33 research outputs found
Properties of AKR from an interferometer analysis of the ISEE-1 and -2 plasma wave data
Both ISEE 1 and 2 are equipped with identical wide-band analog plasma wave receivers which makes long baseline interferometry possible. A cross-correlation of the received signals from each spacecraft during periods of intense Auroral Kilometric Radiation (AKR) provides information on the source size of AKR. From the magnitude of the cross-correlation coefficient, measured over baselines from 40 Km to 8000 Km, an upper limit to the statistical source size can be determined. Thirty-five AKR events at 125 kHz are being analyzed. Preliminary results indicate that the apparent source sizes are smaller than .1 Re
Direction finding measurements of auroral kilometric radiation
Direction finding measurements with plasma wave experiments onboard the Hawkeye-1 and IMP-8 satellites were used to locate the source region of auroral kilometric radiation. The radiation exhibits peak intensities between about 100 kHz and 300 kHz, and emits intense sporadic bursts lasting for between one half hour to several hours. The total power emitted in this frequency range exceeds 10 to the 9th power watts at peak intensity. The occurrence of the radiation is known to be closely associated with bright auroral arcs which occur in the local evening auroral regions
Direction-finding measurements of type 3 radio bursts out of the ecliptic plane
Direction-finding measurements with the plasma wave experiments on the HAWKEYE 1 and IMP 8 satellites are used to find the source locations of type 3 solar radio bursts in heliocentric latitude and longitude in a frequency range from 31.1 kHz to 500 kHz. Using an empirical model for the emission frequency as a function of radial distance from the sun the three-dimensional trajectory of the type 3 radio source can be determined from direction-finding measurements at different frequencies. Since the electrons which produce these radio emissions follow the magnetic field lines from the sun these measurements provide information on the three-dimensional structure of the magnetic field in the solar wind. The source locations projected into the ecliptic plane follow an Archimedian spiral. Perpendicular to the ecliptic plane the source locations usually follow a constant heliocentric latitude. With direction-finding measurements of this type it is also possible to determine the source size from the modulation factor of the received signals
Exchange, interpretation, and database-search of ion mobility spectra supported by data format JCAMP-DX
To assist peak assignment in ion mobility spectrometry it is important to have quality reference data. The reference collection should be stored in a database system which is capable of being searched using spectral or substance information. We propose to build such a database customized for ion mobility spectra. To start off with it is important to quickly reach a critical mass of data in the collection. We wish to obtain as many spectra combined with their IMS parameters as possible. Spectra suppliers will be rewarded for their participation with access to the database. To make the data exchange between users and system administration possible, it is important to define a file format specially made for the requirements of ion mobility spectra. The format should be computer readable and flexible enough for extensive comments to be included. In this document we propose a data exchange format, and we would like you to give comments on it. For the international data exchange it is important, to have a standard data exchange format. We propose to base the definition of this format on the JCAMP-DX protocol, which was developed for the exchange of infrared spectra. This standard made by the Joint Committee on Atomic and Molecular Physical Data is of a flexible design. The aim of this paper is to adopt JCAMP-DX to the special requirements of ion mobility spectra
Dependence of CMI Growth Rates on Electron Velocity Distributions and Perturbation by Solitary Waves
We calculate growth rates and corresponding gains for RX and LO mode
radiation associated with the cyclotron maser instability for parameterized
horseshoe electron velocity distributions. The velocity distribution function
was modeled to closely fit the electron distribution functions observed in the
auroral cavity. We systematically varied the model parameters as well as the
propagation direction to study the dependence of growth rates on model
parameters. The growth rate depends strongly on loss cone opening angle, which
must be less than for significant CMI growth. The growth rate is
sharply peaked for perpendicular radiation (), with a
full-width at half-maximum , in good agreement with observed k-vector
orientations and numerical simulations. The fractional bandwidth varied between
10 and 10, depending most strongly on propagation direction. This
range encompasses nearly all observed fractional AKR burst bandwidths. We find
excellent agreement between the computed RX mode emergent intensities and
observed AKR intensities assuming convective growth length 20-40 km
and group speed 0.15. The only computed LO mode growth rates compatible
observed LO mode radiation levels occurred for number densities more than 100
times the average energetic electron densities measured in auroral cavities.
