Interaction of electromagnetic radiation with a plasma with fully developed ion acoustic turbulence

A study is made of the characteristic features of the reflection and absorption of a monochromatic wave by a plasma with axisymmetric ion acoustic turbulence over a broad frequency range. The absorption anisotropy and the related conversion of an incident, linearly polarized wave into a reflected, elliptically polarized wave are described. The absorption coefficient and the difference in the phase shifts occurring in the reflection of different field components are obtained as explicit functions of the turbulent plasma parameters.     

Excitation of growing wake waves by an electron bunch in a plasma in an intense pump wave

A study is made of the excitation of wake waves by a one-dimensional electron bunch in an electron plasma in the presence of an intense monochromatic pump wave with circular polarization. In the main state (in the absence of a bunch), the interaction between a pump wave and a plasma is described by Maxwell's equations and the nonlinear relativistic hydrodynamic equations for a cold plasma. The excitation of linear waves by a one-dimensional bunch is investigated against a cold plasma background. It is shown that, in a certain range of parameter values of the bunch, pump wave, and plasma, the excitation is resonant in character and the amplitude of the excited wake waves increases with distance from the bunch.     

Wakefield excitation by a relativistic electron bunch in a magnetized plasma

The excitation of a wake wave by a relativistic electron beam in an unbounded magnetized plasma and a plasma waveguide is studied theoretically. It is shown that, in a waveguide partially filled with a plasma, the energy that the electrons of the accelerated beam can gain is 37 times higher than the energy of the electrons of the beam generating wakefield.     

Expansion of a slab of a three-component plasma with negative ions into vacuum

The expansion of a slab of a three-component collisionless plasma with negative ions into vacuum is studied by particle-in-cell numerical simulations. It is found that, when the ion temperatures are low in comparison with the electron temperature, the expansion process goes through several characteristic stages. The breaking phenomenon, the onset of multistream motion, and the development of instability are described.     

Excitation of low-frequency electrostatic oscillations in a collisionless plasma with an anisotropic ion distribution

The stability of an anisotropic ion distribution with unoccupied regions (holes) in velocity space is studied. Such distributions are expected to form near the neutral plane of the Earth's magnetotail. It is shown that, in such systems, electrostatic waves can be excited. The growth rate and propagation direction of these oscillations are determined by the parameters characterizing the ion hole, as well as by the relation between the electron and ion temperatures. The solution to the quasilinear equation for the waves propagating perpendicular to the current sheet is found, and the energy of the excited oscillations as a function of the parameters of the ion hole is evaluated.     

Interaction of intracellular ion buffering with transmembrane-coupled ion transport

The role of the Na/Ca exchanger in the control of cellular excitability and tension development is a subject of current interest in cardiac physiology. It has been suggested that this coupled transporter is responsible for rapid changes in intracellular calcium activity during single beats, generation of plateau currents, which control action potential duration, and control of intracellular sodium during Na/K pump suppression, which may occur during terminal states of ischemia. The actual behavior of this exchanger is likely to be complex for several reasons. First, the exchanger transports two ionic species and thus its instantaneous flux rate depends on both intracellular sodium and calcium activity. Secondly, the alteration in intracellular calcium activity, which is caused by a given transmembrane calcium flux, and which controls the subsequent exchanger rate, is a complex function of available intracellular calcium buffering. The buffers convert the ongoing transmembrane calcium fluxes into changes in activity that are a small and variable fraction of the change in total calcium concentration. Using a number of simple assumptions, we model changes in intracellular calcium and sodium concentration under the influence of Na/Ca exchange, Na/K ATPase and Ca-ATPase pumps, and passive sodium and calcium currents during periods of suppression and reactivation of the Na/K ATPase pump. The goal is to see whether and to what extent general notions of the role of the Na/Ca exchanger used in planning and interpreting experimental studies are consistent with its function as derived from current mechanistic assumptions about the exchanger. We find, for example, that based on even very high estimates of intracellular calcium buffering, it is unlikely that Na/Ca exchange alone can control intracellular sodium during prolonged Na/K pump blockade. It is also shown that Na/Ca exchange can contaminate measurements of Na/K pump currents under a variety of experimental conditions. The way in which these and other functions are affected by the dissociation constants and total capacity of the intracellular calcium buffers are also explored in detail.     

