I-V characteristics of in-plane and out-of-plane strained edge-hydrogenated armchair graphene nanoribbons

The effects of tensile strain on the current-voltage (I-V) characteristics of hydrogenated-edge armchair graphene nanoribbons (HAGNRs) are investigated by using DFT theory. The strain is introduced in two different ways related to the two types of systems studied in this work: in-plane strained systems (A), and out-of-plane strained systems due to bending (B). These two kinds of strain lead to make a distinction among three cases: in-plane strained systems with strained electrodes (A1) and with unstrained electrodes (A2), and out-of-plane homogeneously strained systems with unstrained, fixed electrodes (B). The systematic simulations to calculate the electronic transmission between two electrodes were focused on systems of 8 and 11 dimers in width. The results show that the differences between cases A2 and B are negligible, even though the strain mechanisms are different: in the plane case, the strain is uniaxial along its length, while in the bent case the strain is caused by the arc deformation. Based on the study, a new type of NEMS-solid state switching device is proposed.Comment: 22 pages, 7 figure

Constant Phase Element in the Time Domain: The Problem of Initialization

This research was partially funded by the TIC105 research group of the University of Granada.The constant phase element (CPE) is found in most battery and supercapacitor equivalent circuit models proposed to interpret data in the frequency domain. When these models are used in the time domain, the initial conditions in the fractional differential equations must be correctly imposed. The initial state problem remains controversial and has been analyzed by various authors in the last two decades. This article attempts to clarify this problem by proposing a procedure to prepare the initial state and defining a decay function that reveals the effect of the initial state in several illustrative examples. This decay function depends on the previous history, which is reflected in the time needed to prepare the initial state and on the current profile assumed for this purpose. This effect of the initial state is difficult to separate and can lead to the misinterpretation of the CPE parameter values.University of Granada TIC10

A physics-based fractional-order equivalent circuit model for time and frequency-domain applications in lithium-ion batteries

This work was partially supported by the Regional Government of Andalusia under project P18-RT-3303 from Plan Andaluz de Investigación, Desarrollo e Innovación (PAIDI 2020), by the Spanish Ministry of Science and Innovation and by FEDER funds via Project MCI-20-PID2019-110955RB-I00, by the Principality of Asturias via project AYUD/2021/50994, and by the FPU-UGR-Banco Santander Program for Predoctoral Scholarships. Funding for open access charge: Universidad de Granada / CBUAEquivalent circuit models (ECMs) remain the most popular choice for online applications in lithium-ion batteries because of their simpler parameterization and lower computational requirements in comparison to electrochemical models. Nevertheless, standard ECMs lack physical insight and fail to accurately reproduce cell behavior under a wide range of operating conditions. For this reason, the development of physics-informed ECMs becomes essential so as to provide a better description of the physical processes while maintaining a reduced computational complexity. In this article, we propose a novel physics-based ECM derived directly from an electrochemical model, so that there is a clear correlation between circuit states and internal battery states, as well as circuit and physical parameters. The proposed model yields an RMS error below 1.46 mV for cell voltage, 0.28% for the surface concentration in the active material particles, 0.6% for the electrode-averaged electrolyte concentration and 0.32 mV for the charge-transfer overpotentials. Another key feature of this model is the relationship between circuit parameters and those identified in frequency-domain tests, which allows us to characterize and validate the model experimentally. We understand that the presented model constitutes an alternative to standard ECMs as well as electrochemical models as it combines advantageous characteristics from both of them.Regional Government of Andalusia P18-RT-3303Spanish Ministry of Science and InnovationFEDER: MCI-20-PID2019-110955RB-I00Principality of Asturias AYUD/2021/50994PU-UGR-Banco SantanderUniversidad de Granada / CBU

A fractional-order model for calendar aging with dynamic storage conditions

Funding for open access charge: Universidad de Granada / CBUA.Due to the increasing importance of lithium-ion batteries in electric vehicle and renewable energy applications, battery aging is a subject of intense research. Although many laboratory experiments are performed under well-controlled static conditions, batteries are stored and operated under varying conditions of temperature and state of charge in their real-life performance, so that a suitable model for predicting the effects of calendar aging in lithium-ion batteries with dynamic conditions is highly desirable. In this paper, we review previous models to calculate capacity loss due to calendar aging under variable temperature and state-of-charge conditions according to experimentally observed power-law behavior, and propose a novel model based on fractional calculus. To validate the new model, we compare its predictions with experimental results showing that it can reproduce the non-monotonic behavior that is observed when the state of charge or the temperature change significantly. This is an interesting application of fractional calculus since this characteristic is not obtained with non-fractional models.Universidad de Granada / CBU

