Now showing items 1-20 of 56287

    • Coupled Crust-Mantle Evolution for > 2 Gy in Southern Africa from Exceptionally Strong Crustal Anisotropy

      THYBO, Hans; YOUSSUF, Mohammad; ARTEMIEVA, Irina M. (Acta Geologica Sinica - English Edition, Wiley, 2021-11-27) [Article]
      An enigmatic feature of Precambrian continental lithosphere is its long-term stability, which depends on the degree of coupling between the crust and mantle since cratonisation. Earlier studies infer deformation of the lower lithosphere by mantle flow with fast direction of seismic anisotropy being parallel to present plate motion, and/or report anisotropy frozen into the lithospheric mantle. We demonstrate coupled crust-mantle evolution in southern African cratons for more than 2 billion years based on unexpectedly strong crustal azimuthal anisotropy (Thybo et al., 2019). The direction of the fast axis is uniform within tectonic units and parallel to orogenic strike in the Limpopo and Cape fold belts. It is further parallel to the strike of major dyke swarms which indicates that a large part of the observed anisotropy is controlled by lithosphere fabrics and macroscopic effects. Parallel fast axes in the crust and in the mantle indicate coupled crust-mantle evolution. These conclusions have implications for the rheology of the lower lithosphere and the effects of mantle flow on lithosphere deformation.
    • Perovskite-Nanosheet Sensitizer for Highly Efficient Organic X-ray Imaging Scintillator

      Wang, Jian-Xin; Wang, Xiaojia; Yin, Jun; Gutierrez Arzaluz, Luis; He, Tengyue; Chen, Cailing; Han, Yu; Zhang, Yuhai; Bakr, Osman; Eddaoudi, Mohamed; Mohammed, Omar F. (ACS Energy Letters, American Chemical Society (ACS), 2021-11-27) [Article]
      The weak X-ray capture capability of organic scintillators always leads to poor imaging resolution and detection sensitivity. Here, we realize an efficient and reabsorption-free organic scintillator at the interface of perovskite nanosheets using a very efficient energy transfer strategy. Our steady-state and ultrafast time-resolved experiments supported by density functional theory calculations demonstrate that an efficient interfacial energy transfer from the perovskite nanosheet to the organic chromophore with thermally activated delayed fluorescence (TADF) character can be achieved. Interestingly, we found that the direct harnessing of both singlet and triplet excitons of the TADF chromophores also contributed greatly to its remarkably enhanced radioluminescence intensity and X-ray sensitivity. A high X-ray imaging resolution of 135 μm and a low detection limit of 38.7 nGy/s were achieved in the fabricated X-ray imaging scintillator.
    • Selection of a reference gene for studies on lipid-related aquatic adaptations of toothed whales ( Grampus griseus )

      Senevirathna, Jayan D. M.; Yonezawa, Ryo; Saka, Taiki; Igarashi, Yoji; Funasaka, Noriko; Yoshitake, Kazutoshi; Kinoshita, Shigeharu; Asakawa, Shuichi (Ecology and Evolution, Wiley, 2021-11-26) [Article]
    • Accelerating wheat breeding for end-use quality through association mapping and multivariate genomic prediction

      Zhang-Biehn, Shichen; Fritz, Allan K.; Zhang, Guorong; Evers, Byron; Regan, Rebecca; Poland, Jesse (The Plant Genome, Wiley, 2021-11-24) [Article]
      In hard-winter wheat (Triticum aestivum L.) breeding, the evaluation of end-use quality is expensive and time-consuming, being relegated to the final stages of the breeding program after selection for many traits including disease resistance, agronomic performance, and grain yield. In this study, our objectives were to identify genetic variants underlying baking quality traits through genome-wide association study (GWAS) and develop improved genomic selection (GS) models for the quality traits in hard-winter wheat. Advanced breeding lines (n = 462) from 2015–2017 were genotyped using genotyping-by-sequencing (GBS) and evaluated for baking quality. Significant associations were detected for mixograph mixing time and bake mixing time, most of which were within or in tight linkage to glutenin and gliadin loci and could be suitable for marker-assisted breeding. Candidate genes for newly associated loci are phosphate-dependent decarboxylase and lipid transfer protein genes, which are believed to affect nitrogen metabolism and dough development, respectively. The use of GS can both shorten the breeding cycle time and significantly increase the number of lines that could be selected for quality traits, thus we evaluated various GS models for end-use quality traits. As a baseline, univariate GS models had 0.25–0.55 prediction accuracy in cross-validation and from 0 to 0.41 in forward prediction. By including secondary traits as additional predictor variables (univariate GS with covariates) or correlated response variables (multivariate GS), the prediction accuracies were increased relative to the univariate model using only genomic information. The improved genomic prediction models have great potential to further accelerate wheat breeding for end-use quality.
    • An Interactive Exploration System for Physically-Observable Objective Vortices in Unsteady 2D Flow

