Experiments on stress dependent borehole acoustic waves

In the laboratory setup, a borehole traverses a dry sandstone formation, which is subjected to a controlled uniaxial stress in the direction perpendicular to the borehole axis. Measurements are made in a single loading-unloading stress cycle from zero to 10 MPa and then back down to zero stress. The applied stress and the presence of the borehole induce anisotropy in the bulk of the material and stress concentration around the borehole, both azimuthally and radially. Acoustic waves are generated and detected in the water-filled borehole, including compressional and shear headwaves, as well as modes of monopole, dipole, quadrupole, and higher order azimuthal symmetries. The linear and non-linear elastic parameters of the formation material are independently quantified, and utilized in conjunction with elastic theories to predict the characteristics of various borehole waves at zero and finite stress conditions. For example, an analytic theory is developed which is successfully used to estimate the changes of monopole tube mode at low frequency resulted from uniaxial stress, utilizing the measured material third order elasticity parameters. Comparisons between various measurements as well as that between experiments and theories are also presented.     

Isotopic study of the transition of calcium monomethoxide using laser excitation and population depletion spectroscopy

High resolution excitation spectra have been obtained of the 0–0 band of the transition of four isotopologues, CaO¹²CH₃, CaO¹³CH₃, CaO¹²CD₃ and CaO¹³CD₃ of calcium monomethoxide. The deuterated species were found to have unexpectedly complicated spectra, and definitive rotational assignments were possible only from investigation by optical optical double resonance (OODR) population depletion spectroscopy. This confirmed the assignment of the CaO¹²CD₃ spectrum, and proved crucial in assigning the K-structure and spin components for CaO¹³CD₃. The state was found to be well described by the symmetric rotor model with C_3v symmetry for both hydride species but, for the deuterides, the K-structure and spin rotation splittings were irregular, especially for CaO¹³CD₃ where the K = 0 and 1 levels were heavily perturbed. The changes in the A constant determined for the hydride suggest that the CH₃ umbrella opens by 0.4°, i.e., 0.2° further on excitation to the state than on excitation to the lower-lying state (geometry change established in an earlier experiment by Crozet et al. [P. Crozet, A.J. Ross, C. Linton, A.G. Adam, W.S. Hopkins, R.J. Le Roy, J. Mol. Spectrosc. 229 (2005), 224–230]).     

Laser spectroscopy of LaF: Determination of the separation of the singlet and triplet state manifolds

Tunable dye lasers have been used to excite several known transitions in LaF. Resolved fluorescence spectra obtained after excitation of B¹Π-X¹Σ⁺ and C¹Π-X¹Σ⁺ bands showed transitions to both X¹Σ⁺ and a³Δ states. Analysis of the spectra shows that the state is 1432 cm⁻¹ above X¹Σ⁺, is at 1808 cm⁻¹, and there is an Ω = 2 state (probably ¹Δ) at 5478 cm⁻¹. A new 0⁺-X¹Σ⁺ (v = 0) band has been observed in the vicinity of the B¹Π-X¹Σ⁺ 1-0 band. High resolution excitation spectra of both bands have been obtained, term energies and rotational constants calculated, and the Λ-doubling in B¹Π, v = 1 has been studied. The principal constants (in cm⁻¹) obtained from the analyses wereThe assignments of the low lying states are discussed in terms of their electron configurations and are shown to be in accord with predictions of Ligand Field Theory.     

