Sum-Rate Maximizing Cell Association via Dual-Connectivity

This paper proposes a dual-connectivity (DC) profile allocation algorithm, in which a central macro base station (MBS) is underlaid with randomly scattered small base stations (SBSs), operating on different carrier frequencies. We introduce two dual-connectivity profiles and the differences among them. We utilize the characteristics of dual-connectivity profiles and their applying scenarios to reduce feasible combination set to consider. Algorithm analysis and numerical results verify that our proposed algorithm achieve the optimal algorithm's performance within 5 \% gap with quite low complexity up to $10^6$ times.Comment: 10 pages, 5 figures, conferenc

Bioinspired Nanocomposite Adhesives Based on 3D Microarchitectures and 1D Nanomaterials for Advanced Thermal and Electrical Applications

Department of Mechanical Enginering (Mechanical Engineering)Functional adhesives are essential components in a variety of application fields from daily life to high-tech industries, including precision manufacturing, aerospace, flexible electronics, and wearable devices. However, conventional functional adhesives based on chemically reactive, hot-melt, and viscoelastic adhesive materials generally form uncontrollable mechanical contact, producing bulky, contaminated, or damaged contact interfaces. To address these issues, bioinspired adhesive architectures exhibiting robust, reversible, and residue-free adhesion properties have been proposed. The extraordinary adhesion properties are due to the presence of nano- or micro-hair arrays with protruding tips that maximize van der Waals interactions between surfaces. The photolithography process followed by the replica-molding process has allowed the production of bioinspired artificial adhesives with robust adhesion and high structural stability in a simple, precise, and highly reproducible way. Nevertheless, the manufacturing process narrows the selection of materials to thermal- or UV-curable polymers whose inherently poor thermomechanical and electrical properties hinder the application of bioinspired adhesives in advanced industrial fields. One-dimensional (1D) nanomaterials including carbon nanotubes (CNTs), metallic nanowires, and nanorods have been actively studied as nanofillers to enhance the mechanical, electrical, and thermal properties of polymeric materials. Yet, the existing methods for the application of nanomaterials are not suitable for fabricating three-dimensional (3D) microarchitectures since the high viscosity of nanomaterial???polymer mixtures inhibits the successful formation of the structures. Furthermore, the rough morphology of the nanomaterials hinders the formation of intimate contact interfaces resulting in low adhesion strength. In this dissertation, we present novel design strategies for bioinspired nanocomposite adhesives, in which 1D nanomaterials are integrated into 3D microarchitectures. The strategies include microarchitecture designs, nanomaterial selections, and optimization of integration processes that allow microarchitectures to have enhanced thermal or electrical properties while maintaining superior adhesion performance. In Chapter 2, we propose high-temperature compatible adhesives based on an integration of mushroom-shaped microarchitectures and CNT-based nanocomposites. The nanocomposite microarchitectures are prepared by a photolithography process followed by replica-molding techniques in which polydimethylsiloxane (PDMS) matrices are reinforced with CNT fillers. The excellent thermomechanical properties of the CNTs enable the mushroom-shaped adhesive architectures to have exceptionally enhanced thermomechanical stability compared to pristine PDMS. Moreover, the manufactured adhesives exhibit robust adhesion performances even when exposed to elevated temperatures of ~350 ??Cthus, they could be utilized as versatile high-temperature compatible adhesives with high reversibility. In Chapter 3, we propose a flexible, transparent, and electrically conductive adhesive composed of tentacle-like adhesive architectures and selectively coated percolating silver nanowires (AgNWs). The integrated design provides robust mechanical and low-resistance electrical contacts by forming intimate contact interfaces. The contact interfaces enable efficient electrical connections with active electrodes through attachment without the use of additional contact processes such as mechanical clamping, chemical adhesives, or vacuum deposition, with the contact remaining stable even when highly bent. The superior features of bioinspired conductive adhesives are demonstrated in self-attachable transparent heaters that can form a direct, seamless contact between its AgNWs and the target substrates, providing direct heat-transfer pathways for precise temperature control of the substrate while minimizing energy loss.ope

Strong and Reversible Adhesion of Interlocked 3D-Microarchitectures

Diverse physical interlocking devices have recently been developed based on one-dimensional (1D), high-aspect-ratio inorganic and organic nanomaterials. Although these 1D nanomaterial-based interlocking devices can provide reliable and repeatable shear adhesion, their adhesion in the normal direction is typically very weak. In addition, the high-aspect-ratio, slender structures are mechanically less durable. In this study, we demonstrate a highly flexible and robust interlocking system that exhibits strong and reversible adhesion based on physical interlocking between three-dimensional (3D) microscale architectures. The 3D microstructures have protruding tips on their cylindrical stems, which enable tight mechanical binding between the microstructures. Based on the unique 3D architectures, the interlocking adhesives exhibit remarkable adhesion strengths in both the normal and shear directions. In addition, their adhesion is highly reversible due to the robust mechanical and structural stability of the microstructures. An analytical model is proposed to explain the measured adhesion behavior, which is in good agreement with the experimental results

