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Search Results: 1 - 10 of 497040 matches for " M. F.;Kraus Jr. "
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Variable structure position control of an industrial robotic manipulator
Mendes, M. F.;Kraus Jr., W.;Pieri, E. R. de;
Journal of the Brazilian Society of Mechanical Sciences , 2002, DOI: 10.1590/S0100-73862002000300004
Abstract: the use of a robust position controller for a robotic manipulator moving in free space is presented. the aim is to implement in practice a controller that is robust to uncertainties in the model of the system, as well as being inexpensive from a computational point of view. variable structure theory provides the technique for the design of such controller. the design steps are presented, first from a theoretical perspective and then applied to the control of a two degree-of-freedom manipulator. simulation results that backed the implementation are presented, followed by the experiments conducted and the results that were obtained. the conclusion is that variable structure control is readily applicable to industrial robots for the robust control of positions.
Variable structure position control of an industrial robotic manipulator
Mendes M. F.,Kraus Jr. W.,Pieri E. R. de
Journal of the Brazilian Society of Mechanical Sciences , 2002,
Abstract: The use of a robust position controller for a robotic manipulator moving in free space is presented. The aim is to implement in practice a controller that is robust to uncertainties in the model of the system, as well as being inexpensive from a computational point of view. Variable structure theory provides the technique for the design of such controller. The design steps are presented, first from a theoretical perspective and then applied to the control of a two degree-of-freedom manipulator. Simulation results that backed the implementation are presented, followed by the experiments conducted and the results that were obtained. The conclusion is that variable structure control is readily applicable to industrial robots for the robust control of positions.
A new observational tracer for high-density disc-like structures around B[e] supergiants
A. Aret,M. Kraus,M. F. Muratore,M. Borges Fernandes
Physics , 2012, DOI: 10.1111/j.1365-2966.2012.20871.x
Abstract: The disc formation mechanism of B[e] supergiants is one of the puzzling phenomena in massive star evolution. Rapid stellar rotation seems to play an important role for the non-spherically symmetric mass-loss leading to a high-density disc or ring-like structure of neutral material around these massive and luminous objects. The radial density and temperature structure as well as the kinematics within this high-density material are, however, not well studied. Based on high-resolution optical spectra of a sample of B[e] supergiants in the Magellanic Clouds we especially searched for tracers of the kinematics within their discs. Besides the well-known [O I] lines, we discovered the [Ca II] {\lambda}{\lambda}7291, 7324 lines that can be used as a complementary set of disc tracers. We find that these lines originate from very high-density regions, located closer to the star than the [O I] {\lambda}5577 line-forming region. The line profiles of both the [O I] and the [Ca II] lines indicate that the discs or rings of high-density material are in Keplerian rotation. We estimate plausible ranges of disc inclination angles for the sample of B[e] supergiants and suggest that the star LHA 120-S 22 might have a spiral arm rather than a disc.
Addressing Parental Vaccine Concerns: Engagement, Balance, and Timing
Jason M. Glanz?,Courtney R. Kraus,Matthew F. Daley
PLOS Biology , 2015, DOI: 10.1371/journal.pbio.1002227
Abstract: The recent United States measles epidemic has sparked another contentious national discussion about childhood vaccination. A growing number of parents are expressing concerns about the safety of vaccines, often fueled by misinformation from the internet, books, and other nonmedical sources. Many of these concerned parents are choosing to refuse or delay childhood vaccines, placing their children and surrounding communities at risk for serious diseases that are nearly 100% preventable with vaccination. Between 10% and 15% of parents are asking physicians to space out the timing of vaccines, which often poses an ethical dilemma for physicians. This trend reflects a tension between personal liberty and public health, as parents fight to control the decisions that affect the health of their children and public health officials strive to maintain high immunization rates to prevent outbreaks of vaccine-preventable diseases. Interventions to address this emerging public health issue are needed. We describe a framework by which web-based interventions can be used to help parents make evidence-based decisions about childhood vaccinations.
Many particle theory for luminescence in quantum wells
Pereira Jr., M.F.;
Brazilian Journal of Physics , 2002, DOI: 10.1590/S0103-97332002000500020
Abstract: a green's function theory is applied to the description of luminescence and absorption spectra of low dimensional semiconductors. progress in the numerical solution of the bethe salpeter equation for coupled band quantum wells with a t-matrix structure for the polarisation function and carrier-carrier dephasing is given within an approach that satisfy the kubo-martin-schwinger sum rule and eliminates typical artifacts in computed optical spectra.
Many particle theory for luminescence in quantum wells
Pereira Jr. M.F.
Brazilian Journal of Physics , 2002,
Abstract: A Green's function theory is applied to the description of luminescence and absorption spectra of low dimensional semiconductors. Progress in the numerical solution of the Bethe Salpeter equation for coupled band quantum wells with a T-matrix structure for the polarisation function and carrier-carrier dephasing is given within an approach that satisfy the Kubo-Martin-Schwinger sum rule and eliminates typical artifacts in computed optical spectra.
