Professor Georgii D. Mansfeld The time and frequency control community lost one of its most innovative leaders, Georgii D. Mansfeld, 71, who collapsed and died on his way to work on November 17, 2011. Georgii D. Mansfeld was born in Moscow in 1940. He received the PhD degree from the Moscow Institute of Physics and Technology (1970) and D.Sci. from the Institute of Radioengineering and Electronics (IRE) of the Russian Academy of Sciences for his work “Acoustoelectronic interaction in semiconductors in an AC electric field” (1984). Professor Mansfeld was the Head of the IRE Laboratory for many years. He taught many generations of students at the Moscow Institute of Physics and Technology. During the first years of his career, in the late 1960s, he experimented with microwave BAW generation using a high resistivity depletion layer (either natural, or induced) by a DC field effect close to the surface of a piezoelectric semiconductor. Later in his career, he made significant contributions to the experimental studies of amplification of acoustic waves in semiconductors by electron drift and a variety of acoustoelectronic phenomena in the frequency range 0.5 – 9.4GHz. He confirmed, experimentally, a new mechanism of acoustoelectronic nonlinearity, the so called “electron momentum” nonlinearity. This work was the first direct experimental observation of nonlinear Landau damping in electron plasma in solids. He conducted systematic studies of acoustic waves in polycrystalline ferrites, new piezoelectric materials (particularly quartz-like crystals) and microwave resonators. Professor Mansfeld was originator of microwave resonance acoustic loss spectroscopy of thin piezoelectric films and layers. Using this technique, original data on attenuation constants in thin crystalline layers, carbon nanotubes and Langmuir-Blodgett films at microwave frequencies were obtained. Professor Mansfeld was an active IEEE member, chairing the Russian chapter of the UFFC and participating in the Technical Program Committee of IEEE Frequency Control Symposia. He received the 2005 European Frequency and Time award and the 2011 IEEE Cady Award for pioneering research in physical acoustoelectronics and acoustics. Georgii is survived by his wife, Valentina, his daughter and two grandchildren. People knew Georgii as a kind, gentle and generous man who was always open to his friends, colleagues and students. His bright image will always live in our hearts.