Image effects in transport at metal-molecule interfaces

We present a method for incorporating image-charge effects into the description of charge transport through molecular devices. A simple model allows us to calculate the adjustment of the transport levels, due to the polarization of the electrodes as charge is added to and removed from the molecule. For this, we use the charge distributions of the molecule between two metal electrodes in several charge states, rather than in gas phase, as obtained from a density-functional theory-based transport code. This enables us to efficiently model level shifts and gap renormalization caused by image-charge effects, which are essential for understanding molecular transport experiments. We apply the method to benzene di-amine molecules and compare our results with the standard approach based on gas phase charges. Finally, we give a detailed account of the application of our approach to porphyrin-derivative devices recently studied experimentally by Perrin et al. [Nat. Nanotechnol. 8, 282 (2013)], which demonstrates the importance of accounting for image-charge effects when modeling transport through molecular junctions

Decoloración y detoxificación de aguas de alperujo mediante el empleo de esmectitas e hidrotalcita

2 páginas.-- 1 figura.-- 1 tablas.-- 8 referencias.-- Poster presentado en XXIV Reunión de la Sociedad Española de Arcillas Sevilla. Libro de Resúmenes: Noviembre de 2015 en Sevilla.El alperujo es el residuo sólido del proceso de extracción de aceite de oliva virgen en dos fases, que se produce en grandes cantidades en diversas regiones españolas y cuyo empleo como fertilizante y enmendante de suelos, una vez compostado, facilita una salida sostenible para estos contribuyendo favorablemente al secuestro de carbono (1,2) No obstante también puede dar lugar a algunos efectos adversos: a) Coloración de las aguas, b) Deterioro del suelo por su acidez y sales, c) Solubilización, transporte y lixiviación de algunos metales pesados y plaguicidas (3, 4) y d) Fitotoxicidad sobre plantas y microrganismos acuáticos, si no han sido previamente compostados o tratados (5). Sobre la hipótesis del conocido potencial de los materiales arcillosos de interaccionar con la materia orgánica soluble (MOS) de suelos, sedimentos o residuos (4, 6), el objetivo del presente trabajo ha sido evaluarla capacidad de arcillas catiónicas y aniónicas como adsorbentes de la MOS procedente de alperujo, responsable de los efectos adversos descritos. La finalidad última es el posible desarrollo y utilidad de adsorbentes naturales para reducir la coloración y toxicidad de aguas de lavado de almazaras, o para su posible co-aplicación con alperujo a suelos agrícolas disminuyendo los efectos adversos sobre semillas o plantas o para corregir los efectos de un vertido puntual incontrolado.Este trabajo ha sido financiado a través de los proyectos P07-AGR-03077 y P11-AGR-07400 y AGR-264 de la Junta de Andalucía, cofinanciados por FEDER y FSE; y el Convenio RECUPERA 2020 del MINECO-CSIC.Peer reviewe

Nuevas aportaciones al estudio polínico de sedimentos del Parque Natural de los Alcornocales (Cádiz, sur de España)

Nuevas apotaciones al estudio polínico de sedimentos del Parque Natural de los Alcornocales (Cádiz, Sur de España). En este trabajo se completa el contenido polínico de una columna de sedimento de 300 cm, extraida de una zona semiturbosa de la Sierra del Aljibe en el Parque Natural de los Alcornocales (Cádiz). Se discuten las variaciones polínicas porcentuales de los taxones identificados, consideradas de nuevo aquí a la luz de los nuevos datos, fundamentalmente la datación con radiocarbono, y se interpretan los diagramas polínicos resultantes en términos paleoecológicos. Por otro lado, y en base a estudios previos en el norte de Marruecos, zona de características ecológicas e históricas similares a la zona estudiada, se concluye el uso diferente del territorio a ambos lados del estrecho

Electrochemical study of the repassivation of titanium in different artificial saliva solutions

