Flattened Aggregates Research Articles

New Findings of Diamonds and Diamond Indicator Minerals in the Middle Timan and Prospects of the Search for Their Original Sources

In the poorly studied southeastern part of the Chetlas uplift, ring structures typical for magmatic pipe-type bodies (diatremes) have been established. The main part of the ring structures is located in the areas of the distribution of the Upper Devonian sediments. This fact indicates the lower age threshold of the formation of the objects forming them as Late Devonian, i.e., similar to the age of kimberlites of the Arkhangelsk diamond-bearing province. To assess the prospects of one of the most numerous groups of the ring structures, heavy-mineral concentrate sampling of the modern stream sediments was conducted. While studying the heavy-mineral concentrates, chromium-bearing pyrope—a kimberlite indicator mineral—was revealed, and the first diamond grain was found. About 20% of pyropes are characterized by a high preservation of relict endogenous surfaces. The diamond has the appearance of a flattened aggregate with the distinct octahedron faces modified by surfaces of joint growth with other mineral grains. Findings of diamonds and signs of the formation of the diamond indicator minerals in the stream sediments of the studied area make it possible to detect their nearby original sources.

Flattened aggregate function method for nonlinear programming with many complicated constraints

In this paper, efforts are made to solve nonlinear programming with many complicated constraints more efficiently. The constrained optimization problem is firstly converted to a minimax problem, where the max-value function is approximately smoothed by the so-called flattened aggregate function or its modified version. For carefully updated aggregate parameters, the smooth unconstrained optimization problem is solved by an inexact Newton method. Because the flattened aggregate function can usually reduce greatly the amount of computation for gradients and Hessians, the method is more efficient. Convergence of the proposed method is proven and some numerical results are given to show its efficiency.

The Flattened Aggregate Constraint Homotopy Method for Nonlinear Programming Problems with Many Nonlinear Constraints

The aggregate constraint homotopy method uses a single smoothing constraint instead ofm-constraints to reduce the dimension of its homotopy map, and hence it is expected to be more efficient than the combined homotopy interior point method when the number of constraints is very large. However, the gradient and Hessian of the aggregate constraint function are complicated combinations of gradients and Hessians of all constraint functions, and hence they are expensive to calculate when the number of constraint functions is very large. In order to improve the performance of the aggregate constraint homotopy method for solving nonlinear programming problems, with few variables and many nonlinear constraints, a flattened aggregate constraint homotopy method, that can save much computation of gradients and Hessians of constraint functions, is presented. Under some similar conditions for other homotopy methods, existence and convergence of a smooth homotopy path are proven. A numerical procedure is given to implement the proposed homotopy method, preliminary computational results show its performance, and it is also competitive with the state-of-the-art solver KNITRO for solving large-scale nonlinear optimization.

Three stage multilayer formation kinetics during adsorption of an anionic fluorinated surfactant onto germanium: Solution pH and salt effects

The effects of solution pH, salt type and its concentration on the adsorption kinetics and the structural evolution of an anionic fluorinated surfactant, tetraethylammonium perfluorooctylsulfonate (TEA–FOS), at the hydroxylated Ge/aqueous solution interface are investigated by using Fourier transform infrared spectroscopy in attenuated total reflection mode (ATR-FTIR). The surface excess, the adsorption rate, the durations of three-stage adsorption and the molecular orientation of adsorbed TEA–FOS are all dependent on the pH of the solution. Consistent with the expected effects of solution pH on surface charge of the germanium oxide crystal surface, the most surfactant adsorbs at acidic pH 3.4 although a considerable amount still adsorbs at pH 10.0. Linear dichroism measurements suggest that the adsorbed surfactants prefer to form less-curved (flattened) multilayer admicelles, which pack more closely on the solid surface as the solution pH decreases. Under both acidic (pH 3.4) and basic (pH 10.0) conditions, the equilibrium surface excess first passes through a maximum as NaCl concentration increases, followed by a decrease. This suggests that excessive NaCl concentration is not favorable for multilayer formation due to increased electrostatic shielding which reduces the ion-pairing ability between TEA+ and FOS−. In addition, infrared dichroism measurements of CF2 stretching show that salt type and its concentration influence the structural evolution of adsorbed surfactants. A moderate amount of NaCl favors the assembly of adsorbed micelles into ordered flattened aggregates, but an excess of NaCl makes adsorbed surfactants assemble randomly like spherical aggregates. Compared to Na+ and K+ ions, Ca2+ ions cause the adsorbed surfactants to pack more closely on the solid surface into flattened micellar aggregates. All of the effects of solution pH and salt can be rationalized based on Coulombic interactions between the substrate surface, surfactants and counter-ions.

