Helical Strands Research Articles

Light‐ and Temperature‐Controlled Hybridization, Chiral Induction and Handedness of Helical Foldamers

Helical foldamers have attracted much attention over the last decades given their resemblance to certain biomacromolecules and their potential in domains as different as pharmaceutics, catalysis and photonics. Various research groups have successfully controlled the right‐ or left‐ handedness of these oligomers by introducing stereogenic centers through covalent or non‐covalent chemistry. However, developing helical structures whose handedness can be reversibly switched remains a major challenge for chemists. To date, such an achievement has been reported with light‐responsive single‐stranded foldamers only. Herein, we demonstrate that grafting a unidirectional motor onto foldamer strands constitutes a relevant strategy to i) control the single or double helical state of a foldamer, ii) switch on the chiral induction process from the motor to the helical strands and iii) select the handedness of double helical structures through photochemical and thermal stimulations.

Light- and Temperature-Controlled Hybridization, Chiral Induction and Handedness of Helical Foldamers.

Helical foldamers have attracted much attention over the last decades given their resemblance to certain biomacromolecules and their potential in domains as different as pharmaceutics, catalysis and photonics. Various research groups have successfully controlled the right- or left- handedness of these oligomers by introducing stereogenic centers through covalent or non-covalent chemistry. However, developing helical structures whose handedness can be reversibly switched remains a major challenge for chemists. To date, such an achievement has been reported with light-responsive single-stranded foldamers only. Herein, we demonstrate that grafting a unidirectional motor onto foldamer strands constitutes a relevant strategy to i) control the single or double helical state of a foldamer, ii) switch on the chiral induction process from the motor to the helical strands and iii) select the handedness of double helical structures through photochemical and thermal stimulations.

A new approach to the calculation of variable tangent bending stiffness for helical strands

As the cross-section of the helical strand increases, the effect of its nonlinear bending characteristics becomes significant. To accurately simulate the response of helical strands under such conditions using the finite element method, determining the tangent bending stiffness of helical strands is indispensable. However, the approach of calculating the tangent bending stiffness of helical strands based on the stick-slip state of wires is not universally applicable across all strand models. In this study, we propose an approach for calculating the tangent bending stiffness of strands based on two mechanical models of helical strands. This proposed approach uses the ratio of the “actual increment” to the “theoretical maximum increment” of the nonlinear component of the wire axial force to calculate the contribution of one wire to the tangent bending stiffness of the strand. Significantly, this approach can be applied to different strand models, each of which may adopt different slip criteria. By comparing the results with the numerical solutions, we validate the effectiveness of the proposed approach for calculating the tangent bending stiffness of helical strands on different strand models. Furthermore, it is pointed out that the analytical results of wire sliding may vary significantly depending on the adopted slip criteria.

Rationale and design of INFINITY-SWEDEHEART: A registry-based randomized clinical trial comparing clinical outcomes of the sirolimus-eluting DynamX bioadaptor to the zotarolimus-eluting Resolute Onyx stent

Modern drug-eluting stents have seen significant improvements, yet still create a rigid cage within the coronary artery. There is a 2% to 4% annual incidence of target lesion failure (TLF) beyond 1 year, and half of the patients experience angina after 5 years. The DynamX bioadaptor is a sirolimus-eluting, thin (71 µm) cobalt-chromium platform with helical strands that unlock and separate after in vivo degradation of the bioresorbable polymer coating. This allows the vessel to return to normal physiological function and motion, along with compensatory adaptive remodeling, which may reduce the need for reintervention and alleviate angina following percutaneous coronary intervention (PCI). The INFINITY-SWEDEHEART trial is a single-blind, registry-based randomized clinical trial (R-RCT) to evaluate the safety and effectiveness of the DynamX bioadaptor compared to the Resolute Onyx stent in the treatment of patients with ischemic heart disease with de novo native coronary artery lesions. The R-RCT framework allows for recruitment, randomization, and pragmatic data collection of baseline demographics, medications, and clinical outcomes using existing national clinical registries integrated with the trial database. The primary objective is to demonstrate noninferiority in terms of freedom from TLF (cardiovascular death, target vessel myocardial infarction, or ischemia-driven target lesion revascularization) at 1 year. Powered secondary endpoints will be tested sequentially for superiority from 6 months to the end of follow-up (5 years) for the following: 1) TLF in all subjects, 2) target vessel failure in all subjects, and 3) TLF in subjects with acute coronary syndrome (ACS). Subsequent superiority testing will be performed at a time determined depending on the number of events, ensuring sufficient statistical power. Change in angina-related symptoms, function and quality of life will be assessed using the Seattle Angina Questionnaire-short version. Predefined sub-groups will be analyzed. In total, 2400 patients have been randomized at 20 sites in Sweden. Available baseline characteristic reveal relatively old age (68 years) and a large proportion of ACS patients including 25% STEMI and 37% NSTEMI patients. The INFINITY-SWEDEHEART study is designed to evaluate the long-term safety and efficacy of the DynamX bioadaptor compared to the Resolute Onyx stent in a general PCI patient population.

