Synthesizing plans that contain actions with context-dependent effects1

This paper presents a method of solving planning problems that involve actions whose effects change according to the situations in which they are performed. The approach is an extension of the conventional planning methodology in which plans are constructed through an iterative process of scanning for goals that are not yet satisfied, inserting actions to achieve them, and introducing subgoals to these actions. This methodology was originally developed under the assumption that one would be dealing exclusively with actions that produce the same effects in every situation. The extension involves introducing additional subgoals to actions above and beyond the preconditions of execution normally introduced. These additional subgoals, called secondary preconditions, ensure that the actions are performed in contexts conducive to producing the effects we desire. This paper defines and analyzes secondary preconditions from a mathematically rigorous standpoint and demonstrates how they can be derived from regression operators.     

Parameter Identification in Photothermal Imaging

We propose a technique to reconstruct the geometry of inclusions and their material parameters in thermal scattering near surfaces. The imaging problem is reformulated as a constrained optimization problem with a finite number of stationary constraints. The unknown domains and their parameters are the design variables. A descent method combining topological derivative analysis to find improved guesses of the objects and gradient iterations to correct their material parameters provides reasonable reconstructions.     

X-Ray, Micro-Raman, Optical Absorption/Emission Studies of ErNbO4 Grown by Vapor Transport Equilibration

Vapor transport equilibration (VTE) treatments were performed on a Y-cut bulk Er (1.6 mol%)-doped congruent LiNbO₃ crystal and an X-cut pure congruent crystal, on one surface of which a 40 nm-thick film of erbium metal was coated before the VTE treatment. Scanning electron microscope, powder or single-crystal X-ray diffraction (XRD), polarized infrared absorption/emission of Er³⁺ as well as micro-Raman spectroscopy were used to study the two VTE crystals. The results are discussed in comparison with a corresponding as-grown bulk Er-doped crystal, calcined ErNbO₄ powder, and a locally Er-doped congruent LiNbO₃ crystal prepared by using the standard Er-diffusion technique. The experimental results show that the VTE treatment induces the formation of micrometer-sized ErNbO₄ precipitates with the crystallographic morphology of a flat polyhedron not only on the surfaces of both crystals but also in the bulk of the homogeneously Er-doped one. The optical absorption and emission studies show that the formation of the precipitates results in substantial spectral changes in both the 0.98 and 1.5 μm regions. The micro-Raman studies allow to resolve four additional Raman peaks around 800 cm⁻¹ in the E(TO) spectra of the two VTE crystals. These additional Raman peaks are associated with the characteristic vibrations with respect to the NbO₄³⁻ group. Characteristic XRD, optical absorption, and emission and Raman peaks for identifying the ErNbO₄ phase are proposed. Finally, the formation mechanism and light-scattering effect of the precipitates are discussed.     

Sliding Mode Control with Adaptive Fuzzy Dead-Zone Compensation of an Electro-hydraulic Servo-System

Electro-hydraulic servo-systems are widely employed in industrial applications such as robotic manipulators, active suspensions, precision machine tools and aerospace systems. They provide many advantages over electric motors, including high force to weight ratio, fast response time and compact size. However, precise control of electro-hydraulic systems, due to their inherent nonlinear characteristics, cannot be easily obtained with conventional linear controllers. Most flow control valves can also exhibit some hard nonlinearities such as dead-zone due to valve spool overlap. This work describes the development of an adaptive fuzzy sliding mode controller for an electro-hydraulic system with unknown dead-zone. The boundedness and convergence properties of the closed-loop signals are proven using Lyapunov stability theory and Barbalat’s lemma. Numerical results are presented in order to demonstrate the control system performance.     

