UV Radiation of Low Pressure XeCl* and KrCl* Glow Discharges

The positive column of low pressure DC glow discharges in Xe/Cl₂ and Kr/Cl₂ gas mixtures has been investigated with respect to its UV radiation power and radiative efficiency for a wide range of parameters (total gas pressure: 1–30 mbar, current 10–30 mA, partial pressure of Cl₂: 1–33%). Also the radial distribution of the particle number densities of XeCl* (B) and KrCl* (B) has been determined by absolutely calibrated emission spectroscopy. Optimum UV (190–350 nm) output and efficiency has been found in gas mixtures with a relative Cl₂ partial pressure of 2–3% and total gas pressure of 12–18 mbar. At these parameters, the UV radiation power per column length is greater than 40 Watt/m with a radiative efficiency of 15–18%. These discharges could be used for UV induced photochemical processes.     

Measurement of the Radiative Properties of Frescoed Wall Surfaces Variously Pigmented

A method of radiative heating for frescoed surfaces has recently been proposed to prevent deterioration caused by moisture condensation. A previous study has stressed the importance of the surface absorptivities, in respect both to the power required and temperature disuniformity. In the present research, these absorptivities are measured for wall surfaces, composed and painted with different colors, precisely with the same techniques used at the time of the original construction (XIV–XVI century), and heated by radiating sources with continuous nearly grey spectra and grey-body temperatures between around 3,200 K and 700 K. For temperatures high enough to permit the realization of compact radiating sources (T ≤ 1,300 K), the absorptivities result all sufficiently high, thus not requiring high radiating power, and sufficiently close not to create dangerous internal stresses.     

An improved model to calculate radiative heat transfer in hot combustion gases

Radiative heat transfer plays an important role in the chemical reactions in the combustor. The widely used WSGG model proposed by Smith is established for normal pressure, which shows inevitable computational errors when dealing with radiative heat transfer problems at reduced or elevated pressures. In this paper, an improved global model is established to calculate the radiant energy exchanges between combustion gases and combustor chamber walls. Compared with the Smith model, the new model shows better performance in a wide range of pressure regions. The model accuracy is examined by computing the emissivity, radiative heat flux as well as the radiative source of H₂O–CO₂ gas mixtures at different pressure values. Finally, the radiative heat transfer inside a 3D TBCC(turbine-based combined cycle) engine exhaust system where strong gradients of pressure and temperature exist, is also addressed. The computational results show that the developed model provides approximate results at much less computational costs than the high-precision MSMGFSK-c8 model, which makes it competitive in complicated combustion systems.     

Effects of radiation heat loss on laminar premixed ammonia/air flames

Ammonia (NH₃) direct combustion is attracting attention for energy utilization without CO₂ emissions, but fundamental knowledge related to ammonia combustion is still insufficient. This study was designed to examine effects of radiation heat loss on laminar ammonia/air premixed flames because of their very low flame speeds. After numerical simulations for 1-D planar flames with and without radiation heat loss modeled by the optically thin model were conducted, effects of radiation heat loss on flame speeds, flame structure and emissions were investigated. Simulations were also conducted for methane/air mixtures as a reference. Effects of radiation heat loss on flame speeds were strong only near the flammability limits for methane, but were strong over widely diverse equivalence ratios for ammonia. The lower radiative flame temperature suppressed the thermal decomposition of unburned ammonia to hydrogen (H₂) at rich conditions. The equivalence ratio for a low emission window of ammonia and nitric oxide (NO) in the radiative condition shifted to a lower value than that in the adiabatic condition.     

Kinetic studies of Ar2F* in fast transverse-discharge-excited He-Ar-F2 mixtures

Time-resolved and time-integrated spectra for various He-Ar-F₂ mixtures excited by a fast transverse discharge were recorded. The fluorescence of ArF^* and Ar₂F^* was investigated and the radiative lifetime and emission characteristics of Ar₂F^* were determined. A mechanism for the formation of Ar₂F^* is suggested.     

Special features of electron beam-excited XeCl-laser generation

The results of experimental investigations on generation in Ar(Ne): Xe: CCl₄(HCl) mixtures at excitation by an electron beam are given. It is shown that the use of CCl₄ and HCl with an Ar buffer gas gives equal radiative energies and efficiencies and ā change of Ne for Ar causes a change in generation spectrum. The special features of XeCl-laser generation are discussed.     

Evidence of KrF1 broad band continuum emission at 400 nm

Broad band emission of KrF¹ centered at about 400 nm was observed in various mixtures containing Kr and fluorinated compounds. This emission was resolved against the more intense Kr₂F¹ broad band emission at the same wavelengths due to its temporal behaviour and its different pressure dependence. Its radiative lifetime is 16 ns and it is tentatively ascribed to the 3 ²∑⁺ → 1 ²Π transition.     

