29,869 research outputs found
Evaluation of meteorological airborne Doppler radar
This paper will discuss the capabilities of airborne Doppler radar for atmospheric sciences research. The evaluation is based on airborne and ground based Doppler radar observations of convective storms. The capability of airborne Doppler radar to measure horizontal and vertical air motions is evaluated. Airborne Doppler radar is shown to be a viable tool for atmospheric sciences research
Crossover from a square to a hexagonal pattern in Faraday surface waves
We report on surface wave pattern formation in a Faraday experiment operated
at a very shallow filling level, where modes with a subharmonic and harmonic
time dependence interact. Associated with this distinct temporal behavior are
different pattern selection mechanisms, favoring squares or hexagons,
respectively. In a series of bifurcations running through a pair of
superlattices the surface wave pattern transforms between the two incompatible
symmetries. The close analogy to 2D and 3D crystallography is pointed out.Comment: 4 pages, 4 figure
Gluon Distribution Functions for Very Large Nuclei at Small Transverse Momentum
We show that the gluon distribution function for very large nuclei may be
computed for small transverse momentum as correlation functions of an
ultraviolet finite two dimensional Euclidean field theory. This computation is
valid to all orders in the density of partons per unit area, but to lowest
order in . The gluon distribution function is proportional to ,
and the effect of the finite density of partons is to modify the dependence on
transverse momentum for small transverse momentum.Comment: TPI--MINN--93--52/T, NUC--MINN--93--28/T, UMN--TH--1224/93, LaTex, 11
page
Phase relaxation of Faraday surface waves
Surface waves on a liquid air interface excited by a vertical vibration of a
fluid layer (Faraday waves) are employed to investigate the phase relaxation of
ideally ordered patterns. By means of a combined frequency-amplitude modulation
of the excitation signal a periodic expansion and dilatation of a square wave
pattern is generated, the dynamics of which is well described by a Debye
relaxator. By comparison with the results of a linear theory it is shown that
this practice allows a precise measurement of the phase diffusion constant.Comment: 5 figure
New urea-absorbing polymers for artificial kidney machines
Etherified polymer is made from modified cellulose derivative which is reacted with periodate. It will absorb 2 grams of urea per 100 grams of polymer. Indications are that polymers could be used to help remove uremic wastes in artificial kidneys, or they could be administered orally as therapy for uremia
Aldehyde-containing urea-absorbing polysaccharides
A novel aldehyde containing polymer (ACP) is prepared by reaction of a polysaccharide with periodate to introduce aldehyde groups onto the C2 - C3 carbon atoms. By introduction of ether and ester groups onto the pendant primary hydroxyl solubility characteristics are modified. The ACP is utilized to absorb nitrogen bases such as urea in vitro or in vivo
Solar Orbiter: Exploring the Sun-heliosphere connection
The heliosphere represents a uniquely accessible domain of space, where
fundamental physical processes common to solar, astrophysical and laboratory
plasmas can be studied under conditions impossible to reproduce on Earth and
unfeasible to observe from astronomical distances. Solar Orbiter, the first
mission of ESA's Cosmic Vision 2015-2025 programme, will address the central
question of heliophysics: How does the Sun create and control the heliosphere?
In this paper, we present the scientific goals of the mission and provide an
overview of the mission implementation.Comment: 52 pages, 21 figures, 125 references; accepted for publication in
Solar Physic
N/P GaAs concentrator solar cells with an improved grid and bushbar contact design
The major requirements for a solar cell used in space applications are high efficiency at AMO irradiance and resistance to high energy radiation. Gallium arsenide, with a band gap of 1.43 eV, is one of the most efficient sunlight to electricity converters (25%) when the the simple diode model is used to calculate efficiencies at AMO irradiance, GaAs solar cells are more radiation resistant than silicon solar cells and the N/P GaAs device has been reported to be more radiation resistant than similar P/N solar cells. This higher resistance is probably due to the fact that only 37% of the current is generated in the top N layer of the N/P cell compared to 69% in the top layer of a P/N solar cell. This top layer of the cell is most affected by radiation. It has also been theoretically calculated that the optimized N/P device will prove to have a higher efficiency than a similar P/N device. The use of a GaP window layer on a GaAs solar cell will avoid many of the inherent problems normally associated with a GaAlAs window while still proving good passivation of the GaAs surface. An optimized circular grid design for solar cell concentrators has been shown which incorporates a multi-layer metallization scheme. This multi-layer design allows for a greater current carrying capacity for a unit area of shading, which results in a better output efficiency
Reading between the lines: Prediction of political violence using newspaper text
This article provides a new methodology to predict armed conflict by using newspaper text. Through machine learning, vast quantities of newspaper text are reduced to interpretable topics. These topics are then used in panel regressions to predict the onset of conflict. We propose the use of the within-country variation of these topics to predict the timing of conflict. This allows us to avoid the tendency of predicting conflict only in countries where it occurred before. We show that the within-country variation of topics is a good predictor of conflict and becomes particularly useful when risk in previously peaceful countries arises. Two aspects seem to be responsible for these features. Topics provide depth because they consist of changing, long lists of terms that make them able to capture the changing context of conflict. At the same time, topics provide width because they are summaries of the full text, including stabilizing factors.</jats:p
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