Physical Sciences and Mathematics Commons^™

Viewing A Graph In A Virtual Reality Display Is Three Times As Good As A 2d Diagram, Colin Ware, Glenn Franck

Center for Coastal and Ocean Mapping

An experiment is reported which tests whether network information is more effectively displayed in a three dimensional space than in a two dimensional space. The experimental task is to trace a path in a network and the experiment is carried out in 2D, in a 3D stereo view, in a 2D view with head coupled perspective, and in a 3D stereo view with head coupled perspective; this last condition creates a localized virtual reality display. The results show that the motion parallax obtained from the head coupling of perspective is more important than stereopsis in revealing structural information. Overall the …

Representing Nodes And Arcs In 3d Networks, Glenn Franck, Colin Ware

Center for Coastal and Ocean Mapping

This paper introduces six graphical principles for 30 network displays. These are justified with examples from GraphVisualizer3D, a system developed by the authors to investigate the problems of 30 visualization of information networks. GraphVisualizer3D enables the exploration of sulface color, surface texture, object shape, arc shape and labeling conventions.

Temporal Alternation Between Light- And Nutrient-Limitation Of Phytoplankton Production In A Coastal Plain Estuary., Jonathan Pennock, Jonathan H. Sharp

School of Marine Science and Ocean Engineering

ABSTRACT: The potential for Light- and nutrient-limitation of phytoplankton production was examined in the Delaware Estuary, USA, by combining a hierarchy of expenmental approaches including smallscale bioassay experiments, ecosystem-level analysis of nutrient concentration and stoichiometric ratios, and light-limitation modeling. Light was found to be the predominate regulator of phytoplankton growth throughout the estuary during the winter period as a result of high turbidity and a wellmixed water column. However, during late spring, phosphorus (P) was found to limit growth. This observation was confirmed at each of the experimental levels, and was related to several factors, including elevated input ratios (230:l) …

Soluble Acidic Species In Air And Snow At Summit, Greenland, Jack E. Dibb, R. Talbot, M H. Bergin

Earth Sciences

Simultaneous measurements of the concentrations of soluble acidic species in the gas, aerosol and snow phases at Summit, Greenland were made during summer 1993. Mean concentrations of gas phase HCOOH, CH₃COOH, and HNO₃ (49±28, 32±17 and 0.9±0.6 nmol m⁻³ STP, respectively) exceeded the concentrations of aerosol-associated HCOO⁻, CH₃COO⁻, and NO₃⁻by 1–3 orders of magnitude. On average, SO₂ concentrations (0.9±0.6 nmol m⁻³ STP) were approximately 1/3 those of aerosol SO₄⁼, but this ratio varied widely due largely to changes in the concentration of …

Estimation Of Stratospheric Input To The Arctic Troposphere: 7be And 10be In Aerosols At Alert, Canada, Jack E. Dibb, David Meeker, R C. Finkel, J Southon, Marc W. Caffee, Leonard A. Barrie

Earth Sciences

Concentrations of 7Be and 210Pb in 2 years of weekly high-volume aerosol samples collected at Alert, Northwest Territories, Canada, showed pronounced seasonal variations. We observed a broad winter peak in 210Pb concentration and a spring peak in 7Be. These peaks were similar in magnitude and duration to previously reported results for a number of stations in the Arctic Basin. Beryllium 10 concentrations (determined only during the first year of this study) were well correlated with those of 7Be; the atom ratio 10Be/7Be was nearly constant at 2.2 throughout the year. This relatively high value of 10Be/7Be indicates that the stratosphere …

Comptel Imaging Of The Galactic Disk And The Separation Of Diffuse Emission And Point Sources, H Bloemen, W Hermsen, B Swanenburg, C De Vries, R Diehl, V. Schonfelder, H Steinle, A W. Strong, A Connors, Mark L. Mcconnell, D Morris, G Stacy, K Bennett, C Winkler

