Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polari...Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polarization, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize corrosion morphology and to realize corrosion mechanism of weld regions as opposed to the parent alloy. The microstructure and shear strength of welded joint were fully investigated. The results indicate that, compared with the parent alloy, the weld regions are susceptible to intergranular and pitting attacks in the test solution during immersion time. The obtained results of lap shear testing disclose that tensile shear strength of the welds is 128 MPa which is more than 60% of the strength of parent alloy in lap shear testing. Electrochemical results show that the protection potentials of the WNZ and HAZ regions are more negative than the pitting potential. This means that the WNZ and HAZ regions do not show more tendencies to pitting corrosion. Corrosion resistance of parent alloy is higher than that for the weldments, and the lowest corrosion resistance is related to the heat affected zone. The pitting attacks originate from the edge of intermetallic particles as the cathode compared with the Al matrix due to their high self-corrosion potential. It is supposed that by increasing intermetallic particle distributed throughout the matrix of weld regions, the galvanic corrosion couples are increased, and hence decrease the corrosion resistance of weld regions.展开更多
The author's proposal is to show how an apparently marginal text by Walter Benjamin, "The Destructive Character", can be taken as a hermeneutic model for understanding the connection of Benjamin's with history and...The author's proposal is to show how an apparently marginal text by Walter Benjamin, "The Destructive Character", can be taken as a hermeneutic model for understanding the connection of Benjamin's with history and tradition and for characterizing his thought as philosophy of threshold. It is the author's intention to show how the destructive character, on the threshold between destruction and construction, succeeds in remaining in that transition area that announces a change, showing its creative and conservative features; thus it appears as a figure of coexistence between stillness and movement, passage and interruption, and past and future. What the author wants to point out is that, in the description of this figure, Benjamin is driven by a cognitive demand, which tends to focalize the process of destruction itself rather than the result of the destruction process. The space in which the destructive character is acting is the space of the possibility of change and emancipation, and the space where it is possible to keep together past and future, and memory and redemption. Starting from these reflections, an important question arises about the problem of the relation between history and tradition, and culture and its memory: Neither the destruction of memory by a culture nor its canonization is meaningful. The concept of destructive character then represents a preferential point of observation for analyzing the articulations of Benjamin's thought. From this perspective, a decisive point of Benjamin's reflection seems to emerge on one side, strengthened in the permeation of Hebraic ancestors between destruction and salvation; on the other side, some of the concepts and images of the Berliner philosopher seem to show up in a new light.展开更多
Asphalt mixture is a highly heterogeneous material, which is one of the reasons for high measurements uncertainty when subjected to tests. The results of such tests are often unreliable, which may lead to making bad p...Asphalt mixture is a highly heterogeneous material, which is one of the reasons for high measurements uncertainty when subjected to tests. The results of such tests are often unreliable, which may lead to making bad professional judgments. They can be avoided by carrying out reliable analyses of measurement uncertainty adequate for the research methods used and conducted before the actual research is done. This paper presents the calculation of measurements uncertainty using as an example--the determination of the stiffness modulus of the asphalt mixture, which, in turn, was accomplished using the indirect tension method. The paper also shows the employment of the basic methods of statistical analysis, such as testing two mean values and conformity tests. Essential concepts in measurements uncertainty have been compiled and the determination of the stiffness module parameters are discussed. It has been demonstrated that the biggest source of error in the stiffness modulus measuring process is the displacement measure. The aim of the research was to find the measurement uncertainty for stiffness modulus by an indirect tensile test and the presentation of examples of the used statistical methods.展开更多
In the one-gravity environment on the ground, the simulation of the contact process of two flying objects in the zero-gravity environment of space has been a challenging issue since humans first explored space by flyi...In the one-gravity environment on the ground, the simulation of the contact process of two flying objects in the zero-gravity environment of space has been a challenging issue since humans first explored space by flying objects. Hardware-in-the-loop (HIL) simulation is an important and effective method to test the usability, reliability, and safety of real docking mechanisms in space. There are four main issues for HIL simulation systems: Design of simulators capable of high frequency response, high motion precision, high velocity, and rapid acceleration; compensation for simulation distortion; design of a control model for the HIL simulation process; and experimental verification. Here, we propose a novel HIL simulator system with a 6-DOF 3-3 perpendicular parallel mechanism and a 3-DOF 3-PRS parallel mechanism; discover the principle of simulation distortion; present distortion compensation models for the force measurement system, dynamic response, and structural dynamics of the simulator; and provide a control model for the HIL simulation process. Two kinds of experiments were performed on the pas- sive-undamped elastic rod and the docking mechanisms to test their performances and to verify the effectiveness and usability of the HIL simulator. The HIL simulation system proposed in this paper is useful for developing space docking, berthing, refu- eling, repairing, upgrading, transporting, and rescuing technologies.展开更多
