Spiral-like Structures Research Articles

Spiral-like structure at the centre of nearby clusters of galaxies

<i>Context. <i/>X-ray data analysis have found that fairly complex structures at cluster centres are more common than expected. Many of these structures have similar morphologies, which exhibit spiral-like substructure.<i>Aims. <i/>It is not yet well known how these structures are formed or maintained. Understanding the origin of these spiral-like features at the centre of some clusters is the major motivation behind this work.<i>Methods. <i/>We analyse deep <i>Chandra<i/> observations of 15 nearby galaxy clusters (0.01 <i> < z < <i/> 0.06), and use X-ray temperature and substructure maps to detect small features at the cores of the clusters.<i>Results. <i/>We detect spiral-like features at the centre of 7 clusters: A85, A426, A496, Hydra A cluster, Centaurus, Ophiuchus, and A4059. These patterns are similar to those found in numerical hydrodynamic simulations of cluster mergers with non-zero impact parameter. In some clusters of our sample, a strong radio source also occupies the inner region of the cluster, which indicates a possible connection between the two. Our investigation implies that these spiral-like structures may be caused by off-axis minor mergers. Since these features occur in regions of high density, they may confine radio emission from the central galaxy producing, in some cases, unusual radio morphology.

Overproduction and localization of Mycobacterium tuberculosis ParA and ParB proteins

The ParA and ParB family proteins are required for accurate partitioning of replicated chromosomes. The Mycobacterium tuberculosis genome contains parB, parA and two parA homologs, Rv1708 and Rv3213c. It is unknown if parA and its homologs are functionally related. To understand the roles of ParA and ParB proteins in M. tuberculosis cell cycle, we have evaluated the consequences of their overproduction and visualized their localization patterns in M. smegmatis. We show that cells overproducing ParA, Rv1708 and Rv3213c and ParB are filamentous and multinucleoidal indicating defects in cell-cycle progression. Visualization of green-fluorescent protein fusions of ParA and its homologues showed similar localization patterns with foci at poles, quarter-cell, midcell positions and spiral-like structures indicating that they are functionally related. On the other hand, the ParB- GFP fusion protein localized only to the cell poles. The cyan- and yellow-fluorescent fusion proteins of ParA and ParB, respectively, colocalized at the cell poles indicating that these proteins interact and possibly associate with the chromosomal origin of replication. Collectively our results suggest that the M. tuberculosis Par proteins play important roles in cell-cycle progression.

Dominante spaziale e struttura argomentativa nel V Discorso Sacro di Elio Aristide

Aristides' own definition of the Sacred Tales as diegesis allows us to read them using narratological categories. The work contains circular or, better, spiral-like time structures. The Fifth discourse is dominated by spatial circularity, coexisting with a paradoxical indifference for the real space itself while Aristides' attention focuses on the oneiric one. It has an argumentative structure based on illustration and accumulation; the altered spatio-temporal axis shows that Asclepius' intervention crosses the boundaries between time and space, dream and reality. The Sacred Tales owe their simple stylistic structure, strikingly different from other discourses of Aristides, to many factors, including their psychic and religious content.

Osteoblastic Behavior of Human Bone Marrow Cells Cultured Over Adsorbed Collagen Layer, Over Surface of Collagen Gels, and Inside Collagen Gels

While collagen type I is often used as a substrate for cell culturing and as a coating in biomedical implants, as far as we know a simple systematic study comparing the effects of the different presentations of collagen type I on the osteoblastic behavior of cells is missing. In this work, human bone marrow cells (hBMCs) were cultured under osteoblastic-inducing conditions, for 21 days, over a layer of adsorbed collagen (monomeric) and on the surface and inside collagen gels (fibrillar). Comparison was made based on three classical parameters; cell proliferation/viability, alkaline phosphatase (ALP) activity, and production of mineral deposits. The three types of collagen type I substrates allowed the adhesion, proliferation, and the osteoblastic differentiation of cells. However, hBMCs behavior was influenced by the monomeric/fibrillar and 2-/3-dimensional nature of the collagen substrates, namely: monomeric collagen favored cell attachment; cells on 2D substrates presented higher proliferation rates during the exponential phase of growth with formation of spiral-like multilayered structures; cells seeded inside 3D collagen gels formed a regular dense cellular mesh and had a low proliferating rate; cells cultured over or inside fibrillar collagen differentiated faster, with the 3D cultures presenting higher levels of ALP activity; and the extension of mineralization was greater for the cultures done over or inside fibrillar collagen. Thus, cells cultured over collagen gels showed both the ability for cell proliferation and for earlier differentiation, a fact that can be exploited in the biomaterials field.

