Punctual Source Research Articles

Calibration of Stereo Pairs Using Speckle Metrology.

The accuracy of 3D reconstruction for metrology applications using active stereo pairs depends on the quality of the calibration of the system. Active stereo pairs are generally composed of cameras mounted on tilt/pan mechanisms separated by a constant or variable baseline. This paper presents a calibration approach based on speckle metrology that allows the separation of translation and rotation in the estimation of extrinsic parameters. To achieve speckle-based calibration, a device called an Almost Punctual Speckle Source (APSS) is introduced. Using the APSS, a thorough method for the calibration of extrinsic parameters of stereo pairs is described. Experimental results obtained with a stereo system called the Agile Stereo Pair (ASP) demonstrate that speckle-based calibration achieves better reconstruction performance than methods using standard calibration procedures. Although the experiments were performed with a specific stereo pair, such as the ASP, which is described in the paper, the speckle-based calibration approach using the APSS can be transposed to other stereo setups.

Wind Tunnel Investigation and Numerical Analysis of Fume Behavior in the Vicinity of Rectangular Building Under Moderate Velocity Wind

Abstract A research was conducted to examine the dispersion of pollutants ejected from a chimney around three-dimensional rectangular building. Regarding the experimental study, the wind tunnel experiment comprises data acquired through the dispersion of continuous source tracer discharges from a punctual source situated in a regular network of building-like obstacle, and these data include measurements of mean velocity and turbulence parameters. The relevant data are followed using Particle Image Velocimetry to track various instantaneous and mean dynamic characteristics. Concerning the numerical study, the suggested model simulates both the dynamics and the heat transfer flow field using the overall mean three-dimensional Navier-Stokes equations with an RSM turbulence closure model. The findings of a deep comparison of turbulent flow and dispersion between a full wind tunnel experiment and the model predictions are reported. A high degree of concordance was obtained with the experimental flow and numerical simulation data. The detailed investigation, in which numerical and wind tunnel studies, was performed to evaluate the impact of wind velocity on the pollutant dispersion issued from a chimney around the building in their vicinity. the results clearly showed how wind velocity influenced the environmental air flows and pollutant dispersal pathways. The results of this study show that the shape of the building and the resulting interaction between the wind structure play a determining factor in the distribution of pollutants around a building, thereby affecting the air quality in the various parts of the building.

Comparison between multi-frequency and multi-speed laser lock-in thermography methods for the evaluation of crack depths in metal

ABSTRACT Two original methods using lock-in thermography with a laser excitation are proposed for the estimation without contact of open crack depths in metal. The first uses a modulated punctual thermal source and is well suited for the study of complicated structures. In the second, a continuous moving thermal source allows to scan homogeneous structures. Each method relies on the heat diffusion modifications induced by a crack located in the thermal diffusion area of the synchronised heat source. The thermal signature of the crack is extracted to the amplitude of surface temperature images for various modulation frequencies or various scanning speeds of the thermal source. The thermal signatures are analysed according to a length representative of the thermal diffusion length to give a local evaluation of the crack depth. The obtained results demonstrate the potentiality of active lock-in thermography as a contactless measurement tool for the evaluation of crack depths up to 3 mm.

Point-source dispersion of quasi-neutrally-buoyant inertial particles.

We analyze the evolution of the distribution, both in the phase space and in the physical space, of inertial particles released by a spatially-localized (punctual) source and advected by an incompressible flow. The difference in mass density between fluid and particles is assumed to be small, and represents the basic parameter for a regular perturbative expansion. By means of analytical techniques such as Hermitianization, we derive a chain of equations of the advection-diffusion-reaction type, easily solvable at least numerically. Our procedure provides results also for finite particle inertia, away from the over-damped limit of quasi-tracer dynamics.

