4,601 research outputs found
C3 Photosynthesis in the Gametophyte of the Epiphytic CAM Fern Pyrrosia Longifolia (Polypodiaceae)
This is the publisher's official version, also available at: http://www.jstor.org/stable/2445689Sporophytes of some epiphytic species in the fern genus Pyrrosia exhibit Crassulacean acid metabolism (CAM), generally
considered to be a derived physiological response to xeric habitats. Because these species alternate between independent
sporophytic and gametophytic generations yet only the sporophyte has been characterized physiologically, experiments were
conducted to determine the photosynthetic pathways present in mature sporophytes, immature sporophytes, and gametophytes
of Pyrrosia longifolia. Diurnal C 0 2 exchange and malic acid fluctuations demonstrated that although the mature
sporophytes exhibited CAM, only C3 photosynthesis occurred in the gametophytes and young sporophytes. Consideration
of the above results and those from previous studies, as well as the life cycle of ferns, indicates that the induction of CAM
probably occurs at a certain developmental stage of the sporophyte and/or following exposure to stress. Elucidation of the
precise mechanisms underlying this C^-CAM transition awaits further research
Quantifying structural damage from self-irradiation in a plutonium superconductor
The 18.5 K superconductor PuCoGa5 has many unusual properties, including
those due to damage induced by self-irradiation. The superconducting transition
temperature decreases sharply with time, suggesting a radiation-induced Frenkel
defect concentration much larger than predicted by current radiation damage
theories. Extended x-ray absorption fine-structure measurements demonstrate
that while the local crystal structure in fresh material is well ordered, aged
material is disordered much more strongly than expected from simple defects,
consistent with strong disorder throughout the damage cascade region. These
data highlight the potential impact of local lattice distortions relative to
defects on the properties of irradiated materials and underscore the need for
more atomic-resolution structural comparisons between radiation damage
experiments and theory.Comment: 7 pages, 5 figures, to be published in PR
ESDIS Standards Office (ESO): Requirements, Standards and Practices
The ESDIS Standards Office assists the ESDIS Project in formulating standards policy for NASA Earth Science Data Systems (ESDS), coordinates standards activities within ESDIS, and provides technical expertise and assistance with standards related tasks within the NASA Earth Science Data System Working Groups (ESDSWG). This poster summarizes information found on the earthdata.nasa.gov site that describes the ESO
Self-stresses and Crack Formation by Particle Swelling in Cohesive Granular Media
We present a molecular dynamics study of force patterns, tensile strength and
crack formation in a cohesive granular model where the particles are subjected
to swelling or shrinkage gradients. Non-uniform particle size change generates
self-equilibrated forces that lead to crack initiation as soon as strongest
tensile contacts begin to fail. We find that the coarse-grained stresses are
correctly predicted by an elastic model that incorporates particle size change
as metric evolution. The tensile strength is found to be well below the
theoretical strength as a result of inhomogeneous force transmission in
granular media. The cracks propagate either inward from the edge upon shrinkage
and outward from the center upon swelling
Applying the SPoRT Paradigm to Transitioning the Near Real-Time MAG4 Solar Event Forecast Model into Space Weather Operations
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Small, Low-energy, Dispersive Solar Energetic Particle Events Observed by Parker Solar Probe
The Energetic Particle Instrument–Low Energy (EPI-Lo) experiment has detected several weak, low-energy (~30–300 keV nucleon⁻¹) solar energetic particle (SEP) events during its first two closest approaches to the Sun, providing a unique opportunity to explore the sources of low-energy particle acceleration. As part of the Parker Solar Probe (PSP) Integrated Science Investigation of the Sun (IS⊙IS) suite, EPI-Lo was designed to investigate the physics of energetic particles; however, in the special lowest-energy "time-of-flight only" product used in this study, it also responds to solar photons in a subset of approximately sunward-looking apertures lacking special light-attenuating foils. During the first three perihelia, in a frame rotating with the Sun, PSP undergoes retrograde motion, covering a 17° heliographic longitudinal range three times during the course of the ~11-day perihelion passes, permitting a unique spatial and temporal study into the location, correlation, and persistence of previously unmeasurable SEPs. We examine the signatures of these SEPs (during the first PSP perihelion pass only) and the connection to possible solar sources using remote observations from the Solar Dynamics Observatory (SDO), the Solar TErrestrial RElations Observatory (STEREO), and the ground-based Global Oscillation Network Group (GONG). The orientation of the Sun relative to STEREO, SDO, and GONG makes such identifications challenging, but we do have several candidates, including an equatorial coronal hole at a Carrington longitude of ~335°. To analyze observations from EPI-Lo, which is a new type of particle instrument, we examine instrumental effects and provide a preliminary separation of the ion signal from the photon background
Identification of Phthalates in Medications and Dietary Supplement Formulations in the United States and Canada
Background: In animal studies, some ortho-phthalates, including di(2-ethylhexyl) phthalate (DEHP) and di-n-butyl phthalate (DBP), have been shown to be reproductive and developmental toxicants. Human studies show widespread population exposure to background levels of phthalates. Limited evidence suggests that particularly high exposure levels may result from orally ingested medicinal products containing phthalates as excipients (inactive ingredients)
Multiconfigurational nature of 5f orbitals in uranium and plutonium intermetallics
Uranium and plutonium's 5f electrons are tenuously poised between strongly
bonding with ligand spd-states and residing close to the nucleus. The unusual
properties of these elements and their compounds (eg. the six different
allotropes of elemental plutonium) are widely believed to depend on the related
attributes of f-orbital occupancy and delocalization, for which a quantitative
measure is lacking. By employing resonant x-ray emission spectroscopy (RXES)
and x-ray absorption near-edge structure (XANES) spectroscopy and making
comparisons to specific heat measurements, we demonstrate the presence of
multiconfigurational f-orbital states in the actinide elements U and Pu, and in
a wide range of uranium and plutonium intermetallic compounds. These results
provide a robust experimental basis for a new framework for understanding the
strongly-correlated behavior of actinide materials.Comment: 30 pages, concatenated article and supporting information, 10 figure
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