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Influence of Topological Constraints on the Segmental Motion in the Crystalline Region of Semicrystalline Ultra-High-Molecular-Weight Polyethylene
No full textSemicrystalline polymers constitute crystalline and noncrystalline regions. In the crystalline region, chain segments form a well-defined unit cell. In contrast, the noncrystalline region having a lower density is strongly influenced by the crystallization conditions and considerable variation in the chain conformation/chain topology exists. Here we demonstrate, for the first time, that the mobility of the chain segments in the crystalline region of the same polymer is strongly influenced by the topological/conformational differences of the chain segments in the noncrystalline region. To undertake the study, variability in the topological constraints in the noncrystalline region is achieved by crystallization during polymerization or postpolymerization. Two sets of nascent UHMWPEs are synthesized using a conventional Ziegler–Natta (Z-N) catalytic system and a postmetallocene single-site catalytic system. The polymer obtained from the conventional Z-N catalytic system results in an entangled noncrystalline region, whereas the UHMWPE synthesized using a postmetallocene catalytic system provides a possibility to reduce the entanglement density, reducing the topological constraints. The entanglement density in the Z-N synthesized UHMWPE can be reduced by crystallization of the nascent polymer from a dilute solution. The influence of a tailored entanglement state on the chain mobility in the crystalline region is pursued by solid-state NMR; the 1H spin–lattice relaxation time in the rotating frame (T1ρ,H) indicates that with the decreasing concentration of entanglements the chain-flip motion in the crystalline region increases. The influence of the entanglement density on the chain mobility in the crystalline region is supported by the transfer of polarization from the noncrystalline to crystalline region, arising from the fact that chain segments of the same chain reside in the crystalline as well as noncrystalline region. The ease in transfer of polarization can be expressed by the differences in the entropic barrier between the chain conformations in the noncrystalline and crystalline regions. These observations on the UHMWPE are of a generic nature, allowing us to quantify the differences in the abstract nature of the topological constraints in semicrystalline polymers.This work is supported by KAUST funding (BAS/1/1407). The authors would like to acknowledge Dr. Ravindra P. Gote from Prof. Rastogi’s group for chemical synthesis. The authors would like to acknowledge Dr. Edy Abou-Hamad and Dr. Yaping Zhang from the KAUST Imaging and Characterization core lab for assistance in solid-state NMR experiments and in situ heating SAXS experiments
Advancing coral reef ecological engineering for large-scale seascaping on soft seabeds: a comparison of tiered and biomimetic artificial reef designs
No full textIn a context where entire marine regions are in decline and many coral reef systems have collapsed, creating novel coral reef ecosystems on soft-bottom seascapes can serve as ecological restoration at a regional scale. However, seascaping reef infrastructure in sandy environments presents unique engineering challenges distinct from traditional reef restoration. This study evaluates two artificial reef designs for coral farming: the tiered Marjan Reef and the biomimetic Mushroom Forest Reef (MFR). Both were deployed offshore in Qatar as part of an environmental compensation program involving the transplantation of 4310 coral colonies (10 species) from oil and gas pipeline corridors—843 onto 21 MFR units and 3467 onto 63 Marjan units. Under thermal stress (seawater temperatures reaching 36°C), MFR significantly outperformed the Marjan Reef, with 90% of colonies Healthy, 9.9% Partially-Dead, and 0.49% Dead. In contrast, the Marjan Reef showed 73% Healthy, 25% Partially-Dead, and 4% Dead colonies, likely due to shading, sediment accumulation, and boring sponge colonization on its lower tiers. MFR minimized these stressors, enhancing coral survival and cost-efficiency. For instance, installing 1 ha of coral farming infrastructure would require 51 MFR units, five deployment days, and provide approximately 300 m2 of farming surface. These results support the concept of utilizing the creations of “coral oasis reservoirs” in regional resource management—engineered reef units that function as biodiversity hotspots in soft-bottom marine deserts. These oases offer a scalable solution for coral propagation in novel environments, advancing broader ecological restoration and “Assisted Marine Rewilding” in the Anthropocene.We express our gratitude to the staff