6,161 research outputs found
Feeding ecology of the seagrass-grazing nerite Smaragdia souverbiana (Montrouzier, 1863) in subtropical seagrass beds of eastern Australia
By amalgamating all seagrass-associated grazing invertebrates into an epiphyte-feeding guild, the currently accepted model of seagrass trophic dynamics ignores the diverse range of invertebrates that feed directly on, and do considerable damage to, seagrasses. Of the wide range of invertebrates documented to damage seagrass directly, the gastropod genus Smaragdia has adaptations and ecology that suggests it could be a specialized seagrass-feeding group, of which at least two species are known preferentially to consume seagrass. This paper investigated the dietary associations of Smaragdia souverbiana, one of the most widely distributed but least studied species of the genus, in the subtropical eastern Australian part of its range. Using field-based assessments of grazing damage and targeted laboratory feeding trials, we assessed the dietary associations, digestive ability and feeding preferences of S. souverbiana with local seagrasses (Halophila ovalis, Zostera capricorni and Cymodocea serrulata). We found that this species consumed and damaged all available species, but showed a strong preference for the most abundant and moderately digestible Z. capricorni. Although it avoided seagrass bearing a high epiphyte load in a laboratory context, considerable amounts of epiphytic material were found in the faeces of field-caught individuals. Grazing and digestibility of seagrass cells was higher in Z. capricorni and H. ovalis, and the former was preferred when both were available. This study adds to the growing body of literature demonstrating that S. souverbiana—and potentially many other grazing invertebrates—cause considerable damage to seagrasses directly, rather than targeting epiphytes.Versión del editor1,358
Comparison between disordered quantum spin 1/2 chains
We study the magnetic properties of two types of one dimensional XX spin 1/2
chains. The first type has only nearest neighbor interactions which can be
either antiferromagnetic or ferromagnetic and the second type which has both
nearest neighbor and next nearest neighbor interactions, but only
antiferromagnetic in character. We study these systems in the presence of low
transverse magnetic fields both analytically and numerically. Comparison of
results show a close relation between the two systems, which is in agreement
with results previously found in Heisenberg chains by means of a numerical real
space renormalization group procedure.Comment: 7 page
Effects of varying solar-view geometry and canopy structure on solar-induced chlorophyll fluorescence and PRI
Bond-impurity induced bound states in disordered spin-1/2 ladders
We discuss the effect of weak bond-disorder in two-leg spin ladders on the
dispersion relation of the elementary triplet excitations with a particular
focus on the appearance of bound states in the spin gap. Both the cases of
modified exchange couplings on the rungs and the legs of the ladder are
analyzed. Based on a projection on the single-triplet subspace, the
single-impurity and small cluster problems are treated analytically in the
strong-coupling limit. Numerically, we study the problem of a single impurity
in a spin ladder by exact diagonalization to obtain the low-lying excitations.
At finite concentrations and to leading order in the inter-rung coupling, we
compare the spectra obtained from numerical diagonalization of large systems
within the single-triplet subspace with the results of diagrammatic techniques,
namely low-concentration and coherent-potential approximations. The
contribution of small impurity clusters to the density of states is also
discussed.Comment: 9 pages REVTeX4 including 7 figures, final version; Fig. 5 modifie
Induced Parity Breaking Term at Finite Temperature
We compute the exact induced parity-breaking part of the effective action for
2+1 massive fermions in at finite temperature by calculating the
fermion determinant in a particular background. The result confirms that gauge
invariance of the effective action is respected even when large gauge
transformations are considered.Comment: to be published in Physical Review Letters. 5 pages, Revtex, no
figure
Stabilizing strongly correlated photon fluids with non-Markovian reservoirs
We introduce a frequency-dependent incoherent pump scheme with a square-shaped spectrum as a way to study strongly correlated photons in arrays of coupled nonlinear resonators. This scheme can be implemented via a reservoir of population-inverted two-level emitters with a broad distribution of transition frequencies. Our proposal is predicted to stabilize a nonequilibrium steady state sharing important features with a zero-temperature equilibrium state with a tunable chemical potential. We confirm the efficiency of our proposal for the Bose-Hubbard model by computing numerically the steady state for finite system sizes: first, we predict the occurrence of a sequence of incompressible Mott-insulator-like states with arbitrary integer densities presenting strong robustness against tunneling and losses. Secondly, for stronger tunneling amplitudes or noninteger densities, the system enters a coherent regime analogous to the superfluid state. In addition to an overall agreement with the zero-temperature equilibrium state, exotic nonequilibrium processes leading to a finite entropy generation are pointed out in specific regions of parameter space. The equilibrium ground state is shown to be recovered by adding frequency-dependent losses. The promise of this improved scheme in view of quantum simulation of the zero-temperature many-body physics is highlighted
