Thermoelectric performance in electron and hole doped PtSb2_2

We employ density functional theory to investigate the thermoelectric properties of electron and hole doped PtSb$_2$. Our results show that for doping of 0.04 holes per unit cell (1.5$\times10^{20}$ cm$^{-3}$) PtSb$_2$ shows a high Seebeck coefficient at room temperature, which can also be achieved at other temperatures by controlling the carrier concentration (both electron and hole). The electrical conductivity becomes temperature independent when the doping exceeds about 0.20 electrons/holes per unit cell. The figure of merit at 800 K in electron and hole doped PtSb$_2$ is 0.13 and 0.21, respectively. The thermoelectric efficiency with same host material are predicted for certain doping levels

Colossal Thermoelectric Power Factor in K7/8_{7/8}RhO2_2

We discuss the thermoelectric and optical properties of layered K$_{x}$RhO$_{2}$ (\emph{x} = 1/2 and 7/8) in terms of the electronic structure determined by first principles calculations as well as Boltzmann transport theory. Our optimized lattice constants differ significantly from the experiment, but result in optical and transport properties close to the experiment. The main contribution to the optical spectra are due to intra and inter-band transitions between the Rh 4\emph{d} and O 2\emph{p} states. We find a similar power factor for pristine K$_{x}$RhO$_{2}$ at low and high cation concentartions. Our transport results of hydrated K$_{x}$RhO$_{2}$ at room temperature show highest value of the power factor among the hole-type materials. Specially at 100 K, we obtain a value of 3$\times$10$^{-3}$ K$^{-1}$ for K$_{7/8}$RhO$_{2}$, which is larger than that of Na$_{0.88}$CoO$_{2}$ {[}M. Lee \emph{et al}., Nat. Mater. 5, 537 (2006){]}. In general, the electronic and optical properties of K$_{x}$RhO$_{2}$ are similar to Na$_{x}$CoO$_{2}$ with enhanced transport properties in the hydrated phase

Half-metallicity and giant magneto-optical Kerr effect in N-doped NaTaO3_3

We employ density functional theory using the modified Becke-Johnson (mBJ) approach to investigate the electronic and magneto-optical properties of N-doped NaTaO$_3$. The mBJ results reveal a half metallic nature of NaTaO$_2$N, in contrast to results obtained by the generalized gradient approximation. We find a giant polar Kerr rotation of 2.16$^{\circ}$ at 725 nm wave length (visible region), which is high as compared to other half metallic perovskites as well as to the prototypical half metal PtMnSb

Thickness and strain effects on the thermoelectric transport in nanostructured Bi2Se3

The structural stability, electronic structure, and thermal transport properties of one to six quintuple layers (QLs) of Bi2Se3 are investigated by van der Waals density functional theory and semi-classical Boltzmann theory. The bandgap amounts to 0.41 eV for a single QL and reduces to 0.23 eV when the number of QLs increases to six. A single QL has a significantly higher thermoelectric figure of merit (0.27) than the bulk material (0.10), which can be further enhanced to 0.30 by introducing 2.5% compressive strain. Positive phonon frequencies under strain indicate that the structural stability is maintained

Impact of lattice strain on the tunnel magneto-resistance in Fe/Insulator/Fe and Fe/Insulator/La0.67_{0.67}Sr0.33_{0.33}MnO3_{3} magnetic tunnel junctions

The objective of this work is to describe the tunnel electron current in single barrier magnetic tunnel junctions within a new approach that goes beyond the single-band transport model. We propose a ballistic multi-channel electron transport model that can explain the influence of in-plane lattice strain on the tunnel magnetoresistance as well as the asymmetric voltage behavior. We consider as an example single crystal magnetic Fe(110) electrodes for Fe/Insulator/Fe and Fe/Insulator/La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ tunnel junctions, where the electronic band structures of Fe and La$_{0.67}$Sr$_{0.33}$MnO$_{3}$ are derived by \it{ab-initio} calculations

On Achievable Accuracy of Localization in Magnetic Induction-Based Internet of Underground Things for Oil and Gas Reservoirs

Magnetic Induction (MI) is an efficient wireless communication method to deploy operational internet of underground things (IOUT) for oil and gas reservoirs. The IOUT consists of underground things which are capable of sensing the underground environment and communicating with the surface. The MI-based IOUT enable many applications, such as monitoring of the oil rigs, optimized fracturing, and optimized extraction. Most of these applications are dependent on the location of the underground things and therefore require accurate localization techniques. The existing localization techniques for MI-based underground sensing networks are two-dimensional and do not characterize the achievable accuracy of the developed methods which are both crucial and challenging tasks. Therefore, this paper presents the expression of the Cramer Rao lower bound (CRLB) for three-dimensional MI-based IOUT localization which takes into account the channel parameters of the underground magnetic-induction. The derived CRLB provide the suggestions for an MI-based underground localization system by associating the system parameters with the error trend. Numerical results demonstrate that localization accuracy is affected by different channel and networks parameters such as the number of anchors, noise variance, frequency, and the number of underground things.Comment: Submitted to IEEE Internet of Things Journa

