Electrical and spectroscopic investigations on the reduction mechanism of graphene oxide

Ultra-large graphene oxide sheets of monolayer thickness were obtained by removing ultrasonication during the conventional oxidation process of graphite. In situ electrical conductivity measurement during the reduction by hydrazine monohydrate vapor and thermal annealing revealed the existence of an onset temperature at which electrical conduction started to occur. Corresponding X-ray photoelectron spectra indicated that an approximately 65% restoration of the sp² network led to the occurrence of electrical conduction. Reduction by ring-opening of epoxide group by hydrazine treatment seemed to restore the sp² network, while thermal annealing left a considerable number of defects in the graphene sheet through the formation of volatile gases.     

Performance evolution of NiO/yttria-stabilized zirconia anodes fabricated at different compaction pressures

Nickel oxide (NiO)/yttria-stabilized zirconia (YSZ) anode substrates were fabricated at four compaction pressures, 70, 200, 500 and 1000 MPa, the particle size distributions of NiO and YSZ were investigated with the powders treated at different compaction pressures, and the effects of compaction pressure on the performance of anodes with and without pore-formers were investigated by studying the effects of compaction pressure on the sintering shrinkage, compaction density, sintered density and electrical conductivity of anodes and the performance of cells. Experimental results demonstrated that the mismatch in the sintering shrinkages of YSZ films and the anodes compacted at 70 and 1000 MPa caused gas leakage across the films and thus a higher local temperature than the furnace temperature. The single cell with the anode using pore-former and compacted at 500 MPa exhibited the best output performance of 2.66 W cm⁻² at 800 °C.     

Relationship between molecular structure and dipole orientation of thermally activated delayed fluorescent emitters

The relationship between the chemical structure and the dipole orientation of thermally activated delayed fluorescent (TADF) emitters was examined by synthesizing three TADF emitters with donor and acceptor moieties at ortho-, meta-, and para-positions of a phenyl linker. Two carbazolylcarbazole donor moieties and two CN acceptor moieties were attached to the phenyl linker. The degree of dipole orientation of the three TADF emitters was in the order of para- (0.84)>meta- (0.76)>ortho- (0.72) substitution, demonstrating that extended molecular geometry by para-substitution is a key parameter to induce the dipole orientation of the TADF emitters.     

A Roadmap Review of Thermally Conductive Polymer Composites: Critical Factors,Progress, and Prospects

Recently, the need for miniaturization and high integration have steered a strong technical wave in developing (micro-)electronic devices. However, excessive amounts of heat may be generated during operation/charging, severely affecting device performance and leading to life/property loss. Benefiting from their low density, easy processing and low manufacturing cost, thermally conductive polymer composites have become a research hotspot to mitigate the disadvantage of excessive heat, with potential applications in 5G communication, electronic packaging and energy transmission. By far, the reported thermal conductivity coefficient (λ) of thermally conductive polymer composite is far from expectation. Deeper understanding of heat transfer mechanism is desired for developing next generation thermally conductive composites. This review holistically scopes current advances in this field, while giving special attention to critical factors that affect thermal conductivity in polymer composites as well as the thermal conduction mechanisms on how to enhance the λ value. This review covers critical factors such as interfacial thermal resistance, chain structure of polymer, intrinsic λ value of different thermally conductive fillers, orientation/configuration of nanoparticles, 3D interconnected networks, processing technology, etc. The applications of thermally conductive polymer composites in electronic devices are summarized. The existing problems are also discussed, new challenges and opportunities are prospected.     

