Tuning Thermal Transport Through Atomically Thin Ti3C2Tz MXene by Current Annealing in Vacuum

Heat transport across vertical interfaces of heterogeneous 2D materials is usually governed by the weak Van der Waals interactions of the surface‐terminating atoms. Such interactions play a significant role in thermal transport across transition metal carbide and nitride (MXene) atomic layers due to their hydrophilic nature and variations in surface terminations. Here, the metallicity of atomically thin Ti₃C₂T_z MXene, which is also verified by scanning tunneling spectroscopy for the first time, is exploited to develop a self‐heating/self‐sensing platform to carry out direct‐current annealing experiments in high (<10^?8 bar) vacuum, while simultaneously evaluating the interfacial heat transport across a Ti₃C₂T_z/SiO₂ interface. At room temperature, the thermal boundary conductance (TBC) of this interface is found, on average, to increase from 10 to 27 MW m^?2 K^?1 upon current annealing up to the breakdown limit. In situ heating X‐ray diffraction and X‐ray photo‐electron spectroscopy reveal that the TBC values are mainly affected by interlayer and interface spacing due to the removal of absorbents, while the effect of surface termination is negligible. This study provides key insights into understanding energy transport in MXene nanostructures and other 2D material systems.     

Performance evaluation of co-located IEEE 802.15.4-based wireless body sensor networks

Wireless body sensor networks (WBSNs) are expected to play a pivotal role in health-related and well-being applications. In this paper, we consider a situation in which a large number of people wearing body sensor networks are gathered in very close vicinity (as can happen in sport events or emergency hospitals). Clearly, BSNs compete with each other to gain access to the same frequency which results in experiencing mutual (internal) interference. Therefore, we investigate the “internal interference” and its destructive impacts on the overall performance gain of WBSNs using IEEE 802.15.4 standard protocol. As the number of WBSNs increases in the channel, it becomes highly likely for active periods of neighbouring WBSNs to overlap with each other. The increase in overlapping active periods would increase the probability of packet collisions leading to performance degradation. In this paper, two types of interference mitigation strategies are proposed, namely passive schemes and active scheme. The terms passive and active refer to the absence and presence of the capability of communication between WBSNs to efficiently utilise the same frequency spectrum. According to the passive schemes, WBSNs are enabled to change their operating frequencies whenever required to mitigate the impacts of internal interference, whereas active scheme offers collaborative utilisation of the channel. The simulation results show that the proposed active scheme represents the highest performance gains compared to the proposed practical passive schemes.     

Pool boiling heat transfer characteristics of graphene-based aqueous nanofluids

Journal of Thermal Analysis and Calorimetry - In the present study, experiments on pool boiling heat transfer of graphene nanofluids on a flat heater surface (40&nbsp;mm diameter) were...     

Training a Hidden Markov Model with a Bayesian Spiking Neural Network

It is of some interest to understand how statistically based mechanisms for signal processing might be integrated with biologically motivated mechanisms such as neural networks. This paper explores a novel hybrid approach for classifying segments of sequential data, such as individual spoken works. The approach combines a hidden Markov model (HMM) with a spiking neural network (SNN). The HMM, consisting of states and transitions, forms a fixed backbone with nonadaptive transition probabilities. The SNN, however, implements a biologically based Bayesian computation that derives from the spike timing-dependent plasticity (STDP) learning rule. The emission (observation) probabilities of the HMM are represented in the SNN and trained with the STDP rule. A separate SNN, each with the same architecture, is associated with each of the states of the HMM. Because of the STDP training, each SNN implements an expectation maximization algorithm to learn the emission probabilities for one HMM state. The model was studied on synthesized spike-train data and also on spoken word data. Preliminary results suggest its performance compares favorably with other biologically motivated approaches. Because of the model’s uniqueness and initial promise, it warrants further study. It provides some new ideas on how the brain might implement the equivalent of an HMM in a neural circuit.     

High Performance Microstrip Low Pass Filter for Wireless Communications

A microstrip low-pass filter using T-shaped resonators is designed to achieve an ultra-sharp transition band and high suppression level. The performance of the resonators is investigated based on an LC equivalent circuit and a transfer function to compute the equations of the transmission zeros. This filter has an acceptable stopband with high insertion loss (28 dB) by adopting a rectangular suppressor. Also, the width of the transition band is 0.09 GHz (with – 3 and ? 40 dB attenuation levels), that exhibits a very high sharpness (ξ = 411 dB/GHz). The proposed filter with a 3 dB cut-off frequency (f_c) of 1.32 GHz presents a high return loss in the passband (17 dB) and high figure of merit of 57,073. The designed filter is fabricated and measured, demonstrating sufficient agreement between the simulation and experimental results.

     

Spectral analysis of GFDM modulated signal under nonlinear behavior of power amplifier

Wireless Networks - Generalized frequency division multiplexing (GFDM) is a flexible non-orthogonal waveform candidate for 5G which can offer some advantages such as low out-of-band emission and...     

A catalytic multicomponent protocol to dihydropyridine-3-carboxylate from terminal alkynes,isocyanates, and malonates

Monatshefte für Chemie - Chemical Monthly - A domino catalytic reaction between terminal alkynes, isocyanates, and malonates has been developed. Copper acetylides attack on isocyanates to form...     

Ammonia modification of activated carbon to enhance carbon dioxide adsorption: Effect of pre-oxidation

A commercial granular activated carbon (GAC) was subjected to thermal treatment with ammonia for obtaining an efficient carbon dioxide (CO₂) adsorbent. In general, CO₂ adsorption capacity of activated carbon can be increased by introduction of basic nitrogen functionalities onto the carbon surface. In this work, the effect of oxygen surface groups before introduction of basic nitrogen functionalities to the carbon surface on CO₂ adsorption capacity was investigated. For this purpose two different approaches of ammonia treatment without preliminary oxidation and amination of oxidized samples were studied. Modified carbons were characterized by elemental analysis and Fourier Transform Infrared spectroscopy (FT-IR) to study the impact of changes in surface chemistry and formation of specific surface groups on adsorption properties. The texture of the samples was characterized by conducting N₂ adsorption/desorption at −196 °C. CO₂ capture performance of the samples was investigated using a thermogravimetric analysis (TGA). It was found that in both modification techniques, the presence of nitrogen functionalities on carbon surface generally increased the CO₂ adsorption capacity. The results indicated that oxidation followed by high temperature ammonia treatment (800 °C) considerably enhanced the CO₂ uptake at higher temperatures.     

Enhancing Security in Mobile IPv6

In the Mobile IPv6 (MIPv6) protocol, a mobile node (MN) is a mobile device with a permanent home address (HoA) on its home link. The MN will acquire a care‐of address (CoA) when it roams into a foreign link. It then sends a binding update (BU) message to the home agent (HA) and the correspondent node (CN) to inform them of its current CoA so that future data packets destined for its HoA will be forwarded to the CoA. The BU message, however, is vulnerable to different types of security attacks, such as the man‐in‐the‐middle attack, the session hijacking attack, and the denial‐of‐service attack. The current security protocols in MIPv6 are not able to effectively protect the BU message against these attacks. The private‐key‐based BU (PKBU) protocol is proposed in this research to overcome the shortcomings of some existing MIPv6 protocols. PKBU incorporates a method to assert the address ownership of the MN, thus allowing the CN to validate that the MN is not a malicious node. The results obtained show that it addresses the security requirements while being able to check the address ownership of the MN. PKBU also incorporates a method to verify the reachability of the MN.