The Phoenix survey: the pairing fraction of faint radio sources

The significance of tidal interactions in the evolution of the faint radio population (sub-mJy) is studied using a deep and homogeneous radio survey (1.4 GHz), covering an area of 3.14 deg$^2$ and complete to a flux density of 0.4 mJy. Optical photometric and spectroscopic data are also available for this sample. A statistical approach is employed to identify candidate physical associations between radio sources and optically selected `field' galaxies. We find an excess of close pairs around optically identified faint radio sources, albeit at a low significance level, implying that the pairing fraction of the sub-mJy radio sources is similar to that of `field' galaxies (at the same magnitude limit) but higher than that of local galaxies.Comment: 5 pages, 4 figures. Accepted for publication in MNRAS Letter

The stellar content of brightest cluster galaxies

We present near-infrared K-band spectroscopy of 21 elliptical or cD Brightest Cluster Galaxies (BCGs), for which we have measured the strength of the 2.293 micron CO stellar absorption feature. We find that the strength of this feature is remarkably uniform among these galaxies, with a smaller scatter in equivalent width than for the normal elliptical population in the field or clusters. The scatter for BCGs is 0.156 nm, compared with 0.240 nm for Coma cluster ellipticals, 0.337 nm for ellipticals from a variety of other clusters, and 0.422 nm for field ellipticals. We interpret this homogeneity as being due to a greater age, or more uniform history, of star formation in BCGs than in other ellipticals; only a small fraction of the scatter can be due to metallicity variations, even in the BCGs. Notwithstanding the small scatter, correlations are found between CO strength and various galaxy properties, including R-band absolute magnitude, which could improve the precision of these galaxies as distance indicators in measurements of cosmological parameters and velocity flows.Comment: 7 pages, 8 figures, accepted for publication by MNRA

Spectroscopic Constraints on the Stellar Population of Elliptical Galaxies in the Coma Cluster

Near-IR spectra for a sample of 31 elliptical galaxies in the Coma cluster are obtained. The galaxies are selected to be ellipticals (no lenticulars), with a large spatial distribution, covering both the core and outskirt of the cluster (ie. corresponding to regions with large density contrasts). Spectroscopic CO (2.3 micron) absorption indices, measuring contribution from intermediate-age red giant and supergiant stars to the near-IR light of the ellipticals, are then estimated. It is found that the strength of spectroscopic CO features in elliptical galaxies increases from the core (r 0.2 deg) of the Coma cluster. Using the Mg2 strengths, it is shown that the observed effect is not due to metallicity and is mostly caused by the presence of a younger population (giant and supergiant stars) in ellipticals in outskirts (low density region) of the cluster. Using the spectroscopic CO features, the origin of the scatter on the near-IR Fundamental Plane of elliptical galaxies is studied. Correcting this relation for contributions from the red giant and supergiant stars, the rms scatter reduces from 0.077dex to 0.073dex. Although measurable, the contribution from these intermediate-age stars to the scatter on the near-IR Fundamental Plane of ellipticals is only marginal. A relation is found between the CO and V-K colours of ellipticals with a slope 0.036 +/- 0.016. This is studied using stellar synthesis models.Comment: 17 pages, 7 figures, Accepted for publication in MNRAS Repoprt-no

Fairness in Multiuser Systems with Polymatroid Capacity Region

For a wide class of multi-user systems, a subset of capacity region which includes the corner points and the sum-capacity facet has a special structure known as polymatroid. Multiaccess channels with fixed input distributions and multiple-antenna broadcast channels are examples of such systems. Any interior point of the sum-capacity facet can be achieved by time-sharing among corner points or by an alternative method known as rate-splitting. The main purpose of this paper is to find a point on the sum-capacity facet which satisfies a notion of fairness among active users. This problem is addressed in two cases: (i) where the complexity of achieving interior points is not feasible, and (ii) where the complexity of achieving interior points is feasible. For the first case, the corner point for which the minimum rate of the active users is maximized (max-min corner point) is desired for signaling. A simple greedy algorithm is introduced to find the optimum max-min corner point. For the second case, the polymatroid properties are exploited to locate a rate-vector on the sum-capacity facet which is optimally fair in the sense that the minimum rate among all users is maximized (max-min rate). In the case that the rate of some users can not increase further (attain the max-min value), the algorithm recursively maximizes the minimum rate among the rest of the users. It is shown that the problems of deriving the time-sharing coefficients or rate-spitting scheme can be solved by decomposing the problem to some lower-dimensional subproblems. In addition, a fast algorithm to compute the time-sharing coefficients to attain a general point on the sum-capacity facet is proposed.Comment: Submitted To IEEE Transactions on Information Theory, June 200