Streptococcus pyogenes pSM19035 requires dynamic assembly of ATP-bound ParA and ParB on parS DNA during plasmid segregation

The accurate partitioning of Firmicute plasmid pSM19035 at cell division depends on ATP binding and hydrolysis by homodimeric ATPase δ2 (ParA) and binding of ω2 (ParB) to its cognate parS DNA. The 1.83 Å resolution crystal structure of δ2 in a complex with non-hydrolyzable ATPγS reveals a unique ParA dimer assembly that permits nucleotide exchange without requiring dissociation into monomers. In vitro, δ2 had minimal ATPase activity in the absence of ω2 and parS DNA. However, stoichiometric amounts of ω2 and parS DNA stimulated the δ2 ATPase activity and mediated plasmid pairing, whereas at high (4:1) ω2 : δ2 ratios, stimulation of the ATPase activity was reduced and δ2 polymerized onto DNA. Stimulation of the δ2 ATPase activity and its polymerization on DNA required ability of ω2 to bind parS DNA and its N-terminus. In vivo experiments showed that δ2 alone associated with the nucleoid, and in the presence of ω2 and parS DNA, δ2 oscillated between the nucleoid and the cell poles and formed spiral-like structures. Our studies indicate that the molar ω2 : δ2 ratio regulates the polymerization properties of (δ•ATP•Mg2+)2 on and depolymerization from parS DNA, thereby controlling the temporal and spatial segregation of pSM19035 before cell division.

Making use of dynamic instability at the microtubule‐kinetochore interface

The dynamic behavior of microtubules is essential for their functions. We have obtained the structure of two structural intermediates corresponding to the start and end points in the polymerization cycle that illustrate the conformational consequences of the nucleotide state and how they relate to longitudinal and lateral assembly. We propose that the polymorphism of assembly unique to tubulin reflects an exquisite tuning mechanism for the complex interaction of different microtubule intermediates with cellular factors that need to detect or make direct use of the growing or shortening state of microtubules to play functional roles at the right time and place in the cell. One such cellular component is the yeast Dam1 kinetochore complex. This complex self‐assembles around microtubules into rings and spiral‐like structures, but lacks the classical footprint on the microtubule lattice of motors and structural MAPs, allowing for its passive diffusion on the microtubule. When the microtubule depolymerizes the Dam1 ring uses the conformational strain of GDP tubulin within the lattice as tubulin relaxes into its curved state, to move processively, and without energy consumption of its own. A microtubule‐induced conformational change of the Dam1 complex ensures that ring formation does not precede engagement with a kinetochore microtubule.

Generalized multifractal analysis of the mixing rate across turbulent jet scalar interfaces using the multiscale-minima meshless (M3) method

This work demonstrates generalized multifractal analysis on scalar conditional dissipation rate fields using the multiscale-minima meshless (M3) method. We investigate how the generalized multifractal dimension varies as a function of scale in order to characterize the geometrical structure of the scalar dissipation regions. We also examine how the generalized multifractal dimension varies with the multifractal exponent. The investigation is carried out using a high-resolution experimental two-dimensional image database of fully developed turbulent scalar fields in jets. The conditional dissipation field on scalar interfaces, which represents the mixing rate across the interfaces, is calculated for the outer interface with Taylor's hypothesis in the jet similarity plane. Isosets of multifractal exponents of the dissipation field are identified. Examination of the generalized multifractal dimension of the isosets using the M3 method shows strong dependence on scale. This indicates the presence of scalar conditional dissipation regions whose geometrical structure varies from point-like at the smallest resolved scales, to effectively tube-like at intermediate scales, to effectively space-filling at the largest scales. Since spatially two-dimensional scalar slices of the spatially three-dimensional scalar field were used, this suggests that the scalar conditional dissipation structures in three-dimensional space would be such that they are tube-like at the smallest resolved scales, effectively sheet-like at intermediate scales and effectively space-filling at the largest scales. This suggests the presence of geometrically scale-dependent spiral-like structures and this is consistent with previous observations that the conditional signatures of such structures consist of striation patterns of the dissipation across scalar interfaces. The scale dependence of the generalized multifractal dimension is found to be steepest for the multifractal exponent corresponding to the peak of the probability density function of the multifractal exponents, i.e. for the most probable multifractal exponent. The present findings show that generalized multifractal analysis with the M3 method provides a tool for quantifying the geometrical structure across various scales, including large scales, as well as for capturing scale-dependent aspects of the conditional dissipation rate which are useful capabilities for modeling the mixing rate across turbulent interfaces.

