Continuous surveillance of points by rotating floodlights

Let P and F be sets of n ≥ 2 and m ≥ 2 points in the plane, respectively, so that P∪F is in general position. We study the problem of finding the minimum angle α ∈ [2π/m, 2π] such that one can install at each point of F a stationary rotating floodlight with illumination angle α, initially oriented in a suitable direction, in such a way that, at all times, every target point of P is illuminated by at least one light. All floodlights rotate at unit speed and clockwise. We give an upper bound for the 1-dimensional problem and present results for some instances of the general problem. Specifically, we solve the problem for the case in which we have two floodlights and many points, and give an upper bound for the case in which there are many floodlights and only two target points.Ministerio de Educación y CienciaEuropean Science FoundationMinisterio de Ciencia e InnovaciónComisión Nacional de Investigación Científica y Tecnológica (Chile)Fondo Nacional de Desarrollo Científico y Tecnológico (Chile

Abstracts on Radio Direction Finding (1899 - 1995)

The files on this record represent the various databases that originally composed the CD-ROM issue of "Abstracts on Radio Direction Finding" database, which is now part of the Dudley Knox Library's Abstracts and Selected Full Text Documents on Radio Direction Finding (1899 - 1995) Collection. (See Calhoun record https://calhoun.nps.edu/handle/10945/57364 for further information on this collection and the bibliography). Due to issues of technological obsolescence preventing current and future audiences from accessing the bibliography, DKL exported and converted into the three files on this record the various databases contained in the CD-ROM. The contents of these files are: 1) RDFA_CompleteBibliography_xls.zip [RDFA_CompleteBibliography.xls: Metadata for the complete bibliography, in Excel 97-2003 Workbook format; RDFA_Glossary.xls: Glossary of terms, in Excel 97-2003 Workbookformat; RDFA_Biographies.xls: Biographies of leading figures, in Excel 97-2003 Workbook format]; 2) RDFA_CompleteBibliography_csv.zip [RDFA_CompleteBibliography.TXT: Metadata for the complete bibliography, in CSV format; RDFA_Glossary.TXT: Glossary of terms, in CSV format; RDFA_Biographies.TXT: Biographies of leading figures, in CSV format]; 3) RDFA_CompleteBibliography.pdf: A human readable display of the bibliographic data, as a means of double-checking any possible deviations due to conversion

A systems engineering approach to disturbance minimization for spacecraft utilizing controlled structures technology

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 1991.Includes bibliographical references (leaves 159-163).by Christopher Emil Eyerman.M.S

Evaluation of acoustic noise in magnetic resonance imaging

Magnetic resonance imaging (MRI) is a technique in which strong static and dynamic magnetic fields are used to create virtual slices of the human body. The process of MR imaging is associated with several health and safety issues which may negatively affect patient and radiological health workers. Potentially hazardous are biological effects of both the static and dynamic magnetic fields, the torques of the magnetic fields acting on ferromagnetic objects, thermal effects, and the negative effects of high acoustic sound pressures. The subject of this dissertation is the evaluation and modification of acoustic noise generated during MRI

Antenna Designs for 5G/IoT and Space Applications

This book is intended to shed some light on recent advances in antenna design for these new emerging applications and identify further research areas in this exciting field of communications technologies. Considering the specificity of the operational environment, e.g., huge distance, moving support (satellite), huge temperature drift, small dimension with respect to the distance, etc, antennas, are the fundamental device allowing to maintain a constant interoperability between ground station and satellite, or different satellites. High gain, stable (in temperature, and time) performances, long lifecycle are some of the requirements that necessitates special attention with respect to standard designs. The chapters of this book discuss various aspects of the above-mentioned list presenting the view of the authors. Some of the contributors are working strictly in the field (space), so they have a very targeted view on the subjects, while others with a more academic background, proposes futuristic solutions. We hope that interested reader, will find a fertile source of information, that combined with their interest/background will allow efficiently exploiting the combination of these two perspectives

Proceedings of the Fifth International Mobile Satellite Conference 1997

Satellite-based mobile communications systems provide voice and data communications to users over a vast geographic area. The users may communicate via mobile or hand-held terminals, which may also provide access to terrestrial communications services. While previous International Mobile Satellite Conferences have concentrated on technical advances and the increasing worldwide commercial activities, this conference focuses on the next generation of mobile satellite services. The approximately 80 papers included here cover sessions in the following areas: networking and protocols; code division multiple access technologies; demand, economics and technology issues; current and planned systems; propagation; terminal technology; modulation and coding advances; spacecraft technology; advanced systems; and applications and experiments

Final report on a study of automated rendezvous and docking for ATS 5 despin, volume 1

Investigation of cost effective utilization of space maintenance and repair techniques to despin Applications Technology Satellite number 5 - Vol.

