Open Access. Powered by Scholars. Published by Universities.®
Physical Sciences and Mathematics Commons™
Open Access. Powered by Scholars. Published by Universities.®
Articles 1 - 12 of 12
Full-Text Articles in Physical Sciences and Mathematics
Using Economic Instruments To Develop Effective Management Of Invasive Species: Insights From A Bioeconomic Model, Shana M. Mcdermott, Rebecca E. Irwin, Brad W. Taylor
Using Economic Instruments To Develop Effective Management Of Invasive Species: Insights From A Bioeconomic Model, Shana M. Mcdermott, Rebecca E. Irwin, Brad W. Taylor
Dartmouth Scholarship
Economic growth is recognized as an important factor associated with species invasions. Consequently, there is increasing need to develop solutions that combine economics and ecology to inform invasive species management. We developed a model combining economic, ecological, and sociological factors to assess the degree to which economic policies can be used to control invasive plants. Because invasive plants often spread across numerous properties, we explored whether property owners should manage invaders cooperatively as a group by incorporating the negative effects of invader spread in management decisions (collective management) or independently, whereby the negative effects of invasive plant spread are ignored …
Collisionless Reconnection: Magnetic Field Line Interaction, R A. Treumann, W Baumjohann, W. D. Gonzalez
Collisionless Reconnection: Magnetic Field Line Interaction, R A. Treumann, W Baumjohann, W. D. Gonzalez
Dartmouth Scholarship
Magneticfieldlinesarequantumobjectscarrying onequantum0=2πh ̄/eofmagneticfluxandhavefinite radius λm. Here we argue that they possess a very specific dynamicalinteraction.Parallelfieldlinesrejecteachother. When confined to a certain area they form two-dimensional lattices of hexagonal structure. We estimate the filling factor of such an area. Anti-parallel field lines, on the other hand, at- tract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we de- termine quantum mechanically for two parallel and two anti- parallel field lines. The distortion of the quantum electrody- namic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate …
The Role Of The Bow Shock In Solar Wind-Magnetosphere Coupling, R E. Lopez, V G. Merkin, J G. Lyon
The Role Of The Bow Shock In Solar Wind-Magnetosphere Coupling, R E. Lopez, V G. Merkin, J G. Lyon
Dartmouth Scholarship
No abstract provided.
Field Line Distribution Of Density At L=4.8 Inferred From Observations By Cluster, R E. Denton, P Décréau, M J. Engebretson, F Darrouzet
Field Line Distribution Of Density At L=4.8 Inferred From Observations By Cluster, R E. Denton, P Décréau, M J. Engebretson, F Darrouzet
Dartmouth Scholarship
For two events observed by the CLUSTER space- craft, the field line distribution of mass density ρ was inferred from Alfve ́n wave harmonic frequencies and compared to the electron density ne from plasma wave data and the oxy- gen density nO+ from the ion composition experiment. In one case, the average ion mass M≡ρ/ne was about 5amu (28 October 2002), while in the other it was about 3 amu (10 September 2002). Both events occurred when the CLUSTER 1 (C1) spacecraft was in the plasmatrough. Nevertheless, the electron density ne was significantly lower for the first event (ne =8 …
Pfisr Nightside Observations Of Naturally Enhanced Ion Acoustic Lines, And Their Relation To Boundary Auroral Features, R. G. Michell, K. A. Lynch, C. J. Heinselman, H. C. Stenbaek-Nielsen
Pfisr Nightside Observations Of Naturally Enhanced Ion Acoustic Lines, And Their Relation To Boundary Auroral Features, R. G. Michell, K. A. Lynch, C. J. Heinselman, H. C. Stenbaek-Nielsen
Dartmouth Scholarship
We present results from a coordinated camera and radar study of the auroral ionosphere conducted during March of 2006 from Poker Flat, Alaska. The campaign was conducted to coincide with engineering tests of the first quarter installation of the Poker Flat Incoherent Scatter Radar (PFISR). On 31 March 2006, a moderately intense auroral arc, (~10 kR at 557.7 nm), was located in the local magnetic zenith at Poker Flat. During this event the radar observed 7 distinct periods of abnormally large backscattered power from the F-region. These were only observed in the field-aligned radar beam, and radar spectra from these …
The Chemical Distribution In A Subluminous Type Ia Supernova: Hubble Space Telescope Images Of The Sn 1885 Remnant, Robert A. Fesen, Peter A. Hoflich, Andrew J. S. Hamilton, Molly C. Hammell
The Chemical Distribution In A Subluminous Type Ia Supernova: Hubble Space Telescope Images Of The Sn 1885 Remnant, Robert A. Fesen, Peter A. Hoflich, Andrew J. S. Hamilton, Molly C. Hammell
Dartmouth Scholarship
SN 1885 was a probable subluminous SN Ia that occurred in the bulge of the Andromeda galaxy, M31, at a projected location 16'' from the nucleus. Here we present and analyze Hubble Space Telescope images of the SN 1885 remnant seen in absorption against the M31 bulge via the resonance lines of Ca I, Ca II, Fe I, and Fe II. Viewed in Ca II H and K line absorption, the remnant appears as a nearly black circular spot with an outermost angular radius of 0.40'' ± 0.025'', implying a maximum linear radius of 1.52 ± 0.15 pc at M31's …
Quickest Flows Over Time, Lisa Fleischer, Martin Skutella
Quickest Flows Over Time, Lisa Fleischer, Martin Skutella
Dartmouth Scholarship
