Energy Buildup Research Articles

Magnetic energy buildup in a quadrupole field by photospheric shear motion

Using a two-dimensional, dissipative magnetohydrodynamic model, this paper presents a numerical simulation of the magnetic energy buildup in a quadrupolar field by photospheric shear motion. When electric current density is larger than a certain critical value, an anomalous resistivity is introduced in order to account for the dissipation caused by instabilities in high current regions. It is shown that like a bipolar field, a quadrupolar field can efficiently store magnetic free energy through photospheric shear motion. Electric current formed by shear concentrates on the separatrix and magnetic loops rooted in areas where the shear velocity gradient is large. The atmosphere is heated by anomalous resistive dissipation during the shear. Both magnetic and thermal energy increases nonlinearly with shearing displacement. When the anomalous resistivity increases or the critical current density decreases, the growth rate reduces for magnetic energy but goes up for thermal energy.

Forearc Deformation and Great Subduction Earthquakes: Implications for Cascadia Offshore Earthquake Potential

The maximum size of thrust earthquakes at the world's subduction zones appears to be limited by anelastic deformation of the overriding plate. Anelastic strain in weak forearcs and roughness of the plate interface produced by faults cutting the forearc may limit the size of thrust earthquakes by inhibiting the buildup of elastic strain energy or slip propagation or both. Recently discovered active strike-slip faults in the submarine forearc of the Cascadia subduction zone show that the upper plate there deforms rapidly in response to arc-parallel shear. Thus, Cascadia, as a result of its weak, deforming upper plate, may be the type of subduction zone at which great (moment magnitude approximately 9) thrust earthquakes do not occur.

The Folding of Triangulated Cylinders, Part II: The Folding Process

In the first paper of this series we have introduced a class of foldable triangulated cylinders. In this paper we consider three particular examples of these cylinders and analyse computationally the way they fold. We show that this process is nonuniform and that it consists of two phases. The first unsteady phase involves the gradual buildup of strain energy in a “shape transition region.” In the second phase the transition region moves toward the bottom of the cylinder under almost zero force. Although the behavior of the three example cylinders is qualitatively similar, the peak force on the cylinder, as well as the peak strain, have different magnitudes, in agreement with a result in our first paper.

On the occurrence rate of high-speed solar wind events

We have investigated the rate of occurrence of solar wind phenomena observed between 1972–1984 using power-spectrum analysis. The data have been taken from the high-speed solar wind (HSSW) stream catalogue published by Mavromichalaki, Vassilaki, and Marmatsouri (1988). The power-spectrum analysis of HSSW events indicates that HSSW stream events have a periodicity of 9 days. This periodicity of HSSW events is\(\frac{1}{3}\) of the 27-day period of coronal holes, which are major sources of solar wind events. In our opinion, the 9-day period may be the energy build-up time for coronal hole regions to produce the HSSW stream events.

Hybrid mode locking of a flash-lamp-pumped Ti:Al_2O_3 laser

We demonstrate an all-solid-state hybrid mode-locking technique for flash-lamp-pumped solid-state lasers. The combination of active acousto-optic modulation and fast saturable-absorber action from a low-temperature multiple quantum well allows strong pulse shaping to be achieved during the rapid pulse energy buildup from the flash-lamp pumping. Pulse durations as short as 4.5 ps have been generated. The high-energy storage available from Ti:Al2O3 allows this new mode-locking technique to produce pulses with peak powers of >4 MW at a 10-Hz repetition rate directly from a single laser.

Research needed to improve solar flare and particle forecasting

We briefly review the status of our physical understanding of energy buildup and release in transient active phenomena on the Sun. Such understanding is necessary in order to improve our capabilities to predict such events and their effects in interplanetary space and near-Earth environment. We then discuss the research that we consider is needed for such improvement.

Stable acoustic-emission characteristic of the extent of damage to brittle materials

An experimental study has been made of the dissipation of elastic energy in the course of the inelastic deformation and fracture of brittle materials. The energy characteristics of acoustic emission and the amount of energy expended irreversibly on inelastic deformation were determined simultaneously during uniaxial quasistatic loading. Test samples of grade 600 cement paste, of grade 150 structural ceramic, and of the ceramic ferroelectric materials PKR-1 and TsTS-19 were studied. The results demonstrate the effectiveness of the thermodynamic acoustic-emission damage parameter ω(σ). This parameter characterizes the relative contribution of the rate of the buildup of latent energy of fracture to the overall rate of energy dissipation in the course of the inelastic deformation of a solid.

