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1

Where do imaging clinical trials take place?  

Science.gov (United States)

Imaging clinical trials take place in doctor's offices, cancer centers, other medical centers, community hospitals and clinics, and veterans' and military hospitals in cities and towns across the United States and in other countries. Imaging clinical

2

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

3

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

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

Third Place Learning Environments: Perspective Sharing and Perspective Taking  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 f...

Mara Alagic; Rimmington, Glyn M.; Tatiana Orel

2009-01-01

6

Collisionless Magnetic Reconnection in Space Plasmas  

CERN Document Server

Magnetic reconnection requires the violation of the frozen-in condition which ties gyrating charged particles to the magnetic field inhibiting diffusion. Ongoing reconnection has been identified in near-Earth space as being responsible for the excitation of substorms, magnetic storms, generation of field aligned currents and their consequences, the wealth of auroral phenomena. Its theoretical understanding is now on the verge of being completed. Reconnection takes place in thin current sheets. Analytical concepts proceeded gradually down to the microscopic scale, the scale of the electron skin depth or inertial length, recognizing that current layers that thin do preferentially undergo spontaneous reconnection. Thick current layers start reconnecting when being forced by plasma inflow to thin. For almost half a century the physical mechanism of reconnection has remained a mystery. Spacecraft in situ observations in combination with sophisticated numerical simulations in two and three dimensions recently clari...

Treumann, R A

2014-01-01

7

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

8

Key European Grid event to take place in Geneva  

CERN Document Server

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

9

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

10

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

International Nuclear Information System (INIS)

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 ray busts. The implications of the turbulent reconnection model have not been yet studied insufficient detail. I discuss first order Fermi acceleration of cosmic ray that takes place as the oppositely directed magnetic fluxes move together. This acceleration would work in conjunction with the second order Fermi acceleration that is caused by turbulence in the reconnection region. In partially ionized gas the stochastic reconnection enables fast removal of magneticonnection enables fast removal of magnetic flux from star forming molecular clouds

11

49 CFR 40.41 - Where does a urine collection for a DOT drug test take place?  

Science.gov (United States)

...false Where does a urine collection for a DOT drug test take place? 40...41 Where does a urine collection for a DOT drug test take place? (a) A urine collection for a DOT drug test must take place...

2010-10-01

12

Simulation study of magnetic reconnection  

International Nuclear Information System (INIS)

Dynamical process of collisionless driven reconnection is investigated by means of a two-and-one-half-dimensional particle simulation. Magnetic reconnection develops in two steps in accordance with the formation of ion and electron current layers. The dominant triggering mechanism for electron phase changes from electron meandering motion effect to electron inertia effect as a longitudinal magnetic field increases. It is also found that the energy conversion takes place from electrons to ions through the action of an electrostatic field excited in the downstream and thus the average ion temperature becomes about 1.5 of the average electron temperature. (author)

13

12 CFR 14.50 - Where insurance activities may take place.  

Science.gov (United States)

...2010-01-01 2010-01-01 false Where insurance activities may take place...PROTECTION IN SALES OF INSURANCE § 14.50 Where insurance activities may take place...to the extent practicable, keep the area where the bank conducts transactions...

2010-01-01

14

12 CFR 536.50 - Where insurance activities may take place.  

Science.gov (United States)

...2010-01-01 2010-01-01 false Where insurance activities may take place...PROTECTION IN SALES OF INSURANCE § 536.50 Where insurance activities may take place...extent practicable: (1) Keep the area where the savings association conducts...

2010-01-01

15

12 CFR 208.85 - Where insurance activities may take place.  

Science.gov (United States)

...2010-01-01 2010-01-01 false Where insurance activities may take place...Protection in Sales of Insurance § 208.85 Where insurance activities may take place...to the extent practicable, keep the area where the bank conducts transactions...

2010-01-01

16

12 CFR 343.50 - Where insurance activities may take place.  

Science.gov (United States)

...2010-01-01 2010-01-01 false Where insurance activities may take place...PROTECTION IN SALES OF INSURANCE § 343.50 Where insurance activities may take place...to the extent practicable, keep the area where the bank conducts transactions...

2010-01-01

17

Magnetic Reconnection between Small-scale Loops Observed with the New Vacuum Solar Telescope  

Science.gov (United States)

Using the high tempo-spatial resolution H? images observed with the New Vacuum Solar Telescope, we report solid observational evidence of magnetic reconnection between two sets of small-scale, anti-parallel loops with an X-shaped topology. The reconnection process contains two steps: a slow step with a duration of more than several tens of minutes, and a rapid step lasting for only about three minutes. During the slow reconnection, two sets of anti-parallel loops gradually reconnect, and new loops are formed and stacked together. During the rapid reconnection, the anti-parallel loops approach each other quickly, and then rapid reconnection takes place, resulting in the disappearance of the former loops. In the meantime, new loops are formed and separate. The region between the approaching loops is brightened, and the thickness and length of this region are determined to be about 420 km and 1.4 Mm, respectively. During the rapid reconnection process, obvious brightenings at the reconnection site and apparent material ejections outward along reconnected loops are observed. These observed signatures are consistent with predictions by reconnection models. We suggest that the successive slow reconnection changes the conditions around the reconnection site and triggers instabilities, thus leading to the rapid approach of the anti-parallel loops and resulting in the rapid reconnection.

Yang, Shuhong; Zhang, Jun; Xiang, Yongyuan

2015-01-01

18

49 CFR 40.221 - Where does an alcohol test take place?  

Science.gov (United States)

...2010-10-01 false Where does an alcohol test take place? 40.221 Section...FOR TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Testing Sites, Forms, Equipment and Supplies Used in Alcohol Testing § 40.221 Where...

2010-10-01

19

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

CERN Document Server

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 collisionless reconnection scale. I present a simple criterion for this transition in terms of the upstream plasma density and magnetic field and the global length of the reconnection layer. Second, coronal energy release by reconnection raises the ambient plasma density via chromospheric evaporation and this, in turn, temporarily inhibits subsequent reconnection involving the newly-reconnected loops. Over time, however, radiative cooling gradually lowers the density again below the critical value and fast reconnection again becomes possible. As a ...

Uzdensky, Dmitri A

2007-01-01

20

Sawtooth reconnection  

International Nuclear Information System (INIS)

A model of magnetic field reconnection in tokamak sawteeth is given. The reconnection rate is determined by electron inertia rather than resistivity and this leads to a faster sawtooth collapse than Kadomtsev reconnection. (author). 3 refs, 1 fig

 
 
 
 
21

Mechanisms of impulsive magnetic reconnection: Global and local aspects  

International Nuclear Information System (INIS)

The global and local aspects of mechanisms of impulsive magnetic reconnection are discussed focusing on results from a dedicated laboratory experiment, MRX (Magnetic Reconnection Experiment), as well as fusion experiments. Possible application of the present analysis to reconnection phenomena in solar and space plasmas is also discussed. An external force which drives internal current in a fusion plasma causes magnetic flux to accumulate in a core section of the plasma (flux build-up). When the flux build-up generates a magnetic profile that satisfies a condition for a global magnetohydrodynamic instability to develop, reconnection takes place in an induced current layer generated by the instability leading to a global self-organization of the plasma. Generally the flux build-up phase is significantly longer than the reconnection time, ?H >> ?Rec, thus making the waveform of flux evolution or other plasma parameters sawtooth shaped. In the reconnection layer of collisionless plasmas, the two fluid dynamics would lead to the formation of a narrow electron current channel which tends to become unstable against micro-instabilities, leading to an unsteady or impulsive reconnection. A common feature of impulsive reconnection after flux build-up is presented.

22

Waste Disposal: Processes Taking Place (on the way) from the Repository to the Biosphere  

International Nuclear Information System (INIS)

The main objective of SCK-CEN's R and D programme on the processes taking place on the way from the repository to the biosphere is to provide reliable and defensible models and parameters on the migration of dissolved radionuclides and gases through the host formation (Boom Clay) and the backfill materials of a deep geological repository for high level radioactive waste. The programme and main achievements in this topical area in 1999 are summarised

23

49 CFR 40.41 - Where does a urine collection for a DOT drug test take place?  

Science.gov (United States)

...false Where does a urine collection for a DOT drug test take place...TRANSPORTATION WORKPLACE DRUG AND ALCOHOL TESTING PROGRAMS Collection...Supplies Used in DOT Urine Collections § 40...collection for a DOT drug test take...

2010-10-01

24

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)

25

Collisionless driven reconnection in an open system  

Energy Technology Data Exchange (ETDEWEB)

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)

Horiuchi, Ritoku [National Inst. for Fusion Science, Toki, Gifu (Japan); Pei, Wenbing; Sato, Tetsuya [Graduate University for Advanced Studies, Toki, Gifu (Japan)

2000-06-01

26

Reconnection of magnetic field lines by clouds-in-cells plasma model  

International Nuclear Information System (INIS)

A plasma computer experiment by the clouds-in-cells method is presented for the study of the evolutionary process of the reconnection of magnetic field lines, where initially there is a plane current sheet, i.e. antiparallel magnetic field lines. A plasma flow from outside toward the magnetic neutral sheet will cause the reconnection. The model is two-dimensional and positive and negative charges have the same mass. It is shown that rapid reconnection can easily take place, though the solution is obtained only for the vicinity of the resulting magnetic neutral point. The diffusion rate of the magnetic field at the neutral point is self-adjustable to a given reconnection rate, so that the reconnection rate can take any value up to the local Alfven velocity immediately outisde the field reversal region. (auth.)

27

Particle simulation study of 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 a 2.5 dimensional particle simulation. Magnetic reconnection develops in two steps, i.e., slow reconnection which takes place in the early stage of the compression when the current layer is compressed as thin as the orbit amplitude of an ion meandering motion (ion current layer), and subsequent fast reconnection which takes place in the late stage when the electron current is concentrated into the narrow region with spatial scale comparable to the orbit amplitude of an electron meandering motion (electron current layer). The global dynamic evolution of magnetic reconnection is controlled by the physics of the ion current layer. The maximum reconnection rate is roughly in proportion to the driving electric field. It is also found that both ion heating and electron heating take place in accordance with the formation of two current layers and the ion temperature becomes two or more times as high as the electron temperature. (author)

28

Particle simulation study of collisionless driven reconnection in a sheared magnetic field  

International Nuclear Information System (INIS)

Nonlinear development of collisionless driven reconnection and the consequent energy conversion process between the field and particles in a sheared magnetic field are investigated by means of a two-and-a-half-dimensional particle simulation. Magnetic reconnection takes place in two steps irrespective of a longitudinal magnetic field, but the growth rate of reconnection field varies in proportion to the E x B drift velocity at an input boundary. It is clearly observed that the triggering mechanism of collisionless driven reconnection for the fast growing phase changes from an electron meandering dominance in a weak longitudinal field to an electron inertia dominance in a strong field. The electron acceleration and heating take place in the reconnection area under the influence of reconnection electric field, while the electron energy is converted to the ion energy through the action of electrostatic (ambipolar) field excited by magnetic compression in the downstream. It is also found that, in the presence of a longitudinal magnetic field, the electron acceleration by the reconnection field takes place effectively and the generated force-free current is maintained for a long period while forming an asymmetric spatial profile of current layer. (author)

29

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

30

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

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 mag...

Califano, F.; Faganello, M.; Pegoraro, F.; Valentini, F.

2009-01-01

31

The 'taking place' of health and wellbeing: towards non-representational theory.  

Science.gov (United States)

For the last two decades health geography has focused on the dynamics between health and place. Although the social constructivist perspective of much research has provided many insights into the meanings of health and health care arguably, mirroring progress in the parent discipline of human geography, there could be a far more serious engagement with non-representational theory and the 'taking place' of health and health care. To showcase the importance and potential of this broadly, the idea of wellbeing is re-approached. The paper reflects on the ways wellbeing has been treated in research primarily as a meaningful and relatively prescribed state of life, to the neglect of process. Based on this critique, a qualitative study then illustrates the most immediate and everyday ways wellbeing might arise through 'affect'; the pre-personal mobile energies and intensities that result from physical encounters within assemblages of bodies and objects. Indeed, theoretically the findings support the proposition that, at one level, wellbeing might not be taken from environment but instead might emerge as the affective environment. They certainly raise awareness of how much in health might originate at the surface, prior to meaning, within life's infinite spatial doings, and thus they launch some final thoughts on the wider challenges and opportunities for non-representational health geographies. PMID:24675389

Andrews, Gavin J; Chen, Sandra; Myers, Samantha

2014-05-01

32

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

33

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

34

Magnetic reconnection  

International Nuclear Information System (INIS)

The fundamental physics of magnetic reconnection in laboratory and space plasmas is reviewed by discussing results from theory, numerical simulations, observations from space satellites, and recent results from laboratory plasma experiments. After a brief review of the well-known early work, representative recent experimental and theoretical works are discussed and the essence of significant modern findings are interpreted. In the area of local reconnection physics, many findings have been made with regard to two-fluid 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 microturbulence are discussed to understand the fundamental processes in a local reconnection layer in both 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 discussed.

35

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

36

The study of magnetic reconnection in solar spicules  

CERN Document Server

This work is devoted to study the magnetic reconnection instability under solar spicule conditions. Numerical study of the resistive tearing instability in a current sheet is presented by considering the magnetohydrodynamic (MHD) framework. To investigate the effect of this instability in a stratified atmosphere of solar spicules, we solve linear and non-ideal MHD equations in the x-z plane. In the linear analysis it is assumed that resistivity is only important within the current sheet, and the exponential growth of energies takes place faster as plasma resistivity increases. We are interested to see the occurrence of magnetic reconnection during the lifetime of a typical solar spicule.

Fazel, Z

2014-01-01

37

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

38

Taking back place-names – from dusty library to digital life  

DEFF Research Database (Denmark)

Danish place-names have been under publication since 1922 in the scientific series Danmarks Stednavne (Place-Names of Denmark) but only recently the huge project of a digitization of the series has been undertaken. Around 120,000 name articles are now on their way to the web as part of the Digital atlas of the Danish historical-administrative geography. Digitization and presentation of a scientific place-names edition poses many interesting problems in itself, especially regarding the variation over time in both the selection of names and the build-up of scholarly knowledge. How are we to convey to end users the understanding of the limitations of the early volumes compared to the newer ones, and how are we to avoid confusion due to the uneven distribution of the names selected for publication – even in neighbouring parishes? And, furthermore, how can we transfer the advantage of the physical mobility of the book format into a digital context – by making the content available as an application for mobile devices such as smart phones and iPads? Adding geocodes to the name articles could open up the possibility of a digital place-name lexicon allowing the end user to move around in a place-name environment with a very close connection between place, place-name – and scholarly knowledge of the name.

Knudsen, Bo Nissen

39

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

40

Separatrices: The crux of reconnection  

Science.gov (United States)

abstract-type="normal"> Magnetic 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 it 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 energization of the species, the electromagnetic fields and the instabilities developing at the separatrices.

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

2015-01-01

 
 
 
 
41

Vortex Reconnection as the Dissipative Scattering of Dipoles  

CERN Document Server

We propose a phenomenological model of vortex tube reconnection at high Reynolds numbers. The basic picture is that squeezed vortex lines, formed by stretching in the region of closest approach between filaments, interact like dipoles (monopole-antimonopole pairs) of a confining electrostatic theory. The probability of dipole creation is found from a canonical ensemble spanned by foldings of the vortex tubes, with temperature parameter estimated from the typical energy variation taking place in the reconnection process. Vortex line reshuffling by viscous diffusion is described in terms of directional transitions of the dipoles. The model is used to fit with reasonable accuracy experimental data established long ago on the symmetric collision of vortex rings. We also study along similar lines the asymmetric case, related to the reconnection of non-parallel vortex tubes.

Moriconi, L

1999-01-01

42

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

43

Magnetic Reconnection  

International Nuclear Information System (INIS)

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-fluid 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 briefly discussed.

44

Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment  

International Nuclear Information System (INIS)

Two-dimensional resistive Hall magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX). The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. We successfully reproduce many features of the time evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX. The Hall effect is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late ''steady-state'' Y-phase, when plasma heating takes place. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given

45

Hall MHD Modeling of Two-dimensional Reconnection: Application to MRX Experiment  

Energy Technology Data Exchange (ETDEWEB)

Two-dimensional resistive Hall magnetohydrodynamics (MHD) code is used to investigate the dynamical evolution of driven reconnection in the Magnetic Reconnection Experiment (MRX). The initial conditions and dimensionless parameters of the simulation are set to be similar to the experimental values. We successfully reproduce many features of the time evolution of magnetic configurations for both co- and counter-helicity reconnection in MRX. The Hall effect is shown to be important during the early dynamic X-phase of MRX reconnection, while effectively negligible during the late ''steady-state'' Y-phase, when plasma heating takes place. Based on simple symmetry considerations, an experiment to directly measure the Hall effect in MRX configuration is proposed and numerical evidence for the expected outcome is given.

V.S. Lukin; S.C. Jardin

2003-01-09

46

The auroral and ionospheric flow signatures of dual lobe reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available 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.

S. M. Imber

2006-11-01

47

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

48

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

Energy Technology Data Exchange (ETDEWEB)

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., E-mail: hosseinpour@tabrizu.ac.ir; Mehdizade, M.; Mohammadi, M. A. [Plasma Physics Department, University of Tabriz, Tabriz (Iran, Islamic Republic of)

2014-10-15

49

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

50

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.)

51

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

52

Plasmoid-Induced-Reconnection and Fractal Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

As a key to undertanding the basic mechanism for fast reconnection in solar flares, plasmoid-induced-reconnection and fractal reconnection are proposed and examined. We first briefly summarize recent solar observations that give us hints on the role of plasmoid (flux rope) ejections in flare energy release. We then discuss the plasmoid-induced-reconnection model, which is an extention of the classical two-ribbon-flare model which we refer to as the CSHKP model. An essential ...

Shibata, Kazunari; Tanuma, Syuniti

2000-01-01

53

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

54

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

55

Global Simulations of Magnetotail Reconnection  

Science.gov (United States)

There is a growing number of observational evidences of dynamic quasi-periodical magnetosphere response to continuously southward interplan etary magnetic field (IMF). However, traditional global MHD simulatio ns with magnetic reconnection supported by numerical dissipation and ad hoc anomalous resistivity driven by steady southward IMF often prod uce only quasi-steady configurations with almost stationary near-eart h neutral line. This discrepancy can be explained by the assumption that global MHD simulations significantly underestimate the reconnectio n rate in the magnetotail during substorm expansion phase. Indeed, co mparative studies of magnetic reconnection in small scale geometries demonstrated that traditional resistive MHD did not produce the fast r econnection rates observed in kinetic simulations. The major approxim ation of the traditional MHD approach is an isotropic fluid assumption) with zero off-diagonal pressure tensor components. The approximatio n, however, becomes invalid in the diffusion region around the reconn ection site where ions become unmagnetized and experience nongyrotropic behaviour. Deviation from gyrotropy in particle distribution functi on caused by kinetic effects manifests itself in nongyrotropic pressu re tensor with nonzero off-diagonal components. We use the global MHD code BATS-R-US and replace ad hoc parameters such as "critical curren t density" and "anomalous resistivity" with a physically motivated di ssipation model. The key element of the approach is to identify diffusion regions where the isotropic fluid MHD approximation is not applic able. We developed an algorithm that searches for locations of magnet otail reconnection sites. The algorithm takes advantage of block-based domain-decomposition technique employed by the BATS-R-US. Boundaries of the diffusion region around each reconnection site are estimated from the gyrotropic orbit threshold condition, where the ion gyroradius is equal to the distance to the reconnection site. Inside diffusion regions ions are treated as nongyrotropic fluid with nonzero off-dia gonal components of the pressure tensor. The primary kinetic mechanism controlling the dissipation in the diffusion region is incorporated into global MHD simulations in terms of spatially localized nongyrotropic corrections to the induction equation. The magnitude of the non-g yrotropic corrections to the electric field and spatial scales of the diffusion regions are calculated self-consistently at each time step of the simulation using local MHD plasma and field parameters at the reconnection site without introduction of any ad hoc parameters. We d emonstrated that magnetotail reconnection is inherently unsteady even when the solar wind is steady. Global MHD simulations with nongyrotropic corrections produce bursts of fast reconnection typically observe d in small-scale kinetic simulations. During the bursts the length of the diffusion region does not exceed 2R(sub E) approximates 12(c/ome ga * pi). The bursts of the fast reconnection last only for a few min utes. After reaching the maximum value the reconnection rate decreases while the length of the diffusion region increases. The decreased ra te, however, is still significantly larger that the steady reconnection rate characteristic for MHD simulations with reconnection supported by numerical resistivity alone. Magnetotail reconnection supported b y nongyrotropic effects results in a tailward retreat of the reconnection site with average speed of the order of 100 km/s, accompanied by magnetotail stretching and thin current sheet formation in the near-E arth plasma sheet. Overall magnetotail response to the steady low-mach-number solar wind with southward IMF exhibits quasi-periodic loading /unloading dynamics typical for frequently observed multiple substorm s.

Kuznetsova, M. M.; Hesse, M.; Rastatter, L.; Toth, G.; Gombosi, T.

2007-01-01

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

Plasmoids in Reconnecting Current Sheets: Solar and Terrestrial Contexts Compared  

CERN Document Server

Magnetic reconnection plays a crucial role in violent energy conversion occurring in the environments of high electrical conductivity, such as the solar atmosphere, magnetosphere, and fusion devices. We focus on the morphological features of the process in two different environments, the solar atmosphere and the geomagnetic tail. In addition to indirect evidence that indicates reconnection in progress or having just taken place, such as auroral manifestations in the magnetosphere and the flare loop system in the solar atmosphere, more direct evidence of reconnection in the solar and terrestrial environments is being collected. Such evidence includes the reconnection inflow near the reconnecting current sheet, and the outflow along the sheet characterized by a sequence of plasmoids. Both turbulent and unsteady Petschek-type reconnection processes could account for the observations. We also discuss other relevant observational consequences of both mechanisms in these two settings. While on face value, these are...

Lin, J; Farrugia, C J

2008-01-01

58

“Take place” through the city. Socio-anthropology of urban games and sports practices, self-organized in the city.  

Digital Repository Infrastructure Vision for European Research (DRIVER)

This research combines the benefits of urban sociology and the sociology of sports. It analyzes the logical and practical modalities of fun sports, both organized and self-urban. These practices are not only in the city but are first “from” the city. They are fully in line "to place" in urban public spaces. The investigation involves four communities practicing Paris urban spelunking, base-jump Urban street golf and parkour. Inspired by a socio-anthropological research methodology varies ...

Lebreton, Florian

2009-01-01

59

Research of Place-based 3D Augmented Community-Taking The 3D Virtual Campus as an Example  

Directory of Open Access Journals (Sweden)

Full Text Available Place-based virtual community is the trend of recent researches on pervasive computing. The purpose is to enable users in a physical place to receive ubiquitous services from the environment while they communicate with each other unwittingly. The paper further promotes this idea by allowing remote users to join such a virtual community as well as to interact with members on site and calls this type of community as the place-based 3D augmented (PDA community. With the help of the augmented reality technique, on-the-spot member can visually sense the remote users by their representing avatars. To achieve this goal, the ambient communication environment is required to support message flow among the remote users and people on site. Besides, this environment should be able to discover context passing among members of this community to provide proper services. The context issues and context-awareness approaches of PDA community are fully discussed in the paper. Finally, the infrastructure of this PDA community is also presented along with preliminary result of the prototyping environment.

Chung-Hsien Tsai

2011-05-01

60

Optimization of conditions of tritium label introduction in organic compounds by isotopic exchange with tritium water using guides on processes taking place on catalyst surface  

International Nuclear Information System (INIS)

To light the causes effecting on tritium label introduction by isotopic change with tritium water and to study the mechanism of such reactions an attempt is done to use knowledge on processes taking place in heterogeneous catalysis. Conditions of tritium label introduction into deltametrine, pargyline, trichosanthin, cyprophloxacine, 1,3-dibenzyl glycerine are determined. Preparations with molar radioactivity 9.3, 0.5, 1.8, 35.1, 57.3 Cm/mmol are prepared

 
 
 
 
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

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

63

Colour Reconnection at LEP  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

64

A THEMIS Survey of Flux Ropes and Traveling Compression Regions: Location of the Near-Earth Reconnection Site During Solar Minimum  

Science.gov (United States)

A statistical study of flux ropes and traveling compression regions (TCRs) during the Time History of Events and Macroscale Interactions during Substorms (THEMIS) second tail season has been performed. A combined total of 135 flux ropes and TCRs in the range GSM X approx -14 to -31 R(sub E) were identified, many of these occurring in series of two or more events separated by a few tens of seconds. Those occurring within 10 min of each other were combined into aggregated reconnection events. For the purposes of this survey, these are most likely the products of reconnect ion occurring simultaneously at multiple, closely spaced x-lines as opposed to statistically independent episodes of reconnection. The 135 flux ropes and TCRs were grouped into 87 reconnection events; of these, 28 were moving tailward and 59 were moving Earthward. The average location of the near-Earth x-line determined from statistical analysis of these reconnection events is (X(sub GSM), Y*(sub GSM)) = (-30R(sub E), 5R(sub E)), where Y* includes a correction for the solar aberration angle. A strong east-west asymmetry is present in the tailward events, with >80% being observed at GSM Y* > O. Our results indicate that the Earthward flows are similarly asymmetric in the midtail region, becoming more symmetric inside - 18 R(sub E). Superposed epoch analyses indicate that the occurrence of reconnection closer to the Earth, i.e., X > -20 R(sub E), is associated with elevated solar wind velocity and enhanced negative interplanetary magnetic field B(sub z). Reconnection events taking place closer to the Earth are also far more effective in producing geomagnetic activity, judged by the AL index, than reconnection initiated beyond X approx -25 R(sub E).

Imber, S. M.; Slavin, J. A.; Auster, H. U.; Angelopoulos, V.

2011-01-01

65

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

66

Magnetic reconnection in tokamaks  

International Nuclear Information System (INIS)

Four types of magnetic reconnection occurring in tokamaks play an important role in tokamak operation. They are known as the tearing mode, the sawtooth reconnection, the double tearing mode, and the disruption. Although not observed directly, their effects are detected in a wide range of diagnostic measurements. The basic properties of each type of reconnection and their topology in particular are discussed in detail. General theoretical ideas are illustrated by examples of experimental and numerical results. For better understanding of the subject, close cooperation with astrophysicists might be helpful. (J.U.)

