Bloch oscillations in organic and inorganic polymers.

The transport of polarons above the mobility threshold in organic and inorganic polymers is theoretically investigated in the framework of a one-dimensional tight-binding model that includes lattice relaxation. The computational approach is based on parameters for which the model Hamiltonian suitably describes different polymer lattices in the presence of external electric fields. Our findings show that, above critical field strengths, a dissociated polaron moves through the polymer lattice as a free electron performing Bloch oscillations. These critical electric fields are considerably smaller for inorganic lattices in comparison to organic polymers. Interestingly, for inorganic lattices, the free electron propagates preserving charge and spin densities' localization which is a characteristic of a static polaron. Moreover, in the turning points of the spatial Bloch oscillations, transient polaron levels are formed inside the band gap, thus generating a fully characterized polaron structure. For the organic case, on the other hand, no polaron signature is observed: neither in the shape of the distortion-those polaron profile signatures are absent-nor in the energy levels-as no such polaron levels are formed during the simulation. These results solve controversial aspects concerning Bloch oscillations recently reported in the literature and may enlighten the understanding about the charge transport mechanism in polymers above their mobility edge.

Impact of the electron-phonon coupling symmetry on the polaron stability and mobility in organic molecular semiconductors.

The influence of the interplay between symmetric and antisymmetric inter-molecular electron-phonon (e-ph) coupling mechanisms on the polaron stability and mobility in organic semiconductors has been theoretically investigated at a molecular level. A semi-empirical Holstein-Peierls model is used which in addition to the symmetric and antisymmetric inter-molecular e-ph interactions also includes an antisymmetric intra-molecular e-ph coupling. Our results show that the symmetric e-ph coupling plays the role of destabilizing the polaron as a result of temperature induced phonons that, via the symmetric coupling, affects the charge distribution of the polaron. Considering this kind of coupling, the parameter space for which the polaron is dynamically stable is strongly temperature-dependent. For the combination of symmetric e-ph coupling strength and temperature, which results in a stable polaron, the velocity of the polaron, and therefore also the charge carrier mobility, is not affected by the symmetric e-ph coupling strength.

Modeling the Emission Spectra of Organic Molecules: A Competition between Franck-Condon and Nuclear Ensemble Methods.

The emission spectra of flexible and rigid organic molecules are theoretically investigated in the framework of the Franck-Condon (FC) and nuclear ensemble (NE) approaches, both of which rely on results from density functional theory but differ in the way vibrational contributions are taken into account. Our findings show that the emission spectra obtained using the NE approach are in better agreement with experiment than the ones produced by FC calculations considering both rigid and flexible molecules. Surprisingly, the description of a suitable balance between the vibronic progression and the emission spectra envelope shows dependency on the initial sampling for the NE calculations which must be judiciously selected. Our results intend to provide guidance for a better theoretical description of light emission properties of organic molecules with applications in organic electronic devices.

Impact of the Electron-Phonon Interactions on the Polaron Dynamics in Graphene Nanoribbons.

The influence of the electron-phonon (e-ph) interactions on the filed-included polaron dynamics in armchair graphene nanoribbons (GNRs) is theoretically investigated in the scope of a two-dimensional tight-binding model. The results show that the localization of the polaronic charge increases when the strength of e-ph coupling also increases. Consequently, the polaron saturation velocity decreases for higher e-ph coupling strengths. Interestingly, the interplay between the e-ph coupling strength and the GNR width changes substantially the polaron dynamics properties.

Impurity effects on polaron-exciton formation in conjugated polymers.

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger model and the extended Hubbard model, the collision of two oppositely charged polarons is investigated under the influence of impurity effects using a non-adiabatic evolution method. Results show that electron-electron interactions have direct influence on the charge distribution coupled to the polaron-exciton lattice defect. Additionally, the presence of an impurity in the collisional process reduces the critical electric field for the polaron-exciton formation. In the small electric field regime, the impurity effects open three channels and are of fundamental importance to favor the polaron-exciton creation. The results indicate that the scattering between polarons in the presence of impurities can throw a new light on the description of electroluminescence in conjugated polymer systems.

