Hybrid computer technique yields random signal probability distributions

Hybrid computer determines the probability distributions of instantaneous and peak amplitudes of random signals. This combined digital and analog computer system reduces the errors and delays of manual data analysis

Power and cross-power spectrum analysis by hybrid computers

Power and cross power spectrum analysis by hybrid computer

Solar spin down and neutrino fluxes

Effects of core spin-down process on neutrino flux in solar evolution theor

An investigation of pulsar searching techniques with the Fast Folding Algorithm

Here we present an in-depth study of the behaviour of the Fast Folding Algorithm, an alternative pulsar searching technique to the Fast Fourier Transform. Weaknesses in the Fast Fourier Transform, including a susceptibility to red noise, leave it insensitive to pulsars with long rotational periods (P > 1 s). This sensitivity gap has the potential to bias our understanding of the period distribution of the pulsar population. The Fast Folding Algorithm, a time-domain based pulsar searching technique, has the potential to overcome some of these biases. Modern distributed-computing frameworks now allow for the application of this algorithm to all-sky blind pulsar surveys for the first time. However, many aspects of the behaviour of this search technique remain poorly understood, including its responsiveness to variations in pulse shape and the presence of red noise. Using a custom CPU-based implementation of the Fast Folding Algorithm, ffancy, we have conducted an in-depth study into the behaviour of the Fast Folding Algorithm in both an ideal, white noise regime as well as a trial on observational data from the HTRU-S Low Latitude pulsar survey, including a comparison to the behaviour of the Fast Fourier Transform. We are able to both confirm and expand upon earlier studies that demonstrate the ability of the Fast Folding Algorithm to outperform the Fast Fourier Transform under ideal white noise conditions, and demonstrate a significant improvement in sensitivity to long-period pulsars in real observational data through the use of the Fast Folding Algorithm.Comment: 19 pages, 15 figures, 3 table

Spectra of Atmospheric and Astronomical Molecules

Spectroscopy techniques are focused on spectra of molecules of interest to the Earth’s atmosphere and/or astronomy and astrophysics. Laboratory spectroscopy as well as remote satellite sensing are applied. Using the Fourier transform spectrometer aboard the Atmospheric Chemistry Experiment (ACE) satellite to measure the absorption spectra of the Earth’s atmosphere through solar occultation limb observation demonstrates that volcanic eruption plumes can be located and tracked through their SO2 content. The presence of those plumes is corroborated by overlaying infrared atmospheric aerosol extinction observed by the 1 μm imager on the same satellite. Tracking atmospheric aerosol movement with the ACE imager is also shown to provide key insights into the impact of the unique January 2022 Hunga Tonga-Hunga Ha’apai volcanic eruption on Earth’s atmosphere. ACE satellite data analysis has also been used to better understand seasonal fractionation patterns of NO2 and HNO3 in the stratosphere. Rotational analysis of previously recorded laboratory spectra of the TiO molecule is used to generate new line lists and spectroscopic constants for the E3Π−X3Δ and B3Π−X3Δ electron transitions as well as the A3Φ−X3Δ electron transitions of all four minor TiO isotopologues. New laboratory spectra collected using a Fourier transform infrared spectrometer is shown to improve the known infrared cross sections of cyclohexane

Rapid neutron capture in supernova explosions

Rapid neutron capture in supernova explosion

On the Snow Line in Dusty Protoplanetary Disks

The snow line, in Hayashi's (1981) model, is where the temperature of a black body that absorbed direct sunlight and re-radiated as much as it absorbed, would be 170~K. It is usually assumed that the cores of the giant planets, e.g., Jupiter, form beyond the snow line. Since Hayashi, there have been a series of more detailed models of the absorption by dust of the stellar radiation, and of accretional heating, which alter the location of the snow line. We have attempted a "self-consistent" model of a T Tauri disk in the sense that we used dust properties and calculated surface temperatures that matched observed disks. We then calculated the midplane temperature for those disks, with no accretional heating or with small (<10^-8) accretion rates. Our models bring the snow line in to the neighbourhood of 1 AU; not far enough to explain the close planetary companions to other stars, but much closer than in recent starting lines for orbit migration scenarios.Comment: 9 pages, 1 figure, to appear in ApJ,528,200

Load fluctuations drive actin network growth

The growth of actin filament networks is a fundamental biological process that drives a variety of cellular and intracellular motions. During motility, eukaryotic cells and intracellular pathogens are propelled by actin networks organized by nucleation-promoting factors, which trigger the formation of nascent filaments off the side of existing filaments in the network. A Brownian ratchet (BR) mechanism has been proposed to couple actin polymerization to cellular movements, whereby thermal motions are rectified by the addition of actin monomers at the end of growing filaments. Here, by following actin--propelled microspheres using three--dimensional laser tracking, we find that beads adhered to the growing network move via an object--fluctuating BR. Velocity varies with the amplitude of thermal fluctuation and inversely with viscosity as predicted for a BR. In addition, motion is saltatory with a broad distribution of step sizes that is correlated in time. These data point to a model in which thermal fluctuations of the microsphere or entire actin network, and not individual filaments, govern motility. This conclusion is supported by Monte Carlo simulations of an adhesion--based BR and suggests an important role for membrane tension in the control of actin--based cellular protrusions.Comment: To be published in PNA