A Low Temperature Nonlinear Optical Rotational Anisotropy Spectrometer for the Determination of Crystallographic and Electronic Symmetries

Nonlinear optical generation from a crystalline material can reveal the symmetries of both its lattice structure and underlying ordered electronic phases and can therefore be exploited as a complementary technique to diffraction based scattering probes. Although this technique has been successfully used to study the lattice and magnetic structures of systems such as semiconductor surfaces, multiferroic crystals, magnetic thin films and multilayers, challenging technical requirements have prevented its application to the plethora of complex electronic phases found in strongly correlated electron systems. These requirements include an ability to probe small bulk single crystals at the micron length scale, a need for sensitivity to the entire nonlinear optical susceptibility tensor, oblique light incidence reflection geometry and incident light frequency tunability among others. These measurements are further complicated by the need for extreme sample environments such as ultra low temperatures, high magnetic fields or high pressures. In this review we present a novel experimental construction using a rotating light scattering plane that meets all the aforementioned requirements. We demonstrate the efficacy of our scheme by making symmetry measurements on a micron scale facet of a small bulk single crystal of Sr$_2$IrO$_4$ using optical second and third harmonic generation.Comment: 8 pages, 5 figure

Leo Marx's Legacy

An assessment of Leo Marx’s career, from his youthin New York and Paris, Harvard education, and military servicein World War II, to the major themes in his scholarship during65 years of teaching at Minnesota, Amherst College, and MIT.Best known for his The Machine in the Garden, Marx was oneof the founding scholars of American Studies, but he alsomade seminal contributions to the History of Technology andthe environmental humanities. His work remains a useful legacy forscholars assessing technological solutions proposed to dealwith ecological crises

Harari's world history:Evolution toward intelligence without consciousness?

Yuval Noah Harari’s three books, Sapiens: A Brief History of Hu-mankind, Homo Deus: A Brief History of Tomorrow, and 21 Lessons for the 21st Century, propose a sweeping world history that takes an externalist view of technology, minimizing the importance of cultural difference and individual free will. His deterministic narrative argues that a single world culture is emerging and that artificial intelligence inevitably will replace human consciousness. In this story, technology is increasingly powerful, while inventors, entrepreneurs, and consumers have little influence over events. A far more convincing popular overview based on a more contextual approach could be constructed based on research on technology and culture that Harari disregards.</p

Negative compressibility in platinum sulfide using density-functional theory

Copyright © 2010 The American Physical SocietyThe structural and dynamic properties of the mineral Cooperite (PtS) are investigated using density-functional theory. The results show that a competition with the less symmetric but more compact PdS structure leads to a phase transition when the pressure is increased. However, before the phase transition, PtS displays a rare anomalous elastic behavior by expanding along its long axis under hydrostatic pressure. We report the elastic constants of PtS and interpret this negative linear compressibility in the context of a displacive phase transition. We also show that the real structure of PtS is less symmetric than originally determined by experiment

WHAT WAS THE ASSEMBLY LINE ?

ABSTRACTThe Ford assembly line of 1913 was part of a long series of process innovations that began a century before and that have continued since, notably in the lean production system. This paper examines the historical emergence and synthesis of the five essential elements of the classic assembly line – sub-division of work, interchangeability, single-function machines, organization of machines according to the sequence of assembly, and moving work to the worker, typically using gravity slides or moving belts – and further shows that full electrification was an essential precondition for its creation and proper functioning. In contrast, “scientific management” was not important to the creation of the assembly line