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At least 649 records · Page 36

Concentration-Dependent Transformation Plasticity Effect During Hydrogenation of Technically Pure Titanium Irradiated with an Electron Beam

Using the methods of X-ray diffraction analysis, the concentration-dependent transformation plasticity effect +TPE) is investigated during hydrogenation of the technically pure titanium (VT1-0) irradiated on one side with a low-energy high-current electron beam in a SOLO facility using three 50 μs pulses at the pulse repetition frequency 0.3 s{sup –1} and the beam energy density W = 18 J/cm{sup 2}. Its irradiation is performed in an argon atmosphere at the residual pressure 0.02 Pa. It is found out that the concentration-dependent TPE in the course of hydrogenation is due to the low stability state of the α-Ti crystal lattice formed in the specimen surface layer upon its e-beam irradiation. Relaxation of the elastic plane macrostresses occurs as a result of the development of concentration inhomogeneity of hydrogen or formation of α″-Ti and ω-Ti martensitic phases.

36 MATERIALS SCIENCE↗

Prediction of residual stresses in additively manufactured parts using lumped capacitance and classical lamination theory

Several industries are interested in Laser Powder Bed Fusion (L-PBF) Additively Manufactured (AM) metal parts because their designs can be made arbitrarily complex while retaining bulk-type material properties. However, the residual stresses (RS) and distortions caused by the heat gradients inherent to L-PBF processes are detrimental to the structural integrity of the parts and must be taken into consideration during the part design cycle. Predicting the state of stresses in as-built 3D printed parts is a difficult problem that is typically approached with the use of transient thermomechanical Finite Element Models (FEMs). However, the nonlinearities associated with AM processes are difficult to capture in these FEMs without increasing the computational cost of the simulation, limiting their ability to be incorporated into practical design cycles. This work presents a novel analytical framework that combines lumped capacitance nonlinear heat transfer with time dependent classical lamination theory to efficiently and accurately predict RS in as-built L-PBF parts without the need of FEMs. The simulation was compared to Neutron Diffraction (ND) residual strain measurements taken at Oak Ridge National Laboratories (ORNL) as well as Synchrotron X-ray Diffraction (XRD) strain data published by the National Institute of Standards and Technology (NIST). The simulation predictions and the experimental data showed excellent agreement for the in-plane strain directions, and general agreement for the out of plane strain component, highlighting an area where further development can be implemented.

42 ENGINEERING↗

Traction-separation response of bilayer graphene interfaces: The role of an intercalated single atomic layer of water molecules and hydroxyl groups

Molecular dynamics simulations of the normal and shear traction-separation response of dry and wet bilayer graphene interfaces were performed. The influence of a single, atomic layer of water molecules sandwiched between graphene layers and hydroxyl functionalization on one or both layers were investigated. Hydroxyl groups provided a shielding effect during normal separation while favoring stick-slip friction under sliding conditions. The single, atomic layer of water molecules confined between hydrophilic and asymmetric hydrophobic/hydrophilic surfaces was found to ease sliding friction. The mechanisms arose from the balance between the attractive and repulsive graphene/water interactions through bridges of single water molecules between the two surfaces and the structure of the water monolayer under confinement for which an out-of-plane water/water hydrogen bond network could not be developed. The single, atomic layer of water molecules reduced the sliding friction the most when both surfaces were hydrophilic and lowered the sliding friction of the asymmetric hydrophobic/hydrophilic interfaces to that when both surfaces were hydrophobic. An optimal hydroxyl surface coverage of less than 10% may exist for efficient water lubrication, with diminishing effect with increasing number of hydroxyl groups. Finally, the findings offer a design strategy for assembling bilayer graphene interfaces with tailored friction and sliding contact properties.

36 MATERIALS SCIENCE↗

Charge density wave memory in a cuprate superconductor

Although CDW correlations are a ubiquitous feature of the superconducting cuprates, their disparate properties suggest a crucial role for pinning the CDW to the lattice. Here, we report coherent resonant X-ray speckle correlation analysis, which directly determines the reproducibility of CDW domain patterns in La 1.875 Ba 0.125 CuO 4 (LBCO 1/8) with thermal cycling. While CDW order is only observed below 54 K, where a structural phase transition creates inequivalent Cu-O bonds, we discover remarkably reproducible CDW domain memory upon repeated cycling to far higher temperatures. That memory is only lost on cycling to 240(3) K, which recovers the four-fold symmetry of the CuO 2 planes. We infer that the structural features that develop below 240 K determine the CDW pinning landscape below 54 K. This opens a view into the complex coupling between charge and lattice degrees of freedom in superconducting cuprates.