Polaron Diffusion in Pentathienoacene Crystals.

Molecular crystals have been used as prototypes for studying the energetic and dynamic properties of charge carriers in organic electronics. The growing interest in oligoacenes and fused-ring oligothiophenes in the last two decades is due, in particular, to the success achieved in conceiving pentacene-based organic photovoltaic devices. In the present work, a one-dimensional Holstein-Peierls model is designed to study the temperature-dependent polaron transport in pentathienoacene (PTA) lattices. The tight-binding Hamiltonian employed here takes into account intra and intermolecular electron-lattice interactions. Results reveal that polarons in PTAs can be stable structures even at high temperatures, about 400 K. During the dynamical process, these charge carriers present a typical 1D random walk diffusive motion with a low activation energy of 13 meV and a room temperature diffusivity constant of 1.07 × 10-3 cm2 s-1. Importantly, these critical values for the polaron diffusion and activation energy are related to the choice of model parameters, which are adopted to describe pristine lattices.

Tuning Penta-Graphene Electronic Properties Through Engineered Line Defects.

Penta-graphene is a quasi-two-dimensional carbon allotrope consisting of a pentagonal lattice in which both sp2 and sp3-like carbons are present. Unlike graphene, penta-graphene exhibits a non-zero bandgap, which opens the possibility of its use in optoelectronic applications. However, as the observed bandgap is large, gap tuning strategies such as doping are required. In this work, density functional theory calculations are used to determine the effects of the different number of line defects of substitutional nitrogen or silicon atoms on the penta-graphene electronic behavior. Our results show that this doping can induce semiconductor, semimetallic, or metallic behavior depending on the doping atom and targeted hybridization (sp2 or sp3-like carbons). In particular, we observed that nitrogen doping of sp2-like carbons atoms can produce a bandgap modulation between semimetallic and semiconductor behavior. These results show that engineering line defects can be an effective way to tune penta-graphene electronic behavior.

Bloch Oscillations in Fibonacci lattices: polaron formation.

We investigated the dynamics of an electron subjected to a uniform electric field in the scope of a tight-binding electron-phonon interacting approach. We aimed at describing the transport in a one-dimensional lattice in which the on-site energies are distributed according to a Fibonacci sequence. Within this physical picture, we obtained a novel dynamical process with no counterpart in ordered lattices. Our findings showed that in low-disorder limit, the electron performs spatial Bloch oscillations, generating, in the turning points of its trajectory, composite quasi-particles-namely, polarons. When it comes to highly disordered systems, two strongly localized polarons are formed in the region where the oscillating charge is confined, thus propagating excitations that are present in the lattice.

Electronic structure properties of transition metal dichalcogenide nanotubes: a DFT benchmark.

In this work, we conduct a benchmark study of bandgap energies and density of states of some transition metal dichalcogenide nanotubes by means of density functional theory (DFT) methodology within both CASTEP and DMol3 methodologies. We compare different chiralities and sizes as well as different levels of theory in order to provide the literature with extensive data regarding crucial electronic structure properties of MoS2, MoSe2, mOtE2, WS2, WSe2, and WTe2 nanotubes. Although the two methods were able to rescue experimental evidences, we observed DMol3 to perform better in terms of computational cost, whereas CASTEP has shown to provide an overall greater accuracy at the cost of higher expenditures. The data provided in this work is an important suggestion of which direction future works should follow in further description of these technological promising materials. Graphical Abstract Frontal (left) and side (right) views for the schematic represenation of a zigzag TMD nanotube.

Effective Mass of Quasiparticles in Armchair Graphene Nanoribbons.

