Nonequilibrium Environment Research Articles

The Sagittarius B2 Star-forming Region. III. High-Resolution H52 alpha and H66 alpha Observations of Sagittarius B2 Main

view Abstract Citations (59) References (43) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Sagittarius B2 Star-forming Region. III. High-Resolution H52 alpha and H66 alpha Observations of Sagittarius B2 Main de Pree, C. G. ; Gaume, R. A. ; Goss, W. M. ; Claussen, M. J. Abstract The Galactic center star-forming region Sagittarius B2 Main [Sgr B2 (M)] has been observed with the Very Large Array in the continuum (7 mm and 1.3 cm) and in the radio recombination lines H52α, H66α, and He 66α. The H66α(∼0".25 resolution) and H52α(∼2".5 resolution) data provide high spatial resolution kinematics of the ionized gas associated with the massive stars. Both high spatial resolution and sensitivity to large-scale structures are essential to thoroughly sample the H II regions in Sgr B2 (M) where source sizes of the 36 H II regions range from unresolved (<0".3) to extended (∼10"). H66α recombination line emission has been detected toward 23 of the 36 continuum sources in Sgr B2 (M). The mean velocity of the detected sources is 62±2 km s-1. He 66α line emission is detected toward nine of the 36 continuum sources. The 1.3 cm helium and hydrogen data are used together as a high-resolution probe of Y+ values and variations within Sgr B2 (M). An average singly ionized helium abundance of <Y+> = 10.3%±1.2% is derived. Of the sources where a Y+ value is determined, only Sgr B2 F has an anomalously low value (Y+ ≤ 5%). The recombination line data are examined in detail toward several of the most unusual sources. A very broad radio recombination line (ΔVH66α ∼ 64 km s-1, ΔVH52α ∼ 59 km s-1) is measured, and high electron temperatures [Te(H66α)* = 26,400 K] are derived for Sgr B2 F. The broad lines and high temperatures may be due to a nonequilibrium environment at the edge of an expanding H II region. Assuming that the F and G H II regions have expanded in a dense molecular environment, they appear to be young, with an average age of <τ> = 0.7±0.3 x 104 yr. This lower limit on the age is consistent with the dynamical age of the nearby massive molecular outflow observed by Lis et al. A doubly peaked H66α line has been detected toward the ultracompact H II (UC HII) region Z10.24. This source may be either a very young (τ < 100 yr) shell source or the ionized base of a molecular outflow. The small number of morphological cometary H II regions in Sgr B2 (<5%) and the observed velocity gradients in those regions that do have a cometary morphology indicate that the moving star bow shock model cannot account for any of the H II regions in Sgr B2 (M). Publication: The Astrophysical Journal Pub Date: June 1996 DOI: 10.1086/177364 Bibcode: 1996ApJ...464..788D Keywords: ISM: KINEMATICS AND DYNAMICS; ISM: H II REGIONS; ISM: INDIVIDUAL NAME: SAGITTARIUS B2; GALAXY: CENTER; RADIO LINES: ISM full text sources ADS | data products SIMBAD (47) Related Materials (2) Part 1: 1995ApJ...449..663G Part 2: 1995ApJ...451..284D

Dimensional loss in nonequilibrium quantum systems.

Quantum steady state processes far from equilibrium can be characterized by wave functions whose coefficients (in a fixed basis) evolve onto a fractal set. This is explicitly shown for the prototypical situation of heat flow from hot to cold reservoirs, with two spin-\textonehalf{} particles in a thermal gradient. The resulting dimensional loss, induced by the nonequilibrium environment, is related to the quantum transport process.

Computation of nonequilibrium radiating shock layers

A computational technique of coupling radiative transfer to fluid motion is developed for axisymmetric blunt body shock layer flows in a thermochemical nonequilibrium environment. The coupled formulation of radiation and flowfield leads to a governing set of integro-diffe rential equations. This equation set is solved using a modified Gauss-Seidel line relaxation technique that incorporates the inversion of full block matrix associated with radiative transfer using a block iteration method. The thermodynamic state of the gas is described by three temperatures: 1) translational, 2) rotational, and 3) vibrational-e lectronic. Radiation phenomenon is assumed to be governed by the vibrational-electronic temperature. The radiative properties are described by a spectrally detailed model. The computations are presented for two cases, including the Fire II flight experiment. It is shown that the method converges and the calculated spectra qualitatively agree with the experimental data for the two test cases. The calculated total radiative flux underestimates the measured values owing to the low vibrational-electronic temperature predicted in the flowfield calculation.

