160 research outputs found
Competition Between Stripes and Pairing in a t-t'-J Model
As the number of legs n of an n-leg, t-J ladder increases, density matrix
renormalization group calculations have shown that the doped state tends to be
characterized by a static array of domain walls and that pairing correlations
are suppressed. Here we present results for a t-t'-J model in which a diagonal,
single particle, next-near-neighbor hopping t' is introduced. We find that this
can suppress the formation of stripes and, for t' positive, enhance the
d_{x^2-y^2}-like pairing correlations. The effect of t' > 0 is to cause the
stripes to evaporate into pairs and for t' < 0 to evaporate into
quasi-particles. Results for n=4 and 6-leg ladders are discussed.Comment: Four pages, four encapsulated figure
Local Magnetic Order vs. Superconductivity in a Layered Cuprate
We report on the phase diagram for charge-stripe order in
La(1.6-x)Nd(0.4)Sr(x)CuO(4), determined by neutron and x-ray scattering studies
and resistivity measurements. From an analysis of the in-plane resistivity
motivated by recent nuclear-quadrupole-resonance studies, we conclude that the
transition temperature for local charge ordering decreases monotonically with
x, and hence that local antiferromagnetic order is uniquely correlated with the
anomalous depression of superconductivity at x = 1/8. This result is consistent
with theories in which superconductivity depends on the existence of
charge-stripe correlations.Comment: 4 pages, 4 figures; introduction revised, Fig. 3 removed, last figure
replace
Charge Segregation, Cluster Spin-Glass and Superconductivity in La1.94Sr0.06CuO4
A 63Cu and 139La NMR/NQR study of superconducting (Tc=7 K) La1.94Sr0.06CuO4
single crystal is reported. Coexistence of spin-glass and superconducting
phases is found below ~5 K from 139La NMR relaxation. 63Cu and 139La NMR
spectra show that, upon cooling, CuO2 planes progressively separate into two
magnetic phases, one of them having enhanced antiferromagnetic correlations.
These results establish the AF-cluster nature of the spin-glass. We discuss how
this phase can be related to the microsegregation of mobile holes and to the
possible pinning of charge-stripes.Comment: 4 pages. Modified manuscript with clarification
Effect of a magnetic field on the spin- and charge-density wave order in La1.45Nd0.4Sr0.15CuO4
The spin-density wave (SDW) and charge-density wave (CDW) order in
superconducting La1.45Nd0.4Sr0.15CuO4 were studied under an applied magnetic
field using neutron and X-ray diffraction techniques. In zero field,
incommensurate (IC) SDW order appears below ~ 40 K, which is characterized by
neutron diffraction peaks at (1/2 +/- 0.134, 1/2 +/- 0.134, 0). The intensity
of these IC peaks increases rapidly below T_Nd ~ 8 K due to an ordering of the
Nd^3+ spins. The application of a 1 T magnetic field parallel to the c-axis
markedly diminishes the intensity below T_Nd, while only a slight decrease in
intensity is observed at higher temperatures for fields up to 7 T. Our
interpretation is that the c-axis field suppresses the parasitic Nd^3+ spin
order at the incommensurate wave vector without disturbing the stripe order of
Cu^2+ spins. Consistent with this picture, the CDW order, which appears below
60 K, shows no change for magnetic fields up to 4 T. These results stand in
contrast to the significant field-induced enhancement of the SDW order observed
in superconducting La2-xSrxCuO4 with x ~ 0.12 and stage-4 La2CuO4+y. The
differences can be understood in terms of the relative volume fraction
exhibiting stripe order in zero field, and the collective results are
consistent with the idea that suppression of superconductivity by vortices
nucleates local patches of stripe order.Comment: 7 pages, 5 figure
Differential Glucose-Regulation of MicroRNAs in Pancreatic Islets of Non-Obese Type 2 Diabetes Model Goto-Kakizaki Rat
The Goto-Kakizaki (GK) rat is a well-studied non-obese spontaneous type 2 diabetes (T2D) animal model characterized by impaired glucose-stimulated insulin secretion (GSIS) in the pancreatic beta cells. MicroRNAs (miRNAs) are short regulatory RNAs involved in many fundamental biological processes. We aim to identify miRNAs that are differentially-expressed in the pancreatic islets of the GK rats and investigate both their short- and long term glucose-dependence during glucose-stimulatory conditions
Serum aspirin esterase is strongly associated with glucose and lipids in healthy subjects: different association patterns in subjects with type 2 diabetes mellitus
<p>Abstract</p> <p>Background</p> <p>Aspirin esterase (AE) activity can account for part of aspirin pharmacokinetics in the circulation, possibly being associated with the impairment of aspirin effectiveness as an inhibitor of platelet aggregation.</p> <p>Aims</p> <p>The study was aimed at investigating the correlations of serum AE activity with cholinesterase (ChE) and metabolic variables in healthy subjects in comparison to subjects with type 2 diabetes mellitus (T2DM).</p> <p>Methods</p> <p>In cardiovascular disease-free T2DM subjects and healthy controls, the AE activity levels and/or the correlation patterns between AE and the other variables were analyzed.</p> <p>Results</p> <p>Neither AE nor ChE activities were higher in the subjects with T2DM. Serum AE activity strongly correlated with ChE as well as glucose/lipids variables such as total cholesterol and triglyceride in healthy subjects, while the correlations between AE and glucose/lipids variables were not present in T2DM subjects.</p> <p>Conclusions</p> <p>These data may reflect the pathophysiological changes between healthy and T2DM subjects. Our data may thus provide the basis for future studies to unravel the mechanisms.</p
