Quantum radiation from superluminal refractive index perturbations

We analyze in detail photon production induced by a superluminal refractive index perturbation in realistic experimental operating conditions. The interaction between the refractive index perturbation and the quantum vacuum fluctuations of the electromagnetic field leads to the production of photon pairs.Comment: 4 page

Spacetime geometries and light trapping in travelling refractive index perturbations

In the framework of transformation optics, we show that the propagation of a locally superluminal refractive index perturbation (RIP) in a Kerr medium can be described, in the eikonal approximation, by means of a stationary metric, which we prove to be of Gordon type. Under suitable hypotheses on the RIP, we obtain a stationary but not static metric, which is characterized by an ergosphere and by a peculiar behaviour of the geodesics, which are studied numerically, also accounting for material dispersion. Finally, the equation to be satisfied by an event horizon is also displayed and briefly discussed.Comment: 14 pages, 7 figure

Comparing the Sustainability of Different Powertrains for Urban Use

The real environment impacts the fuel and energy consumption of any vehicle: technology, physical and social phenomena, traffic, drivers’ behaviour, and so on; many of them are difficult to quantify. The authors’ methodology was used to test the real impact of vehicles in “standard” urban conditions, and many generations of hybrid powertrains are compared. One of the latest performance indexes is the percentage of time the vehicle runs with zero emissions (ZEV). For example, the hybrid vehicle tested ran up to 80% with no emissions and fuel consumption below 3 L per 100 km. A few energy performance indicators were compared between five vehicles: one battery electric vehicle (BEV), two hybrid gasoline–electric vehicles (HEVs), and two traditional vehicles (one diesel and one gasoline). Their potential to use only renewable energy is unrivalled, but today’s vehicles’ performances favour hybrid power trains. This paper summarises the most sustainable powertrain for urban use by comparing experimental data from on-road testing. It also evaluates the benefits of reducing emissions by forecasting the Italian car fleet of 2025 and three use cases of the evolution of car fleets, with a focus on Rome

Rogue wave formation scenarios for the focusing nonlinear Schr\"odinger equation with parabolic-profile initial data on a compact support

We study the (1+1) focusing nonlinear Schroedinger (NLS) equation for an initial condition with concave parabolic profile on a compact support and phase depending quadratically on the spatial coordinate. In the absence of dispersion, using the natural class of self-similar solutions of the resulting elliptic system, we generalise a result by Talanov, Guervich and Shvartsburg, finding a criterion on the chirp and modulus coefficients at time equal zero to determine whether the dispersionless solution features asymptotic relaxation or a blow-up at fine time, providing an explicit formula for the time of catastrophe. In the presence of dispersion, we numerically show that the same criterion determines, even beyond the semi-classical regime, whether the solution relaxes or develops a higher order rogue wave, whose amplitude can be several multiples of the height of the initial parabola. In the latter case, for small dispersion, the time of catastrophe for the corresponding dispersionless solution predicts almost exactly the onset time of the rogue wave. In our numerical experiments, the sign of the chirp appears to determine the prevailing scenario, among two competing mechanisms leading to the formation of a rogue wave. For negative values, the simulations are suggestive of the dispersive regularisation of a gradient catastrophe described by Bertola and Tovbis for a different class of smooth, bell-shaped initial data. As the chirp becomes positive, the rogue wave seem to result from the interaction of counter-propagating dispersive dam break flows, as described for the box problem by El, Khamis and Tovbis. As the chirp and amplitude of the initial profile are relatively easy to manipulate in optical devices and water tank wave generators, we expect our observation to be relevant for experiments in nonlinear optics and fluid dynamics.Comment: 17 pages, 5 figures, 1 tabl

Rogue wave formation scenarios for the focusing nonlinear Schrödinger equation with parabolic-profile initial data on a compact support

We study the (1+1) focusing nonlinear Schrödinger equation for an initial condition with compactly supported parabolic profile and phase depending quadratically on the spatial coordinate. In the absence of dispersion, using the natural class of self-similar solutions, we provide a criterion for blowup in finite time, generalizing a result by Talanov et al. In the presence of dispersion, we numerically show that the same criterion determines, even beyond the semiclassical regime, whether the solution relaxes or develops a high-order rogue wave, whose onset time is predicted by the corresponding dispersionless catastrophe time. The sign of the chirp appears to determine the prevailing scenario among two competing mechanisms for rogue wave formation. For negative values, the numerical simulations are suggestive of the dispersive regularization of a gradient catastrophe described by Bertola and Tovbis for a different class of smooth, bell-shaped initial data. As the chirp becomes positive, the rogue wave seems to result from the interaction of counterpropagating dispersive dam break flows, as in the box problem recently studied by El, Khamis, and Tovbis. As the chirp and amplitude of the initial profile are relatively easy to manipulate in optical devices and water tank wave generators, we expect our observation to be relevant for experiments in nonlinear optics and fluid dynamics

Levelling foods for priority micronutrient value can provide more meaningful environmental footprint comparisons