The chemiluminescent flame spectrum of SiO

The band systems of the SiO molecule have been excited in a flame produced by the chemiluminescence of SiCl₄ vapor reacting with oxygen atoms in the presence of an argon atmosphere. A general survey has been made of the emission spectrum of this flame and the various band systems lying in the region 2300–4600 Å have been identified. Many new bands have been observed and have been assigned to the SiO molecule. The emission bands tentatively attributed to a new ¹Σ⁻-¹Σ⁻ transition of neutral SiO [H. Bredohl, R. Cornet, I. Dubois, and F. Remy, Can. J. Phys. 51, 2322 (1973)] and reassigned by R. F. Barrow and T. J. Stone [J. Phys. B. 8, L13 (1975)] to belong to the known E¹Σ⁺-X¹Σ⁺ system of SiO have been extended in the present source. They are shown to confirm the Barrow and Stone assignments. A few bandheads corresponding to the isotopic species ²⁹SiO and ³⁰SiO have been observed for A¹Π-X¹Σ⁺ system. In addition, several strong unidentified bands have been reported.     

Interassociates of the bicyclic semigroup

An interassociate of a semigroup \((S,\cdot )\) is a semigroup \((S, *)\) such that for all \(a, b, c \in S\), \(a\cdot (b*c)=(a\cdot b) *c\) and \(a*(b\cdot c)=(a*b) \cdot c\). We investigate the bicyclic semigroup C and its interassociates. In particular, if p and q are the generators of the bicyclic semigroup and m and n are fixed nonnegative integers, the operation \(a*_{m,n} b= aq^mp^n b\) is known to be an interassociate. We show that for distinct pairs (m, n) and (s, t), the interassociates \((C, *_{m,n})\) and \((C, *_{s,t})\) are not isomorphic. We also generalize a result regarding homomorphisms on C to homomorphisms on its interassociates.     

Effect of granular media on the vibrational response of a resonant structure: theory and experiment

The acoustic response of a structure that contains a cavity filled with a loose granular material is analyzed. The inputs to the theory are the effective masses of each subsystem: that of the empty-cavity resonating structure and that of the granular medium within the cavity. This theory accurately predicts the frequencies, widths, and relative amplitudes of the various flexural mode resonances observed with rectangular bars, each having a cavity filled with loose tungsten granules. Inasmuch as the dominant mechanism for damping is due to adsorbed water at the grain-grain contacts, the significant effects of humidity on both the effective mass of the granular medium as well as on the response of the grain-loaded bars are monitored. Here, depending upon the humidity and the preparation protocol, it is possible to observe one, two, or three distinct resonances in a wide frequency range (1-5 kHz) over which the empty bar has but one resonance. These effects are understood in terms of the theoretical framework, which may simplify in terms of perturbation theories.     

Effects of porous covering on sound attenuation by periodic arrays of cylinders

The acoustic transmission loss of a finite periodic array of long rigid cylinders, without and with porous absorbent covering, is studied both theoretically and in the laboratory. A multiple scattering model is extended to allow for the covering and its acoustical properties are described by a single parameter semi-empirical model. Data from laboratory measurements and numerical results are found to be in reasonable agreement. These data and predictions show that porous covering reduces the variation of transmission loss with frequency due to the stop/pass band structure observed with an array of rigid cylinders with similar overall radius and improves the overall attenuation in the higher frequency range. The predicted sensitivities to covering thickness and effective flow resistivity are explored. It is predicted that a random covered array also gives better attenuation than a random array of rigid cylinders with the same overall radius and volume fraction.     

The extraction and analysis of 1,4-dioxane from water using solid-phase microextraction coupled with gas chromatography and gas chromatography-mass spectrometry

In this study, two methods are developed for the extraction of 1,4-dioxane (dioxane) from water using 80-microm carboxen-polydimethylsiloxane solid-phase microextraction fibers followed by either gas chromatography (GC)-flame ionization detection (FID) or GC-mass spectrometry (MS). With GC-FID, the lower limit of detection (LOD) for 1,4-dioxane is 2.5 microg/L (ppb) with a linear range of 5 to 10,000 microg/L, obtained by immersing the fiber in the sample for 20 min with agitation. Using GC-MS, the lower limit of quantitation is 0.5 microg/L, and the LOD is 0.25 microg/L. The upper linear range limit is 100 microg/L. Samples are extracted in 20 min using either heated headspace with agitation or direct immersion with agitation.