Unequal Gaps Research Articles

Multiband superconductivity in V3Si determined from studying the response to controlled disorder

The London penetration depth, $\lambda(T)$, was measured in a single crystal V$_{3}$Si. The superfluid density obtained from this measurement shows a distinct signature of two almost decoupled superconducting gaps. This alone is insufficient to distinguish between $s_{\pm}$ and $s_{++}$ pairing states, but it can be achieved by studying the effect of a controlled non-magnetic disorder on the superconducting transition temperature, $T_{c}$. For this purpose, the same $\text{V}_{3}\text{Si}$ crystal was sequentially irradiated by 2.5 MeV electrons three times, repeating the measurement between the irradiation runs. A total dose of 10 C/cm$^{2}$ ($6.24\times10^{19}$ electrons/$\textrm{cm}^{2}$) was accumulated, for which $T_{c}$ has changed from 16.4 K in a pristine state to 14.7 K (9.3 $\%$). This substantial suppression is impossible for a single isotropic gap, but also it is not large enough for a sign-changing $s_{\pm}$ pairing state. Our electronic band-structure calculations show how five bands crossing the Fermi energy can be naturally grouped to support two effective gaps, not dissimilar from the iron pnictides physics. We analyze the results using two-gap models for both, $\lambda(T)$ and $T_{c}$, which describe the data very well. Thus, the experimental results and theoretical analysis provide strong support for an $s_{++}$ superconductivity with two unequal gaps, $\Delta_{1}\left(0\right)\approx2.53\;\textrm{meV}$ and $\Delta_{2}\left(0\right)\approx1.42\;\textrm{meV}$, and a very weak inter-band coupling in $\text{V}_{3}\text{Si}$ superconductor.

Construction of theoretical models for the lifting mechanism of the foundry crane

In the lifting drive of the foundry crane, there are emergency situations provoked by failures of bolted connections in the insert of the split drum. The latter is explained by the appearance of unequal gaps in the gearboxes of the «left» and «right» electromechanical systems driven by asynchronous motors with short-circuited rotors powered by individual frequency converters. With high rigidity of the mechanical characteristics of the engines, small deviations in nominal slides can cause a significant variation in engine loads and, as a result, unequal loading of gearboxes and a skew in the loading of the insert. This leads to a violation of the stability of the speed regime of both parts of the drum and to the appearance of additional dynamic loads in the lifting ropes and vibrations of the bucket with metal. The proposed design schemes of the lifting mechanism of the foundry crane allow tracing the nature of simplifications and focusing on possible emergency situations. Lifting models of electromechanical systems make it possible to study their dynamics in typical operating modes. The presence of a gap in the insert when one of the motors is switched off leads to an oscillatory process in electromechanical systems; this especially affects the movement of the insert elements — there are areas of gap opening, which leads to additional dynamic loads in bolted connections and their premature failure. It is recommended to take the elastic moment in the insert as a diagnostic value, by the nature of the change of which it is possible to judge the development of an emergency situation in electromechanical lifting systems.

Role of Interactions in the Energy of the Spin Resonance Peak in Fe-Based Superconductors

We consider the spin response within the five-orbital model for iron-based superconductors and study two cases: equal and unequal gaps in different bands. In the first case, the spin resonance peak in the superconducting state appears below the characteristic energy scale determined by the gap magnitude, 2ΔL. In the second case, the energy scale corresponds to the sum of smaller and larger gap magnitudes, ΔL+ΔS. Increasing the values of the Hubbard interaction and the Hund's exchange, we observe a shift of the spin resonance energy to lower frequencies.

Transflective blue-phase liquid crystal display with polar opposite electrodes

ABSTRACTA submillisecond response, wide view and single-cell-gap transflective (TR) display employing a blue-phase liquid crystal is proposed. The device employs polar opposite in-plane switching (IPS) electrodes. To balance the optical phase retardation between transmissive (T) and reflective (R) regions, the IPS electrodes are formed with unequal gaps in the two regions. This display exhibits reasonably high optical efficiency and well-matched voltage-dependent transmittance and reflectance curves.

Step-wise medial collateral ligament needle puncturing in extension leads to a safe and predictable reduction in medial compartment pressure during TKA.

