arXiv subjects

Charles A. Hagedorn

Publications and source records attributed to Charles A. Hagedorn.

5 recordsLinked to original sources

arXiv2019

Inter-Party Avalanche Involvements May Increase Quadratically With Party Density

We estimate, from first-principles, the rate of inter-party avalanche involvements. The model suggests that the likelihood of inter-party involvements is quadratic in the density of parties -- twice as many parties quadruples the likelihood. The model predicts that when the product of the party-density and the area of a day's potential avalanches approaches one, inter-party avalanche involvements will become a substantial fraction of all avalanche involvements. As a corollary, the relative rate of inter-party involvements is expected to increase with avalanche size. We argue, with selected North American inter-party incidents from 2001-2019, that inter-party involvements are a timely concern. To spur conversation, we enumerate a variety of strategies that may mitigate inter-party hazard.

physics.soc-ph↗

arXiv2019

Constraints on axionlike dark matter with masses down to $10^{-23}$ eV/c$^2$

We analyzed an 6.7-year span of data from a rotating torsion-pendulum containing $\approx 10^{23}$ polarized electrons to search for the "wind" arising from ultralight, axionlike dark matter with masses between $10^{-23}$ and $10^{-18}$ eV/c$^2$. Over most of this range we obtain a 95\% confidence limit $F_{\rm a}/C_{\rm e} \geq 1 \times 10^{15}$ eV on the axionlike decay constant.

astro-ph.CO↗

arXiv2014

A high-precision mechanical absolute-rotation sensor

We have developed a mechanical absolute-rotation sensor capable of resolving ground rotation angle of less than 1 nrad$/\sqrt{\text{Hz}}$ above $30$ mHz and 0.2 nrad$/\sqrt{\text{Hz}}$ above $100$ mHz about a single horizontal axis. The device consists of a meter-scale beam balance, suspended by a pair of flexures, with a resonance frequency of 10.8 mHz. The center of mass is located 3 $μ$m above the pivot, giving an excellent horizontal displacement rejection of better than $3\times10^{-5}$ rad/m. The angle of the beam is read out optically using a high-sensitivity autocollimator. We have also built a tiltmeter with better than 1 nrad$/\sqrt{\text{Hz}}$ sensitivity above 30 mHz. Co-located measurements using the two instruments allowed us to distinguish between background rotation signal at low frequencies and intrinsic instrument noise. The rotation sensor is useful for rotational seismology and for rejecting background rotation signal from seismometers in experiments demanding high levels of seismic isolation, such as Advanced LIGO.

physics.ins-det↗

arXiv2011

Picoradian deflection measurement with an interferometric quasi-autocollimator using weak value amplification

We present an "interferometric quasi-autocollimator" that employs weak value amplification to measure angular deflections of a target mirror. The device has been designed to be insensitive to all translations of the target. We present a conceptual explanation of the amplification effect used by the device. An implementation of the device demonstrates sensitivities better than 10 picoradians per root hertz between 10 and 200 hertz.

physics.ins-det↗

arXiv2010

Indirect Evidence for Lévy Walks in Squeeze Film Damping

Molecular flow gas damping of mechanical motion in confined geometries, and its associated noise, is important in a variety of fields, including precision measurement, gravitational wave detection, and MEMS devices. We used two torsion balance instruments to measure the strength and distance-dependence of `squeeze film' damping. Measured quality factors derived from free decay of oscillation are consistent with gas particle superdiffusion in Lévy walks and inconsistent with those expected from traditional Gaussian random walk particle motion. The distance-dependence of squeeze film damping observed in our experiments is in agreement with a parameter-free Monte Carlo simulation. The squeeze film damping of the motion of a plate suspended a distance d away from a parallel surface scales with a fractional power between 1/d and 1/d^2.

gr-qc↗