Physics & Astronomy

The first MeV image of the inner Galaxy obtained with the COMPTEL telescope aboard the Compton Gamma-Ray Observatory shows a structured ridge of emisssion along the Galactic equator which probably consists of diffuse radiation and unresolved discrete sources. The intensity distribution of this ridge distinctly differs from the expected distribution for a simple model of the diffuse radiation. Most remarkable are the observed excursions out of the disk, which may hint at the presence of gamma-ray point sources located several degrees away from the mid-plane, but a diffuse origin cannot be excluded. If these are indeed discrete sources, a substantial …

Application Of A Maximum Likelihood Processor To Acoustic Backscatter For The Estimation Of Seafloor Roughness Parameters, Zoi-Heleni Michalopoulou, Christian De Moustier

Center for Coastal and Ocean Mapping

Maximum likelihood (ML) estimation is used to extract seafloor roughness parameters from records of acoustic backscatter. The method relies on the Helmholtz–Kirchhoff approximation under the assumption of a power‐law roughness spectrum and on the statistical modeling of bottom reverberation. The result is a globally optimum, highly automated technique that is a useful tool in the context of seafloor classification via remote acoustic sensing. The general geometry of the Sea Beam bathymetric system is incorporated into the design of the ML processor in order to make it applicable to real acoustic data collected by this system. The processor is initially tested …

Observations Of Gamma-Ray Bursts By Comptel, L O. Hanlon, K Bennett, W Collmar, A Connors, R Diehl, R Van Dijk, J Greiner, J W. Den Herder, W Hermsen, R M. Kippen, L Kuiper, Mark L. Mcconnell, James M. Ryan, V. Schonfelder, H Steinle, A W. Strong, M Varendorff, C Winkler

Physics & Astronomy

During the first year of operation, 22 cosmic gamma-ray bursts were detected within the field of view of the COMPTEL instrument on board the Compton Gamma Ray Observatory. Spectra and time histories for the strongest of these bursts have been obtained from both the main instrument (0.75-30 MeV) and the burst modules (0.3-10 MeV). The deconvolved photon spectra for the majority of bursts are fit by a single power law model with spectral index between -1.6 and -2.8. One strong burst, GRB 910814, exhibited significant curvature and could not be fit by a single power law model. A broken power …

Observations Of Cygnus X-1 Comptel During 1991, Mark L. Mcconnell, D J. Forrest, James M. Ryan, W Collmar, V. Schonfelder, H Steinle, A W. Strong, R Van Dijk, W Hermsen, K Bennett

Physics & Astronomy

The Compton Telescope (COMPTEL) experiment on the Compton Gamma-Ray Observatory (CGRO) has observed the Cygnus region on two occasions during the first (sky survey) phase of its mission. These data represent the most sensitive observations to date of Cygnus X-1 in the 0.75-30 MeV range. The observations in 1991 June and August both showed evidence for emission in the 0.75-2 MeV energy range. The flux level was larger by about a factor of 2 during the August observation. The spectral data were analyzed in the context of a Wien spectral model (the high-energy limit of the Sunyaev-Titarchuk Comptonization spectrum). Fits …

Comptel Measurements Of The Gamma-Ray Burst Grb 930131, James M. Ryan, K Bennett, W Collmar, A Connors, Gerald J. Fishman, J Greiner, L O. Hanlon, W Hermsen, R M. Kippen, C Kouveliotou, L Kuiper, G G. Lichti, John R. Macri, J. Mattox, Mark L. Mcconnell, B Mcnamara, C Meegan, V. Schonfelder, R Vandijk, M Varendorff, W Webber, C Winkler

Physics & Astronomy

On 1993 January 31 at 1857:12 Universal Time (UT), the Imaging Compton Telescope COMPTEL onboard the Compton Gamma Ray Observatory (CGRO) detected the cosmic gamma-ray burst GRB 930131. COMPTEL's MeV imaging capability was employed to locate the source to better than 2 deg (1 sigma error radius) within 7 hr of the event, initiating a world-wide search for an optical and radio counterpart. The maximum likelihood position of the burst from the COMPTEL data is alpha₂₀₀₀ = 12h 18m, delta₂₀₀₀ = -9 deg 42 min, consistent with independent CGRO-Burst and Transient Source Experiment (CGRO-BATSE) and Energetic Gamma Ray …