36 MATERIALS SCIENCE↗

ON VERTICALLY GLOBAL, HORIZONTALLY LOCAL MODELS FOR ASTROPHYSICAL DISKS

Disks with a barotropic equilibrium structure, for which the pressure is only a function of the density, rotate on cylinders in the presence of a gravitational potential, so that the angular frequency of such a disk is independent of height. Such disks with barotropic equilibria can be approximately modeled using the shearing box framework, representing a small disk volume with height-independent angular frequency. If the disk is in baroclinic equilibrium, the angular frequency does generally depend on height, and it is thus necessary to go beyond the standard shearing box approach. In this paper, we show that given a global disk model, it is possible to develop approximate models that are local in horizontal planes without an expansion in height with shearing-periodic boundary conditions. We refer to the resulting framework as the vertically global shearing box (VGSB). These models can be non-axisymmetric for globally barotropic equilibria but should be axisymmetric for globally baroclinic equilibria. We provide explicit equations for this VGSB which can be implemented in standard magnetohydrodynamic codes by generalizing the shearing-periodic boundary conditions to allow for a height-dependent angular frequency and shear rate. We also discuss the limitations that result from the radial approximations that are needed in order to impose height-dependent shearing periodic boundary conditions. We illustrate the potential of this framework by studying a vertical shear instability and examining the modes associated with the magnetorotational instability.

79 ASTRONOMY AND ASTROPHYSICS↗

Auxiliary-field quantum Monte Carlo calculations with multiple-projector pseudopotentials

We have implemented recently developed multiple-projector pseudopotentials into the plane-wave-based auxiliary-field quantum Monte Carlo (pw-AFQMC) method. Multiple-projector pseudopotentials can yield smaller plane-wave cutoffs while maintaining or improving transferability. This reduces the computational cost of pw-AFQMC, increasing its reach to larger and more complicated systems. We discuss the use of nonlocal pseudopotentials in the separable Kleinman-Bylander form, and the implementation in pw-AFQMC of the multiple-projector optimized norm-conserving pseudopotential ONCVPSP of Hamann. The accuracy of the method is first demonstrated by equation-of-state calculations of the ionic insulator NaCl and more strongly correlated metal Cu. The method is then applied to calibrate the accuracy of density-functional theory (DFT) predictions of the phase stability of recently discovered high temperature and pressure superconducting sulfur hydride systems. We find that DFT results are in good agreement with pw-AFQMC, due to the near cancellation of electron-electron correlation effects between different structures.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗

Unconventional Spin-Orbit Torques Due to Reduced Crystal Symmetries

Spin-orbit torques have emerged as a powerful mechanism for manipulating magnetic moments in spintronic devices, offering a pathway to more efficient and scalable memory and logic technologies. While conventional spin-orbit torques generated in heavy metals and topological insulators have been extensively studied, recent advancements in unconventional spin-orbit torques demonstrated out-of-plane spin polarizations that could effectively switch perpendicular magnetizations without the need for additional external in-plane magnetic fields, promising significant implications for the development of energy-efficient and compact spintronic devices. Unconventional spin-orbit torques are usually found in materials with low symmetries, such as transition metal dichalcogenides, topological insulators, and 2-D materials. Here, we provide a brief overview of unconventional spin-orbit torques and present two example material systems: CrPt 3 and MoTe 2 , both exhibiting strong spin-orbit coupling and phase-dependent spin-orbit torques, and focus on their unique origins and potential applications. We discuss the roles of magnetic and crystallographic orders in generating unconventional spin-orbit torques, highlighting how these factors contribute to the observed anisotropic and directional dependencies.

