Isotropic properties of the photonic band gap in quasicrystals with low-index contrast

We report on the formation and development of the photonic band gap in two-dimensional 8-, 10- and 12-fold symmetry quasicrystalline lattices of low index contrast. Finite size structures made of dielectric cylindrical rods were studied and measured in the microwave region, and their properties compared with a conventional hexagonal crystal. Band gap characteristics were investigated by changing the direction of propagation of the incident beam inside the crystal. Various angles of incidence from 0 \degree to 30\degree were used in order to investigate the isotropic nature of the band gap. The arbitrarily high rotational symmetry of aperiodically ordered structures could be practically exploited to manufacture isotropic band gap materials, which are perfectly suitable for hosting waveguides or cavities.Comment: 16 pages, 7 figures, submitted to PR

Photonic band gaps analysis of Thue-Morse multilayers made of porous silicon

Dielectric aperiodic Thue-Morse structures up to 128 layers have been fabricated by using porous silicon technology. The photonic band gap properties of Thue-Morse multilayers have been theoretically investigated by means of the transfer matrix method and the integrated density of states. The theoretical approach has been compared and discussed with the reflectivity measurements at variable angles for both the transverse electric and transverse magnetic polarizations of light. The photonic band gap regions, wide 70 nm and 90 nm, included between 0 and 30°, have been observed for the sixth and seventh orders, respectively

Probing the formation history of the nuclear star cluster at the Galactic Centre with millisecond pulsars

The origin of the Nuclear Star Cluster in the centre of our Galaxy is still unknown. One possibility is that it formed after the disruption of stellar clusters that spiralled into the Galactic Centre due to dynamical friction. We trace the formation of the Nuclear Star Cluster around the central black hole, using state-of-the-art N-body simulations, and follow the dynamics of the neutron stars born in the clusters. We then estimate the number of Millisecond Pulsars (MSPs) that are released in the Nuclear Star Cluster, during its formation. The assembly and tidal dismemberment of globular clusters lead to a population of MSPs distributed over a radius of about 20 pc, with a peak near 3 pc. No clustering is found on the sub-parsec scale. We simulate the detectability of this population with future radio telescopes like the MeerKAT radio telescope and SKA1, and find that about of order ten MSPs can be observed over this large volume, with a paucity of MSPs within the central parsec. This helps discriminating this scenario from the in-situ formation model for the Nuclear Star Cluster that would predict an over abundance of MSPs closer to the black hole. We then discuss the potential contribution of our MSP population to the gamma-ray excess at the Galactic Centre.Comment: 11 pages, 8 figures, accepted for publication in MNRA

Rediscovering the scientific and didactic value of minor herbarium collections: the seeds and fruits collection by Gustavo Bonaventura

Seeds and fruits collections are very important from a systematic point of view and represent useful references in several disciplines and research fields. The Herbarium of Sapienza University of Rome (RO) hosts a Spermoteque/Carpoteque, which was organized by Gustavo Bonaventura (1902-1976). The purpose of this paper is to describe the heritage of Bonaventura's collection. It consists of 42 wooden boxes, globally hosting 3411 glass tubes containing seeds, fruits, and other materials. The collection was first of all catalogued; then, analysis were conducted regarding taxonomic composition, temporal and geographic coverage, institutions of provenience, collectors, content, and preservation status. The specimens refer to 2740 taxa, belonging to 890 genera and 135 families. Many genera of agricultural interest are present, each one with different cultivars. The collection spans across 130 years (1843-1975) and hosts specimens coming from all over the world. Materials were provided by several herbaria, botanical gardens and agrarian institutes, and by 50 collectors. The Bonaventura's collection is still a useful reference collection, testifying biodiversity over times and thus being useful for diachronic studies; moreover, it documents the interests of collectors and the past network activity between institutions

Interleukin-18 mediates cardiac dysfunction induced by western diet independent of obesity and hyperglycemia in the mouse

