Dual-beam Methods Research Articles

The results of optical guidance of flowing particles to the probe volume of Dual-Beam Velocimetry

In this study, a new method of microscopic particle’s size and condensation measurement by dual-beam methods is investigated. In this method microscopic particles in a turbulent fluid such as aerosols guide to the interfering fringes of two shifted frequency laser beams by an optical tube (e.g., single-charged Bessel-Gaussian laser beams) instead of mechanical guiding of them. Optical forces such as radiation and photophoretic forces on a particle in a fluid was obtained. It was shown theoretically the Signal-to-Noise Ratio, SNR, and the number of detected photons scattered from the particles cross the fringes will be significantly increased rather than mechanical guiding of them. In addition, the Doppler frequency broadening and angular uncertainty are decreased by new measurement. The condensation of aerosols in the lab was measured by counting the signal burst from particles which traverse light fringes after guided them into a single charge Bessel-Gaussian laser beam. Due to the lack of laboratory facilities, our group can’t determine the frequency Doppler shifted of laser beam to determine the particle’s dimensions.

Velocity map imaging the dynamics of the reactions of Cl atoms with neopentane and tetramethylsilane

The reactions of ground state Cl((2)P(3/2)) atoms with neopentane and tetramethylsilane have been studied at collision energies of 7.9+/-2.0 and 8.2+/-2.0 kcal mol(-1), respectively. The nascent HCl(v=0,J) products were probed using resonance enhanced multiphoton ionization spectroscopy combined with velocity map imaging (VMI) to determine the rotational level population distributions, differential cross sections (DCSs), and product translational energy distributions. The outcomes from PHOTOLOC and dual beam methods are compared and are discussed in light of previous studies of the reactions of Cl atoms with other saturated hydrocarbons, including a recent crossed molecular beam and VMI investigation of the reaction of Cl atoms with neopentane [Estillore et al., J. Chem. Phys. 132, 164313 (2010)]. Rotational distributions were observed to be cold, consistent with the reactions proceeding via a transition state with a collinear Cl-H-C moiety. The DCSs for both reactions are forward peaked but show scatter across a broad angular range. Interpretation using a model based on linear dependence of scattering angle on impact parameter indicates that the probability of reaction is approximately constant across all allowed impact parameters. Product translational energy distributions from dual beam experiments have mean values, expressed as fractions of the total available energy, of 0.67 (Cl+neopentane) and 0.64 (Cl+tetramethylsilane) that are consistent with a kinematic model for the reaction in which the translational energy of the reactants is conserved into product translational energy.

Developing dual beam methods for the study of polymers

The use of a combined Focussed Ion Beam/Environmental Scanning Electron Microscope (FIB/ESEM) offers new possibilities for imaging complex heterogeneous polymeric structures. The use of the focussed ion beam, using positively charged gallium ions in conjunction with a measured ‘defocused’ low energy primary electron beam has permitted milling through the heterostructure to be achieved in a controlled way, exposing the inner structure without introducing significant charge damage into the sample. The use of the Environmental Scanning Electron Microscope for imaging the revealed milled sections has then enabled insulating polymer structures to be imaged without charging problems, despite the absence of a conductive coating. Cross sections of a 900nm thick spun cast film of phase separated polystyrene-polybutadiene blends have been successfully milled and imaged, the results agreeing with previous experiments produced using ultramicrotomy and TEM. In addition, elliptical shaped titanium dioxide particles approximately 220nm in diameter have been dispersed in commercial film forming latices at concentrations between 0 and 100 percent volume. The films have been cast, milled 2μm deep and imaged. Results on the arrangement of titanium dioxide particles in the polymer matrices are presented.

