Littérature scientifique sur le sujet « Wake recover »

Abstract. Understanding wind turbine wake recovery is important for developing models of wind turbine interaction employed in the design of energy-efficient wind farm layouts. Wake recovery is often assumed or explained to be a shear-driven process; however, this is generally not accurate. In this work we show that wind turbine wakes recover mainly due to the divergence (lateral and vertical gradients) of Reynolds shear stresses, which transport momentum from the freestream towards the wake center. The wake recovery mechanisms are illustrated using a simple analytic model and results of large-eddy simulation.

Depletion of fossil fuel caused mankind to look for sustainable and green energy resources. The characteristic of hydrokinetic turbine with ability to operate at low head stream and at low cost made it a good choice for use to harness hydro source of energy. As hydrokinetic turbine gain attention from the industry player, many experimental and Computational Fluid Dynamics (CFD) studies related to hydrokinetic turbine have been carried out. Yet the relationship of flow depth variation and wake recovery behind the turbine is still not fully understood. There is limited study about the effects of flow depth variations on the wake recovery behind the turbine. In this paper, a CFD model investigation was done based on published experimental work. A hydrokinetic water turbine was drawn using the MHKF1-180 and NACA4418 foils dimensions. The transient CFD study was conducted using SST k-w turbulence model and dynamic mesh method. The results showed that in near wake region, the wake at deeper depth will recover faster seemingly due to pressure change at that depth and the faster rate of momentum transfer of the fluid. It can be concluded that the deeper the placement of the turbine inside the water channel, the faster the wake recovers. The wake recovery results as presented in this paper should be considered when placing set of turbines especially in array arrangement to obtain a more efficient energy conversion.

The flow recovery in the wake of a surface-mounted flat plate is investigated in an open channel. The plate with a thickness-to-chord ratio (t/c) of 0.12 is placed with the chord parallel to the flow. The characteristics of the mean velocity and higher-order statistics obtained along the wake axis upstream and downstream of the plate are discussed in the presence of bed roughness. Inner scaling of the mean velocity profile shows a depression in the outer region of the flow. The near-wall portion of the velocity profile in the plate wake region was found to recover faster to the upstream state. The profiles of the turbulent intensity in the plate wake deviate from the upstream profiles and recover gradually with downstream distance. The upstream turbulent intensities for the wire-mesh rough surface peak at farther wall normal locations compared to those of the sand grain and smooth surfaces. A similar roughness effect was observed at the downstream locations amidst the distorted flow, especially, in the intermediate and far wake regions. In the near- and intermediate-wake regions, both the velocity skewness and flatness factors data for the rough walls were higher compared to the data for the smooth surface. For all surfaces, even at the last measuring station (x = 200t) considered in the study, the skewness and flatness factors were found to be still recovering to the upstream condition.

Abstract. Large eddy simulations (LESs) are performed to study the wakes of a multi-rotor wind turbine configuration comprising four identical rotors mounted on a single tower. The multi-rotor turbine wakes are compared to the wake of a conventional turbine comprising a single rotor per tower with the same frontal area, hub height and thrust coefficient. The multi-rotor turbine wakes are found to recover faster, while the turbulence intensity in the wake is smaller, compared to the wake of the conventional turbine. The differences with the wake of a conventional turbine increase as the spacing between the tips of the rotors in the multi-rotor configuration increases. The differences are also sensitive to the thrust coefficients used for all rotors, with more pronounced differences for larger thrust coefficients. The interaction between multiple multi-rotor turbines is contrasted with that between multiple single-rotor turbines by considering wind farms with five turbine units aligned perfectly with each other and with the wind direction. Similar to the isolated turbine results, multi-rotor wind farms show smaller wake losses and smaller turbulence intensity compared to wind farms comprised of conventional single-rotor turbines. The benefits of multi-rotor wind farms over single-rotor wind farms increase with increasing tip spacing, irrespective of the axial spacing and thrust coefficient. The mean velocity profiles and relative powers of turbines obtained from the LES results are predicted reasonably accurately by an analytical model assuming Gaussian radial profiles of the velocity deficits and a hybrid linear-quadratic model for the merging of wakes. These results show that a larger power density can be achieved without significantly increased fatigue loads by using multi-rotor turbines instead of conventional, single-rotor turbines.

The tidal turbines represent a new frontier for extracting energy from tides source. Despite the technology being mature, new solutions aimed at improving performance, reliability with reduced environmental impact, manufacturing and installation costs are currently under investigation. The Rim-driven turbine (abbreviated as RDT) was recently proposed. A RDT resembles a ducted turbine (abbreviated as DT), as both contain blades and a duct. The present study aims at investigating the detail performance and flow field of a RDT in a real flow based on the China Zhaitang Island’s tidal current data. To show the difference between the RDT and DT, simulations are also performed on the corresponding DT. It is found that the power and thrust for the two configurations exhibit time-periodic behavior that is consistent with the wave frequency. At axial flow, the fluctuation amplitude on the power and thrust increase with the increase of tip speed ratio. The RDT has higher power output when operating at lower tip speed ratio and has a potential reduction in flow resistance and disturbance with respect to the DT. At yawed flow, the fluctuation amplitude on the power and thrust decrease with the increase of yaw angle. The RDT has less capable of compensating the effect of yawed inflow in reducing the power than the DT at larger yaw angle. In addition, the power and thrust generates micro-amplitude fluctuation integrated into the main waveform, which the frequency is consistent with the turbine rotation frequency. The wake characteristics analysis reveals that the yawed flow field is more turbulent, and the two configurations suffer strong unsteady flow separation along the whole span. Strong interactions are observed between the rotor’s main wake and the duct’s upper wake. The yaw angle primarily determines the downstream wake deflection direction and significantly changes the wake shape and vortex structures. Meanwhile, the wake flow is found to recover more quickly at larger yaw angle. Besides, due to the open-center of RDT, a part free-stream flow is allowed to travel through and forms an obvious high velocity zone. The presence of open-center of RDT has avoided the low velocity zone, improved the wake structure and accelerated wakes recover, which seems to give an advantageous effect in operating a RDT.

