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1

Is channeling of fission tracks taking place?  

International Nuclear Information System (INIS)

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.

1999-01-01

2

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; Glyn M. Rimmington; Tatiana Orel

2009-01-01

3

Does olfactory specific satiety take place in a natural setting?  

UK PubMed Central (United Kingdom)

Olfactory-specific satiety (OSS) is characterized by a specific decrease in the odor pleasantness of a food eaten to satiety or smelled without ingestion. The usual protocol for studying OSS takes place in laboratory, a setting rather removed from the real world. Here, we set out to examine OSS in a natural setting: during a meal in a restaurant. We hypothesized that an aroma contained in a food that is eaten at the beginning of a meal decreases the pleasantness of the flavor of a food with the same aroma eaten at the end of the meal. In the first experiment (Experiment 1), a test group received an appetizer flavored with a test aroma (anise) at the beginning of the meal. After the main dish, they received a dessert flavored with the same aroma. A control group received the same aromatized dessert, but after a non-aromatized appetizer. This experiment was replicated (Experiment 2) using verbena as the test aroma. For both experiments, results revealed that aroma pleasantness, but not intensity or familiarity, significantly decreased in the test groups vs. the control groups. These findings extend the concept of OSS to a realistic eating context.

Fernandez P; Bensafi M; Rouby C; Giboreau A

2013-01-01

4

Kiwifruit: taking its place in the global fruit bowl.  

UK PubMed Central (United Kingdom)

While the world total production of kiwifruit has increased by over 50% during the last decade, the kiwifruit remains a niche fruit, taking up an estimated 0.22% of the global fruit bowl, which is dominated by apples, oranges, and bananas. Even though kiwifruit's share of the global fruit bowl has remained largely unchanged over the past 15 years, the scope for growth in the category is significant, with the nutritional and production characteristics of kiwifruit being on the right side of key global consumer trends around health and sustainability. Taking advantage of these consumer trends is one of two key challenges for the global kiwifruit industry. The second challenge is to harness the diverse natural and cultivated range of kiwifruit varieties (colors, flavors, sizes, and shapes) to stimulate the interest of consumers and grow the share of kiwifruit in the fruit basket through selecting cultivars that can develop meaningful market segments and meet consumer demand.

Ward C; Courtney D

2013-01-01

5

Magnetic reconnection in sheared solar magnetic arcades  

Energy Technology Data Exchange (ETDEWEB)

The evolution of solar magnetic arcades is investigated with the use of MHD simulations imposing resistivity on sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnection can take place in an arcade-like field geometry to create a magnetic island. The process leading to reconnection cannot be solely attributed to a tearing instability, but rather to a reactive evolution of the magnetic arcade under resistivity. The natures of the arcade reconnection are governed by the spatial pattern of resistivity. A fast reconnection with a small shock angle can only be achieved when the diffusion region is localized. In this case, a highly collimated reconnection outflow can tear the plasmoid into a pair, and most of principal features in solar eruptive processes are reproduced.

Choe, G.S.

1996-12-31

6

Key European Grid event to take place in Geneva  

CERN Multimedia

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

2006-01-01

7

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

CERN Multimedia

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

8

Study of multiple X line reconnection at the dayside magnetopause  

International Nuclear Information System (INIS)

[en] Interaction between the interplanetary magnetic field and the earth's geomagnetic field at the dayside magnetopause is studied by a global two-dimensional incompressible MHD simulation. It is found that for a large magnetic Reynolds number (R/sub m/?400), the multiple X line reconnection (MXR) becomes the major dayside reconnection process, while for a small magnetic Reynolds number (R/sub m/?100), the classical single X line reconnection takes place. Since the magnetic Reynolds number at the dayside magnetopause is probably very high (R/sub m/>103), it may be suggested that MXR will dominate the dayside reconnection pattern. As a result of the MXR process, magnetic islands are formed on the dayside magnetopause surface. The dependence of the dayside reconnection geometry of the solar wind Alfven Mach number is also examined. copyright American Geophysical Union 1988

1988-01-01

9

UHECRs from magnetic reconnection in relativistic jets  

CERN Document Server

Ultra-high energy cosmic rays (UHECRs) may be produced in active galactic nuclei (AGN) or gamma-ray burst (GRB) jets. I argue that magnetic reconnection in jets can accelerate UHECRs rather independently of physical processes in the magnetic dissipation region. First order Fermi acceleration can efficiently take place in the region where the unreconnected (upstream) magnetized fluid converges into the reconnection layer. I find that protons can reach energies up to E~10^{20} eV in GRB and powerful AGN jets while iron nuclei can reach similar energies in AGN jets of more moderate luminosity.

Giannios, Dimitrios

2010-01-01

10

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)

2000-01-01

11

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

12

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)

1994-01-01

13

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

14

Reconnection Electric Field and Hardness of X-Ray Emission of Solar Flares  

CERN Multimedia

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

Liu, Chang

2009-01-01

15

miRNA repression of translation in vitro takes place during 43S ribosomal scanning.  

UK PubMed Central (United Kingdom)

microRNAs (miRNAs) regulate gene expression at multiple levels by repressing translation, stimulating deadenylation and inducing the premature decay of target messenger RNAs (mRNAs). Although the mechanism by which miRNAs repress translation has been widely studied, the precise step targeted and the molecular insights of such repression are still evasive. Here, we have used our newly designed in vitro system, which allows to study miRNA effect on translation independently of deadenylation. By using specific inhibitors of various stages of protein synthesis, we first show that miRNAs target exclusively the early steps of translation with no effect on 60S ribosomal subunit joining, elongation or termination. Then, by using viral proteases and IRES-driven mRNA constructs, we found that translational inhibition takes place during 43S ribosomal scanning and requires both the poly(A) binding protein and eIF4G independently from their physical interaction.

Ricci EP; Limousin T; Soto-Rifo R; Rubilar PS; Decimo D; Ohlmann T

2013-01-01

16

Onset of Hall-mediated magnetic reconnection in weakly ionized astrophysical plasmas  

Science.gov (United States)

We consider transition to Hall-magnetohydrodynamics regimes of the resistive tearing instability in weakly ionized plasmas. A particular emphasis is put on a possible role of the resulting fast magnetic reconnection in such astrophysical objects as solar chromosphere, interstellar molecular clouds and protostellar discs. It is shown that Hall-mediated reconnection can be relevant to explosive phenomena in the latter, though it is unlikely to take place in the former two environments.

Vekstein, Grigory; Kusano, Kanya

2013-09-01

17

Fast reconnection of magnetic fields in a plasma  

International Nuclear Information System (INIS)

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

1983-01-01

18

A model of heat transfer taking place in thermographic test stand  

Directory of Open Access Journals (Sweden)

Full Text Available Purpose: The aim of this paper is to present a model describing heat transfer taking place during thermovision testing of polymer composites. Thermographic tests were undertaken to identify thermal properties of searched material and to correlate them with operational characteristics.Design/methodology/approach: Heat transfer model of thermographic testing stand of our own design was elaborated. The model was applied as a tool of tested material characteristics identification, forming the basis of laminate degradation degree diagnosis.Findings: The most essential result of the project is the physical heat transfer model. Good conformity between model predictions and exemplary experimental results was achieved. The set of physical characteristics describing thermal state of composite was identified and introduced into the model.Research limitations/implications: Experimental results of heat transfer through the composite mounted in thermographic testing stand proved the correctness of developed model. Results of physical properties identification showed the possibility of non-destructive diagnosis of wide class of materials, namely polymeric composites.Practical implications: Results of presented project together with results of planned experimental programme devoted to elaboration of diagnostic relations enable to apply thermography directly to the state of polymeric structural materials assessment. Especially the degree of material degradation may be estimated.Originality/value: Originality of the project is based on possibility of practical application of the model to simulate heat transfer through tested sample mounted in thermographic test stand. Proposed scope of diagnostic tests was not interesting for scientists till now.

J. Kaczmarczyk; M. Rojek; G. Wróbel; J. Stabik

2008-01-01

19

ERCP in acute pancreatitis: What takes place in routine clinical practice?  

Directory of Open Access Journals (Sweden)

Full Text Available AIM: To evaluate the data from a survey carried out in Italy regarding the endoscopic approach to acute pancreatitis in order to obtain a picture of what takes place after the release of an educational project on acute pancreatitis sponsored by the Italian Association for the Study of the Pancreas.METHODS: Of the 1 173 patients enrolled in our survey, the most frequent etiological category was biliary forms (69.3%) and most patients had mild pancreatitis (85.8%).RESULTS: 344/1 173 (29.3%) underwent endoscopic retrograde cholangiopancreatography (ERCP). The mean interval between the onset of symptoms and ERCP was 6.7 ± 5.0 d; only 89 examinations (25.9%) were performed within 72 h from the onset of symptoms. The main indications for ERCP were suspicion of common bile duct stones (90.3%), jaundice (44.5%), clinical worsening of acute pancreatitis (14.2%) and cholangitis (6.1%). Biliary and pancreatic ducts were visualized in 305 patients (88.7%) and in 93 patients (27.0%) respectively. The success rate in obtaining a cholangiogram was statistically higher (P = 0.003) in patients with mild acute pancreatitis (90.6%) than in patients with severe disease (72.2%). Biliary endoscopic sphincterotomy was performed in 295 of the 305 patients (96.7%) with no difference between mild and severe disease (P = 0.985). ERCP morbidity was 6.1% and mortality was 1.7%; the mortality was due to the complications of acute pancreatitis and not the endoscopic procedure.CONCLUSION: The results of this survey, as with those carried out in other countries, indicate a lack of compliance with the guidelines for the indications for interventional endoscopy.

Armando Gabbrielli; Raffaele Pezzilli; Generoso Uomo; Alessandro Zerbi; Luca Frulloni; Paolo De Rai; Laura Castoldi; Guido Costamagna; Claudio Bassi; Valerio Di Carlo

2010-01-01

20

Electromagnetic energy conversion at reconnection fronts.  

UK PubMed Central (United Kingdom)

Earth's magnetotail contains magnetic energy derived from the kinetic energy of the solar wind. Conversion of that energy back to particle energy ultimately powers Earth's auroras, heats the magnetospheric plasma, and energizes the Van Allen radiation belts. Where and how such electromagnetic energy conversion occurs has been unclear. Using a conjunction between eight spacecraft, we show that this conversion takes place within fronts of recently reconnected magnetic flux, predominantly at 1- to 10-electron inertial length scale, intense electrical current sheets (tens to hundreds of nanoamperes per square meter). Launched continually during intervals of geomagnetic activity, these reconnection outflow flux fronts convert ~10 to 100 gigawatts per square Earth radius of power, consistent with local magnetic flux transport, and a few times 10(15) joules of magnetic energy, consistent with global magnetotail flux reduction.

Angelopoulos V; Runov A; Zhou XZ; Turner DL; Kiehas SA; Li SS; Shinohara I

2013-09-01

 
 
 
 
21

Magnetic Reconnection In Sheared Solar Magnetic Arcades  

UK PubMed Central (United Kingdom)

The evolution of solar magnetic arcades is investigated with the use of MHD simulations imposing resistivityon sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnectioncan take place in an arcade-like field geometry to create a magnetic island. The process leading to reconnectioncannot be solely attributed to a tearing instability, but rather to a reactive evolution of the magnetic arcadeunder resistivity. The natures of the arcade reconnection are governed by the spatial pattern of resistivity. A fastreconnection with a small shock angle can only be achieved when the diffusion region is localized. In this case, ahighly collimated reconnection outflow can tear the plasmoid into a pair, and most of principal features in solareruptive processes are reproduced.Key Words : Sun: magnetic fields, Sun: flares, MHDI. INTRODUCTIONIt is widely believed that magnetic reconnectionplays an important role in solar eruptive phenomena...

G. S. Choe

22

Electromagnetic energy conversion at reconnection fronts.  

Science.gov (United States)

Earth's magnetotail contains magnetic energy derived from the kinetic energy of the solar wind. Conversion of that energy back to particle energy ultimately powers Earth's auroras, heats the magnetospheric plasma, and energizes the Van Allen radiation belts. Where and how such electromagnetic energy conversion occurs has been unclear. Using a conjunction between eight spacecraft, we show that this conversion takes place within fronts of recently reconnected magnetic flux, predominantly at 1- to 10-electron inertial length scale, intense electrical current sheets (tens to hundreds of nanoamperes per square meter). Launched continually during intervals of geomagnetic activity, these reconnection outflow flux fronts convert ~10 to 100 gigawatts per square Earth radius of power, consistent with local magnetic flux transport, and a few times 10(15) joules of magnetic energy, consistent with global magnetotail flux reduction. PMID:24072917

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

2013-09-27

23

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.

2009-01-01

24

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

25

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

Science.gov (United States)

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

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

2009-05-01

26

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; S. E. Milan; B. Hubert

2006-01-01

27

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

Science.gov (United States)

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

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

2013-09-01

28

ON THE NATURE OF RECONNECTION AT A SOLAR CORONAL NULL POINT ABOVE A SEPARATRIX DOME  

Energy Technology Data Exchange (ETDEWEB)

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

Pontin, D. I. [Division of Mathematics, University of Dundee, Dundee DD1 4HN (United Kingdom); Priest, E. R. [School of Mathematics and Statistics, University of St Andrews, Fife KY16 9SS (United Kingdom); Galsgaard, K., E-mail: dpontin@maths.dundee.ac.uk [Niels Bohr Institute, Copenhagen DK-2100 (Denmark)

2013-09-10

29

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

CERN Multimedia

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

Pontin, D I; Galsgaard, K

2013-01-01

30

A Magnetic Reconnection Origin for the Soft X-Ray Excess in an Active Galactic Nucleus  

Science.gov (United States)

We present a new scenario to explain the soft X-ray excess in an active galactic nucleus (AGN). Magnetic reconnection could happen in a thin layer on the surface of an accretion disk. Electrons are accelerated by a shock wave and turbulence is triggered by magnetic reconnection. Inverse Compton scattering then takes place above the accretion disk, producing soft X-rays. Based on the standard disk model, we estimate the magnetic field strength and the energy released by magnetic reconnection along the accretion disk and find that the luminosity arising from magnetic reconnection is mostly emitted in the inner disk, which is dominated by radiation pressure. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess.

Zhong, Xiaogu; Wang, Jiancheng

2013-08-01

31

A magnetic reconnection origin for the soft X-ray excess in AGN  

CERN Multimedia

We present a new scenario to explain the soft X-ray excess in Active Galactic Nucleus. The magnetic reconnection could happen in a thin layer on the surface of accretion disk. Electrons are accelerated by shock wave and turbulence triggered by magnetic reconnection, then they take place inverse Compton scattering above accretion disk which contributes soft X-rays. Based on standard disk model, we estimate the magnetic field strength and the energy released by magnetic reconnection along accretion disk, and find that the luminosity caused by magnetic reconnection mainly emits in the inner disk which is dominated by radiation pressure. We then apply the model to fit the spectra of AGNs with strong soft X-ray excess.

Zhong, Xiaogu

2013-01-01

32

CHEMICAL PROCESSES MATHEMATICALLY MODELLED WHICH TAKES PLACE IN COAL EXTRACTION WITH SOLVENTS  

Directory of Open Access Journals (Sweden)

Full Text Available The liquefaction of coals followed by the extraction of the black products with the help of some solvents is a very complex process. For this reason, the knowledge of this process’s mechanism was extremely difficult to decipher. Hiel’s studies led to the proposal of several possible reaction mechanisms. Paying particular attention to the study of the Jiu Valley coal’s liquefaction, there could be underlined a mathematical pattern of the reactions that took place during the process. This model complies with the ones proposed by the speciality literature in this filed.

Clementina Moldovan; I. Ganescu; V. Magearu; C. Ionescu

2006-01-01

33

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

Directory of Open Access Journals (Sweden)

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

ZENG Qi-hong; YUAN Shu-ai

2011-01-01

34

A theory of patchy and intermettent reconnections for magnetospheric flux transfer events  

Energy Technology Data Exchange (ETDEWEB)

The author proposes that the elbow-shaped flux transfer events (FTEs) of Russell and Elphic (1979) are initiated by a specific normal mode of three-dimensional tearing of magnetopause current sheet, resulting in a three-dimensional component reconnection driven by the solar wind. The patchy nature of the proposed three-dimensional tearing reconnection is determined by the structure of the three-dimensional tearing on the dayside magnetopause, leading to isolated reconnection sites; the intermittent nature is governed externally by the fluctuation of the interplanetary magnetic field (IMF) and internally regulated by the ionosphere line-tying effect. The proposed 3 DT reconnection can occur simultaneously with the single x line intermittent or quasi-steady reconnection if the IMF drapes over the dayside magnetopause, which takes place when the solar wind speed exceeds the MHD fast-mode speed. Magnetic field signatures of the 3DT reconnection are consistent with the elbow-shaped FTE signatures. Electric fields associated with the elbow-shaped FTEs can be expected to be spiky, peaking near the center of the localized FTE reconnection sites. The spiky electric field of FTEs is expected to produce channels of enhanced magnetospheric convection. The observed multiple field-aligned current sheets and auroral arcs fanning out from the cusp region along enhanced convection channels can be expected as consequences of the proposed 3DT reconnection on the dayside magnetopause. The polar cap potential due to the elbow-shaped FTEs is predicted to have a dependence on the IMF polar angle somewhat different from that of the single x line reconnection.

Kan, J.R. (Univ. of Alaska, Fairbanks (USA))

1988-06-01

35

Taking the High Ground: Geothermal's Place in the Revolving Energy Market  

Energy Technology Data Exchange (ETDEWEB)

It's a genuine privilege for me to be here today. As Dr. Mock mentioned, I have been President of California Energy for not yet three months and have a total tenure in the industry of only one year. As a newcomer to the industry, I am honored to address this group and share my views on ''The Opportunities and Challenges for Expanding Geothermal Energy''. You will see that my outlook for our industry is generally optimistic, shaped in part, perhaps by a newcomer's enthusiasm, but largely I think by my analysis of the opportunities which are open to us as an industry. Many of you and your predecessors over the last 20 years pioneered the geothermal industry in the United States. The risks were great, the results sometimes rewarding, sometimes disappointing. Government and the private sector forged an alliance that moved the industry ahead. Developers, utilities and federal land managers worked together to bring projects on line. Government helped identify geothermal areas, in many cases doing exploration work. The geothermal pioneers had to form entirely new, multi-disciplinary teams to solve problems unique to this resource. From discovery of fields, to environmental mitigation, to management of reservoirs and all of the steps in between, new teams had to be assembled. Geologists, geochemists, hydrologists, reservoir engineers and drilling technologists now apply their skills. Even anthropologists and biologists routinely get into the act in the environmental assessment phase of development. The care that our industry is taking today to do the job right reflects a maturing industry with high standards of performance. To be sure, mistakes were made in the early years, but the industry learned from them. We all know the value of responsible development and resource management to the long-term future of our industry. Improvements in technology and more efficient operations have helped lower our costs and improve our competitiveness. Our industry's progress has also been affected by outside factors. The price of and demand for electric power has fluctuated through economic cycles and changes in fuel prices. As our industry evolved and matured, we experienced a shakeout of ownership, with new companies arriving on the scene. We can be encouraged that today, some stable companies with solid projects lead in the development of the earth's natural steam. As more geothermal companies offer projects in competitive bidding, their names are becoming familiar to utility executives. Names like UNOCAL, Magma Power, Oxbow, Calpine, OESI, and yes, my company, California Energy. We compete, but we also benefit from one another's successes. Well-run, cost-effective geothermal plants elevate our small industry. We have matured from experimenting with emerging technologies to providing an established, reliable source of power.

Jaros, Richard

1992-03-24

36

Jupiter's polar auroral emissions-signatures of magnetic reconnection.  

Science.gov (United States)

The polar auroral emissions at Jupiter can be divided into three regions fixed in magnetic local time: the dawnside dark region, the poleward swirl region and the duskside active region in which flares and arc-like features are observed. Previous studies related the polar emissions to the solar wind driven Dungey cycle and Vasyliunas flow cycle. Based on HST STIS and ACS images we study extensively the time variations of the morphology and brightness of various polar auroral features as well as their duration and reoccurrence.We magnetically map their location in the equatorial plane and we compare their spatial size and time scales with the reconnection events taking place in the Jovian magnetotail. We discuss the possibility that some polar auroral features are signatures of magnetic reconnection.

Radioti, A.; Gérard, J.-C.; Grodent, D.; Bonfond, B.

2007-08-01

37

Explosive Turbulent Magnetic Reconnection  

CERN Document Server

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.

Higashimori, Katsuaki; Hoshino, Masahiro

2013-01-01

38

Explosive turbulent magnetic reconnection.  

UK PubMed Central (United Kingdom)

We report simulation results for turbulent magnetic reconnection obtained using a newly developed Reynolds-averaged magnetohydrodynamics model. We find that the initial Harris current sheet develops in three ways, depending on the strength of turbulence: laminar reconnection, turbulent reconnection, and turbulent diffusion. The turbulent reconnection explosively converts the magnetic field energy into both kinetic and thermal energy of plasmas, and generates open fast reconnection jets. This fast turbulent reconnection is achieved by the localization of turbulent diffusion. Additionally, localized structure forms through the interaction of the mean field and turbulence.

Higashimori K; Yokoi N; Hoshino M

2013-06-01

39

Reconnection of Magnetic Fields  

Science.gov (United States)

Preface; Part I. Introduction: 1.1 The Sun E. R. Priest; 1.2 Earth's magnetosphere J. Birn; Part II. Basic Theory of MHD Reconnection: 2.1 Classical theory of two-dimensional reconnection T. G. Forbes; 2.2 Fundamental concepts G. Hornig; 2.3 Three-dimensional reconnection in the absence of magnetic null points G. Hornig; 2.4 Three-dimensional reconnection at magnetic null points D. Pontin; 2.5 Three-dimensional flux tube reconnection M. Linton; Part III. Basic Theory of Collisionless Reconnection: 3.1 Fundamentals of collisionless reconnection J. Drake; 3.2 Diffusion region physics M. Hesse; 3.3 Onset of magnetic reconnection P. Pritchett; 3.4 Hall-MHD reconnection A. Bhattacharjee and J. Dorelli; 3.5 Role of current-aligned instabilities J. Büchner and W. Daughton; 3.6 Nonthermal particle acceleration M. Hoshino; Part IV. Reconnection in the Magnetosphere: 4.1 Reconnection at the magnetopause: concepts and models J. G. Dorelli and A. Bhattacharjee; 4.2 Observations of magnetopause reconnection K.-H. Trattner; 4.3 On the stability of the magnetotail K. Schindler; 4.4 Simulations of reconnection in the magnetotail J. Birn; 4.5 Observations of tail reconnection W. Baumjohann and R. Nakamura; 4.6 Remote sensing of reconnection M. Freeman; Part V. Reconnection in the Sun's Atmosphere: 5.1 Coronal heating E. R. Priest; 5.2 Separator reconnection D. Longcope; 5.3 Pinching of coronal fields V. Titov; 5.4 Numerical experiments on coronal heating K. Galsgaard; 5.5 Solar flares K. Kusano; 5.6 Particle acceleration in flares: theory T. Neukirch; 5.7 Fast particles in flares: observations L. Fletcher; 6. Open problems J. Birn and E. R. Priest; Bibliography; Index.

Birn, J.; Priest, E. R.

2007-01-01

40

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

Energy Technology Data Exchange (ETDEWEB)

The effect of gamma irradiation ({sup 60}Co) with doses of 5-30 kGy on the amylose-lipid complex transition and retrogradation occurring in gels containing ca. 50% and ca. 20% wheat starch was studied by differential scanning calorimetry (DSC) during heating-cooling-heating cycles (up to three cycles). Transition of the amylose-lipid complex occurs in all the irradiated samples at a lower temperature as compared to the non-irradiated starch. That effect was larger when the radiation dose was higher. A further thermal treatment causes a decrease of the transition temperature in the irradiated samples, with no effect or increase of that temperature observed for the non-irradiated ones. Irradiation hinders retrogradation taking place in 50% gels but facilitates the process occurring in 20% gels. The differences between the irradiated and the non-irradiated samples are more evident in the every next heating or cooling cycle as well as after storage and in the case of ca. 50% suspensions as compared to ca. 20% suspensions. The results point out to the deterioration of the structure of the complexes formed in the irradiated starch as compared to the non-irradiated one.

Ciesla, K. [Institute of Nuclear Chemistry and Technology, Dorodna 16 str., 03-195 Warsaw (Poland)], E-mail: kciesla@orange.ichtj.waw.pl; Eliasson, A.C. [Department of Food Technology Engineering and Nutrition, Division of Food Technology, University of Lund, P.O. Box 124, S-221 00 Lund (Sweden)

2007-12-15

 
 
 
 
41

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

UK PubMed Central (United Kingdom)

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

Borowski LS; Dziembowski A; Hejnowicz MS; Stepien PP; Szczesny RJ

2013-01-01

42

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

International Nuclear Information System (INIS)

The effect of gamma irradiation (60Co) with doses of 5-30 kGy on the amylose-lipid complex transition and retrogradation occurring in gels containing ca. 50% and ca. 20% wheat starch was studied by differential scanning calorimetry (DSC) during heating-cooling-heating cycles (up to three cycles). Transition of the amylose-lipid complex occurs in all the irradiated samples at a lower temperature as compared to the non-irradiated starch. That effect was larger when the radiation dose was higher. A further thermal treatment causes a decrease of the transition temperature in the irradiated samples, with no effect or increase of that temperature observed for the non-irradiated ones. Irradiation hinders retrogradation taking place in 50% gels but facilitates the process occurring in 20% gels. The differences between the irradiated and the non-irradiated samples are more evident in the every next heating or cooling cycle as well as after storage and in the case of ca. 50% suspensions as compared to ca. 20% suspensions. The results point out to the deterioration of the structure of the complexes formed in the irradiated starch as compared to the non-irradiated one.

2007-01-01

43

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

International Nuclear Information System (INIS)

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

2013-04-20

44

Plasmoid-Induced-Reconnection and Fractal Reconnection  

CERN Document Server

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 ingredient of the new model is the formation and ejection of a plasmoid which play an essential role in the storage of magnetic energy (by inhibiting reconnection) and the induction of a strong inflow into reconnection region. Using a simple analytical model, we show that the plasmoid ejection and acceleration are closely coupled with the reconnection process, leading to a nonlinear instability for the whole dynamics that determines the macroscopic reconnection rate uniquely. Next we show that the current sheet tends to have a fractal stru...

