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Iowa State University

1987

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Articles 1 - 30 of 45

Full-Text Articles in Physics

Effect Of Hybridization On 4d→4f Spectra In Light Lanthanides, David W. Lynch, R. D. Cowan Dec 1987

Effect Of Hybridization On 4d→4f Spectra In Light Lanthanides, David W. Lynch, R. D. Cowan

Physics and Astronomy Publications

The effect of the hybridization of 4f electrons on La, Ce, and Pr tripositive ions with ligand states or conduction electrons was simulated by reducing the Slater integrals involving the 4f electrons by 10% or 20%, depending on whether the integrand involves one or two 4f electrons, respectively. The dipole-allowed 4d→4f spectra were calculated. Observable effects, changes in line energies, and oscillator strengths, were compared with limited data available for ionic and metallic solids containing these lanthanides, and for Ce vapor. Many of the observed changes in the 4d→4f spectra attributed to hybridization effects are ...


Theoretical Study Of The Environmental Effects On The Hyperfine Fields Of Ni And Fe In Ni0.75fe0.25, H. Ebert, H. Winter, B. Gyorffy, Duane D. Johnson, F. J. Pinski Nov 1987

Theoretical Study Of The Environmental Effects On The Hyperfine Fields Of Ni And Fe In Ni0.75fe0.25, H. Ebert, H. Winter, B. Gyorffy, Duane D. Johnson, F. J. Pinski

Duane D. Johnson

The dependence of the hyperfine fields Bhf of Ni and Fe in Ni0.75Fe0.25 on the surrounding atomic configuration has been studied by performing charge selfconsistent 6 shell-cluster Korringa-Kohn-Rostoker Coherent Potential Approximation (KKR-CPA) bandstructure calculations. By replacing the CPA- scatterers in the various shells around the central atom by Ni - or Fe-atoms, respectively, it could be shown that the hyperfine fields vary linearly with the number of Fe-atoms within a given shell and that the changes of Bhf due to simultaneous changes of the atomic configurations of different shells are additive. The changes of the hyperfine fields upon ordering ...


Effect Of Liquids On The Drude Dielectric Function Of Ag And Au Films, Liang-Yao Chen, David W. Lynch Jul 1987

Effect Of Liquids On The Drude Dielectric Function Of Ag And Au Films, Liang-Yao Chen, David W. Lynch

Physics and Astronomy Publications

Spectroscopic ellipsometric measurements were made of the free-electron dielectric functions of Ag and Au films in air and immersed in dielectric liquids of different refractive indexes. The effects seen by Gugger et al. were reproduced for Ag and Au films prepared similarly to theirs, and in Ag films with larger grains. Different effects were seen with an (oxidized) single crystal of Ag and a single crystal of Au. The ‘‘anomalous’’ data could be fitted with an effective-medium model by assuming that the liquid penetrates all, or most, of the intergrain regions within the optical penetration depth. The dielectric functions of ...


La 4d→4f Resonance Absorption In Laf3: Temperature Dependence, C. G. Olson, David W. Lynch May 1987

La 4d→4f Resonance Absorption In Laf3: Temperature Dependence, C. G. Olson, David W. Lynch

Physics and Astronomy Publications

Temperature-modulated transmission spectra in the region of the 4d→4f excitations in LaF3 show a variety of effects, none of which can be explained by the free-atom model hitherto used to describe this absorption. The sharp lines below threshold are shown to broaden with increasing temperature and to shift slightly. The broad ‘‘autoionization’’ region is shown to be composed of several structures, only one of which is included in the atomic picture. The effects of the lattice on these transitions ‘‘within’’ the La3+ ion are significant.


Ultrasonic Studies Of Stresses And Plastic Deformation In Steel During Tension And Compression, J. Frankel, W. Scholz Jan 1987

Ultrasonic Studies Of Stresses And Plastic Deformation In Steel During Tension And Compression, J. Frankel, W. Scholz

Review of Progress in Quantitative Nondestructive Evaluation

A steel bar subjected to four-point bending was instrumented so that various strains and sound velocities could be measured during elastic and plastic deformation on both the tension and compression side of the bar. During plastic deformation, the load was reduced several times before it was increased again. We present the acoustoelastic constants and the corresponding third-order elastic constants 1, m, and n in both tension and compression in the “as-treated” specimen and after various amounts of plastic deformation. The changes in various sound velocities with plastic deformation are also discussed.


