Nonlinear first sound response of liquid helium at 1, 3 and 10 MHz

The first sound response of liquid helium at 1, 3 and 10 MHz is studied using piezoelectric ceramic transducers. Above specific threshold displacement amplitudes, subharmonic frequencies ($\text{?}{}_0\text{2}$, $\text{?}{}_0\text{3}$,…) and ultraharmonic frequencies ($\text{3?}{}_0\text{2}$, $\text{5?}{}_0\text{2}$,…) appear in the response spectrum. The magnitude of the threshold displacement amplitudes for the production of subharmonics suggests that vapor microbubble oscillation appears not to be the primary generation mechanism.     

Measurement of background noise in sound-insulated rooms

Problems concerning measurement of stationary background noise levels below the dynamic limits of normal transducers are studied. The use of very sensitive large transducers is possible, but in general is restricted to rather low frequencies due to their extreme directional characteristics. Thus a 10 inch transducer may be used up to approximately 250 Hz. Two-transducer approaches based on correlation techniques cover a much wider frequency range because ordinary small transducers are applicable. Measurement errors due to diffraction or to unavoidable spacing of the two transducers generally become significant for transducer diameters in excess of one-quarter of a wavelength at the upper limiting frequency, although an exception to this occurs in the particular case of a plane progressive wave. The use of extremely small insensitive transducers is restricted by the necessity of having very impractical integration times. If measurements of levels down to ?20 dB re 20 μPa are carried out with condenser microphones in one-third octave frequency bands a practical compromise seems to be employment of $\text{1}\text{2}$ inch microphones in the range of center frequencies from 25 Hz to 5 kHz. This range may in practice be doubled (e.g., extended to 10 kHz) if measurements in the range 2·5–5 kHz are carried out with both 1 inch and $\text{1}\text{2}$ inch transducers so that corrections can be obtained for extended range measurements from 5 kHz performed with $\text{1}\text{2}$ inch transducers only.     

Velocity and attenuation of ultrasonic waves in n-GaAs at low temperatures

Measurements of velocity and attenuation of ultrasonic waves in n-type GaAs have been made between 4.2 and 240 K. They are interpreted in terms of available theory dealing with sound propagation in piezoelectric semiconductors. We find the piezoelectric constant $\text{e}{}_{14}\text{=}\text{0.16 C}\text{m}{}^2$.     

Statistical analysis from a sound level meter

Increasingly, and particularly for motorway noise, sound level meters are being used to estimate $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$, the noise level just exceeded for 10 per cent of the time, by noting the meter readings at regular intervals and manually analysing the array of data so obtained. In this paper we describe a simple attachment to a sound level meter, which is intended to ease the operator's task in making such measurements and to minimise operator bias. Comparisons are made between the results of sound level meter measurements of three types of noise and the results obtained using the more conventional technique which employs a level recorder and statistical analyser.It is concluded that, at least for motorway noise, the sound level meter technique gives values of $\text{L}{}_{\mathrm{<mtext>10</mtext>}}$ and of $\text{L}{}_{\mathrm{<mtext>90</mtext>}}$ within 1 dB(A) of the values obtained by the normal method. Furthermore, it is probable that the technique will be useful for the measurement of other types of noise in statistical terms, but further investigations of accuracy are required.     

Strain dependence of the piezoelectric polarization of z-cut lithium niobate

Measurements of the piezoelectric polarization of z-cut lithium niobate are accomplished for dynamic compressive strains of from 8.9 × 10^?4 to 6 × 10^?3. Values for the linear piezoelectric constant, $\text{e}$₃₃ and its strain derivative are determined. The logarithmic strain derivatives of the longitudinal piezoelectric constants of x-cut quartz and z-cut lithium niobate are found to be approximately equal.     

M1 transitions in the (sdg) boson model

Using the $\text{1}\text{N}$ expansion technique we derive expressions for β→g, γ→g and γ→γ M1 transitions in a general boson model. The M1 matrix elements in the sdg-boson model are similar in form to those in the neutron-proton IBM. Comparisons are made to some selected M1 data exhibiting collective character.     

