Unequal Gap Research Articles

Emergent half-metal at finite temperatures in a Mott insulator

Sustaining exotic quantum mechanical phases at high temperatures is a long-standing goal of condensed matter physics. Among them, half-metals are spin-polarized conductors that are essential for realizing room-temperature spin current sources. However, typical half-metals are low-temperature phases whose spin polarization rapidly deteriorates with temperature increase. Here, we first show that a low-temperature insulator with an unequal charge gap for the two spin channels can arise from competing Mott and band insulating tendencies. We establish that thermal fluctuations can drive this insulator to a half-metal through a first-order phase transition by closing the charge gap for one spin channel. This half-metal has 100% spin polarization at the onset temperature of metallization. Further, varying the strength of electron repulsion can enhance the onset temperature while preserving spin polarization. We outline experimental scenarios for realizing this tunable finite temperature half-metal.

An Initial States Recognition (ISR) Method for Start-Up of 1Ф BLDC Motor in Hall-Sensor-Less Fan Applications

The initial state is very important for a single-phase brushless DC (BLDC) fan motor when starting, especially in fan application with a nonstatic motor. The direction of self-rotation caused by the external thrust needs to be considered to avoid the starting fail or wrong running direction. This article proposes an initial states recognition (ISR) method to smartize the starting procedure. However, the self-rotation direction identification of single-phase BLDC motors is a challenge, which is even more difficult in some applications without rotor position sensors. The unequal air gap, which is designed by the geometric variation on the pole shoe to form the asymmetric stator, is generally the necessary design for the single-phase BLDC motor to dodge the null torque position (dead point) and determine the operation direction; and it will further form the asymmetrical waveform of the back electromotive force (EMF) voltage. The asymmetric distribution of back EMF waveform will be opposite in half cycle (positive or negative half cycle) with the rotation direction. The proposed ISR method utilizes this trait to achieve the self-rotation direction recognition before starting a dynamic single-phase BLDC fan motor. Finally, under the architecture of Hall-sensor-less control, the experimental results prove that the proposed method is reliable and feasible.

Numerical Study of Flow Past Three Rectangular Rods at Unequal Gap Spacing

Objectives: To examine the effect of unequal gap spacing for flow past over three rectangular rods a fixed Re (Reynolds number) and Aspect Ratio (AR). Methodology: A two dimensional (2-D) numerical study of flow over three rectangular rods is conducted by using Single Relaxation Time Lattice Boltzmann Method (SRT-LBM). The gap spacing (g) between the rods is varied from 0.5 to 7 with fixed Reynolds number i.e., Re = 150 (Re = .U∞d/ υ., where U∞ is uniform velocity, d is size of an object and υ is the kinematic viscosity) and aspect ratio AR = 0.25 (where, AR = l/w, l is the length and w is the width of the rods). Different flow structures, power spectra analysis of lift coefficients and force statistics are studied for this analysis at small, moderate and large gap spacing. Findings: The present study revealed that the gap spacing between the rods has a great impact on the flow behaviour. Therefore, different flow patterns are observed and some of them are outlined as, i). Shear layer reattachment (SLR), ii). Semi developed single bluff body (SDSBB), iii). Fully developed vortex shedding (FDVS), iv). Semi developed irregular vortex shedding, v) Fully generated two row single bluff body, vi). Semi developed irregular single bluff body (SDISBB) and vii). Critical flow (CF) patterns. The critical flow behaviour is observed at the gap spacing (g1 , g2 ) = (5, 2.5), (here, g1 is the gap between upstream rods to middle one and g2 is the gap between middle rods to downstream rectangular rod). In force statistics analysis, the values of Cdmean and Strouhal number are computed at different spacing ratios. The value of mean drags coefficients for all three rodsat g1 = 3 is approximately same, but at g1 = 1 and 5, the maximum value of Cdmean is observed for C2 as compared to C1 and C3, that is 6.91. Furthermore, Strouhal number values are much less than the single rod (SR) value for all three chosen small, moderate and large gap spacing values. The maximum value of St is examined at (g1, g2) = (1, 1) i.e 0.19. Keywords: Drag Coefficient; Rectangular Rods, Single Relaxation Time Lattice Boltzmann Method, Vortex Shedding Suppression

