WorldWideScience
1

Is channeling of fission tracks taking place?  

CERN Document Server

A single crystal of natural zircon which is sliced to have (010) basal plane and thinned by ion thinning is electron microscopically observed after slow neutron irradiation to ascertain whether channeling of the nuclear fission fragments is taking place or not. A fairly large number of the induced fission tracks are recognized at low magnification images where a considerable number of them are parallel to low-index lattice planes such as 100, 001, 101, 301, 103 though their directions changed some time up to several degrees. High resolution images of fission tracks often show a variety of zigzag passing of the tracks along low-index lattice planes in atomistic level. The rate of the tracks which are parallel to these low-index lattice planes is fairly high as about 45%, which strongly suggests that channeling of the fission tracks is taking place.

Yada, K

1999-01-01

2

Taking Design Games Seriously : Re-connecting Situated Power Relations of People and Materials  

DEFF Research Database (Denmark)

Using design games at Participatory Design (PD) events is well acknowledged as a fruitful way of staging participation. As PD researchers, we have many such experiences, and we have argued that design games connect participants and promote equalizing power relations. However, in this paper, we will (self) critically re-connect and reflect on how people (humans) and materials (non-humans) continually participate and intertwine in various power relations in design game situations. The analysis is of detailed situated actions with one of our recent games, UrbanTransition. Core concepts mainly from Bruno Latour’s work on Actor-Network-Theory are applied. The aim is to take design games seriously by e.g. exploring how assemblages of humans and non-humans are intertwined in tacitly-but-tactically staging participation, and opening up for or hindering negotiations and decision-making, thus starting to relate research on various PD techniques and power issues more directly.

Eriksen, Mette Agger; Brandt, Eva

2014-01-01

3

Reconnection in Planetary Magnetospheres  

Science.gov (United States)

Current sheets in planetary magnetospheres that lie between regions of ``oppositely-directed'' magnetic field are either magnetopause-like, separating plasmas with different properties, or tail-like, separating plasmas of rather similar properties. The magnetopause current sheets generally have a nearly limitless supply of magnetized plasma that can reconnect, possibly setting up steady-state reconnection. In contrast, the plasma on either side of a tail current sheet is stratified so that, as reconnection occurs, the plasma properties, in particular the Alfven velocity, change. If the density drops and the magnetic field increases markedly perpendicular to the sheet, explosive reconnection can occur. Even though steady state reconnection can take place at magnetopause current sheets, the process often appears to be periodic as if a certain low average rate was demanded by the conditions but only a rapid rate was available. Reconnection of sheared fields has been postulated to create magnetic ropes in the solar corona, at the Earth's magnetopause, and in the magnetotail. However, this is not the only way to produce magnetic ropes as the Venus ionosphere shows. The geometry of the reconnecting regions and the plasma conditions both can affect the rate of reconnection. Sorting out the various controlling factors can be assisted through the examination of reconnection in planetary settings. In particular we observe similar small-scale tearing in the magnetopause current layers of the Earth, Saturn. Uranus and Neptune and the magnetodisk current sheet at Jupiter. These sites may be seeds for rapid reconnection if the reconnection site reaches a high Alfven velocity region. In the Jupiter magnetosphere this appears to be achieved with resultant substorm activity. Similar seeds may be present in the Earth's magnetotail with the first one to reach explosive growth dominating the dynamics of the tail

Russell, C. T.

4

Third Place Learning Environments: Perspective Sharing and Perspective Taking  

Directory of Open Access Journals (Sweden)

Full Text Available In this paper we deliberate on intercultural and global communication strategies of perspective sharing and perspective taking, and potential perspective transformation. Consideration to these strategies is given within the two instances of third place learning environments: (a Role-play simulation environment in which learners develop experiment with strategies for resolving intercultural misconceptions, and (b a professional virtual learning network that may provide just-in-time support for its members encountering disorienting dilemma. The central purpose of the second environment is actually development of knowledge basis for understanding of Third Place Learning.

Mara Alagic

2009-11-01

5

Book review: Cyber war will not take place  

OpenAIRE

"Cyber War Will Not Take Place." Thomas Rid. Hurst. April 2013. --- In 2005, the U.S. Air Force boasted it would now fly, fight, and win in cyberspace, the ‘fifth domain’ of warfare. This book takes stock to consider whether or not cyber war is a real threat. Thomas Rid argues that the focus on war and winning distracts from the real challenge of cyberspace: non-violent confrontation that may rival or even replace violence in surprising ways. Tracing the most significant hacks and att...

Muravska, Julia

2013-01-01

6

Astrophysical Implications of Turbulent Reconnection: from cosmic rays to star formation  

CERN Document Server

Turbulent reconnection allows fast magnetic reconnection of astrophysical magnetic fields. This entails numerous astrophysical implications and opens new ways to approach long standing problems. I briefly discuss a model of turbulent reconnection within which the stochasticity of 3D magnetic field enables rapid reconnection through both allowing multiple reconnection events to take place simultaneously and by restricting the extension of current sheets. In fully ionized gas the model in Lazarian and Vishniac 99 predicts reconnection rates that depend only on the intensity of turbulence. In partially ionized gas a modification of the original model in Lazarian, Vishniac and Cho 04 predicts the reconnection rates that, apart from the turbulence intensity depend on the degree of ionization. In both cases the reconnection may be slow and fast depending on the level of turbulence in the system. As the result, the reconnection gets bursty, which provides a possible explanation to Solar flares and possibly to gamma ...

Lazarian, A

2005-01-01

7

Magnetic Reconnection under Anisotropic MHD Approximation  

CERN Document Server

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless MHD codes based on the double adiabatic approximation and the Landau closure model. We bridge the gap between the Petschek-type MHD reconnection model accompanied by a pair of slow shocks and the observational evidence of the rare occasion of in-situ slow shock observation. Our results showed that once magnetic reconnection takes place, a firehose-sense pressure anisotropy arises in the downstream region, and the generated slow shocks are quite weak comparing with those in an isotropic MHD. In spite of the weakness of the shocks, however, the resultant reconnection rate is 10-30% higher than that in an isotropic case. This result implies that the slow shock does not necessarily play an important role in the energy conversion in the reconnection system, and is consistent with the satellite observation in the Earth's magnetosphere.

Hirabayashi, K

2013-01-01

8

Out in the Pinwheel Galaxy, a rare event takes place  

Science.gov (United States)

Astronomers forgo sleep; eyes fixed on star's explosionhttp://www.usatoday.com/tech/science/space/story/2011-09-07/Astronomers-forgo-sleep-eyes-fixed-on-stars-explosion/50303380/1#.TmjMWp9vWhAHow to See a Supernova From Your Backyard this Weekendhttp://www.universetoday.com/88617/how-to-see-a-supernova-from-your-backyard-this-weekend/A Stellar Explosion In The Big Dipperhttp://www.npr.org/2011/09/03/140163733/a-stellar-explosion-in-the-big-dippers-handleThe Hubble Space Telescopehttp://hubble.nasa.gov/The Pinwheel Galaxyhttp://www.ing.iac.es/PR/press/m101.htmlWhite Dwarfshttp://imagine.gsfc.nasa.gov/docs/science/know_l2/dwarfs.htmlAstronomers and others who peer into the night sky are getting quite excited about a rather rare event this Friday. A supernova (an exploding star) out in the Pinwheel Galaxy is expected to peak in brightness, and at only a mere 21 million light years away, it is the closest of its kind to be seen in 40 years. In a recent interview, Peter Nugent of the Lawrence Berkeley National Laboratory summed up the sentiments of many when he said "I'm running on adrenaline right now. A good night is four hours sleep." A number of observatories around the world are casting their telescopes out into the Pinwheel Galaxy to observe and document this rather unusual and fascinating event. This particular supernova is part of the "Type 1a" group, born from a runaway thermonuclear combustion from a white dwarf star. While the blast is quite "close" (cosmically speaking), if it had occurred in the Milky Way galaxy, the light from such an event would be visible during the daytime. Those individuals without their own personal high-end space observatory should not dismay, as a 6-inch telescope or a powerful set of binoculars will let them see part of this magnificent event. The first link will take visitors to a piece from Thursday's USA TODAY about this rather unusual and rare event. The second link will whisk users away to a great video clip from Universe Today that features astrophysicist Peter Nugent talking about how amateur astronauts can best view this event. Moving along, the third link will take users to a nice piece from NPR's Weekend Edition that provides a bit more insight into this supernova. The fourth link leads to NASA's homepage for the Hubble Space Telescope. Here visitors can learn about this technological triumph, and also read about its work examining the Pinwheel Galaxy. The fifth link leads to an amazing photograph of the Pinwheel Galaxy, courtesy of the Isaac Newton Telescope. The last link will take users to a page created by NASA's Goddard Space Flight Center that provides some background on white dwarfs.

Grinnell, Max

2011-09-16

9

Key European Grid event to take place in Geneva  

CERN Multimedia

EGEE'06 is the main conference of the EGEE project, which is co-funded by the European Union and hosted by CERN. More than 90 partners all over Europe and beyond are working together in EGEE to provide researchers in both academia and industry with access to major computing resources, independent of their geographic location. The largest user community of the EGEE Grid is the High-Energy Physics community and in particular the LHC experiments, which are already making heavy use of the infrastructure to prepare for data taking. However, with the many new challenges faced by EGEE in its second phase that started in April this year, an even broader audience than at previous EGEE conferences is expected. In particular, a large number of related Grid projects will feature prominently in both plenary and parallel sessions during the 5 days of this event. Industry will also be well represented, highlighting the EGEE project's commitment to technology transfer to industry. CERN is the host of the conference, which i...

2006-01-01

10

Particle trajectories and acceleration during 3D fan reconnection  

Science.gov (United States)

Context: The primary energy release in solar flares is almost certainly due to magnetic reconnection, making this a strong candidate as a mechanism for particle acceleration. While particle acceleration in 2D geometries has been widely studied, investigations in 3D are a recent development. Two main classes of reconnection regimes at a 3D magnetic null point have been identified: fan and spine reconnection Aims: Here we investigate particle trajectories and acceleration during reconnection at a 3D null point, using a test particle numerical code, and compare the efficiency of the fan and spine regimes in generating an energetic particle population. Methods: We calculated the time evolution of the energy spectra. We discuss the geometry of particle escape from the two configurations and characterise the trapped and escaped populations. Results: We find that fan reconnection is less efficent than spine reconnection in providing seed particles to the region of strong electric field where acceleration is possible. The establishment of a steady-state spectrum requires approximately double the time in fan reconnection. The steady-state energy spectrum at intermediate energies (protons 1 keV to 0.1 MeV) is comparable in the fan and spine regimes. While in spine reconnection particle escape takes place in two symmetric jets along the spine, in fan reconnection no jets are produced and particles escape in the fan plane, in a ribbon-like structure.

Dalla, S.; Browning, P. K.

2008-11-01

11

4th openlab Board of Sponsors Meeting takes place at CERN on July 6, 2005  

CERN Multimedia

The 4th openlab Board of Sponsors Meeting is taking place at CERN, room 513, 1-024, the 6th July 2005. The meeting will open with an Executive Session in the presence of Dr. Robert Aymar, Director General of CERN

Patrice Loïez

2005-01-01

12

Criticism of reconnection models of the magnetosphere  

International Nuclear Information System (INIS)

Reconnection involves singular lines called X-lines on the day and night sides of the magnetosphere, and the reconnection rate is proportional to the component of the electric field along the X-line. Although there is some indirect support for this model there is no direct evidence to indicate that the reconnection process does actually take place in the magnetosphere. There are however a number of observations that provide some indirect support. In this paper it is pointed out that some recent observations provide possibilities for direct tests of the theoretical predictions. However it is shown that the direct evidence is clearly contradictory. Some of it is so compelling as to require drastic revision, even rejection, of current concepts in magnetospheric physics. (author)

13

Collisionless driven reconnection in an open system  

International Nuclear Information System (INIS)

Particle simulation studies of collisionless driven reconnection in an open system are presented. Collisionless reconnection evolves in two steps in accordance with the formation of two current layers, i.e., an ion current layer in the early ion phase and an electron current layer in the late electron phase. After the electron current layer is formed inside the ion current layer, the system relaxes gradually to a steady state when convergent plasma flow is driven by an external electric field with a narrow input window. On the other hand, when the convergent plasma flow is driven from the wide input window, magnetic reconnection takes place in an intermittent manner, due to the frequent formation of magnetic islands in the vicinity of neutral sheet. (author)

14

Questions and Answers Regarding Actions to Take When Ending Shelter-in-Place  

Energy Technology Data Exchange (ETDEWEB)

Shelter-in-place has found increasing acceptance as an effective protective action option for communities participating in the Chemical Stockpile Emergency Preparedness Program. Studies have confirmed that it can provide optimum protection under certain accident conditions. However, emergency managers and planners, as well as the public, continue to be troubled by the need to end sheltering when the plume has passed in order to avoid sustained exposure to the small amount of agent that has penetrated the shelter. One of the concerns posed by this necessity is uncertainty regarding what hazards will then be faced in the environment outside the shelter and what actions can be taken to avoid those hazards. This report attempts to address those uncertainties. It recognizes that there is an extremely low probability that the environment outside the shelter will be contaminated with chemical agent residue. However, as people comply with an official recommendation to leave their shelters, they probably can't be certain that the environment is free from contamination. Therefore, this report identifies and explains specific and simple actions they can take to avoid the possibility of exposure to chemical agent hazards outside their shelters. It addresses such issues as the actions people should take upon ending shelter-in-place, what clothing they should wear, how they should handle animals, and what they should do about food in their homes and produce in their gardens.

Shumpert, B.

2003-12-30

15

[Marketing approval and market surveillance of medical devices in Germany: Where does policy integration take place?].  

Science.gov (United States)

Since 2011 new regulatory measures regarding medical devices have been set up with the aim to eliminate obstacles to innovations and to find more coordinated ways to marketing authorisation and market surveillance. This essay investigates whether these new and existing coordination mechanisms build up to a Joined-up Government approach. The analysis shows that the regulatory process should be adjusted along several dimensions. First, many organisations lack awareness regarding their stakeholders and focus solely on their immediate organisational activities. Second, the regulatory process (marketing authorisation and market surveillance) is too fragmented for an effective communication to take place. Finally, the underlying strategy process is an ad-hoc approach lacking continuity and continued involvement of, in particular, the responsible federal ministries. PMID:25066351

Lang, Achim

2014-01-01

16

Repair of DNA interstrand crosslinks may take place at the nuclear matrix.  

Science.gov (United States)

Host cell reactivation assay using Trioxsalen-crosslinked plasmid pEGFP-N1 showed that human cells were able to repair Trioxsalen interstrand crosslinks (ICL). To study the mechanism of this repair pathway, cells were transfected with the plasmids pEGFP-1, which did not contain the promoter of the egfp gene, and with pEGFP-G-, which did not contain the egfp gene. Neither of these plasmids alone was able to express the green fluorescent protein. After cotransfection with the two plasmids, 1%-2% of the cells developed fluorescent signal, which showed that recombination events had taken place in these cells to create DNA constructs containing the promoter and the gene properly aligned. When one or both of the plasmids were crosslinked with Trioxsalen, the recombination rate increased several fold. To identify the nuclear compartment where recombination takes place, cells were transfected with crosslinked pEGFP-N1 and the amount of plasmid DNA in the different nuclear fractions was determined. The results showed that Trioxsalen crosslinking increased the percentage of matrix attached plasmid DNA in a dose-dependent way. Immunoblotting experiments showed that after transfection with Trioxsalen crosslinked plasmids the homologous recombination protein Rad51 also associated with the nuclear matrix fraction. These studies provide a model system for investigating the precise molecular mechanisms that appear to couple repair of DNA ICL with nuclear matrix attachment. PMID:16052506

Atanassov, Boyko; Gospodinov, Anastas; Stoimenov, Ivaylo; Mladenov, Emil; Russev, George; Tsaneva, Irina; Anachkova, Boyka

2005-09-01

17

Multiscale Processes in Magnetic Reconnection  

Science.gov (United States)

The characteristic scales of the plasma processes in magnetic reconnection range from the elec-tron skin-depth to the magnetohydrodynamic (MHD) scale, and cross-scale coupling among them play a key role. Modeling these processes requires different physical models, viz. kinetic, electron-magnetohydrodynamics (EMHD), Hall-MHD, and MHD. The shortest scale processes are at the electron scale and these are modeled using an EMHD code, which provides many features of the multiscale behavior. In simulations using initial conditions consisting of pertur-bations with many scale sizes the reconnection takes place at many sites and the plasma flows from these interact with each other. This leads to thin current sheets with length less than 10 electron skin depths. The plasma flows also generate current sheets with multiple peaks, as observed by Cluster. The quadrupole structure of the magnetic field during reconnection starts on the electron scale and the interaction of inflow to the secondary sites and outflow from the dominant site generates a nested structure. In the outflow regions, the interaction of the electron outflows generated at the neighboring sites lead to the development of electron vortices. A signature of the nested structure of the Hall field is seen in Cluster observations, and more details of these features are expected from MMS.

Surjalal Sharma, A.; Jain, Neeraj

18

Self-organized Te Redistribution during Driven Reconnection Processes in High Temperature Plasmas  

International Nuclear Information System (INIS)

Two-dimensional (2-D) images of electron temperature fluctuations with a high temporal and spatial resolution were employed to study the sawtooth oscillation in TEXTOR tokamak plasmas. The new findings are: (1) 2-D images revealed that the reconnection is localized and permitted the determination of the physical dimensions of the reconnection zone in the poloidal and toroidal planes. (2) The combination of a pressure driven mode and a kink instability leads to an 'X-point' reconnection process. (3) Reconnection can take place anywhere along the q?1 rational magnetic surface (both high and low field sides). (4) Heat flow from the core to the outside of the inversion radius during the reconnection time is highly asymmetric and the behavior is collective. These new findings are compared with the characteristics of various theoretical models and experimental results for the study of the sawtooth oscillation in tokamak plasmas

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Self-organized T(sub)e Redistribution during Driven Reconnection Processes in High Temperature Plasmas  

Energy Technology Data Exchange (ETDEWEB)

Two-dimensional (2-D) images of electron temperature fluctuations with a high temporal and spatial resolution were employed to study the sawtooth oscillation in TEXTOR tokamak plasmas. The new findings are: 1) 2-D images revealed that the reconnection is localized and permitted the determination of the physical dimensions of the reconnection zone in the poloidal and toroidal planes. 2) The combination of a pressure driven mode and a kink instability leads to an "X-point" reconnection process. 3) Reconnection can take place anywhere along the q~1 rational magnetic surface (both high and low field sides). 4) Heat flow from the core to the outside of the inversion radius during the reconnection time is highly asymmetric and the behavior is collective. These new findings are compared with the characteristics of various theoretical models and experimental results for the study of the sawtooth oscillation in tokamak plasmas.

Park, H.K.; Mazzucato, E.; Luhmann, N.C., Jr.; Domier, C.W.; Xia, Z.; Munsat, T.; Donné, A.J.H.; Classen, I.G.J.; van de Pol, M.J.; TEXTOR team

2005-12-01

20

NEW SOLAR TELESCOPE OBSERVATIONS OF MAGNETIC RECONNECTION OCCURRING IN THE CHROMOSPHERE OF THE QUIET SUN  

International Nuclear Information System (INIS)

Magnetic reconnection is a process in which field-line connectivity changes in a magnetized plasma. On the solar surface, it often occurs with the cancellation of two magnetic fragments of opposite polarity. Using the 1.6 m New Solar Telescope, we observed the morphology and dynamics of plasma visible in the H? line, which is associated with a canceling magnetic feature (CMF) in the quiet Sun. The region can be divided into four magnetic domains: two pre-reconnection and two post-reconnection. In one post-reconnection domain, a small cloud erupted, with a plane-of-sky speed of 10 km s-1, while in the other one, brightening began at points and then tiny bright loops appeared and subsequently shrank. These features support the notion that magnetic reconnection taking place in the chromosphere is responsible for CMFs.

21

Acceleration of Energetic Particles through Reconnection of Weakly Stochastic Magnetic Field  

CERN Document Server

Astrophysical media are turbulent and therefore reconnection should be treated in the presence of pre-existing turbulence. We consider the model of fast magnetic reconnection in Lazarian & Vishniac (1999) which predicts that the rate of reconnection is controlled by the intensity and the injection scale of turbulent motions. We provide new evidence of successful testing of the model and argue that the model presents a generic set up for astrophysical reconnection events. We study particle acceleration that takes place in volumes of driven turbulence as well turbulent volumes in the presence of large scale reconnection. We show that in the latter case the acceleration is of the first order Fermi type thus supporting the model of acceleration proposed in Gouveia dal Pino & Lazarian (2005).

Lazarian, A; Pino, E Gouveia dal; Vishniac, E

2012-01-01

22

Makro- and micromorphological evidence of processes taking place during Albeluvisol development in S Norway  

Science.gov (United States)

We studied two soil chronosequences in S Norway to identify processes involved in Albeluvisol formation. For this purpose, field observation of vertical and horizontal sections of soil profiles, soil chemical and mineralogical analyses were carried out, and in particular, micromorphological analysis was applied. The study area is located at the western and eastern side of the Oslofjord, S Norway, in the counties Vestfold and Østfold. This region is characterized by continuous glacio-isostatic uplift over the entire Holocene. Hence, the age of the land surface continuously increases from the coast towards higher elevations. Twelve soil profiles in loamy marine sediments were studied. Based on macro- and micromorphological observations and analytical data progressive soil formation is characterized as follows: As soon as the land surface is raised above sea level, five major processes are initiated: 1) development of deep desiccation cracks, forming a polygonal pattern; 2) compaction, taking place as soon as the coarse pores have been drained; 3) pyrite oxidation and release of sulfuric acid; 4) carbonate dissolution by acids from pyrite and iron oxidation resulting in rapid decarbonatization of the originally calcareous sediments; 5) precipitation of iron hypocoatings and coatings in the capillary fringe Soon after these very early processes have taken place, limited water permeability of the fine-textured sediments leads to horizon differentiation into Ah, Eg and Btg horizons within less than 2.1 ka. Eg horizons become lighter in colour with time. Also illuvial clay is already observed in the 2.1 ka-old soil. Soil pH in the upper part of the E horizon of this soil is already too low for significant clay mobilization. Clay illuviation is still active in all soils studied, but the upper boundary of the zone where pH favours clay mobilization is at 20-50 cm depth. Progressive clay illuviation over time is recorded in increasing thickness of clay coatings and proportion of voids having clay coatings. Clay mobilization and iron co-eluviation in the upper Eg horizon ceases within less than 2.1 ka, whereas weathering and formation of clay minerals and iron oxides continue, leading to formation of a BE horizon in the upper part of the Eg horizon. Albeluvic tongues start to form after 4.6-6.2 ka, developing preferably along desiccation cracks. Albeluvic material is washed into the cracks, and also enhanced leaching of bases and clay eluviation take place in the cracks. As both processes proceed, the albeluvic tongues get longer and wider. Clayey intercalations occur in the older soils (Stagnic Albeluvisols), and the following concept is suggested to explain their genesis: When after snow melt or a rainy period infiltrating water arrives at the lower end of an albeluvic tongue, the tongue fills up with water. Perched water accumulates also on top of the dense Btg horizon. Water, carrying suspended clay, penetrates under the pressure of the overlying water column from the tongue into the Btg horizon, where additional clay is mobilized. The clay settles when the velocity of the water decreases, forming clayey intercalations in the dense matrix of the Btg horizon.

Sauer, Daniela; Schülli-Maurer, Isabelle; Sperstad, Ragnhild; Sørensen, Rolf

2014-05-01

23

Fast reconnection of magnetic fields in a plasma  

International Nuclear Information System (INIS)

Reconnection process of magnetic fields in a plasma is analytically studied by perturbing the boundary conditions on a slab of incompressible plasma with a resonant surface inside. It is found, for small resistivity, that the reconnection takes place on Alfven time scale and continues into a slow time scale t1 = eta/sup 1/3/t. Both time scales are faster than the usual tearing time scale. Furthermore, the plasma evolves globally from its initial equilibrium on the slow time scale and settles down to a different final equilibrium

24

OECD Global Science Forum's Astronomy Workshop to take place in Munich  

Science.gov (United States)

On December 1 to 3, the city of Munich (Bavaria, Germany) will be the venue for a "Workshop on Large Scale Programmes and Projects in Astronomy and Astrophysics" organised by the Organisation for Economic Co-operation and Development (OECD) Global Science Forum in co-operation with the European Southern Observatory (ESO). The Workshop will be chaired by Ian Corbett (ESO). The Global Science Forum brings together science policy officials from the OECD countries. The delegates, who meet twice a year, look at a range of generic issues in science funding and seek to identify and maximise opportunities for international co-operation in basic scientific research. This Workshop was proposed by Germany and agreed by the delegates to the Global Science Forum in June. Government officials and scientists will be able to review in detail the information and the observational and technological advances needed for major progress in the field during the next 15- 20 years. The research subjects reviewed will cover the full range from planets, solar systems, life in the Universe, stars, galaxies, extreme objects to cosmology. Related technological challenges, virtual observatories and other data handling issues will also be considered. The primary objective is to specify the policy issues relating to priority-setting, planning, funding and, above all, international co-ordination and co-operation. The Workshop will focus on issues relevant to the process through which astronomy advances, and will highlight means to enhance that process in light of longer-term scientific and political trends. There will probably be a follow-up meeting early in 2004, from which a policy level report will be prepared for consideration by the Global Science Forum and so transmitted to governments. Eighteen delegations, from non-OECD as well as OECD countries, will attend, each consisting of senior programme managers from the national ministry, funding agency or research council, and one or more senior members of the national astronomical community. The International Astronomical Union (IAU) and the European Southern Observatory (ESO) are explicitly represented. Experts from the world-wide astronomy community have been invited to set the stage and provide input for the discussions. The choice by Germany and the OECD to make Munich the venue of this Global Science Forum Workshop is no coincidence. It is a recognition of the important role played by many institutions in the Munich region in the field of Astronomy and Astrophysics. They include the Ludwig-Maximilians-Universität where the Workshop will take place, the Max-Planck-Institut für Astrophysik, the Max-Planck Institut für Extraterrestrische Physik and the European Southern Observatory. These institutions are all participating in large programmes and projects in astronomy. ESO, for its part, is at the leading edge of world astronomy with its flagship facility, the Very Large Telescope in Paranal (Chile) and the newly started ALMA project at Chajnantor (Chile), being carried out in partnership between Europe and North America. Public Talks (Munich) on December 1, 2003 As a prelude to the Workshop, two public keynote presentations will take place on December 1 at the Deutsches Museum in Munich at 18:00 CET. The speakers are Malcolm Longair, Jacksonian Professor of Natural Philosophy and Head of Laboratory, Cavendish Laboratory, Cambridge (UK) and Martin Harwit, Professor Emeritus of Astronomy, Cornell University, and former Director of the National Air and Space Museum, Washington, DC (USA). The talks will be given in English and the entry to this public event is free. Professor Longair will speak on "Astrophysics and Cosmology in the Twenty-First Century" and Professor Harwit will speak on "The Growth of Understanding of our Universe". You can find more informaton on the Public Talks web page.

2003-11-01

25

DSC studies of retrogradation and amylose-lipid transition taking place in gamma-irradiated wheat starch  

International Nuclear Information System (INIS)

It has been already shown that degradation resulting from gamma irradiation induces a decrease in order of starch granules and influences gelatinisation taking place during heating of starch and flour suspensions. In presented paper, DSC (differential scanning calorimetry) studies were carried out for wheat starch, non-irradiated and irradiated using doses in the range from 5 to 30 kGy. The influence of the conditions applied during DSC measurements on the possibility to observe differences between the amylose-lipid complex transition and retrogradation taking place in the non-irradiated and particularly irradiated starch samples was checked. The better differentiation between the amylose-lipid complex transition taking place in particular samples accompanied by the better reproducity were obtained in the case of dense suspensions as compared to the watery suspensions as well as during the first analysis performed for the recrystallised gels

26

The role of reconnection in the pulsar magnetosphere  

CERN Document Server

The present work is our first attempt to understand the role of reconnection in the pulsar magnetosphere. Our discussion is based on the observationaly infered fact that, as the pulsar spins down, the region of closed corotating dipolar field lines grows with time. This implies that reconnection must take place in the magnetosphere. We argue that non-dissipative reconnection along the equatorial current sheet allows for the continuous channeling of pulsar spindown energy into particle energy, all the way from the light cylinder to the pulsar wind termination shock, and we propose that this effect may account for the low \\sigma values inferred by observations. We present a simple model that allows us to relate the magnetic diffusivity in the equatorial current sheet to an observable pulsar parameter, the braking index n. When n~1, the global structure of the magnetosphere approaches that of a relativistic split monopole where the pulsar spindown energy is carried by the electromagnetic field. However, for valu...

Contopoulos, I

2006-01-01

27

Separatrices: the crux of reconnection  

CERN Document Server

Reconnection is one of the key processes in astrophysical and laboratory plasmas: it is the opposite of a dynamo. Looking at energy, a dynamo transforms kinetic energy in magnetic energy while reconnection takes magnetic energy and returns is to its kinetic form. Most plasma processes at their core involve first storing magnetic energy accumulated over time and then releasing it suddenly. We focus here on this release. A key concept in analysing reconnection is that of the separatrix, a surface (line in 2D) that separates the fresh unperturbed plasma embedded in magnetic field lines not yet reconnected with the hotter exhaust embedded in reconnected field lines. In kinetic physics, the separatrices become a layer where many key processes develop. We present here new results relative to the processes at the separatrices that regulate the plasma flow, the energisation of the species, the electromagnetic fields and the instabilities developing at the separatrices.

Lapenta, Giovanni; Divin, Andrey; Newman, David; Goldman, Martin

2014-01-01

28

An Experimental Investigation of the Process of Isotope Exchange that Takes Place when Heavy Water Is Exposed to the Atmosphere  

Science.gov (United States)

We have used the recently developed method for rapid measurement of maximum density temperature to determine the rate at which hydrogen and deuterium isotope exchange takes place when a sample of heavy water is exposed to the atmosphere. We also provide a simple explanation for the observed linear rate of transition. (Contains 2 figures.)

Deeney, F. A.; O'Leary, J. P.

2009-01-01

29

Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

We review the fundamental physics of magnetic reconnection in laboratory and space plasmas, by discussing results from theory, numerical simulations, observations from space satellites, and the recent results from laboratory plasma experiments. After a brief review of the well-known early work, we discuss representative recent experimental and theoretical work and attempt to interpret the essence of significant modern findings. In the area of local reconnection physics, many significant findings have been made with regard to two- uid physics and are related to the cause of fast reconnection. Profiles of the neutral sheet, Hall currents, and the effects of guide field, collisions, and micro-turbulence are discussed to understand the fundamental processes in a local reconnection layer both in space and laboratory plasmas. While the understanding of the global reconnection dynamics is less developed, notable findings have been made on this issue through detailed documentation of magnetic self-organization phenomena in fusion plasmas. Application of magnetic reconnection physics to astrophysical plasmas is also brie y discussed.

Masaaki Yamada, Russell Kulsrud and Hantao Ji

2009-09-17

30

Country Road Take Me Home: Migration Patterns in the Appalachia America and Place-Based Policy  

OpenAIRE

This research fills a void in the regional development literature by assessing how labor force migration affects regional adjustment in peripheral regions and whether it differs than the rest of the country. We do this by comparing patterns for the lagging Appalachian region to the U.S. as a whole for the 1990s and post-2000 periods. We appraise whether successful job creation helps the original residents seeking employment, or primarily goes to outsiders, rendering place-based development po...

Partridge, Mark; Betz, Mike

2012-01-01

31

On the nature of reconnection at a solar coronal null point above a separatrix dome  

CERN Document Server

Three-dimensional magnetic null points are ubiquitous in the solar corona, and in any generic mixed-polarity magnetic field. We consider magnetic reconnection at an isolated coronal null point, whose fan field lines form a dome structure. We demonstrate using analytical and computational models several features of spine-fan reconnection at such a null, including the fact that substantial magnetic flux transfer from one region of field line connectivity to another can occur. The flux transfer occurs across the current sheet that forms around the null point during spine-fan reconnection, and there is no separator present. Also, flipping of magnetic field lines takes place in a manner similar to that observed in quasi-separatrix layer or slip-running reconnection.

Pontin, D I; Galsgaard, K

2013-01-01

32

On the Nature of Reconnection at a Solar Coronal Null Point above a Separatrix Dome  

Science.gov (United States)

Three-dimensional magnetic null points are ubiquitous in the solar corona and in any generic mixed-polarity magnetic field. We consider magnetic reconnection at an isolated coronal null point whose fan field lines form a dome structure. Using analytical and computational models, we demonstrate several features of spine-fan reconnection at such a null, including the fact that substantial magnetic flux transfer from one region of field line connectivity to another can occur. The flux transfer occurs across the current sheet that forms around the null point during spine-fan reconnection, and there is no separator present. Also, flipping of magnetic field lines takes place in a manner similar to that observed in the quasi-separatrix layer or slip-running reconnection.

Pontin, D. I.; Priest, E. R.; Galsgaard, K.

2013-09-01

33

A Study on the Place Attachment Differences of Residents in Tourism Destination: Take Gulangyu Island as an Example  

Directory of Open Access Journals (Sweden)

Full Text Available Place attachment is a long time research topic in tourism geography. However, when Chinese people do tourism planning and manage the destination, most of them also pay attention to the management of real enviroment or recreation faclilities. Few people study the place attachment relationship between the resident and the destination. This study takes Gulangyu as an example. By a large number of questionnaires, using relevant statistical software and methematical analysis, the paper analyzes the relationship between place attachment and the background, ways of tourism and frequency of visitation of local residents, the result shows that such as gender, cultural level, living time, occupation and whether the local people have an impact on the place attachment of residents. However,such as age and activities have no impact on the place attachment of residents, some differences of residents' place attachment are found. On the basis of the study, the paper analyzes the residents cluster basing on the difference of place attachment. Four types of resident are identified:"the daily life", "the emotion approval", "the sparsely leaving" and "the vital function".

YUAN Shu-ai

2011-11-01

34

The auroral and ionospheric flow signatures of dual lobe reconnection  

Science.gov (United States)

We present the first substantial evidence for the occurrence of dual lobe reconnection from ionospheric flows and auroral signatures. The process of dual lobe reconnection refers to an interplanetary magnetic field line reconnecting with lobe field lines in both the northern and southern hemispheres. Two bursts of sunward plasma flow across the noon portion of the open/closed field line boundary (OCB), indicating magnetic flux closure at the dayside, were observed in SuperDARN radar data during a period of strongly northward IMF. The OCB is identified from spacecraft, radar backscatter, and auroral observations. In order for dual lobe reconnection to take place, we estimate that the interplanetary magnetic field clock angle must be within ±10° of zero (North). The total flux crossing the OCB during each burst is small (1.8% and 0.6% of the flux contained within the polar cap for the two flows). A brightening of the noon portion of the northern auroral oval was observed as the clock angle passed through zero, and is thought to be due to enhanced precipitating particle fluxes due to the occurrence of reconnection at two locations along the field line. The number of solar wind protons captured by the flux closure process was estimated to be ~2.5×1030 (4 tonnes by mass), sufficient to populate the cold, dense plasma sheet observed following this interval.

Imber, S. M.; Milan, S. E.; Hubert, B.

2006-11-01

35

Solar Wind Transport Into Magnetosphere Caused by Magnetic Reconnection During Southward and Northward IMF  

Science.gov (United States)

Reconnection is considered as the dominant mechanism of the solar wind transport into magnetosphere. Here, two cases under southward and northward IMF respectively are analyzed, with the results as follows: Firstly, by analyzing measurements from Cluster, an event of magnetopause crossing has been investigated. At the latitude of about 40' and MLT of 13:20 during southward IMF, a transition layer was observed, with the magnetospheric field configuration and cold dense plasma features of magnetosheath. The particle energy- time spectrograms inside the layer were similar to but still a little different from those in magnetosheath, obviously indicating solar wind entry into magnetosphere. The direction and magnitude of the accelerated ion flow implied that reconnection might possibly cause such a solar wind entry phenomenon. The bipolar signature of the normal magnetic component BN in magnetopause coordinates further supported happening of reconnection there. Solar wind plasma flowed toward magnetopause and entered magnetosphere along the reconnected flux tube. The magnetospheric branch of the reconnected flux tube was still inside the magnetosphere after reconnection and supplied the path for solar wind entry into the dayside magnetosphere. Secondly, an event of Cluster-Double Star conjunction observations of magnetic reconnection at high latitude magnetopause nightside of the cusp and solar wind transport into magnetosphere caused by such a reconnection process has been investigated. During northward IMF, Cluster/SC1 observed accelerated flows and ion heating associated with magnetic reconnection at high latitude magnetopause nightside of southern cusp. And Double Star observed cold dense solar wind plasma transported into dayside magnetosphere. The analysis on such conjunction observations shows that: during northward IMF, magnetic reconnection occurs at high latitude nightside of southern cusp, accompanied by accelerated flows that are observed by Cluster/SC1; the direction of the accelerated flows, with its sunward component Vx, dawnward component Vy, northward component Vz, is quite consistent with the theoretical anticipation under the condition of northward IMF with dawnward component By; reconnection can heat plasma more in parallel direction than in perpendicular direction, to a level of about 4 keV; with reconnection taking place at high latitude magnetopause nightside of the southern cusp, TC-1 observed cold and dense plasma transported into magnetosphere; by reconnection at high latitude magnetopause nightside of both cusps, solar wind flux tube can be captured by magnetosphere and pulled into dayside magnetosphere. The case analysis gave more detail and observational evidence of the solar wind transport into magnetosphere by reconnection under southward or northward IMF.

Yan, G.; Shen, C.; Liu, Z.; Dunlop, M. W.; Lucek, E.; Reme, H.; Carr, C.; Bogdanova, Y. V.; Zhang, T.; Balogh, A.; Fazakerley, A.

2009-05-01

36

Comparison of test particle acceleration in torsional spine and fan reconnection regimes  

Science.gov (United States)

Magnetic reconnection is a common phenomenon taking place in astrophysical and space plasmas, especially in solar flares which are rich sources of highly energetic particles. Torsional spine and fan reconnections are important mechanisms proposed for steady-state three-dimensional null-point reconnection. By using the magnetic and electric fields for these regimes, we numerically investigate the features of test particle acceleration in both regimes with input parameters for the solar corona. By comparison, torsional spine reconnection is found to be more efficient than torsional fan reconnection in an acceleration of a proton to a high kinetic energy. A proton can gain as high as 100 MeV of relativistic kinetic energy within only a few milliseconds. Moreover, in torsional spine reconnection, an accelerated particle can escape either along the spine axis or on the fan plane depending on its injection position. However, in torsional fan reconnection, the particle is only allowed to accelerate along the spine axis. In addition, in both regimes, the particle's trajectory and final kinetic energy depend on the injection position but adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory.

Hosseinpour, M.; Mehdizade, M.; Mohammadi, M. A.

2014-10-01

37

Comparison of test particle acceleration in torsional spine and fan reconnection regimes  

International Nuclear Information System (INIS)

Magnetic reconnection is a common phenomenon taking place in astrophysical and space plasmas, especially in solar flares which are rich sources of highly energetic particles. Torsional spine and fan reconnections are important mechanisms proposed for steady-state three-dimensional null-point reconnection. By using the magnetic and electric fields for these regimes, we numerically investigate the features of test particle acceleration in both regimes with input parameters for the solar corona. By comparison, torsional spine reconnection is found to be more efficient than torsional fan reconnection in an acceleration of a proton to a high kinetic energy. A proton can gain as high as 100?MeV of relativistic kinetic energy within only a few milliseconds. Moreover, in torsional spine reconnection, an accelerated particle can escape either along the spine axis or on the fan plane depending on its injection position. However, in torsional fan reconnection, the particle is only allowed to accelerate along the spine axis. In addition, in both regimes, the particle's trajectory and final kinetic energy depend on the injection position but adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory

38

Barrier breakers : women battling the odds to take places in engineering and oil  

Energy Technology Data Exchange (ETDEWEB)

The future role of women in Canada's engineering and petroleum industry was discussed. Women make up almost half of Canada's labour force, but they occupy only 24.2 per cent of the petroleum sector. This article briefly discussed some of the complex reasons why women continue to be under-represented in the oil and gas sector. In Alberta, job opportunities in engineering and the petroleum industry are alluring to both genders. Profiles of some young women just entering the work force after finishing their university education were also presented. Work experience, internships and networking were considered to be major factors in succeeding in male-dominated fields. It was suggested that it takes both genders to create the diverse thinking and experience needed to move forward technologically.

Rucker, D.

2001-04-02

39

Magnetic reconnection  

International Nuclear Information System (INIS)

A review is given of the theory of magnetic reconnection in the framework of resistive magnetohydrodynamics (MHD). While most of the material refers to two-dimensional systems, the final sections give a brief outlook of problems arising in fully three-dimensional configurations. (orig.)

40

The structure of the magnetic reconnection exhaust boundary  

Science.gov (United States)

Switch-off slow shocks (SSS) are the key structure of driving the outflow in Petschek's reconnection model. Observations of reconnection in the solar wind in particular seem to suggest that reconnection X-lines and associated exhausts grow to very large scales and resemble the open outflow geometry predicted by Petschek. However, direct observations of SSSs in the Earth's magnetosphere and the solar wind are infrequent. Since it is the release of magnetic energy downstream from the X-line that ultimately drives the outflow rather than the dynamics close to the X-line, the absence of the SSS in observations and kinetic simulations calls into question the conjecture that fast collisionless reconnection actually can scale to very large systems. Thus, a key requirement for demonstrating the fast energy release of reconnection that takes place in large systems is to pin down the specific mechanism driving the Alfvenic outflow. We present a large 2-D reconnection simulation and its companion Riemann problem using a Particle-In-Cell code. The self-generated firehose-sense temperature anisotropy (i.e., T| > T) by counterstreaming ions is found to be important in determining the structure of reconnection exhausts. This temperature anisotropy slows down the intermediate mode while speeds up the slow mode, and consequently prevents the formation of classical Switch-off Slow shocks in Petschek's model. Instead, the nonlinear coupling between the slow and intermediate waves constitutes the shock transition. A plateau of the firehose stability parameter 1-(?|-?)/2 at value 0.25 is observed inside these hybrid waves, which should also be observable in Earth's magnetotail and the solar wind. This special value is significant because it is the degeneracy point of slow and intermediate waves in anisotropic plasmas. The anisotropic Rankine-Hugoniot jump conditions are derived and compared with our simulations, while the pseudo-potentials of shocks are analyzed to explain the dynamics of forming these transition structures. The Wal'en relation is shown to fail at the core of reconnection exhausts, where the firehose instability is unstable. (Ref: Yi-Hsin Liu, J. F. Drake and M. Swisdak, The structure of the magnetic reconnection exhaust boundary, Phys. of Plasmas, 19, 022110, 2012)

Liu, Yi-Hsin

2012-10-01

41

Magnetic Reconnection in the Interior of Interplanetary Coronal Mass Ejections  

Science.gov (United States)

Recent in situ observations of interplanetary coronal mass ejections (ICMEs) found signatures of reconnection exhausts in their interior or trailing edge. Whereas reconnection on the leading edge of an ICME would indicate an interaction with the coronal or interplanetary environment, this result suggests that the internal magnetic field reconnects with itself. In light of this data, we consider the stability properties of flux ropes first developed in the context of astrophysics, then further elaborated upon in the context of reversed field pinches (RFPs). It was shown that the lowest energy state of a flux rope corresponds to ?×B=?B with ? a constant, the so-called Taylor state. Variations from this state will result in the magnetic field trying to reorient itself into the Taylor state solution, subject to the constraints that the toroidal flux and magnetic helicity are invariant. In reversed field pinches, this relaxation is mediated by the reconnection of the magnetic field, resulting in a sawtooth crash. If we likewise treat the ICME as a flux rope, any deviation from the Taylor state will result in reconnection within the interior of the flux tube, in agreement with the observations by Gosling et al. Such a departure from the Taylor state takes place as the flux tube cross section expands in the latitudinal direction, as seen in magnetohydrodynamic (MHD) simulations of flux tubes propagating through the interplanetary medium. We show analytically that this elongation results in a state which is no longer in the minimum energy Taylor state. We then present magnetohydrodynamic simulations of an elongated flux tube which has evolved away from the Taylor state and show that reconnection at many surfaces produces a complex stochastic magnetic field as the system evolves back to a minimum energy state configuration.

Fermo, R. L.; Opher, M.; Drake, J. F.

2014-07-01

42

25 CFR 1000.465 - May a Tribe/Consortium negotiate AFA provisions on conflicts of interest to take the place of...  

Science.gov (United States)

...negotiate AFA provisions on conflicts of interest to take the place of this...SELF-DETERMINATION AND EDUCATION ACT Conflicts of Interest § 1000.465 May a Tribe...negotiate AFA provisions on conflicts of interest to take the place of...

2010-04-01

43

Modelling Magnetic Reconnection and Nano-flare Heating in the Solar Corona  

Science.gov (United States)

Current models describing magnetic reconnection in the solar corona assume single reconnection events occurring at random crossings between magnetic flux tubes. However, in the avalanche model of magnetic reconnection, multiple reconnections are expected to occur. The purpose of this research is to first, calculate the point of the greatest stress between magnetic flux tubes and then to allow for dynamic evolution utilising the avalanche model. This represents a significant increase in sophistication over previous models. This undertaking is not purely theoretical since we compare the results of our modelling with HI-C data. Using key inputs from the HIC and AIA observations such as loop length and magnetic field strength, we predict the number of reconnection events likely to take place. As a single reconnection event cannot currently be directly observed, the distribution of flare events are recorded instead. The power law fit yielded as a result of our simulations is within the expected range given the observational evidence of flare distributions and temperature values in the corona. This provides further evidence to support the role of Nano-flares in the heating of the corona.

Biggs, George; Asgari-Targhi, Mahboubeh

2015-01-01

44

RECONNECTION ELECTRIC FIELD AND HARDNESS OF X-RAY EMISSION OF SOLAR FLARES  

International Nuclear Information System (INIS)

Magnetic reconnection is believed to be the prime mechanism that triggers solar flares and accelerates electrons up to energies of MeV. In the classical two-dimensional reconnection model, the separation motion of chromospheric ribbons, manifests the successive reconnection that takes place higher up in the corona. Meanwhile, downward traveling energetic electrons bombard the dense chromosphere and create hard X-ray (HXR) emissions, which provide a valuable diagnostic of electron acceleration. Analyses of ribbon dynamics and the HXR spectrum have been carried out separately. In this Letter, we report a study of the comparison of reconnection electric field measured from ribbon motion and hardness (spectral index) of X-ray emission derived from X-ray spectrum. Our survey of the maximum average reconnection electric field and the minimum overall spectral index for 13 two-ribbon flares shows that they are strongly anticorrelated. The former is also strongly correlated with flare magnitude measured using the peak flux of soft X-ray emissions. These provide strong support for electron acceleration models based on the electric field generated at reconnecting current sheet during flares.

45

Test particle acceleration in torsional spine magnetic reconnection  

Science.gov (United States)

Three-dimensional (3D) magnetic reconnection is taking place commonly in astrophysical and space plasmas, especially in solar flares which are rich sources of highly energetic particles. One of the proposed mechanisms for steady-state 3D magnetic reconnection is "torsional spine reconnection". By using the magnetic and electric fields for "torsional spine reconnection", we numerically investigate the features of test particle acceleration with input parameters for the solar corona. We show that efficient acceleration of a relativistic proton is possible near the null point where it can gain up to 100 MeV of kinetic energy within a few milliseconds. However, varying the injection position results in different scenarios for proton acceleration. A proton is most efficiently accelerated when it is injected at the point where the magnetic field lines change their curvature in the fan plane. Moreover, a proton injected far away from the null point cannot be accelerated and, even in some cases, it is trapped in the magnetic field. In addition, adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory.

