Emeritus Professor of Electronics, Department of Informatics and Telecommunications, University of Athens, Greece. He was born in Patras, Greece, on the 5th of August, 1928 and passed away on December 5, 2021 in Athens. He received the B.Sc. in Physics from the University of Athens, Greece (1953), the M.Sc. in Radioelectrology from the same University (1956), the Certif. Electr. Orsay (1961), the 3me cycle from CEA/Saclay (1961), a Ph.D. from the University of Athens, Greece (1963) and the Doctorat d’ Etat, from the University of Paris (1964). He has been Maitre de Research at the CNRS (France), Chief Assistant at the Laboratory of Electronics of the Physics Department of the University of Athens, Greece, Professor of Electronics at the Department of Physics, University of Athens (until 1989), Chairman of this Department for seven years (1982-1989), Director of the Section of Applied Physics and Director of the Electronics Laboratory of the same Department, Director of the Section of Telecommunications and Signal Processing of the Department of Informatics and Telecommunications, Director of the Ionospheric ￼Institute of the National Observatory of Athens, Greece and President of the Advisory Committee for Research and Technology of the Government of Greece (1983). His scientific interests included the radio observations of the Sun, ionospheric physics and the antennas, digital signal processing, and digital telecommunications.
Dimitri M. Mihalas (1939 - 2013)
Dimitri Mihalas died on Thursday the 21st of November 2013.
World-renowned astrophysicist Dimitri Mihalas passed away in his sleep at his home in Santa Fe, New Mexico on November 21, 2013. Dr. Mihalas retired from the University of Illinois at Urbana- Champaign in 1999 and from the Los Alamos National Laboratory in 2012. Dimitri, to his friends and family, has donated his body to the University of New Mexico Medical School and his library to New Mexico Tech.
Dimitri was born on March 20, 1939 in Los Angeles, California where he grew up. He received his B.A., with Highest Honors, in three majors, Physics, Mathematics, and Astronomy, from the University of California at Los Angeles at age 20. Four years later he received his Ph.D. in Astronomy and Physics from the California Institute of Technology. He was a pioneer in computational astrophysics, and has remained a world leader in the fields of radiation transport, radiation hydrodynamics, and astrophysical quantitative spectroscopy for decades. His broad knowledge and immense contributions earned him election to the U.S. National Academy of Sciences in 1981 at age 42.
Dimitri had an exceptional record of work. He published more than 150 papers and technical reports, authored or co-authored eight books, and co-edited three others. Three of his books have been used as textbooks for both undergraduate and graduate students worldwide and have been translated into other languages, including Russian. His book Foundations of Radiation Hydrodynamics has become the “bible” of the radiation hydrodynamics community.
Dimitri wrote his Ph.D. thesis on theoretical modelings for hydrogen and helium line strengths and profiles in O-stars. He interpreted the observational data with the best theoretical analysis possible at the time. The models were computed using the then prevailing simplifying approximation of local thermodynamic equilibrium (LTE). As shown by its high number of citations, this work, primitive by todays standards, had a major impact on the field.
After joining the faculty of the Department of Astrophysical Sciences at Princeton University, Dimitri undertook new analyses of stellar abundances, devised a method for constructing a constant-flux atmosphere with convection in the full transport (not diffusion) regime, computed the first line-blanketed spectrum of a hot B star which showed that continuum- only models overestimated the effective temperature by 10% (hence luminosity by 40%), and computed a sample of H line-blanketed models accounting for the distortion of the continuum by the confluence of the hydrogen Balmer lines near 3650Å.
Dimitri realized that the widely accepted approximation of LTE in stellar atmospheres is inadequate, so he undertook a major initiative to solve the analogous non-LTE problem. This is an exceptionally difficult problem owing to the need to solve self-consistently a set of coupled, highly nonlinear effects. Only the highly idealized case of a two-level atom with a single line and two continua had been solved previously.
