Spectral characteristics of a barrier discharge in cadmium dihalide vapor-inert gas mixtures

Spectral characteristics of a barrier-discharge plasma produced in atmospheric-pressure mixtures of cadmium diiodide and cadmium dibromide vapors with neon, krypton, and xenon at a repetition rate of sine voltage pulses up to 130 kHz are studied. The emission from the discharge is studied within the spectral range 200–900 nm with a resolution of 0.05 nm. Emission of exciplex molecules CdI(B → X) and CdBr(C, B → X), and cadmium and inert gas atoms is revealed, as well as emission of exciplex molecules XeI(B → X, A) and XeBr(B → X, A) in xenon-containing mixtures. The emission of xenon halides prevails in the spectra at a mixture temperature up to 200°C. With a further temperature increase, the emission of cadmium halides becomes dominating. It is ascertained that the most intense emissions of CdI(B → X) and CdI₂/CdBr₂/Xe/Kr and CdBr(B → X) molecules are observed, respectively, in CdI₂/CdBr₂/Xe/Kr and CdI₂/CdBr₂/Xe mixtures. The cadmium dihalide-inert gas mixtures are of interest for the use as a radiating gas in a multiwavelength and broadband excilamp emitting in the UV and visible spectral ranges.     

CO concentration and temperature measurements in a shock tube for Martian mixtures by coupling OES and TDLAS

CO concentration and gas temperature distribution are diagnosed behind a strong shock wave simulating the Martian atmosphere entry processes by coupling optical emission spectroscopy (OES) and tunable diode laser absorption spectroscopy (TDLAS). The strong shock wave (6.31 ± 0.11 km/s) is established in a shock tube driven by combustion of hydrogen and oxygen. Temperature of the shock-heated gas is inferred through a precise analysis of the high temporal and spatial resolution experimental spectral of CN violet system (B ² Σ ⁺ →X ² Σ ⁺, Δv = 0 sequence) using OES. A CO absorption line near 2,335.778 nm is utilized for detecting the CO concentration using scanned-wavelength direct absorption mode with 50 kHz repetition rate. Combined with temperature results from OES, CO concentration in the thermal equilibrium region is derived. The current experimental results are complementary for determining an accurate rate coefficient of CO₂ dissociation and validation relevant chemical kinetics models in Mars atmosphere entry processes.     

Fifth to tenth virial coefficients of a hard-sphere fluid

The best known value of the fifth virial coefficient for a hard-sphere fluid was until now: B₅/tB⁴₂ = 0.110277 ± 0.000014, B₂ being the second virial coefficient. In the present work, B₅ is determined more accurately, the result being B₅/tB⁴₂ = 0.110252±0.000001. Moreover, the values of B₆ and B₇ given in the literature are re-examined and slightly modified. Then, estimates of B₈, B₉ and B₁₀ are given using several approximations.     

Emission characteristics of an ultraviolet emitter based on mixtures of krypton with low-aggressive halogen carriers pumped by a barrier discharge

The emission characteristics of a pulse-periodic excilamp with three dielectric barriers based on the 222-nm KrCl(X-B) and 248-nm KrF(X-B) emission bands have been investigated. The working gases of the lamp were mixtures of krypton with low-aggressivity halogen carriers (SF₆, CCl₄). Optimal compositions of Kr-SF₆ and Kr-CCl₄ mixtures for obtaining the maximum intensity of the system of 222-nm KrCl(X-B) and 248-nm KrF(X-B) bands have been determined. The results of lamp optimization depending on the parameters of the source of pulse-periodic short-duration barrier discharge are presented.     

Exchange and correlation energy of an inhomogeneous electron gas

A convenient expression is derived for the coefficient, B_xc(n), which determines the first gradient corrections to the exchange and correlation energy of an inhomogeneous electron gas. The result is exact to all orders in $\text{e}$² and is expressed in terms of the single particle progagator. A method of approximation, which is exact at high density, is given for the explicit evaluation of B_xc. Numerical results are given for B_xc in the metallic density range.     

