Unclustered Distribution Research Articles

Late Paleocene pipe swarm in the Great South – Canterbury Basin (New Zealand)

We have identified a deeply buried fluid escape pipe province in Cretaceous - late Paleocene sediments of the Great South–Canterbury Basin (NZ). The seismic observations and interpretations point to an unusually vast fossil system of pipes. These features are exceptional in number (>2000 edifices) and appear to have formed from a common root zone. The areal extent of the analysed pipe system (2500 km 2 ) is among the largest systems of fluid expulsion features ever observed in three-dimensional seismic data. The unclustered distribution of the pipes suggests no specific link to faults or buried sedimentary features and, at their maximum vertical development, the pipes are equally distributed above depocentres or structural highs. The majority of pipes terminate at two discrete levels in the late Paleocene. Based on the geometrical relationship of the pipe edifices to the overburden, and the basinal setting of the hosting units, we interpret these horizons as representing the seabed at the time of pipe formation. This interpretation allows us to date the timing of pipe formation as prominently late Paleocene. We envisage that the pipes originated during discrete episodes of fluid venting in this time interval, disrupting the typical progressive basinal compaction-driven pore fluid expulsion. The pipes are associated with biogenic gas expulsion. We discuss their triggers, mechanical processes, and global significance for understanding fluid flow processes in sedimentary basins. Creation of the initial overpressure could be related to in situ biogenic gas generation in the stratigraphic interval coincident with the root zone of the pipes. We hypothesise that the main episode of gas release and pipe formation was associated with a sea-level fall during the contemporaneous late Paleocene Carbon Isotope Maximum. This case study shows a unique example of a preserved Paleogene fluid migration system and highlights how the observation and the interpretation of massive fossil systems of fluid-escape features provides invaluable information in terms of overpressure generation and basin fluid expulsion history. • Unusually vast fossil system of fluid escape pipes discovered offshore New Zealand. • The >2000 pipe edifices formed in the late Paleocene and are at present deeply buried. • They are associated to overpressure development linked to biogenic gas generation. • Gas release likely associated with late Paleocene Carbon Isotope Maximum sea-level fall.

Clustering of vector control interventions has important consequences for their effectiveness: a modelling study.

Vector control interventions have resulted in considerable reductions in malaria morbidity and mortality. When universal coverage cannot be achieved for financial or logistical reasons, the spatial arrangement of vector control is potentially important for optimizing benefits. This study investigated the effect of spatial clustering of vector control interventions on reducing the population of biting mosquitoes. A discrete-space continuous-time mathematical model of mosquito population dynamics and dispersal was extended to incorporate vector control interventions of insecticide treated bednets (ITNs), Indoor residual Spraying (IRS), and larviciding. Simulations were run at varying levels of coverage and degree of spatial clustering. At medium to high coverage levels of each of the interventions or in combination was more effective to spatially spread these interventions than to cluster them. Suggesting that when financial resources are limited, unclustered distribution of these interventions is more effective. Although it is often stated that locally high coverage is needed to achieve a community effect of ITNs or IRS, our results suggest that if the coverage of ITNs or IRS are insufficient to achieve universal coverage, and there is no targeting of high risk areas, the overall effects on mosquito densities are much greater if they are distributed in an unclustered way, rather than clustered in specific localities. Also, given that interventions are often delivered preferentially to accessible areas, and are therefore clustered, our model results show this may be inefficient. This study provides evidence that the effectiveness of an intervention can be highly dependent on its spatial distribution. Vector control plans should consider the spatial arrangement of any intervention package to ensure effectiveness is maximized.

Distribution of lipid raft markers in live cells

GPI (glycosylphosphatidylinositol)-anchored proteins are characteristic components of biochemically defined lipid rafts. Rafts may be involved in T-cell stimulation, but it is not clear whether molecules involved in TCR (T-cell receptor) signalling are partitioned to T-cell synapses through raft microdomains or through specific protein-protein interactions. We have used FRET (fluorescence resonance energy transfer) analysis to study the distribution of GPI-anchored fluorescent proteins in the plasma membrane of live cells. Multiple criteria suggested that FRET between different GPI-anchored fluorescent proteins in COS-7 or unstimulated Jurkat T-cells is generated by a random, unclustered distribution. Stimulation of TCR signalling in Jurkat T-cells by beads coated with antibodies against TCR subunits resulted in localized increases in fluorescence of raft markers. However, measurements of FRET and ratio imaging showed that there was no detectable clustering and no overall enrichment of raft markers in these regions.

