67639 research outputs found
Sort by
Optical Intelligent Reflecting Surfaces Empowering Non-Terrestrial Communications
No full textIn this work, we propose an innovative system that combines high-altitude platforms (HAPs) and optical intelligent reflecting surfaces (OIRS) to address line-of-sight (LOS) challenges in urban environments. Our three-hops system setup includes an optical ground station (OGS), a HAP, an OIRS, and a user. Signals are transmitted from the OGS to the HAP via a free space optical (FSO) link, with the HAP functioning as an amplify-and-forward (AF) relay that redirects signals through an OIRS, effectively bypassing obstacles such as buildings and trees to improve connectivity for non-line-of-sight (NLOS) User. For the OIRS link, we address key channel impairments, including atmospheric turbulence, pointing errors, attenuation, and geometric and misalignment losses (GML). An accurate approximation for the Hoyt-distributed GML model is derived, enabling us to obtain closed-form expressions for outage probability (OP) and various performance metrics, such as average bit error rate (BER) and channel capacity of the OIRS-assisted FSO link. Furthermore, we analyze the end-to-end signal-to-noise ratio (SNR) and derive closed-form expressions for OP and performance metrics. Asymptotic expressions are provided for high-SNR regimes, allowing the system’s diversity order to be calculated
Covalent organic frameworks with dual-active sites for efficient catalytic cycloaddition of CO<sub>2</sub> with epoxides under mild conditions
No full textA covalent organic frameworks material (iCOF-OH/AB-50) with high content of dual-active sites (hydroxyl and bromide anion), surface area and CO2 uptake was prepared through Schiff-base reaction between 2,4,6-tri(4-aminophenyl)-1,3,5-triazine (TAPT) and 2,5-dihydroxyterephthalaldehyde (DHTA), followed by ionic liquid post-synthetic modification with (2-bromoethyl)trimethylammonium bromide (AB). It can act as a recyclable heterogeneous catalyst in the CO2 cycloaddition with a series of epoxides into cyclic carbonates under mild conditions (1 atm and 50 °C) without solvent, co-catalyst and metal. The remarkable catalytic activity was attributed to the abundant porosity, good CO2 affinity, as well as the synergistic effect of hydroxyl as hydrogen-bond donor and bromide anion as nucleophile. In addition, density functional theory (DFT) calculations were performed to afford insight into the energy barriers of different processes based on the proposed four-step catalytic mechanism, indicating that the rate-determining process, i.e., ring-opening process of epoxides, was accelerated by the synergistic effect of hydroxyl active site and bromide anion site. This work demonstrates the essential role of fabricating effective dual-active sites into COFs with rich porosity and good CO2 affinity in achieving a high catalytic activity for CO2 cycloaddition.The authors acknowledge the support from the Nanqiang Youth Scholar program of Xiamen University, President Research Funds from Xiamen University (ZK1117), and National Natural Science Foundation of China (22201209)
A chemically bonded monolayer interface enables enhanced thermal stability and efficiency in Pb-Sn perovskite solar cells
No full textAdvances in narrow-band-gap (NBG) mixed lead-tin (Pb-Sn) perovskites have enabled increasingly efficient all-perovskite tandem solar cells, yet device stability remains limited by acidic poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) hole transport materials (HTMs). Although carbazole-based self-assembled monolayers (SAMs) were considered as alternatives, they also degrade rapidly (T80 < 200 h) under external stresses. We identified weak chemical interaction at the transparent conductive oxide:SAM:perovskite interface and hypothesized that stronger binding could enhance stability. Introducing bifunctional SAMs with thiol groups established robust S-Pb chemical coordination, improving fracture energy by 30%. Replacing acidic phosphonic groups with milder carboxylic groups and optimizing SAM chain length led to selecting 16-mercaptohexadecanoic acid (16-MHDA), balancing coverage, energy alignment, and series resistance. This approach doubled photocarrier lifetime and increased thermal degradation resistance by 1.3×. Single-junction Pb-Sn cells achieved 24% power conversion efficiency (PCE) and encapsulated devices retained 80% efficiency after 680 h under 1-sun illumination at a heatsink temperature of 50°C.This work was supported by the Trienens Institute for Sustainability and Energy at Northwestern University. This work is partially supported by award 70NANB19H005 from US Department of Commerce, National Institute of Standards and Technology as part of the Center for Hierarchical Materials Design (CHiMaD). This work made use of the NUFAB facility of Northwestern University's NUANCE Center, which has received support from the SHyNE Resource (NSF