Local error analysis for the Stokes equations with a punctual source term

The solution of the Stokes problem with a punctual force in source term is not $$H^1 \times \mathbb {L}^2$$ and therefore the approximation by a finite element method is suboptimal. In the case of Poisson problem with a Dirac mass in the right-hand side, an optimal convergence for the Lagrange finite elements has been shown on a subdomain which excludes the singularity in $$\mathbb {L}^2$$ -norm by Koppl and Wohlmuth. Here we show a quasi-optimal local convergence in $$H^1 \times \mathbb {L}^2$$ -norm for a $$\mathbb {P}_{k}/\mathbb {P}_{k-1}$$ -finite element method, $$k \geqslant 2$$ , and for the $$\mathbb {P}_{1}{\mathrm{b}}/\mathbb {P}_{1}$$ . The error is still analysed on a subdomain which does not contain the singularity. The proof is based on local Arnold and Liu error estimates, a weak version of Aubin–Nitsche duality lemma applied to the Stokes problem and discrete inf-sup conditions. These theoretical results are generalized to a wide class of finite element methods, before being illustrated by numerical simulations.

Ecological risk assessment of sedimentary hydrocarbons in a subtropical estuary as tools to select priority areas for environmental management

The concentration, distribution, and ecological risk of hydrocarbons, as well as bulk parameters, were determined in surface sediments of the Babitonga Bay, a subtropical human-impacted estuary in South Atlantic. Total aliphatic and polycyclic aromatic hydrocarbons (PAHs) ranged between 0.8 and 201.2 μg g−1 and from 8.7 to 5489 ng g−1, respectively. Saguaçú Lagoon, the region near the ferry boat and the vicinity of São Francisco harbour (SFH), presented high hydrocarbon concentrations. Despite the low accumulation trend in this region, the SFH and city may act as a punctual hydrocarbon source. The inner portion of the estuary had the finest sediment grains and the highest concentrations of carbon, nitrogen, and sulphur, indicating its importance as a depositional and cumulative area. The occurrence of unresolved complex mixture suggested chronic oil contamination. Petrogenic (based on the high percentage of alkylated PAHs) and pyrolytic (according to the diagnostic ratios of PAH isomer pairs) sources were confirmed. Ecological risk assessment was evaluated by the risk quotient (RQ). All samples had at least one priority PAH present at above the negligible concentration, including naphthalene, which was observed in all samples. Only the sites near the ferry boat and at the Saguaçú Lagoon contained compounds with concentrations above their maximum permissible concentrations, while all other sampling sites are classified as “Low-risk.” The spatial distribution of RQs coincides with PAHs distribution, indicating that the regions near SFH, ferry-boat, and the Saguaçú Lagoon should be considered to be priority areas when making environmental monitoring policies.

Thermal diffusivity measurement in thin metallic filaments using the mirage method with multiple probe beams and a digital camera.

Photothermal beam deflection is a well-established technique for measuring thermal diffusivity. In this technique, a pump laser beam generates temperature variations on the surface of the sample to be studied. These variations transfer heat to the surrounding medium, which may be air or any other fluid. The medium in turn experiences a change in the refractive index, which will be proportional to the temperature field on the sample surface when the distance to this surface is small. A probe laser beam will suffer a deflection due to the refractive index periodical changes, which is usually monitored by means of a quadrant photodetector or a similar device aided by lock-in amplification. A linear relationship that arises in this technique is that given by the phase lag of the thermal wave as a function of the distance to a punctual heat source when unidimensional heat diffusion can be guaranteed. This relationship is useful in the calculation of the sample's thermal diffusivity, which can be obtained straightforwardly by the so-called slope method, if the pump beam modulation frequency is well-known. The measurement procedure requires the experimenter to displace the probe beam at a given distance from the heat source, measure the phase lag at that offset, and repeat this for as many points as desired. This process can be quite lengthy in dependence of the number points. In this paper, we propose a detection scheme, which overcomes this limitation and simplifies the experimental setup using a digital camera that substitutes all detection hardware utilizing motion detection techniques and software digital signal lock-in post-processing. In this work, the method is demonstrated using thin metallic filaments as samples.

