Analytic approximations for the broadening of the spectral lines of hydrogen-like ions

Broadband approximate expressions for calculating the broadening of the spectral lines of hydrogen-like ions in a multicomponent plasma are derived taking into account both the influence of the interaction between plasma particles on the distribution function of the plasma microfield and the effect of the microfield dynamics on the broadening of the central component of the spectral line. With the approximate expressions proposed, the calculation of the shape of a given spectral line of a certain ion in a plasma with a given ion composition requires only a few seconds of computer time. The approximate expressions provide a good computational accuracy not only for the central component of the spectral line but also for the spectral line wings.     

Diagnostics of a current-sheet plasma with the use of helium spectral lines with forbidden components

Results are presented from the first measurements of the profiles of the HeI 447.1-nm and HeI 492.2-nm neutral helium spectral lines emitted by the plasma of a current sheet formed in the CS-3D experimental device. A theoretical analysis of these profiles is performed with the model microfield method. A comparison of the theoretical and experimental profiles shows that the electron density in the peripheral regions of the current sheets amounts to (1.0–2.0)×10¹⁵ cm^?3.     

Hydrogen lines in the infrared region and spectral background for the thomson scattering diagnostics of the iter divertor plasma

Calculations are made of the plasma spectral background, which is important for the Thomson scattering diagnostics in the ITER divertor. Theoretical grounds have been elaborated for computing the hydrogen spectral line shapes in the infrared spectral region for a divertor plasma in ITER. The shape of the P-7 Paschen line (transition n = 7 → n = 3) located near the laser scattering signal has been calculated for various lines of sight in the ITER divertor. Contributions from different mechanisms of broadening the P-7 line have been examined. The spectral intensities of bremsstrahlung and photorecombination continuum have been calculated. All calculations use data on the spatial distribution of temperatures and densities of all species of plasma particles computed with the SOLPS4.3 code for basic operation regimes of the ITER divertor.     

Microfield model of quasi-independent particles and nonideal plasma

An original model of a plasma microfield constructed from first principles is much more advantageous than the earlier ones. The validity of the model is confirmed by optical measurements. The thermodynamics of a gaseous plasma is qualitatively described by a new ionization equilibrium model in which the interaction between charged particles is accounted for by means of a self-consistent plasma microfield. Numerical simulations show that, in this new model, nonideal effects are insignificant even at high plasma densities, and there are no phase transitions in a gaseous plasma, a conclusion that agrees with experimental data. The model is tested against the popular models of nonideal plasma and the SESAM database.     

Molecular dynamic simulations of electric microfield distributions in a nonideal electron-positron plasma

A symmetric model of a two-component plasma is considered and the distributions of electric microfields acting on charged and neutral particles are calculated using the method of molecular dynamics at a fixed temperature of T = 30000 K and different values of the coupling parameter 0.2 ≤ Γ ≤ 1.2. Changes in these distributions with varying Γ are discussed. Special attention is paid to the behavior of the distribution tails. The behavior of these tails at a neutral point is shown to agree with the tails of the Holtsmark distribution, whereas the tails of the distribution at a charge are considerably heavier and are characterized by the exponent that varies within the range from −2.2 up to −1.8 as Γ increases.     

Features of the chemical models of a nonideal atomic plasma at high temperatures

The equation of state for a hydrogen plasma at high temperatures is considered in a physical and a chemical model. A simple expression is obtained that relates the pressure correction in chemical models to the high-temperature limit of the atom partition function. This expression ensures a correct asymptotic behavior of the equation of state in the high-temperature limit. It is explained why the familiar astrophysical model of Hummer, Mihalas, and Däppen, as applied to helioseismology, yields worse results than a physical model. A modification of the astrophysical model is proposed that makes it possible to use the nearest neighbor approximation to calculate the atom partition function in chemical models in solving astrophysical problems and problems concerning low-temperature plasmas.     

Inhomogeneous broadening in spectral bands of carbonmonoxymyoglobin. The connection between spectral and functional heterogeneity.

