A fast-neutron spectrometer of advanced design

Fast neutron spectrometer combines helium filled proportional counters with solid-state detectors to achieve the properties of high efficiency, good resolution, rapid response, and effective gamma ray rejection

Application of the Moessbauer technique to the study of probable lunar and planetary surface material and to the study of returned lunar surface samples Final report

Preliminary results from Mossbauer instrumental analysis of Apollo 12 lunar rock and soil sample

Fluctuation Superconductivity in Mesoscopic Aluminum Rings

Fluctuations are important near phase transitions, where they can be difficult to describe quantitatively. Superconductivity in mesoscopic rings is particularly intriguing because the critical temperature is an oscillatory function of magnetic field. There is an exact theory for thermal fluctuations in one-dimensional superconducting rings, which are therefore expected to be an excellent model system. We measure the susceptibility of many rings, one ring at a time, using a scanning SQUID that can isolate magnetic signals from seven orders of magnitude larger background applied flux. We find that the fluctuation theory describes the results and that a single parameter characterizes the ways in which the fluctuations are especially important at magnetic fields where the critical temperature is suppressed.Comment: Reprinted with permission from AAA

Anisotropic thermodynamics of d-wave superconductors in the vortex state

We show that the density of states and the thermodynamic properties of a 2D d-wave superconductor in the vortex state with applied magnetic field $\bf H$ in the plane depend on the angle between $\bf H$ and the order parameter nodes. Within a semiclassical treatment of the extended quasiparticle states, we obtain fourfold oscillations of the specific heat, measurement of which provides a simple probe of gap symmetry. The frequency dependence of the density of states and the temperature dependence of thermodynamic properties obey different power laws for field in the nodal and anti-nodal direction. The fourfold pattern is changed to twofold when orthorhombicity is considered.Comment: 5 pages, figures included, minor changes, published versio

A Terraced Scanning Superconducting Quantum Interference Device Susceptometer with Sub-Micron Pickup Loops

Superconducting Quantum Interference Devices (SQUIDs) can have excellent spin sensitivity depending on their magnetic flux noise, pick-up loop diameter, and distance from the sample. We report a family of scanning SQUID susceptometers with terraced tips that position the pick-up loops 300 nm from the sample. The 600 nm - 2 um pickup loops, defined by focused ion beam, are integrated into a 12-layer optical lithography process allowing flux-locked feedback, in situ background subtraction and optimized flux noise. These features enable a sensitivity of ~70 electron spins per root Hertz at 4K.Comment: See http://stanford.edu/group/moler/publications.html for an auxiliary document containing additional fabrication details and discussio

Computing Inferences for Large-Scale Continuous-Time Markov Chains by Combining Lumping with Imprecision

If the state space of a homogeneous continuous-time Markov chain is too large, making inferences - here limited to determining marginal or limit expectations - becomes computationally infeasible. Fortunately, the state space of such a chain is usually too detailed for the inferences we are interested in, in the sense that a less detailed - smaller - state space suffices to unambiguously formalise the inference. However, in general this so-called lumped state space inhibits computing exact inferences because the corresponding dynamics are unknown and/or intractable to obtain. We address this issue by considering an imprecise continuous-time Markov chain. In this way, we are able to provide guaranteed lower and upper bounds for the inferences of interest, without suffering from the curse of dimensionality.Comment: 9th International Conference on Soft Methods in Probability and Statistics (SMPS 2018