Studi Potensi Lokal Kampung Cilegong Desa Mekarwangi dengan Analisis Spirit of Place

New city development, with a gated community approach by private property developers in the Tangerang Regency area, has potentially reducing the quality of local informal settlements to slums. Construction o concrete walls that separate formal and informal housing or between the rich and the poor produces an unequal gap and the absence of shared space. Mekarwangi Village is one of the affected villages. Avoiding negative impacts in the future, it needs good and sustainable planning, which is based on the study of local potential that can be integrated into formal housing with an analysis of spirit of place. The case study of this activity is located in Cilegong Kampong in Mekarwangi Village. What is the local potential of Kampung Cilegong? To get a depht analysis, this study uses qualitative methods. The purpose of this study is to find the local potential of Mekarwangi Village that can be developed in the future. The final result shows, that Cilegong Kampong in Mekarwangi Village has the potential as a Green Tourism Village.

Numerical investigation of fluid-solid interaction for flow around three square cylinders

In this work, fluid-solid interactions are numerically investigated for flow around three equally/unequally spaced square cylinders using the lattice Boltzmann method. Two major trends of shear layers observed for equal gap spacings between cylinders: (i) without roll up (W), and (ii) with roll up (R). While for unequal gap spacings, four major trends of shear layers observed: (i) without roll up in both gaps (WW), (ii) without rollup in first gap and with roll up in second gap (WR), (iii) with roll up in first gap and without roll up in second gap (RW), and (iv) with roll up in both gaps (RR). g = 3 is found to be the critical equal spacing value. Also g = 1.5 is found to be suitable equal spacing in terms of minimum drag force. While the suitable unequal gap spacing combinations found in this study are (g1, g2) = (1.5, 0.5), (g1, g2) = (3, 0.5) and (g1, g2) = (5, 0.5). Results show that flow induced forces can be suppressed by suitable unequal gap spacing combinations.

The effect of Reynolds numbers for unequal gap spacings on flow past three square cylinders arranged in-line

Numerical investigations are carried out to study the effect of Reynolds numbers (Re) for unequal gap spacing on the flow past three square cylinders arranged in-line. Three different cases of unequal gap spacing between the cylinders are chosen in this work: the first case is related to the subcritical spacing range (g 1, g 2) = (1, 1.5) and (g 1, g 2) = (1.5, 1), the second one is related to the post-critical spacing range (g 1, g 2) = (4.5, 5) and (g 1, g 2) = (5, 4.5) and the third one is related to critical gap spacing (g 1, g 2) = (3, 4) and (g 1, g 2) = (4, 3). The Re values are varied from 75 to 175. Effect of equal gap spacing at Re = 150 is also discussed. A two-dimensional single-relaxation time lattice Boltzmann code was employed to simulate the important flow characteristics. In this study, three major cases concerning the behavior of shear layers, emerging from first cylinder, are observed: (a) without reattachment and without roll up, (b) without reattachment and with roll up and (c) with reattachment and with roll up. For equal spacing case, it is found that the critical spacing lies between 2–4. In the subcritical unequal spacing range, the single slender body flow is observed while the reattachment and binary vortex streets are observed in the post-critical unequal spacing range. The mean drag coefficient, Strouhal number, root-mean-square values of drag and lift coefficients are also calculated and compared with the experimental and numerical data in existing literature. It is found that the value of critical Re is 75 where maximum changes in the flow characteristics are observed.

Comparison of wake structures and force measurements behind three side-by-side cylinders

The research presents a numerical investigation of flow past three side-by-side square cylinders using the multi-relaxation-time lattice Boltzmann method. A comparison is made between equal and unequal gap spacings behind the three cylinders. Fluid forces acting on the cylinders, wake structure mechanism, time-trace analysis of drag and lift coefficients and vortex shedding frequencies are investigated systematically for different equal and unequal gap spacings. The Reynolds number is kept at 150 and unequal gap spacings (g 1, g 2) = (0.5, 0.6), (0.6, 0.5), (1.5, 1.6), (1.6, 1.5), (2.5, 2.6), (2.6, 2.5), (4, 4.1) and (4.1, 4) are selected for the investigation. For comparison we have also investigated the effect of equal gap spacings varied from 0.5 to 4. The results show that the wake structure and fluid forces are responsible for a slight change in gap spacing between any two cylinders. It is observed that the effects of unequal gap spacings on force statistics such as drag and lift coefficients, Strouhal number and the vortex shedding mechanism are notable at (g 1, g 2) = (0.5, 0.6), (0.6, 0.5), (1.5, 1.6) and (1.6, 1.5) and are completely different from those at equal gap spacings (g = 0.5 and 1.5). The results further show that at (g 1, g 2) = (4, 4.1) and (4.1, 4) the unequal gap spacing effect almost diminishes and only the primary vortex shedding frequency is observed. The bistable, asymmetric, inphase–antiphase and modulated synchronized flow patterns observed in this study.

