Form Of Internal Energy Research Articles

Particle-in-cell simulations of Alfvén wave parametric decay in a low-beta plasma

We study the parametric decay instability of parallel-propagating Alfvén waves in a low-beta plasma using one-dimensional fully kinetic simulations. We focus for the first time on the conversion of the energy stored in the initial Alfvén wave into particle internal energy, and on its partition between particle species. We show that compressible fluctuations generated by the decay of the pump wave into a secondary ion-acoustic mode and a reflected Alfvén wave contribute to the gain of internal energy via two distinct mechanisms. First, the ion-acoustic mode leads nonlinearly to proton trapping and proton phase-space mixing, in agreement with previous work based on hybrid simulations. Second, during the nonlinear stage, a compressible front of the fast type develops at the steepened edge of the backward Alfvén wave leading to a field-aligned proton beam propagating backwards at the Alfvén speed. We find that parametric decay heats preferentially protons, which gain approximately 50 % of the pump wave energy in the form of internal energy. However, we find that electrons are also energized and that they contribute to the total energy balance by gaining 10 % of the pump wave energy. By investigating energy partition and particle heating during parametric decay, our results contribute to the determination of the role of compressible and kinetic effects in wave-driven models of the solar wind.

Multi-ignition of cornstarch dusts in a vessel with compartments

The aim of this work is to study the effects of a multi-source ignition in a wide energy range on a dust explosion. More particularly, we focus on the pressure history inside a partitioned vessel. The initiation is introduced in the form of internal energy and a calculation methodology, particularly interesting in the field of the risk assessment is used to simulate the transmission of the explosion from one compartment to another adjacent one by the means of the hot flow through the shared orifice and finally to generalise this methodology to a complex multi-partitioned structure.The basic characteristics of the model have been developed for the ignition and the combustion of propulsive powders and adapted to dust suspensions with appropriate parameters linked to simplified kinetics. A simple representation of the combustion phenomena based on energy transfers and the action of specific molecular species is presented. The model allows the study of the influence of various parameters such as the dust concentration, the different ignition energies and their locations, the size of the inner openings or the venting areas. The theoretical results have been compared with many data available in the literature and indicate correct preliminary trends.

Origin of negative temperatures in systems interacting with external fields

The controversial existence of negative temperatures has stirred interesting debates that have reached the foundations of thermodynamics, including questions on the second law, the Carnot efficiency and the statistical definition of entropy. Here we show that for systems interacting with an external field, negative temperatures may arise when the interaction energy with the field is treated as a form of internal energy. We discuss how negative temperatures are avoided when using a thermodynamic formalism that accounts for the intensive and extensive variables associated to the external field. We use the paramagnetic system and a perfect gas in a gravitational field to illustrate these ideas. Considerations about the isothermal and adiabatic work done by the field or the system also shed light on the inconsistency of super-Carnot efficiencies.

An enthalpy-based finite element method for solving two-phase Stefan problem

Stefan problem is a problem involving phase transition from solid to liquid or vice versa where boundary between solid and liquid regions moves as function of time. This paper presents numerical solution of one-dimensional two-phase Stefan problem by using finite element method. The governing equations involved in Stefan problem consist of heat conduction equation for solid and liquid regions, and also transition equation in interface position (moving boundary). The equations are difficult to solve by ordinary numerical method because of the presence of moving boundary. As consequence, the equations is reformulated into the form of internal energy (enthalpy). By the enthalpy formulation, solution of the heat conduction equations is no longer concerning the phase state of material. The advantage of the enthalpy formulation is that, finite element method can be easily implemented to solve Stefan problem. Numerical simulation of interface position, temperature profile, and temperature history has good agreement with the exact solution. The approximation of interface position using finite element method was found that it is more accurate than the approximation by using Godunov method. The simulation results also reveal that the finite element method for solving Stefan problem have smaller mean absolute error than the Godunov method.