67

Three-dimensional steady-state magnetic reconnection  

International Nuclear Information System (INIS)

A family of three-dimensional models of reconnection is presented in which the different members of the family are characterized by the vorticity with which plasma flows towards the reconnection site. The nature of this inflow also determines the size and speed of the outflow jet that carries reconnected field lines away from the reconnection site, and the shape of the MHD shocks that bound it. Flows with positive vorticity are of a flux pile-up type, for which the outflow jet is fastest and narrowest. Among those with negative vorticity is the three-dimensional analogue of Petschek reconnection. Not all combinations of vorticity and reconnection rate are possible; for those solutions with negative vorticity, there is a maximum reconnection rate. As the magnetic Reynolds number Rme or the current density is increased, this maximum is reduced and the possible types of solution become more polarized towards the two extremes of flux pile-up and slow compression regimes. Given a distribution of vorticities and inflow speeds, these models give the corresponding distribution of possible steady-state reconnection rates. As an illustrative example, we take Gaussian distributions of both to show that the resulting distribution is dominated by the flux pile-up regime. (author)

68

Model for magnetic reconnection  

International Nuclear Information System (INIS)

A forced reconnection problem was modeled by two infinite wires that are embedded in a plasma which carry parallel currents. They are brought together at a specified rate. The distance between the wires is taken as 2a(1-e/sup ?t/). For small displacements, the hydromagnetic equations can be linearized and solved asymptotically. For larger displacements, the plasma behavior can be estimated by use of scaling arguments. We determine a local velocity of magnetic reconnection and show that it is essentially equal to the maximum possible reconnection velocity (that of the corresponding vacuum case) up to the time when this velocity approaches the local Alfven speed. We compare the details of our solution with the Sweet-Parker and Petschek reconnection theories

69

Cyclic Magnetic Field Reconnection  

Science.gov (United States)

Using a 2.5D electromagnetic particle-in-cell model, we study the magnetic field reconnection around the rotating plasma embedded in a magnetic field. Considering plasma rotation driven by an external electric field, it was found that during one rotational cycle, first the magnetic field energy increases and then decreases to its initial value. The magnetic reconnection occurring during this cycle plays two roles: first, it produces the closed magnetic islands and later on it reopens them to the initial form of magnetic field lines. Thus, the magnetic reconnection can be cyclically repeated in following plasma rotations. Simultaneously, the kinetic particle energy in the system increases due to dissipative processes in this externally driven plasma system. We think that this cyclic reconnection can operate around rapidly rotating stars and in the plasma vortices formed in unstable plasma flows.

Karlický, Marian

2009-02-01

70

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

71

Fast Turbulent Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Reconnection is the process by which magnetic fields in a conducting fluid change their topology. This process is essential for understanding a wide variety of astrophysical processes, including stellar and galactic dynamos and astrophysical turbulence. To account for solar flares, solar cycles and the structure of the galactic magnetic field reconnection must be fast, propagating with a speed close to the Alfven speed. We show that the presence of a random magnetic field co...

Lazarian, A.; Vishniac, E.

2000-01-01

72

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

73

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

Scientific Electronic Library Online (English)

Full Text Available SciELO Brazil | Language: English Abstract in english 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 w [...] e 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; Gonzalo, Bello; Mariza G, Morgado.

2007-08-01

74

Skewed magnetic field lines reconnection  

International Nuclear Information System (INIS)

Three-dimensional time-dependent reconnection of skewed magnetic field lines is studied. Reconnection is shown to be possible only in the limited oval-shaped part of the current sheet, which was called the reconnection zone. The size of the reconnection zone is defined by the reconnection line length, the behaviour of the electric field in the diffusion region as well as by the angle between the reconnecting fields. Reconnected magnetic flux has the same direction as it has in the Petschek's model near the reconnection line (normal flux), but it changes its sign in the rest of the reconnection zone (anomalous flux). The magnetic energy is converted into the kinetic one in the normal flux region, and the reverse process occurs in the anomalous flux region, so the energy balance is fulfilled within the reconnection region. An electric double layer emerges along the reconnection zone, which emits Alfven waves, these carryin away the energy released in the reconnection process. The solution obtained may be useful in various problems of cosmic plasma physics, e.g. MHD waves generation on the Sun, carrying magnetic flux away from its surface, origin of solar cosmic rays, etc

75

The structure of reconnection layers: Application to the earth's magnetopause  

International Nuclear Information System (INIS)

Using ideal magnetohydrodynamics, the structure of the reconnection layer in the Petschek reconnection model has been analyzed as a function of inflow parameters by Heyn et al. (1988). The authors examine the application of this analysis to conditions which are appropriate to the Earth's magnetopause. For non-antiparallel magnetic field configurations, the field rotation from one inflow region to the other is achieved through two Alfven waves bounding the reconnection layer, although the rotation on the magnetosheath edge is much stronger. Slow shocks or slow expansion waves are needed in addition in order to form a match between the field strengths, and their appearance and strength depends on the degree of asymmetry of the inflow region parameters. Tangential velocities in the inflow regions give rise to a structure of the reconnection layer which is different above and below the reconnection line. In the presence of these tangential velocities, the Kelvin-Helmholtz stability of the magnetopause needs to be considered. If a region of the magnetopause is Kelvin-Helmholtz unstable, it is possible that Petschek-type reconnection is prevented from occurring in this region. Thus they can place constraints on the occurrence of Petschek reconnection

76

THE COLLAPSE OF TURBULENT CORES AND RECONNECTION DIFFUSION  

Energy Technology Data Exchange (ETDEWEB)

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.

Leão, M. R. M.; De Gouveia Dal Pino, E. M.; Santos-Lima, R. [Instituto de Astronomia, Geofísica e Ciências Atmosféricas, Universidade de São Paulo, R. do Matão, 1226, São Paulo, SP 05508-090 (Brazil); Lazarian, A., E-mail: mleao@ime.unicamp.br, E-mail: dalpino@astro.iag.usp.br, E-mail: rlima@astro.iag.usp.br, E-mail: alazarian@facstaff.wisc.edu [Department of Astronomy, University of Wisconsin, Madison, WI 53706 (United States)

2013-11-01

77

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

78

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

79

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

80

Numerical evidence of undriven, fast reconnection in the solar-wind interaction with earth's magnetosphere: formation of electromagnetic coherent structures.  

Science.gov (United States)

We give evidence for the first time of the onset of undriven fast, collisionless magnetic reconnection during the evolution of an initially homogeneous magnetic field advected in a sheared velocity field. We consider the interaction of the solar wind with the magnetospheric plasma at low latitude and show that reconnection takes place in the layer between adjacent vortices generated by the Kelvin-Helmholtz instability. This process generates coherent magnetic structures with a size comparable to the ion inertial scale, much smaller than the system dimensions but much larger than the electron inertial scale. These magnetic structures are further advected in the plasma in a complex pattern but remain stable over a time interval much longer than their formation time. These results can be crucial for the interpretation of satellite data showing coherent magnetic structures in the Earth's magnetosheath or the magnetotail. PMID:18851219

Faganello, M; Califano, F; Pegoraro, F

2008-09-01

 
 
 
 
81

The role of reconnection diffusion in the gravitational collapse of turbulent cloud cores  

Science.gov (United States)

For a molecular cloud clump to form stars some transport of magnetic flux is required from the denser, inner regions to the outer regions of the cloud, otherwise this can prevent the collapse. Fast magnetic reconnection which takes place in the presence of turbulence can induce a process of reconnection diffusion (RD). Extending earlier numerical studies of reconnection diffusion in cylindrical clouds, we consider more realistic clouds with spherical gravitational potentials and also account for the effects of the gas self-gravity. We demonstrate that within our setup RD 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, confirming that RD is able to remove magnetic flux from collapsing clumps, but only a few of them become nearly critical or supercritical, sub-Alfvénic cores, which is consistent with the observations. Besides, we have found that the supercritical cores built up in our simulations develop a predominantly helical magnetic field geometry which is also consistent with observations. Finally, we have evaluated the effective values of the turbulent reconnection diffusion coefficient and found that they are much larger than the numerical diffusion, especially for initially trans-Alfvénic clouds, ensuring that the detected magnetic flux removal is due to to the action of the RD rather than to numerical diffusivity.

Leão, M. R. M.; de Gouveia Dal Pino, E. M.; Santos-Lima, R.; Lazarian, A.

2014-10-01

82

Three-Dimensional Magnetic Reconnection  

CERN Document Server

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) reconnection have been determined. For instance, 3D reconnection (i) occurs with or without nulls, (ii) occurs continuously and continually throughout a diffusion region and (iii) is driven by counter rotating flows. Furthermore, analysis of resistive 3D MHD magnetic experiments have revealed some intriguing effects relating to where and how reconnection occurs. To illustrate these new features, a series of constant-resistivity experiments, involving the interaction of two opposite-polarity magnetic sources in an overlying field, are con...

Parnell, Clare E

2009-01-01

83

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

84

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

85

Turbulent General Magnetic Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 ma...

Eyink, Gregory L.

2014-01-01

86

Reconnecting to the Biosphere  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Humanity has emerged as a major force in the operation of the biosphere, with a significant imprint on the Earth System, challenging social–ecological resilience. This new situation calls for a fundamental shift in perspectives, world views, and institutions. Human development and progress must be reconnected to the capacity of the biosphere and essential ecosystem services to be sustained. Governance challenges include a highly interconnected and faster world, cascading social–ecological...

Folke, Carl; Jansson, A?sa; Rockstro?m, Johan; Olsson, Per; Carpenter, Stephen R.; Chapin, F. Stuart; Cre?pin, Anne-sophie; Daily, Gretchen; Danell, Kjell; Ebbesson, Jonas; Elmqvist, Thomas; Galaz, Victor; Moberg, Fredrik; Nilsson, Ma?ns; O?sterblom, Henrik

2011-01-01

87

Reconnection of colliding vortex rings.  

Science.gov (United States)

We investigate numerically the Navier-Stokes dynamics of reconnecting vortex rings at small Reynolds number for a variety of configurations. We find that reconnections are dissipative due to the smoothing of vorticity gradients at reconnection kinks and to the formation of secondary structures of stretched antiparallel vorticity which transfer kinetic energy to small scales where it is subsequently dissipated efficiently. In addition, the relaxation of the reconnection kinks excites Kelvin waves which due to strong damping are of low wave number and affect directly only large scale properties of the flow. PMID:12633362

Chatelain, Philippe; Kivotides, Demosthenes; Leonard, Anthony

2003-02-01

88

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.

89

Impulsive Magnetic Reconnection in Plasma  

Science.gov (United States)

Transient effect of magnetic reconnection has been investigated in the TS-4 torus plasma merging device. The two loop merging with pull reconnection converts one common flux to two private fluxes. Under strongly driven inflow, the plasma and magnetic flux inflow exceeded the outflow ones, causing flux and density piled-up in the current sheet. This pile-up effect was found to increase the inflow speed without anomalous resistivity effect. Under strong guiding field, a plasmoid grew in the current sheet during plasma pile-up. When flux pile-up reached a critical value, the plasmoid was ejected from the reconnection region and the reconnection speed transiently increased. The plasmoid ejection made the reconnection rate maximum when its acceleration was maximized.

Hayashi, Yoshinori; , Toru, II; Inomoto, Michiaki; Ono, Yasushi

90

Impulsive magnetic reconnection in plasma  

International Nuclear Information System (INIS)

Transient effect of magnetic reconnection has been investigated in the TS-4 torus plasma merging device. The two loop merging with pull reconnection converts one common flux to two private fluxes. Under strongly driven inflow, the plasma and magnetic flux inflow exceeded the outflow ones, causing flux and density piled-up in the current sheet. This pile-up effect was found to increase the inflow speed without anomalous resistivity effect. Under strong guiding field, a plasmoid grew in the current sheet during plasma pile-up. When flux pile-up reached a critical value, the plasmoid was ejected from the reconnection region and the reconnection speed transiently increased. The plasmoid ejection made the reconnection rate maximum when its acceleration was maximized. (author)

91

Reconnection rates of magnetic fields  

International Nuclear Information System (INIS)

The Sweet-Parker and Petschek scalings of magnetic reconnection rate are modified to include the effect of the viscosity. The modified scalings show that the viscous effect can be important in high-? plasmas. The theoretical reconnection scalings are compared with numerical simulation results in a tokamak geometry for three different cases: a forced reconnection driven by external coils, the nonlinear m = 1 resistive internal kink, and the nonlinear m = 2 tearing mode. In the first two cases, the numerical reconnection rate agrees well with the modified Sweet-Parker scaling, when the viscosity is sufficiently large. When the viscosity is negligible, a steady state which was assumed in the derivation of the reconnection scalings is not reached and the current sheet in the reconnection layer either remains stable through sloshing motions of the plasma or breaks up to higher m modes. When the current sheet remains stable, a rough comparison with the Sweet-Parker scaling is obtained. In the nonlinear m = 2 tearing mode case where the instability is purely resistive, the reconnection occurs on the slower dissipation time scale (Psi/sub s/ approx. eta). In addition, experimental data of the nonlinear m = 1 resistive internal kink in tokamak discharges are analyzed and are found to give reasonable agreement with the modified Sweet-Parker scaling

92

Wave associated anomalous drag during magnetic field reconnection  

International Nuclear Information System (INIS)

The anomalous drag, D, due to large amplitude plasma waves is used for the first time, in place of ?*j, to estimate dissipation at the sub-solar magnetopause and to determine the extent to which this drag accounts for the reconnection electric field. This anomalous drag is determined by measuring correlations of the fluctuations in the electric field and plasma density. Large amplitude electric fields occurred more than 60% of the time in the more than 100 sub-solar, low latitude magnetopause crossings of the THEMIS satellite. They occurred mainly near the magnetospheric separatrix in the form of electrostatic lower hybrid and whistler waves. The anomalous drag at the separatrix was generally <10% of the average reconnection electric field, and it was <1% of the field in the current sheet. Thus, anomalous drag due to waves is not a significant driver of reconnection or of the required dissipation at the sub-solar magnetopause.

93

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)

94

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

95

Reconnection of superfluid vortex bundles.  

Science.gov (United States)

Using the vortex filament model and the Gross-Pitaevskii nonlinear Schroedinger equation, we show that bundles of quantized vortex lines in He II are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence and show that, during the bundle reconnection process, kelvin waves of large amplitude are generated, in agreement with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows. PMID:19113421

Alamri, Sultan Z; Youd, Anthony J; Barenghi, Carlo F

2008-11-21

96

NS [Nuclear Safety] update. Current safety and security activities and developments taking place in the Department of Nuclear Safety and Security, Issue no. 6, March 2008  

International Nuclear Information System (INIS)

The current issue presents information about the following activities: 1) International Conference on Illicit Nuclear Trafficking which took place in November 2007 in Edinburgh. The principal aim of the conference was to examine the threat and context of illicit nuclear trafficking of radioactive material, specifically, what is being done to combat such trafficking and where more needs to be done. The conference was also to consider how the obligations and commitments of the legally binding and non-binding international instruments could be and are being implemented by various States. 2) INSAG Message on Nuclear Safety Infrastructure in which the INSAG Chairman Richard Meserve addressed nuclear safety in the current context and various issues that warrant special attention. 3) approved for publication the Safety Requirements publication on Safety of Nuclear Fuel Cycle Facilities. 4) The Asian Nuclear Safety Network (ANSN)

97

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

98

SPONTANEOUS CURRENT-LAYER FRAGMENTATION AND CASCADING RECONNECTION IN SOLAR FLARES. I. MODEL AND ANALYSIS  

International Nuclear Information System (INIS)

Magnetic reconnection is commonly considered to be 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 of 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 a high-resolution MHD simulation. The simulation results indicate that the magnetic-energy transfer to small scales is realized via a cascade of consecutively smaller and smaller flux ropes (plasmoids), analogous to the vortex-tube cascade in (incompressible) fluid dynamics. Both tearing and (driven) 'fragmenting coalescence' processes are equally important for the consecutive fragmentation of the magnetic field (and associated current density) into smaller elements. At the later stages, a dynamic balance between tearing and coalescence processes reveals a steady (power-law) scaling typical of cascading processes. It is shown that cascading reconnection also addresses other open issues in solar-flare research, such as the duality between the regular large-scale picture of (eruptive) flares and the observed signatures of fragmented (chaotic) energy release, as well as the huge number of accelerated particles. Indeed, spontaneous current-layer fragmentation and the formation of multiple channelized dissipative/acceleration regions embeized dissipative/acceleration regions embedded in the current layer appear to be intrinsic to the cascading process. The multiple small-scale current sheets may also facilitate the acceleration of a large number of particles. The structure, distribution, and dynamics of the embedded potential acceleration regions in a current layer fragmented by cascading reconnection are studied and discussed.

99

Diagnostics of solar flare reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We present new diagnostics of the solar flare reconnection, mainly based on the plasma radio emission. We propose that the high-frequency (600-2000 MHz slowly drifting pulsating structures map the flare magnetic field reconnection. These structures correspond to the radio emission from plasmoids which are formed in the extended current sheet due to tearing and coalescence processes. An increase of the frequency drift of the drifting structures is interpreted as an increase of the reconnection rate. Using this model, time scales of slowly drifting pulsating structure observed during the 12 April 2001 flare by the Trieste radiopolarimeter with high time resolution (1 ms are interpreted as a radio manifestation of electron beams accelerated in the multi-scale reconnection process. For short periods Fourier spectra of the observed structure have a power-law form with power-law indices in the 1.3-1.6 range. For comparison the 2-D MHD numerical modeling of the multi-scale reconnection is made and it is shown that Fourier spectrum of the reconnection dissipation power has also a power-law form, but with power-law index 2. Furthermore, we compute a time evolution of plasma parameters (density, magnetic field etc in the 2-D MHD model of the reconnection. Then assuming a plasma radio emission from locations, where the 'double-resonance' instability generates the upper-hybrid waves due to unstable distribution function of suprathermal electrons, we model radio spectra. Effects of the MHD turbulence are included. The resulting spectra are compared with those observed. It is found, that depending on model parameters the lace bursts and the decimetric spikes can be reproduced. Thus, it is shown that the model can be used for diagnostics of the flare reconnection process. We also point out possible radio signatures of reconnection outflow termination shocks. They are detected as type II-like herringbone structures in the 200-700 MHz frequency range. Finally, we mention H? spectra of the 18 September 1995 eruptive prominence which indicate the bi-directional plasma flow as expected in the reconnection process.

M. Karlický

2004-01-01

100

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

 
 
 
 
101

Fast reconnection does not explain internal disruption  

International Nuclear Information System (INIS)

It is shown that a fast reconnection in non viscous plasmas converts a significant part of the liberated magnetic energy into kinetic eddies: such a process cannot persist long enough to allow complete reconnection

102

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

103

A review of astrophysical reconnection  

Science.gov (United States)

Magnetic reconnection is a basic plasma process involving rapid rearrangement of magnetic field topology. It often leads to violent release of magnetic energy and its conversion to the plasma thermal and kinetic energy as well as nonthermal particle acceleration. It is thus believed to power numerous types of explosive phenomena both inside and outside the Solar system, including various kinds of high-energy flares. In this talk I will first give an overview of astrophysical systems where reconnection is believed to play an important role. Examples include pulsed high-energy emission in pulsar magnetospheres; gamma-ray flares in pulsar wind nebulae and AGN/blazar jets; Gamma-Ray Bursts; and giant flares in magnetar systems. I will also analyze the physical conditions of the plasma in some of these astrophysical systems and will discuss the fundamental physical differences between various astrophysical instances of magnetic reconnection and the more familiar solar and space examples of reconnection. In particular, I will demonstrate the importance of including radiative effects in order to understand astrophysical magnetic reconnection and in order to connect our theoretical models with the observed radiation signatures.

Uzdensky, Dmitri

104

Helicity, Reconnection, and Dynamo Effects  

Energy Technology Data Exchange (ETDEWEB)

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.

Ji, Hantao

1998-11-01

105

Magnetic Reconnection in the MST Reversed Field Pinch  

International Nuclear Information System (INIS)

Magnetic field line reconnection is a process whereby magnetic field lines which are otherwise topologically preserved by, and frozen into, a plasma can break and reconnect to form field lines with different topologies. It plays a significant role in a wide variety of plasmas, including stellar, space and laboratory plasmas. The focus of this dissertation is the underlying dynamics of reconnection in one particular kind of laboratory plasma: the Reversed Field Pinch (RFP). Specifically, this dissertation reports measurements, made using a pair of insertable diagnostics in conjunction with arrays of magnetic sensing coils positioned near the plasma surface, of the spatial structure of the magnetic and parallel current density fluctuations associated with reconnection in the edge of MST. At least 4 significant results are obtained form such measurements. First we observe direct evidence of reconnection which takes the form of tearing modes in an RFP. Specifically we measure a (radial) magnetic field fluctuation that causes reconnection in the so-called reversal surface, or q = 0 surface, in the edge of MST. Notably this evidence of reconnection at the reversal surface is the first of its kind in an RFP. Second, we measure the radial width of the associated current sheet, or fluctuation in the component of the current density parallel to the equilibrium magnetic field. Such current sheets are a characteristic feature of the reconnection process but their radial widths arnection process but their radial widths are sensitive to the specific effects that allow reconnection to occur sometimes call non-ideal effects because reconnection is forbidden by ideal MHD. We compare the observed width to those expected from models of reconnection that incorporate different non-ideal effects in Ohm's law. In particular we see that the observed width is significantly larger than those expected form resistivity in the context of linearly unstable tearing modes and electron inertia. It is a factor of a few larger than the width expected form the electron pressure gradient effect. It is significantly smaller than the width expected from the ion inertia, but this width is not expected to be relevant to a strongly magnetized plasma such as an RFP. Notably it is comparable to the width of the magnetic island produced by the associated tearing mode. This is consistent with expectation for saturated or fully developed resistive tearing modes such as MST is believed to exhibit. It is also consistent with the broadening of a smaller width current sheet through current transport due to parallel streaming of charge carriers (along the field lines of the associated island). Third we obtain estimates of the radial charge transport or radial current density due to streaming charge of carriers along magnetic field lines that results from reconnection in the edge of MST. We find that in contradiction with the theoretical expectation for isolated tearing modes it is non-vanishing and in fact large enough to imply both the existence of another charge transport mechanism to maintain charge neutrality and a significant difference in the radial ion and electron particle fluxes due to parallel streaming of particles. Fourth we interpret the flux surface average of j and b as a J x B force density on the plasma. We observe in agreement with theory and observation for interacting tearing modes in an RFP that the radial structure of the force density during sawtooth crashes is such as to flatten the equilibrium radial gradient in toroidal velocity. We observe also that it is sufficiently large as to imply the existence of other force densities on the plasma

106

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

107

Experimental studies of magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Laboratory magnetic reconnection experiments have been performed for nearly 20 years. Elegant experiments by Stenzel and Gekelman [R. L. Stenzel and W. Gekelman, Phys. Rev. Lett. {bold 42}, 1055 (1979); W. Gekelman and R. L. Stenzel, Phys. Rev. Lett. {bold 54}, 2414 (1985)] focused on the measurement of field quantities with a single movable probe in a highly reproducible plasma. Observations included a very thin current sheet (on the order of c/{omega}{sub pe}), accelerated electrons, and whistler waves. The argon ions were unmagnetized in these experiments. Recent magnetohydrodynamic (MHD) experiments by Yamada and Ono have used merging plasmoids [M. Yamada, Y. Ono, A. Hayakawa, M. Katsurai, and F. W. Perkins, Phys. Rev. Lett. {bold 65}, 721 (1990); Y. Ono, M. Yamada, T. Akao, T. Tajima, and R. Matsumoto, Phys. Rev. Lett. {bold 76}, 3328 (1996)] and have measured three dimensional effects and ion acceleration. We have observed correlations between magnetic reconnection and energetic ion flow events with merging force free spheromaks at the Swarthmore Spheromak Experiment (SSX) [T. W. Kornack, P. K. Sollins, and M. R. Brown, Phys. Rev. E {bold 58}, R36 (1998)]. The reconnection layer is measured with linear and two dimensional probe arrays and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The outflow velocity is nearly Alfv{acute e}nic in the reconnection plane and the scale of the magnetic structures is consistent with collisionless reconnection theories (on the order of c/{omega}{sub pi}). Results from the two dimensional array show the formation of magnetic islands correlated with super-Alfv{acute e}nic ions accelerated normal to the layer. {copyright} {ital 1999 American Institute of Physics.}

Brown, M.R. [Department of Physics and Astronomy, Swarthmore College, Swarthmore, Pennsylvania 19081-1397 (United States)

1999-05-01

108

Experimental studies of magnetic reconnection  

International Nuclear Information System (INIS)

Laboratory magnetic reconnection experiments have been performed for nearly 20 years. Elegant experiments by Stenzel and Gekelman [R. L. Stenzel and W. Gekelman, Phys. Rev. Lett. 42, 1055 (1979); W. Gekelman and R. L. Stenzel, Phys. Rev. Lett. 54, 2414 (1985)] focused on the measurement of field quantities with a single movable probe in a highly reproducible plasma. Observations included a very thin current sheet (on the order of c/?pe), accelerated electrons, and whistler waves. The argon ions were unmagnetized in these experiments. Recent magnetohydrodynamic (MHD) experiments by Yamada and Ono have used merging plasmoids [M. Yamada, Y. Ono, A. Hayakawa, M. Katsurai, and F. W. Perkins, Phys. Rev. Lett. 65, 721 (1990); Y. Ono, M. Yamada, T. Akao, T. Tajima, and R. Matsumoto, Phys. Rev. Lett. 76, 3328 (1996)] and have measured three dimensional effects and ion acceleration. We have observed correlations between magnetic reconnection and energetic ion flow events with merging force free spheromaks at the Swarthmore Spheromak Experiment (SSX) [T. W. Kornack, P. K. Sollins, and M. R. Brown, Phys. Rev. E 58, R36 (1998)]. The reconnection layer is measured with linear and two dimensional probe arrays and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The outflow velocity is nearly Alfvenic in the reconnection plane and the scale of the magnetic structurne and the scale of the magnetic structures is consistent with collisionless reconnection theories (on the order of c/?pi). Results from the two dimensional array show the formation of magnetic islands correlated with super-Alfvenic ions accelerated normal to the layer. copyright 1999 American Institute of Physics

109

Experimental studies of magnetic reconnection  

Science.gov (United States)

Laboratory magnetic reconnection experiments have been performed for nearly 20 years. Elegant experiments by Stenzel and Gekelman [R. L. Stenzel and W. Gekelman, Phys. Rev. Lett. 42, 1055 (1979); W. Gekelman and R. L. Stenzel, Phys. Rev. Lett. 54, 2414 (1985)] focused on the measurement of field quantities with a single movable probe in a highly reproducible plasma. Observations included a very thin current sheet (on the order of c/?pe), accelerated electrons, and whistler waves. The argon ions were unmagnetized in these experiments. Recent magnetohydrodynamic (MHD) experiments by Yamada and Ono have used merging plasmoids [M. Yamada, Y. Ono, A. Hayakawa, M. Katsurai, and F. W. Perkins, Phys. Rev. Lett. 65, 721 (1990); Y. Ono, M. Yamada, T. Akao, T. Tajima, and R. Matsumoto, Phys. Rev. Lett. 76, 3328 (1996)] and have measured three dimensional effects and ion acceleration. We have observed correlations between magnetic reconnection and energetic ion flow events with merging force free spheromaks at the Swarthmore Spheromak Experiment (SSX) [T. W. Kornack, P. K. Sollins, and M. R. Brown, Phys. Rev. E 58, R36 (1998)]. The reconnection layer is measured with linear and two dimensional probe arrays and ion flow is directly measured with a retarding grid energy analyzer. Flow has been measured both in the plane of the reconnection layer and out of the plane. The outflow velocity is nearly Alfvénic in the reconnection plane and the scale of the magnetic structures is consistent with collisionless reconnection theories (on the order of c/?pi). Results from the two dimensional array show the formation of magnetic islands correlated with super-Alfvénic ions accelerated normal to the layer.

