3,342 research outputs found
Persistent currents in Bose gases confined in annular traps
We examine the problem of stability of persistent currents in a mixture of
two Bose gases trapped in an annular potential. We evaluate the critical
coupling for metastability in the transition from quasi-one to two-dimensional
motion. We also evaluate the critical coupling for metastability in a mixture
of two species as function of the population imbalance. The stability of the
currents is shown to be sensitive to the deviation from one-dimensional motion.Comment: 6 pages, 4 figure
On the Trade-Off Between Quality Factor and Tuning Ratio in Tunable High-Frequency Capacitors
A benchmark of tunable and switchable devices at microwave frequencies is presented on the basis of physical limitations to show their potential for reconfigurable cellular applications. Performance limitations are outlined for each given technology focusing on the quality factor (Q) and tuning ratio (eta) as figures of merit. The state of the art in terms of these figures of merit of several tunable and switchable technologies is visualized and discussed. If the performance of these criteria is not met, the application will not be feasible. The quality factor can typically be traded off for tuning ratio. The benchmark of tunable capacitor technologies shows that transistor-switched capacitors, varactor diodes, and ferroelectric varactors perform well at 2 GHz for tuning ratios below 3, with an advantage for GaAs varactor diodes. Planar microelectromechanical capacitive switches have the potential to outperform all other technologies at tuning ratios higher than 8. Capacitors based on tunable dielectrics have the highest miniaturization potential, whereas semiconductor devices benefit from the existing manufacturing infrastructure
Phase diagram of a rapidly-rotating two-component Bose gas
We derive analytically the phase diagram of a two-component Bose gas confined
in an anharmonic potential, which becomes exact and universal in the limit of
weak interactions and small anharmonicity of the trapping potential. The
transitions between the different phases, which consist of vortex states of
single and multiple quantization, are all continuous because of the addition of
the second component.Comment: 5 pages, 3 figure
Rotational properties of non-dipolar and dipolar Bose-Einstein condensates confined in annular potentials
We investigate the rotational response of both non-dipolar and dipolar
Bose-Einstein condensates confined in an annular potential. For the non-dipolar
case we identify certain critical rotational frequencies associated with the
formation of vortices. For the dipolar case, assuming that the dipoles are
aligned along some arbitrary and tunable direction, we study the same problem
as a function of the orientation angle of the dipole moment of the atoms.Comment: 5 pages, 4 figure
Dipolar particles in a double-trap confinement: Response to tilting the dipolar orientation
We analyze the microscopic few-body properties of dipolar particles confined
in two parallel quasi-one-dimensional harmonic traps. In particular, we show
that an adiabatic rotation of the dipole orientation about the trap axes can
drive an initially non-localized few-fermion state into a localized state with
strong inter-trap pairing. For an instant, non-adiabatic rotation, however,
localization is inhibited and a highly excited state is reached. This state may
be interpreted as the few-body analog of a super-Tonks-Girardeau state, known
from one-dimensional systems with contact interactions
Distribution and characterisation of Glucagon-like peptide-1 receptor expressing cells in the mouse brain.
© 2015 The Authors.Objective: Although Glucagon-like peptide 1 is a key regulator of energy metabolism and food intake, the precise location of GLP-1 receptors and the physiological relevance of certain populations is debatable. This study investigated the novel GLP-1R-Cre mouse as a functional tool to address this question. Methods: Mice expressing Cre-recombinase under the Glp1r promoter were crossed with either a ROSA26 eYFP or tdRFP reporter strain to identify GLP-1R expressing cells. Patch-clamp recordings were performed on tdRFP-positive neurons in acute coronal brain slices from adult mice and selective targeting of GLP-1R cells in vivo was achieved using viral gene delivery. Results: Large numbers of eYFP or tdRFP immunoreactive cells were found in the circumventricular organs, amygdala, hypothalamic nuclei and the ventrolateral medulla. Smaller numbers were observed in the nucleus of the solitary tract and the thalamic paraventricular nucleus. However, tdRFP positive neurons were also found in areas without preproglucagon-neuronal projections like hippocampus and cortex. GLP-1R cells were not immunoreactive for GFAP or parvalbumin although some were catecholaminergic. GLP-1R expression was confirmed in whole-cell recordings from BNST, hippocampus and PVN, where 100 nM GLP-1 elicited a reversible inward current or depolarisation. Additionally, a unilateral stereotaxic injection of a cre-dependent AAV into the PVN demonstrated that tdRFP-positive cells express cre-recombinase facilitating virally-mediated eYFP expression. Conclusions: This study is a comprehensive description and phenotypic analysis of GLP-1R expression in the mouse CNS. We demonstrate the power of combining the GLP-1R-CRE mouse with a virus to generate a selective molecular handle enabling future in vivo investigation as to their physiological importance
