Recent Submissions

  • Data for "Competition on Spatial Statistics for Large Datasets"

    Huang, Huang; Abdulah, Sameh; Sun, Ying; Ltaief, Hatem; Keyes, David E.; Genton, Marc G. (KAUST Research Repository, 2021-05-10) [Dataset]
    The enclosed datasets have been generated by the internal spatial data generator tool included in the ExaGeoStat software (https://github.com/ecrc/exageostat). It was used for the 2021 KAUST Competition on Spatial Statistics for Large Datasets (https://cemse.kaust.edu.sa/stsds/kaust-competition-spatial-statistics-large-datasets). The competition had four parts (Sub-competition 1a, Sub-competition 1b, Sub-competition 2a, and Sub-competition 2b). The main purpose of the competition was to reassess existing approximation methods on large spatial datasets in a uniform way that guarantees a fair comparison. The true parameters used for generating each dataset are provided in the PDF file attached with the datasets.
  • Nutrient pollution enhances productivity and framework dissolution in algae- but not in coral-dominated reef communities

    Roth, Florian; El-Khaled, Yusuf C.; Karcher, Denis B.; Rädecker, Nils; Carvalho, Susana; Duarte, Carlos M.; Silva, Luis; Calleja, Maria Ll.; Morán, Xosé Anxelu G.; Jones, Burton H.; Voolstra, Christian R.; Wild, Christian (Marine Pollution Bulletin, Elsevier BV, 2021-05-10) [Article]
    Ecosystem services provided by coral reefs may be susceptible to the combined effects of benthic species shifts and anthropogenic nutrient pollution, but related field studies are scarce. We thus investigated in situ how dissolved inorganic nutrient enrichment, maintained for two months, affected community-wide biogeochemical functions of intact coral- and degraded algae-dominated reef patches in the central Red Sea. Results from benthic chamber incubations revealed 87% increased gross productivity and a shift from net calcification to dissolution in algae-dominated communities after nutrient enrichment, but the same processes were unaffected by nutrients in neighboring coral communities. Both community types changed from net dissolved organic nitrogen sinks to sources, but the increase in net release was 56% higher in algae-dominated communities. Nutrient pollution may, thus, amplify the effects of community shifts on key ecosystem services of coral reefs, possibly leading to a loss of structurally complex habitats with carbonate dissolution and altered nutrient recycling.
  • Temperature Responses of Heterotrophic Bacteria in Co-culture With a Red Sea Synechococcus Strain

    Labban, Abbrar; Palacio, Antonio S.; García, Francisca C.; Hadaidi, Ghaida A.; Ansari, Mohd Ikram; López-Urrutia, Ángel; Alonso-Sáez, Laura; Hong, Pei-Ying; Moran, Xose Anxelu G. (Frontiers in Microbiology, Frontiers Media SA, 2021-05-10) [Article]
    Interactions between autotrophic and heterotrophic bacteria are fundamental for marine biogeochemical cycling. How global warming will affect the dynamics of these essential microbial players is not fully understood. The aims of this study were to identify the major groups of heterotrophic bacteria present in a Synechococcus culture originally isolated from the Red Sea and assess their joint responses to experimental warming within the metabolic ecology framework. A co-culture of Synechococcus sp. RS9907 and their associated heterotrophic bacteria, after determining their taxonomic affiliation by 16S rRNA gene sequencing, was acclimated and maintained in the lab at different temperatures (24–34°C). The abundance and cellular properties of Synechococcus and the three dominant heterotrophic bacterial groups (pertaining to the genera Paracoccus, Marinobacter, and Muricauda) were monitored by flow cytometry. The activation energy of Synechococcus, which grew at 0.94–1.38 d–1, was very similar (0.34 ± 0.02 eV) to the value hypothesized by the metabolic theory of ecology (MTE) for autotrophs (0.32 eV), while the values of the three heterotrophic bacteria ranged from 0.16 to 1.15 eV and were negatively correlated with their corresponding specific growth rates (2.38–24.4 d–1). The corresponding carrying capacities did not always follow the inverse relationship with temperature predicted by MTE, nor did we observe a consistent response of bacterial cell size and temperature. Our results show that the responses to future ocean warming of autotrophic and heterotrophic bacteria in microbial consortia might not be well described by theoretical universal rules.
  • Predicting anti-PD-1 responders in malignant melanoma from the frequency of S100A9+ monocytes in the blood.

