APEC Focus: Accomplishment and Challenge

The economic opportunities and the challenges the United States faces in the Asia Pacific region are both daunting and exhilarating. Prospects are describable only in megaterms: the doubling of energy needs within the decade; one trillion dollars of new infrastructure projects envisaged over ten years; the integration not only of China into the regional economy, but also the emergence of India, with a population which is expected to exceed China\u27s in the next century; the massive environmental rehabilitation requirements, for example, in China; staggering food supply requirements; exploding telecommunications networks and educational exchange opportunities. Developments in Asia and the Pacific are dramatically transforming the global geo-economic structure. The Asia Pacific Economic Cooperation ( APEC ) forum has suddenly emerged as the principal vehicle for facilitating this transformation. Our common goal should be to make sure that this is done in a way which not only preserves the equities of all but also ensures the birth of a beneficent and cooperative Pacific community which sustains the dynamic development which has characterized the region in recent years. The challenge was captured in the Vision Statement issued at the conclusion of the historic Seattle APEC Leaders meeting on November 20, 1993. In their vision, APEC Leaders committed to deepening our spirit of community based on our shared vision of achieving stability, security and prosperity for our peoples. That commitment encapsulated the political commitment of the leaders to building a Pacific community, as called for in Seattle by President Clinton

Migratory patterns and population genetic structure in a declining wetland-dependent songbird

Understanding migratory connectivity is essential for assessing the drivers behind population dynamics and for implementing effective management in migratory species. Genetic markers provide a means to describe migratory connectivity, as well as incorporate population genetic analyses, however genetic markers can be uninformative for species with weak genetic structure. In this study, we evaluate range-wide population genetic structure and migratory connectivity in the prothonotary warbler, Protonotaria citrea, a wetland-dependent neotropical migratory songbird, using high-resolution genetic markers. We reveal regional genetic structure between sampling sites in the Mississippi River Valley and the Atlantic Seaboard with overall weak genetic differentiation among populations (FST = 0.0051). By ranking loci by FST and using subsets of the most differentiated genetic markers (200 – 3000), we identify a maximum assignment accuracy (89.7% to site, 94.3% to region) using 600 single nucleotide polymorphisms. We assign samples from unknown origin nonbreeding sites to a breeding region, illustrating weak migratory connectivity between prothonotary warbler breeding and nonbreeding grounds. Our results highlight the importance of using high-resolution markers in studies of migratory connectivity with species exhibiting weak genetic structure. Using similar techniques, studies may begin to describe population genetic structure that was previously undocumented, allowing us to infer the migratory patterns of an increasing number of species

Offspring Sex Ratio in Double Brooding Prothonotary Warblers

Prothonotary warblers are bright, golden birds who, with their loud calls, make themselves known in wetland habitats in the spring after returning from their winter homes in the Neotropics to breed. This migratory species is important to study because of their need for these habitats and are declining in population due to the degradation of wetland environments across the western hemisphere. VCU started a project in 1987 to study prothonotary warblers including population genetics, breeding biology, and migration ecology. Since then, with the help of Richmond Audubon Society, the project has erected over 600 nesting boxes along the James River contributing to a database going back 30 years. This makes them an accessible bird to study and, with the collected information, help to better understand the causes of their declin

Anisotropic solitons in dipolar Bose-Einstein Condensates

Starting with a Gaussian variational ansatz, we predict anisotropic bright solitons in quasi-2D Bose-Einstein condensates consisting of atoms with dipole moments polarized \emph{perpendicular} to the confinement direction. Unlike isotropic solitons predicted for the moments aligned with the confinement axis [Phys. Rev. Lett. \textbf{95}, 200404 (2005)], no sign reversal of the dipole-dipole interaction is necessary to support the solitons. Direct 3D simulations confirm their stability.Comment: 5 pages, 4 figure

Vector solitons in (2+1) dimensions

We address the problem of existence and stability of vector spatial solitons formed by two incoherently interacting optical beams in bulk Kerr and saturable media. We identify families of (2+1)-dimensional two-mode self-trapped beams, with and without a topological charge, and describe their properties analytically and numerically.Comment: 3 pages, 5 figures, submitted to Opt. Let

Gaussian pulse dynamics in gain media with Kerr nonlinearity

Using the Kantorovitch method in combination with a Gaussian ansatz, we derive the equations of motion for spatial, temporal and spatiotemporal optical propagation in a dispersive Kerr medium with a general transverse and spectral gain profile. By rewriting the variational equations as differential equations for the temporal and spatial Gaussian q parameters, optical ABCD matrices for the Kerr effect, a general transverse gain profile and nonparabolic spectral gain filtering are obtained. Further effects can easily be taken into account by adding the corresponding ABCD matrices. Applications include the temporal pulse dynamics in gain fibers and the beam propagation or spatiotemporal pulse evolution in bulk gain media. As an example, the steady-state spatiotemporal Gaussian pulse dynamics in a Kerr-lens mode-locked laser resonator is studied

Stable two-dimensional solitons supported by radially inhomogeneous self-focusing nonlinearity

We demonstrate that modulation of the local strength of the cubic self-focusing (SF) nonlinearity in the two-dimensional (2D) geometry, in the form of a circle with contrast $\Delta g$ of the SF coefficient relative to the ambient medium with a weaker nonlinearity, stabilizes a family of fundamental solitons against the critical collapse. The result is obtained in an analytical form, using the variational approximation (VA) and Vakhitov-Kolokolov (VK) stability criterion, and corroborated by numerical computations. For the small contrast, the stability interval of the soliton's norm scales as $\Delta N\sim \Delta g$ (the replacement of the circle by an annulus leads to a reduction of the stability region by perturbations breaking the axial symmetry). To further illustrate this mechanism, we demonstrate, in an exact form, the stabilization of 1D solitons against the critical collapse under the action of a locally enhanced quintic SF nonlinearity.Comment: 3 pages, 2 figure, to appear in Optics Letter

Conversion of a chirped Gaussian pulse to a soliton or a bound multisoliton state in quasi-lossless and lossy optical fiber spans

The formation of single-soliton or bound-multisoliton states from a single linearly chirped Gaussian pulse in quasi-lossless and lossy fiber spans is examined. The conversion of an input-chirped pulse into soliton states is carried out by virtue of the so-called direct Zakharov-Shabat spectral problem, the solution of which allows one to single out the radiative (dispersive) and soliton constituents of the beam and determine the parameters of the emerging bound state(s). We describe here how the emerging pulse characteristics (the number of bound solitons, the relative soliton power) depend on the input pulse chirp and amplitude

Interaction of pulses in nonlinear Schroedinger model

The interaction of two rectangular pulses in nonlinear Schroedinger model is studied by solving the appropriate Zakharov-Shabat system. It is shown that two real pulses may result in appearance of moving solitons. Different limiting cases, such as a single pulse with a phase jump, a single chirped pulse, in-phase and out-of-phase pulses, and pulses with frequency separation, are analyzed. The thresholds of creation of new solitons and multi-soliton states are found.Comment: 9 pages, 7 figures. Accepted to Phys. Rev. E, 200

Matter wave soliton collisions in the quasi one dimensional potential

We consider soliton solutions of a two-dimensional nonlinear system with the self-focusing nonlinearity and a quasi-1D confining potential, taking harmonic potential as an example. We investigate a single soliton in detail and find criterion for possible collapse. This information is then used to investigate the dynamics of the two soliton collision. In this dynamics we identify three regimes according to the relation between nonlinear interaction and the excitation energy: elastic collision, excitation and collapse regime. We show that surprisingly accurate predictions can be obtained from variational analysis.Comment: 8 pages 7 figure