Doppler sodar measurements and evaluations in complex terrain

Summary Doppler Sodar data recorded in a complex terrain (Levantina Valley and Gotthard Pass, Switzerland) during the first TRANSALP campaign (an international experimental programme, started in 1989, that is a part of the EUROTRAC-TRACT Subproject) are shown. The exercises consisted of tracer experiments coupled to comprehensive meteorological measurements. The measurements performed by a joint team ENEL-CNR, with the ENEL 3-D Doppler sodar system and the relative elaborations are presented and discussed with the aim of showing the performances of such an instrument in a rather complex terrain and its ability to give information useful for atmospheric-dispersion modelling. To strengthen this statement, a few results from the second TRANSALP campaign are also shown. These results cannot be extrapolated to other sites unless proper tests are carried out.     

二元微透镜的位相平衡设计及叠加积分衍射分析

本文用位相平衡设计法设计了优化的二元光学微透镜，这是对Ｄａｍｍａｎｎ阶梯波带片设计方法的一种改进。文中用叠加积分作了二元微透镜的衍射分析，并与Ｄａｍｍａｎｎ法作了比较，计算结果说明本方法的衍射效率及象质都优于Ｄａｍｍａｎｎ法。且能设计更大相对口径（Ｄ／ｆ）。具有任意物象距的二元微透镜。     

Innovative Phase Doppler Systems and their Applications

Theoretical and practical limits on the applicability of PDA are established, using generalized theoretical formulations of various physical processes governing the operation of a phase Doppler system. Furthermore, several innovative solutions are introduced to prevent the commonly occuring problems of PDA, such as Gaussian profile effect, non-monotonic response and 2π-ambiguity. Generalized formulations have also enabled new applications, such as sizing of submicron particles, particle material recognition, measurements with non-standard geometries. Selected results of measurements in particulate flows, using innovative PDA systems, are also presented.     

Analysis and applications of the Voronoi Implicit Interface Method

We analyze a new mathematical and numerical framework, the “Voronoi Implicit Interface Method” (“VIIM”), first introduced in Saye and Sethian (2011) [R.I. Saye, J.A. Sethian, The Voronoi Implicit Interface Method for computing multiphase physics, PNAS 108 (49) (2011) 19498–19503] for tracking multiple interacting and evolving regions (“phases”) whose motion is determined by complex physics (fluids, mechanics, elasticity, etc.). From a mathematical point of view, the method provides a theoretical framework for moving interface problems that involve multiple junctions, defining the motion as the formal limit of a sequence of related problems. Discretizing this theoretical framework provides a numerical methodolology which automatically handles multiple junctions, triple points and quadruple points in two dimensions, as well as triple lines, etc. in higher dimensions. Topological changes in the system occur naturally, with no surgery required. In this paper, we present the method in detail, and demonstrate several new extensions of the method to different physical phenomena, including curvature flow with surface energy densities defined on a per-phase basis, as well as multiphase fluid flow in which density, viscosity and surface tension can be defined on a per-phase basis.We test this method in a variety of ways. We perform rigorous analysis and demonstrate convergence in both two and three dimensions for a variety of evolving interface problems, including verification of von Neumann–Mullins’ law in two dimensions (and its analog in three dimensions), as well as normal driven flow and curvature flow with and without constraints, demonstrating topological change and the effects of different boundary conditions. We couple the method to a second order projection method solver for incompressible fluid flow, and study the effects of membrane permeability and impermeability, large shearing torsional forces, and the effects of varying density, viscosity and surface tension on a per-phase basis. Finally, we demonstrate convergence in both space and time of a topological change in a multiphase foam.     

Particle Trajectory Effects in Phase Doppler Systems: Computations and experiments

The effects of the particle trajectories on phase Doppler measurements were explored numerically using generalized Lorenz-Mie theory. Computations were performed for a commercial phase Doppler system and various schemes for elimination of the trajectory effects were examined. It is shown that these effects cannot be completely suppressed if the ratio of the two measured phase shifts from a single receiving unit is used to validate the measurements. On the other hand, the errors due to particle trajectories can be eliminated satisfactorily by employing an additional receiving unit, which allows one to detect the asymmetry of the scattered light pattern due to displacement of the particle trajectory from the centre of the measuring volume. A preliminary experimental evaluation of this method is presented and discussed.     