Dynamics and information

The dynamical and information aspects of the behaviour of complex physical systems are considered. In classical physics the information coupling appears in the interaction of nonlinear systems with stohastic behaviour when a small external perturbation may greatly alter the paths of a classical system in phase space. In quantum systems the information coupling to the environment appears in measurement processes when the coherence of the wave function of a quantum object is destroyed and corresponding information appears in the external environment. These processes can be described in terms of the collapse of wave functions. Numerous examples of the collapse are considered, including those leading to the classical behaviour of macroscopic bodies with the information coupling to a nonequilibrium environment. The Einstein–Podolsky–Rosen paradox is discussed in detail together with its possible role in the processes of information transfer over a distance.

Magnetic field effects on the computed flow over a Mars return aerobrake

A numerical algorithm is developed to calculate the electromagnetic phenomena simultaneously with the fluid flow in the shock layer over an axisymmetric blunt body in a thermal equilibrium, chemical nonequilibrium environment. The flowfield is solved using an explicit time-marching, first-order spatially accurate scheme. The electromagnetic phenomena are coupled to the real-gas flow solver through an iterative procedure. The electromagnetic terms introduce a strong stiffness, which was overcome by using significantly smaller time steps for the electromagnetic conservation equation. The technique is applied in calculating the flow over a Mars return aerobrake vehicle entering the Earth's atmosphere. For the case where no external field is applied, the electromagnetic effects have little impact on the flowfield. With the application of an external magnetic field of 0.05 to 0.1 T, the solution indicates an increase in stagnation line shock standoff distance, wall pressure, and radiative heat transfer and a decrease in convective heat transfer.

Dynamics of Cluster-Surface Collisions

The structure, energetics, and dynamics of shock conditions generated in a nano-cluster upon impact on a crystalline surface are investigated with molecular-dynamics simulations for a 561-atom argon cluster incident with a velocity of 3 kilometers per second onto a sodium chloride surface. The "piling-up" shock phenomenon occurring upon impact, coupled with cascades of energy and momentum transfer processes and inertial confinement of material in the interior of the cluster, creates a transient medium lasting for about a picosecond and characterized by extreme local density, pressure, and kinetic temperature. The nano-shock conditions and impulsive nature of interactions in the newly formed compressed nonequilibrium environment open avenues for studying chemical reactivity and dynamics catalysed via cluster impact.

Ordering kinetics at surfaces

Aspects of the kinetics of ordering at surfaces are briefly reviewed, including discussions of the growth law and diffusion in a nonequilibrium environment both for phase coexistence and for single stable phases. Examples of two-dimensional ordering are given, including a low-energy electron diffraction study of O/ W(110) and a scanning tunneling microscopy (STM) study of the initial stages of growth of Si on Si(001). Ordering kinetics involving the third dimension are illustrated, with an STM study of step bunching on vicinal Si(111) and model calculations using rate equations for A-on-A epitaxial growth.

Dense ‘‘diamondlike’’ hydrocarbons as random covalent networks

Dense ‘‘diamondlike’’ hydrocarbon films (a-C:H) are a class of amorphous solids which can be condensed as thin films from nonequilibrium environments by several plasma deposition techniques. Films with hydrogen atom fractions from 0.5 to 0.6 select a structure with an average coordination number close to the theoretical value at which stabilization by bonding and destabilization by strain energy are balanced. This coordination number is achieved by the incorporation of the hydrogen and by the presence of trigonally (sp2) bonded carbon in the carbon skeletal network. Theory predicts a range of hydrogen atom fraction, outside of which fully constrained, random hydrocarbon networks cannot exist. The dense hydrocarbon films show extreme values of physical properties, including hardness and argon diffusivity, which can be related to their unusual structure.

Fokker-Planck equation approach to fluctuations about nonequilibrium steady states

We examine the properties of steady states in systems which interact at the boundary with a nonequilibrium environment. The examination is based on a nonlinear Fokker-Planck equation, the structure of which is determined by the fact that it also governs the time evolution of the equilibrium fluctuations of the system. The nonlinearities in the Fokker-Planck equation may have two origins: thermodynamic nonlinearities which arise if the thermodynamic potential is not a bilinear function of the state variables, and nonlinear mode coupling which arises if the transport coefficients depend on the state. While these nonlinearities have only a small effect on the equilibrium fluctuations of a system away from critical points, they are shown to be important for the determination of fluctuations about nonequilibrium steady states. In particular the state dependence of the transport coefficients may lead to deviations from local equilibrium and to a breakdown of detail balance. An explicit formula for the time correlations of fluctuations about the nonequilibrium steady state is obtained. The formula leads to long-range correlations in fluids in the presence of a temperature gradient. The result is compared with earlier approaches to the same problem. Finally, we study the linear response to external forces and obtain a generalization of the fluctuation-dissipation formula relating the response functions with the nonequilibrium correlation functions.

