Thin-layer agar for detection of resistance to rifampicin, ofloxacin and kanamycin in Mycobacterium tuberculosis isolates

BACKGROUND: In low-income countries there is a great need for economical methods for testing the susceptibility of Mycobacterium tuberculosis to antibiotics. OBJECTIVE: To evaluate the thin-layer agar (TLA) for rapid detection of resistance to rifampicin (RMP), ofloxacin (OFX) and kanamycin (KM) in M. tuberculosis clinical isolates and to determine the sensitivity, specificity and time to positivity compared to the gold standard method. METHODS: One hundred and forty-seven clinical isolates of M. tuberculosis were studied. For the TLA method, a quadrant Petri plate containing 7H11 agar with RMP, OFX and KM was used. Results were compared to the Bactec MGIT960 for RMP and the proportion method for OFX and KM. RESULTS: The sensitivity and specificity for RMP and OFX were 100% and for KM they were 100% and 98.7%, respectively. The use of a TLA quadrant plate enables the rapid detection of resistance to the three anti-tuberculosis drugs RMP, OFX and KM in a median of 10 days. CONCLUSION: TLA was an accurate method for the detection of resistance in the three drugs studied. This faster method is simple to perform, providing an alternative method when more sophisticated techniques are not available in low-resource settings

Genuine converging solution of self-consistent field equations for extended many-electron systems

Calculations of the ground state of inhomogeneous many-electron systems involve a solving of the Poisson equation for Coulomb potential and the Schroedinger equation for single-particle orbitals. Due to nonlinearity and complexity this set of equations, one believes in the iterative method for the solution that should consist in consecutive improvement of the potential and the electron density until the self-consistency is attained. Though this approach exists for a long time there are two grave problems accompanying its implementation to infinitely extended systems. The first of them is related with the Poisson equation and lies in possible incompatibility of the boundary conditions for the potential with the electron density distribution. The analysis of this difficulty and suggested resolution are presented for both infinite conducting systems in jellium approximation and periodic solids. It provides the existence of self-consistent solution for the potential at every iteration step due to realization of a screening effect. The second problem results from the existence of continuous spectrum of Hamiltonian eigenvalues for unbounded systems. It needs to have a definition of Hilbert space basis with eigenfunctions of continuous spectrum as elements, which would be convenient in numerical applications. The definition of scalar product specifying the Hilbert space is proposed that incorporates a limiting transition. It provides self-adjointness of Hamiltonian and, respectively, the orthogonality of eigenfunctions corresponding to the different eigenvalues. In addition, it allows to normalize them effectively to delta-function and to prove in the general case the orthogonality of the 'right' and 'left' eigenfunctions belonging to twofold degenerate eigenvalues.Comment: 12 pages. Reported on Interdisciplinary Workshop "Nonequilibrium Green's Functions III", August 22 - 26, 2005, University Kiel, Germany. To be published in Journal of Physics: Conference Series, 2006; Typos in Eqs. (37), (53) and (54) are corrected. The content of the footnote is changed. Published version available free online at http://www.iop.org/EJ/abstract/1742-6596/35/1/01

The Nature of Electronic States in Atomically Thin MoS2 Field-Effect Transistors

We present low temperature electrical transport experiments in five field effect transistor devices consisting of monolayer, bilayer and trilayer MoS2 films, mechanically exfoliated onto Si/SiO2 substrate. Our experiments reveal that the electronic states in all films are localized well up to the room temperature over the experimentally accessible range of gate voltage. This manifests in two dimensional (2D) variable range hopping (VRH) at high temperatures, while below \sim 30 K the conductivity displays oscillatory structures in gate voltage arising from resonant tunneling at the localized sites. From the correlation energy (T0) of VRH and gate voltage dependence of conductivity, we suggest that Coulomb potential from trapped charges in the substrate are the dominant source of disorder in MoS2 field effect devices, which leads to carrier localization as well.Comment: 10 pages, 5 figures; ACS Nano (2011

Solitonic approach to the dimerization problem in correlated one-dimensional systems

Using exact diagonalizations we consider self-consistently the lattice distortions in odd Peierls-Hubbard and spin-Peierls periodic rings in the adiabatic harmonic approximation. From the tails of the inherent spin soliton the dimerization d_\infty of regular even rings is found by extrapolations to infinite ring lengths. Considering a wide region of electron-electron onsite interaction values U>0 compared with the band width 4t_0 at intermediately strong electron-phonon interaction g, known relationships obtained by other methods are reproduced and/or refined within one unified approach: such as the maximum of d_\infty at U \simeq 3 t_0 for g \simeq 0.5 and its shift to zero for g \to g_c \approx 0.7. The hyperbolic tangent shape of the spin soliton is retained for any U and g <~ 0.6. In the spin-Peierls limit the d_\infty are found to be in agreement with results of DMRG computations.Comment: 4 pages, 4 figures, Physical Review B, Rapid Communications, v. 56 (1997) accepte

Control of crystallinity of vinylene-linked two-dimensional conjugated polymers by rational monomer design