magnetic films↗

WE-G-213-01: Roentgen and the Birth of Modern Medical Physics

Roentgen and the Birth of Modern Medical Physics – Perry Sprawls Wilhelm Roentgen is well known for his discovery of x-radiation. What is less known and appreciated is his intensive research following the discovery to determine the characteristics of the “new kind of radiation” and demonstrate its great value for medical purposes. In this presentation we will imagine ourselves in Roentgen’s mind and follow his thinking, including questions and doubts, as he designs and conducts a series of innovative experiments that provided the foundation for the rapid growth of medical physics. Learning Objectives: Become familiar with the personal characteristics and work of Prof. Roentgen that establishes him as an inspiring model for the medical physics profession. Observe the thought process and experiments that determined and demonstrated the comprehensive characteristics of x-radiation. The AAPM Award Eponyms: William D. Coolidge, Edith H. Quimby, and Marvin M.D. Williams - Who were they and what did they do? – Lawrence N. Rothenberg William David Coolidge (1873–1975) William Coolidge was born in Hudson, NY in 1873. He obtained his BS at the Massacusetts Institute of Technology in 1896. Coolidge then went to the University of Leipzig, Germany for graduate study with physicists Paul Drude and Gustave Wiedemann and received a Ph.D. in 1899. While in Germany he met Wilhelm Roentgen. Coolidge returned to the US to teach at MIT where he was associated with Arthur A. Noyes of the Chemistry Department, working on the electrical conductivity of aqueous solutions. Willis R. Whitney, under whom Coolidge had worked before going to Germany, became head of the newly formed General Electric Research Laboratory and he invited Coolidge to work with him. In 1905, Coolidge joined the staff of the GE laboratory and was associated with it for the remainder of his life. He developed ductile tungsten filaments to replace fragile carbon filaments as the material for electric light bulb filaments. Until that innovation light bulbs had a notoriously short life. He later incorporated the ductile tungsten as a filament material for a hot cathode, fully evacuated x-ray tube, first described in 1912, which allowed higher current and x-ray output, and greater reliability than had previously been possible. These “Coolidge x-ray tubes” were far superior to the cold cathode, partial pressure gas x-ray tubes that had been in use since Roentgen’s discovery of x-rays in 1895. The Coolidge tube with incremental developments is now the key component for x-ray production in all of our modern x-ray imaging devices, such as CT scanners, interventional radiology systems, and mammography units. Coolidge was also involved in the development of sectional x-ray tubes for research and treatment that were initially designed to reach 800 kV. Additional improvements led to 1 MV and 2 MV devices. In 1932 Coolidge became director of the General Electric Research Laboratory, and in 1940, was made Vice-President and Director of Research. In 1945 he retired and was named Director Emeritus of the laboratory. Coolidge held 83 patents and was recognized for these and many other achievements by election to the National Academy of Engineers, a place in the Engineering Hall of Fame and the National Inventor’s Hall of Fame. The AAPM’s highest honor, the Coolidge Award, was named after him. He accepted Honorary Membership in the AAPM and was the first recipient of the AAPM Coolidge Award, which was presented to him in a special ceremony in Schenectady, NY in 1972 when he was 100 years old. Edith Hinckley Quimby (1891–1982) Edith Quimby was born in Rockford, IL in 1891. She graduated from Whitman College in Walla Walla, WA with a B.S. in 1913, and then obtained a masters degree from the University of California at Berkeley. Later in her career, after many significant achievements, Quimby was awarded honorary doctorates by Whitman College and Rutgers University. Edith Quimby was hired by Giacchino Failla as a radiation physicist at Memorial Hospital for Cancer in New York City. Failla had studied with Madame Curie and obtained his doctoral degree in her laboratory. After many groundbreaking medical physics studies from 1919 until 1942, they both moved to Columbia University. Dr. Quimby developed a widely employed dosimetry system for single plane implants with radium and radon seeds, and a dosimetry methodology for internal radionuclides. She was author of more than 75 scientific publications, and of significant textbooks including the first comprehensive physics textbook for radiologists “Physical Foundations of Radiology”, which was co-authored with Otto Glasser, Lauriston Taylor and James Weatherwax in the first edition, with Russell Morgan added for the second edition and Paul Goodwin for the fourth edition. With Sergei Feitelberg, M.D. she published two editions of “Radioactive Isotopes in Medicine and Biology: Basic Physics and Instrumentation”. Quimby became a renowned examiner for the American Board of Radiology when the third ABR examination, given in 1936, added physics. She served as President of the American Radium Society, received the RSNA Gold Medal, and also numerous prestigious awards given to women in science. Edith Quimby was a Charter Member of AAPM. The AAPM Lifetime Achievement Award was renamed the Edith H. Quimby Lifetime Achievement Award in her honor in 2011. Marvin Martin Dixon Williams (1902–1981) Marvin Williams was born in Walla Walla, WA in 1902, and attended the same college as Edith Quimby, graduating from Whitman College in 1926. He was greatly influenced to go into medical physics by her accomplishments. During his early career, Williams worked with James Weatherwax in Philadelphia while he was working toward an M.S. from the University of Pennsylvania. In 1931 Williams was awarded a Ph.D. in Biophysics from the University of Minnesota, with the work actually performed at the Mayo Clinic Graduate School of the University. While completing his Ph.D. studies, Marvin met Dr. Paul Hodges who had returned from the Peiping Union Medical College in Peiping (now Beijing), China. Hodges suggested that a physicist be sent to Peiping to install x-ray therapy equipment and a radon plant. Williams accepted the position and, in 1931, he and his wife Orpha left for China. Before going to China, Williams had spent time with the physics group at Memorial Hospital to learn about the operation of a radon plant. In China, he constructed the radon plant, employing 0.25 g of radium, and also installed the x-ray therapy unit. Williams and his wife returned to the US in 1935, and he accepted a research position at the Mayo Clinic. In 1950, he became Professor of Biophysics at Mayo, where he taught physics and biophysics until his retirement in 1967. Williams was also very active in the American Board of Radiology where, from 1944 through 1977, he examined over 3000 radiologists and 250 physicists. Marvin Williams was a Charter member of AAPM, served as the fourth President of AAPM in 1963, and was the fourth recipient the AAPM Coolidge Award in 1975. The Marvin Williams Award was originally established as the highest award of the American College of Medical Physics. When various functions of the ACMP were absorbed into the AAPM in 2012, the Marvin M D Williams Professional Achievement Award became one of the AAPM’s highest honors. Learning Objectives: Become familiar with the persons in whose honor the three major AAPM Award are named Learn about the achievements and activities which influenced the AAPM to name these awards in their honor.

