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Superconductivity of indium and tin under uniform compression
Starting from leaf reflectance and transmittance measurements, we calculated two substantially different values of the Photochemical Reflectance Index (PRI) for each of 22 corn leaves having leaf chlorophyll concentrations ranging from high to low. Leaf reflectance and transmittance were measured simultaneously, precluding changes in leaf light use efficiency (LEU) between measurements. We propose the proportion of leaves reflecting v. transmitting direct beam sunlight toward a canopy reflectance sensor is a potential source of variability in estimates of canopy bidirectional PRI.
This study evaluates a direct remote sensing approach from space for the determination of ecosystem photosynthetic light use efficiency (LUE), through measurement of vegetation reflectance changes expressed with the Photochemical Reflectance Index (PRI). The PRI is a normalized difference index based on spectral changes at a physiologically active wavelength (approximately 531 nanometers) as compared to a reference waveband, and is only available from a very few satellites. These include the two Moderate-Resolution Imaging Spectroradiometers (MODIS) on the Aqua and Terra satellites each of which have a narrow (10-nanometer) ocean band centered at 531 nanometers. We examined several PRI variations computed with candidate reference bands, since MODIS lacks the traditional 570-nanometer reference band. The PRI computed using MODIS land band 1 (620-670 nanometers) gave the best performance for daily LUE estimation. Through rigorous statistical analyses over a large image collection (n equals 420), the success of relating in situ daily tower-derived LUE to MODIS observations for northern forests was strongly influenced by satellite viewing geometry. LUE was calculated from CO2 fluxes (moles per moles of carbon absorbed quanta) measured at instrumented Canadian Carbon Program flux towers in four Canadian forests: a mature fir site in British Columbia, mature aspen and black spruce sites in Saskatchewan, and a mixed deciduous/coniferous forest site in Ontario. All aspects of the viewing geometry had significant effects on the MODIS-PRI, including the view zenith angle (VZA), the view azimuth angle, and the displacement of the view azimuth relative to the solar principal plane, in addition to illumination related variables.Nevertheless, we show that forward scatter sector views (VZA, 16 degrees-45 degrees) provided the strongest relationships to daily LUE, especially those collected in the early afternoon by Aqua (r squared = 0.83, RMSE (root mean square error) equals 0.003 moles per moles of carbon absorbed quanta). Nadir (VZA, 0 degrees plus or minus 15 degrees) and backscatter views (VZA, −16 degrees to −45 degrees) had lower performance in estimating LUE (nadir: r squared approximately equal to 0.62-0.67; backscatter: r squared approximately equal to 0.54-0.59) and similar estimation error (RMSE equals 0.004-0.005).When directional effects were not considered, only a moderately successful MODIS-PRI vs. LUE relationship (r squared equals 0.34, RMSE equals 0.007) was obtained in the full dataset (all views & sites, both satellites), but site-specific relationships were able to discriminate between coniferous and deciduous forests. Overall, MODIS-PRI values from Terra (late morning) were higher than those from Aqua (early afternoon), before/after the onset of diurnal stress responses expressed spectrally. Therefore, we identified ninety-two Terra-Aqua "same day" pairs, for which the sum of Terra morning and Aqua afternoon MODIS-PRI values (PRI (sub sum) using all available directional observations was linearly correlated with daily tower LUE (r squared equals 0.622, RMSE equals 0.013) and independent of site differences or meteorological information. Our study highlights the value of off-nadir directional reflectance observations, and the value of pairing morning and afternoon satellite observations to monitor stress responses that inhibit carbon uptake in Canadian forest ecosystems. In addition, we show that MODIS-PRI values, when derived from either: (i) forward views only, or (ii) Terra/Aqua same day (any view) combined observations, provided more accurate estimates of tower-measured daily LUE than those derived from either nadir or backscatter views or those calculated by the widely used semi-operational MODIS GPP model (MOD17) which is based on a theoretical maximum LUE and environmental data. Consequently, we demonstrate the importance of diurnal as well as off-nadir satellite observations for detecting vegetation physiological processes.