Uniaxial Stress Effects On The Low-Field Magnetoacoustic Interactions In Low And Medium Carbon Steels, D. Utrata, M. Namkung Jan 1987

Uniaxial Stress Effects On The Low-Field Magnetoacoustic Interactions In Low And Medium Carbon Steels, D. Utrata, M. Namkung

Review of Progress in Quantitative Nondestructive Evaluation

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.


Radiographic Detection Of 100 Å Thickness Variations In 1-Μm-Thick Coatings On Submillimeter-Diameter Laser Fusion Targets, David M. Stupin Jan 1987

Radiographic Detection Of 100 Å Thickness Variations In 1-Μm-Thick Coatings On Submillimeter-Diameter Laser Fusion Targets, David M. Stupin

Review of Progress in Quantitative Nondestructive Evaluation

We have developed x-ray radiography to measure thickness variations of coatings on laser fusion targets. Our technique is based on measuring the variation in x-ray transmission through the targets. The simplest targets are hollow glass microshells* or microballoons** 100 to 500 μm in diameter (Fig. 1), that have several layers of metals or plastics, 1 to 100 ym thick (Fig. 2). Our goal is to examine these opaque coatings for thickness variations as small as 1% or 0.1%, depending on the type of defect. Using contact radiography we have obtained the desired sensitivity for concentric and elliptical defects of ...


Process Monitoring Of Polymer Matrix Composites Using Fluorescence Probes, Bruno Fanconi, Francis Wang, Robert Lowry Jan 1987

Process Monitoring Of Polymer Matrix Composites Using Fluorescence Probes, Bruno Fanconi, Francis Wang, Robert Lowry

Review of Progress in Quantitative Nondestructive Evaluation

On-line process monitoring and control are prerequisites for more efficient and reliable manufacture of polymer matrix composites. The cure process involves complex chemical and physical changes that must be adequately controlled to consistently produce high quality products. Of various changes that occur, the viscosity is particularly important as it influences fiber wetting, uniformity of resin distribution and consolidation of the reinforcement plies. In the usual cure cycle, the viscosity of the resin initially decreases as the temperature of the resin rises owing to the higher temperature of the autoclave and heat released by the exothermic chemical reactions of the cross-linking ...


Thermal And Plasma Waves In Semiconductors, Jon Opsal Jan 1987

Thermal And Plasma Waves In Semiconductors, Jon Opsal

Review of Progress in Quantitative Nondestructive Evaluation

The absorption of an intensity modulated laser beam results in a modulated temperature profile having the properties of a critically damped wave, i. e., a thermal wave [1]. In a semiconductor such as silicon, if the energy per photon exceeds the band gap energy, then, in addition to the thermal wave, one has a photo-generated electron-hole plasma density that can also be characterized as a critically damped propagating wave, i. e., a plasma wave [2]. In this paper, we present a theoretical description of these two phenomena that shows how they can be used to obtain information about transport and ...


Thermal Wave Characterization Of Coated Surfaces, J. Jaarinen, C. B. Reyes, I. C. Oppenheim, L. D. Favro, P. K. Kuo, R. L. Thomas Jan 1987

Thermal Wave Characterization Of Coated Surfaces, J. Jaarinen, C. B. Reyes, I. C. Oppenheim, L. D. Favro, P. K. Kuo, R. L. Thomas

Review of Progress in Quantitative Nondestructive Evaluation

The experimental techniques and theory for utilizing the mirage effect, or optical probe beam detection, of thermal waves in opaque solids for determining their thermal diffusivities have been described in detail elsewhere. [1–4] An application to a coated nickel-based alloy has also been described elsewhere. [1] In previous papers [5,6] we presented a theoretical expression which describes the mirage effect signal in a three-layer medium (gas-coating-sample system), taking into consideration the effects of the sizes of the heating and probe beams. In this paper we extend the results of numerical calculations from that expression to the case of ...


