Search

The advent of twisted moiré heterostructures as a playground for strongly correlated electron physics has led to a plethora of experimental and theoretical efforts seeking to unravel the nature of the emergent superconducting and insulating states. Among these layered compositions of two-dimensional materials, transition metal dichalcogenides are now appreciated as highly tunable platforms to simulate reinforced electronic interactions in the presence of low-energy bands with almost negligible bandwidth. Here, we focus on the twisted homobilayer WSe2 and the insulating phase at half-filling of the flat bands reported therein. More specifically, we explore the possibility of realizing quantum spin liquid (QSL) physics on the basis of a strong coupling description, including up to second-nearest neighbor Heisenberg couplings J1 and J2 as well as Dzyaloshinskii–Moriya (DM) interactions. Mapping out the global phase diagram as a function of an out-of-plane displacement field, we indeed find evidence for putative QSL states, albeit only close to SU(2) symmetric points. In the presence of finite DM couplings and XXZ anisotropy, long-range order is predominantly present with a mix of both commensurate and incommensurate magnetic phases., D.K. thanks L. Gresista and T. Müller for related work on the PFFRGSolver.jl package74 used for the FRG calculations. The DMRG calculations are based on the Tenpy package.75 D.K. and C.H. acknowledge support from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation), Project No. 277146847, SFB 1238 (Project No. C03). Y.H. and D.M.K. acknowledge funding by the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Grant No. RTG 1995 within the Priority Program SPP 2244 “2DMP” and within Germany’s Excellence Strategy—Cluster of Excellence Matter and Light for Quantum Computing (ML4Q) Grant No. EXC 2004/1-390534769. This work was supported by the Max Planck-New York City Center for Nonequilibrium Quantum Phenomena. The numerical simulations were performed on the CHEOPS cluster at RRZK Cologne, the JURECA Booster76 and JUWELS cluster77 at the Forschungszentrum Juelich, and the Raven cluster at MPCDF of the Max Planck society.

Significance Micrometer-sized uniform four-layer (ABCA) rhombohedral graphene is realized by introducing a small twist angle between two bilayers of Bernal graphene. By means of scanning tunneling spectroscopy we observe an extremely sharp van Hove singularity of 3–5-meV half-width and a correlated many-body gap of 9.5 meV at neutrality, thus making small twisted double-bilayer graphene a unique platform to realize electronic correlations in the absence of a moiré potential. Furthermore, ABCA graphene domain walls display tunable topological edge states, of great interest in Floquet engineering., Atomically thin van der Waals materials stacked with an interlayer twist have proven to be an excellent platform toward achieving gate-tunable correlated phenomena linked to the formation of flat electronic bands. In this work we demonstrate the formation of emergent correlated phases in multilayer rhombohedral graphene––a simple material that also exhibits a flat electronic band edge but without the need of having a moiré superlattice induced by twisted van der Waals layers. We show that two layers of bilayer graphene that are twisted by an arbitrary tiny angle host large (micrometer-scale) regions of uniform rhombohedral four-layer (ABCA) graphene that can be independently studied. Scanning tunneling spectroscopy reveals that ABCA graphene hosts an unprecedentedly sharp van Hove singularity of 3–5-meV half-width. We demonstrate that when this van Hove singularity straddles the Fermi level, a correlated many-body gap emerges with peak-to-peak value of 9.5 meV at charge neutrality. Mean-field theoretical calculations for model with short-ranged interactions indicate that two primary candidates for the appearance of this broken symmetry state are a charge-transfer excitonic insulator and a ferrimagnet. Finally, we show that ABCA graphene hosts surface topological helical edge states at natural interfaces with ABAB graphene which can be turned on and off with gate voltage, implying that small-angle twisted double-bilayer graphene is an ideal programmable topological quantum material.

Background The burden of non-tuberculous mycobacterial (NTM) disease is increasing worldwide but still its diagnosis is delayed and it is mistaken as multidrug-resistant tuberculosis (MDR-TB).The present study was performed to develop a multiplex PCR assay for detection and identification of clinically most common NTM to the species level from pulmonary samples. Results Out of 50 isolates, 26 were identified as Mycobacterium kansasii (MK), 20 were identified as Mycobacterium abscessus (MA) and 4 were identified as Mycobacterium avium complex (MAC) through multiplex PCR and further confirmed by sequencing. Conclusion Our study showed that multiplex PCR assay is a simple, convenient, and reliable technique for detection and differential identification of major NTM species.