A quantitative echo sounder with multiple beams, model KFC-3000

We have developed a quantitative echo sounder with various features such as effective combination of dual beam and split beam methods. This system is designed in accordance with the established designing method of a quantitative echo sounder. The method specifies source power, operating frequency, and so on for a given measuring object and range under the principle of minimum estimation error. Ideal omnidirectional and symmetrical simultaneous split beam methods detect the three-dimensional position of an individual target. An omnibus display on the multiwindows provides full echo information. Raw data for post-processing is used for accurate biomass evaluation. The easy operation of this system offers a wider range of users more adequate and reliable data for fishery resource surveys.

A comparison of single- and dual-beam methods for maximum velocity estimation

The purpose of this study was to compare the precision and accuracy of maximum velocity estimation when the target direction is known (a string phantom), and when the target direction is unknown (a flow model of arterial stenosis with stenoses of 0–80% by area). Maximum velocity was estimated using single- and dual-beam methods. A linear-array system was used to acquire Doppler spectra from a single-beam direction. The same array was used for sequential acquisition of Doppler spectra from 2 beam directions; the velocity estimates from these were then compounded in a vector manner. The variation of estimated maximum velocity with beam-string angle over the range 40–80° was 27% for conventional Doppler, 2.6% for angle correction from the edge of the array and 1.6% for the vector Doppler. In the stenosis model, for the single-beam methods, the highest frequency shift was obtained just prior to the point of minimum lumen. At this location, the variation with beam-vessel angle over the range 40–80° was 35% for conventional Doppler, 7.4% for the correction factor method and 6.9% for correction from the edge of the array. For the vector method, the maximum velocity is obtained from within the poststenotic jet, the variation was 2% over the range 40–80°. It is recommended that existing Doppler systems use the correction-factor method to reduce variation in measured maximum velocity. The use of the vector technique by future generations of Doppler systems may lead to angle-independent velocity estimation.

Comparison of the response of raw wool to simultaneous neutron and γ-ray (neugat) transmission and simultaneous dual energy γ-ray (gamgat) transmission

Dual radiation beam methods are important for composition measurement where the material can be described as a binary mixture. In this paper the neutron/gamma transmission (neugat) response to the wool yield of raw wool has been determined to identify potential value in specifying this multicomponent product by this approach. A comparison is made with the gamma/gamma transmission (gamgat) method.

Thermal lens spectrophotometry of phosphorus using a near-infrared semiconductor laser

A thermal lens spectrophotometer consisting of a near-infrared semiconductor laser was constructed. The theoretical sensitivity of the present spectrophotometer using a 10-mW laser was 61 times better than the conventional spectrophotometer for the sample in chloroform. When the sample of phosphorus was measured directly in the aqueous phase based on a heteropoly blue method, the detection limit was 2.2 ppb and 0.7 ppb for single and dual beam methods, respectively. When the sample was measured after solvent extraction into 2-butanol, the detection limits were improved to 0.2 ppb for both the methods, which corresponds to an absorbance of 2 x 10/sup -4/. The achieved detection limits were about an order of magnitude better than absorption spectrometry using a conventional 1-cm sample cell. The minimum detectability was mainly limited by blank absorption occurring from the solvent. The determination was also carried out after ion-pair solvent extraction with Zephiramine into chloroform. The solvent blank was much lower for chloroform, but the detection limit remained identical with the previous results. The minimum detectability was limited by reagent blank in this case. 24 references, 3 figures, 1 table.

Mode selection and optimization of parameters for recording high-performance thin-layer chromatograms by transmission measurements

Optimum conditions to maximize the observed resolution and signal-to-noise ratio of a scanning densitometer for high-performance thin-layer chromatography are described. Transmission measurements are compared in three operating modes; two being pseudo dual-beam methods and the third a dual-wavelength single-beam mode. In all modes resolution is shown to be independent of those parameters which control the dimensions of the measuring beam within their accessible ranges. Signal-to-noise ratios depend on both the operating mode and the dimensions of the measuring beam. In particular, signal shows a marked dependence on the ratio of slit height to spot diameter. Similar values for resolution and better signal-to-noise characteristics may be obtained in the transmission mode compared to reflectance for substances absorbing in the visible range.