Physical and mechanical characterization of phyllites and metagreywackes in central Portugal

This work defines the physical and mechanical characteristics of phyllites and metagreywackes belonging to a schist–greywacke complex in central Portugal. The index properties, point load strength, uniaxial compressive strength, slake durability and Schmidt rebound hardness were determined. In general, the metagreywackes gave a higher strength than phyllites with the same weathering degree. Possible correlations and estimation models were established and compared with the equations obtained by different researchers.     

Soft Nanopatterning on Light‐Emitting Inorganic–Organic Composites

In this work we demonstrate the nanopatterning of nanocomposites made by luminescent zinc oxide nanoparticles and light‐emitting conjugated polymers by means of soft molding lithography. Vertical nanofluidics is exploited to overcome the polymer transport difficulties intrinsic in materials incorporating nanocrystals, and the rheology, fluorescence, absolute quantum yield, and emission directionality of the nanostructured composites are investigated. We study the effect of patterned gratings on the directionality of light emitted from the nanocomposites, finding evidence of the enhancement of forward emitted light, due to the printed wavelength‐scale periodicity. These results open new possibilities for the realization of nanopatterned devices based on hybrid organic‐inorganic systems.     

Directional Estimation of Block-Fading MIMO Channels Using Spherical Harmonics Expansion and Tensor Analysis

The well-known benefits of multiple input multiple output (MIMO) wireless communication systems suppose an efficient use of spatial diversity at both the transmitter and receiver. An important and not well-explored path toward improving MIMO system performance using spatial diversity takes into account the interactions among the antennas and the (physical) propagation medium. In this work, spherical harmonics and tensor analysis are originally combined into the problem of MIMO channel modeling and estimation. The use of spherical harmonics allows to represent the antenna radiation patterns in terms of coefficients of an expansion of spatially orthogonal functions, thus decoupling the transmit and receive antenna array responses from the physical propagation medium. Assuming a single-scattering propagation scenario driven by a finite number of specular multipaths, the parallel factor model is used to decompose the spherical modes of the MIMO channel into a sum of rank-one spherical mode tensors, whose dimensions are transmit modes, receive modes, and time. Then, we extend the tensor modeling framework to double scattering channels by resorting to the PARATUCK model that captures the interactions between multiple-scattering clusters. Capitalizing on the structure of these tensor models, we derive tensor-based alternating least squares algorithms for estimating directional MIMO channels in the spherical harmonics domain, from which the directions of arrival and directions of departure are extracted by means of a MUSIC-based method. Simulation results are provided to assess the performance of the proposed algorithms in selected system configurations. Our results also show the impact of the spherical expansion order on the accuracy of DoD/DoA estimates using the proposed algorithms.     

Four state binary QAM trellis code better than known codes

Presents a new one-memory quaternary four-state trellis code, and its four-state binary equivalent code based on a QAM constellation which is 0.52 dB better than the four-state Ungerboeck code.<>     

Spectroscopic ellipsometry for monitoring and control of molecular beam epitaxially grown HgCdTe heterostructures

A systematic study of the effect of measurement perturbation on in situ monitoring of the composition of molecular beam epitaxially (MBE) grown Hg_1−xCd_xTe using spectroscopic ellipsometry was carried out. Of the five variables investigated, which included angle of incidence, wavelength of the light beam, modulator rotation, analyzer rotation, and modulator amplitude, the angle of incidence and the modulator rotation had the strongest effect on the in situ Hg_1−xCd_xTe composition monitoring process. A wobble-free sample manipulator was installed to reduce the impact of these two variables. With these improvements, the spectroscopic ellipsometer is now routinely used to monitor Hg _1−xCd_xTe compositions during MBE growth of heterostructures and is a useful tool in diagnosing growth-related problems. Examples are included for both application areas, that include the control of the interface between Hg_1−xCd_xTe layers of different compositions, i.e. device engineering.     

