An approach to CMG steering using feedback linearization

This paper presents an approach for controlling spacecraft equipped with control moment gyroscopes. A technique from feedback linearization theory is used to transform the original nonlinear problem to an equivalent linear form without approximating assumptions. In this form, the spacecraft dynamics appear linearly, and are decoupled from redundancy in the system of gyroscopes. A general approach to distributing control effort among the available actuators is described which includes provisions for redistribution of rotors, explicit bounds in gimbal rates, and guaranteed operation at or near singular configurations. A particular algorithm is developed for systems of double-gimbal devices, and demonstrated in two examples for which existing approaches fail to give adequate performance

Broadband Multi-wavelength Properties of M87 during the 2017 Event Horizon Telescope Campaign

Abstract: In 2017, the Event Horizon Telescope (EHT) Collaboration succeeded in capturing the first direct image of the center of the M87 galaxy. The asymmetric ring morphology and size are consistent with theoretical expectations for a weakly accreting supermassive black hole of mass ∼6.5 × 109 M ⊙. The EHTC also partnered with several international facilities in space and on the ground, to arrange an extensive, quasi-simultaneous multi-wavelength campaign. This Letter presents the results and analysis of this campaign, as well as the multi-wavelength data as a legacy data repository. We captured M87 in a historically low state, and the core flux dominates over HST-1 at high energies, making it possible to combine core flux constraints with the more spatially precise very long baseline interferometry data. We present the most complete simultaneous multi-wavelength spectrum of the active nucleus to date, and discuss the complexity and caveats of combining data from different spatial scales into one broadband spectrum. We apply two heuristic, isotropic leptonic single-zone models to provide insight into the basic source properties, but conclude that a structured jet is necessary to explain M87’s spectrum. We can exclude that the simultaneous γ-ray emission is produced via inverse Compton emission in the same region producing the EHT mm-band emission, and further conclude that the γ-rays can only be produced in the inner jets (inward of HST-1) if there are strongly particle-dominated regions. Direct synchrotron emission from accelerated protons and secondaries cannot yet be excluded

Auditory display of spatial information

The problem of designing an auditory display for a binaural mobility aid for the blind is investigated. The basis for the project was the binaural linear F.M. echolocation mobility aid proposed by Prof. L. Kay. The sciences of engineering and psychophysics are freely intermixed to define the optimal form of the azimuthal dimension of an auditory spatial display". It is shown that to take advantage of the frequency domain range coding it is necessary to use interaural amplitude difference (IAD) as the localization cue. A series of experiments confirmed this and suggested a modification to the system concept. An extensive psychophysical investigation of auditory localization with IAD determined the parametric-form of the localization function, from which the azimuthal dimension of the display was specified and analysed. The problem of generating this display from an echolocation system is discussed. Measures of the resolution capability of the auditory system in a static. Two object environment are presented. A computer simulation of the auditory display was used to justify the use of data derived from dichotic experiments to specify a display for use with head movement. Adaptive strategies for estimating the localization function are described

Human Rights Violations at the U.S.-Mexican Border

In the past nine years, Sinclair Community College students and faculty have visited the U.S. Mexican Border each year as part of geography and sociology course on this topic. Over, eighty students and five faculty have participated. Two of the faculty have participated every year and have witnessed the increasing human rights violations on the border. Using data, photographs, and newspapers collected over the past nine years, presenters will discuss the increasing militarization on the border and the effect it has had on increasing human rights violations. For example, ten years ago numerous humanitarian groups were on the border living in campgrounds bringing water to undocumented migrants, whereas today vigilante groups are vandalizing water left in the desert to keep people from dying and even posting videos online. Along with the increased militarization of the border, has come more stringent criminal prosecution (Operation Streamline), imprisonment of undocumented migrants, declining treatment of women including reports of rape and criminalization of various forms of humanitarian aid. Many humanitarian groups are referring to the U.S.-Mexican Border has a form of genocide. In particular they point out the majority of the people dying are poor people of color. We will argue that the State of Arizona has basically become a militarized state. Amnesty International has issued several statements about the State of Arizona and the state is featured in a report “Jailed Without Justice

Quantitative Comparison of Alternative Sensory Displays for Mobility Aids for the Blind

This paper proposes a method to compare quantitatively various auditory display schemes communicating the course a blind traveler should follow to comply with information a blind mobility aid has acquired, and the optimal scheme is sought for that traveler. A computer system emulates different display devices which use amplitude modulation to indicate the error of a subject's location from the indicated course. The real-time Selspot-based TRACK system measures the location of the human subject in real time, and the error is presented to the subject via each of the emulated devices. The indicated course, human trajectory, and error are recorded in computer disk memory. The performance of the human in each task is evaluated by calculation of a transfer function of the human with each display and then using this transfer function as the criterion for comparison. The feasibility of designing the display schemes of blind mobility aids using this procedure is demonstrated. Thus, an optimal choice for the specific blind person can be made via this system before committing a particular mobility aid design to the lengthy development process

System dynamics : an introduction/ Rowell

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System dynamics : an introduction/ Rowell

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Variability of master gutta-percha cones

The common technique to hermetically fill prepared root canals involves the use of “standardised” guttapercha cones that are selected to fit the apical portion of the prepared canal space. These guttapercha cones are manufactured to conform to a standard size and taper which should correspond to the size and taper of standard root canal instruments. Clinical observation of commercially available guttapercha cones seemed to indicate that there is wide variation in the diameter and taper of “standardised” gutta-percha cones within the size range 25–35. The present study was undertaken to determine how closely current commercially available gutta-percha cones sizes 25, 30 and 35 conformed to the current ISO standard, and was initiated by the above clinical observation. It was not the purpose of this study to compare the results from different brands or manufacturers, but rather to establish whether commercially available gutta-percha cones collectively conformed to expected standardised sizes. One phial of cones for each of the sizes 25, 30 and 35 of eight different brands was selected for examination. The diameter of each of ten cones for each size from each brand was measured at two points, at 1 mm and at 6 mm from the tip of the cone. The results obtained for each size and each brand were tabulated and compared with ISO 6877:1995 for dental root canal obturating cones. This study demonstrated wide variability for cones from all brands, for all sizes, when individual cones of the same size were compared. While collectively the arithmetic means showed a closer correlation to the ISO Standard, irrespective of the brand size of the cone, or whether the cone was measured at 1 mm or 6 mm, many individual cones showed a great variation from the ideal. The need for less variability is discussed. It is concluded that ISO standard 6877:1995 is inappropriate and allows for too much variation in the size of “standardised” gutta-percha cones