1,313 research outputs found
On Aharonov-Casher bound states
In this work bound states for the Aharonov-Casher problem are considered.
According to Hagen's work on the exact equivalence between spin-1/2
Aharonov-Bohm and Aharonov-Casher effects, is known that the
term cannot be neglected in the
Hamiltonian if the spin of particle is considered. This term leads to the
existence of a singular potential at the origin. By modeling the problem by
boundary conditions at the origin which arises by the self-adjoint extension of
the Hamiltonian, we derive for the first time an expression for the bound state
energy of the Aharonov-Casher problem. As an application, we consider the
Aharonov-Casher plus a two-dimensional harmonic oscillator. We derive the
expression for the harmonic oscillator energies and compare it with the
expression obtained in the case without singularity. At the end, an approach
for determination of the self-adjoint extension parameter is given. In our
approach, the parameter is obtained essentially in terms of physics of the
problem.Comment: 11 pages, matches published versio
Blood Pressure in Patients with Intermittent Claudication Increases Continuously During Walking
ObjectivesThe purpose of this study was to compare the circulatory responses to walking in patients with peripheral atherosclerotic disease (PAD) and healthy controls.MethodsThe participants were eleven patients with diagnosed PAD, and a control group of six healthy age-matched adults. Blood pressure, heart rate (HR), and acral skin perfusion were recorded continuously before, during and after a walking exercise on a treadmill.ResultsThe patients walked to maximum claudication distance (MCD) on a treadmill, median walking distance 103 (34–223) metres [median (range)], at 3.3 (1.0–4.5) km/h. There was a steep increase in HR and mean arterial pressure (MAP) while the patients were walking. At claudication the median rise in MAP was 46.6 (10.3–61.3) mmHg, systolic blood pressure (SP) increased by 84.9 (31.4–124.9) mmHg, and diastolic blood pressure (DP) by 21.7 (−2.1–31.7) mmHg. HR increased by 34.9 (12.9–48.1) beats/min. The control group walked for 5 minutes at 3.2 (3.0–3.3) km/h. In the control group the blood pressure initially increased moderately but stabilised thereafter. Median rise in MAP during walking was 8.5 (5.6–14.6) mmHg, SP increased by 30.9 (6.6–41.5) mmHg, and DP was reduced by −1.4 (−5.4–1.5) mmHg. HR increased by 27.1 (18.8–34.9) beats/min. We found no significant differences in acral skin perfusion during walking exercise between the patients and control group.ConclusionsIn patients with PAD, blood pressure increased continuously and significantly when walking to MCD (dynamic exercise). The level of increase in blood pressure was similar to that caused in response to isometric exercise
Integrating Imagery from Hull Mounted Sidescan Sonars with Multibeam Bathymetry
Multibeam echo sounders produce high quality bathymetric data, however, for acoustic imaging their alongtrack beamwidth is much wider than what is used on conventional sidescan sonars, so the imagery produced by sidescan sonars are of a better quality and are often preferred. A hullmounted combination instrument package that integrates both the accurate multibeam bathymetry and the high resolution sidescan imagery is an attractive and relatively low cost solution for detailed surveys of harbors, canals, rivers and other shallow areas. Especially in these shallow water areas the sidescan sonar benefits from being hull mounted rather than towed, since this arrangement is easier and safer to handle and the sensor position is known with high accuracy. The paper addresses how the backscatter from the hull-mounted sidescan sonar system can be radiometrically and geometrically corrected, by using the bathymetry from the multibeam echo sounder, and how the 2 data sets can be presented together in 2D and 3D. A practical experiment is described, whereby EM 3002D multibeam echo sounder and a hull mounted EA 400 sidescan sonar system are mounted together and deployed over the bow of a small survey launch. The co-registered data sets are analyzed using the UNH GEOCODER processing scheme, and the results are presented and interpreted in terms of capability to resolve small objects. A comparison is made between the EA 400 sidescan backscatter and the EM 3002D seabed imagery
Interacting damage models mapped onto Ising and percolation models
We introduce a class of damage models on regular lattices with isotropic
interactions, as e.g. quasistatic fiber bundles. The system starts intact with
a surface-energy threshold required to break any cell sampled from an
uncorrelated quenched-disorder distribution. The evolution of this
heterogeneous system is ruled by Griffith's principle which states that a cell
breaks when the release in elastic energy in the system exceeds the
