5632 research outputs found
Sort by
Probabilistic Guarantees for Nonlinear Safety-Critical Optimal Control
No full textLeveraging recent developments in black-box risk-aware verification, we provide three algorithms that generate probabilistic guarantees on (1) optimality of solutions, (2) recursive feasibility, and (3) maximum controller runtimes for general nonlinear safety-critical finite-time optimal controllers. These methods forego the usual (perhaps) restrictive assumptions required for typical theoretical guarantees, e.g. terminal set calculation for recursive feasibility in Nonlinear Model Predictive Control, or convexification of optimal controllers to ensure optimality. Furthermore, we show that these methods can directly be applied to hardware systems to generate controller guarantees on their respective systems
Editorial: Atmospheric chemistry in the urban air
No full textUrban atmospheric chemical processes directly affect air quality of megacities. Owing to the synergistic effect of various pollutants in urban atmosphere, urban air pollution is complex and puzzling. Sustainable urban development is being hindered and urban air quality is deteriorating. Moreover, with the fast urbanization and industrialization in many developing (e.g., (China) and developed countries, more and more people live in cities or city clusters. From the statistics by United Nations Department of Economic and Social Affairs, more than 50% of the world’s population are living in urban areas, and the proportion is expected to increase to 68% by 2050. Urban air quality is crucial to human health, especially for people living in urban areas. The recent examples observed in various urban atmospheric environments especially in China have demonstrated the need to broaden the research field of urban atmospheric chemistry and refine more theoretical modeling mechanisms
A Convergent Total Synthesis of (+)-Ineleganolide
No full textWe report the total synthesis of the furanobutenolide-derived diterpenoid (+)-ineleganolide. The synthetic approach relies on a convergent strategy, based on the coupling of two enantioenriched fragments which are derived from (-)-linalool and (+)-norcarvone respectively. A high-yielding, one-step Michael addition and aldol cascade furnishes a pentacyclic framework as a single diastereomer, overcoming previous challenges in controlling stereochemistry. The endgame features an O₂ facilitated C-H oxidation and a samarium diiodide induced semi-pinacol rearrangement to furnish the highly rigid central seven membered ring
Finite Source Properties of Large Strike-Slip Earthquakes
No full textEarthquake ruptures are complex physical processes that may vary with the structure and tectonics of the region in which they occur. Characterizing the factors controlling this variability would provide fundamental constraints on the physics of earthquakes and faults. We investigate this by determining finite source properties from second moments of the stress glut for a global dataset of large strike-slip earthquakes. Our approach uses a Bayesian inverse formulation with teleseismic body and surface waves, which yields a low-dimensional probabilistic description of rupture properties including spatial extent, directivity, and duration. This technique is useful for comparing events because it makes only minor geometric constraints, avoids bias due to rupture velocity parameterization, and yields a full ensemble of possible solutions given the uncertainties of the data. We apply this framework to all great strike-slip earthquakes of the past three decades, and we use the resultant second moments to compare source quantities like directivity ratio, rectilinearity, stress drop, and depth extent. We find that most strike-slip earthquakes have a large component of unilateral directivity, and many of these earthquakes show a mixture of unilateral and bilateral behavior. We also notice that oceanic intraplate earthquakes usually rupture a much larger width of the seismogenic zone than other strike-slip earthquakes, suggesting these earthquakes consistently breach the expected thermal boundary for oceanic ruptures. We also use these second moments to resolve nodal plane ambiguity for the large oceanic intraplate earthquakes and find that the rupture orientation is usually unaligned with encompassing fossil fracture zones
Neural Operators for Solving PDEs and Inverse Design
No full textDeep learning surrogate models have shown promise in modeling complex physical phenomena such as photonics, fluid flows, molecular dynamics and material properties. However, standard neural networks assume finite-dimensional inputs and outputs, and hence, cannot withstand a change in resolution or discretization between training and testing. We introduce Fourier neural operators that can learn operators, which are mappings between infinite dimensional spaces. They are discretization-invariant and can generalize beyond the discretization or resolution of training data. They can efficiently solve partial differential equations (PDEs) on general geometries. We consider a variety of PDEs for both forward modeling and inverse design problems, as well as show practical gains in the lithography domain
Dynamics of the Caltech SSPP deployable structures: structure–mechanism interaction and deployment envelope
No full textThe Caltech Space Solar Power Project has been developing ultralight deployable space structures consisting of thin-shell composite strips that support photovoltaic and RF elements. These modular, square structures can potentially be scaled to tens of meters in size. This paper studies the interaction between the deployment dynamics of the structure and the deployment mechanism, both experimentally and numerically. Instead of considering a full structure, a quadrant is considered to reduce the number of components and to better focus on the main parameters that affect the deployment behavior. Outcomes of this research will not only benefit the Caltech project but will also contribute to the design of future lightweight deployable space structures that undergo unconstrained dynamic deployment
