Inversion Calculations Research Articles

Imaging of small defects in nonmagnetic tubing using a SQUID magnetometer

Using a recently developed superconducting quantum interference device (SQUID) magnetometer system which offers higher resolution and greater sensitivity than previous designs, we have created high-resolution spatial maps of the magnetic anomalies created by small defects in thin-walled, nonmagnetic tubes. Images obtained using three different sensing methods (injected current, induced current, and ferromagnetic decoration) are presented, and compared in terms of sensitivity and signal-to-noise ratio (SNR). All three methods possess the sensitivity to detect holes on a tube's outer diameter as small as 0.37 mm diameter×0.54 mm deep, with varying SNR, as well as holes on the tube's inner diameter as small as 1.0 mm diameter×0.3 mm deep. The ferromagnetic decoration method produces the strongest signals and excellent SNRs. Using this approach, we have detected inner- and outer-diameter slots with dimensions 0.76×0.15×0.08 mm3. In addition, we examine results of numerical inversion calculations applied to the experimental images. With inversion techniques it is possible to determine the original current density distribution given the measured magnetic field, hence revealing the approximate shape and location of defects.

Imaging of Small Defects in Nonmagnetic Tubing Using a SQUID Magnetometer

Abstract Using a recently developed superconducting quantum interference device (SQUID) magnetometer system which offers higher resolution and greater sensitivity than previous designs, we have created high-resolution spatial maps of the magnetic anomalies created by small defects in thin-walled, nonmagnetic tubes. Images obtained using three different sensing methods (injected current, induced current, and ferromagnetic decoration) are presented, and compared in terms of sensitivity and signal-to-noise ratio (SNR). All three methods possess the sensitivity to detect holes on a tube's outer diameter as small as 0.37 mm diameter × 0.54 mm deep, with varying SNR, as well as holes on the tube's inner diameter as small as 1.0 mm diameter × 0.3 mm deep. The ferromagnetic decoration method produces the strongest signals and excellent SNRs. Using this approach, we have detected inner- and outer-diameter slots with dimensions 0.76 × 0.15 × 0.08 mm3. In addition, we examine results of numerical inversion calculations applied to the experimental images. With inversion techniques it is possible to determine the original current density distribution given the measured magnetic field, hence revealing the approximate shape and location of defects.

Measurement of elastic properties of single-crystal CaO up to 1200 K

The elastic moduli of a single-crystal calcium oxide, CaO, are measured in the temperature range from 300 to 1200 K (1.8 times of the Debye temperature) by the resonant sphere technique (RST). The lowest 18 modes are identified in the frequency range from 0.6 to 1.4 MHz for the vibrating spherical specimen, which is 5.6564 mm in diameter and 3.3493 g/cm3 in density at room temperature, and the resonant frequencies are traced as a function of temperature. The adiabatic elastic moduli are determined in the present temperature range from the observed frequencies by inversion calculations. Most of the elastic moduli, except forC 12 modulus, decrease as temperature increases. The temperature curves ofC s andC 44 moduli cross at 372 K. This means that the CaO specimen has an isotropic elasticity at the temperature. The temperature derivatives (∂C 11/∂T) P and (∂C s/∂T) P become slightly less negative with temperature increase and (∂C s /∂T) P and (∂C 44/∂T) P are almost constant. Combining the present elastic data with thermal expansion and specimen heat capacity data of CaO, we present the temperature dependence of thermodynamic parameters important in the studies of earth's interior.

P-4He scattering: Inversion of phase shifts at 64.9 MeV.

We perform S-matrix--to--potential inversion calculations for recently published phase shift fits for protons scattering from $^{4}\mathrm{He}$ at 64.9-MeV laboratory energy. Certain features of the local potential corresponding to these phase shifts appear to be well determined and are unexpected. These include a ``tail'' in the surface of the real potential, and conspicuous regions of emissivity. We also present the equivalent scalar plus vector Dirac potentials.

Venus I. Carbon monoxide distribution and molecular-line searches

An observational program to study variations of the vertical distribution of CO in the Venus atmosphere is presented. Measurements of the J = 0 → 1 absorption line at 2.6 mm wavelength are reported for two phase angles in 1977, one near eastern elongation (Feb.) and the other near inferior conjunction (Apr.). The two spectra are significantly different, with the April absorption line being narrower and deeper. The results of numerical inversion calculations show that the CO mixing ratio increases a factor of ∼ 100 between 78 and 100 km and that the CO abundance above ∼ 100 km is greatest on the night-side hemisphere. These conclusions are in qualitative agreement with theoretical models. In addition to the CO observations, a search for other molecules was made to provide further information on the composition of the Venus middle atmosphere. The J = 0 → 1 transition of 13CO was detected and upper limits were derived for nine other molecules.

The reconstruction of the Laurentide Ice Sheet of North America from sea level data: Method and preliminary results

Usually, ice sheets are reconstructed using the flow law of ice and a number of assumptions regarding ice sheet temperature, accumulation rate, and basal sliding resistance. In this paper, an alternative and independent reconstruction method is given. The weight of the ice sheets deformed the earth's surface and its geoid. The amount of deformation, which can be determined from presently emerged shorelines, is related to the thickness of the overlying ice burden. Therefore elevation and age data of sea levels from North America during the past 17,000 yr can be inverted to determine the history of the most recent North American ice sheet (Laurentide ice sheet), assuming the earth behaves as a viscoelastic material. Because of errors in the data and a number of simplifying assumptions, quadratic programing methods were necessary to insure that the predicted ice thicknesses of the past were always greater than at present. The predicted ice sheet is relatively thin (2000–3000 m), which suggests that it was very dynamic and probably not in a steady state. But poor resolution indicates that other ice thickness models, perhaps of greater thickness, may fit the sea level data as well. The fit to the data is, in general, good, and it indicates that a large proportion of the North American sea level data can be explained by glacial isostatic processes. However, at regions distant from the ice sheet (e.g., Florida) the fit is poor, because the assumption that water‐loading effects can be ignored is no longer valid. For regions close to a fluctuating ice sheet margin (e.g., Connecticut) the fit to the data suffers because of the assumption that the areal extent of the ice sheet remained fixed through time. Methods are developed which obviate both of these unrealistic assumptions so that future inversion calculations will be more realistic. Furthermore, proglacial lake deleveling data can be used to extend the data set throughout the interior of North America so that the entire perimeter of the ice sheet is close to the constraining data. The error of fit and resolution may thus be improved considerably.

The crystal and molecular structure of the 1-carbomethoxy derivative of 5,7,12,14,16(4)-tetracyclo[9,2,2,14,11,08,16]hexadecapentaene, with 1H and 13C n.m.r. studies of ring inversion and strain-energy calculations

The crystal and molecular structure of the 1-carbomethoxy derivative of 5,7,12,14,16(4)-tetracyclo[9,2,2,1^4,11,0^8,16]hexadecapentaene, with ¹H and ¹³C n.m.r. studies of ring inversion and strain-energy calculations

Population inversion calculations using near-resonant charge exchange as a pumping mechanism

Theoretical results are presented for population inversions in a Ca–Xe system. Preliminary results show that it is possible to obtain inversions greater than 1014 m−3 with inversion times up to 8 × 10−7 sec. A possible charge-exchange laser system using an MPD arc plasma accelerator is also described.