AbstractFor marine hydrokinetic energy to become viable, it is essential to develop energy conversion devices that are able to extract energy with high efficiency from a wide range of flow conditions and to field test them in an environment similar to the one they are designed to eventually operate in. FloDesign Inc. developed and built a mixer-ejector hydrokinetic turbine (MEHT) that encloses the turbine in a specially designed shroud that promotes wake mixing to enable increased mass flow through the turbine rotor. A scaled version of this turbine was evaluated experimentally, deployed below a purpose-built floating test platform at two open-water tidal energy test sites in New Hampshire and Massachusetts and also in a large cross-section tow tank. State-of-the-art instrumentation was used to measure the tidal energy resource and turbine wake flow velocities, turbine power extraction, test platform loadings, and platform motion induced by sea state. The MEHT was able to generate power from tidal currents over a wide range of conditions, with low-velocity start-up. The mean velocity deficit in the wake downstream of the turbine was found to recover more quickly with increasing levels of free stream turbulence, which has implications for turbine spacing in arrays.

AbstractRoughness-induced transition is one of the main parameters contributing to performance loss of airfoils. Within this paper, the disturbance evolution downstream of a single, cylindrical roughness element, which is placed in a laminar boundary layer in an airfoil leading edge region, is investigated. The experiments focus on medium height roughness elements with respect to the local boundary layer displacement thickness. Hence, transition is not directly tripped at the roughness element. The roughness diameter is comparable to the streamwise wavelength of the most amplified (linear) disturbance eigenmodes. The vortical structures observed downstream of the roughness are in agreement with previous findings in the literature. In the near roughness wake, a distinct growth of high-frequency (fundamental) modes, that is modes with a high $\def \xmlpi #1{}\def \mathsfbi #1{\boldsymbol {\mathsf {#1}}}\let \le =\leqslant \let \leq =\leqslant \let \ge =\geqslant \let \geq =\geqslant \def \Pr {\mathit {Pr}}\def \Fr {\mathit {Fr}}\def \Rey {\mathit {Re}}n$-factor at the roughness location, is observed. In the far roughness wake, these fundamental modes recover linear stability characteristics due to a possible relaxation of the mean flow. However, an interaction of particularly two-dimensional fundamental modes and by the roughness interference excited oblique fundamental modes results in an excitation of subharmonic type, low-frequency combination modes, which are associated with a phase-locked interaction mechanism. Depending on the initial growth of the fundamental modes in the near wake, the low-frequency modes can experience a nonlinear growth in the far roughness wake and, thereby, trip turbulence. The fundamental mode growth rate in the near wake in turn is a weak function of the disturbance frequency and of the pressure gradient, whereas it is decisively increasing with the roughness height, that is with the mean flow distortion caused by the roughness.

The viable but nonculturable (VBNC) state is a survival strategy for bacteria when encountered with unfavorable conditions. Under favorable environments such as nutrient supplementation, external stress elimination, or supplementation with resuscitation-promoting substances, bacteria will recover from the VBNC state, which is termed “resuscitation”. The resuscitation phenomenon is necessary for proof of VBNC existence, which has been confirmed in different ways to exclude the possibility of culturable-cell regrowth. The resuscitation of VBNC cells has been widely studied for the purpose of risk control of recovered pathogenic or spoilage bacteria. From another aspect, the resuscitation of functional bacteria can also be considered a promising field to explore. To support this point, the resuscitation mechanisms were comprehensively reviewed, which could provide the theoretical foundations for the application of resuscitated VBNC cells. In addition, the proposed applications, as well as the prospects for further applications of resuscitated VBNC bacteria in the food industry are discussed in this review.

Direct numerical simulations of the flow past a fixed oblate spheroidal bubble are carried out to determine the range of parameters within which the flow may be unstable, and to gain some insight into the instability mechanism. The bubble aspect ratio χ (i.e. the ratio of the major axis length over the minor axis length) is varied from 2.0 to 2.5 while the Reynolds number (based on the upstream velocity and equivalent bubble diameter) is varied in the range 102 ≤ Re ≤ 3 × 103. As vorticity generation at the bubble surface is at the root of the instability, theoretical estimates for the maximum of the surface vorticity and the surface vorticity flux are first derived. It is shown that, for large aspect ratios and high Reynolds numbers, the former evolves as χ8/3 while the latter is proportional to χ7/2Re−1/2. Then it is found numerically that the flow first becomes unstable for χ = χc ≈ 2.21. As the surface vorticity becomes independent of Re for large enough Reynolds number, the flow is unstable only within a finite range of Re, this range being an increasing function of χ − χc. An empirical criterion based on the maximum of the vorticity generated at the body surface is built to determine whether the flow is stable or not. It is shown that this criterion also predicts the correct threshold for the wake instability past a rigid sphere, suggesting that the nature of the body surface does not really matter in the instability mechanism. Also the first two bifurcations of the flow are similar in nature to those found in flows past rigid axisymmetric bluff bodies, such as a sphere or a disk. Wake dynamics become more complex at higher Reynolds number, until the Re−1/2-dependency of the surface vorticity flux makes the flow recover its steadiness and eventually its axisymmetry. A qualitative analysis of the azimuthal vorticity field in the base flow at the rear of the bubble is finally carried out to make some progress in the understanding of the primary instability. It is suggested that the instability originates in a thin region of the flow where the vorticity gradients have to turn almost at right angle to satisfy two different constraints, one at the bubble surface, the other within the standing eddy.

Abstract Introduction. Advance care planning (ACP) allows individuals to plan ahead and express their preferences for medical treatment and care options to health care providers, family, and loved ones before they are no longer able to make or voice decisions due to the event of a serious illness or injury. Advance directives (ADs) allow individuals to record their preferences. While unintentional injuries are the leading cause of death among young adults, limited studies focus on ACP, ADs, and end-of-life treatment and care. Our study aims to (1) examine the perspectives of young adults towards Five Wishes, and (2) measure their preferences related to personal, emotional, spiritual, and medical values in end-of-life care planning. Methods. Data were collected using Five Wishes and a one-time questionnaire. Participants include graduate students (n=30) at a New York State university. The average age was 24 years old (60% were female, 60% White, and 27% Black). Results. In the case of permanent and severe brain damage without expectation to wake up or recover, 63% do not want life-support treatment. In the event of coma without expectation to wake up or recover, 53% do not want life-support treatment. When close to death, 80% want to have religious or spiritual readings and well-loved - poems read aloud. Conclusions. Young adults are capable of making their decisions regarding appointing a health care proxy and giving specific instructions for personal, emotional, spiritual, and medical care. The present findings intend to make contributions in promoting population-based healthcare decision-making, education, and awareness.

