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At least 793 records · Page 44
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Intensity of hydrostimulation for the induction of root hydrotropism and its sensing by the root cap

Roots of Pisum sativum L. and Zea mays L. were exposed to different moisture gradients established by placing both wet cheesecloth (hydrostimulant) and saturated aqueous solutions of various salts in a closed chamber. Atmospheric conditions with different relative humidity (RH) in a range between 98 and 86% RH were obtained at root level, 2 to 3mm from the water-saturated hydrostimulant. Roots of Silver Queen corn placed vertically with the tips down curved sideways toward the hydrostimulant in response to approximately 94% RH but did not respond positively to RH higher than approximately 95%. The positive hydrotropic response increased linearly as RH was lowered from 95 to 90%. A maximum response was observed at RH between 90 and 86%. However, RH required for the induction of hydrotropism as well as the responsiveness differed among plant species used; gravitropically sensitive roots appeared to require a somewhat greater moisture gradient for the induction of hydrotropism. Decapped roots of corn failed to curve hydrotropically, suggesting the root cap as a major site of hydrosensing.

NASA Discipline Plant Biology↗
NASA NTRS2004

Comparison Between Lidar and Nephelometer Measurements of Aerosol Hygroscopicity at the Southern Great Plains Atmospheric Radiation Measurement Site

Aerosol hygroscopicity has a significant effect on radiative properties of aerosols. Here a lidar method, applicable to cloud-capped, well-mixed atmospheric boundary layers, is employed to determine the hygroscopic growth factor f(RH) under unperturbed, ambient atmospheric conditions. The data used for the analysis were collected under a wide range of atmospheric aerosol levels during both routine measurement periods and during the intensive operations period (IOP) in May 2003 at the Southern Great Plains (SGP) Climate Research Facility in Oklahoma, USA, as part of the Atmospheric Radiation Measurement (ARM) program. There is a good correlation (approx. 0.7) between a lidar-derived growth factor (measured over the range 85% RH to 96% RH) with a nephelometer-derived growth factor measured over the RH range 40% to 85%. For these RH ranges, the slope of the lidar-derived growth factor is much steeper than that of the nephelometer-derived growth factor, reflecting the rapid increase in particle size with increasing RH. The results are corroborated by aerosol model calculations of lidar and nephelometer equivalent f(RH) based on in situ aerosol size and composition measurements during the IOP. It is suggested that the lidar method can provide useful measurements of the dependence of aerosol optical properties on relative humidity, and under conditions closer to saturation than can currently be achieved with humidified nephelometers.

Pahlow, M.↗
NASA NTRS2008

Accuracy Assessment and Correction of Vaisala RS92 Radiosonde Water Vapor Measurements

Relative humidity (RH) measurements from Vaisala RS92 radiosondes are widely used in both research and operational applications, although the measurement accuracy is not well characterized as a function of its known dependences on height, RH, and time of day (or solar altitude angle). This study characterizes RS92 mean bias error as a function of its dependences by comparing simultaneous measurements from RS92 radiosondes and from three reference instruments of known accuracy. The cryogenic frostpoint hygrometer (CFH) gives the RS92 accuracy above the 700 mb level; the ARM microwave radiometer gives the RS92 accuracy in the lower troposphere; and the ARM SurTHref system gives the RS92 accuracy at the surface using 6 RH probes with NIST-traceable calibrations. These RS92 assessments are combined using the principle of Consensus Referencing to yield a detailed estimate of RS92 accuracy from the surface to the lowermost stratosphere. An empirical bias correction is derived to remove the mean bias error, yielding corrected RS92 measurements whose mean accuracy is estimated to be +/-3% of the measured RH value for nighttime soundings and +/-4% for daytime soundings, plus an RH offset uncertainty of +/-0.5%RH that is significant for dry conditions. The accuracy of individual RS92 soundings is further characterized by the 1-sigma "production variability," estimated to be +/-1.5% of the measured RH value. The daytime bias correction should not be applied to cloudy daytime soundings, because clouds affect the solar radiation error in a complicated and uncharacterized way.