      Zhang, Xingdi (2021-11-24) [Thesis]
      Advisor: Hadwiger, Markus
      Committee members: Pottmann, Helmut; Viola, Ivan
      Vortex detection has been a long-standing and challenging topic in fluid analysis. Recent state-of-the-art extraction and visualization of vortices in unsteady fluid flow employ objective vortex criteria, which makes feature extraction independent of reference frames or observers. However, even objectivity can only guarantee that different observers reach the same conclusions, but not necessarily guarantee that these conclusions are the only physically meaningful or relevant ones. Moreover, a significant challenge is that a single observer is often not sufficient to accurately observe multiple vortices that follow different motions. This thesis presents a novel mathematical framework that represents physically realizable observers as the Lie algebra of the Killing fields on the underlying manifold, together with a software system that enables the exploration and use of an interactively chosen set of observers, resulting in relative velocity fields and objective vortex structures in real-time. Based on our mathematical framework, our system facilitates the objective detection and visualization of vortices relative to well-adapted reference frame motions, while at the same time guaranteeing that these observers are physically realizable. We show how our framework speeds up the exploration of objective vortices in unsteady 2D flow, on planar as well as on spherical domains.
    • Exploring the Structure and Performance of Cd–Chalcogenide Photocatalysts in Selective Trifluoromethylation

      Muralirajan, Krishnamoorthy; Kancherla, Rajesh; Bau, Jeremy; Taksande, Mayur Rahul; Qureshi, Muhammad; Takanabe, Kazuhiro; Rueping, Magnus (ACS Catalysis, American Chemical Society (ACS), 2021-11-24) [Article]
      The field of heterogeneous photoredox catalysis has grown substantially and impacted organic synthesis because of the affordability and reusability of catalysts. This study reports radical trifluoromethylation with Cd–chalcogenide semiconductors. Cd semiconductors, particularly CdSe, are readily available, commercial, visible-light-responsive, heterogeneous photocatalysts. The potential of readily available Cd semiconductors, particularly CdSe, is confirmed by their increased photocatalytic activity toward trifluoromethylation with various substrates, such as (hetero)arenes and vinylic amides/acids, via addition, cyclization, and decarboxylation under visible light. The economic significance of this strategy is also highlighted through the scalable synthesis of biologically active molecules followed by catalyst reuse. Moreover, these catalysts are relatively inexpensive compared with transition metal-based homogeneous photocatalysts, presently used in organic synthesis.
    • A Homozygous Missense Variant in PPP1R1B/DARPP-32 Is Associated With Generalized Complex Dystonia

