Resonant, broadband and highly efficient optical frequency conversion in semiconductor nanowire gratings at visible and UV wavelengths

Using a hydrodynamic approach we examine bulk- and surface-induced second and third harmonic generation from semiconductor nanowire gratings having a resonant nonlinearity in the absorption region. We demonstrate resonant, broadband and highly efficient optical frequency conversion: contrary to conventional wisdom, we show that harmonic generation can take full advantage of resonant nonlinearities in a spectral range where nonlinear optical coefficients are boosted well beyond what is achievable in the transparent, long-wavelength, non-resonant regime. Using femtosecond pulses with approximately 500 MW/cm2 peak power density, we predict third harmonic conversion efficiencies of approximately 1% in a silicon nanowire array, at nearly any desired UV or visible wavelength, including the range of negative dielectric constant. We also predict surface second harmonic conversion efficiencies of order 0.01%, depending on the electronic effective mass, bistable behavior of the signals as a result of a reshaped resonance, and the onset fifth order nonlinear effects. These remarkable findings, arising from the combined effects of nonlinear resonance dispersion, field localization, and phase-locking, could significantly extend the operational spectral bandwidth of silicon photonics, and strongly suggest that neither linear absorption nor skin depth should be motivating factors to exclude either semiconductors or metals from the list of useful or practical nonlinear materials in any spectral range.Comment: 12 pages, 4 figure

Genomic analysis of three cheese-borne pseudomonas lactis with biofilm and spoilage-associated behavior

Psychrotrophic pseudomonads cause spoilage of cold fresh cheeses and their shelf-life reduction. Three cheese-borne Pseudomonas sp., ITEM 17295, ITEM 17298, and ITEM 17299 strains, previously isolated from mozzarella cheese, revealed distinctive spoilage traits based on molecular determinants requiring further investigations. Genomic indexes (ANI, isDDH), MLST-based phylogeny of four housekeeping genes (16S rRNA, gyrB, rpoB and rpoD) and genome-based phylogeny reclassified them as Pseudomonas lactis. Each strain showed distinctive phenotypic traits at 15 and 30◦C: ITEM 17298 was the highest biofilm producer at both temperatures, whilst ITEM 17295 and ITEM 17299 showed the strongest proteolytic activity at 30◦C. A wider pattern of pigments was found for ITEM 17298, while ITEM 17295 colonies were not pigmented. Although the high genomic similarity, some relevant molecular differences supported this phenotypic diversity: ITEM 17295, producing low biofilm amount, missed the pel operon involved in EPS synthesis and the biofilm-related Toxin-Antitoxin systems (mqsR/mqsA, chpB/chpS); pvdS, required for the pyoverdine synthesis, was a truncated gene in ITEM 17295, harboring, instead, a second aprA involved in milk proteolysis. This work provided new insight into the food spoiler microbiota by identifying these mozzarella cheese spoilers as P. lactis; molecular targets to be exploited in the development of novel preservative strategies were also revealed

Bare carbon electrodes as simple and efficient sensors for the quantification of caffeine in commercial beverages

This work has been supported by the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement no. 642014 (IPCOS). Ĺ.Š. would like to acknowledge the Grant Agency of the Slovak Republic (grant no. 1/0489/16)

Commentary: Principles, Approaches and Challenges of Applying Big Data in Safety Psychology Research

This commentary builds upon the recent theoretical paper by Kang et al. (2019) to advance the debate currently going on about psychology and big data. The aim is to discuss the feasibility of extending the conceptualization proposed by the authors\u2014i.e., Big Data of Safety Psychology (BDSP)\u2014to other branches of psychology going beyond the only safety domain, ultimately pointing out a big data of whatever psychology scenario. This will lead to suggest a perspective enrichment from a solely big data applied to psychology paradigm toward a much less advocated psychology applied to big data

Gender differences in cyclists\u2019 crashes: an analysis of routinely recorded crash data

Previous research on gender differences in road crashes has focussed uniquely on car drivers and there has been little research examining such differences among cyclists. In this study, we investigated gender differences in bicycle crashes, using routinely recorded crash data. The present paper focussed on characteristics related to the type of crashes (type of collision and opponent vehicle), the infrastructure (road type and type of road segment), the environmental (season, road surface condition and weather) and time period (time of the day and day of the week). Results revealed that, compared to women cyclists, men cyclists were more likely to be involved in a crash regardless the cyclists\u2019 age. Moreover, we found gender differences in terms of type of road segment, type of opponent vehicle, type of manoeuvre of the opponent vehicle and of the cyclists, type of collision, time of the day, day of the week and season

Atom interferometry gravity-gradiometer for the determination of the Newtonian gravitational constant G

We developed a gravity-gradiometer based on atom interferometry for the determination of the Newtonian gravitational constant \textit{G}. The apparatus, combining a Rb fountain, Raman interferometry and a juggling scheme for fast launch of two atomic clouds, was specifically designed to reduce possible systematic effects. We present instrument performances and show that the sensor is able to detect the gravitational field induced by source masses. A discussion of projected accuracy for \textit{G} measurement using this new scheme shows that the results of the experiment will be significant to discriminate between previous inconsistent values.Comment: 9 pages,9 figures, Submitte

Núcleo de apoio a projetos: monitoramento de projetos e captação de recursos.

bitstream/item/25640/1/194-10.pd

Modelling and nanofabrication of chiral dielectric metasurfaces

Polarization control through all-dielectric metasurfaces holds great potential in different fields, such as telecommunications, biochemistry and holography. Asymmetric chiral metasurfaces supporting quasi-bound states in the continuum may prove very useful for controlling and manipulating the polarization state of light. A crucial quantity for characterizing the optical chirality is the circular dichroism (CD). In this work we analyse how the CD and quality factor of the optical mode can be strongly influenced by a nanofabrication error. Modelling the nanofabrication uncertainties on the gaps of the chiral metasurface, the imperfections of the etchings process or the modification of the asymmetry factor, we found that the proper engineering of the gap between the nanostructures of the unit cell is the most important parameter to achieve a high-quality factor and enhanced optical dichroism. An optimization of the nanofabrication processes, such as dose factor, dwell time and plasma etching demonstrates that, for a writing field of 100 & mu;m2, it is possible to obtain morphologically precise chiral metasurfaces, with fabrication uncertainties lower than those that would limit Q factor and chirality property

On the stochastic mechanics of the free relativistic particle

Given a positive energy solution of the Klein-Gordon equation, the motion of the free, spinless, relativistic particle is described in a fixed Lorentz frame by a Markov diffusion process with non-constant diffusion coefficient. Proper time is an increasing stochastic process and we derive a probabilistic generalization of the equation $(d\tau)^2=-\frac{1}{c^2}dX_{\nu}dX_{\nu}$. A random time-change transformation provides the bridge between the $t$ and the $\tau$ domain. In the $\tau$ domain, we obtain an \M^4-valued Markov process with singular and constant diffusion coefficient. The square modulus of the Klein-Gordon solution is an invariant, non integrable density for this Markov process. It satisfies a relativistically covariant continuity equation