304 research outputs found
Microsite occupancy and spatial structure of regeneration in three late-successional Norway spruce forests in northern Europe
A comparison of microsite occupancy and the spatial structure of regeneration in three areas of late-successional Norway spruce dominated forest. Pallas-Ylläs is understood to have been influenced only by small-scale disturbance; Dvina-Pinega has had sporadic larger-scale disturbances; Kazkim has been affected by fire. All spruce and birch trees with diameter at breast height (DBH) ?10 cm were mapped in five stands on 40 m x 400 m transects, and those with DBH < 10 cm on 2 or 4 m x 400 m subplots. Microsite type was inventoried at 1m intervals along the centre line and for each tree with DBH < 10 cm. At all study areas small seedlings (h < 0.3 m, DBH < 10 cm) preferentially occupied disturbed microsites. In contrast, spruce saplings (h ? 1.3 m, DBH <10 cm) at all study areas showed less, or no, preference. At Pallas-Ylläs spruce seedlings (h < 1.3 m, DBH < 10 cm) and saplings (h ? 1.3 m, DBH < 10 cm) exhibited spatial correlation at scales from 32-52 m. At Dvina-Pinega saplings of both spruce and birch exhibited spatial correlation at scales from 32-81 m. At Kazkim spatial correlation of seedlings and saplings of both species was exhibited over variable distances. No spatial cross-correlation was found between overstorey basal area (DBH ? 10 cm) and regeneration (h ? 1.3 m, DBH < 10 cm) at any study area. The results confirm the importance of disturbed microsites for seedling establishment, but suggest that undisturbed microsites may sometimes be more advantageous for long-term tree survival. The regeneration gap concept may not be useful in describing the regeneration dynamics of late-successional boreal forests
Pastoral theology and use of power
https://place.asburyseminary.edu/ecommonsatsdissertations/1121/thumbnail.jp
Evolution and Spectral Response of a Steam Atmosphere for Early Earth with a coupled climate-interior model
The evolution of Earth's early atmosphere and the emergence of habitable
conditions on our planet are intricately coupled with the development and
duration of the magma ocean phase during the early Hadean period (4 to 4.5 Ga).
In this paper, we deal with the evolution of the steam atmosphere during the
magma ocean period. We obtain the outgoing longwave radiation using a
line-by-line radiative transfer code GARLIC. Our study suggests that an
atmosphere consisting of pure HO, built as a result of outgassing extends
the magma ocean lifetime to several million years. The thermal emission as a
function of solidification timescale of magma ocean is shown. We study the
effect of thermal dissociation of HO at higher temperatures by applying
atmospheric chemical equilibrium which results in the formation of H and
O during the early phase of the magma ocean. A 1-6\% reduction in the OLR
is seen. We also obtain the effective height of the atmosphere by calculating
the transmission spectra for the whole duration of the magma ocean. An
atmosphere of depth ~100 km is seen for pure water atmospheres. The effect of
thermal dissociation on the effective height of the atmosphere is also shown.
Due to the difference in the absorption behavior at different altitudes, the
spectral features of H and O are seen at different altitudes of the
atmosphere. Therefore, these species along with HO have a significant
contribution to the transmission spectra and could be useful for placing
observational constraints upon magma ocean exoplanets.Comment: 22 pages, 17 Figures, accepted for publication in ApJ on March
Uncertainty in phosphine photochemistry in the Venus atmosphere prevents a firm biosignature attribution
Context. The possible detection of phosphine (PH3) in the clouds of Venus has raised the question as to which processes could produce such large abundances of PH3. Previous studies suggested that abiotic processes including photochemical production cannot explain the claimed PH3 concentrations. However, the photochemistry of phosphorus-bearing species in the atmosphere of Venus is not well known.
Aims. We aim to assess the abiotic production of PH3 considering the effect of uncertainties in the chemical rate coefficients of phosphorus-containing reactions.
Methods. Using a photochemical column model, we simulated Venus-like conditions and varied the chemical rate coefficients with a Monte Carlo (MC) approach in order to estimate the associated error in the PH3 abundances throughout the atmosphere.