Sulfate And Msa In The Air And Snow On The Greenland Ice Sheet, J L. Jaffrezo, C Davidson, M Legrand, Jack E. Dibb

Earth Sciences

Sulfate and methanesulfonic acid (MSA) concentrations in aerosol, surface snow, and snowpit samples have been measured at two sites on the Greenland Ice Sheet. Seasonal variations of the concentrations observed for these chemical species in the atmosphere are reproduced in the surface snow and preserved in the snowpit sequence. The amplitude of the variations over a year are smaller in the snow than in the air, but the ratios of the concentrations are comparable. The seasonal variations for sulfate are different at the altitude of the Ice Sheet compared to those observed at sea level, with low concentrations in winter …

An Overview Of Solar Flare Results From Comptel, Mark L. Mcconnell

Space Science Center

The COMPTEL experiment on the Compton Gamma Ray Observatory (CGRO) has been operating in orbit since April of 1991. During that time, COMPTEL has observed several large flares, the most notable of which were several X‐class flares which took place in June of 1991. As a solar instrument, COMPTEL has the capability to measure solar flare radiation in two parallel observing modes. In its telescope mode, COMPTEL is capable of measuring both solar flare photons (in the 0.75–30 MeV range) and solar flare neutrons (in the 20–150 MeV range) using the double scatter technique with a field‐of‐view of ∼1 steradian. …

First Results Of The Batse/Comptel/Nmsu Rapid Burst Response Campaign, R M. Kippen, A Connors, John R. Macri, Mark L. Mcconnell, James M. Ryan, W Collmar, J Greiner, V Schonfelder, M Varendorff, Gerald J. Fishman, C Meegan, C Kouveliotou, B Mcnamara, T Harrison, W Hermsen, L Kuiper, K Bennett, L O. Hanlon, C Winkler

Space Science Center

The Imaging Compton Telescope (COMPTEL) on board the Compton Gamma Ray Observatory regularly observes gamma‐ray bursts which occur inside the instrument’s ∼1 sr field‐of‐view. COMPTEL images bursts in the 0.75–30 MeV energy range with a typical location accuracy of 1–3 degrees, depending on burst strength, position, duration, and spectrum. COMPTEL’s imaging capability has been exploited in order to search for fading gamma‐ray burst counterparts at other wavelengths through the establishment of a BATSE/COMPTEL/NMSU rapid burst response campaign. This campaign utilizes near real‐time identification and preliminary burst location by BATSE, accelerated COMPTEL imaging, and a world‐wide network of observers to search …

Empirical Modeling Of The Quiet Time Nightside Magnetosphere, A. T. Y. Lui, Harlan E. Spence, D. P. Stern

Physics & Astronomy

Empirical modeling of plasma pressure and magnetic field for the quiet time nightside magnetosphere is investigated. Two models are constructed for this study. One model, referred to here as T89R, is basically the magnetic field model of Tsyganenko (1989) but is modified by the addition of an inner eastward ring current at a radial distance of ∼3 RE as suggested by observation. The other is a combination of the T89R model and the long version of the magnetic field model of Tsyganenko (1987) such that the former dominates the magnetic field in the inner magnetosphere, whereas the latter prevails in …

137cs Gamma-Ray Detection At Summit, Greenland, P. P. Dunphy, Jack E. Dibb

Earth Sciences

Global fall-out from atmospheric testing of thermonuclear weapons produced horizon markers corresponding to the initiation of testing in 1953 and the maximum fall-out in 1963. The radioactive isotope 137Cs associated with these events has a half-life of 30.2 years. Therefore, with the appropriate radiation detectors, this fall-out can be used as a long-term temporal indicator in glaciers and snowpack. A prototype γ-ray detector system was successfully tested and was used to make in-situ measurements of the 137Cs marker in a borehole at Summit, Greenland. The system consisted of a 7.6 cm by 7.6 cm NaI (Tl) scintillation crystal/photomultiplier detector, commercial …

An Ice-Core-Based Record Of Biomass Burning In The Arctic And Subarctic, 1750-1980, Sallie I. Whitlow, Paul A. Mayewski, Jack E. Dibb, Mark S. Twickler, G Holdsworth

Earth Sciences

No abstract provided.