Medial soft tissue release in a varus deformity knee during total knee arthroplasty is essential for accurate balancing of the reconstruction. This study attempts to quantify the effect of sequential needle puncturing of the medial collateral ligament (MCL) using a pressure sensor insert (Verasense by OrthoSensor) and gap measurement under tension. Cruciate-retaining arthroplasties were placed in 14 cadaveric knees. The MCL was elongated by step-wise perforation, in five sets of five perforations, with the use of an 18-gauge needle, followed by valgus stress. Following the fifth set of needle perforations, blade perforation was performed on the remaining tense fibers of the MCL. Following each step-wise perforation, corresponding medial compartment pressures and gap measurements under tension were recorded. Sensor measurements correlated closely with step-wise tissue release (R = 0.73, p < 0.0001), and a significant decrease in pressure was found in early needle puncturing (mean 49N after 5, 83N after 15, p values < 0.05), although changes diminished at later stages of needle perforation (90N after 20). Gap measurement demonstrated small gradual changes with early puncturing, but showed significant opening in the later stages of release. There was minimal variation in pressure or gap measurements in flexion versus extension. This finding suggests that MCL needle puncture will not lead to unequal gaps between flexion and extension. There were no cases of MCL over-release after 15 punctures, one case after 20 punctures, and three after blade perforation. Needle puncturing of the MCL in extension for up to 15 punctures can be a safe and predictable way to achieve medial opening when balancing a varus knee during TKA as demonstrated in this cadaveric model. Blade perforation should be used with caution to avoid over-release. The needle puncture method can be used by surgeons to achieve reliable reductions in medial compartment pressures, to help achieve a balanced TKA, with minimal risk of over-release.

HORIZONTAL INEQUALITIES AND ETHNIC CONFLICTS: IMPLICATIONS ON DEVELOPMENT POLICIES IN NIGERIA

The epicenter of every development discourse is for humanity--placing individuals firmly as the major concern for analysis and policy. With its economic and political implications which can frustrate development, Horizontal Inequalities (multi-dimensional inequalities among identity groups rather than individuals) is an important dimension of wellbeing and correcting Horizontal Inequalities should form a significant aspect of development policy design. People act according to perceived injustices and hence perceptions of Horizontal Inequalities affect the likelihood of conflict. This paper focuses on the group dimension of inequalities which seems to be ignored/ relegated but is a recurrent causative factor of ethnic conflicts in heterogeneous societies. It also explores the power and employment distribution amongst ethnic groups in Nigeria. The paper recommends mainstreaming the perspective of Horizontal inequalities in development cooperation in Nigeria vis-a-visa redefinition of ethnic/ regional make up; re-creation of local government areas based on population rather than land mass; adequate compensation for resource based areas; putting time line to the catchment area policy and achieving a representative bureaucracy through effective employment equity policies/programmes. These will help to close up the unequal gaps, reduce ethnic grievances and thus, promote stability and development. Article visualizations:

Roles of anisotropic and unequal gaps in the quasiparticle interference of superconducting iron pnictides

We investigate the role of gap characteristics such as anisotropy or inequality of the gaps in the quasiparticle interferences of iron pnictides using a five-orbital tight-binding model. We examine how the difference in the sensitivities exhibited by the sign-changing and -preserving s-wave superconductivity in an annular region around (π,0), which can be used to determine the sign change of the superconducting gap, gets affected when the gaps are unequal on the electron and hole pockets. In addition, we also discuss how robust these differentiating features are on changing the quasiparticle energy or when the gap is anisotropic.

Spin resonance peak in Fe-based superconductors with unequal gaps

We study the spin resonance in superconducting state of iron-based materials within multiband models with two unequal gaps, $\Delta_L$ and $\Delta_S$, on different Fermi surface pockets. We show that due to the indirect nature of the gap entering the spin susceptibility at the nesting wave vector $\mathbf{Q}$ the total gap $\tilde\Delta$ in the bare susceptibility is determined by the sum of gaps on two different Fermi surface sheets connected by $\mathbf{Q}$. For the Fermi surface geometry characteristic to the most of iron pnictides and chalcogenides, the indirect gap is either $\tilde\Delta = \Delta_L + \Delta_S$ or $\tilde\Delta = 2\Delta_L$. In the $s_{++}$ state, spin excitations below $\tilde\Delta$ are absent unless additional scattering mechanisms are assumed. The spin resonance appears in the $s_\pm$ superconducting state at frequency $\omega_R \leq \tilde\Delta$. Comparison with available inelastic neutron scattering data confirms that what is seen is the true spin resonance and not a peak inherent to the $s_{++}$ state.

