3,278 research outputs found
Fission decay of N = Z nuclei at high angular momentum: Zn
Using a unique two-arm detector system for heavy ions (the BRS, binary
reaction spectrometer) coincident fission events have been measured from the
decay of Zn compound nuclei formed at 88MeV excitation energy in the
reactions with Ar beams on a Mg target at Ar) =
195 MeV. The detectors consisted of two large area position sensitive (x,y) gas
telescopes with Bragg-ionization chambers. From the binary coincidences in the
two detectors inclusive and exclusive cross sections for fission channels with
differing losses of charge were obtained. Narrow out-of-plane correlations
corresponding to coplanar decay are observed for two fragments emitted in
binary events, and in the data for ternary decay with missing charges from 4 up
to 8. After subtraction of broad components these narrow correlations are
interpreted as a ternary fission process at high angular momentum through an
elongated shape. The lighter mass in the neck region consists dominantly of two
or three-particles. Differential cross sections for the different mass splits
for binary and ternary fission are presented. The relative yields of the binary
and ternary events are explained using the statistical model based on the
extended Hauser-Feshbach formalism for compound nucleus decay. The ternary
fission process can be described by the decay of hyper-deformed states with
angular momentum around 45-52 .Comment: 23 pages, 25 figure
Atmospheric studies of habitability in the Gliese 581 system
The M-type star Gliese 581 is orbited by at least one terrestrial planet
candidate in the habitable zone, i.e. GL 581 d. Orbital simulations have shown
that additional planets inside the habitable zone of GL 581 would be
dynamically stable. Recently, two further planet candidates have been claimed,
one of them in the habitable zone.
In view of the ongoing search for planets around M stars which is expected to
result in numerous detections of potentially habitable Super-Earths, we take
the GL 581 system as an example to investigate such planets. In contrast to
previous studies of habitability in the GL 581 system, we use a consistent
atmospheric model to assess surface conditions and habitability. Furthermore,
we perform detailed atmospheric simulations for a much larger subset of
potential planetary and atmospheric scenarios than previously considered.
A 1D radiative-convective atmosphere model is used to calculate temperature
and pressure profiles of model atmospheres, which we assumed to be composed of
molecular nitrogen, water, and carbon dioxide. In these calculations, key
parameters such as surface pressure and CO2 concentration as well as orbital
distance and planetary mass are varied.
Results imply that surface temperatures above freezing could be obtained,
independent of the here considered atmospheric scenarios, at an orbital
distance of 0.117 AU. For an orbital distance of 0.146 AU, CO2 concentrations
as low as 10 times the present Earth's value are sufficient to warm the surface
above the freezing point of water. At 0.175 AU, only scenarios with CO2
concentrations of 5% and 95% were found to be habitable. Hence, an additional
Super-Earth planet in the GL 581 system in the previously determined dynamical
stability range would be considered a potentially habitable planet.Comment: 5 pages, 4 figures, accepted in Astronomy&Astrophysic
The population of deformed bands in Cr by emission of Be from the S + Mg reaction
Using particle- coincidences we have studied the population of final
states after the emission of 2 -particles and of Be in nuclei
formed in S+Mg reactions at an energy of . The data were obtained in a setup
consisting of the GASP -ray detection array and the multidetector array
ISIS. Particle identification is obtained from the E and E signals of
the ISIS silicon detector telescopes, the Be being identified by the
instantaneous pile up of the E and E pulses. -ray decays of the
Cr nucleus are identified with coincidences set on 2 -particles
and on Be. Some transitions of the side-band with show
stronger population for Be emission relative to that of 2
-particles (by a factor ). This observation is interpreted as
due to an enhanced emission of Be into a more deformed nucleus.
Calculations based on the extended Hauser-Feshbach compound decay formalism
confirm this observation quantitatively.Comment: 17 pages, 9 figures accepted for publication in J. Phys.