Observations Of The 1991 June 11 Solar Flare With Comptel, G Rank, R Diehl, G G. Lichti, V Schonfelder, M Varendorff, B Swanenburg, R Vandijk, D J. Forrest, John R. Macri, Mark L. Mcconnell, M Loomis, James M. Ryan, K Bennett, C Winkler

Space Science Center

The COMPTEL instrument onboard of the Compton Gamma‐Ray Observatory (CGRO) is sensitive to γ‐rays in the energy range from 0.75 to 30 MeV and to neutrons in the energy range from 10 to 100 MeV.

During the period of unexpectedly high solar activity in June 1991, several flares from active region 6659 were observed by COMPTEL. For the flare on June 11, we have analyzed the COMPTEL telescope data, finding strong 2.223 MeV line emission, that declines with a time constant of 11.8 minutes during the satellite orbit in which the flare occurs. It remains visible for at least 4 …

Comptel’S Solar Flare Catalog, R Suleiman, D J. Forrest, Mark L. Mcconnell, James M. Ryan, R Diehl, G G. Lichti, G Rank, V Schonfelder, A W. Strong, M Varendorff, K Bennett, L O. Hanlon, C Winkler, H Bloemen, W Hermsen, B Swanenburg

Space Science Center

COMPTEL, the imaging gamma‐ray telescope, capable of detecting gamma rays in the range of 0.1–30 MeV, is one of four instruments aboard NASA’s Compton Gamma‐Ray Observatory. The Comptel burst detectors (single Defector Mode) have a field of view of ∼2.5 π sr. These detectors of COMPTEL permit measurements of energy spectra and time histories of solar flare gamma‐ray emission. A search through the Single Detector Mode’s data is being conducted. We summarize the preliminary results of this search.

Comptel Observations Of Gamma‐Ray Flares In October 1991, M Varendorff, D J. Forrest, Mark L. Mcconnell, James M. Ryan, R Suleiman, R Diehl, G G. Lichti, G Rank, V Schonfelder, K Bennett, L O. Hanlon, C Winkler, B Swanenburg

Space Science Center

The COMPTEL experiment on GRO images 0.75–30 MeV celestial gamma‐radiation that falls within its 1 steradian field of view. During observation 12 (primary target Cen A) in October 1991 the sun had been in the fov and several solar flares associated with the active region 6891 had been observed. Time profile and energy spectra had been produced, using COMPTEL’s primary mode of operation (the telescope mode). Additionally the number of counts received in the D2‐single burst detector (the secondary mode of operation) are given. We summarize the preliminary results on all of these flares.

Neutron And Gamma‐Ray Measurements Of The Solar Flare Of 1991 June 9, James M. Ryan, D J. Forrest, J Lockwood, M Loomis, Mark L. Mcconnell, D Morris, W Webber, K Bennett, L O. Hanlon, C Winkler, H Debrunner, G Rank, V Schonfelder, B Swanenburg

Space Science Center

The COMPTEL Imaging Compton Telescope on‐board the Compton Gamma Ray Observatory measured significant neutron and γ‐ray fluxes from the solar flare of 9 June 1991. The γ‐ray flux had an integrated intensity (≳1 MeV) of ∼30 cm⁻², extending in time from 0136 UT to 0143 UT, while the time of energetic neutron emission extended approximately 10 minutes longer, indicating either extended proton acceleration to high energies or trapping and precipitation of energetic protons. The production of neutrons without accompanying γ‐rays in the proper proportion indicates a significant hardening of the precipitating proton spectrum through either the trapping or …

Comptel Detection Of The Variable Radio Source Gt 0236+610, R Vandijk, H Bloemen, W Hermsen, W Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, K Bennett, M Much, Mark L. Mcconnell, A Connors

Space Science Center

The highly variable and non‐thermal radio source GT 0236+610 exhibits outbursts with a period of 26.496 days, modulated by a four‐year period. Recent EGRET observations confirmed that this source is the counterpart of the COS‐B source 2CG 135+01.

