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Wideband LP to CP Converter Using a Reflectarray Based on Modulated Admittance Surfaces Capable of Wide‐Range Beam‐Scanning for Ku/K Band Applications

Radio Science - Thu, 08/01/2024 - 07:00
Abstract

This study provides the design and demonstration of a Ku/K band horn-fed linear polarization (LP) to circular polarization (CP) converter using a reflectarray antenna based on the holographic technique and the generalized law of total reflection without any iterative algorithms. The proposed hologram performs wide-range frequency beam scanning with minimum gain losses and cross-polarization levels. It comprises 2,500 diagonal slotted octagonal subwavelength metasurfaces with a periodicity of 0.266λ 0 = 4 mm at 20 GHz as the center frequency. Two equations are defined to compute Y 11 of the proposed unit cell regarding its dimensions for TE(0,0) and TM(0,0) Floquet modes. They significantly simplify the coding procedure and reduce the computational time for synthesizing the hologram. The antenna is simulated using the CST software from 14 to 25 GHz. As a confirmation, a prototype is manufactured and measured at 16, 18, 20, 22, and 24 GHz to verify its performance. The simulated and measured results are well-matched. The presented hologram achieves 40% 1.8-dB axial ratio (AR) bandwidth (16–25 GHz), 40% 3.3-dB gain bandwidth (16–24 GHz), and above 30% 2-dB gain bandwidth (16–22 GHz). Moreover, the antenna can perform beam scanning from 42° to 24° by changing the frequency from 16 to 24 GHz with peak gain values greater than 20.33 dBi. The LHCP pencil beams are at least 24° off-broadside, so the proposed hologram avoids the feed blockage. These achievements make the hologram one of the best candidates for satellite communications, radar applications, short-range communication, and point-to-point communication.

Forecasting Inundation of Catastrophic Landslides From Precursory Creep

GRL - Thu, 08/01/2024 - 06:56
Abstract

Forecasting landslide inundation upon catastrophic failure is crucial for reducing casualties, yet it remains a long-standing challenge owing to the complex nature of landslides. Recent global studies indicate that catastrophic hillslope failures are commonly preceded by a period of precursory creep, motivating a novel scheme to foresee their hazard. Here, we showcase an approach to hindcast landslide inundation by linking satellite-captured precursory displacements to modeling of consequent granular-fluid flows. We present its application to the 2021 Chunchi, Ecuador landslide, which failed catastrophically and evolved into a mobile debris flow after four months of precursory creep, destroying 68 homes along its lengthy flow path. Underpinned by uncertainty quantification and in situ validations, we highlight the feasibility and potential of forecasting landslide inundation damage using observable precursors. This forecast approach is broadly applicable for flow hazards initiated from geomaterial failures.

Cold Waves Accelerate the Spread of Infectious Diseases

GRL - Thu, 08/01/2024 - 06:44
Abstract

Climate change is creating a new era of infectious disease crises, further exacerbated by extreme weather. However, the relationship between extreme weather and infectious disease remain unclear. Here, we provide a new quantitative study on the impact of cold wave on COVID-19 as an example. We found that during cold waves, extreme cold temperatures coupled with rapid aerosol transport accelerated COVID-19 outbreaks. It directly increased the number of COVID-19 cases in Beijing by 28.1% in the winter of year 2022. More urgently, cold temperatures led to a higher risk of death during infectious disease outbreaks, with a 7.07% increase in confirmed deaths and a 16.61% increase in excess mortality. Our findings emphasize the urgent need to promote a synergistic policy for responding to infectious diseases during cold wave disasters in order to minimize the risk of death among the elderly and those with underlying diseases.

Standardizing sea level

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 503-503, August 2024.

Valuing animal lives

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 502-502, August 2024.

Additive manufacturing of highly entangled polymer networks

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 566-572, August 2024.

Event-responsive scanning transmission electron microscopy

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 549-553, August 2024.

A molecular anion pump

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 544-549, August 2024.

Recent tropical Andean glacier retreat is unprecedented in the Holocene

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 517-521, August 2024.

A reluctant chemist

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 574-574, August 2024.

In Other Journals

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 510-511, August 2024.

Lessons from ancient pathogens

Science - Thu, 08/01/2024 - 05:58
Science, Volume 385, Issue 6708, Page 490-492, August 2024.

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