Brown, M. R.

1999-05-01

110

Effects of color reconnection on final states at the LHC  

Science.gov (United States)

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 events can be used to further constrain these models and reduce the associated modeling uncertainty.

Argyropoulos, Spyros; Sjöstrand, Torbjörn

2014-11-01

111

Three-dimensional inverse energy transfer induced by vortex reconnections  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In low-temperature superfluid helium, viscosity is zero, and vorticity takes the form of discrete, vortex filaments of fixed circulation and atomic thickness. We present numerical evidence of three-dimensional inverse energy transfer from small length scales to large length scales in superfluid turbulence generated by a flow of vortex rings. We argue that the effect arises from the anisotropy of the flow, which favours vortex reconnections of vortex loops of the same polarit...

Baggaley, Andrew W.; Barenghi, Carlo F.; Sergeev, Yuri A.

2012-01-01

112

Magnetopause reconnection and interlinked flux tubes  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic reconnection can be a continuous or a transient process. Global magnetohydrodynamics (MHD simulations are important tools to understand the relevant magnetic reconnection mechanisms and the resulting magnetic structures. We have studied magnetopause reconnection using a global 3-D MHD simulation in which the interplanetary magnetic field (IMF has been set to large positive By and large negative Bz components, i.e., a south-duskward direction. Flux tubes have been observed even during these constant solar wind conditions. We have focused on the interlinked flux tubes event resulting from time-dependent, patchy and multiple reconnection. At the event onset, two reconnection modes seem to occur simultaneously: a time-dependent, patchy and multiple reconnection for the subsolar region; and, a steady and large-scale reconnection for the regions far from the subsolar site.

F. R. Cardoso

2013-10-01

113

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)

114

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 10(5) 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 × 10(5) 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. PMID:22322399

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

2012-03-01

115

Where does acid hydrolysis take place?  

Science.gov (United States)

We present the results of computations on the dissociation of HCl and HNO(3) at the air-water interface. Molecular dynamics simulations of the acid molecule and 200 water molecules were propagated for several nanoseconds, and the resulting structures were used as input to QM/MM geometry optimization runs. Approximately 20-30 water molecules were included along with the acid in the QM portion of the calculation, which was carried out at the B3LYP/6-31+G(d) level. Whereas dissociation to ions is always spontaneous in the bulk, we find that acid molecules confined to the water surface dissociate only with the participation of two additional water molecules, forming a "critical cluster" about the solute. Thus acid dissociation may occur in the near-surface zone at a dynamic air-water interface, in agreement with our earlier experimental conclusions [Clifford et al., Phys. Chem. Chem. Phys.. 2007, 9, 1362]. PMID:19290333

Ardura, Diego; Donaldson, D J

2009-02-01

116

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

117

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

118

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

119

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

120

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

 
 
 
 
121

Impulsive nature in collisional driven reconnection  

International Nuclear Information System (INIS)

Compressible magnetohydrodynamic simulation is carried out in order to investigate energy relaxation process of the driven magnetic reconnection in an open finite system through a long time calculation. It is found that a very impulsive energy release occurs in an intermittent fashion through magnetic reconnection for a continuous magnetic flux injection on the boundary. In the impulsive phase, the reconnection rate is remarkably enhanced up to more than ten times of the driving rate on the boundary. (author)

122

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

123

In-Situ Observations of Magnetic Reconnection in Thin Current Sheets  

Science.gov (United States)

A key question in plasma physics is how electromagnetic energy is converted into energy of charged particles. Magnetic reconnection is a universal process that is responsible for mayor energy conversion in laboratory plasma, in the solar corona and solar wind, in planetary mag-netospheres and that is considered to play an important role in distant astrophysical objects. Reconnection is inherently a multi-scale process where electron, ion and MHD scales are strongly coupled. Reconnection is initiated rapidly in thin current sheets and subsequently generates fast flows that affect large volumes of space for long time. Understanding the fundamental physics of reconnection from an experimental point of view requires observations at different scales. The only place where such observations are currently possible is the near-Earth space where si-multaneous multi-point measurements are available in-situ through ESA/Cluster and NASA/THEMIS spacecraft, in particular high-resolution measurements that are able to resolve particle distri-bution functions and electromagnetic fields down to the smallest scales. Here we present a few examples of Cluster observations within reconnecting thin current sheets in the terrestrial magnetosheath, magnetopause and magnetotail and we discuss our current knowledge and open issues of the microphysics of reconnection. We briefly discuss how fu-ture measurements such as those from NASA/MMS spacecraft will contribute to improve our understanding of the microphysics.

Retinò, Alessandro; Nakamura, Rumi; Vaivads, Andris; Sundkvist, David; Tanaka, Kentaro; Kasahara, Satoshi; Khotyaintsev, Yuri; Mozer, Forrest; Fujimoto, Masaki; Baumjohann, Wolfgang; Bale, Stuart

124

Reconnecting flux-rope dynamo.  

Science.gov (United States)

We develop a model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multiscale model of turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. This model can be viewed as an implementation of the asymptotic limit R_{m}-->infinity for a continuous magnetic field, where magnetic dissipation is strongly localized to small regions of strong-field gradients. We investigate the kinetic-energy release into heat mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux-rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3 , consistent with the solar corona heating by nanoflares. PMID:20365033

Baggaley, Andrew W; Barenghi, Carlo F; Shukurov, Anvar; Subramanian, Kandaswamy

2009-11-01

125

A Reconnecting Flux Rope Dynamo  

CERN Document Server

We develop a new model of the fluctuation dynamo in which the magnetic field is confined in thin flux ropes advected by a multi-scale flow modeling turbulence. Magnetic dissipation occurs only via reconnection of the flux ropes. We investigate the kinetic energy release into heat, mediated by the dynamo action, both in our model and by solving the induction equation with the same flow. We find that a flux rope dynamo is an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy release in reconnections has a power-law form with the slope -3, consistent with the Solar corona heating by nanoflares.

Baggaley, Andrew W; Shukurov, Anvar; Subramanian, Kandaswamy

2009-01-01

126

Determining Heating Rates in Reconnection Formed Flare Loops  

Science.gov (United States)

High-resolution UV and EUV observations have revealed that flare loops are formed and heated by reconnection events taking place successively. Our recent work (Qiu et al. 2012) suggests that the rapid rise of UV brightness at the foot-points of individual flare loops could be used to infer the impulsive heating rate in these loops. Using these heating rates and the Enthalpy-Based Thermal Evolution of Loops (EBTEL, Klimchuk et al. 2008, Cargrill et al. 2012) model, we can compute plasma evolution in thousands of flare loops anchored at the UV foot-points, and calculate the synthetic coronal radiation by these loops to compare with observations. Therefore, the method uses observations to constrain the heating rates from both the input and output of the loop heating model. In this study, we apply this method to two M-class flares occurred on 2005 May 13 and 2011 March 07, respectively, and show that the synthetic soft X-ray and EUV spectra and light curves compare favorably with the observations by RHESSI and EVE. With a steady-state assumption, we also compute the transition-region DEM at the base of each flare loop during its decay phase, and compare the predicted UV and EUV emission at the foot-points with AIA observations. This experiment provides another independent constraint to determination of the heating rates. Furthermore, using RHESSI hard X-ray observations, we also infer the fraction of non-thermal beam heating in the total heating rate of flare loops, and discuss its effect on plasma evolution. For the 2005 May 13 M8.0 flare that exhibits significant thick-target hard X-ray emissions, the lower limit of the total energy used to heat the flare loops is $1.2 \\times 10^31$ ergs, out of which, less than 20% is carried by beam-driven upflows during the impulsive phase.

Liu, Wenjuan; Qiu, J.; Longcope, D.; Caspi, A.; Courtney, C.; O'Hara, J.

2013-07-01

127

Catastrophe Model for Fast Magnetic Reconnection Onset  

International Nuclear Information System (INIS)

A catastrophe model for the onset of fast magnetic reconnection is presented that suggests why plasma systems with magnetic free energy remain apparently stable for long times and then suddenly release their energy. For a given set of plasma parameters there are generally two stable reconnection solutions: a slow (Sweet-Parker) solution and a fast (Alfvenic) Hall reconnection solution. Below a critical resistivity the slow solution disappears and fast reconnection dominates. Scaling arguments predicting the two solutions and the critical resistivity are confirmed with two-fluid simulations

128

Relation of astrophysical turbulence and magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Astrophysical fluids are generically turbulent and this must be taken into account for most transport processes. We discuss how the preexisting turbulence modifies magnetic reconnection and how magnetic reconnection affects the MHD turbulent cascade. We show the intrinsic interdependence and interrelation of magnetic turbulence and magnetic reconnection, in particular, that strong magnetic turbulence in 3D requires reconnection and 3D magnetic turbulence entails fast reconnection. We follow the approach in Eyink et al.[Astrophys. J. 743, 51 (2011)] to show that the expressions of fast magnetic reconnection in A. Lazarian and E. T. Vishniac [Astrophys. J. 517, 700 (1999)] can be recovered if Richardson diffusion of turbulent flows is used instead of ordinary Ohmic diffusion. This does not revive, however, the concept of magnetic turbulent diffusion which assumes that magnetic fields can be mixed up in a passive way down to a very small dissipation scales. On the contrary, we are dealing the reconnection of dynamically important magnetic field bundles which strongly resist bending and have well defined mean direction weakly perturbed by turbulence. We argue that in the presence of turbulence the very concept of flux-freezing requires modification. The diffusion that arises from magnetic turbulence can be called reconnection diffusion as it based on reconnection of magnetic field lines. The reconnection diffusion has important implications for the continuous transport processes in magnetized plasmas and for star formation. In addition, fast magnetic reconnection in turbulent media induces the First order Fermi acceleration of energetic particles, can explain solar flares and gamma ray bursts. However, the most dramatic consequence of these developments is the fact that the standard flux freezing concept must be radically modified in the presence of turbulence.

Lazarian, A. [Department of Astronomy, University of Wisconsin, 475 North Charter Street, Madison, Wisconsin 53706 (United States); Eyink, Gregory L. [Department of Applied Mathematics and Statistics, Johns Hopkins University, Baltimore, Maryland 21218 (United States); Vishniac, E. T. [Department of Physics and Astronomy, McMaster University, 1280 Main Street West, Hamilton, Ontario L8S 4M1 (Canada)

2012-01-15

129

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

130

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.

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

2014-09-01

131

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

132

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

133

Plans for a 3D reconnection experiment  

Science.gov (United States)

Plasma-filled, current-carrying magnetic flux tubes are the essence of tokamaks, RFP's, spheromaks, solar coronal loops, and astrophysical jets. Relevant behaviors/issues are magnetic helicity content and injection, motion of the tube axis (hoop force, kinking), plasma confinement (balance between hydrodynamic pressure and pinch force), axial jet flows (acceleration and stagnation), waves, particle orbits, reconnection, and open v. closed field lines. These behaviors/issues and their mutual interaction are being investigated via Alfven time-scale imaging and conventional diagnostics in highly reproducible experiments having the simplest relevant geometry. High-speed movies clearly show flux tube kinking, motion of the flux tube axis due to hoop force, axial jet flows, an unusual particle orbit associated with flows counter to the electrical current, and reconnection between adjacent co- or counter-helicity flux tubes. A new experiment now under construction will have two slightly offset plasma-filled, current carrying flux tubes locally reconnect in 3D to form a single long flux tube. The setup requires two floating power supplies to drive the pre-reconnection currents as post-reconnection the power supplies become series-connected. A means for overcoming the topologically unavoidable mutual repulsion between the pre-reconnection currents is also required. It is anticipated that Alfven waves will radiate from the 3D localized reconnection region.

Bellan, Paul

2010-11-01

134

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

135

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

136

The role of the Weibel instability at the reconnection jet front in relativistic pair plasma reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The role of the Weibel instability is investigated for the first time in the context of the large-scale magnetic reconnection problem. A late-time evolution of magnetic reconnection in relativistic pair plasmas is demonstrated by particle-in-cell (PIC) simulations. In the outflow regions, powerful reconnection jet piles up the magnetic fields and then a tangential discontinuity appears there. Further downstream, it is found that the two-dimensional extension of the relativis...

Zenitani, S.; Hesse, M.

2007-01-01

137

Magnetic reconnection in the terrestrial magnetosphere  

Energy Technology Data Exchange (ETDEWEB)

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.

Feldman, W.C.

1984-01-01

138

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

139

Analytical solutions for reconnective magnetic annihilation  

International Nuclear Information System (INIS)

Exact solutions of the resistive magnetohydrodynamics (MHD) equations for a stationary and incompressible plasma are presented. These solutions describe a particular kind of magnetic reconnection known as magnetic reconnective annihilation. The two dimensional (2D) case in polar coordinates is described first. Subsequently two ansatzs for 3D solutions in cylindrical and cartesian coordinates are presented. The former consists of a generalization of the previously described form for 2D solutions in curvilinear coordinates. The latter is its analogous counterpart in cartesian coordinates and it allows to derive new 3D solutions for fan reconnection

140

Taking Medication  

Science.gov (United States)

... Educator Questions, Comments, Concerns? 800 . 338 . 3633 Taking Medication Diabetes is a progressive condition. Depending on what ... healthcare team will be able to determine which medications they should be taking and help them understand ...

 
 
 
 
141

Taking Medication  

Medline Plus

Full Text Available ... Educator Questions, Comments, Concerns? 800 . 338 . 3633 Taking Medication Diabetes is a progressive condition. Depending on what ... healthcare team will be able to determine which medications they should be taking and help them understand ...

142

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

143

Magnetic Reconnection in Extreme Astrophysical Environments  

CERN Document Server

Magnetic reconnection is a basic plasma process of dramatic rearrangement of magnetic topology, often leading to a violent release of magnetic energy. It is important in magnetic fusion and in space and solar physics --- areas that have so far provided the context for most of reconnection research. Importantly, these environments consist just of electrons and ions and the dissipated energy always stays with the plasma. In contrast, in this paper I introduce a new direction of research, motivated by several important problems in high-energy astrophysics --- reconnection in high energy density (HED) radiative plasmas, where radiation pressure and radiative cooling become dominant factors in the pressure and energy balance. I identify the key processes distinguishing HED reconnection: special-relativistic effects; radiative effects (radiative cooling, radiation pressure, and Compton resistivity); and, at the most extreme end, QED effects, including pair creation. I then discuss the main astrophysical application...

Uzdensky, Dmitri A

2011-01-01

144

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

145

Forcing continuous reconnection in hybrid simulations  

International Nuclear Information System (INIS)

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

146

Gyrokinetic simulations of collisionless magnetic reconnection  

International Nuclear Information System (INIS)

Linear and nonlinear gyrokinetic simulations of collisionless magnetic reconnection in the presence of a strong guide field are presented. A periodic slab system is considered with a sinusoidally varying reconnecting magnetic field component. The linear growth rates of the tearing mode in both the large and small ?' regimes are compared to kinetic and fluid theory calculations. In the nonlinear regime, focusing on the limit of large ?', the nonlinear reconnection rates in the gyrokinetic simulations are found to be comparable to those obtained from a two-fluid model. In contrast to the fluid system, however, for Ti>>Te and very small initial perturbation amplitudes, the reconnection in the gyrokinetic system saturates in the early nonlinear phase. This saturation can be overcome if the simulation is seeded initially with sufficient random noise

147

Reconnection of Vortex Bundles Lines with Sinusoidally  

Directory of Open Access Journals (Sweden)

Full Text Available Using the vortex filament model with the full Biot-Savart law, we show that non-straight bundles of quantized vortex lines in HeII are structurally robust and can reconnect with each other maintaining their identity. We discuss vortex stretching in superfluid turbulence in many cases. We show that, during the bundle reconnection process, Kelvin waves of large amplitude are generated, in agreement with previous work and with the finding that helicity is produced by nearly singular vortex interactions in classical Euler flows. The reconnection events lead to changes in velocities, radius, number of points and total length. The existence of reconnections was confirmed by other authors using the model of nonlinear Schrödinger equation (NLSE. Our results are agreed with the finding of other authors and extension to our numerical experiments.

Sultan Z. Alamri

2013-06-01

148

The Diffusion Region in Collisionless Magnetic Reconnection  

Science.gov (United States)

A review of present understanding of the dissipation region in magnetic reconnection is presented. The review focuses on results of the thermal inertia-based dissipation mechanism but alternative mechanisms are mentioned as well. For the former process, a combination of analytical theory and numerical modeling is presented. Furthermore, a new relation between the electric field expressions for anti-parallel and guide field reconnection is developed.

Hesse, Michael; Neukirch, Thomas; Schindler, Karl; Kuznetsova, Masha; Zenitani, Seiji

2011-01-01

149

Sound emission due to superfluid vortex reconnections  

Digital Repository Infrastructure Vision for European Research (DRIVER)

By performing numerical simulations of superfluid vortex ring collisions we make direct quantitative measurements of the sound energy released due to vortex reconnections. We show that the energy radiated expressed in terms of the loss of vortex line length is a simple function of the reconnection angle. In addition, we study the temporal and spatial distribution of the radiation and show that energy is emitted in the form of a rarefaction pulse. The pulse evolves into a sou...

Leadbeater, M.; Winiecki, T.; Samuels, D. C.; Barenghi, C. F.; Adams, C. S.

2000-01-01

150

Proton deflectometry of a magnetic reconnection geometry  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Laser-driven magnetic reconnection is investigated using proton deflectometry. Two laser beams of nanosecond duration were focused in close proximity on a solid target to intensities of I?1× 1015 W cm-2. Through the well known ? ne ×? Te mechanism, azimuthal magnetic fields are generated around each focal spot. During the expansion of the two plasmas, oppositely oriented field lines are brought together resulting in magnetic reconnection in the region between the two focal spots. The ...

Willingale, L.; Nilson, Pm; Kaluza, Mc; Dangor, Ae; Evans, Rg; Fernandes, P.; Haines, Mg; Kamperidis, C.; Kingham, Rj; Ridgers, Cp; Sherlock, M.; Thomas, Agr; Wei, Ms; Najmudin, Z.; Krushelnick, K.

2010-01-01

151

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

152

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

153

Taking Medication  

Medline Plus

Full Text Available ... or labels with you when you go to health appointments. Ask a family member to go to an appointment with you adn take notes so your not confused when you get home. Also, ask them to remind you to take your medications or labels when you go for any medical appointment.

154

Taking Medication  

Medline Plus

Full Text Available ... when you go to health appointments. Ask a family member to go to an appointment with you adn take notes so your not confused when you get home. Also, ask them to remind you to take your medications or labels when you go for any medical appointment.

155

Taking Medication  

Medline Plus

Full Text Available ... you go to health appointments. Ask a family member to go to an appointment with you adn take notes so your not confused when you get home. Also, ask them to remind you to take your medications or labels when you go for any medical appointment.

156

Place Values  

Science.gov (United States)

This site has explanatory lessons, interactive practice, and challenge games all dealing with place value. Includes information, practice, and games on place value of two, three, six and seven digit numbers and expandend notation for two, three, six, and seven digit numbers. Problems are randomly selected and students receive immediate feedback with the correct response. The bottom of each lesson page contains timed exercises.

AAA Math

2007-12-12

157

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

158

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

159

Quantitative analytical model for magnetic reconnection in hall magnetohydrodynamics  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection is of fundamental importance for laboratory and naturally occurring plasmas. Reconnection usually develops on time scales which are much shorter than those associated with classical collisional dissipation processes, and which are not fully understood. While such dissipation-independent (or 'fast') reconnection rates have been observed in particle and Hall magnetohydrodynamics (MHD) simulations and predicted analytically in electron MHD, a quantitative analytical theory of fast reconnection valid for arbitrary ion inertial lengths d{sub i} has been lacking. Here we propose such a theory without a guide field. The theory describes two-dimensional magnetic field diffusion regions, provides expressions for the reconnection rates, and derives a formal criterion for fast reconnection in terms of dissipation parameters and di. It also demonstrates that both open X-point and elongated diffusion regions allow dissipation-independent reconnection and reveals a possibility of strong dependence of the reconnection rates on d{sub i}.

Simakov, Andrei N [Los Alamos National Laboratory

2008-01-01

160

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

 
 
 
 
161

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 ...

162

Suprathermal electron acceleration during reconnection onset in the magnetotail  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We study one event of reconnection onset associated to a small substorm on 27 September 2006 by using Cluster observations at inter-spacecraft separation of about 10 000 km. We focus on the acceleration of suprathermal electrons during different stages of reconnection. We show that several distinct stages of acceleration occur: (1) moderate acceleration during reconnection of pre-existing plasma sheet flux tubes, (2) stronger acceleration during reconnection of lobe flux tubes, (3) production...

Vaivads, A.; Retino?, A.; Khotyaintsev, Yu V.; Andre?, M.

2011-01-01

163

Separatrix regions of magnetic reconnection at the magnetopause  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Using data from the four Cluster spacecraft we study the separatrix regions of magnetic reconnection sites at the dayside magnetopause under conditions when reconnection is occurring in the magnetopause current layer which separates magnetosheath plasma from the hot magnetospheric plasma sheet. We define the separatrix region as the region between the separatrix – the first field line opened by reconnection – and the reconnection jet (outflow region). We analyze eight separatrix region cr...

Lindstedt, T.; Khotyaintsev, Yu V.; Vaivads, A.; Andre?, M.; Fear, R. C.; Lavraud, B.; Haaland, S.; Owen, C. J.

2009-01-01

164

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

165

Electromagnetic energy conversion at reconnection fronts  

Science.gov (United States)

Using a fortuitous conjunction between the ARTEMIS, THEMIS, Geotail and GOES we show that bursty bulk flows and plasmoids are observed symmetrically about the reconnection site during the course of a substorm. Flow bursts and proto-plasmoids have similar plasma acceleration/heating signatures, as well as positive and negative-excursion fronts of Z-component magnetic field within them. Observed on the two sides of the reconnection site these fronts are herein dubbed reconnection fronts. Multiple reconnection sites can be remotely sensed using energetic particles, enabling us to determine the location and motion of the X-points at the meridian of the aligned constellation: we find the active region moves down tail after onset; when it moves past X=-60Re a new (nearer-Earth) X-point starts and the global tail reconnection rate increases. Power conversion at kinetic structures within the fronts is significant. Using ARTEMIS total pressure estimates, pressure balance at the magnetopause, and a simple, monotonic profile of the flaring angle as function of distance we can obtain the total lobe flux. Integration of local electromagnetic power conversion at the fronts agrees with the global energy conversion measured by ARTEMIS, suggesting that these fronts are the dominant site of lobe magnetic energy conversion in the magnetotail.

Angelopoulos, V.; Runov, A.; Zhou, X.; Turner, D. L.; Kiehas, S. A.; Li, S.; Shinohara, I.

2013-12-01

166

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

167

Explosive energy conversion mechanism by magnetic field reconnection  

International Nuclear Information System (INIS)

The self-consistent coupling between magnetic reconnection flow and anomalous plasma resistivity is studied. It is shown that, coupled to an anomalous resistivity due to a current-driven microinstability, magnetic reconnection grows very rapidly. The fast reconnection mechanism, eventually established, provides a very powerful energy converter quite responsible for catastrophic events, such as solar flares, geomagnetic substorms and tokamak disruptions. (author)

168

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

169

Driven reconnection and bursty bulk flows  

Directory of Open Access Journals (Sweden)

Full Text Available The energetics of driven magnetic reconnections induced by the deformation of the magnetopause boundary due to the solar wind-magnetosphere interaction are studied. The bursty type reconnection ensues due to the forcing of the magnetopause boundary by the solar wind. For typical plasma parameters in the inner central plasma sheet (ICPS, the magnetic energy release during the reconnection is estimated and it is found that the available free energy is comparable to the observed kinetic energy of typical bursty bulk flows. It implies that the part of the free energy goes into the heating of the ICPS particles, whereas the rest goes into its acceleration. The accelerated particle manifests itself as bursty flows.

Key words. Magnetospheric physics (magnetotail; storms and substorms

B. P. Pandey

170

Magnetic Reconnection in a Weakly Ionized Plasma  

CERN Document Server

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. 2012 \\cite{Leake2012} 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 sca...

