Twist Terms Research Articles

Physics origin of the parallel drift and the effective parallel magnetic field of a guiding center in curved magnetic fields

We study the physical origins of parallel guiding center drift and parallel velocity-dependent effective magnetic field (B‖*) appearing in the Hamiltonian formulation of a particle motion in a curved magnetic field. The magnetic twist term is shown to be responsible for both of them. The parallel guiding center drift originates from the change in the effective parallel velocity due to the combined effect of the initial perpendicular motion (v⊥0) and the magnetic twist. The effective magnetic field arises from the collated effect of the change in v⊥0 due to its initial parallel guiding center motion and the conservation of magnetic moment. This understanding clearly shows that the appearance of B‖* is a consequence of magnetic moment conservation in curved magnetic fields.

Neural inverse procedural modeling of knitting yarns from images

We investigate the capabilities of neural inverse procedural modeling to infer high-quality procedural yarn models with fiber-level details from single images of depicted yarn samples. While directly inferring all parameters of the underlying yarn model based on a single neural network may seem an intuitive choice, we show that the complexity of yarn structures in terms of twisting and migration characteristics of the involved fibers can be better encountered in terms of ensembles of networks that focus on individual characteristics. We analyze the effect of different loss functions including a parameter loss to penalize the deviation of inferred parameters to ground truth annotations, a reconstruction loss to enforce similar statistics of the image generated for the estimated parameters in comparison to training images as well as an additional regularization term to explicitly penalize deviations between latent codes of synthetic images and the average latent code of real images in the encoder’s latent space. We demonstrate that the combination of a carefully designed parametric, procedural yarn model with respective network ensembles as well as loss functions even allows robust parameter inference when solely trained on synthetic data. Since our approach relies on the availability of a yarn database with parameter annotations and we are not aware of such a respectively available dataset, we additionally provide, to the best of our knowledge, the first dataset of yarn images with annotations regarding the respective yarn parameters. For this purpose, we use a novel yarn generator that improves the realism of the produced results over previous approaches.

Structures and Reactivities of N-Alkenyl-Substituted Anilides: The "Magic" Methyl Effect on Alkene.

Methyl substitution at the double bond of N-alkenyl anilides influences both the preferred conformation and the susceptibility to acidic hydrolysis. The R1-substituted amide favors the trans conformation, whereas amides substituted at R2 or R3 favor the cis conformation. Substitution at the R1 and R3 positions increases the ratio of the trans conformer. DFT study indicated that these conformational preferences can be explained in terms of substituent-induced torsion twisting of the N-alkenyl moiety relative to the amide plane. R1 substitution enhances the susceptibility to acidic hydrolysis, whereas R2 or R3 substitution increases the stability. The effect of the double bond on the conformational effect was showcased by contrasting the preferred conformation of R1-substituted anilide (trans) and hydrogenated N-isopropyl amide (cis).

Bitangents to plane quartics via tropical geometry: rationality, $$\mathbb {A}^1$$-enumeration, and real signed count

We explore extensions of tropical methods to arithmetic enumerative problems such as $$\mathbb {A}^1$$ -enumeration with values in the Grothendieck–Witt ring and rationality over Henselian valued fields, using bitangents to plane quartics as a test case. We consider quartic curves over valued fields whose tropicalizations are smooth and satisfy a mild genericity condition. We then express obstructions to rationality of bitangents and their points of tangency in terms of twisting of edges of the tropicalization; the latter depends only on the tropicalization and the initial coefficients of the defining equation modulo squares. We also show that the $${{\,\textrm{GW}\,}}$$ -multiplicity of a tropical bitangent, i.e. the multiplicity with which its lifts contribute to the $$\mathbb {A}^1$$ -enumeration of bitangents as defined by Larson and Vogt (Res Math Sci 8(26):1–21, 2021), can be computed from the tropicalization of the quartic together with the initial coefficients of the defining equation. As an application, we show that the four lifts of most tropical bitangent classes contribute $$2\mathbb {H}$$ , twice the class of the hyperbolic plane, to the $$\mathbb {A}^1$$ -enumeration. These results rely on a degeneration theorem relating the Grothendieck–Witt ring of a Henselian valued field to the Grothendieck–Witt ring of its residue field, in residue characteristic not equal to two.

