Fine Structure Of Filaments Research Articles

Fine structure of cocoon and cocoon filaments from Braconidae insect

Fine structure of cocoon and cocoon filaments from Braconidae insect

Standing Waves in Near-Parallel Vortex Filaments

A model derived in (Klein et al., J Fluid Mech 288:201–248, 1995) for n near-parallel vortex filaments in a three dimensional fluid region takes into consideration the pairwise interaction between the filaments along with an approximation for motion by self-induction. The same system of equations appears in descriptions of the fine structure of vortex filaments in the Gross–Pitaevski model of Bose–Einstein condensates. In this paper we construct families of standing waves for this model, in the form of n co-rotating near-parallel vortex filaments that are situated in a central configuration. This result applies to any pair of vortex filaments with the same circulation, corresponding to the case n = 2. The model equations can be formulated as a system of Hamiltonian PDEs, and the construction of standing waves is a small divisor problem. The methods are a combination of the analysis of infinite dimensional Hamiltonian dynamical systems and linear theory related to Anderson localization. The main technique of the construction is the Nash–Moser method applied to a Lyapunov–Schmidt reduction, giving rise to a bifurcation equation over a Cantor set of parameters.

Structure of sunspot penumbral filaments: a remarkable uniformity of properties

The sunspot penumbra comprises numerous thin, radially elongated filaments that are central for heat transport within the penumbra, but whose structure is still not clear. To investigate the fine-scale structure of these filaments, we perform a depth-dependent inversion of spectropolarimetric data of a sunspot very close to solar disk center obtained by Hinode (SOT/SP). We have used a recently developed spatially coupled 2D inversion scheme which allows us to analyze the fine structure of individual penumbral filaments up to the diffraction limit of the telescope. Filaments of different sizes in all parts of penumbra display very similar magnetic field strengths, inclinations and velocity patterns. The similarities allowed us to average all these filaments and to extract the physical properties common to all of them. This average filament shows upflows associated with an upward pointing field at its inner, umbral end and along its axis, downflows along the lateral edge and strong downflows in the outer end associated with a nearly vertical, strong and downward pointing field. The upflowing plasma is significantly hotter than the downflowing plasma. The hot, tear-shaped head of the averaged filament can be associated with a penumbral grain. The central part of the filament shows nearly horizontal fields with strengths of ~1kG. The field above the filament converges, whereas a diverging trend is seen in the deepest layers near the head of the filament. We put forward a unified observational picture of a sunspot penumbral filament. It is consistent with such a filament being a magneto-convective cell, in line with recent MHD simulations. The uniformity of its properties over the penumbra sets constraints on penumbral models and simulations. The complex and inhomogeneous structure of the filament provides a natural explanation for a number of long-running controversies in the literature.

Puzzling nature of the fine structure of quiescent prominences and filaments

Even after more than 160 years of observations and modelling of solar prominences their true nature contains many open questions. In this work we argue that current 2D prominence fine structure models can help us to understand the puzzling connection between quasi-vertical fine structures often seen in quiescent prominences observed on the solar limb and horizontally aligned dark fibrils representing the fine structures of prominences observed in absorption against the solar disk (filaments).

THE THERMAL INSTABILITY OF SOLAR PROMINENCE THREADS

The fine structure of solar prominences and filaments appears as thin and long threads in high-resolution images. In H-alpha observations of filaments, some threads can be observed for only 5 - 20 minutes before they seem to fade and eventually disappear, suggesting that these threads may have very short lifetimes. The presence of an instability might be the cause of this quick disappearance. Here, we study the thermal instability of prominence threads as an explanation of their sudden disappearance from H-alpha observations. We model a prominence thread as a magnetic tube with prominence conditions embedded in a coronal environment. We assume a variation of the physical properties in the transverse direction, so that the temperature and density continuously change from internal to external values in an inhomogeneous transitional layer representing the particular prominence-corona transition region (PCTR) of the thread. We use the nonadiabatic and resistive magnetohydrodynamic equations, which include terms due to thermal conduction parallel and perpendicular to the magnetic field, radiative losses, heating, and magnetic diffusion. We combine both analytical and numerical methods to study linear perturbations from the equilibrium state, focusing on unstable thermal solutions. We find that thermal modes are unstable in the PCTR for temperatures higher than 80,000 K, approximately. These modes are related to temperature disturbances that can lead to changes in the equilibrium due to rapid plasma heating or cooling. For typical prominence parameters, the instability time scale is of the order of a few minutes and is independent of the form of the temperature profile within the PCTR of the thread. This result indicates that thermal instability may play an important role for the short lifetimes of threads in the observations.