After several preliminary explorations of methodology with Auer, they reformulated the non-LTE stellar atmosphere problem in a completely original manner; applying the Newton- Raphson technique to the full nonlinear system, and iterating to convergence. This method was a breakthrough in the field – it revolutionized all further work on computing stellar atmospheres. Through his idea of “variable Eddington factors,” the method was made even more efficient.
With this new methodology, Dimitri constructed an extensive, widely cited, sample of non-LTE models for hot stars, and used them to evaluate the effects of departures from LTE on observable stellar line and continuum indices. These results allowed Mihalas and Auer to perform several critical studies which were not previously possible, achieving for the first time good agreement between the computed and observed strengths of the hydrogen and helium lines, and surface gravities consistent with the stars observed masses and element abundances obtained
from nebular analyses. This work has been widely cited, both for the quality of fit to observations, as well as a “gold standard” for verification of present-day calculations using much faster iterative methods. Work with Hummer led to the discovery of the physical mechanism producing the emission the N III emission lines at wavelengths 4634 – 4650Å in O((f)) stars.
In the 1970s, Dimitri devised the now standard method for solving the line-transfer problem in expanding spherical atmospheres in the comoving frame. This work was summarized in the heavily cited 2nd edition of his textbook Stellar Atmospheres, which remains the standard in the field even after 25 years. A third edition (with I. Hubeny) which describes modern fast, iterative methods to solve the transfer equation, including realistic line-blanketing, is in press.
In the period 1981 – 1998, as a consultant to LANL, Dimitri gave lectures on radiation hydrodynamics, for which, he received a number of “Certificate of Appreciation” by X-Division for “Outstanding Service to the Applied Theoretical Division”. In 1984 Dimitri completed the above-mentioned Foundations of Radiation Hydrodynamics. In 1999 Dover Publications reprinted it in inexpensive paperbound form at the urging of many scientists from LANL, LLNL, NRL, and the academic community.
In the period 1987 – 1994 Dimitri worked with Anderson, Hummer, and B. Mihalas on the development of a modern EOS code for stellar envelopes, in support of the large British – American Opacity Project (OP) led by Professor M. J. Seaton. It emerged that the OP results are in excellent agreement (better than 10%) with the independent LLNL OPAL computations. These new opacity data significantly impact stellar evolution calculations, and have helped resolve several previous discrepancies between calculation and observation, especially with the interpretation of Cepheid variable pulsations.
Jointly with Stone, Dimitri showed that the computational oscillations or diffusion, typically found in numerical simulations of a propagating radiation front in vacuum, could be eliminated by using upwind monotonic interpolation methods. They (and M. Norman) also collaborated on incorporating 2-D radiative transfer in the radiation magnetohydrodynamics code ZEUS 2-D developed at the University of Illinois and extensively used by astrophysicists.
In collaboration with K.-H. Winkler and M. Norman, Dimitri developed novel implicit adaptive grid methods to solve 1-D radiation hydrodynamics problems having multiple time and space scales ranging over many orders of magnitude. Dimitri derived the “adaptive-grid transport theorem” rigorously. In 1994 – 1997, Dimitri developed TITAN, a 1-D implicit adaptive-grid code. In collaboration with Cheng at Los Alamos, Dimitri used TITAN to compute the best-ever numerical solution of the infamous Noh stagnating shock problem in planar, cylindrical, and spherical geometry. In 1999, in collaboration with Gehmeyr, and Sincell, Dimitri studied the famous Zeldovich and Heaslet/Baldwin supercritical shock problem and was able to compute the first numerical solutions for this problem. Also in the same year, Dimitri and Auer wrote “An X-6 Radiation Hydrodynamics Primer” intended for LANL use, and in 2001 they published an incisive discussion on exact relativistic laboratory-frame radiation hydrodynamics.
Dimitri was honored for his many scientific contributions at the International Conference in Honor of Dimitri Mihalas for his Lifetime Scientific Contributions on the Occasion of his 70th Birthday held in Boulder, CO in late March 2009.
