A multiscale simulation has been performed to determine the effect of the cutting speed on the deformation mechanism and cutting forces in nanometric cutting of single crystal copper. The multiscale simulation model, ...A multiscale simulation has been performed to determine the effect of the cutting speed on the deformation mechanism and cutting forces in nanometric cutting of single crystal copper. The multiscale simulation model, which links the finite element method and the molecular dynamics method, captures the atomistic mechanisms during nanometric cutting from the free surface without the computational cost of full atomistic simulations. Simulation results show the material deformation mechanism of single crystal copper greatly changes when the cutting speed exceeds the material static propagation speed of plastic wave. At such a high cutting speed, the average magnitudes of tangential and normal forces increase rapidly. In addition, the variation of strain energy of work material atoms in different cutting speeds is investigated.展开更多
Cerium-lanthanum alloy is widely used in the green energy industry,and the nanoscale smooth surface of this material is in demand.Nanometric cutting is an effective approach to achieving the ultra-precision machining ...Cerium-lanthanum alloy is widely used in the green energy industry,and the nanoscale smooth surface of this material is in demand.Nanometric cutting is an effective approach to achieving the ultra-precision machining surface.Molecular dynamics(MD)simulation is usually used to reveal the atomic-scale details of the material removal mechanism in nanometric cutting.In this study,the effects of cutting speed and undeformed chip thickness(UCT)on cutting force and subsurface deformation of the cerium-lanthanum alloy during nanometric cutting are analyzed through MD simulation.The results illustrate that the dislocations,stacking faults,and phase transitions occur in the subsurface during cutting.The dislocations are mainly Shockley partial dislocation,and the increase of temperature and pressure during the cutting process leads to the phase transformation ofγ-Ce(FCC)intoβ-Ce(HCP)andδ-Ce(BCC).β-Ce is mainly distributed in the stacking fault area,whileδ-Ce is distributed in the boundary area between the dislocation atoms andγ-Ce atoms.The cutting speed and UCT affect the distribution of subsurface damage.A thicker deformed layer including dislocations,stacking faults and phase-transformation atoms on the machined surface is generated with the increase in the cutting speed and UCT.Simultaneously,the cutting speed and UCT significantly affect the cutting force,material removal rate,and generated subsurface state.The fluctuations in the cutting force are related to the generation and disappearance of dislocations.This research first studied the nanometric cutting mechanism of the cerium-lanthanum ally,providing a theoretical basis for the development of ultra-precision machining techniques of these materials.展开更多
Thermal stabilities of diethylaluminum azide were studied by means of theoretical analysis and expriments.The results have shown that diethylaluminum and azid be heated to vigorous refluxing under vacuum(400 Pa) at te...Thermal stabilities of diethylaluminum azide were studied by means of theoretical analysis and expriments.The results have shown that diethylaluminum and azid be heated to vigorous refluxing under vacuum(400 Pa) at temperature as high as 420℃ without incident of explosion and decomposes smoothly during 460 ～580℃ to form nanometric particles of aluminum nitride in the aerosol synthesis reactor. A new way of preparing nanometric parties of aluminum nitrideis found.展开更多
The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A sm...The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively展开更多
Due to its difficulty and complexity,the cleavage and subsequent functionalization of the C(sp^(3))-C(sp^(3))single bond has received less attention than the C-C bond formation reactions that have been extensively stu...Due to its difficulty and complexity,the cleavage and subsequent functionalization of the C(sp^(3))-C(sp^(3))single bond has received less attention than the C-C bond formation reactions that have been extensively studied.Herein,by utilizing Cu/g-C_(3)N_(4)nanometric semiconductor as a recyclable photocatalyst,an aerobic oxidative C-C bond cleavage of aldehydes was developed with the promotion of amines under visible light irradiation.Based on the reaction,phenylacetaldehyde was selected as a highly efficient formylation reagent for amines.Under blue light irradiation,good to excellent yields of formamides were achieved for various amines in 1 atm oxygen atmosphere at room temperature.This methodology offers a practical,neutral and gentle alternative to the preparation of formamides.展开更多
Three-dimensional molecular dynamics simulations are carried out to study the mechanism of nanometric processing of ion implanted monocrystalline silicon surfaces. Lattice transformation is observed during implantatio...Three-dimensional molecular dynamics simulations are carried out to study the mechanism of nanometric processing of ion implanted monocrystalline silicon surfaces. Lattice transformation is observed during implantation and nano-indentation using radial distribution function and geometric criterion damage detection. Nano-indentation is simulated to study the changes of mechanical property. Implantation analysis shows the existence of amorphous phase. Indentation process shows the lattice evolution, which is beneficial for reducing fractures during processing. The indentation results reveal the reduction of brittleness and hardness of the implanted surface. The ion fluence is in direct proportion to the damage, and inverse to the hardness of the material. Experiments of ion implar, tation, nanoindentation, nano-scratching and nanometric cutting were carried out to verify the simulation results.展开更多
