2,382 research outputs found
Factors Affecting Recovery from Defoliation during Drought in Two Aridland Tussock Grasses
The importance of several factors in limiting recovery from defoliation was investigated in field-grown plants of Agropyron desertorum and Agropyron spicatum exposed to drought , natural or irrigated conditions. Leaf extension rate, components of leaf area production, number of metabolically active axillary buds and carbohydrate availability were examined on the same plants immediately after defoliation and/or in the following spring from 1984 until 1986.
The diurnal course of leaf growth did not relate to turgor pressure in the expanded portion of leaf laminae. Rather growth was apparently associated with air temperature. Leaf extension rate was lower under drought than under better moisture levels during 1984 to 1986. For both species, reduced growth rates and shorter growth periods resulted in reduced tiller height, leaf number and leaf size under drought compared with natural or irrigated conditions in 1985 and 1986, but not in 1984. As a result, leaf area and/or yields were also lower under drought in 1985 and 1986, and lowest under drought plus defoliation in 1986. Production of daughter tillers immediately after defoliation was also lowest under drought.
Regrowth capacity of both species was not limited by axillary bud number, size or viability immediately after defoliation under any water level in 1986. In early spring, however, tiller number and growth were lower on clipped than on unclipped plants of both species under drought and irrigated conditions in 1986, and under all water levels in 1987; this resulted in considerably reduced photosynthetic canopies on clipped plants.
Crown and root total nonstructural carbohydrate (TNC) pools were higher under drought than under better moisture levels in A. desertorum and A. spicatum in early spring 1986. These high pools of TNC apparently enhanced the production of etiolated regrowth in both species when meristematic limitations did not exist in early spring.
The productive potential of both Agropyron species will probably not be affected following a late and severe defoliation under drought. However, vegetative growth and/or productivity, and probably the persistence of these species in the community, will be reduced after two or more years of late and heavy defoliations under drought
DXA-Based Detection of Low Muscle Mass Using the Total Body Muscularity Assessment Index (TB-MAXI): A New Index with Cutoff Values from the NHANES 1999â2004
Evolution, Explosion and Nucleosynthesis of Core Collapse Supernovae
We present a new set of presupernova evolutions and explosive yields of
massive stars of initial solar composition (Y=0.285, Z=0.02) in the mass range
13-35 Msun. All the models have been computed with the latest version (4.97) of
the FRANEC code that now includes a nuclear network extending from neutrons to
Mo98. The explosive nucleosynthesis has been computed twice: a first one with
an hydro code and a second one following the simpler radiation dominated shock
approximation (RDA).Comment: 20 pages, 10 figures, 12 tables. Accepted for publication on Ap
The peculiar horizontal branch morphology of the Galactic globular clusters NGC 6388 and NGC 6441: new insights from UV observations
Context. In this paper we present multiband optical and UV Hubble Space Telescope photometry of the two Galactic globular clusters NGC 6388 and NGC 6441.
Aims. We investigate the properties of their anomalous horizontal branches in different photometric planes in order to shed light on the nature of the physical mechanism(s) responsible for the existence of an extended blue tail and of a slope in the horizontal branch, visible in all the color-magnitude diagrams.
Methods. New photometric data have been collected and carefully reduced. Empirical data have been compared with updated stellar models of low-mass, metal-rich, He-burning structures, transformed to the observational plane with appropriate model atmospheres.