Possible Molecular Spiral Arms in the Protoplanetary Disk of AB Aurigae

The circumstellar dust disk of the Herbig Ae star AB Aur has been found to exhibit complex spiral-like structures in the near-IR image obtained with the Subaru Telescope. We present maps of the disk in both 12CO (3-2) and dust continuum at 345 GHz with the Submillimeter Array at an angular resolution of 10 × 07 (144 × 100 AU). The continuum emission traces a dust disk with a central depression and a maximum overall dimension of 450 AU (FWHM). This dust disk exhibits several distinct peaks that appear to coincide with bright features in the near-IR image, in particular the brightest inner spiral arm. The CO emission traces a rotating gas disk of size 530 × 330 AU with a deprojected maximum velocity of 2.8 km s-1 at 450 AU. In contrast with the dust disk, the gas disk exhibits an intensity peak at the stellar position. Furthermore, the CO emission in several velocity channels traces the innermost spiral arm seen in the near-IR. We compare the observed spatial-kinematic structure of the CO emission to a simple model of a disk in Keplerian rotation and find that only the emission tracing the main spiral arm clearly lies outside the confines of our model. This emission has a net outward radial motion compared with the radial velocity predicted by the model at the location of the main spiral arms. The disk of AB Aur is therefore quite different from the Keplerian disks seen around many Herbig Ae stars. The spiral-like structures of the disk with non-Keplerian motions we revealed in 12CO (3-2), together with the central depression of the dust disk, could be explained to be driven by the possible existence of a giant planet forming in the disk.

K-band observations of boxy bulges - I. Morphology and surface brightness profiles

Kn-band images, unsharp-masked images, as well as major-axis and vertically- summed surface brightness profiles are presented for 30 edge-on spiral galaxies, most with a boxy or peanut-shaped (B/PS) bulge. Such galaxies have more complex morphologies than galaxies of other bulge types, more often showing (off-)centered X structures, secondary major-axis maxima and spiral-like structures. Those features are also observed in N-body simulations of barred discs and may trace the main bar orbit families. The surface brightness profiles of galaxies with a B/PS bulge are also more complex, with typically 3 or more clearly separated regions, including a flat intermediate region (Freeman Type II profiles). Those radial breaks offer evidence for bar-driven transfer of angular momentum and radial redistribution of material. The profiles also suggest a rapid variation of the scaleheight of the disc material, contrary to conventional wisdom but again as expected from vertical resonances and instabilities in barred discs. The steep inner region of the surface brightness profiles is often shorter than the isophotally thick part of the galaxies, itself always shorter than the flat region of the profiles. Contrary to the standard `bulge + disc' model, we thus propose that galaxies with a B/PS bulge are composed of a thin concentrated disc (a disc-like bulge) contained within a partially thick bar (the B/PS bulge) and a thin outer disc. The inner disc likely formed secularly through bar-driven processes and is responsible for the steep inner region of the surface brightness profiles, while the bar is responsible for the flat region and the thick complex morphological structures observed. Those components are strongly coupled dynamically and are formed mostly of the same (disc) material. [Abridged]

Trapping of a Spiral-Like Intermediate of the Bacterial Cytokinetic Protein FtsZ

The earliest stage in bacterial cell division is the formation of a ring, composed of the tubulin-like protein FtsZ, at the division site. Tight spatial and temporal regulation of Z-ring formation is required to ensure that division occurs precisely at midcell between two replicated chromosomes. However, the mechanism of Z-ring formation and its regulation in vivo remain unresolved. Here we identify the defect of an interesting temperature-sensitive ftsZ mutant (ts1) of Bacillus subtilis. At the nonpermissive temperature, the mutant protein, FtsZ(Ts1), assembles into spiral-like structures between chromosomes. When shifted back down to the permissive temperature, functional Z rings form and division resumes. Our observations support a model in which Z-ring formation at the division site arises from reorganization of a long cytoskeletal spiral form of FtsZ and suggest that the FtsZ(Ts1) protein is captured as a shorter spiral-forming intermediate that is unable to complete this reorganization step. The ts1 mutant is likely to be very valuable in revealing how FtsZ assembles into a ring and how this occurs precisely at the division site.