Although previous studies on structural equation modeling (SEM) have indicated that the second-order latent growth model (SOLGM) is a more appropriate approach to longitudinal intervention effects, its application still requires researchers to collect at least three-wave data (e.g. randomized pretest, posttest, and follow-up design). However, in some circumstances, researchers can only collect two-wave data for resource limitations. With only two-wave data, the SOLGM can not be identified and researchers often choose alternative SEM models to fit two-wave data. Recent studies show that the two-wave longitudinal common factor model (2W-LCFM) and latent change score model (2W-LCSM) can perform well for comparing latent change between groups. However, there still lacks empirical evidence about how accurately these two-wave models can estimate the group effects of latent change obtained by three-wave SOLGM (3W-SOLGM). The main purpose of this dissertation, therefore, is trying to examine to what extent the fixed effects of the tree-wave SOLGM can be recovered from the parameter estimates of the two-wave LCFM and LCSM given different simulation conditions. Fundamentally, the supplementary study (study 2) using three-wave LCFM was established to help justify the logistics of different model comparisons in our main study (study 1). The data generating model in both studies is 3W-SOLGM and there are in total 5 simulation factors (sample size, group differences in intercept and slope, the covariance between the slope and intercept, size of time-specific residual, change the pattern of time-specific residual). Three main types of evaluation indices were used to assess the quality of estimation (bias/relative bias, standard error, and power/type I error rate). The results in the supplementary study show that the performance of 3W-LCFM and 3W-LCSM are equivalent, which further justifies the different models' comparison in the main study. The point estimates for the fixed effect parameters obtained from the two-wave models are unbiased or identical to the ones from the three-wave model. However, using two-wave models could reduce the estimation precision and statistical power when the time-specific residual variance is large and changing pattern is heteroscedastic (non-constant). Finally, two real datasets were used to illustrate the simulation results
Doctor of Philosophy
To collect and analyze the longitudinal data is a very important approach to understand the phenomenon of development in the real world. Ideally, researchers who are interested in using a longitudinal framework would prefer collecting data at more than two points in time because it can provide a deeper understanding of the developmental processes. However, in real scenarios, data may only be collected at two-time points. With only two-wave data, the second-order latent growth model (SOLGM) could not be used. The current dissertation compared the performance of two-wave models (longitudinal common factor model and latent change score model) with the three-wave SOLGM in order to better understand how the estimation quality of two-wave models could be comparable to the tree-wave model. The results show that on average, the estimation from two-wave models is identical to the ones from the three-wave model. So in real data analysis with only one sample, the point estimate by two-wave models should be very closed to that of the three-wave model. But this estimation may not be as accurate as it is obtained by the three-wave model when the latent variable has large variability in the first or last time point. This latent variable is more likely to exist as a statelike construct in the real world. Therefore, the current study could provide a reference framework for substantial researchers who could only have access to two-wave data but are still interested in estimating the growth effect that supposed to obtain by three-wave SOLGM.

This thesis is based on the research project of a W-band gyrotron backward wave oscillator (gyro-BWO) using a helically corrugated waveguide which is currently being built and upgraded in the University of Strathclyde. The gyro-BWO was optimally designed through numerical simulations to achieve an output maximum power of ~ 10 kW with a -3 dB frequency tuning range of 84 - 104 GHz. To increase the overall efficiency of the W-band gyro-BWO, an energy recovery system of four-stage depressed collector was designed, numerically optimized and fabricated on the gyro-BWO. Microwave components including the Bragg reflectors, the side-wall coupler, the three-layer microwave window and the pillbox window were designed, simulated and measured to facilitate the practical use of the energy recovery system. This thesis includes the analytically calculated results, the numerical simulations as well as the experimental results of the said components and system. A 14-section Bragg reflector together with the side-wall coupler located at the upstream of the helically corrugated interaction cavity was used to couple the microwave radiation out. This allowed the installation of the depressed collector at the downstream side of the gyro-BWO. The transmission coefficient of the coupler was numerically optimized to achieve -1.0 dB over the frequency tuning range, from 84 - 104 GHz. The Bragg reflector measurement agrees well with the simulation. The input coupler achieves an average -13 dB reflection over the frequency in the measurement. Theoretical analysis of the pillbox type window and multi-layer window based on mode-matching method was carried out. The simulation and optimization of the pillbox window achieved a reflection of less than -15 dB in the whole operating frequency range of 84 - 104 GHz. The three-layer window can achieve less than 30 dB reflection in the frequency range of 84 - 104 GHz in the simulation. A three-layer window and a pillbox window which particularly optimized in frequency range of 90 - 100 GHz (the operating frequency range of the gyro- TW A that shares the same experimental setup as the gyro-BWO) were fabricated. With manufacturing constraints the design of the three-layer window achieved an average -10 dB measured reflection in 84 - 104 GHz and better than -15 dB in 90 - 100 GHz. In the downstream side of the gyro-BWO, another 18-section Bragg reflector was used to reflect the radiation back into the upstream interaction cavity. And the transmission coefficient of -30 dB was obtained in the microwave measurements using a VNA, which means the microwave power leakage was less than 1%. The measurement results agreed well with the simulations. A four-stage depressed collector was designed to recover the energy from the spent electrons. The 3D PlC code MAGIC and a genetic algorithm were used to simulate and optimize the geometry of the electrodes. Secondary electron emissions were simulated and a few emission models were compared to investigate their effects on the overall recovery efficiency and the backstreaming rate for the multistage collector. The optimization of the shape and dimensions of each stage of the collector using a genetic algorithm achieved an overall recovery efficiency of about 70%, with a minimized backstreaming rate of 4.9%. The heat distribution on the collector was calculated and the maximum heat density on the electrodes was 240W/cm2 and the generation of "hot spots" could be avoided. The electric field distribution inside the depressed collector was calculated and the geometries of these electrodes were properly shaped to avoid the voltage breakdown in vacuum.

In the past decade there has been a significant increase in focus on the effect upper body vibration (UBV) has on the recovery of skeletal muscle after exercise-induced muscle damage. Recovery can be defined and investigated using a wide variety of methods. This study used three different measurements to track muscle recovery over 7 days following an exercise muscle damage protocol and applied vibration to a mathematical model. A visual analog scale (VAS) was used to measure muscle pain, a strain gauge was used to obtain maximum voluntary isometric contraction (MVIC) strength measurements, and shear wave elastography (SWE) represented muscle stiffness over the 7-day experiment. Thirty-three participants were divided into three groups. The first was a control group (C) that experienced no exercise and no therapy. The no vibration group (NV) performed the damage an exercise protocol but received no therapy. The vibration group (V) performed the same exercise protocol but also received vibration therapy. The exercise protocol consisted of 100 dumbbell curls at starting at 50% of their MVIC with one minute of rest after each set of ten. The data provided convincing evidence (27.2%, p < 0.0001) that group NV was not back to its normal stiffness after 7 days unlike group V, which was shown not to be any different from its baseline at the end of the week (9.15%, p = 0.137). Three vibration factors (����1, ����2, ����3) were added to a skeletal muscle regeneration model (SK) to simulate how vibration affects muscle regeneration. The three factors were determined by analyzing previous research to understand how vibration affects cells in the regeneration process. Adding these into SK decreased the time to recovery from about 13 days to about 7 days. Recovery was defined by reaching 10% of the original number of myofibers within the damaged muscle.