Hosseinpour, M.

2014-10-01

46

DSC Studies of Retrogradation and Amylose-Lipid Complex Transition Taking Place in Gamma Irradiated Wheat Starch  

International Nuclear Information System (INIS)

Degradation resulting from gamma irradiation induces decrease in order of starch granules and influences the processes occurring in starch-water system. Differential scanning calorimetry (DSC) was applied at present for studying the effect of radiation with doses of 5 - 30 kGy on amylose-lipid complex transition and retrogradation occurring in wheat starch gels. Influence of the conditions applied during DSC measurements and intermediate storage was tested on the possibility to observe radiation effect. Wheat starch was irradiated with 60Co gamma rays in a gamma cell Issledovatiel placed in the Department of Radiation Chemistry, INCT. DSC measurements were performed for ca. 50% and ca. 20% gels during heating - cooling - heating cycles (up to 3 cycles) in the temperature range 10 - 150 degree at heating and cooling rates of 10, 5 and 2.5 degree min-1. The Seiko DSC 6200 calorimeter was used. Decrease in amylose-lipid complex transition temperature was found already after irradiation of wheat starch with a dose of 5 kGy showing modificatin of the complex structure. The differences between the irradiated and the non-irradiated samples became the easier seen in the every foregoing heating or cooling cycle as compared to the preceeding one. It is because that thermal treatment causes decrease of transition temperature in all the irradiated samples, with no effect or increase of that temperature observed in the non-irradiated ones. Irradiation hinders retrogradation taking place in ca. 50% gels but facilitates retrogradation occurring in ca. 20 % gels. Moreover, the expanded differences between the amylose-lipid complex formed in the irradiated and non-irradiated gels result due to their recrystallisation. Storage of the gels induces decrease in the temperature of the complex transition as compared to the last cycle of the first analysis. That decrease was, however, more significant in the case of all the irradiated samples than in the case of the initial sample. In result, the differences between the irradiated and the non-irradiated samples are easier detected after storage. The better differentiation between the amylose-lipid complex transition taking place in particular samples accompanied by the better reproducity were obtained in the case of ca. 50% suspensions as compared to ca. 20% suspensions submitted to the same treatment. The results are discussed in terms of the structural changes resulting in starch due to irradiation. The work was sponsored in the frame of research grant 2P06T 026 27 of Polish Ministry of Scientific Research and Information Technology

47

Human mitochondrial RNA decay mediated by PNPase–hSuv3 complex takes place in distinct foci  

Science.gov (United States)

RNA decay is usually mediated by protein complexes and can occur in specific foci such as P-bodies in the cytoplasm of eukaryotes. In human mitochondria nothing is known about the spatial organization of the RNA decay machinery, and the ribonuclease responsible for RNA degradation has not been identified. We demonstrate that silencing of human polynucleotide phosphorylase (PNPase) causes accumulation of RNA decay intermediates and increases the half-life of mitochondrial transcripts. A combination of fluorescence lifetime imaging microscopy with Förster resonance energy transfer and bimolecular fluorescence complementation (BiFC) experiments prove that PNPase and hSuv3 helicase (Suv3, hSuv3p and SUPV3L1) form the RNA-degrading complex in vivo in human mitochondria. This complex, referred to as the degradosome, is formed only in specific foci (named D-foci), which co-localize with mitochondrial RNA and nucleoids. Notably, interaction between PNPase and hSuv3 is essential for efficient mitochondrial RNA degradation. This provides indirect evidence that degradosome-dependent mitochondrial RNA decay takes place in foci. PMID:23221631

Borowski, Lukasz S.; Dziembowski, Andrzej; Hejnowicz, Monika S.; Stepien, Piotr P.; Szczesny, Roman J.

2013-01-01

48

Modeling of the thermohydraulic phenomena taking place during the quench of a superconducting magnet cooled with superfluid helium  

International Nuclear Information System (INIS)

One of the main issues related to the conception of a superconducting magnet cooled by a superfluid helium bath (like the Iseult magnet) is to insure the magnet safety as well as the whole cryogenic facility safety in case of accidental quench. In order to find a solution to this problem, we first have to identify the physical mechanisms which drive the pressure rise during a quench. This is why our study deals with the modeling of the thermohydraulic phenomena taking place during such a magnet quench. First of all, we performed and analyzed local pressure rise experiments in a heated helium channel. A numerical thermohydraulic model was developed for this study. Quench experiments were then performed on an 8-T (Seht) superconducting coil cooled by a superfluid helium bath. These experiments allowed us to make a detailed analysis of the physical mechanisms which drive the global pressure rise in case of quench as well as the strong coupling between this pressure rise and the normal zone propagation. Following this analysis, a complete model of normal zone propagation and pressure rising during a quench was developed. This model is a first step toward predictive modeling of the pressure rise during the quench of a superconducting magnet cooled by a superfluid helium bath. (author)

49

Jupiter's magnetopause: A search for wave and reconnection signatures  

Science.gov (United States)

Surface waves and magnetic reconnection are two key processes taking place at the planetary magnetopause. They allow the coupling, through energy (and particle) transfer, of the interplanetary medium and the magnetosphere. The relative importance of large scale Dungey reconnection and viscous interaction (including small-scale intermittent reconnection associated with Kelvin-Helmholtz vortices) are expected to be different at Jupiter compared to the Earth's case. Such differences would be due to the combination of a) a weaker solar wind pressure and Alfvén velocity as the distance to the Sun increases, b) a high- ? plasma sheet, originating from Io's outgassing, which inflates the Jovian magnetosphere, c) the rapid rotation of the planet relative to its size (e.g. Desroche et al. 2012). Here we analyse the signatures of wave activity and reconnection on the magnetopause of Jupiter, based on magnetic field and energetic particle measurements from the successive spacecraft that explored the Jovian system. Up to now, 7 spacecraft equipped with a magnetometer have crossed the Jovian magnetopause: Pioneer 10, Pioneer 11, Voyager 1, Voyager 2, Ulysses,Galileo and Cassini. We make use of several normal direction finding techniques, such as the Minimum Variance Analysis, in order to identify waves and Kelvin-Helmholtz vortices. As far as the reconnection is concerned, small scale signatures of flux-tube events (FTEs) had been identified by Walker and Russell (1985), based on a limited data-set from the Pioneers' and Voyagers' fly-bys. Here we will extend this search to the extensive dataset from all the missions that explored Jupiter's system.

Bonfond, B.; Kivelson, M. G.; Khurana, K. K.; Delamere, P. A.; Stauffer, B. H.; Radioti, A.

2014-04-01

50

Solar flare mechanism based on magnetic arcade reconnection and island merging  

Energy Technology Data Exchange (ETDEWEB)

The authors propose a model describing physical processes of solar flares based on resistive reconnection of magnetic field subject to continuous increase of magnetic shear in the arcade. The individual flaring process consists of magnetic reconnection of arcade field lines, generation of magnetic islands in the magnetic arcade, and coalescence of magnetic islands. When a magnetic arcade is sheared (either by foot point motion or by flux emergence), a current sheet is formed and magnetic reconnection can take place to form a magnetic island. A continuing increase of magnetic shear can trigger a new reconnection process and create a new island in the under lying arcade below the magnetic island. The new born island rises faster than the preceding island and merges with it to form one island. Before completing the island merging process, the new born island exhibits two phases of rising motion: a first phase with a slower rising speed and a second phase with a faster rising speed. The flare plasma heating occurs mainly due to magnetic reconnection in the current sheet under the new born island. The new born island represents the X-ray plasma ejecta which shows two phases of rising motion observed by Yohkoh [Ohyama and Shibata (1997)]. The first phase with slower new born island rising speed corresponds to the early phase of reconnection of line-tied field in the underlying current sheet and is considered as the preflare phase. In the second phase, the island coalescence takes place, and the underlying current sheet is elongated so that the line-tied arcade field reconnection rate is enhanced. This phase is interpreted as the impulsive phase or the flash phase of flares. The obtained reconnection electric field is large enough to accelerate electrons to an energy level higher than 10 keV, which is necessary for observed hard X-ray emissions. After merging of the islands is completed, magnetic reconnection continues in the current sheet under the integrated island for a longer period, which is considered as the main phase of flares. The sequence of all these processes is repeated with some time interval while a shear-increasing motion continues. The authors propose that these repetitive flaring processes constitute a set of homologous flares.

C.Z. Chen; G.S. Choe

2000-06-15

51

Solar wind interaction with the Earth's magnetosphere: the role of reconnection in the presence of a large scale sheared flow  

Directory of Open Access Journals (Sweden)

Full Text Available The Earth's magnetosphere and solar wind environment is a laboratory of excellence for the study of the physics of collisionless magnetic reconnection. At low latitude magnetopause, magnetic reconnection develops as a secondary instability due to the stretching of magnetic field lines advected by large scale Kelvin-Helmholtz vortices. In particular, reconnection takes place in the sheared magnetic layer that forms between adjacent vortices during vortex pairing. The process generates magnetic islands with typical size of the order of the ion inertial length, much smaller than the MHD scale of the vortices and much larger than the electron inertial length. The process of reconnection and island formation sets up spontaneously, without any need for special boundary conditions or initial conditions, and independently of the initial in-plane magnetic field topology, whether homogeneous or sheared.

F. Califano

2009-01-01

52

The Effect of Single Particle Dynamics in Collisionless Reconnection  

Science.gov (United States)

The question of which mechanisms can allow rapid changes of the magnetic field topology in collisionless plasmas is addressed in a laboratory experiment, based on the MIT Versatile Toroidal Facility (VTF). In this presentation we focus on mechanisms that are present at the level of single particle orbits, for cases in which the strength of the magnetic field perpendicular to the reconnection plane (the guide field) is comparable to, or smaller than that of the field on the reconnection plane (the cusp field). Similarly to space plasmas, the electron mean free path is much longer than the characteristic length of particle orbits, considered for the VTF case of the order of the dimensions of the plasma cross-section. Hence, particle orbits are expected to influence the macroscopic plasma dynamics during the development and sustainment of reconnection. We find analytically and demonstrate experimentally that reconnection driven by an electric field along the X--line can take place in a collisionless plasma, in a magnetic cusp with a relatively weak guide field without a macroscopic current layer, consistently with the effect of particle orbits. This study led to three main conclusions. First, because particles are mirror trapped, a reconnection electric field, Ez, does not provide acceleration of the particles in its direction parallel to the X--line. This allows the reconnection to proceed at the externally imposed rate, the same as in vacuum. Second, in the limit of massless particles, an electrostatic potential, ? , is developed self-consistently by the plasma on the reconnection plane to avoid charge separation. This potential was calculated analytically and has been measured experimentally for the first time. Third, particles drift across the plane perpendicular to the X--line at the Ware--pinch velocity (Ez/Bxy). This drift speed is independent of the electrostatic potential ? . This ``frozen in law'' at the single particle level is expected to break along the separatrix where different mechanisms can remove the steep gradients in ? . High resolution measurements of the structure of the electrostatic potential are being performed to identify such mechanisms, and will be discussed at the conference. This work is partly funded by DoE Junior Faculty Development Award DE-FG02-00ER54601.

Egedal, J.; Fasoli, A.; Migliazzo, J.; Nazemi, J.

2001-05-01

53

PLASMOID EJECTIONS AND LOOP CONTRACTIONS IN AN ERUPTIVE M7.7 SOLAR FLARE: EVIDENCE OF PARTICLE ACCELERATION AND HEATING IN MAGNETIC RECONNECTION OUTFLOWS  

Energy Technology Data Exchange (ETDEWEB)

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km s{sup -1} up to 1050 km s{sup -1}. These outflows are associated with spatially separated double coronal X-ray sources with centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descent, which we ascribe to the interplay among multiple processes including the upward development of reconnection and the downward contractions of reconnected loops. The impulsive phase onset is delayed by 10 minutes from the start of the descent, but coincides with the rapid speed increases of the upward plasmoids, the individual loop shrinkages, and the overall loop-top descent, suggestive of an intimate relation of the energy release rate and reconnection outflow speed.

Liu Wei [Lockheed Martin Solar and Astrophysics Laboratory, Building 252, 3251 Hanover Street, Palo Alto, CA 94304 (United States); Chen Qingrong; Petrosian, Vahe [Department of Physics, Stanford University, Stanford, CA 94305 (United States)

2013-04-20

54

Fast Collisionless Reconnection Condition and Self-Organization of Solar Coronal Heating  

OpenAIRE

I propose that solar coronal heating is a self-regulating process that keeps the coronal plasma roughly marginally collisionless. The self-regulating mechanism is based on the interplay of two effects. First, plasma density controls coronal energy release via the transition between the slow collisional Sweet-Parker regime and the fast collisionless reconnection regime. This transition takes place when the Sweet--Parker layer becomes thinner than the characteristic collisionl...

Uzdensky, Dmitri A.

2007-01-01

55

Explosive Turbulent Magnetic Reconnection  

OpenAIRE

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconn...

Higashimori, Katsuaki; Yokoi, Nobumitsu; Hoshino, Masahiro

2013-01-01

56

Reconnection rates in driven magnetic reconnection  

International Nuclear Information System (INIS)

Using resistive magnetohydrodynamic simulations, we investigate the influence of various parameters on the reconnection rate in two scenarios of magnetic reconnection. The first scenario consists of the ''Newton Challenge'' problem [Birn et al., Geophys. Res. Lett. 32, L06105 (2005)]. In this scenario, reconnection is initiated in a plane Harris-type current sheet by temporally limited, spatially varying, inflow of magnetic flux. The second scenario consists of the well-studied island coalescence problem. This scenario starts from an equilibrium containing periodic magnetic islands with parallel current filaments. Due to the attraction between parallel currents, pairs of islands may move toward each other, forming a current sheet in between. This leads to reconnection and ultimately the merging of islands. In either scenario, magnetic reconnection may be considered as being driven by external or internal forcing. Consistent with that interpretation we find that in either case the maximum reconnection rate (electric field) depends approximately linearly on the maximum driving electric field, when other parameters remain unchanged. However, this can be understood mostly from the change of characteristic background parameters; particularly, the increase of the magnetic field strength in the inflow region due to the added magnetic flux. This interpretation is consistent with the result that the maximum of the reconnection electric field is assumed significantly later (ten field is assumed significantly later (tens of Alfven times) than the maximum driving and typically does not match the instantaneous driving electric field. Furthermore, the reconnection rate also depends on the resistivity and the time scale of the driving

57

Modeling Swarthmore spheromak reconnection experiment using hybrid code  

International Nuclear Information System (INIS)

A three-dimensional (3D) hybrid-particle model is developed for investigation of magnetic reconnection in the Swarthmore Spheromak Experiment (SSX). In this numerical model, ions are treated as fully kinetic particles, and electrons are treated as a massless fluid. The plasma responds to the electromagnetic fields in a self-consistent manner. The simulation is performed in a cylindrical domain. Initially, a pair of counter-helicity spheromaks are assumed, in which the magnetic field and plasma pressure are set up according to the MHD equilibrium. The ion particles are loaded with a Maxwellian distribution function. As the simulation proceeds, magnetic reconnection takes place at the current sheet between the pair of spheromak fields. Plasma is ejected away from the X line towards the central axis, where heating of the transmitted ion is found. Meanwhile, quadrupole out-of-plane magnetic field structure associated with the Hall effects is present around the reconnection site. The preliminary simulation shows consistency with the SSX experiment in several aspects

58

Microphysics of Magnetic Reconnection: Experiments on RSX and Simulation  

Science.gov (United States)

Using a unique LANL laboratory facility, the Reconnection Scaling Experiment (RSX), and a state-of-the-art LANL numerical code, CELESTE3D, we are beginning an experimental and numerical study of the microphysics of 2D and 3D "fast magnetic reconnection". RSX at Los Alamos National Laboratory is already operational and producing research plasmas. In RSX, the radial boundaries and thus the reconnection geometry are not constrained to two dimensions. It is capable of investigating 3D magnetic reconnection occurring in a free-boundary 3D linear geometry during the coalescence of two parallel current plasma channels, which are produced by using plasma gun technology. RSX can also scale the guide field (ion gyroradius) independently of other reconnection parameters. Frontier reconnection research invokes (1) `anomalous' microinstability-induced resistivity, which enhances dissipation rates inside the reconnection layer and (2) terms of the two-fluid generalized Ohm's law which introduce whistler and kinetic Alfvén wave dynamics. The two-fluid approach predicts (a) a two-spatial-scale spatial structure of the reconnection layer, with outer (inner) thickness equal to the ion (electron) skin depth and (b) Hall currents in the reconnection plane and out-of-plane magnetic field on the electron scale. We will show spatially resolved RSX experimental measurements of the dynamics of the reconnection layer, and take advantage of our scaling capabilities to address the applicability of the two-fluid approach.

Intrator, T. P.; Furno, I. G.; Hsu, S. C.; Lapenta, G.; Ricci, P.

2003-12-01

59

Taking culture to court: anthropology, expert witnesses and aboriginal sense of place in the Interior Plateau of British Columbia  

OpenAIRE

This thesis examines the way in which indigenous oral knowledge is treated in court by Crown anthropological expert witnesses. I argue that the theoretical frameworks that guide these expert opinions are in defiance of widely taught contemporary academic cannons. My specific focus is indigenous sense of place, an issue that is intensely scrutinized in Aboriginal rights and title cases. As I show, Crown expert evidence ignores contemporary academic paradigms and practices, thereby denying indi...

Banks, Judith

2009-01-01

60

Fast Magnetic Reconnection in Free Space: Self-similar Evolution Process  

Science.gov (United States)

We present a new model for the time evolution of fast magnetic reconnection in free space, which is characterized by self-similarity. Reconnection triggered by locally enhanced resistivity assumed at the center of the current sheet can self-similarly and unlimitedly evolve until external factors affect the evolution. The possibility and stability of this type of evolution are verified by numerical simulations in a very wide spatial dynamic range. Actual astrophysical reconnection in solar flares and geomagnetospheric substorms can be treated as an evolutionary process in free space, because the resultant scale is much larger than the initial scale. In spite of this fact, most of the previous numerical works focused on the evolutionary characters strongly affected by artificial boundary conditions on the simulation boundary. Our new model clarifies a realistic evolution for such cases. The characteristic structure around the diffusion region is quite similar to the Petschek model, which is characterized by a pair of slow-mode shocks and the fast-mode rarefaction-dominated inflow. However, in the outer region, a vortex-like return flow driven by the fast-mode compression caused by the piston effect of the plasmoid takes place. The entire reconnection system expands self-similarly.

Nitta, S.; Tanuma, S.; Shibata, K.; Maezawa, K.

2001-04-01

61

Stuck between a ROC and a hard place? Barriers to the take up of green energy in the UK  

International Nuclear Information System (INIS)

This paper examines the UK mechanisms for ensuring future investment in renewable energy through consumer adoption of green energy tariffs and the Renewable Obligation Certificate (ROC) system. Using a national survey and focus groups the stated willingness by UK customers to pay a premium for renewable or green energy and actual take up of such tariffs is assessed. Substantial differences between willingness to pay for and the adoption of green energy tariffs are reported. This disparity is linked to a range of factors including consumer confusion, lack of supply, complexities of constructing 'green source' tariffs under the ROC system and a lack of customer trust. It is concluded that the re-definition of the green energy market in favour of 'green source' tariffs, greater direct compliance with the Renewable Obligation by addressing supply constraints, and efforts in providing clearer information and choices for consumers via a compulsory green energy accreditation scheme are required if willing consumers' are to contribute to investment in renewable energy. (author)

62

Reconnection in Three Dimensions  

Science.gov (United States)

Analyzing the qualitative three-dimensional magnetic structure of a plasmoid, we were led to reconsider the concept of magnetic reconnection from a general point of view. The properties of relatively simple magnetic field models provide a strong preference for one of two definitions of magnetic reconnection that exist in the literature. Any concept of magnetic reconnection defined in terms of magnetic topology seems naturally restricted to cases where the magnetic field vanishes somewhere in the nonideal (diffusion) region. The main part of this paper is concerned with magnetic reconnection in nonvanishing magnetic fields (finite-B reconnection), which has attracted less attention in the past. We show that the electric field component parallel to the magnetic field plays a crucial physical role in finite-B reconnection, and we present two theorems involving the former. The first states a necessary and sufficient condition on the parallel electric field for global reconnection to occur. Here the term "global" means the generic case where the breakdown of magnetic connection occurs for plasma elements that stay outside the nonideal region. The second theorem relates the change of magnetic helicity to the parallel electric field for cases where the electric field vanishes at large distances. That these results provide new insight into three-dimensional reconnection processes is illustrated in terms of the plasmoid configuration, which was our starting point.

Hesse, Michael

1999-01-01

63

The characteristic of the magnetopause reconnection X-line deduced from low-altitude satellite observations of cusp ions  

Science.gov (United States)

We present an analysis of a 'quasi-steady' cusp ion dispersion signature observed at low altitudes. We reconstruct the field-parallel part of the Cowley-D ion distribution function, injected into the open low-latitude boundary layer (LLBL) in the vicinity of the reconnection X-line. From this we find the field parallel magnetosheath flow at the X-line was only 20 +/- 60 km/s, placing the reconnection site close to the flow streamline which is perpendicular to the magnetosheath field. Using interplanetary data and assuming the subsolar magnetopause is in pressure balance, we derive a wealth of information about the X-line, including: the density, flow, magnetic field and Alfven speed of the magnetosheath; the magnetic shear across the X-line; the de-Hoffman Teller speed with which field lines emerge from the X-line; the magnetospheric field; and the ion transmission factor across the magnetopause. The results indicate that some heating takes place near the X-line as the ions cross the magnetopause, and that sheath densities may be reduced in a plasma depletion layer. We also compute the reconnection rate. Despite its quasi-steady appearance on an ion spectrogram, this cusp is found to reveal a large pulse of enhanced reconnection rate.

Lockwood, M.; Onsager, T. G.; Davis, C. J.; Smith, M. F.; Denig, W. F.

1994-01-01

64

On the possibility of Alfvén wave resonance in collisionless magnetic reconnection  

Science.gov (United States)

Alfvén wave resonance and magnetic reconnection are among the potential candidates for efficient dissipation of magnetic energy in space and astrophysical plasmas. In this paper, the correspondence between Alfvén resonance and the electron-inertia driven reconnection in a sheared force-free magnetic field is discussed. By analytical scaling the linear regimes of compressible tearing instability in the two-fluid magnetohydrodynamic (MHD) model, we present parametric conditions for the possibility of Alfvén resonance existence. Meanwhile, it is argued that the slow MHD Alfvénic resonance can take place only in the "intermediate" - called Hall-MHD regime when ? > ? . ? is the ratio of plasma thermal pressure to the pressure in equilibrium magnetic field and ? is the electron to ion mass ratio. There is no room for such a resonant dissipation phenomenon either in the single-fluid MHD or the electron-MHD regimes.

Hosseinpour, M.

2015-02-01

65

Asymmetric nonstationary reconnection and erosion of the magnetopause  

International Nuclear Information System (INIS)

Two-dimensional problem on nonstationary reconnection of different-size magnetic fields with formation of Petchek travelling shock waves is solved. It is shown, that plasma with shock waves is accelerated up to the Alfven rates average, which correspond to reconnecting fields. Reconnection line shift perpendicular to the current layer in the direction of large magnetic field is the peculiarity of nonstationary asymmetrical reconnction. When reconnection is finished, shock waves scatter along the current layer, the current layer, shifted concerning the initial one at the distance, directly proportional to the reconnected magnetic flux, is reduced at the diffusion region place. Shift values agree well with magnetopause erosion effect. The shock waves front moves along the current layer with large Alfven rate, the back one - with lower rate, while normal components of the rate and magnetic field with root-mean square rate

66

Asymmetric Magnetic Reconnection in Weakly Ionized Chromospheric Plasmas  

CERN Document Server

Realistic models of magnetic reconnection in the solar chromosphere must take into account that the plasma is partially ionized and that plasma conditions within any two magnetic flux bundles undergoing reconnection may not be the same. Asymmetric reconnection in the chromosphere may occur when newly emerged flux interacts with pre-existing, overlying flux. We present 2.5D simulations of asymmetric reconnection in weakly ionized, reacting plasmas where the magnetic field strengths, ion and neutral densities, and temperatures are different in each upstream region. The plasma and neutral components are evolved separately to allow non-equilibrium ionization. As in previous simulations of chromospheric reconnection, the current sheet thins to the scale of the neutral-ion mean free path and the ion and neutral outflows are strongly coupled. However, the ion and neutral inflows are asymmetrically decoupled. In cases with magnetic asymmetry, a net flow of neutrals through the current sheet from the weak field (high ...

Murphy, Nicholas A

2015-01-01

67

Magnetic Reconnection in Astrophysical Environments  

CERN Document Server

Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turbulence in most astrophysical settings is of pre-existing nature, but it also can be induced by magnetic reconnection itself. In this situation turbulent magnetic field wandering opens up reconnection outflow regions, making reconnection fast. We discuss Lazarian \\& Vishniac (1999) model of turbulent reconnection, its numerical and observational testings, as well as its connection to the modern understanding of the Lagrangian properties of turbulent fluids. We show that the predicted dependences of the reconnection rates on the level of...

Lazarian, A; Vishniac, E; Kowal, G

2014-01-01

68

Fragment Driven Magnetic Reconnection  

CERN Document Server

In this paper, we investigate a simple model where two, initially unconnected, flux systems are forced to interact in response to the imposed boundary driving by solving the non-ideal 3D MHD equations numerically. The reconnection rate of the dynamical process is determined and compared with the corresponding rate for the potential evolution of the magnetic field. This shows that the dynamic reconnection rate is about a factor of two smaller than the potential (perfect, instantaneous) rate for realistic solar driving velocities demonstrating that this three-dimensional magnetic reconnection process is fast. The energy input for a fixed advection distance is found to be independent of the driving velocity. The Joule dissipation associated with the reconnection process is also found to be basically dependent on the advection distance rather than driving velocity. This implies that the timescale for the event determines the effect the heating has on the temperature increase. Finally, the numerical experiments in...

Galsgaard, K

2004-01-01

69

Model of Hall reconnection.  

Science.gov (United States)

The rate of quasistationary, two-dimensional magnetic reconnection is calculated in the framework of incompressible Hall magnetohydrodynamics, which includes the Hall and electron pressure terms in Ohm's law. The Hall-magnetohydrodynamics equations are solved in a local region across the reconnection electron layer, including only the upstream region and the layer center. In the case when the ion inertial length di is larger than the Sweet-Parker reconnection layer thickness, the dimensionless reconnection rate is found to be independent of the electrical resistivity and equal to di/L, where L is the scale length of the external magnetic field in the upstream region outside the electron layer and the ion layer thickness is found to be di. PMID:19113486

Malyshkin, Leonid M

2008-11-28

70

Fragment Driven Magnetic Reconnection  

OpenAIRE

In this paper, we investigate a simple model where two, initially unconnected, flux systems are forced to interact in response to the imposed boundary driving by solving the non-ideal 3D MHD equations numerically. The reconnection rate of the dynamical process is determined and compared with the corresponding rate for the potential evolution of the magnetic field. This shows that the dynamic reconnection rate is about a factor of two smaller than the potential (perfect, inst...

Galsgaard, K.; Parnell, C.

2004-01-01

71

Spontaneous 3D Reconnection in Electron MHD Plasmas  

Science.gov (United States)

Experiments on spontaneous magnetic reconnection have been performed in a large (1 m × 2.5 m), dense (10^12 cm-3, 4 eV), weakly (B = 5 G) magnetized laboratory plasma in the parameter regime of electron MHD. A three-dimensional (3D) field topology is formed by superimposing on a uniform background magnetic field an opposing, stronger field of a Helmholtz coil (30 cm diam). The Helmholtz coil current is applied for a time sufficient for the field to penetrate into the plasma (30 ?s), then switched off rapidly (experiments. Plasma parameters are obtained from Langmuir probes. Energetic electrons are also detected optically. A stable field-reverse configuration (FRC) is maintained for many whistler transit times by an electron current sheet driven by inductive electric fields. The FRC decays due to dissipation in the toroidal neutral sheet where E allel J, and ion sound and whistler turbulence are observed. Closed field lines are annihilated at the null layer rather than reconnected at the 3D cusp null points. Strong electron heating is observed in the current sheet. Light emission indicates the presence of fast electrons (> 10 eV). Insignificant electron energization takes place in the 3D null points. Most of the magnetic energy is dissipated rather than convected.

Stenzel, Reiner L.

2001-10-01

72

Signatures of interchange reconnection: STEREO, ACE and Hinode observations combined  

Directory of Open Access Journals (Sweden)

Full Text Available Combining STEREO, ACE and Hinode observations has presented an opportunity to follow a filament eruption and coronal mass ejection (CME on 17 October 2007 from an active region (AR inside a coronal hole (CH into the heliosphere. This particular combination of "open" and closed magnetic topologies provides an ideal scenario for interchange reconnection to take place. With Hinode and STEREO data we were able to identify the emergence time and type of structure seen in the in-situ data four days later. On the 21st, ACE observed in-situ the passage of an ICME with "open" magnetic topology. The magnetic field configuration of the source, a mature AR located inside an equatorial CH, has important implications for the solar and interplanetary signatures of the eruption. We interpret the formation of an "anemone" structure of the erupting AR and the passage in-situ of the ICME being disconnected at one leg, as manifested by uni-directional suprathermal electron flux in the ICME, to be a direct result of interchange reconnection between closed loops of the CME originating from the AR and "open" field lines of the surrounding CH.

D. Baker

2009-10-01

73

Winding, Fingering and Reconnection Mechanisms of Closely Interacting Vortex Tubes in Three Dimensions.  

Science.gov (United States)

Three-dimensional Navier-Stokes equations (with/without hyperviscosity) are solved using a Fourier-pseudospectral method to simulate the evolution of the following generic cases: (I) Orthogonal vortex tubes with equal strengths. (II) Orthogonal vortex tubes with unequal strengths. (III) Vortex/Dipole, Dipole/Dipole tubes with equal strengths. (IV) Single perturbed vortex tube with/without axial flow. The maximum resolution used is 96^3 collocation points. For runs having nu and vortices of equal strength, the Reynolds number Gamma/nu is varied from 690 to 2100. For case I, sudden early-time fingering is followed by reconnection. It is discovered that the fingering process originates from the non-uniform axial vorticity amplification and the displacement of the core vorticity contours due to a lift force set-up by the initial configuration. The growth rate of the mean square rate of strain and vorticity is found to be at least exponential during the reconnection process. The strain components are found to exhibit a strong temporal and spatial dependence. Perfect alignment between the vorticity vector and the mid-eigenvalue eigenvector of the strain rate tensor is observed during reconnection. This result is in agreement with both turbulent flow simulations (54), (3), (114) and with Vieillefosse's model (134). Comparison of the results with Saffman's model (108) showed discrepancies in the growth rates of vorticity and strain, in the time scale of reconnection and in the Reynolds number dependence of the results. Unlike Pumir and Siggia's results (98), the reconnection process is found to be strongly three -dimensional. Disagreements have been detected with Melander and Hussain's (76) simulations: No obvious helicity generation is observed during reconnection. The reconnection process is found to take place near the upper stagnation segment of the dipole due to the nature of the vortex stretching dynamics. For case II, a helical winding process is observed followed by a newly discovered deformation mechanism named as 'vortex plowing'. For case III, a fingering process is observed similar to case I. For case IV, axial flow is found to decrease the rotation of the perturbation. For large axial flows, vortex break-up is observed.

Boratav, Olus Naili

74

Molecular evidence that human immunodeficiency virus type 1 dissemination in a small Brazilian city was already taking place in the early 1990s  

Directory of Open Access Journals (Sweden)

Full Text Available We recently performed a molecular epidemiology survey of human immunodeficiency virus type 1 (HIV-1 infection in Miracema, a small city in Southeast Brazil, and found multiple monophyletic clusters, consistent with independent introductions and spread of different viral lineages in the city. Here we apply Bayesian coalescent-based methods to the two largest subtype B clusters and estimate that the most recent common ancestors that gave rise to these two transmission chains were in circulation around 1991-1992. The finding that HIV-1 spread in this Brazilian small city was already taking place at a time Aids was considered a problem restricted to large urban centers may have important public health implications.

Walter A Eyer-Silva

2007-08-01

75

Magnetic Reconnection in Astrophysical Environments  

OpenAIRE

Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turb...

Lazarian, A.; Eyink, G.; Vishniac, E.; Kowal, G.

2014-01-01

76

THE COLLAPSE OF TURBULENT CORES AND RECONNECTION DIFFUSION  

International Nuclear Information System (INIS)

In order for a molecular cloud clump to form stars, some transport of magnetic flux is required from the denser internal regions to the outer regions; otherwise, this can prevent the gravitational collapse. Fast magnetic reconnection, which takes place in the presence of turbulence, can induce a process of reconnection diffusion that has been elaborated on in earlier theoretical works. We have named this process turbulent reconnection diffusion, or simply RD. This paper continues our numerical study of this process and its implications. In particular, we extend our studies of RD in cylindrical clouds and consider more realistic clouds with spherical gravitational potentials (from embedded stars); we also account for the effects of the gas self-gravity. We demonstrate that, within our setup reconnection, diffusion is efficient. We have also identified the conditions under which RD becomes strong enough to make an initially subcritical cloud clump supercritical and induce its collapse. Our results indicate that the formation of a supercritical core is regulated by a complex interplay between gravity, self-gravity, the magnetic field strength, and nearly transonic and trans-Alfvénic turbulence; therefore, it is very sensitive to the initial conditions of the system. In particular, self-gravity helps RD and, as a result, the magnetic field decoupling from the collapsing gas becomes more efficient compared with the case of an external gravitational field. Our simulations confirm that RD can transport magnetic flux from the core of collapsing clumps to the envelope, but only a few of them become nearly critical or supercritical sub-Alfvénic cores, which is consistent with the observations. Furthermore, we have found that the supercritical cores built up in our simulations develop a predominantly helical magnetic field geometry that is also consistent with recent observations. Finally, we have also evaluated the effective values of the turbulent RD coefficient in our simulations and found that they are much larger than the numerical diffusion coefficient, especially for initially trans-Alfvénic clouds, thus ensuring that the detected magnetic flux removal is due to the action of turbulent RD rather than numerical diffusivity

77

Experimental Investigation of the Neutral sheet Profile During Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

During magnetic reconnection, a ''neutral sheet'' current is induced, heating the plasma. The resultant plasma thermal pressure forms a stationary equilibrium with the opposing magnetic fields. The reconnection layer profile holds significant clues about the physical mechanisms which control reconnection. On the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)], a quasi steady-state and axisymmetric neutral sheet profile has been measured precisely using a magnetic probe array with spatial resolution equal to one quarter of the ion gyro-radius. It was found that the reconnecting field profile fits well with a Harris-type profile [E. G. Harris, Il Nuovo Cimento 23, 115 (1962)], B(x) approximately tanh(x/delta). This agreement is remarkable since the Harris theory does not take into account reconnection and associated electric fields and dissipation. An explanation for this agreement is presented. The sheet thickness delta is found to be approximately 0.4 times the ion skin depth, which agrees with a generalized Harris theory incorporating non-isothermal electron and ion temperatures and finite electric field. The detailed study of additional local features of the reconnection region is also presented.

F. Trintchouk; H. Ji; M. Yamada; R. Kulsrud; S. Hsu; T. Carter

1999-11-01

78

Hall magnetic reconnection rate  

International Nuclear Information System (INIS)

Two-dimensional Hall magnetohydrodynamic simulations are used to determine the magnetic reconnection rate in the Hall limit. The simulations are run until a steady state is achieved for four initial current sheet thicknesses: L=1,5,10, and 20c/?pi, where c/?pi is the ion inertial length. It is found that the asymptotic (i.e., time independent) state of the system is nearly independent of the initial current sheet width. Specifically, the Hall reconnection rate is weakly dependent on the initial current layer width and is ??/?t(less-or-similar sign)0.1VA0B0, where ? the reconnected flux, and VA0 and B0 are the Alfven velocity and magnetic field strength in the upstream region. Moreover, this rate appears to be independent of the scale length on which the electron 'frozen-in' condition is broken (as long as it is pi) and of the system size

79

Magnetic fluxtube reconnection  

Science.gov (United States)

We present the results of 3D numerical simulations of initially discrete magnetic fluxtubes interacting via magnetic reconnection. The initial topology consists of two orthogonal fluxtubes. Each fluxtube has a uniform twist, force-free magnetic field specified by the Gold-Hoyle model. The fluxtubes are then forced together by an initial flow configuration consisting of two superimposed stagnation point flows. We observe three distinct types of interaction, which depend on the twist and on the Lundquist numbers, between the fluxtubes. For low twist the fluxtubes experience an elastic collision. For a higher twist complete reconnection is observed. If the Lundquist numbers are raised fluxtube tunneling occurs.

Dahlburg, R. B.; Antiochos, S. K.

1997-01-01

80

Forced magnetic reconnection  

International Nuclear Information System (INIS)

By studying a simple model problem, we examine the time evolution of magnetic field islands which are induced by perturbing the boundary surrounding an incompressible plasma with a resonant surface inside. We find that for sufficiently small boundary perturbations, the reconnection and island formation process occurs on the tearing mode time scale defined by Furth, Killeen, and Rosenbluth. For larger perturbations the time scale is that defined by Rutherford. The resulting asymptotic equilibrium is such that surface currents in the resonant region vanish. A detailed analytical picture of this reconnection process is presented

81

Interchange Reconnection Alfven Wave Generation  

CERN Document Server

Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfven waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly-open field lines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high frequency component associated with the current sheet/reconnection site and an extended low frequency component associ...

Lynch, B J; Li, Y

2014-01-01

82

Reconnection in tokamaks  

International Nuclear Information System (INIS)

Calculations with several different computer codes based on the resistive MHD equations have shown that (m = 1, n = 1) tearing modes in tokamak plasmas grow by magnetic reconnection. The observable behavior predicted by the codes has been confirmed in detail from the waveforms of signals from x-ray detectors and recently by x-ray tomographic imaging

83

Magnetic reconnection of plasma toroids with co- and counter-helicity  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection phenomena are investigated taking into account all three vector components of the magnetic field in a laboratory experiment. Two toroidal magnetized plasmas carrying identical toroidal currents and poloidal field configurations are made to collide, thereby inducing magnetic reconnections, The directions of the toroidal field play an important role in the merging process. It is found that plasmas of anti-parallel helicity merge much faster than those of parallel helicity. It is also found that the reconnection rate is proportional to the initial relative velocity of the two plasma tori, suggesting that magnetic reconnection, in the present experiment, is forced phenomenon. 16 refs., 5 figs.

Yamada, M.; Ono, Y.; Hayakawa, A.; Katsurai, M. (Tokyo Univ. (Japan). Dept. of Electrical Engineering); Perkins, F.W. (Princeton Univ., NJ (USA). Plasma Physics Lab.)

1990-07-01

84

Three-dimensional magnetic reconnection  

International Nuclear Information System (INIS)

Complete text of publication follows. Three-dimensional reconnection is much more diverse than two-dimensional reconnection. In deed, the characteristics of these two types of reconnection are very different. For instance, three-dimensional reconnection can occur both in the vicinity of null points, as well as in the absence of null points. It occurs continuously and continually throughout a diffusion region, as opposed to at a single point, as it does in two dimensions. This means that in three-dimensions field lines do not reconnect in pairs of lines or even in sets of surfaces making understanding three-dimensional reconnection difficult. One important location for three-dimensional reconnection is at separators, special field lines that connect pairs of null points and lie along the intersection of the two separatrix surfaces emanating from the null points. By focussing on a series of three-dimensional resistive MHD experiments involving separator reconnection I reveal the local requirements and nature of reconnection along separators, as well as describing some of the global consequences of reconnection at multiple separators.

85

Reconnection in turbulent astrophysical fluids  

CERN Document Server

Magnetic reconnection is a fundamental process of magnetic field topology change. We analyze the connection of this process with turbulence which is ubiquitous in astrophysical environments. We show how Lazarian & Vishniac (1999) model of turbulent reconnection is connected to the experimentally proven concept of Richardson diffusion and discuss how turbulence violates the generally accepted notion of magnetic flux freezing. We note that in environments that are laminar initially turbulence can develop as a result of magnetic reconnection and this can result in flares of magnetic reconnection in magnetically dominated media. In particular, magnetic reconnection can initially develop through tearing, but the transition to the turbulent state is expected for astrophysical systems. We show that turbulent reconnection predictions corresponds to the Solar and solar wind data.

Lazarian, A; Vishniac, E; Kowal, G

2014-01-01

86

Three-Dimensional Magnetic Reconnection  

OpenAIRE

The importance of magnetic reconnection as an energy release mechanism in many solar, stellar, magnetospheric and astrophysical phenomena has long been recognised. Reconnection is the only mechanism by which magnetic fields can globally restructure, enabling them to access a lower energy state. Over the past decade, there have been some major advances in our understanding of three-dimensional reconnection. In particular, the key characteristics of 3D magnetohydrodynamic (MHD...

Parnell, Clare E.; Haynes, Andrew L.

2009-01-01

87

Interchange Reconnection Alfvén Wave Generation  

Science.gov (United States)

Given recent observational results of interchange reconnection processes in the solar corona and the theoretical development of the S-Web model for the slow solar wind, we extend the analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. ( Astrophys. J. 707, 1427, 2009). Specifically, we analyze the consequences of the dynamic streamer-belt jump that corresponds to flux opening by interchange reconnection. Information about the magnetic field restructuring by interchange reconnection is carried throughout the system by Alfvén waves propagating away from the reconnection region, distributing the shear and twist imparted by the driving flows, including shedding the injected stress-energy and accumulated magnetic helicity along newly open fieldlines. We quantify the properties of the reconnection-generated wave activity in the simulation. There is a localized high-frequency component associated with the current sheet/reconnection site and an extended low-frequency component associated with the large-scale torsional Alfvén wave generated from the interchange reconnection field restructuring. The characteristic wavelengths of the torsional Alfvén wave reflect the spatial size of the energized bipolar flux region. Lastly, we discuss avenues of future research by modeling these interchange reconnection-driven waves and investigating their observational signatures.

Lynch, B. J.; Edmondson, J. K.; Li, Y.

2014-08-01

88

Colour reconnections in Herwig++  

Energy Technology Data Exchange (ETDEWEB)

We describe the implementation details of the colour reconnection model in the event generator Herwig++. We study the impact on final-state observables in detail and confirm the model idea from colour preconfinement on the basis of studies within the cluster hadronization model. Moreover, we show that the description of minimum bias and underlying event data at the LHC is improved with this model and present results of a tune to available data. (orig.)

Gieseke, Stefan; Roehr, Christian [Karlsruhe Institute of Technology (KIT), Institut fuer Theoretische Physik, Karlsruhe (Germany); Siodmok, Andrzej [Karlsruhe Institute of Technology (KIT), Institut fuer Theoretische Physik, Karlsruhe (Germany); The University of Manchester, Consortium for Fundamental Physics, School of Physics and Astronomy, Manchester (United Kingdom)

2012-11-15

89

Colour reconnection in Herwig  

Energy Technology Data Exchange (ETDEWEB)

As the LHC's quick step-up in luminosity necessarily comes with increasing pile-up activity accompanying every event of interest, the Monte Carlo event generators have to come up with proper models of soft inclusive hadron collisions. Moreover, an irreducible background of hadronic activity, the underlying event, is adherent to the single hard hadron collisions themselves. We report on colour reconnection in Herwig, which provides improvements in these two fields of current research.

Roehr, Christian; Gieseke, Stefan [Karlsruhe Institute of Technology, Karlsruhe (Germany); Siodmok, Andrzej [The University of Manchester, Manchester (United Kingdom)

2012-07-01

90

Hall magnetic reconnection rate.  

Science.gov (United States)

Two-dimensional Hall magnetohydrodynamic simulations are used to determine the magnetic reconnection rate in the Hall limit. The simulations are run until a steady state is achieved for four initial current sheet thicknesses: L=1,5,10, and 20c/omega(pi), where c/omega(pi) is the ion inertial length. It is found that the asymptotic (i.e., time independent) state of the system is nearly independent of the initial current sheet width. Specifically, the Hall reconnection rate is weakly dependent on the initial current layer width and is partial differential Phi/ partial differential t less, similar 0.1V(A0)B0, where Phi the reconnected flux, and V(A0) and B0 are the Alfvén velocity and magnetic field strength in the upstream region. Moreover, this rate appears to be independent of the scale length on which the electron "frozen-in" condition is broken (as long as it is

Huba, J D; Rudakov, L I

2004-10-22

91

Como ocorrem as inovações em serviços? um estudo exploratório de empresas no Brasil / Understanding how innovation takes place in service companies - an exploratory study of companies in Brazil  

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: Portuguese Abstract in portuguese O objetivo deste artigo é o de buscar uma melhor compreensão sobre o fenômeno da inovação nas empresas de serviços. Procurou-se seguir uma linha de abordagem segundo a qual, para se estudar e compreender o funcionamento do processo inovativo nestas empresas, se faz necessário um estudo com maior pro [...] fundidade nas organizações, investigando como ocorreram - em detalhes - as inovações. Para essa finalidade foram conduzidos estudos de casos em cinco diferentes organizações de serviços no setor de telecomunicações e atividades de informática no Brasil. Para melhor descrever o processo de inovação foi empregado o conceito de cadeia de inovação proposto por Hansen e Birkinshaw (2007), isto é, uma visão expandida do fenômeno da inovação que forma uma espécie de cadeia composta pelas seguintes fases: geração de ideias (intradepartamental, interdepartamental e interinstitucional); a conversão (seleção de ideias, incluindo a triagem, o financiamento e o desenvolvimento) e a difusão (sua disseminação na organização e no mercado). Por meio dos casos percebeu-se também que a inovação em serviços segue uma lógica similar em relação às inovações encontradas na literatura para bens físicos, sobretudo no que se refere ao uso da metodologia dos Stage-Gates proposto por Cooper (1993). Abstract in english The main objective of this paper is to improve the understanding of the phenomenon of innovation in service companies. It focuses on the idea that in order to study and understand how innovation processes take place, a more in depth study of these companies was required. Several case studies were co [...] nducted in five different service enterprises in the sector of telecommunications and computer-related activities. To describe the innovation process, the concept of "Chain of Innovation" proposed by Hansen and Birkinshaw (2007) was applied, i.e. an expanded view of the phenomenon of innovation that forms a type of chain composed by the following phases: generation of ideas; conversion (selection of ideas, including the selection, financing, and development), and diffusion. Through the cases studied, it can be seen that innovation in services follows a similar logic to that found in the literature for physical goods, especially concerning the use of the Stage-Gates' classic model proposed by Cooper (1993).

Luís Henrique Rigato, Vasconcellos; Roberto, Marx.

92

Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows  

CERN Document Server

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially separated double coronal X-ray sources with centroid separation decreasing with energy. The highest temperature is located near the nonthermal X-ray loop-top source well below the original heights of contracting cusps near the inferred reconnection site. These observations suggest that the primary loci of particle acceleration and plasma heating are in the reconnection outflow regions, rather than the reconnection site itself. In addition, there is an initial ascent of the X-ray and EUV loop-top source prior to its recently recognized descen...

