1,398 research outputs found
40 years of Studies on the Relationships Between Grass Species, N Turnover and Nutrient Cycling in the Lamto Reserve in the Ivory Coast (Côte d’Ivoire)
The Lamto Station, dominated by grass savannas, was created in 1963. Among other problems, the relationships between savanna grasses (mainly Andropogoneae supertribe) and nutrient cycling, mainly nitrogen (N), have been intensively studied. Such grass systems are of major interest. Savannas represent 25% of terrestrial biomes and are second to tropical forests in the contribution to terrestrial primary production and are predominant in African social and economic environments. The Andropogoneae grasses are of particular interest for pastures. Second, savannas are generally extremely nutrient-poor, especially for N, which often limits productivity. Third, little is known about possible controls of grasses on N processes (e.g. nitrification) which could provide plants with potential advantages in competing for N, and induce changes in system N balance. Finally, these areas are considered to be non-emitting for NO and N2O as a result of extremely low nitrificatio
Pair Correlation Functions and a Free-Energy Functional for the Nematic Phase
In this paper we have presented the calculation of pair correlation functions
in a nematic phase for a model of spherical particles with the long-range
anisotropic interaction from the mean spherical approximation(MSA) and the
Percus-Yevick (PY) integral equation theories. The results found from the MSA
theory have been compared with those found analytically by Holovko and
Sokolovska (J. Mol. Liq. , 161(1999)). A free energy functional which
involves both the symmetry conserving and symmetry broken parts of the direct
pair correlation function has been used to study the properties of the nematic
phase. We have also examined the possibility of constructing a free energy
functional with the direct pair correlation function which includes only the
principal order parameter of the ordered phase and found that the resulting
functional gives results that are in good agreement with the original
functional. The isotropic-nematic transition has been located using the grand
thermodynamic potential. The PY theory has been found to give nematic phase
with pair correlation function harmonic coefficients having all the desired
features. In a nematic phase the harmonic coefficient of the total pair
correlation function connected with the correlations
of the director transverse fluctuations should develop a long-range tail. This
feature has been found in both the MSA and PY theories.Comment: 27 pages, 11 figures, Accepted in J. Chem. Phy
Marine fisheries of Orissa
A brief account of marine fish landings in Orissa during 1985 to
1995 is given in this paper. Gearwise, groupwise and districtwise marine
fish landings in this state was also discussed together with a critical analysis
of marine fishery of the state during the last five decade
Cathodoluminescence hyperspectral imaging of trench-like defects in InGaN/GaN quantum well structures
Optoelectronic devices based on the III-nitride system exhibit remarkably good optical efficiencies despite suffering from a large density of defects. In this work we use cathodoluminescence (CL) hyperspectral imaging to study InGaN/GaN multiple quantum well (MQW) structures. Different types of trench defects with varying trench width, namely wide or narrow trenches forming closed loops and open loops, are investigated in the same hyperspectral CL measurement. A strong redshift (90 meV) and intensity increase of the MQW emission is demonstrated for regions enclosed by wide trenches, whereas those within narrower trenches only exhibit a small redshift (10 meV) and a slight reduction of intensity compared with the defect-free surrounding area. Transmission electron microscopy (TEM) showed that some trench defects consist of a raised central area, which is caused by an increase of about 40% in the thickness of the InGaN wells. The causes of the changes in luminescences are also discussed in relation to TEM results identifying the underlying structure of the defect. Understanding these defects and their emission characteristics is important for further enhancement and development of light-emitting diodes
Pre-main-sequence population in NGC 1893 region: X-ray properties
Continuing the attempt to understand the properties of the stellar content in
the young cluster NGC 1893 we have carried out a comprehensive multi-wavelength
study of the region. The present study focuses on the X-ray properties of
T-Tauri Stars (TTSs) in the NGC 1893 region. We found a correlation between the
X-ray luminosity, , and the stellar mass (in the range 0.22.0 \msun) of
TTSs in the NGC 1893 region, similar to those reported in some other young
clusters, however the value of the power-law slope obtained in the present
study ( 0.9) for NGC 1893 is smaller than those (1.4 - 3.6)
reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions.
However, the slope in the case of Class III sources (Weak line TTSs) is found
to be comparable to that reported in the case of NGC 6611 ( 1.1). It is
found that the presence of circumstellar disks has no influence on the X-ray
emission. The X-ray luminosity for both CTTSs and WTTSs is found to decrease
systematically with age (in the range 0.4 Myr - 5 Myr). The decrease of
the X-ray luminosity of TTSs (slope -0.6) in the case of NGC 1893 seems
to be faster than observed in the case of other star-forming regions (slope
-0.2 to -0.5). There is indication that the sources having relatively large NIR
excess have relatively lower values. TTSs in NGC 1893 do not follow the
well established X-ray activity - rotation relation as in the case of
main-sequence stars.Comment: 10 pages, 7 figures, Accepted for publication in New Astronom
Nitrogen Management in Grasslands and Forage-Based Production Systems–Role of Biological Nitrification Inhibition (BNI)
Nitrogen (N), being the most critical and essential nutrient for plant growth, largely determines the productivity in both extensive- and intensive- grassland systems. Nitrification and denitrification processes in the soil are the primary drivers generating reactive-N: NO3-, N2O, and NO, and is largely responsible for N-loss and degradation of grasslands. Suppressing nitrification can thus facilitate the retention of soil-N to sustain long-term productivity of grasslands and forage-based production systems. Certain plants can suppress soil nitrification by releasing inhibitors from roots, a phenomenon termed ‘biological nitrification inhibition’ (BNI). Recent methodological developments (e.g. bioluminescence assay to detect BNIs from plant-root systems) led to significant advances in our ability to quantify and characterize BNI function in pasture grasses. Among grass-pastures, BNI-capacity is strongest in low-N adapted grasses such as Brachiaria humidicola and weakest in high-N environment grasses such as Italian ryegrass (Lolium perenne) and B. brizantha. The chemical identity of some of the BNIs produced in plant tissues and released from roots has now been established and their mode of inhibitory action determined on nitrifying bacteria Nitrosomonas. Synthesis and release of BNIs is a highly regulated and localized process, triggered by the presence of NH4+ in the rhizosphere, which facilitates the release of BNIs close to soil-nitrifier sites. Substantial genotypic variation is found for BNI-capacity in B. humidicola, which opens the way for its geneticmanipulation. Field studies suggest that Brachiaria grasses suppress nitrification and N2O emissions from soil. The potential for exploiting BNI function (from a genetic improvement and a system perspective) to develop production systems that are low-nitrifying, low N2O-emitting, economically efficient and ecologically sustainable, will be the subject of discussion
Estimated marine fish landings (in tonnes)in India during 2002 and 2003
Estimated marine fishing landing in India during 2002 and 2003 is 2.59 and 2.58 millon tonnes respectively. Gear wise landing were also estimated during this period
Effect of QW growth temperature on the optical properties of blue and green InGaN/GaN QW structures
In this paper we report on the impact that the quantum well growth temperature has on the internal quantum efficiency and carrier recombination dynamics of two sets of InGaN/GaN multiple quantum well samples, designed to emit at 460 and 530 nm, in which the indium content of the quantum wells within each sample set was maintained. Measurements of the internal quantum efficiency of each sample set showed a systematic variation, with quantum wells grown at a higher temperature exhibiting higher internal quantum efficiency and this variation was preserved at all excitation power densities. By investigating the carrier dynamics at both 10 K and 300 K we were able to attribute this change in internal quantum efficiency to a decrease in the non-radiative recombination rate as the QW growth temperature was increased which we attribute to a decrease in incorporation of the point defects
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