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The brown anole (Anolis sagrei) as a model for studying life-history adaptation to seasonality
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VHF and UHF Electromagnetic Radiation Produced by Streamers in Lightning
Get PDFIn this letter, we report simulation results of streamer propagation and collision that produce electromagnetic radiation in the very high frequency (VHF) and ultra high frequency (UHF) bands. The streamers are initiated in overbreakdown field conditions, 1.5E(k)and2E(k), respectively, which may be found during the corona flash stage of negative leader stepping processes. We find that while streamer propagation produces stronger VHF radiation, the head-on collision of streamers dominates UHF, and even higher-frequency radiation. Analysis of the energy spectral densities obtained from different simulation cases shows that the total length and radii of colliding streamers, as well as the ambient field, are important parameters for the UHF radiation produced by streamer collisions. The larger those parameters are, the stronger UHF radiation produced. Finally, by comparing with the measured spectral magnitude of lightning field in the VHF range, it is found that there are probably 10(5)-10(7) streamers involved during the lightning corona flash stage. Plain Language Summary Despite being a familiar phenomenon, the physics of lightning initiation and propagation is not well understood. An effective approach to study lightning is to observe their radio frequency (RF) signals, which is especially critical for understanding the lightning activities inside thunderstorms, because clouds are opaque for other signals. The RF signals with frequencies above about 10MHz are commonly used to map/image lightning development. They are believed to be produced by the physical process electrically breaking down virgin air. Previous work has shown that electrical breakdown processes known as streamers, which are the precursors of lightning, can produce RF radiation below hundreds of megahertz. Our study investigates a physical process that enables lightning to produce RF radiation above hundreds of megahertz. We find that collisions between streamers can generate rapid increases of electrical current to produce RF emissions extending to tens of gigahertz. The results will be helpful for understanding and interpreting RF observations/measurements of lightning and will generate impact in the field of atmospheric and space electricity.PublishedYe
'As plain as water's water': The Symbolic Function of Water in Romola
No full textArticle from the George Eliot Review, digitized and hosted by the George Eliot Review Online.Publishe
Modeling of a New Electron Acceleration Mechanism Ahead of Streamers
Get PDFHead‐on collisions between negative and positive streamers have been proposed as a mechanism behind X‐ray emissions by laboratory spark discharges. Recent simulations using plasma fluid and particle in cell models of a single head‐on collision of two streamers of opposite polarities in ground pressure air predicted an insignificant number of thermal runaway electrons >1 keV and hence weak undetectable X‐ray emissions. Because the current available models of a single streamer collision failed to explain the observations, we first use a Monte Carlo model coupled with multiple static dielectric ellipsoids immersed in a subbreakdown ambient electric field as a description of multiple streamer environment and we investigate the ability of multiple streamer‐streamer head‐on collisions to accelerate runaway electrons >1 keV up to energies ∼200–300 keV instead of just one single head‐on collision. The results of simulations show that the streamer head‐on collision mechanism fails to accelerate electrons; instead, they decelerate in the positive streamer channel. In a second part, we use a streamer plasma fluid model to simulate a new streamer‐electron acceleration mechanism based on a collision of a large negative streamer with a small neutral plasma patch in different Laplacian electric fields |E 0|= (35, 40, 45) kV/cm, respectively. We observe the formation of a secondary short propagating negative streamer with a strong peak electric field >250 up to 378 kV/cm over a time duration of ∼0.16 ns at the moment of the collision. The mechanism produces up to 106 runaway electrons with an upper energy limit of 24 keV.Publishe
Support Scholars Who Share: Combating the Mismatch between Openness Policies and Professional Rewards
Get PDFAre institutional policies designed to advance open scholarship capable of accomplishing that end? What other consequences might they have for the practice of research? These mandates undoubtedly increase the number of publicly-available articles and datasets in the short-term, but there is also an expectation that as researchers become accustomed to the new requirements, the culture within their disciplines will shift to support open research, for instance through the founding of new open-access journals or platforms. Is this reasonable? The answer depends on the fate of individual scholars who support openness within their fields. While disciplinary norms are not biological traits, they can be said to evolve as new attitudes take root and proliferate in the population of members. Cultural change is only sustainable when those who hold the new attitudes can remain in the population.