      Khan, Amjad; Molitor, Anne; Mayeur, Sylvain; Zhang, Gaoqun; Rinaldi, Bruno; Lannes, Béatrice; Lhermitte, Benoît; Umair, Muhammad; Arold, Stefan T.; Friant, Sylvie; Rastegar, Sepand; Anheim, Mathieu; Bahram, Seiamak; Carapito, Raphael (Movement Disorders, Wiley, 2021-11-24) [Article]
      Background The dystonias are a heterogeneous group of hyperkinetic disorders characterized by sustained or intermittent muscle contractions that cause abnormal movements and/or postures. Although more than 200 causal genes are known, many cases of primary dystonia have no clear genetic cause. Objectives To identify the causal gene in a consanguineous family with three siblings affected by a complex persistent generalized dystonia, generalized epilepsy, and mild intellectual disability. Methods We performed exome sequencing in the parents and two affected siblings and characterized the expression of the identified gene by immunohistochemistry in control human and zebrafish brains. Results We identified a novel missense variant (c.142G>A (NM_032192); p.Glu48Lys) in the protein phosphatase 1 regulatory inhibitor subunit 1B gene (PPP1R1B) that was homozygous in all three siblings and heterozygous in the parents. This gene is also known as dopamine and cAMP-regulated neuronal phosphoprotein 32 (DARPP-32) and has been involved in the pathophysiology of abnormal movements. The uncovered variant is absent in public databases and modifies the conserved glutamate 48 localized close to the serine 45 phosphorylation site. The PPP1R1B protein was shown to be expressed in cells and regions involved in movement control, including projection neurons of the caudate-putamen, substantia nigra neuropil, and cerebellar Purkinje cells. The latter cells were also confirmed to be positive for PPP1R1B expression in the zebrafish brain. Conclusions We report the association of a PPP1R1B/DARPP-32 variant with generalized dystonia in man. It might be relevant to include the sequencing of this new gene in the diagnosis of patients with otherwise unexplained movement disorders. © 2021 International Parkinson and Movement Disorder Society
    • Selective Separation of Lithium Chloride by Organogels Containing Strapped Calix[4]pyrroles

      Wang, Hu; Jones, Leighton O.; Hwang, Inhong; Allen, Marshall J.; Tao, Daliao; Lynch, Vincent M.; Freeman, Benny D.; Khashab, Niveen M.; Schatz, George C; Page, Zachariah A.; Sessler, Jonathan L. (Journal of the American Chemical Society, American Chemical Society (ACS), 2021-11-23) [Article]
      Reported herein are two functionalized crown ether strapped calix[4]pyrroles, H1 and H2. As inferred from competitive salt binding experiments carried out in nitrobenzene-d5 and acetonitrile-d3, these hosts capture LiCl selectively over four other test salts, viz. NaCl, KCl, MgCl2, and CaCl2. Support for the selectivity came from density functional theory (DFT) calculations carried out in a solvent continuum. These theoretical analyses revealed a higher innate affinity for LiCl in the case of H1, but a greater selectivity relative to NaCl in the case of H2, recapitulating that observed experimentally. Receptors H1 and H2 were outfitted with methacrylate handles and subject to copolymerization with acrylate monomers and cross-linkers to yield gels, G1 and G2, respectively. These two gels were found to adsorb lithium chloride preferentially from an acetonitrile solution containing a mixture of LiCl, NaCl, KCl, MgCl2, and CaCl2 and then release the lithium chloride in methanol. The gels could then be recycled for reuse in the selective adsorption of LiCl. As such, the present study highlights the use of solvent polarity switching to drive separations with potential applications in lithium purification and recycling.
    • Green Synthesis of Silver-Peptide Nanoparticles Generated by the Photoionization Process for Anti-Biofilm Application

      Seferji, Kholoud; Susapto, Hepi Hari; Khan, Babar Khalid; Rehman, Zahid Ur; Abbas, Manzar; Emwas, Abdul-Hamid M.; Hauser, Charlotte (ACS Applied Bio Materials, American Chemical Society (ACS), 2021-11-23) [Article]
      An alarming increase in antibiotic-resistant bacterial strains is driving clinical demand for new antibacterial agents. One of the oldest antimicrobial agents is elementary silver (Ag), which has been used for thousands of years. Even today, elementary Ag is used for medical purposes such as treating burns, wounds, and microbial infections. In consideration of the effectiveness of elementary Ag, the present researchers generated effective antibacterial/antibiofilm agents by combining elementary Ag with biocompatible ultrashort peptide compounds. The innovative antibacterial agents comprised a hybrid peptide bound to Ag nanoparticles (IVFK/Ag NPs). These were generated by photoionizing a biocompatible ultrashort peptide, thus reducing Ag ions to form Ag NPs with a diameter of 6 nm. The IVFK/Ag NPs demonstrated promising antibacterial/antibiofilm activity against reference Gram-positive and Gram-negative bacteria compared with commercial Ag NPs. Through morphological changes in Escherichia coli and Staphylococcus aureus, we proposed that the mechanism of action for IVFK/Ag NPs derives from their ability to disrupt bacterial membranes. In terms of safety, the IVFK/Ag NPs demonstrated biocompatibility in the presence of human dermal fibroblast cells, and concentrations within the minimal inhibitory concentration had no significant effect on cell viability. These results demonstrated that hybrid peptide/Ag NPs hold promise as a biocompatible material with strong antibacterial/antibiofilm properties, allowing them to be applied across a wide range of applications in tissue engineering and regenerative medicine.
    • Oriented Two-Dimensional Covalent Organic Framework Membranes with High Ion Flux and Smart Gating Nanofluidic Transport

