Analytical considerations of flow boiling heat transfer in metal-foam filled tubes

Flow boiling in metal-foam filled tube was analytically investigated based on a modified microstructure model, an original boiling heat transfer model and fin analysis for metal foams. Microstructure model of metal foams was established, by which fiber diameter and surface area density were precisely predicted. The heat transfer model for flow boiling in metal foams was based on annular pattern, in which two phase fluid was composed by vapor region in the center of the tube and liquid region near the wall. However, it was assumed that nucleate boiling performed only in the liquid region. Fin analysis and heat transfer network for metal foams were integrated to obtain the convective heat transfer coefficient at interface. The analytical solution was verified by its good agreement with experimental data. The parametric study on heat transfer coefficient and boiling mechanism was also carried out

Analysis of the Transmission Performance Limits for a Multi-layer Transmitarray Unit Cell

This communication presents a theoretical study that establishes the performance limits for a multi-layer transmitarray unit cell. This is the first study to be applicable to unit cells in which the conducting resonators, on the different layers, are shaped differently. A theoretical calculation is derived at the beginning. The theoretical calculations predict that, for an S21 amplitude of -1 dB, unit cells having two and three conducting layers provide a phase shifting range of 170° and 360°, respectively. Additionally, for a given phase shifting range of S21, a new methodology for analyzing the maximum S21 amplitude, based on different substrates, is proposed. For the first time, we prove that it is efficient to attain the maximum S21 amplitudes by employing a smaller substrate permittivity or a quarter-of-wavelength substrate electrical thickness. Finally, the theoretical calculations have been validated through computer simulation

Cognitive Principles in Robust Multimodal Interpretation

Multimodal conversational interfaces provide a natural means for users to communicate with computer systems through multiple modalities such as speech and gesture. To build effective multimodal interfaces, automated interpretation of user multimodal inputs is important. Inspired by the previous investigation on cognitive status in multimodal human machine interaction, we have developed a greedy algorithm for interpreting user referring expressions (i.e., multimodal reference resolution). This algorithm incorporates the cognitive principles of Conversational Implicature and Givenness Hierarchy and applies constraints from various sources (e.g., temporal, semantic, and contextual) to resolve references. Our empirical results have shown the advantage of this algorithm in efficiently resolving a variety of user references. Because of its simplicity and generality, this approach has the potential to improve the robustness of multimodal input interpretation

A Reconfigurable Microstrip Patch Antenna with Switchable Liquid-Metal Ground Plane

This letter presents a novel reconfigurable microstrip patch antenna that is reconfigured using liquid metal. The proposed antenna employs two approaches in unison to switch the direction of the main beam. Specifically, the antenna uses the parasitic steering approach together with a novel switchable ground plane. The antenna operates at 5.9 GHz. It consists of a driven patch surrounded by four parasitics. All five elements are circular disk resonators. Each of the parasitic resonators incorporates a drill hole. The drill holes can be filled or emptied of liquid metal to control the behavior of the parasitics. The ground plane incorporates two reconfigurable segments. The switchable ground plane can be reshaped by adding or removing the additional segments of ground plane which are formed from liquid metal. To the best of the authors' knowledge, this is the first antenna that is capable of reconfiguring its radiation pattern by reshaping the ground plane using liquid metal. A hardware prototype of the antenna was fabricated and measured. The measurement results show that the antenna can switch between five different beam directions, namely: 0°, ±20°, and ±40°. The design has only 0.5 dB of scan loss across the beam switching range

Continuous Beam Steering Realized by Tunable Ground in a Patch Antenna

A continuously steerable patch antenna employing liquid metal is presented. The proposed antenna employs a novel tunable ground plane together with parasitic steering to steer the direction of the main beam. The tunable ground plane consists of a permanent region, made from copper, and two tunable regions formed from liquid metal. The liquid metal channels were fabricated using 3D printing technology. By continuously injecting liquid metal into channels, the proposed patch antenna can provide continuous beam steering from -30 to +30 in the elevation plane, while achieving low side lobe level performance combined with low scan loss performance. Such an approach has never been tried before and it is only possible due to the unique properties of liquid metal. To the best of the authors’ knowledge, this is the first time that tunable ground plane has been used for a patch antenna to achieve continuous beam steering. The proposed antenna operates at 5.3 GHz. The antenna is fabricated and measured. Measurement results agree well with the simulation results and validate the effectiveness of the proposed beam steering technique. The proposed antenna has a measured gain of 8.1 dBi at 5.3 GHz and wide bandwidth performance. The tunable ground technique proposed in this work will find numerous applications within future wireless communications systems

Low Cyclic Fatigue of HG70-steel Mining Dump Truck Frame Under Low-Temperature: Chaboche Model and Finite Element Analysis

This paper investigates the low cyclic fatigue behavior of a heavy-duty mining dump truck frame manufactured of HG70-steel under low-temperature conditions. The Chaboche cyclic plastic constitutive model is adopted to characterize the viscoplastic properties of the steel. A finite element model of the frame is subsequently implemented to investigate its structural strength and low cycle performance, integrating the intrinsic stress-strain hysteresis loop. The study reveals the softening stages of HG70-steel under low-temperature low cycle fatigue testing conditions, and investigates the stress concentration regions and maximum displacements in the structured frame. The coded in-house program can be used to assess the low cycle fatigue behavior of steels and components, providing valuable insights into the design and safety analysis of heavy-duty mining dump trucks

Fe-doping induced superconductivity in charge-density-wave system 1T-TaS2

We report the interplay between charge-density-wave (CDW) and superconductivity of 1$T$-Fe$_{x}$Ta$_{1-x}$S$_{2}$ ($0\leq x \leq 0.05$) single crystals. The CDW order is gradually suppressed by Fe-doping, accompanied by the disappearance of pseudogap/Mott-gap as shown by the density functional theory (DFT) calculations. The superconducting state develops at low temperatures within the CDW state for the samples with the moderate doping levels. The superconductivity strongly depends on $x$ within a narrow range, and the maximum superconducting transition temperature is 2.8 K as $x=0.02$. We propose that the induced superconductivity and CDW phases are separated in real space. For high doping level ($x>0.04$), the Anderson localization (AL) state appears, resulting in a large increase of resistivity. We present a complete electronic phase diagram of 1$T$-Fe$_{x}$Ta$_{1-x}$S$_{2}$ system that shows a dome-like $T_{c}(x)$