Liu, Wei; Petrosian, Vahe'

2013-01-01

93

Magnetic Reconnection in Astrophysical Environments  

Science.gov (United States)

Magnetic reconnection is a process that changes magnetic field topology in highly conducting fluids. Traditionally, magnetic reconnection was associated mostly with solar flares. In reality, the process must be ubiquitous as astrophysical fluids are magnetized and motions of fluid elements necessarily entail crossing of magnetic frozen in field lines and magnetic reconnection. We consider magnetic reconnection in realistic 3D geometry in the presence of turbulence. This turbulence in most astrophysical settings is of pre-existing nature, but it also can be induced by magnetic reconnection itself. In this situation turbulent magnetic field wandering opens up reconnection outflow regions, making reconnection fast. We discuss Lazarian and Vishniac (1999) model of turbulent reconnection, its numerical and observational testings, as well as its connection to the modern understanding of the Lagrangian properties of turbulent fluids. We show that the predicted dependences of the reconnection rates on the level of MHD turbulence make the generally accepted Goldreich and Sridhar (1995) model of turbulence self-consistent. Similarly, we argue that the well-known Alfvén theorem on flux freezing is not valid for the turbulent fluids and therefore magnetic fields diffuse within turbulent volumes. This is an element of magnetic field dynamics that was not accounted by earlier theories. For instance, the theory of star formation that was developing assuming that it is only the drift of neutrals that can violate the otherwise perfect flux freezing, is affected and we discuss the consequences of the turbulent diffusion of magnetic fields mediated by reconnection. Finally, we briefly address the first order Fermi acceleration induced by magnetic reconnection in turbulent fluids.

Lazarian, Alex; Eyink, Gregory L.; Vishniac, Ethan T.; Kowal, Grzegorz

94

Reconnection and acoustic emission of quantized vortices in superfluid by the numerical analysis of the Gross-Pitaevskii equation  

OpenAIRE

We study numerically the reconnection of quantized vortices and the concurrent acoustic emission by the analysis of the Gross-Pitaevskii equation. Two quantized vortices reconnect following the process similar to classical vortices; they approach, twist themselves locally so that they become anti-parallel at the closest place, reconnect and leave separately.The investigation of the motion of the singular lines where the amplitude of the wave function vanishes in the vortex c...

Ogawa, S.; Tsubota, M.; Hattori, Y.

2001-01-01

95

Colour Reconnection at LEP2  

CERN Document Server

Two measurements are presented of estimators sensitive to the Colour Reconnection effect in WW events at LEP2. The results are compared with various phenomenological Monte Carlo implementations of the effect. A feasibility study is performed to reduce the total uncertainty in the direct W boson mass measurement at LEP2 by use of the inferred information about the Colour Reconnection effect.

D'Hondt, J

2004-01-01

96

Energetic particles in magnetotail reconnection  

Science.gov (United States)

We carried out a 3D fully kinetic simulation of Earth's magnetotail magnetic reconnection to study the dynamics of energetic particles. We developed and implemented a new relativistic particle mover in iPIC3D, an implicit Particle-in-Cell code, to correctly model the dynamics of energetic particles. Before the onset of magnetic reconnection, energetic electrons are found localized close to current sheet and accelerated by lower hybrid drift instability. During magnetic reconnection, energetic particles are found in the reconnection region along the x-line and in the separatrices region. The energetic electrons are first present in localized stripes of the separatrices and finally cover all the separatrix surfaces. Along the separatrices, regions with strong electron deceleration are found. In the reconnection region, two categories of electron trajectory are identified. First, part of the electrons are trapped in the reconnection region, bouncing a few times between the outflow jets. Second, part of the electrons pass the reconnection region without being trapped. Different from electrons, energetic ions are localized on the reconnection fronts of the outflow jets.

Peng, Ivy Bo; Vencels, Juris; Lapenta, Giovanni; Divin, Andrey; Vaivads, Andris; Laure, Erwin; Markidis, Stefano; Markidis

2015-04-01

97

Reconnections of Wave Vortex Lines  

Science.gov (United States)

When wave vortices, that is nodal lines of a complex scalar wavefunction in space, approach transversely, their typical crossing and reconnection is a two-stage process incorporating two well-understood elementary events in which locally coplanar hyperbolas switch branches. The explicit description of this reconnection is a pedagogically useful…

Berry, M. V.; Dennis, M. R.

2012-01-01

98

Estimating proximity to the asymmetric reconnection X-line  

Science.gov (United States)

Magnetic reconnection is a process that changes magnetic topology, allows plasma transport across boundaries, and converts field potential energy to particle kinetic energy. All of these processes are tied to the X-line, or site of reconnection, yet current methods of locating the reconnection site either do not uniquely identify the the X-line or have not been tested when asymmetries in field strength and plasma density and temperature are present. Furthermore, identification of spacial structures (such as the X-line) as they traverse satellites is limited by hardware constraints. This thesis proposes a new method of locating the reconnection site for asymmetric magnetic reconnection (AMR), and an algorithm for merging fluxgate and searchcoil magnetometer datasets to improve data fidelity in a specific frequency range. Cluster observations show that asymmetries present during reconnection cause a variety of transitions in the reconnecting component of the magnetic field, ion density, ion outflow jets, and the normal component of the electric field across the magnetopause. Simulations in 2D and 3D and a laboratory experiment, both with and without guide field, contain similar offsets. Only within 5 electron inertial lengths of the X-line do transitions occur simultaneously. Farther away, transitions offset from one another in a systematic way. Electron distribution functions serve as an independent check of the method, as they take on a triangular shape that is unique to the X-line. Normal electric field offsets and outflow upstream from the X-line are linked to the presence of a guide field. This new methodology is applied to Cluster AMR events to demonstrate its use. One Cluster event in close proximity to the X-line exhibits triangle-shaped distributions and enhanced currents.

Argall, Matthew R.

99

Turbulent General Magnetic Reconnection  

CERN Document Server

Plasma flows with an MHD-like turbulent inertial range, such as the solar wind, require a generalization of General Magnetic Reconnection (GMR) theory. We introduce the slip-velocity source vector, which gives the rate of development of slip velocity per unit arc length of field line. The slip source vector is the ratio of the curl of the non ideal electric field in the Generalized Ohm's Law and the magnetic field strength. It diverges at magnetic nulls, unifying GMR with magnetic null-point reconnection. Only under restrictive assumptions is the slip velocity related to the gradient of the quasi potential (integral of parallel electric field along field lines). In a turbulent inertial range the curl becomes extremely large while the parallel component is tiny, so that line slippage occurs even while ideal MHD becomes accurate. The resolution of this paradox is that ideal MHD is valid for a turbulent inertial-range only in a weak sense which does not imply magnetic line freezing. The notion of weak solution i...

Eyink, Gregory L

2014-01-01

100

Magnetic reconnection in doublets  

Science.gov (United States)

Doublet [Ohkawa, 1968] is a magnetic configuration with the prospect of being able to confine plasmas for thermonuclear fusion. Because of this prospect Doublet research was carried out at GA for a number of years. The Doublet configuration is axisymmetric and it employs a strong toroidal magnetic field. The poloidal magnetic field forms one hyperbolic magnetic axis located in the midplane and two elliptic axes above and below the midplane. Thus a separatrix with a cross sectional shape of a figure "8" is formed. Experimentally, Doublets were found subject to two sudden, mostly axisymettric deformations. During one of these the plasma split into two separate plasmas, each with one elliptic axis much like two separate tokamak plasmas. During the other the three magnetic axes tended first to merge at the midplane and secondly the plasma became unstable toward motion either up or down. These deformations involve magnetic reconnections. In the first, field lines which initially link all three magnetic axes reconnect to link only one of the elliptic magnetic axes while the reverse is true for the second type of deformation.

Jensen, Torkil H.

101

Intuitive approach to magnetic reconnection  

International Nuclear Information System (INIS)

Two reconnection problems are considered. The first problem concerns global physics. The plasma in the global reconnection region is in magnetostatic equilibrium. It is shown that this equilibrium can be uniquely characterized by a set of constraints. During reconnection and independently of the local reconnection physics, these constraints can be uniquely evolved from any initial state. The second problem concerns Petschek reconnection. Petschek's model for fast reconnection, which is governed by resistive MHD equations with constant resistivity is not validated by numerical simulations. Malyshkin et al.[Phys. Plasmas 12, 102920 (2005)], showed that the reason for the discrepancy is that Petschek did not employ Ohm's law throughout the local diffusion region, but only at the X-point. A derivation of Petschek reconnection, including Ohm's law throughout the entire diffusion region, removes the discrepancy. This derivation is based largely on Petschek's original 1964 calculation [in AAS-NASA Symposium on Solar Flares (National Aeronautics and Space Administration, Washington, D.C., 1964), NASA SP50, p. 425]. A useful physical interpretation of the role which Ohm's law plays in the diffusion region is presented.

102

Reconnection of magnetic field lines  

International Nuclear Information System (INIS)

Magnetic field line diffusion in a plasma is studied on the basis of the non-linear boundary layer equations of dissipative, incompressible magnetohydrodynamics. Non-linear steady state solutions for a class of plasma parameters have been obtained which are consistent with the boundary conditions appropriate for reconnection. The solutions are self-consistent in connecting a stagnation point flow of a plasma with reconnecting magnetic field lines. The range of the validity of the solutions, their relation to other fluid models of reconnection, and their possible applications to space plasma configurations are pointed out. (Author)

103

Turbulent Reconnection and Its Implications  

CERN Document Server

Magnetic reconnection is a process of magnetic field topology change, which is one of the most fundamental processes in magnetized plasmas. In most astrophysical environments the Reynolds numbers are large and therefore the transition to turbulence is inevitable. This turbulence must be taken into account for any theory of magnetic reconnection, since the initially laminar configurations can transit to the turbulence state, what is demonstrated by 3D high resolution numerical simulations. We discuss ideas of how turbulence can modify reconnection with the focus on the Lazarian & Vishniac (1999) reconnection model and present numerical evidence supporting the model and demonstrate that it is closely connected to the concept of Richardson diffusion and compatible with the Lagrangian dynamics of magnetized fluids. We point out that the Generalized Ohm's Law, that accounts for turbulent motion, predicts the subdominance of the microphysical plasma effects for a realistically turbulent media. We show that on o...

Lazarian, Alex; Vishniac, Ethan T; Kowal, Grzegorz

2015-01-01

104

Reconnection of Colliding Cosmic Strings  

OpenAIRE

For vortex strings in the Abelian Higgs model and D-strings in superstring theory, both of which can be regarded as cosmic strings, we give analytical study of reconnection (recombination, inter-commutation) when they collide, by using effective field theories on the strings. First, for the vortex strings, via a string sigma model, we verify analytically that the reconnection is classically inevitable for small collision velocity and small relative angle. Evolution of the sh...

Hanany, Amihay; Hashimoto, Koji

2005-01-01

105

3D Configuration of Anti-parallel and Component Reconnection: Reconstruction of Cluster Measurements  

Science.gov (United States)

Magnetic reconnection (MR) has been commonly studied in two dimensional geometry and usually classified into two categories: anti-parallel and component, the terminology widely used in magnetospheric physics. However, MR is three dimensional (3D) in nature. It is thus necessary to reveal the 3D configuration of anti-parallel and component reconnection in reality. In this presentation we study an event in the magnetotail by reconstructing the magnetic field structure in the MR region based on Cluster four spacecraft measurements. The details of the reconstruction approach can be found in He et al. (2008). It is found that in the event both anti-parallel and component reconnection processes can be detected. The reconstruction shows that in both processes two fan surfaces can be identified and intersect to form a separator. The MR process takes place just on the separator line. In the plane locally perpendicular to the separator, the magnetic field lines display the X-type topology. In the component MR process observed, a null-pair appears at the two ends of the separator. The magnetic field magnitude is found significant in the middle of the separator. On the other hand in the anti-parallel MR process observed, the magnetic field magnitude of the separator is however very weak everywhere. In short, this study shows that the 3D separator MR model can be applied for both processes, i.e., both component and anti-parallel MR processes require a null pair. Component and anti-parallel configurations are just the local manifestations of the 3D separator MR process.

Guo, R.; Pu, Z.; Wang, X.; Xiao, C.; Xie, L.; Fu, S.; Zhong, J.

2011-12-01

106

Magnetic reconnection in space plasmas  

Energy Technology Data Exchange (ETDEWEB)

This is the final report of a three-year, Laboratory-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Magnetic reconnection produces fundamental changes in the magnetic field topology of plasmas and leads ultimately to substantial plasma heating and acceleration. The transfer of stored magnetic field energy to the plasma occurs primarily at thin conversion layers that extend outward from the reconnection site. We performed a comparative study of the structure and nature of these conversion layers as observed during reconnection at Earth`s magnetopause and in the geomagnetic tail. Our research utilized plasma and magnetic field data from the Earth-orbiting ISEE satellites during crossings of the conversion layers at the magnetopause and in the geomagnetic tail, as well as data obtained during a long-duration balloon flight in Antarctica and simultaneously from satellites in geosynchronous orbit. We have found that the reconnection layer at the magnetopause usually does not contain a slow mode shock, contrary to earlier theoretical expectations. Through a coordinated analysis of data obtained from balloon altitudes and at geosynchronous orbit, we obtained evidence that reconnection can occur simultaneously in both hemispheres at the magnetopause above the polar caps. The final year of our study was oriented primarily towards the question of determining the magnetic topology of disturbances in the solar wind associated with coronal mass ejections (CMEs) and understanding how that topology is affected by magnetic reconnection occurring near the Sun.

Gosling, J.; Feldman, W. [Los Alamos National Lab., NM (United States); Walthour, D. [Dartmouth Coll., Hanover, NH (United States)

1996-04-01

107

NS [Nuclear Safety] update. Current safety and security activities and developments taking place in the Department of Nuclear Safety and Security, Issue no. 8, September 2008  

International Nuclear Information System (INIS)

The current issue presents information about the following activities: 1) International Workshops on Denial of Shipments raise awareness of suppliers, recipients, regulators, carriers/consignors and international organizations of the problems relating to denials of radioactive shipments to determine effective measures to prevent or reduce the instances of shipment denials and delays. 2) Communication and knowledge Management in the Department of Nuclear Safety and Security (NS). 3) Nuclear Security at the Beijing Olympics - an excellent example of the IAEA's work in protecting large scale public events. 4) The Incident and Emergency Centre's Participation in the ConvEx 3 Exercise, 9-10 July 2008, which took place at the Laguna Verde nuclear power plant in Mexico. During the 43 hour long exercise, the Incident and Emergency Centre (IEC) was fully activated. Staff members participating in the exercise represented different departments within the IAEA and the diversity of their knowledge and experience ensured an effective response

108

Steady state reconnection at a single 3D magnetic null point  

CERN Document Server

To systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics which may provide scaling relations for various characteristic parameters of the system. The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state in unlikely to be realised as the current layer tends to grow until restricted by the geometry of the computational domain and imposed driving profile. However, ratios between characteristic quantities clearly settle after some...

Galsgaard, K

2011-01-01

109

Steady state reconnection at a single 3D magnetic null point  

Science.gov (United States)

Aims: We systematically stress a rotationally symmetric 3D magnetic null point by advecting the opposite footpoints of the spine axis in opposite directions. This stress eventually concentrates in the vicinity of the null point, thereby forming a local current sheet through which magnetic reconnection takes place. The aim is to look for a steady state evolution of the current sheet dynamics, which may provide scaling relations for various characteristic parameters of the system. Methods: The evolution is followed by solving numerically the non-ideal MHD equations in a Cartesian domain. The null point is embedded in an initially constant density and temperature plasma. Results: It is shown that a quasi-steady reconnection process can be set up at a 3D null by continuous shear driving. It appears that a true steady state is unlikely to be realised because the current layer tends to grow until it is restricted by the geometry of the computational domain and the imposed driving profile. However, ratios between characteristic quantities clearly settle after some time to stable values, so that the evolution is quasi-steady. The experiments show a number of scaling relations, but they do not provide a clear consensus for extending to lower magnetic resistivity or faster driving velocities. More investigations are needed to fully clarify the properties of current sheets at magnetic null points.

Galsgaard, K.; Pontin, D. I.

2011-05-01

110

Spontaneous current-layer fragmentation and cascading reconnection in solar flares: I. Model and analysis  

CERN Document Server

Magnetic reconnection is commonly considered as a mechanism of solar (eruptive) flares. A deeper study of this scenario reveals, however, a number of open issues. Among them is the fundamental question, how the magnetic energy is transferred from large, accumulation scales to plasma scales where its actual dissipation takes place. In order to investigate this transfer over a broad range of scales we address this question by means of high-resolution MHD simulation. The simulation results indicate, that the magnetic-energy transfer to small scales is realized via a cascade of consecutive smaller and smaller flux-ropes (plasmoids), in analogy with the vortex-tube cascade in (incompressible) fluid dynamics. Both tearing and (driven) coalescence processes are equally important for the consecutive fragmentation of the magnetic field (and associated current density) to smaller elements. At the later stages a dynamic balance between tearing and coalescence processes reveals a steady (power-law) scaling typical for ca...

Bárta, Miroslav; Karlický, Marian; Skála, Jan

2010-01-01

111

Plasmoid Ejections and Loop Contractions in an Eruptive M7.7 Solar Flare: Evidence of Particle Acceleration and Heating in Magnetic Reconnection Outflows  

OpenAIRE

Where particle acceleration and plasma heating take place in relation to magnetic reconnection is a fundamental question for solar flares. We report analysis of an M7.7 flare on 2012 July 19 observed by SDO/AIA and RHESSI. Bi-directional outflows in forms of plasmoid ejections and contracting cusp-shaped loops originate between an erupting flux rope and underlying flare loops at speeds of typically 200-300 km/s up to 1050 km/s. These outflows are associated with spatially se...

Liu, Wei; Chen, Qingrong; Petrosian, Vahe

2013-01-01

112

Take Five  

Science.gov (United States)

What if you could learn about how to prepare for emergency situations, explore the legends of the Alamo, and the rise of wireless communications all in one place? Sounds like a pretty good deal, and it is all possible via the Take Five website. Presented by the University of Texas at Austin, the Take Five website presents videos of various faculty members talking about their areas of expertise in an accessible and engaging format. Since the spring of 2003, the Take Five project has presented five new lectures each semester (hence the name of the project), and visitors to the site have access to all of these materials. The presentations are uniformly quite good, and along with the previously mentioned topics, they also cover such areas as minority entrepreneurship and the role of technology in addressing the worldâ??s major health problems.

113

NS [Nuclear Safety] update. Current safety and security activities and developments taking place in the Department of Nuclear Safety and Security. Issue no. 2, January 2007  

International Nuclear Information System (INIS)

This newsletter reports on the training of cardiologists in radiation protection, IAEA's safety review services and the operational safety assessment review team (OSART), the international conference on management of spent fuel and the recent INSAG (International Nuclear Safety Group) publications. The IAEA has begun a major international initiative to train interventional cardiologists in radiation protection. Starting with the first course in May 2004, so far 6 regional and 3 national training courses have been conducted with the participation of over 400 health professionals putting the IAEA in a leading role in this area. A programme of two days' training has been developed, covering possible and observed radiation effects among patients and staff, international standards, dose management techniques, examples of good and bad practice and examples indicating prevention of possible injuries as a result of good practice in radiation protection. The training material is freely available on CD and will be placed on the Radiological Protection of Patients website at http://rpop.iaea.org/

114

Place-focused physical activity research, human agency, and social justice in public health: taking agency seriously in studies of the built environment.  

Science.gov (United States)

Built environment characteristics have been linked to health outcomes and health disparities. However, the effects of an environment on behavior may depend on human perception, interpretation, motivation, and other forms of human agency. We draw on epidemiological and ethical concepts to articulate a critique of research on the built environment and physical activity. We identify problematic assumptions and enumerate both scientific and ethical reasons to incorporate subjective perspectives and public engagement strategies into built environment research and interventions. We maintain that taking agency seriously is essential to the pursuit of health equity and the broader demands of social justice in public health, an important consideration as studies of the built environment and physical activity increasingly focus on socially disadvantaged communities. Attention to how people understand their environment and navigate competing demands can improve the scientific value of ongoing efforts to promote active living and health, while also better fulfilling our ethical obligations to the individuals and communities whose health we strive to protect. PMID:21940195

Blacksher, Erika; Lovasi, Gina S

2012-03-01

115

Reconnection at the Heliopause  

CERN Document Server

In this MHD-model of the heliosphere, we assume a Parker-type flow, and a Parker-type spiral magnetic field, which is extrapolated further downstream from the termination shock to the heliopause. We raise the question whether the heliopause nose region may be leaky with respect to fields and plasmas due to nonideal plasma dynamics, implying a breakdown of the magnetic barrier. We analyse some simple scenarios to find reconnection rates and circumstances, under which the heliosphere can be an "open" or a "closed" magnetosphere. We do not pretend to offer a complete solution for the heliosphere, on the basis of nonideal MHD theory, but present a prescription to find such a solution on the basis of potential fields including the knowledge of neutral points. As an example we imitate the Parker spiral as a monopole with a superposition of homogeneous asymptotical boundary conditions. We use this toy model for x < -R where R = 100 AU is the distance of the termination shock to describe the situation in the nose ...

Nickeler, D H; Nickeler, Dieter H.; Fahr, Hans-Joerg

2005-01-01

116

Helicity, Reconnection, and Dynamo Effects  

International Nuclear Information System (INIS)

The inter-relationships between magnetic helicity, magnetic reconnection, and dynamo effects are discussed. In laboratory experiments, where two plasmas are driven to merge, the helicity content of each plasma strongly affects the reconnection rate, as well as the shape of the diffusion region. Conversely, magnetic reconnection events also strongly affect the global helicity, resulting in efficient helicity cancellation (but not dissipation) during counter-helicity reconnection and a finite helicity increase or decrease (but less efficiently than dissipation of magnetic energy) during co-helicity reconnection. Close relationships also exist between magnetic helicity and dynamo effects. The turbulent electromotive force along the mean magnetic field (alpha-effect), due to either electrostatic turbulence or the electron diamagnetic effect, transports mean-field helicity across space without dissipation. This has been supported by direct measurements of helicity flux in a laboratory plasma. When the dynamo effect is driven by electromagnetic turbulence, helicity in the turbulent field is converted to mean-field helicity. In all cases, however, dynamo processes conserve total helicity except for a small battery effect, consistent with the observation that the helicity is approximately conserved during magnetic relaxation

117

Magnetic reconnection via current sheets  

International Nuclear Information System (INIS)

A general picture of magnetic reconnection in the framework of 2-D incompressible resistive magnetohydrodynamic theory is presented. Numerical studies of (quasi-) steady-state driven reconnection reveal current sheet formation for Mach numbers M = u/v/sub A/ exceeding the Sweet--Parker reconnection rate M/sub SP/ = (eta/Lv/sub A/)1/sup //2. Since the thickness delta of the current sheet is found to be invariant to a change of the resistivity eta, its length ? increases rapidly with decreasing eta or increasing M, which can be written in the form ?approx.(M/M/sub SP/)4, so that ? reaches the global system size L within a short range of the parameter M/M/sub SP/. The results are rather insensitive to the particular choice of boundary conditions. Because of the presence of a current sheet, the overall reconnection process is quite slow. This picture essentially agrees with Syrovatsky's [Sov. Phys. JETP 33, 933 (1971)] theory and disproves Petschek's [AAS/NASA Symposium on the Physics of Solar Flares, (NASA, Washington, DC, 1964) p. 425] mechanism of fast magnetic reconnection. A theory of the solution in the external and in the diffusion region is developed and analytical expressions in agreement with the simulation results are obtained by means of a variational principle

118

Dipolarization Fronts from Reconnection Onset  

Science.gov (United States)

Dipolarization fronts observed in the magnetotail are often viewed as signatures of bursty magnetic reconnection. However, until recently spontaneous reconnection was considered to be fully prohibited in the magnetotail geometry because of the linear stability of the ion tearing mode. Recent theoretical studies showed that spontaneous reconnection could be possible in the magnetotail geometries with the accumulation of magnetic flux at the tailward end of the thin current sheet, a distinctive feature of the magnetotail prior to substorm onset. That result was confirmed by open-boundary full-particle simulations of 2D current sheet equilibria, where two magnetotails were separated by an equilibrium X-line and weak external electric field was imposed to nudge the system toward the instability threshold. To investigate the roles of the equilibrium X-line, driving electric field and other parameters in the reconnection onset process we performed a set of 2D PIC runs with different initial settings. The investigated parameter space includes the critical current sheet thickness, flux tube volume per unit magnetic flux and the north-south component of the magnetic field. Such an investigation is critically important for the implementation of kinetic reconnection onset criteria into global MHD codes. The results are compared with Geotail visualization of the magnetotail during substorms, as well as Cluster and THEMIS observations of dipolarization fronts.

Sitnov, M. I.; Swisdak, M. M.; Merkin, V. G.; Buzulukova, N.; Moore, T. E.

2012-12-01

119

Multiple Spacecraft Study of the Impact of Turbulence on Reconnection Rates  

Science.gov (United States)

Magnetic turbulence and secondary island formation have reemerged as possible explanations for fast reconnection. Recent three-dimensional simulations reveal the formation of secondary islands that serve to shorten the current sheet and increase the accelerating electric field, while both simulations and observations witness electron holes whose collapse energizes electrons. However, few data studies have explicitly investigated the effect of turbulence and islands on the reconnection rate. We present a more comprehensive analysis of the effect of turbulence and islands on reconnection rates observed in space. Our approach takes advantage of multiple spacecraft to find the location of the spacecraft relative to the inflow and the outflow, to estimate the reconnection electric field, to indicate the presence and size of islands, and to determine wave vectors indicating turbulence. A superposed epoch analysis provides independent estimates of spatial scales and a reconnection electric field. We apply k-filtering and a new method adopted from seismological analyses to identify the wavevectors. From several case studies of reconnection events, we obtain preliminary estimates of the spectral scaling law, identify wave modes, and present a method for finding the reconnection electric field associated with the wave modes.

Wendel, Deirdre; Goldstein, Melvyn; Figueroa-Vinas, Adolfo; Adrian, Mark; Sahraoui, Fouad

2011-01-01

120

Magnetotail reconnection onset: 3D full-particle simulation results  

Science.gov (United States)

Magnetotails accumulate energy of the solar wind-magnetosphere interaction and then explosively release it. The most plausible mechanism of explosions is reconnection of magnetic field lines that are almost antiparallel in the tails. However, tail configurations, which have a potential for spontaneous reconnection, also facilitate interchange motions of sharply curved flux tubes. The magnetic tension in those tubes creates an effective gravity force, and a Rayleigh-Taylor-type instability becomes possible when sufficient magnetic flux is accumulated in the tail. Multi-spacecraft observations of Earth's magnetotail show signatures of both reconnection and interchange motions. They also reveal strong north-south oscillations of the tail plasma sheet making it similar to a flapping flag, with an important and puzzling distinction from the latter in that the magnetotail flapping waves propagate almost normal to the Sun-Earth direction. Understanding roles of these different plasma motions in magnetotail explosions requires three-dimensional plasma simulations taking into account kinetic effects of particle motion. Here we report on the results of 3-D full-particle simulations of a two-dimensional magnetotail equilibrium with accumulated magnetic flux in the mid tail. Simulations show that far enough from the planet, where a limited region of the extended tail is modeled using open boundary conditions for fields and particles, reconnection motions dominate interchange ones. They are also accompanied by flapping motions, consistent with their more frequent observations in the mid tail compared to its near-Earth regions.

Sitnov, Mikhail; Swisdak, Marc; Merkin, Viacheslav

121

Model for Incomplete Reconnection in Sawtooth Crashes  

CERN Document Server

A model for incomplete reconnection in sawtooth crashes is presented. The reconnection inflow during the crash phase of sawteeth self-consistently convects the high pressure core toward the reconnection site, raising the pressure gradient there. Reconnection shuts off if the diamagnetic drift speed at the reconnection site exceeds a threshold, which may explain incomplete reconnection. The relaxation of magnetic shear after reconnection stops may explain the destabilization of ideal interchange instabilities reported previously. Proof-of-principle two-fluid simulations confirm this basic picture. Predictions of the model compare favorably to data from the Mega Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are discussed. The results should apply across tokamaks, including ITER.

Beidler, Matthew T

2011-01-01

122

Can amorphization take place in nanoscale interconnects?  

Science.gov (United States)

The trend of miniaturization has highlighted the problems of heat dissipation and electromigration in nanoelectronic device interconnects, but not amorphization. While amorphization is known to be a high pressure and/or temperature phenomenon, we argue that defect density is the key factor, while temperature and pressure are only the means. For nanoscale interconnects carrying modest current density, large vacancy concentrations may be generated without the necessity of high temperature or pressure due to the large fraction of grain boundaries and triple points. To investigate this hypothesis, we performed in situ transmission electron microscope (TEM) experiments on 200 nm thick (80 nm average grain size) aluminum specimens. Electron diffraction patterns indicate partial amorphization at modest current density of about 105 A cm-2, which is too low to trigger electromigration. Since amorphization results in drastic decrease in mechanical ductility as well as electrical and thermal conductivity, further increase in current density to about 7 × 105 A cm-2 resulted in brittle fracture failure. Our molecular dynamics (MD) simulations predict the formation of amorphous regions in response to large mechanical stresses (due to nanoscale grain size) and excess vacancies at the cathode side of the thin films. The findings of this study suggest that amorphization can precede electromigration and thereby play a vital role in the reliability of micro/nanoelectronic devices.

Kumar, S.; Joshi, K. L.; van Duin, A. C. T.; Haque, M. A.

2012-03-01

123

Major growth in coke production takes place  

International Nuclear Information System (INIS)

U.S. petroleum coke production has increased 64% during the 10-year period from 1980 to 1990. This dramatic rise makes it timely to discuss the history and future of U.S. coking capacity, production, and processing. The article covers the properties and uses of the various grades of petroleum coke, as well as pricing and market trends

124

Can amorphization take place in nanoscale interconnects?  

International Nuclear Information System (INIS)

The trend of miniaturization has highlighted the problems of heat dissipation and electromigration in nanoelectronic device interconnects, but not amorphization. While amorphization is known to be a high pressure and/or temperature phenomenon, we argue that defect density is the key factor, while temperature and pressure are only the means. For nanoscale interconnects carrying modest current density, large vacancy concentrations may be generated without the necessity of high temperature or pressure due to the large fraction of grain boundaries and triple points. To investigate this hypothesis, we performed in situ transmission electron microscope (TEM) experiments on 200 nm thick (80 nm average grain size) aluminum specimens. Electron diffraction patterns indicate partial amorphization at modest current density of about 105 A cm?2, which is too low to trigger electromigration. Since amorphization results in drastic decrease in mechanical ductility as well as electrical and thermal conductivity, further increase in current density to about 7 × 105 A cm?2 resulted in brittle fracture failure. Our molecular dynamics (MD) simulations predict the formation of amorphous regions in response to large mechanical stresses (due to nanoscale grain size) and excess vacancies at the cathode side of the thin films. The findings of this study suggest that amorphization can precede electromigration and thereby play a vital role in the rnd thereby play a vital role in the reliability of micro/nanoelectronic devices. (paper)

125

Summer Place Value  

Science.gov (United States)

Play some fun games with your new place value skills Match the number words to the standard form to find the place value mystery picture. Can you solve the place value puzzler? Click on easy and follow the instructions. Check your score after the picture is shown. How many tries did it take you to be able to see the picture. If it ...

Mrs. Korth

2009-07-27

126

On phase diagrams of magnetic reconnection  

International Nuclear Information System (INIS)

Recently, “phase diagrams” of magnetic reconnection were developed to graphically organize the present knowledge of what type, or phase, of reconnection is dominant in systems with given characteristic plasma parameters. Here, a number of considerations that require caution in using the diagrams are pointed out. First, two known properties of reconnection are omitted from the diagrams: the history dependence of reconnection and the absence of reconnection for small Lundquist number. Second, the phase diagrams mask a number of features. For one, the predicted transition to Hall reconnection should be thought of as an upper bound on the Lundquist number, and it may happen for considerably smaller values. Second, reconnection is never “slow,” it is always “fast” in the sense that the normalized reconnection rate is always at least 0.01. This has important implications for reconnection onset models. Finally, the definition of the relevant Lundquist number is nuanced and may differ greatly from the value based on characteristic scales. These considerations are important for applications of the phase diagrams. This is demonstrated by example for solar flares, where it is argued that it is unlikely that collisional reconnection can occur in the corona

127

Driven reconnection in a quadrupole cusp field  

Science.gov (United States)

Driven magnetic reconnection in a quadrupole cusp field is examined numerically in various collisionality regimes. Quasi-steady-state reconnection rates far in excess of often-quoted limits are observed. As expected, the rate is determined by external boundary conditions and appears to be limited only by computational concerns; thus, in this configuration the slow reconnection is differentiated from the fast one only by changes in the reconnection-layer geometry. Collisional reconnection exhibits the typical extended current layer of the Sweet-Parker model, whereas the collisionless reconnection mediated by kinetic-Alvén or whistler waves has the Petschek-type "X-layer" configuration. The current density at the X point is reduced in the collisionless cases, in qualitative agreement with the results from the Versatile Toroidal Facility experiment.

Aydemir, A. Y.

2005-08-01

128

Driven reconnection in a quadrupole cusp field  

International Nuclear Information System (INIS)

Driven magnetic reconnection in a quadrupole cusp field is examined numerically in various collisionality regimes. Quasi-steady-state reconnection rates far in excess of often-quoted limits are observed. As expected, the rate is determined by external boundary conditions and appears to be limited only by computational concerns; thus, in this configuration the slow reconnection is differentiated from the fast one only by changes in the reconnection-layer geometry. Collisional reconnection exhibits the typical extended current layer of the Sweet-Parker model, whereas the collisionless reconnection mediated by kinetic-Alven or whistler waves has the Petschek-type 'X-layer' configuration. The current density at the X point is reduced in the collisionless cases, in qualitative agreement with the results from the Versatile Toroidal Facility experiment

129

Patchy Reconnection in the Solar Corona  

CERN Document Server

Supra-arcade downflows (SADs) and supra-arcade downflowing loops (SADLs) descending from reconnection regions toward solar post-flare arcades seem to be two different observational signatures of retracting, isolated reconnected flux tubes with irreducible three-dimensional geometries. This dissertation describes work in refining and improving a novel model of patchy reconnection, where only a small bundle of field lines is reconnected across a current sheet and forms a reconnected thin flux tube. Traditional models have not been able to explain why some of the observed SADs appear to be hot and relatively devoid of plasma. The present work shows that plasma depletion naturally occurs in flux tubes that are reconnected across nonuniform current sheets and slide trough regions of decreasing magnetic field magnitude. Moreover, through a detailed theoretical analysis of generalized thin flux tube equations, we show that the addition to the model of pressure-driven parallel dynamics, as well as temperature-depende...

Guidoni, Silvina E

2011-01-01

130

Particle acceleration at a reconnecting magnetic separator  

CERN Document Server

While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. The effect upon particle behaviour of initial position, pitch angle and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains ...

Threlfall, J; Parnell, C E; Oskoui, S Eradat

2014-01-01

131

Indeterminacy and instability in Petschek reconnection  

Energy Technology Data Exchange (ETDEWEB)

We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate.

Forbes, Terry G. [Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, New Hampshire 03824 (United States); Priest, Eric R. [Institute of Mathematics, University of St. Andrews, Fife KY16 9SS, Scotland (United Kingdom); Seaton, Daniel B. [SIDC-Royal Observatory of Belgium, Ringlaan 3, 1180 Brussels (Belgium); Litvinenko, Yuri E. [Department of Mathematics, University of Waikato, P.O. 3105, Hamilton (New Zealand)

2013-05-15

132

Indeterminacy and instability in Petschek reconnection  

International Nuclear Information System (INIS)

We explain two puzzling aspects of Petschek's model for fast reconnection. One is its failure to occur in plasma simulations with uniform resistivity. The other is its inability to provide anything more than an upper limit for the reconnection rate. We have found that previously published analytical solutions based on Petschek's model are structurally unstable if the electrical resistivity is uniform. The structural instability is associated with the presence of an essential singularity at the X-line that is unphysical. By requiring that such a singularity does not exist, we obtain a formula that predicts a specific rate of reconnection. For uniform resistivity, reconnection can only occur at the slow, Sweet-Parker rate. For nonuniform resistivity, reconnection can occur at a much faster rate provided that the resistivity profile is not too flat near the X-line. If this condition is satisfied, then the scale length of the nonuniformity determines the reconnection rate

133

On the Rate of Spontaneous Magnetic Reconnection  

CERN Document Server

Magnetic reconnection is a topological rearrangement of the magnetic field lines, leading to the release of magnetic energy, which is thought to be associated with solar flares, coronal mass ejections and magnetospheric storms. Despite magnetic field lines are supposed to be frozen into the well-conducting plasma, the reconnection observed in nature is, typically, fast, so that the rate of convergence of the magnetic field lines is the fraction of the Alfven speed, v_A. The Sweet-Parker solution predicts reconnection rates which are negligible for the solar or astrophysical conditions, this have prompted research into collisionless reconnection. The stochasticity of magnetic field lines due to ambient turbulence leads to fast reconnection and the rate was predicted to be proportional to kinetic energy density of ambient turbulence. Also, tearing instability of the thin current sheet was proposed as a driver of resistivity-independent reconnection, which was shown to be consistent with two-dimensional simulati...

Beresnyak, Andrey

2013-01-01

134

The Physics of Asymmetric Magnetic Field Reconnection (Invited)  

Science.gov (United States)

Asymmetric magnetic field reconnection differs from symmetric magnetic field reconnection in that the Hall term in the Generalized Ohm's Law, which depends on the magnetic field strength divided by the plasma density, is greater on one side of the reconnection region than on the other side. While symmetric reconnection is prevalent in the magnetospheric tail, it is rare during dayside reconnection. The effects on dayside reconnection of the asymmetry in the Hall term are reviewed by comparison of satellite data and computer simulations

Mozer, F.

2013-12-01

135

Gravitational Wave Bursts from Cosmic Superstring Reconnections  

OpenAIRE

We compute the gravitational waveform produced by cosmic superstring reconnections. This is done by first constructing the superstring reconnection trajectory, which closely resembles that of classical, instantaneous reconnection but with the singularities smoothed out due to the string path integral. We then evaluate the graviton vertex operator in this background to obtain the burst amplitude. The result is compared to the detection threshold for current and future gravita...

Jackson, Mark G.; Siemens, Xavier

2009-01-01

136

Particle acceleration at a reconnecting magnetic separator  

OpenAIRE

While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerator...

Threlfall, J.; Neukirch, T.; Parnell, C. E.; Oskoui, S. Eradat

2014-01-01

137

Solar flares: an extremum of reconnection  

International Nuclear Information System (INIS)

Three points are emphasized: that the solar flare is that particular astrophysical phenomenon that is the extremum of reconnection, no other phenomenon demands as rapid magnetic flux annihilation as is seen in the solar flare; that plasma physics experiments can and should be performed in the laboratory that model reconnection as we observe it in astrophysics; and that stochastic field lines derived from something similar to Alfven wave turbulence are a necessary part of reconnection

138

Dissipation in Relativistic Pair-Plasma Reconnection  

Science.gov (United States)

We present an investigation of the relativistic dissipation in magnetic reconnection. The investigated system consists of an electron-positron plasma. A relativistic generalization of Ohm's law is derived. We analyze a set of numerical simulations, composed of runs with and without guide magnetic field, and of runs with different species temperatures. The calculations indicate that the thermal inertia-based dissipation process survives in relativistic plasmas. For anti-parallel reconnection, it is found that the pressure tensor divergence remains the sole contributor to the reconnection electric field, whereas relativistic guide field reconnection exhibits a similarly important role of the bulk inertia terms.

Hesse, Michael; Zenitani, Seiji

2007-01-01

139

Stellarator studies of magnetic reconnection  

Science.gov (United States)

Vacuum magnetic fields in a stellarator can be controlled to give a magnetic island of desired width on any selected rational magnetic surface, which makes stellarators uniquely suitable for reconnection experiments. In a pressureless ideal plasma, a delta function current arises to prevent changes in the island width. The magnetic field produced by this current can be measured outside of the plasma. As the current decays due to plasma dissipation, the time and spatial structure of the resulting field give a non-invasive diagnostic of reconnection. Important parameters include the Alfvén speed, the ion gyroradius using the sound speed, the electron collisionless skin depth, the plasma rotation, which can give a trigger-like phenomenon, and the width of the saturated, or vacuum, island. Plasmas can be produced in a given stellarator device over a broad range of densities, temperatures, and species types, and the saturated island width can be adjusted to any size up to a large fraction of the plasma radius without causing a plasma disruption. Consequently, various regimes of magnetic reconnection can be systematically studied.

Boozer, Allen

2006-10-01

140

Reconnection in orthogonally interacting vortex tubes: Direct numerical simulations and quantifications  

Science.gov (United States)

The three-dimensional time evolution of two orthogonally offset cylindrical vortices of equal strength is simulated by solving the hyperviscosity-regularized incompressible Navier-Stokes equations. A Fourier pseudospectral method with a time-split integration scheme is used for the solution. Four runs with different Reynolds numbers ranging between 690-2100 are performed, each with a resolution of 963 collocation points. The sequence of important physical processes and the evolution of local and global quantities such as vorticity, velocity, and mean-square strain rate are presented. It is found that the growth rate of the maximum vorticity is at most exponential. The Reynolds number dependence of the time scale of reconnection, the vorticity growth rate, and the time at which the maximum vorticity is attained are examined and differences between the present results and Saffman's essentially two-dimensional model predictions are encountered and elucidated. The distributions of the eigenvalues ?, ?, ? and the corresponding eigenvectors s?, s?, s? of the rate of strain tensor Sij are calculated at different times. It is found that as the mean-square strain rate ? increases during the evolution, s? and the vorticity vector ? are perfectly aligned and ?>0 in high ? regions. Strong temporal, spatial, and Reynolds number dependence of the strain fields is also seen. Evidence is presented that, during reconnection, the vorticity growth in newly forming bridges takes place in the vicinity of the upper stagnation line segment of the vortex dipole due to the nature of the vortex stretching term. Also examined is the initial finger formation and it is found that the initial nonuniform axial stretching and the displacement of the vortex cores due to a lift force play an important role in this process.

Boratav, O. N.; Pelz, R. B.; Zabusky, N. J.

1992-03-01

141

Interchange Reconnection Forced by the Filament Eruption Inside a Pseudo-streamer  

Science.gov (United States)

We present rare observational signatures of interchange reconnection (IR) forced by the filament eruption inside a pseudo-streamer (PS). The PS was centered above a positive-polarity region bounded by two negative-polarity coronal holes (CHs), and thus its base contained two polarity inversion lines and a pair of loop arcades where two filaments were harbored. In white-light coronagraph data from two different views, it showed up as a fan-shaped structure consisting of fine rays and a coronal streamer. Followed by a two-ribbon flare and a coronal mass ejection, one of the filaments and its overlying arcade erupted away from the nearby CH and flew over the other arcade to interact with the PS's remote CH. As a result, distinct ribbon-like remote brightenings formed along the remote CH boundary and were connected to the positive-polarity flare ribbon by a loop system, but the nearby open-field region largely remained unchanged except that compact brightenings and a following small coronal dimming appeared close to one end of the erupted filament. In combination with the coronal magnetic configuration that derived from the potential-field source-surface model, these observations can be interpreted as follows: the erupting field was first deflected and guided by the nearby CH's open field and then reconnected with the oppositely oriented open field of the remote CH, during which both the closed field bridging the erupted filament and the remoter CH's open field were transported in the opposite direction. The observations thus supported the idea that PSs provide favorable environments for IR to take place and remote brightenings along their CH boundaries represent a credible IR signature on the solar surface.

Yang, Jiayan; Jiang, Yunchun; Xu, Zhe; Bi, Yi; Hong, Junchao

2015-04-01

142

Magnetic reconnection between colliding magnetized laser-produced plasma plumes.  

Science.gov (United States)

Observations of magnetic reconnection between colliding plumes of magnetized laser-produced plasma are presented. Two counterpropagating plasma flows are created by irradiating oppositely placed plastic (CH) targets with 1.8-kJ, 2-ns laser beams on the Omega EP Laser System. The interaction region between the plumes is prefilled with a low-density background plasma and magnetized by an externally applied magnetic field, imposed perpendicular to the plasma flow, and initialized with an X-type null point geometry with B=0 at the midplane and B=8??T at the targets. The counterflowing plumes sweep up and compress the background plasma and the magnetic field into a pair of magnetized ribbons, which collide, stagnate, and reconnect at the midplane, allowing the first detailed observations of a stretched current sheet in laser-driven reconnection experiments. The dynamics of current sheet formation are in good agreement with first-principles particle-in-cell simulations that model the experiments. PMID:25238366

Fiksel, G; Fox, W; Bhattacharjee, A; Barnak, D H; Chang, P-Y; Germaschewski, K; Hu, S X; Nilson, P M

2014-09-01

143

A reconnection mechanism for the generation of anomalous cosmic rays  

Science.gov (United States)

The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyagers 1 and 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, compresses across the termination shock and reconnects in the subsonic flow of the heliosheath. Dropouts in the intensity of energetic electrons and the most energetic ACR ions as Voyager 2 exits the sector zone support the hypothesis that the heliosheath sectored field has reconnected. The sector structure is examined with global MHD simultions of the heliosphere. Particle-in-cell (PIC) simulations in 2-D and 3-D reveal that the sectors break up into a bath of elongated magnetic islands and that most of the magnetic energy released goes into energetic ions with significant but smaller amounts of energy going into electrons. The most energetic particles gain energy as they circulate in contracting magnetic islands, a first order Fermi process. The simulations also reveal that the firehose condition plays an essential role in the reconnection dynamics and particle acceleration. An analytic model is constructed in which the Fermi drive, modulated by the approach to firehose marginality, is balanced by convective loss. The ACR differential energy spectrum takes the form of a power law with a spectral index slightly above 1.5. The model has the potential to explain several key ACR observations, including the similarities in the spectra of different ion species.

Drake, James; Opher, Merav; Swisdak, Marc; Schoeffler, K.

2012-07-01

144

Energy partition in magnetic reconnection outflows  

Science.gov (United States)

The basic plasma process of magnetic reconnection plays an important role in plasma dynamics in a variety of solar, space, and astrophysical environments. In particular, it converts stored magnetic energy into directed jets and particle heating. An important issue is therefore to understand how magnetic reconnection distributes the released energy into different forms. The partition of energy in reconnection outflows has mainly been investigated in the context of the Earth's magnetotail and solar flares using single fluid simulations. However, the recent discovery of significant Poynting flux associated with kinetic Alfven wave structure emanating from the diffusion region along and near the separatrices means that a re-assessment of the energy partition in reconnection outflows is required, particularly from the experimental point of view. Here we present new measurements of plasma energetics in the vicinity of the diffusion region. Using data from Cluster and examining a series of reconnection events observed in the Earth's magnetotail, we present an analysis of the statistical properties of plasma in the ion diffusion region associated with the magnetic reconnection X-line. In particular, we investigate the partition of energy between the enthalpy, kinetic energy and Poynting fluxes, and the spatial structure of these fluxes relative to the geometry of the diffusion region. The Poynting flux, dominated by Hall electric and magnetic fields created by differential ion and electron motion is surprisingly large. This has significant implications for our understanding of reconnection energetics, because this signal propagates away from the reconnection site at speeds significantly greater than the Alfven speed.

Eastwood, J. P.; Phan, T.; Drake, J. F.; Shay, M. A.