This implies that LO mode radiation is not produced directly by the CMI
mechanism but more likely results from mode conversion of RX mode radiation. We
find that perturbation of the model velocity distribution by large ion solitary
waves (ion holes) can enhance the growth rate by a factor of 2-4. This will
result in a gain enhancement more than 40 dB depending on the convective growth
length within the structure. Similar enhancements may be caused by EMIC waves.Comment: 21 pages, 11 figures. J. Geophys. Res. 2007 (accepted
Striated AKR Emission: A Remote Tracer of Ion Solitary Structures
We describe the statistical properties of narrowband drifting auroral
kilometric radiation ('striated' AKR) based on observations from the Cluster
wideband receiver during 2002-2005. We show that the observed characteristics,
including frequency drift rate and direction, narrow bandwidth, observed
intensity, and beaming angular sizes are all consistent with triggering by
upward traveling ion solitary structures (`ion holes'). We calculate the
expected perturbation of a horseshoe electron distribution function by an ion
hole by integrating the resonance condition for a cyclotron maser instability
(CMI) using the perturbed velocity distribution. We find that the CMI growth
rate can be strongly enhanced as the horseshoe velocity distribution contracts
inside the passing ion hole, resulting in a power gain increase greater than
100 dB. The gain curve is sharply peaked just above the R-mode cut-off
frequency, with an effective bandwidth ~50 Hz, consistent with the observed
bandwidth of striated AKR emission. Ion holes are observed in situ in the
acceleration region moving upward with spatial scales and speeds consistent
with the observed bandwidth and slopes of SAKR bursts. Hence, we suggest that
SAKR bursts are a remote sensor of ion holes and can be used to determine the
frequency of occurrence, locations in the acceleration region, and lifetimes of
these structures.Comment: 10 pages, 10 figures. J .Geophys. Res. (in press
Stakeholder Salience for Small Businesses : A Social Proximity Perspective
This paper advances stakeholder salience theory from the viewpoint of small businesses. It is argued that the stakeholder salience process for small businesses is influenced by their local embeddedness, captured by the idea of social proximity, and characterised by multiple relationships that the owner-manager and stakeholders share beyond the business context. It is further stated that the ethics of care is a valuable ethical lens through which to understand social proximity in small businesses. The contribution of the study conceptualises how the perceived social proximity between local stakeholders and small business owner-managers influences managerial considerations of the legitimacy, power and urgency of stakeholders and their claims. Specifically, the paradoxical nature of close relationships in the salience process is acknowledged and discussed.Peer reviewe
Computer interfaces using vision based gesture recognition
Bibliography: p. 138-150The primary objective of this thesis is to obtain information from a non-instrumented hand - including precise points of contact between the real hand and the virtual environment, and the recognition of meaningful hand postures - so that they can be used to replace standard input devices. Two different methods are presented in this thesis, ERSolitaire and finger classification, which recognize hand postures for use in a natural interface. ERSolitaire provides a grab-move-release interface to the standard game of solitaire, which allows the user to interact with virtual cards in a similar fashion as they would with real cards. The finger classification system provides a virtual touch interface by individually recognizing each of the five fingers. This provides greater power and flexibility than other similar systems, as well as a new technique for hand posture recognition
The Aerodynamics of Frisbee Flight
This project will describe the physics of a common Frisbee in flight. The aerodynamic forces acting on the Frisbee are lift and drag, with lift being explained by Bernoulli‘s equation and drag by the Prandtl relationship. Using V. R. Morrison‘s model for the 2-dimensional trajectory of a Frisbee, equations for the x- and y- components of the Frisbee‘s motion were written in Microsoft Excel and the path of the Frisbee was illustrated. Variables such as angle of attack, area, and attack velocity were altered to see their effect on the Frisbee‘s path and to speculate on ways to achieve maximum distance and height