Strings Of Beads Research Articles

Apparent boudinage in dykes

Intrusive rocks may be arranged in the form of strings of lenses or beads, as found on the Cap de Creus Peninsula, NE Spain, and in the South Finland Migmatite–Granite Belt. These structures first appear to be the result of stretching and boudinage of intrusive sheets or dykes. However, closer examination reveals that they are not boudins, but are instead primary intrusive structures. A detailed study was performed on a swarm of pegmatite intrusions at Cap de Creus. Layering is often continuous between beads, and, in some cases, individual beads exhibit a very irregular shape. These observations are shown to be incompatible with an origin by boudinage. Analogue experiments were used to test the effect of the two models (boudinage and emplacement) on the structures around beads, and show that an emplacement model of local expansion and collapse of magmatic sheets is the most compatible with field observations. Such structures can only form when dykes intrude hot rocks, when magma solidifies slowly enough to allow enough ductile flow of the wall rock to accommodate the formation of the beads. The fact that the pegmatite bead strings are not boudins has repercussions for the interpretation of the deformation at Cap de Creus and necessitates caution in the interpretation of deformation based on apparent boudins in intrusive rocks in other areas.

Morphosynthesis of Nanostructured Polymer Gels by Polymerization within Reverse Hexagonal Mesophases

Free radical polymerization of divinyl benzene (DVB) and styrene (St) was performed within reverse hexagonal phases of the anionic surfactant bis(2-ethylhexyl) sulfosuccinate sodium salt (AOT). The morphologies before and after polymerization were studied by small-angle X-ray scattering (SAXS), polarized light microscopy, and scanning and transmission electron microscopy. Polarized light microscopy and SAXS show no significant changes in textures and order during polymerization. A detailed investigation of the polymer matrix after polymerization and removal of the template reveals the formation of regular micrometer-sized layerlike morphologies. The polymer layers have a hierarchical structure, as they consist of aligned strings of polymer beads with diameters of about 100 nm. Structure formation is directed by the lyotropic phase during polymerization-induced phase separation on a nanometer scale. A mechanism of morphosynthesis is discussed on the basis of characteristic distortions within liquid crystals that are induced by the polymer phase. Parameters such as cross-linking degree and initiator or monomer concentration have a strong influence on the morphologies formed due to a kinetically controlled nucleation and growth mechanism. Finally, the structures formed by polymerization within reverse hexagonal phases are compared to those obtained from lamellar phases of the same surfactant.

Surface of poly(ethylene terephthalate/isophthalate) copolyesters studied by atomic force microscopy

An atomic force microscope (AFM) operating in Tapping™ and contact modes has been used to study the surface topography and the molecular organization of poly(ethylene terephthalate) (PET) films containing 2% (PET-2I) and 10% (PET-10I) isophthalate, and of injection/blow molded bottles containing 2.6% (PET-2.6I) and 10% isophthalate. Large-scale (15-μm × 15-μm) AFM images have shown that both surfaces are fairly flat and heterogeneous in nature, often containing inclusions. Whereas the PET surface appears to be formed mainly by microfibrils, isophthalic acid (IPA) incorporation at the 2–10 mol % level gives the surface a granular appearance. The IPA-containing PET surfaces are frequently coated by a lacelike film consisting of submicron “beads” joined together by filaments. These “strings of beads” form bundles and can also connect bundles. AFM images of PET-2I closely resemble those generated for PET films. By contrast, the lacelike structure becomes a dominant feature of the PET-10I surface. The level of inclusions observed on film surfaces appears to correlate with the levels of extractable oligomers present in the polymers. Nanometer-scale AFM images of PET-10I exhibit surfaces composed of short stacks of plates or rods, with 30–50-nm voids or pores between these stacks. Whereas surface deposits of what we suggest is most likely an oligomer correlates with isophthalate concentration, we see no gross structural features in PET-2I and PET-10I that explain the observed improvement in gas diffusion barrier in these polymers. © 2001 John Wiley & Sons, Inc. J Appl Polym Sci 80: 750–762, 2001

Deformation Mechanisms of Semi-Crystalline Polymers on the Submicron Scale

Micromechanical deformation mechanisms of two slightly branched polyethylenes have been studied by transmission electron microscopy and scanning force microscopy. Using an ethylene/hexene copolymer the transformation of the lamellar structure in the oriented structure inside a notch-tip craze and using a binary blend of different ethylene/1-hexene copolymers the deformation at elastomeric particles were investigated in detail. In particular, the micro-block arrangement in lamellae and the transformation in structures like strings of beads have been studied using microscopy at higher magnifications.