Leake, James E; Linton, Mark G

2013-01-01

171

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

172

Role of compressibility on driven magnetic reconnection  

International Nuclear Information System (INIS)

Whether it is induced by an ideal (current driven) instability or by an external force, plasma flow causes a change in the magnetic field configuration and often gives rise to a current intensification locally, thereby a fast driven reconnection being driven there. Many dramatic phenomena in magnetically confined plasmas such as magnetospheric substorms, solar flares, MHD self-organization and tokamak sawtooth crash, may be attributed to this fast driven reconnection. Using a fourth order MHD simulation code it is confirmed that compressibility of the plasma plays a crucial role in leading to a fast (MHD time scale) driven reconnection. This indicates that the incompressible representation is not always applicable to the study of a global dynamical behavior of a magnetically confined plasma. (author)

173

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

174

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

175

Particle-in-cell simulations of shock-driven reconnection in relativistic striped winds  

International Nuclear Information System (INIS)

By means of two- and three-dimensional particle-in-cell simulations, we investigate the process of driven magnetic reconnection at the termination shock of relativistic striped flows. In pulsar winds and in magnetar-powered relativistic jets, the flow consists of stripes of alternating magnetic field polarity, separated by current sheets of hot plasma. At the wind termination shock, the flow compresses and the alternating fields annihilate by driven magnetic reconnection. Irrespective of the stripe wavelength ? or the wind magnetization ? (in the regime ? ? 1 of magnetically dominated flows), shock-driven reconnection transfers all the magnetic energy of alternating fields to the particles, whose average Lorentz factor increases by a factor of ? with respect to the pre-shock value. In the limit ?/(rL?) ? 1, where rL is the relativistic Larmor radius in the wind, the post-shock particle spectrum approaches a flat power-law tail with slope around ?1.5, populated by particles accelerated by the reconnection electric field. The presence of a current-aligned ‘guide’ magnetic field suppresses the acceleration of particles only when the guide field is stronger than the alternating component. Our findings place important constraints on the models of non-thermal radiation from Pulsar Wind Nebulae and relativistic jets. (paper)

176

Taking Medication  

Medline Plus

Full Text Available ... to inject insulin or explain how diabetes pills work and when to take them. Effective drug therapy in combination with healthy lifestyle choices, can lower blood glucose levels, reduce the risk for diabetes complications and produce other clinical benefits. The goal is ...

177

Taking Medication  

Medline Plus

Full Text Available ... Store Events Make a Donation Access My Learning Access AADE7 System Find a Diabetes Educator Questions, Comments, Concerns? 800 . 338 . 3633 Taking Medication Diabetes is a progressive condition. Depending on what type a person has, their healthcare team will be able to determine which medications ...

178

A mechanism of collisionless magnetic reconnection  

International Nuclear Information System (INIS)

Forced reconnection in a collisionless magnetized plasma is studied using an implicit particle simulation. A coalescence of magnetic islands induces the electric field Et at the x-point via the displacement current. A quasi-steady reconnection is achieved with Et ? 0, the poloidal electric field Ep generated by electrostatic shielding, and the current Jt continuously removed via the Ep x B plasma convection. Transit acceleration of electrons by unshielded parallel electric field Eparallel ? Et at the x-point yields the Ohm's law Et ? ?eqJt with ?eq the inertia (kinetic) resistivity. (author)

179

Magnetopause stability treshold for patchy reconnection  

International Nuclear Information System (INIS)

The magnetopause is considered as a transition layer in which the magnetic field vector rotates at a finite angle determined by the direction of the interplanetary magnetic field. The Vlasov kinetic approach is used to study the stability of magnetic surfaces within the layer. Magnetic surfaces can be destroyed by the growth and overlapping of magnetic islands, which can be considered to be a macroscopic but spatially localized magnetic field reconnection process. The thresholds and growth rates of such a reconnection are calculated. The preliminary results of theoretical consideration are discussed in relation with recent ISEE magnetopause measurements. (J.U.)

180

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

 
 
 
 
181

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

182

Fast magnetic reconnection in laser-produced plasma bubbles  

CERN Document Server

Recent experiments have observed magnetic reconnection in high-energy-density, laser-produced plasma bubbles, with reconnection rates observed to be much higher than can be explained by classical theory. Based on fully kinetic particle simulations we find that fast reconnection in these strongly driven systems can be explained by magnetic flux pile-up at the shoulder of the current sheet and subsequent fast reconnection via two-fluid, collisionless mechanisms. In the strong drive regime with two-fluid effects, we find that the ultimate reconnection time is insensitive to the nominal system Alfven time.

Fox, W; Germaschewski, K

2011-01-01

183

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

184

Magnetic skeletons and 3D magnetic reconnection  

Science.gov (United States)

The upper atmosphere of the sun, the solar corona, is approximately 1,000,000K hotter than the surface of the Sun, a property which cannot be explained by the normal processes of heat conduction and radiation. It is now commonly believed that the magnetic fields which fill the solar atmosphere, and propagate down into the interior of the Sun, are important for transferring and transforming energy from the strong plasma flows inside the Sun into the corona as heat. I have investigated an elementary flux interaction which forms a fundamental building block of the coronal heating process. This interaction involves two opposite polarity sources on the Sun's surface in the presence of an overlying magnetic field. To fully understand how this interaction transfers heat into the solar corona, the magnetic skeleton is required, which shows possible sites of heating that are due to magnetic reconnection. A magnetic field is best described by its magnetic skeleton. The most important parts of the magnetic skeleton to find are the null points, from which separatrix surfaces extend that divide magnetic flux of different topology. Part of this thesis proposes a new method of finding null points, for which the accuracy is shown and then compared with another commonly used method (which gave false results). Using these techniques for finding the magnetic skeleton in the magnetic interaction above, the evolution of the skeleton was found to head through seven distinct states, some of which were far more complicated than expected. This included a high number of separators (the intersection of two separatrix surfaces), which are a known location of magnetic reconnection. This separator reconnection was shown to be the main heating mechanism in this interaction, from which the total amount and rates of reconnection in the experiment was calculated. This led to the discovery of recursive reconnection, a process where magnetic flux is reconnected before reconnecting back to its original state, to allow for the process to repeat a gain. This recursive reconnection was shown to allow far more reconnection than would have been previously expected, all of which releases heat into the neighbouring areas of the atmosphere. Finally, the interaction was modelled with sources of different magnetic radii but of equal flux. This showed that when the antisymmetric nature of the previous interactions was removed, there was little change in the reconnection rates, but when the strength of the overlying magnetic field was increased, the reconnection rates were found to increase. This increase in the overlying magnetic field strength also produced a new magnetic feature called a bald-edge, which was found to replace some of the null points. These bald-edges were found to be associated with surfaces similar to separatrix surfaces that divide flux of different topology but do not extend from a null point. Also features similar to separators extend from these bald-edges.

Haynes, Andrew L.

2008-06-01

185

The role of the Weibel instability at the reconnection jet front in relativistic pair plasma reconnection  

CERN Document Server

We study the role of the Weibel instability in the context of the magnetic reconnection problem. A late-time evolution of magnetic reconnection in relativistic pair plasmas is investigated by particle-in-cell (PIC) simulations. In the outflow regions, powerful reconnection jet piles up the magnetic fields and then a contact discontinuity appears there. Further downstream, we find that the two-dimensional extension of the relativistic Weibel instability generates electro-magnetic fields, which are comparable to the anti-parallel or piled-up fields. In a microscopic viewpoint, the instability allows plasma's multiple interactions with the discontinuity. In a macroscopic viewpoint, the instability leads to rapid expansion of the current sheet and then the reconnection jet front further propagates into the downstream. Possible application to the three-dimensional case is briefly discussed.

Zenitani, S

2007-01-01

186

The role of the Weibel instability at the reconnection jet front in relativistic pair plasma reconnection  

International Nuclear Information System (INIS)

The role of the Weibel instability is investigated for the first time in the context of the large-scale magnetic reconnection problem. A late-time evolution of magnetic reconnection in relativistic pair plasmas is demonstrated by particle-in-cell simulations. In the outflow regions, powerful reconnection jets pile up the magnetic fields and then a contact discontinuity appears there. Further downstream, it is found that the two-dimensional extension of the relativistic Weibel instability generates electromagnetic fields, which are comparable to the antiparallel or piled-up fields. In a microscopic viewpoint, the instability allows the plasma's multiple interactions with the discontinuity. In a macroscopic viewpoint, the instability leads to rapid expansion of the current sheet and then the reconnection jet front further propagates into the downstream. Possible application to the three-dimensional case is briefly discussed

187

Magnetic reconnection with radiative cooling. I. Optically thin regime  

International Nuclear Information System (INIS)

Magnetic reconnection processes in many high-energy-density astrophysical and laboratory plasma systems are significantly affected by radiation; hence traditional, nonradiative reconnection models are not applicable to these systems. Motivated by this observation, the present paper develops a Sweet-Parker-like theory of resistive magnetic reconnection with strong radiative cooling. It is found that, in the case with zero guide field, intense radiative cooling leads to a strong plasma compression, resulting in a higher reconnection rate. The compression ratio and the reconnection layer temperature are determined by the balance between ohmic heating and radiative cooling. The lower temperature in a radiatively cooled layer leads to a higher Spitzer resistivity and, hence, a higher reconnection rate. Several specific radiative processes (bremsstrahlung, cyclotron, and inverse Compton) in the optically thin regime are considered for both the zero- and strong-guide-field cases, and concrete expressions for the reconnection parameters are derived, along with the applicability conditions.

188

Study of the effects of guide field on Hall reconnection  

Energy Technology Data Exchange (ETDEWEB)

The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations.

Tharp, T. D.; Yamada, M.; Ji, H.; Lawrence, E.; Dorfman, S.; Myers, C.; Yoo, J. [Center for Magnetic Self-Organization, Princeton Plasma Physics Laboratory, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States); Huang, Y.-M.; Bhattacharjee, A. [Space Science Center, University of New Hampshire and Max Planck-Princeton Research Center for Plasma Physics, Princeton University, P.O. Box 451, Princeton, New Jersey 08543-0451 (United States)

2013-05-15

189

Study of the effects of guide field on Hall reconnection  

International Nuclear Information System (INIS)

The results from guide field studies on the Magnetic Reconnection Experiment (MRX) are compared with results from Hall magnetohydrodynamic (HMHD) reconnection simulation with guide field. The quadrupole field, a signature of two-fluid reconnection at zero guide field, is modified by the presence of a finite guide field in a manner consistent with HMHD simulation. The modified Hall current profile contains reduced electron flows in the reconnection plane, which quantitatively explains the observed reduction of the reconnection rate. The present results are consistent with the hypothesis that the local reconnection dynamics is dominated by Hall effects in the collisionless regime of the MRX plasmas. While very good agreement is seen between experiment and simulations, we note that an important global feature of the experiments, a compression of the guide field by the reconnecting plasma, is not represented in the simulations

190

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

191

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: ACCESS 2000 - niveau 1 : 13 & 14.11.03 (2 jours) C++ for Particle Physicists : 17 ? 21.11.03 (6 X 3-hour lectures) Programmation automate Schneider TSX Premium ? niveau 2 : 18 ? 21.11.03 (4 jours) JAVA 2 Enterprise Edition ? Part 1 : WEB Applications : 20 & ...

2003-01-01

192

Three-dimensional inverse energy cascade induced by vortex reconnections  

CERN Document Server

A recent study of homogeneous isotropic turbulence by Biferale, Musacchio and Toschi has determined that a three-dimensional inverse energy cascade is possible if the nonlinearity of the Navier-Stokes equation is restricted in Fourier space to helical modes of the same sign. In low-temperature superfluid helium, viscosity is zero, vorticity takes the form of discrete, thin vortex filaments of fixed circulation, and turbulence is a tangle of such filaments. We exploit the simpler nature of quantum vorticity to show that the three-dimensional inverse energy cascade can arise from reconnections of vortex loops of the same polarity which shift energy from small length scales to large length scales, in analogy to what was envisaged by Biferale and collaborators in classical Navier-Stokes turbulence. We discuss superfluid turbulence experiments and the observed generation of the classical Kolmogorov energy spectrum in view of this finding.

Baggaley, Andrew W; Sergeev, Yuri A

2012-01-01

193

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

194

Color-reconnection in Z ? 3 jets  

International Nuclear Information System (INIS)

The electric charge distribution of gluon jets with a rapidity gap is sensitive to possible effects of color reordering in the final quark-gluon cascade. High statistics data from the ALEPH experiment at LEP-1 are used to test the predictions of different color reconnection models. (author)

195

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

196

VINETA II: A linear magnetic reconnection experiment  

Energy Technology Data Exchange (ETDEWEB)

A linear experiment dedicated to the study of driven magnetic reconnection is presented. The new device (VINETA II) is suitable for investigating both collisional and near collisionless reconnection. Reconnection is achieved by externally driving magnetic field lines towards an X-point, inducing a current in the background plasma which consequently modifies the magnetic field topology. Owing to the open field line configuration of the experiment, the current is limited by the axial sheath boundary conditions. A plasma gun is used as an additional electron source in order to counterbalance the charge separation effects and supply the required current. Two drive methods are used in the device. First, an oscillating current through two parallel conductors drive the reconnection. Second, a stationary X-point topology is formed by the parallel conductors, and the drive is achieved by an oscillating current through a third conductor. In the first setup, the magnetic field of the axial plasma current dominates the field topology near the X-point throughout most of the drive. The second setup allows for the amplitude of the plasma current as well as the motion of the flux to be set independently of the X-point topology of the parallel conductors.

Bohlin, H., E-mail: hannes.bohlin@ipp.mpg.de; Von Stechow, A.; Rahbarnia, K.; Grulke, O. [Max-Planck-Institute for Plasma Physics, EURATOM Association, Wendelsteinstr. 1, 17491 Greifswald (Germany); Klinger, T. [Max-Planck-Institute for Plasma Physics, EURATOM Association, Wendelsteinstr. 1, 17491 Greifswald (Germany); Ernst-Moritz-Arndt University, Domstr. 11, 17489 Greifswald (Germany)

2014-02-15

197

On the periodicity of oscillatory reconnection  

Science.gov (United States)

Context. Oscillatory reconnection is a time-dependent magnetic reconnection mechanism that naturally produces periodic outputs from aperiodic drivers. Aims: This paper aims to quantify and measure the periodic nature of oscillatory reconnection for the first time. Methods: We solve the compressible, resistive, nonlinear magnetohydrodynamics (MHD) equations using 2.5D numerical simulations. Results: 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-1, 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 associated with both phases. Conclusions: We conclude that the oscillatory reconnection mechanism behaves akin to a damped harmonic oscillator.

McLaughlin, J. A.; Thurgood, J. O.; MacTaggart, D.

2012-12-01

198

Relating magnetic reconnection to coronal heating  

CERN Document Server

It is clear that the solar corona is begin heated and that coronal magnetic fields undergo reconnection all the time. Here we attempt to show that these two facts are in fact related - i.e. coronal reconnection generates heat. This attempt must address the fact that topological change of field lines does not automatically generate heat. We present one case of flux emergence where we have measured the rate of coronal magnetic reconnection and the rate of energy dissipation in the corona. The ratio of these two, $P/\\dot{\\Phi}$, is a current comparable to the amount of current expected to flow along the boundary separating the emerged flux from the pre-existing flux overlying it. We can generalize this relation to the overall corona in quiet Sun or in active regions. Doing so yields estimates for the contribution to corona heating from magnetic reconnection. These estimated rates are comparable to the amount required to maintain the corona at its observed temperature.

Longcope, Dana W

2015-01-01

199

ASYMMETRIC MAGNETIC RECONNECTION IN SOLAR FLARE AND CORONAL MASS EJECTION CURRENT SHEETS  

Energy Technology Data Exchange (ETDEWEB)

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 there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.

Murphy, N. A.; Miralles, M. P.; Pope, C. L.; Raymond, J. C.; Winter, H. D.; Reeves, K. K.; Van Ballegooijen, A. A.; Lin, J. [Harvard-Smithsonian Center for Astrophysics, 60 Garden Street, Cambridge, MA 02138 (United States); Seaton, D. B. [SIDC-Royal Observatory of Belgium, Avenue Circulaire 3, 1180 Brussels (Belgium)

2012-05-20

200

ASYMMETRIC MAGNETIC RECONNECTION IN SOLAR FLARE AND CORONAL MASS EJECTION CURRENT SHEETS  

International Nuclear Information System (INIS)

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 there than at the strong magnetic field footpoint. The footpoint on the weak magnetic field side is predicted to move more quickly because of the requirement in two dimensions that equal amounts of flux must be reconnected from each upstream region. The X-line drifts away from the conducting wall in all simulations with asymmetric outflow and into the strong magnetic field region during most of the simulations with asymmetric inflow. There is net plasma flow across the X-line for both the inflow and outflow directions. The reconnection exhaust directed away from the obstructing wall is signifi away from the obstructing wall is significantly faster than the exhaust directed toward it. The asymmetric inflow condition allows net vorticity in the rising outflow plasmoid which would appear as rolling motions about the flux rope axis.

 
 
 
 
201

Collisionless magnetic reconnection under anisotropic MHD approximation  

Science.gov (United States)

We study the formation of slow-mode shocks in collisionless magnetic reconnection by using one- and two-dimensional collisionless magneto-hydro-dynamic (MHD) simulations based on the double adiabatic approximation, which is an important step to 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. According to our results, a pair of slow shocks does form in the reconnection layer. The resultant shock waves, however, are quite weak compared with those in an isotropic MHD from the point of view of the plasma compression and the amount of the magnetic energy released across the shock. Once the slow shock forms, the downstream plasma are heated in highly anisotropic manner and a firehose-sense (P_{||}>P_{?}) pressure anisotropy arises. The maximum anisotropy is limited by the marginal firehose criterion, 1-(P_{||}-P_{?})/B(2) =0. In spite of the weakness of the shocks, the resultant reconnection rate is kept at the same level compared with that in the corresponding ordinary MHD simulations. It is also revealed that the sequential order of propagation of the slow shock and the rotational discontinuity, which appears when the guide field component exists, changes depending on the magnitude of the guide field. Especially, when no guide field exists, the rotational discontinuity degenerates with the contact discontinuity remaining at the position of the initial current sheet, while with the slow shock in the isotropic MHD. Our 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, Kota; Hoshino, Masahiro

202

Interchange Reconnection and Coronal Hole Dynamics  

Science.gov (United States)

We investigate the effect of magnetic reconnection between open and closed field, (often referred to as "interchange" reconnection), on the dynamics and topology of coronal hole boundaries. The most important and most prevalent 3D topology of the interchange process is that of a small-scale bipolar magnetic field interacting with a large-scale background field. We determine the evolution of such a magnetic topology by numerical solution of the fully 3D MHD equations in spherical coordinates. First, we calculate the evolution of a small-scale bipole that initially is completely inside an open field region and then is driven across a coronal hole boundary by photospheric motions. Next the reverse situation is calculated in which the bipole is initially inside the closed region and driven toward the coronal hole boundary. In both cases we find that the stress imparted by the photospheric motions results in deformation of the separatrix surface between the closed field of the bipole and the background field, leading to rapid current sheet formation and to efficient reconnection. When the bipole is inside the open field region, the reconnection is of the interchange type in that it exchanges open and closed field. We examine, in detail, the topology of the field as the bipole moves across the coronal hole boundary, and find that the field remains well-connected throughout this process. Our results imply that open flux cannot penetrate deeply into the closed field region below a helmet streamer and, hence, support the quasi-steady models in which open and closed flux remain topologically distinct. Our results also support the uniqueness hypothesis for open field regions as postulated by Antiochos et al. We discuss the implications of this work for coronal observations. Subject Headings: Sun: corona Sun: magnetic fields Sun: reconnection Sun: coronal hole

Edmondson, J. K.; Antiochos, S. K.; DeVore, C. R.; Lynch, B. J.; Zurbuchen, T. H.

2011-01-01

203

PLACES AVAILABLE  

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Monique Duval

2002-01-01

204

Polar cap boundary and the reconnection electric field  

Science.gov (United States)

Magnetic reconnection on the dayside magnetopause and in the nightside magnetotail are the main factors controlling the solar wind energy transfer into the magnetosphere and the ionosphere. Reconnection on the dayside magnetopause creates open magnetic flux and moves the polar cap boundary in the equatorward direction. Reconnection in the magnetotail, either at the distant neutral line or at the near-Earth neutral line during substorm conditions, closes magnetic field lines and moves the polar cap boundary into the poleward direction. The combined effect of dayside and nightside reconnection determines finally the dynamics of the polar cap boundary. A quantity that is related to changes in the amount of open magnetic flux is the reconnection electric field. In this talk, we will review some of the results obtained by using the EISCAT radar facility and supporting instruments (e.g. the MIRACLE magnetometers, the Cluster satellite, and global UVI imagers on Polar and IMAGE satellites) in estimating the motions of the polar cap boundary and the associated reconnection electric field. We have e.g. shown that the nightside reconnection close to substorm onset consists of a series of short-lived reconnection bursts and that isolated reconnection events may occur during the substorm recovery phase. We will also show, quantitatively for the first time to our knowledge, that intensifications in the local reconnection electric field have one-to-one correlation with the appearance of auroral poleward boundary intensifications (PBIs) within the same MLT location. These PBIs are observed by the Polar UVI instrument.

Aikio, A.; Pitkänen, T.; Kozlovsky, A.; Amm, O.; Fontaine, D.; Hubert, B.; Fazakerley, A.

2009-04-01

205

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2003-01-01

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2003-01-01

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2003-01-01

208

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2004-01-01

209

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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: MATLAB Fundamentals and Programming Techniques (ML01) :2 & 3.12.03 (2 days) Oracle 8i : SQL : 3 - 5.12.03 (3 days) The EDMS MTF in practice : 5.12.03 (afternoon, free of charge) Modeling Dynamic Systems with Simulink (SL01) : 8 & 9.12.03 (2 days) Signal Processing with MATLAB (SG01) : 11 & ...

2003-01-01

210

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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) 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

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2003-01-01

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2003-01-01

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2003-01-01

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2003-01-01

215

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2003-01-01

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2003-01-01

217

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

218

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

219

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: C++ Programming Level 2 - Traps & Pitfalls:  16 - 19.7.02 (4 days) Frontpage 2000 - level 1 :  22 - 23.7.02  (2 days) Introduction à Windows 2000 au CERN : 24.7.02 (après-midi) CLEAN-2002 : Travailler en salle blanche (cours gratuit) : 13.08.2002 (matin) 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 Monique Duval Tel.74924 monique.duval@cern.ch

Monique Duval

2002-01-01

220

PLACES AVAILABLE  

CERN Multimedia

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

 
 
 
 
221

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: LabView Base 1 : 27-29.3.01 (3 jours) Contract Follow-up : 9.4.01 (3 heures) Introduction à PowerPoint : 24.4.01 (1 journée) Publier sur le Web : 25-27.4.01 (3 demi-journées) Programmation TSX Premium 2 : 15-16.5.01 (5 jours) LabView Base 2 : 27-29.3.01 (2 jours) Hands-on Object-oriented Analysis, Design & Programming with C++ :  23-27.4.01 (5 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

222

PLACES AVAILABLE  

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

223

PLACES AVAILABLE  

CERN Multimedia

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

224

PLACES AVAILABLE  

CERN Multimedia

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

225

PLACES AVAIABLE  

CERN Multimedia

Places are available in the following courses: The Java programming language (Level 1) : 8 - 9.2.01 (2 days) Architecture d'automatisme : 20 - 21.2.01 (2 jours) Programmation TSX Premium 1 (Schneider) : 26.2 - 2.3.01 (5 jours) C++ for Particle Physicists : 5 - 9.3.01 (6*3 hour lectures) The Java programming language (Level 2) : 12 - 14.3.2001 (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

226

Places available **  

CERN Multimedia

Places are available in the following courses: PIPES-2003 - Pratique du Sertissage de tubes métalliques et multicouches : 26.8.03 (stage pratique) The CERN Engineering Data Management System (EDMS) for Engineers : 27.8.03 (1 day, free of charge) CLEAN-2002 : Travailler en salle blanche : 4.9.03 (une demi-journée, séminaire gratuit) The CERN Engineering Data Management System (EDMS) for Local Administrators : 24 & 25.9.03 (2 days, free of charge) Siemens SIMATIC Training : Programmation STEP7 - niveau 1 : 29 - 2.10.03 (4 jours) - ouverture des inscriptions fin août Programmation STEP7 - niveau 2 : 13 - 17.10.03 (5 jours) - ouverture des inscriptions fin août Réseau Simatic Net : 22 & 23.10.03 (2 jours) - ouverture des inscriptions fin août CLEAN-2002 : Working in a Cleanroom : 23.20.03 (half day, free of charge) These courses will be given in French or Englis...

2003-01-01

227

PLACES AVAILABLE  

CERN Multimedia

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

228

PLACES AVAILABLE  

CERN Multimedia

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

229

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: November 2002   Introduction to PVSS (free of charge): 11.11.02  (afternoon) EXCEL 2000 - niveau 1 :  12 & 13.11.02  (2 jours) CLEAN-2002: Working in a Cleanroom (English, free of charge):  13.11.2002  (afternoon) AutoCAD 2002 - niveau 1 :  14, 15, 21, 22.11.02  (4 jours) Hands-on Object-Oriented Design and Programming with C++:  19 - 21.11.02  (3 days)  EXCEL 2000 - niveau 2 :  25 & 26.11.02  (2 jours) FrontPage 2000 - niveau 1 :  27 & 28.11.02  (2 jours) 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 ...

Monique Duval

2002-01-01

230

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: October 2002   Introduction to the CERN Engineering Data Management System (free of charge):  29.10.2002  (1 day) The CERN EDMS for Advanced users (free of charge):  30.10.2002  (1 day) November 2002   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 ...

Monique Duval

2002-01-01

231

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: 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) Sécurité dans les installations cryogéniques : 21 - 22.11.2001 (2 demi-journées) 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) 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...

Technical Training; Tel. 74924

2001-01-01

232

Taking Leave?  

CERN Document Server

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

233

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

234

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

235

Aspects of collisionless magnetic reconnection in asymmetric systems  

Energy Technology Data Exchange (ETDEWEB)

Asymmetric reconnection is being investigated by means of particle-in-cell simulations. The research has two foci: the direction of the reconnection line in configurations with nonvanishing magnetic fields; and the question why reconnection can be faster if a guide field is added to an otherwise unchanged asymmetric configuration. We find that reconnection prefers a direction, which maximizes the available magnetic energy, and show that this direction coincides with the bisection of the angle between the asymptotic magnetic fields. Regarding the difference in reconnection rates between planar and guide field models, we demonstrate that a guide field can provide essential confinement for particles in the reconnection region, which the weaker magnetic field in one of the inflow directions cannot necessarily provide.

Hesse, Michael; Aunai, Nicolas; Kuznetsova, Masha [Heliophysics Science Division, Code 670, NASA Goddard Space Flight Center, Greenbelt, Maryland 20771 (United States); Zenitani, Seiji [National Astronomical Observatory of Japan, Tokyo (Japan); Birn, Joachim [Space Science Institute, Boulder, Colorado 80301 (United States)

2013-06-15

236

Theory of magnetic reconnection in solar and astrophysical plasmas  

CERN Document Server

Magnetic reconnection is a fundamental process in a plasma that facilitates the release of energy stored in the magnetic field by permitting a change in the magnetic topology. In this article we present a review of the current state of understanding of magnetic reconnection. We discuss theoretical results regarding the formation of current sheets in complex 3D magnetic fields, and describe the fundamental differences between reconnection in two and three dimensions. We go on to outline recent developments in modelling of reconnection with kinetic theory, as well as in the MHD framework where a number of new 3D reconnection regimes have been identified. We discuss evidence from observations and simulations of solar system plasmas that support this theory, and summarise some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.

