Twisted Bundle Research Articles

Chiral and achiral mechanisms of self-limiting assembly of twisted bundles.

A generalized theory of the self-limiting assembly of twisted bundles of filaments and columns is presented. Bundles and fibers form in a broad variety of supramolecular systems, from biological to synthetic materials. A widely-invoked mechanism to explain their finite diameter relies on chirality transfer from the molecular constituents to collective twist of the assembly, the effect of which frustrates the lateral assembly and can select equilibrium, finite diameters of bundles. In this article, the thermodynamics of twisted-bundle assembly is analyzed to understand if chirality transfer is necessary for self-limitation, or instead, if spontaneously-twisting, achiral bundles also exhibit self-limited assembly. A generalized description is invoked for the elastic costs imposed by twist for bundles of various states of intra-bundle order from nematic to crystalline, as well as a generic mechanism for generating twist, classified both by chirality but also the twist susceptibility of inter-filament alignment. The theory provides a comprehensive set of predictions for the equilibrium twist and size of bundles as a function of surface energy as well as chirality, twist susceptibility, and elasticity of bundles. Moreover, it shows that while spontaneous twist can lead to self-limitation, assembly of twisted achiral bundles can be distinguished qualitatively in terms of their range of equilibrium sizes and thermodynamic stability relative to bulk (untwisted) states.

A Vanishing Theorem for the Twisted Normal Bundle of Curves in ,

AbstractWe prove the existence of a smooth and non-degenerate curve$X\subset \mathbb{P}^{n}$,$n\geqslant 8$, with$\deg (X)=d$,$p_{a}(X)=g$,$h^{1}(N_{X}(-1))=0$, and general moduli for all$(d,g,n)$such that$d\geqslant (n-3)\lceil g/2\rceil +n+3$. It was proved by C. Walter that, for$n\geqslant 4$, the inequality$2d\geqslant (n-3)g+4$is a necessary condition for the existence of a curve with$h^{1}(N_{X}(-1))=0$.

Constant spacing in filament bundles

Assemblies of one-dimensional filaments appear in a wide range of physical systems: from biopolymer bundles, columnar liquid crystals, and superconductor vortex arrays; to familiar macroscopic materials, like ropes, cables, and textiles. Interactions between the constituent filaments in such systems are most sensitive to the distance of closest approach between the central curves which approximate their configuration, subjecting these distinct assemblies to common geometric constraints. In this paper, we consider two distinct notions of constant spacing in multi-filament packings in : equidistance, where the distance of closest approach is constant along the length of filament pairs; and isometry, where the distances of closest approach between all neighboring filaments are constant and equal. We show that, although any smooth curve in permits one dimensional families of collinear equidistant curves belonging to a ruled surface, there are only two families of tangent fields with mutually equidistant integral curves in . The relative shapes and configurations of curves in these families are highly constrained: they must be either (isometric) developable domains, which can bend, but not twist; or (non-isometric) constant-pitch helical bundles, which can twist, but not bend. Thus, filament textures that are simultaneously bent and twisted, such as twisted toroids of condensed DNA plasmids or wire ropes, are doubly frustrated: twist frustrates constant neighbor spacing in the cross-section, while non-equidistance requires additional longitudinal variations of spacing along the filaments. To illustrate the consequences of the failure of equidistance, we compare spacing in three ‘almost equidistant’ ansatzes for twisted toroidal bundles and use our formulation of equidistance to construct upper bounds on the growth of longitudinal variations of spacing with bundle thickness.