Results. Current uncertainties and missing data in photochemical rate coefficients lead to a variation of about six orders of magnitude in the modelled PH3 abundance on Venus, assuming photochemical production of PH3 from tetraphosphorus hexoxide (P4O6) pathways. Our results suggest an abiotically produced upper limit of 2 ppb PH3 between 50 and 60 km. These concentrations are in the range of a recent reanalysis of Atacama Large Millimeter Array (ALMA) data, suggesting planet-averaged abundances in PH3 of 1–4 ppb above 55 km. Future observations of phosphorus monoxide (PO) on Venus would be beneficial for increasing our confidence in assessing PH3 as a biosignature.
Conclusions. We conclude that due to the large uncertainties in phosphorus chemistry, even a firm detection of several ppb PH3 in the Venus atmosphere would not necessarily mean a biological origin
The Role of N2 as a Geo-Biosignature for the Detection and Characterization of Earth-like Habitats
Since the Archean, N2 has been a major atmospheric constituent in Earth's
atmosphere. Nitrogen is an essential element in the building blocks of life,
therefore the geobiological nitrogen cycle is a fundamental factor in the long
term evolution of both Earth and Earth-like exoplanets. We discuss the
development of the Earth's N2 atmosphere since the planet's formation and its
relation with the geobiological cycle. Then we suggest atmospheric evolution
scenarios and their possible interaction with life forms: firstly, for a
stagnant-lid anoxic world, secondly for a tectonically active anoxic world, and
thirdly for an oxidized tectonically active world. Furthermore, we discuss a
possible demise of present Earth's biosphere and its effects on the atmosphere.
Since life forms are the most efficient means for recycling deposited nitrogen
back into the atmosphere nowadays, they sustain its surface partial pressure at
high levels. Also, the simultaneous presence of significant N2 and O2 is
chemically incompatible in an atmosphere over geological timescales. Thus, we
argue that an N2-dominated atmosphere in combination with O2 on Earth-like
planets within circumstellar habitable zones can be considered as a
geo-biosignature. Terrestrial planets with such atmospheres will have an
operating tectonic regime connected with an aerobe biosphere, whereas other
scenarios in most cases end up with a CO2-dominated atmosphere. We conclude
with implications for the search for life on Earth-like exoplanets inside the
habitable zones of M to K-stars
Spectral features of Earth-like planets and their detectability at different orbital distances around F, G, and K-type stars
We investigate the spectral appearance of Earth-like exoplanets in the HZ of
different main sequence stars at different orbital distances. We furthermore
discuss for which of these scenarios biomarker absorption bands may be detected
during primary or secondary transit with near-future telescopes and
instruments.We analyze the spectra taking into account different filter
bandpasses of two photometric instruments planned to be mounted to the JWST. We
analyze in which filters and for which scenarios molecular absorption bands are
detectable when using the space-borne JWST or the ground-based telescope E-ELT.
Absorption bands of CO2, H2O, CH4 and O3 are clearly visible in high-resolution
spectra as well as in the filters of photometric instruments. However, only
during primary eclipse bands of CO2, H2O and O3 are detectable for all
scenarios when using photometric instruments and an E-ELT telescope setup. CH4
is only detectable at the outer HZ of the K star since here the atmospheric
modeling results in very high abundances. Since the detectable CO2 and H2O
bands overlap, separate bands need to be observed to prove their existence in
the atmosphere. In order to detect H2O in a separate band, a S/N>7 needs to be
achieved for E-ELT observations, e.g. by co-adding at least 10 transit
observations. Using a spaceborne telescope like the JWST enables the detection
of CO2 at 4.3mu, which is not possible for ground-based observations due to the
Earth's atmospheric absorption. Hence combining observations of spaceborne and
groundbased telescopes might allow to detect the presence of the biomarker
molecule O3 and the related compounds H2O and CO2 in a planetary atmosphere.
