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Results demonstrate that three steps of photocycloaddition, cis-hydroxylation, and nucleophilic addition contribute for the quaternary carbons of the cyclooctane and four stereogenic centers of taxol mediated by bis-2-pyridone.

Three tetrasubstituted carbons can be formed simultaneously in the (4+4) photocycloaddition of pyridones tethered by a four-carbon chain at the 3- and 6'-positions. The reaction was found to be sensitive to substitution at the carbons involved in bond formation. The silyl ether tether substituent fully controls photocycloaddition of the taxanes to afford a photoproduct with five stereogenic centers and both quaternary carbons found in taxol.

Flake graphite-diamond/Cu–Cr–Zr composites with good two-dimensional thermophysical properties were prepared by vacuum hot-pressing technology. The influence and working mechanism of the hot-pressing temperature on the relative density and thermal conductivity of the composites were studied to obtain the optimum sintering process. The results showed that with a pressing pressure of 10 ∼ 20 MPa, the relative density and thermal conductivity of the composite materials increased as the sintering temperature increased from 950 to 1010°C. When the temperature rose to 1010 ∼ 1040°C, a near fully dense composite material was obtained and thermal conductivity reached maxima of 410 and 119 W/m K parallel and perpendicular to the graphite planes, respectively, both of which are close to the theoretical value. However, relative density and thermal conductivity drastically decreased as the temperature continued to increase beyond 1070°C. This is attributed to the combined effect of sintering temperature and wettability between the matrix and the reinforcements. [ABSTRACT FROM AUTHOR]

The 2024Al matrix composites reinforced by 30 vol% SiCp and 10 vol% Al2O3fas wear-resistant materials are prepared by pressure infiltration. The graphite powders are added during the preparation of the preform to support shaping. In this article, the effect of the size of the graphite powder on the friction and wear properties of the composites is researched. The results showed that at a given conditions, namely, the size of the SiCp is 14 µm and the diameter of the Al2O3fiber is 4–5 µm, the composites made from 5 ∼ 30 µm have a more stable friction coefficience and lower wear rate than those from 30 ∼ 50 µm and 50 ∼ 70 µm graphite because the diameter of the generated pores in the corresponding preforms is smaller and more concentrated, resulting in a uniform distribution of the reinforcements in the matrix. The detailed effect mechanisms of different graphite sizes on wear and friction properties of the composites as well as the porosity of the corresponding preforms are also discussed. [ABSTRACT FROM PUBLISHER]

The article focuses on a study on e-learning environments using transactional distance theory (TDT) and adopting an ecological systems model. It discusses the effectiveness of the learner-teacher dialogue, the engagement through effective teaching presence, and levels of infrastructure for supporting transactional distances. It analyses how within the framework of e-learning transactional distance, effective e-learning can be improved by short transactional distances for teaching presence.

Self-powered flexible sensors are highly favored and considered auspicious for wearable electronics due to their preferable flexibility and facilitation to integrate with various apparel products. As a wearable product, the sensors can be designed by a self-powered strategy powered with harvested low-grade heat from human body to meet the daily long-term use. The flexible thermoelectric generator (f-TEG) can harvest the human body heat to generate a thermovoltage driving the sensor directly. Herewith we report a wearable self-powered human motion sensor made from highly stretchable quasi-solid state hydrogel, which shows 2800% elongation at break and good strain sensitivity (GF=4, when the strain is 200%) and detects the movement and sound of human body. Further, the hydrogel based sensor can harvest the human body heat and generate a thermovoltage to drive the sensor directly, which exhibits an impressive gigantic Seebeck coefficient of approximate 11.5 mV K−1 at ambient temperature. Combining the merits of flexibility, environment friendly, sensitivity and thermoelectric performance at room temperature range together, we believe that the hydrogel based sensor will offer amble opportunities to numerous self-powered sensor applications like wearable electronics, sports, health and wellbeing. The dual-network hydrogel based self-powered sensor can harvest human body heat and generate thermovoltage to detect the human motion. [Display omitted] • A self-powered strain sensor realized by a flexible thermoelectric generator is reported. • The hydrogel based sensor can directly harvest the human body heat and generate a thermovoltage to drive the sensor. • A gigantic Seebeck efficient of 11.5 m V K−1 is obtained. • The hydrogel based sensor can detect large and subtle human motion. [ABSTRACT FROM AUTHOR]

