62,557 research outputs found
A suggested search for 207Pb nuclear Schiff moment in PbTiO3 ferroelectric
We suggest two types of experiments, NMR and macroscopic magnetometry, with
solid PbTiO3 to search for the nuclear Schiff moment of 207Pb. Both kinds of
experiments promise substantial improvement over the presently achieved
sensitivities. Statistical considerations show that the improvement of the
current sensitivity can be up to 10 orders of magnitude for the magnetometry
experiment and up to 6 orders of magnitude for the NMR experiment. Such
significant enhancement is due to the strong internal electric field of the
ferroelectric, as well as due to the possibility to cool the nuclear-spin
subsystem in the compound down to nanokelvin temperatures.Comment: 4 pages; revised sensitivity estimate for NMR experimen
Superconductivity from purely repulsive interactions in the strong coupling approach : Application of the SU(2) slave-rotor theory to the Hubbard model
We propose a mechanism of superconductivity from purely repulsive
interactions in the strong coupling regime, where the BCS
(Bardeen-Cooper-Schrieffer) mechanism such as the spin-fluctuation approach is
difficult to apply. Based on the SU(2) slave-rotor representation of the
Hubbard model, we find that the single energy scale for the amplitude formation
of Cooper pairs and their phase coherence is separated into two energy scales,
allowing the so called pseudogap state where such Cooper pairs are coherent
locally but not globally, interpreted as realization of the density-phase
uncertainty principle. This superconducting state shows the temperature-linear
decreasing ratio of superfluid weight, resulting from strong phase
fluctuations
New experimental limits on non-Newtonian forces in the micrometer-range
We report measurements of the short-range forces between two macroscopic
gold-coated plates using a torsion pendulum. The force is measured for
separations between 0.7 m and 7 m, and is well described by a
combination of the Casimir force, including the finite-temperature correction,
and an electrostatic force due to patch potentials on the plate surfaces. We
use our data to place constraints on the Yukawa-type "new" forces predicted by
theories with extra dimensions. We establish a new best bound for force ranges
0.4 m to 4 m, and, for forces mediated by gauge bosons propagating in
dimensions and coupling to the baryon number, extract a
-dimensional Planck scale lower limit of TeV.Comment: 4 pages, 2 figure
Tunnelling series in terms of perturbation theory for quantum spin systems
Considered is quantum tunnelling in anisotropic spin systems in a magnetic
field perpendicular to the anisotropy axis. In the domain of small field the
problem of calculating tunnelling splitting of energy levels is reduced to
constructing the perturbatio n series with degeneracy, the order of degeneracy
being proportional to a spin value. Partial summation of this series taking
into account ''dangerous terms'' with small denominators is performed and the
value of tunnelling splitting is calculated with allowance for the first
correction with respect to a magnetic field.Comment: 7 pages, REVTeX 3.
Foam-like compression behavior of fibrin networks
The rheological properties of fibrin networks have been of long-standing
interest. As such there is a wealth of studies of their shear and tensile
responses, but their compressive behavior remains unexplored. Here, by
characterization of the network structure with synchronous measurement of the
fibrin storage and loss moduli at increasing degrees of compression, we show
that the compressive behavior of fibrin networks is similar to that of cellular
solids. A non-linear stress-strain response of fibrin consists of three
regimes: 1) an initial linear regime, in which most fibers are straight, 2) a
plateau regime, in which more and more fibers buckle and collapse, and 3) a
markedly non-linear regime, in which network densification occurs {{by bending
of buckled fibers}} and inter-fiber contacts. Importantly, the spatially
non-uniform network deformation included formation of a moving "compression
front" along the axis of strain, which segregated the fibrin network into
compartments with different fiber densities and structure. The Young's modulus
of the linear phase depends quadratically on the fibrin volume fraction while
that in the densified phase depends cubically on it. The viscoelastic plateau
regime corresponds to a mixture of these two phases in which the fractions of
the two phases change during compression. We model this regime using a
continuum theory of phase transitions and analytically predict the storage and
loss moduli which are in good agreement with the experimental data. Our work
shows that fibrin networks are a member of a broad class of natural cellular
materials which includes cancellous bone, wood and cork
- …