Metal-insulator transition in the quarter- filled frustrated checkerboard lattice

We study the electronic structure and correlations in the geometrically frustrated two dimensional checkerboard lattice. In the large U limit considered here we start from an extended Hubbard model of spinless fermions at half-filling. We investigate the model within two distinct Green's function approaches: In the first approach a single-site representation decoupling scheme is used that includes the effect of nearest neighbor charge fluctuations. In the second approach a cluster representation leading to a 'multiorbital' model is investigated which includes intra-cluster correlations exactly and those between clusters on a mean field basis. It is demonstrated that with increasing nearest-neighbor Coulomb interaction V both approaches lead to a metal-insulator transition with an associated 'Mott-Hubbard' like gap caused by V. Within the single site approach we also explore the possibility of charge order. Furthermore we investigate the evolution of the quasiparticle bands as funtion of V

Initial correlations in nonequilibrium Falicov-Kimball model

The Keldysh boundary problem in a nonequilibrium Falicov-Kimball model in infinite dimensions is studied within the truncated and self-consistent perturbation theories, and the dynamical mean-field theory. Within the model the system is started in equilibrium, and later a uniform electric field is turned on. The Kadanoff-Baym-Wagner equations for the nonequilibrium Green functions are derived, and numerically solved. The contributions of initial correlations are studied by monitoring the system evolution. It is found that the initial correlations are essential for establishing full electron correlations of the system and independent on the starting time of preparing the system in equilibrium. By examining the contributions of the initial correlations to the electric current and the double occupation, we find that the contributions are small in relation to the total value of those physical quantities when the interaction is weak, and significantly increase when the interaction is strong. The neglect of initial correlations may cause artifacts in the nonequilibrium properties of the system, especially in the strong interaction case

Analyses spectroscopiques du liquide céphalo-rachidien de rat en ex vivo et du noyau du raphé dorsal in vivo

Les propriétés d'absorption et de fluorescence du liquide céphalo-rachidien (LCR) ponctionné au niveau de la cisterna magna du rat, sont analysées puis comparées à l'émission mesurée in situ dans le noyau du raphe dorsal du rat libre de tous mouvements. Les mesures de fluorescence en ex vivo du LCR et in vivo du noyau raphé dorsal, ont été réalisées par la mise en œuvre d'un microcapteur à fibre optique (FOCS). La fluorescence mesurée in vivo sous excitation à 337 nm, présente 2 pics d'émission situés vers 410 et 460 nm. Les spectres d'absorption, d'émission en fluorescence statique et en fluorescence induite par laser sont rapportés. Avec des domaines de longueur d'onde d'excitation de 300-315 nm, 320-355 nm et 360-470 nm, les spectres d'émission du LCR en ex vivo montrent respectivement des pics centrés vers 340 nm, 390 nm et 530 nm. Malgré les limites liées aux différences de localisation anatomique, ces approches ainsi que celles de la littérature permettent de suggérer que le signal de fluorescence mesuré in vivo à 460nm pourrait dépendre pour une grande partie du NADH intracellulaire

Kinetics of Viremia and NS1 Antigenemia Are Shaped by Immune Status and Virus Serotype in Adults with Dengue

Dengue is an acute viral disease that affects tens of millions of people annually in tropical and sub-tropical countries. In some cases, this infection happens to be severe and even life threatening. Severe cases have been associated with higher levels of virus in the blood. Several hypotheses have been proposed to explain the occurrence of these cases notably by involving the patient's history of previous DEN virus infection(s). Little is known about the relationships between the evolution over time of virus levels in the blood, the clinical outcome and the previous infection(s) history—a better understanding of these features could help in anti-viral drug development. To analyze these relationships, we studied well characterized patients who participated in a clinical trial. The majority of these patients were infected by DENV-1 serotype and had higher levels of virus than those infected by DENV-2 and sometimes DENV-3 serotypes. We also found that patients with more severe symptoms had higher levels of virus in the first days of their illness. We found as well that the virus was cleared faster and earlier from the blood of patients previously infected. These findings are of major importance for further anti-viral drug testing

