Central Filament Research Articles

Selenium affects biosilica formation in the demosponge Suberites domuncula

Selenium is a trace element found in freshwater and the marine environment. We show that it plays a major role in spicule formation in the demosponge Suberites domuncula. If added to primmorphs, an in vitro sponge cell culture system, it stimulates the formation of siliceous spicules. Using differential display of transcripts, we demonstrate that, after a 72-h exposure of primmorphs to selenium, two genes are up-regulated; one codes for selenoprotein M and the other for a novel spicule-associated protein. The deduced protein sequence of selenoprotein M (14 kDa) shows characteristic features of metazoan selenoproteins. The spicule-associated protein (26 kDa) comprises six characteristic repeats of 20 amino acids, composed of 10 distinct hydrophobic regions ( approximately 9 amino acids in length). Recombinant proteins were prepared, and antibodies were raised against these two proteins. Both were found to stain the central axial filament, which comprises the silicatein, as well as the surface of the spicules. In the presence of selenium, only the genes for selenoprotein M and spicule-associated protein are up-regulated, whereas the expression of the silicatein gene remains unchanged. Finally we show that, in the presence of selenium, larger silica aggregates are formed. We conclude that selenium has a stimulatory effect on the formation of siliceous spicules in sponges, and it may be involved in the enzymatic synthesis of biosilica components.

Bi-2212 Phase Formation Process in Multifilamentary Bi-2212/Ag Wires and Tapes

We investigated phase formations of multifilamentary Bi-2212/Ag wires during the heat-treatment. We carried out systematic quenching experiments. In the partial-melting process in pure O/sub 2/, when heating rate was 10/spl deg/C/h, melting of filaments was started from central filaments and spread to the edge-located filaments. However, when heating rate was 5/spl deg/C/h, melting of filaments was caused uniformly. In the partial-melting process in 8% O/sub 2/ also, melting of filaments occurred caused uniformly. Phase identification indicates that the existing alkaline earth cuprate was 2:1 alkaline earth cuprate in 8% O/sub 2/ while alkaline earth cuprate was 14:24 alkaline earth cuprate in pure O/sub 2/. These results showed effect of O/sub 2/ partial pressure in filaments. In the slow solidification process, the Bi-2212 phase grew up greatly and broke through the silver matrix in pure O/sub 2/, but the grain growth was suppressed in 8% O/sub 2/, resulting in the suppressing of bridging of Bi-2212 filaments.

Novel photoreception system in sponges?

Sponges (phylum Porifera) of the classes Hexactinellida and Demospongiae possess a skeleton composed of siliceous spicules, which are synthesized enzymatically. The longest spicules are found among the Hexactinellida, with the stalk spicules (length: 30 cm; diameter: 300 microm) of Hyalonema sieboldi as prominent examples. These spicules are constructed around a central axial filament, which is formed by approximately 40 siliceous layers. The stratified spicules function as optical glass fibers with unique properties. If free-spaced coupled with a white light source (WLS), the entire fiber is illuminated. Special features of the light transmission: (i) only wavelengths between 615 and 1310 nm can pass through the fibers and (ii) light below wavelengths of 615 nm and above 1310 nm is completely cut-off. The transmission efficiency is around 60% (measured at 1080-1100 nm [length of the fiber: 5 cm]). The spicules acts as sharp high- and low-pass filters, suggesting that these silica-based fibers might be involved in a photoreception system. This assumption is supported by the finding that sponges are provided with a bioluminescent system. It is hypothesized that the spicules/siliceous fibers might be involved in a photoreception system in these animals.