The width of the lattice distortion and the localization energy for a strong-coupled piezoelectric polaron

It is shown that the width of the lattice distortion for a strong-coupled piezoelectric polaron is proportional to $\text{a}{}^{\mathrm{<mtext>?3</mtext><mtext>2</mtext>}}{}_{\mathrm{<mtext>piezo</mtext>}}$. The well-known functional form of the localization energy follows from this result.     

Analysis of derivative spectrum of indirect exciton absorption in silicon

It is shown that an analysis of the wavelength modulated absorption spectrum enables us to estimate the transition matrix elements in indirect absorption. The transition matrix elements in silicon are determined to be $\text{0.110}\text{h}\text{?}\text{A}\text{?}$ for indirect absorption with the TO phonon, $\text{0.0367}\text{h}\text{?}\text{A}\text{?}$ for the LO phonon and 0.0178 $\text{h}\text{?}\text{A}\text{?}$ for the TA phonon.     

Photoproduction of charm and beauty

The photoproduction of charm and beauty are reexamined within QCD. In addition to the photon-gluon amalgamation mechanism, $\text{q}$q → b$\text{b}$ or c$\text{c}$ is also examined. It turns out that for beauty production at SPS photon beams, the $\text{q}$q → b$\text{b}$ mechanism is dominant over γ-g amalgamation for Buras-Gaemers gluon distributions. The possibility of experimental measurement is briefly discussed.     

Nuclear matrix elements in the first-forbidden β-decay of 125Sb

Nuclear matrix elements in the $\text{7}\text{2}$⁺(444 keV β^?)$\text{9}\text{2}$^?(177 keV γ)$\text{11}\text{2}$^? β-γ cascade in have been extracted from the available experimental data. A significant cancellation in the Coulomb-enhanced matrix element combination permits good limits of error to be placed on the individual matrix elements, even though there is not a large amount of experimental data available.     

Comment on the leptonic decay mode of the τ-lepton

The energy spectrum of the e-μ events from τ-decay is analyzed in an attempt to rule out the possibility that the ν_τ is spin-$\text{3}\text{2}$ independent of the observation of the pionic decay mode. While spin-$\text{3}\text{2}$ cannot be completely ruled out in this way, it is only viable for a fairly narrow range of values of a Michel parameter.     

The unitary representations of G̶L(4, R)

In the paper, nine series of unitary representations of the group $\text{G}\text{?}$L(4, R) are found. Moreover, there are obtained matrix elements of the generators of $\text{G}\text{?}$L(4, R) in an orthonormal basis. The elements of the basis are classified over the subgroup SU(2)?SU(2).     

Neutral B-meson decay and the search for hybrid mesons

We discuss the possibility that the decay of the neutral B mesons via a non-spectator mechanism might have a significant branching fraction into $\text{(}\text{q}\text{q}\text{g}\text{)}$ states. The lightest such hybrid mesons would be recognizable as narroe state of mass 1.6 ± 0.4$\text{GeV}\text{c}{}^2$ decaying predominantly into hadrons containing strange quarks.     

The needle in the large pT haystack: Higgs versus quark or gluon jets together with Z0 in hadronic reactions

The possibility of observing a Higgs particle via high p_T bremsstrahlung from a weak Z₀ in p$\text{p}$ and pp collisions is examined. It appears that, although very weak, some signal might be observed in the future p$\text{p}$ collision experiments.     

