Analytical and numerical solutions of the potential and electric field generated by different electrode arrays in a tumor tissue under electrotherapy

<p>Abstract</p> <p>Background</p> <p>Electrotherapy is a relatively well established and efficient method of tumor treatment. In this paper we focus on analytical and numerical calculations of the potential and electric field distributions inside a tumor tissue in a two-dimensional model (2D-model) generated by means of electrode arrays with shapes of different conic sections (ellipse, parabola and hyperbola).</p> <p>Methods</p> <p>Analytical calculations of the potential and electric field distributions based on 2D-models for different electrode arrays are performed by solving the Laplace equation, meanwhile the numerical solution is solved by means of finite element method in two dimensions.</p> <p>Results</p> <p>Both analytical and numerical solutions reveal significant differences between the electric field distributions generated by electrode arrays with shapes of circle and different conic sections (elliptic, parabolic and hyperbolic). Electrode arrays with circular, elliptical and hyperbolic shapes have the advantage of concentrating the electric field lines in the tumor.</p> <p>Conclusion</p> <p>The mathematical approach presented in this study provides a useful tool for the design of electrode arrays with different shapes of conic sections by means of the use of the unifying principle. At the same time, we verify the good correspondence between the analytical and numerical solutions for the potential and electric field distributions generated by the electrode array with different conic sections.</p

Role of the central cations in the mechanical unfolding of DNA and RNA G-quadruplexes.

Cations are known to mediate diverse interactions in nucleic acids duplexes but they are critical in the arrangement of four-stranded structures. Here, we use all-atom molecular dynamics simulations with explicit solvent to analyse the mechanical unfolding of representative intramolecular G-quadruplex structures: a parallel, a hybrid and an antiparallel DNA and a parallel RNA, in the presence of stabilising cations. We confirm the stability of these conformations in the presence of [Formula: see text] central ions and observe distortions from the tetrad topology in their absence. Force-induced unfolding dynamics is then investigated. We show that the unfolding events in the force-extension curves are concomitant to the loss of coordination between the central ions and the guanines of the G-quadruplex. We found lower ruptures forces for the parallel configuration with respect to the antiparallel one, while the behaviour of the force pattern of the parallel RNA appears similar to the parallel DNA. We anticipate that our results will be essential to interpret the fine structure rupture profiles in stretching assays at high resolution and will shed light on the mechanochemical activity of G-quadruplex-binding machinery

Slingshot non-sequential double ionization as a gate to anti-correlated two electron escape

At intensities below-the-recollision threshold, we show that re-collision-induced excitation with one electron escaping fast after re-collision and the other electron escaping with a time delay via a Coulomb slingshot motion is one of the most important mechanisms of non-sequential double ionization, for strongly-driven He at 400 nm. Slingshot-NSDI is a general mechanism present for a wide range of low intensities and pulse durations. Anti-correlated two-electron escape is its striking hallmark. This mechanism offers an alternative explanation of anti-correlated two-electron escape obtained in previous studies.Comment: 6 pages, 3 figure

Two-color ionization of hydrogen by short intense pulses

Photoelectron energy spectra resulting by the interaction of hydrogen with two short pulses having carrier frequencies, respectively, in the range of the infrared and XUV regions have been calculated. The effects of the pulse duration and timing of the X-ray pulse on the photoelectron energy spectra are discussed. Analysis of the spectra obtained for very long pulses show that certain features may be explained in terms of quantum interferences in the time domain. It is found that, depending on the duration of the X-ray pulse, ripples in the energy spectra separated by the infrared photon energy may appear. Moreover, the temporal shape of the low frequency radiation field may be inferred by the breadth of the photoelectron energy spectra.Comment: 12 pages, 8 figure

El perfil y la actuacion profesional del enfermero/a en el centro de atención psicosocial