Shibata, K; Shibata, Kazunari; Tanuma, Syuniti

2001-01-01

45

Plasmoids in Reconnecting Current Sheets: Solar and Terrestrial Contexts Compared  

CERN Multimedia

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

46

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

International Nuclear Information System (INIS)

[en] One of the main issues related to the conception of a superconducting magnet cooled by a superfluid helium bath (like the Iseult magnet) is to insure the magnet safety as well as the whole cryogenic facility safety in case of accidental quench. In order to find a solution to this problem, we first have to identify the physical mechanisms which drive the pressure rise during a quench. This is why our study deals with the modeling of the thermohydraulic phenomena taking place during such a magnet quench. First of all, we performed and analyzed local pressure rise experiments in a heated helium channel. A numerical thermohydraulic model was developed for this study. Quench experiments were then performed on an 8-T (Seht) superconducting coil cooled by a superfluid helium bath. These experiments allowed us to make a detailed analysis of the physical mechanisms which drive the global pressure rise in case of quench as well as the strong coupling between this pressure rise and the normal zone propagation. Following this analysis, a complete model of normal zone propagation and pressure rising during a quench was developed. This model is a first step toward predictive modeling of the pressure rise during the quench of a superconducting magnet cooled by a superfluid helium bath. (author)[fr] Une des problematiques liees a la conception des aimants supraconducteurs refroidis par un bain d'helium superfluide (de type Iseult) est d'assurer la securite de l'aimant ainsi que celle de toute l'installation cryogenique en cas de quench accidentel. Afin de repondre a cette problematique, il est necessaire de comprendre quels sont les mecanismes physiques responsables de la montee de pression lors d'un quench. C'est pour cette raison que notre etude a consiste a modeliser les phenomenes thermohydrauliques intervenant lors du quench d'un tel aimant. Pour ce faire, on a tout d'abord realise et analyse des experiences de montees de pressions locales dans un canal d'helium chauffe. Un modele numerique de thermohydraulique a ete developpe dans le cadre de ces analyses. Puis, on a realise des essais de quench sur un aimant supraconducteur de 8 T (Seht) refroidi par un bain d'helium superfluide. Ces essais nous ont permis d'analyser en detail les mecanismes physiques responsables de la montee de pression globale en cas de quench ainsi que le fort couplage entre cette montee de pression et la propagation de la zone normale. Suite a cette analyse, un modele complet de propagation de la zone normale et de montee de pression en cas de quench a ete developpe. Ce modele est un premier pas vers la modelisation predictive de la montee de pression en cas de quench d'un aimant supraconducteur refroidi par un bain d'helium superfluide

2010-01-01

47

Sustainable Landscape Planning The Reconnection Agenda  

CERN Multimedia

This book takes as its starting point the need to examine critically the case for landscape reconnection. It looks at alleged disconnections and their supposed consequences. It explores the arguments about reconnecting the natural and human elements of whole landscapes. More broadly, it considers landscape as an arena within which science, humanities and professions can find common ground, and in which vivid social learning can occur about key social and environmental issues. It takes a dynamic view of landscape, in contrast to the popular image of timeless, traditional scenery. It accepts tha

Selman, Paul

2012-01-01

48

Magnetic reconnection in solar atmosphere observed by Hinode  

International Nuclear Information System (INIS)

Complete text of publication follows. The Hinode spacecraft was launched on 2006 September 22 UT. It is a Japanese mission collaborating with US and UK with three instruments on board; the Solar Optical Telescope (SOT), the X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS). Hinode reveals the three-dimensional structure and dynamics in the various activities of the Sun. One of the most interesting topics in solar physics is magnetic reconnection, because magnetic reconnection is one of the rapidest processes of energy conversion from stored magnetic energy to thermal energy and kinetic energy or non-thermal particle energy. In this talk, we present Hinode observation related to magnetic reconnection. One of the most interesting/astonishing Hinode's findings is that the magnetic reconnection can be taken place everywhere in solar atmosphere. We can clearly see the observational evidence of magnetic reconnection in not only solar corona but also chromosphere. SOT can observe the photospheric/chromospheric dynamics, and XRT/EIS can observe coronal dynamics. With those three telescopes, we can discuss magnetic reconnections from photosphere to upper corona. Generally the physical conditions of plasma are quite different between solar corona and chromosphere (for example, temperature, density, and so on). Thus, we can compare the magnetic reconnection in different physical condition and discuss the fundamental characteristics of magnetic reconnection with Hinode. We will discuss the major difference of the magnetic reconnection in the solar corona and photosphere/chromosphere in this talk.

2009-01-01

49

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; Huan-Chao Keh; Shu-Shen Wai; Ji-jen Wu; Chung-Hsien Tsai

2011-01-01

50

A fully magnetohydrodynamic simulation of three-dimensional non-null reconnection  

International Nuclear Information System (INIS)

A knowledge of the nature of fully three-dimensional magnetic reconnection is crucial in understanding a great many processes in plasmas. It has been previously shown that in the kinematic regime the evolution of magnetic flux in three-dimensional reconnection is very different from two dimensions. In this paper a numerical fully magnetohydrodynamic simulation is described, in which this evolution is investigated. The reconnection takes place in the absence of a magnetic null point, and the nonideal region is localized in the center of the domain. The effect of differently prescribed resistivities is considered. The magnetic field is stressed by shear boundary motions, and a current concentration grows within the volume. A stagnation-point flow develops, with strong outflow jets emanating from the reconnection region. The behavior of the magnetic flux matches closely that discovered in the kinematic regime. In particular, it is found that no unique field line velocity exists, and that as a result field lines change their connections continually and continuously throughout the nonideal region. In order to describe the motion of magnetic flux within the domain, it is therefore necessary to use two different field line velocities. The importance of a component of the electric field parallel to the magnetic field is also demonstrated.

2005-01-01

51

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

Energy Technology Data Exchange (ETDEWEB)

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)

Diaz-Rainey, Ivan [Norwich Business School, University of East Anglia, Norwich NR4 7TJ (United Kingdom); Ashton, John K. [Norwich Business School, University of East Anglia, Norwich NR4 7TJ (United Kingdom); ESRC Centre for Competition Policy, University of East Anglia, Norwich NR4 7TJ (United Kingdom)

2008-08-15

52

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.

2008-01-01

53

Placing the power of real options analysis into the hands of natural resource managers - taking the next step.  

UK PubMed Central (United Kingdom)

This paper explores heuristic methods with potential to place the analytical power of real options analysis into the hands of natural resource managers. The complexity of real options analysis has led to patchy or ephemeral adoption even by corporate managers familiar with the financial-market origins of valuation methods. Intuitively accessible methods for estimating the value of real options have begun to evolve, but their evaluation has mostly been limited to researcher-driven applications. In this paper we work closely with Bush Heritage Australia to evaluate the potential of real options analysis to support the intuitive judgement of conservation estate managers in covenanting land with uncertain future conservation value due to climate change. The results show that modified decision trees have potential to estimate the option value of covenanting individual properties while time and ongoing research resolves their future conservation value. Complementing this, Luehrman's option space has potential to assist managers with limited budgets to increase the portfolio value of multiple properties with different conservation attributes.

Nelson R; Howden M; Hayman P

2013-07-01

54

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

1978-01-01

55

Catastrophic eruption of magnetic flux rope in the corona and solar wind with and without magnetic reconnection  

CERN Multimedia

It is generally believed that the magnetic free energy accumulated in the corona serves as a main energy source for solar explosions such as coronal mass ejections (CMEs). In the framework of the flux rope catastrophe model for CMEs, the energy may be abruptly released either by an ideal magnetohydrodynamic (MHD) catastrophe, which belongs to a global magnetic topological instability of the system, or by a fast magnetic reconnection across preexisting or rapidly-developing electric current sheets. Both ways of magnetic energy release are thought to be important to CME dynamics. To disentangle their contributions, we construct a flux rope catastrophe model in the corona and solar wind and compare different cases in which we either prohibit or allow magnetic reconnection to take place across rapidly-growing current sheets during the eruption. It is demonstrated that CMEs, even fast ones, can be produced taking the ideal MHD catastrophe as the only process of magnetic energy release. Nevertheless, the eruptive s...

Chen, Y; Sun, S J

2007-01-01

56

Anti-parallel reconnection. Dynamics and reconnection rate  

International Nuclear Information System (INIS)

[en] Complete text of publication follows. Two of the more elusive characteristics of magnetic reconnection are the dynamics of the reconnection line and the reconnection rate. For in situ measurements at the Earth's magnetopause, the location of the reconnection line is difficult to determine unless the line crosses over the spacecraft. In these rare events, the spacecraft observes a reversal in the high-speed flow jets associated with reconnection. Changes in the location of the reconnection line are equally difficult to determine from in situ measurements because the location is known only when the line passes over the spacecraft. This talk focuses on an event when the Cluster spacecraft were at the high latitude magnetopause and observed the reconnection line pass over the spacecraft twice in a 10 minute period. Using velocity cutoffs in the ion distributions, the location of the reconnection line relative to the spacecraft is determined in the intervening time between spacecraft encounters of the line. The reconnection line appears to track the location on the magnetopause where the magnetosheath and magnetospheric magnetic fields are very close to anti-parallel. With this knowledge of the location of the reconnection site, a two-spacecraft method for determining the reconnection rate is applied to simultaneous observations in the boundary layer. This rate is compared to theory and to previous measurements of reconnection rates from other events.

2009-01-01

57

Spontaneous non-steady magnetic reconnection within the solar environment  

CERN Multimedia

This work presents a 2.5-dimensional simulation study of the instability of current-sheets located in a medium with a strong density variation along the current layer. The initial force-free configuration is observed to undergo a two-stage evolution consisting of an abrupt regime transition from a slow to a fast reconnection process leading the system to a final chaotic configuration. Yet, the onset of the fast phase is not determined by the presence of any anomalous enhancement in plasma's local resistivity, but rather is the result of a new mechanism discovered in Lapenta (2008)* and captured only when sufficient resolution is present. Hence, the effects of the global resistivity, the global viscosity and the plasma beta on the overall dynamics are considered. This mechanism allowing the transition from slow to fast reconnection provides a simple but effective model of several processes taking place within the solar atmosphere from the high chromosphere up to the low corona. In fact, the understanding of a ...

Bettarini, Lapo

2009-01-01

58

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

Directory of Open Access Journals (Sweden)

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

D. Baker; A. P. Rouillard; L. van Driel-Gesztelyi; P. Démoulin; L. K. Harra; B. Lavraud; J. A. Davies; A. Opitz; J. G. Luhmann; J.-A. Sauvaud; A. B. Galvin

2009-01-01

59

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

1986-01-01

60

Understanding the structural changes that take place in a polypyrrole film during its oxi-reduction process: a molecular dynamics simulation study  

Science.gov (United States)

Oxi-reduction processes of conducting polymer are the base of a great number of technological developments in the fields of polymeric actuators (artificial muscles) or smart windows. Hence, the understanding the structural changes that take place in the polymer as a function of its oxidation seems to be crucial for a proper understanding of these complicated systems. In this sense, a model with atomic detail has been simulated by Molecular Dynamics Simulation, which provides an insight of how the electrical response of the system depends of the structural changes that take place inside the polymer. In this regard, the conducting polymer, water and counterions were modeled with atomic detail with the goal of obtaining an insight of the ring orientation and reorientational relaxation time of the pyrrole rings at different oxidation states of the polymer. In addition, we studied how the above properties are greatly affected by the oxidation state of the polymer and the variation these properties changes from the polypyrrole/water interface to the polypyrrole bulk. Finally, we correlated the reorientational dynamics of pyrrole rings with the oxidation kinetic observed from a macroscopic point of view.

Lopez Cascales, J. J.; Otero, T. F.

2005-06-01

 
 
 
 
61

Collisionless driven magnetic reconnection  

International Nuclear Information System (INIS)

Driven magnetic reconnection in a collisionless plasma is investigated by means of a two-and-one-half dimensional particle simulation. The dynamical compression by plasma inflow forms a peaked profile of current density in the neutral sheet. When the width of current layer is compressed as thin as the ion Larmor radius, the charge separation becomes distinct abruptly at the center of the current layer due to the finite ion Larmor radius effect. The charge separation in the central current region and the subsequent spatial modification of the current profile result in excitation of collisionless driven magnetic reconnection. In the cause of collisionless driven magnetic reconnection an efficient energy conversion from field energy to particle energy is observed. (author).

1993-01-01

62

Magnetic field line reconnection  

Energy Technology Data Exchange (ETDEWEB)

The term 'magnetic field line reconnection' has arisen in the physics of rarefied plasmas with very high conductivity. When such a plasma is in motion, the remarkable property of field line 'freezing in' of the plasma manifests itself. However, situations sometimes occur in real plasma motion where this condition is violated. The process of reconnection results in a marked change in the field line topology and is accompanied by the formation of current layers and the conversion of magnetic energy into kinetic and thermal plasma energies. Magnetic field line reconnection plays a key role in many processes in the near-Earth, space and laboratory fusion plasmas.

Kadomtsev, B.B.

1987-02-01

63

Experimental investigation of the neutral sheet profile during magnetic reconnection  

International Nuclear Information System (INIS)

During magnetic reconnection, a ''neutral sheet'' current is induced, heating the plasma. The resultant plasma thermal pressure forms a stationary equilibrium with the opposing magnetic fields. The reconnection layer profile holds significant clues about the physical mechanisms which control reconnection. In the Magnetic Reconnection Experiment [M. Yamada et al., Phys. Plasmas 4, 1936 (1997)], a quasi steady-state and axisymmetric neutral sheet profile has been measured precisely using a magnetic probe array with spatial resolution equal to one quarter of the ion gyro-radius. It was found that the reconnecting field profile fits well with a Harris-type profile [E. G. Harris, Il Nuovo Cimento 23, 115 (1962)], B(x)?tanh(x/?). This agreement is remarkable since the Harris theory does not take into account reconnection and associated electric fields and dissipation. An explanation for this agreement is presented. The sheet thickness ? is found to be ?0.4 times the ion skin depth, which agrees with a generalized Harris theory incorporating nonisothermal electron and ion temperatures and finite electric field. The detailed study of additional local features of the reconnection region is also presented. (c) 2000 American Institute of Physics.

2000-01-01

64

Explosive events and magnetic reconnection in the solar atmosphere  

Energy Technology Data Exchange (ETDEWEB)

Explosive events are highly energetic, small-scale phenomena which are frequently detected throughout the quiet and active Sun. They are seen in profiles of spectral lines formed at transition zone temperatures as exceptionally Doppler-shifted features, typically at 100 km s{sup {minus}1} to the red and/or blue of the rest wavelength. Sufficient observational evidence has now been developed to demonstrate that some explosive events are associated with the emergence of new magnetic flux. In these cases it is likely that the acceleration of plasma is caused by the magnetic reconnection resulting from flux emergence. The authors take as a working hypothesis the proposal that all explosive events are the result of magnetic reconnection. Since explosive events tend to occur on the edges of high photospheric magnetic field regions, they identify them with reconnection that occurs during the cancellation of photospheric magnetic flux (Martin, 1984; Livi et al., 1985). The combined observational characteristics of photospheric flux cancellation and transition zone explosive events provide powerful diagnostic information concerning the nature of magnetic reconnection. Reconnection in the quiet solar atmosphere apparently proceeds in bursts at sites much smaller than the boundary between opposite polarity flux elements that are observed to cancel in magnetograph sequences. Equating the velocity of the expelled transition zone plasma with the Alfven speed yields magnetic field strengths of 20 G at the site of reconnection. The speed at which the reconnection proceeds is commensurate with the rapid rates predicted by Petschek (1964).

Dere, K.P.; Bartoe, J.D.F.; Brueckner, G.E. (Naval Research Lab., Washington, DC (USA)); Ewing, J. (Applied Research Corp., Washington, DC (USA)); Lund, P. (Inertia Switch Aerospace, Inc., Washington, DC (USA))

1991-06-01

65

Reconnection via the Tearing Instability  

CERN Multimedia

We discuss the role of tearing instabilities in magnetic reconnection. In three dimensions this instability leads to the formation of strong Alfvenic waves that remove plasma efficiently from the reconnection layer. As a result the instability proceeds at high rates while staying close to the linear regime. Our calculations show that for a resistive fluid the reconnection speed scales as the product of the Alfven speed V_A over the magnetic Reynolds number to the power -0.3. In the limit of vanishing resistivity, tearing modes proceed at a non-zero rate, driven by the electron inertia term, giving rise to a reconnection speed V_A (c/ømega_p L_x)^{3/5}, where ømega_p is the plasma frequency and L_x is the transverse scale of the reconnection layer. Formally this solves the problem of fast reconnection, but in practice this reconnection speed is small.

Lazarian, A; Vishniac, Ethan T.

1998-01-01

66

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; Gonzalo Bello; Mariza G Morgado

2007-01-01

67

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

1983-01-01

68

Two Energy Release Processes for CMEs: MHD Catastrophe and Magnetic Reconnection  

CERN Multimedia

It remains an open question how magnetic energy is rapidly released in the solar corona so as to create solar explosions such as solar flares and coronal mass ejections (CMEs). Recent studies have confirmed that a system consisting of a flux rope embedded in a background field exhibits a catastrophic behavior, and the energy threshold at the catastrophic point may exceed the associated open field energy. The accumulated free energy in the corona is abruptly released when the catastrophe takes place, and it probably serves as the main means of energy release for CMEs at least in the initial phase. Such a release proceeds via an ideal MHD process in contrast with nonideal ones such as magnetic reconnection. The catastrophe results in a sudden formation of electric current sheets, which naturally provide proper sites for fast magnetic reconnection. The reconnection may be identified with a solar flare associated with the CME on one hand, and produces a further acceleration of the CME on the other. On this basis,...

Chen, Y; Xia, L D

2007-01-01

69

Comparison of secondary islands in collisional reconnection to Hall reconnection  

CERN Document Server

Large-scale resistive Hall-magnetohydrodynamic (Hall-MHD) simulations of the transition from Sweet-Parker (collisional) to Hall (collisionless) magnetic reconnection are presented, the first to separate effects of secondary islands from collisionless effects. Three main results are described. There exists a regime in which secondary islands occur without collisionless effects when the thickness of the dissipation regions exceed ion gyroscales. The reconnection rate with secondary islands is faster than Sweet-Parker but significantly slower than Hall reconnection. This implies that secondary islands are not the cause of the fastest reconnection rates. Because Hall reconnection is much faster, its onset causes the ejection of secondary islands from the vicinity of the X-line. These results imply that most of the energy release occurs during Hall reconnection. Coronal applications are discussed.

Shepherd, L S

2010-01-01

70

The role of lateral magnetic reconnection in solar eruptive events  

Directory of Open Access Journals (Sweden)

Full Text Available On 10–11 December 2005 a slow CME occurred in between two coronal streamers in the Western Hemisphere. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere consisting of a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the expanding CME affects both of the lateral streamers and induces the release of plasma within or close to them. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion that occurs either inside the streamer current sheet or between the CME flanks and the streamer. Our observations show that CMEs can be associated to not only a single reconnection process at a single location in the corona, but also to many reconnection processes occurring at different times and locations around the flux rope. Numerical simulations are used to demonstrate that the observed lateral reconnections can be reproduced. The observed secondary reconnections associated to CMEs may facilitate the CME release by globally decreasing the magnetic tension of the corona. Future CME models should therefore take into account the lateral reconnection effect.

A. Soenen; A. Bemporad; C. Jacobs; S. Poedts

2009-01-01

71

Modulation of Bmp4 signalling in the epithelial-mesenchymal interactions that take place in early thymus and parathyroid development in avian embryos.  

UK PubMed Central (United Kingdom)

Epithelial-mesenchymal interactions are crucial for the development of the endoderm of the pharyngeal pouches into the epithelia of thymus and parathyroid glands. Here we investigated the dynamics of epithelial-mesenchymal interactions that take place at the earliest stages of thymic and parathyroid organogenesis using the quail-chick model together with a co-culture system capable of reproducing these early events in vitro. The presumptive territories of thymus and parathyroid epithelia were identified in three-dimensionally preserved pharyngeal endoderm of embryonic day 4.5 chick embryos on the basis of the expression of Foxn1 and Gcm2, respectively: the thymic rudiment is located in the dorsal domain of the third and fourth pouches, while the parathyroid rudiment occupies a more medial/anterior pouch domain. Using in vitro quail-chick tissue associations combined with in ovo transplantations, we show that the somatopleural but not the limb bud mesenchyme, can mimic the role of neural crest-derived pharyngeal mesenchyme to sustain development of these glands up to terminal differentiation. Furthermore, mesenchymal-derived Bmp4 appears to be essential to promote early stages of endoderm development during a short window of time, irrespective of the mesenchymal source. In vivo studies using the quail-chick system and implantation of growth factor soaked-beads further showed that expression of Bmp4 by the mesenchyme is necessary during a 24 h-period of time. After this period however, Bmp4 is no longer required and another signalling factor produced by the mesenchyme, Fgf10, influences later differentiation of the pouch endoderm. These results show that morphological development and cell differentiation of thymus and parathyroid epithelia require a succession of signals emanating from the associated mesenchyme, among which Bmp4 plays a pivotal role for triggering thymic epithelium specification.

Neves H; Dupin E; Parreira L; Le Douarin NM

2012-01-01

72

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

CERN Document Server

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

Liu, Wei; Petrosian, Vahe'

2013-01-01

73

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 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 profundidade nas organizações, investigando como ocorreram - em detalhes - as inovações. Para essa finalidade foram conduzidos estudos de casos em cinco diferentes orga (more) nizações 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 conducted in five different service enterprises in the sector of telecommunications and computer-related activities. To describe the innovation process, the concept of "Chain of (more) 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).

Vasconcellos, Luís Henrique Rigato; Marx, Roberto

2011-01-01

74

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  

Directory of Open Access Journals (Sweden)

Full Text Available 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 profundidade 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).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 conducted 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

2011-01-01

75

Magnetic reconnection launcher  

Energy Technology Data Exchange (ETDEWEB)

An electromagnetic launcher includes a plurality of electrical stages which are energized sequentially in synchrony with the passage of a projectile. Each stage of the launcher includes two or more coils which are arranged coaxially on either closed-loop or straight lines to form gaps between their ends. The projectile has an electrically conductive gap-portion that passes through all the gaps of all the stages in a direction transverse to the axes of the coils. The coils receive an electric current, store magnetic energy, and convert a significant portion of the stored magnetic energy into kinetic energy of the projectile by magnetic reconnection as the gap portion of the projectile moves through the gap. The magnetic polarity of the opposing coils is in the same direction, e.g. N-S-N-S. A gap portion of the projectile may be made from aluminum and is propelled by the reconnection of magnetic flux stored in the coils which causes accelerating forces to act upon the projectile at both the rear vertical surface of the projectile and at the horizontal surfaces of the projectile near its rear. The gap portion of the projectile may be flat, rectangular and longer than the length of the opposing coils and fit loosely within the gap between the opposing coils.

Cowan, Maynard (Albuquerque, NM)

1989-01-01

76

Effect of interchange instability on magnetic reconnection  

Science.gov (United States)

We present here the results of a study of interacting magnetic fields that involves a force normal to the reconnection layer. In the presence of such force, the reconnection layer becomes unstable to interchange disturbances. The interchange instability results in formation of tongues of heated plasma that leaves the reconnection layer through its wide surface rather than through its narrow ends, as is the case in traditional magnetic reconnection models. This plasma flow out of the reconnection layer facilitates the removal of plasma from the layer and leads to fast reconnection. The proposed mechanism provides fast reconnection of interacting magnetic fields and does not depend on the thickness of the reconnection layer. This instability explains the strong turbulence and bidirectional streaming of plasma that is directed toward and away from the reconnection layer that is observed frequently above reconnection layers. The force normal to the reconnection layer also accelerates the removal of plasma islands appearing in the reconnection layer during turbulent reconnection. In the presence of this force normal to the reconnection layer, these islands are removed from the reconnection layer by the "buoyancy force", as happens in the case of interchange instability that arises due to the polarization electric field generated at the boundaries of the islands.

Lyatsky, W.; Goldstein, M. L.

2013-06-01

77

Effect of interchange instability on magnetic reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We present here the results of a study of interacting magnetic fields that involves a force normal to the reconnection layer. In the presence of such force, the reconnection layer becomes unstable to interchange disturbances. The interchange instability results in formation of tongues of heated plasma that leaves the reconnection layer through its wide surface rather than through its narrow ends, as is the case in traditional magnetic reconnection models. This plasma flow out of the reconnection layer facilitates the removal of plasma from the layer and leads to fast reconnection. The proposed mechanism provides fast reconnection of interacting magnetic fields and does not depend on the thickness of the reconnection layer. This instability explains the strong turbulence and bidirectional streaming of plasma that is directed toward and away from the reconnection layer that is observed frequently above reconnection layers. The force normal to the reconnection layer also accelerates the removal of plasma islands appearing in the reconnection layer during turbulent reconnection. In the presence of this force normal to the reconnection layer, these islands are removed from the reconnection layer by the "buoyancy force", as happens in the case of interchange instability that arises due to the polarization electric field generated at the boundaries of the islands.

W. Lyatsky; M. L. Goldstein

2013-01-01

78

A model of Hall reconnection  

CERN Multimedia

The rate of quasi-stationary, two-dimensional magnetic reconnection is calculated in the framework of incompressible Hall magnetohydrodynamics (MHD). The calculation is based on the solution of Hall-MHD equations that include Hall and electron pressure terms for electric current. These equations are solved in a local region across the reconnection electron layer, including only the upstream region and the layer center. In the case when the ion inertial length d_i is larger than the Sweet-Parker reconnection layer thickness, the dimensionless reconnection rate is found to be independent of the electrical resistivity and equal to d_i/L, where L is the scale length of the external magnetic field in the upstream region outside the electron layer.

Malyshkin, Leonid M

2008-01-01

79

Multiple Spacecraft Study of the Effect 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, 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. Comparison with results from the wavevector and wave mode analyses measures the effect of turbulence or islands on the reconnection rate. From several case studies of reconnection events, we obtain preliminary estimates of the spectral scaling law, associated wave modes , and the resulting effective reconnection electric field.

Wendel, D. E.; Goldstein, M. L.; Vinas, A. F.; Sahraoui, F.; Adrian, M. L.

2010-12-01

80

Colour reconnection at LEP2  

Energy Technology Data Exchange (ETDEWEB)

Two measurements are presented of estimators sensitive to the Colour Reconnection effect in W{sup +}W{sup -} 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 m{sub W} measurement at LEP2 by use of the inferred information about the Colour Reconnection effect. (orig.)

D' Hondt, Jorgen [Inter-University Institute for High Energies (IIHE), Vrije Universiteit Brussel (VUB) (Belgium)

2004-07-01

 
 
 
 
81

Magnetic reconnection in space plasmas  

Energy Technology Data Exchange (ETDEWEB)

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

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

1996-04-01

82

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; M. Bárta

2004-01-01

83

Reconnection at the Heliopause  

CERN Multimedia

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

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

2005-01-01

84

Steady state reconnection at a single 3D magnetic null point  

CERN Multimedia

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

Galsgaard, K

2011-01-01

85

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

86

Magnetic Reconnection : MHD and Beyond.  

Energy Technology Data Exchange (ETDEWEB)

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

Lapenta, G. M. (Giovanni M.)

2002-01-01

87

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)

[en] 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

2008-01-01

88

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)

2008-01-01

89

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

International Nuclear Information System (INIS)

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

2006-01-01

90

Model for incomplete reconnection in sawtooth crashes.  

Science.gov (United States)

A model for incomplete reconnection in sawtooth crashes is presented. The reconnection inflow during the crash phase of sawteeth self-consistently convects the high pressure core toward the reconnection site, raising the pressure gradient there. Reconnection shuts off if the diamagnetic drift speed at the reconnection site exceeds a threshold, which may explain incomplete reconnection. The relaxation of magnetic shear after reconnection stops may explain the destabilization of ideal interchange instabilities reported previously. Proof-of-principle two-fluid simulations confirm this basic picture. Predictions of the model compare favorably to data from the Mega Ampere Spherical Tokamak. Applications to transport modeling of sawteeth are discussed. The results should apply across tokamaks, including ITER. PMID:22243083

Beidler, M T; Cassak, P A

2011-12-13

91

Model for Incomplete Reconnection in Sawtooth Crashes  

CERN Document Server

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

Beidler, Matthew T

2011-01-01

92

Model for incomplete reconnection in sawtooth crashes.  

UK PubMed Central (United Kingdom)

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

Beidler MT; Cassak PA

2011-12-01

93

Manifold reconnection in chaotic regimes  

CERN Document Server

In this paper we extend the concept of separatrix reconnection into chaotic regimes. We show that even under chaotic conditions one can still understand abrupt jumps of diffusive-like processes in the relevant phase-space in terms of relatively smooth realignments of stable and unstable manifolds of unstable fixed points.

Corso, G

1998-01-01

94

Reconnection in magnetic field lines  

International Nuclear Information System (INIS)

Magnetic surfaces are described for MHD equilibrium plasma with central hole plasma current density, confined in large aspect-ratio tokamaks, perturbed by external helical windings. The integrable case is first considered, where reconnection phenomenon is described for the field lines. A toroidal correction causes the integrability loss, leading to the onset of chaotic field lines. (author). 7 refs, 4 figs

1994-11-04

95

Patchy Reconnection in the Solar Corona  

CERN Multimedia

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

96

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

97

Major growth in coke production takes place  

International Nuclear Information System (INIS)

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

1991-03-06

98

Can amorphization take place in nanoscale interconnects?  