Identification of chemical and structural impurities in YBa 2Cu 3O 7−δ films by Raman spectroscopy

Raman spectroscopy has been applied to the identification of chemical and crystal structural impurities on the surfaces of YBa 2Cu 3O 7−δ (YBCO) films. The surfaces of the two YBCO films studied have been shown to contain significant a-oriented components. Film A was prepared at a higher temperature than film B, with oxygen partial pressure remaining about the same. Compared with film A, film B presented a more uniform and shiny surface when observed with the naked eye. On film A, the surface was decorated by mutually perpendicular or parallel strings of beads (or particulates), while on film B, the particulates were more randomly distributed. The particulates were found to be BaCuO 2, but the bead strings were mixtures of BaCuO 2 and Ba 2Cu 3O 5.9, grown concurrently with YBCO during vacuum deposition.

Influence of the microstructure on the sensory quality of whey protein gels

A full two-level factorial experimental design was used to study particulate whey protein gels. The processing conditions, pH, heating rate and the addition of salt were used as design factors. The results were evaluated by using a response surface model, and analysis of variance, M(ANOVA), was performed. The microstructure of particulate whey protein gels has been characterized previously, and the two-dimensional images from light microscopy and transmission electron microscopy were quantified by a stereological approach, while the more three-dimensional scanning electron micrographs were quantified by an expert panel of microscopists. In this study the texture of the same gels was analysed by a sensory panel. Correlations were made between the microstructure and sensory descriptors, and the panellists were able to detect differences between very small particles <1 μm 3 in volume. The sensory descriptors grainy appearance, gritty texture, creamy texture and tendency to fall apart had a logarithmic dependence on the microstructural parameters, particle size, and size of small and large pores. Multivariate techniques were used to create models to describe groups of the sensory descriptors by some of the microstructural parameters. A model with good correlation (r~ 0.8–0.9) was found for grainy appearance, gritty texture, creamy texture and falling apart. They were all dependent on the star volume of particles and small and large pores. The soft and springy textures were influenced by combinations of microstructural parameters, where the formation of strands into strings of beads or in clusters and conglomerates seemed to play an important role. The sticky texture was negatively correlated to the proportion of threads within the pores.

Size and Shape of Allophane Particles in Dispersed Aqueous Systems

AbstractAqueous suspensions of allophane show relatively high viscosity, presumably because of strong particle interaction between the unit particles. To test this hypothesis, we measured the particle weight and particle size of allophane during a dispersion using the light scattering method. The particle weight was more than several hundred times larger than that of the unit particle, and the size was 100–400 nm, whereas the Stokes’ diameter of the particles in the sample was less than 50 nm. Particle weight and size varied with the pH of the sample. Particle sizes were cross-checked by ultrafiltration through membrane filters. The experimental findings show that the unit particles of allophane within dilute dispersions appear to be associated like strings of beads, forming domains (primary floccules) about 100 nm in diameter. When these domains coagulate under certain conditions, they do not grow analogously but form clusters, such as secondary floccules, then precipitate. Formation of secondary flocculation of loose structure accounts for the maximum relative viscosity at the transition pH between dispersion and coagulation.

Did Galaxies Like Our Own Start Life in Chains?

New observations by the Hubble Space Telescope and the Keck Telescope may have spotted ancestors of present-day spiral galaxies, some 10 billion light-years from Earth. The faint galaxies, which looklike strings of beads, could fill a gap in the early history of galactic evolution, but the evidence is not yet complete.

Knots for Molecular Strings of Beads

Knots for Molecular Strings of Beads

Single‐Walled Tubes and Encapsulation of Nanocrystals into Carbon Clusters

Single‐walled carbon nanotubes can be prepared in an arc discharge between graphite electrodes of which the anode contains transition metals and their mixtures. Gram‐quantities of single‐walled tubes (SWT) can be obtained when a mixture of Fe/Ni, Fe/Co, or Ni/Co is used in the anode. Diameters of the SWT produced from Ni or Fe fall in the range of 0.70 to 1.00 nm compared to 0.85 to 1.30 nm of those produced with mixed Fe/Ni or Ni/Co. The SWT are a few microns long and capped at both ends. They do not associate directly to the metal particles. In contract, filled anode produced short SWT radiating from the particles. For B, Mg, Mn, Fe, Co, Ni, Cu, Y, Nb, Mo, and Ta, crystals of the carbides are encapsulated into the growing carbon nanoclusters. For Si, Cr, Zn, Pd, Ag, W, and Pt the nanotubes are formed but no encapsulation is observed. The presence of Ti, however, inhibits the formation of the carbon cages. The thermodynamics of the formation of the carbides is considered to set criteria and predict the encapsulation into the nanotubes. The growth of the strings of beads is discussed in conjunction with existing growth models.