3D meso-scale modeling of bond behavior between helical strand and concrete

Excellent interfacial bonding is the foundation for the strand and concrete working together. Helical structure of strand causes its rotation during the pull-out process, which makes it difficult to quantify the bond-slip at the interface. A three-dimensional (3D) meso-scale numerical model is first established to investigate the bond behavior at strand-concrete interface in this study. A refined modeling method is proposed to build a helical strand with the longitudinal helix shape and transverse flower-like shape. The heterogeneous concrete composed of three-phase composite material is built based on the random aggregate model. The interaction between strand and concrete is implemented by the surface-to-surface contact strategy. The rationality of the proposed model is verified by the experimental results. The effects of the helical structure of strand, the lay length of strand, aggregate content and eccentricity of strand on interfacial bond behavior are discussed. The results indicate that considering the helical structure of strand and heterogeneity of concrete can more accurately describe the stress distribution at the strand -concrete interface. The proportion of twisting slip is lower than that of longitudinal slip in the whole pull-out process, and its proportion increases first and then decreases. The interfacial bond strength increases first and then decreases with the increase of lay length of strand and aggregate content, and it reaches the best when the lay length is 14 time of diameter with the aggregate content of 45 %.

Three-dimensional fusion imaging to assess apposition of low-profile visualized intraluminal support stent for intracranial aneurysm coiling

ObjectiveTo investigate on three-dimensional (3D) fusion images the apposition of low-profile visualized intraluminal support (LVIS) stents in intracranial aneurysms after treatment and assess inter-rater reliability. Materials and methodsRecords of all patients with unruptured intracranial aneurysms who were treated with the LVIS stent were retrospectively accessed and included in this study. Two neurosurgeons evaluated the presence of malapposition between the vessel walls and the stent trunk (crescent sign) and the vessel wall and the stent edges (edge malappostion) on 3D fusion images. These images were high-resolution cone-beam computed tomography images of the LVIS stent fused with 3D-digital subtraction angiography images of the vessels. Associations between malapposition and aneurysm location were assessed by Fisher's exact test, and inter-rater agreement was estimated using Cohen's kappa statistic. ResultsForty consecutive patients were included. In all patients, 3D fusion imaging successfully visualized the tantalum helical strands and the closed-cell structure of the nitinol material of the low-profile visualized intraluminal support. A crescent sign was observed in 27.5 % and edge malapposition in 47.5 % of the patients. Malapposition was not significantly associated with location (p = 0.23 crescent sign, p = 0.07 edge malapposition). Almost perfect (κ = 0.88) and substantial (κ = 0.76) agreements between the two raters were found for the detection of crescent signs and edge appositions, respectively. Conclusions3D fusion imaging provided clear visualization of the LVIS stent and parent arteries, and could detect malapposition with excellent inter-rater reliability. This technique may provide valuable guidance for surgeons in determining postoperative management.

Crystal structure and Hirshfeld surface analysis of 4,4'-di-meth-oxy-biphenyl-3,3',5,5'-tetra-carb-oxy-lic acid dihydrate.

In the crystal of the title compound, C18H14O10·2H2O, the arene rings of the biphenyl moiety are tilted at an angle of 24.3 (1)°, while the planes passing through the carboxyl groups are rotated at angles of 8.6 (1) and 7.7 (1)° out of the plane of the benzene ring to which they are attached. The crystal structure is essentially stabilized by O-H⋯O bonds. Here, the carboxyl groups of neighbouring host mol-ecules are connected by cyclic R 2 2(8) synthons, leading to the formation of a three-dimensional network. The water mol-ecules in turn form helical supra-molecular strands running in the direction of the crystallographic c-axis (chain-like water clusters). The second H atom of each water mol-ecule provides a link to a meth-oxy O atom of the host mol-ecule. A Hirshfeld surface analysis was performed to qu-antify the contributions of the different inter-molecular inter-actions, indicating that the most important contributions to the crystal packing are from H⋯O/O⋯H (37.0%), H⋯H (26.3%), H⋯C/C⋯H (18.5%) and C⋯O/O⋯C (9.5%) inter-actions.