Whiteman, David N.↗
NASA NTRS2017

Beyond 3 Au from the Sun: the Hypervolatiles CH4, C2H6, and CO in the Distant Comet C2006 W3 (Christensen)

Comet C/2006 W3 (Christensen) remained outside a heliocentric distance (Rh) of 3.1 au throughout its apparition, but it presented an exceptional opportunity to directly sense a suite of molecules released from its nucleus. The Cryogenic Infrared Echelle Spectrograph at ESO-VLT detected infrared emissions from the three hypervolatiles (CO, CH4, and C2H6) that have the lowest sublimation temperatures among species that are commonly studied in comets by remote sensing. Even at Rh 3.25 au, the production rate of each molecule exceeded those measured for the same species in a number of other comets, although these comets were observed much closer to the Sun. Detections of CO at Rh = 3.25, 4.03, and 4.73 au constrained its post-perihelion decrease in production rate, which most likely dominated the outgassing. At 3.25 au, our measured abundances scaled as CO/CH4/C2H6 approx. = 100/4.4/2.1. The C2H6/CH4 ratio falls within the range of previously studied comets at Rh < 2 au, while CO/CH4 is comparatively high and similar to in situ measurements from Rosetta at approx.10 km from the nucleus of 67P/Churyumov-Gerasimenko conducted at a very similar Rh (3.15 au). The independent detections of H2O (Herschel Space Observatory) and CO (this work) imply a coma abundance H2O/CO approx. = 20% in C/2006 W3 near Rh = 5 au. All these measurements are of high value for constraining models of nucleus sublimation (plausibly CO-driven) beyond Rh = 3au, where molecular detections in comets are still especially sparse.

Bonev, Boncho P.↗
DOE OSTI2020

Materials Data on TaRh3 by Materials Project

Rh3Ta is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ta is bonded to twelve equivalent Rh atoms to form TaRh12 cuboctahedra that share corners with twelve equivalent TaRh12 cuboctahedra, edges with twenty-four equivalent RhTa4Rh8 cuboctahedra, faces with six equivalent TaRh12 cuboctahedra, and faces with twelve equivalent RhTa4Rh8 cuboctahedra. All Ta–Rh bond lengths are 2.76 Å. Rh is bonded to four equivalent Ta and eight equivalent Rh atoms to form distorted RhTa4Rh8 cuboctahedra that share corners with twelve equivalent RhTa4Rh8 cuboctahedra, edges with eight equivalent TaRh12 cuboctahedra, edges with sixteen equivalent RhTa4Rh8 cuboctahedra, faces with four equivalent TaRh12 cuboctahedra, and faces with fourteen equivalent RhTa4Rh8 cuboctahedra. All Rh–Rh bond lengths are 2.76 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TiRh3 by Materials Project

Rh3Ti is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Ti is bonded to twelve equivalent Rh atoms to form TiRh12 cuboctahedra that share corners with twelve equivalent TiRh12 cuboctahedra, edges with twenty-four equivalent RhTi4Rh8 cuboctahedra, faces with six equivalent TiRh12 cuboctahedra, and faces with twelve equivalent RhTi4Rh8 cuboctahedra. All Ti–Rh bond lengths are 2.73 Å. Rh is bonded to four equivalent Ti and eight equivalent Rh atoms to form distorted RhTi4Rh8 cuboctahedra that share corners with twelve equivalent RhTi4Rh8 cuboctahedra, edges with eight equivalent TiRh12 cuboctahedra, edges with sixteen equivalent RhTi4Rh8 cuboctahedra, faces with four equivalent TiRh12 cuboctahedra, and faces with fourteen equivalent RhTi4Rh8 cuboctahedra. All Rh–Rh bond lengths are 2.73 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on VRh3 by Materials Project

Rh3V is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. V is bonded to twelve equivalent Rh atoms to form VRh12 cuboctahedra that share corners with twelve equivalent VRh12 cuboctahedra, edges with twenty-four equivalent RhV4Rh8 cuboctahedra, faces with six equivalent VRh12 cuboctahedra, and faces with twelve equivalent RhV4Rh8 cuboctahedra. All V–Rh bond lengths are 2.70 Å. Rh is bonded to four equivalent V and eight equivalent Rh atoms to form distorted RhV4Rh8 cuboctahedra that share corners with twelve equivalent RhV4Rh8 cuboctahedra, edges with eight equivalent VRh12 cuboctahedra, edges with sixteen equivalent RhV4Rh8 cuboctahedra, faces with four equivalent VRh12 cuboctahedra, and faces with fourteen equivalent RhV4Rh8 cuboctahedra. All Rh–Rh bond lengths are 2.70 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrRh3 by Materials Project