Determining the health and vigor of vegetation using high spectral resolution remote sensing is an important goal which has application to monitoring agriculture and ecosystem productivity and carbon exchange. Two spectral indices used to assess whether vegetation is performing near-optimally or exhibiting symptoms of environmental stress (e.g., drought or nutrient deficiency, non-optimal temperatures, etc.) are the Photochemical Reflectance Index (PRI) and solar-induced red and far-red Chlorophyll Fluorescence (Fs). Both the PRI and Fs capture the dynamics of photoprotection mechanisms within green foliage: the PRI is based on the association of the reflected radiation in the green spectrum with the xanthophyll cycle, whereas Fs measures the emitted radiation in the red and far-red spectrum. Fs was determined from retrievals in the atmospheric oxygen absorption features centered at 688 and 760 nm using a modified Fraunhofer Line Depth (FLD) method. We previously demonstrated diurnal and seasonal PRI differences for sunlit vs. shaded foliage in a conifer forest canopy, as expressed in the hotspot and darkspot of the Bidirectional Reflectance Function (BRF). In a USDA-ARS experimental field site located in Beltsville, MD, USA, measurements were acquired over a corn crop from a nadir view in 2008 with an ASD FieldSpec Pro (Analytical Spectral Devices, Inc., Boulder, CO, USA) to study the behavior of the PRI for sunlit and shaded foliage as captured in reflectance variations associated with the BRF, in a I m tall canopy in the vegetative growth stage. Those observations were compared to simulations obtained from two radiative transfer models. Measurements were then acquired to examine whether the PRI and Fs were influenced by view zenith and azimuth geometries at different times of day. Those measurements were made in 2010 with the Ocean Optics USB4000 Miniature Fiber Optic Spectrometer (Ocean Optics Inc., Dunedin, Florida, USA) at several times during the day on multiple days throughout the growing season. We found that the PRI consistently had higher values, indicating lower stress, in the BRF darkspot associated with shaded foliage than in the hotspot associated with sunlit foliage. We also found that Fs exhibited differences associated with sunlit and shaded canopy sectors, which were most pronounced for the red/far-red Fs ratio. Values indicated greater physiological stress in afternoons compared to mornings, and in the early senescent canopy as compared to the vegetative growth stage, BRFs for both the PRI and the red/far-red Fs ratio were bowl-shaped for the full azimuth sweep of the canopy. These two spectral indices (PRI, Fs ratio) provided complementary information on the photosynthetic function of the corn canopy.
In remote sensing, the Photochemical Reflectance Index (PRI) provides insight into physiological processes occurring inside the leaves in a stand of plants. Developed by Gamon et al., (1990 and 1992), PRI evolved from laboratory measurements of the reflectance of individual leaves (Bilger et al.,1989). Yet in a remotely sensed image, a pixel measurement may include light from both reflecting and transmitting leaves. We conducted laboratory experiments comparing values of PRI based upon polarized reflectance and transmittance measurements of water and nutrient stressed leaves. We illuminated single detached leaves using a current controlled light source (Oriel model 66881) and measured the leaf weight using an analytical balance (Mettler model AE 260) and the light reflected and transmitted by the leaf during dry down using two Analytical Spectral Devices spectroradiometers. Polarizers on the incident and reflected light beams allowed us to divide the leaf reflectance into two parts: a polarized surface reflectance and a non-polarized 'leaf interior' reflectance. Our results underscore the importance when calculating PRI of removing the leaf surface reflection, which contains no information about physiological processes ongoing in the leaf interior. The results show that the leaf physiology information is in the leaf interior reflectance, not the leaf transmittance. Applied to a plant stand, these results suggest use of polarization measurements in sun-view directions that minimize the number of sunlit transmitting leaves in the sensor field of view.
