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Articles 1 - 13 of 13
Full-Text Articles in Physics
Formation Of Even-Numbered Hydrogen Cluster Cations In Ultracold Helium Droplets, S. Jaksch, A. Mauracher, A. Bacher, S. Denifl, F. Ferreira De Silva, H. Schoebel, Olof E. Echt, T. D. Maerk, M. Probst, D. K. Bohme, P. Scheier
Formation Of Even-Numbered Hydrogen Cluster Cations In Ultracold Helium Droplets, S. Jaksch, A. Mauracher, A. Bacher, S. Denifl, F. Ferreira De Silva, H. Schoebel, Olof E. Echt, T. D. Maerk, M. Probst, D. K. Bohme, P. Scheier
Physics & Astronomy
Neutral hydrogen clusters are grown in ultracold helium nanodroplets by successive pickup of hydrogen molecules. Even-numbered hydrogen cluster cations are observed upon electron-impact ionization with and without attached helium atoms and in addition to the familiar odd-numbered H(n)(+). The helium matrix affects the fragmentation dynamics that usually lead to the formation of overwhelmingly odd-numbered H(n)(+). The use of high-resolution mass spectrometry allows the unambiguous identification of even-numbered H(n)(+) up to n congruent to 120 by their mass excess that distinguishes them from He(n)(+), mixed He(m)H(n)(+), and background ions. The large range in size of these hydrogen cluster ions is unprecedented, …
Molecular Nanoscience And Engineering On Surfaces, Willi Auwarter, Agustin Schiffrin, Alexander Weber-Bargioni, Yan Pennec, Andreas Riemann, Johannes V. Barth
Molecular Nanoscience And Engineering On Surfaces, Willi Auwarter, Agustin Schiffrin, Alexander Weber-Bargioni, Yan Pennec, Andreas Riemann, Johannes V. Barth
Physics & Astronomy
Molecular engineering of low-dimensional materials exploiting controlled self-assembly and positioning of individual atoms or molecules at surfaces opens up new pathways to control matter at the nanoscale. Our research thus focuses on the study of functional molecules and supramolecular architectures on metal substrates. As principal experimental tools we employ low-temperature scanning tunneling microscopy and spectroscopy. Here we review recent studies in our lab at UBC: Controlled manipulation of single CO molecules, self-assembled biomolecular nanogratings on Ag(111) and their use for electron confinement, as well as the organisation, conformation, metalation and electronic structure of adsorbed porphyrins.
Posteruptive Phenomena In Coronal Mass Ejections And Substorms: Indicators Of A Universal Process?, K. K. Reeves, T. B. Guild, W. J. Hughes, K. E. Korreck, J. Lin, J. Raymond, S. Savage, Nathan A. Schwadron, Harlan E. Spence, D. F. Webb, M. Wiltberger
Posteruptive Phenomena In Coronal Mass Ejections And Substorms: Indicators Of A Universal Process?, K. K. Reeves, T. B. Guild, W. J. Hughes, K. E. Korreck, J. Lin, J. Raymond, S. Savage, Nathan A. Schwadron, Harlan E. Spence, D. F. Webb, M. Wiltberger
Physics & Astronomy
[1] We examine phenomena associated with eruptions in the two different regimes of the solar corona and the terrestrial magnetosphere. We find striking similarities between the speeds of shrinking magnetic field lines in the corona and dipolarization fronts traversing the magnetosphere. We also examine the similarities between supra-arcade downflows observed during solar flares and bursty bulk flows seen in the magnetotail and find that these phenomena have remarkably similar speeds, velocity profiles, and size scales. Thus we show manifest similarities in the magnetic reconfiguration in response to the ejection of coronal mass ejections in the corona and the ejection of …
