Search

The thermal desorption (TD) technique is widely employed in modern mass spectrometry to facilitate the detection of non-volatile analytes. In this study, we developed a compact TD device based on a small resistance wire and coupled it with a self-aspirating corona discharge ionization (CDI) source to conduct direct MS analysis of various liquid and solid samples. Due to its small size and low heat capacity, the temperature of the TD module can be flexibly and rapidly modulated by controlling the power sequence. Multiple heating modes, including pulse heating (PH), isothermal heating, and step heating (SH), are realized and characterized, and then applied for the detection of different real samples. In particular, the PH mode is suitable for the simultaneous detection of multiple components in samples with relatively simple matrices, while the SH mode is capable of component separation. In addition, the sensitivity and quantitative capability of the TD-CDI system for DEP solutions were tested, showing acceptable stability with a relative standard deviation of about 6.7% and a detection limit of 0.088 ng. Overall, the developed TD-CDI system provides a simple, convenient, and versatile tool for direct mass spectrometry analysis of real samples.

A series of novel and modular ferrorence-based amino-phosphine-binol (f-amphbinol) ligands have been successfully synthesized. The f-amphbinol ligands exhibited extremely high air stability and catalytic efficiency in the Ir-catalyzed stereoselective hydrogenation of various ketones to afford corresponding stereodefined alcohols with excellent results (full conversions, cis/trans >99:1, and 83% → 99% ee, TON up to 500 000). Control experiments have shown that −OH and −NH groups played a key role in this stereoselective hydrogenation.

A new machining method that combines textured surface and water lubrication is proposed in this paper to improve the friction characteristics of ground silicon carbide (SiC). The effects of water film thickness and grinding speed on the nano-machining behavior of monocrystal cubic SiC are revealed using molecular dynamics simulation. Moreover, a Rayleigh chip thickness model is employed to predict surface roughness. According to the obtained results, friction characteristics and machinability of textured samples are strengthened compared with the non-textured sample. Behavior characteristics are further improved in water-lubricated conditions, which show that the temperature, grinding force, and friction coefficient decrease, while the hydrostatic stress and the von Mises stress increase. Therefore, tool wear and sub-surface damage are improved. Furthermore, an improved material removal performance is also achieved under high-speed grinding. Lastly, it is observed that surface roughness of ground SiC is improved in water lubrication and under high-speed grinding.

To solve problems of low machining efficiency and surface/subsurface damage of silicon carbide (SiC), mechanisms of material dislodging and subsurface destruction of bicrystal SiC under nano-cutting were studied by using three-dimensional molecular dynamics (MD) simulation method. Effects of grain boundary (GB) tilt angle and cutting speed on stress, hydrostatic pressure, cutting force, temperature, and subsurface damage depth were analyzed. Results show that GB slope angle has important influence on the spread of strain, hydrostatic stress, and temperature, especially on subsurface damage depth. Specifically, with the increase in GB slope angle, subsurface damage layer decreases, and machined surface morphology improves. The machinability of small GB angle is better than the large GB angle, and the model with grain boundary angle of 4.24° has the best machinability. It is also found that with the increase in cutting velocity, the temperature increases, whereas cutting force and friction coefficient are reduced, which indicates that the increase in cutting velocity can effectively improve surface machined morphology. The research results provide a theoretical reference for future experimental research.

This paper aims to study the mechanism of ion implantation. Molecular dynamics software was used to simulate the process of 3C-SiC workpiece being ion implanted with different implant parameters. The influence of ion implantation parameters on workpiece damage, as well as on workpiece temperature, potential energy, dislocation defects, surface morphology, cutting force, stress and other processing parameters, is analyzed. The results show that with the increase of dose, the damage range inside the workpiece shows a periodic change, the potential energy and temperature generally show a rising trend, and the internal normal stress exhibits an increasing trend. In addition, the temperature, potential energy, cutting force and stress of the workpiece increase with the increasing inclination angle. Furthermore, the channel effect is obvious when the inclination angle of ion implantation is between 30° and 50°. Alternatively, for inclination angle greater than 70°, a scattering effect is distinctly observed. Moreover, the average cutting force decreases with the increase of injection distance. Lastly, the average temperature is lowest when the ion implantation region is in the middle of the workpiece, and the farther the implantation region is, the faster is the rise in temperature and potential energy.

To improve the machinability of the brittle material 3C-SiC, a new method of ion implantation surface modification is proposed. Molecular dynamics simulations were employed to investigate the mechanical properties and defect evolution of ion-implanted single-crystal 3C-SiC under nano-indentation. The effects of implantation dose, implantation energy, and implantation angle on the force, dislocation, hardness, and elastic modulus were discussed. The results revealed that ion implantation can reduce the hardness and elastic modulus, and improve the plasticity. Besides, the nucleation of dislocation is suppressed by ion implantation. It showed that the higher the implantation dose, the lower the force, the lower the hardness and elastic modulus, whereas those of implantation energy were the opposite. Therefore, the optimum implantation dose and energy can be obtained by comparing the above characteristics. Moreover, the channel effect was revealed under different implantation angles. Finally, through theoretical model analysis, it demonstrated that ion implantation affects the direction and size of normal stress. Thus, this method is favorable to material advanced manufacturing processes for enhancing the plasticity of the brittle single-crystal SiC.

