509 research outputs found
A Comparison of the Ovulation Method With the CUE Ovulation Predictor in Determining the Fertile Period
The purpose of this study was to compare the CUE Ovulation Predictor with the ovulation method in determining the fertile period. Eleven regularly ovulating women measured their salivary and vaginal electrical resistance (ER) with the CUE, observed their cervical-vaginal mucus, and measured their urine for a luteinizing hormone (LH) surge on a daily basis. Data from 21 menstrual cycles showed no statistical difference (T= 0.33, p= 0.63) between the CUE fertile period, which ranged from 5 to 10 days (mean = 6.7 days, SD = 1.6), and the fertile period of the ovulation method, which ranged from 4 to 9 days (mean = 6.5 days, SD = 2.0). The CUE has potential as an adjunctive device in the learning and use of natural family planning methods
Transport properties of heterogeneous materials derived from Gaussian random fields: Bounds and Simulation
We investigate the effective conductivity () of a class of
amorphous media defined by the level-cut of a Gaussian random field. The three
point solid-solid correlation function is derived and utilised in the
evaluation of the Beran-Milton bounds. Simulations are used to calculate
for a variety of fields and volume fractions at several different
conductivity contrasts. Relatively large differences in are observed
between the Gaussian media and the identical overlapping sphere model used
previously as a `model' amorphous medium. In contrast shows little
variability between different Gaussian media.Comment: 15 pages, 14 figure
Probing Pseudogap by Josephson Tunneling
We propose here an experiment aimed to determine whether there are
superconducting pairing fluctuations in the pseudogap regime of the high-
materials. In the experimental setup, two samples above are brought into
contact at a single point and the differential AC conductivity in the presence
of a constant applied bias voltage between the samples, , should be
measured. We argue the the pairing fluctuations will produce randomly
fluctuating Josephson current with zero mean, however the current-current
correlator will have a characteristic frequency given by Josephson frequency
. We predict that the differential AC conductivity
should have a peak at the Josephson frequency with the width determined by the
phase fluctuations time.Comment: 4 pages, 2 eps figure
Low-Frequency Crossover of the Fractional Power-Law Conductivity in SrRuO\u3csub\u3e3\u3c/sub\u3e
We combine the results of terahertz time-domain spectroscopy with far-infrared transmission and reflectivity to obtain the conductivity of SrRuO 3 over an unprecedented continuous range in frequency, allowing us to characterize the approach to zero frequency as a function of temperature. We show that the conductivity follows a simple phenomenological form, with an analytic structure fundamentally different from that predicted by the standard theory of metals
Magnetic field induced charge and spin instabilities in cuprate superconductors
A d-wave superconductor, subject to strong phase fluctuations, is known to
suffer an antiferromagnetic instability closely related to the chiral symmetry
breaking in (2+1)-dimensional quantum electrodynamics (QED3). On the basis of
this idea we formulate a "QED3 in a box" theory of local instabilities of a
d-wave superconductor in the vicinity of a single pinned vortex undergoing
quantum fluctuations around its equilibrium position. As a generic outcome we
find an incommensurate 2D spin density wave forming in the neighborhood of a
vortex with a concomitant "checkerboard" pattern in the local electronic
density of states, in agreement with recent neutron scattering and tunneling
spectroscopy measurements.Comment: 4 pages REVTeX + 2 PostScript figures included in text. Version to
appear in PRL (minor stylistic changes, references updated). For related work
and info visit http://www.physics.ubc.ca/~fran
Algebraic Fermi liquid from phase fluctuations: "topological" fermions, vortex "berryons" and QED3 theory of cuprate superconductors
Within the phase fluctuation model for the pseudogap state of cuprate
superconductors we identify a novel statistical "Berry phase" interaction
between the nodal quasiparticles and fluctuating vortices. The effective action
describing this model assumes the form of an anisotropic Euclidean quantum
electrodynamics in (2+1) dimensions (QED_3) and naturally generates the
marginal Fermi liquid behavior for its fermionic excitations. The doping axis
in the x-T phase diagram emerges as a quantum critical line which regulates low
energy fermiology. We examine the merits of our theory in light of available
experiments.Comment: 5 pages REVTeX + 2 PostScript Figures. Final version to appear in PR
Charge Ordering Fluctuation and Optical Pseudogap in LaCaMnO
Optical spectroscopy was used to investigate the optical gap (2) due
to charge ordering (CO) and related pseudogap developments with x and
temperature (T) in LaCaMnO (0.48 <= x <= 0.67).
Surprisingly, we found 2/k_{B}T_{CO} is as large as 30 for x ~0.5, and
decreases rapidly with increasing x. Simultaneously, the optical pseudogap,
possibly starting from T^* far above T_{CO} becomes drastically enhanced near
x=0.5, producing non-BCS T-dependence of 2 with the large magnitude
far above T_{CO}, and systematic increase of T^* for x~0.5. These results
unequivocally indicate systematically-enhanced CO correlation when x approaches
0.5 even though T_{CO} decreases.Comment: 5 pages, 4 figures embedded, submitted to Phys. Rev. Let
Antiferromagnetism from phase disordering of a d-wave superconductor
The unbinding of vortex defects in the superconducting condensate with d-wave
symmetry at T=0 is shown to lead to the insulator with incommensurate
spin-density-wave order. The transition is similar to the spontaneous
generation of the "chiral" mass in the three dimensional quantum
electrodynamics, at which the global chiral symmetry one can define in the
superconducting state is spontaneously broken. Other symmetry related states
and possible relations to recent experiments on uderdoped cuprates are briefly
discussed.Comment: RevTex, 4 pages, one ps figure; comments on confinement in the SDW
added, references updated; final versio
The superfluid density in cuprate high-Tc superconductors - a new paradigm
The doping dependence of the superfluid density, r_s, of high-Tc
superconductors is usually considered in the context of the Uemura relation,
namely Tc proportional to rs, which is generally assumed to apply in the
underdoped regime. We show that a modified plot of Tc/Do versus rs, where Do is
the maximum d-wave gap at T=0, exhibits universal features that point to an
alternative interpretation of the underlying physics. In the underdoped region
this plot exhibits the canonical negative curvature expected when a
ground-state correlation competes with superconductivity (SC) by opening up a
gap in the normal-state DOS. In particular rs is suppressed much faster than
Tc/Do or indeed Tc. The pseudogap is found to strongly modify the SC ground
state.Comment: 9 pages, 5 figures, submitted Phys. Rev. Let
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