Spinally projecting preproglucagon axons preferentially innervate sympathetic preganglionic neurons
Glucagon-like peptide-1 (GLP-1) affects central autonomic neurons, including those controlling the cardiovascular system, thermogenesis, and energy balance. Preproglucagon (PPG) neurons, located mainly in the nucleus tractus solitarius (NTS) and medullary reticular formation, produce GLP-1. In transgenic mice expressing glucagon promoter-driven yellow fluorescent protein (YFP), these brainstem PPG neurons project to many central autonomic regions where GLP-1 receptors are expressed. The spinal cord also contains GLP-1 receptor mRNA but the distribution of spinal PPG axons is unknown. Here, we used two-color immunoperoxidase labeling to examine PPG innervation of spinal segments T1–S4 in YFP-PPG mice. Immunoreactivity for YFP identified spinal PPG axons and perikarya. We classified spinal neurons receiving PPG input by immunoreactivity for choline acetyltransferase (ChAT), nitric oxide synthase (NOS) and/or Fluorogold (FG) retrogradely transported from the peritoneal cavity. FG microinjected at T9 defined cell bodies that supplied spinal PPG innervation. The deep dorsal horn of lower lumbar cord contained YFP-immunoreactive neurons. Non-varicose, YFP-immunoreactive axons were prominent in the lateral funiculus, ventral white commissure and around the ventral median fissure. In T1–L2, varicose, YFP-containing axons closely apposed many ChAT-immunoreactive sympathetic preganglionic neurons (SPN) in the intermediolateral cell column (IML) and dorsal lamina X. In the sacral parasympathetic nucleus, about 10% of ChAT-immunoreactive preganglionic neurons received YFP appositions, as did occasional ChAT-positive motor neurons throughout the rostrocaudal extent of the ventral horn. YFP appositions also occurred on NOS-immunoreactive spinal interneurons and on spinal YFP-immunoreactive neurons. Injecting FG at T9 retrogradely labeled many YFP-PPG cell bodies in the medulla but none of the spinal YFP-immunoreactive neurons. These results show that brainstem PPG neurons innervate spinal autonomic and somatic motor neurons. The distributions of spinal PPG axons and spinal GLP-1 receptors correlate well. SPN receive the densest PPG innervation. Brainstem PPG neurons could directly modulate sympathetic outflow through their spinal inputs to SPN or interneurons
Mixtures of Bose gases confined in concentrically coupled annular traps
A two-component Bose-Einstein condensate confined in an axially-symmetric
potential with two local minima, resembling two concentric annular traps, is
investigated. The system shows a number of quantum phase transitions that
result from the competition between phase coexistence, and radial/azimuthal
phase separation. The ground-state phase diagram, as well as the rotational
properties, including the (meta)stability of currents in this system, are
analysed.Comment: 6 pages, 5 figures, minor revision
Hexagons become second if symmetry is broken
Pattern formation on the free surface of a magnetic fluid subjected to a
magnetic field is investigated experimentally. By tilting the magnetic field
the symmetry can be broken in a controllable manner. When increasing the
amplitude of the tilted field, the flat surface gives way to liquid ridges. A
further increase results in a hysteretic transition to a pattern of stretched
hexagons. The instabilities are detected by means of a linear array of magnetic
hall sensors and compared with theoretical predictions.Comment: accepted for publication by Physical Review E/Rapid Communicatio
Spin-orbit-coupled Bose-Einstein-condensed atoms confined in annular potentials
A spin-orbit-coupled Bose-Einstein-condensed cloud of atoms confined in an
annular trapping potential shows a variety of phases that we investigate in the
present study. Starting with the non-interacting problem, the homogeneous phase
that is present in an untrapped system is replaced by a sinusoidal density
variation in the limit of a very narrow annulus. In the case of an untrapped
system there is another phase with a striped-like density distribution, and its
counterpart is also found in the limit of a very narrow annulus. As the width
of the annulus increases, this picture persists qualitatively. Depending on the
relative strength between the inter- and the intra-components, interactions
either favor the striped phase, or suppress it, in which case either a
homogeneous, or a sinusoidal-like phase appears. Interactions also give rise to
novel solutions with a nonzero circulation.Comment: Final, slightly revised versio
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