Passive Coding Technique Applied to Synthetic Aperture Interferometric Radiometer

For real-time and high-resolution radiometric imaging, the synthetic aperture interferometric radiometer (SAIR) technique seems to solve the tradeoff between imaging resolution and aperture size. Indeed, it can synthesize a large antenna array by sparsely arranging a small number of antennas to achieve high spatial resolution. Nevertheless, a conventional interferometric radiometer requires as many receivers as antennas needed. This constraint is one of the limitations of SAIR regarding the hardware cost, the system complexity, and the computation load. In this letter, a compressed acquisition technique is proposed to collect the antenna signals. In this method, the antenna’s signals are coded and combined red with a passive microwave device. From the measured waveforms at the receiver’s outputs, a decoding process is performed to estimate the received signal by each antenna. This allows the computation of the visibility function required for image reconstruction. The effectiveness of the proposed method has been tested by means of simulations analysis and has experimentally been applied to a punctual noise source detection. The results reveal that this method can be an efficient alternative for the simplification of the conventional interferometric radiometers’ architectures.

The Selection and Characterization of the Absorptive Coatings Used to Laser Surface Treatments of Tool Steel Parts

The paper presents the experimental results on the surface quenching by CO2 continuous wave laser action of solid phase steel with 1%C obtained, using different absorptive (ZnO, TiO2, ZrO2, graphite) powder coatings. The absorptivity of these coatings was determined by resolving the thermal conductivity equation for the irradiation with an energy punctual source on the massive body. Among the four investigated powders, for thermal treatment with laser of tools carbon steel it is recommend the powder of zinc oxide as coating with most efficient absorption capacity.

Microcautery based on zinc metallic nanoparticles photodeposited on the core of an optical fiber

The experimental arrangement of a microcautery implemented by an optical fiber with zinc nanoparticles (ZnNPs) photodeposited on its core for the cauterization and coagulation in blood vessels hemostasis processes is presented. The interaction between a laser radiation source and the ZnNPS on the fiber core produces a controllable punctual heat source through the radiation intensity, which is capable of reaching a temperature up to 200°C covering an area of approximately ten micrometers. By using three-to-four-month-old rats of CIIZ-V strain, we made several microcauterization experimental tests to stop blood flow. The findings show that the microcautery obliterates the smooth muscle of the blood vessels concatenating mutually to tissue in an average time of three seconds, at the same time, the blood elements responsible for the coagulation are thermally activated and thus the bleeding is stopped.

Different carbon sources affect PCB accumulation by marine bivalves

Pampean creeks were evaluated in the present study as potential land-based sources of PCB marine contamination. Different carbon and nitrogen sources from such creeks were analysed as boosters of PCB bioaccumulation by the filter feeder bivalve Brachidontes rodriguezii and grazer limpet Siphonaria lessoni. Carbon of different source than marine and anthropogenic nitrogen assimilated by organisms were estimated through their C and N isotopic composition. PCB concentration in surface sediments and mollusc samples ranged from 2.68 to 6.46 ng g−1 (wet weight) and from 1074 to 4583 ng g−1 lipid, respectively, reflecting a punctual source of PCB contamination related to a landfill area. Thus, despite the low flow of creeks, they should not be underestimated as contamination vectors to the marine environment. On the other hand, mussels PCB bioaccumulation was related with the carbon source uptake which highlights the importance to consider this factor when studying PCB distribution in organisms of coastal systems.

