Adaptive Beamforming Approaches to Improve Passive Radar Performance in Sea and Wind Farms' Clutter.

This article presents the problem of passive radar vessel detection in a real coastal scenario in the presence of sea and wind farms' clutter, which are characterised by high spatial and time variability due to the influence of weather conditions. Deterministic and adaptive beamforming techniques are proposed and evaluated using real data. Key points such as interference localisation and characterisation are tackled in the passive bistatic scenario with omnidirectional illuminators that critically increase the area of potential clutter sources to areas far from the surveillance area. Adaptive beamforming approaches provide significant Signal-to-Interference improvements and important radar coverage improvements. In the presented case study, an aerial target is detected 28 km far from the passive radar receiver, fulfilling highly demanding performance requirements.

Improved 2D Ground Target Tracking in GPS-Based Passive Radar Scenarios.

Global Positioning System (GPS) satellites offer promising opportunity for Passive Radar systems due to their global coverage and the availability of multiple satellites throughout the world. However, their low power at ground level limits system coverage. In this paper, a GPS based Passive Radar which exploits a single illumination source, and uses digital array processing for ground targets localization is presented. To face signal power problems, a processing scheme combining reconstructed reference signals, adaptive filtering techniques and spatial filtering is implemented. Conventional beamforming techniques are used to increase the level of the target echo before the detection stage, and high resolution DoA estimation techniques are applied to estimate targets azimuth. Ground target localization in local Cartesian space is performed taking into account the system geometry, range and azimuth information. Both synthetic and real radar data are used to analyse system operation. During the measurement campaign, a cooperative vehicle was used for validation purposes. Results confirm that ground targets detection and localization are feasible using a single GPS transmitter.

Covid-19 in Central America: Firm resilience and policy responses on employment.

This paper examines how government support interacts with firm-level resilience capabilities in the reduction of layoffs among formal firms in Central America. Our analysis suggests that government support measures play a role in reducing the probability of layoffs among firms with only dynamic resilience capabilities (i.e., those that are developed after the pandemic onset). The effect of government support is not statistically different from the effect of static resilience capabilities alone (i.e., those that were present before the pandemic); thus, in firms with such capabilities, the effect of government support will be marginal. These results hold across sectors - exhibiting a marginally higher treatment effect in service sectors. Our results do not imply that Covid-19 supportive measures are to be disregarded, but instead raise the question of how government support policies could improve the allocation of support among firms in times of crises. Moreover, it underlines the necessity of policies that enhance resilience more broadly - a task that hints at structural issues and requires continuous government support in lieu of ad-hoc measures.

Design and Validation of a Reflectarray Antenna with Optimized Beam for Ground Target Monitoring with a DVB-S-Based Passive Radar.

A reflectarray antenna with an optimized sectorial beam is designed for the surveillance channel of a DVB-S-based passive radar (PR). The employment of satellite illuminators requires a high gain antenna to counteract the losses due to the great distance from the transmitter, but without forgetting a beamwidth wide enough to provide angular coverage. A method based on optimizing the position of several contiguous beams is proposed to achieve the required sectorial pattern. Different reflectarray elements are designed to achieve S-curves with smooth slopes and covering all the required phases (the S-curve represents the reflection phase of a single element, as a function of size, rotation and incidence angle). The real phase and modulus of the reflection coefficient of each element are considered in the optimization process to achieve the best real prototype. Geometry has been studied and adapted to employ commercial elements for the feed, feed-arm and the structure that holds the aperture. The designed prototype has been characterized in an anechoic chamber achieving a stable gain greater than 19 dBi in almost the complete DVB-S band, from 10.5 GHz to 12 GHz with a sectorial beam of 8.7∘×5.2∘. The prototype has also been validated in PR trials in terrestrial scenarios allowing the detection of cars at distances up to 600 m away from the PR, improving the performance achieved with commercial parabolic dish antennas.

Feasibility Study of EO SARs as Opportunity Illuminators in Passive Radars: PAZ-Based Case Study.

Passive radars exploit the signal transmitted by other systems, known as opportunity illuminators (OIs), instead of using their own transmitter. Due to its almost total invulnerability to natural disasters or physical attacks, satellite OIs are of special interest. In this line, a feasibility study of Earth Observation Synthetic Aperture Radar (EO SAR) systems as OIs is carried out taking into consideration signal waveform, availability, bistatic geometry, instrumented coverage area and incident power density. A case study based on the use of PAZ, the first Spanish EO SAR, is presented. PAZ transmitted waveform, operation modes, orbit characteristics and antenna and transmitter parameters are analyzed to estimate potential coverages and resolutions. The study concludes that, due to its working in on-demand operating mode, passive radars based on PAZ-type illuminators can be proposed as complementing tools during the sensor commissioning phase, for system maintenance and for improving its performance by providing additional information about the area of interest and/or increasing the data updating speed, exploiting other sensors during the time PAZ is not available.

