| 451. |
- Alves, Dimas I, et al.
(författare)
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Statistical Analysis for Wavelength-Resolution SARImage Stacks : New Case Studies
- 2020
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Ingår i: XXXVIII SIMPÓSIO BRASILEIRO DE TELECOMUNICAÇÕES E PROCESSAMENTO DE SINAIS.
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Konferensbidrag (refereegranskat)abstract
- This paper presents new case studies for thestatistical analysis for wavelength resolution SAR image stacks.The statistical analysis considers the Anderson-Darling goodnessof-fit test in a set of pixel samples from the same position obtainedfrom a SAR image stack. The test is applied in wavelengthresolution SAR image stacks. The present work consists of twocase studies based on the use of multiple-pass stacks and TypeI error using the False Discovery Rate controlling procedures.In addition, an application scenario is presented for the studiedscenarios.
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| 452. |
- Alves, Dimas Irion, et al.
(författare)
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Wavelength-Resolution SAR Change Detection Using Bayes' Theorem
- 2020
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Ingår i: IEEE Journal of Selected Topics in Applied Earth Observations and Remote Sensing. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1939-1404 .- 2151-1535. ; 13, s. 5560-5568
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Tidskriftsartikel (refereegranskat)abstract
- This article presents Bayes' theorem for wavelength-resolution synthetic aperture radar (SAR) change detection method development. Different change detection methods can be derived using Bayes' theorem in combination with the target model, clutter-plus-noise model, iterative implementation, and noniterative implementation. As an example of the Bayes' theorem use for wavelength-resolution SAR change detection method development, we propose a simple change detection method with a clutter-plus-noise model and noniterative implementation. In spite of simplicity, the proposed method provides a very competitive performance in terms of probability of detection and false alarm rate. The best result was a probability of detection of $\text{98.7}\%$ versus a false alarm rate of one per square kilometer.
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| 453. |
- Alves, F. O., et al.
(författare)
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Magnetic field in a young circumbinary disk
- 2018
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 616
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Tidskriftsartikel (refereegranskat)abstract
- Context. Polarized continuum emission at millimeter-to-submillimeter wavelengths is usually attributed to thermal emission from dust grains aligned through radiative torques with the magnetic field. However, recent theoretical work has shown that under specific conditions polarization may arise from self-scattering of thermal emission and by radiation fields from a nearby stellar object. Aims. We use multi-frequency polarization observations of a circumbinary disk to investigate how the polarization properties change at distinct frequency bands. Our goal is to discern the main mechanism responsible for the polarization through comparison between our observations and model predictions for each of the proposed mechanisms. Methods. We used the Atacama Large Millimeter/submillimeter Array to perform full polarization observations at 97.5 GHz (Band 3), 233 GHz (Band 6) and 343.5 GHz (Band 7). The ALMA data have a mean spatial resolution of 28 AU. The target is the Class I object BHB07-11, which is the youngest object in the Barnard 59 protocluster. Complementary Karl G. Jansky Very Large Array observations at 34.5 GHz were also performed and revealed a binary system at centimetric continuum emission within the disk. Results. We detect an extended and structured polarization pattern that is remarkably consistent between the three bands. The distribution of polarized intensity resembles a horseshoe shape with polarization angles following this morphology. From the spectral index between Bands 3 and 7, we derived a dust opacity index β ~ 1 consistent with maximum grain sizes larger than expected to produce self-scattering polarization in each band. The polarization morphology and the polarization levels do not match predictions from self-scattering. On the other hand, marginal correspondence is seen between our maps and predictions from a radiation field model assuming the brightest binary component as main radiation source. Previous molecular line data from BHB07-11 indicates disk rotation. We used the DustPol module of the ARTIST radiative transfer tool to produce synthetic polarization maps from a rotating magnetized disk model assuming combined poloidal and toroidal magnetic field components. The magnetic field vectors (i.e., the polarization vectors rotated by 90°) are better represented by a model with poloidal magnetic field strength about three times the toroidal one. Conclusions. The similarity of our polarization patterns among the three bands provides a strong evidence against self-scattering and radiation fields. On the other hand, our data are reasonably well reproduced by a model of disk with toroidal magnetic field components slightly smaller than poloidal ones. The residual is likely to be due to the internal twisting of the magnetic field due to the binary system dynamics, which is not considered in our model.
