MXenes are a large class of materials that are chemically exfoliated from metal-aluminum-carbon (MAX) bulk crystals into low-dimensional sheets. While many MXenes have been theoretically predicted, the careful balance...
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MXenes are a large class of materials that are chemically exfoliated from metal-aluminum-carbon (MAX) bulk crystals into low-dimensional sheets. While many MXenes have been theoretically predicted, the careful balance required in the exfoliation between breaking the inter-layer bonds without damaging the intra-layer bonds of the sheets has limited synthesis and experimental study. Here, we developed the synthesis of cr2c from its parent cr2Alc MAX phase and showed the etching is optimized using sodium fluoride and hydrogen chloride with a modified minimally intensive layer delamination (mMILD) method in a cold environment of 9 celcius. We further optimized the intercalation and delamination using sonication and washing methods. The resulting cr2ccrystal structure was characterized. These results open up cr2c to experimental study, including of its predicted emergent magnetic properties, and develop guidelines for synthesizing new MXene materials.
coimplantation of equal concentrations of c and Al in 6H- and 4H-Sic has been investigated comparatively with implantation of Al alone in the Al concentration range of N-AI = 8x10(19) to 2 x 10(21) cm(-3). c-Al coimpl...
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coimplantation of equal concentrations of c and Al in 6H- and 4H-Sic has been investigated comparatively with implantation of Al alone in the Al concentration range of N-AI = 8x10(19) to 2 x 10(21) cm(-3). c-Al coimplantation at either room temperature (RT) or 600 degrees c, when implanted with N-Al > 1 x 10(20) cm(-3), gives improvements over Al alone implantation in the specificcontact resistance pc of Al ohmiccontacts on the implanted surfaces. The lowest median values of pc obtained are 3 x and 6 x 10(-5) Omega cm(2) for 6H- and JH-S1c. respectively. Ln the mid to high 1020 cm(-3) N-AI range, sheet resistivity. of the p-type implanted layers are also reduced by the coimplantation at RT, Temperature-dependent Hall-effect measurements reveal the correlated trends in increased impurity-band conduction and high-temperature (>400 K) hole concentration. implantation at 600 degrees c, by either coimplantation or Al atone implantation, degrades the electrical characteristics in the mid 10(20) cm(-3) N-AI range, which implies that amorphization of as-implanted Layers is necessary for effective activation of Al acceptors, It will be shown that c-AI coimplantation at RT can produce p(+)-n diodes with low reverse leakage currents and high forward current capability as evidenced by the 110 A/cm(2) forward current density at 2.8 V and 19 nA/cm(2) Leakage current density at -100 V for 4H-Sic p(+)-n diodes created by c-AI coimplantation at RT.
Herein, we report the effects of the catalyst support surface chemical/physical state of commercially available high -surface-area carbons on the electrochemical performance of Pt/c electrocatalysts synthesized using ...
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Herein, we report the effects of the catalyst support surface chemical/physical state of commercially available high -surface-area carbons on the electrochemical performance of Pt/c electrocatalysts synthesized using carbons as the support for platinum nanoparticles (Pt-NPs). A series of Pt/c electrocatalysts were synthesized through a microwave-assisted polyol process. The support carbons and the Pt/ccatalysts were characterized for their structural characteristics including crystallinity, microstructure (morphology and particle size distribution), physical surface area, porosity, thermal behavior, and surface chemical state. Evaluation of the electrocatalytic performances and durability parameters of the Pt/ccatalysts was performed through cyclic voltammetry and an accelerated stress test (AST). The results showed that the support carbons have similar physical properties except for the amounts and types of oxygen-containing surface functional groups. The Pt/ccatalysts supported on the carbon with a higher surface oxygen content were found more durable during the AST, as compared to their corresponding counterparts supported on the carbon with a lower surface oxygen content. This was attributed to the presence of oxygen functional groups that may function as the active sites for the nucleation of new Pt-NPs, hence inhibiting Ostwald ripening to some extent. This study provides valuable catalyst support selection criteria and synthesis parameters at different pressures.
