Spherical Wave Diffraction by a Slit in an Impedance Screen

An exact solution is developed for the problem of diffraction of an E-polarized and an H-polarized spherical waves by a slit in an impedance screen. This consideration is important in the sense that point sources are regarded as better substitutes for real sources than line sources/plane waves. The two independent problems are solved using the Fourier transform, the Wiener-Hopf technique and asymptotic approximations.     

Determination of citric acid in fermentation media by pyrolysis mass spectrometry

Rapid and sensitive determination of citric acid in fermentation media by pyrolysis mass spectrometry (Py–MS) is proposed. Owing to high specificity of this method, distinguishing the citric acid from the matrix and by-products formed in the Krebs cycle is possible. Selected ion monitoring (SIM) mode is used for quantitative measurements, in which mass to charge (m/z) values of 175 of citric acid and 138 of 3-nitroaniline as internal standard are chosen. Limit of detection (LOD) for this method has been found to be 1 ng ml⁻¹ and the linear working range was 10 ng ml⁻¹–100 mg ml⁻¹. Relative standard deviation (R.S.D.) of the method for five replicates was 0.84%. Results of Py–MS are compared with those obtained by UV–vis spectrophotometric method. Also, factor analysis is used for evaluating the influence of pH, molasses concentration, time and shaker intensity on the production of citric acid by Aspergillus niger.     

New and efficient one-pot synthesis of functionalized γ-spirolactones mediated by vinyltriphenylphosphonium salts

The addition of dimethyl acetylenedicarboxylate to isatin derivatives in the presence of triphenylphosphine leading to new highly functionalized γ-spirolactones is reported.     

On the Inclination of Planetary Orbits

Assuming that planets were formed in the equatorial plane of the Sun and that there was a small perturbation at the start, it is shown that relativistic effects could lead to the planetary orbit tilting observed. On the baais of this analysis, a prediction is made for the velocity of the planet Mercury out of its orbital 'plane'. This prediction is a lower limit. Further, this explanation may possibly provide a method for determining the solar angular momentum.     

Unsteady Flow of an Oscillating Porous Disk and a Fluid at Infinity

An exact analytic solution of the unsteady Navier–Stokes equations is obtained for the flow caused by the non-coaxial rotations of a porous disk and a fluid at infinity. The porous disk is executing oscillations in its own plane with superimposed injection or suction. An increasing or decreasing velocity amplitude of the oscillating porous disk is also discussed. Further, it is shown that a combination of suction/injection and decreasing/increasing velocity amplitude is possible as well. In addition, the flow due to porous oscillating disk and a fluid at infinity rotating about an axis parallel to the z-axis is attempted as a second problem. Sommario. Si studia il flusso non stazionario prodotto dall'oscillazione di un disco poroso in un fluido e si fornisce una soluzione analitica delle equazioni di Navier–Stokes. Si discute l'effetto di una suzione/iniezione e di una variazione sull'ampiezza della velocità' di oscillazione. Infine si studia il flusso dovuto alle oscillazioni non coassiali di un disco poroso e di un fluido all'infinito.     

Some Steady MHD Flows of the Second Order Fluid

The exact analytic solutions of two problems of a second order fluid in presence of a uniform transverse magnetic field are investigated. The governing equation is of fourth order ordinary differential equation and is solved using perturbation method. In the first problem we discuss the flow of a second order fluid due to non-coaxial rotations of a porous disk and a fluid at infinity. In second problem the flow of a second order conducting fluid between two infinite plates rotating about the same axis is investigated, with suction or blowing along the axial direction. For second order conducting fluid it is observed that asymptotic solution exists for the velocity both in the case of suction and blowing.     