Strings of liquid beads for gas‐liquid contact operations

AbstractA novel device for gas–liquid contact operations is proposed to feed a liquid onto wires (or threads) hanging down in a gas stream is proposed. The liquid disintegrates into beads strung on each wire at regular intervals; if the wire is moderately wettable, a thin film forms to sheathe the wire, thereby interconnecting the beads. Since the beads fall down slowly, which possibly renews the film flowing down even more slowly a sufficient gas‐liquid contact time is available even in a contactor with considerably limited height. An approximate calculation method is developed for predicting the variation in the temperature effectiveness for the liquid (the fractional approach of the liquid exit temperature to the gas inlet temperature) with the falling distance, assuming an applicability of strings‐of‐beads contactors to thermal energy recovery from hot gas streams.

Image analysis determination of particle size distribution

Three different methods for the determination of particle sizes by means of light microscopy combined with image analysis have been evaluated for dispersions of spherical starch particles. (i) Individual particles. This method was used to separate particles that formed clusters into individual particles. The size of the particles was determined by the diameters of the circles which could be inscribed in the cluster. (ii) Clusters. This method was used to measure all the connecting particles as one object, regardless of whether they were separated or in clusters. The area of the clusters was measured and the diameter of an equivalent circle was calculated. (iii) Strings of beads. This is a special case of clusters where particles were associated in one direction and formed strings. The diameter was the maximum distance between two parallel lines touching the object. Statistical evaluation of the results showed that there was very little variance between slides, frames and samples from the same batch. Thus repeated measurements with the image analysis system appear to be accurate. For the three image analysis methods the mean values of the particle size were between one micron to three microns.

Localization of a chymotrypsin-like protease to the perivitelline space of Xenopus laevis eggs

A chymotrypsin-like protease is released from Xenopus laevis eggs at activation and is involved in conversion of the vitelline envelope to the fertilization envelope. To localize this enzyme in unactivated and activated eggs, we used the synthetic peptide substrate succinylalanylalanylprolylphenylalanyl-4-methoxy-2-naphthylamide whose product can be visualized using transmission electron microscopy. Protease product was localized within the perivitelline space of unactivated eggs, appearing as strings of beads. No protease activity was detected in activated eggs, which is consistent with the observation that the protease is released from the egg at activation.

Charge-transfer reactions of fullerene dications with aromatic hydrocarbon and fullerene molecules in the gas phase

Results of selected-ion flow tube experiments are reported for reactions of C 2+ 60 and C 2+ 70 with benzene, naphthalene, anthracene, C 60 (buckminsterfullerene) and C 70 at 294 ± 2 K in helium gas at 0.35–0.40 Torr. Charge transfer was the only observed product channel. No evidence was obtained for the occurrence of adduct formation. This rules out the ability of doubly-charged fullerene molecules to act as nuclei for the condensation of aromatic molecules and the formation of doubly-charged “strings of fullerene beads” by successive additions of fullerene molecules under these operating conditions.

Immunogold labelling of human von Willebrand factor adsorbed to collagen

von Willebrand factor (vWF) mediates adhesion of platelets to the exposed subendothelium at sites of vascular injury. This function is expressed through binding of vWF to both collagen and receptors on the platelet membrane. We have developed a new method using immunogold staining and electron microscopy, permitting visualization of human vWF adsorbed to collagen fibrils. The electron micrographs revealed strings of gold beads reflecting the polymeric structure of vWF. Our data showed dramatic differences in the binding of vWF to collagens of different sources: high binding density was observed using a collagen preparation isolated from aortic tissue whereas colloidal gold was virtually absent from tendon collagen. Using the immunogold labelling method we demonstrated that high shear rate enhanced vWF binding to aortic collagen.