High-Efficiency Resonant Rf Spin Rotator With Broad Phase Space Acceptance For Pulsed Polarized Cold Neutron Beams, P. N. Seo, L. Barron-Palos, J. D. Bowman, T. E. Chupp, C Crawford, M. Dabaghyan, M. Dawkins, S. J. Freedman, T. Gentile, M. T. Gericke, R. C. Gillis, G. L. Greene, F. William Hersman, G. L. Jones, M. Kandes, S. Lamoreaux, B. Lauss, M. B. Lueschner, R. Mahurin, M. Mason, J. Mei, G. S. Mitchell, H. Nann, S. A. Page, S. I. Penttila, W. D. Ramsay, A. Salas Bacci, S. Santra, M. Sharma, T. B. Smith, W. M. Snow, W. S. Wilburn, H. Zhu
High-Efficiency Resonant Rf Spin Rotator With Broad Phase Space Acceptance For Pulsed Polarized Cold Neutron Beams, P. N. Seo, L. Barron-Palos, J. D. Bowman, T. E. Chupp, C Crawford, M. Dabaghyan, M. Dawkins, S. J. Freedman, T. Gentile, M. T. Gericke, R. C. Gillis, G. L. Greene, F. William Hersman, G. L. Jones, M. Kandes, S. Lamoreaux, B. Lauss, M. B. Lueschner, R. Mahurin, M. Mason, J. Mei, G. S. Mitchell, H. Nann, S. A. Page, S. I. Penttila, W. D. Ramsay, A. Salas Bacci, S. Santra, M. Sharma, T. B. Smith, W. M. Snow, W. S. Wilburn, H. Zhu
Physics & Astronomy
High precision fundamental neutron physics experiments have been proposed for the intense pulsed spallation neutron beams at JSNS, LANSCE, and SNS to test the standard model and search for new physics. Certain systematic effects in some of these experiments have to be controlled at the few ppb level. The NPDGamma experiment, a search for the small parity-violating gamma-ray asymmetry A(gamma) in polarized cold neutron capture on parahydrogen, is one example. For the NPDGamma experiment we developed a radio-frequency resonant spin rotator to reverse the neutron polarization in a 9.5 cm x 9.5 cm pulsed cold neutron beam with high efficiency …
Metrics For Solar Wind Prediction Models: Comparison Of Empirical, Hybrid, And Physics‐Based Schemes With 8 Years Of L1 Observations, M. J. Owens, Harlan E. Spence, S. Mcgregor, W. J. Hughes, J. M. Quinn, C. N. Arge, P. Riley, J. Linker, D. Odstrcil
Metrics For Solar Wind Prediction Models: Comparison Of Empirical, Hybrid, And Physics‐Based Schemes With 8 Years Of L1 Observations, M. J. Owens, Harlan E. Spence, S. Mcgregor, W. J. Hughes, J. M. Quinn, C. N. Arge, P. Riley, J. Linker, D. Odstrcil
Physics & Astronomy
[1] Space weather effects on technological systems originate with energy carried from the Sun to the terrestrial environment by the solar wind. In this study, we present results of modeling of solar corona-heliosphere processes to predict solar wind conditions at the L1 Lagrangian point upstream of Earth. In particular we calculate performance metrics for (1) empirical, (2) hybrid empirical/physics-based, and (3) full physics-based coupled corona-heliosphere models over an 8-year period (1995–2002). L1 measurements of the radial solar wind speed are the primary basis for validation of the coronal and heliosphere models studied, though other solar wind parameters are also considered. …
Ambient Solar Wind's Effect On Icme Transit Times, A. W. Case, Harlan E. Spence, M. J. Owens, P. Riley, D. Odstrcil
Ambient Solar Wind's Effect On Icme Transit Times, A. W. Case, Harlan E. Spence, M. J. Owens, P. Riley, D. Odstrcil
Physics & Astronomy
[1] Most empirical and numerical models of Interplanetary Coronal Mass Ejection (ICME) propagation use the initial CME velocity as their primary, if not only, observational input. These models generally predict a wide spread of 1 AU transit times for ICMEs with the same initial velocity. We use a 3D coupled MHD model of the corona and heliosphere to determine the ambient solar wind's effect on the propagation of ICMEs from 30 solar radii to 1 AU. We quantitatively characterize this deceleration by the velocity of the upstream ambient solar wind. The effects of varying solar wind parameters on the ICME …