Field dependence of a.c. Electroluminescence in ZnS: Mn,Cu, Cl film panels

Electroluminescent (EL) film panels of ZnS: Mn, Cu, Cl operated by a.c. electric field are studied at room temperature. The emission spectrum consists of a single peak at 590 nm. The EL emittance B varies with frequency f of the applied a.c. electric field as B = B_s ? B_m exp ? f/f_c where B_s, B_m and f_c are constants. This equation indicates that B approaches a saturation value B_s when f?f_c and a linear relation between B and f when f?f_c. At a fixed frequency f, B is found to depend on the applied voltage V as B = A exp [-G/F + V^{$\text{1}\text{2}$})] where A, G and F are constants. This formula is valid at all stages of the operating life of the film panel.     

Thermal hadron production in high energy heavy ion collisions

We provide a method to test if hadrons produced in high energy heavy ion collisions were emitted at freeze-out from an equilibrium hadron gas. Our considerations are based on an ideal gas at fixed temperatureT _f , baryon number densityn _B , and vanishing total strangeness. The constituents of this gas are all hadron resonances up to a mass of 2 GeV; they are taken to decay according to the experimentally observed branching ratios. The ratios of the various resulting hadron production rates are tabulated as functions ofT _f andn _B . These tables can be used for the equilibration analysis of any heavy ion data; we illustrate this for some specific cases.     

Photoluminescence study in Ce activated M6B5AlO15 (M = Sr,Ca, Ba) and mixed host aluminoborate phosphors

In this paper we report the modified solid state synthesis of Ce³⁺ activated Sr₆B₅AlO₁₅, Ca₆B₅AlO₁₅ Ba₆B₅AlO₁₅ and mixed host aluminoborate phosphors. The prepared phosphors were characterized by photoluminescence technique. The PL excitation spectra showed the excitation peaks ranging from 300 to 400 nm and emission spectra are observed in UV-blue region of spectrum and it varied for different hosts. This kind of emission is due to 4f⁶5d → 4f⁷ transition of Ce³⁺ ion. Further PLE and PL emission spectra for various compositions Ca₅Sr₁B₅AlO₁₅, Ca₄Sr₂B₅AlO₁₅, Ca₃Sr₃B₅AlO₁₅, Ca₂Sr₄B₅AlO₁₅, CaSr₅B₅AlO₁₅ are also taken which shows Ce³⁺ emission at 428 nm, 425 nm, 432 nm, 427 nm, 438 nm respectively. The calculated ²F_J (J = 7/2, 5/2) energy gap of Ce³⁺ in all hosts have been calculated and obtained values for Sr₆B₅AlO₁₅, Ba₆B₅AlO₁₅ phosphors are 1888 cm⁻¹ and 1330 cm⁻¹ respectively. PL emission spectra of mixed host aluminoborates have shown slight variations in positions of emission peaks.     

The influence of CO adsorption on the galvanomagnetic and magnetic properties of evaporated nickel films

The influence of CO adsorption on the ordinary Hall coefficient, R_HO, the extraordinary Hall coefficient, R_HE, the perpendicular magnetoresistivity ΔR_{mag O} and the saturation magnetization, B_S, of Ni films with thicknesses between 1 and 200 nm has been studies as a function of the CO coverage at 77 and 273 K. There is a maximum in ΔR_HE at a coverage of about half a monolayer. ΔR_HO, ΔΔR_{mag O} and ΔB_S exhibit an oscillating behaviour.     

Theory of the hot free carrier intraband-absorption coefficient of n-inversion layers

The absorption coefficient K of a quasi two dimensional (2D) hot free electron gas is calculated for the first time as a function of the lattice temperature T, the photon angular frequency w, the carrier density N_s as well as the electron temperature T_e when the carriers are scattered by ionized impurities, acoustic phonons and polar optical phonons. Analytical expressions are derived in the limiting cases of non-degeneracy and degeneracy of the electron system. In the quantum limit ħw/k_BT_e ≳ 1 where the interaction between the electron and the photon is inelastic K sensitively depends on the limiting scattering mechanism showing that the electron motion is completely controlled by the photon field. In the classical limit ħw/k_BT_e ⪡ 1 the absorption decreases proportional to w¹ independent of the limiting scattering mechanism in agreement with the experimental data deduced from far-infrared absorptivity measurements on GaAs heterolayers.     

