Stochastic energetics of a Brownian motor and refrigerator driven by non-uniform temperature

The energetics of a Brownian heat engine and heat pump driven by position dependent temperature, known as the B\"uttiker-Landauer heat engine and heat pump, is investigated by numerical simulations of the inertial Langevin equation. We identify parameter values for optimal performance of the heat engine and heat pump. Our results qualitatively differ from approaches based on the overdamped model. The behavior of the heat engine and heat pump, in the linear response regime is examined under finite time conditions and we find that the efficiency is lower than that of an endoreversible engine working under the same condition. Finally, we investigate the role of different potential and temperature profiles to enhance the efficiency of the system. Our simulations show that optimizing the potential and temperature profile leads only to a marginal enhancement of the system performance due to the large entropy production via the Brownian particle's kinetic energy.Comment: 14 pages, 15 figures (latest version with modified figures and text

Understanding students’ instrumental goals, motivation deficits and achievement: Through the Lens of a Latent Profile Analysis

Building on the future oriented and regulated nature of instrumental goals, Lens and colleagues developed a 2 (proximal-distal) x 2 (internal-external) motivational framework. The current study aimed to test this framework from a person-centred perspective, while equally taking into account students’ lack of motivation as to extend the empirical and theoretical borders of the model. Latent Profile Analyses were used to test the viability of two to five motivational profiles among Japanese second-year students (N = 781). A solution with three latent subgroups fitted the sample best, explaining 6% to 62% of the variance in the measured variables. The profiles were labelled “low future oriented motivational profile”, “average motivated profile”, and “highly motivated profile”. The highly motivated subgroup reported the most adaptive pattern of motivation and highest levels of deep level learning, while few differences were found for surface learning and GPA. Theoretical and practical implications are discussed.published_or_final_versio

On the impact of video stalling and video quality in the case of camera switching during adaptive streaming of sports content

The widespread usage of second screens, in combination with mobile video streaming technologies like HTTP Adaptive Streaming (HAS), enable new means for taking end-users' Quality of Experience (QoE) to the next level. For sports events, these technological evolutions can, for example, enhance the overall engagement of remote fans or give them more control over the content. In this paper, we consider the case of adaptively streaming multi-camera sports content to tablet devices, enabling the end-user to dynamically switch cameras. Our goal is to subjectively evaluate the trade-off between video stalling duration (as a result of requesting another camera feed) and initial video quality of the new feed. Our results show that short video stallings do not significantly influence overall quality ratings, that quality perception is highly influenced by the video quality at the moment of camera switching and that large quality fluctuations should be avoided

A heat pump at a molecular scale controlled by a mechanical force

We show that a mesoscopic system such as Feynman's ratchet may operate as a heat pump, and clarify a underlying physical picture. We consider a system of a particle moving along an asymmetric periodic structure . When put into a contact with two distinct heat baths of equal temperature, the system transfers heat between two baths as the particle is dragged. We examine Onsager relation for the heat flow and the particle flow, and show that the reciprocity coefficient is a product of the characteristic heat and the diffusion constant of the particle. The characteristic heat is the heat transfer between the baths associated with a barrier-overcoming process. Because of the correlation between the heat flow and the particle flow, the system can work as a heat pump when the particle is dragged. This pump is particularly effective at molecular scales where the energy barrier is of the order of the thermal energy.Comment: 7 pages, 5 figures; revise

Symmetric Weighted First-Order Model Counting

The FO Model Counting problem (FOMC) is the following: given a sentence $\Phi$ in FO and a number $n$, compute the number of models of $\Phi$ over a domain of size $n$; the Weighted variant (WFOMC) generalizes the problem by associating a weight to each tuple and defining the weight of a model to be the product of weights of its tuples. In this paper we study the complexity of the symmetric WFOMC, where all tuples of a given relation have the same weight. Our motivation comes from an important application, inference in Knowledge Bases with soft constraints, like Markov Logic Networks, but the problem is also of independent theoretical interest. We study both the data complexity, and the combined complexity of FOMC and WFOMC. For the data complexity we prove the existence of an FO$^{3}$ formula for which FOMC is #P$_1$-complete, and the existence of a Conjunctive Query for which WFOMC is #P$_1$-complete. We also prove that all $\gamma$-acyclic queries have polynomial time data complexity. For the combined complexity, we prove that, for every fragment FO$^{k}$, $k\geq 2$, the combined complexity of FOMC (or WFOMC) is #P-complete.Comment: To appear at PODS'1

Biological evaluation of the Belgian beaches by means of terrestrial invertebrates