Characterization of mussel gill cells in vivo and in vitro

Mussel gill cells are attractive models in ecotoxicological studies because gills are the first uptake site for many toxicants in the aquatic environment; gill cells are thus often affected by exposure to pollutants. Our aim was to characterize mussel gill cells in vivo and in vitro by using morphological, histochemical and functional end-points. In paraffin sections stained with haematoxylin-eosin, three zones were distinguished in the long central gill filaments: frontal, intermediate and abfrontal. Various types of ciliated cells were present in the frontal zone, and both ciliated and non-ciliated cells were found in the abfrontal zone. The intermediate zone was comprised of flattened endothelial cells. Lipofuscin granules occurred in the three zones in variable amounts, depending on the specimen. Haemocytes were found in the haemolymph sinus of gill filaments. Mucocytes were identified in both frontal and abfrontal zones by means of periodic acid Schiff-alcian blue (PAS-AB) staining. In cryostat sections, succinate dehydrogenase (SDH) activity was mainly found in ciliated cells, whereas neutral lipids and acid-phosphatase-reactive lysosomes were present in all portions of the gill filament, mostly being related to lipofuscin granules. In mussels exposed to 5'-bromo-2'-deoxyuridine in vivo, proliferating cells were scattered throughout the gill filament. Gill cells (typically 2x10(7) cells/ml per mussel; 95% viability) were isolated by dissociation with dispase. Gill cell suspensions were heterogeneous: 58% were ciliated epithelial cells (positive for SDH), 42% were non-ciliated cells (including epithelial cells and haemocytes), 2.3% were mucocytes (positive for PAS-AB) and 4.25% were haemocytes (able to phagocytose neutral red-stained zymosan). Gill cell cultures were maintained up to 18 days without changing the culture medium, viability decreasing below 50% at day 18. Primary cultures of mussel gill cells might therefore be useful models for the in vitro assessment of xenobiotic impacts on coastal and estuarine ecosystems.

Thermal characterisation of a direction dependent flow sensor

A calorimetric sensor for detection of gas velocity and flow direction was constructed by sacrificial porous silicon micromachining technique. The sensing element contains four temperature sensing resistors arranged symmetrically around a central filament heater. Finite volume flow simulations (FVM) for velocity vector and temperature distribution around the system elements led to the conclusion that the laminar flow conditions, essential for accurate calorimetric sensing, can be maintained by adequate selection of device dimensions and channel depth. Predictions by the flow and thermal simulations were aimed at defining the optimum geometric design. The results of functional tests performed on the fabricated structure were interpreted in terms of changes of parameters in the thermal equivalent circuit of the device.

Multiple filamentation induced by input-beam ellipticity.

We provide what is to our knowledge the first experimental evidence that multiple filamentation (MF) of ultra-short pulses can be induced by input beam ellipticity. Unlike noise-induced MF, which results in complete beam breakup, the MF pattern induced by small input beam ellipticity appears as a result of nucleation of annular rings surrounding the central filament. Moreover, our experiments show that input beam ellipticity can dominate the effect of noise (transverse modulational instability), giving rise to predictable and highly reproducible MF patterns. The results are explained with a theoretical model and simulations.

Coronal oscillations and internal loop structure

The transverse oscillations of a coronal magnetic loop whose ends are rigidly fixed in the photosphere are investigated. The loop is assumed to be inhomogeneous and to comprise two internal structural components: a central dense hot filament and a coaxial rarefied shell around it, in which the plasma density is lower than the density of the surrounding coronal plasma. The Alfven speed in the shell, VAm, is higher than that in the central filament and in the corona: VAm>VAe>VAi. It is shown that, in the perfectly conducting plasma approximation, such a loop can generate two fast magnetosonic waves. The higher velocity wave is emitted in a radial direction, thereby ensuring the effect of the radiative damping of oscillations at the frequency of the m=1 cylindrical mode. The results of calculating the effect of radiative losses show that, for typical loop parameters (corresponding to those of the loops observed in the solar corona), the quality factor of oscillations may be fairly low (Q≈40). Under the conditions in question, the second (lower velocity) fast magnetosonic wave is not emitted (in contrast to the first) but rather turns out to be trapped in the magnetic flux tube.

Drag Reduction by Plasma Filaments over Supersonic Forebodies

Inviscid flow over a supersonic cone-cylinder with thermal plasma filaments projecting upstream of its nose is analyzed numerically. The plasma filaments are idealized as concentric annular layer heat sources. Two limiting cases are assumed. These are, respectively, gas pressure p and gas density p constant inside the layers during their formation. For the first case, the drag reduction energetic efficiency remains less than unity for Mach numbers M = 1.7-7 for an assumed layer configuration. In the second, the efficiency becomes greater than unity for M = 2.5 and reaches its maximum value at M = 5 for an optimal layer arrangement. This configuration consists of one central filament and another layer projecting from the cone surface at a radial distance from the cone axis of symmetry one-third of the cylinder radius

Possible significance of different DNA content ranges of gametophytic and tetrasporophytic nuclei in two species of Laurencia (Rhodomelaceae, Rhodophyta)