Efficient finite element modelling of helical strand cables utilising periodicity

This paper proposes a repeated unit cell (RUC) FE modelling strategy for multilayered helical strand cables subject to tensile loading and bending with an initial tensile load. The approach utilises the axial periodicity in helical structures to reduce computational domain to two cable periods. A novel mesh creation method allowing the exact geometry of helical strands to be discretised into solid elements while maintaining flat end surfaces is proposed. Periodic boundary conditions (PBC) allowing for geometric and material nonlinearity are used to implement cyclic loads to study hysteresis in single and multilayered cables. Comparisons made to existing experimental and analytical results validate the models ability to capture hysteresis due to plasticity and geometric effects such as the stick–slip transition in bending. Examination of the cross-sectional stress distribution shows plasticity initiates at contact points at loads which are 25% of the load at which the cable tensile response deviates from linearity.

On propagation characteristics of ultrasonic guided waves in helical strands

Steel strands have been widely used in industrial fields as a reliable load-bearing component. Under the influence of environmental erosion and fatigue stress, different types of damage, such as corrosion and fracture, will occur in the in-service steel strands, which will cause unpredictable loss of personnel and property. Ultrasonic nondestructive testing technology has become an ideal testing method for long-distance metal structures in recent years due to the advantages of long detection distance and high efficiency. The detection effect of ultrasonic nondestructive testing technology largely depends on the propagation characteristics of the selected guided wave modes. However, due to the influence of the helical structure of the steel strands and the contact between the wires, the propagation characteristics of the guided waves in the steel strands are very complicated. In this paper, a method for analyzing the dispersion characteristics of steel strands based on the Floquet boundary conditions (Floquet BCs) is proposed. The essence of this method is the mutual transformation principle of wave solution and vibration solution. To adapt to the helical structure of steel strands, this paper proposes a helical coordinate system and twisted coordinate system and deduces the corresponding wavenumber conversion formula. The results of Floquet BCs are consistent with the semi-analytical finite element method and sweep frequency finite element modeling method, which proves the correctness of the Floquet BC method from both theoretical and experimental perspectives. This paper provides a new idea for analyzing the dispersion characteristics of complex waveguides such as steel strands.

Ultraductile Bar with Bioinspired Helical Strands

Ultraductile Bar with Bioinspired Helical Strands

Structural insights into a spindle-shaped archaeal virus with a sevenfold symmetrical tail

Archaeal viruses with a spindle-shaped virion are abundant and widespread in extremely diverse environments. However, efforts to obtain the high-resolution structure of a spindle-shaped virus have been unsuccessful. Here, we present the structure of SSV19, a spindle-shaped virus infecting the hyperthermophilic archaeon Sulfolobus sp. E11-6. Our near-atomic structure reveals an unusual sevenfold symmetrical virus tail consisting of the tailspike, nozzle, and adaptor proteins. The spindle-shaped capsid shell is formed by seven left-handed helical strands, constructed of the hydrophobic major capsid protein, emanating from the highly glycosylated tail assembly. Sliding between adjacent strands is responsible for the variation of a virion in size. Ultrathin sections of the SSV19-infected cells show that SSV19 virions adsorb to the host cell membrane through the tail after penetrating the S-layer. The tailspike harbors a putative endo-mannanase domain, which shares structural similarity to a Bacteroides thetaiotaomicro endo-mannanase. Molecules of glycerol dibiphytanyl glycerol tetraether lipid were observed in hydrophobic clefts between the tail and the capsid shell. The nozzle protein resembles the stem and clip domains of the portals of herpesviruses and bacteriophages, implying an evolutionary relationship among the archaeal, bacterial, and eukaryotic viruses.

DNA-like Helices as Nanosized Polarizers of Electromagnetic Waves

The possibility of using a conducting double DNA-like helix as the basis of an electromagnetic wave polarizer, which converts an incident linearly polarized wave into a reflected wave with circular polarization, has been shown. A high-frequency resonance is studied, at which the wavelength of the incident radiation is approximately equal to the length of a helical turn. The simulation of a double DNA-like helix has been carried out. The electric currents arising in the helical strands under waves with circular polarization at high-frequency resonance have been analyzed. Fundamentally different behavior of the double DNA-like helix concerning waves with right-hand or left-hand circular polarization has been established, which can be called the effect of polarization selectivity. This effect is manifested in the fact that a double DNA-like helix at high-frequency resonance can create a reflected wave having only one sign of circular polarization. The electric vector of the reflected wave produces a turn in space with the opposite winding direction compared to the double helix. These studies also highlight the electromagnetic forces of interaction between helical strands. The equilibrium of the double DNA-like helix has been studied, including as an element of metamaterials and as an object with a high potential for use in nanotechnology.