    Rad Pour, Soudabeh; Pico de Coaña, Yago; Demorentin, Xavier Martinez; Melief, Jeroen; Thimma, Manjula; Wolodarski, Maria; Gomez-Cabrero, David; Hansson, Johan; Kiessling, Rolf; Tegner, Jesper (Journal for immunotherapy of cancer, BMJ, 2021-05-08) [Article]
    BackgroundWhile programmed cell death receptor 1 (PD-1) blockade treatment has revolutionized treatment of patients with melanoma, clinical outcomes are highly variable, and only a fraction of patients show durable responses. Therefore, there is a clear need for predictive biomarkers to select patients who will benefit from the treatment.MethodTo identify potential predictive markers for response to PD-1 checkpoint blockade immunotherapy, we conducted single-cell RNA sequencing analyses of peripheral blood mononuclear cells (PBMC) (n=8), as well as an in-depth immune monitoring study (n=20) by flow cytometry in patients with advanced melanoma undergoing treatment with nivolumab at Karolinska University Hospital. Blood samples were collected before the start of treatment and at the time of the second dose.ResultsUnbiased single-cell RNA sequencing of PBMC in patients with melanoma uncovered that a higher frequency of monocytes and a lower ratio of CD4+ T cells to monocyte were inversely associated with overall survival. Similarly, S100A9 expression in the monocytic subset was correlated inversely with overall survival. These results were confirmed by a flow cytometry-based analysis in an independent patient cohort.ConclusionOur results suggest that monocytic cell populations can critically determine the outcome of PD-1 blockade, particularly the subset expressing S100A9, which should be further explored as a possible predictive biomarker. Detailed knowledge of the biological role of S100A9+ monocytes is of high translational relevance.
  • Genetic mapping of the early responses to salt stress in Arabidopsis thaliana

    Awlia, Mariam Sahal Abdulaziz; Alshareef, Nouf Owdah Hameed; Saber, Noha; Korte, Arthur; Oakey, Helena; Panzarová, Klára; Trtílek, Martin; Negrão, Sónia; Tester, Mark A.; Julkowska, Magdalena M. (The Plant Journal, Wiley, 2021-05-08) [Article]
    Salt stress decreases plant growth prior to significant ion accumulation in the shoot. However, the processes underlying this rapid reduction in growth are still unknown. To understand the changes in salt stress responses through time and at multiple physiological levels, examining different plant processes within a single setup is required. Recent advances in phenotyping has allowed the image-based estimation of plant growth, morphology, colour and photosynthetic activity. In this study, we examined the salt stress-induced responses of 191 Arabidopsis accessions from one hour to seven days after treatment using high-throughput phenotyping. Multivariate analyses and machine learning algorithms identified that quantum yield measured in the light-adapted state (Fv´/Fm´) greatly affected growth maintenance in the early phase of salt stress, while maximum quantum yield (QY max) was crucial at a later stage. In addition, our genome-wide association study (GWAS) identified 770 loci that were specific to salt stress, in which two loci associated with QY max and Fv´/Fm´ were selected for validation using T-DNA insertion lines. We characterised an unknown protein kinase found in the QY max locus, which reduced photosynthetic efficiency and growth maintenance under salt stress. Understanding the molecular context of the identified candidate genes will provide valuable insights into the early plant responses to salt stress. Furthermore, our work incorporates high-throughput phenotyping, multivariate analyses and GWAS, uncovering details of temporal stress responses, while identifying associations across different traits and time points, which likely constitute the genetic components of salinity tolerance.
  • Application of Dempster–Shafer Networks to a Real-Time Unmanned Systems Risk Analysis Framework

