Magnetic measurements in resonance systems

Existing methods of measuring uhf properties of ferromagnetic substances in a resonator (and in lumped resonance systems) become inapplicable even for small samples as the Q of the electromagnetic system is increased. By regarding the magnetization oscillations in the specimen as an oscillatory system with two degrees of freedom, the possibility of measuring ferromagnetic resonance parameters in high-Q electromagnetic systems is studied.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 8, pp. 87–91, August, 1971.     

Acoustic streaming with resonance gas oscillations in a cylindrical tube

Acoustic streaming accompanying acoustic resonance oscillations of gas in a tube is considered. The effect of both the Prandtl number and the wall loss on the velocity of acoustic streaming in a viscous heat-conducting medium is investigated. Expressions for the longitudinal and transverse components of the flow velocity are obtained.     

利用PASCO传感器研究管中声波的共振

利用PASCO传感器测量了共振管中的声压分布,结果与基于多重反射的理论分析符合很好.在此基础上,测量了共振管开口端对管内声波的反射系数及其对频率的依赖关系.     

In situ optical measurements of bacterial endospore breakdown in a shock tube

The interaction of endospore-laden bioaerosols and shock waves is monitored with a combination of laser absorption and scattering. Tests are performed in the Stanford aerosol shock tube for post-shock temperatures ranging from 400–1100 K. In situ laser measurements at 266 and 665 nm provide a real-time monitor of endospore morphology. Scatter of visible light measures the integrity of endospore structure, while absorption of UV light provides a monitor of biochemicals released by endospore rupture. For post-shock temperatures greater than 750 K endospore morphological breakdown is observed. A simple theoretical model is employed to quantify the optical measurements, and mechanisms leading to the observed data are discussed.     

Turbulence in a Maxwell fluid

Three-dimensional homogeneous isotropic turbulence is formulated in terms of a discrete stochastic process in Fourier space. The time-dependent joint probability distribution of the stochastic Fourier modes is governed by a multivariate master equation. It is demonstrated that the characteristic functional of the stochastic process obeys the Hopf functional equation. As a first application of the method stochastic simulations of the Burgers's turbulence model are performed and shown to yield the expected energy spectrum.     

Turbulence in a gas laser

We test a recent assertion [A. Muriel, Physica A 388 (4) (2009) 311] that a gas consisting of excited molecules is turbulent, in contrast to the laminar state of a gas of ground state molecules. Since a lasing gas is made up of excited molecules, we examine if a lasing gas system is indeed turbulent. Surprisingly, from a literature search, it appears that turbulence in a lasing gas medium has never been addressed. To test for turbulence, we use a recently proposed criterion for the existence of turbulence, the presence of multivalued steady-state velocity fields [P. Getreur, A. Albano, A. Muriel, Phys. Lett. A 366 (2007) 101]. To study this subject, we improve an old model of a gas of two-level atoms in a one-dimensional model [A. Muriel, M. Dresden, Physica D 94 (1996) 103] by including the effect of a radiation field with the use of Einstein A and B coefficients. A set of coupled equations for the velocity fields in one dimension are derived. The zeroth order implementation of an iterative solution establishes that the steady-state velocity fields are multivalued, given by the Lambert function. We obtain signature characteristics of turbulence such as velocity reversals, infinite gradients, and stagnation points.     

Simple sound transmission loss measurements using a modified impedance tube technique

A method of comparing the sound transmission characteristics of various materials, and combinations of materials, is presented, using a modified impedance tube technique. The procedure proved to be relatively quick and inexpensive in comparison with standard reverberation suite tests, and is therefore particularly useful for the qualitative ranking of multiple samples.The limitations of the technique are discussed in some detail, and particular emphasis is given to the problems of small sample size and method of mounting in the apparatus.     

Investigation of sample size effects in impedance tube measurements

A series of careful impedance tube measurements using different sizes of glass fibre and felt samples have demonstrated that frame resonance effects result from slightly oversize samples. The appropriate size of a sample is investigated while also avoiding air leakage. Diameters of 0.5 or 1.0 mm less than the inner diameter of the tube are found to avoid these effects.     

Ethanol ignition in a high-pressure shock tube: Ignition delay time and high-repetition-rate imaging measurements

Ethanol is known to be prone to pre-ignition in internal combustion engines under high-load conditions and its ignition shows large deviations from ideal, spatially, and temporally-homogeneous ignition in shock tubes at moderate temperatures (800–950 K). In this context, the ignition of stoichiometric ethanol/O₂ mixtures with various levels of inert gas dilution was investigated in a high-pressure shock tube at ?20 bar between 800 and 1250 K. Ignition delay times were determined from spatially integral detection of chemiluminescence emission. Additionally, high-repetition-rate color imaging enabled the differentiation of the luminescence in time, space, and spectral range between various ignition modes. In the low-temperature range (800–860 K), different inhomogeneous ignition modes were identified. The addition of small amounts of helium into the undiluted fuel/air mixture was found to be efficient to mitigate pre-ignition, attributed to a variation in heat transfer and thus suppression of the build-up of local temperature inhomogeneities. The experiments in case of spatially homogeneous ignition show very good agreement with the predictions based on three detailed kinetics mechanisms (Zhang et al., CNF 190 (2018) 74, Frassoldati et al., CNF 159 (2012) 2295, and Zhou et al. CNF 197 (2018) 423), inhomogeneities, however, resulted in a shortening of the ignition delay times up to a factor of 2.6.     