Simulating precursor steps for fibril formation in methylcellulose solutions

We use coarse-grained molecular dynamics simulations to study the precursor steps for fibril formation in methylcellulose solutions. Simulations of ring stacking between two collapsed methylcellulose chains demonstrate the existence of a capture radius that is much larger than that predicted by polymer diffusion alone. When two rings are in very close proximity, they stack together to form a fibril precursor. Simulations of stacks of such rings suggest that this structure is metastable. In contrast, chains that are within the capture radius but not in close proximity, as well as for systems containing both ringlike and relaxed chains, fibril-like structures form via a distinctly different mechanism. Irrespective of their initial arrangement, the chains undergo two specific conformational changes: (i) a part of either a ring or a randomly coiled chain splays out and (ii) the splayed chain subsequently engulfs a nearby chain if it is within a certain capture distance. The latter results are consistent with recent experimental measurements of fibril formation by short methylcellulose chains, which suggests the formation of a twisted bundle.

Parametric study on heat transfer and pressure drop of twisted oval tube bundle with in line layout

A numerical research is conducted to investigate air side heat transfer and pressure drop performance of twisted oval tube bundles with in line layout in cross flow. The effects of five geometric parameters (the ratio of outer major axis to outer minor axis (A/B), twist pitch length (S), transverse tube pitch (St), longitudinal tube pitch (Sl) and number of longitudinal tube rows (Z)) on the air side heat transfer and pressure drop performance are examined in the range of Reynolds number (Re) from 500 to 23,000. The velocity field and temperature field are repeated periodically every S/2 along the length of the twisted oval tube, which reveals that the twisted oval tube is a streamlined tube that is independent of the angle of attack. Twisted oval tube bundles perform excellent heat transfer performance compared with other tube bundles (circular tube bundle with the same tube layout as the twisted oval tube bundle, elliptic tube bundle with staggered manner, spirally corrugated tube bundle with in line layout) in cross flow. And the staggered tube layout is beneficial to enhance heat transfer performance compared with in line tube layout. Correlations for Nusselt number (Nu) and Euler number (Eu) from this paper are presented.

Characterization of Electromagnetic Wave Coupling With a Twisted Bundle of Twisted Wire Pairs (TBTWPs) Above a Ground Plane

A multiconductor transmission line model is developed to characterize electromagnetic wave coupling with a twisted bundle of twisted wire pairs (TBTWPs) running above a ground plane. A set of parametric equations of each wire in each bundle is derived at first, together with its unit tangent vector defined analytically. Furthermore, its averaged per-unit-length parameters are determined according to the derived analytical equations, and the equivalent voltages for describing field–wire coupling are presented. The proposed model is employed for predicting both common mode and differential mode currents induced at different terminal loads of the TBTWP, where fire-side, end-fire, broad-side, and arbitrary electromagnetic wave incidences are investigated. The numerical results of our model are validated in comparison with that of the commercial software FEKO, with good agreement achieved between them. Furthermore, such TBTWP model can be extended for studying electromagnetic wave coupling with multiple TBTWPs employed in many cable systems.

Siu’s lemma, optimal $$L^2$$ extension and applications to twisted pluricanonical sheaves

We prove a general version of Siu’s lemma for plurisubharmonic functions with nontrivial multiplier ideal sheaves and use it to prove an optimal $$L^2$$ extension theorem and an optimal $$L^{\frac{2}{m}}$$ extension theorem for Kahler fibrations. These results are used to prove the positivity of twisted relative pluricanonical bundles and their direct images for Kahler fibrations and to answer a comparison question about singular metrics of twisted pluricanonical bundles.

Equivariant complex bundles, fixed points and equivariant unitary bordism

We study the fixed points of the universal G-equivariant n-dimensional complex vector bundle and obtain a decomposition formula in terms of twisted equivariant universal complex vector bundles of smaller dimension. We use this decomposition to describe the fixed points of the complex equivariant K-theory spectrum and the equivariant unitary bordism groups for adjacent families of subgroups.

Heat transfer and pressure drop for twisted oval tube bundles with staggered layout in crossflow of air

Twisted oval tube is also a finned tube in a sense, especially when used in crossflow, although the fins of the twisted oval tube are invisible. An experimental research on heat transfer and pressure drop performance of twisted oval tube bundle with staggered layout is conducted. The correlations of Nusselt number and pressure drop coefficient deduced from this paper are well compatible with experimental data, which could provide a theoretical reference of twisted oval tubes for industrial applications.

