Agricultural development and the opportunities for aquatic resources research in China

China is a large and rapidly developing country. Fisheries and aquaculture have been prominent sectors in the contribution to GDP and the provision of food security, export revenue, and livelihoods for the poor. The rapid development has come at some cost to the environment and the sustainability of natural resources. Levels of marine fisheries catches are stagnant. Some of the rivers and major lakes are polluted and the restoration of the productivity of these lakes is of key concern. These Proceedings, made up of four papers that leading Chinese experts presented to WorldFish Center in 2002, review four aspects of these trends: agricultural development, environmental issues and the contribution of aquaculture and fisheries to development in China.Agricultural development, Aquaculture development, Living resources, Research, WorldFish Center, WorldFish Center Contrib. No. 1668, China,

Magnetic remanent states in antiferromagnetically coupled multilayers

In antiferromagnetically coupled multilayers with perpendicular anisotropy unusual multidomain textures can be stabilized due to a close competition between long-range demagnetization fields and short-range interlayer exchange coupling. In particular, the formation and evolution of specific topologically stable planar defects within the antiferromagnetic ground state, i.e. wall-like structures with a ferromagnetic configuration extended over a finite width, explain configurational hysteresis phenomena recently observed in [Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers. Within a phenomenological theory, we have analytically derived the equilibrium sizes of these "ferroband" defects as functions of the antiferromagnetic exchange, a bias magnetic field, and geometrical parameters of the multilayers. In the magnetic phase diagram, the existence region of the ferrobands mediates between the regions of patterns with sharp antiferromagnetic domain walls and regular arrays of ferromagnetic stripes. The theoretical results are supported by magnetic force microscopy images of the remanent states observed in [Co/Pt]/Ru.Comment: Paper submitted by the Joint European Magnetics Symposia 2008, Dublin (4 pages, 3 figures

Looking for defects in the 2PI correlator

Truncations of the 2PI effective action are seen as a promising way of studying non-equilibrium dynamics in quantum field theories. We probe their applicability in the non-perturbative setting of topological defect formation in a symmetry-breaking phase transition, by comparing full classical lattice field simulations and the 2PI formulation for classical fields in an O($N$) symmetric scalar field theory. At next-to-leading order in 1/N, the 2PI formalism fails to reproduce any signals of defects in the two-point function. This suggests that one should be careful when applying the 2PI formalism for symmetry breaking phase transitions.Comment: 22 pages, 6 figure

More on scattering of Chern-Simons vortices

I derive a general formalism for finding kinetic terms of the effective Lagrangian for slowly moving Chern-Simons vortices. Deformations of fields linear in velocities are taken into account. From the equations they must satisfy I extract the kinetic term in the limit of coincident vortices. For vortices passing one over the other there is locally the right-angle scattering. The method is based on analysis of field equations instead of action functional so it may be useful also for nonvariational equations in nonrelativistic models of Condensed Matter Physics.Comment: discussion around Eq.(45) is generalised, one more condition for the local right-angle scattering is adde

AdS pp-waves

We obtain the pp-waves of D=5 and D=4 gauged supergravities supported by $U(1)^3$ and $U(1)^4$ gauge field strengths respectively. We show that generically these solutions preserve 1/4 of the supersymmetry, but supernumerary supersymmetry can arise for appropriately constrained harmonic functions associated with the pp-waves. In particular it implies that the solutions are independent of the light-cone coordinate $x^+$. We also obtain the pp-waves in the Freedman-Schwarz model.Comment: Latex, 19 pages, minor changes, to appear in JHE

Coherent resonant tunneling in ac fields

We have analyzed the tunneling transmission probability and electronic current density through resonant heterostructures in the presence of an external electromagnetic field. In this work, we compare two different models for a double barrier : In the first case the effect of the external field is taken into account by spatially dependent AC voltages and in the second one the electromagnetic field is described in terms of a photon field that irradiates homogeneously the whole sample. While in the first description the tunneling takes place mainly through photo sidebands in the case of homogeneous illumination the main effective tunneling channels correspond to the coupling between different electronic states due to photon absorption and emission. The difference of tunneling mechanisms between these configurations is strongly reflected in the transmission and current density which present very different features in both cases. In order to analyze these effects we have obtained, within the Transfer Hamiltonian framework, a general expression for the transition probability for coherent resonant tunneling in terms of the Green's function of the system.Comment: 16 pages,Figures available upon request,to appear in Phys.Rev B (15 April 1996

