An implicit stabilized finite element method for the compressible Navier–Stokes equations using finite calculus

A new implicit stabilized formulation for the numerical solution of the compressible NavierStokes equations is presented. The method is based on the Finite Calculus (FIC) scheme using the Galerkin finite element method (FEM) on triangular grids. Via the FIC formulation, two stabilization terms, called streamline term and transverse term, are added to the original conservation equations in the space-time domain. The non-linear system of equations resulting from the spatial discretization is solved implicitly using a damped Newton method benefiting from the exact Jacobian matrix. The matrix system is solved at each iteration with a preconditioned GMRES method. The efficiency of the proposed stabilization technique is checked out in the solution of 2D inviscid and laminar viscous flow problems where appropriate solutions are obtained especially near the boundary layer and shock waves. The work presented here can be considered as a follow up of a previous work of the authors [24]. In that paper, the stabilized Galerkin FEM based on the FIC formulation was derived for the Euler equations together with an explicit scheme. In the present paper, the extension of this work to the Navier-Stokes equations using an implicit scheme is presented

Adaptive envelope shaping for low and medium power amplifiers with dynamic supply

This letter presents an adaptive envelope shaping (AES) method to linearize low and medium power amplifiers (PAs) with dynamic supply. This straightforward linearization solution results very useful for small cell or handset transmitters, where reducing power consumption and computational complexity of the digital part is crucial. With the AES method, there is no need of an a priori characterization of the PA to shape the supply voltage signal targeting maximum linearity. Excellent linearization results are obtained when the PA presents good AM-PM linearity, otherwise, additional phase distortion linearization has to be included to meet the ACLR specifications.This work was partially supported by the Spanish Government (MINECO) and FEDER under projects TEC2014-58341-C4-01-R and 03-R; by the Catalan Government under project 2014-SGR-1103; and by CATRENE under the project named CORTIF CA116

Renewable Energy Consumption, Water Crises, and Environmental Degradation with Moderating Role of Governance: Dynamic Panel Analysis under Cross-Sectional Dependence

This study aims to investigate the relationship between renewable energy consumption, water availability, and environmental degradation with the moderating effect of governance in the South Asian region. This study collected data for renewable energy, water availability, governance, and environmental degradation for the period of 1988 to 2018 from the World Development Indicator. In panel data estimation, if cross-sectional dependence exists, it produces biased estimates. Therefore, this study applied a newly developed technique, dynamic common correlated effect, which produces efficient estimates in the presence of cross-sectional dependence. This study found that foreign direct investment positively and significantly increases environment degradation (β = 0.69 *, * indicates the significance level at less than 1%) while renewable energy and water availability cause to reduce environment degradation (β = −0.08 **, β = −0.09 **, **indicates the significance level at less than 5%). Moreover, the study also found that governance significantly strengthens the relationship of renewable energy and water availability with environment degradation (β = 0.37 **, β = 0.24 **) while governance significantly weakens the relationship of foreign direct investment and environmental degradation (β = −0.34 *). The study suggests that South Asian countries should improve political institutions, and promote renewable energy, water availability, and clean production to improve the environment quality

Comparison of model order reduction techniques for digital predistortion of power amplifiers

This paper compares and discusses four techniques for model order reduction based on compressed sensing (CS), less relevant basis removal (LRBR), principal component analysis (PCA) and partial least squares (PLS). CS and PCA have already been used for reducing the order of power amplifier (PA) behavioral models for digital predistortion (DPD) purposes. While PLS, despite being popular in some signal processing areas, to the best author’s knowledge, still has not been used in the PA linearization field. Finally, the LRBR is an iterative search algorithm proposed by the authors in this paper for the sake of comparison. Experimental results are presented and the advantages and drawbacks of each method discussed.This work was partially supported by the Spanish Government (MINECO) and FEDER, projects TEC2014-58341-C4-01-R and 03-R; and by the Catalan Government, project 2014-SGR-1103

A low-complexity memoryless model for envelope tracking RF power amplifiers

This paper presents a new kind of behavioral model structure for characterizing static nonlinearities in dynamically supplied RF power amplifiers. The proposed architecture is based on the combination of several basic cells and it is focused to simplify the real-time design and implementation of adaptive shaping functions devoted to improve the efficiency in systems controlled by digital signal processors with tight computational capabilities, such is the case of handsets and small-cells.This work was supported by the Spanish Ministry MINECO under projects TEC2011-29126-C03 (-01 and -02)

The digital predistorter goes multi-dimensional: DPD for concurrent multi-band envelope tracking and outphasing power amplifiers