This study employed a qualitative approach to explore the factors that contribute to positive change and growth following a natural disaster. The qualitative methodology included narrative interviews and family group interviews that were conducted with six families in Florida that had experienced two or three hurricanes within six weeks in 2004. Narrative analysis and thematic analysis were used to discover what factors contributed to participants experiencing positive growth. Participants described the experience of surviving and coping with the hurricane. Participants reported that preparation before a hurricane was a three-part process that involved physical, mental, and emotional preparation. Four actions were referred to as helpful to stay positive during a hurricane: (a) drawing on family, friends, and neighbors for continual emotional support; (b) keeping occupied with a fun activity; (c) leaning on religious faith; (d) and listening to up-to-date information. Families described nine sources of support that enabled them to cope after the hurricane: (a) the government, (b) charitable organizations, (c) homeowner's insurance, (d) family, (e) friends, (f) religious faith, (g) stories, (h) life perspective, and (i) music. Participants reported eight factors that encouraged adversarial growth. Communicating emotional support within relationships was the most commonly cited factor in recovery and growth after a hurricane, followed by worldview, appreciation, religious faith, patience, self-reliance, teamwork, and creativity. A holistic approach to disaster planning that includes consideration of those elements that contribute to positive growth for the survivor is recommended. Further research is needed to understand how to facilitate adversarial growth among disaster survivors through emotional support and interpersonal networks.

Plane-wave decomposition by sparse recovery is a reliable and accurate technique for plane-wave decomposition which can be used for source localization, beamforming, etc. In this work, we introduce techniques to accelerate the plane-wave decomposition by sparse recovery. The method consists of two main algorithms which are spherical Fourier transformation (SFT) and sparse recovery. Comparing the two algorithms, the sparse recovery is the most computationally intensive. We implement the SFT on an FPGA and the sparse recovery on a multithreaded computing platform. Then the multithreaded computing platform could be fully utilized for the sparse recovery. On the other hand, implementing the SFT on an FPGA helps to flexibly integrate the microphones and improve the portability of the microphone array. For implementing the SFT on an FPGA, we develop a scalable FPGA design model that enables the quick design of the SFT architecture on FPGAs. The model considers the number of microphones, the number of SFT channels and the cost of the FPGA and provides the design of a resource optimized and cost-effective FPGA architecture as the output. Then we investigate the performance of the sparse recovery algorithm executed on various multithreaded computing platforms (i.e., chip-multiprocessor, multiprocessor, GPU, manycore). Finally, we investigate the influence of modifying the dictionary size on the computational performance and the accuracy of the sparse recovery algorithms. We introduce novel sparse-recovery techniques which use non-uniform dictionaries to improve the performance of the sparse recovery on a parallel architecture.

Nei nodi wireless per applicazioni IoT, i ricetrasmettitori (transceiver) a radio-frequenza (RF) sono responsabili della maggior parte del consumo di potenza. Inoltre, se da un lato il picco di potenza assorbita avviene in corrispondenza degli istanti di trasmissione, dall’altro il ricevitore, che deve essere mantenuto sempre attivo anche quando il resto del sistema è in stato di “idle”, consuma una buona frazione dell’energia totale. Al fine di ridurre questo consumo, una particolare tipologia di ricevitori detti di “wake-up” sono tra i principali oggetti di ricerca nell’ambito dell’IoT. Essi hanno prestazioni ridotte e consumo molto basso, poiché devono restare sempre attivi mentre il resto del nodo è in stato di “idle”. Tale Wake-Up Radio (WUR) ha il compito di “ascoltare” il canale e attivare il ricevitore principale ed il microcontrollore solo quando c’è qualche richiesta in arrivo. Una parte integrante del ricevitore Wake-Up è il circuito per la decodifica dei byte trasmessi, che di solito comprendono almeno un codice d’indirizzo, che deve essere estratto e confrontato con l’indirizzo memorizzato nel ricevitore. Soltanto se questo confronto ha esito positivo viene attivato il resto del sistema. L’obiettivo di questo lavoro di tesi è il progetto di un sistema di clock recovery basato su PLL analogico a bassissimo consumo per sistemi Wake-Up Radio di tipo short-range caratterizzati da una bit rate di 1 kbps. Tale sistema deve fornire alla rete di controllo un clock allineato in fase e frequenza con i dati ricevuti. Rispetto ad altri sistemi in cui si deve semplicemente decodificare un indirizzo, la soluzione basata su PLL oggetto di questo studio (poiché implica consumi e tempi di aggancio non trascurabili) è particolarmente adatta per lunghe trasmissioni. Nel progetto di un PLL a basso consumo l’obiettivo consiste nell’ottimizzare il trade-off tra consumo (con correnti nell’ordine del nanowatt) e tempo di aggancio.

Over the years it has been speculated that the performance of multi-stage axial flow compressors is enhanced by the passage of a wake through a blade row prior to being mixed-out by viscous diffusion. The link between wake mixing and performance depends on the ability to recover the total pressure deficit of a wake by a reversible flow process. This paper shows that such a process exists, it is unsteady, and is associated with the kinematics of the wake vorticity field. The analysis shows that the benefits of wake total pressure recovery can be estimated from linear theory and quantified in terms of a volume integral involving the deterministic stress and the mean strain rate. In the limit of large reduced frequency the recovery process is shown to be a direct function of blade circulation. Results are presented which show that the recovery process can reduce the wake mixing loss by as much as seventy percent. Under certain circumstances this can lead to nearly a point improvement in stage efficiency, a nontrivial amount.