First Order Vortex Dynamics

A non-dissipative model for vortex motion in thin superconductors is considered. The Lagrangian is a Galilean invariant version of the Ginzburg--Landau model for time-dependent fields, with kinetic terms linear in the first time derivatives of the fields. It is shown how, for certain values of the coupling constants, the field dynamics can be reduced to first order differential equations for the vortex positions. Two vortices circle around one another at constant speed and separation in this model.Comment: 22pages, no figures, tex fil

The multifrequency Siberian Radioheliograph

The 10-antenna prototype of the multifrequency Siberian radioheliograph is described. The prototype consists of four parts: antennas with broadband front-ends, analog back-ends, digital receivers and a correlator. The prototype antennas are mounted on the outermost stations of the Siberian Solar Radio Telescope (SSRT) array. A signal from each antenna is transmitted to a workroom by an analog fiber optical link, laid in an underground tunnel. After mixing, all signals are digitized and processed by digital receivers before the data are transmitted to the correlator. The digital receivers and the correlator are accessible by the LAN. The frequency range of the prototype is from 4 to 8 GHz. Currently the frequency switching observing mode is used. The prototype data include both circular polarizations at a number of frequencies given by a list. This prototype is the first stage of the multifrequency Siberian radioheliograph development. It is assumed that the radioheliograph will consist of 96 antennas and will occupy stations of the West-East-South subarray of the SSRT. The radioheliograph will be fully constructed in autumn of 2012. We plan to reach the brightness temperature sensitivity about 100 K for the snapshot image, a spatial resolution up to 13 arcseconds at 8 GHz and polarization measurement accuracy about a few percent. First results with the 10-antenna prototype are presented of observations of solar microwave bursts. The prototype abilities to estimate source size and locations at different frequencies are discussed

Spin dynamics in high-mobility two-dimensional electron systems

Understanding the spin dynamics in semiconductor heterostructures is highly important for future semiconductor spintronic devices. In high-mobility two-dimensional electron systems (2DES), the spin lifetime strongly depends on the initial degree of spin polarization due to the electron-electron interaction. The Hartree-Fock (HF) term of the Coulomb interaction acts like an effective out-of-plane magnetic field and thus reduces the spin-flip rate. By time-resolved Faraday rotation (TRFR) techniques, we demonstrate that the spin lifetime is increased by an order of magnitude as the initial spin polarization degree is raised from the low-polarization limit to several percent. We perform control experiments to decouple the excitation density in the sample from the spin polarization degree and investigate the interplay of the internal HF field and an external perpendicular magnetic field. The lifetime of spins oriented in the plane of a [001]-grown 2DES is strongly anisotropic if the Rashba and Dresselhaus spin-orbit fields are of the same order of magnitude. This anisotropy, which stems from the interference of the Rashba and the Dresselhaus spin-orbit fields, is highly density-dependent: as the electron density is increased, the kubic Dresselhaus term becomes dominant and reduces the anisotropy.Comment: 13 pages, 6 figure

Time dependent solitons of noncommutative Chern-Simons theory coupled to scalar fields

We study one- and two-soliton solutions of noncommutative Chern-Simons theory coupled to a nonrelativistic or a relativistic scalar field. In the nonrelativistic case, we find a tower of new stationary time-dependent solutions, all with the same charge density, but with increasing energies. The dynamics of these solitons cannot be studied using traditional moduli space techniques, but we do find a nontrivial symplectic form on the phase space indicating that the moduli space is not flat. In the relativistic case we find the metric on the two soliton moduli space.Comment: 22 pages, 2 figures, JHEP3 style. v2: This paper is a thoroughly revised version. We thank P.A. Horvathy, L. Martina and P.C. Stichel for illuminating comments that led us to reconsider some of our previously reported results; see note added at the end of the paper. v3: Acknowledgements adde