Results from DAMA/LIBRA at Gran Sasso

The DAMA project is an observatory for rare processes and it is operative deep underground at the Gran Sasso National Laboratory of the I.N.F.N. In particular, the DAMA/LIBRA (Large sodium Iodide Bulk for RAre processes) set-up consists of highly radiopure NaI(Tl) detectors for a total sensitive exposed mass of ?250 kg. Recent results, obtained by this set-up by exploiting the model independent annual modulation signature of Dark Matter (DM) particles, have confirmed and improved those obtained by the former DAMA/NaI experiment. A model independent evidence for the presence of Dark Matter particles in the galactic halo is cumulatively obtained at 8.2?σ C.L. No systematics or side reactions able to account for the measured modulation amplitude and to contemporaneously satisfy all the many specific requirements of the signature have been found or suggested by anyone over more than a decade. An example of one of the many possible model dependent corollary quests for the candidate particles and for the related astrophysical, nuclear and particle physics scenarios is presented considering the whole cumulative exposure. Future perspectives are shortly addressed.     

Improving monochromaticity of upconversion luminescence by codoping Eu ions in Y2O3:Ho, Yb nanocrystals

Upconversion (UC) luminescence of Y₂O₃:Ho³⁺, Yb³⁺ nanocrystals codoped with different concentrations of Eu³⁺ ions were investigated to improve the monochromaticity of the UC emission. The results show that the monochromaticity, quantified by a parameter SR, increases as the concentration of Eu³⁺ ions becomes higher, which is due to the energy transfer between ⁵I₇ (Ho³⁺) and ⁷F₆ (Eu³⁺). The energy transfer accelerates the relaxation of Ho³⁺ ions from the ⁵I₇ to ⁵I₈ state and then quenches the red emission. The influence of the Eu³⁺ concentration on the pump power dependence of the red UC fluorescence in Y₂O₃:Ho³⁺, Yb³⁺, Eu³⁺ nanocrystals is verified using the steady-state rate equation theory.     

Microwave-assisted synthesis of Fe3O4 nanorods and nanowires in an ionic liquid

Without using inert gas to prevent the oxidation of Fe²⁺, Fe₃O₄ nanorods and nanowires have been successfully synthesized via a microwave-assisted ionic liquid method (MAIL). Compared to the traditional methods, the whole reaction process can be carried out more easily and faster. Our result shows that temperature and time of microwave heat played important roles in the formation of Fe₃O₄ with different morphologies. These products were characterized by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), thermogravimetric analysis (TG) and FT-IR spectra.     

Simulation of current spreading for GaN-based light-emitting diodes

Uniform current spreading is crucial for the performance of light-emitting diodes (LEDs). It has been reported that the reliability and light distribution are affected by non-uniform current spreading. In this paper, the impact of different electrode patterns on the performance of LED chips is investigated. A hybrid modeling method is employed to analyze the electrical and thermal characteristics of LEDs with two different electrode mesa structures. Corresponding experiments are also carried out to validate the calculation results. It is found that increasing amount of p-electrodes in interdigitated electrode patterns is effective in improving the performance of LEDs.     

Electrorheology: Statics and dynamics

The interaction between nanoparticles and an electric field is explored from the electrorheological (ER) point of view, using variational formulations for both the static and dynamic characteristics. In the first part the static characteristics of the ER fluid, consisting of a dispersion of solid particles in a liquid, is detailed by using the spectral representation approach for the effective dielectric constant. Predictions concerning the ground state structure, yield stress, upper bounds on the ER effect are presented together with comparisons to experimental results. The giant ER effect, involving a different paradigm of permanent electric dipoles, is described phenomenologically. In the second part the ER fluid dynamics is formulated via the variational principle of Onsager. Predictions of the model are compared with experiments. It is shown that the phenomenon of the diminishing ER effect at high shear rates may be mitigated by the planar interdigital electrode configuration.     

Multiple Čerenkov second-harmonic waves in a two-dimensional nonlinear photonic structure

We report simultaneous generation of multiple conical second-harmonic waves in a two-dimensional nonlinear photonic structure when illuminated by two overlapping noncollinear fundamental beams. We show that this phenomenon is caused by the nonlinear ?erenkov radiation emitted due to the interaction of photons from each constituent fundamental beam as well as the virtual one propagating along the bisector of the two beams. In addition, by studying the asymmetric geometry of the interaction, we uniquely verify the effects of reciprocal vectors on the ?erenkov-type second-harmonic generation in nonlinear photonic structures.     

An effective adaptive trust region algorithm for nonsmooth minimization

In this paper, an adaptive trust region algorithm that uses Moreau–Yosida regularization is proposed for solving nonsmooth unconstrained optimization problems. The proposed algorithm combines a modified secant equation with the BFGS update formula and an adaptive trust region radius, and the new trust region radius utilizes not only the function information but also the gradient information. The global convergence and the local superlinear convergence of the proposed algorithm are proven under suitable conditions. Finally, the preliminary results from comparing the proposed algorithm with some existing algorithms using numerical experiments reveal that the proposed algorithm is quite promising for solving nonsmooth unconstrained optimization problems.     

序半群Quantale完备化的进一步结果

本文给出了序半群上幂集Quantale的最大拓扑闭包的具体形式,即序半群的最小Quantale完备化.在此基础上,证明了Quantale范畴Quant是序半群范畴OSGrp*的满的反射子范畴.最后,给出了序半群Quantale完备化的一个应用.     

Optimal Harvesting for a Stochastic Predator-prey Model with S-type Distributed Time Delays

In this paper, the optimization problem of harvesting for a stochastic predator-prey model with S-type distributed time delays (which contain both discrete time delays and continuously distributed time delays) is studied by using ergodic method. Sufficient and necessary conditions for the existence of optimal harvesting strategy are obtained. Moreover, the optimal harvesting effort (OHE, for short) and the maximum of expectation of sustainable yield (MESY, for short) are given. Some numerical simulations are introduced to illustrate our main results.