Coating Thickness Determination Using Time Dependent Surface Temperature Measurements, J. C. Murphy, L. C. Aamodt, G. C. Wetsel Jr. Jan 1987

Coating Thickness Determination Using Time Dependent Surface Temperature Measurements, J. C. Murphy, L. C. Aamodt, G. C. Wetsel Jr.

Review of Progress in Quantitative Nondestructive Evaluation

Thin film coatings are used to protect metal alloys from oxidation. To be effective they must have adequate thickness and be well bonded to the metal substrate. This is especially important for metals subject to high temperatures or to highly oxidizing environments. As a consequence, there is a need for a non-destructive method for evaluating coating thickness, bonding, and other coating properties.


Optical Generation Of Coherent Ultrahigh Frequency Surface Waves, Sheryl M. Gracewski, R. J. Dwayne Miller Jan 1987

Optical Generation Of Coherent Ultrahigh Frequency Surface Waves, Sheryl M. Gracewski, R. J. Dwayne Miller

Review of Progress in Quantitative Nondestructive Evaluation

It has been demonstrated [1–4] that coherent bulk acoustic waves can be holographically induced by the interference pattern of two intersecting picosecond laser pulses. The coupling between the optical and elastic fields can either be due to electrostriction or optical absorption which produces thermal stresses. The resulting waveform can then be detected by a third time-delayed laser pulse which diffracts off the density grating of the wave field. The elastic response within the laser spot caused by either coupling mechanism has been shown to consist of 1-D counter-propagating pressure waves. From the frequency and attenuation of the diffracted signal ...


Detection Of Ultrasonic Waves Propagating In Boron/Aluminum And Steel/Lucite Composite Materials, Stephen Huber, William R. Scott, Randall Sands Jan 1987

Detection Of Ultrasonic Waves Propagating In Boron/Aluminum And Steel/Lucite Composite Materials, Stephen Huber, William R. Scott, Randall Sands

Review of Progress in Quantitative Nondestructive Evaluation

In this paper we report preliminary results of investigations into the nature of ultrasonic wave propagation and resulting surface displacements in two selected fiber reinforced composite materials: aluminum with boron fiber reinforcement and Lucite with steel rod reinforcement. These materials have reinforcing fiber diameters that are small and large respectively when compared with the propagating ultrasonic wavelengths. The ultrasonic waves are observed by detecting surface displacements using a scanning micro-interferometer designed for this purpose and discussed in detail elsewhere.


Nde Of Polymer Composites Using Magnetic Resonance Techniques, Wayne A. Bryden, Theodore O. Poehler Jan 1987

Nde Of Polymer Composites Using Magnetic Resonance Techniques, Wayne A. Bryden, Theodore O. Poehler

Review of Progress in Quantitative Nondestructive Evaluation

Polymer based materials have become increasingly important in structural applications primarily due to their high strength to weight ratio. As the use of polymer-based composites has increased, so has the need for reliable non-destructive evaluation techniques. In this paper, a new NDE method for these materials is proposed. The technique relies on the observation of an electron paramagnetic resonance (epr) absorption at the site of damage in a polymer. Using applied magnetic field gradients the physical location of damage can be discerned and an image of the damage site can be obtained. This should allow the detection of cracks and ...


Eddy-Current Probe Interaction With Subsurface Cracks, John R. Bowler Jan 1987

Eddy-Current Probe Interaction With Subsurface Cracks, John R. Bowler

Review of Progress in Quantitative Nondestructive Evaluation

Electric current will flow around on open crack in a conductor and give rise to very abrupt variations in the field. If the crack has a negligible opening it acts as a surface barrier where the field is virtually discontinuous. Effectively the crack is then equivalent to a layer of current dipoles with the dipole orientation normal to the surface and pointing upstream. An integral equation for the dipole density has been derived for an idealised subsurface crack using the Green’s function method [1]. Numerical solutions have been found by assuming a piecewise constant dipole density and satisfying boundary ...


