Spin Dynamics of the Triangular Heisenberg Antiferromagnet: A Schwinger Boson Approach

We have analyzed the two-dimensional antiferromagnetic Heisenberg model on the triangular lattice using a Schwinger boson mean-field theory. By expanding around a state with local $120^\circ$ order, we obtain, in the limit of infinite spin, results for the excitation spectrum in complete agreement with linear spin wave theory (LSWT). In contrast to LSWT, however, the modes at the ordering wave vectors acquire a mass for finite spin. We discuss the origin of this effect.Comment: 15 pages REVTEX 3.0 preprint, 6 postscript figures ( uuencoded and compressed using the script uufiles ) are submitted separately

Possible Quantum Spin Liquid States on the Triangular and Kagome Lattices

The frustrated spin-one-half Heisenberg model on triangualr and Kagome Lattices is mapped onto a single specis of fermion carrying statistical flux. The corresponding Chern-Simons gauge theory is analyzed at the Gaussian level and found to be massive. This provides a new motivation for the spin-liquid Kalmeyer-Laughlin wave function. Good overlap of this wave function with the numerical ground state is found for small clusters.Comment: 13 pages, revtex. IUCM-920

Efficiency of Exciton and Charge Carrier Photogeneration in a Semiconducting Polymer

Euan Hendry, Juleon M. Schins, L. P. Candeias, L. D. A. Siebbeles, and Mischa Bonn, Physical Review Letters, Vol. 92, article 196601 (2004). "Copyright © 2004 by the American Physical Society."We determine the efficiencies for the formation of excitons and charge carriers following ultrafast photoexcitation of a semiconducting polymer (MEH-PPV). The simultaneous, quantitative determination of exciton and charge photoyields is achieved through subpicosecond studies of both the real and the imaginary components of the complex conductivity over a wide frequency range. Predominantly excitons, with near-unity quantum efficiency, are generated on excitation, while only a very small fraction (<10-2) of free charges are initially excited, consistent with rapid (∼100  fs) hot exciton dissociation. These initial charges are very short lived, decaying on subpicosecond time scales

Functional Characterization of Two Mutations Located in the Ligand Binding Domain in the SF1

Purpose: Since SF1 gene mutations located in the ligand binding domain are associated with a wide phenotypic spectrum in 46,XY subjects, the functional and structural characterization of these variations is of great interest. The aim of this study is to evaluate the clinical phenotype, hormonal pattern and molecular studies (genetic, functional data and protein structural analysis) in two non-related 46,XY disorder of sex development (DSD) index patients. Methods: Clinical characteristics, genomic DNA sequencing analysis, protein prediction software study and protein structure analysis, and functional characterization of the mutations was carried out. Results: Both index DSD patients showed a similar phenotype, however several affected members of Family 1 showed variable phenotypes. While in Family 1 a previously reported heterozygous missense point mutation (p.Arg313His) was found, in Family 2 a novel heterozygous missense point mutation (p.Ser303Arg) was detected. Both mutations were predicted to be as “probably damaging”. The transcriptional activity of SF1 mutants p.Arg313His and p.Ser303Arg, studied using two different promoters in two cell lines, exhibited significant reductions of transactivation activity. Structural analysis showed differences between both mutants, such as changes in the flexibility of the receptor backbone and in the tertiary structure around the ligand and in the AF-2 domain. Conclusions: One of these ligand binding domain mutations in SF1 showed phenotypic heterogeneity among family members, while both variations showed similarities in prepubertal phenotype, as well as in damage prediction and experimental decreases in transcriptional activity, but marked differences in structural consequence predictions. Finally the present study reinforces the concept of the wide variability in the clinical phenotype in affected 46,XY DSD patients.Fil: Perez Garrido, Natalia Isabel. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Saraco, Nora Isabel. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Marino, R.. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Ramirez, P.. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Ciaccio, Marta Graciela Cristina. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Costanzo, M.. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Guercio, Gabriela Viviana. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Warman, M.. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Minini, L.. Universidad de la República. Facultad de Ciencias; UruguayFil: Portillo Ledesma, S.. Universidad de la República. Facultad de Ciencias; UruguayFil: Rivarola, Marco Aurelio. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; ArgentinaFil: Coitiño, E. L.. Universidad de la República. Facultad de Ciencias; UruguayFil: Belgorosky, Alicia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Gobierno de la Ciudad de Buenos Aires. Hospital de Pediatría "Juan P. Garrahan"; Argentin

Orbitofrontal cortex, emotional decision-making and response to cognitive behavioural therapy for psychosis

Grey matter volume (GMV) in the orbitofrontal cortex (OFC) may relate to better response to cognitive behavioural therapy for psychosis (CBTp) because of the region's role in emotional decision-making and cognitive flexibility. This study aimed to determine the relation between pre-therapy OFC GMV or asymmetry and CBTp responsiveness and emotional decision-making as measured by the Iowa Gambling Task (IGT). Thirty patients received CBTp + standard care (CBTp+SC; 25 completers) for 6-8 months. All patients (before receiving CBTp) and 25 healthy participants underwent structural magnetic resonance imaging and performed the IGT. Patients' symptoms were assessed before and after therapy. Pre-therapy OFC GMV, measured using a region-of-interest approach, and IGT performance, measured as overall learning, attention to reward, memory for past outcomes and choice consistency, were comparable between patient and healthy groups. In the CBTp+SC group, greater OFC GMV was correlated with positive symptom improvement, specifically hallucinations and persecution. Greater rightward OFC asymmetry correlated with improvement in several negative and general psychopathology symptoms. Greater left OFC GMV was associated with lower IGT attention to reward. The findings suggest that greater OFC volume and rightward asymmetry, which maintain the OFC's function in emotional decision-making and cognitive flexibility, are beneficial for CBTp responsiveness