Over at least the last two decades, digital predistortion (DPD) has become the most common and widespread solution to cope with the power amplifier's (PA's) inherent linearity-versus-efficiency tradeoff. When compared with other linearization techniques, such as Cartesian feedback or feedforward, DPD has proven able to adapt to the always-growing demands of technology: wider bandwidths, stringent spectrum masks, and reconfigurability. The principles of predistortion linearization (in its analog or digital forms) are straightforward, and the linearization subsystem precedes the PA (a nonlinear function in a digital signal processor in the case of DPD or nonlinear device in the case of analog predistortion and counteracts the nonlinear characteristic of the PA. Some excellent overviews on DPD can be found in [1]-[4]. Let us now look at the challenges that DPD linearization has faced and will continue to face in the near future with 5G new radio (5G-NR).This work has been supported in part by the Spanish Government and FEDER under MICINN projects TEC2017-83343-C4-1-R and TEC2017-83343-C4-2-R and by the Generalitat de Catalunya under Grant 2017 SGR 813

Volatility Co-Movement in Stock Markets

The volatility and log-price collective movements among stocks of a given market are studied in this work using co-movement functions inspired by similar functions in the physics of many-body systems, where the collective motions are a signal of structural rearrangement. This methodology is aimed to identify the cause of coherent changes in volatility or price. The function is calculated using the product of the variations in volatility (or price) of a pair of stocks, averaged over all pair particles. In addition to the global volatility co-movement, its distribution according to the volatility of the stocks is also studied. We find that stocks with similar volatility tend to have a greater co-movement than stocks with dissimilar volatility, with a general decrease in co-movement with increasing volatility. On the other hand, when the average volatility (or log-price) is subtracted from the stock volatility (or log-price), the co-movement decreases notably and becomes almost zero. This result, interpreted within the background of many body physics, allows us to identify the index motion as the main source for the co-movement. Finally, we confirm that during crisis periods, the volatility and log-price co-movement are much higher than in calmer periods

A New Look on Financial Markets Co-Movement through Cooperative Dynamics in Many-Body Physics

One of the main contributions of the Capital Assets Pricing Model (CAPM) to portfolio theory was to explain the correlation between assets through its relationship with the market index. According to this approach, the market index is expected to explain the co-movement between two different stocks to a great extent. In this paper, we try to verify this hypothesis using a sample of 3.000 stocks of the USA market (attending to liquidity, capitalization, and free float criteria) by using some functions inspired by cooperative dynamics in physical particle systems. We will show that all of the co-movement among the stocks is completely explained by the market, even without considering the market beta of the stocks

A dual-band outphasing transmitter using broadband class E power amplifiers

In this paper, a dual-band outphasing transmitter (able of operating either at 770 MHz or 960 MHz frequency bands) is presented. Two broadband RF power amplifiers (PAs) have been designed over packaged GaN HEMT devices, switching close to the nominal zero-voltage and zero-voltage-derivative class E conditions. A reactive combiner, using transmission lines of appropriate electrical lengths at both bands, together with compensating reactances, allows positioning the drain impedance loci to produce high efficiency and good dynamic range profiles. Average drain efficiency figures over 68% and 38% have been measured for WCDMA signals with a peak-to-average power ratio (PAPR) of 5.1 dB and 8.4 dB, respectively.This work was supported by MINECO through projects TEC2011-29126-C03 (-01, co funded with FEDER, and -02), and Consolider CSD2008-00068

Constant-gain envelope tracking in a UHF outphasing transmitter based on continuous-mode class-E GaN HEMT PAs

A UHF outphasing transmitter, based on continuous-mode class-E power amplifiers (PAs) and implementing a constant-gain envelope tracking (ET) strategy, is presented in this paper. Drain terminating and biasing networks are designed to provide near optima impedance values at the fundamental and higher order harmonics to the selected GaN HEMT device. A high-efficiency wideband performance, 80% for a 630-890 MHz range, is obtained, besides being amenable for load-modulation through a compact outphasing scheme, incorporating a series Chireix combiner and an impedance transformer. Once characterized in a pure output power phasecoding regime, the observed limitation in dynamic range is overcome by operating the amplifiers in a sort of continuous class-J mode, while forcing the load impedance to follow a constant-gain trajectory. A 1c-WCDMA signal, with peak-toaverage power ratio (PAPR) of 8.4 dB is shown to be reproduced, satisfying the linearity requirements, with an average efficiency of 58%.This work was supported by the Ministry of Economy and Competitiveness (MINECO) through TEC2014-58341-C4-1- R, TEC2014-58341-C4-2-R and TEC2014-58341-C4-3-R projects, co-funded with FEDER. José R. Pérez-Cisneros also thanks the support to his stay at the Univ. of Cantabria provided by the pre-doctoral mobility grant EEBB-I-15-10447