9,608 research outputs found
Selection of Ontologies for the Semantic Web
The development of the Semantic Web has encouraged the creation of ontologies in a great variety of domains. Web users currently looking for ontologies in order to incorporate them into their systems, just use their experience and intuition. This makes it difficult for them to justify their choices. Mainly, this is due to the lack of methods that help the user to measure that the most appropriate ontologies for the new system are. To solve this deficiency, this work proposes a method which allows the users to measure the suitability of the existent ontologies, regarding the requirements of their systems
ASSESSING THE FINANCIAL RISKS OF DIVERSIFIED COFFEE PRODUCTION SYSTEMS: AN ALTERNATIVE NONNORMAL CDF ESTIMATION APPROACH
Recently developed techniques are adapted and combined for the modeling and simulation of crop yields and prices that can be mutually correlated, exhibit heteroskedasticity or autocorrelation, and follow nonnormal probability density functions. The techniques are applied to the modeling and simulation of probability distribution functions for the returns of three tropical agroforestry systems for coffee production. The importance of using distribution functions that can more closely reflect the statistical behavior of yields and prices for risk analysis is discussed and illustrated.Risk and Uncertainty,
Performance Characterization of a Solenoid-type Gas Valve for the Magnetron Source at FNAL
The magnetron-style ion sources currently in operation at Fermilab
use piezoelectric gas valves to function. This kind of gas valve is sensitive
to small changes in ambient temperature, which affect the stability and
performance of the ion source. This motivates the need to find an alternative
way of feeding H2 gas into the source. A solenoid-type gas valve has been
characterized in a dedicated off-line test stand to assess the feasibility of
its use in the operational ion sources. ion beams have been extracted
at 35 keV using this valve. In this study, the performance of the solenoid gas
valve has been characterized measuring the beam current output of the magnetron
source with respect to the voltage and pulse width of the signal applied to the
gas valve.Comment: 4 pp. arXiv admin note: text overlap with arXiv:1701.0175
Experimenta-quÃmica. Un ejemplo de aprendizaje no formal en entornos tecnológicos
Experimenta es un proyecto interinstitucional de la UNAM, cuyo propósito es inculcar el pensamiento cientÃfico y favorecer el interés por las ciencias en los estudiantes de bachillerato. A la fecha Experimenta ha atendido a cinco mil estudiantes. En la práctica, los estudiantes asisten a cinco sesiones consecutivas de cuatro horas. Ahà desarrollan investigaciones enfocadas a un tema común en laboratorios de biologÃa, fÃsica, matemáticas, quÃmica y tecnologÃa. En cada sesión se presentan a los estudiantes, fenómenos atractivos y se les anima a plantear hipótesis sobre las diferentes variables. Estas hipótesis, son probadas por procedimientos experimentales que ellos diseñan y que incluyen el uso de interfases y sensores. Al final de cada sesión en una discusión conjunta los estudiantes cuestionan, comparan y argumentan cientÃficamente los resultados obtenidos
Implementation of Design Changes Towards a More Reliable, Hands-off Magnetron Ion Source
As the main ion source for the accelerator complex, magnetron ion
sources have been used at Fermilab since the 1970s. At the offline test stand,
new R&D is carried out to develop and upgrade the present magnetron-type
sources of ions of up to 80 mA and 35 keV beam energy in the context of
the Proton Improvement Plan. The aim of this plan is to provide high-power
proton beams for the experiments at FNAL. In order to reduce the amount of
tuning and monitoring of these ion sources, a new electronic system consisting
of a current-regulated arc discharge modulator allow the ion source to run at a
constant arc current for improved beam output and operation. A solenoid-type
gas valve feeds gas into the source precisely and independently of
ambient temperature. This summary will cover several studies and design changes
that have been tested and will eventually be implemented on the operational
magnetron sources at Fermilab. Innovative results for this type of ion source
include cathode geometries, solenoid gas valves, current controlled arc pulser,
cesium boiler redesign, gas mixtures of hydrogen and nitrogen, and duty factor
reduction, with the aim to improve source lifetime, stability, and reducing the
amount of tuning needed. In this summary, I will highlight the advances made in
ion sources at Fermilab and will outline the directions of the continuing R&D
effort.Comment: 4 pp. arXiv admin note: substantial text overlap with
arXiv:1701.0175
Characterization of periodic cavitation in an optical tweezer
Microscopic vapor explosions or cavitation bubbles can be generated
periodically in an optical tweezer with a microparticle that partially absorbs
at the trapping laser wavelength. In this work we measure the size distribution
and the production rate of cavitation bubbles for microparticles with a
diameter of 3 m using high speed video recording and a fast photodiode. We
find that there is a lower bound for the maximum bubble radius m which can be explained in terms of the microparticle size. More than
of the measured are in the range between 2 and 6 m,
while the same percentage of the measured individual frequencies or
production rates are between 10 and 200 Hz. The photodiode signal yields an
upper bound for the lifetime of the bubbles, which is at most twice the value
predicted by the Rayleigh equation. We also report empirical relations between
, and the bubble lifetimes.Comment: 5 pages, 3 figure
- …