Interaction of a modulated electron beam with an inhomogeneous plasma: Two-dimensional electrostatic simulations

Nonlinear beam-plasma interaction in a two-dimensional geometry was studied via numerical simulations. The generation of Langmuir waves and transverse oscillations of the beam electrons, as well as the formation of cavities of the plasma density, was observed. Correlation between the electric field structure in the stage of electron nonlinearity and the shape of cavities in the late stage of interaction is revealed.     

Interaction of an ion beam with the target in electron microscope applications

When based on the power-potential law of Lindhard et al. (Mat. Fys. Dan. Vid. Selsk, 33: 1–42, 1963) for ionic impact phenomena on the surfaces of a target, the universal curves of nuclear and electronic energy loss-energy, their resulting yield-energy relationships of sputtering and secondary electron emission yield-energy and range-energy have consistently been derived.According to the results obtained from the above experimental data, a diffusion model of an ion beam penetrating a target is proposed, which takes place throughout a hemisphere with its centre located at half the diffusion depth, and which is found to agree well with the empirical data of ion beam penetration, energy-dissipation profiles and the backscattering coefficient as a function of the reduced depth.Owing to the diffusion model's data, the total secondary electron emission yield due to both primary and backscattering ions is obtained. More importantly, radiation damage in ion beam applications is consistently evaluated as a function of the reduced energy ratio.     

ICR heating of a plasma with a complex ion composition

Two methods for simultaneously heating ions with different masses and, accordingly, with different gyrofrequencies are considered. The first is heating in a steady uniform magnetic field by a nonmonochromatic RF field, and the second is heating in a nonuniform magnetic field by a monochromatic RF field. In the first method, the cyclotron resonance condition is ensured by the finite width of the RF field spectrum, while in the second one, by a drop in the magnetic field along the system. The study is based on the previously developed analytic model of the excitation of RF fields by current-carrying antennas. Nonlinear effects caused by variations in the longitudinal ion velocities during the ICR interaction are taken into account. It is found that ions with atomic masses in the range 85 < A < 150 (fragments of a spent nuclear fuel) can be efficiently heated in systems with moderate parameters.     

Interaction of phospholipase A with an axon plasma membrane preparation.

The rates at which the phosphalipase A catalyzed inactivation of the axonal cholinergic binding macromolecule (ACBM), activation of acetylcholinesterase, and hydrolysis of fatty acid acyl esters were measured in an axon plasma membrane preparation from lobster nerves. The inactivation of ACBM was shown not to be caused by products of the reaction. The solubilized ACBM was also sensitive to phospholipase A inactivation. These results indicated a direct role for the phospholipid in the binding of cholinergic ligands to ACBM. It is suggested that ACBM may be a postsynaptic cholinergic receptor that is in a different lipid environment in the axon plasma membrane. A comparison with the effect of phospholipase A on axonal conduction in intact nerves suggests that the ACBM is directly involved in this process.     

Interaction of bovine factor XIIa with an inhibitor from bovine plasma

An inhibitor of factor XIIa has been purified from bovine plasma and characterized (Thornton, R.D. and Kirby, E.P. (1987) J. Biol. Chem. 262, 12714-12721). This inhibitor interacts with XIIa to form a very stable complex with a 1:1 stoichiometry. The active site of XIIa, located on the light chain, is directly involved in the interaction, and complex formation between factor XIIa inhibitor and XIIa can be blocked by diisopropyl fluorophosphate, corn trypsin inhibitor, or the chromogenic substrate S2302. Incubation of the complex with excess XIIa does not result in cleavage of the complex. The complex does not spontaneously dissociate and is stable to boiling, SDS, thiocyanate, acid, and hydroxylamine or Tris at pH 7-10. In addition to complex formation, a cleaved form of factor XIIa inhibitor can be observed. We suggest that the inhibitor is acting as a mechanism-based inactivator, using the criteria of time-dependent inactivation under pseudo-first-order conditions, 1:1 stoichiometry, active site involvement, kinetic protection by substrate or by an active site inhibitor, and partitioning between cleavage of factor XIIa inhibitor and inactivation by complex formation.     