Fundamentals Of Thermal Wave Physics, Jon Opsal Jan 1987

Fundamentals Of Thermal Wave Physics, Jon Opsal

Review of Progress in Quantitative Nondestructive Evaluation

In this talk, we present the basic elements of thermal wave physics with a particular emphasis on the propagation and scattering of thermal waves. The most significant aspects of thermal waves in terms of their potential for materials characterization will be shown using simple examples and a minimum of mathematical analysis. Although most practical applications require a full 3-dimensional analysis for quantitative interpretation, much of the physics can be qualitatively understood in terms of a simpler 1-dimensional treatment appropriately modified to account for 3-dimensional effects. Following a prescription for the rigorous 3-dimensional analysis we discuss some of the implications in ...


Classical And Quantum Mechanical Aspects Of Thermal Wave Physics, Andreas Mandelis Jan 1987

Classical And Quantum Mechanical Aspects Of Thermal Wave Physics, Andreas Mandelis

Review of Progress in Quantitative Nondestructive Evaluation

The ability of thermal waves to perform non-destructive depth-profiling studies in materials with spatially variable thermal/thermodynamic properties has been exploited mostly qualitatively so far. The lack of appropriate general theoretical models in the literature has been largely responsible for the near absence of quantitative depth-profiling, especially in media with large thermal property variations within depths on the order of the thermal wavelength. As a result of mathematical difficulties, theoretical treatments have been essentially confined to discrete, multilayered solid structures with constant thermal and thermodynamic properties within each thin layer [1,2]. Furthermore, Afromowitz et al. [3] have applied discrete ...


Temporal Behavior Of Modulated Reflectance Signal In Silicon, Allen Rosencwaig, Jon Opsal, Michael W. Taylor Jan 1987

Temporal Behavior Of Modulated Reflectance Signal In Silicon, Allen Rosencwaig, Jon Opsal, Michael W. Taylor

Review of Progress in Quantitative Nondestructive Evaluation

In another paper in these proceedings, Opsal [1] discusses the origin of the modulated reflectance signal observed in silicon under the experimental conditions employed in the Therma-Probe system [2]. These experimental conditions are described in the paper by Smith, Hahn and Arst in these proceedings [3]. Table I lists the major differences between our type of modulated optical reflectance experiments and the more conventional photoreflectance experiments [4–10].


Modulated Reflectance Measurement Of Reactive-Ion And Plasma Etch Damage In Silicon Wafers, W. Lee Smith, Patrice Geraghty Jan 1987

Modulated Reflectance Measurement Of Reactive-Ion And Plasma Etch Damage In Silicon Wafers, W. Lee Smith, Patrice Geraghty

Review of Progress in Quantitative Nondestructive Evaluation

Reactive ion etching (RIE) and plasma etching (PE) are vital processes for the attainment of densely-packed, micron-scaled structures for VLSI integrated circuits. However, it is widely recognized that undesirable modifications of semiconductor or insulator materials may accompany the use of these dry etch processes. For example, during the RIE process, samples are exposed to high energy ions, UV photons and x-rays, all of which can result in radiation damage [1] in the form of non-annealable structural defects in gate oxide or Si/Si02 interface regions, deep level traps or surface states. In terms of IC device performance, these effects cause ...


Picosecond Transient Thermoreflectance: Time-Resolved Studies Of Thin Film Thermal Transport, Gary L. Eesley Jan 1987

Picosecond Transient Thermoreflectance: Time-Resolved Studies Of Thin Film Thermal Transport, Gary L. Eesley

Review of Progress in Quantitative Nondestructive Evaluation

The advent of new and sophisticated material growth processes (molecular beam epitaxy, chemical vapor deposition and ion sputter deposition) has produced new exotic materials such as amorphous alloys and compositionally modulated structures [1]. The atomic level structure of these materials can be proved by techniques such as x-ray diffraction. The electrical and thermal transport properties are also used to characterize these materials, which are usually deposited as thin films onto supporting substrates. Although the substrate may be electrically isolated from the film, complete thermal isolation is more difficult to achieve and thermal transport measurements are complicated.


