Escape rate of muonium from micelles — As determined by competition kinetics

A competition was established for the reaction of muonium atoms (Mu) between nitrate ions in water and benzene or styrene solubilized in micelles. The nitrate was 3.3-times more efficient at inhibiting muonated free radical formation with benzene than with styrene as the radical-producing solute. Kinetic analysis of this system indicates that Mu emerges from micelles, on average, at least three times during its short (ns) lifetime, these being medium sized micelles carrying on average 3 benzene molecules. So Mu is certainly not trapped, nor even localized. Its escape rate is estimated to be 9×10⁸ s^–1, which is commensurate with an ordinary diffusion time. The results were obtained by determining the yield of muonated free radicals formed within the micelles using muon-level-crossing-resonance spectroscopy.     

Autoignition of surrogate fuels at elevated temperatures and pressures

Autoignition of Jet-A and mixtures of benzene, hexane, and decane in air has been studied using a heated shock tube at mean post-shock pressures of 8.5 ± 1 atm within the temperature range of 1000–1700 K with the objective of identifying surrogate fuels for aviation kerosene. The influence of each component on ignition delay time and on critical conditions required for strong ignition of the mixture has been deduced from experimental observations. Correlation equation for Jet-A ignition times has been derived from the measurements. It is found that within the scatter of experimental data dilution of n-decane with benzene and n-hexane leads to slight increase in ignition times at low temperatures and does not change critical temperatures required for direct initiation of detonations in comparison with pure n-decane/air mixtures. Ignition times in 20% hexane/80% decane (HD), 20% benzene/80% decane (BD) and 18.2% benzene/9.1% hexane/72.7% decane (BHD) mixtures at temperature range of T  1450–1750 K correlate well with induction time of Jet-A fuel suggesting that these mixtures could serve as surrogates for aviation kerosene. At the same time, HD, BD and BHD surrogate fuels demonstrate a stronger autoignition and peak velocities of reflected shock front in comparison with Jet-A and n-decane/air mixtures.     

Competition between benzene and styrene in forming radicals under different solvent conditions observed by muon level crossing resonance

The muon level-crossing-resonance technique has been used to resolve major discrepancies that exist in muon-spin-resonance studies (both free-radical formation and muonium decay rates) in the competition between benzene and styrene. The results, obtained for 30 mM solutions in ethanol and for 2.5 mM aqueous micelles solutions, show that muonium atoms (Mu) react 8 (±2) times faster with styrene than with benzene. In the above cases thermalized Mu is unquestionably the reactive species, which is known to show nucleophilic intra-molecular selectivity in the case of styrene. But a similar value, 9 (±2), was also obtained for undiluted mixtures of liquid benzene and styrene (neat mixture) — where the precursor might have been hot Mu (which should display weaker selectivity than Mu) or cations derived from ⁺ (which should show higher selectivity). These results support the view that thermalized Mu is the predominant reactive species in liquid benzene and styrene.     

Gas formation in liquid in initial stages of a pulsed discharge

Gas formation in electrolytes with=10^–2–10^–4–1cm^–1, distilled water = 10^–5-1.5 ·10^{–6 –1}cm^–1, and chemically pure n-hexane in the initial stages of formation of discharge with rectangular voltage pulses of 0.67 and 1.85 sec duration is investigated. The experimental results are compared with the results of approximate calculations.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii Fizika, No. 11, pp. 42–47, November, 1972.The authors thank V. V. Ryumin for taking part in the discussion of the results and V. V. Lopatin for participation in the experiments with electron-optical light amplifier.     

