Pressure recovery system for a high-power HF/DF laser: implementation practice

The matter of development of a high-performance pressure recovery system (PRS) for a high-power HF/DF laser is discussed. A sequence of design steps is proposed, which involves estimation of basic characteristics of PRS components with the help of one-dimensional integral and semi-empirical procedures; simulation, to be performed using three-dimensional non-stationary Navier — Stokes equations; experimental modelling aimed at verification of the calculation procedures and at refinement of obtained parameters; and a fullscale experiment. An ejector-type system providing for recovery of pressure from 12 Torr to atmospheric pressure in the gas-dynamic system of an HF/DF laser of several-tens-kilowatt power is developed. Matching conditions for parameters of individual PRS components as well as joint functioning of the PRS with a continuous chemical laser in an integral complex are analysed. Conditions for minimization of mass-dimensional characteristics of the laser-PRS complex necessary for the development of ground-based mobile systems are identified.     

Radiative decays of ρ and ω mesons

The results of the measurements of radiative decays of ρ and ω mesons with the Neutral Detector at thee ⁺ e ^? collider VEPP-2M are presented. The branching ratio of the decay ω→π ⁰γ was measured with higher than in previous experiments accuracy: $${\rm B}(\omega \to \pi ^0 \gamma ) = 0.0888 \pm 0.0062$$ . The ρ⁰→π ⁰ γ branching ratio was measured for the first time: $$B(\rho ^0 \to \pi ^0 \gamma ) = (7.9 \pm 2.0) \cdot 10^{ - 4} $$ . The decays ρ, ω→ηγ were studied. Their branching ratios with the assumption of constructive ρ?ω interference are: $$\begin{gathered} B(\omega \to \eta \gamma ) = (7.3 \pm 2.9) \cdot 10^{ - 4} , \hfill \\ B(\rho \to \eta \gamma ) = (4.0 \pm 1.1) \cdot 10^{ - 4} \hfill \\ \end{gathered} $$ . The branching ratios of ρ, ω→ηγ and ω→e ⁺ e ^? decays were also measured: $$\begin{gathered} B(\omega \to \pi ^ + \pi ^ - \pi ^0 ) = 0.8942 \pm 0.0062, \hfill \\ B(\omega \to e^ + e^ - ) = (7.14 \pm 0.36) \cdot 10^{ - 5} \hfill \\ \end{gathered} $$ . The upper limit for the ω→π ⁰ π ⁰ γ branching ratio was placed: B(ω→π ⁰ π ⁰ γ)<4·10^?4 at 90% confidence level.     

Chemiluminescence Determination of Cyanide Ions

It was found that alkaline solutions of luminol exhibit chemiluminescence in the presence of p-nitrobenzaldehyde (p-NBA), hemin, and cyanide ions. Air oxygen dissolved in the solutions is an essential component of the process. The kinetics of luminol chemiluminescence in the presence of p-NBA, hemin, and cyanide ions indicates the catalytic nature of the process. A scheme was proposed for the series of reactions resulting in chemiluminescence and generated by superoxide radicals formed in the p-NBA-catalyzed reaction between hemin-activated air oxygen and hydrated p-NBA species. A procedure was developed with a determination limit of (1.0 ± 0.3) × 10^?7 mg/mL (n = 5, P = 0.95) for cyanide ions.     

Fast intramolecular charge transfer with a planar rigidized electron donor/acceptor molecule

The planar rigidized molecule fluorazene (FPP) undergoes fast reversible intramolecular charge transfer (ICT) in the excited state, with a reaction time of 12 ps in the polar solvent ethyl cyanide at -45 degrees C. The ICT state of FPP has a dipole moment mu(e)(ICT) of 13 D, much larger than that of the locally excited state LE (1 D). The ICT behavior of FPP is similar to that of its flexible counterpart N-phenylpyrrole (PP), for which mu(e)(ICT) = 12 D. These results show that intramolecular charge transfer to a planar ICT state can occur efficiently. In designing ICT systems capable of rapid switching, it is therefore important to realize that large amplitude motions such as those necessary for the formation of a twisted intramolecular charge transfer (TICT) state are not required.     

Reactions of CF3-enones with ethyl nitroacetate and nitromethane: synthesis of CF3-γ-nitroketones

Reactions of α,β-unsaturated CF₃-ketones with nitromethane and ethyl nitroacetate have been investigated. We found that α,β-unsaturated trifluoromethylketones react with ethyl nitroacetate in the presence of calcinated potassium fluoride to form two classes of 1,4-conjugated addition products: CF₃-γ-nitroketones and 6,6,6-trifluoro-2-nitro-5-oxohexanoates in nearly quantitative yields. The products obtained are precursors for CF₃-pyrrolidine synthesis.     

