Twisted Lines Research Articles

Transition induced by a bursting vortex ring in channel flow

We investigate the influence of vortices remote from the boundary on the near-wall flow dynamics in wall-bounded flows. A vortex ring with precisely controlled local twist is introduced into the outer layer of a channel flow at a moderate Reynolds number. We find that the minimum vorticity flux for triggering the transition to turbulence is significantly reduced from the initial disturbance of an untwisted vortex ring to that of a twisted ring. In particular, the latter disturbance can cause vortex bursting in the early transitional stage. The impact of vortex bursting on the transition process is characterised by the near-wall, wall-normal velocity with the rapid distortion theory. The wall-normal velocity grows during vortex bursting, and leads to streak formation and then the transition to turbulence. The notable wall-normal velocity is induced by the large di-vorticity generated in vortex bursting. We model the growing radial component of the di-vorticity in terms of the local twist, and demonstrate that its surge is due to the generation of highly twisted vortex lines in vortex bursting. Then, we derive that the generation of the di-vorticity in the outer layer enhances the wall-normal velocity in the inner layer via the Poisson equation with the image method and the multipole expansion. Thus, we elucidate that the vortex bursting can have an effect on the transition process.

Energy absorption characteristics of novel bionic H-type whip restraints for nuclear power plants

To enhance the efficiency of energy absorption in H-type whip restraints for nuclear power plants, this study takes inspiration from the asymmetric twisted lines observed in the Nautilus shell, introducing the Nautilus Bionic Hierarchical Multi-Cell (NBHMC) structure. For different high-energy pipeline sizes and energy absorption quantities, the proposed structures are miniaturized and can be combined into H-type whip restraint by multiple tubes to meet the requirements. The NBHMC structures are investigated based on the validated finite element method, the results demonstrate that the energy absorption per unit mass of the new structure can reach up to 180% of that of the hollow tube, with the maximum enhancement in energy absorption efficiency being 47%. Through parameter analysis of the cross-sectional wall thickness, the highest energy absorption efficiency obtained is 99.62%, with a specific energy absorption of 31.29J/g. Furthermore, utilizing the TOPSIS method, all proposed parameter combinations are ranked, leading to the determination of the optimal parameter combination. Additionally, a theoretical model predicting the mean crushing force is introduced, exhibiting good agreement with numerical simulations. The results presented in this work provide innovative insights for the design of efficient pipe whip restraints.

Twisted pair transmission line coil – a flexible, self-decoupled and robust element for 7 T MRI

ObjectiveThis study evaluates the performance of a twisted pair transmission line coil as a transceive element for 7 T MRI in terms of physical flexibility, robustness to shape deformations, and interelement decoupling. MethodsEach coil element was created by shaping a twisted pair of wires into a circle. One wire was interrupted at the top, while the other was interrupted at the bottom, and connected to the matching circuit. Electromagnetic simulations were conducted to determine the optimal number of twists per length (in terms of B₁+ field efficiency, SAR efficiency, sensitivity to elongation, and interelement decoupling properties) and for investigating the fundamental operational principle of the coil through fields streamline visualisation. A comparison between the twisted pair coil and a conventional loop coil in terms of B₁+ fields, maxSAR₁₀g, and stability of S₁₁ when the coil was deformed was performed. Experimentally measured interelement coupling between individual elements of multichannel arrays was also investigated. ResultsIncreasing the number of twists per length resulted in a more physically robust coil. Poynting vector streamline visualisation showed that the twisted pair coil concentrated most of the energy in the near field. The twisted pair coil exhibited comparable B₁+ fields and improved maxSAR₁₀g to the conventional coil but demonstrated exceptional stability with respect to coil deformation and a strong self-decoupling nature when placed in an array configuration. DiscussionThe findings highlight the robustness of the twisted pair coil, showcasing its stability under shape variations. This coil holds great potential as a flexible RF coil for various imaging applications using multiple-element arrays, benefiting from its inherent decoupling.

Straight and twisted open nodal-line phonon states in the CaI2 family of materials.