On the effect of Reynolds number for flow past three side-by-side square cylinders for unequal gap spacings

Flow patterns and aerodynamic characteristics behind three side-by-side square cylinders has been found depending upon the unequal gap spacing (g1 = s1/d and g2 = s2/d) between the three cylinders and the Reynolds number (Re) using the Lattice Boltzmann method. The effect of Reynolds numbers on the flow behind three cylinders are numerically studied for 75 ≤ Re ≤ 175 and chosen unequal gap spacings such as (g1, g2) = (1.5, 1), (3, 4) and (7, 6). We also investigate the effect of g2 while keeping g1 fixed for Re = 150. It is found that a Reynolds number have a strong effect on the flow at small unequal gap spacing (g1, g2) = (1.5, 1.0). It is also found that the secondary cylinder interaction frequency significantly contributes for unequal gap spacing for all chosen Reynolds numbers. It is observed that at intermediate unequal gap spacing (g1, g2) = (3, 4) the primary vortex shedding frequency plays a major role and the effect of secondary cylinder interaction frequencies almost disappear. Some vortices merge near the exit and as a result small modulation found in drag and lift coefficients. This means that with the increase in the Reynolds numbers and unequal gap spacing shows weakens wakes interaction between the cylinders. At large unequal gap spacing (g1, g2) = (7, 6) the flow is fully periodic and no small modulation found in drag and lift coefficients signals. It is found that the jet flows for unequal gap spacing strongly influenced the wake interaction by varying the Reynolds number. These unequal gap spacing separate wake patterns for different Reynolds numbers: flip-flopping, in-phase and anti-phase modulation synchronized, in-phase and anti-phase synchronized. It is also observed that in case of equal gap spacing between the cylinders the effect of gap spacing is stronger than the Reynolds number. On the other hand, in case of unequal gap spacing between the cylinders the wake patterns strongly depends on both unequal gap spacing and Reynolds number. The vorticity contour visualization, time history analysis of drag and lift coefficients, power spectrum analysis of lift coefficient and force statistics are systematically discussed for all chosen unequal gap spacings and Reynolds numbers to fully understand this valuable and practical problem.

Life Course Transitions and Housework: Marriage, Parenthood, and Time on Housework

We examine the effects of transitions in marital and parenthood status on 1,091 men’s and women’s housework hours using two waves of data from an Australian panel survey titled Negotiating the Life Course. We examine transitions between cohabitation and marriage, and from cohabitation or marriage to separation, as well as transitions to first and higher‐order births. We find extraordinary stability in men’s housework time across most transitions but considerable change for women in relation to transitions in parenthood. Our results suggest that the transition to parenthood is a critical moment in the development of an unequal gap in time spent on routine household labor.

Ac Josephson effect in asymmetric superconducting quantum point contacts

We investigate ac Josephson effects between two superconductors connected by a single-mode quantum point contact, where the gap amplitudes in the two superconductors are unequal. In these systems, it was found in previous studies on the dc effects that, besides the Andreev bound-states, the continuum states can also contribute to the current. Using the quasiclassical formulation, we calculate the current-voltage characteristics for general transmission $D$ of the point contact. To emphasize bound versus continuum states, we examine in detail the low bias, ballistic (D=1) limit. It is shown that in this limit the current-voltage characteristics can be determined from the current-phase relation, if we pay particular attention to the different behaviors of these states under the bias voltage. For unequal gap configurations, the continuum states give rise to non-zero sine components. We also demonstrate that in this limit the temperature dependence of the dc component follows $\tanh(\Delta_s/2T)$, where $\Delta_s$ is the smaller gap, with the contribution coming entirely from the bound state.

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.