The crystal structure of SnYb3Rh4Sn12, a new ternary superconducting stannide

The crystal structure of superconducting SnYb₃Rh₄Sn₁₂ has been determined from single-crystal X-ray diffraction data. This compound is cubic, space group Pm3n, $\text{a}{}_{\mathrm{o}}\text{= 9.676}\text{A}\text{?}$ (1) and has two formulae per unit cell. The structure was solved from Patterson and subsequent Fourier synthesis. The least squares refinement was based on 375 independent reflections. The final R and wR factors were 0.015 and 0.014, respectively. The two Sn(1) atoms occupy the 2a (000) positions, the six Yb atoms the 6d ($\text{1}\text{4}$$\text{1}\text{2}$ 0) positions, the eight Rh atoms the 8e ($\text{1}\text{4}$$\text{1}\text{4}$$\text{1}\text{4}$) positions and the twenty-four Sn(2) atoms the 24k (Oyz) positions (y ～ 0.31, z ～ 0.15). The Sn(2) atoms form a tridimensional array of corner-sharing trigonal prisms whose centers are occupied by the rhodium atoms. The Sn(1) and the Yb atoms occupy the icosahedral and cuboctahedral holes of this array, respectively. They form a sublattice which has the arrangement found in the structure of the A15 compounds. The structure of SnYb₃Rh₄Sn₁₂ can be described as containing two interpenetrated structures, namely Yb₃Sn and RhSn₃, or as having an A15 arrangement of clusters of atoms such as (SnSn₁₂) and (YbSn₁₂). These clusters are bound together by face-sharing among them; and by the rhodium atoms. An analogy is drawn between SnYb₃Rh₄Sn₁₂ and the perovskite-like ternary oxides A′A″₃B₄O₁₂.     

Electromagnetic mixing of narrow baryonium states

We discuss the theoretical possibility that electromagnetic mixing in the recently discovered narrow baryon-antibaryon resonances might be comparable to quark configuration mixing, because of the expected smallness of OZI rule violations of those masses. Nearly “pure” quark states could result. This phenomenon could reveal itself in large violations of isospin and G parity at a single peak and could explain the absence of the S(1936) in $\text{p}$p → $\text{n}$n. It should manifest itself most clearly in $\text{p}$n and $\text{n}$p scattering.     

The p-approximations and inverse problems of expansion and contraction of n-fermion operators

The orthogonal projectors from the space $\text{L}$(n) of n-fermion operators onto its sub-spaces $\text{L}$_p(n) consisting of p-reducible elements of $\text{L}$(n>), as well as those from $\text{L}$(n) onto $\text{L}$_p(n)?$\text{L}$_p?1(n) are constructed. Using the above projectors the inverse problems of contraction and expansion are solved.     

Algebraic approach to the theory of chronological products of currents: Part I

An algebra $\text{F}$ of generating functionals for sets of symmetric n-point functions is investigated. It contains a twosided ideal $\text{T}$ of functionals which vanish on mass-shell. Since scattering processes are described by on-mass-shell values of these functionals, it is proposed to formulate the physical conditions of unitarity, relativity and causality (locality) in terms of elements of the algebra $\text{U}\text{′ =}\text{F}\text{/}\text{T}$ of equivalence classes modulo $\text{T}$. In Part I the extended form of the unitarity and relativity condition is discussed. An example of the algebra of coherent functionals is considered. The causality condition will be treated in the second part of this paper.     

Signal processing for damage detection using two different array transducers

This work describes an investigation into the development of a new health monitoring system for aeronautical applications. The health monitoring system is based on the emission and reception of Lamb waves by multi-element piezoelectric transducers (i.e., arrays) bonded to the structure. The emitter array consists of three different elementary bar transducers. These transducers have the same thickness and length but different widths. The receiver array has 32 same elements. This system offers the possibility to understand the nature of the generated waves and to determine the sensitivity of each mode to possible damage. It presents two principal advantages: Firstly, by exciting all elements in phase, it is possible to generate several Lamb modes in the same time. Secondly, the two-dimensional fourier transform (2D-FT) of the received signal can be easily computed. Experimental results concerning an aluminum plate with different hole sizes will be shown. The A0-, S0-, A1-, S1- and S2-modes are generated at the same time. This study shows that the A0 mode seems particularly interesting to detect flaws of this geometrical type.