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| 454. |
- Alves, F. O., et al.
(författare)
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Molecular outflow launched beyond the disk edge
- 2017
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 603, s. Article no L3 -
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Tidskriftsartikel (refereegranskat)abstract
- One of the long-standing problems of star formation is the excess of angular momentum of the parent molecular cloud. In the classical picture, a fraction of angular momentum of the circumstellar material is removed by the magneto-centrifugally driven disk wind that is launched from a wide region throughout the disk. In this work, we investigate the kinematics in the envelope-disk transition zone of the Class I object BHB07-11, in the B59 core. For this purpose, we used the Atacama Large Millimeter/submillimeter Array in extended configuration to observe the thermal dust continuum emission (lambda(0) similar to 1.3 mm) and molecular lines (CO, (CO)-O-18 and H2CO), which are suitable tracers of disk, envelope, and outflow dynamics at a spatial resolution of similar to 30 AU. We report a bipolar outflow that was launched at symmetric positions with respect to the disk (similar to 80 AU in radius), but was concentrated at a distance of 90-130 AU from the disk center. The two outflow lobes had a conical shape and the gas inside was accelerating. The large off set of the launching position coincided with the landing site of the infall materials from the extended spiral structure (seen in dust) onto the disk. This indicates that bipolar outflows are efficiently launched within a narrow region outside the disk edge. We also identify a sharp transition in the gas kinematics across the tip of the spiral structure, which pinpoints the location of the so-called centrifugal barrier.
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| 455. |
- Alves, F. O., et al.
(författare)
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The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers
- 2012
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Ingår i: Proceedings of the International Astronomical Union. - 1743-9213 .- 1743-9221. ; 8:5287, s. 74-78
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Konferensbidrag (refereegranskat)abstract
- H2O masers are important magnetic field tracers in very high density gas. We show one of the first magnetic field determinations at such high density in a low-mass protostar: IRAS 16293-2422. We used the Very Large Array (VLA) to carry out spectro-polarimetric observations of the 22 GHz Zeeman emission of H2O masers. A blend of at least three maser features can be inferred from our data. They are excited in zones of compressed gas produced by shocks between the outflows ejected by this source and the ambient gas. The post-shock particle density is in the range 1 - 3 × 109 cmt−3, and the line-of-sight component of the magnetic field is estimated as ~ 113 mG. The outflow dynamics is likely magnetically dominated.
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| 456. |
- Alves, F. O., et al.
(författare)
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The magnetic field of IRAS 16293-2422 as traced by shock-induced H2O masers
- 2012
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Ingår i: Astronomy and Astrophysics. - : EDP Sciences. - 0004-6361 .- 1432-0746. ; 542
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Tidskriftsartikel (refereegranskat)abstract
- Context. Shock-induced H2O masers are important magnetic field tracers of very high density gas. Water masers are found in both high-and low-mass star-forming regions, and are a powerful tool for comparing magnetic field morphologies in both mass regimes. Aims. We present one of the first magnetic field determinations for the low-mass protostellar core IRAS 16293-2422 at volume densities as high as 10(8-10) cm(-3). Our goal is to determine wether the collapsing regime of this source is controlled by magnetic fields or other factors such as turbulence. Methods. We used the Very Large Array (VLA) to carry out spectropolarimetric observations of the 22 GHz Zeeman emission from H2O masers. From the Stokes V line profile, we are then able to estimate the magnetic field strength in the dense regions around the protostar. Results. A blend of at least three maser features can be inferred from our relatively high spatial resolution data set (similar to 0.1 ''), which is reproduced as a clear non-Gaussian line profile. The emission is very stable in terms of polarization fraction and position angle across the channels. The maser spots are aligned with some components of the complex outflow configuration of IRAS 16293-2422, and are excited in zones of compressed gas produced by shocks. The post-shock particle density is in the range of 1-3 x 10(9) cm(-3), consistent with typical water-maser pumping densities. Zeeman emission is produced by a very strong line-of-sight magnetic field (B similar to 113 mG). Conclusions. The magnetic field pressure derived from our data is comparable to the ram pressure of the outflow dynamics. This indicates that the magnetic field is energetically important to the dynamical evolution of IRAS 16293-2422.
