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/

Engaging consumers on new integrated multichannel retail settings: challenges for retailers

The rapid diffusion of more channels for shopping posits new challenges for retailers, who need to compete in a complex environment for avoiding the problem of consumer cross-channel free riding. To discourage this behaviour, we propose a new environment where one retailer simultaneously handles more channels. The emerging integrated environment would engage more consumers if compared to the single handled channel, which in turn would avoid switching behaviours towards competitors’ channels. Our empirical research, based on the stimulus-organism-response paradigm, involves a sample of 237 consumers who were asked to explore the new retail settings simulated in a university lab. The results lead us to suggest the effective combination of multiple channels managed by one retailer as the new challenge for scholars and practitioners. We note that our participants showed positive emotional reactions towards the environment, which lead them to choose this environment for purchases

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

Shopping centres revisited: exploring new attributes of attractiveness

Traditional retailing is facing tough challenges, driven not least by the trend towards online shopping. This paper revisits shopping centres research in light of the recent increasing role of technologies, leisure activities and changes in consumer behaviour. Drawing upon 10,544 consumers’ unsolicited communications on Twitter relating to the 19 main shopping centres in UK that were posted in May 2019, this research seeks to understand how retail attributes are unevenly distributed across consumers’ evaluations to define the attributes driving consumers’ evaluations of retail-leisure complexes. Results demonstrate the impact of each identified attribute on preferences for retail-leisure complexes. In particular, findings provide important insights for scholars and practitioners related to the design of future attractive shopping centres. Shopping centres can play an important role in contributing to the viability and vitality of towns. We consider the findings in the light of wider policy and regulatory debates

Inclusive or exclusive? Investigating how retail technology can reduce old consumers’ barriers to shopping

This paper investigates older consumers in-store shopping experiences and the barriers that they face. The aim is to understand how new retail technologies (e.g., interactive in-store displays, self-service tills, robots etc.) can help seniors access satisfying, autonomous retail experiences, helping them to achieve a sense of inclusion in physical retail settings. Drawing upon the social inclusion/exclusion theory and information overload theory, the research employs a qualitative approach based on an inductive design, including face-to-face semi structured interviews with 36 consumers aged 75+. The findings highlight (i) old consumers have scarce interactions with in-store technologies (adding knowledge to motivations literature), (ii) the need to develop new technologies to support these consumers, and (iii) the extent to which these technologies are excluding rather than including old consumers (adding knowledge to the drivers of the field of exclusion). Results provide guidelines for retailers to enhance the sense of inclusion for old consumers through a better usage of new technologies

"Home alone" no more: How does the internet of things (IoT) enhance travellers\u27 subjective well-being

Although extensive research has recognized the importance of both IoT technologies and human well-being, the impact of Internet of Things (IoT) technologies on travellers\u27 subjective well-being (SWB) in the information technology literature remains limited. This study aims to explore the factors and extent to which IoT technologies affect travellers\u27 SWB during short-term trips. To this end, an integrated model was developed. The proposed model was empirically evaluated using survey data collected from a sample of 1028 British and 970 Chinese short-term travellers. A multigroup analysis has been conducted using Structural Equations Modelling (SEM) with Amos 26.0 software. The results reveal TTF has a positive indirect effect on consumers\u27 SWB via perceived benefits in both groups and a positive direct impact in the case of the British group. However, no significant relationship was observed between TTF and travellers\u27 SWB in the case of the Chinese group. Theoretically, this study first empirically explores and advances our knowledge of how the SWB of short-term travellers is affected by the use of IoT technologies across countries. From a practical viewpoint, this study may guide marketers toward a better understanding of how to use IoT technologies to enhance their consumers\u27 subjective well-being in different countrie

Cerebral hemodynamics on MR perfusion images before and after bypass surgery in patients with giant intracranial aneurysms

