discoveries, we performed fecal microbiota transplantation (FMT) and sterile fecal filtrate (SFF) to inoculate DSS-treated mice. Microbiota from EGCG-dosed mice alleviated the colitis over microbiota from control mice and SFF shown by superiorly anti-inflammatory effect and colonic barrier integrity, and also enriched bacteria such as
Akkermansia
and SCFAs. Collectively, the attenuation of colitis by oral EGCG suggests an intimate involvement of SCFAs-producing bacteria
Akkermansia
, and SCFAs, which was further demonstrated by prophylaxis and FMT.
Conclusions
This study provides the first data indicating that oral EGCG ameliorated the colonic inflammation in a gut microbiota-dependent manner. Our findings provide novel insights into EGCG-mediated remission of IBD and EGCG as a potential modulator for gut microbiota to prevent and treat IBD.
The study of ambient air particulate matter (PM2.5)-associated health and economic burdens of cardiovascular disease are crucial for air pollution control and disease prevention strategies. ...Quantified evidence remains inadequate.
This study aimed to estimate the PM2.5 associated risk in cardiovascular hospital admission as well as attributable health burdens and economic costs.
A total of 2,202,244 hospital admission records of cardiovascular disease and six common clinical subtypes in Beijing were included. A time-stratified case-crossover design was applied to estimate the associations and the concentration-response curve. Then, the annual average additional hospital admissions, days of hospital stay, and hospital expenditures were evaluated from 2013 to 2017 and compared between 2017 and 2013.
The results showed that each 10 μg/m3 increase in previous-day PM2.5 concentration was associated with a risk increase of 0.44% (95%CI: 0.40%, 0.47%) for cardiovascular disease, 0.66% (95%CI: 0.58%, 0.73%) for angina pectoris, 0.53% (95%CI: 0.39%, 0.66%) for chronic ischemic heart disease, 0.48% (95%CI: 0.34%, 0.63%) for myocardial infarction, 0.44% (95%CI: 0.29%, 0.60%) for hypertensive heart disease and 0.40% (95%CI: 0.27%, 0.52%) for ischemic stroke. There were 1938 PM2.5 attributed additional hospital admissions, resulting in 21,668 additional days in hospital, along with 5527.12 and 1947.04 ten-thousand of additional total hospital cost and self-afforded cost, respectively. Compared with 2013, the above-mentioned four burdens decreased by 18.17%, 28.80%, 18.90% and 13.72% in 2017, respectively.
PM2.5 exposure was significantly associated with substantial burdens of cardiovascular hospital admission and economic expenditures. The results highlight the necessity of continuous PM2.5 control from the perspective of healthy and sustainable city development in urban China.
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•A case-crossover design based on large individual records of hospital admission.•PM2.5 related cause-specific hospital admissions and economic costs were estimated.•Co-benefit of PM2.5 pollution control in saving medical resources was evaluated.
Miniaturized image classifiers are potential for revolutionizing their applications in optical communication, autonomous vehicles, and healthcare. With subwavelength structure enabled directional ...diffraction and dispersion engineering, the light propagation through multi-layer metasurfaces achieves wavelength-selective image recognitions on a silicon photonic platform at telecommunication wavelength. The metasystems implement high-throughput vector-by-matrix multiplications, enabled by near 10
nanoscale phase shifters as weight elements within 0.135 mm
footprints. The diffraction manifested computing capability incorporates the fabrication and measurement related phase fluctuations, and thus the pre-trained metasystem can handle uncertainties in inputs without post-tuning. Here we demonstrate three functional metasystems: a 15-pixel spatial pattern classifier that reaches near 90% accuracy with femtosecond inputs, a multi-channel wavelength demultiplexer, and a hyperspectral image classifier. The diffractive metasystem provides an alternative machine learning architecture for photonic integrated circuits, with densely integrated phase shifters, spatially multiplexed throughput, and data processing capabilities.
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