1,048 research outputs found
One-electron atomic-molecular ions containing Lithium in a strong magnetic field
The one-electron Li-containing Coulomb systems of atomic type and
molecular type , and are studied in
the presence of a strong magnetic field a.u. in the
non-relativistic framework. They are considered at the Born-Oppenheimer
approximation of zero order (infinitely massive centers) within the parallel
configuration (molecular axis parallel to the magnetic field). The variational
and Lagrange-mesh methods are employed in complement to each other. It is
demonstrated that the molecular systems , and
can exist for sufficiently strong magnetic fields a.u. and that can even be stable at
magnetic fields typical of magnetars.Comment: 22 pages, 9 figures, 4 table
Climate Variability, Communities\u27 Perceptions and Land Management Strategies in Lay Gayint Woreda, Northwest Ethiopia
Climate variability is the fluctuation of climatic elements from the normal or baseline values. Agrarian communities are the most sensitive social groups to climate variability and associate extreme weather-induced hazards due to the fact that climate variability affects the two most important direct agricultural production inputs, such as rainfall and temperature. As Ethiopia is heavily dependent on agriculture its economic development is being hindered by climate variability coupled with many other deriving forces. Therefore, the objective of this study is to examine climate variability, local communities\u27 perceptions and land management strategies to reduce the adverse impact of climate variability in Lay Gayint Woreda, Ethiopia. Both primary and secondary data were used to complete this study. Primary data were collected and analyzed from a total of 200 randomly selected respondents reside in different agro-ecological areas. Metrology data were gathered from Nefas Mewcha Station from the years 1979 to 2010. Standardized rainfall anomaly index (SRAI), crop diversification index (CDI) and other descriptive statistical techniques were used to analyze the data. The results obtained from the climate data revealed an increase in temperature, and decrease and/or erratic in rainfall distribution. Time series SRAI from 1979 to 2010 indicates that 2002 and 2008 were characterized by extreme and severe dry conditions in order of importance with high impact on crop yields whist only 1984 and 1990 received near normal rainfall amount. Similarly, the survey result reveals that out of the total household heads, 87.5 % perceived that there was an increase in temperature over the last 20 years. The survey result also disclosed that significant numbers of households are more likely to adopt different land management strategies to reduce the negative impact of climate variability. Constructing terraces and check dams as well as planting trees were the major land management strategies used by the local communities. However, crop diversification index (CDI) was found to be 0.11 as the cultivated area is stanch to one crop indicating very low alternative crop production in the study area. Although the study area receives variable and inefficient rainfall the rugged topography and poor soil conditions have hindered the development of irrigation facilities. Local context-specific integrated watershed management activities, small-scale irrigation schemes and extension services need to be strengthened to reduce the impact of climate variability. Policy makers need also to substantially invest in establishing information dissemination systems in order to provide reliable weather information for farmers given that crop production is largely dependent on it
Radiative transitions of the helium atom in highly magnetized neutron star atmospheres
Recent observations of thermally emitting isolated neutron stars revealed
spectral features that could be interpreted as radiative transitions of He in a
magnetized neutron star atmosphere. We present Hartree-Fock calculations of the
polarization-dependent photoionization cross sections of the He atom in strong
magnetic fields ranging from 10^12 G to 10^14 G. Convenient fitting formulae
for the cross sections are given as well as related oscillator strengths for
various bound-bound transitions. The effects of finite nucleus mass on the
radiative absorption cross sections are examined using perturbation theory.Comment: 14 pages, 7 figures. Minor changes. MNRAS in pres
The disarrayed mutation results in cell cycle and neurogenesis defects during retinal development in zebrafish
BACKGROUND: The vertebrate retina is derived from proliferative neuroepithelial cells of the optic cup. During retinal development, cell proliferation and the processes of cell cycle exit and neurogenesis are coordinated in neuroepithelial progenitor cells. Previous studies have demonstrated reciprocal influences between the cell cycle and neurogenesis. However the specific mechanisms and exact relationships of cell cycle regulation and neurogenesis in the vertebrate retina remain largely unknown. RESULTS: We have isolated and characterized a zebrafish mutant, disarrayed (dry(a64)), which exhibits retinal defects in cell cycle regulation and neurogenesis. By 42 hours post fertilization, disarrayed mutants show small eyes and a reduced forebrain. Other aspects of development appear normal. Although retinogenesis is delayed, mutant retinal cells eventually differentiate to all major cell types. Examination of the disarrayed mitotic cycle using BrdU and direct imaging techniques revealed that retinal neuroepithelial cells have an extended cell cycle period and reduced rate of cell cycle exit and neurogenesis, despite the fact that neurogenesis initiates at the appropriate time of development. Genetic mosaic analyses indicate that the cell cycle phenotype of disarrayed is cell-non-autonomous. CONCLUSION: The disarrayed mutant shows defects in both cell cycle regulation and neurogenesis and provides insights into the coordinated regulation of these processes during retinal development
Interference effects in the Coulomb dissociation of 15,17,19C
In this work the semiclassical model of pure Coulomb excitation was applied
to the breakup of 15,17,19C. The ground state wave functions were calculated in
the particle-rotor model including core excitation. The importance of
interference terms in the dipole strength arising after including core degrees
of freedom is analyzed for each isotope. It is shown that Coulomb interference
effects are important for the case of 17C.Comment: 17 pages, 5 figures accepted to Physical Review
A generalized Tullock contest
We construct a generalized Tullock contest under complete information where contingent upon winning or losing, the payoff of a player is a linear function of prizes, own effort, and the effort of the rival. This structure nests a number of existing contests in the literature and can be used to analyze new types of contests. We characterize the unique symmetric equilibrium and show that small parameter modifications may lead to substantially different types of contests and hence different equilibrium effort levels
Relation between widths of proton resonances and neutron asymptotic normalization coefficients in mirror states of light nuclei in a microscopic cluster model
It has been suggested recently ({\it Phys. Rev. Lett.} 91, 232501 (2003))
that the widths of narrow proton resonances are related to neutron Asymptotic
Normalization Coefficients (ANCs) of their bound mirror analogs because of
charge symmetry of nucleon-nucleon interactions.
This relation is approximated by a simple analytical formula which involves
proton resonance energies, neutron separation energies, charges of residual
nuclei and the range of their strong interaction with the last nucleon. In the
present paper, we perform microscopic-cluster model calculations for the ratio
of proton widths to neutron ANCs squared in mirror states for several light
nuclei. We compare them to predictions of the analytical formula and to
estimates made within a single-particle potential model. A knowledge of this
ratio can be used to predict unknown proton widths for very narrow low-lying
resonances in the neutron-deficient region of the - and -shells, which
is important for understanding the nucleosynthesis in the -process.Comment: 13 pages, 5 figures, submitted to PR
Microscopic description of the beta delayed deuteron emission from \bbox{^6}He
The beta delayed deuteron emission from He is studied in a dynamical
microscopic cluster model. This model gives a reasonably good description for
all the subsystems of He and Li in a coherent way, without any free
parameter. The beta decay transition probability to the Li ground state is
underestimated by a few percents. The theoretical beta delayed deuteron
spectrum is close to experiment but it is also underestimated by about a factor
1.7. We argue that, in spite of their different magnitudes, both
underestimations might have a common origin. The model confirms that the
neutron halo part of the He wave function plays a crucial role in quenching
the beta decay toward the + d channel.Comment: LATEX with REVTEX, Submitted to Phys. Rev. C, 11 pages, 3 figures
(not included) are available upon request. ATOMKI-93/
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