Effect of cortical cooling on interictal epileptiform activities

AbstractObjectiveTo determine if applying chilled solution to exposed cerebral cortex can reduce interictal epileptiform activities in patients during surgery.MethodsElectrocorticography was used to record the epileptiform activity of 12 patients (ages 18–53) undergoing cortical mapping and resection surgery. Interictal spikes were counted at baseline and compared with spikes after applying room temperature and chilled Lactated Ringer's or normal saline solution.ResultsCortical irrigation with 150-cm3, chilled (4°C) normal saline solution reduced the mean number of interictal spikes from 11.46 to 4.87 spikes per minute (p=0.04). There was no significant reduction in the epileptic spike frequency when room temperature normal saline was used.ConclusionThe application of chilled solution directly to the cortex can reduce interictal epileptiform activities, suggesting that seizure potential can be suppressed to avoid evoked seizures during intraoperative surgery

How Digital Natives Learn and Thrive in the Digital Age: Evidence from an Emerging Economy

As a generation of ‘digital natives,’ secondary students who were born from 2002 to 2010 have various approaches to acquiring digital knowledge. Digital literacy and resilience are crucial for them to navigate the digital world as much as the real world; however, these remain under-researched subjects, especially in developing countries. In Vietnam, the education system has put considerable effort into teaching students these skills to promote quality education as part of the United Nations-defined Sustainable Development Goal 4 (SDG4). This issue has proven especially salient amid the COVID−19 pandemic lockdowns, which had obliged most schools to switch to online forms of teaching. This study, which utilizes a dataset of 1061 Vietnamese students taken from the United Nations Educational, Scientific, and Cultural Organization (UNESCO)’s “Digital Kids Asia Pacific (DKAP)” project, employs Bayesian statistics to explore the relationship between the students’ background and their digital abilities. Results show that economic status and parents’ level of education are positively correlated with digital literacy. Students from urban schools have only a slightly higher level of digital literacy than their rural counterparts, suggesting that school location may not be a defining explanatory element in the variation of digital literacy and resilience among Vietnamese students. Students’ digital literacy and, especially resilience, also have associations with their gender. Moreover, as students are digitally literate, they are more likely to be digitally resilient. Following SDG4, i.e., Quality Education, it is advisable for schools, and especially parents, to seriously invest in creating a safe, educational environment to enhance digital literacy among students

Remote monitoring of natural slopes. Insights from the first Terrestrial INSAR campaign In Vietnam