Mycobacterium tuberculosis Cells Growing in Macrophages Are Filamentous and Deficient in FtsZ Rings

FtsZ, a bacterial homolog of tubulin, forms a structural element called the FtsZ ring (Z ring) at the predivisional midcell site and sets up a scaffold for the assembly of other cell division proteins. The genetic aspects of FtsZ-catalyzed cell division and its assembly dynamics in Mycobacterium tuberculosis are unknown. Here, with an M. tuberculosis strain containing FtsZ(TB) tagged with green fluorescent protein as the sole source of FtsZ, we examined FtsZ structures under various growth conditions. We found that midcell Z rings are present in approximately 11% of actively growing cells, suggesting that the low frequency of Z rings is reflective of their slow growth rate. Next, we showed that SRI-3072, a reported FtsZ(TB) inhibitor, disrupted Z-ring assembly and inhibited cell division and growth of M. tuberculosis. We also showed that M. tuberculosis cells grown in macrophages are filamentous and that only a small fraction had midcell Z rings. The majority of filamentous cells contained nonring, spiral-like FtsZ structures along their entire length. The levels of FtsZ in bacteria grown in macrophages or in broth were comparable, suggesting that Z-ring formation at midcell sites was compromised during intracellular growth. Our results suggest that the intraphagosomal milieu alters the expression of M. tuberculosis genes affecting Z-ring formation and thereby cell division.

Mdv1 Interacts with Assembled Dnm1 to Promote Mitochondrial Division

The dynamin-related GTPase, Dnm1, self-assembles into punctate structures that are targeted to the outer mitochondrial membrane where they mediate mitochondrial division. Post-targeting, Dnm1-dependent division is controlled by the actions of the WD repeat protein, Mdv1, and the mitochondrial tetratricopeptide repeat-like outer membrane protein, Fis1. Our previous studies suggest a model where at this step Mdv1 functions as an adaptor linking Fis1 with Dnm1. To gain insight into the exact role of the Fis1.Mdv1.Dnm1 complex in mitochondrial division, we performed a structure-function analysis of the Mdv1 adaptor. Our analysis suggests that dynamic interactions between Mdv1 and Dnm1 play a key role in division by regulating Dnm1 self-assembly.

Subcellular sites for bacterial protein export.

Most bacterial proteins destined to leave the cytoplasm are exported to extracellular compartments or imported into the cytoplasmic membrane via the highly conserved SecA-YEG pathway. In the present studies, the subcellular distributions of core components of this pathway, SecA and SecY, and of the secretory protein pre-AmyQ, were analysed using green fluorescent protein fusions, immunostaining and/or immunogold labelling techniques. It is shown that SecA, SecY and (pre-)AmyQ are located at specific sites near and/or in the cytoplasmic membrane of Bacillus subtilis. The localization patterns of these proteins suggest that the Sec machinery is organized in spiral-like structures along the cell, with most of the translocases organized in specific clusters along these structures. However, this localization appears to be independent of the helicoidal structures formed by the actin-like cytoskeletal proteins, MreB or Mbl. Interestingly, the specific localization of SecA is dynamic, and depends on active translation. Moreover, reducing the phosphatidylglycerol phospholipids content in the bacterial membrane results in delocalization of SecA, suggesting the involvement of membrane phospholipids in the localization process. These data show for the first time that, in contrast to the recently reported uni-ExPortal site in the coccoïd Streptococcus pyogenes, multiple sites dedicated to protein export are present in the cytoplasmic membrane of rod-shaped B. subtilis.

Instabilité et particularités de l'évolution d'une nappe tourbillonnaire

The instability and the features of vortex sheet evolution are studied. We consider the self-organization of localized vortices (in two-dimensional flows) into clusters-like and spiral-like structures and show that quasi-final states do not ‘forget’ conditions of their initial origin. We discuss the physical significance of the obtained results. To cite this article: V. Pavlov et al., C. R. Mecanique 330 (2002) 757–762.