UK PubMed Central (United Kingdom)

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.

Kumar S; Joshi KL; van Duin AC; Haque MA

2012-03-01

99

Method for heating sauna room, bio sauna room or steam bath, involves providing hybrid heating that takes place by cascading of heat sources heated by switchable electric heater, and arranging heating elements in cascade manner  

UK PubMed Central (United Kingdom)

The method involves providing hybrid heating that takes place by cascading of heat sources, where the heat sources are connected and heated by a switchable electric heater using domestic heating technique. Warm air transportation is performed under utilization of gravitational force circulation, where the gravitational force circulation is supported by fans. Heating power of the electrical heat source is controlled by adjustable thermostats. Multiple heating elements (5) are arranged in a cascade manner. An independent claim is also included for a device for heating a sauna room, bio sauna room or steam bath.

SCHUELER MARTIN

100

Impulsive nature in collisional driven reconnection  

Energy Technology Data Exchange (ETDEWEB)

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).

Kitabata, Hideyuki; Hayashi, Takaya; Sato, Tetsuya

1995-11-01

 
 
 
 
101

New electric field in asymmetric magnetic reconnection.  

UK PubMed Central (United Kingdom)

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 mission to locate reconnection sites as we expect it to appear on the magnetospheric side, pointing earthward, at the dayside magnetopause reconnection site.

Malakit K; Shay MA; Cassak PA; Ruffolo D

2013-09-01

102

Solar flares: an extremum of reconnection  

Energy Technology Data Exchange (ETDEWEB)

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.

Colgate, S.A.

1983-12-22

103

Turbulent Magnetic Reconnection in Two Dimensions  

CERN Multimedia

Two-dimensional numerical simulations of the effect of background turbulence on 2D resistive magnetic reconnection are presented. For sufficiently small values of the resistivity ($\\eta$) and moderate values of the turbulent power ($\\epsilon$), the reconnection rate is found to have a much weaker dependence on $\\eta$ than the Sweet-Parker scaling of $\\eta^{1/2}$ and is even consistent with an $\\eta-$independent value. For a given value of $\\eta$, the dependence of the reconnection rate on the turbulent power exhibits a critical threshold in $\\epsilon$ above which the reconnection rate is significantly enhanced.

Loureiro, N F; Schekochihin, A A; Cowley, S C; Yousef, T A

2009-01-01

104

Relation of astrophysical turbulence and magnetic reconnection  

International Nuclear Information System (INIS)

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.

2012-01-01

105

Theoretical analysis of driven magnetic reconnection experiments  

Energy Technology Data Exchange (ETDEWEB)

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

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

1995-11-01

106

Collisionless reconnection and the sawtooth crash  

International Nuclear Information System (INIS)

A model of the sawtooth crash is presented in which electron inertia combined with anomalous diffusion of the current replace classical resistivity in allowing magnetic reconnection to occur. Experimental measurements of the sawtooth crash time ?c in the TFTR and JET tokamaks range from 20-2,000 ?sec. The crash time, based on a Sweet=Parker model of reconnection by the m = 1 tearing mode, is of order 2,000 ?sec, which is short enough to explain the slow crashes, but not the fast crashes. In this paper the authors show that the electric field E induced during magnetic reconnection during the sawtooth crash greatly exceeds the Dreicer field ED and therefore classical resistivity cannot play a role in this process. Including electron inertia in Ohm's law allows reconnection to proceed. They present numerical simulations which demonstrate that the current layer during collisionless reconnection using this new Ohm's law collapses to a thickness which is much smaller than the electron collisionless skin depth ? = c/?pe, contrary to conventional scientific wisdom. This narrow current layer throttles the nonlinear reconnection rate and, as a consequence, inertial reconnection cannot, by itself, cause the fast sawtooth crash. The extremely narrow current layers induced during collisionless reconnection are strongly unstable to the collisionless current convective instability. They estimate the anomalous current diffusion rate due to this instability to be Dperpendicular = ?e??perpendicularvparallele. Electron inertia combined with anomalous current diffusion given by the expression produce sawtooth crash times which are in reasonable agreement with observations. 2 refs.

1991-01-01

107

Collisionless magnetic reconnection in a plasmoid chain  

CERN Document Server

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

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

2012-01-01

108

Magnetic reconnection and particle accelerationinitiated by flux emergence  

Science.gov (United States)

So as to perform an MHD simulation of the evolution of the corona driven by the evolution of the photosphere, a key aspect is the definition of the boundary conditions for reaching a good compromise between physical conditions and numerical constraints. In this work, we focused on the simulation of a confined flare observed on Nov 16, 2002. As initial configuration, we considered a uniform temperature corona, with a magnetic field resulting from a 3D potential field extrapolation from a SOHO/MDI magnetogram. We prescribed a velocity field at the photospheric boundary of the domain, so as to mimic the observed flow pattern associated to a flux emergence. This resulted in a combination of ``slipping reconnection'' in a halo of QSLs surrounding a 3D null point, through which a ``fan reconnection'' regime took place. This simplified approach of flux emergence has successfully reproduced the main characteristics of the observed flare: the flare ribbons observed in the EUV with TRACE being due to the chromospheric impact of particles accelerated along reconnecting field lines, this bimodal regime could explain both the shapes and dynamics of these ribbons. We foresee that this kind of modeling should be able to simulate the evolution of slipping magnetic flux tubes in open configurations, allowing to predict the spatio-temporal evolution of particle beams injected into the heliosphere.

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

2008-11-01

109

Reconnection process involving nonpendular islands  

Energy Technology Data Exchange (ETDEWEB)

A new type of Hamiltonian nonlinear resonant island is analyzed in the present paper. In the usual case where the resonant island is pendulum-like, chains bifurcated out of the central elliptic point undergo infinite cascades of period-doubling bifurcations as they approach the island boundary. In the present case we find that those chains undergo either period doubling or inverse saddle-node bifurcations, depending on the strength of perturbing terms. In the saddle-node case we show that just after a reconnection process, external chains cross the island boundary to collapse against the bifurcated internal chains. (author). 8 refs., 2 figs.

Corso, G.; Rizzato, F.B. [Rio Grande do Sul Univ., Porto Alegre, RS (Brazil). Inst. de Fisica

1995-12-31

110

Reconnection process involving nonpendular islands  

International Nuclear Information System (INIS)

A new type of Hamiltonian nonlinear resonant island is analyzed in the present paper. In the usual case where the resonant island is pendulum-like, chains bifurcated out of the central elliptic point undergo infinite cascades of period-doubling bifurcations as they approach the island boundary. In the present case we find that those chains undergo either period doubling or inverse saddle-node bifurcations, depending on the strength of perturbing terms. In the saddle-node case we show that just after a reconnection process, external chains cross the island boundary to collapse against the bifurcated internal chains. (author). 8 refs., 2 figs.

1995-01-01

111

Scaling of the magnetic reconnection rate with symmetric shear flow  

Energy Technology Data Exchange (ETDEWEB)

The scaling of the reconnection rate during (fast) Hall magnetic reconnection in the presence of an oppositely directed bulk shear flow parallel to the reconnecting magnetic field is studied using two-dimensional numerical simulations of Hall reconnection with two different codes. Previous studies noted that the reconnection rate falls with increasing flow speed and shuts off entirely for super-Alfvenic flow, but no quantitative expression for the reconnection rate in sub-Alfvenic shear flows is known. An expression for the scaling of the reconnection rate is presented.

Cassak, P. A. [Department of Physics, West Virginia University, Morgantown, West Virginia 26506 (United States); Otto, A. [Geophysical Institute, University of Alaska-Fairbanks, Fairbanks, Alaska 99775 (United States)

2011-07-15

112

Magnetic Chirality and Coronal Reconnection  

UK PubMed Central (United Kingdom)

We have used Mees Solar Observatory vector magnetogramsand Yohkoh Soft X-Ray Telescope images to study the role of magneticchirality in the trans-equatorial reconnection of active regions. We concludethat active regions reconnect preferentially with others of the samechirality. We explain this result with a simple model of the closure oftheir current systems.1. IntroductionHelicity is a topological parameter of magnetic fields and plasma flows, and ismanifested by twist, linkage, and knottedness. Measures of helicity include themagnetic helicity density Hm :Hm = A Delta B; (1)the current helicity density H c :H c = B Delta r Theta B; (2)and the force--free field parameter ff:r Theta B = ffB: (3)For a linear force--free field,Hm = ffGamma1B2; (4)H c = ffB2; (5)whereB is the magnetic induction,A is the magnetic vector potential,B = r Theta A:Chirality measures the handedness of twist; like sign, it has only two values.Positive sign of ...

Richard C. Canfield; Alexei A. Pevtsov; Alexander N. Mcclymont

113

Continuous magnetic reconnection at Earth's magnetopause.  

Science.gov (United States)

The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar flares and magnetospheric substorms--two phenomena believed to be initiated by reconnection--are highly burst-like occurrences, raising the possibility that the reconnection process is intrinsically intermittent, storing and releasing magnetic energy in an explosive and uncontrolled manner. Here we show that reconnection at Earth's high-latitude magnetopause is driven directly by the solar wind, and can be continuous and even quasi-steady over an extended period of time. The dayside proton auroral spot in the ionosphere--the remote signature of high-latitude magnetopause reconnection--is present continuously for many hours. We infer that reconnection is not intrinsically intermittent; its steadiness depends on the way that the process is driven. PMID:14654835

Frey, H U; Phan, T D; Fuselier, S A; Mende, S B

2003-12-01

114

Continuous magnetic reconnection at Earth's magnetopause.  

UK PubMed Central (United Kingdom)

The most important process that allows solar-wind plasma to cross the magnetopause and enter Earth's magnetosphere is the merging between solar-wind and terrestrial magnetic fields of opposite sense-magnetic reconnection. It is at present not known whether reconnection can happen in a continuous fashion or whether it is always intermittent. Solar flares and magnetospheric substorms--two phenomena believed to be initiated by reconnection--are highly burst-like occurrences, raising the possibility that the reconnection process is intrinsically intermittent, storing and releasing magnetic energy in an explosive and uncontrolled manner. Here we show that reconnection at Earth's high-latitude magnetopause is driven directly by the solar wind, and can be continuous and even quasi-steady over an extended period of time. The dayside proton auroral spot in the ionosphere--the remote signature of high-latitude magnetopause reconnection--is present continuously for many hours. We infer that reconnection is not intrinsically intermittent; its steadiness depends on the way that the process is driven.

Frey HU; Phan TD; Fuselier SA; Mende SB

2003-12-01

115

Evolution of magnetic helicity under kinetic magnetic reconnection: Part II B ? 0 reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available We investigate the evolution of magnetic helicity under kinetic magnetic reconnection in thin current sheets. We use Harris sheet equilibria and superimpose an external magnetic guide field. Consequently, the classical 2D magnetic neutral line becomes a field line here, causing a B ? 0 reconnection. While without a guide field, the Hall effect leads to a quadrupolar structure in the perpendicular magnetic field and the helicity density, this effect vanishes in the B ? 0 reconnection. The reason is that electrons are magnetized in the guide field and the Hall current does not occur. While a B = 0 reconnection leads just to a bending of the field lines in the reconnection area, thus conserving the helicity, the initial helicity is reduced for a B ? 0 reconnection. The helicity reduction is, however, slower than the magnetic field dissipation. The simulations have been carried out by the numerical integration of the Vlasov-equation.

T. Wiegelmann; J. Büchner

2002-01-01

116

Collisionless magnetic reconnection via Alfven eigenmodes.  

UK PubMed Central (United Kingdom)

We propose an analytic approach to the problem of collisionless magnetic reconnection formulated as a process of Alfvén eigenmodes' generation and dissipation. Alfvén eigenmodes are confined by the current sheet in the same way that quantum mechanical waves are confined by the tanh;{2} potential. The dynamical time scale of reconnection is the system scale divided by the eigenvalue propagation velocity of the n = 1 mode. The prediction of the n = 1 mode shows good agreement with the in situ measurement of the reconnection-associated Hall fields.

Dai L

2009-06-01

117

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

118

Magnetic reconnection in the terrestrial magnetosphere  

International Nuclear Information System (INIS)

[en] 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

1984-01-01

119

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

120

Magnetic Reconnection in Extreme Astrophysical Environments  

CERN Multimedia

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

 
 
 
 
121

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; Abeer A. Alenezi

2013-01-01

122

Fast Shocks From Magnetic Reconnection Outflows  

CERN Document Server

Magnetic reconnection is commonly perceived to drive flow and particle acceleration in flares of solar, stellar, and astrophysical disk coronae but the relative roles of different acceleration mecha- nisms in a given reconnection environment are not well understood. We show via direct numerical simulations that reconnection outflows produce weak fast shocks, when conditions for fast recon- nection are met and the outflows encounter an obstacle. The associated compression ratios lead to a Fermi acceleration particle spectrum that is significantly steeper than the strong fast shocks commonly studied, but consistent with the demands of solar flares. While this is not the only acceleration mechanism operating in a reconnection environment, it is plausibly a ubiquitous one.

Workman, Jared C; Ren, Chuang

2011-01-01

123

Resistive Magnetohydrodynamic Simulations of Relativistic Magnetic Reconnection  

CERN Multimedia

Resistive relativistic magnetohydrodynamic (RRMHD) simulations are applied to investigate the system evolution of relativistic magnetic reconnection. A time-split Harten--Lan--van Leer (HLL) method is employed. Under a localized resistivity, the system exhibits a fast reconnection jet with an Alfv\\'{e}nic Lorentz factor inside a narrow Petschek-type exhaust. Various shock structures are resolved in and around the plasmoid such as the post-plasmoid vertical shocks and the "diamond--chain" structure due to multiple shock reflections. Under a uniform resistivity, Sweet--Parker-type reconnection slowly evolves. Under a current-dependent resistivity, plasmoids are repeatedly formed in an elongated current sheet. It is concluded that the resistivity model is of critical importance for RRMHD modeling of relativistic magnetic reconnection.

Zenitani, Seiji; Klimas, Alex

2010-01-01

124

Reconnection in a Weakly Stochastic Field  

CERN Multimedia

We examine the effect of weak, small scale magnetic field structure on the rate of reconnection in a strongly magnetized plasma. We recover lower and upper limits on the reconnection rate, depending on the reaction of the magnetic field to stresses exerted from within the reconnection layer. Using Goldreich and Sridhar's model of strong turbulence in a magnetized plasma with negligible intermittency, we find that the lower limit for the reconnection speed is the Alfven speed times the magnetic Reynolds number to the power (-3/16). The upper limit on the reconnection speed is typically a large fraction of Alfven speed. We argue that generic reconnection in turbulent plasmas will normally occur at close to this upper limit. The fraction of magnetic energy that goes directly into electron heating scales as magnetic Reynolds number to the power (-2/5) and the thickness of the current sheet scales as Rm to the power (-3/5). A large fraction of the magnetic energy goes into high frequency Alfven waves. We claim tha...

Lazarian, A

1999-01-01

125

Collisionless magnetic reconnection in a plasmoid chain  

Directory of Open Access Journals (Sweden)

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

S. Markidis; P. Henri; G. Lapenta; A. Divin; M. V. Goldman; D. Newman; S. Eriksson

2012-01-01

126

Reconnection in a slow Coronal Mass Ejection  

Directory of Open Access Journals (Sweden)

Full Text Available This paper aims at studying reconnection occurring in the aftermath of the 28 May 2004, CME, first imaged by the LASCO (Large Angle and Spectrometric Coronagraph) C2 at 11:06 UT. The CME was observed in White Light and UV radiation: images acquired by the LASCO C2 and C3 coronagraphs and spectra acquired by UVCS (Ultraviolet Coronagraph Spectrometer) allowed us to identify the level at which field lines, stretched outwards by the CME ejection, reconnect below the CME bubble. As the CME propagates outwards, reconnection occurs at increasingly higher levels. The process goes on at a low pace for several hours: here we give the profile of the reconnection rate vs. heliocentric distance over a time interval of ?14 h after the CME onset, extending estimates of the reconnection rate to larger distances than previously inferred by other authors. The reconnection rate appears to decrease with time/altitude. We also calculate upper and lower limits to the density in the diffusion region between 4 and 7 R? and conclude by comparing estimates of the classical and anomalous resistivity in the diffusion region with the value inferred from the data. The latter turns out to be ?5 order of magnitudes larger than predicted by classical or anomalous theories, pointing to the need of identifying the process responsible for the observed value.

G. Poletto; A. Bemporad; F. Landini; M. Romoli

2008-01-01

127

Reconnection Processes in the Sun and Heliopshere  

Science.gov (United States)

Solar flare, coronal mass ejection and many other interesting plasma and magnetic field structures in the heliosphere are believed to be generated by a powerful plasma process widely known as reconnection of magnetic field lines. The basic understanding of this reconnection process is described by considering a simple model suggested by Dungey that contains a kind of consistent flow of plasma around an x-type neutral point. There are, however, several comprehensive MHD models, some of which are also discussed in this article. Spontaneous reconnection based on tearing mode instability is described very briefly for completeness. The crucial role played by magnetic reconnection in violent energy conversion occurring in solar flare, coronal mass ejection and other related phenomena like hard x-ray and soft x-ray emissions is highlighted. Several convincing observational evidences that support reconnection model are presented. Numerical simulation is seen to be an essential part of this study that enhances our understanding of the evolution of plasmoid and multiple shocks due to reconnection of field lines. Some challenges are mentioned towards the end of the presentation.

Das, A. C.

128

Place Memes  

Digital Repository Infrastructure Vision for European Research (DRIVER)

In this paper I introduce the concept of the place meme, a ‘unit’ of cultural information about place. Place memes originate in the human brain. Place cells in the hippocampus convert short to long term memory through a repetitive ‘mapping’ of neural clusters, operating according to Edelman’s Theory...

Eades, Gwilym

129

Achieving fast reconnection in resistive MHD models via turbulent means  

Directory of Open Access Journals (Sweden)

Full Text Available Astrophysical fluids are generally turbulent and this preexisting turbulence must be taken into account for models of magnetic reconnection in astrophysical, solar or heliospheric environments. In addition, reconnection itself induces turbulence which provides an important feedback on the reconnection process. In this paper we discuss both the theoretical model and numerical evidence that magnetic reconnection becomes fast in the approximation of resistive MHD. We consider the relation between the Lazarian and Vishniac turbulent reconnection theory and Lapenta's numerical experiments testifying of the spontaneous onset of turbulent reconnection in systems which are initially laminar.

G. Lapenta; A. Lazarian

2012-01-01

130

Taking Medication  

Medline Plus

Full Text Available ... Forgot your ID or password? Priority Code: 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 ...

131

Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence  

International Nuclear Information System (INIS)

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

1971-01-00

132

Reconnection events in two-dimensional Hall magnetohydrodynamic turbulence  

Energy Technology Data Exchange (ETDEWEB)

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

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

2012-09-15

133

Magnetic Reconnection in Turbulent Plasmas and Gamma Ray Bursts  

CERN Document Server

We discuss how the model of magnetic reconnection in the presence of turbulence proposed inLazarian & Vishniac 1999 makes the reconnection rate independent either of resistivity or microscopic plasma effects, but determined entirely by the magnetic field line wandering induced by turbulence. We explain that the model accounts for both fast and slow regimes of reconnection and that this property naturally induces flares of reconnection in low beta plasma environments. In addition, we show that the model involves volume reconnection which can convert a substantial part of the energy into energetic particles. It is important that the reconnection induces an efficient acceleration of the first order Fermi type. Finally, we relate the properties of the reconnection with the observed properties of gamma ray bursts and provide evidence supporting the explanation of gamma ray bursts based on energy release via reconnection.

Lazarian, A

2013-01-01

134

Numerical Tests of Fast Reconnection in Weakly Stochastic Magnetic Fields  

CERN Multimedia

We study the effects of turbulence on magnetic reconnection using 3D numerical simulations. This is the first attempt to test a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian & Vishniac (1999). This model predicts that weak turbulence, generically present in most of astrophysical systems, enhances the rate of reconnection by reducing the transverse scale for reconnection events and by allowing many independent flux reconnection events to occur simultaneously. As a result the reconnection speed becomes independent of Ohmic resistivity and is determined by the magnetic field wandering induced by turbulence. To quantify the reconnection speed we use both an intuitive definition, i.e. the speed of the reconnected flux inflow, as well as a more sophisticated definition based on a formally derived analytical expression. Our results confirm the predictions of the Lazarian & Vishniac model. In particular, we find that Vrec Pinj^(1/2), as predicted by the model. The...

Kowal, G; Vishniac, E T; Otmianowska-Mazur, K

2009-01-01

135

Colour reconnection effects in WW production at LEP  

Energy Technology Data Exchange (ETDEWEB)

Preliminary results from the search for colour reconnection effects by the four LEP experiments and a first combination of their measurements of the inclusive particle flow distributions in four-jet events are presented. Data are compared with predictions of various models with and without colour reconnection. The extreme scenario of the SKI model, where almost all events are reconnected, is ruled out and a limit on the model parameter, controlling the fraction of reconnected events, is set.

Bouhova-Thacker, E

2003-04-01

136

Flow-turbulence interaction in magnetic reconnection  

International Nuclear Information System (INIS)

Roles of turbulence in the context of magnetic reconnection are investigated with special emphasis on the mutual interaction between flow (large-scale inhomogeneous structure) and turbulence. In order to evaluate the effective transport due to turbulence, in addition to the intensity information of turbulence represented by the turbulent energy, the structure information represented by pseudoscalar statistical quantities (helicities) is important. On the basis of the evolution equation, mechanisms that provide turbulence with cross helicity are presented. Magnetic-flux freezing in highly turbulent media is considered with special emphasis on the spatial distribution of the turbulent cross helicity. The cross-helicity effects in the context of magnetic reconnection are also investigated. It is shown that the large-scale flow and magnetic-field configurations favorable for the cross-helicity generation is compatible with the fast reconnection. Difference between the spatial distributions of the turbulent MHD energy and cross helicity plays an essential role for localizing the reconnection region. In this sense, turbulence and large-scale structures promote magnetic reconnection mediated by the turbulent cross helicity.

2011-01-01

137

Density Enhancements and Voids following Patchy Reconnection  

CERN Multimedia

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

138

Continuous versus pulsed reconnection at the magnetopause  

International Nuclear Information System (INIS)

[en] Complete text of publication follows. Decades of research have established that magnetic reconnection is the dominant mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy and momentum to flow into the magnetosphere. Observations and data analysis methods have reached the maturity to analyze the details of this universal process. One of the persistent problems of magnetic reconnection is the question of whether the process is continuous or intermittent. Observations from imagers that record FUV emissions caused by precipitating cusp ions demonstrate the global nature of magnetic reconnection. Those images show continuous ionospheric emissions even during changing IMF conditions. On the other hand, in situ observations from polar orbiting satellites show distinctive cusp structures in the ion flux distortion of precipitating ions; the tell-tale signature of intermittent reconnection. In this study we will investigate those cusp structures by analyzing the time since reconnection occurred to determine if the time profile is continuous or stepped.

2009-01-01

139

Formation of Plasmoid Chains in Magnetic Reconnection  

International Nuclear Information System (INIS)

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

2009-09-04

140

Formation of plasmoid chains in magnetic reconnection.  

UK PubMed Central (United Kingdom)

A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (10(4) reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>10(4).

Samtaney R; Loureiro NF; Uzdensky DA; Schekochihin AA; Cowley SC

2009-09-01

 
 
 
 
141

Formation of plasmoid chains in magnetic reconnection.  

Science.gov (United States)

A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers (10(4) plasmoid (magnetic-island) chains. The plasmoid number scales as S(3/8) and the instability growth rate in the linear stage as S(1/4), in agreement with the theory by Loureiro et al. [Phys. Plasmas 14, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasistationary picture for S>10(4). PMID:19792323

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

2009-09-04

142

Gyro-induced acceleration of magnetic reconnection  

CERN Multimedia

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

143

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

144

Formation of Plasmoid Chains in Magnetic Reconnection  

CERN Document Server

A detailed numerical study of magnetic reconnection in resistive MHD for very large, previously inaccessible, Lundquist numbers ($10^4\\le S\\le 10^8$) is reported. Large-aspect-ratio Sweet-Parker current sheets are shown to be unstable to super-Alfv\\'enically fast formation of plasmoid (magnetic-island) chains. The plasmoid number scales as $S^{3/8}$ and the instability growth rate in the linear stage as $S^{1/4}$, in agreement with the theory by Loureiro et al. [Phys. Plasmas {\\bf 14}, 100703 (2007)]. In the nonlinear regime, plasmoids continue to grow faster than they are ejected and completely disrupt the reconnection layer. These results suggest that high-Lundquist-number reconnection is inherently time-dependent and hence call for a substantial revision of the standard Sweet-Parker quasi-stationary picture for $S>10^4$.

Samtaney, R; Uzdensky, D A; Schekochihin, A A; Cowley, S C

2009-01-01

145

Formation of Plasmoid Chains in Magnetic Reconnection  

International Nuclear Information System (INIS)

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

2009-01-01

146

Computer simulation of reconnection in planetary magnetospheres  

Energy Technology Data Exchange (ETDEWEB)

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.

Birn, J.

1983-01-01

147

Formation of Plasmoid Chains in Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

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

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

2009-09-09

148

Computer simulation of reconnection in planetary magnetospheres  

International Nuclear Information System (INIS)

[en] 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

1983-01-01

149

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).

1991-01-01

150

The structure of the magnetic reconnection exhaust boundary  

CERN Multimedia

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

Liu, Yi-Hsin; Swisdak, M

2011-01-01

151

DENSITY ENHANCEMENTS AND VOIDS FOLLOWING PATCHY RECONNECTION  

International Nuclear Information System (INIS)

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 Syrovatskii (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 its edges. 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 supersonic flows that collide at the center of the tube. There, gas-dynamic shocks that compress and heat the plasma are launched outwardly. The descending tube moves through the bottom part of the CS where it expands laterally in response to the decreasing background magnetic pressure. This effect may decrease plasma density by 30%-50% of background levels. This tube will arrive at the top of the arcade that will slow it to a stop. Here, the perpendicular dynamics is halted, but the parallel dynamics continues along its legs; the RDs are shut down, and the gas is rarified to even lower densities. The hot post-shock regions continue evolving, determining a long lasting hot region on top of the arcade. We provide an observational method based on total emission measure and mean temperature that indicates where in the CS the tube has been reconnected.

2011-04-01

152

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.).

1984-01-01

153

Computer modeling of fast collisionless reconnection  

Energy Technology Data Exchange (ETDEWEB)

Particle simulations of collisionless tearing, reconnection and coalescence of magnetic fields for a sheet-pinch configuration show that reconnection is Sweet-Parker like in the tearing and island formation phase. It is much faster to explosive in the island coalescence state. Island coalescence is the most energetic process and leads to large ion temperature increase and oscillations in the merged state. Similar phenomena have been observed in equivalent MHD simulations. Coalescence and its effects, as observed in our simulations, may explain many of the features of solar flares and coronal x-ray brightening.

Leboeuf, J.N.; Brunel, F.; Tajima, T.; Sakai, J.; Wu, C.C.; Dawson, J.M.

1984-01-01

154

Observations of Turbulence Generated by Magnetic Reconnection  

International Nuclear Information System (INIS)

Spacecraft observations of turbulence within a magnetic reconnection (guide field ?0) ion diffusion region are presented. In the inertial subrange, electric and magnetic fluctuations both followed a -5/3 power law; at higher frequencies, the spectral indices were -1 and -8/3, respectively. The dispersion relation was found to be consistent with fast-mode-whistler waves rather than kinetic Alfven-ion cyclotron waves. Lower hybrid waves, which could be enhanced by whistler mode conversion, were observed, but the associated anomalous resistivity was not found to significantly modify the reconnection rate.