A coupling configuration of double-wall cooling and exterior surface thermal barrier coating (TBC) is one of the most promising thermal protection methods of hot components of modern gas turbine. The combined influences of coating thickness, impingement layout, and cooling air flowrate on the overall thermal performances of such configuration were discussed deeply, to provide the valuable guidance of design. Overall effectiveness measurements were implemented under engine-matched Biot numbers and mainstream-to-coolant temperature ratio. Conjugate heat transfer simulations provided the additional information difficult to be acquired by the measurements. The results indicated that the contribution of TBC is much larger than that of increasing the cooling air amount. The thicker TBC can produce the stronger insulation, while the higher risk of thermal damage of itself. The larger coolant flowrate enlarges the benefit of TBC, while the trend is suppressed by the thick TBC. The constant coating thickness cannot bring to the uniform metal temperature, which can be solved through properly adjusting the backside impingement. The trends in overall effectiveness with TBC’s thickness are independent on the change of internal impingement.

This paper presents a comparative experimental and numerical study of the heat transfer and pressure loss in a swirl multi-pass channel with tangential jet slots, and another baseline multi-pass channel with 180-deg U-bends as comparison baseline has also been investigated. Transient liquid crystal thermography is used to obtain the detailed heat transfer distribution on the internal surfaces of the multi-pass serpentine channels. The heat transfer patterns in the swirl multi-pass channel are quite different from that of the baseline multi-pass channel. Compared with the baseline multi-pass channel, the experimental globally averaged Nusselt number ratios of the last two passes in the swirl multi-pass channel can be increased by up to 82.9%, 104.8% and 124.6% for the Reynolds numbers 20,000, 40,000 and 60,000, respectively. The high and circumferentially uniform heat transfer is mainly due to the large-scale swirling flow induced by the tangential slots. More detailly, the large-scale swirling flow impinges onto the surface and further induces high tangential velocity near the wall, which destroys the boundary layer flow and thus improves the heat transfer rates at the wall. However, the notable pressure loss of the swirl multi-pass channel should be further controlled reasonably, which is about 5.4 times that of the baseline multi-pass channel. As supplements to the experiments, three-dimensional numerical computations provide more insights into the turbulent flow structure in the two kinds of multi-pass serpentine channels.

With the acceleration of globalization and regionalization of the world economy, port is playing an increasingly important role for that it is an international transportation hub port interface and the support of the international trade platform. How to effectively reduce labor costs, improve the working environment, stable productivity, reduce the production cuts caused by human intervention and improve the management of real-time monitoring of all the major ports has become a common issue faced. In order to achieve the automatically stacking and reclaiming process of Stacker-Reclaimer in the bulk material yard, the source of its control is expected to identify the stockpile in the bulk yard, including length, width, height, the starting address, destination address, as well as Three-dimensional shape of the stockpile, since in the operation process, stockpile changes the shape dynamically. As a result, the real-time three-dimensional shape and coordinate of piles should be achieved. Based on the existing Stacker-Reclaimer in Qinhuangdao Port coal, we study the large field of view real-time three-dimensional laser scanning imaging theory and technology. The overall system design to achieving the three-dimensional laser scanning image is presented. The working principle of the three-dimensional laser scanning imaging system is analysised. Moreover, the parameter designation, the technical parameters and the composition of the whole system are all given. The research of the thesis is also used for other large-scale three-dimensional modeling of piles and the volume computing. In a world, the method has wide application prospect.

Abstract: Two linear regression models based on absorption features extracted from CE-1 IIM image data are presented to discuss the relationship between absorption features and titanium content. We computed five absorption parameters (Full Wave at Half Maximum (FWHM), absorption position, absorption area, absorption depth and absorption asymmetry) of the spectra collected at Apollo 17 landing sites to build two regression models, one with FWHM and the other without FWHM due to the low relation coefficient between FWHM and Ti content. Finally Ti content measured from Apollo 17 samples and Apollo 16 samples was used to test the accuracy. The results show that the predicted values of the model with FWHM have many singular values and the result of model without FWHM is more stable. The two models are relatively accurate for high-Ti districts, while seem inexact and disable for low-Ti districts.

We developed an oxidant- and transition-metal-free approach to construct six-membered cyclic phosphinamides via an intramolecular electrochemical C–H phosphinamidation process. With nBu4NBr as the catalyst and electrolyte, cyclic phosphinamides bearing a variety of functional groups (22 examples) were readily accessed under mild conditions. Meanwhile, this protocol provided an alternative route to organic electroluminescent materials and P–N ligands.

As a new two-dimensional material with unique friction and wear properties, graphene often serves as a solid lubricant. In order to better understand the lubrication effect of graphene in the process of three-body polishing of single crystal silicon with diamond abrasive, a molecular dynamics model of this process was established in this study. Further, the changes of coordination number, friction coefficient, temperature, potential energy, stress, and surface/subsurface damage in the process of three-body polishing were analyzed in detail. The results showed that graphene lubrication could enhance the heat dissipation and reduce the number of defect atoms, friction coefficient, potential energy, stress, and chips. Therefore, less subsurface damage and material resistance were observed in the workpiece with graphene lubrication during machining. In general, graphene can be used as a high-quality solid lubricant in the three-body polishing of single crystal silicon using diamond abrasive because of its excellent lubricating effect.

In this paper, molecular dynamics simulations were performed to simulate ion implantation and diamond grinding processes of SiC. Moreover, workpiece surface roughness was predicted based on Rayleigh probability distribution. Effects of ion implantation energy on the temperature, potential energy, cutting force, friction coefficient, and surface morphology of the workpiece during machining were analyzed. It has been revealed that the higher the ion implantation energy, the higher the proportion of internal damage, the lower the temperature rise rate in the workpiece, the lower the cutting force, the smaller the length and number of dislocations, the higher the removal efficiency of single abrasive particles, and the higher the final surface roughness. Among them, the changing trend of surface roughness is qualitative analysis under specific experimental conditions. In conclusion, ion implantation is favorable to SiC processing, and revealing its influence mechanisms has important guiding significance for practical applications.