Resistive switching can be achieved in a Mott insulator by applying current/voltage, which triggers an insulator-metal transition (IMT). This phenomenon is key for understanding IMT physics and developing novel memory elements and brain-inspired technology. Despite this, the roles of electric field and Joule heating in the switching process remain controversial. Using nanowires of two archetypal Mott insulators—VO2 and V2O3 we unequivocally show that a purely non-thermal electrical IMT can occur in both materials. The mechanism behind this effect is identified as field-assisted carrier generation leading to a doping driven IMT. This effect can be controlled by similar means in both VO2 and V2O3, suggesting that the proposed mechanism is generally applicable to Mott insulators. The energy consumption associated with the non-thermal IMT is extremely low, rivaling that of state-of-the-art electronics and biological neurons. These findings pave the way towards highly energy-efficient applications of Mott insulators., Despite intensive research on the electrically driven insulator-to-metal transition, this phenomenon is not well understood. Using quasi 1D nanowires of two Mott insulators, the authors reveal the central role of defects in enabling a non-thermal doping driven insulator-to metal transition.

Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020; Aachen 1 Online-Ressource (IX, 305 Seiten) : Illustrationen, Diagramme (2020). = Dissertation, Rheinisch-Westfälische Technische Hochschule Aachen, 2020, The rapid evolution of electronics and their performance progress in the past decades call for extremely fast, scalable and power efficient memory technologies at the lowest cost. The dominating contemporary memory types of information technology (dynamic random access memory “DRAM” and Flash) shortly approach their physical and technological limits beyond which no further scaling is neither possible nor economically feasible. Hence, there is an urgent need for research of alternative memory and logic concepts. One novel memory class consists of a very simple two terminal device structure of an electrically active thin film sandwiched between two electrodes. After its working principle, it is called resistive switching random access memory (“ReRAM” or “RRAM”). Stored information is represented by the resistance of the electrically active thin film which can be switched between at least two distinguishable states. Macroscopically, resistive switching is controlled by applying an appropriate electrical potential to the device. Depending on the nanoscopic switching mechanism, the device responds with a volatile or a non-volatile change in resistance. In the past few years, ReRAM technology increased in popularity due to its promising device properties with excelling speed, scalability, energy efficiency and endurance. Nowadays, it is seen as one hot candidate to be able to compete both with DRAM as well as Flash and could even open new fields of computation towards neuromorphic circuits. In this thesis, the potential of (and control over) resistive switching mechanisms in undoped and chromium doped vanadium oxide thin films is explored. The material class of vanadium oxides is well known for its abundance of extraordinary electric and magnetic properties such as the presence of electron correlations and the formation of Mott-insulating states in VO2 and Cr-doped V2O3. Therefore, three different synthesis processes are established to determine the (crucial) influence of defect density on electrical switching properties. Low oxygen content thin films are reactively sputtered at room temperature (I) which result in amorphous undoped and Cr-doped VOx=1.5-2, at elevated temperatures (II, > 673 K) for crystalline Cr-doped V2±ΔyO3 and at room temperature with a post-reduction step (III), resulting in Cr-doped V2O3 with excellent stoichiometry. The three established synthesis processes generate largely different morphological and electrical properties in the same type of material. Moreover, resistive switching mechanisms and kinetics of ReRAM devices are investigated in a large temperature range between 80 K and 370 K. At least two volatile and at least four non-volatile types of switching mechanisms have been identified and have been classified with respect to crystallinity, defect density, Cr-doping, stack symmetry, device size and current compliance. Two volatile switching types could be tracked back to mechanisms such as crystallographic phase change in (Cr:)VO2 and a thermal feedback event in Cr:V2O3. Four non-volatile mechanisms may result as consequence of ionic drift, local valence change (e.g. by oxygen vacancies), thermochemical redox reactions and electron-electron correlations. Lastly, the resistive switching performance of ultra-thin (10 nm) Cr-doped V2O3 films is probed by local conducting atomic force microscopy in ultra-high vacuum. A mix of volatile and non-volatile characteristics can provide a multitude of operation principles in the same device. Finally, strong scaling potential below dimensions of less than 250 nm³ makes the material class attractive for selector as well as memory applications., Published by Aachen

