1,933 research outputs found
Direct measurement of swimming and diving kinematics of giant Atlantic bluefin tuna (Thunnus thynnus)
Tunas possess a range of physiological and mechanical adaptations geared towards high-performance swimming that are of considerable interest to physiologists, ecologists and engineers. Advances in biologging have provided significant improvements in understanding tuna migrations and vertical movement patterns, yet our understanding of the locomotion and swimming mechanics of these fish under natural conditions is limited. We equipped Atlantic bluefin tuna (Thunnus thynnus) with motion-sensitive tags and video cameras to quantify the gaits and kinematics used by wild fish. Our data reveal significant variety in the locomotory kinematics of Atlantic bluefin tuna, ranging from continuous locomotion to two types of intermittent locomotion. The tuna sustained swimming speeds in excess of 1.5 m s−1 (0.6 body lengths s−1), while beating their tail at a frequency of approximately 1 Hz. While diving, some descents were entirely composed of passive glides, with slower descent rates featuring more gliding, while ascents were primarily composed of active swimming. The observed swimming behaviour of Atlantic bluefin tuna is consistent with theoretical models predicting such intermittent locomotion to result in mechanical and physiological advantages. Our results confirm that Atlantic bluefin tuna possess behavioural specializations to increase their locomotory performance, which together with their unique physiology improve their capacity to use pelagic and mesopelagic habitats
Conformal Field Theory Approach to the 2-Impurity Kondo Problem: Comparison with Numerical Renormalization Group Results
Numerical renormalization group and conformal field theory work indicate that
the two impurity Kondo Hamiltonian has a non-Fermi liquid critical point
separating the Kondo-screening phase from the inter-impurity singlet phase when
particle-hole (P-H) symmetry is maintained. We clarify the circumstances under
which this critical point occurs, pointing out that there are two types of P-H
symmetry. Only one of them guarantees the occurance of the critical point. Much
of the previous numerical work was done on models with the other type of P-H
symmetry. We analyse this critical point using the boundary conformal field
theory technique. The finite-size spectrum is presented in detail and compared
with about 50 energy levels obtained using the numerical renormalization group.
Various Green's functions, general renormalization group behaviour, and a
hidden are analysed.Comment: 38 pages, RevTex. 2 new sections clarify the circumstances under
which a model will exhibit the non-trivial critical point (hence potentially
resolving disagreements with other Authors) and explain the hidden SO(7)
symmetry of the model, relating it to an alternative approach of Sire et al.
and Ga
N identical particles under quantum confinement: A many-body dimensional perturbation theory approach
Systems that involve N identical interacting particles under quantum
confinement appear throughout many areas of physics, including chemical,
condensed matter, and atomic physics. In this paper, we present the methods of
dimensional perturbation theory, a powerful set of tools that uses symmetry to
yield simple results for studying such many-body systems. We present a detailed
discussion of the dimensional continuation of the N-particle Schrodinger
equation, the spatial dimension D -> infinity equilibrium (D^0) structure, and
the normal-mode (D^{-1}) structure. We use the FG matrix method to derive
general, analytical expressions for the many-body normal-mode vibrational
frequencies, and we give specific analytical results for three confined N-body
quantum systems: the N-electron atom, N-electron quantum dot, and N-atom
inhomogeneous Bose-Einstein condensate with a repulsive hardcore potential
Coordinate Representation of the One-Spinon One-Holon Wavefunction and Spinon-Holon Interaction
By deriving and studying the coordinate representation for the one-spinon
one-holon wavefunction we show that spinons and holons in the supersymmetric model with interaction attract each other. The interaction causes
a probability enhancement in the one-spinon one-holon wavefunction at short
separation between the particles. We express the hole spectral function for a
finite lattice in terms of the probability enhancement, given by the one-spinon
one-holon wavefunction at zero separation. In the thermodynamic limit, the
spinon-holon attraction turns into the square-root divergence in the hole
spectral function.Comment: 20 pages, 3 .eps figure
A framework to predict, validate and review the acoustic footprints of operating tidal turbines [abstract]
A framework to predict, validate and review the acoustic footprints of operating tidal turbines [abstract
Generalized Drinfeld-Sokolov Reductions and KdV Type Hierarchies
Generalized Drinfeld-Sokolov (DS) hierarchies are constructed through local
