A thermodynamically consistent Markovian master equation beyond the secular approximation

Markovian master equations provide a versatile tool for describing open quantum systems when memory effects of the environment may be neglected. As these equations are of an approximate nature, they often do not respect the laws of thermodynamics when no secular approximation is performed in their derivation. Here we introduce a Markovian master equation that is thermodynamically consistent and provides an accurate description whenever memory effects can be neglected. The thermodynamic consistency is obtained through a rescaled Hamiltonian for the thermodynamic bookkeeping, exploiting the fact that a Markovian description implies a limited resolution for heat. Our results enable a thermodynamically consistent description of a variety of systems where the secular approximation breaks down.

Scrutinizing GW-Based Methods Using the Hubbard Dimer

Using the simple (symmetric) Hubbard dimer, we analyze some important features of the GW approximation. We show that the problem of the existence of multiple quasiparticle solutions in the (perturbative) one-shot GW method and its partially self-consistent version is solved by full self-consistency. We also analyze the neutral excitation spectrum using the Bethe-Salpeter equation (BSE) formalism within the standard GW approximation and find, in particular, that 1) some neutral excitation energies become complex when the electron-electron interaction U increases, which can be traced back to the approximate nature of the GW quasiparticle energies; 2) the BSE formalism yields accurate correlation energies over a wide range of U when the trace (or plasmon) formula is employed; 3) the trace formula is sensitive to the occurrence of complex excitation energies (especially singlet), while the expression obtained from the adiabatic-connection fluctuation-dissipation theorem (ACFDT) is more stable (yet less accurate); 4) the trace formula has the correct behavior for weak (i.e., small U) interaction, unlike the ACFDT expression.

Understandable and trustworthy explainable robots: A sensemaking perspective

This article discusses the fundamental requirements for making explainable robots trustworthy and comprehensible for non-expert users. To this extent, we identify three main issues to solve: the approximate nature of explanations, their dependence on the interaction context and the intrinsic limitations of human understanding. The article proposes an organic solution for the design of explainable robots rooted in a sensemaking perspective. The establishment of contextual interaction boundaries, combined with the adoption of plausibility as the main criterion for the evaluation of explanations and of interactive and multi-modal explanations, forms the core of this proposal.

Optimizing Energy Consumption in Transportation: Literature Review, Insights, and Research Opportunities

From airplanes to electric vehicles and trains, modern transportation systems require large quantities of energy. These vast amounts of energy have to be produced somewhere—ideally by using sustainable sources—and then brought to the transportation system. Energy is a scarce and costly resource, which cannot always be produced from renewable sources. Therefore, it is critical to consume energy as efficiently as possible, that is, transportation activities need to be carried out with an optimal intake of energetic means. This paper reviews existing work on the optimization of energy consumption in the area of transportation, including road freight, passenger rail, maritime, and air transportation modes. The paper also analyzes how optimization methods—of both exact and approximate nature—have been used to deal with these energy-optimization problems. Finally, it provides insights and discusses open research opportunities regarding the use of new intelligent algorithms—combining metaheuristics with simulation and machine learning—to improve the efficiency of energy consumption in transportation.

Partial Perception and Approximate Understanding

What is discussed in the present paper is the assumption concerning a human narrowed sense of perception of external world and, resulting from this, a basically approximate nature of concepts that are to portray it. Apart from the perceptual vagueness, other types of vagueness are also discussed, involving both the nature of things, indeterminacy of linguistic expressions and psycho-sociological conditioning of discourse actions in one language and in translational contexts. The second part of the paper discusses the concept of conceptual and linguistic resemblance (similarity, equivalence) and discourse approximating strategies and proposes a Resemblance Matrix, presenting ways used to narrow the approximation gap between the interacting parties in monolingual and translational discourses.

Synthesis of RCCC Linkages to Visit Four Given Poses

This paper focuses on the problem of synthesis of spatial four-bar linkages of the RCCC type for rigid-body guidance with four given poses, R denoting a revolute, C a cylindrical kinematic pair. While synthesis equations for CC and RC dyads are available in the literature, the synthesis of spatial RCCC four-bar linkages requires special attention, due to its asymmetric topology. We revisit the problem to cope robustly with the asymmetry, namely, the approximate nature of the RC dyad and the infinity of exact solutions of the CC dyad for the number of given poses. Our approach includes a robust formulation of the synthesis of CC dyads, for the determination of axis-congruences. Moreover, we formulate a uniform synthesis equation, which enables us to treat both RC and CC dyads, with properly selected constraints for both cases. Two design examples are included.

