5632 research outputs found
Sort by
Bayesian Active Sensing for Fault Estimation with Belief Space Tree Search
No full textAutonomous spacecraft missions must be robust to system component faults such as sensor and actuator failures. An important setting to study fault tolerance is the Bayesian Active Sensing problem, where the system plans control inputs to gain information and estimate system failures quickly and with high confidence. We model the problem as a belief-state planning problem enabling simultaneous estimation of sensor and actuator failures in the presence of noise. Current belief-state tree search planners provide anytime, approximate solutions, but their underlying particle-filter belief update inhibits performance for information-gathering tasks. To address this issue, we propose POMCPMF, a belief-state tree search that uses an exact belief update in the tree search by exploiting the active sensing problem structure to decouple the belief update as a Kalman filter on the physical state and a particle filter on the failure modes. We validate our method on numerical experiments of spacecraft models with unknown sensor and actuator faults to demonstrate (i) the need for an active and planned sensing solution (as opposed to a passive and greedy solution) and (ii) the superior scalability of our method compared to existing active and planned methods. We then demonstrate the applicability of our algorithm to real systems by extending to a non-linear model and deploying our algorithm on a spacecraft simulator robot
Mechanically gated formation of donor–acceptor Stenhouse adducts enabling mechanochemical multicolour soft lithography
No full textStress-sensitive molecules called mechanophores undergo productive chemical transformations in response to mechanical force. A variety of mechanochromic mechanophores, which change colour in response to stress, have been developed, but modulating the properties of the dyes generally requires the independent preparation of discrete derivatives. Here we introduce a mechanophore platform enabling mechanically gated multicolour chromogenic reactivity. The mechanophore is based on an activated furan precursor to donor–acceptor Stenhouse adducts (DASAs) masked as a hetero-Diels–Alder adduct. Mechanochemical activation of the mechanophore unveils the DASA precursor, and subsequent reaction with a secondary amine generates an intensely coloured DASA. Critically, the properties of the DASA are controlled by the amine, and thus a single mechanophore can be differentiated post-activation to produce a wide range of functionally diverse DASAs. We highlight this system by establishing the concept of mechanochemical multicolour soft lithography whereby a complex multicolour composite image is printed into a mechanochemically active elastomer through an iterative process of localized compression followed by reaction with different amines
Periclase deforms more slowly than bridgmanite under mantle conditions
No full textTransport of heat from the interior of the Earth drives convection in the mantle, which involves the deformation of solid rocks over billions of years. The lower mantle of the Earth is mostly composed of iron-bearing bridgmanite MgSiO₃ and approximately 25% volume periclase MgO (also with some iron). It is commonly accepted that ferropericlase is weaker than bridgmanite. Considerable progress has been made in recent years to study assemblages representative of the lower mantle under the relevant pressure and temperature conditions. However, the natural strain rates are 8 to 10 orders of magnitude lower than in the laboratory, and are still inaccessible to us. Once the deformation mechanisms of rocks and their constituent minerals have been identified, it is possible to overcome this limitation thanks to multiscale numerical modelling, and to determine rheological properties for inaccessible strain rates. In this work we use 2.5-dimensional dislocation dynamics to model the low-stress creep of MgO periclase at lower mantle pressures and temperatures. We show that periclase deforms very slowly under these conditions, in particular, much more slowly than bridgmanite deforming by pure climb creep. This is due to slow diffusion of oxygen in periclase under pressure. In the assemblage, this secondary phase hardly participates in the deformation, so that the rheology of the lower mantle is very well described by that of bridgmanite. Our results show that drastic changes in deformation mechanisms can occur as a function of the strain rate
Multivalent optical cycling centers: towards control of polyatomics with multi-electron degrees of freedom
No full textOptical control of polyatomic molecules promises new opportunities in precision metrology and fundamental chemistry, as well as quantum information and many-body science. Contemporary experimental and theoretical efforts have mostly focused on cycling photons via excitation of a single electron localized to an alkaline earth (group 2)-like metal center. In this paper, we consider pathways towards optical cycling in polyatomic molecules with multi-electron degrees of freedom, which arise from two or more cycling electrons localized to p-block post-transition metal and metalloid (group 13, 14, and 15) centers. We characterize the electronic structure and rovibrational branching of several prototypical candidates using ab initio quantum chemical methods. Despite increased internal complexity and challenging design parameters, we find several molecules possessing quasi-closed photon cycling schemes with highly diagonal, visible and near-infrared transitions. Furthermore, we identify new heuristics for engineering optically controllable and laser-coolable polyatomic molecules with multi-electron cycling centers. Our results help elucidate the interplay between hybridization, repulsion, and ionicity in optically active species and provide new directions for using polyatomic molecules with complex electronic structure as a resource for quantum science and measurement
Characterization of the Solid Electrolyte Interphase at the Li Metal–Ionic Liquid Interface
No full textThe solid electrolyte interphase (SEI) forms on electrode surfaces from decomposition of the electrolyte. However, there is almost no atomistic detail of SEI formation on Li metal anode, a major obstacle in understanding the highly complex battery electrochemistry sufficiently to design high performance batteries. Herein, a realistic atomistic model (39 000 atoms) for the SEI formation at the interface between the Li metal anode and ionic liquid electrolyte using reactive molecular dynamics simulations is provided. A ≈10 nm thick SEI composed of a dense ordered inorganic layer near the Li-metal anode and a porous organic layer near the electrolyte is found. These results provide new insights into a deeper understanding of the complex SEI that should be useful in developing a new generation of highly efficient batteries