Muscles in “Concert”: Study of Primary Motor Cortex Upper Limb Functional Topography
BACKGROUND: Previous studies with Transcranial Magnetic Stimulation (TMS) have focused on the cortical representation of limited group of muscles. No attempts have been carried out so far to get simultaneous recordings from hand, forearm and arm with TMS in order to disentangle a 'functional' map providing information on the rules orchestrating muscle coupling and overlap. The aim of the present study is to disentangle functional associations between 12 upper limb muscles using two measures: cortical overlapping and cortical covariation of each pair of muscles. Interhemispheric differences and the influence of posture were evaluated as well. METHODOLOGY/PRINCIPAL FINDINGS: TMS mapping studies of 12 muscles belonging to hand, forearm and arm were performed. Findings demonstrate significant differences between the 66 pairs of muscles in terms of cortical overlapping: extremely high for hand-forearm muscles and very low for arm vs hand/forearm muscles. When right and left hemispheres were compared, overlapping between all possible pairs of muscles in the left hemisphere (62.5%) was significantly higher than in the right one (53.5% ). The arm/hand posture influenced both measures of cortical association, the effect of Position being significant [p = .021] on overlapping, resulting in 59.5% with prone vs 53.2% with supine hand, but only for pairs of muscles belonging to hand and forearm, while no changes occurred in the overlapping of proximal muscles with those of more distal districts. CONCLUSIONS/SIGNIFICANCE: Larger overlapping in the left hemisphere could be related to its lifetime higher training of all twelve muscles studied with respect to the right hemisphere, resulting in larger intra-cortical connectivity within primary motor cortex. Altogether, findings with prone hand might be ascribed to mechanisms facilitating coupling of muscles for object grasping and lifting -with more proximal involvement for joint stabilization- compared to supine hand facilitating actions like catching. TMS multiple-muscle mapping studies permit a better understanding of motor control and 'plastic' reorganization of motor system
Induced Parity Breaking Term in Arbitrary Odd Dimensions at Finite Temperature
We calculate the exact parity odd part of the effective action
() for massive Dirac fermions in 2d+1 dimensions at finite
temperature, for a certain class of gauge field configurations. We consider
first Abelian external gauge fields, and then we deal with the case of a
non-Abelian gauge group containing an Abelian U(1) subgroup. For both cases, it
is possible to show that the result depends on topological invariants of the
gauge field configurations, and that the gauge transformation properties of
depend only on those invariants and on the winding number
of the gauge transformation.Comment: 10 pages, revtex, no figure
Alginate Formulations: Current Developments in the Race for Hydrogel-Based Cardiac Regeneration
Cardiovascular diseases, including myocardial infarction (MI), represent the main worldwide cause of mortality and morbidity. In this scenario, to contrast the irreversible damages following MI, cardiac regeneration has emerged as a novel and promising solution for in situ cellular regeneration, preserving cell behavior and tissue cytoarchitecture. Among the huge variety of natural, synthetic, and hybrid compounds used for tissue regeneration, alginate emerged as a good candidate for cellular preservation and delivery, becoming one of the first biomaterial tested in pre-clinical research and clinical trials concerning cardiovascular diseases. Although promising results have been obtained, recellularization and revascularization of the infarcted area present still major limitations. Therefore, the demand is rising for alginate functionalization and its combination with molecules, factors, and drugs capable to boost the regenerative potential of the cardiac tissue. The focus of this review is to elucidate the promising properties of alginate and to highlight its benefits in clinical trials in relation to cardiac regeneration. The definition of hydrogels, the alginate characteristics, and recent biomedical applications are herewith described. Afterward, the review examines in depth the ongoing developments to refine the material relevance in cardiac recovery and regeneration after MI and presents current clinical trials based on alginate
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