Siro false twist spun yarn structure and the knitted fabric performance

False twisting has been used to reduce yarn twists while keeping yarn tenacity, which is vital to improve fabric softness. In this paper, a false twisting device was integrated into a siro spinning system to develop a novel yarn structure with enhanced softness, in which the fibers were uniformly arranged. Siro false twist spun yarn was compared with a conventional siro spun yarn with the same count and twist in terms of yarn diameter, tenacity, hairiness, evenness, and packing density. The cross-sectional packing density of the yarns was analyzed based on micro X-ray computed tomography. The results showed that the siro false twist spun yarn has advantages in hairiness and evenness. The siro false twist spun yarn has an increased diameter by 10.4–19.0% and a more uniform cross-sectional packing density than the siro spun yarn. The two yarns were knitted into fabrics, and test results showed that the fabric produced with the siro false twist spun yarns had better compressibility, air permeability and light transmission. The findings from this study demonstrated that the siro false twist spun yarn improved fullness and its fabric has superior softness.

Transverse structure of the pion beyond leading twist with basis light-front quantization

We investigate the twist-3 transverse-momentum-dependent parton distribution functions (TMDs) of the pion with basis light-front quantization. The twist-3 TMDs are not independent and can be decomposed into twist-2 and genuine twist-3 terms from the equations of motion (EOM). We compute the TMDs from the resulting light-front wave functions obtained by diagonalizing the light-front QCD Hamiltonian, determined for pion's constituent quark-antiquark and quark-antiquark-gluon Fock sectors, with three-dimensional confinement. We also obtain the twist-3 parton distribution functions (PDFs) and show that they preserve the sum rule, which affirms the robustness of our approach. This is the first time that theoretical predictions are made for subleading twist structures of the pion containing interference terms between two light-front Fock sectors.

An Elastic Quartic Twist Theory for Chromonic Liquid Crystals

Chromonic liquid crystals are lyotropic materials which are attracting growing interest for their adaptability to living systems. To describe their elastic properties, the classical Oseen-Frank theory requires anomalously small twist constants and (comparatively) large saddle-splay constants, so large as to violate one of Ericksen’s inequalities, which guarantee that the Oseen-Frank stored-energy density is bounded below. While such a violation does not prevent the existence and stability of equilibrium distortions in problems with fixed geometric confinement, the study of free-boundary problems for droplets has revealed a number of paradoxical consequences. Minimizing sequences driving the total energy to negative infinity have been constructed by employing ever growing needle-shaped tactoids incorporating a diverging twist (Paparini and Virga in Phys. Rev. E 106: 044703, 2022). To overcome these difficulties, we propose here a novel elastic theory that extends for chromonics the classical Oseen-Frank stored energy by adding a quartic twist term. We show that the total energy of droplets is bounded below in the quartic twist theory, so that the known paradoxes are ruled out. The quartic term introduces a phenomenological length in the theory; this affects the equilibrium of chromonics confined within capillary tubes. Use of published experimental data allows us to estimate .

Generating linear categories of partitions

We present an algorithm for approximating linear categories of partitions (of sets). We report on concrete computer experiments based on this algorithm which we used to obtain first examples of so-called noneasy linear categories of partitions. All of the examples that we constructed are proved to be indeed new and noneasy. We interpret some of the new categories in terms of quantum group anticommutative twists.

Computational Design of a Soft Robotic Myocardium for Biomimetic Motion and Function

AbstractSoft robotic devices containing multiple actuating elements have successfully recapitulated complex biological motion, leading to their utility in biomedical applications. However, there are inherent nonlinear mechanics associated with soft composite materials where soft actuators are embedded in elastomeric matrices. Predicting their overall behavior prior to fabrication and subsequent experimental characterization can therefore present a hurdle in the design process and in efficiently satisfying functional requirements and specifications. In this work, a computational design framework for optimizing the motion and function of biomimetic soft robotic composites is demonstrated by conducting a design case study of soft robotic cardiac muscle (myocardium) with a particular focus on applications including replicating and assisting cardiac motion and function. A finite element model of a soft robotic myocardium is built, in which actuators are prescribed with anisotropic strain to simulate local deformation, and various design parameters are investigated by evaluating the performance of each configuration in terms of ventricular twist, volumetric output, and pressure generation. Then, an optimized design is proposed that recapitulates the physiological motion and hemodynamics of the heart, and its thrombogenicity is further explored using a fluid‐structure interaction model. This framework has broader utility in predicting the performance of other soft robotic embedded composites.