Node trust evaluation in mobile ad hoc networks based on multi-dimensional fuzzy and Markov SCGM(1, 1) model

Due to the nature of distribution and self-organization, mobile ad hoc networks rely on cooperation between nodes to transfer information. One of the key factors to ensure high communication quality is an efficient assessment scheme for risks and trust of choosing next potential cooperative nodes. Trust model, an abstract psychological cognitive process, is one of the most complex concepts in social relationships, involving factors such as assumptions, expectations and behaviors. All of the above make it difficult to quantify and forecast trust accurately. In this paper, based on the theories of fuzzy recognition with feedback, SCGM(1, 1) model and Markov chain, we present a pattern of prediction making. The analysis and experimental computation show that this scheme is efficient in trust prediction for ad hoc networks.     

Parallel machine scheduling to minimize the sum of quadratic completion times

We consider the parallel machine scheduling problem of minimizing the sum of quadratic job completion times. We first prove that the problem is strongly NP-hard. We then demonstrate by probabilistic analysis that the shortest processing time rule solves the problem asymptotically. The relative error of the rule converges in probability to zero under the assumption that the job processing times are independent random variables uniformly distributed in (0, 1). We finally provide some computational results, which show that the rule is effective in solving the problem in practice.     

Finite element model updating and structural damage identification using OMAX data

The main limitations in the finite element (FE) model updating technique lie in the ability of the FE model to represent the true behavior of the structure (modelling problem), and in the ability to identify enough modal parameters with sufficient accuracy, especially for large structures that are tested in operational conditions (identification problem). In this paper, the identification problem is solved with an OMAX approach, where an artificial force is used in operational conditions and a structural model is identified that takes both the forced and the ambient excitation into account. From an extensive case study on a real three-span bridge, it is observed that, while updating the FE model using the experimental output-only data yields a good fit, discrepancies show up when the more extensive set of OMAX data is used for validation, or even for updating. It can be concluded that an OMAX approach not only increases the well-posedness of the updating problem, it also allows to detect potential inaccuracies in the FE model.     

Recovery of surface orientation from diffuse polarization.

When unpolarized light is reflected from a smooth dielectric surface, it becomes partially polarized. This is due to the orientation of dipoles induced in the reflecting medium and applies to both specular and diffuse reflection. This paper is concerned with exploiting polarization by surface reflection, using images of smooth dielectric objects, to recover surface normals and, hence, height. This paper presents the underlying physics of polarization by reflection, starting with the Fresnel equations. These equations are used to interpret images taken with a linear polarizer and digital camera, revealing the shape of the objects. Experimental results are presented that illustrate that the technique is accurate near object limbs, as the theory predicts, with less precise, but still useful, results elsewhere. A detailed analysis of the accuracy of the technique for a variety of materials is presented. A method for estimating refractive indices using a laser and linear polarizer is also given.     

Applying trust enhancements to reactive routing protocols in mobile ad hoc networks

Due to the characteristics of mobile ad hoc networks, such networks are more susceptible to the destruction of malicious attacks or denial of cooperation. It would be easy for an adversary or a malicious node to launch attacks on routing function, especially attacks on packet routing. In order to mitigate these hazards, we incorporate the concept of ‘trust’ into MANETs, and abstract a decentralized trust inference model. The core of this model is trust computation, which is divided into two parts: historical trust assessment and trust prediction. We can quantify a node’s historical trust based on its historical behaviors via introducing multiple trust attributes. The fuzzy AHP method based on entropy weights is used to calculate the weight of trust attributes. By making use of the obtained historical trust data sequence, we propose an improved dynamic grey-Markov chain prediction measure to effectively estimate node’s trust prediction. In order to verify the validity of our trust model, we propose a trust-enhanced unicast routing protocol and a trust-enhanced multicast routing protocol, respectively. Both of the two new protocols can provide a feasible approach to kick out the untrustworthy nodes and choose the optimal trusted routing path. Moreover, the new proposed data-driven route maintenance mechanisms can reduce the routing overhead. The persuasive experiments have been conducted to evaluate the effectiveness of the new proposed trust-enhanced routing protocols in the aspects of packets delivery ratio, end-to-end latency, malicious node detection and attack resistance.