Dynamics of Associative Polymers with High Density of Reversible Bonds.

An associative polymer carries many stickers that can form reversible associations. For more than 30 years, the understanding has been that reversible associations change the shape of linear viscoelastic spectra by adding a rubbery plateau in the intermediate frequency range, at which associations have not yet relaxed and thus effectively act as crosslinks. Here, we design and synthesize new classes of unentangled associative polymers carrying unprecedentedly high fractions of stickers, up to eight per Kuhn segment, that can form strong pairwise hydrogen bonding of ∼20k_{B}T without microphase separation. We experimentally show that reversible bonds significantly slow down the polymer dynamics but nearly do not change the shape of linear viscoelastic spectra. This behavior can be explained by a renormalized Rouse model that highlights an unexpected influence of reversible bonds on the structural relaxation of associative polymers.

Force-driven active dynamics of thin nanorods in unentangled polymer melts.

Recent advances in the functional material and biomedical applications of nanorods call for a fundamental understanding of the active motion of nanorods in a viscoelastic medium. Molecular dynamics simulations are performed to investigate a model system consisting of force-driven active thin nanorods in a melt of unentangled polymers. The activeness of a thin nanorod arises from a constant external force applied uniformly along the rod. The simulations demonstrate that the active force overcomes the randomness of the diffusive motion and results in a ballistic motion along the direction of the applied force at long timescales. The constant speed of the force-driven ballistic motion is determined by the balance of the active force and the friction from the coupling of the nanorod with the polymer viscosity. The friction coefficient, which is computed as the ratio of the active force and the speed, decreases as the active force increases. The origin of the reduction in the friction coefficient is the high speed that allows the nanorod to renew its local environment faster than the relaxation time of melt chains. A scaling theory is developed to quantify the dependence of the friction coefficient on the strength of the active force. The simulations also demonstrate that the force-driven ballistic motion suppresses the rotational diffusion of the rod and cuts off the de-correlation of the rod axis with time. On the scaling level, the long-time trajectory of a force-driven active nanorod piercing through unentangled polymers may be described as a stretched array of "active blobs", where the short-time random-walk trajectory within an active blob is unperturbed by the active force.

Generation of tunable linearly chirped signals with long temporal duration in the photonic time-stretched coherent radar.

Linearly chirped signals with long temporal duration are generated by adding a dispersive loop in the photonic time-stretched coherent radar. The signal-to-noise ratio (SNR) variation of the optical pulse recirculation is analyzed and simulated to evaluate the multiple extension of temporal duration. The achievable temporal duration is confined by the dispersion and the amplified spontaneous emission noise accumulation. The experimental results verify the SNR variation of the optical pulse recirculation. Moreover, tunable linearly chirped signals with temporal duration of 100 ns and a bandwidth of 4 GHz at X or Ku band are generated. With the improvement of the time-bandwidth product, a drone can be successfully observed.

Maintenance of broadband detection in photonic time-stretched coherent radar employing phase diversity.

Frequency response fluctuation in a radar system distorts the envelope of the output signal after matched filtering, thereby impairing its broadband detection performance. Simulations are made under various types and degrees of fluctuation. The results prove that the peak power and range resolution of broadband detection suffer different levels of deterioration. Moreover, simulation results also show that two outputs with orthogonal phase diversity have complementary variation trends and their combination can effectively enhance the broadband detection performance. Based on theoretical analysis, we employ the combination of two orthogonal phase diversity to achieve broadband detection in the photonic time-stretched coherent radar. Compared with using an ordinary modulator, a dual-output-Mach-Zehnder-modulator-based system makes the dispersion-penalty-induced frequency response fluctuation decrease by 9.7 dB. For single target detection, the peak power is increased by 6.7 dB and the range resolution is improved from 8.4 cm to 4.8 cm. For two-target detection, a 6-cm spatial interval is distinguished reliably.

Signal-to-noise ratio improvement of photonic time-stretch coherent radar enabling high-sensitivity ultrabroad W-band operation.

The signal-to-noise ratio (SNR) of the photonic time-stretching receiver in the photonic time-stretch coherent radar (PTS-CR) system is theoretically analyzed. According to the analysis based on the erbium-doped fiber amplifier (EDFA) characteristic, it is found that the SNR is dominantly determined by the input optical power of the EDFA. With the improvement of the SNR of the photonic time-stretching receiver, the radar detection sensitivity is consequently enhanced. Furthermore, a PTS-CR system operating at W band with the ultrabroad bandwidth of 12 GHz is experimentally enabled, leading to the range resolution of ∼1.48 cm in dual-target detection.

Gut microbiota mediates the anti-colitis effects of polysaccharides derived from Rhopilema esculentum Kishinouye in mice.