In species of the red algal genus Laurencia the life cycle is isomorphic, with haploid gametophytic and diploid tetrasporophytic thalli similar or identical in shape. Identical total nuclear DNA contents are postulated in the literature for homologous somatic thallus cells of both generations. However, in the closely related genus Osmundea differences in DNA content were observed between some homologous somatic cells of the isomorphic gametophytes and tetrasporophytes. To find out if differences between nuclear gametophytic and tetrasporophytic DNA contents also exist in Laurencia, comparative studies were carried out in two species of this genus. Microfluorometric measurements of nuclear DNA contents in the uninucleate cells of the central filaments in distal portions of thalli of Laurencia majuscula and Laurencia sp. were up to 64C for tetrasporophytes and up to 32C for gametophytes. Most probably nuclei of apical cells in G2 phase were 128C in tetrasporophytes and 64C in gametophytes. Nuclei of the multinucleate medullary, cortical and epidermal cells were mostly 8C and 4C in tetrasporophytes and gametophytes. Flow charts for nuclear DNA contents starting with apical cells are presented. Average C-levels of gametophytic nuclei were lower than those of homologous tetrasporophytic nuclei, reflecting the respective haploid and diploid states in these isomorphic generations. Because homologous gametophytic and tetrasporophytic cells had identical numbers of nuclei, total nuclear DNA contents per cell were also different. Nuclear DNA content ranges in multinucleate cells were 1C – 16C in gametophytes and 2C – 32C in tetrasporophytes. So, some tetrasporophytic nuclei had C-values identical to those of some gametophytic nuclei. Tetrasporophytic and gametophytic nuclei with identical C-levels are considered to be responsible for isomorphy of the two generations. We suggest that low C-levels in trichoblasts of gametophytes and high C-levels in cortical and epidermal cells of tetrasporophytes control the development of gametangia and tetrasporangia, respectively. Previous reports that nuclear DNA contents in homologous gametophytic and tetrasporophytic cells are identical in Laurencia are not confirmed.

G0.087-0.087, a highly polarized flat spectrum filament near the Galactic CentreArc

32 GHz observations with the Effelsberg 100-m telescope revealed a highly polarized Galactic Centre filament: G0.087-0.087, running parallel to the well-known Arc structure. It has a similar flat spectrum, but it is an order of magnitude weaker. G0.087-0.087 is about $2\farcm 5$ or 6.2 pc long and located at the western boundary of the expanding molecular cloud G0.11-0.11. This unusual cloud is also visible in X-rays and known to interact on its eastern periphery with the Arc. Acceleration of highly relativistic particles at the surface of G0.11-0.11 seems necessary to explain the properties of both structures. The new filament supports previous findings on the existence of a strong poloidal magnetic field throughout the Galactic Centre region.

Numerical modelling of Bi-2223 multifilamentary tapes with position-dependent Jc

Different measurement techniques have demonstrated that due to better alignment during the manufacturing process, the central filaments in multifilamentary Bi-2223 tapes have higher critical current density than the outer filaments. A numerical model of non-twisted tapes has been used in finite-element-method simulations. The model incorporates non-uniform lateral J c distribution in accordance with direct I c measurements, made along the width of a Bi-2223 tape. Two types of simulations are performed on 7 and 19-filamentary tapes with applied transport current––one with constant J c in all filaments, and another with a J c( x) dependence. The current distribution and AC loss in each filament are numerically calculated and compared. It is demonstrated that the current density distribution and power dissipation vary considerably in the different filaments, which is due to the position of the filament with respect to the edge of the tape and the different J c values along the width.

Branched integumental structures in Sinornithosaurus and the origin of feathers.

The evolutionary origin of feathers has long been obscured because no morphological antecedents were known to the earliest, structurally modern feathers of Archaeopteryx. It has been proposed that the filamentous integumental appendages on several theropod dinosaurs are primitive feathers; but the homology between these filamentous structures and feathers has been disputed, and two taxa with true feathers (Caudipteryx and Protarchaeopteryx) have been proposed to be flightless birds. Confirmation of the theropod origin of feathers requires documentation of unambiguously feather-like structures in a clearly non-avian theropod. Here we describe our observations of the filamentous integumental appendages of the basal dromaeosaurid dinosaur Sinornithosaurus millenii, which indicate that they are compound structures composed of multiple filaments. Furthermore, these appendages exhibit two types of branching structure that are unique to avian feathers: filaments joined in a basal tuft, and filaments joined at their bases in series along a central filament. Combined with the independent phylogenetic evidence supporting the theropod ancestry of birds, these observations strongly corroborate the hypothesis that the integumental appendages of Sinornithosaurus are homologous with avian feathers. The plesiomorphic feathers of Sinornithosaurus also conform to the predictions of an independent, developmental model of the evolutionary origin of feathers.

