A non-contact technique for evaluation of elastic structures at large stand-off distances: applications to classification of fluids in steel vessels

A novel technique for non-contact evaluation of structures in air at large stand-off distances (on the order of several meters) has been developed. It utilizes a recently constructed air-coupled, parametric acoustic array to excite the resonance vibrations of elastic, fluid-filled vessels. The parametric array is advantageous for NDE applications in that it is capable of producing a much narrower beamwidth and broader bandwidth than typical devices that operate under linear acoustic principles. In the present experiments, the array operates at a carrier frequency of 217 kHz, and the sound field several meters from the source is described spectrally by the envelope of the drive voltage. An operating bandwidth of more than 25 kHz at a center frequency of 15 kHz is demonstrated. For the present application, the array is used to excite vibrations of fluid-filled, steel containers at stand-off distances of greater than 3 m. The vibratory response of a container is detected with a laser vibrometer in a monostatic configuration with the acoustic source. By analyzing the change in the response of the lowest order, antisymmetric Lamb wave as the interior fluid loading conditions of the container are changed, the fluid contained within the steel vessel is classified.     

Measurement of the transverse kinetic energies of argon recoil ions produced in 120 MeV -Ar collisions

Measurements were carried out to deduce the transverse kinetic energies of highly charged argon recoil ions produced in single collisions of 120 MeV ions with argon atoms in which the post collision charge states of the projectiles were not determined. A time of flight spectrometer was designed and fabricated to detect the charge states of recoils. Experimental procedures for optimizing the spectrometer for extraction, transmission and detection of recoils are described. A simple approach for determining the transverse kinetic energy of the recoil ions from FWHM of the peaks is reported. This method is shown to be independent of the choice of collision partners and requires only the knowledge of the physical values of “optimized parameters” of time-of-flight spectrometer used in the experiment. The transverse kinetic energy of the recoil ions determined from the present approach is found to vary from 0.03 eV for to 4.02 eV for Ar¹⁰⁺. These values are compared with the results reported by earlier workers and are shown to follow a q²-behaviour up to a charge state q =8+ of the recoil ions. Received: 5 February 1998 / Revised: 8 June 1998 / Accepted: 11 June 1998     

Gamma ray photon-induced modifications in Triafol-TN and Triafol-BN polymeric track detectors

Photon induced modifications in Triafol-TN and Triafol-BN polymers have been studied in the dose range of 10¹–10⁶ Gy at room temperature using a ⁶⁰Co source. To monitor the chemical and structural changes induced by gamma rays, UV, IR, and ESR studies were carried out. Thermal studies were also conducted for understanding the effects of gamma irradiations on these polymers. Variation of track etching characteristics and activation energy for bulk etching have been studied at different gamma rays doses. The experimental results are presented and discussed.     

Transfer measurements for the Ti+Ni systems at near barrier energies

Large enhancements have been observed in the sub-barrier fusion cross sections for Ti+Ni systems in our previous studies. Coupled channel calculations incorporating couplings to 2⁺ and 3⁻ states failed to explain these enhancements completely. A possibilty of transfer channels contributing to the residual enhancements had been suggested. In order to investigate the role of relevant transfer channels, measurements of one- and two-nucleon transfer were carried out for ^46,48Ti+⁶¹Ni systems. The present paper gives the results of these studies.     

Schrödinger Operators with Empty Singularly Continuous Spectra

Let H be a semibounded perturbation of the Laplacian H ₀ in L ²( ^d ). For an admissible function sufficient conditions are given for the completeness of the scattering system (H), (H ₀). If is the exponential function and if e^{– H} is an integral operator we denote the kernel of the difference D = e^{– H} – e^{– H} ₀ by D (x, y), > 0. The singularly continuous spectrum of H is empty if^d dx ^d dy |D(x,y)| (1 + |y|²)< for some > 1. This result is applied to potential perturbations and to perturbations by imposing Dirichlet boundary conditions.     

