Trajectory-dependent energy loss for swift He atoms axially scattered off a silver surface

Angle- and energy-loss- resolved distributions of helium atoms grazingly scattered from a Ag(110) surface along low indexed crystallographic directions are investigated considering impact energies in the few keV range. Final projectile distributions are evaluated within a semi-classical formalism that includes dissipative effects due to electron-hole excitations through a friction force. For mono-energetic beams impinging along the $[1\bar{1}0]$, $[1\bar{1}2]$ and $[1\bar{1}0]$ directions, the model predicts the presence of multiple peak structures in energy-loss spectra. Such structures provide detailed information about the trajectory-dependent energy loss. However, when the experimental dispersion of the incident beam is taken into account, these energy-loss peaks are completely washed out, giving rise to a smooth energy-loss distribution, in fairly good agreement with available experimental data

Continuum variational and diffusion quantum Monte Carlo calculations

This topical review describes the methodology of continuum variational and diffusion quantum Monte Carlo calculations. These stochastic methods are based on many-body wave functions and are capable of achieving very high accuracy. The algorithms are intrinsically parallel and well-suited to petascale computers, and the computational cost scales as a polynomial of the number of particles. A guide to the systems and topics which have been investigated using these methods is given. The bulk of the article is devoted to an overview of the basic quantum Monte Carlo methods, the forms and optimisation of wave functions, performing calculations within periodic boundary conditions, using pseudopotentials, excited-state calculations, sources of calculational inaccuracy, and calculating energy differences and forces

Thickness of the buccal bone wall and root angulation in the maxilla and mandible: an approach to cone beam computed tomography

Background: The objective of this paper is to anatomically describe the bone morphology in the maxillary and mandibular tooth areas, which might help in planning post-extraction implants. Methods: CBCT images (Planmeca ProMax 3D) of 403 teeth (208 upper teeth and 195 lower teeth) were obtained from 49 patients referred to the Dental School of Seville from January to December 2014. The thickness of the facial wall was measured at the crest, point A, 4mm below, point B, and at the apex, point C. The second parameter was the angle formed between the dental axis and the axis of the basal bone. Results: A total of 403 teeth were measured. In the maxilla, 89.4% of incisors, 93.94% of canines, 78% of premolars and 70.5% of molars had a buccal bone wall thickness less than the ideal 2mm. In the mandible, 73.5% of incisors, 49% of canines, 64% of premolars and 53% of molars had <1mm buccal bone thickness as measured at point B. The mean angulation in the maxilla was 11.67±6.37° for incisors, 16.88±7.93° for canines, 13.93±8.6° for premolars, and 9.89±4.8° for molars. In the mandible, the mean values were 10.63±8.76° for incisors, 10.98±7.36° for canines, 10.54±5.82° for premolars and 16.19±11.22° for molars. Conclusions: The high incidence of a buccal wall thickness of less than 2mm in over 80% of the assessed sites indicates the need for additional regeneration procedures, and several locations may also require custom abutments to solve the angulation problems for screw-retained crowns

Notes on a short-cut to the proof of the M3\mathbf{M}_3-N5\mathbf{N}_5 Theorem

This paper presents two shortcuts to a classical proof of the $\mathbf{M}_3$-$\mathbf{N}_5$ Theorem, which can be found in B. Davey and H. Priestley [2] and S. Burris and H. Sankappanavar [1]. To be precise, the shortcuts pertain a particular step of the proof that requires showing an algebraic equality. In addition, we briefly discuss how to compare the lengths of the three proofs (the original and our two proposed shortcuts). To do so, we introduce two methods to compare the lengths of proofs based on algebraic lattice expressions. We call them the proof count method and the proof poset method. Both methods indicate that our proofs are shorter but the difference is more pronounced in the former. Keywords: lattices, posetsComment: 10 Page

Desarrollo del razonamiento sobre pruebas de significación de estudiantes de bachillerato en un ambiente tecnológico

Se describe el desarrollo del razonamiento de 36 estudiantes de bachillerato, organizados en parejas, acerca de la técnica de pruebas de significación estadística con el apoyo de un software educativo de estadística (Fathom); dicho desarrollo es visto a través de sus respuestas a 4 problemas de pruebas de significación; estos se resolvieron en sendas sesiones en las que además se realizaron cortas intervenciones del profesor, se enseñó a utilizar el software y se discutieron dudas de los problemas vistos en la sesión previa respectiva. Las respuestas a cada problema se clasificaron en niveles SOLO. Los resultados muestran avances en la calidad de las respuestas de los participantes, superándose en cada actividad algunos errores cometidos en la previa, esto lleva conjeturar que los estudiantes se van apropiando del esquema de pruebas de significación. No obstante, se presentan algunas dificultades similares a las ya reportadas en la literatura