2009-01-23

155

Sound emission due to superfluid vortex reconnections  

CERN Multimedia

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 sound wave with a wavelength of 6-8 healing lengths.

Leadbeater, M L; Samuels, D C; Barenghi, C F; Adams, C S

2001-01-01

156

Patchy Reconnection in a Y-Type Current Sheet  

CERN Multimedia

We study the evolution of the magnetic field in a Y-type current sheet subject to a brief, localized magnetic reconnection event. The reconnection produces up- and down-flowing reconnected flux tubes which rapidly decelerate when they hit the Y-lines and underlying magnetic arcade loops at the ends of the current sheet. This localized reconnection outflow followed by a rapid deceleration reproduces the observed behavior of post-CME downflowing coronal voids. These simulations support the hypothesis that these observed coronal downflows are the retraction of magnetic fields reconnected in localized patches in the high corona.

Linton, M G; Longcope, D W

2007-01-01

157

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.

Math, Aaa; Banfill, J. C.

2007-12-12

158

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

CERN Multimedia

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

159

Antiparallel and component reconnection at the dayside magnetopause  

Science.gov (United States)

Two types of reconnection occur at the Earth's magnetopause: component and antiparallel reconnection. Recently, an empirical model was developed that purportedly determines under what solar wind conditions one or the other type of reconnection is dominant. This empirical model is tested using observations at the magnetopause from the Cluster spacecraft. For a range of interplanetary magnetic field orientations, there are regions on the magnetopause where these two types of reconnection can be distinguished from one another by the direction of the flow of reconnection jets observed in magnetopause boundary layers. Cluster spacecraft observations at the magnetopause under these specific interplanetary magnetic field (IMF) orientations confirm model predictions of the type of reconnection. In addition, these observations show evidence of possible multiple reconnection (both component and antiparallel) occurring at the magnetopause.

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

2011-10-01

160

Three-dimensional null point reconnection regimes  

International Nuclear Information System (INIS)

Recent advances in theory and computational experiments have shown the need to refine the previous categorization of magnetic reconnection at three-dimensional null points--points at which the magnetic field vanishes. We propose here a division into three different types, depending on the nature of the flow near the spine and fan of the null. The spine is an isolated field line which approaches the null (or recedes from it), while the fan is a surface of field lines which recede from it (or approach it). So-called torsional spine reconnection occurs when field lines in the vicinity of the fan rotate, with current becoming concentrated along the spine so that nearby field lines undergo rotational slippage. In torsional fan reconnection field lines near the spine rotate and create a current that is concentrated in the fan with a rotational flux mismatch and rotational slippage. In both of these regimes, the spine and fan are perpendicular and there is no flux transfer across spine or fan. The third regime, called spine-fan reconnection, is the most common in practice and combines elements of the previous spine and fan models. In this case, in response to a generic shearing motion, the null point collapses to form a current sheet that is focused at the null itself, in a sheet that locally spans both the spine and fan. In this regime the spine and fan are no longer perpendicular and there is flux transfer across both of them.

2009-01-01

 
 
 
 
161

Generation of Alfven Waves by Magnetic Reconnection  

CERN Multimedia

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

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

2010-01-01

162

Gyro-induced acceleration of magnetic reconnection  

Science.gov (United States)

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

Comisso, L.; Grasso, D.; Waelbroeck, F. L.; Borgogno, D.

2013-09-01

163

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

164

A MAGNETIC RECONNECTION MECHANISM FOR THE GENERATION OF ANOMALOUS COSMIC RAYS  

International Nuclear Information System (INIS)

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

2010-02-01

165

Three-dimensional magnetic reconnection through a moving magnetic null  

Directory of Open Access Journals (Sweden)

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

V. S. Lukin; M. G. Linton

2011-01-01

166

Experimental study of ion heating and acceleration during magnetic reconnection  

International Nuclear Information System (INIS)

[en] 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

2000-01-01

167

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

168

Mystic Places  

Science.gov (United States)

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

169

Theory of magnetic reconnection in solar and astrophysical plasmas.  

Science.gov (United States)

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 paper, 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 three-dimensional 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 magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas. PMID:22665898

Pontin, David I

2012-07-13

170

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; Y. V. Khotyaintsev; M. André; A. Vaivads; H. Rème

2010-01-01

171

Intermittent magnetic reconnection in TS-3 merging experiment  

International Nuclear Information System (INIS)

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

2011-01-01

172

Statistics of magnetic reconnection in two-dimensional magnetohydrodynamic turbulence  

International Nuclear Information System (INIS)

The nonlinear dynamics of magnetic reconnection in turbulence is investigated through direct numerical simulations of decaying, incompressible, two-dimensional magnetohydrodynamics. Recently, it was shown by Servidio et al. [Phys. Rev. Lett. 102, 115003 (2009)] that in fully developed turbulence complex processes of reconnection occur locally. Here, the main statistical features of these multiscale reconnection events are further described, providing details on the methodology. It is found that is possible to describe the reconnection process in turbulence as a generalized local Sweet-Parker process in which the parameters are locally controlled by the turbulence cascade, thus providing a step toward reconciling classical turbulence analysis with reconnection theory. This general description of reconnection may be useful for laboratory and space plasmas, where the presence of turbulence plays a crucial role.

1971-01-00

173

The role of magnetic reconnection in magnetotail plasmoid dynamics  

International Nuclear Information System (INIS)

[en] In taillike configurations magnetic reconnection necessarily leads to the formation of plasmoids. This paper analyses the dynamical evolution of the developing plasmoids and the influence of magnetic reconnection on the propertie of plasmoids. By two dimensional resistive MHD calculations it is shown that plasmoid properties depend very much on the reconnection process especially when the reconnection rate is large. Thus the early plasmoid formation is dominated by magnetic reconnection. At later times the main plasmoid acceleration is due to pressure forces while the tension of open interplanetary fieldlines is negligible. The comparison of different resistivity and equilibrium modells reveals a definite influence of the microscopic dissipation and the initial state on magnetic reconnection and the resulting evolution of plasmoids. (author). 8 refs.; 6 figs

1989-01-01

174

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

175

Particle trajectories and acceleration during 3D fan reconnection  

CERN Multimedia

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

Dalla, S; 10.1051/0004-6361:200809771

2008-01-01

176

Theory of magnetic reconnection in solar and astrophysical plasmas.  

UK PubMed Central (United Kingdom)

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 paper, 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 three-dimensional 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 magnetohydrodynamic framework where a number of new three-dimensional reconnection regimes have been identified. We discuss evidence from observations and simulations of Solar System plasmas that support this theory and summarize some prominent locations in which this new reconnection theory is relevant in astrophysical plasmas.

Pontin DI

2012-07-01

177

Places available  

CERN Document Server

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

178

Three-dimensional kinematic reconnection of plasmoids  

Energy Technology Data Exchange (ETDEWEB)

The kinematic reconnection model of Lau and Finn (1990) is applied in a theoretical investigation of three-dimensional plasmoid morphology, as seen in the solar corona and earth magnetotail. The derivation of the governing equations is outlined; long, short, and periodic plasmoid models are developed; and the evolution of the stable and unstable manifolds in these models is presented graphically. It is inferred that sheet currents and tangential discontinuities can form on surfaces topologically identical to those where Delta(phi) about equal to Delta(z) singularities occur in the kinematic reconnection model, and can be broadened in a similar way by nonideal effects. Two such surfaces exist in long plasmoids, and also in short plasmoids in the presence of finite resistivity; the intertwined surfaces characteristic of the periodic plasmoid form a fractal set but merge in the presence of finite resistivity, producing structures similar to those proposed by the sheet-current theory of Parker (1983). 35 refs.

Lau, Yuntung; Finn, J.M. (Maryland Univ., College Park (USA))

1991-01-01

179

Kelvin wave turbulence generated by vortex reconnections  

Science.gov (United States)

Reconnections of quantum vortex filaments create sharp bends, which degenerate into propagating Kelvin waves. These waves cascade their energy down-scale and their wave action up-scale via weakly nonlinear interactions, and this is the main mechanism of turbulence at scales less than the inter-vortex distance. In the case of an idealized forcing concentrated around a single scale k 0, the turbulence spectrum exponent has a pure direct cascade form -17/5 at scales k > k 0 [B. V. Svistunov, Phys. Rev. B 52, 3647 (1995)] and a pure inverse cascade form -3 at k Nazarenko, JETP Lett. 83, 198 (2005)]. The main result is that the direct cascade scaling dominates; i.e., the reconnection forcing is more or less equivalent to a low-frequency forcing.

Nazarenko, S.

2007-02-01

180

Nonlinear Acceleration Mechanism of Collisionless Magnetic Reconnection  

CERN Multimedia

A mechanism for fast magnetic reconnection in collisionless plasma is studied for understanding sawtooth collapse in tokamak discharges. Nonlinear growth of the tearing mode driven by electron inertia is analytically estimated by invoking the energy principle for the first time. Decrease of potential energy in the nonlinear regime (where the island width exceeds the electron skin depth) is found to be steeper than in the linear regime, resulting in acceleration of the reconnection. Release of free energy by such ideal fluid motion leads to unsteady and strong convective flow, which theoretically corroborates the inertia-driven collapse model of the sawtooth crash [D. Biskamp and J. F. Drake, Phys. Rev. Lett. 73, 971 (1994)].

Hirota, M; Ishii, Y; Yagi, M; Aiba, N

2012-01-01

 
 
 
 
181

Kinetic aspects of reconnection at the magnetopause  

Energy Technology Data Exchange (ETDEWEB)

Observations presented here support the kinetic (or single particle) description of reconnection where ions interacting with the magnetopause conserve their pitch angles or change them by equal amounts as in adiabatic motion. These observations include ion reflection and transmission at the magnetopause and time of flight effects associated with the magnetopause layers, with an emphasis here on ion reflection. Velocities of the reflected distributions predicted from this kinetic description are in good agreement with observed velocities. However, predicted velocities for the transmitted distributions are often higher than observed ones. Reflected distributions are also heated at the magnetopause; however, this heating is less important than the large scale ion motion. Reflection coefficients at the magnetopause are high (averaging 30%), appear to be the same on either side of the magnetopause, and have little or no dependence on ion mass. Time of flight effects result from the finite extent of the reconnection layers and are best observed at the edges of the layers.

Fuselier, S.A.

1994-04-01

182

. Reconnection in two dimensions --- a conceptual framework  

UK PubMed Central (United Kingdom)

le by the magnetic field (Petschek,1964; Sonnerup, 1970; Hassam, 1992; Craig and McClymont,1993), a situation known as fast reconnection.These conflicting results can largely be attributedto different versions of Ohms law in the models. Fullynon-linear solutions using a uniform resistivity typicallyexhibit slow reconnection occurring at an elongated currentlayer (Biskamp, 1986). Non-uniform (anomalous)resistivity (Ugai and Tsuda, 1977; Scholer and Roth,1987) or non-resistive terms in Ohm's law (Biskampet al., 1997; Shay et al., 1998), can lead to fast reconnectionoccurring at a compact X-point.In spite of their differences, most two-dimensional reconnectionmodels can be understood in terms of a commonglobal picture whose key landmarks are indicatedin fig. 1 (Craig, 1994). The common starting point is anequilibrium magnetic field containing an X-point, whereboth planar components of the field vanish (Dungey,1958; Chapman and Kendall, 1963). Among its m

D. W. Longcope; C. C. Kankelborg

183

Observational studies of reconnection in the solar corona  

Energy Technology Data Exchange (ETDEWEB)

In recent years, observational studies of the corona have shifted focus. Where they were once purely qualitative morphological explorations seeking to support the presence of reconnection, more investigations are providing empirical estimates of the physical conditions in the reconnecting corona. These studies are enabled and enhanced by orbiting telescopes with high angular and temporal resolution. In this article, some recent findings about the empirical quantities are reviewed, including recent estimates of the flux transferred in individual patchy reconnection episodes, the size distribution of post-reconnection flux tubes, and the energy released by the flux tubes as they shrink.

McKenzie, David E. [Department of Physics, Montana State University, P.O. Box 173840, Bozeman, Montana 59717-3840 (United States)

2011-11-15

184

Numerical examination of plasmoid-induced reconnection model for solar flares: the relation between plasmoid velocity and reconnection rate  

CERN Document Server

The plasmoid-induced-reconnection model explaining solar flares based on bursty reconnection produced by an ejecting plasmoid suggests a possible relation between the ejection velocity of a plasmoid and the rate of magnetic reconnection. In this study, we focus on the quantitative description of this relation. We performed magnetohydrodynamic (MHD) simulations of solar flares by changing the values of resistivity and the plasmoid velocity. The plasmoid velocity has been changed by applying an additional force to the plasmoid to see how the plasmoid velocity affects the reconnection rate. An important result is that the reconnection rate has a positive correlation with the plasmoid velocity, which is consistent with the plasmoid-induced-reconnection model for solar flares. We also discuss an observational result supporting this positive correlation.

Nishida, Keisuke; Shiota, Daikou; Takasaki, Hiroyuki; Magara, Tetsuya; Shibata, Kazunari

2008-01-01

185

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

Energy Technology Data Exchange (ETDEWEB)

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

Russell Kulsrud; Hantao Ji; Will Fox; Masaaki Yamada

2005-06-07

186

3D Null Point Reconnection Regimes  

CERN Multimedia

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

Priest, E R

2009-01-01

187

Multiple Reconnection Lines at the Dayside Magnetopause  

Science.gov (United States)

Recent 2.5D global hybrid simulations investigated the formation of flux transfer events (FTEs) and their convection and interaction with the cusp. Multiple FTEs have been reported with a size range from a few hundred to thousands of km. Based on these simulations, we have analyzed several Polar cusp crossings in the northern hemisphere to search for the signature of such FTEs in the energy distribution of downward precipitating ions: overlapping, parallel to the ambient magnetic field, streaming ion beams. Overlapping ion distributions have been analyzed before and are usually attributed to a combination of variable ion acceleration on crossing the magnetopause with the time-of-flight effect from the entry point to the observing satellite. Most step-up cusp ion structures only overlap for pitch angle scattered ions and not for the parallel streaming distribution. This feature is the tell-tale sign for pulsed reconnection, where the reconnection rate at the magnetopause decreased to zero, physically separating convecting flux tubes and their parallel streaming ions. However, several Polar cusp events also show overlapping ion distributions in the parallel-streaming precipitating ions. This condition might be caused by re-opening an already reconnected field line, forming a magnetic island (flux rope) at the magnetopause. In this presentation we will discuss several events that show parallel, overlapping ion energy dispersions consistent with the formation of such magnetic flux tubes.

Trattner, Karlheinz; Petrinec, Steven; Fuselier, Stephen; Omidi, Nick; Sibeck, Dave

2010-05-01

188

The Alfvén edge in asymmetric reconnection  

Directory of Open Access Journals (Sweden)

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

A. Vaivads; A. Retinò; Yu. V. Khotyaintsev; M. André

2010-01-01

189

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: Nouveautés de FileMaker : 20 - 23.03.01 (4 matins) Contract Follow-up : 9.4.01 (3 heures) 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

190

Places available**  

CERN Document Server

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. ** 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 : EXCEL 2000 - niveau 1 : 20 & 22.10.03 (2 jours) CLEAN-2002 : Working in a Cleanroom (free of charge) : 23.10.03 (half day) The EDMS-MTF in practice (free of charge) :  28 -  30.10.03 (6 half-day sessions) AutoCAD 2002 - Level 1 : 3, 4, 12, 13.11.03 (4 days) LabVIEW TestStand ver. 3 : 4 & 5.11.03 (2 days) Introduction to Pspice : 4.11.03 p.m. (half-day) Hands-on Introduction to Python Programm...

2003-01-01

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: Project Planning with MS-Project : 15 & 22.1.2004 (2 days) Joint PVSS JCOP Framework Course : 2 sessions : 2 - 6.2.2004 and 16 - 20-2-2004 (5 days) Hands-on Introduction to Python Programming : 16 - 18.2.2004 (3 days - free of charge) C++ for Particle Physicists : 8 - 12.3.2004 ( 6 X 4-hour sessions)

2003-01-01

192

Places available **  

CERN Multimedia

Des places sont disponibles dans les cours suivants : Places are available in the following courses : DISP-2003 - Spring I Term : Introduction to Digital Signal Processing : 20, 27.2, 6, 13, 20, 27.3, 3.4.03 (7 X 2-hour lectures) AXEL-2003 - Introduction to Accelerators : 24 - 28.2.03 (10 X 1-hour lectures) AutoCAD 2002 - niveau 1 : 24, 25.2 & 3, 4.3.03 (4 jours) Introduction à Windows 2000 au CERN : 25.2.03 (1/2 journée) LabView base 2/LabView Basics 2 : 10 & 11.3.03 (2 jours/2 days) langue à définir/Language to be decided C++ for Particle Physicists : 10 - 14.3.03 (6 X 3-hour lectures) Introduction to PVSS : 10.3.03 (half day, afternoon) Basic PVSS : 11 - 13.3.03 (3 days) LabView avancé /LabView Advanced : 12 - 14.3.03 (3 jours/3days) Langue à définir/language to be decided AutoCAD Mechanical 6 PowerPack (F) : 12, 13, 17, 18, 24 & 25.3.03 (6 jours) PVSS - JCOP Framework Tutorial : 14.3.03 (1 day) CLEAN-2002 : Working in a cleanroom : 2.4.03 (half-day, afternoon, free course, regis...

2003-01-01

193

Places available**  

CERN Document Server

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

2004-01-01

194

Places available **  

CERN Multimedia

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

2003-01-01

195

Places available **  

CERN Multimedia

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

2003-01-01

196

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: 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

197

Places available **  

CERN Document Server

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

2003-01-01

198

Places available **  

CERN Document Server

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

2003-01-01

199

Places available**  

CERN Document Server

Places are available in the following courses: 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) Programmation automate Schneider : Programmation automate Schneider TSX Premium - 2ème niveau : 24 - 27.6.03 (4 jours) - audience : toute personne qui veux maitriser la mise en uvre et la programmation des fonctions spécialisées d'un automate TSX Premium - objectifs : maitriser la mise en uvre et la programmation des fonctions spécialisées d'un automate TSX Premium Cours de sécurité : Etre TSO au CERN : Prochaines sessions : 24, 25 & 27.6.03 - 4, 5 & 7.11.03 (session de 3 jours) ** The number of places available may vary. Please check our Web site to find out the current availability. If you wish to participate in one of these courses, pl...

2003-01-01

200

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

 
 
 
 
201

PLACES AVAILABLE  

CERN Document Server

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

202

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: CLEAN-2002 : Travailler en salle blanche (cours gratuit) : 13.08.2002 (matin) Introduction to the CERN Enginnering Data Management System :  27.8.02  (1 day) The CERN Engineering Data Management System for Advanced Users :  28.8.02  (1 day) 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

203

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

204

PLACES AVAILABLE  

CERN Document Server

Places are available in the following courses: December 2002   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) Introduction à la CAO Cadence (cours gratuit) :  10 & 11.12.02  (2 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). 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

205

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

206

PLACES AVAILABLE  

CERN Document Server

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

Monique Duval

2002-01-01

207

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

208

PLACES AVAILABLE  

CERN Document Server

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

209

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

210

Places disponibles*/Places available **  

CERN Document Server

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

211

Taking Leave?  

CERN Multimedia

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

2000-01-01

212

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

213

Two-dimensional MHD model of the reconnection diffusion region  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic reconnection is an important process providing a fast conversion of magnetic energy into thermal and kinetic plasma energy. In this concern, a key problem is that of the resistive diffusion region where the reconnection process is initiated. In this paper, the diffusion region is associated with a nonuniform conductivity localized to a small region. The nonsteady resistive incompressible MHD equations are solved numerically for the case of symmetric reconnection of antiparallel magnetic fields. A Petschek type steady-state solution is obtained as a result of time relaxation of the reconnection layer structure from an arbitrary initial stage. The structure of the diffusion region is studied for various ratios of maximum and minimum values of the plasma resistivity. The effective length of the diffusion region and the reconnection rate are determined as functions of the length scale and the maximum of the resistivity. For sufficiently small length scale of the resistivity, the reconnection rate is shown to be consistent with Petschek's formula. By increasing the resistivity length scale and decreasing the resistivity maximum, the reconnection layer tends to be wider, and correspondingly, the reconnection rate tends to be more consistent with that of the Parker-Sweet regime.

N. V. Erkaev; V. S. Semenov; H. K. Biernat

2002-01-01

214

Magnetic mirror effect as a trigger of collisionless magnetic reconnection  

International Nuclear Information System (INIS)

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

1994-01-01

215

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

216

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

217

PLACES AVAILABLE  

CERN Document Server

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

218

PLACES AVAILABLE  

CERN Document Server

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

219

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

220

PLACES AVAILABLE  

CERN Document Server

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

 
 
 
 
221

PLACES AVAILABLE  

CERN Document Server

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

222

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

223

PLACES AVAILABLE  

CERN Document Server

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

Monique Duval

2002-01-01

224

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

225

PLACES AVAILABLE  

CERN Multimedia

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

Monique Duval

2002-01-01

226

PLACES AVAILABLE  

CERN Multimedia

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

Monique Duval

2002-01-01

227

PLACES AVAILABLE  

CERN Multimedia

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

Monique Duval

2002-01-01

228

PLACES AVAILABLE  

CERN Document Server

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

229

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

230

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

231

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

232

Places available**  

CERN Document Server

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

233

Places available**  

CERN Multimedia

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

234

Places available**  

CERN Document Server

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

2003-01-01

235

PLACES AVAILABLE  

CERN Document Server

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

236

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

237

PLACES AVAILABLE  

CERN Document Server

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

Monique Duval

2002-01-01

238

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

239

Places available**  

CERN Document Server

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

240

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

 
 
 
 
241

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

242

PLACES AVAILABLE  

CERN Document Server

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

243

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

244

Places available**  

CERN Document Server

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

2003-01-01

245

PLACES AVAILABLE  

CERN Multimedia

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

Monique Duval

2002-01-01

246

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

247

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

248

Taking drugs very seriously.  

UK PubMed Central (United Kingdom)

Neither anti-illegal drug proponents nor their detractors have wholly plausible arguments for their positions, because neither takes responsibility for drug use sufficiently seriously. Instead, only a policy that places users' responsibility at the forefront of the problem is acceptable, one that is sufficiently respectful of actual or potential nonusers' rights not to be wrongfully harmed, directly or indirectly, by drug use, or coerced to support it in any way.

Corlett JA

2013-04-01

249

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

250

The Acceleration of Ions in Solar Flares During Magnetic Reconnection  

CERN Multimedia

The acceleration of solar flare ions during magnetic reconnection is explored via particle-in-cell simulations that self-consistently follow the motions of both protons and $\\alpha$ particles. We demonstrate that the dominant ion heating during reconnection with a guide field (a magnetic component perpendicular to the reconnection plane) results from pickup behavior during the entry into reconnection exhausts. In contrast with anti-parallel reconnection, the temperature increment is dominantly transverse, rather than parallel, to the local magnetic field. The comparison of protons and alphas reveals a mass-to-charge ($M/Q$) threshold in pickup behavior that favors heating of high $M/Q$ ions over protons, which is consistent with impulsive flare observations.

Knizhnik, Kalman; Drake, James F

2011-01-01

251

Plasmoid Instability in High-Lundquist-Number Magnetic Reconnection  

CERN Multimedia

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

252

Reconnection in weakly stochastic B-fields in 2D  

CERN Document Server

We study two dimensional turbulent magnetic reconnection in a compressible fluid in the gas pressure dominated limit. We use open boundary conditions and start from a Harris current sheet configuration with a uniform total pressure. A small perturbation to the vector potential initiates laminar reconnection at the Sweet-Parker rate, which is allowed to evolve for several dynamical times. Subsequently sub-Alfvenic turbulence is produced through random forcing at small wave numbers. The magnetic field topology near the current sheet is strongly affected by the turbulence. However, we find that the resulting reconnection speed depends on the resistivity. In contrast to previous results in three dimensions, we find no evidence for fast reconnection. The reconnection speed exhibits large variations but the time averages increase smoothly with the strength of the turbulence.

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

2009-01-01

253

Magnetic field reconnection in collisionless plasmas  

International Nuclear Information System (INIS)

Magnetic reconnection in collisionless regimes, where electron inertia is responsible for the decoupling of the plasma motion from that of the magnetic field, can now be observed in laboratory plasmas produced by tokamaks such as JET. At the high plasma temperatures of these experiments, internal plasma relaxations can occur on a time scale shorter than the electron-ion collision time. Recently, the linear theory of the m = 1 kink-tearing modes has been extended to experimentally relevant regimes, leading to the conclusion that these modes can remain virulent at low collisionality with an initial growth rate that compares favorably with that observed in the experiments. The nonlinear evolution of this process can be analyzed on the basis of a two-dimensional incompressible fluid model. A numerical and analytical solution of this model that neglects ion Larmor radius and electron pressure effects has been presented. The reconnection process is accompanied by the formation of a current density sublayer narrower than the skin depth and that keeps shrinking with time. This numerical solution was obtained with a pseudospectral code that can no longer resolve the sublayer after the early nonlinear phase is entered. With the aim of resolving this sublayer we adopted a different approach based on a finite-difference method. (1) Under the same initial and boundary conditions, we can reproduce the results obtained with the pseudospectral code. In particular we find the same quasi-explosive behavior of the reconnection process in the early non linear phase. (2) The code is implemented with a non-uniform grid and this increases our ability to follow the evolution of the microscale inside the current-sheet. (3) Now, we can extend this model and generalize its equations so as to include the effect of the thermal ion Larmor radius which is of the order of, or larger than, the electron skin depth in the regimes of interest.

1996-01-01

254

Magnetic field reconnection in collisionless plasmas  

Energy Technology Data Exchange (ETDEWEB)

Magnetic reconnection in collisionless regimes, where electron inertia is responsible for the decoupling of the plasma motion from that of the magnetic field, can now be observed in laboratory plasmas produced by tokamaks such as JET. At the high plasma temperatures of these experiments, internal plasma relaxations can occur on a time scale shorter than the electron-ion collision time. Recently, the linear theory of the m = 1 kink-tearing modes has been extended to experimentally relevant regimes, leading to the conclusion that these modes can remain virulent at low collisionality with an initial growth rate that compares favorably with that observed in the experiments. The nonlinear evolution of this process can be analyzed on the basis of a two-dimensional incompressible fluid model. A numerical and analytical solution of this model that neglects ion Larmor radius and electron pressure effects has been presented. The reconnection process is accompanied by the formation of a current density sublayer narrower than the skin depth and that keeps shrinking with time. This numerical solution was obtained with a pseudospectral code that can no longer resolve the sublayer after the early nonlinear phase is entered. With the aim of resolving this sublayer we adopted a different approach based on a finite-difference method. (1) Under the same initial and boundary conditions, we can reproduce the results obtained with the pseudospectral code. In particular we find the same quasi-explosive behavior of the reconnection process in the early non linear phase. (2) The code is implemented with a non-uniform grid and this increases our ability to follow the evolution of the microscale inside the current-sheet. (3) Now, we can extend this model and generalize its equations so as to include the effect of the thermal ion Larmor radius which is of the order of, or larger than, the electron skin depth in the regimes of interest.