An investigation of some problems such as chip formation and surface generation in nanometric cutting mechanism based on molecular dynamics(MD) simulation is presented.It shows that chip formation is similar to that o...An investigation of some problems such as chip formation and surface generation in nanometric cutting mechanism based on molecular dynamics(MD) simulation is presented.It shows that chip formation is similar to that observed in macro scale cutting.The movement of some micro dislocation is the main cause of formation of chip and surface.Surface generation is notably affected by very small cutting force vibration.The highest stress appears in tool cutting edge,and it may cause wear,so it is necessary to build a MD model of tool wear.展开更多
Objective: To determine the ultrastructural findings on Rectal Mucosa (RM) of patients with HIV/AIDS and anorectal pathologies (ARP), at micrometric and nanometric scales. Materials and methods: 5 patients were evalua...Objective: To determine the ultrastructural findings on Rectal Mucosa (RM) of patients with HIV/AIDS and anorectal pathologies (ARP), at micrometric and nanometric scales. Materials and methods: 5 patients were evaluated, 18 - 55 years old, with ARP (HIV co-infection with HPV, n = 4, and HIV-negative patient with HPV infection) (control n = 1), who were referred to the Coloproctology Unit of the HUC, and subjected to rectoscopy and biopsy. RM samples were identified, placed in a sterile plastic bottle with 1 mL of 2% glutaraldehyde and immediately transported for routine processing of fine cut (60 - 90 nm) to be evaluated via Transmission Electron Microscopy (TEM). They were fixed with Karnovsky solution with Millonig phosphate buffer (pH 7.4 and 320 mOsm) and post-fixed with OsO4 under the same conditions of pH and osmolarity. Results: Ultrastructural findings, at 10−6 scale: 1) Intestinal mucosa: vacuoles of mucus of different sizes that seem to be fused. 2) Smooth muscle cells: loss of definition of contractile myofilaments mass. 3) Unmyelinated axons and terminals of Schwann cells (SC): Edema and loss of their plasma membranes in some areas of association with axon terminals as well as abundant collagen fibers associated with SC. Ultrastructural findings, at 10−9 scale: 1) Smooth muscle cells: folded wrapper cores and edema of mitochondria and rough endoplasmic reticulum cisterns (RER). 2) Myelinated axon terminals: Loss of synaptic vesicles. 3) Fibroblasts: One observes mitochondria and cisterns of RER with alterations. All these alterations can generate intestinal and anorectal dysfunction in these patients. Conclusions: The HIV causes changes in rectal and muscular mucosa despite HAART treatment with undetectable viral load.展开更多
Understanding the basic action of how material removing in nanoscale is a critical issue of producing well-formed components.In order to clarify thermal effects on material removal at atomic level,molecular dynamics(M...Understanding the basic action of how material removing in nanoscale is a critical issue of producing well-formed components.In order to clarify thermal effects on material removal at atomic level,molecular dynamics(MD)simulations of nanometric cutting of mono-crystalline copper are performed with Morse,EAM and Tersoff potential.The effects of cutting speed on temperature distribution are investigated.The simulation results demonstrate that the temperature distribution shows a roughly concentric shape around shear zone and a steep temperature gradient lies in diamond tool,a relative high temperature is located in shear zone and machined surface,but the highest temperature is found in chip.At a high cutting speed mode,the atoms in shear zone with high temperature implies a large stress is built up in a local region.展开更多
Development in industry is asking for improved resolution and higher accuracy in dimensional metrology. In this paper,we proposed a control displacement method based on a polarization ellipsometirc interferometer and ...Development in industry is asking for improved resolution and higher accuracy in dimensional metrology. In this paper,we proposed a control displacement method based on a polarization ellipsometirc interferometer and phase-locked loop technique. The proposed principle was set up. The experimental results of step and step displacements with a step value of 5 nm were presented. We also analyzed the resolution,the potential minimal displacement of the established system. The results show that the position error induced by the ellipticty deviation of the light beam becomes negligible thanks to our signal processing circuit with high-order filter. This method could be useful for many applications in nano dimensional metrology and semiconductor industry.展开更多
Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in ...Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in the actions of the cutting tool. The stacking fault tetrahedral was formed by a series of dislocation reactions, and it maintained the stable structure after the dislocation reactions. In addition, evidence of crystal transition and recovery was found by analyzing the number variations in different types of atoms in the primary shear zone, amorphous region, and crystalline region. The effects of machining speed on the cutting force, chip and subsurface defects, and temperature of the contact zone between the tool and workpiece were investigated. The results suggest that higher the machining speed, larger is the cutting force. The degree of amorphousness of chip atoms and the depth and extent of subsurface defects increase with the machining speed. The average friction coefficient first decreases and then increases with the machining speed because of the temperature difference between the chip and machining surface.展开更多
The effects of the substituents on the cyclopentadienyl ring and the reducing agents on the catalytic activity and the stability of titanocene/NaH or n BuLi systems for the hydrogenation of olefins were investiga...The effects of the substituents on the cyclopentadienyl ring and the reducing agents on the catalytic activity and the stability of titanocene/NaH or n BuLi systems for the hydrogenation of olefins were investigated. For the catalyst systems composed of titanocene/NaH or n BuLi, the nature and the number of the substituents on the cyclopentadienyl ring control the catalytic behavior of those two systems. The effect of the reducing agent on the catalytic activity is relatively small. In addition, the characters of the hydrogenation of various olefins catalyzed respectively by Cp 2TiCl 2/NaH or n BuLi systems were compared.展开更多
基于分子动力学的基本原理,构建了钛的纳米切削分子动力学仿真模型。工件原子间采用嵌入原子势EAM(Embedded atom method),工件原子与刀具原子间采用Morse势函数,研究了在不同刃口半径和刀具前角条件下,钛纳米切削过程中工件形态、系统...基于分子动力学的基本原理,构建了钛的纳米切削分子动力学仿真模型。工件原子间采用嵌入原子势EAM(Embedded atom method),工件原子与刀具原子间采用Morse势函数,研究了在不同刃口半径和刀具前角条件下,钛纳米切削过程中工件形态、系统势能、切削力以及工件温度等的变化规律。结果表明:随着刀具刃口半径增大,加工表面粗糙度增加,切削力和工件温度降低,切屑变薄;当刀具前角由负值增加到正值,钛工件承受的压应力逐渐变为剪应力,正前角刀具更有利于切削,同时在不同的刀具前角下,切向力和法向力的大小也有显著变化。展开更多
Epoxy resin modified by nanometric γ-alumina or multi-walled carbon nanotubes (MCNTs) was prepared with solution mixingmethod, and the wear resistance of the composite was studied. The results show that when an optim...Epoxy resin modified by nanometric γ-alumina or multi-walled carbon nanotubes (MCNTs) was prepared with solution mixingmethod, and the wear resistance of the composite was studied. The results show that when an optimum amount of nanometricalumina or MCNTs is filled in epikote51 (E51), the wear resistance of the composite will increase. When 8 wt pct nanometricγ-alumina is filled in E51, the wear resistance of the composite increases to 230%. When 10% MCNTs is filled in E51, thewear resistance of the composite increases to 226%. When nanometric alumina is filled in, the wear resistance of modifiedepikote51 will increase as the cure temperature is heightened.展开更多
An aerosol process for making aluminum nitride nano-powder by decompositionof single compound diethylalumimm az-ide was described. X-ray diffraction (XRD) and transmissionelectron microscopy (TEM) were used to study c...An aerosol process for making aluminum nitride nano-powder by decompositionof single compound diethylalumimm az-ide was described. X-ray diffraction (XRD) and transmissionelectron microscopy (TEM) were used to study characters of the A1N powder. It is shown that theprocess can produce spherical A1N powder with mean particle diameters ranging from 10 to 50 nm at500-800°C. The generated amorphous A1N powder is characterized by a BET (Brunauer-Emmett-Teller)surface area of 103 m2/g and is very reactive to moisture.展开更多
The present work reports the preliminary results about solid state reactions of Cr-ZnO solid solutions and ZnCr2O4 nanometric particles obtained with triethanolamine (TEA). Different compositions were prepared from 0....The present work reports the preliminary results about solid state reactions of Cr-ZnO solid solutions and ZnCr2O4 nanometric particles obtained with triethanolamine (TEA). Different compositions were prepared from 0.65 to 33.3 at % chromium, the last one corresponding to ZnCr2O4 cubic spinel composition. Fourier Transform Infrared Spectroscopy (FTIR) together with X-ray diffraction (XRD) patterns of powders with Cr3+ between 0.65 and 16.0 at % were assigned to Cr-ZnO solid solution due to the only presence of ZnO structure, FTIR spectra indicating that Cr-O bonding exists even if there was no presence of ZnCr2O4. With low chromium atomic percent, lattice parameters increase, but as the chromium content exceeds of 3 at %, there is basically no further expansion of the cell. From Williamson-Hall and Rietveld methods the lattice dimensions were assigned to chromium incorporation in ZnO structure and the lattice contraction by particle size refinement. After annealing all samples from 0.65 to 16.0 at % at 400°C in oxygen, the analysis showed that nanoparticles of Cr-ZnO solid solution still remain.展开更多