Heat transfer and flow behavior in the mini tube bank were examined. The tube bank was composed of 1 mm diameter nickel wires and a 30 mm wide × 15 mm high flow channel. Experiments were performed in the range of the rod Re = 5 ~ 430 by using water. Numerical analyses were also conducted with the commercial CFD code STAR-CD. The heat transfer coefficient after the second row was lower than first row's one. The flow visualization results indicated that the wake region was stagnant when the Reynolds number was low. This flow stagnation seemed to cause the heat transfer coefficient deterioration in the tube bank. As the Reynolds number was increased, the flow state in the wake region gradually changed from the stagnant condition to the more disturbed condition. The deeper the row was, the more disturbed the wake was. The heat transfer coefficient began to recover to the first row value at certain Reynolds number. The recovery started from the most downstream row; fifth row in the present experiments and was propagated to the upstream row. The Reynolds number when the recovery was initiated decreased as the spacing between rods was increased. The analytical results of the STAR-CD code supported the experimental results. When the wake was stagnant, the heat transfer coefficient distribution around the rear rod, i.e. the rod in the wake, showed a large dip in the front region of the rod. It was considered that this dip caused the heat transfer coefficient decrease after the second row observed in the experiments.

The stern boat deployment system was investigated to evaluate the capability of launching and recovering RHIB via the stern ramp. The main parameters to launch and recover RHIB were tested at the design stage. The combined hydrodynamic effect of the stern wake and the water jet flow made it difficult to maintain the maneuvering and seakeeping ability of RHIB approaching to the stern ramp. The safe recovery course was proposed to maintain the directional control of RHIB and to reduce the combined hydrodynamic effect in the transom zone. To evaluate the feasibility of RHIB recovery, the stern sill depth was measured in various conditions and the ramp availability time was obtained. Also, the experimental PTO test was performed by the number of successive launching and recovering operations.

PIV measurements were made to investigate the turbulent wake flow generated by a vertical sharp-edged flat plate suspended in a shallow channel flow with a gap near the bed. The purpose of this study is to investigate the behaviour of large vortical structures in the wake flow. The investigation focused on the horizontal velocity field in the mid-distance between the bottom bed and the top free surface. Two different gap heights between the channel bed and the bottom edge of the bluff body was studied. These two cases were compared to the no-gap flow case which is considered as a reference case. The Reynolds number based on the water depth was 45,000. The large vortical structures were exposed by analyzing the PIV velocity fields using the proper orthogonal decomposition (POD) method. Only few modes were used for the POD reconstruction of the velocity fields to recover ∼50% of the turbulent kinetic energy. A vortex identification algorithm was then employed to quantify the number, size, circulation, and direction of rotation of the exposed vortices. A statistical analysis of the distribution of number, size, and strength of the identified vortices was carried out to explore the characteristics of the vortical structures. The results revealed that the number of vortical structures increased as a result of the gap flow with a corresponding decrease in the vortex size and strength. This behaviour is attributed to the production of new vortices and the enhancement of the tearing process.

Heat transfer and flow behavior in a mini-tube bank was examined. The tube bank was simulated with wires of 1 mm diameter. The wires were arranged in the 5×5 in-line array and the 5×5 staggered array with the arranging pitch = 3. Experiments were performed in the range of the tube Reynolds number Re = 4 ∼ 3,500. Numerical analyses were also performed with the commercial CFD code of STAR-CD. The heat transfer coefficient of the tube of the first row was well expressed with the existing heat transfer correlations. In the case of the in-line array, unlike usual sized tube banks, the measured heat transfer coefficients of the tubes after the second row were lower than those of the first row and the difference between those increased as the Reynolds number was increased. At approximately Reynolds number ≃ 50, the difference turned to decrease; the heat transfer coefficients initiate to recover to the first row value. Then, the heat transfer coefficient in the rear row became larger at approximately Re ≃ 1,000 than that of the first row. In the case of the staggered array, the decrease in the heat transfer coefficient in the rear row was smaller than that in the case of the in-line array. The recovery of the heat transfer coefficient to the first row value started at a little bit lower Reynolds number and it exceeded the first row value at approximately Re ≃ 700. The flow visualization results and also the STAR-CD analytical results indicated that when the Reynolds number was low, the wake region of the preceding tube was stagnant. This flow stagnation caused the heat transfer deterioration in the front part of the rear tube, which resulted in the lower heat transfer coefficient of the rear tube than that of the first row. As the Reynolds number was increased, the flow state in the wake region changed from the stagnant condition to the more disturbed condition by periodical shedding of the Karman vortex. This change caused the recovery of the heat transfer in the front region of the rear tube, which resulted in the recovery of the heat transfer coefficient of the rear tube.

Abstract A numerical analysis based on Computational Fluid Dynamics (CFD) is carried out to investigate the influence of the fuselage transition and axial offset, on the inlet distortion and performance of a tail mounted fan, for a short-haul commuter aircraft. For the examined configurations, it is predicted that varying the angle of the fuselage transition does not have a significant impact on the radial distortion, for a typical fan mounted at the centreline of the fuselage. The wake behind the fuselage is predicted to increase in size as the slope of the fuselage is increased, however, the positive suction from the fan is sufficient for the flow to fully recover before the fan duct inlet. Nevertheless, it is predicted that offsetting the fan from the fuselage centreline produces a more significant increase in distortion in the circumferential direction. The propulsive power of the fan is predicted to increase slightly with increasing offset mainly due to the side of the fan which is less obstructed by the fuselage. However, the wake on the opposite side is predicted to increase significantly persisting almost to the inlet of the fan duct. A vortex formed upstream of the fan increases in strength with increasing offset. This vortex helps to offset the increase in circumferential distortion by re-energizing the flow in the wake of the fuselage. This causes the circumferential distortion to remain roughly constant between offsets of 25% and 50% of the fuselage radius. It is likely though that this vortex will deteriorate the performance of the fan.

Abstract The development of the wind energy sector has to come with an increase in wind turbine and wind farm efficiency. This increase can be achieved through the use of CFD tools that allow to accurately predict, at a reasonable cost, the efficiency of new wind turbine designs, wind farm layouts and control strategies. In this context, high order CFD tools such as the ones based on the LES approach are required to develop and calibrate lower order models that can be used for industry purposes. The aim of the present study is to assess the ability of CERFACS’ LES solver developed for turbo-machinery applications — AVBP — to perform high fidelity simulations of wind turbine flows. To this end, a wall-modelled approach was chosen to describe the boundary layer on the blades. In addition, A static mesh adaptation method was developed to optimise the mesh size while accurately resolving the turbine wake. Finally, a Pressure Gradient Scaling method [1] was applied to artificially relax the compressible flow CFL condition to a low-mach one and increase the time step. The aforementioned framework was assessed on reduced wind turbine configurations developed and experimentally investigated by NTNU. Although the Reynolds number of these configurations is one to two orders of magnitude inferior to real wind turbine one, the controlled boundary conditions and the available experimental data make these configurations particularly interesting for code validation. Two configurations have been simulated. The results show the ability of the numerical approach to capture the transition between near and far wake and the interaction between inflow turbulence and the wake. The comparison with experimental measurements shows that simulations accurately predict the velocity deficit and recover the right amount of turbulent kinetic energy at the beginning of the far wake. As a conclusion, the framework developed in this study is adapted to reduced turbine computation yet it has to be further validated on real scale wind turbines.

