Supersymmetry in models with strong on-site Coulomb repulsion - application to t-J model

A supersymmetric way of imposing the constraint of no double occupancy in models with strong on-site Coulomb repulsion is presented in this paper. In this formulation the physical operators in the constrainted Hilbert space are invariant under local unitary transformations mixing boson and fermion representations. As an illustration the formulation is applied to the $t-J$ model. The model is studied in the mean-field level in the J=0 limit where we show how both the slave-boson and slave-fermion formulations are included naturally in the present approach and how further results beyond both approaches are obtained.Comment: 12 pages, Latex file, 1 figur

Atomic Model of Susy Hubbard Operators

We apply the recently proposed susy Hubbard operators to an atomic model. In the limiting case of free spins, we derive exact results for the entropy which are compared with a mean field + gaussian corrections description. We show how these results can be extended to the case of charge fluctuations and calculate exact results for the partition function, free energy and heat capacity of an atomic model for some simple examples. Wavefunctions of possible states are listed. We compare the accuracy of large N expansions of the susy spin operators with those obtained using `Schwinger bosons' and `Abrikosov pseudo-fermions'. For the atomic model, we compare results of slave boson, slave fermion, and susy Hubbard operator approximations in the physically interesting but uncontrolled limiting case of N->2. For a mixed representation of spins we estimate the accuracy of large N expansions of the atomic model. In the single box limit, we find that the lowest energy saddle-point solution reduces to simply either slave bosons or slave fermions, while for higher boxes this is not the case. The highest energy saddle-point solution has the interesting feature that it admits a small region of a mixed representation, which bears a superficial resemblance to that seen experimentally close to an antiferromagnetic quantum critical point.Comment: 17 pages + 7 pages Appendices, 14 figures. Substantial revision

Spintronic transport and Kondo effect in quantum dots

We investigate the spin-dependent transport properties of quantum-dot based structures where Kondo correlations dominate the electronic dynamics. The coupling to ferromagnetic leads with parallel magnetizations is known to give rise to nontrivial effects in the local density of states of a single quantum dot. We show that this influence strongly depends on whether charge fluctuations are present or absent in the dot. This result is confirmed with numerical renormalization group calculations and perturbation theory in the on-site interaction. In the Fermi-liquid fixed point, we determine the correlations of the electric current at zero temperature (shot noise) and demonstrate that the Fano factor is suppressed below the Poissonian limit for the symmetric point of the Anderson Hamiltonian even for nonzero lead magnetizations. We discuss possible avenues of future research in this field: coupling to the low energy excitations of the ferromagnets (magnons), extension to double quantum dot systems with interdot antiferromagnetic interaction and effect of spin-polarized currents on higher symmetry Kondo states such as SU(4).Comment: 11 pages, 5 figures. Proceedings of the 3rd Intl. Conf. on Physics and Applications of Spin-Related Phenomena in Semiconductors, Santa Barbara, 200

Mean-Field Description of Phase String Effect in the t−Jt-J Model

A mean-field treatment of the phase string effect in the $t-J$ model is presented. Such a theory is able to unite the antiferromagnetic (AF) phase at half-filling and metallic phase at finite doping within a single theoretical framework. We find that the low-temperature occurrence of the AF long range ordering (AFLRO) at half-filling and superconducting condensation in metallic phase are all due to Bose condensations of spinons and holons, respectively, on the top of a spin background described by bosonic resonating-valence-bond (RVB) pairing. The fact that both spinon and holon here are bosonic objects, as the result of the phase string effect, represents a crucial difference from the conventional slave-boson and slave-fermion approaches. This theory also allows an underdoped metallic regime where the Bose condensation of spinons can still exist. Even though the AFLRO is gone here, such a regime corresponds to a microscopic charge inhomogeneity with short-ranged spin ordering. We discuss some characteristic experimental consequences for those different metallic regimes. A perspective on broader issues based on the phase string theory is also discussed.Comment: 18 pages, five figure

Fractionalization patterns in strongly correlated electron systems: Spin-charge separation and beyond