Large-scale jets from active galactic nuclei as a source of intracluster medium heating: cavities and shocks

The evolution of powerful extragalactic jets is not only interesting by itself, but also for its impact on the evolution of the host galaxy and its surroundings. We have performed long-term axisymmetric numerical simulations of relativistic jets with different powers to study their evolution through an environment with a pressure and density gradient. Our results show key differences in the evolution of jets with different powers in terms of the spatial and temporal scales of energy deposition. According to our results, the observed morphology in X-ray cavities requires that an important fraction of the jet's energetic budget is in the form of internal energy. Thus, light, lepton-dominated jets are favoured. In all cases, heating is mainly produced by shocks. Cavity overpressure is sustained by an important population of thermal particles. Our simulations reproduce the cool-core structure in projected, luminosity-weighted temperature. We have performed an additional simulation of a slow, massive jet and discuss the differences with its relativistic counterparts. Important qualitative and quantitative differences are found between the non-relativistic and the relativistic jets. Our conclusions point towards a dual-mode of AGN kinetic feedback, depending on the jet power.

The matter Lagrangian and the energy-momentum tensor in modified gravity with nonminimal coupling between matter and geometry

We show that in modified $f(R)$ type gravity models with nonminimal coupling between matter and geometry, both the matter Lagrangian and the energy-momentum tensor are completely and uniquely determined by the form of the coupling. This result is obtained by using the variational formulation for the derivation of the equations of motion in the modified gravity models with geometry-matter coupling, and the Newtonian limit for a fluid obeying a barotropic equation of state. The corresponding energy-momentum tensor of the matter in modified gravity models with nonminimal coupling is more general than the usual general-relativistic energy-momentum tensor for perfect fluids, and it contains a supplementary, equation of state dependent term, which could be related to the elastic stresses in the body, or to other forms of internal energy. Therefore, the extra force induced by the coupling between matter and geometry never vanishes as a consequence of the thermodynamic properties of the system, or for a specific choice of the matter Lagrangian, and it is nonzero in the case of a fluid of dust particles.

Auroral arcs as current transformers

We treat the effects of an electric field tangential to an auroral arc on the basis of an analytical model according to which auroral arcs are energized by the release of magnetic shear stresses and associated internal energy (Haerendel, 2007). If the tangential field exceeds a certain (low) threshold, the ionosphere acts as a current generator, or better transformer, and the magnetosphere as the load. The reason is that energy supplied by a longitudinal Type I current system, as defined by Boström in 1964, is transformed into energy of the latitudinal Type II current system attached to the arc and is mostly consumed by the auroral acceleration process. Closure of the transformer current in the upper magnetosphere and energy deposition in form of internal energy and shear stresses, although small, are crucial for the operation of this process. It can be visualized as a dragging of magnetic field and plasma along the arc in the direction of higher magnetospheric pressure enforced by the electric polarization field. This energy deposition from below is superimposed on the release of free energy supplied by the magnetospheric generator. Formulation of this scenario leads to a set of algebraic equations, whose solution provides quantitative answers on the interdependence of current closure, energy deposition, and enhanced auroral energy flux in relation to the imposed tangential electric field. Contrary to earlier expectations, the polarization field appears not as a consequence of current blockage, but as manifestation of its continuation by field‐aligned currents and their closure in the magnetosphere. Another consequence of the energy deposition from below is a small modification of the arc's proper motion in the ambient plasma frame. A procedure for evaluating applicable measurements in terms of the underlying physics is given and a concrete example added.