The Snake: A Reconnecting Coil in a Twisted Magnetic Flux Tube

We propose that the curious Galactic center filament known as the Snake is a twisted giant magnetic flux tube, anchored in rotating molecular clouds. The MHD kink instability generates coils in the tube and subsequent magnetic reconnection injects relativistic electrons. Energy-dependent diffusion of electrons away from the coil produces a flat spectral index at large distances from it. Our fit to the existing data shows that the magnetic field of ~0.4 mG is large compared to the ambient ~7 μG field, indicating that the flux tube is force-free. If the relative level of turbulence in the Snake and the general interstellar medium are similar, then electrons have been diffusing in the Snake for about 3 × 105 yr, comparable to the timescale at which magnetic energy is annihilated in the major kink. Estimates of the magnetic field in the G359.19-0.05 molecular complex are similar to our estimate of the magnetic field in the Snake, suggesting a strong connection between the physics of the anchoring molecular regions and the Snake. We suggest that the physical processes considered here may be relevant to other radio filaments near the Galactic center. We also suggest further observations of the Snake and other filaments that would be useful for obtaining further insights into the physics of these objects.

Parametric forcing of scroll-wave patterns in three-dimensional excitable media

The dynamics of axisymmetric and twisted scroll rings under homogeneous periodic forcing is studied numerically. The collapse of axisymmetric rings can be enhanced or retarded significantly with resonant forcing. Twisted scroll rings exhibit the phenomenon of resonant drift in a direction normal to the axis of the central filament. The scaling of mean and fluctuating axial drift due to forcing is determined. Evidence is provided showing that the appropriate symmetry group for the dynamics of the unforced twisted scroll ring is SE(2)× R . Ordinary differential equations based on symmetry considerations explain the dynamics without resorting to laws of filament motion and the local geometry hypothesis.

Sexual development and sex chromosomes in hop.

The stages of floral development in staminate and pistillate plants of hop (Humulus lupulus) were defined using scanning electron microscopy and light microscopy. Vegetative meristems of male and female plants are morphologically indistinguishable. On transition to the reproductive phase, inflorescence apices reduce greatly in size and striking developmental sex differences become apparent. The first sex-specific differences occur extremely early in floral ontogeny. Both male and female plants initiate inflorescence meristems at each leaf node, each meristem being enclosed within a bract. Male secondary inflorescence meristems give rise to clusters of asynchronously developing flowers. Female inflorescence meristems produce flowers arranged in 'cones'. Each male floral meristem initiates a whorl of five sepal primordia, followed by an inner whorl of five stamen primordia. There is no sign of carpel development at any stage. In females, two carpel primordia are initiated, surrounded at their base by a vestigial perianth whorl. No stamen development is observed. Several monoecious lines carry bisexual flowers, either within cymose panicles or within the basal bracts of terminal female inflorescences. Bisexual flowers usually possess perianth, stamen and carpel whorls. The central whorls are often highly variable, and range from a pair of stigmas fused to a thin central filament to a well developed gynoecium. Chimaeric central whorls consisting of fused staminoid-carpelloid structures also occur. Sex differences in unisexual hop flowers are determined at an extremely early stage in ontogeny. The inappropriate set of sex organs is suppressed before it becomes visible or, more probably, it is not initiated at all. Genes directing the development of sex are likely to act at an extremely early stage, well in advance of floral organogenesis. The sex chromosomes of dioecious hop plants are described, as well as the chromosome constitutions of monoecious plants and those carrying bisexual flowers.

Potential formalism for an axial energy cumulation process

A central filament is assumed to be axially positioned inside a collapsing cylindrical thin shell. A cumulation process is induced by generating a high magnetic field between the shell and the filament. Assuming a dissipationless approach, it is shown that this problem is equivalent to two point particles moving in a potential.

Current distribution and microstructure studies of isolated filamentsextracted from Ag-sheathed Bi(2223) tapes

All the filaments extracted from an Ag-sheathed (Bi,Pb)2Sr2Ca2Cu3O10+x tape, prepared by theoxide-powder-in-tube technique, have been isolated by chemical etching of thesilver matrix, and individually characterized by keeping track of theirposition inside the conductor. Different types of measurements have beenperformed on each filament: magnetization hysteresis loops and zero-fieldcooled DC susceptibility by SQUID magnetometry; electrical resistivity by thefour-probe method; phase purity and texture by x-ray diffraction analysis; andstoichiometry by scanning electron microscopy/energy dispersive x-rayanalysis. The critical-current density jc of every filament has beencalculated from the magnetization hysteresis loops. At 77 K it has been foundthat the innermost filament carries a jc of 53 kA cm-2,i.e. much larger than for all the filaments of the outer shell (with jcranging between 25 and 40 kA cm-2). These results areconsistent with the variation in room temperature electrical resistivityobserved on the same samples. To some extent the observed current distributioncan be imputed to the different amount of cold working experienced by thefilaments. On the other hand, we have found that the average stoichiometry ofthe central filament matches well with that of the initial precursor powders,while in the filaments of the outer shell a consistent loss of Pb has beenobserved. The outer filaments also present a lower oxygencontent.