Lipid raft proteins have a random distribution during localized activation of the T-cell receptor.

The extent to which lipid raft proteins are organized in functional clusters within the plasma membrane is central to the debate on structure and function of rafts. Glycosylphosphatidylinositol (GPI)-linked proteins are characteristic components of biochemically defined rafts. Several studies report a function for rafts in T-cell stimulation, but it is unclear whether molecules involved in T-cell receptor (TCR) signalling are recruited to (or excluded from) T-cell synapses through asymmetric distribution of raft microdomains or through specific protein-protein interactions. Here we used FRET analysis in live cells to determine whether GPI-linked proteins are clustered in the plasma membrane of unstimulated cells, and at regions where TCR signalling has been activated using antibody-coated beads. Multiple criteria suggested that FRET between different GPI-linked fluorescent proteins in COS-7 or unstimulated Jurkat T-cells is generated by a random, un-clustered distribution. Stimulation of TCR signalling in Jurkat cells resulted in localized increases in fluorescence of GPI-linked fluorescent proteins and cholera toxin B-subunit (CTB). However, measurements of FRET and ratio imaging showed that there was no detectable clustering and no overall enrichment of GPI-linked proteins or CTB in these regions.

A Study of Quasar Clustering at z>2.7 From the Palomar Transit GRISM Survey

The quest for structure indicators at earlier and earlier times in the evolution of the universe has led to the search for objects with ever higher redshifts. The Palomar Transit Grism Survey has produced a large sample of high redshift quasars ($z>2.7$), allowing statistical analysis of correlation between quasar positions. In this study, clustering is identified through comparison with $100 000$ Monte Carlo generated, randomly populated volumes, which are identical to the observed region in spatial coordinates, redshift distribution, and number of quasars. Three pairs have been observed with comoving separations of 11.34, 12.97, and 24.13 h_{50}^{-1}Mpc (assuming $q_0=0.5$), smaller separations than would be expected to arise by chance in an unclustered distribution. Selection effects are ruled out as a false source of clustering by scrambling the observed quasar coordinates and redshifts, which gives a pair separation distribution nearly identical to that of the Monte Carlo distribution. Tests using the distribution of pair separations and nearest neighbor distances show that the observed pairs have a probability less than 0.1% of arising in an unclustered distribution. Using a maximum likelihood technique to estimate the correlation length $r_0$, assuming $\xi(r) = (r/r_0)^{-1.8}$, we find $r_0 = 35\pm15 h_{50}^{-1}Mpc$ (comoving, $q_0=0.5$, 1$\sigma$ errors), a value much larger than the correlation length of present-day galaxies.

Gravitational Microlensing by Clustered MACHOs

It has been proposed that the MACHOs in our galaxy could be clumped in globular cluster--like associations or RAMBOs (robust associations of massive baryonic objects) (Moore \& Silk 1995). Here we investigate the effect such clustering has on the microlensing of stars in the Large Magellanic Cloud. We find that the lensing in a one square degree field could be dominated by just a few clusters. As a result the lensing properties vary widely depending on the position and velocity of those clusters which happen to lie between us and the LMC. Moreover we find a large variance in time scale distributions that suggests that the small number statistics could easily be dominated by events in the tails of the unclustered distribution ({\it e.g.} by long periods). We compare our results with the MACHO collaboration's data and find that a ``standard'' halo made entirely of MACHOs is not strongly disfavored if the clusters have masses of $10^6 M_{\odot}$. For less massive clusters such a halo is not as likely. For $10^4 M_{\odot}$ clusters the microlensing statistics are essentially unchanged from the unclustered case. It may be possible to detect very massive clusters from the distribution of events in time-scale and space. We provide some example time- scale distributions.

