Uma formulação de volumes finitos para a solulção de problemas convectivos-difusivos, para quaisquer números de Peclet

Apresenta-se uma metodologia de volumes finitos para solucáo de problemas convectivos difusivos, que pode ser aplicada a escoamentos envolvendo quaisquer valores de números locais de Peclet. O método tem por base a integracáo do termo de adveccáo ao longo da linha de corrente e uma integras50 especial dos termos difusivos, pela utilizaciio de médias de fluxos nas fronteiras dos volumes de controle. O método proposto mostrou-se bastante eficaz e acurado para resolver problemas complexos que normalmente levam a dispersoes e difusóes numéricas.A finite volume method for the solution of convective-diffusive problems is presented, which can be applied to flows with any Peclet numbers. The method is based on the integration of the advective term along a stream line and a special integration of the diffusive terms, using average flow at the boundary at the control volumes. The proposed method has shown to be efficient and acurate in complex applications normally leading to numeric dispersion and diffusion.Peer Reviewe

Uma formulação de volumes finitos para a solulção de problemas convectivos-difusivos, para quaisquer números de Peclet

Apresenta-se uma metodologia de volumes finitos para solucáo de problemas convectivos difusivos, que pode ser aplicada a escoamentos envolvendo quaisquer valores de números locais de Peclet. O método tem por base a integracáo do termo de adveccáo ao longo da linha de corrente e uma integras50 especial dos termos difusivos, pela utilizaciio de médias de fluxos nas fronteiras dos volumes de controle. O método proposto mostrou-se bastante eficaz e acurado para resolver problemas complexos que normalmente levam a dispersoes e difusóes numéricas.A finite volume method for the solution of convective-diffusive problems is presented, which can be applied to flows with any Peclet numbers. The method is based on the integration of the advective term along a stream line and a special integration of the diffusive terms, using average flow at the boundary at the control volumes. The proposed method has shown to be efficient and acurate in complex applications normally leading to numeric dispersion and diffusion.Peer Reviewe

O utjecaju pojedinih parametara ložišta izvedenih iz Rothermelovog modela ravnoteže toplinske energije na stopu širenja požara

We analysed the role of some fuel bed properties on forest fire-spread rate based on the thermal energy balance upon which the well-known fire-spread rate model of Rothermel (1972) was developed, showing that neither fuel bed height, load or density directly influence the thermal energy balance. The influence of such parameters, often inferred from empirical descriptions of spread rate, must result from indirect effects on heat transfer mechanisms. The fraction of heat transferred from the flame to the unburned fuel depends mostly on fuel moisture content and is independent of spread rate and flame geometry. Because empirical models usually implicitly assume the underlying mechanisms of fire spread for describing fire behaviour, this study results can assist at idealizing and delineating future experiments and approaches.Analizirana je uloga pojedinih svojstava ložišta u stopi širenja šumskog požara, na temelju ravnoteže toplinske energije, iz koje je razvijen poznati Rothermelov model širenja požara (1972), pokazujući da niti visina ložišta, jednako kao ni količina i gustoća ne utječu izravno na ravnotežu toplinske energije. Utjecaj tih parametara, često izvedenih iz empirijskih opisa stope širenja, nužno proizlazi iz neizravnih utjecaja na mehanizme prijenosa topline. Udio topline prenesen iz plamena na nesagorijelo gorivo, pretežno ovisi o sadržaju vlage u gorivu te je neovisan od stope širenja te oblika plamena. S obzirom na to da empirijski modeli uglavnom impliciraju mehanizme širenja požara u opisivanju njegovog ponašanja, rezultati ove studije mogu biti od pomoći u osmišljavanju i ocrtavanju budućih eksperimenata i pristupa

Experimental Demonstration of a Structured Material with Extreme Effective Parameters at Microwaves

Following our recent theoretical studies [M. G. Silveirinha, C. A. Fernandes, Phys. Rev. B, 78, 033108, 2008], it is experimentally verified that an array of crossed metallic wires may behave as a nonresonant material with extremely large index of refraction at microwaves, and may enable the realization of ultra-subwavelength waveguides.Comment: accepted for publication in Applied Physics Letters (in press). Applied Physics Letters (in press) (2008

Towards long-term intracranial pressure monitoring based on implantable wireless microsystems and wireless sensor networks