Effects of neon matrix environment on three vibronic emission systems of PbS

Laser sources have been used to explore three emission band systems of the PbS molecule in solid neon matrices. The D → X emission (origin near 29 630 cm^?1), excited biphotonically, consists of broad bands originating from V′ = 0. With laser excitation tuned into the region of the band system origin near 21 860 cm^?1, the B → X system shows emission narrowing of inhomogeneously broadened absorption. Hot luminescence from the B state is also reported. In the a → X system near 14 625 cm^?1 the intensities of phonon sidebands on the high-frequency side of the zero-phonon lines are found to be very sensitive to laser power. Lifetimes of the a, A, and B states of PbS in solid argon have been measured as 260, 0.95, and 1.8 μsec.     

Structural and photoluminescence properties of Dy3+ doped different modifier oxide-based lithium borate glasses

Structural and photoluminescence properties of Dy³⁺ doped lithium fluoro-borate glasses with the compositions Li₂B₄O₇–BaF₂–NaF–MO (where M=Mg, Ca, Cd and Pb), Li₂B₄O₇–BaF₂–NaF–MgO–CaO and Li₂B₄O₇–BaF₂–NaF–CdO–PbO have been investigated through XRD, FTIR, optical absorption, emission and decay measurements. From the optical absorption spectra, Judd–Ofelt intensity parameters (Ω_λ, λ=2, 4 and 6) have been evaluated and are in turn used to predict radiative properties such as radiative transition probabilities (A_T), branching ratios (β_r) and stimulated emission cross sections (σ_p) for all emission levels of Dy³⁺ ion in different lithium fluoro-borate glass matrices. From the emission spectra, chromaticity color coordinates have been calculated and indicated emission color for all glass matrices. The nature of decay profiles of ⁴F_9/2 state of Dy³⁺ in all the glass matrices are analyzed.     

On the non-BoltzmannA-X emission in Na2 following laser excitation of theB state

A ¹Σ _u ⁺ -X ¹Σ _g ⁺ emission in Na₂ is observed following excitation ofB ¹π _u by various lines of an argon ion laser. The excitation energy ofB ¹π _u is collisionally transferred to the (2)¹Σ _g ⁺ which then radiatively populates theA ¹Σ _u ⁺ state. The Na vapour is contained in a stainless steel crossed heat pipe with Ar buffer gas and temperature around 600°C. For all laser lines except 4579 Å, the coarse features ofA-X emission are independent of the laser wavelength. However, at high resolution the finer differences between different laser line excitation are explained. Variousv′-v″ transitions in this emission are identified. Computer simulation is presented to help explain some features of this emission.     

Dynamics of magnetic insulation failure and self-organization of an electron flow in a magnetron diode

The dynamics of back cathode bombardment (BCB) instability in a magnetron diode (a coaxial diode in a magnetic field, B ≡ B _0z ≡ B ₀) is numerically simulated. The quasi-stationary regime of electron leakage across the high magnetic field (B ₀/B _cr > 1.1, where B _cr is the insulation critical field) is realized. An electron beam in the electrode gap is split into a series of bunches in the azimuthal direction and generates the electric field component E _θ(r, θ, t), which accelerates some of the electrons. Having gained an extra energy, these electrons bombard the cathode, causing secondary electron emission. The rest of the electrons lose kinetic energy and move toward the anode. Instability is sustained if the primary emission from the cathode is low and the secondary emission coefficient k _se=I _se/I _{e, BCB} is greater than unity. The results of numerical simulation are shown to agree well with experimental data. A physical model of back-bombardment instability is suggested. Collective oscillations of charged flows take place in the gap with crossed electric and magnetic fields (E × B field) when the electrons and E × B field exchange momentum and energy. The self-generation and self-organization of flows are due to secondary electron emission from the cathode.     

Correlation of volumetric properties of binary mixtures of some ionic liquids with alcohols using equation of state

In our previous paper, we extended the Tao and Mason equation of state (TM EOS) to pure ionic liquids. Here we apply TM EOS based on statistical?Cmechanical perturbation theory to binary mixtures of ionic liquids. Three temperature-dependent quantities are needed to use the equation of state: the second virial coefficient, B ₂, effective van der Waals co-volume, b, and a scaling factor, ??. The second virial coefficients are calculated from a correlation that uses the normal boiling temperature and normal boiling density. ?? and b can also be calculated from the second virial coefficient by scaling. In this procedure, the number of input parameters, for calculation of B ₂, ??, and b reduced from 5 (i.e., critical temperature, critical pressure, acetric factor, Boyle temperature T _B, and the Boyle volume ?? _B) to 2 (i.e., T _bp and ?? _bp). At close inspection of the deviations given in this work, the TM EOS predicts the densities with a mean AAD of 1.69%. The density of selected system obtained from the TM EOS has been compared with those calculated from perturbed-hard-sphere equation of state. Our results are in favor of the preference of the TM EOS over another equation of state. The overall average absolute deviation for 428 data points that calculated by perturbed-hard-sphere equation of state is 2.60%.     