Comparison of the design of composite prestressed concrete hollow-core floor units between Eurocode 2 and ACI 318

A typical 1200 mm (48 in.) wide × 200 mm (8 in.) deep prestressed concrete hollow-core floor unit is analyzed and designed as a composite slab with a 75 mm (3 in.) deep structural topping to make a comparison between Eurocode 2: Design of Concrete Structures (EC2-1-1) and the American Concrete Institute’s Building Code Requirements for Structural Concrete (ACI 318-08) and Commentary (ACI 318R- 08). This is the second of two papers. The first was published in PCI Journal in the March–April 2021 issue and designed a noncomposite hollow-core unit. The present comparison includes two-stage composite service and ultimate moments of resistance, ultimate composite shear capacities, camber and deflections, and interface shear between the hollow-core unit and cast-in-place concrete topping. Precast concrete cylin­der strength was 40 N/mm2 (5800 psi) and the cast-in-place concrete topping was 25 N/mm2 (3625 psi). The hollow-core unit was pretensioned using 10 number seven-wire helical strands. Worked examples are pre­sented in parallel formation for EC2 and ACI 318.

Solvent media as the driving force in the formation of one-dimensional silver(I) coordination polymers with 2-methylidene-1,3-bis(nicotinoyloxy)propane.

Two kinds of silver(I) coordination polymers consisting of the same chemical composition, [Ag(CF3SO3)(L)] [L is 2-methylidene-1,3-bis(nicotinoyloxy)propane], were synthesized and characterized by infrared (IR) and photoluminescence (PL) spectroscopy, elemental and thermal analyses, and single-crystal X-ray diffractometry; these are catena-poly[[(trifluoromethanesulfonato-κO)silver(I)]-μ-2-methylenepropane-1,3-diyl dinicotinate-κ2N:N'], [Ag(CF3SO3)(C16H14N2O4)]n, and its chloroform monosolvate, {[Ag(CF3SO3)(C16H14N2O4)]·CHCl3}n. The X-ray crystallographic measurements revealed that the silver(I) compounds exhibit one-dimensional sinusoidal or helical molecular structures depending on the solvent used for crystallization. Self-assembly in a methanol/chloroform mixture produces the sinusoidal molecular strand, whereas recrystallization from acetonitrile medium affords a racemic mixture of the helical strands. These compounds display a fluorescence emission arising from both the ligand-centred transition and the ligand-to-metal charge transfer (LMCT) in the solid state under ambient conditions.

An ortho-rhom-bic polymorph of 2-(1,3,5-di-thia-zinan-5-yl)ethanol or MEA-di-thia-zine.

Substituted triazines are a class of compounds utilized for scavenging and sequestering hydrogen sulfide in oil and gas production operations. The reaction of one of these triazines under field conditions resulted in the formation of the title compound, 2-(1,3,5-di-thia-zinan-5-yl)ethanol, C5H11NOS2, or MEA-di-thia-zine. Polymorphic form I, in space group I41/a, was first reported in 2004 and its extended structure displays one-dimensional, helical strands connected through O-H⋯O hydrogen bonds. We describe here the form II polymorph of the title compound, which crystallizes in the ortho-rhom-bic space group Pbca as centrosymmetric dimers through pairwise O-H⋯N hydrogen bonds from the hydroxyl moiety to the nitro-gen atom of an adjacent mol-ecule.

Self-Assembly of Double-Helical Metallopolymers.

Metal-containing polymers, or metallopolymers, have diverse applications in the fields of sensors, catalysis, information storage, optoelectronics, and neuromorphic computing, among other areas. The approach of metal-templated subcomponent self-assembly using dynamic covalent linkages allows complex architectures to be formed with relative synthetic ease. The dynamic nature of the linkages between subunits in these systems facilitates error checking during the assembly process and also provides a route to disassemble the structure, rendering these materials recyclable. This Account summarizes a class of double-helical metallopolymers. These metallopolymers are formed via subcomponent self-assembly and consist of two conjugated helical strands wrapping a linear array of CuI centers. Starting from discrete model helicates, we discuss how, through the judicious design of subcomponents, long helical metallopolymers can be obtained and detail their subsequent assembly into nanometer-scale aggregates. Two approaches to generate these helical metallopolymers are compared. We describe methods to govern (i) the length of the metallopolymers, (ii) the relative orientations (head-to-head vs head-to-tail) of the two organic strands, and (iii) the screw-sense of the double helix. Achieving structural control allowed the growth behavior of these systems to be probed. The structure influenced properties in ways that are relevant to specific applications; for example, the length of the metallopolymer determines the color of the light it emits in solution. In the solid state, the ionic nature of these helices renders them useful as both emitters and ionic additives in light-emitting electrochemical cells. Moreover, recent experimental work has clarified the role of the linear array of Cu ions in the transport of charge through these materials. The conductivity displayed by a film of metallopolymer depends upon its history of applied voltage and current, behavior characteristic of a memristor. In addition to the prospective applications already identified, others may be on the horizon, potentially combing stimuli-responsive electronic behavior with the chirality of the helical twist.