In addition to his many scientific contributions, he also published several collections of his poetry and other writings. These other writings include "A Primer on Depression and Bipolar Disorder" and "Depression, Bipolar Disorder, and Spiritual Growth." These books have had as profound an impact as his professional textbooks and articles.
Throughout his long career, Dimitri gave generously of himself to all with whom he interacted. As an advisor, role model, confidant, and friend, he saw each person as an individual, acknowledging strengths, helping overcome weaknesses, giving encouragement, and enthusiastically praising their success. He touched the lives and careers of many students and colleagues and has left a lasting legacy to be cherished by those who knew him.
Reprinted with permission from Physics Today.
Baolian Cheng, LANL, Los Alamos, NM John Castor, LLNL, Livermore, CA
Jim Stone, Princeton University, Princeton, NJ
Barbanis Vassilios, (1926-2006)
Professor (Emeritus), Department of Physics, Aristotle University of Thessaloniki, Greece. He was born in Athens, Greece, on the 26th of October, 1926. He received the B.Sc. in Mathematics from the University of Athens, Greece (1953) and the Ph.D. in Astronomy from the University of Thessaloniki (1953). He worked at the Department of Physics at the same University and reached the position of the Docent (1968). He has been elected as Professor of Astronomy of the University of Patras, Greece (1969-1979) and, finally, he was elected as Professor of Astronomy at the University of Thessaloniki, Greece. For one year (1955-56) he has worked as Research Associate at the Department of Astronomy of the Columbia University of N.Y., U.S.A. His scientific interests included the Dynamics of Stellar systems, stellar paths in galactic models and the chaotic behaviour of dynamical systems with two and three degrees of freedom. He had published many papers in refereed scientific journals and proceedings of international meetings as well as 6 textbooks and one scientific book.
1964, Dept. of Physics, Charles University of Prague, Τσεχία
He was born in Ziakas, Greece on the 6th of May, 1937. He received an M.S. in Nuclear Physics (1961) from the Charles University, Prague and a Postgraduate Degree (1964) from the Institute of Plasma Physics in Prague, then Czechoslovakia. He moved to the University of Chicago, U.S.A. working at the Laboratory for Astrophysics, while in 1981 he joined the Enrico Fermi Laboratory of the same University (1981) as Senior Research Associate and later as Senior Scientist. He has worked on Chemical analyses of planetary bodies by Alpha Backscattering technique (with A. Turkevich - Surveyor Alpha backscattering experiment 1967-68), in Instrument development for Viking missions, in penetrator missions to comets and asteroids. Also, he worked as coinvestigator on the Alpha-X experiment onboard the Soviet Phobos 1 and 2 spacecrafts in 1986-89 and on the Alpha-Proton-X-ray for the Russian Mars-96 missions to Mars. He was the Principal Investigator for the X-ray mode of this experiment and Co-Principal Investigator on the APX Spectrometer on NASAs Mars Pathfinder mission in 1993 - 1997 and the Principal Investigator for the X-ray mode of the APXS experiment on the Pathfinder Mission. He was a Member of Program Science Group for the Pathfinder mission, Team member of Mineralogy/Geochemistry Science Operation Group for the Pathfinder and a Member of many NASA mission evaluation teams (1970 - present). He also worked on the Analysis of Mars Pathfinder APXS data. In generally, he has been building instruments for interplanetary spacecraft since the mid-1960s. His areas of expertise are Chemical Analysis, Mars Rovers and Robotic Spacecraft Instrumentation. He is associated with three of NASA’s robotic missions: the Mars Exploration Rovers, the Cassini mission to Mars, and the now-complete Stardust mission to Comet Wild-2, which has been redirected to a second cometary target. He also built the Alpha Proton X-ray Spectrometer that successfully performed the first chemical analysis of Martian rocks aboard the Mars Pathfinder rover in 1997. Working in the laboratory of Anthony Turkevich, he contributed to the alpha backscattering experiment of three robotic Surveyor space probes that landed on the moon in 1967-68. With Turkevich during the 1970s and 1980s, he also conducted basic nuclear physics research on
￼￼￼￼￼￼￼the subatomic structure of matter using the most advanced particle accelerators at Los Alamos, Argonne and Fermi National Accelerator laboratories. During the 1990s they performed an important double beta decay experiment of Uranium-238 to Plutonium-238, suggesting for the first time that neutrinos consist of a small quantity of mass. He has published more than 90 papers in scientific refereed journals. He has been presented with the NASA award for the APXS on the Pathfinder Mission and with the National Air and Space Museum 1998 Achievement Trophy for the Pathfinder Team. He is a Member AAAS, of the American Geophysical Union, of the European Geophysical Society and of the LAMPF users group.
