Electrical and chemical properties of XeCl*(308 nm) exciplex lamp created by a dielectric barrier discharge

The aim of this work is to highlight, through numerical modeling, the chemical and the electrical characteristics of xenon chloride mixture in XeCl* (308 nm) excimer lamp created by a dielectric barrier discharge. A temporal model, based on the Xe/Cl₂ mixture chemistry, the circuit and the Boltzmann equations, is constructed. The effects of operating voltage, Cl₂ percentage in the Xe/Cl₂ gas mixture, dielectric capacitance, as well as gas pressure on the 308-nm photon generation, under typical experimental operating conditions, have been investigated and discussed. The importance of charged and excited species, including the major electronic and ionic processes, is also demonstrated. The present calculations show clearly that the model predicts the optimal operating conditions and describes the electrical and chemical properties of the XeCl* exciplex lamp.     

Effect of a pulsed high-current discharge on hydrogen-air mixtures

A self-consistent model describing the influence of a pulsed discharge on H₂-air mixtures is developed. The model includes the processes of ionization, dissociation, and excitation of the gas molecules by electron impacts; a set of ion-molecular reactions determining the time evolution of the charged particle densities; the processes involving electronically excited atoms and molecules; and a set of reactions describing the ignition of hydrogen-oxygen mixtures. Results are presented from simulations of the oxidation dynamics of hydrogen molecules in a stoichiometric H₂-air mixture and the ignition of such a mixture under the action of a pulsed high-current discharge. The simulation results are compared with available experimental data and calculations performed by other authors.     

2D gasdynamic simulation of the kinetics of an oxygen-iodine laser with electric-discharge generation of singlet oxygen

The kinetic processes occurring in an electric-discharge oxygen-iodine laser are analyzed with the help of a 2D (r, z) gasdynamic model taking into account transport of excited oxygen, singlet oxygen, and radicals from the electric discharge and their mixing with the iodine-containing gas. The main processes affecting the dynamics of the gas temperature and gain are revealed. The simulation results obtained using the 2D model agree well with the experimental data on the mixture gain. A subsonic oxygen-iodine laser in which singlet oxygen is generated by a 350 W transverse RF discharge excited in an oxygen flow at a pressure P = 10 Torr and the discharge tube wall is covered with mercury oxide is simulated. The simulated mixing system is optimized in terms of the flow rate and the degree of preliminary dissociation of the iodine flow. The optimal regime of continuous operation of a subsonic electric-discharge oxygen-iodine laser is found.     

Modeling of a Ne/Xe dielectric barrier discharge excilamp for improvement of VUV radiation production

This work is devoted to excimer lamp efficiency optimization by using a homogenous discharge model of a dielectric barrier discharge in a Ne?Xe mixture. The model includes the plasma chemistry, electrical circuit, and Boltzmann equation. In this paper, we are particularly interested in the electrical and kinetic properties and light output generated by the DBD. Xenon is chosen for its high luminescence in the range of vacuum UV radiation around 173 nm. Our study is motivated by interest in this type of discharge in many industrial applications, including the achievement of high light output lamps. In this work, we used an applied sinusoidal voltage, frequency, gas pressure, and concentration in the ranges of 2–8 kV, 10–200 kHz, 100–800 Torr, and 10–50%, respectively. The analyzed results concern the voltage V _p across the gap, the dielectric voltage V _d, the discharge current I, and the particles densities. We also investigated the effect of the electric parameters and xenon concentration on the lamp efficiency. This investigation will allow one to find out the appropriate parameters for Ne/Xe DBD excilamps to improve their efficiency.     