Application of advanced technology to space automation

Automated operations in space provide the key to optimized mission design and data acquisition at minimum cost for the future. The results of this study strongly accentuate this statement and should provide further incentive for immediate development of specific automtion technology as defined herein. Essential automation technology requirements were identified for future programs. The study was undertaken to address the future role of automation in the space program, the potential benefits to be derived, and the technology efforts that should be directed toward obtaining these benefits

A method for validating a transperineal ultrasound system for intrafraction monitoring of the prostate during external beam radiotherapy

Introduction: The Clarity Autoscan 40 transperineal ultrasound (TPUS) system (Eiekta, Sweden) for prostate motion management employs a vertically-oriented 20 ultrasound array that is continuously swept mechanically to repeatedly produce 30 images containing the prostate [1]. The target position relative to a pre-fraction reference scan is determined multiple times per second. Other investigators have studied the tracking accuracy of the system using displacements of ~1 0 mm from the initial normalisation point typical to a clinical treatment [1-4]. The primary aim of this work was to utilise clinically available equipment to compare the target positions reported by the Clarity Autoscan system to known target positions over the full imaging volume. A scanning dosimetry water tank was used, however refraction in the 20 mm PMMA wall of the tank presented a significant complication. The potential variation in target dose due to intervention based on the Clarity prostate motion management was also investigated. Method: A prostate analogue was mounted to the scanning mechanism of a MP3-XS scanning water tank "' (PTW, Germany). The Clarity probe was positioned externally against the wall of the scanning tank in the treatment orientation. The scanning mechanism was programmed to make in-plane, cross-plane and diagonal 'profiles' in the horizontal plane ranging approximately ±30 mm from the isocentre. Seven sets of these four 'profiles' were acquired between ±30 mm in the vertical direction yielding data throughout a 60 cm-sided cube centred on the isocentre. A bi-layer 30 refraction correction algorithm was derived to account for refraction caused by differences between the speed of sound in both PMMA and water from the speed of sound in soft tissue assumed by the Clarity system. The prostate analogue was then replaced with a Farmer-type ionisation chamber and monitored by the Clarity system during beam delivery. Programmed movements of the chamber triggered manual or automatic suspension of the beam and the resulting measured doses compared. Results: Without refraction correction the maximum difference in the reported positions from the programmed positions was 9.3 mm and the mean(±SD) difference was 4.0±1.8 mm. Refraction correction reduced this to a maximum of 3.4 mm, and a mean(±SD) of 1.0±0.5 mm. The worst results were at the peripheries of the imaged volume and near the transducer where the Clarity system had difficulty maintaining tracking due to narrowing of the swept imaging volume. At the lateral (left-right) and vertical (anterior-posterior) extremities, the prostate analogue images were visibly distorted which may have affected the accuracy of the Clarity centroid position calculation. There was no significant difference in measured dose between manual and automatic beam suspension in a 10x10 cm2 field when the target moved along the beam axis. Furthermore, there was only a minimal difference in measured dose to the centre of the 'prostate' between intervention and no intervention when the 'prostate' was programmed to move ±20 mm along the beam axis during a 180 MU 1 Ox1 0 cm2 field beam. However, it was found that there was a delay of 5.4±0.9 s between threshold crossing and beam suspension which could become significant at higher dose rates. Conclusions: The target positions reported by the Elekta Clarity Autoscan system can be validated using a programmable scanning water tank by employing a refraction correction if care is taken in the initial positioning of the transducer. Further improvement might be achieved by using a smaller target analogue and associated volume to reduce the effect of the refraction-induced distortion on the Clarity centroid calculation. Intervention following detected prostate motion along the beam axis will have minimal effect on the dose to the centre of the prostate; however, motion in any direction will compromise target coverage and dose minimisation to healthy tissue.Thesis (MPhil) -- University of Adelaide, School of Physical Sciences, 201

A radio census of the young massive stellar cluster Westerlund 1

Observations were made of the massive stellar cluster Westerlund 1 (Wd1) using the Australia Telescope Compact Array (ATCA), with a total on source integration time of ~ 16 hours, collected over the autumn and winter of 2015, with follow up observations carried out in the summer of 2016. This thesis presents a full radio census of the massive stellar cluster. This thesis aims to investigate in full the dataset of radio observations, looking at the radio emission detected from the most massive stars in the cluster, as well as the majority of the post-main sequence massive stars present, including several Wolf-Rayet stars, yellow hypergiants, red supergiants, and a luminous blue variable. A full description outlining the data reduction process and the analysis carried out showcases current methods for handling radio interferometric data from ATCA when considering a crowded field full of extended and complex sources. The scientific results gained provide a follow-up to previous ATCA observations taken in the late 1990s and early 2000s. The more recent observations that are the focus of this thesis demonstrate an increase in both the sensitivity and resolution possible with the use of ATCA. New radio detections are made for ten members of the known stellar population of Wd1. The radio observations could be compared to complementary observations at millimetre wavelengths to determine spectral indices and index limits, which allowed for the nature of the radio emission to be constrained. Conclusions could be made from the spectral indices and index limits about the potential binarity of the stellar sources. For all stars where the radio emission could be validly approximated to a thermally emitting stellar wind, updated constraints could be found for the mass-loss rates of these sources. Comparisons between radio and millimetre wavebands allowed for a consideration of clumping factors