Performance improvements of ultraviolet/infrared dual-band detectors

Results are reported on dual-band detectors based on a GaN/AlGaN structure operating in both the ultraviolet–midinfrared (UV–MIR) and ultraviolet–farinfrared (UV–FIR) regions. The UV detection is due to an interband process, while the MIR/FIR detection is from free carrier absorption in the emitter/contact followed by internal photoemission over the barrier at the GaN/AlGaN interface. The UV detection, which was observed from 300 K to 4.2 K, has a threshold of 360 nm with a peak responsivity of 0.6 mA/W at 300 K. The detector shows a free carrier IR response in the 3–7 μm range up to 120 K, and an impurity response around 54 μm up to 30 K. A response in the range 7–13 μm, which is tentatively assigned to transitions from C impurities and N vacancies in the barrier region, was also observed. It should also be possible to develop a detector operating in the UV–visible–IR regions by choosing the appropriate material system. A dual-band detector design, which allows not only to measure the two components of the photocurrent generated by UV and IR radiation simultaneously but also to optimize the UV and IR responses independently, is proposed.     

Flow-injection determination of ascorbic acid and cysteine simultaneously with spectrofluorometric detection.

A simple and sensitive spectrofluorometric method was developed for the simultaneous determination of ascorbic acid and cysteine by a flow-injection system. This method is based on the reduction of Tl(III) with ascorbic acid or cysteine in acidic media, producing fluorescence reagent, TlCl3(2-) (lambdaex = 227 nm, lambdaem = 419 nm). The injected sample solution was divided into two separate streams. The first stream was treated with Tl(III) at pH 3.0 and then passed through a 270 cm reaction coil to the flow cell of the spectrofluorometer, where the fluorescence intensity was measured. This signal is related to ascorbic acid and cysteine concentration. The second part of the injected sample solution was treated with Tl(III) in HCl solution and then passed through a 50 cm reaction coil to the flow cell and the fluorescence intensity was measured. This signal is related only to cysteine. Thus, the ascorbic acid content was determined directly by the difference according to the calibration curve. Ascorbic acid and cysteine can be determined in the range of 1 x 10(-6) to 5.0 x 10(-5) M, at a rate of 16 samples per hour. The limits of detection (S/N = 3) were 8 x 10(-7) M for ascorbic acid and 7 x 10(-7) M for cysteine. The influence of potential interfering substances was studied. The proposed method was successfully applied to the simultaneous determination of both analytes in real samples.     

Study of neutron induced charged particle reactions on 40K: (I). Thermal neutrons

The (n_th, α) (n_th, p) and (n_th, γα) reactions spectroscopical data are reported on ⁴⁰K and ¹⁴³Nd. For ⁴⁰K, values of σ_α = 0.39 ± 0.08 b, σ_p = 4.4 ± 0.9 b, σ_γα = 26 ± 4 mb are obtained and accurate measurements of E_α0 = 3491.7 ± 7 keV and E_po = 2232.9 ± 3 keV have been performed, α₁, and p₁ transitions and the ⁴⁰K(n_th, γp) reaction have not been observed. The ⁴⁰K(n_th, γα)³⁷Cl and ¹⁴³Nd(n_th, γα)¹⁴⁰Ce spectra are presented. The multipolarity of the primary low energy γ-rays is deduced from the γ-α spectra.     

Half-lives andP n values of delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145

Further results are presented on half-lives and neutron emission probabilities (P _n ) of short-lived delayed-neutron precursors in the mass chains 85–87, 92, 135, 136 and 145 obtained with the recoil focussing parabola-type mass separator for unslowed fission products LOHENGRIN installed at the Grenoble high-flux reactor. A newP _n -value of (44±14)% is given for the (0.73±0.06)s⁸⁷As; theP _n -values of seven precursor nuclides have been redetermined: (1.9±0.1)s⁸⁵As with (22±8)%, 0.9s⁸⁶As with (10.5±2.2)%, (0.35±0.04)s⁹²Br with (21±8)%, (1.6±0.15)s¹³⁵Sb with (14±1)%, (0.9±0.1)s¹³⁶Sb with (19±9)%, (17.5±0.2)s¹³⁶Te with (2.0±1.0)% and 0.6s¹⁴⁵Cs with (12.5±3.0)%. The results are compared with the existing data, and the neutron emission probabilities are discussed within a simple semi-empirical picture.