High-Luminance QD-LED Device With Digital and Dynamic Lighting Functions for Efficient Automotive Systems

The work of F. M. Gomez-Campos and S. Rodriguez-Bolivar was supported by the Spanish Junta de Andalucia under Project P18-RT-3303.Thiswork reports the design of a 60-segment photoluminescence quantum dot light emitting device (QD-LED) for automotive lighting systems. The QD-LED device was fabricated using a quantum dot film (QDF), incorporating two kinds of quantum dots (QDs) synthesized to emit at 531 nm (green) and 624 nm (red). When the QDF is excited with blue wavelength at 465 nm, a white color output is obtained. Likewise, by using different color filters, all the automotive lighting functions (interior and exterior) can be achieved. In addition, an electronic control module, based on the state-of-the-art multichannel automotive lighting emitting diode (LED) drivers, was specifically designed to control each segment individually to enable the possibility of external digital communication with the vehicle surroundings. That is key to develop the autonomous vehicle by incorporating what is known as car-to-X communication, used to transmit information to other vehicles and road users through light. Furthermore, this work is remarkable due to the low power consumption of the QD-LED device designed, which implies a high electrical efficiency, something critical for the electrical vehicle development. Besides, figures ofmerit and performance indicators are measured, offering promising values to use this nanotechnology in the next future of the vehicle transportation lighting systems.Junta de Andalucia P18-RT-330

A compact model of the ZARC for circuit simulators in the frequency and time domains

Equivalent-circuit models containing fractional-order elements are often employed to make use of fractionalorder calculus in the frequency and time domains in a variety of applications. Many of these circuits contain constant-phase elements that appear in parallel with a resistor in a configuration called ZARC. But to avoid fractional order derivatives and include it in circuit simulators, the ZARC itself can also be replaced by equivalent circuit models that only contain integer order elements, such as resistors and capacitors. In this article, a novel compact model is presented to substitute the ZARC by a multiple-RC network. This model is valid for a continuous value of the order exponent and is applicable over a very wide range of frequencies, making it useful in both the frequency and time domains. Since it uses only basic functions and operators, it has been easily implemented as a subcircuit in circuit simulators. The validity of the model has been verified and it has been compared with some previously proposed passive circuit models. The model has also been discussed in relation to the initialization problem, which is an often overlooked challenge in fractional-order circuits.Universidad de Granada/CBU

Cumulative Inflammation and HbA1c Levels Correlate with Increased Intima‐Media Thickness in Patients with Severe Hidradenitis Suppurativa

Hidradenitis suppurativa (HS) is a chronic inflammatory skin disease that has been associated with a greater risk of metabolic and cardiovascular comorbidities. The aim of this study is to assess cardiovascular risk by means of intima‐media thickness (IMT), metabolic syndrome, and other potential biomarkers in patients with severe hidradenitis suppurativa who are candidates for biologic therapy and to explore potentially associated factors. A cross‐sectional study was performed. Body mass index (BMI), carotid intima‐media thickness (IMT), and blood tests, including glycemic and lipid profile, insulin, vitamin D, and inflammation markers were performed. Fifty patients were included in the study; the male/female ratio was 3:2. The mean age was 38 years, and the mean disease duration was 21.8 years. The mean carotid IMT was 651.39 μm. A positive association of IMT with disease duration, tobacco consumption, and HbA1c levels was observed. HbA1c correlated with the age of onset, hypertension, metabolic syndrome, and glucose levels. Vitamin D levels inversely correlated with the number of areas affected. In conclusion, patients with severe HS present a higher cardiovascular risk, but it is not distributed equally within the patients: Tobacco consumption, inadequate glycemic control, and disease duration could be useful clinical and biochemical markers to identify patients at higher risk

Optical Absorption in N-Dimensional Colloidal Quantum Dot Arrays: Influence of Stoichiometry and Applications in Intermediate Band Solar Cells

We present a theoretical atomistic study of the optical properties of non-toxic InX (X = P, As, Sb) colloidal quantum dot arrays for application in photovoltaics. We focus on the electronic structure and optical absorption and on their dependence on array dimensionality and surface stoichiometry motivated by the rapid development of experimental techniques to achieve high periodicity and colloidal quantum dot characteristics. The homogeneous response of colloidal quantum dot arrays to different light polarizations is also investigated. Our results shed light on the optical behaviour of these novel multi-dimensional nanomaterials and identify some of them as ideal building blocks for intermediate band solar cells.Junta de Andalucia P18-RT-3303School of Electronic and Electrical Engineering, University of LeedsUK Research & Innovation (UKRI)Engineering & Physical Sciences Research Council (EPSRC)Junta de Andaluci

