A Compact Five-Channel VLF Wave Receiver for CubeSat Missions

Very low frequency (VLF) waves play an important role in controlling the evolution of energetic electron distributions in near-Earth space. This paper describes the design of a VLF receiver for the Climatology of Anthropogenic and Natural VLF Wave Activity in Space (CANVAS) CubeSat mission, designed to make continuous observations of VLF waves in low-Earth orbit originating from lightning and ground-based transmitters. The CANVAS VLF receiver will observe five components of VLF waves in the 0.3–40 kHz frequency range, using three orthogonal magnetic search coils deployed on the end of a 1-meter carbon fiber boom and four deployable electric field antennas operated as two orthogonal dipoles. Together, these five wave components will be used to calculate real and imaginary spectral matrix components using real-time fast Fourier transforms calculated in an onboard FPGA. Spectral matrix components will be averaged to obtain 1 second time resolution and frequency resolution better than 10%. The averaged spectral matrix will be used to determine the complete set of wave parameters, including Poynting flux, polarization, planarity, and k-vector direction. CANVAS is currently in the manufacturing and assembly phase and is planned to launch at the end of 2022

Conjugate Generators of Knot and Link Groups

This note shows that if two elements of equal trace (e.g., conjugate elements) generate an arithmetic two-bridge knot or link group, then the elements are parabolic. This includes the figure-eight knot and Whitehead link groups. Similarly, if two conjugate elements generate the trefoil knot group, then the elements are peripheral.Comment: 10 pages, submitted to Journal of Knot Theory and Its Ramification

Are 3C249.1 and 3C334 restarted quasars?

This Research Note follows up a Letter in which I posit that J1211+743 is a restarted radio source. This means that its structure, where the jet points to the relic lobe, is only apparently paradoxical. Here, I propose the same scenario and apply the same mathematical model to 3C249.1 and 3C334. The ultimate result of my investigation is that these two well-known radio-loud quasars can be understood best so far if it was assumed that they, too, had been restarted.Comment: 4 pages, accepted for publication in A&A as a Research Not

Frequency of shearing increases growth of fibre and changes objective and subjective attributes of Angora goat fleeces

The impact of genotype and of frequency and timing of shearing, on mohair attributes and production of modern Angora goats was studied. Goats in the southern hemisphere grazed pastures between February 2004 and 2006. There were seven shearing treatments by three genetic strains with four or eight replicates of individual goats. Treatments were: three different 6-month shearing intervals and two of 12-month shearing intervals with different months of shearing, a 7-month winter shearing interval and a 3-month shearing interval. Genetic strain was based on sire line: 1&middot;0 South African; 1&middot;0 Texan; and Mixed 0&middot;5 South African and 0&middot;5 Texan. Annual greasy mohair production was 5&middot;08 kg, and average clean fleece production was 4&middot;37 kg. The Angora goats produced an annual clean fleece equivalent to 0&middot;122 of their mean fleece-free live weight which was equal to 0&middot;34 g/kg/day. Measurements were analysed over the period of spring 2004 shearing to spring 2005 shearing, excluding the June&ndash;December shearing treatment. Increased frequency of shearing increased fleece growth and affected 13 objective and subjective attributes of mohair that were evaluated including clean washing yield, fibre diameter and fibre diameter variation, incidence of medullated fibres, staple length, fibre curvature, crimp frequency, style, staple definition, staple fibre entanglement and staple tip shape. The direction of these effects were generally favourable and for most attributes the magnitude of the response was linear and commercially important. Each additional shearing resulted in an additional 149 g of clean mohair representing 0&middot;034 of the annual clean mohair production. This increase was associated with a 0&middot;6 cm increase in staple length and 0&middot;32 &mu;m increase in mean fibre diameter. In conclusion, Angora goats shorn less frequently grew less mohair that was more likely to be entangled in spring. Managers of Angora goats should take note of these findings.<br /

The CANVAS Mission: Quantifying the Very-Low-Frequency Radio Energy Input from the Ground into the Earth\u27s Magnetosphere