60 APPLIED LIFE SCIENCES↗

WE-G-213-00: History Symposium: Radiological Physics Pioneers: Roentgen and the AAPM Award Eponyms - William Coolidge, Edith Quimby, and Marvin Williams - Who Were They and What Did They Do?

Roentgen and the Birth of Modern Medical Physics – Perry Sprawls Wilhelm Roentgen is well known for his discovery of x-radiation. What is less known and appreciated is his intensive research following the discovery to determine the characteristics of the “new kind of radiation” and demonstrate its great value for medical purposes. In this presentation we will imagine ourselves in Roentgen’s mind and follow his thinking, including questions and doubts, as he designs and conducts a series of innovative experiments that provided the foundation for the rapid growth of medical physics. Learning Objectives: Become familiar with the personal characteristics and work of Prof. Roentgen that establishes him as an inspiring model for the medical physics profession. Observe the thought process and experiments that determined and demonstrated the comprehensive characteristics of x-radiation. The AAPM Award Eponyms: William D. Coolidge, Edith H. Quimby, and Marvin M.D. Williams - Who were they and what did they do? – Lawrence N. Rothenberg William David Coolidge (1873–1975) William Coolidge was born in Hudson, NY in 1873. He obtained his BS at the Massacusetts Institute of Technology in 1896. Coolidge then went to the University of Leipzig, Germany for graduate study with physicists Paul Drude and Gustave Wiedemann and received a Ph.D. in 1899. While in Germany he met Wilhelm Roentgen. Coolidge returned to the US to teach at MIT where he was associated with Arthur A. Noyes of the Chemistry Department, working on the electrical conductivity of aqueous solutions. Willis R. Whitney, under whom Coolidge had worked before going to Germany, became head of the newly formed General Electric Research Laboratory and he invited Coolidge to work with him. In 1905, Coolidge joined the staff of the GE laboratory and was associated with it for the remainder of his life. He developed ductile tungsten filaments to replace fragile carbon filaments as the material for electric light bulb filaments. Until that innovation light bulbs had a notoriously short life. He later incorporated the ductile tungsten as a filament material for a hot cathode, fully evacuated x-ray tube, first described in 1912, which allowed higher current and x-ray output, and greater reliability than had previously been possible. These “Coolidge x-ray tubes” were far superior to the cold cathode, partial pressure gas x-ray tubes that had been in use since Roentgen’s discovery of x-rays in 1895. The Coolidge tube with incremental developments is now the key component for x-ray production in all of our modern x-ray imaging devices, such as CT scanners, interventional radiology systems, and mammography units. Coolidge was also involved in the development of sectional x-ray tubes for research and treatment that were initially designed to reach 800 kV. Additional improvements led to 1 MV and 2 MV devices. In 1932 Coolidge became director of the General Electric Research Laboratory, and in 1940, was made Vice-President and Director of Research. In 1945 he retired and was named Director Emeritus of the laboratory. Coolidge held 83 patents and was recognized for these and many other achievements by election to the National Academy of Engineers, a place in the Engineering Hall of Fame and the National Inventor’s Hall of Fame. The AAPM’s highest honor, the Coolidge Award, was named after him. He accepted Honorary Membership in the AAPM and was the first recipient of the AAPM Coolidge Award, which was presented to him in a special ceremony in Schenectady, NY in 1972 when he was 100 years old. Edith Hinckley Quimby (1891–1982) Edith Quimby was born in Rockford, IL in 1891. She graduated from Whitman College