Papagiannis Michael (1932 – 1997)
Emeritus Professor, Boston University, U.S.A. He obtained his B.Sc. in Chemical Engineering from the National Technical University, Athens, Greece (1955), the M.Sc. in Physics from the University of Virginia, U.S.A. and the Ph.D. from the Harvard University, U.S.A. (1964). He served as Visiting Professor at the University of Athens, Greece (1971-72) and at the University of Crete, Greece (1986). He had been elected Fellow of the American Association for the Advancement of Science. He had served as the first Chairman of Commission 51 of the International Astronomical Union (IAU) on Bioastronomy (1982-85). Prof. Papagiannis was interested in Space Physics and Astrophysics but more strongly on Bioastronomy, and he published over 100 papers and one textbook on these subjects.
Petros Serghiou Florides is a Greek Cypriot mathematical physicist whose career has been based in Ireland.
He was born in Lapithos, Cyprus, and in 1958 received his bachelors degree from the University of London. His 1960 PhD from Royal Holloway on "Problems in Relativity Theory and Relativistic Cosmology" was supervised by William McCrea. After a postdoc with John L Synge at the Dublin Institute of Advanced Studies, he settled at Trinity College Dublin in 1962. There he spent over four decades, rising to the rank of senior fellow and pro-chancellor. In 1964 he was awarded a Master of Arts (juri officii).
He was member of the Reviewing Body of the “Mathematical Reviews” (1963-1980), member of the Preparatory Committee for the Establishment of the University of Cyprus (1988-1992), chairman of the Selection Committee for the Mathematics and Statistics Department of the University of Cyprus (1990-1996), chairman of the Peer Review Group for the first Quality Assessment of Third Level Institutions in Greece (1995), and chairman of the Local Organising Committee of the 17th International Conference on General Relativity and Gravitation, held in Dublin at the RDS Convention Centre from July 18 – 23, 2004 (2001-2004). He is life member of the International Society on General Relativity and Gravitation, fellow of the Royal Astronomical Society, London (since 1963), and a patron (and past president) of the Irish Hellenic Society. He was a former pro-chancellor of Trinity College Dublin from 2010–2012.
Jean-Henri Focas (1909-1969) was born in Corfu on July 20, 1909. An amateur astronomer, he perfected himself and finally entered the National Observatory of Athens. Under the direction of Eginitis and Plakidis, he received the deep traditional training as an observer. In Athens, he devoted himself particularly to the study of planets with the 40 cm Doridis equatorial telescope, and later with the 65 cm refractor for which he contributed in a decisive way to be installed at the astronomical station of Penteli in 1954. He stayed in France to observe the opposition of the planet Mars from 1954 to the Pic du Midi. Returning to Athens, he began a close collaboration with the Observatory of Meudon. For this reason, he visited France every year. In 1961, under the direction of Audouin Dollfus (1924-2010), he obtained a university thesis entitled: Photometric and Polarimetric Study of the Seasonal Phenomena of Mars. Then, in 1964, he came to settle permanently in France to run the photographic documentation center on the planets of the UAI in Meudon. Jean-Henri Focas died suddenly of a heart attack in Athens on January 3, 1969.
His name was given to a lunar crater.