Whether the two-dimensional Eulerian turbulence evolves to a unique final state

The relaxation of two-dimensional Eulerian turbulence to a quasifinal state is studied. We consider the self-organization of localized vortices (in two-dimensional flows) into clusterlike and spiral-like structures and show that quasifinal states do not “forget” conditions of their initial origin. The numerical study confirms a possibility of the “vortex crystals” formation that have been observed in the plasma experiments. We discuss the physical significance of the obtained results.

Diffuse and Gravitationally Stable Molecular Gas in the Post-Starburst Galaxy NGC 5195

Abstract The Nobeyama Millimeter Array (NMA) has been used to make aperture synthesis CO($1-0$) observations of the post-starburst galaxy NGC 5195. CO($1-0$) and HCN($1-0$) observations of NGC 5195 using the Nobeyama 45 m telescope are also presented. High-resolution (${1\rlap {.}{}^{\mathrm {\prime \prime }}9} \times {1\rlap {.}{}^{\mathrm {\prime \prime }}8}$ or $86 \,\mathrm{pc} \times 81 \,\mathrm{pc}$ resolution at $D = 9.3 \,\mathrm{Mpc}$) NMA maps show a strong concentration of CO emission toward the central a few $\times 100 \,\mathrm{pc}$ region of NGC 5195, despite the fact that the current massive star formation is suppressed there. The face-on gas surface density, $\Sigma_\mathrm{gas}$, within the $r&amp;lt;2{}^{\prime\prime}$ or 90 pc region reaches $3.7 \times 10^3 M_\odot$ pc$^{-2}$ if a Galactic $N_\mathrm{H_2}/I_\mathrm{CO}$ conversion factor is applied. The extent of the central CO peak is about $5{}^{\prime\prime}$, or 230 pc, and is elongated along the E-W direction with two-armed spiral-like structures, which are typical for barred disk galaxies. The HCN-to-CO integrated intensity ratio on the brightness temperature scale, $R_\mathrm{HCN/CO}$, is about 0.02 within the central $r &amp;lt; 400$ pc region. This $R_\mathrm{HCN/CO}$ is smaller than those in starburst regions by a factor of $5 \hbox{--} 15$. These molecular-gas properties would explain why NGC 5195 is in a post-starburst phase; most of the dense molecular cores (i.e., the very sites of massive star formation) have been consumed away by a past starburst event, and therefore a burst of massive star formation can no longer last, although a large amount of low density gas still exists. We find a steep rise of the rotation velocity toward the center of NGC 5195. As a consequence, the critical gas surface density for a local gravitational instability of the gas disk becomes very high ($\Sigma_\mathrm{crit} \sim 6.9 \times 10^3 \,{{{M}_{\odot}}} \,\mathrm{pc}^{-2}$), suggesting that the molecular gas in the central region of NGC 5195 is gravitationally stable, in contrast to that of starburst galaxies. We propose that dense molecular gas can not be formed from remaining diffuse molecular gas because the molecular gas in the center of NGC 5195 is too stable to form dense cores via gravitational instabilities of diffuse molecular gas. The deduced very high threshold density seems to be due to a high mass concentration in NGC 5195. The known trends on the occurrence and luminosity of nuclear star formation in early-type galaxies can be understood naturally if the high threshold density is characteristic for early-type galaxies.

An HST emission-line imaging survey of 3CR radio galaxies

We present narrow-band images of sixty-four 3CR radio sources observed in lines of [OII] 3727 Å, [OIII] 5007 Å, and H α using the WFPC2 camera on-board HST. The images reveal a wide variety of emission lime morphologies, from compact nuclear regions to large-scale emission knots, filaments, and spiral-like structures. Many objects give evidence of ionization cones. In general we find a close correspondence between the emission-line and radio axes; most are aligned within 40 degrees. There is also evidence for a positive correlation between radio luminosity and the spatial extent of the emission-line region. Properties of interesting individual objects are discussed.

Candida albicans Int1p interacts with the septin ring in yeast and hyphal cells.