      Cao, Li; Liu, Xiaowei; Shinde, Digambar; Chen, Cailing; Chen, I-Chun; Li, Zhen; Zhou, Zongyao; Yang, Zhongyu; Han, Yu; Lai, Zhiping (Angewandte Chemie, Wiley, 2021-11-23) [Article]
      Nanofluidic ion transport holds high promise in bio-sensing and energy conversion applications. However, smart nanofluidic devices with high ion flux and modulable ion transport capabilities remain to be realised. Herein, we demonstrate smart nanofluidic devices based on oriented two-dimensional covalent organic framework (2D COF) membranes with vertically aligned nanochannel arrays that achieved a 2–3 orders of magnitude higher ion flux compared with that of conventional single-channel nanofluidic devices. The surface-charge-governed ion conductance is dominant for electrolyte concentration up to 0.01 M. Moreover, owing to the customisable pH-responsivity of imine and phenol hydroxyl groups, the COF-DT membranes attained an actively modulable ion transport with a high pH-gating on/off ratio of ~100. The customisable structure and rich chemistry of COF materials will offer a promising platform for manufacturing nanofluidic devices with modifiable ion/molecular transport features.
    • High conductivity n-Al06Ga04N by ammonia-assisted molecular beam epitaxy for buried tunnel junctions in UV emitters

      Wang, Jianfeng; SaifAddin, Burhan K.; Zollner, Christian J.; Bonef, Bastien; Almogbel, Abdullah S.; Yao, Yifan; Iza, Michael; Zhang, Yuewei; Fireman, Micha N.; Young, Erin C.; DenBaars, Steven P.; Nakamura, Shuji; Speck, James S. (Optics Express, The Optical Society, 2021-11-23) [Article]
    • Investigation of the Antiscaling Performance of Phosphonated Chitosan for Upstream Petroleum Industry Application

      Mady, Mohamed F.; Abdel-Azeim, Safwat; Kelland, Malcolm A. (ACS Sustainable Chemistry & Engineering, American Chemical Society (ACS), 2021-11-23) [Article]
    • Synthesis and Characterization of Asymmetric A1BA2 Supramolecular Triblock Copolymers via Noncovalent Interactions: A Solution and Solid-State Study

      Bhaumik, Saibal; Shan, Wenpeng; Thomas, Edwin L.; Hadjichristidis, Nikos (Macromolecules, American Chemical Society (ACS), 2021-11-22) [Article]
      We present the design, synthesis, and characterization of triple hydrogen-bond-forming precursors and their supramolecular triblock copolymers. Thymine end-functionalized polystyrene-b-polyisoprene (PS-b-PI-Thy) and diaminotriazine end-functionalized polystyrene (PS-DAT) were successfully synthesized via anionic polymerization followed by suitable organic reactions and then solution-mixed to form supramolecular triblocks via hydrogen-bonding interactions. Three different types of asymmetric A1-b-B-sb-A2 supramolecular triblock copolymers were prepared by varying the molecular weight of the A1-b-B diblock copolymers and A2 homopolymers. Proton nuclear magnetic resonance spectroscopy was used for the detailed structural characterization of the polymers in solution, and gel permeation chromatography was used to determine the molecular weight and polydispersity index of all homopolymers and block copolymers. Additionally, transmission electron microscopy and small-angle X-ray scattering measurements were employed to assess the solid-state morphological structures of the supramolecular triple hydrogen-bond triblocks, the diblocks, and single hydrogen-bond mixtures of diblocks with homopolymers.
    • The development of integrated circuits based on two-dimensional materials