Trata-se de um estudo qualitativo, envolvendo quatorze enfermeiros de onze Centros de Atenção Psicossocial. Os objetivos do estudo são: caracterizar o perfil profissional do enfermeiro que trabalha no CAPS, e verificar as ações desse profissional no atual modelo de assistência à saúde mental. RESULTADOS: o sexo feminino prevalece; a maioria é formada há mais de 10 anos; a inserção na área de saúde mental se dá tardiamente, e está associada à falta de opção de trabalho e proximidade do serviço com a residência do profissional. Uma parcela demonstra dificuldade para definir sua função num serviço extra-hospitalar. Outra parcela acredita que a ação no CAPS é flexível e identifica um saber que pode ser compartilhado com a equipe multiprofissional. Baixos salários, infraestrutura deficiente e falta de reconhecimento pelos membros da equipe produzem insatisfação no trabalho. A Reforma Psiquiátrica é associada à desospitalização.This qualitative study was performed with fourteen nurses of eleven psychosocial care services. The objectives of the study were the following: to characterize the professional profile of the nurses who work in community psychiatric services and to verify those nurses' practice according to the current model of mental health care. RESULTS: there was a prevalence of females; most had over 10 years since their graduation; their entrance in the mental health area is late and is associated with the lack of job opportunities and the fact that the service is close to their home. One part of the nurses found it difficult to define their work at an extra-hospital environment. On the other hand, another group of nurses believes that the nursing work in mental health services is flexible and it is shared with other workers of the multidisciplinary team. Low salaries, poor infrastructure and the lack of team member acknowledgement generate dissatisfaction at work. The Brazilian Psychiatric Reform is associated with dehospitalization.Se trata de un estudio cualitativo que tiene como sujetos de análisis a catorce enfermeros de once Centros de Atención Psicosocial de la ciudad de São Paulo (Brasil). El objetivo del estudio es caracterizar el perfil profesional del enfermero/a que desempeña sus funciones en un CAPS y verificar sus acciones en el modelo vigente de asistencia a la salud mental. Los datos fueron recogidos a través de entrevistas, empleándose las premisas de Bourdieu. RESULTADOS: prevalece el sexo femenino, la mayoría está graduada hace más de diez años, la inserción en el área de salud mental se produce en forma tardía y está asociada a la falta de opciones de trabajo y a la cercanía del servicio con el domicilio del profesional. Una parte de los entrevistados muestra dificultad para definir su función en un servicio extra hospitalario. Otra parte cree que el trabajo en el CAPS es flexible, e identifica un saber que puede ser compartido con el equipo multidisciplinario. Bajos salarios, infraestructura deficiente y falta de reconocimiento por parta de los miembros del equipo producen insatisfacción en el trabajo. La Reforma Psiquiátrica está asociada a la deshospitalización

Sequential single-photon and direct two-photon absorption processes for Xe interacting with attosecond XUV pulses

We investigate the interaction of Xe with isolated attosecond XUV pulses. Specifically, we calculate the ion yields and determine the pathways leading to the formation of ionic charged states up to Xe$^{5+}$. To do so, in our formulation we account for single-photon absorption, sequential multi-photon absorption, direct two-photon absorption, single and double Auger decays, and shake-off. We compare our results for the ion yields and for ion yield ratios with recent experimental results obtained for 93 eV and 115 eV attosecond XUV pulses. In particular, we investigate the role that a sequence of two single-photon ionization processes plays in the formation of Xe$^{4+}$. We find that each one of these two processes ionizes a core electron and thus leads to the formation of a double core-hole state. Remarkably, we find that the formation of Xe$^{5+}$ involves a direct two-photon absorption process and the absorption of a total of three photons.Comment: 8 pages, 4 figure

Unfolding mechanism and free energy landscape of single, stable, alpha helices at low pull speeds

Single alpha helices (SAHs) stable in isolated form are often found in motor proteins where they bridge functional domains. Understanding the mechanical response of SAHs is thus critical to understand their function. The quasi-static force-extension relation of a small number of SAHs is known from single-molecule experiments. Unknown, or still controversial, are the molecular scale details behind those observations. We show that the deformation mechanism of SAHs pulled from the termini at pull speeds approaching the quasi-static limit differs from that of typical helices found in proteins, which are stable only when interacting with other protein domains. Using molecular dynamics simulations with atomistic resolution at low pull speeds previously inaccessible to simulation, we show that SAHs start unfolding from the termini at all pull speeds we investigated. Unfolding proceeds residue-by-residue and hydrogen bond breaking is not the main event determining the barrier to unfolding. We use the molecular simulation data to test the cooperative Sticky Chain model. This model yields excellent fits of the force-extension curves and quantifies the distance, xE = 0.13 nm, to the transition state, the natural frequency of bond vibration, ν0 = 0.82 ns−1, and the height, V0=2.9 kcal/mol, of the free energy barrier associated with the deformation of single residues. Our results demonstrate that the Sticky Chain model could advantageously be used to analyze experimental force-extension curves of SAHs and other biopolymers