Quantum whistling in superfluid 4He

Fundamental considerations predict that macroscopic quantum systems such as superfluids and the electrons in superconductors will exhibit oscillatory motion when pushed through a small constriction. Here we report the observation of these oscillations between two reservoirs of superfluid 4He partitioned by an array of nanometer-sized apertures. They obey the Josephson frequency equation and are coherent amongst all the apertures. This discovery at the relatively high temperature of 2K (2000 times higher than related phenomena in 3He) may pave the way for a new class of practical rotation sensors of unprecedented precision.Comment: 6 pages, 3 figures, to be published in Natur

Archaeological Investigations at the Box Plant Site, Henry County, Virginia

Research Report No. 13, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Archaeological Investigations at the Philpott Site, Henry County, Virginia

Research Report No. 19, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Archaeological Investigations at the Dallas Hylton Site, Henry County, Virginia

Research Report No. 18, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Archaeological Investigations at the Gravely Site, Henry County, Virginia

Research Report No. 17, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Archaeological Investigations at the Stockton Site, Henry County, Virginia

Research Report No. 14, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Archaeological Investigations at the Wells Site, Henry County, Virginia

Research Report No. 16, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

Archaeological Investigations at the Belmont Site, Henry County, Virginia

Research Report No. 15, Research Laboratories of Archaeology, University of North Carolina at Chapel Hill. Reports in this series discuss the findings of archaeological excavations and research projects undertaken by the RLA between 1984 and present

The effect of boundary conditions on resonant ultrasonic spherical chains

The response of a resonant chain of spheres to changes in holder material and pre-compression is studied at ultrasonic frequencies. The system is found to be very sensitive to these parameters, with the creation of impulsive waveforms from a narrow bandwidth input seen only for certain chain lengths and holder materials. In addition, careful experiments were performed using known amounts of pre-compression force, using a calibrated stylus arrangement. At negligible pre-compression levels, impulses were generated within the chain, which were then suppressed by increased pre-compression. This was accompanied by large changes in propagation velocity as the system gradually changes from being strongly nonlinear to being more linear. Simulations using a discrete model for the motion of each sphere agree well with experimental data

Ultrasonic propagation in finite-length granular chains

A narrowband ultrasound source has been used to generate solitary wave impulses in finite-length chains of spheres. Once the input signal is of sufficient amplitude, both harmonics and sub-harmonics of the input frequency can be generated as non-linear normal modes of the system, allowing a train of impulses to be established from a sinusoidal input. The characteristics of the response have been studied as a function of the physical properties of the chain, the input waveform and the level of static pre-compression. The results agree with the predictions of a theoretical model, based on a set of discrete dynamic equations for the spheres for finite-length chains. Impulses are only created for very small pre-compression forces of the order of 0.01 N, where strongly non-linear behaviour is expected