Magnetic field control of cycloidal domains and electric polarization in multiferroic BiFeO3_3

The magnetic field induced rearrangement of the cycloidal spin structure in ferroelectric mono-domain single crystals of the room-temperature multiferroic BiFeO$_3$ is studied using small-angle neutron scattering (SANS). The cycloid propagation vectors are observed to rotate when magnetic fields applied perpendicular to the rhombohedral (polar) axis exceed a pinning threshold value of $\sim$5\,T. In light of these experimental results, a phenomenological model is proposed that captures the rearrangement of the cycloidal domains, and we revisit the microscopic origin of the magnetoelectric effect. A new coupling between the magnetic anisotropy and the polarization is proposed that explains the recently discovered magnetoelectric polarization to the rhombohedral axis

A Hybrid Lagrangian Variation Method for Bose-Einstein Condensates in Optical Lattices

Solving the Gross--Pitaevskii (GP) equation describing a Bose--Einstein condensate (BEC) immersed in an optical lattice potential can be a numerically demanding task. We present a variational technique for providing fast, accurate solutions of the GP equation for systems where the external potential exhibits rapid varation along one spatial direction. Examples of such systems include a BEC subjected to a one--dimensional optical lattice or a Bragg pulse. This variational method is a hybrid form of the Lagrangian Variational Method for the GP equation in which a hybrid trial wavefunction assumes a gaussian form in two coordinates while being totally unspecified in the third coordinate. The resulting equations of motion consist of a quasi--one--dimensional GP equation coupled to ordinary differential equations for the widths of the transverse gaussians. We use this method to investigate how an optical lattice can be used to move a condensate non--adiabatically.Comment: 16 pages and 1 figur

Characterization of esophageal motility and esophagogastric junction in preterm infants with bronchopulmonary dysplasia

Background: To characterize esophageal motility and function of the esophagogastric junction (EGJ) in preterm infants with bronchopulmonary dysplasia (BPD). Methods: High-resolution manometry with impedance was used to investigate esophageal motility and EGJ function in 28 tube-fed preterm infants with BPD. Patients with BPD were studied at term age during oral feeding. Thirteen healthy term-aged infants were included as controls. Esophageal analysis derived objective measures to evaluate esophageal contractile vigor, bolus distension pressure, EGJ relaxation, and EGJ barrier function (in rest and during respiration). In addition, we investigated the effect of BPD severity on these measures. Key results: A total of 140 nutritive swallows were analyzed (BPD, n = 92; controls, n = 48). Normal esophageal peristaltic wave patterns were observed in all infants. BPD patients had higher distal contractile esophageal strength compared with controls (Kruskal-Wallis (KW) P =.048), and their deglutitive EGJ relaxation was comparable to controls. Severe BPD patients showed higher bolus distension pressures, higher EGJ resting pressures, and increased EGJ contractile integrals compared with mild BPD patients (Mann-Whitney U P =.009, KW P =.012 and KW P =.028, respectively). Conclusions and Inferences: Preterm infants with BPD consistently present with normal peristaltic esophageal patterns following nutritive liquid swallows. The EGJ barrier tone and relaxation pressure appeared normal. In general, infants with BPD do not have altered esophageal motor function. There is however evidence for increased flow resistance at the EGJ in severe BPD patients possibly related to an increased contractility of the diaphragm

A Hybrid Lagrangian Variational Method for Bose–Einstein Condensates in Optical Lattices

Solving the Gross–Pitaevskii (GP) equation describing a Bose–Einstein condensate (BEC) immersed in an optical lattice potential can be a numerically demanding task. We present a variational technique for providing fast, accurate solutions of the GP equation for systems where the external potential exhibits rapid variation along one spatial direction. Examples of such systems include a BEC subjected to a one-dimensional optical lattice or a Bragg pulse. This variational method is a hybrid form of the Lagrangian variational method for the GP equation in which a hybrid trial wavefunction assumes a Gaussian form in two coordinates while being totally unspecified in the third coordinate. The resulting equations of motion consist of a quasi-one-dimensional GP equation coupled to ordinary differential equations for the widths of the transverse Gaussians. We use this method to investigate how an optical lattice can be used to move a condensate non-adiabatically