Nonlinear Ultrasonic Properties of As-Quenched Steels

We have investigated the effect of carbon content on the nonlinear ultrasonic parameter β and the longitudinal phase velocity v L in a series of martensitic steel specimens. The specimens were measured in the as-quenched state to insure that the carbon was present primarily as an interstitial in the martensite. Experimentally, β increased with increasing mass percent carbon (or hardness), while v Lremained virtually the same for all specimens. Therefore we conclude that β is sensitive to microstructural variations between the specimens, but v L is not. X-ray diffraction experiments indicate that the dislocation density in the specimens is high (∼1011/cm2) and increases with increasing carbon content. These results support the hypothesis that the observed increase in β may be attributed to dislocations affected by internal stresses in the quenched specimens

Nonlinear acoustic and microwave absorption in glasses

A theory of weakly-nonlinear low-temperature relaxational absorption of acoustic and electromagnetic waves in dielectric and metallic glasses is developed. Basing upon the model of two-level tunneling systems we show that the nonlinear contribution to the absorption can be anomalously large. This is the case at low enough frequencies, where freqeuency times the minimal relaxation time for the two-level system are much less than one. In dielectric glasses, the lowest-order nonlinear contribution is proportional to the wave's intensity. It is negative and exhibits anomalous frequency and temperature dependencies. In metallic glasses, the nonlinear contribution is also negative, and it is proportional to the square root of the wave's intensity and to the frequency. Numerical estimates show that the predicted nonlinear contribution can be measured experimentally

Enormous shrinkage of carbon nanotubes by supersonic stress and low-acceleration electron beam irradiation

The authors demonstrated a new method for inducing enormous shrinkage in single-walled carbon nanotube bundles by applying low energy electron beam irradiation along with supersonic vibration, and a maximum shrinkage rate of −100% cm2/C was obtained under electron acceleration of 1 keV. The characteristic feature of the shrunken single-walled carbon nanotubes was a wavy deformation that affected the entire bundle. The authors believe that a uniaxial stress induced by the supersonic vibration broke the equilibrium of the internal stress and allowed the uniform accumulation of defects under low energy electron beam excitation. The wavy deformation of the single-walled carbon nanotubes resulted in the enormous shrinkage of the bundle

Histomorphometric analysis of minimodeling in the vertebrae in postmenopausal patients treated with anti-osteoporotic agents

AbstractMinimodeling is a type of focal bone formation that is characterized by the lack of precedent bone erosion by osteoclasts. Although this form of bone formation has been described for more than a decade, how anti-osteoporotic agents that are currently used in clinical practice affect the kinetics of minimodeling is not fully understood. We performed a bone morphometric analysis using human vertebral specimens collected from postmenopausal patients who underwent spinal surgery. Patients were divided into three groups according to osteoporosis medication; non-treated, Eldecalcitol (ELD, a vitamin D derivative that has recently been approved to treat patients with osteoporosis in Japan)-treated, and bisphosphonate-treated groups. Five to six patients were enrolled in each group. There was a trend toward enhanced minimodeling in ELD-treated patients and suppressed of it in bisphosphonate-treated patients compared with untreated patients. The differences of minimodeling activity between ELD-treated and bisphosphonate-treated patients were statistically significant. The present study suggests that ELD and bisphosphonates have opposite effects on minimodeling from one another, and show that minimodeling also takes place in vertebrae as has been described for the ilium and femoral head in humans

Nonlinear acoustic and microwave absorption in disordered semiconductors

Nonlinear hopping absorption of ultrasound and electromagnetic waves in amorphous and doped semiconductors is considered. It is shown that even at low amplitudes of the electric (or acoustic) field the nonlinear corrections to the relaxational absorption appear anomalously large. The physical reason for such behavior is that the nonlinear contribution is dominated by a small group of close impurity pairs having one electron per pair. Since the group is small, it is strongly influenced by the field. An external magnetic field strongly influences the absorption by changing the overlap between the pair components' wave functions. It is important that the influence is substantially different for the linear and nonlinear contributions. This property provides an additional tool to extract nonlinear effects.Comment: correction : misspelled name in references correcte

Acoustic Harmonic Generation Measurements for Materials Characterization

In the first presentation of the Otto Buck memorial session, Dr. Donald Thompson described contributions of Dr. Otto Buck on the theories of finite amplitude waves and elastic constants and his experimental work involving reflections from stress free interfaces and harmonic generation. The speakers following Dr. Thompson described many more of Dr. Buck’s contributions in a wide variety of topics. Listening to the sessions speakers talk of their work with Otto made this author realize just how wide Otto’s interests and expertise were. Here, we come full circle and discussed the preliminary results of work which relates directly to contributions remembered by Dr. Thompson regarding harmonic generation. This work was initiated by Dr. Buck at the Ames Laboratory and continues there.</p

Dislocation Kinks in Copper: Widths, Barriers, Effective Masses, and Quantum Tunneling

We calculate the widths, migration barriers, effective masses, and quantum tunneling rates of kinks and jogs in extended screw dislocations in copper, using an effective medium theory interatomic potential. The energy barriers and effective masses for moving a unit jog one lattice constant are close to typical atomic energies and masses: tunneling will be rare. The energy barriers and effective masses for the motion of kinks are unexpectedly small due to the spreading of the kinks over a large number of atoms. The effective masses of the kinks are so small that quantum fluctuations will be important. We discuss implications for quantum creep, kink--based tunneling centers, and Kondo resonances

Damage detection in a laboratory wind turbine blade using techniques of ultrasonic NDT and SHM

This paper presents a case study in the use of ultrasonic NDE/SHM techniques for detecting and locating damage in a real (but small) wind turbine blade. Two techniques are considered: (1) non-linear acoustics, and (2) guided-wave “pitch-catch” SHM. While the non-linear acoustics approach proved disappointingly insensitive to damage induced experimentally in the blade, the guided-wave approach not only detected the damage but also proved capable of locating it, using a “network of novelty detectors” methodology. A first, slightly ill-conceived, programme of guided-wave tests actually provided valuable insight into attenuation of waves in the structure of interest and supported the idea that actuator-sensor networks of a feasible density could be used for wind turbine blade SHM