Wormhole Structure Research Articles

Conditions affecting the re-alignment of the antimicrobial peptide PGLa in membranes as monitored by solid state 2H-NMR

The cationic antimicrobial peptide PGLa is electrostatically attracted to bacterial membranes, binds as an amphiphilic α-helix, and is thus able to permeabilize the lipid bilayer. Using solid state 2H-NMR of non-perturbing Ala-d 3 labels on the peptide, we have characterized the helix alignment under a range of different conditions. Even at a very high peptide-to-lipid ratio (1:20) and in the presence of negatively charged lipids, there was no indication of a toroidal wormhole structure. Instead, PGLa re-aligns from a surface-bound S-state to an obliquely tilted T-state, which is presumably dimeric. An intermediate structure half-way between the S- and T-state was observed in fully hydrated multilamellar DMPC vesicles at 1:50, suggesting a fast exchange between the two states on the time scale of >50 kHz. We demonstrate that this equilibrium is shifted from the S- towards the T-state either upon (i) increasing the peptide concentration, (ii) adding negatively charged DMPG, or (iii) decreasing the level of hydration. The threshold concentration for re-alignment in DMPC is found to be between 1:200 and 1:100 in oriented samples at 96% humidity. In fully hydrated multilamellar DMPC vesicles, it shifts to an effective peptide-to-lipid ratio of 1:50 as some peptides are able to escape into the bulk water phase.

Effects of SBS addition and temperature on 3D siliceous mesostructured cellular foam

Siliceous mesostructured cellular foam with three-dimensional (3D) wormhole structure (MSU-type) is prepared by using triblock copolymer (poly(styrene- b-butadiene- b-styrene), SBS) with both hydrophobic head and tail group as template in strong acid condition via microemulsion method. The effects of SBS addition and temperature on the morphology and physicochemical properties, such as pore diameters, surface areas and pore volumes of the materials have been investigated by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), field emission scanning electron microscope (FE-SEM) and nitrogen adsorption–desorption analysis. The results show that the pore volumes, pore sizes and specific surface areas depend strongly on the SBS amount and forming micelles temperature. Moreover, the materials obtained with high wall thickness exhibit a relatively good thermal stability.

A Fractal Wormhole Model for Cold Heavy Oil Production

Abstract Wormholes are believed to be generated during the process of cold production and are responsible for enhanced production rates. Understanding the wormhole patterns generated inside the reservoir formation is critical to improve the recovery efficiency and to model the fluid flow behaviour in the cold production process. In this paper, we have proposed that the wormhole growth can be described by the Diffusion-Limited Aggregation (DLA) model, which naturally relates to a broad variety of branchinggrowth patterns through the physics of the processes. The physical processes that were described using fractal models include the following: the growth of a drainage network; the formation of cavities; the dissolution of porous materials; and, the growth of random dendrites in the thin films. The DLA model has important implications in petroleum geology and engineering. Based on the experimental results published in the literature, which were specifically designed to investigate the wormhole dynamics by a Computed-Tomography X-Ray scanner, the wormhole diameter distribution along the wormhole path has been analyzed using the Area Version of Gaussian Function. Then, the material balance method has been applied to the sand production data to determine the possible range of the wormhole structure around the wellbore, assuming that the sand particles are solely produced along the paths of wormholes. Finally, a numerical method has been developed to analyze the field sand production data. The studies have shown that the fractal wormhole model can be used to diagnose the characteristics of the wormhole structures, and that it can be applied to optimize well placement in cold heavy oil production. The model will greatly enhance the analyses of the inflow performance and the pressure response of wells in wormholed reservoirs. Results acquired from this study can also be implemented in field scale numerical simulations for the cold flow process. Introduction Cold production is a non-thermal process in which sand is aggressively produced to reach a higher oil production rate. In the cold flow process, sand and oil are produced together under primary conditions and oil production rates can typically increase by a factor of 10 or more(1–5). For example, primary oil production rates of 8 – 12 m3/d are roughly 10 times greater than those calculated for the radial flow in the Celtic field using Darcy's law(2). The unusual sand production in cold production was observed in several oil fields. Records have indicated that the production of about 708 m3 of sand in the first four months, and in nearly all the wells in S.E. Pauls Valley Field, Oklahoma, produced 10 – 50% sand initially, declining a few months later to 0.1 – 2%, regardless of completion method(5). The cumulative gross fluid production of about 9,000 m3 with an associated sand production of 200 m3 within a period of 1,000 days was observed in the Lindbergh and Frog Lake Fields, Alberta(1).

Thiol-Functionalized Silica with Mesocellular Foam and Hybrid Mesocellular Foam−Wormhole Structures

We report the direct supramolecular assembly of organofunctional compositions of the type (SiO2)1-x-(LSiO1.5)x (L = mercaptopropyl) with a mesocellular foam structure (x = 0.20), along with a new h...

