Catalina Alvarez | Universidad Central de Venezuela (original) (raw)
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Papers by Catalina Alvarez
Astronomy & Astrophysics, 2004
We use a Monte Carlo code to generate synthetic near-IR reflection nebulae that resemble those (n... more We use a Monte Carlo code to generate synthetic near-IR reflection nebulae that resemble those (normally associated with a bipolar outflow cavity) seen towards massive young stellar objects (YSOs). The 2D axi-symmetric calculations use an analytic expression for a flattened infalling rotating envelope with a bipolar cavity representing an outflow. We are interested in which aspects of the circumstellar density distribution can be constrained by observations of these reflection nebulae. We therefore keeep the line of sight optical depth constant in the model grid, as this is often constrained independently by observations. It is found that envelopes with density distributions corresponding to mass infall rates of ∼ 10 −4 M ⊙ yr −1 (for an envelope radius of 4700 AU) seen at an inclination angle of ∼45 • approximately reproduce the morphology and extension of the sub-arcsecond nebulae observed in massive YSOs. Based on the flux ratio between the approaching and receding lobe of the nebula, we can constrain the system inclination angle. The cavity opening angle is well constrained from the nebula opening angle. Our simulations indicate that to constrain the outflow cavity shape and the degree of flattening in the envelope, near-IR imaging with higher resolution and dynamic range than speckle imaging in 4m-class telescopes is needed. The radiative transfer code is also used to simulate the near-IR sub-arcsecond nebula seen in Mon R2 IRS3. We find indications of a shallower opacity law in this massive YSO than in the interstellar medium, or possibly a sharp drop in the envelope density distribution at distances of ∼ 1000 AU from the illuminating source.
Astronomy & Astrophysics, 2004
We present near-IR speckle images of 21 massive Young Stellar Objects (YSOs) associated with outf... more We present near-IR speckle images of 21 massive Young Stellar Objects (YSOs) associated with outflows. The aim of this study is to search for sub-arcsecond reflection nebulae associated with the outflow cavity. We find that 6 of the massive YSOs show a conical nebula which can be interpreted in terms of reflected light from the dusty walls of the outflow cavity. In all cases, the small scale structures seen in our images are compared with outflow indicators found in the literature. No clear correlation is found between the presence of the reflection nebulosity and any property such as degree of embeddedness. We also note that 3 of the sources show close companions, one of them belonging also to the sample with conical nebula.
Inverse Problems, 2005
We study the following inverse problem: an inaccessible rigid body D is immersed in a viscous flu... more We study the following inverse problem: an inaccessible rigid body D is immersed in a viscous fluid, in such a way that D plays the role of an obstacle around which the fluid is flowing in a greater bounded domain , and we wish to determine D (i.e., its form and location) via boundary measurement on the boundary ∂ . Both for the stationary and the evolution problem, we show that under reasonable smoothness assumptions on and D, one can identify D via the measurement of the velocity of the fluid and the Cauchy forces on some part of the boundary ∂ . We also show that the dependence of the Cauchy forces on deformations of D is analytic, and give some stability results for the inverse problem.
Physical Review D, 1997
We consider the empirical validity of the equivalence principle for non-baryonic matter. Working ... more We consider the empirical validity of the equivalence principle for non-baryonic matter. Working in the context of the TH\epsilon\mu formalism, we evaluate the constraints experiments place on parameters associated with violation of the equivalence principle (EVPs) over as wide a sector of the standard model as possible. Specific examples include new parameter constraints which arise from torsion balance experiments, gravitational red shift, variation of the fine structure constant, time-dilation measurements, and matter/antimatter experiments. We find several new bounds on EVPs in the leptonic and kaon sectors.
Physical Review D, 1996
The Einstein Equivalence Principle has as one of its implications that the non-gravitational laws... more The Einstein Equivalence Principle has as one of its implications that the non-gravitational laws of physics are those of special relativity in any local freely-falling frame. We consider possible tests of this hypothesis for systems whose energies are due to radiative corrections, i.e. which arise purely as a consequence of quantum field theoretic loop effects. Specifically, we evaluate the Lamb shift transition (as given by the energy splitting between the 2S1/22S_{1/2}2S1/2 and 2P1/22P_{1/2}2P1/2 atomic states) within the context of violations of local position invariance and local Lorentz invariance, as described by the THepsilonmuT H \epsilon\muTHepsilonmu formalism. We compute the associated red shift and time dilation parameters, and discuss how (high-precision) measurements of these quantities could provide new information on the validity of the equivalence principle.