Tectonics, alteration and the fractal distribution of hydrothermal veins in the lower ocean crust

Gabbros from Hole 735B preserve the igneous, structural and metamorphic history beneath the Southwest Indian Ridge down to middle amphibolite facies conditions. The gabbro was isolated from the zone of lithospheric necking by detachment faulting, unroofing and block uplift at the inside-corner high of the Atlantis II Transform. Lower crustal accretion, as preserved in the core, is a complex integration of igneous, hydrothermal and tectonic processes. Alteration began at anhydrous granulite conditions as surface faulting penetrated the brittle-ductile transition to form brittle-ductile shear zones. In the amphibolite facies, hydrous alteration around these zones was extensive, while undeformed sections remained virtually unaltered. Amphibole veins formed during the brittle-ductile deformation have a high fractal dimension, reflecting an unclustered distribution, consistent with high strain and cracking rates in the zone of lithospheric necking beneath the ridge. However, the fractal dimensions of the two major gneissic amphibolite zones in Hole 735B are different and suggest that they represent discrete fault zones formed at different times. Below middle amphibolite facies a dramatic drop in the extent of alteration reflects cooling, cracking and alteration under static conditions, similar to layered intrusions. Initially, fracture and vein formation exploited undeformed sections, where elastic strain accumulated during cooling from high temperatures was unrelieved by recrystallization. Plagioclase-diopside veins formed at this time have the same orientation as higher temperature veins, but a mineralogy reflecting much lower rock permeabilities, and a low fractal dimension, reflecting a tight clustering of veins, as would be anticipated for crack formation at low strain rates. Late zeolite and carbonate veins and irregular, smectite-lined, near-vertical cracks also have a very low fractal dimension, reflecting clustering appropriate to low strain, near static conditions. These, however, show no preference for undeformed sections of the core and are oriented with subvertical and subhorizontal maxima. This indicates crack formation under the present day stress field. Thus, elastic strain, due to cooling from high temperatures and extension during lithospheric necking, dissipated after plagioclase-diopside vein formation.

Widespread lateral processes of glial cells in the immature striate cortex of the cat

The topographies of intrinsic tangential connections of cells in the striate cortex of cats were determined in animals ranging in age between 1 day and 30 days. Implants of the carbocyanin dye. Dil, were found to label cellular elements which are classified by morphological criteria as astrocytes, in addition to neurons. Labeled astrocytes are seen in all cortical layers and in the superficial and deep white matter. Most labeled astrocytes occur underneath the Dil implant, but a number of them are also located horizontally at various distances from the implant. The horizontal span of the glial processes is the same as that for neuronal processes; in contrast to neurons however, the laterally distributed astrocytes assume a flat and unclustered distribution in the horizontal plane. Our observations suggest that the program for determining the span of laterally directed projections in the cat striate cortex is likely to bethe same for neurons and astrocyte-like neuroglia.

Anchorage-dependent surface distribution and partition during freeze-fracture of viral transmembrane glycoproteins.

We have compared in the same cell type the surface distribution and partition in freeze-fractured plasma membranes of Sindbis virus glycoproteins in three different situations: (i) in permanently transformed cells that express the glycoproteins as the only viral product; (ii) in cells in which prebound viruses were forced to fuse with the plasma membrane by low pH treatment; (iii) in virus-infected cells. We report here that the viral proteins expressed on the surface of transfected cells show a uniform and unclustered distribution; conversely, in Sindbis virus-infected cells they appear clustered, regionally distributed, and always associated with budding viruses (i.e., interacting with the nucleocapsid on the cytosolic side of the membrane). Furthermore, the viral proteins expressed on transfected cells or implanted by low pH-mediated fusion partition during freeze-fracture with the exoplasmic faces of the cell plasma membranes, whereas an opposite partition is observed in infected cells. These results strongly suggest that in infected cells the clustering and the partition with the protoplasmic faces of the plasma membrane depend only on the strong "anchorage" of the glycoproteins to the nucleocapsid.

