83 research outputs found
Nanostructured rigid polyurethane foams with improved specific thermo-mechanical properties using Bacterial Nanocellulose as a Hard Segment
Bacterial nanocellulose (BNC) was used to synthesize rigid polyurethane foams
(RPUFs) based on its reaction with the isocyanate precursor (ISO route) and
also by using the conventional procedure (POL route). The results indicated
that at only 0.1 wt. % of BNC, drastic improvements of specific elastic
compressive modulus (+244.2 %) and strength (+77.5 %) were found. The reaction
of BNC with the precursor was corroborated through the measurement of
isocyanate number and the BNC caused a significant nucleation effect,
decreasing the cell size up to 39.7%. DSC analysis revealed that the BNC had a
strong effect on post-cure enthalpy, decreasing its value when the ISO route
was implemented. DMA analysis revealed that the RPUFs developed using the ISO
route proved to have an improved damping factor, regardless of BNC
concentration. These results emphasize the importance of using the ISO route to
achieve foamed nanocomposites with improved specific mechanical properties
Partial Covering Arrays: Algorithms and Asymptotics
A covering array is an array with entries
in , for which every subarray contains each
-tuple of among its rows. Covering arrays find
application in interaction testing, including software and hardware testing,
advanced materials development, and biological systems. A central question is
to determine or bound , the minimum number of rows of
a . The well known bound
is not too far from being
asymptotically optimal. Sensible relaxations of the covering requirement arise
when (1) the set need only be contained among the rows
of at least of the subarrays and (2) the
rows of every subarray need only contain a (large) subset of . In this paper, using probabilistic methods, significant
improvements on the covering array upper bound are established for both
relaxations, and for the conjunction of the two. In each case, a randomized
algorithm constructs such arrays in expected polynomial time
ECOSTRESS: NASA's next generation mission to measure evapotranspiration from the International Space Station
The ECOsystem Spaceborne Thermal Radiometer Experiment on Space Station ECOSTRESS) was launched to the International Space Station on June 29, 2018. The primary science focus of ECOSTRESS is centered on evapotranspiration (ET), which is produced as levelâ3 (L3) latent heat flux (LE) data products. These data are generated from the levelâ2 land surface temperature and emissivity product (L2_LSTE), in conjunction with ancillary surface and atmospheric data. Here, we provide the first validation (Stage 1, preliminary) of the global ECOSTRESS clearâsky ET product (L3_ET_PTâJPL, version 6.0) against LE measurements at 82 eddy covariance sites around the world. Overall, the ECOSTRESS ET product performs well against the site measurements (clearâsky instantaneous/time of overpass: r2 = 0.88; overall bias = 8%; normalized RMSE = 6%). ET uncertainty was generally consistent across climate zones, biome types, and times of day (ECOSTRESS samples the diurnal cycle), though temperate sites are overârepresented. The 70 m high spatial resolution of ECOSTRESS improved correlations by 85%, and RMSE by 62%, relative to 1 km pixels. This paper serves as a reference for the ECOSTRESS L3 ET accuracy and Stage 1 validation status for subsequent science that follows using these data
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