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Observations of Lamb shifts in H using spatially periodic potentials.
Resonance effects between H levels by induced electric dipole transitions, using spatially periodic potential barriers
Measurement of the Lamb shift in the O-16/7+/ ion.
The energy difference between the 2S(sub 1/2) levels in the O-16(7+) ion has been determined by means of a Stark-quenching experiment to be 2215.6 plus or minus 7.5 GHz. The uncertainty is based on measured quantities only. This result is shown to be in agreement with the results of similar measurements made by other authors.
Observability of hyperfine structure and Lamb, nuclear-volume shifts in 1snl-1snl' transitions of heliumlike ions.
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Precision measurement of transition energies and Lamb shifts in two-electron argon and potassium in solar-flare spectra
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Measurement of wavelengths and lamb shifts for inner-shell transitions in Fe XVIII-XXIV
The wavelengths of inner-shell 1s-2p transitions in the ions Fe XVIII-XXIV have been measured in solar flare spectra recorded by the Naval Research Laboratory crystal spectrometer (SOLFLEX) on the Air Force P78-1 spacecraft. The measurements are compared with previous measurements and with recently calculated wavelengths. It is found that the measured wavelengths are systematically larger than the wavelengths calculated using the Z-expansion method by up to 0.65 mA. For the more highly charged ions, these differences can be attributed to the QED contributions to the transition energies that are not included in the Z-expansion calculations.
Scattering of Lamb waves in a composite plate
A combined analytical and finite element technique is developed to gain a better understanding of the scattering of elastic waves by defects. This hybrid method is capable of predicting scattered displacements from arbitrary shaped defects as well as inclusions of different material. The continuity of traction and displacements at the boundaries of the two areas provided the necessary equations to find the nodal displacements and expansion coefficients. Results clearly illustrate the influence of increasing crack depth on the scattered signal.
Lamb Wave Nondestructive Evaluation and Imaging on Plate-Like Structures
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Effect of Time-Dependent Strength Recovery of Composite Materials: Quantification Through Higher Order Ultrasonic Non-Linearity Using Lamb Waves
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Laser Based Remote and Rapid Inspection for Composite Plates
Composites have been extensively used in aero structure and become the predominate components in the new airframes. Thus, rapid and effective inspection for composite structures is highly desired in aerospace engineering in order to shorten the certificate cycle for new structures or provide safety guarantee for existing ones. In this paper, a laser based remote Lamb wave inspection system is presented and implemented on composite plates for simulated damage detection. The system employs pulsed laser (PL) and scanning laser Doppler vibrometer (SLDV) for noncontact and remote Lamb wave actuation and wavefield sensing. A composite plate with simulated defect (surface bonded quartz rod) is inspected with the PL-SLDV laser system. Wave scattering are observed in the SLDV acquired wavefield and the damage is further evaluated with wavefield imaging and frequency wavenumber analysis. Potential application towards automatic PL Lamb wave excitation is also explored through employing an industry robotic arm towards rapid inspection.
NDE of simulated Space Shuttle tile disbonds
A technique which involves the use of ultrasonic Lamb waves for assaying the structural integrity of adhesive bonds between layered materials on thin metal plates, particularly with regard to the Shuttle TPS, is presented. The Lamb waves are generated by a pulse impact, resulting in surface waves propagating radially at 2.4 mm/microsec. Trials were performed with the sound waves applied to samples, of aluminum similar to the Orbiter external skin, which were coated with Teflon and a RTV silicone screed. The goal was to detect localized debonded areas or potentially debonded areas, which, during reentry, could result in blistering of the aluminum skin. The ultrasonic probes are described, noting the usage of broadband ultrasonic harmonics and a minicomputer processor. The testing system was found to accurately identify weakened bonds by the ratio of high and low frequency component areas of the received signal of the Lamb waves sent across the surface.
Ultrasonic System Measures Elastic Properties Of Composites
Measurements with leaky Lamb waves yield data on properties and defects of panels. System nondestructively measures elastic properties of, and defects in, panel of laminated fiber/matrix material. Ultrasonic transducers operating in pitch/catch mode excite and detect leaky Lamb waves in specimen. Elastic properties of specimen and defects within it characterized from dispersion curves of Lamb waves.
Use of Guided Acoustic Waves to Assess the Effects of Thermal-Mechanical Cycling on Composite Stiffness
The introduction of new, advanced composite materials into aviation systems requires it thorough understanding of the long-term effects of combined thermal and mechanical loading. As part of a study to evaluate the effects of thermal-mechanical cycling, it guided acoustic (Lamb) wave measurement system was used to measure the bending and out-of-plane stiffness coefficients of composite laminates undergoing thermal-mechanical loading. The system uses a pulse/receive technique that excites an antisymmetric Lamb mode and measures the time-of-flight over a wide frequency range. Given the material density and plate thickness, the bending and out-of-plane shear stiffnesses are calculated from a reconstruction of the velocity dispersion curve. A series of 16 and 32-ply composite laminates were subjected to it thermal-mechanical loading profile in load frames equipped with special environmental chambers. The composite systems studied were it graphite fiber reinforced amorphous thermoplastic polyimide and it graphite fiber reinforced bismaleimide thermoset. The samples were exposed to both high and low temperature extremes its well as high and low strain profiles. The bending and out-of-plane stiffnesses for composite sample that have undergone over 6,000 cycles of thermal-mechanical loading are reported. The Lamb wave generated elastic stiffness results have shown decreases of up to 20% at 4,936 loading cycles for the graphite/thermoplastic samples and up to 64% at 4,706 loading cycles for the graphite/thermoset samples.
