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Search Results: 1 - 10 of 414491 matches for " D. R.;Silva "
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Analytical Signal and Reduction to Pole Interpretation of Total Magnetic Field Data at Eppawala Phosphate Deposit  [PDF]
N. D. Subasinghe, W. K. D. G. D. R. Charles, S. N. De Silva
Journal of Geoscience and Environment Protection (GEP) , 2014, DOI: 10.4236/gep.2014.23023

A magnetic survey was carried out to find out the possibilities of demarcating a phosphate deposit from the surrounding country rocks. It is a well-established fact that the magnetic mapping can be utilised to investigate the subsurface objects, materials or different rock types based on their magnetic properties. Those rocks with ferro-magnetic minerals such as magnetite generate magnetic anomalies which in turn help to investigate the subsurface occurrence of mineral deposits. An economic phosphate deposit in Sri Lanka, known as Eppawala Phosphate deposit was selected for this study. The deposit was formed as an accumulation of secondary products of an apatite-rich carbonatite. Due to weathering of iron-rich carbonatite, magnetite and its derivatives are intimately bound with the said deposit. Therefore, the magnetic signature of the phosphate body is different to that of the surrounding country rocks. Despite some studies on different aspects of the deposit, subsurface extents of the ore body are so far not adequately studied. Therefore, this study was conducted to identify the boundaries of the phosphate body. The study was carried over an area of 12 km2 5 km north from the current mining site and survey was conducted. GSM-19 Overhouser system with integrated GPS was used to collect field data. Magnetic anomalies were plotted using a predefined grid. The maximum positive and negative anomalies encountered in the survey area are 690 nT and 829 nT respectively. This study showed that magnetite is not distributed evenly in the area and the deposit extended along the north south direction. Further, processing of analytical signal using the anomalies showed that the carbonatite occurs as a continuous body trending in North South direction. Low magnetic latitudes magnetic data interpretation is difficult because the vector nature of the magnetic field. Therefore, “reduction to pole” concept and “analytical signal concept” were used for the data analysis. Reduction to pole map and analytical signal map are comparatively similar and the change of declination value has no significant effect on the map of reduction to pole.

Application of Photo-Fenton Process for the Treatment of Kraft Pulp Mill Effluent  [PDF]
M. D. Rabelo, C. R. Bellato, C. M. Silva, R. B. Ruy, C. A. B. da Silva, W. G. Nunes
Advances in Chemical Engineering and Science (ACES) , 2014, DOI: 10.4236/aces.2014.44050
Abstract: The present work evaluated the use of photo-Fenton process for the treatment of kraft pulp mill effluent. The photo-Fenton best operating conditions, such as pH, concentration, and H2O2: Fe2+ ratio were evaluated. The efficiency of the treatment was measured by COD (chemical oxygen demand) removal. The results showed that the optimum pH for the photo-Fenton process was equal to 3. The increase in H2O2 application resulted in an efficiency increase of the photo-Fenton process, although this was not a directly proportional relation. For most cases, the H2O2: Fe2+ proportion of 100:1 yielded the best results for COD removal. Solar radiation was more efficient than artificial UV to the COD removal. During the treatment the organic matter of the effluent was more oxidized than mineralized, showing a higher removal of COD than BOD (biochemical oxygen demand) and TOC (total organic carbon), respectively. So, photo-Fenton process increased the BOD/ COD ration but decreased the BOD/TOC ratio.
Long Period Variables in NGC 5128: I. Catalogue
M. Rejkuba,D. Minniti,D. R. Silva
Physics , 2003, DOI: 10.1051/0004-6361:20030683
Abstract: The first variable star catalogue in a giant elliptical galaxy NGC 5128 (Centaurus A) is presented. Using multi-epoch observations with ISAAC at the VLT we have detected 1504 red variables in two halo fields covering 10.46 arcmin square. For the variables with at least 10 good measurements, periods and amplitudes were determined using Fourier analysis and non-linear sine-curve fitting algorithms. The final catalogue contains 1146 long period variables with well established light curve parameters. Periods, amplitudes, JsHKs photometry as well as individual Ks-band magnitudes are provided for all the variables. The distribution of amplitudes ranges from 0.3 to a few magnitudes in the Ks-band, with a median value around 0.7 mag. The amplitudes, mean magnitudes and periods indicate that the majority of variables belong to the class of long period variables with semiregular and Mira variables. Exhaustive simulations were performed in order to assess the completeness of our catalogue and the accuracy of the derived periods.