Inherent Length-Scales Of Periodic Solar Wind Number Density Structures, N. M. Viall, L. Kepko, Harlan E. Spence
Inherent Length-Scales Of Periodic Solar Wind Number Density Structures, N. M. Viall, L. Kepko, Harlan E. Spence
Physics & Astronomy
[1] We present an analysis of the radial length-scales of periodic solar wind number density structures. We converted 11 years (1995–2005) of solar wind number density data into radial length series segments and Fourier analyzed them to identify all spectral peaks with radial wavelengths between 72 (116) and 900 (900) Mm for slow (fast) wind intervals. Our window length for the spectral analysis was 9072 Mm, approximately equivalent to 7 (4) h of data for the slow (fast) solar wind. We required that spectral peaks pass both an amplitude test and a harmonic F-test at the 95% confidence level simultaneously. …
An Event Study To Provide Validation Of Ting And Cmit Geomagnetic Middle-Latitude Electron Densities At The F2 Peak, A. G. Burns, W. Wang, M. Wiltberger, S. C. Soloman, Harlan E. Spence, T. L. Killeen, R. E. Lopez, J. E. Landivar
An Event Study To Provide Validation Of Ting And Cmit Geomagnetic Middle-Latitude Electron Densities At The F2 Peak, A. G. Burns, W. Wang, M. Wiltberger, S. C. Soloman, Harlan E. Spence, T. L. Killeen, R. E. Lopez, J. E. Landivar
Physics & Astronomy
[1] The coupled thermosphere-ionosphere magnetosphere (CMIT) model and the Thermosphere Ionosphere Nested Grid (TING) model have been run to simulate the 15 May 1997 interplanetary coronal mass ejection's (ICME) effects on the Earth's ionosphere and thermosphere. Comparisons were made between these model runs, the IRI-2007 model, and geomagnetic middle-latitude ionosonde data (NmF2) from the World Data Center to determine how well the models simulated the event and to understand the causes of model-data disagreement. The following conclusions were drawn from this study: (1) skill scores were more often negative than positive on average; (2) the best and the worst skill …
A Quantitative Assessment Of Empirical Magnetic Field Models At Geosynchronous Orbit During Magnetic Storms, Chia-Lin L. Huang, Harlan E. Spence, H. J. Singer, N. A. Tsyganenko
A Quantitative Assessment Of Empirical Magnetic Field Models At Geosynchronous Orbit During Magnetic Storms, Chia-Lin L. Huang, Harlan E. Spence, H. J. Singer, N. A. Tsyganenko
Physics & Astronomy
[1] We evaluate the performance of recent empirical magnetic field models (Tsyganenko, 1996, 2002a, 2002b; Tsyganenko and Sitnov, 2005, hereafter referred to as T96, T02 and TS05, respectively) during magnetic storm times including both pre- and post-storm intervals. The model outputs are compared with GOES observations of the magnetic field at geosynchronous orbit. In the case of a major magnetic storm, the T96 and T02 models predict anomalously strong negative Bz at geostationary orbit on the nightside due to input values exceeding the model limits, whereas a comprehensive magnetic field data survey using GOES does not support that prediction. On …
Geotail And Lfm Comparisons Of Plasma Sheet Climatology: 2. Flow Variability, T. B. Guild, Harlan E. Spence, E. L. Kepko, V. Merkin, J. G. Lyon, M. Wiltberger, C. C. Goodrich
Geotail And Lfm Comparisons Of Plasma Sheet Climatology: 2. Flow Variability, T. B. Guild, Harlan E. Spence, E. L. Kepko, V. Merkin, J. G. Lyon, M. Wiltberger, C. C. Goodrich
Physics & Astronomy