Obesity and diabetes are independent risk factors for heart failure and are associated with the consumption of diet rich in saturated fat and sugar, Western diet (WD), known to induce cardiac dysfunction in the mouse through incompletely characterized inflammatory mechanisms. We hypothesized that the detrimental cardiac effects of WD are mediated by interleukin-18 (IL-18), pro-inflammatory cytokine linked to cardiac dysfunction. C57BL/6J wild-type male mice and IL-18 knockout male mice were fed high-saturated fat and high-sugar diet for 8 weeks. We measured food intake, body weight and fasting glycemia. We assessed left ventricular (LV) systolic and diastolic function by Doppler echocardiography and cardiac catheterization. In wild-type mice, WD induced a significant increase in isovolumetric relaxation time, myocardial performance index and left ventricular end-diastolic pressure, reflecting an impairment in diastolic function, paired with a mild reduction in LV ejection fraction. IL-18 KO mice had higher food intake and greater increase in body weight without significant differences in hyperglycemia. Despite displaying greater obesity, IL-18 knockout mice fed with WD for 8 weeks had preserved cardiac diastolic function and higher left ventricular ejection fraction. IL-18 mediates diet-induced cardiac dysfunction, independent of food intake and obesity, thus highlighting a disconnect between the metabolic and cardiac effects of IL-18

Priming Effects on Commitment to Help and on Real Helping Behavior

Years of research on bystander apathy have demonstrated that the physical presence of others can reduce the tendency to help individuals needing assistance. Recent research on the implicit bystander effect has suggested that simply imagining the presence of others can lead to less helping behavior on a subsequent unrelated task. The present study was designed to contribute to previous findings on the implicit bystander effect by demonstrating these effects on commitment to help and on real helping behavior, rather than simply on intentions to help. Studies 1a and 1b demonstrate that merely priming participants with the construct of being in a group at Time 1 created significantly less commitment to future helping on a subsequent task at Time 2. Study 2 aimed to extend this effect to behavioral measures and verified that participants exposed to a group prime helped less than those who were exposed to a single-person prime. The implications of these findings for the literature on the bystander effect are discussed

Radiation and magnetic field effects on new semiconductor power devices for HL-LHC experiments

The radiation hardness of commercial Silicon Carbide and Gallium Nitride power MOSFETs is presented in this paper, for Total Ionizing Dose effects and Single Event Effects, under gamma, neutrons, protons and heavy ions. Similar tests are discussed for commercial DC-DC converters, also tested in operation under magnetic field

Evolution of the electronic structure across the filling-control and bandwidth-control metal-insulator transitions in pyrochlore-type Ru oxides

We have performed photoemission and soft x-ray absorption studies of pyrochlore-type Ru oxides, namely, the filling-control system Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$ and the bandwidth-control system Sm$_{2-x}$Bi$_x$Ru$_2$O$_7$, which show insulator-to-metal transition with increasing Ca and Bi concentration, respectively. Core levels and the O 2$p$ valence band in Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$ show almost the same amount of monotonous upward energy shifts with Ca concentration, which indicates that the chemical potential is shifted downward due to hole doping. The Ru 4$d$ band in Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$ is also shifted toward the Fermi level ($E_F$) with hole doping and the density of states (DOS) at $E_F$ increases. The core levels in Sm$_{2-x}$Bi$_x$Ru$_2$O$_7$, on the other hand, do not show clear energy shifts except for the Ru 3$d$ core level, whose line shape change also reflects the increase of metallic screening with Bi concentration. We observe pronounced spectral weight transfer from the incoherent to the coherent parts of the Ru 4d $t_{2g}$ band with Bi concentration, which is expected for a bandwidth-control Mott-Hubbard system. The increase of the DOS at $E_F$ is more abrupt in the bandwidth-control Sm$_{2-x}$Bi$_x$Ru$_2$O$_7$ than in the filling-control Sm$_{2-x}$Ca$_x$Ru$_2$O$_7$, in accordance with a recent theoretical prediction. Effects of charge transfer between the Bi 6$sp$ band and the Ru 4$d$ band are also discussed.Comment: 11 pages, 6 figure

An Empirical Approach to the Bond Additivity Model in Quantitative Interpretation of Sum Frequency Generation Vibrational Spectra

A complete empirical approach from known Raman and IR spectra is used to make corrections to the bond additivity model for quantitative interpretation of Sum Frequency generation Vibrational Spectra (SFG-VS) from molecular interfaces. This empirical correction successfully addresses the failures of the simple bond additivity model. This empirical approach not only provides new understandings of the effectiveness and limitations of the bond additivity model, but also provides a practical roadmap for its application in SFG-VS studies of molecular interfaces