2012-12-01

145

Theoretical analysis of driven magnetic reconnection experiments  

International Nuclear Information System (INIS)

In this paper the authors develop a theoretical framework for the Magnetic Reconnection Experiment (MRX) in order to understand the basic physics of the experiment, including the effect of the external driving force, and the difference between co and counterhelicity cases of the experiment. In order to simplify the problem they reduce it to a 1-D resistive MHD model. Also, they define a special class of holonomic boundary conditions under which a unique sequence of global equilibria can be obtained, independent of the rate of reconnection. This enables them to break the whole problem into two parts: a global problem for the ideal region, and a local problem for the resistive reconnection layer. The authors carry out the calculations and obtain the global solution for the ideal region in one particular case of holonomic constraints, the so called 'constant force'' regime, for both the co and counterhelicity cases. After the sequence of equilibria in the ideal region is found, they tackle the problem of the rate of reconnection in the resistive reconnection region. This rate tells how fast they proceed through the sequence of global equilibria but does not affects the sequence itself. Assuming the Sweet-Parker model for the reconnection layer, they calculate the reconnection rate, and demonstrate the difference between the co and counterhelicity cases, as well as the role of the external forces. The authors find their results to be in reasonable agreement with the experiment. Magnetic reconnection is important both in laboratory experiments and in astrophysics

146

Theoretical analysis of driven magnetic reconnection experiments  

Energy Technology Data Exchange (ETDEWEB)

In this paper the authors develop a theoretical framework for the Magnetic Reconnection Experiment (MRX) in order to understand the basic physics of the experiment, including the effect of the external driving force, and the difference between co and counterhelicity cases of the experiment. In order to simplify the problem they reduce it to a 1-D resistive MHD model. Also, they define a special class of holonomic boundary conditions under which a unique sequence of global equilibria can be obtained, independent of the rate of reconnection. This enables them to break the whole problem into two parts: a global problem for the ideal region, and a local problem for the resistive reconnection layer. The authors carry out the calculations and obtain the global solution for the ideal region in one particular case of holonomic constraints, the so called `constant force`` regime, for both the co and counterhelicity cases. After the sequence of equilibria in the ideal region is found, they tackle the problem of the rate of reconnection in the resistive reconnection region. This rate tells how fast they proceed through the sequence of global equilibria but does not affects the sequence itself. Assuming the Sweet-Parker model for the reconnection layer, they calculate the reconnection rate, and demonstrate the difference between the co and counterhelicity cases, as well as the role of the external forces. The authors find their results to be in reasonable agreement with the experiment. Magnetic reconnection is important both in laboratory experiments and in astrophysics.

Uzdensky, D.A.; Kulsrud, R.M.; Yamada, Masaaki [Princeton Univ., NJ (United States)

1995-11-01

147

Lessons on collisionless reconnection from quantum fluids  

Science.gov (United States)

Magnetic reconnection in space plasmas remains a challenge in physics in that the phenomenon is associated with the breakdown of frozen-in magnetic field in a collisionless medium. Such a topology change can also be found in superfluidity, known as the quantum vortex reconnection. We give a plasma physicists' view of superfluidity to obtain insights on essential processes in collisionless reconnection, including discussion of the kinetic and fluid pictures, wave dynamics, and time reversal asymmetry. The most important lesson from the quantum fluid is the scenario that reconnection is controlled by the physics of topological defects on the microscopic scale, and by the physics of turbulence on the macroscopic scale. Quantum vortex reconnection is accompanied by wave emission in the form of Kelvin waves and sound waves, which imprints the time reversal asymmetry.

Narita, Yasuhito; Baumjohann, Wolfgang

2014-12-01

148

Relating RHESSI Footpoints to Reconnection: the Importance of Spines and Separators  

Science.gov (United States)

In order to improve the understanding of both flare initiation and evolution, we take advantage of powerful new topological methods and the high spatial resolution of RHESSI to examine where magnetic reconnection takes place in flare-producing solar active regions. We use the MPOLE (http://solar.physics.montana.edu/dana/mpole/) software to extrapolate the observed line of sight photospheric magnetic field into the corona. MPOLE is a suite of IDL programs that implements the Minimum Current Corona Model (Longcope 1996). Recently it has been improved to use a hierarchy of topological features (Beveridge 2006). The coronal extrapolation gives the location of topological features such as poles, nulls, separatricies, separators, and spine lines. For several flares well observed by RHESSI and MDI, we examine the locations of flare HXR emission in the context of these topological features. Two noteworthy relationships are found. First, when footpoints move, they move along spine lines. Second, when separators significantly change over the course of a flare, only those associated with the flare footpoints do so. In this poster, we present observations supporting the relationship between spine lines and footpoint tracks, demonstrate the importance of separator analysis in the study of flares, explore uncertainties in the MPOLE and RHESSI analyses, and survey possible interpretations of the reported results. This work is supported by NASA.

Des Jardins, A.; Canfield, R.; Longcope, D.; McLinden, E.; Fordyce, C.; Waitukaitis, S.

2006-12-01

149

The Onset of Magnetic Reconnection  

Science.gov (United States)

A fundamental question concerning magnetic energy release on the Sun is why the release occurs only after substantial stresses have been built up in the field. If reconnection were to occur readily, the released energy would be insufficient to explain coronal heating, CMEs, flares, jets, spicules, etc. How can we explain this switch-on property? What is the physical nature of the onset conditions? One idea involves the "secondary instability" of current sheets, which switches on when the rotation of the magnetic field across a current sheet reaches a critical angle. Such conditions would occur at the boundaries of flux tubes that become tangled and twisted by turbulent photospheric convection, for example. Other ideas involve a critical thickness for the current sheet. We report here on the preliminary results of our investigation of reconnect onset. Unlike our earlier work on the secondary instability (Dahlburg, Klimchuk, and Antiochos 2005), we treat the coupled chromosphere-corona system. Using the BATS-R-US MHD code, we simulate a single current sheet in a sheared magnetic field that extends from the chromosphere into the corona. Driver motions are applied at the base of the model. The configuration and chromosphere are both idealized, but capture the essential physics of the problem. The advantage of this unique approach is that it resolves the current sheet to the greatest extent possible while maintaining a realistic solar atmosphere. It thus bridges the gap between "reconnection in a box" studies and studies of large-scale systems such as active regions. One question we will address is whether onset conditions are met first in the chromosphere or corona. We will report on the work done on the project.

Daldorff, Lars K. S.; Klimchuk, James A.; van der Holst, Bart

2015-04-01

150

2D numerical simulation of the resistive reconnection layer  

International Nuclear Information System (INIS)

In this paper the authors present a two-dimensional numerical simulation of a reconnection current layer in incompressible resistive magnetohydrodynamics with uniform resistivity in the limit of very large Lundquist numbers. They use realistic boundary conditions derived consistently from the outside magnetic field, and they also take into account the effect of the backpressure from flow into the separatrix region. They find that within a few Alfven times the system reaches a steady state consistent with the Sweet-Parker model, even if the initial state is Petschek-like

151

Asymmetric Magnetic Reconnection in Solar Flare and Coronal Mass Ejection Current Sheets  

CERN Document Server

We present two-dimensional resistive magnetohydrodynamic simulations of line-tied asymmetric magnetic reconnection in the context of solar flare and coronal mass ejection current sheets. The reconnection process is made asymmetric along the inflow direction by allowing the initial upstream magnetic field strengths and densities to differ, and along the outflow direction by placing the initial perturbation near a conducting wall boundary that represents the photosphere. When the upstream magnetic fields are asymmetric, the post-flare loop structure is distorted into a characteristic skewed candle flame shape. The simulations can thus be used to provide constraints on the reconnection asymmetry in post-flare loops. More hard X-ray emission is expected to occur at the footpoint on the weak magnetic field side because energetic particles are more likely to escape the magnetic mirror. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that e...

Murphy, N A; Pope, C L; Raymond, J C; Winter, H D; Reeves, K K; Seaton, D B; van Ballegooijen, A A; Lin, J

2012-01-01

152

Physics of Reconnection and MMS Mission  

Science.gov (United States)

Reconnection is the most important process driving the Earth's magnetosphere. Key to the success of the MMS science plan is the coupling of theory and observation. Determining the kinetic processes occurring in the diffusion region and physical parameters that control the rate of magnetic reconnection are among primary objectives of the MMS mission. Analysis of the role played by particle inertial effects in the diffusion region where the plasma is unmagnetized will be presented. The reconnection electric field in he diffusion region is supported primarily by particle non-gyrotropic effects. At the quasi-steady stage the reconnection electric field serves to accelerate and heat the incoming plasma population to maintain the current flow in the diffusion region the pressure balance. The primary mechanism controlling the dissipation in the vicinity of the reconnection site is incorporated into the fluid description in terms of non-gyrotropic corrections to the. induction and energy equations. The results of kinetic and fluid simulations illustrating the physics of magnetic reconnection will be presented. We will dem:tistrate that kinetic nongyrotropic effects can significantly alter the global magnetosphere evolution and location of reconnection sites.

Kuznetsova, M. M.; Hesse, M.; Gombosi, T.

2009-01-01

153

Evolutions of nonsteady state magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

The full evolutions of collisionless non-steady-state magnetic reconnection are studied with full kinetic particle-in-cell simulations. There are different stages of reconnection: the onset or early growing stage when the out-of-plane electric field (Ey) structure is a monopole at the X-point, the bipolar stage when the Ey structure is bipolar and the outer electron diffusion region (EDR) is being elongated over time, and the possible final steady-state stage when E{sub y} is uniform in the reconnection plane. We find the change of reconnection rate is not empowered or dependent on the length of the EDR. During the early growing stage, the EDR is elongated while the reconnection rate is growing. During the later stage, the reconnection rate may significantly decrease but the length of the inner EDR is largely stable. The results indicate that reconnection is not controlled by the downstream physics, but rather by the availability of plasma inflows from upstream. The physical mechanism of the EDR elongation is studied. The Hall current induced by the quadrupole magnetic field (B{sub y}) is discovered to play an important role in this process. The condition of forming an extended electron super-Alfvenic outflow jet structure in nature is discussed. The jet structure could be elongated during the bipolar stage, and remains stable during steady state. The sufficiency of the electron inflow is crucial for the elongation. Open boundary conditions are applied in the outflow direction.

Wan, Weigang [Los Alamos National Laboratory; Lapenta, Giovanni [KATHOLIEKE UNIV

2008-01-01

154

Magnetic reconnection in a weakly ionized plasma  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al.[“Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” Astrophys. J. 760, 109 (2012)] by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates, it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows, and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets.

Leake, James E. [College of Science, George Mason University, 4400 University Drive, Fairfax, Virginia 22030 (United States); Lukin, Vyacheslav S.; Linton, Mark G. [U.S. Naval Research Lab, 4555 Overlook Ave., SW Washington, DC 20375 (United States)

2013-06-15

155

Magnetic reconnection in a weakly ionized plasma  

International Nuclear Information System (INIS)

Magnetic reconnection in partially ionized plasmas is a ubiquitous phenomenon spanning the range from laboratory to intergalactic scales, yet it remains poorly understood and relatively little studied. Here, we present results from a self-consistent multi-fluid simulation of magnetic reconnection in a weakly ionized reacting plasma with a particular focus on the parameter regime of the solar chromosphere. The numerical model includes collisional transport, interaction and reactions between the species, and optically thin radiative losses. This model improves upon our previous work in Leake et al.[“Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma,” Astrophys. J. 760, 109 (2012)] by considering realistic chromospheric transport coefficients, and by solving a generalized Ohm's law that accounts for finite ion-inertia and electron-neutral drag. We find that during the two dimensional reconnection of a Harris current sheet with an initial width larger than the neutral-ion collisional coupling scale, the current sheet thins until its width becomes less than this coupling scale, and the neutral and ion fluids decouple upstream from the reconnection site. During this process of decoupling, we observe reconnection faster than the single-fluid Sweet-Parker prediction, with recombination and plasma outflow both playing a role in determining the reconnection rate. As the current sheet thins further and elongates, it becomes unstable to the secondary tearing instability, and plasmoids are seen. The reconnection rate, outflows, and plasmoids observed in this simulation provide evidence that magnetic reconnection in the chromosphere could be responsible for jet-like transient phenomena such as spicules and chromospheric jets

156

Magnetic reconnection in the terrestrial magnetosphere  

International Nuclear Information System (INIS)

An overview is given of quantitative comparisons between measured phenomena in the terrestrial magnetosphere thought to be associated with magnetic reconnection, and related theoretical predictions based on Petschek's simple model. Although such a comparison cannot be comprehensive because of the extended nature of the process and the relatively few in situ multipoint measurements made to date, the agreement is impressive where comparisons have been possible. This result leaves little doubt that magnetic reconnection does indeed occur in the terrestrial magnetosphere. The maximum reconnection rate, expressed in terms of the inflow Mach number, M/sub A/, is measured to be M/sub A/ = 0.2 +- 0.1

157

Redistribution of energetic ions during reconnection events in NSTX  

International Nuclear Information System (INIS)

Experiments on the spherical torus NSTX show that reconnection events (sawtooth crashes, internal reconnection events et.) can result in strong, by a factor of two, drops of the neutron yield, which are an evidence of losses of energetic ions. In the present work, mechanisms of the energetic ion redistributions during sawtooth crashes are analyzed, and strong drops of the neutral emission in a particular NSTX experiment are explained. It is found that in NSTX shots with a low magnetic field the main mechanisms of the particle redistribution during the crash are the particle resonance with the 1/1 harmonic of the perturbation and the stochastization of the particle motion. The latter is considerably enhanced by the diamagnetic perturbation of the magnetic field strength. The conclusion is drawn that the loss is sensitive to the safety factor profile, the plasma pressure and the particle precession rate, which, in turn, depends on the particle energy and pitch angle, the plasma elongation etc. The NSTX shot 104505, where drops of the neutron yield by a factor of 2 were observed during reconnection events, was selected for detailed analysis. A semi-analytical model of the electromagnetic field evolution during a Kadomtsev-type reconnection, which takes into account the perturbation of the magnetic field strength, is suggested and incorporated into the code GYROXY, which calculates the particle motion without using the guiding-center approximation. It is found that the moter approximation. It is found that the motion of a considerable fraction of 80-keV ions is stochastic during the reconnection, and this stochasticity can lead to a particle loss. The observed stochasticity results from the overlap of resonance islands, in particular, secondary islands near the separatrix of the 1/1 resonance and islands produced through a nonlinear mechanism. To calculate the post-crash distribution function of energetic ions and the loss of these ions, Monte-Carlo simulations of the particle motion in the evolving magnetic field are carried out. Using this distribution, the change of the neutron reactivity is calculated and compared with the experiment. (author)

158

Forcing continuous reconnection in hybrid simulations  

Energy Technology Data Exchange (ETDEWEB)

We have performed hybrid simulations of driven continuous reconnection with open boundary conditions. Reconnection is started by a collision of two subsonic plasma fronts with opposite magnetic fields, without any specified magnetic field configuration as initial condition. Due to continued forced plasma inflow, a current sheet co-located with a dense and hot plasma sheet develops. The translational symmetry of the current sheet is broken by applying a spatial gradient in the inflow speed. We compare runs with and without localized resistivity: reconnection is initiated in both cases, but localized resistivity stabilizes it and enhances its efficiency. The outflow speed reaches about half of Alfvén speed. We quantify the conversion of magnetic energy to kinetic energy of protons and to Joule heating and show that with localized resistivity, kinetic energy of protons is increased on average five-fold in the reconnection in our simulation case.

Laitinen, T. V., E-mail: tiera.laitinen@fmi.fi; Janhunen, P. [Finnish Meteorological Institute, PL 503, FI-00101 Helsinki (Finland); Jarvinen, R. [Finnish Meteorological Institute, PL 503, FI-00101 Helsinki (Finland); Laboratory for Atmospheric and Space Physics, University of Colorado Boulder, 3665 Discovery Drive, Boulder, Colorado 80303 (United States); Kallio, E. [School of Electrical Engineering, Aalto University, PL 13000, FI-00076 Aalto, Espoo (Finland); Finnish Meteorological Institute, PL 503, FI-00101 Helsinki (Finland)

2014-07-15

159

Three-dimensional Hall magnetic reconnection  

International Nuclear Information System (INIS)

New numerical results of three-dimensional magnetic reconnection in the Hall limit (Lpi where c/?pi is the ion inertial length) are presented. The reconnection process is initiated with a magnetic field perturbation localized along the current channel in a reversed field plasma configuration. The perturbation induces a magnetic wave structure that propagates opposite to the current, and leads to the asymmetric thinning of the plasma layer, strong plasma flows in the direction of the current, and rapid magnetic reconnection. The propagating wave structure is a Hall phenomenon associated with magnetic field curvature. The reconnection rate is independent of a (weak) guide field and the boundary conditions (i.e., periodic or outflowing)

160

Forced magnetic reconnection in the Hall limit  

Science.gov (United States)

Steady state systems have been obtained in 2D Hall magnetic reconnection simulation studies [e.g., Huba and Rudakov, 2004]. For these cases, the inflow and outflow of plasma and magnetic field at the boundaries are determined by the dynamics of the reconnection region. However, in many space physics systems the boundary conditions are imposed, for example, the solar wind/magnetopause interaction. In this paper we present 2D and 3D magnetic reconnection studies of forced reconnection in the Hall limit where the inflow boundary conditions are prescribed. A subset of this work will focus on a generalization of the `Newton challenge' project [Birn et al., 2005]. Preliminary simulations suggest that steady state solutions are not obtained. Huba, J.D. and L.I. Rudakov, Phys. Rev. Lett. 93, 175003, 2004. Birn et al., Geophys. Res. Lett. 32, L06105, doi: 10.1029 / 2004GL022058, 2005. Research supported by NASA and ONR.

Huba, J. D.

2005-12-01

161

Interchange reconnection in a turbulent Corona  

CERN Document Server

Magnetic reconnection at the interface between coronal holes and loops, so-called interchange reconnection, can release the hotter, denser plasma from magnetically confined regions into the heliosphere, contributing to the formation of the highly variable slow solar wind. The interchange process is often thought to develop at the apex of streamers or pseudo-streamers, near Y and X-type neutral points, but slow streams with loop composition have been recently observed along fanlike open field lines adjacent to closed regions, far from the apex. However, coronal heating models, with magnetic field lines shuffled by convective motions, show that reconnection can occur continuously in unipolar magnetic field regions with no neutral points: photospheric motions induce a magnetohydrodynamic turbulent cascade in the coronal field that creates the necessary small scales, where a sheared magnetic field component orthogonal to the strong axial field is created locally and can reconnect. We propose that a similar mechan...

Rappazzo, A F; Ruffolo, D; Servidio, S; Velli, M

2012-01-01

162

Particle acceleration in the driven relativistic reconnection  

OpenAIRE

We study the compression driven magnetic reconnection in the relativistic electron-positron plasma. Making use of a 2.5D particle-in-cell code, we simulated compression of a magnetized plasma layer containing a current sheet within it. We found that the particle spectrum within the reconnecting sheet becomes non-thermal; it could be approximated by a power-law distribution with an index of -1 and an exponential cutoff.

Lyubarsky, Yuri; Liverts, Michael

2008-01-01

163

Reconnection of Non-Abelian Cosmic Strings  

OpenAIRE

Cosmic strings in non-abelian gauge theories naturally gain a spectrum of massless, or light, excitations arising from their embedding in color and flavor space. This opens up the possibility that colliding strings miss each other in the internal space, reducing the probability of reconnection. We study the topology of the non-abelian vortex moduli space to determine the outcome of string collision. Surprisingly we find that the probability of classical reconnection in this ...

Hashimoto, Koji; Tong, David

2005-01-01

164

On the Rate of Spontaneous Magnetic Reconnection  

OpenAIRE

Magnetic reconnection is a topological rearrangement of the magnetic field lines, leading to the release of magnetic energy, which is thought to be associated with solar flares, coronal mass ejections and magnetospheric storms. Despite magnetic field lines are supposed to be frozen into the well-conducting plasma, the reconnection observed in nature is, typically, fast, so that the rate of convergence of the magnetic field lines is the fraction of the Alfven speed, v_A. The ...

Beresnyak, Andrey

2013-01-01

165

Collisionless magnetic reconnection in a plasmoid chain  

Directory of Open Access Journals (Sweden)

Full Text Available The kinetic features of plasmoid chain formation and evolution are investigated by two dimensional Particle-in-Cell simulations. Magnetic reconnection is initiated in multiple X points by the tearing instability. Plasmoids form and grow in size by continuously coalescing. Each chain plasmoid exhibits a strong out-of plane core magnetic field and an out-of-plane electron current that drives the coalescing process. The disappearance of the X points in the coalescence process are due to anti-reconnection, a magnetic reconnection where the plasma inflow and outflow are reversed with respect to the original reconnection flow pattern. Anti-reconnection is characterized by the Hall magnetic field quadrupole signature. Two new kinetic features, not reported by previous studies of plasmoid chain evolution, are here revealed. First, intense electric fields develop in-plane normally to the separatrices and drive the ion dynamics in the plasmoids. Second, several bipolar electric field structures are localized in proximity of the plasmoid chain. The analysis of the electron distribution function and phase space reveals the presence of counter-streaming electron beams, unstable to the two stream instability, and phase space electron holes along the reconnection separatrices.

S. Markidis

2012-02-01

166

Particle acceleration at a reconnecting magnetic separator  

Science.gov (United States)

Context. While the exact acceleration mechanism of energetic particles during solar flares is (as yet) unknown, magnetic reconnection plays a key role both in the release of stored magnetic energy of the solar corona and the magnetic restructuring during a flare. Recent work has shown that special field lines, called separators, are common sites of reconnection in 3D numerical experiments. To date, 3D separator reconnection sites have received little attention as particle accelerators. Aims: We investigate the effectiveness of separator reconnection as a particle acceleration mechanism for electrons and protons. Methods: We study the particle acceleration using a relativistic guiding-centre particle code in a time-dependent kinematic model of magnetic reconnection at a separator. Results: The effect upon particle behaviour of initial position, pitch angle, and initial kinetic energy are examined in detail, both for specific (single) particle examples and for large distributions of initial conditions. The separator reconnection model contains several free parameters, and we study the effect of changing these parameters upon particle acceleration, in particular in view of the final particle energy ranges that agree with observed energy spectra.

Threlfall, J.; Neukirch, T.; Parnell, C. E.; Eradat Oskoui, S.

2015-02-01

167

Test particle acceleration in torsional fan reconnection  

Science.gov (United States)

Magnetic reconnection is understood to be a potential mechanism for particle acceleration in astrophysical and space plasmas, especially in solar flares. Torsional fan reconnection is one of the proposed mechanisms for steady-state three-dimensional (3D) magnetic reconnection. By using the magnetic and electric fields for `torsional fan reconnection', the features of test particle acceleration with input parameters for the solar corona are investigated numerically. We show that torsional fan reconnection is potentially an efficient particle accelerator and a proton can gain up to tens of MeV of kinetic energy within only a few milliseconds. Although the final kinetic energy of the accelerated particle depends on the injection position but there exists only one scenario for the particle's trajectory with different initial positions in which the particle is accelerated on the fan plane. Moreover, adopting either spatially uniform or non-uniform localized plasma resistivity does not much influence the features of trajectory. These results are compared with those of torsional spine reconnection.

Hosseinpour, M.

2014-12-01

168

Coupling between reconnection and Kelvin-Helmholtz instabilities in collisionless plasmas  

Directory of Open Access Journals (Sweden)

Full Text Available In a collisionless plasma, when reconnection instability takes place, strong shear flows may develop. Under appropriate conditions these shear flows become unstable to the Kelvin-Helmholtz instability. Here, we investigate the coupling between these instabilities in the framework of a four-field model. Firstly, we recover the known results in the low ? limit, ? being the ratio between the plasma and the magnetic pressure. We concentrate our attention on the dynamical evolution of the current density and vorticity sheets which evolve coupled together according to a laminar or a turbulent regime. A three-dimensional extension in this limit is also discussed. Secondly, we consider finite values of the ? parameter, allowing for compression of the magnetic and velocity fields along the ignorable direction. We find that the current density and vorticity sheets now evolve separately. The Kelvin-Helmholtz instability involves only the vorticity field, which ends up in a turbulent regime, while the current density maintains a laminar structure.

D. Grasso

2009-04-01

169

Healthy Places  

Centers for Disease Control (CDC) Podcasts

Every person has a stake in environmental public health. As the environment deteriorates, so does the physical and mental health of the people within it. Healthy places are those designed and built to improve the quality of life for all people who live, work, worship, learn, and play within their borders -- where every person is free to make choices amid a variety of healthy, available, accessible, and affordable options. The CDC recognizes significant health issues and places that are vital in developing the Healthy Places program and provides examples in this report.  Created: 4/10/2007 by CDC National Center for Environmental Health.   Date Released: 4/13/2007.

2007-04-10

170

Turbulent Reconnection Rates from Cluster Observations in the Magnetosheath  

Science.gov (United States)

The role of turbulence in producing fast reconnection rates is an important unresolved question. Scant in situ analyses exist. We apply multiple spacecraft techniques to a case of nonlinear turbulent reconnection in the magnetosheath to test various theoretical results for turbulent reconnection rates. To date, in situ estimates of the contribution of turbulence to reconnection rates have been calculated from an effective electric field derived through linear wave theory. However, estimates of reconnection rates based on fully nonlinear turbulence theories and simulations exist that are amenable to multiple spacecraft analyses. Here we present the linear and nonlinear theories and apply some of the nonlinear rates to Cluster observations of reconnecting, turbulent current sheets in the magnetosheath. We compare the results to the net reconnection rate found from the inflow speed. Ultimately, we intend to test and compare linear and nonlinear estimates of the turbulent contribution to reconnection rates and to measure the relative contributions of turbulence and the Hall effect.

Wendel, Deirdre

2011-01-01

171

Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence  

Energy Technology Data Exchange (ETDEWEB)

The statistical study of magnetic reconnection events in two-dimensional turbulence has been performed by comparing numerical simulations of magnetohydrodynamics (MHD) and Hall magnetohydrodynamics (HMHD). The analysis reveals that the Hall term plays an important role in turbulence, in which magnetic islands simultaneously reconnect in a complex way. In particular, an increase of the Hall parameter, the ratio of ion skin depth to system size, broadens the distribution of reconnection rates relative to the MHD case. Moreover, in HMHD the local geometry of the reconnection region changes, manifesting bifurcated current sheets and quadrupolar magnetic field structures in analogy to laminar studies, leading locally to faster reconnection processes in this case of reconnection embedded in turbulence. This study supports the idea that the global rate of energy dissipation is controlled by the large scale turbulence, but suggests that the distribution of the reconnection rates within the turbulent system is sensitive to the microphysics at the reconnection sites.

Donato, S.; Servidio, S.; Carbone, V. [Dipartimento di Fisica, Universita della Calabria, I-87036 Cosenza (Italy); Dmitruk, P. [Departamento de Fisica, Facultad de Ciencias Exactas y Naturales, Universidad de Buenos Aires and Instituto de Fisica de Buenos Aires, CONICET, Buenos Aires (Argentina); Shay, M. A.; Matthaeus, W. H. [Bartol Research Institute and Department of Physics and Astronomy, University of Delaware, Newark, Delaware 19716 (United States); Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States)

2012-09-15

172

Experimental Study of Ion Heating and Acceleration During Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma out flow is sub-Alfvonic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that the ions are heated largely due to non-classical mechanisms. The Ti rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations indicate strongly that non-classical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process.

S.C. Hsu; T.A. Carter; G. Fiksel; H. Ji; R.M. Kulsrud; M. Yamada

2000-10-24

173

Experimental Study of Ion Heating and Acceleration During Magnetic Reconnection  

International Nuclear Information System (INIS)

Ion heating and acceleration has been studied in the well-characterized reconnection layer of the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)]. Ion temperature in the layer rises substantially during null-helicity reconnection in which reconnecting field lines are anti-parallel. The plasma out flow is sub-Alfvonic due to a downstream back pressure. An ion energy balance calculation based on the data and including classical viscous heating indicates that the ions are heated largely due to non-classical mechanisms. The Ti rise is much smaller during co-helicity reconnection in which field lines reconnect obliquely. This is consistent with a slower reconnection rate and a smaller resistivity enhancement over the Spitzer value. These observations indicate strongly that non-classical dissipation mechanisms can play an important role both in heating the ions and in facilitating the reconnection process

174

Externally driven magnetic reconnection in a collisionless plasma  

International Nuclear Information System (INIS)

Driven magnetic reconnection in a collisionless plasma, 'collisionless driven reconnection', is investigated by means of two-and-one-half dimensional particle simulation. Magnetic reconnection develops in two steps in accordance with the formation of two current layers, i.e., an ion current layer and an electron current layer. It is found that the global dynamical evolution of magnetic reconnection is controlled by the physics of the ion current layer. (author). 5 refs, 3 figs

175

Stochastic sawtooth reconnection in ASDEX Upgrade  

International Nuclear Information System (INIS)

In this paper we investigate non-complete sawtooth reconnection in the ASDEX Upgrade tokamak. Such reconnection phenomena are associated with internal m/n = 1/1 kink mode which does not vanish after the crash phase (as would be the case for complete reconnection). It is shown that this sawtooth cannot be fully described by pure m/n = 1/1 mode and that higher harmonics play an important role during the sawtooth crash phase. We employ the Hamiltonian formalism and reconstructed perturbations to model incomplete sawtooth reconnection. It is demonstrated that stochastization appears due to the excitation of low-order resonances which are present in the corresponding q-profiles inside the q = 1 surface which reflects the key role of the q0 value. Depending on this value two completely different situations are possible for one and the same mode perturbations: (i) the resonant surfaces are present in the q-profile leading to stochasticity and sawtooth crash (q0 ? 0.7 ± 0.1); (ii) the resonant surfaces are not present, which means no stochasticity in the system and no crash event (q0 ? 0.9 ± 0.05). Accordingly the central safety factor value is always less than unity in the case of a non-complete sawtooth reconnection. Our investigations show that the stochastic model agrees well with the experimental observations and can be proposed as a promising candidate for an explanation of the sawtooth reconnectionion

176

Some comments on solar reconnection problems  

International Nuclear Information System (INIS)

Comments are given on solar reconnection problems, noting that reconnection of magnetic flux tubes is a widespread phenomenon both on and inside the sun. The solar convection zone, some 200,000 km deep, contains vast numbers of flux tubes, all in pressure equilibrium with the nonmagnetic surroundings. Twisted tubes may well be reconnected in a manner resembling spot welding rather than by Petschek's mechanism. By a sequence of processes, flux ropes are built and float to the surface to produce sunspots. This is a vital part of the solar cycle, and the help of theoreticians in studying it is requested. It is belived that reconnection also occurs in prominences and will be easier to study there than in flares. A massive program is recommended for daily observation of quiescent prominences from limb to limb to establish their typical three dimensional structures. Only after the field geometry is any further work justified on the theory of prominences and related reconnection phenomena. Unanswered questions remaining and observations that could help are noted

177

Hall Magnetic Reconnection: Guide Field Dependence  

Science.gov (United States)

Two (2D) and three (3D) dimensional Hall magnetohydrodynamic (MHD) simulations are used to study the dependence of a guide field on magnetic reconnection. The 2D simulations are run until a steady state is achieved for B gf/B0 = 0, 0.1, 0.2, 0.5, 1.0, 2.0 and 5.0 where B gf is the guide field and B0 is the reversed field. It is found that the reconnection rate and plasma energization are reduced for increasing guide field strength. This is caused by a J × B force associated with Hall currents and the guide field that reduce the inflow and outflow velocities. However, the reconnection rate and plasma energization are only reduced by a factor of 2 for B gf = 5 B0. Additionally, the quadrupole field associated with Hall reconnection is eliminated for B gf ? B0/3. The 3D simulations demonstrate asymmetric development of a reconnection line [similar to the no guide field case reported by Huba and Rudakov (2002)], as well as the development of a (braided) magnetic flux tube. Applications to magnetospheric plasmas are discussed. Huba, J.D. and L.I. Rudakov, Phys. Plasmas 9, 4435 (2002). Research supported by NASA and ONR.

Rudakov, L.; Huba, J.

2004-12-01

178

Density Enhancements and Voids following Patchy Reconnection  

CERN Document Server

We show, through a simple patchy reconnection model, that retracting reconnected flux tubes may present elongated regions relatively devoid of plasma, as well as long lasting, dense central hot regions. Reconnection is assumed to happen in a small patch across a Syrovatski\\'i (non-uniform) current sheet (CS) with skewed magnetic fields. The background magnetic pressure has its maximum at the center of the CS plane, and decreases toward the edges of the plane. The reconnection patch creates two V-shaped reconnected tubes that shorten as they retract in opposite directions, due to magnetic tension. One of them moves upward toward the top edge of the CS, and the other one moves downward toward the top of the underlying arcade. Rotational discontinuities (RDs) propagate along the legs of the tubes and generate parallel super-sonic flows that collide at the center of the tube. There, gas dynamics shocks that compress and heat the plasma are launched outwardly. The descending tube moves through the bottom part of t...

Guidoni, S E

2011-01-01

179

Fast sawtooth reconnection at realistic Lundquist numbers  

Science.gov (United States)

Magnetic reconnection, a ubiquitous phenomenon in astrophysics, space science and magnetic confinement research, frequently proceeds much faster than predicted by simple resistive MHD theory. Acceleration can result from the break-up of the thin Sweet–Parker current sheet into plasmoids, or from two-fluid effects decoupling mass and magnetic flux transport over the ion inertial length {{v}A}/{?ci} or the drift scale \\sqrt{{{T}e}/{{m}i}}/{?ci}, depending on the absence or presence of a strong magnetic guide field. We describe new results on the modelling of sawtooth reconnection in a simple tokamak geometry (circular cylindrical equilibrium) pushed to realistic Lundquist numbers for present day tokamaks. For the resistive MHD case, the onset criteria and the influence of plasmoids on the reconnection process agree well with earlier results found in the case of vanishing magnetic guide fields. While plasmoids are also observed in two-fluid calculations, they do not dominate the reconnection process for the range of plasma parameters considered in this study. In the two-fluid case they form as a transient phenomenon only. The reconnection times become weakly dependent on the S-value and for the most complete model—including two-fluid effects and equilibrium temperature and density gradients—agree well with those experimentally found on ASDEX Upgrade ?ft(?slant 100 ? s\\right).

Günter, S.; Yu, Q.; Lackner, K.; Bhattacharjee, A.; Huang, Y.-M.

2015-01-01

180

Quantifying 3D Reconnection in Fragmented Current Layers  

CERN Document Server

There is growing evidence that when magnetic reconnection occurs in high Lundquist number plasmas such as in the Solar Corona or the Earth's Magnetosphere it does so within a fragmented, rather than a smooth current layer. Within the extent of these fragmented current regions the associated magnetic flux transfer and energy release occurs simultaneously in many different places. This investigation focusses on how best to quantify the rate at which reconnection occurs in such layers. An analytical theory is developed which describes the manner in which new connections form within fragmented current layers in the absence of magnetic nulls. It is shown that the collective rate at which new connections form can be characterized by two measures; a total rate which measures the true rate at which new connections are formed and a net rate which measures the net change of connection associated with the largest value of the integral of $E_{\\|}$ through all of the non-ideal regions. Two simple analytical models are pre...

Wyper, Peter F

2015-01-01

181

Taking Medication  

Medline Plus

Full Text Available ... schedule. Be sure to bring all medications or labels with you when you go to health appointments. ... to remind you to take your medications or labels when you go for any medical appointment.

182

Taking Medication  

Medline Plus

Full Text Available ... on what type a person has, their healthcare team will be able to determine which medications they should be taking and help them understand how your medications work. They can demonstrate how to inject insulin or ...

183

Taking Medicines  

Science.gov (United States)

... of this page please turn Javascript on. Taking Medicines Drugs in the Body Medicines can enter the body in many different ways, ... many steps happen along the way. Understanding how medicines work in your body can help you learn ...

184

Taking Medication  

Medline Plus

Full Text Available ... Make a Donation Access My Learning Access AADE7 System Find a Diabetes Educator Questions, Comments, Concerns? Taking Medication Diabetes is a progressive condition. Depending on what type a person has, their healthcare team will be ...

185

Places to Go: Moodle  

Science.gov (United States)

Educators are becoming increasingly interested in alternatives to learning management systems (LMS) Blackboard and WebCT. Stephen Downes's column Places to Go turns to one internationally popular open source LMS--Moodle. Downes takes the reader through Moodle's Web site, which is simultaneously a Web site about its LMS and an example of what its…

Downes, Stephen

2006-01-01

186

Drifting airglow patches in relation to tail reconnection  

Science.gov (United States)

In this study we present optical ground-based signatures of drifting airglow patches in the polar ionospheric F-layer, in the evening/nighttime MLT sector. The patches were observed under predominately IMF BZ 0 conditions, which are favorable for high-density sunlit plasma to be entrained into the polar cap with the large afternoon cell in the northern hemisphere. The patch morphology, such as altitude, meridional convection speed, and repetition rate was investigated using a meridian scanning photometer, and put into the context of activity changes in the auroral substorm. It was found that the meridional patch speed was modulated by the ongoing substorms, and that the patches crossed the open/closed field line boundary (OCB), even during late recovery, and subsequent growth phase. We take this as an indication of ongoing tail reconnection, and we therefore propose that the patches can be used as a tracer for tail reconnection when they cross the OCB and enter the nighttime auroral oval.

Lorentzen, D. A.; Shumilov, N.; Moen, J.

2004-01-01

187

The structure of the magnetic reconnection exhaust boundary  

CERN Document Server

The structure of shocks that form at the exhaust boundaries during collisionless reconnection of anti-parallel fields is studied using particle-in-cell (PIC) simulations and modeling based on the anisotropic magnetohydrodynamic equations. Large-scale PIC simulations of reconnection and companion Riemann simulations of shock development demonstrate that the pressure anisotropy produced by counterstreaming ions within the exhaust prevents the development of classical Petschek switch-off-slow shocks (SSS). The shock structure that does develop is controlled by the firehose stability parameter epsilon=1-mu_0(P_parallel-P_perpendicular)/ B^2 through its influence on the speed order of the intermediate and slow waves. Here P_parallel and P_perpendicular are the pressure parallel and perpendicular to the local magnetic field. The exhaust boundary is made up of a series of two shocks and a rotational wave. The first shock takes epsilon from unity upstream to a plateau of 0.25 downstream. The condition epsilon =0.25 i...

Liu, Yi-Hsin; Swisdak, M

2011-01-01

188

Gyro-induced acceleration of magnetic reconnection  

CERN Document Server

The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large \\Delta '), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence o...

Comisso, Luca; Waelbroeck, François L; Borgogno, Dario

2013-01-01

189

Formation of Plasmoid Chains in Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (104 ? S ? 108) is reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be unstable to super-Alfvenically fast formation of plasmoid (magnetic-island) chains. The plasmoid number scales as S3/8 and the instability growth rate in the linear stage as S1/4, in agreement with the theory by Loureiro et al. [Phys. Plasmas 14, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>104.

Samtaney, R.; Loureiro, N. F.; Uzdensky, D. A.; Schekochihin, A. A.; Cowley, S. C.

2009-09-09

190

Particle Demagnetization in Collisionless Magnetic Reconnection  

Science.gov (United States)

The dissipation mechanism of magnetic reconnection remains a subject of intense scientific interest. On one hand, one set of recent studies have shown that particle inertia-based processes, which include thermal and bulk inertial effects, provide the reconnection electric field in the diffusion region. In this presentation, we present analytical theory results, as well as 2.5 and three-dimensional PIC simulations of guide field magnetic reconnection. We will show that diffusion region scale sizes in moderate and large guide field cases are determined by electron Larmor radii, and that analytical estimates of diffusion region dimensions need to include description of the heat flux tensor. The dominant electron dissipation process appears to be based on thermal electron inertia, expressed through nongyrotropic electron pressure tensors. We will argue that this process remains viable in three dimensions by means of a detailed comparison of high resolution particle-in-cell simulations.

Hesse, Michael

2006-01-01

191

Computer simulation of reconnection in planetary magnetospheres  

International Nuclear Information System (INIS)

The earth's magnetosphere provides an ideal opportunity to model reconnection in well known geometries that are close enough to the idealized analytic models to make a comparison of the computer models with analytic theory meaningful. In addition more detailed, even three-dimensional, models can be used for a comparison with extended data from in situ observations. The computer studies have basically confirmed the reconnection picture that was based on two-dimensional steady state models and linear analytic theory. The three-dimensional models in particular have also added a lot more information on the reconnection process and the structure of flow, magnetic fields, and currents including many features that are consistent with observations and empirical models of geomagnetic substorms

192

Formation of Plasmoid Chains in Magnetic Reconnection  

International Nuclear Information System (INIS)

A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (104 (le) S (le) 108) is reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be unstable to super-Alfvenically fast formation of plasmoid (magnetic-island) chains. The plasmoid number scales as S3/8 and the instability growth rate in the linear stage as S1/4, in agreement with the theory by Loureiro et al. (Phys. Plasmas 14, 100703 (2007)). In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S > 104.

193

Time-dependent reconnection for anisotropic pressure  

Science.gov (United States)

An analysis of the reconnection process which extends the famous solution obtained by Petschek for the steady-state case to incorporate the effects of unsteady reconnection in an anisotropic plasma is presented. The case of so-called switch-off shocks, where the Alfvén discontinuity and the slow shock degenerate to one discontinuity and the downstream magnetic field vanishes in lowest order, so that the plasma is isotropic in the field reversal region is studied. It is shown that the plasma anisotropy can essentially modify the plasma acceleration, the magnetic field intensity, and the shape of the moving slow shocks. Characteristics of reconnection in several limits, such as the isotropic limit and extreme pressure anisotropy cases corresponding to the fire hose and the mirror instability are analyzed.

Mühlbachler, S.; Ivanova, V. V.; Semenov, V. S.; Biernat, H. K.; Langmayr, D.; Vogl, D. F.

2003-03-01

194

Time-dependent reconnection for anisotropic pressure  

International Nuclear Information System (INIS)

An analysis of the reconnection process which extends the famous solution obtained by Petschek for the steady-state case to incorporate the effects of unsteady reconnection in an anisotropic plasma is presented. The case of so-called switch-off shocks, where the Alfven discontinuity and the slow shock degenerate to one discontinuity and the downstream magnetic field vanishes in lowest order, so that the plasma is isotropic in the field reversal region is studied. It is shown that the plasma anisotropy can essentially modify the plasma acceleration, the magnetic field intensity, and the shape of the moving slow shocks. Characteristics of reconnection in several limits, such as the isotropic limit and extreme pressure anisotropy cases corresponding to the fire hose and the mirror instability are analyzed

195

Cosmic Ray Acceleration in Magnetic Reconnection Sites  

CERN Document Server

Cosmic Ray (CR) acceleration still challenges the researchers. Fast particles may be accelerated in astrophysical environments by a variety of processes. Acceleration in magnetic reconnection sites in particular, has lately attracted the attention of researchers not only for its potential importance in the solar system context, but also in other astrophysical environments, like compact stellar sources, AGNs and GRBs, and even in diffusive media like the ISM and the IGM, especially when the environment is magnetically dominated. In this talk we review this process and also present three-dimensional collisional MHD simulations with the injection of thousands of test particles showing from the evolution of their energy spectrum that they can be efficiently accelerated by reconnection through a first-order Fermi process within large scale magnetic current sheets (especially when local turbulence is present which makes reconnection fast and the acceleration layer thicker).

Pino, Elisabete M de Gouveia Dal; Lazarian, Alex

2014-01-01

196

Mystic Places  

Science.gov (United States)

This Website from The Discovery Channel of Canada explores "some of the world's most enigmatic places." It features separate sections on three famous sites -- Easter Island, Nazca Lines, and Stonehenge -- discussing the construction, cultural significance, and physical history of the extraordinary structures erected at each. The site also offers a slideshow presenting dozens of dramatic photographs from the three places as well as links to pertinent news releases and features archived on the Discovery site. The discussions and images provided are extensive and can serve as a stand-alone source of information, suitable for individual or secondary education.

197

Go Places.  

Science.gov (United States)

This brochure provides information about the individual colleges, universities, community colleges, and technical colleges within the Minnesota State Colleges and Universities system. The opening section titled, "How To Go Places," offers brief overviews on costs, choosing between two- and four-year colleges, options for international study,…

Minnesota State Colleges and Universities System, St. Paul.

198

Effects of color reconnection on $t\\bar{t}$ final states at the LHC  

CERN Document Server

The modeling of color reconnection has become one of the dominant sources of systematic uncertainty in the top mass determination at hadron colliders. The uncertainty on the top mass due to color reconnection is conventionally estimated by taking the difference in the predictions of a model with and a model without color reconnection. We show that this procedure underestimates the uncertainty when applied to the existing models in {\\sc Pythia}~8. We introduce two new classes of color reconnection models, each containing several variants, which encompass a variety of scenarios that could be realized in nature and we study how they affect the reconstruction of the top mass. After tuning the new models to existing LHC data, the remaining spread of predictions is used to derive a more realistic uncertainty for the top mass, which is found to be around 500 MeV. We also propose how future LHC measurements with $t\\bar{t}$ events can be used to further constrain these models and reduce the associated modeling uncerta...

Argyropoulos, Spyros

2014-01-01

199

Effects of color reconnection on t anti t final states at the LHC  

Energy Technology Data Exchange (ETDEWEB)

The modeling of color reconnection has become one of the dominant sources of systematic uncertainty in the top mass determination at hadron colliders. The uncertainty on the top mass due to color reconnection is conventionally estimated by taking the difference in the predictions of a model with and a model without color reconnection. We show that this procedure underestimates the uncertainty when applied to the existing models in PYTHIA 8. We introduce two new classes of color reconnection models, each containing several variants, which encompass a variety of scenarios that could be realized in nature and we study how they affect the reconstruction of the top mass. After tuning the new models to existing LHC data, the remaining spread of predictions is used to derive a more realistic uncertainty for the top mass, which is found to be around 500 MeV. We also propose how future LHC measurements with t anti t events can be used to further constrain these models and reduce the associated modeling uncertainty.

Argyropoulos, Spyros [Univ. Lund (Sweden). Dept. of Astronomy and Theoretical Physics; Deutsches Elektronen-Synchrotron (DESY), Hamburg (Germany); Sjoestrand, Torbjoern [Univ. Lund (Sweden). Dept. of Astronomy and Theoretical Physics

2014-07-15

200

Collisionless magnetic reconnection in a toroidal cusp  

International Nuclear Information System (INIS)

Fast collisionless magnetic reconnection is driven and observed in a toroidal magnetic cusp. For low values of the toroidal (guide) magnetic field, reconnection occurs without the formation of a macroscopic current channel. In the absence of a current channel, the measured plasma potential and poloidal flows are consistent with predictions based upon single particle theory. Only for large values of the toroidal magnetic field compared to cusp poloidal field is a current channel present. Also in this case single particle orbit theory provides a good description of the anomalous resistivity observed experimentally

201

Easily Repairable Networks: Reconnecting Nodes after Damage  

Science.gov (United States)

We introduce a simple class of distribution networks that withstand damage by being repairable instead of redundant. Instead of asking how hard it is to disconnect nodes through damage, we ask how easy it is to reconnect nodes after damage. We prove that optimal networks on regular lattices have an expected cost of reconnection proportional to the lattice length, and that such networks have exactly three levels of structural hierarchy. We extend our results to networks subject to repeated attacks, in which the repairs themselves must be repairable. We find that, in exchange for a modest increase in repair cost, such networks are able to withstand any number of attacks.

Farr, Robert S.; Harer, John L.; Fink, Thomas M. A.

2014-09-01

202

Particle acceleration at a reconnecting magnetic separator  

Science.gov (United States)

We present first results of test particle orbit calculations in a time-dependent electro-magnetic field configuration which models separator reconnection in three dimensions. The test particle orbits are calculated using the relativistic guiding-centre approximation. The test particles are accelerated to high kinetic energies by the parallel electric field generically associated with three-dimensional magnetic reconnection, with the final energy depending on the choice of model parameters. We will discuss how the test-particle orbits and the energy gain depend on the initial conditions, and how observations (for example, of solar flares) may be used to constrain our model parameters.

Threlfall, James; Neukirch, Thomas; Parnell, Clare; Eradat Oskoui, Solmaz

2014-05-01

203

Reconnection properties in collisionless plasma with open boundary conditions  

International Nuclear Information System (INIS)

Collisionless magnetic reconnection in a Harris current sheet with different initial thicknesses is investigated using a 21/2 -D Darwin particle-in-cell simulation with the magnetosonic open boundary condition. It is found that the thicknesses of the ion dissipation region and the reconnection current sheet, when the reconnection rate Er reaches its first peak, are independent of the initial thickness of the current sheet; while the peak reconnection rate depends on it. The peak reconnection rate increases with decrease of the current sheet thickness as Er?a?1/2, where a is the initial current sheet half-thickness

204

Place cells and place navigation.  