Beaches belong to the least studied ecosystems, although they contain typical habitats for a large amount of specialised terrestrial invertebrates. This specific beach fauna was quite diverse along the Belgian coast at the beginning of the twentieth century. Especially species bound to organic matter, washed up on the tide line, were well represented. As a result of the development of mass tourism, most of our beaches are subject to mechanical beach cleaning and the suppletion of sand. These activities are believed to be responsible for the degradation of the original habitat. However, documentation on this topic was scarce and evidence of negative effects on local biodiversity was lacking. Therefore, the main goal of this research was to make an inventory of the terrestrial arthropod fauna on Flemish beaches and analysing temporal and spatial variation, in function of abiotic components such as the degree of recreation and the intensity of mechanical beach cleaning. The main conclusion is that a high degree of recreation and mechanical beach cleaning indeed has a negative influence on the richness of the species bound to organic detritus and also induces a change in community structure of terrestrial invertebrates along the Flemish coast. Secondly, predators and even parasites are also indirectly influenced by these anthropogenic disturbances, as a result of the declining prey population. Excluding or at least reducing these impacts along certain sections of the Flemish coast, might ensure the preservation of the organic detritus on the tide line and hence its associated beach fauna

Efficiency at maximum power: An analytically solvable model for stochastic heat engines

We study a class of cyclic Brownian heat engines in the framework of finite-time thermodynamics. For infinitely long cycle times, the engine works at the Carnot efficiency limit producing, however, zero power. For the efficiency at maximum power, we find a universal expression, different from the endoreversible Curzon-Ahlborn efficiency. Our results are illustrated with a simple one-dimensional engine working in and with a time-dependent harmonic potential.Comment: 6 pages, 3 figure

Compaction control and related stress–strain behaviour of off-shore land reclamations with calcareous sands

AbstractWhen constructing off-shore land reclamations, one aims to ensure that the final soil mass fulfills certain minimal criteria related to shear strength, stiffness and resistance against liquefaction. In general, these characteristics improve with increasing density of the soil mass, which means that the above criteria are usually condensed into a single one: ‘adequate densification’.Quality control of reclamation constructions therefore focuses on the latter. Technical requirements are written based on one single parameter: the relative density Dr. On the site, this parameter is commonly determined indirectly using correlations with the cone penetration resistance qc, making the CPT the main tool for quality control.The paper presents data gathered during the design and construction of an off-shore land reclamation using calcareous sands. For this specific project, density control had to be done through the use of CPT.Calibration chamber tests were performed to establish the CPT qc–Dr correlation for the specific soil material. This correlation was used to analyse CPT results during construction of the site in order to determine the quality of compaction.In a further stage, an elaborate laboratory study was performed to establish additional correlations between soil parameters and the stress–strain parameters. Furthermore, seismic CPT tests were executed on the site to test the relevance of the laboratory correlations and the ‘relative density approach’ in general.It is shown that off-shore land reclamations have a very erratic stress-history, due to the different processes of depositing the soil material and the various densification methods. This stress-history is of great importance in the stress–strain behaviour of the site. Results also suggest that the CPT does not provide enough data to reliably predict soil stiffness when dealing with crushable materials. Specifically, in situ measurements show that there is no direct correlation between the small strain shear modulus G0 and qc

A simplified method to account for vertical human-structure interaction

This is the final version. Available on open access from Elsevier via the DOI in this recordTo account for vertical human-structure interaction (HSI) in the vibration serviceability analysis, the contact force between the pedestrian and the structure can be modelled as the superposition of the force induced by the pedestrian on a rigid surface and the force resulting from the mechanical interaction between the structure and the human body. For the case of large crowds, this approach leads to (timevariant) models with a very high number of degrees of freedom (DOFs). To simplify analysis, this paper investigates the performance of an equivalent single-degree-of-freedom approach whereby the effect of HSI is translated into an effective natural frequency and modal damping ratio for each mode of the supporting structure. First, the numerical study considers a footbridge structure that is modelled as a simply-supported beam for which only the fundamental vertical bending mode is taken into account. For a relevant range of structure and crowd parameters, the comparison is made between the structural response predicted by the simplified model and the more accurate reference model that accounts for all DOFs of the coupled crowd-structure model. Where the simplified model is found to underestimate the structural response, although to a limited extent, this is compensated for by introducing a correction factor for the effective damping ratio. Second, the performance of the simplified method is evaluated through the application on a real footbridge. The results show that the simplified method allows for a good and mildly conservative estimate of the structural acceleration response that is within 10-20% of the predictions of the reference crowd-structure model.Research Foundation Flanders (FWO