Organic glass scintillators: Material properties, performance characterization, and applications
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Pozzi, S.A.↗
Engineering topics
Schneider, E.
Publications and source records attributed to Schneider, E..
Heavy ion induced mutations in mammalian cells: Cross sections and molecular analysis
Our investigations of heavy ion-induced mutations in mammalian cells, which had been begun a few years ago, were systematically continued. For the first time, it was possible to cover a large LET range with a few kinds of ions. To do this, both UNILAC and SIS were used to yield comparable data for a large energy range. This is a necessary condition for a comprehensive description of the influence of such ion parameters as energy and LET. In these experiments, the induced resistance against the poison 6-thioguanin (6-TG), which is linked to the HPRT locus on the genome, is being used as mutation system. In addition to the mutation-induction cross-section measurements, the molecular changes of the DNA are being investigated by means of Multiplex PCR ('Polymerase Chain Reaction') gene amplification. From these experiments we expect further elucidation of the mutation-inducing mechanisms composing the biological action of heavy-ion radiation.
Stoll, U.↗
Heavy ion action on single cells: Cellular inactivation capability of single accelerated heavy ions
Heavy ions (HZE-particles) constitute an important part of radiation in space. Although their number is small the high amount of energy transferred by individual particles may cause severe biological effects. Their investigation requires special techniques which were tested by experiments performed at the UNILAC at the GSI (Darmstadt). Diploid yeast was used which is a suitable eucaryotic test system because of its resistance to extreme conditions like dryness and vacuum. Cells were placed on nuclear track detector foils and exposed to ions of different atomic number and energy. To assess the action of one single ion on an individual cell, track parameters and the respective colony forming abilities (CFA) were determined with the help of computer aided image analysis. There is mounting evidence that not only the amount of energy deposited along the particle path, commonly given by the LET, is of importance but also the spatial problem of energy deposition at a submicroscopical scale. It is virtually impossible to investigate track structure effects in detail with whole cell populations and (globally applied) high particle fluences. It is, therefore, necessary to detect the action of simple ions in individual cells. The results show that the biological action depends on atomic number and specific energy of the impinging ions, which can be compared with model calculations of recent track structure models.
Kost, M.↗
X-ray-provoked non-Mendelian transgenerational oncodeterminants
Cancer is the most important risk of radiation exposure. There is a definite lack of suitable test systems, human epidemiological data are only available for certain radiation types, especially not for charged particles. We use the Xiphophorus model which is genetically well characterized. As a prelude to experiments with heavy ions we report here on results obtained with x-rays to establish the necessary baseline for future studies. Apart from this direct aim we hope to obtain also a better insight in the genetical determination of cancer formation.
Anders, A.↗
The simulated Indian monsoon: A GCM sensitivity study
A series of sensitivity experiments are conducted in an attempt to understand and correct deficiencies in the simulation of the seasonal mean Indian monsoon with a global atmospheric general circulation model. The seasonal mean precipitation is less than half that observed. This poor simulation in seasonal integrations is independent of the choice of initial conditions and global sea surface temperature data used. Experiments are performed to test the sensitivity of the Indian monsoon simulation to changes in orography, vegetation, soil, wetness, and cloudiness. The authors find that the deficiency of the model precipitation simulation may be attributed to the use of an enhanced orography in the integrations. Replacement of this orography with a mean orography results in a much more realistic simulation of Indian monsoon circulation and rainfall. Experiments with a linear primitive equation model on the sphere suggest that this striking improvement is due to modulations of the orographically forced waves in the lower troposphere. This improvement in the monsoon simulation is due to the kinematic and dynamical effects of changing the topography, rather than the thermal effects, which were minimal. The magnitude of the impact on the Indian monsoon of the other sensitivity experiments varied considerably, but was consistently less than the impact of using the mean orography. However, results from the soil moisture sensitivity experiments suggest a possibly important role for soil moisture in simulating tropical precipitation, including that associated with the Indian monsoon.