Pontin, D I

2012-01-01

237

Local influence of magnetosheath plasma beta fluctuations on magnetopause reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We present observations from two subsolar Cluster magnetopause crossings under southward interplanetary magnetic field and strong mirror mode fluctuations in the magnetosheath. In both events the reconnection outflow jets show strong variations on the timescale of one minute. We show that at least some of the recorded variations are truly temporal, not spatial. On the same timescale, mirror mode fluctuations appear as strong magnetic fluctuations in the magnetosheath next to the magnetopause. This suggests that mirror modes can cause the variations either through modulation of continuous reconnection or through triggering of bursty reconnection. Using a theoretical scaling law for asymmetric reconnection we show that modulation of reconnection at a single x-line can explain the observations of the first event. The second event cannot be explained by a single modulated x-line: there the evidence points to patchy and bursty reconnection.

T. V. Laitinen

2010-05-01

238

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

239

Comment on "Reconnection of quantized vortex filaments and the Kolmogorov spectrum"  

CERN Document Server

In this comment we would like to emphasize that in [Phys. Rev. B 90, 104506 (2014)] the calculated energy spectrum takes into account only the small interaction (cross) term and, additionally, this term is only calculated at the instant when the two vortices reconnect. The majority of the kinetic energy is contained in the self-energy term which has a characteristic spectrum of $1/k$. If this, and the additional average over time, is taken into account the suggested Kolmogorov type $k^{-5/3}$ spectrum is likely not visible in the kinetic energy spectrum which contains both terms. Therefore, we find the suggestion misleading that the Kolmogorov spectrum in superfluids arises from the reconnection of vortices.

Hänninen, R

2014-01-01

240

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

 
 
 
 
241

A general hybrid kinetic-fluid model for collisionless magnetic reconnection  

International Nuclear Information System (INIS)

A general set of equations appropriate for the description of the plasma dynamics within a collisionless magnetized plasma during the process of magnetic reconnection is derived. The particular geometry considered is that of a Harris pinch with a guide field and full kinetic equations for the perturbations are found, valid within the singular layer around the reconnecting region. Ion equations take into account finite Larmor radius effects while electron dynamics is based on the gyro-averaged drift kinetic equation. A more manageable model is obtained by resorting to fluid equations for the ions and retaining electron kinetic effects. It is shown that these equations give the same results obtained from the two-fluid theory in the limit of the collisionless tearing mode for different regimes

242

Magnetic Weibel field generation in thin collisionless current sheets in reconnection in space plasma  

CERN Document Server

In collisionless reconnection in space plasma like the magnetospheric tail or magnetopause current layer, magnetic fields can grow from thermal level by the action of the non-magnetic Weibel instability driven in thin ($\\Delta<$ few $\\lambda_i$) current layers by the counter-streaming electron inflow from the `ion diffusion' (ion inertial Hall) region into the inner current (electron inertial) region from where the ambient magnetic fields are excluded when released by the inflowing electrons which become non-magnetic on scales $<$ few $\\lambda_e$. It is shown that under magnetospheric tail conditions it takes $\\sim 40$ e-folding times ($\\sim 20$ s) for the Weibel field to reach observable amplitudes $|{\\bf b}_{\\rm W}|\\sim 1$ nT. In counter-streaming inflows these fields are predominantly of guide field type. In non-symmetric inflows the field may possess a component normal to the current which would be capable of initiating reconnection onset.

Treumann, R A

2009-01-01

243

New Measure of the Dissipation Region in Collisionless Magnetic Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 sit...

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

2011-01-01

244

Magnetic reconnection in the heliosphere: impulsive dynamics and particle acceleration  

International Nuclear Information System (INIS)

Magnetic reconnection in the heliosphere is often time-dependent and impulsive, as in the classic instance of solar flares. A large fraction of the energy liberated during such events shows up in the energy of accelerated particles. Collisionless reconnection theory can account for significant features of these observations, but several open questions remain. Recent theoretical developments and observations that shed light on impulsive reconnection dynamics and particle acceleration mechanisms will be reviewed. (author)

245

Analysis of the reconnection process in nontwist cubic maps  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The reconnection process in the dynamics of cubic nontwist maps, introduced in [3], is studied. The present paper extends the work presented in [8]. As in that work, in order to describe the route to reconnection of the involved Poincar\\'{e}--Birkhoff chains or dimerised chains we investigate an approximate interpolating Hamiltonian of the map under study revealing again that the scenario of reconnection of cubic nontwist maps is different from that occurring in the dynamics...

Tigan, Gheorghe

2005-01-01

246

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: Electromagnetic Compatibility (EMC): Introduction (bilingual) :  3.12.01 (half-day) Habilitation électrique : superviseurs : 5.12.01 (1/2 journée) Introduction to the CERN Engineering Data Management System : 07.12.2001 (1 day) 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) C++ Programming Level 2 - Traps and Pitfalls :  15 - 18.1.2002  (4 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) Introduction au PC et à Windows 2000 au CERN : 29 - 30.1....

Technical Traininf; Tel. 74924

2001-01-01

247

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

248

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

249

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

250

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: MS-Project 1er niveau : 20 - 23.2.01 (4 matins) Architecture d'automatisme : 20 - 21.2.01 (2 jours) Introduction à PowerPoint : 26.2.01 (1 journée) Programmation TSX Premium 1 (Schneider) : 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) 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 accepted in the order of their receipt.

TECHNICAL TRAINING; Tel. 74460

2001-01-01

251

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

252

Places available**  

CERN Multimedia

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 days) FrontPage 2000 - niveau 1 : 20 & 21.11.03 (2 jours) MAGNE-03 : Magnétisme pour l'électrotechnique : 25 - 27.11.03 (3 jours) ...

2003-01-01

253

Places available**  

CERN Multimedia

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

254

PLACES AVAILABLE  

CERN Multimedia

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

255

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

256

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

257

Places available**  

CERN Multimedia

Places are available in the following courses: PIPES-2003 - Pratique du sertissage de tubes métalliques et multicouches :26.8.03(stage pratique) The CERN EDMS for Engineers (free of charge) : 27.8.03 (1 day) 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...

2003-01-01

258

Places available**  

CERN Multimedia

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

259

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

260

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

 
 
 
 
261

Places available**  

CERN Multimedia

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

262

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

263

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: LabVIEW Basics 2: 13 & 14.5.02 (2 days) 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) The CERN Engineering Data Management System for Advanced users:  30.5.02  (1 day) LabVIEW Basics 1:  3 - 5.6.02  (3 days) AutoCAD 2002 - condensé : 4 - 6.6.02 (3 jours) LabVIEW DAQ (E):  6 & 7.6.02  (2 days) AutoCAD 2002 - Level 1:  10 - 12 and 24 - 26.6.02  (6 days) If you wish to participate in one of these courses, please discuss with your supervisor and apply electronically directly from the c...

Monique Duval

2002-01-01

264

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: 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) The CERN Engineering Data Management System for Advanced users:  30.5.02  (1 day) LabVIEW Basics 1:  3 - 5.6.02  (3 days) AutoCAD 2002 - condensé : 4 - 6.6.02 (3 jours) LabVIEW DAQ (E):  6 & 7.6.02  (2 days) AutoCAD 2002 - Level 1:  10 - ...

Monique Duval

2002-01-01

265

PLACES AVAILABLE  

CERN Multimedia

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

266

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

267

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

268

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

269

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

270

PLACES AVAILABLE  

CERN Multimedia

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

271

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

272

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

273

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

274

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

275

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

276

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

277

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

278

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

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 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

 
 
 
 
281

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

282

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) 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

283

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

284

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) PowerPoint 2000 : 1 et 2.10.01 (2 jours) EXCEL 2000 - niveau 1 : 3 et 4.10.01 (2 jours) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) Introduction à Outlook : 5.10.01 (1 journée) Frontpage 2000 - niveau 1 : 8 et 9.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) C++ for Particle Physicists : 8 - 12.10.01 (6 3-hour lectures) MS-Project 2000 - niveau 1 : 15 - 18.10.01 (4 demi-journées) LabView Basics 1 :  15 - 17.10.01  (3 days) 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...

Technical Training; Tel. 74924

2001-01-01

285

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

286

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

287

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) Automates et réseaux de terrain : 3 - 4.10.2001 (2 jours) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) Programmation TSX Premium 1 : 15 - 19.10.01 (5 jours) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) Programming TSX Premium 2: 19 - 23.11.01 (5 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) Autocad Migration support courses: a detailed calendar will be published shortly for this series of sessions which will start on 15.10.2001. Registration is already open AutoCAD : Mise à jour AutoCAD r-14 vers 2002 (2 jours) AutoCAD Mechanical PowerPack 6 basé sur AutoCAD 2002 (5 jours) The following LabView courses will be given in either English or French according to demand LabVIEW - Base 1 / LabVIEW - Basics 1 : 10 - 12.9.01 (3 jours / 3 days)...

Technical training; Tel. 74924

2001-01-01

288

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: PVSS Basics : 20 - 24.8.01 (5 days) PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) Programming TSX Premium 1: 15 - 19.10.01 (5 days) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) Programming TSX Premium 2: 19 - 23.11.01 (5 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) The following LabView courses will be given in either English or French according to demand LabVIEW - Base 1 / LabVIEW - Basics 1 : 10 - 12.9.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 13 - 14.9.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 15 - 17.10.01 (3 jours / 3 days) LabVIEW - Base 2 / LabVIEW - Basics 2 : 18 - 19.10.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 12 - 14.11.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 15 - 16.11.01 (2 jours / 2...

Technical training; Tel. 74924

2001-01-01

289

PLACES AVAILABLES  

CERN Multimedia

Places are available in the following courses: PVSS Basics : 20 - 24.8.01 (5 days) PROFIBUS : 25 - 26.9.01 (2 jours) PROFIBUS : 27 - 28.9.01 (2 days) PCAD Schémas - débutants : 4 - 5.10.01 (2 jours) PCAD PCB - débutants : 8 - 10.10.01 (3 jours) Programming TSX Premium 1: 15 - 19.10.01 (5 days) Programmation TSX Premium 1 : 22 - 26.10.01 (5 jours) Programming TSX Premium 2: 19 - 23.11.01 (5 days) Programmation TSX Premium 2 : 26 - 30.11.01 (5 jours) The following LabView courses will be given in either English or French according to demand LabVIEW - Base 1 / LabVIEW - Basics 1 : 10 - 12.9.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 13 - 14.9.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 15 - 17.10.01 (3 jours / 3 days) LabVIEW - Base 2 / LabVIEW - Basics 2 : 18 - 19.10.01 (2 jours / 2 days) LabVIEW - Base 1 / LabVIEW - Basics 1 : 12 - 14.11.01 (3 jours / 3 days) LabVIEW - DAQ / LabVIEW - DAQ : 15 - 16.11.01 (2 jours / 2...

Technical Training; Tel. 74924

2001-01-01

290

Places available**  

CERN Document Server

Places are available in the following courses : FrontPage 2000 - niveau 1: 20 & 21.5.03 (2 jours) PIPES-2003 : Pratique du sertissage de tubes métalliques et multicouches: 21.5.03 (1 jour) Introduction à la CAO Cadence: de la saisie de schéma Concept-HDL au PCB : 20 & 22.5.03 (2 jours) AutoCAD Mechanical 6 PowerPack (E): 5, 6, 12, 13, 26, 27.6.03 (6 days) EXCEL 2000 - niveau 1: 10 & 11.6.03 (2 jours) Conception de PCB rapides dans le flot Cadence: 11.6.03 (matin) EXCEL 2000 - level 1: 12 & 13.6.03 (2 days) Introduction to PVSS: 16.6.03 (half-day, pm) Basic PVSS: 17 - 19.6.03 (3 days) Réalisation de PCB rapides dans le flot Cadence: 17.6.03 (matin) LabView DSC (language to be defined): 19 & 20.6.03 PVSS - JCOP Framework Tutorial: 20.6.03 (1 day) EXCEL 2000 - niveau 2: 24 & 25.6.03 (2 jours) Siemens SIMATIC Training: Introduction to STEP7: 3 & 4.6.03 (2 days) STEP7 Programming: 16 - 20.6.03 (5 days) Simatic Net Network: 26 & 27.6.03 (2 days) These courses will be given...

2003-01-01

291

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

292

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

293

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: 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 : 11 - 13.02.02 (3 days) C++ for Particle Physicists : 11 - 15.3.2002 (6 * 3 hour lectures) 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 ...

Technical Training; Tel 74924

2002-01-01

294

Places available**  

CERN Document Server

Places are available in the following courses : FrontPage 2000 - niveau 1 : 20 & 21.5.03 (2 jours) PIPES-2003 : Pratique du sertissage de tubes métalliques et multicouches : 21.5.03 (1 jour) Introduction à la CAO Cadence : de la saisie de schéma Concept-HDL au PCB : 20 & 22.5.03 (2 jours) AutoCAD 2002 - niveau 2 : 3 & 4.6.03 (2 jours) AutoCAD Mechanical 6 PowerPack (F) : 5, 6, 12, 13, 26, 27.6.03 (6 jours) EXCEL 2000 - niveau 1 : 10 & 11.6.03 (2 jours) Conception de PCB rapides dans le flot Cadence : 11.6.03 (matin) EXCEL 2000 - level 1 : 12 & 13.6.03 (2 days) PowerPoint 2000 (F) : 17 & 18.6.03 (2 jours) Réalisation de PCB rapides dans le flot Cadence : 17.6.03 (matin) FrontPage 2000 - niveau 2 : 19 & 20.6.03 (2 jours) LabView DSC (langue à décider/language to be defined) : 19 & 20.6.03 EXCEL 2000 - niveau 2 : 24 & 25.6.03 (2 jours) Siemens SIMATIC Training: Introduction to STEP7 : 3 & 4.6.03 (2 days) STEP7 Programming : 16 - 20.6.03 (5 days) Simatic...

2003-01-01

295

Places available**  

CERN Multimedia

Places are available in the following courses : EXCEL 2000 - niveau 1 : 10 & 11.6.03 (2 jours) Conception de PCB rapides dans le flot Cadence : 11.6.03 (matin) EXCEL 2000 - level 1 : 12 & 13.6.03 (2 days) Introduction to PVSS : 16.6.03 (p.m.) Basic PVSS : 17 - 19.6.03 (3 days) Réalisation de PCB rapides dans le flot Cadence : 17.6.03 (matin) PVSS - JCOP Framework Tutorial : 20.6.03 (1 day) EXCEL 2000 - niveau 2 : 24 & 25.6.03 (2 jours) Siemens SIMATIC Training : Introduction to STEP7 : 3 & 4.6.03 (2 jours/2 days) STEP7 Programming : 16 - 20.6.03 (5 jours/5 days) Simatic Net Network : 26 & 27.6.03 (2 jours/2 days) These courses will be given in French or English following the requests. Programmation automate Schneider : Programmation automate Schneider TSX Premium - 1er niveau : 10 - 13.6.03 (4 jours) - audience : toute personne qui veux maitriser la msie en uvre et la programmation d'un automate TSX Premium - objectifs : maitriser la mise en uvre et la programmation d'un autom...

2003-01-01

296

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: 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  (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) The CERN Engineering Data Management System for Advanced users :  21.2.02  (1 day) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) 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 electr...

Monique Duval

2002-01-01

297

PLACES AVAILABLE  

CERN Multimedia

Places are available in the following courses: 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 : 22, 24 & 25.01.02 (3 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 :  11 - 13.02.02 (3 days) PVSS basics :  11 - 15.2.02 (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) The CERN Engineering Data Management System for Advanced users :  21.2.02  (1 day) C++ for Particle Physicists :  11 - 15.3.2002  (6 * 3 hour lectures) Cours sur la migration AutoCAD : AutoCAD : Mise à...

Technical Training; Tel. 74924

2002-01-01

298

Nonlinear magnetic reconnection in low collisionality plasmas  

Energy Technology Data Exchange (ETDEWEB)

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 {rho}/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.

Ottaviani, M. [Commission of the European Communities, Abingdon (United Kingdom). JET Joint Undertaking; Porcelli, F. [Politecnico di Torino, Turin (Italy)

1994-07-01

299

PARTIAL SLINGSHOT RECONNECTION BETWEEN TWO FILAMENTS  

International Nuclear Information System (INIS)

We present a rare observation of an interaction between two filaments around AR 11358 and AR 11361 on 2011 December 3 that is strongly suggestive of the occurrence of slingshot reconnection. A small elbow-shaped active-region filament (F12) underwent a failed eruption that brought it into contact with a nearby larger, thicker filament (F34). Accompanied by the appearance of complicated internal structures below the erupting F12, its two legs separated away from each other and then connected into F34. This process led the filaments to change their connectivity to form two newly linked filaments, and one of them showed a clear inverse ?-shape. However, the alteration in the filament connectivity was imperfect since F34 is discernible after the eruption. These observations can be interpreted as a partial slingshot reconnection between two filaments that had unequal axial magnetic flux.

300

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

 
 
 
 
301

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

302

Places disponibles/Places available  

CERN Document Server

Si vous désirez participer à l'un des cours suivants, veuillez en discuter avec votre superviseur et vous inscrire électroniquement en direct depuis les pages de description des cours dans le Web que vous trouvez à l'adresse : http://www.cern.ch/Training/ ou remplissez une « demande de formation » disponible auprès du Secrétariat de votre Division ou de votre DTO (Délégué divisionnaire à la formation). Les places seront attribuées dans l'ordre de réception des inscriptions. 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 Off...

2004-01-01

303

INTERCHANGE RECONNECTION AND CORONAL HOLE DYNAMICS  

International Nuclear Information System (INIS)

We investigate the effect of magnetic reconnection between open and closed fields, often referred to as 'interchange' reconnection, on the dynamics and topology of coronal hole boundaries. The most important and most prevalent three-dimensional topology of the interchange process is that of a small-scale bipolar magnetic field interacting with a large-scale background field. We determine the evolution of such a magnetic topology by numerical solution of the fully three-dimensional MHD equations in spherical coordinates. First, we calculate the evolution of a small-scale bipole that initially is completely inside an open field region and then is driven across a coronal hole boundary by photospheric motions. Next the reverse situation is calculated in which the bipole is initially inside the closed region and driven toward the coronal hole boundary. In both cases, we find that the stress imparted by the photospheric motions results in deformation of the separatrix surface between the closed field of the bipole and the background field, leading to rapid current sheet formation and to efficient reconnection. When the bipole is inside the open field region, the reconnection is of the interchange type in that it exchanges open and closed fields. We examine, in detail, the topology of the field as the bipole moves across the coronal hole boundary and find that the field remains well connected throughout this process. Our results, therefore, provide essential support for the refore, provide essential support for the quasi-steady models of the open field, because in these models the open and closed flux are assumed to remain topologically distinct as the photosphere evolves. Our results also support the uniqueness hypothesis for open field regions as postulated by Antiochos et al. On the other hand, the results argue against models in which open flux is assumed to diffusively penetrate deeply inside the closed field region under a helmet streamer. We discuss the implications of this work for coronal observations.

304

Global Magnetospheric Modeling of 3D Reconnection  

Science.gov (United States)

A review of approaches to the global modeling of the terrestrial magnetosphere, how these approaches are utilized to interpret satellite data, and how these approaches have been successful at predicting magnetospheric phenomena will be presented. In addition, the importance of the ionospheric boundary and its effect on the globally topology of the magnetospheric magnetic field will be reviewed. In particular, numerical results that are rapidly changing our view of magnetospheric reconnection within the magnetospheric magnetic field will be discussed.

Spicer, Daniel S.

1999-01-01

305

Kinetic Vlasov Simulations of collisionless magnetic Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

A fully kinetic Vlasov simulation of the Geospace Environment Modeling (GEM) Magnetic Reconnection Challenge is presented. Good agreement is found with previous kinetic simulations using particle in cell (PIC) codes, confirming both the PIC and the Vlasov code. In the latter the complete distribution functions $f_k$ ($k=i,e$) are discretised on a numerical grid in phase space. In contrast to PIC simulations, the Vlasov code does not suffer from numerical noise and allows a m...

Schmitz, H.; Grauer, R.

2006-01-01

306

Rapidity gaps in gluon jets / color reconnection at LEP  

CERN Document Server

Gluon jets with a large gap in the rapidity distribution of particles within the jet are very sensitive to color reconnection effects. Gluon jets of this type, selected from hadronic Z0 decay events produced in e+e- annihilations at LEP, are used to test three QCD models which include a simulation of color reconnection: one in the Ariadne Monte Carlo, one in the Herwig Monte Carlo, and the other by Rathsman in the Pythia Monte Carlo. We conclude that color reconnection as implemented by the Rathsman and Ariadne models is disfavored. We don't obtain a definite conclusion concerning the Herwig color reconnection model.

Giunta, M

2003-01-01

307

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

308

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

309

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

310

Magnetic reconnection in electron-magnetohydrodynamics  

International Nuclear Information System (INIS)

The magnetic field dynamics and reconnection processes in a highly conducting plasma are investigated in regimes where Ohm's law is dominated by the Hall term using a single (electron) fluid description (Electron-magnetohydrodynamics). In these regimes, which correspond to the frequency range of the so-called whistler mode, the electromagnetic field is nearly force-free: (jxB)/c+eneE=0. Small scale magnetic reconnection occurs near surfaces where k·B=0, and tearing-type modes can be unstable due to the effect of electron inertia. The evolution of the magnetic field in the vicinity of an X-line is discussed and the propagation of whistler waves is shown to result in the steepening of their wave front and in the increase of the electric current density. A class of exact self-similar solutions is obtained which describe, within the scope of a local approximation, the magnetic collapse of three-dimensional magnetic configurations leading to the formation of flat electric current sheets. Finally, the rate of reconnection in the electron-hydrodynamic frequency range is estimated in a steady state approximation. (author) 7 refs

311

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

312

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

313

THEMIS, ARTEMIS and allied Heliophysics System Observatory spacecraft studies of magnetotail reconnection and its global consequences  

Science.gov (United States)

On several occasions over the last two years, conjuctions between THEMIS and ARTEMIS in the magnetotail enabled multi-point studies of localized Earthward flows - accompanied by dipolarization fronts and localized tailward flows / plasmoids accompanied by "anti-dipolarization fronts", allowing us to explore their common progenitor: a single reconnection point somewhere in the magnetotail. We use timing of particle injections and kinetic modeling to infer the location and motion of that common source as function of substorm phase. In agreement with past Geotail studies, the two-spacecraft ARTEMIS dataset also indicates a poor correlation between plasmoids in the mid-tail region and substorms, consistent with the localized nature of the activations on the tailward side of a near-Earth reconnection point. Using a network of ground magnetometer stations we are able to place the flux transport and field aligned current generation accomplished by the observed magnetotail signatures in a global substorm context. We find that individual localized reconnection impulses, resulting in localized plasmoids on one side and bursty flows on the other, build up the large scale substorm instability.

Angelopoulos, V.; Zhou, X.; Kiehas, S. A.; Li, S.; Runov, A.; Weygand, J. M.

2012-12-01

314

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. PMID:25628139

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

2015-01-01

315

The Time-Dependent Structure of the Electron Reconnection Layer  

Science.gov (United States)

Collisionless magnetic reconnection is often associated with time-dependent behavior. Specifically, current layers in the diffusion region can become unstable to tearing-type instabilities on one hand, or to instabilities with current-aligned wave vectors on the other. In the former case, the growth of tearing instabilities typically leads to the production of magnetic islands, which potentially provide feedback on the reconnection process itself, as well as on the rate of reconnection. The second class of instabilities tend to modulate the current layer along the direction of the current flow, for instance generating kink-type perturbations, or smaller-scale turbulence with the potential to broaden the current layer. All of these processes contribute to rendering magnetic reconnection time-dependent. In this presentation, we will provide a summary of these effects, and a discussion of how much they contribute to the overall magnetic reconnection rate.

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

2009-01-01

316

Suprathermal electron acceleration during reconnection onset in the magnetotail  

Science.gov (United States)

We study one event of reconnection onset associated to a small substorm on 27 September 2006 by using Cluster observations at inter-spacecraft separation of about 10,000 km. We focus on the acceleration of suprathermal electrons during different stages of reconnection. We show that several distinct stages of acceleration occur: 1) moderate acceleration during reconnection of pre-existing plasma sheet flux tubes 2) stronger acceleration during reconnection of lobe flux tubes 3) production of the most energetic electrons within dipolarization fronts / magnetic pile-up boundaries. The strongest acceleration is reached at the location of Bz maxima inside the magnetic pile-up region where the reconnection jet stops. Very strong localized dawn-dusk electric field are observed within the magnetic pile-up regions and are associated to most of the magnetic flux transport.

Vaivads, A.; Retino, A.; Khotyaintsev, Y. V.; Andre, M.

2011-12-01

317

Suprathermal electron acceleration during reconnection onset in the magnetotail  

Directory of Open Access Journals (Sweden)

Full Text Available We study one event of reconnection onset associated to a small substorm on 27 September 2006 by using Cluster observations at inter-spacecraft separation of about 10 000 km. We focus on the acceleration of suprathermal electrons during different stages of reconnection. We show that several distinct stages of acceleration occur: (1 moderate acceleration during reconnection of pre-existing plasma sheet flux tubes, (2 stronger acceleration during reconnection of lobe flux tubes, (3 production of the most energetic electrons within dipolarization fronts (magnetic pile-up regions. The strongest acceleration is reached at the location of Bz maxima inside the magnetic pile-up region where the reconnection jet stops. Very strong localized dawn-dusk electric field are observed within the magnetic pile-up regions and are associated to most of the magnetic flux transport.

A. Vaivads

2011-10-01

318

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

319

Two-Fluid MHD Simulations of Relativistic Magnetic Reconnection  

CERN Document Server

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 evolution thanks to an open boundary condition, and find that the Petschek-type structure is stable over the long time period. Simulation results and theoretical analyses exhibit that the Petschek outflow channel becomes narrower when the reconnection inflow contains more magnetic energy, as previously claimed. Meanwhile, we find that the reconnection rate goes up to ~1 in extreme cases, which is faster than previously thought. The role of the resistivity, implications for reconnection models in the magnetically dominated limit, and relevan...

