Phase Winding a Two-Component BEC in an Elongated Trap: Experimental Observation of Moving Magnetic Orders and Dark-bright Solitons

We experimentally investigate the phase winding dynamics of a harmonically trapped two-component BEC subject to microwave induced Rabi oscillations between two pseudospin components. While the single particle dynamics can be explained by mapping the system to a two-component Bose-Hubbard model, nonlinearities due to the interatomic repulsion lead to new effects observed in the experiments: In the presence of a linear magnetic field gradient, a qualitatively stable moving magnetic order that is similar to antiferromagnetic order is observed after critical winding is achieved. We also demonstrate how the phase winding can be used as a new tool to generate copious dark-bright solitons in a two-component BEC, opening the door for new experimental studies of these nonlinear features.Comment: 5 pages, 4 figure

Beating dark-dark solitons in Bose-Einstein condensates

Motivated by recent experimental results, we study beating dark-dark solitons as a prototypical coherent structure that emerges in two-component Bose-Einstein condensates. We showcase their connection to dark- bright solitons via SO(2) rotation, and infer from it both their intrinsic beating frequency and their frequency of oscillation inside a parabolic trap. We identify them as exact periodic orbits in the Manakov limit of equal inter- and intra-species nonlinearity strengths with and without the trap and showcase the persistence of such states upon weak deviations from this limit. We also consider large deviations from the Manakov limit illustrating that this breathing state may be broken apart into dark-antidark soliton states. Finally, we consider the dynamics and interactions of two beating dark-dark solitons in the absence and in the presence of the trap, inferring their typically repulsive interaction.Comment: 13 pages, 14 figure

Dynamics of Dark-Bright Solitons in Cigar-Shaped Bose-Einstein Condensates

We explore the stability and dynamics of dark-bright solitons in two-component elongated Bose-Einstein condensates by developing effective 1D vector equations as well as solving the corresponding 3D Gross-Pitaevskii equations. A strong dependence of the oscillation frequency and of the stability of the dark-bright (DB) soliton on the atom number of its components is found. Spontaneous symmetry breaking leads to oscillatory dynamics in the transverse degrees of freedom for a large occupation of the component supporting the dark soliton. Moreover, the interactions of two DB solitons are investigated with special emphasis on the importance of their relative phases. Experimental results showcasing dark-bright soliton dynamics and collisions in a BEC consisting of two hyperfine states of $^{87}$Rb confined in an elongated optical dipole trap are presented.Comment: 4 pages, 5 figure

If you could see what we see, would it bother you?

Objective The purpose of our study was to determine whether the anatomic threshold for pelvic organ prolapse (POP) diagnosis and surgical success remains valid when the patient sees what we see on exam. Methods Two hundred participants were assigned, by computer-generated block randomization, to see one of four videos. Each video contained the same six clips representative of various degrees of anterior vaginal wall support. Participants were asked questions immediately after each clip. They were asked: “In your opinion, does this patient have a bulge or something falling out that she can see or feel in the vaginal area?” Similarly, they were asked to give their opinion on surgical outcome on a 4-point Likert scale. Results The proportion of participants who identified the presence of a vaginal bulge increased substantially at the level of early stage 2 prolapse (1 cm above the hymen), with 67 % answering yes to the question regarding bulge. The proportion of participants who felt that surgical outcome was less desirable also increased substantially at early stage 2 prolapse (1 cm above the hymen), with 52 % describing that outcome as “not at all” or “somewhat” successful. Conclusion Early stage 2 POP (1 cm above the hymen) is the anatomic threshold at which women identify both a vaginal bulge and a less desirable surgical outcome when they see what we see on examination

Grey solitons in a strongly interacting superfluid Fermi Gas

The Bardeen-Cooper-Schrieffer to Bose-Einstein condensate (BCS to BEC) crossover problem is solved for stationary grey solitons via the Boguliubov-de Gennes equations at zero temperature. These \emph{crossover solitons} exhibit a localized notch in the gap and a characteristic phase difference across the notch for all interaction strengths, from BEC to BCS regimes. However, they do not follow the well-known Josephson-like sinusoidal relationship between velocity and phase difference except in the far BEC limit: at unitary the velocity has a nearly linear dependence on phase difference over an extended range. For fixed phase difference the soliton is of nearly constant depth from the BEC limit to unitarity and then grows progressively shallower into the BCS limit, and on the BCS side Friedel oscillations are apparent in both gap amplitude and phase. The crossover soliton appears fundamentally in the gap; we show, however, that the density closely follows the gap, and the soliton is therefore observable. We develop an approximate power law relationship to express this fact: the density of grey crossover solitons varies as the square of the gap amplitude in the BEC limit and a power of about 1.5 at unitarity.Comment: 10 pages, 6 figures, part of New Journal of Physics focus issue "Strongly Correlated Quantum Fluids: From Ultracold Quantum Gases to QCD Plasmas," in pres

Photoperiodism in Relation to Hormones as Factors in Floral Initiation and Development

