1,600 research outputs found
Gutzwiller Charge Phase Diagram of Cuprates, including Electron-Phonon Coupling Effects
Besides significant electronic correlations, high-temperature superconductors
also show a strong coupling of electrons to a number of lattice modes. Combined
with the experimental detection of electronic inhomogeneities and ordering
phenomena in many high-T_c compounds, these features raise the question as to
what extent phonons are involved in the associated instabilities. Here we
address this problem based on the Hubbard model including a coupling to phonons
in order to capture several salient features of the phase diagram of hole-doped
cuprates. Charge degrees of freedom, which are suppressed by the large Hubbard
U near half-filling, are found to become active at a fairly low doping level.
We find that possible charge order is mainly driven by Fermi surface nesting,
with competition between a near-(pi,pi) order at low doping and antinodal
nesting at higher doping, very similar to the momentum structure of magnetic
fluctuations. The resulting nesting vectors are generally consistent with
photoemission and tunneling observations, evidence for charge density wave
(CDW) order in YBa_2Cu_3O_{7-delta} including Kohn anomalies, and suggestions
of competition between one- and two-q-vector nesting.Comment: This is a revised version of arXiv:1207.5715. 25 pages, 5 figures,
plus Supplement [7 pages, 7 figures], available as a pdf [click on other,
then Download Source, & extract pdf file from zip] Manuscript is under
consideration at the NJ
Remnant Fermi Surfaces in Photoemission
Recent experiments have introduced a new concept for analyzing the
photoemission spectra of correlated electrons -- the remnant Fermi surface
(rFs), which can be measured even in systems which lack a conventional Fermi
surface. Here, we analyze the rFs in a number of interacting electron models,
and find that the results fall into two classes. For systems with pairing
instabilities, the rFs is an accurate replica of the true Fermi surface. In the
presence of nesting instabilities, the rFs is a map of the resulting
superlattice Brillouin zone. The results suggest that the gap in Ca_2CuO_2Cl_2
is of nesting origin.Comment: 4 pages LaTex, 3 ps figure
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Threats to safe transitions from hospital to home: a consensus study in North West London primary care.
BACKGROUND: Transitions between healthcare settings are vulnerable points for patients. AIM: To identify key threats to safe patient transitions from hospital to primary care settings. DESIGN AND SETTING: Three-round web-based Delphi consensus process among clinical and non-clinical staff from 39 primary care practices in North West London, England. METHOD: Round 1 was a free-text idea-generating round. Rounds 2 and 3 were consensus-obtaining rating rounds. Practices were encouraged to complete the questionnaires at team meetings. Aggregate ratings of perceived level of importance for each threat were calculated (1-3: 'not important', 4-6: 'somewhat important', 7-9: 'very important'). Percentage of votes cast for each patient or medication group were recorded; consensus was defined as ≥75%. RESULTS: A total of 39 practices completed round 1, 36/39 (92%) completed round 2, and 30/36 (83%) completed round 3. Round 1 identified nine threats encompassing problems involving communication, service organisation, medication provision, and patients who were most at risk. 'Poor quality of handover instructions from secondary to primary care teams' achieved the highest rating (mean rating at round 3 = 8.43) and a 100% consensus that it was a 'very important' threat. Older individuals (97%) and patients with complex medical problems taking >5 medications (80%) were voted the most vulnerable. Anticoagulants (77%) were considered to pose the greatest risk to patients. CONCLUSION: This study identified specific threats to safe patient transitions from hospital to primary care, providing policymakers and healthcare providers with targets for quality improvement strategies. Further work would need to identify factors underpinning these threats so that interventions can be tailored to the relevant behavioural and environmental contexts in which these threats arise
Using MATLAB software with Tomcat server and Java platform for remote image analysis in pathology
