Alignment-Dependent Ionization of N2_2, O2_2, and CO2_2 in Intense Laser Fields

The ionization probability of N$_2$, O$_2$, and CO$_2$ in intense laser fields is studied theoretically as a function of the alignment angle by solving the time-dependent Schr\"odinger equation numerically assuming only the single-active-electron approximation. The results are compared to recent experimental data [D.~Pavi{\v{c}}i{\'c} et al., Phys.\,Rev.\,Lett.\ {\bf 98}, 243001 (2007)] and good agreement is found for N$_2$ and O$_2$. For CO$_2$ a possible explanation is provided for the failure of simplified single-active-electron models to reproduce the experimentally observed narrow ionization distribution. It is based on a field-induced coherent core-trapping effect.Comment: 5 pages, 2 figure

Caracterización de Capas Delgadas de Tungsteno obtenidas mediante High Power Impulse Magnetron Sputtering (HiPIMS)

Práctica dirigida (Bachillerato en Ingeniería en Ciencias de los Materiales) Instituto Tecnológico de Costa Rica, Escuela de Ingeniería en Ciencias de los Materiales, 2019.High Power Impulse Magnetron Sputtering (HiPIMS) is a novel thin film processing method to achieve include higher density, better substrate adhesion, and smoother surfaces compared to conventional DC sputtering (DCms). The Max-Planck Institute for Plasma Physics is seeking to enable a HiPIMS device to maintain its leading position in scientific research in advanced coatings. In this work, the first results of W coatings on Si and W obtained with a new HiPIMS power source, P = 200 W, tpulse = 10 μs and f = 2000 Hz, were evaluated. Physical properties such as microstructure, density, roughness, and impurity content were compared with films obtained via DCms under the similar processing conditions. It was found that the HiPIMS method achieves a ~10% increase in density, and eliminates the β-W phase in W over Si films, compared to films obtained with the conventional DCms method. The addition of a bias voltage Vb = -120 V decreased the root mean square (RMS) of the roughness in W films over W substrate obtained by both DCms and HiPIM

Water molecules in ultrashort intense laser fields

Ionization and excitation of water molecules in intense laser pulses are studied theoretically by solvingthe three-dimensional time-dependent electronic Schrödinger equation within the single-active-electronapproximation. The possibility to image orbital densities by measurement of the orientation-dependentionization of H2O in few-cycle, 800 nm linear-polarized laser pulses is investigated. While the highest-occupied molecular orbital 1b1is found to dominate the overall ionization behavior, contributions fromthe energetically lower lying 3a1orbital dominate the ionization yield in the nodal plane of the 1b1orbi-tal. The ratio of the ionization yields of the two orbitals depends on the intensity. Furthermore, even forlaser pulses as long as 8 cycles the orientation-dependent ion yield depends on the carrier-envelopephase. In the interpretation of the orientation-dependent ionization as an imaging tool these effects haveto be considered

Wavelength- and alignment-dependent photoionization of N2 and O2

The ionization behavior of the two diatomic molecules nitrogen and oxygen in strong laser fields has been investigated. For this purpose, the time-dependent Schr\uf6dinger equation is solved numerically within the many-electron single-determinant approximation. Three different orientations of the molecular axis with respect to the laser field have been considered: 0 18,45 18, and 90 18. The photon wavelength has been varied from 25 to 800 nm, covering a range from XUV to infrared radiation. Nitrogen and oxygen were chosen as they possess the same molecular symmetry but different orbital structures. The ionization from different orbitals is discussed

The curved Mimetic Finite Difference method: allowing grids with curved faces

We present a new mimetic finite difference method for diffusion problems that converges on grids with \textit{curved} (i.e., non-planar) faces. Crucially, it gives a symmetric discrete problem that uses only one discrete unknown per curved face. The principle at the core of our construction is to abandon the standard definition of local consistency of mimetic finite difference methods. Instead, we exploit the novel and global concept of $P_{0}$-consistency. Numerical examples confirm the consistency and the optimal convergence rate of the proposed mimetic method for cubic grids with randomly perturbed nodes as well as grids with curved boundaries.Comment: Accepted manuscrip

Evaluación de la interactividad del Plasma Atmosférico No-Equilibrado (APNP) sobre la viabilidad celular de fibroblastos murinos cultivados in vitro

Proyecto de Investigación (Código: 1801079) Instituto Tecnológico de Costa Rica. Vicerrectoría de Investigación y Extensión (VIE). Escuela de Biología, Escuela de Física, 2017Plasma Medicine es un área prometedora que ha tenido un gran desarrollo en los últimos años. Sus aplicaciones van desde la esterilización de equipos, heridas, cauterización de tejidos, hasta tratamientos para el cierre de heridas crónicas y potencial co-adyuvante y/o tratamiento contra el cáncer. El fin para el cual se destine el plasma definirá el tipo de fuente y descarga que se generará. En el presente estudio, se buscó evaluar la respuesta in vitro de fibroblastos murinos de la línea NHI-3T3 a descargas de plasma atmosférico no equilibrado. Para esto, se desarrolló un prototipo que pudiera generar una descarga uniforme, en un ambiente como la cámara de flujo laminar, que posee un flujo vertical constante que podría interferir con la generación de la descarga. El dispositivo generado tipo DBD (dielectric barrier discharge) utilizando el gas helio, fue escogido como el más adecuado según las condiciones presentadas. Para la evaluación de la respuesta de los fibroblastos a la descarga de plasma, se utilizó una prueba de viabilidad que utiliza el reactivo MTT, así como un ensayo de scratch wound healing (SWH), este con el fin de evaluar la existencia de un efecto sobre la migración celular. Los resultados encontrados muestran que las dosis evaluadas de irradiación no producen un efecto diferencial en la viabilidad celular respecto al control. Sin embargo, fue posible observar un aumento en la pérdida de la adhesión celular en los cultivos al utilizar un medio de cultivo menos nutritivo para el ensayo de SWH. Dado que en la dinámica de interacción de una descarga de plasma con un cultivo celular interviene una gran cantidad de variables, se recomienda evaluar la irradiación en condiciones de cultivo que permitan una interacción directa del plasma con el cultivo disminuyendo la interferencia del medio de cultivo y la geometría de los platos de cultivo que pudieron afectar la homogeneidad de la irradiación en el presente estudio. De igual manera, se recomienda tomar en cuenta ajustar las dosis de irradiación (potencia y tiempo de irradiación) según el tipo de ensayo, de manera que se pueda evaluar la interacción del plasma con el cultivo

Insight Report: COVID-19 Community Involvement - “Let’s Talk About…HIV Care”

This informal session led by the Patient Experience Research Centre (PERC), in collaboration with Positively UK, invited people living with, affected by, or working in HIV to share their experience, views, questions and concerns on accessing HIV care during COVID-19. The aim of the call was to gather feedback on specific areas to help guide a proposed qualitative (interview-based study) looking to explore experiences, specifically on: 1. Challenges and concerns in managing HIV care during COVID-19 2. Challenges in the provision of HIV care during COVID-19 3. Opportunities presented for HIV care during COVID-19 We also wished to inspire new ways to rapidly engage and involve communities remotely during a public health emergency, through strengthening partnerships with existing groups (in this case, Positively UK)