Problematic bedding-plane markings from the Middle Proterozoic Manganese Subgroup, Bangemall Basin, Western Australia

Enigmatic bedding-plane markings, impressions resembling isolated strings of beads, occur in sandy and argillaceous strata of the Stag Arrow Formation in the Middle Proterozoic Manganese Subgroup, Bangemall Group, of the Bangemall Basin, east of Newman, Western Australia. Markings are abundant at two localities and traces are found at a third. Structures similar in both morphology and dimension have previously been reported from the Appekunny Formation in the Middle Proterozoic Belt Supergroup of U.S.A. The Manganese Subgroup structures provide further details of morphology, enabling comparison with a variety of biogenic and non-biogenic structures. A source for the markings still cannot be determined with certainty, but a biogenic origin is favoured, and affinities with the green or brown algae suggested. Such an origin is consistent with records of megascopic algae from rocks of similar age.

Bending energy of vesicle membranes: General expressions for the first, second, and third variation of the shape energy and applications to spheres and cylinders.

A general equation of mechanical equilibrium of fluid membranes subject to bending elasticity [reported in Phys. Rev. Lett. 59, 2486 (1987)] is derived in detail. The second variation of the shape energy, also obtained for arbitrary shapes, is used to analyze stability with respect to deformational modes for spherical and cylindrical vesicles. The former analysis is well known, while the latter is presented here for the first time. The theoretical results are shown to agree very well with previous numerical calculations. In addition, they provide the energies controlling the shape fluctuations and show that spontaneous curvature may transform cylinders into tapes or strings of beads. The study of the energy of infinitesimal deformations is finally extended to include the third variation. Applying the general result to the sphere, we obtain the critical value of spontaneous curvature below which oblate ellipsoids of a deformed sphere are more stable than prolate ones. It is shown to be the same regardless of whether volume or pressure is kept constant.

Interaction of human low density lipoprotein and apolipoprotein B with ternary lipid microemulsion. Physical and functional properties.

Based on data from sedimentation velocity experiments, electrophoresis, electron microscopy, cellular uptake studies, scanning molecular sieve chromatography using a quasi-three-dimensional data display and flow performance liquid chromatography (FPLC), models for the interaction of human serum low density lipoprotein (LDL) and of apolipoprotein B (apo B) with a ternary lipid microemulsion (ME) are proposed. The initial step in the interaction of LDL (Stokes radius 110 A) with the ternary microemulsion (Stokes radius 270 A) appears to be attachment of the LDL to emulsion particles. This attachment is followed by a very slow fusion into particles having a radius of approx. 280 A. Sonication of this mixture yields large aggregates. Electron micrographs of deoxycholate-solubilized apo B indicate an arrangement of apo B resembling strings of beads. During incubation, these particles also attach to the ternary microemulsion particles and, upon sonication, spherical particles result which resemble native LDL particles in size. Scanning chromatography corroborates the electron microscopy results. By appropriate choice of display angles in a quasi-three-dimensional display of the scanning data (corrected for gel apparent absorbance) taken at equal time intervals during passage of a sample through the column, changes in molecular radius of less than 10 A can be detected visually. Such a display gives a quantitative estimate of 101 +/- 2 A for these particles (compared to 110 A for native LDL). The LDL-ME particles and apo B-ME particles compete efficiently with native LDL for cellular binding and uptake. Cellular association studies indicate that both LDL- and apo B-ME particles are effective vehicles for lipid delivery into cells.

Bisection of Circle Colorings

Consider $2n$ beads of k colors arranged on a necklace, using $2a$, beads of color i. A bisection is a set of disjoint strings (“intervals”) of beads whose union captures half the beads of each color. We prove that any arrangement with k colors has a bisection using at most $\lceil k / 2 \rceil $ intervals. In addition, if k is odd, an endpoint of one interval can be specified arbitrarily. The result is best possible. For fixed k, there is a polynomial-time algorithm to find such a bisection; it runs in $O ( n^{k - 2} )$ for $k\geqq 3$. We consider continuous and linear versions of the problem and use them to obtain applications in geometry, VLSI circuit design, and orthogonal functions.

Putative association of mitochondria with a subpopulation of intermediate-sized filaments in cultured human skin fibroblasts

Cultured cell Triton cytoskeletons enriched in intermediate filaments by extraction in high and low salt show, in addition to known intermediate-filament proteins and actin, a few other tenaciously bound polypeptides. An antibody raised against one of these polypeptides (IEF 24) is shown to react specifically with mitochondria of different cell types. With methanol-acetone fixation, required for the antibody reaction, the characteristically long mitochondria of human skin fibroblasts fragment into strings of beads, as identified by antibody staining in the light microscope and whole-mount electron microscopy. From the colinear organization of these beads, their codistribution with the intermediate-filament network and their retention in salt-extracted cytoskeletons, it is suggested that a subpopulation of the intermediate filaments can serve as an anchorage site for mitochondria.