The passive film presented at the dental implant surfaces can be damaged or eventually destroyed during insertion and implantation into hard tissue due to abrasion/wear with bone or other materials. However, when the wear action stops, the surface will tend to regenerate immediately, and a new passive film will be formed. In such conditions we are in the presence of a tribo-electrochemical phenomenon which comprises the analysis of two different processes and of the synergism effects between them. In fact, the mechanisms of mechanical degradation due to wear might be influenced by the presence of a corrosive environments, but the electrochemical behaviour of the material is likely to be modified by the presence of the mechanical solicitation and by the presence of wear debris and/or the formation of tribolayers. Also, the repassivation kinetics of the tribocorrosion system during or after mechanical damage becomes an important issue to be studied. This work deals with the study of the repassivation of titanium when in contact with artificial saliva solutions, after mechanical damage. Samples were immersed in different kinds of artificial saliva solutions (artificial saliva (AS), AS + citric acid, AS + anodic, cathodic or organic inhibitor). After stabilisation the passive film was mechanically disrupted and the open-circuit potential (OCP) was monitored both during the mechanical damage and until the repassivation was completed. Additionally, and in order to evaluate the quality of the passive film, EIS measurements were performed before and after mechanical disruption of the passive film. The effect of pH variation and of electrolyte composition on the repassivation evolution was also investigated. Considering the evolution of the open circuit potential represented in figure 1 the approximation ln(E) = ln(k) + b*ln(t) was used to study the repassivation evolution with the time. As it can be observed, the open circuit potential achieved before and after the mechanical damage varies, which indicates that the nature of the electrolyte influences the properties of the passive film. As indicated by the b values presented in Table 1, after repassivation, the AS + citric acid is the solution that provides better repassivation evolution with the time. In contrast, the AS + cathodic inhibitor is the solution that provides worst repassivation evolution. However, the EIS results suggests that AS solution is that providing the most stable and thick passive film. The results obtained with the AS + cathodic or + organic solution shows that these solutions do not have a good influence on the film growth

Tribocorrosion behaviour of titanium in artificial saliva solutions

Dental implants are used to replace teeth lost due to decay, trauma or periodontal disease. In last years, the demand for such implants has increased exponentially due mostly to the ageing of the population and/or increased reliability of implant therapy. To choose a material for a particular rehabilitation treatment different characteristics must be considered such as mechanical strength, elastic properties, machinability, chemical resistance, etc. There is, however, one aspect that is always of prime importance; namely how the tissue at the implant site responds to the chemical disturbance imposed by the presence of a foreign material. In this work, commercially pure titanium (grade 2) was selected mainly due to its excellent corrosion behaviour and biocompatibility, that make this material one of the most used in dentistry. The tribocorrosion behaviour of the material in conditions simulating mastication, when in contact with artificial saliva solutions was investigated. Corundum was used as counterface material. The tests were performed, at MTM- KULeuven (Belgium), in a fretting machine specially adapted for tribocorrosion experiments. A normal load of 2 N was applied to the specimens and a displacement amplitude of 200µm at a frequency of 1 Hz. The number of cycles was varied between 5.000 and 10.000. In order to simulate different environmental conditions, simple artificial saliva (0.7%KCl + 1,2%NaCl; pH =6), artificial saliva with corrosion catalyst (citric acid), and artificial saliva with anodic, cathodic and organic corrosion inhibitors (sodium nitrite, calcium carbonate or benzotriazole, respectively), was used. The tribocorrosion degradation mechanisms were investigated by Electrochemical Noise technique (TEN), which combines Electrochemical Emission Spectroscopy with fretting tests [1]. After being tested, the surface of the samples was investigated by SEM and EDX. Roughness measurements and wear volume measurements were also performed. The depassivation/repassivation phenomena occurring during the tests were clearly detected, and are discussed. Considering the influence of the corrosion inhibitors, it was possible to observe that the degree of protection varies with the nature of the inhibitor.(undefined

Assessing The Impact Of Medical Malpractice Awards, Tort Reform, And Investment Returns Upon Medical Malpractice Insurance Premiums

For most doctors, obtaining medical malpractice insurance coverage each year represents a significant expense.  During the past three decades, researchers have developed several competing theories to explain changes in the cost of obtaining medical malpractice insurance in the United States.  This article focuses on the relationship, on a nationwide basis, between medical malpractice awards, the presence of tort reform, investment returns by insurers, and the impact of each upon the cost of obtaining medical malpractice insurance.  The results of a multivariate equation are then used to analyze the relative impacts of these competing theories

Influence of pH and corrosion inhibitors on the tribocorrrosion of titanium in artificial saliva

Dental implants are used to replace teeth lost due to decay, trauma, or periodontal iseases. Dental implants are most of the times ubjected tomicro-movements at the implant/bone interface or implant/porcelain interface (due to the transmitted mastication loads) and chemical solicitations (oral environment). Such implant becomes part of tribocorrosion system, which may undergo a complex degradation process that can lead to implant failure. In this work, the fretting–corrosion behaviour of titanium grade 2 in contact with artificial saliva was investigated under fretting test conditions. Citric acid was added to artificial saliva to investigate a pH variation on the tribocorrosion behaviour of the material. Additionally, three different inhibitors were added to investigate cathodic and anodic reactions on the electrochemical response. Also, the influence of inhibitors included in the formulation of tooth cleaning agents or medicines was investigated. Degradation mechanisms were investigated by electrochemical noise technique that provided information on the evolution of corrosion potential and corrosion current during fretting tests. Depassivation and repassivation phenomena occurring during the tests were detected and discussed. Considering the influence of corrosion inhibitors, it was observed that the degree of protection varies with the nature of the inhibitors