多普勒展宽和多普勒频移在光谱分析中的应用

分析了多普勒展宽和多普勒频移区别,讨论了高斯拟合和弦积分线形分布的差异。利用多道光学分析仪（OSMA）测量HT-6M托卡马克限制器前Hα线形分布,通过高斯拟合由多普勒展宽和多普勒频移分别得出等离子温度和粒子入射速度。     

Multichannel Nomarski microscope with polarization modulation: performance and applications

Using a two-dimensional CCD array, a photoelastic modulator, and a commercial Nomarski microscope, we built a differential polarization interferometer. Multichannel lock-in detection of the signal allowed us to reach a shot-noise limit corresponding to 5-pm path differences for a few seconds of recording time. This interferometer was used as a surface profilometer as well as a system for imaging through scattering media.     

双频相位测量轮廓术及其误差分析

提出一种双频相位测量轮廓术，利用这一技术。在相位恢复过程中，对有断点及边界区域也能得到正确的去包裹相位值，把这一技术用于三维面形测量中，得到了较好的实验结果。最后，分析实验产生误差的原因。     

Laboratory, ground-based, and airborne tunable diode laser systems: performance characteristics and applications in atmospheric studies

2 O) used as the target gas. One method utilizes the Allan variance. When our present aircraft system is operated in the laboratory, the Allan variance indicates a CH₂O detection limit of 0.031 ppbv for integration times of 25 s. This sensitivity corresponds to a minimum detectable absorbance of 1.0×10^-6, and this is within a factor of two of that reported by Werle et al. who used high-frequency modulation spectroscopy. The present instrument utilizes conventional low-frequency (2f=100 kHz) wavelength modulation. Instrument performance, obtained from replicate measurements of CH₂O standards acquired over time periods as long as 1.5 hours, on average resulted in a factor of two poorer precision than indicated by the Allan variance. Since replicate measurements precisely simulate the acquisition procedures employed, including the acquisition of sample and background spectra, they present a more meaningful measure of instrument performance. Preliminary evidence suggests that slow drifts in the laser wavelength control during acquisition of replicate measurements may play an important role in the above disparity. The resultant laser wavelength correction voltage, which is applied to counter such drifts, may also be a factor in this disparity. A limited number of replicate measurements with minimal drift in the laser wavelength yield much closer agreement between replicate and Allan variance precisions. Received: 19 March 1998/Revised version: 2 June 1998     

A Method for Increasing the Sensitivity of Phase Doppler Interferometry to seed particles in liquid spray flows

A method has been developed to increase the sensitivity of phase Doppler interferometry-based particle sizing systems to small particles in the presence of a spray containing large and small droplets; an important consideration when using seed particles to track the gas-phase velocity in multi-phase flows. The method, applicable to PDPA systems configured to operate in first and higher order refraction mode, involves doping the sprayed liquid with a dye that is strongly absorbing at the incident laser wavelengths. This results in greatly diminished scattered intensity from larger droplets, thus allowing the photomultiplier gain to be set to a level sufficient to easily detect small particles without saturation. Tests conducted indicate that, at a collection angle of 30° and droplet absorptivity of γ = 0.014/μm, the PDPA can accurately size absorbing droplets up to approximately 200 μm. This upper limit can be extended by changing selection angle. Tests performed with an actual spray demonstrated that the method allowed detection of 1 μm to 235 μm droplets; more than four times the instrument's usual range of 50: 1. A data correction scheme to determine the effective probe volume radius for each particle size class has been developed for absorbing particles, as standard correction schemes derived for non-absorbing droplets excessively weigh distributions toward smaller particles.     

The Canonical Function Method and its applications in quantum physics

The Canonical Function Method (CFM) is a powerful method that solves the radial Schrödinger equation for the eigenvalues directly, without having to evaluate the eigenfunctions. It is applied to various quantum mechanical problems in Atomic and Molecular physics in the presence of regular or singular potentials. It has also been developed to handle single and multiple channel scattering problems, where phaseshift is required for the evaluation of the scattering cross-section. Its controllable accuracy makes it a valuable tool for the evaluation of vibrational levels of cold molecules, a sensitive test of the Bohr correspondence principle and a powerful method for tackling local and non-local spin dependent problems.     