Results. We have obtained the first UV color-magnitude diagrams for NGC 6388 and NGC 6441. These diagrams confirm previous results, obtained in optical bands, about the presence of a sizeable stellar population of extremely hot horizontal branch stars. At least in NGC 6388, we find a clear indication that at the hot end of the horizontal branch the distribution of stars forms a hook-like feature, closely resembling those observed in NGC 2808 and Omega Cen. We briefly review the theoretical scenarios that have been suggested for interpreting this observational feature. We also investigate the tilted horizontal branch morphology and provide further evidence that supports early suggestions that this feature cannot be interpreted as an effect of differential reddening. We show that a possible solution of the puzzle is to assume that a small fraction - ranging between 10-20% - of the stellar population in the two clusters is strongly helium-enriched (Y ~ 0.40 in NGC 6388 and Y ~ 0.35 in NGC 6441). The occurrence of a spread in the He abundance between the canonical value (Y ~ 0.26) and the quoted upper limits can significantly help in explaining the "whole" morphology of the horizontal branch and the pulsational properties of the variable stars in the target clusters
Dimensions of Adversity, Physiological Reactivity, and Externalizing Psychopathology in Adolescence: Deprivation and Threat
Dysregulation of autonomic nervous system (ANS) and hypothalamic-pituitary-adrenal (HPA) axis function is a putative intermediate phenotype linking childhood adversity (CA) with later psychopathology. However, associations of CAs with ANS and HPA-axis function vary widely across studies. Here, we test a novel conceptual model discriminating between distinct forms of CA (deprivation and threat) and examine their independent associations with physiological reactivity and psychopathology
Seed Production and Resource Allocation in Three Cultivars of \u3cem\u3eAchnatherum Hymenoides\u3c/em\u3e, Nevada, USA
Plant production is partially determined by resource allocation among various organs (Monsi & Murata, 1970), however, studies on dry matter partitioning among different plant organs are scarce in general (Marceli, 1996), and lacking in Achnatherum hymenoides. This study compared dry matter production and partitioning among three commercial cultivars (Paloma, Nezpar and Rimrock) of A. hymenoides and identified growth and developmental characteristics that could indicate potential seed production. In addition, the relationship between an organ weight as a percent of total aerial plant biomass was assessed
Discovery of Blue Hook Stars in the Massive Globular Cluster M54
We present BV photometry centered on the globular cluster M54 (NGC 6715). The
color-magnitude diagram clearly shows a blue horizontal branch extending
anomalously beyond the zero age horizontal branch theoretical models. These
kinds of horizontal branch stars (also called ``blue hook'' stars), which go
beyond the lower limit of the envelope mass of canonical horizontal branch hot
stars, have so far been known to exist in only a few globular clusters: NGC
2808, Omega Centauri (NGC 5139), NGC 6273, and NGC 6388. Those clusters, like
M54, are among the most luminous in our Galaxy, indicating a possible
correlation between the existence of these types of horizontal branch stars and
the total mass of the cluster. A gap in the observed horizontal branch of M54
around T(eff)= 27000 K could be interpreted within the late helium flash
theoretical scenario, a possible explanation for the origin of those stars.Comment: 10 pages, 2 figures, accepted for publication in the Astrophysical
Journa
On the Origin of the Early Solar System Radioactivities. Problems with the AGB and Massive Star Scenarios
Recent improvements in stellar models for intermediate-mass and massive stars
are recalled, together with their expectations for the synthesis of radioactive
nuclei of lifetime Myr, in order to re-examine the origins
of now extinct radioactivities, which were alive in the solar nebula. The
Galactic inheritance broadly explains most of them, especially if -process
nuclei are produced by neutron star merging according to recent models.
Instead, Al, Ca, Cs and possibly Fe require
nucleosynthesis events close to the solar formation. We outline the persisting
difficulties to account for these nuclei by Intermediate Mass Stars (2
M/M). Models of their final stages now
predict the ubiquitous formation of a C reservoir as a neutron capture
source; hence, even in presence of Al production from Deep Mixing or Hot
Bottom Burning, the ratio Al/Pd remains incompatible with
measured data, with a large excess in Pd. This is shown for two recent
approaches to Deep Mixing. Even a late contamination by a Massive Star meets
problems. In fact, inhomogeneous addition of Supernova debris predicts
non-measured excesses on stable isotopes. Revisions invoking specific low-mass
supernovae and/or the sequential contamination of the pre-solar molecular cloud
might be affected by similar problems, although our conclusions here are
weakened by our schematic approach to the addition of SN ejecta. The limited
parameter space remaining to be explored for solving this puzzle is discussed.Comment: Accepted for publication on Ap
Effects of neuromuscular electrical stimulation therapy on physical function in patients with COVID-19 associated pneumonia: Study protocol of a randomized controlled trial
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