Moments of the characteristic polynomial in the three ensembles of random matrices

Moments of the characteristic polynomial of a random matrix taken from any of the three ensembles, orthogonal, unitary or symplectic, are given either as a determinant or a pfaffian or as a sum of determinants. For gaussian ensembles comparing the two expressions of the same moment one gets two remarkable identities, one between an $n\times n$ determinant and an $m\times m$ determinant and another between the pfaffian of a $2n\times 2n$ anti-symmetric matrix and a sum of $m\times m$ determinants.Comment: tex, 1 file, 15 pages [SPhT-T01/016], published J. Phys. A: Math. Gen. 34 (2001) 1-1

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

Statistical and Clinical Aspects of Hospital Outcomes Profiling

Hospital profiling involves a comparison of a health care provider's structure, processes of care, or outcomes to a standard, often in the form of a report card. Given the ubiquity of report cards and similar consumer ratings in contemporary American culture, it is notable that these are a relatively recent phenomenon in health care. Prior to the 1986 release of Medicare hospital outcome data, little such information was publicly available. We review the historical evolution of hospital profiling with special emphasis on outcomes; present a detailed history of cardiac surgery report cards, the paradigm for modern provider profiling; discuss the potential unintended negative consequences of public report cards; and describe various statistical methodologies for quantifying the relative performance of cardiac surgery programs. Outstanding statistical issues are also described.Comment: Published in at http://dx.doi.org/10.1214/088342307000000096 the Statistical Science (http://www.imstat.org/sts/) by the Institute of Mathematical Statistics (http://www.imstat.org

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 $746 per patient (se$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

Magnon Dispersion in the Field-Induced Magnetically Ordered Phase of TlCuCl3

The magnetic properties of the interacting dimer system TlCuCl3 are investigated within a bond-operator formulation. The observed field-induced staggered magnetic order perpendicular to the field is described as a Bose condensation of magnons which are linear combinations of dimer singlet and triplet modes. This technique accounts for the magnetization curve and for the field dependence of the magnon dispersion curves observed by high-field neutron scattering measurements.Comment: 4 pages, 4 figures, REVTeX