    Dunham, Joel; Johnson, Eric; Feron, Eric; German, Brian (Journal of Aerospace Information Systems, American Institute of Aeronautics and Astronautics (AIAA), 2021-05-07) [Article]
    Unmanned aerial systems (UASs) are continuing to proliferate. Quantitative risk assessment for UAS operations, both a priori and during the operation, are necessary for governing authorities and insurance companies to understand the risks and properly approve operations and assign insurance premiums, respectively. In this paper, the problem of UAS risk analysis and decision making is treated through a novel application of Dempster–Shafer (DS) networks using auto-updating transition matrices. This method was motivated by the results of the 2018 UAS Safety Symposium held at the Georgia Institute of Technology, which was conducted as part of the research detailed in this paper. The paper describes training a DS network based on simulated operation data, testing the capabilities of the trained network to make real-time decisions on a small UAS against a baseline system in a representative mission, and exploring how this system would extend to a more inclusive UAS ecosystem. Conclusions are drawn with respect to the research performed, and additional research directions are proposed.
  • Compartmentalization of bacterial and fungal microbiomes in the gut of adult honeybees

    Callegari, Matteo; Crotti, Elena; Fusi, Marco; Marasco, Ramona; Gonella, Elena; De Noni, Ivano; Romano, Diego; Borin, Sara; Tsiamis, George; Cherif, Ameur; Alma, Alberto; Daffonchio, Daniele (npj Biofilms and Microbiomes, Springer Science and Business Media LLC, 2021-05-07) [Article]
    AbstractThe core gut microbiome of adult honeybee comprises a set of recurring bacterial phylotypes, accompanied by lineage-specific, variable, and less abundant environmental bacterial phylotypes. Several mutual interactions and functional services to the host, including the support provided for growth, hormonal signaling, and behavior, are attributed to the core and lineage-specific taxa. By contrast, the diversity and distribution of the minor environmental phylotypes and fungal members in the gut remain overlooked. In the present study, we hypothesized that the microbial components of forager honeybees (i.e., core bacteria, minor environmental phylotypes, and fungal members) are compartmentalized along the gut portions. The diversity and distribution of such three microbial components were investigated in the context of the physico-chemical conditions of different gut compartments. We observed that changes in the distribution and abundance of microbial components in the gut are consistently compartment-specific for all the three microbial components, indicating that the ecological and physiological interactions among the host and microbiome vary with changing physico-chemical and metabolic conditions of the gut.
  • A decentralized water/electricity cogeneration system integrating concentrated photovoltaic/thermal collectors and vacuum multi-effect membrane distillation

    Chen, Qian; Burhan, Muhammad; Akhtar, Faheem; Ybyraiymkul, Doskhan; Shahzad, Muhammad Wakil; Li, Yong; Ng, Kim Choon (Energy, Elsevier BV, 2021-05-07) [Article]
    Cogeneration of electricity and freshwater by integrating photovoltaic/thermal collectors and desalination systems is one of the most promising methods to tackle the challenges of water and energy shortage in remote areas. This study investigates a decentralized water/electricity cogeneration system combining concentrated photovoltaic/thermal collectors and a vacuum multi-effect membrane distillation system. The merits of such a configuration include high compactness and improved thermodynamic efficiency. To evaluate the long-term production potential of the proposed system, a thermodynamic analysis is firstly conducted. Under the climatic conditions of Makkah, Saudi Arabia, the system can convert ∼70% of the solar irradiance into useful energy. The annual productivity of electricity and distilled water are 562 kWh and 5.25 m3, respectively, per m2 of the solar collector area. Electricity and water production rates are found to be impacted by hot water flowrate, feed seawater flowrate and heat storage tank dimension, while the overall exergy efficiency stabilizes at 25-27%. Based on the production rates, an economic analysis is conducted through life-cycle cost analysis. The final desalination cost is calculated to be $0.7-4.3/m3, depending on the solar collector cost and the electricity price. The derived results will enable a more in-depth understanding of the proposed solar-driven water/electricity cogeneration system.
  • A Robust Wearable Point-of-Care CNT-Based Strain Sensor for Wirelessly Monitoring Throat-Related Illnesses

