Search

Your search keyword '"Staab T"' showing total 118 results
Start Over Author "Staab T"
118 results on '"Staab T"'

2. On the Role of Grain Boundaries During Sintering

Author

Staab T, Helm R, and Diegeler A

Subjects
Materials science, Metallurgy, Sintering, Grain boundary
Abstract

We present new results in positron annihilation lifetime spectroscopy (PALS), thermo-optical dilatometry and microscopy, which are indicating a strong correlation between grain-boundaries and mass transport during the sintering process of carbonyl iron powder. In this particular system we were able to show that the change in particle shape and size with increasing temperature yields an anisotropy in shrinkage, which manifests itself in a higher shrinkage perpendicular to the compaction axis. In the intermediate stage of sintering, where the major mass transport occurs, the average distance between two grain boundaries could be determined to (3,73 ± 0,18) μm at T = 744°C. This is in good agreement with previous calculations of positron pathways in defect free particles. Furthermore, due to sintering temperatures far above the annealing temperature of dislocations in iron, the existence of dislocations in the bulk of the particles is very unlikely. These claims are reflected by the collected positron data, which exhibit a clear grain boundary signal of ∼ 250ps while no vacancy or dislocation signal (typically ∼ 160 ps) is evident in the intermediate stage of sintering.

Published
2021
Full Text
View/download PDF

12. Limitations on the Positron Lifetime Spectra Decomposability Applying the Iterative Least-Square Re-Convolution Method Using the Instrumental Responses Obtained from 207Bi and 60Co.

Author

PETSCHKE, D., HELM, R., HAAKS, M., and STAAB, T. E. M.

Subjects
POSITRONS, COMPTON effect, COMPTON scattering, INVERSE problems, MATHEMATICAL convolutions, PHENOMENOLOGICAL theory (Physics), POSITRON annihilation
Abstract

Since the decomposition of positron lifetime spectra requires solving an ill-posed and inverse problem, the accurate knowledge of the spectrometer's instrument response function is crucial for extracting the true underlying physical information of the phenomenon under investigation. In general, the instrument response function is modelled by a superposition of Gaussian functions, since an analytical solution for the convolution with an exponential distribution function exists and, hence, the characteristic lifetimes and its corresponding contributions can be obtained by non-linear least-squares fitting. In contrast, the iterative least-squares re-convolution approach determines the best fit of the recorded lifetime spectrum by re-convoluting a sum of N expected exponential decays with the numerical data of the experimentally obtained instrument response function. For a laboratory setup, two methods exist to estimate the shape of the instrument response function from experiment: (1) the direct method using a 60Co isotope and an indirect method by graphically deconvoluting the monoexponential lifetime spectrum obtained from 207Bi. For both variants, the energies of the incident gamma-rays are considerably different to the energies accompanying the creation (1274 keV) and annihilation (511 keV) of a positron using 22Na: 60Co (1173 keV, 1333 keV), 207Bi (570 keV, 1064 keV). Here we present a detailed study on the basis of plastic scintillators regarding the spectra decomposability by using the re-convolution technique with experimentally obtained instrument response functions. We can clearly show that beyond incident gamma-ray energy differences, the Compton scattering effects and pile-up events represent the limiting factors in this approach. [ABSTRACT FROM AUTHOR]

Published
2020
Full Text
View/download PDF

13. Study of defects in electron irradiated CulnSe2 by positron lifetime spectroscopy.

Author

Polity, A., Krause-Rehberg, R., Staab, T. E. M., Puska, M. J., Klais, J., Möller, H. J., and Meyer, B. K.

Subjects
SPECTRUM analysis
Abstract

Studies the defects in electron irradiated CulnSe2 by using positron lifetime spectroscopy. Growing of bulk crystals of CulnSe2 by the Bridgeman method; Information on the positron annihilation spectroscopy; Theoretical calculations of positron lifetimes; Statistical information supporting the results of the study.

