Electrodynamics of Amorphous Media at Low Temperatures

Amorphous solids exhibit intrinsic, local structural transitions, that give rise to the well known quantum-mechanical two-level systems at low temperatures. We explain the microscopic origin of the electric dipole moment of these two-level systems: The dipole emerges as a result of polarization fluctuations between near degenerate local configurations, which have nearly frozen in at the glass transition. An estimate of the dipole's magnitude, based on the random first order transition theory, is obtained and is found to be consistent with experiment. The interaction between the dipoles is estimated and is shown to contribute significantly to the Gr\"{u}neisen parameter anomaly in low $T$ glasses. In completely amorphous media, the dipole moments are expected to be modest in size despite their collective origin. In partially crystalline materials, however, very large dipoles may arise, possibly explaining the findings of Bauer and Kador, J. Chem. Phys. {\bf 118}, 9069 (2003).Comment: Submitted for publication; April 27, 2005 versio

Detection of Aircraft Component Defects Using Low Voltage Excitation of Ultrasonic Transducers

Large areas of composite primary structure are now to be found both on civil and military aircraft throughout the world and the inspection of these structures contributes significantly to overall operating costs. Therefore methods to reduce the inspection time, whilst maintaining an acceptable minimum defect detection capability, are required in order to optimize the potential cost saving benefits offered by using that carbon fiber composite material

Mapping a nation’s landslides: a novel multi-stage methodology

Through combining new technologies and traditional mapping techniques, the British Geological Survey (BGS) has developed a novel, multi-stage methodology for landslide mapping. 3-D aerial photograph interpretation, variable-perspective 3-D topographic visualisation and field mapping with digital data capture are being used to map the UK’s landslides. The resulting ESRI ArcGIS polygons are published on BGS 1:50,000 geological maps and as digital data products. Data collected during mapping are also uploaded directly into the National Landslides Database maintaining a systematic, nationally-uniform landslide inventory. Repeat monitoring of selected landslides using terrestrial LIDAR and dGPS allows the database to be frequently updated and the proactive Landslide Response Team means that new landslide events can be mapped within days, if not hours, of their occurrence. The long-term aim is to apply this methodology throughout the UK, providing a wealth of data for scientific research and hazard assessment. This methodology is also suitable for application in an international context

Theoretical Study of High Frequency Ultrasonic Wave Attenuation in Polycrystalline Materials

Three different regimes for scattering of ultrasonic waves in poly-crystalline materials exist, depending on the ratio of the mean grain size to the wavelength: (i) the low frequency (Rayleigh) region with scattering-induced attenuation proportional to the fourth power of the frequency and to the cube of the mean grain diameter, (ii) the medium frequency (stochastic) region with scattering proportional to the square of the frequency and to the mean grain diameter, and (iii) the high-frequency (geometric) region with scattering independent of frequency

Evaluating the Integrity of Adhesive Bonds by the Measurement of Acoustic Properties under Stresses

Adhesively bonded components and structures are widely used in many critical aerospace applications. Several techniques have been developed to evaluate the integrity of adhesive bonds nondestructively. Most of the techniques rely on the ability to correlate the bond integrity to the behavior of the bondline region to elastic wave propagation. Testing for the relative rigidity between the adherend and adhesive layer at the bond interface will yield reliable information of the bond integrity. This can be achieved by either applying stress in the bondline region externally, or be induced internally

Leadership for change

This edited volume reveals how the journey of transformation at the University of the Free State (UFS) became interwoven with student leadership development and global learning. The UFS initiated two intersecting co-curricular programmes, namely, the First-Year Leadership for Change (F1L4C) programme in 2010; and the triennial Global Leadership Summit (GLS) in 2012. Although these programmes changed over time, their core focus remained to be the development of transformational student leaders through the creation of global learning spaces. From its inception in 2010 to the last GLS in 2018, the UFS global learning project involved 780 students and 259 staff members from 109 institutions, across four continents. The goal of this edited volume is to create a deeper understanding of how the UFS F1L4C and GLS programmes enhanced student leadership development through global learning, especially in the context of higher education transformation

Uniaxial Stress Effects on the Low-Field Magnetoacoustic Interactions in Low and Medium Carbon Steels

In the past, we have shown that the low-field magnetoacoustic technique is capable of detecting uniaxial compression in steel components without necessiating a calibration standard [1,2]. This is because the initial slope of the AF(B)/F curve (fractional frequency change of phase-locked acoustic waves as a function of net magnetic induction) is negative only under compression and positive otherwise, when the specimens are magnetized along the static unaxial stress axis.</p

Measurement of Viscosity in Liquids Using Reflection Coefficient: Phase Difference Method

Measurement of viscosity of fluids is a critical parameter in determining the state of the fluid (ie. edible products), and the state of the forming solid (ie. molten metals and glasses). Experiments to measure viscosity using ultrasound, have been carried out since as early as 1951 [1]. Ultrasound has potentially offered a non-invasive, in-line method of property and process monitoring [2,3]. Early research has demonstrated that viscosity measurement can be accomplished by ultrasound using different linear and nonlinear techniques [4]. This paper is devoted to furthering the technique called shear reflectance method [5]

Precision Ultrasonic Thickness Measurements of Thin Steel Disks

The accurate in-situ measurement of part dimensions during fabrication is of much interest to the manufacturing industry, especially for untended manufacturing. The goal of this work is to apply non-contacting ultrasonic techniques to the precise thickness measurement, during machining, of metal parts of rotation having a nominal wall thickness of 1.5 mm. The desired accuracy is ±.0025 mm at all points on the approximately 200 mm diameter steel shells, where part access is restricted to one side at a time for the measurement. In a feasibility study, dimensional information using eddy current techniques was overwhelmed by conductivity variations in the 304-stainless steel samples [1]. The approach here is to precisely measure ultrasonic echo transit times, and calulate part dimensions, knowing the material sound speed. To that end, feasibility results on flat disk specimens possessing a wide range of grain sizes representative of the shell’s variable metallurgy are reported here. Factors affecting ultrasonic dimensional precision including grain size, texture, sample temperature and surface roughness are discussed, with an emphasis on precision limitations due to finite grain sizes in thin parts. Both longitudinal (10 to 30 MHz) and shear (3 MHz) wave measurements were made, the latter using electromagnetic acoustic transducers (EMATS).</p

Leadership for change

This edited volume reveals how the journey of transformation at the University of the Free State (UFS) became interwoven with student leadership development and global learning. The UFS initiated two intersecting co-curricular programmes, namely, the First-Year Leadership for Change (F1L4C) programme in 2010; and the triennial Global Leadership Summit (GLS) in 2012. Although these programmes changed over time, their core focus remained to be the development of transformational student leaders through the creation of global learning spaces. From its inception in 2010 to the last GLS in 2018, the UFS global learning project involved 780 students and 259 staff members from 109 institutions, across four continents. The goal of this edited volume is to create a deeper understanding of how the UFS F1L4C and GLS programmes enhanced student leadership development through global learning, especially in the context of higher education transformation