1. A description is given of a simple method whereby one portion of a plant may be subjected to one photoperiod while another portion of the same plant is being subjected to another photoperiod. 2. Floral initiation in Xanthium pennsylvanicum results if plants are subjected to photoperiods shorter than 15 hours with accompanying dark periods of longer than 8 hours. If Xanthium plants are subjected continuously to photoperiods longer than 16 hours with accompanying dark periods shorter than 8 hours they remain strictly vegetative. 3. The initial effect of the photoperiodic stimulus is perceived by the leaves which are subjected to short photoperiod. However, this stimulus, resulting in floral initiation, may be transported from these leaves to other portions of the same plant which are maintained under conditions of long photoperiod and may also move across a diffusion contact from a plant subjected to short photoperiod to a plant subjected to long photoperiod. The stimulus to floral initiation may therefore be attributed to a substance or substances manufactured in leaves subjected to short photoperiod. 4. The response of Xanthium to photoperiod is primarily a response to length of dark period rather than to duration of photoperiod. Thus reactions resulting in the formation of floral initiation substances may take place during the dark period. These reactions are adversely affected by light and by low temperature. 5. Fully expanded leaves on receptor branches subjected to long photoperiod may exert some influence inhibitory to floral initiation; under similar circumstances young expanding leaves exert a promotive effect on floral initiation and flower development. 6. In Xanthium the development of mature flowers and fruits from floral primordia is also promoted by a substance or substances formed in portions of the plant which are exposed to short photoperiod and which may move across a diffusion contact. Whether or not this substance or substances is identical with the floral initiation substance has not as yet been determined. 7. A portion of a plant maintained under long photoperiod may be influenced by a portion of the same plant subjected to short photoperiods in such a way that it may behave as though it has been photoperiodically induced by direct exposure to short photoperiod. Flowers and fruits continue to develop on such portions of a branch which has never itself been subjected to short photoperiods. 8. Evidence is presented that the floral initiation substance is not identical with any of the following known plant growth factors: vitamins B₁, B₂, and B₆, ascorbic acid, nicotinic acid, pantothenic acid, theelin, theelol, inositol, or indoleacetic acid

Photoperiodism in Relation to Hormones as Factors in Floral Initiation and Development

1. A description is given of a simple method whereby one portion of a plant may be subjected to one photoperiod while another portion of the same plant is being subjected to another photoperiod. 2. Floral initiation in Xanthium pennsylvanicum results if plants are subjected to photoperiods shorter than 15 hours with accompanying dark periods of longer than 8 hours. If Xanthium plants are subjected continuously to photoperiods longer than 16 hours with accompanying dark periods shorter than 8 hours they remain strictly vegetative. 3. The initial effect of the photoperiodic stimulus is perceived by the leaves which are subjected to short photoperiod. However, this stimulus, resulting in floral initiation, may be transported from these leaves to other portions of the same plant which are maintained under conditions of long photoperiod and may also move across a diffusion contact from a plant subjected to short photoperiod to a plant subjected to long photoperiod. The stimulus to floral initiation may therefore be attributed to a substance or substances manufactured in leaves subjected to short photoperiod. 4. The response of Xanthium to photoperiod is primarily a response to length of dark period rather than to duration of photoperiod. Thus reactions resulting in the formation of floral initiation substances may take place during the dark period. These reactions are adversely affected by light and by low temperature. 5. Fully expanded leaves on receptor branches subjected to long photoperiod may exert some influence inhibitory to floral initiation; under similar circumstances young expanding leaves exert a promotive effect on floral initiation and flower development. 6. In Xanthium the development of mature flowers and fruits from floral primordia is also promoted by a substance or substances formed in portions of the plant which are exposed to short photoperiod and which may move across a diffusion contact. Whether or not this substance or substances is identical with the floral initiation substance has not as yet been determined. 7. A portion of a plant maintained under long photoperiod may be influenced by a portion of the same plant subjected to short photoperiods in such a way that it may behave as though it has been photoperiodically induced by direct exposure to short photoperiod. Flowers and fruits continue to develop on such portions of a branch which has never itself been subjected to short photoperiods. 8. Evidence is presented that the floral initiation substance is not identical with any of the following known plant growth factors: vitamins B₁, B₂, and B₆, ascorbic acid, nicotinic acid, pantothenic acid, theelin, theelol, inositol, or indoleacetic acid

Solitary waves in the Nonlinear Dirac Equation

In the present work, we consider the existence, stability, and dynamics of solitary waves in the nonlinear Dirac equation. We start by introducing the Soler model of self-interacting spinors, and discuss its localized waveforms in one, two, and three spatial dimensions and the equations they satisfy. We present the associated explicit solutions in one dimension and numerically obtain their analogues in higher dimensions. The stability is subsequently discussed from a theoretical perspective and then complemented with numerical computations. Finally, the dynamics of the solutions is explored and compared to its non-relativistic analogue, which is the nonlinear Schr{\"o}dinger equation. A few special topics are also explored, including the discrete variant of the nonlinear Dirac equation and its solitary wave properties, as well as the PT-symmetric variant of the model

Ocean acidification reduces demersal zooplankton that reside in tropical coral reefs

The in situ effects of ocean acidification on zooplankton communities remain largely unexplored. Using natural volcanic CO2 seep sites around tropical coral communities, we show a threefold reduction in the biomass of demersal zooplankton in high-CO2 sites compared with sites with ambient CO2. Differences were consistent across two reefs and three expeditions. Abundances were reduced in most taxonomic groups. There were no regime shifts in zooplankton community composition and no differences in fatty acid composition between CO2 levels, suggesting that ocean acidification affects the food quantity but not the quality for nocturnal plankton feeders. Emergence trap data show that the observed reduction in demersal plankton may be partly attributable to altered habitat. Ocean acidification changes coral community composition from branching to massive bouldering coral species, and our data suggest that bouldering corals represent inferior daytime shelter for demersal zooplankton. Since zooplankton represent a major source of nutrients for corals, fish and other planktivores, this ecological feedback may represent an additional mechanism of how coral reefs will be affected by ocean acidification