Influence of the chlorine concentration on the radiation efficiency of a XeCl exciplex lamp

The influence of the chlorine concentration on the radiation efficiency of coaxial exciplex lamps (excilamps) excited by a dielectric barrier discharge (DBD) in binary Xe-Cl₂ mixtures at pressures of 240–250 Torr is investigated experimentally and theoretically. The experiments were carried out at Cl₂ concentrations in the range of 0.01–1%. The DBD characteristics were calculated in the framework of a one-dimensional hydrodynamic model at Cl₂ concentrations in the range of 0.1–5%. It is found that the radiation intensities of the emission bands of Xe*₂(172 nm) and XeCl* (308 nm) are comparable when the chlorine concentration in the mixture is in the range of 0.01–0.1%. In this case, in the mixture, the radiation intensity of the Xe*₂ molecule rapidly decreases with increasing Cl₂ concentration and, at a chlorine concentration of ≥0.2%, the radiation of the B → X band of XeCl* molecules with a peak at 308 nm dominates in the discharge radiation. The radiation efficiency of this band reaches its maximum value at chlorine concentrations in the range of 0.4–0.5%. The calculated efficiencies of DBD radiation exceed those obtained experimentally. This is due to limitations of the one-dimensional model, which assumes the discharge to be uniform in the transverse direction, whereas the actual excilamp discharge is highly inhomogeneous. The influence of the chlorine concentration on the properties of the DBD plasma in binary Xe-Cl₂ mixtures is studied numerically. It is shown that an increase in the Cl₂ concentration in the mixture leads to the attachment of electrons to chlorine atoms and a decrease in the electron density and discharge conductivity. As a result, the electric field and the voltage drop across the discharge gap increase, which, in turn, leads to an increase in the average electron energy and the probability of dissociation of Cl₂ molecules and ionization of Xe atoms and Cl₂ molecules. The total energy deposited in the discharge rises with increasing chlorine concentration due to an increase in the power spent on the heating of positive and negative ions. The power dissipated by electrons decreases with increasing chlorine concentration in the working mixture. Recommendations on the choice of the chlorine content in the mixture for reducing the intensity of VUV radiation of the second continuum of the Xe*₂ excimer without a substantial decrease in the excilamp efficiency are formulated.     

Breakdown in helium in high-voltage open discharge with subnanosecond current front rise

Investigations of high-voltage open discharge in helium have shown a possibility of generation of current pulses with subnanosecond front rise, due to ultra-fast breakdown development. The open discharge is ignited between two planar cathodes with mesh anode in the middle between them. For gas pressure 6 Torr and 20 kV applied voltage, the rate of current rise reaches 500 A/(cm² ns) for current density 200 A/cm² and more. The time of breakdown development was measured for different helium pressures and a kinetic model of breakdown in open discharge is presented, based on elementary reactions for electrons, ions and fast atoms. The model also includes various cathode emission processes due to cathode bombardment by ions, fast atoms, electrons and photons of resonant radiation with Doppler shift of frequency. It is shown, that the dominating emission processes depend on the evolution of the discharge voltage during the breakdown. In the simulations, two cases of voltage behavior were considered: (i) the voltage is kept constant during the breakdown; (ii) the voltage is reduced with the growth of current. For the first case, the exponentially growing current is maintained due to photoemission by the resonant photons with Doppler-shifted frequency. For the second case, the dominating factor of current growth is the secondary electron emission. In both cases, the subnanosecond rise of discharge current was obtained. Also the effect of gas pressure on breakdown development was considered. It was found that for 20 Torr gas pressure the time of current rise decreases to 0.1 ns, which is in agreement with experimental data.     

凑型准分子激光器的发展及其在医学中的应用

由于在绝缘材料和气体放电技术方面的进展,处于紫外波段的准分子激光器已经在工业、科学研究,特别是医学等领域成为主要应用工具.在本文中,我们将介绍新颖紧凑型准分子激光器在医学中的应用.此外,在文章中对紧凑型准分子激光器所采用的关键技术,诸如固态开关、电晕预电离和金属/陶瓷腔等技术进行了详细的讨论.     