Multiple ionization of argon in coincidence with projectile ions in 60–120 MeV Si q+-Ar collisions

A projectile ion-recoil ion coincidence technique has been employed to study the multiple ionization and the charge transfer processes in collisions of 60–120 MeV Si ^q+ (q = 4−14) ions with neutral argon atoms. The relative contribution of different ionization channels, namely; direct ionization, electron capture and electron loss leading to the production of slow moving multiply charged argon recoil ions have been investigated. The data reported on the present collision system result from a direct measurement in the considered impact energy for the first time. The total ionization cross-sections for the recoil ions are shown to scale as q ^1.7/E _p ^0.5 , where E _p is the energy in MeV of the projectile and q its charge state. The recoil fractions for the cases of total- and direct ionizations are found to decrease with increasing recoil charge state j. The total ionization fractions of the recoils are seen to depend on q and to show the presence of a ‘shell-effect’ of the target. Further, the fractions are found to vary as 1/j ² upto j = 8+. The average recoil charge state 〈j〉 increases slowly with q and with the number of lost or captured electrons from or into the projectile respectively. The projectile charge changing cross-sections σ _qq′ are found to decrease with increasing q for loss ionization and to increase with q for direct-and capture ionization processes respectively. The physics behind various scaling rules that are found to follow our data for different ionization processes is reviewed and discussed.     

Study of band offsets in InN/Ge heterojunctions

InN layers were directly grown on Ge substrate by plasma-assisted molecular beam epitaxy (PAMBE). The valence band offset (VBO) of wurtzite InN/Ge heterojunction is determined by X-ray photoemission spectroscopy (XPS). The valence band of Ge is found to be 0.18 ± 0.04 eV above that of InN and a type-II heterojunction with a conduction band offset (CBO) of ~ 0.16 eV is found. The accurate determination of the VBO and CBO is important for the design of InN/Ge based electronic devices.     

Structural and ac electrical properties of a newly synthesized single phase rare earth double perovskite oxide: Ba2CeNbO6

A single phase rare earth double perovskite oxide Ba₂CeNbO₆ (BCN) is synthesized by solid-state reaction technique for the first time. The X-ray diffraction pattern of the sample at room temperature shows monoclinic structure, with the lattice parameters, a=5.9763 Å, b=5.975 Å and c=8.48 Å and β=90.04°. Impedance spectroscopy is used to study the ac electrical behavior of this material as a function of frequency (10²-10⁶ Hz) at various temperatures (30-450 °C). A relaxation is observed in the entire temperature range. Conduction mechanism is investigated by fitting the complex impedance data to Cole-Cole equation. Complex impedance plane plots show only one semicircular arc, indicating only the grain contribution of dielectric relaxation. The scaling behavior of imaginary part of electric modulus (M″) and imaginary part of electrical impedance (Z″) suggests that the relaxation describes the same mechanism at various temperatures. The frequency dependence of conductivity is interpreted in terms of the jump relaxation model and is fitted to Jonscher's power law. The values of dc conductivities extracted from the Jonscher power law varies from 2.79×10⁻⁷ to 3.5×10⁻⁵ Sm⁻¹ with the increase in temperature from 100 to 450 °C. The activation energies (0.37 eV) extracted from M″(ω) and Z″(ω) peaks are found to follow the Arrhenius law.     

Sub- and above-barrier fusion of loosely bound 6Li with 28Si

Fusion excitation functions are measured for the system ⁶Li + ²⁸Si using the characteristic $ \gamma$ -ray method, encompassing both the sub-barrier and above-barrier regions, viz, E _lab = 7-24 MeV. Two separate experiments were performed, one for the above-barrier region ( E _lab = 11-24 MeV) and another for the below-barrier region ( E _lab = 7-10 MeV). The results were compared with our previously measured fusion cross-section for the ⁷Li + ²⁸Si system. We observed the enhancement of the fusion cross-section at sub-barrier regions for both ⁶Li and ⁷Li , but the yield was substantially larger for ⁶Li . However, for well-above-barrier regions, a similar type of suppression was identified for both the systems.     

Acousto-optic mode coupling of partially coherent light in two-mode optical fibers

An acoustic pulse propagating on a two-mode fiber can act as a beam splitter in a scanning interferometer. When this device is employed in white-light interferometry, the effects of distributed coupling and dispersive interferometer arms need to be considered. A theory suitable for treating acousto-optic interaction of partially coherent light in a moving interaction region was developed. It was found that differential optical dispersion should be negligible and the acoustic pulse length short. Also the coherence time should be short but long compared to the intermodal group delay difference over a pulse length. Experiments with long acoustic pulses were performed, and fairly good agreement with theory was obtained.