The interest in two-dimensional conjugated polymers (2D CPs) has increased significantly in recent years. In particular, vinylene-linked 2D CPs with fully in-plane sp2-carbon-conjugated structures, high thermal and chemical stability, have become the focus of attention. Although the Horner-Wadsworth-Emmons (HWE) reaction has been recently demonstrated in synthesizing vinylene-linked 2D CPs, it remains largely unexplored due to the challenge in synthesis. In this work, we reveal the control of crystallinity of 2D CPs during the solvothermal synthesis of 2D-poly(phenylene-quinoxaline-vinylene)s (2D-PPQVs) and 2D-poly(phenylene-vinylene)s through the HWE polycondensation. The employment of fluorinated phosphonates and rigid aldehyde building blocks is demonstrated as crucial factors in enhancing the crystallinity of the obtained 2D CPs. Density functional theory (DFT) calculations reveal the critical role of the fluorinated phosphonate in enhancing the reversibility of the (semi)reversible C−C single bond formation

Interfacial charge transfer in nanoscale polymer transistors

Interfacial charge transfer plays an essential role in establishing the relative alignment of the metal Fermi level and the energy bands of organic semiconductors. While the details remain elusive in many systems, this charge transfer has been inferred in a number of photoemission experiments. We present electronic transport measurements in very short channel ($L < 100$ nm) transistors made from poly(3-hexylthiophene) (P3HT). As channel length is reduced, the evolution of the contact resistance and the zero-gate-voltage conductance are consistent with such charge transfer. Short channel conduction in devices with Pt contacts is greatly enhanced compared to analogous devices with Au contacts, consistent with charge transfer expectations. Alternating current scanning tunneling microscopy (ACSTM) provides further evidence that holes are transferred from Pt into P3HT, while much less charge transfer takes place at the Au/P3HT interface.Comment: 19 preprint pages, 6 figure

Establishing a meaningful human rights due diligence process for corporations : learning from experience of human rights impact assessment

The United Nations Special Representative of the Secretary-General on Business and Human Rights, Professor John Ruggie, has constructed a new international framework, which is set to become the cornerstone for all action on human rights and business at the international level. The principle of human rights due diligence (HRDD) is the central component of the corporate duty to respect human rights within that framework. This article argues that Ruggie's HRDD principle contains the majority of the core procedural elements that a reasonable human rights impact assessment (HRIA) process should incorporate. It is likely that the majority of corporations will adopt HRIA as a mechanism for meeting their due diligence responsibilities. However, in the context of the contentious debate around corporate human rights performance, the current state of the art in HRIA gives rise to concerns about the credibility and robustness of likely practice. Additional requirements are therefore essential if HRDD is to have a significant impact on corporate human rights performance – requirements in relation to transparency; external participation and verification; and independent monitoring and review

Fully sp²‐carbon‐linked crystalline two‐dimensional conjugated polymers: insight into 2D poly(phenylenecyanovinylene) formation and their optoelectronic properties

Cyano‐substituted polyphenylene vinylenes (PPVs) have been in the focus of research for several decades due to their interesting optoelectronic properties and potential applications in organic electronics. With the advent of organic two‐dimensional (2D) crystals, the question arose how the chemical and optoelectronic advantages of PPVs evolve in 2D compared to their linear counterparts. In this work, we present the efficent synthesis of two novel 2D fully sp²‐carbon‐linked crystalline PPVs and investigate the essentiality of inorganic bases for their catalytic formation. Notably, among all bases screened, cesium carbonate (Cs₂CO₃) plays a crucial role and enables reversibility in the first step with subsequent structure locking by formation of a C=C double bond to maintain crystallinity, which is supported by density functional theory (DFT) calculation. We propose a quantifiable energy diagram of a “quasi‐reversible reaction” which allows to identify further suitable C‐C bond formation reactions for 2D polymerizations. Moreover, we delineate the narrowing of the HOMO‐LUMO gap by expanding conjugation into two dimensions. To enable environmentally benign processing, we further perform the post‐modification of 2D PPVs, which renders stable dispersions in the aqueous phase

Self-consistent solution of Kohn-Sham equations for infinitely extended systems with inhomogeneous electron gas

The density functional approach in the Kohn-Sham approximation is widely used to study properties of many-electron systems. Due to the nonlinearity of the Kohn-Sham equations, the general self-consistence searching method involves iterations with alternate solving of the Poisson and Schr\"{o}dinger equations. One of problems of such an approach is that the charge distribution renewed by means of the Schr\"{o}dinger equation solution does not conform to boundary conditions of Poisson equation for Coulomb potential. The resulting instability or even divergence of iterations manifests itself most appreciably in the case of infinitely extended systems. The published attempts to deal with this problem are reduced in fact to abandoning the original iterative method and replacing it with some approximate calculation scheme, which is usually semi-empirical and does not permit to evaluate the extent of deviation from the exact solution. In this work, we realize the iterative scheme of solving the Kohn-Sham equations for extended systems with inhomogeneous electron gas, which is based on eliminating the long-range character of Coulomb interaction as the cause of tight coupling between charge distribution and boundary conditions. The suggested algorithm is employed to calculate energy spectrum, self-consistent potential, and electrostatic capacitance of the semi-infinite degenerate electron gas bounded by infinitely high barrier, as well as the work function and surface energy of simple metals in the jellium model. The difference between self-consistent Hartree solutions and those taking into account the exchange-correlation interaction is analyzed. The case study of the metal-semiconductor tunnel contact shows this method being applied to an infinitely extended system where the steady-state current can flow.Comment: 38 pages, 9 figures, to be published in ZhETF (J. Exp. Theor. Phys.