Polariton excitation in epsilon-near-zero slabs: transient trapping of slow light

We numerically investigate the propagation of a spatially localized and quasi-monochromatic electromagnetic pulse through a slab with Lorentz dielectric response in the epsilon-near-zero regime, where the real part of the permittivity vanishes at the pulse carrier frequency. We show that the pulse is able to excite a set of virtual polariton modes supported by the slab, the excitation undergoing a generally slow damping due to absorption and radiation leakage. Our numerical and analytical approaches indicate that in its transient dynamics the electromagnetic field displays the very same enhancement of the field component perpendicular to the slab, as in the monochromatic regime. The transient trapping is inherently accompanied by a significantly reduced group velocity ensuing from the small dielectric permittivity, thus providing a novel platform for achieving control and manipulation of slow light

Multipolar terahertz absorption spectroscopy ignited by graphene plasmons

AbstractTerahertz absorption spectroscopy plays a key role in physical, chemical and biological systems as a powerful tool to identify molecular species through their rotational spectrum fingerprint. Owing to the sub-nanometer scale of molecules, radiation-matter coupling is typically dominated by dipolar interaction. Here we show that multipolar rotational spectroscopy of molecules in proximity of localized graphene structures can be accessed through the extraordinary enhancement of their multipolar transitions provided by terahertz plasmons. In particular, specializing our calculations to homonuclear diatomic molecules, we demonstrate that a micron-sized graphene ring with a nano-hole at the core combines a strong near-field enhancement and an inherently pronounced field localization enabling the enhancement of the dipole-forbidden terahertz absorption cross-section of $${{\rm{H}}}_{2}^{+}$$ H 2 + by 8 orders of magnitude. Our results shed light on the strong potential offered by nano-structured graphene as a robust and electrically tunable platform for multipolar terahertz absorption spectroscopy at the nanoscale

Collision quenching in the ultrafast dynamics of plasmonic materials

We explore the nonlinear response of plasmonic materials driven by ultrashort pulses of electromagnetic radiation with temporal duration of few femtoseconds and high peak intensity. By developing the Fokker-Planck-Landau theory of electron collisions, we solve analytically the collisional integral and derive a novel set of hydrodynamical equations accounting for plasma dynamics at ultrashort time scales. While in the limit of small light intensities we recover the well established Drude model of plasmas, in the high intensity limit we observe nonlinear quenching of collision-induced damping leading to absorption saturation. Our results provide a general background to understand electron dynamics in plasmonic materials with promising photonic applications in the manipulation of plasma waves with reduced absorption at the femtosecond time scale

effects of upgraded cooling system and new blade materials on a real gas turbine performance

Abstract The aim of this paper is to study the effects on the performance of a real heavy-duty gas turbine of two different solutions for enhancing turbine blades thermal resistance. An upgrade of the first stator cooling system and the adoption of improved blade materials are simulated exploiting an in-house simulation tool (ESMS). The changes are studied separately in order to point out the positive effects as well as the related risks, such as the side effect of temperature increase on downstream blade rows, to be considered in service operations

Wealth effects, the Taylor rule and the liquidity trap

This paper analyzes the dynamic properties of the Taylor rule with the zero lower bound on the nominal interest rate in an optimizing monetary model with overlapping generations. The main result is that the presence of wealth effects is not sufficient to rule out the possibility of infinite equilibrium paths with decelerating inflation. In particular, the operation of wealth effects does not avoid the occurrence of liquidity traps when the central bank implements a Taylor-type interest-rate feedback rule

Attraction comes from many sources. Attentional and comparative processes in decoy effects

The attraction effect emerges when adding a seemingly irrelevant option(decoy) to a binary choice shifts preference towardsa target option. This suggests that choice behaviour is dynamic, i.e., choice values are developed during deliberation, rather thanmanifesting some pre-existing preference set. Whereas several models of multialternative and multiattribute decision makingconsider dynamic choice processes as crucial to explain the attraction effect, empirically investigating the exact nature of suchprocesses requires complementing choice output with other data. In this study, we focused on asymmetrically dominateddecoys (i.e., decoys that are clearly dominated only by the target option) to examine the attentional and comparative processesresponsible for the attraction effect. Through an eye-tracker paradigm, we showed that the decoy option can affect subjects’preferences in two different and not mutually exclusive ways: by focusing the attention on the salient option and the dominanceattribute, and by increasing comparisons with the choice dominant pattern.Although conceptually and procedurally distinct,both pathways for decoy effects produce an increase in preferencesfor the target option, in line with attentional and dynamicmodels of decision making. Eye-tracking data provide further details to theverification of such models, by highlighting thecontext-dependent nature of attention and the development of similarity-driven competitive decisional processes