Preparation, Characterization, and Applications of Carbonaceous Mesophase: A Review

Carbonaceous mesophase with a nematic liquid crystal structure possesses an easily graphitizable characteristic and can be used as a promising raw material to prepare anisotropic carbon and graphite materials with high performance and multifunction. Therefore, the carbonaceous mesophase occupies a pivotal and irreplaceable position in many frontier and cutting-edge fields. The controllable preparation and characterization of carbonaceous mesophase derived from a model molecule (i.e., naphthalene) are presented, especially the formation, development, and transformation of anisotropic liquid crystalline mesophase in the synthetic naphthalene pitch during the process of liquid-phase carbonization (350–450°C). The increasing applications of naphthalene-based carbonaceous mesophase as an ideal precursor material for fabricating representative advanced carbon materials with high added value (e.g., mesophase pitch-derived coke, mesocarbon microbeads, mesophase pitch-based carbon foam, high-modulus mesophase pitch-based carbon fibers, and high-thermal-conductivity carbon-based composites, etc.) are reviewed in detail in this chapter

Polyimide-Derived Graphite Films with High Thermal Conductivity

Nowadays, polyimide-derived graphite films with high thermal conductivity have been increasingly applied in many cutting-edge fields needing thermal management, such as highly integrated microelectronics and wireless communication technologies. This chapter first introduces a variety of functional graphite films with high thermal conductivity of 500–2000 W/m K in the planar direction, then provides the preparation technology (including lab-scale preparation and industrial production) and quality control strategy of high-thermal-conductivity graphite films, which are derived from a special polymer- polyimide (PI) by carbonization and graphitization treatments through a suitable molding press in a vacuum furnace. The morphology, microstructure and physical properties as well as the microstructural evolution and transformation mechanism of PI films during the whole process of high-temperature treatment are comprehensively introduced. The nature of PI precursor (e.g., the molecular structure and planar molecular orientation) and preparation technics (e.g., heat-treatment temperature and molding pressure) are critical factors influencing their final physical properties. Currently challenged by the emerging of graphene-based graphite films, the latest developments and future prospects of various PI-derived carbons and composites (beyond films) with high thermal conductivity have been summarized at the end. This chapter may shed light on a promising and versatile utilization of PI-derived functional carbon materials for advanced thermal management

Responses of the Ocular Anterior Segment and Refraction to 0.5% Tropicamide in Chinese School-Aged Children of Myopia, Emmetropia, and Hyperopia

Purpose. To investigate the changes of anterior segment after cycloplegia and estimate the association of such changes with the changes of refraction in Chinese school-aged children of myopia, emmetropia, and hyperopia. Methods. 309 children were recruited and eligible subjects were assigned to three groups: hyperopia, emmetropia, or myopia. Cycloplegia was achieved with five cycles of 0.5% tropicamide. The Pentacam system was used to measure the parameters of interest before and after cycloplegia. Results. In the myopic group, the lenses were thinner and the lens position was significantly more posterior than that of the emmetropic and hyperopic groups in the cycloplegic status. The correlations between refraction and lens thickness (age adjusted; r=0.26, P<0.01), and lens position (age adjusted; r=-0.31, P<0.01) were found. After cycloplegia, ACD and ACV significantly increased, while ACA significantly decreased. Changes in refraction, ACD, ACV, and ACA were significantly different among the three groups (P<0.05, all). Changes of refraction were correlated with changes of ACD (r=0.41, P<0.01). Conclusions. Myopia presented thinner lenses and smaller changes of anterior segment and refraction after cycloplegia when compared to emmetropia and hyperopia. Changes of anterior chamber depth were correlated with refraction changes. This may contribute to a better understanding of the relationship between anterior segment and myopia

Identification of optimal endogenous reference RNAs for RT-qPCR normalization in hindgut of rat models with anorectal malformations

Background Quantitative real-time polymerase chain reaction (RT-qPCR) is a sensitive method for quantifying mRNA abundance. With relative expression analysis, however, reliable data output is dependent on stably expressed reference genes across the samples being studied. In anorectal malformations (ARMs), there is limited data on the selection of appropriate reference genes. Purpose This study was aimed to investigate the optimal reference genes for PCR in ARM rat models. Methods We selected 15 commonly used reference genes (Rps18, Actb, B2m, Gapdh, Ppia, Hprt1, Pgk1, Ywhaz, Tbp, Ubc, Rps16, Rpl13a, Rplp1, Sdha, and Hmbs) as candidate reference genes and detected their mRNA expression in ARM samples by RT-qPCR. The expression stability and variability of these transcripts were subsequently evaluated using four methods (geNorm, NormFinder, comparative ΔCt, and BestKeeper). Results The abundance of the candidate reference genes was qualified by RT-qPCR and the cycle threshold (Ct) values ranged between 14.07 (Rplp1) and 21.89 (Sdha). In the overall candidate genes, different variations existed across the different algorithms. A comprehensive analysis revealed that Rpl13a ranked first among the relatively stable genes, followed by Ywhaz, Rps18, Sdha, and Hmbs. Conclusions The most stable reference genes for RT-qPCR were Rpl13a, Ywhaz, and Rps18 in ETU-induced ARMs in rat fetus. This study provided a foundation for reference gene selection for future gene expression analyses

Possible Luttinger liquid behavior of edge transport in monolayer transition metal dichalcogenide crystals.

In atomically-thin two-dimensional (2D) semiconductors, the nonuniformity in current flow due to its edge states may alter and even dictate the charge transport properties of the entire device. However, the influence of the edge states on electrical transport in 2D materials has not been sufficiently explored to date. Here, we systematically quantify the edge state contribution to electrical transport in monolayer MoS2/WSe2 field-effect transistors, revealing that the charge transport at low temperature is dominated by the edge conduction with the nonlinear behavior. The metallic edge states are revealed by scanning probe microscopy, scanning Kelvin probe force microscopy and first-principle calculations. Further analyses demonstrate that the edge-state dominated nonlinear transport shows a universal power-law scaling relationship with both temperature and bias voltage, which can be well explained by the 1D Luttinger liquid theory. These findings demonstrate the Luttinger liquid behavior in 2D materials and offer important insights into designing 2D electronics

Effect of carbon fiber crystallite size on the formation of hafnium carbide coating and the mechanism of the reaction of hafnium with carbon fibers

The effect of carbon source crystallite size on the formation of hafnium carbide (HfC) coating was investigated via direct reaction of hafnium powders with mesophase pitch-based carbon fibers (CFs) heat-treated at various temperatures. X-ray diffraction, scanning electron microscopy and energy dispersive X-ray spectroscopy analyses reveal that uniform and dense HfC coatings are preferentially formed on CFs containing larger and more ordered graphite crystallites. The carbide synthesis temperature and the sizes of crystallites in the CFs have a remarkable influence on the integrity and thickness of the coatings. The formation the HfC coatings can be attributed to the surface diffusion of hafnium and the bi-directional diffusion of hafnium and carbon sources inside the HfC coating. The reaction of HfC coated carbon fibers with zirconium powders leads to the growth of ZrC on the HfC coating and this has been shown to occur by the diffusion of carbon from the carbon fiber core through the carbide coating to its surface