Based on first-principles calculations and symmetry analysis, we propose that trigonal CaI2 with the space group P3̄m1 possesses straight and twisted open nodal-line phonon states with linear dispersion. The symmetry analysis indicates that joint symmetry PT and rotational symmetry C3z protect the straight nodal lines along Γ-A and K-H while PT and mirror symmetry M010 (M110) maintain the twisted nodal lines that traverse Γ-M (Γ-K) and A-L (A-H). The calculated π Berry phase suggests that all the nodal lines are nontrivial and the corresponding drumhead-like surface states are clearly visible in the observation window, which is less than 6 THz, suggesting a significant chance for them to be measured using meV-resolution inelastic X-ray scattering. The distribution of the nodal lines in the Brillouin zone is also confirmed by the phononic tight-binding model. Furthermore, the isostructural compounds MgBr2 and MgI2 show similar phonon spectra and topological nontrivial surface states. This work provides promising candidates for investigating straight and twisted open nodal-line phonon states in a single material, which will facilitate future experimental observation.

Wideband Millimeter-Wave Substrate Integrated Suspended Twisted Line for High-Speed Transmission

This paper proposes a novel substrate integrated suspended twisted line (SISTL), which can broaden the transmission bandwidth of the transmitted signal and reduce the external radiation of the transmission line through a self-packaging format. Specifically, the wide transmission bandwidth is obtained in this designed structure by combining theoretical analysis and optimizing the variables. The mixed-mode scattering parameters and eye diagrams are employed to measure the quality of the transmitted signal, demonstrating the feasibility of the proposed design. Moreover, the results show that the max bandwidth of SISTL is more than 50 GHz, and at this time, the data transmission rate can be up to 32 Gbps with an exemplary eye diagram and a low bite error rate.

Twisted Chiral Algebras of Class {mathcal {S}} and Mixed Feigin–Frenkel Gluing

The correspondence between four-dimensional {mathcal {N}}=2 superconformal field theories and vertex operator algebras, when applied to theories of class {mathcal {S}}, leads to a rich family of VOAs that have been given the monicker chiral algebras of class{mathcal {S}}. A remarkably uniform construction of these vertex operator algebras has been put forward by Tomoyuki Arakawa in Arakawa (Chiral algebras of class {mathcal {S}} and Moore–Tachikawa symplectic varieties, 2018. arXiv:1811.01577 [math.RT]). The construction of Arakawa (2018) takes as input a choice of simple Lie algebra {mathfrak {g}}, and applies equally well regardless of whether {mathfrak {g}} is simply laced or not. In the non-simply laced case, however, the resulting VOAs do not correspond in any clear way to known four-dimensional theories. On the other hand, the standard realisation of class {{{mathcal {S}}}} theories involving non-simply laced symmetry algebras requires the inclusion of outer automorphism twist lines, and this requires a further development of the approach of Arakawa (2018). In this paper, we give an account of those further developments and propose definitions of most chiral algebras of class {{{mathcal {S}}}} with outer automorphism twist lines. We show that our definition passes some consistency checks and point out some important open problems.

A 19.1–25.5-GHz Compact Dual-Mode Rotary Traveling-Wave Oscillator With 195.4-dBc/Hz FoM

In this letter, a dual-mode rotary traveling-wave oscillator (RTWO) is proposed to achieve wide operation bandwidth and multiple phases. Two twisted differential transmission lines are coupled together to form the dual-mode traveling-wave resonator. Sixteen pairs of back-to-back inverters and capacitors are connected to the resonators to introduce the multicore multi-phase operation. The mode switches are used to control the coupling direction and select the desired mode without degrading the quality factor. Verified in a 40-nm CMOS process, the proposed dual-mode RTWO exhibits a dual-mode frequency range from 19.1 to 25.5 GHz with the core size of 0.08 mm <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$^{\textbf {2}}$ </tex-math></inline-formula> . The measured 10-MHz phase noise at 25.30 and 22.12 GHz is −129.6 and −131.5 dBc/Hz, respectively. The best FoM and FoMT are 186.2 and 195.4 dBc/Hz, respectively.

