1,124 research outputs found
On the use of the systems approach to certify advanced aviation technologies
The field of human factors is as varied and diverse as the human subject itself. But one of its most important applications is the facilitation of safety and efficiency in a particular working environment through the implementation of paradigms known about humans and their working relationship with machines and systems. During the period since World War II (which is often viewed as the birth of Human Factors) no area has been the subject of more human factors research than aviation. And in no time during that epoch is the influence of human factors more important, nor more imperative than it is today. As technology driven designs have been finding their way into the national airspace system (NAS), there has been growing concern within the aviation industry itself, the Federal Aviation Administration (FAA), and the general public for a means by which to certify complex systems and the advanced aviation technologies that will be responsible for transporting, directing, and maintaining our airborne travel. While it is widely agreed human factors certification is desirable, the philosophy that will underlie the approach is debatable. There are, in general, two different approaches to certification: (1) the top-down or systems approach; and, (2) the bottom-up or monadical approach. The top-down approach is characterized by the underlying assumption that certification can be best achieved by looking at the system as a whole, understanding its objectives and operating environment, then examining the constituent parts. In an aircraft cockpit, this would be accomplished by first examining what the aircraft is supposed to be (e.g., fighter, general aviation, passenger), identifying its operating environment (IFR, VMC, combat, etc.) and looking at the entire working system which includes the hardware, software, liveware and their interactions; then, evaluative measures can be applied to the subsystems (e.g., individual instruments, CRT displays, controls). The bottom-up approach is founded on the philosophy that the whole can be best served by first examining it constituent elements. This approach would perform the above certification completely antithetically, by looking at the individual parts and certifying good human factors applications to those parts under the basic assumption that the whole is equal to the sum of its parts
Knowledge, Attitudes and Practices on Child Feeding and Care: Preliminary Insights from the Project on Linkages between Child Nutrition and Agricultural Growth
Food Consumption/Nutrition/Food Safety, Downloads May 2008-June 2009: 46,
Spatially Extended 21 cm Signal from Strongly Clustered UV and X-Ray Sources in the Early Universe
We present our prediction for the local 21 cm differential brightness
temperature () from a set of strongly clustered sources of
Population III (Pop III) and II (Pop II) objects in the early Universe, by a
numerical simulation of their formation and radiative feedback. These objects
are located inside a highly biased environment, which is a rare, high-density
peak ("Rarepeak") extending to comoving Mpc. We study the impact of
ultraviolet (UV) and X-ray photons on the intergalactic medium (IGM) and the
resulting , when Pop III stars are assumed to emit X-ray photons
by forming X-ray binaries very efficiently. We parameterize the rest-frame
spectral energy distribution (SED) of X-ray photons, which regulates X-ray
photon-trapping, IGM-heating, secondary Lyman-alpha pumping and the resulting
morphology of . A combination of emission () and
absorption () regions appears in varying amplitudes and angular
scales. The boost of the signal by the high-density environment
() and on a relatively large scale combine to make Rarepeak a
discernible, spatially-extended () object for 21 cm observation
at , which is found to be detectable as a single object
by SKA with integration time of hours. Power spectrum analysis by
some of the SKA precursors (LOFAR, MWA, PAPER) of such rare peaks is found
difficult due to the rarity of these peaks, and the contribution only by these
rare peaks to the total power spectrum remains subdominant compared to that by
all astrophysical sources.Comment: Accepted for publication in ApJ; Major revision done on the
cosmological 21-cm line transfer, allowing for generic cases with peculiar
motion of gas and non-negligible optical dept
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