In this paper, we report the results obtained from different phases of metal hydrides. The synthesis and characterization of tantalum hydrides were obtained “in situ” during mechanical milling. Elemental Ta with pur...In this paper, we report the results obtained from different phases of metal hydrides. The synthesis and characterization of tantalum hydrides were obtained “in situ” during mechanical milling. Elemental Ta with purity of 99.8% was used in this investigation to obtain the hydrides. A highenergy ball milling technique was utilized to prepare hydrogenated phases. Ta hydrides and oxides were formed as function of milling process time. Milling times of 5, 10 and 20 hours were programmed, and the ball-to-powder weight ratio was 10:1. The material was first characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Before and after hydrogenation process the material was also analyzed by TGA. X-ray diffraction analysis demonstrated that only tantalum hydrides (Ta2H and TaH0.5) were obtained after 20 h of milling. We will discuss the effect of the ball-milling process about formation “in situ” of nanometric tantalum hydrides with methanol as a hydrogen source.展开更多
Fe3O4 magnetic nanoparticles were prepared by the aqueous co-precipitation of FeCl3-6H2O and FeCl2-4H2O with addition of ammonium hydroxide. The conditions for the preparation of Fe3O4 magnetic nanoparticles were opti...Fe3O4 magnetic nanoparticles were prepared by the aqueous co-precipitation of FeCl3-6H2O and FeCl2-4H2O with addition of ammonium hydroxide. The conditions for the preparation of Fe3O4 magnetic nanoparticles were optimized, and Fe3O4 magnetic nanoparticles obtained were characterized systematically by means of transmission electron microscope （TEM）, dynamic laser scattering analyzer （DLS） and X-ray diffraction （XRD）. The results revealed that the magnetic nanoparticles were cubic shaped and dispersive, with narrow size distribution and average diameter of 11.4 nm. It was found that the homogeneous variation of pH value in the solution via the control on the dropping rate of aqueous ammonia played a critical role in size distribution. The magnetic response of the product in the magnetic field was also analyzed and evaluated carefully. A 32.6 mT magnetic field which is produced by four ferromagnets was found to be sufficient to excite the dipole moments of 0.05 g Fe3O4 powder 2 cm far away from the ferromagnets. In conclusion, the Fe3O4 magnetic nanoparticles with excellent properties were competent for the magnetic carders of targeted-drug in future application.展开更多
Enhanced photoluminescence （PL） at room temperature from thermally annealed a-Si：H/SiO2 multilayers is observed through the step-by-step thermal post-treatment. The correlation between the PL and the crystallizatio...Enhanced photoluminescence （PL） at room temperature from thermally annealed a-Si：H/SiO2 multilayers is observed through the step-by-step thermal post-treatment. The correlation between the PL and the crystallization process is studied using temperature-dependent PL, Raman, cross section high-resolution transmission electron microscopy （XHRTEM） and x-ray diffraction （XRD） techniques. An intensified PL band around 820 nm is discovered from the sample annealed near the crystallization onset temperature, which is composed of two peaks centred at 773 nm and 863 nm, respectively. It is found that the PL band centred at 863 nm is related to the pseudo nanocrystal （p-nc-Si） silicon, and the PL band centred at 773 nm is attributed to Si = O bonds stabilized in the p-nc-Si surface.展开更多
Optical responses in dilute composites are controlled through the local dielectric resonance of metallic clusters. We consider two located metallic clusters close to each other with admittances ε1 and ε2. Through va...Optical responses in dilute composites are controlled through the local dielectric resonance of metallic clusters. We consider two located metallic clusters close to each other with admittances ε1 and ε2. Through varying the difference admittance ratio η[= （ε2 - ε0）/（ε1 - ε0）], we find that their optical responses are determined by the local resonance. There is a blueshift of absorption peaks with the increase of η- Simultaneously, it is known that the absorption peaks will be redshifted by enlarging the cluster size. By adjusting the nano-metallic cluster geometry, size and admittances, we can control the positions and intensities of absorption peaks effectively. We have also deduced the effective linear optical responses of three-component composites εe=ε0 （1＋∑^n n=1[（γn1＋ηγn2）/（ε0（s-sn））]） and the sum rule of cross sections：∑^n n=1（γn1＋ηγn2）=Nh1＋Nh2,, where Nh1and Nh2 are the numbers of εl and ε2 bonds along the electric field, respectively. These results may be beneficial to the study of surface plasmon resonances on a nanometre scale.展开更多
基金supported by National Natural Science Foundation of China(Nos.50675050 and 50705023)Outstanding Youth Science Foundation of Hei-longjiang Province (No.JC200614)
文摘A multiscale simulation has been performed to determine the effect of the cutting speed on the deformation mechanism and cutting forces in nanometric cutting of single crystal copper. The multiscale simulation model, which links the finite element method and the molecular dynamics method, captures the atomistic mechanisms during nanometric cutting from the free surface without the computational cost of full atomistic simulations. Simulation results show the material deformation mechanism of single crystal copper greatly changes when the cutting speed exceeds the material static propagation speed of plastic wave. At such a high cutting speed, the average magnitudes of tangential and normal forces increase rapidly. In addition, the variation of strain energy of work material atoms in different cutting speeds is investigated.