Ianbruceite, ideally [Zn2(OH)(H2O)(AsO4)](H2O)2, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure

AbstractIanbruceite, ideally [Zn2(OH)(H2O)(AsO4)](H2O)2, is a new supergene mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia. It occurs as thin platy crystals up to 80 μm long and a few μm thick, which form flattened aggregates up to 0.10 mm across, and ellipsoidal aggregates up to 0.5 mm across. It is associated with coarse white leiteite, dark blue köttigite, minor legrandite and adamite. Ianbruceite is sky blue to very pale blue with a white streak and a vitreous lustre; it does not fluoresce under ultraviolet light. It has perfect cleavage parallel to (100), is flexible, and deforms plastically. The Mohs hardness is 1 and the calculated density is 3.197 g cm-3. The refractive indices are α = 1.601, β = 1.660, γ = 1.662, all ±0.002; 2Vobs= 18(2)°, 2Vcalc= 20°, and the dispersion isr<v, weak. Ianbruceite is monoclinic, space groupP21/c, a= 11.793(2),b= 9.1138(14),c= 6.8265(10) Å, β = 103.859(9)°,V= 712.3(3) Å3,Z= 4,a:b:c= 1.2940:1:0.7490. The seven strongest lines in the X-ray powder diffraction pattern [d(Å),I, (hkl)] are as follows: 11.29, 100, (100); 2.922, 17, (130); 3.143, 15, (202); 3.744, 11, (300); 2.655, 9, (230); 1.598, 8, (152); 2.252, 7, (222). Chemical analysis by electron microprobe gave As2O536.27, As2O31.26, Al2O30.37, ZnO 49.72, MnO 0.32, FeO 0.71, K2O 0.25, H2Ocalc19.89, sum 108.79 wt.%; the very high oxide sum is due to the fact that the calculated H2O content is determined from crystal-structure analysis, but H2O is lost under vacuum in the electron microprobe.The crystal structure of ianbruceite was solved by direct methods and refined to anR1index of 8.6%. The As is tetrahedrally coordinated by four O anions with a mean As O distance of 1.687 Å. Zigzag [[5]Zn[6]Znϕ7] chains extend in thecdirection and are linked in thebdirection by sharing corners with (AsO4) tetrahedra to form slabs with a composition [Zn2(OH)(H2O)(AsO4)]. The space between these slabs is filled with disordered (H2O) groups and minor lone-pair stereoactive As3+. The ideal formula derived from chemical analysis and crystal-structure solution and refinement is [Zn2(OH)(H2O)(AsO4)](H2O)2.

Macrothrombocytopenia: Investigating the Ultrastructure of Platelets and Fibrin Networks Using Scanning and Transmission Electron Microscopy

Macrothrombocytopenia is a rare condition where large, circulating platelets ranging between ~5 and 20 μm are found (typically platelets size range from 1.5 to 2.5 μm). The condition is also characterized by the prevalence of decreased numbers of circulating platelets, bleeding, short circulating times in blood, as well as abnormal platelet destruction. The current research investigates the scanning electron microscopy (SEM) and transmission electron microscopy (TEM) of platelet aggregates and fibrin networks of a family diagnosed with macrothrombocytopenia. Although TEM analysis of macrothrombocytopenia is not novel, little is known regarding the SEM analysis of platelet aggregates and fibrin networks. Here the authors show that macrothrombocytopenia have two different variations of giant platelet aggregates: a bulbous, giant aggregate that is very similar to control aggregates, and a giant flattened aggregate, with a compressed outer rim and a centrally placed area that forms a bulbous pseudopodia-like core. TEM micrographs of controls showed that, as previously seen in the literature, an aggregate contains dense bodies and alpha granules that carry, among other compounds, fibrinogen. TEM micrographs of the individuals with macrothrombocytopenia revealed aggregates with large vacuoles and areas mostly devoid of dense bodies and alpha granules. An interesting observation was that, in the presence of added human thrombin (to initially form the clot), fibrin fiber networks, comparable to that of control fibrin networks, were formed. This might be of clinical interest in the treatment regime and should be investigated further.

