Contribution to the theory of Lorentzian ionization

The probability w _L of Lorentzian ionization, which arises when an atom or ion moves in a constant magnetic field, is calculated in the quasiclassical approximation. The nonrelativistic (v≲e ²/ℏ=1, v is the velocity of the atom) and ultrarelativistic (v→c=137) cases are examined and the stabilization factor S, which takes account of the effect of the magnetic field on tunneling of an electron, is found. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 5, 391–396 (10 March 1997)     

An absolute method for determination of misalignment of an immersion ultrasonic transducer

An absolute methodology has been developed for quantification of misalignment of an ultrasonic transducer using a corner-cube retroreflector. The amplitude based and the time of flight (TOF) based C-scans of the reflector are obtained for various misalignments of the transducer. At zero degree orientation of the transducer, the vertical positions of the maximum amplitude and the minimum TOF in the C-scan coincide. At any other orientation of the transducer with the horizontal plane, there is a vertical shift in the position of the maximum amplitude with respect to the minimum TOF. The position of the minimum (TOF) remains the same irrespective of the orientation of the transducer and hence is used as a reference for any misalignment of the transducer. With the measurement of the vertical shift and the horizontal distance between the transducer and the vertex of the reflector, the misalignment of the transducer is quantified. Based on the methodology developed in the present study, retroreflectors are placed in the Indian 500 MWe Prototype Fast Breeder Reactor for assessment of the orientation of the ultrasonic transducer prior to the under-sodium ultrasonic scanning for detection of any protrusion of the subassemblies.     

压电盘簧换能器灵敏度研究

本文介绍的压电盘簧换能器,利用结构对应力具有放大作用的原理,通过利用扭矩实现应力放大,可有效地提高换能器的灵敏度。同时通过设计极化的方法使得g₁₅压电模式得到应用。理论分析和计算结果表明,这种换能器具有很高的灵敏度。     

Contribution to the determination of the energy stability of structural types in crystals

Within the framework of the pair approximation the paper discusses how the interaction radius (measured in units of the coordination spheres of the lattice) must be taken into account so that a given superlattice in a lattice could be energetically stable. An original group-theoretical treatment permits this problem to be solved, even if the required number k of coordination spheres is fairly large (e.g., for the -W structural type on the basis of an auxiliary simple cubic lattice k=14).Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 72–77, June, 1985.     

Experimental determination of sensitivity of piezoquartz microweighing using an electrochemical method

The sensitivity of a piezoquartz microweighing device was determined experimentally using an electrochemical method working in a real time mode. The results obtained confirmed the linearity of the dependence of the piezoquartz generator’s basic frequency drift on the mass of an applied metal for a wide measurement range.     

具有大指向性开角及高发射电压响应的发射换能器

应用复合变幅杆及夹心式换能器结构,研制了一种指向性开角较大且发射电压响应较高的发射换能器。应用有限元方法对换能器的工作频率,发射电压响应及指向性进行了理论计算。并与实验结果进行了比较,结果较吻合。本文研制的换能器工作频率为75.6kHz,发射电压响应级达到1 56dB(基准值1V/μPa),-3dB发射指向性开角100°     

Control of an ultrasonic transducer to realize low speed driven

This paper deals with the control of a transducer to realize low speed. A new PWM control is proposed to fit the transducer. By this control method, the transducer is directly excited by pulses whose width can be modulated. The noise induced by conventional PWM control is eliminated and the motor works more steadily and more quietly. Instead of the general method of decreasing vibrating amplitude of ultrasonic motor to realize low speed, in this paper, two fast contrary elliptical vibrations of the transducer's two Langevin vibrators are excited to restrain skip-slip influence on ultrasonic motor's low speed performance and the driven is realized by the difference of the two vibrators' vibrating amplitudes. Experiments had been carried out by driving an aerostatic guide and fuzzy control is applied. The controlled speed reached 0.1 mm/s.     

Receiving sensitivity and transmitting voltage response of a fluid loaded spherical piezoelectric transducer with an elastic coating

A method is presented to determine the response of a spherical acoustic transducer that consists of a fluid-filled piezoelectric sphere with an elastic coating embedded in infinite fluid to electrical and plane-wave acoustic excitations. The exact spherically symmetric, linear, differential, governing equations are used for the interior and exterior fluids, and elastic and piezoelectric materials. Under acoustic excitation and open circuit boundary condition, the equation governing the piezoelectric sphere is homogeneous and the solution is expressed in terms of Bessel functions. Under electrical excitation, the equation governing the piezoelectric sphere is inhomogeneous and the complementary solution is expressed in terms of Bessel functions and the particular integral is expressed in terms of a power series. Numerical results are presented to illustrate the effect of dimensions of the piezoelectric sphere, fluid loading, elastic coating and internal material losses on the open-circuit receiving sensitivity and transmitting voltage response of the transducer.     

