An Analytical Antenna Modeling of Electromagnetic Wave Propagation in Inhomogeneous Media Using FDTD: A Comprehensive Study.

This paper discusses the challenges in characterizing electromagnetic (EM) waves propagating through inhomogeneous media, such as reinforced cement concrete and hot mix asphalt. Understanding the EM properties of materials, including their dielectric constant, conductivity, and magnetic permeability, is crucial to analyzing the behavior of these waves. The focus of this study is to develop a numerical model for EM antennas using the finite difference time domain (FDTD) method, and to gain a deeper understanding of various EM wave phenomena. Additionally, we verify the accuracy of our model by comparing its results with experimental data. We analyze several antenna models with different materials, including the absorber, high-density polyethylene and perfect electrical conductors, to obtain an analytical signal response that is verified against the experimental response. Furthermore, we model the inhomogeneous mixture of randomly distributed aggregates and voids within a medium. We verify the practicality and reliability of our inhomogeneous models using experimental radar responses on an inhomogeneous medium.

Wave Dispersion Behavior in Quasi-Solid State Concrete Hydration.

This paper aims to investigate wave dispersion behavior in the quasi-solid state of concrete to better understand microstructure hydration interactions. The quasi-solid state refers to the consistency of the mixture between the initial liquid-solid stage and the hardened stage, where the concrete has not yet fully solidified but still exhibits viscous behavior. The study seeks to enable a more accurate evaluation of the optimal time for the quasi-liquid product of concrete using both contact and noncontact sensors, as current set time measurement approaches based on group velocity may not provide a comprehensive understanding of the hydration phenomenon. To achieve this goal, the wave dispersion behavior of P-wave and surface wave with transducers and sensors is studied. The dispersion behavior with different concrete mixtures and the phase velocity comparison of dispersion behavior are investigated. The analytical solutions are used to validate the measured data. The laboratory test specimen with w/c = 0.5 was subjected to an impulse in a frequency range of 40 kHz to 150 kHz. The results demonstrate that the P-wave results exhibit well-fitted waveform trends with analytical solutions, showing a maximum phase velocity when the impulse frequency is at 50 kHz. The surface wave phase velocity shows distinct patterns at different scanning times, which is attributed to the effect of the microstructure on the wave dispersion behavior. This investigation delivers profound knowledge of hydration and quality control in the quasi-solid state of concrete with wave dispersion behavior, providing a new approach for determining the optimal time of the quasi-liquid product. The criteria and methods developed in this paper can be applied to optimal timing for additive manufacturing of concrete material for 3D printers by utilizing sensors.

Power-Delay Area-Efficient Processing-In-Memory Based on Nanocrystalline Hafnia Ferroelectric Field-Effect Transistors.

Ferroelectric field-effect transistors (FeFETs) have attracted enormous attention for low-power and high-density nonvolatile memory devices in processing-in-memory (PIM). However, their small memory window (MW) and limited endurance severely degrade the area efficiency and reliability of PIM devices. Herein, we overcome such challenges using key approaches covering from the material to the device and array architecture. High ferroelectricity was successfully demonstrated considering the thermodynamics and kinetics, even in a relatively thick (≥30 nm) ferroelectric material that was unexplored so far. Moreover, we employed a metal-ferroelectric-metal-insulator-semiconductor architecture that enabled desirable voltage division between the ferroelectric and the metal-oxide-semiconductor FET, leading to a large MW (∼11 V), fast operation speed (<20 ns), and high endurance (∼1011 cycles) characteristics. Subsequently, reliable and energy-efficient multiply-and-accumulation (MAC) operations were verified using a fabricated FeFET-PIM array. Furthermore, a system-level simulation demonstrated the high energy efficiency of the FeFET-PIM array, which was attributed to charge-domain computing. Finally, the proposed signed weight MAC computation achieved high accuracy on the CIFAR-10 dataset using the VGG-8 network.

Steep-Slope Transistor with an Imprinted Antiferroelectric Film.

The effect of negative capacitance (NC), which can internally boost the voltage applied to a transistor, has been considered to overcome the fundamental Boltzmann limit of a transistor. To stabilize the NC effect, the dielectric (DE) must be integrated into a heterostructure with a ferroelectric (FE) film. However, in a multidomain hafnia, the charge boosting effect is reduced owing to a lowering of the depolarization field originating from the stray field at each domain, and simultaneously, the operating voltage increases owing to the voltage division at the DE. Here, we demonstrate core approaches to the gate stack of energy-efficient device technology using a transient NC. Electrical measurements of the transistor with imprinted antiferroelectric and high CDE/CFE structures exhibit low subthreshold slopes below 20 mV/dec, a low voltage operation of 0.5 V, a fast operation of 20 ns, hysteresis-free Id-Vg, and high endurance characteristics of 1012 cycles. We expect that this will lead to the rapid implementation of the NC effect in high-speed switching device applications with significantly improved energy efficiency.

Remembering rewarding futures: A simulation-selection model of the hippocampus.

Despite tremendous progress, the neural circuit dynamics underlying hippocampal mnemonic processing remain poorly understood. We propose a new model for hippocampal function-the simulation-selection model-based on recent experimental findings and neuroecological considerations. Under this model, the mammalian hippocampus evolved to simulate and evaluate arbitrary navigation sequences. Specifically, we suggest that CA3 simulates unexperienced navigation sequences in addition to remembering experienced ones, and CA1 selects from among these CA3-generated sequences, reinforcing those that are likely to maximize reward during offline idling states. High-value sequences reinforced in CA1 may allow flexible navigation toward a potential rewarding location during subsequent navigation. We argue that the simulation-selection functions of the hippocampus have evolved in mammals mostly because of the unique navigational needs of land mammals. Our model may account for why the mammalian hippocampus has evolved not only to remember, but also to imagine episodes, and how this might be implemented in its neural circuits.

Role of the hippocampal CA1 region in incremental value learning.

It is generally believed that the hippocampus plays a crucial role in declarative memory-remembering facts and events-but not in gradual stimulus-response association or incremental value learning. Based on the finding that CA1 conveys strong value signals during dynamic foraging, we investigated the possibility that the hippocampus contributes to incremental value learning. Specifically, we examined effects of inactivating different subregions of the dorsal hippocampus on behavioral performance of mice performing a dynamic foraging task in a modified T-maze. A reinforcement learning model-based analysis indicated that inactivation of CA1, but not dentate gyrus, CA3, or CA2, impaired trial-by-trial updating of chosen value without affecting value-dependent action selection. As a result, it took longer for CA1-inactivated mice to bias their choices toward the higher-reward-probability target after changes in reward probability. Our results indicate, contrary to the traditional view, that the hippocampus, especially CA1, might contribute to incremental value learning under certain circumstances.