Crop Performance and Yield of Groundnut, Sesame and Roselle in an Agroforesty Cropping System with Acacia senegal in North Kordofan (Sudan)
Crop performance and yield of groundnut (Arachis hypogea), sesame (Sesamum indicum) and roselle (Hibiscus sabdariffa) were investigated in an intercropping system with Acacia senegal and compared with sole cropping. The study was conducted in North Kordofan (Sudan) on loamy sand. Experimental design was a randomized complete block with split plots.Crop performance and crop yield of groundnut, sesame and roselle were significantly (p 0.05) reduced in the intercropping system compared to sole cropping. However, yield reduction in groundnut (53%) was much higher than in sesame (6%) and roselle (14%). The reduction in yield of the intercropping plots could be due to the high tree density, which results in water and light competition between the trees and the agricultural crops
The use of plasma ashers and Monte Carlo modeling for the projection of atomic oxygen durability of protected polymers in low Earth orbit
The results of ground laboratory and in-space exposure of polymeric materials to atomic oxygen has enabled the development of a Monte Carlo computational model which simulates the oxidation processes of both environments. The cost effective projection of long-term low-Earth-orbital durability of protected polymeric materials such as SiO(x)-coated polyimide Kapton photovoltaic array blankets will require ground-based testing to assure power system reliability. Although silicon dioxide thin film protective coatings can greatly extend the useful life of polymeric materials in ground-based testing, the projection of in-space durability based on these results can be made more reliable through the use of modeling which simulates the mechanistic properties of atomic oxygen interaction, and replicates test results in both environments. Techniques to project long-term performance of protected materials, such as the Space Station Freedom solar array blankets, are developed based on ground laboratory experiments, in-space experiments, and computational modeling
Monte Carlo modeling of atomic oxygen attack of polymers with protective coatings on LDEF
Characterization of the behavior of atomic oxygen interaction with materials on the Long Duration Exposure Facility (LDEF) assists in understanding of the mechanisms involved. Thus the reliability of predicting in-space durability of materials based on ground laboratory testing should be improved. A computational model which simulates atomic oxygen interaction with protected polymers was developed using Monte Carlo techniques. Through the use of an assumed mechanistic behavior of atomic oxygen interaction based on in-space atomic oxygen erosion of unprotected polymers and ground laboratory atomic oxygen interaction with protected polymers, prediction of atomic oxygen interaction with protected polymers on LDEF was accomplished. However, the results of these predictions are not consistent with the observed LDEF results at defect sites in protected polymers. Improved agreement between observed LDEF results and predicted Monte Carlo modeling can be achieved by modifying of the atomic oxygen interactive assumptions used in the model. LDEF atomic oxygen undercutting results, modeling assumptions, and implications are presented
Detectability of atmospheric features of Earth-like planets in the habitable zone around M dwarfs
We investigate the detectability of atmospheric spectral features of
Earth-like planets in the habitable zone (HZ) around M dwarfs with the future
James Webb Space Telescope (JWST). We use a coupled 1D climate-chemistry-model
to simulate the influence of a range of observed and modelled M-dwarf spectra
on Earth-like planets. The simulated atmospheres served as input for the
calculation of the transmission spectra of the hypothetical planets, using a
line-by-line spectral radiative transfer model. To investigate the
spectroscopic detectability of absorption bands with JWST we further developed
a signal-to-noise ratio (S/N) model and applied it to our transmission spectra.
High abundances of CH and HO in the atmosphere of Earth-like planets
around mid to late M dwarfs increase the detectability of the corresponding
spectral features compared to early M-dwarf planets. Increased temperatures in
the middle atmosphere of mid- to late-type M-dwarf planets expand the
atmosphere and further increase the detectability of absorption bands. To
detect CH, HO, and CO in the atmosphere of an Earth-like planet
around a mid to late M dwarf observing only one transit with JWST could be
enough up to a distance of 4 pc and less than ten transits up to a distance of
10 pc. As a consequence of saturation limits of JWST and less pronounced
absorption bands, the detection of spectral features of hypothetical Earth-like
planets around most early M dwarfs would require more than ten transits. We
identify 276 existing M dwarfs (including GJ 1132, TRAPPIST-1, GJ 1214, and LHS
1140) around which atmospheric absorption features of hypothetical Earth-like
planets could be detected by co-adding just a few transits. We show that using
transmission spectroscopy, JWST could provide enough precision to be able to
partly characterise the atmosphere of Earth-like TESS planets around mid to
late M dwarfs.Comment: 18 pages, 10 figure
Big Five personality and religiosity: Bidirectional cross-lagged effects and their moderation by culture
Objective: Personality has long been assumed to be a cause of religiosity, not a consequence. Yet, recent research suggests that religiosity may well cause personality change. Consequently, longitudinal research is required that examines the bi-directionality between personality and religiosity. The required research must also attend to cultural religiosity - a critical moderator in previous cross-sectional research. Method: We conducted four-wave, cross-lagged panel models assessing the bi-directional effects between religiosity (measured as religious attendance) and the Big Five personality traits over 12 years in 14 samples (Ntotal = 44,485). Each sample used population-representative data from a different German federal state - states that vary widely in religiosity. Results: The findings were the following: (1) Agreeableness, openness, and conscientiousness were associated with changes in religiosity, with the latter two effects being culture-contingent. (2) Religiosity was associated with changes in agreeableness and openness, with the latter effect being culture-contingent. (3) The cross-lagged effects of personality on religiosity were overall stronger than the reverse effects. Conclusions: The directionality between the Big Five and religiosity seems to go both ways and culture matters for those effects. We discuss the power of religiosity to alter personality and the role of culture for this effect and for personality change more generally
Very high-energy γ-ray observations of the Crab nebula and other potential sources with the GRAAL experiment
The “γ-ray astronomy at Almeria” (GRAAL) experiment uses 63 heliostat-mirrors with a total mirror area of ≈2500 m2 from the CESA-1 field at the “Plataforma Solar de Almeria” to collect Cherenkov light from air showers. The detector is located in a central solar tower and detects photon-induced showers with an energy threshold of 250±110 GeV and an asymptotic effective detection area of about 15 000 m2. A comparison between the results of detailed Monte-Carlo simulations and data is presented.
Data sets taken in the period September 1999–September 2000 in the direction of the Crab pulsar, the active galaxy 3C 454.3, the unidentified γ-ray source 3EG J1835+59 and a “pseudosource” were analyzed for high energy γ-ray emission. Evidence for a γ-ray flux from the Crab pulsar with an integral flux of 2.2±0.4 above threshold and a significance of 4.5σ in a total measuring time of 7 h and 10 min on source was found. No evidence for emission from the other sources was found.
Some difficulties with the use of heliostat fields for γ-ray astronomy are pointed out. In particular the effect of field-of-view restricted to the central part of a detected air shower on the lateral distribution and timing properties of Cherenkov light are discussed. Upon restriction the spread of the timing front of proton-induced showers sharply decreases and the reconstructed direction becomes biased towards the pointing direction. This is shown to make efficient γ-hadron separation difficult
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