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504 results on '"MacLennan C"'

101. Solar Energetic Particle Spectral Breaks.

Author

Mewaldt, R. A., Cohen, C. M. S., Mason, G. M., Labrador, A. W., Looper, M. L., Haggerty, D. E., Maclennan, C. G., Cummings, A. C., Desai, M. I., Leske, R. A., Li, G., Mazur, J. E., Stone, E. C., and Wiedenbeck, M. E.

Subjects
SPECTRUM analysis, INTERMEDIATES (Chemistry), PROPERTIES of matter, PARTICLES (Nuclear physics), ORGANIC compounds, CARBENES
Abstract

The five large solar particle events during October–November 2003 presented an opportunity to test shock acceleration models with in-situ observations. We use solar particle spectra of H to Fe ions, measured by instruments on ACE, SAMPEX, and GOES-11, to investigate the Q/M-dependence of spectral breaks in the 28 October 2003 event. We find that the break energies scale as (Q/M)b with b ≤ 1.56 to 1.75, somewhat less than predicted. We also conclude that SEP spectra >100 MeV/nucleon are best fit by a double power-law shape. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

Published
2005
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107. High-latitude Ulysses observations of the H/He intensity ratio under solar minimum and solar maximum conditions.

Author

Lario, D., Maclennan, C. G., Roelof, E. C., Gosling, J. T., Ho, G. C., and Hawkins, S. E.

Subjects
*SOLAR activity, *COSMIC abundances
Abstract

We analyze measurements of the 0.5-1.0 MeV/nucleon H/He intensity ratio from the Ulysses spacecraft during its first (1992-1994) and second (1999-2000) ascents to southern high latitude regions of the heliosphere. These cover a broad range of heliocentric distances (from 5.2 to 2.0 AU) and out-of-ecliptic latitudes (from 18°S to 80°S). During Ulysses' first southern pass, the HI-SCALE instrument measured a series of enhanced particle fluxes associated with the passage of a recurrent corotating interaction region (CIR). Low values (∼6) of the H/He ratio were observed in these recurrent corotating events, with a clear minimum following the passage of the corotating reverse shock. When Ulysses reached high southern latitudes (>40°S), the H/He ratio always remained below ∼10 except during two transient solar events that brought the ratio to high (>20) values. Ulysses' second southern pass was characterized by a higher average value of the H/He ratio. No recurrent pattern was observed in the energetic ion intensity, which was dominated by the occurrence of transient events of solar origin. Numerous stream interaction regions (SIRs) were observed in the solar wind and magnetic field data, many of which were bounded by forward and reverse shock pairs. The arrival of those SIRs at Ulysses usually produced an energetic particle flux enhancement, but they were not always characterized by a decrease of the H/He ratio; on the contrary, many SIRs showed a higher H/He ratio than some transient events. Within a SIR, however, the H/He ratio usually increased around the forward shock and decreased towards the reverse shock. Throughout the second ascent to southern heliolatitudes, the H/He ratio seldom decreased below ∼10 even at high latitudes (>40°S). We interpret these higher values of the H/He ratio in terms of the increasing level of solar activity together with the poor definition and short life that corotating solar wind structures have under... [ABSTRACT FROM AUTHOR]

Published
2001

108. Charged particle composition in the inner heliosphere during the rise to maximum of Solar Cycle 23.

Author

Maclennan, C. G., Lanzerotti, L. J., Fisk, L. A., and Gold, R. E.

Subjects
*PARTICLES (Nuclear physics), *COSMIC abundances
Abstract

Flux distributions and abundances relative to oxygen of interplanetary ions (Z > 1) are statistically studied and compared for measurements made at 1 and at ∼ 5 AU on the ACE and the Ulysses spacecraft near the ecliptic plane. Over the nearly two year interval studied, the distributions of the relative abundances and the fluxes of particles at the two locations are found to be approximately log normal. The statistical distributions of the relative abundances are found to be similar at the two helioradii. On a statistical basis, the fluxes at Ulysses times the distance of the measurements appear to be proportional to the fluxes at ACE. This radial dependence of the fluxes is consistent with the interpretation that, statistically, the ion parallel diffusion coefficient is large. [ABSTRACT FROM AUTHOR]

Published
2000

109. Coherent frequency variations in electron fluxes at 1 and 5 AU in the inner heliosphere.

Author

Thomson, D. J., Lanzerotti, L. J., and Maclennan, C. G.