Eruption of a multi-flux-rope system in solar active region 12673 leading to the two largest flares in Solar Cycle 24

Context. Solar active region (AR) 12673 in 2017 September produced the two largest flares in Solar Cycle 24: the X9.3 flare on September 6 and the X8.2 flare on September 10. Aims. We attempt to investigate the evolutions of the two large flares and their associated complex magnetic system in detail. Methods. Combining observations from the Solar Dynamics Observatory and results of nonlinear force-free field (NLFFF) modeling, we identify various magnetic structures in the AR core region and examine the evolution of these structures during the flares. Results. Aided by the NLFFF modeling, we identify a double-decker flux rope configuration above the polarity inversion line (PIL) in the AR core region. The north ends of these two flux ropes were rooted in a negative- polarity magnetic patch, which began to move along the PIL and rotate anticlockwise before the X9.3 flare on September 6. The strong shearing motion and rotation contributed to the destabilization of the two magnetic flux ropes, of which the upper one subsequently erupted upward due to the kink-instability. Then another two sets of twisted loop bundles beside these ropes were disturbed and successively erupted within five minutes like a chain reaction. Similarly, multiple ejecta components were detected as consecutively erupting during the X8.2 flare occurring in the same AR on September 10. We examine the evolution of the AR magnetic fields from September 3 to 6 and find that five dipoles emerged successively at the east of the main sunspot. The interactions between these dipoles took place continuously, accompanied by magnetic flux cancellations and strong shearing motions. Conclusions. In AR 12673, significant flux emergence and successive interactions between the different emerging dipoles resulted in a complex magnetic system, accompanied by the formations of multiple flux ropes and twisted loop bundles. We propose that the eruptions of a multi-flux-rope system resulted in the two largest flares in Solar Cycle 24.

The Moduli Spaces of Parabolic Connections with a Quadratic Differential and Isomonodromic Deformations

In this paper, we study the moduli spaces of parabolic connections with a quadratic differential. We endow these moduli spaces with symplectic structures by using the fundamental 2-forms on the moduli spaces of parabolic connections (which are phase spaces of isomonodromic deformation systems). Moreover, we see that the moduli spaces of parabolic connections with a quadratic differential are equipped with structures of twisted cotangent bundles.

Quasi-static and dynamic interfacial evaluations of plasma functionalized carbon nanotube fiber

Carbon nanotube (CNT) fibers composed of well-oriented and twisted CNT bundles are desirable as a strong and lightweight reinforcement for the high-performance composites. Herein, CNT fibers were functionalized by atmospheric pressure helium/oxygen plasma to build up the sufficient fiber/matrix interfacial bonding. The micro-bond test (quasi-static test) and electrical resistance measurement under cyclic loading (dynamic test) were carried out to evaluate the interfacial properties between CNT fiber and epoxy resin. The results illustrated 84.6% improvement in the interfacial shear strength (IFSS) of the functionalized CNT fiber and epoxy from 17.37 MPa to 32.08 MPa, since the generated oxygenic groups and roughed morphology on CNT fiber surface. Moreover, the linear and repeatable gauge factors (between 1.1 and 1.4) of the functionalized CNT fiber embedded in epoxy under dynamic cyclic loading demonstrated their good interfacial bonding as well. In addition, the tensile strength of the functionalized CNT fiber showed 49.5% increment. Our study for the first time reveals the interface interaction in a fiber-matrix system to provide the direct evidence for the interfacial enhancement of the plasma functionalized CNT fiber. The interface-enhanced CNT fiber can be generally applied in composites with much improved mechanical and electrical performance.

Putative Neural Network Within an Olfactory Sensory Unit for Nestmate and Non-nestmate Discrimination in the Japanese Carpenter Ant: The Ultra-structures and Mathematical Simulation.

