Interstellar-dust properties as deduced from FIR and millimetric observations

Summary We have considered some millimetric observations of our Galaxy and of the Large Magellanic Cloud (LMC) taken at the Italian Base in Antarctica. Using other submm data and fitting all the observations with a modified Planck curve, we have obtained useful information about the temperaureT and the spectral index α of the dust grains both for the Galaxy and the LMC. For the galactic spectrum two different couples ofT and α match the detected fluxes:a)T=7K, α=2;b)T=15K, α=1.1. We have tried to identify the nature of the dust grains responsible for the submm and mm emission by comparing these results with the spectral trend of some cosmic analogues studied in laboratory. Paper presented at the 6th Cosmic Physics National Conference, Palermo, 3–7 November 1992.     

Proton quantum coherence observed in water confined in silica nanopores

Deep inelastic neutron scattering measurements of water confined in nanoporous xerogel powders, with average pore diameters of 24 and 82 A, have been carried out for pore fillings ranging from 76% to nearly full coverage. DINS measurements provide direct information on the momentum distribution n(p) of protons, probing the local structure of the molecular system. The observed scattering is interpreted within the framework of the impulse approximation and the longitudinal momentum distribution determined using a model independent approach. The results show that the proton momentum distribution is highly non-Gaussian. A bimodal distribution appears in the 24 A pore, indicating coherent motion of the proton over distances d of approximately 0.3 A. The proton mean kinetic energy W of the confined water molecule is determined from the second moment of n(p). The W values, higher than in bulk water, are ascribed to changes of the proton dynamics induced by the interaction between interfacial water and the confining surface.     

Maximum-exponent scaling behavior of optical second-harmonic generation in finite multilayer photonic crystals

Scaling laws of second-harmonic generation (SHG) in nonlinear Bragg stacks (or finite one-dimensional photonic crystals) as a function of the number N of periods are explored. While it is known that SHG scales like the sixth power of N when phase matching is achieved, we find maximal scaling like the eighth power of N under appropriate non-phase-matching conditions with the pump and harmonic waves being resonant with band-edge states. In this framework we introduce the concept of self-adaptive coherence length that scales with the system length. An analytical treatment based on coupled-mode equations clarifies the conditions for obtaining different scaling laws as a function of filling factor in the photonic gap map.     

A family of optimal weighted conjugate-gradient-type methods for strictly convex quadratic minimization

Numerical Algorithms - We introduce a family of weighted conjugate-gradient-type methods, for strictly convex quadratic functions, whose parameters are determined by a minimization model based on a...     

Global Convergence of Algorithms Under Constant Rank Conditions for Nonlinear Second-Order Cone Programming

In Andreani et al. (Weak notions of nondegeneracy in nonlinear semidefinite programming, 2020), the classical notion of nondegeneracy (or transversality) and Robinson’s constraint qualification have been revisited in the context of nonlinear semidefinite programming exploiting the structure of the problem, namely its eigendecomposition. This allows formulating the conditions equivalently in terms of (positive) linear independence of significantly smaller sets of vectors. In this paper, we extend these ideas to the context of nonlinear second-order cone programming. For instance, for an m-dimensional second-order cone, instead of stating nondegeneracy at the vertex as the linear independence of m derivative vectors, we do it in terms of several statements of linear independence of 2 derivative vectors. This allows embedding the structure of the second-order cone into the formulation of nondegeneracy and, by extension, Robinson’s constraint qualification as well. This point of view is shown to be crucial in defining significantly weaker constraint qualifications such as the constant rank constraint qualification and the constant positive linear dependence condition. Also, these conditions are shown to be sufficient for guaranteeing global convergence of several algorithms, while still implying metric subregularity and without requiring boundedness of the set of Lagrange multipliers.

     

Far-field emission profiles from L3 photonic crystal cavity modes

We experimentally characterize the spatial far-field emission profiles for the two lowest confined modes of a photonic crystal cavity of the L3 type, finding a good agreement with FDTD simulations. We then link the far-field profiles to relevant features of the cavity mode near-fields, using a simple Fabry–Perot resonator model. The effect of disorder on far-field cavity profiles is clarified through comparison between experiments and simulations. These results can be useful for emission engineering from active centers embedded in the cavity.