Fennessy, M. J.↗
A CAM-based LZ data compression IC
A custom CMOS processor is introduced that implements the Data Compression Lempel-Ziv (DCLZ) standard, a variation of the LZ2 Algorithm. This component presently achieves a sustained compression and decompression rate of 10 megabytes/second by employing an on-chip content-addressable memory for string table storage.
Winters, K.↗
A study of the dynamics of the Intertropical Convergence Zone (ITCZ) in a symmetric atmosphere-ocean model
A numerical model of the circulation of a coupled axisymmetric atmosphere-ocean system was constructed to investigate the physical factors governing the location and intensity of the Intertropical Convergence Zone (ITCZ) over oceans and over land. The results of several numerical integrations are presented to illustrate the interaction of the individual atmospheric and oceanic circulations. It is shown that the ITCA cannot be located at the equator because the atmosphere-ocean system is unstable for lateral displacements of the ITCA from an equilibrium position at the equator.
Charney, J. G.↗
Acoustoelastic constants in dilute two-phase alloys
Acoustoelastic constants are calculated for two-phase alloys containing dilute concentrations of precipitates in a solid-solution matrix, on the basis of a model in which the precipitates are represented as a dilute elastic suspension of spherical particle inclusions in an infinite matrix. The longitudinal propagation velocity in the alloy is thereby obtained in terms of the precipitates' concentration and the elastic moduli of the two phases. Results are presented which indicate that the acoustoelastic constant of longitudinal waves in a dilute two-phase alloy varies linearly with the concentration of second-phase precipitates, in agreement with recent measurements in aluminum and steel alloys where the acoustoelastic constants changed linearly with the second phase's volume fraction.
Salama, K.↗
Nondestructive determination of mechanical properties
The sensitivity of the velocity of ultrasonic waves to the elasticity of the materials (acousto-elastic constant - AEC) as controlled by the microstructure of the materials was examined experimentally. Rolled-plate specimens of five different Al alloys were subjected to tensile tests while being monitored for the velocity change of a 10 MHz longitudinal wave as a function of the applied tensile stress. The acoustic propagation velocity was measured perpendicularly to the stress. Determinations were made of the yield strength and the hardnesses of the specimens. Samples of the plate materials examined microscopically to characterize the solid phases. The AECs varied linearly with the percentage of solid solution phase of the alloys. The trend for strain-hardened samples was, however, opposite from that in the precipitation-hardened alloys. The results underscore the necessity of considering the microstructural dependencies of the AECs when using ultrasonic NDE methods, and also opened the potential of determining some mechanical properties with NDE techniques.
Schneider, E.↗
Nondestructive determination of mechanical properties
Aluminum alloys of types 1100, 3003, 5052, 6061, and 2024 were used to study the sensitivity of the acousto-elastic constant to changes in the microstructure. Results show that there is a strong relationship between the acousto-elastic constants and the yield strength and hardness. This relationship depends on whether the alloy is strain hardened or precipitation hardened. In strain hardened alloys, the constants increase as the amount of solid solution is decreased, while the behavior is the opposite in precipitation hardened alloys.
Schneider, E.↗
Morphology and chemistry of projectile residue in small experimental impact craters
Small-scale impact craters (5-7 mm in diameter) were produced with a light gas gun in high purity Au and Cu targets using soda lime glass (SL) and man-made basalt glass (BG) as projectiles. Maximum impact velocity was 6.4 km/s resulting in peak pressures of approximately 120-150 GPa. Copious amounts of projectile melts are preserved as thin glass liners draping the entire crater cavity; some of this liner may be lost by spallation, however. SEM investigations reveal complex surface textures including multistage flow phenomena and distinct temporal deposition sequences of small droplets. Inasmuch as some of the melts were generated at peak pressures greater than 120 GPa, these glasses represent the most severely shocked silicates recovered from laboratory experiments to date. Major element analyses reveal partial loss of alkalis; Na2O loss of 10-15 percent is observed, while K2O loss may be as high as 30-50 percent. Although the observed volatile loss in these projectile melts is significant, it still remains uncertain whether target melts produced on planetary surfaces are severely fractionated by selective volatilization processes.