Two bio-indicators, the Photochemical Reflectance Index (PRI) and solar-induced red and far-red Chlorophyll Fluorescence (SIF), were derived from directional hyperspectral observations and studied in a cornfield on two contrasting days in the growing season. Both red and far-red SIF exhibited higher values on the day when the canopy in the early senescent stage, but only the far-red SIF showed sensitivity to viewing geometry. Consequently, the red/far-red SIF ratio varied greatly among azimuth positions while the largest values were obtained for the "hotspot" at both growth stages. This ratio was lower (approx.0.88 +/- 0.4) in early July than in August when the ratio approached equivalence (near approx.1). In concert, the PRI exhibited stronger responses to both zenith and azimuth angles and different values on the two growth stages. The potential of using these indices to monitor photosynthetic activities needs further investigation
Even though over half of the world's soil organic carbon (SOC) is stored in subsoils (>20 cm deep), and the old ages of subsoil OC indicate its cycling differs from surface SOC, there are few studies examining in situ decomposition processes in deep soils. The purpose of this dataset is to elucidate these processes. In this study we added 13C-labeled fine roots to 15, 55, and 95 cm depths of a well-characterized coniferous forest Alfisol and monitored the amount of root-derived C remaining over 6, 12, and 30 months. We recovered the root-derived C in microbial phospholipid fatty acids (PLFAs) after 6 months and in coarse (>2 mm) particulate, fine (<2 mm) particulate, and dense, mineral-associated pools after 6, 12, and 30 months. Overall, root decomposition in the first 6 months was similar among all depths but significantly diverged at 30 months with faster decomposition at 15 cm than at 95 cm. There were more fungal and Gram negative-associated PLFAs at 15 cm than at 95 cm, and 13C analysis revealed those microbial groups preferred the added root carbon to native SOC. Mineral-associations were not the cause of slower decomposition at depth because similar amounts of applied root C was recovered in the dense fraction at all depths. The largest difference among depths was in the amount of root C recovered in the coarse particulate fraction, which was greater at 95 cm (50%) than at 15 cm (15%). Slower decomposition of the particulate pool at depth likely contributed to the increase in C:N ratios and depletion of δ13C values below 60 cm depth in our soil profiles. Simulations of these soils using the CORPSE model, which incorporates microbial priming effects and mineral stabilization of SOC, reproduced patterns of particulate and mineral-associated SOC over both time and depth and suggested that a lack of priming by root exudates at depth could account for the slower decomposition rate of particulate root material. Decomposition of deep particulate SOC may increase if root exudation or dissolved OC transport to depth increases.This dataset includes (1) characterization of the soil pits prior to litter addition, (2) characterization of how the litter changed after 6, 12, and 30 months, and (3) the CORPSE model structure, parameterization, and output.
YPr is beta-derived structured and crystallizes in the trigonal R3m space group. The structure is three-dimensional. there are four inequivalent Pr sites. In the first Pr site, Pr is bonded to nine Pr and three equivalent Y atoms to form PrPr9Y3 cuboctahedra that share corners with six equivalent PrPr9Y3 cuboctahedra, corners with twelve YPr3Y9 cuboctahedra, edges with six equivalent YPr3Y9 cuboctahedra, edges with twelve PrPr9Y3 cuboctahedra, faces with eight YPr3Y9 cuboctahedra, and faces with twelve PrPr9Y3 cuboctahedra. There are six shorter (3.67 Å) and three longer (3.72 Å) Pr–Pr bond lengths. All Pr–Y bond lengths are 3.60 Å. In the second Pr site, Pr is bonded to six equivalent Pr and six Y atoms to form PrPr6Y6 cuboctahedra that share corners with six equivalent YPr3Y9 cuboctahedra, corners with twelve PrPr6Y6 cuboctahedra, edges with six equivalent PrPr6Y6 cuboctahedra, edges with twelve YPr3Y9 cuboctahedra, faces with seven PrPr6Y6 cuboctahedra, and faces with thirteen YPr3Y9 cuboctahedra. All Pr–Pr bond lengths are 3.67 Å. There are three shorter (3.62 