Stellar populations in NGC 5128 with the VLT: evidence for recent star formation
M. Rejkuba,D. Minniti,D. R. Silva,T. R. Bedding
Physics , 2001, DOI: 10.1051/0004-6361:20011315
Abstract: We resolve stars of the nearest giant elliptical galaxy NGC 5128 using VLT with FORS1 and ISAAC. We construct deep U, V and Ks color-magnitude and color-color diagrams in two different halo fields (in the halo and in the north-eastern diffuse shell). In the outer, shell field, at ~14 kpc from the center of the galaxy, there is a significant recent star formation with stars as young as 10 Myr, approximately aligned with the prominent radio and x-ray jet from the nucleus of the host AGN. Ionized gas filaments are evident in ultraviolet images near the area where neutral HI and CO molecular gas was previously observed. The underlying stellar population of the halo of the giant elliptical is predominantly old with a very broad metallicity distribution. The presence of an extended giant branch reaching M_bol=-5 mag suggests the existence of a significant intermediate-age AGB population in the halo of this galaxy.
High Galactic latitude runaway stars as tracers of the spiral arms
M. D. V. Silva,R. Napiwotzki
Physics , 2013, DOI: 10.1093/mnras/stt177
Abstract: A direct observation of the spiral structure of the Galaxy is hindered by our position in the middle of the Galactic plane. We propose a method based on the analysis of the birthplaces of high Galactic latitude runaway stars to map the spiral arms and determine their dynamics. As a proof of concept, the method is applied to a local sample of early-type stars and a sample of runaways stars to obtain estimates of the pattern speed and the spiral arm's phase angle. We also estimate the performance of this method once the data gathered by Gaia, in particular for runaway stars observed on the other side of the Galaxy, is available.
Ejection velocities of high Galactic latitude runaway stars
M. D. V. Silva,R. Napiwotzki
Physics , 2010, DOI: 10.1111/j.1365-2966.2010.17864.x
Abstract: We estimate the distribution of ejection velocities for the known population of high galactic latitude runaway stars. The initial sample is a collection of 174 early-type stars selected from the literature. The stars are first classified according to their evolutionary status in order to obtain a homogeneous sample of 96 genuine main sequence stars. Their present velocities and flight times are then estimated using proper motion data from various astrometric catalogues (including Tycho-2, UCAC2, and USNO-B) and the ejection velocities are computed by tracing their orbits back in time, based on a galactic potential. The potential used is constructed from a mass density model chosen to fit the most recent observational constraints. We find evidence for two different populations of runaway stars: a "high" velocity population, with a maximum ejection velocity of about 400 - 500 km/s, and a "low" velocity population, with a maximum ejection velocity of about 300 km/s. We argue that the observed limit of 500 km/s and the bimodality of the observed ejection velocity distribution are natural consequences of the so-called Binary Ejection Mechanism. We discuss the connection between the "high" velocity population and the so-called hypervelocity stars, showing how previously studied hypervelocity stars are consistent with the results obtained. We also find that some stars that were once thought to be best explained as being formed in the Halo are compatible with a runaway hypothesis once proper motions are included in the analysis. However, three stars in the selected sample appear to be inconsistent with ejection from the galactic disc. Possible scenarios are discussed, including a possible formation in the galactic halo.
Colored noise and memory effects on formal spiking neuron models
L. A. da Silva,R. D. Vilela
Quantitative Biology , 2015, DOI: 10.1103/PhysRevE.91.062702
Abstract: Simplified neuronal models capture the essence of the electrical activity of a generic neuron, besides being more interesting from the computational point of view when compared to higher dimensional models such as the Hodgkin-Huxley one. In this work, we propose a generalized resonate-and-fire model described by a generalized Langevin equation that takes into account memory effects and colored noise. We perform a comprehensive numerical analysis to study the dynamics and the point process statistics of the proposed model, highlighting interesting new features like: i) non-monotonic behavior (emergence of peak structures, enhanced by the choice of colored noise characteristic time-scale) of the coefficient of variation (CV) as a function of memory characteristic time-scale, ii) colored noise-induced shift in the CV, and iii) emergence and suppression of multimodality in the interspike interval (ISI) distribution due to memory-induced subthreshold oscillations. Moreover, in the noise-induced spike regime, we study how memory and colored noise affects the coherence resonance (CR) phenomenon. We found that for sufficiently long memory, CR is not only suppressed, but also the minimum of the CV $\times$ noise intensity curve that characterizes the presence of CR may be replaced by a maximum. The aforementioned features allow to interpret the interplay between memory and colored noise as an effective control mechanism to neuronal variability. Since both variability and non-trivial temporal patterns in the ISI distribution are ubiquitous in biological cells, we hope the present model can be useful in modeling real aspects of neurons.