Direct syntheses using a fluorinated surfactant of silicas containing organofluorinated groups

Direct syntheses of silicas containing organofluorinated groups have been achieved by co-condensation of tetraethylorthosilicate (TEOS) and a organofluorinated triethoxysilane, RF(CH2)2Si(OEt)3 [RF = CF3(CF2)5 or CF3], in the presence of either the neutral fluorinated surfactant n-CF3(CF2)7(CH2)2NH2 or the cationic one, n-CF3(CF2)7(CH2)2NMe3+I−. Microporous silica with a wormhole structure containing the C8 fluorinated chain was obtained in the presence of the nonionic surfactant. It was shown that the use of fluorinated surfactants allows the incorporation of an amount of (fluorinated) chains located in the channel pores that is superior to that obtained by using a hydrogenated surfactant. The cationic surfactant used under acidic conditions allowed the incorporation of only a low amount of the C8 fluorinated chain, leading to a poorly structured material. In contrast, a mesoporous silica containing the CF3(CH2)2 group and showing a hexagonal arrangement was obtained under the same experimental conditions.

Structured mesoporous organosilicas from an acetonitrile–water template system

The synthesis of templated mesoporous silicas with a narrow pore size distribution can be achieved in a water/acetonitrile/n-dodecylamine system. The benefits of using this system compared to aqueous ethanol to prepare silicas are the much enhanced wall thickness, leading to greater structural stability, as well as a lack of co-surfactancy from acetonitrile, which means that the pore size remains constant over a wide range of solvent compositions. The particles obtained from this route are cylindrical, with partially aligned mesopores, in contrast to those obtained from aqueous ethanol, which are spherical and have a wormhole structure. A further major advantage is that the amine-functionalised materials, formed by direct co-condensation, are nucleophilic, in contrast to those prepared from aqueous ethanol. This latter feature allows for the elaboration of these amine functions to attach a range of more complex functionality, examples of which are given.

Exactly soluble quantum wormhole in two dimensions

We are presenting a quantum traversable wormhole in an exactly soluble two-dimensional model. This is different from previous works since the exotic negative energy that supports the wormhole is generated from the quantization of classical energy-momentum tensors. This explicit illustration shows the quantum-mechanical energy can be used as a candidate for the exotic source. As for the traversability, after a particle travels through the wormhole, the static initial wormhole geometry gets a back reaction which spoils the wormhole structure. However, it may still maintain the initial structure along with the appropriate boundary condition.

Comparison of Au Catalysts Supported on Mesoporous Titania and Silica: Investigation of Au Particle Size Effects and Metal-Support Interactions

Au catalysts supported on mesoporous silica and titania supports were synthesized and tested for the oxidation of CO. Two approaches were used to prepare the silica-supported catalysts utilizing complexing triamine ligands which resulted in mesoporous silica with wormhole and hexagonal structures. The use of triamine ligands is the key for the formation of uniformly sized 2–3 nm Au nanoparticles in the silica pores. On mesoporous titania, high gold dispersions were obtained without the need of a functional ligand. Au supported on titania exhibited a much higher activity for CO oxidation, even though the Au particle sizes were essentially identical on the titania and the wormhole silica supports. The results suggest that the presence of 2–3 nm particle size alone is not sufficient to achieve high activity in CO oxidation. Instead, the support may influence the activity through other possible ways including stabilization of active sub-nanometer particles, formation of active oxygen-containing reactant intermediates (such as hydroxyls or O2−), or stabilization of optimal Au structures.

Mesostructured Fe Oxide Synthesized by Ligand-Assisted Templating with a Chelating Triol Surfactant

The synthesis and properties of sulfate- and phosphate-free mesostructured iron oxide prepared using a chelating triol surfactant are reported. Materials synthesized using metal−surfactant ratios of 1:1, 2:1, 3:1, and 4:1 all showed a broad single reflection in the XRD at low angle corresponding to a wormhole mesostructure, as well as small higher angle peaks consistent with the presence of a small amount of maghemite and hemitite. TEM images confirmed the wormhole structure of the mesophase, while also revealing rodlike crystals corresponding to one or both of the two known phases of iron oxide observed in the XRD. Attempts to remove the surfactant by washing or chemical treatment were unsuccessful. Calcination led to a complete collapse of the structure and crystallization of the mesophase into maghemite. Magnetic studies provided evidence for the formation of superparamagnetic iron oxide particles within the walls of the mesostructure in addition to a small magnetic contribution arising from the presence of larger maghemite crystallites, while the calcined materials behaved more like a soft ferromagnet.

New SO2 Resistant Mesoporous La—Co—Zr Mixed Oxide Catalysts for Hydrocarbon Oxidation.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Aluminosilicate Mesostructures with Improved Acidity and Hydrothermal Stability

AbstractFor Abstract see ChemInform Abstract in Full Text.

