Formal Analysis and Redesign of a Neural Network-Based Aircraft Taxiing System with VerifAI

We demonstrate a unified approach to rigorous design of safety-critical autonomous systems using the VerifAI toolkit for formal analysis of AI-based systems. VerifAI provides an integrated toolchain for tasks spanning the design process, including modeling, falsification, debugging, and ML component retraining. We evaluate all of these applications in an industrial case study on an experimental autonomous aircraft taxiing system developed by Boeing, which uses a neural network to track the centerline of a runway. We define runway scenarios using the Scenic probabilistic programming language, and use them to drive tests in the X-Plane flight simulator. We first perform falsification, automatically finding environment conditions causing the system to violate its specification by deviating significantly from the centerline (or even leaving the runway entirely). Next, we use counterexample analysis to identify distinct failure cases, and confirm their root causes with specialized testing. Finally, we use the results of falsification and debugging to retrain the network, eliminating several failure cases and improving the overall performance of the closed-loop system.Comment: Full version of a CAV 2020 pape

Distribution-Aware Sampling and Weighted Model Counting for SAT

Given a CNF formula and a weight for each assignment of values to variables, two natural problems are weighted model counting and distribution-aware sampling of satisfying assignments. Both problems have a wide variety of important applications. Due to the inherent complexity of the exact versions of the problems, interest has focused on solving them approximately. Prior work in this area scaled only to small problems in practice, or failed to provide strong theoretical guarantees, or employed a computationally-expensive maximum a posteriori probability (MAP) oracle that assumes prior knowledge of a factored representation of the weight distribution. We present a novel approach that works with a black-box oracle for weights of assignments and requires only an {\NP}-oracle (in practice, a SAT-solver) to solve both the counting and sampling problems. Our approach works under mild assumptions on the distribution of weights of satisfying assignments, provides strong theoretical guarantees, and scales to problems involving several thousand variables. We also show that the assumptions can be significantly relaxed while improving computational efficiency if a factored representation of the weights is known.Comment: This is a full version of AAAI 2014 pape

Déterminisme et variabilité génétique du poids de l'épiphyse et de la concentration plasmatique de mélatonine chez les ovins

La mélatonine, hormone sécrétée par la glande pinéale lors de la phase obscure du nycthémère, intervient dans le contrôle du cycle annuel de reproduction des ovins. Les concentrations plasmatiques nocturnes de mélatonine présentent une grande variabilité inter-individuelle. Cette variabilité est corrélée à une grande variabilité inter-individuelle du poids de la glande pinéale et serait sous contrôle génétique important. L'objectif de cette étude est d'examiner l'origine génétique de la variabilité inter-individuelle des concentrations plasmatiques nocturnes de mélatonine et du poids de la glande pinéale. Différents facteurs de variation du poids de la glande pinéale et des concentrations plasmatiques nocturnes de mélatonine ont été testés. Le modèle retenu pour décrire la variabilité du poids de la glande pinéale est un modèle linéaire à trois effets fixes : l'année d'abattage, le père et le type génétique (back-cross ou F2). Le modèle retenu pour le caractère "concentration plasmatique de mélatonine" comprend deux effets fixes (l'année d'abattage et le père), ainsi que deux covariables (le poids de la glande pinéale et le poids de carcasse). A partir de ces deux modèles, les héritabilités du poids de la glande pinéale et de la concentration plasmatique nocturne de mélatonine ont été estimées. Une valeur identique (0,42) a été obtenue pour les deux caractères. Pour tester l'hypothèse selon laquelle ces caractères seraient gouvernés par des gènes majeurs, une analyse de ségrégation a été réalisée. Cette analyse a montré l'existence de gènes majeurs contrôlant le poids de la glande pinéale et la concentration plasmatique de mélatonine. Enfin, une analyse QTL limitée à 11 marqueurs du chromosome 2 n'a pas révélé la présence de ces gènes majeurs sur cette partie du génome de la brebis. Le typage des agneaux pour un nombre plus impotant de marqueurs permettra de confirmer l'existence d'un gène majeur pour ces caractères et de localise ce gène

Control Improvisation

We formalize and analyze a new automata-theoretic problem termed control improvisation. Given an automaton, the problem is to produce an improviser, a probabilistic algorithm that randomly generates words in its language, subject to two additional constraints: the satisfaction of an admissibility predicate, and the exhibition of a specified amount of randomness. Control improvisation has multiple applications, including, for example, generating musical improvisations that satisfy rhythmic and melodic constraints, where admissibility is determined by some bounded divergence from a reference melody. We analyze the complexity of the control improvisation problem, giving cases where it is efficiently solvable and cases where it is #P-hard or undecidable. We also show how symbolic techniques based on Boolean satisfiability (SAT) solvers can be used to approximately solve some of the intractable cases

Biomechanical interactions of endodontically treated tooth implant-supported prosthesis under fatigue test with acoustic emission monitoring

International audienc

A gorilla adenovirus-based vaccine against Zika virus induces durable immunity and confers protection in pregnancy

The teratogenic potential of Zika virus (ZIKV) has made the development of an effective vaccine a global health priority. Here, we generate two gorilla adenovirus-based ZIKV vaccines that encode for pre-membrane (prM) and envelope (E) proteins (GAd-Zvp) or prM and the ectodomain of E protein (GAd-Eecto). Both vaccines induce humoral and cell-mediated immune responses and prevent lethality after ZIKV challenge in mice. Protection is antibody dependent, CD

Crystal structure of the cowpox virus-encoded NKG2D ligand OMCP

The NKG2D receptor is expressed on the surface of NK, T, and macrophage lineage cells and plays an important role in antiviral and antitumor immunity. To evade NKG2D recognition, herpesviruses block the expression of NKG2D ligands on the surface of infected cells using a diverse repertoire of sabotage methods. Cowpox and monkeypox viruses have taken an alternate approach by encoding a soluble NKG2D ligand, the orthopoxvirus major histocompatibility complex (MHC) class I-like protein (OMCP), which can block NKG2D-mediated cytotoxicity. This approach has the advantage of targeting a single conserved receptor instead of numerous host ligands that exhibit significant sequence diversity. Here, we show that OMCP binds the NKG2D homodimer as a monomer and competitively blocks host ligand engagement. We have also determined the 2.25-Å-resolution crystal structure of OMCP from the cowpox virus Brighton Red strain, revealing a truncated MHC class I-like platform domain consisting of a beta sheet flanked with two antiparallel alpha helices. OMCP is generally similar in structure to known host NKG2D ligands but has notable variations in regions typically used to engage NKG2D. Additionally, the determinants responsible for the 14-fold-higher affinity of OMCP for human than for murine NKG2D were mapped to a single loop in the NKG2D ligand-binding pocket