Short Pitch Research Articles

Periodic pattern formation in an achiral bent core nematic

We investigated a periodic flexoelectric domain pattern, which appeared as regular parallel stripes in an achiral bent core nematic liquid crystal when dc electric field was applied. We found that such a pattern was first formed at the substrate surface and took place in sandwich cells with a gap larger than 2μm. The field-induced periodic pattern was preserved in the field-off state by a polymer network formed in the cell and was found to exhibit a polar as well as a linear electro-optic response due to in-plane switching of the sample optic axis. A comparison between this response and the one obtained in short cholesteric liquid crystals, aligned in ULH (uniform lying helix) texture, and short pitch ferroelectric liquid crystals, respectively, suggested that a heliconical molecular order is most probably formed in the field-induced periodic stripe pattern, with the helix axis orthogonal to the stripes. To our knowledge, this is the first experimental evidence of field-induced chiral-symmetry breaking in the flexoelectric periodic stripe pattern in achiral bent core nematic, resulting in heliconical molecular order, resembling the one of twist-bend (TB) nematic phase in this kind of nematics.

Numerical investigation of the effects of rail vibration absorbers on wear behaviour of rail surface

Rail corrugation refers to the periodic wear of the top working surfaces of rails. This problem has plagued the railway industry over a hundred years. In the present paper, the effects of rail vibration absorbers on wear behaviour of the rail surface have been studied. The dynamic model of a wheel–rail–absorber system is established. The friction contact coupling between the wheel and the rail are fully considered in this model. A wear model, in which the mass loss of unit area in contact patch is proportional to frictional work per unit area between the wheel and the rail, is developed to analyse the wear behaviour of the rail surface. Numerical results show that the saturated creep force-induced self-excited vibration of the wheel–rail system can result in short pitch rail corrugation on the rail surface. The maximum wear depth occurs at the positions close to mid-span of each sleeper bay. After the installation of rail vibration absorbers, the formation of short pitch rail corrugation can be suppressed effectively, and the wear on the rail surface becomes uniform and the growth rate of rail corrugation reduces considerably. Increasing the connection damping between the absorber and the rail web is beneficial to preventing the formation of short pitch rail corrugation.

Stability analysis on Nb3Sn sample conductor of CFETR central solenoid model coil

The magnet system of China fusion engineering test reactor (CFETR) includes toroidal field, central solenoid (CS) and poloidal field coils. The design and fabrication of CS coil are most significant and challenging for China due to the lack of experience. As the core technique of CS coil, cable-in-conduit-conductor (CICC) has been chosen to ITER CS conductor with the short twist pitch (STP) cable pattern. STP cable pattern has been demonstrated to avoid the performance degradation of conductor after electromagnetic cycling and warm-up-cool-down thermal cycles during operation. For qualifying the manufacturing process and performance of conductor, two short sample conductors were manufactured at ASIPP and tested at Swiss Plasma Center. Performance tests include DC test, Tcs, AC loss and MQE (Minimum Quench Energy) measurements. This paper is mainly about the stability analysis, and the energy margins of the conductor at various operation conditions are investigated with test data and model simulation.

The Control of Vocal Pitch in Human Laryngeal Motor Cortex

In speech, the highly flexible modulation of vocal pitch creates intonation patterns that speakers use to convey linguistic meaning. This human ability is unique among primates. Here, we used high-density cortical recordings directly from the human brain to determine the encoding of vocal pitch during natural speech. We found neural populations in bilateral dorsal laryngeal motor cortex (dLMC) that selectively encoded produced pitch but not non-laryngeal articulatory movements. This neural population controlled short pitch accents to express prosodic emphasis on a word in a sentence. Other larynx cortical representations controlling voicing and longer pitch phrase contours were found at separate sites. dLMC sites also encoded vocal pitch during a non-speech singing task. Finally, direct focal stimulation of dLMC evoked laryngeal movements and involuntary vocalization, confirming its causal role in feedforward control. Together, these results reveal the neural basis for the voluntary control of vocal pitch in human speech. VIDEO ABSTRACT.

