The following aerospace firms have been cited in the works published from 1955 through 1974:  None of the reported experimental breakthroughs published during the 1950s and 1960s have been recognized by the aerospace community. Various reports indicated Brown's gravitators were the main experimental focus of the gravity control propulsion research. According to G. Harry Stine and Intel, research on Brown's gravitators became classified immediately after demonstrations of 30% weight reductions. Thomas Townsend Brown had obtained a British patent for high voltage, symmetric, parallel plate capacitors, that he called gravitators, in 1928. Brown claimed they would produce a net thrust in the direction of the anode of the capacitor that varied slightly with the positions of the Moon. The scientific community rejected such claims as products of pseudoscience and/or misinterpretations of ion wind effects. Independent research found small amounts of lift from Brown's gravitator based on an inefficient use of ionic propulsion. The devices were named Ion Lifters or Ionocraft and were reported to be able to lift the empty shell of a vehicle under ideal conditions, but not the additional machinery required to generate the electric field. Gravity effects were not found in the independent research. In July 1960, "Missiles and Rockets" reported Martin N. Kaplan, Senior Research Engineer, Electronics Division, Ryan Aeronautical Company, San Diego, had conducted anti-gravitational experiments yielding the promise of impulses, accelerations, and decelerations one hundred times the pull of gravity. Neither comments nor criticism of the report appeared in subsequent articles during the period of intensified gravity control propulsion research (see Section 1 of tractor beam for similar reports). Robert L. Forward, Hughes Research Laboratories, Malibu, described the theoretical generation of dipole gravitational fields by accelerating a super-dense fluid through pipes wound around a torus. Many of the contributors to general relativity have been supported by and/or associated with the ARL, RIAS, and/or the Gravity Research Foundation. The decades preceding the 1955 revelation of the gravity control propulsion research were a low water mark for general relativity. The following summarizes how the components of that research had stimulated the resurgence of general relativity:  Even though some of the physicists who attended the Gravity Day Conferences quietly mocked the anti-gravity mission of the Foundation, it provided significant contributions to mainstream physics. The "International Journal of Modern Physics D" has featured selected papers from the Gravity Research Foundation essay competition. Many have been incorporated with the collections of the Niels Bohr Library. A few of the Foundation essay contest winners became Nobel laureates (e.g., Ilya Prigogine, Maurice Allais, George F. Smoot).