Cellular dosimetry calculations for Strontium-90 using Monte Carlo code PENELOPE

Purpose: To improve risk assessments associated with chronic exposure to Strontium-90 (Sr-90), for both the environment and human health, it is necessary to know the energy distribution in specific cells or tissue. Monte Carlo (MC) simulation codes are extremely useful tools for calculating deposition energy. The present work was focused on the validation of the MC code PENetration and Energy LOss of Positrons and Electrons (PENELOPE) and the assessment of dose distribution to bone marrow cells from punctual Sr-90 source localized within the cortical bone part.Materials and methods: S-values (absorbed dose per unit cumulated activity) calculations using Monte Carlo simulations were performed by using PENELOPE and Monte Carlo N-Particle eXtended (MCNPX). Cytoplasm, nucleus, cell surface, mouse femur bone and Sr-90 radiation source were simulated. Cells are assumed to be spherical with the radii of the cell and cell nucleus ranging from 2–10 μm. The Sr-90 source is assumed to be uniformly distributed in cell nucleus, cytoplasm and cell surface.Results: The comparison of S-values calculated with PENELOPE to MCNPX results and the Medical Internal Radiation Dose (MIRD) values agreed very well since the relative deviations were less than 4.5%. The dose distribution to mouse bone marrow cells showed that the cells localized near the cortical part received the maximum dose.Conclusion: The MC code PENELOPE may prove useful for cellular dosimetry involving radiation transport through materials other than water, or for complex distributions of radionuclides and geometries.

A simplified approach for the calculation of acoustic emission in the case of friction-induced noise and vibration

The acoustic response associated with squeal noise radiations is a hard issue due to the need to consider non-linearities of contact and friction, to solve the associated nonlinear dynamic problem and to calculate the noise emissions due to self-excited vibrations. In this work, the focus is on the calculation of the sound pressure in free space generated during squeal events.The calculation of the sound pressure can be performed by the Boundary Element Method (BEM). The inputs of this method are a boundary element model, a field of normal velocity characterized by a unique frequency. However, the field of velocity associated with friction-induced vibrations is composed of several harmonic components. So, the BEM equation has to be solved for each frequency and in most cases, the number of harmonic components is significant. Therefore, the computation time can be prohibitive.The reduction of the number of harmonic component is a key point for the quick estimation of the squeal noise. The proposed approach is based on the detection and the selection of the predominant harmonic components in the mean square velocity. It is applied on two cases of squeal and allows us to consider only few frequencies.In this study, a new method will be proposed in order to quickly well estimate the noise emission in free space. This approach will be based on an approximated acoustic power of brake system which is assumed to be a punctual source, an interpolated directivity and the decrease of the acoustic power levels.This method is applied on two classical cases of squeal with one and two unstable modes. It allows us to well reconstruct the acoustic power levels map. Several error estimators are introduced and show that the reconstructed field is close to the reference calculated with a complete BEM.

Historical mercury trends recorded in sediments from the Laguna del Plata, Córdoba, Argentina

The main carrying phases of mercury (Hg) were analyzed in a 120cm sediment core taken at the Laguna del Plata (LP), a small lake connected to the main water body of Laguna Mar Chiquita (LMC) during highstands. LMC is considered to be one of the largest saline lakes in the world representing a sensitive climatic indicator due to its frequent lake level variations at millennial and interdecadal scale like the last ones that started early in the 1970s and after 2004. Total particulate Hg (HgTP) concentrations vary between ∼13 and ∼131μgkg−1 indicating a system with low pollution. Selective extractions with ascorbate, HCl and H2O2 were performed in the sediments and they revealed that Hg is associated mainly to reactive sulphides in the base of the core, while in the middle and upper part the organic matter seems to be the main Hg-bearing phase. The highest and most important peak was found in sediments accumulated between 1991 and 1995. More than a punctual source of pollution, this peak is likely related to two eruptive events occurred in the Andean Cordillera in this period: the eruption of Hudson volcano in southern Patagonia that occurred in 1991 and the one of the Láscar volcano in northern Chile that occurred in 1993. In both cases, the respective ash plumes were documented to have reached the Laguna del Plata region.