Band-like transport in “green” quantum dot films: The effect of composition and stoichiometry

ACKNOWLEDGMENTS This work was undertaken on ARC3, part of the High Performance Computing Facilities at the University of Leeds, UK. P.R. gratefully acknowledges financial support from EPSRC through a Doctoral Training Grant. F.M.G.C., S.R.B., and E.S.S.-G. received financial support from Project No. P18-RT-3303 from the Spanish Junta de Andalucia. M.C. is thankful to the School of Electronic and Electrical Engineering, University of Leeds, for financial support.SUPPLEMENTARY MATERIAL https://www.scitation.org/doi/suppl/10.1063/5.0078375 See the supplementary material for the mobility calculations for the rest of the materials considered here. The lowermost conduction miniband visualization in the reciprocal space is also included, along with the tables of flight times and fitting parameters.Two-dimensional quantum dot (QD) arrays are considered as promising candidates for a wide range of applications that heavily rely on their transport properties. Existing QD films, however, are mainly made of either toxic or heavy-metal-based materials, limiting their applications and the commercialization of devices. In this theoretical study, we provide a detailed analysis of the transport properties of “green” colloidal QD films (In-based and Ga-based), identifying possible alternatives to their currently used toxic counterparts. We show how changing the composition, stoichiometry, and the distance between the QDs in the array affects the resulting carrier mobility for different operating temperatures. We find that InAs QD films exhibit high carrier mobilities, even higher compared to previously modeled CdSe (zb) QD films. We also provide the first insights into the transport properties of properly passivated InP and GaSb QD films and envisage how realistic systems could benefit from those properties. Ideally passivated InP QD films can exhibit mobilities an order of magnitude larger compared to what is presently achievable experimentally, which show the smallest variation with (i) increasing temperature when the QDs in the array are very close and (ii) an increasing interdot distance at low operating temperatures (70 K), among the materials considered here, making InP a potentially ideal replacement for PbS. Finally, we show that by engineering the QD stoichiometry, it is possible to enhance the film’s transport properties, paving the way for the synthesis of higher performance devices.Spanish Junta de AndaluciaEngineering and Physical Sciences Research Council P18-RT-330

Time- and Amplitude-Controlled Power Noise Generator against SPA Attacks for FPGA-Based IoT Devices

Power noise generation for masking power traces is a powerful countermeasure against Simple Power Analysis (SPA), and it has also been used against Differential Power Analysis (DPA) or Correlation Power Analysis (CPA) in the case of cryptographic circuits. This technique makes use of power consumption generators as basic modules, which are usually based on ring oscillators when implemented on FPGAs. These modules can be used to generate power noise and to also extract digital signatures through the power side channel for Intellectual Property (IP) protection purposes. In this paper, a new power consumption generator, named Xored High Consuming Module (XHCM), is proposed. XHCM improves, when compared to others proposals in the literature, the amount of current consumption per LUT when implemented on FPGAs. Experimental results show that these modules can achieve current increments in the range from 2.4 mA (with only 16 LUTs on Artix-7 devices with a power consumption density of 0.75 mW/LUT when using a single HCM) to 11.1 mA (with 67 LUTs when using 8 XHCMs, with a power consumption density of 0.83 mW/LUT). Moreover, a version controlled by Pulse-Width Modulation (PWM) has been developed, named PWM-XHCM, which is, as XHCM, suitable for power watermarking. In order to build countermeasures against SPA attacks, a multi-level XHCM (ML-XHCM) is also presented, which is capable of generating different power consumption levels with minimal area overhead (27 six-input LUTS for generating 16 different amplitude levels on Artix-7 devices). Finally, a randomized version, named RML-XHCM, has also been developed using two True Random Number Generators (TRNGs) to generate current consumption peaks with random amplitudes at random times. RML-XHCM requires less than 150 LUTs on Artix-7 devices. Taking into account these characteristics, two main contributions have been carried out in this article: first, XHCM and PWM-XHCM provide an efficient power consumption generator for extracting digital signatures through the power side channel, and on the other hand, ML-XHCM and RML-XHCM are powerful tools for the protection of processing units against SPA attacks in IoT devices implemented on FPGAs.Junta de AndaluciaEuropean Commission B-TIC-588-UGR2