We discuss possible patterns of electron fractionalization in strongly interacting electron systems. A popular possibility is one in which the charge of the electron has been liberated from its Fermi statistics. Such a fractionalized phase contains in it the seed of superconductivity. Another possibility occurs when the spin of the electron, rather than its charge, is liberated from its Fermi statistics. Such a phase contains in it the seed of magnetism, rather than superconductivity. We consider models in which both of these phases occur and study possible phase transitions between them. We describe other fractionalized phases, distinct from these, in which fractions of the electron themselves fractionalize, and discuss the topological characterization of such phases. These ideas are illustrated with specific models of p-wave superconductors, Kondo lattices, and coexistence between d-wave superconductivity and antiferromagnetism.Comment: 28 pages, 11 fig

Diagnostic tests for oral cancer and potentially malignant disorders in patients presenting with clinically evident lesions

Background: Oral squamous cell carcinoma is the most common form of malignancy of the lip and oral cavity, often being proceeded by potentially malignant disorders (PMD). Early detection can reduce the malignant transformation of PMD and can improve the survival rate for oral cancer. The current standard of scalpel biopsy with histology is painful for patients and involves a delay whilst histology is completed; other tests are available that are unobtrusive and provide immediate results.Objectives: Primary objective: To estimate the diagnostic accuracy of index tests for the detection of oral cancer and PMD of the lip and oral cavity, in people presenting with clinically evident lesions. Secondary objective: To estimate the relative accuracy of the different index tests.Search methods: The electronic databases were searched on 30 April 2013. We searched MEDLINE (OVID) (1946 to April 2013) and four other electronic databases (the Cochrane Diagnostic Test Accuracy Studies Register, the Cochrane Oral Health Group's Trials Register, EMBASE (OVID) and MEDION (Ovid)). There were no restrictions on language in the searches of the electronic databases. We conducted citation searches and screened reference lists of included studies for additional references.Selection criteria: We selected studies that reported the diagnostic test accuracy of the following index tests when used as an adjunct to conventional oral examination in detecting PMD or oral squamous cell carcinoma of the lip or oral cavity: vital staining, oral cytology, light-based detection and oral spectroscopy, blood or saliva analysis (which test for the presence of biomarkers in blood or saliva).Data collection and analysis: Two review authors independently screened titles and abstracts for relevance. Eligibility, data extraction and quality assessment were carried out by at least two authors, independently and in duplicate. Studies were assessed for methodological quality using QUADAS-2. Meta-analysis was used to combine the results of studies for each index test using the bivariate approach to estimate the expected values of sensitivity and specificity.Main results: We included 41 studies, recruiting 4002 participants, in this review. These studies evaluated the diagnostic accuracy of conventional oral examination with: vital staining (14 studies), oral cytology (13 studies), light-based detection or oral spectroscopy (13 studies). Six studies assessed two combined index tests. There were no eligible diagnostic accuracy studies evaluating blood or salivary sample analysis. The summary estimates for vital staining obtained fromthemeta-analysis were sensitivity of 0.84 (95%CI 0.74 to 0.90) with specificity of 0.70 (0.59 to 0.79), with 14 studies were included in themeta-analysis. For cytology, sensitivity was 0.91 (0.81 to 0.96) and specificity was 0.91 (0.81 to 0.95) with 12 studies included in the meta-analysis. For light-based detection, sensitivity was 0.91 (0.77 to 0.97) and specificity was 0.58 (0.22 to 0.87) with 11 studies included in the meta-analysis. The relative test accuracy was assessed by adding covariates to the bivariate analysis, no difference in model fit was observed.Authors' conclusions: The overall quality of the included studies was poor.None of the adjunctive tests can be recommended as a replacement for the currently used standard of a scalpel biopsy and histological assessment. Given the relatively high values of the summary estimates of sensitivity and specificity for cytology, this would appear to offer themost potential. Combined adjunctive tests involving cytology warrant further investigation.</p

