The preparation of self-assembled DNA nanostructure with different sizes and shapes has been one of the most promising research areas in recent years, while the application of these DNA ...nanostructures in biosensors is far from fully developed. Here, we presented a novel carrier system to construct an electrochemiluminescence (ECL) aptasensor for ultrasensitive determination of lipopolysaccharides (LPS) on the basis of self-assembled tetrahedron DNA dendrimers. Doxorubicin (Dox), a well-known intercalator of double stranded DNA (dsDNA), was conjugated with the ECL luminophore of N-(aminobutyl)-N-(ethylisoluminol) (ABEI) to form a new type of ECL indicators (Dox-ABEI), which could noncovalently attach to dsDNA through intercalation. Based on this property, self-assembled tetrahedron DNA dendrimers were employed as an efficient nanocarrier to achieve a high loading efficiency for Dox-ABEI with significantly amplified ECL signal output. Streptavidin (SA) and biotin, a typical ligand–receptor pair, has been chosen to anchor the tetrahedron DNA dendrimers on the electrode surface. Moreover, by converting LPS content into DNA output, catalyzed hairpin assembly (CHA) target recycling signal amplification strategy was also adopted to enhance the sensitivity of the ECL aptasensor. With combining the loading power of the tetrahedron DNA dendrimers for ECL indicators, the inherent high sensitivity of ECL technique and target recycling for signal amplification, the proposed strategy showed a detection limit of 0.18 fg/mL for LPS.
A ferrocene-switched electrochemiluminescence "off-on" sensor is proposed on the basis of target transduction and a DNA walking machine for the sensitive detection of cardiac troponin I (cTnI). The ...proposed method offers high selectivity with a low detection limit of 0.016 pg mL(-1), and provides a universal platform for detecting a wide range of targets, including other proteins and DNAs, by changing the molecular recognition elements to the corresponding antibodies, aptamers or DNA probes.
With the development of manufacturing technology, five-axis milling has been one of the most important solution strategies in machining field. To deepen the understanding of multi-axis processing and ...improve the application level of the technology, the current work was carried out. This paper investigated the effects of tilt and lead angle on the scallop height, surface roughness, surface topography, and surface damages in five-axis ball-end milling process. Both geometrical analysis and experiment research are conducted to investigate the scallop height after five-axis milling, and variation of the surface roughness and surface topography with tool inclination angle obtained from the experiments was analyzed. Surface damages under the different inclination angles were also observed and analyzed with optical profiler. Several conclusions are made as follows. The inclination angles of the ball-end mill have no effect on the scallop height when only the spherical part of the cutter participates in the cutting process according to the geometrical analysis. Surface roughness with regard to tilt angles presents symmetrical characteristic around 0°. Surface texture feature, especially the texture direction, is closely related with the tool posture. The surface concave pits, convex marks, microscopic cracks, and spot corrosions are mainly the damage forms of the machined surface. More surface blemishes appeared when small inclination angles are adopted in cutting. As a result, the recommendatory inclination angle values for inclination angle are proposed. A better understanding of the five-axis machining process would be given by the detailed analysis of generation reason of the machined surface features, and the results could provide support for process parameter optimization.
In this paper, samples of xCeO2·(100-x) (SiO2·Al2O3·CaO) (x: 0∼15) glass solidified body was prepared by a high temperature melting method. The structural characteristics and thermal stability of ...CeO2 silicate glass-cured bodies were characterized by means of density porosity test, XRD, Raman, DSC and SEM. The results show that the addition of CeO2 does not change the basic structure of the glass, which is located in the pores of the silicate glass grid and plays a network modification role. When the added amount is less than 5% wt, homogeneous glass is easily formed. CeO2 is uniformly distributed in the glass body, and no enrichment occurs. When the added amount is more than 8% wt, CeO2 easily crystallizes during cooling.