Armchair graphene nanoribbons (AGNRs) may present intrinsic semiconducting bandgaps, being of potential interest in developing new organic-based optoelectronic devices. The induction of a bandgap in AGNRs results from quantum confinement effects, which reduce charge mobility. In this sense, quasiparticles' effective mass becomes relevant for the understanding of charge transport in these systems. In the present work, we theoretically investigate the drift of different quasiparticle species in AGNRs employing a 2D generalization of the Su-Schrieffer-Heeger Hamiltonian. Remarkably, our findings reveal that the effective mass strongly depends on the nanoribbon width and its value can reach 60 times the mass of one electron for narrow lattices. Such underlying property for quasiparticles, within the framework of gap tuning engineering in AGNRs, impact the design of their electronic devices.

Charge Carrier Scattering in Polymers: A New Neutral Coupled Soliton Channel.

The dynamical scattering of two oppositely charged bipolarons in non-degenerate organic semiconducting lattices is numerically investigated in the framework of a one-dimensional tight-biding-Hubbard model that includes lattice relaxation. Our findings show that it is possible for the bipolaron pair to merge into a state composed of a confined soliton-antisoliton pair, which is characterized by the appearance of states within less than 0.1 eV from the Fermi level. This compound is in a narrow analogy to a meson confining a quark-antiquark pair. Interestingly, solitons are quasi-particles theoretically predicted to arise only in polymer lattices with degenerate ground state: in the general case of non-degenerate ground state polymers, isolated solitons are not allowed.

On the Angular Distribution of the H+Li2 Cross Sections: a Converged Time-Independent Quantum Scattering Study.

A thorough time-independent quantum scattering study is performed on a benchmark potential energy surface for the H+Li2 reaction at the fundamental electronic state. Integral and differential cross sections are calculated along with thermal rate coefficients until convergence is reached. Our findings show that vibrational and rotational excitations of the reactant hinder reactivity, though for the latter a considerable reaction promotion was spotted as we increase the reactant rotational quantum number until the critical value of j = 4. Such a promotion then begins to retract, eventually becoming an actual inhibition for larger j. In a straightforward manner, the concept of time-independent methods implemented in this study allowed this accurate state-to-state analysis. Furthermore, a nearly isotropic behaviour of the scattering is noted to take place from the angular point of view. Remarkably, our computational protocol is ideally suited to yield converged thermal rate coefficients, revealing a non-Arrhenius pattern and showing that J-shifting approach fails to describe this particular reaction. Our results, when compared to previous and independent ones, reinforce the latest theoretical reference for future validation in the experimental field.

Spin-Orbit Effects on the Dynamical Properties of Polarons in Graphene Nanoribbons.

The dynamical properties of polarons in armchair graphene nanoribbons (GNR) is numerically investigated in the framework of a two-dimensional tight-binding model that considers spin-orbit (SO) coupling and electron-lattice (e-l) interactions. Within this physical picture, novel polaron properties with no counterparts to results obtained from conventional tight-binding models are obtained. Our findings show that, depending on the system's width, the presence of SO coupling changes the polaron's charge localization giving rise to different degrees of stability for the charge carrier. For instance, the joint action of SO coupling and e-l interactions could promote a slight increase on the charge concentration in the center of the lattice deformation associated to the polaron. As a straightforward consequence, this process of increasing stability would lead to a depreciation in the polaron's motion by decreasing its saturation velocity. Our finds are in good agreement with recent experimental investigations for the charge localization in GNR, mostly when it comes to the influence of SO coupling. Moreover, the contributions reported here provide a reliable method for future works to evaluate spin-orbit influence on the performance of graphene nanoribbons.

Bond length pattern associated with charge carriers in armchair graphene nanoribbons.

The geometry configuration of charged armchair graphene nanoribbons (AGNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model that includes lattice relaxation. Our findings show that the charge distribution and, consequently, the bond length pattern is dependent on the parity of the nanoribbon width. In this sense, the lattice distortions decrease smoothly for increasingly wider GNRs. As should be expected, AGNRs belonging to a particular family present similar patterns for the bond lengths. The interplay between the electron-phonon coupling and band gap is also investigated. The results show that the electron-phonon coupling strength is fundamental to promote the transition from metallic towards semiconducting-like behavior for the band gap. Most important, such strength is crucial on defining the degree of lattice distortions in AGNRs.

