The lack of short baselines, referred to as the short-spacing problem (SSP), is a well-known limitation of the performance of radio interferometers, causing a reduction of the ux detected from source structure on large angular scales. The very large number of antennas operated in the Atacama Large Millimeter/sub-millimeter Array (ALMA) generates situations for which the impact of the SSP takes a complex form, not simply measurable by a single number, such as the maximal recoverable scale. In particular, extended antenna congurations, complemented by a small group of closeby antennas at the centre of the array, may result in a double-humped baseline distribution with a signicant gap between the two groups. In such cases one should adopt as the effective maximal recoverable scale the one associated with the extended array and use only the central array to recover missing ux, as one would do with single dish or ACA (Atacama Compact Array) observations. The impact of the missing baselines can be very important and may easily be underestimated, or even overlooked. The present study uses ALMA archival data of the 29SiO(8-7) line emission of the AGB star W Hydrae for a demonstration. A critical discussion of the reliability of the observations away from the star is presented together with comments of a broader scope. Properties of the circumstellar envelope of W Hya within 15 au from the star, many of which are not mentioned in the published literature, are brie y described and compared with R Doradus, an AGB star having properties very similar to W Hya.

Currently, there are very few papers that have examined the efficiency of Vietnamese ports. Of those that have, some of them take into account only a few container ports in Northern Vietnam. Others focus on comparing all types of ports in Vietnam with regard to the differences in efficiency scores when applying different methods to evaluate efficiency. However, there is no paper that specifically analyzes the efficiency of Vietnamese container ports throughout the country or that compares Vietnamese container ports with those of other countries in terms of efficiency. In order to provide more accurate and interesting information for container port authorities, in this study, 21 major Vietnamese container ports and seven major Korean container ports are selected and examined with regard to their levels of efficiency in 2016 using data envelopment analysis (DEA). This paper applies both constant return to scale (CRS) and variable return to scale (VRS) to explore the differences among overall technical efficiency, pure technical efficiency, and scale efficiency of the selected container ports. This study also indicate slacks and sets projections for inefficient ports.