Zenitani, Seiji; Klimas, Alex

2009-01-01

320

Plasmoid Instability in High-Lundquist-Number Magnetic Reconnection  

CERN Document Server

Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist ($S$) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when $S$ exceeds a critical value $\\sim10^{4}$, the Sweet-Parker current sheet is unstable to a super-Alfv\\'enic plasmoid instability, with a linear growth rate that scales as $S^{1/4}$. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of $S$, and the distribution function $f(\\psi)$ of plasmoid magnetic flux $\\psi$ follows a power law $f(\\psi)\\sim\\psi^{-1}$. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion f...

Huang, Yi-Min

2013-01-01

 
 
 
 
321

Two-dimensional magnetic reconnection model for incompressible plasmas  

International Nuclear Information System (INIS)

A modified two-dimensional magnetic reconnection model is presented which focuses on the role of electrostatic field generated by charge separation in magnetic reconnection, and the E cross B drift causing the Alfvenic outflows. This reconnection model reveals that the reconnection rate described in Sweet-Parker model is strongly dependent on the ratio of the electron mass and the ion mass, and the effective local resistivity normalized by the Spitzer resistivity is proportional to the square of the ratio of the ion skin depth to the width of the current sheet. The relativistic effect and creation of electron-positron pairs in high temperature plasmas can enhance the reconnection rate. The excitation of electromagnetic waves is necessary for dissipation of magnetic energy. (authors)

322

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

323

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

324

When Should Surgical Cytoreduction in Advanced Ovarian Cancer Take Place?  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Initial surgical management is commonly accepted to date as paramount in the treatment of women presenting with epithelial ovarian cancer and permits the assessment of the disease (staging), the histological confirmation of disease type and grade, and the practice of maximal debulking preceding platinum-based chemotherapy. Many studies have shown that the volume of residual disease after initial surgical cytoreduction inversely correlates with survival. Thus, women with optimal debulking perf...

Sean Kehoe; Martinek, Igor E.

2009-01-01

325

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

326

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

327

Hall MHD reconnection in cometary magnetotail  

International Nuclear Information System (INIS)

The fine structure of cometary tails (swirls, loops and blobs) is studied in the framework of resistive magnetic reconnection without a guide field in a dusty plasma. For a high-beta plasma (? ? 1) consisting of electrons, ions, and immobile dust grains, a two-fluid description is used to study electromagnetic perturbations with the frequency below ?i, propagating at an arbitrary angle, and including the effects of Hall current. A zero-order current associated with the anti-parallel magnetic configuration may exist even in the limit of zero plasma temperature in a dusty plasma due to a symmetry breaking between electrons and ions by dust grains that yields an E-vector x B-vector current. In the perturbed state, a new linear electromagnetic mode is found in dusty plasma which is evanescent below the Rao cut-off frequency and has the characteristic wavelength comparable to the ion skin depth, which enables the reconnection at short spatial scales. The role of the dust is found to be twofold, yielding a new mode outside of the current sheet and altering the continuity conditions at its edge by an inhomogeneous Doppler shift associated with the E-vector x B-vector current

328

Fluctuation dynamo based on magnetic reconnections  

CERN Document Server

We develop a new model of the fluctuation dynamo in which the magnetic field is confined to thin flux ropes advected by a multi-scale flow which models turbulence. Magnetic dissipation occurs only via reconnections of flux ropes. The model is particularly suitable for rarefied plasma, such as the Solar corona or galactic halos. We investigate the kinetic energy release into heat, mediated by dynamo action, both in our model and by solving the induction equation with the same flow. We find that the flux rope dynamo is more than an order of magnitude more efficient at converting mechanical energy into heat. The probability density of the magnetic energy released during reconnections has a power-law form with the slope -3, consistent with the Solar corona heating by nanoflares. We also present a nonlinear extension of the model. This shows that a plausible saturation mechanism of the fluctuation dynamo is the suppression of turbulent magnetic diffusivity, due to suppression of random stretching at the location o...

Baggaley, Andrew W; Shukurov, Anvar; Subramanian, Kandaswamy

2009-01-01

329

Collisionless reconnection: magnetic field line interaction  

Science.gov (United States)

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.

Treumann, R. A.; Baumjohann, W.; Gonzalez, W. D.

2012-10-01

330

Study of driven magnetic reconnection in a laboratory plasma  

International Nuclear Information System (INIS)

The Magnetic Reconnection Experiment (MRX) has been constructed to investigate the fundamental physics of magnetic reconnection in a well controlled laboratory setting. This device creates an environment satisfying the criteria for a magnetohydrodynamic (MHD) plasma (S much-gt 1, ?i much-lt L). The boundary conditions can be controlled externally, and experiments with fully three-dimensional reconnection are now possible. In the initial experiments, the effects of the third vector component of reconnecting fields have been studied. Two distinctively different shapes of neutral sheet current layers, depending on the third component, are identified during driven magnetic reconnection. Without the third component (anti-parallel or null-helicity reconnection), a thin double-Y shaped diffusion region is identified. A neutral sheet current profile is measured accurately to be as narrow as order ion gyro-radius. In the presence of an appreciable third component (co-helicity reconnection), an O-shaped diffusion region appears and grows into a spheromak configuration

331

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

332

Reconstruction of the reconnection rate from Cluster measurements: First results  

Science.gov (United States)

A model of transient time-dependent magnetic reconnection is used to describe the behavior of nightside flux transfers (NFTEs) in the Earth's magnetotail. On the basis of the analytical approach to reconnection developed by Heyn and Semenov (1996) and Semenov et al. (2004a) we calculate the magnetic field and plasma bulk velocity time series observed by a satellite. The solution for the plasma parameters is given in the form of a convolution integral. The calculation of the reconnection electric field is an ill-posed inverse problem, which we treat in the frame of the theory of regularization. This method is applied to Cluster measurements from 8 September 2002, where a series of earthward propagating 1-min scale magnetic field and plasma flow variations are observed outside of the plasma sheet, which are consistent with the theoretical picture of NFTEs. We analyzed three NFTEs and reconstructed the reconnection electric field. Additionally, the position of the satellite with respect to the reconnection site as well as the Alfvén velocity are estimated because they are necessary input parameters for the model. The reconnection electric field is found to be about 1-2 mV/m, while the reconnection site is located about 29-31 RE in the magnetotail.

Semenov, V. S.; Penz, T.; Ivanova, V. V.; Sergeev, V. A.; Biernat, H. K.; Nakamura, R.; Heyn, M. F.; Kubyshkin, I. V.; Ivanov, I. B.

2005-11-01

333

Magnetic field topology for northward IMF reconnection: Ion observations  

Science.gov (United States)

observations from the Cluster spacecraft are used to investigate magnetopause reconnection for northward Interplanetary Magnetic Field (IMF) conditions. When the spacecraft cross the magnetopause and enter the magnetosphere at low latitudes, equatorward of the magnetospheric cusps, multiple ion populations of magnetosheath origin are almost always observed. The bulk flow velocities of these separate populations are consistent with their entry at high northern and southern latitudes. Furthermore, characteristics of the pitch angle distributions provide a means to estimate the entry point of the magnetosheath ions and the relative timing of the reconnections in opposite hemispheres. In the example presented, these entry points are poleward of both magnetospheric cusps, and the reconnections are separated by minutes. In a survey of magnetopause crossing events, most ion observations and associated electron observations are consistent with this dual-lobe reconnection process as long as the reconnections are separated in time by several minutes. A small percentage of events are not consistent with this reconnection model and may indicate reconnection at other locations, such as equatorward of the cusp.

Fuselier, S. A.; Petrinec, S. M.; Trattner, K. J.; Lavraud, B.

2014-11-01

334

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 ...

335

Ion acceleration during internal magnetic reconnection events in TST-2  

International Nuclear Information System (INIS)

Characteristics of ion acceleration in the internal magnetic reconnection events (IRE) have been studied by means of a neutral particle energy analyzer (NPA) in Tokyo Spherical Tokamak (TST-2). The major and minor radii are 0.38 m and 0.25 m, respectively. The magnetic field strength is 0.3 T and the maximum plasma current is up to 140 kA. The electron and ion temperatures are 0.4 - 0.5 keV and 0.1 keV, respectively and the electron density is ? 1019 m-3. The NPA can be scanned toroidally from ? = 74 degrees (cw) to ? = 114 degrees (ccw), where ? = 90 degrees corresponds to the perpendicular sight-line. The direction of the plasma current is cw. The NPA signals are digitized at every 50 ?s. The NPA is calibrated in the energy range of 0.1 keV i) increases by 80 eV at IREs. The angle ? dependence of increment of Ti shows that ?Ti (? equals 74 degrees) is higher than that for ? = 114 degrees. This observation suggests that an ion is accelerated initially in the direction of magnetic field lines. The time evolution of the ion distribution function is simulated with a Fokker-Planck code taking into account the electric field effects. (authors)

336

Epidemiology and bioethics: a plea for reconnecting with the public.  

Science.gov (United States)

The author takes the position that both epidemiology and bioethics, as practiced within academic establishments, have largely although not entirely abstracted the public context of health and well-being from their respective disciplines. It is argued that by and large both disciplines have been highly successful at what they do. However, this success can in part be attributed to each limiting its ability to look beyond its respective academic niche and thus embrace challenges which are socially challenging, politically charged, and academically messy. This narrow focus has become self-serving and ultimately detracts from fundamental remits of both disciplines in protecting the public from harm. Furthermore, it may re-enforce the inequalities of research into health overall, whereby the greatest concentration of effort remains firmly focused upon those who already have the most. Currently marginalized approaches to each of these disciplines - such as social epidemiology, global bioethics, and critical bioethics - provide us with platforms that challenge mainstream academic epidemiologists and bioethicists to seek out and reconnect their expertise with questions that are more relevant to real-world situations. PMID:21485959

Outram, Simon M

2011-01-01

337

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

338

Hybrid studies of collisionless magnetic reconnection on tearing mode  

International Nuclear Information System (INIS)

In this work, we performed two-dimensional hybrid (kinetic particle ions, massless fluid electrons) studies of collisionless magnetic reconnection on tearing mode, which is characteristic of magnetosphere and high temperature fusion device plasmas. Results include the full electron pressure tensor (instead of a localized resistivity) in the generalized Ohm's law to initiate reconnection, and an initial perturbation to the Harris equilibrium is applied. It was found that the reconnection rate has similar results to those obtained on magnetohydrodynamic (MHD) models and kinetic models.

339

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

340

On the relationship between quadrupolar magnetic field and collisionless reconnection  

Energy Technology Data Exchange (ETDEWEB)

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.

Smets, R., E-mail: roch.smets@lpp.polytechnique.fr; Belmont, G. [LPP, University P. and M. Curie, CNRS, Ecole Polytechnique, F-91128 Palaiseau (France); Aunai, N. [IRAP, University Paul Sabatier, F-31028 Toulouse (France); Boniface, C. [CEA/DAM, DIF, F-91297 Arpajon (France); Fuchs, J. [LULI, Ecole Polytechnique, CNRS, CEA, University P. and M. Curie, F-91128 Palaiseau (France)

2014-06-15

 
 
 
 
341

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

342

A New Electric Field in Asymmetric Magnetic Reconnection  

CERN Document Server

We present a theory and numerical evidence for the existence of a previously unexplored in-plane electric field in collisionless asymmetric magnetic reconnection. This electric field, dubbed the "Larmor electric field," is associated with finite Larmor radius effects and is distinct from the known Hall electric field. Potentially, it could be an important indicator for the upcoming Magnetospheric Multiscale (MMS) mission to locate reconnection sites as we expect it to appear on the magnetospheric side, pointing Earthward, at the dayside magnetopause reconnection site.

Malakit, Kittipat; Cassak, Paul A; Ruffolo, David

2013-01-01

343

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

344

ARTEMIS-THEMIS observations of magnetotail dynamics driven by magnetic reconnection  

Science.gov (United States)

The ARTEMIS (Acceleration, Reconnection, Turbulence, and Electrodynamics of the Moon's Interaction with the Sun) mission consists of two satellites (probes) extracted from the Earth-orbiting five probe THEMIS mission in 2009 and placed in lunar orbit in mid-2011. Prior to their insertion into lunar orbit, from October 2010 the two ARTEMIS probes P1 and P2 occupied Lissajous orbits around the 1st and 2nd lunar Lagrange points respectively (phase LL1,2). In Jan 2011, both probes were placed in orbit around the near-Earth Lagrange point (phase LL1). From this location, and complemented by the remaining THEMIS probes, ARTEMIS provided a new multi-spacecraft view of the Earth's mid-magnetotail, with a spacecraft separation baseline of 10 - 20 RE. A key goal of the ARTEMIS mission is to characterize the nature of magnetotail dynamics using two point measurements, with particular reference to the development of magnetic reconnection and formation of X-lines. To address this goal, we present the results of a survey for fast plasma flow in the magnetotail, made using ARTEMIS data acquired during the LL1,2 and LL1 mission phases. Between October 2010 and June 2011, the two ARTEMIS probes made 9 magnetotail crossings, each lasting 4 - 6 days. More than 80 intervals of interest are identified, including (a) examples of flow observed only by one spacecraft even with both in the plasma sheet, (b) examples where plasma sheet flow bursts were simultaneously observed by both spacecraft, (c) examples of simultaneous magnetosheath and magnetotail observation, including observations of boundary dynamics. Using case studies and statistical analysis, the typical properties of fast plasma flow bursts driven by reconnection in the magnetotail in the vicinity of lunar orbit are identified.

Eastwood, J. P.; Phan, T.; Oieroset, M.; Angelopoulos, V.; McFadden, J. P.; Auster, H.

2011-12-01

345

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

346

Reconnection in Spheromak formation and sustainment  

International Nuclear Information System (INIS)

The Spheromak is a magnetic confinement device that is being explored in both the US and Japanese fusion programs. It is a member of the Compact Torus family of magnetic structures characterized by a set of closed, nested toroidal flux surfaces but without any coils, transformer cores, etc. protruding through the hole in the torus. The Speromak is closely elated to the Reversed Field Pinch (RFP) in that most of the magnetic field is produced by plasma currents flowing along the magnetic field lines (a near force free field) rather than by external coils. The Spheromak has magnetic field components of comparable strength in both the toroidal (azimuthal) and poloidal (in the plane perpendicular to the azimuthal unit vector) directions. The large internal magnetic energy in the Spheromak makes it rich in magnetohydrodynamic phenomena and reconnection, in particular, plays an important role in the formation, resistive decay and instability processes

347

Plasma Reconnection in HI-1 Helicity Injector  

Science.gov (United States)

The intensive research on the spheromaks in steady state conditions are studied in 1980's as well as the fundamental numerical simulations. However, the experimental understanding of the plasma production phase with the drastic reconnection process are out of DOE's main focus. In this meeting an experimental findings closely related to the electrode polarity effect are introduced as well as the fundamental results especially on the stagnation point. The fundamental parameters are already shown in the last meeting in LUISVILLE. This device is a simulator of future FBX-III BURNER EXPERIMENT and operated under a 30kA,10Pa coaxial discharge up to 0.1 Tesla axial magnetic field. Bull.American Phys.Soc., 40,11(1995) OCT, 1764

Irie, Masaru; Yoshikawa, Shirou

1996-11-01

348

Reconnection of vortex filaments and Kolmogorov spectrum  

CERN Document Server

The energy spectrum of the 3D velocity field, induced by collapsing vortex filaments is studied. One of the aims of this work is to clarify the appearance of the Kolmogorov type energy spectrum $E(k)\\varpropto k^{-5/3}$, observed in many numerical works on discrete vortex tubes (quantized vortex filaments in quantum fluids). Usually, explaining classical turbulent properties of quantum turbulence, the model of vortex bundles, is used. This model is necessary to mimic the vortex stretching, which is responsible for the energy transfer in classical turbulence. In our consideration we do not appeal to the possible "bundle arrangement" but explore alternative idea that the turbulent spectra appear from singular solution, which describe the collapsing line at moments of reconnection. One more aim is related to an important and intensively discussed topic - a role of hydrodynamic collapse in the formation of turbulent spectra. We demonstrated that the specific vortex filament configuration generated the spectrum $E...

Nemirovskii, Sergey K

2014-01-01

349

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

350

Observations of slow electron holes at a magnetic reconnection site.  

Science.gov (United States)

We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process. PMID:21230981

Khotyaintsev, Yu V; Vaivads, A; André, M; Fujimoto, M; Retinò, A; Owen, C J

2010-10-15

351

Integrating Kinetic Effects into Global Models for Reconnection  

Science.gov (United States)

Magnetic reconnection is the most striking example of how the coupling between global and kinetic scales can lead to fast energy release. Explosive solar activity, such as coronal mass ejections and flares for example, is widely believed to be due to the release of magnetic energy stored on global scales by magnetic reconnection operating on kinetic scales. Understanding how processes couple across spatial scales is one of the most difficult challenges in all of physics, and is undoubtedly the main obstacle to developing predictive models for the Sun's activity. Consequently, the NASA Living With a Star Program selected a Focused Science Team to attack the problem of cross-scale coupling in reconnection. In this talk I will present some of the results of the Team and review our latest theories and methods for modeling the global-local coupling in solar reconnection.

Antiochos, S. K.

2012-01-01

352

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

353

Multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma  

CERN Document Server

We present results from the first self-consistent multi-fluid simulations of chromospheric magnetic reconnection in a weakly ionized reacting plasma. We simulate two dimensional magnetic reconnection in a Harris current sheet with a numerical model which includes ion-neutral scattering collisions, ionization, recombination, optically thin radiative loss, collisional heating, and thermal conduction. In the resulting tearing mode reconnection the neutral and ion fluids become decoupled upstream from the reconnection site, creating an excess of ions in the reconnection region and therefore an ionization imbalance. Ion recombination in the reconnection region, combined with Alfv\\'{e}nic outflows, quickly removes ions from the reconnection site, leading to a fast reconnection rate independent of Lundquist number. In addition to allowing fast reconnection, we find that these non-equilibria partial ionization effects lead to the onset of the nonlinear secondary tearing instability at lower values of the Lundquist nu...

Leake, James E; Linton, Mark G; Meier, Eric T

2012-01-01

354

Signatures of secondary collisionless magnetic reconnection driven by kink instability of a flux rope  

Science.gov (United States)

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 reconnection events in space, astrophysical and fusion plasmas.

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

2014-06-01

355

Is Guide Field Reconnection Inherently Turbulent?  

Science.gov (United States)

At the Earth’s magnetopause, magnetic reconnection is thought to develop within ion-scale current sheets in the presence of a finite guide field. As the dynamics develops, 2D kinetic simulations have demonstrated that new electron-scale current layers are formed extending outwards from the diffusion region, and these are often unstable to the formation of secondary islands. In this work, we demonstrate there are some profound differences in extending these previous 2D results to real 3D systems. With a finite guide field, tearing modes are unstable at resonant surfaces across the initial layer, corresponding to oblique angles relative to the standard 2D geometry. The 2D models artificially suppress these oblique modes and greatly restrict the manner in which magnetic islands can interact. In real 3D systems, both primary and secondary islands correspond to extended flux ropes, which can interact in a variety of complex ways not possible in 2D. Here, we address these challenges using Vlasov theory and 3D kinetic simulations. The theoretical results are used to gain insight into the range of unstable oblique modes and to guide and interpret 3D petascale kinetic simulations. These unprecedented simulations, using up to ~1.3 trillion particles, have revealed an inherently 3D evolution featuring the formation and interaction of flux ropes within the initial current layer, followed by the subsequent generation of secondary flux ropes within the elongated current sheets extending outward from the diffusion region as well as along the separatrices. These results may have far-reaching implications for a range of basic issues, including the structure of the exhaust, the dissipation rate of magnetic energy, the generation of stochastic magnetic fields and the transport of particles. Implications for MMS and the detections of reconnection at the dayside magnetopause are discussed

Daughton, W. S.; Roytershteyn, V.; Karimabadi, H.; Quest, K. B.; Yin, L.; Albright, B. J.; Bowers, K. J.

2010-12-01

356

Observations of significant flux closure by dual lobe reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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 footpr...

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

2007-01-01

357

Magnetic reconnection associated fluctuations in the deep magnetotail: ARTEMIS results  

Digital Repository Infrastructure Vision for European Research (DRIVER)

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

358

Plasmoid instability in high-Lundquist-number magnetic reconnection  

International Nuclear Information System (INIS)

Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist (S) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when S exceeds a critical value ?104, the Sweet-Parker current sheet is unstable to a super-Alfvénic plasmoid instability, with a linear growth rate that scales as S1/4. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of S, and the distribution function f(?) of plasmoid magnetic flux ? follows a power law f(?)???1. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion for onset is not satisfied. The rich variety of possible reconnection dynamics is organized in the framework of a phase diagram

359

Origins of effective resistivity in collisionless magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

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 (?{sub npg}) in the electron diffusion region (EDR). We derive an analytical relation for the effective resistivity (?{sub kin}) by momentum balance in a control volume in the EDR. Both ?{sub npg} and ?{sub kin} mutually compare well and they also compare well with the resistivity required to support reconnection electric field E{sub rec} 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 (d{sub i}), 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???d{sub i}, 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 [Electrical and Computer Engineering, University of Alabama, Huntsville, Alabama 35899 (United States)

2014-07-15

360

Origins of effective resistivity in collisionless magnetic reconnection  

International Nuclear Information System (INIS)

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

 
 
 
 
361

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

362

Plasmoid instability in high-Lundquist-number magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Our understanding of magnetic reconnection in resistive magnetohydrodynamics has gone through a fundamental change in recent years. The conventional wisdom is that magnetic reconnection mediated by resistivity is slow in laminar high Lundquist (S) plasmas, constrained by the scaling of the reconnection rate predicted by Sweet-Parker theory. However, recent studies have shown that when S exceeds a critical value ?10{sup 4}, the Sweet-Parker current sheet is unstable to a super-Alfvénic plasmoid instability, with a linear growth rate that scales as S{sup 1/4}. In the fully developed statistical steady state of two-dimensional resistive magnetohydrodynamic simulations, the normalized average reconnection rate is approximately 0.01, nearly independent of S, and the distribution function f(?) of plasmoid magnetic flux ? follows a power law f(?)??{sup ?1}. When Hall effects are included, the plasmoid instability may trigger onset of Hall reconnection even when the conventional criterion for onset is not satisfied. The rich variety of possible reconnection dynamics is organized in the framework of a phase diagram.

Huang, Yi-Min [Center for Integrated Computation and Analysis of Reconnection and Turbulence, Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, Space Science Center, University of New Hampshire, Durham, New Hampshire 03824 (United States); Bhattacharjee, A. [Center for Integrated Computation and Analysis of Reconnection and Turbulence, Center for Magnetic Self-Organization in Laboratory and Astrophysical Plasmas, Max Planck-Princeton Center for Plasma Physics and Princeton Plasma Physics Laboratory, Princeton, New Jersey 08543 (United States)

2013-05-15

363

Magnetic Reconnection and Intermittent Turbulence in the Solar Wind  

Science.gov (United States)

A statistical relationship between magnetic reconnection, current sheets, and intermittent turbulence in the solar wind is reported for the first time using in situ measurements from the Wind spacecraft at 1 AU. We identify intermittency as non-Gaussian fluctuations in increments of the magnetic field vector B that are spatially and temporally nonuniform. The reconnection events and current sheets are found to be concentrated in intervals of intermittent turbulence, identified using the partial variance of increments method: within the most non-Gaussian 1% of fluctuations in B, we find 87%-92% of reconnection exhausts and ˜9% of current sheets. Also, the likelihood that an identified current sheet will also correspond to a reconnection exhaust increases dramatically as the least intermittent fluctuations are removed from the data set. Hence, the turbulent solar wind contains a hierarchy of intermittent magnetic field structures that are increasingly linked to current sheets, which in turn are progressively more likely to correspond to sites of magnetic reconnection. These results could have far reaching implications for laboratory and astrophysical plasmas where turbulence and magnetic reconnection are ubiquitous.

Osman, K. T.; Matthaeus, W. H.; Gosling, J. T.; Greco, A.; Servidio, S.; Hnat, B.; Chapman, S. C.; Phan, T. D.

2014-05-01

364

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

365

Transience and Place: Exploring Tourists' Experiences of Place  

Directory of Open Access Journals (Sweden)

Full Text Available This paper explores tourists' transient place experiences. The focus is on what is commonly called sightseeing, confined mainly to experiences of locations not previously visited. This type of travel experience, seeing actual places or objects for one's self and taking photographs, is regarded here as an important ritual in modernity. With reference to the concept of adventurer, the paper attempts to describe various aspects of novel travel experiences. For instance, ephemeral tourist sensations of place are compared to «love at first sight», a blissful experience of meeting with a place to which one feels strongly attracted. While transient encounters may also provide access to dreamlike place experiences, adventurous tourists are always in danger of being caught up in other roles, or of becoming embroiled in a new everyday life with accompanying routines. By way of conclusion, it is proposed that the restrictions on time inherent in today's holiday tours usually result in transient place experiences as the only alternative for those desiring to gain first-time impressions of several places or larger geographic areas.

Jens Kristian Steen Jacobsen

1998-02-01

366

Fast magnetic reconnection with plasmoid / current sheet ejection events in laboratory experiments  

Science.gov (United States)

Non-steady and fast magnetic reconnections due to plasmoid or current sheet ejection events have been investigated in laboratory experiments using TS-3, TS-4 and UTST plasma merging devices in the University of Tokyo. In these devices, magnetic reconnection is induced by two different schemes, a) push reconnection driven by flux injection from the upstream region, b) pull reconnection driven by flux extraction to the downstream region. Current sheet or plasmoid ejection events are observed in these reconnection experiments particularly with strong guide magnetic field parallel to the reconnection electric field. In push reconnection experiments, anomalous resistivity is induced by the ion's kinetic effect (meandering motion) when the current sheet width is compressed shorter than the ion gyroradius by the strongly injected inflow flux. This fast reconnection regime does not involve plasmoid / current sheet ejection events. On the other hand, the guide field reduces the ion gyroradius and suppresses the onset of the anomalous resistivity, providing slow and steady magnetic reconnection. Impulsive fast reconnection with strong guide field develops, nevertheless, due to plasmoid / current sheet ejection events in pull and push reconnection experiments with extremely large external driving forces. In such a situation, the inflow flux is forcedly pushed into the reconnection region even faster than the maximal reconnection rate, resulting in flux pile up in front of the diffusion region. This piled flux induces large current density inside the current sheet in which plasmoid structure with closed flux surface is formed in pull reconnection case. The induced large current density or plasmoid is then ejected from the diffusion region with significant increase of reconnection electric field. As a result, magnetic reconnection condition with even larger reconnection rate than that obtained by anomalous resistivity was achieved under strong guide field and large external driving force.