Nonlinear Atmospheric Adjustment to Thermal Forcing

Abstract A nonlinear, numerical model of a compressible atmosphere is used to simulate the hydrostatic and geostrophic adjustment to a localized prescribed heating applied over five minutes with a size characteristic of an isolated, deep, cumulus cloud. This thermal forcing generates both buoyancy waves and a horizontally propagating Lamb wave packet as well as a steady state rich in potential vorticity. The adjustments in three model atmospheres (an isothermal, a constant lapse rate, and one with a stratosphere) are studied. The Lamb wave packet and the two lowest-order buoyancy waves are relatively unaffected by nonlinearities but the higher-order modes and the steady state are. The heating generates a vertically stacked dipole of potential vorticity with a cyclonic perturbation below an anticyclonic perturbation. In contrast to the linear results, the nonlinear dipole is severely distorted by vertical and horizontal advections. In addition, the Lamb wave packet contains some weak positive perturbation potential vorticity. The energetics is examined using traditional and Eulerian available energetics. Traditional energetics consists of kinetic, internal, and potential energies. It is shown that the Lamb wave packet contains more total traditional energy than that input to the atmosphere by the heating. The traditional energy in the packet resides primarily in the form of internal energy and only secondarily in the form of potential energy. The passage of the Lamb wave packet produces an atmosphere that, overall, is cooler, less dense, and with less total traditional energy than the initial atmosphere. Eulerian available energetics consists of kinetic, available potential, and available elastic energies. The heating generates both available elastic and potential energy that is then converted into kinetic energy. Most of the available elastic energy projects onto the Lamb packet, while almost all of the available potential energy is associated with the buoyancy waves and the steady state. The effects of varying the spatial and temporal scale of the heating, while keeping the net heating the same, are examined. As the duration of the heating decreases, the amount of energy projected onto the waves increases. Increasing the size of the heating decreases the amount of energy projected onto the waves. The adjustment is kinetically more vigorous in the nonisothermal atmospheres because of the reduction in the base-state static stability. The presence of a stratosphere produces large anomalies at and above the tropopause that are linked to the vertical motions of the buoyancy wave field.

Deceleration phase of inertial confinement fusion implosions

A model for the deceleration phase and marginal ignition of imploding capsules is derived by solving a set of ordinary differential equations describing the hot-spot energy balance and the shell dynamics including the return shock propagation. It is found that heat flux leaving the hot spot goes back in the form of internal energy and PdV work of the material ablated off the inner-shell surface. Though the hot-spot temperature is reduced by the heat conduction losses, the hot-spot density increases due to the ablated material in such a way that the hot-spot pressure is approximately independent of heat conduction. For hot-spot temperatures exceeding approximately 7 keV, the ignition conditions are not affected by heat conduction losses that are recycled into the hot spot by ablation. Instead, the only significant internal energy loss is due to the hot-spot expansion tamped by the surrounding shell. The change of adiabat induced by the shock is also calculated for marginally igniting shells, and the relation between the in-flight and stagnation adiabats is in general agreement with the numerical fit of LASNEX simulations by Herrmann et al. [Nucl. Fusion 41, 99 (2001)] and the self-similar solution of Kemp et al. [Phys. Rev. Lett. 15, 3336 (2001)]. The minimum kinetic energy required for ignition is also calculated from the same model and shown to be in good agreement with the numerical fit of LASNEX simulations. It is also found that mass ablation leads to a significant reduction of the deceleration phase Rayleigh–Taylor instability growth rates and to the suppression of short wavelength modes.

Hot-spot dynamics and deceleration-phase Rayleigh–Taylor instability of imploding inertial confinement fusion capsules

A model for the deceleration phase of imploding inertial confinement fusion capsules is derived by solving the conservation equations for the hot spot. It is found that heat flux leaving the hot spot goes back in the form of internal energy and pdV work of the material ablated off the inner shell surface. Though the hot-spot temperature is reduced by the heat conduction losses, the hot-spot density increases due to the ablated material in such a way that the hot-spot pressure is approximately independent of heat conduction. For direct-drive National Ignition Facility-like capsules, the ablation velocity off the shell inner surface is of the order of tens μm/ns, the deceleration of the order of thousands μm/ns2, and the density-gradient scale length of the order a few μm. Using the well-established theory of the ablative Rayleigh–Taylor instability, it is shown that the growth rates of the deceleration phase instability are significantly reduced by the finite ablative flow and the unstable spectrum exhibits a cutoff for mode numbers of about l≈90.

Isotope effects in the bimolecular reactions of gaseous ions. Concepts, techniques, and reactions

AbstractFoundations of isotope effects are examined in terms of concepts, models, and theories. Leading instrumental methods for bimoleculur reactions are reviewed: the guided ion beum mass spectrometer (GIBMS) and the selected ion flow tube (SIFT). In their most elaborate forms, both methods can select the translational energies of the reacting ions and the temperatures of the neutral molecules. This capability gives extraordinary control over bimolecular ion/molecule reactions. Experiments on simple systems can sometimes identify the effects of particular forms of internal energy. Isotope effects appear in numerous reaction types and behave in several ways as functions of ion translational energy and temperature. For endothermic reactions, they can become very large at low temperatures, a matter of much interest in astrophysics. © 1996 John Wiley & Sons, Inc.