Quality assurance of stereotactic alignment and patient positioning mechanical accuracy for robotized Gamma Knife radiosurgery

The automatic patient positioning system and its alignment is critical and specified to be less than 0.35 mm for a radiosurgical treatment with the latest robotized Gamma Knife Perfexion (GKPFX). In this study, we developed a quantitative QA procedure to verify the accuracy and robustness of such a system. In particular, we applied the test to a unit that has performed >1000 procedures at our institution. For the test, a radiochromic film was first placed inside a spherical film phantom and then irradiated with a sequence of linearly placed shots of equal collimator size (e.g. 4 mm) via the Leksell Gamma Knife Perfexion system (PFX). The shots were positioned with either equal or unequal gaps of approximately 8 mm both at center and off-center positions of the patient positioning system. Two independent methods of localizing the irradiation shot center coordinates were employed to measure the gap spacing between adjacent shots. The measured distance was then compared with the initial preset values for the test. On average, the positioning uncertainty for the PFX delivery system was found to be 0.03 ± 0.2 mm (2σ). No significant difference in the positioning uncertainty was noted among measurements in the x-, y- and z-axis orientations. In conclusion, a simple, fast, and quantitative test was developed and demonstrated for routine QA of the submillimeter PFX patient positioning system. This test also enables independent verification of any patient-specific shot positioning for a critical treatment such as a tumor in the brainstem.

A forecasting model for small non-equigap data sets considering data weights and occurrence possibilities

In the early stages of manufacturing systems, it is often difficult to obtain sufficient data to make accurate forecasts. Grey system theory is one of the approaches to deal with this issue, as it uses fairly small sets to construct forecasting models. Among published grey models, the current non-equigap grey models can deal with data having unequal gaps, and have been applied in various fields. However, these models usually use fixed modeling procedures that do not consider data growth trend differences. This paper utilizes the trend and potency tracking method to determine the parameter α of the background value to build an adaptive non-equigap grey model to improve forecasting performance. The experimental results indicate that the proposed method considers that data occurrence properties can obtain better forecasting results.

Temperature distribution study during the friction stir welding process of Al2024-T3 aluminum alloy

Heat flux characteristics are critical to good quality welding obtained in the important engineering alloy Al2024-T3 by the friction stir welding (FSW) process. In the present study, thermocouples in three different configurations were affixed on the welding samples to measure the temperatures: in the first configuration, four thermocouples were placed at equivalent positions along one side of the welding direction; the second configuration involved two equivalent thermocouple locations on either side of the welding path; while the third configuration had all the thermocouples on one side of the layout but with unequal gaps from the welding line. A three-dimensional, non-linear ANSYS computational model, based on an approach applied to Al2024-T3 for the first time, was used to simulate the welding temperature profiles obtained experimentally. The experimental thermal profiles on the whole were found to be in agreement with those calculated by the ANSYS model. The broad agreement between the two kinds of profiles validates the basis for derivation of the simulation model and provides an approach for the FSW simulation in Al2024-T3 and is potentially more useful than models derived previously.

Analysis and Enhancing of Self-Breakdown Voltages of a Multistage Gas Switch

A six-stage gas switch developed for linear transformer drivers is presented in this paper. The switch features an easy-handling structure consisting of stackable cylindrical insulators and brimmed toroidal electrodes. Following an electrode conditioning procedure, the switch and one of its gaps undergo self-breakdown tests by which normal distribution parameters of the self-breakdown voltage at each experimental air pressure are determined. Assuming that all gaps are the same, the switch's voltage with a 50% self-breakdown probability is predicted as the summed voltage of six gaps which individually have a 10.9% self-breakdown probability of voltage being calculated by using the experimentally determined normal function. The calculated result is 7-14 kV higher than the measured voltage because of a nonuniform voltage distribution which is later confirmed by using unequal gaps. For a more uniform voltage distribution, electrodes are revised to suppress corona discharge, and this revision has finally increased the switch hold-off voltage by 4-6 kV, which is the same as a resistive divider.