Analysis of the parameters of a barrier discharge in Kr-I2 and Xe-I2 mixtures

The barrier discharges in Kr-I₂ and Xe-I₂ mixtures are investigated as possible light sources at wavelengths λ=185 and 253 nm. The spectral and current-voltage characteristics of the barrier discharges are obtained. The concentrations of mixture components are calculated, and the kinetic diagrams of the reactions are constructed. The emission efficiencies are estimated to be approximately 20% for both wavelengths. The optimum conditions for emission at these wavelengths in the mixtures Xe-I₂ (400 ± 15 Torr) and Kr-I₂ (200 ± 0.1 Torr) are determined.     

Spectrophotometric Determination of the Stability Constants of Co(II) and DPKBH (DI-2-Pyridyl Ketone Benzoylhydrazone)

Abstract

In order to have more information about the thermodynamic properties of the complexes formed by Cobalt(II) and DPKBH (di-2-pyridyl ketone benzoylhydrazone) and for the development of speciation methods for cobalt, the respective stepwise formation constants were determined in ethanolic solution 50% (V/V), at pH 5.3 and 25.0°C. The spectrophotometric method of corresponding solutions was used and the following overall formation constants were obtained: β₁ = 5.305 × 10⁶ M^?1 and β₂ = 8.476 × 10¹⁰ M^?2. The molar absorptivities of the 1:1 (ε₁) and 1:2 (ε₂) complexes (Co(II):DPKBH) were determined to be 4.475 × 10 and 2.994 × 10 (M^?1cm^?1), respectively. The calculated distribution diagram shows the percentage of the species at equilibrium as a function of the free DPKBH concentration.     

Experimental investigations and modelling studies of ozone producing corona discharges

The ozone generation by negative corona discharge in coaxial cylindrical system of electrodes have been studied experimentally in Ar+O₂ and N₂+O₂ mixtures. Both in argon and nitrogen mixtures with oxygen the monotonous decrease in ozone concentration [O₃] was observed at decreasing oxygen content in mixtures and the constant input energy density η. The rate coefficients for the ozone generation and ozone decomposition were obtained by fitting experimentally measured data [O₃]=f(η) with Vasiljev-Eremin formula. The calculated rate coefficient for ozone generation in N₂+O₂ mixtures at low content of oxygen (below 20%) was found considerably higher than that in Ar+O₂ mixtures. Increase in the rate coefficients for ozone generation and decomposition was observed with decreasing content of oxygen in both mixtures. The experimental results are in qualitative agreement with the simple model incorporating five main chemical processes in mechanism of ozone generation. The research was partially supported by Slovak Grant Agency under project 1/765920 The UK EPSRC (Grant GM/98944) and NATO Joint Project PST CLG 976544.     

Infrared luminescence of erbium-doped sodium lead germanate glass

The infrared optical properties of Er³⁺ ions are reported for 60GeO₂–20PbO–20Na₂O glass for two Er₂O₃ concentrations. From the optical absorption spectra, the Judd–Ofelt (J–O) parameters have been obtained and have been used to calculate radiative lifetimes and stimulated emission cross sections. A narrow emission band peaked at 1536 nm with exponential decay for both Er concentrations is observed. The measured lifetime decreases for increasing Er concentration, its value being very close, in the case of the lowest doping level, to the radiative lifetime calculated from J–O analysis. This, together with the relatively high emission cross section makes this glass suitable for laser applications.     

The dielectric relaxation study of 2(2-alkoxyethoxy)ethanol-water mixtures using time domain reflectometry

Complex permittivity spectra of 2(2-alkoxyethoxy)ethanol-water mixtures for the entire concentration range and at 25 °C have been measured using time domain reflectometry technique up to 30 GHz. The relaxation processes have been obtained by fitting the complex permittivity spectra of the binary mixtures in 2-Debye equation. In glycol ether-water mixtures except for pure water and its rich region the double relaxation times, primary process (τ₁) and secondary process (τ₂) have been observed. The primary relaxation process (τ₁) may be due to cooperative relaxation of the H-bond network of mixture constituents and the secondary relaxation process (τ₂) may be due to its flexible parts attached to the carbon chain. The intra and intermolecular hydrogen bonding of 2(2-alkoxyethoxy)ethanol in pure form as well as in binary mixtures of water have been discussed using Kirkwood correlation factor, Excess dielectric properties and the Bruggeman factor.     

Spectroscopic study of neodymium-doped potassium-lead double chloride Nd3+:KPb2Cl5 crystals

Optical spectra, radiative and nonradiative transition intensities, and luminescence kinetics of neodymium-doped potassium-lead double chloride crystals Nd³⁺:KPb₂Cl₅, (Nd³⁺:KPC) are investigated. Crystals were grown by the Stockbarger-Bridgman technique. Experimental studies of absorption and luminescence spectra are performed, intensity parameters are obtained by the Judd-Ofelt method, radiative transition probabilities and branching ratios are calculated, and nonradiative transition probabilities are estimated. Luminescence kinetics of ² K _13/2, ² P _3/2, and ⁴ D _3/2 radiative levels of neodymium under selective excitation in the 355-nm region are studied.     