Although most studies have indicated that biochar can boost rice (Oryza sativa) growth, the material may also suppress it, depending on ratios of carbon (c) to nitrogen (N) and available N to available phosphorous (P)...
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Although most studies have indicated that biochar can boost rice (Oryza sativa) growth, the material may also suppress it, depending on ratios of carbon (c) to nitrogen (N) and available N to available phosphorous (P). The current study sought to examine the impacts of biochar on rice growth and to identify underlying mechanisms. A pot experiment was conducted using two soils of high (3.05%) and low (0.54%) organiccarbon (Oc) content, mixed with 0, 1.5, 3, 6, and 12% biochar and planted with rice. Rice growth components, five rice tissue nutrients, and nine soil properties were measured. The results showed that the response of rice growth to biochar rates could be described using an exponential-growth function in high-Oc soil but an inverted U-shaped curve in low-Oc soil. In high-Oc soil, the 12% biochar rate led to the greatest total biomass, increased by 47%, whereas in low-Oc soil, the 3 and 6% rates exhibited the highest total biomass, increased by 44%, compared to the no-biochar added soils. Biochar elevated the c:N ratio from 11.5 to 39.1, with an optimal range of 20-30 corresponding to the highest rice growth. Biochar declined the ratio of NH4-N to Mehlich-1 P, causing N deficiency. In brief, high biochar rates may suppress rice growth when the soil c:N ratio exceeds 30. The applied biochar rate should be considered based on soil properties typically Oc and N content to obtain the c:N ratio between 20 and 30 for optimal rice growth.
A new surface micromachining way of ultrashort plus laser for c/Siccomposites with high quality and efficiency was demonstrated, including picosecond and femtosecond laser. Surface morphologies, element content and b...
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A new surface micromachining way of ultrashort plus laser for c/Siccomposites with high quality and efficiency was demonstrated, including picosecond and femtosecond laser. Surface morphologies, element content and bonding states of c/Siccomposites were analysed in detail after machined by picosecond and femtosecond laser power respectively. For femtosecond laser machining, the amount of nanoparticles increased with increasing laser power. At 20 and 50mW, Si-c, c-c and Si-O bonds existed in nanoparticles, while Si-c bonds disappeared at 70mW. For picosecond laser machining, cauliflower-like particles and periodic ripple with certain depth were formed distinctly. Furthermore, thermal ablation phenomenon occurred, and only Si-O bonds existed in particles due to the oxidation of the carbon fibres and Sic matrix. The results showed that femtosecond laser with low power was more suitable to the surface machining due to better machining quality and less machining damage compared with high power picosecond laser.
Despite its maturity and popularity, the c programming language still lacks tool support for reliably performing even simple refactoring, browsing, or analysis operations. This is primarily due to identifier scope com...
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Despite its maturity and popularity, the c programming language still lacks tool support for reliably performing even simple refactoring, browsing, or analysis operations. This is primarily due to identifier scope complications introduced by the c preprocessor. The cScout refactoring browser analyses complete program families by tagging the original identifiers with their precise location and classifying them into equivalence classes orthogonal to the c language's namespace and scope extents. A web-based user interface provides programmers with an intuitive source code analysis and navigation front-end, while an SQL-based back-end allows more complex source code analysis and manipulation. cScout has been successfully applied to many medium and large-sized proprietary and open-source projects identifying thousands of modest refactoring opportunities. (c) 2009 Elsevier B.V. All rights reserved.
An improved high-solid-loading slurry impregnation process was developed to introduce HfB2 particles into a low-density c/c preform efficiently, and precursor infiltration and pyrolysis process was used for densificat...
