Non-Adiabatic Vibrational Damping of Molecular Adsorbates: Insights into Electronic Friction and the Role of Electronic Coherence

We present a perturbation approach rooted in time-dependent density-functional theory to calculate electron hole (eh)-pair excitation spectra during the non-adiabatic vibrational damping of adsorbates on metal surfaces. Our analysis for the benchmark systems CO on Cu(100) and Pt(111) elucidates the surprisingly strong influence of rather short electronic coherence times. We demonstrate how in the limit of short electronic coherence times, as implicitly assumed in prevalent quantum nuclear theories for the vibrational lifetimes as well as electronic friction, band structure effects are washed out. Our results suggest that more accurate lifetime or chemicurrent-like experimental measurements could characterize the electronic coherence.Comment: Article as accepted for publication in Physical Review Letter

Electronic friction-based vibrational lifetimes of molecular adsorbates: Beyond the independent atom approximation

We assess the accuracy of vibrational damping rates of diatomic adsorbates on metal surfaces as calculated within the local-density friction approximation (LDFA). An atoms-in-molecules (AIM) type charge partitioning scheme accounts for intra-molecular contributions and overcomes the systematic underestimation of the non-adiabatic losses obtained within the prevalent independent atom approximation. The quantitative agreement obtained with theoretical and experimental benchmark data suggests the LDFA-AIM as an efficient and reliable approach to account for electronic dissipation in ab initio molecular dynamics simulations of surface chemical reactions.Comment: 5 pages including 2 figure

Cosmic Ray Nuclei (CRN) detector investigation

The Cosmic Ray Nuclei (CRN) detector was designed to measure elemental composition and energy spectra of cosmic radiation nuclei ranging from lithium to iron. CRN was flown as part of Spacelab 2 in 1985, and consisted of three basic components: a gas Cerenkov counter, a transition radiation detector, and plastic scintillators. The results of the experiment indicate that the relative abundance of elements in this range, traveling at near relativistic velocities, is similar to those reported at lower energy

Making the local count: social change communication and participation in HIV prevention

Introduction: Migrant and mobile seasonal farm workers face multiple challenges in preventing sexual transmission of HIV. They also fall beyond direct reach of district health promotion services and national HIV prevention communication interventions. HIV prevalence rates in rural farming communities are significantly higher than provincial averages. An integrated health promotion intervention was initiated in 2005 on commercial farms in Hoedspruit, Limpopo province, through the International Organization for Migration. In terms of HIV prevention the Hlokomela project’s key innovation was to employ a local process of participatory communication, with and within the farm worker community, in order to create a local context enabling of health promotion and within which efforts to prevent HIV could be more effective. The research sought to explore the social processes and actions related to the on-going process of dialogue at the core of the participatory communication process. The objective was to describe and analyse the role of dialogue during regular purposive face to face interactions with farm worker change agents, in promoting health and addressing vulnerability to HIV. Method: The study population comprised Hlokomela coordinators, farm worker change agents (Nompilos and Gingirikani) and key farm stakeholders from the 59 partner farms. Research was conducted in Hoedspruit, at the Hlokomela Wellness Centre and on a partner farm. A grounded theory approach was used for sampling: participants were selected through purposive sampling for the initial study sample, and theoretical sampling for the balance. Data was gathered monthly, in three stages between August and November 2010, through: 10 semi-structured in-depth individual interviews; 5 focus group discussions, and observation of 2 monthly meetings and a special event organised by the change agents. Data was analysed using a grounded theory approach. Findings: Farm workers perceive and experience the process of on-going dialogue in face to face interactions as being intertwined with other aspects of the intervention, in particular identification and action to enable access to health services. Hlokomela Coordinators guide and support the process as a means to empower a corps of primary farm worker Change Agents (Nompilos). Nompilos, in turn, apply the system to benefit and empower a wider group of farm worker as second level change agents (Gingirikani). Through this system farm workers have found ways to negotiate HIV-related stigma and cultural taboos on speaking about sex, and to address interpersonal tensions and violence, often gender related, on farms. They have come to consider themselves leaders and role models. Individuals have been enabled to define for themselves appropriate HIV-protective behaviours, and new HIV protective social norms which enable protective behaviours, have gained local currency. These norms include placing value on the opportunity and ability to communicate, to learn from each other, to develop different views, and to attain or protect family, physical and spiritual wellness. Discussion: The process of engagement and regular dialogue, nested in processes related to the other elements of the projects, has positively altered the material, experiential and symbolic context on partner farms. It constitutes effective communication for social change, and has enabled health promotion, as described by the Ottawa Charter, to be realised. This demonstrates that an on-going, participatory process of local communication can create an enabling environment for health promotion. A community of communication practice has been developed in the farming community; this constitutes a reservoir of social capital and capacity to communicate and addresses the need for innovative communication in rural settings. A discursive space and public of discourse around wellness and HIV has been created, and new leaders and alternative narratives, which constitute self and collectively defined “AIDS competency” in a marginalised setting, are becoming visible, suggesting pathways for future interventions to enable equivalent responses in similar settings. Conclusion: An opportunity exists to make more effective use of the power of face to face communication in defined local settings, in order to enable disempowered individuals to claim their human and health rights, to protect themselves from HIV, and to help activate and realise synergies in health and development objectives such as the Millennium Development Goals