reductions of Hamiltonian flows generated by monodromy invariants on the dual
of a loop algebra. Following earlier work of De Groot et al, reductions based
upon graded regular elements of arbitrary Heisenberg subalgebras are
considered. We show that, in the case of the nontwisted loop algebra
, graded regular elements exist only in those Heisenberg
subalgebras which correspond either to the partitions of into the sum of
equal numbers or to equal numbers plus one . We prove that the
reduction belonging to the grade regular elements in the case yields
the matrix version of the Gelfand-Dickey -KdV hierarchy,
generalizing the scalar case considered by DS. The methods of DS are
utilized throughout the analysis, but formulating the reduction entirely within
the Hamiltonian framework provided by the classical r-matrix approach leads to
some simplifications even for .Comment: 43 page
Niobium based intermetallics as a source of high-current/high-magnetic field superconductors
The article is focused on low temperature intermetallic A15 superconducting
wires development for Nuclear Magnetic Resonance, NMR, and Nuclear Magnetic
Imaging, MRI, magnets and also on cryogen-free magnets. There are many other
applications which would benefit from new development such as future Large
Hadron Collider to be built from A15 intermetallic conductors. This paper
highlights the current status of development of the niobium based
intermetallics with special attention to Nb 3 (Al 1-x, Ge x). Discussion is
focused on the materials science aspects of conductor manufacture, such as
b-phase (A15) formation, with particular emphasis on the maximisation of the
superconducting parameters, such as critical current density, Jc, critical
temperature, Tc, and upper critical field, Hc2 . Many successful manufacturing
techniques of the potential niobium-aluminide intermetallic superconducting
conductors, such as solid-state processing, liquid-solid processing, rapid
heating/cooling processes, are described, compared and assessed. Special
emphasis has been laid on conditions under which the Jc (B) peak effect occurs
in some of the Nb3(Al,Ge) wires. A novel electrodeoxidizing method developed in
Cambridge whereby the alloys and intermetallics are produced cheaply making all
superconducting electromagnetic devices, using low cost LTCs, more cost
effective is presented.This new technique has potential to revolutionise the
existing superconducting industry enabling reduction of cost orders of
magnitude.Comment: Paper presented at EUCAS'01 conference, Copenhagen, 26-30 August 200
Personality Traits in Juvenile Delinquents: Associations with Peer and Family Relations
Objective: To establish family and peer correlates of personality traits shown to be predictive of future criminal recidivism.
Method: 137 incarcerated boys aged 13-18 (x = 16 ± 1.2), 35% black, 21% Hispanic, 43% white, and 1% other completed the Weinberger Adjustment Inventory (WAI) and a psychosocial history obtained by a social worker. Records were summarized using two raters who assigned numerical ratings to dimensions of family and peer relations.
Results: As expected, observer ratings of family and peer relationships were correlated with the personality characteristics of distress, denial and restraint as measured by the WAI.
Conclusion: Family and peer relations are associated with certain personality traits that are predictive of criminal recidivism in delinquents. This study further expands the knowledge base regarding the social and interpersonal correlates of individual traits predicting criminal recidivism
Enhancement of the Two-channel Kondo Effect in Single-Electron boxes
The charging of a quantum box, coupled to a lead by tunneling through a
single resonant level, is studied near the degeneracy points of the Coulomb
blockade. Combining Wilson's numerical renormalization-group method with
perturbative scaling approaches, the corresponding low-energy Hamiltonian is
solved for arbitrary temperatures, gate voltages, tunneling rates, and energies
of the impurity level. Similar to the case of a weak tunnel barrier, the shape
of the charge step is governed at low temperatures by the non-Fermi-liquid
fixed point of the two-channel Kondo effect. However, the associated Kondo
temperature TK is strongly modified. Most notably, TK is proportional to the
width of the level if the transmission through the impurity is close to unity
at the Fermi energy, and is no longer exponentially small in one over the
tunneling matrix element. Focusing on a particle-hole symmetric level, the
two-channel Kondo effect is found to be robust against the inclusion of an
on-site repulsion on the level. For a large on-site repulsion and a large
asymmetry in the tunneling rates to box and to the lead, there is a sequence of
Kondo effects: first the local magnetic moment that forms on the level
undergoes single-channel screening, followed by two-channel overscreening of
the charge fluctuations inside the box.Comment: 21 pages, 19 figure
- …