A comprehensive study of the behavior of the Mott insulator ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ under electrical current drive is performed by combining two experimental probes: the macroscopic electrical transport and the microscopic x-ray diffraction. The resistivity, $\ensuremath{\rho}$, versus electric current density, $J$, and temperature, $T,\ensuremath{\rho}(J,T)$, resistivity map is drawn. In particular, the metastable state, induced between the insulating and the metallic thermodynamic states by current biasing ${\mathrm{Ca}}_{2}{\mathrm{RuO}}_{4}$ single crystals, is investigated. Such an analysis, combined with the study of the resulting ${\mathrm{RuO}}_{6}$ octahedra energy levels, reveals that a metallic crystal phase emerges in the metastable regime. The peculiar properties of such a phase, coexisting with the well-established orthorhombic insulating and tetragonal metallic phases, allow one to explain some of the unconventional and puzzling behaviors observed in the experiments as a negative differential resistivity.

Background Success of India’s TB control program relies on rapid case detection, monitoring, care and treatment of drug resistance. Patients on multidrug resistance (MDR) treatment are monitored by follow up cultures. Discordant results (culture and smear positive while capilia negative) are usually declared negative Mycobacterium tuberculosis complex (MTBC). This study was designed to understand the possible causes of discordant results. Methods The capilia kit was evaluated to test its utility among 4737 follow up MDR patients enrolled during a period of 1 year. A total of 889 were liquid culture positive, 3375 were negative and 473 were contaminated. Of the 889 cultures positive, 829 were found positive by ZN smear, capilia test and MTBDR plus assay. The cultures which gave a positive result on Mycobacterium Growth Indicator Tube 960 (MGIT 960) and ZN smear but were negative on capilia test with no growth on Brain Heart Infusion agar (BHI) were included in this study. The conflicting results of capilia were compared with other molecular techniques; MTBDR plus assay and DNA sequence analysis of MPT64 gene. Results Out of 889 culture positive, 60 (6.7%) were found positive on liquid culture and ZN smear but were negative on capilia. Of these 60 cultures, 10 (16.7%) were found positive by both MTBDR plus assay and PCR. The sequencing analysis revealed that all of the capilia negative isolates had mutations within the MPT64 gene. Conclusion Re-evaluation of culture positive but capilia negative isolates should be done before declaring them as Mycobacterium other than tuberculosis (MOTT) because such cases can act as chronic carriers of TB in the population which can lead to the rise of this lethal disease.

Out of equilibrium phenomena are a major issue of modern physics. In particular, correlated materials such as Mott insulators experience fascinating long-lived exotic states under a strong electric field. Yet, the origin of their destabilization by the electric field is not elucidated. Here we present a comprehensive study of the electrical response of canonical Mott insulators GaM4Q8 (M=V, Nb, Ta, Mo; Q=S, Se) in the context of a microscopic theory of electrical breakdown where in-gap states allow for a description in terms of a two-temperature model. Our results show how the nonlinearities and the resistive transition originate from a massive creation of hot electrons under an electric field. These results give new insights for the control of the long-lived states reached under an electric field in these systems which has recently open the way to new functionalities used in neuromorphic applications. Fil: Diener, P.. Universite de Nantes; Francia Fil: Janod, E.. Universite de Nantes; Francia Fil: Corraze, B.. Universite de Nantes; Francia Fil: Querré, M.. Universite de Rennes I. Institut Des Sciences Chimiques de Rennes.; Francia. Universite de Nantes; Francia Fil: Adda, C.. Universite de Nantes; Francia Fil: Guilloux Viry, M.. Universite de Rennes I. Institut Des Sciences Chimiques de Rennes.; Francia Fil: Cordier, S.. Universite de Rennes I. Institut Des Sciences Chimiques de Rennes.; Francia Fil: Camjayi, Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Ciudad Universitaria. Instituto de Física de Buenos Aires. Universidad de Buenos Aires. Facultad de Ciencias Exactas y Naturales. Instituto de Física de Buenos Aires; Argentina Fil: Rozenberg, Marcelo Javier. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Université Paris Sud; Francia Fil: Besland, M. P.. Universite de Nantes; Francia Fil: Cario, L.. Universite de Nantes; Francia