in Walla Walla, WA with a B.S. in 1913, and then obtained a masters degree from the University of California at Berkeley. Later in her career, after many significant achievements, Quimby was awarded honorary doctorates by Whitman College and Rutgers University. Edith Quimby was hired by Giacchino Failla as a radiation physicist at Memorial Hospital for Cancer in New York City. Failla had studied with Madame Curie and obtained his doctoral degree in her laboratory. After many groundbreaking medical physics studies from 1919 until 1942, they both moved to Columbia University. Dr. Quimby developed a widely employed dosimetry system for single plane implants with radium and radon seeds, and a dosimetry methodology for internal radionuclides. She was author of more than 75 scientific publications, and of significant textbooks including the first comprehensive physics textbook for radiologists “Physical Foundations of Radiology”, which was co-authored with Otto Glasser, Lauriston Taylor and James Weatherwax in the first edition, with Russell Morgan added for the second edition and Paul Goodwin for the fourth edition. With Sergei Feitelberg, M.D. she published two editions of “Radioactive Isotopes in Medicine and Biology: Basic Physics and Instrumentation”. Quimby became a renowned examiner for the American Board of Radiology when the third ABR examination, given in 1936, added physics. She served as President of the American Radium Society, received the RSNA Gold Medal, and also numerous prestigious awards given to women in science. Edith Quimby was a Charter Member of AAPM. The AAPM Lifetime Achievement Award was renamed the Edith H. Quimby Lifetime Achievement Award in her honor in 2011. Marvin Martin Dixon Williams (1902–1981) Marvin Williams was born in Walla Walla, WA in 1902, and attended the same college as Edith Quimby, graduating from Whitman College in 1926. He was greatly influenced to go into medical physics by her accomplishments. During his early career, Williams worked with James Weatherwax in Philadelphia while he was working toward an M.S. from the University of Pennsylvania. In 1931 Williams was awarded a Ph.D. in Biophysics from the University of Minnesota, with the work actually performed at the Mayo Clinic Graduate School of the University. While completing his Ph.D. studies, Marvin met Dr. Paul Hodges who had returned from the Peiping Union Medical College in Peiping (now Beijing), China. Hodges suggested that a physicist be sent to Peiping to install x-ray therapy equipment and a radon plant. Williams accepted the position and, in 1931, he and his wife Orpha left for China. Before going to China, Williams had spent time with the physics group at Memorial Hospital to learn about the operation of a radon plant. In China, he constructed the radon plant, employing 0.25 g of radium, and also installed the x-ray therapy unit. Williams and his wife returned to the US in 1935, and he accepted a research position at the Mayo Clinic. In 1950, he became Professor of Biophysics at Mayo, where he taught physics and biophysics until his retirement in 1967. Williams was also very active in the American Board of Radiology where, from 1944 through 1977, he examined over 3000 radiologists and 250 physicists. Marvin Williams was a Charter member of AAPM, served as the fourth President of AAPM in 1963, and was the fourth recipient the AAPM Coolidge Award in 1975. The Marvin Williams Award was originally established as the highest award of the American College of Medical Physics. When various functions of the ACMP were absorbed into the AAPM in 2012, the Marvin M D Williams Professional Achievement Award became one of the AAPM’s highest honors. Learning Objectives: Become familiar with the persons in whose honor the three major AAPM Award are named Learn about the achievements and activities which influenced the AAPM to name these awards in their honor.