X-ray spectra of accreting degenerate stars
X-ray emission from accreting nonmagnetic degenerate dwarfs is discussed. Emphasis is placed on the numerical calculations by Kylafis and Lamb (1979) with regard to the entire range of accretion rates and stellar masses. It is concluded that at moderate and high accretion rates the spectral temperature varies dramatically and the star exhibits a pronounced correlation between X-ray spectral temperature and luminosity. Also considered are the results of Lamb and Masters (1979) of calculations of high-harmonic cyclotron emission from a hot plasma, from which they developed a model of X-ray and UV emission from accreting magnetic degenerate dwarfs. It is found that the position and relative strength of the spectral components change with variations in the accretion rate and differ for different magnetic fields; in addition, magnetic degenerate dwarfs are predicted to be strong UV sources with only a few percent of the total accretion luminosity ordinarily appearing as soft and hard X-rays.
Advanced infrared astronomy
The CO2 laser heterodyne spectrometer was used at the 3-m IRTF on Mauna Kea to make measurements of Mars during the 1984 opposition. Analysis of the observations of the mesospheric non-thermal emission demonstrated the existence of a warming of the Mars polar mesosphere, similar to the seasonal effects which are well known to occur at the Earth's mesopause. A search for CO2 and NH3 on Comet Halley was done with the new Kitt Peak system as well as with the IRTF heterodyne system. A Lamb-dip absorption cell was designed and constructed. Its use will allow extreme frequency stabilization of the laser local oscillator, which will greatly facilitate measurements of winds and dynamical phenomena. The Lamb-dip cell was used at Kitt Peak to study zonal and meridional winds in the atmosphere of Venus. Water vapor was detected in Comet Halley using Fourier transform spectrometer. The 2.65 micrometer upsilon sub 3 band was seen in emission, confirming non-thermal-equilibrium excitation models for comets. A study was made of the variability of Jovian ethane emission. The average volume mixing ratio of ethane in the Jovian stratosphere was found to be 3x10 to the -6 power, with the greatest variability seen in the auroral regions.
A model of sonoluminescence
A bubble of air, trapped at the center of a spherical container of water on the surface of which spherical sound waves are maintained by transducers, may emit light, a phenomenon known as sonoluminescence. The surface of the bubble expands and contracts in obedience to the Rayleigh-Lamb equation, which requires knowledge of the gas pressure on the surface of the bubble. In many investigations of bubble pulsations, it is assumed that the air in the bubble moves adiabatically. To understand sonoluminescence, however, it is necessary to allow for the possibility that shocks are generated within the bubble. We couple the Rayleigh-Lamb equation governing the bubble radius to Euler's equations governing the motion of air in the bubble, and solve the two equations simultaneously. The air is modelled by a van der Waals gas. Results are presented for a number of slightly different conditions of excitation, but in which the response of the system is widely different.
Broad-Band Measurements of Cen X-3 With XTE and CGRO
Centaurus X-3 has played a key role in the development of our understanding of galactic x-ray binary sources. Timing analysis of the UHURU x-ray observations for the luminous Cen X-3 source (L approximately 10(exp 38) erg/s) revealed the first evidence for coherent x-ray pulsations from an object in a binary system (Giaconni 1971; Schreier 1972). It was quickly understood that the luminous pulsed x-ray emission could be generated by the accretion of matter from a companion star onto a rotating neutron star and led to the adoption of binary star models as the fundamental model for galactic x-ray sources (e.g. Pringle and Rees 1972; Lamb 1973). Based on modeling and refined observations since the original measurements, we now believe that Cen X-3 is a high mass x-ray binary system that contains a disk-fed pulsar with a period of 4.84 seconds that is in a 2.087 day orbit around an O-star companion. Since the pulsar discovery, its period has been intermittently monitored and those studies show a long term spin-up of the pulsar punctuated by short intervals of spin-down (e.g. Finger 1994). The implied torques are thought to originate from the interaction of an accretion disk with the magnetic field of a neutron star (Ghosh and Lamb 1979).
XTE Science Briefing from KSCNF
The X-ray Timing Explorer (XTE), launched on Dec. 30, 1995, is a Satellite that observes the fast-moving, high-energy worlds of black holes, neutron stars, x-ray pulsars and bursts of X-rays that light up the sky and then disappear forever. This videotape presents a pre-launch science briefing to the press by a few of the scientist and managers associated with the XTE satellite. The moderator for the press briefing is Jim Sahli, from the Public Affairs Office at Goddard Space Flight Center (GSFC). He introduces Alan Bunner, of the High Energy Astrophysics at NASA Headquarters; Fred Lamb, from the University of Illinois; Richard Mashotzky, X Ray Scientist at GSFC; Rick Rothschild, Principal Investigator from the University of California at San Diego; and Dale Schultz, the XTE project manager at GSFC. Dr. Bunner explains the electromagnetic spectrum, the placement of x-rays and the importance of the XTE observations to a better understanding of the Universe. Dr. Lamb, explains the difference between white dwarfs, neutron stars and black holes, and the type of observations that the XTE will give to a further understanding of these phenomena. Dr. Mashotzky expands the viewpoint to beyond the galaxy, and explains the interests of scientists who hope to use XTE to further study Quasars and Active Galactic Nuclei. Dr. Rothschild reviews some of the features of XTE, using a diagram to show the features of interest, such as the X ray Telescopes, and the collecting Proportional Counter Array (PCA.) Mr. Schultz presents a videotape tour of the XTE, in which he shows the scientific instruments and the other features of the satellite. In this tour, the source of each of the instruments is noted. Questions from the members of the press are then fielded. Many of the questions are about the cost of the XTE and any problems that are anticipated in regards to the launch.