Rock avalanches are catastrophic events involving important granular rock masses (>106 m3) and traveling long distances. In exceptional cases, the runout can reach up to tens of kilometers. Even if they are highly ...Rock avalanches are catastrophic events involving important granular rock masses (>106 m3) and traveling long distances. In exceptional cases, the runout can reach up to tens of kilometers. Even if they are highly destructive and uncontrollable events, they give important insights to understand interactions between the displaced masses and landscape conditions. However, those events are not frequent. Therefore, the analogue and numerical modelling gives fundamental inputs to better understand their behavior. The objective of the research is to understand the propagation and spreading of granular mass released at the top of a simple geometry. The flow is unconfined, spreading freely along a 45° slope and deposit on a horizontal surface. The evolution of this analogue rock avalanche was measured from the initiation to its deposition with high speed camera. To simulate the analogue granular flow, a numerical model based on the continuum mechanics approach and the solving of the shallow water equations was used. In this model, the avalanche is described from a eulerian point of view within a continuum framework as single phase of incompressible granular material. The interaction of the flowing layer with the substratum follows a Mohr-Coulomb friction law. Within same initial conditions (slope, volume, basal friction, height of fall and initial velocity), results obtained with the numerical model are similar to those observed in the analogue. In both cases, the runout of the mass is comparable and the size of both deposits matches well. Moreover, both analogue and numerical modeling gave same magnitude of velocities. In this study, we highlighted the importance of the friction on a flowing mass and the influence of the numerical resolution on the propagation. The combination of the fluid dynamic equation with the frictional law enables the self-channelization and the stop of the granular mass.展开更多
We discuss novel advanced concepts suitable for the practical design of gamma-ray sources of directed energy. One concept is based on the self-channeling of a powerful optical laser in a gas within a metal tube. Anoth...We discuss novel advanced concepts suitable for the practical design of gamma-ray sources of directed energy. One concept is based on the self-channeling of a powerful optical laser in a gas within a metal tube. Another concept employs a direct excitation of a quadrupole nuclear level by a powerful optical laser. The third concept is based on the process of a high-order harmonic generation by an x-ray laser. All three concepts can be used for designing gamma-ray lasers that would have significant advantages over x-ray lasers. First, missile defense systems employing gamma-ray lasers would be weather independent. Second, the gamma-ray laser radiation can penetrate through the sand, which could be suspended in the air in a desert either naturally (due to strong winds) or artificially (as a protective “shield”). Besides, the first out of the three concepts can beemployed for creating non-laser gamma-ray sources of directed energy to be used for detecting stored radioactive materials, including the radioactive materials carried by an aircraft or a satellite. Last but not least: these concepts can be also used for remotely destroying biological and chemical weapons as a preemptive strike or during its delivery phase, as well as for distinguishing a nuclear warhead from decoy warheads. Thus, the defense capabilities of the proposed gamma-ray lasers can save numerous lives.展开更多
In underdense plasmas, the transverse ponderomotive force of an intense laser beam with Ganssian transverse profile expels electrons radially, and it can lead to an electron cavitstion. An improved cavitation model wi...In underdense plasmas, the transverse ponderomotive force of an intense laser beam with Ganssian transverse profile expels electrons radially, and it can lead to an electron cavitstion. An improved cavitation model with charge conservation constraint is applied to the determination of the width of the electron cavity. The envelope equation for spot size derived by using source-dependent expansion method is extended to including the electron cavity. The condition for self-guiding is given and illuminated by an effective potential for the laser spot size. The effects of the laser power, plasma density and energy dissipation on the self-guiding condition are discussed.展开更多
Theoretical investigation on the propagation characteristics of a new class of laser beams known as multi Gaussian(M.G)laser beams has been presented.To investigate the linear characteristics,propagation of the laser ...Theoretical investigation on the propagation characteristics of a new class of laser beams known as multi Gaussian(M.G)laser beams has been presented.To investigate the linear characteristics,propagation of the laser beam in vacuum has been considered.Whereas,the nonlinear characteristics have been investigated in plasmas.Optical nonlinearity of the plasma has been modeled by relativistic mass nonlinearity of the plasma electrons in the field of laser beam.Formulation is based on finding the semi analytical solution of the wave equation for the slowly varying envelope of the laser beam.Particularly,the dynamical evolutions of the beam width and longitudinal phase of the laser beam have been investigated in detail.展开更多