We explore the ground-state properties of the two-band Hubbard model with degenerate electronic bands, parametrized by nearest-neighbor hopping $t$, intra- and inter-orbital on-site Coulomb repulsions $U$ and $U^\prime$, and Hund coupling $J$, focusing on the case with $J>0$. Using Jastrow-Slater wave functions, we consider both states with and without magnetic/orbital order. Electron pairing can also be included in the wave function, in order to detect the occurrence of superconductivity for generic electron densities $n$. When no magnetic/orbital order is considered, the Mott transition is continuous for $n=1$ (quarter filling); instead, at $n=2$ (half filling), it is first order for small values of $J/U$, while it turns out to be continuous when the ratio $J/U$ is increased. A significant triplet pairing is present in a broad region around $n=2$. By contrast, singlet superconductivity (with $d$-wave symmetry) is detected only for small values of the Hund coupling and very close to half filling. When including magnetic and orbital order, the Mott insulator acquires antiferromagnetic order for $n=2$; instead, for $n=1$ the insulator has ferromagnetic and antiferro-orbital orders. In the latter case, a metallic phase is present for small values of $U/t$ and the metal-insulator transition becomes first order. In the region with $1, Comment: 11 pages, 10 figures

Dissertation, RWTH Aachen University, 2017; Aachen, 1 Online-Ressource (ii, 184 Seiten) : Illustrationen, Diagramme (2017). = Dissertation, RWTH Aachen University, 2017, Metal-semiconductor junctions are playing a crucial role for almost all semiconductor technology based devices. Here, the main drawback is the formation of a Schottky-barrier at the silicon surface which reduces the transmission of carriers. Conventional measures for a Schottky-barrier reduction are approaching their economical and physical limits. While the most common approach is based on doping by minimizing the effect oft he Schottky-barrier the here in this thesis studied concept focuses on the root of the Schottky-barrier. The incorporation of an ultra thin silicon nitride layer with a thickness of a few atoms (0.8nm) resolves the Fermi-level pinning at the silicon surface. These thermally grown silicon nitride layers offer an excellent and passivated tunneling barrier to suppress the metal induced silicon gap states . Both qualities lead to a decoupling of the Fermi-level and the huge interface state density so that the metal free carrier concentration dominates almost the silicon surface.Ultra thin silicon nitride layers with thicknesses between 0.6nm up to 3.7nm were thermally grown in an ammona atmosphere. These layers are characterized by their excellent thickness conformity on wafer scale, huge etching resistance and high density. The main pillars of this work are dopant-free: metal-oxide-silicon-field effect transistors (MOSFET), diodes, metal-insulator-silicon-solar celss and resonant tunneling diodes realized by ultra thin silicon nitride layers. The ambipolar characteristics of Schottky-barrier MOSFETs is suppressed by the incorporation of an ultra thin silicon nitride layer. Hence, for the first time unipolar N-type and P-type MOSFETs without contact doping are successfully fabricated. Furthermore, the combination of low and high work function metals with silicon nitride enable Schottky-Mott diodes which exhibit forward voltages of approximately 1V, reverse capacitance below 5pF and a temperature coefficient close to 2mV/K proving the existence of a Schottky-Mott diodes at the silicon-silicon nitride-metal. Increasing the insulator thickness reduces the forward voltage. Highly doped substrates lead to an one-side Schottky-Mott junction which exhibits Schottky diode behavior owing to the small junction depth. In addition, it could be demonstrated for the first time that holes can propagate on a long distance in a low doped substrate despite the fact of the carrier freeze-out state.Micro- and nanostencil masks are the keys to satisfy the claim of a highly pure fabrication procedure for Schottky-Mott diodes and increasing the overall yield. For the first time, metal-insulator-silicon solar cells made of ultra thin silicon nitride layer were fabricated and take advantage of the ohmic tunneling junction which demonstrated a fill factor of 0.74. Thinking of energy selective contacts, first-time resonant tunneling diodes consisting of silicon nitride-silicon nanocrystals-silicon nitride sandwiches were realized by crystallization prior to the second nitridation.In summary, this thesis confirmed on various domains of application the cost-effective, dopant-free and successful ultra thin silicon nitride interface engineering., Published by Aachen

