An analysis of soft terms in Calabi-Yau compactifications

We perform an analysis of the soft supersymmetry-breaking terms arising in Calabi-Yau compactifications. The sigma-model contribution and the instanton correction to the Kähler potential are included in the computation. The existence of off-diagonal moduli and matter metrics gives rise to specific features as the possibility of having scalars heavier than gauginos or the presence of tachyons. Although non-universal soft terms is a natural situation, we point out that there is an interesting limit where universality is achieved. Finally, we compare these results with those of orbifold compactifications. Although they are qualitatively similar some features indeed change. For example, sum rules found in orbifold models which imply that on average the scalars are lighter than gauginos can be violated in Calabi-Yau manifolds.     

Distributed measurement of chromatic dispersion by four-wave mixing and Brillouin optical-time-domain analysis

A new nondestructive method for measuring the spatial distribution of chromatic dispersion along an optical fiber is presented. It is based on using Brillouin optical time-domain analysis to probe the power distribution of the four-wave mixing generated by two continuous-wave lasers. The results obtained prove that this new method is capable of providing better performance than comparable techniques. Furthermore, sensing the variations of Brillouin gain maximum produces additional information about the fiber, such as presence of strain and concentration of GeO2.     

Polarity effects on ZnO films grown along the nonpolar [1120] direction

The surface electrical properties of ZnO thin films grown along the nonpolar [1120] direction have been investigated by Kelvin probe microscopy on a nanometer scale. Two different charge domains, with a 75 meV work function difference, coexist within the ZnO surface, which is covered by rhombohedral pyramids whose sidewalls are shown to be {1011}-type planes. The presence and relative orientation of the two kinds of charge domains are explained in terms of the atomic arrangement at the {1011} polar surfaces.     

Tuning of optical resonances in asymmetric microtube cavities

We tune optical resonances in rolled-up SiO/SiO(2) microtube cavities by gradually modifying the tube structure through asymmetrical postdeposition of SiO(2). Spectral blueshifts followed by redshifts of the resonant modes are observed in a thin-walled microtube (tube-I), which is attributed to a competition between shape deformation and effective increase of tube wall thickness. In contrast, only a monotonic redshift is detected when asymmetrical deposition is performed on a thick-walled microtube (tube-II). Distinct wavelength-dependent tuning was revealed in both kinds of tubes. Numerical calculations based on perturbation theory are carried out to explain and confirm the experimental results.     

Photonic temporal integration of broadband intensity waveforms over long operation time windows

We propose and experimentally demonstrate a novel design for temporal integration of microwave and optical intensity waveforms with combined high processing speed and a long operation time window. It is based on concatenating in series a discrete-time (low-speed) photonic integrator and a high-speed analog time-limited intensity integrator. This scheme is demonstrated here using a cascaded fiber-based interferometers' system (as a passive eight-point discrete-time integrator) and an analog time-limited intensity integrator. The latter is based on temporal intensity modulation of the input waveform with a rectangular-like incoherent energy spectrum followed by linear dispersion. Using this setup, we experimentally achieve accurate time integration of intensity signals with ~36 GHz bandwidths over an operation time window of ~4 ns, corresponding to a processing time-bandwidth product of >144.     

Synthesis and characterization of silicon-doped gallium oxide nanowires for optoelectronic UV applications

Silicon-doped gallium oxide nanowires have been synthesized by thermal methods using either a mixture of gallium oxide and silicon powders or metallic gallium with silicon powder as precursor materials. The growth mechanism has been found to be a vapour–liquid–solid (VLS) or vapour–solid (VS) process, respectively, depending on the precursor used. In the former case, silicon oxide droplets at the end of the nanowires have been observed. Their possible role during the growth of the nanostructures is discussed. Structural and morphological characterization of the doped nanowires has been performed by transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The results show a high crystalline quality and a uniform distribution of silicon along the nanowires. Room temperature cathodoluminescence (CL) in the SEM shows that slight variations in the composed UV–blue emission band appear due to the influence of Si impurities in the oxygen vacancy defect structure.     

Design of two-dimensional random surfaces with specified scattering properties

A method is proposed for designing a two-dimensional randomly rough Dirichlet surface that, when illuminated at normal incidence, scatters a scalar plane wave with a specified angular distribution of its intensity. The method is validated by computer simulation calculations.     

Analysis of the Abraham-Minkowski Controversy by Means of Two Simple Examples

Using a very simple example, H. M. Lai [1] argued in favor of Abraham's proposal for defining electromagnetic field momentum density. Later, using another simple device, Johnson et al. [2] argued in favor of Minkowski's proposal. This indicates that the Abraham-Minkowski controversy remains open. Both models consider nonmagnetic media ( = 1). In this work we analyze both models pointing out some weak points and extend the analysis to magnetic media ( 1). We show that in this case Minkowski's proposal is better than Abraham's. Our analysis throws some light on this very old controversy.