文摘Rock avalanches are catastrophic events involving important granular rock masses (>106 m3) and traveling long distances. In exceptional cases, the runout can reach up to tens of kilometers. Even if they are highly destructive and uncontrollable events, they give important insights to understand interactions between the displaced masses and landscape conditions. However, those events are not frequent. Therefore, the analogue and numerical modelling gives fundamental inputs to better understand their behavior. The objective of the research is to understand the propagation and spreading of granular mass released at the top of a simple geometry. The flow is unconfined, spreading freely along a 45° slope and deposit on a horizontal surface. The evolution of this analogue rock avalanche was measured from the initiation to its deposition with high speed camera. To simulate the analogue granular flow, a numerical model based on the continuum mechanics approach and the solving of the shallow water equations was used. In this model, the avalanche is described from a eulerian point of view within a continuum framework as single phase of incompressible granular material. The interaction of the flowing layer with the substratum follows a Mohr-Coulomb friction law. Within same initial conditions (slope, volume, basal friction, height of fall and initial velocity), results obtained with the numerical model are similar to those observed in the analogue. In both cases, the runout of the mass is comparable and the size of both deposits matches well. Moreover, both analogue and numerical modeling gave same magnitude of velocities. In this study, we highlighted the importance of the friction on a flowing mass and the influence of the numerical resolution on the propagation. The combination of the fluid dynamic equation with the frictional law enables the self-channelization and the stop of the granular mass.
文摘We discuss novel advanced concepts suitable for the practical design of gamma-ray sources of directed energy. One concept is based on the self-channeling of a powerful optical laser in a gas within a metal tube. Another concept employs a direct excitation of a quadrupole nuclear level by a powerful optical laser. The third concept is based on the process of a high-order harmonic generation by an x-ray laser. All three concepts can be used for designing gamma-ray lasers that would have significant advantages over x-ray lasers. First, missile defense systems employing gamma-ray lasers would be weather independent. Second, the gamma-ray laser radiation can penetrate through the sand, which could be suspended in the air in a desert either naturally (due to strong winds) or artificially (as a protective “shield”). Besides, the first out of the three concepts can beemployed for creating non-laser gamma-ray sources of directed energy to be used for detecting stored radioactive materials, including the radioactive materials carried by an aircraft or a satellite. Last but not least: these concepts can be also used for remotely destroying biological and chemical weapons as a preemptive strike or during its delivery phase, as well as for distinguishing a nuclear warhead from decoy warheads. Thus, the defense capabilities of the proposed gamma-ray lasers can save numerous lives.
基金Project supported by the National High Technology Inertial Confinement Fusion Foundation （Grant No 10335020/A0506）, the National Natural Science Foundation of China （Grant Nce 10474081 and 10576035）, and Natural Science Foundation of Shanghai （Grant No 05ZR14159）.
文摘In underdense plasmas, the transverse ponderomotive force of an intense laser beam with Ganssian transverse profile expels electrons radially, and it can lead to an electron cavitstion. An improved cavitation model with charge conservation constraint is applied to the determination of the width of the electron cavity. The envelope equation for spot size derived by using source-dependent expansion method is extended to including the electron cavity. The condition for self-guiding is given and illuminated by an effective potential for the laser spot size. The effects of the laser power, plasma density and energy dissipation on the self-guiding condition are discussed.
文摘Theoretical investigation on the propagation characteristics of a new class of laser beams known as multi Gaussian(M.G)laser beams has been presented.To investigate the linear characteristics,propagation of the laser beam in vacuum has been considered.Whereas,the nonlinear characteristics have been investigated in plasmas.Optical nonlinearity of the plasma has been modeled by relativistic mass nonlinearity of the plasma electrons in the field of laser beam.Formulation is based on finding the semi analytical solution of the wave equation for the slowly varying envelope of the laser beam.Particularly,the dynamical evolutions of the beam width and longitudinal phase of the laser beam have been investigated in detail.