A flare caused by interacting coronal loops

view Abstract Citations (37) References (13) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS A Flare Caused by Interacting Coronal Loops Hanaoka, Yoichiro Abstract The observation of a flare on 1992 July 15 with the Soft X-ray Telescope (SXT) on board the Yohkoh satellite shows that the energy buildup in the corona was caused by the increasing shear of the magnetic field due to the photospheric flow and that the flare occurred through the interaction of sheared coronal loops. About 24 hr before the flare, the coronal loops were only weakly sheared. After that time, a rapid spot motion with the velocity of 0.25 km/s was observed, and the coronal loops were changed to a sheared structure by this motion. Finally, a flare occurred at the intersection of the sheared loops. Such a scenario of the energy buildup and release processes has been suggested from the various indirect evidence. However, the SXT, which takes both soft X-ray and optical pictures, shows for the first time that the photospheric motion actually produces the sheared coronal loop structure. Furthermore, the observational results of the flare prove the validity of the loop-loop interaction model for flares. Publication: The Astrophysical Journal Pub Date: January 1994 DOI: 10.1086/187157 Bibcode: 1994ApJ...420L..37H Keywords: Coronal Loops; Light (Visible Radiation); Magnetic Energy Storage; Photosphere; Shear; Solar Flares; Solar Magnetic Field; Sunspots; X Ray Astronomy; Magnetic Signatures; Radio Spectra; Satellite-Borne Instruments; Solar Maximum Mission; X Ray Imagery; X Ray Telescopes; Solar Physics; SUN: CORONA; SUN: FLARES; SUN: MAGNETIC FIELDS full text sources ADS |

Synthetic strategies towards C70: molecular mechanics and MNDO calculations on pinakene, C28H14 and related molecules

Molecular mechanics (MM2) calculations have been performed to estimate the strain energies of hydrocarbons derived from the fragments of C70 which retain C5 or C2 symmetry. There are two ways of dissecting C70 retaining C2 symmetry, C2(a) and C2(b). The key fragment along the C2(a) route is pinakene. C28H14(12). It exists in a bowl shape. Its strain energy is close to that of the corresponding C28 fragment of C70. The bowl depth was calculated to be 2.03 A at the MNDO level, and the ‘bowl-to-bowl’ inversion barrier calculated to be about 48.6 kcal mol–1, implying that this is a very rigid bowl. The strain energy build-up from the sequential placement of methylene bridges in going from dibenzo[fg,op] naphthacene (26) to pinakene was estimated. Methyl derivatives of dibenzo[fg,op]naphthacene were taken as the key precursors in this study. Strain energies of various positional isomers were also evaluated. Synthetic strategies towards pinakene are delineated.

Generation of Electric Currents in Two-dimensional Magnetic Nulls

view Abstract Citations (3) References (19) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Generation of Electric Currents in Two-dimensional Magnetic Nulls Fontenla, Juan M. Abstract We present detailed calculations and results for a model case of two-dimensional small distortions of static, current-free equilibrium around a null-line magnetic configuration. This setup has been studied for fast energy release in flares, but has not been studied before in the context of the magnetic energy buildup that precedes the flare. Our analytical results are new because they include gas pressure and provide explicit formulae for the expressions of all quantities (and especially the electric current) and energy storage as functions of the values of boundary conditions. A general solution is shown as a combination of eigenfunctions, with coefficients resulting from the boundary conditions. These boundary conditions are given in terms of any arbitrary plasma acceleration at a boundary enclosing the domain we study. The approach used here studies the MHD evolution of the electric current and plasma density variations driven by external forces. We find that both pressure and Lorentz forces are important, and that their boundary values select between a wide range of solutions, many of which have been found previously in numerical simulations. Most of the modes we find display strong current sheets, velocities, and pressure variations at the separatrices Also we find that Joule and other dissipative terms are not important for typical cases, except at an extremely narrow inner core, and near the separatrices We discuss our results and their relationship to numerical MHD simulations. Publication: The Astrophysical Journal Pub Date: December 1993 DOI: 10.1086/173535 Bibcode: 1993ApJ...419..837F Keywords: MAGNETOHYDRODYNAMICS: MHD; SUN: MAGNETIC FIELDS full text sources ADS |

Effect of switching on nanosecond rf-pulse shaping

Recursion relations are obtained for the shaping of rf pulses produced by the buildup and release of microwave energy from resonant cavities based on rectangular tees. Within the framework of the adopted model of switching process, a theoretical analysis of its impact on the rf-pulse parameters is performed. The analysis results are compared with experimental data. Suggestions on the design of nanosecond rf-pulse shapers are given.

