A virtual test facility for the efficient simulation of solid material response under strong shock and detonation wave loading

A virtual test facility (VTF) for studying the three-dimensional dynamic response of solid materials subject to strong shock and detonation waves has been constructed as part of the research program of the Center for Simulating the Dynamic Response of Materials at the California Institute of Technology. The compressible fluid flow is simulated with a Cartesian finite volume method and treating the solid as an embedded moving body, while a Lagrangian finite element scheme is employed to describe the structural response to the hydrodynamic pressure loading. A temporal splitting method is applied to update the position and velocity of the boundary between time steps. The boundary is represented implicitly in the fluid solver with a level set function that is constructed on-the-fly from the unstructured solid surface mesh. Block-structured mesh adaptation with time step refinement in the fluid allows for the efficient consideration of disparate fluid and solid time scales. We detail the design of the employed object-oriented mesh refinement framework AMROC and outline its effective extension for fluid–structure interaction problems. Further, we describe the parallelization of the most important algorithmic components for distributed memory machines and discuss the applied partitioning strategies. As computational examples for typical VTF applications, we present the dynamic deformation of a tantalum cylinder due to the detonation of an interior solid explosive and the impact of an explosion-induced shock wave on a multi-material soft tissue body.     

Structured prediction with reinforcement learning

We formalize the problem of Structured Prediction as a Reinforcement Learning task. We first define a Structured Prediction Markov Decision Process (SP-MDP), an instantiation of Markov Decision Processes for Structured Prediction and show that learning an optimal policy for this SP-MDP is equivalent to minimizing the empirical loss. This link between the supervised learning formulation of structured prediction and reinforcement learning (RL) allows us to use approximate RL methods for learning the policy. The proposed model makes weak assumptions both on the nature of the Structured Prediction problem and on the supervision process. It does not make any assumption on the decomposition of loss functions, on data encoding, or on the availability of optimal policies for training. It then allows us to cope with a large range of structured prediction problems. Besides, it scales well and can be used for solving both complex and large-scale real-world problems. We describe two series of experiments. The first one provides an analysis of RL on classical sequence prediction benchmarks and compares our approach with state-of-the-art SP algorithms. The second one introduces a tree transformation problem where most previous models fail. This is a complex instance of the general labeled tree mapping problem. We show that RL exploration is effective and leads to successful results on this challenging task. This is a clear confirmation that RL could be used for large size and complex structured prediction problems.     

Photopolymerization of Pollen Based Biosourced Composites and Applications in 3D and 4D Printing

Pollen have the potential to be effective plant-based biorenewable reinforcing fillers for polymers due to their chemical stability and unique micro- or nano-structured surfaces. Pollen-polymer composites can form the basis for a new class of light-weight and sustainable materials if compatible polymer-filler systems can be engineered through photopolymerization, but this idea is previously unexplored. The first demonstration of photopolymerization and 3D printing with the incorporation of pine pollen as filler in poly(ethylene glycol) diacrylate are presented. The filler properties affecting the related depth of cure and the mechanical, thermal, and functional properties are examined in detail. In addition, the lithography technique is applied to the photocomposites for the production of 3D patterns. 4D printing behavior is also possible through the water swelling and dehydration induced actuation of the 3D printed composites with spatial resolution features. This work is expected to provide a new way to a field for photopolymerization reactions in natural material-resin composites and thereby to expand potential applications in 3D and 4D printing.     

Integrative Study of the Structural and Dynamical Properties of a KirBac3.1 Mutant: Functional Implication of a Highly Conserved Tryptophan in the Transmembrane Domain

ATP-sensitive potassium (K-ATP) channels are ubiquitously expressed on the plasma membrane of cells in several organs, including the heart, pancreas, and brain, and they govern a wide range of physiological processes. In pancreatic β-cells, K-ATP channels composed of Kir6.2 and SUR1 play a key role in coupling blood glucose and insulin secretion. A tryptophan residue located at the cytosolic end of the transmembrane helix is highly conserved in eukaryote and prokaryote Kir channels. Any mutation on this amino acid causes a gain of function and neonatal diabetes mellitus. In this study, we have investigated the effect of mutation on this highly conserved residue on a KirBac channel (prokaryotic homolog of mammalian Kir6.2). We provide the crystal structure of the mutant KirBac3.1 W46R (equivalent to W68R in Kir6.2) and its conformational flexibility properties using HDX-MS. In addition, the detailed dynamical view of the mutant during the gating was investigated using the in silico method. Finally, functional assays have been performed. A comparison of important structural determinants for the gating mechanism between the wild type KirBac and the mutant W46R suggests interesting structural and dynamical clues and a mechanism of action of the mutation that leads to the gain of function.     

