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Andres Jordan - One of the best experts on this subject based on the ideXlab platform.

  • the acs virgo cluster survey x half light radii of globular clusters in early type galaxies environmental dependencies and a standard ruler for Distance Estimation
    The Astrophysical Journal, 2005
    Co-Authors: Andres Jordan, Patrick Cote, John P Blakeslee, Laura Ferrarese, Dean E Mclaughlin, Eric W Peng, John L Tonry
    Abstract:

    We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric Distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of rh with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average rh depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed by Jordan. We discuss these findings in light of two simple pictures for the origin of the rh of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius, and underlying surface brightness, we show that the average GC half-light radii rh can be successfully used as a standard ruler for Distance Estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this Distance estimator with future observing facilities. We find rh = 2.7 ± 0.35 pc for GCs with (g - z) = 1.2 mag in a galaxy with color (g - z)gal = 1.5 mag and at an underlying surface z-band brightness of μz = 21 mag arcsec-2. Using this technique, we place an upper limit of 3.4 Mpc on the 1 σ line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the rh distribution for our sample galaxies and provide an analytic expression that successfully describes this distribution.

  • the acs virgo cluster survey x half light radii of globular clusters in early type galaxies environmental dependencies and a standard ruler for Distance Estimation
    arXiv: Astrophysics, 2005
    Co-Authors: Andres Jordan, Patrick Cote, John P Blakeslee, Laura Ferrarese, Dean E Mclaughlin, S Mei, Eric W Peng
    Abstract:

    We have measured half-light radii, r_h, for globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured r_h on both the properties of the GCs themselves and their host galaxies reveals that the average r_h increases with increasing galactocentric Distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average r_h decreases with the host galaxy color. We also show that there is no evidence for a variation of r_h with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average r_h depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed in Jordan (2004). We discuss these findings in light of two simple pictures for the origin of the r_h of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies found we show that the average GC half-light radii can be successfully used as a standard ruler for Distance Estimation. We outline the methodology, and provide a calibration for its use. We find = 2.7 +- 0.35 pc for GCs with (g-z)=1.2 mag in a galaxy with color (g-z)_{gal}=1.5 mag and at an underlying surface z-band brightness of mu_z = 21 mag arcsec^{-2}. Using this technique, we place an upper limit of 3.4 Mpc on the 1-sigma line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the r_h distribution for our sample galaxies and provide an analytic expression which successfully describes this distribution. (Abridged)

Andrew G. Ag Dempster - One of the best experts on this subject based on the ideXlab platform.

  • Dynamic Path Loss Exponent and Distance Estimation in a Vehicular Network Using Doppler Effect and Received Signal Strength
    2010 IEEE 72nd Vehicular Technology Conference - Fall, 2010
    Co-Authors: Nima Alam, Asghar Tabatabaie Balaie, Andrew G. Ag Dempster
    Abstract:

    Global Navigation Satellite Systems (GNSS) can be used for navigation purposes in vehicular environments. However, the limited accuracy of GNSS makes it unsuitable for applications such as vehicle collision avoidance. Improving the positioning accuracy in vehicular networks, Cooperative Positioning (CP) algorithms have emerged. CP algorithms are based on data communication among vehicles and Estimation of the Distance between the nodes of the network. Among the variety of radio ranging techniques, Received Signal Strength (RSS) is very popular due to its simplicity and lower cost compared to other methods like Time of Arrival (TOA), and Time Difference of Arrival (TDOA). The main drawback of RSS-based ranging is its inaccuracy, which mostly originates from the uncertainty of the path loss exponent. Without knowing the environment path loss exponent, which is a time-varying parameter in the mobile networks, RSS is effectively useless for Distance Estimation. There are many approaches and techniques proposed in the literature for dynamic Estimation of the path loss exponent within a certain environment. Most of these methods are not functional for mobile applications or their efficiency decreases dramatically with increasing mobility of the nodes. In this paper, we propose a method for dynamic Estimation of the path loss exponent and Distance based on the Doppler Effect and RSS. Since this method is fundamentally based on the Doppler Effect, it can be implemented within networks with mobile nodes. The higher the mobility of the nodes, the better performance of the proposed technique. This contribution is important because vehicles will be equipped with Dedicated Short Range Communication (DSRC) in the near future.