To determinate car capacity at bus stops with mixed traffic, a new theoretical approach was developed on the basis of additive-conflict-flows procedure. The procedure was extended from homogeneous traffic flow to mixe...To determinate car capacity at bus stops with mixed traffic, a new theoretical approach was developed on the basis of additive-conflict-flows procedure. The procedure was extended from homogeneous traffic flow to mixed traffic flow. The conflicts among cars, buses and bicycles near the stop can be described by the extended procedure. The procedure can be understood more easily than the theory of gap acceptance. Car capacity near the stop is the function of both bus stream and bicycle stream. The proposed model can also analyze the cases of pedestrian effects and limited priority of bicyclists. Numerical results show that the car capacity decreases with the increasing flow rates of other streams. In addition, pedestrian effects and bicyclist's limited priority have negative effects on car capacity near bus stops with mixed traffic flow.展开更多
A Lagrangian compatible radiation hydrodynamic algorithm and the nuclear dynamics computing module are developed and implemented in the LARED Integration code, which is a radiation hydrodynamic code based on the 2-D c...A Lagrangian compatible radiation hydrodynamic algorithm and the nuclear dynamics computing module are developed and implemented in the LARED Integration code, which is a radiation hydrodynamic code based on the 2-D cylindrical coordinates for the numerical simulation of the indirect-drive Inertial Confined Fusion. A number of 1-D and 2-D ignition implosion numerical simulations by using the improved LARED Integration code (ILARED) are presented which show that the 1-D numerical results are consistent with those computed by the 1-D radiation hydrodynamic code RDMG, while the simulation results of the 2-D low-mode radiative asymmetry and hydrodynamic instability growth,according to the physical analysis and anticipation, are satisfactory. The capsules driven by the sources from SGII experiments are also simulated by ILARED, and the fuel shapes agree well with the experimental results. The numerical simulations demonstrate that ILARED can be used in the simulation of the 1-D and 2-D ignition capsule implosion using the multi-group diffusion model for radiation.展开更多
In this paper, the continuous-time independent edge-Markovian random graph process model is constructed. The authors also define the interval isolated nodes of the random graph process, study the distribution sequence...In this paper, the continuous-time independent edge-Markovian random graph process model is constructed. The authors also define the interval isolated nodes of the random graph process, study the distribution sequence of the number of isolated nodes and the probability of having no isolated nodes when the initial distribution of the random graph process is stationary distribution, derive the lower limit of the probability in which two arbitrary nodes are connected and the random graph is also connected, and prove that the random graph is almost everywhere connected when the number of nodes is sufficiently large.展开更多
文摘Corrosion behavior of friction stir lap welded AA6061-T6 aluminum alloy was investigated by immersion tests in sodium chloride + hydrogen peroxide solution. Electrochemical measurement by cyclic potentiodynamic polarization, scanning electron microscopy, and energy dispersive spectroscopy were employed to characterize corrosion morphology and to realize corrosion mechanism of weld regions as opposed to the parent alloy. The microstructure and shear strength of welded joint were fully investigated. The results indicate that, compared with the parent alloy, the weld regions are susceptible to intergranular and pitting attacks in the test solution during immersion time. The obtained results of lap shear testing disclose that tensile shear strength of the welds is 128 MPa which is more than 60% of the strength of parent alloy in lap shear testing. Electrochemical results show that the protection potentials of the WNZ and HAZ regions are more negative than the pitting potential. This means that the WNZ and HAZ regions do not show more tendencies to pitting corrosion. Corrosion resistance of parent alloy is higher than that for the weldments, and the lowest corrosion resistance is related to the heat affected zone. The pitting attacks originate from the edge of intermetallic particles as the cathode compared with the Al matrix due to their high self-corrosion potential. It is supposed that by increasing intermetallic particle distributed throughout the matrix of weld regions, the galvanic corrosion couples are increased, and hence decrease the corrosion resistance of weld regions.
文摘The author's proposal is to show how an apparently marginal text by Walter Benjamin, "The Destructive Character", can be taken as a hermeneutic model for understanding the connection of Benjamin's with history and tradition and for characterizing his thought as philosophy of threshold. It is the author's intention to show how the destructive character, on the threshold between destruction and construction, succeeds in remaining in that transition area that announces a change, showing its creative and conservative features; thus it appears as a figure of coexistence between stillness and movement, passage and interruption, and past and future. What the author wants to point out is that, in the description of this figure, Benjamin is driven by a cognitive demand, which tends to focalize the process of destruction itself rather than the result of the destruction process. The space in which the destructive character is acting is the space of the possibility of change and emancipation, and the space where it is possible to keep together past and future, and memory and redemption. Starting from these reflections, an important question arises about the problem of the relation between history and tradition, and culture and its memory: Neither the destruction of memory by a culture nor its canonization is meaningful. The concept of destructive character then represents a preferential point of observation for analyzing the articulations of Benjamin's thought. From this perspective, a decisive point of Benjamin's reflection seems to emerge on one side, strengthened in the permeation of Hebraic ancestors between destruction and salvation; on the other side, some of the concepts and images of the Berliner philosopher seem to show up in a new light.
