Large-scale Loop Research Articles

Signatures of magnetic reconnection in solar radio observations?

Magnetic reconnection occurs during eruptive processes (flares, CMEs) in the solar corona. This leads to a change of magnetic connectivity. Nonthermal electrons propagate along the coronal magnetic field thereby exciting dm- and m-wave radio burst emission after acceleration during reconnection or other energy release processes in heights of some Mm to ⩾700 Mm. We summarize the results of some case studies which can be interpreted as radio evidence of magnetic reconnection: under certain conditions, simple spectral structures (pulsation pulses, reverse drift bursts) are formed by simultaneously acting but widely spaced radio sources. Narrowband spikes are emitted as a side-effect during large-scale coronal loop collisions. In dynamic radio spectra, the lower fast mode shock formed in the reconnection outflow appears as type II burst-like but nondrifting emission lane. It has been several times observed at the harmonic mode of the local plasma frequency between 250 and 500 MHz and at heights of ≈200 Mm.

The temperature map of the loop and coronal sources of an occulted solar flare

An occulted solar flare occurred at about 06:07 UT on 2002, November 2. The RHESSI X-ray images show two separate parts. The lower part consists of a complete loop and the upper part a coronal source which well extends above the solar limb. The loop source shrank for about 3 min with a speed of ∼24 km s −1 during the early impulsive phase and then expanded at ∼7 km s −1, while the coronal source presented an upward motion at about 6 km s −1. We obtained the temperature map of the loop source from RHESSI image spectrum. The temperature of the loop increases with altitude, indicating that the reconnection X-point of this flare is located above the loop source. However, the apparent coronal source is the top of another independent large-scale loop.

Full-Height Thermal-Hydraulic Scaling Analysis of Pb-Bi-Cooled Fast Reactor PEACER

A liquid-metal–cooled fast reactor Proliferation-resistant Environment-friendly Accident-tolerant Continuable-energy Economical Reactor (PEACER) is being developed at Seoul National University with metallic-type U-Pu-Th fuel and lead-bismuth (Pb-Bi) coolant, employing the steam-generating Rankine cycle without an intermediate loop. The natural circulation potential is a key ingredient of the liquid-metal reactor design. PEACER is designed as a loop system, which increases the natural circulation capacity and reduces the maintenance cost. This work is concerned with design of a large-scale test loop Heavy Eutectic Loop Integrated Operation System (HELIOS) to simulate thermal-hydraulic behavior of Pb-Bi in the PEACER system following a single-phase one-dimensional flow loop model. The full-height loop is being constructed for Pb-Bi natural-circulation testing and operating procedure development. Electrically heated rods are used in the heating section, and a water-cooling method is adopted in the cooling section. HELIOS has the same elevation difference between thermal centers of the heat source and heat sink but reduced piping diameters.

Modelling of enzymatic reaction in an internal loop airlift reactor

AbstractGas-liquid reaction carried out in an internal loop airlift reactor was modelled and subjected to the scale-up procedure. Homogeneous oxidation of glucose to gluconic acid catalyzed by Gluzyme 10000 BG, a commercial product containing the enzymes glucose oxidase and catalase as active components, was chosen as the model system. The kinetic parameters were obtained using a 12-L airlift reactor considered as a CSTR. The behaviour of a large-scale internal loop airlift reactor was modelled dividing the reactor sections into a series of tank reactors. The reliability of the model was verified by comparing experimental measurements with the simulation results obtained employing 40-L and 200-L airlift reactors. The designed model could be suitable to predict the behaviour of large-scale internal loop airlift reactors.