Other absorption bands using the JWST can only be detected for much higher
S/Ns, which is not achievable by just co-adding transit observations since this
would be far beyond the planned mission time of JWST.(abridged)Comment: 15 pages, 8 figure
Biomarker Response to Galactic Cosmic Ray-Induced NOx and the Methane Greenhouse Effect in the Atmosphere of an Earthlike Planet Orbiting an M-Dwarf Star
Planets orbiting in the habitable zone (HZ) of M-Dwarf stars are subject to
high levels of galactic cosmic rays (GCRs) which produce nitrogen oxides in
earthlike atmospheres. We investigate to what extent this NOx may modify
biomarker compounds such as ozone (O3) and nitrous oxide (N2O), as well as
related compounds such as water (H2O) (essential for life) and methane (CH4)
(which has both abiotic and biotic sources) . Our model results suggest that
such signals are robust, changing in the M-star world atmospheric column by up
to 20% due to the GCR NOx effects compared to an M-star run without GCR effects
and can therefore survive at least the effects of galactic cosmic rays. We have
not however investigated stellar cosmic rays here. CH4 levels are about 10
times higher than on the Earth related to a lowering in hydroxyl (OH) in
response to changes in UV. The increase is less than reported in previous
studies. This difference arose partly because we used different biogenic input.
For example, we employed 23% lower CH4 fluxes compared to those studies. Unlike
on the Earth, relatively modest changes in these fluxes can lead to larger
changes in the concentrations of biomarker and related species on the M-star
world. We calculate a CH4 greenhouse heating effect of up to 4K. O3
photochemistry in terms of the smog mechanism and the catalytic loss cycles on
the M-star world differs considerably compared with the Earth
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The effect of National defense education act counseling institutes on the measured interests of institute enrollees
In the 1961-62 academic year there were thirteen National
Defense Education Act Counseling and Guidance Training Institutes
established at institutions of higher education about the country.
The purpose of these institutes was to upgrade the counseling and
guidance skills of personnel employed as half-time counselors in
secondary schools. As a part of the evaluation process of these
institutes, students were administered a number of tests at the beginning
and at the end of the institute experience. One of these
evaluative tools was the Strong Vocational Interest Blank for Men.
Three problems were investigated. The first was to determine
the effect of the intensive Counseling and Guidance Training
Institute program on the Institute enrollees' interests as measured
by the Strong Vocational Interest Blank. The second was to determine
if there were common interest patterns among the enrollees.
The third problem was to investigate the relationship between
interest patterns and the enrollees' ratings of success in counseling
by Institute staff.
In this study it was hypothesized that the intensive nature of
the institute experience would cause marked shifts in interest patterns
on the part of the enrollees. These shifts would be toward
Group V, Welfare and Social Service, Group VIII, Administrative
Detail, and Group X, Communications, and away from Group I,
Biological Science, Group II, Physical Science, Group III, Technical,
and Group IX, Sales. It was also expected that enrollees would have
common profile patterns on admission to the institute, and that
these profile patterns would be especially similar for those who had
been grouped in the top, average, or low rated group of enrollees.
Using the t-test of mean differences, it was found that there
were no statistically significant differences at acceptable levels of
confidence between the interest patterns of enrollees from the pretest
to the post-test administration of the Strong Vocational Interest
Blank. In addition, there were no common profile patterns among
the enrollees on admission to the institute, nor were there any
common interest patterns among those who were rated by staff as
being in the top, average, or low group of enrollees. Approximately
63 percent of the enrollees had a primary interest pattern in the
social service area. Thirty-six percent had primary interest
patterns in administrative detail, and all of the other primary pattern
groups contained less than 30 percent of the enrollees. Likewise,
61 percent of the enrollees had reject patterns in Group II,
Physical Science, while 34 percent had a reject pattern in Group VI,
Musician, and Group I, Biological Science. There were no significant
changes in interest pattern profiles from the pre-test to the
post-test and there were no significant differences in the profile
patterns of those in the top-rated, low-rated, or average groups of
enrollees
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