Transcription factors (TFs) tightly control plant development by regulating gene expression. The phase separation of TFs plays a vital role in gene regulation. Many plant TFs have the potential to form phase-separated protein condensates; however, little is known about which TFs are regulated by phase separation and how it affects their roles in plant development. Here, we report that the rice (Oryza sativa) single Myb TF TELOMERE REPEAT-BINDING FACTOR 2 (TRBF2) is highly expressed in fast-growing tissues at the seedling stage. TRBF2 is a transcriptional repressor that binds to the transcriptional start site of thousands of genes. Mutation of TRBF2 leads to pleiotropic developmental defects and misexpression of many genes. TRBF2 displays characteristics consistent with phase separation in vivo and forms phase-separated condensates in vitro. The H1/H5 domain of TRBF2 plays a crucial role in phase separation, chromatin targeting, and gene repression. Replacing the H1/H5 domain by a phase-separated intrinsically disordered region from Arabidopsis (Arabidopsis thaliana) AtSERRATE partially recovers the function of TRBF2 in gene repression in vitro and in transgenic plants. We also found that TRBF2 is required for trimethylation of histone H3 Lys27 (H3K27me3) deposition at specific genes and genome wide. Our findings reveal that phase separation of TRBF2 facilitates gene repression in rice development. An essential protein domain of a transcriptional repressor promotes its phase separation, chromatin targeting, and gene repression during rice development. [ABSTRACT FROM AUTHOR]

The interaction between interstitial oxygen atoms and -type screw dislocations was investigated via first-principles calculations to elucidate the effect of oxygen solutes on the deformation behaviors of Mg. The results show that repulsive interactions exist between basal screw dislocation cores and oxygen atoms, which would enable the full basal dislocation to bypass the oxygen atoms in the dislocation glide plane through the cross-slip process. This repulsion also increases the resistance to the motion of dissociated basal dislocations. Moreover, the energy of prismatic -type screw dislocation cores is reduced by the presence of oxygen, which would stabilize the screw dislocation core on the prismatic plane, accordingly facilitating the prismatic slip. This information can complement the fundamental knowledge of alloying Mg using interstitial solutes. [ABSTRACT FROM AUTHOR]

The surrounding rocks of underground engineering are usually subjected to the coupling of compressive and shear stresses. The mechanical characteristics of underground geomaterials subjected submitted to compression-shear loading have received considerable attention recently. The complex response arises from the microstructure redistribution under high in-situ stress and the resulting fracture behaviors at multiaxial stress states. Understanding the compression-shear behavior and failure mechanism of rocks is of essential importance for mechanical characterization and construction safety in deep underground engineering applications. In this study, variable-angle shear tests are conducted for cubic sandstone samples to investigate damage evolution under compression-shear loading, and the acoustic emission (AE) and electromagnetic radiation (EMR) are simultaneously monitored to record crack development. The mechanical behaviors of rock with AE and EMR responses in variable-angle shear tests with shear angle of 30°, 45° and 60° are analyzed. Then, correlation between AE and EMR is evaluated. Damage evolution of the rock specimen is described based on AE and EMR energy. Fractal dimension and b-value of AE and EMR time series are calculated to further reveal the microscopic crack mechanism of rocks. The results suggest that the continuous decline of fractal dimension and b-value of AE and EMR can act as the precursor of rock failure. • Variable-angle shear tests are conducted for cubic samples to investigate damage evolution under compression-shear loading. • Acoustic emission and electromagnetic radiation responses during failure process are analyzed. • Correlations between acoustic emission and electromagnetic radiation are quantitatively evaluated • Damage evolution of the rock specimen is described based on acoustic emission and electromagnetic radiation energy. • Fractal dimension and b-value of AE and EMR are calculated to further reveal the microscopic crack mechanism of rocks. [ABSTRACT FROM AUTHOR]