基金Supported by Science Challenge Project(Grant No.TZ2018006-0201-01)National Natural Science Foundation of China(Grant Nos.51605327 and 52035009).
文摘Cerium-lanthanum alloy is widely used in the green energy industry,and the nanoscale smooth surface of this material is in demand.Nanometric cutting is an effective approach to achieving the ultra-precision machining surface.Molecular dynamics(MD)simulation is usually used to reveal the atomic-scale details of the material removal mechanism in nanometric cutting.In this study,the effects of cutting speed and undeformed chip thickness(UCT)on cutting force and subsurface deformation of the cerium-lanthanum alloy during nanometric cutting are analyzed through MD simulation.The results illustrate that the dislocations,stacking faults,and phase transitions occur in the subsurface during cutting.The dislocations are mainly Shockley partial dislocation,and the increase of temperature and pressure during the cutting process leads to the phase transformation ofγ-Ce(FCC)intoβ-Ce(HCP)andδ-Ce(BCC).β-Ce is mainly distributed in the stacking fault area,whileδ-Ce is distributed in the boundary area between the dislocation atoms andγ-Ce atoms.The cutting speed and UCT affect the distribution of subsurface damage.A thicker deformed layer including dislocations,stacking faults and phase-transformation atoms on the machined surface is generated with the increase in the cutting speed and UCT.Simultaneously,the cutting speed and UCT significantly affect the cutting force,material removal rate,and generated subsurface state.The fluctuations in the cutting force are related to the generation and disappearance of dislocations.This research first studied the nanometric cutting mechanism of the cerium-lanthanum ally,providing a theoretical basis for the development of ultra-precision machining techniques of these materials.
文摘Thermal stabilities of diethylaluminum azide were studied by means of theoretical analysis and expriments.The results have shown that diethylaluminum and azid be heated to vigorous refluxing under vacuum(400 Pa) at temperature as high as 420℃ without incident of explosion and decomposes smoothly during 460 ～580℃ to form nanometric particles of aluminum nitride in the aerosol synthesis reactor. A new way of preparing nanometric parties of aluminum nitrideis found.
文摘The crystallization behaviour of the laser synthesized nanometric amorphous Si3N4 powders with the particle size of 15 nm in diameter has been studied between 1200° and 1700℃ by XRD,TEM and FTIR techniques. A small amount of β-Si3N4 formed at 1250℃ and increased slowly until the α- β transformation happened at 1700℃, whereas α-Si3N4 appeared at 1300℃ andincreased rapidly between 1500-1600℃. The formation of β phase at the lower temperature was caused by the nitridation of free Si due to the preexisted β-nuclei in the Si3N4 particles, whereasthe α phase was formed by solid crystallization from the amorphous matrix. There were α and β SiC formed at 1700℃ due to the presence of Sio and Co gases in the system. FTIR analysis shows that two new IR absorption at 1356 and 1420 cm-1, and an overall strong absorption in wide wavenumber range resulted from the powders annealed at 1600 and 1700℃ respectively
基金the financial support from the National Natural Science Foundation of China(Nos.21772091,21472092 to X.Yao)funded by the Priority Academic Program Development of Jiangsu Higher Education Institutions。
文摘Due to its difficulty and complexity,the cleavage and subsequent functionalization of the C(sp^(3))-C(sp^(3))single bond has received less attention than the C-C bond formation reactions that have been extensively studied.Herein,by utilizing Cu/g-C_(3)N_(4)nanometric semiconductor as a recyclable photocatalyst,an aerobic oxidative C-C bond cleavage of aldehydes was developed with the promotion of amines under visible light irradiation.Based on the reaction,phenylacetaldehyde was selected as a highly efficient formylation reagent for amines.Under blue light irradiation,good to excellent yields of formamides were achieved for various amines in 1 atm oxygen atmosphere at room temperature.This methodology offers a practical,neutral and gentle alternative to the preparation of formamides.
