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Composite solid propellants demand fine and stable mechanical properties, creep resistance and stress relaxation performance during their long storage and usage time. In this study, modified hyperbranched polyester (MHBPE) was prepared and introduced into HTPE/AP/Al/RDX (HTPE, hydroxyl‐terminated polyether; AP, ammonium perchlorate; RDX, cyclotrimethylenetrinitramine) solid propellant as an effective additive. The static tensile and dynamic mechanical properties of this propellant before and after the introduction of MHBPE were evaluated. The elevated interfacial interaction by using MHBPE between the binder and RDX fillers improved the toughness and elasticity of the propellant. The enhancement mechanisms were also confirmed by the influence on the fracture surface morphology of the binder which was investigated by SEM. In addition, some influence on the dynamic mechanical properties of HTPE/AP/Al/RDX propellant caused by MHBPE was investigated by dynamic mechanical analysis. The creep behaviors of the HTPE/AP/Al/RDX propellants with and without MHBPE were also investigated at different stresses and temperatures. Reduced creep strain rate and strain were obtained for the modified propellant, implying enhanced creep resistance performance. The creep properties were quantitatively evaluated using a six‐element model and the long‐term creep performance of the propellant was predicted using the time–temperature superposition principle. A creep behavior of nearly 106 s at 30 °C could be acquired in a short‐term experiment (800 s) at 30–70 °C. Moreover, the stress relaxation investigation of the propellants with and without MHBPE at −40 °C, 20 °C and 70 °C suggested that MHBPE/HTPE/AP/Al/RDX propellant possessed better response ability to deformation. Thus, the application of MHBPE provides an efficient route of reinforcement to enhance the creep resistance and stress relaxation properties. © 2020 Society of Chemical Industry [ABSTRACT FROM AUTHOR]

The development of a nanographite (NG)‐based fluorescent biosensor for detecting microRNA (miRNA) is reported. Duplex‐specific nuclease (DSN)‐assisted signal amplification was key to its function. In the absence of a target, with the assistance of p‐stacking interactions, the NG adsorbed the double carboxyfluorescein (FAM)‐labelled probe (DFP) whose surface was perfectly complementary to miRNA, leading to quenching of FAM fluorescence. In the presence of a target, double‐stranded DNA/RNA hybrids were repelled by the NG and fluorescence was restored. Meanwhile, the considerable increase in signal strength and sensitivity suggests DSN‐mediated target recycling as an application. The detection limit of the proposed biosensor for miRNA was 10 pmol/L; there was a linear correlation when the miRNA concentration ranged from 50 pmol/L to 5 nmol/L. Additionally, the method could distinguish let‐7b from most let‐7 miRNA family members and was successfully used in a sample assay. This biosensor is a novel and highly sensitive tool for miRNA detection and has great potential for biochemical research, disease diagnosis, and therapy. [ABSTRACT FROM AUTHOR]

Although collaborative filtering achieves satisfying performance in recommender systems, many studies suggest that it is vulnerable by shilling attack aimed to manipulate the recommending frequency of a target item by injecting malicious user profiles. The existing attack methods usually generate malicious profiles by rating the item selected randomly. However, as these rating patterns are different from the real users, who have their own preferences on items, these attack methods can be easily detected by shilling attack detection, which significantly reduces the attack ability. Although some attack methods consider disguise ability, these methods require too much information from real users. This study proposes a shilling attack which generates malicious samples with strong attack ability and similarity to real users. To imitate the rating behavior of genuine users, our attack model considers both rated item correlation and item popularity when choosing items to rate. The profiles generated by our attack model is expected to be more similar to real user profiles, which increases the disguise ability. We also investigate whether and how rated item correlation of real user profiles is different from the ones generated by our method and the existing shilling attack. The experimental results confirm that our method achieves the highest attack ability after removing the suspected profiles identified by PCA-based and SVM-based shilling attack detection. The study confirms the correlation of rated item is a critical factor of the robustness of recommender systems. [ABSTRACT FROM AUTHOR]

Soyasaponin Ab (SA) is a typical oleanane triterpene saponin isolated from soybean and represents effects of antioxidation and anti-inflammation. In this study, we found the expressions of some phase II detoxifying enzymes were stimulated by SA via the signaling pathway of nuclear factor erythroid 2-related factor 2 (Nrf2) in HepG2 cells. Luciferase assay results demonstrated that SA promoted the Nrf2 transcription via binding to the antioxidant response element. In addition, a combining of luciferase assay and Western blotting suggested that SA activated ERK1/2 signaling pathways, and made Nrf2 translocated from cytoplasm to nucleus. SA also upregulated some Nrf2-related antioxidant enzymes such as heme oxygenase-1 (HO-1), NAD(P)H quinone oxidoreductase-1 (NQO1), and glutamate cysteine ligase catalytic subunit (GCLC). Inhibition of si-Nrf2 resisted expressions of SA-induced antioxidant genes. Collectively, these results suggest that SA exerted its protection against oxidative stress via the Nrf2/HO-1/NQO1 signaling pathways. [ABSTRACT FROM AUTHOR]

The authors describe a low-cost and sensitive method for the fluorometric determination of Salmonella enteritidis (S. enteritidis). It is based on the use of nanographite (NG) as a quencher of fluorescence, and on cyclic signal amplification by using deoxyribonuclease I (DNase I). The probe containing a capture probe and two short sequences (probe 1 and probe 2) labeled with carboxyfluorescein (FAM) are used as the signal probe that is adsorbed on the surface of NG via p-stacking interactions. Adsorption results in quenching of the fluorescence of FAM. If S. enteridis is introduced, fluorescence is restored due to the displacement of the probe from the surface of the NG due competitive binding. The signal is considerably amplified by applying DNase I-mediated target recycling. The assay has a linear response that covers the 1 to 50 nM concentration range, with a 0.5 nM lower limit of detection (LOD). A milk sample spiked with S. enteritidis was analyzed and the detection limit is as low as 50 colony-forming units (CFU) per mL. Accordingly, this biosensor is highly sensitive and selective but also cost-effective. Conceivably, the detection scheme may be extended to the detection of other biomolecules. [ABSTRACT FROM AUTHOR]