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Nucleobases are nitrogenous bases composed of monomers that are a major constituent of RNA and DNA, which are an essential part of any cellular life on the Earth. The search for nucleobases in the interstellar medium remains a major challenge, however, the recent detection of nucleobases in meteorite samples and laboratory synthesis in simulated analogue experiments have confirmed their abiotic origin and a possible route for their delivery to the Earth. Nevertheless, cellular life is based on the interacting network of complex structures, and there is substantial lack of information on the possible routes by which such ordered structures may be formed in the prebiotic environment. In the current study, we present the evidence for the synthesis of complex structures due to shock processing of nucleobases. The nucleobases were subjected to the reflected shock temperature of 3500–7000 K (estimated) and pressure of about 15–34 bar for over ~2 ms timescale. Under such extreme thermodynamic conditions, the nucleobases sample experiences superheating and subsequent cooling. Electron microscopic studies of shock processed residue show that nucleobases result in spontaneous formation of complex structures when subjected to extreme conditions of shock. These results suggest that impact shock processes might have contributed to the self-assembly of biologically relevant structures and the origin of life.
Whether enjoying the lucid prose of a favourite author or slogging through some other writer’s cumbersome, heavy-set prattle (full of parentheses, em dashes, compound adjectives, and Oxford commas), readers will notice stylistic signatures not only in word choice and grammar but also in punctuation itself. Indeed, visual sequences of punctuation from different authors produce marvellously different (and visually striking) sequences. Punctuation is a largely overlooked stylistic feature in stylometry, the quantitative analysis of written text. In this paper, we examine punctuation sequences in a corpus of literary documents and ask the following questions: Are the properties of such sequences a distinctive feature of different authors? Is it possible to distinguish literary genres based on their punctuation sequences? Do the punctuation styles of authors evolve over time? Are we on to something interesting in trying to do stylometry without words, or are we full of sound and fury (signifying nothing)?
In our investigation, we examine a large corpus of documents from Project Gutenberg (a digital library with many possible editorial influences). We extract punctuation sequences from each document in our corpus and record the number of words that separate punctuation marks. Using such information about punctuation-usage patterns, we attempt both author and genre recognition, and we also examine the evolution of punctuation usage over time. Our efforts at author recognition are particularly successful. Among the features that we consider, the one that seems to carry the most explanatory power is an empirical approximation of the joint probability of the successive occurrence of two punctuation marks. In our conclusions, we suggest several directions for future work, including the application of similar analyses for investigating translations and other types of categorical time series.
In chemical process engineering, surrogate models of complex systems are often necessary for tasks of domain exploration, sensitivity analysis of the design parameters, and optimization. A suite of computational fluid dynamics (CFD) simulations geared toward chemical process equipment modeling has been developed and validated with experimental results from the literature. Various regression-based active learning strategies are explored with these CFD simulators in-the-loop under the constraints of a limited function evaluation budget. Specifically, five different sampling strategies and five regression techniques are compared, considering a set of four test cases of industrial significance and varying complexity. Gaussian process regression was observed to have a consistently good performance for these applications. The present quantitative study outlines the pros and cons of the different available techniques and highlights the best practices for their adoption. The test cases and tools are available with an open-source license to ensure reproducibility and engage the wider research community in contributing to both the CFD models and developing and benchmarking new improved algorithms tailored to this field.
Solar coronal dimmings have been observed extensively in the past two decades and are believed to have close association with coronal mass ejections (CMEs). Recent study found that coronal dimming is the only signature that could differentiate powerful flares that have CMEs from those that do not. Therefore, dimming might be one of the best candidates to observe the stellar CMEs on distant Sun-like stars. In this study, we investigate the possibility of using coronal dimming as a proxy to diagnose stellar CMEs. By simulating a realistic solar CME event and corresponding coronal dimming using a global magnetohydrodynamics model (AWSoM: Alfvén-wave Solar Model), we first demonstrate the capability of the model to reproduce solar observations. We then extend the model for simulating stellar CMEs by modifying the input magnetic flux density as well as the initial magnetic energy of the CME flux rope. Our result suggests that with improved instrument sensitivity, it is possible to detect the coronal dimming signals induced by the stellar CMEs.
