Dynamics of Silent Universes

We investigate the local non--linear dynamics of irrotational dust with vanishing magnetic part of the Weyl tensor, $H_{ab}$. Once coded in the initial conditions, this dynamical restriction is respected by the relativistic evolution equations. Thus, the outcome of the latter are {\it exact solutions} for special initial conditions with $H_{ab}=0$, but with no symmetries: they describe inhomogeneous triaxial dynamics generalizing that of a fluid element in a Tolman--Bondi, Kantowski--Sachs or Szekeres geometry. A subset of these solutions may be seen as (special) perturbations of Friedmann models, in the sense that there are trajectories in phase--space that pass arbitrarily close to the isotropic ones. We find that the final fate of ever--expanding configurations is a spherical void, locally corresponding to a Milne universe. For collapsing configurations we find a whole family of triaxial attractors, with vanishing local density parameter $\Omega$. These attractors locally correspond to Kasner vacuum solutions: there is a single physical configuration collapsing to a degenerate {\it pancake}, while the generic configuration collapses to a triaxial {\it spindle} singularity. These {\it silent universe} models may provide a fair representation of the universe on super horizon scales. Moreover, one might conjecture that the non--local information carried by $H_{ab}$ becomes negligible during the late highly non--linear stages of collapse, so that the attractors we find may give all of the relevant expansion or collapse configurations of irrotational dust.Comment: 40 pages with 4 figures, compressed and uuencoded PostScript file, submitted to ApJ, SISSA preprint Ref. 85/94/

Second-order matter perturbations in a LambdaCDM cosmology and non-Gaussianity

We obtain exact expressions for the effect of primordial non-Gaussianity on the matter density perturbation up to second order in a LambdaCDM cosmology, fully accounting for the general relativistic corrections arising on scales comparable with the Hubble radius. We present our results both in the Poisson gauge and in the comoving and synchronous gauge, which are relevant for comparison to different cosmological observables.Comment: 15 pages. LaTeX file. Invited article for CQG issue on non-linear cosmolog

Reconstruction subgrid models for nonpremixed combustion

Large-eddy simulation of combustion problems involves highly nonlinear terms that, when filtered, result in a contribution from subgrid fluctuations of scalars, Z, to the dynamics of the filtered value. This subgrid contribution requires modeling. Reconstruction models try to recover as much information as possible from the resolved field Z, based on a deconvolution procedure to obtain an intermediate field ZM. The approximate reconstruction using moments (ARM) method combines approximate reconstruction, a purely mathematical procedure, with additional physics-based information required to match specific scalar moments, in the simplest case, the Reynolds-averaged value of the subgrid variance. Here, results from the analysis of the ARM model in the case of a spatially evolving turbulent plane jet are presented. A priori and a posteriori evaluations using data from direct numerical simulation are carried out. The nonlinearities considered are representative of reacting flows: power functions, the dependence of the density on the mixture fraction (relevant for conserved scalar approaches) and the Arrhenius nonlinearity (very localized in Z space). Comparisons are made against the more popular beta probability density function (PDF) approach in the a priori analysis, trying to define ranges of validity for each approach. The results show that the ARM model is able to capture the subgrid part of the variance accurately over a wide range of filter sizes and performs well for the different nonlinearities, giving uniformly better predictions than the beta PDF for the polynomial case. In the case of the density and Arrhenius nonlinearities, the relative performance of the ARM and traditional PDF approaches depends on the size of the subgrid variance with respect to a characteristic scale of each function. Furthermore, the sources of error associated with the ARM method are considered and analytical bounds on that error are obtained

Making sense of consumers' tweets: sentiment outcomes for fast fashion retailers through big data analytics

Purpose- Consumers online interactions, posts, rating and ranking, reviews of products/attractions/restaurants and so on lead to a massive amount of data that marketers might access to improve the decision-making process, by impacting the competitive and marketing intelligence. The aim of this research is to help to develop understanding of consumers online generated contents in terms of positive or negative comments to increase marketing intelligence. Design/Methodology/Approach- The research focuses on the collection of 9,652 tweets referring to three fast fashion retailers of different sizes operating in the UK market, which have been shared among consumers and between consumer and firm, and subsequently evaluated through a sentiment analysis based on machine learning. Findings- Findings provide the comparison and contrast of consumers’ response towards the different retailers, while providing useful guidelines to systematically making sense of consumers’ tweets and enhancing marketing intelligence. Practical Implications- Our research provides an effective and systemic approach to (i) accessing the rich data set on consumers’ experiences based the massive number of contents that consumers generate and share online, and (ii) investigating this massive amount of data to achieve insights able to impact on retailers’ marketing intelligence. Originality/Value- To best of our knowledge, while other authors tried to identify the effect of positive or negative online comments/posts/reviews, the present study is the first one to show how to systematically detect the positive or negative sentiments of shared tweets for improving the marketing intelligence of fast fashion retailers