Luminescence of ZnO Having a Superstoichiometric Content of Oxygen

Using a unique method of radical-beam heteroepitaxy (RBHE) based on annealing of the crystals of the II–VI (ZnSe) compounds in a flow of radicals of a metalloid component — oxygen O — ZnO layers with a superstoichiometric content of oxygen were obtained. The conductivity of the layers = 10² ·cm, the mobility of the holes = 23 cm²/V·sec, and the concentration N _A = 10¹⁵ cm^–3. The luminescence spectra of pure ZnO single crystals and those doped with Li and Na, both treated by the RBHE method, are studied at helium temperatures. The luminescence centers associated with the intrinsic defects (V _Zn) are identified.     

The UV absorption spectrum of the phenyl radical isolated in solid argon

Phenyl radicals have been generated by photodecomposition of nitrosobenzene isolated in solid argon at 12 K. In this medium the origin of the first UV absorption band of nitrosobenzene corresponding to theS ₀ S ₂ transition is found at 30260 cm^–1. Excitation with an excess energy of 2200 cm^–1 results in very efficient photodissociation. The fragments NO and phenyl are stable for many hours. Annealing of the sample above 35 K led to partial recombination and recovery of the absorption spectrum of nitrosobenzene. The UV spectrum of the phenyl radical was obtained in the wavenumber range 25000–45000 cm^–1, apparently without contamination by other species. It shows sharp lines at 25220, 33880, and 34820 cm^–1 and two broader maxima at 38360 and 41060 cm^–1. Of these only the line at 34820 cm^–1 had been assigned to the phenyl radical in earlier work. These data are compared to recent molecular orbital calculations.Dedicated to Prof. F. P. Schäfer on the occasion of his 65th birthday.     

Observation of muonic HF molecule formation with TF μ− SR

Negative muon polarization has been measured in pure gaseous Ne (24 atm) and in Ne+H₂ mixtures (24 atm Ne+1.8 atm H₂, 8 atm H₂ and 16 atm H₂). The experiment was performed at JINR (Dubna) on aSR-spectrometer [1] with 200 G transverse magnetic field at room temperature. In pure Ne no polarization was observed (a ₀=0.09±0.1%) while in Ne+H₂ mixtures clear precession signals were detected at the free-muon frequency with asymmetries a_1.8=0.33±0.13%,a ₈=0.33±0.14% anda ₁₆=0.59±0.09%. The fact that polarization appears in the muonic HF molecule shows that at the moment of the molecule formation (t10^–10 s) the muon is not completely depolarized. The estimate of the reaction constantk=(2.3±1.6)×10^–11cm³ s^–1 agrees with the experimental values obtained by other methods. The result achieved demonstrates that ^– SR-method can be applied for studying fast kinetics processes in the gas phase and in particular for measuring chemical reaction rates of halogen atoms and ions.     

Photoinduced Electron Transfer From Carbazole to Halomethanes in a Gas Phase

Intermolecular photoinduced electron transfer (PET) in a gas phase was studied using carbazole vapor fluorescence quenching by halomethanes (CHCl₃, CH₂Br₂, CCl₄, CHBr₃). The fluorescence quenching rate constants k _q changing from 2.3·10⁵ sec^–1·torr^–1 in mixtures with CHCl₃ to 4.6·10⁶ sec^–1·torr^–1 in mixtures with CHBr₃ at a constant temperature of 403 K were estimated. The dependence of the carbazole fluorescence decay rates in the presence of halomethanes on the free energy change G during transfer of the electron from carbazole to halomethanes is considered. It is suggested to take into account the influence of the vibrational energy of the carbazole molecule E _vib and its temperature changes in estimation of the G values. The differences between PET in the gas and liquid phases were analyzed. It is found that for mixtures with CCl₄ and CHBr₃ the negative temperature dependence of k _q is observed, when the decay rates and efficiencies of the intermolecular PET decreased with temperature increase in the range 403–573 K, i.e. these mixtures the electron transfer is not a barrier-restricted process.     