Characterization of aliphatic and aromatic polyester hyperbranched dendrimers by AFM imaging

The aggregates of aliphatic (AL-PE) and aromatic polyester (AR-PE) hyperbranched dendrimers were imaged by tapping mode atomic force microscopy (AFM). The second and third generations of AL-PE dendrimers were adsorbed on mica in large aggregates of 150- and 166-nm diameters with little heights (ca. 1–2 nm). The origin of such flattened aggregates is attributed to their favorable adsorption on mica in view of the presence of –OH surface groups. AR-PE did not show such flattened aggregates instead small aggregates of 63 nm were observed in an organized manner beaving a cavity in the center of each aggregate. The organized aggregates of AR-PE with smaller dimension than AL-PE are ascribed to less favorable adsorption of the latter on mica in view of its stronger hydrophobicity.

Morphology microstructure, and development of colonies of Acetobacter xylinum.

Development of the morphology and microstructure of colonies of Acetobacter xylinum growing on agar was studied by optical microscopy, and transmission and scanning electron microscopy. The mass of rapidly dividing cells surrounded by a sheath of cellulose microfibrils passes from a smooth spheroid to a flattened aggregate with a characteristic "pillowed" surface. This morphology is the result of a repeated extrusion of cells from the confirming sheath, followed by regeneration of a new portion of the sheath on the extrusion of cells from the confirming sheath, followed by regeneration of a new portion of the sheath on the extruded cell mass. Relations of this mechanism to others which produce similar shapes are indicated.

Liquid-Tissue Mechanics in Amphibian Gastrulation: Germ-Layer Assembly inRana Pipiens

During amphibian gastrulation, migrating subsurface germ layers may flow past one another like immiscible viscous liquids in response to tissue surface tension forces. We describe here two physical tests for liquid-tissue morphogenesis in cultured aggregates of subsurface ectoderm (E), mesoderm (M) and endoderm (N) excised from mid-yolk-plug Rana pipiens gastrulae. (i) Liquids are coherent substances in which subunits can slip past one another to relax internal shear stresses. We find, in cross-sections of cell aggregates fixed during compression, that cells within flattened aggregates are intially deformed, but do, as predicted, gradually reassume their original, undistorted shapes, (ii) Surface tensions (γ's) govern ordinary liquid-droplet spreading; e.g. , if equal-sized droplets A and B fuse in medium O, B spreads around A when γAO γBO. When pairs of subsurface aggregates are cultured together, N surrounds M and E, and M surrounds E. To see if γEO > γMO > γNO. we flatten aggregates with quartz fibers calibrated to measure the force of compression. As predicted, under the same flattening force, E aggregates are rounder than M aggregates, which are rounder than N aggregates. Furthermore, a second surface tension relationship can account for the autonomous involution of M between E and N; and these surface tension relationships can also explain the inversion of E, M and N by coated ectoderm to produce normal gastrular germ-layer arrangements. We conclude that, combined with active cell shape changes in solid-like surface cell layers and also with autonomous elongation of dorsal lip mesoderm, tissue surface tension control of liquid-tissue flow in subsurface germ layers is a key morphogenetic mechanism in amphibian gastrulation which might be regulated by changes in intercellular adhesiveness.

The Local Supercluster

The first quantitative evidence for a large scale density excess or “metagalactic cloud” including the Local Group was obtained by Holmberg (1937) and confirmed by Reiz (1941). the present concept of the Local Supercluster (LSC) as a flattened aggregate of field galaxies, small groups and larger clouds centered at the Virgo cluster was formulated 25 years ago (de Vaucouleurs 1953) even before large-scale superclustering was recognized as a general phenomenon. See review papers in Vistas in Astronomy (1956), Soviet Astronomy (1960), Science (1970), Publ. Astron. Soc. Pacific (1971), and IAU Symp. No. 63 (Abell 1974).

A mutation affecting both rate and pattern of morphogenesis in Dictyostelium discoideum

At high population densities, mutant Fr-17 of D. discoideum forms only irregular flattened aggregates rather than the mature fruiting structures of the wild type. Yet many of the end products of the normal morphogenesis are present in the mutant. These include: spores, ensheathed clusters of stalk cells, a variety of polysaccharides, antigens known to be associated with the spores and stalks of the wild type, and pigment. In addition the temporal succession of these morphogenetic events is greatly accelerated.