Optical properties of P3HT and N2200 polymers: a performance study of an optimally tuned DFT functional.

The optical properties of systems composed of the polymers PolyeraActivInk™ N2200 and P3HT are experimentally and theoretically investigated using UV-Vis spectroscopy and time-dependent density functional theory calculations, respectively. From a theoretical point of view, we carried out an analysis considering several functionals and model oligomers of different sizes to mimic the polymers. As our studies were performed with and without solvents, a first important result regards the fact that, by considering solvent effects, a better agreement between theoretical and experimental results could be achieved. Our findings also show that an optimally tuned functional is better suited to describe the experimental absorption profile than a hybrid one for the flexible polymer (P3HT). For the almost rigid polymer considered here (N2200), on the other hand, hybrid functionals may perform better than tuned functionals.

Transport of Polarons in Graphene Nanoribbons.

The field-induced dynamics of polarons in armchair graphene nanoribbons (GNRs) is theoretically investigated in the framework of a two-dimensional tight-binding model with lattice relaxation. Our findings show that the semiconductor behavior, fundamental to polaron transport to take place, depends upon of a suitable balance between the GNR width and the electron-phonon (e-ph) coupling strength. In a similar way, we found that the parameter space for which the polaron is dynamically stable is limited to an even narrower region of the GNR width and the e-ph coupling strength. Interestingly, the interplay between the external electric field and the e-ph coupling plays the role to define a phase transition from subsonic to supersonic velocities for polarons in GNRs.

Dynamical study of impurity effects on bipolaron-bipolaron and bipolaron-polaron scattering in conjugated polymers.

Combining the one-dimensional tight-binding Su-Schrieffer-Heeger (SSH) model and the extended Hubbard model (EHM), the scattering of two oppositely charged bipolarons and a bipolaron-polaron pair is investigated under the influence of impurity effects using a nonadiabatic evolution method. These novel results for bipolarons show that the oppositely charged quasi-particles scatter into a mixed state composed of bipolarons and excitons. The excitation yield depends sensitively on the strength of the applied electric field. In the presence of an impurity, the critical electric field regime for formation of a state composed by bipolarons and excitons is increased. Additionally, we were able to obtain critical values of electric fields that played the role of drastically modifying the system dynamics. These facts suggest that the scattering between bipolarons and a bipolaron-polaron pair in the presence of impurities is crucial for the understanding of electroluminescence in optoelectronics devices, such as polymer light emitting diodes.

Análise histopatológica do melanoma em cabeça e pescoço / Histopathological analysis of head and neck melanoma

Introdução: Os habitantes da região de Blumenau têm pele clara e são expostos a uma radiação solar com elevado índice ultra-violeta durante o ano. Essas situações associadas favorecem o surgimento do melanoma. Objetivo: estudar o comportamento histológico dos melanomas na região de cabeça e pescoço. Pacientes e Método: Foram analisados todos os casos de melanoma na região de cabeça e pescoço diagnosticados no Laboratório de Anatomia Patológica CIPAC durante o período de janeiro de 2002 e abril de 2005, perfazendo 20 casos. Foram estudadas as seguintes variáveis dos casos: gênero, idade, margens (livres ou comprometidas), presença ou ausência de regressão, invasão angiolinfática e ulceração, além dos critérios de Breslow e Clark. Resultados: Dos 20 casos, 11 correspondiam a mulheres. A idade média foi de 56 anos. Houve predominância histológica do tipo difusão superficial, com 65%. Oito casos tiveram Breslow menor ou igual a 1mm, com Clark II ou III e oito casos tiveram Breslow maior que 1mm, com Clark II ou III. Em três casos, o Breslow era maior que 1mm, com Clark IV ou V. Ulceração ocorreu em 40% dos casos e as margens comprometidas ocorreram em 25%. Conclusão: Os fatores prognósticos de Breslow, Clark, ulceração e índice mitótico estão relacionados ao padrão de crescimento (crescimento superficial, crescimento vertical e ulceração). Os melanomas em região de cabeça e pescoço possuem um comportamento diferente daqueles que aparecem em outras partes do corpo, tendo evolução e prognóstico diferente.