Published
1998
Full Text
View/download PDF

15. Divacancy in 3C- and 4H-SiC : An extremely stable defect

Author

Torpo, L., Staab, T. E. M., Nieminen, Risto M., Perustieteiden korkeakoulu, School of Science, Teknillisen fysiikan laitos, Department of Applied Physics, Aalto-yliopisto, and Aalto University

Subjects
SiC, Physics, relaxed geometries, divacancy defects, stability, ionization levels, formation energies
Abstract

Using first-principles calculations for divacancy defects in 3C− and 4H−SiC, we determine their formation energies and stability, their ionization levels, and relaxed geometries (symmetry point groups) for neutral as well as for charged states. For 4H−SiC all four possible nearest-neighbor divacancy configurations are considered. We find not only a remarkable high binding energy of about 4 eV, but also a strong site dependence (cubic or hexagonal lattice sites) of the formation energies. Applying a Madelung-type correction to deal with the electrostatic interactions between charged supercells, our results indicate a negative-U behavior at EV+0.7 eV between the charge states 1+/1− only for nearest-neighbor divacancies on different lattice sites (mixed cubic and hexagonal) in 4H−SiC, but not for all the other cases (pure cubic or pure hexagonal) in 4H− or for the cubic divacancy in 3C−SiC.

Published
2002

17. The Rapid Syndrome Validation Project (RSVP)

Author

Zelicoff, A., Brillman, J., Forslund, D. W., George, J. E., Zink, S., Koenig, S., Staab, T., Simpson, G., Umland, E., and Bersell, K.

Subjects
Health Personnel, Syndrome, Bioterrorism, humanities, United States, Disease Outbreaks, Computer Communication Networks, Government Agencies, Computer Systems, Population Surveillance, Humans, Emergency Service, Hospital, Public Health Administration, Software, Research Article, Information Systems
Abstract

The Rapid Syndrome Validation Project (RSVP) is a collaboration of several institutions: Sandia and Los Alamos National Laboratories, the University of New Mexico Department of Emergency Medicine, and the NM Department of Health Office of Epidemiology. RSVP is a system that operates at the intersection of individual health care providers, public health and bioterrorism. Physicians quickly enter clinical and demographic information on patients exhibiting symptoms and signs of the syndromes of interest. It provides early warning and response to emerging biological threats, as well as emerging epidemics and diseases. RSVP provides real time clinical information to the provider and any other potential user such as the DOH, about current symptoms, disease prevalence and location. The system also serves as a mechanism for the Department of Health to inform health care providers of health alerts and to facilitate the process of collecting data on reportable diseases. We describe here the purpose an the architecture of a network-based surveillance system that is currently implemented in an Emergency Department.

Published
2001

18. Neutron activations for lower s-process temperatures

Author

Heftrich Tanja, Al-Khasawleh Kafa, Borzek Sandra, Brückner Benjamin, Dellmann Sophia Florence, Dogan Ozan Can, El Mard Asmaa, Erbacher Philipp, Gail Madeleine, Göbel Kathrin, Habermehl Fabian, Heybeck Benedict, Kisselbach Timo, Kurtulgil Deniz, Mourad Rim, Reich Markus, Reifarth René, Sheriff Silas, Staab Tom, Volknandt Meiko, and Weigand Mario

Subjects
Physics, QC1-999
Abstract

The slow neutron capture process produces heavy elements in different stellar sites at different temperatures. Neutron capture cross sections for stellar temperatures between kBT = 5 keV and kBT = 100 keV are crucial for a quantitative understanding of the s-process abundance distribution. Over the last decade activation measurements were performed at the Goethe University Frankfurt to study cross sections at a temperature of kBT = 25 keV. We developed a new method to measure neutron capture cross sections at kBT = 6 keV.

Published
2023
Full Text
View/download PDF

Catalog

Books, media, physical & digital resources
See catalog results