Strong-field molecular ionization: determination of ionization probabilities calibrated with field-free alignment

We report an original optical method providing the probability of molecular ionization induced by femtosecond laser pulses. The approach consists of exploiting molecular alignment to extract reliable information about ionization. The cross defocusing technique implemented for this purpose reveals a sensitivity with respect to postpulse alignment, as well as to the free electron density induced by the ultrashort laser pulse. The analysis of the resulting signal thus gives access to absolute single-ionization probabilities calibrated through the degree of alignment, provided that free electrons are produced mainly by single ionization. The relevance of the method is assessed in N2.     

高感光度测定研究

研究了感光材料高感光度测定方法 ,并将工作标准感光仪改造成适合高感光度范围的感光测定仪 ,解决了现有感光仪无法测定高感光度的问题。     

Methodologies for determination of soil ionization gradient

In this paper the results of the research being carried out on the impulse characteristics of soils and more specifically the ionization voltage gradient are presented. The determination of the soil ionization voltage and the respective gradient using a universally accepted method is yet to be established. Aiming at meeting this need, the present paper critically presents these methods and records the ionization gradient values for soil types, which have derived from different experimental approaches. The comprehensive study of these methods is intended to serve as a guide for researchers studying the nonlinear phenomena developed in the soil.     

Liquid ionization chambers for LET determination

Modern radiotherapy facilities for cancer treatment such as the Heavy Ion Therapy Centre (HIT) in Heidelberg (Germany) enable sub millimetre precision in dose deposition. For the measurement of such dose distributions and characterization of the particle beams, detectors with high spatial resolution and high sensitivity are necessary. For exact dosimetry which is done using ionization chambers (ICs), the recombination taking place in the IC has to be known. Up to now, recombination is corrected phenomenologically and more practical approaches are currently used. Nevertheless, Jaffés theory of columnar recombination was designed to model the detector efficiency of an ionization chamber. Here, we have shown that despite the approximations and simplification made, the theory is correct for the LETs typically found in clinical radiotherapy employing particles from protons to carbon ions. As no exact closed solution is available, a numerical solver was programmed.     

The relative ionization gauge sensitivity of some unsaturated hydrocarbons

By studying the water desorption rate from an oxygen covered Pd surface which is exposed to some unsaturated hydrocarbons (and hydrogen) the relative ionization gauge sensitivity of the hydrocarbons: acetylene, ethylene, propene, 1- and 2-butene, propadiene, 1,3-butadiene, propyne and butyne has been determined.     

On driving a transducer to produce pulses shorter than the natural period of the transducer

When an acoustical transducer is given a short electrical impulse, the pressure wave produced is usually some sort of damped sine wave whose exact shape is determined by the physical properties of the transducer and the medium to which it is coupled. In order to produce pressure pulses shorter than this, it is necessary to drive the transducer with a more complex waveform. This paper describes how to calculate and produce the voltage waveform for any desired pressure waveform and shows some examples of the voltage waveforms necessary to drive a loudspeaker to produce pulses shorter than the natural resonant period of the loudspeaker.     

Sound field of an electromagnetic acoustic transducer

The characteristic of radiated sound field excitated within a non-ferromagnetic aluminum by an electromagnetic acoustic transducer consisting of circle-spiral coil and vertical bias magnetic field is studied.This article presents an improved force source model according to the principle of electromagnetic induction.Then the analytic displacement solution of sound field produced by that force source model is deduced.The tangential and normal directivities of shear and longitudinal sounds are calculated numerically and compared with experimental results.Experimental results conform well to the theoretical prediction,which not only shows that the electromagnetic acoustic transducer of this conformation has a good directivity of vertical shear-wave radiation,but also confirms the given force source model is effective to describe the actual physical behavior of the probe.Theoretical and experimental study lays a foundation for optimization design and engineering application of the electromagnetic acoustic probe.     

Increasing the sensitivity of atomic absorption determination of iron

We have studied the effect of the nature and concentration of surfactants on the atomic absorption of iron. We show that using sodium dodecylbenzenesulfonate as the modifier in flame atomic absorption determination of iron in real samples makes it possible to make the measurements in a low-temperature flame (propane-butane-air type) with increased sensitivity and selectivity and also a lower detection limit for iron. We have developed a procedure for atomic absorption determination of iron in food products using sodium dodecylbenzenesulfonate as the modifier. The detection limit for iron is C_min = 0.008 μg/cm³. Report given at the International Congress of Analytical Sciences, ICAS-2006, 20–30 June 2006, Moscow, Russia __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 2, pp. 263–266, March–April, 2007.     

Contribution to the determination of the Fermi surface of V3Si by positron annihilation

The angular correlation of the positron annihilation radiation has been measured with a bi-dimensional apparatus in the (100) and (110) planes of V₃Si. The main features of the Fermi Surface are determined.