38 research outputs found
Electronic Liquid Crystal Physics of Underdoped Cuprates
Recent observations of broken symmetries have partly demystified the
pseudogap phase. Here we review evidence for long-range intra-unit-cell(IUC)
nematic order and its unexpectedly strong coupling to the phase of the
fluctuating stripes in the pseudogap states of underdoped
BiSrCaCuO. In particular, we focus on the analysis
techniques that reveal this evidence in scanning tunneling spectroscopy data,
the definition of the extracted IUC nematic order parameter, and a
phenomenological theory of the coupling between the IUC nematic order and the
previously reported coexisting fluctuating stripes. We also present a
microscopic mechanism of IUC nematic order driven by on-site and near-neighbor
repulsions. Finally we discuss open questions in the context of these results.Comment: 26 pages, 10 figures. To be published in Physica
Stripes and electronic quasiparticles in the pseudogap state of cuprate superconductors
This article is devoted to a discussion of stripe and electron-nematic order
and their connection to electronic properties in the pseudogap regime of
copper-oxide superconductors. We review basic properties of these
symmetry-breaking ordering phenomena as well as proposals which connect them to
quantum-oscillation measurements. Experimental data indicate that these orders
are unlikely to be the cause of the pseudogap phenomenon, implying that they
occur on top of the pseudogap state which itself is of different origin.
Specifically, we discuss the idea that the non-superconducting pseudogap ground
state hosts electron-like quasiparticles which coexist with a spin liquid,
realizing a variant of a fractionalized Fermi liquid. We speculate on how
stripe order in such a pseudogap state might offer a consistent description of
ARPES, NMR, quantum-oscillation, and transport data.Comment: 15 pages, 6 figs. Article prepared for a Physica C special issue on
"Stripes and Electronic Liquid Crystals
The association between low level exposures to ambient air pollution and term low birth weight: a retrospective cohort study
BACKGROUND: Studies in areas with relatively high levels of air pollution have found some positive associations between exposures to ambient levels of air pollution and several birth outcomes including low birth weight (LBW). The purpose of this study was to examine the association between LBW among term infants and ambient air pollution, by trimester of exposure, in a region of lower level exposures. METHODS: The relationship between LBW and ambient levels of particulate matter up to 10 um in diameter (PM(10)), sulfur dioxide (SO(2)) and ground-level ozone (O(3)) was evaluated using the Nova Scotia Atlee Perinatal Database and ambient air monitoring data from the Environment Canada National Air Pollution Surveillance Network and the Nova Scotia Department of Environment. The cohort consisted of live singleton births (≥37 weeks of gestation) between January1,1988 and December31,2000. Maternal exposures to air pollution were assigned to women living within 25 km of a monitoring station at the time of birth. Air pollution was evaluated as a continuous and categorical variable (using quartile exposures) for each trimester and relative risks were estimated from logistic regression, adjusted for confounding variables. RESULTS: There were 74,284 women with a term, singleton birth during the study period and with exposure data. In the analyses unadjusted for year of birth, first trimester exposures in the highest quartile for SO(2 )and PM(10)suggested an increased risk of delivering a LBW infant (relative risk = 1.36, 95% confidence interval = 1.04 to 1.78 for SO(2 )exposure and relative risk = 1.33, 95% confidence interval = 1.02 to 1.74 for PM(10)). After adjustment for birth year, the relative risks were attenuated somewhat and not statistically significant. A dose-response relationship for SO(2 )was noted with increasing levels of exposure. No statistically significant effects were noted for ozone. CONCLUSION: Our results suggest that exposure during the first trimester to relatively low levels of some air pollutants may be associated with a reduction in birth weight in term-born infants. These findings have implications for the development of effective risk management strategies to minimize the public health impacts for pregnant women
Gap structure in the electron-doped Iron-Arsenide Superconductor Ba(Fe0.92Co0.08)2As2: low-temperature specific heat study
We report the field and temperature dependence of the low-temperature
specific heat down to 400 mK and in magnetic fields up to 9 T of the
electron-doped Ba(Fe0.92Co0.08)2As2 superconductor. Using the phonon specific
heat obtained from pure BaFe2As2 we find the normal state Sommerfeld
coefficient to be 18 mJ/mol.K^2 and a condensation energy of 1.27 J/mol. The
temperature dependence of the electronic specific heat clearly indicate the
presence of the low-energy excitations in the system. The magnetic field
variation of field-induced specific heat cannot be described by single clean s-
or d-wave models. Rather, the data require an anisotropic gap scenario which
may or may not have nodes. We discuss the implications of these results.Comment: New Journal of Physics in press, 10 pages, 5 figure
Magnetic-field-induced charge-stripe order in the high temperature superconductor YBa2Cu3Oy
Electronic charges introduced in copper-oxide planes generate high-transition
temperature superconductivity but, under special circumstances, they can also
order into filaments called stripes. Whether an underlying tendency of charges
to order is present in all cuprates and whether this has any relationship with
superconductivity are, however, two highly controversial issues. In order to
uncover underlying electronic orders, magnetic fields strong enough to
destabilise superconductivity can be used. Such experiments, including quantum
oscillations in YBa2Cu3Oy (a notoriously clean cuprate where charge order is
not observed) have suggested that superconductivity competes with spin, rather
than charge, order. Here, using nuclear magnetic resonance, we demonstrate that
high magnetic fields actually induce charge order, without spin order, in the
CuO2 planes of YBa2Cu3Oy. The observed static, unidirectional, modulation of
the charge density breaks translational symmetry, thus explaining quantum
oscillation results, and we argue that it is most likely the same 4a-periodic
modulation as in stripe-ordered cuprates. The discovery that it develops only
when superconductivity fades away and near the same 1/8th hole doping as in
La2-xBaxCuO4 suggests that charge order, although visibly pinned by CuO chains
in YBa2Cu3Oy, is an intrinsic propensity of the superconducting planes of high
Tc cuprates.Comment: For a final version, see
http://www.nature.com/nature/journal/v477/n7363/full/nature10345.htm
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Exercise interventions are delayed in critically ill patients: a cohort study in an Australian tertiary intensive care unit
Objectives: This study aims to (i) describe the time to exercise commencement (sitting and upright activities) relative to ICU admission and relative to achievement of initial neurological, respiratory and cardiovascular stability; (ii) examine factors associated with whether sitting and upright activities occurred in ICU; and (iii) examine factors associated with time taken to commence these activities after stability has been achieved.
Design: Five-year historical cohort study.
Setting: An Australian tertiary mixed medical, surgical, trauma ICU.
Participants: The cohort (n = 3222, mean (SD) age 54 (18) years, 67% male) included consecutive ICU patients with length of stay over 48 hours admitted to a tertiary ICU who achieved stability.
Main outcome measures: Time from stability to patients’ first completed sitting and upright activities was calculated. Logistic regression (and Cox proportional hazard models) examined whether sitting and upright activities in ICU occurred (and time to these events).
Interventions: None.
Results: For patients who completed exercise interventions (n = 1845/3222, 57%), this commenced a median (IQR) 2.3 (1.3–4.4) days after stability for upright activities and 2.7 (1.5–5.7) days for sitting. A large proportion of patients did not complete exercise interventions despite achieving stability (n = 1377/3222, 43%). Elective surgical admissions, lower illness severity and older age were associated with completion (and earlier completion) of sitting and upright activity (P < 0.01).
Conclusions: Many stable patients did not commence sitting or upright activity in ICU despite known benefits, or commencement was somewhat delayed. Opportunities may exist to improve patient outcomes through timely implementation of exercise-based interventions