CrRh3 is Uranium Silicide structured and crystallizes in the cubic Pm-3m space group. The structure is three-dimensional. Cr is bonded to twelve equivalent Rh atoms to form CrRh12 cuboctahedra that share corners with twelve equivalent CrRh12 cuboctahedra, edges with twenty-four equivalent RhCr4Rh8 cuboctahedra, faces with six equivalent CrRh12 cuboctahedra, and faces with twelve equivalent RhCr4Rh8 cuboctahedra. All Cr–Rh bond lengths are 2.69 Å. Rh is bonded to four equivalent Cr and eight equivalent Rh atoms to form distorted RhCr4Rh8 cuboctahedra that share corners with twelve equivalent RhCr4Rh8 cuboctahedra, edges with eight equivalent CrRh12 cuboctahedra, edges with sixteen equivalent RhCr4Rh8 cuboctahedra, faces with four equivalent CrRh12 cuboctahedra, and faces with fourteen equivalent RhCr4Rh8 cuboctahedra. All Rh–Rh bond lengths are 2.69 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on MoRh by Materials Project

MoRh is beta-prime cadmium gold structured and crystallizes in the orthorhombic Pmma space group. The structure is three-dimensional. Mo is bonded to four equivalent Mo and eight equivalent Rh atoms to form MoMo4Rh8 cuboctahedra that share corners with eight equivalent RhMo8Rh4 cuboctahedra, corners with ten equivalent MoMo4Rh8 cuboctahedra, edges with six equivalent MoMo4Rh8 cuboctahedra, edges with twelve equivalent RhMo8Rh4 cuboctahedra, faces with eight equivalent RhMo8Rh4 cuboctahedra, and faces with twelve equivalent MoMo4Rh8 cuboctahedra. There are two shorter (2.76 Å) and two longer (2.77 Å) Mo–Mo bond lengths. There are a spread of Mo–Rh bond distances ranging from 2.72–2.80 Å. Rh is bonded to eight equivalent Mo and four equivalent Rh atoms to form RhMo8Rh4 cuboctahedra that share corners with eight equivalent MoMo4Rh8 cuboctahedra, corners with ten equivalent RhMo8Rh4 cuboctahedra, edges with six equivalent RhMo8Rh4 cuboctahedra, edges with twelve equivalent MoMo4Rh8 cuboctahedra, faces with eight equivalent MoMo4Rh8 cuboctahedra, and faces with twelve equivalent RhMo8Rh4 cuboctahedra. There are two shorter (2.76 Å) and two longer (2.79 Å) Rh–Rh bond lengths.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on PrGe3Rh by Materials Project

PrRhGe3 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Pr is bonded in a 12-coordinate geometry to five equivalent Rh and twelve Ge atoms. There are one shorter (3.46 Å) and four longer (3.54 Å) Pr–Rh bond lengths. There are a spread of Pr–Ge bond distances ranging from 3.23–3.48 Å. Rh is bonded in a 5-coordinate geometry to five equivalent Pr and five Ge atoms. There are one shorter (2.41 Å) and four longer (2.46 Å) Rh–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 2-coordinate geometry to four equivalent Pr, two equivalent Rh, and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.75 Å. In the second Ge site, Ge is bonded in a 1-coordinate geometry to four equivalent Pr, one Rh, and four equivalent Ge atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on TbRh2 by Materials Project

TbRh2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Tb is bonded in a 12-coordinate geometry to twelve equivalent Rh atoms. All Tb–Rh bond lengths are 3.14 Å. Rh is bonded to six equivalent Tb and six equivalent Rh atoms to form a mixture of edge, corner, and face-sharing RhTb6Rh6 cuboctahedra. All Rh–Rh bond lengths are 2.68 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CeGe3Rh by Materials Project

CeRhGe3 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. Ce is bonded in a 12-coordinate geometry to five equivalent Rh and twelve Ge atoms. There are one shorter (3.37 Å) and four longer (3.54 Å) Ce–Rh bond lengths. There are eight shorter (3.22 Å) and four longer (3.47 Å) Ce–Ge bond lengths. Rh is bonded in a 5-coordinate geometry to five equivalent Ce and five Ge atoms. There are one shorter (2.40 Å) and four longer (2.44 Å) Rh–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 2-coordinate geometry to four equivalent Ce, two equivalent Rh, and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.73 Å. In the second Ge site, Ge is bonded in a 1-coordinate geometry to four equivalent Ce, one Rh, and four equivalent Ge atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on LaGe3Rh by Materials Project