A growing literature in Life Cycle Assessment seeks to better inform consumers, food policymakers, food supply chain actors, and other relevant stakeholders about how individual foods contribute to sustainable diets. One major challenge involves accurately capturing potential trade-offs between nutritional provision and environmental impacts associated with food production. In response, food system sustainability literature has turned increasingly to nutritional Life Cycle Assessment, which assesses the environmental footprints of different foods while accounting for nutritional value. Here we provide examples that show how environmental footprints based on a priority micronutrient-focused functional unit can provide nutritionally meaningful insights about the complexities involved in sustainable food systems. We reinforce the idea that there are limitations in using single-value nutrition-environment scores to inform food guidance, as they do not adequately capture the complex multi-dimensionality and variation involved in healthy and sustainable food systems. In our discussion we highlight the need for future agri-food sustainability assessments to pay attention to regional nutritional and environmental variation within and between commodities, and to better interpret trade-offs involved in food substitutions

Chemical defence by sterols in the freshwater ciliate Stentor polymorphus

Heterotrich ciliates typically retain toxic substances in specialized ejectable organelles, called extrusomes, which are used in predator-prey interactions. In this study, we analysed the chemical defence strategy of the freshwater heterotrich ciliate Stentor polymorphus against the predatory ciliate Coleps hirtus, and the microturbellarian flatworm Stenostomum sphagnetorum. The results showed that S. polymorphus is able to defend itself against these two predators by deploying a mix of bioactive sterols contained in its extrusomes. Sterols were isolated in vivo and characterized by liquid chromatography-mass spectrometry (LC-MS), and nuclear magnetic resonance (NMR), as ergosterol, 7-dehydroporiferasterol, and their two peroxidized analogues. The assessment of the toxicity of ergosterol and ergosterol peroxide against various organisms, indicated that these sterols are essential for the effectiveness of the chemical defence in S. polymorphus

Birkhoff strata of the Grassmannian Gr(2)\mathrm{^{(2)}}: Algebraic curves

Algebraic varieties and curves arising in Birkhoff strata of the Sato Grassmannian Gr${^{(2)}}$ are studied. It is shown that the big cell $\Sigma_0$ contains the tower of families of the normal rational curves of all odd orders. Strata $\Sigma_{2n}$, $n=1,2,3,...$ contain hyperelliptic curves of genus $n$ and their coordinate rings. Strata $\Sigma_{2n+1}$, $n=0,1,2,3,...$ contain $(2m+1,2m+3)-$plane curves for $n=2m,2m-1$ $(m \geq 2)$ and $(3,4)$ and $(3,5)$ curves in $\Sigma_3$, $\Sigma_5$ respectively. Curves in the strata $\Sigma_{2n+1}$ have zero genus.Comment: 14 pages, no figures, improved some definitions, typos correcte

energy consumption of a last generation full hybrid vehicle compared with a conventional vehicle in real drive conditions

Abstract Hybrid vehicles are one of the most important choices to improve efficiency and reduce CO2 production of vehicles. Benefits in using hybrid powertrains are generally found in urban environment where lower average speeds, higher accelerations make the internal combustion engine run at lower efficiency points. The originality of the present paper consists in the data elaboration and analysis collected in a measurement campaign on road in real driving conditions, on an ad hoc path planned according to the average national daily mileage in metropolitan urban context, which thus acquires a significance generalizable in that specific context, which led to the consumption quantification and an analysis of the main factors that determine the reduction in consumption of full-hybrid vs conventional vehicles. Another important and original aspect of this paper is the analysis of the operating times in ZEV mode of hybrid vehicles, which shows how this solution leads to a significant reduction of pollutant emissions in urban contest. An on-road experimental campaign has been done by comparing two different versions of the same model (Toyota Yaris Hybrid and a conventional one, Toyota Yaris 1.5 gasoline) and a hybrid vehicle with different characteristics (the hybrid born - Toyota Prius), like size, traction battery capacity, generator/motor electric power. Thirty drivers on a fixed path have done this experimental campaign and in this paper, the results are reported. The results show that a strong influence on consumption is due not only to the type of vehicle, but also to driving style and speed. The comparison between the two versions of Yaris, shows a strong reduction in consumption using hybrid vehicle for low and medium speeds (for 20 km/h about 50%), such benefit decreases with the increasing speed and for values higher than 90 km/h both the vehicles have the same consumption. The reduced consumption of the hybrid vehicle at low speeds is due, on the one hand, to the greater efficiency of the hybrid vehicle engine compared to the conventional one and on the other hand to the high functioning in ZEV mode, with the engine off, (63% of time) thanks to the use of the electric motor. The comparison between the two hybrid vehicles with different characteristics (YarisHy and Prius) shows that the consumption trend vs. speeds is similar but the Prius has lower consumption due above all to the high efficiency of the braking energy recovery system, despite the greatest mass. This lead then to significant consumption reduction, but also lower emissions in places where such parameters have an important role: the urban environment

Reply to Comment on: Hawking radiation from ultrashort laser pulse filaments

A comment by R. Schutzhold et al. raises possible concerns and questions regarding recent measurements of analogue Hawking radiation. We briefly reply to the opinions expressed in the comment and sustain that the origin of the radiation may be understood in terms of Hawking emission