Intelligent image interpretation for high‐compression high‐quality sequence coding

AbstractVideo transmission at very low bit rate has got growing attention in recent years. In this paper we propose an approach for the compression of 144 x 176 pixels Q‐CIF video conference sequences. The compression ratio well exceeds 200 : 1 (thus leading to bit‐rates under 10 kbit/s for 10 frames/s) with very good psycovisual quality of the reconstructed images. The algorithm integrates and improves different feature extraction and image coding techniques. At first the speaker's head is detected by means of active snakes. A new form of internal energy is defined that allows a very robust and fast head tracking. After head detection, internal facial features (i.e., eyes, nose, and mouth) are located by means of a new algorithm. The image is decomposed into different parts with different psicovisual relevance. This information is used to guide in an intelligent way the subsequent processing of the motion compensated difference image. The important areas are coded more accurately while the less relevant areas are coded in a coarser way. This approach grants very high compression while the image quality remains high. Subpixel block matching is used to obtain a motion compensated difference image. This image is segmented into homogeneous regions that are then coded by means of a technique based on differential chain code.

Ignition and Flame Propagation Modeling with an Improved Propane Oxidation Mechanism

Abstract An improved chemical mechanism for the combustion of propane has been developed which describes experimental results for a broad range of ignition and combustion phenomena. Simulations of shock tube induction times, measurements of chemical component concentrations in flow reactor experiments, flame speeds, and flame compositions have been carried out with a reasonable degree of success. The rate-determining reactions for some of the experimental simulations have been determined with “brute force” sensitivity analysis Minimum ignition energies were also calculated for spherical ignitions where the ignition energy was added in the form of internal energy which served only to increase the temperature of the gas (heat). The calculated minimum ignition energy gave reasonable agreement with the experimental value for near-stoichiometric mixtures. The H = 02 = OH + O reaction was shown to play a dominant role in determining the minimum ignition energy. This paper also attempts to correct errors which appeared in the previous methane-air mechanism (Sloanc, 1989) Previous ignition experiments have shown that for methane-air mixtures the equivalence ratio yielding the lowest minimum ignition energy is leaner than for propane-air mixtures. Modeling studies by others employing a one-step chemical mechanism have suggested that this is due to the different diffusivities of the two fuels relative to oxygen. That explanation was determined in this work to also hold when a detailed chemical kinetics mechanism was used in the model.

Numerical Simulation of Electric Spark Ignition in Atmospheric Pressure Methane-Air Mixtures

Abstract A model has been developed to describe the growth of an ignition kernel produced by an electric spark in quiescent methane-air mixtures at atmospheric pressure. The model involves the solution of the conservation equations of mass, momentum, and energy in a chemically reacting fluid in one-dimensional spherical coordinates. Detailed chemical kinetics for methane oxidation are included in the equations, along with an accurate method of calculating the transport coefficients. The electric spark energy is added in the form of internal energy; ionization in the discharge is neglected. The temporal and spatial dependence of this internal energy addition can be taken from the current, voltage, and duration of the discharge which produces the ignition kernel being modeled. The agreement with experimental results for arc and glow discharges is quite good.

Ignition and Flame Propagation Modeling With an Improved Methane Oxidation Mechanism

Abstract An improved chemical mechanism for the combustion of propane has been developed which describes experimental results for a broad range of ignition and combustion phenomena. Simulations of shock tube induction times, measurements of chemical component concentrations in flow reactor experiments, flame speeds, and flame compositions have been carried out with a reasonable degree of success. The rate-determining reactions for some of the experimental simulations have been determined with “brute force” sensitivity analysis Minimum ignition energies were also calculated for spherical ignitions where the ignition energy was added in the form of internal energy which served only to increase the temperature of the gas (heat). The calculated minimum ignition energy gave reasonable agreement with the experimental value for near-stoichiometric mixtures. The H = 02 = OH + O reaction was shown to play a dominant role in determining the minimum ignition energy. This paper also attempts to correct errors which a...

