Molecular Dissociation in Presence of a Catalyst II: The bond breaking role of the transition from virtual to localized states

We address a molecular dissociation mechanism that is known to occur when a H 2 molecule approaches a catalyst with its molecular axis parallel to the surface. It is found that molecular dissociation is a form of quantum dynamical phase transition associated to an ana- lytic discontinuity of quite unusual nature: the molecule is destabilized by the transition from non-physical virtual states into actual local- ized states. Current description complements our recent results for a molecule approaching the catalyst with its molecular axis perpendicu- lar to the surface. Also, such a description can be seen as a further successful implementation of a non-Hermitian Hamiltonian in a well defined model

Molecular dissociation in the presence of catalysts: Interpreting bond breaking as a quantum dynamical phase transition

In this work we show that molecular chemical bond formation and dissociation in the presence of the d-band of a metal catalyst can be described as a quantum dynamical phase transition (QDPT). This agrees with DFT calculations that predict sudden jumps in some observables as the molecule breaks. According to our model this phenomenon emerges because the catalyst provides for a non-Hermitian Hamiltonian. We show that when the molecule approaches the surface, as occurs in the Heyrovsky reaction of H2, the bonding H2 orbital has a smooth crossover into a bonding molecular orbital built with the closest H orbital and the surface metal d-states. The same occurs for the antibonding state. Meanwhile, two resonances appear within the continuous spectrum of the d-band, which are associated with bonding and antibonding orbitals between the furthest H atom and the d-states at the second metallic layer. These move toward the band center, where they collapse into a pure metallic resonance and an almost isolated H orbital. This phenomenon constitutes a striking example of the non-trivial physics enabled when one deals with non-Hermitian Hamiltonian beyond the usual wide band approximation.Fil: Ruderman, Andres. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Dente, Axel Damián. Invap S. E.; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Pastawski, Horacio Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Key role of anions in the 2D-3D electrochemical deposition of Rh on Ag electrodes

We have studied the electrochemical deposition of Rh on polycrystalline Ag substrates from electrolytes containing chloride and sulphate anions. Chronoamperometry and cyclic voltammetry have been employed in order to elucidate the growth mechanism. Anions play a key role in the growth mechanism and the resulting structures. In the presence of sulphate anions Rh deposition follows a 3D nucleation - growth mechanism, while a 2D nucleation - growth is obeyed in the case of electrolytes containing chloride anions. Ab initio thermodynamics studies support the hypothesis that chloride anions stabilize the Rh deposition favouring a 2D mechanism at low overpotentials in good agreements with the experimental data.Fil: Schulz, Eduardo Nicolás. Universitat Ulm; AlemaniaFil: Ruderman, Andres. Universitat Ulm; AlemaniaFil: Soldano, Germán. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: García, Silvana G.. Universidad Nacional del Sur. Departamento de Ingeniería Química. Instituto de Ingeniería Electroquímica y Corrosión; ArgentinaFil: Santos, Elizabeth del Carmen. Universitat Ulm; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentin

Hydrogen Evolution Reaction on Nanostructures Electrodes—a Scenario on Stepped Silver Surfaces

We have investigated the scenario for the hydrogen evolution reaction at stepped silver surfaces in acid solutions at high overpotentials using a simple kinetic model. Two independent types of sites, at the steps and at the terraces, were considered. The rate constants for the Volmer and Heyrovsky reactions were estimated. Both reactions occur with rate constant about two orders of magnitude larger at step sites than at terrace sites. Calculations of the activation energy for these reactions using our theory of electrocatalysis give similar results. [Figure not available: see fulltext.].Fil: Juárez, M. F.. Universitat Ulm; AlemaniaFil: Avila, Milagros. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Ruderman, Andres. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Santos, Elizabeth del Carmen. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universitat Ulm; AlemaniaFil: Leiva, Ezequiel Pedro M.. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Oviedo, Oscar Alejandro. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; Argentin

Testing a counseling message for increasing uptake of self-injectable contraception in southern Malawi: A mixed-methods, clustered randomized controlled study.

