Paulo Cardoso

2-Arylthienyl-Substituted 1,3-Benzothiazoles as New Nonlinear Optical Chromophores

A series of nonlinear optical chromophores 6 containing a substituted benzothiazole ring have been synthesized and characterized. 1,3-Benzothiazoles 6 were prepared by treating various formyl derivatives of thienyl compounds withortho-aminobenzenethiol in fair to excellent yields. These in turn were prepared by Suzuki coupling between aryl and thienyl precursors. The electronic interactions between donor and acceptor end groups in the conjugated 1,3-benzothiazoles 6 are revealed by the intense and markedly solvatochromic CT transitions. The solvatochromic behaviour of compounds 6 was determined by linear regression analyses of absorption maxima in several solvents, where benzothiazole 6f was found to be a very appropriate indicator dye whose absorption wavenumbers (Δmax = 1590 cm–1) in aliphatic and dipolar aprotic and in aromatic and chlorinated solvents correlated excellently with the π* values defined by Kamlet and Taft. Hyper-Rayleigh scattering was used to measure the first hyperpolarizabilities β of the aforementioned compounds. Thermogravimetric analysis (TGA) was used to evaluate their thermal stability. The experimental results indicate that good nonlinearity and thermal stability are well balanced for chromophores 6, making them good candidates for device applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Effect of filler dispersion on the electromechanical response of epoxy/vapor-grown carbon nanofiber composites

The piezoresistive response of epoxy/vapor-grown carbon nanofiber composites prepared by four different dispersion methods achieving different dispersion levels has been investigated. The composite response was measured as a function of carbon nanofiber loading for the different dispersion methods. Strain sensing by variation of the electrical resistance was tested through four-point bending experiments, and the dependence of the gauge factor as a function of the deformation and velocity of deformation was calculated as well as the stability of the electrical response. The composites demonstrated an appropriate response for being used as a piezoresistive sensor. Specific findings were that the intrinsic piezoresistive response was only effective around the percolation threshold and that good cluster dispersion was more appropriate for a good piezoresistive response than a uniform dispersion of individual nanofibers. The application limits of these materials for sensor applications are also addressed.

Yarn Diameter Measurements Using Coherent Optical Signal Processing

A method to measure variations in yarn diameter using coherent optical signal processing based on a single photodiode plus additional electronics is described. The approach enables us to quantify yarn irregularities associated with diameter variations which are linearly correlated with yarn mass variations. A robust method of system auto-calibration, eliminating the need for a temperature and humidity controlled environment, is also demonstrated. Two yarns that span the diameter ranges commonly used in the textile industry were used to verify the system linearity and ascertain its resolution. The results obtained have been verified using image analysis. Moreover, a diameter characterization was performed under real-world conditions for three types of yarns and a correlation with capacitive measurements is also presented. The system with sensitivity of 0.034 V/mm2 is able to detect minute variations of yarn diameter and characterize irregularities starting at very low thresholds (commercial systems generally characterize variations of 30% or greater relative to the average value).

Optical Yarn Hairiness Measurement System

This paper presents a system developed for measuring yarn hairiness using a coherent optical signal processing technique, in steps of 1 mm. The system hardware is divided into two main parts: optical, for establishing an image regarding yarn hairiness and electronic, which converts the optical signal to a proportional voltage signal. Additionally, software using LabVIEWTM was also designed to acquire the output voltage with a data acquisition board (DAQ) and to perform the corresponding data processing. This system is able to quantify the traditional commercial hairniness parameters, as sH (%), CVH (%), H and spectral analysis based on FFT. In addition several other parameters, novel in textile characterization, such as DRH (%), IDRH (%), UH (%) and spectral analysis based on FWHT and FDFI are readily available. The results obtained using this system to characterize a 4.20 g/Km cotton yarn are presented.

