1,311 research outputs found
Destruction of chain-superconductivity in YBa_2Cu_4O_8 in a weak magnetic field
We report measurements of the temperature dependent components of the
magnetic penetration depth {\lambda}(T) in single crystal samples of
YBa_2Cu_4O_8 using a radio frequency tunnel diode oscillator technique. We
observe a downturn in {\lambda}(T) at low temperatures for currents flowing
along the b and c axes but not along the a axis. The downturn in {\lambda}_b is
suppressed by a small dc field of ~0.25 T. This and the zero field anisotropy
of {\lambda}(T) likely result from proximity induced superconducting on the CuO
chains, however we also discuss the possibility that a significant part of the
anisotropy might originate from the CuO2 planes.Comment: 5 page
a systematic review protocol
Introduction Varicella zoster virus (VZV) causes varicella (chicken pox) and
herpes zoster (shingles). Worldwide, these diseases are associated with
significant morbidity. Most of the epidemiological data on VZV come from high
income countries. There are few data on VZV in Africa, where tropical climates
and high HIV/AIDS prevalence rates are expected to impact the epidemiology of
VZV. Safe and effective vaccinations for both varicella and herpes zoster
exist, but are not routinely used in Africa. There are very few data available
on VZV disease burden in Africa to guide the introduction of these vaccines on
the continent. Our aim is to conduct a systematic review of the VZV-associated
morbidity and mortality in Africa, which will provide critical information
that could be used to develop vaccination policies against these diseases in
Africa. Methods and analysis Electronic databases will be searched and all
studies published after 1974 that meet predefined criteria will be assessed.
The primary outcomes for the study are VZV incidence/prevalence,
hospitalisation rates and total death rates. The secondary outcome for this
study is the proportion of VZV hospitalisations and/or deaths associated with
HIV/AIDS. Two reviewers will screen the titles and abstracts, and then
independently review the full texts, to determine if studies are eligible for
inclusion. A risk of bias and quality assessment tool will be used to score
all included studies. Following standardised data extraction, a trend analysis
using R-programming software will be conducted to investigate the trend of
VZV. Depending on the characteristics of included studies, subgroup analyses
will be performed. This review will be reported according to the Preferred
Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) guidelines.
Ethics and dissemination As this is a protocol for a systematic review, which
will use already published data, no ethics approval is required. Findings will
be disseminated in peer-reviewed journals. Trial registration number
CRD4201502614
The 3D printing of a polymeric electrochemical cell body and its characterisation
An undivided flow cell was designed and constructed using additive manufacturing technology and its mass transport characteristics were evaluated using the reduction of ferricyanide, hexacyanoferrate (III) ions at a nickel surface. The dimensionless mass transfer correlation Sh = aRebScdLee was obtained using the convective-diffusion limiting current observed in linear sweep voltammetry; this correlation compared closely with that reported in the literature from traditionally machined plane parallel rectangular flow channel reactors. The ability of 3D printer technology, aided by computational graphics, to rapidly and conveniently design, manufacture and re-design the geometrical characteristics of the flow cell ishighlighted
Phenomenology of the normal state in-plane transport properties of high- cuprates
In this article, I review progress towards an understanding of the normal
state (in-plane) transport properties of high- cuprates in the light of
recent developments in both spectroscopic and transport measurement techniques.
Against a backdrop of mounting evidence for anisotropic single-particle
lifetimes in cuprate superconductors, new results have emerged that advocate
similar momentum dependence in the transport decay rate ({\bf k}). In
addition, enhancement of the energy scale (up to the bare bandwidth) over which
spectroscopic information on the quasiparticle response can be obtained has led
to the discovery of new, unforeseen features that surprisingly, may have a
significant bearing on the transport properties at the dc limit. With these two
key developments in mind, I consider here whether all the ingredients necessary
for a complete phenomenological description of the anomalous normal state
transport properties of high- cuprates are now in place.Comment: 31 pages, 10 figure
Neutron interferometric measurement of the scattering length difference between the triplet and singlet states of n-He
We report a determination of the n-He scattering length difference
(
(statistical) (systematic)) fm between the triplet and singlet
states using a neutron interferometer. This revises our previous result (-5.610 (statistical) (systematic)
fm obtained using the same technique in 2008. This revision is due to a
re-analysis of the 2008 experiment that includes a more robust treatment of the
phase shift caused by magnetic field gradients near the He cell.