Neutron Scattering Study of Spin Density Wave Order in the Superconducting State of Excess-Oxygen-Doped La2CuO4+y
We report neutron scattering measurements of spin density wave order within
the superconducting state of a single crystal of predominately stage-4
La2CuO4+y with a Tc(onset) of 42 K. The low temperature elastic magnetic
scattering is incommensurate with the lattice and is characterized by
long-range order in the copper-oxide plane with the spin direction identical to
that in the insulator. Between neighboring planes, the spins exhibit
short-range correlations with a stacking arrangement reminiscent of that in the
undoped antiferromagnetic insulator. The elastic magnetic peak intensity
appears at the same temperature within the errors as the superconductivity,
suggesting that the two phenomena are strongly correlated. These observations
directly reveal the persistent influence of the antiferromagnetic order as the
doping level increases from the insulator to the superconductor. In addition,
our results confirm that spin density wave order for incommensurabilities near
1/8 is a robust feature of the La2CuO4-based superconductors.Comment: 14 pages, LaTeX, includes 8 figure
Glassy nature of stripe ordering in La(1.6-x)Nd(0.4)Sr(x)CuO(4)
We present the results of neutron-scattering studies on various aspects of
crystalline and magnetic structure in single crystals of
La(1.6-x)Nd(0.4)Sr(x)CuO(4) with x=0.12 and 0.15. In particular, we have
reexamined the degree of stripe order in an x=0.12 sample. Measurements of the
width for an elastic magnetic peak show that it saturates at a finite value
below 30 K, corresponding to a spin-spin correlation length of 200 A. A model
calculation indicates that the differing widths of magnetic and (previously
reported) charge-order peaks, together with the lack of commensurability, can
be consistently explained by disorder in the stripe spacing. Above 30 K, the
width of the nominally elastic signal begins to increase. Interpreting the
signal as critical scattering from slowly fluctuating spins, the temperature
dependence of the width is consistent with renormalized classical behavior of a
2-dimensional anisotropic Heisenberg antiferromagnet. Inelastic scattering
measurements show that incommensurate spin excitations survive at and above 50
K, where the elastic signal is neglible. We also report several results related
to the LTO-to-LTT transition.Comment: 13 pp, 2-col. REVTeX, 11 figures embedded with psfig; expanded
discussion of T-dep. of magnetic peak width; version to appear in Phys. Rev.
B (01Jun99
Digital intervention increases influenza vaccination rates for people with diabetes in a decentralized randomized trial
People with diabetes (PWD) have an increased risk of developing influenza-related complications, including pneumonia, abnormal glycemic events, and hospitalization. Annual influenza vaccination is recommended for PWD, but vaccination rates are suboptimal. The study aimed to increase influenza vaccination rate in people with self-reported diabetes. This study was a prospective, 1:1 randomized controlled trial of a 6-month Digital Diabetes Intervention in U.S. adults with diabetes. The intervention group received monthly messages through an online health platform. The control group received no intervention. Difference in self-reported vaccination rates was tested using multivariable logistic regression controlling for demographics and comorbidities. The study was registered at clinicaltrials.gov: NCT03870997. A total of 10,429 participants reported influenza vaccination status (5158 intervention, mean age (±SD) = 46.8 (11.1), 78.5% female; 5271 control, Mean age (±SD) = 46.7 (11.2), 79.4% female). After a 6-month intervention, 64.2% of the intervention arm reported influenza vaccination, vers us 61.1% in the control arm (diff = 3.1, RR = 1.05, 95% CI [1.02, 1.08], p = 0.0013, number needed to treat = 33 to obtain 1 additional vaccination). Completion of one or more intervention messages was associated with up to an 8% increase in vaccination rate (OR 1.27, 95% CI [1.17, 1.38], p < 0.0001). The intervention improved influenza vaccination rates in PWD, suggesting that leveraging new technology to deliver knowledge and information can improve influenza vaccination rates in high-risk populations to reduce public health burden of influenza. Rapid cycle innovation could maximize the effects of these digital interventions in the future with other populations and vaccines
Topological doping and the stability of stripe phases
We analyze the properties of a general Ginzburg-Landau free energy with
competing order parameters, long-range interactions, and global constraints
(e.g., a fixed value of a total ``charge'') to address the physics of stripe
phases in underdoped high-Tc and related materials. For a local free energy
limited to quadratic terms of the gradient expansion, only uniform or
phase-separated configurations are thermodynamically stable. ``Stripe'' or
other non-uniform phases can be stabilized by long-range forces, but can only
have non-topological (in-phase) domain walls where the components of the
antiferromagnetic order parameter never change sign, and the periods of charge
and spin density waves coincide. The antiphase domain walls observed
experimentally require physics on an intermediate lengthscale, and they are
absent from a model that involves only long-distance physics. Dense stripe
phases can be stable even in the absence of long-range forces, but domain walls
always attract at large distances, i.e., there is a ubiquitous tendency to
phase separation at small doping. The implications for the phase diagram of
underdoped cuprates are discussed.Comment: 18 two-column pages, 2 figures, revtex+eps
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