Das Ziel der Arbeit ist es, die elektronische Struktur der Oberfläche der Übergangsmetalldichalkogenide 1T-TaSe2 und 1T-TiSe2 zu untersuchen. 1T-TaSe2 zeigt einen Metall-Isolator-Übergang der mit Mott-Physik in Verbindung gebracht wird und sich in der Volumenleitfähigkeit nicht nachweisen lässt. Zeit- und winkelaufgelöste Photoelektronenspektroskopie wurde genutzt, um die Dynamik der elektronischen Struktur an der Oberfläche von 1T-TaSe2 impulsaufgelöst nach Anregung mit einem Infrarot-Laserpuls zu untersuchen. Es konnten zwei zeitlich getrennte Abläufe beobachtet werden: Zum einen der quasi sofortige Verlust der elektronischen Ordnung im Bereich der Zeitauflösung von t < 40 fs und zum anderen die kohärente Unterdrückung der periodischen Gitterverzerrung auf der Zeitskala der Oszillationsfrequenz eines kohärenten Phonons. Die schnellen Reaktionszeiten zeigen, dass tatsächlich elektronische Wechselwirkung die Ursache dieses Metall-Isolator-Übergangs ist. Des Weiteren wurde die Tiefenabhängigkeit der Ladungsdichtewelle in 1T-TaSe2 bei tiefen Temperaturen anhand der Aufspaltung der Ta-4f-Rumpfniveaus von 1T-TaSe2 studiert. Die Analyse zeigt eine Vergrößerung der Aufspaltung von 40 meV an der Oberfläche und damit eine Stärkung der Ladungsdichtewelle. Die Größe der Aufspaltung korreliert mit der des thermischen Metall-Isolator-Übergangs, welcher folglich lediglich an der Oberfläche des Materials auftritt. Im zweiten Teil der Arbeit wird der gezielte Einfluss von Elektronendotierung auf die elektronische Bandstruktur an der Oberfläche des Ladungsdichtewelle-Materials 1T-TiSe2 mit winkelauflösender Photoelektronenspektroskopie analysiert. Im Detail wird der Einfluss der zusätzlichen Ladungsträger auf die Ladungsdichtewelle untersucht. Bei hohen Elektronendotierung konnte eine vollständige energetische Entkopplung der obersten Einheitszelle nachgewiesen werden. The goal of the present work is to investigate the electronic structure of the surfaces of the transition-metal dichalcogenides 1T-TaSe2 and 1T-TiSe2. In particular the modification of the electronic structure by enhanced interactions at the surface is studied. 1T-TaSe2 shows a pronounced metal-to-insulator transition, which may be related to Mott physics and is not observable in bulk sensitive transport measurements. The first part of this work investigates the origin and the spatial extend of this transition. Time- and angle-resolved extreme ultraviolet photoelectron spectroscopy is used to determine the momentum-dependent electronic structure dynamics in the layered material 1T-TaSe2. Extracted spectroscopic order parameters display a global two-time-scale dynamics indicating a quasi-instantaneous loss of the electronic orders and a subsequent coherent suppression of the lattice distortion on a time scale related to the frequency of the charge-density-wave amplitude mode. The fast reaction of the system reveals electronic interplay as the driving force to this phase transition. Moreover, the depth dependency of the charge-density wave in 1T-TaSe2 at low temperatures is studied by hard X-ray photoelectron spectroscopy. The additional charge- density-wave-induced splitting of the Ta-4f-core levels, which serves as an excellent order parameter for the strength of the charge-density wave, is investigated. The findings corroborate the idea of a surface confined metal-to-insulator transition triggered by an enhancement of the charge-density wave at the surface. The second part of the present work focuses on the modification of the electronic structure at the surface of 1T-TiSe2 enforced by electron doping. Angle-resolved photo- electron spectroscopy is used to investigate the influence on the charge-density wave in this material in detail. At high doping levels the charge-density wave vanishes and the complete electronically decoupling of the uppermost layer is observed.

The phase diagram of a half-filled hard core boson two-leg ladder in a flux is investigated by means of numerical simulations based on the Density Matrix Renormalization Group (DMRG) algorithm and bosonization. We calculate experimentally accessible observables such as the momentum distribution, as well as rung current, density wave and bond-order wave correlation functions, allowing us to identify the Mott Meissner and Mott Vortex states. We follow the transition from commensurate Meissner to incommensurate Vortex state at increasing interchain hopping till the critical value [Piraud et al. Phys. Rev. B v. 91, p. 140406 (2015)] above which the Meissner state is stable at any flux. For flux close to $\pi$, and below the critical hopping, we observe the formation of a second incommensuration in the Mott Vortex state that could be detectable in current experiments., Comment: RevTeX 4, 5 pages + 8 pages supplemental, 6 EPS figures; (v2) references added, corrected the discussion of the Meissner state at high interchain hopping

In this thesis we investigated magnetic excitations in the iridate compound Sr2IrO4. As a layered strongly correlated system it can be described by the two-dimensional one-band Hubbard model, describing interacting particles in effective spin-1/2 states. Based on the previously calculated band structure model, it becomes an effective model with one free parameter, the one-site interaction strength U. Using Green's functions at the mean field level, we calculated the dynamic magnetic susceptibility and thereby the spin wave dispersion. We compared the spin wave dispersion with resonant inelastic X-ray scattering experiments and used it to fit the Hubbard interaction strength U. We found the t-t'-t''-U-Hubbard model based on the band structure energies to provide a good description of the spin wave dispersion for U=1.1eV.