ECCS-2025633), the IIN, and Northwestern's MRSEC program (NSF DMR-2308691). A.S.R.B. acknowledges support from King Abdullah University of Science and Technology (KAUST) through the Ibn Rushd Postdoctoral Fellowship Award. Part of the research described in this paper was performed at the CLS, a national research facility of the University of Saskatchewan, which is supported by the Canada Foundation for Innovation (CFI), the Natural Sciences and Engineering Research Council (NSERC), the National Research Council (NRC), the Canadian Institutes of Health Research (CIHR), the Government of Saskatchewan, and the University of Saskatchewan. DFT calculations were conducted in the Resnick High Performance Computing Center, a facility supported by Resnick Sustainability Institute at the California Institute of Technology. DFT calculations were also supported through computational resources and staff contributions provided for the Quest high-performance computing facility at Northwestern University which is jointly supported by the Office of the Provost, the Office of Research, and Northwestern University Information Technology. J.A.S. acknowledges financial support from the Australian Research Council (DE230100173). The in situ GIWAXS data were collected at NCD-SWEET beamline at ALBA synchrotron (Spain) with the collaboration of ALBA staff. C.B.M. and W.A.G. acknowledge support from the Liquid Sunlight Alliance, which is supported by the US Department of Energy, Office of Science, Office of Basic Energy Sciences, Fuels from Sunlight Hub under award number DE-SC0021266. U.R. acknowledges funding from the SNSF under grant no. 200020_219440 and computational resources from the Swiss National Computing Center CSCS. N.R. acknowledges support from the National Science Foundation under grant no. 2339233. The authors thank Selina Olthof for useful discussions
CIMNAS: A Joint Framework for Compute-In-Memory-Aware Neural Architecture Search
No full textTo maximize hardware efficiency and performance accuracy in Compute-In-Memory (CIM)-based neural network accelerators for Artificial Intelligence (AI) applications, co-optimizing both software and hardware design parameters is essential. Manual tuning is impractical due to the vast number of parameters and their complex interdependencies. To effectively automate the design and optimization of CIM-based neural network accelerators, hardware-aware neural architecture search (HW-NAS) techniques can be applied. This work introduces CIMNAS, a joint model-quantization-hardware optimization framework for CIM architectures. CIMNAS simultaneously searches across software parameters, quantization policies, and a broad range of hardware parameters, incorporating device-, circuit-, and architecture-level co-optimizations. CIMNAS experiments were conducted over a search space of 9.9x10^85 potential parameter combinations with the MobileNet model as a baseline and RRAM-based CIM architecture. Evaluated on the ImageNet dataset, CIMNAS achieved a reduction in energy-delay-area product (EDAP) ranging from 90.1x to 104.5x, an improvement in TOPS/W between 4.68x and 4.82x, and an enhancement in TOPS/mm^2 from 11.3x to 12.78x relative to various baselines, all while maintaining an accuracy of 73.81%. The adaptability and robustness of CIMNAS are demonstrated by extending the framework to support the SRAM-based ResNet50 architecture, achieving up to an 819.5x reduction in EDAP. Unlike other state-of-the-art methods, CIMNAS achieves EDAP-focused optimization without any accuracy loss, generating diverse software-hardware parameter combinations for high-performance CIM-based neural network designs. The source code of CIMNAS is available at https://github.com/OlgaKrestinskaya/CIMNAS.This work was supported by the King Abdullah University of Science and Technology through the Competitive Research Grant program under grant URF/1/4704-01-01
Bridging the Educational Divide: A Delay-Tolerant Networking Approach for Equitable Digital Learning in Rural Areas
No full textAccess to quality education remains unequal, particularly in rural areas where Internet connectivity is limited or nonexistent. This paper introduces a framework for a digital learning platform that uses Delay Tolerant Networking (DTN) to extend educational opportunities to underserved communities. Unlike conventional models that rely on continuous Internet access, DTN offers an affordable and sustainable solution by leveraging existing transportation infrastructure. Beyond its technical contributions, the framework addresses ethical imperatives by promoting educational equity and digital inclusion. We present a prototype tested on a university campus, demonstrating the feasibility of DTN for educational delivery. By addressing the digital divide, this framework aligns with global goals of inclusive education and sustainable development
Aerosol Monitoring at the Western Arabian Peninsula and North region of KSA (NEOM).
