The time-domain electromagnetic interference measurement system

A novel real-time broad-band time-domain electromagnetic interference (TDEMI) measurement system for the 30-1000-MHz frequency range is described. The signals from the antenna are sampled, analog-to-digital (A/D) converted and digitally processed. The fast-Fourier transform (FFT), the Welch- and Bartlett periodograms are digitally computed. Compared with state-of-the-art EMI measurement systems, the novel described TDEMI system samples the complete phase and amplitude information of the EMI simultaneously over the whole frequency band under consideration. With the presented time domain measurement system the measurement time can be reduced by a factor of 10. The digital processing of EMI measurements allows emulation in real-time of the various modes of conventional analogous equipment, e.g., peak, average, rms and quasi-peak detector and also introduces new concepts of analysis, e.g., phase spectra, short-time spectra, statistical evaluation and FFT-based time-frequency analysis methods.     

Ground-state properties of LiV2O4 and Li1-xZnx(V1-yTiy)2O4

We present susceptibility, microwave resistivity, NMR and heat-capacity results for Li_1-xZn_x(V_1-yTi_y)₂O₄ with 0 ? x ? 0.3 and 0 ? y ? 0.3. For all doping levels the susceptibility curves can be fitted with a Curie-Weiss law. The paramagnetic Curie-Weiss temperatures remain negative with an average value close to that of the pure compound Θ≈ - 36 K. Spin-glass anomalies are observed in the susceptibility, heat-capacity and NMR measurements for both type of dopants. From the temperature dependence of the spin-lattice relaxation rate we found critical-dynamic behavior in the Zn doped compounds at the freezing temperatures. For the Ti-doped samples two successive freezing transitions into disordered low-temperature states can be detected. The temperature dependence of the heat capacity for Zn-doped compounds does not resemble that of canonical spin glasses and only a small fraction of the total vanadium entropy is frozen at the spin-glass transitions. For pure LiV₂O₄ the spin-glass transition is completely suppressed. The temperature dependence of the heat capacity for LiV₂O₄ can be described using a nuclear Schottky contribution and the non-Fermi liquid model, appropriate for a system close to a spin-glass quantum critical point. Finally an ( x / y , T )-phase diagram for the low-doping regime is presented. Received 16 March 2001 and Received in final form 30 October 2001     

Atomization of Al in a tungsten coil electrothermal atomic absorption spectrophotometer

Electrothermal atomic absorption spectrophotometry of Al in a tungsten coil atomizer was evaluated and applied for its determination in hemodialysis fluid. The system was mounted on a Varian Spectra AA-40 spectrophotometer with continuum background correction and all measurements, in peak height absorbance, were done at 309.3 nm. The purge gas was a mixture of 90% Ar plus 10% H(2). Observation height, gas flow, drying, pyrolysis and atomization steps were optimized. The heating program was carried out by employing a heating cycle in four steps: dry, pyrolysis, atomization and clean. The determination of Al in hemodialysis solutions was performed by using a matrix-matching procedure. Al in hemodialysis solutions was determined by TCA and by electrothermal atomization with a graphite tube atomizer. There is no differences between results obtained by both methods at a confidence level of 95%. The characteristic mass of Al by using the TCA was 39 pg and the detection limit was 2.0 mug l(-1).     

Formation of Zn(1-x)MnxS nanowires within mesoporous silica of different pore sizes

Arrays of highly ordered Zn(1-x)MnxS quantum wires with x ranging from 0.01 to 0.3 and with lateral dimensions of 3, 6, and 9 nm were synthesized within mesoporous SiO2 host structures of the MCM-41 and SBA-15 type. The hexagonal symmetry of these arrays (space group p6m) and the high degree of order was confirmed by X-ray diffraction and transmission electron microscopy (TEM) studies. Physisorption measurements show the progressive filling of the pores of the SiO2 host structures, while TEM and Raman studies reveal the wire-like character of the incorporated Zn(1-x)MnxS nanostructures. X-ray absorption near-edge structure, extended X-ray absorption fine structure, photoluminescence excitation (PLE), and electron paramagnetic resonance studies confirm the good crystalline quality of the incorporated Zn(1-x)MnxS guest species and, in particular, that the Mn2+ ions are randomly distributed and are situated on tetrahedrally coordinated cation sites of the Zn(1-x)MnxS wires for all x up to 0.3. The amount of Mn2+ ions loosely bound to the surface of the Zn(1-x)MnxS nanowires is less than 4% of the total Mn content even for the 3 nm nanostructures up to the highest Mn content of x = 0.3. The effects of the reduction of the lateral dimensions on electronic properties of the diluted magnetic semiconductor were studied by PLE spectroscopy. Due to the quantum confinement of the excitons in the wires an increase of the direct band gap with decreasing particle size is observed.     