Preoperative assessment of the anatomy and dynamics of cerebral circulation for patients with giant intracranial aneurysm can improve both outcome prediction and therapeutic approach. The aim of our study was to use perfusion MR imaging to evaluate cerebral hemodynamics in such patients before and after extraintracranial high-flow bypass surgery. METHODS: Five patients with a giant aneurysm of the intracranial internal carotid artery underwent MR studies before, 1 week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiography, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)-internal carotid artery bypass with saphenous vein grafts (n = 4) or MCA-external carotid artery bypass (n = 1). RESULTS: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, characterized by significantly reduced mean cerebral blood flow (CBF), whereas mean transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good canalization of the bypass graft. MR perfusion data obtained after surgery showed improved cerebral hemodynamics in all cases, with a return of CBF index (CBFi), MTT, and rCBV to nearly normal values. CONCLUSION: Increased MTT with increased or preserved rCBV can be interpreted as a compensatory vasodilatory response to reduced perfusion pressure, presumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer compensate for diminished perfusion by vasodilation, and rCBV and CBFi diminish. Bypass surgery improves hemodynamics, increasing perfusion pressure and, thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodynamics in patients with intracranial giant aneurysm.BACKGROUND AND PURPOSE: Preoperative assessment of the anatomy and dynamics of cerebral circulation for patients with giant intracranial aneurysm can improve both outcome prediction and therapeutic approach. The aim of our study was to use perfusion MR imaging to evaluate cerebral hemodynamics in such patients before and after extraintracranial high-flow bypass surgery. METHODS: Five patients with a giant aneurysm of the intracranial internal carotid artery underwent MR studies before, 1 week after, and 1 month after high-flow bypass surgery. We performed MR and digital subtraction angiography, and conventional and functional MR sequences (diffusion and perfusion). Surgery consisted of middle cerebral artery (MCA)-internal carotid artery bypass with saphenous vein grafts (n = 4) or MCA-external carotid artery bypass (n = 1). RESULTS: In four patients, MR perfusion study showed impaired hemodynamics in the vascular territory supplied by the MCA of the aneurysm side, characterized by significantly reduced mean cerebral blood flow (CBF), whereas mean transit time (MTT) and regional cerebral blood volume (rCBV) were either preserved, reduced, or increased. After surgery, angiography showed good canalization of the bypass graft. MR perfusion data obtained after surgery showed improved cerebral hemodynamics in all cases, with a return of CBF index (CBFi), MTT, and rCBV to nearly normal values. CONCLUSION: Increased MTT with increased or preserved rCBV can be interpreted as a compensatory vasodilatory response to reduced perfusion pressure, presumably from compression and disturbed flow in the giant aneurysmal sac. When maximal vasodilation has occurred, however, the brain can no longer compensate for diminished perfusion by vasodilation, and rCBV and CBFi diminish. Bypass surgery improves hemodynamics, increasing perfusion pressure and, thus, CBFi. Perfusion MR imaging can be used to evaluate cerebral hemodynamics in patients with intracranial giant aneurysm

To immerse or not? Experimenting with two virtual retail environments

Purpose: The aim of this paper is to examine the determinants of users’ simulated experience in a virtual store and to show the subsequent impact of that experience on engagement. The outcome of that engagement is examined in relation to enjoyment, satisfaction and purchase intentions. Design/methodology/approach: The method comprised an experiment comparing users’ perceptions of a standard 2D online clothing store with an enhanced, immersive one that aimed to provide shopping value approaching that of a traditional store by using a 3D experience where participants wore special glasses and a data glove. Findings: Results demonstrate the major role of telepresence components in simulated experience and the critical role of that experience, along with hedonic and utilitarian values, in engagement. Purchase intention is influenced by satisfaction, which is in turn influenced by enjoyment and engagement. Engagement in turn is influenced by utilitarian and hedonic value and the experience of product simulation or telepresence, which is composed of control, colour and graphics vividness, and 3D authenticity. In the immersive, 3D environment experience is more associated with engagement and enjoyment, leading to greater purchase intention. The immersive, 3D environment thus has the potential to rival traditional shopping in terms of experience, resulting in higher sales for retailers and satisfaction for consumers. Originality: This work has evaluated a robust model of purchase intention and demonstrated it to hold not only in a 3D environment on a conventional computer platform, but also in an immersive one, where participants wear special glasses and a data glove

Short-Facelift Approach in Temporal Artery Biopsy: Is It Safe?

Giant cell arteritis (GCA) is a quite common panarteritis of the elderly that affects medium- and large-size arteries. Despite the increasing role of imaging with advancing technology, the gold standard for the diagnosis of GCA is still the temporal artery biopsy. A described complication of superficial temporal artery biopsy (STAB), for which incidence is not clear, is the accidental damage of the frontal branch of the facial nerve. In this paper, we described the short-scar facelift surgical approach for STAB on 23 consecutive patients who underwent unilateral superficial temporal artery biopsy for GCA suspicion. We collected data in terms of postoperative complications, biopsy specimen length, biopsy result and cosmetic appearance of the scar. In our experience, this surgical approach combines the advantage of avoiding incisions within the dangerous anatomical area, minimizing the risk of facial nerve damage, with an acceptable complication rate and a good final aesthetic result which avoids visible scarring

Testing the Dispersion of Nanoparticles in a Nanocomposite with an Ultra-Low Fill Content Using a Novel Non-Destructive Evaluation Technique

A non-destructive evaluation (NDE) technique capable of testing the dispersion of nanoparticles in a nanocomposite would be of great use to the industry to check the quality of the products made and to ensure compliance with their specifications. Very few NDE techniques found in the literature can evaluate the level of dispersion of the nanoparticles in the whole nanocomposite. Here, a recently developed NDE technique based on pulsed phase thermography (PPT) in transmission mode was used to assess the particle dispersion in ultra-low, less than 0.05 wt%, Ag enriched polymeric based nanocomposite manufactured with an innovative nano-coating fragmentation technique. The phasegrams obtained with the presented technique clearly showed clusters or bundles of Ag nanoparticles when present, down to the size of 6 µm. Therefore, the new NDE approach can be applied to verify that the expected levels of dispersion are met in the production process