1,425 research outputs found
The simplest Regge calculus model in the canonical form
Dynamics of a Regge three-dimensional (3D) manifold in a continuous time is
considered. The manifold is closed consisting of the two tetrahedrons with
identified corresponding vertices. The action of the model is that obtained via
limiting procedure from the general relativity (GR) action for the completely
discrete 4D Regge calculus. It closely resembles the continuous general
relativity action in the Hilbert-Palatini (HP) form but possesses finite number
of the degrees of freedom. The canonical structure of the theory is described.
Central point is appearance of the new relations with time derivatives not
following from the Lagrangian but serving to ensure completely discrete 4D
Regge calculus origin of the system. In particular, taking these into account
turns out to be necessary to obtain the true number of the degrees of freedom
being the number of linklengths of the 3D Regge manifold at a given moment of
time.Comment: LaTeX, 7 page
Magnetotransport of lanthanum doped RuSr2GdCu2O8 - the role of gadolinium
Strongly underdoped RuSr_1.9La_0.1GdCu_2O_8 has been comprehensively studied
by dc magnetization, microwave measurements, magnetoresistivity and Hall
resistivity in fields up to 9 T and temperatures down to 1.75 K. Electron
doping by La reduces the hole concentration in the CuO2 planes and completely
suppresses superconductivity. Microwave absorption, dc resistivity and ordinary
Hall effect data indicate that the carrier concentration is reduced and a
semiconductor-like temperature dependence is observed. Two magnetic ordering
transitions are observed. The ruthenium sublattice orders antiferromagnetically
at 155 K for low applied magnetic field and the gadolinium sublattice
antiferromagnetically orders at 2.8 K. The magnetoresistivity exhibits a
complicated temperature dependence due to the combination of the two magnetic
orderings and spin fluctuations. It is shown that the ruthenium magnetism
influences the conductivity in the RuO2 layers while the gadolinium magnetism
influences the conductivity in the CuO2 layers. The magnetoresistivity is
isotropic above 4 K, but it becomes anisotropic when gadolinium orders
antiferromagnetically.Comment: 7 pages, 9 figures, submitted to European Physical Journal
On the area expectation values in area tensor Regge calculus in the Lorentzian domain
Wick rotation in area tensor Regge calculus is considered. The heuristical
expectation is confirmed that the Lorentzian quantum measure on a spacelike
area should coincide with the Euclidean measure at the same argument. The
consequence is validity of probabilistic interpretation of the Lorentzian
measure as well (on the real, i.e. spacelike areas).Comment: LaTeX, 7 pages, introduction and discussion given in more detail,
references adde
Wearable device to assist independent living.
Older people increasingly want to remain living independently in their own homes. The aim of the ENABLE project is to develop a wearable device that can be used both within and outside of the home to support older people in their daily lives and which can monitor their health status, detect potential problems, provide activity reminders and offer communication and alarm services. In order to determine the specifications and functionality required for development of the device user surveys and focus groups were undertaken and use case analysis and scenario modeling carried out. The project has resulted in the development of a wrist worn device and mobile phone combination that can support and assist older and vulnerable wearers with a range of activities and services both inside and outside of their homes. The device is currently undergoing pilot trials in five European countries. The aim of this paper is to describe the ENABLE device, its features and services, and the infrastructure within which it operates
Quantum algorithm for smoothed particle hydrodynamics
We present a quantum computing algorithm for the smoothed particle hydrodynamics (SPH) method. We use a normalization procedure to encode the SPH operators and domain discretization in a quantum register. We then perform the SPH summation via an inner product of quantum registers. Using a one-dimensional function, we test the approach in a classical sense for the kernel sum and first and second derivatives of a one-dimensional function, using both the Gaussian and Wendland kernel functions, and compare various register sizes against analytical results. Error convergence is exponentially fast in the number of qubits. We extend the method to solve the one-dimensional advection and diffusion partial differential equations, which are commonly encountered in fluids simulations. This work provides a foundation for a more general SPH algorithm, eventually leading to highly efficient simulations of complex engineering problems on gate-based quantum computers
Vortex structure in d-density wave scenario of pseudogap
We investigate the vortex structure assuming the d-density wave scenario of
the pseudogap. We discuss the profiles of the order parameters in the vicinity
of the vortex, effective vortex charge and the local density of states. We find
a pronounced modification of these quantities when compared to a purely
superconducting case. Results have been obtained for a clean system as well as
in the presence of a nonmagnetic impurity. We show that the competition between
superconductivity and the density wave may explain some experimental data
recently obtained for high-temperature superconductors. In particular, we show
that the d-density wave scenario explains the asymmetry of the gap observed in
the vicinity of the vortex core.Comment: 8 pages, 10 figure
Coupled-mode theory for Bose-Einstein condensates
We apply the concepts of nonlinear guided-wave optics to a Bose-Einstein
condensate (BEC) trapped in an external potential. As an example, we consider a
parabolic double-well potential and derive coupled-mode equations for the
complex amplitudes of the BEC macroscopic collective modes. Our equations
describe different regimes of the condensate dynamics, including the nonlinear
Josephson effect for any separation between the wells. We demonstrate
macroscopic self-trapping for both repulsive and attractive interactions, and
confirm our results by numerical simulations.Comment: 4 pages, 5 figures; typos removed, figures amended; submitted to PR
"Forbidden" transitions between quantum Hall and insulating phases in p-SiGe heterostructures
We show that in dilute metallic p-SiGe heterostructures, magnetic field can
cause multiple quantum Hall-insulator-quantum Hall transitions. The insulating
states are observed between quantum Hall states with filling factors \nu=1 and
2 and, for the first time, between \nu=2 and 3 and between \nu=4 and 6. The
latter are in contradiction with the original global phase diagram for the
quantum Hall effect. We suggest that the application of a (perpendicular)
magnetic field induces insulating behavior in metallic p-SiGe heterostructures
in the same way as in Si MOSFETs. This insulator is then in competition with,
and interrupted by, integer quantum Hall states leading to the multiple
re-entrant transitions. The phase diagram which accounts for these transition
is similar to that previously obtained in Si MOSFETs thus confirming its
universal character
Vortex states in binary mixture of Bose-Einstein condensates
The vortex configurations in the Bose-Einstein condensate of the mixture of
two different spin states |F=1,m_f=-1> and |2,1> of ^{87}Rb atoms corresponding
to the recent experiments by Matthews et. al. (Phys. Rev. Lett. 83, 2498
(1999)) are considered in the framework of the Thomas-Fermi approximation as
functions of N_2/N_1, where N_1 is the number of atoms in the state |1,-1> and
N_2 - in the state |2,1>. It is shown that for nonrotating condensates the
configuration with the |1,-1> fluid forming the shell about the |2,1> fluid
(configuration "a") has lower energy than the opposite configuration
(configuration "b") for all values of N_2/N_1. When the |1,-1> fluid has net
angular momentum and forms an equatorial ring around the resting central
condensate |2,1>, the total energy of the system is higher than the ground
energy, but the configuration "a" has lower energy than the configuration "b"
for all N_2/N_1. On the other hand, when the |2> fluid has the net angular
momentum, for the lowest value of the angular momentum \hbar l (l=1) there is
the range of the ratio N_2/N_1 where the configuration "b" has lower energy
than the configuration "a". For higher values of the angular momentum the
configuration "b" is stable for all values of N_2/N_1.Comment: minor changes, references adde
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