3,266 research outputs found
Voyage of the Northern Light : newspaper reports and articles.
No full textCover title.; For private circulation only.; Contains typescript copy of a letter from the author to the Daily telegraph.; Library's N copy is inscribed "To the Editor Bulletin, Joshua Slocum ... Strictly private". ANL; Electronic reproduction. Canberra, A.C.T. : National Library of Australia, 2009
Joshua Davis: Author of Spare Parts
No full textCitation: K-State First (2016). Joshua Davis: Author of Spare Parts [Flier]. Manhattan, Kansas: K-State First.Flyer advertising Joshua Davis's author talk at Kansas State University
Indigeous author talk
No full textA unique online author event celebrating the diversity of literature created by and for Two-Spirit and Indigiqueer people. This event features writers and creators T’áncháy Redvers and Joshua Whitehead in conversation with host Taya Jardine.Other UBCNon UBCUnreviewedOthe
Hebrew made easy [electronic resource] : or, a brief introduction to the Hebrew grammar, (upon a new and delightful plan); Whereby our British Gentlemen and Ladies may, in so very short a Time as Twenty-Four Days, learn the most necessary and essential Variations of that incomparable Language, without the Help of the Latin, or the Assistance of a Master. The second edition, with additions. By the author of The great importance of the Hebrew language.
No full textThe author of "The great importance of the Hebrew language" = Joshua Kettilby.Kettilby's 'Hebrew made easy' was first published in [1760?] (c.f.t123545). 'The excellency and great importance of the Hebrew language ... by Joshua Kettilby, author of Hebrew made easy' was published in 1762 (c.f.t183663)Electronic reproduction.English Short Title Catalog,Reproduction of original from Bodleian Library (Oxford)
Reply to Joshua Meltzer
No full textA reply to Joshua Meltzer\u27s comment on the author\u27s paper Bridging Fragmentation and Unity: International Law as a Universe of Inter-Connected Island
Satellite swarms for auroral plasma science
No full textWith the growing accessibility of space, this thesis work sets out to explore space-based swarms to do multipoint magnetometer measurements of current systems embedded within the Aurora Borealis as an initial foray into concepts for space physics applications using swarms of small spacecraft.
As a pathfinder, ANDESITE---a 6U CubeSat with eight deployable picosatellites---was built as part of this research. The mission will fly a local network of magnetometers above the Northern Lights. With the spacecraft due to launch on an upcoming ELaNa mission, here we discuss the details of the science motivation, the mathematical framework for current field reconstruction, the particular hardware implementation selected, the calibration procedures, and the pragmatic management needed to realize the spacecraft.
After describing ANDESITE and defining its capability, we also propose a follow-on that uses propulsive nodes in a swarm, allowing measurements that can adaptively change to capture the physical phenomena of interest. To do this a flock of satellites needs to fall into the desired formation and maintain it for the duration of the science mission. A simple optimal controller is developed to model the deployment of the satellites. Using a Monte Carlo approach for the uncertain initial conditions, we bound the fuel cost of the mission and test the feasibility of the concept.
To illustrate the system analysis needed to effectively design such swarms, this thesis also develops a framework that characterizes the spatial frequency response of the kilometer-scale filter created by the swarm as it flies through various current density structures in the ionospheric plasma. We then subjugate a nominal ANDESITE formation and the controlled swarm specified to the same analysis framework. The choice of sampling scheme and rigorous basic mathematical analysis are essential in the development of a multipoint-measurement mission.
We then turn to a novel capability exploiting current trends in the commercial industry. Magnetometers deployed on the largest constellation to date are leveraged as a space-based magnetometer network. The constellation, operated by Planet Labs Inc., consists of nearly 200 satellites in two polar sun-synchronous orbits, with median spacecraft separations on the order of 375 km, and some occasions of opportunity providing much closer spacing. Each spacecraft contains a magneto-inductive magnetometer, able to sample the ambient magnetic field at 0.1 Hz to 10 Hz with <200 nT sensitivity. A feasibility study is presented wherein seven satellites from the Planet constellation were used to investigate space-time patterns in the current systems overlying an active auroral arc over a 10-minute interval.
Throughout the this work advantages, limitations, and caveats in exploiting networks of lower quality magnetometers are discussed, pointing out the path forward to creating a global network that can monitor the space environment
Key to the genera of the Cerambycidae of western North America
No full textJames R. LaBonte, Joshua B. Dunlap, Daniel R. Clark, Thomas E. Valente, Joshua J. Vlach, Oregon Department of Agriculture.Title from PDF cover (viewed on October 20, 2021).Covers OCLC #1277514227 and OCLC #1226522396.This archived document is maintained by the State Library of Oregon as part of the Oregon Documents Depository Program. It is for informational purposes and may not be suitable for legal purposes.Mode of access: Internet from the Oregon Government Publications Collection.Text in English
Quantifying loss of current sheet scattered electrons during the substorm growth phase
No full textParticles trapped in the magnetosphere are naturally accelerated by the exchange of electromagnetic and kinetic energy, resulting in relativistic plasma populations. Through a number of processes, these particles can be scattered into the atmosphere and lost to interactions. Such precipitating particles can affect radio communications, ozone chemistry, and thermal structures. For these reasons, it is important to characterize loss mechanisms and quantify precipitation rates. This thesis examines one particular loss mechanism known as current sheet scattering (CSS).
