Spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on Cu(111) surfaces.

It has been demonstrated previously that electrons interact differently with chiral molecules depending on their polarization. For enantiomeric pure monolayers of heptahelicene, opposite asymmetries in spin polarization were reported and attributed to the so-called chirality-induced spin selectivity effect. However, these promising proof-of-concept photoemission experiments lack the angular and energy resolution that could provide the necessary insights into the mechanism of this phenomenon. In order to fill in the missing gaps, we provide a detailed spin- and angle-resolved photoemission spectroscopy study of heptahelicene layers on a Cu(111) substrate. Throughout the large accessible energy and angle range, no chirality induced spin asymmetry in photoemission could be observed. Possible reasons for the absence of signatures of the spin-dependent electron transmission through the chiral molecular layer are briefly discussed.

Cost-benefit analysis of controlling rabies: placing economics at the heart of rabies control to focus political will.

Rabies is an economically important zoonosis. This paper describes the extent of the economic impacts of the disease and some of the types of economic analyses used to understand those impacts, as well as the trade-offs between efforts to manage rabies and efforts to eliminate it. In many cases, the elimination of rabies proves more cost-effective over time than the continual administration of postexposure prophylaxis, animal testing and animal vaccination. Economic analyses are used to inform and drive policy decisions and focus political will, placing economics at the heart of rabies control.

La rage est une zoonose importante au plan économique. Les auteurs décrivent la portée de l'impact économique de la rage et présentent quelques modèles d'analyse économique utilisés pour comprendre ces effets ; ils analysent également les compromis à trouver entre les efforts consacrés à la gestion de la rage et ceux dédiés à son élimination. Dans bien des cas, il est plus rentable sur le long terme d'éliminer la rage que de procéder à la gestion continue de la prophylaxie post-exposition chez l'homme et au dépistage et à la vaccination des animaux. Les analyses économiques servent à documenter et à orienter les décisions concernant les mesures à prendre afin de mobiliser la volonté politique nécessaire, en plaçant l'économie au coeur de la lutte contre la rage.

La rabia es una zoonosis que reviste importancia económica. Los autores exponen la magnitud del impacto económico de la enfermedad y algunas de las modalidades de análisis económico utilizadas para aprehender esas consecuencias, así como el juego de equilibrios entre las medidas de gestión de la rabia y las actividades destinadas a eliminarla. En muchos casos, la eliminación de la enfermedad ofrece a la larga mayor eficacia, en relación con el costo, que la continua labor de administración de profilaxis tras exposición, realización de pruebas en animales y vacunación de estos. Los análisis económicos sirven para fundamentar y encauzar las decisiones de planificación y para aglutinar la voluntad política, haciendo de los aspectos económicos un eje de la lucha contra la rabia.

Pentagonal tiling with buckybowls: pentamethylcorannulene on Cu(111).

We present scanning tunnelling microscopy studies and first principles calculation on the 2D crystallization of pentagonal pentamethylcorannulene on a Cu(111) surface under ultrahigh vacuum in the temperature range of 50 K to 400 K. The observed 2D crystal phases and their packing densities are compared to tiling options of hard pentagons. Temperature change-induced reversible phase transitions reveal entropic effects in 2D crystallization. Only inclusion of dispersion interactions into density functional theory yields structures observed experimentally at low temperatures.

Two-dimensional separation of [7]helicene enantiomers on Cu(111).

The adsorption of heptahelicene, a helically shaped polyaromatic hydrocarbon (C(30)H(18)), on a Cu(111) surface was studied by means of thermal desorption mass spectrometry (TDMS) and low energy electron diffraction (LEED) at temperatures between 130-1,000 K under ultrahigh vacuum (UHV) conditions. The molecule in the monolayer remains intact up to 400 K. Above that temperature it decomposes in several steps into carbon and hydrogen, desorbing subsequently as H(2). In the saturated monolayer of the racemate the enantiomers are separated into two different domains on the surface which are mirror images of each other. After adsorption of one enantiomer only, no mirror domains were observed.

Sum-frequency vibrational spectroscopy on chiral liquids: a novel technique to probe molecular chirality.

Optical activity in sum-frequency vibrational spectra has been observed for the first time in chiral liquids. The electric-dipole allowed chiral element of the nonlinear susceptibility appears to be 3 orders of magnitude smaller than typical allowed achiral elements. This is partly because the observed chirality requires a breakdown of the Born-Oppenheimer approximation.