The ability to switch between yeast and hyphal morphologies is an important virulence factor for the opportunistic pathogen Candida albicans. Although the kinetics of appearance of the filamentous ring that forms at the incipient septum differ in yeast and cells forming hyphae (germ tubes) (), the molecular mechanisms that regulate this difference are not known. Int1p, a C. albicans gene product with similarity in its C terminus to Saccharomyces cerevisiae Bud4p, has a role in hyphal morphogenesis. Here we report that in S. cerevisiae, Int1p expression results in the growth of highly polarized cells with delocalized chitin and defects in cytokinesis and bud-site selection patterns, phenotypes that are also seen in S. cerevisiae septin mutant strains. Expression of high levels of Int1p in S. cerevisiae generated elaborate spiral-like structures at the periphery of the polarized cells that contained septins and Int1p. In addition, Int1p coimmunoprecipitated with the Cdc11p and Cdc12p septins, and Cdc12p is required for the establishment and maintenance of these Int1p/septin spirals. Although Swe1p kinase contributes to INT1-induced filamentous growth in S. cerevisiae, it is not required for the formation of ectopic Int1p/septin structures. In C. albicans, Int1p was important for the axial budding pattern and colocalized with Cdc3p septin in a ring at the mother-bud neck of yeast and pseudohyphal cells. Under conditions that induce hyphae, both Cdc3p and Int1p localized to a ring distal to the junction of the mother cell and germ tube. Thus, placement of the Int1p/septin ring with respect to the mother-daughter cell junction distinguishes yeast/pseudohyphal growth from hyphal growth in C. albicans.

Squared-spin-modulated versus spiral-like magnetic structures inGdNi2B2C: A155GdMössbauer-effect investigation

${}^{155}\mathrm{Gd}$ M\"ossbauer spectroscopy has been used to study the magnetic properties of ${\mathrm{GdNi}}_{2}{\mathrm{B}}_{2}\mathrm{C}.$ It was shown that below ${T}_{R}\ensuremath{\cong}14\mathrm{K}$ this compound orders in a bunched spiral-like magnetic structure with gadolinium magnetic moments rotating within the $(\mathbf{b},\mathbf{c})$ plane. Between $T=14\mathrm{K}$ and the N\'eel temperature of ${T}_{N}\ensuremath{\cong}20\mathrm{K}$ the magnetic structure is of sine-modulated type with gadolinium moments perpendicular to the tetragonal c axis. The observation of high-order harmonics indicates, however, a partial squaring of the sine modulation.

Measuring non-axisymmetry in spiral galaxies

We present a method for measuring small deviations from axisymmetry of the potential of a filled gas disc. The method is based on a higher order harmonic expansion of the full velocity field of the disc. This expansion is made by first fitting a tilted-ring model to the velocity field of the gas disc and subsequently expanding the velocity field along each ring into its harmonic terms. We use epicycle theory to derive equations for the harmonic terms in a distorted potential. The phase of each component of the distortion can vary with radius. We show that if the potential has a distortion of harmonic number m, the velocity field as seen on the sky exhibits an m − 1 and m + 1 distortion. As is to be expected, the effects of a global elongation of the halo are similar to an m = 2 spiral arm. The main difference is that the phase of the spiral arm can vary with radius. Our method allows a measurement of ϵ pot sin 2 ϕ2, where épot is the elongation of the potential and ϕ2 is one of the viewing angles. The advantage of this method over previous approaches to measure the elongations of disc galaxies is that, by using Hi data, one can probe the potential at radii beyond the stellar disc, into the regime where dark matter is thought to be the dominant dynamical component. The method is applied to the spiral galaxies NGC 2403 and 3198 and the harmonic terms are measured up to ninth order. The residual velocity field of NGC 2403 shows some spiral-like structures. The harmonic analysis indicates that the m = 3 term is dominant, with an average value of ∼0.02 υ c. This is consistent with an average ellipticity of the potential of ϵpot sin 2 ϕ2 = 0.064 ± 0.003, but spiral arms may couple significantly to this result. In the harmonic analysis of the kinematics of NGC 3198 the m= 2 and m= 3 terms are strongest (∼0.01υc). The inferred average elongation of the potential is 0.019 ± 0.003. Since the amplitude of the elongation is coupled to the viewing angles and may be influenced by spiral arms, more galaxies should be examined to separate these effects from true elongation in a statistical way.