Horz, F.↗
Millimeter-wave sensing of the environment: A bibliographic survey
This literature survey was conducted to examine the field of millimeter wave remote sensing of the environment and collect all relevant observations made in the atmospheric windows near 90, 140, and 230 GHz of ocean, terrain, man-made features, and the atmosphere. Over 170 articles and reports were examined; bibliographic references are provided for all and abstracts are quoted when available. Selected highlights were extracted from the pertinent articles.
Schneider, E.↗
Microcraters on lunar samples
The lunar microcrater phenomenology is described. The morphology of the lunar craters is in almost all aspects simulated in laboratory experiments in the diameter range from less than 1 nu to several millimeters and up to 60 km/s impact velocity. An empirically derived formula is given for the conversion of crater diameters into projectile diameters and masses for given impact velocities and projectile and target densities. The production size frequency distribution for lunar craters in the crater size range from approximately 1 nu to several millimeters in diameter is derived from various microcrater measurements within a factor of up to 5. Particle track exposure age measurements for a variety of lunar samples have been performed. They allow the conversion of the lunar crater size frequency production distributions into particle fluxes. The development of crater populations on lunar rocks under self-destruction by subsequent meteoroid impacts and crater overlap is discussed and theoretically described. Erosion rates on lunar rocks on the order of several millimeters per 10 yr are calculated. Chemical investigations of the glass linings of lunar craters yield clear evidence of admixture of projectile material only in one case, where the remnants of an iron-nickel micrometeorite have been identified.
Fechtig, H.↗
Catastrophic rupture of lunar rocks - A Monte Carlo simulation
A computer model based on Monte Carlo techniques was developed to simulate the destruction of lunar rocks by 'catastrophic rupture' due to meteoroid impact. Energies necessary to accomplish catastrophic rupture were derived from laboratory experiments. A crater-production rate derived from lunar rocks was utilized to calculate absolute time scales. Calculated median survival times for crystalline lunar rocks are 1.9, 4.6, 10.3, and 22 m.y. for rock masses of 10, 100, 1000, and 10,000 g, respectively. Corresponding times of 6, 14.5, 32, and 68 million years are required before the probability of destruction reaches 0.99. These results are consistent with absolute exposure ages measured on returned rocks. Some results also substantiate previous conclusions that the catastrophic-rupture process is significantly more effective in obliterating lunar rocks than mass wasting by single-particle abrasion. The view is also corroborated that most rocks presently on the lunar surface either are exhumed from the regolith or are fragments of much larger boulders rather than primary ejecta excavated from pristine bedrock.
Hoerz, F.↗
Lunar microcraters - Implications for the micrometeoroid complex
(For abstract see issue 03, p. 459, Accession no. A75-13187)
Hoerz, F.↗
Microcrater populations on Apollo 17 rocks
Approximately 6000 microcraters were investigated using binocular microscope techniques on Apollo 17 rocks 70215, 72215, 72235, 72395, 72435, 73216, 73218, 73275, 74275, 76135, 76136, and 79155. The crater populations observed have identical characteristics to those obtained from previous missions. Special emphasis was placed on assessing the influence of target properties on the observable crater populations. Although these properties cannot be quantitatively evaluated at present, the empirical results indicate that crater populations on glass, breccia, and crystalline rock surfaces may differ fundamentally. As a consequence, lunar surface exposure ages of individual rocks based on micrometeoroid craters may be subject to criticism.
Schneider, E.↗
Micrometeoroid abrasion of lunar rocks - A Monte Carlo simulation
A Monte Carlo computer model simulating the randomness of the impact process both in space and in time is developed in order to provide insight into lunar rock erosion by single particle abrasion and into bombardment history of fractional surface areas of lunar rocks. Microcrater frequencies derived from lunar rocks are used to calculate magnitude and probability of each cratering event, and experimental cratering results are employed to determine the eroded volumina for individual crater sizes. It is shown that a fractional surface area of a lunar rock sample may have a completely different bombardment history, and that the exposure histories and actual erosion depths of the surfaces vary accordingly and are highly heterogeneous. A minimum erosion rate of 0.3 to 0.6 mm for the past one million years is obtained.
Hoerz, F.↗