60 APPLIED LIFE SCIENCES↗

WE-G-213-02: The AAPM Award Eponyms: William D. Coolidge, Edith H. Quimby, and Marvin M.D. Williams - Who Were They and What Did They Do?

Roentgen and the Birth of Modern Medical Physics – Perry Sprawls Wilhelm Roentgen is well known for his discovery of x-radiation. What is less known and appreciated is his intensive research following the discovery to determine the characteristics of the “new kind of radiation” and demonstrate its great value for medical purposes. In this presentation we will imagine ourselves in Roentgen’s mind and follow his thinking, including questions and doubts, as he designs and conducts a series of innovative experiments that provided the foundation for the rapid growth of medical physics. Learning Objectives: Become familiar with the personal characteristics and work of Prof. Roentgen that establishes him as an inspiring model for the medical physics profession. Observe the thought process and experiments that determined and demonstrated the comprehensive characteristics of x-radiation. The AAPM Award Eponyms: William D. Coolidge, Edith H. Quimby, and Marvin M.D. Williams - Who were they and what did they do? – Lawrence N. Rothenberg William David Coolidge (1873–1975) William Coolidge was born in Hudson, NY in 1873. He obtained his BS at the Massacusetts Institute of Technology in 1896. Coolidge then went to the University of Leipzig, Germany for graduate study with physicists Paul Drude and Gustave Wiedemann and received a Ph.D. in 1899. While in Germany he met Wilhelm Roentgen. Coolidge returned to the US to teach at MIT where he was associated with Arthur A. Noyes of the Chemistry Department, working on the electrical conductivity of aqueous solutions. Willis R. Whitney, under whom Coolidge had worked before going to Germany, became head of the newly formed General Electric Research Laboratory and he invited Coolidge to work with him. In 1905, Coolidge joined the staff of the GE laboratory and was associated with it for the remainder of his life. He developed ductile tungsten filaments to replace fragile carbon filaments as the material for electric light bulb filaments. Until that innovation light bulbs had a notoriously short life. He later incorporated the ductile tungsten as a filament material for a hot cathode, fully evacuated x-ray tube, first described in 1912, which allowed higher current and x-ray output, and greater reliability than had previously been possible. These “Coolidge x-ray tubes” were far superior to the cold cathode, partial pressure gas x-ray tubes that had been in use since Roentgen’s discovery of x-rays in 1895. The Coolidge tube with incremental developments is now the key component for x-ray production in all of our modern x-ray imaging devices, such as CT scanners, interventional radiology systems, and mammography units. Coolidge was also involved in the development of sectional x-ray tubes for research and treatment that were initially designed to reach 800 kV. Additional improvements led to 1 MV and 2 MV devices. In 1932 Coolidge became director of the General Electric Research Laboratory, and in 1940, was made Vice-President and Director of Research. In 1945 he retired and was named Director Emeritus of the laboratory. Coolidge held 83 patents and was recognized for these and many other achievements by election to the National Academy of Engineers, a place in the Engineering Hall of Fame and the National Inventor’s Hall of Fame. The AAPM’s highest honor, the Coolidge Award, was named after him. He accepted Honorary Membership in the AAPM and was the first recipient of the AAPM Coolidge Award, which was presented to him in a special ceremony in Schenectady, NY in 1972 when he was 100 years old. Edith Hinckley Quimby (1891–1982) Edith Quimby was born in Rockford, IL in 1891. She graduated from Whitman College in Walla Walla, WA with a B.S. in 1913, and then obtained a masters degree from the University of California at Berkeley. Later in her career, after many significant achievements, Quimby was awarded honorary doctorates by Whitman College and Rutgers University. Edith Quimby was hired by Giacchino Failla as a radiation physicist at Memorial Hospital for Cancer in New York City. Failla had studied with Madame Curie and obtained his doctoral degree in her laboratory. After many groundbreaking medical physics studies from 1919 until 1942, they both moved to Columbia University. Dr. Quimby developed a widely employed dosimetry system for single plane implants with radium and radon seeds, and a dosimetry methodology for internal radionuclides. She was author of more than 75 scientific publications, and of significant textbooks including the first comprehensive physics textbook for radiologists “Physical Foundations of Radiology”, which was co-authored with Otto Glasser, Lauriston Taylor and James Weatherwax in the first edition, with Russell Morgan added for the second edition and Paul Goodwin for the fourth edition. With Sergei Feitelberg, M.D. she published two editions of “Radioactive Isotopes in Medicine and Biology: Basic Physics and Instrumentation”. Quimby became a renowned examiner for the American Board of Radiology when the third ABR examination, given in 1936, added physics. She served as President of the American Radium Society, received the RSNA Gold Medal, and also numerous prestigious awards given to women in science. Edith Quimby was a Charter Member of AAPM. The AAPM Lifetime Achievement Award was renamed the Edith H. Quimby Lifetime Achievement Award in her honor in 2011. Marvin Martin Dixon Williams (1902–1981) Marvin Williams was born in Walla Walla, WA in 1902, and attended the same college as Edith Quimby, graduating from Whitman College in 1926. He was greatly influenced to go into medical physics by her accomplishments. During his early career, Williams worked with James Weatherwax in Philadelphia while he was working toward an M.S. from the University of Pennsylvania. In 1931 Williams was awarded a Ph.D. in Biophysics from the University of Minnesota, with the work actually performed at the Mayo Clinic Graduate School of the University. While completing his Ph.D. studies, Marvin met Dr. Paul Hodges who had returned from the Peiping Union Medical College in Peiping (now Beijing), China. Hodges suggested that a physicist be sent to Peiping to install x-ray therapy equipment and a radon plant. Williams accepted the position and, in 1931, he and his wife Orpha left for China. Before going to China, Williams had spent time with the physics group at Memorial Hospital to learn about the operation of a radon plant. In China, he constructed the radon plant, employing 0.25 g of radium, and also installed the x-ray therapy unit. Williams and his wife returned to the US in 1935, and he accepted a research position at the Mayo Clinic. In 1950, he became Professor of Biophysics at Mayo, where he taught physics and biophysics until his retirement in 1967. Williams was also very active in the American Board of Radiology where, from 1944 through 1977, he examined over 3000 radiologists and 250 physicists. Marvin Williams was a Charter member of AAPM, served as the fourth President of AAPM in 1963, and was the fourth recipient the AAPM Coolidge Award in 1975. The Marvin Williams Award was originally established as the highest award of the American College of Medical Physics. When various functions of the ACMP were absorbed into the AAPM in 2012, the Marvin M D Williams Professional Achievement Award became one of the AAPM’s highest honors. Learning Objectives: Become familiar with the persons in whose honor the three major AAPM Award are named Learn about the achievements and activities which influenced the AAPM to name these awards in their honor.