Intramolecular charge transfer with the planarized 4-aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6)

Fast and efficient intramolecular charge transfer (ICT) and dual fluorescence is observed with the planarized aminobenzonitrile 1-tert-butyl-6-cyano-1,2,3,4-tetrahydroquinoline (NTC6) in a series of solvents from n-hexane to acetonitrile and methanol. Such a reaction does not take place for the related molecules with 1-isopropyl (NIC6) and 1-methyl (NMC6) groups, nor with the 1-alkyl-5-cyanoindolines with methyl (NMC5), isopropyl (NIC5), or tert-butyl (NTC5) substituents. For these molecules, a single fluorescence band from a locally excited (LE) state is found. The charge transfer reaction of NTC6 is favored by its relatively small energy gap DeltaE(S(1),S(2)), in accordance with the PICT model for ICT in aminobenzonitriles. For the ICT state of NTC6, a dipole moment of around 19 D is obtained from solvatochromic measurements, similar to micro(e)(ICT) = 17 D of 4-(dimethylamino)benzonitrile (DMABN). For NMC5, NIC5, NTC5, NMC6, and NIC6, a dipole moment of around 10 D is determined by solvatochromic analysis, the same as that of the LE state of DMABN. For NTC6 in diethyl ether at -70 degrees C, the forward ICT rate constant (1.3 x 10(11) s(-1)) is much smaller than that of the back reaction (5.9 x 10(9) s(-1)), showing that the equilibrium is on the ICT side. The results presented here make clear that ICT can very well take place with a planarized molecule such as NTC6, when DeltaE(S(1),S(2)) is sufficiently small, indicating that a perpendicular twist of the amino group relative to the rest of the molecule is not necessary for reaching an ICT state with a large dipole moment. The six-membered alicyclic ring in NMC6, for example, prevents ICT by increasing DeltaE(S(1),S(2)) relative to that of DMABN.     

Self-Sustained Oscillations of the Torque under High-Pressure Torsion in an NdFeB Alloy

JETP Letters - The behavior of an NdFeB-based multicomponent alloy subjected to high-pressure torsion has been studied. The high-pressure torsion results in the partial amorphization of the alloy,...     

Intramolecular Fluorescence Quenching of Crowned 7-Aminocoumarins as Potential Fluorescent Chemosensors

The effects of the nature of solvent, temperature and complex formation with alkali and alkaline-earth metal cations, as well as protonation, on the efficiency and the kinetics of fluorescence of 3-azacrowned 7-diethylaminocoumarins have been studied. For the crown-ethers under investigation, the ratio of a dipole moment to the radius of Onsager cavity delta micro/rho is a constant value, and a macrocycle does not affect delta micro, and rho. The fluorescence of coumarin 1 in acetonitrile is quenched by an electron donor, triethylamine, with the Stern-Volmer constant being equal to (0.474+/-0.009) M(-1). The decrease in coumarin 1 fluorescence quantum yield upon the introduction of N-alkylazacrown moiety into position 3 is caused by an intramolecular photoinduced electron transfer from the nitrogen atom of macroheterocycle to the coumarin moiety, where the excitation is localized. The fluorescence quenching has an activation energy 2.32+/-0.05 kcal/mol in various hydrocarbons, and does not depend on the solvent viscosity. The fluorescence kinetics of free crowned coumarins in methanol is not monoexponential because of the existence of macrocycle conformers, or because of the hydrogen bond complex formation between the solvent and the nitrogen atom of macrocycle, in which the efficiency of intramolecular electron transfer is different. Upon complex formation with alkali and alkaline-earth metal cations and upon protonation, the fluorescence quantum yield increases and fluorescence decay becomes monoexponential.     

Measurement of the relative probability of the decay φ → η′γ in the channel η′ → ηπ0π0, η → γγ

The process e ⁺ e ^? → η′γ, η′ → η π⁰π⁰, η → γγ is investigated by an SND detector in experiment on a VEPP-2M equipment with colliding electron-positron beams. The analysis of experimental data yields a value of B(? → η′γ)=(6.7 _?4.2 ^+5.0 ±1.5)×10^?5 for the decay probability. Taking into account a previous measurement of this quantity by an SND detector in the decay channel η′ → π⁺π^?η, one finally obtains B(?→η ′γ)=(6.7 _?2.4 ^+2.8 ±0.8)×10^?5.