Solid and 3D beam finite element models for the nonlinear elastic analysis of helical strands within a computational homogenization framework

This paper proposes a computational approach for studying the overall behaviour and local stress state of strand-type structures. This method is based on the homogenization theory of periodic beamlike structures, with the local problem posed on the strand axial period being solved using the finite element method. This approach fully utilises the strand’s helical symmetry, thus minimising the size of the computational domain. Consequently, accounting for geometric complexity and contact interactions, which are of paramount importance for bending loads, is more straightforward. The numerical model mesh size can also be reduced thanks to the use of beam elements, and one objective of this paper is to assess the accuracy of such a model in comparison with solid element models and analytical results. These comparisons are performed on both single-layer and multi-layer strands. Results demonstrate the capability of the proposed computational approach to accurately capture the nonlinear bending behaviour stemming from the stick-slip transition as well as local stress distributions. As for the beam model, it apparently offers a very good compromise between accuracy and numerical efficiency.

Comparative study of the service life of a central core and a helical strand constituting the same rope

The purpose of this study is to characterize the mechanical behavior of the central core strand and of a helical strand taken from the same wire rope during the use. In addition, to predict the evolution of their damage and their instantaneous reliability. This is fulfilled by comparing the lifetime of the central core strand to as well as the helical strand based on static tensile tests performed on virgin specimen and others that are artificially damaged by breaking the wires making up the central core and the helical strand. Moreover, three damage models have been used to define the damage stages, from which, we can locate the critical life fraction βc in order to know which first element (centrale core strand or helical strand) will be broken. The intersection between the curve of damage and that of reliability enable us to find the element having the short lifetime.

Meso-scale modeling of concrete cracking induced by 3D corrosion expansion of helical strands

A meso-scale numerical model is established to simulate concrete cracking induced by the three-dimensional (3D) corrosion expansion of helical strands in the present study. A 3D corrosion expansion model is proposed to consider the longitudinal helix shape and transverse flower-like shape of the strand. The concrete in the model is considered as a three-phase composite material consisting of a mortar matrix, aggregate, and interfacial transition zones (ITZ) between the mortar matrix and aggregate. The rationality of the proposed model is validated, and the effects of the space helix structure and the lay length of the strand on corrosion-induced cracking are discussed. The results indicate that considering the space helix structure of a strand can effectively improve the prediction accuracy of strand corrosion-induced concrete cracking. The change in strand lay length has little effect on the critical corrosion loss of the initial damage occurrence. The critical corrosion loss at cover cracking increases with increasing strand lay length, whereas the corrosion-induced crack width decreases with increasing strand lay length.

Tunable helical structures formed by blending ABC triblock copolymers and C homopolymers in nanopores

AbstractABC triblock copolymers with frustrated interactions of χACN ≪ χABN ~ χBCN confined in nanopores with A‐block‐attracting surfaces can self‐assemble into helical morphologies, where the B blocks form helical domains wrapping around C‐core cylinders within the A shell. It has been suggested that the number of helical strands (m) increases as the volume fraction of C block (fC) decreases, while the increasing m is restricted because C blocks forming domains cannot maintain a cylindrical shape as fC gradually decreases, and the B block domains transform from helical structures to toroidal domains. To prevent the restriction of increasing m, in the current study we added C homopolymers into nanopores. For a given triblock copolymer with (χABN, χBCN, χACN) = (80, 80, 20) and (fA, fB, fC) = (0.7, 0.1, 0.2), varying the concentration (ϕH) and the chain length (γ) of the C homopolymers, as well as the diameter (D) of the nanopores, we constructed different two‐dimensional phase diagrams with respect to two of these control parameters using self‐consistent field theory. A number of helical structures with strands ranging from 1 to 6 are predicted. Our calculations indicate that m increases with increasing γ and D and decreasing ϕH. The theoretical results demonstrate that blending of homopolymer with one given triblock terpolymer could provide an efficient route to fabricate different complex helical nanostructures. © 2021 Society of Industrial Chemistry.