Integrating External and Internal Load for Monitoring Fitness and Fatigue Status in Standard Microcycles in Elite Rink Hockey.

The aims of this study were 3-fold: firstly, to present an integrative approach to external and internal load dynamics for monitoring fitness and fatigue status of specific in-court rink hockey training sessions in a standard microcycle; secondly, to assess the differences between training sessions and matches; the third and final aim was to assess the association between external and internal load metrics. The external load, using a local positioning system, and internal load, using the declared rate of perceived exertion, were measured during 23 in-season microcycles for nine top-level players. Training load data were analysed with regard to the number of days before or after a match [match day (MD) minus or plus]. In relation to the first aim, internal and external load metrics merged into a single integrated system using pooled data z-scores provided an invisible monitoring tool that places the players in the fitness-fatigue continuum throughout the different microcycle sessions. In this regard, MD-4 and MD-1 sessions tend to place, with a low dispersion, the players in a "low external and internal load" zone. On the contrary, in MD-3 and MD-2 sessions, as well as in MD, in which higher loads were recorded, most of the players were within a "high external and internal load" zone with a tendency towards dispersion towards the fitness or fatigue zones. Finally, and with regard to the second and third aims, an inverted "U-shape" load dynamic related to the specific goals of each training session was the main finding in terms of comparison between MD; a load peak between MD-3 and MD-2 sessions and a significant decrease in all the load variables in MD-1 sessions were found; and high-to-low correlations were found between external and internal load metrics. This study presents an integrative approach to the external and internal load of players for monitoring fitness and fatigue status during a standard microcycle in rink hockey that might provide team sport staff members with a deeper understanding of load distribution in the microcycle in relation to the match.

Brugada Phenocopy Induced by a Lethal Methanol Intoxication.

Brugada phenocopies (BrP) are clinical entities that present with an ECG pattern identical to either the type 1 or type 2 Brugada pattern without true congenital Brugada syndrome. This ECG pattern is associated with an identifiable condition and normalizes upon resolution or treatment of the underlying cause. We present a case of a 54-year-old man with extreme metabolic acidosis, hyperkalaemia and a Brugada type 1 ECG pattern in the setting of a suicidal methanol (MeOH) poisoning. Upon correction of these metabolic derangements with bicarbonate infusions and continuous veno-venous haemodiafiltration (CVVH), the Brugada type 1 ECG pattern normalized. Unfortunately, the patient developed signs of cerebral herniation followed by brain death and died on the first day of ICU admission. LEARNING POINTS: Brugada-like ECG patterns are described in several metabolic conditions such as extreme hyperglycaemia, glucose/insulin challenge, isolated hyperkalaemia or in association with hyponatraemia and acidosis.Until now, there have been no published case reports of BrP in association with methanol intoxication.Correction of hyperkalaemia and acidosis and specific therapy for methanol intoxication leads to a complete resolution of a Brugada type 1 ECG pattern.

Vitamins C and e reduce retinal oxidative stress and nitric oxide metabolites and prevent ultrastructural alterations in porcine hypercholesterolemia.

PURPOSE: Oxidative stress is thought to be involved in the pathogenesis of age-related diseases, such as atherosclerosis and retinal degeneration. The current study was conducted to examine vitreoretinal oxidative status in a model of porcine hypercholesterolemia to identify morphologic alterations and analyze the effect of dietary supplementation with vitamins C and E. METHODS: Adult miniature pigs were fed standard chow, cholesterol-rich chow, or a cholesterol-rich diet supplemented with vitamins C and E. Total cholesterol, triglycerides, high-density lipoproteins, lipid peroxidation, and tocopherol were measured in plasma. Lipid peroxidation and nitric oxide (NO) metabolites were measured in vitreous and retinal homogenates. Superoxide anion release in the retinal pigment epithelium (RPE) was analyzed by chemiluminescence. Retinal morphology was studied by transmission electron microscopy. RESULTS: The high-cholesterol group, with increased retinal oxidative stress (P < 0.01) and NO metabolites in the retina (P < 0.05), had increased superoxide anion release (P < 0.05) and showed development of pyknosis, irregular nuclear membranes, and cytoplasmic accumulation of lipids and autophagocytic vacuoles in the RPE cells. Vitamins C and E prevented biochemical changes and most ultrastructural alterations in the RPE. CONCLUSIONS: The results suggest an evolving role for hypercholesterolemia through increased retinal oxidative stress and NO synthesis that could be responsible for retinal ultrastructural alterations. The beneficial effects of vitamins C and E in the retinal tissue further support this hypothesis.