Ambient Assisted Living (AAL) aims to provide support to healthcare professionals making use of sensing, and information and communication technologies. Brain related information is becoming more and more relevant for many pathologies, but access to long-term information from brain to feed such AAL technologies is still giving the first steps. One main issue when recording signal from the brain is the available room for sensing device placement. Since available room is limited, battery-less solutions are welcome. Also, AAL solutions to be developed should consider not only the sensing device, but also the entire supporting framework. This paper introduces a solution for long-term monitoring of intracranial pressure using a wireless microdevice and a wireless sensor network. This work introduces a solution to achieve an enough miniaturized pressure sensor, powered by a wireless link, and analyzes the suitability of a wireless sensor network to support the data dissemination.This work was supported by Portuguese Foundation for Science and Technology: FCT-PTDC/EEI-TEL/2881/2012, Programa Operacional Temático Fatores de Competitividade (COMPETE) and Fundo Comunitário Europeu FEDER. 2015info:eu-repo/semantics/publishedVersio

Experimental analysis on the functional properties of rendering mortars with superficial addition of TiO2 nanoparticles

Recent developments in the area of nanomaterials science and nanotechnology are changing the field of construction and building industry. The construction industry has been increasingly identified as an important market for the use of nanomaterial´s since this can make buildings cleaner (minimizing the pollution effects and also reducing the building facades maintenance costs), resistant and energy efficient (thermal energy storage). In order to contribute for the development of this area, this work aims the production of rendering plastering mortars with multifunctional properties such as photocatalytic capacity and improving thermal capabilities. Standard plastering mortars were modified by spraying titanium dioxide (TiO2) from a water-based TiO2 nanoparticles solution. Two mortar compositions, which are representative of rendering mortars, namely composition, 1:1:6 and 1:2:9 (cement:lime:sand) in volume, were considered. Additionally, two distinct water/binder ratios were considered to induce distinct porosities and thus to evaluate the differences on the mechanical and physical properties of the mortars after the addition of the TiO2 nanoparticles

Target Selection in Multistatic Microwave Breast Imaging Setup Using Dielectric Lens

Microwave Imaging (MWI) has been studied to aid early breast cancer detection. Current prototypes in more advanced stages of development include both monostatic or multistatic setups. However, multistatic configurations usually include a high number of antennas which consequently require complex and computationally-intensive signal processing algorithms to ensure a good target detection. We previously presented a novel approach using a dielectric lens which reduces the signal processing burden of multistatic setups, while ensuring good spatial resolution. In this paper, we evaluate this novel setup using an anatomically realistic breast phantom and its capability of selecting targets inside the breast. We show a successful detection of the targets using an artefact removal algorithm based on singular value decomposition when the Bessel beam is centered at the target location.info:eu-repo/semantics/publishedVersio

Study of the Refraction Effects in Microwave Breast Imaging Using a Dry Setup

Medical Microwave Imaging (MWI) has been studied as a technique to aid breast cancer diagnosis. Several different prototypes have been proposed but most of them require the use of a coupling medium between the antennas and the breast, in order to reduce skin backscattering and avoid refraction effects. The use of dry setups has been addressed and recent publications show promising results. In this paper, we assess the importance of considering refraction effects in the image reconstruction algorithms. To this end, we consider a simplified homogeneous spherical model of the breast and analytically compute the propagating rays through the air-body interface. The comparison of results considering only direct ray propagation or refracted rays shows negligible impact on the accuracy of the images for moderately high permittivity media. Thus, we may avoid the computational burden of calculating the refracted rays in complex shapes.info:eu-repo/semantics/publishedVersio

Experimental Evaluation of an Axillary Microwave Imaging System to Aid Breast Cancer Staging

The number of metastasised Axillary Lymph Nodes (ALNs) is a key indicator for breast cancer staging. Its correct assessment affects subsequent therapeutic decisions. Common ALN screening modalities lack high enough sensitivity and specificity. Level I ALNs produce detectable backscattering of microwaves, opening the way for Microwave Imaging (MWI) as a complementary screening modality. Radar-based MWI is a low-cost, noninvasive technique, widely studied for breast cancer and brain stroke detection. However, new specific challenges arise for ALN detection, which deter a simple extension of existing MWI methods. The geometry of the axillary region is more complex, limiting the antenna travel range required for maximum resolution. Additionally, unlike breast MWI setups, it is impractical to use liquid immersion to enhance energy coupling to the body; therefore, higher skin reflection masks ALNs response. We present a complete study that proposes dedicated imaging algorithms to detect ALNs dealing with the above constraints, and evaluate their effectiveness experimentally. We describe the developed setup based on a 3D-printed anthropomorphic phantom, and the antenna-positioning configuration. To the authors’ knowledge, this is the first ALN-MWI study involving a fully functional anatomically compliant setup. A Vivaldi antenna, operating in a monostatic radar mode at 2-5 GHz, scans the axillary region. Pre-clinical assessment in different representative scenarios shows Signal-to-ClutterRatio higher than 2.8 dB and Location Error lower than 15mm, which is smaller than considered ALN dimensions. Our study shows promising level I ALN detection results despite the new challenges, confirming MWI potential to aid breast cancer staging.info:eu-repo/semantics/publishedVersio