The rebinding kinetics of CO to myoglobin after flash photolysis is nonexponential in time below approximately 180 K; the kinetics is governed by a distribution of enthalpic barriers. This distribution results from inhomogeneities in the protein conformation, referred to as conformational substates. Hole-burning experiments on the Soret and IR CO-stretch bands test the assumption that an inhomogeneous distribution of conformational substates results in inhomogeneously broadened spectra. CO was slowly photolyzed at different wavelengths in the Soret band at 10 K. Both the Soret band and the CO-stretch band A1, centered at 1,945 cm-1, shift during photolysis, demonstrating that different wavelengths excite different parts of the distributed population. We have also done kinetic hole-burning experiments by measuring peak shifts in the Soret and A1 bands as the CO molecules rebind. The shifts indicate that the spectral and enthalpic distributions are correlated. In the A1 band, the spectral and enthalpic distributions are highly correlated while in the Soret the correlation is weak. From the peak shifts in the spectral and kinetic hole-burning experiments the inhomogeneous broadening is estimated to be approximately 15% of the total width in the Soret band and approximately 60% in A1. We have previously measured the tilt angle alpha between the bound CO and the heme normal (Ormos, P., D. Braunstein, H. Frauenfelder, M. K. Hong, S.-L. Lin, T. B. Sauke, and R. D. Young. 1988. Proc. Natl. Acad. Sci. USA. 85:8492-8496) and observed a wave number dependence of the tilt angles within the CO-stretch A bands. Thus the spectral and enthalpic distributions of the A bands are coupled to a heterogeneity of the structure.     

Fluctuation approach to description of nonideal plasma. II: Collisional recombination in nonequilibrium plasma

A model capable of describing the kinetics of collisional recombination in nonideal plasmas by the methods of molecular dynamics is developed. The dependence of the collisional recombination rate on the coupling parameter is found to differ substantially from the extrapolation of the three-body recombination rate in nonideal plasmas. A sharp decrease in the recombination rate in strongly nonideal plasmas is revealed. As the coupling parameter decreases, collisional recombination transforms into three-body recombination.     

Investigation of the helicon discharge plasma parameters in a hybrid RF plasma system

Results of an experimental study of the helicon discharge plasma parameters in a prototype of a hybrid RF plasma system equipped with a solenoidal antenna are described. It is shown that an increase in the external magnetic field leads to the formation of a plasma column and a shift of the maximum ion current along the discharge axis toward the bottom flange of the system. The shape of the plasma column can be controlled via varying the configuration of the magnetic field.     

A reexamination of the mechanisms underlying the arteriovenous chloride shift

The chloride shift is the movement of Cl(-) from the plasma into erythrocytes as blood moves from the arterial to the venous end of systemic capillaries. The traditional explanation for the chloride shift emphasizes the causative roles of the rise in Pco(2) and the exclusive presence of carbonic anhydrase within the red blood cell. The purpose of this article is, first, to reexamine two aspects of the chloride shift that we feel are traditionally underemphasized. They are the role of hemoglobin in causing the chloride shift and the affect of the chloride shift on the acid-base status of the blood. Second, we wish to reconcile more recent work with the traditional understanding of the chloride shift. The chloride shift has never been modeled from the perspective of the Stewart strong ion approach. Similarly, the traditional understanding has generally treated Cl(-) as a passive participant in the chloride shift whose role was simply to replace the lost negative charge of the outward moving HCO-3. More recent work has suggested that the ingoing Cl(-) is important for both O(2) unloading and acid-base balance of the blood. We conclude this article with a model of the chloride shift that uses the Stewart approach and, though harmonious with the traditional understanding, highlights the importance of hemoglobin and Cl(-) in the chloride shift.     

Spatial and spectral resolution of the plasma Doppler reflectometry

An approach to numerical simulations of microwave scattering in Doppler reflectometry is developed that is based on calculations of the two-dimensional spatial weighting function in the Born approximation. The knowledge of the spatial weighting (or instrumental) function, which contains complete information on both forward and backward scattering processes, allows one to calculate the output signal of a quadrature diagnostic detector for any given distribution of the electron plasma density fluctuations. The weighting functions were computed for axisymmetric distributions of the background plasma density and for arbitrarily specified fields in the mouths of the emitting and receiving antennas. Simulations carried out for different model representations of the scattering fluctuations yielded quantitative estimates of both the spatial and wavenumber resolutions of Doppler reflectometry. The simulations showed that the resolution of the method proposed worsens with increasing curvature of the cut-off surface. Conditions are determined under which the resolution of the diagnostics in small-and medium-size tokamaks can be substantially improved by using converging microwave beams. The possibility of utilizing focused probing microwave beams in Doppler reflectometry on ITER-scale devices is discussed.     