Crystal growth, Judd-Ofelt analysis and fluorescence properties of Tm: CaNb2O6 crystal

Tm³⁺-doped CaNb₂O₆ single crystal was successfully grown by the Czochralski technique. Based on the Judd-Ofelt theory, three spectroscopic parameters Ω_t (t=2,4,6), radiative transition probabilities, radiative lifetimes, branching ratios and oscillator strengths were obtained according to the absorption spectra and the fluorescence spectra. Both the radiative lifetimes corresponding to the ³F₄→³H₆ transition for the bulk and the powder samples were recorded, and the final value of the radiative lifetime was obtained to be 2.25 ms, which indicates the existence of the luminescence re-absorption in the bulk sample. The corresponding quantum efficiency of the ³F₄ level was calculated to be 96%.     

Spectral investigations of Sm3+ doped lead bismuth magnesium borophosphate glasses

The multicomponent lead bismuth magnesium borophosphate glass systems (LBMBPS) doped with Samarium ions with the molar compositions of (50?x)PbOxBi₂O₃25MgHPO₄24B₂O₃1Sm₂O₃ (where x=10, 20, 30, and 40) were fabricated using conventional melt quenching technique. The amorphous nature of these glass samples was confirmed with XRD studies. The spectral data from the optical absorption studies were employed to compute various spectroscopic parameters such as Judd–Ofelt intensity parameters. The Judd–Ofelt parameterization employed reflects the covalency and vibration frequencies of the ligands with Samarium ions. The radiative parameters such as radiative transition probabilities (A), the total radiative transitional probabilities (A_T), radiative life times (τ_R), branching ratios (β) and absorption cross sections (Σ) were computed for certain lasing levels. The glass systems thus developed indicate their potential lasing candidature. The emission cross sections (σ_E) for the significant lasing transitions ⁴G_5/2→⁶H_5/2, ⁴G_5/2→⁶H_7/2, and ⁴G_5/2→⁶H_9/2 evaluated from the photoluminescence spectra were reported. The radiative properties obtained in our investigations suggest their lasing candidature.     

Transport mean free path for magneto-transverse light diffusion: an alternative approach

Abstract

This paper presents a derivation of the transport mean free path for magneto-transverse light diffusion, ?*_⊥, in an arbitrary random mixture of Faraday-active and non-Faraday-active Mie scatterers. This derivation is based on the standard radiative transfer equation. The expression of the transport mean free path obtained previously from the Bethe–Salpeter equation, for the case where only Faraday-active scatterers are present, is recovered. This simpler formulation can include the case of homogeneous mixtures of Faraday-active and non-Faraday-active scatterers.     

A multi-spectral reordering technique for the full spectrum SLMB modeling of radiative heat transfer in nonuniform gaseous mixtures

A Multi-Spectral Reordering (MSR) scheme is introduced to improve the performances of the Spectral-Line Moment-Based (SLMB) modeling for the handling of full spectrum radiative heat transfer calculations in nonuniform media. Using this simultaneous reordering of the spectrum for several thermophysical conditions together with employing approximate formulations to evaluate path-averaged transmission functions for nonisothermal and nonhomogenous gaseous paths, a novel full spectrum gas radiation modeling method in nonuniform gaseous mixtures is constituted. The method is presented in details as well as the building of associated databases for CO₂ and H₂O at atmospheric pressure and for the temperature range of 300-2700 K. The new model is validated against line-by-line reference computations for a series of existing benchmarks and for a flame configuration. The MSR-SLMB modeling is shown to perform accurately and better than the standard SLMB one, while involving reasonable additional computational costs.     

Orientational order and molecular parameters of two nematogenic mixtures from X-ray studies: confirmation of electro-optical results

This study entails the report of X-ray studies conducted on two nematogenic mixtures (code names ZLI 1221 and ZLI 1291) containing identical moieties: phenyl cyclohexane, biphenyl cyclohexane and cyclohexyl benzoate, but exhibiting different mesogenic ranges and properties. X-ray studies have been undertaken with a view to investigate the difference in the mesogenic behaviour of the said mixtures at the molecular level. The average apparent molecular length ‘l?’ and intermolecular distance ‘D’ of the two mixtures and their variations with temperature have been determined from X-ray data. The orientational order parameters ?P ₂? and ?P ₄? and their thermal variations have also been obtained. Comparison has been made with the ?P ₂? values obtained from X-ray study with those obtained from optical study. The average apparent molecular lengths of the two mixtures corroborate the findings regarding the relative molecular weights of the two samples obtained from optical and dielectric data.     

Improved conversion efficiency of XeCl radiation to the first stokes at high pump energy

An XeCl laser beam has been used to investigate stimulated Raman scattering in H₂ and in various H₂-foreign gas mixtures. Helium, neon, argon, and nitrogen have been tested as foreign gases. In all the investigated mixtures with 50% of H₂, the energy conversion efficiency to the first Stokes (353 nm) was more than 70% higher than that obtained in H₂ at the same total pressure (40 bar) and pump energy (60 mJ). The dependence of the energy conversion efficiency on pump beam divergence has also been investigated.