Self-Calibration for MEMS With Comb Drives: Measurement of Gap

We present a practical method for measuring planar gaps of microelectromechanical systems (MEMS) with comb drives by on- or off-chip electrical probing. We show that our method is practical, accurate, precise, and repeatable. The option of on-chip postpackaged electrical measurement enables MEMS to be autonomously self-calibratable. We use the measurement of gap to determine the geometrical difference between layout and fabrication, which can lead to measurements of other properties such as displacement, force, stiffness, and mass. Our method consists of applying enough voltage to close two unequal gaps and measuring the resulting changes in capacitances. Many MEMS designs with comb drives can be easily modified to implement our technology. Our results are an order better than convention and suggest means for further improvement.

The effect of rotor position on pulp properties in a twozoned low consistency refiner

Earlier studies have shown that plate gaps are sometimes unequal in two-zoned low consistency refiners and that unequal gaps render unevenly refined pulp. It is also known that optimisation of plat ...

Numerical Estimations of Carrier Generation–Recombination Processes and the Photon Recycling Effect in HgCdTe Heterostructure Photodiodes

An enhanced computer program has been applied to explain in detail the photon recycling effect which drastically limits the influence of radiative recombination on the performance of p-on-n HgCdTe heterostructure photodiodes. The computer program is based on a solution of the carrier transport equations, as well as the photon transport equations for semiconductor heterostructures. We distinguish photons in two energy ranges according to p+ and n region with unequal band gaps. As a result, both the distribution of thermal carrier generation and recombination rates and spatial photon density distribution in photodiode structures have been obtained. The general conclusion, similar to our earlier work concerning 3-μm n-on-p HgCdTe heterostructure photodiodes, confirms the previous assertion by Humphreys that radiative recombination does not limit HgCdTe photodiode performance.

Novel topology of unequal air gap in a single-phase brushless DC motor

Most single-phase brushless DC (BLDC) motors have unequal air gaps to eliminate the dead point where the developed torque value is zero. These unequal air gaps deteriorate the motor characteristics in cogging torque. Thus in this paper a new topology of the unequal air gaps is proposed to solve this problem. As a result, it is proved by the finite element analysis and experimental results that the proposed air gap topology is very effective in reducing the cogging torque.

Vibration of Harmonically Excited Oscillators With Asymmetric Constraints

investigation is carried out for a class of piecewise linear oscillators with asymmetric characteristics. The damping and restoring forces are general trilinear functions of the system velocity and displacement, respectively, while the excitation is harmonic in time. First, an analysis is presented which determines harmonic and subharmonic steady-state response. Then, a special formulation is employed in examining the stability of located periodic motions. Finally, numerical results are presented for several representative sets of the system parameters. Effects of asymmetries in the response due to unequal gaps as well as unequal stiffness and damping coefficients are analyzed in detail. Asymmetric response of a system with symmetric technical characteristics is also investigated. The behavior of the systems examined resembles response of similar nonlinear systems with continuous characteristics, like the response of the Duffing and van der Pol oscillators. Complicated nonperiodic response is also encountered and analyzed.

Microwave mixing and direct detection using SIS and SIS' quasiparticle tunnel junctions

Quasiparticle mixers have shown strong quantum effects, conversion gain, and noise levels approaching the quantum limit, but only in tunnel junctions with very low sub-gap leakage conductance. It has been suggested that SIS' tunnel junctions, made from two different conductors with unequal gaps, will function as high gain mixers since the dynamic conductance below the gap is negative. We report results of the first SIS' mixing and direct detection experiments. At 36 GHz, a conversion efficiency of -4 dB with a noise temperature of 33 K (SSB) has been obtained. A novel gain mechanism for SIS' direct detectors is predicted. A direct detector responsivity of 250 A/W was measured. We compare our results to quantum theory models. In addition, we demonstrate quasiparticle harmonic mixing of a 36 GHz signal with an 18 GHz local oscillator in tin SIS junctions. Harmonic mixers can have important advantages at high microwave frequencies where insufficient local oscillator power is available.

Periodic multielement strip gratings

A method of analysis for strip gratings with more than one conducting strip per period is given. The method is then applied to a periodic twin-strip grating with two unequal gaps. The scattering parameters are found from a set of linear equations which may be solved numerically.