LaRhGe3 crystallizes in the tetragonal I4mm space group. The structure is three-dimensional. La is bonded in a 12-coordinate geometry to five equivalent Rh and twelve Ge atoms. There are one shorter (3.47 Å) and four longer (3.55 Å) La–Rh bond lengths. There are a spread of La–Ge bond distances ranging from 3.25–3.49 Å. Rh is bonded in a 5-coordinate geometry to five equivalent La and five Ge atoms. There are one shorter (2.43 Å) and four longer (2.47 Å) Rh–Ge bond lengths. There are two inequivalent Ge sites. In the first Ge site, Ge is bonded in a 2-coordinate geometry to four equivalent La, two equivalent Rh, and two equivalent Ge atoms. Both Ge–Ge bond lengths are 2.76 Å. In the second Ge site, Ge is bonded in a 1-coordinate geometry to four equivalent La, one Rh, and four equivalent Ge atoms.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on SrRh2 by Materials Project

SrRh2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Sr is bonded in a 12-coordinate geometry to twelve equivalent Rh atoms. All Sr–Rh bond lengths are 3.23 Å. Rh is bonded to six equivalent Sr and six equivalent Rh atoms to form a mixture of corner, edge, and face-sharing RhSr6Rh6 cuboctahedra. All Rh–Rh bond lengths are 2.75 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Zn13Rh by Materials Project

RhZn13 crystallizes in the monoclinic C2/m space group. The structure is three-dimensional. Rh is bonded to twelve Zn atoms to form corner-sharing RhZn12 cuboctahedra. There are a spread of Rh–Zn bond distances ranging from 2.58–2.69 Å. There are five inequivalent Zn sites. In the first Zn site, Zn is bonded in a distorted linear geometry to two equivalent Rh and two equivalent Zn atoms. Both Zn–Zn bond lengths are 2.79 Å. In the second Zn site, Zn is bonded in a 1-coordinate geometry to one Rh and four Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.60–2.84 Å. In the third Zn site, Zn is bonded in a 1-coordinate geometry to one Rh and four Zn atoms. There are a spread of Zn–Zn bond distances ranging from 2.65–2.85 Å. In the fourth Zn site, Zn is bonded in a 1-coordinate geometry to one Rh and ten Zn atoms. The Zn–Zn bond length is 2.59 Å. In the fifth Zn site, Zn is bonded in a 10-coordinate geometry to ten Zn atoms. The Zn–Zn bond length is 2.72 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on DyRh2 by Materials Project

DyRh2 is Cubic Laves structured and crystallizes in the cubic Fd-3m space group. The structure is three-dimensional. Dy is bonded in a 12-coordinate geometry to twelve equivalent Rh atoms. All Dy–Rh bond lengths are 3.13 Å. Rh is bonded to six equivalent Dy and six equivalent Rh atoms to form a mixture of face, edge, and corner-sharing RhDy6Rh6 cuboctahedra. All Rh–Rh bond lengths are 2.67 Å.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on Rh3(PbS)2 by Materials Project

Rh3(PbS)2 crystallizes in the trigonal R-3m space group. The structure is three-dimensional. Rh is bonded in a distorted linear geometry to four Pb and two equivalent S atoms. There are two shorter (2.89 Å) and two longer (2.91 Å) Rh–Pb bond lengths. Both Rh–S bond lengths are 2.34 Å. There are two inequivalent Pb sites. In the first Pb site, Pb is bonded to six equivalent Rh and two equivalent S atoms to form corner-sharing PbRh6S2 hexagonal bipyramids. Both Pb–S bond lengths are 3.08 Å. In the second Pb site, Pb is bonded in a hexagonal planar geometry to six equivalent Rh atoms. S is bonded in a 4-coordinate geometry to three equivalent Rh and one Pb atom.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Materials Data on CrAsRh by Materials Project

CrRhAs crystallizes in the hexagonal P-62m space group. The structure is three-dimensional. Cr is bonded in a 11-coordinate geometry to six equivalent Rh and five As atoms. There are two shorter (2.88 Å) and four longer (2.98 Å) Cr–Rh bond lengths. There are one shorter (2.65 Å) and four longer (2.72 Å) Cr–As bond lengths. Rh is bonded in a 12-coordinate geometry to six equivalent Cr and four As atoms. There are two shorter (2.46 Å) and two longer (2.50 Å) Rh–As bond lengths. There are two inequivalent As sites. In the first As site, As is bonded in a 9-coordinate geometry to six equivalent Cr and three equivalent Rh atoms. In the second As site, As is bonded in a 9-coordinate geometry to three equivalent Cr and six equivalent Rh atoms.

36 MATERIALS SCIENCE↗