Emergence and refinement of clustered horizontal connections in cat striate cortex

Pyramidal cells in layer 2/3 of adult cat striate cortex have long, intrinsic horizontal axon collaterals within both layer 2/3 and layer 5. These collaterals form periodic "clusters" of finer axon branches that link columns of similar orientation selectivity. We have investigated the sequence of events and possible mechanisms underlying the development of these clustered intrinsic horizontal connections using a combination of neuronal tracers and intracellular staining. Small injections of fluorescent latex microspheres made during the first postnatal week (at P4-6), when examined in tangential sections, produced an even, unclustered distribution of retrogradely labeled cells up to 2 mm from the injection site. At P8, retrograde labeling extended over a larger area and clustering was discernible, primarily among the most distant labeled cells. At both P6 and P8, labeling was similar in layers 2/3 and 5, indicating that the transition from clustered to unclustered connections occurred simultaneously for cells in superficial and deep laminae. By the end of the second postnatal week (P12-15), retrogradely labeled cells were far more clustered both within and beyond the extent of P6 label; the density of labeled cells was high throughout the labeled region, but much higher within clusters. The periodicity of these nascent clusters was similar to that in the adult. Despite obvious clustering, the pattern of retrograde label observed following injections at 2-3 weeks (P12-21) differed markedly from the adult, in that the regions between clusters contained many labeled cells. Over the next 3 weeks, the connections were refined, so that by the sixth postnatal week (P36-38), regions between clusters contained very few retrogradely labeled cells and the overall pattern of retrograde label was indistinguishable from that in adults. Despite differences in postmigratory ages of neurons from the superficial and deep laminae, clustering of retrogradely labeled cells from these 2 populations was similar at all ages. Experiments in which 2-3 weeks elapsed between the time microsphere injections were made and animals were killed demonstrated that neither the initial formation of crude clusters nor their refinement was due to cell death. Instead, cluster refinement resulted from specific process elimination. When a red microsphere injection at P15 was followed by a green microsphere injection at exactly the same location on P29, the earlier injection resulted in crude clustering, as expected. Virtually all of the cells double-labeled by the later injection were within the densest clusters of label from the early injection.(ABSTRACT TRUNCATED AT 400 WORDS)

Distribution and mobility of murine histocompatibility H-2Kk antigen in the cytoplasmic membrane.

The topographical distributions and mobilities of the murine histocompatibility antigen H-2Kk and of concanavalin A (Con A) binding sites have been studied on a murine lymphoma cell line. The spatial distribution of H-2Kk antigens, the average distance between H-2Kk antigens and Con A binding sites, and the separation of different determinants on the H-2Kk antigen itself were determined by using fluorescence resonance energy-transfer measurements with a dual-laser flow sorter. From the lack of energy transfer between bound monoclonal anti-H-2Kk antibodies conjugated with fluorescein (donor) and rhodamine (acceptor), we conclude that the H-2Kk antigen exists without appreciable clustering on the cell surface. Substantial energy transfer between appropriately labeled Con A and antibodies bound to the H-2Kk antigen shows that the two populations are interspersed. Donor/acceptor pairs of monoclonal antibodies binding to different determinants on the same H-2Kk antigen exhibited a degree of energy transfer indicative of a mean separation of 8.6 nm between the sites. Time-resolved phosphorescence anisotropy measurements with anti-H-2Kk antibodies labeled with eosin or erythrosin yielded rotational mobility information for the antigen-antibody complexes on the cell membrane. The rotational correlation time of 10-20 mus and the finite residual anisotropy are compatible with an uniaxial mode of rotation of monomeric antigen around its transmembrane portion and, thus, provide additional evidence for an unclustered distribution. Capping by rabbit anti-mouse IgG immobilized the antigen-antibody complex. Fluorescence recovery after photobleaching was used to calculate an apparent lateral diffusion coefficient of 5 +/- 3 X 10(-10) cm2 . s-1 for the H-2Kk antigen labeled with fluoresceinated IgG or its corresponding Fab fragment.