and colleagues of the ESC-QU, Mr. Reyniel M. Gasang, Mr. Faisal M. Al-Quaiti, and Mr. Mehmet Demirel during field activities; Ms. A. Begum for the administrative support; our manager Dr. A. Leitão; Ms. S. Saliba in the project management; and special credits to Prof. H. A. Al-Saad Al-Kuwari, Director of the ESC, and lead of this industry project. Thanks also to the crew and the Captain of the ESC-QU R/V Janan. We also thank the representatives from the Ministry of Environment and Climate Change (MECC) of Qatar and the Coast Guard. Our appreciation goes to the engineering and staff at SMEET Precast regarding the used artificial reefs; to the staff at GHD Group Pty Ltd (formerly known as Gutteridge Haskins & Davey) for their assistance in the coral removal, transplantation, and monitoring, as well as the deployment of the modules, particularly for Mr. S. Healy and Mr. N. Chacko; and Seaboost for the Marjan AR. Lastly, we are especially grateful to Qatar Energy LNG for their funding (no. STC/C/NFE/4967/20/QUEX-ESC-QG-20/21-1) and commitment to the R&D, accepting to use the MFR in their coral restoration offset as an experimental technology, enabling the achievement of the coral restoration experiments. The authors have no relevant financial or non-financial interests to disclose. Authors from Qatar Energy, despite being employed by the funding agent, were not involved in the conceptualization, monitoring, or data preparation, and declared that they have no financial interests
For What the Bell Tolls
No full textWith today's exascale computers requiring 20 to 40 MW and some cloud centers exceeding 100MW, with no slacking of demand in sight, computing is a nonnegligible factor in climate change. For the past three years, we have been finalists in the Gordon Bell Prize with computations that do more with less - that scale up while squeezing out operations and data transfers that do not ultimately impact application accuracy requirements
Information Retrieval in the Age of Generative AI: The RGB Model
No full textThe advent of Large Language Models (LLMs) and generative AI is fundamentally transforming information retrieval and processing on the Internet, bringing both great potential and significant concerns regarding content authenticity and reliability. This paper presents a novel quantitative approach to shed light on the complex information dynamics arising from the growing use of generative AI tools. Despite their significant impact on the digital ecosystem, these dynamics remain largely uncharted and poorly understood. We propose a stochastic model to characterize the generation, indexing, and dissemination of information in response to new topics. This scenario particularly challenges current LLMs, which often rely on real-time Retrieval-Augmented Generation (RAG) techniques to overcome their static knowledge limitations. Our findings suggest that the rapid pace of generative AI adoption, combined with increasing user reliance, can outpace human verification, escalating the risk of inaccurate information proliferation across digital resources. An in-depth analysis of Stack Exchange data confirms that high-quality answers inevitably require substantial time and human effort to emerge. This underscores the considerable risks associated with generating persuasive text in response to new questions and highlights the critical need for responsible development and deployment of future generative AI tools
Integrating ultra-high resolution mass spectrometry into analytical workflows for comprehensive characterization of streams from waste- and biorefinery
No full textThis doctoral thesis addresses key analytical challenges in integrating advanced techniques into traditional workflows to study compositional changes and reaction networks in unconventional feedstocks, proposing methods for translation of qualitative molecular information into a quantitative description.
The first result chapter deals with the hydrocracking of vacuum gas oil (VGO) blended with oxygenated plastics, such as PMMA and PET. A multi-technique approach, combining gas chromatography, bulk elemental analysis, and Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS), elucidates heteroatom removal mechanisms in waste-refinery blends. The results point to a direct relationship between the polymer structure (linear vs. aromatic) with enhanced heteroatom removal efficiency.
Next, the thesis explores blends of VGO and pyrolysis waxes from HDPE, introducing a method to transform qualitative FT-ICR MS data into a quantitative description. This chapter focuses on exposing the feasibility of integrating data from different techniques to calculate a mass-fraction based distribution, while using results from routine analysis like simulated distillation to define compositional space limits.