      Zhu, Kaichen; Wen, Chao; Aljarb, Areej A.; Xue, Fei; Xu, Xiangming; Tung, Vincent; Zhang, Xixiang; Alshareef, Husam N.; Lanza, Mario (Nature Electronics, Springer Science and Business Media LLC, 2021-11-22) [Article]
      Two-dimensional (2D) materials could potentially be used to develop advanced monolithic integrated circuits. However, despite impressive demonstrations of single devices and simple circuits—in some cases with performance superior to those of silicon-based circuits—reports on the fabrication of integrated circuits using 2D materials are limited and the creation of large-scale circuits remains in its infancy. Here we examine the development of integrated circuits based on 2D layered materials. We assess the most advanced circuits fabricated so far and explore the key challenges that need to be addressed to deliver highly scaled circuits. We also propose a roadmap for the future development of integrated circuits based on 2D layered materials.
    • Monotonicity methods for Mean-Field Games

      Tada, Teruo (2021-11-22) [Dissertation]
      Advisor: Gomes, Diogo A.
      Committee members: Genton, Marc G.; Tempone, Raul; Di Fazio, Giussepe
      Mean-field games (MFGs) model the behavior of large populations of rational agents. Each agent seeks to minimize an individual cost that depends on the statistical distribution of the population. Roughly speaking, MFGs are given by the limit of differential games with N agents as N goes to infinity. This limit describes an average effect of the population’s behavior. Instead of modeling large systems for all agents, we consider two coupled equations: the Hamilton–Jacobi equation and the Fokker–Planck equation. A solution to MFGs is given by two functions: a value function and a population density. From the point of view of mathematics, monotonicity conditions for MFGs are a natural way to obtain the uniqueness of solutions and the stability of systems. In this thesis, we develop a new framework to establish the existence of solutions to MFGs through monotonicity. First, we study first-order stationary monotone MFGs with Dirichlet boundary conditions. In MFGs, boundary conditions arise when agents can leave the domain. There are exit costs for agents given by Dirichlet boundary conditions. Here, we establish the existence of solutions to MFGs that fulfill those boundary conditions in the trace sense. In particular, our solution is continuous up to the boundary in the one-dimensional case. Second, we consider time-dependent monotone MFGs with space-periodic boundary conditions. To solve the time-dependent monotone MFG, we introduce a mono- tone high-order regularized elliptic problem in Rn+1, although the original MFG is a parabolic type. To preserve monotonicity, we need to determine the specific boundary conditions for the time variable. Then, we can apply our method of stationary MFGs to this regularization. In particular, we prove that a solution to the problem exists for any terminal time. Third, we investigate stationary MFGs with hypoelliptic operators that are degenerate differential operators. Those models arise from stochastic control problems with the Stratonovich integration. We study a hypoelliptic MFG with the standard quadratic Hamiltonian. Under standard assumptions, although there is no uniform elliptic condition in hypoelliptic operators, we verify that there is a unique solution to our hypoelliptic MFG.
    • Threat Adaptive Byzantine Fault Tolerant State-Machine Replication

      Silva, Douglas Simões; Graczyk, Rafal; Decouchant, Jérémie; Völp, Marcus; Esteves-Verissimo, Paulo (IEEE, 2021-11-22) [Conference Paper]
      Critical infrastructures have to withstand advanced and persistent threats, which can be addressed using Byzantine fault tolerant state-machine replication (BFT-SMR). In practice, unattended cyberdefense systems rely on threat level detectors that synchronously inform them of changing threat levels. However, to have a BFT-SMR protocol operate unattended, the state-of-the-art is still to configure them to withstand the highest possible number of faulty replicas $f$ they might encounter, which limits their performance, or to make the strong assumption that a trusted external reconfiguration service is available, which introduces a single point of failure. In this work, we present ThreatAdaptive the first BFT-SMR protocol that is automatically strengthened or optimized by its replicas in reaction to threat level changes. We first determine under which conditions replicas can safely reconfigure a BFT-SMR system, i.e., adapt the number of replicas $n$ and the fault threshold $f$ so as to outpace an adversary. Since replicas typically communicate with each other using an asynchronous network they cannot rely on consensus to decide how the system should be reconfigured. ThreatAdaptive avoids this pitfall by proactively preparing the reconfiguration that may be triggered by an increasing threat when it optimizes its performance. Our evaluation shows that ThreatAdaptive can meet the latency and throughput of BFT baselines configured statically for a particular level of threat, and adapt 30% faster than previous methods, which make stronger assumptions to provide safety.
    • Characterizing the Impact of Network Delay on Bitcoin Mining

