33 research outputs found
Discovery of Fulminic Acid, HCNO, in Dark Clouds
We report on the first detection in space of fulminic acid, HCNO. This isomer
of HNCO has been observed in three starless cores, B1, L1544 and L183, and in
the low mass star forming region L1527 with a measured abundance ratio of
HNCO/HCNO between 40-70. However, HCNO was not detected towards the direction
of the cyanopolyyne peak of TMC-1 or towards the Orion Hot Core region. The
derived HNCO/HCNO abundance ratio in these cases is greater than 350 and 1000
in TMC-1 and Orion, respectively. We find that CH_2 + NO \to HCNO + H is a key
reaction for the formation of fulminic acid. A value of 5.5 10^{-12} cm^3
s^{-1} of the corresponding reaction rate coefficient, as given by Miller et
al. (2003), allows to reproduce the observed abundances of fulminic acid in
both the observed dark clouds and low mass star forming core, where the
determined abundance of HNCO in these regions with respect to molecular
hydrogen is 1-5 10^{-10}.Comment: 5 pages, 1 figure, accepted for publication in ApJ
Inverse scattering method and vector higher order nonlinear Schrodinger equation
A generalised inverse scattering method has been developed for arbitrary n
dimensional Lax equations. Subsequently, the method has been used to obtain N
soliton solutions of a vector higher order nonlinear Schrodinger equation,
proposed by us. It has been shown that under suitable reduction, vector higher
order nonlinear Schrodinger equation reduces to higher order nonlinear
Schrodinger equation. The infinite number of conserved quantities have been
obtained by solving a set of coupled Riccati equation. A gauge equivalence is
shown between the vector higher order nonlinear Schrodinger equation and the
generalized Landau Lifshitz equation and the Lax pair for the latter equation
has also been constructed in terms of the spin field, establishing direct
integrability of the spin system.Comment: 28 page
Modulational instability and nonlocality management in coupled NLS system
The modulational instability of two interacting waves in a nonlocal Kerr-type
medium is considered analytically and numerically. For a generic choice of wave
amplitudes, we give a complete description of stable/unstable regimes for zero
group-velocity mismatch. It is shown that nonlocality suppresses considerably
the growth rate and bandwidth of instability. For nonzero group-velocity
mismatch we perform a geometrical analysis of a nonlocality management which
can provide stability of waves otherwise unstable in a local medium.Comment: 15 pages, 12 figures, to be published in Physica Script
Pan-African Genetic Structure in the African Buffalo (Syncerus caffer): Investigating Intraspecific Divergence
The African buffalo (Syncerus caffer) exhibits extreme morphological variability, which has led to controversies about the validity and taxonomic status of the various recognized subspecies. The present study aims to clarify these by inferring the pan-African spatial distribution of genetic diversity, using a comprehensive set of mitochondrial D-loop sequences from across the entire range of the species. All analyses converged on the existence of two distinct lineages, corresponding to a group encompassing West and Central African populations and a group encompassing East and Southern African populations. The former is currently assigned to two to three subspecies (S. c. nanus, S. c. brachyceros, S. c. aequinoctialis) and the latter to a separate subspecies (S. c. caffer). Forty-two per cent of the total amount of genetic diversity is explained by the between-lineage component, with one to seventeen female migrants per generation inferred as consistent with the isolation-with-migration model. The two lineages diverged between 145 000 to 449 000 years ago, with strong indications for a population expansion in both lineages, as revealed by coalescent-based analyses, summary statistics and a star-like topology of the haplotype network for the S. c. caffer lineage. A Bayesian analysis identified the most probable historical migration routes, with the Cape buffalo undertaking successive colonization events from Eastern toward Southern Africa. Furthermore, our analyses indicate that, in the West-Central African lineage, the forest ecophenotype may be a derived form of the savanna ecophenotype and not vice versa, as has previously been proposed. The African buffalo most likely expanded and diverged in the late to middle Pleistocene from an ancestral population located around the current-day Central African Republic, adapting morphologically to colonize new habitats, hence developing the variety of ecophenotypes observed today
Heel impact forces during barefoot versus minimally shod walking among Tarahumara subsistence farmers and urban Americans
A new approach to the analysis of the soliton: Nonuniform finite difference beam propagation method
Ferromagnetic properties of epitaxial manganite films on SrTiO\u3csub\u3e3\u3c/sub\u3e/Si heterostructures
We report on the magnetic properties of epitaxial La0.7Ba0.3MnO3 and La0.7Sr0.3MnO3 films on Si (100) and Si (111) substrates using SrTiO3 template layer, which demonstrate magnetic and electrical properties at and above room temperature. The magnetization data show magnetic transition and magnetic hysteresis at and above room temperature. The films show well-defined magnetic domains. The ferromagnetic resonance studies show anisotropic effects related to ferromagnetic properties of films. The smaller grain size of about 20 nm in manganite films on SrTiO3 /Si may be one of the reasons to minimize the strain effect through strain relaxation at the interface between SrTiO3and manganites through the formation of three-dimensional islands