Furthermore, we more than doubled our original data set from 2008 by acquiring
six months of additional data in 2013. Both the new data set and a re-analysis
of the older data are in good agreement. Scattering lengths of low Z isotopes
are valued for use in few-body nuclear effective field theories, provide
important tests of modern nuclear potential models and in the case of He
aid in the interpretation of neutron scattering from quantum liquids. The
difference was determined by measuring the relative phase
shift between two incident neutron polarizations caused by the spin-dependent
interaction with a polarized He target. The target He gas was sealed
inside a small, flat windowed glass cell that was placed in one beam path of
the interferometer. The relaxation of He polarization was monitored
continuously with neutron transmission measurements. The neutron polarization
and spin flipper efficiency were determined separately using He analyzers
and two different polarimetry analysis methods. A summary of the measured
scattering lengths for n-He with a comparison to nucleon interaction models
is given
Fermiology and electronic homogeneity of the superconducting overdoped cuprate Tl-2201 revealed by quantum oscillations
We report an angular quantum oscillation study of Tl_2Ba_2CuO_{6+delta} for
two different doping levels (Tc = 10K and 26 K) and determine the Fermi surface
size and topology in considerable detail. Our results show that Fermi liquid
behavior is not confined to the edge of the superconducting dome and is robust
up to at least T_c^{max}/3.5. Superconductivity is found to survive up to a
larger doping p_c = 0.31 than in La_{2-x}Sr_xCuO_4. Our data imply that
electronic inhomogeneity does not play a significant role in the loss of
superconductivity and superfluid density in overdoped cuprates, and point
towards a purely magnetic or electronic pairing mechanismComment: 4 page
Direct Search for a Ferromagnetic Phase in a Heavily Overdoped Nonsuperconducting Copper Oxide
The doping of charge carriers into the CuO2 planes of copper oxide Mott
insulators causes a gradual destruction of antiferromagnetism and the emergence
of high-temperature superconductivity. Optimal superconductivity is achieved at
a doping concentration p beyond which further increases in doping cause a
weakening and eventual disappearance of superconductivity. A potential
explanation for this demise is that ferromagnetic fluctuations compete with
superconductivity in the overdoped regime. In this case a ferromagnetic phase
at very low temperatures is predicted to exist beyond the doping concentration
at which superconductivity disappears. Here we report on a direct examination
of this scenario in overdoped La2-xSrxCuO4 using the technique of muon spin
relaxation. We detect the onset of static magnetic moments of electronic origin
at low temperature in the heavily overdoped nonsuperconducting region. However,
the magnetism does not exist in a commensurate long-range ordered state.
Instead it appears as a dilute concentration of static magnetic moments. This
finding places severe restrictions on the form of ferromagnetism that may exist
in the overdoped regime. Although an extrinsic impurity cannot be absolutely
ruled out as the source of the magnetism that does occur, the results presented
here lend support to electronic band calculations that predict the occurrence
of weak localized ferromagnetism at high doping.Comment: 13 pages, 5 figure
Shubnikov-de Haas oscillations in YBa_2Cu_4O_8
We report the observation of Shubnikov-de Haas oscillations in the underdoped
cuprate superconductor YBaCuO (Y124). For field aligned along the
c-axis, the frequency of the oscillations is T, which corresponds
to % of the total area of the first Brillouin zone. The effective
mass of the quasiparticles on this orbit is measured to be times
the free electron mass. Both the frequency and mass are comparable to those
recently observed for ortho-II YBaCuO (Y123-II). We show that
although small Fermi surface pockets may be expected from band structure
calculations in Y123-II, no such pockets are predicted for Y124. Our results
therefore imply that these small pockets are a generic feature of the copper
oxide plane in underdoped cuprates.Comment: v2: Version of paper accepted for publication in Physical Review
Letters. Only minor changes to the text and reference
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