文摘Asphalt mixture is a highly heterogeneous material, which is one of the reasons for high measurements uncertainty when subjected to tests. The results of such tests are often unreliable, which may lead to making bad professional judgments. They can be avoided by carrying out reliable analyses of measurement uncertainty adequate for the research methods used and conducted before the actual research is done. This paper presents the calculation of measurements uncertainty using as an example--the determination of the stiffness modulus of the asphalt mixture, which, in turn, was accomplished using the indirect tension method. The paper also shows the employment of the basic methods of statistical analysis, such as testing two mean values and conformity tests. Essential concepts in measurements uncertainty have been compiled and the determination of the stiffness module parameters are discussed. It has been demonstrated that the biggest source of error in the stiffness modulus measuring process is the displacement measure. The aim of the research was to find the measurement uncertainty for stiffness modulus by an indirect tensile test and the presentation of examples of the used statistical methods.
基金supported by the National Basic Research Program of China(“973”Project)(Grant No.2013CB035501)the National Natural Science Foundation of China(Grant Nos.51335007&61473187)
文摘In the one-gravity environment on the ground, the simulation of the contact process of two flying objects in the zero-gravity environment of space has been a challenging issue since humans first explored space by flying objects. Hardware-in-the-loop (HIL) simulation is an important and effective method to test the usability, reliability, and safety of real docking mechanisms in space. There are four main issues for HIL simulation systems: Design of simulators capable of high frequency response, high motion precision, high velocity, and rapid acceleration; compensation for simulation distortion; design of a control model for the HIL simulation process; and experimental verification. Here, we propose a novel HIL simulator system with a 6-DOF 3-3 perpendicular parallel mechanism and a 3-DOF 3-PRS parallel mechanism; discover the principle of simulation distortion; present distortion compensation models for the force measurement system, dynamic response, and structural dynamics of the simulator; and provide a control model for the HIL simulation process. Two kinds of experiments were performed on the pas- sive-undamped elastic rod and the docking mechanisms to test their performances and to verify the effectiveness and usability of the HIL simulator. The HIL simulation system proposed in this paper is useful for developing space docking, berthing, refu- eling, repairing, upgrading, transporting, and rescuing technologies.
基金supported by the National Basic Research Program of China (Grant No. 2006CB705503)National Natural Science Foundation of China (Grant Nos. 70901005, 70631001, 71071016)Specialized Research Fund for the Doctoral Program of Higher Education of China (Grant No. 20090009120015)
文摘To determinate car capacity at bus stops with mixed traffic, a new theoretical approach was developed on the basis of additive-conflict-flows procedure. The procedure was extended from homogeneous traffic flow to mixed traffic flow. The conflicts among cars, buses and bicycles near the stop can be described by the extended procedure. The procedure can be understood more easily than the theory of gap acceptance. Car capacity near the stop is the function of both bus stream and bicycle stream. The proposed model can also analyze the cases of pedestrian effects and limited priority of bicyclists. Numerical results show that the car capacity decreases with the increasing flow rates of other streams. In addition, pedestrian effects and bicyclist's limited priority have negative effects on car capacity near bus stops with mixed traffic flow.
基金Supported by the National Natural Science Foundation of China under Grant Nos.10901021,91130002,11126134and11105013the China Academy of Engineering Physics Project under Grant No.2012A0202010+1 种基金the National High Technology Research and Development Program of China under Grant No.2012AA01A303the National Hi-Tech Inertial Confinement Fusion Committee of China
文摘A Lagrangian compatible radiation hydrodynamic algorithm and the nuclear dynamics computing module are developed and implemented in the LARED Integration code, which is a radiation hydrodynamic code based on the 2-D cylindrical coordinates for the numerical simulation of the indirect-drive Inertial Confined Fusion. A number of 1-D and 2-D ignition implosion numerical simulations by using the improved LARED Integration code (ILARED) are presented which show that the 1-D numerical results are consistent with those computed by the 1-D radiation hydrodynamic code RDMG, while the simulation results of the 2-D low-mode radiative asymmetry and hydrodynamic instability growth,according to the physical analysis and anticipation, are satisfactory. The capsules driven by the sources from SGII experiments are also simulated by ILARED, and the fuel shapes agree well with the experimental results. The numerical simulations demonstrate that ILARED can be used in the simulation of the 1-D and 2-D ignition capsule implosion using the multi-group diffusion model for radiation.
基金supported by the National Natural Science Foundation of China(Nos.60872060,11101265)the Shanghai Natural Science Foundation of China(No.12ZR1421000)the Shanghai Education Commission Innovation Project Fund(Nos.12ZZ193,14YZ152,15ZZ099)
文摘In this paper, the continuous-time independent edge-Markovian random graph process model is constructed. The authors also define the interval isolated nodes of the random graph process, study the distribution sequence of the number of isolated nodes and the probability of having no isolated nodes when the initial distribution of the random graph process is stationary distribution, derive the lower limit of the probability in which two arbitrary nodes are connected and the random graph is also connected, and prove that the random graph is almost everywhere connected when the number of nodes is sufficiently large.