A fragment-based approach to understanding inhibition of 1-deoxy-D-xylulose-5-phosphate reductoisomerase

The inhibition of 1-deoxy-D-xylulose-5-phosphate reductoisomerase (DXR) by fosmidomycin was studied by using a kinetic assay based on the consumption of NADPH and synthetic substrate. Fosmidomycin is a slow tight-binding inhibitor of DXR that shows strong negative cooperativity (absolute value(h) = 0.3) in binding. Cooperativity is displayed during the initial (weak, K0.5 = 10 microM) binding event and does not change as the binding tightens to the equilibrium value of 0.9 nM over a period of seconds to minutes. A series of fosmidomycin fragments was examined, but all showed much weaker inhibition, in the mM range. A series of cyclic fosmidomycin analogues was also synthesised and tested, but these showed high-microM binding at best. None of the synthetic compounds showed time-dependent inhibition. We concluded that the slow tight-binding behaviour, and perhaps also cooperativity, are mediated by significant reorganisation of the active site upon fosmidomycin binding. This makes the rational design of new inhibitors of DXR difficult at best.     

Searching information with a natural language dialogue system: a comparison of spoken vs. written modalities

This paper examines the effects of spoken vs. written dialogue modalities on the effectiveness of information search with a computerized retrieval system. Forty-eight adults familiar with the use of computers were asked to carry out six information retrieval tasks, engaging with the system using either spoken or written communication. The written modality was more efficient with regard to the number of dialogue turns, length of interaction with the system and mental workload. Even though the turns lasted longer in the written mode, they appeared to yield less mental workload. Moreover, spoken and written dialogues did not differ as regards the use of pronouns and articles. The implications for the development of natural-language dialogue systems are discussed.     

Reduction of aqueous chromate by Fe(II)/Fe(III) carbonate green rust: kinetic and mechanistic studies

This work describes the heterogeneous reaction between FeII in carbonate green rust and aqueous chromate, in NaHCO3 solutions at 25 degrees C, and at pH values of 9.3-9.6. Evidence for reduction of CrVI to CrIII and concomitant solid-state oxidation of lattice FeII to FeIII was found from FeII titration and from structural analysis of the solids using FTIR, XRD, SEM, and XPS methods. Results indicate the formation of ferric oxyhydroxycarbonate and the concomitant precipitation of CrIII monolayers at the surface of the iron compound that induce passivation effects and progressive rate limitations. The number of CrIII monolayers formed at the completion of the reaction depends on [FeII]t=0, the molar concentration of FeII(solid) at t=0; on [n(o)]t=0, the molar concentration of reaction sites present at the surface of the solid phase at t=0; and on [CrVI]t=0, the molar concentration of CrVI at t=0. Kinetic data were modeled using a model based on the formation of successive CrIII monolayers, -(d[CrVI]/dt) = sigma(1)j k(i)[S] [CrVI]([n(i - 1)] - [n(i)]) with k(i)[S] (in s(-1) L mol(-1)), the rate coefficient of formation of CrIII monolayer i, and [n(i)] and [n(i - 1)], the molar concentration of CrIII precipitated in monolayer i and monolayer i - 1, respectively. Good matching curves were obtained with kinetic coefficients: k(1)[S] = 5-8 x 10(-4), k(2)[S] = 0.5-3 x 10(-5), and k(3)[S] about 1.7 x 10(-6) s(-1) m(-2) L. The CrVI removal efficiency progressively decreases along with the accumulation of CrIII monolayers at the surface of carbonate green rust particles. In the case of thick green rust particles resulting from the corrosion of iron in permeable reactive barriers, the quantity of FeII readily accessible for efficient CrVI removal should be rather low.     

Is Dimethyldecanal a Common Aggregation Pheromone of Tribolium Flour Beetles?

Flour beetles are cosmopolitan and common pests in grain stores and flour mills. Their ability to exploit a wide variety of stored products has contributed to their status as major pests of stored food. Although it was previously reported that the same aggregation pheromone, 4,8-dimethyldecanal (DMD), is shared by three flour beetles species (Tribolium castaneum, T. confusum, and T. freemani), the volatiles released by the other Tribolium species associated with stored products have not yet been examined. In the present study, the volatiles produced by males and females of eight Tribolium species were examined by solid phase microextraction (SPME). SPME samples were analyzed by gas chromatography coupled to mass spectrometry (GC-MS). Experiments were conducted to identify volatiles emitted by the adults of different Tribolium species and to determine whether DMD is a common aggregation pheromone. We observed that DMD is not a common pheromone of the eight species tested, but is common to T. castaneum, T. confusum, T. freemani, and T. madens. Two other volatiles were detected, 1-pentadecene, which is shown here to be a common semiochemical of flour beetles, and 1,6-pentadecadiene, which was detected in five species (T. audax, T. brevicornis, T. destructor, T. freemani, and T. madens).