SciCombinator

Discover the most talked about and latest scientific content & concepts.

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A new nucleation theory is presented. This theory is based on the assumption that a critical nucleus of the new phase can be regarded as an activated complex that passes through the top of the energy barrier. In the framework of the proposed approach, an equation in a general form for the nucleation rate is obtained. This equation is used to obtain the calculated data in the case of homogeneous nucleation at the vapor-liquid, liquid-vapor, and liquid-solid phase transitions. A comparison of the calculated data with the available experimental data as well as with the calculated data obtained in the framework of the classical nucleation theory is carried out. From a comparison between the calculated data obtained in the framework of the presented theory and the experimental data for the supercooled water-ice phase transition, the dependence on temperature of the surface tension coefficient between supercooled water and ice is determined.

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The instability of an electrolyte surface to a high-frequency, 10 to 200kHz, electric field, normal to the interface is investigated theoretically. From a practical viewpoint, such a high frequency leads to the absence of undesired electrochemical reactions and provides an additional control parameter. The theory of unsteady electric double layer by Barrero and Ramos is exploited. At such a high frequency, which is much larger than the eigenfrequency of the mechanical system, the nonlinear mechanical term does not “feel” the fast part of the Coulomb force, but it feels its slower component. In fact, the system behaves as if the electric field were a DC field. The observed instability is qualitatively close to the Tonks-Frenkel instability. The problem of the linear stability of the 1D quiescent stationary solution is solved analytically. For the important limiting cases, simple analytical formulas are derived. The linear stability analysis is complemented by the DNS of the full nonlinear system of equations with broadband low-amplitude white-noise initial conditions. After a transition period, the linear instability mechanism filters out the broad spectrum except for a narrow band near the maximum growth rate in rather good agreement with the linear stability analysis. If the external field is large enough, the nonlinear evolution results in coherent structures with sharp tips resembling to a Taylor cone. An evaluation of the cone angle for different conditions gives its value of about 30° to 60° , which is smaller than the angle of 98.6° for DC field and qualitatively corresponds to the experiments (L.Y. Yeo et al., Phys. Rev. Lett. 92, 133902 (2004)) for the high-frequency AC field and to the theoretical evaluation of the AC Taylor cones in E.A. Demekhin et al., Phys. Rev. E 84, 035301® (2011).

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The novel N-acyldehydrotyrosine analogues known as thalassotalic acids A-C were isolated from a marine bacterium by Deering et al. in 2016. These molecules were shown to have tyrosinase inhibition activity and thus are an attractive set of molecules for further study and optimization. To this end, a concise and modular synthesis has been devised and executed to produce thalassotalic acids A-C and two unnatural analogues. This synthesis has confirmed the identity and inhibitory data of thalassotalic acids A-C, more potent synthetic analogues (IC50 = 65 μM), and provides a route for further structure-activity relationship studies to optimize these molecules.

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Chronic hepatitis B virus (HBV) infection remains a major cause of morbidity and mortality worldwide. HBV surface antigen loss is considered a functional cure, and is an ideal goal for antiviral therapy. However, current treatment regimens, including nucleos(t)ide analogues or interferons monotherapy and combination therapy, rarely achieve this goal in chronic hepatitis B patients. NAs, as well as many direct antiviral drugs in ongoing development, are able to inhibit HBV replication and gene expression, but it is hard to achieve immune control and prevent recurrence after therapy cessation. Host immunity, especially HBV-specific T cell response, is proven to play a critical role in control or clearance of HBV infection. Considering HBV chronically infected patients display varying degrees of dysfunction regarding their immune system, novel approaches to enhancing antiviral immune responses are thus necessary in order to combine with current antiviral agents. In this review, we focus on the role of innate and adaptive immune responses in HBV immunopathogenesis, and discuss attractive strategies or drugs that aim to activate or rebuild antiviral immunity to achieve the goal for HBV functional cure.

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MnO2 has been explored for various applications in environmental and energy aspects. However, the thermal sensitivity of the MnO2 crystal structure never been studied. As a potential cathode material for fuel cell, α-MnO2 has a higher specific activity than Pt/C based on per metals cost. In this work, the physical and electrochemical properties of α-MnO2 nanorods were explored for the first time under thermal treatment with different temperatures (300, 400, and 500 °C). Under thermal treatment, oxygen vacancies were induced. The high-angle annular dark-field (HAADF) images and electron energy loss spectroscopy (EELS) have been taken to explore oxygen vacancies of α-MnO2 materials. From EELS and X-ray photoelectron spectroscopy (XPS) analysis, the oxygen vacancies on the α-MnO2 nanorods were strengthened with the temperature increasing. The sample with 400 °C treatment exhibited the best performance toward ORR, excellent methanol tolerance and higher stability compared to commercial Pt/C in alkaline media due to its combination of preferable growth on (211) plane and moderate oxygen vacancies as well as coexistence of Mn (IV)/ Mn (III) species. It was also observed the α-MnO2 nanorods tended to become longer and thinner with increasing temperature. This work suggests that the α-MnO2 nanorods are thermal sensitive materials and their performance for ORR can be boosted under certain temperatures.