Visualization Methods for Viability Studies of Inspection Modules for the Space Shuttle

An effective simulation of an object, process, or task must be similar to that object, process, or task. A simulation could consist of a physical device, a set of mathematical equations, a computer program, a person, or some combination of these. There are many reasons for the use of simulators. Although some of the reasons are unique to a specific situation, there are many general reasons and purposes for using simulators. Some are listed but not limited to (1) Safety, (2) Scarce resources, (3) Teaching/education, (4) Additional capabilities, (5) Flexibility and (6) Cost. Robot simulators are in use for all of these reasons. Virtual environments such as simulators will eliminate physical contact with humans and hence will increase the safety of work environment. Corporations with limited funding and resources may utilize simulators to accomplish their goals while saving manpower and money. A computer simulation is safer than working with a real robot. Robots are typically a scarce resource. Schools typically don t have a large number of robots, if any. Factories don t want the robots not performing useful work unless absolutely necessary. Robot simulators are useful in teaching robotics. A simulator gives a student hands-on experience, if only with a simulator. The simulator is more flexible. A user can quickly change the robot configuration, workcell, or even replace the robot with a different one altogether. In order to be useful, a robot simulator must create a model that accurately performs like the real robot. A powerful simulator is usually thought of as a combination of a CAD package with simulation capabilities. Computer Aided Design (CAD) techniques are used extensively by engineers in virtually all areas of engineering. Parts are designed interactively aided by the graphical display of both wireframe and more realistic shaded renderings. Once a part s dimensions have been specified to the CAD package, designers can view the part from any direction to examine how it will look and perform in relation to other parts. If changes are deemed necessary, the designer can easily make the changes and view the results graphically. However, a complex process of moving parts intended for operation in a complex environment can only be fully understood through the process of animated graphical simulation. A CAD package with simulation capabilities allows the designer to develop geometrical models of the process being designed, as well as the environment in which the process will be used, and then test the process in graphical animation much as the actual physical system would be run . By being able to operate the system of moving and stationary parts, the designer is able to see in simulation how the system will perform under a wide variety of conditions. If, for example, undesired collisions occur between parts of the system, design changes can be easily made without the expense or potential danger of testing the physical system

Evidence for the Evolution of Young Early-Type Galaxies in the GOODS/CDF-S Field

We have developed an efficient photometric technique for identifying young early-type galaxy candidates using a combination of photometric redshifts, spectral-type classification, and optical/near-infrared colors. Applying our technique to the GOODS HST/ACS and VLT/ISAAC data we have selected a complete and homogeneous sample of young elliptical candidates among early-type field galaxies. The distribution of structural parameters for these candidates shows that their selection, which is based on early spectral types, is fully consistent with early morphological types. We investigate the evolution of their luminosities and colors as a function of redshift and galaxy mass and find evidence for an increasing starburst mass fraction in these young early-type galaxy candidates at higher redshifts, which we interpret in terms of massive field galaxies experiencing more massive/intense starbursts at higher redshifts. Moreover, we find indications for a systematically larger young elliptical fraction among sub-L*/2 early-type galaxies compared to their brighter counterparts. The total fraction among the field early-type galaxies increases with redshift, irrespective of galaxy luminosity. Our results are most consistent with galaxy formation scenarios in which stars in massive early-type field galaxies are assembled earlier than in their low-mass counterparts.Comment: 11 pages, 10 figures, accepted for publication in A