Anisotropic conductivity of silver thin films grown on silicon (100) vicinal surfaces

The electrical conductivity between 4 and 300 K of Ag thin films (up to 30 mm grown at room temperature on Si(100) vicinal surfaces has been measured and their morphology imaged with an atomic force microscope. A noticeable anisotropy of the resistivity of the films which is related to the structure of the films has been found)Laboratories du CNRS Departamento de Física Materia Condensada. Universidad Autónoma.Peer reviewe

Reliability of the resonance frequency analysis values in new prototype transepithelial abutments: A prospective clinical study

Resonance frequency analysis (RFA) requires abutment disconnection to monitor implant stability. To overcome this limitation, an experimental transepithelial abutment was designed to allow a SmartPeg to be screwed onto it, in order to determine the prototype abutments repeatability and reproducibility using Osstell ISQ and to assess whether implant length and diameter have an influence on the reliability of these measurements. RFA was conducted with a SmartPeg screwed directly into the implant and onto experimental abutments of different heights of 2, 3.5 and 5 mm. A total of 32 patients (116 implants) were tested. RFA measurements were taken twice for each group from mesial, distal, buccal and palatal/lingual surfaces. Mean values and SD were calculated and Intraclass Correlation Coefficients (ICC) (p < 0.05, IC 95%). The implant stability quotient (ISQ) mean values were 72.581 measured directly to implant and 72.899 (2 mm), 72.391 (3.5 mm) and 71.458 (5 mm) measured from the prototypes. ICC between measurements made directly to implant and through 2-, 3.5-and 5-mm abutments were 0.908, 0.919 and 0.939, respectively. RFA values registered through the experimental transepithelial abutments achieved a high reliability. Neither the implant length nor the diameter had any influence on the measurements’ reliability

Estudio in vitro de la actividad citotóxica de resinas dentales tipo BIS-GMA

Las resinas composites se emplean desde hace varias décadas en distintas aplicaciones estomatológicas, volviéndose indispensables para lograr una alta calidad en los servicios modernos. Uno de los monómeros acrílicos más utilizados en estos materiales poliméricos de recubrimiento es el 2-bis-[p-(2-hidroxi-3-metacriloxipropoxi) fenil] propano, conocido comúnmente como Bis- GMA. El conocimiento de las interacciones de estos materiales con el sistema biológico es de vital importancia debido al uso tan difundido de los mismos en la práctica clínica. El comportamiento de una célula viva en contacto con un material extraño es un problema esencial en las aplicaciones biomédicas de polímeros sintéticos. Los ensayos in vitro son sistemas muy útiles para la evaluación de los efectos biológicos de los biomateriales. En el laboratorio de Inmunofarmacología del INOR se llevó a cabo la evaluación de la toxicidad de dos resinas dentales tipo Bis-GMA producidas por el Centro de Biomateriales de la Universidad de La Habana: el Obtudent Fotocurado (FC), resina fotopolimerizable para restauraciones dentales y el Cubridem Autocurado (AC), sellante dental para fosas y fisuras. Este estudio forma parte de las evaluaciones preclínicas biológicas de biomateriales y equipos médicos implantables que se lleva a cabo en Cuba a través de la Red Funcional de Implantología del Ministerio de Salud Pública. Se aplicó el método de citotoxicidad in vitro descrito por Stanley para la evaluación toxicológica de materiales dentales. Ambos composites resultaron citotóxicos para la línea de fibroblastos L929, lo que se corresponde con lo descrito en la literatura para este tipo de material. Su citotoxicidad se encontró en el rango de la de los análogos comerciales evaluados.Peer Reviewe

Tribological and mechanical properties of graphene nanoplatelet/PEEK composites

Poly(ether ether ketone) (PEEK) is a relevant thermoplastic in industry and in the biomedical sector. In this work, the lubricant capability of graphene nanoplatelets (GNPs) is used for improving the PEEK wear properties. Nanocomposites were prepared by solvent-free melt-blending and injection molding at various compositions between 1 and 10 wt. % of GNPs. The Raman G band shows a progressive increment proportional to the bulk GNP percentage. From calorimetric data, the polymer matrix structure is interpreted in terms of a 3-phase model, in which the crystalline phase fluctuates from 39 to 34% upon GNP addition. Thermal conductivity varies in accordance with the polymer crystallinity. Tensile and flexural tests show a progressive increase in the modulus, as well as a decrease in the fracture strength and the work of fracture. Most important, the composite surface undergoes a substantial improvement in hardness (60%), together with a decrease in the coefficient of friction (-38%) and a great reduction in the wear factor (-83%). Abrasion and fatigue wear mechanisms are predominant at the lowest and highest GNP concentrations respectively. In conclusion, GNPs are used without any chemical functionalization as the filler in PEEK-based materials, improving the surface hardness and the tribological properties