Extreme fractal structures in chaotic mechanical systems: riddled basins of attraction

Chaotic dynamical systems with certain phase space symmetries may exhibit riddled basins of attraction, which can be viewed as extreme fractal structures in the sense that, regardless of how small is the uncertainty in the determination of an initial condition, we cannot decrease the fraction of such points that are certain to converge to a given attractor. We investigate a mechanical system exhibiting riddled basins of attraction: a particle under a two-dimensional potential with friction and time-periodic forcing. The verification of riddling is made by checking its mathematical requirements through computation of finite-time Lyapunov exponents as well as by scaling laws describing the fine structure of basin filaments densely intertwined in phase space.

Fine structure of the cocoon filaments of the silkworm differing relative amounts of sericin

Fine structure of the cocoon filaments of the silkworm differing relative amounts of sericin

On the Fine Structure and Formation of Sunspot Penumbrae

Recent high-resolution observations with the 1 m Swedish Solar Telescope (SST) on La Palma reveal the fine substructure of penumbral filaments and new properties of their dynamics. These findings provide both the basis and constraints for novel models of the penumbra. We present new observations of a large isolated sunspot near Sun center obtained with the SST in 2006. Our data, taken simultaneously in the 4305 A G-band and 4364 A continuum bandpasses and compiled in high-cadence movies, confirm the previous results and reveal new features of penumbral filament dynamics. We find that individual filaments are cylindrical helices with the apparent properties of vortex tubes exhibiting flow patterns similar to kinked flux tubes. Measured pitch/radius ratios of helical filaments indicate their dynamic stability. We propose a mechanism that explains the fine structure of penumbral filaments, their observed dynamics, and their formation process in association with sunspot properties. The mechanism assumes that the umbra itself is a dense conglomerate of twisted, interlaced flux tubes with peripheral filaments branching out from the trunk at different heights due to ongoing reconnection processes and arcing downward to the photosphere. The twist of individual filaments, and the resulting distribution of magnetic fields and temperature, is due to the onset of the well-known screw pinch instability, the parameters of which can be measured from our data.

Ultrastructural characteristics of tau filaments in tauopathies: Immuno‐electron microscopic demonstration of tau filaments in tauopathies

The microtubule-associated protein tau aggregates into filaments in the form of neurofibrillary tangles, neuropil threads and argyrophilic grains in neurons, in the form of variable astrocytic tangles in astrocytes and in the form of coiled bodies and argyrophilic threads in oligodendrocytes. These tau filaments may be classified into two types, straight filaments or tubules with 9-18 nm diameters and "twisted ribbons" composed of two parallel aligned components. In the same disease, the fine structure of tau filaments in glial cells roughly resembles that in neurons. In sporadic tauopathies, individual tau filaments show characteristic sizes, shapes and arrangements, and therefore contribute to neuropathologic differential diagnosis. In frontotemporal dementias caused by tau gene mutations, variable filamentous profiles were observed in association with mutation sites and insoluble tau isoforms, including straight filaments or tubules, paired helical filament-like filaments, and twisted ribbons. Pre-embedding immunoelectron microscopic studies were carried out using anti-3-repeat tau and anti-4-repeat tau specific antibodies, RD3 and RD4. Straight tubules in neuronal and astrocytic Pick bodies were immunolabeled by the anti-3-repeat tau antibody. The anti-4-repeat tau antibody recognized abnormal tubules comprising neurofibrillary tangles, coiled bodies and argyrophilic threads in progressive supranuclear palsy (PSP) and corticobasal degeneration. In the pre-embedding immunoelectron microscopic study using the phosphorylated tau AT8 antibody, tuft-shaped astrocytes of PSP were found to be composed of bundles of abnormal tubules in processes and perikarya of protoplasmic astrocytes. In this study, the 3-repeat tau or 4-repeat tau epitope was detected in situ at the ultrastructural level in abnormal tubules in representative pathological lesions in Pick's disease, PSP and corticobasal degeneration.