傾斜坑井掘削時の掘屑運搬挙動に関する実験的研究

Cuttings transport behavior in drilling directional wells was experimentally investigated using a once-through type large-scale flow loop apparatus, the Cuttings Transport Flow Loop System (CTFLS) in the Japan Oil, Gas and Metals National Corporation Kashiwazaki Test Field. The annular test section of the CTFLS is 9-m long and consists of a 5" ID transparent casing pipe and a 2.063" OD drillpipe. The inclination of the test section can be set at an angle from 0 to 90° in 15° increments. Drillpipe can be mounted either in concentric or eccentric mode.Experiments using two types of drilling mud, water and 0.15% PHPA solution, were conducted to focus on the effects of parameters such as hole inclination angle, drillpipe eccentricity, mud flow rate, mud rheology and rate of penetration (ROP). In the test procedure, mud was circulated and cuttings were fed into the test section both at constant rates, supposing a condition of drilling with constant ROP. Then, for predetermined mud flow rates, quantitative data in steady-state condition such as volumetric concentration of cuttings in the annulus, cuttings bed height and frictional pressure loss were measured. Critical flow rate determination based on a cuttings concentration criteria defined in this study was also presented, and optimum mud flow rate in actual field operation was discussed from a more practical point of view.

Three dimensional computer simulation of magnetic loop associated with magnetic reconnection

The dynamics of large-scale magnetic loop in three dimensions is studied by MHD simulations. The spontaneous fast reconnection model is used in this study. Once a current-driven anomalous resistivity is ignited in a local region in a current sheet, the fast reconnection mechanism spontaneously evolves. As a result, large magnetic loop is developed, and very localized high pressure region appears outside of the magnetic loop. Near the region between magnetic loop and the high pressure region, very large vortex flow appears, and then, the high pressure region more and more localized due to this vortex. On the other hand, we suggest that the spatial size of initial disturbance to the direction of current is very important to evolve of three dimensional fast reconnection processes.

Non-thermal processes associated with rising structures and waves during a “halo” type CME

We analyse structures and events connected with a flare-associated “halo” type coronal mass ejection (CME) observed on December 18, 2000. A GOES C7.0 class X-ray flare started at 11:02 UT in NOAA Active Region 9269, located at N14 E03. Yohkoh SXT observed slowly rising soft X-ray loops already some 5 min before flare start. H α images show a two-ribbon flare, remote brightenings, and a partly disappearing filament near the active region. A metric radio precursor was observed to start at 11:06:30 UT, simultaneously with impulsive emission in hard X-rays and microwaves. The frequency-drifting precursor envelope was superposed with J- and reverse drift bursts. The radio bursts traced large-scale soft X-ray loop structures about 160 000 km away from the flare core, and hard X-ray emission was observed at the ends of some of these loops. The precursor emission points to a rising structure where electron acceleration takes place. Later on, a radio type II burst (signature of a propagating shock, driven either by an ejecta or a blast wave) and an EIT wave were observed. We conclude that possible sources for the rising structure and accelerator of electron beams are (1) large-scale loops that connect the flare core region and the precursor site in the close vicinity of two separate rising filaments, and (2) a growing shock that accelerates electrons along closed field lines until the multipolar field is opened and the CME is lifted off. As neither X-ray nor EUV ejecta could be observed whether in the direction of the type II burst or near the radio precursor, we find some support for the shock wave scenario.

Experimental and Theoretical Simulation of Gravel-Pack Displacement in Extended Horizontal-Offshore Wells

Summary This article presents the development of a computational tool to guide horizontal gravel-pack design for long horizontal offshore wells. Mechanistic model hypotheses, experimentation at a large-scale flow loop, and software development are detailed. The computer simulation results are then compared with field data collected in the Campos basin operations, offshore Brazil. A discussion on design alternatives for a long horizontal well at low fracture-gradient formations is presented. This discussion includes a sensibility analysis on screen eccentricity, open and closed blowout-preventer(BOP) configurations, and alpha (alone) vs. alpha plus beta wave displacement options.

Functionality maps of the ATP binding site of DNA gyrase B: generation of a consensus model of ligand binding.

