Invisibility and PT Symmetry: A Simple Geometrical Viewpoint

We give a simplified account of the properties of the transfer matrix for a complex one-dimensional potential, paying special attention to the particular instance of unidirectional invisibility. In appropriate variables, invisible potentials appear as performing null rotations, which lead to the helicity-gauge symmetry of massless particles. In hyperbolic geometry, this can be interpreted, via M\"{o}bius transformations, as parallel displacements, a geometric action that has no Euclidean analogy.Comment: 13 pages. No figure. Accepted for publication in Symmetr

The many facets of the Fabry-Perot

We address the response, both in amplitude and intensity, of a Fabry-Perot from a variety of viewpoints. These complementary pictures conspire to achieve a comprehensive and consistent theory of the operation of this system.Comment: 15 pages, 9 figure

Tourism's Impact on Long-Run Mexican Economic Growth

Tourism is one of the most important factors in the productivity of Mexican economy with significant multiplier effects on economic activity. This paper investigates possible causal relationships among tourism expenditure, real exchange rate and economic growth by using quarterly data. Johansen cointegration analysis shows the existence of one cointegrated vector among real GDP, tourism expenditure and real exchange rate where the corresponding elasticities are positive. The tourism-led growth hypothesis is confirmed through cointegration and causality testing. Tourism expenditure and Real Exchange Rate (RER) are weakly exogenous to real GDP. A modified version of the Granger Causality test shows that causality goes unidirectionally from tourism expenditure and RER to real GDP. Impulse response analysis shows that a shock in tourism expenditure produces a short fall and then a positive effect on growth.economic growth Johansen cointegration test Granger causality tourism-led growth hypothesis.

Size-Controlled Water-Soluble Ag Nanoparticles

Ag nanoparticles of two different sizes (1 and 4 nm) were prepared within an apoferritin cavity by using an Ag+-loaded apoferritin as a nanoconfined environment for their construction. The initial amount of Ag' ions injected in the apoferritin cavity dictates the size of the final Ag particles. The protein shell prevents bulk aggregation of the metal particles, which renders them water soluble and extremely stable

El sistema ejecutivo y las lesiones frontales en el niño

Frontal lobe syndrome in adulthood is characterised by executive function deficits leading to altered behavioural control with difficulties in social interactions and in maintaining stable jobs and interpersonal relationships. Generalisation of this concept to children with early frontal lobe damage is not straightforward. There are complex interactions between the effects of the lesion itself and the effects in other interconnected regions, timing of lesion, how long it was since the lesion occurred to the time of evaluation, and how old the child is at examination. These facts lead to consider that there might be a number of 'frontal syndromes' in childhood rather than a unique one. We report 9 cases of children with early frontal lobe lesions who were followed up for an average of 10 years. CONCLUSION: A variety of different outcomes suggests that prognosis for these patients might be better that previously reported

Effects of lactisole on pancreatic islet B-cells electrophysiology

Sucralose mimics the effects of glucose upon several variables of pancreatic islet B-cell metabolism and function, including bioelectrical activity. The present study aimed at investigating whether lactisole, which was recently found to act as an antagonist of the sweet taste receptor TIR3 in pancreatic islet B-cells, also opposes the effects of glucose and/or sucralose upon B-cell electrophysiology. A dual effect of lactisole, both inhibitory and stimulatory, was observed upon the electrical activity of mouse pancreatic islet B-cells. The present findings thus document that agents supposed to act specifically on the TIR3 sweet receptor may either mimic or oppose the effect of glucose upon islet B-cell electrical activity

Brewster quasi bound states in the continuum in all-dielectric metasurfaces from single magnetic-dipole resonance meta-atoms

Bound states in the continuum (BICs) are ubiquitous in many areas of physics, attracting especial interest for their ability to confine waves with infinite lifetimes. Metasurfaces provide a suitable platform to realize them in photonics; such BICs are remarkably robust, being however complex to tune in frequency-wavevector space.Here we propose a scheme to engineer BICs and quasi-BICs with single magnetic-dipole resonance meta-atoms. Upon changing the orientation of the magnetic-dipole resonances, we show that the resulting quasi-BICs,emerging from the symmetry-protected BIC at normal incidence, become transparent for plane-wave illumination exactly at the magnetic-dipole angle, due to a Brewster-like effect. While yielding infinite Q-factors at normalincidence(canonical BIC), these are termed Brewster quasi-BICs since a transmission channel is always allowed that slightly widens resonances at oblique incidences. This is demonstrated experimentally through reflectance measurements in the microwave regime with high-refractive-index mm-disk metasurfaces. Such Brewster-inspired configuration is a plausible scenario to achieve quasi-BICs throughout the electromagnetic spectrum inaccessible through plane-wave illumination at given angles, which could be extrapolated to other kind of waves.Comment: 15 pages, 7 figures; typos corrected, Figs. 3 & 5 modified, new Fig. 7 & references adde