Multidisciplinary aeroelastic optimization of a 10MW-scale wind turbine rotor targeting to reduced LCoE

In the present paper, multidisciplinary optimization (MDAO) is applied with the aim to reduce the levelized cost of energy (LCoE) of the DTU-10MW Reference Wind Turbine (RWT) rotor. As application paradigm, the widely applied in the literature passive load control method of Bend Twist Coupling (BTC) is considered. The integrated optimization framework combines in a common loop, rotor aerodynamic and full wind turbine structural elasto-dynamic analyses, aiming at determining the optimum rotor diameter, the planform of the blade in terms of twist and chord distributions, the offset ply angle for BTC and the inner structure of the blade with cost function directly the LCoE. It is based on an in-house servo-aero-elastic analysis tool for determining the ultimate loads along the span of the blades and the power yield, whereas a cross-sectional analysis tool is employed for acquiring structural properties of the modified blade and stresses distributions over the blade sections. A cost model of the overall wind turbine is implemented by combining existing in the literature models and open data. The new rotor design is found to have a reduced LCoE by 0.71% and to produce 2.4% higher energy annually due to its increased by 3.7% diameter.

Homogeneous Yang-Baxter deformations as undeformed yet twisted models

The homogeneous Yang-Baxter deformation is part of a larger web of integrable deformations and dualities that recently have been studied with motivations in integrable σ-models, solution-generating techniques in supergravity and Double Field Theory, and possible generalisations of the AdS/CFT correspondence. The σ-models obtained by the homogeneous Yang-Baxter deformation with periodic boundary conditions on the worldsheet are on-shell equivalent to undeformed models, yet with twisted boundary conditions. While this has been known for some time, the expression provided so far for the twist features non-localities (in terms of the degrees of freedom of the deformed model) that prevent practical calculations, and in particular the construction of the classical spectral curve. We solve this problem by rewriting the equation defining the twist in terms of the degrees of freedom of the undeformed yet twisted model, and we show that we are able to solve it in full generality. Remarkably, this solution is a local expression. We discuss the consequences of the twist at the level of the monodromy matrix and of the classical spectral curve, analysing in particular the concrete examples of abelian, almost abelian and Jordanian deformations of the Yang-Baxter class.

3D Behaviour of Buildings due to Tunnel Induced Ground Movement

Ground subsidence from tunnel excavation below existing buildings may result in building distortion and develop structural damage. Previous case histories have shown that buildings may deform three-dimensionally when the tunnel alignment is orientated to the building facade. The authors incorporated a three-dimensional distortion parameter called twist into damage assessment by extending the current beam model to three dimensions. In this study, the new method is reviewed, and the concepts of the local and global twists are discussed. Results of a 3D Finite Element (FE) parametric study of global and local twist deformations of buildings due to tunnel-induced ground movement are compared in temporary and permanent cases during and after the construction of the tunnel. To investigate the behaviour of a twisted building, varying building stiffness, building geometry, and orientation angle are considered in the analyses. Comparison of the global and local twist shows that the global twist is not always the maximum twist during or after excavation of the tunnel. However, because of the temporary nature of the local twist, the global twist is still considered more critical than the local twist in terms of damage to the building. A new modification factor for the twist for different building stiffness factor is being proposed in the form of design graph. The design graph is included in the current three-stage procedure for assessing potential building damage. The modified procedure is used to predict the performance of a case study building affected by tunnel construction.