Inomoto, Michiaki; Ono, Yasushi; Hayashi, Yoshinori

2012-07-01

367

When School Are Not Safe Places: Reconnecting Gay and Lesbian Young People to Schools.  

Science.gov (United States)

Describes how two schools have made themselves more open to gay, lesbian, bisexual, and transgender students. Recommends that schools develop policies that protect students, train teachers and counselors in suicide- and violence prevention, provide support groups for straight and gay students, make information available in school libraries, and…

Mallon, Gerald P.

1997-01-01

368

Internal and External Reconnection Series Homologous Solar Flares  

Science.gov (United States)

Using data from the extreme ultraviolet imaging telescope (EIT) on SOHO and the soft X-ray telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in National Oceanic and Atmospheric Administration (NOAA) active region 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X rays. In EIT each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities approx. 20 km/ s. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions but are modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare, postflare loops, and a coronal mass ejection (CME). External reconnection, first occurring between the escaping CME and the coronal hole field and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting in morphologically homologous eruptions. Our inferred magnetic topology is similar to that suggested in the "breakout model" of eruptions although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, primarily by the internal reconnection.

Sterling, Alphonse C.; Moore, Ronald L.

2001-01-01

369

Impulsive reconnection: 3D onset and stagnation in turbulent paradigms  

Energy Technology Data Exchange (ETDEWEB)

Reconnection processes are ubiquitous in solar coronal loops, the earth's magnetotail, galactic jets, and laboratory configurations such as spheromaks and Z pinches. It is believed that reconnection dynamics are often closely linked to turbulence. In these phenomena, the bursty onset of reconnection is partly determined by a balance of macroscopic MHD forces. In a turbulent paradigm, it is reasonable to suppose that there exist many individual reconnection sites, each X-line being finite in axial extent and thus intrinsically three-dimensional (3D) in structure. The balance between MHD forces and flux pile-up continuously shifts as mutually tangled flux ropes merge or bounce. The spatial scale and thus the rate of reconnection are therefore intimately related to the turbulence statistics both in space and in time. We study intermittent 3D reconnection along spatially localized X-lines between two or more flux ropes. The threshold of MHD instability which in this case is the kink threshold is varied by modifying the line-tying boundary conditions. For fast inflow speed of approaching ropes, there is merging and magnetic reconnection which is a well known and expected consequence of the 2D coalescence instability. On the other hand, for slower inflow speed the flux ropes bounce. The threshold appears to be the Sweet Parker speed v{sub A}/S{sup 1/2}, where v{sub A} is the Alfven speed and S is the Lundquist number. Computations by collaborators at University of Wisconsin, Madison, Katholieke Universiteit Leuven, and LANL complement the experiment.

Sears, Jason A [Los Alamos National Laboratory; Intrator, Thomas P [Los Alamos National Laboratory; Weber, Tom [Los Alamos National Laboratory; Lapenta, Giovanni [KATHOLIEKE UNIV.; Lazarian, Alexander [UNIV OF WISCONSIN

2010-12-14

370

CAN THE SOLAR WIND BE DRIVEN BY MAGNETIC RECONNECTION IN THE SUN'S MAGNETIC CARPET?  

International Nuclear Information System (INIS)

The physical processes that heat the solar corona and accelerate the solar wind remain unknown after many years of study. Some have suggested that the wind is driven by waves and turbulence in open magnetic flux tubes, and others have suggested that plasma is injected into the open tubes by magnetic reconnection with closed loops. In order to test the latter idea, we developed Monte Carlo simulations of the photospheric 'magnetic carpet' and extrapolated the time-varying coronal field. These models were constructed for a range of different magnetic flux imbalance ratios. Completely balanced models represent quiet regions on the Sun and source regions of slow solar wind streams. Highly imbalanced models represent coronal holes and source regions of fast wind streams. The models agree with observed emergence rates, surface flux densities, and number distributions of magnetic elements. Despite having no imposed supergranular motions in the models, a realistic network of magnetic 'funnels' appeared spontaneously. We computed the rate at which closed field lines open up (i.e., recycling times for open flux), and we estimated the energy flux released in reconnection events involving the opening up of closed flux tubes. For quiet regions and mixed-polarity coronal holes, these energy fluxes were found to be much lower than that which is required to accelerate the solar wind. For the most imbalanced coronal holes, the energy fluxes may be large enough to power the solar wind,y be large enough to power the solar wind, but the recycling times are far longer than the time it takes the solar wind to accelerate into the low corona. Thus, it is unlikely that either the slow or fast solar wind is driven by reconnection and loop-opening processes in the magnetic carpet.

371

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

372

Holography of D-Brane Reconnection  

CERN Document Server

Gukov, Martinec, Moore and Strominger found that the D1-D5-D5' system with the D5-D5' angle at 45 degrees admits a deformation "rho" preserving supersymmetry. Under this deformation, the D5-branes and D5'-branes reconnect along a single special Lagrangian manifold. We construct the near-horizon limit of this brane setup (for which no supergravity solution is currently known), imposing the requisite symmetries perturbatively in the deformation rho. Reducing to the three-dimensional effective gauged supergravity, we compute the scalar potential and verify the presence of a deformation with the expected properties. We compute the conformal dimensions as functions of rho. This spectrum naturally organizes into N=3 supermultiplets, corresponding to the 3/16 preserved by the brane system. We give some remarks on the symmetric orbifold CFT for Q_D5=Q_D5', outline the computation of rho-deformed correlators in this theory, and probe computations in our rho-deformed background.

Berg, M; Samtleben, H; Berg, Marcus; Hohm, Olaf; Samtleben, Henning

2007-01-01

373

Magnetic field reconnection in a collisionless plasma  

International Nuclear Information System (INIS)

In a collisionless plasma, steady-state reconnection flows require some form of anomalous dissipation in order to limit the current in the neutral region. As a possible anomalous resistance process, we consider the current-driven ion acoustic instability for plasmas with comparable electron and ion temperatures. Although the marginally stable electron drift speed is high, small increases above marginal stability lead to large ion acoustic growth rates. A nonlinear turbulence theory for the instability is developed, and the saturation amplitude is calculated as a function of electron drift and electron-to-ion temperature ratio. For reasonable DC electric fields the ion acoustic anomalous resistance is strong enough to limit the electron drift to slightly above marginal stability. The physical consequences of the anomalous resistance are incorporated into a hydromagnetic model of the flow in the neutral region. The neutral region solution is matched to an approximate solution for the flow external to the resistive region. From the matching conditions we find that if the upstream ratio of thermal pressure to magnetic pressure is less than about 5, the ion acoustic instability will be excited

374

Computer simulations on three-dimensional magnetic loop dynamics by the spontaneous fast reconnection model  

International Nuclear Information System (INIS)

Three-dimensional (3D) dynamics of a large-scale magnetic loop is studied by precise magnetohydrodynamic simulations on the basis of the spontaneous fast reconnection model. Once a (current-driven) anomalous resistivity is ignited, the fast reconnection mechanism drastically evolves by the positive feedback between the (3D) global reconnection flow and the anomalous resistivity; on the nonlinear saturation phase, the global reconnection flow has grown so that the reconnection (diffusion) region shrinks to a small extent, and the fast reconnection mechanism involving a pair of standing slow shocks is established in the finite extent. When the 3D plasmoid, formed ahead of the fast reconnection jet, collides with the mirror plane boundary, the reconnected field lines are piled up, leading to formation of a large-scale 3D magnetic loop. Since the resulting 3D fast reconnection jet becomes supersonic, a definite fast shock builds up at the interface between the magnetic loop top and the fast reconnection jet. The 3D fast reconnection jet is limited in a narrow channel between the pair of slow shocks, so that the resulting fast shock is also limited to a small extent ahead of the magnetic loop top. On the other hand, for the uniform resistivity model the 3D fast reconnection mechanism cannot be realized without any vital positive feedback between the reconnection flow and the local magnetic diffusion; hence, such an effective resistivity that can be self-consistently enhancivity that can be self-consistently enhanced locally at the X reconnection point by the global reconnection flow is essential for the fast reconnection mechanism to be realized in actual systems

375

Demonstration of Anisotropic Fluid Closure Capturing the Kinetic Structure of Magnetic Reconnection  

Digital Repository Infrastructure Vision for European Research (DRIVER)

Collisionless magnetic reconnection in high-temperature plasmas has been widely studied through fluid-based models. Here, we present results of fluid simulation implementing new equations of state for guide-field reconnection. The new fluid closure accurately accounts for the anisotropic electron pressure that builds in the reconnection region due to electric and magnetic trapping of electrons. In contrast to previous fluid models, our fluid simulation reproduces the detailed reconnection reg...

Ohia, Obioma O.; Egedal, J.; Lukin, V. S.; Daughton, W.

2012-01-01

376

Places for Pedagogies, Pedagogies for Places  

Science.gov (United States)

Working with an understanding of assemblage as the ad hoc groupings of vibrant materials and elements, this article argues that conceptualizing place as an assemblage opens possibilities for bridging the gap between subjects and objects that continue to structure pedagogy. Considering "place" as an assemblage of humans and their multiple "others"…

Duhn, Iris

2012-01-01

377

Energy balance in the course of relativistic magnetic reconnection  

Science.gov (United States)

Magnetic reconnection plays an important role in space physics, for example, in Earth's magnetosphere, on the Sun, in the magnetospheres of magnetars, pulsars, black holes, etc. Reconnection starts with abrupt drop of plasma conductivity in a small part of a current sheet, so called, diffusion region. As a result electric field is generated and is transferred by relativistic MHD surface wave from the diffusion region to the current sheet which leads to decay of the disturbed part of the current sheet into a system of slow shocks. Plasma is highly accelerated and heated at the shock fronts forming outflow region with relativistic plasma jets and weak magnetic field (Semenov & Bernikov 1991). At some stage the reconnection process has to switch-off, then outflow regions must detach from the site where the electric field was initiated, and propagate along the current sheet as solitary waves (Tolstykh et al. 2005). The energy balance of relativistic reconnection is investigated in details. It is shown that magnetic and thermal energy from the inflow region is spent for acceleration and heating of the plasma in jets. It is interesting that the temperature of the plasma in the wake of the propagating outflow regions drops after each pulse of reconnection. This differ from usual explosion which heats the plasma behind the shock front (Tolstykh et al. 2007).

Semenov, V. S.; Tolstykh, Yu. V.; Dyadechkin, S. A.

378

Crossed flux tubes 3D magnetic reconnection experiment  

Science.gov (United States)

The formation and dynamics of writhing, plasma-filled, twisted open magnetic flux tubes is being investigated using laboratory experiments. The behavior of these flux tubes is relevant to solar corona loops, astrophysical jets, spheromak formation, and open field lines in tokamaks and RFP's. MHD forces have been determined to drive fast axial plasma flows into the flux tube from the boundary it intercepts. These flows fill the flux tubes with plasma while simultaneously injecting linked frozen-in azimuthal flux; helicity injection is thus associated with mass injection. An upgraded experiment under construction will have two adjacent arched plasma-filled flux tubes cross over each other. It is anticipated that a localized 3D reconnection will occur at the cross-over. This reconnection should result in half-twists in the post re-connection topology and subsequent Alfven wave propagation to equilibrate the half-twists along the post-reconnection flux tubes. The electrical circuitry requires two initially independent floating capacitor bank power supplies that become series-connected as a result of reconnection.

Bellan, Paul

2011-11-01

379

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

380

Reconnection in photospheric-chromospheric current sheet and coronal heating  

Energy Technology Data Exchange (ETDEWEB)

It has been observed by various ground and space based solar missions that magnetic reconnection occurs frequently in the photosphere-chromosphere region as well as in the solar corona. The purpose of this article is to examine the process of reconnection in thin current sheet formed between two oppositely directed magnetic flux tubes in photospheric-chromospheric region. Using the data of different atmospheric models for the solar photosphere and chromosphere, we have estimated the rate of magnetic reconnection in terms of Alfvenic Mach number, growth rate of tearing mode, island length scales, and energy dissipation rate necessary to heat the chromospheric plasma. It is found that magnetic Reynolds number for the current sheet in the chromosphere varies from 1.14 Multiplication-Sign 10{sup 3} to 7.14 Multiplication-Sign 10{sup 6} which indicates that the field lines in the photosphere and chromosphere reconnect with speed, that is, 0.00034 to 0.0297 times the Alfven speed. Frequency of the MHD waves generated in the chromosphere reconnection region is of the order of 100 Hz, so these high-frequency waves may be the sources of coronal heating and solar wind acceleration.

Kumar, P. [Hindu College, Department of Physics (India); Kumar, N. [M.M.H. College, Department of Mathematics (India); Uddin, W. [Aryabhatta Research Institute of Observational Sciences (ARIES) (India)

2011-02-15

 
 
 
 
381

Non-linear development of streaming instabilities in magnetic reconnection with a strong guide field  

Science.gov (United States)

Magnetic reconnection has been recognized as a dominant mechanism for converting magnetic energy into the convective and thermal energy of particles, and has been thought as the driver of explosive events in nature and laboratory, such as solar and stellar flares, magnetic substorms and disruptions in fusion experiments. Magnetic reconnection (Sweet-Parker and Petscheck model) is often modeled using resistive magnetohydrodynamics, in which collisions play the key role in facilitating the release of energy in the explosive events. However, in space plasma the collisional resistivity is far below the required resistivity to explain the observed energy release rate. Turbulence is common in plasmas and the anomalous resistivity induced by the turbulence has been proposed as a mechanism for breaking the frozen-in condition in magnetic reconnection. Turbulence-driven resistivity has remained a poorly understood, but widely invoked mechanism for nearly 50 years. The goal of this project is to understand what role anomalous resistivity plays in fast magnetic reconnection. Turbulence has been observed in the intense current layers that develop during magnetic reconnection in the Earth's magnetosphere. Electron streaming is believed to be the source of this turbulence. Using kinetic theory and 3D particlein- cell simulations, we study the nonlinear development of streaming instabilities in 3D magnetic reconnection with a strong guide field. Early in time an intense current sheet develops around the x-line and drives the Buneman instability. Electron holes, which are bipolar spatial localized electric field structures, form and then self-destruct creating a region of strong turbulence around the x-line. At late time turbulence with a characteristic frequency in the lower hybrid range also develops, leading to a very complex mix of interactions. A major challenge is to investigate what occurs after the saturation of Buneman instability and how the momentum and energy are exchanged among the waves and particles by the turbulence. The difficulty we face in this project is how to address a long-standing problem in nonlinear kinetic theory: how to treat large amplitude perturbations and the associated strong wave-particle interactions. In my thesis, I address this long-standing problem using particle-in-cell simulations and linear kinetic theory. The kinetic process of 3D magnetic reconnection is complicated. To separate problem of turbulent driven drag from reconnection, we carry out 3D simulations in which we specify the initial streaming velocities of particles to mimic the configuration of the x-line during magnetic reconnection. The geometry is chosen so that reconnection does not develop. Some important physics have been revealed. (1) At late time the lower hybrid instability (LHI) dominates the dynamics in low b plasma in combination with either the electron-electron two-stream instability (ETS) or the Buneman instability (BI), depending on the parallel phase speed of the LHI. If its parallel phase speed is sufficiently large and leaves sufficient velocity space for the ETS to grow, the ETS takes over the BI and interacts with the LHI to slow the streaming electrons. If not, the BI acts with the LHI to slow the high speed electrons. (2) An instability with a high phase speed is required to tap the energy of the high velocity electrons. The BI with its low phase speed, can not do this. The ETS and the LHI, both have high phase speed. (3) The condition for the formation of stable electron holes requires |" v p - v g |" < [Special characters omitted.] where|"[straight phi]|" is the amplitude of the electric potential, and v p and v g are the phase and group velocity of the relevant waves. Like the BI and ETS the LHI can form electron holes. (4) The overlapping resonance in phase space is the dominant mechanism for transporting the momentum and energy from high velocity electrons to low velocity electrons, which then couple to the ions. These resonances also lead to the chaotic motion of electrons in phase spa

Che, Haihong

2009-06-01

382

Experimental Verification of the Hall Effect during Magnetic Reconnection in a Laboratory Plasma  

International Nuclear Information System (INIS)

In this letter we report a clear and unambiguous observation of the out-of-plane quadrupole magnetic field suggested by numerical simulations in the reconnecting current sheet in the Magnetic Reconnection Experiment (MRX). Measurements show that the Hall effect is large in collisionless regime and becomes small as the collisionality increases, indicating that the Hall effect plays an important role in collisionless reconnection

383

Definition of reconnection rate of solar flares registered in 2011-2012 years  

CERN Document Server

Was defined reconnection rate of solar flares observed with the SOHO Michelson Doppler Imager (MDI). Measured physical parameters of 15 flares, such as the temporal scale, size and magnetic flux density. Estimated reconnection inflow velocity, coronal Alfven velocity, and reconnection rate using the observed values.

Sarsembayeva, A T

2012-01-01

384

Relativistic Magnetic Reconnection in Pair Plasmas and Its Astrophysical Applications  

Science.gov (United States)

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, D.; Sironi, L.; Cerutti, B.; Giannios, D.

2015-01-01

385

Occurrence of Magnetic Reconnection in the Deep Magnetotail: ARTEMIS Results  

Science.gov (United States)

Using two-probe ARTEMIS magnetic field and plasma measurements we have accomplished a survey of the occurrence of magnetic reconnection signatures in the distant magnetotail between October 2010 and June 2011. We have considered highly accelerated electron and fast bulk plasma flow events during ARTEMIS tail crossings. Our findings suggest that the deep-tail region between -60{R}E < X({GSM}) < -40{R}E is rather active. Fourteen events have been found exhibiting signatures of magnetic reconnection occurrence during 29 days of plasma sheet crossings. Comparisons with mid-tail surveys of reconnection statistics indicate that the deep-tail region can play a significant role in global magnetosphere dynamics.

Vörös, Zoltán; Runov, Andrei; Kendl, Alexander

386

Collisionless magnetic reconnection associated with coalescence of flux bundles  

International Nuclear Information System (INIS)

The basic process of collisionless reconnection is studied in terms of coalescence of magnetized flux bundles using an implicit particle simulation of two-dimensions. The toroidal electric field that directly relates to magnetic reconnection is generated solenoidally in a region much broader than the current sheet whose width is a few electron skin depths. The reconnected flux increases linearly in time, but it is insensitive to finite Larmor radii of the ions in this Sweet-Parker regime. The toroidal electric field is controlled by a balance of transit acceleration of finite-mass electrons and their removal by sub-Alfvenic E x B drift outflow. The simulation results supports the collisionless Ohm's law Et??eqJt with ?eq the inertia resistivity. (author)

387

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

388

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

389

Solar Particle Acceleration at Reconnecting 3D Null Points  

CERN Document Server

Context: The strong electric fields associated with magnetic reconnection in solar flares are a plausible mechanism to accelerate populations of high energy, non-thermal particles. One such reconnection scenario occurs at a 3D magnetic null point, where global plasma flows give rise to strong currents in the spine axis or fan plane. Aims: To understand the mechanism of charged particle energy gain in both the external drift region and the diffusion region associated with 3D magnetic reconnection. In doing so we evaluate the efficiency of resistive spine and fan models for particle acceleration, and find possible observables for each. Method: We use a full orbit test particle approach to study proton trajectories within electromagnetic fields that are exact solutions to the steady and incompressible magnetohydrodynamic equations. We study single particle trajectories and find energy spectra from many particle simulations. The scaling properties of the accelerated particles with respect to field and plasma para...

Stanier, Adam J; Dalla, Silvia

2012-01-01

390

Magnetic Reconnection in the Spheromak: Physics and Consequences  

International Nuclear Information System (INIS)

Magnetic reconnection in the spheromak changes magnetic topology by conversion of injected toroidal flux into poloidal flux and by magnetic surface closure (or opening) in a slowly decaying spheromak. Results from the Sustained Spheromak Physics Experiment, SSPX, are compared with resistive MHD simulations using the NIMROD code. Voltage spikes on the SSPX gun during spheromak formation are interpreted as reconnection across a negative-current layer close to the mean-field x-point. Field lines are chaotic during these events, resulting in rapid electron energy loss to the walls and the low Te e) can occur between voltage spikes if they are sufficiently far apart in time; these topology changes are not reflected in the impedance of the axisymmetric gun. Possible future experimental scenarios in SSPX are examined in the presence of the constraints imposed by reconnection physics

391

SHOCKS AND THERMAL CONDUCTION FRONTS IN RETRACTING RECONNECTED FLUX TUBES  

International Nuclear Information System (INIS)

We present a model for plasma heating produced by time-dependent, spatially localized reconnection within a flare current sheet separating skewed magnetic fields. The reconnection creates flux tubes of new connectivity which subsequently retract at Alfvenic speeds from the reconnection site. Heating occurs in gas-dynamic shocks (GDSs) which develop inside these tubes. Here we present generalized thin flux tube equations for the dynamics of reconnected flux tubes, including pressure-driven parallel dynamics as well as temperature-dependent, anisotropic viscosity and thermal conductivity. The evolution of tubes embedded in a uniform, skewed magnetic field, following reconnection in a patch, is studied through numerical solutions of these equations, for solar coronal conditions. Even though viscosity and thermal conductivity are negligible in the quiet solar corona, the strong GDSs generated by compressing plasma inside reconnected flux tubes generate large velocity and temperature gradients along the tube, rendering the diffusive processes dominant. They determine the thickness of the shock that evolves up to a steady state value, although this condition may not be reached in the short times involved in a flare. For realistic solar coronal parameters, this steady state shock thickness might be as long as the entire flux tube. For strong shocks at low Prandtl numbers, typical of the solar corona, the GDS consists of an isothermal sub-shock where all the compression and c sub-shock where all the compression and cooling occur, preceded by a thermal front where the temperature increases and most of the heating occurs. We estimate the length of each of these sub-regions and the speed of their propagation.

392

Reconnection in substorms and solar flares: analogies and differences  

Directory of Open Access Journals (Sweden)

Full Text Available 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 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 a 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. Further similarities might exist in the role of collapsing magnetic flux tubes, as a consequence of reconnection, in the heating and acceleration of charged particles.

J. Birn

2009-03-01

393

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

394

Anomalous Resistivity and Particle Kinetic Effects in Collisionless Driven Reconnection  

Science.gov (United States)

Roles of plasma instabilities and particle kinetic effects in collisionless reconnection are investigated by means of three-dimensional full particle simulations based on an open boundary model. In the early stage of simulation non-ideal effects such as inertia effect and meandering effect breaks the frozen-in condition of magnetic field in the central current region, and it leads to the penetration of the driving electric field into the current sheet. When the electric field reaches the neutral sheet, collisionless reconnection is triggered and the generated fast reconnection flow carries the magnetic flux towards the downstream region. The current sheet is split as a result of collisionless reconnection, and thus small islands appear in the downstream. Magnetic islands move toward the downstream boundary, accumulating the magnetic flux carried by the fast reconnection flow. When the magnetic islands move out though the boundary, the extra energy is suddenly expelled from the system together with the magnetic islands. After this epoch, the system relaxes into a quasi-steady state in which the energy inflow is balanced with the energy outflow. A low-frequency electromagnetic (EM) instability, drift-kink instability (DKI), is excited near the central region in this quasi-steady state. The current sheet is modified along the axis normal to the reconnection plane. The electron flow crossing the neutral sheet is generated by the excited EM waves. This flow operates as resistivity on the equilibrium current flowing along the neutral sheet. This mode has a peak in the frequency spectrum near the ion cyclotron frequency. Furthermore, the width of current sheet is comparable to the ion meandering amplitude. It is concluded that the DKI can be a cause of anomalous resistivity in the thin current sheet and the ion dynamics is a key process to control the anomalous resistivity in quasi-steady state.

Horiuchi, Ritoku; Ohtani, Hiroaki; Ishizawa, Akihiro

2004-11-01

395

Reciprocatory magnetic reconnection in a coronal bright point  

Science.gov (United States)

Context. Coronal bright points (CBPs) are small-scale and long-duration brightenings in the lower solar corona. They are often explained in terms of magnetic reconnection. Aims: We aim to study the substructures of a CBP and clarify the relationship among the brightenings of different patches inside the CBP. Methods: The event was observed by the X-ray Telescope (XRT) aboard the Hinode spacecraft on 2009 August 22-23. Results: The CBP showed repeated brightenings (or CBP flashes). During each of the two successive CBP flashes, that is, weak and strong flashes that were separated by ~2 hr, the XRT images revealed that the CBP was composed of two chambers, patches A and B. During the weak flash, patch A brightened first, and patch B brightened ~2 min later. During the transition, the right leg of a large-scale coronal loop drifted from the right side of the CBP to the left side. During the strong flash, patch B brightened first, and patch A brightened ~2 min later. During the transition, the right leg of the large-scale coronal loop drifted from the left side of the CBP to the right side. In each flash, the rapid change of the connectivity of the large-scale coronal loop is strongly suggestive of the interchange reconnection. Conclusions: For the first time we found reciprocatory reconnection in the CBP, which means that reconnected loops in the outflow region of the first reconnection process serve as the inflow of the second reconnection process. Movies associated with Figs. 2 and 5 are available in electronic form at http://www.aanda.org

Zhang, Q. M.; Chen, P. F.; Ding, M. D.; Ji, H. S.

2014-08-01

396

Physical Conditions in the Reconnection Layer in Pulsar Magnetospheres  

Science.gov (United States)

The magnetosphere of a rotating pulsar naturally develops a current sheet (CS) beyond the light cylinder (LC). Magnetic reconnection in this CS 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 a 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 CS, these basic parameters are uniquely determined by the strength of the reconnecting upstream magnetic field. For the case of the Crab pulsar, we find them to be of order 10 GeV, 1013 cm-3, and 10 cm, respectively. After accounting for the bulk Doppler boosting due to the pulsar wind, the synchrotron and inverse-Compton emission from the reconnecting CS can explain the observed pulsed high-energy (GeV) and very high energy (~100 GeV) radiation, respectively. Also, we suggest that the rapid relative motions of the secondary plasmoids in the hierarchical chain may contribute to the production of the pulsar radio emission.