Ulcerative colitis (UC) is closely associated with the disturbance of gut microbiota. Crude polysaccharide-rich extract from Rhopilema esculentum Kishinouye has been proven to alleviate dextran sulfate sodium (DSS)-triggered colitis. However, it remains unclear whether the polysaccharides from Rhopilema esculentum (REP) in the extract play a predominant role in ameliorating colitis and whether gut microbiota mediates the beneficial effect of REP. Herein, we aimed to investigate the anti-colitis effects of REP and its mechanisms and to explore the role of REP-modulated gut microbiota in alleviating colitis in mice. Oral REP supplementation ameliorated the symptoms, inflammatory responses, colonic damage and gut microbial dysbiosis in colitic mice. REP significantly enriched SCFA-producing bacteria such as Roseburia and probiotics such as Bifidobacterium and restored the level of SCFAs especially butyric acid and propionic acid. Next, we found that transplantation of microbiota from REP-treated mice alleviated DSS-induced acute colitis, evidenced by improved gut barrier integrity and lower inflammation compared with mice receiving microbiota from control mice. Notably, dramatically enriched Bifidobacterium, Faecalibaculum and SCFA-producing bacteria including Butyricicoccus and Roseburia were found in mice receiving microbiota from the REP-treated donor mice. Lastly, the protective effect of REP supplementation on colitis was abolished in the antibiotic-treated mice. Overall, our findings suggest that REP could alleviate DSS-induced colitis in mice by regulating the imbalance of the microbiome. The polysaccharides of Rhopilema esculentum Kishinouye have the potential to be developed into promising prebiotic agents for rectifying dysbiosis of gut microbiota and preventing UC.

Fermented Sargassum fusiforme Mitigates Ulcerative Colitis in Mice by Regulating the Intestinal Barrier, Oxidative Stress, and the NF-κB Pathway.

In recent years, Sargassum fusiforme has gained increasing attention for its ability to improve human health and reduce the risk of disease. Nevertheless, there have been few reports on the beneficial functions of fermented Sargassum fusiforme. In this study, the role of fermented Sargassum fusiforme in the mitigation of ulcerative colitis was investigated. Both fermented and unfermented Sargassum fusiforme demonstrated significant improvement in weight loss, diarrhea, bloody stools, and colon shortening in mice with acute colitis. Fermented Sargassum fusiforme further protected against goblet cell loss, decreased intestinal epithelium permeability, and enhanced the expression of tight junction proteins. Fermented Sargassum fusiforme reduced oxidative stress, which was demonstrated by a decrease in nitric oxide (NO), myeloperoxidase (MPO), and malondialdehyde (MDA) concentrations in the colon of mice and an increase in total superoxide dismutase (T-SOD) activity in the colon. Meanwhile, catalase (CAT) concentrations in both the colon and serum of mice were significantly increased. Fermented Sargassum fusiforme also attenuated the inflammatory response, which was evidenced by the decreased level of pro-inflammatory cytokines in the colon. Moreover, fermented Sargassum fusiforme inhibited the nuclear factor-κB (NF-κB) signaling pathway and increased the production of short-chain fatty acids in the intestine. These findings indicate that fermented Sargassum fusiforme may have the potential to be developed as an alternative strategy for alleviating colitis.

Isinglass Polysaccharides Regulate Intestinal-Barrier Function and Alleviate Obesity in High-Fat Diet Mice through the HO-1/Nrf2 Pathway and Intestinal Microbiome Environment.

Plant polysaccharide intervention has shown significant potential to combat obesity. However, studies on animal polysaccharides are indeed rare. The aim of this study was to investigate the potential functions of CIP (IL) on obesity, intestinal microflora dysbiosis, and the possible protection of intestinal barrier in mice fed with high-fat diet (HFD). Our results revealed that after 13 weeks, the HFD+L (high-fat diet + 25 mg/kg CIP) group showed significantly more weight loss and fat accumulation relative to the HFD+H (high-fat diet + 50 mg/kg CIP) group. Furthermore, CIP intervention modulated lipid metabolism and mRNA levels of inflammatory mediators in liver. Overall, CIP clearly improved the intestinal barrier in HFD-fed mice. Additionally, we observed that CIP intervention improved intestinal microbiota community richness and diversity in HFD-fed mice. The CIP intervention mice group showed a relatively low Firmicutes to Bacteroidetes ratio compared to the HFD group. This study concluded that CIP could be used as a functional food to prevent adipocyte accumulation, reduce systemic inflammation, and protect the intestinal barrier.

All-optical central-frequency-programmable and bandwidth-tailorable radar.

Radar has been widely used for military, security, and rescue purposes, and modern radar should be reconfigurable at multi-bands and have programmable central frequencies and considerable bandwidth agility. Microwave photonics or photonics-assisted radio-frequency technology is a unique solution to providing such capabilities. Here, we demonstrate an all-optical central-frequency-programmable and bandwidth-tailorable radar architecture that provides a coherent system and utilizes one mode-locked laser for both signal generation and reception. Heterodyning of two individually filtered optical pulses that are pre-chirped via wavelength-to-time mapping generates a wideband linearly chirped radar signal. The working bands can be flexibly tailored with the desired bandwidth at a user-preferred carrier frequency. Radar echoes are first modulated onto the pre-chirped optical pulse, which is also used for signal generation, and then stretched in time or compressed in frequency several fold based on the time-stretch principle. Thus, digitization is facilitated without loss of detection ability. We believe that our results demonstrate an innovative radar architecture with an ultra-high-range resolution.