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A radar-based stochastic model for the time-space arrivals of the rain fields onto a geographical region (1989)

Kavvas, M. L. ; Chen, Z.

Springer

Stochastic environmental research and risk assessment 3 (1989), S. 261-280

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ISSN: 1436-3259

Keywords: Rain fields ; time-space arrivals ; stochastic model

Source: Springer Online Journal Archives 1860-2000

Topics: Architecture, Civil Engineering, Surveying , Energy, Environment Protection, Nuclear Power Engineering , Geography , Geosciences

Notes: Abstract Rainfall in time at any ground location can be described by the rain intensity distribution over the subtrajectories which are drawn by the ground location point on the radar-detected incremental rain fields (IRFs) that pass over this location. Based on this conceptualization, this study develops a stochastic description of the arrivals of IRF subtrajectories (SIRFs) onto any given set of ground locations over a geographical region. The arrivals of SIRFs is described by a multivariate doubly stochastic Poisson process, excited by the time-space arrival process of IRFs onto the designated geographical region. The arrival process of IRFs is described by a 3-level time-space nonhomogeneous Poisson cluster model. At the primary level of this model are the arrivals of synoptic cyclonic systems; at the secondary level are the arrivals of large mesoscale rain areas (LMSAs) and at the tertiary level are the arrivals of IRFs onto the designated geographical region, all detected by the weather radar. The models are substantiated both by the graphical analysis of rain fields, as detected on a radar scope, and by the statistical analysis of the arrivals data at all of the four levels at three different ground locations over a rectangular geographical region in Northern Kentucky. It is pointed out that a doubly stochastic Poisson process is basically a Poisson cluster process. Hence, the final process of SIRF arrivals onto any ground location may be interpreted as a 4-level Poisson cluster process. Finally, heavy tails in the sample covariance density functions of the IRF and SIRF arrivals are detected. This study shows that the appropriate incorporation of clustering at all observable distinct scales of the rain fields models the heavy tail behavior of the covariance density adequately.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF01543460

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Properties and phase separation of reaction injection molded and solution polymerized polyureas as a function of hard block content (1988)

Willkomm, Wayne R. ; Chen, Z. S. ; Macosko, C. W. ; [et al.]

Stamford, Conn. [u.a.] : Wiley-Blackwell

Polymer Engineering and Science 28 (1988), S. 888-900

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ISSN: 0032-3888

Keywords: Chemistry ; Chemical Engineering

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology , Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics , Physics

Notes: A series of amine terminated polypropylene oxide based thermoplastic polyureas with hard segment contents of 30%, 50%, and 70 percent were synthesized via solution polymerization and reaction injection molding (RIM). Amine terminated polypropylene oxide (PPO-NH2) of Mn = 2000 was used as the soft segment and 4,4′-diphenylme-thanediisocyanate (MDI) extended with diethyltoluenediamine (DETDA) as the hard segment. These polyureas are linear, amorphous, and phase separated. Polymers were characterized by gel permeation chromatography (GPC), differential scanning calorimetry (DSC), dynamic mechanical spectroscopy (DMS), small angle X-ray scattering (SAXS), and tensile testing. RIM polyureas had significantly lower molecular weights than solution polymerized polyureas, but their mechanical properties did not suffer, RIM polyureas have poorer phase separation than solution polyureas as evidenced by DSC, DMS, and SAXS, especially at high hard segment levels. SAXS shows phase separation levels of up to 100 percent for low hard segment polyureas and down to 10 percent for high hard segment RIM polyurea. DSC found no evidence of a hard segment glass transition, and the evidence from DMS was inconclusive. In addition to polymer characterization, demolding behavior was studied. The 30 percent hard segment was always tough and elastomeric, while the 70 percent hard segment was always very brittle. The 50 percent hard segment showed the greatest variation in properties, ranging from very brittle to very though as mold temperature and in-mold time were increased. Demold brittleness is explained by the presence of low molecular weight DETDA/MDI oligomers on demolding, which continue to react on aging.

Additional Material: 11 Ill.