No full textDeserts are the primary source of atmospheric dust. Covering over one-third of the Earth’s land surface, deserts play a pivotal role in influencing planetary albedo and dust dynamics.The Arabian Peninsula is one of the world’s largest dust source regions. It is also affected by natural and anthropogenic pollution of African, Asian, and European origin. As the Arabian Peninsula is highly under-sampled, we have since 2012 established and maintained aerosol monitoring sites at King Abdullah University of Science and Technology (KAUST), as well as in the North-Western part of the Arabian Peninsula, and the Red Sea coast.The sites incorporate the following instrumentation:1.Two CIMEL sun photometers operational since 2012 as a part of the NASA Aerosol Robotic NETwork (AERONET), providing aerosol parameters, reporting data to the NASA Goddard website (http://aeronet.gsfc.nasa.gov/cgi-bin/type_piece_of_map_opera_v2_new).2.Hand-held sun photometer (Microtops II). The data are reported to the NASA Maritime Network (http://aeronet.gsfc.nasa.gov/new_web/maritime_aerosol_network.html).3.Micro Pulse Lidar (MPL) operating as a part of the NASA MPLNET (http://kimura.gsfc.nasa.gov/site--‐page?site=Kaust). Monitoring the vertical distribution of Aerosols.4.We measure aerosol deposition rates on a monthly basis using passive samplers in different several locations (KAUST, 2015-2023; Al Wajh Lagoon, 2021-2022; DUBA & Tabuk,2022 -2023; NEOM project area (NESTOR; ENOWA), 2024 - now)5.Mineralogical analysis of deposited aerosols by X-ray diffractometry (XRD)6.Measured particle size distributions using Mastersizer3000.In this study we conduct an analysis of the combined effects of natural and anthropogenic pollution on air quality, climate, and application of renewable energy across the Arabian Peninsula, providing a scientific foundation for model calibration in this region.Here we report on the data sets collected in 2021- 2025:•KAUST campus site: Two dust deposition samplers, AERONET, MPL•Al Wajh Lagoon site: Nine dust deposition samplers•Duba site: Two dust deposition samplers•Tabuk site: Two dust deposition samplers•NEOM, NESTOR Project: Two dust deposition samplersThese data sets, in combination with the available satellite observations, were integrated into the meteorology-chemistry-aerosol model, WRF-Chem, to quantify the aerosol environmental impacts and support environmental decision-making in the region
A Large Area Hybrid Phototransistor Platform with Large Detectivity and Fast Response to NIR Light
No full textWithin multijunction organic and hybrid photodetectors (PDs), organic and hybrid phototransistors (HPTs) hold promises for high sensitivity (S) and specific detectivity (D*). However, it is difficult to achieve a trade-off between a large sensing area, a fast response, and a high D*. Here, we propose an alternative phototransistor concept relying on a geometrically engineered tri-channel (Tr-iC) architecture with a 4-mm2 large sensing area, applied to a multilayer HPT whose active region is comprised of an inorganic In2O3/ZnO n-type field-effect channel and solution-processed organic bulk heterojunction (BHJ) or hybrid perovskite light-sensing layer. The resulting HPTs combine a responsivity (R) up to 105 A/W, thanks to the efficient charge transport (at the bottom In2O3/ZnO layer) and a D* estimated at 1015Jones, which allows to measure low light power densities down to 10 nW cm−2. These figures of merit are coupled to a fast response (risetime <10 ms and falltime of ≈100 ms for illumination, in the µW/cm2 range), which is comparable to the time-response of organic PDs in a diode architecture. The experimental data are supported by a comprehensive device modeling, which helps highlighting the peculiar advantages of the proposed large area, Tr-iC, and multilayer HPT architecture.F.P. and W.S.A. contributed equally to this work. This work received funding from the European Union's Horizon 2020 research and innovation program under grant agreement no. 101016706 (h-ALO) and from PNRR MUR Project ECS_00000033_ECOSISTER
Photocatalytic H2O2 Production with >30% Quantum Efficiency via Monovalent Copper Dynamics
No full textPhotocatalytic O2 reduction to H2O2 is a green and promising technology with advantages in cost-effectiveness, sustainability, and environmental friendliness, but its efficiency is constrained by limited selectivity for the two-electron oxygen reduction reaction (ORR) pathway. Here, we anchored isolated Cu atoms with tunable oxidation states onto WO3 as effective active centers to enhance photocatalytic H2O2 production. Due to the charge compensation between single atoms and the support, the oxidation state of Cu species exhibited a loading-dependent transition between +2 and +1 valence. Experimental and theoretical analyses indicate that Cu(I) sites exhibit outstanding O2 adsorption and activation capabilities, transforming the thermodynamically unfavorable hydrogenation of the *OOH intermediate (the rate-determining step in the two-electron ORR pathway) into an exothermic process, thereby significantly improving selectivity and efficiency. The Cu(I)-SA/WO3 photocatalyst exhibited a H2O2 production rate of 102 μmol h-1 under visible light irradiation, much higher than other reported photocatalysts. More importantly, it achieves an impressive apparent quantum efficiency of 30% at 420 nm, making a significant breakthrough in this field. This work provides novel perspectives for designing single-atom catalysts for efficient H2O2 synthesis via electronic state modulation.This work was supported by the King Abdullah University of Science and Technology and the Center of Excellence for Renewable Energy and Storage Technologies under award number 5937. Fan Yang is thankful for support from the China Scholarship Council, the National Natural Science Foundation of China (22408278), and the Key Laboratory of Functional Inorganic Material Chemistry (Heilongjiang University), Ministry of Education