Grasso, D.; Pegoraro, F. [Univ. of Torino (Italy); Cafaro, E. [Polytechnic of Torino (Italy)] [and others

1996-12-31

255

MHD simulations of magnetic reconnection in a skewed three-dimensional tail configuration  

Energy Technology Data Exchange (ETDEWEB)

Using the three-dimensional MHD code, the authors have studied the dynamic evolution of a non-symmetric magnetotail configuration, initiated by the sudden occurence of (anomalous) resistivity. The initial configuration included variations in all three space dimensions, consistent with average tail observations. In addition, it was skewed due to the presence of a net cross-tail magnetic field component B{sub yN} with a magnitude as typically observed, so that it lacked commonly assumed mirror symmetries around the midnight meridian and the equatorial planes. The field evolution was found to be very similar to that of a symmetric configuration studied earlier, indicating plasmoid formation and ejection. The most noticeable new feature in the evolution of the individual field components is a reduction of B{sub y} on the reconnected dipole-like field lines earthward from the reconnection region. The topological structure of the magnetic field, however, defined by the field line connections, shows remarkable differences from the symmetric case, consistent with conclusions by Hughes and Sibeck (1987) and Birn et al. (1989). The plasmoid, which is a magnetically separate entity in the symmetric case, becomes open, connected initially with the Earth, but getting gradually connected with the interplanetary field, as reconnection of lobe field lines proceeds from the midnight region to the flanks of the tail. The separation of the plasmoid from the Earth is thus found to take a finite amount of time. When the plasmoid begins to separate from the Earth, a filamentary structure of field connections develops, not present in the spatial variation of the fields; this confirms predictions by Birn et al. (1989). A localization of the electric field parallel to the magnetic field is found consistent with conclusions on general magnetic reconnection.

Birn, J.; Hesse, M. (Los Alamos National Lab., NM (USA))

1991-01-01

256

MHD simulations of magnetic reconnection in a skewed three-dimensional tail configuration  

International Nuclear Information System (INIS)

Using the three-dimensional MHD code, the authors have studied the dynamic evolution of a non-symmetric magnetotail configuration, initiated by the sudden occurence of (anomalous) resistivity. The initial configuration included variations in all three space dimensions, consistent with average tail observations. In addition, it was skewed due to the presence of a net cross-tail magnetic field component ByN with a magnitude as typically observed, so that it lacked commonly assumed mirror symmetries around the midnight meridian and the equatorial planes. The field evolution was found to be very similar to that of a symmetric configuration studied earlier, indicating plasmoid formation and ejection. The most noticeable new feature in the evolution of the individual field components is a reduction of By on the reconnected dipole-like field lines earthward from the reconnection region. The topological structure of the magnetic field, however, defined by the field line connections, shows remarkable differences from the symmetric case, consistent with conclusions by Hughes and Sibeck (1987) and Birn et al. (1989). The plasmoid, which is a magnetically separate entity in the symmetric case, becomes open, connected initially with the Earth, but getting gradually connected with the interplanetary field, as reconnection of lobe field lines proceeds from the midnight region to the flanks of the tail. The separation of the plasmoid from the Earth is thus found to take a finite amount of time. When the plasmoid begins to separate from the Earth, a filamentary structure of field connections develops, not present in the spatial variation of the fields; this confirms predictions by Birn et al. (1989). A localization of the electric field parallel to the magnetic field is found consistent with conclusions on general magnetic reconnection.

1991-01-01

257

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

0000-01-01

258

Head of household education level as a factor influencing whether delivery takes place in the presence of a skilled birth attendant in Busia, Uganda: a cross-sectional household study.  

UK PubMed Central (United Kingdom)

BACKGROUND: Assistance during delivery by a skilled attendant is recommended as a means to reduce child and maternal mortality. Globally, higher levels of maternal education have been associated with better health behaviours at delivery. However, given that heads of households tend to be the decision makers regarding accessing healthcare, some educated mothers may find themselves prevented from accessing healthcare at the point of delivery. METHODS: We examined the association between head of household education level and health seeking behaviours at delivery across a sample of 392 households. Chi-squared analysis and odds ratios were calculated to measure the strength of the relationship between no, some primary, or some secondary or higher education attained by the head of household and the presence or absence of a skilled birth attendant at that child's birth, and whether the birth took place at a health facility. RESULTS: Heads of household (n = 392) were predominantly male (93.4% [(90.9%, 95.8%), a = 0.05]). We found a significant difference in skilled birth attendance between heads of households with some primary education and heads of household with some secondary education or higher (?2 (1) = 6.231, p <0.05) whereby those with secondary or higher education were significantly more likely to seek a skilled birth attendant (OR = 1.5,[1.1,2.1]). The difference in health centre delivery between heads of household with a primary education and heads of household with a secondary or higher education was also significant (?2 (1) = 7.519, p <0.05). Those with secondary or higher education were significantly more likely to deliver in a health facility (OR = 1.6,[1.2,2.1]). CONCLUSIONS: The results of our analysis, which identified the vast majority of heads of households as men, suggests that education, or rather limited or a lack of education for the head of household, may be a barrier to women's use of health care in Uganda and therefore reinforces the need to increase educational access among male heads of households. Improving the rates of health centre deliveries and utilization of services provided by skilled health workers might lie, in part, in increasing overall education levels of heads of households, specifically the education of male heads of households.

Vallières F; Hansen A; McAuliffe E; Cassidy EL; Owora P; Kappler S; Gathuru E

2013-01-01

259

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; W. Baumjohann; W. D. Gonzalez

2012-01-01

260

Direct implicit simulation of collisionless magnetic reconnection  

Energy Technology Data Exchange (ETDEWEB)

Collisionless reconnection of magnetic field lines depends upon electron inertia effects and details of the electron and ion distribution functions, thus requiring a kinetic description of both. Though traditional explicit PIC techniques provide this description in principle, they are severely limited in parameters by time step constraints. This parameter regime has been expanded in this work by using the recently constructed 2.5 D electromagnetic code AVANTI. The code runs stably with arbitrarily large {Delta}t and is quite robust with respect to large fluctuations occurring due to small numbers of particles per cell. We find excellent agreement with linear electron tearing theory for early simulation times, provided electrostatic effects are included in the theory. In the non-linear regime following tearing, we observe electrostatic ringing of electrons and trapped flux into the magnetic island, superposed on linear growth determined by the ion sound velocity. It is found that the inclusion of a guide magnetic field (magnetic shear) severely slows the initial stages of reconnection and damps out the electrostatic ringing if local values of the guide field are above a threshold determined by questions of electron mobility. 21 refs., 8 figs.

Francis, G.E.; Hewett, D.W.; Max, C.E.

1989-07-12

 
 
 
 
261

Microflare Activity driven by Forced Magnetic Reconnection  

CERN Multimedia

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

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

2010-01-01

262

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

263

Local influence of mirror mode fluctuations on magnetopause reconnection  

International Nuclear Information System (INIS)

Complete text of publication follows. We present observations from two subsolar Cluster magnetopause crossings with 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 the first of our events is compatible with the modulation hypothesis. The second event also exhibits flow reversals, pointing to patchy and bursty reconnection, but mirror modes may play a role in triggering the variations. A hybrid simulation shows formation of magnetic islands at the magnetopause, which also would be compatible with patchy reconnection. These examples illustrate that to understand magnetopause reconnection in depth, it is necessary to know the local boundary conditions in the magnetosheath, not just the IMF direction. The rather small-scale mirror mode fluctuations can strongly influence the total energy conversion at a magnetic boundary, and should be common when the solar wind, or a stellar wind, hits a magnetised celestial object.

2009-01-01

264

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

1990-01-01

265

Study of driven magnetic reconnection in a laboratory plasma  

Energy Technology Data Exchange (ETDEWEB)

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, {rho}{sub 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.

Yamada, Masaaki; Ji, H.; Hsu, S.; Carter, T.; Kulsrud, R.; Bretz, N.; Jobes, F.; Ono, Yasushi; Perkins, F.

1998-12-31

266

SCALING LAW OF RELATIVISTIC SWEET-PARKER-TYPE MAGNETIC RECONNECTION  

International Nuclear Information System (INIS)

Relativistic Sweet-Parker-type magnetic reconnection is investigated by relativistic resistive magnetohydrodynamic (RRMHD) simulations. As an initial setting, we assume anti-parallel magnetic fields and a spatially uniform resistivity. A perturbation imposed on the magnetic fields triggers magnetic reconnection around a current sheet, and the plasma inflows into the reconnection region. The inflows are then heated due to ohmic dissipation in the diffusion region and finally become relativistically hot outflows. The outflows are not accelerated to ultrarelativistic speeds (i.e., Lorentz factor ? 1), even when the magnetic energy dominates the thermal and rest mass energies in the inflow region. Most of the magnetic energy in the inflow region is converted into the thermal energy of the outflow during the reconnection process. The energy conversion from magnetic to thermal energy in the diffusion region results in an increase in the plasma inertia. This prevents the outflows from being accelerated to ultrarelativistic speeds. We find that the reconnection rate R obeys the scaling relation R?S-0.5, where S is the Lundquist number. This feature is the same as that of non-relativistic reconnection. Our results are consistent with the theoretical predictions of Lyubarsky for Sweet-Parker-type magnetic reconnection.

2011-10-01

267

Impulsive reconnection: 3D onset and stagnation in turbulent paradigms  

International Nuclear Information System (INIS)

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 vA/S1/2, where vA 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.

2010-01-01

268

Study of driven magnetic reconnection in a laboratory plasma  

International Nuclear Information System (INIS)

[en] 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

1998-01-01

269

Three-dimensional magnetic reconnection regimes: A review  

CERN Multimedia

The magnetic field in many astrophysical plasmas -- such as the Solar corona and Earth's magnetosphere -- has been shown to have a highly complex, three-dimensional structure. Recent advances in theory and computational simulations have shown that reconnection in these fields also has a three-dimensional nature, in contrast to the widely used two-dimensional (or 2.5-dimensional) models. Here we discuss the underlying theory of three-dimensional magnetic reconnection. We also review a selection of new models that illustrate the current state of the art, as well as highlighting the complexity of energy release processes mediated by reconnection in complicated three-dimensional magnetic fields.

Pontin, D I

2011-01-01

270

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

271

Hybrid studies of collisionless magnetic reconnection on tearing mode  

Energy Technology Data Exchange (ETDEWEB)

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.

Avendano, J D; Devia, A [Laboratorio de Fisica del Plasma, Departamento de Fisica y Quimica, Universidad Nacional de Colombia, Sede Manizales, Manizales (Colombia)], E-mail: adevia@une.net.co

2008-10-15

272

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.

2008-01-01

273

New Measure of the Dissipation Region in Collisionless Magnetic Reconnection  

International Nuclear Information System (INIS)

[en] 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.

2011-05-13

274

Laboratory study of Hall reconnection in partially ionized plasmas.  

UK PubMed Central (United Kingdom)

The effects of partial ionization (n(i) / n(n) ? 1%) on magnetic reconnection in the Hall regime have been studied systematically in the Magnetic Reconnection Experiment. It is shown that, when neutrals are added, the Hall quadrupole field pattern and thus electron flow are unchanged while the ion outflow speed is reduced due to ion-neutral drag. However, in contrast to theoretical predictions, the ion diffusion layer width does not change appreciably. Therefore, the total ion outflow flux and the normalized reconnection rate are reduced.

Lawrence EE; Ji H; Yamada M; Yoo J

2013-01-01

275

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

CERN Document Server

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

Wyper, Peter F

2013-01-01

276

What are the ionospheric signatures of magnetotail reconnection?  

Science.gov (United States)

In a recent case study based on the combined Cluster and Polar PIXIE data we reported that an inverted-V structure caused by a field aligned potential drop of 30 kV producing very strong X-ray aurora was found in connection with tail reconnection. However, the insitu particle measurements by Cluster indicate clearly that the particles responsible for the X-ray aurora were not accelerated by the reconection process. In this paper we report predicted and observed ionospheric signatures of 13 reconnection events where Cluster passed through the reconnection ion diffusion region. For the 6 events where global auroral imaging data were available our results indicate that reconnection is an azimuthally expanding (or extended) process observed along the poleward boundary of the aurora. Furthermore, the ionospheric emissions indicate that there has to be acceleration mechanism in addition to the local acceleration in the ion diffusion region.

Ostgaard, N.; Borg, A. L.; Asnes, A.; Pedersen, A.; Oieroset, M.; Phan, T.; Snekvik, K.

2007-12-01

277

Potential reconnection configurations and flows at Jupiter’s magnetopause  

Science.gov (United States)

We are developing a model at Jupiter based on the Cooling model of reconnected flux tube motion on Earth’s magnetopause. (Cooling et al, JGR 106, 2001) Our model will test for possible reconnection sites at the magnetopause and map the subsequent flux tube motion. We begin this study by mapping out the Khurana magnetic field (which includes a plasma sheet, radial currents, and magnetopause currents) and the draping of the IMF at the magnetopause to test for regions of possible reconnection by considering the relative field orientations. (Khurana and Schwarzl, JGR 110, 2005) We consider the sensitivity of the magnetospheric field to IMF orientation when a Tsyganenko-like model of IMF penetration is included. The model of Stahara and Spreiter is employed to determine the solar wind flow around Jupiter. (Stahara, et al, JGR 94, 1989) With reasonable models of the flows and fields on either side of the magnetopause, we calculate flux tube motion following reconnection.

Desroche, M. J.; Bagenal, F.; Delamere, P. A.

2009-12-01

278

Magnetic Reconnection in Non-Equilibrium Ionization Plasma  

CERN Multimedia

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

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

2011-01-01

279

Analytic Solution of the Approach of Quantum Vortices Towards Reconnection  

Science.gov (United States)

Experimental and simulational studies of the dynamics of vortex reconnections in quantum fluids showed that the distance d between the reconnecting vortices is close to a universal time dependence d=D[?|t0-t|]? with ? fluctuating around 1/2 and ?=h/m is the quantum of circulation. Dimensional analysis, based on the assumption that the quantum of circulation ?=h/m is the only relevant parameter in the problem, predicts ?=1/2. The theoretical calculation of the dimensionless coefficient D in this formula remained an open problem. In this Letter we present an analytic calculation of D in terms of the given geometry of the reconnecting vortices. We start from the numerically observed generic geometry on the way to vortex reconnection and demonstrate that the dynamics is well described by a self-similar analytic solution which provides the wanted information.

Boué, Laurent; Khomenko, Dmytro; L'vov, Victor S.; Procaccia, Itamar

2013-10-01

280

Scaling Law of Relativistic Sweet-Parker Type Magnetic Reconnection  

CERN Document Server

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

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

2011-01-01

 
 
 
 
281

Particle Acceleration in Turbulence and Weakly Stochastic Reconnection  

CERN Multimedia

Fast particles are accelerated in astrophysical environments by a variety of processes. Acceleration in reconnection sites has attracted the attention of researchers recently. In this letter we analyze the energy distribution evolution of test particles injected in three dimensional (3D) magnetohydrodynamic (MHD) simulations of different magnetic reconnection configurations. When considering a single Sweet-Parker topology, the particles accelerate predominantly through a first-order Fermi process, as predicted in previous work (de Gouveia Dal Pino & Lazarian, 2005) and demonstrated numerically in Kowal, de Gouveia Dal Pino & Lazarian (2011). When turbulence is included within the current sheet, the acceleration rate, which depends on the reconnection rate, is highly enhanced. This is because reconnection in the presence of turbulence becomes fast and independent of resistivity (Lazarian & Vishniac, 1999; Kowal et al., 2009) and allows the formation of a thick volume filled with multiple simultaneo...

Kowal, Grzegorz; Lazarian, Alex

2012-01-01

282

From flares to nanoflares: magnetic reconnection on the Sun  

Science.gov (United States)

Peter Cargill discusses the history and current thinking on magnetic reconnection, in the first James Dungey Lecture, which was given in the presence of Jim Dungey himself at the RAS on 11 January 2013.

Cargill, Peter

2013-06-01

283

Extended Magnetic Reconnection across the Dayside Magnetopause  

International Nuclear Information System (INIS)

The extent of where magnetic reconnection (MR), the dominant process responsible for energy and plasma transport into the magnetosphere, operates across Earth's dayside magnetopause has previously been only indirectly shown by observations. We report the first direct evidence of X-line structure resulting from the operation of MR at each of two widely separated locations along the tilted, subsolar line of maximum current on Earth's magnetopause, confirming the operation of MR at two or more sites across the extended region where MR is expected to occur. The evidence results from in-situ observations of the associated ion and electron plasma distributions, present within each magnetic X-line structure, taken by two spacecraft passing through the active MR regions simultaneously.

2011-07-08

284

Fast Magnetic Reconnection and Spontaneous Stochasticity  

CERN Document Server

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

Eyink, Gregory L; Vishniac, Ethan T

2011-01-01

285

Resistive instabilities and field line reconnection  

International Nuclear Information System (INIS)

[en] A review is given of the linear theory of reconnection for a plane current layer. The three basic modes are the Rippling Mode, the Gravitational Interchange Mode, and the Tearing Mode. A derivation is given of the magnetic field energy which provides the driving force for the tearing mode. The necessary concepts for the analysis of tearing modes in cylindrical geometry are introduced. The equations governing tearing mode evolution in a tokamak are expanded to lowest order in the inverse aspect ratio. The tearing mode in a toroidal device is closely related to the ideal magnetohydrodynamic kink mode, and this relationship is stressed in the derivations of the linear growth rates for modes with poloidal model number m > 2 and for the quite different m = 1 mode. The nonlinear theory of tearing mode development and the implications of this theory for the understanding of toroidal magnetic confinement devices is reviewed

1980-01-01

286

Resistive instabilities and field line reconnection  

Energy Technology Data Exchange (ETDEWEB)

A review is given of the linear theory of reconnection for a plane current layer. The three basic modes are the Rippling Mode, the Gravitational Interchange Mode, and the Tearing Mode. A derivation is given of the magnetic field energy which provides the driving force for the tearing mode. The necessary concepts for the analysis of tearing modes in cylindrical geometry are introduced. The equations governing tearing mode evolution in a tokamak are expanded to lowest order in the inverse aspect ratio. The tearing mode in a toroidal device is closely related to the ideal magnetohydrodynamic kink mode, and this relationship is stressed in the derivations of the linear growth rates for modes with poloidal model number m > 2 and for the quite different m = 1 mode. The nonlinear theory of tearing mode development and the implications of this theory for the understanding of toroidal magnetic confinement devices is reviewed.

White, R.B.

1980-05-01

287

Fluid and particle signatures of dayside reconnection  

Directory of Open Access Journals (Sweden)

Full Text Available Using measurements of the AMPTE/IRM spacecraft, we study reconnection signatures at the dayside magnetopause. If the magnetopause is open, it should have the properties of a rotational discontinuity. Applying the fluid concept of a rotational discontinuity, we check for the existence of a de Hoffmann-Teller frame and the tangential stress balance (Walén relation). For 13 out of 40 magnetopause crossings in a statistical survey we find a reasonable agreement between observed plasma flows and those predicted by the Walén relation. In addition, we check if the measured distribution functions show single particle signatures which are expected on open field lines. We find the following types of signatures: field-aligned streaming of ring current particles, "D-shaped" distributions of solar wind particles, counterstreaming of solar wind and cold ionospheric ions, two-beam distributions of solar wind ions, and distributions of solar wind particles associated with field-aligned heat flux. While a particular type of particle signature is observed only for the minority of magnetopause crossings, 24 of the 40 crossings show at least one type of signature. Both the particle signatures and the fit to the Walén relation can be used to infer the sign of the normal magnetic field, Bn. We find that the two ways of inferring the sign of Bn lead primarily to the same result. Thus, both the particle signatures and a reasonable agreement with the Walén  relation can, in a statistical sense, be considered as a useful indicator of open field lines. On the other hand, many crossings do not show any reconnection signatures. We discuss the possible reasons for their absence.Key words. Magnetopause, cusp and boundary layers; magnetosheath; solar wind – magnetosphere interactions

T. M. Bauer; G. Paschmann; N. Sckopke; R. A. Treumann; W. Baumjohann; T.-D. Phan

0000-01-01

288

Fluid and Magnetofluid Modeling of Relativistic Magnetic Reconnection  

CERN Multimedia

The fluid-scale evolution of relativistic magnetic reconnection is investigated by using two-fluid and magnetofluid simulation models. Relativistic two-fluid simulations demonstrate the meso-scale evolution beyond the kinetic scales, and exhibit quasi-steady Petschek-type reconnection. Resistive relativistic MHD simulations further show new shock structures in and around the downstream magnetic island (plasmoid). These structures will be ubiquitous in both relativistic and nonrelativistic regimes.

Zenitani, Seiji; Klimas, Alex

2011-01-01

289

Low frequency Whistler waves excited in fast magnetic reconnection processes  

Science.gov (United States)

Whistler waves generated in fast magnetic reconnection processes of collisionless high beta plasmas are reviewed in experiments and satellite observations, as well as in theory and simulation, and further studied in the two-fluid theory. It is found that low frequency whistler waves can be excited in the ion inertial range of the reconnection region. The wave is found right-handed polarized with a quadrupolar out-of-plane magnetic perturbation, in accord with satellite observations in the geomagnetosphere.

Wang, Xiao-Gang; Luan, Qi-Bin

2013-08-01

290

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

2008-01-01

291

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

Energy Technology Data Exchange (ETDEWEB)

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

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

2008-12-03

292

The Dimensions of Place Meanings  

Directory of Open Access Journals (Sweden)

Full Text Available This article aims to give an overview of how place meanings are created and how they influence people's sense of belonging. It should be noted that the current literature has various shortcomings which mostly result from the lack of interdisciplinary research. The studies in place attachment usually focus on personal sense of belonging leaving aside those extending over various scales -- such as, for instance, national identity. Also, place meanings and identity are primarily discussed as the very personal phenomena. On the contrary, place making and shaping is usually seen through more structural viewpoint by claiming that places mainly change in result of political or economic processes. Nowadays, there are even claims that due to the influx of globalization place no more matters and similar processes will happen everywhere. This notion does not take into account the special character of every place and the fact that outside forces come together in different ways in every place. Authors suggest that these different perspectives need to be united in order to fully grasp the character of place making and place meanings. In current articles, authors have adopted the multi-disciplinary approach and understood the place as uniting different processes starting from deeply personal meaning creation and ending with changes happening in global scale.

Hannes Palang; Maarja Saar

2009-01-01

293

Take back needs logistics  

Energy Technology Data Exchange (ETDEWEB)

In order to establish effective take back systems in industrialized countries an area-wide logistic network for the redistribution of used (electronic) products will be necessary. Today the logistic costs present up to 70% of the total recycling costs - and consequently logistics is important in the realization of sustainable policy and recycling. The development of logistic solutions for the redistribution of products using existing chains of distribution, channels to be newly established, or other ones already existing, taking into account all technical and organizational components, one has to consider that varying quantity flows, branchings and combinations of the material flow have to take place in the recycling process for the quantity flow of the production from raw material suppliers via supplier to the manufacturer. This also requires the development of networks for a systematic information flow from the recycling process back to the construction of recycling-based products as well as for the information from the construction to the product recycling - e.g. working plans for dismantling, lists of parts containing hazardous substances, certificates on the further use of components, etc. (orig.)

Hansen, U. [Univ. of Applied Sciences RheinAhrCampus, Remagen (Germany)

2004-07-01

294

The location of reconnection at the magnetopause: Testing the maximum magnetic shear model with THEMIS observations  

Science.gov (United States)

Reconnection at the Earth's magnetopause is the mechanism by which magnetic fields in different regions change topology to create open magnetic field lines that allow energy and momentum to flow into the magnetosphere. One of the long-standing open questions about magnetic reconnection is the location of the reconnection line. There are two reconnection scenarios discussed in the literature: (1) antiparallel reconnection where shear angles between the magnetospheric field and the interplanetary magnetic field (IMF) are near 180° and (2) component reconnection where a tilted reconnection line which crosses the magnetopause in the subsolar region at shear angles not near 180°. Early satellite observations were limited to the detection of accelerated ion beams in the magnetopause boundary layer to determine the general direction of the reconnection line location with respect to the satellite. An improved view of the reconnection location at the magnetopause was determined from ionospheric emissions observed by polar-orbiting imagers which revealed that both scenarios occur. The time-of-flight effect of precipitating ions in the cusp in connection with the low-velocity cutoff method pinpointed reconnection locations and their dependency on IMF conditions. These results are summarized by the maximum magnetic shear model. This study uses confirmed magnetic reconnection locations from the THEMIS mission to test the predictions of this reconnection location model. The results reveal that the maximum magnetic shear model predicts the observed reconnection locations for dominant IMF BY conditions very well but needs further improvement and modifications for dominant southward IMF conditions.

Trattner, K. J.; Petrinec, S. M.; Fuselier, S. A.; Phan, T. D.

2012-01-01

295

Fermi Acceleration in Plasmoids interacting with Fast Shocks of Reconnection via Fractal Reconnection  

CERN Document Server

We propose the particle acceleration model coupled with multiple plasmoid ejections in a solar flare. Unsteady reconnection produces plasmoids in a current sheet and ejects them out to the fast shocks, where particles in a plasmoid are reflected upstream the shock front by magnetic mirror effect. As the plasmoid passes through the shock front, the reflection distance becomes shorter and shorter driving Fermi acceleration, until it becomes proton Larmor radius. The fractal distribution of plasmoids may also have a role in naturally explaining the power-law spectrum in nonthermal emissions.

Nishizuka, N

2013-01-01

296

Fermi acceleration in plasmoids interacting with fast shocks of reconnection via fractal reconnection.  

UK PubMed Central (United Kingdom)

We propose the particle acceleration model coupled with multiple plasmoid ejections in a solar flare. Unsteady reconnection produces plasmoids in a current sheet and ejects them out to the fast shocks, where particles in a plasmoid are reflected upstream the shock front by magnetic mirror effect. As the plasmoid passes through the shock front, the reflection distance becomes shorter and shorter driving Fermi acceleration, until it becomes proton Larmor radius. The fractal distribution of plasmoids may also have a role in naturally explaining the power-law spectrum in nonthermal emissions.

Nishizuka N; Shibata K

2013-02-01

297

Fermi acceleration in plasmoids interacting with fast shocks of reconnection via fractal reconnection.  

Science.gov (United States)

We propose the particle acceleration model coupled with multiple plasmoid ejections in a solar flare. Unsteady reconnection produces plasmoids in a current sheet and ejects them out to the fast shocks, where particles in a plasmoid are reflected upstream the shock front by magnetic mirror effect. As the plasmoid passes through the shock front, the reflection distance becomes shorter and shorter driving Fermi acceleration, until it becomes proton Larmor radius. The fractal distribution of plasmoids may also have a role in naturally explaining the power-law spectrum in nonthermal emissions. PMID:23414011

Nishizuka, Naoto; Shibata, Kazunari

2013-01-30

298

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.

299

Reconnection-Driven Alfven (RDA) Waves in the Solar Corona  

Science.gov (United States)

The mechanisms for heating the corona and accelerating the solar wind remain active areas of solar and heliospheric research. Currently, two relatively distinct paradigms confront these problems: a waves/turbulence paradigm, and a magnetic reconnection/dissipation paradigm. The fact that magnetic reconnection generates Alfvén waves suggests that the heating of the low-beta corona and the acceleration of the wind are likely the result of both paradigms operating simultaneously. This research aims to unify the two competing viewpoints. We present 3D MHD simulations of magnetic reconnection/dissipation processes in the solar corona that provide a self-consistent mechanism for producing the energy injection spectrum required by the waves/turbulence paradigm. We analyze the simulations to quantify the amount of magnetic energy released in the reconnection process and the material and energy fluxes carried by large-amplitude, nonlinear, reconnection-driven Alfvén (RDA) waves. In addition to isolating the RDA waves, characterizing their physical properties, and investigating their evolution in a low-beta, gravitationally stratified model corona, we examine their time-dependent material and energy outflows and discuss their observable consequences in the corona and inner heliosphere.

Edmondson, J. K.; Lynch, B. J.; DeVore, C. R.; Velli, M.