Semiconductor optical amplifiers will be important components for high-repetition rate optical systems, such as optical time division multiplexed systems [1]. Several groups have studied the properties of optical amplifiers when used with ultrashort input optical pulses [2-4]. If the input pulse is sufficiently energetic, it can compress (saturate) the gain of the amplifier by removal of a fraction of carriers from the active region by stimulated emission [2,4]. After passage of the input pulse, the amplifier gain will recover with a time constant, τ. When the separation between input pulses becomes comparable to or smaller than τ, the gain experienced by a particular pulse will depend on the previous pulse pattern incident on the amplifier, because the gain may not have time to recover to its original value between pulses. Thus, it is important to understand the effect of gain recovery on the gain experienced by a randomly modulated pulse stream, because the finite gain recovery time may lead to inter-symbol interference (ISI). To gain insight into this problem, we study gain compression of an InGaAsP optical amplifier when used with multi-gigahertz repetition rate pulse streams.

In the combustor inlet diffuser section of gas turbine engine, high-velocity air from compressor flows into the diffuser, where a considerable portion of the inlet velocity head PT3 − PS3 is converted to static pressure (PS) before the airflow enters the combustor. Modern high through-flow turbine engine compressors are highly loaded and usually have high inlet Mach numbers. With high compressor exit Mach numbers, the velocity head at the compressor exit station may be as high as 10% of the total pressure. The function of the diffuser is to recover a large proportion of this energy. Otherwise, the resulting higher total pressure loss would result in a significantly higher level of engine specific fuel consumption. The diffuser performance must also be sensitive to inlet velocity profiles and geometrical variations of the combustor relative to the location of the pre-diffuser exit flow path. Low diffuser pressure losses with high Mach numbers are more rapidly achieved with increasing length. However, diffuser length must be short to minimize engine length and weight. A good diffuser design should have a well considered balance between the confliction requirements for low pressure losses and short engine lengths. The present paper describes the effect of divergence angle on diffuser performance for gas turbine combustion chamber using Computational Fluid Dynamic Approach. The flow through the diffuser is numerically solved for divergence angles ranging from 5 to 25°. The flow separation and formation of wake regions are studied.

Recent publications have demonstrated the influence of unsteady work terms on the inviscid recovery of wake momentum. So far, this so-called wake differential work effect was only validated based on selected locations and time steps in turbine rotors. The magnitude of this effect over a whole blade passing cycle and the local unsteady work mechanisms causing it are still not fully understood. Using a numerical simulation, the unsteady static pressure field of a turbine rotor is assessed. Three regions are identified in which work is transfered unsteadily to the fluid, caused by the fluid interaction with the unsteady rotor pressure field. A Lagrangian analysis is performed to validate and quantify the wake differential work concept. To be representative, a large number of wake and free stream fluid particle paths are evaluated. Overall, a 7 per cent lower wake work in the rotor is identified, averaged over a whole blade passing cycle. From a particle point of view, the rotor pressure field acts as a pressure wave propagating in circumferential direction. Due to inviscid unsteady work, this pressure wave influences the stagnation enthalpy of the fluid particles. It is shown that this effect is more dominant for wake fluid, as the wake velocity is closer to the propagation velocity of the pressure wave. A mathematical model of this so-called “wake surfing effect” and the two other unteady work mechanisms reveals how the wake momentum is recovered depending on the initial wake velocity vector. If exploited well, this unsteady work mechanism could cause a reduction of wake mixing loss, leading to an increased turbine efficiency.

The report shows that wages and the purchasing power of households have been dented considerably during the past three years, first by the COVID-19 pandemic and then, as the world economy started to recover from that crisis, by the global rise in inflation. Available evidence for 2022 suggests that rising inflation is causing real wage growth to dip into negative figures in many countries, reducing the purchasing power of the middle class and hitting low-income groups particularly hard. This cost-ofliving crisis comes on top of significant losses in the total wage bill for workers and their families during the COVID-19 crisis, which in many countries had the greatest impact on low-income groups. In the absence of adequate policy responses, the near future could see a sharp erosion of the real incomes of workers and their families and an increase in inequality, threatening the economic recovery and possibly fuelling further social unrest.