COMPTEL observed this source during three observations in Phase I. We report here on the detections in each of the observations, the time‐averaged spectrum, and address the question of time variability with respect to the radio phase.

Comptel Upper Limits For Seyfert Galaxies, M Maisack, W Collmar, G G. Lichti, V Schonfelder, H Steinle, H Bloemen, W Hermsen, Mark L. Mcconnell, G Stacy, P Barr, O R. Williams

Space Science Center

The gamma‐ray emission of Seyfert galaxies has fallen far short of pre‐GRO expectations. No single object of this class has been detected by either COMPTEL or EGRET, and OSSE has detected only a fraction of the Seyferts expected. To derive a more stringent upper limit to the emission from these objects in the energy ranges 0.75 to 1 and 1 to 3 MeV, we have summed a large number of COMPTEL observations acquired during Phase 1 of the GRO mission. From a total of 47 observations of 23 individual X‐ray selected Seyfert galaxies, we derive preliminary upper limits of 8×10 …

Comptel Gamma‐Ray Observations Of The Quasars Cta 102 And 3c 454.3, J J. Blom, H Bloemen, W Hermsen, W Collmar, V Schonfelder, H Steinle, A W. Strong, Mark L. Mcconnell, G Stacy, K Bennett, C Winkler

Space Science Center

The blazer‐type active galactic nuclei (AGNs) CTA 102 (QSO 2230+114) and 3C 454.3 (QSO 2251+158), located about 7° apart on the sky, were observed by the Compton Gamma Ray Observatory at four epochs in 1992. Both were detected by EGRET and here we present theCOMPTEL observations of the two quasars. These observations clearly indicate that the power‐law spectra measured by EGRET above ∼50 MeV show a flattening at lower MeV energies. A comparison with observations at other wavelengths shows that the power spectra of CTA 102 and 3C 454.3 peak at MeV energies. This behavior appears to be a …

Comptel Observations Of The Quasar Pks 0528+134, W Collmar, R Diehl, G G. Lichti, V Schonfelder, H Steinle, A W. Strong, H Bloemen, W Hermsen, Mark L. Mcconnell, James M. Ryan, G Stacy, K Bennett, O R. Williams, C Winkler

Space Science Center

During Phase I and Phase II of the CGRO‐mission, the quasar PKS 0528+134 was in the field of view of the COMPTEL instrument during several viewing periods. The quasar was detected by COMPTEL mainly at energies above 10 MeV. Below 10 MeV there is evidence for the source during some CGRO viewing periods, while below 3 MeV no signal is detected. The detections and non‐detections during different viewing periods follow the trend seen by EGRET, thereby indicating a time‐variable MEV‐flux of the quasar. The COMPTEL spectral results together with the simultaneously measured EGRET spectrum, indicate a spectral break in the …

Tracking And Imaging Gamma Ray Experiment (Tigre) For 1 To 100 Mev Gamma Ray Astronomy, A Alpar, D Bhattacharya, R Buccheri, K Dotson, D J. Forrest, W N. Johnson, G Kanbach, U Kiziloglu, R Kroeger, J Kurfess, M L. Mcconnell, H Ogelman, B O'Neill, Terence J. O'Neill, A Owens, B Pi, B Pierce, James M. Ryan, B Sacco, G Simnett, O T. Tumer, W Wheaton, R S. White, Allen Zych

Space Science Center

A large international collaboration from the high energy astrophysics community has proposed the Tracking and Imaging Gamma Ray Experiment (TIGRE) for future space observations. TIGRE will image and perform energy spectroscopy measurements on celestial sources of gamma rays in the energy range from 1 to 100 MeV. This has been a difficult energy range experimentally for gamma ray astronomy but is vital for the future considering the recent exciting measurements below 1 and above 100 MeV. TIGRE is both a double scatter Compton and gamma ray pair telescope with direct imaging of individual gamma ray events.