Theoretical investigation into the formation mechanism and mitigation measures of short pitch rail corrugation in resilient tracks of metros

Severe rail corrugation occurs at both the curved and tangent tracks of the metro in Shanghai, where resilient rail fasteners are used to reduce ground-borne vibration by isolating the transmission of track vibration to the infrastructure. The wavelength of corrugation is about 25–30 mm. It could be assumed that this short pitch rail corrugation is caused by the pinned–pinned resonance. However, rail fasteners with low stiffness were believed to be able to suppress the pinned–pinned resonance thereby resulting in corrugation. To investigate the formation mechanism of this specific rail corrugation, a multiple wheel–rail interaction model is used to calculate the wheel–rail dynamic forces caused due to the multiple wheel–rail interactions, which are considered to play a major role in the formation of corrugation. Then the influences on wear and corrugation growth are analyzed in terms of both amplitude and phase of the wheel–rail dynamic forces. By combining the properties of multiple wheel–rail interactions with their influences on wear and corrugation, the growth rates of rail corrugation at different wavelengths (frequencies) are studied to obtain the characteristic wavelength (frequency), at which the highest corrugation growth rate appears. The obtained characteristic wavelength is in good agreement with observation in the practice of Shanghai metro. It is found that the wave reflection from the wheels on the rail is responsible for the short pitch rail corrugation in the resilient tracks. Finally, tuned rail dampers are applied in the multiple wheel–rail interaction models to investigate their effects on rail corrugation growth. The simulation results show that use of tuned rail dampers is effective in suppressing the short pitch rail corrugation occurring at resilient tracks.

Reducing the pitch length: Effects on junior cricket

The pitch lengths used for junior cricket are a subject of debate but to date there have been no studies of their influence on the game. This study evaluated the effect of reducing the pitch length on batting, bowling and fielding. County under 10 and club under 11 matches were analysed, 10 played on pitch lengths currently recommended by the England and Wales Cricket Board, 19 yd (17.37 m) or 20 yd (18.28 m), respectively, and 10 played on 16 yd (14.63 m) pitches. Differences between measures of batting, bowling and fielding were calculated to assess the effects of the shorter pitch length. In club and county matches on 16 yd, running between the wickets increased by 22 and 39%, respectively, while boundary fours and sixes decreased by 54 and 68%. Deliveries played to the Mid-wicket area decreased by 44% in club and 33% in county matches, both accompanied by a more even distribution of fielding opportunities. Club matches saw a 15% increase in playable deliveries, largely due to fewer deliveries bouncing twice. Attempted shots, full toss No balls and Wide balls changed negligibly. Playing on a shorter pitch had positive impacts for bowlers, batters and fielders, consequently resulting in matches which were more engaging. Coaches and governing bodies should consider shorter pitches as a means of enhancing junior cricket.

A Superconducting Induction Motor with a High Temperature Superconducting Armature: Electromagnetic Theory, Design and Analysis

Large electric superconducting machines are being sought to solve emissions challenges in aircraft and provide a solution to >12 MW wind turbine electricity generation. Superconducting motors with only high temperature superconducting (HTS) armatures can offer advantages of high reliability, high power density, and high efficiency compared with conventional superconducting motors. In this paper, a novel HTS squirrel-cage induction motor is proposed for high speed operation, which adopts the structure of HTS windings with a certain inclination angle in the stator slots. Due to the limitation of curvature radius of superconducting tapes, the pitch of HTS windings can be only set to 1 and adopt the short pitch arrangement structure, which such design details of the HTS motor would ensure the superconducting coils can undertake larger current and reduce AC losses. In order to keep the HTS windings in superconducting state and larger current density, a special fixed cryogenic cooling system below 70 K with the method of gas extraction and decompression, which is made of aramid fiber, has been fabricated and the whole structure of the stator is placed in liquid nitrogen. According to the motor control principles and electromagnetic field theory, the electrical performances of the novel designed stator-HTS motor, which driven by the variable-voltage variable-frequency (VVVF) inverter, are analyzed including the flux density distributions, the torque, the induced electromotive force, losses and efficiency by using the finite element method. Finally, the components of HTS squirrel-cage induction motor have been manufactured according to the designed parameters. Next step, the motor will be assembled and tested.

