1,348 research outputs found
Fluidic low speed wind sensor research study Final report, Oct. 1968 - Oct. 1969
Cross flow and parallel flow concepts of fluidic wind speed sensor
Very low velocity flow sensor uses fluidic techniques
Parallel-flow wind sensor provides differential pressure output which is nearly linear and relatively insensitive to supply pressure over a wide range of wind velocities. Cross-flow wind sensor outputs are input to a fluidic amplifier to obtain high pressure output for low wind velocities without changing output characteristics
Classical solutions of sigma models in curved backgrounds by the Poisson-Lie T-plurality
Classical equations of motion for three-dimensional sigma-models in curved
background are solved by a transformation that follows from the Poisson-Lie
T-plurality and transform them into the equations in the flat background.
Transformations of coordinates that make the metric constant are found and used
for solving the flat model. The Poisson-Lie transformation is explicitly
performed by solving the PDE's for auxiliary functions and finding the relevant
transformation of coordinates in the Drinfel'd double. String conditions for
the solutions are preserved by the Poisson-Lie transformations. Therefore we
are able to specify the type of sigma-model solutions that solve also equations
of motion of three dimensional relativistic strings in the curved backgrounds.
Simple examples are given
Flat coordinates and dilaton fields for three--dimensional conformal sigma models
Riemannian coordinates for flat metrics corresponding to three--dimensional
conformal Poisson--Lie T--dualizable sigma models are found by solving partial
differential equations that follow from the transformations of the connection
components. They are then used for finding general forms of the dilaton fields
satisfying the vanishing beta equations of the sigma models.Comment: 16 pages, no figure
Quasiparticle decay rate of Josephson charge qubit oscillations
We analyze the decay of Rabi oscillations in a charge qubit consisting of a
Cooper pair box connected to a finite-size superconductor by a Josephson
junction. We concentrate on the contribution of quasiparticles in the
superconductors to the decay rate. Passing of a quasiparticle through the
Josephson junction tunes the qubit away from the charge degeneracy, thus
spoiling the Rabi oscillations. We find the temperature dependence of the
quasiparticle contribution to the decay rate for open and isolated systems. The
former case is realized if a normal-state trap is included in the circuit, or
if just one vortex resides in the qubit; the decay rate has an activational
temperature dependence with the activation energy equal to the superconducting
gap . In a superconducting qubit isolated from the environment, the
activation energy equals if the number of electrons is even, while
for an odd number of electrons the decay rate of an excited qubit state remains
finite in the limit of zero temperature. We estimate the decay rate for
realistic parameters of a qubit.Comment: 8 pages, 3 figures, final version as published in PRB, minor change
Transport properties of single atoms
We present a systematic study of the ballistic electron conductance through
sp and 3d transition metal atoms attached to copper and palladium crystalline
electrodes. We employ the 'ab initio' screened Korringa-Kohn-Rostoker Green's
function method to calculate the electronic structure of nanocontacts while the
ballistic transmission and conductance eigenchannels were obtained by means of
the Kubo approach as formulated by Baranger and Stone. We demonstrate that the
conductance of the systems is mainly determined by the electronic properties of
the atom bridging the macroscopic leads. We classify the conducting
eigenchannels according to the atomic orbitals of the contact atom and the
irreducible representations of the symmetry point group of the system that
leads to the microscopic understanding of the conductance. We show that if
impurity resonances in the density of states of the contact atom appear at the
Fermi energy, additional channels of appropriate symmetry could open. On the
other hand the transmission of the existing channels could be blocked by
impurity scattering.Comment: RevTEX4, 9 pages, 9 figure
Study of loss in superconducting coplanar waveguide resonators
Superconducting coplanar waveguide (SCPW) resonators have a wide range of
applications due to the combination of their planar geometry and high quality
factors relative to normal metals. However, their performance is sensitive to
both the details of their geometry and the materials and processes that are
used in their fabrication. In this paper, we study the dependence of SCPW
resonator performance on materials and geometry as a function of temperature
and excitation power. We measure quality factors greater than at
high excitation power and at a power comparable to that generated
by a single microwave photon circulating in the resonator. We examine the
limits to the high excitation power performance of the resonators and find it
to be consistent with a model of radiation loss. We further observe that while
in all cases the quality factors are degraded as the temperature and power are
reduced due to dielectric loss, the size of this effect is dependent on
resonator materials and geometry. Finally, we demonstrate that the dielectric
loss can be controlled in principle using a separate excitation near the
resonance frequencies of the resonator.Comment: Replacing original version. Changes made based on referee comments.
Fixed typo in equation (3) and added appendi
Spin-dependent Transparency of Ferromagnet/Superconductor Interfaces
Because the physical interpretation of the spin-polarization of a ferromagnet
determined by point-contact Andreev reflection (PCAR) is non-trivial, we have
carried out parameter-free calculations of PCAR spectra based upon a
scattering-theory formulation of Andreev reflection generalized to
spin-polarized systems and a tight-binding linear muffin tin orbital method for
calculating the corresponding scattering matrices. PCAR is found to measure the
spin-dependent interface transparency rather than the bulk polarization of the
ferromagnet which is strongly overestimated by free electron model fitting.Comment: 4 pages, 1figure. submitte
Helical edge and surface states in HgTe quantum wells and bulk insulators
The quantum spin Hall (QSH) effect is the property of a new state of matter
which preserves time-reversal, has an energy gap in the bulk, but has
topologically robust gapless states at the edge. Recently, it has been shown
that HgTe quantum wells realize this novel effect. In this work, we start from
realistic tight-binding models and demonstrate the existence of the helical
edge states in HgTe quantum wells and calculate their physical properties. We
also show that 3d HgTe is a topological insulator under uniaxial strain, and
show that the surface states are described by single-component massless
relativistic Dirac fermions in 2+1 dimensions. Experimental predictions are
made based on the quantitative results obtained from realistic calculations.Comment: 5 page
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