13,050 research outputs found
GM crops and gender issues
Correspondence in the December issue by Jonathan Gressel not only states that gender issues in rural settings have not been adequately addressed with respect to weed control biotech but also asserts that such technology can increase the quality of life of rural women in developing countries. Improved weed control is a labor-saving technology that can result in less employment in a labor surplus rural economy. Often in rural areas, wage income is the main source of income and an important determinant of the quality of life, particularly where employment opportunities are generally limited. Apart from soil preparation, planting and weeding, harvesting is also 'femanual' work that can generate more employment if yields are higher. Biotech can enhance the quality of life of women but only if the technology is associated with overall generation of rural employment
Effect of oxygen concentration on the structural and magnetic properties of LaRh1/2Mn1/2O3 thin films
Epitaxial LaRh1/2Mn1/2O3 thin films have been grown on (001)-oriented LaAlO3
and SrTiO3 substrates using pulsed laser deposition. The optimized thin film
samples are semiconducting and ferromagnetic with a Curie temperature close to
100 K, a coercive field of 1200 Oe, and a saturation magnetization of 1.7muB
per formula unit. The surface texture, structural, electrical, and magnetic
properties of the LaRh1/2Mn1/2O3 films was examined as a function of the oxygen
concentration during deposition. While an elevated oxygen concentration yields
thin films with optimal magnetic properties, slightly lower oxygen
concentrations result in films with improved texture and crystallinity
Non-collinear Magnetic Order in the Double Perovskites: Double Exchange on a Geometrically Frustrated Lattice
Double perovskites of the form A_2BB'O_6 usually involve a transition metal
ion, B, with a large magnetic moment, and a non magnetic ion B'. While many
double perovskites are ferromagnetic, studies on the underlying model reveal
the possibility of antiferromagnetic phases as well driven by electron
delocalisation. In this paper we present a comprehensive study of the magnetic
ground state and T_c scales of the minimal double perovskite model in three
dimensions using a combination of spin-fermion Monte Carlo and variational
calculations. In contrast to two dimensions, where the effective magnetic
lattice is bipartite, three dimensions involves a geometrically frustrated face
centered cubic (FCC) lattice. This promotes non-collinear spiral states and
`flux' like phases in addition to collinear anti-ferromagnetic order. We map
out the possible magnetic phases for varying electron density, `level
separation' epsilon_B - epsilon_B', and the crucial B'-B' (next neighbour)
hopping t'.Comment: 15 pages pdflatex + 19 figs, revision: removed redundant comment
Dielectric and polarization experiments in high loss dielectrics: a word of caution
The recent quest for improved functional materials like high permittivity
dielectrics and/or multiferroics has triggered an intense wave of research.
Many materials have been checked for their dielectric permittivity or their
polarization state. In this report, we call for caution when samples are
simultaneously displaying insulating behavior and defect-related conductivity.
Many oxides containing mixed valent cations or oxygen vacancies fall in this
category. In such cases, most of standard experiments may result in effective
high dielectric permittivity which cannot be related to ferroelectric
polarization. Here we list few examples of possible discrepancies between
measured parameters and their expected microscopic origin
Heating and Turbulence Driving by Galaxy Motions in Galaxy Clusters
Using three-dimensional hydrodynamic simulations, we investigate heating and
turbulence driving in an intracluster medium (ICM) by orbital motions of
galaxies in a galaxy cluster. We consider Ng member galaxies on isothermal and
isotropic orbits through an ICM typical of rich clusters. An introduction of
the galaxies immediately produces gravitational wakes, providing perturbations
that can potentially grow via resonant interaction with the background gas.
When Ng^{1/2}Mg_11 < 100, where Mg_11 is each galaxy mass in units of 10^{11}
Msun, the perturbations are in the linear regime and the resonant excitation of
gravity waves is efficient to generate kinetic energy in the ICM, resulting in
the velocity dispersion sigma_v ~ 2.2 Ng^{1/2}Mg_11 km/s. When Ng^{1/2}Mg_11 >
100, on the other hand, nonlinear fluctuations of the background ICM destroy
galaxy wakes and thus render resonant excitation weak or absent. In this case,
the kinetic energy saturates at the level corresponding to sigma_v ~ 220 km/s.
The angle-averaged velocity power spectra of turbulence driven in our models
have slopes in the range of -3.7 to -4.3. With the nonlinear saturation of
resonant excitation, none of the cooling models considered are able to halt
cooling catastrophe, suggesting that the galaxy motions alone are unlikely to
solve the cooling flow problem.Comment: 12 pages including 3 figures, To appear in ApJ
A Unified treatment of small and large- scale dynamos in helical turbulence
Helical turbulence is thought to provide the key to the generation of
large-scale magnetic fields. Turbulence also generically leads to rapidly
growing small-scale magnetic fields correlated on the turbulence scales. These
two processes are usually studied separately. We give here a unified treatment
of both processes, in the case of random fields, incorporating also a simple
model non-linear drift. In the process we uncover an interesting plausible
saturated state of the small-scale dynamo and a novel analogy between quantum
mechanical (QM) tunneling and the generation of large scale fields. The steady
state problem of the combined small/large scale dynamo, is mapped to a
zero-energy, QM potential problem; but a potential which, for non-zero mean
helicity, allows tunneling of bound states. A field generated by the
small-scale dynamo, can 'tunnel' to produce large-scale correlations, which in
steady state, correspond to a force-free 'mean' field.Comment: 4 pages, 1 figure, Physical Review Letters, in pres
Unconventional superconducting pairing symmetry induced by phonons
The possibility of non-s-wave superconductivity induced by phonons is
investigated using a simple model that is inspired by SrRuO. The model
assumes a two-dimensional electronic structure, a two-dimensional
spin-fluctuation spectrum, and three-dimensional electron-phonon coupling.
Taken separately, each interaction favors formation of spin-singlet pairs (of s
symmetry for the phonon interaction and d symmetry for the spin
interaction), but in combination, a variety of more unusual singlet and triplet
states are found, depending on the interaction parameters. This may have
important implications for SrRuO, providing a plausible explanation of
how the observed spin fluctuations, which clearly favor d pairing,
may still be instrumental in creating a superconducting state with a different
(e.g., p-wave) symmetry. It also suggests an interpretation of the large
isotope effect observed in SrRuO. These results indicate that phonons
could play a key role in establishing the order-parameter symmetry in
SrRuO, and possibly in other unconventional superconductors.Comment: 6 pages, 5 figures, submitted to Phys. Rev.
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