Towards the Internet of X-things: New Possibilities for Underwater, Underground, and Outer Space Exploration

The rapid growth of the world's population demands more natural resources, food, and space. World-renowned physicist Stephan Hawking has argued that soon we will require another world to live on because we are running out of space and natural resources. This ever-increasing demand for resources and space needs novel technologies to explore natural resources, produce more crops, and explore outer space. Internet of X-things (X-IoT) is an enabling technology to overcome all of the above issues. In this article, we have presented an overview of a unified framework of X-IoT. The framework of X-IoT consists of three major categories. The first one is the Internet of underwater things (IoUT) for smart oceans. The second category is the Internet of underground things (IoUGT) for smart agriculture, seismic monitoring, and Oil/Gas fields. The third category is the Internet of space things (IoST) for outer space exploration, to provide global coverage, and to enable inter-satellite communications. Through this framework, we get to know what has been done since recently and how the technical challenges across the broad spectrum of emerging use cases under the water, underground and over the space are converging toward future solutions.Comment: Accepted in IEEE ComSoc News (CTN

Outlier Detection and Optimal Anchor Placement for 3D Underwater Optical Wireless Sensor Networks Localization

Location is one of the basic information required for underwater optical wireless sensor networks (UOWSNs) for different purposes such as relating the sensing measurements with precise sensor positions, enabling efficient geographic routing techniques, and sustaining link connectivity between the nodes. Even though various two-dimensional UOWSNs localization methods have been proposed in the past, the directive nature of optical wireless communications and three-dimensional (3D) deployment of sensors require to develop 3D underwater localization methods. Additionally, the localization accuracy of the network strongly depends on the placement of the anchors. Therefore, we propose a robust 3D localization method for partially connected UOWSNs which can accommodate the outliers and optimize the placement of the anchors to improve the localization accuracy. The proposed method formulates the problem of missing pairwise distances and outliers as an optimization problem which is solved through half quadratic minimization. Furthermore, analysis is provided to optimally place the anchors in the network which improves the localization accuracy. The problem of optimal anchor placement is formulated as a combination of Fisher information matrices for the sensor nodes where the condition of D-optimality is satisfied. The numerical results indicate that the proposed method outperforms the literature substantially in the presence of outliers.Comment: 14 pages, 11 figures, Accepted for Publication in IEEE Transactions on Communication

Towards the Internet of Underground Things: A Systematic Survey

This paper provides recent advances in the area of Internet of Underground Things (IoUT) with emphasis on enabling communication technologies, networking issues, and localization techniques. IoUT is enabled by underground things (sensors), communication technology, and networking protocols. This new paradigm of IoUT facilitates the integration of sensing and communication in the underground environment for various industries such as oil and gas, agriculture, seismic mapping, and border monitoring. These applications require to gather relevant information from the deployed underground things. However, the harsh underground propagation environment including sand, rock, and watersheds do not allow the use of single communication technology for information transfer between the surface and the underground things. Therefore, various wireless and wired communication technologies are used for underground communication. The wireless technologies are based on acoustic waves, electromagnetic waves, magnetic induction and visible light communication while the wired technologies use coaxial cable and optical fibers. In this paper, state-of-art communication technologies are surveyed, and the respective networking and localization techniques for IoUT are presented. Moreover, the advances and applications of IoUT are also reported. Also, new research challenges for the design and implementation of IoUT are identified.Comment: IEEE Communication Surveys & Tutorial

Underwater Optical Wireless Communications, Networking, and Localization: A Survey

Underwater wireless communications can be carried out through acoustic, radio frequency (RF), and optical waves. Compared to its bandwidth limited acoustic and RF counterparts, underwater optical wireless communications (UOWCs) can support higher data rates at low latency levels. However, severe aquatic channel conditions (e.g., absorption, scattering, turbulence, etc.) pose great challenges for UOWCs and significantly reduce the attainable communication ranges, which necessitates efficient networking and localization solutions. Therefore, we provide a comprehensive survey on the challenges, advances, and prospects of underwater optical wireless networks (UOWNs) from a layer by layer perspective which includes: 1) Potential network architectures; 2) Physical layer issues including propagation characteristics, channel modeling, and modulation techniques 3) Data link layer problems covering link configurations, link budgets, performance metrics, and multiple access schemes; 4) Network layer topics containing relaying techniques and potential routing algorithms; 5) Transport layer subjects such as connectivity, reliability, flow and congestion control; 6) Application layer goals and state-of-the-art UOWN applications, and 7) Localization and its impacts on UOWN layers. Finally, we outline the open research challenges and point out the future directions for underwater optical wireless communications, networking, and localization research.Comment: This manuscript is submitted to IEEE Communication Surveys and Tutorials for possible publicatio