High speed milling experiments using nitrogen-oil-mist as the cutting medium were carried out to investigate the characteristics of chip formation for Ti-6Al-4V alloy.Within the range of conditions employed(cutting sp...High speed milling experiments using nitrogen-oil-mist as the cutting medium were carried out to investigate the characteristics of chip formation for Ti-6Al-4V alloy.Within the range of conditions employed(cutting speed,vc=190-300 m/min;cutting depth of axial,ap=5,7 mm),saw-tooth chips were produced in these experiments.During the macro and micro analysis of the Ti-6Al-4V chips,an optical microscope and a scanning electron microscope(SEM)were used to study the microstructure and the morphology of the chips,and the X-ray photoelectron spectroscopy(XPS)was employed for chemical analysis.Comparisons were made to study the influence of different cutting media(nitrogen-oil-mist,air-oil-mist and dry cutting condition)on chip formation.Results indicate that cutting media have significant effects on chip formation.Nitrogen-oil-mist is more suitable for improving the contact condition at chip-tool interface and increasing the tool life in high speed milling of Ti-6Al-4V alloy than air-oil-mist and dry cutting.展开更多
A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil...A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root sys- tems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excava- tion/drilling location is of prime importance. Ground penetrating radar （GPR） provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the perfor- mance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled envi- ronment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radar- grams were subject to the influence of the following factors： size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T2 （p〈0.001, t=0.795）. Because GPR root detection is highly site-specific, this study provides a local refer- ence for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.展开更多
Hydrothermal carbon （HTC） is typically well- dispersed, but it remains a great challenge for HTC to become conductive. Co-doping with heteroatoms has been confirmed to be an effective strategy to significantly promo...Hydrothermal carbon （HTC） is typically well- dispersed, but it remains a great challenge for HTC to become conductive. Co-doping with heteroatoms has been confirmed to be an effective strategy to significantly promote the electrical conductivity of carbon. Moreover, there is no simple and green method to construct sensitive HTC based electro- chemical biosensors until now. In this paper, N and S dual-doped carbon （NS-C） with ultra-low charge transfer resistance is easily synthesized from L-cysteine and glucose in a hydrothermal reaction system. The morphology, structural prop- erties and electrochemical properties of the as-prepared NS-C are analyzed. In comparison with the undoped hydrothermal （UC） modified glassy carbon electrode （GCE）, the charge transfer resistance of UC （476 Ω） is ten times the value of NS- C （46 Ω）. The developed biosensor shows a better performance to detect glucose in a wide concentration range （50-2500 μmol L^-1） with the detection limit of 1.77 μmol L^-1 （S/N-3） and a high sensitivity （0.0554 μA cm^-2μmol^-1 L）. The apparent Michaelis-Menten constant value of GCE/NS-C/GOx/nafion modified electrode is 0.769 mmol L^-1, indicating a high affinity of glucose oxidase to glucose. These results demonstrate that the hydrothermal method is an effective way for prepar- ing high electrical conductivity carbon with excellent performances in biosensor application.展开更多
基金the National Natural Science Foundation of China (Grant No. 50175051)
文摘High speed milling experiments using nitrogen-oil-mist as the cutting medium were carried out to investigate the characteristics of chip formation for Ti-6Al-4V alloy.Within the range of conditions employed(cutting speed,vc=190-300 m/min;cutting depth of axial,ap=5,7 mm),saw-tooth chips were produced in these experiments.During the macro and micro analysis of the Ti-6Al-4V chips,an optical microscope and a scanning electron microscope(SEM)were used to study the microstructure and the morphology of the chips,and the X-ray photoelectron spectroscopy(XPS)was employed for chemical analysis.Comparisons were made to study the influence of different cutting media(nitrogen-oil-mist,air-oil-mist and dry cutting condition)on chip formation.Results indicate that cutting media have significant effects on chip formation.Nitrogen-oil-mist is more suitable for improving the contact condition at chip-tool interface and increasing the tool life in high speed milling of Ti-6Al-4V alloy than air-oil-mist and dry cutting.
基金the Research Grants Council of the Hong Kong Special Administrative Region (HKSAR) (Grant Nos. HKUST9/CRF/ 09, HKUST6/CRF/12R)
文摘A plant is stabilized by its root system. In congested urban cities such as Hong Kong, ground trenching is frequently seen due to the installation of utility lines along the roadside. Soil nailing, which involves soil coring in slopes, is a common solution to improve the slope stability. However, both activities inevitably pose a risk to the integrity of any root sys- tems present, and thus reduce the root anchorage. To prevent or minimize such damage, a careful design of the excava- tion/drilling location is of prime importance. Ground penetrating radar （GPR） provides a non-destructive method for locating roots by examining the contrast between the dielectric properties of the roots and the surrounding soil. To examine the perfor- mance of GPR and promote its use in Hong Kong, a test bed was prepared using local materials to create a controlled envi- ronment in which to conduct a series of systematic tests evaluating the performance of a 900 MHz GPR. The reflected radar- grams were subject to the influence of the following factors： size and depth of roots, horizontal distance between roots, and contrast between the root and soil water content. Correlations between root size and a number of waveform parameters were also explored. Limiting values for root size, root embedded depth, horizontal separation distance between roots, and water content contrast between root and soil were obtained. A significant correlation was found between the root diameter and time travel parameter T2 （p〈0.001, t=0.795）. Because GPR root detection is highly site-specific, this study provides a local refer- ence for GPR performance in the Hong Kong environment. The findings demonstrate that the 900 MHz GPR is applicable in Hong Kong for the detection of main roots.
基金supported by the National Basic Research Program of China (973 Program,2014CB931900)UCAS Young Teacher Research Fund (Y55103NY00,Y55103EY00,and Y25102TN00)+1 种基金Beijing Natural Science Foundation (Z160002)The Chinese Academy of Sciences Key Project Foundation (KFZD-SW-202)
文摘Hydrothermal carbon （HTC） is typically well- dispersed, but it remains a great challenge for HTC to become conductive. Co-doping with heteroatoms has been confirmed to be an effective strategy to significantly promote the electrical conductivity of carbon. Moreover, there is no simple and green method to construct sensitive HTC based electro- chemical biosensors until now. In this paper, N and S dual-doped carbon （NS-C） with ultra-low charge transfer resistance is easily synthesized from L-cysteine and glucose in a hydrothermal reaction system. The morphology, structural prop- erties and electrochemical properties of the as-prepared NS-C are analyzed. In comparison with the undoped hydrothermal （UC） modified glassy carbon electrode （GCE）, the charge transfer resistance of UC （476 Ω） is ten times the value of NS- C （46 Ω）. The developed biosensor shows a better performance to detect glucose in a wide concentration range （50-2500 μmol L^-1） with the detection limit of 1.77 μmol L^-1 （S/N-3） and a high sensitivity （0.0554 μA cm^-2μmol^-1 L）. The apparent Michaelis-Menten constant value of GCE/NS-C/GOx/nafion modified electrode is 0.769 mmol L^-1, indicating a high affinity of glucose oxidase to glucose. These results demonstrate that the hydrothermal method is an effective way for prepar- ing high electrical conductivity carbon with excellent performances in biosensor application.