Sulphate preconcentration by anion exchange resin in flow injection and its turbidimetric determination in water

A preconcentration procedure was established for sulphate determination in rain waters at the mg/l level, employing a small column packed with the AG1-X8 (200-400 mesh) anionic resin inserted into a flow injection system. Sulphate determination was performed by using the turbidimetric method based on reaction with barium. For concentrations within 0.10 and 2.0 MgSO(2-)(4)/l, a throughput of 50 determinations/hr was achieved, and the relative standard deviation of results was better than 2%.     

Imine insertion into a late metal-carbon bond to form a stable amido complex

An arylrhodium(I) complex containing a labile dative ligand was prepared, and its reactivity toward aryl imines was investigated. The arylrhodium(I) complex (DPPE)Rh(C5H5N)(p-tol), 2, was isolated in 65% yield from [(DPPE)Rh(mu-Cl)]2, pyridine, and p-tolyllithium. Reaction of 2 with the aldimine (p-tol)CH=N(C6H4-p-CO2Me) (3a-Tol) gave the Rh amide insertion product 4 in 88% isolated yield. The solid-state structure of 4 was determined by single-crystal X-ray diffraction. The reaction of 2 with the electron-neutral and electron-rich aldimines (Ph)CH=NPh (3b) and (p-tol)CH=N(C6H4-p-OMe) (3c) also appeared to involve insertion, but the amido complexes formed from these insertions were not stable. Thus, reaction of 2 with 3b, followed by addition of Et3NHCl, gave the amine and ketimine products (Ph)(p-tol)CH-NHPh, 5, and (p-tol)(Ph)C=N(Ph), 6, in 25% and 50% yields. Several lines of data indicate that these products are formed by a sequence of transformations involving insertion of imine to give a Rh amide intermediate, beta-hydrogen elimination, cyclometalation to form a bound imine and H2, and protonolysis of the metallacycle upon addition of Et3NHCl. Consistent with this proposal, the proposed metallacycle containing the ortho-metalated ketimine ligand (p-tol)2C=N(C6H4-p-OMe) was isolated and characterized by single-crystal X-ray diffraction.     

Quantitative determination of chloride by means of flow injection analysis with spectrophotometric detection in the UV/VIS range

Chloride is determined indirectly by Spectrophotometric flow injection analysis. Two systems are compared, both based on the principle of ion exchange of easily detectable anions versus chloride from suitable mercury salts. The first method is based on the exchange of chloride with chloranilate which is detected at 332 nm or at 306 nm in neutral or in acidic medium respectively. In the second case, chloride reacts with Hg(SCN)₂. The liberated thiocyanate forms a strongly coloured complex with Fe(III) in acidic solution with an absorption maximum at 460 nm. Both methods have a detection limit of about 5 mol Cl^–/l (175 ng/ml). In the case of the thiocyanate method, the relative standard deviation is about 2% (7 measurements) in the range of 5 to 150 mol/l and decreases significantly to a value of approximately 0.2% at higher concentrations; for the chloranilate method it is 10% for lower and about 1% for higher concentrations respectively.     

On-line electrolytic dissolution of alloys in flow-injection analysis : Part 1. Principles and application in the determination of soluble aluminium in steels

A fast system for steel analysis is described. Immediately after collection, the solidified sample is polished and placed on a small electrochemical dissolution unit. The dissolution step is accomplished in a few seconds, and the dissolved material is passed directly “on line” to a flow-injection manifold. The feasibility of the approach is demonstrated by determining soluble aluminium in steels (0.01–0.13% w/w) spectrophotometrically. Dissolution conditions such as current density, electrolysis duration, composition and flow rate of the electrolyte carrier stream are described. The proposed system is very stable and the consumption of reagents is low; 20–40 samples per hour can be handled. The results compare well with the values for reference standard steels.