Introduction: The inhabitants of the region of Blumenau City have fair skin and are displayed to solar radiation with high UV index during the year. All those associated situations favor the melanoma sprouting. Objective: to study the histological behavior of the melanomas in the head and neck area. Materials and methods: All cases of melanoma in the head and neck diagnosed in CIPAC Laboratory of Pathology between January, 2002 and April, 2005 were analyzed. The following variable were studied in each case: gender, age, margins (free or not), Clark level, Breslow thickness and presence or absence of regression, angiolymphatic invasion and ulceration. Results: 20 cases were analyzed. Eleven patients were women. The average age was 56. The superficial spread melanoma occurred in 65% of the cases. In 8 cases the Breslow thickness was < 1mm and the Clark level was II or III. In 8 cases the Breslow thickness was > 1mm and the Clark level was II or III. In 3 cases the Clark level was IV or V (the Breslow thickness was >1mm). Ulceration was detected in 40%, and the margins were not free in 25%. Conclusions: The prognostic factors Breslow thickness, Clark level, ulceration and mitotic index are related to the growth behavior of the tumor (radial growth, vertical growth and ulceration). The melanomas in the head and neck have a distinct behavior from those who occur in other parts of the body. As a result, they have different evolution and prognosis.

Tratamento da hiperplasia benigna da prostata por laser: experiencia preliminar com 36 pacientes / Treatment of benign prostatic hyperplasia by laser: preliminary experience with 36 patients

A ablaçao visual da prostata por laser constitui metodo eficaz, confiavel e de baixa morbidade para o tratamento da hiperplasia benigna da prostata sintomatica. O procedimento e realizado sob anestesia peridural, nao se acompanha de sangramento e permite que o paciente deixe o hospital algumas horas depois. Trinta e cinco pacientes foram submetidos a prostatectomia por laser e a avaliaçao pre e pos-operatoria de 25 casos e apresentada. A melhora dos doentes obtida com essa nova modalidade terapeutica foi bastante evidente, uma vez que a media do fluxo urinario maximo aumentou de 10 ml/seg para 21 ml/seg, enquanto o escore de sintomas se reduziu, na media, de 25 para cinco. As complicaçoes da terapia por laser foram infrequentes e tiveram pequeno significado clinico, ressaltando-se retençao urinaria mais prolongada em tres casos, que resolveram espontaneamente, e ocorrencia frequente de disuria e polaciuria durante duas a seis semanas apos o tratamento. Concluimos que a ablaçao visual da prostata por laser representa uma alternativa terapeutica muito atraente, produzindo resultados iniciais comparaveis aqueles apresentados com a ressecçao transuretral

Embolia gordurosa / Fat embolism

A importância do diagnóstico de embolia gordurosa nos pacientes vítimados de politraumatismo tem sido cada vez mais reconhecida. Sei diagnóstico é difícil, principalmente nos casos de não-aparecimento da sintomatologia pulmonar antecedendo a deterioração neurológica, pela falta de um padrão-ouro de diagnóstico e por falta de critérios definidores. Os autores relatam um caso de embolia gordurosa em paciente vítima de trauma fechado, no qual o diagnóstico foi possível graças ao uso da ressonância nuclear magnética de crânio. Fazem também uma revisão sobre o quadro clínico e o diagnóstico de embolia gordurosa, com especial ênfase aos quadros de embolização cerebral sem acometimento pulmonar primário. A alta especificidade da ressonância nuclear magnética permitiu a confirmação do diagnóstico de embolia gordurosa cerebral, sem os sinais de embolização pulmonar prévia. Os autores acreditam que a solicitação da ressonância nuclear magnética cerebral deva ser estendida a outros casos similares