Robert Schober - One of the best experts on this subject based on the ideXlab platform.

  • bounds on Distance Estimation via diffusive molecular communication
    Global Communications Conference, 2014
    Co-Authors: Adam Noel, Karen C. Cheung, Robert Schober
    Abstract:

    This paper studies Distance Estimation for diffusive molecular communication. The strength of the channel impulse response generally decreases with Distance, so it is measured to estimate the Distance. The Cramer-Rao lower bound on the variance of the Distance Estimation error is derived. The lower bound is derived for a physically unbounded environment with molecule degradation and steady uniform flow. The maximum likelihood Distance estimator is derived and its accuracy is shown via simulation to perform very close to the Cramer-Rao lower bound. An existing protocol is shown to be equivalent to the maximum likelihood Distance estimator if only one observation is made. Simulation results also show the accuracy of existing protocols with respect to the Cramer-Rao lower bound.

  • Bounds on Distance Estimation via Diffusive Molecular Communication
    2014 IEEE Global Communications Conference, 2014
    Co-Authors: Adam Noel, Karen C. Cheung, Robert Schober
    Abstract:

    This paper studies Distance Estimation for diffusive molecular communication. The Cramer-Rao lower bound on the variance of the Distance Estimation error is derived. The lower bound is derived for a physically unbounded environment with molecule degradation and steady uniform flow. The maximum likelihood Distance estimator is derived and its accuracy is shown via simulation to perform very close to the Cramer-Rao lower bound. An existing protocol is shown to be equivalent to the maximum likelihood Distance estimator if only one observation is made. Simulation results also show the accuracy of existing protocols with respect to the Cramer-Rao lower bound.

Laura Ferrarese - One of the best experts on this subject based on the ideXlab platform.

  • the acs virgo cluster survey x half light radii of globular clusters in early type galaxies environmental dependencies and a standard ruler for Distance Estimation
    The Astrophysical Journal, 2005
    Co-Authors: Andres Jordan, Patrick Cote, John P Blakeslee, Laura Ferrarese, Dean E Mclaughlin, Eric W Peng, John L Tonry
    Abstract:

    We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric Distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of rh with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average rh depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed by Jordan. We discuss these findings in light of two simple pictures for the origin of the rh of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius, and underlying surface brightness, we show that the average GC half-light radii rh can be successfully used as a standard ruler for Distance Estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this Distance estimator with future observing facilities. We find rh = 2.7 ± 0.35 pc for GCs with (g - z) = 1.2 mag in a galaxy with color (g - z)gal = 1.5 mag and at an underlying surface z-band brightness of μz = 21 mag arcsec-2. Using this technique, we place an upper limit of 3.4 Mpc on the 1 σ line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the rh distribution for our sample galaxies and provide an analytic expression that successfully describes this distribution.

  • the acs virgo cluster survey x half light radii of globular clusters in early type galaxies environmental dependencies and a standard ruler for Distance Estimation
    arXiv: Astrophysics, 2005
    Co-Authors: Andres Jordan, Patrick Cote, John P Blakeslee, Laura Ferrarese, Dean E Mclaughlin, S Mei, Eric W Peng
    Abstract:

    We have measured half-light radii, r_h, for globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured r_h on both the properties of the GCs themselves and their host galaxies reveals that the average r_h increases with increasing galactocentric Distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average r_h decreases with the host galaxy color. We also show that there is no evidence for a variation of r_h with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average r_h depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed in Jordan (2004). We discuss these findings in light of two simple pictures for the origin of the r_h of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies found we show that the average GC half-light radii can be successfully used as a standard ruler for Distance Estimation. We outline the methodology, and provide a calibration for its use. We find = 2.7 +- 0.35 pc for GCs with (g-z)=1.2 mag in a galaxy with color (g-z)_{gal}=1.5 mag and at an underlying surface z-band brightness of mu_z = 21 mag arcsec^{-2}. Using this technique, we place an upper limit of 3.4 Mpc on the 1-sigma line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the r_h distribution for our sample galaxies and provide an analytic expression which successfully describes this distribution. (Abridged)

Patrick Cote - One of the best experts on this subject based on the ideXlab platform.