Persistent organic pollutants in sea bass (Dicentrarchus labrax L.) in two fish farms in the Mediterranean Sea

We analyzed polychlorobiphenyls (PCBs), perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA) in the edible part of farmed sea bass reared in two fish farms in Liguria (Northern Italy). The aim was to determine the contamination levels and human exposure to these chemicals through fish consumption. Concentrations of “dioxin-like” PCBs (DL-PCBs) ranged from 0.033 to 0.759pg ΣTEQ-PCBg−1 whole weight (w.w.) in fish farm 1 and from 0.032 to 1.60pg ΣTEQ-PCBg−1 w.w. in fish farm 2, and the six indicators of “non-dioxin-like” (NDL-PCBs) from 0.538 to 9.33ng Σ6PCBg−1 w.w. and from 1.62 to 27.6ng Σ6PCBg−1 w.w. Concentrations were generally lower in farm 1 than in farm 2. One reason for this difference might be the proximity of farm 2 to the seaport of La Spezia, which could be a punctual source of pollutants influencing the contamination of the water in the farm. Principal component analysis (PCA) showed differences also in the congeners profiles for the two sites, with higher-chlorinated PCBs more abundant in farm 1, and lower-chlorinated PCBs were more abundant in farm 2. Most of the concentrations of PFOS and PFOA were below the limit of detection (LOD 0.05ngg−1 w.w.). Only about 10% of the samples analyzed had levels slightly higher than the LOD. Assessments of exposure using these data showed that consumption of farmed fish may contribute significantly to PCBs through the diet, whereas the contribution of PFOS and PFOA seems to be low.

Shedding light on night myopia

First described during the 18th century, the cause of night myopia remains a controversial topic. Whereas several explanations have been suggested in the literature, particularly related with accommodation or chromatic shift in scotopic light conditions, no definitive explanation for its aetiology has been provided. We describe an experiment in which ocular refractive state was objectively and subjectively measured while viewing two kind of stimulus: letters on a bright background and a punctual source of light in a dark background. We found that under photopic conditions the optimum refractive state of the accommodating eye is significantly more myopic when maximizing perceived quality of a point source on a dark background compared to a conventional letter chart with black letters on a white background. Optical modeling suggested this difference in refractive state is due to spherical aberration. Since isolated point sources are more likely encountered at night, whereas extended objects are more likely encountered in the daytime, our results suggest that a significant part of the night myopia phenomenon is determined by the nature of the visual stimulus and the visual task used to assess ocular refractive state.

Electric motor winding temperature prediction using a simple two‐resistance thermal circuit

PurposeThe purpose of this paper is to propose a simplified thermal circuit to estimate the temperature rise in the winding of a totally enclosed fan cooled electric motor for different loads and/or cooling conditions since the motor has already been tested for a known condition.Design/methodology/approachThe determination of the convection resistance is based on classical Nusselt correlations and the value of conduction resistance is provided from a known load condition and the corresponding temperature rise in the winding.FindingsPredicted temperature values showed good agreement with the experimental results, demonstrating that the hypothesis of simplification to a punctual source of thermal energy is acceptable.Research limitations/implicationsIt is necessary that the motor has already been tested for a known condition (losses, temperature, and ventilation). Although the basic idea of this methodology is based on the use of a reference test condition of the same motor, as a suggestion, with small modifications the same methodology can be used to estimate the thermal behavior of different sized motors, provided a similar motor has already been tested.Practical implicationsThis approach results in a fast methodology to estimate the thermal behavior of an electric motor in different loads and/or cooling conditions.Originality/valueThe differential of this circuit is the use of only two thermal resistances, one for the whole conduction and the other for the convection. This approach is a way to overcome the difficulties related to the determination of the thermal contact resistance and the equivalent conduction resistance between the winding and the different isolation systems inside the slots.