凑型准分子激光器的发展及其在医学中的应用

由于在绝缘材料和气体放电技术方面的进展,处于紫外波段的准分子激光器已经在工业、科学研究,特别是医学等领域成为主要应用工具。在本文中,我们将介绍新颖紧凑型准分子激光器在医学中的应用。此外,在文章中对紧凑型准分子激光器所采用的关键技术,诸如固态开关、电晕预电离和金属,陶瓷腔等技术进行了详细的讨论。     

Resonance microwave discharge as a source of UV radiation

Results are presented from theoretical and experimental studies of an optical radiation source based on a microwave discharge excited in an Ar + Hg mixture. The main attention is paid to the so-called “resonance” discharge operating at low pressures of the working gas (argon). It is shown that a decrease in the Ar pressure leads to significant increase in the Hg radiation intensity (including biologically active UV radiation) and considerable decrease in the intensity of argon emission lines. The intensity of discharge radiation is calculated in the framework of the collisional-radiative model. The results of calculation agree qualitatively with experimental data.     

Population of vibrational levels of krypton excimer states excited by an electric discharge

The effect of admixtures and excitation conditions on the population distribution of the vibrational levels of krypton excimer states is investigated. The emission spectra of a krypton discharge plasma in a supersonic jet, an extended capillary discharge, and a barrier discharge are considered. It is found that the population distribution in a barrier discharge best fits the equilibrium conditions.     

Phenylethynylpyrene-labeled oligonucleotide probes for excimer fluorescence SNP analysis of 23S rRNA gene in clarithromycin-resistant Helicobacter pylori strains

The use of phenylethynylpyrene excimer forming pair in the design of specific fluorescent probes for determination of A2144G (A2143G and/or A2143C) mutations in 23S rRNA gene of Helicobacter pylori is described. Analysis of fluorescence spectra of model duplexes revealed optimal positions of fluorophore residues in the probe sequences for maximum efficiency of SNP detection. Application of excimer forming probes for analysis of DNA samples isolated from natural bacterial strains of H. pylori was demonstrated.     

Hydrocarbon plasma chemistry in a continuous microwave discharge

A study is made of the relation between the kinetic processes involving carbon-containing species and the intensity ratios of different emission lines in synthesizing diamond films in a microwave discharge plasma. The intensity ratios of the emission lines are measured as functions of the pressure, composition, and flow rate of the gas mixture. The kinetic processes involving carbon-containing components are simulated under conditions close to the experimental ones. It is shown that the intensity ratios of different pairs of lines can be used to control diamond film deposition.     

Dipyrenylphosphatidylcholines as membrane fluidity probes. Relationship between intramolecular and intermolecular excimer formation rates.

In the intramolecular excimeric membrane probe, dipyrenylphosphatidylcholine (dipyn PC), pyrene moieties are linked to the terminal carbons of the two acyl chains, each of which contains n carbons. We show here how the probe intramolecular excimer production rate, K, may be determined from the excimer/monomer intensity ratio, rl, by making use of the fluorescence titrations of the related monopyrenyl probe, pyn PC, analyzed according to the milling crowd model. rl and the rate K of dipy10 PC in four model membrane systems were measured over a wide temperature range and both parameters are shown to be sensitive functions of the lateral fluidity of the host matrix. A model for relating the intramolecular and intermolecular excimer formation rates is proposed according to which both processes are limited by the reorientational rate of the pyrene moiety. Above the fluid-gel transition temperature, Tc, the diffusion rate (f) of the monopyrenyl probe (pyn PC) is accordingly related to K by: pE approximately K/(K + 1/2f + tau -1M), where pE is the probability of excimer formation between nearest neighbor pyn PC probes, and tau M is the monomer lifetime. Values of pE derived in this way are found to be consistent with pE values derived from the milling crowd analysis of fluorescence yield titration experiments. K for dipy10 PC in DMPC multibilayers ranges from 0.21 x 10(7) s-1 at 10 degrees C in the gel phase, to 5.7 x 10(7) s-1 at 60 degrees C in the fluid phase, whereas the lateral diffusion coefficient, D, for py10 PC in the same bilayers ranged from 8 to 34 microns2 s-1, when calculated with D = fL2/4, L being the average lipid-lipid spacing of the host membrane. Above Tc and at the same reduced temperature, (T - Tc)/Tc, both f for py10 PC, and K for dipy10 PC were found to have relative magnitudes in the order: DPPC greater than DMPC greater than POPC greater than DOPC. This and the similarity of the activation energies for f and K suggest that the rotation of the the pyrene moiety is the rate-limiting step for both the lateral mobility of py10 PC and intramolecular excimer formation in dipy10 PC.     