Theoretical analysis for the mechanical behavior caused by an electromagnetic cycle in ITER $$\hbox {Nb}_{3}\hbox {Sn}$$ Nb 3 Sn cable-in-conduit conductors

The central solenoid (CS) is one of the key components of the International Thermonuclear Experimental Reactor (ITER) tokamak and which is often considered as the heart of this fusion reactor. This solenoid will be built by using \(\hbox {Nb}_{3}\hbox {Sn}\) cable-in-conduit conductors (CICC), capable of generating a 13 T magnetic field. In order to assess the performance of the \(\hbox {Nb}_{3}\hbox {Sn}\) CICC in nearly the ITER condition, many short samples have been evaluated at the SULTAN test facility (the background magnetic field is of 10.85 T with the uniform length of 400 mm at 1% homogeneity) in Centre de Recherches en Physique des Plasma (CRPP). It is found that the samples with pseudo-long twist pitch (including baseline specimens) show a significant degradation in the current-sharing temperature (Tcs), while the qualification tests of all short twist pitch (STP) samples, which show no degradation versus electromagnetic cycling, even exhibits an increase of Tcs. This behavior was perfectly reproduced in the coil experiments at the central solenoid model coil (CSMC) facility last year. In this paper, the complex structure of the \(\hbox {Nb}_{3}\hbox {Sn}\) CICC would be simplified into a wire rope consisting of six petals and a cooling spiral. An analytical formula for the Tcs behavior as a function of the axial strain of the cable is presented. Based on this, the effects of twist pitch, axial and transverse stiffness, thermal mismatch, cycling number, magnetic distribution, etc., on the axial strain are discussed systematically. The calculated Tcs behavior with cycle number show consistency with the previous experimental results qualitatively and quantitatively. Lastly, we focus on the relationship between Tcs and axial strain of the cable, and we conclude that the Tcs behavior caused by electromagnetic cycles is determined by the cable axial strain. Once the cable is in a compression situation, this compression strain and its accumulation would lead to the Tcs degradation. The experimental observation of the Tcs enhancement in the CS STP samples should be considered as a contribution of the shorter length of the high field zone in SULTAN and CSMC devices, as well as the tight cable structure.

Design of polar self-assembling lactic acid derivatives possessing submicrometre helical pitch.

Several new lactic acid derivatives containing the keto linkage group far from the chiral part and short alkyl chains have been synthesized and characterised by polarising optical microscopy, differential scanning calorimetry, as well as electro-optic and dielectric spectroscopy. The materials possess a self-assembling behaviour on the nanoscale level as they form polar smectic liquid crystalline mesophases, namely the orthogonal paraelectric SmA* and the tilted ferroelectric SmC* phases, in a broad temperature range down to room temperature. A short helical pitch (≈120–320 nm), relatively high spontaneous polarisation (≈150 nC/cm2) and reasonable tilt angle values have been determined within the temperature range of the tilted ferroelectric SmC* phase. The obtained results make the new materials useful for the advanced mixture design and for further utilisation in electro-optic devices based on the deformed helix ferroelectric effect.

The effect of dopant chirality on the properties of self-assembling materials with a ferroelectric order.

