Molecular gas freeze-out in the pre-stellar core L1689B

C17O (J=2-1) observations have been carried out towards the pre-stellar core L1689B. By comparing the relative strengths of the hyperfine components of this line, the emission is shown to be optically thin. This allows accurate CO column densities to be determined and, for reference, this calculation is described in detail. The hydrogen column densities that these measurements imply are substantially smaller than those calculated from SCUBA dust emission data. Furthermore, the C17O column densities are approximately constant across L1689B whereas the SCUBA column densities are peaked towards the centre. The most likely explanation is that CO is depleted from the central regions of L1689B. Simple models of pre-stellar cores with an inner depleted region are compared with the results. This enables the magnitude of the CO depletion to be quantified and also allows the spatial extent of the freeze-out to be firmly established. We estimate that within about 5000 AU of the centre of L1689B, over 90% of the CO has frozen onto grains. This level of depletion can only be achieved after a duration that is at least comparable to the free-fall timescale.Comment: MNRAS letters. 5 pages, 5 figure

The Taming of the Site: Helping Users Find What They Need Where They Expect It

Helping users find the need-to-know information on a library website can be difficult, especially if the site’s structure itself confuses them or leads them to unexpected places. A library site may start small but grow larger and more unwieldy every year until users are lost in a maze of disconnected, outdated, or even missing pages. In this episode, you\u27ll find out how to update your site\u27s information architecture (IA) and simplify your navigational structure. You’ll also learn how identifying content owners makes content clean-up easier to finish and simpler to maintain. We’ll walk through steps to make sure your IA informs site navigation in a way that leads users the way they need to go. We’ll also discuss how to identify important content and distill it in a way that helps users get what they need without becoming frustrated. After this episode, you\u27ll be able to help users easily find what they need and make sure it\u27s still relevant when they get there

Prediction of unsteady aerodynamic loadings caused by leading edge and trailing edge control surface motions in subsonic compressible flow: Analysis and results

A theoretical analysis and computer program was developed for the prediction of unsteady lifting surface loadings caused by motions of leading edge and trailing edge control surfaces having sealed gaps. The final form of the downwash integral equation was formulated by isolating the singularities from the nonsingular terms and using a preferred solution process to remove and evaluate the downwash discontinuities in a systematic manner. Comparisons of theoretical and experimental pressure data are made for several control surface configurations. The comparisons indicate that reasonably accurate theoretical pressure distributions and generalized forces may be obtained for a wide variety of control surface configurations. Spanwise symmetry or antisymmetry of motion, and up to six control surfaces on each half span can be accommodated

Drive-Thru User Testing

User testing doesn’t have to be expensive or tedious. Join us to find out more about drive-thru user testing: cheap, quick, and easy ways to find out what your users expect from your services. Find out when to use different types of user testing to figure out the specific answers to your questions -- and which methods may seem easy when they aren’t

Surface electrical properties experiment, part 1

The work is reported which was performed on the Surface Electrical Properties Experiment Data Acquisition System. Areas discussed include: data handling and processing, installation and external signal application, operation of the equipment, and digital output. Detailed circuit descriptions are included

COMSAT Laboratories' on-board baseband switch development

Work performed at COMSAT Laboratories to develop a prototype on-board baseband switch is summarized. The switch design is modular to accommodate different service types, and the architecture features a high-speed optical ring operating at 1 Gbit/s to route input (up-link) channels to output (down-link) channels. The switch is inherently a packet switch, but can process either circuit-switched or packet-switched traffic. If the traffic arrives at the satellite in a circuit-switched mode, the input processor packetizes it and passes it on to the switch. The main advantage of the packet approach lies in its simplified control structure. Details of the switch architecture and design, and the status of its implementation, are presented

Ready, set, oh no? Prepare for possible online accessibility issues before they arise

Trying to make your online resources more accessible but aren\u27t sure where the vendor\u27s interface might cause problems? Do you collect Accessibility Compliance Reports (sometimes referred to as a Voluntary Product Accessibility Template or VPAT) and file it away without doing anything with the information contained within? Find out how the Online Resources and Services Librarian at the University of North Dakota’s School of Medicine and Health Sciences Library Resources has partnered with UND’s Equity Compliance and Education Manager to take accessibility compliance to the next level. We’ve augmented the basic University requirement to check a box into a more comprehensive process that ensures we’re proactively attending to our users’ current and future needs. We work internally and with vendors to identify and track the potential failing points of our online resources as identified in their ACR. We then, prior to purchase approval or renewal, develop a plan to mitigate the accessibility barriers within the platform and provide equally effective alternative access to the material. Once the resource is made available within our ILS, we inform users of known accessibility barriers and make sure they know how to contact us with questions or for assistance. In this lightning talk, we’ll discuss going beyond basic internal requirements to establish more rigorous measures that better meets users where they are and before they know they need help. You’ll discover how to identify and track potential problems, how to communicate to your users regarding accessibility concerns, and how to maintain contact with your vendors and publishers to advocate for your users

The creation of the Helix planetary nebula (NGC 7293) by multiple events

A deep, continuum-subtracted, image of NGC 7293 has been obtained in the light of the Halpha+[N II] emission lines. New images of two filamentary halo stuctures have been obtained and the possible detection of a collimated outflow made. Spatially resolved, longslit profiles of the Halpha+[N II] lines have been observed across several of these features with the MES combined with the SPM 2.1m telescope; these are compared with the [N II]6584, [O III]5007, HeII 6560 and Halpha profiles obtained over the nebular core. The central HeII emission is originating in a ~0.34pc diameter spherical volume expanding at <=12km/s which is surrounded, and partially coincident with an [O III] emitting inner shell expanding at 12km/s. The bright helical structure surrounding this inner region is modelled as a bi-polar nebula with lobe expansions of 25km/s whose axis is tilted at 37deg to the sight line but with a toroidal waist itself expanding at 14 km/s. These observations are compared with the expectations of the interacting two winds model for the formation of PNe. Only after the fast wind has switched off could this global velocity structure be generated. Ablated flows must complicate any interpretation. It is suggested that the clumpy nature of much of the material could play a part in creating the radial `spokes' shown here to be apparently present close to the central star. These `spokes' could in fact be the persistant tails of cometary globules whose heads have now photo-evaporated completely. A halo arc projecting from the north-east of the bright core has a conterpart to the south-east. Anomolies in the position-velocity arrays of line profiles could suggest that these are part of an expanding disc not aligned with the central helical structure though expanding bi-polar lobes along a tilted axis are not ruled out.Comment: 17 pages, 11 figures, accepted for publication in MNRA