  • the acs virgo cluster survey x half light radii of globular clusters in early type galaxies environmental dependencies and a standard ruler for Distance Estimation
    The Astrophysical Journal, 2005
    Co-Authors: Andres Jordan, Patrick Cote, John P Blakeslee, Laura Ferrarese, Dean E Mclaughlin, Eric W Peng, John L Tonry
    Abstract:

    We have measured half-light radii, rh, for thousands of globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured half-light radii on both the properties of the GCs themselves and their host galaxies reveals that, in analogy with GCs in the Galaxy but in a milder fashion, the average half-light radius increases with increasing galactocentric Distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average half-light radius decreases with the host galaxy color. We also show that there is no evidence for a variation of rh with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average rh depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed by Jordan. We discuss these findings in light of two simple pictures for the origin of the rh of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies on galaxy color, galactocentric radius, and underlying surface brightness, we show that the average GC half-light radii rh can be successfully used as a standard ruler for Distance Estimation. We outline the methodology, provide a calibration for its use, and discuss the prospects for this Distance estimator with future observing facilities. We find rh = 2.7 ± 0.35 pc for GCs with (g - z) = 1.2 mag in a galaxy with color (g - z)gal = 1.5 mag and at an underlying surface z-band brightness of μz = 21 mag arcsec-2. Using this technique, we place an upper limit of 3.4 Mpc on the 1 σ line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the rh distribution for our sample galaxies and provide an analytic expression that successfully describes this distribution.

  • the acs virgo cluster survey x half light radii of globular clusters in early type galaxies environmental dependencies and a standard ruler for Distance Estimation
    arXiv: Astrophysics, 2005
    Co-Authors: Andres Jordan, Patrick Cote, John P Blakeslee, Laura Ferrarese, Dean E Mclaughlin, S Mei, Eric W Peng
    Abstract:

    We have measured half-light radii, r_h, for globular clusters (GCs) belonging to the 100 early-type galaxies observed in the ACS Virgo Cluster Survey and the elliptical galaxy NGC 4697. An analysis of the dependencies of the measured r_h on both the properties of the GCs themselves and their host galaxies reveals that the average r_h increases with increasing galactocentric Distance or, alternatively, with decreasing galaxy surface brightness. For the first time, we find that the average r_h decreases with the host galaxy color. We also show that there is no evidence for a variation of r_h with the luminosity of the GCs. Finally, we find in agreement with previous observations that the average r_h depends on the color of GCs, with red GCs being ~17% smaller than their blue counterparts. We show that this difference is probably a consequence of an intrinsic mechanism, rather than projection effects, and that it is in good agreement with the mechanism proposed in Jordan (2004). We discuss these findings in light of two simple pictures for the origin of the r_h of GCs and show that both lead to a behavior in rough agreement with the observations. After accounting for the dependencies found we show that the average GC half-light radii can be successfully used as a standard ruler for Distance Estimation. We outline the methodology, and provide a calibration for its use. We find = 2.7 +- 0.35 pc for GCs with (g-z)=1.2 mag in a galaxy with color (g-z)_{gal}=1.5 mag and at an underlying surface z-band brightness of mu_z = 21 mag arcsec^{-2}. Using this technique, we place an upper limit of 3.4 Mpc on the 1-sigma line-of-sight depth of the Virgo Cluster. Finally, we examine the form of the r_h distribution for our sample galaxies and provide an analytic expression which successfully describes this distribution. (Abridged)