    Qaiser, Nadeem; Al-Modaf, Fhad; Khan, Sherjeel Munsif; Shaikh, Sohail F.; El-Atab, Nazek; Hussain, Muhammad Mustafa (Advanced Functional Materials, Wiley, 2021-05-07) [Article]
    Point-of-care testing (POC) has the ability to detect chronic and infectious diseases early or at the time of occurrence and provide a state-of-the-art personalized healthcare system. Recently, wearable and flexible sensors have been employed to analyze sweat, glucose, blood, and human skin conditions. However, a flexible sensing system that allows for the real-time monitoring of throat-related illnesses, such as salivary parotid gland swelling caused by flu and mumps, is necessary. Here, for the first time, a wearable, highly flexible, and stretchable piezoresistive sensing patch based on carbon nanotubes (CNTs) is reported, which can record muscle expansion or relaxation in real-time, and thus act as a next-generation POC sensor. The patch offers an excellent gauge factor for in-plane stretching and spatial expansion with low hysteresis. The actual extent of muscle expansion is calculated and the gauge factor for applications entailing volumetric deformations is redefined. Additionally, a bluetooth-low-energy system that tracks muscle activity in real-time and transmits the output signals wirelessly to a smartphone app is utilized. Numerical calculations verify that the low stress and strain lead to excellent mechanical reliability and repeatability. Finally, a dummy muscle is inflated using a pneumatic-based actuator to demonstrate the application of the affixed wearable next-generation POC sensor.
  • Alternative glycosylation controls endoplasmic reticulum dynamics and tubular extension in mammalian cells

    Kerselidou, Despoina; Dohai, Bushra Saeed; Nelson, David R.; Daakour, Sarah; De Cock, Nicolas; Hassoun, Zahra Al Oula; Kim, Dae-Kyum; Olivet, Julien; El Assal, Diana C.; Jaiswal, Ashish; Alzahmi, Amnah; Saha, Deeya; Pain, Charlotte; Matthijssens, Filip; Lemaitre, Pierre; Herfs, Michael; Chapuis, Julien; Ghesquiere, Bart; Vertommen, Didier; Kriechbaumer, Verena; Knoops, Kèvin; Lopez-Iglesias, Carmen; van Zandvoort, Marc; Lambert, Jean-Charles; Hanson, Julien; Desmet, Christophe; Thiry, Marc; Lauersen, Kyle J.; Vidal, Marc; Van Vlierberghe, Pieter; Dequiedt, Franck; Salehi-Ashtiani, Kourosh; Twizere, Jean-Claude (Science Advances, American Association for the Advancement of Science (AAAS), 2021-05-07) [Article]
    The endoplasmic reticulum (ER) is a central eukaryotic organelle with a tubular network made of hairpin proteins linked by hydrolysis of guanosine triphosphate nucleotides. Among posttranslational modifications initiated at the ER level, glycosylation is the most common reaction. However, our understanding of the impact of glycosylation on the ER structure remains unclear. Here, we show that exostosin-1 (EXT1) glycosyltransferase, an enzyme involved in N-glycosylation, is a key regulator of ER morphology and dynamics. We have integrated multiomics and superresolution imaging to characterize the broad effect of EXT1 inactivation, including the ER shape-dynamics-function relationships in mammalian cells. We have observed that inactivating EXT1 induces cell enlargement and enhances metabolic switches such as protein secretion. In particular, suppressing EXT1 in mouse thymocytes causes developmental dysfunctions associated with the ER network extension. Last, our data illuminate the physical and functional aspects of the ER proteome-glycome-lipidome structure axis, with implications in biotechnology and medicine.
  • Manipulation of carotenoid metabolism stimulates biomass and stress tolerance in tomato

    Vallarino, José G; Mi, Jianing; Pet?ík, Ivan; Novak, Ondrej; Correa, Sandra Marcela; Kosmacz, Monika; Havaux, Michel; Rodriguez-Concepcion, Manuel; Al-Babili, Salim; Fernie, Alisdair R.; Skirycz, Aleksandra; Moreno, Juan C (Cold Spring Harbor Laboratory, 2021-05-07) [Preprint]
    Improving yield, nutritional value and tolerance to abiotic stress are major targets of current breeding and biotechnological approaches that aim at increasing crop production and ensuring food security. Metabolic engineering of carotenoids, the precursor of Vitamin-A and plant hormones that regulate plant growth and response to adverse growth conditions, has been mainly focusing on provitamin A biofortification or the production of high-value carotenoids. Here, we show that the introduction of a single gene of the carotenoid biosynthetic pathway in different tomato cultivars simultaneously improved photosynthetic capacity and tolerance to various abiotic stresses (e.g., high light, salt, and drought), caused an up to 77% fruit yield increase and enhanced fruit's provitamin A content and shelf life. Our findings pave the way for developing a new generation of crops that combine high productivity and increased nutritional value with the capability to cope with climate change-related environmental challenges.
  • Extensive Screening of Solvent-Linked Porous Polymers through Friedel-Crafts Reaction for Gas Adsorption

