Current Star Formation in Post-Starburst Galaxies?

Radio continuum observations are a probe of star formation in galaxies, and are unaffected by dust extinction. Observations of the distant rich cluster Cl 0939+4713 have detected radio galaxies classified as post-starburst (``k+a'') on the basis of their optical spectra, and presumably this situation arises from heavily dust-obscured star formation (Smail et al. 1999). We present the results of a radio continuum survey of post-starburst galaxies identified from the Las Campanas Redshift Survey by Zabludoff et al. (1996). This sample was selected using very stringent criteria, and therefore provides an estimate on the incidence of potential star formation in galaxies whose optical spectra exhibit the strongest post-starburst features. We detected two of fifteen such galaxies at radio luminosities consistent with moderate levels of star formation. This result underscores the potential importance of dust extinction when investigating star formation in galaxies.Comment: Replaced with corrected version of Table

Impact and promise of NASA aeropropulsion technology

The aeropropulsion industry in the U.S. has established an enviable record of leading the world in aeropropulsion for commercial and military aircraft. NASA's aeropropulsion program (primarily conducted through the Lewis Research Center) has significantly contributed to that success through research and technology advances and technology demonstration. Some past NASA contributions to engines in current aircraft are reviewed, and technologies emerging from current research programs for the aircraft of the 1990's are described. Finally, current program thrusts toward improving propulsion systems in the 2000's for subsonic commercial aircraft and higher speed aircraft such as the High-Speed Civil Transport and the National Aerospace Plane are discussed

A cost function for similarity-based hierarchical clustering

The development of algorithms for hierarchical clustering has been hampered by a shortage of precise objective functions. To help address this situation, we introduce a simple cost function on hierarchies over a set of points, given pairwise similarities between those points. We show that this criterion behaves sensibly in canonical instances and that it admits a top-down construction procedure with a provably good approximation ratio

The Highest Price Ever: The Great NYSE Seat Sale of 1928-1929 and Capacity Constraints

A surge in orders during the stock market boom of the late 1920s collided against the constraint created by the fixed number of brokers on the New York Stock Exchange. Estimates of the determinants of individual stock bid-ask spreads from panel data reveal that spreads jumped when volume spiked, confirming contemporary observers complaints that there were insufficient counterparties. When the position of the NYSE as the dominant exchange became threatened, the management of the exchange proposed a 25 percent increase in the number of seats in February 1929 by issuing a quarter-seat dividend to all members. While such a "stock split" would be expected to leave the aggregate value of the NYSE unchanged, an event study reveals that its value rose in anticipation of increased efficiency. These expectations were justified as bid-ask spreads became less sensitive to peak volume days after the increase in seats.

Prediction of forces and moments for hypersonic flight vehicle control effectors

This research project includes three distinct phases. For completeness, all three phases of the work are briefly described in this report. The goal was to develop methods of predicting flight control forces and moments for hypersonic vehicles which could be used in a preliminary design environment. The first phase included a preliminary assessment of subsonic/supersonic panel methods and hypersonic local flow inclination methods for such predictions. While these findings clearly indicated the usefulness of such methods for conceptual design activities, deficiencies exist in some areas. Thus, a second phase of research was conducted in which a better understanding was sought for the reasons behind the successes and failures of the methods considered, particularly for the cases at hypersonic Mach numbers. This second phase involved using computational fluid dynamics methods to examine the flow fields in detail. Through these detailed predictions, the deficiencies in the simple surface inclination methods were determined. In the third phase of this work, an improvement to the surface inclination methods was developed. This used a novel method for including viscous effects by modifying the geometry to include the viscous/shock layer

Hadron Masses and Screening from AdS Wilson Loops

We show that in strongly coupled N=4 SYM the binding energy of a heavy and a light quark is independent of the strength of the coupling constant. As a consequence we are able to show that in the presence of light quarks the analog of the QCD string can snap and color charges are screened. The resulting neutral mesons interact with each other only via pion exchange and we estimate the massesComment: 4 pages, revte

Telluric correction in the near-infrared: Standard star or synthetic transmission?