Subjects
PARTICLES (Nuclear physics), NUCLEAR physics
Abstract

Several years ago we reported evidence for distinct modal structure in particle flux data from Ulysses and other interplanetary spacecraft, based on detailed time series analyses (1). Furthermore, we concluded that numerous discrete frequencies could be identified with known solar p-mode frequencies and with several calculated solar g-mode frequencies. This paper continues to explore the nature of the modal structure of the interplanetary medium by investigating the statistics of the coherence in electron fluxes measured at two separate locations in the near-ecliptic heliosphere, at 1 AU and at 5 AU, on the ACE and the Ulysses spacecraft, respectively. We demonstrate that there are highly significant coincident frequency peaks at the two locations in data taken at different times, and that, for data acquired at the same time at the two locations, there are high levels of coherence at multiple frequency pairs across a wide spectral band. [ABSTRACT FROM AUTHOR]

Published
2000

114. A multipoint determination of the propagation velocity of a sudden commencement across the polar ionosphere

Author

Engebretson, M. J., primary, Murr, D. L., additional, Hughes, W. J., additional, Lühr, H., additional, Moretto, T., additional, Posch, J. L., additional, Weatherwax, A. T., additional, Rosenberg, T. J., additional, Maclennan, C. G., additional, Lanzerotti, L. J., additional, Marcucci, F., additional, Dennis, S., additional, Burns, G., additional, Bitterly, J., additional, and Bitterly, M., additional

Published
1999
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117. Ionospheric convection response to slow, strong variations in a northward interplanetary magnetic field: A case study for January 14, 1988

Author

Knipp, D. J., Emery, B. A., Richmond, A. D., Crooker, N. U., Hairston, M. R., Cumnock, J. A., Denig, W. F., Rich, F. J., de la Beaujardiere, O., Ruohoniemi, J. M., Rodger, A. S., Crowley, G., Ahn, B. -H., Evans, D. S., Fuller -Rowell, T. J., Friis -Christensen, E., Lockwood, M., Kroehl, H. W., Maclennan, C. G., McEwin, A., Pellinen, R. J., Morris, R. J., Burns, G. B., Papitashvili, V., Zaitzev, A., Troshichev, O., Sato, N., Sutcliffe, P., Tomlinson, L., Knipp, D. J., Emery, B. A., Richmond, A. D., Crooker, N. U., Hairston, M. R., Cumnock, J. A., Denig, W. F., Rich, F. J., de la Beaujardiere, O., Ruohoniemi, J. M., Rodger, A. S., Crowley, G., Ahn, B. -H., Evans, D. S., Fuller -Rowell, T. J., Friis -Christensen, E., Lockwood, M., Kroehl, H. W., Maclennan, C. G., McEwin, A., Pellinen, R. J., Morris, R. J., Burns, G. B., Papitashvili, V., Zaitzev, A., Troshichev, O., Sato, N., Sutcliffe, P., and Tomlinson, L.

Abstract

We analyze ionospheric convection patterns over the polar regions during the passage of an interplanetary magnetic cloud on January 14, 1988, when the interplanetary magnetic field (IMF) rotated slowly in direction and had a large amplitude. Using the assimilative mapping of ionospheric electrodynamics (AMIE) procedure, we combine simultaneous observations of ionospheric drifts and magnetic perturbations from many different instruments into consistent patterns of high-latitude electrodynamics, focusing on the period of northward IMF. By combining satellite data with ground-based observations, we have generated one of the most comprehensive data sets yet assembled and used it to produce convection maps for both hemispheres. We present evidence that a lobe convection cell was embedded within normal merging convection during a period when the IMF By and Bz components were large and positive. As the IMF became predominantly northward, a strong reversed convection pattern (afternoon-to-morning potential drop of around 100 kV) appeared in the southern (summer) polar cap, while convection in the northern (winter) hemisphere became weak and disordered with a dawn-to-dusk potential drop of the order of 30 kV. These patterns persisted for about 3 hours, until the IMF rotated significantly toward the west. We interpret this behavior in terms of a recently proposed merging model for northward IMF under solstice conditions, for which lobe field lines from the hemisphere tilted toward the Sun (summer hemisphere) drape over the dayside magnetosphere, producing reverse convection in the summer hemisphere and impeding direct contact between the solar wind and field lines connected to the winter polar cap. The positive IMF Bx component present at this time could have contributed to the observed hemispheric asymmetry. Reverse convection in the summer hemisphere broke down rapidly after the ratio |By/Bz| exceeded unity, while convection in the winter hemisphere strengthened. A dominant

Published
1993

129. Design of Glycoconjugate Vaccines against Invasive African Salmonella entericaSerovar Typhimurium

Author

Rondini, S., Micoli, F., Lanzilao, L., Gavini, M., Alfini, R., Brandt, C., Clare, S., Mastroeni, P., Saul, A., and MacLennan, C. A.