基金Supported by the National Basic Research Program of China("973" Program,No.2011CB706703)
文摘Three-dimensional molecular dynamics simulations are carried out to study the mechanism of nanometric processing of ion implanted monocrystalline silicon surfaces. Lattice transformation is observed during implantation and nano-indentation using radial distribution function and geometric criterion damage detection. Nano-indentation is simulated to study the changes of mechanical property. Implantation analysis shows the existence of amorphous phase. Indentation process shows the lattice evolution, which is beneficial for reducing fractures during processing. The indentation results reveal the reduction of brittleness and hardness of the implanted surface. The ion fluence is in direct proportion to the damage, and inverse to the hardness of the material. Experiments of ion implar, tation, nanoindentation, nano-scratching and nanometric cutting were carried out to verify the simulation results.
文摘An investigation of some problems such as chip formation and surface generation in nanometric cutting mechanism based on molecular dynamics(MD) simulation is presented.It shows that chip formation is similar to that observed in macro scale cutting.The movement of some micro dislocation is the main cause of formation of chip and surface.Surface generation is notably affected by very small cutting force vibration.The highest stress appears in tool cutting edge,and it may cause wear,so it is necessary to build a MD model of tool wear.
文摘Objective: To determine the ultrastructural findings on Rectal Mucosa (RM) of patients with HIV/AIDS and anorectal pathologies (ARP), at micrometric and nanometric scales. Materials and methods: 5 patients were evaluated, 18 - 55 years old, with ARP (HIV co-infection with HPV, n = 4, and HIV-negative patient with HPV infection) (control n = 1), who were referred to the Coloproctology Unit of the HUC, and subjected to rectoscopy and biopsy. RM samples were identified, placed in a sterile plastic bottle with 1 mL of 2% glutaraldehyde and immediately transported for routine processing of fine cut (60 - 90 nm) to be evaluated via Transmission Electron Microscopy (TEM). They were fixed with Karnovsky solution with Millonig phosphate buffer (pH 7.4 and 320 mOsm) and post-fixed with OsO4 under the same conditions of pH and osmolarity. Results: Ultrastructural findings, at 10−6 scale: 1) Intestinal mucosa: vacuoles of mucus of different sizes that seem to be fused. 2) Smooth muscle cells: loss of definition of contractile myofilaments mass. 3) Unmyelinated axons and terminals of Schwann cells (SC): Edema and loss of their plasma membranes in some areas of association with axon terminals as well as abundant collagen fibers associated with SC. Ultrastructural findings, at 10−9 scale: 1) Smooth muscle cells: folded wrapper cores and edema of mitochondria and rough endoplasmic reticulum cisterns (RER). 2) Myelinated axon terminals: Loss of synaptic vesicles. 3) Fibroblasts: One observes mitochondria and cisterns of RER with alterations. All these alterations can generate intestinal and anorectal dysfunction in these patients. Conclusions: The HIV causes changes in rectal and muscular mucosa despite HAART treatment with undetectable viral load.
基金supported by the National Natural Science Foundation of China(Grant No.50675050)the Outstanding Youth Fund of Heilongjiang Province(Grant No.JC200614)
文摘Understanding the basic action of how material removing in nanoscale is a critical issue of producing well-formed components.In order to clarify thermal effects on material removal at atomic level,molecular dynamics(MD)simulations of nanometric cutting of mono-crystalline copper are performed with Morse,EAM and Tersoff potential.The effects of cutting speed on temperature distribution are investigated.The simulation results demonstrate that the temperature distribution shows a roughly concentric shape around shear zone and a steep temperature gradient lies in diamond tool,a relative high temperature is located in shear zone and machined surface,but the highest temperature is found in chip.At a high cutting speed mode,the atoms in shear zone with high temperature implies a large stress is built up in a local region.