Context. The atmospheric absorption of the Earth is an important limiting factor for ground-based spectroscopic observations and the near-infrared and infrared regions are the most affected. Several software packages that produce a synthetic atmospheric transmission spectrum have been developed to correct for the telluric absorption; these are Molecfit, TelFit, and TAPAS. Aims. Our goal is to compare the correction achieved using these three telluric correction packages and the division by a telluric standard star. We want to evaluate the best method to correct near-infrared high-resolution spectra as well as the limitations of each software package and methodology. Methods. We applied the telluric correction methods to CRIRES archival data taken in the J and K bands. We explored how the achieved correction level varies depending on the atmospheric T-P profile used in the modelling, the depth of the atmospheric lines, and the molecules creating the absorption. Results. We found that the Molecfit and TelFit corrections lead to smaller residuals for the water lines. The standard star method corrects best the oxygen lines. The Molecfit package and the standard star method corrections result in global offsets always below 0.5% for all lines; the offset is similar with TelFit and TAPAS for the H2O lines and around 1% for the O2 lines. All methods and software packages result in a scatter between 3% and 7% inside the telluric lines. The use of a tailored atmospheric profile for the observatory leads to a scatter two times smaller, and the correction level improves with lower values of precipitable water vapour. Conclusions. The synthetic transmission methods lead to an improved correction compared to the standard star method for the water lines in the J band with no loss of telescope time, but the oxygen lines were better corrected by the standard star method.Comment: 18 pages, 13 figures, Accepted to A&

Energy efficiency of the rowing oar from catch to square-off

The mechanical efficiency of a rowing oar during the drive phrase may be defined as that proportion of the energy put into the oar by the rower which is "usefully" dissipated in overcoming hull and aerodynamic drag as the boat is propelled forwards. Ignoring friction in the oar gate/pivot, the remaining energy is "uselessly" dissipated by the blade as it shifts and churns water. As an example of energy analysis of propulsion systems, the energy efficiency for a slipping and a non-slipping car wheel is derived. The same method applied to the oar, shows that the efficiency of the oar is inextricably related to the direction of the water reaction force on the blade. If, as is usually assumed, the force is normal to the oar-shaft direction, the efficiency of the oar can be expressed as V sin(A)/(omega l), where V is the hull speed through the water, omega is the rotational speed of the oar, l is the distance from the gate to the centre of force on the blade, and A is the angle of the oar-shaft to the boat forward direction. We consider the efficiency of the oar from catch to square-off, using data gathered from an elite eight rowing at the Australian Institute of Sport. We show that, except for a degree or two of oar-sweep at the catch, when the force is negligible, the efficiency is greatest towards square-off, where a greater portion of the blade force is directed forward, which agrees with the results of Affeld et al. (Int. J. Sports Medicine, 14:S39-S41, 1993). Correlations of force profile shape with average efficiency show that a later application of the maximum force, nearer square-off, is generally more efficient than an earlier application. However, since the oar efficiency increases with boat speed, less efficient oars, for which the maximum force is applied near the catch, cause a greater increase of the boat speed early in the stroke, and this tends to enhance the efficiency of all the oars later in the stroke

Measuring gravitational lens time delays using low-resolution radio monitoring observations

Obtaining lensing time delay measurements requires long-term monitoring campaigns with a high enough resolution (< 1 arcsec) to separate the multiple images. In the radio, a limited number of high-resolution interferometer arrays make these observations difficult to schedule. To overcome this problem, we propose a technique for measuring gravitational time delays which relies on monitoring the total flux density with low-resolution but high-sensitivity radio telescopes to follow the variation of the brighter image. This is then used to trigger high-resolution observations in optimal numbers which then reveal the variation in the fainter image. We present simulations to assess the efficiency of this method together with a pilot project observing radio lens systems with the Westerbork Synthesis Radio Telescope (WSRT) to trigger Very Large Array (VLA) observations. This new method is promising for measuring time delays because it uses relatively small amounts of time on high-resolution telescopes. This will be important because instruments that have high sensitivity but limited resolution, together with an optimum usage of followup high-resolution observations from appropriate radio telescopes may in the future be useful for gravitational lensing time delay measurements by means of this new method.Comment: 10 pages, 7 figures, accepted by MNRA