The Multiple Copy Simultaneous Search method (MCSS) was used to construct consensus functionality maps for functional group binding in the ATP binding site of DNA gyrase B. To account for the conformational flexibility of the protein active site, which involves small side chain fluctuations as well as large-scale loop motions, the calculations were done for three different conformations of the 24 kDa subdomain of DNA gyrase B. A postprocessing procedure that employs a continuum dielectric model to include solvent effects was used to calculate the binding free energy for every functional group. These results were ranked according to their affinity for DNA gyrase B and clustered using a new procedure based on van der Waals contacts that is better adapted for cases where multiple conformations are being considered. A total of 23 different functional groups were tested. The results gave consensus maps that indicate those functional group binding sites that are insensitive to the specific protein conformation. The maps also demonstrate that functional groups other than those found in the known ligands may bind competitively in the binding sites of known ligands. This suggests numerous scaffolds that can be used in the development of new ligands for the ATP and coumarinic binding sites in DNA gyrase B. Finally, the calculations show the existence of alternative binding sites near the known binding sites that could be targeted in the rational design for new inhibitors.

Effects of film cooling hole shape on heat transfer

AbstractThe effects of hole shapes, secondary injection Reynolds numbers, and blowing ratios on the heat transfer downstream of film cooling holes have been investigated by using a large‐scale low‐speed loop wind tunnel. The test model consists of five film cooling holes. Experiments on dustpan‐shaped holes, fan‐shaped holes, and round holes have been conducted with injection Reynolds number ranging from 10,000 to 25,000 and blowing ratio ranging from 0.3 to 2.0. Measurements are taken under 26 conditions. Results show that the critical blowing ratio is 1.3 for the dustpan‐ and fan‐shaped holes, 0.7 for the round holes. The turbulence generated by air injection through round holes is stronger than those through dustpan‐ and fan‐shaped holes. © 2004 Wiley Periodicals, Inc. Heat Trans Asian Res, 33(2): 73–80, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/htj.20005

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

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

A model for elemental coronal flux loops

The photosphere possesses many small, intense patches of magnetic flux. Each of these patches (or sources) is connected magnetically through the corona to several sources of opposite polarity. An elemental flux loop consists of all of the flux joining one such source to another. We find that each source is connected to twenty other sources, on average, and that the typical flux and diameter of elemental loops in the corona are 10 16 Mx and 200 km; there are approximately 17 separators for each source. We also model a typical large-scale coronal loop consisting of many elemental loops and determine its complex internal topology. Each upright null lies at the end of about 22 separatrices, which tend to be clustered together in trunk-like structures, analogous to river- valleys in a geographical contour map. Prone nulls correspond to saddle points, while their spines are analogous to watersheds.

Forced Convection Heat Transfer and Temperature Fluctuations of Lithium under Transverse Magnetic Fields

The MHD effects on a heat transfer of liquid lithium flowing in an annular channel were studied, using a newly constructed comparatively large-scale lithium loop. The data on the heat transfer characteristics were arranged in Nu-St diagrams where St=Ha2/Re. The diagrams indicate that Nu decreases as St increases as a whole trend. However, singular peaks of Nu were observed at about St=13, corresponding to the singular increments of temperature fluctuations, whereas the peaks occurred at St=1.5 in the previous experiment with a smaller channel. In considering a predominant MHD effect due to conductive wall duct, the current load factor KP for external circuit was taken into account. And Miyazaki number Mi=KPSt, which means the effective electromagnetic interaction, was adopted in substitution for St and the heater pin diameter was taken as the characteristic length in place of the conventional hydraulic equivalent diameter. Thus, an appreciably good agreement was obtained concerning the peaks at Mi=0.13 in the previous and at Mi=0.14 in the present experiments. Generation of vortex series in the singular phenomena was suggested from both the periodicity of temperature fluctuations in their PSD analysis and the proportionality between peak frequency and mean flow velocity, resulting in a 32 mm interval length of series.

Physical mechanism of spontaneous fast reconnection evolution

Large dissipative events, such as solar flares and geomagnetic substorms, result from sudden onset of magnetic reconnection, so that it is a long-standing problem to find the physical mechanism that makes magnetic reconnection explosive. As recognized by Petschek, standing slow shocks enable the effective magnetic energy conversion in space plasmas of extremely large magnetic Reynolds number. Hence, a basic question is how the fast reconnection mechanism involving slow shocks can be realized as an eventual solution? We have proposed the spontaneous fast reconnection model, which describes a new type of nonlinear instability that grows by the positive feedback between plasma microphysics (current-driven anomalous resistivity) and macrophysics (global reconnection flow). It is demonstrated that the fast reconnection mechanism explosively grows by the positive feedback in a variety of physical situations; for the larger threshold of anomalous resistivity, the fast reconnection evolves more drastically. Also, distinct plasma processes, such as large-scale plasmoid and magnetic loop dynamics, result directly from the fast reconnection evolution. Even in general asymmetric situations, the spontaneous fast reconnection model effectively works, giving rise to drastic magnetic flux transfer.