Hybrid neural simulation of a fed-batch bioreactor for a nonideal recombinant fermentation

Fermentations employing genetically modified microbes under industrial conditions are difficult to monitor on line or to describe by simple, good mathematical models. So, a practically convenient approach is to combine mathematical models of some aspects with artificial neural networks of those aspects which are difficult to measure or model. Such hybrid models have been applied earlier to laboratory-scale bioreactors. In the present work, a model based on laboratory data for the synthesis of recombinant #-galactosidase was corrupted by adding imperfect mixing and noise in the feed stream to generate data mimicking a real nonideal operation. These data were used to train a recurrent Elman neural network and a hybrid neural network, and it was seen that a hybrid network provides more accurate estimates of both extra-cellular and intra-cellular variables. The benefit is enhanced by the hybrid network's superiority being more pronounced for the intra-cellular recombinant protein, #-galactosidase, which is the main product of interest.     

Uncovering the basis for nonideal behavior of biological molecules

The molecular origin of the nonideal behavior for concentrated binary solutions of biochemical compounds is examined. The difference between activities expressed in the molar and molal conventions can be large. Considering the range from dilute to concentrated, we show that molar activity coefficients can be represented by simple but rigorous equations involving between one and three parameters only. We derive a universal relationship interconverting the scales of molarity and molality without requiring the density of the solution. The equations are developed from first principles using a statistical thermodynamic theory of molar activity coefficients. It is shown how to express activity coefficients in different concentration scales, and the advantages and disadvantages of using certain scales are discussed and compared with the experimental data. Several classes of biochemically relevant compounds, many of which are naturally occurring osmolytes, are discussed: six saccharides (glucose, xylose, maltose, mannose, raffinose, and sucrose), four polyols (glycerol, mannitol, erythritol, and sorbitol), five amino acids (glycine, alanine, sarcosine, glycine betaine, and proline), and urea. Of the 16 solutes, 10 could be described in terms of a single parameter that is due to pure first-order effects (packing, hydration, or space limitation). The remaining six exhibit significant second-order effects (solute-solute interactions) and require two additional parameters, one typically identified with the volume occupied per solute molecule in the pure solute (crystal or liquid) and the other with a self-association constant. The activity coefficients of the osmolytes roughly display the rank order found with respect to their ability to stabilize proteins. These findings are discussed in terms of the physical principles that give rise to the activity coefficients.     

Fluorescence emission spectral shift measurements of membrane potential in single cells.

Previous measurements of transmembrane potential using the electrochromic probe di-8-ANEPPS have used the excitation spectral shift response by alternating excitation between two wavelengths centered at voltage-sensitive portions of the excitation spectrum and recording at a single wavelength near the peak of the emission spectrum. Recently, the emission spectral shift associated with the change in transmembrane potential has been used for continuous membrane potential monitoring. To characterize this form of the electrochromic response from di-8-ANEPPS, we have obtained fluorescence signals from single cells in response to step changes in transmembrane potentials set with a patch electrode, using single wavelength excitation near the peak of the dye absorption spectrum. Fluorescence changes at two wavelengths near voltage-sensitive portions of the emission spectrum and shifts in the complete emission spectrum were determined for emission from plasma membrane and internal membrane. We found that the fluorescence ratio from either dual-wavelength recordings, or from opposite sides of the emission spectrum, varied linearly with the amplitude of the transmembrane potential step between -80 and +60 mV. Voltage dependence of difference spectra exhibit a crossover point near the peak of the emission spectra with approximately equal gain and loss of fluorescence intensity on each side of the spectrum and equal response amplitude for depolarization and hyperpolarization. These results are consistent with an electrochromic mechanism of action and demonstrate how the emission spectral shift response can be used to measure the transmembrane potential in single cells.     

Possibility of X-ray spectral diagnostics of a plasma in the tracks of fast multicharged ions

A plasma model of the relaxation of a medium within the tracks of heavy ions in condensed matter is proposed that is based on solving time-dependent radiative collisional kinetic equations with the initial condition corresponding to a medium’s state described by the classical model of multiple ionization of the target atoms by the field of fast multicharged ions. It is shown that the plasma model allows one to describe X-ray spectra recorded in the interaction of ion beams with condensed targets. An X-ray spectral method for plasma diagnostics is proposed that is based on the plasma model. The results obtained can also be used to study the initial stage of the formation of defects in solid bodies under the action of individual fast heavy ions.