Å) and three longer (3.64 Å) Pr–Y bond lengths. In the third Pr site, Pr is bonded to nine Pr and three equivalent Y atoms to form PrPr9Y3 cuboctahedra that share corners with three equivalent YPr3Y9 cuboctahedra, corners with twelve PrPr6Y6 cuboctahedra, edges with nine YPr3Y9 cuboctahedra, edges with twelve PrPr9Y3 cuboctahedra, faces with six equivalent YPr6Y6 cuboctahedra, and faces with thirteen PrPr9Y3 cuboctahedra. All Pr–Pr bond lengths are 3.67 Å. All Pr–Y bond lengths are 3.62 Å. In the fourth Pr site, Pr is bonded to six equivalent Pr and six Y atoms to form PrPr6Y6 cuboctahedra that share corners with six equivalent YPr3Y9 cuboctahedra, corners with twelve PrPr9Y3 cuboctahedra, edges with six equivalent PrPr6Y6 cuboctahedra, edges with twelve YPr6Y6 cuboctahedra, faces with seven PrPr9Y3 cuboctahedra, and faces with thirteen YPr3Y9 cuboctahedra. All Pr–Pr bond lengths are 3.67 Å. There are three shorter (3.62 Å) and three longer (3.64 Å) Pr–Y bond lengths. There are four inequivalent Y sites. In the first Y site, Y is bonded to three equivalent Pr and nine Y atoms to form YPr3Y9 cuboctahedra that share corners with six equivalent PrPr9Y3 cuboctahedra, corners with nine YPr3Y9 cuboctahedra, edges with six equivalent PrPr6Y6 cuboctahedra, edges with fifteen YPr6Y6 cuboctahedra, faces with seven PrPr9Y3 cuboctahedra, and faces with twelve YPr3Y9 cuboctahedra. There are three shorter (3.57 Å) and six longer (3.67 Å) Y–Y bond lengths. In the second Y site, Y is bonded to six Pr and six equivalent Y atoms to form YPr6Y6 cuboctahedra that share corners with six equivalent PrPr9Y3 cuboctahedra, corners with nine YPr3Y9 cuboctahedra, edges with nine YPr3Y9 cuboctahedra, edges with twelve PrPr9Y3 cuboctahedra, faces with six equivalent YPr6Y6 cuboctahedra, and faces with thirteen PrPr9Y3 cuboctahedra. All Y–Y bond lengths are 3.67 Å. In the third Y site, Y is bonded to three equivalent Pr and nine Y atoms to form YPr3Y9 cuboctahedra that share corners with six equivalent YPr3Y9 cuboctahedra, corners with nine PrPr6Y6 cuboctahedra, edges with nine PrPr9Y3 cuboctahedra, edges with twelve YPr3Y9 cuboctahedra, faces with seven PrPr9Y3 cuboctahedra, and faces with twelve YPr3Y9 cuboctahedra. All Y–Y bond lengths are 3.67 Å. In the fourth Y site, Y is bonded to six Pr and six equivalent Y atoms to form YPr6Y6 cuboctahedra that share corners with six equivalent PrPr9Y3 cuboctahedra, corners with nine YPr3Y9 cuboctahedra, edges with nine YPr6Y6 cuboctahedra, edges with twelve PrPr9Y3 cuboctahedra, faces with six equivalent YPr6Y6 cuboctahedra, and faces with thirteen PrPr9Y3 cuboctahedra. All Y–Pr bond lengths are 3.62 Å. All Y–Y bond lengths are 3.67 Å.
The synthesis, structural, magnetic, thermal, and transport properties are reported for polycrystalline PrIr 3 . At room temperature PrIr 3 displays the rhombohedral space group R–3m and a PuNi 3 -type structure. At around 70 K a phase transition to a monoclinic C2/m structure is observed and continued cooling reveals temperature independent behavior of the unit cell volume. Further, PrIr 3 undergoes a paramagnetic to ferromagnetic transition with T c =7.5K. The temperature dependent magnetic susceptibility follows the Curie-Weiss law with a positive Curie-Weiss temperature, and an effective moment that is close to the theoretical effective moment for a free Pr +3 ion. Finally, the structural transition introduces further complexity into the behavior of PuNi 3 -type materials and highlights the importance of temperature-dependent structural studies to complement physical property measurements in intermetallic compounds.
Post-buckling behavior of cylindrical shells - axial compression and external pressure effects
Investigation of upper atmosphere by satellites cosmos iii and cosmos v
Safety measures against radiation hazard during vostok iii and iv space flights
Earth radiation measurements by meteorological satellites
Atmospheric density measurement using manometers mounted in unoriented satellite
Temperature measurement of atmosphere with satellite-borne instruments
Accelerometric precordial ballistocardiogram in hypertension
Stellar evolution & liberation of gravitational energy from charged particle collision
Rhythm variations of neurons of reticular formation during lateral overloads