Recent Developments in Understanding Two-dimensional Turbulence and the Nastrom–Gage Spectrum

Two-dimensional turbulence appears to be a more formidable problem than three-dimensional turbulence despite the numerical advantage of working with one less dimension. In the present paper we review recent numerical investigations of the phenomenology of two-dimensional turbulence as well as recent theoretical breakthroughs by various leading researchers. We also review efforts to reconcile the observed energy spectrum of the atmosphere (the Nastrom–Gage spectrum) with the predictions of two-dimensional turbulence and quasigeostrophic turbulence.     

Indexing and progressive top-k similarity retrieval of trajectories

In this work, we study the performance of state-of-the-art access methods to efficiently store and retrieve trajectories in spatial networks. First, we study how efficiently such methods can manage trajectory data to support indexing for data demanding applications where trajectory retrieval must be fast. At the same time, trajectory insertions, deletions and modifications should also be executed efficiently. Secondly, we compare the performance of progressive processing of trajectory similarity top-k queries, which is a common query in spatial applications. Specifically, we examine FNR-trees (Frentzos 2003) and MON-trees (de Almeida and Gueting, 2005), which have been proposed for trajectory management, against a novel variation of our proposed Cluster-extended Adjacency Lists (CeAL) (Tiakas and Rafailidis 2015). In particular: (a) we extend the above access methods to efficiently handle trajectories of objects that move in large spatial networks, and (b) to enhance their performance, we create an entirely new implementation framework to generate trajectories and to test the trajectory management and retrieval for each approach. With respect to the generation of trajectories, we extend the generator by Brinkhoff (2000) to efficiently support very large spatial networks. Finally, we conduct extensive experimentation which demonstrates that the proposed method CeAL prevails in space and time complexity.

     

Assessing the performance of short multi-item questionnaires in aesthetic evaluation of websites

In recent years, website aesthetics has received a fair amount of attention from the HCI community. This has led to the creation of a variety of multi-item questionnaires aimed at capturing users’ aesthetic judgments. Researchers have used these questionnaires in several HCI studies to investigate the relationship between aesthetics and other evaluative constructs such as usability. However, their usefulness as evaluation tools in visual design practice remains underexplored. Lengthy multi-item questionnaires can be particularly problematic especially in studies where participants must evaluate multiple designs or when they are required to give responses repeatedly in predefined time intervals. Despite the criticism, single-item scales have been used in many past studies in which questionnaire length could be problematic. Another alternative available to practitioners/researchers are short versions of standardised multi-item questionnaires that have been created for the aesthetic evaluations of websites. In this paper, we present a study in which we compare the performance of three such condensed aesthetic questionnaires (i.e. aesthetics scale, AttrakDiff, VisAWI) during a website redesign project. The short versions of those questionnaires were used by 187 users during an evaluation of 7 alternative website designs. The questionnaires were compared on performance criteria such as reliability, validity, and predictive ability. Data analysis showed that although AttrakDiff’s overall performance was better, a considerable amount of variance in aesthetic judgment could not be accounted for by any of the questionnaires.     

A Synthesis of Tactical Fleet Planning Models for the Car Rental Industry

Daily tactical planning of the vehicle fleet is critical for a car rental business. In this decision-making process planners have to address the conflicting concerns of field management, namely, assuring adequate vehicle availability to satisfy customer demand while maintaining a high degree of utilization for each car in the fleet; this is achieved by the appropriate fleet deployment among car rental locations. This work was inspired by a series of problems encountered by the decision-makers of a major US car rental company. We first present the formulation of the tactical fleet planning model. Based on its structure, we decompose the model into a fleet deployment model and a transportation model. We develop optimal conditions for both subproblems and then we present a heuristic to reduce the gap from optimality for the complete model. We further present the application of the entire solution methodology via a case analysis for the State of Florida. Finally, we develop three extensions to the fleet deployment model to capture the cost of unsatisfied demand and fleet surplus, the service level, and a general price-demand function. We provide optimal closed-form conditions for all the extensions.     

Conjugated Graetz problems—I: General formalism and a class of solid-fluid problems

Conjugated Graetz problems arise where two (or more) phases, with at least one phase in fully developed flow, exchange energy or mass across an intervening surface. In these problems the temperature or concentration fields are coupled through the conjugating conditions which express the continuity of fluxes and the rate of transfer. A general formalism is presented first for the analysis of these problems, employing a matrix differential operator with respect to the radial variable and following the decomposition technique of [1–3]. The aforementioned operator is shown to be symmetric in its domain, possessing a denumerable set of eigenvalues and a complete set of eigenvectors. A class of solid-fluid problems, involving the removal of heat from a heated solid cylinder by a surrounding annular-flow fluid, is then discussed in detail; analytical solutions are obtained by expansion in terms of the above eigenvectors. These solid-fluid problems may be viewed as extensions of the extended, one-phase, Graetz problem with prescribed wall flux [2].     

Polyurethane/poly(vinylidene fluoride)/MWCNT composite foam for broadband airborne sound absorption

A polyurethane/poly(vinylidene fluoride)/multi-walled carbon nanotubes (PU/PVDF/MWCNT) (83/15/2) composite foam was designed and fabricated. The foam exhibited high airborne sound absorption performance in a wide-frequency range. The sound absorption coefficient reached the value of 0.85 at 1 kHz, which is a significant improvement over PU foam. It was found that PVDF formed a separate immiscible phase and part of it was crystallized in a polar phase in the PU scaffold in the PU/PVDF/MWCNT composite, which could benefit the sound absorption performance by introducing interfacial damping and local piezoelectric damping effects. The introduction of the conductive MWCNT filament in the composite foam further improved sound absorption, possibly by facilitating the dissipation of the electrical charges generated from local piezoelectric effect and enhancing both the interfacial damping effect and local piezoelectric damping effect. With PU as the main ingredient, the fabrication scalability of the foam can be improved with significantly reduced material and production cost in comparison with PVDF foam. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 47868.     

Evaluation of cost-effective methods in the pesticide residue analysis of non-fatty baby foods

Three non-fatty ready-to-eat baby food matrices (fruits: juice, purée and cocktail plus rice flour/starch and sugar) were fortified with 0.01, 0.05, 0.1 and 0.2 mg/kg of dimethoate, chlorpyrifos, methidathion, phosalone and diazinon. Simple methods including extraction by ethyl acetate [EtAc] and acetone partition and determination by gas chromatography with Nitrogen–Phosphorus Detector (GC–NPD) were used. Acceptable pesticides recoveries (70–110%), low detection and quantification limits (0.001 to >0.1 mg/kg and 0.005 to 0.04 mg/kg, respectively) and repeatabilities (%RSDs), in 0.01 mg/kg, within 2.9–13.9% were observed. However, analytes recoveries were affected (p < 0.05) by both the baby food formulation and the extraction method used. Specifically, fruits purée and cocktail EtAc extracts gave excessively over-(dimethoate recoveries of 119.7–153.5%) or underestimation (phosalone and especially diazinon recoveries of 19.3–79.2%) in contrast to fruits juice (e.g., 61.3–87.9%). Also, EtAc extracts showed higher amount of lipophilic compounds and provided lower recoveries for non-polar analytes than those of acetone partition. Consequently, the examined methods may be successfully applied in non-fatty baby foods with the matrix-matched standards determination, following improvements of certain parameters in relation to the clean-up of samples.