Structural Identification of a 52-Story High-Rise in Downtown Los Angeles Based on Short-Term Wind Vibration Measurements
No full textThis paper presents a case study of a realistic application and evaluation of a promising structural health monitoring approach that exploits some topological features of building-like structures to develop a reduced-order, reduced-complexity, not-necessarily-linear, substructure model. The approach not only reliably detects the occurrence of anomalous features that can reflect incipient damage and deterioration but also provides the locations of the structure’s regions where a single or multiple changes have been detected. The target structure used in this study is a 52-story building in Los Angeles that is instrumented with a relatively dense sensor array and is being continuously monitored through the efforts of the community seismic network (CSN). Two qualitatively different system identification approaches (global and substructuring) are applied to the large data set of ambient acceleration measurements produced by a strong wind event (“Santa Ana winds”) to identify the dominant modal characteristics of the building. The results are shown to match the corresponding results from a high-resolution computational model of the building based on a widely used structural analysis software package (ETABS) developed by Computers and Structures, Inc. The main contribution of this study is to demonstrate the practical feasibility of the proposed substructuring approach with a high-order system using both wind and low-amplitude ambient vibration measurements. The approach also assesses the accuracy and reliability of the estimates of the dominant modal features of the structure to subsequently provide a probabilistic measure of confidence in the extent and location of changes if an anomaly is detected. Due to the minimal computational resources needed to implement the proposed substructuring approach, it is efficient for near-real-time applications where important structures need to be continuously monitored for sustainability as well as resiliency requirements. The method is applicable to linear, nonlinear nonhysteretic, and hysteretic systems, with no restriction on the source of the signal for identification purposes
In Situ Deposited Polyaromatic Layer Generates Robust Copper Catalyst for Selective Electrochemical CO₂ Reduction at Variable pH
No full textElectrochemical reduction of CO₂ (CO₂R) by Cu metal holds promise to convert CO₂ to valuable C₂₊ chemicals at scale using electricity and water but suffers from poor selectivity. Coating of metal electrodes with small organic molecules or polymers has been shown to effectively enhance catalytic performance but remains underexplored. Herein, facile modification of Cu surfaces by a polyaromatic layer was found to boost both selectivity and activity toward C₂₊ products. Using phenyldiazonium or diphenyliodonium salts to graft an organic layer onto the surface of Cu foil electrodes resulted in up to 75% Faradaic efficiency (FE) for C₂₊ at neutral pH. Modified electrodes have electrochemical active surface areas and proton diffusion coefficients similar to those of bare Cu. High CO₂R performance was maintained in a gas diffusion electrode, with a pH ≈ 1 electrolyte (1 M H₃PO₄, 1 M KCl; −100 mA/cm²), producing 65% FE for C₂₊ over 5 h, with no delamination
Microbiome in Anxiety and Other Psychiatric Disorders
No full textInitial studies suggested that the fluctuations in the quantity, variety, and composition of the gut microbiota can significantly affect disease processes. This change in the gut microbiota causing negative health benefits was coined dysbiosis. Initial research focused on gastrointestinal illnesses. However, the gut microbiome was found to affect more than just gastrointestinal diseases. Numerous studies have proven that the gut microbiome can influence neuropsychiatric diseases such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis
Tracking Hidden Magnetospheric Fluctuations in Accretion-powered Pulsars With a Kalman Filter
No full textX-ray flux and pulse period fluctuations in an accretion-powered pulsar convey important information about the disk–magnetosphere interaction. It is shown that simultaneous flux and period measurements can be analysed with a Kalman filter based on the standard magnetocentrifugal accretion torque to generate accurate time-dependent estimates of three hidden state variables, which fluctuate stochastically and cannot be measured directly: the mass accretion rate, the Maxwell stress at the disk–magnetosphere boundary, and the radiative efficiency of accretion onto the stellar surface. The inferred fluctuation statistics carry implications for the physics of hydromagnetic instabilities at the disk–magnetosphere boundary and searches for continuous gravitational radiation from low-mass X-ray binaries
Optimization of the visibility of a tunable dual-phase x-ray grating interferometer
No full textDual-phase x-ray grating interferometry (DP-XGI) is a recently developed imaging technique that can retrieve structural information in the sub-micro scale over areas in the millimeter range. This is performed by use of the scattering signal, which is sensitive to structures that lie below the intrinsic spatial resolution of the imaging system. A quantitative understanding of the microstructure is possible when the scattering signal is retrieved within a range of auto-correlation lengths of the features of interest. High visibility of fringes in this length range is desirable, but no straightforward framework exists for choosing design parameters of the imaging system for such optimization. The purpose of this work is to present an optimization protocol for DP-XGI based on a Fresnel propagation simulation framework which evaluates different parameters of the optical system, utilizing the mean visibility of the fringes at the detector plane as a figure of merit to optimize the DP-XGI for a conventional lab x-ray source. The performance of the numerical simulation with realistic component parameters is validated with the experimental results obtained at a lab-based setup. The results of the validation confirm the robustness of the model for the evaluation of the different components of the interferometer and its optimization at low and high energies