2011-12-01

300

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

 
 
 
 
301

Time-dependent localized reconnection of skewed magnetic fields  

International Nuclear Information System (INIS)

The authors describe and analyze a model for time-varying, localized reconnection in a current sheet with skewed magnetic field orientations on opposite sides. As in Petschek's description, disruption is initiated in a localized part of the current sheet known as the diffusion region, and the disturbances are subsequently propagated into the system at large through magnetohydrodynamic (MHD) waves. The MHD waves therefore play the dominant role in energy conversion, and collectively they form an outflow for plasma streaming toward the current sheet and a field reversal region joining magnetic field lines from opposite sides. They restrict the analysis to an incompressible plasma, in which case the Alfven wave and the slow shock merge to form shocks bounding the field reversal or outflow region, and the case of weak reconnection, which implies that the reconnection electric field is much smaller than the product of the characteristic values of the external field strength and Alfven speed. Reconnection also acts as a source of surface waves, and their analysis determines the behavior of the perpendicular field and flow components and the shape of the shocks. Lastly, the field reversal region can be considered as a thin boundary layer in the treatment, and the external disturbances can therefore be solved in a way similar to the flow around a thin aerofoil. The model presented here can be applied to the Earth's magnetopause, where reconnection is considered to be the dominant process coupling the solar wind and the magnetosphere.

1992-01-01

302

Observations of significant flux closure by dual lobe reconnection  

Directory of Open Access Journals (Sweden)

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

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

2007-01-01

303

Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate  

International Nuclear Information System (INIS)

A physical mechanism of flares, in particular for the flare rise phase, has emerged from our 2-1/2-dimensional resistive MHD simulations. The dynamical evolution of current-sheet formation and magnetic reconnection and flux-rope acceleration subject to continuous, slow increase of magnetic shear in the arcade are studied by employing a non-uniform anomalous resistivity in the reconnecting current sheet under gravity. The simulation results directly relate the flux rope's accelerated rising motion with an enhanced magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. The simulation results provide good quantitative agreements with observations of the acceleration of flux rope, which manifests in the form of SXR ejecta or erupting filament or CMEs, in the low corona. Moreover, for the X-class flare events studied in this paper the peak reconnection electric field is about O(102 V/m) or larger, enough to accelerate p articles to over 100 keV in a field-aligned distance of 10 km. Nonthermal electrons thus generated can produce hard X-rays, consistent with impulsive HXR emission observed during the flare rise phase

2003-01-01

304

Flux Rope Acceleration and Enhanced Magnetic Reconnection Rate  

Energy Technology Data Exchange (ETDEWEB)

A physical mechanism of flares, in particular for the flare rise phase, has emerged from our 2-1/2-dimensional resistive MHD simulations. The dynamical evolution of current-sheet formation and magnetic reconnection and flux-rope acceleration subject to continuous, slow increase of magnetic shear in the arcade are studied by employing a non-uniform anomalous resistivity in the reconnecting current sheet under gravity. The simulation results directly relate the flux rope's accelerated rising motion with an enhanced magnetic reconnection rate and thus an enhanced reconnection electric field in the current sheet during the flare rise phase. The simulation results provide good quantitative agreements with observations of the acceleration of flux rope, which manifests in the form of SXR ejecta or erupting filament or CMEs, in the low corona. Moreover, for the X-class flare events studied in this paper the peak reconnection electric field is about O(10{sup 2} V/m) or larger, enough to accelerate p articles to over 100 keV in a field-aligned distance of 10 km. Nonthermal electrons thus generated can produce hard X-rays, consistent with impulsive HXR emission observed during the flare rise phase.

C.Z. Cheng; Y. Ren; G.S. Choe; Y.-J. Moon

2003-03-25

305

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

306

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.

2005-01-01

307

Place cells and place?navigation  

Digital Repository Infrastructure Vision for European Research (DRIVER)

The assumption that hippocampal place cells (PCs) form the neural substrate of cognitive maps can be experimentally tested by comparing the effect of experimental interventions on PC activity and place navigation. Conditions that interfere with place navigation (darkness, cholinergic blockade) but l...

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

308

Numerical simulations of magnetic reconnection in the lower solar atmosphere  

International Nuclear Information System (INIS)

Observations indicate that Ellerman bombs (EBs) and chromospheric microflares both occur in the lower solar atmosphere, and share many common features, such as temperature enhancements, accompanying jet-like mass motions, short lifetime, and so on. These strongly suggest that EBs and chromospheric microflares could both probably be induced by magnetic reconnection in the lower solar atmosphere. With gravity, ionization and radiation considered, we perform two-dimensional numerical simulations of magnetic reconnection in the lower solar atmosphere. The influence of different parameters, such as intensity of the magnetic field and anomalous resistivity, on the results are investigated. Our result demonstrates that the temperature increases are mainly due to the joule dissipation caused by magnetic reconnection. The spectral profiles of EBs and chromospheric microflares are calculated with the non-LTE radiative transfer theory and compared with observations. It is found that the typical features of the two phenomena can be qualitatively reproduced.

2011-01-01

309

Collisionless magnetic reconnection associated with coalescence of flux bundles  

International Nuclear Information System (INIS)

[en] 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)

1994-01-01

310

Kelvin-wave turbulence generated by vortex reconnections  

CERN Multimedia

Reconnections of quantum vortex filaments create sharp bends which degenerate into propagating Kelvin waves. These waves cascade their energy down-scale and their waveaction up-scale via weakly nonlinear interactions, and this is the main mechanism of turbulence at the scales less than the inter-vortex distance. In case of an idealised forcing concentrated around a single scale k0, the turbulence spectrum exponent has a pure direct cascade form -17/5 at scales k>k0 and a pure inverse cascade form -3 at kreconnections contains a broad range of Fourier modes. What scaling should one expect in this case? In this Letter I obtain an answer to this question using the differential model for the Kelvin wave turbulence. The main result is that the direct cascade scaling dominates, i.e. the reconnection forcing is more or less equivalent to a low-frequency forcing.

Nazarenko, S

2006-01-01

311

A new paradigm for 3D collisionless magnetic reconnection  

International Nuclear Information System (INIS)

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

2002-01-01

312

Solar Particle Acceleration at Reconnecting 3D Null Points  

CERN Multimedia

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

313

Numerical simulation of a magnetic reconnection in the solar corona  

International Nuclear Information System (INIS)

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

1990-01-01

314

Relativistic Magnetic Reconnection in Pair Plasmas in Three Dimensions  

CERN Document Server

We investigate guide-field magnetic reconnection and particle acceleration in relativistic pair plasmas with three-dimensional particle-in-cell (PIC) simulations of a kinetic-scale current sheet in a periodic geometry at low magnetizations. The tearing instability is the dominant mode in the current sheet for all guide field strengths, while the linear kink mode is less important even without guide field. Oblique modes seem to be suppressed entirely. In its nonlinear evolution, the reconnection layer develops a network of interconnected and interacting magnetic flux ropes. As smaller flux ropes merge into larger ones, the reconnection layer evolves toward a three-dimensional, disordered state in which the resulting flux rope segments contain magnetic substructure on plasma skin depth scales. Embedded in the flux ropes, we detect spatially and temporally intermittent sites of dissipation reflected in peaks in the parallel electric field. Magnetic dissipation and particle acceleration persist until the end of t...

Kagan, Daniel; Spitkovsky, Anatoly

2012-01-01

315

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 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.

2010-08-01

316

Energy partition in magnetic reconnection in Earth's magnetotail.  

UK PubMed Central (United Kingdom)

The partition of energy flux in magnetic reconnection is examined experimentally using Cluster satellite observations of collisionless reconnection in Earth's magnetotail. In this plasma regime, the dominant component of the energy flux is ion enthalpy flux, with smaller contributions from the electron enthalpy and heat flux and the ion kinetic energy flux. However, the Poynting flux is not negligible, and in certain parts of the ion diffusion region the Poynting flux in fact dominates. Evidence for earthward-tailward asymmetry is ascribed to the presence of Earth's dipole fields.

Eastwood JP; Phan TD; Drake JF; Shay MA; Borg AL; Lavraud B; Taylor MG

2013-05-01

317

Color Reconnection and Flowlike Patterns in pp Collisions.  

UK PubMed Central (United Kingdom)

Increasingly, with the data collected at the LHC we are confronted with the possible existence of flow in pp collisions. In this work, we show that PYTHIA 8 produces flowlike effects in events with multiple hard subcollisions due to color string formations between final partons from independent hard scatterings, the so-called color reconnection. We present studies of different identified hadron observables in pp collisions at 7 TeV. Studies have been done both for minimum bias and multiplicity intervals in events with and without color reconnection to isolate the flowlike effect.

Ortiz Velasquez A; Christiansen P; Cuautle Flores E; Maldonado Cervantes IA; Pai? G

2013-07-01

318

Color Reconnection and Flowlike Patterns in pp Collisions.  

Science.gov (United States)

Increasingly, with the data collected at the LHC we are confronted with the possible existence of flow in pp collisions. In this work, we show that PYTHIA 8 produces flowlike effects in events with multiple hard subcollisions due to color string formations between final partons from independent hard scatterings, the so-called color reconnection. We present studies of different identified hadron observables in pp collisions at 7 TeV. Studies have been done both for minimum bias and multiplicity intervals in events with and without color reconnection to isolate the flowlike effect. PMID:23931356

Ortiz Velasquez, A; Christiansen, P; Cuautle Flores, E; Maldonado Cervantes, I A; Pai?, G

2013-07-22

319

Fast magnetic reconnection in the plasmoid-dominated regime.  

Science.gov (United States)

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. PMID:21231473

Uzdensky, D A; Loureiro, N F; Schekochihin, A A

2010-12-01

320

Plasmoid-induced turbulence in collisionless magnetic reconnection.  

Science.gov (United States)

The dissipation mechanism in collisionless magnetic reconnection in a quasisteady period is investigated for the antiparallel field configuration. A three-dimensional simulation in a fully kinetic system reveals that a current-aligned electromagnetic mode produces turbulent electron flow that facilitates the transport of the momentum responsible for the current density. It is found that the electromagnetic turbulence is drastically enhanced by plasmoid formations and has a significant impact on the dissipation at the magnetic x-line. The linear analyses confirm that the mode survives in the real ion-to-electron mass ratio, which assures the importance of the turbulence in collisionless reconnection. PMID:23368574

Fujimoto, Keizo; Sydora, Richard D

2012-12-28

 
 
 
 
321

Plasmoid-induced turbulence in collisionless magnetic reconnection.  

UK PubMed Central (United Kingdom)

The dissipation mechanism in collisionless magnetic reconnection in a quasisteady period is investigated for the antiparallel field configuration. A three-dimensional simulation in a fully kinetic system reveals that a current-aligned electromagnetic mode produces turbulent electron flow that facilitates the transport of the momentum responsible for the current density. It is found that the electromagnetic turbulence is drastically enhanced by plasmoid formations and has a significant impact on the dissipation at the magnetic x-line. The linear analyses confirm that the mode survives in the real ion-to-electron mass ratio, which assures the importance of the turbulence in collisionless reconnection.

Fujimoto K; Sydora RD

2012-12-01

322

Fast magnetic reconnection in the plasmoid-dominated regime  

CERN Multimedia

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 magnetohydrodynamic to collisionless regime is provided.

Uzdensky, D A; Schekochihin, A A

2010-01-01

323

Fast Magnetic Reconnection in the Plasmoid-Dominated Regime  

International Nuclear Information System (INIS)

[en] 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.

2010-12-03

324

Fast magnetic reconnection in the plasmoid-dominated regime.  

UK PubMed Central (United Kingdom)

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.

Uzdensky DA; Loureiro NF; Schekochihin AA

2010-12-01

325

Measurement of the Transverse Spitzer Resistivity during Collisional Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

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.

Trintchouk, F.; Yamada, M.; Ji, H.; Kulsrud, R.M.; Carter, T.A.

2000-09-18

326

Solar Flares as Cascades of Reconnecting Magnetic Loops  

CERN Multimedia

A model for the solar coronal magnetic field is proposed where multiple directed loops evolve in space and time. Loops injected at small scales are anchored by footpoints of opposite polarity moving randomly on a surface. Nearby footpoints of the same polarity aggregate, and loops can reconnect when they collide. This may trigger a cascade of further reconnection, representing a solar flare. Numerical simulations show that a power law distribution of flare energies emerges, associated with a scale free network of loops, indicating self-organized criticality.

Hughes, D; Dendy, R O; Helander, P; McClements, K G

2003-01-01

327

Color reconnection and flowlike patterns in pp collisions.  

UK PubMed Central (United Kingdom)

Increasingly, with the data collected at the LHC we are confronted with the possible existence of flow in pp collisions. In this work, we show that PYTHIA 8 produces flowlike effects in events with multiple hard subcollisions due to color string formations between final partons from independent hard scatterings, the so-called color reconnection. We present studies of different identified hadron observables in pp collisions at 7 TeV. Studies have been done both for minimum bias and multiplicity intervals in events with and without color reconnection to isolate the flowlike effect.

Ortiz Velasquez A; Christiansen P; Cuautle Flores E; Maldonado Cervantes IA; Pai? G

2013-07-01

328

Color reconnection and flow-like patterns in pp collisions  

CERN Multimedia

Increasingly, with the data collected at the LHC we are confronted with the possible existence of flow in pp collisions. In this work we show that PYTHIA 8 produces flow-like effects in events with multiple hard subcollisions due to color string formations between final partons from independent hard scatterings, the so called color reconnection. We present studies of different identified hadron observables in pp collisions at 7 TeV with the tune 4C. Studies have been done both for minimum bias and multiplicity intervals in events with and without color reconnection to isolate the flow like effect.

Ortiz, Antonio; Cuautle, Eleazar; Maldonado, Ivonne; Paic, Guy

2013-01-01

329

The origin of collisionless dissipation in magnetic reconnection  

International Nuclear Information System (INIS)

The mechanism of collisionless reconnection in magnetized plasmas is studied in terms of coalescence of two flux tubes using implicit particle simulation. The motional electric field resulting from magnetic attraction generates the non-MHD (magneto-hydrodynamic), scalar electrical potential of a quadrupole configuration across the x-point. This electric field transports the plasma and magnetic flux into and out of the diffusion layer, and also accelerates the finite mass electrons to produce the current Jparallel along the helical magnetic field. These processes provide equivalent dissipation which makes magnetic reconnection possible in collisionless magnetized plasmas. (author).

1993-01-01

330

Magnetic topologies of coronal mass ejection events: Effects of 3-dimensional reconnection  

Energy Technology Data Exchange (ETDEWEB)

New magnetic loops formed in the corona following coronal mass ejection, CME, liftoffs provide strong evidence that magnetic reconnection commonly occurs within the magnetic ``legs`` of the departing CMEs. Such reconnection is inherently 3-dimensional and naturally produces CMEs having magnetic flux rope topologies. Sustained reconnection behind CMEs can produce a mixture of open and disconnected field lines threading the CMES. In contrast to the results of 2-dimensional reconnection. the disconnected field lines are attached to the outer heliosphere at both ends. A variety of solar and solar wind observations are consistent with the concept of sustained 3-dimensional reconnection within the magnetic legs of CMEs close to the Sun.

Gosling, J.T.

1995-09-01

331

Reconnection at three dimensional magnetic null points: Effect of current sheet asymmetry  

Science.gov (United States)

Asymmetric current sheets are likely to be prevalent in both astrophysical and laboratory plasmas with complex three dimensional (3D) magnetic topologies. This work presents kinematic analytical models for spine and fan reconnection at a radially symmetric 3D null (i.e., a null where the eigenvalues associated with the fan plane are equal) with asymmetric current sheets. Asymmetric fan reconnection is characterized by an asymmetric reconnection of flux past each spine line and a bulk flow of plasma across the null point. In contrast, asymmetric spine reconnection is characterized by the reconnection of an equal quantity of flux across the fan plane in both directions. The higher modes of spine reconnection also include localized wedges of vortical flux transport in each half of the fan. In this situation, two definitions for reconnection rate become appropriate: a local reconnection rate quantifying how much flux is genuinely reconnected across the fan plane and a global rate associated with the net flux driven across each semi-plane. Through a scaling analysis, it is shown that when the ohmic dissipation in the layer is assumed to be constant, the increase in the local rate bleeds from the global rate as the sheet deformation is increased. Both models suggest that asymmetry in the current sheet dimensions will have a profound effect on the reconnection rate and manner of flux transport in reconnection involving 3D nulls.

Wyper, P. F.; Jain, Rekha

2013-05-01

332

Magnetic flux transport in the Dungey cycle: A survey of dayside and nightside reconnection rates  

Science.gov (United States)

Changes in the open flux content of the ionospheric polar cap, estimated from auroral, radar, and low-Earth orbit particle measurements, are used to determine dayside and nightside reconnection rates during 73 hours of observation spread over nine intervals. We identify 25 episodes of nightside reconnection and examine statistically the rates and durations of reconnection, as well as possible triggers for the onset of reconnection, such as changes in solar wind ram pressure or orientation of the interplanetary magnetic field. Approximately half of the events can possibly be identified with a trigger, the other half appearing spontaneous. On average 0.3 GWb of open flux are closed in each event, with average durations and reconnection rates being 70 min and 85 kV. We find no evidence for a low background rate of nightside reconnection between these events and conclude that substorms and other large reconnection bursts provide the major or only source of flux closure on the nightside.

Milan, S. E.; Provan, G.; Hubert, B.

2007-01-01

333

Placing Dental Implants  

Science.gov (United States)

Placing Dental Implants Before Placing an Implant Placing the Implants Complications from Surgery Implant Failure When you get implants, more than one dental professional may treat you. An oral surgeon, periodontist ...

334

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; D. Korovinskiy; A. Divin; N. Erkaev; H. Biernat

2009-01-01

335

Is null-point reconnection important for solar flux emergence?  

CERN Multimedia

The role of null-point reconnection in a 3D numerical MHD model of solar emerging flux is investigated. The model consists of a twisted magnetic flux tube rising through a stratified convection zone and atmosphere to interact and reconnect with a horizontal overlying magnetic field in the atmosphere. Null points appear as the reconnection begins and persist throughout the rest of the emergence, where they can be found mostly in the model photosphere and transition region, forming two loose clusters on either side of the emerging flux tube. Up to 26 nulls are present at any one time, and tracking in time shows that there is a total of 305 overall, despite the initial simplicity of the magnetic field configuration. We find evidence for the reality of the nulls in terms of their methods of creation and destruction, their balance of signs, their long lifetimes, and their geometrical stability. We then show that due to the low parallel electric fields associated with the nulls, null-point reconnection is not the m...

Maclean, R C; Galsgaard, K

2009-01-01

336

Colour Annealing - a Toy Model of Colour Reconnections.  

Science.gov (United States)

We present a simple toy model for colour reconnections at the nonperturbative level. The model resembles an annealing-type algorithm and is applicable to any collider and process type, though we argue for a possible enhancement of the effect in hadron-had...

M. Sandhoff P. Skands

2005-01-01

337

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; R. Nakamura; A. Runov; H. Rème; E. A. Lucek

2007-01-01

338

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

339

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

340

Particle acceleration from reconnection in the geomagnetic tail  

Energy Technology Data Exchange (ETDEWEB)

Acceleration of charged particles in the near geomagnetic tail, associated with a dynamic magnetic reconnection process, was investigated by a combined effort of data analysis, using Los Alamos data from geosynchronous orbit, MHD modeling of the dynamic evolution of the magnetotail, and test particle tracing in the electric and magnetic fields obtained from the MHD simulation.

Birn, J.; Borovsky, J.E.; Thomsen, M.F.; McComas, D.J.; Reeves, G.D.; Belian, R.D. [Los Alamos National Lab., NM (United States); Hesse, M. [National Aeronautics and Space Administration, Greenbelt, MD (United States). Goddard Space Flight Center; Schindler, K. [Ruhr-Univ., Bochum (Germany)

1997-08-01

 
 
 
 
341

Predicted signatures of pulsed reconnection in ESR data  

Directory of Open Access Journals (Sweden)

Full Text Available Early in 1996, the latest of the European incoherent-scatter (EISCAT) radars came into operation on the Svalbard islands. The EISCAT Svalbard Radar (ESR) has been built in order to study the ionosphere in the northern polar cap and in particular, the dayside cusp. Conditions in the upper atmosphere in the cusp region are complex, with magnetosheath plasma cascading freely into the atmosphere along open magnetic field lines as a result of magnetic reconnection at the dayside magnetopause. A model has been developed to predict the effects of pulsed reconnection and the subsequent cusp precipitation in the ionosphere. Using this model we have successfully recreated some of the major features seen in photometer and satellite data within the cusp. In this paper, the work is extended to predict the signatures of pulsed reconnection in ESR data when the radar is pointed along the magnetic field. It is expected that enhancements in both electron concentration and electron temperature will be observed. Whether these enhancements are continuous in time or occur as a series of separate events is shown to depend critically on where the open/closed field-line boundary is with respect to the radar. This is shown to be particularly true when reconnection pulses are superposed on a steady background rate.

C. J. Davis; M. Lockwood

0000-01-01

342

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).

1983-01-01

343

Conditions for substorm onset by the fast reconnection mechanism  

Directory of Open Access Journals (Sweden)

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

2008-01-01

344

Energy release and conversion by reconnection in the magnetotail  

Directory of Open Access Journals (Sweden)

Full Text Available Magnetic reconnection is the crucial process in the release of magnetic energy previously stored in the magnetotail in association with substorms. However, energy transfer and dissipation in the vicinity of the reconnection site is only a minor part of the energy conversion. We discuss the energy release, transport, and conversion based on large-scale resistive MHD simulations of magnetotail dynamics and more localized full particle simulations of reconnection. We address in particular, where the energy is released, how it propagates and where and how it is converted from one form into another. We find that Joule (or ohmic) dissipation plays only a minor role in the overall energy transfer. Bulk kinetic energy, although locally significant in the outflow from the reconnection site, plays a more important role as mediator or catalyst in the transfer between magnetic and thermal energy. Generator regions with potential auroral consequences are located primarily off the equatorial plane in the boundary regions of the plasma sheet.

J. Birn; M. Hesse

2005-01-01

345

Conditions for substorm onset by the fast reconnection mechanism  

Science.gov (United States)

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.

Ugai, M.

2008-12-01

346

Generalised models for torsional spine and fan magnetic reconnection  

CERN Document Server

Three-dimensional null points are present in abundance in the solar corona, and the same is likely to be true in other astrophysical environments. Recent studies suggest that reconnection at such 3D nulls may play an important role in the coronal dynamics. In this paper the properties of the torsional spine and torsional fan modes of magnetic reconnection at 3D nulls are investigated. New analytical models are developed, which for the first time include a current layer that is spatially localised around the null, extending along either the spine or the fan of the null. These are complemented with numerical simulations. The principal aim is to investigate the effect of varying the degree of asymmetry of the null point magnetic field on the resulting reconnection process - where previous studies always considered a non-generic radially symmetric null. The geometry of the current layers within which torsional spine and torsional fan reconnection occur is found to be strongly dependent on the symmetry of the magn...

Pontin, D I; Galsgaard, K

2011-01-01

347

Interchange Slip-Running Reconnection and Sweeping SEP Beams  

CERN Multimedia

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

348

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

349

The Theory of Magnetic Reconnection: Past, Present, and Future  

Science.gov (United States)

Magnetic reconnection underlies the energy release observed in eruptive events in the solar corona (such as solar flares and coronal mass ejections) and in the Earth's magnetosphere. The theory of magnetic reconnection was originally developed to understand observations by Ron Giovanelli, who discovered that solar flares occur where the coronal magnetic field changes directions. Pioneers in space plasma theory such as James Dungey, Peter Sweet, Eugene Parker, and Harry Petschek first elucidated the underlying physical effects that lead to this massive energy release. Since then, much effort has been made to understand what process or processes cause magnetic reconnection to be fast enough to be consistent with observations, such as anomalous resistivity, secondary instabilities, and the Hall effect. However, a thorough understanding of this important process remains a topic of intense study. In celebration of the 50th anniversary of Parker's paper predicting the high-speed solar wind, this talk will review the history of the theory of magnetic reconnection. The present status of the field will be discussed, and remaining unanswered questions will be summarized.

Cassak, P. A.

2008-05-01

350

MESSENGER Observations of Magnetic Reconnection in Mercury's Magnetosphere  

Science.gov (United States)

During MESSENGER's second flyby of Mercury on October 6, 2008, very intense reconnection was observed between the planet's magnetic field and a steady southward interplanetary magnetic field (IMF). The dawn magnetopause was threaded by a strong magnetic field normal to its surface, 14 nT, that implies a rate of reconnection 10 times the typical rate at Earth and a cross-magnetospheric electric potential drop of 30 kV. The highest magnetic field observed during this second flyby, 160 nT, was found at the core of a large dayside flux transfer event (FTE). This FTE is estimated to contain magnetic flux equal to 5% that of Mercury's magnetic tail or approximately one order of magnitude higher fraction of the tail flux than is typically found for FTEs at Earth. Plasmoid and traveling compression region (TCR) signatures were observed throughout MESSENGER's traversal of Mercury's magnetotail with a repetition rate comparable to the Dungey cycle time of 2 min. The TCR signatures changed from south-north, indicating tailward motion, to north-south, indicating sunward motion, at a distance 2.6 RM (where RM is Mercury's radius) behind the terminator indicating that the near-Mercury magnetotail neutral line was crossed at that point. Overall, these new MESSENGER observations suggest that magnetic reconnection at the dayside magnetopause is very intense relative to what is found at Earth and other planets, while reconnection in Mercury's tail is similar to that in other planetary magnetospheres, but with a very short Dungey cycle time.

Slavin, J. A.; Acuna, M. H.; Anderson, B. J.; Baker, D. N.; Boardsen, S. A.; Korth, H.; Krimigis, S. M.; McNutt, R. L., Jr.; Solomon, S. C.; Zurbuchen, T. H.

2009-04-01

351

Conditions for fast magnetic reconnection in astrophysical plasmas  

Digital Repository Infrastructure Vision for European Research (DRIVER)

We investigate favourable circumstances for fast magnetic reconnection in astrophysical plasmas based on recent results by Rogers et al. (2001). Given that a critical magnetic field structure with antiparallel field lines exists, our analysis demonstrates that a sufficient condition for fast reconne...

Hanasz, Micha?; Lesch, Harald

352

Field line topology determined by energetic particles during a possible magnetopause reconnection event  

International Nuclear Information System (INIS)

The September 8, 1978, crossing of the magnetopause by ISEE 1 and 2 has been studied in the light of energetic ion and electron data in order to derive the magnetic field topology. The plasma and magnetic field observations during this crossing provided evidence for the occurrence of plasma acceleration intrinsic to reconnection between interplanetary and magnetospheric magnetic field lines. The energetic particle observations result in two different pictures of the open and closed field lines within the magnetosphere, depending on either the ion or electron observations. According to the ion measurements, the high-speed flow can be placed exclusively on open field lines. The electrons, however, exhibit trapped distributions during these times. This apparent dilemma can be resolved by invoking magnetic mirroring of the electrons off the increased magnetosheath field, as shown in a companion paper by Daly and Fritz (1982)

1982-08-01

353

Stress at Work Place  

Directory of Open Access Journals (Sweden)

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

Mohammad A. Shahrour

2010-01-01

354

Sondrestrom radar measurements of the reconnection electric field  

International Nuclear Information System (INIS)

Solar wind energy is transferred to and from the closed field line region of the magnetosphere by transport across the boundary between open and closed field lines (the separatrix). The rate of this transfer is measured by the reconnection electric field, which is tangential to the separatrix. Although it is not possible to measure directly the reconnection electric field in the magnetosphere, the electric field in the ionosphere can readily be used to calculate the magnetic reconnection rate. This paper describes a technique for using the Sondrestrom incoherent scatter radar in Greenland to estimate this rate from measurements of the plasma velocity in the separatrix reference frame. The ionospheric plasma drift and the separatrix location and velocity are determined from the radar observations, and the separatrix orientation is inferred from all-sky images. This technique has been applied to obtain measurements of the reconnection electric field in the midnight sector, with 3- to 5-min time resolution during the night of January 14-15, 1989. The reconnection electric field was found to be less than 15 mV/m during periods of local polar cap expansion, which corresponded to substorm recovery phases, and to be 30 to 40 mV/m during times of polar cap contraction, which corresponded to substorm expansive phases. During a short interval, the measurements showed the separatrix moving equatorward faster than the plasma, which implies that there was plasma transfer from closed to open field lines, rather than the usual nightside transfer from open to closed field lines.