High power electron spin echo modulation studies of silver atom solvation and desolvation in ice matrices: Geometrical models for silver cation and silver atom aqueous solvation shells

High power electron spin echo modulation patterns have been obtained at 4.2 K and analyzed for presolvated silver atoms produced at 4.2 K in a nonequilibrium environment by radiolysis of deuterated ice matrices containing AgF, and for solvated silver atoms produced by brief annealing at 77 K. The analysis shows that presolvated Ag0 is surrounded by eight equivalent deuterons at 3.1±0.1 Å with zero isotropic hyperfine coupling which suggests a tetrahedral model of four waters with their dipoles pointed away from Ag0 (i.e., a solvated Ag+ geometry). Solvated Ag0 has one deuteron at 1.7±0.05 Å with a 1.8 MHz isotropic hyperfine coupling and seven deuterons at 3.1±0.1 Å with zero isotropic hyperfine coupling. The solvation process appears to occur by rotation of one water around one of its OD bonds with no change in the Ag–O distance.

Hot hydrogen atoms reactions of interest in molecular evolution and interstellar chemistry.

Hot hydrogen atoms which are photochemically generated initiate reactions among mixtures of methane, ethane, water and ammonia, to produce ethanol, organic amines, organic acids, and amino acids. Both ethanol and ethyl amine can also act as substrates for formation of amino acids. The one carbon substrate methane is sufficient as a carbon source to produce amino acids. Typical quantum yields for formation of amino acids are approximately 2–4 · 10-5. In one experiment, 6 protein amino acids were identified and 8 non-protein amino acids verified utilizing gas chromatography-mass spectroscopy. We propose that hot atoms, especially hydrogen, initiate reactions in the thermodynamic non-equilibrium environment of interstellar space as well as in the atmospheres of planets.

On the Validity of Kirchhoff's Law in a Nonequilibrium Environment

In the heat radiation literature, the words absorptivity and emissivity have both been used in different senses. This can lead to confusion, and in one case it was argued that Kirchhoffs law of equality between emissivity and absorptivity does not apply to the radiation from a material for which the stimulated emission depends on the temperature of the environment. We clarify the proper thermodynamic definition of absorptivity (and emissivity) and show that Kirchhoff's law stated in terms of those definitions correctly predicts the results of experiments. This follows even when there are large deviations from equilibrium, or when there is nonlinear absorption or emission.

Nonequilibrium Processes

Nonequilibrium phenomena have been studied for over half a century, particularly as a means to understanding the mechanism of energy transfer. Application of the insights and techniques of molecular physics to chemistry has resulted in a view of chemistry as constituting an aspect of the study of strong collisions, and chemical reaction as a special type of energy transfer. Increasing use has been made in experimental work of nonequilibrium environments for the study of chemical processes. The nature and purpose of such experiments are reviewed here, very briefly, and an attempt is made to point to areas that appear ripe for development over the coming decade.

Membrane excitability and dissipative instabilities

Electrical excitation is interpreted in terms of a cooperative structural transition of membrane protomers coupled with the translocation of a permeant molecule in a non-equilibrium environment. Equations for flow of permeant and for membrane conformation are derived for the simple case of a single non-charged permeant. On the basis of a few simple physical assumptions, the theory predicts several important properties of electrically excitable membranes: the steepness of the relation between membrane conductance and potential, the presence of a negative conductance, and the occurrence of instabilities following rapid perturbations of membrane environment, giving rise to some simple cases of action potentials. Several experimental tests of the membrane with its changes of electrical properties are proposed. From a thermodynamic point of view, an electrically excitable membrane, in its resting state, lies beyond a dissipative instability and consequently is in a non-equilibrium state but with stable organization, a "dissipative structure" of Prigogine. Membrane excitation following a small perturbation of the environment would correspond to a jump from such an organization to another stable organization but close to thermodynamic equilibrium. It is shown how the cooperative molecular properties of the membrane are amplified by energy dissipation at the macroscopic level.

1183. Measurement of the enthalpy of formation of barium hydride: A F Vorobev et al, Dokl Akad Nauk SSSR, 179 (5), 11 th April 1968, 1129–1132 ( in Russian)