A series of achiral hockey stick-shaped molecules forming a tilted smectic I liquid crystal phase as well as one non-mesogenic chiral bistereogenic analogue were synthesized and characterized. Herein, we report an example of an achiral hockey stick-shaped compound exhibiting a smectic I phase with a direct transition to the isotropic phase for the first time. This occurrence was confirmed via polarized light microscopy, dielectric spectroscopy, and XRD studies. Homologues with an odd number of carbon atoms in the oligomethylene spacer chain exhibit a lower clearing point than members posessing an even number of carbon atoms in this chain; thus, a characteristic odd-even effect has been observed. The influence of the synthesized compounds with different degrees of chirality and similar chemical structures on the properties of the host compound with a chiral smectic C phase was investigated. A chiral compound forming a wide-temperature chiral smectic C phase without any additional mesophase and having a short helical pitch was selected as the host material for the creation of two bicomponent systems. The mesomorphism of each binary mixture was characterized using optical microscopy and differential scanning calorimetry. The helical pitch of every binary mixture, forming a chiral smectic C phase, was studied within its full phase temperature range. As expected, the chiral host compound in the smectic C* phase doped with the hockey stick-shaped mesogen exhibited a longer helical pitch and lower spontaneous polarization than the chiral host material. On the other hand, for the chiral host compound doped with a non-mesogenic analogue containing two chiral centres, the helical pitch was shorter, and the spontaneous polarization was higher. These results should be potentially applicable for the design of advanced functional multi-component mixtures useful for various applications. The mesogenic behaviour of one binary mixture, forming both the chiral smectic I and titled chiral smectic C phases, was deeply studied via X-ray diffraction and dielectric spectroscopy techniques.

Effect of lactate group in the chiral chain of new compounds exhibiting short-pitch cholesteric or TGBA phase

ABSTRACTWe have synthesised and studied lactic acid derivatives based on chlorine substituted molecular core, which is created from two biphenyls linked by an ester, and terminated with one or two lactic units in a chiral chain. The compounds with one lactate group exhibit cholesteric phase with rather short helix pitch (200 nm) in a broad temperature range. On contrary, compound with two lactate units reveals a stable TGBA phase, with transition temperatures substantially lower than those for one-lactate derivatives. We have studied mesophase behaviour and electro-optical properties, mostly based on the texture observation in polarising microscope. Additionally, we have used AFM and x-ray techniques to confirm mesophase identification and establish structural properties.

Coupling Loss Characteristics of Nb3Sn CIC Conductor for CFETR CS Model Coil

An Nb 3 Sn cable-in-conduit (CIC) conductor with short twist pitch structure has been developed at Institute of Plasma Physics Chinese Academy of Sciences, Hefei, China, to meet the central solenoid model coil (CSMC) project of China fusion engineering test reactor (CFETR). 12 T magnetic field and 1.5 T/s field change are the most basic design target. The coupling loss characteristics of Nb 3 Sn CIC conductor is the key design requirement for CSMS because the deposited energy in magnets from ac losses can decrease the safe margin in the nuclear fusion device. In order to evaluate the coupling loss performance of the Nb 3 Sn CIC conductor, the ac loss measurement for Nb 3 Sn CIC conductor sample was carried out at SULTAN facility. This paper presents the specific structure design of the Nb 3 Sn CIC conductor and ac losses test results first. Then, the coupling losses characteristics are discussed with Multizones PArtial Shielding model and the key fit parameters are obtained from measurement results. Finally, two typical field cases are considered to evaluate the coupling loss energy of Nb 3 Sn CIC conductor for safe operation of the CFETR CSMC and the optimization of the cryogenic system.

