Pablo S. Moya

Line Shapes in Infrared Absorption by Solids and by Atomic or Molecular Species Embedded in Solids

When the target is in the solid state, most infrared spectral features are manifestly asymmetric; hence, a line shape function well-grounded in theory is necessary to ascertain the net energy taken by the associated electronic transition. The main sources for spectral line broadening, asymmetry, and shift, no matter the transferred energy, are multiphonon events involving the acoustic vibrational modes. A simple closed-form mathematical expression for the phonon-broadened lineshapes, shown to be valid at low temperatures, and linewidths on the order of the Debye energy of the solid or smaller, giving remarkable agreement with experiment is studied in connection with its utility for analyzing infrared spectral features.

Linear Kinetic Waves in Plasmas Described by Kappa Distributions

In this chapter we present an overview of the excitation, propagation, and absorption of linear plasma waves in collisionless, spatially uniform, multicomponent, magnetized non-Maxwellian plasma characterized by a kappa velocity distribution based on a Vlasov kinetic description. Although traditional plasma physics texts are replete with examples of linear waves and instabilities in plasmas whose charged particles are modeled by the thermal Maxwellian velocity distribution, very few works exist that bring together in one place the analogous results for plasmas modeled by a kappa distribution—a more appropriate and versatile model for space and other collisionless plasmas. The treatment, which uses Vlasov kinetic theory coupled with Maxwells equations, covers the range from low-frequency waves, where ion dynamics dominates the dispersion properties of the waves, up to frequencies in excess of the plasma frequency, where the electron physics plays the dominant role. For reasons of tractability, the primary focus is on waves and instabilities that propagate parallel to the ambient magnetic field, but both electrostatic as well as electromagnetic plasma waves are considered. The chapter begins with the fundamental concepts of nonequilibrium statistical mechanics and electrodynamics. The established kinetic theory of waves in a multispecies plasma with arbitrary velocity distribution is used to introduce the general dielectric tensor, which characterizes the plasma response to fluctuating electromagnetic fields. The general dielectric tensor is then derived using a drifting bi-kappa distribution for the special case of parallel propagation. Using this dielectric tensor in the Fourier-transformed wave equation, various fundamental parallel propagating longitudinal (electrostatic) and transverse (electromagnetic) plasma wave modes are discussed within the context of the bi-kappa velocity distribution. Both analytical and numerical results for the excitation (growth) and absorption (damping) of plasma waves in plasmas with a kappa velocity distribution will be discussed.

Relativistic Cyclotron Instability in Anisotropic Plasmas

CONICyT through FONDECyT 1150718 1130273 1161711 1161700 11150055 FONDECyT Postdoctoral Grant 3150262 CEDENNA CONICyT PIA ACT1405 NASA-Wind/SWE project Universidad de Concepcion through VRID-Enlace 215.011.059-1.0

Electromagnetic Electron Cyclotron Instability in the Solar Wind

The abundant reports on the existence of electromagnetic high-frequency fluctuations in space plasmas have increased the expectations that theoretical modeling may help understand their origins and implications (e.g., kinetic instabilities and dissipation). This paper presents an extended quasi-linear approach of the electromagnetic electron cyclotron instability in conditions typical for the solar wind, where the anisotropic electrons (T⊥>T∥) exhibit a dual distribution combining a bi-Maxwellian core and bi-Kappa halo. Involving both the core and halo populations, the instability is triggered by the cumulative effects of these components, mainly depending of their anisotropies. The instability is not very sensitive to the shape of halo distribution function conditioned in this case by the power index κ. This result seems to be a direct consequence of the low density of electron halo, which is assumed more dilute than the core component in conformity with the observations in the ecliptic. Quasi-linear time evolutions predicted by the theory are confirmed by the particle-in-cell simulations, which also suggest possible explanations for the inherent differences determined by theoretical constraints. These results provide premises for an advanced methodology to characterize, realistically, the electromagnetic electron cyclotron instability and its implication in the solar wind.

Processes in auroral oval and outer electron radiation belt

We have analyzed the role of auroral processes in the formation of the outer radiation belt, considering that the main part of the auroral oval maps to the outer part of the ring current, instead of the plasma sheet as is commonly postulated. In this approach, the outer ring current is the region where transverse magnetospheric currents close inside the magnetosphere. Specifically, we analyzed the role of magnetospheric substorms in the appearance of relativistic electrons in the outer radiation belt. We present experimental evidence that the presence of substorms during a geomagnetic storm recovery phase is, in fact, very important for the appearance of a new radiation belt during this phase. We discuss the possible role of adiabatic acceleration of relativistic electrons during storm recovery phase and show that this mechanism may accelerate the relativistic electrons by more than one order of magnitude.

What is the temperature of a moving body

The construction of a relativistic thermodynamics theory is still controversial after more than 110 years. To the date there is no agreement on which set of relativistic transformations of thermodynamic quantities is the correct one, or if the problem even has a solution. Starting from Planck and Einstein, several authors have proposed their own reasoning, concluding that a moving body could appear cooler, hotter or at the same temperature as measured by a local observer. In this article we present a review of the main theories of relativistic thermodynamics, with an special emphasis on the physical assumptions adopted by each one. We also present a set of relativistic transformations that we have derived by assuming the laws of Thermodynamics to be covariant. We found that under such assumptions a moving body appears to be hotter. Since relativistic thermodynamics is a topic that can be treated as part of an undergraduate course of classical thermodynamics or modern physics, the review and our own derivations presented here aim to encourage undergraduate physics students to open a discussion on the fundamental assumptions in thermodynamics and to engage in research activities early in their scientific career.