<p>Abstract</p> <p>Background</p> <p>The Matlab software is a one of the most advanced development tool for application in engineering practice. From our point of view the most important is the image processing toolbox, offering many built-in functions, including mathematical morphology, and implementation of a many artificial neural networks as AI. It is very popular platform for creation of the specialized program for image analysis, also in pathology. Based on the latest version of Matlab Builder Java toolbox, it is possible to create the software, serving as a remote system for image analysis in pathology via internet communication. The internet platform can be realized based on Java Servlet Pages with Tomcat server as servlet container.</p> <p>Methods</p> <p>In presented software implementation we propose remote image analysis realized by Matlab algorithms. These algorithms can be compiled to executable <it>jar</it> file with the help of Matlab Builder Java toolbox. The Matlab function must be declared with the set of input data, output structure with numerical results and Matlab web figure. Any function prepared in that manner can be used as a Java function in Java Servlet Pages (JSP). The graphical user interface providing the input data and displaying the results (also in graphical form) must be implemented in JSP. Additionally the data storage to database can be implemented within algorithm written in Matlab with the help of Matlab Database Toolbox directly with the image processing. The complete JSP page can be run by Tomcat server.</p> <p>Results</p> <p>The proposed tool for remote image analysis was tested on the Computerized Analysis of Medical Images (CAMI) software developed by author. The user provides image and case information (diagnosis, staining, image parameter etc.). When analysis is initialized, input data with image are sent to servlet on Tomcat. When analysis is done, client obtains the graphical results as an image with marked recognized cells and also the quantitative output. Additionally, the results are stored in a server database. The internet platform was tested on PC Intel Core2 Duo T9600 2.8GHz 4GB RAM server with 768x576 pixel size, 1.28Mb tiff format images reffering to meningioma tumour (x400, Ki-67/MIB-1). The time consumption was as following: at analysis by CAMI, locally on a server – 3.5 seconds, at remote analysis – 26 seconds, from which 22 seconds were used for data transfer via internet connection. At jpg format image (102 Kb) the consumption time was reduced to 14 seconds.</p> <p>Conclusions</p> <p>The results have confirmed that designed remote platform can be useful for pathology image analysis. The time consumption is depended mainly on the image size and speed of the internet connections. The presented implementation can be used for many types of analysis at different staining, tissue, morphometry approaches, etc. The significant problem is the implementation of the JSP page in the multithread form, that can be used parallelly by many users. The presented platform for image analysis in pathology can be especially useful for small laboratory without its own image analysis system.</p
Entropic Origin of Pseudogap Physics and a Mott-Slater Transition in Cuprates
We propose a new approach to understand the origin of the pseudogap in the
cuprates, in terms of bosonic entropy. The near-simultaneous softening of a
large number of different -bosons yields an extended range of short-range
order, wherein the growth of magnetic correlations with decreasing temperature
is anomalously slow. These entropic effects cause the spectral weight
associated with the Van Hove singularity (VHS) to shift rapidly and nearly
linearly toward half filling at higher , consistent with a picture of the
VHS driving the pseudogap transition at a temperature . As a
byproduct, we develop an order-parameter classification scheme that predicts
supertransitions between families of order parameters. As one example, we find
that by tuning the hopping parameters, it is possible to drive the cuprates
across a {\it transition between Mott and Slater physics}, where a
spin-frustrated state emerges at the crossover.Comment: 24 pgs, 15 figs + Supp. Material [6pgs, 3 figs]. Major revision of
arXiv:1505.0477
Pinned Balseiro-Falicov Model of Tunneling and Photoemission in the Cuprates
The smooth evolution of the tunneling gap of Bi_2Sr_2CaCu_2O_8 with doping
from a pseudogap state in the underdoped cuprates to a superconducting state at
optimal and overdoping, has been interpreted as evidence that the pseudogap
must be due to precursor pairing. We suggest an alternative explanation, that
the smoothness reflects a hidden SO(N) symmetry near the (pi,0) points of the
Brillouin zone (with N = 3, 4, 5, or 6). Because of this symmetry, the
pseudogap could actually be due to any of a number of nesting instabilities,
including charge or spin density waves or more exotic phases. We present a
detailed analysis of this competition for one particular model: the pinned