Abstract

ABSTRACTNontyphoidal salmonellae, particularly Salmonella entericaserovar Typhimurium, are a major cause of invasive disease in Africa, affecting mainly young children and HIV-infected individuals. Glycoconjugate vaccines provide a safe and reliable strategy against invasive polysaccharide-encapsulated pathogens, and lipopolysaccharide (LPS) is a target of protective immune responses. With the aim of designing an effective vaccine against S. Typhimurium, we have synthesized different glycoconjugates, by linking O-antigen and core sugars (OAg) of LPS to the nontoxic mutant of diphtheria toxin (CRM197). The OAg-CRM197conjugates varied in (i) OAg source, with three S. Typhimurium strains used for OAg extraction, producing OAg with differences in structural specificities, (ii) OAg chain length, and (iii) OAg/CRM197ratio. All glycoconjugates were compared for immunogenicity and ability to induce serum bactericidal activity in mice. In vivoenhancement of bacterial clearance was assessed for a selected S. Typhimurium glycoconjugate by challenge with live Salmonella. We found that the largest anti-OAg antibody responses were elicited by (i) vaccines synthesized from OAg with the highest glucosylation levels, (ii) OAg composed of mixed- or medium-molecular-weight populations, and (iii) a lower OAg/CRM197ratio. In addition, we found that bactericidal activity can be influenced by S. Typhimurium OAg strain, most likely as a result of differences in OAg O-acetylation and glucosylation. Finally, we confirmed that mice immunized with the selected OAg-conjugate were protected against S. Typhimurium colonization of the spleen and liver. In conclusion, our findings indicate that differences in the design of OAg-based glycoconjugate vaccines against invasive African S. Typhimurium can have profound effects on immunogenicity and therefore optimal vaccine design requires careful consideration.

Published
2015
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138. Observation by Ulysses of hot (∼270 keV) coronal particles at 32° south heliolatitude and 4.6 AU

Author

Armstrong, T. P., primary, Haggerty, D., additional, Lanzerotti, L. J., additional, Maclennan, C. G., additional, Roelof, E. C., additional, Pick, M., additional, Simnett, G. M., additional, Gold, R. E., additional, Krimigis, S. M., additional, Anderson, K. A., additional, Lin, R. P., additional, Sarris, E. T., additional, Forsyth, R., additional, and Balogh, A., additional

Published
1994
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140. Correction to “Ionospheric convection response to slow, strong variations in a northward interplanetary magnetic field: A case study for January 14, 1988”

Author

Knipp, D. J., primary, Emery, B. A., additional, Richmond, A. D., additional, Crooker, N. U., additional, Hairston, M. R., additional, Cumnock, J. A., additional, Denig, W. F., additional, Rich, F. J., additional, de la Beaujariere, O., additional, Ruohoniemi, J. M., additional, Rodger, A. S., additional, Crowley, G., additional, Ahn, B. -H., additional, Evans, D. S., additional, Fuller-Rowell, T. J., additional, Friis-Christensen, E., additional, Lockwood, M., additional, Kroehl, H. W., additional, Maclennan, C. G., additional, McEwin, A., additional, Pellinen, R. J., additional, Morris, R. J., additional, Burns, G. B., additional, Papitashvili, V., additional, Zaitzev, A., additional, Troshichev, O., additional, Sato, N., additional, Sutcliffe, P., additional, and Tomlinson, L., additional

Published
1994
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142. Ionospheric convection response to slow, strong variations in a northward interplanetary magnetic field: A case study for January 14, 1988

Author

Knipp, D. J., primary, Emery, B. A., additional, Richmond, A. D., additional, Crooker, N. U., additional, Hairston, M. R., additional, Cumnock, J. A., additional, Denig, W. F., additional, Rich, F. J., additional, de la Beaujardiere, O., additional, Ruohoniemi, J. M., additional, Rodger, A. S., additional, Crowley, G., additional, Ahn, B. -H., additional, Evans, D. S., additional, Fuller -Rowell, T. J., additional, Friis -Christensen, E., additional, Lockwood, M., additional, Kroehl, H. W., additional, Maclennan, C. G., additional, McEwin, A., additional, Pellinen, R. J., additional, Morris, R. J., additional, Burns, G. B., additional, Papitashvili, V., additional, Zaitzev, A., additional, Troshichev, O., additional, Sato, N., additional, Sutcliffe, P., additional, and Tomlinson, L., additional

Published
1993
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