Information Imperfection as an Inherent Characteristic of Adaptive Hypermedia

daptive hypermedia applications are aimed at tailoring hypermedia structures according to some form of user model, in an attempt to increase the usability and utility of the application for each individual or group. Existing research in the field has resulted in many systems, techniques, and paradigms, both for modelling user data and for the subsequent exploitation of such model for the sake of personalisation. As a matter of fact, the majority of adaptive hypermedia systems work with user models that are imperfect in some way, and the theories or hypotheses that guide adaptation are also often of a heuristic or approximate nature. Although some existing systems provide explicit means for dealing with imperfection in one or several of its multiple facets, there exists a lack of support for information imperfection in adaptive hypermedia models and architectures. In an attempt to provide such conceptual support, the MAZE model was proposed as a generalisation of an existing abstract hypermedia model, providing built-in support for fuzzy set-theoretic notions. This chapter provides an overall account of the MAZE model, along with its rationale, and an overview of a possible instance of a MAZE-based architecture. In addition, the use of MAZE to model common adaptive hypermedia technologies is illustrated through a concrete case study.

Look-Ahead NURBS-PH Interpolation for High Speed CNC Machining

Various methods for parametric interpolation of NURBS curves have been proposed in the past. However, the errors caused by the approximate nature of the NURBS interpolator were rarely taken into account. This paper proposes an integrated look-ahead algorithm for parametric interpolation along NURBS curves. The algorithm interpolates the sharp corners on the curve with the Pythagorean-hodograph (PH) interpolation. This will minimize the geometric and interpolator approximation errors simultaneously. The algorithm consists of four different modules: a sharp corner detection module, a PH construction module, a jerk-limited module, and a dynamics module. Simulations are performed to show correctness of the proposed algorithm. Experiments on an X-Y table confirm that the developed method improves tracking and contour accuracies significantly when compared to previously proposed adaptive-feedrate and curvature-feedrate algorithms.

Development of Finite Element Analysis Lab Module in the Second Course of Solid Mechanics

Many universities have started introducing Finite Element Analysis (FEA) at an earlier point in the curriculum. However, there is a wide diversity of university backgrounds, course content and sequence, pedagogical objectives and approaches, etc. This paper describes the development of FEA lab modules in the second course of solid mechanics in our specific context. Students in this course were introduced to FEA earlier in the first course of statics and solid mechanics. They had learned the basic steps in FEA for axially loaded and planar truss structures. In the second course, the FEA was extended to the planar cases. One of the objectives was to make the students aware of the descretization and numerical errors of the FEA. Hence there was a particular focus on element displacement fields and how they influence element behavior in comparison with an actual structure behavior. The lab modules were designed to be complementary to the class room learning. Approximate nature of the FEA was taught via the lab modules on descretization errors and numerical errors. The descretization error was demonstrated in the first part of the lab wherein different types of elements for planar problems were compared. One cantilever beam problem was solved with different types of elements and the results were compared with the theoretical value. Numerical error was studied in the second part of the lab wherein the effect of the element shape quality on the results was studied. A systematic study of the effect of mesh distortion was undertaken. ANSYS Parametric Design Language (APDL) macros were developed to change the mesh distortion quickly in a controlled fashion. A study of convergence of the results followed in the third part of the lab. A reasonable convergence was obtained for a plate with a central hole for which the theoretical results are known. Once the students grasped the need of convergence, a real life problem was attempted in the fourth part of the lab. The actual results are not known in the real life and a reasonable convergence needs to be established for acceptable results and for subsequent analysis and design. Design of a seat belt buckle was undertaken. A Pro/E CAD model was imported into ANSYS. The students used the subset of the CAD model to build their FE model considering only the relevant part, the symmetry and the mid plane. At the end of the semester, the students used the FEA tools for a real life design problem with a firm grasp of the approximate nature of the method.