Flows over time (also called dynamic flows) generalize standard network flows by introducing an element of time. They naturally model problems where travel and transmission are not instantaneous. Traditionally, flows over time are solved in time‐expanded networks that contain one copy of the original network for each discrete time step. While this method makes available the whole algorithmic toolbox developed for static flows, its main and often fatal drawback is the enormous size of the time‐expanded network. We present several approaches for coping with this difficulty. First, inspired by the work of Ford and Fulkerson on maximal s‐t …
Discovery Of Outlying High-Velocity Oxygen-Rich Ejecta In Cassiopeia A, Robert A. Fesen, Molly C. Hammell, Jon Morse, Roger A. Chevalier, Kazimierz J. Borkowski, Michael A. Dopita, Christopher L. Gerardy, Stephen S. Lawrence, John C. Raymond, Sydney Van Den Bergh
Discovery Of Outlying High-Velocity Oxygen-Rich Ejecta In Cassiopeia A, Robert A. Fesen, Molly C. Hammell, Jon Morse, Roger A. Chevalier, Kazimierz J. Borkowski, Michael A. Dopita, Christopher L. Gerardy, Stephen S. Lawrence, John C. Raymond, Sydney Van Den Bergh
Dartmouth Scholarship
Analysis of broadband HST ACS and WFPC2 images of the young Galactic supernova remnant Cassiopeia A reveals a far larger population of outlying, high-velocity knots of ejecta with a broader range of chemical properties than previously suspected. ACS filte r flux ratios along with follow-up, ground-based spectra are used to investigate some of the kinema tic and chemical properties of these outermost ejecta. In this paper, we concentrate on a ≃ 1.5 sq arcmin region located along the eastern limb of the remnant where numerous outer emission knots are optica lly visible due to an interaction with a local circumstellar …
Model Simulations Of A Shock‐Cloud Interaction In The Cygnus Loop, Daniel J. Patnaude, Robert A. Fesen
Model Simulations Of A Shock‐Cloud Interaction In The Cygnus Loop, Daniel J. Patnaude, Robert A. Fesen
Dartmouth Scholarship
We present optical observations and two-dimensional hydrodynamic modeling of an isolated shocked ISM cloud. Hα images taken in 1992.6 and 2003.7 of a small optical emission cloud along the southwestern limb of the Cygnus Loop were used to measure positional displacements of ~01 yr-1 for surrounding Balmer-dominated emission filaments and 0025-0055 yr-1 for internal cloud emission features. These measurements imply transverse velocities of 250 and 80-140 km s-1 for ambient ISM and internal cloud shocks, respectively. A lack of observed turbulent gas stripping at the cloud-ISM boundary in the Hα images suggests that there is not an …
Simulations Of Resonant Alfvén Waves Generated By Artificial Hf Heating Of The Auroral Ionosphere, D Pokhotelov, W Lotko, A V. Streltsov
Simulations Of Resonant Alfvén Waves Generated By Artificial Hf Heating Of The Auroral Ionosphere, D Pokhotelov, W Lotko, A V. Streltsov
Dartmouth Scholarship
Numerical two-dimensional two-fluid MHD sim- ulations of dynamic magnetosphere-ionosphere (MI) cou- pling have been performed to model the effects imposed on the auroral ionosphere by a powerful HF radio wave trans- mitter. The simulations demonstrate that modifications of the ionospheric plasma temperature and recombination due to artificial heating may trigger the ionospheric feedback in- stability when the coupled MI system is close to the state of marginal stability. The linear dispersion analysis of MI coupling has been performed to find the favorable conditions for marginal stability of the system. The development of the ionospheric feedback instability leads to the generation …
High-Latitude Propagation Studies Using A Meridional Chain Of Lf/Mf/Hf Receivers, J Labelle
High-Latitude Propagation Studies Using A Meridional Chain Of Lf/Mf/Hf Receivers, J Labelle
Dartmouth Scholarship
For over a decade, Dartmouth College has oper- ated programmable radio receivers at multiple high-latitude sites covering the frequency range 100–5000 kHz with about a 1-s resolution. Besides detecting radio emissions of auro- ral origin, these receivers record characteristics of the iono- spheric propagation of natural and man-made signals, docu- menting well-known effects, such as the diurnal variation in the propagation characteristics of short and long waves, and also revealing more subtle effects. For example, at auroral zone sites in equinoctial conditions, the amplitudes of dis- tant transmissions on MF/HF frequencies are often enhanced by a few dB just before …
A Study Of Pc-5 Ulf Oscillations, M K. Hudson, R E. Denton, M R. Lessard, E G. Miftakhova, R R. Anderson
A Study Of Pc-5 Ulf Oscillations, M K. Hudson, R E. Denton, M R. Lessard, E G. Miftakhova, R R. Anderson
Dartmouth Scholarship
A study of Pc-5 magnetic pulsations using data from the Combined Release and Radiation Effects Satellite (CRRES) was carried out. Three-component dynamic mag- netic field spectrograms have been used to survey ULF pul- sation activity for the approximate fourteen month lifetime of CRRES. Two-hour panels of dynamic spectra were exam- ined to find events which fall into two basic categories: 1) toroidal modes (fundamental and harmonic resonances) and 2) poloidal modes, which include compressional oscillations. The occurence rates were determined as a function of L value and local time. The main result is a comparable probabil- ity of occurence of …