Synthetic cathinones related fatalities: an update

Synthetic cathinones, more commonly known as "bath salts", are synthetic drugs chemically related to cathinone, a psychostimulant found in the khat plant. They are the first most consumed products among new psychoactive substances, which cause psychostimulant and hallucinogenic effects determining a number of fatalities worldwide.  In this paper, we have systematically reviewed cases of synthetic cathinones-related fatalities analytically confirmed, which have occurred in the last few years.OBJECTIVE: Synthetic cathinones, more commonly known as “bath salts”, are synthetic drugs chemically related to cathinone, a psychostimulant found in the khat plant. They are the first most consumed products among new psychoactive substances, which cause psychostimulant and hallucinogenic effects determining a number of fatalities worldwide. In this paper, we have systematically reviewed cases of synthetic cathinones-related fatalities analytically confirmed, which have occurred in the last few years. MATERIALS AND METHODS: Relevant scientific articles were identified in Medline, Cochrane Central, Scopus, Web of Science and Institutional/ government websites up to November 2017 using the following keywords: synthetic cathinones, mephedrone, methylenedioxypyrovalerone, MDPV, methylone, ethylone, buthylone, fatal intoxication, fatalities and death. RESULTS: In total, 20 citations met the criteria for inclusion, representing several fatal cases with analytically confirmed synthetic cathinones in biological sample/s of the deceased. The death was attributed to hyperthermia, hypertension, cardiac arrest and more in general to the classic serotonin syndrome. Only rarely did the concentration of the parent drug causing fatality overcome the value of 1 mg/L in post-mortem biological fluids. CONCLUSIONS: Abuse of synthetic cathinones still represents a serious public health issue. Systematic clinical studies on both the animal and human model are lacking; therefore, the only available data are from the users who experience the possible hazardous consequences. Analytical methodologies for the identification of parent compounds and eventual metabolites both in ante-mortem and post-mortem cases need to be developed and validated. Analytical data should be shared through different communication platforms with the aim of stopping this serious health threat for drug users

An instructional experience for pre-service teachers: integrating simulations and hands-on activities in physics teaching

Simulations are a valuable tool in teaching modern science. We report on an experiment in a physics laboratory on electricity using both simulations as well as hands-on activities. The laboratory was implemented as part of a course for pre-service secondary school physics teachers. The 45 participants were divided into two groups, one performing first simulations and then hands-on activities, the other in the reversed order. The laboratory activities focused on DC circuits related to real-life situations, like a multiple socket or a chandelier modeled with simple wires, batteries and bulbs. The participants were asked to make predictions of the outcome before conducting each task and to compare their predictions with the observations and measurements they made during the activities. The participants were asked to make predictions of the outcome before conducting each task and to compare their predictions with the observations and measurements they made during the activities. No significant differences in performance were observed between the two groups, suggesting that in this experiment simulations did not help the pre-service teachers in transferring their conceptual knowledge to practical application

Does the innovation-orientation lead to retail industry growth? Empirical evidence from patent analysis

Competitiveness and complexity in the retail industry are increasing due to rapid technological changes and diffusion. Patent analysis is largely used in innovation studies to assess and monitor technological changes in different sectors. The aim of this paper is to provide a comprehensive view of the innovative forces affecting the retailing sector, by focusing on the evaluation of innovation levels through the classification and analysis of patented innovations. The findings show that retailers might shift to more innovation-oriented strategies in order to propose innovative consumer solutions, due to the support of the technology advancements highlighted by the strong patent track record. Our study contributes to the literature by providing empirical evidence of critical areas for innovation in retailing and by offering bibliometric and patent analytical methods measures relative to the innovative forces affecting retailing, which might push the sector to be increasingly an innovation-oriented one. Finally, the high level of property rights (defined by the huge amount of patents) pushes retailers to invest more on acquiring patented technologies to achieve advantages over competitors or to adopt novel management practices as substitutes for patents

To what extent luxury retailing can be smart?

The aim of this paper is to explore how luxury brands use new technologies in the context of smart retailing. Building on qualitative data from multiple cases from the luxury industry, our analysis reveals that this sector is conscious of the benefits of using smart technologies as marketing tools, while the effective use of these innovative systems is still limited. However, studies on innovation forces affecting the retail industry are still limited in luxury sectors. The study provides an empirical contribution to the emerging topic of smart retailing with an emphasis on the luxury sector through its in-depth investigation of the usage of smart technologies by the firms studied

The use of new technologies for corporate marketing communication in luxury retailing: preliminary findings

The aim of this paper is to explore the extent to which luxury brand retailers employ new technologies as a tool for corporate marketing communication. We employed a multiple-case study consisting of five information-rich cases, with the similar characteristics of large firms selling luxury brands which are aware of the importance of innovation. In each company, we interviewed the key person in charge of marketing innovation strategies, and we collected data from annual reports, press releases, and direct observation of all the new technology categories used. Our findings reveal that this sector is considerably aware of the benefits of using new media as a marketing communication tool, while the effective use of these new media is still limited. The study provides an empirical contribution to the emerging topic of innovation and technology management in retailing, with the emphasis being placed on the luxury sector through an in-depth investigation of the usage of new technologies by the firms studied. This study is the first one investigating thoroughly the luxury sector usage of new technologies to improve corporate marketing communication

An electrical model for the Korteweg-de Vries equation

In this paper we describe an electrical network, whose current evolution does agree with a Korteweg\u2013de Vries equation. Our aim is to prepare pupils to understand the analytical aspects of nonlinear and dispersive phenomena, which very often are neglected in high-school and graduate textbooks. Some historical remarks introduce the topic and a bibliography is provided. \ua9 1984, American Association of Physics Teachers