The last disconnection events in Comet Halley in April 1986

Disconnection event (DE) in cometary plasma physics is the regular loss of the entire plasma tail and the growth of the new one. Analysis of a sequence of DEs that occurred 13-18 April, 1986 shows that they correlate well with a magnetic, sector-boundary crossing and a complex magnetic structure in the solar wind with polarity reversals that occurred about one day later. These events are entirely consistent with sunward, magnetic reconnection as the DE mechanism

Evolution on large-scale plasma structures in comets: Kinematics and physics

The disconnection event (DE) consists of the periodic loss of a comet's entire plasma tail and the growth of a new one. This spectacular phenomenon is not understood. The strategy was to assemble a data base of specific events studied in detail, determine the solar wind conditions responsible for DEs, and develop a consistent physical model. Analysis is complete for the sequence of DEs that took place during 13 to 18 April 1986. The first DE correlates well with a sector boundary crossing for the comet and a group of DEs that occurred approximately a day later could have produced by polarity reversals seen in the IMP-8 data. Thus, these DEs are consistent with the frontside, magnetic reconnection mechanism

Evolution of large-sclae plasma structures in comets: Kinematics and physics

Disconnection Events are the dramatic part of the periodic morphology involving the separation of the entire plasma tail from the head region of the comet and the growth of a new plasma. The coordinated observations of Comet Halley recorded approximately 30 DEs during the 7 months of plasma activity; 19 of these are obvious. The plasma physics of these events were approached via a detailed, kinematic investigation of specific DEs and the solar-wind environment associated with it. As the detailed investigations are completed, researchers should be able to answer the question of a single or multiple mechanism(s) for DEs and determine which mechanism(s) are important. At present, the mechanism of sunward magnetic reconnection caused by interplanetary sector boundary crossing in consistent with the data available

Large-scale interaction of the solar wind with comets Halley and Giacobini-Zinner

In-situ measurements of comets Halley and Giacobini-Zinner have confirmed the accepted basic physics of comet/solar wind interaction. The solar wind magnetic field is captured by the comet through the mechanism of field-line loading by cometary ions and the field lines drape around the cometary ionosphere. With this basic model in hand, the large-scale structure of the plasma tail as revealed by submissions to the Large Scale Phenomena Network of the International Halley Watch is reviewed. The turn-on and turn-off of plasma activity seem consistent with theory. Some 16 obvious disconnection events (DEs) have been recorded. Preliminary results showed agreement with the sector-boundary model; a detailed analysis of all DEs will be required in order to make a definitive statement. A study of plasma activity around the time of the VEGA encounters provides strong support for the sector-boundary model and illustrates once again the power of simultaneous remote and in-situ measurements

The Population of Small Comets: Optimum Techniques for Detection

The goals of this project were: (1) to present evidence to the scientific community for the importance of the small comet population and (2) to develop techniques for optimum detection in order to characterize the population. Our work on techniques has been to develop algorithms for searching images for SCs based on the distinctive properties of comets; (1) motion with respect to background stars; (2) extended source with most light coming from the coma rather than the nucleus; and characteristic spectral signature

Evolution of large-scale plasma structures in comets: Kinematics and physics

Cometary and solar wind data from December 1985 through April 1986 are presented for the purpose of determining the solar wind conditions associated with comet plasma tail disconnection events (DE's). The cometary data are from The International Halley Watch Atlas of Large-Scale Phenomena (Brandt, Niedner, and Rahe, 1992). In addition, we present the kinematic analysis of 4 DE's, those of Dec. 13.5 and 31.2, 1985, and Feb. 21.7 and 28.7, 1986. The circumstances of these DE's clearly illustrate the need to analyze DE's in groups. In situ solar wind measurements from IMP-8, ICE, and PVO were used to construct the variation of solar wind speed, density, and dynamic pressure during this interval. Data from these same spacecraft plus Vega-1 were used to determine the time of 48 current sheet crossings. These data were fitted to heliospheric current sheet curves extrapolated from the corona into the heliosphere in order to determine the best-fit source surface radius for each Carrington rotation. Comparison of the solar wind conditions and 16 DE's in Halley's comet (the four DE's discussed in this paper and 12 DE's in the literature) leaves little doubt that DE's are associated primarily with crossings of the heliospheric current sheet and apparently not with any other property of the solar wind. If we assume that there is a single or primary physical mechanism and that Halley's DE's are representative, efforts at simulation should concentrate on conditions at current sheet crossings. The mechanisms consistent with this result are sunward magnetic reconnection and tailward magnetic reconnection, if tailward reconnection can be triggered by the sector boundary crossing

Initial overview of disconnection events in Halley's Comet 1986

We present an initial overview of the disconnection events (DE's) in Comet Halley in 1986. Although disconnection events are arguably the most spectacular of all dynamic comet phenomena, the mechanisms by which they occur are not fully understood. It is generally believed that the solar wind plays a major role in determining when disconnection events occur, but the details of the solar wind/cometary interactions responsible for initiating the tail disconnection are still under debate. The three most widely accepted models are: (1) high speed streams in the solar wind cause the tail to disconnect due to pressure effects; (2) decreased production of cometary ions in a high speed stream allows magnetic field to slip away from the comet; and (3) the tail disconnects after frontside reconnection of the interplanetary magnetic field (IMF) as the comet crosses a magnetic field sector boundary. We find that the front-side magnetic reconnection model is the best explanation for the DE's we have considered

Adsorption of hydantoins on activated carbon.

http://archive.org/details/adsorptionofhyda00branNAN

Electric field formulation for thin film magnetization problems

We derive a variational formulation for thin film magnetization problems in type-II superconductors written in terms of two variables, the electric field and the magnetization function. A numerical method, based on this formulation, makes it possible to accurately compute all variables of interest, including the electric field, for any value of the power in the power law current-voltage relation characterizing the superconducting material. For high power values we obtain a good approximation to the critical state model solution. Numerical simulation results are presented for simply and multiply connected films, and also for an inhomogeneous film.Comment: 15 p., submitte