Physics Letters B, 1997
We consider the possibility of using measurements of anomalous magnetic moments of elementary par... more We consider the possibility of using measurements of anomalous magnetic moments of elementary particles as a possible test of the Einstein Equivalence Principle (EEP). For the class non-metric theories of gravity described by the T Hǫµ formalism we find several novel mechanisms for breaking the EEP, and discuss the possibilities of setting new empirical constraints on such effects. 1
We consider the possibility of using measurements of anomalous magnetic moments of elementary par... more We consider the possibility of using measurements of anomalous magnetic moments of elementary particles as a possible test of the Einstein Equivalence Principle (EEP). For the class non-metric theories of gravity described by the T Hǫµ formalism we find several novel mechanisms for breaking the EEP, and discuss the possibilities of setting new empirical constraints on such effects. 1
Physical Review D, 1996
We investigate the possibility of testing of the Einstein Equivalence Principle (EEP) using measu... more We investigate the possibility of testing of the Einstein Equivalence Principle (EEP) using measurements of anomalous magnetic moments of elementary particles. We compute the one loop correction for the g−2g-2g−2 anomaly within the class of non metric theories of gravity described by the \tmu formalism. We find several novel mechanisms for breaking the EEP whose origin is due purely to radiative corrections. We discuss the possibilities of setting new empirical constraints on these effects.
Dynamic Voltage Restorers (DVR) have been successfully applied for voltage dip mitigation in the ... more Dynamic Voltage Restorers (DVR) have been successfully applied for voltage dip mitigation in the last years. Especially in systems with nonlinear loads and wind turbine generation DVR units support the Power Quality enhancement. The reliability and quality of DVR operation depends mostly on fast and accurate voltage dip detection. Detection methodologies must be able to detect a voltage dip as fast as possible and be immune to other types of perturbations. In this paper we address the problem of voltage dip estimation using carefully selected advanced signal processing methods such as Fourier based algorithm, Kalman filtering and Wavelets. Additionally, the traditional and common technique of RMS value tracking has been mentioned. The algorithms have been tested under different conditions: voltage dip with phase jump, noise, frequency variations.
Astronomy & Astrophysics, 2004
We use a Monte Carlo code to generate synthetic near-IR reflection nebulae that resemble those (n... more We use a Monte Carlo code to generate synthetic near-IR reflection nebulae that resemble those (normally associated with a bipolar outflow cavity) seen towards massive young stellar objects (YSOs). The 2D axi-symmetric calculations use an analytic expression for a flattened infalling rotating envelope with a bipolar cavity representing an outflow. We are interested in which aspects of the circumstellar density distribution can be constrained by observations of these reflection nebulae. We therefore keeep the line of sight optical depth constant in the model grid, as this is often constrained independently by observations. It is found that envelopes with density distributions corresponding to mass infall rates of ∼ 10 −4 M ⊙ yr −1 (for an envelope radius of 4700 AU) seen at an inclination angle of ∼45 • approximately reproduce the morphology and extension of the sub-arcsecond nebulae observed in massive YSOs. Based on the flux ratio between the approaching and receding lobe of the nebula, we can constrain the system inclination angle. The cavity opening angle is well constrained from the nebula opening angle. Our simulations indicate that to constrain the outflow cavity shape and the degree of flattening in the envelope, near-IR imaging with higher resolution and dynamic range than speckle imaging in 4m-class telescopes is needed. The radiative transfer code is also used to simulate the near-IR sub-arcsecond nebula seen in Mon R2 IRS3. We find indications of a shallower opacity law in this massive YSO than in the interstellar medium, or possibly a sharp drop in the envelope density distribution at distances of ∼ 1000 AU from the illuminating source.
Astronomy & Astrophysics, 2004
We present near-IR speckle images of 21 massive Young Stellar Objects (YSOs) associated with outf... more We present near-IR speckle images of 21 massive Young Stellar Objects (YSOs) associated with outflows. The aim of this study is to search for sub-arcsecond reflection nebulae associated with the outflow cavity. We find that 6 of the massive YSOs show a conical nebula which can be interpreted in terms of reflected light from the dusty walls of the outflow cavity. In all cases, the small scale structures seen in our images are compared with outflow indicators found in the literature. No clear correlation is found between the presence of the reflection nebulosity and any property such as degree of embeddedness. We also note that 3 of the sources show close companions, one of them belonging also to the sample with conical nebula.
