Size effects and interactions in La0.7Ca0.3MnO3 nanoparticles

La_0.7Ca_0.3MnO₃ (LCMO) nanoparticles with average diameter of 16-73 nm were prepared by reactive milling and thermal processing methods. Interaction and size effects on the magnetic properties of the LCMO nanoparticle samples were investigated. Phenomena related to the interparticle interaction, such as an un-overlapping of the M(H_ext,T)/M_S vs. H_ext/T scaling plots and a Curie-Weiss rather than Curie law behavior of the dc susceptibility at high temperatures were analyzed. The magnetization curves of interacting nanoparticles were well described by using the mean-field approximation. The dependence of the blocking temperature T_B on the strength of the interactions, magnetic anisotropy, as well as the thermal dependence of magnetization deviates from the expected Bloch law was also estimated.     

Subsurface crack determination by one-sided ultrasonic measurements

Corrosion of steel reinforcement in concrete is a common type of damage. The cracks propagate from the steel bar to the surface without giving any visual sign prior to surface crack formation. As long as the surface material is intact, the sensitivity of the longitudinal wave velocity to the subsurface cracks is doubtful. In this paper, cracks were created in steel fiber reinforced concrete specimens by four point bending. Wave measurements took place on the intact surfaces (compression side) using common acoustic emission transducers. Although there was no visual sign of the crack, Rayleigh as well as longitudinal wave velocities clearly decreased relative to those of the sound material. Other parameters like the amplitude and the experimental scatter of the waves were much more sensitive to damage. Numerical simulations were conducted in order to make a parametric study concerning the depth of the sound layer, the propagating wavelength and the measured wave parameters and propose a firm methodology. It is concluded that by scanning a surface with simple acoustic one-sided measurements, the identification of the location of the subsurface damage is possible, while the propagating wave gives information about the depth of the crack.     

Determining elastic properties of skin by measuring surface waves from an impulse mechanical stimulus using phase-sensitive optical coherence tomography

The mechanical properties of skin are important tissue parameters that are useful for understanding skin patho-physiology, which can aid disease diagnosis and treatment. This paper presents an innovative method that employs phase-sensitive spectral-domain optical coherence tomography (PhS-OCT) to characterize the biomechanical properties of skin by measuring surface waves induced by short impulses from a home-made shaker. Experiments are carried out on single and double-layer agar–agar phantoms, of different concentrations and thickness, and on in vivo human skin, at the forearm and the palm. For each experiment, the surface wave phase-velocity dispersion curves were calculated, from which the elasticity of each layer of the sample was determined. It is demonstrated that the experimental results agree well with previous work. This study provides a novel combination of PhS-OCT technology with a simple and an inexpensive mechanical impulse surface wave stimulation that can be used to non-invasively evaluate the mechanical properties of skin in vivo, and may offer potential use in clinical situations.     

Ultrasonic Evaluation of Adhesive Bonding

The capabilities of existing ultrasonic nondestructive evaluation (NDE) methods for the strength-related properties of bonds in structural components is reviewed. The severe limitations of conventional NDE methods in yielding quantitative results are indicated. Some recent results of a joint theoretical and experimental program of research using leaky Lamb waves (LLW) in laboratory specimens are presented. The LLW technique is shown to have several advantages over conventional techniques. Potential applications of the technique to determine non-destructively the quality of bonds in a variety of models are discussed.     

Microwave magnetoresistance in Ge:Mn nanowires and nanofilms

Abstract

The Lorentzian and spin-scattering components of magnetoresistance were found and distinguished in Ge:Mn thin films. The suppression of microwave magnetoresistance by the limitation of the dimensionality of Ge nanowires doped with Mn has been revealed. Spin-wave resonance in the long-ordered magnetic state and ferromagnetic resonance in GeMn clusters have been detected.     

Effect of different temperature–time combinations on physicochemical,microbiological, textural and structural features of sous-vide cooked lamb loins

Lamb loins were subjected to sous-vide cooking at different combinations of temperature (60, 70, and 80 °C) and time (6, 12, and 24 h). Different physicochemical, histological and structural parameters were studied. Increasing cooking temperatures led to higher weight losses and lower moisture contents, whereas the effect of cooking time on these variables was limited. Samples cooked at 60 °C showed the highest lightness and redness, while increasing cooking temperature and cooking time produced higher yellowness values. Most textural variables in a texture profile analysis showed a marked interaction between cooking temperature and time. Samples cooked for 24 h showed significantly lower values for most of the studied textural parameters for all the temperatures considered. Connective tissue granulation at 60 °C and gelation at 70 °C were observed in the SEM micrographs. The sous-vide cooking of lamb loins dramatically reduced microbial population even with the less intense heat treatment studied (60 °C–6 h).     

Pressure waves as a tool for leak detection in closed conduits

In recent decades, growing water demand and a scarcity of easily exploitable high-quality water sources has reinvigorated interest in the further development of already stressed groundwater resources. Since leakage reduction often means the acquisition of new high-quality water resources, utility managers are realizing that water loss must be considered in plans to extend water supply and leak detection is now perceived as a money-saving expense. Among leak detection methodologies, those based on transient analysis can be some of the fastest and cheapest. This article briefly outlines the properties of pressure waves in closed single pipe systems. Past findings from the analysis of pressure signals within the time domain framework are reviewed and time series of pressure variations acquired in laboratory experiments at one measurement section are examined. Emphasis is placed on the analysis of transient test results in the frequency domain and the use of the wavelet transform for interpreting pressure signals. Both a single pipe system and a wastewater outfall system are examined and discussed.     

Spectral calculations in magnetohydrodynamics using the Jacobi–Davidson method

For the solution of the generalized complex non-Hermitian eigenvalue problems Ax=λBx occurring in the spectral study of linearized resistive magnetohydrodynamics (MHD) a new parallel solver based on the recently developed Jacobi–Davidson [SIAM J. Matrix Anal. Appl. 17 (1996) 401] method has been developed. A brief presentation of the implementation of the solver is given here. The new solver is very well suited for the computation of some selected interior eigenvalues related to the resistive Alfvén wave spectrum and is well parallelizable. All features of the spectrum are easily and accurately computed with only a few target shifts.     

Analysis of plate wave propagation in anisotropic laminates using a wavelet transform

A new approach is presented for the analysis of transient waves propagating in anisotropic composite laminates. The wavelet transform (WT) using the Gabor wavelet is applied to the time-frequency analysis of dispersive flexural waves in these plates. It can be shown that the peaks of the magnitude of WT in a time-frequency domain is related to the arrival times of the group velocity. Experiments were performed using a lead break as the simulated acoustic emission source on the surface of unidirectional and quasi-isotropic laminates. A method was developed to obtain the group velocity of the flexural mode as a function of frequency. Theoretical predictions were made using the Mindlin plate theory, which includes the effects of shear deformation and rotatory inertia. Our predictions on the dispersion of the flexural mode showed good agreement with the experimental results.