Search

The distance effect of the doped heteroatoms away from the catalytic centers has rarely been reported. In this work, we conducted density functional theory calculations to thoroughly investigate the influence of heteroatom (N, P, B, and S atoms) doping distance on the oxygen reduction reaction (ORR) activity of graphene-based FeN4 sites. We uncovered a Sabatier-like relationship between heteroatom doping distance and ORR activity of FeN4 sites. The nearest doping does not significantly improve and even block the ORR activity of FeN4 sites. Optimal ORR activity is achieved when the heteroatoms are 4–5 Å (N, P, and S atoms) or 6–7 Å (B atoms) away from the Fe atoms. Analysis of electronic structure indicates that distance effect can modulate the local chemical environment of Fe atoms, thereby account for the changes in ORR activity along with the doping distance and doping atoms. This study provides insights into the influence of heteroatom doping on the chemical environment of reaction active centers, and provides the theoretical guidance for controlling the doping distance of heteroatoms to achieve optimal catalytic activity and selectivity. [ABSTRACT FROM AUTHOR]

This study aimed to establish a method for the simultaneous determination of isoquercitrin, trifolin and afzelin in A. persica flowers by high performance liquid chromatography (HPLC) with ionic liquid as extractant and ultrasonic-assisted extraction. The effects of ionic liquid concentration, solid–liquid ratio, number of crushing mesh, ultrasonic time, extraction temperature, and ultrasonic power on the extraction yield of three target compounds were investigated using the extraction yield of target analytes as the index. According to the results of single factor experiment, the Box-Behnken design-response surface methodology (BBD) was used to optimize the extraction method and compared with the traditional extraction method. The results showed that, calibration curves had excellent linearity (R2 > 0.9990) within the test ranges. In combination with other validation data, this method demonstrated good reliability and sensitivity, and can be conveniently used for the quantification of isoquercitrin, trifolin and afzelinin A. persica flowers. And the contents of isoquercitrin, trifolin and afzelin were 64.08, 20.55 and 75.63 μg/g, respectively. The optimal process obtained by BBD was as follows: ionic liquid concentration was 1.0 mol/L, solid–liquid ratio was 1:40 g/ml, mesh sieve was 50 mesh, ultrasonic time was 40 min, extraction temperature was 50 °C, and ultrasonic power was 400 W. Under the optimal conditions, the theoretical predicted total extraction yield of the three target compounds was 159.77 μg/g, which was close to the actual extraction value (160.26 μg/g, n = 3), this result indicating that the optimal process parameters obtained by response surface methodology analysis were accurate and reliable. The method was simple, accurate and rapid for determination the contents of three active ingredients in A. persica flowers. [ABSTRACT FROM AUTHOR]

At present, steam-assisted gravity drainage technology has failed to meet the requirement for the large-scale development of abundant oil sands resources due to high production cost and serious environmental pollution caused by huge amounts of carbon emissions. Therefore, this paper proposes a radio frequency technology for heating oil sands and establishes a corresponding mathematical model that considers the phase transition of water. Then, a lab-scale experimental setup is designed to experimentally investigate the performance of radio frequency heating based on the phase change. Finally, the influences of phase transition of water on the temperature distribution of oil sand samples are analyzed in detail. The results show that the mathematical model of radio frequency heating can accurately predict the temperature distribution prior to the phase transition of water due to the little effect of phase transition on the thermal properties and density of oil sand samples. The failure to consider the effect of phase transition of water on electrical conductivity of oil sand in the mathematical model accounts for a large deviation between the measured temperature data and numerical results. So, in order to make the calculated temperature results more accurate, this effect should be considered during numerical simulation. [ABSTRACT FROM AUTHOR]

Multifunctional textiles were fabricated by one-step in-situ synthesis of zeolite imidazole skeleton-8 (ZIF-8) on polydopamine (pDA) templated cotton fabrics. A homogenous distribution of ZIF-8 nanoparticles on cotton fiber surface was achieved as per surface morphology study by SEM and TEM, and the heterogeneous nucleation mechanism of depositing the dense ZIF-8 film on pDA-templated cotton fabrics was proposed. FTIR spectra, XPS, and XRD have indicated the presence and confirmed the chemical composition of ZIF-8 on coated cotton fabrics. The fabricated ZIF-8/cotton fabrics showed excellent photocatalysis for Methylene blue decomposition under ultraviolet radiation, and the photocatalysis mechanism was discussed. In addition, the coated fabrics showed robust antimicrobial activity towards Escherichia coli. This facile and affordable fabrication method based on dopamine and ZIF-8 is promising for large-scale production of multifunctional textiles. [ABSTRACT FROM AUTHOR]

Compared with the chemical vapor deposition method, the high-pressure and high-temperature (HPHT) method has some advantages, such as fast diamond crystal growth speed, mature technology and easy mass production. HPHT method synthetic diamond is widely used industrially, but gem-quality synthetic diamond from China has rarely been reported. In this work, the gem-quality diamond synthesized by State Key Laboratory of Superhard Materials, Jilin University, China (SKLSHM), using the cubic hinge press equipment by the HPHT method, was investigated by microscopy, field-emission scanning electron microscopy (FE-SEM) and Diamond View observations as well as infrared spectrometer, ultraviolet–visible spectrometer (UV spectrometer) and energy-dispersive x-ray fluorescence tests. FE-SEM observation showed that regular growth steps and obvious growth pits were common on the {100} surface, and they were consistent with the distribution of internal metal inclusions. In most cases, the {111} plane is significantly flatter than the {100} plane, which may be related to the surface atomic state. It also can be seen that the internal metal inclusions are easily aligned along the internal growth boundary,which may be due to the different growth rates of different crystal faces during diamond growth. The fluorescent image under Diamond View shows the special geometric growth zone structure. Cubes, octahedrons and rhombohedral dodecahedrons have different intensities of orange, yellow, blue and other uneven fluorescences, which can be used as the most important diagnostic evidence. [ABSTRACT FROM AUTHOR]

