Maximum Resilience of Artificial Neural Networks

The deployment of Artificial Neural Networks (ANNs) in safety-critical applications poses a number of new verification and certification challenges. In particular, for ANN-enabled self-driving vehicles it is important to establish properties about the resilience of ANNs to noisy or even maliciously manipulated sensory input. We are addressing these challenges by defining resilience properties of ANN-based classifiers as the maximal amount of input or sensor perturbation which is still tolerated. This problem of computing maximal perturbation bounds for ANNs is then reduced to solving mixed integer optimization problems (MIP). A number of MIP encoding heuristics are developed for drastically reducing MIP-solver runtimes, and using parallelization of MIP-solvers results in an almost linear speed-up in the number (up to a certain limit) of computing cores in our experiments. We demonstrate the effectiveness and scalability of our approach by means of computing maximal resilience bounds for a number of ANN benchmark sets ranging from typical image recognition scenarios to the autonomous maneuvering of robots.Comment: Timestamp research work conducted in the project. version 2: fix some typos, rephrase the definition, and add some more existing wor

Electron dynamics in gold and gold–silver alloy nanoparticles: The influence of a nonequilibrium electron distribution and the size dependence of the electron–phonon relaxation

©1999 American Institute of Physics. The electronic version of this article is the complete one and can be found online at: http://link.aip.org/link/?JCPSA6/111/1255/1DOI: 10.1063/1.479310Electron dynamics in gold nanoparticles with an average diameter between 9 and 48 nm have been studied by femtosecond transient absorption spectroscopy. Following the plasmon bleach recovery after low power excitation indicates that a non-Fermi electron distribution thermalizes by electron–electron relaxation on a time scale of 500 fs to a Fermi distribution. This effect is only observed at low excitation power and when the electron distribution is perturbed by mixing with the intraband transitions within the conduction band (i.e., when the excitation wavelength is 630 or 800 nm). However, exciting the interband transitions at 400 nm does not allow following the early electron thermalization process. Electron thermalization with the lattice of the nanoparticle by electron–phonon interactions occurs within 1.7 ps under these conditions, independent of the excitation wavelength. In agreement with the experiments, simulations of the optical response arising from thermalized and nonthermalized electron distributions show that a non-Fermi electron distribution leads to a less intense bleach of the plasmon absorption. Furthermore, the difference between the response from the two electron distributions is greater for small temperature changes of the electron gas (low excitation powers). No size dependence of the electron thermalization dynamics is observed for gold nanoparticles with diameters between 9 and 48 nm. High-resolution transmission electron microscopy (HRTEM) reveals that these gold nanoparticles possess defect structures. The effect of this on the electron–phonon relaxation processes is discussed. 18 nm gold–silver alloy nanoparticles with a gold mole fraction of 0.8 are compared to 15 nm gold nanoparticles. While mixing silver leads to a blue-shift of the plasmon absorption in the ground-state absorption spectrum, no difference is observed in the femtosecond dynamics of the system

Development of indole sulfonamides as cannabinoid receptor negative allosteric modulators

This Letter was supported by the Biotechnology and Biological Sciences Research Council (BBSRC) and the Scottish Universities Life Sciences Alliance (SULSA) in 2011Peer reviewedPostprin

Discussion of "Riverbed degradation below large capacity reservoirs"

CER58-9.Includes bibliographical references.Proc. paper 788

Speed Range for Breakdown Waves

Considering the electrons as the main element in breakdown wave propagation and using a one-dimensional, steady-state, three-fluid, hydrodynamical model, previous investigations have resulted in the completion of a set of equations for conservation of mass, momentum, and energy. We will use the terms proforce and antiforce waves, depending on whether the applied electric field force on electrons is with or against the direction of wave propagation. In the case of antiforce waves, the electron gas temperature and therefore the electron fluid pressure is assumed to be large enough to sustain the wave propagation down the discharge tube. For strong discontinuity and based on the conditions existent at the leading edge of the wave, previous investigations have concluded a minimum wave velocity condition for breakdown waves. However, allowing for a temperature derivative discontinuity at the shock front, we have been able to derive a new set of conditions at the shock front and therefore a lower range of electron drift velocity. This conforms with the experimentally observed wave speeds. The solution to the set of electron fluid-dynamical equations involves a previously discovered method of integration of the equations through the sheath (dynamical transition) region. For a wide range of wave speeds, the appropriate set of electron fluid-dynamical equations has been integrated through the sheath region

Diversity and Specialization in Collaborative Swarm Systems

This paper addresses qualitative and quantitative diversity and specialization issues in the frame- work of self-organizing, distributed, artificial systems. Both diversity and specialization are obtained via distributed learning from initially homogeneous swarms. While measuring diversity essentially quantifies differences among the individuals, assessing the degree of specialization implies to correlate the swarm’s heterogeneity with its overall performance. Starting from a stick-pulling experiment in collective robotics, a task that requires the collaboration of two robots, we abstract and generalize in simulation the task constraints to k robots collaborating sequentially or in parallel. We investi- gate quantitatively the influence of task constraints and type of reinforcement signals on diversity and specialization in these collaborative experiments. Results show that, though diversity is not explicitly rewarded in our learning algorithm and there is no explicit communication among agents, the swarm becomes specialized after learning. The degree of specialization is affected strongly by environmental conditions and task constraints, and reveals characteristics related to performance and learning in a more consistent and clearer way than diversity does