Effectiveness of ultrasound for the destruction of Mycobacterium sp. strain (6PY1)

Ultrasound is widely used to disinfect drinking water and wastewater due to its strong physical and chemical effects on microorganisms. The aim of this study was to investigate the effect of ultrasound on the destruction of Mycobacterium strain 6PY1. Ultrasound waves (20 kHz or 612 kHz) were used to treat aqueous suspensions of Mycobacterium at different volumes, initial bacterial concentrations, and power densities. At the same power density and the same exposure time, sonication at high frequency resulted in a lower destruction of Mycobacterium sp. 6PY1 (35.5%) than sonication at low frequency (93%). The percentage of removal was not significantly affected by the volume of the irradiated suspension (150–300 ml) or the initial cell concentration (2.15 × 10⁻³–1.4 × 10⁻² mg protein L⁻¹). At low frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density, with a constant level reached after a certain power density. At high frequency, the removal percentage of Mycobacterium sp. 6PY1 increased with increasing the power density. The mechanism of cell killing was investigated by examining the effects of OH radical scavengers such as sodium carbonate. At high frequency the presence of sodium carbonate suppressed the removal process. However, at low frequency the removal process was not affected, thus indicating that OH radicals have a negligible role in this case. The latter result was supported by ten time’s H₂O₂ production at high frequency greater than that at low frequency.     

Infrared absorption of silane,ammonia, acetylene and diborane in the range of the CO2 laser emission lines: Measurements and modelling

Absorption spectra of the gases SiH₄, NH₃, C₂H₂ and of SiH₄/Ar and SiH₄/B₂H₆ mixtures have been measured in the spectral range of the CO₂ laser from 9.2 to 10.8 µm. In agreement with literature, silane shows the highest absorption (absorption coefficient = 3.3 × 10^–2 Pa^–1 m^–1). The deviation of the measured absorption behaviour of silane from literature, as far as the pressure dependence is concerned, can be explained by the enhanced spectral energy density in our experiment. This is confirmed by a rate-equation model involving the basic mechanisms of V-V and V-T energy transfer between vibrationally excited silane molecules. In contrast to silane, the absorption coefficient of NH₃ at the 10P(20) laser line is 4.5 × 10^–4 Pa^–1 m^–1 atp = 20 kPa and has its maximum of 4.5 × 10^–3 Pa^–1 m^–1 at the 10R(6) laser line. For C₂H₂ and B₂H₆, is even less ( 2.1 Ò 10^–5 Pa^–1 m^–1 for C₂H₂).     

Volume and grain boundary diffusion of implanted 113Sn in aluminium

Volume and grain boundary diffusion of ¹¹³Sn in aluminium was investigated with the radiotracer method. The implantation technique was used for tracer deposition to avoid problems of tracer hold-up caused by the oxide layer always present on aluminium. The diffusion penetration was chosen large enough to permit serial sectioning of samples with the aid of a microtome.The temperature dependence of the volume diffusivity was determined as D(T)=4.54×10^–5×exp[–(114.5±1.2)kJmol^–1/RT] m ² s ^–1. This confirms previous measurements from our group which already showed that Sn is the fastest foreign metal diffusor so far investigated in aluminium.Grain boundary diffusion of ¹¹³Sn in Al polycrystals was measured in the type-B kinetic regime. The grain boundary diffusion product P=sD _gb (s=segregation factor, =grain boundary width, D _gb=grain boundary diffusivity) was found to be strongly affected by the impurity content of aluminium. For Al polycrystals of 99.9992% nominal purity we obtained P _5N(T)=1.08×10^–8exp [–(96.9±7.5) kJ mol^–1/RT] m³ s^–1 and for less pure Al polycrystals of 99.99% nominal purity P _4N(T)=3.0×10^–10 exp [–(90.1±4.2) kJ mol^–1/RT] m³ s^–1 was determined. The grain boundary diffusion product in the purer material is more than one order of magnitude higher than in the less pure material. Very likely this is an effect of co-segregation of non-diffusant impurities into the grain boundaries.     

