Investigation of carbon nanotube antennas using thin wire integral equations

In this paper the characteristics of small carbon nanotube (CNT) dipole antennas are investigated on the basis of the thin wire Hallén integral equation (IE). A surface impedance model for the CNT is adopted to account for the specific material properties resulting in a modified kernel function for the integral equation. A numerical solution for the IE gives the current distribution along the CNT. From the current distribution the antenna driving point impedance and the antenna efficiency are computed. The presented numerical examples demonstrate the strong dependence of the antenna characteristics on the used material and show the limitations of nanoscale antennas

Seismic waveform tomography of the central and eastern Mediterranean upper mantle

Abstract. We present a seismic waveform tomography of the upper mantle beneath the central and eastern Mediterranean down to the mantle transition zone. Our methodology incorporates in a consistent manner the information from body and multimode surface waves, source effects, frequency dependence, wavefront healing, anisotropy and attenuation. This allows us to jointly image multiple parameters of the crust and upper mantle. Based on the data from ∼ 17 000 unique source–receiver pairs, gathered from 80 earthquakes, we image radially anisotropic S velocity, P velocity and density. We use a multi-scale approach in which the longest periods (100–150 s) are inverted first, broadening to a period band of 28–150 s. Thanks to a strategy that combines long-period signals and a separation of body and surface wave signals, we are able to image down to the mantle transition zone in most of the model domain. Our model shows considerable detail in especially the northern part of the domain, where data coverage is very dense, and displays a number of clear and coherent high-velocity structures across the domain that can be linked to episodes of current and past subduction. These include the Hellenic subduction zone, the Cyprus subduction zone and high-velocity anomalies beneath the Italian peninsula and the Dinarides. This model is able to explain data from new events that were not included in the inversion.</jats:p

TLM modeling and system identification of optimized antenna structures

The transmission line matrix (TLM) method in conjunction with the genetic algorithm (GA) is presented for the bandwidth optimization of a low profile patch antenna. The optimization routine is supplemented by a system identification (SI) procedure. By the SI the model parameters of the structure are estimated which is used for a reduction of the total TLM simulation time. The SI utilizes a new stability criterion of the physical poles for the parameter extraction

Short-range ordering in the Li-rich disordered rock salt cathode material Li2_{2}VO2_{2}F revealed by Raman spectroscopy

Li‐rich disordered rock salt (DRS) materials are new promising high‐capacity cathode candidates for Li‐ion batteries. DRS structures were initially assumed to have a completely random cation and anion distribution, but recent reports suggest that some of these structures can exhibit local atomic arrangements, or short‐range ordering (SRO). Here, we prove the existence of SRO in the Li‐rich DRS material Li$_{2}$VO$_{2}$F by employing Raman spectroscopy supported by density functional theory (DFT) calculations. Our results suggest that this combination of Raman spectroscopy with computational tools is useful for SRO estimation in this new class of Li‐rich DRS cathode materials

From Fully Strained to Relaxed: Epitaxial Ferroelectric Al_1-xSc_xN for III-N Technology

The recent emergence of wurtzite-type nitride ferroelectrics such as Al1-xScxN has paved the way for the introduction of all-epitaxial, all-wurtzite-type ferroelectric III-N semiconductor heterostructures. This paper presents the first in-depth structural and electrical characterization of such an epitaxial heterostructure by investigating sputter deposited Al1-xScxN solid solutions with x between 0.19 and 0.28 grown over doped n-GaN. The results of detailed structural investigations on the strain state and the initial unit-cell polarity with the peculiarities observed in the ferroelectric response are correlated. Among these, a Sc-content dependent splitting of the ferroelectric displacement current into separate peaks, which can be correlated with the presence of multiple strain states in the Al1-xScxN films is discussed. Unlike in previously reported studies on ferroelectric Al1-xScxN, all films thicker than 30 nm grown on the metal (M)-polar GaN template feature an initial multidomain state. The results support that regions with opposed polarities in as-grown films do not result as a direct consequence of the in-plane strain distribution, but are rather mediated by the competition between M-polar epitaxial growth on an M-polar template and a deposition process that favors nitrogen (N)-polar growth

Analysing socioeconomic diversity and scaling effects on residential electricity load profiles in the context of low carbon technology uptake

Adequately accounting for interactions between Low Carbon Technologies (LCTs) at the building level and the overarching energy system means capturing the granularity associated with decentralised heat and power supply in residential buildings. The approach presented here adds novelty in terms of a realistic socioeconomic differentiation by employing dwelling/household archetypes (DHAs) and neighbourhood clusters at the Output Area (OA) level. These archetypes are combined with a mixed integer linear program (MILP) to generate optimum (minimum cost) technology configurations and operation schedules. Even in the baseline case, without any LCT penetration, a substantial deviation from the standard load profile (SLP) is encountered, suggesting that for some neighbourhoods this profile is not appropriate. With the application of LCTs, including heat pumps, micro-CHP and photovoltaic (PV), this effect is much stronger, including more negative residual load, more variability, and higher ramps with increased LCT penetration, and crucially different between neighbourhood clusters. The main policy implication of the study is the importance of understanding electrical load profiles at the neighbourhood level, because of the consequences they have for investment in the overarching energy system, including transmission and distribution infrastructure, and centralised generation plant. Further work should focus on attaining a superior socioeconomic differentiation between households