Probing Through The Gas-Solid Interface With Thermal Waves: A Study Of The Temperature Distribution In The Gas And In The Solid, L. J. Inglehart, J. Jaarinen, P. K. Kuo, E. H. Le Gal La Salle Jan 1987

Probing Through The Gas-Solid Interface With Thermal Waves: A Study Of The Temperature Distribution In The Gas And In The Solid, L. J. Inglehart, J. Jaarinen, P. K. Kuo, E. H. Le Gal La Salle

Review of Progress in Quantitative Nondestructive Evaluation

Thermal wave nondestructive evaluation is one of the few NDE methods applicable to the characterization of ceramic and composite materials. As a near surface characterization technique, it has been shown to be useful for metals and semiconductors and has been developed for use with those materials. Limited work has been done with the technique on ceramics, with little effort to investigate the resulting fundamental differences which can occur in the case of insulating materials.


Reflection-Mirage Measurements Of Thermal Diffusivity, C. B. Reyes, J. Jaarinen, L. D. Favro, P. K. Kuo, R. L. Thomas Jan 1987

Reflection-Mirage Measurements Of Thermal Diffusivity, C. B. Reyes, J. Jaarinen, L. D. Favro, P. K. Kuo, R. L. Thomas

Review of Progress in Quantitative Nondestructive Evaluation

The experimental technique for the measurement of thermal diffusivity using the mirage effect, or optical probe beam detection of thermal waves in opaque solids has been described elsewhere. [1–3] This is carried out by scanning the probe beam relative to the heating beam with a constant height, h. The separation, x0, of the two points on either side of the center of such a scan where the phase of the transverse deflection signal reaches ninety decrees effectively measures the thermal wavelength, λ = 2(πα /f)1/2 in the solid. The determination of the thermal diffusivity, a, is accomplished ...


Nondestructive Characterization Of Coatings On Metal Alloys, G. C. Wetsel Jr., J. C. Murphy, L. C. Aamodt Jan 1987

Nondestructive Characterization Of Coatings On Metal Alloys, G. C. Wetsel Jr., J. C. Murphy, L. C. Aamodt

Review of Progress in Quantitative Nondestructive Evaluation

There is a need to nondestructively evaluate coatings on metal alloys that must endure high-temperature or highly oxidizing environments, such as for aircraft turbine blades. Such coatings are opaque and of the order of 25 μm in thickness. Characteristics of interest include the uniformity and thickness of the coating, which must be sufficient to protect the substrate from oxidation at high temperatures.


Internal Monitoring Of Acoustic Emission In Graphite-Epoxy Composites Using Imbedded Optical Fiber Sensors, K. D. Bennett, R. O. Claus, M. J. Pindera Jan 1987

Internal Monitoring Of Acoustic Emission In Graphite-Epoxy Composites Using Imbedded Optical Fiber Sensors, K. D. Bennett, R. O. Claus, M. J. Pindera

Review of Progress in Quantitative Nondestructive Evaluation

The monitoring of acoustic emission (AE) is an important technique for the nondestructive characterization of strained materials because time and frequency domain analyses of AE events yield information about the type, geometry, and location of defects, as well as how material failure may occur. The quantitative interpretation of AE event signatures is critically dependent upon the faithfulness of the acoustic transduction and signal processing system in reproducing localized stress wave amplitude as a function of time. Although the usual sensor for acoustic emission is the piezoelectric transducer, several investigators have considered the application of interferometric optical sensing techniques which offer ...


Application Of Pattern Recognition Techniques To Acoustic Emission From Steel And Aluminum, Mark A. Friesel Jan 1987

Application Of Pattern Recognition Techniques To Acoustic Emission From Steel And Aluminum, Mark A. Friesel

Review of Progress in Quantitative Nondestructive Evaluation

Much of the interest in using acoustic emission to monitor structural components is a result of the ability of the technique to detect growing cracks. The greatest problem standing in the way of applying this technique is the presence of signals from innocuous sources, which can make identification of crack-produced emission difficult, especially in those circumstances when cracks must be detected in real time and without other reliable correlation parameters. The test results presented here suggest an approach to eliminate spurious signals from acoustic emission data, which may be applicable to real time analysis and amenable to a variety-of monitoring ...