Set-theoretic Yang–Baxter equation, braces and Drinfeld twists

We consider involutive, non-degenerate, finite set-theoretic solutions of the Yang–Baxter equation (YBE). Such solutions can be always obtained using certain algebraic structures that generalize nilpotent rings called braces. Our main aim here is to express such solutions in terms of admissible Drinfeld twists substantially extending recent preliminary results. We first identify the generic form of the twists associated to set-theoretic solutions and we show that these twists are admissible, i.e. they satisfy a certain co-cycle condition. These findings are also valid for Baxterized solutions of the YBE constructed from the set-theoretical ones.

Effect of Log Heat Treatment on Release of Growth Stresses in Eucalyptus Nitens

The use of Eucalyptus nitens has diversified the Chilean lumber industry in unprecedented ways. However, growth-induced strains cause splitting and warping. The objective of this investigation was to determine the effect of the heat treatment applied to logs of Eucalyptus niten s on the reduction of growth stresses and improvement of quality in sawn wood. Logs were extracted at different heights of the tree for 15-yr and 20-yr-old trees. The sawmill process was allowed to obtain radial, mixed, and tangential plane pieces, at two thicknesses (25 and 50 mm). The evaluation of MC and warping was according to Chilean National Standards. The results obtained in this research suggest that by applying the heat treatment to Eucalyptus nitens logs, a significant reduction in growth strains can be achieved. Heat treatment also increased the quality of the pieces in terms of bow, crooking, and twisting. Therefore, there are substantial benefits of using heat treatments to reduce defects caused by growth strains and thus increase the quality of the wood and reduce its warp.

Train-track interactions over vulnerable railway turnout systems exposed to flooding conditions

Track twists used in modern railways indicate the warpage of a particular track plane to identify track quality. In some cases, a twist is intentionally introduced on tracks to facilitate motions in curves. Nevertheless, twists can exceed above certain thresholds resulting in twist faults, which impose direct risk to safety and a potential cause for derailments. Twist faults are commonly observed in ballasted tracks, which consists of crushed rock particles and have low endurance to resist against dynamic track forces. In general, the deterioration in ballast structure progresses slowly. However, in reality, there are some catalysts such as extreme events that can speed up the deterioration of the ballast bed. Extreme events have rare occurrences but a high potential to damage structures and environment in a short duration. Even though the term ‘rare’ is still used to define extreme events, a consensus among the environmental scientists on the increased frequency of extreme events could be found in open literatures. In this study, the impacts of flooding, one of the most common extreme events, on the dynamic phenomena of a turnout structure is investigated in terms of dynamic twists. The emphasis is placed on railway turnouts of which the asymmetrical structure is expected to amplify twist responses. A 3-dimensional finite element method (FEM) model has been developed and many hypothetical scenarios ranging from various materials to vehicle speeds have been tested in virtual environments. It should be noted that the developed model is the modified version of a previously validated model and therefore, validation of the model is done by a comparison with the parent model. This study is the world's first to demonstrate that the dynamic performance of composite and plastic bearers is relatively poor in comparison to concrete bearers when considering dynamic twist phenomena. Our new results also exhibit that partially damaged turnout structures in the case of flooding is the most critical and vulnerable situation, which could result in detrimental train derailments. This vulnerability cannot practically be inspected by naked and untrained eyes. On this ground, when exposed to flooding conditions, it is recommended to halt any railway operations over vulnerable switches and crossings, and to avoid the approach of ‘reach the station first’ in emergency cases.

A one-dimensional variational problem for cholesteric liquid crystals with disparate elastic constants

We consider a one-dimensional variational problem arising in connection with a model for cholesteric liquid crystals. The principal feature of our study is the assumption that the twist deformation of the nematic director incurs much higher energy penalty than other modes of deformation. The appropriate ratio of the elastic constants then gives a small parameter ε entering an Allen-Cahn-type energy functional augmented by a twist term. We consider the behavior of the energy as ε tends to zero. We demonstrate existence of the local energy minimizers classified by their overall twist, find the Γ-limit of the relaxed energies and show that it consists of the twist and jump terms. Further, we extend our results to include the situation when the cholesteric pitch vanishes along with ε.

