Hybrid photonic-bandgap accelerating cavities

In a recent investigation, we studied two-dimensional point-defected photonic bandgap cavities composed of dielectric rods arranged according to various representative periodic and aperiodic lattices, with special emphasis on possible applications to particle acceleration (along the longitudinal axis). In this paper, we present a new study aimed at highlighting the possible advantages of using hybrid structures based on the above dielectric configurations, but featuring metallic rods in the outermost regions, for the design of extremely-high quality factor, bandgap-based, accelerating resonators. In this framework, we consider diverse configurations, with different (periodic and aperiodic) lattice geometries, sizes, and dielectric/metal fractions. Moreover, we also explore possible improvements attainable via the use of superconducting plates to confine the electromagnetic field in the longitudinal direction. Results from our comparative studies, based on numerical full-wave simulations backed by experimental validations (at room and cryogenic temperatures) in the microwave region, identify the candidate parametric configurations capable of yielding the highest quality factor.Comment: 13 pages, 5 figures, 3 tables. One figure and one reference added; minor changes in the tex

Deep near-infrared imaging of W3 Main: constraints on stellar cluster formation

Embedded clusters like W3 Main are complex and dynamically evolving systems that represent an important phase of the star formation process. We aim at the characterization of the entire stellar content of W3 Main in a statistical sense to identify possible differences in evolutionary phase of the stellar populations and find clues about the formation mechanism of this massive embedded cluster. Methods. Deep JHKs imaging is used to derive the disk fraction, Ks-band luminosity functions and mass functions for several subregions in W3 Main. A two dimensional completeness analysis using artificial star experiments is applied as a crucial ingredient to assess realistic completeness limits for our photometry. We find an overall disk fraction of 7.7 $\pm$ 2.3%, radially varying from 9.4 $\pm$ 3.0 % in the central 1 pc to 5.6 $\pm$ 2.2 % in the outer parts of W3 Main. The mass functions derived for three subregions are consistent with a Kroupa and Chabrier mass function. The mass function of IRSN3 is complete down to 0.14 Msun and shows a break at M $\sim$ 0.5 Msun. We interpret the higher disk fraction in the center as evidence for a younger age of the cluster center. We find that the evolutionary sequence observed in the low-mass stellar population is consistent with the observed age spread among the massive stars. An analysis of the mass function variations does not show evidence for mass segregation. W3 Main is currently still actively forming stars, showing that the ionizing feedback of OB stars is confined to small areas ($\sim$ 0.5 pc). The FUV feedback might be influencing large regions of the cluster as suggested by the low overall disk fraction.Comment: 15 pages, 13 figures, accepted by A&

Self-Reported Route Familiarity and Road Safety Negative Outcomes: First Results from a Transnational Survey-Based Study

Previous research has shown the influence of drivers' route familiarity on road safety. The drivers' familiarity was possibly related to some negative safety outcomes such as speeding, violations, inattention. On the other hand, drivers unfamiliar with the route (especially if foreigners) were related to over-involvement in specific types or at-fault crashes. Drivers' route familiarity is mainly identifiable from frequency-based self-reported scales and distance from residence scales. In this study, another perspective was used, by relying on surveys. The familiarity with given routes and the behavioral differences with respect to generic routes was self-reported by drivers, who have answered to a specifically designed survey. Other questions were related to other safety issues and negative outcomes, such as accidents and sanctions/violations. The survey was submitted to both Italian and Norwegian young drivers, to explore also possible cultural/geographic differences of the phenomenon. The first results from the study are presented here, by focusing on the relevant aspects emerged from both the Italian and Norwegian surveys. In particular, the representation of the habitual routes is different between Italy and Norway. Some stated behavioral differences emerge from the comparison between answers related to the generic routes travelled and those specifically related to the habitual routes. Most accidents occur on routes frequently traveled, while there is a relevant part of fines which occur on roads rarely/never travelled. Those tendencies should be confirmed and other possible relationships should be explored after having enlarged the sample of respondents

Analysis of the performance of driver MOX fuel in the MYRRHA reactor under Beam Power Jump transient irradiation conditions

This work focuses on the performance analysis of driver fuel pins under transient irradiation conditions in the MYRRHA reactor, which must be considered besides the normal operation towards the design optimization and licensing of the facility. The considered transient scenario is a Beam Power Jump (BPJ) caused by a trip of the MYRRHA accelerator coupled to the sub-critical reactor core. Based on the outcomes of the analysis of the nominal MYRRHA irradiation - NED 386 (2022) 111581, the impact of this over-power scenario on the pin response is investigated both at the beginning and at the end of irradiation as the most critical moments for the fuel maximum temperature and for the potential fuel-cladding mechanical interaction, respectively. The simu- lation results are achieved with the TRANSURANUS fuel performance code equipped with advanced models for thermal–mechanical properties of U-Pu mixed-oxide (MOX) fuels, for inert gas behaviour and for the specific mechanical response of DIN 1.4970 cladding. The comparison with design limit criteria adopted highlights the safety of the MYRRHA fuel pins under irradiation, complying with satisfactory margins even considering the occurrence of BPJ transients

