Polycyclic aromatic hydrocarbon processing in interstellar shocks

Context: PAHs appear to be an ubiquitous interstellar dust component but the effects of shocks waves upon them have never been fully investigated. Aims: To study the effects of energetic (~0.01-1 keV) ion (H, He and C) and electron collisions on PAHs in interstellar shock waves.Methods: We calculate the ion-PAH and electron-PAH nuclear and electronic interactions, above the threshold for carbon atom loss from a PAH, in 50-200 km/s shock waves in the warm intercloud medium. Results: Interstellar PAHs (Nc = 50) do not survive in shocks with velocities greater than 100 km/s and larger PAHs (Nc = 200) are destroyed for shocks with velocities greater/equal to 125 km/s. For shocks in the ~75 - 100 km/s range, where destruction is not complete, the PAH structure is likely to be severely denatured by the loss of an important fraction (20-40%) of the carbon atoms. We derive typical PAH lifetimes of the order of a few x10^8 yr for the Galaxy. These results are robust and independent of the uncertainties in some key parameters that have yet to be well-determined experimentally. Conclusions: The observation of PAH emission in shock regions implies that that emission either arises outside the shocked region or that those regions entrain denser clumps that, unless they are completely ablated and eroded in the shocked gas, allow dust and PAHs to survive in extreme environments.Comment: 19 pages, 11 figures, 3 tables, typos corrected and PAH acronym in the title substituted with full name to match version published in Astronomy and Astrophysic

Aberration-corrected electron microscopy of nanoparticles

The early history of scanning transmission electron microscopy (STEM) is reviewed as a way to frame the technical issues that make aberration correction an essential upgrade for the study of nanoparticles using STEM. The principles of aberration correction are explained, and the use of aberration-corrected microscopy in the study of nanostructures is exemplified in order to remark the features and challenges in the use of this measuring techniqu

The affordance of compassion for animals: a filmic exploration of industrial linear rhythms

Compassion is an emotion that could be useful for improving the lives of animals within the intensive and factory farming system (IFFS). Rhythms that exist within this system play a role in making compassion difficult to realize, which formulates the research question: How do the rhythms of the IFFS shape the affordance of compassion for animals? Drawing on a cultural mode of analysis informed by Henri Lefebvre’s work on rhythms, this paper explored the rhythms of three films that focus on the treatment of animals in this system: Meat; Our Daily Bread and Never Let Me Go. Industrial linear rhythms seem to compromise the compassion offered to animals in the IFFS by manipulating the cyclical rhythms of animals and animalized bodies from birth, through life and at death. Compassion for animals and animalized bodies in the IFFS, this paper concludes, is often provided in a piecemeal and localized manner

Ptychography

Ptychography is a computational imaging technique. A detector records an extensive data set consisting of many inference patterns obtained as an object is displaced to various positions relative to an illumination field. A computer algorithm of some type is then used to invert these data into an image. It has three key advantages: it does not depend upon a good-quality lens, or indeed on using any lens at all; it can obtain the image wave in phase as well as in intensity; and it can self-calibrate in the sense that errors that arise in the experimental set up can be accounted for and their effects removed. Its transfer function is in theory perfect, with resolution being wavelength limited. Although the main concepts of ptychography were developed many years ago, it has only recently (over the last 10 years) become widely adopted. This chapter surveys visible light, x-ray, electron, and EUV ptychography as applied to microscopic imaging. It describes the principal experimental arrangements used at these various wavelengths. It reviews the most common inversion algorithms that are nowadays employed, giving examples of meta code to implement these. It describes, for those new to the field, how to avoid the most common pitfalls in obtaining good quality reconstructions. It also discusses more advanced techniques such as modal decomposition and strategies to cope with three-dimensional () multiple scattering

Photoelectron microscopy of organic surfaces: The effect of substrate reflectivity

5 pagesPhotoelectron measurements of thin organic films deposited on a metal substrate may contain information from deep within the sample, derived from reflected ultraviolet light. This effect depends on the reflectivity of the substrate, the sample thickness and optical absorption coefficient, and the photoelectron escape depth. Calculations are given for phthalocyanine as a specific example. Contrast reversal and apparent seethrough effects resulting from reflection are predicted in overlapping thin films. Photoelectron micrographs of thin films and grid patterns of phthalocyanine show that the reflection model is essentially correct. This effect can be substantially reduced by using a nitrocellulose-coated carbon substrate