Comparison of FDTD Hard Source With FDTD Soft Source and Accuracy Assessment in Debye Media

To radiate electromagnetic energy from a single point of a finite difference time domain (FDTD) grid, there are typically two general classes of electromagnetic wave sources; the soft source which consists of impressing a current, and the hard source which consists of impressing an electric field. The physical meaning of the soft source is well understood and its analytical solution is known, whereas there is no analytical solution for the hard source excitation. Nevertheless, many FDTD works utilize the hard source for its practicality. A novel aspect is that the derivation of a field radiated from the hard source towards the free space is identical to the field radiated from the soft source, provided that a certain relationship holds between the source excitations. This provides us with an analytical solution for the field radiated from the hard source. The assessment of accuracy is then considered for a wide band field radiated from a punctual source into frequency-dependent FDTD Debye media. The quantification of the deviation of the waveform observed in the FDTD space from the analytical solution is demonstrated. The numerical experiments with this quantification show that the waveform observed with the soft source excitation matches the one with the hard source excitation when the minimum wavelength to the spatial discretization ratio is greater than 10. It turns out that the soft source outperforms the hard source when the minimum wavelength relative to the spatial discretization is less than 10 in the case of lossless media. Equivalent accuracy is achievable for both lossless and lossy media even when the minimum wavelength to the spatial discretization ratio is lower than 10 due to the loss tangent which absorbs the spurious frequencies related to the numerical noise.

Modelo aplicado à dinâmica da água e do potássio no solo sob irrigação por gotejamento: análise de sensibilidade

A compreensão do transporte simultâneo da água e de solutos, a partir de uma fonte pontual, permite desenvolver estratégias eficientes na fertirrigação, sendo importante no dimensionamento, na operação e no manejo de sistemas de irrigação localizada. O presente trabalho teve como objetivo apresentar a análise de sensibilidade de um modelo matemático, desenvolvido para simular o deslocamento simultâneo de água e de potássio na irrigação por gotejamento. A análise de sensibilidade foi realizada com respeito às variações individuais da condutividade hidráulica do solo saturado, umidade inicial e saturada do solo, dispersividade, fator de retardamento e vazão do emissor. Os resultados obtidos revelaram que o modelo matemático, com relação à distribuição de água, é bastante sensível à umidade de saturação e inicial do solo e, em relação à distribuição de potássio, é bastante sensível a variações negativas da condutividade hidráulica do solo saturado e da vazão do gotejador; já em relação aos parâmetros de transporte de solutos no solo, é bastante sensível a variações negativas do fator de retardamento e pouco sensível às variações da dispersividade do solo.

Comparaison entre OSEM-3D et rétroprojection filtrée pour les images traitées par SISCOM dans l’épilepsie temporale

Introduction When ictal and interictal brain SPECT are reconstructed with filtered backprojection (FBP), the noise level of subtraction images is frequently high and requires the use of thresholding methods. The aim of this study was to compare the subtraction images for cerebral SPECT reconstructed either with FBP or with a 3D iterative reconstruction method (OSEM-3D). Material and methods After optimisation of the reconstruction parameters on phantom, the subtraction SPECT images, which were obtained with FBP or with OSEM-3D and coregistered with MRI images, were analyzed in 15 patients with refractory temporal epilepsy. Results On phantom and with the constrain of high enough spatial resolution (full width at half of maximum for a punctual source less than or equal to 11 mm) were reached using: (i) a Butterworth filter with a cut-off frequency of 0.4 Nyquist at order 6 for FBP and (ii) five iterations, 16 subsets and a 9 mm gaussian filter for OSEM-3D. On the subtraction images, which were obtained with these optimal parameters, the temporal foci from patients were smaller with OSEM-3D than with FBP (11 ± 6 cm 3 versus 17 ± 10 cm 3, P = 0.02), mean voxel activities were equivalent between the two methods within temporal foci (6.30 ± 3.13 counts versus 6.34 ± 4.93 counts) but these activities were dramatically reduced by OSEM-3D within background regions (0.02 ± 0.02 counts versus 0.19 ± 0.12 counts, P < 0.001). Conclusion For the ictal–interictal subtraction SPECT images, which are obtained in patients with refractory temporal epilepsy, the use of an optimized OSEM-3D method leads to dramatically reduce the volume of temporal foci, as well as the background noise level, two properties that are likely to facilitate the detection and localisation of epilepsy foci.