Protonated dye-surfactant ion pair formation between neutral red and anionic surfactants in aqueous submicellar solutions

Spectral and surface tension behavior of aqueous neutral red in the presence of sodium dodecyl sulfate (SDS), sodium dodecyl benzene sulfonate (SDBS) and sodium dodecyl sulfonate (SDSN) have been studied to understand the nature of the interactions in their submicellar concentration ranges. The variations in spectra and surface tension with variation in the concentrations of the surfactants suggest the formation of a 1:1 close-packed dye-surfactant ion pair, HNR⁺S⁻ between the acid form, HNR⁺ of the dye and the surfactant anion at very low concentrations of the surfactant below critical micelle concentration (cmc) of the pure surfactant. The dye-surfactant ion pair behaves like a nonionic surfactant having higher efficiency and lower cmc than that of the corresponding pure anionic surfactant. The ion pairs are adsorbed on the air/water interface at very low concentrations of the surfactant. As the concentration of the surfactant increases and the ion pairs form micelles of their own, the dye in the ion pair is protonated to form H₂NR²⁺S⁻. As the cmc of the pure surfactant is approached, the protonation equilibrium gradually reverses and pure surfactant ions gradually replace the ion pairs at the interface. Finally, a homogeneous monolayer of pure surfactant anions exists at the air/water interface and the dye remain solubilized in pure micelles above the cmc of the pure surfactant. The equilibrium constants, K_c for the close-packed protonated dye-surfactant ion pair (PDSIP) formation have been determined at varying pH. The submicellar interaction has been found to be stronger with SDS than SDBS. The plots of logarithm of K_c vs. pH have been found to be quite linear which consolidates the assumption of formation of the species, H₂NR²⁺S⁻. The interaction is driven by enthalpy as well as entropy.     

A photometer to measure light scattering in optical glass

A photometer is described for the measurement of light-scattering in high-quality, optical bulk glass. The photometer operates continuously over the wavelength range 0.5 to 1m and can measure scattering coefficients down to a level of 5×10^–7 cm^–1. A photon counting technique is used for light measurement and calibration is by reflection of the incident beam from an ideal diffusing screen. Measurements with high-purity benzene are in good agreement with computed and previous experimental values. Results of scattering from two samples of optical glass are given.     

Absolute CH concentrations in low-pressure flames measured with laser-induced fluorescence

Laser-induced fluorescence in both theA–X andB–X band systems was used to measure absolute number densities of CH radicals in 40 Torr propane/air flames at temperatures near 1600 K. The fluorescence signal was calibrated against Rayleigh scattering in N₂ and Raman scattering in H₂. In a rich flame, = 1.15, the concentration at the peak of the CH distribution was 5.8 ± 1.5 ppm, or (1.4 ± 0.4) × 10¹² cm^–3, with independent values obtained using both band systems and calibration methods in good agreement. This result compares well with a prediction of 8 ppm from a kinetic model of this flame.     

Measurement of complex dielectric constant of inhomogeneous materials in the range 102–107 Hz

A method of measuring the complex dielectric constant of a mixture composed of a disperse substance and water by insertion of dielectric spacers between the electrodes and the investigated substance is discussed. This system exhibits relaxation of the Maxwell-Wagner type in the conductivity range 10^–8–10^{–2 –1}·m^–1. By constructing and analyzing Cole-Cole diagrams it is possible to determine the complex dielectric constant of mixtures with a water content of 1–100 wt.% in the frequency range 10²–10⁷ Hz.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 40–46, September, 1978.     

Parton distributions for high energy collisions

Recent data from deep inelastic scattering experiments atx10^–2 are used to fix the parton distributions down tox10^–4 andQ ²0.3 GeV². The predicted extrapolations are uniquely determined by the requirement of avalence-like structure ofall parton distributions at some low resolution scale and are furthermore shown to be insensitive in the small-x region, 10^–4x10^–2, to the detailed experimental input at the presently accessiblex>10^–2. Simple parameterizations of the resulting parton distributions are presented in the range 10^–5x<1 and=">Q ²10⁸ GeV² as obtained from the leading- and higher-order evolution equations.     