Thermal Wave Techniques For Imaging And Characterization Of Materials, L. D. Favro, P. K. Kuo, R. L. Thomas Jan 1987

Thermal Wave Techniques For Imaging And Characterization Of Materials, L. D. Favro, P. K. Kuo, R. L. Thomas

Review of Progress in Quantitative Nondestructive Evaluation

Thermal wave imaging is proving to be a useful technique for the nondestructive evaluation (NDE) of subsurface features of opaque solids. This imaging is achieved with various intensity-modulated heat sources, such as laser or particle beams, and with various detectors, such as microphones, ultrasonic transducers, infrared detectors, and laser probes. The authors have recently reviewed these techniques and their application to NDE [1], Common to the techniques is the fact that they each involve the interaction of a highly damped thermal wave with surface or subsurface thermal features. They also have in common the fact that the source is localized ...


Effect Of Temperature And Heat Treatment On Crack Growth Acoustic Emission In 7075 Aluminum, S. L. Mcbride, J. L. Harvey Jan 1987

Effect Of Temperature And Heat Treatment On Crack Growth Acoustic Emission In 7075 Aluminum, S. L. Mcbride, J. L. Harvey

Review of Progress in Quantitative Nondestructive Evaluation

The acoustic emission activity due to crack advance in 7075 aluminum alloys has been found to vary with both temperature and heat treatment. An Increase in temperature or overaging of material in the -T6 condition each reduces the acoustic emission activity by changing the probability of occurrence of acoustic emission events and lowering their amplitudes. These observations suggest that the acoustic emission source mechanism is not inclusion fracture but rather is a property of the ductile matrix.


Acoustic Transducers And Lens Design For Acoustic Microscopy, C.-H. Chou, B. T. Khuri-Yakub Jan 1987

Acoustic Transducers And Lens Design For Acoustic Microscopy, C.-H. Chou, B. T. Khuri-Yakub

Review of Progress in Quantitative Nondestructive Evaluation

The transducer-lens system is one major component in the performance of an acoustic microscope. The design criteria for the various types of applications of an acoustic microscope are different. For surface imaging applications, it is desired to have a small spot size and low sidelobe level. For materials characterization and subsurface imaging applications (such as subsurface crack imaging), it is required to have high surface wave excitation efficiency. Several researchers addressed the problem of surface imaging.1-5 Also, some work has been done to investigate materials properties indirectly by using so-called V(z) curves.6-8 The resolution obtained in the ...


Optical Range Finder, G. Q. Xiao, D. B. Patterson, G. S. Kino Jan 1987

Optical Range Finder, G. Q. Xiao, D. B. Patterson, G. S. Kino

Review of Progress in Quantitative Nondestructive Evaluation

Recently, a great deal of interest has been shown in making accurate range measurements with good transverse definition. This capability makes it possible, in machine vision systems, to extract geometrical shape information from the images. In robot position sensing, it is important to determine the absolute distance instead of distance change so that noncontinuous measurements can be made without the need for calibration at start-up. A third application of great importance is to measure the shape and size of machined parts with a noncontacting sensor.


The Effect Of Oxygen On The Ion-Acoustic Signal Generation Process, F. G. Satkiewicz, J. C. Murphy, J. W. Maclachlan, L. C. Aamodt Jan 1987

The Effect Of Oxygen On The Ion-Acoustic Signal Generation Process, F. G. Satkiewicz, J. C. Murphy, J. W. Maclachlan, L. C. Aamodt

Review of Progress in Quantitative Nondestructive Evaluation

Thermal wave imaging (TWI) describes a family of methods for materials characterization based on temperature changes induced by an external source. The source can be a laser [1,2,3] or an electron [4,5,6] beam modulated to produce time-varying surface and bulk temperatures in the specimen. Recently, ion sources have been used for excitation [7,8,9] and share some imaging features in common with laser and electron sources. All three types of sources have the ability to detect buried defects in opaque solids and to locate tightly closed cracks [10]. However, the fundamental physical mechanisms of signal ...