Very-low-frequency (VLF) electromagnetic waves, emitted by ground-based sources including lightning and VLF transmitters, can impact the lower ionosphere and magnetosphere through their interaction with the local plasma and energetic particle environments. Quantifying the impacts of these waves requires an accurate assessment of the propagation and attenuation of these waves. The Climatology of Anthropogenic and Natural VLF wave Activity in Space (CANVAS) mission is designed to measure VLF waves in low Earth orbit originating from these ground-based sources. The mission aims to characterize the VLF environment in low Earth orbit to address two main goals: i) constrain the VLF wave injection from the ground into the magnetosphere, and ii) improve models of VLF wave attenuation during propagation through the ionosphere. CANVAS will measure VLF waves using three search coil magnetometers and two electric field dipole antennas that comprise its payload. The search coils are integrated into a 3D-printed Carbon PEEK holder, along with the magnetic field preamplifier board. The search coil system is deployed 1 meter from the spacecraft using a carbon fiber deployable boom, in order to isolate the sensitive search coils from spacecraft noise. The electric field system is composed of four 40 cm monopole antennas, making two orthogonal dipole antennas, integrated into the spacecraft “crown”, along with a custom preamplifier circuit for each monopole. The payload is completed by a custom analog receiver board, providing amplification, anti-alias filtering, and centering for the analog-to-digital converters (ADCs); and a custom digital board, which includes an FPGA for onboard signal processing. Spectral data spanning 0.3–40 kHz are saved at 1-second cadence, providing a continuous “fast survey” data mode for the duration of the mission. The CANVAS spacecraft is a 4U CubeSat, 10 × 10 × 45 cm and under 6 kg. In addition to the 1-meter deployable carbon fiber boom and electric field antennas, the spacecraft incorporates deployable solar panels and a monopole antenna for UHF communications. Data is downlinked in S-band. The spacecraft structure and avionics are custom-designed and built at CU Boulder, while the radios and attitude determination and control system (ADCS) are vendor-supplied components. The CANVAS mission is designed to operate at ∼500 km altitude in a moderate-inclination orbit (∼50 degrees), to ensure global coverage of lightning-generating regions; most lightning globally is confined to within ±50 degrees latitude. Spectra at 1-second cadence account for ∼424 MB of data per day, after housekeeping and encoding overhead. A one-year mission will ensure seasonal coverage to observe the Marshall 1 36th Annual Small Satellite Conference variability in global lightning activity. This paper presents a detailed overview of the CANVAS science goals, payload, spacecraft, and mission. The instrument is now completed and undergoing functional testing and performance characterization, and the spacecraft is beginning integration, expected to be completed in Fall 2022. The CANVAS mission will be ready to launch in early 2023

Developing a Novel Platform for Characterizing Thermoelectric Materials for Uncooled Detectors for Land Imaging Applications

Thermal land imaging (imaging at ~8-14 micron optical wavelength) is an essential tool for understanding and managing terrestrial freshwater resources. Current thermal imaging instruments employ low temperature detectors, which require cryocoolers. Consequently, cost-saving reductions in size, weight, and power can be achieved by employing uncooled detectors. One uncooled detector concept, which NASA is pursuing, is a thermopile detector with sub-micron thick doped-Si thermoelectric materials. In order to characterize the thermoelectric properties of the doped silicon, we designed and optimized a novel apparatus. This simple apparatus measures the Seebeck coefficient with thermally isolated stages and LABVIEW automation. We optimized thermal stability using PID tuning and optimized the thermal contact between the thin film samples and stages using electrically conductive springs. Utilizing our apparatus, we measured the Seebeck coefficient of 0.45 micron thick phosphorus-doped single crystal Si samples bonded to alumina substrates. Using these Seebeck coefficient measurements and four-wire electrical resistivity measurements, we determined the relationship between the thermoelectric figure of merit and dopant concentration. These characterization results for doped-Si will guide our thermopile detector design to provide an optimal and competitive detector alternative for future thermal imaging instruments

