A DFT study of electron-phonon interactions for theC2CNandVNNBdefects in hexagonal boron nitride: investigating the role of the transition dipole direction.

Quantum emitters in two-dimensional hexagonal boron nitride (h-BN) have generated significant interest due to observations of ultra-bright emission made at room temperature. The expectation that solid-state emitters exhibit broad zero-phonon lines at elevated temperatures has been put in question by recent observations of Fourier transform (FT) limited photons emitted from h-BN flakes at room temperature. All decoupled emitters produce photons that are directed in-plane, suggesting that the dipoles are perpendicular to the h-BN plane. Motivated by the promise of an efficient and scalable source of indistinguishable photons that can operate at room temperature, we have developed an approach using density functional theory (DFT) to determine the electron-phonon coupling for defects that have in- and out-of-plane transition dipole moments. Our DFT calculations reveal that the transition dipole for theC2CNdefect is parallel to the h-BN plane, and for theVNNBdefect is perpendicular to the plane. We calculate both the phonon density of states and the electron-phonon matrix elements associated with the h-BN defective structures. We find no indication that an out-of-plane transition dipole by itself will result in the low electron-phonon coupling that is expected to produce FT-limited photons at room temperature. Our work provides direction to future DFT software developments and adds to the growing list of calculations relevant to researchers in the field of solid-state quantum information processing.

Thermo-electro-optical properties of seamless metallic nanowire networks for transparent conductor applications.

Rapid reaction time, high attainable temperatures, minimum operating voltage, excellent optical transmittance, and tunable sheet resistance are all desirable properties of transparent conductors, which are important thin-film components in numerous electronic devices. A seamless nanowire network (NWN) refers to a structure composed of nanowires that lack interwire contact junctions, resulting in a continuous and uninterrupted network arrangement. This seamless nature leads to unique properties, including high conductivity and surface area-to-volume ratios, which make it a promising candidate for a vast application range in nanotechnology. Here, we have conducted an in-depth computational investigation to study the thermo-electro-optical properties of seamless nanowire networks and understand their geometrical features using in-house computational implementations and a coupled electrothermal model built in COMSOL Multiphysics software. Sheet resistance calculations were performed using Ohm's law combined with Kirchhoff circuit laws for a random resistor network and compared with those obtained employing COMSOL. In this work, aluminium, gold, copper, and silver nanowires are the materials of choice for testing the transparent conduction performance of our systems. We have studied a wide range of tuning parameters, including the network area fraction, the width-to-depth aspect ratio, and the length of the nanowire segments. We obtained corresponding figures of merit (optical transmittance versus sheet resistance) and temperature distributions to provide a complete characterization of the performance of real-world transparent conductors idealized with seamless NWNs. Our analysis accounted for the thermo-electro-optical responses of the NWNs and the inspection of various controlling parameters depending on system design considerations to shed light on how the electrical transport, optical qualities, and thermal management of these systems can be optimized.

Decoding the conductance of disordered nanostructures: a quantum inverse problem.

Obtaining conductance spectra for a concentration of disordered impurities distributed over a nanoscale device with sensing capabilities is a well-defined problem. However, to do this inversely, i.e., extracting information about the scatters from the conductance spectrum alone, is not an easy task. In the presence of impurities, even advanced techniques of inversion can become particularly challenging. This article extends the applicability of a methodology we proposed capable of extracting composition information about a nanoscale sensing device using the conductance spectrum. The inversion tool decodes the conductance spectrum to yield the concentration and nature of the disorders responsible for conductance fluctuations in the spectra. We present the method for simple one-dimensional systems like an electron gas with randomly distributed delta functions and a linear chain of atoms. We prove the generality and robustness of the method using materials with complex electronic structures like hexagonal boron nitride, graphene nanoribbons, and carbon nanotubes. We also go on to probe distribution of disorders on the sublattice structure of the materials using the proposed inversion tool.

Finite-size correction scheme for supercell calculations in Dirac-point two-dimensional materials.

Modern electronic structure calculations are predominantly implemented within the super cell representation in which unit cells are periodically arranged in space. Even in the case of non-crystalline materials, defect-embedded unit cells are commonly used to describe doped structures. However, this type of computation becomes prohibitively demanding when convergence rates are sufficiently slow and may require calculations with very large unit cells. Here we show that a hitherto unexplored feature displayed by several 2D materials may be used to achieve convergence in formation- and adsorption-energy calculations with relatively small unit-cell sizes. The generality of our method is illustrated with Density Functional Theory calculations for different 2D hosts doped with different impurities, all of which providing accuracy levels that would otherwise require enormously large unit cells. This approach provides an efficient route to calculating the physical properties of 2D systems in general but is particularly suitable for Dirac-point materials doped with impurities that break their sublattice symmetry.

Efeito do tipo de alimentação de cães saudáveis sobre análises clínicas e aspectos comportamentais / Effect of the diet of healthy dogs on clinical analysis and behavioral aspects

Objetivou-se estudar o efeito da alimentação caseira, da ração comercial a granel e da ração comercial fechada para cães adultos sobre análises clínicas e aspectos comportamentais de ingestão das dietas. O delineamento experimental foi inteiramente ao acaso, com três tratamentos, sendo o tratamento 1 constituído de dieta caseira, o tratamento 2 por ração a granel tipo premium, e o tratamento 3 por ração comercial fechada do tipo premium. Foram utilizados três cães em cada um dos tratamentos, totalizando nove animais. As variáveis analisadas foram: teste de glicemia, odor fecal, escore fecal, volume fecal, análise química da urina (pH urinário, presença de proteína, sangue, corpos cetônicos, bilirrubina e glicose), avaliação visual do pelo e consumo voluntário da dieta. Os cães submetidos à dieta caseira apresentaram menor resultado de glicemia sanguínea (83,90). A urina apresentou pH mais alcalino para cães que receberam a ração a granel (8,06). Cães da dieta caseira apresentaram o mais alto escore para a qualidade do pelo. Houve um maior volume das fezes de cães que receberam a dieta de ração a granel. Cães que receberam a dieta de alimentação caseira ou a ração comercial fechada apresentaram um consumo total do alimento em menos de 10 minutos. A maioria dos resultados foi semelhante entre a dieta caseira e a ração fechada do tipo premium. A ração a granel apresentou os piores resultados.(AU)