Synthesis of stable mesostructured zirconia: Tween surfactant and controlled template removal

Mesostructured zirconia has been synthesized by using zirconium chloride and PEO nonionic ethoxylated sorbitan ester (Tween-20, -40, -60 or -80) as a zirconium source and structure-directing agent in an aqueous medium. To remove the occluded surfactants, UV/ozone treatment has been utilized instead of calcination due to thermal instability. This results from a special molecular structure of Tween surfactant. From XRD, SEM and TEM analyses, the materials treated with UV light and in-situ generated ozone has a wormhole structure and ill-defined or well-defined spherical particles.

New SO2resistant mesoporous La–Co–Zr mixed oxide catalysts for hydrocarbon oxidation

A new approach for the synthesis of a new type of ternary mesoporous La–Co–Zr mixed oxides with various atomic (La + Co/La + Co + Zr) ratios is reported. The synthesis method combines the advantages of the preparation of the clear soluble homogeneous metal oxides containing a cationic surfactant in acidic medium followed by the precipitation of this mixture in basic medium and hydrothermal treatment. These solids have high surface area, uniform mesopore size with a worm-hole like pore structure, good thermal stability and high component dispersion. They exhibit unusually high catalytic activity and resistance to SO2 poisoning in the complete methane oxidation as compared to bulk LaCoO3 perovskites.

Macro-cellular silica foams: synthesis during the natural creaming process of an oil-in-water emulsion.

The room-temperature synthesis of a macro-mesoporous silica material during the natural creaming process of an oil-in-water emulsion is reported. The material has 3-dimensional interconnected macropores with a strut-like structure similar to meso-cellular silica foams with mesoporous walls of worm-hole structure. The material has very high surface area (approximately 800 m2 g(-1)) with narrow mesopore size distribution.

Aluminosilicate mesostructures with improved acidity and hydrothermal stability

Significant improvements in both the hydrothermal stability and the acidity of mesostructured aluminosilcates have been reported recently. New assembly pathways, along with post-synthesis treatment methods, have made it possible to form structures with thick and more highly crosslinked framework walls. The resulting structures are slow to degrade under hydrothermal conditions in comparison to conventional analogs. Also, improved methodologies for grafting Al centers into the walls of pre-assembled frameworks have afforded aluminosilicate mesostructures with enhanced acidity. The most promising strategy for improving the hydrothermal stability and acidity of aluminosilicate mesostructures, however, is based on the use of protozeolitic nanoclusters. These so-called “zeolite seeds” can be directly assembled into hexagonal, cubic, wormhole, and foamlike framework structures under a variety of assembly conditions. They also can be grafted into the walls of pre-assembled frameworks to form more stable acidic derivatives.

Single crystal particles of a mesoporous mixed transition metal oxide with a wormhole structure.

A new type of mesoporous mixed transition metal oxide of Nb and Ta (NbTa-TIT-1) has been prepared through a two-step calcination, which consists of single crystal particles with wormhole mesoporous structure.

Influence of transport and reaction on wormhole formation in porous media

AbstractThe transport and reaction of fluids in porous media results in unique pore growth and channel evolution as the media are dissolved. This often leads to the formation of highly conductive flow channels, commonly referred to as wormholes. The objective of this work is to predict the influence of transport and reaction on the structure of the wormhole channels. An experimental and theoretical investigation of a variety of fluid systems, including strong acids, weak acids, and chelating agents, provides a wide range of conditions for studying wormhole formation. A generalized description of the dissolution phenomenon is introduced, and a common dependence on the Damköhler number is demonstrated. The Damköhler number is shown to dictate the type of wormhole structure formed by systems with various degrees of transport and reaction limitations. An optimum Damköhler number for channel formation is observed at a value of approximately 0.29 for all of the fluid systems investigated. The stochastic nature of the dissolution phenomenon is described using network models. Results from a 2‐D network model and a 3‐D physically representative network model agree qualitatively with experimental results and substantiate the existence of an optimum Damköhler number.

Dynamics of gravitating magnetic monopoles.

According to previous work on magnetic monopoles, static regular solutions are nonexistent if the vacuum expectation value of the Higgs field $\eta$ is larger than a critical value $\eta_{{\rm cr}}$, which is of the order of the Planck mass. In order to understand the properties of monopoles for $\eta>\eta_{{\rm cr}}$, we investigate their dynamics numerically. If $\eta$ is large enough ($\gg\eta_{{\rm cr}}$), a monopole expands exponentially and a wormhole structure appears around it, regardless of coupling constants and initial configuration. If $\eta$ is around $\eta_{{\rm cr}}$, there are three types of solutions, depending on coupling constants and initial configuration: a monopole either expands as stated above, collapses into a black hole, or comes to take a stable configuration.

Lorentzian wormholes from the gravitationally squeezed vacuum

Minkowski-signature wormhole solutions of the Einstein field equations entail violations of the weak energy condition in the vicinity of the wormhole throat. Squeezed states of matter provide a natural source of violation for this condition. The matter vacuum is automatically squeezed as a result of the gravitational interaction, and gives rise to the negative energy densities required for supporting a wormhole structure in spacetime.