Inverse Problems, 2005
We study the following inverse problem: an inaccessible rigid body D is immersed in a viscous flu... more We study the following inverse problem: an inaccessible rigid body D is immersed in a viscous fluid, in such a way that D plays the role of an obstacle around which the fluid is flowing in a greater bounded domain , and we wish to determine D (i.e., its form and location) via boundary measurement on the boundary ∂ . Both for the stationary and the evolution problem, we show that under reasonable smoothness assumptions on and D, one can identify D via the measurement of the velocity of the fluid and the Cauchy forces on some part of the boundary ∂ . We also show that the dependence of the Cauchy forces on deformations of D is analytic, and give some stability results for the inverse problem.
Physical Review D, 1997
We consider the empirical validity of the equivalence principle for non-baryonic matter. Working ... more We consider the empirical validity of the equivalence principle for non-baryonic matter. Working in the context of the TH\epsilon\mu formalism, we evaluate the constraints experiments place on parameters associated with violation of the equivalence principle (EVPs) over as wide a sector of the standard model as possible. Specific examples include new parameter constraints which arise from torsion balance experiments, gravitational red shift, variation of the fine structure constant, time-dilation measurements, and matter/antimatter experiments. We find several new bounds on EVPs in the leptonic and kaon sectors.
Physical Review D, 1996
The Einstein Equivalence Principle has as one of its implications that the non-gravitational laws... more The Einstein Equivalence Principle has as one of its implications that the non-gravitational laws of physics are those of special relativity in any local freely-falling frame. We consider possible tests of this hypothesis for systems whose energies are due to radiative corrections, i.e. which arise purely as a consequence of quantum field theoretic loop effects. Specifically, we evaluate the Lamb shift transition (as given by the energy splitting between the 2S1/22S_{1/2}2S1/2 and 2P1/22P_{1/2}2P1/2 atomic states) within the context of violations of local position invariance and local Lorentz invariance, as described by the THepsilonmuT H \epsilon\muTHepsilonmu formalism. We compute the associated red shift and time dilation parameters, and discuss how (high-precision) measurements of these quantities could provide new information on the validity of the equivalence principle.
Physics Letters B, 1997
We consider the possibility of using measurements of anomalous magnetic moments of elementary par... more We consider the possibility of using measurements of anomalous magnetic moments of elementary particles as a possible test of the Einstein Equivalence Principle (EEP). For the class non-metric theories of gravity described by the T Hǫµ formalism we find several novel mechanisms for breaking the EEP, and discuss the possibilities of setting new empirical constraints on such effects. 1
We consider the possibility of using measurements of anomalous magnetic moments of elementary par... more We consider the possibility of using measurements of anomalous magnetic moments of elementary particles as a possible test of the Einstein Equivalence Principle (EEP). For the class non-metric theories of gravity described by the T Hǫµ formalism we find several novel mechanisms for breaking the EEP, and discuss the possibilities of setting new empirical constraints on such effects. 1
Physical Review D, 1996
We investigate the possibility of testing of the Einstein Equivalence Principle (EEP) using measu... more We investigate the possibility of testing of the Einstein Equivalence Principle (EEP) using measurements of anomalous magnetic moments of elementary particles. We compute the one loop correction for the g−2g-2g−2 anomaly within the class of non metric theories of gravity described by the \tmu formalism. We find several novel mechanisms for breaking the EEP whose origin is due purely to radiative corrections. We discuss the possibilities of setting new empirical constraints on these effects.
Dynamic Voltage Restorers (DVR) have been successfully applied for voltage dip mitigation in the ... more Dynamic Voltage Restorers (DVR) have been successfully applied for voltage dip mitigation in the last years. Especially in systems with nonlinear loads and wind turbine generation DVR units support the Power Quality enhancement. The reliability and quality of DVR operation depends mostly on fast and accurate voltage dip detection. Detection methodologies must be able to detect a voltage dip as fast as possible and be immune to other types of perturbations. In this paper we address the problem of voltage dip estimation using carefully selected advanced signal processing methods such as Fourier based algorithm, Kalman filtering and Wavelets. Additionally, the traditional and common technique of RMS value tracking has been mentioned. The algorithms have been tested under different conditions: voltage dip with phase jump, noise, frequency variations.