One‐dimensional and Pseudo–Two‐dimensional Hydrodynamic Simulations of Solar X‐Ray Jets

We present results of one-dimensional hydrodynamic simulations of the chromospheric evaporation produced by a microflare in a large-scale loop as a model of X-ray jets. The initial conditions of the simulations are based on the observations of X-ray jets. We deposit thermal energy (~1 × 1028 ergs) in the corona. The deposited energy is rapidly transported to the chromosphere by conduction, which heats the dense plasma in the upper chromosphere. As a result, the gas pressure is increased and drives a strong upflow of dense, hot plasma along the magnetic loop. We found the following features of evaporation in the results of our simulations: (1) the maximum temperature of the evaporating plasma is determined by the balance between the conductive flux and the heating flux; (2) the total mass of evaporating plasma is controlled by the balance between the conductive flux and enthalpy flux; (3) the relationship between the density neva, height of energy deposition sflare, and heating rate Fh is described as neva ∝ F/s; (4) the X-ray intensity along the evaporation-flow plasma decreases exponentially with distance from the footpoint, and that exponential intensity distribution holds from the early phase to the decay phase; (5) in the single-loop model, the temperature decreases with distance from the energy deposition site (on the other hand, a hot region is present in front of the evaporation front in the multiple-loop model); (6) we compare the physical parameters of the evaporation flow with the observations of the X-ray jet that occurred on 1992 September 3 and find that the physical parameters of evaporating plasma are similar to those of the Yohkoh-observed X-ray jet. Since these properties of the evaporation flow are similar to the observed properties of X-ray jets, we suggest that an X-ray jet is the evaporation flow produced by a flare near the footpoint of a large-scale loop. Furthermore, according to the X-ray intensity distribution along the evaporation flow, we suggest that a multiple-loop model based on the magnetic reconnection mechanism can reproduce the properties of an X-ray jet better than the single-loop model.

Parallel processing of network calculations in order to speed up transient stability analysis

AbstractPower systems have become very large, and in addition the forthcoming open electricity market will make power system operation more complex. Therefore, power system operation must become more efficient and flexible. Very fast power system simulation is a means of achieving more sophisticated power system on‐line monitoring and control, and parallel computing is a key technology for very fast power system simulation. This paper proposes an efficient and fast parallel network calculation algorithm that will contribute to the development of fast power system simulation programs. Numerical examples show that the proposed method using six processors is about 4.0 times as fast as the usual serial algorithm when applied to a large‐scale radial power system and about 3.2 times as fast when applied to a large‐scale loop power system. © 2001 Scripta Technica, Electr Eng Jpn, 135(3): 26–36, 2001

Hessian-free low-mode conformational search for large-scale protein loop optimization: application to c-jun N-terminal kinase JNK3

A Hessian-free low-mode search algorithm has been developed for large-scale conformational searching. The new method is termed LLMOD, and it utilizes the ARPACK package to compute low-mode eigenvectors of a Hessian matrix that is only referenced implicitly, through its product with a series of vectors. The Hessian × vector product is calculated utilizing a finite difference formula based on gradients. LLMOD is the first conformational search method that can be applied to fully flexible, unconstrained protein structures for complex loop optimization problems. LLMOD has been tested on a particularly difficult model system, c-jun N-terminal kinase JNK3. We demonstrate that LLMOD was able to correct a P38/ERK2/HCL-based homology model that grossly misplaced the crucial glycine-rich loop in the ATP-binding site. © 2000 John Wiley & Sons, Inc. J Comput Chem 22: 21–30, 2001

過渡安定度計算高速化のための系統計算の並列処理アルゴリズムの開発

Power system has become so large and, furthermore, forthcoming open electricity market will make power system operation more complex. Therefore, power system operation is required to become more efficient and flexible. Very fast power system simulation method is a ticket to more sophisticated power system on-line monitoring and control, and parallel computing technology is a key technology to very fast power system simulation method. In this paper, an efficient and fast parallel algorithm of network calculation is proposed, which will contribute to the development of fast power system simulation program. Numerical examples show that the proposed method using 6 processors is about 4.0 times faster than usual serial algorithm when applied to a large scale radial power system and about 3.2 times faster when applied to a large scale loop power system.

