Finite element analysis of flow,heat transfer,and free interfaces in an electron-beam vaporization system for metals

A numerical analysis is made of the liquid flow and energy transport in a system to evaporate metals. The energy from an electron-beam heats an axisymmetric metal disk supported by a water-cooled platform. Metal evaporates from the surface of a hot pool of liquid which is surrounded by a shell of its own solid. Flow in the pool is strongly driven by temperature-induced buoyancy and capillary forces, and is located in the transition region between laminar and turbulent flow. The evaporation rate is strongly influenced by the locations of the free boundaries. A modified finite element method is used to calculate the steady state flow and temperature fields coupled with the interface locations. The mesh is structured with spines that stretch and pivot as the interfaces move. The discretized equations are arranged in an ‘arrow’ matrix and are solved using the Newton–Raphson method. The electron-beam power and platform contact resistance are varied for cases involving the evaporation of aluminum. The results reveal the interaction of liquid flow, heat transfer and free interfaces. © 1998 John Wiley & Sons, Ltd.     

Time-dependent liquid metal flows with free convection and a deformable free surface

The finite element method is employed to investigate time-dependent liquid metal flows with free convection, free surfaces and Marangoni effects. The liquid circulates in a two-dimensional shallow trough with differentially heated vertical walls. The spatial formulation incorporates mixed Lagrangian approximations to the velocity, pressure, temperature and free surface position. The time integration is performed with the backward Euler and trapezoid rule methods with step size control. The Galerkin method is used to reduce the problem to a set of non-linear equations which are solved with the Newton–Raphson method. Calculations are performed for conditions relevant to the electron beam vaporization of refractory metals. The Prandtl number is 0·015 and Grashof number are in the transition range between laminar and turbulent flow. The results reveal the effects of flow intensity, surface tension gradients, mesh refinement and time integration strategy.     

Demonstration of a passive subpicostrain fiber strain sensor

We demonstrate a fiber Fabry-Perot (FFP) sensor that is capable of detecting subpicostrain signals, from 100 Hz and extending beyond 100 kHz, using the Pound-Drever-Hall (PDH) frequency locking technique. A low-power diode laser at 1550 nm is locked to a free-space reference cavity to suppress its free-running frequency noise, thereby stabilizing the laser. The stabilized laser is then used to interrogate a FFP sensor whose PDH error signal yields the instantaneous fiber strain.     

Experimental demonstration of variable-reflectivity signal recycling for interferometric gravitational-wave detectors

The results of an experimental demonstration of a benchtop Michelson interferometer with a variable-reflectivity signal mirror are presented. This variable reflectivity is achieved by employment of a second Michelson interferometer. The results are presented in the form of the frequency responses obtained from this configuration with a signal laser injection method. It is shown that the frequency response can be dynamically tuned with independent peak frequency and bandwidth control. Such a configuration gives a tunable frequency response and has an application as a flexible gravitational-wave detector.     

Direct bound-free photodesorption of physisorbed molecules

Because light, weakly adsorbed atoms and molecules have very few bound states, the harmonic oscillator Δv = 1 optical selection rule is invalid for vibrational transitions of the physisorption bond. For such systems, we show that very low power (50 mW) infrared radiation should be sufficient to cause a direct one-photon optical transition from the ground state to continuum translational levels, resulting in photodesorption. Using a simple one-dimensional model, we present computations of the photodesorption rate as a function of photon energy for the Morse potential and several dipole moment functions. The threshold behavior at long wavelengths is analyzed.     

Elastic π± + 3He scattering

Differential cross sections have been measured at θ≈20–120° at 50, 100 and 200 MeV. Salient features of the angular distributions are Coulomb interference effects at 50 MeV and clear spin-flip contributions to π^? compared to π⁺ scattering in the angular region of θ≈80° dominated by the πN p-wave minimum. Comparison with optical model calculations account for the data up to 200 MeV while this first-order scattering theory misses conspicuous features of data at 295 MeV.