Misfit dislocation distributions in capped (buried) strained semiconductor layers

An elastic continuum model is used to investigate distributions of misfit dislocations in a capped layer structure. Effects of the free surface at the top of the cap and of interactions between dislocations have been rigorously incorporated, making the study applicable to structures with caps of arbitrary thickness and to the process of strain relaxation in layers already containing misfit dislocations. Two dislocation types are considered in detail: single dislocations (singles) residing at the lower interface, between the strained layer and the substrate, and dislocation dipoles, i.e., pairs of parallel dislocations with opposite Burgers vectors, one at the lower interface and the other at the upper interface, between the strained layer and the cap. Although singles cause unwanted long-range distortion in the cap, which is not caused by dipoles, dipoles give rise to increased localised distortion, due to the presence of the additional dislocation, at the upper interface. Hence singles and dipoles compete as misfit dislocation types in capped layers, with the dominant type being determined by the parameters of the layer structure. It is demonstrated that interactions between dislocations are crucial, and that experimental observations cannot be explained by consideration of an isolated single or dipole. Interactions between singles in an array at the lower interface result in a buildup of strain energy in the cap. The rapidity of this buildup with dislocation density demands a transition from relaxation by singles to relaxation by arrays of dipoles; such a transition would not be predicted by a consideration of isolated singles or dipoles. Energy evaluations are performed to incorporate such interactions between dislocations while providing a sequential view of strain relaxation, with singles and dipoles entering the structure one at a time. It is thus demonstrated that a mixture of singles and dipoles is expected in many capped layers of practical interest. An example calculation predicts a mixture that is consistent with experimental observation.

Frequency distributions and correlations of solar X-ray flare parameters

We have determined frequency distributions of flare parameters from over 12000 solar flares recorded with the Hard X-Ray Burst Spectrometer (HXRBS) on the Solar Maximum Mission (SMM) satellite. These parameters include the flare duration, the peak counting rate, the peak hard X-ray flux, the total energy in electrons, and the peak energy flux in electrons (the latter two computed assuming a thick-target flare model). The energies were computed above a threshold energy between 25 and 50 keV. All of the distributions can be represented by power laws above the HXRBS sensitivity threshold. Correlations among these parameters are determined from linear regression fits as well as from the slopes of the frequency distributions. Variations of the frequency distributions were investigated with respect to the solar activity cycle. Theoretical models for the frequency distribution of flare parameters depend on the probability of flaring and the temporal evolution of the flare energy build-up. Our results are consistent with stochastic flaring and exponential energy build-up, with an average build-up time constant that is 0.5 times the mean time between flares. The measured distributions of flares are also consistent with predicted distributions of flares from computer simulations of avalanche models that are governed by the principle of self-organized criticality.

Theoretical study of the resonant behaviour of an ion confined to a potential well in a combination of AC and DC magnetic fields.

Numerical solutions are presented to the equation of motion for an ion confined to a region of space by a restoring force and subject to DC and AC magnetic fields. We have expanded on the theoretical work of Durney et al. [1988] by including a potential well as a confining factor. This additional term in the equation of motion, being nondissipative, could allow for the buildup of stored energy within the system to a level necessary for a macroscopic resonant phenomenon. Resonant behaviour has been studied, including calculation of the trajectory and energy (kinetic and potential) of a confined ion, with emphases on the appearance of both amplitude and frequency windows. The results are discussed in relation to ion transport through transmembrane channels exposed to magnetic fields. When realistic values of the frictional and restoring-force coefficients are considered, all predicted resonant behaviour disappears, except at very high field strengths.

Magnetic Field Topology in Solar Active Regions

AbstractIn solar active regions, over extended periods of time the plasma-magnetic field configuration evolves quasistatically through a sequence of nearly force-free equilibrium states. This evolution may be understood as the continual distortion of an existing equilibrium by wavelike disturbances propagating upward from the photosphere and subsequent fast relaxation to a new, neighbouring equilibrium. In the present paper the build-up of magnetic energy, which is presumably necessary for flares and other explosive events, during a quasistatic evolution is considered. If during the slow evolution the magnetic energy is increased, then the relaxation processes represent inverse cascades of energy. We study the conditions under which such cascades are possible within the framework of mean-field MHD. In contrast to the convection zone, where the dynamo for the global magnetic field of the Sun works, the solar atmosphere is convectively stable and the first order smoothing approximation justified. It turns out then that current helicity (B.∇ × B) is an important quantity decisive for whether magnetic energy can be built up.