Spatial configuration of a plasma bunch formed under gyromagnetic resonance in a magnetic mirror trap

The spatial configuration of a relativistic plasma bunch generated under the gyromagnetic autoresonance and confined in a magnetic mirror trap has been studied experimentally and numerically. The characteristics of bremsstrahlung generated by the plasma bunch from the gas and chamber walls were investigated using X-ray spectroscopy and radiometry, which made it possible to determine the localization of the bunch and analyze the dynamics of its confinement.     

Interaction of thiamine diphosphate with magnesium ion

The action of magnesium ion on the exchange rate of the proton in C2 of thiamine and thiamine diphosphate is studied at different values of pD. Above pD 5 the ion Mg2+ increases this exchange rate. The phenomenon is markedly enhanced for TDP rather than thiamine and increases with pD. Below pD 5 magnesium decreases the exchange rate. This decrease is greater for TDP than for thiamine. The maximum effect is reached at a magnesium concentration of 0.5/1 for thiamine and of 1/1 for TDP. T1 measurements are made for different pH values with and without magnesium ion. Results seem to prove that an increase in pD values from 3.9 to 5.9 leads to an accentuation of the molecules "folded" form. Nevertheless for a given pD value the TDP-Mg complex seems to have a more "folded" form than TDP.     

Interaction of cupric ion with parvalbumin.

Cod parvalbumin, a calcium-binding protein, possesses a specific Zn2+ (or Cu2+) binding site per molecule. This work employed fluorescence energy transfer techniques to measure the distance between the Zn2+ (Cu2+) site and the stronger Ca(2+)-binding site in parvalbumin. Specifically, the distance between Tb3+ bound at the Ca2+ site and Co2+ bound to the Zn2+ (Cu2+) binding site was 10.3 +/- 0.9 A. Lastly, the effects of Cu2+ on the physico-chemical properties of parvalbumin were studied by measuring the accessibility of protein thiol groups to 5,5'-dithio bis(2-nitrobenzoic acid) and by its affinity for the fluorescent probe 4,4'-bis[1-(phenylamino)-8-naphthalene sulfonic acid] dipotassium salt. The thiol group accessibility decreased and the affinity to the fluorescent probe increased upon complexation of Cu2+ to the protein. It appears that the binding of Cu2+ converts parvalbumin to an apo-like state.     

Interaction of plasma gelsolin with ADP-actin

In the presence of Ca2+, gelsolin forms a very tight, stoichiometric complex with 2 molecules of ADP-G-actin. Removal of free Ca2+ causes the 1:2 complex to dissociate to a 1:1 complex. Gelsolin accelerates the very slow polymerization of ADP-actin, apparently by accelerating the rate of nucleation, but the number concentration of filaments formed is probably less than the gelsolin concentration, indicating that the GA2 complex is not a true nucleus. These results are similar to those obtained for the interaction of gelsolin with ATP-G-actin. Both kinetic and equilibrium measurements demonstrate that the critical concentration of gelsolin-capped ADP-actin filaments (8 microM in 1 mM MgCl2 and 0.2 mM ADP) is the same as for the uncapped filaments, proving that the critical concentration is the same at both ends of the equilibrium polymer in ADP as predicted by theory. The association and dissociation rate constants for the addition of ADP-G-actin at the pointed end of an ADP-F-actin filament are estimated to be 4.6 X 10(4) M-1 s-1 and 0.4 s-1, respectively, about 15-fold lower than the rate constants at the barbed end.     