Ants are known to use a colony-specific blend of cuticular hydrocarbons (CHCs) as a pheromone to discriminate between nestmates and non-nestmates and the CHCs were sensed in the basiconic type of antennal sensilla (S. basiconica). To investigate the functional design of this type of antennal sensilla, we observed the ultra-structures at 2D and 3D in the Japanese carpenter ant, Camponotus japonicus, using a serial block-face scanning electron microscope (SBF-SEM), and conventional and high-voltage transmission electron microscopes. Based on the serial images of 352 cross sections of SBF-SEM, we reconstructed a 3D model of the sensillum revealing that each S. basiconica houses > 100 unbranched dendritic processes, which extend from the same number of olfactory receptor neurons (ORNs). The dendritic processes had characteristic beaded-structures and formed a twisted bundle within the sensillum. At the “beads,” the cell membranes of the processes were closely adjacent in the interdigitated profiles, suggesting functional interactions via gap junctions (GJs). Immunohistochemistry with anti-innexin (invertebrate GJ protein) antisera revealed positive labeling in the antennae of C. japonicus. Innexin 3, one of the five antennal innexin subtypes, was detected as a dotted signal within the S. basiconica as a sensory organ for nestmate recognition. These morphological results suggest that ORNs form an electrical network via GJs between dendritic processes. We were unable to functionally certify the electric connections in an olfactory sensory unit comprising such multiple ORNs; however, with the aid of simulation of a mathematical model, we examined the putative function of this novel chemosensory information network, which possibly contributes to the distinct discrimination of colony-specific blends of CHCs or other odor detection.

Experimental study on heat transfer and pressure drop of twisted oval tube bundle in cross flow

An experimental research on air side heat transfer and pressure drop performance of twisted oval tube bundle with staggered layout in cross flow is conducted. The comprehensive performance of present twisted oval tube bundle is larger than that of round tube bundle with the same layout by 25.5–33.3% during the experimental range of Remax (7500–18,000). The economic operation Remax among the experimental range is from 7500 to 13,000 for present twist oval tube bundle in cross flow. The correlations for Nusselt number and Euler number deduced from this paper are well compatible with experimental data, which could provide a theoretical reference of twisted oval tube bundle for industrial applications.

Persistence of Perfect Packing in Twisted Bundles of Elastic Filaments.

It is generally understood that geometric frustration prevents maximal hexagonal packings in uniform filament bundles upon twist. We demonstrate that a hexagonal packed elastic filament bundle can preserve its order over a wide range of twist due to a subtle counteraction of geometric expansion with elastic contraction. Using x-ray scanning and by locating each filament in the bundle, we show the remarkable persistence of order even as the twist is increased well above 360°, by measuring the spatial correlation function across the bundle cross section. We introduce a model which analyzes the combined effects of elasticity including filament stretching and radial and hoop compression necessary to explain this generic preservation of order observed with Hookean filaments.

Twisted hollow fiber membrane modules for reverse osmosis-driven desalination

We show how a simple design adaptation creates desirable flow structures that dramatically enhance performance in hollow fiber membrane (HFM) water desalination modules using computational fluid dynamics (CFD) simulations. Conventional HFM desalination modules encase thousands of co-axially aligned HFMs in a mutually parallel flow of brackish water. HFMs are subject to a phenomenon called concentration polarization (CP), which leads to fouling and will eventually prevent clean water production. We found that the twisted HFM module mitigates CP effects and increases transmembrane permeate flux by 5–9% for three flow rates considered. Twisted HFM bundles induce swirling flow structures inside desalination modules that increase momentum mixing throughout. Frictional energy losses and increased pumping power associated with this subtle design alteration are small relative to projected gains in clean water production. We predict system performance increases about 70% for the twisted modules herein considered, and there are in principle no additional required components associated with this geometry adaptation. With our findings, we identify how the twisted module design induces desirable flow structures that increase membrane separation performance by mitigating CP effects and increasing HFM efficacy.