Quadrupolar Magnetic Reconnection in Solar Flares. I. Three‐dimensional Geometry Inferred fromYohkohObservations

We analyze the three-dimensional geometry of solar flares that show so-called interacting flare loops in soft X-ray, hard X-ray, and radio emission, as previously identified by Hanaoka and Nishio. The two flare loops that appear brightest after the flare are assumed to represent the outcome of a quadrupolar magnetic reconnection process, during which the connectivity of magnetic polarities is exchanged between the four loop footpoints. We parameterize the three-dimensional geometry of the four involved magnetic field lines with circular segments, additionally constrained by the geometric condition that the two pre-reconnection field lines have to intersect each other at the onset of the reconnection process, leading to a 10 parameter model. We fit this 10 parameter model to Yohkoh Soft and Hard X-Ray Telescopes (SXT and HXT) data of 10 solar flares and determine in this way the loop sizes and relative orientation of interacting field lines before and after reconnection. We apply a flare model by Melrose to calculate the magnetic flux transfer and energy released when two current-carrying field lines reconnect to form a new current-carrying system in a quadrupolar geometry. The findings and conclusions are the following. (1) The pre-reconnection field lines always show a strong asymmetry in size, consistent with the scenario of newly emerging small-scale loops that reconnect with preexisting large-scale loops. (2) The relative angle between reconnecting field lines is nearly collinear in half of the cases, and nearly perpendicular in the other half, contrary to the antiparallel configuration that is considered to be most efficient for magnetic reconnection. (3) The angle between interacting field lines is reduced by ≈10°-50° after quadrupolar reconnection. (4) The small-scale flare loop experiences a shrinkage by a factor of 1.31 ± 0.44, which is consistent with the scaling law found from previous electron time-of-flight measurements, suggesting that electron acceleration occurs near the cusp of quadrupolar configurations. (5) The large-scale loop is found to dominate the total induction between current-carrying loops, providing a simple estimate of the maximum magnetic energy available for flare energy release because of current transfer, which scales as ΔEI ≈ 1029.63(r2/109 cm)(I2/1011A)2 (with r2 the curvature radius and I2 the current of the large-scale loop) and is found to correlate with observed flare energies deduced from soft X-ray and hard X-ray fluxes. Most of the energy is transferred to small-scale loops that have one-half of the large-scale current (I1 = I2/2). (6) The quadrupolar reconnection geometry provides also a solution of Canfield's dilemma of the offset between the maximum of vertical currents and the HXR flare loop footpoints. (7) The quadrupolar geometry provides not only a framework for interacting double-loop flares, but it can also be considered as a generalized version of (cusp-shaped) single-loop flares.

Modelling and scale-up of a loop reactor for hydrogenation processes

A dynamic model for the scale-up of semibatch loop reactors was developed. The mathematical model comprises the essential parts of the loop reactor: the reaction vessel, the ejector and the circulation loop. Tanks-in-series and axial dispersion concepts were applied on the description of the non-ideal flow pattern of the reactor. The dynamic axial dispersion model was discretized with finite differences with respect to the spatial coordinate, and the created ordinary differential equations were solved with the backward difference method suitable for stiff differential equations. The loop reactor model was tested with a case study, a homogeneously-heterogeneously catalyzed reaction system, reductive alkylation of aromatic amines. Simulations showed that rate equations obtained from laboratory-scale experiments can be successfully combined to the flow model of the loop reactor: the behaviour of a large-scale loop reactor was predicted with satisfactory accuracy.