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Ferulic acid (FA) is a major polyphenolic compound and has been shown to improve the glucose and lipid homeostasis in high-fat diet-induced obese mice. Here, we found the optimal level of dietary FA to ameliorate obesity and obesity-correlated disorders, and identified the responses of gut microbiota to dietary FA in genetic leptin-deficient obese (ob/ob)mice. The ob/ob mice exhibited persistent higher body weights, feed efficiency, white adipose tissue weights and hepatic lipid accumulation, compared with those of the WT mice. However, 0.5% dietary FA suppressed these symptoms in ob/ob mice. The diversity of gut microbiota and the total abundance of obesity- and anti-obesity-related genera were not influenced after FA intervention in ob/ob mice. These data suggest that sufficient intake of FA (0.5%) could be useful for treating obesity or obesity-related diseases, and this weight-control effect is possibly not correlated with the gut-brain axis.

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Large-scale production of natural products, such as terpenes, presents a significant scientific and technological challenge. One promising approach to tackle this problem is chemical synthesis inside nano-capsules, although enzyme-like control of such chemistry has not yet been achieved. In order to better understand the complex chemistry inside nano-capsules, we design a multiscale nano-reactor simulation approach. The nano-reactor simulation protocol consists of hybrid quantum mechanics-molecular mechanics-based high temperature Langevin molecular dynamics simulations. Using this approach we model the tail-to-head formation of monoterpenes inside a resor-cin[4]arene-based capsule (capsule I). We provide a rationale for the experimentally observed kinetics of monoterpene product for-mation and product distribution using capsule I, and we explain why additional stable monoterpenes, like camphene, are not observed. Based on the in-capsule I simulations, and mechanistic insights, we propose that feeding the capsule with pinene can yield camphene, and this proposal is verified experimentally. This suggests that the capsule may direct the dynamic reaction cascades by virtue of π-cation interactions.

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Explicit control of the crystalline phases and morphology of semiconducting BiVO4 crystals has been successfully synthesized via microwave-hydrothermal condition (MW-HT) without requiring any template/surfactant, doping of metal ions, and altering pH of reaction solution. Unambiguously, the crystalline phase of BiVO4 crystal has transformed from tetragonal zircon type ( tz) to monoclinic scheelite ( m) via mixed-phase ( m- tz) by altering microwave-irradiation time at fixed microwave-irradiation power (800 W) without changing any precursor concentrations throughout the reaction. X-ray diffraction and Rietveld refinement studies confirmed the phase transformation of BiVO4 crystals that occurs by controlling the irradiation time (10-22 min) and temperature (116-195 °C). The changes in VO43- tetrahedron bond strength and bond length attributed to phase transitions in BiVO4 crystals were corroborated by Raman spectra. Field emission scanning electron microscope revealed the sequential growth and rational morphological evolution of spherical-shaped zircon type tz-BiVO4 particles to preferentially oriented (010) and (110)-faceted decahedron-shaped scheelite m-BiVO4 crystals. The UV-reflectance and photoluminescence analyses revealed reduction in the optical bandgap and efficient charge separation with tunneling of excitons through interfaces, owing to phase transitions from tetragonal to monoclinic in BiVO4 crystals. High-resolution transmission electron microscopy images revealed the formation of heterojunctions between both the phases of BiVO4 crystals. The photocatalytic degradation of Rhodamine-B dye under natural sunlight showed maximum efficiency of 95% with highest rate kinetics (κavg = 0.0718/min) using mixed-phase BiVO4 ( m: tz-60:40) crystals, whereas under simulated sunlight, monoclinic phase BiVO4 crystals showed high degradation efficiency of 87% with low rate kinetics (κavg= 0.0436/min) for 200 min. The free-radical trapping tests revealed that superoxide radical (•O2) and hydroxyl radical (•OH) are active radicals during photocatalysis. Significantly, the MW-HT synthesized mixed-phase BiVO4 retained photocatalytic activity and structural stability even after three cycles. These findings open possibilities for innovative design of highly efficient semiconductor photocatalyst for environmental remediation applications.

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Coronary heart disease (CHD) is a cardiovascular disease that threatens human health with its complex metabolic disorders, the identify of potential biometabolic markers of different syndrome types may help to decipher its pathophysiological mechanisms and discover new targets for diagnosis and treatment. Based on UPLC-Q-TOF-MS metabolomics technology, urine samples of 1072 subjects from 9 centers, including normal control, phlegm and blood stasis (PBS) syndrome and Qi and Yin deficiency (QYD) syndrome, and other syndromes of CHD, were conducted to find biomarkers. Among them, the discovery set (n = 125) and the test set (n = 337) were used to identify and validate biomarkers, and the validation set (n = 610) was used for the application and evaluation of the support vector machine (SVM) prediction model. We discovered 15 CHD-PBS syndrome biomarkers and 12 CHD-QYD syndrome biomarkers, and the receiver-operator characteristic (ROC) area-under-the-curve (AUC) values of them were 0.963 and 0.990. The established SVM model has a good diagnostic ability and can well distinguish the two syndromes of CHD with a high predicted accuracy > 98.0%. The discovery of biomarkers and metabolic pathways in different syndrome types of coronary heart disease provides a basis for the diagnosis and evaluation of coronary heart disease, thereby improving the accurate diagnosis and precise treatment level of Chinese medicine.

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In two oil-wastewater treatment stations of Shengli Oilfield, cyclic volatile methylsiloxanes (cVMS, D4-D6) in the wastewater stream were found to undergo chlorination during electro-oxidation process for wastewater containing chlorine ions (16.1-42.0 g/L). Their converted fractions were 4.71-28.0% for monochlorinated D4-D6 and 0.22-7.96% for dichlorinated D4, which were ∼2 orders of magnitude higher than those for hydroxylated products. Furthermore, portions of chlorinated methylsiloxanes retained in excess sludge were released to the surrounding soils. In soil samples ( n = 500), chlorinated methylsiloxanes concentrations (