13,062 research outputs found
Field Redefinitions at Finite Density
The apparent dependence of nuclear matter observables on off-shell properties
of the two-nucleon potential is re-examined in the context of the effective
field theory (EFT) approach. Finite density (thermodynamic) observables are
invariant under field redefinitions, which extends the well-known theorem about
the invariance of S-matrix elements. Simple examples demonstrate how field
redefinitions can shift contributions between purely off-shell two-body
interactions and many-body forces, leaving both scattering and finite-density
observables unchanged. If only the transformed two-body potentials are kept,
however, the nuclear matter binding curves will depend on the off-shell part
(generating ``Coester bands''). The correspondence between field redefinitions
and unitary transformations, which have traditionally been used to generate
``phase-equivalent'' nucleon-nucleon potentials, is also demonstrated.Comment: 23 pages, RevTex, 9 ps figures, included with epsf.tex, minor change
On the origin of <i>Halipeurus heraldicus</i> on Round Island petrels: cophylogenetic relationships between petrels and their chewing lice
Lice phylogenetic relationships have often been used to elucidate host relationships and vice versa. In this study, we investigate the louse genus Halipeurus which parasitizes bird hosts in the families Procellariidae, Hydrobatidae and Pelecanoididae. The presence of two lice species on Pterodroma arminjoniana in different breeding grounds (Halipeurus heraldicus on Round Island, off Mauritius in the Indian Ocean and Halipeurus kermadecensis on Trindade Island in the Atlantic Ocean) has led to some confusion in the distribution of Pt. arminjoniana and its close relatives Pt. heraldica and Pt. neglecta. By using a cophylogenetic approach that incorporates uncertainties in phylogenetic reconstructions, we show significant overall coevolution between Halipeurus lice and their hosts. However, the study also indicates that the presence of H. heraldicus on Pt. arminjoniana and Pt. neglecta on Round Island and on Pt. heraldica on Gambier Island are the result of a host switch whereas H. kermadecensis is the ancestral parasite of Pt. arminjoniana. This suggests that H. kermadecensis was lost during or after colonisation of Round Island by Pt. arminjoniana. We conclude that cophylogenetic analyses are central to inferring the evolutionary history and biogeographical patterns of hosts and their parasites
Analytical approach to dielectric optical bent slab waveguides
A rigorous classical analytic frequency domain model of con?ned optical wave propagation along 2D bent slab waveguides and curved dielectric interfaces is investigated, based on a piecewise ansatz for bend mode profiles in terms of Bessel and Hankel functions. This approach provides a clear picture of the behaviour of bend modes, concerning their decay for large radial arguments or effects of varying bend radius. Fast and accurate routines are required to evaluate Bessel functions with large complex orders and large arguments. Our implementation enabled detailed studies of bent waveguide properties, including higher order bend modes and whispering gallery modes, their interference patterns, and issues related to bend mode normalization and orthogonality properties
Orthogonality relations for triple modes at dielectric boundary surfaces
We work out the orthogonality relations for the set of Carniglia-Mandel
triple modes which provide a set of normal modes for the source-free
electromagnetic field in a background consisting of a passive dielectric
half-space and the vacuum, respectively. Due to the inherent computational
complexity of the problem, an efficient strategy to accomplish this task is
desirable, which is presented in the paper. Furthermore, we provide all main
steps for the various proofs pertaining to different combinations of triple
modes in the orthogonality integral.Comment: 15 page
A study of commuter airplane design optimization
Problems of commuter airplane configuration design were studied to affect a minimization of direct operating costs. Factors considered were the minimization of fuselage drag, methods of wing design, and the estimated drag of an airplane submerged in a propellor slipstream; all design criteria were studied under a set of fixed performance, mission, and stability constraints. Configuration design data were assembled for application by a computerized design methodology program similar to the NASA-Ames General Aviation Synthesis Program
Density Functional Theory: Methods and Problems
The application of density functional theory to nuclear structure is
discussed, highlighting the current status of the effective action approach
using effective field theory, and outlining future challenges.Comment: 10 pages, 14 figures, invited talk at INT workshop on Nuclear Forces
and the Quantum Many-Body Problem, Seattle, October 200
Potential Energy Surface for H_2 Dissociation over Pd(100)
The potential energy surface (PES) of dissociative adsorption of H_2 on
Pd(100) is investigated using density functional theory and the full-potential
linear augmented plane wave (FP-LAPW) method. Several dissociation pathways are
identified which have a vanishing energy barrier. A pronounced dependence of
the potential energy on ``cartwheel'' rotations of the molecular axis is found.
The calculated PES shows no indication of the presence of a precursor state in
front of the surface. Both results indicate that steering effects determine the
observed decrease of the sticking coefficient at low energies of the H_2
molecules. We show that the topology of the PES is related to the dependence of
the covalent H(s)-Pd(d) interactions on the orientation of the H_2 molecule.Comment: RevTeX, 8 pages, 5 figures in uufiles forma
An optical fibre dynamic instrumented palpation sensor for the characterisation of biological tissue
AbstractThe diagnosis of prostate cancer using invasive techniques (such as biopsy and blood tests for prostate-specific antigen) and non-invasive techniques (such as digital rectal examination and trans-rectal ultrasonography) may be enhanced by using an additional dynamic instrumented palpation approach to prostate tissue classification. A dynamically actuated membrane sensor/actuator has been developed that incorporates an optical fibre Fabry–Pérot interferometer to record the displacement of the membrane when it is pressed on to different tissue samples. The membrane sensor was tested on a silicon elastomer prostate model with enlarged and stiffer material on one side to simulate early stage prostate cancer. The interferometer measurement was found to have high dynamic range and accuracy, with a minimum displacement resolution of ±0.4μm over a 721μm measurement range. The dynamic response of the membrane sensor when applied to different tissue types changed depending on the stiffness of the tissue being measured. This demonstrates the feasibility of an optically tracked dynamic palpation technique for classifying tissue type based on the dynamic response of the sensor/actuator
'It Has to Go Down A Little, In Order to Go Around'- Following Feynman on the Gyroscope
In this paper we show that with the help of accessible, teaching quality
equipment, some interesting details of the motion of a gyroscope, typically
overlooked in introductory courses, can be measured and compared to theory. We
begin by deriving a simple relation between the asymptotic dip angle of a
gyroscope released from rest and its precession velocity. We then describe an
experiment which measures these parameters. The data gives excellent agreement
with the model. The idea for this project was suggested by the discussion of
gyroscopic motion in The Feynman Lectures on Physics. Feynman's conclusion
(stated in colloquial terms and quoted in the title) is confirmed and, in
addition, conservation of angular momentum, which underlies this effect, is
quantitatively demonstrated.Comment: 6 pages, 4 figure
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