Abstract
The application potential of bentonite is closely related to the content of montmorillonite from it, and the purification of bentonite is conducive to expanding its industrial application. ...In this paper, purification method of Keerjian bentonite with low to medium grade were studied systematically. A comparative study of natural settlement, chemical dispersion and high-speed centrifugation was carried out. In addition, one-factor experiment and orthogonal experiment on a compound purification method, chemical dispersion following by high-speed centrifugation, were conducted. According to the experimental result, the optimal parameters of the compound purification, namely slurry ratio 1:8, dispersant amount 1.2% and soaking time 24h, were obtained. This study solved the problem of low utilization level and low purification efficiency, which shade light in the application of Keerjian bentonite with high efficiency and high economic benefits.
Abstract
In this paper, low- to medium-grade bentonite derived in Keerjian of Toksun county were characterized. A method combined by chemical dispersion and high-speed centrifugation was used for the ...purification of the bentonite. Absorption of methylene blue and X-ray diffraction analysis were used to evaluate the effect of purification methods. The result showed that the optimal slurry solid-liquid ratio, dispersant amount, sedimentation time, centrifugal speed, and time of centrifugation was 1:8, 1.2% of the bentonite mass, 24h, 2000 r/min, and 5 min, respectively. The investigation provided experimental evidence for the better development and application of bentonite in this mining area.
High-speed face milling of AISI H13 hardened steel is conducted in order to investigate the effects of cutting parameters on tool life and wear mechanisms of the cubic boron nitride (CBN) tools. ...Cutting speeds ranging from 400 to 1,600 m/min are selected. For each cutting speed, the metal removal rate and axial depth of cut are fixed, and different combinations of radial depth of cut and feed per tooth are adopted. The tool life, tool wear progression, and tool wear mechanisms are analyzed for different combinations of cutting parameters. It is found that for most of the selected cutting speeds, the tool life increases with radial depth cut and then decreases. For each cutting speed, the CBN tool life can be enhanced by means of adopting suitable combination of cutting parameters. When the cutting speed increases, the normal wear stage becomes shorter and the tool wear rate grows larger. Because of the variations of cutting force and tool temperature, the tool wear mechanisms change with different combinations of cutting parameters even at the same cutting speed. At relatively low cutting speed, in order to acquire high tool life of the CBN tool, the tool material should possess sufficient capability of resisting adhesion from the workpiece. When relatively high cutting speed is adopted, retention of mechanical properties to high cutting temperature and resistance to mechanical impact are crucial for the enhancement of the CBN tool life.
High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main ...tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.
Abstract
In this paper, samples of xCeO
2
·(100-x) (SiO
2
·Al
2
O
3
·CaO) (x: 0∼15) glass solidified body was prepared by a high temperature melting method. The structural characteristics and thermal ...stability of CeO
2
silicate glass-cured bodies were characterized by means of density porosity test, XRD, Raman, DSC and SEM. The results show that the addition of CeO
2
does not change the basic structure of the glass, which is located in the pores of the silicate glass grid and plays a network modification role. When the added amount is less than 5% wt, homogeneous glass is easily formed. CeO
2
is uniformly distributed in the glass body, and no enrichment occurs. When the added amount is more than 8% wt, CeO
2
easily crystallizes during cooling.
Sialon–Si3N4 graded composite ceramic materials were fabricated by hot press sintering. The mechanical properties and microstructure of the composites were examined. The thermal shock and thermal ...fatigue resistance of the Sialon–Si3N4 graded composite ceramic materials were investigated by means of the water quenching method. The microstructure of the composites was characterized with transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results showed that the graded ceramic exhibited higher retained flexural strength under all thermal shock temperature differences compared to the homogeneous reference one, indicating the higher thermal shock resistance of the graded ceramic. The highest critical temperature difference of the graded composites was 600°C. The crack growth (∆c) of graded ceramic materials was much lower than that of homogeneous ceramic materials, which revealed the higher thermal fatigue resistance of the graded ceramics. The improvement of the thermal shock and thermal fatigue resistance was attributed to the formation of compressive residual stress in the surface layer and the enhanced mechanical properties induced by the graded compositional structure.
►High properties of Sialon–Si3N4 graded composite ceramics are obtained. ►The thermal shock resistance of graded ceramic is higher than that of homogeneous one. ►Graded structure contributes to the thermal shock resistance of material.
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