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| 457. |
- Alves, Guido, et al.
(författare)
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Cerebrospinal fluid amyloid-β and phenotypic heterogeneity in de novo Parkinson's disease.
- 2013
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Ingår i: Journal of neurology, neurosurgery, and psychiatry. - : BMJ. - 1468-330X .- 0022-3050. ; 84:5, s. 537-43
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Tidskriftsartikel (refereegranskat)abstract
- In Parkinson's disease (PD), the motor presentation characterised by postural instability/gait difficulties (PIGD) heralds accelerated motor, functional and cognitive decline, as compared with the more benign tremor-dominant (TD) variant. This makes the PIGD complex an attractive target for the discovery of prognostic biomarkers in PD.
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| 458. |
- Alves, G., et al.
(författare)
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CSF A beta(42) predicts early-onset dementia in Parkinson disease
- 2014
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Ingår i: Neurology. - : Ovid Technologies (Wolters Kluwer Health). - 0028-3878 .- 1526-632X. ; 82:20, s. 1784-1790
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Tidskriftsartikel (refereegranskat)abstract
- Objective:To test in vivo the proposal from clinicopathologic studies that -amyloid (A) pathology shortens the time to dementia in Parkinson disease (PD), and to explore the utility of CSF A and related measures as early prognostic biomarkers of dementia in an incident PD cohort.Methods:We assessed a population-based incident cohort of 104 patients with PD who underwent lumbar puncture at diagnosis. We analyzed CSF concentrations of A42, A40, and A38 using a multiplexed immunoassay with electrochemiluminescence (ECL) detection and levels of A42, total tau, and phosphorylated tau using ELISA. Patients were followed prospectively for 5 years. Dementia was diagnosed according to published criteria.Results:CSF levels of A42 were significantly decreased in patients who developed dementia (n = 20, 19.2%) compared to those who did not (n = 84, 80.8%), as measured by ECL (-33%, p = 0.006) as well as ELISA (-36%, p < 0.001). No differences were observed for other markers. Low A42 values predicted a substantially increased risk for subsequent dementia at high sensitivity (85%), with hazard ratios of 9.9 (95% confidence interval 2.3-43.5, p = 0.002) for A42(ECL) <376 pg/mL and 7.6 (2.2-26.4, p = 0.001) for A42(ELISA) <443 pg/mL, after adjustment for baseline age and PD-mild cognitive impairment (MCI) status. A42 reductions tended to precede the onset of PD-MCI that progressed to dementia.Conclusions:These in vivo data support the role of A pathology in the etiology and highlight the potential utility of CSF A42 as an early prognostic biomarker of dementia associated with PD.
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| 459. |
- Alves, Guido, et al.
(författare)
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CSF Aβ42 predicts early-onset dementia in Parkinson disease.
- 2014
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Ingår i: Neurology. - 1526-632X. ; 82:20, s. 1784-90
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Tidskriftsartikel (refereegranskat)abstract
- To test in vivo the proposal from clinicopathologic studies that β-amyloid (Aβ) pathology shortens the time to dementia in Parkinson disease (PD), and to explore the utility of CSF Aβ and related measures as early prognostic biomarkers of dementia in an incident PD cohort.
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| 460. |
- Alves, G.R., et al.
(författare)
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Using VISIR in a large undergraduate course : Preliminary assessment results
- 2011
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Konferensbidrag (refereegranskat)abstract
- The use of remote labs in undergraduate courses has been reported in literature several times since the mid 90's. Nevertheless, very few articles present results about the learning gains obtained by students using them, especially with a large number of students, thus suggesting a lack of data concerning their pedagogical effectiveness. This paper addresses such a gap by presenting some preliminary results concerning the use of a remote laboratory, known as VISIR, in a large undergraduate course on Applied Physics, with over 500 students enrolled.
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