Impurity ‘Hot Spots’ in MBE HgCdTe/CdZnTe

In this work, impurity ‘hot spot’ macro-defects—high impurity level macro-defect contaminates were examined. ‘Hot spots’ have very high localized concentrations of: K, Mg, Ni, Cr, Mn, Ca, Al, Na, Fe, and Cu. For example, these ‘hot spot’ macro-defects can have Cu concentrations >?1?×?10¹⁸ cm^?3. Focused ion beam scanning transmission electron microscopy analysis of four ‘hot spots’ was performed. The origin of ‘hot spot’ defects is unresolved—however, our analysis has shown ‘hot spots’ can arise due to molecular beam epitaxy spit defects and CdZnTe substrate defects. The estimated ‘hot spot’ density is ～?30 cm^?2. The presence of impurity ‘hot spot’ macro-defects in HgCdTe/CdZnTe is confirming evidence for the occurrence of L. Bubulac’s impurity ‘pipe’ mechanism.     

A visible-light and infrared video database for performance evaluation of video/image fusion methods

Multidimensional Systems and Signal Processing - In general, the fusion of visible-light and infrared images produces a composite representation where both data are pictured in a single image. The...     

Étude des structures planaires en très hautes fréquences par une nouvelle formulation de la méthode des moments dans le domaine spatial

An efficient analytical integration technique for computation of spatial method of moments (MoM) integrals in conjunction with numerical matched loads is presented. The current distribution on the device is solved by using the well-known Galerkin’s MoM procedure applied to mixed potential integral equation in the spatial domain. The scattering parameters are determined by considering infinite lines at each port where only the fundamental mode is assumed to propagate. The contribution of this work is the development of an integration technique for the computation of spatial domain integrals, that is fast and rigorous. This technique is based on a Taylor series expansion of the integrands involving only polynomial functions. The use of polynomial forms in the integrals leads an immediate analytical integration, and the computation time will be considerably reduced.     

Long wavelength infrared, molecular beam epitaxy, HgCdTe-on-Si diode performance

In the past several years, we have made significant progress in the growth of CdTe buffer layers on Si wafers using molecular beam epitaxy (MBE) as well as the growth of HgCdTe onto this substrate as an alternative to the growth of HgCdTe on bulk CdZnTe wafers. These developments have focused primarily on mid-wavelength infrared (MWIR) HgCdTe and have led to successful demonstrations of high-performance 1024×1024 focal plane arrays (FPAs) using Rockwell Scientific’s double-layer planar heterostructure (DLPH) architecture. We are currently attempting to extend the HgCdTe-on-Si technology to the long wavelength infrared (LWIR) and very long wavelength infrared (VLWIR) regimes. This is made difficult because the large lattice-parameter mismatch between Si and CdTe/HgCdTe results in a high density of threading dislocations (typically, >5E6 cm⁻²), and these dislocations act as conductive pathways for tunneling currents that reduce the R_oA and increase the dark current of the diodes. To assess the current state of the LWIR art, we fabricated a set of test diodes from LWIR HgCdTe grown on Si. Silicon wafers with either CdTe or CdSeTe buffer layers were used. Test results at both 78 K and 40 K are presented and discussed in terms of threading dislocation density. Diode characteristics are compared with LWIR HgCdTe grown on bulk CdZnTe.     

An active star topology for improving fault confinement in CAN networks

The controller area network (CAN) is a field bus that is nowadays widespread in distributed embedded systems due to its electrical robustness, low price, and deterministic access delay. However, its use in safety-critical applications has been controversial due to dependability limitations, such as those arising from its bus topology. In particular, in a CAN bus, there are multiple components such that if any of them is faulty, a general failure of the communication system may happen. In this paper, we propose a design for an active star topology called CANcentrate. Our design solves the limitations indicated above by means of an active hub, which prevents error propagation from any of its ports to the others. Due to the specific characteristics of this hub, CANcentrate is fully compatible with existing CAN controllers. This paper compares bus and star topologies, analyzes related work, describes the CANcentrate basics, paying special attention to the mechanisms used for detecting faulty ports, and finally describes the implementation and test of a CANcentrate prototype.