Photoelectric properties of Pb1−x−y Sn x Ge y Te:In epitaxial films

Pb_1–x–y Sn _x Ge _y Te:In epitaxial films are examined in a wide temperature interval and at various background fluxes. These films have high sensitivity to infrared radiation in the spectral range <20m. The lifetime depends exponentially on temperature and varies from several seconds at T=10 K to 10^–2 s at T=20 K. The two-electron model of Jahn-Teller centers is proposed to explain the results. Multielement photoresistors based on these films are fabricated and D*=1.7×10¹³ cm Hz^1/2 W^–1 at T=25 K is achieved. Noise of the photoresistors is independent of background flux when it varies from 10¹² cm^–2 s^–1 to 10¹⁸ cm^–2 s^–1. As compared with Si:Ga and Ge:Hg photoresistors, the responsitivity is several orders larger at the operating temperature 25–30 K.     

Pitfalls in the Use of Common Luminescent Probes for Oxidative and Nitrosative Stress

Lucigenin (LC²⁺, bis-N-methylacridinium) and 2,7-dichlorofluorescin (DCFH₂) are widely used as chemiluminescent or fluorescent probes for cellular oxidative stress, to reflect levels of superoxide (O₂ ^·–) and hydrogen peroxide, respectively. We report mechanistic studies that add to the growing evidence for the unsuitability of either probe except in very well-defined circumstances. The ability for lucigenin to generate superoxide via reduction of LC²⁺ to LC^·+ and redox cycling with oxygen depends on the reduction potential of the LC²⁺/LC^·+ couple. Redox equilibrium between LC^·+ and the redox indicator benzyl viologen is established in microseconds after generation of the radicals by pulse radiolysis and indicated E(LC²⁺/LC^·+) –0.28 V vs. NHE. Reaction of LC^·+ with O₂ to generate O₂ ^·– was also observed directly similarly, occurring in milliseconds, with a rate constant k 3 × 10⁶ M ^–1 s^–1. Quinones act as redox mediators in LC^·+/O₂ redox cycling. Oxidation of DCFH₂ to fluorescent DCF is not achieved by O₂ ^·– or H₂O₂, but NO₂ ^·) reacts rapidly: k 1 × 10⁷ M ^–1 s^–1. Oxidation by H₂O₂ requires a catalyst: cytochrome c (released into the cytosol in apoptosis) is very effective (even 10 nM). Fluorescence reflects catalyst level as much as O₂ ^·–) production.     

The first and second nearest neighbour Cr3+ pairs in ruby

The optical spectrum of the exchange coupled first nearest neighbour Cr³⁺ pairs in ruby was studied by absorption, fluorescence and excitation spectroscopy. It was analysed by means of the group theoretical considerations given in part I [1]. The analysis could be verified by measuring the Zeeman effect in fields up to 150 KG. The Zeeman splitting deviates considerably from that of pure spin states even for the orbital singulet of the pair ground state. The exchange integrals of the ground state are found to beJ=–115 cm^–1 andj=–0.7 cm^–1.This work was supported by the Deutsche Forschungsgemeinschaft, SFB 65     

Anomalous behaviour of transient creep in commercially pure aluminium

Transient creep of pure and commercial aluminium was studied under a constant stress of 18·6 MPa at different temperatures ranging from 613 to 698 K. The anomalous values of transient creep parameters, n ranging from 0·003–0·055 (±0·001) and 0·5–1·0 (±0·05) respectively, which were found in this temperature rangs, might bs ascribed to the superplastic behaviour of pure and commercial aluminium. The activation energy of transient creep for pure Al was found to be about (2·4 +0·07) × 10^–22) kJ/atom. characterizing a dislocation glide-cross slipping mechanism.