8,810 research outputs found
Predicting the arrival times of solar particles
A procedure has been developed to generate a computerized time-intensity profile of the solar proton intensity expected at the earth after the occurrence of a significant solar flare on the sun. This procedure is a combination of many pieces of independent research and theoretical results. Many of the concepts used were first reported by Smart and Shea (1979) and are summarized by Smart and Shea (1985). Extracts from the general procedure that relate to predicting the expected onset time and time of maximum at the earth after the occurrence of a solar flare are presented
An update on the correlation between the cosmic radiation intensity and the geomagnetic AA index
A statistical study between the cosmic ray intensity, as observed by a neutron monitor, and of the geomagnetic aa index, as representative of perturbations in the plasma and interplanetary magnetic field in the heliosphere, has been updated to specifically exclude time periods around the reversal of the solar magnetic field. The results of this study show a strong negative correlation for the period 1960 through 1968 with a correlation coefficient of approximately -0.86. However, there is essentially no correlation between the cosmic ray intensity and the aa index for the period 1972-1979 (i.e. correlation coefficient less than 0.16). These results would appear to support the theory of preferential particle propagation into the heliosphere vis the ecliptic during the period 1960-1968 and via the solar polar regions during 1972-1979
Exploring the relationship between the Engineering and Physical Sciences and the Health and Life Sciences by advanced bibliometric methods
We investigate the extent to which advances in the health and life sciences
(HLS) are dependent on research in the engineering and physical sciences (EPS),
particularly physics, chemistry, mathematics, and engineering. The analysis
combines two different bibliometric approaches. The first approach to analyze
the 'EPS-HLS interface' is based on term map visualizations of HLS research
fields. We consider 16 clinical fields and five life science fields. On the
basis of expert judgment, EPS research in these fields is studied by
identifying EPS-related terms in the term maps. In the second approach, a
large-scale citation-based network analysis is applied to publications from all
fields of science. We work with about 22,000 clusters of publications, each
representing a topic in the scientific literature. Citation relations are used
to identify topics at the EPS-HLS interface. The two approaches complement each
other. The advantages of working with textual data compensate for the
limitations of working with citation relations and the other way around. An
important advantage of working with textual data is in the in-depth qualitative
insights it provides. Working with citation relations, on the other hand,
yields many relevant quantitative statistics. We find that EPS research
contributes to HLS developments mainly in the following five ways: new
materials and their properties; chemical methods for analysis and molecular
synthesis; imaging of parts of the body as well as of biomaterial surfaces;
medical engineering mainly related to imaging, radiation therapy, signal
processing technology, and other medical instrumentation; mathematical and
statistical methods for data analysis. In our analysis, about 10% of all EPS
and HLS publications are classified as being at the EPS-HLS interface. This
percentage has remained more or less constant during the past decade
Fast Desynchronization For Decentralized Multichannel Medium Access Control
Distributed desynchronization algorithms are key to wireless sensor networks
as they allow for medium access control in a decentralized manner. In this
paper, we view desynchronization primitives as iterative methods that solve
optimization problems. In particular, by formalizing a well established
desynchronization algorithm as a gradient descent method, we establish novel
upper bounds on the number of iterations required to reach convergence.
Moreover, by using Nesterov's accelerated gradient method, we propose a novel
desynchronization primitive that provides for faster convergence to the steady
state. Importantly, we propose a novel algorithm that leads to decentralized
time-synchronous multichannel TDMA coordination by formulating this task as an
optimization problem. Our simulations and experiments on a densely-connected
IEEE 802.15.4-based wireless sensor network demonstrate that our scheme
provides for faster convergence to the steady state, robustness to hidden
nodes, higher network throughput and comparable power dissipation with respect
to the recently standardized IEEE 802.15.4e-2012 time-synchronized channel
hopping (TSCH) scheme.Comment: to appear in IEEE Transactions on Communication
The use of the McIlwain L-parameter to estimate cosmic ray vertical cutoff rigidities for different epochs of the geomagnetic field
Secular changes in the geomagnetic field between 1955 and 1980 have been large enough to produce significant differences in both the verical cutoff rigidities and in the L-value for a specified position. A useful relationship employing the McIlwain L-parameter to estimate vertical cutoff rigidities has been derived for the twenty-five year period
Research study of droplet sizing technology leading to the development of an advanced droplet sizing system
An instrument to measure the size and velocity of droplets was developed. The instrument uses one of two techniques, as appropriate. In the first technique two small laser beams of one color identify the center of a larger laser beam of a different color. This defines a region of almost uniform intensity where the light scattered by the individual droplets can be related to their size. The first technique uses the visibility of a Doppler burst and validates it against the peak intensity of the signal's pedestal. Results are presented for monodisperse, bimodal, trimodal, and polydisperse sprays produced by the Berglund-Liu droplet generator and a pressure nozzle. Size distributions of a given spray obtained using three different size ranges show excellent self-consistency in the overlapping region. Measurements of sprays of known characteristics exhibit errors in the order of 10%. The principles of operation and design criteria of the instrument are discussed in great detail
Empirical model for the Earth's cosmic ray shadow at 400 KM: Prohibited cosmic ray access
The possibility to construct a unit sphere of access that describes the cosmic radiation allowed to an Earth-orbiting spacecraft is discussed. It is found that it is possible to model the occluded portion of the cosmic ray sphere of access as a circular projection with a diameter bounded by the satellite-Earth horizon. Maintaining tangency at the eastern edge of the spacecraft-Earth horizon, this optically occluded area is projected downward by an angle beta which is a function of the magnetic field inclination and cosmic ray arrival direction. This projected plane, corresponding to the forbidden area of cosmic ray access, is bounded by the spacecraft-Earth horizon in easterly directions, and is rotated around the vertical axis by an angle alpha from the eastern direction, where the angle alpha is a function of the offset dipole latitude of the spacecraft
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