The previous chapters have highlighted electron induced processes taking place with a wide variety of atoms and molecules, at incident energies from ionization threshold (∼15 eV) to about 2000 eV. These studies seek to provide fundamental knowledge and develop insights into these processes that enable us to interpret the relevant phenomena occurring in both natural and technological environments. In this chapter we aim to highlight various applications of such electron scattering data from different atomic–molecular targets. Electrons are almost everywhere in the universe and provide one of the simplest probes for exploring matter in its different forms. Electron collisions with atoms, molecules and ions are dominant in many of the naturally occurring phenomena including the Earth's atmosphere and in the atmospheres of other planets and their satellites, in comets and in far-off molecular clouds of the interstellar medium, where they may play a key role in producing the molecular precursors of life. Primarily the ionosphere of the Earth and other planets is formed by ionization produced by solar UV and X-rays, with some of the photoelectrons produced being energetic enough to cause further ionization along with excitation, leading to the magnificent phenomena of the aurora. The solar wind contains not only electrons (average energy ∼12 eV) but protons and other charged particles which produce secondary electrons upon interaction with our upper atmosphere. Furthermore relativistic electrons, though in lower concentrations, are continuously arriving on the Earth as a part of cosmic rays coming from far-off galaxies, etc.
Thus the upper atmospheres of the Earth and planets are a veritable electron collision laboratory in nature. Cross sections for interaction processes of electrons are therefore necessary inputs into the models for understanding physico-chemical and dynamic properties of atmospheres/ionospheres of the Earth and other planets as discussed by Haider et al. (2010, 2012) and others. Energy degradation of electrons resulting from ionization and other inelastic processes in specific atmospheres can be investigated by employing Monte Carlo models as demonstrated in Bhardwaj and Mukundan (2015), and references therein.
Electron scattering discussed in the previous chapters is basically a microscopic, i.e.
Electron collisions with atoms and molecules are commonplace. In the natural world they occur in lightning strikes, aurorae, and the Earth's ionosphere in general; outside our planet they are important for similar processes in other planets. The glow of Jupiter's aurora can clearly be seen using telescopes from the Earth. Electron collisions also form a primary process in cometary tails that are bathed in the solar wind, and in many other astrophysical processes. Plasma is the fourth state of matter which involves partial ionization of the atomic and molecular components. Plasmas occur naturally in flames, stars, and elsewhere. Humankind has increasingly harnessed the power of electron collisions in many ways: to start cars with spark plugs, in the traditional light bulb, and in many lasers. Much of modern industry is driven by the use of electron collisions to create plasmas which etch silicon and other materials into ever more complex structures or to provide surface coatings to alter, enhance, or protect the properties of materials. The quest to harness the Sun's power on Earth via fusion involves making a vast hot plasma with a wealth of electron collision processes requiring detailed study. In the current century it has also been realized that the damage experienced by bio-systems as a consequence of all types of high energy particles and radiation is predominantly caused by collisions involving secondary electrons. These electrons are created by the ionizing effect of the original high-energy collision particle independent of the nature of the colliding species. In medical applications these collisions can be harmful, causing double strand breaks of DNA, or beneficial as in radiation therapy, which is widely used to exorcize malignant tumours.
Electrons colliding with atoms and particularly molecules can initiate a variety of processes. Probably the most important of these is the creation of ions (charged species) either through impact ionization or by electron attachment leading to positively and negatively charged ions respectively. These ionized species are chemically active and act as initiators of many of the processes mentioned above.
Electrons are ubiquitous in nature and throughout modern industry, and therefore there are varieties of situations in which electrons interact with atoms and molecules producing diverse physical and chemical phenomena. Extensive studies, both experimental and theoretical, have been carried out on the interactions of electrons with different atomic and molecular targets; indeed the last few decades have witnessed rapid developments in the techniques and methodology for exploring electron–atom/molecule scattering. The wider recognition of the role of fundamental electron interactions in natural phenomena (for example, the observation of aurorae on other planets and the contribution of electron interactions in astrochemistry), in underpinning novel technologies such as Focussed Electron Beam Induced Deposition (FEBID), and as a major source of radiation damage by ionizing radiation has led to an increase in the size of the international community studying electron collisions in all phases of matter.
In this book, our aim is to provide an overview of the field with a focus on theoretical methods used to describe the collisions of intermediate to high energy (exceeding about 15 eV) electrons. The book has six chapters and begins with a discussion of the subject by outlining the necessary textbook background on atoms, molecules, and quantum scattering theories. Attention has been devoted (in Chapter 1) to atomic sizes or ‘radii’ – something that is normally missing in most books and reviews of this kind. A brief survey of atomic radii, running across the periodic table of elements, is outlined.
The major part of this monograph provides an up-to-date review of electron scattering from atoms and molecules, summarizing recent publications. Although the title of the present book mentions ionization specifically, the contents are comprehensive in that we highlight several important inelastic processes ocurring in the background of elastic scattering. For many atoms and a large number of molecules, recent theoretical results are discussed along with experimental and other data, and wherever possible recommended data are presented to provide the user with data sets for models and simulations of processes in which electron interactions play a significant role.