A 2,250 mm whirlpool foundation pit is located in Donghai Island, Zhanjiang City, Guangdong Province, China. The layers of the island are composed of multi-aquifers and multi-aquitards (MAMA). The aquifers are intersected by partial aquitard lenses. A large confined aquifer is frequently interbedded and separated into several sub-confined aquifers by partial aquitards. In the 2,250 mm foundation pit, the water level of two confined aquifers was reduced to satisfy excavation requirements and prevent water inrush. Construction of the 32.55 m deep foundation pit encountered MAMA and potential defects of the diaphragm wall. The pumping wells in the second confined aquifer were used to reduce the water level to ensure the safety of bottom excavation. The pumping wells in the first confined aquifer were used to reduce the water level under emergency conditions to prevent potential water inrush and piping from the defects of the diaphragm wall. Field pumping tests and numerical simulations were performed to determine the risk of leakage and verify the capability of the pumping wells to reduce the water level. Quicksand occurred during shallow excavation because of leakage although the confined aquifer had been cut off and pumped for a long time. Three pumping wells were installed to reduce the water level. When the foundation pit was excavated to a depth of 24 m, water inrush occurred at the middle of the pit bottom although the water level of the dewatered aquifer had been reduced to below the excavation face. A 90 m deep borehole was found where the underlying confined aquifer below the first aquifer induced the water inrush. Although the upper water level was reduced, the high water level in the deep part still induced water inrush. The pumping wells in the second aquifer were all opened, and the water level of the underlying confined aquifer was reduced. After the water level was reduced to below the pit bottom, the borehole was filled, and the water inrush stopped. However, water inrush occurred on the cracks of the diaphragm wall as predicted. The pre-installed pumping wells were opened to control the water inrush. The deepest foundation pit on the island was constructed successfully after dealing with the water inrush and leakages. [ABSTRACT FROM AUTHOR]

A series of novel KLaSr3−x(PO4)3F:xEu2+ phosphors were synthesized for the first time. The crystal structure, photoluminescence properties, concentration quenching, decay analysis, and the temperature dependent luminescence properties were investigated in detail. The unit cell parameters for KLaSr3(PO4)3F were estimated to be a = 9.8997 Å, c = 7.4075 Å, and V = 628.7 Å3. The photoluminescence excitation spectrum of KLaSr3(PO4)3F:Eu2+ shows a broad band from 225 nm to 450 nm with a maximum at about 320 nm. KLaSr3−x(PO4)3F:xEu2+ phosphors exhibit a wide emission band ranging from 425 to 550 nm. KLaSr3(PO4)3F:Eu2+ phosphors exhibit good thermal stability up to 423 K. KLaSr3(PO4)3F:Eu2+ was fabricated with commercial green (Ba,Sr)SiO4:Eu2+ and red CaAlSiN3:Eu2+ phosphors to obtain a white-light-emitting diode. All the results demonstrate that KLaSr3(PO4)3F:Eu2+ are promising blue phosphors for white-light ultraviolet light-emitting diode applications. [ABSTRACT FROM PUBLISHER]

Two kinds of natural apatite minerals were obtained from two different phosphate deposits in northern China, FanShan, Hebei province and HeiYingShan, Inner Mongolia province. Their chemical compositions, phase structure, and cathodoluminescence (CL) have been comparatively investigated. X-ray diffraction (XRD) analysis indicated that the raw phosphate minerals from FanShan mainly are composed of FanShan apatite (FA) and FanShan mica, respectively, while the ore sample from HeiYingShan contained HeiYingshan apatite (HA) and HeiYingshan magnetite. The mineralogical characteristics and crystal structure of FA and HA were further determined by XRD, scanning electron microscopy, x-ray fluorescence spectrometer, and inductively coupled plasma-mass spectrometry, respectively. These results indicate that FA belongs to fluorapatite, while the HA belongs to hydroxyapatite. The existence of some trace elements has also been verified by the measured CL spectrum. The origin of the observed CL peaks has been discussed, and the relationship of the CL and the chemical composition has also been investigated. [ABSTRACT FROM AUTHOR]

Purpose: The purpose of this article is to evaluate fast-track rehabilitation program and conventional care after esophagectomy using a retrospective controlled cohort study in esophageal cancer patients. Methods: Fifty-five patients underwent fast-track rehabilitation program and 57 patients underwent conventional care after esophagectomy. Fast-track rehabilitation program was performed to patients who have early movement, epidural analgesia control, fluid infusion volume control and enteral nutrition for early discharge. The other 57 patients underwent conventional care after esophagectomy. The average of hospital stay and complications were calculated in the patients between the two groups. Results: The median length of hospital stay in the patients was significantly shorter after fast-track rehabilitation program than after conventional care (7.7 vs 14.8 day, P < 0.01). The percentage of patients who developed complications was significantly lower 30 day after fast-track rehabilitation program than after conventional care (29.1 vs 47.4 %, P < 0.05). 87.3 % in patients of the fast-track rehabilitation program group and 54.4 % in those of the conventional care group reported excellent to very good satisfaction with their pain control ( P = 0.000). Conclusions: The fast-track rehabilitation program results in fewer complications, less postoperative pain, a reduction in the hospital length of stay, and quicker return to work and normal activities after esophagectomy. [ABSTRACT FROM AUTHOR]

A new general optimal principle of designing explicit finite difference method was obtained. Several applied cases were put forward to explain the uses of the principle. The validity of the principal was tested by a numeric example. [ABSTRACT FROM AUTHOR]