If interactions are negligible, charged particles in a magnetic field have approximately conserved quantities that characterize their motion provided the background field changes sufficiently slowly over space and time. The first of these ‘adiabatic invariants,’ the magnetic moment, is related to the particle’s mirror point along its bounce trajectory—the location at which the particle reverses direction in its journey from weaker to stronger B. In the equatorial region of the near-Earth magnetotail, where the radius of field line curvature of the magnetic field can become comparable to the gyroradius of ≈ 100 keV electrons, the homogeneity conditions needed for conservation of the magnetic moment of this population are broken. Upon passing through this location, known as the current sheet, these particles experience a chaotic change in their magnetic moment, and thus an alteration of their mirror point. This is the phenomenon of CSS. If the resulting mirror point lies within the atmosphere, the particle will most likely be lost through interactions.
CSS is often investigated for highly relativistic electrons. However, recent observations suggest that this mechanism may account for a significant proportion of precipitating electrons between 100 and 300 keV during the substorm growth phase, a common space weather event wherein magnetic field lines in the near-Earth magnetotail become highly stretched. In this thesis, we test the efficacy of CSS as a loss mechanism for < 300 keV electrons by developing a relativistic charged particle tracer capable of solving complex trajectories in realistic magnetospheric magnetic field models. We then find distributional characteristics through Monte Carlo methods, comparing simulated ratios of loss- to total-flux with observations of the same quantities for a single substorm event. These observations are obtained by comparison of in situ measurements made by THEMIS (Time History of Events and Macroscale Interactions during Substorms) with ionospheric energy flux remotely sensed by PFISR (Poker Flat Incoherent Scatter Radar).
Given an input distribution from THEMIS satellite measurements, we find agreement between observed and simulated loss- to total-flux ratios within an order of magnitude, with closer agreement for electrons between 100 and 300 keV. This implies CSS can explain a significant proportion of observed precipitation for the event studied and demonstrates its role as a prominent radiation belt loss mechanism. In particular, these findings suggest that the measured loss flux of < 300 keV electrons during such events can be immediately related to the geometry of the near-Earth magnetotail. This is further supported by a parametric study of initially field aligned distributions spawned at various nightside locations, showing a low-energy peak in the loss- to total-flux ratio at the boundary between the outermost radiation belt and the magnetotail. Measurements of particle orientation taken from THEMIS are low resolution, and agreement between simulated and observed loss- to total-flux ratios can be increased by assuming a more field aligned distribution for electrons below 100 keV. This suggests the presence of other physical processes besides CSS that may preferentially structure the pitch angle distributions of low energy electrons to be field aligned. Additional analysis is needed to identify these possible mechanisms.
In summary, findings from this work support the role of CSS as an important contributor to < 300 keV electron loss during the substorm growth phase. Though there is an underestimation of loss for < 100 keV electrons, it is known that the empirical magnetic field models employed overestimate the radius of curvature in the current sheet. Furthermore, the dawn-dusk electric field has been neglected, though it has the possibility to produce field aligned electrons through current sheet acceleration. The inclusion of these effects in future studies may further improve agreement between simulation and observations
Data driven techniques to advance our understanding of the STEVE phenomenon
No full textStrong Thermal Emission Velocity Enhancement (STEVE) is an optical phenomenon in Earth’s ionosphere that has recently captured the attention of both citizen and professional scientists. STEVE appears as a mauve-white elongated band stretching for a few thousand kilometers across the night sky during the recovery phase of an auroral substorm. It is sometimes accompanied by quasiperiodic collimated green rays known as the ‘picket fence’. The picket fence has been observed to be localized to a section of the STEVE.
STEVE has been observed to occur during the recovery phase of a substorm, which is an abrupt global-scale change in Earth’s magnetotail that releases energy stored in the nightside magnetosphere into two nightside polar ionospheres via field-aligned currents and particle precipitation.
This thesis employs data fusion and image processing methodologies from a remote sensing perspective to advance our understanding of the STEVE phenomenon. Additionally, it offers insights into the application of deep learning techniques in this field.
This thesis is divided into three parts. In the first part, we examine the morphology and velocity of features based on citizen science observations of STEVE. High-resolution imaging of the complete life cycle of a STEVE with a picket fence reveals fine-scale white pillar-like structures seemingly accelerating as they move westward, with an average velocity of ~13km/s. Individual pickets of the picket fence move much slower, at speeds of ~1km/s. This provides weak evidence for acceleration of features in STEVE, though we are limited by the geometry of the system.
The second part examines Total Electron Content (TEC) variations during a STEVE. TEC is a measurement of the ionospheric activity and has not been examined for a STEVE in the literature yet, largely due to a lack of Global Navigation Satellite System (GNSS) receivers in locations where a STEVE exists. We observe high-resolution (15-second) changes in TEC during a STEVE event on the 26 March 2008, which occurred over a region with a large amount of GNSS receivers. We observe a sudden jump in TEC as the STEVE propagates towards the equator and another jump as the auroral oval expands. For another substorm in the same region on 1 March 2011, we do not see this two-stage jump.
The third part examines the feasibility of detecting a STEVE as it occurs, based on data from ASIs. We adapt and enhance an algorithm originally designed for identifying faint sources in astronomical images to detect STEVE phenomena within faint and noisy All-Sky Imager (ASI) images. We then examine the performance of the ConvNeXt computer vision model in classifying ASI images with and without STEVE. We finally discuss the difficulty in applying computer vision models for the detection of this phenomenon, which is largely due to the low occurrence rate, and give some insight into strategies such as active learning and open set recognition which can potentially be used to identify STEVE in different ASI data
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