    Rozyyev, Vepa; Hong, Yeongran; Yavuz, Mustafa S.; Thirion, Damien; Yavuz, Cafer T. (Advanced Energy and Sustainability Research, Wiley, 2021-05-07) [Article]
    Scalability, cost and feasibility of porous structures in gas capture are prerequisites for emerging materials to be promising in industry. Here, we present a simpler variant of Friedel-Crafts synthesis of highly porous covalent organic polymers (COPs) based on an unprecedented solvent mediated cross-linking. Alkyl chlorides behave as both solvents and linkers in the presence of AlCl3. Studies on three classes of 18 different monomers using dichloromethane, chloroform, and 1,2-dichloroethane lead to produce 29 new COPs (124-152). Polymers were characterized by Fourier-transform infrared spectroscopy (FTIR), nuclear magnetic resonance (NMR) spectroscopy, elemental composition analysis, scanning electron microscopy (SEM), thermogravimetric analysis (TGA) and porosity analyzer. The synthesized COPs exhibited structures from nonporous to highly porous morphologies with Brunauer–Emmett–Teller (BET) surface areas as high as 1685 m2 g-1. These COPs showed high gas uptake towards CO2 (up to 4.71 mmol g-1 at 273 K, 1.1 bar), CH4 (up to 1.31 mmol g-1 at 273 K, 1.1 bar), and H2 (up to 2.02 wt.% at 77 K, 1.1 bar). The findings point to significant potential in producing sustainable porous materials through simple and scalable methodology developed here.
  • Synthesis and characterization of second-generation phosphorus-nitrogen PN 3 P-rhodium (I) pincer complexes via ligand post-modification

    Zhou, Chunhui; Hu, Jinsong; Chakraborty, Priyanka; Huang, Kuo-Wei (Zeitschrift für anorganische und allgemeine Chemie, Wiley, 2021-05-07) [Article]
    A pseudo-dearomatized PN3P*Rh−CO complex reacts with various alkyl/benzyl halides to furnish a series of second-generation PN3P-pincer carbonyl complexes via the ligand post-modification strategy. These synthesized complexes were fully characterized by NMR, FTIR, HRMS, and single-crystal X-ray crystallography. A plausible mechanism for the formation of 2nd-generation PN3P complexes was proposed based on the isolation of the minor dialkylated products.
  • Accelerating Geostatistical Modeling and Prediction With Mixed-Precision Computations: A High-Productivity Approach with PaRSEC

    Abdulah, Sameh; Cao, Qinglei; Pei, Yu; Bosilca, George; Dongarra, Jack; Genton, Marc G.; Keyes, David E.; Ltaief, Hatem; Sun, Ying (2021-05-06) [Technical Report]
    Geostatistical modeling, one of the prime motivating applications for exascale computing, is a technique for predicting desired quantities from geographically distributed data, based on statistical models and optimization of parameters. Spatial data is assumed to possess properties of stationarity or non-stationarity via a kernel fitted to a covariance matrix. A primary workhorse of stationary spatial statistics is Gaussian maximum log-likelihood estimation (MLE), whose central data structure is a dense, symmetric positive definite covariance matrix of dimension of the number of correlated observations. Two essential operations in MLE are the application of the inverse and evaluation of the determinant of the covariance matrix. These can be rendered through the Cholesky decomposition and triangular solution. In this contribution, we reduce the precision of weakly correlated locations to single- or half- precision based on distance. We thus exploit mathematical structure to migrate MLE to a three-precision approximation that takes advantage of contemporary architectures offering BLAS3-like operations in a single instruction that are extremely fast for reduced precision. We illustrate application-expected accuracy worthy of double-precision from a majority half-precision computation, in a context where uniform single precision is by itself insufficient. In tackling the complexity and imbalance caused by the mixing of three precisions, we deploy the PaRSEC runtime system. PaRSEC delivers on-demand casting of precisions while orchestrating tasks and data movement in a multi-GPU distributed-memory environment within a tile-based Cholesky factorization. Application-expected accuracy is maintained while achieving up to 1.59 by mixing FP64/FP32 operations on 1536 nodes of HAWK or 4096 nodes of Shaheen-II, and up to 2.64X by mixing FP64/FP32/FP16 operations on 128 nodes of Summit, relative to FP64-only operations, This translates into up to 4.5, 4.7, and 9.1 (mixed) PFlop/s sustained performance, respectively, demonstrating a synergistic combination of exascale architecture, dynamic runtime software, and algorithmic adaptation applied to challenging environmental problems.
  • Decentralized Task Reallocation on Parallel Computing Architectures Targeting an Avionics Application