This investigation has been devoted to the theoretical description and computer modeling of atomic processes giving rise to radiative emission in energetic electron and ion beam interactions and in laboratory plasmas. We are also interested in the effects of directed electron and ion collisions and of anisotropic electric and magnetic fields. In the kinetic-theory description, we treat excitation, de-excitation, ionization, and recombination in electron and ion encounters with partially ionized atomic systems, including the indirect contributions from processes involving autoionizing resonances. These fundamental collisional and electromagnetic interactions also provide particle and photon transport mechanisms. From the spectral perspective, the analysis of atomic radiative emission can reveal detailed information on the physical properties in the plasma environment, such as non-equilibrium electron and charge-state distributions as well as electric and magnetic field distributions. In this investigation, a reduced-density-matrix formulation is developed for the microscopic description of atomic electromagnetic interactions in the presence of environmental (collisional and radiative) relaxation and decoherence processes. Our central objective is a fundamental microscopic description of atomic electromagnetic processes, in which both bound-state and autoionization-resonance phenomena can be treated in a unified and self-consistent manner. The time-domain (equation-of-motion) and frequency-domain (resolvent-operator) formulations of the reduced-density-matrix approach are developed in a unified and self-consistent manner. This is necessary for our ultimate goal of a systematic and self-consistent treatment of non-equilibrium (possibly coherent) atomic-state kinetics and high-resolution (possibly overlapping) spectral-line shapes. We thereby propose the introduction of a generalized collisional-radiative atomic-state kinetics model based on a reduced-density-matrix formulation. It will become apparent that the full atomic data needs for the precise modeling of extreme non-equilibrium plasma environments extend beyond the conventional radiative-transition-probability and collisional-cross-section data sets.

Kinetic salt effects on the reactions of hydrated electrons produced photochemically from ferrocyanide ions

When applied to a reaction between ions occurring in the vicinity of a highly charged ion, the theory developed in the previous paper predicts much larger kinetic salt effects than were suggested by the activity coefficient method. This disagreement seems to be due, essentially, to an error in calculating activity coefficients of ions with a non-equilibrium environment. A comparison of theoretical predictions with the experimental results of Airey and Dainton showing high salt effects for hydrated electrons produced photochemically from ferrocyanide ions indicates a discrepancy of two orders of magnitude between the experimental conditions and those where such behaviour is expected. An explanation is that the hydrated electron may undergo reaction nearer to the parent ion than one would calculate from the solute concentrations and rate constants if the dissociation of the photoexcited ferrocyanide ion is influenced by the proximity of an acceptor.

Measurements of hydrogen-atom recombination rates behind shock waves

Hydrogen-atom recombination rates, with either hydrogen molecules or hydrogen atoms acting as the third bodies, have been measured over the temperature range from 2500° to 7000°K. The rates were determined from spectrum-line reversal measurements of the temperature changes caused by dissociation behind incident shock waves in mixtures containing from 20% to 60% hydrogen in argon. The rate with molecular hydrogen exhibits a temperature dependence of T−3/2 and decreases from 1.4×1015cm6 mole−2 sec−1 at 2500°K to 3.9×1014 cm6 mole−2 at 7000°K. Extrapolation of this rate to lower temperatures agrees well with flame data and a recent room-temperature evaluation. The rate with argon is inferred to be about one-fifth that with molecular hydrogen. The rate with atomic hydrogen shows a dependence of T−7 and decreases from 9×1016 cm6 mole−2 sec−1 at 2500°K to 3.7×1014 cm6 mole−2 sec−1 at 5500°K. These values of the rates are critically compared with existing shock-wave data. The strong temperature dependence for the rate with atomic hydrogen confirms that observed in a previous experiment over a less-extensive temperature range. Possible reasons for this dependence are discussed, and it is concluded that either it arises from the possibly invalid use of equilibrium concepts in the nonequilibrium environment of the shock or it is a real dependence and interpretable on the basis of the “chaperon” theory of recombination processes.

Diffusion and Chemical Surface Catalysis in a Low-Temperature Plasmajet: The Determination of Atom Concentrations in Nonequilibrium Supersonic Streams of Activated Nitrogen

Chemical and thermal methods have been used to estimate the free atom concentration in a nonequilibrium supersonic jet of activated nitrogen emerging from a direct-current, high pressure, glow discharge. Emphasis is given to differential catalytic probe techniques, several variations of which are discussed. For nonequilibrium dissociated streams of low stagnation enthalpy, a differential catalytic thermometer is described which, in principle, offers the advantages of: (a) Linearity of probe response; (b) sensitivity independent of catalyst activity, details of gas dynamic environment, and catalyst geometry. A simple thermometric probe has been constructed and its output has been studied over a small range of electrical power dissipation. Evidence is given in support of the view that the probe responds principally to the same component of activated nitrogen that is depleted by chemical reaction with ethylene and propylene. Both catalytic probe measurements and the limiting amount of hydrogen cyanide production yielded about the same atom concentration (mole fractions of about 2 per cent). For electrical discharges operating at higher power densities, radiation losses from the catalytic thermometer surfaces necessitate design compromises which reduce the potential accuracy of the thermometric technique applied herein. This difficulty can be circumvented by using cooled catalytic probes (calorimeters), one type of which is currently under investigation. In general, it appears that the aerodynamic uncertainties involved in the catalytic probe theories presented are minor compared to the physicochemical questions raised by the use of such probes in nonequilibrium environments. Particular attention must be devoted to the role of excited species (other than ground state atoms) on the accuracy of both differential thermal detectors and chemical reactivity methods of analysis.