Il presente lavoro, realizzato nell'ambito di un progetto di ricerca finanziato dal Vietnamese Space Science & Technology Program, mostra i primi risultati di una campagna di monitoraggio da remoto della frana di Nam Dan (Vietnam settentrionale) dove, per la prima volta nel Paese, è stata utilizzata la tecnica dell'Interferometria SAR Terrestre (TInSAR). Tale tecnica si basa sull’utilizzo di un sensore radar installato su una piattaforma terrestre che trasmette il segnale nel campo delle microonde (banda Ku) e ne riceve gli echi di ritorno dai target riflettenti. Il sensore utilizzato è costituito da due antenne (una trasmittente e una ricevente) e si muove seguendo una traiettoria lineare lungo un binario. Grazie a questa tecnica è possibile effettuare da remoto il monitoraggio delle deformazioni del terreno, raggiungendo una precisione sub-millimetrica in condizioni ideali (ad es. breve distanza, alta riflettività, etc.). Le attività di monitoraggio sono state condotte nel villaggio di Nam Dan, dove una frana attiva con diverse evidenze geomorfologiche quali scarpate, crepe, contropendenze con ristagni d’acqua, abitazioni e beni pubblici gravemente danneggiati, costituisce una seria minaccia per la popolazione locale. L’area di Nam Dan (22°36'N; 104°29'E) si trova nella parte meridionale del distretto di Xin Man, in prossimità del confine tra Vietnam e Cina. Tale distretto, caratterizzato da un clima monsonico umido subtropicale, si estende su un'area di circa 582 km2ed è caratterizzato da una topografia complessa con catene montuose, pendii terrazzati e valli molto profonde con processi erosivi avanzati. Gli archivi locali riportano che in tale area, dal 2012 al 2016, si sono verificate 967 frane, principalmente durante l'estate in corrispondenza delle piogge monsoniche del sud-ovest. Secondo recenti indagini e osservazioni sul campo, la frana oggetto di studio, verificatasi nel luglio del 2012 in seguito a forti precipitazioni, può classificarsi come uno scivolamento traslativo di detrito e si estende su un'area di circa 12.000 m2 con una profondità media di circa 22,5 metri. Nell'agosto del 2013 la frana ha causato nuovi gravi danni a 5 abitazioni, al mercato comunale e alla strada provinciale n. 178 e rappresenta tutt’oggi un grave pericolo per la popolazione residente. Le attività di monitoraggio sono state effettuate tra agosto e dicembre 2019 attraverso un nuovo interferometro radar denominato Phoenix, che è stato utilizzato in una delle sue prime applicazioni sul campo. Il monitoraggio tramite Interferometria SAR Terrestre ha avuto l’obiettivo di controllare l’evoluzione del versante instabile ed ha portato alla realizzazione di mappe di spostamento e delle relative serie temporali, fornendo informazioni dettagliate sulla localizzazione e sui tassi di deformazione dei processi gravitativi di versante presenti. Sebbene nel periodo monitorato non siano state registrate deformazioni significative, l'utilizzo di questa tecnica di telerilevamento, insieme alla strumentazione a contatto precedentemente installata (inclinometri, piezometri, pluviometri) ed alle indagini sul campo, hanno contribuito a migliorare la conoscenza della frana di Nam Dan e la comprensione del suo cinematismo, con particolare riguardo all'evoluzione temporale delle deformazioni superficiali, anche tenendo conto delle condizioni meteorologiche locali. I risultati ottenuti durante la campagna di monitoraggio, in combinazione con i dati precedentemente acquisiti ed elaborati, confermano che il versante oggetto di studio è caratterizzato da fenomeni di instabilità gravitativa, che possono essere innescati da precipitazioni intense che solitamente avvengono nell’area durante la stagione estiva. In considerazione dei contesti ambientali dell'area, quali le severe condizioni climatiche e le aree impervie da percorrere in assenza di infrastrutture viarie adeguate, è stato posto l'accento sulle attività operative sul campo e sull'individuazione di soluzioni tecnologiche appropriate, che hanno rappresentato aspetti particolarmente sfidanti per il monitoraggio di fenomeni franosi tramite tecniche di telerilevamento.The present work, realized in the framework of a research project funded by the Vietnamese Space Science & Technology Program, shows the first insights of remote monitoring at the Nam Dan landslide (Northern Vietnam). The Terrestrial SAR Interferometry (TInSAR) technique was used for the first time in the Country.The activities were performed in Nam Dan village, where an active landslide with several geomorphological evidences as open cracks and scarps, severely damaged dwellings and public assets, constituting a serious hazard to the local inhabitants. The monitoring activities were carried out between August and December 2019 through a new TInSAR device called Phoenix which it was used for one of its first on-field applications. The Terrestrial SAR was aimed at creating displacement maps and related time series, providing detailed information on the location and deformation rate of the processes under investigation. The use of such a remote sensing technique, coupled with contact instrumentation (inclinometers, piezometers, rain gauge) and field surveys have contributed to improving the knowledge about the Nam Dan landslide and the understanding of its behaviour, with particular regard to the time evolution of deformations

Flexural-strengthening efficiency of cfrp sheets for unbonded post-tensioned concrete T-beams

There has been a limited number of studies about the flexural behavior of unbonded post-tensioned concrete (UPC) beams strengthened with carbon fibre reinforced polymer (CFRP) and these studies have not systematically examined the effect of CFRP sheets on the tendon strain as well as the strengthening efficiency. Moreover, current design guides for the FRP strengthening techniques have not provided any design procedure for UPC structures. This study, thus, investigates the influence of CFRP sheet ratio on the flexural behavior of CFRP-strengthened UPC T-beams and quantifies its effect upon tendon behavior in this kind of UPC beams. The testing program consisted of nine large-scale UPC T-beams strengthened by different layers of CFRP sheets with or without CFRP U-wrapped anchors. The experimental results have shown that the use of CFRP sheets and CFRP U-wrapped anchors significantly affected the tendon strain. The FRP reinforcement ratio governed the flexural capacity, the crack width, the mid-span displacement, and the ductility of the beams in which the strengthening efficiency reduces with the increased number of CFRP layers. The configuration of the CFRP U-wrapped anchors affected the strain of the CFRP sheets, the failure mode and thus the beam behavior. In addition, semi-empirical equations were proposed to estimate the actual strain of unbonded tendons in which the effect of the CFRP sheets and CFRP U-wrapped anchors have been taken into consideration. The proposed equations, which are simple to use, yield reliable predictions with a small variation