Monodon baculovirus from Australia:ultrastructural observations

The cytopathology, virogenesis and replication of monodon baculovirus (MBV) in Penaeus monodon from Australia are described. Electron-dense unenveloped nucleocapsids, not previously described for MBV, are shown in the cytoplasm and attached to the nuclear envelope of infected hepatopancreatocytes. These nucleocapsids comprise a missing link in the published literature on the replication cycle of MBV by providing evidence for the means by which the viral genome travels from the plasma membrane of the hepatopancreatocyte to the nucleus. Features similar to those of MBV from other areas, but not previously reported for MBV from Australia include empty capsids attached to the nuclear pore, central filaments in developing capsids, capsids partly filled with nucleic acid, and filaments in subapical envelope expansions. A model for virogenesis and replication is illustrated which takes into account the new observations as well as previously described ultrastructural characteristics of the developing viral particle.

A high spatial resolution double-pulse Thomson scattering diagnostic; description, assessment of accuracy and examples of applications

A high spatial resolution (3 mm full width half maximum, i.e. 2% of the minor radius) double-pulse multiposition Thomson scattering system was in operation at the Rijnhuizen tokamak project RTP from March 1996 until September 1998. It upgrades the previously installed single-pulse Thomson scattering system. Two measurements of full electron temperature, Te, and density, ne, profiles can be performed in rapid succession during one plasma discharge, using a double-pulsed laser and a dual charge-coupled-device camera system. The temporal resolution is determined by the separation time between the two subsequent laser pulses and can be tuned in the range 20-800 µs. Typical relative experimental errors are 3-5% for Te and 2-4% for ne at ne = 5 × 1019 m-3. Plasma experiments show the application of the diagnostic; double-pulse Thomson scattering measurements have been performed on high-ne ohmic plasmas with large m/n = 2/1 magnetohydrodynamic activity, centrally heated plasmas with filaments (i.e. high Te peaks) applying electron cyclotron heating, plasmas with a transient central Te-rise after oblique pellet injection showing central filaments, and off-axis heated plasmas with off-axis sawtooth activity. The double-pulse feature of the diagnostic enables the study of the dynamics of Te and ne profiles in these plasmas.

Fine Structure and Evolutionary Significance of Sagittocysts of Convolutriloba longifissura (Acoela, Platyhelminthes)

Sagittocysts are extrusomes found only in acoel turbellarians. They are needlelike secretory products, on the order of 18-50 pxm long and 1-5 pxm wide, and consist of a fibrous cortex, a central filament, and an intermediate lucent layer. We discovered sagittocysts in Convolutriloba longifissura, for which they had not been known before, by using confocal microscopy and a phalloidin-conjugated fluorescent stain that strongly labeled a mantle of muscle around the distal neck of the sagittocyst-secreting cell, the sagittocyte. The muscle mantle apparently plays a role in ejecting the sagittocyst. Positions of the sagittocysts revealed by confocal microscopy suggests their role in defense as well as in prey capture. By electron microscopy, the differentiation of sagittocysts was evident in the proximal part of the sagittocyte. The muscle mantle on the neck of the sagittocyte is conical in shape; its ribbon-like myocyte enwraps the neck in a tight spiral. Extrusion of sagittocysts could be induced by stimulation with electrical pulses, light pulses, or weak hydrochloric acid; only the whole sagittocyst was ejected, not its central filament. The presence of sagittocysts in species of Convolutriloba is sufficient to reassign the genus to the family Sagittiferidae. We establish the new subfamily Convolutrilobinae, with 3 species in the genus Convolutriloba, and new subfamilies for the remaining sagittiferids as well. As extrusomes, sagittocysts are comparable to nematocysts, colloblasts, rhabdites, and other extrusomes common especially to lower eumetazoans, and the origin of all such extrusomes may correlate with the origin of the eumetazoan