60 APPLIED LIFE SCIENCES↗

Propagation of radio frequency waves through turbulent plasmas

The practical and economic viability of tokamak fusion reactors depends, in a significant way, on the efficiency of radio frequency (RF) waves to deliver energy and momentum to the plasma in the core of the reactor. The RF electromagnetic waves, excited by antenna structures placed near the wall of a tokamak, have to propagate through the turbulent edge plasma along their path to the core of the fusion device. In present day experiments, the radial width of the edge region and scrape-off layer is of the order of a few centimeters. In ITER, and in future fusion reactors, this width will be of the order of tens of centimeters. Any effects on RF waves due to plasma turbulence have to be properly understood in order to optimize the delivery of RF energy and momentum into the core. This paper is on a multi-pronged, theoretical and computational, approach that is being pursued to quantify the effect of edge plasma turbulence on the propagation of RF waves. The theoretical and analytical models are based on solutions of the Faraday-Ampere equation in a magnetized plasma and on the Kirchhoff tangent plane approximation. An effective medium approach has been developed so as to approximate the permittivity of a turbulent plasma by analytical expressions. The computations are being carried out with a newly developed code ScaRF that is based on the finite difference finite domain technique for solving Maxwell's equations. The plasma permittivity can be assigned as desired. The code is being used to validate the analytical and theoretical models and to evaluate their limitations.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗

The circumferentially notched cylindrical bar as a fracture toughness test specimen

The present work reviews the use of the notched cylinder as a screening specimen for use in sorting materials with respect to their relative levels of plane strain fracture toughness. Irwin's work in developing an estimate of stress intensity factors for the circumferentially cracked cylinder is reviewed. Some discrepancies between stress intensity factors determined with fatigue cracked notched cylinders and those determined with plate specimens are discussed. Problems in the technical realization of fatigue cracking a specimen are briefly discussed, and the problem of ensuring low eccentricity of loading when testing notch cylindrical specimens is considered. Finally, specimen size requirements for testing are examined.