Finally, the thesis extends this quantitative approach to bio-oils, addressing challenges such as the absence of commercial internal standards or model compounds. It evaluates the influence of water content and ionization source on method applicability to bio-oils with varying hydrodeoxygenation (HDO) levels. The results highlight the relevance of applying the acquired knowledge from complex petroleum samples and their limitations to oxygen-rich biomass-derived oils
On the Exergoeconomics of the Thermochemical Recycling of End-of-Life Tires by Pyrolysis
No full textThis work presents the exergoeconomic assessment of a 1000 kg/h model industrial plant for the pyrolysis of end-of-life tires (ELTs) to produce raw recovered carbon black (RRCB), tire pyrolysis gas (TPG), and tire pyrolysis oil (TPO) for subsequent distillation. TPG is deemed to be used for both supplying the energy needed for pyrolysis and generating electricity through an internal combustion gas engine (ICGE). The resulting hot flue gases from the ICGE are proposed to provide the energy for the TPO distillation stage. The thermodynamic characteristics of the streams were determined based on results obtained at laboratory scale. After mass, energy, and exergy balances, the exergoeconomic principles were applied to estimate the exergy and monetary cost of the plant products. Exergy destruction in each subsystem was estimated, as well as the production costs of the TPO, its distillate fractions, the TPG, and the RRCB, among others, considering a variation of the ELTs price between -10 USD/t and 400 USD/t. An alternative approach was also evaluated in which electric heaters instead of combustion gases drive the pyrolysis and TPO distillation processes. Although technically feasible, this alternative plant could be more sensitive to heat losses which compromises its energy self-sufficiency. However, the current trend toward chemical industry electrification and the ability to precisely control pyrolysis and distillation parameters to improve product quality make this route highly attractive. These analyses aim to consolidate the advantages of scaling up the pyrolysis process and its potential to pursue the circularity of ELTs and the defossilization of the tire industry.The authors would like to express their gratitude to COLCIENCIAS for the financial support to the research project 1210-715-51742. F. Campuzano acknowledges COLCIENCIAS for the Ph.D. scholarship 757-2016. This work was also supported by the Grupo de Investigaciones Ambientales (GIA) at Universidad Pontificia Bolivariana (UPB) and the Clean Combustion Research Platform (CERP) at King Abdullah University of Science and Technology (KAUST)
Zeolite–Water Chemistry: Characterization Methods to Unveil Zeolite Structure
No full textThis review provides comprehensive aspects of the interaction of water with zeolites, focusing on its influence on the structural and catalytic properties of zeolites. It details how water can alter zeolite acidity by forming hydrogen bonding or hydronium ions through different modes of water in zeolite topologies. Moreover, it summarizes the risks of zeolite stability loss via hydrolysis of Si−O−T bonds to influence the stability, structure, and catalytic reactivity of zeolites. To address water interference, various strategies for water removal from zeolite frameworks are reviewed and proposed from the structural perspective of the zeolites. By combining advanced in-situ techniques, FTIR and solid-state NMR have proven effective in providing atomic-level insights, as they eliminate the masking effects of water to enable precise characterization of the zeolite framework. This work underscores the importance of these methods in minimizing the influence of water, enhancing the reliability of zeolite characterization for catalytic applications, and providing insights into recent advancements, challenges, and future directions in the related fields.Funding for this work was provided by baseline grant (BAS/1/1402\u201001\u201001) from King Abdullah University of Science and Technology (KAUST), Saudi Arabia. This work was also supported by the Soonchunhyang University Research Fund
Fundamental limits via CRB of semi-blind channel estimation in Massive MIMO systems
No full textThis paper investigates the asymptotic behavior of the deterministic and stochastic Cramér-Rao Bounds (CRB) for semi-blind channel estimation in massive multiple-input multiple-output (MIMO) systems. We derive and analyze mathematically tractable expressions for both metrics under various asymptotic regimes, which govern the growth rates of the number of antennas, the number of users, the training sequence length, and the transmission block length. Unlike the existing work, our results show that the CRB can be made arbitrarily small as the transmission block length increases, but only when the training sequence length grows at the same rate and the number of users remains fixed. However, if the number of training sequences remains proportional to the number of users, the CRB converges to a non-vanishing constant. Numerical results are presented to support our findings and demonstrate the advantages of semi-blind channel estimation in reducing the required number of training sequences
CCDC 2426060: Experimental Crystal Structure Determination :
No full textAn entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures
Spiideo SoccerNet SynLoc: Single Frame World Coordinate Athlete Detection and Localization with Synthetic Data
No full textCurrently, most research and public datasets for video sports analytics are base on detecting players as bounding boxes in broadcast videos. Going from there to precise locations on the pitch is however hard. Modern solutions are making dedicated static cameras covering the entire pitch more readily accessible, and they are now used more and more even in lower tiers. To promote research that can take benefits of such cameras and produce more precise pitch locations, we introduce the Spiideo SoccerNet SynLoc dataset. It consists of synthetic athletes rendered on top of images from real world installation of such cameras. We also introduce a new task of detecting the players in the world pitch coordinate system and a new metric based solely on real world physical properties where the representation in the image is irrelevant. The dataset and code are publicly available at https://github.com/Spiideo/sskit