44,015 research outputs found
Lightweight helmet-mounted eye movement measurement system
The helmet-mounted eye movement measuring system, weighs 1,530 grams; the weight of the present aviators' helmet in standard form with the visor is 1,545 grams. The optical head is standard NAC Eye-Mark. This optical head was mounted on a magnesium yoke which in turn was attached to a slide cam mounted on the flight helmet. The slide cam allows one to adjust the eye-to-optics system distance quite easily and to secure it so that the system will remain in calibration. The design of the yoke and slide cam is such that the subject can, in an emergency, move the optical head forward and upward to the stowed and locked position atop the helmet. This feature was necessary for flight safety. The television camera that is used in the system is a solid state General Electric TN-2000 with a charged induced device imager used as the vidicon
Some services of the Time and Frequency Division of the National Bureau of Standards
The Time and Frequency Division of the National Bureau of Standards (NBS) provides several services to the general public. The radio broadcasts of WWV, WWVH, and WWVB supply reliable, unambiguous time signals to many users. The NBS telephone time-of-day service attracts several hundreds of thousands of calls each year. Periodically, the NBS provides courses on specific topics relating to time and frequency technology. In addition to numerous technical papers published each year, the NBS has prepared the first volume of a comprehensive monograph on time and frequency. The results of research in the Time and Frequency Division of the NBS have had significant impact. An active TV time system capable of serving most of the U.S. currently awaits a ruling by the FCC on a petition filed last year on behalf of the NBS by the Department of Commerce. Three more recent developments are: (1) a TV frequency comparator (patent applied for); (2) a method to perform an independent (absolute) frequency evaluation of commercial cesium beam oscillators; and (3) a method of removing one source of frequency drift in commercial cesium beam oscillators
Spatial dependences in the distant solar wind: Pioneers 10 and 11
Pioneer 10, 11 observations of the solar wind and magnetic field between 1 and 20 AU are reviewed. Spatial dependences, which are emphasized, must be inferred in the presence of large temporal variations including solar cycle effects. The separation of spatial and temporal dependences is achieved principally through the use of multipoint observations including baseline measurements at 1 AU. Measurements of the solar wind parameters (radial speed, flux, proton temperature) and of the magnetic field magnitude and components are compared with two theories, the Parker theory which assumes radial, azimuthally symmetric flow and the Goldstein-Jokipii theory which includes effects associated with stream-stream interactions. The observed radial gradients in the proton density and velocity and the magnetic field are consistent with the Parker model. A qualitative dependence of field magnitude on heliomagnetic latitude, i.e., referred to the observed location of the heliospheric current sheet, was derived. The field strength was found to decrease with distance from the current sheet
Lie groups of conformal motions acting on null orbits
Space-times admitting a 3-dimensional Lie group of conformal motions
acting on null orbits are studied. Coordinate expressions for the metric and
the conformal Killing vectors (CKV) are provided (irrespectively of the matter
content) and then all possible perfect fluid solutions are found, although none
of these verify the weak and dominant energy conditions over the whole
space-time manifold.Comment: 5 pages, Late
A school for humanity: Confronting division and trauma through lived values in Burundi
The Burundi American International Academy is an independent school in central Africa. It was established eight years ago expressly to generate potential leaders motivated to build peace, humanity and economic development in an impoverished country beset by political, ethnic, environmental and development challenges. The purpose of this research is to evaluate progress toward achieving the school’s aims to create such leaders through instilling and modelling the values of integrity, excellence, responsibility, passion, compassion and respect.
The study used qualitative approaches including semi-structured conversations, observations, video, questionnaires and follow-up interviews to provide data. Data was analysed using Grounded Theory to identify the characteristics of a model intended to deliver sustainable positive change in social processes through education.
Significant findings were that the school had developed a strong, united, persuasive and perhaps self-fulfilling narrative about its successes. This narrative shared between teachers, students, governors and parents, included convincing evidence of deep understanding of the relationship between values and action at macro and micro levels. The strong motivation among teachers and other adult participants towards sustaining its aims was reinforced by evidence of frequent values discussions and values-focussed in-service training.
Theory arising from grounded research led to discussion on staff training and curriculum coverage. This included suggestions on involving connections to the school’s humanitarian values and philosophy, cross-curricular approaches to Sustainable Development Goals and closer relations between the subject disciplines. Establishing inclusive values within a privileged minority in a divided and impoverished society and balancing charitable attitudes with aspirations to high status, were revealed as significant challenges for the school. While student admission to North American universities may result in losing of some promising future leaders, the school offers a globally transferrable example of how to establish and sustain a values-creating school
On the Symmetries of the Edgar-Ludwig Metric
The conformal Killing equations for the most general (non-plane wave)
conformally flat pure radiation field are solved to find the conformal Killing
vectors. As expected fifteen independent conformal Killing vectors exist, but
in general the metric admits no Killing or homothetic vectors. However for
certain special cases a one-dimensional group of homotheties or motions may
exist and in one very special case, overlooked by previous investigators, a
two-dimensional homethety group exists. No higher dimensional groups of motions
or homotheties are admitted by these metrics.Comment: Plain TeX, 7 pages, No figure
On the measurement of frequency and of its sample variance with high-resolution counters
A frequency counter measures the input frequency averaged over a
suitable time , versus the reference clock. High resolution is achieved
by interpolating the clock signal. Further increased resolution is obtained by
averaging multiple frequency measurements highly overlapped. In the presence of
additive white noise or white phase noise, the square uncertainty improves from
to .
Surprisingly, when a file of contiguous data is fed into the formula of the
two-sample (Allan) variance
of
the fractional frequency fluctuation , the result is the \emph{modified}
Allan variance mod . But if a sufficient number of contiguous
measures are averaged in order to get a longer and the data are fed into
the same formula, the results is the (non-modified) Allan variance. Of course
interpretation mistakes are around the corner if the counter internal process
is not well understood.Comment: 14 pages, 5 figures, 1 table, 18 reference
Unleashing the Power of Distributed CPU/GPU Architectures: Massive Astronomical Data Analysis and Visualization case study
Upcoming and future astronomy research facilities will systematically
generate terabyte-sized data sets moving astronomy into the Petascale data era.
While such facilities will provide astronomers with unprecedented levels of
accuracy and coverage, the increases in dataset size and dimensionality will
pose serious computational challenges for many current astronomy data analysis
and visualization tools. With such data sizes, even simple data analysis tasks
(e.g. calculating a histogram or computing data minimum/maximum) may not be
achievable without access to a supercomputing facility.
To effectively handle such dataset sizes, which exceed today's single machine
memory and processing limits, we present a framework that exploits the
distributed power of GPUs and many-core CPUs, with a goal of providing data
analysis and visualizing tasks as a service for astronomers. By mixing shared
and distributed memory architectures, our framework effectively utilizes the
underlying hardware infrastructure handling both batched and real-time data
analysis and visualization tasks. Offering such functionality as a service in a
"software as a service" manner will reduce the total cost of ownership, provide
an easy to use tool to the wider astronomical community, and enable a more
optimized utilization of the underlying hardware infrastructure.Comment: 4 Pages, 1 figures, To appear in the proceedings of ADASS XXI, ed.
P.Ballester and D.Egret, ASP Conf. Serie
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