Brown, W. F., Jr.↗

Volumetric pattern analysis of fuselage-mounted airborne antennas

A volumetric pattern analysis of fuselage-mounted airborne antennas at high frequencies was investigated. The primary goal of the investigation was to develop a numerical solution for predicting radiation patterns of airborne antennas in an accurate and efficient manner. An analytical study of airborne antenna pattern problems is presented in which the antenna is mounted on the fuselage near the top or bottom. Since this is a study of general-type commercial aircraft, the aircraft was modeled in its most basic form. The fuselage was assumed to be an infinitely long perfectly conducting elliptic cylinder in its cross-section and a composite elliptic cylinder in its elevation profile. The wing, cockpit, stabilizers (horizontal and vertical) and landing gear are modeled by "N" sided bent or flat plates which can be arbitrarily attached to the fuselage. The volumetric solution developed utilizes two elliptic cylinders, namely, the roll plane and elevation plane models to approximate the principal surface profile (longitudinal and transverse) at the antenna location. With the belt concept and the aid of appropriate coordinate system transformations the solution can be used to predict the volumetric patterns of airborne antennas in an accurate and efficient manner. Applications of this solution to various airborne antenna problems show good agreement with scale model measurements. Extensive data are presented for a microwave landing antenna system.

Yu, C. L.↗

Guidance of an aeromaneuvering orbit-to-orbit shuttle through a statistically varying atmosphere

One candidate for a reusable upper stage to be carried by the space shuttle is an aeromaneuvering orbit-to-orbit shuttle (AMOOS). This concept uses the drag of the vehicle during a pass through the atmosphere rather than the propulsion system to slow the vehicle on a return from a high energy orbit. The nature and magnitude of the sensitivity of AMOOS to uncertainties in the properties of the atmosphere are shown. Various guidance schemes for correcting for the effects that the unpredictable variations in the atmosphere have on the trajectory are discussed. For the mission studied here, a payload retrieval from geosynchronous orbit with aerodynamic plane change, a linear feedback guidance scheme was developed. A relatively simple heuristic law was used to demonstrate the concept. Using optimal control theory a feedback law was developed analytically. Testing with a large number of different atmospheres showed this law to be a feasible means of controlling the AMOOS trajectory. Refinements to the technique offer promise of significant improvement, and these are discussed.

Rehder, J. J.↗

Turbulent boundary layers with large streamline curvature effects

It has been shown that turbulent flows are greatly affected by streamline curvature. In spite of this and the fact that curved shear flows are frequently encountered in engineering applications, the predictions of such flows are relatively less developed than the predictions of two-dimensional plane flows. Recently, various attempts were made by different investigators; however, their methods are only successful when the product of the boundary layer thickness to the local surface curvature is approximately 0.05. The present paper investigates the more general case where this product is in the range from 0.1 to 0.5. Results show that the calculated boundary-layer characteristics for arbitrary free stream conditions are in good agreement with measurements.

So, R. M. C.↗

A semiclassical approach to collisional ionization with application to the Ar-He system

A semiclassical approach based on the propagation of classical trajectories on potential surfaces analytically continued into the complex plane, together with a discretization procedure, has been developed for the problem of collisional ionization. Based on Franck-Condon considerations the formalism is reduced to that of the two-state approximation. Preionization loss and tunnelling beyond turning points have not been considered. Calculated partial ionization cross sections for the Ar-He system show good agreement with a fully quantum mechanical treatment.

Lam, K.-S.↗

Finite dynamic element formulation for a plane triangular element

Higher order correction terms for the stiffness and inertia matrices associated with a triangular plane stress-strain finite dynamic element are developed in detail. Numerical results are presented which indicate that the adoption of these matrices along with a suitable quadratic matrix eigenproblem solver effects a significant economy in the free vibration solution of structure when compared with the analysis based on the usual finite element procedure. Finally, a FORTRAN IV computer program listing of the various relevant matrices is given.

Gupta, K. K.↗