Fluorescence decay of 1-methylpyrene in small unilamellar l-alpha-dimyristoylphosphatidylcholine vesicles. A temperature and concentration dependence study

The fluorescence decay kinetics of 1-methylpyrene in small unilamellar l-alpha-dimyristoylphosphatidylcholine vesicles above the phase transition temperature has been studied as a function of concentration and temperature. When the 1-methylpyrene/phospholipid ratio equals 1:2000 no excimer is observed and the fluorescence decay is monoexponential. When this ratio is equal to or higher than 1 200, excimer is observed and the monomer and excimer decays can be adequately described by two exponential terms. The deviation of the monomer decays from monoexponentiality cannot be described by a model where the diffusion-controlled excimer formation is time dependent. The observed decays are compatible with the excimer formation scheme which is valid in an isotropic medium. The activation energy of excimer formation is found to be 29-9 +/-1.4 kJ mol . The (apparent) excimer formation constant and the excimer lifetime at different temperatures have been determined. The diffusion coefficient associated with the excimer formation process varies between 2 x 10(-10) m(2)/s at 70 degrees C to 4 x 10(-11) m(2)/s at 25 degrees C.     

Optimization of excimer-forming two-probe nucleic acid hybridization method with pyrene as a fluorophore.

A previously presented homogeneous assay method, named the excimer-forming two-probe nucleic acid hybridization (ETPH) method, is based on specific excimer formation between two pyrenes attached at the neighboring terminals of two sequential probe oligonucleotides complementary to a single target. In this study, we investigated assay conditions and optimal molecular design of probes for intense excimer emission using a pyrenemethyliodoacetamide-introduced 16mer probe, a pyrene butanoic acid-introduced 16merprobe and a target 32mer. The length of the linker between the pyrene residue and the terminal sugar moiety remarkably influenced the quantum efficiency of excimer emission; the pair of linker arms of these two probes was optimal. The quantum efficiency was also dependent upon the concentrations of dimethylformamide and NaCl added to the assay solution. Spectroscopic measurements and T m analysis showed that an optimal configuration of the two pyrene residues for intense excimer emission might be affected by pyrene-pyrene interaction, pyrene-duplex interaction (intercalation/stacking) and solvent conditions as a whole. We then demonstrated the practicality of the ETPH method with the optimal hybridization conditions thus attained by determining that the concentration of 16S rRNA in extracts from Vibrio mimicus ATCC 33655 cells in exponential growth phase is 18 500 16S rRNA molecules/cell on average.     

Domain formation in a fluid mixed lipid bilayer modulated through binding of the C2 protein motif

The role and mechanism of formation of lipid domains in a functional membrane have generally received limited attention. Our approach, based on the hypothesis that thermodynamic coupling between lipid-lipid and protein-lipid interactions can lead to domain formation, uses a combination of an experimental lipid bilayer model system and Monte Carlo computer simulations of a simple model of that system. The experimental system is a fluid bilayer composed of a binary mixture of phosphatidylcholine (PC) and phosphatidylserine (PS), containing 4% of a pyrene-labeled anionic phospholipid. Addition of the C2 protein motif (a structural domain found in proteins implicated in eukaryotic signal transduction and cellular trafficking processes) to the bilayer first increases and then decreases the excimer/monomer ratio of the pyrene fluorescence. We interpret this to mean that protein binding induces anionic lipid domain formation until the anionic lipid becomes saturated with protein. Monte Carlo simulations were performed on a lattice representing the lipid bilayer to which proteins were added. The important parameters are an unlike lipid-lipid interaction term and an experimentally derived preferential protein-lipid interaction term. The simulations support the experimental conclusion and indicate the existence of a maximum in PS domain size as a function of protein concentration. Thus, lipid-protein coupling is a possible mechanism for both lipid and protein clustering on a fluid bilayer. Such domains could be precursors of larger lipid-protein clusters ('rafts'), which could be important in various biological processes such as signal transduction at the level of the cell membrane.     