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An improved high-solid-loading slurry impregnation process was developed to introduce HfB2 particles into a low-density c/c preform efficiently, and precursor infiltration and pyrolysis process was used for densification to obtain a c/c-HfB2-Siccomposite. The microstructure characterization revealed that HfB2 particles uniformly filled the pores in the c/c preform, and Sic well densified the interstices between HfB2 particles and the small pores in the carbon fiber bundles. After being tested, the c/c-HfB2-Siccomposite had a density of 4.07 g/cm3 and a bending strength of 344.8 MPa, and exhibited a non-brittle fracture behavior. After ablation with oxyacetylene flame at 2500 for 120 s, the mass ablation rate and linear ablation rate of the c/c-HfB2-Siccomposite were 0.5 mg/s and 0.415 mu m/s, respectively. The good ablation performance is attributed to the hindering effect of the HfO2 scale on oxygen diffusion at high temperature.
Metastasis is the primary cause of death in cancer patients. cXcR4/cXcL12 chemokine axis provides directional cues for breast cancer cells to metastasize to specific organs. Despite their potential clinical importance...
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Metastasis is the primary cause of death in cancer patients. cXcR4/cXcL12 chemokine axis provides directional cues for breast cancer cells to metastasize to specific organs. Despite their potential clinical importance, how cXcR4 expression in breast cancer cells is regulated at the molecular level is not well understood. We identified an isoform of c/EBP, liver-enriched inhibitory protein (LIP), as a previously unrecognized transcriptional regulator of cXcR4 in breast cancer cells. LIP up-regulated the transcription of cXcR4 through direct interaction with the cXcR4 promoter. The increase in cXcR4 mRNA was paralleled by an increased cell surface expression of the cXcR4, which in turn promoted cXcR4-mediated breast cancer cell migration. A significant positive correlation between LIP and cXcR4 expression was observed in stage III and IV human breast carcinoma specimens. Neuregulin 1 (or NRG1, hereafter referred to as heregulin) increased cXcR4 expression in breast cancer cells, and this coincided with increased LIP binding on the cXcR4 promoter. These findings may have important implications for understanding the molecular basis of cXcR4-mediated breast cancer cell metastasis and could potentially allow us to develop novel strategies to reduce morbidity and mortality in patients with metastatic breast cancer.
We describe a production quality implementation of Scheme. Its design, and therefore the program, is based around objects although it is written in c, a language not specifically intended for object-oriented programmi...
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We describe a production quality implementation of Scheme. Its design, and therefore the program, is based around objects although it is written in c, a language not specifically intended for object-oriented programming. This was a fortuitous choice as it allowed us to recover from a design mistake that was not discovered until implementation time. Moreover, as we designed the program around objects and were not constrained by a strict object-oriented notation, this created a program that others have found easy to understand, extend and tune for improved performance.
The carbonaceous residue (coke) formed on HZSM-5 during the conversion of methanol to gasoline was studied by 13 c n.m.r. spectroscopy using cross-polarization and magic angle spinning and by e.p.r. spectroscopy. Meas...
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The carbonaceous residue (coke) formed on HZSM-5 during the conversion of methanol to gasoline was studied by 13 c n.m.r. spectroscopy using cross-polarization and magic angle spinning and by e.p.r. spectroscopy. Measurements were made on samples with different coke contents and on samples from which some external coke had been removed by treatment with an oxygen plasma. It was found that the amount of carbon visible by n.m.r. differed from that expected from the measured coke contents and that the ratio of these amounts varied with the degree of coking. We concluded that the n.m.r.-visible carbon was most probably composed of methyl-substituted polycyclic aromatic hydrocarbons, the degree of methyl substitution and ring condensation changing with the coke content. It was inferred that these methyl-substituted polycyclic aromatics were present in the channels of the zeolite whereas the coke invisible to n.m.r. could be highly condensed polycyclic aromatics or “graphitic” structures on the external surfaces of the zeolite crystals. It appears that initial coke formation is internal and that external coke forms at latter stages in the deactivation process.
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