基金supported by the National Natural Science Foundation of China (Grant No.50905170)
文摘Development in industry is asking for improved resolution and higher accuracy in dimensional metrology. In this paper,we proposed a control displacement method based on a polarization ellipsometirc interferometer and phase-locked loop technique. The proposed principle was set up. The experimental results of step and step displacements with a step value of 5 nm were presented. We also analyzed the resolution,the potential minimal displacement of the established system. The results show that the position error induced by the ellipticty deviation of the light beam becomes negligible thanks to our signal processing circuit with high-order filter. This method could be useful for many applications in nano dimensional metrology and semiconductor industry.
基金supported by the National Natural Science Foundation of China(Grant Nos,51375082)
文摘Molecular dynamics simulations are employed to study the nanometric machining process of single crystal nickel. Atoms from different machining zones had different atomic crystal structures owing to the differences in the actions of the cutting tool. The stacking fault tetrahedral was formed by a series of dislocation reactions, and it maintained the stable structure after the dislocation reactions. In addition, evidence of crystal transition and recovery was found by analyzing the number variations in different types of atoms in the primary shear zone, amorphous region, and crystalline region. The effects of machining speed on the cutting force, chip and subsurface defects, and temperature of the contact zone between the tool and workpiece were investigated. The results suggest that higher the machining speed, larger is the cutting force. The degree of amorphousness of chip atoms and the depth and extent of subsurface defects increase with the machining speed. The average friction coefficient first decreases and then increases with the machining speed because of the temperature difference between the chip and machining surface.
基金Supported by the Educational Com mittee of L iaoning Province
文摘The effects of the substituents on the cyclopentadienyl ring and the reducing agents on the catalytic activity and the stability of titanocene/NaH or n BuLi systems for the hydrogenation of olefins were investigated. For the catalyst systems composed of titanocene/NaH or n BuLi, the nature and the number of the substituents on the cyclopentadienyl ring control the catalytic behavior of those two systems. The effect of the reducing agent on the catalytic activity is relatively small. In addition, the characters of the hydrogenation of various olefins catalyzed respectively by Cp 2TiCl 2/NaH or n BuLi systems were compared.
基金supported by Science Foundation of AVIC I,Project(No.2007ZE54011)
文摘基于分子动力学的基本原理,构建了钛的纳米切削分子动力学仿真模型。工件原子间采用嵌入原子势EAM(Embedded atom method),工件原子与刀具原子间采用Morse势函数,研究了在不同刃口半径和刀具前角条件下,钛纳米切削过程中工件形态、系统势能、切削力以及工件温度等的变化规律。结果表明:随着刀具刃口半径增大,加工表面粗糙度增加,切削力和工件温度降低,切屑变薄;当刀具前角由负值增加到正值,钛工件承受的压应力逐渐变为剪应力,正前角刀具更有利于切削,同时在不同的刀具前角下,切向力和法向力的大小也有显著变化。
文摘Epoxy resin modified by nanometric γ-alumina or multi-walled carbon nanotubes (MCNTs) was prepared with solution mixingmethod, and the wear resistance of the composite was studied. The results show that when an optimum amount of nanometricalumina or MCNTs is filled in epikote51 (E51), the wear resistance of the composite will increase. When 8 wt pct nanometricγ-alumina is filled in E51, the wear resistance of the composite increases to 230%. When 10% MCNTs is filled in E51, thewear resistance of the composite increases to 226%. When nanometric alumina is filled in, the wear resistance of modifiedepikote51 will increase as the cure temperature is heightened.
文摘An aerosol process for making aluminum nitride nano-powder by decompositionof single compound diethylalumimm az-ide was described. X-ray diffraction (XRD) and transmissionelectron microscopy (TEM) were used to study characters of the A1N powder. It is shown that theprocess can produce spherical A1N powder with mean particle diameters ranging from 10 to 50 nm at500-800°C. The generated amorphous A1N powder is characterized by a BET (Brunauer-Emmett-Teller)surface area of 103 m2/g and is very reactive to moisture.
文摘The present work reports the preliminary results about solid state reactions of Cr-ZnO solid solutions and ZnCr2O4 nanometric particles obtained with triethanolamine (TEA). Different compositions were prepared from 0.65 to 33.3 at % chromium, the last one corresponding to ZnCr2O4 cubic spinel composition. Fourier Transform Infrared Spectroscopy (FTIR) together with X-ray diffraction (XRD) patterns of powders with Cr3+ between 0.65 and 16.0 at % were assigned to Cr-ZnO solid solution due to the only presence of ZnO structure, FTIR spectra indicating that Cr-O bonding exists even if there was no presence of ZnCr2O4. With low chromium atomic percent, lattice parameters increase, but as the chromium content exceeds of 3 at %, there is basically no further expansion of the cell. From Williamson-Hall and Rietveld methods the lattice dimensions were assigned to chromium incorporation in ZnO structure and the lattice contraction by particle size refinement. After annealing all samples from 0.65 to 16.0 at % at 400°C in oxygen, the analysis showed that nanoparticles of Cr-ZnO solid solution still remain.