1991-01-01

355

Place Names and Identities  

Directory of Open Access Journals (Sweden)

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

Botolv Helleland

2012-01-01

356

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; Ray McDermott; Jason Raley; Matthew Thibeault; Kimberly Powell; Daniel J. Levitin

2008-01-01

357

Take Your Medicines Safely  

Medline Plus

Full Text Available ... not completely give what they call a "bactericidal effect." That means taking the bacteria completely out of ... taking this medicine? What are the possible side effects and what do I do if they occur? ...

358

Particle-in-Cell Simulations of Fast Magnetic Reconnection in Laser-Plasma Interaction  

Science.gov (United States)

Recent experiments have observed magnetic reconnection in laser-produced high-energy-density (HED) plasma bubbles. We perform two-dimensional (2-D) particle-in-cell (PIC) simulations to investigate magnetic reconnection between two approaching HED plasma bubbles. It is found that the expanding velocity of the bubbles has a great influence on the process of magnetic reconnection. When the expanding velocity is small, a single X line reconnection is formed. However, when the expanding velocity is sufficiently large, we can observe a plasmoid in the vicinity of the X line. At the same time, the structures of the electromagnetic field in HED plasma reconnection are similar to that in Harris current sheet reconnection.

Zhang, Ze-Chen; Lu, Quan-Ming; Dong, Quan-Li; Lu, San; Huang, Can; Wu, Ming-Yu; Sheng, Zheng-Ming; Wang, Shui; Zhang, Jie

2013-04-01

359

Statistical study of magnetic reconnection in the solar wind at 1 AU  

Science.gov (United States)

Magnetic reconnection is a phenomenon where the energy stored in the magnetic field dissipates into heating and plasma acceleration. It can occur on boundaries connecting plasma with different magnetic field orientations. In spacecraft observations, we can identify magnetic reconnection as its exhaust where the plasma on reconnected field lines leaves the reconnection site. We present a statistical study based on data from the WIND spacecraft during a period of 1995-2012. We track the signatures of magnetic reconnection exhaust such as a rotation of the magnetic field or acceleration and heating of the plasma. Our statistics focuses on such parameters as the velocity change, temperature, and density enhancements or the shear angle of reconnection.

Enzl, Jakub; Prech, Lubomir; Safrankova, Jana; Nemecek, Zdenek

2013-04-01

360

The dependence of magnetic reconnection on plasma ? and magnetic shear: Evidence from magnetopause observations  

Science.gov (United States)

We have performed a statistical study of THEMIS spacecraft crossings of the asymmetric dayside magnetopause to test the prediction that the diamagnetic drift of the X-line due to a plasma pressure gradient across the magnetopause can suppress magnetic reconnection. The study includes crossings both when reconnection exhausts were present and when they were absent in the current sheet. When we restrict the survey to the subsolar region (10 MLT < 14), we find that for low ?? (the difference of plasma ? on the two sides of the current sheet) the majority of reconnection events occurred over a large range of magnetic shears, whereas when ?? was high reconnection events occurred only for high shears. Furthermore, nonreconnection events occurred primarily in the ??-shear regime in which reconnection is predicted to be suppressed, in good agreement with theory. The ??-shear condition should have general consequences for the occurrence of reconnection in space and laboratory plasmas.

Phan, T. D.; Paschmann, G.; Gosling, J. T.; Oieroset, M.; Fujimoto, M.; Drake, J. F.; Angelopoulos, V.

2013-01-01

 
 
 
 
361

Reconnection at the Earth's dayside magnetopause in the presence of sheared flows and skewed fields  

International Nuclear Information System (INIS)

We study the reconnection layer for different regions of the Earth's magnetopause using a Petschek-type reconnection model which allows for tangential plasma flows and skewed magnetic fields. In particular, we use parameters of the magnetosheath appropriate to the subsolar, the cusp and the flank regions. The skew of the ambient magnetic fields and the velocity shear across the magnetopause differ greatly in the various regions we study, and the properties of the reconnection layer show a corresponding variation.

1990-01-01

362

Propagation and dispersion of whistler waves generated by fast reconnection onset  

International Nuclear Information System (INIS)

The role of whistler mode during the onset of magnetic reconnection (MR) has been widely suggested, but the manifestations of its highly dispersive and anisotropic propagation properties in reconnection events remain largely unclear. Comparing results from a recently developed theoretical model for reconnection in terms of whistler's dispersive behavior with those reported from laboratory experiments on fast spontaneous magnetic reconnection, we demonstrate that the onset of fast reconnection in electron current layers (ECLs) emits whistler wave packets. The time scale of the explosively fast reconnection events are inversely related to the whistler mode frequencies at the lower end of the whistler frequency band. The wave packets in this frequency band have a characteristic angular dispersion, which marks the initial opening of the reconnection exhaust angle. The multidimensional propagation of the whistler for the reconnection with a strong guide magnetic field is investigated, showing that the measured propagation velocities of the reconnection electric field along the guide field in the Versatile Toroidal Facility at MIT quantitatively compare with the group velocities of the whistler wave packets. The whistler mode dispersive properties measured in laboratory experiments without a guide magnetic field in the magnetic reconnection experiments at Princeton also compare well with the theoretically predicted dispersion of the wave packets depending on the ECL width. Fast normalized reconnection rates extending to ?0.35 at the MR onset in thin ECLs imply whistler wave propagation away from the onset location. We also present evidences for the whistler wave packets being emitted from reconnection diffusion region as seen in simulations and satellite observations.

2013-01-01

363

Local Measurement of Non-Classical Ion Heating During Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

Local ion temperature is measured directly in the well-characterized reconnection layer of a laboratory plasma. These measurements demonstrate definitively that ions are heated due to reconnection and that more than half of the reconnected field energy is converted to ion kinetic energy. Neither classical Ohmic dissipation nor thermalization of energetic flows is sufficient to account for the energy converted, suggesting the importance of non-classical dissipation mechanisms such as wave-particle interactions.

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

1999-11-01

364

Three dimensional density cavities in guide field collisionless magnetic reconnection  

CERN Document Server

Particle-in-Cell simulations of collisionless magnetic reconnection with a guide field reveal for the first time the three dimensional features of the low density regions along the magnetic reconnection separatrices, the so-called "cavities". It is found that structures with further lower density develop within the cavities. Because their appearance is similar to the rib shape, these formations are here called "low density ribs". Their location remains approximately fixed in time and their density progressively decreases, as electron currents along the cavities evacuate them. They develop along the magnetic field lines and are supported by a strong perpendicular electric field that oscillates in space. In addition, bipolar parallel electric field structures form as isolated spheres between the cavities and the outflow plasma, along the direction of the low density ribs and of magnetic field lines.

Markidis, Stefano; Divin, Andrey; Goldman, Martin V; Newman, D; Andersson, Laila

2012-01-01

365

Kinetic simulation of magnetic reconnection in the presence of shear  

International Nuclear Information System (INIS)

The basic physical processes associated with collisionless magnetic reconnection are investigated using the implicit PIC code AVANTI. The code is based on a 2.5-D fully electromagnetic direct implicit algorithm which has proven stable for arbitrary time step. This stability makes it possible to separate out the respective roles of the highly magnetized electrons and the un-magnetized ions for large ion-electron mass ratios. It is found that the inclusion of a guide magnetic field (magnetic shear) severely slows the initial stages of reconnection and damps out the electrostatic ringing if local values of the guide field are above a threshold determined by questions of electron mobility. 9 refs., 6 figs.

1988-01-01

366

Kinetic simulation of magnetic reconnection in the presence of shear  

Energy Technology Data Exchange (ETDEWEB)

The basic physical processes associated with collisionless magnetic reconnection are investigated using the implicit PIC code AVANTI. The code is based on a 2.5-D fully electromagnetic direct implicit algorithm which has proven stable for arbitrary time step. This stability makes it possible to separate out the respective roles of the highly magnetized electrons and the un-magnetized ions for large ion-electron mass ratios. It is found that the inclusion of a guide magnetic field (magnetic shear) severely slows the initial stages of reconnection and damps out the electrostatic ringing if local values of the guide field are above a threshold determined by questions of electron mobility. 9 refs., 6 figs.

Francis, G.E.; Hewett, D.W.; Max, C.E.

1988-09-05

367

Radio signatures of upper and lower reconnection outflow shocks  

Energy Technology Data Exchange (ETDEWEB)

For the flare of 28 September 2001, we discuss simultaneously appearing slow drift (type II-like) bursts at about 327 and 58 MHz as radio signature of the upper and lower reconnection outflow termination shock (TS). The features appear during the impulsive phase, but well after the regular traveling-shock type II burst, and during the rise of a CME. The sequence of the regular type II and the following standing shock signatures are well in accordance with the energy release diagnostic from the time derivative of the GOES flux. The upper and lower TS features are suggestive of a flux anti-correlation tendency. We use radio imaging data (Nancay radio heliograph), SOHO EIT and Yohkoh SXT images to support the TS hypothesis. The result gives new observational support for assuming magnetic reconnection as flare energy release mechanism. (orig.)

Aurass, H.

2004-08-01

368

Radio signatures of upper and lower reconnection outflow shocks  

International Nuclear Information System (INIS)

[en] For the flare of 28 September 2001, we discuss simultaneously appearing slow drift (type II-like) bursts at about 327 and 58 MHz as radio signature of the upper and lower reconnection outflow termination shock (TS). The features appear during the impulsive phase, but well after the regular traveling-shock type II burst, and during the rise of a CME. The sequence of the regular type II and the following standing shock signatures are well in accordance with the energy release diagnostic from the time derivative of the GOES flux. The upper and lower TS features are suggestive of a flux anti-correlation tendency. We use radio imaging data (Nancay radio heliograph), SOHO EIT and Yohkoh SXT images to support the TS hypothesis. The result gives new observational support for assuming magnetic reconnection as flare energy release mechanism. (orig.)

2001-09-28

369

Magnetic reconnection mediated by hyper-resistive plasmoid instability  

Science.gov (United States)

Magnetic reconnection mediated by the hyper-resistive plasmoid instability is studied with both linear analysis and nonlinear simulations. The linear growth rate is found to scale as SH1/6 with respect to the hyper-resistive Lundquist number SH?L3VA/?H, where L is the system size, VA is the Alfvén velocity, and ?H is the hyper-resistivity. In the nonlinear regime, reconnection rate becomes nearly independent of SH, the number of plasmoids scales as SH1/2, and the secondary current sheet length and width both scale as SH-1/2. These scalings are consistent with a heuristic argument assuming secondary current sheets are close to marginal stability. The distribution of plasmoids as a function of the enclosed flux ? is found to obey a ?-1 power law over an extended range, followed by a rapid fall off for large plasmoids. These results are compared with those from resistive magnetohydrodynamic studies.

Huang, Yi-Min; Bhattacharjee, A.; Forbes, Terry G.

2013-08-01

370

The plasmoid instability during asymmetric inflow magnetic reconnection  

CERN Document Server

Theoretical studies of the plasmoid instability generally assume that the reconnecting magnetic fields are symmetric. We relax this assumption by performing two-dimensional resistive magnetohydrodynamic simulations of the plasmoid instability during asymmetric inflow magnetic reconnection. Magnetic asymmetry modifies the onset, scaling, and dynamics of this instability. Magnetic islands develop preferentially into the weak magnetic field upstream region. Outflow jets from individual X-points impact plasmoids obliquely rather than directly as in the symmetric case. Consequently, deposition of momentum by the outflow jets into the plasmoids is less efficient, the plasmoids develop net vorticity, and shear flow slows down secondary merging between islands. Secondary merging events have asymmetry along both the inflow and outflow directions. Downstream plasma is more turbulent in cases with magnetic asymmetry because islands are able to roll around each other after exiting the current sheet. As in the symmetric c...

Murphy, Nicholas A; Shen, Chengcai; Lin, Jun; Ni, Lei

2013-01-01

371

Nonlinear variational method for predicting fast collisionless magnetic reconnection  

Science.gov (United States)

A mechanism for fast magnetic reconnection in collisionless plasma is studied for understanding sawtooth collapse in tokamak discharges using a two-fluid model for cold ions and electrons. Explosive growth of the tearing mode enabled by electron inertia is analytically estimated using an energy principle with a nonlinear displacement map. Decrease in the potential energy in the nonlinear regime (where the island width exceeds the electron skin depth) is found to be steeper than in the linear regime, resulting in accelerated reconnection. Release of potential energy by such a fluid displacement leads to unsteady and strong convective flow, which is not damped by the small dissipation effects in high-temperature tokamak plasmas. Direct numerical simulation in slab geometry substantiates the theoretical prediction of the nonlinear growth.

Hirota, M.; Morrison, P. J.; Ishii, Y.; Yagi, M.; Aiba, N.

2013-06-01

372

Magnetic Reconnection Instabilities in Soft-Gamma Repeaters  

CERN Document Server

We examine an external trigger mechanism that gives rise to the intense soft gamma-ray repeater (SGR) giant flares. Out of the three giant flares, two showcased the existence of a precursor, which we show to have had initiated the main flare. We develop a reconnection model based on the hypothesis that shearing motion of the footpoints causes the materialization of a Sweet-Parker current layer in the magnetosphere. The thinning of this macroscopic layer due to the development of an embedded super-hot turbulent current layer switches on the impulsive Hall reconnection, which powers the giant flare. We show that the thinning time is on the order of the pre-flare quiescent time.

Heyl, Jeremy S

2013-01-01

373

Nonlinear variational method for predicting fast collisionless magnetic reconnection  

CERN Multimedia

A mechanism for fast magnetic reconnection in collisionless plasma is studied for understanding sawtooth collapse in tokamak discharges. Explosive growth of the tearing mode driven by electron inertia is analytically estimated by using an energy principle with a nonlinear displacement map. Decrease of the potential energy in the nonlinear regime (where the island width exceeds the electron skin depth) is found to be steeper than in the linear regime, resulting in accelerated reconnection. Release of free energy by such ideal fluid motion leads to unsteady and strong convective flow, which is not deterred by the small dissipation effects in high-temperature tokamak plasmas. Direct numerical simulation in slab geometry substantiates the theoretical prediction of the nonlinear growth.

Hirota, M; Ishii, Y; Yagi, M; Aiba, N

2013-01-01

374

The generalized Ohm's law in collisionless magnetic reconnection  

International Nuclear Information System (INIS)

[en] The generalized Ohm close-quote s law and the force balance near neutral lines in collisionless magnetic reconnection is studied based on two-dimensional full particle simulations in which the ion endash electron mass ratio is set to be 1836. The off-diagonal elements of a plasma pressure tensor are found to be responsible for the breakdown of the frozen-in condition in collisionless reconnection. While the off-diagonal elements of the electron pressure tensor are dominant terms in the generalized Ohm close-quote s law near neutral lines, the ion off-diagonal pressure terms are of significant importance when ions are main current carriers. The spatial scale of electron off-diagonal pressure term Pxy(e) is also found to be proportional to the Dungey length scale, (meEy/e?2)1/3, where ?=?Bz/?x. copyright 1997 American Institute of Physics

375

Mechanisms of field-aligned current formation in magnetic reconnection  

Science.gov (United States)

Satellite observations provide strong evidence for the generation of significant field-aligned currents (FACs) during magnetic reconnection. Reconnection of antiparallel magnetic field does not generate FACs in magnetohydrodynamics (MHD) due to coplanarity in MHD shocks. However, a guide magnetic field and a sheared velocity component are almost always present at the magnetopause and their absence is a singular case. It is illustrated that the presence of these noncoplanar fields requires FACs. Contrary to intuition, such currents are generated more efficiently for a small guide field and are more likely to be a result of the redistribution of already present FACs for large guide fields. It is demonstrated that moderate values of shear flow can generate significant ionospheric FACs. Similar to shear flow, the presence of Hall physics leads to significant FACs and we examine the scaling of these current with the ion inertia length.

Ma, Xuanye; Otto, Antonius

2013-08-01

376

Remote estimation of reconnection parameters in the Earth's magnetotail: model and observations  

Directory of Open Access Journals (Sweden)

Full Text Available We develop a method to estimate the reconnected magnetic flux and the location of the reconnection site using properties of magnetic field and plasma velocity disturbances in the regions surrounding the reconnection plasma flow. Our analysis is based on a 3-D non-steady reconnection model with a finite-sized X-line length. In this framework, we obtain a system of equations capturing the relationships between the disturbances of the magnetic field and plasma flow from one side and the reconnection characteristics from another side. These equations allow us to determine the reconnection characteristics from one-point remote observations of the reconnection fast flow, propagated in the magnetotail current sheet. We apply the model to magnetic field and plasma observations at (?43, ?11.2, ?6.9) RE GSM obtained by the THEMIS/ARTEMIS spacecraft, located in the tail lobe during a substorm event. We found that the reconnection region was located at ~ (?27, 3.5, 0) RE GSM. The X-line appeared to be close to the local time of the substorm current wedge identified from ground-based observations. We estimated the total magnetic flux, which was reconnected in the event as ~5 MWb. That corresponds to a small fraction of the total amount of magnetic flux transferred during a substorm.

A. Alexandrova; R. Nakamura; V. S. Semenov; I. V. Kubyshkin; S. Apatenkov; E. V. Panov; D. Korovinskiy; H. Biernat; W. Baumjohann; K.-H. Glassmeier; J. P. McFadden

2012-01-01

377

New Insights into Dissipation in the Electron Layer During Magnetic Reconnection  

Energy Technology Data Exchange (ETDEWEB)

ELECTRON DISSIPATION IN RECONNECTION Detailed comparisons are reported between laboratory observations of electron scale dissipation layers near a reconnecting X-line and direct two-dimensional full-particle simulations. Many experimental features of the electron layers, such as insensitivity to the ion mass, are reproduced by the simulations; the layer thickness, however, is about 3 - 5 times larger than the predictions. Consequently, the leading candidate 2D mechanism based on collisionless electron nongyrotropic pressure is insuffcient to explain the observed reconnection rates. These results suggest that, in addition to the residual collisions, 3D effects play an important role in electron-scale dissipation during fast reconnection.

H. Ji, Y. Ren, M. Yamada, S. Dorfman, W. Daughton and S.P. Gerhardt

2008-07-18

378

Measuring the dayside reconnection rate during an interval of due northward interplanetary magnetic field  

Directory of Open Access Journals (Sweden)

Full Text Available This study presents, for the first time, detailed spatiotemporal measurements of the reconnection electric field in the Northern Hemisphere ionosphere during an extended interval of northward interplanetary magnetic field. Global convection mapping using the SuperDARN HF radar network provides global estimates of the convection electric field in the northern polar ionosphere. These are combined with measurements of the ionospheric footprint of the reconnection X-line to determine the spatiotemporal variation of the reconnection electric field along the whole X-line. The shape of the spatial variation is stable throughout the interval, although its magnitude does change with time. Consequently, the total reconnection potential along the X-line is temporally variable but its typical magnitude is consistent with the cross-polar cap potential measured by low-altitude satellite overpasses. The reconnection measurements are mapped out from the ionosphere along Tsyganenko model magnetic field lines to determine the most likely reconnection location on the lobe magnetopause. The X-line length on the lobe magnetopause is estimated to be ~6–11 RE in extent, depending on the assumptions made when determining the length of the ionospheric X-line. The reconnection electric field on the lobe magnetopause is estimated to be ~0.2mV/m in the peak reconnection region. Key words. Space plasma physics (Magnetic reconnection) – Magnetospheric physics (Magnetopause, cusp and boundary layers) – Ionosphere (Plasma convection)

G. Chisham; M. P. Freeman; I. J. Coleman; M. Pinnock; M. R. Hairston; M. Lester; G. Sofko

2004-01-01

379

Comparison of analytical and numerical models for steadily driven magnetic reconnection  

International Nuclear Information System (INIS)

The effect of boundary conditions in both analytical and numerical solutions of steadily driven reconnection on the reconnection of antiparallel magnetic fields is considered, with special attention given to the mathematical problem of properly specifying boundary conditions for the MHD equation. A unified formulation developed by Priest and Forbes (1986) for steady state reconnection, which includes the Petschek solution and the Sonnerup (1970) solution as special cases, is used to reinterpret the previous numerical experiments of steadily driven reconnection. It is shown that many contradictory features of these experiments were caused by the use of boundary conditions which are different from those required by Petschek's (1964) theory. 117 references.

1987-01-01

380

Colour reconnection and Bose-Einstein studies with WW decays in ALEPH  

International Nuclear Information System (INIS)

The production of WW pairs at LEP allows interference effect between the hadronic systems of the two W bosons to be studied, such as Bose-Einstein interference and possible signatures for 'colour reconnection' have been investigated. As yet, ALEPH sees no compelling evidence for colour reconnection nor for Bose-Einstein interference between the W systems. In related studies of the predictions of various Monte Carlo models for colour reconnection effects, it is noted that there is no large multiplicity shift due to colour reconnection in the Herwig model when appropriately re-tuned to correctly describe the Z data.

1999-01-01

 
 
 
 
381

Direct observation of high-speed plasma outflows produced by magnetic reconnection in solar impulsive events  

CERN Multimedia

Spectroscopic observations of a solar limb flare recorded by SUMER on SOHO reveal, for the first time, hot fast magnetic reconnection outflows in the corona. As the reconnection site rises across the SUMER spectrometer slit, significant blue- and red-shift signatures are observed in sequence in the Fe XIX line, reflecting upflows and downflows of hot plasma jets, respectively. With the projection effect corrected, the measured outflow speed is between 900-3500 km/s, consistent with theoretical predictions of the Alfvenic outflows in magnetic reconnection region in solar impulsive events. Based on theoretic models, the magnetic field strength near the reconnection region is estimated to be 19-37 Gauss.

Wang, Tongjiang; Qiu, Jiong

2007-01-01

382

Remote estimation of reconnection parameters in the Earth's magnetotail: model and observations  

Science.gov (United States)

We develop a method to estimate the reconnected magnetic flux and the location of the reconnection site using properties of magnetic field and plasma velocity disturbances in the regions surrounding the reconnection plasma flow. Our analysis is based on a 3-D non-steady reconnection model with a finite-sized X-line length. In this framework, we obtain a system of equations capturing the relationships between the disturbances of the magnetic field and plasma flow from one side and the reconnection characteristics from another side. These equations allow us to determine the reconnection characteristics from one-point remote observations of the reconnection fast flow, propagated in the magnetotail current sheet. We apply the model to magnetic field and plasma observations at (-43, -11.2, -6.9) RE GSM obtained by the THEMIS/ARTEMIS spacecraft, located in the tail lobe during a substorm event. We found that the reconnection region was located at ~ (-27, 3.5, 0) RE GSM. The X-line appeared to be close to the local time of the substorm current wedge identified from ground-based observations. We estimated the total magnetic flux, which was reconnected in the event as ~5 MWb. That corresponds to a small fraction of the total amount of magnetic flux transferred during a substorm.

Alexandrova, A.; Nakamura, R.; Semenov, V. S.; Kubyshkin, I. V.; Apatenkov, S.; Panov, E. V.; Korovinskiy, D.; Biernat, H.; Baumjohann, W.; Glassmeier, K.-H.; McFadden, J. P.

2012-12-01

383

Properties of Near-Earth Magnetic Reconnection from In-Situ Observations  

Science.gov (United States)

Many properties of magnetic reconnection have been determined from in-situ spacecraft observations in the Earth's magnetosphere. Recent studies have focused on ion scale lengths and have largely confirmed theoretical predictions. In addition, some interesting features of reconnection regions on electron scale lengths have been identified. These recent studies have demonstrated the need for combined plasma and field measurements on electron scale lengths in the reconnection diffusion regions at the magnetopause and in the magnetotail. They have also indicated that measurements, such as those that will be made by the Magnetospheric Multiscale mission in the near future, will have a significant impact on understanding magnetic reconnection as a fundamental plasma process.

Fuselier, S. A.; Lewis, W. S.

2011-10-01

384

Dynamical reconnection and stability constraints on cortical network architecture.  

Science.gov (United States)

Stability under dynamical changes to network connectivity is invoked alongside previous criteria to constrain brain network architecture. A new hierarchical network is introduced that satisfies all these constraints, unlike more commonly studied regular, random, and small-world networks. It is shown that hierarchical networks can simultaneously have high clustering, short path lengths, and low wiring costs, while being robustly stable under large scale reconnection of substructures. PMID:19792345

Robinson, P A; Henderson, J A; Matar, E; Riley, P; Gray, R T

2009-09-04

385

First-order Fermi acceleration driven by magnetic reconnection  

Science.gov (United States)

A box model is used to study first-order Fermi acceleration driven by magnetic reconnection. It is shown, at least in this simple model, that the spectral index of the accelerated particles is related to the total compression in the same way as in diffusive shock acceleration and is not, as has been suggested, a universal E-5/2 spectrum. The acceleration time-scale is estimated and some comments made about the applicability of the process.

Drury, L. O'C.

2012-05-01

386

Reconnection studies under different types of turbulence driving  

Directory of Open Access Journals (Sweden)

Full Text Available We study a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian and Vishniac (1999) using three-dimensional direct numerical simulations. The model has been already successfully tested in Kowal et al. (2009) confirming the dependencies of the reconnection speed Vrec on the turbulence injection power Pinj and the injection scale linj expressed by a constraint Vrec ~ Pinj1/2linj3/4and no observed dependency on Ohmic resistivity. In Kowal et al. (2009), in order to drive turbulence, we injected velocity fluctuations in Fourier space with frequencies concentrated around kinj = 1/linj, as described in Alvelius (1999). In this paper, we extend our previous studies by comparing fast magnetic reconnection under different mechanisms of turbulence injection by introducing a new way of turbulence driving. The new method injects velocity or magnetic eddies with a specified amplitude and scale in random locations directly in real space. We provide exact relations between the eddy parameters and turbulent power and injection scale. We performed simulations with new forcing in order to study turbulent power and injection scale dependencies. The results show no discrepancy between models with two different methods of turbulence driving exposing the same scalings in both cases. This is in agreement with the Lazarian and Vishniac (1999) predictions. In addition, we performed a series of models with varying viscosity ?. Although Lazarian and Vishniac (1999) do not provide any prediction for this dependence, we report a weak relation between the reconnection speed with viscosity, Vrec ~ ??1/4.

G. Kowal; A. Lazarian; E. T. Vishniac; K. Otmianowska-Mazur

2012-01-01

387

Acceleration mechanisms flares, magnetic reconnection and shock waves  

International Nuclear Information System (INIS)

Several mechanisms are briefly discussed for the acceleration of particles in the astrophysical environment. Included are hydrodynamic acceleration, spherically convergent shocks, shock and a density gradient, coherent electromagnetic acceleration, the flux tube origin, symmetries and instabilities, reconnection, galactic flares, intergalactic acceleration, stochastic acceleration, and astrophysical shocks. It is noted that the supernova shock wave models still depend critically on the presupernova star structure and the assumption of highly compact presupernova models for type I supernovae. 37 references

1979-08-23

388

First order Fermi acceleration driven by magnetic reconnection  

CERN Multimedia

A box model is used to study first order Fermi acceleration driven by magnetic reconnection. It is shown, at least in this simple model, that the spectral index of the accelerated particles is related to the total compression in the same way as in diffusive shock acceleration and is not, as has been suggested, a universal $E^{-5/2}$ spectrum. The acceleration time-scale is estimated and some comments made about the applicability of the process.

Drury, Luke O'C

2012-01-01

389

AN ANALYTICAL MODEL FOR RECONNECTION OUTFLOW JETS INCLUDING THERMAL CONDUCTION  

International Nuclear Information System (INIS)

We develop a model that predicts the velocity, density, and temperature of coronal reconnection jets in the presence of thermal conduction. Our model is based on the quasi-one-dimensional treatment of reconnecting current sheets developed by B. Somov and V. S. Titov using the magnetohydrodynamics nozzle equations. We incorporate thermal conduction into the Somov-Titov framework using slow-shock jump conditions modified to include losses due the conduction of thermal energy along field lines mapping to the chromosphere. We find that thermal conduction has a significant effect on the fast-mode Mach number of the reconnection outflow, producing Mach numbers possibly as high as 7 for some solar-flare conditions. This value is three times greater than previously calculated. We conclude that these termination shocks are considerably more efficient at producing particle acceleration than previously thought since the efficiency of particle acceleration at shocks increases dramatically with Mach number. We compare this model with numerical simulations by T. Yokoyama and K. Shibata and find good agreement.

