3,119 research outputs found
Improved ferrous shielding for flat cables
To improve shielding of flat multicore cables, a thin, seamless ferrous shield around all cores optimizes low frequency magnetic shielding. Such shielding is covered with an ultrathin seamless coat of highly conductive nonferrous material
On quantum and parallel transport in a Hilbert bundle over spacetime
We study the Hilbert bundle description of stochastic quantum mechanics in
curved spacetime developed by Prugove\v{c}ki, which gives a powerful new
framework for exploring the quantum mechanical propagation of states in curved
spacetime. We concentrate on the quantum transport law in the bundle,
specifically on the information which can be obtained from the flat space
limit. We give a detailed proof that quantum transport coincides with parallel
transport in the bundle in this limit, confirming statements of Prugove\v{c}ki.
We furthermore show that the quantum-geometric propagator in curved spacetime
proposed by Prugove\v{c}ki, yielding a Feynman path integral-like formula
involving integrations over intermediate phase space variables, is Poincar\'e
gauge covariant (i.e. is gauge invariant except for transformations at the
endpoints of the path) provided the integration measure is interpreted as a
``contact point measure'' in the soldered stochastic phase space bundle raised
over curved spacetime.Comment: 25 pages, Plain TeX, harvmac/lanlma
Absence of fermionic quasi-particles in the superfluid state of the attractive Fermi gas
We calculate the effect of order parameter fluctuations on the fermionic
single-particle excitations in the superfluid state of neutral fermions
interacting with short range attractive forces. We show that in dimensions D
\leq 3 the singular effective interaction between the fermions mediated by the
gapless Bogoliubov-Anderson mode prohibits the existence of well-defined
quasi-particles. We explicitly calculate the single-particle spectral function
in the BEC regime in D=3 and show that in this case the quasi-particle residue
and the density of states are logarithmically suppressed.Comment: 4 RevTex pages, 3 figures; title changed, new Figure 1, added
references. We argue that in the entire regime of the BCS-BEC crossover the
quasi-particle picture breaks down in D <=3 for neutral fermions (but NOT for
charged fermions
Renormalization of the BCS-BEC crossover by order parameter fluctuations
We use the functional renormalization group approach with partial
bosonization in the particle-particle channel to study the effect of order
parameter fluctuations on the BCS-BEC crossover of superfluid fermions in three
dimensions. Our approach is based on a new truncation of the vertex expansion
where the renormalization group flow of bosonic two-point functions is closed
by means of Dyson-Schwinger equations and the superfluid order parameter is
related to the single particle gap via a Ward identity. We explicitly calculate
the chemical potential, the single-particle gap, and the superfluid order
parameter at the unitary point and compare our results with experiments and
previous calculations.Comment: 5 pages, 3 figure
Field-induced gapless electron pocket in the superconducting vortex phase of YNi2B2C as probed by magnetoacoustic quantum oscillations
By use of ultrasound studies we resolved magneto-acoustic quantum oscillation
deep into the mixed state of the multiband nonmagnetic superconductor YNi2B2C.
Below the upper critical field, only a very weak additional damping appears
that can be well explained by the field inhomogeneity caused by the flux-line
lattice in the mixed state. This is clear evidence for no or a vanishingly
small gap for one of the bands, namely, the spheroidal alpha band. This
contrasts de Haas--van Alphen data obtained by use of torque magnetometry for
the same sample, with a rapidly vanishing oscillation signal in the mixed
state. This points to a strongly distorted flux-line lattice in the latter case
that, in general, can hamper a reliable extraction of gap parameters by use of
such techniques.Comment: 6 pages, 6 figure
Saturation field of frustrated chain cuprates: broad regions of predominant interchain coupling
An efficient and precise thermodynamic method to extract the interchain
coupling (IC) of spatially anisotropic 2D or 3D spin-1/2 systems from their
empirical saturation field H_s (T=0) is proposed. Using density-matrix
renormalization group, hard-core boson, and spin-wave theory we study how H_s
is affected by an antiferromagnetic (AFM) IC between frustrated chains
described in the J_1-J_2-spin model with ferromagnetic 1st and AFM 2nd neighbor
in-chain exchange. A complex 3D-phase diagram has been found. For Li2CuO2 and
Y2Ca2Cu5O10, we show that H_s is solely determined by the IC and predict H_s
approx 61 T for the latter.Using H_s approx 55 T from our high-field pulsed
measurements one reads out a weak IC for Li2CuO2 close to that from neutron
scattering.Comment: 4 pages, 6 figures, slightly revised version including a slightly
changed title and abstract, one new figure and an EPAPS-supplementatary part
have been adde
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