基于量子计算的医疗数据敏感度度量

针对传统的医疗数据敏感度度量方法存在的度量开销大、数据查准率和查全率低的问题,提出基于量子计算的医疗数据敏感度度量方法。首先采用分布式样本重构方法重组医疗数据的分布式结构,建立医疗数据敏感度度量的统计分析模型;其次采用量化回归分析方法进行医疗数据的模糊融合和聚类分析,建立其定量递归分析模型;最后采用量子计算方法进行医疗数据敏感度度量过程中的自适应寻优控制,建立量子寻优约束进化模型,采用动态全局规划方法实现对医疗数据敏感度的度量。实验结果表明,采用该方法进行医疗数据敏感度度量的统计分析能力较强,且度量时间开销较小、对敏感数据的查准率和查全率较高,提高了对医疗数据的检索和特征分辨能力,有效实现了对医疗数据的统计分析和检测度量。     

Tin–graphite materials prepared by reduction of SnCl4 in organic medium: Synthesis,characterization and electrochemical lithiation

Tin–graphite materials were prepared by chemical reduction of SnCl₄ by t-BuONa-activated NaH. TEM imaging showed that the crude material is composed of an amorphous organic matrix containing tin present either as nanosized particles deposited on the graphite surface or as free aggregates. Subsequent washings with ethanol and water allow removal of side products as well as most part of the organic matrix. Electrochemical insertion of lithium occurred in graphite and in tin. The initial reversible massic capacity of 630 mAh g⁻¹ decayed to a stable value of 415 mAh g⁻¹ after 12 cycles. This capacity value was lower than the expected maximum one of 650 mAh g⁻¹ corresponding to a Sn/12C molar composition and assuming the formation of LiC₆ and Li₂₂Sn₅. Even if this massic capacity is not much improved by comparison with that of graphite, it must be pointed out that the volume capacity of this graphite/Sn material is much larger (2137 mAh cm⁻³) than that corresponding to graphite (837 mAh cm⁻³). It was hypothesized that the part of tin bound to graphite could be responsible for the stable reversible capacity. To the contrary, graphite unsupported tin aggregates would contribute to the observed gradual decline in the storage capacity. Therefore, the improvement in cycleability, compared to that of massive metals, could be attributed both to the nanoscale dimension of the metal particles and to interactions between graphite and metal the nature of which remaining to be precised.     

A few things transport regulators should know about risk and the cost of capital

In reviewing contracts, establishing price limits, or arbitrating conflicts, regulatory agencies and policy advisors face significant information asymmetry in determining the appropriate allowed rate of return, or discount rate. The information gap is especially important in determining the degree of market risk—often a critical component of the cost of capital demanded by operators.Alexander, Estache, and Oliveri consider various methodological problems in the transport sector in establishing the link between regulatory regime and degree of market risk.The results of quantitative studies confirm that even for the transport sector—where there is intermodal competition and where contracts are often shorter and regulatory decisions may be less pressing than for utilities—the choice of regulatory regime greatly affects the degree of market risk a company faces. This has important implications for regulatory agencies and actions.When a regulatory agency undertakes a price review, or when issues arise about concession contracts, it is important that regulators assess correctly the required rate of return and cost of capital. They must also assess correctly the level of risk, which affects the required rate of return and the cost of capital.Most regulators in developing countries have a problem: the regulated companies are unquoted or undertake many activities for a range of industries and even sectors. For them this methodology for measuring the cost of capital, calculating the measure of market risk, and estimating the impact of various regulatory regimes on market risk may be useful.     

A-site cation deficiency tuned oxygen transport dynamics of perovskite Pr0.5Ba0.25-xCa0.25CoO3-δ oxide for intermediate temperature solid oxide fuel cells

Perovskite oxides with ionic and electronic conductivity are the key cathode materials of solid oxide fuel cells. Most of these materials, however, exhibit large cathodic polarization resistance which is mainly determined by their tardy oxygen transport kinetics. Herein, Pr_0.5Ba_0.25-xCa_0.25CoO_3-δ is studied to understand the roles of Ba-deficiency in tuning oxygen transport and electrochemical behaviors in the system. Our findings indicate that Ba-deficiency can significantly accelerate oxygen surface exchange process and bring ∼77% reduction of polarization resistance in this process. It is interesting to note that Ba-deficiency can slightly slow oxygen ion bulk diffusion rate and induce a minor increase of polarization resistance in the corresponding process, which associates with the inhibited oxygen vacancy mobility caused by the interactions between negatively charged Ba vacancy and positively charged oxygen vacancy. These new findings pave a new path for solid oxide fuel cell design and chemical sensor developments.