The radio source population at high frequency: follow-up of the 15-GHz 9C survey

We have carried out extensive radio and optical follow-up of 176 sources from the 15 GHz 9th Cambridge survey. Optical identifications have been found for 155 of the radio sources; optical images are given with radio maps overlaid. The continuum radio spectrum of each source spanning the frequency range 1.4 - 43 GHz is also given. Two flux-limited samples are defined, one containing 124 sources complete to 25 mJy and one of 70 sources complete to 60 mJy. Between one fifth and one quarter of sources from these flux-limited samples display convex radio spectra, rising between 1.4 and 4.8 GHz. These rising-spectrum sources make up a much larger fraction of the radio source population at this high selection frequency than in lower frequency surveys. We find that by using non-simultaneous survey flux density measurements at 1.4 and 15 GHz to remove steep spectrum objects, the efficiency of selecting objects with spectra rising between 1.4 and 4.8 GHz (as seen in simultaneous measurements) can be raised to 49 percent without compromising the completeness of the rising spectrum sample.Comment: 40 pages, 223 figures. Accepted for publication in MNRAS. Version with full size images (A4 paper) avaliable at http://www.mrao.cam.ac.uk/publications/papers files ME777.ps and ME777.pd

A Study of 3CR Radio Galaxies from z = 0.15 to 0.65. II. Evidence for an Evolving Radio Structure

Radio structure parameters were measured from the highest quality radio maps available for a sample of 3CR radio galaxies in the redshift range 0.15 < z < 0.65. Combined with similar data for quasars in the same redshift range, these morphology data are used in conjunction with a quantification of the richness of the cluster environment around these objects (the amplitude of the galaxy-galaxy spatial covariance function, Bgg) to search for indirect evidence of a dense intracluster medium (ICM). This is done by searching for confinement and distortions of the radio structure that are correlated with Bgg. Correlations between physical size and hot spot placement with Bgg show evidence for an ICM only at z 0.4, suggesting an epoch of z ~ 0.4 for the formation of an ICM in these Abell richness class 0-1, FR2-selected clusters. X-ray selected clusters at comparable redshifts, which contain FR1 type sources exclusively, are demonstrably richer than the FR2-selected clusters found in this study. The majority of the radio sources with high Bgg values at z < 0.4 can be described as ``fat doubles'' or intermediate FR2/FR1s. The lack of correlation between Bgg and bending angle or Bgg and lobe length asymmetry suggests that these types of radio source distortion are caused by something other than interaction with a dense ICM. Thus, a large bending angle cannot be used as an unambiguous indicator of a rich cluster around powerful radio sources. These results support the hypothesis made in Paper 1 that cluster quasars fade to become FR2s, then FR1s, on a timescale of 0.9 Gyrs (for H0 = 50 km s^-1 Mpc^-1).Comment: 44 pages, 8 figures, 2 tables; to be published in the September 2002 issue of The Astronomical Journa

Spectroscopic and Mechanistic Studies of Heterodimetallic Forms of Metallo-β-lactamase NDM-1

In an effort to characterize the roles of each metal ion in metallo-β-lactamase NDM-1, heterodimetallic analogues (CoCo-, ZnCo-, and CoCd-) of the enzyme were generated and characterized. UV–vis, 1H NMR, EPR, and EXAFS spectroscopies were used to confirm the fidelity of the metal substitutions, including the presence of a homogeneous, heterodimetallic cluster, with a single-atom bridge. This marks the first preparation of a metallo-β-lactamase selectively substituted with a paramagnetic metal ion, Co(II), either in the Zn1 (CoCd-NDM-1) or in the Zn2 site (ZnCo-NDM-1), as well as both (CoCo-NDM-1). We then used these metal-substituted forms of the enzyme to probe the reaction mechanism, using steady-state and stopped-flow kinetics, stopped-flow fluorescence, and rapid-freeze-quench EPR. Both metal sites show significant effects on the kinetic constants, and both paramagnetic variants (CoCd- and ZnCo-NDM-1) showed significant structural changes on reaction with substrate. These changes are discussed in terms of a minimal kinetic mechanism that incorporates all of the data