299 research outputs found
Modeling a striped pseudogap state
We study the electronic structure within a system of phase-decoupled
one-dimensional superconductors coexisting with stripe spin and charge density
wave order. This system has a nodal Fermi surface (Fermi arc) in the form of a
hole pocket and an antinodal pseudogap. The spectral function in the antinodes
is approximately particle-hole symmetric contrary to the gapped regions just
outside the pocket. We find that states at the Fermi energy are extended
whereas states near the pseudogap energy have localization lengths as short as
the inter-stripe spacing. We consider pairing which has either local d-wave or
s-wave symmetry and find similar results in both cases, consistent with the
pseudogap being an effect of local pair correlations. We suggest that this
state is a stripe ordered caricature of the pseudogap phase in underdoped
cuprates with coexisting spin-, charge-, and pair-density wave correlations.
Lastly, we also model a superconducting state which 1) evolves smoothly from
the pseudogap state, 2) has a signature subgap peak in the density of states,
and 3) has the coherent pair density concentrated to the nodal region.Comment: 12 pages, 12 figures, extended discussion, added references; v3,
added figure of antinodal spectra for normal/pseudo/sc state
Multichannel Kondo Screening in a One-Dimensional Correlated Electron System
We present the exact Bethe Ansatz solution of a multichannel model of one-
dimensional correlated electrons coupled antiferromagnetically to a magnetic
impurity of arbitrary spin S. The solution reveals that interactions in the
bulk make the magnetic impurity drive both spin and charge fluctuations,
producing a mixed valence at the impurity site, with an associated effective
spin S_eff > S in the presence of a magnetic field. The screening of the
impurity spin is controlled by its size independently of the number of
channels, in contrast to the multichannel Kondo effect for free electrons.Comment: 5 pages Revtex. Final revised version to appear in Europhys. Let
Disturbance interval modulates the starting point for vegetation succession
Increased frequency and new types of disturbances caused by global change calls
for deepened insights into possible alterations of successional pathways. Despite current interest
in disturbance interactions there is a striking lack of studies focusing on the implication of
decreasing times between disturbances. We surveyed forest-floor vegetation (vascular plants
and bryophytes) in a Pinus sylvestrisâdominated, even-aged production forest landscape,
unique because of the presence of stands under a precisely dated disturbance interval gradient,
ranging from 0 to 123 yr between clearcutting and a subsequent megafire. Despite a dominance
of early-successional species in all burned stands 5 yr after fire, progression of succession
was linked to time since the preceding clearcutting disturbance. This was most clearly seen in
increased frequency with time since clearcutting of the dominant, late-successional dwarf
shrub Vaccinium myrtillus, with surviving rhizomes as an important mechanism for postfire
recovery. Our results demonstrate the role of legacy species as significant drivers of succession.
We conclude that the starting point for succession is modulated by disturbance interval, so that
shortened intervals risk reducing development towards late-successional stages. We suggest
that a decrease in long successional sequences caused by more frequent disturbances may represent
a general pattern, relevant also for other forest types and ecosystems
Magnetic impurities in the one-dimensional spin-orbital model
Using one-dimensional spin-orbital model as a typical example of quantum spin
systems with richer symmetries, we study the effect of an isolated impurity on
its low energy dynamics in the gapless phase through bosonization and
renormalization group methods. In the case of internal impurities, depending on
the symmetry, the boundary fixed points can be either an open chain with a
residual spin or (and) orbital triplet left behind, or a periodic chain.
However, these two fixed points are indistinguishable in the sense that in both
cases, the lead-correction-to-scaling boundary operators (LCBO) only show
Fermi-liquid like corrections to thermodynamical quantities. (Except the
possible Curie-like contributions from the residual moments in the latter
cases.) In the case of external (Kondo) impurities, the boundary fixed points,
depending on the sign of orbital couplings, can be either an open chain with an
isolated orbital doublet due to Kondo screening or it will flow to an
intermediate fixed point with the same LCBO as that of the two-channel Kondo
problem. Comparison with the Kondo effect in one-dimensional (1D) Heisenberg
spin chain and multi-band Hubbard models is also made.Comment: 7 pages, No figur
Association between cerebrospinal fluid biomarkers of neuronal injury or amyloidosis and cognitive decline after major surgery
BACKGROUND: Postoperative neurocognitive decline is a frequent complication in adult patients undergoing major surgery with increased risk for morbidity and mortality. The mechanisms behind cognitive decline after anaesthesia and surgery are not known. We studied the association between CSF and blood biomarkers of neuronal injury or brain amyloidosis and long-term changes in neurocognitive function. METHODS: In patients undergoing major orthopaedic surgery (knee or hip replacement), blood and CSF samples were obtained before surgery and then at 4, 8, 24, 32, and 48 h after skin incision through an indwelling spinal catheter. CSF and blood concentrations of total tau (T-tau), neurofilament light, neurone-specific enolase and amyloid ÎČ (AÎČ1-42) were measured. Neurocognitive function was assessed using the International Study of Postoperative Cognitive Dysfunction (ISPOCD) test battery 1â2 weeks before surgery, at discharge from the hospital (2â5 days after surgery), and at 3 months after surgery. RESULTS: CSF and blood concentrations of T-tau, neurone-specific enolase, and AÎČ1-42 increased after surgery. A similar increase in serum neurofilament light was seen with no overall changes in CSF concentrations. There were no differences between patients having a poor or good late postoperative neurocognitive outcome with respect to these biomarkers of neuronal injury and AÎČ1-42. CONCLUSIONS: The findings of the present explorative study showed that major orthopaedic surgery causes a release of CSF markers of neural injury and brain amyloidosis, suggesting neuronal damage or stress. We were unable to detect an association between the magnitude of biomarker changes and long-term postoperative neurocognitive dysfunction
A systematic review of randomised controlled trials on the effectiveness of exercise programs on lumbo pelvic pain among postnatal women
Background: A substantial number of women tend to be affected by Lumbo Pelvic Pain (LPP) following child birth.