Interaction of local anesthetics with model ion channels

A theoretical study of intermolecular interactions between local anesthetics of the acetanilide series and model ionic channels was performed. A dimer of gramicidine A and melittin were used as models of ionic channels. The geometry of molecules was determined by the method of molecular mechanics. Statistically significant correlation equations were derived, which relate the indices of local anesthetizing activity to the characteristics of intermolecular interactions in the anesthetic-peptide system. A comparative analysis of intermolecular interactions in anesthetic-gramicidine A and anesthetic-melittin systems was carried out.     

Interaction of cremophor EL with human plasma

1. Interaction of cremophor EL (CRM) with human plasma lipoproteins and nonlipoproteins has been investigated by ultracentrifugation. 2. VLDL has only a low or negligible capacity to bind CRM, i.e. there is little or no change in the optical absorption at 280 nm of VLDL when CRM is added. 3. A low density subfraction of low density lipoproteins seems to associate substantially with CRM at relatively low CRM concentrations (1-3 mg/ml), but such association is not evident for CRM concentrations in the region 12-116 mg/ml. 4. Low density lipoproteins (LDL) may act as a carrier for CRM-emulsions, yet there seems to be no concomitant change in the 280 nm optical absorption of the proteins of LDL. 5. The position in the gradient (i.e. in the centrifugation tube after centrifugation) of high density lipoproteins (HDL) is shifted towards lower density in the presence of 1-4 mg CRM/ml. For higher concentrations of CRM, a destruction of HDL can be observed: the HDL distribution is converted into a bimodal distribution of respectively lighter and heavier "HDL"-particles than the normal ones; the densities at the peaks of these distributions are approximately 1.07 g/ml (light), 1.20 g/ml (heavy) and 1.11 g/ml (normal HDL). The optical extinction coefficient is apparently the same for the proteins of normal--and modified HDL. 6. Even high CRM concentrations (less than or equal to 116 mg/ml) have no perceptible effect on the gradient positions and profile of human serum albumin (HSA) and/or other heavy proteins. 7. The possible biological significance of these findings is briefly touched upon.     

Interaction of insecticides with human plasma lipoproteins

The binding of chlorinated hydrocarbon, carbamate and organophosphate insecticides to human low density plasma lipoproteins (LDL) and high density plasma lipoproteins (HDL) was studied at pH 7.0 and 16°C and 26°C by equilibrium dialysis, difference spectra and fluorescence. The results suggest interaction to be a partitioning rather than a stoichiometric binding process. Distribution is related to lipid content and composition of the lipoproteins. The K-values vary from 3 × 10⁵ M^?1 for 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT) to less than 10 M^?1 for nicotine and aldicarb, and ΔG_tr° is in the range of 7400 cal for DDT to less than 1000 cal for aldicarb and nicotine. The K and ΔG_tr° are inversely related to the water solubility of the insecticides. A significant role of plasma lipoproteins in the transport of slightly water soluble insecticides is suggested.     

Interaction of plasma apolipoproteins with lipid monolayers

The monolayer technique has been used to study the interaction of lipids with plasma apolipoproteins. Apolipoprotein C-II and C-III from human very low density lipoproteins, apolipoprotein A-I from human high density lipoproteins and arginine-rich protein from swine very low density lipoproteins were studied. The injection of each apoprotein underneath a monolayer of egg phosphatidyl[¹⁴C]choline at 20 mN/m caused an increase in surface pressure to approximately 30 mN/m. With apolipoprotein C-II and apolipoprotein C-III there was a decrease in surface radioactivity indicating that the apoproteins were removing phospholipid from the interface; the removal of phospholipid was specific for apolipoprotein C-II and apolipoprotein C-III. Although there was a removal of phospholipid from the monolayer, the surface pressure remained constant and was due to the accumulation of apoprotein at the interface. The rate of surface radioactivity decrease was a function of protein concentration, required lipid in a fluid state and, of the lipids tested, was specific for phosphatidylcholine. Cholesterol and phosphatidylinositol were not removed from the interface. The addition of 33 mol% cholesterol to the phosphatidylcholine monolayer did not affect the removal of phospholipid by apolipoprotein C-III.The addition of phospholipid liposomes to the subphase greatly facilitated the apolipoprotein C-II-mediated removal of phospholipid from the interface.