Science.gov (United States)

The assumption that hippocampal place cells (PCs) form the neural substrate of cognitive maps can be experimentally tested by comparing the effect of experimental interventions on PC activity and place navigation. Conditions that interfere with place navigation (darkness, cholinergic blockade) but leave PC activity unaffected obviously disrupt spatial memory at a post-PC level. Situations creating a conflict between egocentric and allocentric orientation (place navigation in the Morris water maze filled with slowly rotating water) slow down spatial learning. PC recording in rats searching food pellets in a rotating arena makes it possible to determine which firing fields are stable relative to the room (allocentrically dependent on sighted extramaze landmarks), to the surface of the arena (dependent on egocentric path integration mechanisms and intra-arena cues), or disappear during rotation. Such comparison is made possible by the computerized tracking system simultaneously displaying a rat's locomotion and the respective firing rate maps both in the room reference and arena reference frames. More severe conflict between allocentric and egocentric inputs is produced in the field clamp situation when the rat searching food in a ring-shaped arena is always returned by rotation of the arena to the same allocentric position. Ten-minute exposure to this condition caused subsequent disintegration or remapping of 70% PCs (n = 100). Simultaneous examination of PC activity and navigation is possible in the place avoidance task. A rat searching food in a stationary or rotating arena learns to avoid an allocentrically or egocentrically defined location where it receives mild electric footshock. In the place preference task the rat releases pellet delivery by entering an unmarked goal area and staying in it for a criterion time. Both tasks allow direct comparison of the spatial reference frames used by the PCs and by the behaving animal. PMID:8990211

Bures, J; Fenton, A A; Kaminsky, Y; Zinyuk, L

1997-01-01

205

Double Take  

Science.gov (United States)

This paper begins by discussing the results of two studies recently conducted in Australia. According to the two studies, taking a gap year between high school and college may help students complete a degree once they return to school. The gap year can involve such activities as travel, service learning, or work. Then, the paper presents links to…

Educational Leadership, 2011

2011-01-01

206

Catastrophic onset of fast magnetic reconnection with a guide field  

International Nuclear Information System (INIS)

It was recently shown that the slow (collisional) Sweet-Parker and the fast (collisionless) Hall magnetic reconnection solutions simultaneously exist for a wide range of resistivities; reconnection is bistable [Cassak, Shay, and Drake, Phys. Rev. Lett., 95, 235002 (2005)]. When the thickness of the dissipation region becomes smaller than a critical value, the Sweet-Parker solution disappears and fast reconnection ensues, potentially explaining how large amounts of magnetic free energy can accrue without significant release before the onset of fast reconnection. Two-fluid numerical simulations extending the previous results for anti-parallel reconnection (where the critical thickness is the ion skin depth) to component reconnection with a large guide field (where the critical thickness is the thermal ion Larmor radius) are presented. Applications to laboratory experiments of magnetic reconnection and the sawtooth crash are discussed

207

Effect of collisions and magnetic convergence on electron acceleration and transport in reconnecting twisted solar flare loops  

CERN Document Server

We study a model of particle acceleration coupled with an MHD model of magnetic reconnection in unstable twisted coronal loops. The kink instability leads to the formation of helical currents with strong parallel electric fields resulting in electron acceleration. The motion of electrons in the electric and magnetic fields of the reconnecting loop is investigated using a test-particle approach taking into account collisional scattering. We discuss the effects of Coulomb collisions and magnetic convergence near loop footpoints on the spatial distribution and energy spectra of high-energy electron populations and possible implications on the hard X-ray emission in solar flares.

Gordovskyy, M; Kontar, E P; Bian, N H

2015-01-01

208

Places available  

CERN Multimedia

If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. Places available The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses : Introduction à Outlook : 19.8.2004 (1 journée) Outlook (short course I) : E-mail : 31.8.2004 (2 hours, morning) Outlook (short course II) : Calendar, Tasks and Notes : 31.8.2004 (2 hours, afternoon) Instructor-led WBTechT Study or Follow-up for Microsoft Applications : 7.9.2004 (morning) Outlook (short course III) : Meetings and Delegation : 7.9.2004 (2 hours, afternoon) Introduction ...

2004-01-01

209

Places disponibles*/Places available **  

CERN Multimedia

Des places sont disponibles dans les cours suivants : Places are available in the following course : Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 20 - 22.1.03 (3 days) Introduction to PVSS : 27.1.03 (Afternoon) free course but registration necessary Basic PVSS : 28 - 30.1.03 (3 days) MAGNE-03 - Magnétisme pour l'électrotechnique : 28 - 30.1.03 (3 jours) MAGNE-03 - Magnetism for Technical Electronics : 11 - 13.2.03 (3 days) AutoCAD 2002 - niveau 1 : 24, 25.2 et 3, 4.3.03 (4 jours) AutoCAD 2002 - niveau 2 : 10 & 11.3.03 (2 jours) C++ for Particle Physicists : 10 - 14.3.03 (6 X 3 hour lectures) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 17, 18, 24 & 25.3.03 (6 jours) * Etant donné le délai d'impression du Bulletin, ces places peuvent ne plus être disponibles au moment de sa parution. Veuillez consulter notre site Web pour avoir la dernière mise à jour. ** The number of places available may vary. Please check our Web site to find out the current availability. Si vous désirez ...

2003-01-01

210

A Next Generation Magnetic Reconnection Experiment: Accessing ``Reconnection Phase Diagrams'' for Space and Astrophysical Relevances  

Science.gov (United States)

Ongoing dedicated laboratory experiments, such as Magnetic Reconnection Experiment (MRX), have been productive in providing original and valuable data in achieving much needed understanding of fast reconnection and associated processes. However, further critical contributions to astrophysical plasmas are limited by the achievable parameters. In this paper, we discuss results from our ongoing effortsfootnotetextH. Ji et al., APS 51st DPP Annual Meeting (November, 2009), http://meetings.aps.org/link/BAPS.2009.DPP.TP8.111 to develop plans for a next-generation reconnection experiment based on MRX. Most recent results from two-dimentional, large-scale numerical simulations suggest the existence of a reconnection phase diagram'', which illustrates phase transitions'' between different states'' or regimes. They include collisional MHD without plasmoids regime'', collisional MHD with plasmoids regime'', kinetic and MHD hybrid regime'', and collisionless regime''. The latter three regimes are considered to be relevant to reconnection in solar tachocline, solar corona, and Earth's magnetosphere. A natural goal for the next generation of reconnection experiments is the ability to access all of these regimes so that phase transitions can be studied in a controlled environment and the results are potentially applicable to astrophysical plasmas. Experimental requirements, aided by numerical simulations, will be discussed in detail.

Ji, H.; Yamada, M.; Prager, S.; Daughton, W.; Roytershteyn, V.

2010-11-01

211

Generation of Alfven Waves by Magnetic Reconnection  

CERN Document Server

In this paper, results of 2.5-dimensional magnetohydrodynamical simulations are reported for the magnetic reconnection of non-perfectly antiparallel magnetic fields. The magnetic field has a component perpendicular to the computational plane, that is, guide field. The angle theta between magnetic field lines in two half regions is a key parameter in our simulations whereas the initial distribution of the plasma is assumed to be simple; density and pressure are uniform except for the current sheet region. Alfven waves are generated at the reconnection point and propagate along the reconnected field line. The energy fluxes of the Alfven waves and sound waves generated by the magnetic reconnection are measured. Each flux shows the similar time evolution independent of theta. The percentage of the energies (time integral of energy fluxes) carried by the Alfven waves and sound waves to the released magnetic energy are calculated. The Alfven waves carry 38.9%, 36.0%, and 29.5% of the released magnetic energy at the...

Kigure, Hiromitsu; Shibata, Kazunari; Yokoyama, Takaaki; Nozawa, Satoshi

2010-01-01

212

Crossed Flux Tubes Magnetic Reconnection Experiment  

Science.gov (United States)

The dynamics of arched, plasma-filled flux tubes have been studied in experiments at Caltech. These flux tubes expand, undergo kink instabilities, magnetically reconnect, and are subject to magnetohydrodynamic forces. An upgraded experiment will arrange for two of these flux tubes to cross over each other. It is expected then that the flux tubes will undergo magnetic reconnection at the crossover point, forming one long flux tube and one short flux tube. This reconnection should also result in a half-twist in the flux tubes at the crossover point, which will propagate along each tube as Alfv'en waves. The control circuitry requires two independent floating high energy capacitor power supplies to power the plasma loops, which will be put in series when the plasma loops reconnect. Coordinating these two power supplies requires the building of new systems for controlling plasma generation. Unlike with previous designs, all timing functions are contained on a single printed circuit board, allowing the design to be easily replicated for use with each independent capacitor involved. The control circuit sequencing has been tested successfully in generating a single flux tube. The plasma gun is currently under construction, with its installation pending completion of prior experiments.

Tobin, Zachary; Bellan, Paul

2012-10-01

213

"Streamer Blob" Outflow from Interchange Reconnection  

Science.gov (United States)

Given the recent observational results of interchange reconnection processes in the solar corona and theoretical development of the S-Web model for the slow solar wind, we present further analysis of the 3D MHD simulation of interchange reconnection by Edmondson et al. (2009). Specifically, we will analyze the observable properties of the dynamic streamer belt jump that corresponds to previously closed streamer belt flux opening up via interchange reconnection. We quantify the system's kinetic energy and open flux evolution in time and show that the material released from the reconnection region outflow is qualitatively similar to the transient slow solar wind features known as "streamer blobs". Our simulation results imply that the commonly accepted interpretation of streamer blobs as small-scale magnetic flux-ropes may not be universally applicable. Additionally, we examine the synthetic emission from the density evolution above the surface and show the correspondence between coronal "dimming" and the opening up of previously closed flux. We will discuss future improvements to the MHD simulations that include a solar wind outflow and more rigorous comparisons to observations. BJL and YL acknowledge support from NASA HGI NNX08AJ04G and JKE acknowledges support from the NASA Postdoctoral Program.

Lynch, Benjamin J.; Edmondson, J. K.; Li, Y.

2011-05-01

214

Relaxation, Reconnection and the MHD dynamo  

International Nuclear Information System (INIS)

By considering a turbulence driven reconnection process we calculate the helicity transport across flux surfaces to produce a mean field representation undefined parameters. This model shows that in order to transport helicity, energy must be anomalously dissipated. The implications and results of this model with respect to mean field profiles, anomalous ion heating and edge effects are discussed. (author) 6 refs., 4 figs

215

Gyro-induced acceleration of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large ??), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence of the fact that the peak instantaneous growth rate becomes weakly dependent on the microscopic plasma parameters if the diffusion region thickness is sufficiently smaller than the equilibrium magnetic field scale length. When this condition is satisfied, the peak reconnection rate asymptotes to a constant value.

Comisso, L.; Grasso, D. [Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy); Istituto dei Sistemi Complessi - CNR, Via dei Taurini 19, 00185 Roma (Italy); Waelbroeck, F. L. [Institute for Fusion Studies, The University of Texas at Austin, Austin, Texas 78712-1060 (United States); Borgogno, D. [Dipartimento Energia, Politecnico di Torino, Corso Duca degli Abruzzi 24, 10129 Torino (Italy)

2013-09-15

216

Gyro-induced acceleration of magnetic reconnection  

International Nuclear Information System (INIS)

The linear and nonlinear evolution of magnetic reconnection in collisionless high-temperature plasmas with a strong guide field is analyzed on the basis of a two-dimensional gyrofluid model. The linear growth rate of the reconnecting instability is compared to analytical calculations over the whole spectrum of linearly unstable wave numbers. In the strongly unstable regime (large ??), the nonlinear evolution of the reconnecting instability is found to undergo two distinctive acceleration phases separated by a stall phase in which the instantaneous growth rate decreases. The first acceleration phase is caused by the formation of strong electric fields close to the X-point due to ion gyration, while the second acceleration phase is driven by the development of an open Petschek-like configuration due to both ion and electron temperature effects. Furthermore, the maximum instantaneous growth rate is found to increase dramatically over its linear value for decreasing diffusion layers. This is a consequence of the fact that the peak instantaneous growth rate becomes weakly dependent on the microscopic plasma parameters if the diffusion region thickness is sufficiently smaller than the equilibrium magnetic field scale length. When this condition is satisfied, the peak reconnection rate asymptotes to a constant value

217

A MAGNETIC RECONNECTION MECHANISM FOR THE GENERATION OF ANOMALOUS COSMIC RAYS  

International Nuclear Information System (INIS)

The recent observations of the anomalous cosmic ray (ACR) energy spectrum as Voyager 1 and Voyager 2 crossed the heliospheric termination shock have called into question the conventional shock source of these energetic particles. We suggest that the sectored heliospheric magnetic field, which results from the flapping of the heliospheric current sheet, piles up as it approaches the heliopause, narrowing the current sheets that separate the sectors and triggering the onset of collisionless magnetic reconnection. Particle-in-cell simulations reveal that most of the magnetic energy is released and most of this energy goes into energetic ions with significant but smaller amounts of energy going into electrons. The energy gain of the most energetic ions results from their reflection from the ends of contracting magnetic islands, a first-order Fermi process. The energy gain of the ions in contracting islands increases their parallel (to the magnetic field B) pressure p|| until the marginal fire-hose condition is reached, causing magnetic reconnection and associated particle acceleration to shut down. Thus, the feedback of the self-consistent development of the energetic ion pressure on reconnection is a crucial element of any reconnection-based, particle-acceleration model. The model calls into question the strong scattering assumption used to derive the Parker transport equation and therefore the absence of first-order Fermi acceleration in incompressible flows.ermi acceleration in incompressible flows. A simple one-dimensional model for particle energy gain and loss is presented in which the feedback of the energetic particles on the reconnection drive is included. The ACR differential energy spectrum takes the form of a power law with a spectral index slightly above 1.5. The model has the potential to explain several key Voyager observations, including the similarities in the spectra of different ion species.

218

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If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.TECHNICAL TRAINING Monique Duval tel. 74924 technical.training@cern.ch ** The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses: The JAVA Programming Language Level 1 : 9 & 10.1.2004 (2 days) The JAVA Programming Language Level 2 : 11 to 13.1.2004 (3 days) LabVIEW base 1 : 25 - 27.2.2004 (3 jours) CLEAN-2002 : Working in a Cleanroom : 10.3.2004 (afternoon - free of charge) C++ for Particle Physicists : 8 - 12.3.2004 ( 6 X 4-hour sessions) LabVIEW Basics 1 : 22 - 24.3.20...

2004-01-01

219

Places available**  

CERN Multimedia

If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. TECHNICAL TRAINING Monique Duval Tel. 74924 technical.training@cern.ch ** The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses: JAVA 2 Enterprise Edition - Part 1 : WEB Applications : 20 & 21.11.03(2 days) FrontPage 2000 - niveau 1 : 20 & 21.11.03 (2 jours) Oracle 8i : SQL : 3 - 5.12.03 (3 days) Oracle 8i : Programming with PL/SQL : 8 - 10.12.03 (3 days) The JAVA Programming Language - leve...

2003-01-01

220

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CERN Multimedia

If you wish to participate in one of the following courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at: http://www.cern.ch/Training/ or fill in an "application for training" form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. TECHNICAL TRAINING Monique Duval tel. 74924 technical.training@cern.ch ** The number of places available may vary. Please check our Web site to find out the current availability. Places are available in the following courses: The JAVA Programming Language Level 1 :9 & 10.1.2004 (2 days) The JAVA Programming Language Level 2 : 11 to 13.1.2004 (3 days) Hands-on Introduction to Python Programming : 16 - 18.2.2004 (3 days - free of charge) CLEAN-2002 : Working in a Cleanroom : 10.3.2004 (afternoon - free of charge) C++ for Particle Physicists : 8 - 12.3.2004...

2004-01-01

221

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222

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2003-01-01

223

Places available **  

CERN Multimedia

Des places sont disponibles dans les cours suivants : Places are available in the following courses : C++ for Particle Physicists : 10 - 14.3.03 (6 X 3-hour lectures) Introduction to PVSS : 10.3.03 (half day, afternoon) Basic PVSS : 11 - 13.3.03 (3 days) PVSS - JCOP Framework Tutorial : 14.3.03 (1 day) CLEAN-2002 : Working in a cleanroom : 2.4.03 (half-day, afternoon, free course, registration required) LabView base 1/LabView Basics 1 : 9 - 11.4.03 (3 jours/3 days) Langue à définir/language to be decided DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) AutoCAD 2002 - niveau 1 : 29, 30.4 et 7, 8.5.03 (4 jours) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03 (6 jours) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 11 & 12.3.03 / 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 31.3 - 4.4.03 / 16...

2003-01-01

224

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CERN Multimedia

Des places sont disponibles dans les cours suivants : Places are available in the following courses : Introduction à Windows 2000 au CERN : 25.2.03 (1/2 journée) LabView base 2/LabView Basics 2 : 10 & 11.3.03 (2 jours/2 days) langue à définir/Language to be decided C++ for Particle Physicists : 10 - 14.3.03 (6 X 3-hour lectures) Introduction to PVSS : 10.3.03 (half day, afternoon) Basic PVSS : 11 - 13.3.03 (3 days) LabView avancé /LabView Advanced : 12 - 14.3.03 (3 jours/3days) Langue à définir/Language to be decided AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 17, 18, 24 & 25.3.03 (6 jours) PVSS - JCOP Framework Tutorial : 14.3.03 (1 day) CLEAN-2002 : Working in a cleanroom : 2.4.03 (half-day, afternoon, free course, registration required) LabView base 1/LabView Basics 1 : 9 - 11.4.03 (3 jours/3 days) Langue à définir/Language to be decided DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (...

2003-01-01

225

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Des places sont disponibles dans les cours suivants : Places are available in the following courses : WorldFIP 2003 pour utilisateurs : 11-14.2.03 (4 jours) DISP-2003 ? Spring I Term : Introduction to Digital Signal Processing : 20, 27.2, 6, 13, 20, 27.3, 3.4.03 (7 X 2-hour lectures) AXEL-2003 - Introduction to Accelerators : 24-28.2.03 (10 X 1-hour lectures) AutoCAD 2002 - niveau 1 : 24, 25.2 & 3, 4.3.03 (4 jours) Introduction à Windows 2000 au CERN : 25.2.03 (1/2 journée) LabView base 2/LabView Basics 2 : 10 & 11.3.03 (2 jours/2 days) langue à définir/Language to be decided C++ for Particle Physicists : 10 ? 14.3.03 (6 X 3-hour lectures) Introduction to PVSS : 10.3.03 (half day, afternoon) Basic PVSS : 11 - 13.3.03 (3 days) LabView avancé /LabView Advanced : 12 - 14.3.03 (3 jours/3days) Langue à définir/language to be decided AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 17, 18, 24 & 25.3.03 (6 jours) PVSS - JCOP Framework Tutorial : 14.3.03 (1 day) MAGNE-03 - Magnetism for Technical Ele...

2003-01-01

226

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Places are available in the following courses: Hands-on Introduction to Python Programming: 11-13.08.2003(3 days) Introduction to the CERN Engineering Data Management System (EDMS): 26.08.2003 (1 day) The CERN Engineering Data Management System (EDMS) for Engineers: 27.08.2003 (1 day) CLEAN-2002 : Travailler en salle blanche : 4.09.2003 (une demi-journée) AutoCAD 2002 - Level 1: 4, 5, 15, 16.09.2003 (2 x 2 days) AutoCAD Mechanical 6 PowerPack : 17, 18, 25, 26.09.2003 et 2, 3.10.2003 (3 x 2 journées, français) AutoCAD 2002 - niveau 1 : 23, 24, 30.09.2003 et 1.10.2003 (2 x 2 journées) Introduction to the CERN Engineering Data Management System (EDMS): 23.09.2003 (1 day) The CERN Engineering Data Management System (EDMS) for Local Administrators: 24-25.09.2003 (2 days) AutoCAD 2002 - niveau 2 : 8 et 10.10.2003 (2 journées) CLEAN-2002: Working in a Cleanroom: 23.10.2003 (half day, p.m.) ** The number of places available may vary. Please ch...

2003-01-01

227

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Des places sont disponibles dans les cours suivants : Places are available in the following course : Introduction to the CERN Engineering Data Management System : 28.1.03 (1 day) AutoCAD 2002 - niveau 1 : 24, 25.2 et 3, 4.3.03 (4 jours) AutoCAD 2002 - niveau 2 : 27 & 28.2.03 (2 jours) C++ for Particle Physicists : 10 - 14.3.03 (6 X 3 hour lectures) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 17, 18, 24 & 25.3.03 (6 jours) CLEAN-2002 : Working in a cleanroom : 25.3.03 (half-day, afternoon, free course, registration required) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 11 & 12.3.03 / 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 31.3 - 4.4.03 / 16 - 20.6.03 (5 jours/5 days) Réseau Simatic Net /Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 Ces cours seront donnés en français ou anglais en fonction des demandes / These courses will be given in French or English following the requests. * Etant do...

2003-01-01

228

Privileged Girls: The Place of Femininity and Femininity in Place  

Science.gov (United States)

Constructions of femininity and attendant notions of feminism are being produced in different ways in different places around the world. This is a complicated global process that cannot be reduced to analyses that take place in nation states. This paper seeks to respond to and enhance Angela McRobbie's compelling argument about understandings…

Fahey, Johannah

2014-01-01

229

Three-dimensional magnetic reconnection through a moving magnetic null  

Directory of Open Access Journals (Sweden)

Full Text Available A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fields begin to reconnect at the null, subsequently displacing both the null and the reconnection site. The motion of the reconnection region and the magnetic null are shown to be correlated, with stronger correlation and faster reconnection observed in plasmas with lower thermal to magnetic pressure ratio. It is also shown that ion inertial effects allow for yet faster reconnection, but do not qualitatively change the dynamics of the process. Implications of the coupling between moving magnetic nulls and reconnection sites, as well as of possible mechanisms for fast reconnection through a moving reconnection region, are discussed. The simulations are conducted using both single-fluid and Hall MHD plasma models within the HiFi multi-fluid modeling framework.

V. S. Lukin

2011-11-01

230

Experimental study of ion heating and acceleration during magnetic reconnection  

International Nuclear Information System (INIS)

This dissertation reports an experimental study of ion heating and acceleration during magnetic reconnection, which is the annihilation and topological rearrangement of magnetic flux in a conductive plasma. Reconnection is invoked often to explain particle heating and acceleration in both laboratory and naturally occurring plasmas. However, a simultaneous account of reconnection and its associated energy conversion has been elusive due to the extreme inaccessibility of reconnection events, e.g. in the solar corona, the Earth's magnetosphere, or in fusion research plasmas. Experiments for this work were conducted on MRX (Magnetic Reconnection Experiment), which creates a plasma environment allowing the reconnection process to be isolated, reproduced, and diagnosed in detail. Key findings of this work are the identification of local ion heating during magnetic reconnection and the determination that non-classical effects must provide the heating mechanism. Measured ion flows are sub-Alfvenic and can provide only slight viscous heating, and classical ion-electron interactions can be neglected due to the very long energy equipartition time. The plasma resistivity in the reconnection layer is seen to be enhanced over the classical value, and the ion heating is observed to scale with the enhancement factor, suggesting a relationship between the magnetic energy dissipation mechanism and the ion heating mechanism. The observation of non-classical ion heating during reconnection has significant implications for understanding the role played by non-classical dissipation mechanisms in generating fast reconnection. The findings are relevant for many areas of space and laboratory plasma research, a prime example being the currently unsolved problem of solar coronal heating. In the process of performing this work, local measurements of ion temperature and flows in a well-characterized reconnection layer were obtained for the first time in either laboratory or observational reconnection research. Furthermore, much progress was made in understanding the reconnection process itself

231

Experimental study of ion heating and acceleration during magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

This dissertation reports an experimental study of ion heating and acceleration during magnetic reconnection, which is the annihilation and topological rearrangement of magnetic flux in a conductive plasma. Reconnection is invoked often to explain particle heating and acceleration in both laboratory and naturally occurring plasmas. However, a simultaneous account of reconnection and its associated energy conversion has been elusive due to the extreme inaccessibility of reconnection events, e.g. in the solar corona, the Earth's magnetosphere, or in fusion research plasmas. Experiments for this work were conducted on MRX (Magnetic Reconnection Experiment), which creates a plasma environment allowing the reconnection process to be isolated, reproduced, and diagnosed in detail. Key findings of this work are the identification of local ion heating during magnetic reconnection and the determination that non-classical effects must provide the heating mechanism. Measured ion flows are sub-Alfvenic and can provide only slight viscous heating, and classical ion-electron interactions can be neglected due to the very long energy equipartition time. The plasma resistivity in the reconnection layer is seen to be enhanced over the classical value, and the ion heating is observed to scale with the enhancement factor, suggesting a relationship between the magnetic energy dissipation mechanism and the ion heating mechanism. The observation of non-classical ion heating during reconnection has significant implications for understanding the role played by non-classical dissipation mechanisms in generating fast reconnection. The findings are relevant for many areas of space and laboratory plasma research, a prime example being the currently unsolved problem of solar coronal heating. In the process of performing this work, local measurements of ion temperature and flows in a well-characterized reconnection layer were obtained for the first time in either laboratory or observational reconnection research. Furthermore, much progress was made in understanding the reconnection process itself.

Hsu, S.C.

2000-01-28

232

Highly localized, fully 3-D disruptions of the reconnection layer in the Magnetic Reconnection Experiment  

Science.gov (United States)

Magnetic reconnection is a fundamental process in plasmas which converts magnetic energy to plasma kinetic and thermal energy through topological changes. One of the important goals in magnetic reconnection research is to explain the fast reconnection rate observed in real three-dimensional laboratory and astrophysical systems. In the Magnetic Reconnection Experiment (MRX), an enhancement of the reconnection electric field is often associated with a wholesale disruption of the reconnection current layer, an intrinsically 3-D phenomena observed in the presence of out-of-plane gradients of local quantities such as reconnection layer current and density. During a disruption, the out-of-plane current decreases as current carrying electrons are redirected in the outflow direction. Observed ``O-point'' signatures and density striations suggest that this redirection often occurs though the ejection of 3-D flux rope structures. Large fluctuations in the lower hybrid frequency range are also routinely seen, but the ratio of the phase speed to the diamagnetic drift speed does not match what is predicted by 3-D kinetic simulations without disruptions. A 2-D Hall MHD analysis of the out-of-plane gradients is consistent with the buildup of magnetic energy leading to the event [1], but variation in all three spacial dimensions is required in order to obtain results in agreement with the disruptive behavior observed. Analysis and comparison with 3-D simulations is ongoing to determine if the fluctuations and/or disruptive behavior are responsible for the corresponding discrepancies in the layer structure between the experiments and 2-D kinetic simulations [2,3,4]. Supported by DOE, NASA, and NSF. [4pt] [1] J.D. Huba and L.I. Rudakov, Phys. Plasmas 10, 3139 (2003).[0pt] [2] Y. Ren, et al., Phys. Plasmas 15, 082113 (2008).[0pt] [3] S. Dorfman, et al., Phys. Plasmas 15, 102107 (2008).[0pt] [4] V. Roytershteyn, et al., Phys. Plasmas 17, 055706 (2010).

Dorfman, Seth

2011-11-01

233

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Places are available in the following courses:   LabView hands-on 13.11.00 4 hours LabView Basics 1 14 - 16.11.00 3 days C++ for Particle Physicists 20 - 24.11.00 6 lectures Develop PL/SQL Program Units 20 - 22.11.00 3 days The JAVA programming Language level 2 27 - 29.11.00.00 3 days If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an ?application for training? form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

Enseignement Technique; Technical Training; Monique Duval - Tel. 74924

2000-01-01

234

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Places are available in the following courses: The JAVA programming language level 1: 8 - 9.2.01 (2 days) AutoCAD 2D niveau 1 : 12 - 16.2.01 (5 jours) The JAVA programming language level 2: 19 - 21.2.01 (3 days) C++ for Particle Physicists: 5 - 9.3.01 (20 hrs on 5 days) Contract Follow-up : 12.3.01 (3 heures) The JAVA programming language level 2: 12 - 14.3.01 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

235

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Places are available in the following courses: The CERN Engineering Data Management System for Advanced users :  13.6.02  (1 day) The CERN Engineering Data Management System for Local Administrators :  18.6.02  (1 day) AutoCAD 2002 - niveau 2 : 24 - 25.6.02 (2 jours) Frontpage 2000 - niveau 2 : 25 - 26.6.02 (2 jours) Object-oriented Analysis and Design :  2 - 5.7.02  (4 days) C++ Programming Level 2 - Traps & Pitfalls :  16 - 19.7.02  (4 days) C++ for Particle Physicists :  22 - 26.7.02  (6 * 3 hour lectures) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of the...

Monique Duval

2002-01-01

236

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2001-01-01

237

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2003-01-01

238

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Monique Duval

2002-01-01

239

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CERN Document Server

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Monique Duval

2002-01-01

240

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Places are available in the following courses: November 2002   Hands-on Object-Oriented Design and Programming with C++:  19 - 21.11.02  (3 days)  December 2002   LabVIEW - DSC (English) :  2 - 3.12.02  (2 days) AutoCAD 2002 - niveau 2 :  2 & 3.12.02  (2 jours) FileMaker (Français) :  2 - 5.12.02  (4 jours) PCAD Schémas - Débutants :  5 & 6.12.02  (2 jours) PCAD PCB - Débutants :  9 - 11.12.02  (3 jours) FrontPage 2000 - level 1:  9 & 10.12.02  (2 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisiona...

Monique Duval

2002-01-01

241

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CERN Multimedia

Places are available in the following courses: Introduction to Databases :  3 - 4.7.01 (2 days) The JAVA programming language Level 2 : 4 - 6.7.01 (3 days) Enterprise JavaBeans :  9 - 11.7.01 (3 days) Design Patterns :  10 - 12.7.01 (3 days) C++ for Particle Physicists :  23 - 27.7.01 (6 3-hour lectures) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

Technical Training; Tel. 74924

2001-01-01

242

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CERN Document Server

Places are available in the following courses: Introduction to Perl 5 : 2 - 3.7.01 (2 days) Introduction to Databases :  3 - 4.7.01 (2 days) JAVA programming language Level 2 : 4 - 6.7.01 (3 days) Enterprise JavaBeans :  9 - 11.7.01 (3 days) Design Patterns :  10 - 12.7.01 (3 days) C++ for Particle Physicists :  23 - 27.7.01 (6 3-hour lectures) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

Technical Training; Tel. 74924

2001-01-01

243

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: November 2002   Java Programming Language level 1 :  28 & 29.11.02  (2 days) December 2002   LabVIEW - DSC (English) :  2 - 3.12.02  (2 days) FileMaker (Français) :  2 - 5.12.02  (4 jours) PCAD Schémas - Débutants :  5 & 6.12.02  (2 jours) PCAD PCB - Débutants :  9 - 11.12.02  (3 jours) FrontPage 2000 - level 1:  9 & 10.12.02  (2 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt. Technical Training M...

Monique Duval

2002-01-01

244

Places disponibles*/Places available **  

CERN Multimedia

Des places sont disponibles dans les cours suivants : Places are available in the following course : WorldFIP 2003 pour utilisateurs : 11 - 14.2.03 (4 jours) AutoCAD 2002 - niveau 1 : 24, 25.2 & 3, 4.3.03 (4 jours) Introduction à Windows 2000 au CERN : 25.2.03 (1/2 journée) AutoCAD 2002 - niveau 2 : 27 & 28.2.03 (2 jours) C++ for Particle Physicists : 10 - 14.3.03 (6 X 3 hour lectures) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 17, 18, 24 & 25.3.03 (6 jours) CLEAN-2002 : Working in a cleanroom : 2.4.03 (half-day, afternoon, free course, registration required) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 11 & 12.3.03 / 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 31.3 - 4.4.03 / 16 - 20.6.03 (5 jours/5 days) Réseau Simatic Net /Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 Ces cours seront donnés en français ou anglais en fonction des demandes / These courses will be given in French o...

2003-01-01

245

Reconnection and electron temperature anisotropy in electron scale plasma turbulence  

CERN Document Server

We study the turbulent decay of fluctuations using results from 2D, particle-in-cell (PIC) collisionless plasma simulations with realistic electron-proton mass ratio and a guide field out of the simulation plane. A fluctuation power spectrum with approximately power law form is created down to scales of order the electron gyroradius. Where there is an X-point magnetic field line geometry we find signatures of reconnection such as electron bulk inflows and outflows. The reconnection signatures persist even when the reconnection sites are only several electron gyroradii across. Although the reconnection sites do not dominate the electron temperature variation, they are generally associated with regions of strong parallel electron temperature anisotropy. By tracking simulation particles we find that electrons are accelerated along the guide field near reconnection sites, and that in the reconnection outflows there is a mixing of electrons from spatially separated locations. The topology of magnetic field lines c...

Haynes, Christopher T; Camporeale, Enrico

2013-01-01

246

Particle trajectories and acceleration during 3D fan reconnection  

CERN Document Server

Context. The primary energy release in solar flares is almost certainly due to magnetic reconnection, making this a strong candidate as a mechanism for particle acceleration. While particle acceleration in 2D geometries has been widely studied, investigations in 3D are a recent development. Two main classes of reconnection regimes at a 3D magnetic null point have been identified: fan and spine reconnection Aims. Here we investigate particle trajectories and acceleration during reconnection at a 3D null point, using a test particle numerical code, and compare the efficiency of the fan and spine regimes in generating an energetic particle population. Methods. We calculated the time evolution of the energy spectra. We discuss the geometry of particle escape from the two configurations and characterise the trapped and escaped populations. Results. We find that fan reconnection is less efficent than spine reconnection in providing seed particles to the region of strong electric field where acceleration is possible...

Dalla, S; 10.1051/0004-6361:200809771

2008-01-01

247

Intermittent magnetic reconnection in TS-3 merging experiment  

International Nuclear Information System (INIS)

Ejection of current sheet with plasma mass causes impulsive and intermittent magnetic reconnection in the TS-3 spherical tokamak (ST) merging experiment. Under high guide toroidal field, the sheet resistivity is almost classical due to the sheet thickness much longer than the ion gyroradius. Large inflow flux and low current-sheet resistivity result in flux and plasma pileup followed by rapid growth of the current sheet. When the pileup exceeds a critical limit, the sheet is ejected mechanically from the squeezed X-point area. The reconnection (outflow) speed is slow during the flux/plasma pileup and is fast during the ejection, suggesting that intermittent reconnection similar to the solar flare increases the averaged reconnection speed. These transient effects enable the merging tokamaks to have the fast reconnection as well as the high-power reconnection heating, even when their current-sheet resistivity is low under high guide field.

248

Magnetic Reconnection with Radiative Cooling. I. Optically-Thin Regime  

CERN Document Server

Magnetic reconnection, a fundamental plasma process associated with a rapid dissipation of magnetic energy, is believed to power many disruptive phenomena in laboratory plasma devices, the Earth magnetosphere, and the solar corona. Traditional reconnection research, geared towards these rather tenuous environments, has justifiably ignored the effects of radiation on the reconnection process. However, in many reconnecting systems in high-energy astrophysics (e.g., accretion-disk coronae, relativistic jets, magnetar flares) and, potentially, in powerful laser plasma and z-pinch experiments, the energy density is so high that radiation, in particular radiative cooling, may start to play an important role. This observation motivates the development of a theory of high-energy-density radiative magnetic reconnection. As a first step towards this goal, we present in this paper a simple Sweet--Parker-like theory of non-relativistic resistive-MHD reconnection with strong radiative cooling. First, we show how, in the a...

Uzdensky, Dmitri A

2010-01-01

249

Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere  

CERN Document Server

Twisted coronal loops should be ubiquitous in the solar corona. Twisted magnetic fields contain excess magnetic energy, which can be released during magnetic reconnection, causing solar flares. The aim of this work is to investigate magnetic reconnection, and particle acceleration and transport in kink-unstable twisted coronal loops, with a focus on the effects of resistivity, loop geometry and atmospheric stratification. Another aim is to perform forward-modelling of bremsstrahlung emission and determine the structure of hard X-ray sources. We use a combination of magnetohydrodynamic (MHD) and test-particle methods. First, the evolution of the kinking coronal loop is considered using resistive MHD model, incorporating atmospheric stratification and loop curvature. Then, the obtained electric and magnetic fields and density distributions are used to calculate electron and proton trajectories using a guiding-centre approximation, taking into account Coulomb collisions. It is shown that electric fields in twist...

Gordovskyy, Mykola; Kontar, Eduard; Bian, Nicolas

2015-01-01

250

Magnetic reconnection in space and laboratory plasmas; Proceedings of the Chapman Conference on Magnetic Reconnection, Los Alamos, NM, October 3-7, 1983  

Science.gov (United States)

The physics of magnetic reconnection is discussed in reviews and reports of theoretical and experimental investigations. Topics examined include the theory of magnetic reconnection, reconnection in astronomical objects, reconnection in the earth magnetosphere and magnetotail, computer modeling, and laboratory plasmas. Diagrams, spectra, drawings, graphs, and photographs are provided.

Hones, E. W., Jr. (editor)

1984-01-01

251

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Base 2 : 18 & 19.10.01 (2 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Contract Follow-up (F) : 30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) Automates et réseaux de terrain : 13 & 14.11.01 (2 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introduction to C Programming :  21- 23.11.01 (3 days) The Java programming language Level 2:  26 - 28.11.01 (3 days) Programmation TSX Premium 2 : 26 ...

Technical Training; Tel. 74924

2001-01-01

252

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Cadence Board Design tools : Upgrading to release 14 :  3 1-day sessions on 9, 10 & 11.10.01 MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Base 2 : 18 & 19.10.01 (2 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Contract Follow-up (F) :  30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introduction to C Programming :  21- 23.11.01 (3 days) The Java programming language Level 2:  26 - 28.11.01 (...

Technical Training; Tel. 74924

2001-01-01

253

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à Windows 2000 au CERN : 2 sessions de _ journée les 24 et 25.9.01 PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) EXCEL 2000 - niveau 1 : 3 et 4.10.01 (2 jours) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) Introduction à Outlook : 5.10.01 (1 journée) Frontpage 2000 - niveau 1 : 8 et 9.10.01 (2 jours) C++ for Particle Physicists : 8 - 12.10.01 (6 lectures) MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) Programmation TSX Premium 1 : 15 - 19.10.01 (5 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2...

Technical Training; Tel. 74924

2001-01-01

254

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: EXCEL 2000 - niveau 1 : 3 et 4.10.01 (2 jours) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) Introduction à Outlook : 5.10.01 (1 journée) C++ for Particle Physicists : 8 - 12.10.01 (6 lectures) Cadence Board Design tools : Upgrading to release 14 : 3 1-day sessions on 9, 10 & 11.10.01 MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Base 2 : 18 & 19.10.01 (2 jours) WORD 2000 : importer et manipuler des images : 19.10.01 (1 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) The Java programming language Level 1: 8 - 9.11.01 (2 days) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introd...

Technical Training; Tel. 74924

2001-01-01

255

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: The JAVA programming language level 1 : 22 - 23.1.01 (2 days) Introduction to Databases : 23 - 24.1.01 (2 days) EXCEL : 24 - 25.1.01  et 1 - 2.2.01 (4 jours) Advanced and Modern Databases : 25 - 26.01.01 (2 days) UNIX pour non-programmeurs : 31.1 - 2.2.01 (3 jours) JAVA for non-programmers : 5 - 7.2.01 (3 days) Publier sur le Web :  6 - 8.2.01 (3 demi-journées) Contract Follow-up : 12.2.01 (3 heures) Introduction to Oracle SQL and PL/SQL : 12 - 16.2.01 (5 days) The JAVA programming language level 2 : 19 - 21.2.01 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order...

Technical Training; Tel. 74460

2001-01-01

256

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à PowerPoint : 26.2.01 (1 journée) Programmation TSX Premium 1 : 26.2 - 2.3.01 (5 jours) Premiers pas avec votre PC : 27.2 - 2.3.01 (4 matins) C++ for Particle Physicists :  5 - 9.3.01 (6*3 hour lectures) The CERN Engineering Data Management System for Electronic Design : 6.3.01 (1 day) The CERN Engineering Data Management System for Electronic Design : 7.3.01 (1 day) EXCEL : 6, 7 et 13, 14.3.01 (4 jours) The JAVA programming language level 2 : 12 - 14.3.01 (3 days) Nouveautés de FileMaker : 20 - 23.03.01 (4 matins) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be acc...

Technical Training; Tel. 74460

2001-01-01

257

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to Databases : 23 - 24.1.01 (2 days) Advanced and Modern Databases : 25 - 26.01.01 (2 days) UNIX pour non-programmeurs : 31.1 - 2.2.01 (3 jours) JAVA for non-programmers : 5 - 7.2.01 (3 days) Contract Follow-up : 12.2.01 (3 heures) Introduction to Oracle SQL and PL/SQL : 12 - 16.2.01 (5 days) AutoCAD 2D niveau I : 12 - 16.2.02 (5 jours) The JAVA programming language level 2 : 19 - 21.2.2001 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applications will be accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

258

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) Object-Oriented Analysis & Design: 16 - 19.4.02  (4 days) The CERN Engineering Data Management System for Advanced users:  16.4.02  (1 day) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) AutoCAD - niveau 1 : 22, 23, 29, 30.4 et 6, 7.5.02 (6 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) EXCEL 2000 - niveau 1 : 15 & 16.5.02 (2 jours) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours) LabVIEW Basics 1:  3 - 5.6.02&a...

Monique Duval

2002-01-01

259

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to C Programming :  21- 23.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Contract Follow-up (F) : 26.11.01 (1/2 journée) Habilitation électrique : électriciens network : 27 - 29.11.2001 (3 jours) Object-Oriented Analysis and Design :  27 - 30.11.2001  (4 days) Introduction to the CERN Engineering Data Management System :  30.11.2001 (1 day) Electromagnetic Compatibility (EMC): Introduction (bilingual) :  3.12.01 (half-day) Introduction to the CERN Engineering Data Management System : 07.12.2001 (1 day) LabVIEW - Basics 1 :  10 - 12.12.01 (3 days) LabVIEW - Basics 2 :  13 - 14.12.01 (2 days) EXCEL 2000 - niveau 2 : 15 - 16.1.02 (2 jours) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 days) Nouveautés de WORD 2000 : 18.1.02 (1/2 journée) FileMaker P...

Technical Training; Tel. 74924

2001-01-01

260

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à DesignSpace :  16.10.02  (1 journée) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS 21 - 25.10.02  (5 jours/days) HREF-2002: Helium Refrigeration Techniques (English-French, bilingual) :  21 - 25.10.2002  (7 half days) LabVIEW Basics 1 (English):  21 - 23.10.02  (3 days) LabVIEW Basics 2 (English):  24 & 25.10.02  (2 days) Oracle 8i : Access the Database with Java:  7 & 8.11.02  (2 days) AutoCAD 2002 - niveau 2 :  7 & 8.11.02  (2 jours) AutoCAD 2002 - Level 1:  14, 15, 21, 22.11.02  (4 days) LabVIEW - Advanced (English) :  18 - 20.11.2002  (3 days) AutoCAD 2002 - niveau 1 :  19, 20, 25, 26.11.02 (4 jours) Oracle iDS Designer: First Class:&...

Monique Duval

2002-01-01

261

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to Oracle 8i : SQL and PL/SQL:  7 - 11.10.02  (5 days) CLEAN-2002 : Working in a Cleanroom (free of charge):  10.10.02  (half-day, p.m.) AutoCAD 2002 - niveau 2 :  14 - 15.10.02  (2 jours) Introduction à DesignSpace :  16.10.02  (1 journée) Introduction to DesignSpace:  17.10.02  (1 day) AutoCAD 2002 - Level 1:  17, 18, 24, 25.10.02  (4 days) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS/Introduction to ANSYS (langue à définir suivant demande/ Language to be chosen according to demand):  21 - 25.10.02  (5 jours/days) HREF-2002: Helium Refrigeration Techniques (English-French, bilingual) :  21 - 25.10.2002  (7 half days) HREF-2002: Techniques de la Réfri...

Monique Duval

2002-01-01

262

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction to Oracle 8i : SQL and PL/SQL:  7 - 11.10.02  (5 days) CLEAN-2002 : Working in a Cleanroom (free of charge):  10.10.02  (half-day, p.m.) LabView Hands-on (bilingue/bilingual) : 10.10.02 (matin/morning) LabView DAQ Hands-on (bilingue/bilingual)  10.10.02 (après-midi /afternoon) Introduction à DesignSpace :  16.10.02  (1 journée) Introduction to DesignSpace:  17.10.02  (1 day) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS/Introduction to ANSYS (langue à définir suivant demande/ Language to be chosen according to demand):  21 - 25.10.02  (5 jours/days) HREF-2002: Helium Refrigeration Techniques (English-French, bilingual) :  21 - 25.10.2002  (7 half days) HREF-2002: Techniques de la...

Monique Duval

2002-01-01

263

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: LabView hands-on (bilingue/bilingual): 5.11.02 (matin/morning) LabView DAQ hands-on (bilingue/bilingual):  5.11.02  (après-midi afternoon) Introduction au PC et Windows 2000 au CERN:  6 & 7.11.02  (2 jours) Oracle 8i : Access the Database with Java:  7 & 8.11.02  (2 days) AutoCAD 2002 - niveau 2:  7 & 8.11.02  (2 jours) Introduction to PVSS (free of charge):  11.11.2002 pm  (1/2 day) Basic PVSS:  12 - 14.11.02  (3 days) EXCEL 2000 - niveau 1:  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free of charge):  13.11.2002  (afternoon) LabView Base 1 :  13 - 15.11.02  (3 jours) AutoCAD 2002 - Level 1:  14, 15, 21, 22.11.2002  (4 days) LabVIEW - Advanced:  18 - 20.11.02  (3 days) Auto...

Monique Duval

2002-01-01

264

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: November 2002   LabView hands-on (bilingue/bilingual): 5.11.02 (matin/morning) LabView DAQ hands-on (bilingue/bilingual):  5.11.02  (après-midi afternoon) PCAD Schémas - Débutants :  5 & 6.11.02  (2 jours) PCAD PCB - Débutants :  9 - 11.11.02  (3 jours) Introduction au PC et Windows 2000 au CERN :  6 & 7.11.02  (2 jours) Oracle 8i : Access the Database with Java :  7 & 8.11.02  (2 days) Introduction to PVSS (free of charge):  11.11.2002 pm  (1/2 day) Basic PVSS:  12 - 14.11.02  (3 days) EXCEL 2000 - niveau 1 :  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free of charge):  13.11.2002  (afternoon) LabView Base 1 :  13 - 15.11.02  (3 jours) AutoCAD 2002 - niveau 1 :  14, 15, 21, 22.11.02  (4 jours) LabVIEW - Advanced:  18 - 20.11.02  (3 days) Hands-on Object-Oriented Design and Programming with C++ :  19 - 21.11.02  (3 days)  LabVIEW - Basics 2:  21 - 22.11.02 ...

Monique Duval

2002-01-01

265

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) Programming the Web for Control Applications : 11, 12, 18, 19.3.2002  (4 * 2 hour lectures) Habilitation électrique : recyclage HT/BT (Français) : 13 - 14.3.2002 (2 * 2 heures) Introduction à la CAO CADENCE : 19 & 20.3.02 (2 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fil...

Monique Duval

2002-01-01

266

Places available**  

CERN Multimedia

Places are available in the following courses : DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) Oracle iDS Reports : Build Internet Reports : 5 - 9.5.03 (5 days) LabView DAQ (language to be defined) : 8 & 9.5.03 AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03 (6 jours) AutoCAD 2002 - niveau 2 : 3 & 4.6.03 (2 jours) LabView DSC (language to be defined) : 19 & 20.6.03 Siemens SIMATIC Training : Introduction to STEP7 : 3 & 4.6.03 (2 days) STEP7 Programming : 16 - 20.6.03 (5 days) Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 (sessions of 2 days) These courses will be given in French or English following the requests. Cours de sécurité : Etre TSO au CERN : Prochaines sessions : 24, 25 & 27.6.03 - 4, 5 & 7.11.03 (session de 3 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description ...

