On the dynamics of the collapse of a diffusion-flame hole

The collapse dynamics of a diffusion-flame hole in the presence of a counterflow are studied. We construct unsteady solutions of the one-dimensional edge-flame model of Buckmaster (1996), in which heat and mass transverse losses are algebraic. The flame structure is determined in the classical limit of large activation energy. Solutions for both planar and axisymmetric strain geometry are considered for the particular case of unity Lewis number. It is shown that the final stage of the edge-flame collapse is determined by a dominant balance between the time rate of change of the mass fractions (and temperature) and diffusion, giving a self-similar structure in which the size of the edge-flame hole approaches zero, to leading (zeroth) order, as a 1/2-power of time. This solution suggests an expansion of the full model equations in 1/2-powers of time that allows detailed analysis of the effects of side losses and flow distribution in the edge-flame collapse process. It is found that side loss effects are apparent at the first order, whereas convection by the counterflow is first felt during collapse at the second order in the fractional-time expansion. Numerical integrations of the governing equations are found to verify the analytic results

Large-eddy simulation and multiscale modelling of a Richtmyer–Meshkov instability with reshock

Large-eddy simulations of the Richtmyer–Meshkov instability with reshock are pre- sented and the results are compared with experiments. Several configurations of shocks initially travelling from light (air) to heavy (sulfur hexafluoride, SF6) have been simulated to match previous experiments and good agreement is found in the growth rates of the turbulent mixing zone (TMZ). The stretched-vortex subgrid model used in this study allows for subgrid continuation modelling, where statistics of the unresolved scales of the flow are estimated. In particular, this multiscale modelling allows the anisotropy of the flow to be extended to the dissipation scale, eta, and estimates to be formed for the subgrid probability density function of the mixture fraction of air/SF6 based on the subgrid variance, including the effect of Schmidt number

New technology and tourism industry innovation: evidence from audio-visual patented technologies

Purpose - Patenting behaviour in the tourism sector has received little academic attention due to a wider belief that innovation in tourism commonly involves improving the services in ways that are hardly patentable. The current study aims to address this oversight by focusing on patent analysis as means to evaluate the innovation trends in tourism. Design/methodology/approach - Building on an analysis of historical series of patents worldwide from 1996 to 2016, this paper explores the trends in the tourism sector by focusing on audio-visual technologies. The study used an evaluation of the 8,785 emerging patents, in terms of co-occurrences, applying hierarchical cluster analysis, factor analysis and multidimensional scaling. Findings - The findings suggest that there is a gradually increasing interest in innovation in tourism, which is growing faster than most of the other sectors explored here such as transportation and pharmaceuticals. The outputs also reveal the inventive effort of tourism industry in new technologies for developing utility models for tourists. Originality/value - The study contributes to tourism theory and practice by offering an overview of current/future applications of new technologies in tourism along with future trends, and mapping the main areas that these technologies might affect

A low-numerical dissipation, patch-based adaptive-mesh-refinement method for large-eddy simulation of compressible flows

This paper describes a hybrid finite-difference method for the large-eddy simulation of compressible flows with low-numerical dissipation and structured adaptive mesh refinement (SAMR). A conservative flux-based approach is described with an explicit centered scheme used in turbulent flow regions while a weighted essentially non-oscillatory (WENO) scheme is employed to capture shocks. Three-dimensional numerical simulations of a Richtmyer-Meshkov instability are presented

Shock-resolved Navier–Stokes simulation of the Richtmyer–Meshkov instability start-up at a light–heavy interface

The single-mode Richtmyer–Meshkov instability is investigated using a first-order perturbation of the two-dimensional Navier–Stokes equations about a one-dimensional unsteady shock-resolved base flow. A feature-tracking local refinement scheme is used to fully resolve the viscous internal structure of the shock. This method captures perturbations on the shocks and their influence on the interface growth throughout the simulation, to accurately examine the start-up and early linear growth phases of the instability. Results are compared to analytic models of the instability, showing some agreement with predicted asymptotic growth rates towards the inviscid limit, but significant discrepancies are noted in the transient growth phase. Viscous effects are found to be inadequately predicted by existing models

Enhancing the online decision-making process by using augmented reality: a two country comparison of youth markets