Processing-Controlled Seebeck Modulation in Laser-Induced Graphene for Flexible Temperature Sensors
No full textClassical thermocouples are too rigid for accurate temperature measurement on curved or irregular surfaces, necessitating the development of flexible sensors. These sensors are typically composed of materials such as printed inks and flexible substrates and utilize the Seebeck effect for high sensitivity, with optimized designs enhancing performance in wearable, environmental, and structural monitoring applications. This study proposes a flexible temperature sensor based on the Seebeck effect, fabricated using laser-induced graphene (LIG) technology. Unlike conventional thermocouples composed of two dissimilar materials, each leg of the proposed LIG thermocouple is fabricated by using different laser configurations. Each configuration results in a unique microstructure and defect population, enabling tuning of the Seebeck coefficient by controlling phonon scattering at grain boundaries. Increasing the laser fluence increases the IG/ID ratio, indicating a higher number of defects in LIG, and reduces the crystalline size, thereby increasing grain boundaries and further improving the Seebeck coefficient. Furthermore, a thermopile approach is employed to enhance the Seebeck response by connecting two LIG thermocouples in series, increasing the Seebeck coefficient from 2.68 μV/°C to 5.67 μV/°C. This study demonstrates the advantages and versatility of LIG technology for fabricating flexible thermocouples. The proposed process is rapid, cost-effective, and suitable for large-scale production, making it a promising solution for advanced temperature-sensing applications.The work reported in this publication was financially supported by King Abdullah University of Science and Technology (KAUST), Saudi Arabia, under award number BAS/1/1315-01-01. M.A.A. appreciates the sabbatical leave support from Yanbu Industrial College, the Royal Commission for Jubail and Yanbu, Kingdom of Saudi Arabia
Thermal Modifications of Thin-Film Composite Membranes for Enhanced Removal of Nitrogenous Neutral Organic Micropollutants
No full textConventional thin-film composite membranes prepared via interfacial polymerization often exhibit molecular level ‘defects’ that can compromise their liquid separation performance. This research aimed to develop essentially ‘defect-free’ membranes with enhanced size-sieving properties through facile thermal modifications. Low-molecular weight, nitrogenous neutral organic micropollutants, including urea, 1H-benzotriazole, and N-nitrosodimethylamine, were selected as markers to evaluate membrane performance.
The first methodology examined the sequential application of elevated interfacial polymerization temperature and heat-curing on thin-film composite membranes for efficient urea removal. This systematic study demonstrated that heat-curing effectively minimized ‘defects’ and promoted additional crosslinking. Under brackish water conditions, the modified membranes exhibited a water permeance of 0.8 LMH/bar and urea rejection of 76.7 %. Further optimization of feed solute concentration and transmembrane pressure improved urea rejection to 88.0 %, achieving the highest water/urea selectivity reported to date. Despite such improvements, this thermal modification led to a slight decrease in water permeance.
To overcome this limitation, a second methodology investigated the thermal treatment of hydrated thin-film composite membranes to enhance 1H-benzotriazole rejection. Thermally treated membranes exhibited an unexpected increase in water permeance from 1.0 to 1.6 LMH/bar, while simultaneously maintaining a lower pressure-independent solute flux. This thermal modification effectively produced essentially ‘defect-free’ membranes with enhanced transport properties. Under optimal thermal treatment and operating conditions, thermally treated membranes achieved 97.4 % 1H-benzotriazole rejection.
Lastly, a comparative study evaluated both heat-curing and thermal treatment of hydrated thin-film composite membranes for N-nitrosodimethylamine removal. Both thermal modifications enhanced rejection; however, thermally treated membranes achieved an outstanding rejection of 94.3 % while maintaining a relatively high water permeance of 1.6 LMH/bar. These membranes exhibited the highest N-nitrosodimethylamine rejection reported among state-of-the-art thin-film composite membranes. This research comprehensively demonstrated that the developed methodologies optimize membrane performance for the efficient rejection of a broad range of challenging nitrogenous neutral organic micropollutants, underscoring their potential for diverse advanced liquid separation applications