Magnetic Field Observation with the Solar Flare Telescope

AbstractThe Solar Flare Telescope was constructed at Mitaka in 1989. This instrument comprises four telescopes which respectively observe (a) Hα images, (b) continuum images, (c) vector magnetic fields, and (d) velocity fields in the photosphere. The instrument aims at the study of energy build-up and energy release in solar flares, in cooperation with the Solar-A satellite. The whole system has been in regular operation since 1992 July. The methods of measuring the magnetic and velocity fields are described.

Magnetic diffusion and flare energy buildup

Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear two-dimensional force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field (B0 almost-equal-to 10(3) G) and photospheric velocity field (V(max) almost-equal-to 1 km s-1) are used, it is found that 3-4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal region, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.

Depositional controls on Lower Carboniferous microbial buildups, eastern Midland Valley of Scotland

ABSTRACTIn the eastern Midland Valley of Scotland non‐skeletal carbonate buildup complexes are present in the Charlestown Main Limestone (Brigantian), a thin marine carbonate unit within a lower Carboniferous basin fill otherwise dominated by fluvio‐deltaic sediments and volcanics. The buildups are restricted geographically to West Lothian and Central Fife and correspond to an area of reduced subsidence, the Burntisland High. Buildup geometry and local facies mosaics reflect the relative water depth and position on the Burntisland High that, because of its slight topographical relief and more distal position with respect to the location of fluvio‐deltaic systems, became an area of increased carbonate productivity and hence a locus for buildup development. Away from the Burntisland High, in the Fife‐Midlothian Low, more monotonous argillaceous limestone facies, of low energy and somewhat deeper water aspect, accumulated.Buildup facies contain a diverse marine fauna and are characterized by peloidal, clotted and homogeneous micrites interpreted as predominantly microbial in origin. Two types of buildup complex occur. At Charlestown, vertically stacked, tabular banks (up to 2 m thick and 100 m wide) form the western margin of an asymmetric buildup accumulation. East of this margin a complex mosaic of isolated low relief buildups and inter‐buildup sediments was deposited. Skeletal sand shoals present within these inter‐buildup sediments indicate that high energy conditions prevailed during buildup growth. In contrast, at Roscobie, inter‐buildup sediments are of low energy aspect and buildup geometry is domical rather than tabular. Initiated in slightly deeper and calmer water on the flank of the Burntisland High, the Roscobie buildups (up to 15 m thick and 46 m wide) accreted vertically, rather than laterally as at Charlestown, and coalesced to form an elongate ridge‐shaped buildup complex.

The effect of retardation on the stability of current filaments

We investigate the influence of the finite Alfven velocity on the evolution of an active region filament. In general, variations of a current result in variations of the magnetic fields which spread around with the Alfven velocity. As a consequence of the fact that a magnetic field can only change with the Alfven velocity, a filament will experience the photospheric boundary conditions as these were at an Alfven travel time back in time. The inclusion of this retardation effect in the momentum equation of a filament leads effectively to an extra force term. This force contribution acts in the direction in which the filament moves and has therefore a destabilizing effect on the filament. Because a moving filament acts as an antenna of Alfven waves, the filament loses energy by the emission process. This leads to a radiative damping term in the equation of motion of the filament. In general, the radiative damping will be sufficiently strong to counteract the retardation instability. Numerical simulations show that during the energy build-up phase a filament follows the van Tend-Kuperus equilibrium curve. After the van Tend-Kuperus equilibrium has disappeared the filament goes through a transient phase moving with a sub-Alfvenic velocity upward. At greater heights the repulsive Lorentz force of the photospheric surface current magnetic field is balanced by the radiative damping, resulting in a decreasing filament velocity.

The use of an external cavity with the SCA/FEL

Abstract We have investigated the possibility of coupling the FEL optical beam into an external cavity. The resulting buildup of optical energy in the cavity offers several advantages. First, the sensitivity of the stored energy to source instabilities makes the external cavity a powerful FEL diagnostic. The dependence of the stored energy on several important instabilities will be discussed, as will plans for actually quantifying these instabilities with the external cavity. Second, a large amount of energy can be accumulated in the external cavity. Outcoupling this energy can significantly increase the micropulse energy delivered. Three possible outcoupling schemes will be discussed: “enhanced” outcoupling, photo-activated cavity dumping, and electro-optic cavity dumping.