355 research outputs found
Quantum tunneling of magnetization in dipolar spin-1 condensates under external fields
We study the macroscopic quantum tunneling of magnetization of the F=1 spinor
condensate interacting through dipole-dipole interaction with an external
magnetic field applied along the longitudinal or transverse direction. We show
that the ground state energy and the effective magnetic moment of the system
exhibit an interesting macroscopic quantum oscillation phenomenon originating
from the oscillating dependence of thermodynamic properties of the system on
the vacuum angle. Tunneling between two degenerate minima are analyzed by means
of an effective potential method and the periodic instanton method.Comment: 2 figures, accepted PR
Blends of Amphiphilic, Hyperbranched Polyesters and Different Polyolefins
A hyperbranched polyester based on 3,5-dihydroxybenzoic acid was completely modified with dodecanoyl chloride to result in an amphiphilic, globular polymer, which has a polar core and a nonpolar outer sphere with the ability both to incorporate an organic dye and to interact with a nonpolar matrix. A series of blends were prepared using either polypropylene or polyethylene (HDPE) as the matrix. The content of the polyester as disperse phase was varied between 0.05 and 20 wt %. The blends with polyester contents up to 5% were prepared for colorization of polyolefins using the polyester as a dye carrier. The blends with higher polyester contents were prepared in order to investigate the influence of the hyperbranched material on the material properties. The blends exhibited a heterogeneous morphology with very small particle sizes even at high polyester concentrations. The melt rheology measurements resulted in a reduced complex viscosity for both polyolefins when the hyperbranched polyester was added. The observed melt viscosity of the i-PP blends deviated from the linear mixing rule, whereas the HDPE blends followed it. The use of amphiphilic hyperbranched polyesters as dye carriers allowed a homogeneous distribution of an organic dye in a polyolefin matrix with similar dynamic-mechanical behavior of the blends compared to the case of pure polyolefins. The dyed samples exhibited good stability in extraction experiments
Quantum Dynamics of Atomic Coherence in a Spin-1 Condensate: Mean-Field versus Many-Body Simulation
We analyse and numerically simulate the full many-body quantum dynamics of a
spin-1 condensate in the single spatial mode approximation. Initially, the
condensate is in a ``ferromagnetic'' state with all spins aligned along the
axis and the magnetic field pointing along the z axis. In the course of
evolution the spinor condensate undergoes a characteristic change of symmetry,
which in a real experiment could be a signature of spin-mixing many-body
interactions. The results of our simulations are conveniently visualised within
the picture of irreducible tensor operators.Comment: Accepted for publication for the special issue of "Optics
Communications" on Quantum Control of Light and Matte
Ecology of a North Sea pockmark with an active methane seep
ABSTRACT: At a large North Sea pockmark, with active methane seeps, surface sediments were found
to have higher insoluble sulphide concentrations than sedlments from the surrounding area. The fauna
of the pockmark was characterized by 2 species which have not pi-evlously been reported from the
Fladen Ground in the northern North Sea. These species were a b~valve, Thyasira sarsi (which is known
to contain endosymbiotic sulphur-oxidising bacteria) and a mouthless and gutless nematode,
Astomonerna sp., which also contains endosymbiotic bacteria The nematode was the dominant
meiofauna species in the pockmark sediments. Both macro-lnfauna and total nematodes were in low
abundance in samples taken from the base of the pockmark. Sediment samples from the pockmark
contained numerous otoliths, implying that substantial winnowing of the sediment had taken place.
This was supported by studies on the sulphide concentrations in the sediment which showed multiple
layering of the sediments on the sides of the pockmark, suggesting displacement. The carbon isotope
compositions (6I3c) of the tissues of benthic animals from in and around the pockmark were generally in
the range -16 to -2O%, indicating that little methane-derived carbon was contributing to their
nutrition. T sarsi had the most 13c-depleted tissues, -31.4 to -35.1 L, confirming the nutritional dependence of this species on chemoautotrophic bacteria that utilize reduced sulphur
Quantum phase transition to unconventional multi-orbital superfluidity in optical lattices
Orbital physics plays a significant role for a vast number of important
phenomena in complex condensed matter systems such as high-T
superconductivity and unconventional magnetism. In contrast, phenomena in
superfluids -- especially in ultracold quantum gases -- are commonly well
described by the lowest orbital and a real order parameter. Here, we report on
the observation of a novel multi-orbital superfluid phase with a {\it complex}
order parameter in binary spin mixtures. In this unconventional superfluid, the
local phase angle of the complex order parameter is continuously twisted
between neighboring lattice sites. The nature of this twisted superfluid
quantum phase is an interaction-induced admixture of the p-orbital favored by
the graphene-like band structure of the hexagonal optical lattice used in the
experiment. We observe a second-order quantum phase transition between the
normal superfluid (NSF) and the twisted superfluid phase (TSF) which is
accompanied by a symmetry breaking in momentum space. The experimental results
are consistent with calculated phase diagrams and reveal fundamentally new
aspects of orbital superfluidity in quantum gas mixtures. Our studies might
bridge the gap between conventional superfluidity and complex phenomena of
orbital physics.Comment: 5 pages, 4 figure
Multicomponent Bright Solitons in F = 2 Spinor Bose-Einstein Condensates
We study soliton solutions for the Gross--Pitaevskii equation of the spinor
Bose--Einstein condensates with hyperfine spin F=2 in one-dimension. Analyses
are made in two ways: by assuming single-mode amplitudes and by generalizing
Hirota's direct method for multi-components. We obtain one-solitons of
single-peak type in the ferromagnetic, polar and cyclic states, respectively.
Moreover, twin-peak type solitons both in the ferromagnetic and the polar state
are found.Comment: 15 pages, 8 figure
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