Auto Tracking Antenna Platform

The present invention is an auto tracking antenna platform upon which multiple antenna elements can be mounted to track a common moving object. The antenna tracking platform generally comprises a bottom pedestal enclosing a rotary azimuth actuator for controlled-rotary motion about the single vertical (z) axis, and an upper multi-tier framework housing a horizontal antenna-mounting beam pivotally supported for rotation about a horizontal (x) axis, and a drive assembly for direct-drive rotation of the antenna-mounting bar. Antenna elements are mounted along the horizontal mounting bar and the feeds routed through the azimuth actuator. This enables the use of fiber optic rotary joints or slip rings to pass data and video, instead of RF (waveguide) rotary joints which are required to pass high power RF signals

Velocity Dispersion of Dissolving OB Associations Affected by External Pressure of Formation Environment

This paper presents a possible way to understand dissolution of OB associations (or groups). Assuming rapid escape of parental cloud gas from associations, we show that the shadow of the formation environment for associations can be partially imprinted on the velocity dispersion at their dissolution. This conclusion is not surprising as long as associations are formed in a multiphase interstellar medium, because the external pressure should suppress expansion caused by the internal motion of the parental clouds. Our model predicts a few km s$^{-1}$ as the internal velocity dispersion. Observationally, the internal velocity dispersion is $\sim 1$ km s$^{-1}$ which is smaller than our prediction. This suggests that the dissipation of internal energy happens before the formation of OB associations.Comment: 6 pages. AJ accepte

The Observations Of The X-Ray Source Hz Herculis-Hercules X-1

NASAESASRCAstronom

Fifty Years of IMF Variation: The Intermediate-Mass Stars

I track the history of star count estimates of the Milky Way field star and open cluster IMFs, concentrating on the neglected mass range from 1 to 15 M${_\odot}$. The prevalent belief in a universal IMF appears to be without basis for this mass range. Two recent estimates of the field star IMF using different methods and samples give values of the average logarithmic slope $\Gamma$ between -1.7 and -2.1 in the mass range 1.1 to 4 M${_\odot}$. Two older estimates between 2 and 15 M${_\odot}$ disagree severely; the field IMF in this range is essentially unknown from star counts. Variations in $\Gamma$ among open cluster IMFs in this mass range have not decreased despite numerous detailed studies, even for studies using homogeneous data and reduction procedures and including only clusters with a significant mass range. These cluster variations \textit{might} be due to the combined effects of sampling, systematic errors, stellar evolution uncertainties, dynamical evolution, and unresolved binaries. If so, then the cluster data are consistent with a universal IMF, but are also consistent with sizeable variations. The cluster data do not allow an estimate of an average IMF or $\Gamma$ because the average depends on the choice of weighting procedure and other effects. If the spread in cluster IMFs is in excess of the effects listed above, real IMF variations must occur that do not depend much on physical conditions explored so far. The complexity of the star formation process seen in observations and simulations suggests that large realization-to-realization differences might be expected, in which case an individual cluster IMF would be in part the product of evolutionary contingency in star formation, and the function of interest is the probability distribution of IMF parameters.Comment: 18 pages, including 4 figures: invited talk presented at the conference on "IMF@50: The Stellar Initial Mass Function Fifty Years Later" held at Abbazia di Spineto, Siena, Italy, May 2004; to be published by Kluwer Academic Publishers, edited by E. Corbelli, F. Palla, and H. Zinnecke

contact.engineering -- Create, analyze and publish digital surface twins from topography measurements across many scales

The optimization of surface finish to improve performance occurs largely through trial and error, despite significant advancements in the relevant science. There are three central challenges that account for this disconnect: (1) the challenge of integration of many different types of measurement for the same surface to capture the multi-scale nature of roughness; (2) the technical complexity of implementing spectral analysis methods, and of applying mechanical or numerical models to describe surface performance; (3) a lack of consistency between researchers and industries in how surfaces are measured, quantified, and communicated. Here we present a freely-available internet-based application which attempts to overcome all three challenges. First, the application enables the user to upload many different topography measurements taken from a single surface, including using different techniques, and then integrates all of them together to create a digital surface twin. Second, the application calculates many of the commonly used topography metrics, such as root-mean-square parameters, power spectral density (PSD), and autocorrelation function (ACF), as well as implementing analytical and numerical calculations, such as boundary element modeling (BEM) for elastic and plastic deformation. Third, the application serves as a repository for users to securely store surfaces, and if they choose, to share these with collaborators or even publish them (with a digital object identifier) for all to access. The primary goal of this application is to enable researchers and manufacturers to quickly and easily apply cutting-edge tools for the characterization and properties-modeling of real-world surfaces. An additional goal is to advance the use of open-science principles in surface engineering by providing a FAIR database where researchers can choose to publish surface measurements for all to use.Comment: 19 pages, 6 figure

Photometric study of the young open cluster NGC 3293

Deep and extensive CCD photometric observations $UBV(RI)_{C}H_{\alpha}$ were carried out in the area of the open cluster NGC 3293. The new data set allows to see the entire cluster sequence down to $M_{V} \approx +4.5$, revealing that stars with $M_{V} < -2$ are evolving off the main sequence; stars with $-2 < M_{V} +2$ are placed above it. According to our analysis, the cluster distance is $d = 2750 \pm 250 pc$ ($V_{0}-M_{V} = 12.2 \pm 0.2$) and its nuclear age is $8 \pm 1 Myr$. NGC 3293 contains an important fraction of pre--main sequence (PMS) stars distributed along a parallel band to the ZAMS with masses from 1 to 2.5 \cal M_{\sun} and a mean contraction age of $10 Myr$. This last value does not differ too much from the nuclear age estimate. Actually, if we take into account the many factors that may affect the PMS star positions onto the colour--magnitude diagram, both ages can be perfectly reconciled. The star formation rate, on the other hand, suggests that NGC 3293 stars formed surely in one single event, therefore favouring a coeval process of star formation. Besides, using the $H_{\alpha}$ data, we detected nineteen stars with signs of having $H_{\alpha}$ emission in the region of NGC 3293, giving another indication that the star formation process is still active in the region. The computed initial mass function for the cluster has a slope value $x = 1.2 \pm 0.2$, a bit flatter than the typical slope for field stars and similar to the values found for other young open clusters.Comment: 17 pages, 13 eps figures, in press in Astronomy and Astrophysic