On the Hamel Coefficients and the Boltzmann\u2013Hamel Equations for the Rigid Body

The Boltzmann–Hamel (BH) equations are central in the dynamics and control of nonholonomic systems described in terms of quasi-velocities. The rigid body is a classical example of such systems, and it is well-known that the BH-equations are the Newton–Euler (NE) equations when described in terms of rigid body twists as quasi-velocities. It is further known that the NE-equations are the Euler–Poincaré, respectively, the reduced Euler–Lagrange equations on SE(3) when using body-fixed or spatial representation of rigid body twists. The connection between these equations are the Hamel coefficients, which are immediately identified as the structure constants of SE(3). However, an explicit coordinate-free derivation has not been presented in the literature. In this paper the Hamel coefficients for the rigid body are derived in a coordinate-free way without resorting to local coordinates describing the rigid body motion. The three most relevant choices of quasi-velocities (body-fixed, spatial, and hybrid representation of rigid body twists) are considered. The corresponding BH-equations are derived explicitly for the rotating and free floating body. Further, the Hamel equations for nonholonomically constrained rigid bodies are discussed, and demonstrated for the inhomogenous ball rolling on a plane.

The D\u2217D\u03c0 and B\u2217B\u03c0 couplings from light-cone sum rules

We revisit the calculation of the strong couplings D∗Dπ and B∗Bπ from the QCD light-cone sum rules using the pion light-cone distribution amplitudes. The accuracy of the correlation function, calculated from the operator product expansion near the light-cone, is upgraded by taking into account the gluon radiative corrections to the twist-3 terms. The double spectral density of the correlation function, including the twist-2, 3 terms at mathcal{O}left({alpha}_sright) and the twist-4 LO terms, is presented in an analytical form for the first time. This form allows us to use various versions of the quark-hadron duality regions in the double dispersion relation underlying the sum rules. We predict {g}_{D^{ast } Dpi}={14.1}_{-1.2}^{+1.3} and {g}_{B^{ast } Bpi}={30.0}_{-2.4}^{+2.6} when the decay constants of heavy mesons entering the light-cone sum rule are taken from lattice QCD results. We compare our results with the experimental value for the charmed meson coupling and with the lattice QCD calculations.

Marshall's nucleic acid: From double-helical structure to a potent intercalator

Deoxyribonucleic acid (DNA) not only stores genetic information but also emerged as a popular drug target. Modified nucleotides/nucleosides have been extensively studied in recent years wherein the sugar/nucleobase/phosphate-backbone has been altered. Several such molecules are FDA approved, capable of targeting nucleic acids and proteins. In this article, we modified negatively charged phosphate backbone to marshall's acid-based neutral backbone and analyzed the resultant structures by utilizing Gaussian accelerated molecular dynamics simulations (1 μs) in aqueous media at 150 mM salt concentration. We noted that the double-helical marshall's nucleic acid structure was partially denatured during the course of simulations, however, after using conformationally locked sugar, the marshall's nucleic acid (hereby called MNA) maintained the double-helical structure throughout the simulations. Despite the fact that MNA has a more extended backbone than the regular DNA, surprisingly, both showed similar helical rise (~3.4 Å) along with a comparable Watson-Crick hydrogen bond profile. The backbone difference was majorly compensated in terms of helical twist (~56° (MNA) and ~ 35° (control DNA)). Further, we examined a few MNA based ss-dinucleotides as intercalating ligands for a regular B-DNA. Quite strikingly, the ligands unwinded the DNA and showed intercalating properties with high DNA binding affinities. Hence, the use of small fragments of MNA based molecules in DNA targeted drug discovery is foreseen.

Classification of 5d mathcal{N} = 1 gauge theories

We classify 5d mathcal{N} = 1 gauge theories carrying a simple gauge group that can arise by mass-deforming 5d SCFTs and 6d SCFTs (compactified on a circle, possibly with a twist). For theories having a 6d UV completion, we determine the tensor branch data of the 6d SCFT and capture the twist in terms of the tensor branch data. We also determine the dualities between these 5d gauge theories, thus determining the sets of gauge theories having a common UV completion.