Adaptive Noise Reduction Algorithm to Improve R Peak Detection in ECG Measured by Capacitive ECG Sensors

Electrocardiograms (ECGs) can be conveniently obtained using capacitive ECG sensors. However, motion noise in measured ECGs can degrade R peak detection. To reduce noise, properties of reference signal and ECG measured by the sensors are analyzed and a new method of active noise cancellation (ANC) is proposed in this study. In the proposed algorithm, the original ECG signal at QRS interval is regarded as impulsive noise because the adaptive filter updates its weight as if impulsive noise is added. As the proposed algorithm does not affect impulsive noise, the original signal is not reduced during ANC. Therefore, the proposed algorithm can conserve the power of the original signal within the QRS interval and reduce only the power of noise at other intervals. The proposed algorithm was verified through comparisons with recent research using data from both indoor and outdoor experiments. The proposed algorithm will benefit a noise reduction of noisy biomedical signal measured from sensors.11Ysciescopu

Bioinspired reversible hydrogel adhesives for wet and underwater surfaces

Stable and reversible adhesion to wet surfaces is challenging owing to water molecules at the contact interface. In this study, we develop a hydrogel-based wet adhesive, which can exhibit strong and reversible adhesion to wet and underwater surfaces as well as to dry surfaces. The remarkable wet adhesion of the hydrogel adhesive is realized based on a synergetic integration of bioinspired microarchitectures and water-friendly and water-absorbing properties of the polymeric hydrogel. Under dry conditions, the microstructured hydrogel adhesive exhibits strong van der Waals interaction-based adhesion, while under underwater conditions, it can maximize capillary adhesion. Consequently, the hydrogel adhesive exhibits remarkable adhesion strengths for dry, moist, and submerged substrates. Maximum normal and shear adhesion strengths of 423 and 384, 492 and 340, and 253 and 21 kPa are achieved with the hydrogel adhesive for dry, moist, and submerged substrates, respectively. Our results demonstrate that strong wet and underwater adhesion can be achieved only with the hydrogel-based adhesive with simple microscale architecture

Flexible and Shape-Reconfigurable Hydrogel Interlocking Adhesives for High Adhesion in Wet Environments Based on Anisotropic Swelling of Hydrogel Microstructures

This study presents wet-responsive, shape-reconfigurable, and flexible hydrogel adhesives that exhibit strong adhesion under wet environments based on reversible interlocking between reconfigurable microhook arrays. The experimental investigation on the swelling behavior and structural characterization of the hydrogel microstructures reveal that the microhook arrays undergo anisotropic swelling and shape transformation upon contact with water. The adhesion between the interlocked microhook arrays is greatly enhanced under wet conditions because of the hydration-triggered shape reconfiguration of the hydrogel microstructures. Furthermore, wet adhesion monotonically increases with water-exposure time. A maximum adhesion force of 79.9 N cm-2 in the shear direction is obtained with the hydrogel microhook array after 20 h of swelling, which is 732.3% greater than that under dry conditions (i.e., 9.6 N cm-2). A simple theoretical model is developed to describe the measured adhesion forces. The results are in good agreement with the experimental data

A Pressure-Insensitive Self-Attachable Flexible Strain Sensor with Bioinspired Adhesive and Active CNT Layers

Flexible tactile sensors are required to maintain conformal contact with target objects and to differentiate different tactile stimuli such as strain and pressure to achieve high sensing performance. However, many existing tactile sensors do not have the ability to distinguish strain from pressure. Moreover, because they lack intrinsic adhesion capability, they require additional adhesive tapes for surface attachment. Herein, we present a self-attachable, pressure-insensitive strain sensor that can firmly adhere to target objects and selectively perceive tensile strain with high sensitivity. The proposed strain sensor is mainly composed of a bioinspired micropillar adhesive layer and a selectively coated active carbon nanotube (CNT) layer. We show that the bioinspired adhesive layer enables strong self-attachment of the sensor to diverse planar and nonplanar surfaces with a maximum adhesion strength of 257 kPa, while the thin film configuration of the patterned CNT layer enables high strain sensitivity (gauge factor (GF) of 2.26) and pressure insensitivity

Who is the bigger culprit? Studying impacts of traffic and land use on noise levels in CBD area of Karachi, Pakistan

The trend of urbanization has attracted increased attention towards urban areas around the world. Central business districts (CBDs) serve as the core of commercial activities of urban areas and are often associated with high-density population. Noise pollution in urban areas, especially CBDs, is considered as an important issue for planners and policy makers especially with regard to human health. Noise prediction models for CBD area of Karachi, Pakistan, have been developed in this study using land use and traffic parameters. These models show that traffic and built-up space (especially residential land use) contribute positively and vacant space contributes negatively to the noise levels. However, it was found that traffic volume has higher impact, than land use, in terms of on noise levels in CBD area. The models of this research are anticipated to be used for planning of urban CBD areas in other cities where noise levels do not meet international health standards. In addition, they would be useful in calculating the rate of traffic volume associated with residential land use