3,462 research outputs found
Circulating-current states and ring-exchange interactions in cuprates
We consider the consequences for circulating-current states of a cyclic,
four-spin, ``ring-exchange'' interaction of the type shown recently to be
significant in cuprate systems. The real-space Hartree-Fock approach is used to
establish the existence of charge-current and spin-current phases in a
generalized Hubbard model for the CuO_2 planes in cuprates. We compare the
results of the Hartree-Fock approximation with the correlated states
renormalized by Gutzwiller projection factors which allows us to gauge the
qualitative effects of projection to no double site occupancy. We find that
charge flux states may be competitive in cuprates, whereas spin flux states are
suppressed in the strongly correlated regime. We then include the ring-exchange
interaction and demonstrate its effect on current-carrying states both at and
away from half-filling.Comment: 14 pages, 11 figure
Static impurities in the kagome lattice: dimer freezing and mutual repulsion
We consider the effects of doping the S = 1/2 kagome lattice with static
impurities. We demonstrate that impurities lower the number of low-lying
singlet states, induce dimer-dimer correlations of considerable spatial extent,
and do not generate free spin degrees of freedom. Most importantly, they
experience a highly unconventional mutual repulsion as a direct consequence of
the strong spin frustration. These properties are illustrated by exact
diagonalization, and reproduced to semi-quantitative accuracy within a dimer
resonating-valence-bond description which affords access to longer length
scales. We calculate the local magnetization induced by doped impurities, and
consider its implications for nuclear magnetic resonance measurements on known
kagome systems.Comment: 9 pages, 12 figure
A systematic review of the cost and cost effectiveness of using standard oral nutritional supplements in the hospital setting
Background & aims: There is limited information about the economic impact of nutritional support despite its known clinical benefits. This systematic review examined the cost and cost effectiveness of using standard (non-disease specific) oral nutritional supplements (ONS) administered in the hospital setting only. Methods: A systematic literature search of multiple databases, data synthesis and analysis were undertaken according to recommended procedures. Results: Nine publications comprising four full text papers, two abstracts and three reports, one of which contained 11 cost analyses of controlled cohort studies, were identified. Most of these were based on retrospective analyses of randomised controlled trials designed to assess clinically relevant outcomes. The sample sizes of patients with surgical, orthopaedic and medical problems and combinations of these varied from 40 to 1.16 million. Of 14 cost analyses comparing ONS with no ONS (or routine care), 12 favoured the ONS group, and among those with quantitative data (12 studies) the mean cost saving was 12.2%. In a meta-analysis of five abdominal surgical studies in the UK, the mean net cost saving was 338; P = 0.027). Cost savings were typically associated with significantly improved outcomes, demonstrated through the following meta-analyses: reduced mortality (Risk ratio 0.650, P < 0.05; N = 5 studies), reduced complications (by 35% of the total; P < 0.001, N = 7 studies) and reduced length of hospital stay (by ~2 days, P < 0.05; N = 5 surgical studies) corresponding to ~13.0% reduction in hospital stay. Two studies also found ONS to be cost effective, one by avoiding development of pressure ulcers and releasing hospital beds, and the other by gaining quality adjusted life years. Conclusion: This review suggests that standard ONS in the hospital setting produce a cost saving and are cost effective. The evidence base could be further strengthened by prospective studies in which the primary outcome measures are economic
A systematic review of the cost and cost effectiveness of using standard oral nutritional supplements in community and care home settings
Background & aims: Despite the clinical benefits of using standard (non-disease specific) oral nutritional supplements (ONS) in the community and care homes, there is uncertainty about their economic consequences. Methods: A systematic review was undertaken according to recommended procedures to assess whether ONS can produce cost savings and cost-effective outcomes. Results: 19 publications with and without a hospital component were identified: 9 full text papers, 9 abstracts, and 1 report with retrospective analyses of 6 randomised controlled trials. From these publications a total of 31 cost and 4 cost-effectiveness analyses were identified. Most were retrospective analyses based on clinical data from randomised controlled trials (RCTs). In 9 studies/economic models involving ONS use for 0.05; 5 studies). In RCTs, ONS accounted for less than 5% of the total costs and the investment in the community produced a cost saving in hospital. Meta-analysis indicated that ONS reduced hospitalisation significantly (16.5%; P < 0.001; 9 comparisons) and mortality non-significantly (Relative risk 0.86 (95% CI, 0.61, 1.22); 8 comparisons). Many clinically relevant outcomes favouring ONS were reported: improved quality of life, reduced infections, reduced minor post-operative complications, reduced falls, and functional limitations. Of the cost-effectiveness analyses involving quality adjusted life years or functional limitations, most favoured the ONS group. The care home studies (4 cost analyses; 2 cost-effectiveness analyses) had differing aims, designs and conclusions. Conclusions: Overall, the reviewed studies, mostly based on retrospective cost analyses, indicate that ONS use in the community produce an overall cost advantage or near neutral balance, often in association with clinically relevant outcomes, suggesting cost effectiveness. There is a need for prospective studies designed to examine primary economic outcomes
Discrete port-controlled Hamiltonian dynamics and average passivation
The paper discusses the modeling and control of port-controlled Hamiltonian dynamics in a pure discrete-time domain. The main result stands in a novel differential-difference representation of discrete port-controlled Hamiltonian systems using the discrete gradient. In these terms, a passive output map is exhibited as well as a passivity based damping controller underlying the natural involvement of discrete-time average passivity
On possible superconductivity in the doped ladder compound La_(1-x)Sr_xCuO_2.5
LaCuO_2.5 is a system of coupled, two-chain, cuprate ladders which may be
doped systematically by Sr substitution. Motivated by the recent synthesis of
single crystals, we investigate theoretically the possibility of
superconductivity in this compound. We use a model of spin fluctuation-mediated
superconductivity, where the pairing potential is strongly peaked at \pi in the
ladder direction. We solve the coupled gap equations on the bonding and
antibonding ladder bands to find superconducting solutions across the range of
doping, and discuss their relevance to the real material.Comment: RevTex, 4 pages, 7 figure
Accurate determination of the Gaussian transition in spin-1 chains with single-ion anisotropy
The Gaussian transition in the spin-one Heisenberg chain with single-ion
anisotropy is extremely difficult to treat, both analytically and numerically.
We introduce an improved DMRG procedure with strict error control, which we use
to access very large systems. By considering the bulk entropy, we determine the
Gaussian transition point to 4-digit accuracy, , resolving a long-standing debate in quantum magnetism. With
this value, we obtain high-precision data for the critical behavior of
quantities including the ground-state energy, gap, and transverse string-order
parameter, and for the critical exponent, . Applying our
improved technique at highlights essential differences in
critical behavior along the Gaussian transition line.Comment: 4 pages and 4 figure
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