Two-dimensional Lagrangian calculation of a laser-heated solenoid

A two-dimensional Lagrangian code is used to model a laser-heated solenoid. The results indicate important two-dimensional effects and the global behavior of the plasma is found to be different from the predictions of one-dimensional theories. Most of the laser energy transferred to the plasma appears in the form of internal energy, suggesting that the bleaching wave approach for reactor calculations is correct. The plasma parameters are significantly changed when the peak of the laser beam profile is flattened.

Energy distribution of electrons from U + O 2 associative ionization

The electrons produced in the thermal energy associative ionization reaction U + O 2 → UO + 2 + e were energy analyzed. Most of the exoergicity (≈4 cV) of the reaction appears to be retained by the ion in the form of internal energy while the electron emerges with only a small kinetic energy. Three peaks at equal separations of 0.08 eV are observed in the energy spectrum.

Active mass in relativistic gravity - Theoretical interpretation of the Kreuzer experiment

A 1966 experiment performed by Kreuzer set an upper limit of 5 parts in 10/sup 5/ on the difference in the ratio of active to passive mass between fluorine and bromine. (Active mass of a body is the mass that generates gravity, while passive mass is the mass that responds to gravity.) A parametrized post-Newtonian formalism is introduced for the spacetime metric of a system of charged point particles using parameters (..gamma..,..beta.., ..cap alpha../sub 1/, ..cap alpha../sub 2/, ..cap alpha../sub 3/, zeta/sub 1/, zeta/sub 2/, zeta/subW/, epsilon/sub 1/, epsilon/sub 2/, epsilon/sub 3/) whose values vary from gravitation theory to gravitation theory. The prediction of this formalism for the active gravitational masses of fluorine and bromine nuclei is compared with the results of the Kreuzer experiment and place an upper limit on a combination of these PPN parameters. By making a detailed comparison of the point-mass formalism with the standard perfect-fluid PPN formalism, it is shown that for the theories of gravitation whose perfect-fluid equations are blind to the different forms of internal energy and pressure in the fluid, the perfect-fluid PPN parameters must satisfy the constraint zeta/sub 3/+2zeta/sub 4/-..cap alpha../sub 3/-2/3zeta/sub 1/ =0. For such theories it is demonstrated thatmore » the Kreuzer experiment imposes the limit vertical-barzeta/sub 3/vertical-bar<0.06. Any theory of gravity that possesses post-Newtonian integral conservation laws for total momentum automatically agrees with the Kreuzer experiment. (AIP)« less

The X-ray, Optical and Radio Properties of Young Supernova Remnants

The expansion of hot gas spheres into a cold uniform medium is studied as a model for the evolution of young supernova remnants. The formation of fast optical filaments in a young supernova is attributed to a Rayleigh–Taylor instability as the expanding sphere sweeps up interstellar material. In the expansion, energy is stored in the velocity dispersion of the ejecta and this is made available in the form of internal energy and random motions as the remnant decelerates. Detailed hydrodynamical calculations lead to an estimate of the amount of energy that becomes available and to prediction of the properties of filaments. During the process of filament formation, the ejecta are re-heated to a high temperature as they coalesce to form a thin shell. The thermal X-ray emission of this hot gas can account for the observed X-ray luminosity of Cas A. Secondary instabilities as the filaments disperse provide a natural way of producing a shell of magnetic field in young remnants. It appears that many of the properties of young supernova remnants can be attributed to liberation of this energy stored in the velocity dispersion of the ejecta.

Energy loss in pulsed coaxial plasma guns

The one-dimensional flow of a current-carry ing plasma, driven into neutral gas by its selfmagnetic field, is considered for the case where both the neutral gas and the current have arbitrary distributions in the direction of flow. The conservation laws are used to derive a simple expression for the amount of input power that goes into all forms of internal energy. It is shown that this power depends mainly on the rate at which the current sheet sweeps up neutral gas. In principle, internal energy can be converted into directed energy by expansion; however, it is argued that, in the coaxial plasma accelerators currently used in propulsion studies, most of the internal energy will be lost by excitation and subsequent radiation or ionization before expansion occurs.