Global form of flavor symmetry groups in 4d N=2 theories of class S

We provide a systematic method to deduce the global form of flavor symmetry groups in 4d N=2 theories obtained by compactifying 6d N=(2,0) superconformal field theories (SCFTs) on a Riemann surface carrying regular punctures and possibly outer-automorphism twist lines. Apriori, this method only determines the group associated to the manifest part of the flavor symmetry algebra, but often this information is enough to determine the group associated to the full enhanced flavor symmetry algebra. Such cases include some interesting and well-studied 4d N=2 SCFTs like the Minahan-Nemeschansky theories. The symmetry groups obtained via this method match with the symmetry groups obtained using a Lagrangian description if such a description arises in some duality frame. Moreover, we check that the proposed symmetry groups are consistent with the superconformal indices available in the literature. As another application, our method finds distinct global forms of flavor symmetry group for pairs of interacting 4d N=2 SCFTs (recently pointed out in the literature) whose Coulomb branch dimensions, flavor algebras and levels coincide (along with other invariants), but nonetheless are distinct SCFTs.

2-Group symmetries in class S

2-group symmetries are generalized symmetries that arise when 1-form and 0-form symmetries mix with each other. We uncover the existence of a class of 2-group symmetries in general 4d4d\mathcal{N}=2𝒩=2 theories of Class S that can be constructed by compactifying 6d6d\mathcal{N}=(2,0)𝒩=(2,0) SCFTs on Riemann surfaces carrying arbitrary regular punctures and outer-automorphism twist lines. The 2-group structure can be captured in terms of equivalence classes of line defects plus flavor Wilson lines, which can be thought of as accounting for screening of line defects while keeping track of flavor charges. We describe a method for computing these equivalence classes for a general Class S theory using the data on the Riemman surface used for compactifying its parent 6d6d\mathcal{N}=(2,0)𝒩=(2,0) theory.

Factorized class S theories and surface defects

It is known that some theories of class S are actually factorized into multiple decoupled nontrivial four-dimensional mathcal{N} = 2 theories. We propose a way of constructing examples of this phenomenon using the physics of half-BPS surface defects, and check that it works in one simple example: it correctly reproduces a known realization of two copies of mathcal{N} = 2 superconformal SU(2) QCD, describing this factorized theory as a class S theory of type A3 on a five-punctured sphere with a twist line. Separately, we also present explicit checks that the Coulomb branch of a putative factorized class S theory has the expected product structure, in two examples.

The novel transmission scheme with CAT Ethernet cable and SFP for White Rabbit

White Rabbit (WR) is a deterministic Ethernet-based network for general-purpose data transfer and sub-nanosecond time synchronization in large distributed systems. WR has been used in Large Hadron Collider and Large High-Altitude Air Shower Observatory for physics experiment. WR mainly uses the optical fiber for data transmission between WR devices. Commercial off-the-shelf Direct Attach Cable is not suitable for WR network at 100 m level distance. Considering the lower cost of Category (CAT) Ethernet cable compared to optical fiber and the demand of remote power supply in distributed system at 100 m level length, we developed a novel transmission scheme with CAT Ethernet cable for WR. The novel transmission scheme uses the CAT Ethernet cable and small form-factor pluggable connector which is compatible with the optical links. This scheme only uses two pairs of twisted lines in the CAT Ethernet cable for data uplink and downlink. The other two pairs of twisted lines are used for remote power supply. The novel transmission scheme could use the CAT Ethernet cable to complete remote power supply and time synchronization with expected time offset of less than 100 ps and standard deviation of less than 20 ps in the WR distributed system. The distance of distributed nodes could be 80 m with one CAT 7 Ethernet cable or 150 m with relay transceiver connecting two CAT 7 Ethernet cables. In the short-distance scenarios, the novel transmission scheme has lower cost than the optical fiber and additional power supply function.