文摘In this paper, we report the results obtained from different phases of metal hydrides. The synthesis and characterization of tantalum hydrides were obtained “in situ” during mechanical milling. Elemental Ta with purity of 99.8% was used in this investigation to obtain the hydrides. A highenergy ball milling technique was utilized to prepare hydrogenated phases. Ta hydrides and oxides were formed as function of milling process time. Milling times of 5, 10 and 20 hours were programmed, and the ball-to-powder weight ratio was 10:1. The material was first characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD). Before and after hydrogenation process the material was also analyzed by TGA. X-ray diffraction analysis demonstrated that only tantalum hydrides (Ta2H and TaH0.5) were obtained after 20 h of milling. We will discuss the effect of the ball-milling process about formation “in situ” of nanometric tantalum hydrides with methanol as a hydrogen source.
基金the Technology Project of Jiangxi Provincial Education DepartmentJiangxi Provincial Science Department
文摘Fe3O4 magnetic nanoparticles were prepared by the aqueous co-precipitation of FeCl3-6H2O and FeCl2-4H2O with addition of ammonium hydroxide. The conditions for the preparation of Fe3O4 magnetic nanoparticles were optimized, and Fe3O4 magnetic nanoparticles obtained were characterized systematically by means of transmission electron microscope （TEM）, dynamic laser scattering analyzer （DLS） and X-ray diffraction （XRD）. The results revealed that the magnetic nanoparticles were cubic shaped and dispersive, with narrow size distribution and average diameter of 11.4 nm. It was found that the homogeneous variation of pH value in the solution via the control on the dropping rate of aqueous ammonia played a critical role in size distribution. The magnetic response of the product in the magnetic field was also analyzed and evaluated carefully. A 32.6 mT magnetic field which is produced by four ferromagnets was found to be sufficient to excite the dipole moments of 0.05 g Fe3O4 powder 2 cm far away from the ferromagnets. In conclusion, the Fe3O4 magnetic nanoparticles with excellent properties were competent for the magnetic carders of targeted-drug in future application.
基金Project supported by the Natural Science Foundation of Jiangsu Province, China （Grant No BK 2004410）, the National Natural Science Foundation of China （Grant Nos 60508009, 90301009, 60471021 and 60571008）, and the State Key Program for Basic Research of China （Grant No 2006CB0N0202）.
文摘Enhanced photoluminescence （PL） at room temperature from thermally annealed a-Si：H/SiO2 multilayers is observed through the step-by-step thermal post-treatment. The correlation between the PL and the crystallization process is studied using temperature-dependent PL, Raman, cross section high-resolution transmission electron microscopy （XHRTEM） and x-ray diffraction （XRD） techniques. An intensified PL band around 820 nm is discovered from the sample annealed near the crystallization onset temperature, which is composed of two peaks centred at 773 nm and 863 nm, respectively. It is found that the PL band centred at 863 nm is related to the pseudo nanocrystal （p-nc-Si） silicon, and the PL band centred at 773 nm is attributed to Si = O bonds stabilized in the p-nc-Si surface.
基金Project supported by the National Natural Science Foundation of China（Grant Nos 10304001, 10334010, 10521002, 10434020, 10328407 and 90501007）.
文摘Optical responses in dilute composites are controlled through the local dielectric resonance of metallic clusters. We consider two located metallic clusters close to each other with admittances ε1 and ε2. Through varying the difference admittance ratio η[= （ε2 - ε0）/（ε1 - ε0）], we find that their optical responses are determined by the local resonance. There is a blueshift of absorption peaks with the increase of η- Simultaneously, it is known that the absorption peaks will be redshifted by enlarging the cluster size. By adjusting the nano-metallic cluster geometry, size and admittances, we can control the positions and intensities of absorption peaks effectively. We have also deduced the effective linear optical responses of three-component composites εe=ε0 （1＋∑^n n=1[（γn1＋ηγn2）/（ε0（s-sn））]） and the sum rule of cross sections：∑^n n=1（γn1＋ηγn2）=Nh1＋Nh2,, where Nh1and Nh2 are the numbers of εl and ε2 bonds along the electric field, respectively. These results may be beneficial to the study of surface plasmon resonances on a nanometre scale.