[1] We characterize the variability of central plasma sheet bulk flows with a 6-year Geotail data set and a 2-month Lyon-Fedder-Mobarry (LFM) global MHD simulation at two spatial resolutions. Comparing long databases of observed and simulated parameters enable rigorous statistical tests of the model's ability to predict plasma sheet properties during routine driving conditions and represent a new method of global MHD validation. In this study, we use probability density functions (PDFs) to compare the statistics of plasma sheet velocities in the Geotail observations with those in the LFM simulations. We find that the low-resolution model grossly underestimates the occurrence …
Geotail And Lfm Comparisons Of Plasma Sheet Climatology: 1. Average Values, T. B. Guild, Harlan E. Spence, E. L. Kepko, V. Merkin, J. G. Lyon, M. Wiltberger, C. C. Goodrich
Geotail And Lfm Comparisons Of Plasma Sheet Climatology: 1. Average Values, T. B. Guild, Harlan E. Spence, E. L. Kepko, V. Merkin, J. G. Lyon, M. Wiltberger, C. C. Goodrich
Physics & Astronomy
[1] We compare the statistics of central plasma sheet properties from 6 years of Geotail observations with 2 months of Lyon-Fedder-Mobarry (LFM) global MHD simulations. This statistical validation effort represents an inherently new method of systematically characterizing and quantifying global MHD model performance. For our comparison, we identify the central plasma sheet in the observations and simulation by identical criteria and select the simulation interval to ensure statistically similar distributions of solar wind conditions in both studies. After verifying our plasma sheet selection by inspecting the magnetic signatures of both studies, we compare the resultant number densities, thermal pressures, thermal …
Student Understanding Of Control Of Variables: Deciding Whether Or Not A Variable Influences The Behavior Of A System, Andrew Boudreaux, Peter S. Shaffer, Paula R. L. Heron, Lillian C. Mcdermott
Student Understanding Of Control Of Variables: Deciding Whether Or Not A Variable Influences The Behavior Of A System, Andrew Boudreaux, Peter S. Shaffer, Paula R. L. Heron, Lillian C. Mcdermott
Physics & Astronomy
The ability of adult students to reason on the basis of the control of variables was the subject of an extended investigation. This paper describes the part of the study that focused on the reasoning required to decide whether or not a given variable influences the behavior of a system. The participants were undergraduates taking introductory Physics and K-8 teachers studying physics and physical science in inservice institutes and workshops. Although most of the students recognized the need to control variables, many had significant difficulty with the underlying reasoning. The results indicate serious shortcomings in the preparation of future scientists …
Space Technology 5 Multi-Point Measurements Of Near-Earth Magnetic Fields: Initial Results, J. A. Slavin, G. Le, R. J. Strangeway, Y. Wang, S. A. Boardsen, M. B. Moldwin, Harlan E. Spence
Space Technology 5 Multi-Point Measurements Of Near-Earth Magnetic Fields: Initial Results, J. A. Slavin, G. Le, R. J. Strangeway, Y. Wang, S. A. Boardsen, M. B. Moldwin, Harlan E. Spence
Physics & Astronomy
[1] The Space Technology 5 (ST-5) mission successfully placed three micro-satellites in a 300 × 4500 km dawn-dusk orbit on 22 March 2006. Each spacecraft carried a boom-mounted vector fluxgate magnetometer that returned highly sensitive and accurate measurements of the geomagnetic field. These data allow, for the first time, the separation of temporal and spatial variations in field-aligned current (FAC) perturbations measured in low-Earth orbit on time scales of ∼10 sec to 10 min. The constellation measurements are used to directly determine field-aligned current sheet motion, thickness, and current density. In doing so, we demonstrate two multi-point methods for the …