Balseiro-Falicov model of competing charge density wave and (s-wave)
superconductivity. We show that most of the anomalous features of both
tunneling and photoemission follow naturally from the model, including the
smooth crossover, the general shape of the pseudogap phase diagram, the
shrinking Fermi surface of the pseudogap phase, and the asymmetry of the
tunneling gap away from optimal doping. Below T_c, the sharp peak at Delta_1
and the dip seen in the tunneling and photoemission near 2Delta_1 cannot be
described in detail by this model, but we suggest a simple generalization to
account for inhomogeneity, which does provide an adequate description. We show
that it should be possible, with a combination of photoemission and tunneling,
to demonstrate the extent of pinning of the Fermi level to the Van Hove
singularity. A preliminary analysis of the data suggests pinning in the
underdoped, but not in the overdoped regime.Comment: 18 pages LaTeX, 26 ps. figure
How different Fermi surface maps emerge in photoemission from Bi2212
We report angle-resolved photoemission spectra (ARPES) from the Fermi energy
() over a large area of the () plane using 21.2 eV and 32 eV
photons in two distinct polarizations from an optimally doped single crystal of
BiSrCaCuO (Bi2212), together with extensive
first-principles simulations of the ARPES intensities. The results display a
wide-ranging level of accord between theory and experiment and clarify how
myriad Fermi surface (FS) maps emerge in ARPES under various experimental
conditions. The energy and polarization dependences of the ARPES matrix element
help disentangle primary contributions to the spectrum due to the pristine
lattice from those arising from modulations of the underlying tetragonal
symmetry and provide a route for separating closely placed FS sheets in low
dimensional materials.Comment: submitted to PR
Stripes, Pseudogaps, and Van Hove Nesting in the Three-band tJ Model
Slave boson calculations have been carried out in the three-band tJ model for
the high-T_c cuprates, with the inclusion of coupling to oxygen breathing mode
phonons. Phonon-induced Van Hove nesting leads to a phase separation between a
hole-doped domain and a (magnetic) domain near half filling, with long-range
Coulomb forces limiting the separation to a nanoscopic scale. Strong
correlation effects pin the Fermi level close to, but not precisely at the Van
Hove singularity (VHS), which can enhance the tendency to phase separation. The
resulting dispersions have been calculated, both in the uniform phases and in
the phase separated regime. In the latter case, distinctly different
dispersions are found for large, random domains and for regular (static)
striped arrays, and a hypothetical form is presented for dynamic striped
arrays. The doping dependence of the latter is found to provide an excellent
description of photoemission and thermodynamic experiments on pseudogap
formation in underdoped cuprates. In particular, the multiplicity of observed
gaps is explained as a combination of flux phase plus charge density wave (CDW)
gaps along with a superconducting gap. The largest gap is associated with VHS
nesting. The apparent smooth evolution of this gap with doping masks a
crossover from CDW-like effects near optimal doping to magnetic effects (flux
phase) near half filling. A crossover from large Fermi surface to hole pockets
with increased underdoping is found. In the weakly overdoped regime, the CDW
undergoes a quantum phase transition (), which could be obscured
by phase separation.Comment: 15 pages, Latex, 18 PS figures Corrects a sign error: major changes,
esp. in Sect. 3, Figs 1-4,6 replace
Gutzwiller Magnetic Phase Diagram of the Undoped t-t'-U Hubbard Model
We calculate the magnetic phase diagram of the half-filled t-t'-U Hubbard
model as a function of t' and U, within the Gutzwiller approximation RPA
(GA+RPA). As U increases, the system first crosses over to one of a wide
variety of incommensurate phases, whose origin is clarified in terms of double
nesting. We evaluate the stability regime of the incommensurate phases by
allowing for symmetry-breaking with regard to the formation of spin spirals,
and find a crossover to commensurate phases as U increases and a full gap
opens. The results are compared with a variety of other recent calculations,
and in general good agreement is found. For parameters appropriate to the
cuprates, double occupancy should be only mildly suppressed in the absence of
magnetic order, inconsistent with a strong coupling scenario.Comment: PRB, 4 eps figures, revtex;
http://link.aps.org/doi/10.1103/PhysRevB.81.01451
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