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

Prediction Based Efficient Resource Provisioning and Its Impact on QoS Parameters in the Cloud Environment

The purpose of this paper is to provision the on demand resources to the end users as per their need using prediction method in cloud computing environment. The provisioning of virtualized resources to cloud consumers according to their need is a crucial step in the deployment of applications on the cloud. However, the dynamical management of resources for variable workloads remains a challenging problem for cloud providers. This problem can be solved by using a prediction based adaptive resource provisioning mechanism, which can estimate the upcoming resource demands of applications. The present research introduces a prediction based resource provisioning model for the allocation of resources in advance. The proposed approach facilitates the release of unused resources in the pool with quality of service (QoS), which is defined based on prediction model to perform the allocation of resources in advance. In this work, the model is used to determine the future workload prediction for user requests on web servers, and its impact toward achieving efficient resource provisioning in terms of resource exploitation and QoS. The main contribution of this paper is to develop the prediction model for efficient and dynamic resource provisioning to meet the requirements of end users

Free-energy functional for freezing transitions: Hard sphere systems freezing into crystalline and amorphous structures

A free-energy functional that contains both the symmetry conserved and symmetry broken parts of the direct pair correlation function has been used to investigate the freezing of a system of hard spheres into crystalline and amorphous structures. The freezing parameters for fluid-crystal transition have been found to be in very good agreement with the results found from simulations. We considered amorphous structures found from the molecular dynamics simulations at packing fractions $\eta$ lower than the glass close packing fraction $\eta_{J}$ and investigated their stability compared to that of a homogeneous fluid. The existence of free-energy minimum corresponding to a density distribution of overlapping Gaussians centered around an amorphous lattice depicts the deeply supercooled state with a heterogeneous density profile

Crystallization of Simple Fluids: Relative Stability of f.c.c. and b.c.c Structures

A free-energy functional for a crystal that contains both the symmetry conserved and symmetry broken parts of the direct pair correlation function is developed. The free-energy functional is used to investigate the crystallization of fluids interacting via the inverse power potential ; $u(r)=\epsilon {(\sigma/r)}^n$. In agreement with simulation results we find that for $n=12$ the freezing is into close packed f.c.c structure while for soft repulsions $(n\leq 6)$ b.c.c phase is more stable.Comment: 9 pages, 2 figure

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. $\bf 82$, 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 $h({\bf x_1},{\bf x_2})$ 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

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, $L_X$, and the stellar mass (in the range 0.2$-$2.0 \msun) of TTSs in the NGC 1893 region, similar to those reported in some other young clusters, however the value of the power-law slope obtained in the present study ($\sim$ 0.9) for NGC 1893 is smaller than those ($\sim$1.4 - 3.6) reported in the case of TMC, ONC, IC 348 and Chameleon star forming regions. However, the slope in the case of Class III sources (Weak line TTSs) is found to be comparable to that reported in the case of NGC 6611 ($\sim$ 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 $\sim$ 0.4 Myr - 5 Myr). The decrease of the X-ray luminosity of TTSs (slope $\sim$ -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 $L_X$ 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

Origin and consequences of chromosomal inversions in the virilis group of Drosophila

In Drosophila, large variations in rearrangement rate have been reported among different lineages and among Muller’s elements. Nevertheless, the mechanisms that are involved in the generation of inversions, their increase in frequency, as well as their impact on the genome are not completely understood. This is in part due to the lack of comparative studies on species distantly related to Drosophila melanogaster. Therefore, we sequenced and assembled the genomes of two species of the virilis phylad (Drosophila novamexicana [15010-1031.00] and Drosophila americana [SF12]), which are diverging from D. melanogaster for more than 40 Myr. Based on these data, we identified the precise location of six novel inversion breakpoints. A molecular characterization provided clear evidence that DAIBAM (a miniature inverted–repeat transposable element) was involved in the generation of eight out of the nine inversions identified. In contrast to what has been previously reported for D. melanogaster and close relatives, ectopic recombination is thus the prevalent mechanism of generating inversions in species of the virilis phylad. Using pool-sequencing data for three populations of D. americana, we also show that common polymorphic inversions create a high degree of genetic differentiation between populations for chromosomes X, 4, and 5 over large physical distances. We did not find statistically significant differences in expression levels between D. americana (SF12) and D. novamexicana (15010-1031.00) strains for the three genes surveyed (CG9588, Fig 4, and fab1) flanking three inversion breakpoints.This article is a result of the project Norte-01-0145-FEDER-000008—Porto Neurosciences and Neurologic Disease Research Initiative at I3S, supported by Norte Portugal Regional Operational Programme (NORTE 2020), under the PORTUGAL 2020 Partnership Agreement, through the European Regional Development Fund (FEDER). N.P. and M.R. are funded by the Emmy Noether Programme of the Deutsche Forschungsgemeinschaft (Grant Number: PO 1648/3-1 to N.P.). We would like to thank the Transcriptome Analysis Lab (TAL) (University Medical Center Göttingen, UMG) in Göttingen for the Illumina sequencing