The Immersed Structural Potential Method for haemodynamic applications

In this paper, a new fluid–structure interaction immersed computational methodology, based upon the original Immersed Boundary Method (IBM) [1] is outlined with the final aim of modelling cardiovascular phenomena, specifically, heart valve related problems. The principal characteristic of such immersed techniques is the representation of any deformable or rigid body immersed within an incompressible viscous flow field as a momentum forcing source in the Navier–Stokes equations. A number of shortcomings within the immersed formulation still require further investigation and improvement, including the excessive numerical diffusion caused by the interpolation/spreading process, the need to include realistic viscoelastic composite constitutive models describing more accurately the nature of cardiovascular tissues and also the need to capture more effectively stresses developed at the fluid–structure interface. By following the same philosophy as the original IBM, a more sophisticated formulation is derived in this paper, the “Immersed Structural Potential Method (ISPM)”. The method introduced presents an alternative approach to compute the equivalent fluid–structure interaction forces at the fluid mesh, accounts for a sophisticated viscoelastic fibre-reinforced constitutive model to better describe the mechanics of cardiovascular tissues and utilises a novel time-integration methodology for the computation of the deformation gradient tensor which ensures compliance with the incompressibility constraint. A series of numerical examples will be presented in order to demonstrate the robustness and applicability of this new methodology.     

Phase engineering of one-dimensional defective photonic crystal and applications

It is shown in this paper that many new sensitive phase photonic crystal devices will be developed, if some existing problems can be overcome. The main problems are the rapid change of light intensity around the defect mode and the influence of the substrate. The method for overcoming these problems is to construct the defective photonic crystal in a heterostructure or an asymmetric structure. The phase properties of asymmetric one-dimensional photonic crystals with couple defects are revealed in this paper. As examples, a phase modulator and a phase switch with very high sensitivity are demonstrated. PACS 42.70.Qs; 42.79.-e; 42.60.Da; 74.62.Dh     

Design and performance simulation of a molecular Doppler wind lidar

A mobile molecular Doppler wind lidar at an eye-safe wavelength of 355 nm based on double-edge technique is being built in Hefei （China） for wind measurement from 10-to 40-km altitude. The structure of this lidar system is described. A triple Fabry-Perot etalon is employed as a frequency discriminator whose parameters are optimized. The receiver system is designed to achieve compactness and stability by putting in a standard 19-inch socket bench. Simulation results show that within the wind speed dynamic range of ±100 m/s, the horizontal wind errors due to noise are less than 1 m/s bdow 20-km altitude for 100-m vertical resolution, and less than 5.5 m/s from 20 km up to 40 km for 500-m vertical resolution with 400-mJ laser energy, 30-min temporal resolution, and a 45-cm aperture telescooe.     

Trajectory Ambiguities in Phase Doppler Systems: Study of a near forward and a near-backward geometry

Generalized Lorenz-Mie theory for the scattering of arbitrarily shaped beams by spherical particles has been applied to two standard phase Doppler layouts, employing receiving units at 30° and 150° off-axis locations. It is shown that the particle trajectory effects may lead to inaccurate size measurements for the near-forward receiver and may make the near-backward measurements totally misleading when a large particle size range (1:40) needs to be covered. Only limited improvements can be achieved by using two phase-shift signals from a single receiving unit for discrimination. The errors associated with the trajectories are also detrimental to the concentration measurements based on the existing criteria. However, an extended optical system employing two identical receiving units, located symmetrically about the plane of the laser beams, provides a robust solution to the trajectory ambiguity. It can be used to measure correctly the particle size and the particle location in the measuring volume. The difficulties associated with estimating the effective size of the measuring volume as a function of the particle diameter (in order to determine the true size distribution and the particle number density) may also be resolved by employing an extended system. Hence, despite a higher cost, this arrangement is attractive, at least for obtaining some benchmark simultaneous measurements of sizes and velocities in two-phase particulate flows.     

Influence of the Measurement Volume on the Phase Error in Phase Doppler Anemometry. Part 1: Reflective mode operation

In phase Doppler anemometry (PDA), phase difference errors are caused by the Gaussian intensity distribution of the laser beam and the curvature of the phase fronts outside of the beam waist. This results in erroneous particle sizes. Based on a physical analysis by geometrical optics [1], this phase difference error is evaluated for reflected mode operation (Part I) and for refracted mode operation (Part II). By varying the particle trajectories statistically, the error in determining the particle size and the mass flow can be simulated. By the method described the error in the measured phase difference can easily be estimated.     

The transport of slow ions in gases: Experiment, theory, and applications

This review is concerned with the two most important transport phenomena in involving slow ions in gases, namely their drift and diffusion in an externally applied electric field. The energy range of interest extends from thermal values at low temperatures up to about 10 eV. The transport phenomena are first discussed in physical terms, and experimental techniques for measuring ionic drift velocities and diffusion coefficients are then described. Brief coverage is given to ionic transport theory up to the time of Wannier's landmark contributions in 1951–1952; later theoretical developments are treated in more detail. Special emphasis is placed on aspects of modern theory that permit the determination of interaction potentials and collision frequencies for momentum transfer from experimental transport data. The review ends with a discussion of several applications of transport data to ionospheric problems.