Important paradigms of pulmonary disease with nontuberculous mycobacteria (NTM) are currently shifting based on an increasing attention within the field of cystic fibrosis (CF). These shifts are likely to benefit the management of all patients with pulmonary NTM, regardless of underlying pathology. Currently several key areas are being revised: The first outbreak of human NTM transmission has been proven and new evidence of biofilm growth in vivo has been demonstrated. A better understanding of the clinical impact of NTM infection has led to increased diagnostic vigilance and new recommendations for lung transplantation are under way. While recent changes have reinvigorated the interest in NTM disease, the challenge remains, whether such advances can be successfully translated into improved management and care.

Revealing the nature of charge excitations in strongly correlated electron systems is crucial to understanding their exotic properties. Here we use broadband ultrafast pump-probe spectroscopy in the visible range to study low-energy transitions across the Mott-Hubbard gap in the orbitally ordered insulator YVO 3 . Separating thermal and nonthermal contributions to the optical transients, we show that the total spectral weight of the two lowest peaks is conserved, demonstrating that both excitations correspond to the same multiplet. The pump-induced transfer of spectral weight between the two peaks reveals that the low-energy one is a Hubbard exciton, i.e., a resonance or a nearly bound state between a doublon and a holon. Finally, we speculate that the pump-driven spin disorder can be used to quantify the kinetic energy gain of the excitons in a ferromagnetic environment.

Objective To determine the prevalence of non tuberculosis mycobacteria (NTM) among new and previously treated tuberculosis (TB) patients in Nigeria. Methods It was a retrospective study. A total of 102 sputum smear positive samples/culture isolates from pulmonary TB patients (41 new smear positive and 61 smear positive retreatment cases) were sent to the Institute of Tropical Medicine, Antwerp Belgium between 2007-2009. Data on patients' characteristics were retrieved from their treatment cards. Results Among the 102 samples, 25 isolates results (20 were culture negative while 5 were contaminated) were excluded from the study. Data were available for 77 mycobacterium isolates. 70 (90.9%) were identified as Mycobacterium tuberculosis and 7 (9.1%) as atypical mycobacteria. Among the atypical mycobacteria, three of them were Mycobacterium fortuitum, two Mycobacterium intracellulare and two Mycobacterium chelonae. Of the seven isolates with atypical mycobacteria, 4 (57.1%) were from previously treated patients, while 3 (42.9%) were new sputum positive patients. There was no statistically significant difference in NTM infection between new and previously treated pulmonary TB patients (P =0.97). Conclusions The study shows the involvement of atypical mycobacterium in pulmonary infection in both new and previously treated TB patients. Therefore, there is a need to carry out culture and drug susceptibility testing in all pulmonary TB patients especially those who had failed conventional DOTS treatment to rule out NTM infections.

Strong correlation effects, which are often associated to the approach to a Mott insulating state, in some cases may be observed even far from half-filling. This typically happens whenever the inter-site Coulomb repulsion induces a tendency towards charge ordering, an effect that confines the electrons, and in turn favors local moment formation, i.e. Mott localization. A distinct intermediate regime then emerges as a precursor of such a Wigner-Mott transition, which is characterized by both charge and spin correlations, displaying large mass enhancements and strong renormalizations of other Fermi liquid parameters. Here we present a careful study of a quarter filled extended Hubbard model - a simple example where such physics can be studied in detail, and discuss its relevance for the understanding of the phenomenology of low-density two dimensional electron gases., 11 pages, 9 figures

Un experimento fue conducido para estudiar los efectos de enzimas de celulosa y bacterias de ácido láctico sobre las características de fermentación, composición química, valor nutritivo y rendimiento animal de ensilaje de pasto elefante enano cv. Mott. Se realizaron cinco preparativos: melaza (control), melaza y enzimas de celulosa, enzimas de celulosas, concentrado de bacterias de ácido láctico y melaza y concentrado de bacterias de ácido láctico. Se encontraron diferencias significativas (P