Uzdensky, Dmitri A.; Spitkovsky, Anatoly

2014-01-01

397

Acceleration mechanisms 2: force-free reconnection  

International Nuclear Information System (INIS)

We suggest an unconventional view of the origin of most cosmic rays (CRs) in the universe. We propose that nearly every accelerated CR was part of the parallel current that maintains all force-free (f-f) magnetic fields. Charged particles are accelerated by the electric field E|| produced by reconnection parallel to the magnetic field B. The inferred total energy in extragalactic cosmic rays is ? 1060 ergs per galaxy spacing volume, provided that the assumed acceleration mechanisms do not preferentially only accelerate ultra high energy cosmic rays (UHECRs). This total energy is quite large, about 105 times the parent galactic CR or magnetic energy. We argue that the formation energy of supermassive black holes (SMBHs) at galaxy centers, ? 1062 ergs, becomes the only feasible source. We propose an efficient dynamo process which converts gravitational free energy into magnetic energy in an accretion disk around a SMBH. Aided by Keplerian winding, this dynamo converts a poloidal seed field into f-f fields, which are transported into the general intergalactic medium (IGM) eventually. This magnetic energy must also have been efficiently converted into particle energies, as evidenced by the radiation from energetic particles. In this view CRs of the IGM are the result of the continuing dissipation, in a Hubble time, of this free energy, by acceleration in situ within the f-f fields confined within the super-galactic walls and filaments he super-galactic walls and filaments of large scale structures. In addition, UHECRs are diffusively lost to the galactic voids at time scales below the GZK (Greisen-Zatsepin-Kuzmin) attenuation time, ? 108 years. Similarly, within the galaxy we expect that the winding by the disk rotation of the galaxy, by the rotation energy of magnetized neutron stars, and by the Keplerian winding of star formation disks are efficient sources of f-f magnetic field energy and hence the sources of galactic CR acceleration. (authors)

398

Measurement of the Transverse Spitzer Resistivity during Collisional Magnetic Reconnection  

International Nuclear Information System (INIS)

Measurement of the transverse resistivity was carried out in a reconnecting current sheet where the mean free path for the Coulomb collision is smaller than the thickness of the sheet. In a collisional neutral sheet without a guide field, the transverse resistivity is directly related to the reconnection rate. A remarkable agreement is found between the measured resistivity and the classical value derived by L. Spitzer. In his calculation the transverse resistivity for the electrons is higher than the parallel resistivity by a factor of 1.96. The measured values have verified this theory to within 30% errors

399

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.

400

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)

 
 
 
 
401

Shear flow effects on double tearing mode global magnetic reconnection  

International Nuclear Information System (INIS)

The dynamics of a global reconnection in the presence of a poloidal shear flow which is located in between magnetic islands is investigated. Different linear regimes are identified according to the value of the resistivity and the distance between the low-order resonant surfaces. It is found that the presence of a small shear flow affects and significantly delays the global reconnection processes. It is shown that this delay is linked to a breaking of symmetry imposed by the existence of the shear flow and the generation of a mean poloidal flow in the resistive layers. (author)

402

Possible Kelvin-Helmholtz waves driven by reconnection accelerated flows  

International Nuclear Information System (INIS)

The author presents new observations of highly steepened magnetic signals within the dayside magnetopause current layer, having a period of about 5 seconds. These signals are embedded within a reconnection region and he suggests they may be Kelvin-Helmholtz waves driven unstable by the velocity shear associated with reconnection accelerated flows. It is due to the low magnetic field strength and consequent high Alfven Mach number that the signals are confined to the magnetopause. The data consist of high time resolution magnetic field and plasma measurements from the AMPTE-UKS satellite

403

Direct observation of Kelvin waves excited by quantized vortex reconnection.  

Science.gov (United States)

Quantized vortices are key features of quantum fluids such as superfluid helium and Bose-Einstein condensates. The reconnection of quantized vortices and subsequent emission of Kelvin waves along the vortices are thought to be central to dissipation in such systems. By visualizing the motion of submicron particles dispersed in superfluid (4)He, we have directly observed the emission of Kelvin waves from quantized vortex reconnection. We characterize one event in detail, using dimensionless similarity coordinates, and compare it with several theories. Finally, we give evidence for other examples of wavelike behavior in our system. PMID:24704878

Fonda, Enrico; Meichle, David P; Ouellette, Nicholas T; Hormoz, Sahand; Lathrop, Daniel P

2014-03-25

404

Effects of Global Boundary and Local Collisionality on Magnetic Reconnection in a Laboratory Plasma  

Energy Technology Data Exchange (ETDEWEB)

The magnetic reconnection process is studied in a wide range of operating conditions in the well-controlled Magnetic Reconnection Experiment. The reconnection rate is observed to be a function of both global (i.e., system size) and local (collisionality) plasma parameters. When only local collisionality is lowered, the current sheet is shortened while effective resistivity is enhanced, both accelerating reconnection rates. At a fixed collisionality, the current sheet length increases with system size, resulting in the reduction of the reconnection rate. These results quantitatively agree with a generalized Sweet-Parker analysis.

A. Kuritsyn, H. Ji, S.P. Gerhardt, Y. Ren, and M. Yamada

2007-07-24

405

Effects of Global Boundary and Local Collisionality on Magnetic Reconnection in a Laboratory Plasma  

International Nuclear Information System (INIS)

The magnetic reconnection process is studied in a wide range of operating conditions in the well-controlled Magnetic Reconnection Experiment. The reconnection rate is observed to be a function of both global (i.e., system size) and local (collisionality) plasma parameters. When only local collisionality is lowered, the current sheet is shortened while effective resistivity is enhanced, both accelerating reconnection rates. At a fixed collisionality, the current sheet length increases with system size, resulting in the reduction of the reconnection rate. These results quantitatively agree with a generalized Sweet-Parker analysis.

406

Experimental Study of Current-Driven Turbulence During Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

CMPD Final Report Experimental Study of Current-Driven Turbulence During Magnetic Reconnection Miklos Porkolab, PI, Jan Egedal, co-PI, William Fox, graduate student. This is the final report for Grant DE-FC02-04ER54786, �¢����MIT Participation in the Center for Multiscale Plasma Dynamics,�¢��� which was active from 8/1/2004 to 7/31/2010. This Grant supported the thesis work of one MIT graduate student, William Fox, The thesis research consisted of an experimental study of the fluctuations arising during magnetic reconnection in plasmas on the Versatile Toroidal Facility (VTF) at MIT Plasma Science and Fusion Center (PSFC). The thesis was submitted and accepted by the MIT physics Department, �¢����W. Fox, Experimental Study of Current-Driven Turbulence During Magnetic Reconnection, Ph.D. Thesis, MIT (2009)�¢���. In the VTF experiment reconnection and current-sheet formation is driven by quickly changing currents in a specially arranged set of internal conductors. Previous work on this device [Egedal, et al, PRL 98, 015003, (2007)] identified a �¢����spontaneous�¢��� reconnection regime. In this work fluctuations were studied using impedance-matched, high-bandwidth Langmuir probes. Strong, broadband fluctuations, with frequencies extending from near the lower-hybrid frequency [fLH = (fcefci)1/2] to the electron cyclotron frequency fce were found to arise during the reconnection events. Based on frequency and wavelength measurements, lower-hybrid waves and Trivelpiece-Gould waves were identified. The lower-hybrid waves are easiest to drive with strong perpendicular drifts or gradients which arise due to the reconnection events; an appealing possibility is strong temperature gradients. The Trivelpiece-Gould modes can result from kinetic, bump-on-tail instability of a runaway electron population energized by the reconnection events. We also observed that the turbulence is often spiky, consisting of discrete positive-potential spikes, which were identified as �¢����electron phase-space holes,�¢��� a class of nonlinear solitary wave known to evolve from a strong beam-on-tail instability. We established that fast electrons were produced by magnetic reconnection. Overall, these instabilities were found to be a consequence of reconnection, specifically the strong energization of electrons, leading to steep gradients in both coordinate- and velocity-space. Estimates (using quasi-linear theory) of the anomalous resistivity due to these modes did not appear large enough to substantially impact the reconnection process. Relevant publications: �¢���¢ W. Fox, M. Porkolab, et al, Phys. Rev. Lett. 101, 255003 (2008). �¢���¢ W. Fox, M. Porkolab, et al, Phys. Plasmas 17, 072303, (2010).

Miklos Porkolab; Jan Egedal-Pedersen; William Fox

2010-08-31

407

Recent Evolution in the Theory of Magnetic Reconnection and Its Connection with Turbulence  

Science.gov (United States)

The concept of reconnection is found in many fields of physics with the closest analogue to magnetic reconnection being the reconnection of vortex tubes in hydrodynamics. In plasmas, magnetic reconnection plays an important role in release of energy associated with the magnetic shear into particle energy. Although most studies to date have focused on 2D reconnection, the availability of 3D petascale kinetic simulations have brought the complexity of 3D reconnection to the forefront in collisionless reconnection studies. Here we briefly review the latest advances in 2D and compare and contrast the results with recent 3D studies that address role of anomalous transport in reconnection, effects of turbulence on the rate and structure, among others. Another outcome of recent research is the realization of a deeper link between turbulence and reconnection where the common denominator is the generic formation of electron scale sheets which dissipate the energy through reconnection. Finally, we close the review by listing some of the major outstanding problems in reconnection physics.

Karimabadi, Homa; Roytershteyn, Vadim; Daughton, William; Liu, Yi-Hsin

408

Plans, Takes, and Mis-takes  

Directory of Open Access Journals (Sweden)

Full Text Available This paper analyzes what may have been a mistake bypianist Thelonious Monk playing a jazz solo in 1958.Even in a Monk composition designed for patternedmayhem, a note can sound out of pattern. We reframethe question of whether the note was a mistake and askinstead about how Monk handles the problem. Amazingly,he replays the note into a new pattern that resituatesits jarring effect in retrospect. The mistake, orbetter, the mis-take, was “saved” by subsequent notes.Our analysis, supported by reflections from jazz musiciansand the philosopher John Dewey, encourages areformulation of plans, takes, and mis-takes as categoriesfor the interpretation of contingency, surprise, andrepair in all human activities. A final section suggeststhat mistakes are essential to the practical plying andplaying of knowledge into performances, particularlythose that highlight learning.

Nathaniel Klemp

2008-04-01

409

Take Your Medicines Safely  

Medline Plus

Full Text Available ... means taking the bacteria completely out of the system. It might be just putting it to rest and in the next four days, if they stop taking it, the infection will come back twice ...

410

Stochastic acceleration by multi-island contraction during turbulent magnetic reconnection  

CERN Document Server

The acceleration of charged particles in magnetized plasmas is considered during turbulent multi-island magnetic reconnection. The particle acceleration model is constructed for an ensemble of islands which produce adiabatic compression of the particles. The model takes into account the statistical fluctuations in the compression rate experienced by the particles during their transport in the acceleration region. The evolution of the particle distribution function is described as a simultaneous first and second-order Fermi acceleration process. While the efficiency of the first-order process is controlled by the average rate of compression, the second order process involves the variance in the compression rate. Moreover, the acceleration efficiency associated with the second-order process involves both the Eulerian properties of the compression field and the Lagrangian properties of the particles. The stochastic contribution to the acceleration is non-resonant and can dominate the systematic part in the case ...

Bian, Nicolas

2013-01-01

411

Magnetotail Reconnection and Flux Circulation: Jupiter and Saturn Compared  

Science.gov (United States)

The Jovian magnetosphere has been visited by eight spacecraft, and the magnetometer data have been used to identify dozens of plasmoids and 250 field dipolarizations associated with magnetic reconnection in the tail [e.g. Vogt et al., 2010]. Since the arrival of the Cassini spacecraft at Saturn in 2004, the magnetometer instrument has also been used to identify reconnection signatures. The deepest magnetotail orbits were in 2006, and during this time 34 signatures of plasmoids were identified. In this study we compare the statistical properties of plasmoids at Jupiter and Saturn such as duration, size, location, and recurrence period. Such parameters can be influenced by many factors, including the different Dungey cycle timescales and cross-magnetospheric potential drops at the two planets. We present superposed epoch analyses of plasmoids at the two planets to determine their average properties and to infer their role in the reconfiguration of the nightside of the magnetosphere. We examine the contributions of plasmoids to the magnetic flux transfer cycle at both planets. At Jupiter, there is evidence of an extended interval after reconnection where the field remains northward (analogous to the terrestrial post-plasmoid plasma sheet). At Saturn we see a similar feature, and calculate the amount of flux closed on average in reconnection events, leading us to an estimation of the recurrence rate of plasmoid release.

Jackman, C. M.; Vogt, M. F.; Slavin, J. A.; Cowley, S. W. H.; Boardsen, S. A.

2011-01-01

412

Viscous effects in time-dependent planar reconnection  

Science.gov (United States)

Context. Viscous dissipation is expected to play a significant part in energy release in solar flares, yet the role of viscosity in a weakly resistive plasma of the solar corona remains unclear. Aims: We attempt to clarify the role of viscous effects in magnetic reconnection by performing simulations of reconnection in planar periodic geometry in an incompressible viscous resistive plasma. Methods: We consider magnetic reconnection, driven by large-scale vortical flows. We use both the classical shear viscosity and the Braginskii form for the ion parallel viscosity in a magnetised plasma. We determine the scalings of the current sheet parameters and the global rates of resistive and viscous dissipation. We use steady-state exact solutions and scaling arguments to interpret the numerical results. Results: We show that, regardless of the form of viscosity, the resistive non-viscous analytical solutions for flux pile-up merging provide a very good approximation of the numerical results in the reconnecting current sheet. We find no evidence for a visco-resistive scale. Numerical results for a highly sheared magnetic field, however, appear to deviate from the analytical predictions in the case of the Braginskii viscosity.

Armstrong, C. K.; Craig, I. J. D.; Litvinenko, Y. E.

2011-10-01

413

Asymmetric evolution of magnetic reconnection in collisionless accretion disk  

CERN Document Server

An evolution of a magnetic reconnection in a collisionless accretion disk is investigated using a 2.5 dimensional hybrid code simulation. In astrophysical disks, magnetorotational instability (MRI) is considered to play an important role by generating turbulence in the disk and contributes to an effective angular momentum transport through a turbulent viscosity. Magnetic reconnection, on the other hand, also plays an important role on the evolution of the disk through a dissipation of a magnetic field enhanced by a dynamo effect of MRI. In this study, we developed a hybrid code to calculate an evolution of a differentially rotating system. With this code, we first confirmed a linear growth of MRI. We also investigated a behavior of a particular structure of a current sheet, which would exist in the turbulence in the disk. From the calculation of the magnetic reconnection, we found an asymmetric structure in the out-of-plane magnetic field during the evolution of reconnection, which can be understood by a coup...

Shirakawa, Keisuke

2014-01-01

414

Relating reconnection rate, exhaust structure and effective resistivity  

Energy Technology Data Exchange (ETDEWEB)

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 (?{sub e}), the half width (w) of the CDR, the outflow velocity V{sub o}, and the effective resistivity (?{sub 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 E{sub rec} to the current density J{sub y} 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 [Electrical and Computer Engineering, University of Alabama, Huntsville, Alabama 35899 (United States)

2014-03-15

415

Collisionless magnetic reconnection: analytical model and PIC simulation comparison  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic reconnection is believed to be responsible for various explosive processes in the space plasma including magnetospheric substorms. The Hall effect is proved to play a key role in the reconnection process. An analytical model of steady-state magnetic reconnection in a collisionless incompressible plasma is developed using the electron Hall MHD approximation. It is shown that the initial complicated system of equations may split into a system of independent equations, and the solution of the problem is based on the Grad-Shafranov equation for the magnetic potential. The results of the analytical study are further compared with a two-dimensional particle-in-cell simulation of reconnection. It is shown that both methods demonstrate a close agreement in the electron current and the magnetic and electric field structures obtained. The spatial scales of the acceleration region in the simulation and the analytical study are of the same order. Such features like particles trajectories and the in-plane electric field structure appear essentially similar in both models.

V. Semenov

2009-03-01

416

Proxy and in-situ studies of dayside magnetopause reconnection  

Energy Technology Data Exchange (ETDEWEB)

The functional dependence of magnetic reconnection on solar wind parameters is examined utilizing the am geomagnetic index and satellite observations at the magnetopause. Several parameters in the solar wind are found to control geomagnetic activity. Reconnection is found to be most efficient when the interplanetary magnetic field is southward, although some activity remains when the IMF is horizontal and slightly northward. The reconnection efficiency increases with the solar wind dynamic pressure but decreases when the Mach number is greater than 7.5. These results are compared with the functional dependencies found by correlating solar wind and magnetosheath measurements with observations of accelerated tows at the magnetopause. Accelerated tows are found to occur most often when the interplanetary magnetic field is directed southward. However, accelerated flows do occur when the IMF is horizontal and northward. Accelerated flows are also affected by the magnetosheath beta such that higher beta inhibits their occurrence. The location of accelerated tows indicates that reconnection occurs mainly at the subsolar point.

Scurry, L.; Russell, C.T. [California Univ., Los Angeles, CA (United States). Inst. of Geophysics and Planetary Physics; Gosling, J.T. [Los Alamos National Lab., NM (United States)

1992-12-01

417

Proxy and in-situ studies of dayside magnetopause reconnection  

Energy Technology Data Exchange (ETDEWEB)

The functional dependence of magnetic reconnection on solar wind parameters is examined utilizing the am geomagnetic index and satellite observations at the magnetopause. Several parameters in the solar wind are found to control geomagnetic activity. Reconnection is found to be most efficient when the interplanetary magnetic field is southward, although some activity remains when the IMF is horizontal and slightly northward. The reconnection efficiency increases with the solar wind dynamic pressure but decreases when the Mach number is greater than 7.5. These results are compared with the functional dependencies found by correlating solar wind and magnetosheath measurements with observations of accelerated tows at the magnetopause. Accelerated tows are found to occur most often when the interplanetary magnetic field is directed southward. However, accelerated flows do occur when the IMF is horizontal and northward. Accelerated flows are also affected by the magnetosheath beta such that higher beta inhibits their occurrence. The location of accelerated tows indicates that reconnection occurs mainly at the subsolar point.

Scurry, L.; Russell, C.T. (California Univ., Los Angeles, CA (United States). Inst. of Geophysics and Planetary Physics); Gosling, J.T. (Los Alamos National Lab., NM (United States))

1992-01-01

418

Interchange Slip-Running Reconnection and Sweeping SEP Beams  

CERN Document Server

We present a new model to explain how particles (solar energetic particles; SEPs), 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 identifi...

Masson, S; Pariat, E; Klein, K -L

2011-01-01

419

Energy transfer by magnetopause reconnection and the substorm parameter epsilon  

International Nuclear Information System (INIS)

An expression for the magnetopause reconnection power based on the dawn-dusk component of the reconnection electric field, that reduces to the substorm parameter epsilon for the limit that involves equal geomagnetic (B sub(G)) and magnetosheath (B sub(M)) magnetic field amplitudes at the magnetopause, is contrasted with the expression based on the whole reconnection electric field vector obtained by Gonzalez. The correlation examples of this report show that this (more general) expression for the reconnection power seems to correlate with the empirical dissipation parameter U sub(T) from Akasofu, with slightly better correlation coefficients than those obtained from similar correlations between the parameter epsilon and U sub(T). Thus, these (better) correlations show up for the more familiar values of the ratio B sub(G) / B sub(M) > 1. Nevertheless, the (expected) relatively small difference that seems to exist between these correlation coefficients suggests that, for practical purposes, the parameter epsilon could be used as well (instead of the more general expression) in similar correlation studies due to its impler format. On the other hand, studies that refer mainly to the difference in the magnitudes of epsilon and of the more general expression are expected to give results with less negligible differences. (Author)

420

Global and local disturbances in the magnetotail during reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We examine Cluster observations of a reconnection event at xGSM=?15.7 RE in the magnetotail on 11 October 2001, when Cluster recorded the current sheet for an extended period including the entire duration of the reconnection event. The onset of reconnection is associated with a sudden orientation change of the ambient magnetic field, which is also observed simultaneously by Goes-8 at geostationary orbit. Current sheet oscillations are observed both before reconnection and during it. The speed of the flapping motions is found to increase when the current sheet undergoes the transition from quiet to active state, as suggested by an earlier statistical result and now confirmed within one single event. Within the diffusion region both the tailward and earthward parts of the quadrupolar magnetic Hall structure are recorded as an x-line passes Cluster. We report the first observations of the Hall structure conforming to the kinks in the current sheet. This results in relatively strong fluctuations in Bz, which are shown to be the Hall signature tilted in the yz plane with the current sheet.

T. V. Laitinen

2007-05-01

 
 
 
 
421

Magnetic reconnection associated fluctuations in the deep magnetotail: ARTEMIS results  

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Full Text Available 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.

Z. Vörös

2011-11-01

422

The Importance of Electrostatic Instabilities in Magnetic Reconnection  

Science.gov (United States)

Recent simulation studies of kinetic instabilities in reconnecting plasmas suggests that investigation of electromagnetic waves, such as the drift-kink-instability (DKI) and the Kelvin Helmholtz instability (KHI), may yield a theory of reconnection. However, the combined results of linear theory, and explicit and implicit plasma simulations fail to support a direct link between kinking and reconnection. Instead, the surprise has been the unexpected importance of the lower-hybrid-drift instability (LHDI). This electrostatic instability, which simulations suggest saturates at a level that is too low to provide the anomalous resistivity necessary for reconnection, alters current sheets in several important ways. The LHDI causes velocity shear, current sheet thinning, and anisotropic heating of electrons. The velocity shear drives a KHI mode, which explains current sheet kinking at high mass ratios, and the current sheet thinning and anisotropic heating significantly enhance the growth rate of the tearing instability, which may explain onset. Clearly, there is strong motivation for studies of the LHDI under magnetotail conditions.

Brackbill, J. U.

2003-12-01

423

Study of Local Reconnection Physics in a Laboratory Plasma  

International Nuclear Information System (INIS)

A short review of physics results obtained in the Magnetic Reconnection Experiment (MRX) is given with an emphasis on the local features of magnetic reconnection in a controlled environment. Stable two-dimensional current sheets are formed and sustained by induction using two internal coils. The observed reconnection rates are found to be quantitatively consistent with a generalized Sweet-Parker model which incorporates compressibility, unbalanced upstream-downstream pressure, and the effective resistivity. The latter is significantly enhanced over its classical values in the low collisionality regime. Strong local ion heating is measured by an optical probe during the reconnection process, and at least half of the increased ion energy must be due to nonclassical processes, consistent with the resistivity enhancement. Characteristics of high-frequency electrostatic and electromagnetic fluctuations detected in the current sheet suggest presence of the lower-hybrid-drift-like waves with significant magnetic components. The detailed structures of the current sheet are measured and compared with Harris theory and two-fluid theory

424

Study of Local Reconnection Physics in a Laboratory Plasma  

Energy Technology Data Exchange (ETDEWEB)

A short review of physics results obtained in the Magnetic Reconnection Experiment (MRX) is given with an emphasis on the local features of magnetic reconnection in a controlled environment. Stable two-dimensional current sheets are formed and sustained by induction using two internal coils. The observed reconnection rates are found to be quantitatively consistent with a generalized Sweet-Parker model which incorporates compressibility, unbalanced upstream-downstream pressure, and the effective resistivity. The latter is significantly enhanced over its classical values in the low collisionality regime. Strong local ion heating is measured by an optical probe during the reconnection process, and at least half of the increased ion energy must be due to nonclassical processes, consistent with the resistivity enhancement. Characteristics of high-frequency electrostatic and electromagnetic fluctuations detected in the current sheet suggest presence of the lower-hybrid-drift-like waves with significant magnetic components. The detailed structures of the current sheet are measured and compared with Harris theory and two-fluid theory.

Hantao Ji; Troy Carter; Scott Hsu; Masaaki Yamada

2001-06-11

425

Conditions for substorm onset by the fast reconnection mechanism  

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Full Text Available The fast reconnection mechanism, involving slow shocks and Alfvénic fast plasma jets, is most responsible for the explosive conversion of magnetic energy associated with geomagnetic substorms and solar flares. In this paper, the spontaneous fast reconnection model is applied to well-known phenomena of substorms. When the east-west width of the tail current sheet becomes 3–4 times larger than its north-south thickness, the fast reconnection mechanism can fully be established, which may lead to substorm onset. The resulting Alfvénic jet can exactly explain, both qualitatively and quantitatively, the in-situ satellite observations of the traveling compression regions (TCRs associated with large-scale plasmoids propagating down the tail. Also, the earthward fast reconnection jet causes drastic magnetic field dipolarization, so that the sheet current ahead of the magnetic loop of closed field lines suddenly turns its direction toward the loop footpoint and a large-scale current wedge is formed according to the growth of field-aligned currents. It is demonstrated that an MHD generator arises ahead of the magnetic loop and drives the current wedge to distinctly enhance the current density in a pair of thin layers of the loop footpoint, giving rise to drastic heating in the form of two ribbons.

M. Ugai

2008-12-01

426

Simulations of Flare Reconnection in Breakout Coronal Mass Ejections  

Science.gov (United States)

We report 3D MHD simulations of the flare reconnection in the corona below breakout coronal mass ejections (CMEs). The initial setup is a single bipolar active region imbedded in the global-scale background dipolar field of the Sun, forming a quadrupolar magnetic configuration with a coronal null point. Rotational motions applied to the active-region polarities at the base of the atmosphere introduce shear across the polarity inversion line (PIL). Eventually, the magnetic stress and energy reach the critical threshold for runaway breakout reconnection, at which point the sheared core field erupts outward at high speed. The vertical current sheet formed by the stretching of the departing sheared field suffers reconnection that reforms the initial low-lying arcade across the PIL, i.e., creates the flare loops. Our simulation model, the Adaptively Refined MHD Solver, exploits local grid refinement to resolve the detailed structure and evolution of the highly dynamic current sheet. We are analyzing the numerical experiments to identify and interpret observable signatures of the flare reconnection associated with CMEs, e.g., the flare loops and ribbons, coronal jets and shock waves, and possible origins of solar energetic particles. This research was supported by NASA and ONR.

DeVore, C. Richard; Karpen, J. T.; Antiochos, S. K.

2009-05-01

427

Do dispersive waves play a role in collisionless magnetic reconnection?  

Energy Technology Data Exchange (ETDEWEB)

Using fully kinetic simulations, we demonstrate that the properly normalized reconnection rate is fast ?0.1 for guide f