Probing the ejecta of evolved massive stars in transition: A VLT/SINFONI K-band survey
M. E. Oksala,M. Kraus,L. S. Cidale,M. F. Muratore,M. Borges Fernandes
Physics , 2013, DOI: 10.1051/0004-6361/201321568
Abstract: Massive evolved stars in transition phases, such as Luminous Blue Variables (LBVs), B[e] Supergiants (B[e]SGs), and Yellow Hypergiants (YHGs), are not well understood, and yet crucial steps in determining accurate stellar and galactic evolution models. The circumstellar environments of these stars reveal their mass-loss history, identifying clues to both their individual evolutionary status and the connection between objects of different phases. Here we present a survey of 25 such evolved massive stars (16 B[e]SGs, 6 LBVs, 2 YHGs, and 1 Peculiar Oe star), observed in the K-band with the Spectrograph for INtegral Field Observation in the Near-Infrared (SINFONI; R = 4500) on the ESO VLT UT4 8 m telescope. The sample can be split into two categories based on spectral morphology: one group includes all of the B[e]SGs, the Peculiar Oe star, and two of the LBVs, while the other includes the YHGs and the rest of the LBVs. The difference in LBV spectral appearance is due to some objects being in a quiescent phase and some objects being in an active or outburst phase. CO emission features are found in 13 of our targets, with first time detections for MWC 137, LHA 120-S 35, and LHA 115-S 65. From model fits to the CO band heads, the emitting regions appear to be detached from the stellar surface. Each star with ^12CO features also shows ^13CO emission, signaling an evolved nature. Based on the level of ^13C enrichment, we conclude that many of the B[e]SGs are likely in a pre-Red Supergiant phase of their evolution. There appears to be a lower luminosity limit of log L/L_solar = 5.0 below which CO is not detected. The lack of CO features in several high luminosity B[e]SGs and variability in others suggests that they may in fact be LBV candidates, strengthening the connection between these two very similar transition phases.
Parallel MRI at microtesla fields
V. S. Zotev,P. L. Volegov,A. N. Matlashov,M. A. Espy,J. C. Mosher,R. H. Kraus Jr
Physics , 2007, DOI: 10.1016/j.jmr.2008.02.015
Abstract: Parallel imaging techniques have been widely used in high-field magnetic resonance imaging (MRI). Multiple receiver coils have been shown to improve image quality and allow accelerated image acquisition. Magnetic resonance imaging at ultra-low fields (ULF MRI) is a new imaging approach that uses SQUID (superconducting quantum interference device) sensors to measure the spatially encoded precession of pre-polarized nuclear spin populations at microtesla-range measurement fields. In this work, parallel imaging at microtesla fields is systematically studied for the first time. A seven-channel SQUID system, designed for both ULF MRI and magnetoencephalography (MEG), is used to acquire 3D images of a human hand, as well as 2D images of a large water phantom. The imaging is performed at 46 microtesla measurement field with pre-polarization at 40 mT. It is shown how the use of seven channels increases imaging field of view and improves signal-to-noise ratio for the hand images. A simple procedure for approximate correction of concomitant gradient artifacts is described. Noise propagation is analyzed experimentally, and the main source of correlated noise is identified. Accelerated imaging based on one-dimensional undersampling and 1D SENSE (sensitivity encoding) image reconstruction is studied in the case of the 2D phantom. Actual 3-fold imaging acceleration in comparison to single-average fully encoded Fourier imaging is demonstrated. These results show that parallel imaging methods are efficient in ULF MRI, and that imaging performance of SQUID-based instruments improves substantially as the number of channels is increased.
SQUID-based instrumentation for ultra-low-field MRI
V. S. Zotev,A. N. Matlashov,P. L. Volegov,A. V. Urbaitis,M. A. Espy,R. H. Kraus Jr
Physics , 2007, DOI: 10.1088/0953-2048/20/11/S13
Abstract: Magnetic resonance imaging at ultra-low fields (ULF MRI) is a promising new imaging method that uses SQUID sensors to measure the spatially encoded precession of pre-polarized nuclear spin populations at a microtesla-range measurement field. In this work, a seven-channel SQUID system designed for simultaneous 3D ULF MRI and magnetoencephalography (MEG) is described. The system includes seven second-order SQUID gradiometers, characterized by magnetic field resolutions of 1.2 - 2.8 fT/rtHz. It is also equipped with five sets of coils for 3D Fourier imaging with pre-polarization. Essential technical details of the design are discussed. The system's ULF MRI performance is demonstrated by multi-channel 3D images of a preserved sheep brain acquired at 46 microtesla measurement field with pre-polarization at 40 mT. The imaging resolution is 2.5 mm x 2.5 mm x 5 mm. The ULF MRI images are compared to images of the same brain acquired using conventional high-field MRI. Different ways to improve imaging SNR are discussed.
Effelsberg 100-m polarimetric observations of a sample of Compact Steep-Spectrum sources
F. Mantovani,K. -H. Mack,F. M. Montenegro-Montes,A. Rossetti,A. Kraus
Physics , 2009, DOI: 10.1051/0004-6361/200911815
Abstract: We completed observations with the Effelsberg 100-m radio telescope to measure the polarised emission from a complete sample of Compact Steep-Spectrum sources. We observed the sources at four different frequencies. We complemented these measurements with polarisation parameters at 1.4 GHz derived from the NVSS. Previous single dish measurements were taken from the catalogue of Tabara and Inoue. The depolarisation index DP was computed for four pairs of frequencies. A drop in the fractional polarisation appeared in the radio emission when observing at frequencies below about 2 GHz. Rotation measures were derived for about 25% of the sources in the sample. The values range from about -20 rad/m**2} found for 3C138 to 3900 rad/m**2 in 3C119. In all cases, the lambda**2 law is closely followed. The presence of a foreground screen as predicted by the Tribble model or with ``partial coverage'' as defined by ourselves can explain the polarimetric behaviour of the CSS sources detected in polarisation by the present observations. Indication of repolarisation at lower frequencies was found for some sources. A case of possible variability in the fractional polarisation is also suggested. The most unexpected result was found for the distribution of the fractional polarisations versus the linear sizes of the sources. Our results appear to disagree with the findings of Cotton and collaborators and Fanti and collaborators for the B3-VLA sample of CSS sources, the so-called ``Cotton effect''. This apparent contradiction may, however, be caused by the large contamination of the sample by quasars with respect to the B3-VLA.
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