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A thermodynamically consistent density dependent quark mass model has been used to study the velocity of sound in a hot quark–gluon plasma. The results are compared with the recent lattice data.

We investigate the equation of state (EOS) and the corresponding sound velocity of the dense matter in hybrid neutron stars. For the hadron matter, the Bruckner–Hartree–Fock (BHF) many-body theory with Bonn-B potential is adopted. For the quark matter, the Dyson–Schwinger quark model is adopted, with the rainbow approximation and the Gaussian type effective interaction for quark–gluon vertex and gluon propagator. The phase transition is considered with both Maxwell condition and Gibbs condition. Then, the sound velocity in the pure hadron phase, pure quark phase and the mixed phase are obtained. The causality requirement $c_s^2\le 1$ puts a strong constraint on the EOS from BHF theory. In quark matter, it is found that $c_s^2\le 1/3$ and varies slowly. In the mixed phase with Gibbs condition, the sound velocity varies strongly and nonmonotonically.

Ultrasonic properties of bulk TlSr₂ (M_{1 - x}Y_x)Cu₂O₇(M = Ca, Sr) high temperature superconductors have been measured between 80 and 280 K. Sound velocity measurements show that all samples exhibit an overall stiffening trend with decreasing temperature. The longitudinal sound velocity shows a pronounced slope change and attenuation peak around 200 K. The results were explained in terms of phase transition and distortion of Tl and O atoms associated with local oxygen ordering. The calculated acoustic Debye temperature does not show strong correlation with the transition temperature. The electron-phonon coupling constant was calculated using the weak and strong limit of the BCS theory as well as the van Hove scenario.

A series of Al–Mg_x alloys, with x = 0.82, 2.09, 2.28, 2.49 and 4.47 wt.%, respectively were characterized by using positron annihilation lifetime studies (PAL), X-ray diffraction (XRD), and sound velocity and internal friction using a vibrating reed technique (VRT). PAL lifetime values increase linearly as the composition is varied, but texturing or preferential orientation is maximum at an intermediate value of composition (x = 2.49%). The internal friction shows a minimum at the same composition, and the sound velocity changes show the maximum value here too. This means that at this composition the sample is the most ordered and defect free.

The success of modern electronics is built on the possibility to accurately predict system behavior by using simulation tools. This paradigm can be extended to components such as piezoelectric transducers attached to the electronics. The ability to simulate both piezoelectric transducer and electronics together renders possible effective optimizations at system level, i.e. minimizing size, cost and power consumption. In this paper a computer simulation of a combined electronics and piezoelectric transducer system is explored. The analogy between acoustic wave propagation and wave propagation in an electric transmission line is given. The simulation approach is applied to a pulser-receiver setup for the determination of speed of sound and attenuation in liquids. Experiments and simulations are made for fixed temperature and in the frequency range 1–10 MHz using ethanol, methanol, carbon tetrachloride, acetone, benzene and distilled water as test samples. Comparison shows a good agreement between simulation and experiments. Furthermore, the use of an ultrasonic simulation package allows for the development of the associated electronics to amplify and process the received ultrasonic signals.

The longitudinal and shear sound velocity in colossal magnetoresistive La_1-xSr_xMnO₃ (x = 0.0, 0.05, 0.15 and 0.3) were measured using the pulse-echo-overlap technique in the temperature range of 80 to 300 K. An abrupt increase in the longitudinal velocity was observed immediately below the insulator-metal transition (T_im) in the x = 0.05 and 0.15 samples. This anomaly shifted towards higher temperature with an increase in Sr content. The absolute velocities (measured at 80 K) increased with Sr content. Hystereses in the longitudinal and shear velocity were observed in the x = 0.05 and 0.15 samples. A step-like longitudinal sound velocity anomaly between 150 K and 220 K during warming and cooling was observed in the x = 0.05 sample. A sudden hardening was observed for longitudinal and shear sound velocity coinciding with second broad resistance peak at temperature below T_im in x = 0.15 sample. The characteristic Debye temperature increases as Sr content was increased, indicating a hardening trend. These results indicate the importance of phonons in the transport mechanism of these colossal magnetoresistive materials.

Al has unique intrinsic characteristics, which are of interest to scientists as well as engineers. Al and its alloys are slightly paramagnetic materials. Al has very low cross section for thermal neutrons of 0.23 barn, hence Al can be used in nuclear fields as a structural material which is virtually transparent to neutrons. We report VRT as a new technique to study material problems. We also discuss, the results of sound velocity and internal friction, and resonance frequency as a function of temperature range for a pure aluminum sample under investigation. By using VRT, we found that the annealing temperature (450°C) is sufficient to remove the type of defects introduced in the materials under study. The activation energy to remove point defect for Al samples was calculated and found to be about 0.0624 eV. Also, we could easily observe that Q^-1 is a function of annealing time. From these measurements of sound velocity and internal friction we can conclude that VRT is a powerful tool for detecting and probing the physical properties of the material under study. Internal friction is a microscopic property for the indication of the purity of the sample. Sound velocity depends on the state of the materials (which depends on the process of treatment).

Various carbon nanostructures, including graphene, are of great interest nowadays for many applications. It has been shown that graphene has unique physical and mechanical properties and its properties can be controlled by the applied strain. The objective of the present paper is to describe several physical properties of graphene that can be controlled by means of elastic strain engineering. The space of in-plane elastic strain components is divided into regions with different structural configurations and physical properties of graphene. It is shown that a gap in the phonon density of states is observed when graphene is strained close to the appearance of ripples. Sound velocities of unstrained graphene do not depend on the propagation direction but application of strain, apart hydrostatic tension, makes graphene elastically anisotropic. The orientation, amplitude and wavelength of unidirectional ripples in graphene can be controlled by a change in the components of the applied strain.