Giant anomalous Nernst signal in the antiferromagnet YbMnBi2

A large anomalous Nernst effect (ANE) is crucial for thermoelectric energy conversion applications because the associated unique transverse geometry facilitates module fabrication. Topological ferromagnets with large Berry curvatures show large ANEs; however, they face drawbacks such as strong magnetic disturbances and low mobility due to high magnetization. Herein, we demonstrate that YbMnBi2, a canted antiferromagnet, has a large ANE conductivity of ~10 A m−1 K−1 that surpasses large values observed in other ferromagnets (3–5 A m−1 K−1). The canted spin structure of Mn guarantees a non-zero Berry curvature, but generates only a weak magnetization three orders of magnitude lower than that of general ferromagnets. The heavy Bi with a large spin–orbit coupling enables a large ANE and low thermal conductivity, whereas its highly dispersive px/y orbitals ensure low resistivity. The high anomalous transverse thermoelectric performance and extremely small magnetization make YbMnBi2 an excellent candidate for transverse thermoelectrics.

Effect of Welding Sequence and the Transverse Geometry of the Weld Overlay on the Distribution of Residual Stress in the Weld Overlay Repair of T23 Tubes

Water-wall tubes are important components in power plants and are used to absorb the heat from the boilers, and they often fail prematurely due to corrosion, erosion, and fatigue during service. To repair the defects, weld overlay repair is often adopted by forming a compressive stress area around the susceptible area to prevent the cracks from propagating. In order to obtain reasonable process parameters of weld overlay repair, a study combining experiments and numerical simulations was performed to investigate the welding residual stress distribution on the repaired area with different welding repair methods. The results reveal that a compressive stress area is generated on the repaired area after the repair, and a center-to-outside welding sequence is better than either a right-to-left welding sequence or an outside-to-center welding sequence when overlaying a one-layer weld; with an increase in the number of weld layers, the compressive stress area of the repaired area is expanded, and the stress level is increased, which results from the upward movement of the compressive stress area of the subsequent-overlaying layer and the superposition of the compression areas of the subsequent-overlaying layer and previous-overlaying layer, respectively. In addition, the number of the weld passes of each layer should be not less than four with the center-to-outside welding sequence.

Optimisation Studies of Cylinder Water Channel Geometry in an Internal Combustion Engine

This paper presents an analysis of the results of simulation studies of optimisation of water channel geometry placed in the head of an opposed-piston three-cylinder engine. For this purpose, six computation cases were prepared, differing in shape and cross-section field of channels located along the axis of one of the cylinders. The research was conducted by means of Ansys Flutent software. The conditions of initiation and boundary have been obtained from previous studies using AVL Boost RT software. A fixed temperature was assumed on the cylinder wall and a fixed temperature was assumed for the coolant at the inlet to the model. The studies were carried out for the model of the designed engine, which carries out a two-stroke diesel cycle. The engine will be equipped with direct injection of diesel fuel. On the basis of the conducted analysis of the test results, the flow velocity distributions and distributions of speed fields of the working medium in the critical cross-sections, the distribution of temperature and heat flow fields were prepared. Pressure drops and heat dissipation were also determined for individual models. This provided the basis for the determination of the influence of the rib's transverse geometry shape on the amount of heat received from the cylinder's smoothing walls.

Temperature Sensor Based on an Asymmetric Two-Hole Fiber Using a Sagnac Interferometer

We report in this paper a temperature sensor based on an asymmetric two-hole fiber (ATHF) using a Sagnac interferometer (SI) configuration. The operation principle is based on the birefringence change induced by the temperature difference between the air holes and the silica fiber. As a result, the transmitted spectrum of the SI exhibits a sinusoidal profile which is shifted when the temperature is increased. A linear wavelength shift as a function of temperature is observed, and a sensitivity of 2.22 nm/°C was achieved using a 2 m long asymmetric THF, which is in the same order as those previously reported using similar microstructured fibers. The advantage of this system is a linear response, the use of a microstructured fiber with a simpler transverse geometry, and the use of bigger holes which can facilitate the insertion of several materials and improve the sensitivity of the sensor for different applications.

THE FOLIATED LEFSCHETZ HYPERPLANE THEOREM

A foliation$(M,{\mathcal{F}})$is said to be$2$-calibrated if it admits a closed 2-form$\unicode[STIX]{x1D714}$making each leaf symplectic. By using approximately holomorphic techniques, a sequence$W_{k}$of$2$-calibrated submanifolds of codimension-$2$can be found for$(M,{\mathcal{F}},\unicode[STIX]{x1D714})$. Our main result says that the Lefschetz hyperplane theorem holds for the pairs$(F,F\cap W_{k})$, with$F$any leaf of${\mathcal{F}}$. This is applied to draw important consequences on the transverse geometry of such foliations.