1.1 Macroeconomic summary Economic recovery has consistently outperformed the technical staff’s expectations following a steep decline in activity in the second quarter of 2020. At the same time, total and core inflation rates have fallen and remain at low levels, suggesting that a significant element of the reactivation of Colombia’s economy has been related to recovery in potential GDP. This would support the technical staff’s diagnosis of weak aggregate demand and ample excess capacity. The most recently available data on 2020 growth suggests a contraction in economic activity of 6.8%, lower than estimates from January’s Monetary Policy Report (-7.2%). High-frequency indicators suggest that economic performance was significantly more dynamic than expected in January, despite mobility restrictions and quarantine measures. This has also come amid declines in total and core inflation, the latter of which was below January projections if controlling for certain relative price changes. This suggests that the unexpected strength of recent growth contains elements of demand, and that excess capacity, while significant, could be lower than previously estimated. Nevertheless, uncertainty over the measurement of excess capacity continues to be unusually high and marked both by variations in the way different economic sectors and spending components have been affected by the pandemic, and by uneven price behavior. The size of excess capacity, and in particular the evolution of the pandemic in forthcoming quarters, constitute substantial risks to the macroeconomic forecast presented in this report. Despite the unexpected strength of the recovery, the technical staff continues to project ample excess capacity that is expected to remain on the forecast horizon, alongside core inflation that will likely remain below the target. Domestic demand remains below 2019 levels amid unusually significant uncertainty over the size of excess capacity in the economy. High national unemployment (14.6% for February 2021) reflects a loose labor market, while observed total and core inflation continue to be below 2%. Inflationary pressures from the exchange rate are expected to continue to be low, with relatively little pass-through on inflation. This would be compatible with a negative output gap. Excess productive capacity and the expectation of core inflation below the 3% target on the forecast horizon provide a basis for an expansive monetary policy posture. The technical staff’s assessment of certain shocks and their expected effects on the economy, as well as the presence of several sources of uncertainty and related assumptions about their potential macroeconomic impacts, remain a feature of this report. The coronavirus pandemic, in particular, continues to affect the public health environment, and the reopening of Colombia’s economy remains incomplete. The technical staff’s assessment is that the COVID-19 shock has affected both aggregate demand and supply, but that the impact on demand has been deeper and more persistent. Given this persistence, the central forecast accounts for a gradual tightening of the output gap in the absence of new waves of contagion, and as vaccination campaigns progress. The central forecast continues to include an expected increase of total and core inflation rates in the second quarter of 2021, alongside the lapse of the temporary price relief measures put in place in 2020. Additional COVID-19 outbreaks (of uncertain duration and intensity) represent a significant risk factor that could affect these projections. Additionally, the forecast continues to include an upward trend in sovereign risk premiums, reflected by higher levels of public debt that in the wake of the pandemic are likely to persist on the forecast horizon, even in the context of a fiscal adjustment. At the same time, the projection accounts for the shortterm effects on private domestic demand from a fiscal adjustment along the lines of the one currently being proposed by the national government. This would be compatible with a gradual recovery of private domestic demand in 2022. The size and characteristics of the fiscal adjustment that is ultimately implemented, as well as the corresponding market response, represent another source of forecast uncertainty. Newly available information offers evidence of the potential for significant changes to the macroeconomic scenario, though without altering the general diagnosis described above. The most recent data on inflation, growth, fiscal policy, and international financial conditions suggests a more dynamic economy than previously expected. However, a third wave of the pandemic has delayed the re-opening of Colombia’s economy and brought with it a deceleration in economic activity. Detailed descriptions of these considerations and subsequent changes to the macroeconomic forecast are presented below. The expected annual decline in GDP (-0.3%) in the first quarter of 2021 appears to have been less pronounced than projected in January (-4.8%). Partial closures in January to address a second wave of COVID-19 appear to have had a less significant negative impact on the economy than previously estimated. This is reflected in figures related to mobility, energy demand, industry and retail sales, foreign trade, commercial transactions from selected banks, and the national statistics agency’s (DANE) economic tracking indicator (ISE). Output is now expected to have declined annually in the first quarter by 0.3%. Private consumption likely continued to recover, registering levels somewhat above those from the previous year, while public consumption likely increased significantly. While a recovery in investment in both housing and in other buildings and structures is expected, overall investment levels in this case likely continued to be low, and gross fixed capital formation is expected to continue to show significant annual declines. Imports likely recovered to again outpace exports, though both are expected to register significant annual declines. Economic activity that outpaced projections, an increase in oil prices and other export products, and an expected increase in public spending this year account for the upward revision to the 2021 growth forecast (from 4.6% with a range between 2% and 6% in January, to 6.0% with a range between 3% and 7% in April). As a result, the output gap is expected to be smaller and to tighten more rapidly than projected in the previous report, though it is still expected to remain in negative territory on the forecast horizon. Wide forecast intervals reflect the fact that the future evolution of the COVID-19 pandemic remains a significant source of uncertainty on these projections. The delay in the recovery of economic activity as a result of the resurgence of COVID-19 in the first quarter appears to have been less significant than projected in the January report. The central forecast scenario expects this improved performance to continue in 2021 alongside increased consumer and business confidence. Low real interest rates and an active credit supply would also support this dynamic, and the overall conditions would be expected to spur a recovery in consumption and investment. Increased growth in public spending and public works based on the national government’s spending plan (Plan Financiero del Gobierno) are other factors to consider. Additionally, an expected recovery in global demand and higher projected prices for oil and coffee would further contribute to improved external revenues and would favor investment, in particular in the oil sector. Given the above, the technical staff’s 2021 growth forecast has been revised upward from 4.6% in January (range from 2% to 6%) to 6.0% in April (range from 3% to 7%). These projections account for the potential for the third wave of COVID-19 to have a larger and more persistent effect on the economy than the previous wave, while also supposing that there will not be any additional significant waves of the pandemic and that mobility restrictions will be relaxed as a result. Economic growth in 2022 is expected to be 3%, with a range between 1% and 5%. This figure would be lower than projected in the January report (3.6% with a range between 2% and 6%), due to a higher base of comparison given the upward revision to expected GDP in 2021. This forecast also takes into account the likely effects on private demand of a fiscal adjustment of the size currently being proposed by the national government, and which would come into effect in 2022. Excess in productive capacity is now expected to be lower than estimated in January but continues to be significant and affected by high levels of uncertainty, as reflected in the wide forecast intervals. The possibility of new waves of the virus (of uncertain intensity and duration) represents a significant downward risk to projected GDP growth, and is signaled by the lower limits of the ranges provided in this report. Inflation (1.51%) and inflation excluding food and regulated items (0.94%) declined in March compared to December, continuing below the 3% target. The decline in inflation in this period was below projections, explained in large part by unanticipated increases in the costs of certain foods (3.92%) and regulated items (1.52%). An increase in international food and shipping prices, increased foreign demand for beef, and specific upward pressures on perishable food supplies appear to explain a lower-than-expected deceleration in the consumer price index (CPI) for foods. An unexpected increase in regulated items prices came amid unanticipated increases in international fuel prices, on some utilities rates, and for regulated education prices. The decline in annual inflation excluding food and regulated items between December and March was in line with projections from January, though this included downward pressure from a significant reduction in telecommunications rates due to the imminent entry of a new operator. When controlling for the effects of this relative price change, inflation excluding food and regulated items exceeds levels forecast in the previous report. Within this indicator of core inflation, the CPI for goods (1.05%) accelerated due to a reversion of the effects of the VAT-free day in November, which was largely accounted for in February, and possibly by the transmission of a recent depreciation of the peso on domestic prices for certain items (electric and household appliances). For their part, services prices decelerated and showed the lowest rate of annual growth (0.89%) among the large consumer baskets in the CPI. Within the services basket, the annual change in rental prices continued to decline, while those services that continue to experience the most significant restrictions on returning to normal operations (tourism, cinemas, nightlife, etc.) continued to register significant price declines. As previously mentioned, telephone rates also fell significantly due to increased competition in the market. Total inflation is expected to continue to be affected by ample excesses in productive capacity for the remainder of 2021 and 2022, though less so than projected in January. As a result, convergence to the inflation target is now expected to be somewhat faster than estimated in the previous report, assuming the absence of significant additional outbreaks of COVID-19. The technical staff’s year-end inflation projections for 2021 and 2022 have increased, suggesting figures around 3% due largely to variation in food and regulated items prices. The projection for inflation excluding food and regulated items also increased, but remains below 3%. Price relief measures on indirect taxes implemented in 2020 are expected to lapse in the second quarter of 2021, generating a one-off effect on prices and temporarily affecting inflation excluding food and regulated items. However, indexation to low levels of past inflation, weak demand, and ample excess productive capacity are expected to keep core inflation below the target, near 2.3% at the end of 2021 (previously 2.1%). The reversion in 2021 of the effects of some price relief measures on utility rates from 2020 should lead to an increase in the CPI for regulated items in the second half of this year. Annual price changes are now expected to be higher than estimated in the January report due to an increased expected path for fuel prices and unanticipated increases in regulated education prices. The projection for the CPI for foods has increased compared to the previous report, taking into account certain factors that were not anticipated in January (a less favorable agricultural cycle, increased pressure from international prices, and transport costs). Given the above, year-end annual inflation for 2021 and 2022 is now expected to be 3% and 2.8%, respectively, which would be above projections from January (2.3% and 2,7%). For its part, expected inflation based on analyst surveys suggests year-end inflation in 2021 and 2022 of 2.8% and 3.1%, respectively. There remains significant uncertainty surrounding the inflation forecasts included in this report due to several factors: 1) the evolution of the pandemic; 2) the difficulty in evaluating the size and persistence of excess productive capacity; 3) the timing and manner in which price relief measures will lapse; and 4) the future behavior of food prices. Projected 2021 growth in foreign demand (4.4% to 5.2%) and the supposed average oil price (USD 53 to USD 61 per Brent benchmark barrel) were both revised upward. An increase in long-term international interest rates has been reflected in a depreciation of the peso and could result in relatively tighter external financial conditions for emerging market economies, including Colombia. Average growth among Colombia’s trade partners was greater than expected in the fourth quarter of 2020. This, together with a sizable fiscal stimulus approved in the United States and the onset of a massive global vaccination campaign, largely explains the projected increase in foreign demand growth in 2021. The resilience of the goods market in the face of global crisis and an expected normalization in international trade are additional factors. These considerations and the expected continuation of a gradual reduction of mobility restrictions abroad suggest that Colombia’s trade partners could grow on average by 5.2% in 2021 and around 3.4% in 2022. The improved prospects for global economic growth have led to an increase in current and expected oil prices. Production interruptions due to a heavy winter, reduced inventories, and increased supply restrictions instituted by producing countries have also contributed to the increase. Meanwhile, market forecasts and recent Federal Reserve pronouncements suggest that the benchmark interest rate in the U.S. will remain stable for the next two years. Nevertheless, a significant increase in public spending in the country has fostered expectations for greater growth and inflation, as well as increased uncertainty over the moment in which a normalization of monetary policy might begin. This has been reflected in an increase in long-term interest rates. In this context, emerging market economies in the region, including Colombia, have registered increases in sovereign risk premiums and long-term domestic interest rates, and a depreciation of local currencies against the dollar. Recent outbreaks of COVID-19 in several of these economies; limits on vaccine supply and the slow pace of immunization campaigns in some countries; a significant increase in public debt; and tensions between the United States and China, among other factors, all add to a high level of uncertainty surrounding interest rate spreads, external financing conditions, and the future performance of risk premiums. The impact that this environment could have on the exchange rate and on domestic financing conditions represent risks to the macroeconomic and monetary policy forecasts. Domestic financial conditions continue to favor recovery in economic activity. The transmission of reductions to the policy interest rate on credit rates has been significant. The banking portfolio continues to recover amid circumstances that have affected both the supply and demand for loans, and in which some credit risks have materialized. Preferential and ordinary commercial interest rates have fallen to a similar degree as the benchmark interest rate. As is generally the case, this transmission has come at a slower pace for consumer credit rates, and has been further delayed in the case of mortgage rates. Commercial credit levels stabilized above pre-pandemic levels in March, following an increase resulting from significant liquidity requirements for businesses in the second quarter of 2020. The consumer credit portfolio continued to recover and has now surpassed February 2020 levels, though overall growth in the portfolio remains low. At the same time, portfolio projections and default indicators have increased, and credit establishment earnings have come down. Despite this, credit disbursements continue to recover and solvency indicators remain well above regulatory minimums. 1.2 Monetary policy decision In its meetings in March and April the BDBR left the benchmark interest rate unchanged at 1.75%.