Black hole evaporation in a spherically symmetric non-commutative space-time

Recent work in the literature has studied the quantum-mechanical decay of a Schwarzschild-like black hole, formed by gravitational collapse, into almost-flat space-time and weak radiation at a very late time. The relevant quantum amplitudes have been evaluated for bosonic and fermionic fields, showing that no information is lost in collapse to a black hole. On the other hand, recent developments in noncommutative geometry have shown that, in general relativity, the effects of non-commutativity can be taken into account by keeping the standard form of the Einstein tensor on the left-hand side of the field equations and introducing a modified energy-momentum tensor as a source on the right-hand side. Relying on the recently obtained non-commutativity effect on a static, spherically symmetric metric, we have considered from a new perspective the quantum amplitudes in black hole evaporation. The general relativity analysis of spin-2 amplitudes has been shown to be modified by a multiplicative factor F depending on a constant non-commutativity parameter and on the upper limit R of the radial coordinate. Limiting forms of F have been derived which are compatible with the adiabatic approximation.Comment: 8 pages, Latex file with IOP macros, prepared for the QFEXT07 Conference, Leipzig, September 200

Finite Temperature Effective Potential for Gauge Models in de Sitter Space

The one-loop effective potential for gauge models in static de Sitter space at finite temperatures is computed by means of the $\zeta$--function method. We found a simple relation which links the effective potentials of gauge and scalar fields at all temperatures. In the de Sitter invariant and zero-temperature states the potential for the scalar electrodynamics is explicitly obtained, and its properties in these two vacua are compared. In this theory the two states are shown to behave similarly in the regimes of very large and very small radii a of the background space. For the gauge symmetry broken in the flat limit ($a \to \infty$) there is a critical value of a for which the symmetry is restored in both quantum states. Moreover, the phase transitions which occur at large or at small a are of the first or of the second order, respectively, regardless the vacuum considered. The analytical and numerical analysis of the critical parameters of the above theory is performed. We also established a class of models for which the kind of phase transition occurring depends on the choice of the vacuum.Comment: 23 pages, LaTeX, 5 figure.ep

Delegatable homomorphic encryption with applications to secure outsourcing of computation

In this work we propose a new cryptographic primitive called Delegatable Homomorphic Encryption (DHE). This allows a Trusted Authority to control/delegate the capability to evaluate circuits over encrypted data to untrusted workers/evaluators by issuing tokens. This primitive can be both seen as a public-key counterpart to Verifiable Computation, where input generation and output verification are performed by different entities, or as a generalisation of Fully Homomorphic Encryption enabling control over computations on encrypted data. Our primitive comes with a series of extra features as follows: 1) there is a one-time setup procedure for all circuits; 2) senders do not need to be aware of the functions which will be evaluated on the encrypted data, nor do they need to register keys; 3) tokens are independent of senders and receiver; and 4) receivers are able to verify the correctness of computation given short auxiliary information on the input data and the function, independently of the complexity of the computed circuit. We give a modular construction of such a DHE scheme from three components: Fully Homomorphic Encryption (FHE), Functional Encryption (FE), and a (customised) MAC. As a stepping stone, we first define Verifiable Functional Encryption (VFE), and then show how one can build a secure DHE scheme from a VFE and an FHE scheme. We also show how to build the required VFE from a standard FE together with a MAC scheme. All our results hold in the standard model.Finally, we show how one can build a verifiable computation (VC) scheme generically from a DHE. As a corollary, we get the first VC scheme which remains verifiable even if the attacker can observe verification result

Heat-kernel Coefficients and Spectra of the Vector Laplacians on Spherical Domains with Conical Singularities

The spherical domains $S^d_\beta$ with conical singularities are a convenient arena for studying the properties of tensor Laplacians on arbitrary manifolds with such a kind of singular points. In this paper the vector Laplacian on $S^d_\beta$ is considered and its spectrum is calculated exactly for any dimension $d$. This enables one to find the Schwinger-DeWitt coefficients of this operator by using the residues of the $\zeta$-function. In particular, the second coefficient, defining the conformal anomaly, is explicitly calculated on $S^d_\beta$ and its generalization to arbitrary manifolds is found. As an application of this result, the standard renormalization of the one-loop effective action of gauge fields is demonstrated to be sufficient to remove the ultraviolet divergences up to the first order in the conical deficit angle.Comment: plain LaTeX, 23 pp., revised version, a misprint in expressions (1.8) and (4.38) of the second heat coefficient for the vector Laplacian is corrected. No other change

The WFC3 Galactic Bulge Treasury Program: Relative Ages of Bulge Stars of High and Low Metallicity

Indexación: Scopus.The Hubble Space Telescope/WFC3 multiband photometry spanning from the UV to the near-IR of four fields in the Galactic bulge, together with that for six template globular and open clusters, are used to photometrically tag the metallicity [Fe/H] of stars in these fields after proper-motion rejecting most foreground disk contaminants. Color-magnitude diagrams and luminosity functions (LF) are then constructed, in particular for the most metal-rich and most metal-poor stars in each field. We do not find any significant difference between the I-band and H-band LFs, hence turnoff luminosity and age of the metal-rich and metal-poor components therefore appear essentially coeval. In particular, we find that no more than ∼3% of the metal-rich component can be ∼5 Gyr old, or younger. Conversely, theoretical LFs match well to the observed ones for an age of ∼10 Gyr. Assuming this age is representative for the bulk of bulge stars, we then recall the observed properties of star-forming galaxies at 10 Gyr lookback time, i.e., at z ∼ 2, and speculate about bulge formation in that context. We argue that bar formation and buckling instabilities leading to the observed boxy/peanut, X-shaped bulge may have arisen late in the history of the Milky Way Galaxy, once its gas fraction had decreased compared to the high values typical of high-redshift galaxies. This paper follows the public release of the photometric and astrometric catalogs of the measured stars in the four fields. © 2018. The American Astronomical Society

High performance n(+)/p and p(+)/n germanium diodes at low-temperature activation annealing

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