Chlorhexidine mouthrinse as an adjunctive treatment for gingival health

BACKGROUND: Dental plaque associated gingivitis is a reversible inflammatory condition caused by accumulation and persistence of microbial biofilms (dental plaque) on the teeth. It is characterised by redness and swelling of the gingivae (gums) and a tendency for the gingivae to bleed easily. In susceptible individuals, gingivitis may lead to periodontitis and loss of the soft tissue and bony support for the tooth. It is thought that chlorhexidine mouthrinse may reduce the build-up of plaque thereby reducing gingivitis. OBJECTIVES: To assess the effectiveness of chlorhexidine mouthrinse used as an adjunct to mechanical oral hygiene procedures for the control of gingivitis and plaque compared to mechanical oral hygiene procedures alone or mechanical oral hygiene procedures plus placebo/control mouthrinse. Mechanical oral hygiene procedures were toothbrushing with/without the use of dental floss or interdental cleaning aids and could include professional tooth cleaning/periodontal treatment.To determine whether the effect of chlorhexidine mouthrinse is influenced by chlorhexidine concentration, or frequency of rinsing (once/day versus twice/day).To report and describe any adverse effects associated with chlorhexidine mouthrinse use from included trials. SEARCH METHODS: Cochrane Oral Health's Information Specialist searched the following databases: Cochrane Oral Health's Trials Register (to 28 September 2016); the Cochrane Central Register of Controlled Trials (CENTRAL; 2016, Issue 8) in the Cochrane Library (searched 28 September 2016); MEDLINE Ovid (1946 to 28 September 2016); Embase Ovid (1980 to 28 September 2016); and CINAHL EBSCO (Cumulative Index to Nursing and Allied Health Literature; 1937 to 28 September 2016). We searched ClinicalTrials.gov and the World Health Organization International Clinical Trials Registry Platform for ongoing trials. No restrictions were placed on the language or date of publication when searching the electronic databases. SELECTION CRITERIA: We included randomised controlled trials assessing the effects of chlorhexidine mouthrinse used as an adjunct to mechanical oral hygiene procedures for at least 4 weeks on gingivitis in children and adults. Mechanical oral hygiene procedures were toothbrushing with/without use of dental floss or interdental cleaning aids and could include professional tooth cleaning/periodontal treatment. We included trials where participants had gingivitis or periodontitis, where participants were healthy and where some or all participants had medical conditions or special care needs. DATA COLLECTION AND ANALYSIS: Two review authors independently screened the search results extracted data and assessed the risk of bias of the included studies. We attempted to contact study authors for missing data or clarification where feasible. For continuous outcomes, we used means and standard deviations to obtain the mean difference (MD) and 95% confidence interval (CI). We combined MDs where studies used the same scale and standardised mean differences (SMDs) where studies used different scales. For dichotomous outcomes, we reported risk ratios (RR) and 95% CIs. Due to anticipated heterogeneity we used random-effects models for all meta-analyses. MAIN RESULTS: We included 51 studies that analysed a total of 5345 participants. One study was assessed as being at unclear risk of bias, with the remaining 50 being at high risk of bias, however, this did not affect the quality assessments for gingivitis and plaque as we believe that further research is very unlikely to change our confidence in the estimate of effect. Gingivitis After 4 to 6 weeks of use, chlorhexidine mouthrinse reduced gingivitis (Gingival Index (GI) 0 to 3 scale) by 0.21 (95% CI 0.11 to 0.31) compared to placebo, control or no mouthrinse (10 trials, 805 participants with mild gingival inflammation (mean score 1 on the GI scale) analysed, high-quality evidence). A similar effect size was found for reducing gingivitis at 6 months. There were insufficient data to determine the reduction in gingivitis associated with chlorhexidine mouthrinse use in individuals with mean GI scores of 1.1 to 3 (moderate or severe levels of gingival inflammation). Plaque Plaque was measured by different indices and the SMD at 4 to 6 weeks was 1.45 (95% CI 1.00 to 1.90) standard deviations lower in the chlorhexidine group (12 trials, 950 participants analysed, high-quality evidence), indicating a large reduction in plaque. A similar large reduction was found for chlorhexidine mouthrinse use at 6 months. Extrinsic tooth staining There was a large increase in extrinsic tooth staining in participants using chlorhexidine mouthrinse at 4 to 6 weeks. The SMD was 1.07 (95% CI 0.80 to 1.34) standard deviations higher (eight trials, 415 participants analysed, moderate-quality evidence) in the chlorhexidine mouthrinse group. There was also a large increase in extrinsic tooth staining in participants using chlorhexidine mouthrinse at 7 to 12 weeks and 6 months. Calculus Results for the effect of chlorhexidine mouthrinse on calculus formation were inconclusive. Effect of concentration and frequency of rinsing There were insufficient data to determine whether there was a difference in effect for either chlorhexidine concentration or frequency of rinsing. Other adverse effects The adverse effects most commonly reported in the included studies were taste disturbance/alteration (reported in 11 studies), effects on the oral mucosa including soreness, irritation, mild desquamation and mucosal ulceration/erosions (reported in 13 studies) and a general burning sensation or a burning tongue or both (reported in nine studies). AUTHORS' CONCLUSIONS: There is high-quality evidence from studies that reported the Löe and Silness Gingival Index of a reduction in gingivitis in individuals with mild gingival inflammation on average (mean score of 1 on the 0 to 3 GI scale) that was not considered to be clinically relevant. There is high-quality evidence of a large reduction in dental plaque with chlorhexidine mouthrinse used as an adjunct to mechanical oral hygiene procedures for 4 to 6 weeks and 6 months. There is no evidence that one concentration of chlorhexidine rinse is more effective than another. There is insufficient evidence to determine the reduction in gingivitis associated with chlorhexidine mouthrinse use in individuals with mean GI scores of 1.1 to 3 indicating moderate or severe levels of gingival inflammation. Rinsing with chlorhexidine mouthrinse for 4 weeks or longer causes extrinsic tooth staining. In addition, other adverse effects such as calculus build up, transient taste disturbance and effects on the oral mucosa were reported in the included studies