Development of a Yarn Evenness Measurement and Hairiness Analysis System

This paper presents an automatic yarn characterization system, based on capacitive sensors for evenness measurement and on optical sensors for hairiness analysis. This approach enables direct yarn mass determination in 1 mm range for evenness, an increase by a factor of eight over the most common commercial solutions (8 mm), and will also enable hairiness measurement up to 1 mm with high accuracy. This system determines all parameters commonly used in textile industry, for different sensitivity values defined by the operator. It also presents new parameters, not measured by commercial equipments (integral deviation rate-IDR, different signal processing techniques to detect error patterns (fast Walsh-Hadamard transform-FWHT) and other adapted parameters (deviation rate-DR, spectrograms (fast Fourier transform-FFT), coefficient of variation-CV, mean deviation-U, number and length of faults)

The influence of the dispersion method on the electrical properties of vapor-grown carbon nanofiber/epoxy composites

The influence of the dispersion of vapor-grown carbon nanofibers (VGCNF) on the electrical properties of VGCNF/Epoxy composites has been studied. A homogenous dispersion of the VGCNF does not imply better electrical properties. In fact, it is demonstrated that the most simple of the tested dispersion methods results in higher conductivity, since the presence of well-distributed nanofiber clusters appears to be a key factor for increasing composite conductivity.PACS: 72.80.Tm; 73.63.Fg; 81.05.Qk

RodosVisor - an object-oriented and customizable hypervisor: The CPU virtualization

Abstract RodosVisor is an object-oriented and bare-metal virtual machine monitor (VMM) or hypervisor designed for the aerospace industry, mainly to provide time and spatial separation to the NetworkCentric core avionics machine, Montenegro and Dittrich (2009). The NetworkCentric core avionics machine consists of several harmonized components working together to implement dependable computing in a simple way, with computing units managed by the local real-time operating system RODOS. To support partitioned software architectures such as AIR, Rufino et al. (2009), and MILS, DeLong, R. (2007), RodosVisor adapted the Popek and Goldbergs fidelity, efficiency and resource control virtualization requirements, Popek and Goldberg (1974), to the space application domain by extending them with extra ones, like timing determinism, reactivity and improved dependability. Another distinctive RodosVisor feature is the customized design based on generative programming techniques, such as aspect oriented programming and template meta-programming.

Rodosvisor — An ARINC 653 quasi-compliant hypervisor: CPU, memory and I/O virtualization

This paper presents a novel hypervisor engineered for aerospace applications using an object oriented approach embodying time and space partitioning (TSP) on a PowerPC core embedded in a FPGA, for the NetworkCentric core avionics [1] - an architecture of cooperating components and managed by a real-time operating system to implement dependable computing and targeting simplicity. To support partitioned IMA [2]software architectures our hypervisor adapted to the aerospace application domain the Popek and Goldbergs [3] fidelity, efficiency and resource control virtualization requirements by extending them with additional ones like timing determinism, reactivity and improved dependability. A distinctive feature of the hypervisor is its I/O device virtualization approach that guarantees real-time performance and small trusted computing base.

Cache full-virtualization for the PowerPC 405-S

As real-time embedded systems become overwhelmingly complex, hypervisor-based architectures are increasingly being used. Hypervisor-based architectures can support such level of complexity and, at the same time, provide real-time performance while reducing the size, cost and time-to-market of such systems. Modern processors provide cache facilities which can increase their performance substantially. Similarly, in hypervisor-based architectures, by providing virtual machines (VM) with such facilities a significant improvement in their performance can be obtained as we conclude in this work. This article presents a methodology to fully virtualize the cache facilities of the IBM PowerPC 405-S. To the best of our knowledge, this is the first time cache virtualization is openly described. A careful mapping between a VMs cache-related configuration and the processors configuration is done, accompanied by the emulation of 5 cache-related privileged instructions. Even though some issues have been detected, a simple solution is provided for all of them. The results show that cache virtualization works with minimal virtualization overhead.

Full virtualization on low-end hardware: A case study

Most hypervisors today rely either on (1) full virtualization on high-end hardware (i.e., hardware with virtualization extensions), (2) paravirtualization, or (3) both. These, however, do not fulfill embedded systems requirements, or require legacy software to be modified. Full virtualization on low-end hardware (i.e., hardware without virtualization extensions), on the other end, has none of those disadvantages. However, it is often claimed that it is not feasible due to an unacceptably high virtualization overhead. We were, nevertheless, unable to find real-world quantitative results supporting those claims.