Physical exercise is indicated as a beneficial method to relieve LPP, but individual studies appear to suggest mixed
findings about its effectiveness. This systematic review aimed to synthesise evidence from randomised controlled trials on the effectiveness of exercise on LPP among postnatal women to inform policy, practice and future research.
Methods: A systematic review was conducted of all randomised controlled trials published between January 1990 and July 2014, identified through a comprehensive search of following databases: PubMed, PEDro, Embase, Cinahl, Medline, SPORTDiscus, Cochrane Pregnancy and Childbirth Groupâs Trials Register, and electronic libraries of authorsâinstitutions.
Randomised controlled trials were eligible for inclusion if the intervention comprised of postnatal exercise for women
with LPP onset during pregnancy or within 3 months after delivery and the outcome measures included changes in
LPP. Selected articles were assessed using the PEDro Scale for methodological quality and findings were synthesised narratively as meta-analysis was found to be inappropriate due to heterogeneity among included studies.
Results: Four randomised controlled trials were included, involving 251 postnatal women. Three trials were rated as
of âgoodâ methodological quality. All trials, except one, were at low risk of bias. The trials included physical exercise
programs with varying components, differing modes of delivery, follow up times and outcome measures. Intervention
in one trial, involving physical therapy with specific stabilising exercises, proved to be effective in reducing LPP
intensity. An improvement in gluteal pain on the right side was reported in another trial and a significant difference in
pain frequency in another.
Conclusion: Our review indicates that only few randomised controlled trials have evaluated the effectiveness of
exercise on LPP among postnatal women. There is also a great amount of variability across existing trials in the
components of exercise programs, modes of delivery, follow up times and outcome measures. While there is some
evidence to indicate the effectiveness of exercise for relieving LPP, further good quality trials are needed to ascertain
the most effective elements of postnatal exercise programs suited for LPP treatment
Association of the 894G>T polymorphism in the endothelial nitric oxide synthase gene with risk of acute myocardial infarction
Background: This study was designed to investigate the association of the 894G>T polymorphism in the eNOS gene with risk of acute myocardial infarction (AMI), extent of coronary artery disease (CAD) on coronary angiography, and in-hospital mortality after AMI.
Methods: We studied 1602 consecutive patients who were enrolled in the GEMIG study. The control group was comprised by 727 individuals, who were randomly selected from the general adult population.
Results: The prevalence of the Asp298 variant of eNOS was not found to be significantly and independently associated with risk of AMI (RR = 1.08, 95%CI = 0.77â1.51, P = 0.663), extent of CAD on angiography (OR = 1.18, 95%CI = 0.63â2.23, P = 0.605) and in-hospital mortality (RR = 1.08, 95%CI = 0.29â4.04, P = 0.908).
Conclusion: In contrast to previous reports, homozygosity for the Asp298 variant of the 894G>T polymorphism in the eNOS gene was not found to be associated with risk of AMI, extent of CAD and in-hospital mortality after AM
Mid-Infrared Conductivity from Mid-Gap States Associated with Charge Stripes
The optical conductivity of La(2-x)Sr(x)NiO(4) has been interpreted in
various ways, but so far the proposed interpretations have neglected the fact
that the holes doped into the NiO(2) planes order in diagonal stripes, as
established by neutron and X-ray scattering. Here we present a study of optical
conductivity in La(2)NiO(4+d) with d=2/15, a material in which the charge
stripes order three-dimensionally. We show that the conductivity can be
decomposed into two components, a mid-infrared peak that we attribute to
transitions from the filled valence band into empty mid-gap states associated
with the stripes, and a Drude peak that appears at higher temperatures as
carriers are thermally excited into the mid-gap states. The shift of the mid-IR
peak to lower energy with increasing temperature is explained in terms of the
Franck-Condon effect. The relevance of these results to understanding the
optical conductivity in the cuprates is discussed.Comment: final version of paper (minor changes from previous version
Progress in Neutron Scattering Studies of Spin Excitations in High-Tc Cuprates
Neutron scattering experiments continue to improve our knowledge of spin
fluctuations in layered cuprates, excitations that are symptomatic of the
electronic correlations underlying high-temperature superconductivity.
Time-of-flight spectrometers, together with new and varied single crystal
samples, have provided a more complete characterization of the magnetic energy
spectrum and its variation with carrier concentration. While the spin
excitations appear anomalous in comparison with simple model systems, there is
clear consistency among a variety of cuprate families. Focusing initially on
hole-doped systems, we review the nature of the magnetic spectrum, and
variations in magnetic spectral weight with doping. We consider connections
with the phenomena of charge and spin stripe order, and the potential
generality of such correlations as suggested by studies of magnetic-field and
impurity induced order. We contrast the behavior of the hole-doped systems with
the trends found in the electron-doped superconductors. Returning to hole-doped
cuprates, studies of translation-symmetry-preserving magnetic order are
discussed, along with efforts to explore new systems. We conclude with a
discussion of future challenges.Comment: revised version, to be published in JPSJ, 20 pages, 21 figure
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