    Khamvilai, Thanakorn; Sutter, Louis; Baufreton, Philippe; Neumann, François; Feron, Eric (Journal of Optimization Theory and Applications, Springer Science and Business Media LLC, 2021-05-06) [Article]
    This work presents an online decentralized allocation algorithm of a safety-critical application on parallel computing architectures, where individual Computational Units can be affected by faults. The described method includes representing the architecture by an abstract graph where each node represents a Computational Unit. Applications are also represented by the graph of Computational Units they require for execution. The problem is then to decide how to allocate Computational Units to applications to guarantee execution of a safety-critical application. The problem is formulated as an optimization problem with the form of an Integer Linear Program. A state-of-the-art solver is then used to solve the problem. Decentralizing the allocation process is achieved through redundancy of the allocator executed on the architecture. No centralized element decides on the allocation of the entire architecture, thus improving the reliability of the system. Inspired by multi-core architectures in avionics systems, an experimental illustration of the work is also presented. It is used to demonstrate the capabilities of the proposed allocation process to maintain the operation of a physical system in a decentralized way while individual components fail.
  • Direct proof of unconditional asymptotic consensus in the Hegselmann–Krause model with transmission-type delay

    Haskovec, Jan (Bulletin of the London Mathematical Society, Wiley, 2021-05-06) [Article]
    We present a direct proof of asymptotic consensus in the non-linear Hegselmann–Krause model with transmission-type delay, where the communication weights depend on the particle distance in phase space. Our approach is based on an explicit estimate of the shrinkage of the group diameter on finite time intervals and avoids the usage of Lyapunov-type functionals or results from non-negative matrix theory. It works for both the original formulation of the model with communication weights scaled by the number of agents, and the modification with weights normalized a'la Motsch–Tadmor. We pose only minimal assumptions on the model parameters. In particular, we only assume global positivity of the influence function, without imposing any conditions on its decay rate or monotonicity. Moreover, our result holds for any length of the delay.
  • StyleFlow: Attribute-conditioned Exploration of StyleGAN-Generated Images using Conditional Continuous Normalizing Flows

    Abdal, Rameen; Zhu, Peihao; Mitra, Niloy J.; Wonka, Peter (ACM Transactions on Graphics, Association for Computing Machinery (ACM), 2021-05-06) [Article]
    High-quality, diverse, and photorealistic images can now be generated by unconditional GANs (e.g., StyleGAN). However, limited options exist to control the generation process using (semantic) attributes while still preserving the quality of the output. Further, due to the entangled nature of the GAN latent space, performing edits along one attribute can easily result in unwanted changes along other attributes. In this article, in the context of conditional exploration of entangled latent spaces, we investigate the two sub-problems of attribute-conditioned sampling and attribute-controlled editing. We present StyleFlow as a simple, effective, and robust solution to both the sub-problems by formulating conditional exploration as an instance of conditional continuous normalizing flows in the GAN latent space conditioned by attribute features. We evaluate our method using the face and the car latent space of StyleGAN, and demonstrate fine-grained disentangled edits along various attributes on both real photographs and StyleGAN generated images. For example, for faces, we vary camera pose, illumination variation, expression, facial hair, gender, and age. Finally, via extensive qualitative and quantitative comparisons, we demonstrate the superiority of StyleFlow over prior and several concurrent works. Project Page and Video: https://rameenabdal.github.io/StyleFlow .
  • Activity of loggerhead turtles during the U-shaped dive: insights using angular velocity metrics

