Physiological Aeroecology: Anatomical and Physiological Adaptations for Flight

Flight has evolved independently in birds, bats, and insects and was present in the Mesozoic pterosaurians that have disappeared. Of the roughly one million living animal species, more than three-quarters are flying insects. Flying is an extremely successful way of locomotion. At first glance, this seems surprising because leaving the ground and moving in the air is energetically expensive. We will therefore start with the question: why do some animals spend a substantial proportion of their life in the air? To generate lift, a few key features are required, and yet, animals show incredible diversity in their flight mechanics. We will review constraints imposed by body size including anatomical adaptations of the skeleton, muscles, and organs necessary to stay airborne with a special focus on the wings. Ecology of the aerial organism, such as diet or migration, has diversified flight styles and the physiological adaptations required to optimize performance. For example, animals are exposed to low temperatures and low oxygen pressure at high altitude, whereas overheating can pose a problem at low altitudes. Moreover, aerial prey can be particularly apparent to aerial predators resulting in selection on flight speed and maneuverability of predators and prey. Flight is energetically costly, much more costly than walking, with the majority of the cost dictated by body mass. Hence, adding weight load to fuel flight also adds to the cost of flight. We review energy supply for flight, and special adaptations for long-term flights. Aeroecology has resulted in extraordinary visual and aural sensory systems of predators, which in coordination with the locomotor system are under strong selection to detect and intercept prey in flight

Nonlinear Self-Trapping of Matter Waves in Periodic Potentials

We report the first experimental observation of nonlinear self-trapping of Bose-condensed 87Rb atoms in a one dimensional waveguide with a superimposed deep periodic potential . The trapping effect is confirmed directly by imaging the atomic spatial distribution. Increasing the nonlinearity we move the system from the diffusive regime, characterized by an expansion of the condensate, to the nonlinearity dominated self-trapping regime, where the initial expansion stops and the width remains finite. The data are in quantitative agreement with the solutions of the corresponding discrete nonlinear equation. Our results reveal that the effect of nonlinear self-trapping is of local nature, and is closely related to the macroscopic self-trapping phenomenon already predicted for double-well systems.Comment: 5 pages, 4 figure

Bloch Structures in a Rotating Bose-Einstein Condensate

A rotating Bose-Einstein condensate is shown to exhibit a Bloch band structure without the need of periodic potential. Vortices enter the condensate by a mechanism similar to the Bragg reflection, if the frequency of a rotating drive or the strength of interaction is adiabatically changed. A localized state analogous to a gap soliton in a periodic system is predicted near the edge of the Brillouin zone.Comment: 4 pages, 3 figure

Oscillations and interactions of dark and dark-bright solitons in Bose-Einstein condensates

Solitons are among the most distinguishing fundamental excitations in a wide range of non-linear systems such as water in narrow channels, high speed optical communication, molecular biology and astrophysics. Stabilized by a balance between spreading and focusing, solitons are wavepackets, which share some exceptional generic features like form-stability and particle-like properties. Ultra-cold quantum gases represent very pure and well-controlled non-linear systems, therefore offering unique possibilities to study soliton dynamics. Here we report on the first observation of long-lived dark and dark-bright solitons with lifetimes of up to several seconds as well as their dynamics in highly stable optically trapped $^{87}$Rb Bose-Einstein condensates. In particular, our detailed studies of dark and dark-bright soliton oscillations reveal the particle-like nature of these collective excitations for the first time. In addition, we discuss the collision between these two types of solitary excitations in Bose-Einstein condensates.Comment: 9 pages, 4 figure

Bright gap solitons of atoms with repulsive interaction

We report on the first experimental observation of bright matter-wave solitons for 87Rb atoms with repulsive atom-atom interaction. This counter intuitive situation arises inside a weak periodic potential, where anomalous dispersion can be realized at the Brillouin zone boundary. If the coherent atomic wavepacket is prepared at the corresponding band edge a bright soliton is formed inside the gap. The strength of our system is the precise control of preparation and real time manipulation, allowing the systematic investigation of gap solitons.Comment: 4 pages, 4 figure

Two-dimensional loosely and tightly bound solitons in optical lattices and inverted traps

We study the dynamics of nonlinear localized excitations (solitons) in two-dimensional (2D) Bose-Einstein condensates (BECs) with repulsive interactions, loaded into an optical lattice (OL), which is combined with an external parabolic potential. First, we demonstrate analytically that a broad (loosely bound, LB) soliton state, based on a 2D Bloch function near the edge of the Brillouin zone (BZ), has a negative effective mass (while the mass of a localized state is positive near the BZ center). The negative-mass soliton cannot be held by the usual trap, but it is safely confined by an inverted parabolic potential (anti-trap). Direct simulations demonstrate that the LB solitons (including the ones with intrinsic vorticity) are stable and can freely move on top of the OL. The frequency of elliptic motion of the LB-soliton's center in the anti-trapping potential is very close to the analytical prediction which treats the solition as a quasi-particle. In addition, the LB soliton of the vortex type features real rotation around its center. We also find an abrupt transition, which occurs with the increase of the number of atoms, from the negative-mass LB states to tightly bound (TB) solitons. An estimate demonstrates that, for the zero-vorticity states, the transition occurs when the number of atoms attains a critical number N=10^3, while for the vortex the transition takes place at N=5x10^3 atoms. The positive-mass LB states constructed near the BZ center (including vortices) can move freely too. The effects predicted for BECs also apply to optical spatial solitons in bulk photonic crystals.Comment: 17 pages, 12 figure

Stable two-dimensional dispersion-managed soliton

The existence of a dispersion-managed soliton in two-dimensional nonlinear Schr\"odinger equation with periodically varying dispersion has been explored. The averaged equations for the soliton width and chirp are obtained which successfully describe the long time evolution of the soliton. The slow dynamics of the soliton around the fixed points for the width and chirp are investigated and the corresponding frequencies are calculated. Analytical predictions are confirmed by direct PDE and ODE simulations. Application to a Bose-Einstein condensate in optical lattice is discussed. The existence of a dispersion-managed matter-wave soliton in such system is shown.Comment: 4 pages, 3 figures, Submitted to Phys. Rev.

Kinks in the discrete sine-Gordon model with Kac-Baker long-range interactions

We study effects of Kac-Baker long-range dispersive interaction (LRI) between particles on kink properties in the discrete sine-Gordon model. We show that the kink width increases indefinitely as the range of LRI grows only in the case of strong interparticle coupling. On the contrary, the kink becomes intrinsically localized if the coupling is under some critical value. Correspondingly, the Peierls-Nabarro barrier vanishes as the range of LRI increases for supercritical values of the coupling but remains finite for subcritical values. We demonstrate that LRI essentially transforms the internal dynamics of the kinks, specifically creating their internal localized and quasilocalized modes. We also show that moving kinks radiate plane waves due to break of the Lorentz invariance by LRI.Comment: 11 pages (LaTeX) and 14 figures (Postscript); submitted to Phys. Rev.