Twisted argyle quivers and Higgs bundles

Ordinarily, quiver varieties are constructed as moduli spaces of quiver representations in the category of vector spaces. It is also natural to consider quiver representations in a richer category, namely that of vector bundles on some complex variety equipped with a fixed sheaf that twists the morphisms. Representations of A-type quivers in this twisted category — known in the literature as “holomorphic chains” — have practical use in questions concerning the topology of the moduli space of Higgs bundles. In that problem, the variety is a Riemann surface of genus at least 2, and the twist is its canonical line bundle. We extend the treatment of twisted A-type quiver representations to any genus using the Hitchin stability condition induced by Higgs bundles and computing their deformation theory. We then focus in particular on so-called “argyle quivers”, where the rank labelling alternates between 1 and integers ri≥1. We give explicit geometric identifications of moduli spaces of twisted representations of argyle quivers on P1 using invariant theory for a non-reductive action via Euclidean reduction on polynomials. This leads to a stratification of the moduli space by change of bundle type, which we identify with “collision manifolds” of invariant zeroes of polynomials. We also relate the present work to Bradlow–Daskalopoulos stability and Thaddeus' pullback maps to stable tuples. We apply our results to computing Q-Betti numbers of low-rank twisted Higgs bundle moduli spaces on P1, where the Higgs fields take values in an arbitrary ample line bundle. Our results agree with conjectural Poincaré series arising from the ADHM recursion formula.

Pathway driven self-assembly and living supramolecular polymerization in an amyloid-inspired peptide amphiphile.

Peptide 1 with an Aβ42 amyloid nucleating core demonstrates step-wise self-assembly in water. Variation of temperature or solvent composition arrests the self-assembly to give metastable nanoparticles, which undergo self-assembly on gradual increase in temperature and eventually produce kinetically controlled nanofibers and thermodynamically stable twisted helical bundles. Mechanical agitation of the fibers provided access to short seeds with narrow polydispersity index, which by mediation of seeded supramolecular polymerization establishes perfect control over the length of the nanofibers. Such pathway dependence and the length control of the supramolecular peptide nanofibers is exploited to tune the mechanical strength of the resulting hydrogel materials.

Moduli of non-commutative polarized schemes

We construct, using geometric invariant theory, a quasi-projective Deligne–Mumford stack of stable graded algebras. We also construct a derived enhancement, which classifies twisted bundles of stable graded A_infty -algebras. The tangent complex of the derived scheme is given by graded Hochschild cohomology, which we relate to ordinary Hochschild cohomology. We obtain a version of Hilbert stability for non-commutative projective schemes.

Erosion resistance of high-strength concrete containing forta-ferro fibers against sulfuric acid attack with an optimum design

One important factor affecting the resistance and durability loss of concrete structures is acid attack, and one common method of improving concrete properties against this attack is to use high-strength fiber-reinforced concrete. In this study, high-strength concretes containing different percentages of forta-ferro fibers (consisted of synthetic materials in the form of twisted bundle non-fibrillated monofilament and fibrillated polypropylene network) in the presence of silica fume and nano-silica pozzolans were made. After placing the specimens in 5% sulfuric acid for different days of immersion, the effect of adding fibers and pozzolans to the concrete mix on the strength and durability of the high-strength concrete was examined and the relationships between them were determined. Here, ultrasonic pulse velocity (UPV) test was also performed as a nondestructive test to evaluate the quality of high-strength fibrous concrete. The results indicated that as the volume fraction of fibers in the high-strength concrete exposed to sulfuric acid attack increased, less reduction in weight, crushing load, and ultrasonic pulse velocity occurred. In addition, using silica fume resulted in a greater improvement in the durability of the acid-exposed specimens relative to using nano-silica. Moreover, after 63days immersion in acid, the specimen FF0.6SF10 had the lowest loss in the crushing load, UPV, and weight by demonstrating 4.7, 2.9, and 3.1%, respectively, variations relative to the corresponding reference specimen. Finally, an optimum solution for the design parameters where the crushing load of high-strength fibrous concrete is maximized, was found employing response surface method (RSM).