Although online stores extend the traditional offer of the brick and mortar ones, the limited possibilities to virtually try the product before the effective buying makes the online purchase decision a complex process for consumers. Therefore, online retailers face new challenges for supporting consumers consisting of the introduction of advanced technologies such as augmented reality systems. The present study investigates the effect of augmented reality technologies on consumer behaviour within the online retail environments, by comparing two different cultural settings. Drawing upon the technology acceptance model (TAM), new constructs related to the technology characteristics (e.g. quality of information, aesthetic quality, interactivity, and response time) developed a new conceptual model. This model has been tested for a new technology for virtual try-on (a smart mirror for virtual glasses). Focusing on young consumers, data collected in Italy and Germany yielding a total of 318 participants was used. Findings across these two markets reflect cross-market similarities, but also dissimilarities, related to consumers’ motivation to employ augmented reality systems for supporting their online purchase decision. These insights should prove helpful to retailers in better manage the online channels, that could be easily extended to the mobile one

I, Robot, You, Consumer: Measuring Artificial Intelligence Types and their Effect on Consumers Emotions in Service

This research draws upon the increasing usage of AI in service. It aims at understanding the extent to which AI systems have multiple intelligence types like humans and if these types arouse different emotions in consumers. To this end, the research uses a two-study approach: Study 1 builds and evaluates a scale for measuring different AI intelligence types. Study 2 evaluates consumers’ emotional responses to the different AI intelligences. The findings provide a measurement scale for evaluating different types of artificial intelligence against human ones, thus showing that artificial intelligences are configurable, describable, and measurable (Study 1), and influence positive and negative consumers’ emotions (Study 2). The findings also demonstrate that consumers display different emotions, in terms of happiness, excitement, enthusiasm, pride, inspiration, sadness, fear, anger, shame, and anxiety, and also emotional attachment, satisfaction, and usage intention when interacting with the different types of AI intelligences. Our scale builds upon human intelligence against AI intelligence characteristics while providing a guidance for future development of AI-based systems more similar to human intelligences

Modello numerico per la simulazione e l’ottimizzazione di controlli non distruttivi con ultrasuoni

I controlli non distruttivi basati sull’impiego di ultrasuoni sono ampiamente usati per la loro efficacia e affidabilità nel rilevamento di difetti. La generazione di onde ultrasonore e la propagazione in strutture di forma non regolare sono difficili da analizzare, soprattutto se la sorgente impiegata è un laser. Le tecniche numeriche per la simulazione del fenomeno reperibili in letteratura mostrano limiti di applicabilità per frequenze nel campo dei MHz e lunghezze d’onda molto corte. In questo lavoro presentiamo un metodo numerico in grado di risolvere accuratamente ed efficientemente problemi di generazione di onde ultrasonore tramite laser, con frequenze nel range dei MHz, e di propagazione in corpi relativamente estesi. La ricezione viene simulata con la propagazione degli ultrasuoni in aria, al fine di poter ottimizzare la configurazione completa per controlli non distruttivi con ultrasuoni senza contatto. Diverse configurazioni di ispezione sono state prima simulate tramite l’analisi numerica e poi riprodotte sperimentalmente per confrontare i risultati

Structure and Dynamics of amorphous Silica Surfaces

We use molecular dynamics computer simulations to study the equilibrium properties of the surface of amorphous silica. Two types of geometries are investigated: i) clusters with different diameters (13.5\AA, 19\AA, and 26.5\AA) and ii) a thin film with thickness 29\AA. We find that the shape of the clusters is independent of temperature and that it becomes more spherical with increasing size. The surface energy is in qualitative agreement with the experimental value for the surface tension. The density distribution function shows a small peak just below the surface, the origin of which is traced back to a local chemical ordering at the surface. Close to the surface the partial radial distribution functions as well as the distributions of the bond-bond angles show features which are not observed in the interior of the systems. By calculating the distribution of the length of the Si-O rings we can show that these additional features are related to the presence of two-membered rings at the surface. The surface density of these structures is around 0.6/nm^2 in good agreement with experimental estimates. From the behavior of the mean-squared displacement at low temperatures we conclude that at the surface the cage of the particles is larger than the one in the bulk. Close to the surface the diffusion constant is somewhat larger than the one in the bulk and with decreasing temperature the relative difference grows. The total vibrational density of states at the surface is similar to the one in the bulk. However, if only the one for the silicon atoms is considered, significant differences are found.Comment: 30 pages of Latex, 16 figure

Competing during a pandemic? Retailers’ ups and downs during the COVID-19 outbreak

The COVID-19 pandemic (that started in early 2020) is causing several disruptions in the short- and mid-term, to which businesses have to adapt. Some retailers have reacted to the emergency immediately, displaying a plethora of different intervention types. The authors aim to synthesize the challenges that retailers are facing during the COVID-19 emergency. We do this from the perspective of both consumers and managers, with the goal of providing guidelines on and examples of how retailers can handle this unprecedented situation