High-resolution resonance measurements of the physisorption interaction

Narrow selective adsorption resonances, with line widths given by the natural lifetime of the intermediate resonance state, have been observed directly in the angular distributions of Ne nozzle beams diffracted from a 20 K Cu(110) surface. Using beams of 20Ne and 22Ne isotopes we show that this high-resolution mode of resonance detection permits, even in a case of a small isotope effect, unique assignment of bound level sequences compatible with a single gas-surface potential curve.     

On a Shock Front in Burgers Turbulence

We investigate how chaos propagates in the solution of Burgers equation _t u+u _x u=0 with initial condition u(,0) distributed as a white noise on and 0 on . We describe the evolution of the shock front that travels to the left. Asymptotics are given for both large and small time t.     

Precisiong-factor measurements of electron paramagnetic resonance standards

An attempt is made to measureg-factors of electrons in EPR standard samples with the lowest obtainable uncertainty. An experimental equipment for preciseg-factor measurements is described, working at microwave frequencies in the 9 and 36 GHz region, and at room temperature. The course of the measuring process is mentioned in some detail and the sources of errors, which arise during the measurement, are discussed. As an example, the determination ofg-factors of certain EPR standards (using DPPH single crystals and powdered charred dextrose) is presented. No dispersion ofg-factor value has been observed between 9 and 36 GHz.     

Turbulence of a free surface

We study the free surface of a turbulent channel flow, in particular, the relation between the statistical properties of the wrinkled surface and those of the velocity field beneath it. For an irregular flow shed off a vertical cylinder, surface indentations are strongly correlated with vortices in the subsurface flow. For fully developed turbulence this correlation is dramatically reduced. This is because the large eddies excite random capillary-gravity waves that travel in all directions across the surface. Both their predominant wavelength and their anisotropy are determined by the subsurface turbulence.     

Porosity measurements in natural porous rocks using magnetic resonance imaging

A magnetic resonance imaging (MRI) method is presented to measure localized porosity values inside natural porous rocks for the purpose of obtaining frequency distributions of the porosity (porosity distributions). The method is applied to study six different cores, including three Berea sandstone samples, Casper sandstone, Indiana limestone, and San Andres dolomite. An image of the porosity is shown for a transverse and a longitudinal slice in order to show qualitative variations of the porosity within each core sample. The porosity distribution for the entire core has been acquired, and it is shown with a Gaussian fit to the data. In addition, for cores known to have a layered structure, a bimodal distribution is fit to the data, and the fit is used to estimate the value of the porosity for two characteristic types of layers within the core sample.     

Turbulence as a Problem in Non-equilibrium Statistical Mechanics

First, we obtain decay rates of probabilities of tails of polynomials in several independent random variables with heavy tails. Then we derive stable limit theorems for sums of the form \(\sum _{Nt\ge n\ge 1}F\big (X_{q_1(n)},\ldots ,X_{q_\ell (n)}\big )\) where F is a polynomial, \(q_i(n)\) is either \(n-1+i\) or ni and \(X_n,n\ge 0\) is a sequence of independent identically distributed random variables with heavy tails. Our results can be viewed as an extension to the heavy tails case of the nonconventional functional central limit theorem from Kifer and Varadhan (Ann Probab 42:649–688, 2014).     

In-beam quadrupole interaction measurements by level mixing resonance

A new method to measure the quadrupole interaction of in-beam produced isomeric nuclear states is proposed. A simplified version of the theory, adapted to the particular experimental configuration of an in-beam experiment is described.     

Frequency dependence of the ferromagnetic resonance width in magneto-impedance measurements

Giant magneto-impedance has shown large sensitivities that are of great interest in practical applications. Above certain frequencies the ferromagnetic resonance controls the magneto-impedance behavior, and the resonance width limits the maximum achievable magneto-impedance ratio. In this work we present the evolution of the resonance width as a function of the frequency, determined through magneto-impedance and microwave absorption measurements on a NiFe–Au multilayer thin film. The width of the resonance can be fitted to a curve in the form of Δf∼f⁻¹. This is explained by means of a simple model taking into account all inhomogeneities in the sample through a Gaussian distribution of anisotropy fields, as suggested by the shape of the hysteresis loop.