On the Fine Structure of Solar Filaments

High-resolution Hα images of solar filaments show a variety of dark fine-structure fibrils, most of them aligned with the magnetic field that is sheared with respect to the filament long axis. Here we demonstrate how such fibrils can be explained in terms of the magnetic field dips produced by realistic mass loading due to plasma condensation along the top of a magnetic prominence arcade. Our interpretation is supported by (2+1)-dimensional radiation-magnetohydrostatic simulations that predict quantitatively the properties of such condensations that are suspended in the dipped magnetic field.

Helicity Generation and Signature in Solar Atmosphere

AbstractTo fully understand the origin, evolution and topology of solar magnetic fields, one should comprehend their magnetic helicity. Observationally, non-zero helicity reveals itself in the patterns of electric currents inside active regions, superpenumbral sunspot whirls, the shape of coronal loops and the fine structure of chromospheric filaments. Some patterns may bear information about deep sub-photospheric processes (e.g., dynamo, turbulent convection). Others may originate at or near the photosphere. This presentation reviews the observations of magnetic and current helicity on the Sun, discusses the possible mechanisms of helicity generation, and compares them with the observations.

Fast MHD oscillations of a 3-dimensional prominence fibril

High-resolution observations of quiescent filaments point out that their fine structure is made of small-scale threads or fibrils. These fibrils can be represented as thin loops having cool tops, i.e. the prominence material, while the rest of the loop displays coronal temperatures. Then, the stacking of these thin loops in the vertical and horizontal directions gives place to the fine structure of filaments. On the other hand, two-dimensional, high-resolution observations of oscillations in filaments suggest that individual fibrils or groups of fibrils may oscillate independently with their own periods (Yi et al. [CITE]). Díaz et al. ([CITE], hereafter Paper I) studied the fast magnetohydrodynamic oscillations of a single and isolated slab prominence fibril using a two-dimensional model with no dependence in the y-direction. Here, we introduce a completely different approach which allows us to build up a 3-dimensional model for the fast magnetohydrodynamic oscillations of the fibril configuration used in Paper I. As compared to the results obtained in Paper I, two relevant new features appear; first of all, the cut-off frequency varies with the longitudinal wavenumber, so more modes can be trapped within the fibril; secondly, a much better confinement of the energy of the modes within the fibril appears, diminishing the leakage of energy towards neighbouring fibrils and so difficulting their mutual excitation.

Origin and Evolution of Filament‐Prominence Systems

We present a head-to-tail linkage model for the formation, evolution, and eruption of solar filaments. The magnetic field structure of our model is based on the observation that filaments form exclusively in filament channels with no apparent magnetic connections above the polarity inversion line. The formation of a filament in this configuration is driven by flux convergence and cancellation, which produces looplike filament segments with a half-turn. Filament segments of like chirality may connect and form long quiescent filaments. Such filaments are stabilized through footpoint anchoring until further cancellation at the footpoints causes their eruption. The eruption restores the original filament channel so that filament formation may resume immediately. We then demonstrate that the combined workings of Hale's polarity law, Joy's law, and differential rotation introduce a strong hemispheric preference in the chirality of filaments formed poleward of the sunspot belt, which is in agreement with observations. We analyze the magnetic fine structure of filaments formed through our model and find consistency with the observed hemispheric preference for barb orientation and a simple explanation for barb formation. Finally, we consider the flux tubes retracted below the surface in the process of filament formation. We show that every cancellation event that generates a filament obeying the hemispheric chirality preference injects a flux tube below the surface with a poloidal field opposite that of the ongoing cycle. We suggest that this pattern of submergence of flux represents the specific mechanism for the reversal of the poloidal flux in a Babcock-Leighton-Durney-type model for the solar dynamo.

Ultrastructure of Intermediate Filaments of Nestin- and Vimentin-Immunoreactive Astrocytes in Organotypic Slice Cultures of Hippocampus

Glial cells in rat hippocampal slices cultured for 4 weeks were examined with immunocytochemical and cryoelectron microscopical methods. Astrocytes possessing long processes were similarly stained with antibodies against nestin, vimentin, and glial fibrillary acidic protein as seen by confocal microscopy. The three antibodies also labeled intermediate filaments in these astrocytes. In order to examine the fine structure of these intermediate filaments, slices were rapid-frozen for freeze-substitution and freeze-etching. By freeze-substitution the processes of the astrocytes were packed with large bundles of intermediate filaments. In rapid-freeze deep-etched slices, these filaments were often interconnected with filamentous cross-bridges. These cross-bridges were rather uniform in size and shape (mean 2.9 nm thick and 14.8 nm long). These results suggest that the filament network with these cross-linkers is important for shaping the long processes of nestin- and vimentin-immunoreactive astrocytes in slice cultures.