      Cao, Tong; Decouchant, Jérémie; Yu, Jiangshan; Esteves-Verissimo, Paulo (IEEE, 2021-11-22) [Conference Paper]
      While previous works have discussed the network delay upper bound that guarantees the consistency of Nakamoto consensus, measuring the actual network latencies and evaluating their impact on miners/pools in Bitcoin remain open questions. This paper fills this gap by: (1) defining metrics that quantify the impact of network latency on the mining network; (2) developing a tool, named miner entanglement (ME), to experimentally evaluate these metrics with a focus on the network latency of the top mining pools; and (3) quantifying the impact of the current network delays on Bitcoin's mining network. For example, we evaluated that Poolin, a Bitcoin mining pool, was able to gain between 0.5% and 1.9% of blocks in addition (i.e., from 36.27 BTC to 137.83 BTC) per week thanks to its low network latency. Moreover, as pools are rational in Bitcoin, we model the strategy a pool would follow to improve its network latency (e.g., by leveraging our ME tool) as a two party game. We show that a Bitcoin mining pool could improve its effective hash rate by up to 4.5%. For a multi-party game, we use a state-of-the-art Bitcoin mining simulator to study the situation where all pools attempt to improve their network latency and show that the largest mining pools would improve their revenue and reach a Nash equilibrium while the smaller mining pools would suffer from a decreased access to the network, and therefore a decreased revenue. These conclusions further incentivize the centralisation of the mining network in Bitcoin, and provide an empirical explanation for the observed tendency of pools to design and rely on low latency private networks.
    • Dual Mode Sensing of Binding and Blocking of Cancer Exosomes to Biomimetic Human Primary Stem Cell Surfaces

      Uribe, Johana; Traberg, Walther C.; Hama, Adel; Druet, Victor; Mohamed, Zeinab; Ooi, Amanda Siok Lee; Pappa, Anna-Maria; Huerta, Miriam; Inal, Sahika; Owens, R. M.; Daniel, Susan (ACS Biomaterials Science & Engineering, American Chemical Society (ACS), 2021-11-21) [Article]
      Cancer-derived exosomes (cEXOs) facilitate transfer of information between tumor and human primary stromal cells, favoring cancer progression. Although the mechanisms used during this information exchange are still not completely understood, it is known that binding is the initial contact established between cEXOs and cells. Hence, studying binding and finding strategies to block it are of great therapeutic value. However, such studies are challenging for a variety of reasons, including the need for human primary cell culture, the difficulty in decoupling and isolating binding from internalization and cargo delivery, and the lack of techniques to detect these specific interactions. In this work, we created a supported biomimetic stem cell membrane incorporating membrane components from human primary adipose-derived stem cells (ADSCs). We formed the supported membrane on glass and on multielectrode arrays to offer the dual option of optical or electrical detection of cEXO binding to the membrane surface. Using our platform, we show that cEXOs bind to the stem cell membrane and that binding is blocked when an antibody to integrin β1, a component of ADSC surface, is exposed to the membrane surface prior to cEXOs. To test the biological outcome of blocking this interaction, we first confirm that adding cEXOs to cultured ADSCs leads to the upregulation of vascular endothelial growth factor, a measure of proangiogenic activity. Next, when ADSCs are first blocked with anti-integrin β1 and then exposed to cEXOs, the upregulation of proangiogenic activity and cell proliferation are significantly reduced. This biomimetic membrane platform is the first cell-free label-free in vitro platform for the recapitulation and study of cEXO binding to human primary stem cells with potential for therapeutic molecule screening as it is compatible with scale-up and multiplexing.