Modeling of Damage in Coilable Composite Shell Structures
No full textCoilable composite shell structures, composed of ultra-thin laminates, are ideal for deployable space structures applications. Their ability to be flattened and coiled for packaging, and deployed in their operational configuration makes them suitable for many space missions. Due to the complex states of stresses that occur in a composite shell during these processes (coiling, stowage, and deployment), material failure may be induced. This in turn would negatively affect the deployment, cause shape distortions, reduce the stiffness of the shell, or even lead to catastrophic failure of the mission. Therefore, predicting the failure modes and mechanisms of ultra-thin laminates at the structural scale is critical for design and certification purposes. However, this is often complicated by the complex microstructure and the multiple length-scales (micro and meso) associated with composites. This study presents a finite element model with progressive damage that effectively captures the ply failure modes. This is done through a damage constitutive model, where local cracks in the shell are smeared within a finite element. The fracture properties of interest are experimentally measured and incorporated into the model. The salient features of the model needed to capture failure are identified by comparing the simulation results with experiments. This is achieved by analyzing the coiling of a TRAC longeron shell structure
A stretchable wireless wearable bioelectronic system for multiplexed monitoring and combination treatment of infected chronic wounds
No full textChronic nonhealing wounds are one of the major and rapidly growing clinical complications all over the world. Current therapies frequently require emergent surgical interventions, while abuse and misapplication of therapeutic drugs often lead to an increased morbidity and mortality rate. Here, we introduce a wearable bioelectronic system that wirelessly and continuously monitors the physiological conditions of the wound bed via a custom-developed multiplexed multimodal electrochemical biosensor array and performs noninvasive combination therapy through controlled anti-inflammatory antimicrobial treatment and electrically stimulated tissue regeneration. The wearable patch is fully biocompatible, mechanically flexible, stretchable, and can conformally adhere to the skin wound throughout the entire healing process. Real-time metabolic and inflammatory monitoring in a series of preclinical in vivo experiments showed high accuracy and electrochemical stability of the wearable patch for multiplexed spatial and temporal wound biomarker analysis. The combination therapy enabled substantially accelerated cutaneous chronic wound healing in a rodent model
Genome manipulation by guide-directed Argonaute cleavage
No full textMany prokaryotic argonautes (pAgos) mediate DNA interference by using small DNA guides to cleave target DNA. A recent study shows that CbAgo, a pAgo from Clostridium butyricum, induces DNA interference between homologous sequences and generates double-stranded breaks (DSBs) in target DNAs. This mechanism enables the host to defend against invading DNAs such as plasmids and viruses. However, whether such a CbAgo-mediated DNA cleavage is mutagenic remains unexplored. Here we demonstrate that CbAgo, directed by plasmid-encoded guide sequences, can cleave genome target sites and induce chromosome recombination between downstream homologous sequences in Escherichia coli. The recombination rate correlates well with pAgo DNA cleavage activity and the mechanistic study suggests the recombination involves DSBs and RecBCD processing. In RecA-deficient E. coli strain, guide-directed CbAgo cleavage on chromosomes severely impairs cell growth, which can be utilized as counter-selection to assist Lambda-Red recombineering. These findings demonstrate the guide-directed cleavage of pAgo on the host genome is mutagenic and can lead to different outcomes according to the function of the host DNA repair machinery. We anticipate this novel DNA-guided interference to be useful in broader genetic manipulation. Our study also provides an in vivo assay to characterize or engineer pAgo DNA cleavage activity
Identification of new oxospiro chromane quinoline-carboxylate antimalarials that arrest parasite growth at ring stage
No full textMalaria still threatens half the globe population despite successful Artemisinin-based combination therapy. One of the reasons for our inability to eradicate malaria is the emergence of resistance to current antimalarials. Thus, there is a need to develop new antimalarials targeting Plasmodium proteins. The present study reported the design and synthesis of 4, 6 and 7-substituted quinoline-3-carboxylates 9(a–o) and carboxylic acids 10(a–b) for the inhibition of Plasmodium N-Myristoyltransferases (NMTs) using computational biology tools followed by chemical synthesis and functional analysis. The designed compounds exhibited a glide score of −9.241 to −6.960 kcal/mol for PvNMT and −7.538 kcal/mol for PfNMT model proteins. Development of the synthesized compounds was established via NMR, HRMS and single crystal X-ray diffraction study. The synthesized compounds were evaluated for their in vitro antimalarial efficacy against CQ-sensitive Pf3D7 and CQ-resistant PfINDO lines followed by cell toxicity evaluation. In silico results highlighted the compound ethyl 6-methyl-4-(naphthalen-2-yloxy)quinoline-3-carboxylate (9a) as a promising inhibitor with a glide score of −9.084 kcal/mol for PvNMT and −6.975 kcal/mol for PfNMT with IC50 values of 6.58 µM for Pf3D7 line. Furthermore, compounds 9n and 9o exhibited excellent anti-plasmodial activity (Pf3D7 IC₅₀ = 3.96, 6.71 µM, and PfINDO IC50 = 6.38, 2.8 µM, respectively). The conformational stability of 9a with the active site of the target protein was analyzed through MD simulation and was found concordance with in vitro results. Thus, our study provides scaffolds for the development of potent antimalarials targeting both Plasmodium vivax and Plasmodium falciparum