DC performance measurement and assessment of Nb3Sn Cable-In-Conduit Conductor for CFETR CS model coil

The Central Solenoid Model Coil (CSMC) project of China Fusion Engineering Test Reactor (CFETR) was developed from 2014 at the Institute of Plasma and Physics Chinese Academy of Sciences (ASIPP) to verify the larger-scale superconducting magnet technology. The short twist pitch (STP) option was chosen for Nb3Sn Cable-In-Conduit Conductors (CICC) due to the stronger rigidity which can withstand the higher electromagnetic (EM) cycles effectively. Performance measurement of conductor short samples in SULTAN facility is the most important assessment method. This paper introduces the Nb3Sn strand parameters and CICC design firstly; then the preparation and measurement procedure of conductor short samples for current sharing temperature (Tcs) are described; subsequently, the Tcs vs. cycles, effective strain (εeff) with B×I and transition broadness characteristics compared with strands are assessed qualitatively by power law model. The assessment result shows that the DC performance vs. cycles of the STP design for Nb3Sn CICC is very stable and no degradation. The notable result gives the confidence that life period in the CSMC can be achieved reliably although the number of the EM cycles has been limited to below 10 000 in the measurement. The successful DC performance testing of Nb3Sn CICC will be an important milestone for CSMC project. Lastly, the performance assessment in coil is performed at the typical test waveform. The minimum temperature margin (Tmag) of 0.14K and electric field of 5 uV/m are achieved respectively. Some slow EM cycles is required to decrease the coupling loss deposition before coil testing.

Friction Reduction Induced by Elliptical Surface Patterns under Lubricated Conditions

Recording Stribeck‐like curves is an efficient way to evaluate the frictional performance and efficiency of patterned surfaces. Elliptical patterns with varying area density and structural depth are fabricated by micro‐coining on steel substrates (AISI 304). A ball‐on‐disc tribometer is used to perform unidirectional sliding experiments for the polished reference and the elliptical patterns dependent on the sliding velocity. In this study, a clear connection between structural parameters such as length of long and short axis, aspect ratio, and pitch with the frictional behavior can be found. Comparing patterns with comparable depth and area density underlines that elliptical patterns having larger individual features (increased length of both axes) separated by a larger pitch reduce the COF more significantly. The number of tribologically active individual elliptical structures, recirculation effects of the lubricant, as well as the pattern geometry that may lead to undesired edge effects and stress concentrations need to be taken into consideration to explain those findings. The sample with the smallest structural depth, the smallest area density, and the lowest aspect ratio (A1) leads to the maximum friction reduction (4‐fold) for all velocities which underlines the enormous potential of elliptical structures in terms of friction reduction.

Effect of the applied electric field on new cholesterics with extremely short pitch

ABSTRACTNew lactic acid derivatives have been prepared and studied and found that they form cholesteric phase with the helix pitch length in interval 120–200 nm within a broad temperature range. Due to the positive dielectric anisotropy and the short pitch, the applied electric field causes reversible optical changes in planar cell, in which the applied electric field reorients the long molecular axis. Presence of short pitch and possibility to effectively affect electro-optical properties are promising from the point of view of specific applications.

Numerical and experimental analysis of long period gratings in wavelength scale elliptical microfibers**Project supported by the National Natural Science Foundation of China (Grant No. 61605168), the Natural Science Foundation of Hebei Province, China (Grant No. F2016203392), the College and University Science and Technology Research Project of Hebei Province, China (Grant No. QN2016078), the Science and Technology Project of Qinhuangdao City

We report the fabrication of long-period gratings (LPGs) in elliptical microfibers with femtosecond laser. Based on the numerical analysis of the modes and the mode coupling condition of elliptical microfibers, an LPG is fabricated with a very short pitch of by periodically modifying the fiber surface, which demonstrates very strong polarization-dependent resonances, a very low temperature sensitivity of a few picometers in air, and high temperature sensitivity of −1.62 nm/°C in refractive index oil.

