Thilo M. Brill

Elastic properties of NiTi

The authors present measurements of the elastic constants on a single crystal of the shape-memory alloy NiTi in a wide temperature range. Step-like anomalies and hysteresis are detected at the austenitic-martensitic phase transition which provide evidence for the strain-order parameter coupling in the pre-martensitic phases. The results are discussed in the framework of existing Landau theory models.

MAGNETIC RESONANCES IN THE ONE-DIMENSIONAL S=1 SPIN SYSTEM NENP

Magnetic resonance experiments in the frequency range 55–404 GHz in magnetic fields up to 14 T are presented. Comparison with an existing field theoretical model leads to gap parameters and critical fields that are only slightly different from those obtained by neutron scattering experiments at q=π. Temperature dependent resonance signal intensities of various branches are compared to calculated intensities in the framework of Boltzmann statistics for temperatures between 1.5 K and 18 K. In this way resonance branches are assigned to transitions within a scheme of energy levels.

Use of LaBr 3 for downhole spectroscopic applications

The use of lanthanum bromide (LaBr3) in commercial applications has increased rapidly over the last few years owing to its very favorable properties, e.g., excellent spectral resolution, high speed, high light output, and efficiency.

High-field ESR in the s=1 Heisenberg antiferromagnetic chains of NENP

ESR studies of the excitation spectrum of Haldane spin systems are presented. We performed temperature-dependent high-field and high-frequency ESR measurements up to 21 T and 1042 GHz on the compound NENP [Ni(C2H8N2)2NO2ClO4]. Based on extensive experimental investigations we propose to distinguish between different classes of resonances: first, the transitions between excited states at the boundary of the Brillouin zone (q=π) below the critical field; second, the high-frequency transitions from the ground state (q=0) above the critical field and third, the low-frequency resonances at q=0 in the whole field range. New results are presented in the high-field phase, which exhibit an appreciable temperature dependence of the resonance field and at low temperatures show the existence of multiple high-frequency excitation branches. In the low-frequency regime we also observed an additional ground state excitation.

SPIN-POLARIZED HYDROGEN IN A HIGH FIELD TRAP : TOWARDS A TWO-COMPONENT BOSE GAS

We have loaded spin-polarized hydrogen (SPH) into a magnetostatic Ioffe trap with central fields as high as 1 T and at two different temperatures, 0.25 and 0.4 K, on the way to create a gas of SPH with two distinguishable Bose component. We have measured the magnetic dipole decay rate constant of SPH at these high fields and found good agreement with theory. A measurement technique that allows determination of the absolute number of atoms was developed.

Relaxation dynamics in the high-frequency crystal-field spectroscopy of PrNi5 point contacts

High-frequency point-contact (PC) spectroscopy is used to investigate the kinetics of relaxation processes in the intermetallic rare-earth compound PrNi5. A difference is observed in the spectral response between the conventional low-frequency PC data and the response signal to microwave and far-infrared radiation of PrNi5–Cu point contacts. This difference is connected with the f-shell electronic levels (CEF levels) and phonon temporal dynamics. The phonon reabsorption contribution to the spectra above the Debye energy decreases for microwave and far-infrared frequencies. However, the crystal-field contribution to the spectra at 4.2 meV is enhanced for high frequencies, reflecting the relaxation processes specific for these Fermi-statistics electronic excitations. The characteristic frequency for CEF-level relaxation is evaluated as ∼200 GHz.

Haldane gap observation in TMNIN by electron spin resonance

Abstract Electron spin resonance (ESR) measurements on powder samples of the quasi-one-dimensional S = 1 Heisenberg antiferromagnet (CH 3 ) 4 NNi(NO 2 ) 3 (TMNIN) were performed for the first time in the frequency range 55–400 GHz in magnetic fields up to 14 T at temperatures down to 1.3 K. Resonance lines can be associated with transitions between excited states in the framework of a field theoretical model. The field dependence of the resonance modes points to a zero-field splitting of the triplet states at about 2.9 K due to a planar anisotropy. The temperature dependence of the line intensity confirms the existence of a Haldane gap in TMNIN with Δ / k B = 3.4 K .

Effect of microannulus on ultrasonic pulse-echo resonance, flexural, and extensional Lamb-wave cement-evaluation measurements

Subterranean wells are usually constructed by cementing steel tubes, called casings, inside the borehole. The cement quality is typically verified through ultrasonic measurements deployed from inside the casing. Environmental effects such as cement shrinkage or changes in static pressure can alter the bonding properties between casing and cement with significant effects on the acoustic measurement response. The cement may detach from the casing, opening a gap, called a microannulus. This microannulus is sized from submicrometer to hundreds of micrometers and filled with either gas or liquid. The subwavelength nature of the microannuli does not allow a direct, unambiguous characterization through an ultrasonic measurement. We studied the measurement signature of ultrasonic-pulse-echo resonance, and flexural and extensional Lamb waves for air- and liquid-filled microannuli for various annulus materials and steel-casing thicknesses. This characterization allows statistically linking measured results to micro...

Mapping of ultrasonic Lamb-wave field in elastic, layered structures using acoustic and laser probes

In the oil and gas industry, the nondestructive evaluation of cemented steel pipes in subterranean wells commonly involves the use of ultrasonic, guided Lamb waves. These measurements help ensure that the cement annulus between the rock formation and the steel pipes provide hydraulic isolation between different depth zones of the well. Such techniques employ the excitation of leaky flexural and extensional waves inside the highly contrasting steel layer to distinguish solids from liquids in the inaccessible region outside the pipe. Furthermore, the annular cement layer may exhibit defects such as cracks or channels which may compromise zonal isolation. We present laboratory measurements using piezo-electric needle probes and laser interferometry, as well as comparative modeling results along spatial and temporal dimensions to visualize and quantify leaky-Lamb-wave propagation for a variety of homogeneous liquid and solid layers behind a steel sheet in planar and cylindrical geometries. We characterize sev...

A method to separate flexural and extensional signals from mixed-mode ultrasonic signals

Ultrasonic guided leaky Lamb waves are widely used for nondestructive evaluation of layered, fluid-loaded, elastic structures. When used in fluid-immersed structures with a frequency-thickness product in the range of 1 to 3 MHz·mm, fundamental Lamb modes can be selectively excited by a suitable combination of broadband pulse and oblique incidence angle. Lamb modes exhibit dispersion, and an intersection of group velocity curves happens in the range of operation of the tool. Consequently, an ultrasonic transducer operating in the range of 1 to 3 MHz·mm acquires composite signals consisting of mixed single-mode signals that overlap in the time-frequency plane. We examine in this contribution a new technique designed to separate the mixed single-mode signals. The separation technique performance is analyzed in our target frequency-thickness product range. The time-frequency distribution of the single-mode reconstruction error reveals that most of the error maxima are localized in the regions where the group delay curves are close.