Performance Evaluation of Inverted Tee (IT) Bridge System

The Inverted Tee (IT) girder bridge system was originally developed in 1996 by the University of Nebraska–Lincoln (UNL) researchers and Nebraska Department of Transportation (NDOT) engineers. This bridge system currently accounts for over 110 bridges in Nebraska used for both state highways and local county roads. Extensive longitudinal and transverse deck cracking have been observed and noted in numerous bridge inspection reports. Since the IT girder bridge system is relatively new, limited data and knowledge exist on its structural performance and behavior. This study evaluates the IT girder bridge system by conducting twenty field observations as well as recording accelerometer, strain gauge, and LVDT time histories and lidar scans for a selected subset of these bridges and then a three-dimensional finite element analysis (FEA) was conducted. The field observations included visual inspection for damage and developing deck crack maps to identify a trend for the damage. System identification of the bridge deck and girders helped investigate the global and local structural responses, respectively. Operational modal analysis quantified the natural frequencies, damping ratios, and operational deflected shapes for the instrumented IT girder bridges. These results helped diagnose the reason for the longitudinal deck cracking. The IT girders respond non- uniformly for the first operational deflected shape and independently for higher modes. Two comparable bridges, namely one slab and one NU girder bridge, were instrumented to verify and demonstrate that the IT girder behavior is unique. An advanced geospatial analysis was conducted for the IT girder bridges to develop lidar depth maps of the deck and girders elevations. These depth maps help identify locations of potential water/chloride penetration and girders set at various elevations and/or where the deck thickness is non-uniform. Live load tests helped quantify the transverse dynamic behavior of the bridge girders. Quantifying the transverse dynamic behavior helped validate the source of longitudinal deck cracking in IT girder bridges, which was determined to be the differential deflection between adjacent IT girders. The FEA analysis was conducted to evaluate the live load moment and shear distribution factors and compare that to the predicted values calculated from the AASHTO Standard and LRFD bridge design specifications. The comparison indicated that the predicted distribution factors were conservative. Also, interviews with IT bridge producers and contractors were conducted to determine production and construction advantages and challenges of this bridge system

Speed Cut-Off Point for Antiforce Waves

A one-dimensional, three-component, fluid model has been employed to investigate the existence of a speed cut-off point for antiforce breakdown waves. The term antiforce wave is used to identify breakdown waves for which the electric field force on electrons is in the opposite direction of wave propagation. The electron fluid-dynamical equations for antiforce waves are different from those of proforce waves. This presentation will address the difference in the set of equations for proforce and antiforce waves and the method of integration of the set of equations through the dynamical transition region for antiforce waves. Also, for antiforce waves, the existence and approximate value of a speed cut-off point will be discussed

Size-dependent compressive strength properties of hard rocks and rock-like cementitious brittle materials

Rock engineering projects have always been constructed on different (from micro to macro) scales. This makes understanding rock behaviour at different scales essential. In previous statistical studies on igneous hard rocks, the correlation of uniaxial compressive strength (UCS) values in different diameters with estimations of specimen size effect models was weak. In view of this knowledge gap, the present research proposed a model of appropriate size effect in igneous hard rocks. This research also aimed at discussing the effect of specimen size and grain size on the UCS of concrete specimens. To achieve these aims, studies were conducted in parallel on the previous and new experimental data. Non-linear regression analysis on igneous hard rocks indicated that there is a better agreement between the outputs of the multi-fractal scaling model and the specimen size effect model using the fracture energy theory and the results of previous laboratory tests. In addition, in the experimental study, the grain size effect on the predictions of specimen size effect models was exhibited. The results of this research can be used for designing engineering projects at different scales

Evaluating the immediate and longer term impact of a refusal conversion strategy in a large scale longitudinal study

Refusal conversion is one of the fieldwork strategies commonly used to minimise non-response in surveys. There is, however, relatively little evidence about the effectiveness of this strategy, particularly for face-to-face longitudinal surveys. Moreover, much of the existing evidence is based on observational studies. This paper evaluates the effectiveness of a fieldwork strategy – intensive re-issuing - to convert refusals using evidence from an intervention on a random sub-sample of refusals implemented in wave four of a large scale longitudinal study in the UK: the Millennium Cohort Study. We show that intensive re-issuing is an effective way of reducing the refusal rate. We also show that refusal conversion led to a modest reduction in non-response bias in the survey estimates for several key variables. The longer term impact of refusal conversion is also a key concern in longitudinal surveys. We demonstrate that, although the majority of converted refusals go on to participate in the subsequent wave of the study, there is no overall effect of intensive re-issuing on sample size at this wave