2003-01-01

267

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabView DAQ  (F) : 7 & 8.2.02 (2 jours) Hands-on Object-Oriented Design & Programming with Java :  11 - 13.02.02 (3 days) PVSS basics :  18 - 22.2.02 (5 days) Introduction à Windows 2000 : 18.2.02 (1 demi-journée) Introduction to the CERN Engineering Data Management System :  20.2.02 (1 day) Introduction à la CAO CADENCE : 20 & 21.2.02 (2 jours) The CERN Engineering Data Management System for Advanced users :  21.2.02  (1 day) LabView Basics 1 :  4 - 6.3.02  (3 days) Introduction au VHDL et utilisation du simulateur de CADENCE : 6 & 7.3.02 (2 jours) LabView Base 2 : 11 & 12.3.02 (2 jours) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) LabView Advanced :  13 - 15.3.02 (3 days) Cours sur la migration AutoCAD :   AutoCAD : Mise à...

Monique Duval

2002-01-01

268

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: PVSS basics :  18 - 22.2.02 (5 days) Introduction à la CAO CADENCE : 20 & 21.2.02 (2 jours) LabView Basics 1 :  4 - 6.3.02  (3 days) Introduction au VHDL et utilisation du simulateur de CADENCE : 6 & 7.3.02 (2 jours) LabView Base 2 : 11 & 12.3.02 (2 jours) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) LabView Advanced :  13 - 15.3.02 (3 days) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO...

Monique Duval

2002-01-01

269

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: PVSS Basics :  8 - 12.4.02  (5 days) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) Object-Oriented Analysis & Design: 16 - 19.4.02  (4 days) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) LabVIEW base 1 : 22 - 24.4.02 (3 jours) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) LabVIEW Basics 1:  3 - 5.6.02  (3 days) LabVIEW DAQ (E):  6 & 7.6.02  (2 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that...

Monique Duval

2002-01-01

270

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Habilitation électrique : recyclage HT/BT : 11 - 15.3.2002  (2 * 2 heures) PVSS Basics :  8 - 12.4.02  (5 days) ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Officer). Applica...

Monique Duval

2002-01-01

271

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses : Premiers pas avec votre PC 12 - 15.9.00 (4 demi-journées) WORD 20, 21 et 26, 27.9.2000 (4 jours) JAVA programming level 1 25 - 26.9.2000 (2 days) Gaz inflammables 1 26.9.2000 (1 journée) Advanced aspects of PERL 5 6.10.2000 (1 day) Initiation au WWW 10 - 12.10.00 (3 demi-journées) WORD : importer et manipuler des images 16.10.2000 (1 journée) FileMaker 17, 18 et 24, 25.10.00 (4 jours) Nouveautés de WORD 19 et 20.10.2000 (2 jours) ACCESS 1er niveau 30 - 31.10.00 (2 jours)Introduction à PowerPoint 6.11.00 (1 journée)Nouveautés d?EXCEL 7.11.2000(4 demi-journées)Excel 13, 14 et 20, 21.11.00 (4 jours) LabView hands-on 13.11.2000(4 hours)LabView Basics 1 14 - 16.11.2000 (3 days) MS-Project 1er niveau 14-17.11.00 (4 demi-journées) If you wish to participate in one of these courses, please discuss with your supervisor and apply elec...

Enseignement Technique; Tél. 74924; Technical Training; Monique Duval; Tel. 74924

2000-01-01

272

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Habilitation électrique : superviseurs : 5.12.01 (1/2 journée) LabVIEW - Basics 1 :  10 - 12.12.01 (3 days) Introduction au PC et Windows 2000 : 12 & 14.12.01 (2 jours) LabVIEW - Basics 2 :  13 - 14.12.01 (2 days) Habilitation électrique : superviseurs : 17.12.2001 (1/2 journée) EXCEL 2000 - niveau 2 : 15 - 16.1.02 (2 jours) Sécurité dans les installations cryogéniques: 15-17.1.2002 (2 demi-journées) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 days) ELEC-2002 Winter Term: Readout and system electronics for Physics  15.1.2002 - 7.2.2002 (8 half- days) Nouveautés de WORD 2000 : 18.1.02 (1/2 journée) LabView hands-on : 21.01.02 (1/2 journée) LabView DAQ hands-on : 21.01.02 (1/2 journée) FileMaker Pro : 22 - 25.1.02 (4 jours) Frontpage...

Technical Training; Tel.74924

2001-01-01

273

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabVIEW - Basics 1 :  10 - 12.12.01 (3 days) Introduction to XML :  12 & 13.12.01 (2 days) Introduction au PC et Windows 2000 : 12 & 14.12.01 (2 jours) LabVIEW - Basics 2 :  13 - 14.12.01 (2 days) Habilitation électrique : superviseurs : 17.12.2001 (1/2 journée) MS-Project 2000 : 10 & 11.01.02 (2 jours) EXCEL 2000 - niveau 2 : 15 - 16.1.02 (2 jours) Sécurité dans les installations cryogéniques: 15-17.1.2002 (2 demi-journées) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 days) ELEC-2002 Winter Term: Readout and system electronics for Physics  15.1.2002 - 7.2.2002 (8 half- days) Nouveautés de WORD 2000 : 18.1.02 (1/2 journée) LabView hands-on : 21.01.02 (1/2 journée) LabView DAQ hands-on : 21.01.02 (1/2 journée) FileMaker Pro : 22 -...

Technical Training; Tel. 74924

2001-01-01

274

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: MS-Project 2000 : 10 & 11.01.02 (2 jours) EXCEL 2000 - niveau 2 : 15 - 16.1.02 (2 jours) Sécurité dans les installations cryogéniques: 15-17.1.2002 (2 demi-journées) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 days) ELEC-2002 Winter Term: Readout and system electronics for Physics  15.1.2002 - 7.2.2002 (8 half- days) Nouveautés de WORD 2000 : 18.1.02 (1/2 journée) LabView hands-on : 21.01.02 (1/2 journée) LabView DAQ hands-on : 21.01.02 (1/2 journée) FileMaker Pro : 22 - 25.1.02 (4 jours) MS-Project 2000 : 24 & 25.01.02 (2 jours) Introduction au PC et à Windows 2000 au CERN : 29 - 30.1.02 (2 jours) LabView Base 1 : 4 - 6.2.02 (3 jours) LabView DAQ  (E) :  7 & 8.02.02 (2 days) Hands-on Object-Oriented Design & Programming with Java :&nbs...

Enseignement Technique; Tel. 74924

2001-01-01

275

PLACES AVAILABLES  

CERN Multimedia

Places are available in the following courses:   C++ for Particle Physicists 20 - 24.11.00 6 lectures CANbus 20.11.00 1 journée CANopen 21 et 22.11.00 2 jours Sécutiré dans les installations cryogéniques 21 et 22.11.00 2 demi-journées The JAVA programming language level 2 27 ­ 29.11.00 3 days Contract Follow-up 27.11.00 3 heures 1/2 Cryogénie (introduction) 4 ­ 8.12.00 ANSYS Introduction : langue a décider suivant majorité 5 ­ 7.12.00 3 jours EXCEL 7, 8, 13 et 14.12.00 4 jours Contract Follow-up 15.12.00 3 heures 1/2 If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an ?application for training? form available from your Divisional Secretariat or from your DTO (Divisional Training Officer)....

Technical Training; Tel. 74924

2000-01-01

276

Places available**  

CERN Document Server

Places are available in the following courses: CLEAN-2002 : Travailler en salle blanche (séminaire gratuit) : 4.9.03 (une demi-journée) The CERN EDMS for Local Administrators (free of charge) : 24 & 25.9.03 (2 days) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) AutoCAD Mechanical 6 PowerPack (E) : 23, 24, 30, 31.10 & 12, 13.11.03 (6 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours)...

2003-01-01

277

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Java 2 Enterprise Edition - Part 2: Enterprise JavaBeans:  18 - 20.9.02  (3 days) AutoCAD 2002 - niveau 1 :  19, 20, 26, 27.9.02  (4 jours) LabView Base 1 :  23 - 25.9.02  (3 jours) Object-Oriented Analysis & Design using UML:  25 - 27.9.02  (3 days) LabView DAQ (E):  26 - 27.9.02  (2 days) Introduction to Oracle 8i : SQL and PL/SQL:  7 - 11.10.02  (5 days) CLEAN-2002 : Working in a Cleanroom (free of charge):  10.10.02  (half-day, p.m.) AutoCAD 2002 - niveau 2 :  14 - 15.10.02  (2 jours) Introduction à DesignSpace :  16.10.02  (1 journée) Introduction to DesignSpace:  17.10.02  (1 day) AutoCAD 2002 - Level 1:  17, 18, 24, 25.10.02  (4 days) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11....

Monique Duval

2002-01-01

278

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: LabView Base 1 :  23 - 25.9.02  (3 jours) Object-Oriented Analysis & Design using UML:  25 - 27.9.02  (3 days) LabView DAQ (E):  26 - 27.9.02  (2 days) Introduction to Oracle 8i : SQL and PL/SQL:  7 - 11.10.02  (5 days) CLEAN-2002 : Working in a Cleanroom (free of charge):  10.10.02  (half-day, p.m.) AutoCAD 2002 - niveau 2 :  14 - 15.10.02  (2 jours) Introduction à DesignSpace :  16.10.02  (1 journée) Introduction to DesignSpace:  17.10.02  (1 day) AutoCAD 2002 - Level 1:  17, 18, 24, 25.10.02  (4 days) AutoCAD Mechanical 6 PowerPack (F) :  21, 22, 23.10 et 4, 5, 6.11.02  (6 jours) Introduction à ANSYS/Introduction to ANSYS (langue à définir suivant demande/ Language to be chosen according to demand):...

Monique Duval

2002-01-01

279

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Contract Follow-up (F) : 30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) Nouveautés d'Excel 2000 : 5.11.01 (1/2 journée) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) Introduction à Windows 2000 au CERN : 6.11.01 (1/2 journée) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) LabVIEW DAQ (F) : 15 & 16.11.01 (2 jours) Automates et réseaux de terrain : 13 & 14.11.01 (2 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) LabVIEW - DAQ : 15 - 16.11.01 (2 jours) Introduction to XML :  19 - 20.11.01 (2 days) Introduction to C Programming :  21- 23.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Object-Oriented Analysis and Design :  27 - 30.11.2001 (4 days) Hands...

Technical Training; Tel. 74924

2001-01-01

280

Places available**  

CERN Document Server

Places are available in the following courses : The CERN EDMS for Local Administrators : 24 & 25.9.03 (2 days, free of charge) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom : 23.10.03 (half day, free of charge) AutoCAD 2002 - Level 1 : 3, 4, 12, 13.11.03 (4 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours) ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) AutoCAD Mechanical 6 PowerPack (E) : 17, 18, 24, 25.11 & 1, 2.12.03 (6...

2003-01-01

281

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: Utilisation du simulateur Simplorer : 30.5 - 1.6.01 (3 jours) JAVA programming language level 1: 11-12.6.01 (2 days) LabView hands-on F ou E : 11.6.01 (1/2 journée) Comprehensive VHDL for EPLD/FPGA Design : 11 - 15.6.01 (5 days) Introduction au Langage C : 13 - 15.6.01 (3 jours) LabView Base 1 : 12 - 14.6.01 (3 jours) Habilitation électrique : superviseurs : 2 sessions d'une demi-journée les 12 et 19.6.01 Migration de LabVIEW 5 vers LabVIEW 6i Migration from LabVIEW 5 to LabVIEW 6I :  15.6.01 (1/2 journée/half-day) Introduction to Perl 5 : 2 - 3.7.01 (2 days) JAVA programming language level 2 : 4 - 6.7.01 (3 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : http://www.cern.ch/Training/ or fill in an 'application for training' form available from ...

Technical Training; Tel. 74924

2001-01-01

282

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Nouveautés d'EXCEL : 5.11.01 (1/2 journée) Introduction a Windows 2000 au CERN : 6.11.01 (1/2 journée) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) Design Patterns :  7 - 8.11.01 (2 days) The Java programming language Level 1: 8 - 9.11.01 (2 days) Automates et réseaux de terrain : 13 & 14.11.01 (3 jours) Introduction à Windows 2000 au CERN : 12 - 14.11.01 (1/2 journée) Introduction to Windows 2000 at CERN :  14.11.01  (half-day) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to C Programming :  21- 23.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Contract Follow-up (F) : 26.11.01 (1/2 journée) Object-Oriented Analysis and Design :  27 - 30.11.2001  (4 days) Hands-on Object-Oriented Design and Programming with C++ :  11 - 13.12.2...

Technical Training; Tel. 74924

2001-01-01

283

Places available**  

CERN Document Server

Places are available in the following courses: The CERN EDMS for Local Administrators (free of charge) : 24 & 25.9.03 (2 days) HeREF-2003 : Techniques de la réfrigération Hélium (cours en français avec support en anglais) : 6 - 10.10.2003 (7 demi-journées) The Java Programming Language Level 1 : 6 - 7.10.2003 (2 days) Java 2 Enterprise Edition - Part 2 : Enterprise JavaBeans : 8 - 10.10.2003 (3 days) FileMaker - niveau 1 : 9 & 10.10.03 (2 jours) EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) AutoCAD 2002 - niveau 1 : 20, 21, 27, 28.10.03 (4 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) AutoCAD Mechanical 6 PowerPack (E) : 23, 24, 30, 31.10 & 12, 13.11.03 (6 days) AutoCAD 2002 - niveau 2 : 10 & 11.11.03 (2 jours) ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) FrontPage 2000 - niveau 1 : 20...

2003-01-01

284

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: Contract Follow-up (F) : 30.10.01 (1/2 journée) The CERN Engineering Data Management System for Electronics Design :  30.10.01 (1 day) UNIX pour non-programmeurs : 5 - 7.11.01 (3 jours) Nouveautés d'EXCEL : 5.11.01 (1/2 journée) Introduction a Windows 2000 au CERN : 6.11.01 (1/2 journée) The Java programming language Level 1: 8 - 9.11.01 (2 days) LabView Base 1 : 12 - 14.11.01 (3 jours) Automates et réseaux de terrain : 13 & 14.11.01 (2 jours) Introduction to PERL 5 :  15 - 16.11.01  (2 days) Introduction to XML :  19 - 20.11.01 (2 days) Programming TSX Premium 1 :  19 - 23.11.01  (5 days) Introduction to C Programming :  21- 23.11.01 (3 days) The Java programming language Level 2:  26 - 28.11.01 (3 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Autocad Migration support courses: a detail...

Technical Training; Tel. 74924

2001-01-01

285

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: ELEC-2002 : Spring Term :  9, 11, 16, 18, 23, 25, 30.4.02 (7 * 2.5 hours) Object-Oriented Analysis & Design: 16 - 19.4.02  (4 days) The CERN Engineering Data Management System for Advanced users:  16.4.02  (1 day) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) AutoCAD - niveau 1 : 22, 23, 29, 30.4 et 6, 7.5.02 (6 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) Cotations selon les normes GPS de l'ISO : 29 - 30.4.02 (2 jours) Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2 : 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-...

Monique Duval

2002-01-01

286

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) Cotations selon les normes GPS de l'ISO : 29 - 30.4.02 (2 jours) Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2: 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-14, 17, 21, 27-28.5.02 (6 jours) WorldFIP - Généralités : 14.5.2002 (1/2 journée) WorldFIP - Développer avec MicroFIP HANDLER : 14.5 - après-midi, 15.5.02 - matin (1 jour) WorldFIP - FullFIP FDM : FIP Device Manager (F) : 15.5 - après-midi, 16.5.02 - matin (1 jour) LabVIEW DAQ (F) : 15 & 16.5.02 (2 jours) EXCEL 2000 - niveau 2 : 22 & 23.5.02 (2 jours)...

Monique Duval

2002-01-01

287

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: The CERN Engineering Data Management System for Advanced users : 16.4.02  (1 day) Migration from AutoCAD 14 towards AutoCAD Mechanical6 PowerPack:  17 - 19.4 and 2 &3.5.02  (5 days) AutoCAD - niveau 1 : 22, 23, 29, 30.4 et 6, 7.5.02 (6 jours) LabVIEW base 1 : 22 - 24.4.02 (3 jours) CLEAN 2002 : working in a cleanroom:  24.4.02  (half-day, pm) LabVIEW DSC (F) 25 & 26.4.02 (2 jours) AutoCAD : Mise à jour AutoCAD r-14 vers 2002 : 25 & 26.4.02 (2 jours) Cotations selon les normes GPS de l'ISO : 29 - 30.4.02 (2 jours) Introduction to the CERN Engineering Data Management System:  7.5.02  (1 day) LabVIEW Basics 2: 13 & 14.5.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 13-14, 17, 21, 27-28.5.02 (6 jours) WorldFIP - Généralités : 14.5.2002 (1/2 journée) WorldFIP - Développer avec Micr...

Monique Duval

2002-01-01

288

Places available**  

CERN Multimedia

Places are available in the following courses : CLEAN-2002 : Working in a cleanroom (free course, registration required): 11.4.03 (half-day, afternoon, ) LabView Basics 2 : 10 - 11.4.03 (3 days) DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) AutoCAD 2002 - niveau 1 : 29, 30.4 et 7, 8.5.03 (4 jours) Oracle iDS Reports : Build Internet Reports : 5 - 9.5.03 (5 days) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03(6 jours) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 31.3 - 4.4.03 / 16 - 20.6.03 (5 jours/5 days) Réseau Simatic Net /Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 These courses will be given in French or English following the requests. Cours de sécurité : Etre TSO au CERN : Prochaines sessions : 24, 25 & 27.6...

2003-01-01

289

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Introduction à la CAO CADENCE : 20 & 21.2.02 (2 jours) LabView Basics 1 :  4 - 6.3.02  (3 days) Introduction au VHDL et utilisation du simulateur de CADENCE : 6 & 7.3.02 (2 jours) CLEAN-2002 : Working in a Clean Room :  7.3.2002  (1 day) LabView Base 2 : 11 & 12.3.02 (2 jours) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) LabView Advanced :  13 - 15.3.02 (3 days) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisiona...

Monique Duval

2002-01-01

290

Places available**  

CERN Multimedia

Places are available in the following courses : CLEAN-2002 : Working in a cleanroom (free course, registration required): 11.4.03 (half-day, afternoon) LabView Basics 2 : 10 - 11.4.03 (3 days) DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) AutoCAD 2002 - niveau 1 : 29, 30.4 et 7, 8.5.03 (4 jours) Oracle iDS Reports : Build Internet Reports : 5 - 9.5.03 (5 days) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03(6 jours) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 16 - 20.6.03 (5 jours/5 days) Réseau Simatic Net /Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 These courses will be given in French or English following the requests. Cours de sécurité : Etre TSO au CERN : Prochaines sessions : 24, 25 & 27.6.03 - 4, 5 & 7....

2003-01-01

291

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabView Hands-on (bilingue/bilingual - gratuit/free of charge) : 13.9.02 (a.m.) LabView DAQ Hands-on (bilingue/bilingual - gratuit/free of charge) : 13.9.02 (p.m.) AutoCAD 2002 - niveau 1 : 19, 20, 26, 27.9.02 (4 jours) LabView Base 1 : 23 - 25.9.02 (3 jours) LabView DAQ (E) : 26 - 27.9.02 (2 days) AutoCAD Mechanical 6 PowerPack (F) : 30.9, 1, 2, 9, 10, 11.10.02 (6 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 10.10.02 (half-day, p.m.) AutoCAD 2002 - niveau 2 : 14 - 15.10.02 (2 jours) AutoCAD 2002 - Level 1 : 17, 18, 24, 25.10.02 (4 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the course description pages that can be found on the Web at : Technical Training or fill in an 'application for training' form available from your Divisional Secretariat or from your DTO (Divisional Training Of...

Monique Duval

2002-01-01

292

Places available **  

CERN Multimedia

Places are available in the following courses : CLEAN-2002 : Working in a cleanroom (free course, registration required): 11.4.03 (half-day, afternoon, ) LabView Basics 2 : 10 - 11.4.03 (3 days) DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) AutoCAD 2002 - niveau 1 : 29, 30.4 et 7, 8.5.03 (4 jours) Oracle iDS Reports : Build Internet Reports : 5 - 9.5.03 (5 days) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03 (6 jours) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 31.3 - 4.4.03 / 16 - 20.6.03 (5 jours/5 days) Réseau Simatic Net /Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 These courses will be given in French or English following the requests. Cours de sécurité : Etre TSO au CERN : Prochaines sessions : 24, 25 & 27.6....

2003-01-01

293

Places available**  

CERN Multimedia

Places are available in the following courses : Introduction to PVSS : 10.3.03 (half-day, afternoon) CLEAN-2002 : Working in a cleanroom : 2.4.03 (half-day, afternoon, free course, registration required) LabView Basics 1 : 9 - 11.4.03 (3 days) Language to be decided. DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures). AutoCAD 2002 - niveau 1 : 29, 30.4 et 7, 8.5.03 (4 jours) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03 (6 jours) Siemens SIMATIC Training: Introduction to STEP7 : 3 & 4.6.03 (2 days) STEP7 Programming : 31.3 - 4.4.03 / 16 - 20.6.03 (5 days) Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 These courses will be given in French or English following the requests. Cours de sécurité: Etre TSO au CERN : 3 sessions sont programmées pour 2003 : 25, 26 & 28.3.03 - 24, 25 & 27.6.03 - 4, 5 & 7.11.03 (sessions de 3 jours) ** The number o...

2003-01-01

294

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabView Basics 1 :  4 - 6.3.02  (3 days) CLEAN-2002 : Working in a Clean Room :  7.3.2002  (half day) LabView Base 2 : 11 & 12.3.02 (2 jours) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) Programming the Web for Control Applications : 11, 12, 18, 19.3.2002  (4 * 2 hour lectures) Habilitation électrique : recyclage HT/BT (Français) : 13 - 14.3.2002 (2 * 2 heures) LabView Advanced :  13 - 15.3.02 (3 days) Introduction to the CERN Engineering Data Management System (EDMS) :  20.3.2002  (1 day) The CERN (EDMS) for Advanced Users :  21.3.2002  (1 day) LabVIEW DSC : 25 - 26.4.2002 (2 jours) LabVIEW DAQ : 15 - 16.5.2002 (2 jours) Cours sur la migration AutoCAD :   AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé ...

Monique DUVAL

2002-01-01

295

Places available**  

CERN Multimedia

Places are available in the following courses : CLEAN-2002 : Working in a cleanroom (free course, registration required) : 2.4.03 (half-day, afternoon) LabView base 1/LabView Basics 1 (Langue à définir/ language to be decided) : 9 - 11.4.03 (3 jours/3 days) DISP-2003 - Spring II Term : Advanced Digital Signal Processing : 30.4, 7, 14, 21.5.03 (4 X 2-hour lectures) AutoCAD 2002 - niveau 1 : 29, 30.4 et 7, 8.5.03 (4 jours) AutoCAD 2002 - niveau 2 : 5 & 6.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 20, 21, 27 & 28.5.03(6 jours) Formation Siemens SIMATIC /Siemens SIMATIC Training : Introduction à STEP7 /Introduction to STEP7 : 3 & 4.6.03 (2 jours/2 days) Programmation STEP7/STEP7 Programming : 31.3 - 4.4.03 / 16 - 20.6.03 (5 jours/5 days) Réseau Simatic Net /Simatic Net Network : 15 & 16.4.03 / 26 & 27.6.03 These courses will be given in French or English following the requests. Cours de sécurité : Etre TSO au CERN : 3 sessions sont programmées pour 2003 : 25...

2003-01-01

296

Episodic X-ray Emission Accompanying the Activation of an Eruptive Prominence: Evidence of Episodic Magnetic Reconnection  

CERN Document Server

We present an X-ray imaging and spectroscopic study of a partially occulted C7.7 flare on 2003 April 24 observed by RHESSI that accompanied a prominence eruption observed by TRACE. (1) The activation and rise of the prominence occurs during the preheating phase of the flare. The initial X-ray emission appears as a single coronal source at one leg of the prominence and it then splits into a double source. Such a source splitting happens three times, each coinciding with an increased X-ray flux and plasma temperature, suggestive of fast reconnection in a localized current sheet and an enhanced energy release rate. In the late stage of this phase, the prominence displays a helical structure. These observations are consistent with the tether-cutting or kink instability model for triggering solar eruptions. (2) The eruption of the prominence takes place during the flare impulsive phase. Since then, there appear signatures predicted by the classical CSHKP model of two-ribbon flares occurring in a vertical current s...

Liu, Wei W; Dennis, Brian R; Holman, Gordon D

2009-01-01

297

The auroral and ionospheric flow signatures of dual lobe reconnection  

OpenAIRE

We present the first substantial evidence for the occurrence of dual lobe reconnection from ionospheric flows and auroral signatures. The process of dual lobe reconnection refers to an interplanetary magnetic field line reconnecting with lobe field lines in both the northern and southern hemispheres. Two bursts of sunward plasma flow across the noon portion of the open/closed field line boundary (OCB), indicating magnetic flux closure at the dayside, were observed in SuperDARN radar data duri...

Imber, S. M.; Milan, S. E.; Hubert, B.

2006-01-01

298

Magnetic Reconnection in Non-Equilibrium Ionization Plasma  

OpenAIRE

We have studied the effect of time-dependent ionization and recombination processes on magnetic reconnection in the solar corona. Petschek-type steady reconnection, in which model the magnetic energy is mainly converted at the slow-mode shocks, was assumed. We carried out the time-dependent ionization calculation in the magnetic reconnection structure. We only calculated the transient ionization of iron; the other species were assumed to be in ionization equilibrium. The int...

Imada, S.; Murakami, I.; Watanabe, T.; Hara, H.; Shimizu, T.

2011-01-01

299

Cluster Spacecraft Observations of Magnetopause Reconnection at Multiple Scales  

Science.gov (United States)

Magnetic reconnection is an inherently multi-scale process where the dynamics at small-scales strongly affect the large-scale evolution of the process. The microphysics of reconnection (i.e. the physics at proton scales and below) is particularly important. Key questions are reconnection onset, time evolution (rate) and ion and electron heating/acceleration around reconnection sites. The Earth's magnetopause is an excellent laboratory for studying reconnection, especially at subsolar point where is more steady and easier to study with spacecraft data. Despite of initially being a high-latitude mission, ESA/Cluster spacecraft have crossed the subsolar magnetopause starting from 2008. During such recent orbits two spacecraft were separated by ~10s km (sub-proton/electron scales) while being apart ~ 1000s km (fluid scales) from the others. This special configuration allows studying reconnection at multiple scales. Here we present a few examples of magnetopause reconnection from such recent Cluster multi-scale orbits. For one case of subsolar reconnection, the observation of jet reversals at large scales allows setting the position of the reconnection site in between the spacecraft. Two-point observations at sub-proton/electron scales are then used to identify a very thin rotational discontinuity (having a thickness of about 10 electron gyroradii) and study the microphysics therein. We also show a few other examples of magnetopause reconnection from the Cluster Guest Investigator campaign (2012), for which orbit, spacecraft configuration and instrument modes were tailored to study reconnection at multiple scales. We discuss the relevance of such recent Cluster measurements for the reconnection science of upcoming NASA/MMS and other multi-scale future missions.

Retino, A.; Vaivads, A.; Chasapis, A.; Rossi, C.; Sahraoui, F.; Canu, P.; Nakamura, R.; Mozer, F.

2013-12-01

300

Is null-point reconnection important for solar flux emergence?  

OpenAIRE

The role of null-point reconnection in a 3D numerical MHD model of solar emerging flux is investigated. The model consists of a twisted magnetic flux tube rising through a stratified convection zone and atmosphere to interact and reconnect with a horizontal overlying magnetic field in the atmosphere. Null points appear as the reconnection begins and persist throughout the rest of the emergence, where they can be found mostly in the model photosphere and transition region, fo...

Maclean, R. C.; Parnell, C. E.; Galsgaard, K.

2009-01-01

301

Taking Leave?  

CERN Multimedia

Planning a holiday? Then if you're a member of the personnel, you'll need to use the Laboratory's new leave system that will be put in place on 1 October. Leave allocations don't change - you are entitled to just as much holiday as before - but instead of being credited annually, your leave will be credited on a monthly basis, and this information will be communicated on your salary slip. The reason for the change is that with the various new leave schemes such as Recruitment by Saved Leave (RSL) and the Progressive Retirement Programme (PRP), a streamlined procedure was required for dealing with all kinds of leave. In the new system, each member of the personnel will have leave accounts to which leave will be credited monthly from the payroll and debited each time an absence is registered in the CERN Electronic Document Handling system (EDH). Leave balances will appear on monthly pay slips, and full details of leave transactions and balances will be available through EDH at all times. As the leave will be c...

2000-01-01

302

Take heart!  

CERN Multimedia

Recently, ten new semi-automatic defibrillators were installed at various locations around CERN. This is a preventive measure intended to provide cardiac arrest victims with the best possible response. The first responder could be you!   The Director-General has welcomed the initiative of the Medical Service and Fire Brigade for the installation of ten new semi-automatic defibrillators. You have probably seen them on your way to the restaurant, for example:  brand new semi-automatic defibrillators, ready for an emergency. Housed in a white wall-mounted case, the bright red defibrillators are marked with a white heart symbol crossed by a lightning bolt (see photo). The defibrillator is designed so that anyone can use it. “Anyone can use it, you don’t need to be a health professional,” says Dr Reymond from CERN's Medical Service. Together with the CERN Fire Brigade, he is behind the initiative to have these units put in place. And with good reason, as the unit...

Alizée Dauvergne

2010-01-01

303

Introduction to Plasma Dynamo, Reconnection and Shocks  

Energy Technology Data Exchange (ETDEWEB)

In our plasma universe, most of what we can observe is composed of ionized gas, or plasma. This plasma is a conducting fluid, which advects magnetic fields when it flows. Magnetic structure occurs from the smallest planetary to the largest cosmic scales. We introduce at a basic level some interesting features of non linear magnetohydrodynamics (MHD). For example, in our plasma universe, dynamo creates magnetic fields from gravitationally driven flow energy in an electrically conducting medium, and conversely magnetic reconnection annihilates magnetic field and accelerates particles. Shocks occur when flows move faster than the local velocity (sonic or Alfven speed) for the propagation of information. Both reconnection and shocks can accelerate particles, perhaps to gigantic energies, for example as observed with 10{sup 20} eV cosmic rays.

Intrator, Thomas P. [Los Alamos National Laboratory

2012-08-30

304

Nonlinear magnetic reconnection in low collisionality plasmas  

International Nuclear Information System (INIS)

The magnetic reconnection in collisionless regimes, where electron inertia is responsible for the decoupling of the plasma motion from that of the field lines, is discussed. Since the linear theory of m=1 modes breaks down for very small magnetic island widths, a non linear analysis is called for. Thus, the behaviour of a collisionless, 2-D fluid slab model in the limit ?/d -> 0, is analyzed. The main result is that, when the island size is larger than the linear layer but smaller than the equilibrium scale length, the reconnection rate exhibits a quasi-explosive time behaviour, during which a current density sub-layer narrower than the skin depth is formed. It is believed that the inclusion of the electron initial term in Ohm's law opens the possibility to understand the rapidity of relaxation process observed in low collisionality plasmas. 7 refs., 6 figs

305

Space weather. Ionospheric control of magnetotail reconnection.  

Science.gov (United States)

Observed distributions of high-speed plasma flows at distances of 10 to 30 Earth radii (R(E)) in Earth's magnetotail neutral sheet are highly skewed toward the premidnight sector. The flows are a product of the magnetic reconnection process that converts magnetic energy stored in the magnetotail into plasma kinetic and thermal energy. We show, using global numerical simulations, that the electrodynamic interaction between Earth's magnetosphere and ionosphere produces an asymmetry consistent with observed distributions in nightside reconnection and plasmasheet flows and in accompanying ionospheric convection. The primary causal agent is the meridional gradient in the ionospheric Hall conductance which, through the Cowling effect, regulates the distribution of electrical currents flowing within and between the ionosphere and magnetotail. PMID:25013068

Lotko, William; Smith, Ryan H; Zhang, Binzheng; Ouellette, Jeremy E; Brambles, Oliver J; Lyon, John G

2014-07-11

306

Multipoint observations of dipolarization front formation by magnetotail reconnection  

Science.gov (United States)

We present multipoint observations of magnetotail plasma sheet dynamics during an event in which magnetic reconnection and dipolarization were observed at -16 tail) and at -10 tail reconnection. Large-amplitude magnetic field oscillations were observed in the temporal and spatial vicinity of the reconnection site. Interpreted as current sheet flapping, they enable reconstruction of a complex sheet structure with an embedded thin current sheet of ion inertial scale size. Detailed analysis of the orientation of the dipolarization front and of plasma motions around it reveals that the front of the reconnection jet was interchange unstable.

Runov, A.; Angelopoulos, V.; Zhou, X.-Z.

2012-05-01

307

Distant plasma sheet ion distributions during reconnection  

OpenAIRE

Previous models of the plasma sheet following reconnection and current sheet acceleration predict 'lima-bean' ion distributions. These are inconsistent with observational constraints. We postulate that following initial interaction with the current sheet, a fraction of outflow ions are backscattered and re-encounter the current sheet. Fermi acceleration processes then generate an additional high-energy outflow population. In the backscatter region these ions form a complete shell in velocity ...

Owen, C. J.; Mist, R. T.

2001-01-01

308

Electron Acceleration in 3D Magnetic Reconnection  

CERN Document Server

A kinetic simulation of 3D collisionless magnetic reconnection shows a dramatic enhancement of electron acceleration when compared with a 2D system. In the 2D system, electrons are trapped in magnetic islands which limits their energy gain, whereas in the 3D system the stochastic magnetic field enables the electrons to access volume-filling acceleration regions. The dominant accelerator of the most energetic electrons is Fermi reflection from contracting field lines.

Dahlin, J T; Swisdak, M

2015-01-01

309

An Electromagnetic Drift Instability in the Magnetic Reconnection Experiment (MRX) and its Importance for Magnetic Reconnection  

International Nuclear Information System (INIS)

The role which resistivity plays in breaking magnetic field lines, heating the plasma, and plasma field slippage during magnetic reconnection is discussed. Magnetic fluctuations are observed in the MRX (Magnetic Reconnection Experiment) that are believed to provide resistive friction or wave resistivity. A localized linear theory has been proposed for their origin as an obliquely propagating Lower Hybrid Drift Instability. In this paper, the linear theory of the instability is summarized, and the resulting heating and slippage are calculated from quasi-linear theory. Making use of measured amplitudes of the magnetic fluctuations in the MRX the amount of these effects is estimated. Within the experimental uncertainties they are shown to be quite important for the magnetic reconnection process

310

An Electromagnetic Drift Instability in the Magnetic Reconnection Experiment (MRX) and its Importance for Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

The role which resistivity plays in breaking magnetic field lines, heating the plasma, and plasma field slippage during magnetic reconnection is discussed. Magnetic fluctuations are observed in the MRX (Magnetic Reconnection Experiment) that are believed to provide resistive friction or wave resistivity. A localized linear theory has been proposed for their origin as an obliquely propagating Lower Hybrid Drift Instability. In this paper, the linear theory of the instability is summarized, and the resulting heating and slippage are calculated from quasi-linear theory. Making use of measured amplitudes of the magnetic fluctuations in the MRX the amount of these effects is estimated. Within the experimental uncertainties they are shown to be quite important for the magnetic reconnection process.

Russell Kulsrud; Hantao Ji; Will Fox; Masaaki Yamada

2005-06-07

311

Fermi Acceleration in Magnetic Reconnection Sites  

Science.gov (United States)

The mechanisms that accelerate cosmic relativistic particles are not fully understood yet. A variety of processes has been investigated and the acceleration in magnetic reconnection sites has lately gained increasing attention from researchers not only for its potential importance in the solar system, but also beyond it, in astrophysical environments like compact stellar sources, AGNs and GRBs, and even in diffusive magnetized media as the interstellar medium (ISM) and the intergalactic medium (IGM). In this talk we review this process and, supported by three-dimensional MHD simulations with the injection of thousands of test particles, we show that they can be efficiently accelerated by magnetic reconnection through a first-order Fermi process within large scale magnetic current sheets, even in a collisional fluid (contrary to what was previously believed), especially when local turbulence is present which makes reconnection fast, the acceleration layer thicker and the overall process naturally three-dimensional. Tests of particle acceleration in pure MHD turbulent environments (i.e., without the presence of large scale current sheets), on the other hand, indicate that the dominant acceleration process is a second-order Fermi.

de Gouveia Dal Pino, E. M.; Kowal, G.; Lazarian, A.

2014-09-01

312

The Alfvén edge in asymmetric reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We show that in the case of magnetic reconnection where the Alfvén velocity is much higher in the plasma on one side of the current sheet than the other, an Alfvén edge is formed. This edge is located between the electron and ion edges on the high Alfvén velocity side of the current sheet. The Alfvén edge forms because the Alfvén wave generated near the X-line will propagate faster than the accelerated ions forming the ion edge. We discuss possible generation mechanism and the polarization of the Alfvén wave in the case when higher Alfvén speed is due to larger magnetic field and smaller plasma density, as in the case of magnetopause reconnection. The Alfvén wave can be generated due to Hall dynamics near the X-line. The Alfvén wave pulse has a unipolar electric field and the parallel current will be such that the outer current on the high magnetic field side is flowing away from the X-line. Understanding Alfvén edges is important for understanding the separatrix regions at the boundaries of reconnection jets. We present an example of Alfvén edge observed by the Cluster spacecraft at the magnetopause.

A. Vaivads

2010-06-01

313

3D Null Point Reconnection Regimes  

CERN Document Server

Recent advances in theory and computational experiments have shown the need to refine the previous categorisation of magnetic reconnection at three-dimensional null points -- points at which the magnetic field vanishes. We propose here a division into three different types, depending on the nature of the flow near the spine and fan of the null. The spine is an isolated field line which approaches the null (or recedes from it), while the fan is a surface of field lines which recede from it (or approach it). So-called "torsional spine reconnection" occurs when field lines in the vicinity of the fan rotate, with current becoming concentrated along the spine, so that nearby field lines undergo rotational slippage. In "torsional fan reconnection" field lines near the spine rotate and create a current that is concentrated in the fan with a rotational flux mismatch and rotational slippage. In both of these regimes, the spine and fan are perpendicular and there is no flux transfer across spine or fan. The third regim...

Priest, E R

2009-01-01

314

Redistribution of fast ions during sawtooth reconnection  

Science.gov (United States)

In a tokamak-based fusion power plant, possible scenarios may include regulated sawtooth oscillations to remove thermalized helium from the core of the plasma. During a sawtooth crash, the helium ash and other impurities trapped in the core are driven by the instability to an outer region. However, in a fusion plasma, high energy ions will represent a significant population. We thus study the behaviour of these energetic particles during a sawtooth. This paper presents the modelling of the redistribution of fast ions during a sawtooth reconnection event in a tokamak plasma. Along the lines of the model for the evolution of the flux surfaces during a sawtooth collapse described in Ya.I. Kolesnichenko and Yu.V. Yakovenko 1996 Nucl. Fusion 36 159, we have built a time-dependent electromagnetic model of a sawtooth reconnection. The trajectories of the ions are described by a complete gyro-orbit integration. The fast particles were evolved from specific initial parameters (given energy and uniform spread in pitch) or distributed initially according to a slowing-down distribution created by fusion reactions. Our modelling is used to understand the main equilibrium parameters driving the motions during the collapse and to determine the evolution of the distribution function of energetic ions when different geometries of reconnection are considered.

Jaulmes, F.; Westerhof, E.; de Blank, H. J.

2014-10-01

315

On the Periodicity of Oscillatory Reconnection  

CERN Document Server

Oscillatory reconnection is a time-dependent magnetic reconnection mechanism that naturally produces periodic outputs from aperiodic drivers. This paper aims to quantify and measure the periodic nature of oscillatory reconnection for the first time. We solve the compressible, resistive, nonlinear MHD equations using 2.5D numerical simulations. We identify two distinct periodic regimes: the impulsive and stationary phases. In the impulsive phase, we find the greater the amplitude of the initial velocity driver, the longer the resultant current sheet and the earlier its formation. In the stationary phase, we find that the oscillations are exponentially decaying and for driving amplitudes 6.3 - 126.2 km/s, we measure stationary-phase periods in the range 56.3 - 78.9 s, i.e. these are high frequency (0.01 - 0.02 Hz) oscillations. In both phases, we find that the greater the amplitude of the initial velocity driver, the shorter the resultant period, but note that different physical processes and periods are associ...

McLaughlin, J A; MacTaggart, D; 10.1051/0004-6361/201220234

2012-01-01

316

What is taking place in science classrooms?: A case study analysis of teaching and learning in seventh-grade science of one Alabama school and its impact on African American student learning  

Science.gov (United States)

This qualitative case study investigated the teaching strategies that improve science learning of African American students. This research study further sought the extent the identified teaching strategies that are used to improve African American science learning reflect culturally responsive teaching. Best teaching strategies and culturally responsive teaching have been researched, but there has been minimal research on the impact that both have on science learning, with an emphasis on the African American population. Consequently, the Black-White achievement gap in science persists. The findings revealed the following teaching strategies have a positive impact on African American science learning: (a) lecture-discussion, (b) notetaking, (c) reading strategies, (d) graphic organizers, (e) hands-on activities, (f) laboratory experiences, and (g) cooperative learning. Culturally responsive teaching strategies were evident in the seventh-grade science classrooms observed. Seven themes emerged from this research data: (1) The participating teachers based their research-based teaching strategies used in the classroom on all of the students' learning styles, abilities, attitudes towards science, and motivational levels about learning science, with no emphasis on the African American student population; (2) The participating teachers taught the state content standards simultaneously using the same instructional model daily, incorporating other content areas when possible; (3) The participating African American students believed their seventh-grade science teachers used a variety of teaching strategies to ensure science learning took place, that science learning was fun, and that science learning was engaging; (4) The participating African American students genuinely liked their teacher; (5) The participating African American students revealed high self-efficacy; (6) The African American student participants' parents value education and moved to Success Middle School district for better educational opportunities; and (7) Teachers were not familiar with the term "culturally responsive teaching," but there was evidence that several aspects of it were present in the seventh-grade science classroom environment. Critical Race Theory (CRT) was the framework for analysis and interpretation of this research study. The findings support the following tenets of CRT: (a) racism is normal, (b) interest-convergence or colorblindness, (c) contextual-historical analysis, (d) storytelling or counterstorytelling, and (e) social transformation. These findings indicate that racial inequalities remain an issue in the underachievement of African Americans and may be the solution to improving science learning of African Americans. The outcome of this study contributes to the limited research on utilizing culturally responsive teaching along with best teaching strategies to improve academic achievement of African American students, and CRT exposes the issues that contribute to the Black-White achievement gap in science widening.

Norman, Lashaunda Renea

317

Slip Running Reconnection in Magnetic Flux Ropes  

Science.gov (United States)

Magnetic flux ropes are due to helical currents and form a dense carpet of arches on the surface of the sun. Occasionally one tears loose as a coronal mass ejection and its rope structure can be detected by satellites close to the earth. Current sheets can tear into filaments and these are nothing other than flux ropes. Ropes are not static, they exert mutual ?c{J}×?c{B} forces causing them to twist about each other and eventually merge. Kink instabilities cause them to violently smash into each other and reconnect at the point of contact. We report on experiments on two adjacent ropes done in the large plasma device (LAPD) at UCLA ( ne ˜ 1012, Te ˜ 6 eV, B0z=330G, Brope}\\cong{10G,trep=1 Hz). The currents and magnetic fields form exotic shapes with no ignorable direction and no magnetic nulls. Volumetric space-time data (70,600 spatial locations) show multiple reconnection sites with time-dependent locations. The concept of a quasi-separatrix layer (QSL), a tool to understand and visualize 3D magnetic field lines reconnection without null points is introduced. Three-dimensional measurements of the QSL derived from magnetic field data are presented. Within the QSL field lines that start close to one another rapidly diverge as they pass through one or more reconnection regions. The motion of magnetic field lines are traced as reconnection proceeds and they are observed to slip through the regions of space where the QSL is largest. As the interaction proceeds we double the current in the ropes. This accompanied by intense heating as observed in uv light and plasma flows measured by Mach probes. The interaction of the ropes is clearly seen by vislaulizng magnetic field data , as well as in images from a fast framing camera. Work supported by the Dept. of Energy and The National Science Foundation, done at the Basic Plasma Science Facility at UCLA.Magnetic Field lines (measured) of three flux ropes and the plasma currents associated with them

Gekelman, W. N.; Van Compernolle, B.; Vincena, S. T.; De Hass, T.

2012-12-01

318

The relation between reconnected flux, the parallel electric field, and the reconnection rate in a three-dimensional kinetic simulation of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

We investigate the distribution of parallel electric fields and their relationship to the location and rate of magnetic reconnection in a large particle-in-cell simulation of 3D turbulent magnetic reconnection with open boundary conditions. The simulation's guide field geometry inhibits the formation of simple topological features such as null points. Therefore, we derive the location of potential changes in magnetic connectivity by finding the field lines that experience a large relative change between their endpoints, i.e., the quasi-separatrix layer. We find a good correspondence between the locus of changes in magnetic connectivity or the quasi-separatrix layer and the map of large gradients in the integrated parallel electric field (or quasi-potential). Furthermore, we investigate the distribution of the parallel electric field along the reconnecting field lines. We find the reconnection rate is controlled by only the low-amplitude, zeroth and first–order trends in the parallel electric field while the contribution from fluctuations of the parallel electric field, such as electron holes, is negligible. The results impact the determination of reconnection sites and reconnection rates in models and in situ spacecraft observations of 3D turbulent reconnection. It is difficult through direct observation to isolate the loci of the reconnection parallel electric field amidst the large amplitude fluctuations. However, we demonstrate that a positive slope of the running sum of the parallel electric field along the field line as a function of field line length indicates where reconnection is occurring along the field line.

Wendel, D. E.; Olson, D. K.; Hesse, M.; Kuznetsova, M.; Adrian, M. L. [NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Aunai, N. [Institute for Research in Astrophysics and Planetology, University Paul Sabatier, Toulouse (France); Karimabadi, H. [SciberQuest, Inc., Del Mar, California 92014 (United States); Department of Computer and Electrical Engineering, University of California, San Diego, La Jolla, California 92093 (United States); Daughton, W. [Los Alamos National Laboratory, Los Alamos, New Mexico 87545 (United States)

2013-12-15

319

RHESSI and EIS observations of an above-the-looptop reconnection region  

Science.gov (United States)

A variety of solar flare observations suggest particle acceleration in the corona, at or above the flare looptop. Hard X-ray (HXR) studies, for example, occasionally reveal accelerated electrons above flare looptops, in some cases suggesting the location of the acceleration region. However, since coronal HXR sources are faint and the structure of the flare as seen in extreme ultraviolet (EUV) images is complicated, it is difficult to say where these sources lie with respect to, for example, the reconnection region.HXR and EUV observations can provide complementary information for investigating this topic. EUV imaging spectroscopy reveals bulk flows and locations of line-broadened (potentially turbulent) sources. Such observations can, for example, identify outflows from the reconnection region. HXR imaging places the flare-accelerated electrons in the context of the overall flare geometry, allowing comparison of the locations of accelerated electrons, the reconnection region, and the flare loop.In this work, data from RHESSI and Hinode/EIS are used to investigate above-the-looptop sources in the 2013 May 15 X-class flare. Above-the-looptop EIS flows and loop-top line-broadening are compared with RHESSI HXR sources in the preimpulsive phase of the flare.

