Large-Scale Forces and Small-Scale Experiments: Levitated Optomechanics for Precision Gravitational Measurements
We set out to combine a mechanical system in which classical mechanics breaks down and quantum mechanics must be used with a seemingly unlikely application, measurement of the strength and effects of gravity. Our optomechanical system consists of a silica microsphere levitated in ultra-high vacuum in a magneto-gravitational trap. The microsphere is trapped in a magnetic field gradient created by permanent magnets and ferromagnetic pole pieces using the weak diamagnetism of the particle. With optical position measurements and feedback, the mechanical motion can be cooled by several orders of magnitude, ideally reaching the quantum ground state. The extreme sensitivity of this optomechanical system to external forces makes it a promising approach to a new measurement of the Newtonian gravitational constant. Furthermore, by measuring the decoherence rate of non-classical motional states of the trapped particle, it may be possible to place limits on theories of gravitational decoherence. This material is based upon work supported by the National Science Foundation under Grant No. 1757005
Giannis Mpourmpakis and his students have proposed a bond-centric (BC) model able to capture cohesive energy trends over a range of monometallic and bimetallic nanoparticles and mixing behavior (excess energy) of nanoalloys, in great agreement with DFT calculations. This model utilizes to calculate the energetics of any nanoparticle morphology and chemical composition, thus significantly accelerating nanoalloys design. This work introduces a simple yet very powerful tool for nanoalloy design that can potentially help elucidate the energetics of alloy MNP genomes.
James R. Martin II
Michael Widom and his colleagues showed what happens at the grain boundaries of one particular alloy of the metals nickel and bismuth that makes it brittle in their paper published in Science. Using advanced electron microscopes, Widom’s collaborators at Lehigh University scrutinized these microscopic grain boundaries at an atomic level. In a "very heroic experimental program" they discovered that when grains met, the bismuth and nickel atoms realigned into lattices to form layered superstructures at the grain boundaries. These superstructures had previously been thought to exist only rarely in some alloys. Finding it at many different boundaries led the team to conclude that these superstructures are probably much more common than many people had thought.