Systemic suppression of the shoot metabolism upon rice root nematode infection

Hirschmanniella oryzae is the most common plant-parasitic nematode in flooded rice cultivation systems. These migratory animals penetrate the plant roots and feed on the root cells, creating large cavities, extensive root necrosis and rotting. The objective of this study was to investigate the systemic response of the rice plant upon root infection by this nematode. RNA sequencing was applied on the above-ground parts of the rice plants at 3 and 7 days post inoculation. The data revealed significant modifications in the primary metabolism of the plant shoot, with a general suppression of for instance chlorophyll biosynthesis, the brassinosteroid pathway, and amino acid production. In the secondary metabolism, we detected a repression of the isoprenoid and shikimate pathways. These molecular changes can have dramatic consequences for the growth and yield of the rice plants, and could potentially change their susceptibility to above-ground pathogens and pests

Electron Counting Rules and Electronic Structure in Tetrameric Transition-Metal (T)-Centered Rare-Earth (R) Cluster Complex Halides (X)

Electron partition schemes are a beneficial means to systematize bonding networks and to identify structure-bonding relationships in polar intermetallics. One prolific class of polymetal networks with simple counterions is the broad family of transition-metal (T)-centered rare-earth metal (R) cluster halides (X), which can be isolated or condensed to oligomers and chains. While the electronic structures of R cluster monomers and chains encapsulating T atoms have been studied systematically, the band structures of oligomers, in particular, the most frequent Friauf-type {T4R16} tetramers, have been investigated to a lesser extent. Therefore, the band structures of prototypical compounds with {T4R16}-type tetramers, while maintaining different compositions, were analyzed employing density functional theory based methods. Furthermore, these theoretical examinations provide insight into the origin of the 15 electron rule, which is significant for this class of compounds and correlates with the closed-shell configurations for these structures. Additional research focused on the band structure of monoclinic {Ru4Gd16}Br23, which is composed of rhomboid-shaped {Ru4Gd16} tetramers

Towards Macroporous α-Al2O3—Routes, Possibilities and Limitations

This article combines a systematic literature review on the fabrication of macroporous α-Al2O3 with increased specific surface area with recent results from our group. Publications claiming the fabrication of α-Al2O3 with high specific surface areas (HSSA) are comprehensively assessed and critically reviewed. An account of all major routes towards HSSA α-Al2O3 is given, including hydrothermal methods, pore protection approaches, dopants, anodically oxidized alumina membranes, and sol-gel syntheses. Furthermore, limitations of these routes are disclosed, as thermodynamic calculations suggest that γ-Al2O3 may be the more stable alumina modification for ABET > 175 m2/g. In fact, the highest specific surface area unobjectionably reported to date for α-Al2O3 amounts to 16–24 m2/g and was attained via a sol-gel process. In a second part, we report on some of our own results, including a novel sol-gel synthesis, designated as mutual cross-hydrolysis. Besides, the Mn-assisted α-transition appears to be a promising approach for some alumina materials, whereas pore protection by carbon filling kinetically inhibits the formation of α-Al2O3 seeds. These experimental results are substantiated by attempts to theoretically calculate and predict the specific surface areas of both porous materials and nanopowders