In this paper, I argue that the choices that determine professional gain and loss facing each researcher who wants to advance in their areas of study can be modeled as a prisoner’s dilemma. I first discuss why patterns in researcher behavior and beliefs suggest a prisoner’s dilemma in the area of data sharing, then apply this line of reasoning to the problem of perverse incentives in open access publishing. Finally, I explain what makes certain open access mandates counterproductive and propose alternative solutions that reward researchers who choose to make their work open. This provides a path towards reforming disciplinary norms concerning publishing.Ye
Cluster perturbation theory. IV. Convergence of cluster perturbation series for energies and molecular properties
Get PDFThe theoretical foundation has been developed for establishing whether cluster perturbation (CP) series for the energy, molecular properties, and excitation energies are convergent or divergent and for using a two-state model to describe the convergence rate and convergence patterns of the higher-order terms in the CP series. To establish whether the perturbation series are convergent or divergent, a fictitious system is introduced, for which the perturbation is multiplied by a complex scaling parameter z. The requirement for convergent perturbation series becomes that the energy or molecular property, including an excitation energy, for the fictitious system is an analytic, algebraic function of z that has no singularities when the norm vertical bar z vertical bar is smaller than one. Examples of CP series for the energy and molecular properties, including excitation energies, are also presented, and the two-state model is used for the interpretation of the convergence rate and the convergence patterns of the higher-order terms in these series. The calculations show that the perturbation series effectively become a two-state model at higher orders. Published under license by AIP Publishing.Publishe
Two-Dimensional gcPIC Simulation of Rising-Tone Chorus Waves in a Dipole Magneitic Field
Get PDFRising-tone chorus waves have already been successfully produced in a mirror magnetic field with the use of one- and two-dimensional particle-in-cell (PIC) simulations. However, in reality, the background magnetic field in the inner Earth's magnetosphere is a dipole magnetic field, unlike symmetric mirror fields. In this paper, with the two-dimensional (2-D) general curvilinear PIC (gcPIC) code, we investigate the generation of rising-tone chorus waves in the dipole magnetic field configuration. The plasma consists of three components: immobile ions, cold background, and hot electrons. In order to save computational resource, the topology of the magnetic field is roughly equal to that at L = 0.6 R-E, although the plasma parameters corresponding to those at L = 6 R-E (R-E is the Earth's radius) are used. Whistler mode waves are first excited around the magnetic equator by the hot electrons with a temperature anisotropy. The excited whistler mode waves propagate almost parallel and antiparallel to the background magnetic field in their source region, which is limited at vertical bar lambda vertical bar <= 3 degrees (where lambda is the magnetic latitude). When the waves leave from the source region and propagate toward high latitudes, both their amplitude and wave normal angle become larger. However, the group velocity of the waves is directed toward high latitudes almost along the magnetic field. During such a process, the waves have a frequency chirping, as shown by a rising tone in the frequency-time spectrogram. To our best knowledge, it is for the first time that rising-tone chorus are generated in a dipole magnetic field with a PIC simulation.PublishedYe
On the potential of lignin-containing cellulose nanofibrils (LCNFs): a review on properties and applications
Get PDFThis review outlines the present state and recent progress in the area of lignin-containing cellulose nanofibrils (LCNFs), an emerging family of green cellulose nanomaterials. Different types of LCNF raw materials are described, with main focus on wood-based raw materials, and the properties of the resulting LCNFs are compared. Common problems faced in industrial utilization of CNFs are discussed in the light of potential improvements from LCNFs, covering areas such as chemical and energy consumption, dewatering and redispersibility. Out of the potential applications, barrier films, emulsions and nanocomposites are considered.PublishedYe