ObjectiveWhile self-injection of subcutaneous depot medroxyprogesterone acetate (DMPA-SC) has well-documented benefits, uptake may be improved by addressing client concerns such as fear of self-injury and low self-efficacy. However, current training materials for family planning providers do not address these concerns. We used an iterative process with family planning providers and clients, male community leaders and partners, and stakeholders in Malawi to develop a counseling message addressing user-centered concerns about self-injection. We report on our testing of the effectiveness of this evidence-based message for increasing self-injection uptake in the context of full method choice.MethodsWe randomized 60 public facilities across two districts in southern Malawi to orient their providers to the message (treatment) or not (control). After strengthening data quality, we extracted routine service delivery data from the facilities six months before and after introducing the message. We compared pre- and post-orientation trends for the treatment and control groups using generalized linear mixed models. We conducted eight focus group discussions with a sample of providers oriented to the message.ResultsThe message was feasible to implement and highly acceptable to providers. During June 2020-June 2021, 16,593 new clients used injectables in Mangochi district (52% DMPA-SC; 15% self-injected). In Thyolo district, 7,761 new clients used injectables during July 2020-July 2021 (29% DMPA-SC; 14% self-injected). We observed high variability in number of clients and self-injection uptake across facilities and over time, indicating inconsistent offering of self-injection. In both districts, we found significant increases in self-injection in treatment facilities after message introduction. However, this increase was not sustained, especially when DMPA-SC was unavailable or about to expire.ConclusionBased on the study findings, we recommend the evidence-based message be used in programs offering DMPA-SC self-injection services. However, effective use of the message is contingent upon a consistent supply of DMPA-SC

Current transients for the hydrogen evolution reaction at high overpotentials on silver electrodes in acid solutions: Experiments and modelling

The hydrogen evolution reaction has been investigated on Ag(1 0 0) by potentiostatic current transientsat high overpotentials (- > 0.7 V) in acidic solutions. The reaction proceeds via the Volmer-Heyrovskymechanism, simultaneously coupled with desorption of sulphate/disulphate anions. Volmer is the ratedetermined step, although the Heyrovsky reaction is only slightly faster. The kinetic parameters havebeen obtained under various conditions of pH and concentration of anions. A catalytic effect due to thepresence of anions has been observed. © 2013 Elsevier Ltd. All rights reserved.Fil: Ruderman, Andres. Institute of Theoretical Chemistry; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universitat Ulm; AlemaniaFil: Juarez, Maria Fernanda. Institute of Theoretical Chemistry; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Soldano, Germán. Universidad Nacional de Córdoba. Facultad de Cs.químicas. Departamento de Química Teórica y Computacional; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Investigaciones en Físico-química de Córdoba. Universidad Nacional de Córdoba. Facultad de Ciencias Químicas. Instituto de Investigaciones en Físico-química de Córdoba; ArgentinaFil: Avalle, Lucia Bernardita. Universidad Nacional de Córdoba. Facultad de Matemática, Astronomía y Física; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; ArgentinaFil: Beltramo, Guillermo Nicolás. Institute of complex systems; AlemaniaFil: Giesen, M.. Institute of complex systems; AlemaniaFil: Santos, Elizabeth del Carmen. Institute of Theoretical Chemistry; Alemania. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Física Enrique Gaviola. Universidad Nacional de Córdoba. Instituto de Física Enrique Gaviola; Argentina. Universitat Ulm; Alemani

Obesity, genomic ancestry, and socioeconomic variables in Latin American mestizos

Objectives: This article aims to assess the contribution of genomic ancestry and socioeconomic status to obesity in a sample of admixed Latin Americans. Methods: The study comprised 6776 adult volunteers from Brazil, Chile, Colombia, Mexico, and Peru. Each volunteer completed a questionnaire about socioeconomic variables. Anthropometric variables such as weight, height, waist, and hip circumference were measured to calculate body indices: body mass index, waist‐to‐hip ratio and waist‐to‐height ratio (WHtR). Genetic data were extracted from blood samples, and ancestry was estimated using chip genotypes. Multiple linear regression was used to evaluate the relationship between the indices and ancestry, educational level, and economic well‐being. The body indices were dichotomized to obesity indices by using appropriate thresholds. Odds ratios were calculated for each obesity index. Results: The sample showed high percentages of obesity by all measurements. However, indices did not overlap consistently when classifying obesity. WHtR resulted in the highest prevalence of obesity. Overall, women with low education level and men with high economic wellness were more likely to be obese. American ancestry was statistically associated with obesity indices, although to a lesser extent than socioeconomic variables. Conclusions: The proportion of obesity was heavily dependent on the index and the population. Genomic ancestry has a significant influence on the anthropometric measurements, especially on central adiposity. As a whole, we detected a large interpopulation variation that suggests that better approaches to overweight and obesity phenotypes are needed in order to obtain more precise reference values