The Beck Cognitive Insight Scale (BCIS): translation and validation of the Taiwanese version

<p>Abstract</p> <p>Background</p> <p>Over the last few decades, research concerning the insight of patients with schizophrenia and its relationships with other clinical variables has been given much attention in the clinical setting. Since that time, a series of instruments assessing insight have been developed. The purpose of this study was to examine the reliability and validity of the Taiwanese version of the Beck Cognitive Insight Scale (BCIS). The BCIS is a self-administered instrument designed to evaluate cognitive processes that involves reevaluating patients' anomalous experiences and specific misinterpretations.</p> <p>Methods</p> <p>The English language version of the BCIS was translated into Taiwanese for use in this study. A total of 180 subjects with and without psychosis completed the Taiwanese version of the BCIS and additional evaluations to assess researcher-rated insight scales and psychopathology. Psychometric properties (factor structures and various types of reliability and validity) were assessed for this translated questionnaire.</p> <p>Results</p> <p>Overall, the Taiwanese version of the BCIS showed good reliability and stability over time. This translated scale comprised a two-factor solution corresponding to reflective attitude and certain attitude subscales. Following the validation of the internal structure of the scale, we obtained an R-C (reflective attitude minus certain attitude) index of the translated BCIS, representing the measurement of cognitive insight by subtracting the score of the certain attitude subscale from that of the reflective attitude subscale. As predicted, the differences in mean reflective attitude, certain attitude and R-C index between subjects with and without psychosis were significant. Our data also demonstrated that psychotic patients were significantly less reflective, more confident in their beliefs, and had less cognitive insight compared with nonpsychotic control groups.</p> <p>Conclusions</p> <p>In light of these findings, we believe that the Taiwanese version of BCIS is a valid and reliable instrument for the assessment of cognitive insight in psychotic patients.</p

Spontaneous Inter-layer Coherence in Double-Layer Quantum-Hall Systems I: Charged Vortices and Kosterlitz-Thouless Phase Transitions

At strong magnetic fields double-layer two-dimensional-electron-gas systems can form an unusual broken symmetry state with spontaneous inter-layer phase coherence. In this paper we explore the rich variety of quantum and finite-temperature phase transitions associated with this broken symmetry. We describe the system using a pseudospin language in which the layer degree-of-freedom is mapped to a fictional spin 1/2 degree-of-freedom. With this mapping the spontaneous symmetry breaking is equivalent to that of a spin 1/2 easy-plane ferromagnet. In this language spin-textures can carry a charge. In particular, vortices carry e/2 electrical charge and vortex-antivortex pairs can be neutral or carry charge e. We derive an effective low-energy action and use it to discuss the charged and collective neutral excitations of the system. We have obtained the parameters of the Landau-Ginzburg functional from first-principles estimates and from finite-size exact diagonalization studies. We use these results to estimate the dependence of the critical temperature for the Kosterlitz-Thouless phase transition on layer separation.Comment: 56 pages, 19 figures available upon request at [email protected]. RevTex 3.0. IUCM94-00

Associations of human gene EPB41L3 DNA methylation and cervical intraepithelial neoplasia in women living with HIV-1 in Africa.

OBJECTIVES: To evaluate associations of DNA methylation of the human tumour suppressor gene EPB41L3 with high-grade cervical intraepithelial neoplasia (CIN2+) and HIV-related factors among women living with HIV-1 (WLHIV) in Burkina Faso and South Africa. DESIGN: Case-control study of WLHIV aged 25-50 with histology-determined CIN2+ (cases, N = 152) and ≤CIN1 (controls, N = 210). METHODS: EPB41L3 methylation was measured by pyrosequencing of bisulphite converted DNA from exfoliated cervical specimens at baseline and 16 months later. Median methylation levels were compared across CIN grades using the Mann-Whitney test and Cuzick test for trend. EPB41L3 methylation levels were dichotomized into 'high' and 'low' using the 66.7 percentile point of the distribution in the controls. Associations of EPB41L3 methylation with HIV-related factors were estimated by logistic regression. RESULTS: Among 94 WLHIV in Burkina Faso and 268 in South Africa, median methylation levels at baseline for EPB41L3 increased with increasing CIN grade in both countries (P-trend 5 years vs. ≤5 years; adjusted odds ratio (aOR) = 4.15, 95% CI 1.09-15.83, adjusted for age, CD4 count, high-risk HPV and CIN status], with low CD4 count in both countries (CD4 ≤200 vs. ≥350 cells/μl: aOR = 7.14, 95% CI 1.44-35.37 in Burkina Faso; aOR = 2.55, 95% CI 1.07-6.07 in South Africa), and with prolonged ART use in South Africa (ART >2 years vs. ART-naïve: aOR = 2.40, 95% CI: 1.23-4.69). CONCLUSION: Methylation of EPB41L3 DNA is elevated among WLHIV with CIN2+ and independently associated with lower CD4 count and ART use.European Commission (EC) 7th Framework Programme under grant agreement No. HEALTH-2010-F2-265396, UK Medical Research Council (MRC) PHINDS scheme (PH01/14-39) and Cancer Research UK [Grant number C569/A10404] to QMUL