surface-energy barrier necessary to break the cell. By direct integration over
all possible realizations of the quenched disorder, we obtain the probability
distribution of each damage configuration at any level of the imposed external
deformation. We demonstrate an isomorphism between the distributions so
obtained and standard generalized Ising models, in which the coupling constants
and effective temperature in the Ising model are functions of the nature of the
quenched-disorder distribution and the extent of accumulated damage. In
particular, we show that damage models with global load sharing are isomorphic
to standard percolation theory, that damage models with local load sharing rule
are isomorphic to the standard Ising model, and draw consequences thereof for
the universality class and behavior of the autocorrelation length of the
breakdown transitions corresponding to these models. We also treat damage
models having more general power-law interactions, and classify the breakdown
process as a function of the power-law interaction exponent. Last, we also show
that the probability distribution over configurations is a maximum of Shannon's
entropy under some specific constraints related to the energetic balance of the
fracture process, which firmly relates this type of quenched-disorder based
damage model to standard statistical mechanics.Comment: 16 pages, 3 figure
Morphology of two dimensional fracture surface
We consider the morphology of two dimensional cracks observed in experimental
results obtained from paper samples and compare these results with the
numerical simulations of the random fuse model (RFM). We demonstrate that the
data obey multiscaling at small scales but cross over to self-affine scaling at
larger scales. Next, we show that the roughness exponent of the random fuse
model is recovered by a simpler model that produces a connected crack, while a
directed crack yields a different result, close to a random walk. We discuss
the multiscaling behavior of all these models.Comment: slightly revise
Effect of topological defects and Coulomb charge on the low energy quantum dynamics of gapped graphene
We study the combined effect of a conical topological defect and a Coulomb
charge impurity on the dynamics of Dirac fermions in gapped graphene. Beyond a
certain strength of the Coulomb charge, quantum instability sets in, which
demarcates the boundary between sub and supercritical values of the charge. In
the subcritical regime, for certain values of the system parameters, the
allowed boundary conditions in gapped graphene cone can be classified in terms
of a single real parameter. We show that the observables such as local density
of states, scattering phase shifts and the bound state spectra are sensitive to
the value of this real parameter, which is interesting from an empirical point
of view. For a supercritical Coulomb charge, we analyze the system with a
regularized potential as well as with a zigzag boundary condition and find the
effect of the sample topology on the observable features of the system.Comment: 22 pages, 23 figure
Monte-Carlo study of scaling exponents of rough surfaces and correlated percolation
We calculate the scaling exponents of the two-dimensional correlated
percolation cluster's hull and unscreened perimeter. Correlations are
introduced through an underlying correlated random potential, which is used to
define the state of bonds of a two-dimensional bond percolation model.
Monte-Carlo simulations are run and the values of the scaling exponents are
determined as functions of the Hurst exponent H in the range -0.75 <= H <= 1.
The results confirm the conjectures of earlier studies
Gravitational Geometric Phase in the Presence of Torsion
We investigate the relativistic and non-relativistic quantum dynamics of a
neutral spin-1/2 particle submitted an external electromagnetic field in the
presence of a cosmic dislocation. We analyze the explicit contribution of the
torsion in the geometric phase acquired in the dynamic of this neutral
spinorial particle. We discuss the influence of the torsion in the relativistic
geometric phase. Using the Foldy-Wouthuysen approximation, the non-relativistic
quantum dynamics are studied and the influence of the torsion in the
Aharonov-Casher and He-McKellar-Wilkens effects are discussed.Comment: 14 pages, no figur
Relativistic Landau-Aharonov-Casher quantization based on the Lorentz symmetry violation background
Based on the discussions about the Aharonov-Casher effect in the Lorentz
symmetry violation background, we show that the analogue of the relativistic
Landau quantization in the Aharonov-Casher setup can be achieved in the
Lorentz-symmetry violation background.Comment: 11 pages. published in Journal of Mathematical Physic
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