Showerhead film cooling injection orientation design on the turbine vane leading edge considering representative lean burn combustor outflow

The heat transfer performance of showerhead film cooling on the vane leading edge was numerically investigated considering representative lean burn combustor swirling outflow. Three cases with different inflow conditions (uniform inflow, positive swirling inflow, and negative swirling inflow) and three cases with different film injection angles (45°, 90°, and 135°) were studied. As the first study to explore the showerhead film design principle under swirling inflow, a newly designed asymmetrical counter-inclined (45° and 135°) film cooling was also proposed. To examine the design principles, the cooling effectiveness, heat transfer augmentation, and heat flux reduction of the newly designed asymmetrical case were evaluated compared with the traditional symmetrical case. The results show that the swirling inflow introduces obvious radial pressure gradient on the vane. The radial pressure gradient is the key influence factor to deflect the coolant migration, decrease the cooling effect, and degrade the homogeneity. The film with opposite orientation to the radial pressure gradient can weaken the deflect effect. The radial pressure gradient direction differs in different regions, making it impossible for the film with congruent injection orientation to simultaneously resist the pressure gradient on the entire vane. For the new design, the boundary line of the counter-inclined holes is consistent with the twisted stagnation line to guarantee that the injection orientation of all the film holes is opposite to the radial pressure gradient. As expected, the new design can effectively weaken the deflection effect and show uniform film distribution. The higher coolant mass ratio provides more obvious enhancement effect. At coolant mass ratio 3.71% and 4.56%, the overall area-averaged heat flux reduction (Δ q) is increased by 0.311 and 0.576, and the overall area-averaged relative standard deviation is reduced by 12.17 and 11.66 compared with the traditional design. The results have confirmed the adaptability of the film design principle under swirling inflow.

Second-order total freedom analysis of 3D objects in a single point contact

This paper studies the instantaneous second-order total freedom of two smooth objects initially in contact at a single point. The analytical determination of the set of physically allowed second-order motions is formulated in the Euclidean space using the screw theoretic concepts of twist and twist-derivative. Mathematical expression that characterizes the nature of second-order motion for an arbitrary contact geometry is derived in terms of twist coordinates, twist-derivative coordinates and the principle normal curvatures of the two surfaces at the point of contact. It is shown that the characteristic of this expression is equivalent to that of the derivative of reciprocal product of the instantaneous twist and contact normal line. The efficacy of the theory developed is demonstrated through two illustrative examples.

Comparison of Cylindrical Interplanetary Flux-Rope Model Fitting with Different Boundary Pitch-Angle Treatments

Interplanetary flux ropes (IFRs) observed in the solar wind have been investigated through application of the Lundquist model, which is a cylindrical flux-rope model with a constant- $\alpha $ force-free magnetic-field model. This study evaluated two Lundquist-model fitting methods by applying them to magnetic-obstacle (MO) events observed by the Wind and Solar TErrestrial RElations Observatory (STEREO) spacecraft and by comparing the results. In one method, the pitch angle of the magnetic field at the IFR boundary is assumed to be $90^{\circ}$ , whereas in the other method this restriction is relaxed and the pitch angle is handled as a free parameter [ $\alpha _{\mathrm{p}} $ ]. We found that the angle between the axial and radial directions in radial tangential normal (RTN) coordinates (cone angle) and the magnetic flux of the IFR were significantly different for approximately 30% of these events. However, both methods yielded similar values for the direction of the IFR axis projected onto the T–N plane in the RTN coordinates (tilt angle). We also found that the statistical distribution of $\alpha _{\mathrm{p}}$ , which was estimated using the generalized method, shows a spread of $34^{\circ}$ centered at $82^{\circ}$ , implying that a highly twisted magnetic-field line surrounds the surface of the IFR for approximately 60% of the events. On the other hand, it was noted that a significant number of events (approximately 25%) have a small $\alpha _{\mathrm{p}}$ ( ${<}\,60^{\circ}$ ). These results prove that it is better to use the generalized method than the conventional method for solving the cone angle, magnetic flux, or pitch angle of the flux rope, which would lead to a more accurate derivation of the properties of IFRs.

Applications of Backscattering for the Study of Twisted Pair Transmission Lines

The phenomenon of backscattering in copper cables has been recently observed and initially explicated. It can provide promising techniques to address the problem of loop diagnostic and maintenance. The backscattering is analyzed both in frequency and time domains. To demonstrate the practical use of the phenomenon, we estimate certain properties of the loop using wideband, high-frequency $S_{11}(f)$ measurements performed in the laboratory on real cables. The results corroborate the usefulness and accuracy of the investigated method.

