On the construction and calculation of optimal nonlifting critical airfoils

Numerical calculations are carried out in the hodograph plane to construct optimal critical airfoil shapes and the flow about them. These optimal airfoil shapes give the highest free-stream Mach numberM for a given thickness ratio and tail angle _t (nonlifting) for which the flow is nowhere supersonic. A relationship betweenM and for various _t is given. Analytical and numerical solutions to the same problem are found on the basis of transonic small-disturbance theory. These results provide a limiting case asM 1, 0 and agree well with the calculations of the full problem. Using a numerical method to calculate the flow about general (subsonic) airfoils, a comparison is made between the critical free-stream Mach numbers for some standard airfoil shapes and the optimal free stream Mach number of the corresponding and _t . A significant increase in the critical free-stream Mach number is found for the optimal airfoils.     

Self-injection length in La0.7Ca0.3MnO3-YBa2Cu3O7-δ ferromagnet-superconductor multilayer thin films

We have carried out extensive studies on the self-injection problem in barrierless heterojunctions between La_0.7Ca_0.3MnO₃ (LCMO) and YBa₂Cu₃O_7-δ (YBCO) thin films. The heterojunctions were formed in situ by sequentially growing LCMO and YBCO films on 〈100〉 LaAlO₃ (LAO) substrate using a pulsed laser deposition (PLD) system. YBCO micro-bridges with 64 μm width were patterned both on the LAO (control) and LCMO side of the substrate. Critical current, I _c, was measured at 77 K on both the control side as well as the LCMO side for different YBCO film thickness. It was observed that while the control side showed a J _c of ∼ 2 × 10⁶ A/cm², the LCMO side showed about half the value for the same thickness (1800 ?). The difference in J _c indicates that a certain thickness of YBCO has become ‘effectively’ normal due to self-injection. From the measurement of J _c at two different thicknesses (1800 ? and 1500 ?) of YBCO films both on the LAO as well as the LCMO side, the value of self-injection length (at 77 K) was estimated to be ∼ 900 ?. To the authors’ best knowledge, this is the first time that self-injection length has been quantified. A control experiment carried out with LaNiO₃ deposited by PLD on YBCO did not show any evidence of self-injection.     

Study of magnetoresistance and conductance of bicrystal grain boundary in La0.67Ba0.33MnO3 thin film

La_0.67Ba_0.33MnO₃ (LBMO) thin film is deposited on a 36.7°C SrTiO₃ bicrystal substrate using laser ablation technique. A microbridge is created across bicrystal grain boundary and its characteristics are compared with a microbridge on the LBMO film having no grain boundary. Presence of grain boundary exhibits substantial magnetoresistance ratio (MRR) in the low field and low temperature region. Bicrystal grain boundary contribution in MRR disappears at temperature T>175 K. At low temperature, I-V characteristic of the microbridge across bicrystal grain boundary is nonlinear. Analysis of temperature dependence of dynamic conductance-voltage characteristics of the bicrystal grain boundary indicates that at low temperatures (T<175 K) carrier transport across the grain boundary in LBMO film is dominated by inelastic tunneling via pairs of manganese atoms and tunneling through disordered oxides. At higher temperatures (T>175 K), magnetic scattering process is dominating. Decrease of bicrystal grain boundary contribution in magnetoresistance with the increase in temperature is due to enhanced spin-flip scattering process.     

Molar extinction coefficients of some carbohydrates in aqueous solutions

Molar extinction coefficients of some carbohydrates viz. l-arabinose (C₅H₁₀O₅), d-glucose (C₆H₁₂O₆), d-mannose (C₆H₁₂O₆), d-galactose (C₆H₁₂O₆), d(-) fructose (C₆H₁₂O₆) and maltose (C₁₂H₂₄O₁₂) in aqueous solutions have been determined at 81, 356, 511, 662, 1173 and 1332 keV by gamma ray transmission method in a narrow beam good geometry set-up. These coefficients have been found to depend upon the photon energy following a 4-parameter polynomial. These extinction coefficients for different sugars having the same molecular formula have same values varying within experimental uncertainty. Within concentration ranges studied, Beer-Lambert law is obeyed very well.     

Infrared-microwave two-photon spectroscopy of the ν4 and ν6 bands of D2CO

Transitions in the ν₄ and ν₆ bands of D₂CO have been recorded by means of an infrared-microwave two-photon spectometer. The two-photon frequencies have been combined with frequencies obtained by infrared laser Stark and microwave spectroscopy to obtain rotational and centrifugal distortion constants for the ground, ν₄, and ν₆ states as well as vibrational frequencies and the Coriolis coupling constant for the two excited states. Expressions are reported for the linestrengths of two-photon transitions for an asymmetric rotor for the cases of parallel and perpendicular orientation of the planes of polarization of the infrared and microwave radiation.     

Infrared-microwave double resonance study of the ν4 fundamental band of POF3

Three-level and four-level infrared-microwave double resonance effects have been observed in a POF₃ sample contained in a microwave waveguide Stark cell that was modified to permit transmission of radiation from a CO₂ infrared gas laser. In three-level double resonance experiments laser pumping of rotational states in the ν₄ = 1 vibrational state greatly increased the signal/noise for observation of Stark-shifted rotational transitions in the excited vibrational state. The frequencies of the observed excited state transitions were used to confirm the assignment of laser Stark spectra and to obtain independent measures of the rotational constant B and the dipole moment for ν₄ = 1. The observation of four level double resonances could be explained qualitatively by the assumption of dipole selection rules for collision-induced transitions. However, the intensities of the double-resonance effects could not be explained by this simple model.     

Investigation of the ν5 band of methylacetylene by infrared laser Stark and microwave spectroscopy

Microwave spectra have been studied in the ground and v₅ = 1 (CC stretching mode) states of methylacetylene. From these data, dipole moments and rotational and centrifugal distortion constants have been determined, as follows: μ_D⁽⁰⁾ = 0.7839 ± 0.0010 D, μ_D⁽⁵⁾ = 0.7954 ± 0.0010 D, B₅ = 8508.119 ± 0.003 MHz, D_J⁽⁵⁾ = 1.8 ± 0.2 kHz, and D_JK⁽⁵⁾ = 169 ± 1 kHz. Laser Stark spectra have been obtained for the ν₅ band of this molecule and from these spectra the following vibration-rotation parameters have been determined: ν₅⁰ = 93.27540 ± 0.00007 cm^?1, A₅ - A₀ = ?227.0 ± 2.3 MHz and D_K⁽⁵⁾ - D_K⁽⁰⁾ = ?0.05 ± 0.50 MHz. The higher-J and -K states of the v₅ = 1 state appear to be purturbed.