2009-08-10

390

CME Initiation Driven by Velocity-Shear Kinetic Reconnection Simulations  

Science.gov (United States)

In the standard model for coronal mass ejections (CME) and/or solar flares, the free energy for the event resides in the strongly sheared magnetic field of a filament channel. The pre-eruption force balance consists of an upward force due to the magnetic pressure of the sheared field balanced by a downward tension due to overlying unsheared field. Magnetic reconnection is widely believed to be the mechanism that disrupts this force balance, leading to explosive eruption. For understanding CME/flare initiation, therefore, it is critical to model the onset or reconnection that is driven by the buildup of magnetic shear. In MHD simulations, the application of a magnetic field shear is a trivial matter. However, kinetic effects are important in the diffusion region and thus, it is important to examine this process with PIC simulations as well. The implementation of such a driver in PIC methods is nontrivial and indicates necessity of a true multiscale model for such processes in the Solar environment. The field must be sheared self-consistently/ indirectly to prevent the generation of waves that destroy the desired system. In the work presented here, we discuss methods for applying a velocity shear perpendicular to the plane of reconnection for periodic and nonperiodic systems.

Black, Carrie; Antiochos, S. K.; Karpen, J. T.; Germaschewski, K.; DeVore, C. R.

2013-07-01

391

Magnetic reconnection processes induced by a CME expansion  

Directory of Open Access Journals (Sweden)

Full Text Available On 10–11 December 2005 a slow CME occurred in the Western Hemisphere in between two coronal streamers. SOHO/MDI magnetograms show a multipolar magnetic configuration at the photosphere: a complex of active regions located at the CME source and two bipoles at the base of the lateral coronal streamers. White light observations reveal that the CME expansion affects both of them and induces the release of plasma within or close to the nearby streamers. These transient phenomena are possibly due to magnetic reconnections induced by the CME expansion and occurring inside the streamer current sheet or between the CME flanks and the streamer. These events have been observed by the SOHO/UVCS with the spectrometer slit centered at 1.8 R? over about a full day. In this work we focus on the interaction between the CME and the streamer: the UVCS spectral interval included UV lines from ions at different temperatures of maximum formation such as O VI, Si XIII and Al Xi. These data gave us the opportunity to infer the evolution of plasma temperature and density at the reconnection site and adjacent regions. These are relevant to characterize secondary reconnection processes occurring during a CME development.

A. Bemporad; G. Poletto; F. Landini; M. Romoli

2008-01-01

392

Downward auroral currents from the reconnection Hall-region  

Directory of Open Access Journals (Sweden)

Full Text Available We present a simple (stationary) mechanism capable of generating the auroral downward field-aligned electric field that is needed for accelerating the ionospheric electron component up into the magnetosphere and confining the ionospheric ions at low latitudes (as is required by observation of an ionospheric cavity in the downward auroral current region). The lifted ionospheric electrons carry the downward auroral current. Our model is based on the assumption of collisionless reconnection in the tail current sheet. It makes use of the dynamical difference between electrons and ions in the ion inertial region surrounding the reconnection X-line which causes Hall currents to flow. We show that the spatial confinement of the Hall magnetic field and flux to the ion inertial region centred on the X-point generates a spatially variable electromotive force which is positive near the outer inflow boundaries of the ion inertial region and negative in the central inflow region. Looked at from the ionosphere it functions like a localised meso-scale electric potential. The positive electromotive force gives rise to upward electron flow from the ionosphere during substorms (causing "black aurorae"). A similar positive potential is identified on the earthward side of the fast reconnection outflow region which has the same effect, explaining the observation that auroral upward currents are flanked from both sides by narrow downward currents.

R. A. Treumann; R. Nakamura; W. Baumjohann

2011-01-01

393

Coordinated Cluster/Double Star observations of dayside reconnection signatures  

Directory of Open Access Journals (Sweden)

Full Text Available The recent launch of the equatorial spacecraft of the Double Star mission, TC-1, has provided an unprecedented opportunity to monitor the southern hemisphere dayside magnetopause boundary layer in conjunction with northern hemisphere observations by the quartet of Cluster spacecraft. We present first results of one such situation where, on 6 April 2004, both Cluster and the Double Star TC-1 spacecraft were on outbound transits through the dawnside magnetosphere. The observations are consistent with ongoing reconnection on the dayside magnetopause, resulting in a series of flux transfer events (FTEs) seen both at Cluster and TC-1, which appear to lie north and south of the reconnection line, respectively. In fact, the observed polarity and motion of each FTE signature advocates the existence of an active reconnection region consistently located between the positions of Cluster and TC-1, with Cluster observing northward moving FTEs with +/- polarity, whereas TC-1 sees -/+ polarity FTEs. This assertion is further supported by the application of a model designed to track flux tube motion for the prevailing interplanetary conditions. The results from this model show, in addition, that the low-latitude FTE dynamics are sensitive to changes in convected upstream conditions. In particular, changing the interplanetary magnetic field (IMF) clock angle in the model suggests that TC-1 should miss the resulting FTEs more often than Cluster and this is borne out by the observations.

M. W. Dunlop; M. G. G. T. Taylor; J. A. Davies; C. J. Owen; F. Pitout; A. N. Fazakerley; Z. Pu; H. Laakso; Y. V. Bogdanova; Q.-G. Zong; C. Shen; K. Nykyri; B. Lavraud; S. E. Milan; T. D. Phan; H. Rème; C. P. Escoubet; C. M. Carr; P. Cargill; M. Lockwood; B. Sonnerup

2005-01-01

394

Reconnection Studies Under Different Types of Turbulence Driving  

CERN Multimedia

We study a model of fast magnetic reconnection in the presence of weak turbulence proposed by Lazarian and Vishniac (1999) using three-dimensional direct numerical simulations. The model has been already successfully tested in Kowal et al. (2009) confirming the dependencies of the reconnection speed $V_{rec}$ on the turbulence injection power $P_{inj}$ and the injection scale $l_{inj}$ expressed by a constraint $V_{rec} \\sim P_{inj}^{1/2} l_{inj}^{3/4}$ and no observed dependency on Ohmic resistivity. In Kowal et al. (2009), in order to drive turbulence, we injected velocity fluctuations in Fourier space with frequencies concentrated around $k_{inj}=1/l_{inj}$, as described in Alvelius (1999). In this paper we extend our previous studies by comparing fast magnetic reconnection under different mechanisms of turbulence injection by introducing a new way of turbulence driving. The new method injects velocity or magnetic eddies with a specified amplitude and scale in random locations directly in real space. We pr...

Kowal, Grzegorz; Vishniac, Ethan T; Otmianowska-Mazur, Katarzyna

2012-01-01

395

Model of magnetic reconnection in space and astrophysical plasmas  

Energy Technology Data Exchange (ETDEWEB)

Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

Boozer, Allen H. [Department of Applied Physics and Applied Mathematics, Columbia University, New York, New York 10027 (United States)

2013-03-15

396

Model of magnetic reconnection in space and astrophysical plasmas  

International Nuclear Information System (INIS)

Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

2013-01-01

397

Model of magnetic reconnection in space and astrophysical plasmas  

Science.gov (United States)

Maxwell's equations imply that exponentially smaller non-ideal effects than commonly assumed can give rapid magnetic reconnection in space and astrophysical plasmas. In an ideal evolution, magnetic field lines act as stretchable strings, which can become ever more entangled but cannot be cut. High entanglement makes the lines exponentially sensitive to small non-ideal changes in the magnetic field. The cause is well known in popular culture as the butterfly effect and in the theory of deterministic dynamical systems as a sensitive dependence on initial conditions, but the importance to magnetic reconnection is not generally recognized. Two-coordinate models are too constrained geometrically for the required entanglement, but otherwise the effect is general and can be studied in simple models. A simple model is introduced, which is periodic in the x and y Cartesian coordinates and bounded by perfectly conducting planes in z. Starting from a constant magnetic field in the z direction, reconnection is driven by a spatially smooth, bounded force. The model is complete and could be used to study the impulsive transfer of energy between the magnetic field and the ions and electrons using a kinetic plasma model.

Boozer, Allen H.

2013-03-01

398

Two-dimensional Fully Kinetic Simulations Of Driven Magnetic Reconnection With Boundary Conditions Relevant To The Magnetic Reconnection Experiment  

International Nuclear Information System (INIS)

[en] Two-dimensional fully kinetic simulations are performed using global boundary conditions relevant to model the Magnetic Reconnection Experiment (MRX) (M. Yamada et al., Phys Plasmas 4, 1936 (1997)). The geometry is scaled in terms of the ion kinetic scales in the experiment, and a reconnection layer is created by reducing the toroidal current in the flux cores in a manner similar to the actual experiment. The ion-scale features in these kinetic simulations are in remarkable agreement with those observed in MRX, including the reconnection inflow rate and quadrupole field structure. In contrast, there are significant discrepancies in the simulated structure of the electron layer that remain unexplained. In particular, the measured thickness of the electron layers is 3-5 times thicker in MRX than in the kinetic simulations. The layer length is highly sensitive to downstream boundary conditions as well as the time over which the simulation is driven. However, for a fixed set of chosen boundary conditions, an extrapolation of the scaling with the ion to electron mass ratio implies that at realistic mass ratio both the length and width will be too small compared to the experiment. This discrepancy implies that the basic electron layer physics may differ significantly between MRX and the two-dimensional, collisionless simulations. The two leading possibilities to explain the discrepancy are weak Coulomb collisions and three-dimensional effects that are present in the experiment but not included in the simulation model

2008-01-01

399

Two-dimensional Fully Kinetic Simulations Of Driven Magnetic Reconnection With Boundary Conditions Relevant To The Magnetic Reconnection Experimen  

Energy Technology Data Exchange (ETDEWEB)

Two-dimensional fully kinetic simulations are performed using global boundary conditions relevant to model the Magnetic Reconnection Experiment (MRX) [M. Yamada et al., Phys Plasmas 4, 1936 (1997)]. The geometry is scaled in terms of the ion kinetic scales in the experiment, and a reconnection layer is created by reducing the toroidal current in the flux cores in a manner similar to the actual experiment. The ion-scale features in these kinetic simulations are in remarkable agreement with those observed in MRX, including the reconnection inflow rate and quadrupole field structure. In contrast, there are significant discrepancies in the simulated structure of the electron layer that remain unexplained. In particular, the measured thickness of the electron layers is 3?5 times thicker in MRX than in the kinetic simulations. The layer length is highly sensitive to downstream boundary conditions as well as the time over which the simulation is driven. However, for a fixed set of chosen boundary conditions, an extrapolation of the scaling with the ion to electron mass ratio implies that at realistic mass ratio both the length and width will be too small compared to the experiment. This discrepancy implies that the basic electron layer physics may differ significantly between MRX and the two-dimensional, collisionless simulations. The two leading possibilities to explain the discrepancy are weak Coulomb collisions and three-dimensional effects that are present in the experiment but not included in the simulation model.

S. Dorfman, W. Daughton, V. Roytershteyn, H. Ji, Y. Ren, and M. Yamada

2008-11-06

400

77 FR 23547 - Taking and Importing Marine Mammals; Taking Marine Mammals Incidental to Columbia River Crossing...  

Science.gov (United States)

...and material barges. Columns would be constructed of cast-in-place reinforced concrete or precast concrete. Column construction is estimated to take 120 days for each pier complex. Construction of columns would require cranes, work...

2012-04-19

 
 
 
 
401

Technical training: places available  

CERN Multimedia

CERN Technical Training: Open Courses (April - June 2007) The following course sessions are currently scheduled in the framework of the CERN Technical Training Programme 2007:   AutoCAD 2006 - niveau 1 (course in French): 25.4.- 26.4.2007 & 2.5. - 3.5.2007 (4 days in 2 modules, 5 places available) AutoCAD 2006 - niveau 1 (course in French): 27.6.- 28.6.2007 & 3.7. - 4.7.2007 (4 days in 2 modules, 5 places available) AutoCAD Mechanical 2006 (course in French) 21.6.-22.6.2007 (2 days, 8 places available) * NEW COURSE* Automate de securite S7 (course in French) 14.5.-16.5.2007 (3 days, 4 places available) * NEW COURSE* Automate de securite S7 (course in French): 9.5.-11.5.2007 (3 days, 4 places available) JCOP - Joint PVSS-JCOP Frameswork (course in English): 21.5.-25.5.2007 (5 days, 12 places available) JCOP - Finite State Machines in the JCOP Frameswork (course in English): 12.6.-14.6.2007 (3 days, 12 places available) LabVIEW Basics 1 (in English): 2.-4.5.2007 (3 days, 7 places ...

HR Department

2007-01-01

402

Technical training - places available  

CERN Multimedia

If you would like more information on a course, or for any other inquiry/suggestions, please contact Technical.Training@cern.ch Valeria Perez Reale, Learning Specialist, Technical Programme Coordinator (Tel.: 62424) Eva Stern and Elise Romero, Technical Training Administration (Tel.: 74924) HR Department »Electronics design Next Session Duration Language Availability Comprehensive VHDL for FPGA Design 08-Oct-12 to 12-Oct-12 5 days English 3 places available Foundations of Electromagnetism and Magnet Design (EMAG) 14-Nov-12 to 27-Nov-12 6 days English 20 places available Impacts de la suppression du plomb (RoHS) en électronique 26-Oct-12 to 26-Oct-12 8 hours French 15 places available Introduction to VHDL 10-Oct-12 to 11-Oct-12 2 days English 7 places available LabVIEW Real Time and FPGA 13-Nov-12 to 16-Nov-12 5 days French 5 places available »Mechanical design Next Se...

2012-01-01

403

Overview on numerical studies of reconnection and dissipation in the solar wind  

Science.gov (United States)

In this work, recent advances in numerical studies of local reconnection events in the turbulent plasmas are reviewed. Recently [1], the nonlinear dynamics of magnetic reconnection in turbulence has been investigated through high resolution numerical simulations. Both fluid (MHD and Hall MHD) and kinetic (HybridVlasov) 2D simulations reveal the presence of a large number of X-type neutral points, where magnetic reconnection locally occurs. The associated reconnection rates are distributed over a wide range of values and they depend on the local geometry of the diffusion region. This new approach to the study of magnetic reconnection has broad applications to the turbulent solar wind (SW). Strong magnetic SW discontinuities are in fact strongly related to these intermittent processes of reconnection [2, 3]. Methods employed to identify sets of possible reconnection events along a one-dimensional path through the turbulent field (emulating experimental sampling by a single detector in a highspeed flow) are here reviewed. These local reconnection/discontinuity events may be the main sites of heating and particle acceleration processes [4]. Results from hybrid-Vlasov kinetic simulations support these observations [5, 6]. In the turbulent regime, in fact, kinetic effects manifest through a deformation of the ion distribution function. These patterns of non-Maxwellian features are concentrated in space nearby regions of strong magnetic activity. These results open a new path on the study of kinetic processes such as heating, particle acceleration, and temperature anisotropy, commonly observed in astrophysics.

Donato, S.; Servidio, S.; Dmitruk, P.; Valentini, F.; Greco, A.; Veltri, P.; Wan, M.; Shay, M. A.; Cassak, P. A.; Matthaeus, W. H.

2013-06-01

404

Collisionless magnetic reconnection in the presence of a sheared velocity field  

International Nuclear Information System (INIS)

The linear theory of magnetic field lines reconnection in a two-dimensional configuration in the presence of a (Kelvin-Helmholtz stable) sheared velocity field is investigated within a single fluid model, where the onset of magnetic field line reconnection is made possible by the effect of electron inertia in the so called large ?' regime.

2010-01-01

405

Magnetic reconnection and stochastic plasmoid chains in high-Lundquist-number plasmas  

CERN Document Server

A numerical study of magnetic reconnection in the large-Lundquist-number ($S$), plasmoid-dominated regime is carried out for $S$ up to $10^7$. The theoretical model of Uzdensky {\\it et al.} [Phys. Rev. Lett. {\\bf 105}, 235002 (2010)] is confirmed and partially amended. The normalized reconnection rate is $\

Loureiro, N F; Schekochihin, A A; Uzdensky, D A

2011-01-01

406

Search for colour singlet and colour reconnection effects in hadronic Z decays at LEP  

Energy Technology Data Exchange (ETDEWEB)

A search is performed in symmetric 3-jet hadronic Z-decay events for evidence of colour singlet production or colour reconnection effects. Asymmetries in the angular separation of particles are found to be sensitive indicators of such effects. Upper limits on the level of colour singlet production or of colour reconnection effects are established for a variety of models.

Achard, P.; Adriani, O.; Aguilar-Benitez, M. (and others)

2004-02-12

407

The Location of the Magnetopause Reconnection Site during Southward IMF Conditions  

Science.gov (United States)

Karlheinz Trattner, karlheinz.j.trattner.dr@lmco.com Lockheed Martin Advanced Technology Lab, CA 94304, California, United States Stephen Fuselier, stephen.a.fuselier@lmco.com Lockheed Martin Advanced Technology Lab, Palo Alto, California, United States Steven Petrinec, steven.m.petrinec@lmco.com Lockheed Martin Advanced Technology Lab, Palo Alto, United States There are two reconnection location scenarios discussed in the literature: a) anti-parallel re-connection where shear angles between the magnetospheric field and the IMF are near 180 degrees, and b) component reconnection where shear angles are as low as 50 degrees. One popular component reconnection model is the tilted neutral line model. Recent studies about the location of the reconnection line with single point measurements under stable solar wind and IMF conditions reveal that the so-called tilted X-line, crossing near the dayside sub-solar region, is the dominant reconnection scenario. Specifically, magnetic reconnection will occur along the line of maximum magnetic shear across the dayside magnetopause. Exceptions to this reconnection location are dominant southward IMF conditions (within 25 of southward IMF) or a dominant IMF BX component (more than 70

Trattner, Karlheinz; Fuselier, Stephen; Petrinec, Steven

408

Predicting the behavior of magnetic reconnection processes in fusion burning plasma experiments  

International Nuclear Information System (INIS)

Critical stability issues involving magnetic reconnection, which are likely to influence the successful operation of burning plasma experiments, are addressed. In particular, we discuss: 1) sawtooth oscillations; 2) nonlinear tearing mode stability, including neo-classical effects; reconnection near the X-points of magnetic separatrices. (author)

2003-01-01

409

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

Directory of Open Access Journals (Sweden)

Full Text Available We present an investigation of magnetic flux ropes observed by the four Cluster spacecraft during periods of magnetic reconnection in the Earth's magnetotail. Using a list of 21 Cluster encounters with the reconnection process in the period 2001–2006 identified in Borg et al. (2012), we present the distribution and characteristics of the flux ropes. We find 27 flux ropes embedded in the reconnection outflows of only 11 of the 21 reconnection encounters. Reconnection processes associated with no flux rope observations were not distinguishable from those where flux ropes were observed. Only 7 of the 27 flux ropes show evidence of enhanced energetic electron flux above 50 keV, and there was no clear signature of the flux rope in the thermal particle measurements. We found no clear correlation between the flux rope core field and the prevailing IMF By direction.

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

2012-01-01

410

Analytical Model of Fast Magnetic Reconnection with a Large Guide Field  

CERN Multimedia

Analytical theory of fast magnetic reconnection with a large guide field is presented for the first time. We confirm that two distinct reconnection regimes are possible depending on whether the diffusion region thickness $\\delta$ is larger or smaller than the sound gyroradius $\\rho_s$. The reconnection is slow or Sweet-Parker-like for $\\delta \\gtrsim \\rho_s$, and fast otherwise. In the fast regime, however, we find that ion viscosity $\\mu$ plays a critical role. In particular, for $\\delta < \\rho_s$ the diffusion region thickness is proportional to $Ha^{-1}$ with $Ha \\propto 1/\\sqrt{\\eta \\mu}$ the Hartmann number, and the reconnection rate is proportional to $Pr^{-1/2}$ with $Pr = \\mu/\\eta$ the Prandtl number and $\\eta$ the resistivity. If the perpendicular ion viscosity is employed for $\\mu$ the reconnection rate becomes independent of both plasma $\\beta$ and collision frequencies and therefore potentially fast.

Simakov, Andrei N; Zocco, A

2010-01-01

411

Magnetic Reconnection and Turbulent Mixing From ISM to Clusters of Galaxies  

CERN Multimedia

Magnetic reconnection, or the ability of the magnetic field lines that are frozen in plasma to change their topology, is a fundamental problem of magnetohydrodynamics (MHD). We briefly examine the problem starting with the well-known Sweet-Parker scheme, discuss effects of tearing modes, anomalous resistivity and the concept of hyperresistivity. We show that the field stochasticity by itself provides a way to enable fast reconnection even if, at the scale of individual turbulent wiggles, the reconnection happens at the slow Sweet-Parker rate. We show that fast reconnection allows efficient mixing of magnetic field in the direction perpendicular to the local direction of magnetic field. While the idea of stochastic reconnection still requires numerical confirmation, our numerical simulations testify that mixing motions perpendicular to the local magnetic field are up to high degree hydrodynamical. This suggests that the turbulent heat transport should be similar to that in non-magnetized turbulent fluid, namel...

Lazarian, A

2004-01-01

412

Ionospheric convection observed by SuperDARN during ongoing lobe reconnection revealed by Cluster .  

Science.gov (United States)

Since Dungey's work in the early sixties, who suggested that the interplanetary magnetic field and the geomagnetic field could reconnect, a lot of debate has been going on regarding how the reconnection process exactly occurs at the Earth's magnetopause. In fact, many fundamental questions remain unanswered, in particular regarding the shape and the extension of the reconnection sites for variable IMF orientation. The polar ionospheric convection strongly depends on the orientation of the IMF; such dependence can be explained in the framework of the reconnection between interplanetary and geomagnetic fields. Here we use SuperDARN observations of the ionospheric convection in coordination with space observations provided by the Cluster spacecraft to infer large scale configuration and evolution of the reconnection at the magnetopause during an extended period of Northward IMF.

Marcucci, M. F.; Amata, E.; Ambrosino, D.; Coco, I.; Bavassano Cattaneo, M. B.; Retinò, A.

413

Mobile technology and place  

CERN Multimedia

An international roster of contributors come together in this comprehensive volume to examine the complex interactions between mobile media technologies and issues of place. Balancing philosophical reflection with empirical analysis, this book examines the specific contexts in which place and mobile technologies come into focus, intersect, and interact. Given the far-reaching impact of contemporary mobile technology use - and given the lasting importance of the concept and experiences of place - this book will appeal to a wide range of scholars in media and cultural studies, sociology, and phi

Wilken, Rowan

2013-01-01

414

Management and communication courses – Places available  

CERN Document Server

There are places available in some management and communication courses taking place in the period April to June 2013.   For more information on the course, click on the course title, this will bring you to the training catalogue. You can then sign-up online. For advice, you can contact: - Erwin Mosselmans, tel. 74125, erwin.mosselmans@cern.ch - Nathalie Dumeaux, tel. 78144, nathalie.dumeaux@cern.ch Courses in English (or bilingual) Sessions Duration Language Availability Managing stress 29 and 30 May 2 days English 3 places Making Presentations 30, 31 May & 25 June 3 days English 2 places Communicating Effectively - Residential course 4 to 6 June 3 days Bilingual 9 places Handling difficult conversations (Adapted from Dealing with Conflict) 7 and 14 June and 13 September 3 days English 6 places Voice and Nonverbal Behaviour in Speech Communication 17 and 18 June 1 day 4 hours English 7 plac...

2013-01-01

415

The location and rate of dayside reconnection during an interval of southward interplanetary magnetic field  

Directory of Open Access Journals (Sweden)

Full Text Available Using ionospheric data from the SuperDARN radar network and a DMSP satellite we obtain a comprehensive description of the spatial and temporal pattern of day-side reconnection. During a period of southward interplanetary magnetic field (IMF), the data are used to determine the location of the ionospheric projection of the dayside magnetopause reconnection X-line. From the flow of plasma across the projected X-line, we derive the reconnection rate across 7 h of longitude and estimate it for the total length of the X-line footprint, which was found to be 10 h of longitude. Using the Tsyganenko 96 magnetic field model, the ionospheric data are mapped to the magnetopause, in order to provide an estimate of the extent of the reconnection X-line. This is found to be ~ 38 RE in extent, spanning the whole dayside magnetopause from dawn to dusk flank. Our results are compared with previously reported encounters by the Equator-S and Geotail spacecraft with a reconnecting magnetopause, near the dawn flank, for the same period. The SuperDARN observations allow the satellite data to be set in the context of the whole magnetopause reconnection X-line. The total potential associated with dayside reconnection was ~ 150 kV. The reconnection signatures detected by the Equator-S satellite mapped to a region in the ionosphere showing continuous flow across the polar cap boundary, but the reconnection rate was variable and showed a clear spatial variation, with a distinct minimum at 14:00 magnetic local time which was present throughout the 30-min study period.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetosphere-ionoshere interactions) – Space plasma physics (magnetic reconnection)

M. Pinnock; G. Chisham; I. J. Coleman; M. P. Freeman; M. Hairston; J.-P. Villain

0000-01-01

416

An analysis of the accuracy of magnetopause reconnection rate variations deduced from cusp ion dispersion characteristics  

Directory of Open Access Journals (Sweden)

Full Text Available We present an analysis of the accuracy of the method introduced by Lockwood et al. (1994) for the determination of the magnetopause reconnection rate from the dispersion of precipitating ions in the ionospheric cusp region. Tests are made by applying the method to synthesised data. The simulated cusp ion precipitation data are produced by an analytic model of the evolution of newly-opened field lines, along which magnetosheath ions are firstly injected across the magnetopause and then dispersed as they propagate into the ionosphere. The rate at which these newly opened field lines are generated by reconnection can be varied. The derived reconnection rate estimates are then compared with the input variation to the model and the accuracy of the method assessed. Results are presented for steady-state reconnection, for continuous reconnection showing a sine-wave variation in rate and for reconnection which only occurs in square wave pulses. It is found that the method always yields the total flux reconnected (per unit length of the open-closed field-line boundary) to within an accuracy of better than 5%, but that pulses tend to be smoothed so that the peak reconnection rate within the pulse is underestimated and the pulse length is overestimated. This smoothing is reduced if the separation between energy channels of the instrument is reduced; however this also acts to increase the experimental uncertainty in the estimates, an effect which can be countered by improving the time resolution of the observations. The limited time resolution of the data is shown to set a minimum reconnection rate below which the method gives spurious short-period oscillations about the true value. Various examples of reconnection rate variations derived from cusp observations are discussed in the light of this analysis.

M. Lockwood; C. J. Davis

0000-01-01

417

Taking Acetaminophen Safely  

Medline Plus

Full Text Available ... care professional, such as your pharmacist, doctor, and nurse Taking too much acetaminophen is harmful. Severe liver ... If you have questions talk to your doctor, nurse, or pharmacist. You can visit the FDA at ...

418

Take Your Medicines Safely  

Medline Plus

Full Text Available ... better, the antibiotic is working in killing the bacteria, but it might not completely give what they call a "bactericidal effect." That means taking the bacteria completely out of the system. It might be ...

419

Taking Acetaminophen Safely  

Medline Plus

Full Text Available ... it can be harmful. Acetaminophen can cause serious liver injury. This reference summary discusses: • what acetaminophen is ... taking too much acetaminophen, which can cause serious liver injury, you must follow the information given by: • ...

420

Taking iron supplements  

Science.gov (United States)

... part of treating iron deficiency anemia. However, iron supplements are often needed to build up the iron ... WHO SHOULD TAKE EXTRA IRON Iron supplements may be taken as ... The most common tablet size is 325 mg. Make sure your health ...