The radio/optical alignment and the recent star formation associated with ionized filaments in the halo of NGC 5128 (Centaurus A)
M. Rejkuba,D. Minniti,F. Courbin,D. R. Silva
Physics , 2001, DOI: 10.1086/324500
Abstract: We used the direct CCD camera at the Magellan I telescope at Las Campanas Observatory and FORS1 at Antu VLT at ESO Paranal Observatory to image fields centered on the inner and outer optical filaments in the halo of NGC 5128. In the V vs. U-V color-magnitude diagrams we have identified young blue supergiants associated with these line-emitting filaments located between the inner radio lobe and the northern middle lobe. Around the outer filament stars as young as 10 Myr were detected. They are principally aligned with the direction of the radio jet, but a vertical north-east alignment along the edge of the HI cloud is also present. Young stars in the inner filament field are found inside the bright knots of photoionized gas and are strongly aligned in the direction towards the center of the galaxy at the same position angle as the inner radio jet. Fitting the Padova isochrones on UV color-magnitude diagrams we find that the blue stars around the inner filaments have ages similar to the ones around the outer filaments ~10-15 Myr and the same abundance of Z=0.004. The presence of young blue supergiants clearly shows that the bright blue knots in the north-eastern halo of NGC 5128 are associations of young stars with photoionized gas. The temperature of the brightest stars is T \~ 12000-16000 K, insufficient to account alone for the high excitation lines observed in the surrounding ionized gas. Thus the optical emission jet is principally seen due to its alignment with the radio structure of the AGN. The highly collimated star formation is present only in the north eastern halo of the galaxy, suggesting the interaction of the jet with the gas clouds deposited during the last accretion event as the preferred triggering mechanism. (abridged)
Real Estate Evaluation engineering suported by multicriteria analysis and artificial neural network
Salesian Journal on Information Systems , 2010,
Abstract: To evaluate real estates means estimate its market value, taking into account several factors, such as: the particular characteristics of the property, market conditions and the balance between stakeholders in the negotiation. All these features make the evaluation a complex task, mainly because the real estate market represents an important segment of the national economy requiring more precise results. In this context, we conducted a survey on evaluation methodologies of properties that are used and identified that the main technique, regression analysis, has limitations that may compromise the outcome of the evaluation. This paper presents the research methodology developed using Multicriteria Analysis and Artificial Neural Network to evaluate residential apartments. The results were considered very satisfactory, indicating that the combination of multicriteria analysis and artificial neural network is efficient and promising.
Characterization and Bioaccessibility of Minerals in Seeds of Salvia hispanica L.  [PDF]
Aline D. Barreto, érika M. R. Gutierrez, Mauro R. Silva, Fabiano O. Silva, Nilton O. C. Silva, Inayara C. A. Lacerda, Renata A. Labanca, Raquel L. B. Araújo
American Journal of Plant Sciences (AJPS) , 2016, DOI: 10.4236/ajps.2016.715204
Abstract: Salvia hispanica L. is a herbacia plant that originates from Mexico and Guatemala, and it is currently known by the popular name of chia. Currently, chia seeds have been considered to be of great importance for human health and nutrition because they have a high concentration of polyunsaturated fatty acids. They contain the largest known percentage of fatty α-linolenic acid (ALA) in plants—approximately 68%. Furthermore, they are an excellent source of protein, dietary fiber, calcium, magnesium, iron, vitamin B and phenolic compounds that have antioxidant properties. However, despite the high nutritional value present in the food and the possible health benefits of its nutrients, there is a need to evaluate the bioaccessibility of its micronutrients to measure their effectiveness. Thus, we evaluated the chemical composition of chia seeds from different producers, their lipid profiles and the bioaccessibility of some of their minerals.
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