This report shows that Latin America and the Caribbean faces critical policy challenges going forward. It must accelerate the digital transformation to allow businesses and consumers to adapt to a new normal and leverage pandemic recovery to create stronger economies, and also tackle long-standing barriers to adopting digital technologies and bridging digital divides. These have impeded sustained and equitable economic growth even before the pandemic struck. This crisis should be a wake-up call for governments, the private sector, civil society, and international development partners to come together and take concerted actions to advance on consistent, long-term, and sustainable e-commerce strategies that are at the forefront of national and regional productive development agendas. Just as digital solutions allowed countries to overcome the increased role of distance within the context of the pandemic in shaping consumption and business, they should also be harnessed to increase regional economic integration beyond this emergency situation.

This paper assesses whether the Covid-19 pandemic accelerated automation in developing countries. We studied the case of Colombia, a country with low R&D and productivity and with high labor informality and unemployment. We estimated event-study models to assess the differential effect of the pandemic on job openings and salaried employment by the potential degree of automation of each occupation. Our results suggest that both vacancies and salaried employment fell more in highly automatable occupations during the pandemic and have since experienced a slower recovery. The effect of the pandemic on automation is mostly driven by sectors that were affected by mobility restrictions. We also found heterogeneous effects by age and gender. The acceleration of automation is mainly affecting the labor market for females and individuals over the age of 40. Finally, we explored the differential effect on occupations with wages around the minimum wage. We found that occupations with wages close to the minimum wage exhibit the highest effect, especially at the onset of the pandemic.

For decades, our flawed economic and governance systems have allowed inequality and social exclusion to grow to extreme and dangerous levels, and now coronavirus has driven an even greater wedge between the haves and have nots. Without immediate action, the pandemic could cause the biggest spike in inequality ever seen, and further destabilize the democratic systems we need to ensure a recovery for all. Governments must take action to tackle the inequality and climate crises, rein in extreme wealth and monopoly power, and deliver universal public services and social protection.