Reproducing Field-to-Wire Coupling Effects in Twisted-Wire Pairs by Crosstalk

This paper proposes an alternative test procedure for testing the radiated immunity of units and subsystems interconnected through unshielded twisted-wire pairs (TWPs). The procedure makes use of an additional wire placed in close proximity and parallel to the TWP axis to generate the interference, which is then transferred to the TWP under test through crosstalk coupling. Equivalence with field-to-wire coupling is enforced in terms of equal common mode (CM) currents induced at the TWP terminals, by resorting to the introduction of an equivalent CM straight wire to replace the original twisted line. The proposed equivalence scheme, derived by resorting to transmission-line modeling and full-wave numerical simulation, is eventually validated by measurements in the frequency interval from 1 MHz up to 1 GHz. The experiments prove the accuracy of the proposed procedure in reproducing both the CM and the differential noise induced by field-to-wire coupling in the terminations of the twisted lines.

New dualities and misleading anomaly matchings from outer-automorphism twists

We study four-dimensional mathcal{N}=1, 2 superconformal theories in class mathcal{S} obtained by compactifying the 6d mathcal{N}=left(2, 0right) theory on a Riemann surface mathcal{C} with outer-automorphism twist lines. From the pair-of-pants decompositions of mathcal{C} , we find various dual descriptions for the same theory having distinct gauge groups. We show that the various configurations of the twist line give rise to dual descriptions for the identical theory. We compute the ’t Hooft anomaly coefficients and the superconformal indices to test dualities. Surprisingly, we find that the class mathcal{S} theories with twist lines wrapping 1-cycles of mathcal{C} have the identical ’t Hooft anomalies as the ones without the twist line, whereas the superconformal indices differ. This provides a large set of examples where the anomaly matching is insufficient to test dualities.

Fractographic approach to metallurgical coke failure analysis. Part 1: Cokes of single coal origin

Metallurgical coke is a complex brittle heterogeneous material consisting of carbon derived from fusible, semi-fusible and inert coal particles that forms a porous composite matrix. This paper presents a novel approach to assess and quantify the breakage behaviour and microstructural weaknesses in a pilot oven metallurgical coke. The approach uses fractography, a method commonly applied to determine the fracture behaviour and origin(s) in homogeneous materials, such as metals and ceramics. Determination of the fracture origin(s), paths of crack propagation and microstructural weaknesses in such a complex heterogeneous material as metallurgical coke represents a significant advance in both the application of fractography and the assessment of coke strength and breakage behaviour. Identification of the key features that contribute to the coke’s failure will facilitate better prediction of coke strength from coal properties and ultimately optimisation of the coal blending process.Key features and markings have been clearly identified on fracture surfaces that can either be traced back to the fracture origin or give an indication of the type of fracture or stresses to which the coke has been subjected, including the directionality and strength of those stresses. These markings include hackle, hackle twist and wallner lines, as well as markings generated by conchoidal and overload fractures.A three-step approach was applied to determine the breakage behaviour in stabilized lumps of the pilot oven coke, in which fractured coke surfaces were analysed at the macro, micro and submicron levels. The observed mechanisms of failure were quantified and summarised using a radar diagram.

OPGWの電流サージで生じる光信号の瞬時偏波変動の実測

Polarization of an optical light transmitted through an OPGW is changed by influence of electric current flows in the twisted metal line at the surface of the OPGW. High speed polarization change is caused by serge current such as lightning stroke current or power line fault current. It might induce a trouble of an optical communication system using an OPGW. In order to evaluate the speed of the polarization change at the moment of flowing surge current, polarization state of the optical signal through an OPGW in the field is observed from the summer to the winter. As a result, examples of polarized change according to the falling of a thunderbolt to an OPGW or the other causes are obtained.

Detecting the Triple Resistance Fault in Twisted Pair Telephone Lines

Detecting the Triple Resistance Fault in Twisted Pair Telephone Lines