Characteristics of a transverse RF discharge in Xe/Cl<Subscript>2</Subscript> mixtures

Results are presented from the study of the electrical and optical characteristics of a transverse RF discharge in Xe/Cl₂ mixtures at pressures of p≤400 Pa. The working mixture was excited by a modulated RF discharge (f=1.76 MHz) with a transverse electrode configuration (L≤17 cm). The emission spectrum in the spectral range of 210–600 nm and the waveforms of the discharge current, discharge voltage, and plasma emission intensity were investigated. The UV emission power from the discharge was studied as a function of the pressure and composition of a Xe/Cl₂ mixture. It is shown that a discharge in a xenon-chlorine mixture acts as planar excimer-halogen lamp operating in the spectral range of 220–450 nm, which contains a system of overlapping XeCl(D, B-X; B, C-A) and Cl₂(D′-A′) bands. Transverse RF discharges in Xe/Cl₂ mixtures can be used to create a wideband lamp with two 50-cm² planar apertures and the low circulation rate of the working mixture.     

Pyrene excimer fluorescence: a spatially sensitive probe to monitor lipid-induced helical rearrangement of apolipophorin III

Manduca sexta apolipophorin III (apoLp-III), an 18-kDa, monomeric, insect hemolymph apolipoprotein, is comprised of five amphipathic alpha-helices arranged as a globular bundle in the lipid-free state. Upon lipid binding, it is postulated that the bundle opens, exposing a continuous hydrophobic surface which becomes available for lipid interaction. To investigate lipid binding-induced helical rearrangements, we exploited the unique fluorescence characteristics of N-(1-pyrene)maleimide. Pyrene is a spatially sensitive extrinsic fluorescent probe, which forms excited-state dimers (excimers) upon close encounter with another pyrene molecule. Cysteine residues were introduced into apoLp-III (which otherwise lacks cysteine) at Asn 40 (helix 2) and/or Leu 90 (helix 3), creating two single-cysteine mutants (N40C-apoLp-III and L90C-apoLp-III) and N40C/L90C-apoLp-III, a double-cysteine mutant, which were labeled with pyrene maleimide. Pyrene-labeled N40C/L90C-apoLp-III, but not the pyrene-labeled single-cysteine mutants, exhibited strong excimer fluorescence in the lipid-free, monomeric state. Guanidine hydrochloride titration and temperature studies revealed a loss in excimer fluorescence, accompanied by a loss in the molar ellipticity of the protein. When apoLp-III interacts with phospholipid vesicles to form disklike complexes, a significant loss in excimer fluorescence was noted, indicating that the helices bearing the pyrene moieties diverge from each other. Pyrene excimer fluorescence was further employed to examine the relative orientation of lipid-bound apoLp-III molecules. Pyrene-labeled N40C- or L90C-apoLp-III displayed no excimer fluorescence in the disk complexes, while complexes prepared with an equal mixture of both single-labeled mutants did emit excimer fluorescence, indicating apoLp-III adopts a preferred nonrandom orientation around the perimeter of the bilayer disk. These studies establish pyrene excimer fluorescence as a useful spectroscopic tool to address intra- and intermolecular interactions of exchangeable apolipoproteins upon binding to lipid.     

Kinetics of the processes,plasma parameters,and output characteristics of a UV emitter operating on XeI molecules and iodine molecules and atoms

A kinetic model of the processes occurring in the plasma of a high-power low-pressure gas-discharge lamp is presented, and the output characteristics of the lamp are described. The lamp is excited by a longitudinal glow discharge and emits the I₂(D′-A′) 342-nm and XeI(B-X) 253-nm bands and the 206.2-nm spectral line of atomic iodine. When the emitter operates in a sealed-off mode on the p(He): p(Xe): p(I₂) = 400: 120: (100–200) Pa mixture, the fractions of the UV radiation power of iodine atoms, exciplex molecules of xenon iodide, and iodine molecules comprise 55, 10, and 35%, respectively. At the optimal partial pressure, the maximum total radiation power of the lamp reaches 37 W, the energy efficiency being about 15%.