Effect of angiotensin-converting enzyme inhibitor and angiotensin receptor blocker initiation on organ support-free days in patients hospitalized with COVID-19

IMPORTANCE Overactivation of the renin-angiotensin system (RAS) may contribute to poor clinical outcomes in patients with COVID-19. Objective To determine whether angiotensin-converting enzyme (ACE) inhibitor or angiotensin receptor blocker (ARB) initiation improves outcomes in patients hospitalized for COVID-19. DESIGN, SETTING, AND PARTICIPANTS In an ongoing, adaptive platform randomized clinical trial, 721 critically ill and 58 non–critically ill hospitalized adults were randomized to receive an RAS inhibitor or control between March 16, 2021, and February 25, 2022, at 69 sites in 7 countries (final follow-up on June 1, 2022). INTERVENTIONS Patients were randomized to receive open-label initiation of an ACE inhibitor (n = 257), ARB (n = 248), ARB in combination with DMX-200 (a chemokine receptor-2 inhibitor; n = 10), or no RAS inhibitor (control; n = 264) for up to 10 days. MAIN OUTCOMES AND MEASURES The primary outcome was organ support–free days, a composite of hospital survival and days alive without cardiovascular or respiratory organ support through 21 days. The primary analysis was a bayesian cumulative logistic model. Odds ratios (ORs) greater than 1 represent improved outcomes. RESULTS On February 25, 2022, enrollment was discontinued due to safety concerns. Among 679 critically ill patients with available primary outcome data, the median age was 56 years and 239 participants (35.2%) were women. Median (IQR) organ support–free days among critically ill patients was 10 (–1 to 16) in the ACE inhibitor group (n = 231), 8 (–1 to 17) in the ARB group (n = 217), and 12 (0 to 17) in the control group (n = 231) (median adjusted odds ratios of 0.77 [95% bayesian credible interval, 0.58-1.06] for improvement for ACE inhibitor and 0.76 [95% credible interval, 0.56-1.05] for ARB compared with control). The posterior probabilities that ACE inhibitors and ARBs worsened organ support–free days compared with control were 94.9% and 95.4%, respectively. Hospital survival occurred in 166 of 231 critically ill participants (71.9%) in the ACE inhibitor group, 152 of 217 (70.0%) in the ARB group, and 182 of 231 (78.8%) in the control group (posterior probabilities that ACE inhibitor and ARB worsened hospital survival compared with control were 95.3% and 98.1%, respectively). CONCLUSIONS AND RELEVANCE In this trial, among critically ill adults with COVID-19, initiation of an ACE inhibitor or ARB did not improve, and likely worsened, clinical outcomes. TRIAL REGISTRATION ClinicalTrials.gov Identifier: NCT0273570

Optimisation studies on inclined web wheel using finite elements

The optimisation studies on wheels have generated much interest among the researchers in order to upgrade the wheel performance. Wheels find application as wheel in automobiles, trains, as pulleys, helical gears etc. Optimum shape of wheel is the fundamental objective of designers. Finite Element Method (FEM) is an appropriate technique suitable for computer implementation. This study is mainly concerned about the analysis of stress and deflection of the web of wheel under static loading conditions. Modification of geometric parameters such as web inclination, fillet radius and rim-volume reduce the stress distribution and deflection of wheel axial loading condition. The investigation reveals information on shape optimisation and the resulting stress reduction