Spin-Charge Separation in the t−Jt-J Model: Magnetic and Transport Anomalies

A real spin-charge separation scheme is found based on a saddle-point state of the $t-J$ model. In the one-dimensional (1D) case, such a saddle-point reproduces the correct asymptotic correlations at the strong-coupling fixed-point of the model. In the two-dimensional (2D) case, the transverse gauge field confining spinon and holon is shown to be gapped at {\em finite doping} so that a spin-charge deconfinement is obtained for its first time in 2D. The gap in the gauge fluctuation disappears at half-filling limit, where a long-range antiferromagnetic order is recovered at zero temperature and spinons become confined. The most interesting features of spin dynamics and transport are exhibited at finite doping where exotic {\em residual} couplings between spin and charge degrees of freedom lead to systematic anomalies with regard to a Fermi-liquid system. In spin dynamics, a commensurate antiferromagnetic fluctuation with a small, doping-dependent energy scale is found, which is characterized in momentum space by a Gaussian peak at ($\pi/a$, $\pi/a$) with a doping-dependent width ($\propto \sqrt{\delta}$, $\delta$ is the doping concentration). This commensurate magnetic fluctuation contributes a non-Korringa behavior for the NMR spin-lattice relaxation rate. There also exits a characteristic temperature scale below which a pseudogap behavior appears in the spin dynamics. Furthermore, an incommensurate magnetic fluctuation is also obtained at a {\em finite} energy regime. In transport, a strong short-range phase interference leads to an effective holon Lagrangian which can give rise to a series of interesting phenomena including linear-$T$ resistivity and $T^2$ Hall-angle. We discuss the striking similarities of these theoretical features with those found in the high-$T_c$ cuprates and give aComment: 70 pages, RevTex, hard copies of 7 figures available upon request; minor revisions in the text and references have been made; To be published in July 1 issue of Phys. Rev. B52, (1995

Analysis of the UCHL1 genetic variant in Parkinson's disease among Chinese

10.1016/j.neurobiolaging.2008.11.008Neurobiology of Aging31122194-2196NEAG

Meta- and pooled analyses of the Methylenetetrahydrofolate reductase C677T and A1298C polymorphisms and gastric cancer risk: a HuGE-GSEC Review.

Methylenetetrahydrofolate reductase (MTHFR) is a key enzyme in the metabolism of folate, whose role in gastric carcinogenesis is controversial. The authors performed a meta-analysis and individual data pooled analysis of case-control studies that examined the association between C677T and A1298C polymorphisms (the former being associated with low folate serum levels) and gastric cancer (meta-analyses: 16 studies, 2,727 cases and 4,640 controls for C677T and seven studies, 1,223 cases and 2,015 controls for A1298C; pooled analyses: nine studies, 1,540 cases and 2,577 controls for C677T and five studies, 1,146 cases and 1,549 controls for A1298C). An increased risk was found for MTHFR 677 TT in the meta-analysis (odds ratio (OR) = 1.52, 95% confidence interval (CI): 1.31, 1.77) and pooled analysis (OR = 1.49, 95% CI: 1.14, 1.95). No association resulted for MTHFR 1298 CC (meta-OR = 0.94, 95% CI: 0.65, 1.35; pooled OR = 0.90, 95% CI: 0.69, 1.34). Results from the pooled analysis of four studies on C677T stratified according to folate levels showed an increased risk for individuals with low (OR = 2.05, 95% CI: 1.13, 3.72) versus high (OR = 0.95, 95% CI: 0.54, 1.67) folate levels. Overall, these findings support the hypothesis that folate plays a role in gastric carcinogenesis

Meta- e pooled analisi dei polimorfismi c677t e a1298c del metilenetetraidrofolato reduttasi (MTHFR) e rischio di carcinoma gastrico: una HuGE-GSEC review

OBIETTIVI: Il metilenetetraidrofolato reduttasi (MTHFR) \ue8 un enzima coinvolto nel metabolismo dei folati, da cui dipendono la sintesi del DNA e la regolazione dell???espressione genica. Due polimorfismi (C677T e A1298C) sono associati a ridotta attivit\ue0 enzimatica e al conseguente basso livello ematico di folati. Esistono contrastanti evidenze in letteratura sul possibile ruolo preventivo dei folati nello sviluppo del carcinoma gastrico. Al fine di quantificare l???associazione tra i due polimorfismi di MTHFR e il carcinoma gastrico abbiamo effettuato una meta-analisi di studi pubblicati e una analisi pooled di dati individuali. METODI: Sono stati ricercati su Medline ed Embase articoli di studi osservazionali pubblicati prima di gennaio 2007 sull???associazione tra i polimorfismi C677T e/o A1298C di MTHFR e carcinoma gastrico. Per la metaanalisi \ue8 stato utilizzato il modello ad effetti random. Per la analisi pooled sono stati richiesti i database originali agli autori degli articoli inclusi e sono stati calcolati gli ORs aggiustati mediante analisi multivariata. \uc8 stato quindi calcolato l???OR pooled tramite meta-analisi. RISULTATI: Sono stati inclusi nella meta-analisi 16 studi caso-controllo per C677T e sette per A1298C; i database ottenuti per l???analisi pooled sono stati nove e sei, rispettivamente. Il rischio di carcinoma gastrico \ue8 risultato maggiore per gli individui con genotipo 677TT (meta-analisi-OR=1.52, 95%CI: 1.31-1.77; pooled-OR=1.49, 95% CI: 1.14-1.95). Non \ue8 stata evidenziata alcuna associazione per 1298CC. Nell???analisi pooled, stratificando per consumo di frutta e verdura, alimenti ricchi di folati, il rischio in individui 677TT risulta pi\uf9 elevato nel gruppo con basso consumo (OR=2.05, 95% CI: 1.13-3.72) rispetto al gruppo con alto consumo (OR=0.95, 95% CI: 0.54-1.67; p value dell???eterogeneit\ue0 tra le due stime=0.06). CONCLUSIONI: Gli individui portatori del genotipo 677TT hanno un aumentato rischio di carcinoma gastrico, soprattutto in condizioni di basso consumo di frutta e verdura. Per valutare i possibili benefici di una eventuale supplementazione con folati bisogna attendere i risultati di studi randomizzati controllati

A Review on Adaptive Methods for Structural Control

Adaptive control algorithms are widely used in many technical fields like aeronautics and robotics for controlling systems whose characteristics vary with time or are uncertain. In the last decades, with the diffusion of active and semiactive control applications in civil engineering, adaptive methods started to be adopted for structural control. This paper provides an up-to-date survey on strategies currently available for adaptive control and a literature overview of solutions examined until today for structural applications