Glesener, Lindsay; Hara, Hirohisa; Krucker, Sam

2014-06-01

320

General magnetic reconnection, parallel electric fields, and helicity  

International Nuclear Information System (INIS)

Analyzing the qualitative three-dimensional magnetic structure of a plasmoid, we were led to reconsider the concept of magnetic reconnection from a general point of view. The properties of relatively simple magnetic field models provide a strong preference for one of two definitions of magnetic reconnection that exist in the literature. Any concept of magnetic reconnection defined in terms of magnetic topology seems naturally restricted to cases where the magnetic field vanishes somewhere in the nonideal (diffusion) region. The main part of this paper is concerned with magnetic reconnection in nonvanishing magnetic fields (finite-B reconnection), which has attracted less attention in the past. We show that E/sub parallel/ (the electric field component parallel to the magnetic field) plays a crucial physical role in finite-B reconnection, and we present two theorems involving E/sub parallel/. The first states a necessary and sufficient condition on E/sub parallel/ for global reconnection to occur. Here the term ''global'' means the generic case where the breakdown of magnetic connection occurs for plasma elements that stay outside the nonideal region. The second theorem relates the change of magnetic helicity to E/sub parallel/ for cases where the electric field vanishes at large distances. That these results provide new insight into three-dimensional reconnection processes is illustrated in terms of the plasmoid configuration, which was our starting point. copyright A which was our starting point. copyright American Geophysical Union 1988

321

Measurements of Magnetic Fluctuations in Magnetic Reconnection Experiment  

International Nuclear Information System (INIS)

Magnetic reconnection plays an important role in determining the evolution of magnetic topology in laboratory and astrophysical plasmas. A central question concerns why the observed reconnection rates are much faster than predictions made by classical theories, such as the Sweet-Parker model based on MHD with classical Spitzer resistivity. Often, the local resistivity is conjectured to be enhanced by micro-instabilities to accelerate reconnection rates either in the context of the Sweet-Parker model or by facilitating setup of the Pestchek model. Although it is commonly believed that there is plenty of free energy available at the reconnection region to destabilize some sort of micro-instability, a clear identification of this instability and its exact role in reconnection has never been established experimentally. We report the first such experimental evidence of a clear and positive correlation between magnetic fluctuations in the lower-hybrid frequency range and resistivity enhancement during fast reconnection in the low-collisionality regimes in the Magnetic Reconnection Experiment (MRX). The waves have been identified as right-hand polarized whistler waves, propagating obliquely to the reconnecting field, with a phase velocity comparable to the relative drift velocity. These waves are consistent with the modified two-stream instability driven by large drift speeds compared to the Alfven speed in high-beta plasmas. The short coherence length and large variation alrt coherence length and large variation along the propagation direction indicate their strongly nonlinear nature

322

Magnetic mirror effect as a trigger of collisionless magnetic reconnection  

International Nuclear Information System (INIS)

A new mechanism of collisionless magnetic reconnection is proposed. It is based on the current density redistribution along the magnetic field lines caused by the reflection of meandering particles due to the magnetic mirror effect from the would-be reconnection region. (author)

323

Direct evidence for kinetic effects associated with solar wind reconnection  

Science.gov (United States)

Kinetic effects resulting from the two-fluid physics play a crucial role in the fast collisionless reconnection, which is a process to explosively release massive energy stored in magnetic fields in space and astrophysical plasmas. In-situ observations in the Earth's magnetosphere provide solid consistence with theoretical models on the point that kinetic effects are required in the collisionless reconnection. However, all the observations associated with solar wind reconnection have been analyzed in the context of magnetohydrodynamics (MHD) although a lot of solar wind reconnection exhausts have been reported. Because of the absence of kinetic effects and substantial heating, whether the reconnections are still ongoing when they are detected in the solar wind remains unknown. Here, by dual-spacecraft observations, we report a solar wind reconnection with clear Hall magnetic fields. Its corresponding Alfvenic electron outflow jet, derived from the decouple between ions and electrons, is identified, showing direct evidence for kinetic effects that dominate the collisionless reconnection. The turbulence associated with the exhaust is a kind of background solar wind turbulence, implying that the reconnection generated turbulence has not much developed.

Xu, Xiaojun; Wang, Yi; Wei, Fengsi; Feng, Xueshang; Deng, Xiaohua; Ma, Yonghui; Zhou, Meng; Pang, Ye; Wong, Hon-Cheng

2015-01-01

324

A Model for Patchy Reconnection in Three Dimensions  

CERN Document Server

We show, theoretically and via MHD simulations, how a short burst of reconnection localized in three dimensions on a one-dimensional current sheet creates a pair of reconnected flux tubes. We focus on the post-reconnection evolution of these flux tubes, studying their velocities and shapes. We find that slow-mode shocks propagate along these reconnected flux tubes, releasing magnetic energy as in steady-state Petschek reconnection. The geometry of these three-dimensional shocks, however, differs dramatically from the classical two-dimensional geometry. They propagate along the flux tube legs in four isolated fronts, whereas in the two-dimensional Petschek model, they form a continuous, stationary pair of V-shaped fronts. We find that the cross sections of these reconnected flux tubes appear as teardrop shaped bundles of flux propagating away from the reconnection site. Based on this, we argue that the descending coronal voids seen by Yohkoh SXT, LASCO, and TRACE are reconnected flux tubes descending from a fl...

Linton, M G

2005-01-01

325

Turbulent magnetic reconnection in 2D and 3D  

CERN Document Server

Magnetic field embedded in a perfectly conducting fluid preserves its topology for all time. Although ionized astrophysical objects, like stars and galactic disks, are almost perfectly conducting, they show indications of changes in topology, `magnetic reconnection', on dynamical time scales. Reconnection can be observed directly in the solar corona, but can also be inferred from the existence of large scale dynamo activity inside stellar interiors. Solar flares and gamma ray busts are usually associated with magnetic reconnection. Previous work has concentrated on showing how reconnection can be rapid in plasmas with very small collision rates. Here we present numerical evidence, based on three dimensional simulations, that reconnection in a turbulent fluid occurs at a speed comparable to the rms velocity of the turbulence, regardless of the value of the resistivity. In particular, this is true for turbulent pressures much weaker than the magnetic field pressure so that the magnetic field lines are only slig...

Lazarian, A; Vishniac, E; Kulpa-Dubel, K; Otmianowska-Mazur, K

2010-01-01

326

Relativistic Reconnection: an Efficient Source of Non-Thermal Particles  

CERN Document Server

In magnetized astrophysical outflows, the dissipation of field energy into particle energy via magnetic reconnection is often invoked to explain the observed non-thermal signatures. By means of two- and three-dimensional particle-in-cell simulations, we investigate anti-parallel reconnection in magnetically-dominated electron-positron plasmas. Our simulations extend to unprecedentedly long temporal and spatial scales, so we can capture the asymptotic state of the system beyond the initial transients, and without any artificial limitation by the boundary conditions. At late times, the reconnection layer is organized into a chain of large magnetic islands connected by thin X-lines. The plasmoid instability further fragments each X-line into a series of smaller islands, separated by X-points. At the X-points, the particles become unmagnetized and they get accelerated along the reconnection electric field. We provide definitive evidence that the late-time particle spectrum integrated over the whole reconnection r...

Sironi, Lorenzo

2014-01-01

327

Conservation of writhe helicity under anti-parallel reconnection  

Science.gov (United States)

Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts. PMID:25820408

Laing, Christian E.; Ricca, Renzo L.; Sumners, De Witt L.

2015-01-01

328

On the two-dimensional magnetic reconnection with nonuniform resistivity  

CERN Document Server

In this paper two theoretical approaches for the calculation of the rate of quasi-stationary, two-dimensional magnetic reconnection with nonuniform anomalous resistivity are considered in the framework of incompressible magnetohydrodynamics (MHD). In the first, ``global'' equations approach the MHD equations are approximately solved for a whole reconnection layer, including the upstream and downstream regions and the layer center. In the second, ``local'' equations approach the equations are solved across the reconnection layer, including only the upstream region and the layer center. Both approaches give the same approximate answer for the reconnection rate. Our theoretical model is in agreement with the results of recent simulations of reconnection with spatially nonuniform resistivity by Baty, Priest and Forbes (2006), contrary to their conclusions.

Malyshkin, L; Malyshkin, Leonid; Kulsrud, Russell M.

2006-01-01

329

Conservation of writhe helicity under anti-parallel reconnection.  

Science.gov (United States)

Reconnection is a fundamental event in many areas of science, from the interaction of vortices in classical and quantum fluids, and magnetic flux tubes in magnetohydrodynamics and plasma physics, to the recombination in polymer physics and DNA biology. By using fundamental results in topological fluid mechanics, the helicity of a flux tube can be calculated in terms of writhe and twist contributions. Here we show that the writhe is conserved under anti-parallel reconnection. Hence, for a pair of interacting flux tubes of equal flux, if the twist of the reconnected tube is the sum of the original twists of the interacting tubes, then helicity is conserved during reconnection. Thus, any deviation from helicity conservation is entirely due to the intrinsic twist inserted or deleted locally at the reconnection site. This result has important implications for helicity and energy considerations in various physical contexts. PMID:25820408

Laing, Christian E; Ricca, Renzo L; Sumners, De Witt L

2015-01-01

330

Review of recent experiments on magnetic reconnection in laboratory plasmas  

Energy Technology Data Exchange (ETDEWEB)

The present paper reviews recent laboratory experiments on magnetic reconnection. Examples will be drawn from electron current sheet experiments, merging spheromaks, and from high temperature tokamak plasmas with the Lundquist numbers exceeding 10{sup 7}. These recent laboratory experiments create an environment which satisfies the criteria for MHD plasma and in which the global boundary conditions can be controlled externally. Experiments with fully three dimensional reconnection are now possible. In the most recent TFTR tokamak discharges, Motional Stark effect (MSE) data have verified the existence of a partial reconnection. In the experiment of spheromak merging, a new plasma acceleration parallel to the neutral line has been indicated. Together with the relationship of these observations to the analysis of magnetic reconnection in space and in solar flares, important physics issues such as global boundary conditions, local plasma parameters, merging angle of the field lines, and the 3-D aspects of the reconnection are discussed.

Yamada, M.

1995-02-01

331

Rogowski Coil Array for Collisionless Magnetic Reconnection Experiments at VTF  

Science.gov (United States)

Recent experiments on magnetic reconnection at the Versatile Toroidal Facility (VTF) indicate that the electron current may become filamented during spontaneous reconnection events [1]. A new array of Rogowski coils, which has centimeter-scale resolution, will measure the parallel currents driven by fast reconnection in the presence of a guide magnetic field. The diagnostic should confirm the filamentary structure of the current profile, determine the distribution of filaments around the X-line, and reveal when the filaments are generated with respect to the onset of reconnection. In addition, multi-shot scans performed by moving the Rogowski coil array across a poloidal section and to several different toroidal angles will yield high-resolution measurements of the reproducible features of the current profile that develops during three-dimensional reconnection at VTF. Preliminary data will be presented if available.[1ex] [1] J. Egedal et al., Phys. Rev. Lett., 98, 015003 (2007)

Le, A.; Egedal, J.; Fox, W.; Katz, N.; Vrublevskis, A.; Porkolab, M.

2009-11-01

332

Comment on Lockwood and Davis, "On the longitudinal extent of magnetopause reconnection pulses"  

Directory of Open Access Journals (Sweden)

Full Text Available Lockwood and Davis (1996 present a concise description of magnetopause reconnection pulses, with the claimed support of three types of observations: (1 flux transfer events (FTE, (2 poleward-moving auroral forms on the dayside, and (3 steps in cusp ion dispersion characteristics. However, there are a number of errors and misconceptions in the paper that make their conclusions untenable. They do not properly take account of the fact that the relevant processes operate in the presence of a plasma. They fail to notice that the source of energy (a dynamo with E · J<0 must be close to the region of dissipation (the electrical load with E · J>0 in transient phenomena, since energy (or information cannot travel faster than the group velocity of waves in the medium (here the Alfvén velocity VA. In short, Lockwood and Davis use the wrong contour in their attempt to evaluate the electromotive force (emf. This criticism goes beyond their article: a dynamo is not included in the usual definition of reconnection, only the reconnection load. Without an explicit source of energy in the assumed model, the idea of magnetic reconnection is improperly posed. Recent research has carried out a superposed epoch analysis of conditions near the dayside magnetopause and has found the dynamo and the load, both within the magnetopause current sheet. Since the magnetopause current is from dawn to dusk, the sign of E · J reflects the sign of the electric field. The electric field reverses, within the magnetopause; this can be discovered by an application of Lenz's law using the concept of erosion of the magnetopause. The net result is plasma transfer across the magnetopause to feed the low latitude boundary layer, at least partly on closed field lines, and viscous interaction as the mechanism by which solar wind plasma couples to the magnetosphere.

W. J. Heikkila

333

Formation of current sheets in magnetic reconnection  

International Nuclear Information System (INIS)

An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ? along the lines, ?(?)=?(0)e?(?). The non-ideal effects required to break magnetic field line connections scale as e??, so the breaking of connections is inevitable for ? sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j||/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j||/B occurs. Independent of the original spatial distribution of j||/B, the evolution is into a sheet current, which is stretched by a factor e? in width and contracted by a factor e? in thickness with the current density j|| increasing as e?. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of current flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not

334

FAST MAGNETIC RECONNECTION AND SPONTANEOUS STOCHASTICITY  

International Nuclear Information System (INIS)

Magnetic field lines in astrophysical plasmas are expected to be frozen-in at scales larger than the ion gyroradius. The rapid reconnection of magnetic-flux structures with dimensions vastly larger than the gyroradius requires a breakdown in the standard Alfvén flux-freezing law. We attribute this breakdown to ubiquitous MHD plasma turbulence with power-law scaling ranges of velocity and magnetic energy spectra. Lagrangian particle trajectories in such environments become 'spontaneously stochastic', so that infinitely many magnetic field lines are advected to each point and must be averaged to obtain the resultant magnetic field. The relative distance between initial magnetic field lines which arrive at the same final point depends upon the properties of two-particle turbulent dispersion. We develop predictions based on the phenomenological Goldreich and Sridhar theory of strong MHD turbulence and on weak MHD turbulence theory. We recover the predictions of the Lazarian and Vishniac theory for the reconnection rate of large-scale magnetic structures. Lazarian and Vishniac also invoked 'spontaneous stochasticity', but of the field lines rather than of the Lagrangian trajectories. More recent theories of fast magnetic reconnection appeal to microscopic plasma processes that lead to additional terms in the generalized Ohm's law, such as the collisionless Hall term. We estimate quantitatively the effect of such processes on the inertial-range turbulence dynamics and findertial-range turbulence dynamics and find them to be negligible in most astrophysical environments. For example, the predictions of the Lazarian and Vishniac theory are unchanged in Hall MHD turbulence with an extended inertial range, whenever the ion skin depth ?i is much smaller than the turbulent integral length or injection-scale Li .

335

Formation of current sheets in magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

An ideal evolution of magnetic fields in three spatial dimensions tends to cause neighboring field lines to increase their separation exponentially with distance ? along the lines, ?(?)=?(0)e{sup ?(?)}. The non-ideal effects required to break magnetic field line connections scale as e{sup ??}, so the breaking of connections is inevitable for ? sufficiently large—even though the current density need nowhere be large. When the changes in field line connections occur rapidly compared to an Alfvén transit time, the constancy of j{sub ||}/B along the magnetic field required for a force-free equilibrium is broken in the region where the change occurs, and an Alfvénic relaxation of j{sub ||}/B occurs. Independent of the original spatial distribution of j{sub ||}/B, the evolution is into a sheet current, which is stretched by a factor e{sup ?} in width and contracted by a factor e{sup ?} in thickness with the current density j{sub ||} increasing as e{sup ?}. The dissipation of these sheet currents and their associated vorticity sheets appears to be the mechanism for transferring energy from a reconnecting magnetic field to a plasma. Harris sheets, which are used in models of magnetic reconnection, are shown to break up in the direction of current flow when they have a finite width and are in a plasma in force equilibrium. The dependence of the longterm nature of magnetic reconnection in systems driven by footpoint motion can be studied in a model that allows qualitative variation in the nature of that motion: slow or fast motion compared to the Alfvén transit time and the neighboring footpoints either exponentially separating in time or not.

Boozer, Allen H., E-mail: ahb17@columbia.edu [Department of Applied Physics and Applied Mathematics Columbia University, New York, New York 10027 (United States)

2014-07-15

336

Magnetopause reconnection across wide local time  

Directory of Open Access Journals (Sweden)

Full Text Available During April to July 2007 a combination of 10 spacecraft provided simultaneous monitoring of the dayside magnetopause across a wide range of local times. The array of four Cluster spacecraft, separated at large distances (10 000 km, were traversing the dawn-side magnetopause at high and low latitudes; the five THEMIS spacecraft were often in a 4 + 1 grouped configuration, traversing the low latitude, dusk-side magnetosphere, and the Double star, TC-1 spacecraft was in an equatorial orbit between the local times of the THEMIS and Cluster orbits. We show here a number of near simultaneous conjunctions of all 10 spacecraft at the magnetopause. One conjunction identifies an extended magnetic reconnection X-line, tilted in the low latitude, sub-solar region, which exists together with active anti-parallel reconnection sites extending to locations on the dawn-side flank. Oppositely moving FTE's are observed on all spacecraft, consistent with the initially strong IMF By conditions and the comparative locations of the spacecraft both dusk-ward and dawn-ward of noon. Comparison with other conjunctions of magnetopause crossings, which are also distributed over wide local times, supports the result that reconnection activity may occur at many sites simultaneously across the sub-solar and flank magnetopause, but linked to the large scale (extended configuration of the merging line; broadly depending on IMF orientation. The occurrence of MR therefore inherently follows a "component" driven scenario irrespective of the guide field conditions. Some conjunctions allow the global magnetopause response to IMF changes to be observed and the distribution of spacecraft can directly confirm its shape, motion and deformation at local noon, dawn and dusk-side, simultaneously.

M. W. Dunlop

2011-09-01

337

Fast Magnetic Reconnection and Spontaneous Stochasticity  

Science.gov (United States)

Magnetic field lines in astrophysical plasmas are expected to be frozen-in at scales larger than the ion gyroradius. The rapid reconnection of magnetic-flux structures with dimensions vastly larger than the gyroradius requires a breakdown in the standard Alfvén flux-freezing law. We attribute this breakdown to ubiquitous MHD plasma turbulence with power-law scaling ranges of velocity and magnetic energy spectra. Lagrangian particle trajectories in such environments become "spontaneously stochastic," so that infinitely many magnetic field lines are advected to each point and must be averaged to obtain the resultant magnetic field. The relative distance between initial magnetic field lines which arrive at the same final point depends upon the properties of two-particle turbulent dispersion. We develop predictions based on the phenomenological Goldreich & Sridhar theory of strong MHD turbulence and on weak MHD turbulence theory. We recover the predictions of the Lazarian & Vishniac theory for the reconnection rate of large-scale magnetic structures. Lazarian & Vishniac also invoked "spontaneous stochasticity," but of the field lines rather than of the Lagrangian trajectories. More recent theories of fast magnetic reconnection appeal to microscopic plasma processes that lead to additional terms in the generalized Ohm's law, such as the collisionless Hall term. We estimate quantitatively the effect of such processes on the inertial-range turbulence dynamics and find them to be negligible in most astrophysical environments. For example, the predictions of the Lazarian & Vishniac theory are unchanged in Hall MHD turbulence with an extended inertial range, whenever the ion skin depth ? i is much smaller than the turbulent integral length or injection-scale Li .

Eyink, Gregory L.; Lazarian, A.; Vishniac, E. T.

2011-12-01

338

Triggered-reconnection compact toroid experiment  

International Nuclear Information System (INIS)

A schematic of the MSNW experimental apparatus, which is closely patterned after the Soviet experiment, is shown. A bias field is created by an external quasi-steady solenoid. An additional quasi-steady coil at each end is used to apply a mirror or cusp field configuration. Eight pairs of oppositely directed longitudinal conductors are located as shown to form a pulsed octopole field near the tube wall. In addition, at each end there is a very fast pulsed mirror trigger coil used to force reconnection at the desired time

339

Finding the Right Place for the Person with Alzheimer's Disease  

Science.gov (United States)

Finding the Right Place for the Person with AD Steps to take Assisted living facilities Group homes Nursing homes How to ... well cared for." Steps to take Choosing the right place is a big decision. It's hard to ...

340

BP-Mobil partnership. The common network takes place  

International Nuclear Information System (INIS)

After the partnership between BP and Mobil was signed, the program of transformation of the petrol stations network started in November 1996 in the UK and concern 3300 stations in Europe and 800 stations in France. About 9100 stations will be transformed by the end of 1998. BP France is the operator for petroleum products (petrol, fuel, bitumens, LPG..) with a 70% share holding (30% for Mobil) while Mobil is the major shareholder (51%) for the lubricants and special products activities. The chemical, aviation nd maritime activities are not concerned. Thanks to the fusion of their down-file activities in Europe, the benefits of the partnership should reach 600 to 700 million of US Dollars each year. However the restructuring cost should reach 740 millions of US Dollars in two years, which doubles the initial estimation. Short paper. (J.S.)

341

How Chemical Reactions Take Place in Reactive Ternary Blends  

Science.gov (United States)

Reaction mechanism and kinetics of reactive ternary blends, consisting of a crystallizable polyester, an amorphous polyether, and an acrylate with high glass transition temperature, have been investigated using time-resolved Fourier transform infrared spectroscopy. Since the polyester and polyether have reactive isocyanate units, they are able to react with water vapor in the environment. A specially-designed cell was constructed to obtain reaction kinetics for reactive ternary blends with a variety of thickness at different relative humidity and temperatures. The reaction kinetics obtained are significantly slower than expected for a diffusion-limited mechanism of a homogeneous medium, indicating that curing reactions in the thin dimension are primarily controlled by the reaction-limited mechanism. Morphological features (phase-separated structure, degree of crystallinity, and crystalline domain size), which have been characterized by vibrational spectroscopy, optical microscopy, and atomic force microscopy, are dependent on composition, thermal history, and initial phase behavior. Reaction rates were shown to be highly dependent on sample morphology and composition, being faster with smaller phase-separated domains and lower degrees of crystallinity.

Jeong, Young Gyu

2005-03-01

342

Observations of magnetic flux ropes during magnetic reconnection in the Earth's magnetotail  

OpenAIRE

We present an investigation of magnetic flux ropes observed by the four Cluster spacecraft during periods of magnetic reconnection in the Earth's magnetotail. Using a list of 21 Cluster encounters with the reconnection process in the period 2001–2006 identified in Borg et al. (2012), we present the distribution and characteristics of the flux ropes. We find 27 flux ropes embedded in the reconnection outflows of only 11 of the 21 reconnection encounters. Reconnection processes associate...

Borg, A. L.; Taylor, M. G. G. T.; Eastwood, J. P.

2012-01-01

343

Microflare Activity driven by Forced Magnetic Reconnection  

CERN Document Server

High cadence, multiwavelength, optical observations of a solar active region are presented, obtained with the Swedish Solar Telescope. Two magnetic bright points are seen to separate in opposite directions at a constant velocity of 2.8km/s. After a separation distance of approximately 4400km is reached, multiple Ellerman bombs are observed in both H-alpha and Ca-K images. As a result of the Ellerman bombs, periodic velocity perturbations in the vicinity of the magnetic neutral line, derived from simultaneous MDI data, are generated with amplitude +/- 6km/s and wavelength 1000km. The velocity oscillations are followed by an impulsive brightening visible in H-alpha and Ca-K, with a peak intensity enhancement of 63%. We interpret these velocity perturbations as the magnetic field deformation necessary to trigger forced reconnection. A time delay of approximately 3min between the H-alpha wing and Ca-K observations indicate that the observed magnetic reconnection occurs at a height of 200km above the solar surface...

Jess, D B; Browning, P K; Crockett, P J; Keenan, F P

2010-01-01

344

Microinstabilities in an EMHD reconnection experiment  

Science.gov (United States)

A magnetic null point geometry has been established in a large laboratory plasma with a dipole field opposing a weak uniform magnetic field. The field and plasma parameters fall into the regime of Electron MHD (EMHD). Magnetic nulls are formed in two cusp points and a toroidally closed \\textit{O}-type layer, which carries a toroidal current sheet. The behavior of this field topology is studied during its free relaxation without boundary effects. Magnetic flux is annihilated in the \\textit{O}-type null layer. Magnetic energy is converted into electron heat. Current-driven ion sound turbulence is created in the current sheet. The associated anomalous resistivity explains the rate of energy conversion which is two orders of magnitude faster than predicted by classical diffusion. The temperature rise of the electrons is limited by heat conduction, emission of light, and electromagnetic waves above the plasma frequency. Ion acceleration is negligible during EMHD reconnection. The observed phenomena should be relevant to reconnection in the solar photosphere which has similar parameters as the laboratory plasma.

Stenzel, R. L.; Griskey, M. C.; Urrutia, J. M.; Strohmaier, K. D.

2002-12-01

345

Collisionless reconnection: magnetic field line interaction  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic field lines are quantum objects carrying one quantum ?0 = 2?h/e of magnetic flux and have finite radius ?m. Here we argue that they possess a very specific dynamical interaction. Parallel field lines reject each other. 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, attract each other. We identify the physical mechanism as being due to the action of the gauge potential field, which we determine quantum mechanically for two parallel and two anti-parallel field lines. The distortion of the quantum electrodynamic vacuum causes a cloud of virtual pairs. We calculate the virtual pair production rate from quantum electrodynamics and estimate the virtual pair cloud density, pair current and Lorentz force density acting on the field lines via the pair cloud. These properties of field line dynamics become important in collisionless reconnection, consistently explaining why and how reconnection can spontaneously set on in the field-free centre of a current sheet below the electron-inertial scale.

R. A. Treumann

2012-10-01

346

Balanced reconnection intervals: four case studies  

Science.gov (United States)

During steady magnetospheric convection (SMC) events the magnetosphere is active, yet there are no data signatures of a large scale reconfiguration, such as a substorm. While this definition has been used for years it fails to elucidate the true physics that is occurring within the magnetosphere, which is that the dayside merging rate and the nightside reconnection rate balance. Thus, it is suggested that these events be renamed Balanced Reconnection Intervals (BRIs). This paper investigates four diverse BRI events that support the idea that new name for these events is needed. The 3-4 February 1998 event falls well into the classic definition of an SMC set forth by Sergeev et al. (1996), while the other challenge some previous notions about SMCs. The 15 February 1998 event fails to end with a substorm expansion and concludes as the magnetospheric activity slowly quiets. The third event, 22-23 December 2000, begins with a slow build up of magnetospheric activity, thus there is no initiating substorm expansion. The last event, 17 February 1998, is more active (larger AE, AL and cross polar cap potential) than previously studied SMCs. It also has more small scale activity than the other events studied here.

Dejong, A. D.; Ridley, A. J.; Clauer, C. R.

2008-12-01

347

Balanced reconnection intervals: four case studies  

Directory of Open Access Journals (Sweden)

Full Text Available During steady magnetospheric convection (SMC events the magnetosphere is active, yet there are no data signatures of a large scale reconfiguration, such as a substorm. While this definition has been used for years it fails to elucidate the true physics that is occurring within the magnetosphere, which is that the dayside merging rate and the nightside reconnection rate balance. Thus, it is suggested that these events be renamed Balanced Reconnection Intervals (BRIs. This paper investigates four diverse BRI events that support the idea that new name for these events is needed. The 3–4 February 1998 event falls well into the classic definition of an SMC set forth by Sergeev et al. (1996, while the other challenge some previous notions about SMCs. The 15 February 1998 event fails to end with a substorm expansion and concludes as the magnetospheric activity slowly quiets. The third event, 22–23 December 2000, begins with a slow build up of magnetospheric activity, thus there is no initiating substorm expansion. The last event, 17 February 1998, is more active (larger AE, AL and cross polar cap potential than previously studied SMCs. It also has more small scale activity than the other events studied here.

A. D. DeJong

2008-12-01

348

First Reconnected Flux Tubes in the Near-Earth Tail  

Science.gov (United States)

Following the onset of reconnection, the first reconnecting flux tubes move away from the reconnection site creating an over-dense region in front of their leading edge, with a low density region lagging behind. The initial front observed at the magnetic equator has a fairly well distinguishable magnetic signature, which in space observation constitute a sub category of a broader group classified as magnetic pile-up events (or, alternatively, as dipolarization events). The first reconnecting flux tubes at the magnetic equator do not form a classic shock, but are associated with lower hybrid drift instabilities and whistler waves. As has been shown in work by others, the first reconnecting flux tubes are associated with strong dissipation, especially ion dissipation. In the high density region, the electrons and ions are decelerated and redirected perpendicular to the ejected exhaust. Near the first reconnecting flux tubes the ions gain energy and the electrons consist of two populations, one bi-streaming and the other more energetic (warmer) in the perpendicular direction. One particular magnetospheric disturbance event will be presented form the THEMIS mission where good observations from ground assets exits. Aurora intensification, enhanced 30 keV electrons and ionospheric currents are associated with this event. The radar clearly demonstrate the changes in the convection pattern helping to understand the satellite observations from the THEMIS and the GOES satellites. This reconfiguration event occurs in discrete steps by separate reconnection events.

Andersson, L.; Lapenta, G.; Newman, D. L.; Spanswick, E. L.; Baker, J. B.; Clausen, L.; Larson, D. E.; Frey, H. U.; Singer, H. J.; Angelopoulos, V.; Ergun, R. E.; Bonnell, J. W.; McFadden, J. P.; Glassmeier, K.; Baumjohann, W.

2010-12-01

349

Total magnetic reconnection during a tokamak major disruption  

International Nuclear Information System (INIS)

Magnetic reconnection has long been considered to be the cause of sawtooth oscillations and major disruptions in tokamak experiments. Experimental confirmation of reconnection models has been hampered by the difficulty of direct measurement of reconnection, which would involve tracing field lines for many transits around the tokamak. Perhaps the most stringent test of reconnection in a tokamak involves measurement of the safety factor q. Reconnection arising from a single helical disturbance with mode numbers m and n should raise q to m/n everywhere inside of the original resonant surface. Total reconnection should also flatten the temperature and current density profiles inside of this surface. Disruptive instabilities have been studied in the Tokapole 2, a poloidal divertor tokamak. When Tokapole 2 is operated in the material limiter configuration, a major disruption results in current termination as in most tokamaks. However, when operated in the magnetic limiter configuration current termination is suppressed and major disruptions appear as giant sawtooth oscillations. The objective of this thesis is to determine if total reconnection is occurring during major disruptions. To accomplish this goal, the poloidal magnetic field has been directly measured in Tokapole 2 with internal magnetic coils. A full two-dimensional measurement over the central current channel has been done. From these measurements, the poloidal magnetic flux function is obtained and the magnetic surfaces are plotted. The flux-surface-averaged safety factor is obtained by integrating the local magnetic field line pitch over the experimentally obtained magnetic surface

350

Recent Results from Magnetic Reconnection Experiment (MRX) at PPPL  

Science.gov (United States)

Magnetic reconnection plays a crucial role in determining the topology of magnetic fields in solar flares, magnetospheric substorms, and relaxation processes in laboratory plasmas. Many fundamental issues of magnetic reconnection are being investigated in the MRX (Magnetic Reconnection Experiment) device [1], which creates an environment satisfying the criteria for MHD plasmas with well controlled boundary conditions in a nearly two-dimensional geometry. Detailed structures and key plasma parameters of magnetic reconnection have been measured by extensive diagnostics. Major findings of recent MRX experiments are: (1) The observed reconnection rate can be explained by a generalized Sweet-Parker model [2], which incorporates compressibility, downstream pressure, and the effective resistivity; (2) The reconnection speed and the shape of the diffusion region depend on the merging angle of the reconnecting field; (3) Resistivity is greatly enhanced over the classical values in the collisionless regime; (4) The thickness of current sheet is proportional to ion gyro-radius and ion skin-depth. This result can be translated into a constant drift velocity over a wide range of plasma density, and is closely related to the observed resistivity enhancement. Application of these MRX results to solar flares will be discussed along with the detailed analysis and physics interpretations. [1] M. Yamada, H. Ji et al., Phys. Rev. Lett. 78, 3117(1997). [2] H. Ji, M. Yamada et al., Phys. Rev. Lett. 80, 3256 (1998).

Yamada, M.; Ji, H.

1999-05-01

351

A new fast reconnection model in a collisionless regime  

International Nuclear Information System (INIS)

Based on the first principles [i.e., (i) by balancing the magnetic field advection with the term containing electron pressure tensor nongyrotropic components in the generalized Ohm's law; (ii) using the conservation of mass; and (iii) assuming that the weak magnetic field region width, where electron meandering motion supports electron pressure tensor off-diagonal (nongyrotropic) components, is of the order of electron Larmor radius] a simple model of magnetic reconnection in a collisionless regime is formulated. The model is general, resembling its collisional Sweet-Parker analog in that it is not specific to any initial configuration, e.g., Harris-type tearing unstable current sheet, X-point collapse or otherwise. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate [Mc'less=(c/?pe)2/(rL,eL)] than Sweet-Parker's classical one (Msp=S-1/2). The width of the diffusion region (current sheet) in the collisionless regime is found to be ?c'less=(c/?pe)2/rL,e, which is independent of the global reconnection scale L and is only prescribed by microphysics (electron inertial length, c/?pe, and electron Larmor radius, rL,e). Amongst other issues, the fastness of the reconnection rate alleviates, e.g., the problem of interpretation of sg., the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be a few minutes, as opposed to Sweet-Parker's equivalent value of less than a day. The new theoretical reconnection rate is compared to the Magnetic Reconnection Experiment device experimental data by Yamada et al. [Phys. Plasmas 13, 052119 (2006)] and Ji et al. [Geophys. Res. Lett. 35, 13106 (2008)], and a good agreement is obtained.

352

Effects of electron inertia in collisionless magnetic reconnection  

CERN Document Server

We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our results show that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfv\\'en velocity, which therefore qualifies as fast reconnection.

Andrés, N; Dmitruk, P; Gómez, D

2013-01-01

353

Effects of electron inertia in collisionless magnetic reconnection  

Science.gov (United States)

We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.

Andrés, Nahuel; Martin, Luis; Dmitruk, Pablo; Gómez, Daniel

2014-07-01

354

Effects of electron inertia in collisionless magnetic reconnection  

International Nuclear Information System (INIS)

We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection

355

New Measure of the Dissipation Region in Collisionless Magnetic Reconnection  

Science.gov (United States)

A new measure to identify a small-scale dissipation region in collisionless magnetic reconnection is proposed. The energy transfer from the electromagnetic field to plasmas in the electron s rest frame is formulated as a Lorentz-invariant scalar quantity. The measure is tested by two-dimensional particle-in-cell simulations in typical configurations: symmetric and asymmetric reconnection, with and without the guide field. The innermost region surrounding the reconnection site is accurately located in all cases. We further discuss implications for nonideal MHD dissipation.

Zenitani, Seiji; Hesse, Michael; Klimas, Alex; Kuznetsova, Masha

2012-01-01

356

On the relationship between quadrupolar magnetic field and collisionless reconnection  

International Nuclear Information System (INIS)

Using hybrid simulations, we investigate the onset of fast reconnection between two cylindrical magnetic shells initially close to each other. This initial state mimics the plasma structure in High Energy Density Plasmas induced by a laser-target interaction and the associated self-generated magnetic field. We clearly observe that the classical quadrupolar structure of the out-of-plane magnetic field appears prior to the reconnection onset. Furthermore, a parametric study reveals that, with a non-coplanar initial magnetic topology, the reconnection onset is delayed and possibly suppressed. The relation between the out-of-plane magnetic field and the out-of-plane electric field is discussed

357

Effects of electron inertia in collisionless magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

We present a study of collisionless magnetic reconnection within the framework of full two-fluid MHD for a completely ionized hydrogen plasma, retaining the effects of the Hall current, electron pressure and electron inertia. We performed 2.5D simulations using a pseudo-spectral code with no dissipative effects. We check that the ideal invariants of the problem are conserved down to round-off errors. Our numerical results confirm that the change in the topology of the magnetic field lines is exclusively due to the presence of electron inertia. The computed reconnection rates remain a fair fraction of the Alfvén velocity, which therefore qualifies as fast reconnection.

Andrés, Nahuel, E-mail: nandres@iafe.uba.ar; Gómez, Daniel [Instituto de Astronomía y Física del Espacio, CC. 67, suc. 28, 1428, Buenos Aires (Argentina); Departamento de Física, Facultad de Ciencias Exactas y Naturales, Univrsidad de Buenos Aires, Pabellón I, 1428, Buenos Aires (Argentina); Martin, Luis; Dmitruk, Pablo [Departamento de Física, Facultad de Ciencias Exactas y Naturales, Univrsidad de Buenos Aires, Pabellón I, 1428, Buenos Aires (Argentina)

2014-07-15

358

A hybrid simulation study of magnetic reconnection in anisotropic plasmas  

Science.gov (United States)

The process of magnetic reconnection in anisotropic plasmas is studied numerically using a 2-dimensional, 3-component hybrid simulation. The results of the calculation show that, when the plasma pressure in the direction perpendicular to magnetic field is larger than that in the parallel direction (e.g. P ?/P ? = 1.5 ), instability may greatly increase, speeding up the rate of reconnection. When P? is smaller than P?, (e.g., when P ?/P ? = 0.6 ), fire hose instability appears, which will restrain the tearing mode instability and the process of magnetic reconnection.

Guo, Jun; Li, Yi; Lu, Quan-ming; Wang, Shui

2003-10-01

359

Reconnection at 3D Magnetic Null Points: Effect of Current Sheet Asymmetry  

CERN Document Server

Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a symmetric 3D null with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is inherently equal and opposite in how flux is reconnected across the fan plane. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis it is shown that when the ohmic dissipation in the layer ...

Wyper, Peter F

2013-01-01

360

Place cells and place?navigation  

OpenAIRE

The assumption that hippocampal place cells (PCs) form the neural substrate of cognitive maps can be experimentally tested by comparing the effect of experimental interventions on PC activity and place navigation. Conditions that interfere with place navigation (darkness, cholinergic blockade) but leave PC activity unaffected obviously disrupt spatial memory at a post-PC level. Situations creating a conflict between egocentric and allocentric orientation (place navigation in the Morris water ...

Bures, J.; Fenton, A. ?A; Kaminsky, Yu; Zinyuk, L.

1997-01-01

361

Magnetopause reconnection and the role of the magnetosphere  

Science.gov (United States)

The Earth's dayside magnetopause provides a platform to study magnetic reconnection over a wide range of parameter space. The plasma and magnetic field on both sides of the magnetopause boundary can change significantly. The resulting boundary is the site of asymmetric reconnection spanning a host of parameters and with a range of effects on energy input into the magnetosphere. We present recent spacecraft observations from the THEMIS mission studying the impact of changes on the magnetosphere side of the boundary. This includes changes in plasma density by up to three orders of magnitude (0.1 to 100cm^-3). We find the reconnection structure agrees with asymmetric reconnection theory, however the local parameters in the magnetosheath do not adjust sufficiently to accommodate changes within the magnetoshere.

Walsh, Brian; Sibeck, David; Phan, Tai; Souza, Vitor; Bonnell, John

2015-04-01

362

Magnetic reconnection in Hall-MHD including electron inertia  

Science.gov (United States)

Magnetic reconnection is an important energy conversion process in highly conducting plasmas, such as those present in the solar corona or in planetary magnetospheres. Within the framework of resistive one-fluid MHD, the Sweet-Parker model leads to extremely low reconnection rates for virtually all space physics applications. Kinetic plasma effects introduce new spatial and temporal scales into the theoretical description, which might significantly increase the reconnection rates. Within the more general framework of two-fluid MHD for a fully ionized hydrogen plasma, we retain the effects of the Hall current and electron inertia. We performed 2.5D Hall MHD simulations including electron inertia using a pseudo-spectral code which yields exact conservation (to round-off errors) of all the ideal invariants. We obtain finite reconnection rates even in the case of zero resistivity, thus showing the important influence of the electron inertia.

Gomez, D. O.; Andres, N.; Martin, L. N.; Dmitruk, P.

2013-12-01

363

Relating reconnection rate, exhaust structure and effective resistivity  

Science.gov (United States)

The magnetic reconnection structure consists of a central diffusion region (CDR) and a cone or wedge shaped reconnection exhaust containing accelerated plasma flows and electromagnetic fluctuations. We predict here the relationship among the exhaust half-cone angle (?e), the half width (w) of the CDR, the outflow velocity Vo, and the effective resistivity (?eff), which includes the effects of all the nonideal terms in the generalized Ohm's law. The effective resistivity is defined as the ratio of reconnection electric field Erec to the current density Jy at the X point and it essentially represents the loss of momentum from the current-carrying plasma particles due to scattering by waves, their inertia or outflux from the CDR. The relation is checked against relevant results previously reported from laboratory experiments, space observations, and simulations, showing excellent agreement. The relation can be used for estimating the ad-hoc effective resistivity often used in magnetohydrodynamic modeling of reconnection.

Singh, Nagendra

2014-03-01

364

Scaling Law of Relativistic Sweet-Parker Type Magnetic Reconnection  

CERN Document Server

Relativistic Sweet-Parker type magnetic reconnection is investigated by relativistic resistive magnetohydrodynamic (RRMHD) simulations. As an initial setting, we assume anti-parallel magnetic fields and a spatially uniform resistivity. A perturbation imposed on the magnetic fields triggers magnetic reconnection around a current sheet, and the plasma inflows into the reconnection region. The inflows are then heated due to ohmic dissipation in the diffusion region, and finally become relativistically hot outflows. The outflows are not accelerated to ultra-relativistic speeds (i.e., Lorentz factor ~ 1), even when the magnetic energy dominates the thermal and rest mass energies in the inflow region. Most of the magnetic energy in the inflow region is converted into the thermal energy of the outflow during the reconnection process. The energy conversion from magnetic to thermal energy in the diffusion region results in an increase in the plasma inertia. This prevents the outflows from being accelerated to ultra-re...

Takahashi, Hiroyuki R; Masada, Youhei; Matsumoto, Jin

2011-01-01

365

Magnetic Reconnection in Non-Equilibrium Ionization Plasma  

CERN Document Server

We have studied the effect of time-dependent ionization and recombination processes on magnetic reconnection in the solar corona. Petschek-type steady reconnection, in which model the magnetic energy is mainly converted at the slow-mode shocks, was assumed. We carried out the time-dependent ionization calculation in the magnetic reconnection structure. We only calculated the transient ionization of iron; the other species were assumed to be in ionization equilibrium. The intensity of line emissions at specific wavelengths were also calculated for comparison with {\\it Hinode} or other observations in future. What we found is as follows: (1) iron is mostly in non-equilibrium ionization in the reconnection region, (2) the intensity of line emission estimated by the time-dependent ionization calculation is significantly different from that with the ionization equilibrium assumption, (3) the effect of time-dependent ionization is sensitive to the electron density in the case that the electron density is less than ...

Imada, S; Watanabe, T; Hara, H; Shimizu, T

2011-01-01

366

Singular structure of magnetic islands resulting from reconnection  

International Nuclear Information System (INIS)

Magnetic island equilibria resulting from reconnection in magnetohydrodynamic (MHD) simulations are explored in a two-dimensional slab geometry. Magnetic islands are evolved to finite amplitude with a nonzero resistivity. The resistivity and flows are then set to zero and the system is allowed to relax toward equilibrium. A y-type singular current layer in the equilibrium state is identified for all but systems with the smallest values of the tearing mode stability parameter ?'. It is shown that the length of the equilibrium y line tracks the length of the Sweet-Parker current layer that develops during reconnection. This suggests that the formation of Sweet-Parker current layers during magnetic reconnection in the resistive MHD model is a consequence of the presence of a singularity in post-reconnection state. A threshold in ?' for singular behavior is also identified

367

Theoretical Resolution of Magnetic Reconnection in High Energy Plasmas  

CERN Document Server

The formation of macroscopic reconnected magnetic structures (islands) have been observed in advanced experiments on weakly collisional, well confined plasmas while established theories of the drift-tearing modes, which depend strongly on the electron temperature gradient and can describe the formation of these structures, had predicted practically inaccessible excitation thresholds for them in these regimes. The relevant theoretical dilemma is resolved as mesoscopic modes that depend critically on the ratio of the transverse (to the magnetic field) to the longitudinal thermal conductivity${D^e_{\\perp}/D^e_{\\|}$, can produce large scale magnetic reconnection. These modes are envisioned to emerge from a background, which can be coherent, of collisionless microscopic reconnecting modes driven by the electron temperature gradient, that create a sequence of adjacent strings of magnetic islands and increase considerably the ratio ${D^e_{\\perp}/D^e_{\\|}$ over its classical value. The mesoscopic reconnecting mode is...

Coppi, B

2007-01-01

368

Forced Hall magnetic reconnection: Parametric variation of the 'Newton Challenge'  

International Nuclear Information System (INIS)

A parametric study of forced magnetic reconnection using a 2D Hall magnetohydrodynamic (MHD) code based on the 'Newton Challenge' is presented. The 'Newton Challenge' defined a magnetic reconnection problem in which reconnection was initiated by a spatially and temporally dependent inflow velocity on the upstream boundary. In this study the magnitude and time dependence of the inflow velocity are varied, as well as the length of the system and the boundary conditions. The general conclusion is that reconnection occurs sooner and faster for stronger impulsive drives (e.g., larger inflow velocities and longer time scales). The results are fairly insensitive to system length. Finally, the Hall MHD results are compared to results from a particle-in-cell simulation study

369

Electron response in gyrofluid simulations of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

We investigate the behaviour of an electron population during the evolution of a spontaneous collisionless magnetic reconnection event, reproduced by a two-dimensional version of a Hamiltonian gyrofluid model. This model can be applied in electromagnetic problems where nonlinear effects are important, such as the sawtooth crash in the core of fusion devices. The electron dynamics in the presence of the reconnection fields is reconstructed by means of a test particle code, based on a relativistic Hamiltonian guiding centre formulation of the electron motion. The moments of the electron distribution function and the effects determined by the peculiar structure of the parallel electric field on the electron temperature in the reconnection region are reconstructed and compared with the corresponding quantities evolved by the fluid reconnection model.

Perona, A; Grasso, D; Borgogno, D, E-mail: anna.perona@polito.it

2010-11-01

370

Magnetic reconnection associated fluctuations in the deep magnetotail: ARTEMIS results  

Science.gov (United States)

On the basis of ARTEMIS two-probe mission magnetic reconnection (MR) outflow associated magnetic fluctuations and turbulence are analyzed on 19 February 2011. In the deep-tail, at distances between X = 45 - 51 RE, evidence for reconnection associated plasma sheet thinning was found, accompanied by heating of the plasma sheet. Correlated flow and field reversals and the large-scale Hall-effect signatures indicated the presence of the reconnection X-line. Within fast reconnection plasma outflows, magnetic fluctuations exhibit the same spectral scaling features and kinked spectra as magnetic fluctuations in the solar wind or in various parts of geospace. It was shown that the proton scale magnetic fluctuations are constrained by oblique firehose, proton cyclotron and mirror instability thresholds. For parallel plasma ?|| > 1, where the thresholds converge, perpendicular magnetic fluctuations are enhanced. Magnetic compressibility decreases with the distance to the neutral sheet, however, near the instability thresholds it is comparable to the values obtained in the solar wind.

Vörös, Z.

2011-11-01

371

Experimental Investigation of Trigger Problem in Magnetic Reconnection  

Science.gov (United States)

In order for magnetic reconnection to be explosive there must be a sudden transition from slow to fast reconnection. This so- called ``trigger mechanism,'' which is responsible for the spontaneous and explosive release of magnetic energy in solar flares, magnetospheric substorms, and sawtooth crashes in magnetic fusion devices, is not yet well-understood. We use the Versatile Toroidal Facility (VTF) at MIT to study this transition [1], focusing specifically on its 3D nature. To this end, we use multiple arrays of Langmuir probes, magnetic probes, and Rogowski coils to map out the full 3D structure of the reconnecting plasma. The emerging picture is one in which a global plasma mode (q=2 or q=3) plays a key role in the onset of reconnection, by breaking the axi-symmetry of the device and allowing 3D effects to arise.[1ex] [1] J. Egedal et al., Phys. Rev. Lett. 98, 015003 (2007).