Multi‐layers of Si strip …

Simultaneous Observations Of The Continuum Emission Of The Quasar 3c 273 From Radio To Γ‐Ray Energies, G G. Lichti, C Von Montigny, T Balonek, T Courvoisier, N Johnson, Mark L. Mcconnell, W Paciesas, E I. Robson, A Sadun, C Schalinski, H Steppe, A G. Smith, R Staubert, B Swanenburg, M Turner, M Ulrich, O R. Williams

Space Science Center

From June 15–28, 1991 the Compton Gamma‐Ray Observatory (CGRO) observed the radio‐loud quasar 3C 273. All four CGRO instruments detected radiation from this quasar in their relevant energy range (from 20 keV to 5 GeV). Simultaneous and quasi‐simultaneous observations by instruments sensitive at other wavelengths have also been obtained. The data from all these observations, spanning the frequency range from ∼10⁹ Hz–∼10^{2 6} Hz, were collected and analyzed. Details of the observations and an overall energy‐density spectrum are presented. This spectrum shows two maxima of nearly equal strength. One is in the UV, while the other one is …

Spectral Properties Of Gamma‐Ray Bursts Observed By Comptel, L O. Hanlon, K Bennett, O R. Williams, C Winkler, W Collmar, R Diehl, J Greiner, V Schonfelder, H Steinle, A W. Strong, M Varendorff, R Vandijk, J W. Den Herder, W Hermsen, L Kuiper, A Connors, R M. Kippen, Mark L. Mcconnell, James M. Ryan

Space Science Center

During the first year of operation, the COMPTEL instrument on board the Compton Gamma Ray Observatory detected 22 γ‐ray bursts within its field of view. Spectra and time histories for the strongest 7 of these bursts have been obtained from both the main instrument (0.75–30 MeV) and the burst modules (0.1–10 MeV). The deconvolved photon spectra for the majority of bursts are fit by a single power law model with spectral index between −1.6 and −2.8. One strong burst, GRB 910814, exhibited significant curvature and could not be fit by a single power law model. A broken power law model …

Mev Emission From The Black‐Hole Candidate Gro J0422+32 Measured With Comptel, R Vandijk, H Bloemen, W Hermsen, W Collmar, R Diehl, J Greiner, G G. Lichti, V Schonfelder, A W. Strong, K Bennett, L O. Hanlon, C Winkler, Mark L. Mcconnell, James M. Ryan

Space Science Center

On Aug. 5, 1992 BATSE discovered the bright X‐ray transient GRO J0422+32, also known as Nova Per 1992. The COMPTEL instrument (0.75–30 MeV) aboard CGRO observed this black‐hole candidate twice. During the first observation, which started when the X‐ray flux was at its maximum, GRO J0422+32 was detected up to 2 MeV. The fluxes in the 0.75–1 and 1–2 MeV range were signficantly higher than expected based on an extrapolation of the contemporaneous OSSE data. The COMPTEL spectral points can be interpreted as evidence for a Wien‐type spectral component with temperature k T≊300 keV. During the second observation, 3 …

Recent Results From Comptel Observations Of Cygnus X‐1, Mark L. Mcconnell, D J. Forrest, James M. Ryan, W Collmar, V Schonfelder, H Steinle, A W. Strong, R Vandijk, W Hermsen, K Bennett, R Much

Space Science Center

The COMPTEL experiment on the Compton Gamma‐Ray Observatory (CGRO) has now observed Cyg X‐1 on four separate occasions during phase 1 and phase 2 of its orbital mission (April, 1991 to August, 1993). Here we report on the results of the latest analysis of these data, which provide a spectrum extending to energies greater than 2 MeV. A spectral analysis of these data, in the context of a classical Comptonization model, indicates an electron temperature much higher than previous hard X‐ray measurements would suggest (200 keV vs 60–80 keV). This implies either some limitations in the standard Comptonization model and/or …