Designing independent water transport channels to improve water flooding in ultra-thin nanoporous film cathodes for PEMFCs

Utilization of 3D nanostructured Pt cathodes could obviously improve performances of proton exchange membrane fuel cells (PEMFCs) owing to the reduced tortuosity and the bi-continuous nanoporous structure. However, these cathodes usually suffer from the flooding problem ascribed to the ionomer-free and nanoscale pores which are more susceptible to water condensation. In this paper, ultra-thin nanoporous metal films (100 nm) were utilized to construct PEMFC cathodes and independent transport channels were designed separately for water and gas aiming at the flooding problem. Nanoporous gold (NPG) film was used as the model support for loading Pt nanoparticles owing to its controllable and stable structure. After optimizing the polytetrafluoroethylene (PTFE) content and carbon loading in the gas diffusion layer (GDL), plasma treatment under O₂ atmosphere was used to pattern the GDL with independent water transport channels. The obtained liquid permeation coefficients and oxygen gains demonstrated the obviously improved water and O₂ transport. By using a home-made optimized GDL and a nanoporous film cathode with pore size ～60 nm, the flooding problem could be facilely solved. With a Pt loading of ～16 μg cm^?2, this 3D nanostructured cathode exhibits a PEMFC performance of ～957 mW cm^?2 at 80 °C. The Pt power efficiency is about 4 times higher than that of the commercial Pt/C cathode (50 μg cm^?2, 756 mW cm^?2). Obviously, this study provides a simple but effective methodology to solve the water flooding problem in the ultra-thin nanoporous film cathodes which is applicable for other types of 3D nanostructured PEMFC cathodes.     

Kinetics of light-induced degradation in compensated boron-doped silicon investigated using photoluminescence and numerical simulation

We use photoluminescence to observe light-induced degradation in silicon in real time. Numerical simulations are used to match our results and lifetime decay data from the literature with theoretical models for the generation of the light-induced boron–oxygen defects. It is found that the existing model of the slowly generated defect SRC, where its saturated concentration is a function of the majority carrier concentration, does not explain certain results in both p- and n-type samples. A new model is proposed in which the saturated SRC concentration is controlled by the total hole concentration under illumination.     

Effect of high pressure - low temperature processing on composition and colloidal stability of casein micelles and whey proteins

The aim of this study was to identify the impact of high pressure treatments at sub-zero temperatures (high pressure - low temperature; HPLT) on milk proteins. Whey protein solutions, micellar casein dispersions and two mixtures (micellar caseins:whey proteins, 80:20 and 20:80, w/w) were pressure treated (100–600 MPa) at pH 7.0 or 5.8 at −15 °C, −35 °C and ambient temperature. Solubility data showed that whey proteins could only be affected by HPLT treatments at pH 7.0 if caseins were present, while effects could be induced at pH 5.8 without the presence of caseins. The caseins formed on the one hand large aggregates (flocs) and on the other hand the solubility was increased by the creation of smaller micelles. The formation of flocs could only be observed for HPLT treated samples, which indicates the formation of different protein interactions in milk protein based samples compared with common HP treatments.     

A gradient boosting decision tree approach for insider trading identification: An empirical model evaluation of China stock market

Insider trading is a kind of criminal behavior in stock market by using nonpublic information. In recent years, it has become the major illegal activity in China’s stock market. In this study, a combination approach of GBDT (Gradient Boosting Decision Tree) and DE (Differential Evolution) is proposed to identify insider trading activities by using data of relevant indicators. First, insider trading samples occurred from year 2007 to 2017 and corresponding non-insider trading samples are collected. Next, the proposed method is trained by the GBDT, and initial parameters of the GBDT are optimized by the DE. Finally, out-of-samples are classified by the trained GBDT–DE model and its performances are evaluated. The experiment results show that our proposed method performed the best for insider trading identification under time window length of ninety days, indicating the relevant indicators under 90-days time window length are relatively more useful. Additionally, under all three time window lengths, relative importance result shows that several indicators are consistently crucial for insider trading identification. Furthermore, the proposed approach significantly outperforms other benchmark methods, demonstrating that it could be applied as an intelligent system to improve identification accuracy and efficiency for insider trading regulation in China stock market.     

Effects of anion and cation doping on the thermoelectric properties of n-type PbS

The PbCl_xS_1-x and Pb_1-xBi_xS (x? =?0–0.05) bulks were fabricated with a facile method of hydrothermal synthesis and microwave sintering, and the effect of anionic and cationic donors on the thermoelectric performance of PbS was investigated. Although Cl^? and Bi³⁺ both effectively improved the thermoelectric properties of n-type PbS, more excellent thermoelectric performance was obtained from Cl^? doped samples because of higher electrical property and lower thermal conductivity at higher temperature (T? >?600?K). The thermoelectric figure of merit (ZT) reaches 1.04 for PbCl_0.015S_0.985 at 800?K and increases with temperature increasing without sign of saturation, which is probably the highest value ever reported for single-phase polycrystalline n-type PbS. The results also indicate that the hydrothermal synthesis and microwave sintering can realize anion doping as well as cation doping for n-type PbS at low cost, and PbS should be a robust alternative for PbTe thermoelectric materials.     

Synthesis and electrochemical properties of layered Li[Ni0.333Co0.333Mn0.293Al0.04]O2−zFz cathode materials prepared by the sol–gel method

The cathode-active materials, layered Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_2−zF_z (0 ≤ z ≤ 0.1), were synthesized from a sol–gel precursor at 900 °C in air. The influence of Al–F co-substitution on the structural and electrochemical properties of the as-prepared samples was characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and electrochemical experiments. The results showed that Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_2−zF_z has a typical hexagonal structure with a single phase, the particle sizes of the samples tended to increase with increasing fluorine content. It has been found that Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_1.95F_0.05 showed an improved cathodic behavior and discharge capacity retention compared to the undoped samples in the voltage range of 3.0–4.3 V. The electrodes prepared from Li[Ni_0.333Co_0.333Mn_0.293Al_0.04]O_1.95F_0.05 delivered an initial discharge capacity of 158 mAh⁻¹ g and an initial coulombic efficiency is 91.3%, and the capacity retention at the 20th cycle was 94.9%. Though the F-doped samples had lower initial capacities, they showed better cycle performances compared with F-free samples. Therefore, this is a promising material for a lithium-ion battery.     

高效液相法测定鹅肥肝和鹅肝酱中维生素A

研究了运用高效液相法检测鹅肥肝和鹅肝酱中VA的方法。通过比较3种不同的处理样品方法，选择了其中较为快速、准确的处理方法。实验测定回收率为98．21％，鹅肥肝和鹅肝酱测定的变异系数分别为0.44％和1.14％。     

TCP self-clocking and bandwidth sharing

We propose a simple queueing model for TCP transfers sharing a bottleneck link and examine its behavior when the buffer at the bottleneck is large compared to the bandwidth-delay product. This model explains some behaviors of TCP that have already been observed, and predicts other behaviors that are new. We present measurements that demonstrate these behaviors in the current Internet.     

High mobility,low voltage polymer transistor

We introduce a polymer transistor that operates with low supply voltage and yet has a field-effect mobility higher than the mobilities reported for low voltage polymer transistors. A simple plasma oxidation of the gate metal to form a thin (3.74 nm) top metal oxide layer in the gate metal is involved in the fabrication that acts as the gate dielectric. With ultrathin gate dielectrics, the variation in the dielectric thickness and the surface roughness scattering can severely limit the mobility attainable. The plasma oxidation under certain conditions produces a very smooth oxide surface, leading to the high mobility.