    Gunner, RM; Wilson, RP; Holton, MD; Scott, R; Arkwright, A; Fahlman, A; Ulrich, M; Hopkins, P; Duarte, Carlos M.; Eizaguirre, C (Endangered Species Research, Inter-Research Science Center, 2021-05-06) [Article]
    Understanding the behavioural ecology of endangered taxa can inform conservation strategies. The activity budgets of the loggerhead turtle Caretta caretta are still poorly understood because many tracking methods show only horizontal displacement and ignore dives and associated behaviours. However, time-depth recorders have enabled researchers to identify flat, U-shaped dives (or type 1a dives) and these are conventionally labelled as resting dives on the seabed because they involve no vertical displacement of the animal. Video- and acceleration-based studies have demonstrated this is not always true. Focusing on sea turtles nesting on the Cabo Verde archipelago, we describe a new metric derived from magnetometer data, absolute angular velocity, that integrates indices of angular rotation in the horizontal plane to infer activity. Using this metric, we evaluated the variation in putative resting behaviours during the bottom phase of type 1a dives for 5 individuals over 13 to 17 d at sea during a single inter-nesting interval (over 75 turtle d in total). We defined absolute resting within the bottom phase of type 1a dives as periods with no discernible acceleration or angular movement. Whilst absolute resting constituted a significant proportion of each turtle’s time budget for this 1a dive type, turtles allocated 16-38% of their bottom time to activity, with many dives being episodic, comprised of intermittent bouts of rest and rotational activity. This implies that previously considered resting behaviours are complex and need to be accounted for in energy budgets, particularly since energy budgets may impact conservation strategies.
  • A Reinforcement Learning-based Economic Model Predictive Control Framework for Autonomous Operation of Chemical Reactors

    Alhazmi, Khalid; Albalawi, Fahad; Sarathy, Mani (arXiv, 2021-05-06) [Preprint]
    Economic model predictive control (EMPC) is a promising methodology for optimal operation of dynamical processes that has been shown to improve process economics considerably. However, EMPC performance relies heavily on the accuracy of the process model used. As an alternative to model-based control strategies, reinforcement learning (RL) has been investigated as a model-free control methodology, but issues regarding its safety and stability remain an open research challenge. This work presents a novel framework for integrating EMPC and RL for online model parameter estimation of a class of nonlinear systems. In this framework, EMPC optimally operates the closed loop system while maintaining closed loop stability and recursive feasibility. At the same time, to optimize the process, the RL agent continuously compares the measured state of the process with the model's predictions (nominal states), and modifies model parameters accordingly. The major advantage of this framework is its simplicity; state-of-the-art RL algorithms and EMPC schemes can be employed with minimal modifications. The performance of the proposed framework is illustrated on a network of reactions with challenging dynamics and practical significance. This framework allows control, optimization, and model correction to be performed online and continuously, making autonomous reactor operation more attainable.
  • Highly Accurate Thickness Determination of 2D Materials

    Xiao, Yiping; Zheng, Wenwen; Yuan, Bin; Wen, Chao; Lanza, Mario (Crystal Research and Technology, Wiley, 2021-05-06) [Article]
    Determining the thickness of two-dimensional (2D) materials accurately and reliably is highly necessary for multiple investigations, but at the same time it can be quite complex. Most studies in this field measure a topographic map at the edge of the 2D material using an atomic force microscope (AFM), and plot a single-line cross-section using the software of the AFM. However, this method is highly inaccurate and can result in high relative errors due to surface roughness and line-to-line variability. This is even more important in ultrathin (<4 nm) 2D materials grown by chemical vapor deposition, as these exhibit a larger surface roughness (compared to mechanically exfoliated) due to the high density of local defects. Here it is shown that the thickness of ultrathin 2D materials can be determined statistically with high accuracy and reliability in a very easy way by plotting the histogram height plot. Using this method should enhance the reliability of investigations and research papers in the field of 2D materials.

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