Absorption and emission spectra of matrix-isolated GeTe

Systems of broad bands have been observed in the absorption and laser-induced emission spectra of the GeTe molecule in solid argon and krypton matrices. Hitherto unreported electronic states have been characterized: a, ν₀₀ = 15 500 cm^?1; B, ν₀₀ = 20 070, ω_e = 190 cm^?1; C, ν₀₀ = 23 500, ω_e = 270 cm^?1. Higher energy states are also reported as well as an emission system in the red which is probably due to the Ge₂Te₂.     

Giant quantum oscillations of the magnetothermoelectric coefficient in semimetallic Sb-Bi and Sb-As alloys

Quantum oscillations of the magnetothermoelectric coefficient α_ii(B) are investigated in semimetallic Sb-Bi and Sb-As alloys in stationary magnetic fields up to 15 T and at temperatures from 1.9 to 30 K. Quantum oscillations of α_ii(B) of a giant amplitude are observed when the longitudinal or transverse magnetic field is oriented along a binary C ₂ axis or a bisectory C ₁ axis and also when rotating the transverse magnetic field in angle ranges up to [+55°, ?55°] around them.     

Revised molecular constants,RKR potential,and long-range analysis for the B3Π(0u+) state of Cl2, and rotationally dependent Franck-Condon factors for Cl2 (BX1Σg+)

Literature data for the line frequencies of the B³Π(0_u⁺) ← X¹Σ_g⁺ transition of Cl₂ are fitted directly by least squares to obtain new molecular constants. The constants from individual bands are merged to obtain single-valued estimates of the rotational constants for each vibrational level of the B state. The results are combined with recent data from the B → X system in emission to obtain new RKR turning points for the B and X states, and Franck-Condon factors for the B-X system. The new constants are also used to provide revised long-range parameters for Cl₂(B) which differ from those of earlier work. In particular, the coefficient C₅ of the leading term in the inverse-power long-range potential is now found to be $\text{C}{}_5\text{= 1.16(2) × 10}{}^5\text{A}\text{?}{}^5\text{cm}{}^{\mathrm{?1}}$. Theoretical results for the variation of centrifugal distortion parameters for levels near dissociation are tested for D_v and H_v, and an extrapolation based on this behavior is used to facilitate determination of reliable B_v and G(v) values for the highest observed B-state levels.     

Stress-optical studies of VI B transition metal dichalcogenides

The effect of a uniaxial stress on the excitonic optical spectra are studied for MoS₂, WS₂, MoSe₂ and WSe₂. Stress dichroism appears in the A′, B′ excitons in diselenides, while it is absent in the A, B excitons in the four compounds. The A′, B′ excitons shift oppositely to the A, B excitons, indicating that A, B and A′, B′ are not pair excitons split by interlayer interaction.     

Pressure effect on structural,electronic and thermodynamic investigations of europium filled skutterudite EuFe4Sb12: LDA and LSDA approximations

Numerical calculations based on the full potential muffin-tin orbitals method (FP-LMTO) within the local density approximation (LDA) and the local spin-density approximation (LSDA) to investigate the structural, electronic and thermodynamic properties of filled skutterudite EuFe₄Sb₁₂ are presented. The electronic band structure and density of states profiles prove that this material is a conductor. The present investigation is also extended to the elastic constants, such as the bulk modulus B, anisotropy factor A, shear modulus G, young's modulus E, Poisson's ratio ν, and the B/G ratio with pressure in the range of 0–40 GPa. The sound velocities and Debye temperatures are also predicted from the above constants. The variations of the primitive cell volume, expansion coefficient α, bulk modulus B, heat capacity (C_p and C_v), Debye temperature θ_D, Helmholtz free energy A, Gibbs free energy G, entropy S, and internal energy U with pressure and temperature in the range 0–3000 K are calculated successfully.