The objective of this study was to study the effect of homemade feed, commercial feed in bulk, and closed commercial feed for adult dogs on clinical analysis and behavioral aspects of diet intake. The experimental design was completely randomized with three treatments: homemade diet, bulk premium type feed, and closed commercial feed of the premium type. Three dogs were observed in each of the treatments, totaling nine animals. The variables analyzed were: blood glycemia, fecal odor, fecal score, fecal volume, chemical urine analysis (urinary pH, presence of protein, blood, ketone bodies, bilirubin and glucose), visual evaluation of hair and voluntary dietary intake. Dogs submitted to a home diet showed lower blood glucose results (83.90). Urine was more alkaline pH for dogs that received the bulk feed (8.06). Dogs from the homemade feed presented the highest score for hair quality. There was a greater volume of feces from dogs that received the diet of bulk feed. Dogs that received the diet of home feed or closed commercial feed showed a total consumption of food in less than ten minutes. Most of the results were similar between the homemade feed and the closed-type premium diet. The dogs bulk feed presented the worst results.(AU)

Co-percolation to tune conductive behaviour in dynamical metallic nanowire networks.

Nanowire networks act as self-healing smart materials, whose sheet resistance can be tuned via an externally applied voltage stimulus. This memristive response occurs due to modification of junction resistances to form a connectivity path across the lowest barrier junctions in the network. While most network studies have been performed on expensive noble metal nanowires like silver, networks of inexpensive nickel nanowires with a nickel oxide coating can also demonstrate resistive switching, a common feature of metal oxides with filamentary conduction. However, networks made from solely nickel nanowires have high operation voltages which prohibit large-scale material applications. Here we show, using both experiment and simulation, that a heterogeneous network of nickel and silver nanowires allows optimization of the activation voltage, as well as tuning of the conduction behavior to be either resistive switching, memristive, or a combination of both. Small percentages of silver nanowires, below the percolation threshold, induce these changes in electrical behaviour, even for low area coverage and hence very transparent films. Silver nanowires act as current concentrators, amplifying conductivity locally as shown in our computational dynamical activation framework for networks of junctions. These results demonstrate that a heterogeneous nanowire network can act as a cost-effective adaptive material with minimal use of noble metal nanowires, without losing memristive behaviour that is essential for smart sensing and neuromorphic applications.

Probing optical spectra of carbon nanotubes with external fields.

Here we present a theoretical study of the interplay between electronic and optical properties of carbon nanotubes. External perturbations such as electric and magnetic fields are applied on the systems which are probed by parallel and perpendicularly polarized light sources. We demonstrate that the optical transitions can be fully controlled by the fields. Likewise, extra optical excitations can be induced in different energy ranges of the absorption spectra due to degeneracy splitting of the states. In most of the theoretical works developed in this realm, a remarkable discrepancy between the results obtained via the tight binding approximation and first principle calculations is found. The disagreement can be enhanced when external perturbation fields act on the tubes forcing the realization of demanding charge self-consistent calculations. In this sense, we profit from novel parametrization schemes for the tight binding approach to describe the optical response of nanotubes of any diameter size and with similar accuracy to density functional theory.

[Cervical cancer and DNA microarrays: tumour marker identification]. / Microarreglos de ADN y cáncer cervicouterino: identificación de marcadores tumorales.

Microarray technology has remarkably accelerated the understanding of the molecular events of neoplasias. By means of gene expression profiles, a molecular subclassification of cancer patients and the identification of thousand of genes involved in this pathology have been achieved. Herein, the general use of DNA microarrays in cervical cancer tumorigenesis is reviewed. Finally, putative molecular tumour markers as useful factors in diagnosis, prognosis, and tailor-made therapy for this disease are proposed.

Modeling the effect of dispersed doping agents in carbon nanotubes.

Theoretical studies of how the electronic properties of a nanotube are affected by one isolated doping agent is commonly done by ab-initio electronic structure calculations. Although these calculations are essential to understand how the system responds to doping, they are by no means sufficient, since, in reality, a large disordered array of doping agents must be considered. It is then necessary to combine ab-initio techniques with less-computationally-demanding methods if one wishes to describe the real effect of doping on the electronic properties of nanotubes. Here we propose a method that makes use of ab-initio results for single impurities as an input to generate the parameters of the less-demanding tight-binding technique. The method is based on suitable sum rules for the Green functions of the impurity-free nanotubes and does not rely on any fitting scheme. The resulting parametrization allows us to describe disordered systems without losing the important contributions due to charge transfer and screening. Transport properties are subsequentially investigated.

Electric field effects on the energy spectrum of carbon nanotubes.

Electronic properties of straight carbon nanotubes under an external electric are investigated, following a single-π-orbital tight binding approximation. Metal-insulator transitions in metallic tubes and energy gap modulations in semiconducting ones were found due to the action of the electric field. Reductions in the tube symmetry operations induced by the field are manifested in the energy spectrum as a function of the angle determined by the field direction and equivalent in-plane atomic positions along the circumferential direction. We find that particular energies in the spectra exhibit a periodic oscillation with this dephasing angle. The range and position of those energies, as well the amplitude of the oscillation, can be properly manipulated by changing the strength and direction of the applied electric field.