Katz, N.; Egedal, J.; Fox, W.; Le, A.; Vrublevskis, A.; Bonde, J.; Porkolab, M.

2009-11-01

372

Physical Conditions in the Reconnection Layer in Pulsar Magnetospheres  

CERN Document Server

The magnetosphere of a rotating pulsar naturally develops a current sheet beyond the light cylinder (LC). Magnetic reconnection in this current sheet inevitably dissipates a nontrivial fraction of the pulsar spin-down power within a few LC radii. We develop a basic physical picture of reconnection in this environment and discuss its implications for the observed pulsed gamma-ray emission. We argue that reconnection proceeds in the plasmoid-dominated regime, via an hierarchical chain of multiple secondary islands/flux ropes. The inter-plasmoid reconnection layers are subject to strong synchrotron cooling, leading to significant plasma compression. Using the conditions of pressure balance across these current layers, the balance between the heating by magnetic energy dissipation and synchrotron cooling, and Ampere's law, we obtain simple estimates for key parameters of the layers --- temperature, density, and layer thickness. In the comoving frame of the relativistic pulsar wind just outside of the equatorial c...

Uzdensky, Dmitri A

2012-01-01

373

Imaging coronal magnetic-field reconnection in a solar flare  

CERN Document Server

Magnetic-field reconnection is believed to play a fundamental role in magnetized plasma systems throughout the Universe1, including planetary magnetospheres, magnetars and accretion disks around black holes. This letter present extreme ultraviolet and X-ray observations of a solar flare showing magnetic reconnection with a level of clarity not previously achieved. The multi-wavelength extreme ultraviolet observations from SDO/AIA show inflowing cool loops and newly formed, outflowing hot loops, as predicted. RHESSI X-ray spectra and images simultaneously show the appearance of plasma heated to >10 MK at the expected locations. These two data sets provide solid visual evidence of magnetic reconnection producing a solar flare, validating the basic physical mechanism of popular flare models. However, new features are also observed that need to be included in reconnection and flare studies, such as three-dimensional non-uniform, non-steady and asymmetric evolution.

Su, Yang; Holman, Gordon D; Dennis, Brian R; Wang, Tongjiang; Temmer, Manuela; Gan, Weiqun

2013-01-01

374

TWISTING, RECONNECTING MAGNETOSPHERES AND MAGNETAR SPINDOWN  

International Nuclear Information System (INIS)

We present the first simulations of evolving, strongly twisted magnetar magnetospheres. Slow shearing of the magnetar crust is seen to lead to a series of magnetospheric expansion and reconnection events, corresponding to X-ray flares and bursts. The axisymmetric simulations include rotation of the neutron star and the magnetic wind through the light cylinder. We study how the increasing twist affects the spindown rate of the star, finding that a dramatic increase in spindown occurs. Particularly spectacular are explosive events caused by the sudden opening of large amounts of overtwisted magnetic flux, which may be associated with the observed giant flares. These events are accompanied by a short period of ultrastrong spindown, resulting in an abrupt increase in spin period, such as was observed in the giant flare of SGR 1900+14.

375

Magnetic reconnection driven by current repulsion  

International Nuclear Information System (INIS)

The evolution of an equilibrium consisting of two magnetic islands with oppositely directed currents embedded in a strong magnetic field is investigated, using numerical simulation methods. The rapid development of an ideal magnetohydrodynamic instability is observed, which first rotates and then expels the islands. The growth rate is on the order of the inverse of the Alfven transit time and is much higher than that for magnetic island coalescence. In the nonlinear stage, resistivity becomes important as the reconnection process ensues and dissipates the magnetic energy. The growth rate of the instability is a weak function of the plasma beta and other plasma parameters such as S, the magnetic Reynolds number. An energy principle analysis, based on eigenfunctions obtained from the simulation, confirms the existence of the instability

376

Plasma Astrophysics, Part II Reconnection and Flares  

CERN Document Server

This two-part book is devoted to classic fundamentals and current practices and perspectives of modern plasma astrophysics. This second part discusses the physics of magnetic reconnection and flares of electromagnetic origin in space plasmas in the solar system, single and double stars, relativistic objects, accretion disks and their coronae. More than 25% of the text is updated from the first edition, including the additions of new figures, equations and entire sections on topics such as topological triggers for solar flares and the magnetospheric physics problem. This book is aimed at professional researchers in astrophysics, but it will also be useful to graduate students in space sciences, geophysics, applied physics and mathematics, especially those seeking a unified view of plasma physics and fluid mechanics.

Somov, Boris V

2013-01-01

377

Fast Magnetic Reconnection and Spontaneous Stochasticity  

CERN Document Server

Fast turbulent reconnection based on the MHD description assumes, implicitly, a breakdown of flux-freezing. We suggest that this violation is due to the "spontaneous stochasticity" of Lagrangian particle trajectories, a recently discovered phenomenon which corresponds to non-unique and random trajectories for the same starting point. This phenomenon requires a fundamental reformulation of flux-freezing, which reduces to the standard Alfv\\'en relation for laminar flow but which becomes intrinsically stochastic in a turbulent MHD plasma with an extended inertial-range. Infinitely-many magnetic field-lines are stochastically advected to each point and must be averaged to obtain the resultant magnetic field. The relative distance between initial magnetic field lines which arrive to the same final point depends upon the properties of two-particle turbulent dispersion. We develop predictions for such dispersion based on the Goldreich & Sridhar theory of strong MHD turbulence and on weak MHD turbulence theory. O...

Eyink, Gregory L; Vishniac, Ethan T

2011-01-01

378

Twisting, reconnecting magnetospheres and magnetar spindown  

CERN Document Server

We present the first simulations of evolving, strongly twisted magnetospheres of magnetars. Slow shearing of the magnetar crust is seen to lead to a series of magnetospheric expansion and reconnection events, corresponding to X-ray flares and bursts. The simulations include rotation of the neutron star and the magnetic wind through the light cylinder. We study how the increasing twist affects the spindown rate of the star, finding that a dramatic increase in spindown occurs. Particularly spectacular are explosive events caused by sudden opening of large amounts of overtwisted magnetic flux, which may be associated with the observed giant flares. These events are accompanied by a short period of ultra-strong spindown, resulting in an abrupt increase in spin period, such as was observed in the giant flare of SGR 1900+14.

Parfrey, Kyle; Hui, Lam

2012-01-01

379

Magnetic Reconnection in Space Plasmas : Cluster Spacecraft Observations  

OpenAIRE

Magnetic reconnection is a universal process occurring at boundaries between magnetized plasmas, where changes in the topology of the magnetic field lead to the transport of charged particles across the boundaries and to the conversion of electromagnetic energy into kinetic and thermal energy of the particles. Reconnection occurs in laboratory plasmas, in solar system plasmas and it is considered to play a key role in many other space environments such as magnetized stars and accretion disks ...

Retino?, Alessandro

2007-01-01

380

Electron acceleration and heating in collisionless magnetic reconnection  

OpenAIRE

We discuss electron acceleration and heating during collisionless magnetic reconnection by using the results of implicit kinetic simulations of Harris current sheets. We consider and compare electron dynamics in plasmas with different \\beta values and perform simulations up to the physical mass ratio. We analyze the typical trajectory of electrons passing through the reconnection region, we study the electron velocity, focusing on the out-of-plane velocity, and we discuss th...

Ricci, Paolo; Lapenta, Giovanni; Brackbill, J. U.

2003-01-01

381

A simple model for magnetic reconnection heated corona  

OpenAIRE

We construct a simple model for a magnetic reconnection heated corona above a thin accretion disk in AGNs and Galactic black hole candidates(GBHCs). The basic assumptions are that (1) the magnetic reconnection heat is cooled down overwhelmingly by Compton scattering in the corona and that (2) thermal conduction is dominantly cooled by evaporation of the chromospheric plasma in the disk-corona interface before Compton cooling sets in. With these two basic equations as well as...

Liu, B. F.; Mineshige, S.; Shibata, K.

2002-01-01

382

Two-Fluid Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection  

OpenAIRE

We investigate the large scale evolution of a relativistic magnetic reconnection in an electron-positron pair plasma by a relativistic two-fluid magnetohydrodynamic (MHD) code. We introduce an inter-species friction force as an effective resistivity to dissipate magnetic fields. We demonstrate that magnetic reconnection successfully occurs in our two-fluid system, and that it involves Petschek-type bifurcated current layers in later stage. We further observe a quasi-steady e...

Zenitani, Seiji; Hesse, Michael; Klimas, Alex

2009-01-01

383

Collisionless reconnection in an electron-positron plasma.  

Science.gov (United States)

Electromagnetic particle-in-cell simulations of fast collisionless reconnection in a two-dimensional electron-positron plasma (without an equilibrium guide field) are presented. A generalized Ohm's law in which the Hall current cancels out exactly is given. It is suggested that the key to fast reconnection in this plasma is the localization caused by the off-diagonal components of the pressure tensors, which produce an effect analogous to a spatially localized resistivity. PMID:16384388

Bessho, N; Bhattacharjee, A

2005-12-01

384

Three-dimensional magnetic reconnection through a moving magnetic null  

OpenAIRE

A computational study of three-dimensional magnetic reconnection between two flux ropes through a moving reconnection site is presented. The configuration is considered in the context of two interacting spheromaks constrained by a perfectly conducting cylindrical boundary and oriented to form a single magnetic field null at its center. The initial magnetic field configuration is embedded into a uniform thermal plasma and is unstable to tilting. As the spheromaks tilt, their magnetic fi...

Lukin, V. S.; Linton, M. G.

2011-01-01

385

Magnetic reconnection associated fluctuations in the deep magnetotail: ARTEMIS results  

OpenAIRE

On the basis of ARTEMIS two-probe mission magnetic reconnection (MR) outflow associated magnetic fluctuations and turbulence are analyzed on 19 February 2011. In the deep-tail, at distances between X = 45 – 51 RE, evidence for reconnection associated plasma sheet thinning was found, accompanied by heating of the plasma sheet. Correlated flow and field reversals and the large-scale Hall-effect signatures indicated the pres...

Vo?ro?s, Z.

2011-01-01

386

An Analytic Study of the Perpendicularly Propagating Electromagnetic Drift Instabilities in the Magnetic Reconnection Experiment  

Energy Technology Data Exchange (ETDEWEB)

A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients and modest collisions as in the Magnetic Reconnection Experiment (MRX) [10]. The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of cross-field current. By taking into account the electron-ion collisions and applying the theory in the Harris sheet, we establish that this instability could be excited near the center of the Harris sheet and have enough efoldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (LHDI, MTSI et.) studied previously, we believe the instability we find is a favorable candidate to produce anomalous resistivity because of its unique wave characteristics, such as electromagnetic component, large phase velocity, and small group velocity in the cross current layer direction.

Wang, Y., Kulsrud, R., Ji, H

2008-12-03

387

An Analytic Study of the Perpendicularly Propagating Electromagnetic Drift Instabilities in the Magnetic Reconnection Experiment  

International Nuclear Information System (INIS)

A local linear theory is proposed for a perpendicularly propagating drift instability driven by relative drifts between electrons and ions. The theory takes into account local cross-field current, pressure gradients and modest collisions as in the Magnetic Reconnection Experiment (MRX) (10). The unstable waves have very small group velocities in the direction of the pressure gradient, but have a large phase velocity near the relative drift velocity between electrons and ions in the direction of cross-field current. By taking into account the electron-ion collisions and applying the theory in the Harris sheet, we establish that this instability could be excited near the center of the Harris sheet and have enough efoldings to grow to large amplitude before it propagates out of the unstable region. Comparing with the other magnetic reconnection related instabilities (LHDI, MTSI et.) studied previously, we believe the instability we find is a favorable candidate to produce anomalous resistivity because of its unique wave characteristics, such as electromagnetic component, large phase velocity, and small group velocity in the cross current layer direction

388

Cluster Observations of Magnetopause Reconnection at Sub-Proton Scales  

Science.gov (United States)

Magnetopause reconnection has been studied for decades by using observations from many spacecraft. Yet the microphysics of reconnection, i.e. the physics at proton scales and below, is still poorly understood from an observational point of view. Studying the microphysics is crucial for understanding how reconnection starts (onset), how it evolves in time (rate) and how ions and electrons are heated/accelerated. Here we present novel ESA/Cluster observations of reconnection at the subsolar magnetopause, where two spacecraft are separated by ~10 km (sub-proton scale) while being apart ~ 10000 km (fluid scale) from the others. The two-point measurements at sub-proton scales allow to identify a very thin rotational discontinuity having a thickness of about 10 electron gyroradii. The thin discontinuity is associated to a strong parallel current and electron heating in field-aligned directions. Electromagnetic turbulence in the whistler frequency range is observed within the rotational discontinuity. We interpret the observations as a crossing of the reconnection electron diffusion region. We discuss the relevance of Cluster measurements of reconnection at sub-proton scales for the science of the upcoming NASA/MMS mission.

Retino, A.; Vaivads, A.; Sahraoui, F.; Mozer, F.; Zieger, B.; Nakamura, R.

2011-12-01

389

Origins of effective resistivity in collisionless magnetic reconnection  

Science.gov (United States)

The mechanisms that provide effective resistivity for supporting collisonless magnetic reconnection have remained unsettled despite numerous studies. Some of these studies demonstrated that the electron pressure nongyrotropy generates the resistivity (?npg) in the electron diffusion region (EDR). We derive an analytical relation for the effective resistivity (?kin) by momentum balance in a control volume in the EDR. Both ?npg and ?kin mutually compare well and they also compare well with the resistivity required to support reconnection electric field Erec in multi-dimensional particle-in-cell simulations as well as in satellite observations when reconnection occurs in an EDR. But they are about an order of magnitude or so smaller than that required when the reconnection occurred in a much wider reconnecting current sheet (RCS) of half width (w) of the order of the ion skin depth (di), observed in the Earth magnetosphere. The chaos-induced resistivity reported in the literature is found to be even more deficient. We find that for reconnection in RCS with w ˜ di, anomalous diffusion, such as the universal Bhom diffusion and/or that arising from kinetic Alfven waves, could fairly well account for the required resistivity.

Singh, Nagendra

2014-07-01

390

Current disruption and its spreading in collisionless magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Recent magnetic reconnection experiments (MRX) [Dorfman et al., Geophys. Res. Lett. 40, 233 (2013)] have disclosed current disruption in the absence of an externally imposed guide field. During current disruption in MRX, both the current density and the total observed out-of-reconnection-plane current drop simultaneous with a rise in out-of-reconnection-plane electric field. Here, we show that current disruption is an intrinsic property of the dynamic formation of an X-point configuration of magnetic field in magnetic reconnection, independent of the model used for plasma description and of the dimensionality (2D or 3D) of reconnection. An analytic expression for the current drop is derived from Ampere's Law. Its predictions are verified by 2D and 3D electron-magnetohydrodynamic (EMHD) simulations. Three dimensional EMHD simulations show that the current disruption due to localized magnetic reconnection spreads along the direction of the electron drift velocity with a speed which depends on the wave number of the perturbation. The implications of these results for MRX are discussed.

Jain, Neeraj; Büchner, Jörg [Max-Planck/Princeton Center for Plasma Physics, Max Planck Institute for Solar System Research, 37191 Katlenburg-Lindau (Germany); Dorfman, Seth [University of California Los Angeles, Los Angeles, California 90095 (United States); Ji, Hantao [Max-Planck/Princeton Center for Plasma Physics, Deparment of Astrophysica Sciences and Princeton Plasma Physics Laboratory, Princeton University, Princeton, New Jersey 08540 (United States); Surjalal Sharma, A. [Department of Astronomy, University of Maryland, College Park, Maryland 20742 (United States)

2013-11-15

391

Place Names and Identities  

OpenAIRE

This paper discusses various approaches to the topic "place names and identities", addressing the meaning of place names, their role as links to the past as well as their identity-building capacity. The author argues that there is an intimate relationship between place and place name, and he discusses how place names may reflect or give rise to feelings of individual and collective identity attached to the places in question. Three particular personal experiences of the identity role of place...

Botolv Helleland

2012-01-01

392

Fast Magnetic Reconnection in a Toroidal Magnetic Cusp  

Science.gov (United States)

The first results of a basic laboratory experiment aimed at studying the dynamics of plasmas in the region of a magnetic X--point and the related phenomenon of magnetic reconnection in a collision-less regime are presented. The experiments are based on the MIT Versatile Toroidal Facility, VTF. The plasma is created by electron cyclotron resonance heating using a 50 kW klystron micro-wave source at 2.45 GHz. The magnetic configuration is that of a toroidal cusp. Argon and hydrogen plasmas are created by ECRH resulting in densities and temperatures in the range of 10^18 m-3 and 10 eV. Lundquist numbers of the order of 500--1000 are achieved. These conditions are suitable for the study of magnetic reconnection in a low collisionality regime where the collisional mean free paths of electrons and ions are much larger than the dimensions of the plasma. Reconnection is driven by the E× B drift resulting from the combination of the poloidal magnetic cusp field and the toroidal electric field induced by an ohmic transformer. In the typical magnetic configuration, due to the topology of the particle orbits, no global current is encountered when inducing an electric field. A toroidal current is only observed in the case of a very small poloidal magnetic field cusp field and a strong toroidal magnetic guide field. The reconnection studies are focused on the combined effect of plasma flows and the evolution of the magnetic field line structure. Several diagnostic methods based on magnetic probes, passive optical spectra detection and electrostatic probes are used for the field reconstruction and for the electron dynamics. Active optical methods such as laser induced fluorescence, LIF, will be applied for the determination of the ion response during the reconnection process. During the reconnection process the induced flows are larger than the E× B value. A possible explanation for the enhanced flows, related to fast reconnection, is sought in particle orbit effects.

Egedal, Jan

2000-10-01

393

A New Electric Field in Asymmetric Magnetic Reconnection  

Science.gov (United States)

Magnetic reconnection is an important plasma process that drives the dynamics of the plasma in the magnetosphere and plays a crucial role in the interaction between magnetospheric and magnetosheath plasma. It has been shown that when a reconnection occurs in a collisionless plasma, it exhibits the Hall electric field, an in-plane electric field structure pointing toward the X-line. In this work, we show that when the reconnection has asymmetric inflow conditions such as the reconnection at the day-side magnetopause, a new in-plane electric field structure can exist. This electric field points away from the X-line and is distinct from the known Hall electric field. We argue that the origin of the electric field is associated with the physics of finite Larmor radius. A theory and predictions of the electric field properties are presented and backed up by results from fully kinetic particle-in-cell simulations of asymmetric reconnection with various inflow conditions. Under normal day-side reconnection inflow conditions, the electric field is expected to occur on the magnetospheric side of the X-line pointing Earthward. Hence, it has a potential to be used as a signature for satellites, such as the upcoming Magnetospheric Multi-Scale (MMS) mission, to locate the reconnection sites at the day-side magnetopause. This research was supported by the postdoctoral research sponsorship of Mahidol University (KM), NSF grants ATM-0645271 - Career Award (MAS) and AGS-0953463 (PAC), NASA grants NNX08A083G - MMS IDS, NNX11AD69G, and NNX13AD72G (MAS) and NNX10AN08A (PAC), and the Thailand Research Fund (DR).

Malakit, K.; Shay, M. A.; Cassak, P.; Ruffolo, D. J.

2013-12-01

394

Interchange Slip-Running Reconnection and Sweeping SEP-Beams  

Science.gov (United States)

We present a new model to explain how particles, accelerated at a reconnection site that is not magnetically connected to the Earth, could eventually propagate along the well-connected open flux tube. Our model is based on the results of a low-beta resistive magnetohydrodynamics simulation of a three-dimensional line-tied and initially current-free bipole, that is embedded in a non-uniform open potential field. The topology of this configuration is that of an asymmetric coronal null-point, with a closed fan surface and an open outer spine. When driven by slow photospheric shearing motions, field lines, initially fully anchored below the fan dome, reconnect at the null point, and jump to the open magnetic domain. This is the standard interchange mode as sketched and calculated in 2D. The key result in 3D is that, reconnected open field lines located in the vicinity of the outer spine, keep reconnecting continuously, across an open quasi-separatrix layer, as previously identified for non-open-null-point reconnection. The apparent slipping motion of these field lines leads to form an extended narrow magnetic flux tube at high altitude. Because of the slip-running reconnection, we conjecture that if energetic particles would be travelling through, or be accelerated inside, the diffusion region, they would be successively injected along continuously reconnecting field lines that are connected farther and farther from the spine. At the scale of the full Sun, owing to the super-radial expansion of field lines below 3 solar radius, such energetic particles could easily be injected in field lines slipping over significant distances, and could eventually reach the distant flux tube that is well-connected to the Earth.

Masson, S.; Aulanier, G.; Pariat, E.; Klein, K.-L.

2011-01-01

395

Signatures of Secondary Collisionless Magnetic Reconnection Driven by Kink Instability of a Flux Rope  

CERN Document Server

The kinetic features of secondary magnetic reconnection in a single flux rope undergoing internal kink instability are studied by means of three-dimensional Particle-in-Cell simulations. Several signatures of secondary magnetic reconnection are identified in the plane perpendicular to the flux rope: a quadrupolar electron and ion density structure and a bipolar Hall magnetic field develop in proximity of the reconnection region. The most intense electric fields form perpendicularly to the local magnetic field, and a reconnection electric field is identified in the plane perpendicular to the flux rope. An electron current develops along the reconnection line in the opposite direction of the electron current supporting the flux rope magnetic field structure. Along the reconnection line, several bipolar structures of the electric field parallel to the magnetic field occur making the magnetic reconnection region turbulent. The reported signatures of secondary magnetic reconnection can help to localize magnetic re...

Markidis, S; Delzanno, G L; Henri, P; Goldman, M V; Newman, D L; Intrator, T; Laure, E

2014-01-01

396

Color reconnection and its effects on precise measurements at the LHC  

CERN Document Server

There are experimental evidence for the occurrence of colour reconnection, but the mechanisms involved are far from understood. Previous reconnection studies are briefly summarized, and some potential implications for LHC physics are outlined.

Sjöstrand, Torbjörn

2013-01-01

397

Reconnection Inside a Thick Near-Earth Plasma Sheet and its Evolution into Lobe Reconnection: Control of Substorm phases  

Science.gov (United States)

Reconnection can occur in the center of a thick near-earth nightside plasma sheet when boundary conditions are favorable. Outflow on the earthward side of the X line is provided by the well-known azimuthal convection around the earth. Outflow from the tailward side of the X line occurs by earthward motion of the X line and a magnetic island forms on the tailward side. The "thick-sheet reconnection" occurs at a "critical X line" at the outer boundary of the azimuthal convection channel. The outer boundary occurs where flux tubes become too tail-like to convect to the dayside (~30 Re in a stretched tail). Thick-sheet reconnection is suppressed in the growth phase of substorms due to the time-variation of the topology produced by a large dayside reconnection rate and a small convection rate of flux tubes to the dayside. It is initiated when the time-variation of the topology changes as a result of a decrease in dayside reconnection and/or a large convection to the dayside. It then evolves on a time scale of several minutes into the traditional lobe-merging model. There are two options for the evolution of thick-sheet reconnection into traditional lobe merging and the expansion phase. The simplest is that thick-sheet reconnection eats through plasma sheet field lines until lobe field lines are involved. The more complicated option is that the earthward-moving X line and magnetic island come in contact with sub-auroral magnetic flux. The subsequent coalescence of the island with lower-latitude flux causes the formation of a second X line at distances ~25Re which eats through the plasma sheet flux until lobe field lines are involved.

Atkinson, G.

2004-05-01

398

Places of remembrance in citizenship education  

Directory of Open Access Journals (Sweden)

Full Text Available The text starts with a short introduction. Then the concept of place is defined and its inherent characteristics are described: its symbolism, multi-sided nature and multidisciplinary connotations. Afterwards the principles of place-based pedagogy are presented and it’s eclectic character is pointed out. Then, attempt is made to explain the idea of the places of remembrance from the standpoint of history and pedagogy. In the final part the author relates to educational potential of places of remembrance and takes a stance on the role of places of remembrance in citizenship education.

KInga Majchrzak

2012-06-01

399

RADIO EVIDENCE OF BREAK-OUT RECONNECTION?  

International Nuclear Information System (INIS)

We reconsider the 2003 October 28 X17 flare/coronal mass ejection (CME), studying the five minutes immediately before the impulsive flare phase (not discussed in previous work). To this aim we examine complementary dynamic radio spectrograms, single frequency polarimeter records, radio images, space-based longitudinal field magnetograms, and ultraviolet images. We find widely distributed faint and narrowband meter wave radio sources located outside active regions but associated with the boundaries of magnetic flux connectivity cells, inferred from the potential extrapolation of the observed photospheric longitudinal field as a model for coronal magnetic field structures. The meter wave radio sources occur during the initial decimeter wave effects, which are well known to be associated with filament destabilization in the flaring active region (here NOAA 10486). Antiochos et al. predict in their break-out model for CME initiation that '... huge phenomena ... may be controlled by detailed plasma processes that occur in relatively tiny regions'. They suggest that the expected faint energy release '... on long field lines far away from any neutral line ... may be detectable in radio/microwave emission from nonthermal particles...'. In this paper, we describe meter wave sources whose properties correctly coincide with the quoted predictions of the break-out reconnection model of the CME initiation.

400

Magnetohydrodynamic Turbulence and Reconnection in the Magnetotail  

Science.gov (United States)

We have used a global MHD simulation with high spatial resolution to investigate the origin and properties of turbulence in the plasma sheet. In this simulation we imposed a steady southward IMF with a magnitude of 5 nT at the upstream simulation boundary for more than three hours followed by ninety minutes of northward IMF of the same magnitude. The solar wind number density was 20 cm-3, the thermal pressure was 20 pPa, and the velocity was 500 km/s in the x direction. The moderately high dynamic pressure confined the magnetotail to the high-grid resolution region. Even for these nominal solar wind parameters and steady driving the plasma sheet became turbulent. The power spectral densities and probability distribution functions computed from the simulations were comparable to those obtained from spacecraft observations. The largest scale vortices were associated with reconnection outflows and, in the southward IMF case, with the diversion of high speed flows in the near-Earth region. Both time and space domain analyses revealed that there were three scales present, the large scale of the driving processes, the intermediate inertial scale and the dissipative scale.

El-Alaoui, Mostafa; Richard, Robert L.; Ashour-Abdalla, Maha; Goldstein, Melvyn L.; Walker, Raymond J.

2011-01-01

401

Stress at Work Place  

Directory of Open Access Journals (Sweden)

Full Text Available One of hardest forms of stresses to avoid is that work place or job stress Job stress refers to stress experienced by an individual at or because of issues at their work place The term work related stress has many meanings and it causes different levels of anxiety. Not all challenges at work can be called stress as some of these challenges drive employees upward, and empower them to learn new skills or push them to work harder to achieve a certain goal. So, this type of challenges cannot be considered as true stress True job stress is a condition that not only destroys employee desire to work, but also his or her energy, getting them to suffer both emotionally and physically. Warning signs of stress at work when people feel overwhelmed they feel lacking confidence, become irritated or withdrawn, less productive, less effective and their work less rewarding if these warning passed unnoticed then signs and symptoms of stress will appear. Signs and Symptoms of Excessive 4. Personal conflicts with supervisors Workplace Stress or other employees 5. Feeling insecure at work ( 1. Feeling anxious, agitated, constantly threatened with criticism depressed or apathetic or job loss 2. Loss of interest at work 6. Discrimination ( race, sex or age 3. Difficulty in attention and 7. Discouragement (to feel concentration incompetent and worthless 4. Insomnia and sleep problems 8. Sexual harassment 5. Feeling fatigue 9. Lack of flexibility in work hours 6. Muscle tension and headaches 10. Poor work environment 7. Stomach problems or different 11. Developments in technology body aches 8. Social withdrawal How to Deal with Work Place Stress 9. Loss of sex drive 10. Using alcohol or drugs to cope Fortunately, there is a lot that you can do to manage and reduce stress at work. Different Causes of Job Stress General Guidelines: 1. Poor work conditions and having no say over such conditions A. Taking responsibility for 2. Unreasonable demands from improving your physical and emotional employers ( to do perfect job all the well being. time B. Avoiding pitfalls: by identifying 3. Long hours of stressful work knee jerks habits and negative attitudes

Mohammad A. Shahrour

2010-06-01

402

Observations of significant flux closure by dual lobe reconnection  

Science.gov (United States)

We present an interval of dual lobe reconnection during which interplanetary magnetic field lines are captured by the magnetosphere by reconnecting at high latitudes in both the Northern and the Southern Hemispheres. This event was identified using measurements of the ionospheric convection flow and observations of the aurora using the SuperDARN radars and the IMAGE spacecraft. A cusp spot, characteristic of northward IMF, is clearly visible for a 30 min period enabling the ionospheric footprint of the Northern Hemisphere merging gap to be accurately determined. During the interval a strong burst of sunward flow across the dayside open/closed field line boundary (OCB) is observed, which we interpret as the reconfiguration of the magnetosphere following a burst of reconnection. Noon-midnight and dawn-dusk keograms of the aurora show that the polar cap shrinks during the interval indicating that a large amount of flux was closed by the reconnection. Using the SuperDARN potential maps it is possible to calculate that the amount of flux closed during the interval is 0.13 GWb which represents approximately 10% of the pre-existing polar cap. The number of ions captured by the burst of dual lobe reconnection was calculated to be ~2.2×1031, more than sufficient to populate a cold, dense plasma sheet. That a dense plasma sheet was not subsequently observed is discussed in terms of subsequent changes in the IMF.

Imber, S. M.; Milan, S. E.; Hubert, B.

2007-07-01

403

Collision-less Reconnection in the Versatile Toroidal Facility  

Science.gov (United States)

Magnetic reconnection and the mechanisms that allow rapid changes of magnetic field topology are studied in the collisionless plasmas produced in the Versatile Toroidal Facility. Theoretical arguments and experimental results suggest that particle dynamics plays a fundamental role in the reconnection process. Reconnection is observed to proceed at the externally imposed rate unless the ratio of the guide to the cusp field is large. For low values of this ratio, in the absence of macroscopic current layers, a demonstration of the frozen-in law at a single particle level is provided by the measurements of the flow and of the self-consistent electrostatic potential. The breaking of the frozen-in law around the separatrix is also directly observed experimentally. In the presence of significant plasma current, the dynamical evolution of the current layer is measured along with the plasma density and the potential on the reconnection plane. Broadband fluctuations are observed after the current layer forms, in the region of strong pressure and current density gradients. These observations and their interpretation within the gyro-kinetic model will be discussed, along with experiments aimed at measuring fluctuation spectra and possibly preliminary results on the particle distributions during reconnection measured by laser-induced fluorescence and by electrostatic energy analyzers.

Egedal, Jan; Fasoli, Ambrogio; Nazemi, Jon

2001-10-01

404

Vortex induced collisionless reconnection at the magnetopause - magnetosphere boundary  

Science.gov (United States)

The Earth's Magnetopause can be viewed as the boundary separating the Earth's magnetosphere and the solar wind. Therefore, the understanding of the dynamics at play in this region is of primary importance for space weather modeling. We focus our attention on the low latitude flank of the Magnetosphere where the velocity shear between the Magnetosheath and Magnetospheric plasmas is the energetic source of Kelvin-Helmholtz instability. On the shoulder of the resulting vortex chain, different secondary instabilities are at play depending on the local plasma parameters and compete with the vortex pairing process. Most important, secondary instabilities, among other magnetic reconnection, control the plasma mixing as well as the entry of solar wind plasma in the Magnetosphere. We make use of a two-fluid model, including the Hall term and the electron mass in the generalized Ohm's law, to study the 2D non-linear evolution of the Kelvin-Helmholtz instability at the Magnetopause - Magnetosphere interface, in the intermediate regime between subsonic and supersonic regimes. In the presence of a weak in-plane magnetic field, the dynamics of the Kelvin-Helmholtz rolled-up vortices self-consistently generates thin current sheets where reconnection instability eventually enable spontaneous or induced fast reconnection to develop. This evolution enable to study guide field multiple-island collisionless magnetic reconnection as embedded in a large-scale dynamic system, unlike the classical static reconnection setups. This study provides a clear example of nonlinear, cross-scale, collisionless plasma dynamics.

Henri, P.; Califano, F.; Faganello, M.; Pegoraro, F.

2012-04-01

405

Implications of solar flare dynamics for reconnection in magnetospheric substorms  

Energy Technology Data Exchange (ETDEWEB)

From observations of two-ribbon solar flares, a new line of evidence is presented that magnetic reconnection is of key importance in magnetospheric substorms. It is inferred that in substorms reconnection of closed field lines in the near-Earth thinned plasma sheet both initiates and is driven by the overall MHD instability that drives the tailward expulsion of the reconnected closed field (0 loops). The general basis for this inference is the longstanding notion that two-ribbon flares and substorms are essentially similar phenomena, driven by similar processes. An array of observed similarities that substantiate this view is given. More specifically, our inference for substorms is drawn from observations of filament eruptions in two-ribbon flares, from which we conclude that the heart of the overall instability consists of reconnection and eruption of the closed magnetic field in and around the filament. It is proposed that essentially the same overall instability operates in substorms. Our point is not that the magnetic field configuration or the microphysics in substorms is identical to that in two-ribbon flares, but that the overall instability results from essentially the same combination of reconnection and eruption of closed magnetic field.

Moore, R.L.; Horowitz, J.L.; Green, J.L. (National Aeronautics and Space Administration, Huntsville, AL (USA). George C. Marshall Space Flight Center)

1984-11-01

406

A new fast reconnection model in a collisionless regime  

CERN Document Server

Based on the first principles (by balancing the advection with the electron pressure tensor in the generalised Ohm's law, and using the conservation of mass) a simple model of magnetic reconnection in a collisionless regime is formulated. In addition to its importance from the fundamental point of view, the collisionless reconnection model offers a much faster reconnection rate ($M_{c'less}={(d_i/2)}^{1/2}$) than Sweet-Parker's classical one ($M_{sp}=S^{-1/2}$). The width of the diffusion region (current sheet) in the collisionless regime is found to be $\\delta_{c'less}={(d_i/2)}^{1/2}L$, which is much larger than the Sweet-Parker width ($\\delta_{sp}=S^{-1/2}L$) for the space plasma conditions. Amongst other issues, this alleviates e.g. the problem of interpretation of solar flares by means of reconnection, as for the typical solar coronal parameters the obtained collisionless reconnection time can be $< 10$ minutes, as opposed to Sweet-Parker's equivalent value of $<$ year. The new theoretical reconnec...

Tsiklauri, David

2008-01-01

407

Reconnection in substorms and solar flares: analogies and differences  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection is the crucial process in the release of magnetic energy associated with magnetospheric substorms and with solar flares. On the basis of three-dimensional resistive MHD simulations we investigate similarities and differences between the two scenarios. We address in particular mechanisms that lead to the onset of reconnection and on energy release, transport, and conversion mechanisms. Analogous processes might exist in the motion of field line footpoints on the sun and in magnetic flux addition to the magnetotail. In both cases such processes might lead to a loss of neighboring equilibrium, characterized by the formation of very thin embedded current sheet, which acts as trigger for reconnection. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer associated with reconnection. The dominant transfer of released magnetic energy occurs to electromagnetic energy (Poynting) flux and to thermal energy transport as enthalpy flux. The former dominates in low-beta, specifically initially force-free current sheets expected for the solar corona, while the latter dominates in high-beta current sheets, such as the magnetotail. In both cases the outflow from the reconnection site becomes bursty, i.e. spatially and temporally localized, yet carrying most of the outflow energy. Hence an analogy might exist between bursty bulk flows (BBFs) in the magnetotail and pulses of Poynting flux in solar flares.

Birn, Joachim [Los Alamos National Laboratory

2008-01-01

408

Particle acceleration and transport in reconnecting twisted loops in a stratified atmosphere  

Science.gov (United States)

Context. Twisted coronal loops should be ubiquitous in the solar corona. Twisted magnetic fields contain excess magnetic energy, which can be released during magnetic reconnection, causing solar flares. Aims: The aim of this work is to investigate magnetic reconnection, and particle acceleration and transport in kink-unstable twisted coronal loops, with a focus on the effects of resistivity, loop geometry and atmospheric stratification. Another aim is to perform forward-modelling of bremsstrahlung emission and determine the structure of hard X-ray sources. Methods: We use a combination of magnetohydrodynamic (MHD) and test-particle methods. First, the evolution of the kinking coronal loop is considered using resistive MHD model, incorporating atmospheric stratification and loop curvature. Then, the obtained electric and magnetic fields and density distributions are used to calculate electron and proton trajectories using a guiding-centre approximation, taking into account Coulomb collisions. Results: It is shown that electric fields in twisted coronal loops can effectively accelerate protons and electrons to energies up to 10 MeV. High-energy particles have hard, nearly power-law energy spectra. The volume occupied by high-energy particles demonstrates radial expansion, which results in the expansion of the visible hard X-ray loop and a gradual increase in hard X-ray footpoint area. Synthesised hard X-ray emission reveals strong footpoint sources and the extended coronal source, whose intensity strongly depends on the coronal loop density.

Gordovskyy, M.; Browning, P. K.; Kontar, E. P.; Bian, N. H.

2014-01-01

409

Electron Force Balance in Steady Collisionless-Driven Reconnection  

International Nuclear Information System (INIS)

Steady collisionless-driven reconnection in an open system is investigated by means of full-particle simulations. A long thin electron current sheet extends towards the outflow direction when the system relaxes to a steady state. Although the pressure tensor term along the reconnection electric field contributes to the violation of the electron frozen-in condition, a new force balance in the inflow direction is realized between the Lorentz and electrostatic forces, which is quite different from that in Harris equilibrium. The strong electrostatic field is generated through the combined effect of the Hall term and a driving inflow. This new force balance is more evident in the three-dimensional case due to the growth of an instability along the reconnection electric field. It is also found that the normalized charge density is in proportion to the square of the electron Alfven velocity averaged over the electron dissipation region

410

Evolution of field line helicity during magnetic reconnection  

CERN Document Server

We investigate the evolution of field line helicity for non-zero magnetic fields that connect two boundaries, with emphasis on localized finite-B magnetic reconnection. Total (relative) magnetic helicity is already recognized as an important topological constraint on magnetohydrodynamic processes. Field line helicity offers further advantages because it preserves all topological information and can distinguish between different magnetic fields with the same total helicity. Magnetic reconnection changes field topology and field line helicity reflects these changes; the goal of this paper is to characterize that evolution. We start by deriving the evolution equation for field line helicity and examining its terms, also obtaining a simplified form for cases where dynamics are localized within the domain. The main result, which we support using kinematic examples, is that during localized reconnection in a topologically complex magnetic field, the evolution of field line helicity is dominated by a work-like term ...

Russell, Alexander J B; Hornig, Gunnar; Wilmot-Smith, Antonia L

2015-01-01

411

Numerical simulation of a magnetic reconnection in the solar corona  

International Nuclear Information System (INIS)

In this paper, a kind of magnetic reconnection process caused by the local heating in the closed magnetic field region over the equator in the solar corona is discussed. At first, we use a method in combination with analytical and numerical methods to obtain a coronal magnetic configuration with X-type neutral point. Furthermore we solve numerically the magnetohydrodynamic equations by using the full-implicit continuous Eulerian scheme in the spherical coordinates. The results of numerical simulation show that three different processes of magnetic reconnection are existed. On the other hand, the upward plasma velocity is small when the effect of solar gravitational field is considered. Hence, we suggest that the magnetic reconnection caused by the pure resistivity tearing mode may be unimportant for the coronal mass ejections. (author). 37 refs, 2 figs

412

Reconnection dynamics and normal fluid mutual friction in superfluid turbulence  

CERN Document Server

We investigate the forcing of the normal fluid via mutual friction in finite temperature superfluid turbulence in helium-4, paying particular attention to the role of quantized vortex reconnections. Through the use of the vortex filament model, we produce three experimentally relevant vortex tangles each with different topological properties in steady state conditions. Subsequently we investigate, through statistical analysis, how the mutual friction force upon the normal fluid is affected by the characteristic of each of the vortex tangles. Finally, by monitoring the vortex reconnection events, we show how reconnections produce areas of relatively high curvature and superfluid velocity leading to regions of high normal fluid mutual friction, particularly for the homogeneous and isotropic tangles.

Laurie, Jason

2014-01-01

413

Turbulence, Reconnection and Cosmic Rays in Galaxy Clusters  

CERN Document Server

Recent years have been marked by substantial changes in our understanding of magnetic turbulence and magnetic reconnection, which, in its turn induced better understanding of cosmic ray diffusion and acceleration. Current models of magnetized turbulence are no more ad hoc constructions, but numerically tested theories. In this very short review we summarize topics presented in two talks given at the conference and provide a brief sketch of the vast and rapidly developing field. We discuss how turbulence decreases the efficient mean free path of the particles in the collisionless plasmas in galaxy clusters and claim that this makes MHD turbulence description applicable to a wider range of scales. We discuss the properties of MHD turbulence and its relation to magnetic reconnection. Finally, we overview how turbulence induces particle acceleration via second order Fermi process and affects first order Fermi acceleration in shocks and reconnection regions.

Lazarian, A

2011-01-01

414

Asymmetric Magnetic Reconnection in Coronal Mass Ejection Current Sheets  

Science.gov (United States)

Flux rope models of coronal mass ejections (CMEs) predict the formation ofan elongated current sheet in the wake behind the rising plasmoid. These current sheets have been seen to drift or tilt over time by instruments including SOHO/LASCO and Hinode/XRT. We measure this in multiple observations including the 2008 April 9 "Cartwheel CME" and find an average drift that is far more than can be accounted for via the effects of solar rotation. The observed drift could be due to different parts of the current sheet actively reconnecting at different times (e.g., Savage et al. 2010), macroscopic effects from the rising flux rope pulling the plasma sheet along with it, or asymmetry in the magnetic reconnection process itself. These drift rates are compared with resistive magnetohydrodynamic (MHD) simulations of line-tied reconnection between magnetic fields of different strengths. The observed drift rates are comparable to predictions made by the simulations.

Pope, Crystal; Miralles, M. P.; Murphy, N. A.

2012-01-01

415

Relativistic magnetic reconnection in pair plasmas and its astrophysical applications  

CERN Document Server

This review discusses the physics of magnetic reconnection, a process in which the magnetic field topology changes and magnetic energy is converted to kinetic energy, in pair plasmas in the relativistic regime. We focus on recent progress in the field driven by theory advances and the maturity of particle-in-cell codes. This work shows that fragmentation instabilities at the current sheet can play a critical role in setting the reconnection speed and affect the resulting particle acceleration, anisotropy, bulk flows, and radiation. Then, we discuss how this novel understanding of relativistic reconnection can be applied to high-energy astrophysical phenomena, with an emphasis on pulsars, pulsar wind nebulae, and active galactic nucleus jets.

Kagan, Daniel; Cerutti, Benoit; Giannios, Dimitrios

2014-01-01

416

A new paradigm for 3D collisionless magnetic reconnection.  

Energy Technology Data Exchange (ETDEWEB)

A new paradigm is emerging for 3D magnetic reconnection where the interaction of reconnection processes with current aligned instabilities plays an important role. According to the new paradigm, the initial equilibrium is rendered unstable by current aligned instabilities (lower-hybrid drift instability first, drift-kink instability later) and the non-uniform development of kinking modes leads to a compression of magnetic field lines in certain locations and a rarefaction in others. The areas where the flow is compressional are subjected to a driven reconnection process on the time scale of the driving mechanism (the kink mode). In the present paper we illustrate this series of event with a selection of simulation results.

Lapenta, G. M. (Giovanni M.)

2002-01-01

417

Magnetic reconnection, buoyancy, and flapping motions in magnetotail explosions  

Science.gov (United States)

A key process in the interaction of magnetospheres with the solar wind is the explosive release of energy stored in the magnetotail. Based on observational evidence, magnetic reconnection is widely believed to be responsible. However, the very possibility of spontaneous reconnection in collisionless magnetotail plasmas has been questioned in kinetic theory for more than three decades. In addition, in situ observations by multispacecraft missions (e.g., THEMIS) reveal the development of buoyancy and flapping motions coexisting with reconnection. Never before have kinetic simulations reproduced all three primary modes in realistic 2-D configurations with a finite normal magnetic field. Moreover, 3-D simulations with closed boundaries suggest that the tail activity is dominated by buoyancy-driven instabilities, whereas reconnection is a secondary effect strongly localized in the dawn-dusk direction. In this paper, we use massively parallel 3-D fully kinetic simulations with open boundaries to show that sufficiently far from the planet explosive processes in the tail are dominated by reconnection motions. These motions occur in the form of spontaneously generated dipolarization fronts accompanied by changes in magnetic topology which extend in the dawn-dusk direction over the size of the simulation box, suggesting that reconnection onset causes a macroscale reconfiguration of the real magnetotail. In our simulations, buoyancy and flapping motions significantly disturb the primary dipolarization front but neither destroy it nor change the near 2-D picture of the front evolution critically. Consistent with recent multiprobe observations, dipolarization fronts are also found to be the main regions of energy conversion in the magnetotail.

Sitnov, M. I.; Merkin, V. G.; Swisdak, M.; Motoba, T.; Buzulukova, N.; Moore, T. E.; Mauk, B. H.; Ohtani, S.

2014-09-01

418

Microstructure of magnetic reconnection in earth's magnetotail  

International Nuclear Information System (INIS)

A recent study of magnetic reconnection in the earth's magnetotail identified five events in which a pulse of heated electrons appeared near the end of an interval of fast tailward plasma flow. Further investigation of these events has revealed the following information on their microstructure: (1) Measurments of the electron velocity distribution show that the temperature rise can be characterized as a true heating process, in that the gross evolution of the distribution is from a narrower to a broader Maxwellian. (2) During the heating pulse a bump is often apparent in the tail of the electron distribution function at an energy of 2--5 keV. This bump could be the remnant of a beam produced by a 2- to 5-kV parallel potential drop. Thus a possible mechanism for the heating of electrons is the beam plasma instability. (3) The magnetic field during these events is highly variable in all three components. Part of this variability may result from magnetic turbulence generated by the tearing model instability, but minimum variance analysis suggest that some of the more rapid variations up to 20 nT/s) are caused by rotational or tangential discontinuities. (4) Both the Y and Z components of the magnetic field are quite large (10--20 nT) at times. The strongest southward fields are usually observed near the beginning of the heating pulse, while the strongest Y components generally occur during the pre-heating interval of tailward plasma flow. Transient large-scale changes insma flow. Transient large-scale changes in the normal magnetotail current system are indicated by these observations

419

On transition from Alfvén resonance to forced magnetic reconnection  

International Nuclear Information System (INIS)

We revisit the transition from Alfvén resonance to forced magnetic reconnection with a focus on the property of their singularities. As the driven frequency tends to zero, the logarithmic singularity of Alfvén resonance shifts to the power-law singularity of forced reconnection, due to merging of the two resonance layers. The transition criterion depends on either kinetic effects or dissipations that resolve the singularity. As an example, a small but finite resistivity ? is introduced to investigate the transition process. The transition threshold is then obtained as the driven frequency reaches a level of ?O((?/k)1/3)

420

Fast Magnetic Reconnection in the Plasmoid-Dominated Regime  

International Nuclear Information System (INIS)

A conceptual model of resistive magnetic reconnection via a stochastic plasmoid chain is proposed. The global reconnection rate is shown to be independent of the Lundquist number. The distribution of fluxes in the plasmoids is shown to be an inverse-square law. It is argued that there is a finite probability of emergence of abnormally large plasmoids, which can disrupt the chain (and may be responsible for observable large abrupt events in solar flares and sawtooth crashes). A criterion for the transition from the resistive magnetohydrodynamic to the collisionless regime is provided.

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