541 research outputs found
Synthetic magnetism for photon fluids
We develop a theory of artificial gauge fields in photon fluids for the cases
of both second-order and third-order optical nonlinearities. This applies to
weak excitations in the presence of pump fields carrying orbital angular
momentum, and is thus a type of Bogoliubov theory. The resulting artificial
gauge fields experienced by the weak excitations are an interesting
generalization of previous cases and reflect the PT-symmetry properties of the
underlying non-Hermitian Hamiltonian. We illustrate the observable consequences
of the resulting synthetic magnetic fields for examples involving both
second-order and third-order nonlinearities
BFT Hamiltonian embedding for SU(3) Skyrmion
We newly apply the Batalin, Fradkin and Tyutin (BFT) formalism to the SU(3)
flavor Skyrmion model to investigate the Weyl ordering correction to the
structure of the hyperfine splittings of strange baryons. On the other hand,
the Berry phases and Casimir effects are also discussed.Comment: 14 pages, modified titl
Spin Waves in Random Spin Chains
We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random
antiferromagnetic impurity bonds with modified spin-wave theory. By describing
thermal excitations in the language of spin waves, we successfully observe a
low-temperature Curie susceptibility due to formation of large spin clusters
first predicted by the real-space renormalization-group approach, as well as a
crossover to a pure ferromagnetic spin chain behavior at intermediate and high
temperatures. We compare our results of the modified spin-wave theory to
quantum Monte Carlo simulations.Comment: 3 pages, 3 eps figures, submitted to the 47th Conference on Magnetism
and Magnetic Material
Density Matrix Renormalization Group Study of the Haldane Phase in Random One-Dimensional Antiferromagnets
It is conjectured that the Haldane phase of the S=1 antiferromagnetic
Heisenberg chain and the ferromagnetic-antiferromagnetic alternating
Heisenberg chain is stable against any strength of randomness, because of
imposed breakdown of translational symmetry. This conjecture is confirmed by
the density matrix renormalization group calculation of the string order
parameter and the energy gap distribution.Comment: 4 Pages, 7 figures; Considerable revisions are made in abstract and
main text. Final accepted versio
Low-Temperature Scaling Regime of Random Ferromagnetic-Antiferromagnetic Spin Chains
Using the Continuous Time Quantum Monte Carlo Loop algorithm, we calculate
the temperature dependence of the uniform susceptibility, and the specific heat
of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings,
down to very low temperatures. Our data show a consistent scaling behavior in
both quantities and support strongly the conjecture drawn from the
approximative real-space renormalization group treatment. A statistical
analysis scheme is developed which will be useful for the search scaling
behavior in numerical and experimental data of random spin chains.Comment: 4 pages and 3 figure
Clear-cuts are temporary habitats, not matrix, for endangered grassland burnet moths (Zygaena spp.)
Burnet moths (Zygaena spp.) are day-flying Lepidoptera considered indicative of species-rich grasslands. In the present study, our aim was to clarify whether clear-cuts are habitat, supporting habitat or matrix for three species of Zygaena. We did so by sampling these species with sex pheromones on 48 clear-cuts, varying in amount of host and nectar plants, in southern Sweden. To compare the efficiency of such sampling, we also conducted transect walks on these clearcuts. Overall, host-plants on clear-cuts best explained the abundance of Zygaena spp. recorded, better than nectar-plants or connectivity with nearby grasslands. These results indicate that clear-cuts with an abundance of host plants are used as a fully functional habitat, and not a supporting habitat in the sense of only providing nectar. There is no support in these results for considering clear-cuts as an inert matrix. With about half the work-effort, pheromone traps recorded 100 times more Zygaena spp. as transect walks. The poor correspondence between observations during transects walks and pheromone trap catches suggest Zygaena spp. being difficult to monitor by transect walks. In contrast to grasslands, clear-cuts are short-term in nature requiring repeated recolonization, indicating the importance of permanent grasslands. However, clear-cuts are important temporary insect habitats due to their great acreage, and suitable management can increase the time they remain a habitat
The Low-Energy Fixed Points of Random Quantum Spin Chains
The one-dimensional isotropic quantum Heisenberg spin systems with random
couplings and random spin sizes are investigated using a real-space
renormalization group scheme. It is demonstrated that these systems belong to a
universality class of disordered spin systems, characterized by weakly coupled
large effective spins. In this large-spin phase the uniform magnetic
susceptibility diverges as 1/T with a non-universal Curie constant at low
temperatures T, while the specific heat vanishes as T^delta |ln T| for T->0.
For broad range of initial distributions of couplings and spin sizes the
distribution functions approach a single fixed-point form, where delta \approx
0.44. For some singular initial distributions, however, fixed-point
distributions have non-universal values of delta, suggesting that there is a
line of fixed points.Comment: 19 pages, REVTeX, 13 figure
Thermodynamics of Random Ferromagnetic Antiferromagnetic Spin-1/2 Chains
Using the quantum Monte Carlo Loop algorithm, we calculate the temperature
dependence of the uniform susceptibility, the specific heat, the correlation
length, the generalized staggered susceptibility and magnetization of a
spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings, down
to very low temperatures. Our data show a consistent scaling behavior in all
the quantities and support strongly the conjecture drawn from the approximate
real-space renormalization group treatment.A statistical analysis scheme is
developed which will be useful for the search of scaling behavior in numerical
and experimental data of random spin chains.Comment: 13 pages, 13 figures, RevTe
Predation on migrating eels (Anguilla anguilla L.) from the Western Mediterranean
Nineteen female silver European eels (Anguilla anguilla L.) were tagged with satellite tags and released in the Gulf of Lion in the Mediterranean during the migration seasons 2013 and 2015. Sixteen tags transmitted data: five in the Atlantic Ocean, and eleven in the Mediterranean. Of those, 50% of migrating eels were consumed by marine mammals in each year, all in the Mediterranean. The diving behaviour recorded by the tags after the eels were consumed indicated that the most likely predators were deep diving toothed whales. Measurements of the acoustic target strength of the tag showed a negligible effect on the detectability by whale biosonar. Overall, the observed predation rate was similar to that reported for eels escaping into the Atlantic. However, unlike eels in the Atlantic, which are most vulnerable to predators in the first week of escapement as they traverse the continental shelf and before they reach the refuge of the deep ocean, eels escaping from the Mediterranean were predated in deep water, months after release, likely as a consequence of their migration within a relatively narrow and deep corridor in the Alboran Sea. This emphasises the challenge of accounting for natural mortality in management plans for the long-term recovery of the European eel
Real Space Renormalization Group Study of the S=1/2 XXZ Chains with Fibonacci Exchange Modulation
Ground state properties of the S=1/2 antiferromagnetic XXZ chain with
Fibonacci exchange modulation are studied using the real space renormalization
group method for strong modulation. The quantum dynamical critical behavior
with a new universality class is predicted in the isotropic case. Combining our
results with the weak coupling renormalization group results by Vidal et al.,
the ground state phase diagram is obtained.Comment: 9 pages, 9 figure
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