The architecture and fine structure of gill filaments in the brown mussel,Perna perna

For many years, bivalve molluscs have played a useful role in determining the impact of pollution on marine organisms. In the northern hemisphere, ecologists from countries subscribing to the Inter...

Fine structure of abnormal filaments isolated from Alzheimer's diseased brain: an application of atomic force microscopy

Alzheimer's disease is characterized by the spontaneous assembly of a cytoskeletal protein into highly insoluble filamentous structures which appear, in conventional transmission electron microscopy (EM), as paired helical filaments (PHFs) or straight filaments (SFs). Recent examination of PHF ultrastructure using EM of vertical PtC replicas of isolated PHF indicate that PHFs more closely resemble twisted ribbons than helically wound pairs of filaments. To re-evaluate the fine structure of PHFs we isolated fractions highly enriched in PHF from Alzheimer diseased brains and characterized the fractions with an atomic force microscope. PHFs adhered to both mica and graphite surfaces without pre-treatment of the surfaces and remained fixed to the substrate even after repeated scanning. Using the AFM, PHFs appeared as twisted ribbons and had dimensions similar to those reported for vertically replicated PHF viewed with EM. Rare SFs were found admixed with typical twisted ribbons. These data indicate that high resolution imaging using both PtC replication and AFM give similar quantitative data with respect to PHF dimensions. We conclude that Alzheimer PHFs should be modelled as a twisted ribbon rather than the structure implied by its name.

Fine Structure of Prominences and Filaments

AbstractThe fine structures of prominences and filaments are involved in many phenomena such as formation and magnetostatic support, instabilities and eruptions. After a short introduction (Section 1), we concentrate on quiescent prominences, and we review some recent results about resolved structures (Section 2), statistical properties of “threads” (Section 3), and detailed analysis of average line profiles (Section 4). We mention magnetic field measurements (Section 5) and thermal problems (Section 6). New magnetostatic models (Section 7) are very promising. We discuss briefly the problem of the scale of fine structures, and we suggest some directions for further works (Section 8).

Mechanical instability of Pick bodies and their isolation in an intact form using urea solution

Isolation of Pick bodies was attempted from an autopsied brain of a patient with Pick's disease following a modified method for isolation of senile plaques cores and neurofibrillary tangles in the brains of Alzheimer's disease. Pick bodies were mechanically less stable than senile plaque cores and neurofibrillary tangles since Pick bodies were destroyed by vigorous homogenization or treatment with 1% sodium dodecyl sulfate solution. Pick bodies were released out of mother neuronal cells in an intact form by treatment with 8 M urea solution for several hours at room temperature. Finally, fine structure of Pick filaments released from Pick bodies was compared with the filaments of neurofibrillary tangles.

Dynamical Fine Structure of Filaments and Prominences

We observed a quiescent prominence on the east limb of the Sun, on June 7, 1988 (Mein P. et al 1990) and a quiescent filament (N 5, W 5) on June 17, 1986 (Schmieder et al 1991). These two observations are made with the Multichannel Subtractive Double Pass spectrograph of the turret dome refractor of the Pic du Midi Observatory, providing simultaneous 2D pictures in 9 channels for Hα.

Fine Structure of Mitochondrial Helical Filaments Revealed by Computer Image Analyses

In order to clarify the fine structure of the helical filaments appearing in the outer compartment of the mitochondria, Sprague-Dawley strain male rats were given 30% ethanol in drinking water for 90 days. The hepatic tissues of these animals were fixed with perfusion of glutaraldehyde via the portal vein followed by immersion in OsO4 and were then routinely processed for preparation of thin sections. Transmission electron micrographs of the sections were used for computer image analyses of the intramitochondrial helical filaments. With the application of the image analysis, it was revealed that the helical filaments show a right-hand rotating helix of 4.3 nm in thickness, 13.2 nm in diameter of the helix, and 15.7 nm in pitch. Also, with the multivariate statistical analysis and classification method of the IMAGIC image processing system, it was suggested in the classified images that the helical filament has substructures of rod-shaped particles of 4.3 nm in diameter. These particles are considered to be connected to each other and forming the helical structure of the filament.