New Insights into the Short Pitch Corrugation Enigma Based on 3D-FE Coupled Dynamic Vehicle-Track Modeling of Frictional Rolling Contact

A three-dimensional (3D) finite element (FE) dynamic frictional rolling contact model is presented for the study of short pitch corrugation that considers direct and instantaneous coupling between the contact mechanics and the structural dynamics in a vehicle-track system. In this study, we examine the system responses in terms of vibration modes, contact forces and the resulting wear with smooth rail and corrugated rail with progressively increasing amplitude to infer the conditions for consistent corrugation initiation and growth. Wear is assumed to be the damage mechanism, and short pitch corrugation is modeled using wavelengths from field observations of a Dutch railway. The contribution of this paper is a global perspective of the consistency conditions that govern the evolution of short pitch corrugation. The main insights are as follows: (1) the longitudinal vibration modes are probably dominant for short pitch corrugation initiation; (2) during short pitch corrugation evolution, the interaction and consistency between longitudinal and vertical modes should determine the development of short pitch corrugation, and once a certain severity is reached, vertical modes become dominant; and (3) in the case simulated in this paper, corrugation does not grow probably due to not only the different resulting main frequencies of the vertical and longitudinal contact forces, but also the inconsistency between the frequencies of the vertical and longitudinal vibration modes and the resulting wear. It is inferred that in the continuous process of initiation and growth of the corrugation, there should be a consistency between them, and this could be done by the control of certain track parameters.

Regressor time-shifting to identify longitudinal stability and control derivatives of the Jetstream 3102

The Jetstream 31 G-NFLA aircraft is used as a national flying laboratory test vehicle for flight dynamics research and teaching purposes. It has been the subject of much theoretical and experimental modelling and therefore, the need for generating validation data through flight testing is critical. In this paper, the aircraft's short period pitch oscillation mode characteristics are identified using data from sixteen flight tests. An identification procedure based on the least squares method and reduced order state-space model is used and the need for pre-processing regressors due to the effects of sensor location and instrumentation delays is highlighted. It has been shown that time-shifting the regressors based on relative locations of the angle of attack vanes and the inertial measurement unit results in significant reductions in uncertainty bounds of the estimated aeroderivatives and also a model that provides a closer match to flight test data. The estimated models are validated using separate flight test data and the variations in aeroderivatives over a range of airspeeds and centre of gravity positions are also presented.

The Effect of Indentation Depth on Performances of Nb3Sn Strands in Cables of ITER Central Solenoid

The ITER Central Solenoid (CS) is composed Nb 3 Sn cable-in-conduit conductor. Short twist pitch cable design is appropriate for the CS cables to maintain the current sharing temperature under electromagnetic loading cycles. In the production process of the short twist pitch CS cable, Nb 3 Sn strands, and Cu strands are cabled tightly and compressed to get circular shape. However, these processes induced strong interstrand contact force and the strands deformation. The strand performances are degraded by the severe indentation on the strands at the contact point between the strands, although the strands are deformed before the heat-treatment. Therefore, influence of the indentation on critical current and residual resistive ratio were investigated in two types of bronze-route and an internal-tin Nb 3 Sn strands which are used for the CS cable, in order to determine the threshold of indentation depth in the strands. Also, transverse cross-sectional observation by Electron Probe Micro Analyzer was carried out on the indented strands to investigate the damage in the cross-section. Before August 2016, 37 CS cables were manufactured. On 37 CS cables manufactured before August 2016, numbers of indentations on the Nb 3 Sn strands were investigated to confirm whether there was indentation on the Nb 3 Sn strands which degrades the strand performance.

Impact of Indentation on the Performance of MgB2Round Wire

MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> round wire is a promising material for future fusion Cable in Conduit Conductor applied in low magnetic field, due to its larger T-margin compare with NbTi. It's a competitive candidate for feeders, poloidal field or correction coils. Since MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> is sensitive to strain, a short twist pitch cable pattern will be taken into consideration. During cabling and conductor manufacturing, the compression on the strand is inevitable, for a cable with short twist pitch can make more severe indentation on the strands. Previous studies have shown that indentation can caused degradation of the critical current of Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn and Bi-2212 round wires. So the same research is performed on MgB <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> round wire, in this paper, the critical current of artificially indented samples is measured, and the results are compared with artificially indented Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Sn, NbTi and Bi-2212 round wires.